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diff --git a/doc/gawk.texi b/doc/gawk.texi index fc569ffc..a4567760 100644 --- a/doc/gawk.texi +++ b/doc/gawk.texi @@ -1,4 +1,10 @@ +% **************************************************** +% * DO NOT MODIFY THIS FILE!!!! * +% * It was generated from gawktexi.in by sidebar.awk * +% * Edit gawktexi.in instead. * +% **************************************************** \input texinfo @c -*-texinfo-*- +@c vim: filetype=texinfo @c %**start of header (This is for running Texinfo on a region.) @setfilename gawk.info @settitle The GNU Awk User's Guide @@ -13,6 +19,31 @@ * awk: (gawk)Invoking gawk. Text scanning and processing. @end direntry +@ifset FOR_PRINT +@tex +\gdef\xrefprintnodename#1{``#1''} +@end tex +@end ifset + +@ifclear FOR_PRINT +@c With early 2014 texinfo.tex, restore PDF links and colors +@tex +\gdef\linkcolor{0.5 0.09 0.12} % Dark Red +\gdef\urlcolor{0.5 0.09 0.12} % Also +\global\urefurlonlylinktrue +@end tex +@end ifclear + +@ifnotdocbook +@set BULLET @bullet{} +@set MINUS @minus{} +@end ifnotdocbook + +@ifdocbook +@set BULLET +@set MINUS +@end ifdocbook + @set xref-automatic-section-title @c The following information should be updated here only! @@ -20,15 +51,18 @@ @c applies to and all the info about who's publishing this edition @c These apply across the board. -@set UPDATE-MONTH June, 2011 -@set VERSION 4.0 -@set PATCHLEVEL 0 - -@set FSF +@set UPDATE-MONTH September, 2014 +@set VERSION 4.1 +@set PATCHLEVEL 2 +@ifset FOR_PRINT +@set TITLE Effective awk Programming +@end ifset +@ifclear FOR_PRINT @set TITLE GAWK: Effective AWK Programming +@end ifclear @set SUBTITLE A User's Guide for GNU Awk -@set EDITION 4 +@set EDITION 4.1 @iftex @set DOCUMENT book @@ -38,6 +72,7 @@ @set SUBSECTION subsection @set DARKCORNER @inmargin{@image{lflashlight,1cm}, @image{rflashlight,1cm}} @set COMMONEXT (c.e.) +@set PAGE page @end iftex @ifinfo @set DOCUMENT Info file @@ -47,6 +82,7 @@ @set SUBSECTION node @set DARKCORNER (d.c.) @set COMMONEXT (c.e.) +@set PAGE screen @end ifinfo @ifhtml @set DOCUMENT Web page @@ -56,6 +92,7 @@ @set SUBSECTION subsection @set DARKCORNER (d.c.) @set COMMONEXT (c.e.) +@set PAGE screen @end ifhtml @ifdocbook @set DOCUMENT book @@ -65,7 +102,18 @@ @set SUBSECTION subsection @set DARKCORNER (d.c.) @set COMMONEXT (c.e.) +@set PAGE page @end ifdocbook +@ifxml +@set DOCUMENT book +@set CHAPTER chapter +@set APPENDIX appendix +@set SECTION section +@set SUBSECTION subsection +@set DARKCORNER (d.c.) +@set COMMONEXT (c.e.) +@set PAGE page +@end ifxml @ifplaintext @set DOCUMENT book @set CHAPTER chapter @@ -74,22 +122,94 @@ @set SUBSECTION subsection @set DARKCORNER (d.c.) @set COMMONEXT (c.e.) +@set PAGE page @end ifplaintext +@ifdocbook +@c empty on purpose +@set PART1 +@set PART2 +@set PART3 +@set PART4 +@end ifdocbook + +@ifnotdocbook +@set PART1 Part I:@* +@set PART2 Part II:@* +@set PART3 Part III:@* +@set PART4 Part IV:@* +@end ifnotdocbook + @c some special symbols @iftex @set LEQ @math{@leq} +@set PI @math{@pi} @end iftex +@ifdocbook +@set LEQ @inlineraw{docbook, ≤} +@set PI @inlineraw{docbook, &pgr;} +@end ifdocbook @ifnottex +@ifnotdocbook @set LEQ <= +@set PI @i{pi} +@end ifnotdocbook @end ifnottex @ifnottex +@ifnotdocbook @macro ii{text} @i{\text\} @end macro +@end ifnotdocbook @end ifnottex +@ifdocbook +@macro ii{text} +@inlineraw{docbook,<lineannotation>\text\</lineannotation>} +@end macro +@end ifdocbook + +@c hack for docbook, where comma shouldn't always follow an @ref{} +@ifdocbook +@macro DBREF{text} +@ref{\text\} +@end macro +@macro DBXREF{text} +@xref{\text\} +@end macro +@macro DBPXREF{text} +@pxref{\text\} +@end macro +@end ifdocbook + +@ifnotdocbook +@macro DBREF{text} +@ref{\text\}, +@end macro +@macro DBXREF{text} +@xref{\text\}, +@end macro +@macro DBPXREF{text} +@pxref{\text\}, +@end macro +@end ifnotdocbook + +@ifclear FOR_PRINT +@set FN file name +@set FFN File Name +@set DF data file +@set DDF Data File +@set PVERSION version +@end ifclear +@ifset FOR_PRINT +@set FN filename +@set FFN Filename +@set DF datafile +@set DDF Datafile +@set PVERSION version +@end ifset + @c For HTML, spell out email addresses, to avoid problems with @c address harvesters for spammers. @ifhtml @@ -103,19 +223,36 @@ @end macro @end ifnothtml -@set FN file name -@set FFN File Name -@set DF data file -@set DDF Data File -@set PVERSION version -@set CTL Ctrl +@c Indexing macros +@ifinfo + +@macro cindexawkfunc{name} +@cindex @code{\name\} +@end macro + +@macro cindexgawkfunc{name} +@cindex @code{\name\} +@end macro + +@end ifinfo + +@ifnotinfo + +@macro cindexawkfunc{name} +@cindex @code{\name\()} function +@end macro + +@macro cindexgawkfunc{name} +@cindex @code{\name\()} function (@command{gawk}) +@end macro +@end ifnotinfo @ignore Some comments on the layout for TeX. -1. Use at least texinfo.tex 2000-09-06.09 -2. I have done A LOT of work to make this look good. There are `@page' commands - and use of `@group ... @end group' in a number of places. If you muck - with anything, it's your responsibility not to break the layout. +1. Use at least texinfo.tex 2014-01-30.15 +2. When using @docbook, if the last line is part of a paragraph, end +it with a space and @c so that the lines won't run together. This is a +quirk of the language / makeinfo, and isn't going to change. @end ignore @c merge the function and variable indexes into the concept index @@ -131,6 +268,10 @@ Some comments on the layout for TeX. @syncodeindex fn cp @syncodeindex vr cp @end ifxml +@ifdocbook +@synindex fn cp +@synindex vr cp +@end ifdocbook @c If "finalout" is commented out, the printed output will show @c black boxes that mark lines that are too long. Thus, it is @@ -142,9 +283,30 @@ Some comments on the layout for TeX. @end iftex @copying -Copyright @copyright{} 1989, 1991, 1992, 1993, 1996, 1997, 1998, 1999, -2000, 2001, 2002, 2003, 2004, 2005, 2007, 2009, 2010, 2011 +@docbook +<para> +“To boldly go where no man has gone before” is a +Registered Trademark of Paramount Pictures Corporation.</para> + +<para>Published by:</para> + +<literallayout class="normal">Free Software Foundation +51 Franklin Street, Fifth Floor +Boston, MA 02110-1301 USA +Phone: +1-617-542-5942 +Fax: +1-617-542-2652 +Email: <email>gnu@@gnu.org</email> +URL: <ulink url="http://www.gnu.org">http://www.gnu.org/</ulink></literallayout> + +<literallayout class="normal">Copyright © 1989, 1991, 1992, 1993, 1996–2005, 2007, 2009–2014 Free Software Foundation, Inc. +All Rights Reserved.</literallayout> +@end docbook + +@ifnotdocbook +Copyright @copyright{} 1989, 1991, 1992, 1993, 1996--2005, 2007, 2009--2015 @* +Free Software Foundation, Inc. +@end ifnotdocbook @sp 2 This is Edition @value{EDITION} of @cite{@value{TITLE}: @value{SUBTITLE}}, @@ -154,19 +316,24 @@ implementation of AWK. Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.3 or any later version published by the Free Software Foundation; with the -Invariant Sections being ``GNU General Public License'', the Front-Cover -texts being (a) (see below), and with the Back-Cover Texts being (b) -(see below). A copy of the license is included in the section entitled +Invariant Sections being ``GNU General Public License'', with the +Front-Cover Texts being ``A GNU Manual'', and with the Back-Cover Texts +as in (a) below. +@ifclear FOR_PRINT +A copy of the license is included in the section entitled ``GNU Free Documentation License''. +@end ifclear +@ifset FOR_PRINT +A copy of the license +may be found on the Internet at +@uref{http://www.gnu.org/software/gawk/manual/html_node/GNU-Free-Documentation-License.html, +the GNU Project's website}. +@end ifset @enumerate a @item -``A GNU Manual'' - -@item -``You have the freedom to -copy and modify this GNU manual. Buying copies from the FSF -supports it in developing GNU and promoting software freedom.'' +The FSF's Back-Cover Text is: ``You have the freedom to +copy and modify this GNU manual.'' @end enumerate @end copying @@ -184,6 +351,7 @@ supports it in developing GNU and promoting software freedom.'' @c during editing and review. @setchapternewpage odd +@shorttitlepage GNU Awk @titlepage @title @value{TITLE} @subtitle @value{SUBTITLE} @@ -191,6 +359,7 @@ supports it in developing GNU and promoting software freedom.'' @subtitle @value{UPDATE-MONTH} @author Arnold D. Robbins +@ifnotdocbook @c Include the Distribution inside the titlepage environment so @c that headings are turned off. Headings on and off do not work. @@ -215,6 +384,7 @@ URL: @uref{http://www.gnu.org/} @* ISBN 1-882114-28-0 @* @sp 2 @insertcopying +@end ifnotdocbook @end titlepage @c Thanks to Bob Chassell for directions on doing dedications. @@ -223,15 +393,13 @@ ISBN 1-882114-28-0 @* @page @w{ } @sp 9 -@center @i{To Miriam, for making me complete.} +@center @i{To my parents, for their love, and for the wonderful example they set for me.} @sp 1 -@center @i{To Chana, for the joy you bring us.} +@center @i{To my wife, Miriam, for making me complete. +Thank you for building your life together with me.} @sp 1 -@center @i{To Rivka, for the exponential increase.} +@center @i{To our children, Chana, Rivka, Nachum, and Malka, for enrichening our lives in innumerable ways.} @sp 1 -@center @i{To Nachum, for the added dimension.} -@sp 1 -@center @i{To Malka, for the new beginning.} @w{ } @page @w{ } @@ -239,6 +407,17 @@ ISBN 1-882114-28-0 @* @headings on @end iftex +@docbook +<dedication> +<para>To my parents, for their love, and for the wonderful +example they set for me.</para> +<para>To my wife Miriam, for making me complete. +Thank you for building your life together with me.</para> +<para>To our children Chana, Rivka, Nachum and Malka, +for enrichening our lives in innumerable ways.</para> +</dedication> +@end docbook + @iftex @headings off @evenheading @thispage@ @ @ @strong{@value{TITLE}} @| @| @@ -247,6 +426,7 @@ ISBN 1-882114-28-0 @* @ifnottex @ifnotxml +@ifnotdocbook @node Top @top General Introduction @c Preface node should come right after the Top @@ -258,12 +438,14 @@ particular records in a file and perform operations upon them. @insertcopying +@end ifnotdocbook @end ifnotxml @end ifnottex @menu -* Foreword:: Some nice words about this +* Foreword3:: Some nice words about this @value{DOCUMENT}. +* Foreword4:: More nice words. * Preface:: What this @value{DOCUMENT} is about; brief history and acknowledgments. * Getting Started:: A basic introduction to using @@ -283,20 +465,24 @@ particular records in a file and perform operations upon them. * Arrays:: The description and use of arrays. Also includes array-oriented control statements. * Functions:: Built-in and user-defined functions. -* Internationalization:: Getting @command{gawk} to speak your - language. -* Advanced Features:: Stuff for advanced users, specific to - @command{gawk}. * Library Functions:: A Library of @command{awk} Functions. * Sample Programs:: Many @command{awk} programs with complete explanations. -* Debugger:: The @code{dgawk} debugger. +* Advanced Features:: Stuff for advanced users, specific to + @command{gawk}. +* Internationalization:: Getting @command{gawk} to speak your + language. +* Debugger:: The @code{gawk} debugger. +* Arbitrary Precision Arithmetic:: Arbitrary precision arithmetic with + @command{gawk}. +* Dynamic Extensions:: Adding new built-in functions to + @command{gawk}. * Language History:: The evolution of the @command{awk} language. * Installation:: Installing @command{gawk} under various operating systems. -* Notes:: Notes about @command{gawk} extensions and - possible future work. +* Notes:: Notes about adding things to @command{gawk} + and possible future work. * Basic Concepts:: A very quick introduction to programming concepts. * Glossary:: An explanation of some unfamiliar terms. @@ -306,460 +492,605 @@ particular records in a file and perform operations upon them. * Index:: Concept and Variable Index. @detailmenu -* History:: The history of @command{gawk} and - @command{awk}. -* Names:: What name to use to find @command{awk}. -* This Manual:: Using this @value{DOCUMENT}. Includes - sample input files that you can use. -* Conventions:: Typographical Conventions. -* Manual History:: Brief history of the GNU project and - this @value{DOCUMENT}. -* How To Contribute:: Helping to save the world. -* Acknowledgments:: Acknowledgments. -* Running gawk:: How to run @command{gawk} programs; - includes command-line syntax. -* One-shot:: Running a short throwaway @command{awk} - program. -* Read Terminal:: Using no input files (input from - terminal instead). -* Long:: Putting permanent @command{awk} - programs in files. -* Executable Scripts:: Making self-contained @command{awk} - programs. -* Comments:: Adding documentation to @command{gawk} - programs. -* Quoting:: More discussion of shell quoting - issues. -* DOS Quoting:: Quoting in Windows Batch Files. -* Sample Data Files:: Sample data files for use in the - @command{awk} programs illustrated in - this @value{DOCUMENT}. -* Very Simple:: A very simple example. -* Two Rules:: A less simple one-line example using - two rules. -* More Complex:: A more complex example. -* Statements/Lines:: Subdividing or combining statements - into lines. -* Other Features:: Other Features of @command{awk}. -* When:: When to use @command{gawk} and when to - use other things. -* Command Line:: How to run @command{awk}. -* Options:: Command-line options and their - meanings. -* Other Arguments:: Input file names and variable - assignments. -* Naming Standard Input:: How to specify standard input with - other files. -* Environment Variables:: The environment variables - @command{gawk} uses. -* AWKPATH Variable:: Searching directories for @command{awk} - programs. -* Other Environment Variables:: The environment variables. -* Exit Status:: @command{gawk}'s exit status. -* Include Files:: Including other files into your - program. -* Obsolete:: Obsolete Options and/or features. -* Undocumented:: Undocumented Options and Features. -* Regexp Usage:: How to Use Regular Expressions. -* Escape Sequences:: How to write nonprinting characters. -* Regexp Operators:: Regular Expression Operators. -* Bracket Expressions:: What can go between @samp{[...]}. -* GNU Regexp Operators:: Operators specific to GNU software. -* Case-sensitivity:: How to do case-insensitive matching. -* Leftmost Longest:: How much text matches. -* Computed Regexps:: Using Dynamic Regexps. -* Records:: Controlling how data is split into - records. -* Fields:: An introduction to fields. -* Nonconstant Fields:: Nonconstant Field Numbers. -* Changing Fields:: Changing the Contents of a Field. -* Field Separators:: The field separator and how to change - it. -* Default Field Splitting:: How fields are normally separated. -* Regexp Field Splitting:: Using regexps as the field separator. -* Single Character Fields:: Making each character a separate field. -* Command Line Field Separator:: Setting @code{FS} from the - command-line. -* Field Splitting Summary:: Some final points and a summary table. -* Constant Size:: Reading constant width data. -* Splitting By Content:: Defining Fields By Content -* Multiple Line:: Reading multi-line records. -* Getline:: Reading files under explicit program - control using the @code{getline} - function. -* Plain Getline:: Using @code{getline} with no arguments. -* Getline/Variable:: Using @code{getline} into a variable. -* Getline/File:: Using @code{getline} from a file. -* Getline/Variable/File:: Using @code{getline} into a variable - from a file. -* Getline/Pipe:: Using @code{getline} from a pipe. -* Getline/Variable/Pipe:: Using @code{getline} into a variable - from a pipe. -* Getline/Coprocess:: Using @code{getline} from a coprocess. -* Getline/Variable/Coprocess:: Using @code{getline} into a variable - from a coprocess. -* Getline Notes:: Important things to know about - @code{getline}. -* Getline Summary:: Summary of @code{getline} Variants. -* Command line directories:: What happens if you put a directory on - the command line. -* Print:: The @code{print} statement. -* Print Examples:: Simple examples of @code{print} - statements. -* Output Separators:: The output separators and how to change - them. -* OFMT:: Controlling Numeric Output With - @code{print}. -* Printf:: The @code{printf} statement. -* Basic Printf:: Syntax of the @code{printf} statement. -* Control Letters:: Format-control letters. -* Format Modifiers:: Format-specification modifiers. -* Printf Examples:: Several examples. -* Redirection:: How to redirect output to multiple - files and pipes. -* Special Files:: File name interpretation in - @command{gawk}. @command{gawk} allows - access to inherited file descriptors. -* Special FD:: Special files for I/O. -* Special Network:: Special files for network - communications. -* Special Caveats:: Things to watch out for. -* Close Files And Pipes:: Closing Input and Output Files and - Pipes. -* Values:: Constants, Variables, and Regular - Expressions. -* Constants:: String, numeric and regexp constants. -* Scalar Constants:: Numeric and string constants. -* Nondecimal-numbers:: What are octal and hex numbers. -* Regexp Constants:: Regular Expression constants. -* Using Constant Regexps:: When and how to use a regexp constant. -* Variables:: Variables give names to values for - later use. -* Using Variables:: Using variables in your programs. -* Assignment Options:: Setting variables on the command-line - and a summary of command-line syntax. - This is an advanced method of input. -* Conversion:: The conversion of strings to numbers - and vice versa. -* All Operators:: @command{gawk}'s operators. -* Arithmetic Ops:: Arithmetic operations (@samp{+}, - @samp{-}, etc.) -* Concatenation:: Concatenating strings. -* Assignment Ops:: Changing the value of a variable or a - field. -* Increment Ops:: Incrementing the numeric value of a - variable. -* Truth Values and Conditions:: Testing for true and false. -* Truth Values:: What is ``true'' and what is ``false''. -* Typing and Comparison:: How variables acquire types and how - this affects comparison of numbers and - strings with @samp{<}, etc. -* Variable Typing:: String type versus numeric type. -* Comparison Operators:: The comparison operators. -* POSIX String Comparison:: String comparison with POSIX rules. -* Boolean Ops:: Combining comparison expressions using - boolean operators @samp{||} (``or''), - @samp{&&} (``and'') and @samp{!} - (``not''). -* Conditional Exp:: Conditional expressions select between - two subexpressions under control of a - third subexpression. -* Function Calls:: A function call is an expression. -* Precedence:: How various operators nest. -* Locales:: How the locale affects things. -* Pattern Overview:: What goes into a pattern. -* Regexp Patterns:: Using regexps as patterns. -* Expression Patterns:: Any expression can be used as a - pattern. -* Ranges:: Pairs of patterns specify record - ranges. -* BEGIN/END:: Specifying initialization and cleanup - rules. -* Using BEGIN/END:: How and why to use BEGIN/END rules. -* I/O And BEGIN/END:: I/O issues in BEGIN/END rules. -* BEGINFILE/ENDFILE:: Two special patterns for advanced - control. -* Empty:: The empty pattern, which matches every - record. -* Using Shell Variables:: How to use shell variables with - @command{awk}. -* Action Overview:: What goes into an action. -* Statements:: Describes the various control - statements in detail. -* If Statement:: Conditionally execute some - @command{awk} statements. -* While Statement:: Loop until some condition is satisfied. -* Do Statement:: Do specified action while looping until - some condition is satisfied. -* For Statement:: Another looping statement, that - provides initialization and increment - clauses. -* Switch Statement:: Switch/case evaluation for conditional - execution of statements based on a - value. -* Break Statement:: Immediately exit the innermost - enclosing loop. -* Continue Statement:: Skip to the end of the innermost - enclosing loop. -* Next Statement:: Stop processing the current input - record. -* Nextfile Statement:: Stop processing the current file. -* Exit Statement:: Stop execution of @command{awk}. -* Built-in Variables:: Summarizes the built-in variables. -* User-modified:: Built-in variables that you change to - control @command{awk}. -* Auto-set:: Built-in variables where @command{awk} - gives you information. -* ARGC and ARGV:: Ways to use @code{ARGC} and - @code{ARGV}. -* Array Basics:: The basics of arrays. -* Array Intro:: Introduction to Arrays -* Reference to Elements:: How to examine one element of an array. -* Assigning Elements:: How to change an element of an array. -* Array Example:: Basic Example of an Array -* Scanning an Array:: A variation of the @code{for} - statement. It loops through the indices - of an array's existing elements. -* Delete:: The @code{delete} statement removes an - element from an array. -* Numeric Array Subscripts:: How to use numbers as subscripts in - @command{awk}. -* Uninitialized Subscripts:: Using Uninitialized variables as - subscripts. -* Multi-dimensional:: Emulating multidimensional arrays in - @command{awk}. -* Multi-scanning:: Scanning multidimensional arrays. -* Arrays of Arrays:: True multidimensional arrays. -* Built-in:: Summarizes the built-in functions. -* Calling Built-in:: How to call built-in functions. -* Numeric Functions:: Functions that work with numbers, - including @code{int()}, @code{sin()} - and @code{rand()}. -* String Functions:: Functions for string manipulation, such - as @code{split()}, @code{match()} and - @code{sprintf()}. -* Gory Details:: More than you want to know about - @samp{\} and @samp{&} with - @code{sub()}, @code{gsub()}, and - @code{gensub()}. -* I/O Functions:: Functions for files and shell commands. -* Time Functions:: Functions for dealing with timestamps. -* Bitwise Functions:: Functions for bitwise operations. -* Type Functions:: Functions for type information. -* I18N Functions:: Functions for string translation. -* User-defined:: Describes User-defined functions in - detail. -* Definition Syntax:: How to write definitions and what they - mean. -* Function Example:: An example function definition and what - it does. -* Function Caveats:: Things to watch out for. -* Calling A Function:: Don't use spaces. -* Variable Scope:: Controlling variable scope. -* Pass By Value/Reference:: Passing parameters. -* Return Statement:: Specifying the value a function - returns. -* Dynamic Typing:: How variable types can change at - runtime. -* Indirect Calls:: Choosing the function to call at - runtime. -* I18N and L10N:: Internationalization and Localization. -* Explaining gettext:: How GNU @code{gettext} works. -* Programmer i18n:: Features for the programmer. -* Translator i18n:: Features for the translator. -* String Extraction:: Extracting marked strings. -* Printf Ordering:: Rearranging @code{printf} arguments. -* I18N Portability:: @command{awk}-level portability issues. -* I18N Example:: A simple i18n example. -* Gawk I18N:: @command{gawk} is also - internationalized. -* Nondecimal Data:: Allowing nondecimal input data. -* Array Sorting:: Facilities for controlling array - traversal and sorting arrays. -* Controlling Array Traversal:: How to use PROCINFO["sorted_in"]. -* Controlling Scanning With A Function:: Using a function to control scanning. -* Controlling Scanning:: Controlling the order in which arrays - are scanned. -* Array Sorting Functions:: How to use @code{asort()} and - @code{asorti()}. -* Two-way I/O:: Two-way communications with another - process. -* TCP/IP Networking:: Using @command{gawk} for network - programming. -* Profiling:: Profiling your @command{awk} programs. -* Library Names:: How to best name private global - variables in library functions. -* General Functions:: Functions that are of general use. -* Strtonum Function:: A replacement for the built-in - @code{strtonum()} function. -* Assert Function:: A function for assertions in - @command{awk} programs. -* Round Function:: A function for rounding if - @code{sprintf()} does not do it - correctly. -* Cliff Random Function:: The Cliff Random Number Generator. -* Ordinal Functions:: Functions for using characters as - numbers and vice versa. -* Join Function:: A function to join an array into a - string. -* Gettimeofday Function:: A function to get formatted times. -* Data File Management:: Functions for managing command-line - data files. -* Filetrans Function:: A function for handling data file - transitions. -* Rewind Function:: A function for rereading the current - file. -* File Checking:: Checking that data files are readable. -* Empty Files:: Checking for zero-length files. -* Ignoring Assigns:: Treating assignments as file names. -* Getopt Function:: A function for processing command-line - arguments. -* Passwd Functions:: Functions for getting user information. -* Group Functions:: Functions for getting group - information. -* Walking Arrays:: A function to walk arrays of arrays. -* Running Examples:: How to run these examples. -* Clones:: Clones of common utilities. -* Cut Program:: The @command{cut} utility. -* Egrep Program:: The @command{egrep} utility. -* Id Program:: The @command{id} utility. -* Split Program:: The @command{split} utility. -* Tee Program:: The @command{tee} utility. -* Uniq Program:: The @command{uniq} utility. -* Wc Program:: The @command{wc} utility. -* Miscellaneous Programs:: Some interesting @command{awk} - programs. -* Dupword Program:: Finding duplicated words in a document. -* Alarm Program:: An alarm clock. -* Translate Program:: A program similar to the @command{tr} - utility. -* Labels Program:: Printing mailing labels. -* Word Sorting:: A program to produce a word usage - count. -* History Sorting:: Eliminating duplicate entries from a - history file. -* Extract Program:: Pulling out programs from Texinfo - source files. -* Simple Sed:: A Simple Stream Editor. -* Igawk Program:: A wrapper for @command{awk} that - includes files. -* Anagram Program:: Finding anagrams from a dictionary. -* Signature Program:: People do amazing things with too much - time on their hands. -* Debugging:: Introduction to @command{dgawk}. -* Debugging Concepts:: Debugging In General. -* Debugging Terms:: Additional Debugging Concepts. -* Awk Debugging:: Awk Debugging. -* Sample dgawk session:: Sample @command{dgawk} session. -* dgawk invocation:: @command{dgawk} Invocation. -* Finding The Bug:: Finding The Bug. -* List of Debugger Commands:: Main @command{dgawk} Commands. -* Breakpoint Control:: Control of breakpoints. -* Dgawk Execution Control:: Control of execution. -* Viewing And Changing Data:: Viewing and changing data. -* Dgawk Stack:: Dealing with the stack. -* Dgawk Info:: Obtaining information about the program - and the debugger state. -* Miscellaneous Dgawk Commands:: Miscellaneous Commands. -* Readline Support:: Readline Support. -* Dgawk Limitations:: Limitations and future plans. -* V7/SVR3.1:: The major changes between V7 and System - V Release 3.1. -* SVR4:: Minor changes between System V Releases - 3.1 and 4. -* POSIX:: New features from the POSIX standard. -* BTL:: New features from Brian Kernighan's - version of @command{awk}. -* POSIX/GNU:: The extensions in @command{gawk} not in - POSIX @command{awk}. -* Common Extensions:: Common Extensions Summary. -* Ranges and Locales:: How locales used to affect regexp - ranges. -* Contributors:: The major contributors to - @command{gawk}. -* Gawk Distribution:: What is in the @command{gawk} - distribution. -* Getting:: How to get the distribution. -* Extracting:: How to extract the distribution. -* Distribution contents:: What is in the distribution. -* Unix Installation:: Installing @command{gawk} under various - versions of Unix. -* Quick Installation:: Compiling @command{gawk} under Unix. -* Additional Configuration Options:: Other compile-time options. -* Configuration Philosophy:: How it's all supposed to work. -* Non-Unix Installation:: Installation on Other Operating - Systems. -* PC Installation:: Installing and Compiling @command{gawk} - on MS-DOS and OS/2. -* PC Binary Installation:: Installing a prepared distribution. -* PC Compiling:: Compiling @command{gawk} for MS-DOS, - Windows32, and OS/2. -* PC Testing:: Testing @command{gawk} on PC systems. -* PC Using:: Running @command{gawk} on MS-DOS, - Windows32 and OS/2. -* Cygwin:: Building and running @command{gawk} for - Cygwin. -* MSYS:: Using @command{gawk} In The MSYS - Environment. -* VMS Installation:: Installing @command{gawk} on VMS. -* VMS Compilation:: How to compile @command{gawk} under - VMS. -* VMS Installation Details:: How to install @command{gawk} under - VMS. -* VMS Running:: How to run @command{gawk} under VMS. -* VMS Old Gawk:: An old version comes with some VMS - systems. -* Bugs:: Reporting Problems and Bugs. -* Other Versions:: Other freely available @command{awk} - implementations. -* Compatibility Mode:: How to disable certain @command{gawk} - extensions. -* Additions:: Making Additions To @command{gawk}. -* Accessing The Source:: Accessing the Git repository. -* Adding Code:: Adding code to the main body of - @command{gawk}. -* New Ports:: Porting @command{gawk} to a new - operating system. -* Dynamic Extensions:: Adding new built-in functions to - @command{gawk}. -* Internals:: A brief look at some @command{gawk} - internals. -* Plugin License:: A note about licensing. -* Sample Library:: A example of new functions. -* Internal File Description:: What the new functions will do. -* Internal File Ops:: The code for internal file operations. -* Using Internal File Ops:: How to use an external extension. -* Future Extensions:: New features that may be implemented - one day. -* Basic High Level:: The high level view. -* Basic Data Typing:: A very quick intro to data types. -* Floating Point Issues:: Stuff to know about floating-point - numbers. -* String Conversion Precision:: The String Value Can Lie. -* Unexpected Results:: Floating Point Numbers Are Not Abstract - Numbers. -* POSIX Floating Point Problems:: Standards Versus Existing Practice. +* History:: The history of @command{gawk} and + @command{awk}. +* Names:: What name to use to find + @command{awk}. +* This Manual:: Using this @value{DOCUMENT}. Includes + sample input files that you can use. +* Conventions:: Typographical Conventions. +* Manual History:: Brief history of the GNU project and + this @value{DOCUMENT}. +* How To Contribute:: Helping to save the world. +* Acknowledgments:: Acknowledgments. +* Running gawk:: How to run @command{gawk} programs; + includes command-line syntax. +* One-shot:: Running a short throwaway + @command{awk} program. +* Read Terminal:: Using no input files (input from the + keyboard instead). +* Long:: Putting permanent @command{awk} + programs in files. +* Executable Scripts:: Making self-contained @command{awk} + programs. +* Comments:: Adding documentation to @command{gawk} + programs. +* Quoting:: More discussion of shell quoting + issues. +* DOS Quoting:: Quoting in Windows Batch Files. +* Sample Data Files:: Sample data files for use in the + @command{awk} programs illustrated in + this @value{DOCUMENT}. +* Very Simple:: A very simple example. +* Two Rules:: A less simple one-line example using + two rules. +* More Complex:: A more complex example. +* Statements/Lines:: Subdividing or combining statements + into lines. +* Other Features:: Other Features of @command{awk}. +* When:: When to use @command{gawk} and when to + use other things. +* Intro Summary:: Summary of the introduction. +* Command Line:: How to run @command{awk}. +* Options:: Command-line options and their + meanings. +* Other Arguments:: Input file names and variable + assignments. +* Naming Standard Input:: How to specify standard input with + other files. +* Environment Variables:: The environment variables + @command{gawk} uses. +* AWKPATH Variable:: Searching directories for + @command{awk} programs. +* AWKLIBPATH Variable:: Searching directories for + @command{awk} shared libraries. +* Other Environment Variables:: The environment variables. +* Exit Status:: @command{gawk}'s exit status. +* Include Files:: Including other files into your + program. +* Loading Shared Libraries:: Loading shared libraries into your + program. +* Obsolete:: Obsolete Options and/or features. +* Undocumented:: Undocumented Options and Features. +* Invoking Summary:: Invocation summary. +* Regexp Usage:: How to Use Regular Expressions. +* Escape Sequences:: How to write nonprinting characters. +* Regexp Operators:: Regular Expression Operators. +* Bracket Expressions:: What can go between @samp{[...]}. +* Leftmost Longest:: How much text matches. +* Computed Regexps:: Using Dynamic Regexps. +* GNU Regexp Operators:: Operators specific to GNU software. +* Case-sensitivity:: How to do case-insensitive matching. +* Regexp Summary:: Regular expressions summary. +* Records:: Controlling how data is split into + records. +* awk split records:: How standard @command{awk} splits + records. +* gawk split records:: How @command{gawk} splits records. +* Fields:: An introduction to fields. +* Nonconstant Fields:: Nonconstant Field Numbers. +* Changing Fields:: Changing the Contents of a Field. +* Field Separators:: The field separator and how to change + it. +* Default Field Splitting:: How fields are normally separated. +* Regexp Field Splitting:: Using regexps as the field separator. +* Single Character Fields:: Making each character a separate + field. +* Command Line Field Separator:: Setting @code{FS} from the command + line. +* Full Line Fields:: Making the full line be a single + field. +* Field Splitting Summary:: Some final points and a summary table. +* Constant Size:: Reading constant width data. +* Splitting By Content:: Defining Fields By Content +* Multiple Line:: Reading multiline records. +* Getline:: Reading files under explicit program + control using the @code{getline} + function. +* Plain Getline:: Using @code{getline} with no + arguments. +* Getline/Variable:: Using @code{getline} into a variable. +* Getline/File:: Using @code{getline} from a file. +* Getline/Variable/File:: Using @code{getline} into a variable + from a file. +* Getline/Pipe:: Using @code{getline} from a pipe. +* Getline/Variable/Pipe:: Using @code{getline} into a variable + from a pipe. +* Getline/Coprocess:: Using @code{getline} from a coprocess. +* Getline/Variable/Coprocess:: Using @code{getline} into a variable + from a coprocess. +* Getline Notes:: Important things to know about + @code{getline}. +* Getline Summary:: Summary of @code{getline} Variants. +* Read Timeout:: Reading input with a timeout. +* Command-line directories:: What happens if you put a directory on + the command line. +* Input Summary:: Input summary. +* Input Exercises:: Exercises. +* Print:: The @code{print} statement. +* Print Examples:: Simple examples of @code{print} + statements. +* Output Separators:: The output separators and how to + change them. +* OFMT:: Controlling Numeric Output With + @code{print}. +* Printf:: The @code{printf} statement. +* Basic Printf:: Syntax of the @code{printf} statement. +* Control Letters:: Format-control letters. +* Format Modifiers:: Format-specification modifiers. +* Printf Examples:: Several examples. +* Redirection:: How to redirect output to multiple + files and pipes. +* Special FD:: Special files for I/O. +* Special Files:: File name interpretation in + @command{gawk}. @command{gawk} allows + access to inherited file descriptors. +* Other Inherited Files:: Accessing other open files with + @command{gawk}. +* Special Network:: Special files for network + communications. +* Special Caveats:: Things to watch out for. +* Close Files And Pipes:: Closing Input and Output Files and + Pipes. +* Output Summary:: Output summary. +* Output Exercises:: Exercises. +* Values:: Constants, Variables, and Regular + Expressions. +* Constants:: String, numeric and regexp constants. +* Scalar Constants:: Numeric and string constants. +* Nondecimal-numbers:: What are octal and hex numbers. +* Regexp Constants:: Regular Expression constants. +* Using Constant Regexps:: When and how to use a regexp constant. +* Variables:: Variables give names to values for + later use. +* Using Variables:: Using variables in your programs. +* Assignment Options:: Setting variables on the command line + and a summary of command-line syntax. + This is an advanced method of input. +* Conversion:: The conversion of strings to numbers + and vice versa. +* Strings And Numbers:: How @command{awk} Converts Between + Strings And Numbers. +* Locale influences conversions:: How the locale may affect conversions. +* All Operators:: @command{gawk}'s operators. +* Arithmetic Ops:: Arithmetic operations (@samp{+}, + @samp{-}, etc.) +* Concatenation:: Concatenating strings. +* Assignment Ops:: Changing the value of a variable or a + field. +* Increment Ops:: Incrementing the numeric value of a + variable. +* Truth Values and Conditions:: Testing for true and false. +* Truth Values:: What is ``true'' and what is + ``false''. +* Typing and Comparison:: How variables acquire types and how + this affects comparison of numbers and + strings with @samp{<}, etc. +* Variable Typing:: String type versus numeric type. +* Comparison Operators:: The comparison operators. +* POSIX String Comparison:: String comparison with POSIX rules. +* Boolean Ops:: Combining comparison expressions using + boolean operators @samp{||} (``or''), + @samp{&&} (``and'') and @samp{!} + (``not''). +* Conditional Exp:: Conditional expressions select between + two subexpressions under control of a + third subexpression. +* Function Calls:: A function call is an expression. +* Precedence:: How various operators nest. +* Locales:: How the locale affects things. +* Expressions Summary:: Expressions summary. +* Pattern Overview:: What goes into a pattern. +* Regexp Patterns:: Using regexps as patterns. +* Expression Patterns:: Any expression can be used as a + pattern. +* Ranges:: Pairs of patterns specify record + ranges. +* BEGIN/END:: Specifying initialization and cleanup + rules. +* Using BEGIN/END:: How and why to use BEGIN/END rules. +* I/O And BEGIN/END:: I/O issues in BEGIN/END rules. +* BEGINFILE/ENDFILE:: Two special patterns for advanced + control. +* Empty:: The empty pattern, which matches every + record. +* Using Shell Variables:: How to use shell variables with + @command{awk}. +* Action Overview:: What goes into an action. +* Statements:: Describes the various control + statements in detail. +* If Statement:: Conditionally execute some + @command{awk} statements. +* While Statement:: Loop until some condition is + satisfied. +* Do Statement:: Do specified action while looping + until some condition is satisfied. +* For Statement:: Another looping statement, that + provides initialization and increment + clauses. +* Switch Statement:: Switch/case evaluation for conditional + execution of statements based on a + value. +* Break Statement:: Immediately exit the innermost + enclosing loop. +* Continue Statement:: Skip to the end of the innermost + enclosing loop. +* Next Statement:: Stop processing the current input + record. +* Nextfile Statement:: Stop processing the current file. +* Exit Statement:: Stop execution of @command{awk}. +* Built-in Variables:: Summarizes the predefined variables. +* User-modified:: Built-in variables that you change to + control @command{awk}. +* Auto-set:: Built-in variables where @command{awk} + gives you information. +* ARGC and ARGV:: Ways to use @code{ARGC} and + @code{ARGV}. +* Pattern Action Summary:: Patterns and Actions summary. +* Array Basics:: The basics of arrays. +* Array Intro:: Introduction to Arrays +* Reference to Elements:: How to examine one element of an + array. +* Assigning Elements:: How to change an element of an array. +* Array Example:: Basic Example of an Array +* Scanning an Array:: A variation of the @code{for} + statement. It loops through the + indices of an array's existing + elements. +* Controlling Scanning:: Controlling the order in which arrays + are scanned. +* Numeric Array Subscripts:: How to use numbers as subscripts in + @command{awk}. +* Uninitialized Subscripts:: Using Uninitialized variables as + subscripts. +* Delete:: The @code{delete} statement removes an + element from an array. +* Multidimensional:: Emulating multidimensional arrays in + @command{awk}. +* Multiscanning:: Scanning multidimensional arrays. +* Arrays of Arrays:: True multidimensional arrays. +* Arrays Summary:: Summary of arrays. +* Built-in:: Summarizes the built-in functions. +* Calling Built-in:: How to call built-in functions. +* Numeric Functions:: Functions that work with numbers, + including @code{int()}, @code{sin()} + and @code{rand()}. +* String Functions:: Functions for string manipulation, + such as @code{split()}, @code{match()} + and @code{sprintf()}. +* Gory Details:: More than you want to know about + @samp{\} and @samp{&} with + @code{sub()}, @code{gsub()}, and + @code{gensub()}. +* I/O Functions:: Functions for files and shell + commands. +* Time Functions:: Functions for dealing with timestamps. +* Bitwise Functions:: Functions for bitwise operations. +* Type Functions:: Functions for type information. +* I18N Functions:: Functions for string translation. +* User-defined:: Describes User-defined functions in + detail. +* Definition Syntax:: How to write definitions and what they + mean. +* Function Example:: An example function definition and + what it does. +* Function Caveats:: Things to watch out for. +* Calling A Function:: Don't use spaces. +* Variable Scope:: Controlling variable scope. +* Pass By Value/Reference:: Passing parameters. +* Return Statement:: Specifying the value a function + returns. +* Dynamic Typing:: How variable types can change at + runtime. +* Indirect Calls:: Choosing the function to call at + runtime. +* Functions Summary:: Summary of functions. +* Library Names:: How to best name private global + variables in library functions. +* General Functions:: Functions that are of general use. +* Strtonum Function:: A replacement for the built-in + @code{strtonum()} function. +* Assert Function:: A function for assertions in + @command{awk} programs. +* Round Function:: A function for rounding if + @code{sprintf()} does not do it + correctly. +* Cliff Random Function:: The Cliff Random Number Generator. +* Ordinal Functions:: Functions for using characters as + numbers and vice versa. +* Join Function:: A function to join an array into a + string. +* Getlocaltime Function:: A function to get formatted times. +* Readfile Function:: A function to read an entire file at + once. +* Shell Quoting:: A function to quote strings for the + shell. +* Data File Management:: Functions for managing command-line + data files. +* Filetrans Function:: A function for handling data file + transitions. +* Rewind Function:: A function for rereading the current + file. +* File Checking:: Checking that data files are readable. +* Empty Files:: Checking for zero-length files. +* Ignoring Assigns:: Treating assignments as file names. +* Getopt Function:: A function for processing command-line + arguments. +* Passwd Functions:: Functions for getting user + information. +* Group Functions:: Functions for getting group + information. +* Walking Arrays:: A function to walk arrays of arrays. +* Library Functions Summary:: Summary of library functions. +* Library Exercises:: Exercises. +* Running Examples:: How to run these examples. +* Clones:: Clones of common utilities. +* Cut Program:: The @command{cut} utility. +* Egrep Program:: The @command{egrep} utility. +* Id Program:: The @command{id} utility. +* Split Program:: The @command{split} utility. +* Tee Program:: The @command{tee} utility. +* Uniq Program:: The @command{uniq} utility. +* Wc Program:: The @command{wc} utility. +* Miscellaneous Programs:: Some interesting @command{awk} + programs. +* Dupword Program:: Finding duplicated words in a + document. +* Alarm Program:: An alarm clock. +* Translate Program:: A program similar to the @command{tr} + utility. +* Labels Program:: Printing mailing labels. +* Word Sorting:: A program to produce a word usage + count. +* History Sorting:: Eliminating duplicate entries from a + history file. +* Extract Program:: Pulling out programs from Texinfo + source files. +* Simple Sed:: A Simple Stream Editor. +* Igawk Program:: A wrapper for @command{awk} that + includes files. +* Anagram Program:: Finding anagrams from a dictionary. +* Signature Program:: People do amazing things with too much + time on their hands. +* Programs Summary:: Summary of programs. +* Programs Exercises:: Exercises. +* Nondecimal Data:: Allowing nondecimal input data. +* Array Sorting:: Facilities for controlling array + traversal and sorting arrays. +* Controlling Array Traversal:: How to use PROCINFO["sorted_in"]. +* Array Sorting Functions:: How to use @code{asort()} and + @code{asorti()}. +* Two-way I/O:: Two-way communications with another + process. +* TCP/IP Networking:: Using @command{gawk} for network + programming. +* Profiling:: Profiling your @command{awk} programs. +* Advanced Features Summary:: Summary of advanced features. +* I18N and L10N:: Internationalization and Localization. +* Explaining gettext:: How GNU @command{gettext} works. +* Programmer i18n:: Features for the programmer. +* Translator i18n:: Features for the translator. +* String Extraction:: Extracting marked strings. +* Printf Ordering:: Rearranging @code{printf} arguments. +* I18N Portability:: @command{awk}-level portability + issues. +* I18N Example:: A simple i18n example. +* Gawk I18N:: @command{gawk} is also + internationalized. +* I18N Summary:: Summary of I18N stuff. +* Debugging:: Introduction to @command{gawk} + debugger. +* Debugging Concepts:: Debugging in General. +* Debugging Terms:: Additional Debugging Concepts. +* Awk Debugging:: Awk Debugging. +* Sample Debugging Session:: Sample debugging session. +* Debugger Invocation:: How to Start the Debugger. +* Finding The Bug:: Finding the Bug. +* List of Debugger Commands:: Main debugger commands. +* Breakpoint Control:: Control of Breakpoints. +* Debugger Execution Control:: Control of Execution. +* Viewing And Changing Data:: Viewing and Changing Data. +* Execution Stack:: Dealing with the Stack. +* Debugger Info:: Obtaining Information about the + Program and the Debugger State. +* Miscellaneous Debugger Commands:: Miscellaneous Commands. +* Readline Support:: Readline support. +* Limitations:: Limitations and future plans. +* Debugging Summary:: Debugging summary. +* Computer Arithmetic:: A quick intro to computer math. +* Math Definitions:: Defining terms used. +* MPFR features:: The MPFR features in @command{gawk}. +* FP Math Caution:: Things to know. +* Inexactness of computations:: Floating point math is not exact. +* Inexact representation:: Numbers are not exactly represented. +* Comparing FP Values:: How to compare floating point values. +* Errors accumulate:: Errors get bigger as they go. +* Getting Accuracy:: Getting more accuracy takes some work. +* Try To Round:: Add digits and round. +* Setting precision:: How to set the precision. +* Setting the rounding mode:: How to set the rounding mode. +* Arbitrary Precision Integers:: Arbitrary Precision Integer Arithmetic + with @command{gawk}. +* POSIX Floating Point Problems:: Standards Versus Existing Practice. +* Floating point summary:: Summary of floating point discussion. +* Extension Intro:: What is an extension. +* Plugin License:: A note about licensing. +* Extension Mechanism Outline:: An outline of how it works. +* Extension API Description:: A full description of the API. +* Extension API Functions Introduction:: Introduction to the API functions. +* General Data Types:: The data types. +* Memory Allocation Functions:: Functions for allocating memory. +* Constructor Functions:: Functions for creating values. +* Registration Functions:: Functions to register things with + @command{gawk}. +* Extension Functions:: Registering extension functions. +* Exit Callback Functions:: Registering an exit callback. +* Extension Version String:: Registering a version string. +* Input Parsers:: Registering an input parser. +* Output Wrappers:: Registering an output wrapper. +* Two-way processors:: Registering a two-way processor. +* Printing Messages:: Functions for printing messages. +* Updating @code{ERRNO}:: Functions for updating @code{ERRNO}. +* Requesting Values:: How to get a value. +* Accessing Parameters:: Functions for accessing parameters. +* Symbol Table Access:: Functions for accessing global + variables. +* Symbol table by name:: Accessing variables by name. +* Symbol table by cookie:: Accessing variables by ``cookie''. +* Cached values:: Creating and using cached values. +* Array Manipulation:: Functions for working with arrays. +* Array Data Types:: Data types for working with arrays. +* Array Functions:: Functions for working with arrays. +* Flattening Arrays:: How to flatten arrays. +* Creating Arrays:: How to create and populate arrays. +* Extension API Variables:: Variables provided by the API. +* Extension Versioning:: API Version information. +* Extension API Informational Variables:: Variables providing information about + @command{gawk}'s invocation. +* Extension API Boilerplate:: Boilerplate code for using the API. +* Finding Extensions:: How @command{gawk} finds compiled + extensions. +* Extension Example:: Example C code for an extension. +* Internal File Description:: What the new functions will do. +* Internal File Ops:: The code for internal file operations. +* Using Internal File Ops:: How to use an external extension. +* Extension Samples:: The sample extensions that ship with + @code{gawk}. +* Extension Sample File Functions:: The file functions sample. +* Extension Sample Fnmatch:: An interface to @code{fnmatch()}. +* Extension Sample Fork:: An interface to @code{fork()} and + other process functions. +* Extension Sample Inplace:: Enabling in-place file editing. +* Extension Sample Ord:: Character to value to character + conversions. +* Extension Sample Readdir:: An interface to @code{readdir()}. +* Extension Sample Revout:: Reversing output sample output + wrapper. +* Extension Sample Rev2way:: Reversing data sample two-way + processor. +* Extension Sample Read write array:: Serializing an array to a file. +* Extension Sample Readfile:: Reading an entire file into a string. +* Extension Sample Time:: An interface to @code{gettimeofday()} + and @code{sleep()}. +* Extension Sample API Tests:: Tests for the API. +* gawkextlib:: The @code{gawkextlib} project. +* Extension summary:: Extension summary. +* Extension Exercises:: Exercises. +* V7/SVR3.1:: The major changes between V7 and + System V Release 3.1. +* SVR4:: Minor changes between System V + Releases 3.1 and 4. +* POSIX:: New features from the POSIX standard. +* BTL:: New features from Brian Kernighan's + version of @command{awk}. +* POSIX/GNU:: The extensions in @command{gawk} not + in POSIX @command{awk}. +* Feature History:: The history of the features in + @command{gawk}. +* Common Extensions:: Common Extensions Summary. +* Ranges and Locales:: How locales used to affect regexp + ranges. +* Contributors:: The major contributors to + @command{gawk}. +* History summary:: History summary. +* Gawk Distribution:: What is in the @command{gawk} + distribution. +* Getting:: How to get the distribution. +* Extracting:: How to extract the distribution. +* Distribution contents:: What is in the distribution. +* Unix Installation:: Installing @command{gawk} under + various versions of Unix. +* Quick Installation:: Compiling @command{gawk} under Unix. +* Shell Startup Files:: Shell convenience functions. +* Additional Configuration Options:: Other compile-time options. +* Configuration Philosophy:: How it's all supposed to work. +* Non-Unix Installation:: Installation on Other Operating + Systems. +* PC Installation:: Installing and Compiling + @command{gawk} on MS-DOS and OS/2. +* PC Binary Installation:: Installing a prepared distribution. +* PC Compiling:: Compiling @command{gawk} for MS-DOS, + Windows32, and OS/2. +* PC Testing:: Testing @command{gawk} on PC systems. +* PC Using:: Running @command{gawk} on MS-DOS, + Windows32 and OS/2. +* Cygwin:: Building and running @command{gawk} + for Cygwin. +* MSYS:: Using @command{gawk} In The MSYS + Environment. +* VMS Installation:: Installing @command{gawk} on VMS. +* VMS Compilation:: How to compile @command{gawk} under + VMS. +* VMS Dynamic Extensions:: Compiling @command{gawk} dynamic + extensions on VMS. +* VMS Installation Details:: How to install @command{gawk} under + VMS. +* VMS Running:: How to run @command{gawk} under VMS. +* VMS GNV:: The VMS GNV Project. +* VMS Old Gawk:: An old version comes with some VMS + systems. +* Bugs:: Reporting Problems and Bugs. +* Other Versions:: Other freely available @command{awk} + implementations. +* Installation summary:: Summary of installation. +* Compatibility Mode:: How to disable certain @command{gawk} + extensions. +* Additions:: Making Additions To @command{gawk}. +* Accessing The Source:: Accessing the Git repository. +* Adding Code:: Adding code to the main body of + @command{gawk}. +* New Ports:: Porting @command{gawk} to a new + operating system. +* Derived Files:: Why derived files are kept in the Git + repository. +* Future Extensions:: New features that may be implemented + one day. +* Implementation Limitations:: Some limitations of the + implementation. +* Extension Design:: Design notes about the extension API. +* Old Extension Problems:: Problems with the old mechanism. +* Extension New Mechanism Goals:: Goals for the new mechanism. +* Extension Other Design Decisions:: Some other design decisions. +* Extension Future Growth:: Some room for future growth. +* Old Extension Mechanism:: Some compatibility for old extensions. +* Notes summary:: Summary of implementation notes. +* Basic High Level:: The high level view. +* Basic Data Typing:: A very quick intro to data types. @end detailmenu @end menu @c dedication for Info file @ifinfo -@center To Miriam, for making me complete. -@sp 1 -@center To Chana, for the joy you bring us. +To my parents, for their love, and for the wonderful +example they set for me. @sp 1 -@center To Rivka, for the exponential increase. +To my wife Miriam, for making me complete. +Thank you for building your life together with me. @sp 1 -@center To Nachum, for the added dimension. -@sp 1 -@center To Malka, for the new beginning. +To our children Chana, Rivka, Nachum and Malka, +for enrichening our lives in innumerable ways. @end ifinfo @summarycontents @contents -@node Foreword -@unnumbered Foreword +@node Foreword3 +@unnumbered Foreword to the Third Edition + +@c This bit is post-processed by a script which turns the chapter +@c tag into a preface tag, and moves this stuff to before the title. +@c Bleah. +@docbook + <prefaceinfo> + <author> + <firstname>Michael</firstname> + <surname>Brennan</surname> + <!-- can't put mawk into command tags. sigh. --> + <affiliation><jobtitle>Author of mawk</jobtitle></affiliation> + </author> + <date>March 2001</date> + </prefaceinfo> +@end docbook Arnold Robbins and I are good friends. We were introduced @c 11 years ago @@ -769,21 +1100,23 @@ The circumstances started a couple of years earlier. I was working at a new job and noticed an unplugged Unix computer sitting in the corner. No one knew how to use it, and neither did I. However, -a couple of days later it was running, and +a couple of days later, it was running, and I was @code{root} and the one-and-only user. That day, I began the transition from statistician to Unix programmer. On one of many trips to the library or bookstore in search of -books on Unix, I found the gray AWK book, a.k.a.@: Aho, Kernighan and -Weinberger, @cite{The AWK Programming Language}, Addison-Wesley, -1988. AWK's simple programming paradigm---find a pattern in the +books on Unix, I found the gray AWK book, a.k.a.@: +Alfred V.@: Aho, Brian W.@: Kernighan, and +Peter J.@: Weinberger's @cite{The AWK Programming Language} (Addison-Wesley, +1988). @command{awk}'s simple programming paradigm---find a pattern in the input and then perform an action---often reduced complex or tedious -data manipulations to few lines of code. I was excited to try my +data manipulations to a few lines of code. I was excited to try my hand at programming in AWK. Alas, the @command{awk} on my computer was a limited version of the -language described in the AWK book. I discovered that my computer -had ``old @command{awk}'' and the AWK book described ``new @command{awk}.'' +language described in the gray book. I discovered that my computer +had ``old @command{awk}'' and the book described +``new @command{awk}.'' I learned that this was typical; the old version refused to step aside or relinquish its name. If a system had a new @command{awk}, it was invariably called @command{nawk}, and few systems had it. @@ -801,7 +1134,7 @@ My Unix system started out unplugged from the wall; it certainly was not plugged into a network. So, oblivious to the existence of @command{gawk} and the Unix community in general, and desiring a new @command{awk}, I wrote my own, called @command{mawk}. -Before I was finished I knew about @command{gawk}, +Before I was finished, I knew about @command{gawk}, but it was too late to stop, so I eventually posted to a @code{comp.sources} newsgroup. @@ -810,7 +1143,7 @@ from Arnold introducing himself. He suggested we share design and algorithms and attached a draft of the POSIX standard so that I could update @command{mawk} to support language extensions added -after publication of the AWK book. +after publication of @cite{The AWK Programming Language}. Frankly, if our roles had been reversed, I would not have been so open and we probably would @@ -829,7 +1162,7 @@ standard. On the other hand, the novice AWK programmer can study a wealth of practical programs that emphasize the power of AWK's basic idioms: -data driven control-flow, pattern matching with regular expressions, +data-driven control flow, pattern matching with regular expressions, and associative arrays. Those looking for something new can try out @command{gawk}'s interface to network protocols via special @file{/inet} files. @@ -837,7 +1170,7 @@ interface to network protocols via special @file{/inet} files. The programs in this book make clear that an AWK program is typically much smaller and faster to develop than a counterpart written in C. -Consequently, there is often a payoff to prototype an +Consequently, there is often a payoff to prototyping an algorithm or design in AWK to get it running quickly and expose problems early. Often, the interpreted performance is adequate and the AWK prototype becomes the product. @@ -845,21 +1178,37 @@ and the AWK prototype becomes the product. The new @command{pgawk} (profiling @command{gawk}), produces program execution counts. I recently experimented with an algorithm that for -@math{n} lines of input, exhibited +@ifnotdocbook +@math{n} +@end ifnotdocbook +@ifdocbook +@i{n} +@end ifdocbook +lines of input, exhibited @tex $\sim\! Cn^2$ @end tex @ifnottex +@ifnotdocbook ~ C n^2 +@end ifnotdocbook @end ifnottex +@docbook +<emphasis>∼ Cn<superscript>2</superscript></emphasis> @c +@end docbook performance, while theory predicted @tex $\sim\! Cn\log n$ @end tex @ifnottex +@ifnotdocbook ~ C n log n +@end ifnotdocbook @end ifnottex +@docbook +<emphasis>∼ Cn log n</emphasis> @c +@end docbook behavior. A few minutes poring over the @file{awkprof.out} profile pinpointed the problem to a single line of code. @command{pgawk} is a welcome addition to @@ -869,11 +1218,69 @@ Arnold has distilled over a decade of experience writing and using AWK programs, and developing @command{gawk}, into this book. If you use AWK or want to learn how, then read this book. +@ifnotdocbook +@cindex Brennan, Michael +@display +Michael Brennan +Author of @command{mawk} +March 2001 +@end display +@end ifnotdocbook + +@node Foreword4 +@unnumbered Foreword to the Fourth Edition + +@c This bit is post-processed by a script which turns the chapter +@c tag into a preface tag, and moves this stuff to before the title. +@c Bleah. +@docbook + <prefaceinfo> + <author> + <firstname>Michael</firstname> + <surname>Brennan</surname> + <!-- can't put mawk into command tags. sigh. --> + <affiliation><jobtitle>Author of mawk</jobtitle></affiliation> + </author> + <date>October 2014</date> + </prefaceinfo> +@end docbook + +Some things don't change. Thirteen years ago I wrote: +``If you use AWK or want to learn how, then read this book.'' +True then, and still true today. + +Learning to use a programming language is about more than mastering the +syntax. One needs to acquire an understanding of how to use the +features of the language to solve practical programming problems. +A focus of this book is many examples that show how to use AWK. + +Some things do change. Our computers are much faster and have more memory. +Consequently, speed and storage inefficiencies of a high-level language +matter less. Prototyping in AWK and then rewriting in C for performance +reasons happens less, because more often the prototype is fast enough. + +Of course, there are computing operations that are best done in C or C++. +With @command{gawk} 4.1 and later, you do not have to choose between writing +your program in AWK or in C/C++. You can write most of your +program in AWK and the aspects that require C/C++ capabilities can be written +in C/C++, and then the pieces glued together when the @command{gawk} module loads +the C/C++ module as a dynamic plug-in. +@c Chapter 16 +@ref{Dynamic Extensions}, +has all the +details, and, as expected, many examples to help you learn the ins and outs. + +I enjoy programming in AWK and had fun (re)reading this book. +I think you will too. + +@ifnotdocbook +@cindex Brennan, Michael @display Michael Brennan Author of @command{mawk} -March, 2001 +October 2014 @end display +@end ifnotdocbook @node Preface @unnumbered Preface @@ -882,29 +1289,39 @@ March, 2001 @c @c 12/2000: Chuck wants the preface & intro combined. -Several kinds of tasks occur repeatedly -when working with text files. -You might want to extract certain lines and discard the rest. -Or you may need to make changes wherever certain patterns appear, -but leave the rest of the file alone. -Writing single-use programs for these tasks in languages such as C, C++, -or Java is time-consuming and inconvenient. -Such jobs are often easier with @command{awk}. -The @command{awk} utility interprets a special-purpose programming language -that makes it easy to handle simple data-reformatting jobs. +@c This bit is post-processed by a script which turns the chapter +@c tag into a preface tag, and moves this stuff to before the title. +@c Bleah. +@docbook + <prefaceinfo> + <author> + <firstname>Arnold</firstname> + <surname>Robbins</surname> + <affiliation><jobtitle>Nof Ayalon</jobtitle></affiliation> + <affiliation><jobtitle>Israel</jobtitle></affiliation> + </author> + <date>December 2014</date> + </prefaceinfo> +@end docbook + +Several kinds of tasks occur repeatedly when working with text files. +You might want to extract certain lines and discard the rest. Or you +may need to make changes wherever certain patterns appear, but leave the +rest of the file alone. Such jobs are often easy with @command{awk}. +The @command{awk} utility interprets a special-purpose programming +language that makes it easy to handle simple data-reformatting jobs. The GNU implementation of @command{awk} is called @command{gawk}; if you -invoke it with the proper options or environment variables -(@pxref{Options}), it is fully -compatible with -the POSIX@footnote{The 2008 POSIX standard can be found online at -@url{http://www.opengroup.org/onlinepubs/9699919799/}.} +invoke it with the proper options or environment variables, +it is fully compatible with +the POSIX@footnote{The 2008 POSIX standard is accessible online at +@w{@url{http://www.opengroup.org/onlinepubs/9699919799/}.}} specification of the @command{awk} language and with the Unix version of @command{awk} maintained by Brian Kernighan. This means that all properly written @command{awk} programs should work with @command{gawk}. -Thus, we usually don't distinguish between @command{gawk} and other +So most of the time, we don't distinguish between @command{gawk} and other @command{awk} implementations. @cindex @command{awk}, POSIX and, See Also POSIX @command{awk} @@ -913,9 +1330,9 @@ Thus, we usually don't distinguish between @command{gawk} and other @cindex @command{gawk}, @command{awk} and @cindex @command{awk}, @command{gawk} and @cindex @command{awk}, uses for -Using @command{awk} allows you to: +Using @command{awk} you can: -@itemize @bullet +@itemize @value{BULLET} @item Manage small, personal databases @@ -926,7 +1343,7 @@ Generate reports Validate data @item -Produce indexes and perform other document preparation tasks +Produce indexes and perform other document-preparation tasks @item Experiment with algorithms that you can adapt later to other computer @@ -940,7 +1357,7 @@ In addition, @command{gawk} provides facilities that make it easy to: -@itemize @bullet +@itemize @value{BULLET} @item Extract bits and pieces of data for processing @@ -949,11 +1366,17 @@ Sort data @item Perform simple network communications + +@item +Profile and debug @command{awk} programs + +@item +Extend the language with functions written in C or C++ @end itemize This @value{DOCUMENT} teaches you about the @command{awk} language and how you can use it effectively. You should already be familiar with basic -system commands, such as @command{cat} and @command{ls},@footnote{These commands +system commands, such as @command{cat} and @command{ls},@footnote{These utilities are available on POSIX-compliant systems, as well as on traditional Unix-based systems. If you are using some other operating system, you still need to be familiar with the ideas of I/O redirection and pipes.} as well as basic shell @@ -964,15 +1387,20 @@ Implementations of the @command{awk} language are available for many different computing environments. This @value{DOCUMENT}, while describing the @command{awk} language in general, also describes the particular implementation of @command{awk} called @command{gawk} (which stands for -``GNU awk''). @command{gawk} runs on a broad range of Unix systems, -ranging from Intel@registeredsymbol{}-architecture PC-based computers -up through large-scale systems, -such as Crays. @command{gawk} has also been ported to Mac OS X, -Microsoft Windows (all versions) and OS/2 PCs, -and VMS. -(Some other, obsolete systems to which @command{gawk} was once ported -are no longer supported and the code for those systems -has been removed.) +``GNU @command{awk}''). @command{gawk} runs on a broad range of Unix systems, +ranging from Intel-architecture PC-based computers +up through large-scale systems. +@command{gawk} has also been ported to Mac OS X, +Microsoft Windows +@ifset FOR_PRINT +(all versions), +@end ifset +@ifclear FOR_PRINT +(all versions) and OS/2 PCs, +@end ifclear +and OpenVMS.@footnote{Some other, obsolete systems to which @command{gawk} +was once ported are no longer supported and the code for those systems +has been removed.} @menu * History:: The history of @command{gawk} and @@ -991,27 +1419,54 @@ has been removed.) @unnumberedsec History of @command{awk} and @command{gawk} @cindex recipe for a programming language @cindex programming language, recipe for -@center Recipe For A Programming Language +@cindex sidebar, Recipe for a Programming Language +@ifdocbook +@docbook +<sidebar><title>Recipe for a Programming Language</title> +@end docbook + @multitable {2 parts} {1 part @code{egrep}} {1 part @code{snobol}} @item @tab 1 part @code{egrep} @tab 1 part @code{snobol} @item @tab 2 parts @code{ed} @tab 3 parts C @end multitable -@quotation Blend all parts well using @code{lex} and @code{yacc}. Document minimally and release. After eight years, add another part @code{egrep} and two more parts C. Document very well and release. -@end quotation + +@docbook +</sidebar> +@end docbook +@end ifdocbook + +@ifnotdocbook +@cartouche +@center @b{Recipe for a Programming Language} + + + +@multitable {2 parts} {1 part @code{egrep}} {1 part @code{snobol}} +@item @tab 1 part @code{egrep} @tab 1 part @code{snobol} +@item @tab 2 parts @code{ed} @tab 3 parts C +@end multitable + +Blend all parts well using @code{lex} and @code{yacc}. +Document minimally and release. + +After eight years, add another part @code{egrep} and two +more parts C. Document very well and release. +@end cartouche +@end ifnotdocbook @cindex Aho, Alfred @cindex Weinberger, Peter @cindex Kernighan, Brian @cindex @command{awk}, history of The name @command{awk} comes from the initials of its designers: Alfred V.@: -Aho, Peter J.@: Weinberger and Brian W.@: Kernighan. The original version of +Aho, Peter J.@: Weinberger, and Brian W.@: Kernighan. The original version of @command{awk} was written in 1977 at AT&T Bell Laboratories. In 1985, a new version made the programming language more powerful, introducing user-defined functions, multiple input @@ -1022,22 +1477,22 @@ The version in System V Release 4 (1989) added some new features and cleaned up the behavior in some of the ``dark corners'' of the language. The specification for @command{awk} in the POSIX Command Language and Utilities standard further clarified the language. -Both the @command{gawk} designers and the original Bell Laboratories @command{awk} -designers provided feedback for the POSIX specification. +Both the @command{gawk} designers and the original @command{awk} designers at Bell Laboratories +provided feedback for the POSIX specification. @cindex Rubin, Paul @cindex Fenlason, Jay @cindex Trueman, David -Paul Rubin wrote the GNU implementation, @command{gawk}, in 1986. +Paul Rubin wrote @command{gawk} in 1986. Jay Fenlason completed it, with advice from Richard Stallman. John Woods contributed parts of the code as well. In 1988 and 1989, David Trueman, with help from me, thoroughly reworked @command{gawk} for compatibility with the newer @command{awk}. Circa 1994, I became the primary maintainer. Current development focuses on bug fixes, -performance improvements, standards compliance, and occasionally, new features. +performance improvements, standards compliance, and, occasionally, new features. -In May of 1997, J@"urgen Kahrs felt the need for network access +In May 1997, J@"urgen Kahrs felt the need for network access from @command{awk}, and with a little help from me, set about adding features to do this for @command{gawk}. At that time, he also wrote the bulk of @@ -1048,41 +1503,39 @@ with @command{gawk} @value{PVERSION} 3.1. John Haque rewrote the @command{gawk} internals, in the process providing an @command{awk}-level debugger. This version became available as -@command{gawk} @value{PVERSION} 4.0, in 2011. +@command{gawk} @value{PVERSION} 4.0 in 2011. -@xref{Contributors}, -for a complete list of those who made important contributions to @command{gawk}. +@DBXREF{Contributors} +for a full list of those who have made important contributions to @command{gawk}. @node Names -@section A Rose by Any Other Name +@unnumberedsec A Rose by Any Other Name @cindex @command{awk}, new vs.@: old The @command{awk} language has evolved over the years. Full details are provided in @ref{Language History}. The language described in this @value{DOCUMENT} -is often referred to as ``new @command{awk}'' (@command{nawk}). +is often referred to as ``new @command{awk}.'' +By analogy, the original version of @command{awk} is +referred to as ``old @command{awk}.'' -@cindex @command{awk}, versions of -Because of this, there are systems with multiple -versions of @command{awk}. -Some systems have an @command{awk} utility that implements the -original version of the @command{awk} language and a @command{nawk} utility -for the new version. -Others have an @command{oawk} version for the ``old @command{awk}'' -language and plain @command{awk} for the new one. Still others only -have one version, which is usually the new one.@footnote{Often, these systems -use @command{gawk} for their @command{awk} implementation!} - -@cindex @command{nawk} utility -@cindex @command{oawk} utility -All in all, this makes it difficult for you to know which version of -@command{awk} you should run when writing your programs. The best advice -we can give here is to check your local documentation. Look for @command{awk}, -@command{oawk}, and @command{nawk}, as well as for @command{gawk}. -It is likely that you already -have some version of new @command{awk} on your system, which is what -you should use when running your programs. (Of course, if you're reading -this @value{DOCUMENT}, chances are good that you have @command{gawk}!) +Today, on most systems, when you run the @command{awk} utility +you get some version of new @command{awk}.@footnote{Only +Solaris systems still use an old @command{awk} for the +default @command{awk} utility. A more modern @command{awk} lives in +@file{/usr/xpg6/bin} on these systems.} If your system's standard +@command{awk} is the old one, you will see something like this +if you try the test program: + +@example +$ @kbd{awk 1 /dev/null} +@error{} awk: syntax error near line 1 +@error{} awk: bailing out near line 1 +@end example + +@noindent +In this case, you should find a version of new @command{awk}, +or just install @command{gawk}! Throughout this @value{DOCUMENT}, whenever we refer to a language feature that should be available in any complete implementation of POSIX @command{awk}, @@ -1090,7 +1543,7 @@ we simply use the term @command{awk}. When referring to a feature that is specific to the GNU implementation, we use the term @command{gawk}. @node This Manual -@section Using This Book +@unnumberedsec Using This Book @cindex @command{awk}, terms describing The term @command{awk} refers to a particular program as well as to the language you @@ -1100,7 +1553,7 @@ and the program ``the @command{awk} utility.'' This @value{DOCUMENT} explains both how to write programs in the @command{awk} language and how to run the @command{awk} utility. -The term @dfn{@command{awk} program} refers to a program written by you in +The term ``@command{awk} program'' refers to a program written by you in the @command{awk} programming language. @cindex @command{gawk}, @command{awk} and @@ -1110,52 +1563,79 @@ Primarily, this @value{DOCUMENT} explains the features of @command{awk} as defined in the POSIX standard. It does so in the context of the @command{gawk} implementation. While doing so, it also attempts to describe important differences between @command{gawk} -and other @command{awk} implementations.@footnote{All such differences +and other @command{awk} +@ifclear FOR_PRINT +implementations.@footnote{All such differences appear in the index under the entry ``differences in @command{awk} and @command{gawk}.''} -Finally, any @command{gawk} features that are not in -the POSIX standard for @command{awk} are noted. +@end ifclear +@ifset FOR_PRINT +implementations. +@end ifset +Finally, it notes any @command{gawk} features that are not in +the POSIX standard for @command{awk}. @ifnotinfo This @value{DOCUMENT} has the difficult task of being both a tutorial and a reference. If you are a novice, feel free to skip over details that seem too complex. You should also ignore the many cross-references; they are for the -expert user and for the online Info and HTML versions of the document. +expert user and for the Info and +@uref{http://www.gnu.org/software/gawk/manual/, HTML} +versions of the @value{DOCUMENT}. @end ifnotinfo -There are -subsections labeled -as @strong{Advanced Notes} +There are sidebars scattered throughout the @value{DOCUMENT}. They add a more complete explanation of points that are relevant, but not likely to be of interest on first reading. -All appear in the index, under the heading ``advanced features.'' +@ifclear FOR_PRINT +All appear in the index, under the heading ``sidebar.'' +@end ifclear Most of the time, the examples use complete @command{awk} programs. Some of the more advanced sections show only the part of the @command{awk} -program that illustrates the concept currently being described. +program that illustrates the concept being described. -While this @value{DOCUMENT} is aimed principally at people who have not been +Although this @value{DOCUMENT} is aimed principally at people who have not been exposed to @command{awk}, there is a lot of information here that even the @command{awk} expert should find useful. In particular, the description of POSIX @command{awk} and the example programs in -@ref{Library Functions}, and in +@ref{Library Functions}, and +@ifnotdocbook +in +@end ifnotdocbook @ref{Sample Programs}, should be of interest. +This @value{DOCUMENT} is split into several parts, as follows: + +@c FULLXREF ON + +@itemize @value{BULLET} +@item +Part I describes the @command{awk} language and the @command{gawk} program in detail. +It starts with the basics, and continues through all of the features of @command{awk}. +It contains the following chapters: + +@c nested +@itemize @value{MINUS} +@item @ref{Getting Started}, provides the essentials you need to know to begin using @command{awk}. +@item @ref{Invoking Gawk}, describes how to run @command{gawk}, the meaning of its command-line options, and how it finds @command{awk} program source files. +@item @ref{Regexp}, introduces regular expressions in general, and in particular the flavors supported by POSIX @command{awk} and @command{gawk}. +@item @ref{Reading Files}, describes how @command{awk} reads your data. It introduces the concepts of records and fields, as well @@ -1163,55 +1643,106 @@ as the @code{getline} command. I/O redirection is first described here. Network I/O is also briefly introduced here. +@item @ref{Printing}, describes how @command{awk} programs can produce output with @code{print} and @code{printf}. +@item @ref{Expressions}, describes expressions, which are the basic building blocks for getting most things done in a program. +@item @ref{Patterns and Actions}, describes how to write patterns for matching records, actions for -doing something when a record is matched, and the built-in variables +doing something when a record is matched, and the predefined variables @command{awk} and @command{gawk} use. +@item @ref{Arrays}, -covers @command{awk}'s one-and-only data structure: associative arrays. -Deleting array elements and whole arrays is also described, as well as -sorting arrays in @command{gawk}. It also describes how @command{gawk} -provides arrays of arrays. +covers @command{awk}'s one-and-only data structure: the associative array. +Deleting array elements and whole arrays is described, as well as +sorting arrays in @command{gawk}. The @value{CHAPTER} also describes how +@command{gawk} provides arrays of arrays. +@item @ref{Functions}, -describes the built-in functions @command{awk} and -@command{gawk} provide, as well as how to define -your own functions. +describes the built-in functions @command{awk} and @command{gawk} provide, +as well as how to define your own functions. It also discusses how +@command{gawk} lets you call functions indirectly. +@end itemize -@ref{Internationalization}, -describes special features in @command{gawk} for translating program -messages into different languages at runtime. +@item +Part II shows how to use @command{awk} and @command{gawk} for problem solving. +There is lots of code here for you to read and learn from. +This part contains the following chapters: + +@c nested +@itemize @value{MINUS} +@item +@ref{Library Functions}, provides a number of functions meant to +be used from main @command{awk} programs. + +@item +@ref{Sample Programs}, +provides many sample @command{awk} programs. +@end itemize + +Reading these two chapters allows you to see @command{awk} +solving real problems. +@item +Part III focuses on features specific to @command{gawk}. +It contains the following chapters: + +@c nested +@itemize @value{MINUS} +@item @ref{Advanced Features}, -describes a number of @command{gawk}-specific advanced features. +describes a number of advanced features. Of particular note -are the abilities to have two-way communications with another process, +are the abilities to control the order of array traversal, +have two-way communications with another process, perform TCP/IP networking, and profile your @command{awk} programs. -@ref{Library Functions}, and -@ref{Sample Programs}, -provide many sample @command{awk} programs. -Reading them allows you to see @command{awk} -solving real problems. +@item +@ref{Internationalization}, +describes special features for translating program +messages into different languages at runtime. + +@item +@ref{Debugger}, describes the @command{gawk} debugger. + +@item +@ref{Arbitrary Precision Arithmetic}, +describes advanced arithmetic facilities. -@ref{Debugger}, describes the @command{awk} debugger, -@command{dgawk}. +@item +@ref{Dynamic Extensions}, describes how to add new variables and +functions to @command{gawk} by writing extensions in C or C++. +@end itemize + +@item +@ifclear FOR_PRINT +Part IV provides the appendices, the Glossary, and two licenses that cover +the @command{gawk} source code and this @value{DOCUMENT}, respectively. +It contains the following appendices: +@end ifclear +@ifset FOR_PRINT +Part IV provides the following appendices, +including the GNU General Public License: +@end ifset +@itemize @value{MINUS} +@item @ref{Language History}, describes how the @command{awk} language has evolved since -its first release to present. It also describes how @command{gawk} +its first release to the present. It also describes how @command{gawk} has acquired features over time. +@item @ref{Installation}, describes how to get @command{gawk}, how to compile it on POSIX-compatible systems, @@ -1219,35 +1750,85 @@ and how to compile and use it on different non-POSIX systems. It also describes how to report bugs in @command{gawk} and where to get other freely available @command{awk} implementations. +@end itemize + +@ifset FOR_PRINT +@itemize @value{MINUS} +@item +@ref{Copying}, +presents the license that covers the @command{gawk} source code. +@end itemize + +The version of this @value{DOCUMENT} distributed with @command{gawk} +contains additional appendices and other end material. +To save space, we have omitted them from the +printed edition. You may find them online, as follows: + +@itemize @value{BULLET} +@item +@uref{http://www.gnu.org/software/gawk/manual/html_node/Notes.html, +The appendix on implementation notes} +describes how to disable @command{gawk}'s extensions, how to contribute +new code to @command{gawk}, where to find information on some possible +future directions for @command{gawk} development, and the design decisions +behind the extension API. +@item +@uref{http://www.gnu.org/software/gawk/manual/html_node/Basic-Concepts.html, +The appendix on basic concepts} +provides some very cursory background material for those who +are completely unfamiliar with computer programming. + +@item +@uref{http://www.gnu.org/software/gawk/manual/html_node/Glossary.html, +The Glossary} +defines most, if not all, of the significant terms used +throughout the @value{DOCUMENT}. If you find terms that you aren't familiar with, +try looking them up here. + +@item +@uref{http://www.gnu.org/software/gawk/manual/html_node/GNU-Free-Documentation-License.html, +The GNU FDL} +is the license that covers this @value{DOCUMENT}. +@end itemize + +Some of the chapters have exercise sections; these have also been +omitted from the print edition but are available online. +@end ifset + +@ifclear FOR_PRINT +@itemize @value{MINUS} +@item @ref{Notes}, describes how to disable @command{gawk}'s extensions, as well as how to contribute new code to @command{gawk}, -how to write extension libraries, and some possible -future directions for @command{gawk} development. +and some possible future directions for @command{gawk} development. +@item @ref{Basic Concepts}, provides some very cursory background material for those who are completely unfamiliar with computer programming. -Also centralized there is a discussion of some of the issues -surrounding floating-point numbers. -The -@ref{Glossary}, -defines most, if not all, the significant terms used -throughout the book. -If you find terms that you aren't familiar with, try looking them up here. +The @ref{Glossary}, defines most, if not all, of the significant terms used +throughout the @value{DOCUMENT}. If you find terms that you aren't familiar with, +try looking them up here. +@item @ref{Copying}, and @ref{GNU Free Documentation License}, present the licenses that cover the @command{gawk} source code and this @value{DOCUMENT}, respectively. +@end itemize +@end ifclear +@end itemize + +@c FULLXREF OFF @node Conventions -@section Typographical Conventions +@unnumberedsec Typographical Conventions @cindex Texinfo -This @value{DOCUMENT} is written in @uref{http://texinfo.org, Texinfo}, +This @value{DOCUMENT} is written in @uref{http://www.gnu.org/software/texinfo/, Texinfo}, the GNU documentation formatting language. A single Texinfo source file is used to produce both the printed and online versions of the documentation. @@ -1259,12 +1840,19 @@ are slightly different than in other books you may have read. This @value{SECTION} briefly documents the typographical conventions used in Texinfo. @end ifinfo -Examples you would type at the command-line are preceded by the common +Examples you would type at the command line are preceded by the common shell primary and secondary prompts, @samp{$} and @samp{>}. Input that you type is shown @kbd{like this}. +@c 8/2014: @print{} is stripped from the texi to make docbook. +@ifclear FOR_PRINT Output from the command is preceded by the glyph ``@print{}''. This typically represents the command's standard output. -Error messages, and other output on the command's standard error, are preceded +@end ifclear +@ifset FOR_PRINT +Output from the command, usually its standard output, appears +@code{like this}. +@end ifset +Error messages and other output on the command's standard error are preceded by the glyph ``@error{}''. For example: @example @@ -1289,17 +1877,31 @@ Finally, @value{FN}s are indicated like this: @file{/path/to/ourfile}. Characters that you type at the keyboard look @kbd{like this}. In particular, there are special characters called ``control characters.'' These are characters that you type by holding down both the @kbd{CONTROL} key and -another key, at the same time. For example, a @kbd{@value{CTL}-d} is typed +another key, at the same time. For example, a @kbd{Ctrl-d} is typed by first pressing and holding the @kbd{CONTROL} key, next -pressing the @kbd{d} key and finally releasing both keys. +pressing the @kbd{d} key, and finally releasing both keys. + +For the sake of brevity, throughout this @value{DOCUMENT}, we refer to +Brian Kernighan's version of @command{awk} as ``BWK @command{awk}.'' +(@DBXREF{Other Versions} for information on his and other versions.) + +@ifset FOR_PRINT +@quotation NOTE +Notes of interest look like this. +@end quotation + +@quotation CAUTION +Cautionary or warning notes look like this. +@end quotation +@end ifset @c fakenode --- for prepinfo -@subsubheading Dark Corners +@unnumberedsubsec Dark Corners @cindex Kernighan, Brian @quotation -@i{Dark corners are basically fractal --- no matter how much -you illuminate, there's always a smaller but darker one.}@* -Brian Kernighan +@i{Dark corners are basically fractal---no matter how much +you illuminate, there's always a smaller but darker one.} +@author Brian Kernighan @end quotation @cindex d.c., See dark corner @@ -1313,18 +1915,25 @@ the picture of a flashlight in the margin, as shown here. @value{DARKCORNER} @end iftex @ifnottex -``(d.c.)''. +``(d.c.).'' @end ifnottex +@ifclear FOR_PRINT They also appear in the index under the heading ``dark corner.'' +@end ifclear -As noted by the opening quote, though, any -coverage of dark corners -is, by definition, incomplete. +But, as noted by the opening quote, any coverage of dark +corners is by definition incomplete. +@cindex c.e., See common extensions Extensions to the standard @command{awk} language that are supported by more than one @command{awk} implementation are marked +@ifclear FOR_PRINT ``@value{COMMONEXT},'' and listed in the index under ``common extensions'' and ``extensions, common.'' +@end ifclear +@ifset FOR_PRINT +``@value{COMMONEXT}'' for ``common extension.'' +@end ifset @node Manual History @unnumberedsec The GNU Project and This Book @@ -1341,25 +1950,28 @@ Emacs editor. GNU Emacs is the most widely used version of Emacs today. @cindex GPL (General Public License) @cindex General Public License, See GPL @cindex documentation, online -The GNU@footnote{GNU stands for ``GNU's not Unix.''} +The GNU@footnote{GNU stands for ``GNU's Not Unix.''} Project is an ongoing effort on the part of the Free Software Foundation to create a complete, freely distributable, POSIX-compliant computing environment. -The FSF uses the ``GNU General Public License'' (GPL) to ensure that -their software's -source code is always available to the end user. A -copy of the GPL is included +The FSF uses the GNU General Public License (GPL) to ensure that +its software's +source code is always available to the end user. +@ifclear FOR_PRINT +A copy of the GPL is included @ifnotinfo in this @value{DOCUMENT} @end ifnotinfo for your reference (@pxref{Copying}). +@end ifclear The GPL applies to the C language source code for @command{gawk}. To find out more about the FSF and the GNU Project online, see @uref{http://www.gnu.org, the GNU Project's home page}. This @value{DOCUMENT} may also be read from -@uref{http://www.gnu.org/software/gawk/manual/, their web site}. +@uref{http://www.gnu.org/software/gawk/manual/, GNU's website}. +@ifclear FOR_PRINT A shell, an editor (Emacs), highly portable optimizing C, C++, and Objective-C compilers, a symbolic debugger and dozens of large and small utilities (such as @command{gawk}), have all been completed and are @@ -1370,109 +1982,84 @@ stage of development. @cindex Linux @cindex GNU/Linux @cindex operating systems, BSD-based -@cindex Alpha (DEC) Until the GNU operating system is more fully developed, you should consider using GNU/Linux, a freely distributable, Unix-like operating -system for Intel@registeredsymbol{}, +system for Intel, Power Architecture, Sun SPARC, IBM S/390, and other systems.@footnote{The terminology ``GNU/Linux'' is explained in the @ref{Glossary}.} Many GNU/Linux distributions are available for download from the Internet. - -(There are numerous other freely available, Unix-like operating systems -based on the -Berkeley Software Distribution, and some of them use recent versions -of @command{gawk} for their versions of @command{awk}. -@uref{http://www.netbsd.org, NetBSD}, -@uref{http://www.freebsd.org, FreeBSD}, -and -@uref{http://www.openbsd.org, OpenBSD} -are three of the most popular ones, but there -are others.) +@end ifclear @ifnotinfo The @value{DOCUMENT} you are reading is actually free---at least, the information in it is free to anyone. The machine-readable -source code for the @value{DOCUMENT} comes with @command{gawk}; anyone -may take this @value{DOCUMENT} to a copying machine and make as many -copies as they like. (Take a moment to check the Free Documentation +source code for the @value{DOCUMENT} comes with @command{gawk}. +@ifclear FOR_PRINT +(Take a moment to check the Free Documentation License in @ref{GNU Free Documentation License}.) +@end ifclear @end ifnotinfo -@ignore -@cindex Close, Diane -The @value{DOCUMENT} itself has gone through several previous, -preliminary editions. -Paul Rubin wrote the very first draft of @cite{The GAWK Manual}; -it was around 40 pages in size. -Diane Close and Richard Stallman improved it, yielding the -version which I started working with in the fall of 1988. -It was around 90 pages long and barely described the original, ``old'' -version of @command{awk}. After substantial revision, the first version of -the @cite{The GAWK Manual} to be released was Edition 0.11 Beta in -October of 1989. The manual then underwent more substantial revision -for Edition 0.13 of December 1991. -David Trueman, Pat Rankin and Michal Jaegermann contributed sections -of the manual for Edition 0.13. -That edition was published by the -FSF as a bound book early in 1992. Since then there were several -minor revisions, notably Edition 0.14 of November 1992 that was published -by the FSF in January of 1993 and Edition 0.16 of August 1993. - -Edition 1.0 of @cite{GAWK: The GNU Awk User's Guide} represented a significant re-working -of @cite{The GAWK Manual}, with much additional material. -The FSF and I agreed that I was now the primary author. -@c I also felt that the manual needed a more descriptive title. - -In January 1996, SSC published Edition 1.0 under the title @cite{Effective AWK Programming}. -In February 1997, they published Edition 1.0.3 which had minor changes -as a ``second edition.'' -In 1999, the FSF published this same version as Edition 2 -of @cite{GAWK: The GNU Awk User's Guide}. - -Edition @value{EDITION} maintains the basic structure of Edition 1.0, -but with significant additional material, reflecting the host of new features -in @command{gawk} @value{PVERSION} @value{VERSION}. -Of particular note is -@ref{Array Sorting}, -@ref{Bitwise Functions}, -@ref{Internationalization}, -@ref{Advanced Features}, -and -@ref{Dynamic Extensions}. -@end ignore - @cindex Close, Diane -The @value{DOCUMENT} itself has gone through a number of previous editions. +The @value{DOCUMENT} itself has gone through multiple previous editions. Paul Rubin wrote the very first draft of @cite{The GAWK Manual}; -it was around 40 pages in size. +it was around 40 pages long. Diane Close and Richard Stallman improved it, yielding a version that was -around 90 pages long and barely described the original, ``old'' +around 90 pages and barely described the original, ``old'' version of @command{awk}. I started working with that version in the fall of 1988. As work on it progressed, the FSF published several preliminary versions (numbered 0.@var{x}). -In 1996, Edition 1.0 was released with @command{gawk} 3.0.0. +In 1996, edition 1.0 was released with @command{gawk} 3.0.0. The FSF published the first two editions under the title @cite{The GNU Awk User's Guide}. +@ifset FOR_PRINT +SSC published two editions of the @value{DOCUMENT} under the +title @cite{Effective awk Programming}, and O'Reilly published +the third edition in 2001. +@end ifset This edition maintains the basic structure of the previous editions. -For Edition 4.0, the content has been thoroughly reviewed -and updated. All references to versions prior to 4.0 have been -removed. -Of significant note for this edition is @ref{Debugger}. - -@cite{@value{TITLE}} will undoubtedly continue to evolve. -An electronic version -comes with the @command{gawk} distribution from the FSF. -If you find an error in this @value{DOCUMENT}, please report it! -@xref{Bugs}, for information on submitting -problem reports electronically. +For FSF edition 4.0, the content was thoroughly reviewed and updated. All +references to @command{gawk} versions prior to 4.0 were removed. +Of significant note for that edition was the addition of @ref{Debugger}. + +For FSF edition +@ifclear FOR_PRINT +@value{EDITION}, +@end ifclear +@ifset FOR_PRINT +@value{EDITION} +(the fourth edition as published by O'Reilly), +@end ifset +the content has been reorganized into parts, +and the major new additions are @ref{Arbitrary Precision Arithmetic}, +and @ref{Dynamic Extensions}. + +This @value{DOCUMENT} will undoubtedly continue to evolve. If you +find an error in the @value{DOCUMENT}, please report it! @DBXREF{Bugs} +for information on submitting problem reports electronically. + +@ifset FOR_PRINT +@c fakenode --- for prepinfo +@unnumberedsec How to Stay Current + +You may have a newer version of @command{gawk} than the +one described here. To find out what has changed, +you should first look at the @file{NEWS} file in the @command{gawk} +distribution, which provides a high-level summary of the changes in +each release. +You can then look at the @uref{http://www.gnu.org/software/gawk/manual/, +online version} of this @value{DOCUMENT} to read about any new features. +@end ifset + +@ifclear FOR_PRINT @node How To Contribute @unnumberedsec How to Contribute @@ -1489,20 +2076,26 @@ However, I found that I could not dedicate enough time to managing contributed code: the archive did not grow and the domain went unused for several years. -Fortunately, late in 2008, a volunteer took on the task of setting up -an @command{awk}-related web site---@uref{http://awk.info}---and did a very +Late in 2008, a volunteer took on the task of setting up +an @command{awk}-related website---@uref{http://awk.info}---and did a very nice job. If you have written an interesting @command{awk} program, or have written a @command{gawk} extension that you would like to share with the rest of the world, please see @uref{http://awk.info/?contribute} for how to -contribute it to the web site. +contribute it to the website. + +@ignore +As of this writing, this website is in search of a maintainer; please +contact me if you are interested. +@end ignore @ignore Other links: http://www.reddit.com/r/linux/comments/dtect/composing_music_in_awk/ @end ignore +@end ifclear @node Acknowledgments @unnumberedsec Acknowledgments @@ -1513,7 +2106,7 @@ The initial draft of @cite{The GAWK Manual} had the following acknowledgments: Many people need to be thanked for their assistance in producing this manual. Jay Fenlason contributed many ideas and sample programs. Richard Mlynarik and Robert Chassell gave helpful comments on drafts of this -manual. The paper @cite{A Supplemental Document for @command{awk}} by John W.@: +manual. The paper @cite{A Supplemental Document for AWK} by John W.@: Pierce of the Chemistry Department at UC San Diego, pinpointed several issues relevant both to @command{awk} implementation and to this manual, that would otherwise have escaped us. @@ -1524,12 +2117,18 @@ I would like to acknowledge Richard M.@: Stallman, for his vision of a better world and for his courage in founding the FSF and starting the GNU Project. +@ifclear FOR_PRINT Earlier editions of this @value{DOCUMENT} had the following acknowledgements: +@end ifclear +@ifset FOR_PRINT +The previous edition of this @value{DOCUMENT} had +the following acknowledgements: +@end ifset @quotation The following people (in alphabetical order) provided helpful comments on various -versions of this book, +versions of this book: Rick Adams, Dr.@: Nelson H.F. Beebe, Karl Berry, @@ -1557,7 +2156,7 @@ Robert J.@: Chassell provided much valuable advice on the use of Texinfo. He also deserves special thanks for convincing me @emph{not} to title this @value{DOCUMENT} -@cite{How To Gawk Politely}. +@cite{How to Gawk Politely}. Karl Berry helped significantly with the @TeX{} part of Texinfo. @cindex Hartholz, Marshall @@ -1588,64 +2187,91 @@ The intrepid members of the GNITS mailing list, and most notably Ulrich Drepper, provided invaluable help and feedback for the design of the internationalization features. -Chuck Toporek, Mary Sheehan, and Claire Coutier of O'Reilly & Associates contributed +Chuck Toporek, Mary Sheehan, and Claire Cloutier of O'Reilly & Associates contributed significant editorial help for this @value{DOCUMENT} for the 3.1 release of @command{gawk}. @end quotation -@cindex Beebe, Nelson +@cindex Beebe, Nelson H.F.@: @cindex Buening, Andreas +@cindex Collado, Manuel @cindex Colombo, Antonio @cindex Davies, Stephen @cindex Deifik, Scott -@cindex DuBois, John +@cindex Demaille, Akim @cindex Hankerson, Darrel -@cindex Haque, John @cindex Jaegermann, Michal @cindex Kahrs, J@"urgen @cindex Kasal, Stepan +@cindex Malmberg, John @cindex Pitts, Dave +@cindex Ramey, Chet @cindex Rankin, Pat @cindex Schorr, Andrew @cindex Vinschen, Corinna -@cindex Wallin, Anders @cindex Zaretskii, Eli + Dr.@: Nelson Beebe, Andreas Buening, +Dr.@: Manuel Collado, Antonio Colombo, Stephen Davies, Scott Deifik, -John H. DuBois III, +Akim Demaille, Darrel Hankerson, Michal Jaegermann, J@"urgen Kahrs, -Dave Pitts, Stepan Kasal, +John Malmberg, +Dave Pitts, +Chet Ramey, Pat Rankin, Andrew Schorr, Corinna Vinschen, -Anders Wallin, and Eli Zaretskii (in alphabetical order) -make up the current -@command{gawk} ``crack portability team.'' Without their hard work and -help, @command{gawk} would not be nearly the fine program it is today. It -has been and continues to be a pleasure working with this team of fine -people. - -John Haque contributed the modifications to convert @command{gawk} -into a byte-code interpreter, including the debugger. Stephen Davies -contributed to the effort to bring the byte-code changes into the mainstream -code base. -Efraim Yawitz contributed the initial text of @ref{Debugger}. +make up the current @command{gawk} ``crack portability team.'' Without +their hard work and help, @command{gawk} would not be nearly the robust, +portable program it is today. It has been and continues to be a pleasure +working with this team of fine people. + +Notable code and documentation contributions were made by +a number of people. @DBXREF{Contributors} for the full list. + +@ifset FOR_PRINT +@cindex Oram, Andy +Thanks to Andy Oram of O'Reilly Media for initiating +the fourth edition and for his support during the work. +Thanks to Jasmine Kwityn for her copyediting work. +@end ifset + +Thanks to Michael Brennan for the Forewords. + +@cindex Duman, Patrice +@cindex Berry, Karl +Thanks to Patrice Dumas for the new @command{makeinfo} program. +Thanks to Karl Berry, who continues to work to keep +the Texinfo markup language sane. @cindex Kernighan, Brian -I would like to thank Brian Kernighan for invaluable assistance during the -testing and debugging of @command{gawk}, and for ongoing +@cindex Brennan, Michael +@cindex Day, Robert P.J.@: +Robert P.J.@: Day, Michael Brennan, and Brian Kernighan kindly acted as +reviewers for the 2015 edition of this @value{DOCUMENT}. Their feedback +helped improve the final work. + +I would also like to thank Brian Kernighan for his invaluable assistance during the +testing and debugging of @command{gawk}, and for his ongoing help and advice in clarifying numerous points about the language. - We could not have done nearly as good a job on either @command{gawk} +We could not have done nearly as good a job on either @command{gawk} or its documentation without his help. +Brian is in a class by himself as a programmer and technical +author. I have to thank him (yet again) for his ongoing friendship +and for being a role model to me for close to 30 years! +Having him as a reviewer is an exciting privilege. It has also +been extremely humbling@enddots{} + @cindex Robbins, Miriam @cindex Robbins, Jean @cindex Robbins, Harry @@ -1658,63 +2284,56 @@ which they raised and educated me. Finally, I also must acknowledge my gratitude to G-d, for the many opportunities He has sent my way, as well as for the gifts He has given me with which to take advantage of those opportunities. +@iftex @sp 2 @noindent Arnold Robbins @* Nof Ayalon @* -ISRAEL @* -March, 2011 +Israel @* +December 2014 +@end iftex -@ignore -@c Try this -@iftex -@page -@headings off -@majorheading I@ @ @ @ The @command{awk} Language and @command{gawk} -Part I describes the @command{awk} language and @command{gawk} program in detail. -It starts with the basics, and continues through all of the features of @command{awk} -and @command{gawk}. It contains the following chapters: +@ifnotinfo +@part @value{PART1}The @command{awk} Language +@end ifnotinfo -@itemize @bullet -@item -@ref{Getting Started}. +@ifdocbook -@item -@ref{Regexp}. +Part I describes the @command{awk} language and @command{gawk} program +in detail. It starts with the basics, and continues through all of +the features of @command{awk}. Included also are many, but not all, +of the features of @command{gawk}. This part contains the +following chapters: +@itemize @value{BULLET} @item -@ref{Reading Files}. +@ref{Getting Started} @item -@ref{Printing}. +@ref{Invoking Gawk} @item -@ref{Expressions}. +@ref{Regexp} @item -@ref{Patterns and Actions}. +@ref{Reading Files} @item -@ref{Arrays}. +@ref{Printing} @item -@ref{Functions}. +@ref{Expressions} @item -@ref{Internationalization}. +@ref{Patterns and Actions} @item -@ref{Advanced Features}. +@ref{Arrays} @item -@ref{Invoking Gawk}. +@ref{Functions} @end itemize - -@page -@evenheading @thispage@ @ @ @strong{@value{TITLE}} @| @| -@oddheading @| @| @strong{@thischapter}@ @ @ @thispage -@end iftex -@end ignore +@end ifdocbook @node Getting Started @chapter Getting Started with @command{awk} @@ -1727,17 +2346,17 @@ and @command{gawk}. It contains the following chapters: The basic function of @command{awk} is to search files for lines (or other units of text) that contain certain patterns. When a line matches one of the patterns, @command{awk} performs specified actions on that line. -@command{awk} keeps processing input lines in this way until it reaches +@command{awk} continues to process input lines in this way until it reaches the end of the input files. @cindex @command{awk}, uses for @cindex programming languages@comma{} data-driven vs.@: procedural @cindex @command{awk} programs Programs in @command{awk} are different from programs in most other languages, -because @command{awk} programs are @dfn{data-driven}; that is, you describe -the data you want to work with and then what to do when you find it. +because @command{awk} programs are @dfn{data driven} (i.e., you describe +the data you want to work with and then what to do when you find it). Most other languages are @dfn{procedural}; you have to describe, in great -detail, every step the program is to take. When working with procedural +detail, every step the program should take. When working with procedural languages, it is usually much harder to clearly describe the data your program will process. For this reason, @command{awk} programs are often refreshingly easy to @@ -1747,15 +2366,15 @@ read and write. @cindex rule, definition of When you run @command{awk}, you specify an @command{awk} @dfn{program} that tells @command{awk} what to do. The program consists of a series of -@dfn{rules}. (It may also contain @dfn{function definitions}, -an advanced feature that we will ignore for now. -@xref{User-defined}.) Each rule specifies one +@dfn{rules} (it may also contain @dfn{function definitions}, +an advanced feature that we will ignore for now; +@pxref{User-defined}). Each rule specifies one pattern to search for and one action to perform upon finding the pattern. -Syntactically, a rule consists of a pattern followed by an action. The -action is enclosed in curly braces to separate it from the pattern. -Newlines usually separate rules. Therefore, an @command{awk} +Syntactically, a rule consists of a @dfn{pattern} followed by an +@dfn{action}. The action is enclosed in braces to separate it from the +pattern. Newlines usually separate rules. Therefore, an @command{awk} program looks like this: @example @@ -1778,6 +2397,7 @@ program looks like this: * Other Features:: Other Features of @command{awk}. * When:: When to use @command{gawk} and when to use other things. +* Intro Summary:: Summary of the introduction. @end menu @node Running gawk @@ -1806,7 +2426,7 @@ variations of each. @menu * One-shot:: Running a short throwaway @command{awk} program. -* Read Terminal:: Using no input files (input from terminal +* Read Terminal:: Using no input files (input from the keyboard instead). * Long:: Putting permanent @command{awk} programs in files. @@ -1828,8 +2448,8 @@ awk '@var{program}' @var{input-file1} @var{input-file2} @dots{} @end example @noindent -where @var{program} consists of a series of @var{patterns} and -@var{actions}, as described earlier. +where @var{program} consists of a series of patterns and +actions, as described earlier. @cindex single quote (@code{'}) @cindex @code{'} (single quote) @@ -1848,11 +2468,12 @@ programs from shell scripts, because it avoids the need for a separate file for the @command{awk} program. A self-contained shell script is more reliable because there are no other files to misplace. +Later in this chapter, in +@ifdocbook +the section +@end ifdocbook @ref{Very Simple}, -@ifnotinfo -later in this @value{CHAPTER}, -@end ifnotinfo -presents several short, +we'll see examples of several short, self-contained programs. @node Read Terminal @@ -1870,10 +2491,15 @@ awk '@var{program}' @noindent @command{awk} applies the @var{program} to the @dfn{standard input}, -which usually means whatever you type on the terminal. This continues -until you indicate end-of-file by typing @kbd{@value{CTL}-d}. -(On other operating systems, the end-of-file character may be different. -For example, on OS/2, it is @kbd{@value{CTL}-z}.) +which usually means whatever you type on the keyboard. This continues +until you indicate end-of-file by typing @kbd{Ctrl-d}. +@ifset FOR_PRINT +(On non-POSIX operating systems, the end-of-file character may be different.) +@end ifset +@ifclear FOR_PRINT +(On non-POSIX operating systems, the end-of-file character may be different. +For example, on OS/2, it is @kbd{Ctrl-z}.) +@end ifclear @cindex files, input, See input files @cindex input files, running @command{awk} without @@ -1881,33 +2507,31 @@ For example, on OS/2, it is @kbd{@value{CTL}-z}.) As an example, the following program prints a friendly piece of advice (from Douglas Adams's @cite{The Hitchhiker's Guide to the Galaxy}), to keep you from worrying about the complexities of computer -programming@footnote{If you use Bash as your shell, you should execute -the command @samp{set +H} before running this program interactively, -to disable the C shell-style command history, which treats -@samp{!} as a special character. We recommend putting this command into -your personal startup file.} -(@code{BEGIN} is a feature we haven't discussed yet): +programming: @example -$ @kbd{awk "BEGIN @{ print \"Don't Panic!\" @}"} +$ @kbd{awk 'BEGIN @{ print "Don\47t Panic!" @}'} @print{} Don't Panic! @end example -@cindex quoting -@cindex double quote (@code{"}) -@cindex @code{"} (double quote) -@cindex @code{\} (backslash) -@cindex backslash (@code{\}) -This program does not read any input. The @samp{\} before each of the -inner double quotes is necessary because of the shell's quoting -rules---in particular because it mixes both single quotes and -double quotes.@footnote{Although we generally recommend the use of single -quotes around the program text, double quotes are needed here in order to -put the single quote into the message.} +@command{awk} executes statements associated with @code{BEGIN} before +reading any input. If there are no other statements in your program, +as is the case here, @command{awk} just stops, instead of trying to read +input it doesn't know how to process. +The @samp{\47} is a magic way (explained later) of getting a single quote into +the program, without having to engage in ugly shell quoting tricks. + +@quotation NOTE +If you use Bash as your shell, you should execute the +command @samp{set +H} before running this program interactively, to +disable the C shell-style command history, which treats @samp{!} as a +special character. We recommend putting this command into your personal +startup file. +@end quotation This next simple @command{awk} program emulates the @command{cat} utility; it copies whatever you type on the -keyboard to its standard output (why this works is explained shortly). +keyboard to its standard output (why this works is explained shortly): @example $ @kbd{awk '@{ print @}'} @@ -1919,7 +2543,7 @@ $ @kbd{awk '@{ print @}'} @print{} Four score and seven years ago, ... @kbd{What, me worry?} @print{} What, me worry? -@kbd{@value{CTL}-d} +@kbd{Ctrl-d} @end example @node Long @@ -1928,7 +2552,7 @@ $ @kbd{awk '@{ print @}'} @cindex @command{awk} programs, running @cindex @command{awk} programs, lengthy @cindex files, @command{awk} programs in -Sometimes your @command{awk} programs can be very long. In this case, it is +Sometimes @command{awk} programs are very long. In these cases, it is more convenient to put the program into a separate file. In order to tell @command{awk} to use that file for its program, you type: @@ -1936,12 +2560,12 @@ more convenient to put the program into a separate file. In order to tell awk -f @var{source-file} @var{input-file1} @var{input-file2} @dots{} @end example -@cindex @code{-f} option -@cindex command line, options -@cindex options, command-line -The @option{-f} instructs the @command{awk} utility to get the @command{awk} program -from the file @var{source-file}. Any @value{FN} can be used for -@var{source-file}. For example, you could put the program: +@cindex @option{-f} option +@cindex command line, option @option{-f} +The @option{-f} instructs the @command{awk} utility to get the +@command{awk} program from the file @var{source-file} (@pxref{Options}). +Any @value{FN} can be used for @var{source-file}. For example, you +could put the program: @example BEGIN @{ print "Don't Panic!" @} @@ -1958,10 +2582,10 @@ awk -f advice does the same thing as this one: @example -awk "BEGIN @{ print \"Don't Panic!\" @}" +awk 'BEGIN @{ print "Don\47t Panic!" @}' @end example -@cindex quoting +@cindex quoting in @command{gawk} command lines @noindent This was explained earlier (@pxref{Read Terminal}). @@ -1970,12 +2594,12 @@ specify with @option{-f}, because most @value{FN}s don't contain any of the shel special characters. Notice that in @file{advice}, the @command{awk} program did not have single quotes around it. The quotes are only needed for programs that are provided on the @command{awk} command line. +(Also, placing the program in a file allows us to use a literal single quote in the program +text, instead of the magic @samp{\47}.) -@c STARTOFRANGE sq1x -@cindex single quote (@code{'}) -@c STARTOFRANGE qs2x -@cindex @code{'} (single quote) -If you want to clearly identify your @command{awk} program files as such, +@cindex single quote (@code{'}) in @command{gawk} command lines +@cindex @code{'} (single quote) in @command{gawk} command lines +If you want to clearly identify an @command{awk} program file as such, you can add the extension @file{.awk} to the @value{FN}. This doesn't affect the execution of the @command{awk} program but it does make ``housekeeping'' easier. @@ -1984,15 +2608,13 @@ affect the execution of the @command{awk} program but it does make @subsection Executable @command{awk} Programs @cindex @command{awk} programs @cindex @code{#} (number sign), @code{#!} (executable scripts) -@cindex number sign (@code{#}), @code{#!} (executable scripts) @cindex Unix, @command{awk} scripts and -@cindex @code{#} (number sign), @code{#!} (executable scripts), portability issues with -@cindex number sign (@code{#}), @code{#!} (executable scripts), portability issues with +@cindex number sign (@code{#}), @code{#!} (executable scripts) Once you have learned @command{awk}, you may want to write self-contained @command{awk} scripts, using the @samp{#!} script mechanism. You can do this on many systems.@footnote{The @samp{#!} mechanism works on -GNU/Linux systems, BSD-based systems and commercial Unix systems.} +GNU/Linux systems, BSD-based systems, and commercial Unix systems.} For example, you could update the file @file{advice} to look like this: @example @@ -2004,14 +2626,7 @@ BEGIN @{ print "Don't Panic!" @} @noindent After making this file executable (with the @command{chmod} utility), simply type @samp{advice} -at the shell and the system arranges to run @command{awk}@footnote{The -line beginning with @samp{#!} lists the full @value{FN} of an interpreter -to run and an optional initial command-line argument to pass to that -interpreter. The operating system then runs the interpreter with the given -argument and the full argument list of the executed program. The first argument -in the list is the full @value{FN} of the @command{awk} program. The rest of the -argument list contains either options to @command{awk}, or @value{DF}s, -or both.} as if you had +at the shell and the system arranges to run @command{awk} as if you had typed @samp{awk -f advice}: @example @@ -2029,10 +2644,32 @@ Self-contained @command{awk} scripts are useful when you want to write a program that users can invoke without their having to know that the program is written in @command{awk}. -@c fakenode --- for prepinfo -@subheading Advanced Notes: Portability Issues with @samp{#!} +@cindex sidebar, Understanding @samp{#!} +@ifdocbook +@docbook +<sidebar><title>Understanding @samp{#!}</title> +@end docbook + @cindex portability, @code{#!} (executable scripts) +@command{awk} is an @dfn{interpreted} language. This means that the +@command{awk} utility reads your program and then processes your data +according to the instructions in your program. (This is different +from a @dfn{compiled} language such as C, where your program is first +compiled into machine code that is executed directly by your system's +processor.) The @command{awk} utility is thus termed an @dfn{interpreter}. +Many modern languages are interpreted. + +The line beginning with @samp{#!} lists the full @value{FN} of an +interpreter to run and a single optional initial command-line argument +to pass to that interpreter. The operating system then runs the +interpreter with the given argument and the full argument list of the +executed program. The first argument in the list is the full @value{FN} +of the @command{awk} program. The rest of the argument list contains +either options to @command{awk}, or @value{DF}s, or both. (Note that on +many systems @command{awk} may be found in @file{/usr/bin} instead of +in @file{/bin}.) + Some systems limit the length of the interpreter name to 32 characters. Often, this can be dealt with by using a symbolic link. @@ -2044,8 +2681,7 @@ of some sort from @command{awk}. @cindex @code{ARGC}/@code{ARGV} variables, portability and @cindex portability, @code{ARGV} variable -Finally, -the value of @code{ARGV[0]} +Finally, the value of @code{ARGV[0]} (@pxref{Built-in Variables}) varies depending upon your operating system. Some systems put @samp{awk} there, some put the full pathname @@ -2054,6 +2690,58 @@ of your script (@samp{advice}). @value{DARKCORNER} Don't rely on the value of @code{ARGV[0]} to provide your script name. +@docbook +</sidebar> +@end docbook +@end ifdocbook + +@ifnotdocbook +@cartouche +@center @b{Understanding @samp{#!}} + + +@cindex portability, @code{#!} (executable scripts) + +@command{awk} is an @dfn{interpreted} language. This means that the +@command{awk} utility reads your program and then processes your data +according to the instructions in your program. (This is different +from a @dfn{compiled} language such as C, where your program is first +compiled into machine code that is executed directly by your system's +processor.) The @command{awk} utility is thus termed an @dfn{interpreter}. +Many modern languages are interpreted. + +The line beginning with @samp{#!} lists the full @value{FN} of an +interpreter to run and a single optional initial command-line argument +to pass to that interpreter. The operating system then runs the +interpreter with the given argument and the full argument list of the +executed program. The first argument in the list is the full @value{FN} +of the @command{awk} program. The rest of the argument list contains +either options to @command{awk}, or @value{DF}s, or both. (Note that on +many systems @command{awk} may be found in @file{/usr/bin} instead of +in @file{/bin}.) + +Some systems limit the length of the interpreter name to 32 characters. +Often, this can be dealt with by using a symbolic link. + +You should not put more than one argument on the @samp{#!} +line after the path to @command{awk}. It does not work. The operating system +treats the rest of the line as a single argument and passes it to @command{awk}. +Doing this leads to confusing behavior---most likely a usage diagnostic +of some sort from @command{awk}. + +@cindex @code{ARGC}/@code{ARGV} variables, portability and +@cindex portability, @code{ARGV} variable +Finally, the value of @code{ARGV[0]} +(@pxref{Built-in Variables}) +varies depending upon your operating system. +Some systems put @samp{awk} there, some put the full pathname +of @command{awk} (such as @file{/bin/awk}), and some put the name +of your script (@samp{advice}). @value{DARKCORNER} +Don't rely on the value of @code{ARGV[0]} +to provide your script name. +@end cartouche +@end ifnotdocbook + @node Comments @subsection Comments in @command{awk} Programs @cindex @code{#} (number sign), commenting @@ -2067,14 +2755,14 @@ can explain what the program does and how it works. Nearly all programming languages have provisions for comments, as programs are typically hard to understand without them. -In the @command{awk} language, a comment starts with the sharp sign +In the @command{awk} language, a comment starts with the number sign character (@samp{#}) and continues to the end of the line. The @samp{#} does not have to be the first character on the line. The -@command{awk} language ignores the rest of a line following a sharp sign. +@command{awk} language ignores the rest of a line following a number sign. For example, we could have put the following into @file{advice}: @example -# This program prints a nice friendly message. It helps +# This program prints a nice, friendly message. It helps # keep novice users from being afraid of the computer. BEGIN @{ print "Don't Panic!" @} @end example @@ -2084,13 +2772,14 @@ programs, but this usually isn't very useful; the purpose of a comment is to help you or another person understand the program when reading it at a later time. -@cindex quoting +@cindex quoting, for small awk programs @cindex single quote (@code{'}), vs.@: apostrophe @cindex @code{'} (single quote), vs.@: apostrophe @quotation CAUTION As mentioned in @ref{One-shot}, -you can enclose small to medium programs in single quotes, in order to keep +you can enclose short to medium-sized programs in single quotes, +in order to keep your shell scripts self-contained. When doing so, @emph{don't} put an apostrophe (i.e., a single quote) into a comment (or anywhere else in your program). The shell interprets the quote as the closing @@ -2100,7 +2789,7 @@ runs, it will probably print strange messages about syntax errors. For example, look at the following: @example -$ @kbd{awk '@{ print "hello" @} # let's be cute'} +$ @kbd{awk 'BEGIN @{ print "hello" @} # let's be cute'} > @end example @@ -2119,19 +2808,19 @@ $ @kbd{awk '@{ print "hello" @} # let's be cute'} @cindex @code{\} (backslash) @cindex backslash (@code{\}) Putting a backslash before the single quote in @samp{let's} wouldn't help, -since backslashes are not special inside single quotes. +because backslashes are not special inside single quotes. The next @value{SUBSECTION} describes the shell's quoting rules. @end quotation @node Quoting -@subsection Shell-Quoting Issues -@cindex quoting, rules for +@subsection Shell Quoting Issues +@cindex shell quoting, rules for @menu * DOS Quoting:: Quoting in Windows Batch Files. @end menu -For short to medium length @command{awk} programs, it is most convenient +For short to medium-length @command{awk} programs, it is most convenient to enter the program on the @command{awk} command line. This is best done by enclosing the entire program in single quotes. This is true whether you are entering the program interactively at @@ -2148,7 +2837,27 @@ knowledge of shell quoting rules. The following rules apply only to POSIX-compliant, Bourne-style shells (such as Bash, the GNU Bourne-Again Shell). If you use the C shell, you're on your own. -@itemize @bullet +Before diving into the rules, we introduce a concept that appears +throughout this @value{DOCUMENT}, which is that of the @dfn{null}, +or empty, string. + +The null string is character data that has no value. +In other words, it is empty. It is written in @command{awk} programs +like this: @code{""}. In the shell, it can be written using single +or double quotes: @code{""} or @code{''}. Although the null string has +no characters in it, it does exist. For example, consider this command: + +@example +$ @kbd{echo ""} +@end example + +@noindent +Here, the @command{echo} utility receives a single argument, even +though that argument has no characters in it. In the rest of this +@value{DOCUMENT}, we use the terms @dfn{null string} and @dfn{empty string} +interchangeably. Now, on to the quoting rules: + +@itemize @value{BULLET} @item Quoted items can be concatenated with nonquoted items as well as with other quoted items. The shell turns everything into one argument for @@ -2160,26 +2869,26 @@ that character. The shell removes the backslash and passes the quoted character on to the command. @item -@cindex @code{\} (backslash) -@cindex backslash (@code{\}) -@cindex single quote (@code{'}) -@cindex @code{'} (single quote) +@cindex @code{\} (backslash), in shell commands +@cindex backslash (@code{\}), in shell commands +@cindex single quote (@code{'}), in shell commands +@cindex @code{'} (single quote), in shell commands Single quotes protect everything between the opening and closing quotes. The shell does no interpretation of the quoted text, passing it on verbatim to the command. It is @emph{impossible} to embed a single quote inside single-quoted text. Refer back to -@ref{Comments}, +@DBREF{Comments} for an example of what happens if you try. @item -@cindex double quote (@code{"}) -@cindex @code{"} (double quote) +@cindex double quote (@code{"}), in shell commands +@cindex @code{"} (double quote), in shell commands Double quotes protect most things between the opening and closing quotes. The shell does at least variable and command substitution on the quoted text. Different shells may do additional kinds of processing on double-quoted text. -Since certain characters within double-quoted text are processed by the shell, +Because certain characters within double-quoted text are processed by the shell, they must be @dfn{escaped} within the text. Of note are the characters @samp{$}, @samp{`}, @samp{\}, and @samp{"}, all of which must be preceded by a backslash within double-quoted text if they are to be passed on literally @@ -2188,8 +2897,14 @@ Thus, the example seen @ifnotinfo previously @end ifnotinfo -in @ref{Read Terminal}, -is applicable: +in @ref{Read Terminal}: + +@example +awk 'BEGIN @{ print "Don\47t Panic!" @}' +@end example + +@noindent +could instead be written this way: @example $ @kbd{awk "BEGIN @{ print \"Don't Panic!\" @}"} @@ -2202,7 +2917,7 @@ Note that the single quote is not special within double quotes. @item Null strings are removed when they occur as part of a non-null -command-line argument, while explicit non-null objects are kept. +command-line argument, while explicit null objects are kept. For example, to specify that the field separator @code{FS} should be set to the null string, use: @@ -2211,7 +2926,7 @@ awk -F "" '@var{program}' @var{files} # correct @end example @noindent -@cindex null strings, quoting and +@cindex null strings in @command{gawk} arguments, quoting and Don't use this: @example @@ -2219,12 +2934,12 @@ awk -F"" '@var{program}' @var{files} # wrong! @end example @noindent -In the second case, @command{awk} will attempt to use the text of the program +In the second case, @command{awk} attempts to use the text of the program as the value of @code{FS}, and the first @value{FN} as the text of the program! This results in syntax errors at best, and confusing behavior at worst. @end itemize -@cindex quoting, tricks for +@cindex quoting in @command{gawk} command lines, tricks for Mixing single and double quotes is difficult. You have to resort to shell quoting tricks, like this: @@ -2235,7 +2950,7 @@ $ @kbd{awk 'BEGIN @{ print "Here is a single quote <'"'"'>" @}'} @noindent This program consists of three concatenated quoted strings. The first and the -third are single-quoted, the second is double-quoted. +third are single-quoted, and the second is double-quoted. This can be ``simplified'' to: @@ -2256,8 +2971,6 @@ $ @kbd{awk "BEGIN @{ print \"Here is a single quote <'>\" @}"} @end example @noindent -@c ENDOFRANGE sq1x -@c ENDOFRANGE qs2x This option is also painful, because double quotes, backslashes, and dollar signs are very common in more advanced @command{awk} programs. @@ -2274,19 +2987,22 @@ $ @kbd{awk 'BEGIN @{ print "Here is a double quote <\42>" @}'} @end example @noindent -This works nicely, except that you should comment clearly what the +This works nicely, but you should comment clearly what the escapes mean. A fourth option is to use command-line variable assignment, like this: @example -$ awk -v sq="'" 'BEGIN @{ print "Here is a single quote <" sq ">" @}' +$ @kbd{awk -v sq="'" 'BEGIN @{ print "Here is a single quote <" sq ">" @}'} @print{} Here is a single quote <'> @end example +(Here, the two string constants and the value of @code{sq} are concatenated +into a single string that is printed by @code{print}.) + If you really need both single and double quotes in your @command{awk} program, it is probably best to move it into a separate file, where -the shell won't be part of the picture, and you can say what you mean. +the shell won't be part of the picture and you can say what you mean. @node DOS Quoting @subsubsection Quoting in MS-Windows Batch Files @@ -2323,6 +3039,7 @@ Although this @value{DOCUMENT} generally only worries about POSIX systems and th POSIX shell, the following issue arises often enough for many users that it is worth addressing. +@cindex Brink, Jeroen The ``shells'' on Microsoft Windows systems use the double-quote character for quoting, and make it difficult or impossible to include an escaped double-quote character in a command-line script. @@ -2336,43 +3053,43 @@ gawk "@{ print \"\042\" $0 \"\042\" @}" @var{file} @node Sample Data Files @section @value{DDF}s for the Examples -@c For gawk >= 4.0, update these data files. No-one has such slow modems! @cindex input files, examples -@cindex @code{BBS-list} file +@cindex @code{mail-list} file Many of the examples in this @value{DOCUMENT} take their input from two sample -@value{DF}s. The first, @file{BBS-list}, represents a list of -computer bulletin board systems together with information about those systems. +@value{DF}s. The first, @file{mail-list}, represents a list of peoples' names +together with their email addresses and information about those people. The second @value{DF}, called @file{inventory-shipped}, contains information about monthly shipments. In both files, each line is considered to be one @dfn{record}. -In the @value{DF} @file{BBS-list}, each record contains the name of a computer -bulletin board, its phone number, the board's baud rate(s), and a code for -the number of hours it is operational. An @samp{A} in the last column -means the board operates 24 hours a day. A @samp{B} in the last -column means the board only operates on evening and weekend hours. -A @samp{C} means the board operates only on weekends: +In @file{mail-list}, each record contains the name of a person, +his/her phone number, his/her email address, and a code for his/her relationship +with the author of the list. +The columns are aligned using spaces. +An @samp{A} in the last column +means that the person is an acquaintance. An @samp{F} in the last +column means that the person is a friend. +An @samp{R} means that the person is a relative: -@c 2e: Update the baud rates to reflect today's faster modems @example @c system if test ! -d eg ; then mkdir eg ; fi @c system if test ! -d eg/lib ; then mkdir eg/lib ; fi @c system if test ! -d eg/data ; then mkdir eg/data ; fi @c system if test ! -d eg/prog ; then mkdir eg/prog ; fi @c system if test ! -d eg/misc ; then mkdir eg/misc ; fi -@c file eg/data/BBS-list -aardvark 555-5553 1200/300 B -alpo-net 555-3412 2400/1200/300 A -barfly 555-7685 1200/300 A -bites 555-1675 2400/1200/300 A -camelot 555-0542 300 C -core 555-2912 1200/300 C -fooey 555-1234 2400/1200/300 B -foot 555-6699 1200/300 B -macfoo 555-6480 1200/300 A -sdace 555-3430 2400/1200/300 A -sabafoo 555-2127 1200/300 C +@c file eg/data/mail-list +Amelia 555-5553 amelia.zodiacusque@@gmail.com F +Anthony 555-3412 anthony.asserturo@@hotmail.com A +Becky 555-7685 becky.algebrarum@@gmail.com A +Bill 555-1675 bill.drowning@@hotmail.com A +Broderick 555-0542 broderick.aliquotiens@@yahoo.com R +Camilla 555-2912 camilla.infusarum@@skynet.be R +Fabius 555-1234 fabius.undevicesimus@@ucb.edu F +Julie 555-6699 julie.perscrutabor@@skeeve.com F +Martin 555-6480 martin.codicibus@@hotmail.com A +Samuel 555-3430 samuel.lanceolis@@shu.edu A +Jean-Paul 555-2127 jeanpaul.campanorum@@nyu.edu R @c endfile @end example @@ -2384,6 +3101,7 @@ of green crates shipped, the number of red boxes shipped, the number of orange bags shipped, and the number of blue packages shipped, respectively. There are 16 entries, covering the 12 months of last year and the first four months of the current year. +An empty line separates the data for the two years: @example @c file eg/data/inventory-shipped @@ -2407,45 +3125,30 @@ Apr 21 70 74 514 @c endfile @end example -@ifinfo -If you are reading this in GNU Emacs using Info, you can copy the regions -of text showing these sample files into your own test files. This way you -can try out the examples shown in the remainder of this document. You do -this by using the command @kbd{M-x write-region} to copy text from the Info -file into a file for use with @command{awk} -(@xref{Misc File Ops, , Miscellaneous File Operations, emacs, GNU Emacs Manual}, -for more information). Using this information, create your own -@file{BBS-list} and @file{inventory-shipped} files and practice what you -learn in this @value{DOCUMENT}. - -@cindex Texinfo -If you are using the stand-alone version of Info, -see @ref{Extract Program}, -for an @command{awk} program that extracts these @value{DF}s from -@file{gawk.texi}, the Texinfo source file for this Info file. -@end ifinfo +The sample files are included in the @command{gawk} distribution, +in the directory @file{awklib/eg/data}. @node Very Simple @section Some Simple Examples The following command runs a simple @command{awk} program that searches the -input file @file{BBS-list} for the character string @samp{foo} (a +input file @file{mail-list} for the character string @samp{li} (a grouping of characters is usually called a @dfn{string}; the term @dfn{string} is based on similar usage in English, such -as ``a string of pearls,'' or ``a string of cars in a train''): +as ``a string of pearls'' or ``a string of cars in a train''): @example -awk '/foo/ @{ print $0 @}' BBS-list +awk '/li/ @{ print $0 @}' mail-list @end example @noindent -When lines containing @samp{foo} are found, they are printed because +When lines containing @samp{li} are found, they are printed because @w{@samp{print $0}} means print the current line. (Just @samp{print} by itself means the same thing, so we could have written that instead.) -You will notice that slashes (@samp{/}) surround the string @samp{foo} -in the @command{awk} program. The slashes indicate that @samp{foo} +You will notice that slashes (@samp{/}) surround the string @samp{li} +in the @command{awk} program. The slashes indicate that @samp{li} is the pattern to search for. This type of pattern is called a @dfn{regular expression}, which is covered in more detail later (@pxref{Regexp}). @@ -2457,11 +3160,11 @@ interpret any of it as special shell characters. Here is what this program prints: @example -$ @kbd{awk '/foo/ @{ print $0 @}' BBS-list} -@print{} fooey 555-1234 2400/1200/300 B -@print{} foot 555-6699 1200/300 B -@print{} macfoo 555-6480 1200/300 A -@print{} sabafoo 555-2127 1200/300 C +$ @kbd{awk '/li/ @{ print $0 @}' mail-list} +@print{} Amelia 555-5553 amelia.zodiacusque@@gmail.com F +@print{} Broderick 555-0542 broderick.aliquotiens@@yahoo.com R +@print{} Julie 555-6699 julie.perscrutabor@@skeeve.com F +@print{} Samuel 555-3430 samuel.lanceolis@@shu.edu A @end example @cindex actions, default @@ -2472,18 +3175,18 @@ for @emph{every} input line. If the action is omitted, the default action is to print all lines that match the pattern. @cindex actions, empty -Thus, we could leave out the action (the @code{print} statement and the curly +Thus, we could leave out the action (the @code{print} statement and the braces) in the previous example and the result would be the same: -@command{awk} prints all lines matching the pattern @samp{foo}. By comparison, -omitting the @code{print} statement but retaining the curly braces makes an +@command{awk} prints all lines matching the pattern @samp{li}. By comparison, +omitting the @code{print} statement but retaining the braces makes an empty action that does nothing (i.e., no lines are printed). @cindex @command{awk} programs, one-line examples -Many practical @command{awk} programs are just a line or two. Following is a +Many practical @command{awk} programs are just a line or two long. Following is a collection of useful, short programs to get you started. Some of these programs contain constructs that haven't been covered yet. (The description -of the program will give you a good idea of what is going on, but please -read the rest of the @value{DOCUMENT} to become an @command{awk} expert!) +of the program will give you a good idea of what is going on, but you'll +need to read the rest of the @value{DOCUMENT} to become an @command{awk} expert!) Most of the examples use a @value{DF} named @file{data}. This is just a placeholder; if you use these programs yourself, substitute your own @value{FN}s for @file{data}. @@ -2492,36 +3195,41 @@ one way to do things in @command{awk}. At some point, you may want to look back at these examples and see if you can come up with different ways to do the same things shown here: -@itemize @bullet +@itemize @value{BULLET} @item -Print the length of the longest input line: +Print every line that is longer than 80 characters: @example -awk '@{ if (length($0) > max) max = length($0) @} - END @{ print max @}' data +awk 'length($0) > 80' data @end example +The sole rule has a relational expression as its pattern and has no +action---so it uses the default action, printing the record. + @item -Print every line that is longer than 80 characters: +Print the length of the longest input line: @example -awk 'length($0) > 80' data +awk '@{ if (length($0) > max) max = length($0) @} + END @{ print max @}' data @end example -The sole rule has a relational expression as its pattern and it has no -action---so the default action, printing the record, is used. +The code associated with @code{END} executes after all +input has been read; it's the other side of the coin to @code{BEGIN}. @cindex @command{expand} utility @item Print the length of the longest line in @file{data}: @example -expand data | awk '@{ if (x < length()) x = length() @} - END @{ print "maximum line length is " x @}' +expand data | awk '@{ if (x < length($0)) x = length($0) @} + END @{ print "maximum line length is " x @}' @end example -The input is processed by the @command{expand} utility to change TABs -into spaces, so the widths compared are actually the right-margin columns. +This example differs slightly from the previous one: +the input is processed by the @command{expand} utility to change TABs +into spaces, so the widths compared are actually the right-margin columns, +as opposed to the number of input characters on each line. @item Print every line that has at least one field: @@ -2547,7 +3255,7 @@ Print the total number of bytes used by @var{files}: @example ls -l @var{files} | awk '@{ x += $5 @} - END @{ print "total bytes: " x @}' + END @{ print "total bytes: " x @}' @end example @item @@ -2582,7 +3290,7 @@ Print the even-numbered lines in the @value{DF}: awk 'NR % 2 == 0' data @end example -If you use the expression @samp{NR % 2 == 1} instead, +If you used the expression @samp{NR % 2 == 1} instead, the program would print the odd-numbered lines. @end itemize @@ -2591,15 +3299,20 @@ the program would print the odd-numbered lines. @cindex @command{awk} programs The @command{awk} utility reads the input files one line at a -time. For each line, @command{awk} tries the patterns of each of the rules. -If several patterns match, then several actions are run in the order in +time. For each line, @command{awk} tries the patterns of each rule. +If several patterns match, then several actions execute in the order in which they appear in the @command{awk} program. If no patterns match, then -no actions are run. +no actions run. After processing all the rules that match the line (and perhaps there are none), @command{awk} reads the next line. (However, -@pxref{Next Statement}, -and also @pxref{Nextfile Statement}). +@DBPXREF{Next Statement} +@ifdocbook +and @DBREF{Nextfile Statement}.) +@end ifdocbook +@ifnotdocbook +and also @pxref{Nextfile Statement}.) +@end ifnotdocbook This continues until the program reaches the end of the file. For example, the following @command{awk} program contains two rules: @@ -2619,29 +3332,23 @@ This program prints every line that contains the string strings, it is printed twice, once by each rule. This is what happens if we run this program on our two sample @value{DF}s, -@file{BBS-list} and @file{inventory-shipped}: +@file{mail-list} and @file{inventory-shipped}: @example $ @kbd{awk '/12/ @{ print $0 @}} -> @kbd{/21/ @{ print $0 @}' BBS-list inventory-shipped} -@print{} aardvark 555-5553 1200/300 B -@print{} alpo-net 555-3412 2400/1200/300 A -@print{} barfly 555-7685 1200/300 A -@print{} bites 555-1675 2400/1200/300 A -@print{} core 555-2912 1200/300 C -@print{} fooey 555-1234 2400/1200/300 B -@print{} foot 555-6699 1200/300 B -@print{} macfoo 555-6480 1200/300 A -@print{} sdace 555-3430 2400/1200/300 A -@print{} sabafoo 555-2127 1200/300 C -@print{} sabafoo 555-2127 1200/300 C +> @kbd{/21/ @{ print $0 @}' mail-list inventory-shipped} +@print{} Anthony 555-3412 anthony.asserturo@@hotmail.com A +@print{} Camilla 555-2912 camilla.infusarum@@skynet.be R +@print{} Fabius 555-1234 fabius.undevicesimus@@ucb.edu F +@print{} Jean-Paul 555-2127 jeanpaul.campanorum@@nyu.edu R +@print{} Jean-Paul 555-2127 jeanpaul.campanorum@@nyu.edu R @print{} Jan 21 36 64 620 @print{} Apr 21 70 74 514 @end example @noindent -Note how the line beginning with @samp{sabafoo} -in @file{BBS-list} was printed twice, once for each rule. +Note how the line beginning with @samp{Jean-Paul} +in @file{mail-list} was printed twice, once for each rule. @node More Complex @section A More Complex Example @@ -2654,8 +3361,8 @@ features that haven't been covered yet, so don't worry if you don't understand all the details: @example -LC_ALL=C ls -l | awk '$6 == "Nov" @{ sum += $5 @} - END @{ print sum @}' +ls -l | awk '$6 == "Nov" @{ sum += $5 @} + END @{ print sum @}' @end example @cindex @command{ls} utility @@ -2679,21 +3386,20 @@ the file was last modified. Its output looks like this: @noindent @cindex line continuations, with C shell The first field contains read-write permissions, the second field contains -the number of links to the file, and the third field identifies the owner of -the file. The fourth field identifies the group of the file. -The fifth field contains the size of the file in bytes. The +the number of links to the file, and the third field identifies the file's owner. +The fourth field identifies the file's group. +The fifth field contains the file's size in bytes. The sixth, seventh, and eighth fields contain the month, day, and time, respectively, that the file was last modified. Finally, the ninth field -contains the @value{FN}.@footnote{The @samp{LC_ALL=C} is -needed to produce this traditional-style output from @command{ls}.} +contains the @value{FN}. @c @cindex automatic initialization @cindex initialization, automatic The @samp{$6 == "Nov"} in our @command{awk} program is an expression that tests whether the sixth field of the output from @w{@samp{ls -l}} matches the string @samp{Nov}. Each time a line has the string -@samp{Nov} for its sixth field, the action @samp{sum += $5} is -performed. This adds the fifth field (the file's size) to the variable +@samp{Nov} for its sixth field, @command{awk} performs the action +@samp{sum += $5}. This adds the fifth field (the file's size) to the variable @code{sum}. As a result, when @command{awk} has finished reading all the input lines, @code{sum} is the total of the sizes of the files whose lines matched the pattern. (This works because @command{awk} variables @@ -2720,7 +3426,7 @@ separate rule, like this: @example awk '/12/ @{ print $0 @} - /21/ @{ print $0 @}' BBS-list inventory-shipped + /21/ @{ print $0 @}' mail-list inventory-shipped @end example @cindex @command{gawk}, newlines in @@ -2760,7 +3466,7 @@ We have generally not used backslash continuation in our sample programs. @command{gawk} places no limit on the length of a line, so backslash continuation is never strictly necessary; it just makes programs more readable. For this same reason, as well as -for clarity, we have kept most statements short in the sample programs +for clarity, we have kept most statements short in the programs presented throughout the @value{DOCUMENT}. Backslash continuation is most useful when your @command{awk} program is in a separate source file instead of entered from the command line. You should also note that @@ -2780,7 +3486,7 @@ lines in the middle of a regular expression or a string. with the C shell.} It works for @command{awk} programs in files and for one-shot programs, @emph{provided} you are using a POSIX-compliant shell, such as the Unix Bourne shell or Bash. But the C shell behaves -differently! There, you must use two backslashes in a row, followed by +differently! There you must use two backslashes in a row, followed by a newline. Note also that when using the C shell, @emph{every} newline in your @command{awk} program must be escaped with a backslash. To illustrate: @@ -2821,11 +3527,11 @@ starts a comment, it ignores @emph{everything} on the rest of the line. For example: @example -$ gawk 'BEGIN @{ print "dont panic" # a friendly \ -> BEGIN rule -> @}' +$ @kbd{gawk 'BEGIN @{ print "dont panic" # a friendly \} +> @kbd{ BEGIN rule} +> @kbd{@}'} @error{} gawk: cmd. line:2: BEGIN rule -@error{} gawk: cmd. line:2: ^ parse error +@error{} gawk: cmd. line:2: ^ syntax error @end example @noindent @@ -2835,8 +3541,8 @@ noticed because it is ``hidden'' inside the comment. Thus, the @code{BEGIN} is noted as a syntax error. @cindex statements, multiple -@cindex @code{;} (semicolon) -@cindex semicolon (@code{;}) +@cindex @code{;} (semicolon), separating statements in actions +@cindex semicolon (@code{;}), separating statements in actions When @command{awk} statements within one rule are short, you might want to put more than one of them on a line. This is accomplished by separating the statements with a semicolon (@samp{;}). @@ -2871,9 +3577,9 @@ performing bit manipulation, for runtime string translation (internationalizatio determining the type of a variable, and array sorting. -As we develop our presentation of the @command{awk} language, we introduce +As we develop our presentation of the @command{awk} language, we will introduce most of the variables and many of the functions. They are described -systematically in @ref{Built-in Variables}, and +systematically in @DBREF{Built-in Variables} and in @ref{Built-in}. @node When @@ -2896,34 +3602,74 @@ used once, and thrown away. Because @command{awk} programs are interpreted, you can avoid the (usually lengthy) compilation part of the typical edit-compile-test-debug cycle of software development. +@cindex Brian Kernighan's @command{awk} Complex programs have been written in @command{awk}, including a complete -retargetable assembler for eight-bit microprocessors (@pxref{Glossary}, for -more information), and a microcode assembler for a special-purpose Prolog +retargetable assembler for +@ifclear FOR_PRINT +eight-bit microprocessors (@pxref{Glossary}, for more information), +@end ifclear +@ifset FOR_PRINT +eight-bit microprocessors, +@end ifset +and a microcode assembler for a special-purpose Prolog computer. -While the original @command{awk}'s capabilities were strained by tasks -of such complexity, modern versions are more capable. Even Brian Kernighan's -version of @command{awk} has fewer predefined limits, and those -that it has are much larger than they used to be. +The original @command{awk}'s capabilities were strained by tasks +of such complexity, but modern versions are more capable. @cindex @command{awk} programs, complex -If you find yourself writing @command{awk} scripts of more than, say, a few -hundred lines, you might consider using a different programming -language. Emacs Lisp is a good choice if you need sophisticated string -or pattern matching capabilities. The shell is also good at string and -pattern matching; in addition, it allows powerful use of the system -utilities. More conventional languages, such as C, C++, and Java, offer -better facilities for system programming and for managing the complexity -of large programs. Programs in these languages may require more lines -of source code than the equivalent @command{awk} programs, but they are -easier to maintain and usually run more efficiently. +If you find yourself writing @command{awk} scripts of more than, say, +a few hundred lines, you might consider using a different programming +language. The shell is good at string and pattern matching; in addition, +it allows powerful use of the system utilities. Python offers a nice +balance between high-level ease of programming and access to system +facilities.@footnote{Other popular scripting languages include Ruby +and Perl.} + +@node Intro Summary +@section Summary + +@c FIXME: Review this chapter for summary of builtin functions called. +@itemize @value{BULLET} +@item +Programs in @command{awk} consist of @var{pattern}--@var{action} pairs. + +@item +An @var{action} without a @var{pattern} always runs. The default +@var{action} for a pattern without one is @samp{@{ print $0 @}}. + +@item +Use either +@samp{awk '@var{program}' @var{files}} +or +@samp{awk -f @var{program-file} @var{files}} +to run @command{awk}. + +@item +You may use the special @samp{#!} header line to create @command{awk} +programs that are directly executable. + +@item +Comments in @command{awk} programs start with @samp{#} and continue to +the end of the same line. + +@item +Be aware of quoting issues when writing @command{awk} programs as +part of a larger shell script (or MS-Windows batch file). + +@item +You may use backslash continuation to continue a source line. +Lines are automatically continued after +a comma, open brace, question mark, colon, +@samp{||}, @samp{&&}, @code{do}, and @code{else}. +@end itemize @node Invoking Gawk @chapter Running @command{awk} and @command{gawk} -This @value{CHAPTER} covers how to run awk, both POSIX-standard +This @value{CHAPTER} covers how to run @command{awk}, both POSIX-standard and @command{gawk}-specific command-line options, and what @command{awk} and -@command{gawk} do with non-option arguments. +@command{gawk} do with nonoption arguments. It then proceeds to cover how @command{gawk} searches for source files, reading standard input along with other files, @command{gawk}'s environment variables, @command{gawk}'s exit status, using include files, @@ -2942,8 +3688,10 @@ things in this @value{CHAPTER} that don't interest you right now. * Environment Variables:: The environment variables @command{gawk} uses. * Exit Status:: @command{gawk}'s exit status. * Include Files:: Including other files into your program. +* Loading Shared Libraries:: Loading shared libraries into your program. * Obsolete:: Obsolete Options and/or features. * Undocumented:: Undocumented Options and Features. +* Invoking Summary:: Invocation summary. @end menu @node Command Line @@ -2957,15 +3705,15 @@ There are two ways to run @command{awk}---with an explicit program or with one or more program files. Here are templates for both of them; items enclosed in [@dots{}] in these templates are optional: -@example -awk @r{[@var{options}]} -f progfile @r{[@code{--}]} @var{file} @dots{} -awk @r{[@var{options}]} @r{[@code{--}]} '@var{program}' @var{file} @dots{} -@end example +@display +@command{awk} [@var{options}] @option{-f} @var{progfile} [@option{--}] @var{file} @dots{} +@command{awk} [@var{options}] [@option{--}] @code{'@var{program}'} @var{file} @dots{} +@end display @cindex GNU long options @cindex long options @cindex options, long -Besides traditional one-letter POSIX-style options, @command{gawk} also +In addition to traditional one-letter POSIX-style options, @command{gawk} also supports GNU long options. @cindex dark corner, invoking @command{awk} @@ -2976,7 +3724,7 @@ It is possible to invoke @command{awk} with an empty program: awk '' datafile1 datafile2 @end example -@cindex @code{--lint} option +@cindex @option{--lint} option @noindent Doing so makes little sense, though; @command{awk} exits silently when given an empty program. @@ -2987,20 +3735,16 @@ warning that the program is empty. @node Options @section Command-Line Options -@c STARTOFRANGE ocl @cindex options, command-line -@c STARTOFRANGE clo @cindex command line, options -@c STARTOFRANGE gnulo @cindex GNU long options -@c STARTOFRANGE longo @cindex options, long Options begin with a dash and consist of a single character. GNU-style long options consist of two dashes and a keyword. The keyword can be abbreviated, as long as the abbreviation allows the option -to be uniquely identified. If the option takes an argument, then the -keyword is either immediately followed by an equals sign (@samp{=}) and the +to be uniquely identified. If the option takes an argument, either the +keyword is immediately followed by an equals sign (@samp{=}) and the argument's value, or the keyword and the argument's value are separated by whitespace. If a particular option with a value is given more than once, it is the @@ -3016,27 +3760,27 @@ The following list describes options mandated by the POSIX standard: @table @code @item -F @var{fs} @itemx --field-separator @var{fs} -@cindex @code{-F} option -@cindex @code{--field-separator} option +@cindex @option{-F} option +@cindex @option{--field-separator} option @cindex @code{FS} variable, @code{--field-separator} option and Set the @code{FS} variable to @var{fs} (@pxref{Field Separators}). @item -f @var{source-file} @itemx --file @var{source-file} -@cindex @code{-f} option -@cindex @code{--file} option +@cindex @option{-f} option +@cindex @option{--file} option @cindex @command{awk} programs, location of -Read @command{awk} program source from @var{source-file} -instead of in the first non-option argument. +Read the @command{awk} program source from @var{source-file} +instead of in the first nonoption argument. This option may be given multiple times; the @command{awk} -program consists of the concatenation the contents of +program consists of the concatenation of the contents of each specified @var{source-file}. @item -v @var{var}=@var{val} @itemx --assign @var{var}=@var{val} -@cindex @code{-v} option -@cindex @code{--assign} option +@cindex @option{-v} option +@cindex @option{--assign} option @cindex variables, setting Set the variable @var{var} to the value @var{val} @emph{before} execution of the program begins. Such variable values are available @@ -3047,17 +3791,17 @@ The @option{-v} option can only set one variable, but it can be used more than once, setting another variable each time, like this: @samp{awk @w{-v foo=1} @w{-v bar=2} @dots{}}. -@cindex built-in variables, @code{-v} option@comma{} setting with -@cindex variables, built-in, @code{-v} option@comma{} setting with +@cindex predefined variables, @code{-v} option@comma{} setting with +@cindex variables, predefined @code{-v} option@comma{} setting with @quotation CAUTION Using @option{-v} to set the values of the built-in variables may lead to surprising results. @command{awk} will reset the values of those variables as it needs to, possibly ignoring any -predefined value you may have given. +initial value you may have given. @end quotation @item -W @var{gawk-opt} -@cindex @code{-W} option +@cindex @option{-W} option Provide an implementation-specific option. This is the POSIX convention for providing implementation-specific options. These options @@ -3082,53 +3826,59 @@ by the user that could start with @samp{-}. It is also useful for passing options on to the @command{awk} program; see @ref{Getopt Function}. @end table -@c ENDOFRANGE gnulo -@c ENDOFRANGE longo The following list describes @command{gawk}-specific options: -@table @code -@item -b -@itemx --characters-as-bytes -@cindex @code{-b} option -@cindex @code{--characters-as-bytes} option +@c Have to use @asis here to get docbook to come out right. +@table @asis +@item @option{-b} +@itemx @option{--characters-as-bytes} +@cindex @option{-b} option +@cindex @option{--characters-as-bytes} option Cause @command{gawk} to treat all input data as single-byte characters. +In addition, all output written with @code{print} or @code{printf} +is treated as single-byte characters. + Normally, @command{gawk} follows the POSIX standard and attempts to process -its input data according to the current locale. This can often involve +its input data according to the current locale (@pxref{Locales}). This can often involve converting multibyte characters into wide characters (internally), and can lead to problems or confusion if the input data does not contain valid -multibyte characters. This option is an easy way to tell @command{gawk}: -``hands off my data!''. +multibyte characters. This option is an easy way to tell @command{gawk}, +``Hands off my data!'' -@item -c -@itemx --traditional -@cindex @code{--c} option -@cindex @code{--traditional} option +@item @option{-c} +@itemx @option{--traditional} +@cindex @option{-c} option +@cindex @option{--traditional} option @cindex compatibility mode (@command{gawk}), specifying Specify @dfn{compatibility mode}, in which the GNU extensions to the @command{awk} language are disabled, so that @command{gawk} behaves just -like Brian Kernighan's version @command{awk}. +like BWK @command{awk}. @xref{POSIX/GNU}, -which summarizes the extensions. Also see +which summarizes the extensions. +@ifclear FOR_PRINT +Also see @ref{Compatibility Mode}. +@end ifclear -@item -C -@itemx --copyright -@cindex @code{-C} option -@cindex @code{--copyright} option +@item @option{-C} +@itemx @option{--copyright} +@cindex @option{-C} option +@cindex @option{--copyright} option @cindex GPL (General Public License), printing Print the short version of the General Public License and then exit. -@item -d@r{[}@var{file}@r{]} -@itemx --dump-variables@r{[}=@var{file}@r{]} -@cindex @code{-d} option -@cindex @code{--dump-variables} option -@cindex @code{awkvars.out} file -@cindex files, @code{awkvars.out} +@item @option{-d}[@var{file}] +@itemx @option{--dump-variables}[@code{=}@var{file}] +@cindex @option{-d} option +@cindex @option{--dump-variables} option +@cindex dump all variables of a program +@cindex @file{awkvars.out} file +@cindex files, @file{awkvars.out} @cindex variables, global, printing list of Print a sorted list of global variables, their types, and final values to @var{file}. If no @var{file} is provided, print this -list to the file named @file{awkvars.out} in the current directory. +list to a file named @file{awkvars.out} in the current directory. No space is allowed between the @option{-d} and @var{file}, if @var{file} is supplied. @@ -3141,10 +3891,24 @@ inadvertently use global variables that you meant to be local. (This is a particularly easy mistake to make with simple variable names like @code{i}, @code{j}, etc.) -@item -e @var{program-text} -@itemx --source @var{program-text} -@cindex @code{-e} option -@cindex @code{--source} option +@item @option{-D}[@var{file}] +@itemx @option{--debug}[@code{=}@var{file}] +@cindex @option{-D} option +@cindex @option{--debug} option +@cindex @command{awk} debugging, enabling +Enable debugging of @command{awk} programs +(@pxref{Debugging}). +By default, the debugger reads commands interactively from the keyboard +(standard input). +The optional @var{file} argument allows you to specify a file with a list +of commands for the debugger to execute noninteractively. +No space is allowed between the @option{-D} and @var{file}, if +@var{file} is supplied. + +@item @option{-e} @var{program-text} +@itemx @option{--source} @var{program-text} +@cindex @option{-e} option +@cindex @option{--source} option @cindex source code, mixing Provide program source code in the @var{program-text}. This option allows you to mix source code in files with source @@ -3153,16 +3917,16 @@ This is particularly useful when you have library functions that you want to use from your command-line programs (@pxref{AWKPATH Variable}). -@item -E @var{file} -@itemx --exec @var{file} -@cindex @code{-E} option -@cindex @code{--exec} option +@item @option{-E} @var{file} +@itemx @option{--exec} @var{file} +@cindex @option{-E} option +@cindex @option{--exec} option @cindex @command{awk} programs, location of @cindex CGI, @command{awk} scripts for Similar to @option{-f}, read @command{awk} program text from @var{file}. There are two differences from @option{-f}: -@itemize @bullet +@itemize @value{BULLET} @item This option terminates option processing; anything else on the command line is passed on directly to the @command{awk} program. @@ -3175,7 +3939,13 @@ Command-line variable assignments of the form This option is particularly necessary for World Wide Web CGI applications that pass arguments through the URL; using this option prevents a malicious (or other) user from passing in options, assignments, or @command{awk} source -code (via @option{--source}) to the CGI application. This option should be used +code (via @option{-e}) to the CGI application.@footnote{For more detail, +please see Section 4.4 of @uref{http://www.ietf.org/rfc/rfc3875, +RFC 3875}. Also see the +@uref{http://lists.gnu.org/archive/html/bug-gawk/2014-11/msg00022.html, +explanatory note sent to the @command{gawk} bug +mailing list}.} +This option should be used with @samp{#!} scripts (@pxref{Executable Scripts}), like so: @example @@ -3184,36 +3954,69 @@ with @samp{#!} scripts (@pxref{Executable Scripts}), like so: @var{awk program here @dots{}} @end example -@item -g -@itemx --gen-pot -@cindex @code{-g} option -@cindex @code{--gen-pot} option +@item @option{-g} +@itemx @option{--gen-pot} +@cindex @option{-g} option +@cindex @option{--gen-pot} option @cindex portable object files, generating @cindex files, portable object, generating Analyze the source program and -generate a GNU @code{gettext} Portable Object Template file on standard +generate a GNU @command{gettext} portable object template file on standard output for all string constants that have been marked for translation. @xref{Internationalization}, for information about this option. -@item -h -@itemx --help -@cindex @code{-h} option -@cindex @code{--help} option +@item @option{-h} +@itemx @option{--help} +@cindex @option{-h} option +@cindex @option{--help} option @cindex GNU long options, printing list of @cindex options, printing list of @cindex printing, list of options -Print a ``usage'' message summarizing the short and long style options +Print a ``usage'' message summarizing the short- and long-style options that @command{gawk} accepts and then exit. -@item -L @r{[}value@r{]} -@itemx --lint@r{[}=value@r{]} -@cindex @code{-l} option -@cindex @code{--lint} option +@item @option{-i} @var{source-file} +@itemx @option{--include} @var{source-file} +@cindex @option{-i} option +@cindex @option{--include} option +@cindex @command{awk} programs, location of +Read an @command{awk} source library from @var{source-file}. This option +is completely equivalent to using the @code{@@include} directive inside +your program. It is very similar to the @option{-f} option, +but there are two important differences. First, when @option{-i} is +used, the program source is not loaded if it has been previously +loaded, whereas with @option{-f}, @command{gawk} always loads the file. +Second, because this option is intended to be used with code libraries, +@command{gawk} does not recognize such files as constituting main program +input. Thus, after processing an @option{-i} argument, @command{gawk} +still expects to find the main source code via the @option{-f} option +or on the command line. + +@item @option{-l} @var{ext} +@itemx @option{--load} @var{ext} +@cindex @option{-l} option +@cindex @option{--load} option +@cindex loading, extensions +Load a dynamic extension named @var{ext}. Extensions +are stored as system shared libraries. +This option searches for the library using the @env{AWKLIBPATH} +environment variable. The correct library suffix for your platform will be +supplied by default, so it need not be specified in the extension name. +The extension initialization routine should be named @code{dl_load()}. +An alternative is to use the @code{@@load} keyword inside the program to load +a shared library. This advanced feature is described in detail in @ref{Dynamic Extensions}. + +@item @option{-L}[@var{value}] +@itemx @option{--lint}[@code{=}@var{value}] +@cindex @option{-l} option +@cindex @option{--lint} option @cindex lint checking, issuing warnings @cindex warnings, issuing Warn about constructs that are dubious or nonportable to other @command{awk} implementations. +No space is allowed between the @option{-L} and @var{value}, if +@var{value} is supplied. Some warnings are issued when @command{gawk} first reads your program. Others are issued at runtime, as your program executes. With an optional argument of @samp{fatal}, @@ -3229,10 +4032,18 @@ when eliminating problems pointed out by @option{--lint}, you should take care to search for all occurrences of each inappropriate construct. As @command{awk} programs are usually short, doing so is not burdensome. -@item -n -@itemx --non-decimal-data -@cindex @code{-n} option -@cindex @code{--non-decimal-data} option +@item @option{-M} +@itemx @option{--bignum} +@cindex @option{-M} option +@cindex @option{--bignum} option +Force arbitrary-precision arithmetic on numbers. This option has no effect +if @command{gawk} is not compiled to use the GNU MPFR and MP libraries +(@pxref{Arbitrary Precision Arithmetic}). + +@item @option{-n} +@itemx @option{--non-decimal-data} +@cindex @option{-n} option +@cindex @option{--non-decimal-data} option @cindex hexadecimal values@comma{} enabling interpretation of @cindex octal values@comma{} enabling interpretation of @cindex troubleshooting, @code{--non-decimal-data} option @@ -3241,30 +4052,46 @@ values in input data (@pxref{Nondecimal Data}). @quotation CAUTION -This option can severely break old programs. -Use with care. +This option can severely break old programs. Use with care. Also note +that this option may disappear in a future version of @command{gawk}. @end quotation -@item -N -@itemx --use-lc-numeric -@cindex @code{-N} option -@cindex @code{--use-lc-numeric} option +@item @option{-N} +@itemx @option{--use-lc-numeric} +@cindex @option{-N} option +@cindex @option{--use-lc-numeric} option Force the use of the locale's decimal point character when parsing numeric input data (@pxref{Locales}). -@item -O -@itemx --optimize -@cindex @code{--optimize} option -@cindex @code{-O} option +@item @option{-o}[@var{file}] +@itemx @option{--pretty-print}[@code{=}@var{file}] +@cindex @option{-o} option +@cindex @option{--pretty-print} option +Enable pretty-printing of @command{awk} programs. +By default, the output program is created in a file named @file{awkprof.out} +(@pxref{Profiling}). +The optional @var{file} argument allows you to specify a different +@value{FN} for the output. +No space is allowed between the @option{-o} and @var{file}, if +@var{file} is supplied. + +@quotation NOTE +In the past, this option would also execute your program. +This is no longer the case. +@end quotation + +@item @option{-O} +@itemx @option{--optimize} +@cindex @option{--optimize} option +@cindex @option{-O} option Enable some optimizations on the internal representation of the program. -At the moment this includes just simple constant folding. The @command{gawk} -maintainer hopes to add more optimizations over time. - -@item -p@r{[}@var{file}@r{]} -@itemx --profile@r{[}=@var{file}@r{]} -@cindex @code{-p} option -@cindex @code{--profile} option -@cindex @command{awk} programs, profiling, enabling +At the moment, this includes just simple constant folding. + +@item @option{-p}[@var{file}] +@itemx @option{--profile}[@code{=}@var{file}] +@cindex @option{-p} option +@cindex @option{--profile} option +@cindex @command{awk} profiling, enabling Enable profiling of @command{awk} programs (@pxref{Profiling}). By default, profiles are created in a file named @file{awkprof.out}. @@ -3273,27 +4100,25 @@ The optional @var{file} argument allows you to specify a different No space is allowed between the @option{-p} and @var{file}, if @var{file} is supplied. -When run with @command{gawk}, the profile is just a ``pretty printed'' version -of the program. When run with @command{pgawk}, the profile contains execution -counts for each statement in the program in the left margin, and function -call counts for each function. +The profile contains execution counts for each statement in the program +in the left margin, and function call counts for each function. -@item -P -@itemx --posix -@cindex @code{-P} option -@cindex @code{--posix} option +@item @option{-P} +@itemx @option{--posix} +@cindex @option{-P} option +@cindex @option{--posix} option @cindex POSIX mode @cindex @command{gawk}, extensions@comma{} disabling Operate in strict POSIX mode. This disables all @command{gawk} extensions (just like @option{--traditional}) and disables all extensions not allowed by POSIX. -@xref{Common Extensions}, for a summary of the extensions +@DBXREF{Common Extensions} for a summary of the extensions in @command{gawk} that are disabled by this option. Also, the following additional restrictions apply: -@itemize @bullet +@itemize @value{BULLET} @cindex newlines @cindex whitespace, newlines as @@ -3309,7 +4134,7 @@ Newlines are not allowed after @samp{?} or @samp{:} @cindex @code{FS} variable, as TAB character @item -Specifying @samp{-Ft} on the command-line does not set the value +Specifying @samp{-Ft} on the command line does not set the value of @code{FS} to be a single TAB character (@pxref{Field Separators}). @@ -3322,36 +4147,28 @@ data (@pxref{Locales}). @c @cindex automatic warnings @c @cindex warnings, automatic -@cindex @code{--traditional} option, @code{--posix} option and -@cindex @code{--posix} option, @code{--traditional} option and +@cindex @option{--traditional} option, @code{--posix} option and +@cindex @option{--posix} option, @code{--traditional} option and If you supply both @option{--traditional} and @option{--posix} on the command line, @option{--posix} takes precedence. @command{gawk} -also issues a warning if both options are supplied. +issues a warning if both options are supplied. -@item -r -@itemx --re-interval -@cindex @code{-r} option -@cindex @code{--re-interval} option +@item @option{-r} +@itemx @option{--re-interval} +@cindex @option{-r} option +@cindex @option{--re-interval} option @cindex regular expressions, interval expressions and Allow interval expressions (@pxref{Regexp Operators}) in regexps. This is now @command{gawk}'s default behavior. -Nevertheless, this option remains both for backward compatibility, -and for use in combination with the @option{--traditional} option. - -@item -R @var{file} -@itemx --command=@var{file} -@cindex @code{-R} option -@cindex @code{--command} option -@command{dgawk} only. -Read @command{dgawk} debugger options and commands from @var{file}. -@xref{Dgawk Info}, for more information. - -@item -S -@itemx --sandbox -@cindex @code{-S} option -@cindex @code{--sandbox} option +Nevertheless, this option remains (both for backward compatibility +and for use in combination with @option{--traditional}). + +@item @option{-S} +@itemx @option{--sandbox} +@cindex @option{-S} option +@cindex @option{--sandbox} option @cindex sandbox mode Disable the @code{system()} function, input redirections with @code{getline}, @@ -3359,20 +4176,20 @@ output redirections with @code{print} and @code{printf}, and dynamic extensions. This is particularly useful when you want to run @command{awk} scripts from questionable sources and need to make sure the scripts -can't access your system (other than the specified input data file). +can't access your system (other than the specified input @value{DF}). -@item -t -@itemx --lint-old -@cindex @code{--L} option -@cindex @code{--lint-old} option +@item @option{-t} +@itemx @option{--lint-old} +@cindex @option{-L} option +@cindex @option{--lint-old} option Warn about constructs that are not available in the original version of @command{awk} from Version 7 Unix (@pxref{V7/SVR3.1}). -@item -V -@itemx --version -@cindex @code{-V} option -@cindex @code{--version} option +@item @option{-V} +@itemx @option{--version} +@cindex @option{-V} option +@cindex @option{--version} option @cindex @command{gawk}, versions of, information about@comma{} printing Print version information for this particular copy of @command{gawk}. This allows you to determine if your copy of @command{gawk} is up to date @@ -3386,43 +4203,44 @@ As long as program text has been supplied, any other options are flagged as invalid with a warning message but are otherwise ignored. -@cindex @code{-F} option, @code{-Ft} sets @code{FS} to TAB +@cindex @option{-F} option, @option{-Ft} sets @code{FS} to TAB In compatibility mode, as a special case, if the value of @var{fs} supplied to the @option{-F} option is @samp{t}, then @code{FS} is set to the TAB character (@code{"\t"}). This is true only for @option{--traditional} and not for @option{--posix} (@pxref{Field Separators}). -@cindex @code{-f} option, on command line +@cindex @option{-f} option, multiple uses The @option{-f} option may be used more than once on the command line. If it is, @command{awk} reads its program source from all of the named files, as if they had been concatenated together into one big file. This is useful for creating libraries of @command{awk} functions. These functions can be written once and then retrieved from a standard place, instead -of having to be included into each individual program. +of having to be included in each individual program. +The @option{-i} option is similar in this regard. (As mentioned in @ref{Definition Syntax}, function names must be unique.) With standard @command{awk}, library functions can still be used, even -if the program is entered at the terminal, +if the program is entered at the keyboard, by specifying @samp{-f /dev/tty}. After typing your program, -type @kbd{@value{CTL}-d} (the end-of-file character) to terminate it. +type @kbd{Ctrl-d} (the end-of-file character) to terminate it. (You may also use @samp{-f -} to read program source from the standard -input but then you will not be able to also use the standard input as a +input, but then you will not be able to also use the standard input as a source of data.) -Because it is clumsy using the standard @command{awk} mechanisms to mix source -file and command-line @command{awk} programs, @command{gawk} provides the -@option{--source} option. This does not require you to pre-empt the standard -input for your source code; it allows you to easily mix command-line -and library source code -(@pxref{AWKPATH Variable}). -The @option{--source} option may also be used multiple times on the command line. - -@cindex @code{--source} option -If no @option{-f} or @option{--source} option is specified, then @command{gawk} -uses the first non-option command-line argument as the text of the +Because it is clumsy using the standard @command{awk} mechanisms to mix +source file and command-line @command{awk} programs, @command{gawk} +provides the @option{-e} option. This does not require you to +preempt the standard input for your source code; it allows you to easily +mix command-line and library source code (@pxref{AWKPATH Variable}). +As with @option{-f}, the @option{-e} and @option{-i} +options may also be used multiple times on the command line. + +@cindex @option{-e} option +If no @option{-f} or @option{-e} option is specified, then @command{gawk} +uses the first nonoption command-line argument as the text of the program source code. @cindex @env{POSIXLY_CORRECT} environment variable @@ -3430,7 +4248,7 @@ program source code. @cindex POSIX mode If the environment variable @env{POSIXLY_CORRECT} exists, then @command{gawk} behaves in strict POSIX mode, exactly as if -you had supplied the @option{--posix} command-line option. +you had supplied @option{--posix}. Many GNU programs look for this environment variable to suppress extensions that conflict with POSIX, but @command{gawk} behaves differently: it suppresses all extensions, even those that do not @@ -3461,8 +4279,6 @@ setenv POSIXLY_CORRECT true Having @env{POSIXLY_CORRECT} set is not recommended for daily use, but it is good for testing the portability of your programs to other environments. -@c ENDOFRANGE ocl -@c ENDOFRANGE clo @node Other Arguments @section Other Command-Line Arguments @@ -3473,22 +4289,32 @@ Any additional arguments on the command line are normally treated as input files to be processed in the order specified. However, an argument that has the form @code{@var{var}=@var{value}}, assigns the value @var{value} to the variable @var{var}---it does not specify a -file at all. -(See -@ref{Assignment Options}.) +file at all. (See @ref{Assignment Options}.) In the following example, +@var{count=1} is a variable assignment, not a @value{FN}: + +@example +awk -f program.awk file1 count=1 file2 +@end example @cindex @command{gawk}, @code{ARGIND} variable in @cindex @code{ARGIND} variable, command-line arguments +@cindex @code{ARGV} array, indexing into @cindex @code{ARGC}/@code{ARGV} variables, command-line arguments -All these arguments are made available to your @command{awk} program in the +All the command-line arguments are made available to your @command{awk} program in the @code{ARGV} array (@pxref{Built-in Variables}). Command-line options and the program text (if present) are omitted from @code{ARGV}. All other arguments, including variable assignments, are included. As each element of @code{ARGV} is processed, @command{gawk} -sets the variable @code{ARGIND} to the index in @code{ARGV} of the +sets @code{ARGIND} to the index in @code{ARGV} of the current element. +@c FIXME: One day, move the ARGC and ARGV node closer to here. +Changing @code{ARGC} and @code{ARGV} in your @command{awk} program lets +you control how @command{awk} processes the input files; this is described +in more detail in @ref{ARGC and ARGV}. + @cindex input files, variable assignments and +@cindex variable assignments and input files The distinction between @value{FN} arguments and variable-assignment arguments is made when @command{awk} is about to open the next input file. At that point in execution, it checks the @value{FN} to see whether @@ -3507,7 +4333,7 @@ The variable values given on the command line are processed for escape sequences (@pxref{Escape Sequences}). @value{DARKCORNER} -In some earlier implementations of @command{awk}, when a variable assignment +In some very early implementations of @command{awk}, when a variable assignment occurred before any @value{FN}s, the assignment would happen @emph{before} the @code{BEGIN} rule was executed. @command{awk}'s behavior was thus inconsistent; some command-line assignments were available inside the @@ -3519,7 +4345,7 @@ upon the old behavior. The variable assignment feature is most useful for assigning to variables such as @code{RS}, @code{OFS}, and @code{ORS}, which control input and -output formats before scanning the @value{DF}s. It is also useful for +output formats, before scanning the @value{DF}s. It is also useful for controlling state if multiple passes are needed over a @value{DF}. For example: @@ -3561,11 +4387,12 @@ with @code{getline}. Some other versions of @command{awk} also support this, but it is not standard. (Some operating systems provide a @file{/dev/stdin} file -in the file system, however, @command{gawk} always processes +in the filesystem; however, @command{gawk} always processes this @value{FN} itself.) @node Environment Variables @section The Environment Variables @command{gawk} Uses +@cindex environment variables used by @command{gawk} A number of environment variables influence how @command{gawk} behaves. @@ -3573,104 +4400,153 @@ behaves. @menu * AWKPATH Variable:: Searching directories for @command{awk} programs. +* AWKLIBPATH Variable:: Searching directories for @command{awk} shared + libraries. * Other Environment Variables:: The environment variables. @end menu @node AWKPATH Variable @subsection The @env{AWKPATH} Environment Variable @cindex @env{AWKPATH} environment variable -@cindex directories, searching -@cindex search paths +@cindex directories, searching for source files @cindex search paths, for source files -@cindex differences in @command{awk} and @command{gawk}, @code{AWKPATH} environment variable +@cindex differences in @command{awk} and @command{gawk}, @env{AWKPATH} environment variable @ifinfo The previous @value{SECTION} described how @command{awk} program files can be named -on the command-line with the @option{-f} option. +on the command line with the @option{-f} option. @end ifinfo In most @command{awk} -implementations, you must supply a precise path name for each program +implementations, you must supply a precise pathname for each program file, unless the file is in the current directory. -But in @command{gawk}, if the @value{FN} supplied to the @option{-f} option -does not contain a @samp{/}, then @command{gawk} searches a list of -directories (called the @dfn{search path}), one by one, looking for a +But with @command{gawk}, if the @value{FN} supplied to the @option{-f} +or @option{-i} options +does not contain a directory separator @samp{/}, then @command{gawk} searches a list of +directories (called the @dfn{search path}) one by one, looking for a file with the specified name. The search path is a string consisting of directory names -separated by colons. @command{gawk} gets its search path from the +separated by colons.@footnote{Semicolons on MS-Windows and MS-DOS.} +@command{gawk} gets its search path from the @env{AWKPATH} environment variable. If that variable does not exist, -@command{gawk} uses a default path, -@samp{.:/usr/local/share/awk}.@footnote{Your version of @command{gawk} -may use a different directory; it -will depend upon how @command{gawk} was built and installed. The actual -directory is the value of @samp{$(datadir)} generated when -@command{gawk} was configured. You probably don't need to worry about this, -though.} +or if it has an empty value, +@command{gawk} uses a default path (described shortly). -The search path feature is particularly useful for building libraries +The search path feature is particularly helpful for building libraries of useful @command{awk} functions. The library files can be placed in a standard directory in the default path and then specified on -the command line with a short @value{FN}. Otherwise, the full @value{FN} -would have to be typed for each file. +the command line with a short @value{FN}. Otherwise, you would have to +type the full @value{FN} for each file. -By using both the @option{--source} and @option{-f} options, your command-line +By using the @option{-i} or @option{-f} options, your command-line @command{awk} programs can use facilities in @command{awk} library files (@pxref{Library Functions}). Path searching is not done if @command{gawk} is in compatibility mode. This is true for both @option{--traditional} and @option{--posix}. @xref{Options}. -@quotation NOTE -To include -the current directory in the path, either place -@file{.} explicitly in the path or write a null entry in the -path. (A null entry is indicated by starting or ending the path with a -colon or by placing two colons next to each other (@samp{::}).) -This path search mechanism is similar +If the source code file is not found after the initial search, the path is searched +again after adding the suffix @samp{.awk} to the @value{FN}. + +@command{gawk}'s path search mechanism is similar to the shell's. -@c someday, @cite{The Bourne Again Shell}.... +(See @uref{http://www.gnu.org/software/bash/manual/, +@cite{The Bourne-Again SHell manual}}.) +It treats a null entry in the path as indicating the current +directory. +(A null entry is indicated by starting or ending the path with a +colon or by placing two colons next to each other [@samp{::}].) -However, @command{gawk} always looks in the current directory @emph{before} -searching @env{AWKPATH}, so there is no real reason to include -the current directory in the search path. -@c Prior to 4.0, gawk searched the current directory after the -@c path search, but it's not worth documenting it. +@quotation NOTE +To include the current directory in the path, either place @file{.} +as an entry in the path or write a null entry in the path. + +Different past versions of @command{gawk} would also look explicitly in +the current directory, either before or after the path search. As of +@value{PVERSION} 4.1.2, this no longer happens; if you wish to look +in the current directory, you must include @file{.} either as a separate +entry or as a null entry in the search path. @end quotation -If @env{AWKPATH} is not defined in the -environment, @command{gawk} places its default search path into -@code{ENVIRON["AWKPATH"]}. This makes it easy to determine -the actual search path that @command{gawk} will use -from within an @command{awk} program. +The default value for @env{AWKPATH} is +@samp{.:/usr/local/share/awk}.@footnote{Your version of @command{gawk} +may use a different directory; it +will depend upon how @command{gawk} was built and installed. The actual +directory is the value of @code{$(datadir)} generated when +@command{gawk} was configured. You probably don't need to worry about this, +though.} Since @file{.} is included at the beginning, @command{gawk} +searches first in the current directory and then in @file{/usr/local/share/awk}. +In practice, this means that you will rarely need to change the +value of @env{AWKPATH}. + +@xref{Shell Startup Files}, for information on functions that help to +manipulate the @env{AWKPATH} variable. -While you can change @code{ENVIRON["AWKPATH"]} within your @command{awk} +@command{gawk} places the value of the search path that it used into +@code{ENVIRON["AWKPATH"]}. This provides access to the actual search +path value from within an @command{awk} program. + +Although you can change @code{ENVIRON["AWKPATH"]} within your @command{awk} program, this has no effect on the running program's behavior. This makes sense: the @env{AWKPATH} environment variable is used to find the program source files. Once your program is running, all the files have been found, and @command{gawk} no longer needs to use @env{AWKPATH}. +@node AWKLIBPATH Variable +@subsection The @env{AWKLIBPATH} Environment Variable +@cindex @env{AWKLIBPATH} environment variable +@cindex directories, searching for loadable extensions +@cindex search paths, for loadable extensions +@cindex differences in @command{awk} and @command{gawk}, @code{AWKLIBPATH} environment variable + +The @env{AWKLIBPATH} environment variable is similar to the @env{AWKPATH} +variable, but it is used to search for loadable extensions (stored as +system shared libraries) specified with the @option{-l} option rather +than for source files. If the extension is not found, the path is +searched again after adding the appropriate shared library suffix for +the platform. For example, on GNU/Linux systems, the suffix @samp{.so} +is used. The search path specified is also used for extensions loaded +via the @code{@@load} keyword (@pxref{Loading Shared Libraries}). + +If @env{AWKLIBPATH} does not exist in the environment, or if it has +an empty value, @command{gawk} uses a default path; this +is typically @samp{/usr/local/lib/gawk}, although it can vary depending +upon how @command{gawk} was built. + +@xref{Shell Startup Files}, for information on functions that help to +manipulate the @env{AWKLIBPATH} variable. + +@command{gawk} places the value of the search path that it used into +@code{ENVIRON["AWKLIBPATH"]}. This provides access to the actual search +path value from within an @command{awk} program. + @node Other Environment Variables @subsection Other Environment Variables A number of other environment variables affect @command{gawk}'s behavior, but they are more specialized. Those in the following -list are meant to be used by regular users. +list are meant to be used by regular users: @table @env -@item POSIXLY_CORRECT -Causes @command{gawk} to switch POSIX compatibility -mode, disabling all traditional and GNU extensions. -@xref{Options}. - -@item GAWK_SOCK_RETRIES -Controls the number of time @command{gawk} will attempt to -retry a two-way TCP/IP (socket) connection before giving up. -@xref{TCP/IP Networking}. - @item GAWK_MSEC_SLEEP Specifies the interval between connection retries, in milliseconds. On systems that do not support the @code{usleep()} system call, the value is rounded up to an integral number of seconds. + +@item GAWK_READ_TIMEOUT +Specifies the time, in milliseconds, for @command{gawk} to +wait for input before returning with an error. +@xref{Read Timeout}. + +@item GAWK_SOCK_RETRIES +Controls the number of times @command{gawk} attempts to +retry a two-way TCP/IP (socket) connection before giving up. +@xref{TCP/IP Networking}. + +@item POSIXLY_CORRECT +Causes @command{gawk} to switch to POSIX-compatibility +mode, disabling all traditional and GNU extensions. +@xref{Options}. @end table The environment variables in the following list are meant @@ -3678,13 +4554,18 @@ for use by the @command{gawk} developers for testing and tuning. They are subject to change. The variables are: @table @env -@item AVG_CHAIN_MAX -The average number of items @command{gawk} will maintain on a -hash chain for managing arrays. +@item AWKBUFSIZE +This variable only affects @command{gawk} on POSIX-compliant systems. +With a value of @samp{exact}, @command{gawk} uses the size of each input +file as the size of the memory buffer to allocate for I/O. Otherwise, +the value should be a number, and @command{gawk} uses that number as +the size of the buffer to allocate. (When this variable is not set, +@command{gawk} uses the smaller of the file's size and the ``default'' +blocksize, which is usually the filesystem's I/O blocksize.) @item AWK_HASH If this variable exists with a value of @samp{gst}, @command{gawk} -will switch to using the hash function from GNU Smalltalk for +switches to using the hash function from GNU Smalltalk for managing arrays. This function may be marginally faster than the standard function. @@ -3694,6 +4575,14 @@ files one line at a time, instead of reading in blocks. This exists for debugging problems on filesystems on non-POSIX operating systems where I/O is performed in records, not in blocks. +@item GAWK_MSG_SRC +If this variable exists, @command{gawk} includes the @value{FN} +and line number within the @command{gawk} source code +from which warning and/or fatal messages +are generated. Its purpose is to help isolate the source of a +message, as there are multiple places that produce the +same warning or error message. + @item GAWK_NO_DFA If this variable exists, @command{gawk} does not use the DFA regexp matcher for ``does it match'' kinds of tests. This can cause @command{gawk} @@ -3706,9 +4595,17 @@ coordinate with each other.) This specifies the amount by which @command{gawk} should grow its internal evaluation stack, when needed. +@item INT_CHAIN_MAX +This specifies intended maximum number of items @command{gawk} will maintain on a +hash chain for managing arrays indexed by integers. + +@item STR_CHAIN_MAX +This specifies intended maximum number of items @command{gawk} will maintain on a +hash chain for managing arrays indexed by strings. + @item TIDYMEM If this variable exists, @command{gawk} uses the @code{mtrace()} library -calls from GNU LIBC to help track down possible memory leaks. +calls from the GNU C library to help track down possible memory leaks. @end table @node Exit Status @@ -3727,25 +4624,29 @@ If an error occurs, @command{gawk} exits with the value of the C constant @code{EXIT_FAILURE}. This is usually one. If @command{gawk} exits because of a fatal error, the exit -status is 2. On non-POSIX systems, this value may be mapped +status is two. On non-POSIX systems, this value may be mapped to @code{EXIT_FAILURE}. @node Include Files -@section Including Other Files Into Your Program +@section Including Other Files into Your Program @c Panos Papadopoulos <panos1962@gmail.com> contributed the original @c text for this section. This @value{SECTION} describes a feature that is specific to @command{gawk}. -The @samp{@@include} keyword can be used to read external @command{awk} source +@cindex @code{@@include} directive +@cindex file inclusion, @code{@@include} directive +@cindex including files, @code{@@include} directive +The @code{@@include} keyword can be used to read external @command{awk} source files. This gives you the ability to split large @command{awk} source files into smaller, more manageable pieces, and also lets you reuse common @command{awk} code from various @command{awk} scripts. In other words, you can group -together @command{awk} functions, used to carry out specific tasks, +together @command{awk} functions used to carry out specific tasks into external files. These files can be used just like function libraries, -using the @samp{@@include} keyword in conjunction with the @code{AWKPATH} -environment variable. +using the @code{@@include} keyword in conjunction with the @env{AWKPATH} +environment variable. Note that source files may also be included +using the @option{-i} option. Let's see an example. We'll start with two (trivial) @command{awk} scripts, namely @@ -3772,19 +4673,19 @@ produces the following result: @example $ @kbd{gawk -f test2} -@print{} This is file test1. -@print{} This is file test2. +@print{} This is script test1. +@print{} This is script test2. @end example -@code{gawk} runs the @file{test2} script which includes @file{test1} -using the @samp{@@include} -keyword. So, to include external @command{awk} source files you just -use @samp{@@include} followed by the name of the file to be included, +@code{gawk} runs the @file{test2} script, which includes @file{test1} +using the @code{@@include} +keyword. So, to include external @command{awk} source files, you just +use @code{@@include} followed by the name of the file to be included, enclosed in double quotes. @quotation NOTE Keep in mind that this is a language construct and the @value{FN} cannot -be a string variable, but rather just a literal string in double quotes. +be a string variable, but rather just a literal string constant in double quotes. @end quotation The files to be included may be nested; e.g., given a third @@ -3803,9 +4704,9 @@ following results: @example $ @kbd{gawk -f test3} -@print{} This is file test1. -@print{} This is file test2. -@print{} This is file test3. +@print{} This is script test1. +@print{} This is script test2. +@print{} This is script test3. @end example The @value{FN} can, of course, be a pathname. For example: @@ -3815,57 +4716,99 @@ The @value{FN} can, of course, be a pathname. For example: @end example @noindent -or: +and: @example @@include "/usr/awklib/network" @end example @noindent -are valid. The @code{AWKPATH} environment variable can be of great -value when using @samp{@@include}. The same rules for the use -of the @code{AWKPATH} variable in command-line file searches +are both valid. The @env{AWKPATH} environment variable can be of great +value when using @code{@@include}. The same rules for the use +of the @env{AWKPATH} variable in command-line file searches (@pxref{AWKPATH Variable}) apply to -@samp{@@include} also. +@code{@@include} also. This is very helpful in constructing @command{gawk} function libraries. -If you have a large script with useful, general purpose @command{awk} +If you have a large script with useful, general-purpose @command{awk} functions, you can break it down into library files and put those files -in a special directory. You can then include those ``libraries,'' using -either the full pathnames of the files, or by setting the @code{AWKPATH} -environment variable accordingly and then using @samp{@@include} with -just the file part of the full pathname. Of course you can have more -than one directory to keep library files; the more complex the working +in a special directory. You can then include those ``libraries,'' +either by using the full pathnames of the files, or by setting the @env{AWKPATH} +environment variable accordingly and then using @code{@@include} with +just the file part of the full pathname. Of course, +you can keep library files in more than one directory; +the more complex the working environment is, the more directories you may need to organize the files to be included. Given the ability to specify multiple @option{-f} options, the -@samp{@@include} mechanism is not strictly necessary. -However, the @samp{@@include} keyword +@code{@@include} mechanism is not strictly necessary. +However, the @code{@@include} keyword can help you in constructing self-contained @command{gawk} programs, thus reducing the need for writing complex and tedious command lines. -In particular, @samp{@@include} is very useful for writing CGI scripts +In particular, @code{@@include} is very useful for writing CGI scripts to be run from web pages. As mentioned in @ref{AWKPATH Variable}, the current directory is always -searched first for source files, before searching in @env{AWKPATH}, -and this also applies to files named with @samp{@@include}. +searched first for source files, before searching in @env{AWKPATH}; +this also applies to files named with @code{@@include}. + +@node Loading Shared Libraries +@section Loading Dynamic Extensions into Your Program + +This @value{SECTION} describes a feature that is specific to @command{gawk}. + +@cindex @code{@@load} directive +@cindex loading extensions, @code{@@load} directive +@cindex extensions, loading, @code{@@load} directive +The @code{@@load} keyword can be used to read external @command{awk} extensions +(stored as system shared libraries). +This allows you to link in compiled code that may offer superior +performance and/or give you access to extended capabilities not supported +by the @command{awk} language. The @env{AWKLIBPATH} variable is used to +search for the extension. Using @code{@@load} is completely equivalent +to using the @option{-l} command-line option. + +If the extension is not initially found in @env{AWKLIBPATH}, another +search is conducted after appending the platform's default shared library +suffix to the @value{FN}. For example, on GNU/Linux systems, the suffix +@samp{.so} is used: + +@example +$ @kbd{gawk '@@load "ordchr"; BEGIN @{print chr(65)@}'} +@print{} A +@end example + +@noindent +This is equivalent to the following example: + +@example +$ @kbd{gawk -lordchr 'BEGIN @{print chr(65)@}'} +@print{} A +@end example + +@noindent +For command-line usage, the @option{-l} option is more convenient, +but @code{@@load} is useful for embedding inside an @command{awk} source file +that requires access to an extension. + +@ref{Dynamic Extensions}, describes how to write extensions (in C or C++) +that can be loaded with either @code{@@load} or the @option{-l} option. +It also describes the @code{ordchr} extension. @node Obsolete @section Obsolete Options and/or Features -@cindex features, advanced, See advanced features +@c update this section for each release! + @cindex options, deprecated @cindex features, deprecated @cindex obsolete features This @value{SECTION} describes features and/or command-line options from -previous releases of @command{gawk} that are either not available in the -current version or that are still supported but deprecated (meaning that +previous releases of @command{gawk} that either are not available in the +current version or are still supported but deprecated (meaning that they will @emph{not} be in the next release). -@c update this section for each release! - -@cindex @code{PROCINFO} array The process-related special files @file{/dev/pid}, @file{/dev/ppid}, @file{/dev/pgrpid}, and @file{/dev/user} were deprecated in @command{gawk} 3.1, but still worked. As of @value{PVERSION} 4.0, they are no longer @@ -3887,10 +4830,11 @@ in case some option becomes obsolete in a future version of @command{gawk}. @cindex Jedi knights @cindex Knights, jedi @quotation -@i{Use the Source, Luke!}@* -Obi-Wan +@i{Use the Source, Luke!} +@author Obi-Wan @end quotation +@cindex shells, sea This @value{SECTION} intentionally left blank. @@ -3903,7 +4847,7 @@ blank. @table @code @item -W nostalgia @itemx --nostalgia -Print the message @code{"awk: bailing out near line 1"} and dump core. +Print the message @samp{awk: bailing out near line 1} and dump core. This option was inspired by the common behavior of very early versions of Unix @command{awk} and by a t--shirt. The message is @emph{not} subject to translation in non-English locales. @@ -3919,15 +4863,15 @@ awk '@{ sum += $1 @} END @{ print sum @}' @end example @command{gawk} actually supports this but it is purposely undocumented -because it is considered bad style. The correct way to write such a program -is either +because it is bad style. The correct way to write such a program +is either: @example awk '@{ sum += $1 @} ; END @{ print sum @}' @end example @noindent -or +or: @example awk '@{ sum += $1 @} @@ -3935,8 +4879,7 @@ awk '@{ sum += $1 @} @end example @noindent -@xref{Statements/Lines}, for a fuller -explanation. +@xref{Statements/Lines}, for a fuller explanation. You can insert newlines after the @samp{;} in @code{for} loops. This seems to have been a long-undocumented feature in Unix @command{awk}. @@ -3947,35 +4890,62 @@ long-undocumented ``feature'' of Unix @code{awk}. @end ignore -@ignore -@c Try this -@iftex -@page -@headings off -@majorheading II@ @ @ Using @command{awk} and @command{gawk} -Part II shows how to use @command{awk} and @command{gawk} for problem solving. -There is lots of code here for you to read and learn from. -It contains the following chapters: +@node Invoking Summary +@section Summary -@itemize @bullet +@itemize @value{BULLET} @item -@ref{Library Functions}. +Use either +@samp{awk '@var{program}' @var{files}} +or +@samp{awk -f @var{program-file} @var{files}} +to run @command{awk}. @item -@ref{Sample Programs}. +The three standard options for all versions of @command{awk} are +@option{-f}, @option{-F}, and @option{-v}. @command{gawk} supplies these +and many others, as well as corresponding GNU-style long options. -@end itemize +@item +Nonoption command-line arguments are usually treated as @value{FN}s, +unless they have the form @samp{@var{var}=@var{value}}, in which case +they are taken as variable assignments to be performed at that point +in processing the input. -@page -@evenheading @thispage@ @ @ @strong{@value{TITLE}} @| @| -@oddheading @| @| @strong{@thischapter}@ @ @ @thispage -@end iftex -@end ignore +@item +All nonoption command-line arguments, excluding the program text, +are placed in the @code{ARGV} array. Adjusting @code{ARGC} and @code{ARGV} +affects how @command{awk} processes input. + +@item +You can use a single minus sign (@samp{-}) to refer to standard input +on the command line. @command{gawk} also lets you use the special +@value{FN} @file{/dev/stdin}. + +@item +@command{gawk} pays attention to a number of environment variables. +@env{AWKPATH}, @env{AWKLIBPATH}, and @env{POSIXLY_CORRECT} are the +most important ones. + +@item +@command{gawk}'s exit status conveys information to the program +that invoked it. Use the @code{exit} statement from within +an @command{awk} program to set the exit status. + +@item +@command{gawk} allows you to include other @command{awk} source files into +your program using the @code{@@include} statement and/or the @option{-i} +and @option{-f} command-line options. + +@item +@command{gawk} allows you to load additional functions written in C +or C++ using the @code{@@load} statement and/or the @option{-l} option. +(This advanced feature is described later, in @ref{Dynamic Extensions}.) +@end itemize @node Regexp @chapter Regular Expressions -@cindex regexp, See regular expressions -@c STARTOFRANGE regexp +@cindex regexp @cindex regular expressions A @dfn{regular expression}, or @dfn{regexp}, is a way of describing a @@ -3983,16 +4953,16 @@ set of strings. Because regular expressions are such a fundamental part of @command{awk} programming, their format and use deserve a separate @value{CHAPTER}. -@cindex forward slash (@code{/}) -@cindex @code{/} (forward slash) +@cindex forward slash (@code{/}) to enclose regular expressions +@cindex @code{/} (forward slash) to enclose regular expressions A regular expression enclosed in slashes (@samp{/}) is an @command{awk} pattern that matches every input record whose text belongs to that set. The simplest regular expression is a sequence of letters, numbers, or both. Such a regexp matches any string that contains that sequence. Thus, the regexp @samp{foo} matches any string containing @samp{foo}. -Therefore, the pattern @code{/foo/} matches any input record containing -the three characters @samp{foo} @emph{anywhere} in the record. Other +Thus, the pattern @code{/foo/} matches any input record containing +the three adjacent characters @samp{foo} @emph{anywhere} in the record. Other kinds of regexps let you specify more complicated classes of strings. @ifnotinfo @@ -4006,10 +4976,11 @@ regular expressions work, we present more complicated instances. * Escape Sequences:: How to write nonprinting characters. * Regexp Operators:: Regular Expression Operators. * Bracket Expressions:: What can go between @samp{[...]}. -* GNU Regexp Operators:: Operators specific to GNU software. -* Case-sensitivity:: How to do case-insensitive matching. * Leftmost Longest:: How much text matches. * Computed Regexps:: Using Dynamic Regexps. +* GNU Regexp Operators:: Operators specific to GNU software. +* Case-sensitivity:: How to do case-insensitive matching. +* Regexp Summary:: Regular expressions summary. @end menu @node Regexp Usage @@ -4020,15 +4991,15 @@ A regular expression can be used as a pattern by enclosing it in slashes. Then the regular expression is tested against the entire text of each record. (Normally, it only needs to match some part of the text in order to succeed.) For example, the -following prints the second field of each record that contains the string -@samp{foo} anywhere in it: +following prints the second field of each record where the string +@samp{li} appears anywhere in the record: @example -$ @kbd{awk '/foo/ @{ print $2 @}' BBS-list} -@print{} 555-1234 +$ @kbd{awk '/li/ @{ print $2 @}' mail-list} +@print{} 555-5553 +@print{} 555-0542 @print{} 555-6699 -@print{} 555-6480 -@print{} 555-2127 +@print{} 555-3430 @end example @cindex regular expressions, operators @@ -4040,9 +5011,9 @@ $ @kbd{awk '/foo/ @{ print $2 @}' BBS-list} @cindex @code{!} (exclamation point), @code{!~} operator @cindex exclamation point (@code{!}), @code{!~} operator @c @cindex operators, @code{!~} -@cindex @code{if} statement -@cindex @code{while} statement -@cindex @code{do}-@code{while} statement +@cindex @code{if} statement, use of regexps in +@cindex @code{while} statement, use of regexps in +@cindex @code{do}-@code{while} statement, use of regexps in @c @cindex statements, @code{if} @c @cindex statements, @code{while} @c @cindex statements, @code{do} @@ -4053,17 +5024,16 @@ and @samp{!~} perform regular expression comparisons. Expressions using these operators can be used as patterns, or in @code{if}, @code{while}, @code{for}, and @code{do} statements. (@xref{Statements}.) -For example: +For example, the following is true if the expression @var{exp} (taken +as a string) matches @var{regexp}: @example @var{exp} ~ /@var{regexp}/ @end example @noindent -is true if the expression @var{exp} (taken as a string) -matches @var{regexp}. The following example matches, or selects, -all input records with the uppercase letter @samp{J} somewhere in the -first field: +This example matches, or selects, all input records with the uppercase +letter @samp{J} somewhere in the first field: @example $ @kbd{awk '$1 ~ /J/' inventory-shipped} @@ -4101,6 +5071,7 @@ $ @kbd{awk '$1 !~ /J/' inventory-shipped} @end example @cindex regexp constants +@cindex constant regexps @cindex regular expressions, constants, See regexp constants When a regexp is enclosed in slashes, such as @code{/foo/}, we call it a @dfn{regexp constant}, much like @code{5.27} is a numeric constant and @@ -4109,7 +5080,7 @@ a @dfn{regexp constant}, much like @code{5.27} is a numeric constant and @node Escape Sequences @section Escape Sequences -@cindex escape sequences +@cindex escape sequences, in strings @cindex backslash (@code{\}), in escape sequences @cindex @code{\} (backslash), in escape sequences Some characters cannot be included literally in string constants @@ -4132,11 +5103,11 @@ string or regexp. Thus, the string whose contents are the two characters @samp{"} and @samp{\} must be written @code{"\"\\"}. Other escape sequences represent unprintable characters -such as TAB or newline. While there is nothing to stop you from entering most +such as TAB or newline. There is nothing to stop you from entering most unprintable characters directly in a string constant or regexp constant, -they may look ugly. +but they may look ugly. -The following table lists +The following list presents all the escape sequences used in @command{awk} and what they represent. Unless noted otherwise, all these escape sequences apply to both string constants and regexp constants: @@ -4149,39 +5120,39 @@ A literal backslash, @samp{\}. @cindex @code{\} (backslash), @code{\a} escape sequence @cindex backslash (@code{\}), @code{\a} escape sequence @item \a -The ``alert'' character, @kbd{@value{CTL}-g}, ASCII code 7 (BEL). -(This usually makes some sort of audible noise.) +The ``alert'' character, @kbd{Ctrl-g}, ASCII code 7 (BEL). +(This often makes some sort of audible noise.) @cindex @code{\} (backslash), @code{\b} escape sequence @cindex backslash (@code{\}), @code{\b} escape sequence @item \b -Backspace, @kbd{@value{CTL}-h}, ASCII code 8 (BS). +Backspace, @kbd{Ctrl-h}, ASCII code 8 (BS). @cindex @code{\} (backslash), @code{\f} escape sequence @cindex backslash (@code{\}), @code{\f} escape sequence @item \f -Formfeed, @kbd{@value{CTL}-l}, ASCII code 12 (FF). +Formfeed, @kbd{Ctrl-l}, ASCII code 12 (FF). @cindex @code{\} (backslash), @code{\n} escape sequence @cindex backslash (@code{\}), @code{\n} escape sequence @item \n -Newline, @kbd{@value{CTL}-j}, ASCII code 10 (LF). +Newline, @kbd{Ctrl-j}, ASCII code 10 (LF). @cindex @code{\} (backslash), @code{\r} escape sequence @cindex backslash (@code{\}), @code{\r} escape sequence @item \r -Carriage return, @kbd{@value{CTL}-m}, ASCII code 13 (CR). +Carriage return, @kbd{Ctrl-m}, ASCII code 13 (CR). @cindex @code{\} (backslash), @code{\t} escape sequence @cindex backslash (@code{\}), @code{\t} escape sequence @item \t -Horizontal TAB, @kbd{@value{CTL}-i}, ASCII code 9 (HT). +Horizontal TAB, @kbd{Ctrl-i}, ASCII code 9 (HT). @c @cindex @command{awk} language, V.4 version @cindex @code{\} (backslash), @code{\v} escape sequence @cindex backslash (@code{\}), @code{\v} escape sequence @item \v -Vertical tab, @kbd{@value{CTL}-k}, ASCII code 11 (VT). +Vertical TAB, @kbd{Ctrl-k}, ASCII code 11 (VT). @cindex @code{\} (backslash), @code{\}@var{nnn} escape sequence @cindex backslash (@code{\}), @code{\}@var{nnn} escape sequence @@ -4199,20 +5170,34 @@ between @samp{0} and @samp{7}. For example, the code for the ASCII ESC @item \x@var{hh}@dots{} The hexadecimal value @var{hh}, where @var{hh} stands for a sequence of hexadecimal digits (@samp{0}--@samp{9}, and either @samp{A}--@samp{F} -or @samp{a}--@samp{f}). Like the same construct -in ISO C, the escape sequence continues until the first nonhexadecimal -digit is seen. @value{COMMONEXT} -However, using more than two hexadecimal digits produces -undefined results. (The @samp{\x} escape sequence is not allowed in -POSIX @command{awk}.) +or @samp{a}--@samp{f}). A maximum of two digts are allowed after +the @samp{\x}. Any further hexadecimal digits are treated as simple +letters or numbers. @value{COMMONEXT} +(The @samp{\x} escape sequence is not allowed in POSIX awk.) + +@quotation CAUTION +In ISO C, the escape sequence continues until the first nonhexadecimal +digit is seen. +@c FIXME: Add exact version here. +For many years, @command{gawk} would continue incorporating +hexadecimal digits into the value until a non-hexadecimal digit +or the end of the string was encountered. +However, using more than two hexadecimal digits produced +undefined results. +As of @value{PVERSION} @strong{FIXME:} 4.3.0, only two digits +are processed. +@end quotation @cindex @code{\} (backslash), @code{\/} escape sequence @cindex backslash (@code{\}), @code{\/} escape sequence @item \/ A literal slash (necessary for regexp constants only). This sequence is used when you want to write a regexp -constant that contains a slash. Because the regexp is delimited by -slashes, you need to escape the slash that is part of the pattern, +constant that contains a slash +(such as @code{/.*:\/home\/[[:alnum:]]+:.*/}; the @samp{[[:alnum:]]} +notation is discussed in @ref{Bracket Expressions}). +Because the regexp is delimited by +slashes, you need to escape any slash that is part of the pattern, in order to tell @command{awk} to keep processing the rest of the regexp. @cindex @code{\} (backslash), @code{\"} escape sequence @@ -4220,8 +5205,10 @@ in order to tell @command{awk} to keep processing the rest of the regexp. @item \" A literal double quote (necessary for string constants only). This sequence is used when you want to write a string -constant that contains a double quote. Because the string is delimited by -double quotes, you need to escape the quote that is part of the string, +constant that contains a double quote +(such as @code{"He said \"hi!\" to her."}). +Because the string is delimited by +double quotes, you need to escape any quote that is part of the string, in order to tell @command{awk} to keep processing the rest of the string. @end table @@ -4231,7 +5218,7 @@ with a backslash have special meaning in regexps. In a regexp, a backslash before any character that is not in the previous list and not listed in -@ref{GNU Regexp Operators}, +@DBREF{GNU Regexp Operators} means that the next character should be taken literally, even if it would normally be a regexp operator. For example, @code{/a\+b/} matches the three characters @samp{a+b}. @@ -4240,29 +5227,58 @@ characters @samp{a+b}. @cindex @code{\} (backslash), in escape sequences @cindex portability For complete portability, do not use a backslash before any character not -shown in the previous list. +shown in the previous list or that is not an operator. -To summarize: +@c 11/2014: Moved so as to not stack sidebars +@cindex sidebar, Backslash Before Regular Characters +@ifdocbook +@docbook +<sidebar><title>Backslash Before Regular Characters</title> +@end docbook -@itemize @bullet -@item -The escape sequences in the table above are always processed first, -for both string constants and regexp constants. This happens very early, -as soon as @command{awk} reads your program. +@cindex portability, backslash in escape sequences +@cindex POSIX @command{awk}, backslashes in string constants +@cindex backslash (@code{\}), in escape sequences, POSIX and +@cindex @code{\} (backslash), in escape sequences, POSIX and -@item -@command{gawk} processes both regexp constants and dynamic regexps -(@pxref{Computed Regexps}), -for the special operators listed in -@ref{GNU Regexp Operators}. +@cindex troubleshooting, backslash before nonspecial character +If you place a backslash in a string constant before something that is +not one of the characters previously listed, POSIX @command{awk} purposely +leaves what happens as undefined. There are two choices: + +@c @cindex automatic warnings +@c @cindex warnings, automatic +@cindex Brian Kernighan's @command{awk} +@table @asis +@item Strip the backslash out +This is what BWK @command{awk} and @command{gawk} both do. +For example, @code{"a\qc"} is the same as @code{"aqc"}. +(Because this is such an easy bug both to introduce and to miss, +@command{gawk} warns you about it.) +Consider @samp{FS = @w{"[ \t]+\|[ \t]+"}} to use vertical bars +surrounded by whitespace as the field separator. There should be +two backslashes in the string: @samp{FS = @w{"[ \t]+\\|[ \t]+"}}.) +@c I did this! This is why I added the warning. + +@cindex @command{gawk}, escape sequences +@cindex Unix @command{awk}, backslashes in escape sequences +@cindex @command{mawk} utility +@item Leave the backslash alone +Some other @command{awk} implementations do this. +In such implementations, typing @code{"a\qc"} is the same as typing +@code{"a\\qc"}. +@end table + +@docbook +</sidebar> +@end docbook +@end ifdocbook + +@ifnotdocbook +@cartouche +@center @b{Backslash Before Regular Characters} -@item -A backslash before any other character means to treat that character -literally. -@end itemize -@c fakenode --- for prepinfo -@subheading Advanced Notes: Backslash Before Regular Characters @cindex portability, backslash in escape sequences @cindex POSIX @command{awk}, backslashes in string constants @cindex backslash (@code{\}), in escape sequences, POSIX and @@ -4275,9 +5291,10 @@ leaves what happens as undefined. There are two choices: @c @cindex automatic warnings @c @cindex warnings, automatic +@cindex Brian Kernighan's @command{awk} @table @asis @item Strip the backslash out -This is what Brian Kernighan's @command{awk} and @command{gawk} both do. +This is what BWK @command{awk} and @command{gawk} both do. For example, @code{"a\qc"} is the same as @code{"aqc"}. (Because this is such an easy bug both to introduce and to miss, @command{gawk} warns you about it.) @@ -4288,14 +5305,68 @@ two backslashes in the string: @samp{FS = @w{"[ \t]+\\|[ \t]+"}}.) @cindex @command{gawk}, escape sequences @cindex Unix @command{awk}, backslashes in escape sequences +@cindex @command{mawk} utility @item Leave the backslash alone Some other @command{awk} implementations do this. In such implementations, typing @code{"a\qc"} is the same as typing @code{"a\\qc"}. @end table +@end cartouche +@end ifnotdocbook + +To summarize: + +@itemize @value{BULLET} +@item +The escape sequences in the preceding list are always processed first, +for both string constants and regexp constants. This happens very early, +as soon as @command{awk} reads your program. + +@item +@command{gawk} processes both regexp constants and dynamic regexps +(@pxref{Computed Regexps}), +for the special operators listed in +@ref{GNU Regexp Operators}. + +@item +A backslash before any other character means to treat that character +literally. +@end itemize + +@cindex sidebar, Escape Sequences for Metacharacters +@ifdocbook +@docbook +<sidebar><title>Escape Sequences for Metacharacters</title> +@end docbook + +@cindex metacharacters, escape sequences for + +Suppose you use an octal or hexadecimal +escape to represent a regexp metacharacter. +(See @ref{Regexp Operators}.) +Does @command{awk} treat the character as a literal character or as a regexp +operator? + +@cindex dark corner, escape sequences, for metacharacters +Historically, such characters were taken literally. +@value{DARKCORNER} +However, the POSIX standard indicates that they should be treated +as real metacharacters, which is what @command{gawk} does. +In compatibility mode (@pxref{Options}), +@command{gawk} treats the characters represented by octal and hexadecimal +escape sequences literally when used in regexp constants. Thus, +@code{/a\52b/} is equivalent to @code{/a\*b/}. + +@docbook +</sidebar> +@end docbook +@end ifdocbook + +@ifnotdocbook +@cartouche +@center @b{Escape Sequences for Metacharacters} + -@c fakenode --- for prepinfo -@subheading Advanced Notes: Escape Sequences for Metacharacters @cindex metacharacters, escape sequences for Suppose you use an octal or hexadecimal @@ -4313,11 +5384,13 @@ In compatibility mode (@pxref{Options}), @command{gawk} treats the characters represented by octal and hexadecimal escape sequences literally when used in regexp constants. Thus, @code{/a\52b/} is equivalent to @code{/a\*b/}. +@end cartouche +@end ifnotdocbook @node Regexp Operators @section Regular Expression Operators -@c STARTOFRANGE regexpo @cindex regular expressions, operators +@cindex metacharacters in regular expressions You can combine regular expressions with special characters, called @dfn{regular expression operators} or @dfn{metacharacters}, to @@ -4327,57 +5400,61 @@ The escape sequences described @ifnotinfo earlier @end ifnotinfo -in @ref{Escape Sequences}, +in @DBREF{Escape Sequences} are valid inside a regexp. They are introduced by a @samp{\} and are recognized and converted into corresponding real characters as the very first step in processing regexps. Here is a list of metacharacters. All characters that are not escape -sequences and that are not listed in the table stand for themselves: +sequences and that are not listed here stand for themselves: -@table @code -@cindex backslash (@code{\}) -@cindex @code{\} (backslash) -@item \ -This is used to suppress the special meaning of a character when +@c Use @asis so the docbook comes out ok. Sigh. +@table @asis +@cindex backslash (@code{\}), regexp operator +@cindex @code{\} (backslash), regexp operator +@item @code{\} +This suppresses the special meaning of a character when matching. For example, @samp{\$} matches the character @samp{$}. @cindex regular expressions, anchors in @cindex Texinfo, chapter beginnings in files -@cindex @code{^} (caret) -@cindex caret (@code{^}) -@item ^ -This matches the beginning of a string. For example, @samp{^@@chapter} -matches @samp{@@chapter} at the beginning of a string and can be used +@cindex @code{^} (caret), regexp operator +@cindex caret (@code{^}), regexp operator +@item @code{^} +This matches the beginning of a string. @samp{^@@chapter} +matches @samp{@@chapter} at the beginning of a string, +for example, and can be used to identify chapter beginnings in Texinfo source files. The @samp{^} is known as an @dfn{anchor}, because it anchors the pattern to match only at the beginning of the string. It is important to realize that @samp{^} does not match the beginning of -a line embedded in a string. +a line (the point right after a @samp{\n} newline character) embedded in a string. The condition is not true in the following example: @example if ("line1\nLINE 2" ~ /^L/) @dots{} @end example -@cindex @code{$} (dollar sign) -@cindex dollar sign (@code{$}) -@item $ +@cindex @code{$} (dollar sign), regexp operator +@cindex dollar sign (@code{$}), regexp operator +@item @code{$} This is similar to @samp{^}, but it matches only at the end of a string. For example, @samp{p$} matches a record that ends with a @samp{p}. The @samp{$} is an anchor -and does not match the end of a line embedded in a string. +and does not match the end of a line +(the point right before a @samp{\n} newline character) +embedded in a string. The condition in the following example is not true: @example if ("line1\nLINE 2" ~ /1$/) @dots{} @end example -@cindex @code{.} (period) -@cindex period (@code{.}) -@item . @r{(period)} +@cindex @code{.} (period), regexp operator +@cindex period (@code{.}), regexp operator +@item @code{.} (period) This matches any single character, @emph{including} the newline character. For example, @samp{.P} matches any single character followed by a @samp{P} in a string. Using @@ -4392,12 +5469,13 @@ character, which is a character with all bits equal to zero. Otherwise, @sc{nul} is just another character. Other versions of @command{awk} may not be able to match the @sc{nul} character. -@cindex @code{[]} (square brackets) -@cindex square brackets (@code{[]}) +@cindex @code{[]} (square brackets), regexp operator +@cindex square brackets (@code{[]}), regexp operator @cindex bracket expressions @cindex character sets, See Also bracket expressions @cindex character lists, See bracket expressions -@item [@dots{}] +@cindex character classes, See bracket expressions +@item @code{[}@dots{}@code{]} This is called a @dfn{bracket expression}.@footnote{In other literature, you may see a bracket expression referred to as either a @dfn{character set}, a @dfn{character class}, or a @dfn{character list}.} @@ -4409,7 +5487,7 @@ is given in @ref{Bracket Expressions}. @cindex bracket expressions, complemented -@item [^ @dots{}] +@item @code{[^}@dots{}@code{]} This is a @dfn{complemented bracket expression}. The first character after the @samp{[} @emph{must} be a @samp{^}. It matches any characters @emph{except} those in the square brackets. For example, @samp{[^awk]} @@ -4418,20 +5496,19 @@ or @samp{k}. @cindex @code{|} (vertical bar) @cindex vertical bar (@code{|}) -@item | +@item @code{|} This is the @dfn{alternation operator} and it is used to specify -alternatives. -The @samp{|} has the lowest precedence of all the regular -expression operators. -For example, @samp{^P|[[:digit:]]} -matches any string that matches either @samp{^P} or @samp{[[:digit:]]}. This -means it matches any string that starts with @samp{P} or contains a digit. +alternatives. The @samp{|} has the lowest precedence of all the regular +expression operators. For example, @samp{^P|[aeiouy]} matches any string +that matches either @samp{^P} or @samp{[aeiouy]}. This means it matches +any string that starts with @samp{P} or contains (anywhere within it) +a lowercase English vowel. The alternation applies to the largest possible regexps on either side. -@cindex @code{()} (parentheses) -@cindex parentheses @code{()} -@item (@dots{}) +@cindex @code{()} (parentheses), regexp operator +@cindex parentheses @code{()}, regexp operator +@item @code{(}@dots{}@code{)} Parentheses are used for grouping in regular expressions, as in arithmetic. They can be used to concatenate regular expressions containing the alternation operator, @samp{|}. For example, @@ -4442,47 +5519,42 @@ explained further on in this list.) @cindex @code{*} (asterisk), @code{*} operator, as regexp operator @cindex asterisk (@code{*}), @code{*} operator, as regexp operator -@item * +@item @code{*} This symbol means that the preceding regular expression should be repeated as many times as necessary to find a match. For example, @samp{ph*} applies the @samp{*} symbol to the preceding @samp{h} and looks for matches of one @samp{p} followed by any number of @samp{h}s. This also matches just @samp{p} if no @samp{h}s are present. -The @samp{*} repeats the @emph{smallest} possible preceding expression. -(Use parentheses if you want to repeat a larger expression.) It finds -as many repetitions as possible. For example, -@samp{awk '/\(c[ad][ad]*r x\)/ @{ print @}' sample} -prints every record in @file{sample} containing a string of the form -@samp{(car x)}, @samp{(cdr x)}, @samp{(cadr x)}, and so on. -Notice the escaping of the parentheses by preceding them -with backslashes. - -@cindex @code{+} (plus sign) -@cindex plus sign (@code{+}) -@item + +There are two subtle points to understand about how @samp{*} works. +First, the @samp{*} applies only to the single preceding regular expression +component (e.g., in @samp{ph*}, it applies just to the @samp{h}). +To cause @samp{*} to apply to a larger subexpression, use parentheses: +@samp{(ph)*} matches @samp{ph}, @samp{phph}, @samp{phphph}, and so on. + +Second, @samp{*} finds as many repetitions as possible. If the text +to be matched is @samp{phhhhhhhhhhhhhhooey}, @samp{ph*} matches all of +the @samp{h}s. + +@cindex @code{+} (plus sign), regexp operator +@cindex plus sign (@code{+}), regexp operator +@item @code{+} This symbol is similar to @samp{*}, except that the preceding expression must be matched at least once. This means that @samp{wh+y} would match @samp{why} and @samp{whhy}, but not @samp{wy}, whereas -@samp{wh*y} would match all three of these strings. -The following is a simpler -way of writing the last @samp{*} example: +@samp{wh*y} would match all three. -@example -awk '/\(c[ad]+r x\)/ @{ print @}' sample -@end example - -@cindex @code{?} (question mark) regexp operator -@cindex question mark (@code{?}) regexp operator -@item ? +@cindex @code{?} (question mark), regexp operator +@cindex question mark (@code{?}), regexp operator +@item @code{?} This symbol is similar to @samp{*}, except that the preceding expression can be matched either once or not at all. For example, @samp{fe?d} matches @samp{fed} and @samp{fd}, but nothing else. -@cindex interval expressions -@item @{@var{n}@} -@itemx @{@var{n},@} -@itemx @{@var{n},@var{m}@} +@cindex interval expressions, regexp operator +@item @code{@{}@var{n}@code{@}} +@itemx @code{@{}@var{n}@code{,@}} +@itemx @code{@{}@var{n}@code{,}@var{m}@code{@}} One or two numbers inside braces denote an @dfn{interval expression}. If there is one number in the braces, the preceding regexp is repeated @var{n} times. @@ -4496,10 +5568,10 @@ is repeated at least @var{n} times: Matches @samp{whhhy}, but not @samp{why} or @samp{whhhhy}. @item wh@{3,5@}y -Matches @samp{whhhy}, @samp{whhhhy}, or @samp{whhhhhy}, only. +Matches @samp{whhhy}, @samp{whhhhy}, or @samp{whhhhhy} only. @item wh@{2,@}y -Matches @samp{whhy} or @samp{whhhy}, and so on. +Matches @samp{whhy}, @samp{whhhy}, and so on. @end table @cindex POSIX @command{awk}, interval expressions in @@ -4524,6 +5596,10 @@ it is good practice to always escape them with a backslash. Then the regexp constants are valid and work the way you want them to, using any version of @command{awk}.@footnote{Use two backslashes if you're using a string constant with a regexp operator or function.} + +Finally, when @samp{@{} and @samp{@}} appear in regexp constants +in a way that cannot be interpreted as an interval expression +(such as @code{/q@{a@}/}), then they stand for themselves. @end table @cindex precedence, regexp operators @@ -4544,23 +5620,22 @@ usage as a syntax error. If @command{gawk} is in compatibility mode (@pxref{Options}), interval expressions are not available in regular expressions. -@c ENDOFRANGE regexpo @node Bracket Expressions @section Using Bracket Expressions -@c STARTOFRANGE charlist @cindex bracket expressions @cindex bracket expressions, range expressions @cindex range expressions (regexps) +@cindex character lists in regular expression -As mentioned earlier, a bracket expression matches any character amongst +As mentioned earlier, a bracket expression matches any character among those listed between the opening and closing square brackets. Within a bracket expression, a @dfn{range expression} consists of two characters separated by a hyphen. It matches any single character that sorts between the two characters, based upon the system's native character set. For example, @samp{[0-9]} is equivalent to @samp{[0123456789]}. -(See @ref{Ranges and Locales}, for an explanation of how the POSIX +(See @DBREF{Ranges and Locales} for an explanation of how the POSIX standard and @command{gawk} have changed over time. This is mainly of historical interest.) @@ -4579,12 +5654,15 @@ bracket expression, put a @samp{\} in front of it. For example: @noindent matches either @samp{d} or @samp{]}. +Additionally, if you place @samp{]} right after the opening +@samp{[}, the closing bracket is treated as one of the +characters to be matched. @cindex POSIX @command{awk}, bracket expressions and @cindex Extended Regular Expressions (EREs) @cindex EREs (Extended Regular Expressions) @cindex @command{egrep} utility -This treatment of @samp{\} in bracket expressions +The treatment of @samp{\} in bracket expressions is compatible with other @command{awk} implementations and is also mandated by POSIX. The regular expressions in @command{awk} are a superset @@ -4608,23 +5686,23 @@ a keyword denoting the class, and @samp{:]}. POSIX standard. @float Table,table-char-classes -@caption{POSIX Character Classes} +@caption{POSIX character classes} @multitable @columnfractions .15 .85 @headitem Class @tab Meaning -@item @code{[:alnum:]} @tab Alphanumeric characters. -@item @code{[:alpha:]} @tab Alphabetic characters. -@item @code{[:blank:]} @tab Space and TAB characters. -@item @code{[:cntrl:]} @tab Control characters. -@item @code{[:digit:]} @tab Numeric characters. -@item @code{[:graph:]} @tab Characters that are both printable and visible. -(A space is printable but not visible, whereas an @samp{a} is both.) -@item @code{[:lower:]} @tab Lowercase alphabetic characters. -@item @code{[:print:]} @tab Printable characters (characters that are not control characters). +@item @code{[:alnum:]} @tab Alphanumeric characters +@item @code{[:alpha:]} @tab Alphabetic characters +@item @code{[:blank:]} @tab Space and TAB characters +@item @code{[:cntrl:]} @tab Control characters +@item @code{[:digit:]} @tab Numeric characters +@item @code{[:graph:]} @tab Characters that are both printable and visible +(a space is printable but not visible, whereas an @samp{a} is both) +@item @code{[:lower:]} @tab Lowercase alphabetic characters +@item @code{[:print:]} @tab Printable characters (characters that are not control characters) @item @code{[:punct:]} @tab Punctuation characters (characters that are not letters, digits, -control characters, or space characters). -@item @code{[:space:]} @tab Space characters (such as space, TAB, and formfeed, to name a few). -@item @code{[:upper:]} @tab Uppercase alphabetic characters. -@item @code{[:xdigit:]} @tab Characters that are hexadecimal digits. +control characters, or space characters) +@item @code{[:space:]} @tab Space characters (such as space, TAB, and formfeed, to name a few) +@item @code{[:upper:]} @tab Uppercase alphabetic characters +@item @code{[:xdigit:]} @tab Characters that are hexadecimal digits @end multitable @end float @@ -4636,6 +5714,17 @@ With the POSIX character classes, you can write @code{/[[:alnum:]]/} to match the alphabetic and numeric characters in your character set. +@c Thanks to +@c Date: Tue, 01 Jul 2014 07:39:51 +0200 +@c From: Hermann Peifer <peifer@gmx.eu> +Some utilities that match regular expressions provide a nonstandard +@code{[:ascii:]} character class; @command{awk} does not. However, you +can simulate such a construct using @code{[\x00-\x7F]}. This matches +all values numerically between zero and 127, which is the defined +range of the ASCII character set. Use a complemented character list +(@code{[^\x00-\x7F]}) to match any single-byte characters that are not +in the ASCII range. + @cindex bracket expressions, collating elements @cindex bracket expressions, non-ASCII @cindex collating elements @@ -4653,8 +5742,8 @@ These sequences are: @item Collating symbols Multicharacter collating elements enclosed between @samp{[.} and @samp{.]}. For example, if @samp{ch} is a collating element, -then @code{[[.ch.]]} is a regexp that matches this collating element, whereas -@code{[ch]} is a regexp that matches either @samp{c} or @samp{h}. +then @samp{[[.ch.]]} is a regexp that matches this collating element, whereas +@samp{[ch]} is a regexp that matches either @samp{c} or @samp{h}. @cindex bracket expressions, equivalence classes @item Equivalence classes @@ -4662,7 +5751,7 @@ Locale-specific names for a list of characters that are equal. The name is enclosed between @samp{[=} and @samp{=]}. For example, the name @samp{e} might be used to represent all of -``e,'' ``@`e,'' and ``@'e.'' In this case, @code{[[=e=]]} is a regexp +``e,'' ``@`e,'' and ``@'e.'' In this case, @samp{[[=e=]]} is a regexp that matches any of @samp{e}, @samp{@'e}, or @samp{@`e}. @end table @@ -4677,16 +5766,207 @@ expression matching currently recognize only POSIX character classes; they do not recognize collating symbols or equivalence classes. @end quotation @c maybe one day ... -@c ENDOFRANGE charlist + +@node Leftmost Longest +@section How Much Text Matches? + +@cindex regular expressions, leftmost longest match +@c @cindex matching, leftmost longest +Consider the following: + +@example +echo aaaabcd | awk '@{ sub(/a+/, "<A>"); print @}' +@end example + +This example uses the @code{sub()} function to make a change to the input +record. (@code{sub()} replaces the first instance of any text matched +by the first argument with the string provided as the second argument; +@pxref{String Functions}). Here, the regexp @code{/a+/} indicates ``one +or more @samp{a} characters,'' and the replacement text is @samp{<A>}. + +The input contains four @samp{a} characters. +@command{awk} (and POSIX) regular expressions always match +the leftmost, @emph{longest} sequence of input characters that can +match. Thus, all four @samp{a} characters are +replaced with @samp{<A>} in this example: + +@example +$ @kbd{echo aaaabcd | awk '@{ sub(/a+/, "<A>"); print @}'} +@print{} <A>bcd +@end example + +For simple match/no-match tests, this is not so important. But when doing +text matching and substitutions with the @code{match()}, @code{sub()}, @code{gsub()}, +and @code{gensub()} functions, it is very important. +@ifinfo +@xref{String Functions}, +for more information on these functions. +@end ifinfo +Understanding this principle is also important for regexp-based record +and field splitting (@pxref{Records}, +and also @pxref{Field Separators}). + +@node Computed Regexps +@section Using Dynamic Regexps + +@cindex regular expressions, computed +@cindex regular expressions, dynamic +@cindex @code{~} (tilde), @code{~} operator +@cindex tilde (@code{~}), @code{~} operator +@cindex @code{!} (exclamation point), @code{!~} operator +@cindex exclamation point (@code{!}), @code{!~} operator +@c @cindex operators, @code{~} +@c @cindex operators, @code{!~} +The righthand side of a @samp{~} or @samp{!~} operator need not be a +regexp constant (i.e., a string of characters between slashes). It may +be any expression. The expression is evaluated and converted to a string +if necessary; the contents of the string are then used as the +regexp. A regexp computed in this way is called a @dfn{dynamic +regexp} or a @dfn{computed regexp}: + +@example +BEGIN @{ digits_regexp = "[[:digit:]]+" @} +$0 ~ digits_regexp @{ print @} +@end example + +@noindent +This sets @code{digits_regexp} to a regexp that describes one or more digits, +and tests whether the input record matches this regexp. + +@quotation NOTE +When using the @samp{~} and @samp{!~} +operators, there is a difference between a regexp constant +enclosed in slashes and a string constant enclosed in double quotes. +If you are going to use a string constant, you have to understand that +the string is, in essence, scanned @emph{twice}: the first time when +@command{awk} reads your program, and the second time when it goes to +match the string on the lefthand side of the operator with the pattern +on the right. This is true of any string-valued expression (such as +@code{digits_regexp}, shown previously), not just string constants. +@end quotation + +@cindex regexp constants, slashes vs.@: quotes +@cindex @code{\} (backslash), in regexp constants +@cindex backslash (@code{\}), in regexp constants +@cindex @code{"} (double quote), in regexp constants +@cindex double quote (@code{"}), in regexp constants +What difference does it make if the string is +scanned twice? The answer has to do with escape sequences, and particularly +with backslashes. To get a backslash into a regular expression inside a +string, you have to type two backslashes. + +For example, @code{/\*/} is a regexp constant for a literal @samp{*}. +Only one backslash is needed. To do the same thing with a string, +you have to type @code{"\\*"}. The first backslash escapes the +second one so that the string actually contains the +two characters @samp{\} and @samp{*}. + +@cindex troubleshooting, regexp constants vs.@: string constants +@cindex regexp constants, vs.@: string constants +@cindex string constants, vs.@: regexp constants +Given that you can use both regexp and string constants to describe +regular expressions, which should you use? The answer is ``regexp +constants,'' for several reasons: + +@itemize @value{BULLET} +@item +String constants are more complicated to write and +more difficult to read. Using regexp constants makes your programs +less error-prone. Not understanding the difference between the two +kinds of constants is a common source of errors. + +@item +It is more efficient to use regexp constants. @command{awk} can note +that you have supplied a regexp and store it internally in a form that +makes pattern matching more efficient. When using a string constant, +@command{awk} must first convert the string into this internal form and +then perform the pattern matching. + +@item +Using regexp constants is better form; it shows clearly that you +intend a regexp match. +@end itemize + +@cindex sidebar, Using @code{\n} in Bracket Expressions of Dynamic Regexps +@ifdocbook +@docbook +<sidebar><title>Using @code{\n} in Bracket Expressions of Dynamic Regexps</title> +@end docbook + +@cindex regular expressions, dynamic, with embedded newlines +@cindex newlines, in dynamic regexps + +Some older versions of @command{awk} do not allow the newline +character to be used inside a bracket expression for a dynamic regexp: + +@example +$ @kbd{awk '$0 ~ "[ \t\n]"'} +@error{} awk: newline in character class [ +@error{} ]... +@error{} source line number 1 +@error{} context is +@error{} $0 ~ "[ >>> \t\n]" <<< +@end example + +@cindex newlines, in regexp constants +But a newline in a regexp constant works with no problem: + +@example +$ @kbd{awk '$0 ~ /[ \t\n]/'} +@kbd{here is a sample line} +@print{} here is a sample line +@kbd{Ctrl-d} +@end example + +@command{gawk} does not have this problem, and it isn't likely to +occur often in practice, but it's worth noting for future reference. + +@docbook +</sidebar> +@end docbook +@end ifdocbook + +@ifnotdocbook +@cartouche +@center @b{Using @code{\n} in Bracket Expressions of Dynamic Regexps} + + +@cindex regular expressions, dynamic, with embedded newlines +@cindex newlines, in dynamic regexps + +Some older versions of @command{awk} do not allow the newline +character to be used inside a bracket expression for a dynamic regexp: + +@example +$ @kbd{awk '$0 ~ "[ \t\n]"'} +@error{} awk: newline in character class [ +@error{} ]... +@error{} source line number 1 +@error{} context is +@error{} $0 ~ "[ >>> \t\n]" <<< +@end example + +@cindex newlines, in regexp constants +But a newline in a regexp constant works with no problem: + +@example +$ @kbd{awk '$0 ~ /[ \t\n]/'} +@kbd{here is a sample line} +@print{} here is a sample line +@kbd{Ctrl-d} +@end example + +@command{gawk} does not have this problem, and it isn't likely to +occur often in practice, but it's worth noting for future reference. +@end cartouche +@end ifnotdocbook @node GNU Regexp Operators @section @command{gawk}-Specific Regexp Operators @c This section adapted (long ago) from the regex-0.12 manual -@c STARTOFRANGE regexpg @cindex regular expressions, operators, @command{gawk} -@c STARTOFRANGE gregexp @cindex @command{gawk}, regular expressions, operators @cindex operators, GNU-specific @cindex regular expressions, operators, for words @@ -4706,7 +5986,7 @@ or underscores (@samp{_}): @item \s Matches any whitespace character. Think of it as shorthand for -@w{@code{[[:space:]]}}. +@w{@samp{[[:space:]]}}. @c @cindex operators, @code{\S} (@command{gawk}) @cindex backslash (@code{\}), @code{\S} operator (@command{gawk}) @@ -4714,7 +5994,7 @@ Think of it as shorthand for @item \S Matches any character that is not whitespace. Think of it as shorthand for -@w{@code{[^[:space:]]}}. +@w{@samp{[^[:space:]]}}. @c @cindex operators, @code{\w} (@command{gawk}) @cindex backslash (@code{\}), @code{\w} operator (@command{gawk}) @@ -4722,7 +6002,7 @@ Think of it as shorthand for @item \w Matches any word-constituent character---that is, it matches any letter, digit, or underscore. Think of it as shorthand for -@w{@code{[[:alnum:]_]}}. +@w{@samp{[[:alnum:]_]}}. @c @cindex operators, @code{\W} (@command{gawk}) @cindex backslash (@code{\}), @code{\W} operator (@command{gawk}) @@ -4730,7 +6010,7 @@ letter, digit, or underscore. Think of it as shorthand for @item \W Matches any character that is not word-constituent. Think of it as shorthand for -@w{@code{[^[:alnum:]_]}}. +@w{@samp{[^[:alnum:]_]}}. @c @cindex operators, @code{\<} (@command{gawk}) @cindex backslash (@code{\}), @code{\<} operator (@command{gawk}) @@ -4770,9 +6050,9 @@ word-constituent characters. For example, @cindex regular expressions, operators, for buffers @cindex operators, string-matching, for buffers There are two other operators that work on buffers. In Emacs, a -@dfn{buffer} is, naturally, an Emacs buffer. For other programs, -@command{gawk}'s regexp library routines consider the entire -string to match as the buffer. +@dfn{buffer} is, naturally, an Emacs buffer. +Other GNU programs, including @command{gawk}, +consider the entire string to match as the buffer. The operators are: @table @code @@ -4791,10 +6071,10 @@ Matches the empty string at the end of a buffer (string). @end table -@cindex @code{^} (caret) -@cindex caret (@code{^}) -@cindex @code{?} (question mark) regexp operator -@cindex question mark (@code{?}) regexp operator +@cindex @code{^} (caret), regexp operator +@cindex caret (@code{^}), regexp operator +@cindex @code{?} (question mark), regexp operator +@cindex question mark (@code{?}), regexp operator Because @samp{^} and @samp{$} always work in terms of the beginning and end of strings, these operators don't add any new capabilities for @command{awk}. They are provided for compatibility with other @@ -4811,11 +6091,8 @@ GNU operators, but this was deemed too confusing. The current method of using @samp{\y} for the GNU @samp{\b} appears to be the lesser of two evils. -@c NOTE!!! Keep this in sync with the same table in the summary appendix! -@c -@c Should really do this with file inclusion. @cindex regular expressions, @command{gawk}, command-line options -@cindex @command{gawk}, command-line options +@cindex @command{gawk}, command-line options, and regular expressions The various command-line options (@pxref{Options}) control how @command{gawk} interprets characters in regexps: @@ -4829,20 +6106,23 @@ previously described GNU regexp operators. @end ifnotinfo @ifnottex +@ifnotdocbook GNU regexp operators described in @ref{Regexp Operators}. +@end ifnotdocbook @end ifnottex @item @code{--posix} -Only POSIX regexps are supported; the GNU operators are not special +Match only POSIX regexps; the GNU operators are not special (e.g., @samp{\w} matches a literal @samp{w}). Interval expressions are allowed. +@cindex Brian Kernighan's @command{awk} @item @code{--traditional} -Traditional Unix @command{awk} regexps are matched. The GNU operators +Match traditional Unix @command{awk} regexps. The GNU operators are not special, and interval expressions are not available. -The POSIX character classes (@code{[[:alnum:]]}, etc.) are supported, -as Brian Kernighan's @command{awk} does support them. +Because BWK @command{awk} supports them, +the POSIX character classes (@samp{[[:alnum:]]}, etc.) are available. Characters described by octal and hexadecimal escape sequences are treated literally, even if they represent regexp metacharacters. @@ -4851,15 +6131,11 @@ Allow interval expressions in regexps, if @option{--traditional} has been provided. Otherwise, interval expressions are available by default. @end table -@c ENDOFRANGE gregexp -@c ENDOFRANGE regexpg @node Case-sensitivity @section Case Sensitivity in Matching -@c STARTOFRANGE regexpcs @cindex regular expressions, case sensitivity -@c STARTOFRANGE csregexp @cindex case sensitivity, regexps and Case is normally significant in regular expressions, both when matching ordinary characters (i.e., not metacharacters) and inside bracket @@ -4893,16 +6169,18 @@ This works in any POSIX-compliant @command{awk}. @cindex tilde (@code{~}), @code{~} operator @cindex @code{!} (exclamation point), @code{!~} operator @cindex exclamation point (@code{!}), @code{!~} operator -@cindex @code{IGNORECASE} variable +@cindex @code{IGNORECASE} variable, with @code{~} and @code{!~} operators @cindex @command{gawk}, @code{IGNORECASE} variable in @c @cindex variables, @code{IGNORECASE} Another method, specific to @command{gawk}, is to set the variable @code{IGNORECASE} to a nonzero value (@pxref{Built-in Variables}). When @code{IGNORECASE} is not zero, @emph{all} regexp and string -operations ignore case. Changing the value of -@code{IGNORECASE} dynamically controls the case-sensitivity of the -program as it runs. Case is significant by default because -@code{IGNORECASE} (like most variables) is initialized to zero: +operations ignore case. + +Changing the value of @code{IGNORECASE} dynamically controls the +case sensitivity of the program as it runs. Case is significant by +default because @code{IGNORECASE} (like most variables) is initialized +to zero: @example x = "aB" @@ -4913,7 +6191,7 @@ if (x ~ /ab/) @dots{} # now it will succeed @end example In general, you cannot use @code{IGNORECASE} to make certain rules -case-insensitive and other rules case-sensitive, because there is no +case insensitive and other rules case sensitive, as there is no straightforward way to set @code{IGNORECASE} just for the pattern of a particular rule.@footnote{Experienced C and C++ programmers will note @@ -4924,16 +6202,13 @@ and However, this is somewhat obscure and we don't recommend it.} To do this, use either bracket expressions or @code{tolower()}. However, one thing you can do with @code{IGNORECASE} only is dynamically turn -case-sensitivity on or off for all the rules at once. +case sensitivity on or off for all the rules at once. @code{IGNORECASE} can be set on the command line or in a @code{BEGIN} rule (@pxref{Other Arguments}; also @pxref{Using BEGIN/END}). Setting @code{IGNORECASE} from the command line is a way to make -a program case-insensitive without having to edit it. - -Both regexp and string comparison -operations are affected by @code{IGNORECASE}. +a program case insensitive without having to edit it. @c @cindex ISO 8859-1 @c @cindex ISO Latin-1 @@ -4952,168 +6227,57 @@ the right thing.} The value of @code{IGNORECASE} has no effect if @command{gawk} is in compatibility mode (@pxref{Options}). Case is always significant in compatibility mode. -@c ENDOFRANGE csregexp -@c ENDOFRANGE regexpcs - -@node Leftmost Longest -@section How Much Text Matches? -@cindex regular expressions, leftmost longest match -@c @cindex matching, leftmost longest -Consider the following: +@node Regexp Summary +@section Summary -@example -echo aaaabcd | awk '@{ sub(/a+/, "<A>"); print @}' -@end example - -This example uses the @code{sub()} function (which we haven't discussed yet; -@pxref{String Functions}) -to make a change to the input record. Here, the regexp @code{/a+/} -indicates ``one or more @samp{a} characters,'' and the replacement -text is @samp{<A>}. - -The input contains four @samp{a} characters. -@command{awk} (and POSIX) regular expressions always match -the leftmost, @emph{longest} sequence of input characters that can -match. Thus, all four @samp{a} characters are -replaced with @samp{<A>} in this example: - -@example -$ @kbd{echo aaaabcd | awk '@{ sub(/a+/, "<A>"); print @}'} -@print{} <A>bcd -@end example - -For simple match/no-match tests, this is not so important. But when doing -text matching and substitutions with the @code{match()}, @code{sub()}, @code{gsub()}, -and @code{gensub()} functions, it is very important. -@ifinfo -@xref{String Functions}, -for more information on these functions. -@end ifinfo -Understanding this principle is also important for regexp-based record -and field splitting (@pxref{Records}, -and also @pxref{Field Separators}). - -@node Computed Regexps -@section Using Dynamic Regexps - -@c STARTOFRANGE dregexp -@cindex regular expressions, computed -@c STARTOFRANGE regexpd -@cindex regular expressions, dynamic -@cindex @code{~} (tilde), @code{~} operator -@cindex tilde (@code{~}), @code{~} operator -@cindex @code{!} (exclamation point), @code{!~} operator -@cindex exclamation point (@code{!}), @code{!~} operator -@c @cindex operators, @code{~} -@c @cindex operators, @code{!~} -The righthand side of a @samp{~} or @samp{!~} operator need not be a -regexp constant (i.e., a string of characters between slashes). It may -be any expression. The expression is evaluated and converted to a string -if necessary; the contents of the string are then used as the -regexp. A regexp computed in this way is called a @dfn{dynamic -regexp}: - -@example -BEGIN @{ digits_regexp = "[[:digit:]]+" @} -$0 ~ digits_regexp @{ print @} -@end example - -@noindent -This sets @code{digits_regexp} to a regexp that describes one or more digits, -and tests whether the input record matches this regexp. - -@quotation NOTE -When using the @samp{~} and @samp{!~} -operators, there is a difference between a regexp constant -enclosed in slashes and a string constant enclosed in double quotes. -If you are going to use a string constant, you have to understand that -the string is, in essence, scanned @emph{twice}: the first time when -@command{awk} reads your program, and the second time when it goes to -match the string on the lefthand side of the operator with the pattern -on the right. This is true of any string-valued expression (such as -@code{digits_regexp}, shown previously), not just string constants. -@end quotation - -@cindex regexp constants, slashes vs.@: quotes -@cindex @code{\} (backslash), regexp constants -@cindex backslash (@code{\}), regexp constants -@cindex @code{"} (double quote), regexp constants -@cindex double quote (@code{"}), regexp constants -What difference does it make if the string is -scanned twice? The answer has to do with escape sequences, and particularly -with backslashes. To get a backslash into a regular expression inside a -string, you have to type two backslashes. - -For example, @code{/\*/} is a regexp constant for a literal @samp{*}. -Only one backslash is needed. To do the same thing with a string, -you have to type @code{"\\*"}. The first backslash escapes the -second one so that the string actually contains the -two characters @samp{\} and @samp{*}. - -@cindex troubleshooting, regexp constants vs.@: string constants -@cindex regexp constants, vs.@: string constants -@cindex string constants, vs.@: regexp constants -Given that you can use both regexp and string constants to describe -regular expressions, which should you use? The answer is ``regexp -constants,'' for several reasons: +@itemize @value{BULLET} +@item +Regular expressions describe sets of strings to be matched. +In @command{awk}, regular expression constants are written enclosed +between slashes: @code{/}@dots{}@code{/}. -@itemize @bullet @item -String constants are more complicated to write and -more difficult to read. Using regexp constants makes your programs -less error-prone. Not understanding the difference between the two -kinds of constants is a common source of errors. +Regexp constants may be used standalone in patterns and +in conditional expressions, or as part of matching expressions +using the @samp{~} and @samp{!~} operators. @item -It is more efficient to use regexp constants. @command{awk} can note -that you have supplied a regexp and store it internally in a form that -makes pattern matching more efficient. When using a string constant, -@command{awk} must first convert the string into this internal form and -then perform the pattern matching. +Escape sequences let you represent nonprintable characters and +also let you represent regexp metacharacters as literal characters +to be matched. @item -Using regexp constants is better form; it shows clearly that you -intend a regexp match. -@end itemize +Regexp operators provide grouping, alternation, and repetition. -@c fakenode --- for prepinfo -@subheading Advanced Notes: Using @code{\n} in Bracket Expressions of Dynamic Regexps -@cindex regular expressions, dynamic, with embedded newlines -@cindex newlines, in dynamic regexps +@item +Bracket expressions give you a shorthand for specifying sets +of characters that can match at a particular point in a regexp. +Within bracket expressions, POSIX character classes let you specify +certain groups of characters in a locale-independent fashion. -Some commercial versions of @command{awk} do not allow the newline -character to be used inside a bracket expression for a dynamic regexp: +@item +Regular expressions match the leftmost longest text in the string being +matched. This matters for cases where you need to know the extent of +the match, such as for text substitution and when the record separator +is a regexp. -@example -$ @kbd{awk '$0 ~ "[ \t\n]"'} -@error{} awk: newline in character class [ -@error{} ]... -@error{} source line number 1 -@error{} context is -@error{} >>> <<< -@end example +@item +Matching expressions may use dynamic regexps (i.e., string values +treated as regular expressions). -@cindex newlines, in regexp constants -But a newline in a regexp constant works with no problem: +@item +@command{gawk}'s @code{IGNORECASE} variable lets you control the +case sensitivity of regexp matching. In other @command{awk} +versions, use @code{tolower()} or @code{toupper()}. -@example -$ @kbd{awk '$0 ~ /[ \t\n]/'} -@kbd{here is a sample line} -@print{} here is a sample line -@kbd{@value{CTL}-d} -@end example +@end itemize -@command{gawk} does not have this problem, and it isn't likely to -occur often in practice, but it's worth noting for future reference. -@c ENDOFRANGE dregexp -@c ENDOFRANGE regexpd -@c ENDOFRANGE regexp @node Reading Files @chapter Reading Input Files -@c STARTOFRANGE infir +@cindex reading input files @cindex input files, reading @cindex input files @cindex @code{FILENAME} variable @@ -5123,7 +6287,7 @@ standard input (by default, this is the keyboard, but often it is a pipe from an command) or from files whose names you specify on the @command{awk} command line. If you specify input files, @command{awk} reads them in order, processing all the data from one before going on to the next. -The name of the current input file can be found in the built-in variable +The name of the current input file can be found in the predefined variable @code{FILENAME} (@pxref{Built-in Variables}). @@ -5150,32 +6314,38 @@ used with it do not have to be named on the @command{awk} command line * Field Separators:: The field separator and how to change it. * Constant Size:: Reading constant width data. * Splitting By Content:: Defining Fields By Content -* Multiple Line:: Reading multi-line records. +* Multiple Line:: Reading multiline records. * Getline:: Reading files under explicit program control using the @code{getline} function. -* Command line directories:: What happens if you put a directory on the +* Read Timeout:: Reading input with a timeout. +* Command-line directories:: What happens if you put a directory on the command line. +* Input Summary:: Input summary. +* Input Exercises:: Exercises. @end menu @node Records @section How Input Is Split into Records -@c STARTOFRANGE inspl @cindex input, splitting into records -@c STARTOFRANGE recspl @cindex records, splitting input into @cindex @code{NR} variable @cindex @code{FNR} variable -The @command{awk} utility divides the input for your @command{awk} -program into records and fields. -@command{awk} keeps track of the number of records that have -been read -so far -from the current input file. This value is stored in a -built-in variable called @code{FNR}. It is reset to zero when a new -file is started. Another built-in variable, @code{NR}, records the total -number of input records read so far from all @value{DF}s. It starts at zero, -but is never automatically reset to zero. +@command{awk} divides the input for your program into records and fields. +It keeps track of the number of records that have been read so far from +the current input file. This value is stored in a predefined variable +called @code{FNR}, which is reset to zero every time a new file is started. +Another predefined variable, @code{NR}, records the total number of input +records read so far from all @value{DF}s. It starts at zero, but is +never automatically reset to zero. + +@menu +* awk split records:: How standard @command{awk} splits records. +* gawk split records:: How @command{gawk} splits records. +@end menu + +@node awk split records +@subsection Record Splitting with Standard @command{awk} @cindex separators, for records @cindex record separators @@ -5183,7 +6353,7 @@ Records are separated by a character called the @dfn{record separator}. By default, the record separator is the newline character. This is why records are, by default, single lines. A different character can be used for the record separator by -assigning the character to the built-in variable @code{RS}. +assigning the character to the predefined variable @code{RS}. @cindex newlines, as record separators @cindex @code{RS} variable @@ -5192,75 +6362,86 @@ the value of @code{RS} can be changed in the @command{awk} program with the assignment operator, @samp{=} (@pxref{Assignment Ops}). The new record-separator character should be enclosed in quotation marks, -which indicate a string constant. Often the right time to do this is +which indicate a string constant. Often, the right time to do this is at the beginning of execution, before any input is processed, so that the very first record is read with the proper separator. To do this, use the special @code{BEGIN} pattern (@pxref{BEGIN/END}). For example: -@cindex @code{BEGIN} pattern @example -awk 'BEGIN @{ RS = "/" @} - @{ print $0 @}' BBS-list +awk 'BEGIN @{ RS = "u" @} + @{ print $0 @}' mail-list @end example @noindent -changes the value of @code{RS} to @code{"/"}, before reading any input. -This is a string whose first character is a slash; as a result, records -are separated by slashes. Then the input file is read, and the second +changes the value of @code{RS} to @samp{u}, before reading any input. +This is a string whose first character is the letter ``u''; as a result, records +are separated by the letter ``u.'' Then the input file is read, and the second rule in the @command{awk} program (the action with no pattern) prints each record. Because each @code{print} statement adds a newline at the end of its output, this @command{awk} program copies the input -with each slash changed to a newline. Here are the results of running -the program on @file{BBS-list}: - -@example -$ @kbd{awk 'BEGIN @{ RS = "/" @}} -> @kbd{@{ print $0 @}' BBS-list} -@print{} aardvark 555-5553 1200 -@print{} 300 B -@print{} alpo-net 555-3412 2400 -@print{} 1200 -@print{} 300 A -@print{} barfly 555-7685 1200 -@print{} 300 A -@print{} bites 555-1675 2400 -@print{} 1200 -@print{} 300 A -@print{} camelot 555-0542 300 C -@print{} core 555-2912 1200 -@print{} 300 C -@print{} fooey 555-1234 2400 -@print{} 1200 -@print{} 300 B -@print{} foot 555-6699 1200 -@print{} 300 B -@print{} macfoo 555-6480 1200 -@print{} 300 A -@print{} sdace 555-3430 2400 -@print{} 1200 -@print{} 300 A -@print{} sabafoo 555-2127 1200 -@print{} 300 C +with each @samp{u} changed to a newline. Here are the results of running +the program on @file{mail-list}: + +@example +$ @kbd{awk 'BEGIN @{ RS = "u" @}} +> @kbd{@{ print $0 @}' mail-list} +@print{} Amelia 555-5553 amelia.zodiac +@print{} sq +@print{} e@@gmail.com F +@print{} Anthony 555-3412 anthony.assert +@print{} ro@@hotmail.com A +@print{} Becky 555-7685 becky.algebrar +@print{} m@@gmail.com A +@print{} Bill 555-1675 bill.drowning@@hotmail.com A +@print{} Broderick 555-0542 broderick.aliq +@print{} otiens@@yahoo.com R +@print{} Camilla 555-2912 camilla.inf +@print{} sar +@print{} m@@skynet.be R +@print{} Fabi +@print{} s 555-1234 fabi +@print{} s. +@print{} ndevicesim +@print{} s@@ +@print{} cb.ed +@print{} F +@print{} J +@print{} lie 555-6699 j +@print{} lie.perscr +@print{} tabor@@skeeve.com F +@print{} Martin 555-6480 martin.codicib +@print{} s@@hotmail.com A +@print{} Sam +@print{} el 555-3430 sam +@print{} el.lanceolis@@sh +@print{} .ed +@print{} A +@print{} Jean-Pa +@print{} l 555-2127 jeanpa +@print{} l.campanor +@print{} m@@ny +@print{} .ed +@print{} R @print{} @end example @noindent -Note that the entry for the @samp{camelot} BBS is not split. +Note that the entry for the name @samp{Bill} is not split. In the original @value{DF} (@pxref{Sample Data Files}), the line looks like this: @example -camelot 555-0542 300 C +Bill 555-1675 bill.drowning@@hotmail.com A @end example @noindent -It has one baud rate only, so there are no slashes in the record, -unlike the others which have two or more baud rates. -In fact, this record is treated as part of the record -for the @samp{core} BBS; the newline separating them in the output +It contains no @samp{u} so there is no reason to split the record, +unlike the others which have one or more occurrences of the @samp{u}. +In fact, this record is treated as part of the previous record; +the newline separating them in the output is the original newline in the @value{DF}, not the one added by @command{awk} when it printed the record! @@ -5271,36 +6452,47 @@ using the variable-assignment feature (@pxref{Other Arguments}): @example -awk '@{ print $0 @}' RS="/" BBS-list +awk '@{ print $0 @}' RS="u" mail-list @end example @noindent -This sets @code{RS} to @samp{/} before processing @file{BBS-list}. +This sets @code{RS} to @samp{u} before processing @file{mail-list}. + +Using an alphabetic character such as @samp{u} for the record separator +is highly likely to produce strange results. +Using an unusual character such as @samp{/} is more likely to +produce correct behavior in the majority of cases, but there +are no guarantees. The moral is: Know Your Data. -Using an unusual character such as @samp{/} for the record separator -produces correct behavior in the vast majority of cases. However, -the following (extreme) pipeline prints a surprising @samp{1}: +When using regular characters as the record separator, +there is one unusual case that occurs when @command{gawk} is +being fully POSIX-compliant (@pxref{Options}). +Then, the following (extreme) pipeline prints a surprising @samp{1}: @example -$ echo | awk 'BEGIN @{ RS = "a" @} ; @{ print NF @}' +$ @kbd{echo | gawk --posix 'BEGIN @{ RS = "a" @} ; @{ print NF @}'} @print{} 1 @end example There is one field, consisting of a newline. The value of the built-in variable @code{NF} is the number of fields in the current record. +(In the normal case, @command{gawk} treats the newline as whitespace, +printing @samp{0} as the result. Most other versions of @command{awk} +also act this way.) @cindex dark corner, input files Reaching the end of an input file terminates the current input record, even if the last character in the file is not the character in @code{RS}. @value{DARKCORNER} +@cindex empty strings @cindex null strings @cindex strings, empty, See null strings The empty string @code{""} (a string without any characters) has a special meaning as the value of @code{RS}. It means that records are separated by one or more blank lines and nothing else. -@xref{Multiple Line}, for more details. +@DBXREF{Multiple Line} for more details. If you change the value of @code{RS} in the middle of an @command{awk} run, the new value is used to delimit subsequent records, but the record @@ -5319,6 +6511,9 @@ After the end of the record has been determined, @command{gawk} sets the variable @code{RT} to the text in the input that matched @code{RS}. +@node gawk split records +@subsection Record Splitting with @command{gawk} + @cindex common extensions, @code{RS} as a regexp @cindex extensions, common@comma{} @code{RS} as a regexp When using @command{gawk}, @@ -5350,22 +6545,22 @@ with optional leading and/or trailing whitespace: @example $ @kbd{echo record 1 AAAA record 2 BBBB record 3 |} > @kbd{gawk 'BEGIN @{ RS = "\n|( *[[:upper:]]+ *)" @}} -> @kbd{@{ print "Record =", $0, "and RT =", RT @}'} -@print{} Record = record 1 and RT = AAAA -@print{} Record = record 2 and RT = BBBB -@print{} Record = record 3 and RT = -@print{} +> @kbd{@{ print "Record =", $0,"and RT = [" RT "]" @}'} +@print{} Record = record 1 and RT = [ AAAA ] +@print{} Record = record 2 and RT = [ BBBB ] +@print{} Record = record 3 and RT = [ +@print{} ] @end example @noindent -The final line of output has an extra blank line. This is because the -value of @code{RT} is a newline, and the @code{print} statement -supplies its own terminating newline. -@xref{Simple Sed}, for a more useful example +The square brackets delineate the contents of @code{RT}, letting you +see the leading and trailing whitespace. The final value of +@code{RT} is a newline. +@DBXREF{Simple Sed} for a more useful example of @code{RS} as a regexp and @code{RT}. If you set @code{RS} to a regular expression that allows optional -trailing text, such as @samp{RS = "abc(XYZ)?"} it is possible, due +trailing text, such as @samp{RS = "abc(XYZ)?"}, it is possible, due to implementation constraints, that @command{gawk} may match the leading part of the regular expression, but not the trailing part, particularly if the input text that could match the trailing part is fairly long. @@ -5378,8 +6573,8 @@ metacharacters match the beginning and end of a @emph{string}, and not the beginning and end of a @emph{line}. As a result, something like @samp{RS = "^[[:upper:]]"} can only match at the beginning of a file. This is because @command{gawk} views the input file as one long string -that happens to contain newline characters in it. -It is thus best to avoid anchor characters in the value of @code{RS}. +that happens to contain newline characters. +It is thus best to avoid anchor metacharacters in the value of @code{RS}. @end quotation @cindex differences in @command{awk} and @command{gawk}, @code{RS}/@code{RT} variables @@ -5388,19 +6583,71 @@ variable are @command{gawk} extensions; they are not available in compatibility mode (@pxref{Options}). In compatibility mode, only the first character of the value of -@code{RS} is used to determine the end of the record. +@code{RS} determines the end of the record. -@c fakenode --- for prepinfo -@subheading Advanced Notes: @code{RS = "\0"} Is Not Portable +@cindex sidebar, @code{RS = "\0"} Is Not Portable +@ifdocbook +@docbook +<sidebar><title>@code{RS = "\0"} Is Not Portable</title> +@end docbook + +@cindex portability, data files as single record +There are times when you might want to treat an entire @value{DF} as a +single record. The only way to make this happen is to give @code{RS} +a value that you know doesn't occur in the input file. This is hard +to do in a general way, such that a program always works for arbitrary +input files. + +You might think that for text files, the @sc{nul} character, which +consists of a character with all bits equal to zero, is a good +value to use for @code{RS} in this case: + +@example +BEGIN @{ RS = "\0" @} # whole file becomes one record? +@end example + +@cindex differences in @command{awk} and @command{gawk}, strings, storing +@command{gawk} in fact accepts this, and uses the @sc{nul} +character for the record separator. +This works for certain special files, such as @file{/proc/environ} on +GNU/Linux systems, where the @sc{nul} character is in fact the record separator. +However, this usage is @emph{not} portable +to most other @command{awk} implementations. -@cindex advanced features, @value{DF}s as single record -@cindex portability, @value{DF}s as single record +@cindex dark corner, strings, storing +Almost all other @command{awk} implementations@footnote{At least that we know +about.} store strings internally as C-style strings. C strings use the +@sc{nul} character as the string terminator. In effect, this means that +@samp{RS = "\0"} is the same as @samp{RS = ""}. +@value{DARKCORNER} + +It happens that recent versions of @command{mawk} can use the @sc{nul} +character as a record separator. However, this is a special case: +@command{mawk} does not allow embedded @sc{nul} characters in strings. +(This may change in a future version of @command{mawk}.) + +@cindex records, treating files as +@cindex treating files, as single records +@DBXREF{Readfile Function} for an interesting way to read +whole files. If you are using @command{gawk}, see @DBREF{Extension Sample +Readfile} for another option. + +@docbook +</sidebar> +@end docbook +@end ifdocbook + +@ifnotdocbook +@cartouche +@center @b{@code{RS = "\0"} Is Not Portable} + + +@cindex portability, data files as single record There are times when you might want to treat an entire @value{DF} as a single record. The only way to make this happen is to give @code{RS} a value that you know doesn't occur in the input file. This is hard to do in a general way, such that a program always works for arbitrary input files. -@c can you say `understatement' boys and girls? You might think that for text files, the @sc{nul} character, which consists of a character with all bits equal to zero, is a good @@ -5413,23 +6660,30 @@ BEGIN @{ RS = "\0" @} # whole file becomes one record? @cindex differences in @command{awk} and @command{gawk}, strings, storing @command{gawk} in fact accepts this, and uses the @sc{nul} character for the record separator. +This works for certain special files, such as @file{/proc/environ} on +GNU/Linux systems, where the @sc{nul} character is in fact the record separator. However, this usage is @emph{not} portable -to other @command{awk} implementations. +to most other @command{awk} implementations. @cindex dark corner, strings, storing -All other @command{awk} implementations@footnote{At least that we know +Almost all other @command{awk} implementations@footnote{At least that we know about.} store strings internally as C-style strings. C strings use the @sc{nul} character as the string terminator. In effect, this means that @samp{RS = "\0"} is the same as @samp{RS = ""}. @value{DARKCORNER} +It happens that recent versions of @command{mawk} can use the @sc{nul} +character as a record separator. However, this is a special case: +@command{mawk} does not allow embedded @sc{nul} characters in strings. +(This may change in a future version of @command{mawk}.) + @cindex records, treating files as -@cindex files, as single records -The best way to treat a whole file as a single record is to -simply read the file in, one record at a time, concatenating each -record onto the end of the previous ones. -@c ENDOFRANGE inspl -@c ENDOFRANGE recspl +@cindex treating files, as single records +@DBXREF{Readfile Function} for an interesting way to read +whole files. If you are using @command{gawk}, see @DBREF{Extension Sample +Readfile} for another option. +@end cartouche +@end ifnotdocbook @node Fields @section Examining Fields @@ -5437,7 +6691,6 @@ record onto the end of the previous ones. @cindex examining fields @cindex fields @cindex accessing fields -@c STARTOFRANGE fiex @cindex fields, examining @cindex POSIX @command{awk}, field separators and @cindex field separators, POSIX and @@ -5448,9 +6701,9 @@ called @dfn{fields}. By default, fields are separated by @dfn{whitespace}, like words in a line. Whitespace in @command{awk} means any string of one or more spaces, TABs, or newlines;@footnote{In POSIX @command{awk}, newlines are not -considered whitespace for separating fields.} other characters, such as -formfeed, vertical tab, etc., that are -considered whitespace by other languages, are @emph{not} considered +considered whitespace for separating fields.} other characters +that are considered whitespace by other languages +(such as formfeed, vertical tab, etc.) are @emph{not} considered whitespace by @command{awk}. The purpose of fields is to make it more convenient for you to refer to @@ -5462,12 +6715,12 @@ simple @command{awk} programs so powerful. @cindex @code{$} (dollar sign), @code{$} field operator @cindex dollar sign (@code{$}), @code{$} field operator @cindex field operators@comma{} dollar sign as -A dollar-sign (@samp{$}) is used +You use a dollar-sign (@samp{$}) to refer to a field in an @command{awk} program, followed by the number of the field you want. Thus, @code{$1} refers to the first field, @code{$2} to the second, and so on. (Unlike the Unix shells, the field numbers are not limited to single digits. -@code{$127} is the one hundred twenty-seventh field in the record.) +@code{$127} is the 127th field in the record.) For example, suppose the following is a line of input: @example @@ -5483,7 +6736,7 @@ field. @cindex @code{NF} variable @cindex fields, number of -@code{NF} is a built-in variable whose value is the number of fields +@code{NF} is a predefined variable whose value is the number of fields in the current record. @command{awk} automatically updates the value of @code{NF} each time it reads a record. No matter how many fields there are, the last field in a record can be represented by @code{$NF}. @@ -5493,45 +6746,38 @@ one (such as @code{$8} when the record has only seven fields), you get the empty string. (If used in a numeric operation, you get zero.) The use of @code{$0}, which looks like a reference to the ``zero-th'' field, is -a special case: it represents the whole input record +a special case: it represents the whole input record. Use it when you are not interested in specific fields. Here are some more examples: @example -$ @kbd{awk '$1 ~ /foo/ @{ print $0 @}' BBS-list} -@print{} fooey 555-1234 2400/1200/300 B -@print{} foot 555-6699 1200/300 B -@print{} macfoo 555-6480 1200/300 A -@print{} sabafoo 555-2127 1200/300 C +$ @kbd{awk '$1 ~ /li/ @{ print $0 @}' mail-list} +@print{} Amelia 555-5553 amelia.zodiacusque@@gmail.com F +@print{} Julie 555-6699 julie.perscrutabor@@skeeve.com F @end example @noindent -This example prints each record in the file @file{BBS-list} whose first -field contains the string @samp{foo}. The operator @samp{~} is called a -@dfn{matching operator} -(@pxref{Regexp Usage}); -it tests whether a string (here, the field @code{$1}) matches a given regular -expression. +This example prints each record in the file @file{mail-list} whose first +field contains the string @samp{li}. -By contrast, the following example -looks for @samp{foo} in @emph{the entire record} and prints the first -field and the last field for each matching input record: +By contrast, the following example looks for @samp{li} in @emph{the +entire record} and prints the first and last fields for each matching +input record: @example -$ @kbd{awk '/foo/ @{ print $1, $NF @}' BBS-list} -@print{} fooey B -@print{} foot B -@print{} macfoo A -@print{} sabafoo C +$ @kbd{awk '/li/ @{ print $1, $NF @}' mail-list} +@print{} Amelia F +@print{} Broderick R +@print{} Julie F +@print{} Samuel A @end example -@c ENDOFRANGE fiex @node Nonconstant Fields @section Nonconstant Field Numbers @cindex fields, numbers @cindex field numbers -The number of a field does not need to be a constant. Any expression in +A field number need not be a constant. Any expression in the @command{awk} language can be used after a @samp{$} to refer to a field. The value of the expression specifies the field number. If the value is a string, rather than a number, it is converted to a number. @@ -5543,14 +6789,14 @@ awk '@{ print $NR @}' @noindent Recall that @code{NR} is the number of records read so far: one in the -first record, two in the second, etc. So this example prints the first +first record, two in the second, and so on. So this example prints the first field of the first record, the second field of the second record, and so on. For the twentieth record, field number 20 is printed; most likely, the record has fewer than 20 fields, so this prints a blank line. Here is another example of using expressions as field numbers: @example -awk '@{ print $(2*2) @}' BBS-list +awk '@{ print $(2*2) @}' mail-list @end example @command{awk} evaluates the expression @samp{(2*2)} and uses @@ -5558,9 +6804,13 @@ its value as the number of the field to print. The @samp{*} sign represents multiplication, so the expression @samp{2*2} evaluates to four. The parentheses are used so that the multiplication is done before the @samp{$} operation; they are necessary whenever there is a binary -operator in the field-number expression. This example, then, prints the -hours of operation (the fourth field) for every line of the file -@file{BBS-list}. (All of the @command{awk} operators are listed, in +operator@footnote{A @dfn{binary operator}, such as @samp{*} for +multiplication, is one that takes two operands. The distinction +is required, because @command{awk} also has unary (one-operand) +and ternary (three-operand) operators.} +in the field-number expression. This example, then, prints the +type of relationship (the fourth field) for every line of the file +@file{mail-list}. (All of the @command{awk} operators are listed, in order of decreasing precedence, in @ref{Precedence}.) @@ -5574,14 +6824,13 @@ implementations may behave differently.) As mentioned in @ref{Fields}, @command{awk} stores the current record's number of fields in the built-in -variable @code{NF} (also @pxref{Built-in Variables}). The expression +variable @code{NF} (also @pxref{Built-in Variables}). Thus, the expression @code{$NF} is not a special feature---it is the direct consequence of evaluating @code{NF} and using its value as a field number. @node Changing Fields @section Changing the Contents of a Field -@c STARTOFRANGE ficon @cindex fields, changing contents of The contents of a field, as seen by @command{awk}, can be changed within an @command{awk} program; this changes what @command{awk} perceives as the @@ -5608,7 +6857,7 @@ Then it prints the original and new values for field three. (Someone in the warehouse made a consistent mistake while inventorying the red boxes.) -For this to work, the text in field @code{$3} must make sense +For this to work, the text in @code{$3} must make sense as a number; the string of characters must be converted to a number for the computer to do arithmetic on it. The number resulting from the subtraction is converted back to a string of characters that @@ -5630,12 +6879,12 @@ $ @kbd{awk '@{ $2 = $2 - 10; print $0 @}' inventory-shipped} @dots{} @end example -It is also possible to also assign contents to fields that are out +It is also possible to assign contents to fields that are out of range. For example: @example -$ awk '@{ $6 = ($5 + $4 + $3 + $2) -> print $6 @}' inventory-shipped +$ @kbd{awk '@{ $6 = ($5 + $4 + $3 + $2)} +> @kbd{ print $6 @}' inventory-shipped} @print{} 168 @print{} 297 @print{} 301 @@ -5681,9 +6930,9 @@ else @noindent should print @samp{everything is normal}, because @code{NF+1} is certain -to be out of range. (@xref{If Statement}, +to be out of range. (@DBXREF{If Statement} for more information about @command{awk}'s @code{if-else} statements. -@xref{Typing and Comparison}, +@DBXREF{Typing and Comparison} for more information about the @samp{!=} operator.) It is important to note that making an assignment to an existing field @@ -5699,7 +6948,7 @@ $ @kbd{echo a b c d | awk '@{ OFS = ":"; $2 = ""} @end example @noindent -The field is still there; it just has an empty value, denoted by +The field is still there; it just has an empty value, delimited by the two colons between @samp{a} and @samp{c}. This example shows what happens if you create a new field: @@ -5723,8 +6972,8 @@ after the new value of @code{NF} and recomputes @code{$0}. Here is an example: @example -$ echo a b c d e f | awk '@{ print "NF =", NF; -> NF = 3; print $0 @}' +$ @kbd{echo a b c d e f | awk '@{ print "NF =", NF;} +> @kbd{ NF = 3; print $0 @}'} @print{} NF = 6 @print{} a b c @end example @@ -5732,7 +6981,7 @@ $ echo a b c d e f | awk '@{ print "NF =", NF; @cindex portability, @code{NF} variable@comma{} decrementing @quotation CAUTION Some versions of @command{awk} don't -rebuild @code{$0} when @code{NF} is decremented. Caveat emptor. +rebuild @code{$0} when @code{NF} is decremented. @end quotation Finally, there are times when it is convenient to force @@ -5746,7 +6995,7 @@ print $0 # or whatever else with $0 @end example @noindent -This forces @command{awk} rebuild the record. It does help +This forces @command{awk} to rebuild the record. It does help to add a comment, as we've shown here. There is a flip side to the relationship between @code{$0} and @@ -5756,24 +7005,54 @@ This also applies to any built-in function that updates @code{$0}, such as @code{sub()} and @code{gsub()} (@pxref{String Functions}). -@c fakenode --- for prepinfo -@subheading Advanced Notes: Understanding @code{$0} +@cindex sidebar, Understanding @code{$0} +@ifdocbook +@docbook +<sidebar><title>Understanding @code{$0}</title> +@end docbook + + +It is important to remember that @code{$0} is the @emph{full} +record, exactly as it was read from the input. This includes +any leading or trailing whitespace, and the exact whitespace (or other +characters) that separate the fields. + +It is a common error to try to change the field separators +in a record simply by setting @code{FS} and @code{OFS}, and then +expecting a plain @samp{print} or @samp{print $0} to print the +modified record. + +But this does not work, because nothing was done to change the record +itself. Instead, you must force the record to be rebuilt, typically +with a statement such as @samp{$1 = $1}, as described earlier. + +@docbook +</sidebar> +@end docbook +@end ifdocbook + +@ifnotdocbook +@cartouche +@center @b{Understanding @code{$0}} + + It is important to remember that @code{$0} is the @emph{full} record, exactly as it was read from the input. This includes any leading or trailing whitespace, and the exact whitespace (or other characters) that separate the fields. -It is a not-uncommon error to try to change the field separators +It is a common error to try to change the field separators in a record simply by setting @code{FS} and @code{OFS}, and then expecting a plain @samp{print} or @samp{print $0} to print the modified record. -But this does not work, since nothing was done to change the record +But this does not work, because nothing was done to change the record itself. Instead, you must force the record to be rebuilt, typically with a statement such as @samp{$1 = $1}, as described earlier. +@end cartouche +@end ifnotdocbook -@c ENDOFRANGE ficon @node Field Separators @section Specifying How Fields Are Separated @@ -5782,15 +7061,14 @@ with a statement such as @samp{$1 = $1}, as described earlier. * Default Field Splitting:: How fields are normally separated. * Regexp Field Splitting:: Using regexps as the field separator. * Single Character Fields:: Making each character a separate field. -* Command Line Field Separator:: Setting @code{FS} from the command-line. +* Command Line Field Separator:: Setting @code{FS} from the command line. +* Full Line Fields:: Making the full line be a single field. * Field Splitting Summary:: Some final points and a summary table. @end menu @cindex @code{FS} variable @cindex fields, separating -@c STARTOFRANGE fisepr @cindex field separators -@c STARTOFRANGE fisepg @cindex fields, separating The @dfn{field separator}, which is either a single character or a regular expression, controls the way @command{awk} splits an input record into fields. @@ -5811,7 +7089,7 @@ is split into three fields: @samp{m}, @samp{@bullet{}g}, and Note the leading spaces in the values of the second and third fields. @cindex troubleshooting, @command{awk} uses @code{FS} not @code{IFS} -The field separator is represented by the built-in variable @code{FS}. +The field separator is represented by the predefined variable @code{FS}. Shell programmers take note: @command{awk} does @emph{not} use the name @code{IFS} that is used by the POSIX-compliant shells (such as the Unix Bourne shell, @command{sh}, or Bash). @@ -5819,7 +7097,7 @@ the Unix Bourne shell, @command{sh}, or Bash). @cindex @code{FS} variable, changing value of The value of @code{FS} can be changed in the @command{awk} program with the assignment operator, @samp{=} (@pxref{Assignment Ops}). -Often the right time to do this is at the beginning of execution +Often, the right time to do this is at the beginning of execution before any input has been processed, so that the very first record is read with the proper separator. To do this, use the special @code{BEGIN} pattern @@ -5890,9 +7168,7 @@ rules. @node Regexp Field Splitting @subsection Using Regular Expressions to Separate Fields -@c STARTOFRANGE regexpfs @cindex regular expressions, as field separators -@c STARTOFRANGE fsregexp @cindex field separators, regular expressions as The previous @value{SUBSECTION} discussed the use of single characters or simple strings as the @@ -5950,7 +7226,7 @@ $ @kbd{echo ' a b c d ' | awk 'BEGIN @{ FS = "[ \t\n]+" @}} @cindex null strings @cindex strings, null @cindex empty strings, See null strings -In this case, the first field is @dfn{null} or empty. +In this case, the first field is null, or empty. The stripping of leading and trailing whitespace also comes into play whenever @code{$0} is recomputed. For instance, study this pipeline: @@ -5965,37 +7241,37 @@ $ @kbd{echo ' a b c d' | awk '@{ print; $2 = $2; print @}'} The first @code{print} statement prints the record as it was read, with leading whitespace intact. The assignment to @code{$2} rebuilds @code{$0} by concatenating @code{$1} through @code{$NF} together, -separated by the value of @code{OFS}. Because the leading whitespace -was ignored when finding @code{$1}, it is not part of the new @code{$0}. -Finally, the last @code{print} statement prints the new @code{$0}. +separated by the value of @code{OFS} (which is a space by default). +Because the leading whitespace was ignored when finding @code{$1}, +it is not part of the new @code{$0}. Finally, the last @code{print} +statement prints the new @code{$0}. @cindex @code{FS}, containing @code{^} -@cindex @code{^}, in @code{FS} +@cindex @code{^} (caret), in @code{FS} @cindex dark corner, @code{^}, in @code{FS} There is an additional subtlety to be aware of when using regular expressions for field splitting. -It is not well-specified in the POSIX standard, or anywhere else, what @samp{^} +It is not well specified in the POSIX standard, or anywhere else, what @samp{^} means when splitting fields. Does the @samp{^} match only at the beginning of the entire record? Or is each field separator a new string? It turns out that different @command{awk} versions answer this question differently, and you should not rely on any specific behavior in your programs. @value{DARKCORNER} -As a point of information, Brian Kernighan's @command{awk} allows @samp{^} +@cindex Brian Kernighan's @command{awk} +As a point of information, BWK @command{awk} allows @samp{^} to match only at the beginning of the record. @command{gawk} also works this way. For example: @example $ @kbd{echo 'xxAA xxBxx C' |} > @kbd{gawk -F '(^x+)|( +)' '@{ for (i = 1; i <= NF; i++)} -> @kbd{printf "-->%s<--\n", $i @}'} +> @kbd{ printf "-->%s<--\n", $i @}'} @print{} --><-- @print{} -->AA<-- @print{} -->xxBxx<-- @print{} -->C<-- @end example -@c ENDOFRANGE regexpfs -@c ENDOFRANGE fsregexp @node Single Character Fields @subsection Making Each Character a Separate Field @@ -6024,7 +7300,7 @@ $ @kbd{echo a b | gawk 'BEGIN @{ FS = "" @}} @end example @cindex dark corner, @code{FS} as null string -@cindex FS variable, as null string +@cindex @code{FS} variable, as null string Traditionally, the behavior of @code{FS} equal to @code{""} was not defined. In this case, most versions of Unix @command{awk} simply treat the entire record as only having one field. @@ -6036,10 +7312,8 @@ behaves this way. @node Command Line Field Separator @subsection Setting @code{FS} from the Command Line -@cindex @code{-F} option -@cindex options, command-line -@cindex command line, options -@cindex field separators, on command line +@cindex @option{-F} option, command-line +@cindex field separator, on command line @cindex command line, @code{FS} on@comma{} setting @cindex @code{FS} variable, setting from command line @@ -6053,15 +7327,10 @@ awk -F, '@var{program}' @var{input-files} @noindent sets @code{FS} to the @samp{,} character. Notice that the option uses an uppercase @samp{F} instead of a lowercase @samp{f}. The latter -option (@option{-f}) specifies a file -containing an @command{awk} program. Case is significant in command-line -options: -the @option{-F} and @option{-f} options have nothing to do with each other. -You can use both options at the same time to set the @code{FS} variable -@emph{and} get an @command{awk} program from a file. +option (@option{-f}) specifies a file containing an @command{awk} program. The value used for the argument to @option{-F} is processed in exactly the -same way as assignments to the built-in variable @code{FS}. +same way as assignments to the predefined variable @code{FS}. Any special characters in the field separator must be escaped appropriately. For example, to use a @samp{\} as the field separator on the command line, you would have to type: @@ -6072,8 +7341,8 @@ awk -F\\\\ '@dots{}' files @dots{} @end example @noindent -@cindex @code{\} (backslash), as field separators -@cindex backslash (@code{\}), as field separators +@cindex @code{\} (backslash), as field separator +@cindex backslash (@code{\}), as field separator Because @samp{\} is used for quoting in the shell, @command{awk} sees @samp{-F\\}. Then @command{awk} processes the @samp{\\} for escape characters (@pxref{Escape Sequences}), finally yielding @@ -6088,111 +7357,140 @@ shell, without any quotes, the @samp{\} gets deleted, so @command{awk} figures that you really want your fields to be separated with TABs and not @samp{t}s. Use @samp{-v FS="t"} or @samp{-F"[t]"} on the command line if you really do want to separate your fields with @samp{t}s. +Use @samp{-F '\t'} when not in compatibility mode to specify that TABs +separate fields. -As an example, let's use an @command{awk} program file called @file{baud.awk} -that contains the pattern @code{/300/} and the action @samp{print $1}: +As an example, let's use an @command{awk} program file called @file{edu.awk} +that contains the pattern @code{/edu/} and the action @samp{print $1}: @example -/300/ @{ print $1 @} +/edu/ @{ print $1 @} @end example Let's also set @code{FS} to be the @samp{-} character and run the -program on the file @file{BBS-list}. The following command prints a -list of the names of the bulletin boards that operate at 300 baud and +program on the file @file{mail-list}. The following command prints a +list of the names of the people that work at or attend a university, and the first three digits of their phone numbers: -@c tweaked to make the tex output look better in @smallbook @example -$ @kbd{awk -F- -f baud.awk BBS-list} -@print{} aardvark 555 -@print{} alpo -@print{} barfly 555 -@print{} bites 555 -@print{} camelot 555 -@print{} core 555 -@print{} fooey 555 -@print{} foot 555 -@print{} macfoo 555 -@print{} sdace 555 -@print{} sabafoo 555 +$ @kbd{awk -F- -f edu.awk mail-list} +@print{} Fabius 555 +@print{} Samuel 555 +@print{} Jean @end example @noindent -Note the second line of output. The second line +Note the third line of output. The third line in the original file looked like this: @example -alpo-net 555-3412 2400/1200/300 A +Jean-Paul 555-2127 jeanpaul.campanorum@@nyu.edu R @end example -The @samp{-} as part of the system's name was used as the field +The @samp{-} as part of the person's name was used as the field separator, instead of the @samp{-} in the phone number that was originally intended. This demonstrates why you have to be careful in choosing your field and record separators. @cindex Unix @command{awk}, password files@comma{} field separators and -Perhaps the most common use of a single character as the field -separator occurs when processing the Unix system password file. -On many Unix systems, each user has a separate entry in the system password -file, one line per user. The information in these lines is separated -by colons. The first field is the user's login name and the second is -the user's (encrypted or shadow) password. A password file entry might look -like this: +Perhaps the most common use of a single character as the field separator +occurs when processing the Unix system password file. On many Unix +systems, each user has a separate entry in the system password file, one +line per user. The information in these lines is separated by colons. +The first field is the user's login name and the second is the user's +encrypted or shadow password. (A shadow password is indicated by the +presence of a single @samp{x} in the second field.) A password file +entry might look like this: @cindex Robbins, Arnold @example -arnold:xyzzy:2076:10:Arnold Robbins:/home/arnold:/bin/bash +arnold:x:2076:10:Arnold Robbins:/home/arnold:/bin/bash @end example The following program searches the system password file and prints -the entries for users who have no password: +the entries for users whose full name is not indicated: @example -awk -F: '$2 == ""' /etc/passwd +awk -F: '$5 == ""' /etc/passwd @end example -@node Field Splitting Summary -@subsection Field-Splitting Summary +@node Full Line Fields +@subsection Making the Full Line Be a Single Field -It is important to remember that when you assign a string constant -as the value of @code{FS}, it undergoes normal @command{awk} string -processing. For example, with Unix @command{awk} and @command{gawk}, -the assignment @samp{FS = "\.."} assigns the character string @code{".."} -to @code{FS} (the backslash is stripped). This creates a regexp meaning -``fields are separated by occurrences of any two characters.'' -If instead you want fields to be separated by a literal period followed -by any single character, use @samp{FS = "\\.."}. +Occasionally, it's useful to treat the whole input line as a +single field. This can be done easily and portably simply by +setting @code{FS} to @code{"\n"} (a newline):@footnote{Thanks to +Andrew Schorr for this tip.} -The following table summarizes how fields are split, based on the value -of @code{FS} (@samp{==} means ``is equal to''): +@example +awk -F'\n' '@var{program}' @var{files @dots{}} +@end example -@table @code -@item FS == " " -Fields are separated by runs of whitespace. Leading and trailing -whitespace are ignored. This is the default. +@noindent +When you do this, @code{$1} is the same as @code{$0}. -@item FS == @var{any other single character} -Fields are separated by each occurrence of the character. Multiple -successive occurrences delimit empty fields, as do leading and -trailing occurrences. -The character can even be a regexp metacharacter; it does not need -to be escaped. +@cindex sidebar, Changing @code{FS} Does Not Affect the Fields +@ifdocbook +@docbook +<sidebar><title>Changing @code{FS} Does Not Affect the Fields</title> +@end docbook -@item FS == @var{regexp} -Fields are separated by occurrences of characters that match @var{regexp}. -Leading and trailing matches of @var{regexp} delimit empty fields. -@item FS == "" -Each individual character in the record becomes a separate field. -(This is a @command{gawk} extension; it is not specified by the -POSIX standard.) -@end table +@cindex POSIX @command{awk}, field separators and +@cindex field separator, POSIX and +According to the POSIX standard, @command{awk} is supposed to behave +as if each record is split into fields at the time it is read. +In particular, this means that if you change the value of @code{FS} +after a record is read, the value of the fields (i.e., how they were split) +should reflect the old value of @code{FS}, not the new one. + +@cindex dark corner, field separators +@cindex @command{sed} utility +@cindex stream editors +However, many older implementations of @command{awk} do not work this way. Instead, +they defer splitting the fields until a field is actually +referenced. The fields are split +using the @emph{current} value of @code{FS}! +@value{DARKCORNER} +This behavior can be difficult +to diagnose. The following example illustrates the difference +between the two methods. +(The @command{sed}@footnote{The @command{sed} utility is a ``stream editor.'' +Its behavior is also defined by the POSIX standard.} +command prints just the first line of @file{/etc/passwd}.) + +@example +sed 1q /etc/passwd | awk '@{ FS = ":" ; print $1 @}' +@end example + +@noindent +which usually prints: + +@example +root +@end example + +@noindent +on an incorrect implementation of @command{awk}, while @command{gawk} +prints the full first line of the file, something like: + +@example +root:x:0:0:Root:/: +@end example + +@docbook +</sidebar> +@end docbook +@end ifdocbook + +@ifnotdocbook +@cartouche +@center @b{Changing @code{FS} Does Not Affect the Fields} + -@c fakenode --- for prepinfo -@subheading Advanced Notes: Changing @code{FS} Does Not Affect the Fields @cindex POSIX @command{awk}, field separators and -@cindex field separators, POSIX and +@cindex field separator, POSIX and According to the POSIX standard, @command{awk} is supposed to behave as if each record is split into fields at the time it is read. In particular, this means that if you change the value of @code{FS} @@ -6227,14 +7525,56 @@ root @noindent on an incorrect implementation of @command{awk}, while @command{gawk} -prints something like: +prints the full first line of the file, something like: @example -root:nSijPlPhZZwgE:0:0:Root:/: +root:x:0:0:Root:/: @end example +@end cartouche +@end ifnotdocbook + +@node Field Splitting Summary +@subsection Field-Splitting Summary + +It is important to remember that when you assign a string constant +as the value of @code{FS}, it undergoes normal @command{awk} string +processing. For example, with Unix @command{awk} and @command{gawk}, +the assignment @samp{FS = "\.."} assigns the character string @code{".."} +to @code{FS} (the backslash is stripped). This creates a regexp meaning +``fields are separated by occurrences of any two characters.'' +If instead you want fields to be separated by a literal period followed +by any single character, use @samp{FS = "\\.."}. + +The following list summarizes how fields are split, based on the value +of @code{FS} (@samp{==} means ``is equal to''): + +@table @code +@item FS == " " +Fields are separated by runs of whitespace. Leading and trailing +whitespace are ignored. This is the default. + +@item FS == @var{any other single character} +Fields are separated by each occurrence of the character. Multiple +successive occurrences delimit empty fields, as do leading and +trailing occurrences. +The character can even be a regexp metacharacter; it does not need +to be escaped. + +@item FS == @var{regexp} +Fields are separated by occurrences of characters that match @var{regexp}. +Leading and trailing matches of @var{regexp} delimit empty fields. + +@item FS == "" +Each individual character in the record becomes a separate field. +(This is a common extension; it is not specified by the POSIX standard.) +@end table + +@cindex sidebar, @code{FS} and @code{IGNORECASE} +@ifdocbook +@docbook +<sidebar><title>@code{FS} and @code{IGNORECASE}</title> +@end docbook -@c fakenode --- for prepinfo -@subheading Advanced Notes: @code{FS} and @code{IGNORECASE} The @code{IGNORECASE} variable (@pxref{User-modified}) @@ -6252,37 +7592,59 @@ print $1 @noindent The output is @samp{aCa}. If you really want to split fields on an alphabetic character while ignoring case, use a regexp that will -do it for you. E.g., @samp{FS = "[c]"}. In this case, @code{IGNORECASE} +do it for you (e.g., @samp{FS = "[c]"}). In this case, @code{IGNORECASE} will take effect. -@c ENDOFRANGE fisepr -@c ENDOFRANGE fisepg +@docbook +</sidebar> +@end docbook +@end ifdocbook + +@ifnotdocbook +@cartouche +@center @b{@code{FS} and @code{IGNORECASE}} + + + +The @code{IGNORECASE} variable +(@pxref{User-modified}) +affects field splitting @emph{only} when the value of @code{FS} is a regexp. +It has no effect when @code{FS} is a single character, even if +that character is a letter. Thus, in the following code: + +@example +FS = "c" +IGNORECASE = 1 +$0 = "aCa" +print $1 +@end example + +@noindent +The output is @samp{aCa}. If you really want to split fields on an +alphabetic character while ignoring case, use a regexp that will +do it for you (e.g., @samp{FS = "[c]"}). In this case, @code{IGNORECASE} +will take effect. +@end cartouche +@end ifnotdocbook + @node Constant Size @section Reading Fixed-Width Data -@ifnotinfo -@quotation NOTE +@cindex data, fixed-width +@cindex fixed-width data +@cindex advanced features, fixed-width data + +@c O'Reilly doesn't like it as a note the first thing in the section. This @value{SECTION} discusses an advanced feature of @command{gawk}. If you are a novice @command{awk} user, you might want to skip it on the first reading. -@end quotation -@end ifnotinfo -@ifinfo -(This @value{SECTION} discusses an advanced feature of @command{awk}. -If you are a novice @command{awk} user, you might want to skip it on -the first reading.) -@end ifinfo - -@cindex data, fixed-width -@cindex fixed-width data -@cindex advanced features, fixed-width data -@command{gawk} provides a facility for dealing with -fixed-width fields with no distinctive field separator. For example, -data of this nature arises in the input for old Fortran programs where -numbers are run together, or in the output of programs that did not -anticipate the use of their output as input for other programs. +@command{gawk} provides a facility for dealing with fixed-width fields +with no distinctive field separator. For example, data of this nature +arises in the input for old Fortran programs where numbers are run +together, or in the output of programs that did not anticipate the use +of their output as input for other programs. An example of the latter is a table where all the columns are lined up by the use of a variable number of spaces and @emph{empty fields are just @@ -6321,20 +7683,15 @@ dave ttyq4 26Jun9115days 46 46 wnewmail @end group @end example -The following program takes the above input, converts the idle time to +The following program takes this input, converts the idle time to number of seconds, and prints out the first two fields and the calculated idle time: -@quotation NOTE -This program uses a number of @command{awk} features that -haven't been introduced yet. -@end quotation - @example BEGIN @{ FIELDWIDTHS = "9 6 10 6 7 7 35" @} NR > 2 @{ idle = $4 - sub(/^ */, "", idle) # strip leading spaces + sub(/^ +/, "", idle) # strip leading spaces if (idle == "") idle = 0 if (idle ~ /:/) @{ @@ -6348,6 +7705,11 @@ NR > 2 @{ @} @end example +@quotation NOTE +The preceding program uses a number of @command{awk} features that +haven't been introduced yet. +@end quotation + Running the program on the data produces the following results: @example @@ -6371,10 +7733,6 @@ program for processing such data could use the @code{FIELDWIDTHS} feature to simplify reading the data. (Of course, getting @command{gawk} to run on a system with card readers is another story!) -@ignore -Exercise: Write a ballot card reading program -@end ignore - @cindex @command{gawk}, splitting fields and Assigning a value to @code{FS} causes @command{gawk} to use @code{FS} for field splitting again. Use @samp{FS = FS} to make this happen, @@ -6391,31 +7749,22 @@ if (PROCINFO["FS"] == "FS") else if (PROCINFO["FS"] == "FIELDWIDTHS") @var{fixed-width field splitting} @dots{} else - @var{content-based field splitting} @dots{} (see next @value{SECTION}) + @var{content-based field splitting} @dots{} @ii{(see next @value{SECTION})} @end example This information is useful when writing a function that needs to temporarily change @code{FS} or @code{FIELDWIDTHS}, read some records, and then restore the original settings -(@pxref{Passwd Functions}, +(@DBPXREF{Passwd Functions} for an example of such a function). @node Splitting By Content -@section Defining Fields By Content +@section Defining Fields by Content -@ifnotinfo -@quotation NOTE +@c O'Reilly doesn't like it as a note the first thing in the section. This @value{SECTION} discusses an advanced feature of @command{gawk}. If you are a novice @command{awk} user, you might want to skip it on the first reading. -@end quotation -@end ifnotinfo - -@ifinfo -(This @value{SECTION} discusses an advanced feature of @command{awk}. -If you are a novice @command{awk} user, you might want to skip it on -the first reading.) -@end ifinfo @cindex advanced features, specifying field content Normally, when using @code{FS}, @command{gawk} defines the fields as the @@ -6426,14 +7775,16 @@ However, there are times when you really want to define the fields by what they are, and not by what they are not. The most notorious such case -is so-called @dfn{comma separated value} (CSV) data. Many spreadsheet programs, +is so-called @dfn{comma-separated values} (CSV) data. Many spreadsheet programs, for example, can export their data into text files, where each record is terminated with a newline, and fields are separated by commas. If only commas separated the data, there wouldn't be an issue. The problem comes when -one of the fields contains an @emph{embedded} comma. While there is no -formal standard specification for CSV data@footnote{At least, we don't know of one.}, -in such cases, most programs embed the field in double quotes. So we might -have data like this: +one of the fields contains an @emph{embedded} comma. +In such cases, most programs embed the field in double quotes.@footnote{The +CSV format lacked a formal standard definition for many years. +@uref{http://www.ietf.org/rfc/rfc4180.txt, RFC 4180} +standardizes the most common practices.} +So we might have data like this: @example @c file eg/misc/addresses.csv @@ -6447,7 +7798,7 @@ The @code{FPAT} variable offers a solution for cases like this. The value of @code{FPAT} should be a string that provides a regular expression. This regular expression describes the contents of each field. -In the case of CSV data as presented above, each field is either ``anything that +In the case of CSV data as presented here, each field is either ``anything that is not a comma,'' or ``a double quote, anything that is not a double quote, and a closing double quote.'' If written as a regular expression constant (@pxref{Regexp}), @@ -6504,16 +7855,18 @@ if (substr($i, 1, 1) == "\"") @{ As with @code{FS}, the @code{IGNORECASE} variable (@pxref{User-modified}) affects field splitting with @code{FPAT}. +Assigning a value to @code{FPAT} overrides field splitting +with @code{FS} and with @code{FIELDWIDTHS}. Similar to @code{FIELDWIDTHS}, the value of @code{PROCINFO["FS"]} will be @code{"FPAT"} if content-based field splitting is being used. @quotation NOTE Some programs export CSV data that contains embedded newlines between the double quotes. @command{gawk} provides no way to deal with this. -Since there is no formal specification for CSV data, there isn't much +Even though a formal specification for CSV data exists, there isn't much more to be done; the @code{FPAT} mechanism provides an elegant solution for the majority -of cases, and the @command{gawk} maintainer is satisfied with that. +of cases, and the @command{gawk} developers are satisfied with that. @end quotation As written, the regexp used for @code{FPAT} requires that each field @@ -6527,14 +7880,18 @@ FPAT = "([^,]*)|(\"[^\"]+\")" Finally, the @code{patsplit()} function makes the same functionality available for splitting regular strings (@pxref{String Functions}). +To recap, @command{gawk} provides three independent methods +to split input records into fields. @command{gawk} uses whichever +mechanism was last chosen based on which of the three +variables---@code{FS}, @code{FIELDWIDTHS}, and @code{FPAT}---was +last assigned to. + @node Multiple Line @section Multiple-Line Records -@c STARTOFRANGE recm +@cindex multiple-line records @cindex records, multiline -@c STARTOFRANGE imr @cindex input, multiline records -@c STARTOFRANGE frm @cindex files, reading, multiline records @cindex input, files, See input files In some databases, a single line cannot conveniently hold all the @@ -6574,14 +7931,15 @@ the first nonblank line that follows---no matter how many blank lines appear in a row, they are considered one record separator. @cindex dark corner, multiline records -There is an important difference between @samp{RS = ""} and +However, there is an important difference between @samp{RS = ""} and @samp{RS = "\n\n+"}. In the first case, leading newlines in the input @value{DF} are ignored, and if a file ends without extra blank lines after the last record, the final newline is removed from the record. In the second case, this special processing is not done. @value{DARKCORNER} -@cindex field separators, in multiline records +@cindex field separator, in multiline records +@cindex @code{FS}, in multiline records Now that the input is separated into records, the second step is to separate the fields in the record. One way to do this is to divide each of the lines into fields in the normal manner. This happens by default @@ -6647,7 +8005,7 @@ BEGIN @{ RS = "" ; FS = "\n" @} Running the program produces the following output: @example -$ awk -f addrs.awk addresses +$ @kbd{awk -f addrs.awk addresses} @print{} Name is: Jane Doe @print{} Address is: 123 Main Street @print{} City and State are: Anywhere, SE 12345-6789 @@ -6659,12 +8017,9 @@ $ awk -f addrs.awk addresses @dots{} @end example -@xref{Labels Program}, for a more realistic -program that deals with address lists. -The following -table -summarizes how records are split, based on the -value of +@DBXREF{Labels Program} for a more realistic program dealing with +address lists. The following list summarizes how records are split, +based on the value of @ifinfo @code{RS}. (@samp{==} means ``is equal to.'') @@ -6699,22 +8054,18 @@ POSIX standard.) @cindex @command{gawk}, @code{RT} variable in @cindex @code{RT} variable -In all cases, @command{gawk} sets @code{RT} to the input text that matched the -value specified by @code{RS}. +If not in compatibility mode (@pxref{Options}), @command{gawk} sets +@code{RT} to the input text that matched the value specified by @code{RS}. But if the input file ended without any text that matches @code{RS}, then @command{gawk} sets @code{RT} to the null string. -@c ENDOFRANGE recm -@c ENDOFRANGE imr -@c ENDOFRANGE frm @node Getline @section Explicit Input with @code{getline} -@c STARTOFRANGE getl @cindex @code{getline} command, explicit input with @cindex input, explicit So far we have been getting our input data from @command{awk}'s main -input stream---either the standard input (usually your terminal, sometimes +input stream---either the standard input (usually your keyboard, sometimes the output from another program) or from the files specified on the command line. The @command{awk} language has a special built-in command called @code{getline} that @@ -6725,15 +8076,27 @@ The @code{getline} command is used in several different ways and should The examples that follow the explanation of the @code{getline} command include material that has not been covered yet. Therefore, come back and study the @code{getline} command @emph{after} you have reviewed the -rest of this @value{DOCUMENT} and have a good knowledge of how @command{awk} works. +rest of +@ifinfo +this @value{DOCUMENT} +@end ifinfo +@ifhtml +this @value{DOCUMENT} +@end ifhtml +@ifnotinfo +@ifnothtml +Parts I and II +@end ifnothtml +@end ifnotinfo +and have a good knowledge of how @command{awk} works. @cindex @command{gawk}, @code{ERRNO} variable in -@cindex @code{ERRNO} variable +@cindex @code{ERRNO} variable, with @command{getline} command @cindex differences in @command{awk} and @command{gawk}, @code{getline} command @cindex @code{getline} command, return values -@cindex @code{--sandbox} option, input redirection with @command{getline} +@cindex @option{--sandbox} option, input redirection with @code{getline} -The @code{getline} command returns one if it finds a record and zero if +The @code{getline} command returns 1 if it finds a record and 0 if it encounters the end of the file. If there is some error in getting a record, such as a file that cannot be opened, then @code{getline} returns @minus{}1. In this case, @command{gawk} sets the variable @@ -6744,7 +8107,7 @@ represents a shell command. @quotation NOTE When @option{--sandbox} is specified (@pxref{Options}), -reading lines from files, pipes and coprocesses is disabled. +reading lines from files, pipes, and coprocesses is disabled. @end quotation @menu @@ -6773,44 +8136,63 @@ finished processing the current record, but want to do some special processing on the next record @emph{right now}. For example: @example +# Remove text between /* and */, inclusive @{ - if ((t = index($0, "/*")) != 0) @{ - # value of `tmp' will be "" if t is 1 - tmp = substr($0, 1, t - 1) - u = index(substr($0, t + 2), "*/") - offset = t + 2 - while (u == 0) @{ - if (getline <= 0) @{ - m = "unexpected EOF or error" - m = (m ": " ERRNO) - print m > "/dev/stderr" + if ((i = index($0, "/*")) != 0) @{ + out = substr($0, 1, i - 1) # leading part of the string + rest = substr($0, i + 2) # ... */ ... + j = index(rest, "*/") # is */ in trailing part? + if (j > 0) @{ + rest = substr(rest, j + 2) # remove comment + @} else @{ + while (j == 0) @{ + # get more text + if (getline <= 0) @{ + print("unexpected EOF or error:", ERRNO) > "/dev/stderr" exit - @} - u = index($0, "*/") - offset = 0 - @} - # substr() expression will be "" if */ - # occurred at end of line - $0 = tmp substr($0, offset + u + 2) - @} - print $0 + @} + # build up the line using string concatenation + rest = rest $0 + j = index(rest, "*/") # is */ in trailing part? + if (j != 0) @{ + rest = substr(rest, j + 2) + break + @} + @} + @} + # build up the output line using string concatenation + $0 = out rest + @} + print $0 @} @end example +@c 8/2014: Here is some sample input: +@ignore +mon/*comment*/key +rab/*commen +t*/bit +horse /*comment*/more text +part 1 /*comment*/part 2 /*comment*/part 3 +no comment +@end ignore + This @command{awk} program deletes C-style comments (@samp{/* @dots{} -*/}) from the input. By replacing the @samp{print $0} with other +*/}) from the input. +It uses a number of features we haven't covered yet, including +string concatenation +(@pxref{Concatenation}) +and the @code{index()} and @code{substr()} built-in +functions +(@pxref{String Functions}). +By replacing the @samp{print $0} with other statements, you could perform more complicated processing on the decommented input, such as searching for matches of a regular expression. (This program has a subtle problem---it does not work if one comment ends and another begins on the same line.) -@ignore -Exercise, -write a program that does handle multiple comments on the line. -@end ignore - This form of the @code{getline} command sets @code{NF}, -@code{NR}, @code{FNR}, and the value of @code{$0}. +@code{NR}, @code{FNR}, @code{RT}, and the value of @code{$0}. @quotation NOTE The new value of @code{$0} is used to test @@ -6824,6 +8206,7 @@ rule in the program. @xref{Next Statement}. @node Getline/Variable @subsection Using @code{getline} into a Variable +@cindex @code{getline} into a variable @cindex variables, @code{getline} command into@comma{} using You can use @samp{getline @var{var}} to read the next record from @@ -6867,13 +8250,15 @@ free @end example The @code{getline} command used in this way sets only the variables -@code{NR} and @code{FNR} (and of course, @var{var}). The record is not +@code{NR}, @code{FNR}, and @code{RT} (and of course, @var{var}). +The record is not split into fields, so the values of the fields (including @code{$0}) and the value of @code{NF} do not change. @node Getline/File @subsection Using @code{getline} from a File +@cindex @code{getline} from a file @cindex input redirection @cindex redirection of input @cindex @code{<} (left angle bracket), @code{<} operator (I/O) @@ -6902,15 +8287,16 @@ Because the main input stream is not used, the values of @code{NR} and @code{FNR} are not changed. However, the record it reads is split into fields in the normal manner, so the values of @code{$0} and the other fields are changed, resulting in a new value of @code{NF}. +@code{RT} is also set. @cindex POSIX @command{awk}, @code{<} operator and @c Thanks to Paul Eggert for initial wording here According to POSIX, @samp{getline < @var{expression}} is ambiguous if @var{expression} contains unparenthesized operators other than @samp{$}; for example, @samp{getline < dir "/" file} is ambiguous -because the concatenation operator is not parenthesized. You should -write it as @samp{getline < (dir "/" file)} if you want your program -to be portable to all @command{awk} implementations. +because the concatenation operator (not discussed yet; @pxref{Concatenation}) +is not parenthesized. You should write it as @samp{getline < (dir "/" file)} if +you want your program to be portable to all @command{awk} implementations. @node Getline/Variable/File @subsection Using @code{getline} into a Variable from a File @@ -6918,12 +8304,10 @@ to be portable to all @command{awk} implementations. Use @samp{getline @var{var} < @var{file}} to read input from the file -@var{file}, and put it in the variable @var{var}. As above, @var{file} +@var{file}, and put it in the variable @var{var}. As earlier, @var{file} is a string-valued expression that specifies the file from which to read. -@cindex @command{gawk}, @code{RT} variable in -@cindex @code{RT} variable -In this version of @code{getline}, none of the built-in variables are +In this version of @code{getline}, none of the predefined variables are changed and the record is not split into fields. The only variable changed is @var{var}.@footnote{This is not quite true. @code{RT} could be changed if @code{RS} is a regular expression.} @@ -6945,28 +8329,35 @@ Such a record is replaced by the contents of the file Note here how the name of the extra input file is not built into the program; it is taken directly from the data, specifically from the second field on -the @samp{@@include} line. +the @code{@@include} line. -@cindex @code{close()} function The @code{close()} function is called to ensure that if two identical -@samp{@@include} lines appear in the input, the entire specified file is +@code{@@include} lines appear in the input, the entire specified file is included twice. @xref{Close Files And Pipes}. One deficiency of this program is that it does not process nested -@samp{@@include} statements -(i.e., @samp{@@include} statements in included files) +@code{@@include} statements +(i.e., @code{@@include} statements in included files) the way a true macro preprocessor would. -@xref{Igawk Program}, for a program -that does handle nested @samp{@@include} statements. +@DBXREF{Igawk Program} for a program +that does handle nested @code{@@include} statements. @node Getline/Pipe @subsection Using @code{getline} from a Pipe +@c From private email, dated October 2, 1988. Used by permission, March 2013. +@cindex Kernighan, Brian +@quotation +@i{Omniscience has much to recommend it. +Failing that, attention to details would be useful.} +@author Brian Kernighan +@end quotation + @cindex @code{|} (vertical bar), @code{|} operator (I/O) @cindex vertical bar (@code{|}), @code{|} operator (I/O) @cindex input pipeline -@cindex pipes, input +@cindex pipe, input @cindex operators, input/output The output of a command can also be piped into @code{getline}, using @samp{@var{command} | getline}. In @@ -6990,14 +8381,14 @@ produced by running the rest of the line as a shell command: @end example @noindent -@cindex @code{close()} function The @code{close()} function is called to ensure that if two identical @samp{@@execute} lines appear in the input, the command is run for each one. @ifnottex +@ifnotdocbook @xref{Close Files And Pipes}. +@end ifnotdocbook @end ifnottex -@c Exercise!! @c This example is unrealistic, since you could just use system Given the input: @@ -7026,13 +8417,14 @@ bletch @end example @noindent -Notice that this program ran the command @command{who} and printed the previous result. +Notice that this program ran the command @command{who} and printed the result. (If you try this program yourself, you will of course get different results, depending upon who is logged in on your system.) This variation of @code{getline} splits the record into fields, sets the value of @code{NF}, and recomputes the value of @code{$0}. The values of @code{NR} and @code{FNR} are not changed. +@code{RT} is set. @cindex POSIX @command{awk}, @code{|} I/O operator and @c Thanks to Paul Eggert for initial wording here @@ -7043,12 +8435,14 @@ because the concatenation operator is not parenthesized. You should write it as @samp{(@w{"echo "} "date") | getline} if you want your program to be portable to all @command{awk} implementations. +@cindex Brian Kernighan's @command{awk} +@cindex @command{mawk} utility @quotation NOTE Unfortunately, @command{gawk} has not been consistent in its treatment of a construct like @samp{@w{"echo "} "date" | getline}. Most versions, including the current version, treat it at as @samp{@w{("echo "} "date") | getline}. -(This how Brian Kernighan's @command{awk} behaves.) +(This is also how BWK @command{awk} behaves.) Some versions changed and treated it as @samp{@w{"echo "} ("date" | getline)}. (This is how @command{mawk} behaves.) @@ -7075,8 +8469,8 @@ BEGIN @{ @} @end example -In this version of @code{getline}, none of the built-in variables are -changed and the record is not split into fields. +In this version of @code{getline}, none of the predefined variables are +changed and the record is not split into fields. However, @code{RT} is set. @ifinfo @c Thanks to Paul Eggert for initial wording here @@ -7122,7 +8516,7 @@ The values of @code{NR} and because the main input stream is not used. However, the record is split into fields in the normal manner, thus changing the values of @code{$0}, of the other fields, -and of @code{NF}. +and of @code{NF} and @code{RT}. Coprocesses are an advanced feature. They are discussed here only because this is the @value{SECTION} on @code{getline}. @@ -7137,9 +8531,10 @@ When you use @samp{@var{command} |& getline @var{var}}, the output from the coprocess @var{command} is sent through a two-way pipe to @code{getline} and into the variable @var{var}. -In this version of @code{getline}, none of the built-in variables are +In this version of @code{getline}, none of the predefined variables are changed and the record is not split into fields. The only variable changed is @var{var}. +However, @code{RT} is set. @ifinfo Coprocesses are an advanced feature. They are discussed here only because @@ -7153,7 +8548,7 @@ where coprocesses are discussed in more detail. Here are some miscellaneous points about @code{getline} that you should bear in mind: -@itemize @bullet +@itemize @value{BULLET} @item When @code{getline} changes the value of @code{$0} and @code{NF}, @command{awk} does @emph{not} automatically jump to the start of the @@ -7165,7 +8560,7 @@ However, the new record is tested against any subsequent rules. @cindex @command{awk}, implementations, limits @cindex @command{gawk}, implementation issues, limits @item -Many @command{awk} implementations limit the number of pipelines that an @command{awk} +Some very old @command{awk} implementations limit the number of pipelines that an @command{awk} program may have open to just one. In @command{gawk}, there is no such limit. You can open as many pipelines (and coprocesses) as the underlying operating system permits. @@ -7183,7 +8578,7 @@ causes @command{awk} to set the value of @code{FILENAME}. Normally, @code{FILENAME} does not have a value inside @code{BEGIN} rules, because you have not yet started to process the command-line @value{DF}s. @value{DARKCORNER} -(@xref{BEGIN/END}, +(See @ref{BEGIN/END}; also @pxref{Auto-set}.) @item @@ -7192,16 +8587,45 @@ Using @code{FILENAME} with @code{getline} is likely to be a source for confusion. @command{awk} opens a separate input stream from the current input file. However, by not using a variable, @code{$0} -and @code{NR} are still updated. If you're doing this, it's +and @code{NF} are still updated. If you're doing this, it's probably by accident, and you should reconsider what it is you're trying to accomplish. @item -@ref{Getline Summary}, presents a table summarizing the +@DBREF{Getline Summary} presents a table summarizing the @code{getline} variants and which variables they can affect. It is worth noting that those variants which do not use redirection can cause @code{FILENAME} to be updated if they cause @command{awk} to start reading a new input file. + +@item +@cindex Moore, Duncan +If the variable being assigned is an expression with side effects, +different versions of @command{awk} behave differently upon encountering +end-of-file. Some versions don't evaluate the expression; many versions +(including @command{gawk}) do. Here is an example, due to Duncan Moore: + +@ignore +Date: Sun, 01 Apr 2012 11:49:33 +0100 +From: Duncan Moore <duncan.moore@@gmx.com> +@end ignore + +@example +BEGIN @{ + system("echo 1 > f") + while ((getline a[++c] < "f") > 0) @{ @} + print c +@} +@end example + +@noindent +Here, the side effect is the @samp{++c}. Is @code{c} incremented if +end of file is encountered, before the element in @code{a} is assigned? + +@command{gawk} treats @code{getline} like a function call, and evaluates +the expression @samp{a[++c]} before attempting to read from @file{f}. +However, some versions of @command{awk} only evaluate the expression once they +know that there is a string value to be assigned. @end itemize @node Getline Summary @@ -7210,46 +8634,258 @@ can cause @code{FILENAME} to be updated if they cause @ref{table-getline-variants} summarizes the eight variants of @code{getline}, -listing which built-in variables are set by each one, +listing which predefined variables are set by each one, and whether the variant is standard or a @command{gawk} extension. +Note: for each variant, @command{gawk} sets the @code{RT} predefined variable. @float Table,table-getline-variants -@caption{getline Variants and What They Set} +@caption{@code{getline} variants and what they set} @multitable @columnfractions .33 .38 .27 -@headitem Variant @tab Effect @tab Standard / Extension -@item @code{getline} @tab Sets @code{$0}, @code{NF}, @code{FNR}, and @code{NR} @tab Standard -@item @code{getline} @var{var} @tab Sets @var{var}, @code{FNR}, and @code{NR} @tab Standard -@item @code{getline <} @var{file} @tab Sets @code{$0} and @code{NF} @tab Standard -@item @code{getline @var{var} < @var{file}} @tab Sets @var{var} @tab Standard -@item @var{command} @code{| getline} @tab Sets @code{$0} and @code{NF} @tab Standard -@item @var{command} @code{| getline} @var{var} @tab Sets @var{var} @tab Standard -@item @var{command} @code{|& getline} @tab Sets @code{$0} and @code{NF} @tab Extension -@item @var{command} @code{|& getline} @var{var} @tab Sets @var{var} @tab Extension +@headitem Variant @tab Effect @tab @command{awk} / @command{gawk} +@item @code{getline} @tab Sets @code{$0}, @code{NF}, @code{FNR}, @code{NR}, and @code{RT} @tab @command{awk} +@item @code{getline} @var{var} @tab Sets @var{var}, @code{FNR}, @code{NR}, and @code{RT} @tab @command{awk} +@item @code{getline <} @var{file} @tab Sets @code{$0}, @code{NF}, and @code{RT} @tab @command{awk} +@item @code{getline @var{var} < @var{file}} @tab Sets @var{var} and @code{RT} @tab @command{awk} +@item @var{command} @code{| getline} @tab Sets @code{$0}, @code{NF}, and @code{RT} @tab @command{awk} +@item @var{command} @code{| getline} @var{var} @tab Sets @var{var} and @code{RT} @tab @command{awk} +@item @var{command} @code{|& getline} @tab Sets @code{$0}, @code{NF}, and @code{RT} @tab @command{gawk} +@item @var{command} @code{|& getline} @var{var} @tab Sets @var{var} and @code{RT} @tab @command{gawk} @end multitable @end float -@c ENDOFRANGE getl -@c ENDOFRANGE inex -@c ENDOFRANGE infir -@node Command line directories -@section Directories On The Command Line -@cindex directories, command line +@node Read Timeout +@section Reading Input with a Timeout +@cindex timeout, reading input + +@cindex differences in @command{awk} and @command{gawk}, read timeouts +This @value{SECTION} describes a feature that is specific to @command{gawk}. + +You may specify a timeout in milliseconds for reading input from the keyboard, +a pipe, or two-way communication, including TCP/IP sockets. This can be done +on a per input, command, or connection basis, by setting a special element +in the @code{PROCINFO} array (@pxref{Auto-set}): + +@example +PROCINFO["input_name", "READ_TIMEOUT"] = @var{timeout in milliseconds} +@end example + +When set, this causes @command{gawk} to time out and return failure +if no data is available to read within the specified timeout period. +For example, a TCP client can decide to give up on receiving +any response from the server after a certain amount of time: + +@example +Service = "/inet/tcp/0/localhost/daytime" +PROCINFO[Service, "READ_TIMEOUT"] = 100 +if ((Service |& getline) > 0) + print $0 +else if (ERRNO != "") + print ERRNO +@end example + +Here is how to read interactively from the user@footnote{This assumes +that standard input is the keyboard.} without waiting +for more than five seconds: + +@example +PROCINFO["/dev/stdin", "READ_TIMEOUT"] = 5000 +while ((getline < "/dev/stdin") > 0) + print $0 +@end example + +@command{gawk} terminates the read operation if input does not +arrive after waiting for the timeout period, returns failure +and sets @code{ERRNO} to an appropriate string value. +A negative or zero value for the timeout is the same as specifying +no timeout at all. + +A timeout can also be set for reading from the keyboard in the implicit +loop that reads input records and matches them against patterns, +like so: + +@example +$ @kbd{gawk 'BEGIN @{ PROCINFO["-", "READ_TIMEOUT"] = 5000 @}} +> @kbd{@{ print "You entered: " $0 @}'} +@kbd{gawk} +@print{} You entered: gawk +@end example + +In this case, failure to respond within five seconds results in the following +error message: + +@example +@error{} gawk: cmd. line:2: (FILENAME=- FNR=1) fatal: error reading input file `-': Connection timed out +@end example + +The timeout can be set or changed at any time, and will take effect on the +next attempt to read from the input device. In the following example, +we start with a timeout value of one second, and progressively +reduce it by one-tenth of a second until we wait indefinitely +for the input to arrive: + +@example +PROCINFO[Service, "READ_TIMEOUT"] = 1000 +while ((Service |& getline) > 0) @{ + print $0 + PROCINFO[Service, "READ_TIMEOUT"] -= 100 +@} +@end example + +@quotation NOTE +You should not assume that the read operation will block +exactly after the tenth record has been printed. It is possible that +@command{gawk} will read and buffer more than one record's +worth of data the first time. Because of this, changing the value +of timeout like in the preceding example is not very useful. +@end quotation + +If the @code{PROCINFO} element is not present and the +@env{GAWK_READ_TIMEOUT} environment variable exists, +@command{gawk} uses its value to initialize the timeout value. +The exclusive use of the environment variable to specify timeout +has the disadvantage of not being able to control it +on a per command or connection basis. + +@command{gawk} considers a timeout event to be an error even though +the attempt to read from the underlying device may +succeed in a later attempt. This is a limitation, and it also +means that you cannot use this to multiplex input from +two or more sources. + +Assigning a timeout value prevents read operations from +blocking indefinitely. But bear in mind that there are other ways +@command{gawk} can stall waiting for an input device to be ready. +A network client can sometimes take a long time to establish +a connection before it can start reading any data, +or the attempt to open a FIFO special file for reading can block +indefinitely until some other process opens it for writing. + +@node Command-line directories +@section Directories on the Command Line +@cindex differences in @command{awk} and @command{gawk}, command-line directories +@cindex directories, command-line @cindex command line, directories on According to the POSIX standard, files named on the @command{awk} -command line must be text files. It is a fatal error if they are not. +command line must be text files; it is a fatal error if they are not. Most versions of @command{awk} treat a directory on the command line as a fatal error. By default, @command{gawk} produces a warning for a directory on the -command line, but otherwise ignores it. If either of the @option{--posix} +command line, but otherwise ignores it. This makes it easier to use +shell wildcards with your @command{awk} program: + +@example +$ @kbd{gawk -f whizprog.awk *} @ii{Directories could kill this program} +@end example + +If either of the @option{--posix} or @option{--traditional} options is given, then @command{gawk} reverts to treating a directory on the command line as a fatal error. +@DBXREF{Extension Sample Readdir} for a way to treat directories +as usable data from an @command{awk} program. + +@node Input Summary +@section Summary + +@itemize @value{BULLET} +@item +Input is split into records based on the value of @code{RS}. +The possibilities are as follows: + +@multitable @columnfractions .25 .35 .40 +@headitem Value of @code{RS} @tab Records are split on @dots{} @tab @command{awk} / @command{gawk} +@item Any single character @tab That character @tab @command{awk} +@item The empty string (@code{""}) @tab Runs of two or more newlines @tab @command{awk} +@item A regexp @tab Text that matches the regexp @tab @command{gawk} +@end multitable + +@item +@code{FNR} indicates how many records have been read from the current input file; +@code{NR} indicates how many records have been read in total. + +@item +@command{gawk} sets @code{RT} to the text matched by @code{RS}. + +@item +After splitting the input into records, @command{awk} further splits +the record into individual fields, named @code{$1}, @code{$2}, and so +on. @code{$0} is the whole record, and @code{NF} indicates how many +fields there are. The default way to split fields is between whitespace +characters. + +@item +Fields may be referenced using a variable, as in @code{$NF}. Fields +may also be assigned values, which causes the value of @code{$0} to be +recomputed when it is later referenced. Assigning to a field with a number +greater than @code{NF} creates the field and rebuilds the record, using +@code{OFS} to separate the fields. Incrementing @code{NF} does the same +thing. Decrementing @code{NF} throws away fields and rebuilds the record. + +@item +Field splitting is more complicated than record splitting: + +@multitable @columnfractions .40 .45 .15 +@headitem Field separator value @tab Fields are split @dots{} @tab @command{awk} / @command{gawk} +@item @code{FS == " "} @tab On runs of whitespace @tab @command{awk} +@item @code{FS == @var{any single character}} @tab On that character @tab @command{awk} +@item @code{FS == @var{regexp}} @tab On text matching the regexp @tab @command{awk} +@item @code{FS == ""} @tab Each individual character is a separate field @tab @command{gawk} +@item @code{FIELDWIDTHS == @var{list of columns}} @tab Based on character position @tab @command{gawk} +@item @code{FPAT == @var{regexp}} @tab On the text surrounding text matching the regexp @tab @command{gawk} +@end multitable + +@item +Using @samp{FS = "\n"} causes the entire record to be a single field +(assuming that newlines separate records). + +@item +@code{FS} may be set from the command line using the @option{-F} option. +This can also be done using command-line variable assignment. + +@item +Use @code{PROCINFO["FS"]} to see how fields are being split. + +@item +Use @code{getline} in its various forms to read additional records, +from the default input stream, from a file, or from a pipe or coprocess. + +@item +Use @code{PROCINFO[@var{file}, "READ_TIMEOUT"]} to cause reads to timeout +for @var{file}. + +@item +Directories on the command line are fatal for standard @command{awk}; +@command{gawk} ignores them if not in POSIX mode. + +@end itemize + +@c EXCLUDE START +@node Input Exercises +@section Exercises + +@enumerate +@item +Using the @code{FIELDWIDTHS} variable (@pxref{Constant Size}), +write a program to read election data, where each record represents +one voter's votes. Come up with a way to define which columns are +associated with each ballot item, and print the total votes, +including abstentions, for each item. + +@item +@ref{Plain Getline}, presented a program to remove C-style +comments (@samp{/* @dots{} */}) from the input. That program +does not work if one comment ends on one line and another one +starts later on the same line. +That can be fixed by making one simple change. What is it? + +@end enumerate +@c EXCLUDE END + @node Printing @chapter Printing Output -@c STARTOFRANGE prnt @cindex printing @cindex output, printing, See printing One of the most common programming actions is to @dfn{print}, or output, @@ -7260,12 +8896,11 @@ The @code{print} statement is not limited when computing @emph{which} values to print. However, with two exceptions, you cannot specify @emph{how} to print them---how many columns, whether to use exponential notation or not, and so on. -(For the exceptions, @pxref{Output Separators}, and +(For the exceptions, @DBPXREF{Output Separators} and @ref{OFMT}.) For printing with specifications, you need the @code{printf} statement (@pxref{Printf}). -@c STARTOFRANGE prnts @cindex @code{print} statement @cindex @code{printf} statement Besides basic and formatted printing, this @value{CHAPTER} @@ -7281,17 +8916,20 @@ and discusses the @code{close()} built-in function. * Printf:: The @code{printf} statement. * Redirection:: How to redirect output to multiple files and pipes. +* Special FD:: Special files for I/O. * Special Files:: File name interpretation in @command{gawk}. @command{gawk} allows access to inherited file descriptors. * Close Files And Pipes:: Closing Input and Output Files and Pipes. +* Output Summary:: Output summary. +* Output Exercises:: Exercises. @end menu @node Print @section The @code{print} Statement -The @code{print} statement is used for producing output with simple, standardized -formatting. Specify only the strings or numbers to print, in a +Use the @code{print} statement to produce output with simple, standardized +formatting. You specify only the strings or numbers to print, in a list separated by commas. They are output, separated by single spaces, followed by a newline. The statement looks like this: @@ -7314,13 +8952,17 @@ expression. Numeric values are converted to strings and then printed. @cindex text, printing The simple statement @samp{print} with no items is equivalent to @samp{print $0}: it prints the entire current record. To print a blank -line, use @samp{print ""}, where @code{""} is the empty string. +line, use @samp{print ""}. To print a fixed piece of text, use a string constant, such as @w{@code{"Don't Panic"}}, as one item. If you forget to use the double-quote characters, your text is taken as an @command{awk} expression, and you will probably get an error. Keep in mind that a space is printed between any two items. +Note that the @code{print} statement is a statement and not an +expression---you can't use it in the pattern part of a +@var{pattern}-@var{action} statement, for example. + @node Print Examples @section @code{print} Statement Examples @@ -7330,9 +8972,22 @@ newline, the newline is output along with the rest of the string. A single @code{print} statement can make any number of lines this way. @cindex newlines, printing -The following is an example of printing a string that contains embedded newlines +The following is an example of printing a string that contains embedded +@ifinfo +newlines (the @samp{\n} is an escape sequence, used to represent the newline character; @pxref{Escape Sequences}): +@end ifinfo +@ifhtml +newlines +(the @samp{\n} is an escape sequence, used to represent the newline +character; @pxref{Escape Sequences}): +@end ifhtml +@ifnotinfo +@ifnothtml +newlines: +@end ifnothtml +@end ifnotinfo @example $ @kbd{awk 'BEGIN @{ print "line one\nline two\nline three" @}'} @@ -7374,10 +9029,9 @@ $ @kbd{awk '@{ print $1 $2 @}' inventory-shipped} To someone unfamiliar with the @file{inventory-shipped} file, neither example's output makes much sense. A heading line at the beginning would make it clearer. Let's add some headings to our table of months -(@code{$1}) and green crates shipped (@code{$2}). We do this using the -@code{BEGIN} pattern -(@pxref{BEGIN/END}) -so that the headings are only printed once: +(@code{$1}) and green crates shipped (@code{$2}). We do this using +a @code{BEGIN} rule (@pxref{BEGIN/END}) so that the headings are only +printed once: @example awk 'BEGIN @{ print "Month Crates" @@ -7426,7 +9080,6 @@ You can continue either a @code{print} or @code{printf} statement simply by putting a newline after any comma (@pxref{Statements/Lines}). @end quotation -@c ENDOFRANGE prnts @node Output Separators @section Output Separators @@ -7437,15 +9090,15 @@ of items separated by commas. In the output, the items are normally separated by single spaces. However, this doesn't need to be the case; a single space is simply the default. Any string of characters may be used as the @dfn{output field separator} by setting the -built-in variable @code{OFS}. The initial value of this variable -is the string @w{@code{" "}}---that is, a single space. +predefined variable @code{OFS}. The initial value of this variable +is the string @w{@code{" "}} (i.e., a single space). -The output from an entire @code{print} statement is called an -@dfn{output record}. Each @code{print} statement outputs one output -record, and then outputs a string called the @dfn{output record separator} -(or @code{ORS}). The initial -value of @code{ORS} is the string @code{"\n"}; i.e., a newline -character. Thus, each @code{print} statement normally makes a separate line. +The output from an entire @code{print} statement is called an @dfn{output +record}. Each @code{print} statement outputs one output record, and +then outputs a string called the @dfn{output record separator} (or +@code{ORS}). The initial value of @code{ORS} is the string @code{"\n"} +(i.e., a newline character). Thus, each @code{print} statement normally +makes a separate line. @cindex output, records @cindex output record separator, See @code{ORS} variable @@ -7463,26 +9116,32 @@ The following example prints the first and second fields of each input record, separated by a semicolon, with a blank line added after each newline: -@ignore -Exercise, -Rewrite the -@example -awk 'BEGIN @{ print "Month Crates" - print "----- ------" @} - @{ print $1, " ", $2 @}' inventory-shipped -@end example -program by using a new value of @code{OFS}. -@end ignore @example $ @kbd{awk 'BEGIN @{ OFS = ";"; ORS = "\n\n" @}} -> @kbd{@{ print $1, $2 @}' BBS-list} -@print{} aardvark;555-5553 +> @kbd{@{ print $1, $2 @}' mail-list} +@print{} Amelia;555-5553 @print{} -@print{} alpo-net;555-3412 +@print{} Anthony;555-3412 +@print{} +@print{} Becky;555-7685 +@print{} +@print{} Bill;555-1675 +@print{} +@print{} Broderick;555-0542 +@print{} +@print{} Camilla;555-2912 +@print{} +@print{} Fabius;555-1234 +@print{} +@print{} Julie;555-6699 +@print{} +@print{} Martin;555-6480 +@print{} +@print{} Samuel;555-3430 +@print{} +@print{} Jean-Paul;555-2127 @print{} -@print{} barfly;555-7685 -@dots{} @end example If the value of @code{ORS} does not contain a newline, the program's output @@ -7504,16 +9163,16 @@ numbers can be formatted. The different format specifications are discussed more fully in @ref{Control Letters}. -@cindex @code{sprintf()} function +@cindexawkfunc{sprintf} @cindex @code{OFMT} variable @cindex output, format specifier@comma{} @code{OFMT} -The built-in variable @code{OFMT} contains the default format specification +The predefined variable @code{OFMT} contains the format specification that @code{print} uses with @code{sprintf()} when it wants to convert a number to a string for printing. The default value of @code{OFMT} is @code{"%.6g"}. The way @code{print} prints numbers can be changed -by supplying different format specifications -as the value of @code{OFMT}, as shown in the following example: +by supplying a different format specification +for the value of @code{OFMT}, as shown in the following example: @example $ @kbd{awk 'BEGIN @{} @@ -7533,7 +9192,6 @@ if @code{OFMT} contains anything but a floating-point conversion specification. @node Printf @section Using @code{printf} Statements for Fancier Printing -@c STARTOFRANGE printfs @cindex @code{printf} statement @cindex output, formatted @cindex formatting output @@ -7543,9 +9201,7 @@ With @code{printf} you can specify the width to use for each item, as well as various formatting choices for numbers (such as what output base to use, whether to print an exponent, whether to print a sign, and how many digits to print -after the decimal point). You do this by supplying a string, called -the @dfn{format string}, that controls how and where to print the other -arguments. +after the decimal point). @menu * Basic Printf:: Syntax of the @code{printf} statement. @@ -7565,12 +9221,12 @@ printf @var{format}, @var{item1}, @var{item2}, @dots{} @end example @noindent -The entire list of arguments may optionally be enclosed in parentheses. The -parentheses are necessary if any of the item expressions use the @samp{>} -relational operator; otherwise, it can be confused with an output redirection -(@pxref{Redirection}). +As for @code{print}, the entire list of arguments may optionally be +enclosed in parentheses. Here too, the parentheses are necessary if any +of the item expressions use the @samp{>} relational operator; otherwise, +it can be confused with an output redirection (@pxref{Redirection}). -@cindex format strings +@cindex format specifiers The difference between @code{printf} and @code{print} is the @var{format} argument. This is an expression whose value is taken as a string; it specifies how to output each of the other arguments. It is called the @@ -7591,14 +9247,14 @@ on @code{printf} statements. For example: @example $ @kbd{awk 'BEGIN @{} > @kbd{ORS = "\nOUCH!\n"; OFS = "+"} -> @kbd{msg = "Dont Panic!"} +> @kbd{msg = "Don\47t Panic!"} > @kbd{printf "%s\n", msg} > @kbd{@}'} -@print{} Dont Panic! +@print{} Don't Panic! @end example @noindent -Here, neither the @samp{+} nor the @samp{OUCH} appear in +Here, neither the @samp{+} nor the @samp{OUCH!} appear in the output message. @node Control Letters @@ -7613,25 +9269,16 @@ of value to print. The rest of the format specifier is made up of optional @dfn{modifiers} that control @emph{how} to print the value, such as the field width. Here is a list of the format-control letters: -@table @code -@item %c -Print a number as an ASCII character; thus, @samp{printf "%c", +@c @asis for docbook to come out right +@table @asis +@item @code{%c} +Print a number as a character; thus, @samp{printf "%c", 65} outputs the letter @samp{A}. The output for a string value is the first character of the string. @cindex dark corner, format-control characters @cindex @command{gawk}, format-control characters @quotation NOTE -@ignore -The @samp{%c} format does @emph{not} handle values outside the range -0--255. On most systems, values from 0--127 are within the range of -ASCII and will yield an ASCII character. Values in the range 128--255 -may format as characters in some extended character set, or they may not. -System 390 (IBM architecture mainframe) systems use 8-bit characters, -and thus values from 0--255 yield the corresponding EBCDIC character. -Any value above 255 is treated as modulo 255; i.e., the lowest eight bits -of the value are used. The locale and character set are always ignored. -@end ignore The POSIX standard says the first character of a string is printed. In locales with multibyte characters, @command{gawk} attempts to convert the leading bytes of the string into a valid wide character @@ -7639,6 +9286,8 @@ and then to print the multibyte encoding of that character. Similarly, when printing a numeric value, @command{gawk} allows the value to be within the numeric range of values that can be held in a wide character. +If the conversion to multibyte encoding fails, @command{gawk} +uses the low eight bits of the value as the character to print. Other @command{awk} versions generally restrict themselves to printing the first byte of a string or to numeric values within the range of @@ -7646,12 +9295,12 @@ a single byte (0--255). @end quotation -@item %d@r{,} %i +@item @code{%d}, @code{%i} Print a decimal integer. The two control letters are equivalent. (The @samp{%i} specification is for compatibility with ISO C.) -@item %e@r{,} %E +@item @code{%e}, @code{%E} Print a number in scientific (exponential) notation; for example: @@ -7666,7 +9315,7 @@ which follow the decimal point. discussed in the next @value{SUBSECTION}.) @samp{%E} uses @samp{E} instead of @samp{e} in the output. -@item %f +@item @code{%f} Print a number in floating-point notation. For example: @@ -7680,45 +9329,46 @@ which follow the decimal point. (The @samp{4.3} represents two modifiers, discussed in the next @value{SUBSECTION}.) -On systems supporting IEEE 754 floating point format, values +On systems supporting IEEE 754 floating-point format, values representing negative infinity are formatted as @samp{-inf} or @samp{-infinity}, and positive infinity as -@samp{inf} and @samp{infinity}. -The special ``not a number'' value formats as @samp{-nan} or @samp{nan}. +@samp{inf} or @samp{infinity}. +The special ``not a number'' value formats as @samp{-nan} or @samp{nan} +(@pxref{Math Definitions}). -@item %F +@item @code{%F} Like @samp{%f} but the infinity and ``not a number'' values are spelled using uppercase letters. The @samp{%F} format is a POSIX extension to ISO C; not all systems support it. On those that don't, @command{gawk} uses @samp{%f} instead. -@item %g@r{,} %G +@item @code{%g}, @code{%G} Print a number in either scientific notation or in floating-point notation, whichever uses fewer characters; if the result is printed in scientific notation, @samp{%G} uses @samp{E} instead of @samp{e}. -@item %o +@item @code{%o} Print an unsigned octal integer (@pxref{Nondecimal-numbers}). -@item %s +@item @code{%s} Print a string. -@item %u +@item @code{%u} Print an unsigned decimal integer. (This format is of marginal use, because all numbers in @command{awk} -are floating-point; it is provided primarily for compatibility with C.) +are floating point; it is provided primarily for compatibility with C.) -@item %x@r{,} %X +@item @code{%x}, @code{%X} Print an unsigned hexadecimal integer; @samp{%X} uses the letters @samp{A} through @samp{F} instead of @samp{a} through @samp{f} (@pxref{Nondecimal-numbers}). -@item %% +@item @code{%%} Print a single @samp{%}. This does not consume an argument and it ignores any modifiers. @@ -7739,13 +9389,12 @@ values or do something else entirely. @node Format Modifiers @subsection Modifiers for @code{printf} Formats -@c STARTOFRANGE pfm @cindex @code{printf} statement, modifiers @cindex modifiers@comma{} in format specifiers A format specification can also include @dfn{modifiers} that can control how much of the item's value is printed, as well as how much space it gets. The modifiers come between the @samp{%} and the format-control letter. -We will use the bullet symbol ``@bullet{}'' in the following examples to +We use the bullet symbol ``@bullet{}'' in the following examples to represent spaces in the output. Here are the possible modifiers, in the order in which they may appear: @@ -7753,7 +9402,7 @@ which they may appear: @table @code @cindex differences in @command{awk} and @command{gawk}, @code{print}/@code{printf} statements @cindex @code{printf} statement, positional specifiers -@c the command does NOT start a secondary +@c the code{} does NOT start a secondary @cindex positional specifiers, @code{printf} statement @item @var{N}$ An integer constant followed by a @samp{$} is a @dfn{positional specifier}. @@ -7776,9 +9425,9 @@ It is in fact a @command{gawk} extension, intended for use in translating messages at runtime. @xref{Printf Ordering}, which describes how and why to use positional specifiers. -For now, we will not use them. +For now, we ignore them. -@item - +@item - (Minus) The minus sign, used before the width modifier (see later on in this list), says to left-justify @@ -7803,7 +9452,7 @@ says to always supply a sign for numeric conversions, even if the data to format is positive. The @samp{+} overrides the space modifier. @item # -Use an ``alternate form'' for certain control letters. +Use an ``alternative form'' for certain control letters. For @samp{%o}, supply a leading zero. For @samp{%x} and @samp{%X}, supply a leading @samp{0x} or @samp{0X} for a nonzero result. @@ -7812,7 +9461,7 @@ contains a decimal point. For @samp{%g} and @samp{%G}, trailing zeros are not removed from the result. @item 0 -A leading @samp{0} (zero) acts as a flag that indicates that output should be +A leading @samp{0} (zero) acts as a flag indicating that output should be padded with zeros instead of spaces. This applies only to the numeric output formats. This flag only has an effect when the field width is wider than the @@ -7820,7 +9469,7 @@ value to print. @item ' A single quote or apostrophe character is a POSIX extension to ISO C. -It indicates that the integer part of a floating point value, or the +It indicates that the integer part of a floating-point value, or the entire part of an integer decimal value, should have a thousands-separator character in it. This only works in locales that support such characters. For example: @@ -7829,7 +9478,7 @@ For example: $ @kbd{cat thousands.awk} @ii{Show source program} @print{} BEGIN @{ printf "%'d\n", 1234567 @} $ @kbd{LC_ALL=C gawk -f thousands.awk} -@print{} 1234567 @ii{Results in "C" locale} +@print{} 1234567 @ii{Results in} "C" @ii{locale} $ @kbd{LC_ALL=en_US.UTF-8 gawk -f thousands.awk} @print{} 1,234,567 @ii{Results in US English UTF locale} @end example @@ -7901,7 +9550,7 @@ prints @samp{foob}. @end table The C library @code{printf}'s dynamic @var{width} and @var{prec} -capability (for example, @code{"%*.*s"}) is supported. Instead of +capability (e.g., @code{"%*.*s"}) is supported. Instead of supplying explicit @var{width} and/or @var{prec} values in the format string, they are passed in the argument list. For example: @@ -7939,15 +9588,12 @@ This is not particularly easy to read but it does work. @c @cindex lint checks @cindex troubleshooting, fatal errors, @code{printf} format strings @cindex POSIX @command{awk}, @code{printf} format strings and -C programmers may be used to supplying additional -@samp{l}, @samp{L}, and @samp{h} -modifiers in @code{printf} format strings. These are not valid in @command{awk}. -Most @command{awk} implementations silently ignore them. -If @option{--lint} is provided on the command line -(@pxref{Options}), -@command{gawk} warns about their use. If @option{--posix} is supplied, -their use is a fatal error. -@c ENDOFRANGE pfm +C programmers may be used to supplying additional modifiers (@samp{h}, +@samp{j}, @samp{l}, @samp{L}, @samp{t}, and @samp{z}) in @code{printf} +format strings. These are not valid in @command{awk}. Most @command{awk} +implementations silently ignore them. If @option{--lint} is provided +on the command line (@pxref{Options}), @command{gawk} warns about their +use. If @option{--posix} is supplied, their use is a fatal error. @node Printf Examples @subsection Examples Using @code{printf} @@ -7956,30 +9602,30 @@ The following simple example shows how to use @code{printf} to make an aligned table: @example -awk '@{ printf "%-10s %s\n", $1, $2 @}' BBS-list +awk '@{ printf "%-10s %s\n", $1, $2 @}' mail-list @end example @noindent This command -prints the names of the bulletin boards (@code{$1}) in the file -@file{BBS-list} as a string of 10 characters that are left-justified. It also +prints the names of the people (@code{$1}) in the file +@file{mail-list} as a string of 10 characters that are left-justified. It also prints the phone numbers (@code{$2}) next on the line. This produces an aligned two-column table of names and phone numbers, as shown here: @example -$ @kbd{awk '@{ printf "%-10s %s\n", $1, $2 @}' BBS-list} -@print{} aardvark 555-5553 -@print{} alpo-net 555-3412 -@print{} barfly 555-7685 -@print{} bites 555-1675 -@print{} camelot 555-0542 -@print{} core 555-2912 -@print{} fooey 555-1234 -@print{} foot 555-6699 -@print{} macfoo 555-6480 -@print{} sdace 555-3430 -@print{} sabafoo 555-2127 +$ @kbd{awk '@{ printf "%-10s %s\n", $1, $2 @}' mail-list} +@print{} Amelia 555-5553 +@print{} Anthony 555-3412 +@print{} Becky 555-7685 +@print{} Bill 555-1675 +@print{} Broderick 555-0542 +@print{} Camilla 555-2912 +@print{} Fabius 555-1234 +@print{} Julie 555-6699 +@print{} Martin 555-6480 +@print{} Samuel 555-3430 +@print{} Jean-Paul 555-2127 @end example In this case, the phone numbers had to be printed as strings because @@ -7992,7 +9638,7 @@ they are last on their lines. They don't need to have spaces after them. The table could be made to look even nicer by adding headings to the -tops of the columns. This is done using the @code{BEGIN} pattern +tops of the columns. This is done using a @code{BEGIN} rule (@pxref{BEGIN/END}) so that the headers are only printed once, at the beginning of the @command{awk} program: @@ -8000,17 +9646,17 @@ the @command{awk} program: @example awk 'BEGIN @{ print "Name Number" print "---- ------" @} - @{ printf "%-10s %s\n", $1, $2 @}' BBS-list + @{ printf "%-10s %s\n", $1, $2 @}' mail-list @end example -The above example mixes @code{print} and @code{printf} statements in +The preceding example mixes @code{print} and @code{printf} statements in the same program. Using just @code{printf} statements can produce the same results: @example awk 'BEGIN @{ printf "%-10s %s\n", "Name", "Number" printf "%-10s %s\n", "----", "------" @} - @{ printf "%-10s %s\n", $1, $2 @}' BBS-list + @{ printf "%-10s %s\n", $1, $2 @}' mail-list @end example @noindent @@ -8025,23 +9671,16 @@ emphasized by storing it in a variable, like this: awk 'BEGIN @{ format = "%-10s %s\n" printf format, "Name", "Number" printf format, "----", "------" @} - @{ printf format, $1, $2 @}' BBS-list + @{ printf format, $1, $2 @}' mail-list @end example -@c !!! exercise -At this point, it would be a worthwhile exercise to use the -@code{printf} statement to line up the headings and table data for the -@file{inventory-shipped} example that was covered earlier in the @value{SECTION} -on the @code{print} statement -(@pxref{Print}). -@c ENDOFRANGE printfs @node Redirection @section Redirecting Output of @code{print} and @code{printf} @cindex output redirection @cindex redirection of output -@cindex @code{--sandbox} option, output redirection with @code{print}, @code{printf} +@cindex @option{--sandbox} option, output redirection with @code{print}, @code{printf} So far, the output from @code{print} and @code{printf} has gone to the standard output, usually the screen. Both @code{print} and @code{printf} can @@ -8050,7 +9689,7 @@ This is called @dfn{redirection}. @quotation NOTE When @option{--sandbox} is specified (@pxref{Options}), -redirecting output to files and pipes is disabled. +redirecting output to files, pipes and coprocesses is disabled. @end quotation A redirection appears after the @code{print} or @code{printf} statement. @@ -8058,11 +9697,11 @@ Redirections in @command{awk} are written just like redirections in shell commands, except that they are written inside the @command{awk} program. @c the commas here are part of the see also -@cindex @code{print} statement, See Also redirection, of output -@cindex @code{printf} statement, See Also redirection, of output +@cindex @code{print} statement, See Also redirection@comma{} of output +@cindex @code{printf} statement, See Also redirection@comma{} of output There are four forms of output redirection: output to a file, output appended to a file, output through a pipe to another command, and output -to a coprocess. They are all shown for the @code{print} statement, +to a coprocess. We show them all for the @code{print} statement, but they work identically for @code{printf}: @table @code @@ -8080,20 +9719,20 @@ before the first output is written to it. Subsequent writes to the same @var{output-file} do not erase @var{output-file}, but append to it. (This is different from how you use redirections in shell scripts.) If @var{output-file} does not exist, it is created. For example, here -is how an @command{awk} program can write a list of BBS names to one +is how an @command{awk} program can write a list of peoples' names to one file named @file{name-list}, and a list of phone numbers to another file named @file{phone-list}: @example $ @kbd{awk '@{ print $2 > "phone-list"} -> @kbd{print $1 > "name-list" @}' BBS-list} +> @kbd{print $1 > "name-list" @}' mail-list} $ @kbd{cat phone-list} @print{} 555-5553 @print{} 555-3412 @dots{} $ @kbd{cat name-list} -@print{} aardvark -@print{} alpo-net +@print{} Amelia +@print{} Anthony @dots{} @end example @@ -8111,7 +9750,7 @@ appended to the file. If @var{output-file} does not exist, then it is created. @cindex @code{|} (vertical bar), @code{|} operator (I/O) -@cindex pipes, output +@cindex pipe, output @cindex output, pipes @item print @var{items} | @var{command} It is possible to send output to another program through a pipe @@ -8122,7 +9761,7 @@ to another process created to execute @var{command}. The redirection argument @var{command} is actually an @command{awk} expression. Its value is converted to a string whose contents give the shell command to be run. For example, the following produces two -files, one unsorted list of BBS names, and one list sorted in reverse +files, one unsorted list of peoples' names, and one list sorted in reverse alphabetical order: @ignore @@ -8135,7 +9774,7 @@ alone for now and let's hope no-one notices. @example awk '@{ print $1 > "names.unsorted" command = "sort -r > names.sorted" - print $1 | command @}' BBS-list + print $1 | command @}' mail-list @end example The unsorted list is written with an ordinary redirection, while @@ -8147,27 +9786,21 @@ in an @command{awk} script run periodically for system maintenance: @example report = "mail bug-system" -print "Awk script failed:", $0 | report -m = ("at record number " FNR " of " FILENAME) -print m | report +print("Awk script failed:", $0) | report +print("at record number", FNR, "of", FILENAME) | report close(report) @end example -The message is built using string concatenation and saved in the variable -@code{m}. It's then sent down the pipeline to the @command{mail} program. -(The parentheses group the items to concatenate---see -@ref{Concatenation}.) - The @code{close()} function is called here because it's a good idea to close the pipe as soon as all the intended output has been sent to it. -@xref{Close Files And Pipes}, +@DBXREF{Close Files And Pipes} for more information. This example also illustrates the use of a variable to represent a @var{file} or @var{command}---it is not necessary to always use a string constant. Using a variable is generally a good idea, because (if you mean to refer to that same file or command) -@command{awk} requires that the string value be spelled identically +@command{awk} requires that the string value be written identically every time. @cindex coprocesses @@ -8184,9 +9817,9 @@ but subsidiary to, the @command{awk} program. This feature is a @command{gawk} extension, and is not available in POSIX @command{awk}. -@xref{Getline/Coprocess}, +@DBXREF{Getline/Coprocess} for a brief discussion. -@xref{Two-way I/O}, +@DBXREF{Two-way I/O} for a more complete discussion. @end table @@ -8210,7 +9843,7 @@ print "Avoid improbability generators" >> "guide.txt" @noindent This is indeed how redirections must be used from the shell. But in @command{awk}, it isn't necessary. In this kind of case, a program should -use @samp{>} for all the @code{print} statements, since the output file +use @samp{>} for all the @code{print} statements, because the output file is only opened once. (It happens that if you mix @samp{>} and @samp{>>} that output is produced in the expected order. However, mixing the operators for the same file is definitely poor style, and is confusing to readers @@ -8226,7 +9859,9 @@ As mentioned earlier many @end ifnotinfo @ifnottex +@ifnotdocbook Many +@end ifnotdocbook @end ifnottex older @command{awk} implementations limit the number of pipelines that an @command{awk} @@ -8234,9 +9869,12 @@ program may have open to just one! In @command{gawk}, there is no such limit. @command{gawk} allows a program to open as many pipelines as the underlying operating system permits. -@c fakenode --- for prepinfo -@subheading Advanced Notes: Piping into @command{sh} -@cindex advanced features, piping into @command{sh} +@cindex sidebar, Piping into @command{sh} +@ifdocbook +@docbook +<sidebar><title>Piping into @command{sh}</title> +@end docbook + @cindex shells, piping commands into A particularly powerful way to use redirection is to build command lines @@ -8258,26 +9896,49 @@ uppercase characters converted to lowercase The program builds up a list of command lines, using the @command{mv} utility to rename the files. It then sends the list to the shell for execution. -@c ENDOFRANGE outre -@c ENDOFRANGE reout -@node Special Files -@section Special @value{FFN}s in @command{gawk} -@c STARTOFRANGE gfn -@cindex @command{gawk}, @value{FN}s in +@DBXREF{Shell Quoting} for a function that can help in generating +command lines to be fed to the shell. -@command{gawk} provides a number of special @value{FN}s that it interprets -internally. These @value{FN}s provide access to standard file descriptors -and TCP/IP networking. +@docbook +</sidebar> +@end docbook +@end ifdocbook -@menu -* Special FD:: Special files for I/O. -* Special Network:: Special files for network communications. -* Special Caveats:: Things to watch out for. -@end menu +@ifnotdocbook +@cartouche +@center @b{Piping into @command{sh}} + + +@cindex shells, piping commands into + +A particularly powerful way to use redirection is to build command lines +and pipe them into the shell, @command{sh}. For example, suppose you +have a list of files brought over from a system where all the @value{FN}s +are stored in uppercase, and you wish to rename them to have names in +all lowercase. The following program is both simple and efficient: + +@c @cindex @command{mv} utility +@example +@{ printf("mv %s %s\n", $0, tolower($0)) | "sh" @} + +END @{ close("sh") @} +@end example + +The @code{tolower()} function returns its argument string with all +uppercase characters converted to lowercase +(@pxref{String Functions}). +The program builds up a list of command lines, +using the @command{mv} utility to rename the files. +It then sends the list to the shell for execution. + +@DBXREF{Shell Quoting} for a function that can help in generating +command lines to be fed to the shell. +@end cartouche +@end ifnotdocbook @node Special FD -@subsection Special Files for Standard Descriptors +@section Special Files for Standard Pre-Opened Data Streams @cindex standard input @cindex input, standard @cindex standard output @@ -8288,9 +9949,12 @@ and TCP/IP networking. @cindex files, descriptors, See file descriptors Running programs conventionally have three input and output streams -already available to them for reading and writing. These are known as -the @dfn{standard input}, @dfn{standard output}, and @dfn{standard error -output}. These streams are, by default, connected to your keyboard and screen, but +already available to them for reading and writing. These are known +as the @dfn{standard input}, @dfn{standard output}, and @dfn{standard +error output}. These open streams (and any other open file or pipe) +are often referred to by the technical term @dfn{file descriptors}. + +These streams are, by default, connected to your keyboard and screen, but they are often redirected with the shell, via the @samp{<}, @samp{<<}, @samp{>}, @samp{>>}, @samp{>&}, and @samp{|} operators. Standard error is typically used for writing error messages; the reason there are two separate @@ -8299,7 +9963,7 @@ redirected separately. @cindex differences in @command{awk} and @command{gawk}, error messages @cindex error handling -In other implementations of @command{awk}, the only way to write an error +In traditional implementations of @command{awk}, the only way to write an error message to standard error in an @command{awk} program is as follows: @example @@ -8309,7 +9973,8 @@ print "Serious error detected!" | "cat 1>&2" @noindent This works by opening a pipeline to a shell command that can access the standard error stream that it inherits from the @command{awk} process. -This is far from elegant, and it is also inefficient, because it requires a +@c 8/2014: Mike Brennan says not to cite this as inefficient. So, fixed. +This is far from elegant, and it also requires a separate process. So people writing @command{awk} programs often don't do this. Instead, they send the error messages to the screen, like this: @@ -8324,19 +9989,19 @@ that is connected to your keyboard and screen. It represents the ``terminal,''@footnote{The ``tty'' in @file{/dev/tty} stands for ``Teletype,'' a serial terminal.} which on modern systems is a keyboard and screen, not a serial console.) -This usually has the same effect but not always: although the +This generally has the same effect but not always: although the standard error stream is usually the screen, it can be redirected; when that happens, writing to the screen is not correct. In fact, if @command{awk} is run from a background job, it may not have a terminal at all. Then opening @file{/dev/tty} fails. -@command{gawk} provides special @value{FN}s for accessing the three standard -streams. @value{COMMONEXT}. It also provides syntax for accessing -any other inherited open files. If the @value{FN} matches -one of these special names when @command{gawk} redirects input or output, -then it directly uses the stream that the @value{FN} stands for. -These special @value{FN}s work for all operating systems that @command{gawk} +@command{gawk}, BWK @command{awk}, and @command{mawk} provide +special @value{FN}s for accessing the three standard streams. +If the @value{FN} matches one of these special names when @command{gawk} +(or one of the others) redirects input or output, then it directly uses +the descriptor that the @value{FN} stands for. These special +@value{FN}s work for all operating systems that @command{gawk} has been ported to, not just those that are POSIX-compliant: @cindex common extensions, @code{/dev/stdin} special file @@ -8345,10 +10010,10 @@ has been ported to, not just those that are POSIX-compliant: @cindex extensions, common@comma{} @code{/dev/stdin} special file @cindex extensions, common@comma{} @code{/dev/stdout} special file @cindex extensions, common@comma{} @code{/dev/stderr} special file -@cindex @value{FN}s, standard streams in @command{gawk} -@cindex @code{/dev/@dots{}} special files (@command{gawk}) +@cindex file names, standard streams in @command{gawk} +@cindex @code{/dev/@dots{}} special files @cindex files, @code{/dev/@dots{}} special files -@cindex @code{/dev/fd/@var{N}} special files +@cindex @code{/dev/fd/@var{N}} special files (@command{gawk}) @table @file @item /dev/stdin The standard input (file descriptor 0). @@ -8358,38 +10023,64 @@ The standard output (file descriptor 1). @item /dev/stderr The standard error output (file descriptor 2). - -@item /dev/fd/@var{N} -The file associated with file descriptor @var{N}. Such a file must -be opened by the program initiating the @command{awk} execution (typically -the shell). Unless special pains are taken in the shell from which -@command{gawk} is invoked, only descriptors 0, 1, and 2 are available. @end table -The @value{FN}s @file{/dev/stdin}, @file{/dev/stdout}, and @file{/dev/stderr} -are aliases for @file{/dev/fd/0}, @file{/dev/fd/1}, and @file{/dev/fd/2}, -respectively. However, they are more self-explanatory. -The proper way to write an error message in a @command{gawk} program -is to use @file{/dev/stderr}, like this: +With these facilities, +the proper way to write an error message then becomes: @example print "Serious error detected!" > "/dev/stderr" @end example -@cindex troubleshooting, quotes with @value{FN}s +@cindex troubleshooting, quotes with file names Note the use of quotes around the @value{FN}. Like any other redirection, the value must be a string. It is a common error to omit the quotes, which leads to confusing results. -@c Exercise: What does it do? :-) -Finally, using the @code{close()} function on a @value{FN} of the -form @code{"/dev/fd/@var{N}"}, for file descriptor numbers -above two, will actually close the given file descriptor. +@command{gawk} does not treat these @value{FN}s as special when +in POSIX-compatibility mode. However, because BWK @command{awk} +supports them, @command{gawk} does support them even when +invoked with the @option{--traditional} option (@pxref{Options}). -The @file{/dev/stdin}, @file{/dev/stdout}, and @file{/dev/stderr} -special files are also recognized internally by several other -versions of @command{awk}. +@node Special Files +@section Special @value{FFN}s in @command{gawk} +@cindex @command{gawk}, file names in + +Besides access to standard input, standard output, and standard error, +@command{gawk} provides access to any open file descriptor. +Additionally, there are special @value{FN}s reserved for +TCP/IP networking. + +@menu +* Other Inherited Files:: Accessing other open files with + @command{gawk}. +* Special Network:: Special files for network communications. +* Special Caveats:: Things to watch out for. +@end menu + +@node Other Inherited Files +@subsection Accessing Other Open Files With @command{gawk} + +Besides the @code{/dev/stdin}, @code{/dev/stdout}, and @code{/dev/stderr} +special @value{FN}s mentioned earlier, @command{gawk} provides syntax +for accessing any other inherited open file: + +@table @file +@item /dev/fd/@var{N} +The file associated with file descriptor @var{N}. Such a file must +be opened by the program initiating the @command{awk} execution (typically +the shell). Unless special pains are taken in the shell from which +@command{gawk} is invoked, only descriptors 0, 1, and 2 are available. +@end table + +The @value{FN}s @file{/dev/stdin}, @file{/dev/stdout}, and @file{/dev/stderr} +are essentially aliases for @file{/dev/fd/0}, @file{/dev/fd/1}, and +@file{/dev/fd/2}, respectively. However, those names are more self-explanatory. + +Note that using @code{close()} on a @value{FN} of the +form @code{"/dev/fd/@var{N}"}, for file descriptor numbers +above two, does actually close the given file descriptor. @node Special Network @subsection Special Files for Network Communications @@ -8405,7 +10096,7 @@ This is done using a special @value{FN} of the form: @file{/@var{net-type}/@var{protocol}/@var{local-port}/@var{remote-host}/@var{remote-port}} @end example -The @var{net-type} is one of @samp{inet}, @samp{inet4} or @samp{inet6}. +The @var{net-type} is one of @samp{inet}, @samp{inet4}, or @samp{inet6}. The @var{protocol} is one of @samp{tcp} or @samp{udp}, and the other fields represent the other essential pieces of information for making a networking connection. @@ -8419,15 +10110,20 @@ Full discussion is delayed until @node Special Caveats @subsection Special @value{FFN} Caveats -Here is a list of things to bear in mind when using the +Here are some things to bear in mind when using the special @value{FN}s that @command{gawk} provides: -@itemize @bullet -@cindex compatibility mode (@command{gawk}), @value{FN}s -@cindex @value{FN}s, in compatibility mode +@itemize @value{BULLET} +@cindex compatibility mode (@command{gawk}), file names +@cindex file names, in compatibility mode @item -Recognition of these special @value{FN}s is disabled if @command{gawk} is in -compatibility mode (@pxref{Options}). +Recognition of the @value{FN}s for the three standard pre-opened +files is disabled only in POSIX mode. + +@item +Recognition of the other special @value{FN}s is disabled if @command{gawk} is in +compatibility mode (either @option{--traditional} or @option{--posix}; +@pxref{Options}). @item @command{gawk} @emph{always} @@ -8439,18 +10135,13 @@ the time this does not matter; however, it is important to @emph{not} close any of the files related to file descriptors 0, 1, and 2. Doing so results in unpredictable behavior. @end itemize -@c ENDOFRANGE gfn @node Close Files And Pipes @section Closing Input and Output Redirections @cindex files, output, See output files -@c STARTOFRANGE ifc @cindex input files, closing -@c STARTOFRANGE ofc @cindex output, files@comma{} closing -@c STARTOFRANGE pc -@cindex pipes, closing -@c STARTOFRANGE cc +@cindex pipe, closing @cindex coprocesses, closing @cindex @code{getline} command, coprocesses@comma{} using from @@ -8467,7 +10158,7 @@ the @value{FN} or command associated with it, and subsequent writes to the same file or command are appended to the previous writes. The file or pipe stays open until @command{awk} exits. -@cindex @code{close()} function +@cindexawkfunc{close} This implies that special steps are necessary in order to read the same file again from the beginning, or to rerun a shell command (rather than reading more output from the same command). The @code{close()} function @@ -8519,7 +10210,7 @@ close(sortcom) This helps avoid hard-to-find typographical errors in your @command{awk} programs. Here are some of the reasons for closing an output file: -@itemize @bullet +@itemize @value{BULLET} @item To write a file and read it back later on in the same @command{awk} program. Close the file after writing it, then @@ -8552,6 +10243,7 @@ a separate message. @cindex differences in @command{awk} and @command{gawk}, @code{close()} function @cindex portability, @code{close()} function and +@cindex @code{close()} function, portability If you use more files than the system allows you to have open, @command{gawk} attempts to multiplex the available open files among your @value{DF}s. @command{gawk}'s ability to do this depends upon the @@ -8587,15 +10279,17 @@ more importantly, the file descriptor for the pipe is not closed and released until @code{close()} is called or @command{awk} exits. -@code{close()} will silently do nothing if given an argument that -does not represent a file, pipe or coprocess that was opened with -a redirection. +@code{close()} silently does nothing if given an argument that +does not represent a file, pipe, or coprocess that was opened with +a redirection. In such a case, it returns a negative value, +indicating an error. In addition, @command{gawk} sets @code{ERRNO} +to a string indicating the error. -Note also that @samp{close(FILENAME)} has no -``magic'' effects on the implicit loop that reads through the -files named on the command line. It is, more likely, a close -of a file that was never opened, so @command{awk} silently -does nothing. +Note also that @samp{close(FILENAME)} has no ``magic'' effects on the +implicit loop that reads through the files named on the command line. +It is, more likely, a close of a file that was never opened with a +redirection, so @command{awk} silently does nothing, except return +a negative value. @cindex @code{|} (vertical bar), @code{|&} operator (I/O), pipes@comma{} closing When using the @samp{|&} operator to communicate with a coprocess, @@ -8607,24 +10301,85 @@ the first argument is the name of the command or special file used to start the coprocess. The second argument should be a string, with either of the values @code{"to"} or @code{"from"}. Case does not matter. -As this is an advanced feature, a more complete discussion is +As this is an advanced feature, discussion is delayed until @ref{Two-way I/O}, -which discusses it in more detail and gives an example. +which describes it in more detail and gives an example. + +@cindex sidebar, Using @code{close()}'s Return Value +@ifdocbook +@docbook +<sidebar><title>Using @code{close()}'s Return Value</title> +@end docbook -@c fakenode --- for prepinfo -@subheading Advanced Notes: Using @code{close()}'s Return Value -@cindex advanced features, @code{close()} function @cindex dark corner, @code{close()} function -@cindex @code{close()} function, return values -@cindex return values@comma{} @code{close()} function +@cindex @code{close()} function, return value +@cindex return value@comma{} @code{close()} function @cindex differences in @command{awk} and @command{gawk}, @code{close()} function @cindex Unix @command{awk}, @code{close()} function and -In many versions of Unix @command{awk}, the @code{close()} function -is actually a statement. It is a syntax error to try and use the return +In many older versions of Unix @command{awk}, the @code{close()} function +is actually a statement. +@value{DARKCORNER} +It is a syntax error to try and use the return value from @code{close()}: + +@example +command = "@dots{}" +command | getline info +retval = close(command) # syntax error in many Unix awks +@end example + +@cindex @command{gawk}, @code{ERRNO} variable in +@cindex @code{ERRNO} variable, with @command{close()} function +@command{gawk} treats @code{close()} as a function. +The return value is @minus{}1 if the argument names something +that was never opened with a redirection, or if there is +a system problem closing the file or process. +In these cases, @command{gawk} sets the predefined variable +@code{ERRNO} to a string describing the problem. + +In @command{gawk}, +when closing a pipe or coprocess (input or output), +the return value is the exit status of the command.@footnote{ +This is a full 16-bit value as returned by the @code{wait()} +system call. See the system manual pages for information on +how to decode this value.} +Otherwise, it is the return value from the system's @code{close()} or +@code{fclose()} C functions when closing input or output +files, respectively. +This value is zero if the close succeeds, or @minus{}1 if +it fails. + +The POSIX standard is very vague; it says that @code{close()} +returns zero on success and nonzero otherwise. In general, +different implementations vary in what they report when closing +pipes; thus the return value cannot be used portably. @value{DARKCORNER} +In POSIX mode (@pxref{Options}), @command{gawk} just returns zero +when closing a pipe. + +@docbook +</sidebar> +@end docbook +@end ifdocbook + +@ifnotdocbook +@cartouche +@center @b{Using @code{close()}'s Return Value} + + +@cindex dark corner, @code{close()} function +@cindex @code{close()} function, return value +@cindex return value@comma{} @code{close()} function +@cindex differences in @command{awk} and @command{gawk}, @code{close()} function +@cindex Unix @command{awk}, @code{close()} function and + +In many older versions of Unix @command{awk}, the @code{close()} function +is actually a statement. +@value{DARKCORNER} +It is a syntax error to try and use the return +value from @code{close()}: @example command = "@dots{}" @@ -8633,12 +10388,12 @@ retval = close(command) # syntax error in many Unix awks @end example @cindex @command{gawk}, @code{ERRNO} variable in -@cindex @code{ERRNO} variable +@cindex @code{ERRNO} variable, with @command{close()} function @command{gawk} treats @code{close()} as a function. The return value is @minus{}1 if the argument names something that was never opened with a redirection, or if there is a system problem closing the file or process. -In these cases, @command{gawk} sets the built-in variable +In these cases, @command{gawk} sets the predefined variable @code{ERRNO} to a string describing the problem. In @command{gawk}, @@ -8660,16 +10415,75 @@ pipes; thus the return value cannot be used portably. @value{DARKCORNER} In POSIX mode (@pxref{Options}), @command{gawk} just returns zero when closing a pipe. +@end cartouche +@end ifnotdocbook + + +@node Output Summary +@section Summary + +@itemize @value{BULLET} +@item +The @code{print} statement prints comma-separated expressions. Each +expression is separated by the value of @code{OFS} and terminated by +the value of @code{ORS}. @code{OFMT} provides the conversion format +for numeric values for the @code{print} statement. + +@item +The @code{printf} statement provides finer-grained control over output, +with format control letters for different data types and various flags +that modify the behavior of the format control letters. + +@item +Output from both @code{print} and @code{printf} may be redirected to +files, pipes, and coprocesses. + +@item +@command{gawk} provides special @value{FN}s for access to standard input, +output, and error, and for network communications. + +@item +Use @code{close()} to close open file, pipe, and coprocess redirections. +For coprocesses, it is possible to close only one direction of the +communications. + +@end itemize + +@c EXCLUDE START +@node Output Exercises +@section Exercises + +@enumerate +@item +Rewrite the program: + +@example +awk 'BEGIN @{ print "Month Crates" + print "----- ------" @} + @{ print $1, " ", $2 @}' inventory-shipped +@end example + +@noindent +from @ref{Output Separators}, by using a new value of @code{OFS}. + +@item +Use the @code{printf} statement to line up the headings and table data +for the @file{inventory-shipped} example that was covered in @ref{Print}. + +@item +What happens if you forget the double quotes when redirecting +output, as follows: + +@example +BEGIN @{ print "Serious error detected!" > /dev/stderr @} +@end example + +@end enumerate +@c EXCLUDE END -@c ENDOFRANGE ifc -@c ENDOFRANGE ofc -@c ENDOFRANGE pc -@c ENDOFRANGE cc -@c ENDOFRANGE prnt @node Expressions @chapter Expressions -@c STARTOFRANGE exps @cindex expressions Expressions are the basic building blocks of @command{awk} patterns @@ -8691,10 +10505,11 @@ combinations of these with various operators. * Function Calls:: A function call is an expression. * Precedence:: How various operators nest. * Locales:: How the locale affects things. +* Expressions Summary:: Expressions summary. @end menu @node Values -@section Constants, Variables and Conversions +@section Constants, Variables, and Conversions Expressions are built up from values and the operations performed upon them. This @value{SECTION} describes the elementary objects @@ -8710,6 +10525,7 @@ which provide the values used in expressions. @node Constants @subsection Constant Expressions + @cindex constants, types of The simplest type of expression is the @dfn{constant}, which always has @@ -8718,7 +10534,7 @@ string, and regular expression. Each is used in the appropriate context when you need a data value that isn't going to change. Numeric constants can -have different forms, but are stored identically internally. +have different forms, but are internally stored in an identical manner. @menu * Scalar Constants:: Numeric and string constants. @@ -8729,13 +10545,14 @@ have different forms, but are stored identically internally. @node Scalar Constants @subsubsection Numeric and String Constants -@cindex numeric, constants +@cindex constants, numeric +@cindex numeric constants A @dfn{numeric constant} stands for a number. This number can be an integer, a decimal fraction, or a number in scientific (exponential) notation.@footnote{The internal representation of all numbers, -including integers, uses double precision -floating-point numbers. -On most modern systems, these are in IEEE 754 standard format.} +including integers, uses double-precision floating-point numbers. +On most modern systems, these are in IEEE 754 standard format. +@xref{Arbitrary Precision Arithmetic}, for much more information.} Here are some examples of numeric constants that all have the same value: @@ -8747,7 +10564,7 @@ have the same value: @cindex string constants A string constant consists of a sequence of characters enclosed in -double-quotation marks. For example: +double quotation marks. For example: @example "parrot" @@ -8755,7 +10572,7 @@ double-quotation marks. For example: @noindent @cindex differences in @command{awk} and @command{gawk}, strings -@cindex strings, length of +@cindex strings, length limitations represents the string whose contents are @samp{parrot}. Strings in @command{gawk} can be of any length, and they can contain any of the possible eight-bit ASCII characters including ASCII @sc{nul} (character code zero). @@ -8769,13 +10586,13 @@ implementations may have difficulty with some character codes. @cindex numbers, octal @cindex numbers, hexadecimal -In @command{awk}, all numbers are in decimal; i.e., base 10. Many other +In @command{awk}, all numbers are in decimal (i.e., base 10). Many other programming languages allow you to specify numbers in other bases, often octal (base 8) and hexadecimal (base 16). -In octal, the numbers go 0, 1, 2, 3, 4, 5, 6, 7, 10, 11, 12, etc. +In octal, the numbers go 0, 1, 2, 3, 4, 5, 6, 7, 10, 11, 12, and so on. Just as @samp{11}, in decimal, is 1 times 10 plus 1, so @samp{11}, in octal, is 1 times 8, plus 1. This equals 9 in decimal. -In hexadecimal, there are 16 digits. Since the everyday decimal +In hexadecimal, there are 16 digits. Because the everyday decimal number system only has ten digits (@samp{0}--@samp{9}), the letters @samp{a} through @samp{f} are used to represent the rest. (Case in the letters is usually irrelevant; hexadecimal @samp{a} and @samp{A} @@ -8827,11 +10644,12 @@ you can use the @code{strtonum()} function to convert the data into a number. Most of the time, you will want to use octal or hexadecimal constants when working with the built-in bit manipulation functions; -see @ref{Bitwise Functions}, +see @DBREF{Bitwise Functions} for more information. -Unlike some early C implementations, @samp{8} and @samp{9} are not valid -in octal constants; e.g., @command{gawk} treats @samp{018} as decimal 18: +Unlike some early C implementations, @samp{8} and @samp{9} are not +valid in octal constants. For example, @command{gawk} treats @samp{018} +as decimal 18: @example $ @kbd{gawk 'BEGIN @{ print "021 is", 021 ; print 018 @}'} @@ -8846,9 +10664,35 @@ If @command{gawk} is in compatibility mode (@pxref{Options}), they are not available. -@c fakenode --- for prepinfo -@subheading Advanced Notes: A Constant's Base Does Not Affect Its Value -@cindex advanced features, constants@comma{} values of +@cindex sidebar, A Constant's Base Does Not Affect Its Value +@ifdocbook +@docbook +<sidebar><title>A Constant's Base Does Not Affect Its Value</title> +@end docbook + + +Once a numeric constant has +been converted internally into a number, +@command{gawk} no longer remembers +what the original form of the constant was; the internal value is +always used. This has particular consequences for conversion of +numbers to strings: + +@example +$ @kbd{gawk 'BEGIN @{ printf "0x11 is <%s>\n", 0x11 @}'} +@print{} 0x11 is <17> +@end example + +@docbook +</sidebar> +@end docbook +@end ifdocbook + +@ifnotdocbook +@cartouche +@center @b{A Constant's Base Does Not Affect Its Value} + + Once a numeric constant has been converted internally into a number, @@ -8861,11 +10705,12 @@ numbers to strings: $ @kbd{gawk 'BEGIN @{ printf "0x11 is <%s>\n", 0x11 @}'} @print{} 0x11 is <17> @end example +@end cartouche +@end ifnotdocbook @node Regexp Constants @subsubsection Regular Expression Constants -@c STARTOFRANGE rec @cindex regexp constants @cindex @code{~} (tilde), @code{~} operator @cindex tilde (@code{~}), @code{~} operator @@ -8875,8 +10720,8 @@ A regexp constant is a regular expression description enclosed in slashes, such as @code{@w{/^beginning and end$/}}. Most regexps used in @command{awk} programs are constant, but the @samp{~} and @samp{!~} matching operators can also match computed or dynamic regexps -(which are just ordinary strings or variables that contain a regexp). -@c ENDOFRANGE cnst +(which are typically just ordinary strings or variables that contain a regexp, +but could be a more complex expression). @node Using Constant Regexps @subsection Using Regular Expression Constants @@ -8888,7 +10733,7 @@ matched. However, regexp constants (such as @code{/foo/}) may be used like simple expressions. When a regexp constant appears by itself, it has the same meaning as if it appeared -in a pattern, i.e., @samp{($0 ~ /foo/)} +in a pattern (i.e., @samp{($0 ~ /foo/)}). @value{DARKCORNER} @xref{Expression Patterns}. This means that the following two code segments: @@ -8909,7 +10754,7 @@ if (/barfly/ || /camelot/) @noindent are exactly equivalent. One rather bizarre consequence of this rule is that the following -Boolean expression is valid, but does not do what the user probably +Boolean expression is valid, but does not do what its author probably intended: @example @@ -8943,22 +10788,21 @@ upon the contents of the current input record. @cindex differences in @command{awk} and @command{gawk}, regexp constants @cindex dark corner, regexp constants, as arguments to user-defined functions -@cindex @code{gensub()} function (@command{gawk}) -@cindex @code{sub()} function -@cindex @code{gsub()} function +@cindexgawkfunc{gensub} +@cindexawkfunc{sub} +@cindexawkfunc{gsub} Constant regular expressions are also used as the first argument for the @code{gensub()}, @code{sub()}, and @code{gsub()} functions, as the second argument of the @code{match()} function, -and as the third argument of the @code{patsplit()} function +and as the third argument of the @code{split()} and @code{patsplit()} functions (@pxref{String Functions}). Modern implementations of @command{awk}, including @command{gawk}, allow the third argument of @code{split()} to be a regexp constant, but some older implementations do not. @value{DARKCORNER} -This can lead to confusion when attempting to use regexp constants -as arguments to user-defined functions -(@pxref{User-defined}). -For example: +Because some built-in functions accept regexp constants as arguments, +it can be confusing when attempting to use regexp constants as arguments +to user-defined functions (@pxref{User-defined}). For example: @example function mysub(pat, repl, str, global) @@ -8981,14 +10825,13 @@ function mysub(pat, repl, str, global) @c @cindex automatic warnings @c @cindex warnings, automatic In this example, the programmer wants to pass a regexp constant to the -user-defined function @code{mysub}, which in turn passes it on to +user-defined function @code{mysub()}, which in turn passes it on to either @code{sub()} or @code{gsub()}. However, what really happens is that the @code{pat} parameter is either one or zero, depending upon whether or not @code{$0} matches @code{/hi/}. @command{gawk} issues a warning when it sees a regexp constant used as -a parameter to a user-defined function, since passing a truth value in +a parameter to a user-defined function, because passing a truth value in this way is probably not what was intended. -@c ENDOFRANGE rec @node Variables @subsection Variables @@ -9002,7 +10845,7 @@ on the @command{awk} command line. @menu * Using Variables:: Using variables in your programs. -* Assignment Options:: Setting variables on the command-line and a +* Assignment Options:: Setting variables on the command line and a summary of command-line syntax. This is an advanced method of input. @end menu @@ -9013,7 +10856,11 @@ on the @command{awk} command line. Variables let you give names to values and refer to them later. Variables have already been used in many of the examples. The name of a variable must be a sequence of letters, digits, or underscores, and it may not begin -with a digit. Case is significant in variable names; @code{a} and @code{A} +with a digit. +Here, a @dfn{letter} is any one of the 52 upper- and lowercase +English letters. Other characters that may be defined as letters +in non-English locales are not valid in variable names. +Case is significant in variable names; @code{a} and @code{A} are distinct variables. A variable name is a valid expression by itself; it represents the @@ -9022,24 +10869,24 @@ variable's current value. Variables are given new values with @dfn{decrement operators}. @xref{Assignment Ops}. In addition, the @code{sub()} and @code{gsub()} functions can -change a variable's value, and the @code{match()}, @code{patsplit()} -and @code{split()} functions can change the contents of their +change a variable's value, and the @code{match()}, @code{split()}, +and @code{patsplit()} functions can change the contents of their array parameters. @xref{String Functions}. @cindex variables, built-in @cindex variables, initializing A few variables have special built-in meanings, such as @code{FS} (the field separator), and @code{NF} (the number of fields in the current input -record). @xref{Built-in Variables}, for a list of the built-in variables. -These built-in variables can be used and assigned just like all other +record). @DBXREF{Built-in Variables} for a list of the predefined variables. +These predefined variables can be used and assigned just like all other variables, but their values are also used or changed automatically by -@command{awk}. All built-in variables' names are entirely uppercase. +@command{awk}. All predefined variables' names are entirely uppercase. Variables in @command{awk} can be assigned either numeric or string values. The kind of value a variable holds can change over the life of a program. By default, variables are initialized to the empty string, which is zero if converted to a number. There is no need to explicitly -``initialize'' a variable in @command{awk}, +initialize a variable in @command{awk}, which is what you would do in C and in most other traditional languages. @node Assignment Options @@ -9056,7 +10903,7 @@ Such an assignment has the following form: @var{variable}=@var{text} @end example -@cindex @code{-v} option, variables@comma{} assigning +@cindex @option{-v} option @noindent With it, a variable is set either at the beginning of the @command{awk} run or in between input files. @@ -9071,14 +10918,14 @@ as in the following: the variable is set at the very beginning, even before the @code{BEGIN} rules execute. The @option{-v} option and its assignment must precede all the @value{FN} arguments, as well as the program text. -(@xref{Options}, for more information about +(@DBXREF{Options} for more information about the @option{-v} option.) Otherwise, the variable assignment is performed at a time determined by its position among the input file arguments---after the processing of the preceding input file argument. For example: @example -awk '@{ print $n @}' n=4 inventory-shipped n=2 BBS-list +awk '@{ print $n @}' n=4 inventory-shipped n=2 mail-list @end example @noindent @@ -9087,10 +10934,10 @@ the first file is read, the command line sets the variable @code{n} equal to four. This causes the fourth field to be printed in lines from @file{inventory-shipped}. After the first file has finished, but before the second file is started, @code{n} is set to two, so that the -second field is printed in lines from @file{BBS-list}: +second field is printed in lines from @file{mail-list}: @example -$ @kbd{awk '@{ print $n @}' n=4 inventory-shipped n=2 BBS-list} +$ @kbd{awk '@{ print $n @}' n=4 inventory-shipped n=2 mail-list} @print{} 15 @print{} 24 @dots{} @@ -9111,6 +10958,19 @@ sequences @node Conversion @subsection Conversion of Strings and Numbers +Number-to-string and string-to-number conversion are generally +straightforward. There can be subtleties to be aware of; +this @value{SECTION} discusses this important facet of @command{awk}. + +@menu +* Strings And Numbers:: How @command{awk} Converts Between Strings And + Numbers. +* Locale influences conversions:: How the locale may affect conversions. +@end menu + +@node Strings And Numbers +@subsubsection How @command{awk} Converts Between Strings and Numbers + @cindex converting, strings to numbers @cindex strings, converting @cindex numbers, converting @@ -9140,19 +11000,19 @@ string, concatenate that number with the empty string, @code{""}. To force a string to be converted to a number, add zero to that string. A string is converted to a number by interpreting any numeric prefix of the string as numerals: -@code{"2.5"} converts to 2.5, @code{"1e3"} converts to 1000, and @code{"25fix"} +@code{"2.5"} converts to 2.5, @code{"1e3"} converts to 1,000, and @code{"25fix"} has a numeric value of 25. Strings that can't be interpreted as valid numbers convert to zero. @cindex @code{CONVFMT} variable The exact manner in which numbers are converted into strings is controlled -by the @command{awk} built-in variable @code{CONVFMT} (@pxref{Built-in Variables}). +by the @command{awk} predefined variable @code{CONVFMT} (@pxref{Built-in Variables}). Numbers are converted using the @code{sprintf()} function with @code{CONVFMT} as the format specifier (@pxref{String Functions}). -@code{CONVFMT}'s default value is @code{"%.6g"}, which prints a value with +@code{CONVFMT}'s default value is @code{"%.6g"}, which creates a value with at most six significant digits. For some applications, you might want to change it to specify more precision. On most modern machines, @@ -9180,6 +11040,12 @@ b = a "" @code{b} has the value @code{"12"}, not @code{"12.00"}. @value{DARKCORNER} +@cindex sidebar, Pre-POSIX @command{awk} Used @code{OFMT} for String Conversion +@ifdocbook +@docbook +<sidebar><title>Pre-POSIX @command{awk} Used @code{OFMT} for String Conversion</title> +@end docbook + @cindex POSIX @command{awk}, @code{OFMT} variable and @cindex @code{OFMT} variable @cindex portability, new @command{awk} vs.@: old @command{awk} @@ -9191,64 +11057,91 @@ specifies the output format to use when printing numbers with @code{print}. conversion from the semantics of printing. Both @code{CONVFMT} and @code{OFMT} have the same default value: @code{"%.6g"}. In the vast majority of cases, old @command{awk} programs do not change their behavior. -However, these semantics for @code{OFMT} are something to keep in mind if you must -port your new-style program to older implementations of @command{awk}. -We recommend -that instead of changing your programs, just port @command{gawk} itself. -@xref{Print}, -for more information on the @code{print} statement. - -And, once again, where you are can matter when it comes to converting -between numbers and strings. In @ref{Locales}, we mentioned that -the local character set and language (the locale) can affect how -@command{gawk} matches characters. The locale also affects numeric -formats. In particular, for @command{awk} programs, it affects the -decimal point character. The @code{"C"} locale, and most English-language -locales, use the period character (@samp{.}) as the decimal point. -However, many (if not most) European and non-English locales use the comma -(@samp{,}) as the decimal point character. +@DBXREF{Print} for more information on the @code{print} statement. + +@docbook +</sidebar> +@end docbook +@end ifdocbook + +@ifnotdocbook +@cartouche +@center @b{Pre-POSIX @command{awk} Used @code{OFMT} for String Conversion} + +@cindex POSIX @command{awk}, @code{OFMT} variable and +@cindex @code{OFMT} variable +@cindex portability, new @command{awk} vs.@: old @command{awk} +@cindex @command{awk}, new vs.@: old, @code{OFMT} variable +Prior to the POSIX standard, @command{awk} used the value +of @code{OFMT} for converting numbers to strings. @code{OFMT} +specifies the output format to use when printing numbers with @code{print}. +@code{CONVFMT} was introduced in order to separate the semantics of +conversion from the semantics of printing. Both @code{CONVFMT} and +@code{OFMT} have the same default value: @code{"%.6g"}. In the vast majority +of cases, old @command{awk} programs do not change their behavior. +@DBXREF{Print} for more information on the @code{print} statement. +@end cartouche +@end ifnotdocbook + +@node Locale influences conversions +@subsubsection Locales Can Influence Conversion + +Where you are can matter when it comes to converting between numbers and +strings. The local character set and language---the @dfn{locale}---can +affect numeric formats. In particular, for @command{awk} programs, +it affects the decimal point character and the thousands-separator +character. The @code{"C"} locale, and most English-language locales, +use the period character (@samp{.}) as the decimal point and don't +have a thousands separator. However, many (if not most) European and +non-English locales use the comma (@samp{,}) as the decimal point +character. European locales often use either a space or a period as +the thousands separator, if they have one. + +@cindex dark corner, locale's decimal point character The POSIX standard says that @command{awk} always uses the period as the decimal -point when reading the @command{awk} program source code, and for command-line -variable assignments (@pxref{Other Arguments}). -However, when interpreting input data, for @code{print} and @code{printf} output, -and for number to string conversion, the local decimal point character is used. -Here are some examples indicating the difference in behavior, -on a GNU/Linux system: +point when reading the @command{awk} program source code, and for +command-line variable assignments (@pxref{Other Arguments}). However, +when interpreting input data, for @code{print} and @code{printf} output, +and for number-to-string conversion, the local decimal point character +is used. @value{DARKCORNER} In all cases, numbers in source code and +in input data cannot have a thousands separator. Here are some examples +indicating the difference in behavior, on a GNU/Linux system: @example +$ @kbd{export POSIXLY_CORRECT=1} @ii{Force POSIX behavior} $ @kbd{gawk 'BEGIN @{ printf "%g\n", 3.1415927 @}'} @print{} 3.14159 -$ @kbd{LC_ALL=en_DK gawk 'BEGIN @{ printf "%g\n", 3.1415927 @}'} +$ @kbd{LC_ALL=en_DK.utf-8 gawk 'BEGIN @{ printf "%g\n", 3.1415927 @}'} @print{} 3,14159 $ @kbd{echo 4,321 | gawk '@{ print $1 + 1 @}'} @print{} 5 -$ @kbd{echo 4,321 | LC_ALL=en_DK gawk '@{ print $1 + 1 @}'} +$ @kbd{echo 4,321 | LC_ALL=en_DK.utf-8 gawk '@{ print $1 + 1 @}'} @print{} 5,321 @end example @noindent -The @samp{en_DK} locale is for English in Denmark, where the comma acts as +The @code{en_DK.utf-8} locale is for English in Denmark, where the comma acts as the decimal point separator. In the normal @code{"C"} locale, @command{gawk} -treats @samp{4,321} as @samp{4}, while in the Danish locale, it's treated -as the full number, 4.321. +treats @samp{4,321} as 4, while in the Danish locale, it's treated +as the full number including the fractional part, 4.321. Some earlier versions of @command{gawk} fully complied with this aspect of the standard. However, many users in non-English locales complained -about this behavior, since their data used a period as the decimal +about this behavior, because their data used a period as the decimal point, so the default behavior was restored to use a period as the decimal point character. You can use the @option{--use-lc-numeric} option (@pxref{Options}) to force @command{gawk} to use the locale's decimal point character. (@command{gawk} also uses the locale's decimal point character when in POSIX mode, either via @option{--posix}, or the -@env{POSIXLY_CORRECT} environment variable.) +@env{POSIXLY_CORRECT} environment variable, as shown previously.) @ref{table-locale-affects} describes the cases in which the locale's decimal point character is used and when a period is used. Some of these features have not been described yet. @float Table,table-locale-affects -@caption{Locale Decimal Point versus A Period} +@caption{Locale decimal point versus a period} @multitable @columnfractions .15 .20 .45 @headitem Feature @tab Default @tab @option{--posix} or @option{--use-lc-numeric} @item @code{%'g} @tab Use locale @tab Use locale @@ -9258,13 +11151,13 @@ features have not been described yet. @end multitable @end float -Finally, modern day formal standards and IEEE standard floating point +Finally, modern day formal standards and IEEE standard floating-point representation can have an unusual but important effect on the way @command{gawk} converts some special string values to numbers. The details are presented in @ref{POSIX Floating Point Problems}. @node All Operators -@section Operators: Doing Something With Values +@section Operators: Doing Something with Values This @value{SECTION} introduces the @dfn{operators} which make use of the values provided by constants and variables. @@ -9315,16 +11208,10 @@ $ @kbd{awk '@{ sum = $2 + $3 + $4 ; avg = sum / 3} @print{} Chris 84.3333 @end example -The following list provides the arithmetic operators in @command{awk}, in order from -the highest precedence to the lowest: +The following list provides the arithmetic operators in @command{awk}, +in order from the highest precedence to the lowest: @table @code -@item - @var{x} -Negation. - -@item + @var{x} -Unary plus; the expression is converted to a number. - @cindex common extensions, @code{**} operator @cindex extensions, common@comma{} @code{**} operator @cindex POSIX @command{awk}, arithmetic operators and @@ -9334,6 +11221,12 @@ Exponentiation; @var{x} raised to the @var{y} power. @samp{2 ^ 3} has the value eight; the character sequence @samp{**} is equivalent to @samp{^}. @value{COMMONEXT} +@item - @var{x} +Negation. + +@item + @var{x} +Unary plus; the expression is converted to a number. + @item @var{x} * @var{y} Multiplication. @@ -9343,7 +11236,7 @@ Multiplication. Division; because all numbers in @command{awk} are floating-point numbers, the result is @emph{not} rounded to an integer---@samp{3 / 4} has the value 0.75. (It is a common mistake, especially for C programmers, -to forget that @emph{all} numbers in @command{awk} are floating-point, +to forget that @emph{all} numbers in @command{awk} are floating point, and that division of integer-looking constants produces a real number, not an integer.) @@ -9375,7 +11268,7 @@ b * int(a / b) + (a % b) == a @end example One possibly undesirable effect of this definition of remainder is that -@code{@var{x} % @var{y}} is negative if @var{x} is negative. Thus: +@samp{@var{x} % @var{y}} is negative if @var{x} is negative. Thus: @example -17 % 8 = -1 @@ -9383,7 +11276,7 @@ One possibly undesirable effect of this definition of remainder is that In other @command{awk} implementations, the signedness of the remainder may be machine-dependent. -@c !!! what does posix say? +@c FIXME !!! what does posix say? @cindex portability, @code{**} operator and @cindex @code{*} (asterisk), @code{**} operator @@ -9398,8 +11291,8 @@ For maximum portability, do not use the @samp{**} operator. @subsection String Concatenation @cindex Kernighan, Brian @quotation -@i{It seemed like a good idea at the time.}@* -Brian Kernighan +@i{It seemed like a good idea at the time.} +@author Brian Kernighan @end quotation @cindex string operators @@ -9410,9 +11303,9 @@ specific operator to represent it. Instead, concatenation is performed by writing expressions next to one another, with no operator. For example: @example -$ @kbd{awk '@{ print "Field number one: " $1 @}' BBS-list} -@print{} Field number one: aardvark -@print{} Field number one: alpo-net +$ @kbd{awk '@{ print "Field number one: " $1 @}' mail-list} +@print{} Field number one: Amelia +@print{} Field number one: Anthony @dots{} @end example @@ -9420,15 +11313,15 @@ Without the space in the string constant after the @samp{:}, the line runs together. For example: @example -$ @kbd{awk '@{ print "Field number one:" $1 @}' BBS-list} -@print{} Field number one:aardvark -@print{} Field number one:alpo-net +$ @kbd{awk '@{ print "Field number one:" $1 @}' mail-list} +@print{} Field number one:Amelia +@print{} Field number one:Anthony @dots{} @end example @cindex troubleshooting, string concatenation Because string concatenation does not have an explicit operator, it is -often necessary to insure that it happens at the right time by using +often necessary to ensure that it happens at the right time by using parentheses to enclose the items to concatenate. For example, you might expect that the following code fragment concatenates @code{file} and @code{name}: @@ -9439,9 +11332,11 @@ name = "name" print "something meaningful" > file name @end example +@cindex Brian Kernighan's @command{awk} +@cindex @command{mawk} utility @noindent This produces a syntax error with some versions of Unix -@command{awk}.@footnote{It happens that Brian Kernighan's +@command{awk}.@footnote{It happens that BWK @command{awk}, @command{gawk} and @command{mawk} all ``get it right,'' but you should not rely on this.} It is necessary to use the following: @@ -9467,7 +11362,7 @@ BEGIN @{ @end example @noindent -It is not defined whether the assignment to @code{a} happens +It is not defined whether the second assignment to @code{a} happens before or after the value of @code{a} is retrieved for producing the concatenated value. The result could be either @samp{don't panic}, or @samp{panic panic}. @@ -9526,16 +11421,13 @@ Otherwise, it's parsed as follows: @end display As mentioned earlier, -when doing concatenation, @emph{parenthesize}. Otherwise, +when mixing concatenation with other operators, @emph{parenthesize}. Otherwise, you're never quite sure what you'll get. @node Assignment Ops @subsection Assignment Expressions -@c STARTOFRANGE asop @cindex assignment operators -@c STARTOFRANGE opas @cindex operators, assignment -@c STARTOFRANGE exas @cindex expressions, assignment @cindex @code{=} (equals sign), @code{=} operator @cindex equals sign (@code{=}), @code{=} operator @@ -9589,8 +11481,8 @@ element. (Such values are called @dfn{rvalues}.) @cindex variables, types of It is important to note that variables do @emph{not} have permanent types. -A variable's type is simply the type of whatever value it happens -to hold at the moment. In the following program fragment, the variable +A variable's type is simply the type of whatever value was last assigned +to it. In the following program fragment, the variable @code{foo} has a numeric value at first, and a string value later on: @example @@ -9688,9 +11580,17 @@ The indices of @code{bar} are practically guaranteed to be different, because @code{rand()} returns different values each time it is called. (Arrays and the @code{rand()} function haven't been covered yet. @xref{Arrays}, -and see @ref{Numeric Functions}, for more information). +and +@ifnotdocbook +@DBPXREF{Numeric Functions} +@end ifnotdocbook +@ifdocbook +@DBREF{Numeric Functions} +@end ifdocbook +for more information). This example illustrates an important fact about assignment operators: the lefthand expression is only evaluated @emph{once}. + It is up to the implementation as to which expression is evaluated first, the lefthand or the righthand. Consider this example: @@ -9720,20 +11620,20 @@ to a number. @cindex @code{*} (asterisk), @code{**=} operator @cindex asterisk (@code{*}), @code{**=} operator @float Table,table-assign-ops -@caption{Arithmetic Assignment Operators} +@caption{Arithmetic assignment operators} @multitable @columnfractions .30 .70 @headitem Operator @tab Effect -@item @var{lvalue} @code{+=} @var{increment} @tab Adds @var{increment} to the value of @var{lvalue}. -@item @var{lvalue} @code{-=} @var{decrement} @tab Subtracts @var{decrement} from the value of @var{lvalue}. -@item @var{lvalue} @code{*=} @var{coefficient} @tab Multiplies the value of @var{lvalue} by @var{coefficient}. -@item @var{lvalue} @code{/=} @var{divisor} @tab Divides the value of @var{lvalue} by @var{divisor}. -@item @var{lvalue} @code{%=} @var{modulus} @tab Sets @var{lvalue} to its remainder by @var{modulus}. +@item @var{lvalue} @code{+=} @var{increment} @tab Add @var{increment} to the value of @var{lvalue} +@item @var{lvalue} @code{-=} @var{decrement} @tab Subtract @var{decrement} from the value of @var{lvalue} +@item @var{lvalue} @code{*=} @var{coefficient} @tab Multiply the value of @var{lvalue} by @var{coefficient} +@item @var{lvalue} @code{/=} @var{divisor} @tab Divide the value of @var{lvalue} by @var{divisor} +@item @var{lvalue} @code{%=} @var{modulus} @tab Set @var{lvalue} to its remainder by @var{modulus} @cindex common extensions, @code{**=} operator @cindex extensions, common@comma{} @code{**=} operator @cindex @command{awk} language, POSIX version @cindex POSIX @command{awk} @item @var{lvalue} @code{^=} @var{power} @tab -@item @var{lvalue} @code{**=} @var{power} @tab Raises @var{lvalue} to the power @var{power}. @value{COMMONEXT} +@item @var{lvalue} @code{**=} @var{power} @tab Raise @var{lvalue} to the power @var{power} @value{COMMONEXT} @end multitable @end float @@ -9744,9 +11644,12 @@ Only the @samp{^=} operator is specified by POSIX. For maximum portability, do not use the @samp{**=} operator. @end quotation -@c fakenode --- for prepinfo -@subheading Advanced Notes: Syntactic Ambiguities Between @samp{/=} and Regular Expressions -@cindex advanced features, regexp constants +@cindex sidebar, Syntactic Ambiguities Between @samp{/=} and Regular Expressions +@ifdocbook +@docbook +<sidebar><title>Syntactic Ambiguities Between @samp{/=} and Regular Expressions</title> +@end docbook + @cindex dark corner, regexp constants, @code{/=} operator and @cindex @code{/} (forward slash), @code{/=} operator, vs. @code{/=@dots{}/} regexp constant @cindex forward slash (@code{/}), @code{/=} operator, vs. @code{/=@dots{}/} regexp constant @@ -9755,18 +11658,64 @@ For maximum portability, do not use the @samp{**=} operator. @c derived from email from "Nelson H. F. Beebe" <beebe@math.utah.edu> @c Date: Mon, 1 Sep 1997 13:38:35 -0600 (MDT) -@cindex dark corner +@cindex dark corner, @code{/=} operator vs. @code{/=@dots{}/} regexp constant +@cindex ambiguity, syntactic: @code{/=} operator vs. @code{/=@dots{}/} regexp constant +@cindex syntactic ambiguity: @code{/=} operator vs. @code{/=@dots{}/} regexp constant +@cindex @code{/=} operator vs. @code{/=@dots{}/} regexp constant +There is a syntactic ambiguity between the @code{/=} assignment +operator and regexp constants whose first character is an @samp{=}. +@value{DARKCORNER} +This is most notable in some commercial @command{awk} versions. +For example: + +@example +$ @kbd{awk /==/ /dev/null} +@error{} awk: syntax error at source line 1 +@error{} context is +@error{} >>> /= <<< +@error{} awk: bailing out at source line 1 +@end example + +@noindent +A workaround is: + +@example +awk '/[=]=/' /dev/null +@end example + +@command{gawk} does not have this problem; BWK @command{awk} +and @command{mawk} also do not. + +@docbook +</sidebar> +@end docbook +@end ifdocbook + +@ifnotdocbook +@cartouche +@center @b{Syntactic Ambiguities Between @samp{/=} and Regular Expressions} + + +@cindex dark corner, regexp constants, @code{/=} operator and +@cindex @code{/} (forward slash), @code{/=} operator, vs. @code{/=@dots{}/} regexp constant +@cindex forward slash (@code{/}), @code{/=} operator, vs. @code{/=@dots{}/} regexp constant +@cindex regexp constants, @code{/=@dots{}/}, @code{/=} operator and + +@c derived from email from "Nelson H. F. Beebe" <beebe@math.utah.edu> +@c Date: Mon, 1 Sep 1997 13:38:35 -0600 (MDT) + +@cindex dark corner, @code{/=} operator vs. @code{/=@dots{}/} regexp constant @cindex ambiguity, syntactic: @code{/=} operator vs. @code{/=@dots{}/} regexp constant @cindex syntactic ambiguity: @code{/=} operator vs. @code{/=@dots{}/} regexp constant @cindex @code{/=} operator vs. @code{/=@dots{}/} regexp constant There is a syntactic ambiguity between the @code{/=} assignment operator and regexp constants whose first character is an @samp{=}. @value{DARKCORNER} -This is most notable in commercial @command{awk} versions. +This is most notable in some commercial @command{awk} versions. For example: @example -$ awk /==/ /dev/null +$ @kbd{awk /==/ /dev/null} @error{} awk: syntax error at source line 1 @error{} context is @error{} >>> /= <<< @@ -9780,20 +11729,15 @@ A workaround is: awk '/[=]=/' /dev/null @end example -@command{gawk} does not have this problem, -nor do the other -freely available versions described in -@ref{Other Versions}. -@c ENDOFRANGE exas -@c ENDOFRANGE opas -@c ENDOFRANGE asop +@command{gawk} does not have this problem; BWK @command{awk} +and @command{mawk} also do not. +@end cartouche +@end ifnotdocbook @node Increment Ops @subsection Increment and Decrement Operators -@c STARTOFRANGE inop @cindex increment operators -@c STARTOFRANGE opde @cindex operators, decrement/increment @dfn{Increment} and @dfn{decrement operators} increase or decrease the value of a variable by one. An assignment operator can do the same thing, so @@ -9801,16 +11745,15 @@ the increment operators add no power to the @command{awk} language; however, the are convenient abbreviations for very common operations. @cindex side effects -@cindex @code{+} (plus sign), @code{++} (decrement/increment operators) -@cindex plus sign (@code{+}), @code{++} (decrement/increment operators) +@cindex @code{+} (plus sign), @code{++} operator +@cindex plus sign (@code{+}), @code{++} operator @cindex side effects, decrement/increment operators The operator used for adding one is written @samp{++}. It can be used to increment a variable either before or after taking its value. -To pre-increment a variable @code{v}, write @samp{++v}. This adds +To @dfn{pre-increment} a variable @code{v}, write @samp{++v}. This adds one to the value of @code{v}---that new value is also the value of the -expression. (The assignment expression @samp{v += 1} is completely -equivalent.) -Writing the @samp{++} after the variable specifies post-increment. This +expression. (The assignment expression @samp{v += 1} is completely equivalent.) +Writing the @samp{++} after the variable specifies @dfn{post-increment}. This increments the variable value just the same; the difference is that the value of the increment expression itself is the variable's @emph{old} value. Thus, if @code{foo} has the value four, then the expression @samp{foo++} @@ -9820,9 +11763,20 @@ but with the side effect of incrementing it. The post-increment @samp{foo++} is nearly the same as writing @samp{(foo += 1) - 1}. It is not perfectly equivalent because all numbers in -@command{awk} are floating-point---in floating-point, @samp{foo + 1 - 1} does +@command{awk} are floating point---in floating point, @samp{foo + 1 - 1} does not necessarily equal @code{foo}. But the difference is minute as -long as you stick to numbers that are fairly small (less than 10e12). +long as you stick to numbers that are fairly small (less than +@iftex +@math{10^{12}}). +@end iftex +@ifnottex +@ifnotdocbook +10e12). +@end ifnotdocbook +@end ifnottex +@docbook +10<superscript>12</superscript>). @c +@end docbook @cindex @code{$} (dollar sign), incrementing fields and arrays @cindex dollar sign (@code{$}), incrementing fields and arrays @@ -9863,9 +11817,64 @@ as the value of the expression. like @samp{@var{lvalue}++}, but instead of adding, it subtracts.) @end table -@c fakenode --- for prepinfo -@subheading Advanced Notes: Operator Evaluation Order -@cindex advanced features, operators@comma{} precedence +@cindex sidebar, Operator Evaluation Order +@ifdocbook +@docbook +<sidebar><title>Operator Evaluation Order</title> +@end docbook + +@cindex precedence +@cindex operators, precedence +@cindex portability, operators +@cindex evaluation order +@cindex Marx, Groucho +@quotation +@i{Doctor, doctor! It hurts when I do this!@* +So don't do that!} +@author Groucho Marx +@end quotation + +@noindent +What happens for something like the following? + +@example +b = 6 +print b += b++ +@end example + +@noindent +Or something even stranger? + +@example +b = 6 +b += ++b + b++ +print b +@end example + +@cindex side effects +In other words, when do the various side effects prescribed by the +postfix operators (@samp{b++}) take effect? +When side effects happen is @dfn{implementation defined}. +In other words, it is up to the particular version of @command{awk}. +The result for the first example may be 12 or 13, and for the second, it +may be 22 or 23. + +In short, doing things like this is not recommended and definitely +not anything that you can rely upon for portability. +You should avoid such things in your own programs. +@c You'll sleep better at night and be able to look at yourself +@c in the mirror in the morning. + +@docbook +</sidebar> +@end docbook +@end ifdocbook + +@ifnotdocbook +@cartouche +@center @b{Operator Evaluation Order} + + @cindex precedence @cindex operators, precedence @cindex portability, operators @@ -9873,8 +11882,8 @@ like @samp{@var{lvalue}++}, but instead of adding, it subtracts.) @cindex Marx, Groucho @quotation @i{Doctor, doctor! It hurts when I do this!@* -So don't do that!}@* -Groucho Marx +So don't do that!} +@author Groucho Marx @end quotation @noindent @@ -9907,15 +11916,14 @@ not anything that you can rely upon for portability. You should avoid such things in your own programs. @c You'll sleep better at night and be able to look at yourself @c in the mirror in the morning. -@c ENDOFRANGE inop -@c ENDOFRANGE opde -@c ENDOFRANGE deop +@end cartouche +@end ifnotdocbook @node Truth Values and Conditions @section Truth Values and Conditions -In certain contexts, expression values also serve as ``truth values;'' i.e., -they determine what should happen next as the program runs. This +In certain contexts, expression values also serve as ``truth values''; (i.e., +they determine what should happen next as the program runs). This @value{SECTION} describes how @command{awk} defines ``true'' and ``false'' and how values are compared. @@ -9962,7 +11970,7 @@ BEGIN @{ @} @end example -@cindex dark corner +@cindex dark corner, @code{"0"} is actually true There is a surprising consequence of the ``nonzero or non-null'' rule: the string constant @code{"0"} is actually true, because it is non-null. @value{DARKCORNER} @@ -9970,21 +11978,17 @@ the string constant @code{"0"} is actually true, because it is non-null. @node Typing and Comparison @subsection Variable Typing and Comparison Expressions @quotation -@i{The Guide is definitive. Reality is frequently inaccurate.}@* -The Hitchhiker's Guide to the Galaxy +@i{The Guide is definitive. Reality is frequently inaccurate.} +@author Douglas Adams, @cite{The Hitchhiker's Guide to the Galaxy} @end quotation -@c STARTOFRANGE comex @cindex comparison expressions -@c STARTOFRANGE excom @cindex expressions, comparison @cindex expressions, matching, See comparison expressions @cindex matching, expressions, See comparison expressions @cindex relational operators, See comparison operators @cindex operators, relational, See operators@comma{} comparison -@c STARTOFRANGE varting @cindex variable typing -@c STARTOFRANGE vartypc @cindex variables, types of, comparison expressions and Unlike other programming languages, @command{awk} variables do not have a fixed type. Instead, they can be either a number or a string, depending @@ -9999,25 +12003,21 @@ compares variables. @end menu @node Variable Typing -@subsubsection String Type Versus Numeric Type +@subsubsection String Type versus Numeric Type @cindex numeric, strings @cindex strings, numeric @cindex POSIX @command{awk}, numeric strings and -The 1992 POSIX standard introduced +The POSIX standard introduced the concept of a @dfn{numeric string}, which is simply a string that looks like a number---for example, @code{@w{" +2"}}. This concept is used for determining the type of a variable. The type of the variable is important because the types of two variables determine how they are compared. -The various versions of the POSIX standard did not get the rules -quite right for several editions. Fortunately, as of at least the -2008 standard (and possibly earlier), the standard has been fixed, -and variable typing follows these rules:@footnote{@command{gawk} has -followed these rules for many years, -and it is gratifying that the POSIX standard is also now correct.} +Variable typing follows these rules: + -@itemize @bullet +@itemize @value{BULLET} @item A numeric constant or the result of a numeric operation has the @var{numeric} attribute. @@ -10029,7 +12029,7 @@ attribute. @item Fields, @code{getline} input, @code{FILENAME}, @code{ARGV} elements, @code{ENVIRON} elements, and the elements of an array created by -@code{patsplit()}, @code{split()} and @code{match()} that are numeric +@code{match()}, @code{split()}, and @code{patsplit()} that are numeric strings have the @var{strnum} attribute. Otherwise, they have the @var{string} attribute. Uninitialized variables also have the @var{strnum} attribute. @@ -10103,6 +12103,7 @@ STRNUM &&string &numeric &numeric\cr }}} @end tex @ifnottex +@ifnotdocbook @display +---------------------------------------------- | STRING NUMERIC STRNUM @@ -10115,7 +12116,51 @@ NUMERIC | string numeric numeric STRNUM | string numeric numeric --------+---------------------------------------------- @end display +@end ifnotdocbook @end ifnottex +@docbook +<informaltable> +<tgroup cols="4"> +<colspec colname="1" align="left"/> +<colspec colname="2" align="left"/> +<colspec colname="3" align="left"/> +<colspec colname="4" align="left"/> +<thead> +<row> +<entry/> +<entry>STRING</entry> +<entry>NUMERIC</entry> +<entry>STRNUM</entry> +</row> +</thead> + +<tbody> +<row> +<entry><emphasis role="bold">STRING</emphasis></entry> +<entry>string</entry> +<entry>string</entry> +<entry>string</entry> +</row> + +<row> +<entry><emphasis role="bold">NUMERIC</emphasis></entry> +<entry>string</entry> +<entry>numeric</entry> +<entry>numeric</entry> +</row> + +<row> +<entry><emphasis role="bold">STRNUM</emphasis></entry> +<entry>string</entry> +<entry>numeric</entry> +<entry>numeric</entry> +</row> + +</tbody> +</tgroup> +</informaltable> + +@end docbook The basic idea is that user input that looks numeric---and @emph{only} user input---should be treated as numeric, even though it is actually @@ -10123,7 +12168,7 @@ made of characters and is therefore also a string. Thus, for example, the string constant @w{@code{" +3.14"}}, when it appears in program source code, is a string---even though it looks numeric---and -is @emph{never} treated as number for comparison +is @emph{never} treated as a number for comparison purposes. In short, when one operand is a ``pure'' string, such as a string @@ -10134,27 +12179,28 @@ This point bears additional emphasis: All user input is made of characters, and so is first and foremost of @var{string} type; input strings that look numeric are additionally given the @var{strnum} attribute. Thus, the six-character input string @w{@samp{ +3.14}} receives the -@var{strnum} attribute. In contrast, the eight-character literal -@w{@code{" +3.14"}} appearing in program text is a string constant. +@var{strnum} attribute. In contrast, the eight characters +@w{@code{" +3.14"}} appearing in program text comprise a string constant. The following examples print @samp{1} when the comparison between the two different constants is true, @samp{0} otherwise: +@c 22.9.2014: Tested with mawk and BWK awk, got same results. @example -$ @kbd{echo ' +3.14' | gawk '@{ print $0 == " +3.14" @}'} @ii{True} +$ @kbd{echo ' +3.14' | awk '@{ print($0 == " +3.14") @}'} @ii{True} @print{} 1 -$ @kbd{echo ' +3.14' | gawk '@{ print $0 == "+3.14" @}'} @ii{False} +$ @kbd{echo ' +3.14' | awk '@{ print($0 == "+3.14") @}'} @ii{False} @print{} 0 -$ @kbd{echo ' +3.14' | gawk '@{ print $0 == "3.14" @}'} @ii{False} +$ @kbd{echo ' +3.14' | awk '@{ print($0 == "3.14") @}'} @ii{False} @print{} 0 -$ @kbd{echo ' +3.14' | gawk '@{ print $0 == 3.14 @}'} @ii{True} +$ @kbd{echo ' +3.14' | awk '@{ print($0 == 3.14) @}'} @ii{True} @print{} 1 -$ @kbd{echo ' +3.14' | gawk '@{ print $1 == " +3.14" @}'} @ii{False} +$ @kbd{echo ' +3.14' | awk '@{ print($1 == " +3.14") @}'} @ii{False} @print{} 0 -$ @kbd{echo ' +3.14' | gawk '@{ print $1 == "+3.14" @}'} @ii{True} +$ @kbd{echo ' +3.14' | awk '@{ print($1 == "+3.14") @}'} @ii{True} @print{} 1 -$ @kbd{echo ' +3.14' | gawk '@{ print $1 == "3.14" @}'} @ii{False} +$ @kbd{echo ' +3.14' | awk '@{ print($1 == "3.14") @}'} @ii{False} @print{} 0 -$ @kbd{echo ' +3.14' | gawk '@{ print $1 == 3.14 @}'} @ii{True} +$ @kbd{echo ' +3.14' | awk '@{ print($1 == 3.14) @}'} @ii{True} @print{} 1 @end example @@ -10184,18 +12230,18 @@ operators}, which are a superset of those in C. @cindex exclamation point (@code{!}), @code{!~} operator @cindex @code{in} operator @float Table,table-relational-ops -@caption{Relational Operators} +@caption{Relational operators} @multitable @columnfractions .25 .75 @headitem Expression @tab Result -@item @var{x} @code{<} @var{y} @tab True if @var{x} is less than @var{y}. -@item @var{x} @code{<=} @var{y} @tab True if @var{x} is less than or equal to @var{y}. -@item @var{x} @code{>} @var{y} @tab True if @var{x} is greater than @var{y}. -@item @var{x} @code{>=} @var{y} @tab True if @var{x} is greater than or equal to @var{y}. -@item @var{x} @code{==} @var{y} @tab True if @var{x} is equal to @var{y}. -@item @var{x} @code{!=} @var{y} @tab True if @var{x} is not equal to @var{y}. -@item @var{x} @code{~} @var{y} @tab True if the string @var{x} matches the regexp denoted by @var{y}. -@item @var{x} @code{!~} @var{y} @tab True if the string @var{x} does not match the regexp denoted by @var{y}. -@item @var{subscript} @code{in} @var{array} @tab True if the array @var{array} has an element with the subscript @var{subscript}. +@item @var{x} @code{<} @var{y} @tab True if @var{x} is less than @var{y} +@item @var{x} @code{<=} @var{y} @tab True if @var{x} is less than or equal to @var{y} +@item @var{x} @code{>} @var{y} @tab True if @var{x} is greater than @var{y} +@item @var{x} @code{>=} @var{y} @tab True if @var{x} is greater than or equal to @var{y} +@item @var{x} @code{==} @var{y} @tab True if @var{x} is equal to @var{y} +@item @var{x} @code{!=} @var{y} @tab True if @var{x} is not equal to @var{y} +@item @var{x} @code{~} @var{y} @tab True if the string @var{x} matches the regexp denoted by @var{y} +@item @var{x} @code{!~} @var{y} @tab True if the string @var{x} does not match the regexp denoted by @var{y} +@item @var{subscript} @code{in} @var{array} @tab True if the array @var{array} has an element with the subscript @var{subscript} @end multitable @end float @@ -10228,30 +12274,29 @@ part of the test always succeeds. Because the operators are so similar, this kind of error is very difficult to spot when scanning the source code. -@cindex @command{gawk}, comparison operators and -The following table of expressions illustrates the kind of comparison -@command{gawk} performs, as well as what the result of the comparison is: +The following list of expressions illustrates the kinds of comparisons +@command{awk} performs, as well as what the result of each comparison is: @table @code @item 1.5 <= 2.0 -numeric comparison (true) +Numeric comparison (true) @item "abc" >= "xyz" -string comparison (false) +String comparison (false) @item 1.5 != " +2" -string comparison (true) +String comparison (true) @item "1e2" < "3" -string comparison (true) +String comparison (true) @item a = 2; b = "2" @itemx a == b -string comparison (true) +String comparison (true) @item a = 2; b = " +2" -@item a == b -string comparison (false) +@itemx a == b +String comparison (false) @end table In this example: @@ -10296,15 +12341,15 @@ has the value one if @code{x} contains @samp{foo}, such as @cindex @code{!} (exclamation point), @code{!~} operator @cindex exclamation point (@code{!}), @code{!~} operator The righthand operand of the @samp{~} and @samp{!~} operators may be -either a regexp constant (@code{/@dots{}/}) or an ordinary +either a regexp constant (@code{/}@dots{}@code{/}) or an ordinary expression. In the latter case, the value of the expression as a string is used as a dynamic regexp (@pxref{Regexp Usage}; also @pxref{Computed Regexps}). @cindex @command{awk}, regexp constants and @cindex regexp constants -In modern implementations of @command{awk}, a constant regular -expression in slashes by itself is also an expression. The regexp +A constant regular +expression in slashes by itself is also an expression. @code{/@var{regexp}/} is an abbreviation for the following comparison expression: @example @@ -10318,10 +12363,12 @@ One special place where @code{/foo/} is @emph{not} an abbreviation for where this is discussed in more detail. @node POSIX String Comparison -@subsubsection String Comparison With POSIX Rules +@subsubsection String Comparison with POSIX Rules The POSIX standard says that string comparison is performed based -on the locale's collating order. This is usually very different +on the locale's @dfn{collating order}. This is the order in which +characters sort, as defined by the locale (for more discussion, +@pxref{Locales}). This order is usually very different from the results obtained when doing straight character-by-character comparison.@footnote{Technically, string comparison is supposed to behave the same way as if the strings are compared with the C @@ -10329,7 +12376,7 @@ to behave the same way as if the strings are compared with the C Because this behavior differs considerably from existing practice, @command{gawk} only implements it when in POSIX mode (@pxref{Options}). -Here is an example to illustrate the difference, in an @samp{en_US.UTF-8} +Here is an example to illustrate the difference, in an @code{en_US.UTF-8} locale: @example @@ -10341,19 +12388,13 @@ $ @kbd{gawk --posix 'BEGIN @{ printf("ABC < abc = %s\n",} @print{} ABC < abc = FALSE @end example -@c ENDOFRANGE comex -@c ENDOFRANGE excom -@c ENDOFRANGE vartypc -@c ENDOFRANGE varting @node Boolean Ops @subsection Boolean Expressions @cindex and Boolean-logic operator @cindex or Boolean-logic operator @cindex not Boolean-logic operator -@c STARTOFRANGE exbo @cindex expressions, Boolean -@c STARTOFRANGE boex @cindex Boolean expressions @cindex operators, Boolean, See Boolean expressions @cindex Boolean operators, See Boolean expressions @@ -10384,10 +12425,10 @@ The Boolean operators are: @item @var{boolean1} && @var{boolean2} True if both @var{boolean1} and @var{boolean2} are true. For example, the following statement prints the current input record if it contains -both @samp{2400} and @samp{foo}: +both @samp{edu} and @samp{li}: @example -if ($0 ~ /2400/ && $0 ~ /foo/) print +if ($0 ~ /edu/ && $0 ~ /li/) print @end example @cindex side effects, Boolean operators @@ -10400,16 +12441,19 @@ no substring @samp{foo} in the record. @item @var{boolean1} || @var{boolean2} True if at least one of @var{boolean1} or @var{boolean2} is true. For example, the following statement prints all records in the input -that contain @emph{either} @samp{2400} or -@samp{foo} or both: +that contain @emph{either} @samp{edu} or +@samp{li}: @example -if ($0 ~ /2400/ || $0 ~ /foo/) print +if ($0 ~ /edu/ || $0 ~ /li/) print @end example The subexpression @var{boolean2} is evaluated only if @var{boolean1} is false. This can make a difference when @var{boolean2} contains expressions that have side effects. +(Thus, this test never really distinguishes records that contain both +@samp{edu} and @samp{li}---as soon as @samp{edu} is matched, +the full test succeeds.) @item ! @var{boolean} True if @var{boolean} is false. For example, @@ -10419,7 +12463,7 @@ variable is not defined: @example BEGIN @{ if (! ("HOME" in ENVIRON)) - print "no home!" @} + print "no home!" @} @end example (The @code{in} operator is described in @@ -10438,7 +12482,7 @@ is ``short-circuited'' if the result can be determined part way through its evaluation. @cindex line continuations -Statements that use @samp{&&} or @samp{||} can be continued simply +Statements that end with @samp{&&} or @samp{||} can be continued simply by putting a newline after them. But you cannot put a newline in front of either of these operators without using backslash continuation (@pxref{Statements/Lines}). @@ -10457,7 +12501,7 @@ program is one way to print lines in between special bracketing lines: @example $1 == "START" @{ interested = ! interested; next @} -interested == 1 @{ print @} +interested @{ print @} $1 == "END" @{ interested = ! interested; next @} @end example @@ -10477,6 +12521,16 @@ bogus input data, but the point is to illustrate the use of `!', so we'll leave well enough alone. @end ignore +Most commonly, the @samp{!} operator is used in the conditions of +@code{if} and @code{while} statements, where it often makes more +sense to phrase the logic in the negative: + +@example +if (! @var{some condition} || @var{some other condition}) @{ + @var{@dots{} do whatever processing @dots{}} +@} +@end example + @cindex @code{next} statement @quotation NOTE The @code{next} statement is discussed in @@ -10486,8 +12540,6 @@ next record, and start processing the rules over again at the top. The reason it's there is to avoid printing the bracketing @samp{START} and @samp{END} lines. @end quotation -@c ENDOFRANGE exbo -@c ENDOFRANGE boex @node Conditional Exp @subsection Conditional Expressions @@ -10545,7 +12597,7 @@ However, putting a newline in front of either character does not work without using backslash continuation (@pxref{Statements/Lines}). If @option{--posix} is specified -(@pxref{Options}), then this extension is disabled. +(@pxref{Options}), this extension is disabled. @node Function Calls @section Function Calls @@ -10559,11 +12611,13 @@ example, the function @code{sqrt()} computes the square root of a number. @cindex functions, built-in A fixed set of functions are @dfn{built-in}, which means they are available in every @command{awk} program. The @code{sqrt()} function is one -of these. @xref{Built-in}, for a list of built-in +of these. @DBXREF{Built-in} for a list of built-in functions and their descriptions. In addition, you can define functions for use in your program. -@xref{User-defined}, +@DBXREF{User-defined} for instructions on how to do this. +Finally, @command{gawk} lets you write functions in C or C++ +that may be called from your program (@pxref{Dynamic Extensions}). @cindex arguments, in function calls The way to use a function is with a @dfn{function call} expression, @@ -10582,7 +12636,7 @@ rand() @ii{no arguments} @cindex troubleshooting, function call syntax @quotation CAUTION -Do not put any space between the function name and the open-parenthesis! +Do not put any space between the function name and the opening parenthesis! A user-defined function name looks just like the name of a variable---a space would make the expression look like concatenation of a variable with an expression inside parentheses. @@ -10603,9 +12657,11 @@ Some of the built-in functions have one or more optional arguments. If those arguments are not supplied, the functions use a reasonable default value. -@xref{Built-in}, for full details. If arguments +@DBXREF{Built-in} for full details. If arguments are omitted in calls to user-defined functions, then those arguments are -treated as local variables and initialized to the empty string +treated as local variables. Such local variables act like the +empty string if referenced where a string value is required, +and like zero if referenced where a numeric value is required (@pxref{User-defined}). As an advanced feature, @command{gawk} provides indirect function calls, @@ -10614,12 +12670,12 @@ when you write the source code to your program. We defer discussion of this feature until later; see @ref{Indirect Calls}. @cindex side effects, function calls -Like every other expression, the function call has a value, which is -computed by the function based on the arguments you give it. In this -example, the value of @samp{sqrt(@var{argument})} is the square root of -@var{argument}. -The following program reads numbers, one number per line, and prints the -square root of each one: +Like every other expression, the function call has a value, often +called the @dfn{return value}, which is computed by the function +based on the arguments you give it. In this example, the return value +of @samp{sqrt(@var{argument})} is the square root of @var{argument}. +The following program reads numbers, one number per line, and prints +the square root of each one: @example $ @kbd{awk '@{ print "The square root of", $1, "is", sqrt($1) @}'} @@ -10629,7 +12685,7 @@ $ @kbd{awk '@{ print "The square root of", $1, "is", sqrt($1) @}'} @print{} The square root of 3 is 1.73205 @kbd{5} @print{} The square root of 5 is 2.23607 -@kbd{@value{CTL}-d} +@kbd{Ctrl-d} @end example A function can also have side effects, such as assigning @@ -10662,9 +12718,7 @@ $ @kbd{awk -f matchit.awk} @node Precedence @section Operator Precedence (How Operators Nest) -@c STARTOFRANGE prec @cindex precedence -@c STARTOFRANGE oppr @cindex operators, precedence @dfn{Operator precedence} determines how operators are grouped when @@ -10704,31 +12758,31 @@ expression because the first @samp{$} has higher precedence than the @samp{++}; to avoid the problem the expression can be rewritten as @samp{$($0++)--}. -This table presents @command{awk}'s operators, in order of highest +This list presents @command{awk}'s operators, in order of highest to lowest precedence: -@c use @code in the items, looks better in TeX w/o all the quotes -@table @code -@item (@dots{}) +@c @asis for docbook to come out right +@table @asis +@item @code{(}@dots{}@code{)} Grouping. @cindex @code{$} (dollar sign), @code{$} field operator @cindex dollar sign (@code{$}), @code{$} field operator -@item $ +@item @code{$} Field reference. @cindex @code{+} (plus sign), @code{++} operator @cindex plus sign (@code{+}), @code{++} operator -@cindex @code{-} (hyphen), @code{--} (decrement/increment) operator -@cindex hyphen (@code{-}), @code{--} (decrement/increment) operators -@item ++ -- +@cindex @code{-} (hyphen), @code{--} operator +@cindex hyphen (@code{-}), @code{--} operator +@item @code{++ --} Increment, decrement. @cindex @code{^} (caret), @code{^} operator @cindex caret (@code{^}), @code{^} operator @cindex @code{*} (asterisk), @code{**} operator @cindex asterisk (@code{*}), @code{**} operator -@item ^ ** +@item @code{^ **} Exponentiation. These operators group right-to-left. @cindex @code{+} (plus sign), @code{+} operator @@ -10737,7 +12791,7 @@ Exponentiation. These operators group right-to-left. @cindex hyphen (@code{-}), @code{-} operator @cindex @code{!} (exclamation point), @code{!} operator @cindex exclamation point (@code{!}), @code{!} operator -@item + - ! +@item @code{+ - !} Unary plus, minus, logical ``not.'' @cindex @code{*} (asterisk), @code{*} operator, as multiplication operator @@ -10746,17 +12800,17 @@ Unary plus, minus, logical ``not.'' @cindex forward slash (@code{/}), @code{/} operator @cindex @code{%} (percent sign), @code{%} operator @cindex percent sign (@code{%}), @code{%} operator -@item * / % +@item @code{* / %} Multiplication, division, remainder. @cindex @code{+} (plus sign), @code{+} operator @cindex plus sign (@code{+}), @code{+} operator @cindex @code{-} (hyphen), @code{-} operator @cindex hyphen (@code{-}), @code{-} operator -@item + - +@item @code{+ -} Addition, subtraction. -@item @r{String Concatenation} +@item String concatenation There is no special symbol for concatenation. The operands are simply written side by side (@pxref{Concatenation}). @@ -10782,7 +12836,7 @@ The operands are simply written side by side @cindex @code{|} (vertical bar), @code{|&} operator (I/O) @cindex vertical bar (@code{|}), @code{|&} operator (I/O) @cindex operators, input/output -@item < <= == != > >= >> | |& +@item @code{< <= == != > >= >> | |&} Relational and redirection. The relational operators and the redirections have the same precedence level. Characters such as @samp{>} serve both as relationals and as @@ -10795,7 +12849,7 @@ statements belong to the statement level, not to expressions. The redirection does not produce an expression that could be the operand of another operator. As a result, it does not make sense to use a redirection operator near another operator of lower precedence without -parentheses. Such combinations (for example, @samp{print foo > a ? b : c}), +parentheses. Such combinations (e.g., @samp{print foo > a ? b : c}), result in syntax errors. The correct way to write this statement is @samp{print foo > (a ? b : c)}. @@ -10803,26 +12857,26 @@ The correct way to write this statement is @samp{print foo > (a ? b : c)}. @cindex tilde (@code{~}), @code{~} operator @cindex @code{!} (exclamation point), @code{!~} operator @cindex exclamation point (@code{!}), @code{!~} operator -@item ~ !~ +@item @code{~ !~} Matching, nonmatching. @cindex @code{in} operator -@item in +@item @code{in} Array membership. @cindex @code{&} (ampersand), @code{&&} operator @cindex ampersand (@code{&}), @code{&&} operator -@item && +@item @code{&&} Logical ``and''. @cindex @code{|} (vertical bar), @code{||} operator @cindex vertical bar (@code{|}), @code{||} operator -@item || +@item @code{||} Logical ``or''. @cindex @code{?} (question mark), @code{?:} operator @cindex question mark (@code{?}), @code{?:} operator -@item ?: +@item @code{?:} Conditional. This operator groups right-to-left. @cindex @code{+} (plus sign), @code{+=} operator @@ -10839,7 +12893,7 @@ Conditional. This operator groups right-to-left. @cindex percent sign (@code{%}), @code{%=} operator @cindex @code{^} (caret), @code{^=} operator @cindex caret (@code{^}), @code{^=} operator -@item = += -= *= /= %= ^= **= +@item @code{= += -= *= /= %= ^= **=} Assignment. These operators group right-to-left. @end table @@ -10849,46 +12903,118 @@ Assignment. These operators group right-to-left. The @samp{|&}, @samp{**}, and @samp{**=} operators are not specified by POSIX. For maximum portability, do not use them. @end quotation -@c ENDOFRANGE prec -@c ENDOFRANGE oppr @node Locales -@section Where You Are Makes A Difference +@section Where You Are Makes a Difference @cindex locale, definition of -Modern systems support the notion of @dfn{locales}: a way to tell -the system about the local character set and language. +Modern systems support the notion of @dfn{locales}: a way to tell the +system about the local character set and language. The ISO C standard +defines a default @code{"C"} locale, which is an environment that is +typical of what many C programmers are used to. -Once upon a time, the locale setting used to affect regexp matching -(@pxref{Ranges and Locales}), but this is no longer true. +Once upon a time, the locale setting used to affect regexp matching, +but this is no longer true (@pxref{Ranges and Locales}). -Locales can affect record splitting. -For the normal case of @samp{RS = "\n"}, the locale is largely irrelevant. -For other single-character record separators, setting @samp{LC_ALL=C} -in the environment -will give you much better performance when reading records. Otherwise, +Locales can affect record splitting. For the normal case of @samp{RS = +"\n"}, the locale is largely irrelevant. For other single-character +record separators, setting @samp{LC_ALL=C} in the environment will +give you much better performance when reading records. Otherwise, @command{gawk} has to make several function calls, @emph{per input character}, to find the record terminator. -According to POSIX, string comparison is also affected by locales -(similar to regular expressions). The details are presented in -@ref{POSIX String Comparison}. +Locales can affect how dates and times are formatted (@pxref{Time +Functions}). For example, a common way to abbreviate the date September +4, 2015, in the United States is ``9/4/15.'' In many countries in +Europe, however, it is abbreviated ``4.9.15.'' Thus, the @samp{%x} +specification in a @code{"US"} locale might produce @samp{9/4/15}, +while in a @code{"EUROPE"} locale, it might produce @samp{4.9.15}. + +According to POSIX, string comparison is also affected by locales (similar +to regular expressions). The details are presented in @ref{POSIX String +Comparison}. Finally, the locale affects the value of the decimal point character -used when @command{gawk} parses input data. This is discussed in -detail in @ref{Conversion}. +used when @command{gawk} parses input data. This is discussed in detail +in @ref{Conversion}. + +@node Expressions Summary +@section Summary + +@itemize @value{BULLET} +@item +Expressions are the basic elements of computation in programs. They are +built from constants, variables, function calls, and combinations of the +various kinds of values with operators. + +@item +@command{awk} supplies three kinds of constants: numeric, string, and +regexp. @command{gawk} lets you specify numeric constants in octal +and hexadecimal (bases 8 and 16) as well as decimal (base 10). +In certain contexts, a standalone regexp constant such as @code{/foo/} +has the same meaning as @samp{$0 ~ /foo/}. + +@item +Variables hold values between uses in computations. A number of built-in +variables provide information to your @command{awk} program, and a number +of others let you control how @command{awk} behaves. + +@item +Numbers are automatically converted to strings, and strings to numbers, +as needed by @command{awk}. Numeric values are converted as if they were +formatted with @code{sprintf()} using the format in @code{CONVFMT}. +Locales can influence the conversions. + +@item +@command{awk} provides the usual arithmetic operators (addition, +subtraction, multiplication, division, modulus), and unary plus and minus. +It also provides comparison operators, boolean operators, array membership +testing, and regexp +matching operators. String concatenation is accomplished by placing +two expressions next to each other; there is no explicit operator. +The three-operand @samp{?:} operator provides an ``if-else'' test within +expressions. + +@item +Assignment operators provide convenient shorthands for common arithmetic +operations. + +@item +In @command{awk}, a value is considered to be true if it is non-zero +@emph{or} non-null. Otherwise, the value is false. + +@item +A variable's type is set upon each assignment and may change over its +lifetime. The type determines how it behaves in comparisons (string +or numeric). + +@item +Function calls return a value which may be used as part of a larger +expression. Expressions used to pass parameter values are fully +evaluated before the function is called. @command{awk} provides +built-in and user-defined functions; this is described in +@ref{Functions}. + +@item +Operator precedence specifies the order in which operations are performed, +unless explicitly overridden by parentheses. @command{awk}'s operator +precedence is compatible with that of C. + +@item +Locales can affect the format of data as output by an @command{awk} +program, and occasionally the format for data read as input. + +@end itemize -@c ENDOFRANGE exps @node Patterns and Actions @chapter Patterns, Actions, and Variables -@c STARTOFRANGE pat @cindex patterns As you have already seen, each @command{awk} statement consists of a pattern with an associated action. This @value{CHAPTER} describes how you build patterns and actions, what kinds of things you can do within -actions, and @command{awk}'s built-in variables. +actions, and @command{awk}'s predefined variables. The pattern-action rules and the statements available for use within actions form the core of @command{awk} programming. @@ -10903,7 +13029,8 @@ building something useful. * Action Overview:: What goes into an action. * Statements:: Describes the various control statements in detail. -* Built-in Variables:: Summarizes the built-in variables. +* Built-in Variables:: Summarizes the predefined variables. +* Pattern Action Summary:: Patterns and Actions summary. @end menu @node Pattern Overview @@ -10934,10 +13061,10 @@ A single expression. It matches when its value is nonzero (if a number) or non-null (if a string). (@xref{Expression Patterns}.) -@item @var{pat1}, @var{pat2} -A pair of patterns separated by a comma, specifying a range of records. -The range includes both the initial record that matches @var{pat1} and -the final record that matches @var{pat2}. +@item @var{begpat}, @var{endpat} +A pair of patterns separated by a comma, specifying a @dfn{range} of records. +The range includes both the initial record that matches @var{begpat} and +the final record that matches @var{endpat}. (@xref{Ranges}.) @item BEGIN @@ -10948,8 +13075,8 @@ Special patterns for you to supply startup or cleanup actions for your @item BEGINFILE @itemx ENDFILE -Special patterns for you to supply startup or cleanup actions to -done on a per file basis. +Special patterns for you to supply startup or cleanup actions to be +done on a per-file basis. (@xref{BEGINFILE/ENDFILE}.) @item @var{empty} @@ -10999,7 +13126,7 @@ slashes (@code{/@var{regexp}/}), or any expression whose string value is used as a dynamic regular expression (@pxref{Computed Regexps}). The following example prints the second field of each input record -whose first field is precisely @samp{foo}: +whose first field is precisely @samp{li}: @cindex @code{/} (forward slash), patterns and @cindex forward slash (@code{/}), patterns and @@ -11008,68 +13135,64 @@ whose first field is precisely @samp{foo}: @cindex @code{!} (exclamation point), @code{!~} operator @cindex exclamation point (@code{!}), @code{!~} operator @example -$ @kbd{awk '$1 == "foo" @{ print $2 @}' BBS-list} +$ @kbd{awk '$1 == "li" @{ print $2 @}' mail-list} @end example @noindent -(There is no output, because there is no BBS site with the exact name @samp{foo}.) +(There is no output, because there is no person with the exact name @samp{li}.) Contrast this with the following regular expression match, which -accepts any record with a first field that contains @samp{foo}: +accepts any record with a first field that contains @samp{li}: @example -$ @kbd{awk '$1 ~ /foo/ @{ print $2 @}' BBS-list} -@print{} 555-1234 +$ @kbd{awk '$1 ~ /li/ @{ print $2 @}' mail-list} +@print{} 555-5553 @print{} 555-6699 -@print{} 555-6480 -@print{} 555-2127 @end example @cindex regexp constants, as patterns @cindex patterns, regexp constants as -A regexp constant as a pattern is also a special case of an expression -pattern. The expression @code{/foo/} has the value one if @samp{foo} -appears in the current input record. Thus, as a pattern, @code{/foo/} -matches any record containing @samp{foo}. +pattern. The expression @code{/li/} has the value one if @samp{li} +appears in the current input record. Thus, as a pattern, @code{/li/} +matches any record containing @samp{li}. @cindex Boolean expressions, as patterns Boolean expressions are also commonly used as patterns. Whether the pattern matches an input record depends on whether its subexpressions match. For example, the following command prints all the records in -@file{BBS-list} that contain both @samp{2400} and @samp{foo}: +@file{mail-list} that contain both @samp{edu} and @samp{li}: @example -$ @kbd{awk '/2400/ && /foo/' BBS-list} -@print{} fooey 555-1234 2400/1200/300 B +$ @kbd{awk '/edu/ && /li/' mail-list} +@print{} Samuel 555-3430 samuel.lanceolis@@shu.edu A @end example The following command prints all records in -@file{BBS-list} that contain @emph{either} @samp{2400} or @samp{foo} +@file{mail-list} that contain @emph{either} @samp{edu} or @samp{li} (or both, of course): @example -$ @kbd{awk '/2400/ || /foo/' BBS-list} -@print{} alpo-net 555-3412 2400/1200/300 A -@print{} bites 555-1675 2400/1200/300 A -@print{} fooey 555-1234 2400/1200/300 B -@print{} foot 555-6699 1200/300 B -@print{} macfoo 555-6480 1200/300 A -@print{} sdace 555-3430 2400/1200/300 A -@print{} sabafoo 555-2127 1200/300 C +$ @kbd{awk '/edu/ || /li/' mail-list} +@print{} Amelia 555-5553 amelia.zodiacusque@@gmail.com F +@print{} Broderick 555-0542 broderick.aliquotiens@@yahoo.com R +@print{} Fabius 555-1234 fabius.undevicesimus@@ucb.edu F +@print{} Julie 555-6699 julie.perscrutabor@@skeeve.com F +@print{} Samuel 555-3430 samuel.lanceolis@@shu.edu A +@print{} Jean-Paul 555-2127 jeanpaul.campanorum@@nyu.edu R @end example The following command prints all records in -@file{BBS-list} that do @emph{not} contain the string @samp{foo}: +@file{mail-list} that do @emph{not} contain the string @samp{li}: @example -$ @kbd{awk '! /foo/' BBS-list} -@print{} aardvark 555-5553 1200/300 B -@print{} alpo-net 555-3412 2400/1200/300 A -@print{} barfly 555-7685 1200/300 A -@print{} bites 555-1675 2400/1200/300 A -@print{} camelot 555-0542 300 C -@print{} core 555-2912 1200/300 C -@print{} sdace 555-3430 2400/1200/300 A +$ @kbd{awk '! /li/' mail-list} +@print{} Anthony 555-3412 anthony.asserturo@@hotmail.com A +@print{} Becky 555-7685 becky.algebrarum@@gmail.com A +@print{} Bill 555-1675 bill.drowning@@hotmail.com A +@print{} Camilla 555-2912 camilla.infusarum@@skynet.be R +@print{} Fabius 555-1234 fabius.undevicesimus@@ucb.edu F +@print{} Martin 555-6480 martin.codicibus@@hotmail.com A +@print{} Jean-Paul 555-2127 jeanpaul.campanorum@@nyu.edu R @end example @cindex @code{BEGIN} pattern, Boolean patterns and @@ -11080,7 +13203,7 @@ The subexpressions of a Boolean operator in a pattern can be constant regular expressions, comparisons, or any other @command{awk} expressions. Range patterns are not expressions, so they cannot appear inside Boolean patterns. Likewise, the special patterns @code{BEGIN}, @code{END}, -@code{BEGINFILE} and @code{ENDFILE}, +@code{BEGINFILE}, and @code{ENDFILE}, which never match any input record, are not expressions and cannot appear inside Boolean patterns. @@ -11113,7 +13236,7 @@ input record. When a record matches @var{begpat}, the range pattern is @dfn{turned on} and the range pattern matches this record as well. As long as the range pattern stays turned on, it automatically matches every input record read. The range pattern also matches @var{endpat} against every -input record; when this succeeds, the range pattern is turned off again +input record; when this succeeds, the range pattern is @dfn{turned off} again for the following record. Then the range pattern goes back to checking @var{begpat} against each record. @@ -11173,12 +13296,15 @@ $ @kbd{echo Yes | gawk '(/1/,/2/) || /Yes/'} @error{} gawk: cmd. line:1: ^ syntax error @end example +@cindex range patterns, line continuation and +As a minor point of interest, although it is poor style, +POSIX allows you to put a newline after the comma in +a range pattern. @value{DARKCORNER} + @node BEGIN/END @subsection The @code{BEGIN} and @code{END} Special Patterns -@c STARTOFRANGE beg @cindex @code{BEGIN} pattern -@c STARTOFRANGE end @cindex @code{END} pattern All the patterns described so far are for matching input records. The @code{BEGIN} and @code{END} special patterns are different. @@ -11186,7 +13312,7 @@ They supply startup and cleanup actions for @command{awk} programs. @code{BEGIN} and @code{END} rules must have actions; there is no default action for these rules because there is no current record when they run. @code{BEGIN} and @code{END} rules are often referred to as -``@code{BEGIN} and @code{END} blocks'' by long-time @command{awk} +``@code{BEGIN} and @code{END} blocks'' by longtime @command{awk} programmers. @menu @@ -11197,28 +13323,30 @@ programmers. @node Using BEGIN/END @subsubsection Startup and Cleanup Actions +@cindex @code{BEGIN} pattern +@cindex @code{END} pattern A @code{BEGIN} rule is executed once only, before the first input record is read. Likewise, an @code{END} rule is executed once only, after all the input is read. For example: @example $ @kbd{awk '} -> @kbd{BEGIN @{ print "Analysis of \"foo\"" @}} -> @kbd{/foo/ @{ ++n @}} -> @kbd{END @{ print "\"foo\" appears", n, "times." @}' BBS-list} -@print{} Analysis of "foo" -@print{} "foo" appears 4 times. +> @kbd{BEGIN @{ print "Analysis of \"li\"" @}} +> @kbd{/li/ @{ ++n @}} +> @kbd{END @{ print "\"li\" appears in", n, "records." @}' mail-list} +@print{} Analysis of "li" +@print{} "li" appears in 4 records. @end example @cindex @code{BEGIN} pattern, operators and @cindex @code{END} pattern, operators and -This program finds the number of records in the input file @file{BBS-list} -that contain the string @samp{foo}. The @code{BEGIN} rule prints a title +This program finds the number of records in the input file @file{mail-list} +that contain the string @samp{li}. The @code{BEGIN} rule prints a title for the report. There is no need to use the @code{BEGIN} rule to -initialize the counter @code{n} to zero, since @command{awk} does this +initialize the counter @code{n} to zero, as @command{awk} does this automatically (@pxref{Variables}). The second rule increments the variable @code{n} every time a -record containing the pattern @samp{foo} is read. The @code{END} rule +record containing the pattern @samp{li} is read. The @code{END} rule prints the value of @code{n} at the end of the run. The special patterns @code{BEGIN} and @code{END} cannot be used in ranges @@ -11243,7 +13371,7 @@ The order in which library functions are named on the command line controls the order in which their @code{BEGIN} and @code{END} rules are executed. Therefore, you have to be careful when writing such rules in library files so that the order in which they are executed doesn't matter. -@xref{Options}, for more information on +@DBXREF{Options} for more information on using library functions. @xref{Library Functions}, for a number of useful library functions. @@ -11260,7 +13388,7 @@ rule checks the @code{FNR} and @code{NR} variables. @subsubsection Input/Output from @code{BEGIN} and @code{END} Rules @cindex input/output, from @code{BEGIN} and @code{END} -There are several (sometimes subtle) points to remember when doing I/O +There are several (sometimes subtle) points to be aware of when doing I/O from a @code{BEGIN} or @code{END} rule. The first has to do with the value of @code{$0} in a @code{BEGIN} rule. Because @code{BEGIN} rules are executed before any input is read, @@ -11271,6 +13399,7 @@ to give @code{$0} a real value is to execute a @code{getline} command without a variable (@pxref{Getline}). Another way is simply to assign a value to @code{$0}. +@cindex Brian Kernighan's @command{awk} @cindex differences in @command{awk} and @command{gawk}, @code{BEGIN}/@code{END} patterns @cindex POSIX @command{awk}, @code{BEGIN}/@code{END} patterns @cindex @code{print} statement, @code{BEGIN}/@code{END} patterns and @@ -11283,18 +13412,19 @@ The POSIX standard specifies that @code{NF} is available in an @code{END} rule. It contains the number of fields from the last input record. Most probably due to an oversight, the standard does not say that @code{$0} is also preserved, although logically one would think that it should be. -In fact, @command{gawk} does preserve the value of @code{$0} for use in -@code{END} rules. Be aware, however, that Brian Kernighan's @command{awk}, and possibly -other implementations, do not. +In fact, all of BWK @command{awk}, @command{mawk}, and @command{gawk} +preserve the value of @code{$0} for use in @code{END} rules. Be aware, +however, that some other implementations and many older versions +of Unix @command{awk} do not. The third point follows from the first two. The meaning of @samp{print} inside a @code{BEGIN} or @code{END} rule is the same as always: @samp{print $0}. If @code{$0} is the null string, then this prints an -empty record. Many long time @command{awk} programmers use an unadorned +empty record. Many longtime @command{awk} programmers use an unadorned @samp{print} in @code{BEGIN} and @code{END} rules, to mean @samp{@w{print ""}}, relying on @code{$0} being null. Although one might generally get away with this in @code{BEGIN} rules, it is a very bad idea in @code{END} rules, -at least in @command{gawk}. It is also poor style, since if an empty +at least in @command{gawk}. It is also poor style, because if an empty line is needed in the output, the program should print one explicitly. @cindex @code{next} statement, @code{BEGIN}/@code{END} patterns and @@ -11304,33 +13434,48 @@ line is needed in the output, the program should print one explicitly. Finally, the @code{next} and @code{nextfile} statements are not allowed in a @code{BEGIN} rule, because the implicit read-a-record-and-match-against-the-rules loop has not started yet. Similarly, those statements -are not valid in an @code{END} rule, since all the input has been read. -(@xref{Next Statement}, and see -@ref{Nextfile Statement}.) -@c ENDOFRANGE beg -@c ENDOFRANGE end +are not valid in an @code{END} rule, because all the input has been read. +(@DBXREF{Next Statement} and +@ifnotdocbook +@DBPXREF{Nextfile Statement}.) +@end ifnotdocbook +@ifdocbook +@DBREF{Nextfile Statement}.) +@end ifdocbook @node BEGINFILE/ENDFILE @subsection The @code{BEGINFILE} and @code{ENDFILE} Special Patterns @cindex @code{BEGINFILE} pattern @cindex @code{ENDFILE} pattern +@cindex differences in @command{awk} and @command{gawk}, @code{BEGINFILE}/@code{ENDFILE} patterns This @value{SECTION} describes a @command{gawk}-specific feature. Two special kinds of rule, @code{BEGINFILE} and @code{ENDFILE}, give you ``hooks'' into @command{gawk}'s command-line file processing loop. -As with the @code{BEGIN} and @code{END} rules (@pxref{BEGIN/END}), all -@code{BEGINFILE} rules in a program are merged, in the order they are +As with the @code{BEGIN} and @code{END} rules +@ifnottex +@ifnotdocbook +(@pxref{BEGIN/END}), +@end ifnotdocbook +@end ifnottex +@iftex +(see the previous section), +@end iftex +@ifdocbook +(see the previous section), +@end ifdocbook +all @code{BEGINFILE} rules in a program are merged, in the order they are read by @command{gawk}, and all @code{ENDFILE} rules are merged as well. The body of the @code{BEGINFILE} rules is executed just before @command{gawk} reads the first record from a file. @code{FILENAME} is set to the name of the current file, and @code{FNR} is set to zero. -The @code{BEGINFILE} rule provides you the opportunity for two tasks +The @code{BEGINFILE} rule provides you the opportunity to accomplish two tasks that would otherwise be difficult or impossible to perform: -@itemize @bullet +@itemize @value{BULLET} @item You can test if the file is readable. Normally, it is a fatal error if a file named on the command line cannot be opened for reading. However, @@ -11338,7 +13483,7 @@ you can bypass the fatal error and move on to the next file on the command line. @cindex @command{gawk}, @code{ERRNO} variable in -@cindex @code{ERRNO} variable +@cindex @code{ERRNO} variable, with @code{BEGINFILE} pattern @cindex @code{nextfile} statement, @code{BEGINFILE}/@code{ENDFILE} patterns and You do this by checking if the @code{ERRNO} variable is not the empty string; if so, then @command{gawk} was not able to open the file. In @@ -11348,10 +13493,11 @@ the file entirely. Otherwise, @command{gawk} exits with the usual fatal error. @item -If you have written extensions that modify the record handling (by inserting -an ``open hook''), you can invoke them at this point, before @command{gawk} -has started processing the file. (This is a @emph{very} advanced feature, -currently used only by the @uref{http://xmlgawk.sourceforge.net, XMLgawk project}.) +If you have written extensions that modify the record handling (by +inserting an ``input parser,'' @pxref{Input Parsers}), you can invoke +them at this point, before @command{gawk} has started processing the file. +(This is a @emph{very} advanced feature, currently used only by the +@uref{http://gawkextlib.sourceforge.net, @code{gawkextlib} project}.) @end itemize The @code{ENDFILE} rule is called when @command{gawk} has finished processing @@ -11367,20 +13513,20 @@ level of the @command{awk} program. @cindex @code{next} statement, @code{BEGINFILE}/@code{ENDFILE} patterns and The @code{next} statement (@pxref{Next Statement}) is not allowed inside -either a @code{BEGINFILE} or and @code{ENDFILE} rule. The @code{nextfile} -statement (@pxref{Nextfile Statement}) is allowed only inside a +either a @code{BEGINFILE} or an @code{ENDFILE} rule. The @code{nextfile} +statement is allowed only inside a @code{BEGINFILE} rule, but not inside an @code{ENDFILE} rule. @cindex @code{getline} statement, @code{BEGINFILE}/@code{ENDFILE} patterns and The @code{getline} statement (@pxref{Getline}) is restricted inside -both @code{BEGINFILE} and @code{ENDFILE}. Only the @samp{getline -@var{variable} < @var{file}} form is allowed. +both @code{BEGINFILE} and @code{ENDFILE}: only redirected +forms of @code{getline} are allowed. @code{BEGINFILE} and @code{ENDFILE} are @command{gawk} extensions. In most other @command{awk} implementations, or if @command{gawk} is in compatibility mode (@pxref{Options}), they are not special. -@c FIXME: For 4.1 maybe deal with this? +@c FIXME: For 4.2 maybe deal with this? @ignore Date: Tue, 17 May 2011 02:06:10 PDT From: rankin@pactechdata.com (Pat Rankin) @@ -11411,12 +13557,11 @@ An empty (i.e., nonexistent) pattern is considered to match @emph{every} input record. For example, the program: @example -awk '@{ print $1 @}' BBS-list +awk '@{ print $1 @}' mail-list @end example @noindent prints the first field of every record. -@c ENDOFRANGE pat @node Using Shell Variables @section Using Shell Variables in Programs @@ -11432,9 +13577,9 @@ There are two ways to get the value of the shell variable into the body of the @command{awk} program. @cindex shells, quoting -The most common method is to use shell quoting to substitute +A common method is to use shell quoting to substitute the variable's value into the program inside the script. -For example, in the following program: +For example, consider the following program: @example printf "Enter search pattern: " @@ -11444,11 +13589,11 @@ awk "/$pattern/ "'@{ nmatches++ @} @end example @noindent -the @command{awk} program consists of two pieces of quoted text +The @command{awk} program consists of two pieces of quoted text that are concatenated together to form the program. -The first part is double-quoted, which allows substitution of +The first part is double quoted, which allows substitution of the @code{pattern} shell variable inside the quotes. -The second part is single-quoted. +The second part is single quoted. Variable substitution via quoting works, but can be potentially messy. It requires a good understanding of the shell's quoting rules @@ -11458,8 +13603,8 @@ match up the quotes when reading the program. A better method is to use @command{awk}'s variable assignment feature (@pxref{Assignment Options}) -to assign the shell variable's value to an @command{awk} variable's -value. Then use dynamic regexps to match the pattern +to assign the shell variable's value to an @command{awk} variable. +Then use dynamic regexps to match the pattern (@pxref{Computed Regexps}). The following shows how to redo the previous example using this technique: @@ -11477,7 +13622,7 @@ The assignment @samp{-v pat="$pattern"} still requires double quotes, in case there is whitespace in the value of @code{$pattern}. The @command{awk} variable @code{pat} could be named @code{pattern} too, but that would be more confusing. Using a variable also -provides more flexibility, since the variable can be used anywhere inside +provides more flexibility, as the variable can be used anywhere inside the program---for printing, as an array subscript, or for any other use---without requiring the quoting tricks at every point in the program. @@ -11497,13 +13642,13 @@ both) may be omitted. The purpose of the @dfn{action} is to tell @command{awk} what to do once a match for the pattern is found. Thus, in outline, an @command{awk} program generally looks like this: -@example -@r{[}@var{pattern}@r{]} @{ @var{action} @} - @var{pattern} @r{[}@{ @var{action} @}@r{]} +@display +[@var{pattern}] @code{@{ @var{action} @}} + @var{pattern} [@code{@{ @var{action} @}}] @dots{} -function @var{name}(@var{args}) @{ @dots{} @} +@code{function @var{name}(@var{args}) @{ @dots{} @}} @dots{} -@end example +@end display @cindex @code{@{@}} (braces), actions and @cindex braces (@code{@{@}}), actions and @@ -11512,11 +13657,11 @@ function @var{name}(@var{args}) @{ @dots{} @} @cindex @code{;} (semicolon), separating statements in actions @cindex semicolon (@code{;}), separating statements in actions An action consists of one or more @command{awk} @dfn{statements}, enclosed -in curly braces (@samp{@{@dots{}@}}). Each statement specifies one +in braces (@samp{@{@r{@dots{}}@}}). Each statement specifies one thing to do. The statements are separated by newlines or semicolons. -The curly braces around an action must be used even if the action +The braces around an action must be used even if the action contains only one statement, or if it contains no statements at -all. However, if you omit the action entirely, omit the curly braces as +all. However, if you omit the action entirely, omit the braces as well. An omitted action is equivalent to @samp{@{ print $0 @}}: @example @@ -11542,16 +13687,15 @@ programs. The @command{awk} language gives you C-like constructs special ones (@pxref{Statements}). @item Compound statements -Consist of one or more statements enclosed in -curly braces. A compound statement is used in order to put several -statements together in the body of an @code{if}, @code{while}, @code{do}, -or @code{for} statement. +Enclose one or more statements in braces. A compound statement +is used in order to put several statements together in the body of an +@code{if}, @code{while}, @code{do}, or @code{for} statement. @item Input statements Use the @code{getline} command (@pxref{Getline}). Also supplied in @command{awk} are the @code{next} -statement (@pxref{Next Statement}), +statement (@pxref{Next Statement}) and the @code{nextfile} statement (@pxref{Nextfile Statement}). @@ -11566,11 +13710,8 @@ For deleting array elements. @node Statements @section Control Statements in Actions -@c STARTOFRANGE csta @cindex control statements -@c STARTOFRANGE acs @cindex statements, control, in actions -@c STARTOFRANGE accs @cindex actions, control statements in @dfn{Control statements}, such as @code{if}, @code{while}, and so on, @@ -11591,7 +13732,7 @@ Many control statements contain other statements. For example, the @code{if} statement contains another statement that may or may not be executed. The contained statement is called the @dfn{body}. To include more than one statement in the body, group them into a -single @dfn{compound statement} with curly braces, separating them with +single @dfn{compound statement} with braces, separating them with newlines or semicolons. @menu @@ -11619,9 +13760,9 @@ newlines or semicolons. The @code{if}-@code{else} statement is @command{awk}'s decision-making statement. It looks like this: -@example -if (@var{condition}) @var{then-body} @r{[}else @var{else-body}@r{]} -@end example +@display +@code{if (@var{condition}) @var{then-body}} [@code{else @var{else-body}}] +@end display @noindent The @var{condition} is an expression that controls what the rest of the @@ -11639,13 +13780,13 @@ else print "x is odd" @end example -In this example, if the expression @samp{x % 2 == 0} is true (that is, +In this example, if the expression @samp{x % 2 == 0} is true (i.e., if the value of @code{x} is evenly divisible by two), then the first @code{print} statement is executed; otherwise, the second @code{print} statement is executed. If the @code{else} keyword appears on the same line as @var{then-body} and @var{then-body} is not a compound statement (i.e., not surrounded by -curly braces), then a semicolon must separate @var{then-body} from +braces), then a semicolon must separate @var{then-body} from the @code{else}. To illustrate this, the previous example can be rewritten as: @@ -11664,6 +13805,7 @@ the first thing on its line. @subsection The @code{while} Statement @cindex @code{while} statement @cindex loops +@cindex loops, @code{while} @cindex loops, See Also @code{while} statement In programming, a @dfn{loop} is a part of a program that can @@ -11689,20 +13831,21 @@ If the @var{condition} is true, it executes the statement @var{body}. is not zero and not a null string.) @end ifinfo After @var{body} has been executed, -@var{condition} is tested again, and if it is still true, @var{body} is -executed again. This process repeats until the @var{condition} is no longer -true. If the @var{condition} is initially false, the body of the loop is -never executed and @command{awk} continues with the statement following +@var{condition} is tested again, and if it is still true, @var{body} +executes again. This process repeats until the @var{condition} is no longer +true. If the @var{condition} is initially false, the body of the loop +never executes and @command{awk} continues with the statement following the loop. This example prints the first three fields of each record, one per line: @example -awk '@{ - i = 1 - while (i <= 3) @{ - print $i - i++ - @} +awk ' +@{ + i = 1 + while (i <= 3) @{ + print $i + i++ + @} @}' inventory-shipped @end example @@ -11716,7 +13859,7 @@ field is printed. Then the @samp{i++} increments the value of @code{i} and the loop repeats. The loop terminates when @code{i} reaches four. A newline is not required between the condition and the -body; however using one makes the program clearer unless the body is a +body; however, using one makes the program clearer unless the body is a compound statement or else is very simple. The newline after the open-brace that begins the compound statement is not required either, but the program is harder to read without it. @@ -11724,6 +13867,7 @@ program is harder to read without it. @node Do Statement @subsection The @code{do}-@code{while} Statement @cindex @code{do}-@code{while} statement +@cindex loops, @code{do}-@code{while} The @code{do} loop is a variation of the @code{while} looping statement. The @code{do} loop executes the @var{body} once and then repeats the @@ -11735,14 +13879,14 @@ do while (@var{condition}) @end example -Even if the @var{condition} is false at the start, the @var{body} is -executed at least once (and only once, unless executing @var{body} +Even if the @var{condition} is false at the start, the @var{body} +executes at least once (and only once, unless executing @var{body} makes @var{condition} true). Contrast this with the corresponding @code{while} statement: @example while (@var{condition}) - @var{body} + @var{body} @end example @noindent @@ -11752,23 +13896,24 @@ The following is an example of a @code{do} statement: @example @{ - i = 1 - do @{ - print $0 - i++ - @} while (i <= 10) + i = 1 + do @{ + print $0 + i++ + @} while (i <= 10) @} @end example @noindent This program prints each input record 10 times. However, it isn't a very -realistic example, since in this case an ordinary @code{while} would do +realistic example, because in this case an ordinary @code{while} would do just as well. This situation reflects actual experience; only occasionally is there a real use for a @code{do} statement. @node For Statement @subsection The @code{for} Statement @cindex @code{for} statement +@cindex loops, @code{for}, iterative The @code{for} statement makes it more convenient to count iterations of a loop. The general form of the @code{for} statement looks like this: @@ -11792,9 +13937,10 @@ compares it against the desired number of iterations. For example: @example -awk '@{ - for (i = 1; i <= 3; i++) - print $i +awk ' +@{ + for (i = 1; i <= 3; i++) + print $i @}' inventory-shipped @end example @@ -11822,7 +13968,7 @@ between 1 and 100: @example for (i = 1; i <= 100; i *= 2) - print i + print i @end example If there is nothing to be done, any of the three expressions in the @@ -11857,7 +14003,7 @@ very common in loops. It can be easier to think of this counting as part of looping rather than as something to do inside the loop. @cindex @code{in} operator -There is an alternate version of the @code{for} loop, for iterating over +There is an alternative version of the @code{for} loop, for iterating over all the indices of an array: @example @@ -11866,7 +14012,7 @@ for (i in array) @end example @noindent -@xref{Scanning an Array}, +@DBXREF{Scanning an Array} for more information on this version of the @code{for} loop. @node Switch Statement @@ -11875,6 +14021,10 @@ for more information on this version of the @code{for} loop. @cindex @code{case} keyword @cindex @code{default} keyword +This @value{SECTION} describes a @command{gawk}-specific feature. +If @command{gawk} is in compatibility mode (@pxref{Options}), +it is not available. + The @code{switch} statement allows the evaluation of an expression and the execution of statements based on a @code{case} match. Case statements are checked for a match in the order they are defined. If no suitable @@ -11882,7 +14032,7 @@ are checked for a match in the order they are defined. If no suitable Each @code{case} contains a single constant, be it numeric, string, or regexp. The @code{switch} expression is evaluated, and then each -@code{case}'s constant is compared against the result in turn. The type of constant +@code{case}'s constant is compared against the result in turn. The type of constant determines the comparison: numeric or string do the usual comparisons. A regexp constant does a regular expression match against the string value of the original expression. The general form of the @code{switch} @@ -11904,41 +14054,44 @@ case is made, the case statement bodies execute until a @code{break}, or the end of the @code{switch} statement itself. For example: @example -switch (NR * 2 + 1) @{ -case 3: -case "11": - print NR - 1 - break - -case /2[[:digit:]]+/: - print NR - -default: - print NR + 1 - -case -1: - print NR * -1 +while ((c = getopt(ARGC, ARGV, "aksx")) != -1) @{ + switch (c) @{ + case "a": + # report size of all files + all_files = TRUE; + break + case "k": + BLOCK_SIZE = 1024 # 1K block size + break + case "s": + # do sums only + sum_only = TRUE + break + case "x": + # don't cross filesystems + fts_flags = or(fts_flags, FTS_XDEV) + break + case "?": + default: + usage() + break + @} @} @end example -Note that if none of the statements specified above halt execution +Note that if none of the statements specified here halt execution of a matched @code{case} statement, execution falls through to the -next @code{case} until execution halts. In the above example, for -any case value starting with @samp{2} followed by one or more digits, -the @code{print} statement is executed and then falls through into the -@code{default} section, executing its @code{print} statement. In turn, -the @minus{}1 case will also be executed since the @code{default} does -not halt execution. - -This @code{switch} statement is a @command{gawk} extension. -If @command{gawk} is in compatibility mode -(@pxref{Options}), -it is not available. +next @code{case} until execution halts. In this example, the +@code{case} for @code{"?"} falls through to the @code{default} +case, which is to call a function named @code{usage()}. +(The @code{getopt()} function being called here is +described in @ref{Getopt Function}.) @node Break Statement @subsection The @code{break} Statement @cindex @code{break} statement @cindex loops, exiting +@cindex loops, @code{break} statement and The @code{break} statement jumps out of the innermost @code{for}, @code{while}, or @code{do} loop that encloses it. The following example @@ -11948,15 +14101,15 @@ numbers: @example # find smallest divisor of num @{ - num = $1 - for (div = 2; div * div <= num; div++) @{ - if (num % div == 0) - break - @} - if (num % div == 0) - printf "Smallest divisor of %d is %d\n", num, div - else - printf "%d is prime\n", num + num = $1 + for (div = 2; div * div <= num; div++) @{ + if (num % div == 0) + break + @} + if (num % div == 0) + printf "Smallest divisor of %d is %d\n", num, div + else + printf "%d is prime\n", num @} @end example @@ -11974,17 +14127,17 @@ an @code{if}: @example # find smallest divisor of num @{ - num = $1 - for (div = 2; ; div++) @{ - if (num % div == 0) @{ - printf "Smallest divisor of %d is %d\n", num, div - break - @} - if (div * div > num) @{ - printf "%d is prime\n", num - break + num = $1 + for (div = 2; ; div++) @{ + if (num % div == 0) @{ + printf "Smallest divisor of %d is %d\n", num, div + break + @} + if (div * div > num) @{ + printf "%d is prime\n", num + break + @} @} - @} @} @end example @@ -11998,6 +14151,7 @@ This is discussed in @ref{Switch Statement}. @cindex POSIX @command{awk}, @code{break} statement and @cindex dark corner, @code{break} statement @cindex @command{gawk}, @code{break} statement in +@cindex Brian Kernighan's @command{awk} The @code{break} statement has no meaning when used outside the body of a loop or @code{switch}. However, although it was never documented, @@ -12005,7 +14159,7 @@ historical implementations of @command{awk} treated the @code{break} statement outside of a loop as if it were a @code{next} statement (@pxref{Next Statement}). @value{DARKCORNER} -Recent versions of Brian Kernighan's @command{awk} no longer allow this usage, +Recent versions of BWK @command{awk} no longer allow this usage, nor does @command{gawk}. @node Continue Statement @@ -12054,7 +14208,8 @@ BEGIN @{ @end example @noindent -This program loops forever once @code{x} reaches 5. +This program loops forever once @code{x} reaches 5, because +the increment (@samp{x++}) is never reached. @c @cindex @code{continue}, outside of loops @c @cindex historical features @@ -12062,15 +14217,16 @@ This program loops forever once @code{x} reaches 5. @cindex POSIX @command{awk}, @code{continue} statement and @cindex dark corner, @code{continue} statement @cindex @command{gawk}, @code{continue} statement in +@cindex Brian Kernighan's @command{awk} The @code{continue} statement has no special meaning with respect to the -@code{switch} statement, nor does it any meaning when used outside the body of -a loop. Historical versions of @command{awk} treated a @code{continue} +@code{switch} statement, nor does it have any meaning when used outside the +body of a loop. Historical versions of @command{awk} treated a @code{continue} statement outside a loop the same way they treated a @code{break} statement outside a loop: as if it were a @code{next} statement (@pxref{Next Statement}). @value{DARKCORNER} -Recent versions of Brian Kernighan's @command{awk} no longer work this way, nor +Recent versions of BWK @command{awk} no longer work this way, nor does @command{gawk}. @node Next Statement @@ -12103,9 +14259,8 @@ the beginning, in the following manner: @example NF != 4 @{ - err = sprintf("%s:%d: skipped: NF != 4\n", FILENAME, FNR) - print err > "/dev/stderr" - next + printf("%s:%d: skipped: NF != 4\n", FILENAME, FNR) > "/dev/stderr" + next @} @end example @@ -12114,7 +14269,7 @@ Because of the @code{next} statement, the program's subsequent rules won't see the bad record. The error message is redirected to the standard error output stream, as error messages should be. -For more detail see +For more detail, see @ref{Special Files}. If the @code{next} statement causes the end of the input to be reached, @@ -12131,70 +14286,74 @@ The @code{next} statement is not allowed inside @code{BEGINFILE} and @cindex POSIX @command{awk}, @code{next}/@code{nextfile} statements and @cindex @code{next} statement, user-defined functions and @cindex functions, user-defined, @code{next}/@code{nextfile} statements and -According to the POSIX standard, the behavior is undefined if -the @code{next} statement is used in a @code{BEGIN} or @code{END} rule. -@command{gawk} treats it as a syntax error. -Although POSIX permits it, -some other @command{awk} implementations don't allow the @code{next} -statement inside function bodies -(@pxref{User-defined}). -Just as with any other @code{next} statement, a @code{next} statement inside a -function body reads the next record and starts processing it with the -first rule in the program. +According to the POSIX standard, the behavior is undefined if the +@code{next} statement is used in a @code{BEGIN} or @code{END} rule. +@command{gawk} treats it as a syntax error. Although POSIX does not disallow it, +most other @command{awk} implementations don't allow the @code{next} +statement inside function bodies (@pxref{User-defined}). Just as with any +other @code{next} statement, a @code{next} statement inside a function +body reads the next record and starts processing it with the first rule +in the program. @node Nextfile Statement -@subsection Using @command{gawk}'s @code{nextfile} Statement +@subsection The @code{nextfile} Statement @cindex @code{nextfile} statement -@cindex differences in @command{awk} and @command{gawk}, @code{next}/@code{nextfile} statements -@cindex common extensions, @code{nextfile} statement -@cindex extensions, common@comma{} @code{nextfile} statement -@command{gawk} provides the @code{nextfile} statement, -which is similar to the @code{next} statement. @value{COMMONEXT} +The @code{nextfile} statement +is similar to the @code{next} statement. However, instead of abandoning processing of the current record, the -@code{nextfile} statement instructs @command{gawk} to stop processing the +@code{nextfile} statement instructs @command{awk} to stop processing the current @value{DF}. -The @code{nextfile} statement is a @command{gawk} extension. -In most other @command{awk} implementations, -or if @command{gawk} is in compatibility mode -(@pxref{Options}), -@code{nextfile} is not special. - Upon execution of the @code{nextfile} statement, -any @code{ENDFILE} rules are executed except in the case as -mentioned below, @code{FILENAME} is +@code{FILENAME} is updated to the name of the next @value{DF} listed on the command line, -@code{FNR} is reset to one, @code{ARGIND} is incremented, -any @code{BEGINFILE} rules are executed, and processing +@code{FNR} is reset to one, +and processing starts over with the first rule in the program. -(@code{ARGIND} hasn't been introduced yet. @xref{Built-in Variables}.) If the @code{nextfile} statement causes the end of the input to be reached, then the code in any @code{END} rules is executed. An exception to this is -when the @code{nextfile} is invoked during execution of any statement in an -@code{END} rule; In this case, it causes the program to stop immediately. @xref{BEGIN/END}. +when @code{nextfile} is invoked during execution of any statement in an +@code{END} rule; in this case, it causes the program to stop immediately. +@xref{BEGIN/END}. The @code{nextfile} statement is useful when there are many @value{DF}s to process but it isn't necessary to process every record in every file. -Normally, in order to move on to the next @value{DF}, a program -has to continue scanning the unwanted records. The @code{nextfile} +Without @code{nextfile}, +in order to move on to the next @value{DF}, a program +would have to continue scanning the unwanted records. The @code{nextfile} statement accomplishes this much more efficiently. -In addition, @code{nextfile} is useful inside a @code{BEGINFILE} +In @command{gawk}, execution of @code{nextfile} causes additional things +to happen: any @code{ENDFILE} rules are executed if @command{gawk} is +not currently in an @code{END} or @code{BEGINFILE} rule, @code{ARGIND} is +incremented, and any @code{BEGINFILE} rules are executed. (@code{ARGIND} +hasn't been introduced yet. @xref{Built-in Variables}.) + +With @command{gawk}, @code{nextfile} is useful inside a @code{BEGINFILE} rule to skip over a file that would otherwise cause @command{gawk} to exit with a fatal error. In this case, @code{ENDFILE} rules are not executed. @xref{BEGINFILE/ENDFILE}. -While one might think that @samp{close(FILENAME)} would accomplish +Although it might seem that @samp{close(FILENAME)} would accomplish the same as @code{nextfile}, this isn't true. @code{close()} is reserved for closing files, pipes, and coprocesses that are opened with redirections. It is not related to the main processing that @command{awk} does with the files listed in @code{ARGV}. +@quotation NOTE +For many years, @code{nextfile} was a +common extension. In September 2012, it was accepted for +inclusion into the POSIX standard. +See @uref{http://austingroupbugs.net/view.php?id=607, the Austin Group website}. +@end quotation + @cindex functions, user-defined, @code{next}/@code{nextfile} statements and @cindex @code{nextfile} statement, user-defined functions and -The current version of the Brian Kernighan's @command{awk} (@pxref{Other -Versions}) also supports @code{nextfile}. However, it doesn't allow the +@cindex Brian Kernighan's @command{awk} +@cindex @command{mawk} utility +The current version of BWK @command{awk}, and @command{mawk} +also support @code{nextfile}. However, they don't allow the @code{nextfile} statement inside function bodies (@pxref{User-defined}). @command{gawk} does; a @code{nextfile} inside a function body reads the next record and starts processing it with the first rule in the program, @@ -12208,9 +14367,9 @@ The @code{exit} statement causes @command{awk} to immediately stop executing the current rule and to stop processing input; any remaining input is ignored. The @code{exit} statement is written as follows: -@example -exit @r{[}@var{return code}@r{]} -@end example +@display +@code{exit} [@var{return code}] +@end display @cindex @code{BEGIN} pattern, @code{exit} statement and @cindex @code{END} pattern, @code{exit} statement and @@ -12226,14 +14385,14 @@ the program to stop immediately. An @code{exit} statement that is not part of a @code{BEGIN} or @code{END} rule stops the execution of any further automatic rules for the current record, skips reading any remaining input records, and executes the -@code{END} rule if there is one. -Any @code{ENDFILE} rules are also skipped; they are not executed. +@code{END} rule if there is one. @command{gawk} also skips +any @code{ENDFILE} rules; they do not execute. In such a case, if you don't want the @code{END} rule to do its job, set a variable to nonzero before the @code{exit} statement and check that variable in the @code{END} rule. -@xref{Assert Function}, +@DBXREF{Assert Function} for an example that does this. @cindex dark corner, @code{exit} statement @@ -12243,9 +14402,8 @@ status code for the @command{awk} process. If no argument is supplied, In the case where an argument is supplied to a first @code{exit} statement, and then @code{exit} is called a second time from an @code{END} rule with no argument, -@command{awk} uses the previously supplied exit value. -@value{DARKCORNER} -@xref{Exit Status}, for more information. +@command{awk} uses the previously supplied exit value. @value{DARKCORNER} +@DBXREF{Exit Status} for more information. @cindex programming conventions, @code{exit} statement For example, suppose an error condition occurs that is difficult or @@ -12256,12 +14414,12 @@ in the following example: @example BEGIN @{ - if (("date" | getline date_now) <= 0) @{ - print "Can't get system date" > "/dev/stderr" - exit 1 - @} - print "current date is", date_now - close("date") + if (("date" | getline date_now) <= 0) @{ + print "Can't get system date" > "/dev/stderr" + exit 1 + @} + print "current date is", date_now + close("date") @} @end example @@ -12271,16 +14429,11 @@ Negative values, and values of 127 or greater, may not produce consistent results across different operating systems. @end quotation -@c ENDOFRANGE csta -@c ENDOFRANGE acs -@c ENDOFRANGE accs @node Built-in Variables -@section Built-in Variables -@c STARTOFRANGE bvar -@cindex built-in variables -@c STARTOFRANGE varb -@cindex variables, built-in +@section Predefined Variables +@cindex predefined variables +@cindex variables, predefined Most @command{awk} variables are available to use for your own purposes; they never change unless your program assigns values to @@ -12291,10 +14444,10 @@ to tell @command{awk} how to do certain things. Others are set automatically by @command{awk}, so that they carry information from the internal workings of @command{awk} to your program. -@cindex @command{gawk}, built-in variables and -This @value{SECTION} documents all the built-in variables of -@command{gawk}, most of which are also documented in the chapters -describing their areas of activity. +@cindex @command{gawk}, predefined variables and +This @value{SECTION} documents all of @command{gawk}'s predefined variables, +most of which are also documented in the @value{CHAPTER}s describing +their areas of activity. @menu * User-modified:: Built-in variables that you change to control @@ -12305,51 +14458,43 @@ describing their areas of activity. @end menu @node User-modified -@subsection Built-in Variables That Control @command{awk} -@c STARTOFRANGE bvaru -@cindex built-in variables, user-modifiable -@c STARTOFRANGE nmbv +@subsection Built-In Variables That Control @command{awk} +@cindex predefined variables, user-modifiable @cindex user-modifiable variables The following is an alphabetical list of variables that you can change to -control how @command{awk} does certain things. The variables that are -specific to @command{gawk} are marked with a pound sign@w{ (@samp{#}).} +control how @command{awk} does certain things. + +The variables that are specific to @command{gawk} are marked with a pound +sign (@samp{#}). These variables are @command{gawk} extensions. In other +@command{awk} implementations or if @command{gawk} is in compatibility +mode (@pxref{Options}), they are not special. (Any exceptions are noted +in the description of each variable.) @table @code @cindex @code{BINMODE} variable @cindex binary input/output @cindex input/output, binary -@item BINMODE # -On non-POSIX systems, this variable specifies use of binary mode for all I/O. -Numeric values of one, two, or three specify that input files, output files, or -all files, respectively, should use binary I/O. -A numeric value less than zero is treated as zero, and a numeric value greater than -three is treated as three. -Alternatively, -string values of @code{"r"} or @code{"w"} specify that input files and -output files, respectively, should use binary I/O. -A string value of @code{"rw"} or @code{"wr"} indicates that all -files should use binary I/O. -Any other string value is treated the same as @code{"rw"}, -but causes @command{gawk} -to generate a warning message. -@code{BINMODE} is described in more detail in -@ref{PC Using}. - @cindex differences in @command{awk} and @command{gawk}, @code{BINMODE} variable -This variable is a @command{gawk} extension. -In other @command{awk} implementations -(except @command{mawk}, -@pxref{Other Versions}), -or if @command{gawk} is in compatibility mode -(@pxref{Options}), -it is not special. +@item BINMODE # +On non-POSIX systems, this variable specifies use of binary mode +for all I/O. Numeric values of one, two, or three specify that input +files, output files, or all files, respectively, should use binary I/O. +A numeric value less than zero is treated as zero, and a numeric value +greater than three is treated as three. Alternatively, string values +of @code{"r"} or @code{"w"} specify that input files and output files, +respectively, should use binary I/O. A string value of @code{"rw"} or +@code{"wr"} indicates that all files should use binary I/O. Any other +string value is treated the same as @code{"rw"}, but causes @command{gawk} +to generate a warning message. @code{BINMODE} is described in more +detail in @ref{PC Using}. @command{mawk} (@pxref{Other Versions}), +also supports this variable, but only using numeric values. @cindex @code{CONVFMT} variable @cindex POSIX @command{awk}, @code{CONVFMT} variable and @cindex numbers, converting, to strings @cindex strings, converting, numbers to -@item CONVFMT +@item @code{CONVFMT} This string controls conversion of numbers to strings (@pxref{Conversion}). It works by being passed, in effect, as the first argument to the @@ -12364,16 +14509,11 @@ Its default value is @code{"%.6g"}. @cindex field separators, @code{FIELDWIDTHS} variable and @cindex separators, field, @code{FIELDWIDTHS} variable and @item FIELDWIDTHS # -This is a space-separated list of columns that tells @command{gawk} +A space-separated list of columns that tells @command{gawk} how to split input with fixed columnar boundaries. Assigning a value to @code{FIELDWIDTHS} overrides the use of @code{FS} and @code{FPAT} for field splitting. -@xref{Constant Size}, for more information. - -If @command{gawk} is in compatibility mode -(@pxref{Options}), then @code{FIELDWIDTHS} -has no special meaning, and field-splitting operations occur based -exclusively on the value of @code{FS}. +@DBXREF{Constant Size} for more information. @cindex @command{gawk}, @code{FPAT} variable in @cindex @code{FPAT} variable @@ -12381,24 +14521,18 @@ exclusively on the value of @code{FS}. @cindex field separators, @code{FPAT} variable and @cindex separators, field, @code{FPAT} variable and @item FPAT # -This is a regular expression (as a string) that tells @command{gawk} +A regular expression (as a string) that tells @command{gawk} to create the fields based on text that matches the regular expression. Assigning a value to @code{FPAT} overrides the use of @code{FS} and @code{FIELDWIDTHS} for field splitting. -@xref{Splitting By Content}, for more information. - -If @command{gawk} is in compatibility mode -(@pxref{Options}), then @code{FPAT} -has no special meaning, and field-splitting operations occur based -exclusively on the value of @code{FS}. +@DBXREF{Splitting By Content} for more information. @cindex @code{FS} variable @cindex separators, field @cindex field separators @item FS -This is the input field separator -(@pxref{Field Separators}). -The value is a single-character string or a multi-character regular +The input field separator (@pxref{Field Separators}). +The value is a single-character string or a multicharacter regular expression that matches the separations between fields in an input record. If the value is the null string (@code{""}), then each character in the record becomes a separate field. @@ -12431,8 +14565,8 @@ is to simply say @samp{FS = FS}, perhaps with an explanatory comment. @cindex @command{gawk}, @code{IGNORECASE} variable in @cindex @code{IGNORECASE} variable @cindex differences in @command{awk} and @command{gawk}, @code{IGNORECASE} variable -@cindex case sensitivity, string comparisons and -@cindex case sensitivity, regexps and +@cindex case sensitivity, and string comparisons +@cindex case sensitivity, and regexps @cindex regular expressions, case sensitivity @item IGNORECASE # If @code{IGNORECASE} is nonzero or non-null, then all string comparisons @@ -12447,18 +14581,13 @@ and it does not affect field splitting when using a single-character field separator. @xref{Case-sensitivity}. -If @command{gawk} is in compatibility mode -(@pxref{Options}), -then @code{IGNORECASE} has no special meaning. Thus, string -and regexp operations are always case-sensitive. - @cindex @command{gawk}, @code{LINT} variable in @cindex @code{LINT} variable @cindex differences in @command{awk} and @command{gawk}, @code{LINT} variable @cindex lint checking @item LINT # When this variable is true (nonzero or non-null), @command{gawk} -behaves as if the @option{--lint} command-line option is in effect. +behaves as if the @option{--lint} command-line option is in effect (@pxref{Options}). With a value of @code{"fatal"}, lint warnings become fatal errors. With a value of @code{"invalid"}, only warnings about things that are @@ -12479,13 +14608,13 @@ of @command{awk} being executed. @cindex numbers, converting, to strings @cindex strings, converting, numbers to @item OFMT -This string controls conversion of numbers to +Controls conversion of numbers to strings (@pxref{Conversion}) for printing with the @code{print} statement. It works by being passed as the first argument to the @code{sprintf()} function (@pxref{String Functions}). Its default value is @code{"%.6g"}. Earlier versions of @command{awk} -also used @code{OFMT} to specify the format for converting numbers to +used @code{OFMT} to specify the format for converting numbers to strings in general expressions; this is now done by @code{CONVFMT}. @cindex @code{sprintf()} function, @code{OFMT} variable and @@ -12500,15 +14629,26 @@ default value is @w{@code{" "}}, a string consisting of a single space. @cindex @code{ORS} variable @item ORS -This is the output record separator. It is output at the end of every +The output record separator. It is output at the end of every @code{print} statement. Its default value is @code{"\n"}, the newline character. (@xref{Output Separators}.) +@cindex @code{PREC} variable +@item PREC # +The working precision of arbitrary-precision floating-point numbers, +53 bits by default (@pxref{Setting precision}). + +@cindex @code{ROUNDMODE} variable +@item ROUNDMODE # +The rounding mode to use for arbitrary-precision arithmetic on +numbers, by default @code{"N"} (@samp{roundTiesToEven} in +the IEEE 754 standard; @pxref{Setting the rounding mode}). + @cindex @code{RS} variable @cindex separators, for records @cindex record separators -@item RS -This is @command{awk}'s input record separator. Its default value is a string +@item @code{RS} +The input record separator. Its default value is a string containing a single newline character, which means that an input record consists of a single line of text. It can also be the null string, in which case records are separated by @@ -12527,53 +14667,46 @@ just the first character of @code{RS}'s value is used. @cindex @code{SUBSEP} variable @cindex separators, subscript @cindex subscript separators -@item SUBSEP -This is the subscript separator. It has the default value of +@item @code{SUBSEP} +The subscript separator. It has the default value of @code{"\034"} and is used to separate the parts of the indices of a multidimensional array. Thus, the expression @code{@w{foo["A", "B"]}} really accesses @code{foo["A\034B"]} -(@pxref{Multi-dimensional}). +(@pxref{Multidimensional}). @cindex @command{gawk}, @code{TEXTDOMAIN} variable in @cindex @code{TEXTDOMAIN} variable @cindex differences in @command{awk} and @command{gawk}, @code{TEXTDOMAIN} variable @cindex internationalization, localization @item TEXTDOMAIN # -This variable is used for internationalization of programs at the +Used for internationalization of programs at the @command{awk} level. It sets the default text domain for specially marked string constants in the source text, as well as for the -@code{dcgettext()}, @code{dcngettext()} and @code{bindtextdomain()} functions +@code{dcgettext()}, @code{dcngettext()}, and @code{bindtextdomain()} functions (@pxref{Internationalization}). The default value of @code{TEXTDOMAIN} is @code{"messages"}. - -This variable is a @command{gawk} extension. -In other @command{awk} implementations, -or if @command{gawk} is in compatibility mode -(@pxref{Options}), -it is not special. @end table -@c ENDOFRANGE bvar -@c ENDOFRANGE varb -@c ENDOFRANGE bvaru -@c ENDOFRANGE nmbv @node Auto-set -@subsection Built-in Variables That Convey Information +@subsection Built-In Variables That Convey Information -@c STARTOFRANGE bvconi -@cindex built-in variables, conveying information -@c STARTOFRANGE vbconi -@cindex variables, built-in, conveying information +@cindex predefined variables, conveying information +@cindex variables, predefined conveying information The following is an alphabetical list of variables that @command{awk} sets automatically on certain occasions in order to provide -information to your program. The variables that are specific to -@command{gawk} are marked with a pound sign@w{ (@samp{#}).} +information to your program. -@table @code +The variables that are specific to @command{gawk} are marked with a pound +sign (@samp{#}). These variables are @command{gawk} extensions. In other +@command{awk} implementations or if @command{gawk} is in compatibility +mode (@pxref{Options}), they are not special: + +@c @asis for docbook +@table @asis @cindex @code{ARGC}/@code{ARGV} variables @cindex arguments, command-line @cindex command line, arguments -@item ARGC@r{,} ARGV +@item @code{ARGC}, @code{ARGV} The command-line arguments available to @command{awk} programs are stored in an array called @code{ARGV}. @code{ARGC} is the number of command-line arguments present. @xref{Other Arguments}. @@ -12585,16 +14718,16 @@ In the following example: $ @kbd{awk 'BEGIN @{} > @kbd{for (i = 0; i < ARGC; i++)} > @kbd{print ARGV[i]} -> @kbd{@}' inventory-shipped BBS-list} +> @kbd{@}' inventory-shipped mail-list} @print{} awk @print{} inventory-shipped -@print{} BBS-list +@print{} mail-list @end example @noindent @code{ARGV[0]} contains @samp{awk}, @code{ARGV[1]} contains @samp{inventory-shipped}, and @code{ARGV[2]} contains -@samp{BBS-list}. The value of @code{ARGC} is three, one more than the +@samp{mail-list}. The value of @code{ARGC} is three, one more than the index of the last element in @code{ARGV}, because the elements are numbered from zero. @@ -12607,13 +14740,13 @@ method of accessing command-line arguments. The value of @code{ARGV[0]} can vary from system to system. Also, you should note that the program text is @emph{not} included in @code{ARGV}, nor are any of @command{awk}'s command-line options. -@xref{ARGC and ARGV}, for information +@DBXREF{ARGC and ARGV} for information about how @command{awk} uses these variables. @value{DARKCORNER} @cindex @code{ARGIND} variable @cindex differences in @command{awk} and @command{gawk}, @code{ARGIND} variable -@item ARGIND # +@item @code{ARGIND #} The index in @code{ARGV} of the current file being processed. Every time @command{gawk} opens a new @value{DF} for processing, it sets @code{ARGIND} to the index in @code{ARGV} of the @value{FN}. @@ -12625,128 +14758,138 @@ This variable is useful in file processing; it allows you to tell how far along you are in the list of @value{DF}s as well as to distinguish between successive instances of the same @value{FN} on the command line. -@cindex @value{FN}s, distinguishing +@cindex file names, distinguishing While you can change the value of @code{ARGIND} within your @command{awk} -program, @command{gawk} automatically sets it to a new value when the -next file is opened. - -This variable is a @command{gawk} extension. -In other @command{awk} implementations, -or if @command{gawk} is in compatibility mode -(@pxref{Options}), -it is not special. +program, @command{gawk} automatically sets it to a new value when it +opens the next file. @cindex @code{ENVIRON} array -@cindex environment variables -@item ENVIRON +@cindex environment variables, in @code{ENVIRON} array +@item @code{ENVIRON} An associative array containing the values of the environment. The array indices are the environment variable names; the elements are the values of the particular environment variables. For example, -@code{ENVIRON["HOME"]} might be @file{/home/arnold}. Changing this array -does not affect the environment passed on to any programs that -@command{awk} may spawn via redirection or the @code{system()} function. -@c (In a future version of @command{gawk}, it may do so.) +@code{ENVIRON["HOME"]} might be @code{/home/arnold}. + +For POSIX @command{awk}, changing this array does not affect the +environment passed on to any programs that @command{awk} may spawn via +redirection or the @code{system()} function. + +However, beginning with version 4.2, if not in POSIX +compatibility mode, @command{gawk} does update its own environment when +@code{ENVIRON} is changed, thus changing the environment seen by programs +that it creates. You should therefore be especially careful if you +modify @code{ENVIRON["PATH"]"}, which is the search path for finding +executable programs. + +This can also affect the running @command{gawk} program, since some of the +built-in functions may pay attention to certain environment variables. +The most notable instance of this is @code{mktime()} (@pxref{Time +Functions}), which pays attention the value of the @env{TZ} environment +variable on many systems. Some operating systems may not have environment variables. On such systems, the @code{ENVIRON} array is empty (except for -@w{@code{ENVIRON["AWKPATH"]}}, -@pxref{AWKPATH Variable}). +@w{@code{ENVIRON["AWKPATH"]}} and +@w{@code{ENVIRON["AWKLIBPATH"]}}; +@DBPXREF{AWKPATH Variable} and +@ifdocbook +@DBREF{AWKLIBPATH Variable}). +@end ifdocbook +@ifnotdocbook +@pxref{AWKLIBPATH Variable}). +@end ifnotdocbook @cindex @command{gawk}, @code{ERRNO} variable in @cindex @code{ERRNO} variable @cindex differences in @command{awk} and @command{gawk}, @code{ERRNO} variable @cindex error handling, @code{ERRNO} variable and -@item ERRNO # -If a system error occurs during a redirection for @code{getline}, -during a read for @code{getline}, or during a @code{close()} operation, -then @code{ERRNO} contains a string describing the error. - -In addition, @command{gawk} clears @code{ERRNO} -before opening each command-line input file. This enables checking if -the file is readable inside a @code{BEGINFILE} pattern (@pxref{BEGINFILE/ENDFILE}). - -Otherwise, -@code{ERRNO} works similarly to the C variable @code{errno}. -Except for the case just mentioned, -@command{gawk} @emph{never} clears it (sets it -to zero or @code{""}). Thus, you should only expect its value -to be meaningful when an I/O operation returns a failure -value, such as @code{getline} returning @minus{}1. -You are, of course, free to clear it yourself before doing an -I/O operation. - -This variable is a @command{gawk} extension. -In other @command{awk} implementations, -or if @command{gawk} is in compatibility mode -(@pxref{Options}), -it is not special. +@item @code{ERRNO #} +If a system error occurs during a redirection for @code{getline}, during +a read for @code{getline}, or during a @code{close()} operation, then +@code{ERRNO} contains a string describing the error. + +In addition, @command{gawk} clears @code{ERRNO} before opening each +command-line input file. This enables checking if the file is readable +inside a @code{BEGINFILE} pattern (@pxref{BEGINFILE/ENDFILE}). + +Otherwise, @code{ERRNO} works similarly to the C variable @code{errno}. +Except for the case just mentioned, @command{gawk} @emph{never} clears +it (sets it to zero or @code{""}). Thus, you should only expect its +value to be meaningful when an I/O operation returns a failure value, +such as @code{getline} returning @minus{}1. You are, of course, free +to clear it yourself before doing an I/O operation. @cindex @code{FILENAME} variable @cindex dark corner, @code{FILENAME} variable -@item FILENAME -The name of the file that @command{awk} is currently reading. -When no @value{DF}s are listed on the command line, @command{awk} reads -from the standard input and @code{FILENAME} is set to @code{"-"}. -@code{FILENAME} is changed each time a new file is read -(@pxref{Reading Files}). -Inside a @code{BEGIN} rule, the value of @code{FILENAME} is -@code{""}, since there are no input files being processed -yet.@footnote{Some early implementations of Unix @command{awk} initialized -@code{FILENAME} to @code{"-"}, even if there were @value{DF}s to be -processed. This behavior was incorrect and should not be relied -upon in your programs.} -@value{DARKCORNER} -Note, though, that using @code{getline} -(@pxref{Getline}) -inside a @code{BEGIN} rule can give -@code{FILENAME} a value. +@item @code{FILENAME} +The name of the current input file. When no @value{DF}s are listed +on the command line, @command{awk} reads from the standard input and +@code{FILENAME} is set to @code{"-"}. @code{FILENAME} changes each +time a new file is read (@pxref{Reading Files}). Inside a @code{BEGIN} +rule, the value of @code{FILENAME} is @code{""}, because there are no input +files being processed yet.@footnote{Some early implementations of Unix +@command{awk} initialized @code{FILENAME} to @code{"-"}, even if there +were @value{DF}s to be processed. This behavior was incorrect and should +not be relied upon in your programs.} @value{DARKCORNER} Note, though, +that using @code{getline} (@pxref{Getline}) inside a @code{BEGIN} rule +can give @code{FILENAME} a value. @cindex @code{FNR} variable -@item FNR -The current record number in the current file. @code{FNR} is -incremented each time a new record is read -(@pxref{Records}). It is reinitialized -to zero each time a new input file is started. +@item @code{FNR} +The current record number in the current file. @command{awk} increments +@code{FNR} each time it reads a new record (@pxref{Records}). +@command{awk} resets @code{FNR} to zero each time it starts a new +input file. @cindex @code{NF} variable -@item NF +@item @code{NF} The number of fields in the current input record. @code{NF} is set each time a new record is read, when a new field is created or when @code{$0} changes (@pxref{Fields}). -Unlike most of the variables described in this -@ifnotinfo -section, -@end ifnotinfo -@ifinfo -node, -@end ifinfo +Unlike most of the variables described in this @value{SUBSECTION}, assigning a value to @code{NF} has the potential to affect @command{awk}'s internal workings. In particular, assignments to @code{NF} can be used to create or remove fields from the current record. @xref{Changing Fields}. +@cindex @code{FUNCTAB} array +@cindex @command{gawk}, @code{FUNCTAB} array in +@cindex differences in @command{awk} and @command{gawk}, @code{FUNCTAB} variable +@item @code{FUNCTAB #} +An array whose indices and corresponding values are the names of all +the built-in, user-defined, and extension functions in the program. + +@quotation NOTE +Attempting to use the @code{delete} statement with the @code{FUNCTAB} +array causes a fatal error. Any attempt to assign to an element of +@code{FUNCTAB} also causes a fatal error. +@end quotation + @cindex @code{NR} variable -@item NR +@item @code{NR} The number of input records @command{awk} has processed since the beginning of the program's execution (@pxref{Records}). -@code{NR} is incremented each time a new record is read. +@command{awk} increments @code{NR} each time it reads a new record. @cindex @command{gawk}, @code{PROCINFO} array in @cindex @code{PROCINFO} array @cindex differences in @command{awk} and @command{gawk}, @code{PROCINFO} array -@item PROCINFO # +@item @code{PROCINFO #} The elements of this array provide access to information about the running @command{awk} program. The following elements (listed alphabetically) are guaranteed to be available: @table @code +@cindex effective group ID of @command{gawk} user @item PROCINFO["egid"] The value of the @code{getegid()} system call. @item PROCINFO["euid"] +@cindex effective user ID of @command{gawk} user The value of the @code{geteuid()} system call. @item PROCINFO["FS"] @@ -12755,23 +14898,62 @@ This is @code{"FIELDWIDTHS"} if field splitting with @code{FIELDWIDTHS} is in effect, or @code{"FPAT"} if field matching with @code{FPAT} is in effect. +@item PROCINFO["identifiers"] +@cindex program identifiers +A subarray, indexed by the names of all identifiers used in the text of +the AWK program. An @dfn{identifier} is simply the name of a variable +(be it scalar or array), built-in function, user-defined function, or +extension function. For each identifier, the value of the element is +one of the following: + +@table @code +@item "array" +The identifier is an array. + +@item "builtin" +The identifier is a built-in function. + +@item "extension" +The identifier is an extension function loaded via +@code{@@load} or @option{-l}. + +@item "scalar" +The identifier is a scalar. + +@item "untyped" +The identifier is untyped (could be used as a scalar or array, +@command{gawk} doesn't know yet). + +@item "user" +The identifier is a user-defined function. +@end table + +@noindent +The values indicate what @command{gawk} knows about the identifiers +after it has finished parsing the program; they are @emph{not} updated +while the program runs. + @item PROCINFO["gid"] +@cindex group ID of @command{gawk} user The value of the @code{getgid()} system call. @item PROCINFO["pgrpid"] +@cindex process group idIDof @command{gawk} process The process group ID of the current process. @item PROCINFO["pid"] +@cindex process ID of @command{gawk} process The process ID of the current process. @item PROCINFO["ppid"] +@cindex parent process ID of @command{gawk} process The parent process ID of the current process. @item PROCINFO["sorted_in"] If this element exists in @code{PROCINFO}, its value controls the order in which array indices will be processed by -@samp{for (index in array) @dots{}} loops. -Since this is an advanced feature, we defer the +@samp{for (@var{indx} in @var{array})} loops. +This is an advanced feature, so we defer the full description until later; see @ref{Scanning an Array}. @@ -12784,9 +14966,50 @@ Assigning a new value to this element changes the default. The value of the @code{getuid()} system call. @item PROCINFO["version"] +@cindex version of @command{gawk} +@cindex @command{gawk} version The version of @command{gawk}. @end table +The following additional elements in the array +are available to provide information about the MPFR and GMP libraries +if your version of @command{gawk} supports arbitrary-precision arithmetic +(@pxref{Arbitrary Precision Arithmetic}): + +@table @code +@cindex version of GNU MPFR library +@item PROCINFO["mpfr_version"] +The version of the GNU MPFR library. + +@item PROCINFO["gmp_version"] +@cindex version of GNU MP library +The version of the GNU MP library. + +@item PROCINFO["prec_max"] +@cindex maximum precision supported by MPFR library +The maximum precision supported by MPFR. + +@item PROCINFO["prec_min"] +@cindex minimum precision supported by MPFR library +The minimum precision required by MPFR. +@end table + +The following additional elements in the array are available to provide +information about the version of the extension API, if your version +of @command{gawk} supports dynamic loading of extension functions +(@pxref{Dynamic Extensions}): + +@table @code +@item PROCINFO["api_major"] +@cindex version of @command{gawk} extension API +@cindex extension API, version number +The major version of the extension API. + +@item PROCINFO["api_minor"] +The minor version of the extension API. +@end table + +@cindex supplementary groups of @command{gawk} process On some systems, there may be elements in the array, @code{"group1"} through @code{"group@var{N}"} for some @var{N}. @var{N} is the number of supplementary groups that the process has. Use the @code{in} operator @@ -12794,19 +15017,23 @@ to test for these elements (@pxref{Reference to Elements}). @cindex @command{gawk}, @code{PROCINFO} array in -@cindex @code{PROCINFO} array -The @code{PROCINFO} array is also used to cause coprocesses -to communicate over pseudo-ttys instead of through two-way pipes; -this is discussed further in @ref{Two-way I/O}. +@cindex @code{PROCINFO} array, uses +The @code{PROCINFO} array has the following additional uses: -This array is a @command{gawk} extension. -In other @command{awk} implementations, -or if @command{gawk} is in compatibility mode -(@pxref{Options}), -it is not special. +@itemize @value{BULLET} +@item +It may be used to provide a timeout when reading from any +open input file, pipe, or coprocess. +@DBXREF{Read Timeout} for more information. + +@item +It may be used to cause coprocesses to communicate over pseudo-ttys +instead of through two-way pipes; this is discussed further in +@ref{Two-way I/O}. +@end itemize @cindex @code{RLENGTH} variable -@item RLENGTH +@item @code{RLENGTH} The length of the substring matched by the @code{match()} function (@pxref{String Functions}). @@ -12814,7 +15041,7 @@ The length of the substring matched by the is the length of the matched string, or @minus{}1 if no match is found. @cindex @code{RSTART} variable -@item RSTART +@item @code{RSTART} The start-index in characters of the substring that is matched by the @code{match()} function (@pxref{String Functions}). @@ -12825,24 +15052,75 @@ if no match was found. @cindex @command{gawk}, @code{RT} variable in @cindex @code{RT} variable @cindex differences in @command{awk} and @command{gawk}, @code{RT} variable -@item RT # -This is set each time a record is read. It contains the input text -that matched the text denoted by @code{RS}, the record separator. +@item @code{RT #} +The input text that matched the text denoted by @code{RS}, +the record separator. It is set every time a record is read. -This variable is a @command{gawk} extension. -In other @command{awk} implementations, -or if @command{gawk} is in compatibility mode -(@pxref{Options}), -it is not special. +@cindex @command{gawk}, @code{SYMTAB} array in +@cindex @code{SYMTAB} array +@cindex differences in @command{awk} and @command{gawk}, @code{SYMTAB} variable +@item @code{SYMTAB #} +An array whose indices are the names of all defined global variables and +arrays in the program. @code{SYMTAB} makes @command{gawk}'s symbol table +visible to the @command{awk} programmer. It is built as @command{gawk} +parses the program and is complete before the program starts to run. + +The array may be used for indirect access to read or write the value of +a variable: + +@example +foo = 5 +SYMTAB["foo"] = 4 +print foo # prints 4 +@end example + +@noindent +The @code{isarray()} function (@pxref{Type Functions}) may be used to test +if an element in @code{SYMTAB} is an array. +Also, you may not use the @code{delete} statement with the +@code{SYMTAB} array. + +You may use an index for @code{SYMTAB} that is not a predefined identifier: + +@example +SYMTAB["xxx"] = 5 +print SYMTAB["xxx"] +@end example + +@noindent +This works as expected: in this case @code{SYMTAB} acts just like +a regular array. The only difference is that you can't then delete +@code{SYMTAB["xxx"]}. + +@cindex Schorr, Andrew +The @code{SYMTAB} array is more interesting than it looks. Andrew Schorr +points out that it effectively gives @command{awk} data pointers. Consider his +example: + +@example +# Indirect multiply of any variable by amount, return result + +function multiply(variable, amount) +@{ + return SYMTAB[variable] *= amount +@} +@end example + +@quotation NOTE +In order to avoid severe time-travel paradoxes,@footnote{Not to mention difficult +implementation issues.} neither @code{FUNCTAB} nor @code{SYMTAB} +are available as elements within the @code{SYMTAB} array. +@end quotation @end table -@c ENDOFRANGE bvconi -@c ENDOFRANGE vbconi -@c fakenode --- for prepinfo -@subheading Advanced Notes: Changing @code{NR} and @code{FNR} +@cindex sidebar, Changing @code{NR} and @code{FNR} +@ifdocbook +@docbook +<sidebar><title>Changing @code{NR} and @code{FNR}</title> +@end docbook + @cindex @code{NR} variable, changing @cindex @code{FNR} variable, changing -@cindex advanced features, @code{FNR}/@code{NR} variables @cindex dark corner, @code{FNR}/@code{NR} variables @command{awk} increments @code{NR} and @code{FNR} each time it reads a record, instead of setting them to the absolute @@ -12871,13 +15149,55 @@ many @command{awk} programs used this feature to track the number of records in a file by resetting @code{NR} to zero when @code{FILENAME} changed. +@docbook +</sidebar> +@end docbook +@end ifdocbook + +@ifnotdocbook +@cartouche +@center @b{Changing @code{NR} and @code{FNR}} + + +@cindex @code{NR} variable, changing +@cindex @code{FNR} variable, changing +@cindex dark corner, @code{FNR}/@code{NR} variables +@command{awk} increments @code{NR} and @code{FNR} +each time it reads a record, instead of setting them to the absolute +value of the number of records read. This means that a program can +change these variables and their new values are incremented for +each record. +@value{DARKCORNER} +The following example shows this: + +@example +$ @kbd{echo '1} +> @kbd{2} +> @kbd{3} +> @kbd{4' | awk 'NR == 2 @{ NR = 17 @}} +> @kbd{@{ print NR @}'} +@print{} 1 +@print{} 17 +@print{} 18 +@print{} 19 +@end example + +@noindent +Before @code{FNR} was added to the @command{awk} language +(@pxref{V7/SVR3.1}), +many @command{awk} programs used this feature to track the number of +records in a file by resetting @code{NR} to zero when @code{FILENAME} +changed. +@end cartouche +@end ifnotdocbook + @node ARGC and ARGV @subsection Using @code{ARGC} and @code{ARGV} -@cindex @code{ARGC}/@code{ARGV} variables +@cindex @code{ARGC}/@code{ARGV} variables, how to use @cindex arguments, command-line @cindex command line, arguments -@ref{Auto-set}, +@DBREF{Auto-set} presented the following program describing the information contained in @code{ARGC} and @code{ARGV}: @@ -12885,16 +15205,16 @@ and @code{ARGV}: $ @kbd{awk 'BEGIN @{} > @kbd{for (i = 0; i < ARGC; i++)} > @kbd{print ARGV[i]} -> @kbd{@}' inventory-shipped BBS-list} +> @kbd{@}' inventory-shipped mail-list} @print{} awk @print{} inventory-shipped -@print{} BBS-list +@print{} mail-list @end example @noindent In this example, @code{ARGV[0]} contains @samp{awk}, @code{ARGV[1]} contains @samp{inventory-shipped}, and @code{ARGV[2]} contains -@samp{BBS-list}. +@samp{mail-list}. Notice that the @command{awk} program is not entered in @code{ARGV}. The other command-line options, with their arguments, are also not entered. This includes variable assignments done with the @option{-v} @@ -12947,11 +15267,26 @@ use the @code{delete} statement to remove elements from All of these actions are typically done in the @code{BEGIN} rule, before actual processing of the input begins. -@xref{Split Program}, and see -@ref{Tee Program}, for examples +@DBXREF{Split Program} and +@ifnotdocbook +@DBPXREF{Tee Program} +@end ifnotdocbook +@ifdocbook +@DBREF{Tee Program} +@end ifdocbook +for examples of each way of removing elements from @code{ARGV}. + +To actually get options into an @command{awk} program, +end the @command{awk} options with @option{--} and then supply +the @command{awk} program's options, in the following manner: + +@example +awk -f myprog.awk -- -v -q file1 file2 @dots{} +@end example + The following fragment processes @code{ARGV} in order to examine, and -then remove, command-line options: +then remove, the previously mentioned command-line options: @example BEGIN @{ @@ -12971,36 +15306,104 @@ BEGIN @{ @} @end example -To actually get the options into the @command{awk} program, -end the @command{awk} options with @option{--} and then supply -the @command{awk} program's options, in the following manner: - -@example -awk -f myprog -- -v -q file1 file2 @dots{} -@end example - @cindex differences in @command{awk} and @command{gawk}, @code{ARGC}/@code{ARGV} variables -This is not necessary in @command{gawk}. Unless @option{--posix} has +Ending the @command{awk} options with @option{--} isn't +necessary in @command{gawk}. Unless @option{--posix} has been specified, @command{gawk} silently puts any unrecognized options into @code{ARGV} for the @command{awk} program to deal with. As soon as it sees an unknown option, @command{gawk} stops looking for other -options that it might otherwise recognize. The previous example with +options that it might otherwise recognize. The previous command line with @command{gawk} would be: @example -gawk -f myprog -q -v file1 file2 @dots{} +gawk -f myprog.awk -q -v file1 file2 @dots{} @end example @noindent -Because @option{-q} is not a valid @command{gawk} option, -it and the following @option{-v} -are passed on to the @command{awk} program. -(@xref{Getopt Function}, for an @command{awk} library function -that parses command-line options.) +Because @option{-q} is not a valid @command{gawk} option, it and the +following @option{-v} are passed on to the @command{awk} program. +(@DBXREF{Getopt Function} for an @command{awk} library function that +parses command-line options.) + +When designing your program, you should choose options that don't +conflict with @command{gawk}'s, because it will process any options +that it accepts before passing the rest of the command line on to +your program. Using @samp{#!} with the @option{-E} option may help +(@DBXREF{Executable Scripts} +and +@ifnotdocbook +@DBPXREF{Options}). +@end ifnotdocbook +@ifdocbook +@DBREF{Options}). +@end ifdocbook + +@node Pattern Action Summary +@section Summary + +@itemize @value{BULLET} +@item +Pattern-action pairs make up the basic elements of an @command{awk} +program. Patterns are either normal expressions, range expressions, +regexp constants, one of the special keywords @code{BEGIN}, @code{END}, +@code{BEGINFILE}, @code{ENDFILE}, or empty. The action executes if +the current record matches the pattern. Empty (missing) patterns match +all records. + +@item +I/O from @code{BEGIN} and @code{END} rules have certain constraints. +This is also true, only more so, for @code{BEGINFILE} and @code{ENDFILE} +rules. The latter two give you ``hooks'' into @command{gawk}'s file +processing, allowing you to recover from a file that otherwise would +cause a fatal error (such as a file that cannot be opened). + +@item +Shell variables can be used in @command{awk} programs by careful +use of shell quoting. It is easier to pass a shell variable into +@command{awk} by using the @option{-v} option and an @command{awk} +variable. + +@item +Actions consist of statements enclosed in curly braces. Statements +are built up from expressions, control statements, compound statements, +input and output statements, and deletion statements. + +@item +The control statements in @command{awk} are @code{if}-@code{else}, +@code{while}, @code{for}, and @code{do}-@code{while}. @command{gawk} +adds the @code{switch} statement. There are two flavors of @code{for} +statement: one for performing general looping, and the other for iterating +through an array. + +@item +@code{break} and @code{continue} let you exit early or start the next +iteration of a loop (or get out of a @code{switch}). + +@item +@code{next} and @code{nextfile} let you read the next record and start +over at the top of your program, or skip to the next input file and +start over, respectively. + +@item +The @code{exit} statement terminates your program. When executed +from an action (or function body) it transfers control to the +@code{END} statements. From an @code{END} statement body, it exits +immediately. You may pass an optional numeric value to be used +as @command{awk}'s exit status. + +@item +Some predefined variables provide control over @command{awk}, mainly for I/O. +Other variables convey information from @command{awk} to your program. + +@item +@code{ARGC} and @code{ARGV} make the command-line arguments available +to your program. Manipulating them from a @code{BEGIN} rule lets you +control how @command{awk} will process the provided @value{DF}s. + +@end itemize @node Arrays @chapter Arrays in @command{awk} -@c STARTOFRANGE arrs @cindex arrays An @dfn{array} is a table of values called @dfn{elements}. The @@ -13014,29 +15417,19 @@ It also describes how @command{awk} simulates multidimensional arrays, as well as some of the less obvious points about array usage. The @value{CHAPTER} moves on to discuss @command{gawk}'s facility for sorting arrays, and ends with a brief description of @command{gawk}'s -ability to support true multidimensional arrays. - -@cindex variables, names of -@cindex functions, names of -@cindex arrays, names of -@cindex names, arrays/variables -@cindex namespace issues -@command{awk} maintains a single set -of names that may be used for naming variables, arrays, and functions -(@pxref{User-defined}). -Thus, you cannot have a variable and an array with the same name in the -same @command{awk} program. +ability to support true arrays of arrays. @menu * Array Basics:: The basics of arrays. -* Delete:: The @code{delete} statement removes an element - from an array. * Numeric Array Subscripts:: How to use numbers as subscripts in @command{awk}. * Uninitialized Subscripts:: Using Uninitialized variables as subscripts. -* Multi-dimensional:: Emulating multidimensional arrays in +* Delete:: The @code{delete} statement removes an element + from an array. +* Multidimensional:: Emulating multidimensional arrays in @command{awk}. * Arrays of Arrays:: True multidimensional arrays. +* Arrays Summary:: Summary of arrays. @end menu @node Array Basics @@ -13054,6 +15447,8 @@ an array. * Scanning an Array:: A variation of the @code{for} statement. It loops through the indices of an array's existing elements. +* Controlling Scanning:: Controlling the order in which arrays are + scanned. @end menu @node Array Intro @@ -13062,8 +15457,8 @@ an array. @cindex Wall, Larry @quotation @i{Doing linear scans over an associative array is like trying to club someone -to death with a loaded Uzi.}@* -Larry Wall +to death with a loaded Uzi.} +@author Larry Wall @end quotation The @command{awk} language provides one-dimensional arrays @@ -13076,7 +15471,7 @@ as a variable) in the same @command{awk} program. Arrays in @command{awk} superficially resemble arrays in other programming languages, but there are fundamental differences. In @command{awk}, it isn't necessary to specify the size of an array before starting to use it. -Additionally, any number or string in @command{awk}, not just consecutive integers, +Additionally, any number or string, not just consecutive integers, may be used as an array index. In most other languages, arrays must be @dfn{declared} before use, @@ -13096,65 +15491,107 @@ the array is declared.) A contiguous array of four elements might look like the following example, conceptually, if the element values are 8, @code{"foo"}, -@code{""}, and 30: +@code{""}, and 30 +@ifnotdocbook +as shown in @ref{figure-array-elements}: +@end ifnotdocbook +@ifdocbook +as shown in @inlineraw{docbook, <xref linkend="figure-array-elements"/>}: +@end ifdocbook -@c @strong{FIXME: NEXT ED:} Use real images here -@iftex -@c from Karl Berry, much thanks for the help. -@tex -\bigskip % space above the table (about 1 linespace) -\offinterlineskip -\newdimen\width \width = 1.5cm -\newdimen\hwidth \hwidth = 4\width \advance\hwidth by 2pt % 5 * 0.4pt -\centerline{\vbox{ -\halign{\strut\hfil\ignorespaces#&&\vrule#&\hbox to\width{\hfil#\unskip\hfil}\cr -\noalign{\hrule width\hwidth} - &&{\tt 8} &&{\tt "foo"} &&{\tt ""} &&{\tt 30} &&\quad Value\cr -\noalign{\hrule width\hwidth} -\noalign{\smallskip} - &\omit&0&\omit &1 &\omit&2 &\omit&3 &\omit&\quad Index\cr -} -}} -@end tex -@end iftex -@ifnottex -@example -+---------+---------+--------+---------+ -| 8 | "foo" | "" | 30 | @r{Value} -+---------+---------+--------+---------+ - 0 1 2 3 @r{Index} -@end example -@end ifnottex +@ifnotdocbook +@float Figure,figure-array-elements +@caption{A contiguous array} +@ifinfo +@center @image{array-elements, , , Basic Program Stages, txt} +@end ifinfo +@ifnotinfo +@center @image{array-elements, , , Basic Program Stages} +@end ifnotinfo +@end float +@end ifnotdocbook + +@docbook +<figure id="figure-array-elements" float="0"> +<title>A contiguous array</title> +<mediaobject> +<imageobject role="web"><imagedata fileref="array-elements.png" format="PNG"/></imageobject> +</mediaobject> +</figure> +@end docbook @noindent Only the values are stored; the indices are implicit from the order of the values. Here, 8 is the value at index zero, because 8 appears in the position with zero elements before it. -@c STARTOFRANGE arrin @cindex arrays, indexing -@c STARTOFRANGE inarr @cindex indexing arrays @cindex associative arrays @cindex arrays, associative Arrays in @command{awk} are different---they are @dfn{associative}. This means -that each array is a collection of pairs: an index and its corresponding +that each array is a collection of pairs---an index and its corresponding array element value: +@ifnotdocbook @example @r{Index} 3 @r{Value} 30 @r{Index} 1 @r{Value} "foo" @r{Index} 0 @r{Value} 8 @r{Index} 2 @r{Value} "" @end example +@end ifnotdocbook + +@docbook +<informaltable> +<tgroup cols="2"> +<colspec colname="1" align="center"/> +<colspec colname="2" align="center"/> +<thead> +<row> +<entry>Index</entry> +<entry>Value</entry> +</row> +</thead> + +<tbody> +<row> +<entry><literal>3</literal></entry> +<entry><literal>30</literal></entry> +</row> + +<row> +<entry><literal>1</literal></entry> +<entry><literal>"foo"</literal></entry> +</row> + +<row> +<entry><literal>0</literal></entry> +<entry><literal>8</literal></entry> +</row> + +<row> +<entry><literal>2</literal></entry> +<entry><literal>""</literal></entry> +</row> + +</tbody> +</tgroup> +</informaltable> + +@end docbook @noindent -The pairs are shown in jumbled order because their order is irrelevant. +The pairs are shown in jumbled order because their order is +irrelevant.@footnote{The ordering will vary among @command{awk} +implementations, which typically use hash tables to store array elements +and values.} One advantage of associative arrays is that new pairs can be added at any time. For example, suppose a tenth element is added to the array whose value is @w{@code{"number ten"}}. The result is: +@ifnotdocbook @example @r{Index} 10 @r{Value} "number ten" @r{Index} 3 @r{Value} 30 @@ -13162,6 +15599,51 @@ whose value is @w{@code{"number ten"}}. The result is: @r{Index} 0 @r{Value} 8 @r{Index} 2 @r{Value} "" @end example +@end ifnotdocbook + +@docbook +<informaltable> +<tgroup cols="2"> +<colspec colname="1" align="center"/> +<colspec colname="2" align="center"/> +<thead> +<row> +<entry>Index</entry> +<entry>Value</entry> +</row> +</thead> +<tbody> + +<row> +<entry><literal>10</literal></entry> +<entry><literal>"number ten"</literal></entry> +</row> + +<row> +<entry><literal>3</literal></entry> +<entry><literal>30</literal></entry> +</row> + +<row> +<entry><literal>1</literal></entry> +<entry><literal>"foo"</literal></entry> +</row> + +<row> +<entry><literal>0</literal></entry> +<entry><literal>8</literal></entry> +</row> + +<row> +<entry><literal>2</literal></entry> +<entry><literal>""</literal></entry> +</row> + +</tbody> +</tgroup> +</informaltable> + +@end docbook @noindent @cindex sparse arrays @@ -13174,28 +15656,68 @@ have to be positive integers. Any number, or even a string, can be an index. For example, the following is an array that translates words from English to French: +@ifnotdocbook @example @r{Index} "dog" @r{Value} "chien" @r{Index} "cat" @r{Value} "chat" @r{Index} "one" @r{Value} "un" @r{Index} 1 @r{Value} "un" @end example +@end ifnotdocbook + +@docbook +<informaltable> +<tgroup cols="2"> +<colspec colname="1" align="center"/> +<colspec colname="2" align="center"/> +<thead> +<row> +<entry>Index</entry> +<entry>Value</entry> +</row> +</thead> +<tbody> +<row> +<entry><literal>"dog"</literal></entry> +<entry><literal>"chien"</literal></entry> +</row> + +<row> +<entry><literal>"cat"</literal></entry> +<entry><literal>"chat"</literal></entry> +</row> + +<row> +<entry><literal>"one"</literal></entry> +<entry><literal>"un"</literal></entry> +</row> + +<row> +<entry><literal>1</literal></entry> +<entry><literal>"un"</literal></entry> +</row> + +</tbody> +</tgroup> +</informaltable> + +@end docbook @noindent Here we decided to translate the number one in both spelled-out and numeric form---thus illustrating that a single array can have both numbers and strings as indices. -In fact, array subscripts are always strings; this is discussed -in more detail in -@ref{Numeric Array Subscripts}. -Here, the number @code{1} isn't double-quoted, since @command{awk} +(In fact, array subscripts are always strings. +There are some subtleties to how numbers work when used as +array subscripts; this is discussed in more detail in +@ref{Numeric Array Subscripts}.) +Here, the number @code{1} isn't double quoted, because @command{awk} automatically converts it to a string. @cindex @command{gawk}, @code{IGNORECASE} variable in -@cindex @code{IGNORECASE} variable @cindex case sensitivity, array indices and -@cindex arrays, @code{IGNORECASE} variable and -@cindex @code{IGNORECASE} variable, array subscripts and +@cindex arrays, and @code{IGNORECASE} variable +@cindex @code{IGNORECASE} variable, and array indices The value of @code{IGNORECASE} has no effect upon array subscripting. The identical string value used to store an array element must be used to retrieve it. @@ -13206,13 +15728,12 @@ that array's indices are consecutive integers starting at one. @command{awk}'s arrays are efficient---the time to access an element is independent of the number of elements in the array. -@c ENDOFRANGE arrin -@c ENDOFRANGE inarr @node Reference to Elements @subsection Referring to an Array Element -@cindex arrays, elements, referencing -@cindex elements in arrays +@cindex arrays, referencing elements +@cindex array members +@cindex elements of arrays The principal way to use an array is to refer to one of its elements. An array reference is an expression as follows: @@ -13229,11 +15750,16 @@ The value of the array reference is the current value of that array element. For example, @code{foo[4.3]} is an expression for the element of array @code{foo} at index @samp{4.3}. +@cindex arrays, unassigned elements +@cindex unassigned array elements +@cindex empty array elements A reference to an array element that has no recorded value yields a value of @code{""}, the null string. This includes elements that have not been assigned any value as well as elements that have been deleted (@pxref{Delete}). +@cindex non-existent array elements +@cindex arrays, elements that don't exist @quotation NOTE A reference to an element that does not exist @emph{automatically} creates that array element, with the null string as its value. (In some cases, @@ -13248,25 +15774,28 @@ if (a["foo"] != "") @dots{} @end example @noindent -This is incorrect, since this will @emph{create} @code{a["foo"]} -if it didn't exist before! +This is incorrect for two reasons. First, it @emph{creates} @code{a["foo"]} +if it didn't exist before! Second, it is valid (if a bit unusual) to set +an array element equal to the empty string. @end quotation @c @cindex arrays, @code{in} operator and -@cindex @code{in} operator, arrays and +@cindex @code{in} operator, testing if array element exists To determine whether an element exists in an array at a certain index, use the following expression: @example -@var{ind} in @var{array} +@var{indx} in @var{array} @end example @cindex side effects, array indexing @noindent -This expression tests whether the particular index @var{ind} exists, +This expression tests whether the particular index @var{indx} exists, without the side effect of creating that element if it is not present. -The expression has the value one (true) if @code{@var{array}[@var{ind}]} +The expression has the value one (true) if @code{@var{array}[@var{indx}]} exists and zero (false) if it does not exist. +(We use @var{indx} here, because @samp{index} is the name of a built-in +function.) For example, this statement tests whether the array @code{frequencies} contains the index @samp{2}: @@ -13288,8 +15817,8 @@ if (frequencies[2] != "") @node Assigning Elements @subsection Assigning Array Elements -@cindex arrays, elements, assigning -@cindex elements in arrays, assigning +@cindex arrays, elements, assigning values +@cindex elements in arrays, assigning values Array elements can be assigned values just like @command{awk} variables: @@ -13306,6 +15835,7 @@ assign to that element of the array. @node Array Example @subsection Basic Array Example +@cindex arrays, an example of using The following program takes a list of lines, each beginning with a line number, and prints them out in order of line number. The line numbers @@ -13319,14 +15849,14 @@ begin with a number: @example @c file eg/misc/arraymax.awk @{ - if ($1 > max) - max = $1 - arr[$1] = $0 + if ($1 > max) + max = $1 + arr[$1] = $0 @} END @{ - for (x = 1; x <= max; x++) - print arr[x] + for (x = 1; x <= max; x++) + print arr[x] @} @c endfile @end example @@ -13366,16 +15896,18 @@ program's @code{END} rule, as follows: @example END @{ - for (x = 1; x <= max; x++) - if (x in arr) - print arr[x] + for (x = 1; x <= max; x++) + if (x in arr) + print arr[x] @} @end example @node Scanning an Array @subsection Scanning All Elements of an Array @cindex elements in arrays, scanning +@cindex scanning arrays @cindex arrays, scanning +@cindex loops, @code{for}, array scanning In programs that use arrays, it is often necessary to use a loop that executes once for each element of an array. In other languages, where @@ -13388,16 +15920,16 @@ an array: @example for (@var{var} in @var{array}) - @var{body} + @var{body} @end example @noindent -@cindex @code{in} operator, arrays and +@cindex @code{in} operator, use in loops This loop executes @var{body} once for each index in @var{array} that the program has previously used, with the variable @var{var} set to that index. @cindex arrays, @code{for} statement and -@cindex @code{for} statement, in arrays +@cindex @code{for} statement, looping over arrays The following program uses this form of the @code{for} statement. The first rule scans the input records and notes which words appear (at least once) in the input, by storing a one into the array @code{used} with @@ -13405,7 +15937,7 @@ the word as index. The second rule scans the elements of @code{used} to find all the distinct words that appear in the input. It prints each word that is more than 10 characters long and also prints the number of such words. -@xref{String Functions}, +@DBXREF{String Functions} for more information on the built-in function @code{length()}. @example @@ -13428,143 +15960,228 @@ END @{ @end example @noindent -@xref{Word Sorting}, +@DBXREF{Word Sorting} for a more detailed example of this type. -@cindex arrays, elements, order of -@cindex elements in arrays, order of +@cindex arrays, elements, order of access by @code{in} operator +@cindex elements in arrays, order of access by @code{in} operator +@cindex @code{in} operator, order of array access The order in which elements of the array are accessed by this statement is determined by the internal arrangement of the array elements within -@command{awk} and normally cannot be controlled or changed. This can lead to -problems if new elements are added to @var{array} by statements in -the loop body; it is not predictable whether the @code{for} loop will -reach them. Similarly, changing @var{var} inside the loop may produce -strange results. It is best to avoid such things. - -As an extension, @command{gawk} makes it possible for you to -loop over the elements of an array in order, based on the value of -@code{PROCINFO["sorted_in"]} (@pxref{Auto-set}). -This is an advanced feature, so discussion of it is delayed -until @ref{Controlling Array Traversal}. - -In addition, @command{gawk} provides built-in functions for -sorting arrays; see @ref{Array Sorting Functions}. - -@node Delete -@section The @code{delete} Statement -@cindex @code{delete} statement -@cindex deleting elements in arrays -@cindex arrays, elements, deleting -@cindex elements in arrays, deleting +@command{awk} and in standard @command{awk} cannot be controlled +or changed. This can lead to problems if new elements are added to +@var{array} by statements in the loop body; it is not predictable whether +the @code{for} loop will reach them. Similarly, changing @var{var} inside +the loop may produce strange results. It is best to avoid such things. -To remove an individual element of an array, use the @code{delete} -statement: +As a point of information, @command{gawk} sets up the list of elements +to be iterated over before the loop starts, and does not change it. +But not all @command{awk} versions do so. Consider this program, named +@file{loopcheck.awk}: @example -delete @var{array}[@var{index-expression}] +BEGIN @{ + a["here"] = "here" + a["is"] = "is" + a["a"] = "a" + a["loop"] = "loop" + for (i in a) @{ + j++ + a[j] = j + print i + @} +@} @end example -Once an array element has been deleted, any value the element once -had is no longer available. It is as if the element had never -been referred to or been given a value. -The following is an example of deleting elements in an array: +Here is what happens when run with @command{gawk} (and @command{mawk}): @example -for (i in frequencies) - delete frequencies[i] +$ @kbd{gawk -f loopcheck.awk} +@print{} here +@print{} loop +@print{} a +@print{} is @end example -@noindent -This example removes all the elements from the array @code{frequencies}. -Once an element is deleted, a subsequent @code{for} statement to scan the array -does not report that element and the @code{in} operator to check for -the presence of that element returns zero (i.e., false): +Contrast this to BWK @command{awk}: @example -delete foo[4] -if (4 in foo) - print "This will never be printed" +$ @kbd{nawk -f loopcheck.awk} +@print{} loop +@print{} here +@print{} is +@print{} a +@print{} 1 @end example -@cindex null strings, array elements and -It is important to note that deleting an element is @emph{not} the -same as assigning it a null value (the empty string, @code{""}). -For example: +@node Controlling Scanning +@subsection Using Predefined Array Scanning Orders with @command{gawk} -@example -foo[4] = "" -if (4 in foo) - print "This is printed, even though foo[4] is empty" -@end example +This @value{SUBSECTION} describes a feature that is specific to @command{gawk}. -@cindex lint checking, array elements -It is not an error to delete an element that does not exist. -However, if @option{--lint} is provided on the command line -(@pxref{Options}), -@command{gawk} issues a warning message when an element that -is not in the array is deleted. +By default, when a @code{for} loop traverses an array, the order +is undefined, meaning that the @command{awk} implementation +determines the order in which the array is traversed. +This order is usually based on the internal implementation of arrays +and will vary from one version of @command{awk} to the next. -@cindex common extensions, @code{delete} to delete entire arrays -@cindex extensions, common@comma{} @code{delete} to delete entire arrays -@cindex arrays, deleting entire contents -@cindex deleting entire arrays -@cindex differences in @command{awk} and @command{gawk}, array elements, deleting -All the elements of an array may be deleted with a single statement -@value{COMMONEXT} -by leaving off the subscript in the @code{delete} statement, -as follows: +@cindex array scanning order, controlling +@cindex controlling array scanning order +Often, though, you may wish to do something simple, such as +``traverse the array by comparing the indices in ascending order,'' +or ``traverse the array by comparing the values in descending order.'' +@command{gawk} provides two mechanisms which give you this control. -@example -delete @var{array} -@end example +@itemize @value{BULLET} +@item +Set @code{PROCINFO["sorted_in"]} to one of a set of predefined values. +We describe this now. -This ability is a @command{gawk} extension; it is not available in -compatibility mode (@pxref{Options}). +@item +Set @code{PROCINFO["sorted_in"]} to the name of a user-defined function +to use for comparison of array elements. This advanced feature +is described later in @ref{Array Sorting}. +@end itemize -Using this version of the @code{delete} statement is about three times -more efficient than the equivalent loop that deletes each element one -at a time. +@cindex @code{PROCINFO}, values of @code{sorted_in} +The following special values for @code{PROCINFO["sorted_in"]} are available: -@cindex portability, deleting array elements -@cindex Brennan, Michael -The following statement provides a portable but nonobvious way to clear -out an array:@footnote{Thanks to Michael Brennan for pointing this out.} +@table @code +@item "@@unsorted" +Array elements are processed in arbitrary order, which is the default +@command{awk} behavior. + +@item "@@ind_str_asc" +Order by indices in ascending order compared as strings; this is the most basic sort. +(Internally, array indices are always strings, so with @samp{a[2*5] = 1} +the index is @code{"10"} rather than numeric 10.) + +@item "@@ind_num_asc" +Order by indices in ascending order but force them to be treated as numbers in the process. +Any index with a non-numeric value will end up positioned as if it were zero. + +@item "@@val_type_asc" +Order by element values in ascending order (rather than by indices). +Ordering is by the type assigned to the element +(@pxref{Typing and Comparison}). +All numeric values come before all string values, +which in turn come before all subarrays. +(Subarrays have not been described yet; +@pxref{Arrays of Arrays}.) + +@item "@@val_str_asc" +Order by element values in ascending order (rather than by indices). Scalar values are +compared as strings. Subarrays, if present, come out last. + +@item "@@val_num_asc" +Order by element values in ascending order (rather than by indices). Scalar values are +compared as numbers. Subarrays, if present, come out last. +When numeric values are equal, the string values are used to provide +an ordering: this guarantees consistent results across different +versions of the C @code{qsort()} function,@footnote{When two elements +compare as equal, the C @code{qsort()} function does not guarantee +that they will maintain their original relative order after sorting. +Using the string value to provide a unique ordering when the numeric +values are equal ensures that @command{gawk} behaves consistently +across different environments.} which @command{gawk} uses internally +to perform the sorting. + +@item "@@ind_str_desc" +String indices ordered from high to low. + +@item "@@ind_num_desc" +Numeric indices ordered from high to low. + +@item "@@val_type_desc" +Element values, based on type, ordered from high to low. +Subarrays, if present, come out first. + +@item "@@val_str_desc" +Element values, treated as strings, ordered from high to low. +Subarrays, if present, come out first. + +@item "@@val_num_desc" +Element values, treated as numbers, ordered from high to low. +Subarrays, if present, come out first. +@end table + +The array traversal order is determined before the @code{for} loop +starts to run. Changing @code{PROCINFO["sorted_in"]} in the loop body +does not affect the loop. +For example: @example -split("", array) +$ @kbd{gawk '} +> @kbd{BEGIN @{} +> @kbd{ a[4] = 4} +> @kbd{ a[3] = 3} +> @kbd{ for (i in a)} +> @kbd{ print i, a[i]} +> @kbd{@}'} +@print{} 4 4 +@print{} 3 3 +$ @kbd{gawk '} +> @kbd{BEGIN @{} +> @kbd{ PROCINFO["sorted_in"] = "@@ind_str_asc"} +> @kbd{ a[4] = 4} +> @kbd{ a[3] = 3} +> @kbd{ for (i in a)} +> @kbd{ print i, a[i]} +> @kbd{@}'} +@print{} 3 3 +@print{} 4 4 @end example -@cindex @code{split()} function, array elements@comma{} deleting -The @code{split()} function -(@pxref{String Functions}) -clears out the target array first. This call asks it to split -apart the null string. Because there is no data to split out, the -function simply clears the array and then returns. +When sorting an array by element values, if a value happens to be +a subarray then it is considered to be greater than any string or +numeric value, regardless of what the subarray itself contains, +and all subarrays are treated as being equal to each other. Their +order relative to each other is determined by their index strings. -@quotation CAUTION -Deleting an array does not change its type; you cannot -delete an array and then use the array's name as a scalar -(i.e., a regular variable). For example, the following does not work: +Here are some additional things to bear in mind about sorted +array traversal: + +@itemize @value{BULLET} +@item +The value of @code{PROCINFO["sorted_in"]} is global. That is, it affects +all array traversal @code{for} loops. If you need to change it within your +own code, you should see if it's defined and save and restore the value: @example -a[1] = 3 -delete a -a = 3 +@dots{} +if ("sorted_in" in PROCINFO) @{ + save_sorted = PROCINFO["sorted_in"] + PROCINFO["sorted_in"] = "@@val_str_desc" # or whatever +@} +@dots{} +if (save_sorted) + PROCINFO["sorted_in"] = save_sorted @end example -@end quotation + +@item +As already mentioned, the default array traversal order is represented by +@code{"@@unsorted"}. You can also get the default behavior by assigning +the null string to @code{PROCINFO["sorted_in"]} or by just deleting the +@code{"sorted_in"} element from the @code{PROCINFO} array with +the @code{delete} statement. +(The @code{delete} statement hasn't been described yet; @pxref{Delete}.) +@end itemize + +In addition, @command{gawk} provides built-in functions for +sorting arrays; see @ref{Array Sorting Functions}. @node Numeric Array Subscripts @section Using Numbers to Subscript Arrays @cindex numbers, as array subscripts -@cindex arrays, subscripts +@cindex arrays, numeric subscripts @cindex subscripts in arrays, numbers as -@cindex @code{CONVFMT} variable, array subscripts and +@cindex @code{CONVFMT} variable, and array subscripts An important aspect to remember about arrays is that @emph{array subscripts are always strings}. When a numeric value is used as a subscript, it is converted to a string value before being used for subscripting (@pxref{Conversion}). -This means that the value of the built-in variable @code{CONVFMT} can +This means that the value of the predefined variable @code{CONVFMT} can affect how your program accesses elements of an array. For example: @example @@ -13587,12 +16204,13 @@ The program then changes the value of @code{CONVFMT}. The test @samp{(xyz in data)} generates a new string value from @code{xyz}---this time @code{"12.15"}---because the value of @code{CONVFMT} only allows two significant digits. This test fails, -since @code{"12.15"} is different from @code{"12.153"}. +because @code{"12.15"} is different from @code{"12.153"}. -@cindex converting, during subscripting +@cindex converting integer array subscripts +@cindex integer array indices According to the rules for conversions (@pxref{Conversion}), integer -values are always converted to strings as integers, no matter what the +values always convert to strings as integers, no matter what the value of @code{CONVFMT} may happen to be. So the usual case of the following works: @@ -13604,19 +16222,19 @@ for (i = 1; i <= maxsub; i++) The ``integer values always convert to strings as integers'' rule has an additional consequence for array indexing. Octal and hexadecimal constants +@ifnotdocbook (@pxref{Nondecimal-numbers}) +@end ifnotdocbook +@ifdocbook +(covered in @ref{Nondecimal-numbers}) +@end ifdocbook are converted internally into numbers, and their original form -is forgotten. -This means, for example, that -@code{array[17]}, -@code{array[021]}, -and -@code{array[0x11]} -all refer to the same element! +is forgotten. This means, for example, that @code{array[17]}, +@code{array[021]}, and @code{array[0x11]} all refer to the same element! As with many things in @command{awk}, the majority of the time -things work as one would expect them to. But it is useful to have a precise -knowledge of the actual rules since they can sometimes have a subtle +things work as you would expect them to. But it is useful to have a precise +knowledge of the actual rules, as they can sometimes have a subtle effect on your programs. @node Uninitialized Subscripts @@ -13636,14 +16254,14 @@ $ @kbd{echo 'line 1} > @kbd{line 2} > @kbd{line 3' | awk '@{ l[lines] = $0; ++lines @}} > @kbd{END @{} -> @kbd{for (i = lines-1; i >= 0; --i)} +> @kbd{for (i = lines - 1; i >= 0; i--)} > @kbd{print l[i]} > @kbd{@}'} @print{} line 3 @print{} line 2 @end example -Unfortunately, the very first line of input data did not come out in the +Unfortunately, the very first line of input data did not appear in the output! Upon first glance, we would think that this program should have worked. @@ -13660,7 +16278,7 @@ The following version of the program works correctly: @example @{ l[lines++] = $0 @} END @{ - for (i = lines - 1; i >= 0; --i) + for (i = lines - 1; i >= 0; i--) print l[i] @} @end example @@ -13679,23 +16297,136 @@ Even though it is somewhat unusual, the null string if @option{--lint} is provided on the command line (@pxref{Options}). -@node Multi-dimensional +@node Delete +@section The @code{delete} Statement +@cindex @code{delete} statement +@cindex deleting elements in arrays +@cindex arrays, elements, deleting +@cindex elements in arrays, deleting + +To remove an individual element of an array, use the @code{delete} +statement: + +@example +delete @var{array}[@var{index-expression}] +@end example + +Once an array element has been deleted, any value the element once +had is no longer available. It is as if the element had never +been referred to or been given a value. +The following is an example of deleting elements in an array: + +@example +for (i in frequencies) + delete frequencies[i] +@end example + +@noindent +This example removes all the elements from the array @code{frequencies}. +Once an element is deleted, a subsequent @code{for} statement to scan the array +does not report that element and the @code{in} operator to check for +the presence of that element returns zero (i.e., false): + +@example +delete foo[4] +if (4 in foo) + print "This will never be printed" +@end example + +@cindex null strings, and deleting array elements +It is important to note that deleting an element is @emph{not} the +same as assigning it a null value (the empty string, @code{""}). +For example: + +@example +foo[4] = "" +if (4 in foo) + print "This is printed, even though foo[4] is empty" +@end example + +@cindex lint checking, array elements +It is not an error to delete an element that does not exist. +However, if @option{--lint} is provided on the command line +(@pxref{Options}), +@command{gawk} issues a warning message when an element that +is not in the array is deleted. + +@cindex common extensions, @code{delete} to delete entire arrays +@cindex extensions, common@comma{} @code{delete} to delete entire arrays +@cindex arrays, deleting entire contents +@cindex deleting entire arrays +@cindex @code{delete} @var{array} +@cindex differences in @command{awk} and @command{gawk}, array elements, deleting +All the elements of an array may be deleted with a single statement +by leaving off the subscript in the @code{delete} statement, +as follows: + + +@example +delete @var{array} +@end example + +Using this version of the @code{delete} statement is about three times +more efficient than the equivalent loop that deletes each element one +at a time. + +This form of the @code{delete} statement is also supported +by BWK @command{awk} and @command{mawk}, as well as +by a number of other implementations. + +@cindex Brian Kernighan's @command{awk} +@quotation NOTE +For many years, using @code{delete} without a subscript was a common +extension. In September 2012, it was accepted for inclusion into the +POSIX standard. See @uref{http://austingroupbugs.net/view.php?id=544, +the Austin Group website}. +@end quotation + +@cindex portability, deleting array elements +@cindex Brennan, Michael +The following statement provides a portable but nonobvious way to clear +out an array:@footnote{Thanks to Michael Brennan for pointing this out.} + +@example +split("", array) +@end example + +@cindex @code{split()} function, array elements@comma{} deleting +The @code{split()} function +(@pxref{String Functions}) +clears out the target array first. This call asks it to split +apart the null string. Because there is no data to split out, the +function simply clears the array and then returns. + +@quotation CAUTION +Deleting all the elements from an array does not change its type; you cannot +clear an array and then use the array's name as a scalar +(i.e., a regular variable). For example, the following does not work: + +@example +a[1] = 3 +delete a +a = 3 +@end example +@end quotation + +@node Multidimensional @section Multidimensional Arrays @menu -* Multi-scanning:: Scanning multidimensional arrays. +* Multiscanning:: Scanning multidimensional arrays. @end menu @cindex subscripts in arrays, multidimensional @cindex arrays, multidimensional -A multidimensional array is an array in which an element is identified +A @dfn{multidimensional array} is an array in which an element is identified by a sequence of indices instead of a single index. For example, a -two-dimensional array requires two indices. The usual way (in most +two-dimensional array requires two indices. The usual way (in many languages, including @command{awk}) to refer to an element of a two-dimensional array named @code{grid} is with @code{grid[@var{x},@var{y}]}. -@cindex @code{SUBSEP} variable, multidimensional arrays +@cindex @code{SUBSEP} variable, and multidimensional arrays Multidimensional arrays are supported in @command{awk} through concatenation of indices into one string. @command{awk} converts the indices into strings @@ -13727,16 +16458,18 @@ combined strings that are ambiguous. Suppose that @code{SUBSEP} is "b@@c"]}} are indistinguishable because both are actually stored as @samp{foo["a@@b@@c"]}. +@cindex @code{in} operator, index existence in multidimensional arrays To test whether a particular index sequence exists in a multidimensional array, use the same operator (@code{in}) that is -used for single dimensional arrays. Write the whole sequence of indices +used for single-dimensional arrays. Write the whole sequence of indices in parentheses, separated by commas, as the left operand: @example -(@var{subscript1}, @var{subscript2}, @dots{}) in @var{array} +if ((@var{subscript1}, @var{subscript2}, @dots{}) in @var{array}) + @dots{} @end example -The following example treats its input as a two-dimensional array of +Here is an example that treats its input as a two-dimensional array of fields; it rotates this array 90 degrees clockwise and prints the result. It assumes that all lines have the same number of elements: @@ -13781,16 +16514,18 @@ the program produces the following output: 3 2 1 6 @end example -@node Multi-scanning +@node Multiscanning @subsection Scanning Multidimensional Arrays There is no special @code{for} statement for scanning a -``multidimensional'' array. There cannot be one, because, in truth, there -are no multidimensional arrays or elements---there is only a +``multidimensional'' array. There cannot be one, because, in truth, +@command{awk} does not have +multidimensional arrays or elements---there is only a multidimensional @emph{way of accessing} an array. @cindex subscripts in arrays, multidimensional, scanning @cindex arrays, multidimensional, scanning +@cindex scanning multidimensional arrays However, if your program has an array that is always accessed as multidimensional, you can get the effect of scanning it by combining the scanning @code{for} statement @@ -13813,7 +16548,7 @@ into the individual indices by breaking it apart where the value of @code{SUBSEP} appears. The individual indices then become the elements of the array @code{separate}. -Thus, if a value is previously stored in @code{array[1, "foo"]}; then +Thus, if a value is previously stored in @code{array[1, "foo"]}, then an element with index @code{"1\034foo"} exists in @code{array}. (Recall that the default value of @code{SUBSEP} is the character with code 034.) Sooner or later, the @code{for} statement finds that index and does an @@ -13832,11 +16567,13 @@ separate indices is recovered. @node Arrays of Arrays @section Arrays of Arrays +@cindex arrays of arrays -@command{gawk} supports arrays of +@command{gawk} goes beyond standard @command{awk}'s multidimensional +array access and provides true arrays of arrays. Elements of a subarray are referred to by their own indices enclosed in square brackets, just like the elements of the main array. -For example, the following creates a two-element subarray at index @samp{1} +For example, the following creates a two-element subarray at index @code{1} of the main array @code{a}: @example @@ -13848,7 +16585,7 @@ This simulates a true two-dimensional array. Each subarray element can contain another subarray as a value, which in turn can hold other arrays as well. In this way, you can create arrays of three or more dimensions. The indices can be any @command{awk} expression, including scalars -separated by commas (that is, a regular @command{awk} simulated +separated by commas (i.e., a regular @command{awk} simulated multidimensional subscript). So the following is valid in @command{gawk}: @@ -13859,14 +16596,15 @@ a[1][3][1, "name"] = "barney" Each subarray and the main array can be of different length. In fact, the elements of an array or its subarray do not all have to have the same type. This means that the main array and any of its subarrays can be -non-rectangular, or jagged in structure. One can assign a scalar value to -the index @samp{4} of the main array @code{a}: +non-rectangular, or jagged in structure. You can assign a scalar value to +the index @code{4} of the main array @code{a}, even though @code{a[1]} +is itself an array and not a scalar: @example a[4] = "An element in a jagged array" @end example - -The terms @dfn{dimension}, @dfn{row} and @dfn{column} are + +The terms @dfn{dimension}, @dfn{row}, and @dfn{column} are meaningless when applied to such an array, but we will use ``dimension'' henceforth to imply the maximum number of indices needed to refer to an existing element. The @@ -13881,7 +16619,7 @@ a[4][5][6][7] = "An element in a four-dimensional array" @end example @noindent -This removes the scalar value from index @samp{4} and then inserts a +This removes the scalar value from index @code{4} and then inserts a subarray of subarray of subarray containing a scalar. You can also delete an entire subarray or subarray of subarrays: @@ -13922,14 +16660,14 @@ The @samp{for (item in array)} statement (@pxref{Scanning an Array}) can be nested to scan all the elements of an array of arrays if it is rectangular in structure. In order to print the contents (scalar values) of a two-dimensional array of arrays -(i.e., in which each first-level element is itself an -array, not necessarily of the same length) +(i.e., in which each first-level element is itself an +array, not necessarily of the same length) you could use the following code: @example for (i in array) for (j in array[i]) - print array[i][j] + print array[i][j] @end example The @code{isarray()} function (@pxref{Type Functions}) @@ -13939,15 +16677,17 @@ lets you test if an array element is itself an array: for (i in array) @{ if (isarray(array[i]) @{ for (j in array[i]) @{ - print array[i][j] + print array[i][j] @} @} + else + print array[i] @} @end example If the structure of a jagged array of arrays is known in advance, you can often devise workarounds using control statements. For example, -the following code prints the elements of our main array @code{a}: +the following code prints the elements of our main array @code{a}: @example for (i in a) @{ @@ -13957,13 +16697,13 @@ for (i in a) @{ print a[i][j][k] @} else print a[i][j] - @} + @} @} @end example @noindent -@xref{Walking Arrays}, for a user-defined function that will ``walk'' an -arbitrarily-dimensioned array of arrays. +@DBXREF{Walking Arrays} for a user-defined function that ``walks'' an +arbitrarily dimensioned array of arrays. Recall that a reference to an uninitialized array element yields a value of @code{""}, the null string. This has one important implication when you @@ -13982,20 +16722,76 @@ creating an arbitrary index: $ @kbd{gawk 'BEGIN @{ b[1][1] = ""; split("a b c d", b[1]); print b[1][1] @}'} @print{} a @end example -@c ENDOFRANGE arrs + +@node Arrays Summary +@section Summary + +@itemize @value{BULLET} +@item +Standard @command{awk} provides one-dimensional associative arrays +(arrays indexed by string values). All arrays are associative; numeric +indices are converted automatically to strings. + +@item +Array elements are referenced as @code{@var{array}[@var{indx}]}. +Referencing an element creates it if it did not exist previously. + +@item +The proper way to see if an array has an element with a given index +is to use the @code{in} operator: @samp{@var{indx} in @var{array}}. + +@item +Use @samp{for (@var{indx} in @var{array}) @dots{}} to scan through all the +individual elements of an array. In the body of the loop, @var{indx} takes +on the value of each element's index in turn. + +@item +The order in which a @samp{for (@var{indx} in @var{array})} loop +traverses an array is undefined in POSIX @command{awk} and varies among +implementations. @command{gawk} lets you control the order by assigning +special predefined values to @code{PROCINFO["sorted_in"]}. + +@item +Use @samp{delete @var{array}[@var{indx}]} to delete an individual element. +To delete all of the elements in an array, +use @samp{delete @var{array}}. +This latter feature has been a common extension for many +years and is now standard, but may not be supported by all commercial +versions of @command{awk}. + +@item +Standard @command{awk} simulates multidimensional arrays by separating +subscript values with a comma. The values are concatenated into a +single string, separated by the value of @code{SUBSEP}. The fact +that such a subscript was created in this way is not retained; thus +changing @code{SUBSEP} may have unexpected consequences. You can use +@samp{(@var{sub1}, @var{sub2}, @dots{}) in @var{array}} to see if such +a multidimensional subscript exists in @var{array}. + +@item +@command{gawk} provides true arrays of arrays. You use a separate +set of square brackets for each dimension in such an array: +@code{data[row][col]}, for example. Array elements may thus be either +scalar values (number or string) or another array. + +@item +Use the @code{isarray()} built-in function to determine if an array +element is itself a subarray. + +@end itemize + @node Functions @chapter Functions -@c STARTOFRANGE funcbi @cindex functions, built-in -@c STARTOFRANGE bifunc @cindex built-in functions This @value{CHAPTER} describes @command{awk}'s built-in functions, which fall into three categories: numeric, string, and I/O. @command{gawk} provides additional groups of functions to work with values that represent time, do -bit manipulation, sort arrays, and internationalize and localize programs. +bit manipulation, sort arrays, +provide type information, and internationalize and localize programs. Besides the built-in functions, @command{awk} has provisions for writing new functions that the rest of a program can use. @@ -14006,10 +16802,11 @@ The second half of this @value{CHAPTER} describes these * Built-in:: Summarizes the built-in functions. * User-defined:: Describes User-defined functions in detail. * Indirect Calls:: Choosing the function to call at runtime. +* Functions Summary:: Summary of functions. @end menu @node Built-in -@section Built-in Functions +@section Built-In Functions @dfn{Built-in} functions are always available for your @command{awk} program to call. This @value{SECTION} defines all @@ -14032,7 +16829,7 @@ but are summarized here for your convenience. @end menu @node Calling Built-in -@subsection Calling Built-in Functions +@subsection Calling Built-In Functions To call one of @command{awk}'s built-in functions, write the name of the function followed @@ -14042,7 +16839,7 @@ is a call to the function @code{atan2()} and has two arguments. @cindex programming conventions, functions, calling @cindex whitespace, functions@comma{} calling Whitespace is ignored between the built-in function name and the -open parenthesis, but nonetheless it is good practice to avoid using whitespace +opening parenthesis, but nonetheless it is good practice to avoid using whitespace there. User-defined functions do not permit whitespace in this way, and it is easier to avoid mistakes by following a simple convention that always works---no whitespace after a function name. @@ -14079,7 +16876,7 @@ right to left. For example: @example i = 5 -j = atan2(i++, i *= 2) +j = atan2(++i, i *= 2) @end example If the order of evaluation is left to right, then @code{i} first becomes @@ -14090,41 +16887,68 @@ two arguments 11 and 10. @node Numeric Functions @subsection Numeric Functions +@cindex numeric functions The following list describes all of the built-in functions that work with numbers. Optional parameters are enclosed in square brackets@w{ ([ ]):} -@table @code -@item atan2(@var{y}, @var{x}) -@cindex @code{atan2()} function +@c @asis for docbook +@table @asis +@item @code{atan2(@var{y}, @var{x})} +@cindexawkfunc{atan2} +@cindex arctangent Return the arctangent of @code{@var{y} / @var{x}} in radians. +You can use @samp{pi = atan2(0, -1)} to retrieve the value of +@value{PI}. -@item cos(@var{x}) -@cindex @code{cos()} function +@item @code{cos(@var{x})} +@cindexawkfunc{cos} +@cindex cosine Return the cosine of @var{x}, with @var{x} in radians. -@item exp(@var{x}) -@cindex @code{exp()} function +@item @code{div(@var{numerator}, @var{denominator}, @var{result})} +@cindexawkfunc{div} +@cindex div +Perform integer division, similar to the standard C function of the +same name. First, truncate @code{numerator} and @code{denominator} +towards zero, creating integer values. Clear the @code{result} +array, and then set @code{result["quotient"]} to the result of +@samp{numerator / denominator}, truncated towards zero to an integer, +and set @code{result["remainder"]} to the result of @samp{numerator % +denominator}, truncated towards zero to an integer. This function is +primarily intended for use with arbitrary length integers; it avoids +creating MPFR arbitrary precision floating-point values (@pxref{Arbitrary +Precision Integers}). + +This function is a @code{gawk} extension. It is not available in +compatibility mode (@pxref{Options}). + +@item @code{exp(@var{x})} +@cindexawkfunc{exp} +@cindex exponent Return the exponential of @var{x} (@code{e ^ @var{x}}) or report an error if @var{x} is out of range. The range of values @var{x} can have depends on your machine's floating-point representation. -@item int(@var{x}) -@cindex @code{int()} function +@item @code{int(@var{x})} +@cindexawkfunc{int} +@cindex round to nearest integer Return the nearest integer to @var{x}, located between @var{x} and zero and truncated toward zero. - For example, @code{int(3)} is 3, @code{int(3.9)} is 3, @code{int(-3.9)} is @minus{}3, and @code{int(-3)} is @minus{}3 as well. -@item log(@var{x}) -@cindex @code{log()} function +@item @code{log(@var{x})} +@cindexawkfunc{log} +@cindex logarithm Return the natural logarithm of @var{x}, if @var{x} is positive; -otherwise, report an error. +otherwise, return @code{NaN} (``not a number'') on IEEE 754 systems. +Additionally, @command{gawk} prints a warning message when @code{x} +is negative. -@item rand() -@cindex @code{rand()} function +@item @code{rand()} +@cindexawkfunc{rand} @cindex random numbers, @code{rand()}/@code{srand()} functions Return a random number. The values of @code{rand()} are uniformly distributed between zero and one. @@ -14140,8 +16964,9 @@ Often random integers are needed instead. Following is a user-defined function that can be used to obtain a random non-negative integer less than @var{n}: @example -function randint(n) @{ - return int(n * rand()) +function randint(n) +@{ + return int(n * rand()) @} @end example @@ -14161,12 +16986,11 @@ function roll(n) @{ return 1 + int(rand() * n) @} # Roll 3 six-sided dice and # print total number of points. @{ - printf("%d points\n", - roll(6)+roll(6)+roll(6)) + printf("%d points\n", roll(6) + roll(6) + roll(6)) @} @end example -@cindex numbers, random +@cindex seeding random number generator @cindex random numbers, seed of @quotation CAUTION In most @command{awk} implementations, including @command{gawk}, @@ -14181,25 +17005,27 @@ the seed to a value that is different in each run. To do this, use @code{srand()}. @end quotation -@item sin(@var{x}) -@cindex @code{sin()} function +@item @code{sin(@var{x})} +@cindexawkfunc{sin} +@cindex sine Return the sine of @var{x}, with @var{x} in radians. -@item sqrt(@var{x}) -@cindex @code{sqrt()} function +@item @code{sqrt(@var{x})} +@cindexawkfunc{sqrt} +@cindex square root Return the positive square root of @var{x}. @command{gawk} prints a warning message if @var{x} is negative. Thus, @code{sqrt(4)} is 2. -@item srand(@r{[}@var{x}@r{]}) -@cindex @code{srand()} function +@item @code{srand(}[@var{x}]@code{)} +@cindexawkfunc{srand} Set the starting point, or seed, for generating random numbers to the value @var{x}. Each seed value leads to a particular sequence of random numbers.@footnote{Computer-generated random numbers really are not truly random. They are technically known as ``pseudorandom.'' This means -that while the numbers in a sequence appear to be random, you can in +that although the numbers in a sequence appear to be random, you can in fact generate the same sequence of random numbers over and over again.} Thus, if the seed is set to the same value a second time, the same sequence of random numbers is produced again. @@ -14218,27 +17044,43 @@ numbers that are truly unpredictable. The return value of @code{srand()} is the previous seed. This makes it easy to keep track of the seeds in case you need to consistently reproduce sequences of random numbers. + +POSIX does not specify the initial seed; it differs among @command{awk} +implementations. @end table @node String Functions @subsection String-Manipulation Functions +@cindex string-manipulation functions + +The functions in this @value{SECTION} look at or change the text of one +or more strings. + +@code{gawk} understands locales (@pxref{Locales}), and does all +string processing in terms of @emph{characters}, not @emph{bytes}. +This distinction is particularly important to understand for locales +where one character may be represented by multiple bytes. Thus, for +example, @code{length()} returns the number of characters in a string, +and not the number of bytes used to represent those characters. Similarly, +@code{index()} works with character indices, and not byte indices. -The functions in this @value{SECTION} look at or change the text of one or more -strings. -@code{gawk} understands locales (@pxref{Locales}), and does all string processing in terms of -@emph{characters}, not @emph{bytes}. This distinction is particularly important -to understand for locales where one character -may be represented by multiple bytes. Thus, for example, @code{length()} -returns the number of characters in a string, and not the number of bytes -used to represent those characters, Similarly, @code{index()} works with -character indices, and not byte indices. +@quotation CAUTION +A number of functions deal with indices into strings. For these +functions, the first character of a string is at position (index) one. +This is different from C and the languages descended from it, where the +first character is at position zero. You need to remember this when +doing index calculations, particularly if you are used to C. +@end quotation In the following list, optional parameters are enclosed in square brackets@w{ ([ ]).} Several functions perform string substitution; the full discussion is provided in the description of the @code{sub()} function, which comes -towards the end since the list is presented in alphabetic order. +toward the end, because the list is presented alphabetically. + Those functions that are specific to @command{gawk} are marked with a -pound sign@w{ (@samp{#}):} +pound sign (@samp{#}). They are not available in compatibility mode +(@pxref{Options}): + @menu * Gory Details:: More than you want to know about @samp{\} and @@ -14246,32 +17088,38 @@ pound sign@w{ (@samp{#}):} @code{gensub()}. @end menu -@table @code -@item asort(@var{source} @r{[}, @var{dest} @r{[}, @var{how} @r{]} @r{]}) # +@c @asis for docbook +@table @asis +@item @code{asort(}@var{source} [@code{,} @var{dest} [@code{,} @var{how} ] ]@code{) #} +@itemx @code{asorti(}@var{source} [@code{,} @var{dest} [@code{,} @var{how} ] ]@code{) #} +@cindexgawkfunc{asorti} +@cindex sort array @cindex arrays, elements, retrieving number of -@cindex @code{asort()} function (@command{gawk}) +@cindexgawkfunc{asort} +@cindex sort array indices +These two functions are similar in behavior, so they are described +together. + +@quotation NOTE +The following description ignores the third argument, @var{how}, as it +requires understanding features that we have not discussed yet. Thus, +the discussion here is a deliberate simplification. (We do provide all +the details later on; see @DBREF{Array Sorting Functions} for the full story.) +@end quotation + +Both functions return the number of elements in the array @var{source}. +For @command{asort()}, @command{gawk} sorts the values of @var{source} +and replaces the indices of the sorted values of @var{source} with +sequential integers starting with one. If the optional array @var{dest} +is specified, then @var{source} is duplicated into @var{dest}. @var{dest} +is then sorted, leaving the indices of @var{source} unchanged. + @cindex @command{gawk}, @code{IGNORECASE} variable in -@cindex @code{IGNORECASE} variable -Return the number of elements in the array @var{source}. -@command{gawk} sorts the contents of @var{source} -and replaces the indices -of the sorted values of @var{source} with sequential -integers starting with one. If the optional array @var{dest} is specified, -then @var{source} is duplicated into @var{dest}. @var{dest} is then -sorted, leaving the indices of @var{source} unchanged. The optional third -argument @var{how} is a string which controls the rule for comparing values, -and the sort direction. A single space is required between the -comparison mode, @samp{string} or @samp{number}, and the direction specification, -@samp{ascending} or @samp{descending}. You can omit direction and/or mode -in which case it will default to @samp{ascending} and @samp{string}, respectively. -An empty string "" is the same as the default @code{"ascending string"} -for the value of @var{how}. If the @samp{source} array contains subarrays as values, -they will come out last(first) in the @samp{dest} array for @samp{ascending}(@samp{descending}) -order specification. The value of @code{IGNORECASE} affects the sorting. -The third argument can also be a user-defined function name in which case -the value returned by the function is used to order the array elements -before constructing the result array. -@xref{Array Sorting Functions}, for more information. +When comparing strings, @code{IGNORECASE} affects the sorting +(@pxref{Array Sorting Functions}). If the +@var{source} array contains subarrays as values (@pxref{Arrays of +Arrays}), they will come last, after all scalar values. +Subarrays are @emph{not} recursively sorted. For example, if the contents of @code{a} are as follows: @@ -14297,32 +17145,21 @@ a[2] = "de" a[3] = "sac" @end example -In order to reverse the direction of the sorted results in the above example, -@code{asort()} can be called with three arguments as follows: +The @code{asorti()} function works similarly to @code{asort()}, however, +the @emph{indices} are sorted, instead of the values. Thus, in the +previous example, starting with the same initial set of indices and +values in @code{a}, calling @samp{asorti(a)} would yield: @example -asort(a, a, "descending") +a[1] = "first" +a[2] = "last" +a[3] = "middle" @end example -The @code{asort()} function is described in more detail in -@ref{Array Sorting Functions}. -@code{asort()} is a @command{gawk} extension; it is not available -in compatibility mode (@pxref{Options}). - -@item asorti(@var{source} @r{[}, @var{dest} @r{[}, @var{how} @r{]} @r{]}) # -@cindex @code{asorti()} function (@command{gawk}) -Return the number of elements in the array @var{source}. -It works similarly to @code{asort()}, however, the @emph{indices} -are sorted, instead of the values. (Here too, -@code{IGNORECASE} affects the sorting.) - -The @code{asorti()} function is described in more detail in -@ref{Array Sorting Functions}. -@code{asorti()} is a @command{gawk} extension; it is not available -in compatibility mode (@pxref{Options}). - -@item gensub(@var{regexp}, @var{replacement}, @var{how} @r{[}, @var{target}@r{]}) # -@cindex @code{gensub()} function (@command{gawk}) +@item @code{gensub(@var{regexp}, @var{replacement}, @var{how}} [@code{, @var{target}}]@code{) #} +@cindexgawkfunc{gensub} +@cindex search and replace in strings +@cindex substitute in string Search the target string @var{target} for matches of the regular expression @var{regexp}. If @var{how} is a string beginning with @samp{g} or @samp{G} (short for ``global''), then replace all matches of @var{regexp} with @@ -14331,7 +17168,7 @@ which match of @var{regexp} to replace. If no @var{target} is supplied, use @code{$0}. It returns the modified string as the result of the function and the original target string is @emph{not} changed. -@code{gensub()} is a general substitution function. It's purpose is +@code{gensub()} is a general substitution function. Its purpose is to provide more features than the standard @code{sub()} and @code{gsub()} functions. @@ -14381,11 +17218,8 @@ a warning message. If @var{regexp} does not match @var{target}, @code{gensub()}'s return value is the original unchanged value of @var{target}. -@code{gensub()} is a @command{gawk} extension; it is not available -in compatibility mode (@pxref{Options}). - -@item gsub(@var{regexp}, @var{replacement} @r{[}, @var{target}@r{]}) -@cindex @code{gsub()} function +@item @code{gsub(@var{regexp}, @var{replacement}} [@code{, @var{target}}]@code{)} +@cindexawkfunc{gsub} Search @var{target} for @emph{all} of the longest, leftmost, @emph{nonoverlapping} matching substrings it can find and replace them with @var{replacement}. @@ -14406,9 +17240,10 @@ omitted, then the entire input record (@code{$0}) is used. As in @code{sub()}, the characters @samp{&} and @samp{\} are special, and the third argument must be assignable. -@item index(@var{in}, @var{find}) -@cindex @code{index()} function -@cindex searching +@item @code{index(@var{in}, @var{find})} +@cindexawkfunc{index} +@cindex search in string +@cindex find substring in string Search the string @var{in} for the first occurrence of the string @var{find}, and return the position in characters where that occurrence begins in the string @var{in}. Consider the following example: @@ -14420,17 +17255,37 @@ $ @kbd{awk 'BEGIN @{ print index("peanut", "an") @}'} @noindent If @var{find} is not found, @code{index()} returns zero. -(Remember that string indices in @command{awk} start at one.) -@item length(@r{[}@var{string}@r{]}) -@cindex @code{length()} function +@cindex dark corner, regexp as second argument to @code{index()} +With BWK @command{awk} and @command{gawk}, +it is a fatal error to use a regexp constant for @var{find}. +Other implementations allow it, simply treating the regexp +constant as an expression meaning @samp{$0 ~ /regexp/}. @value{DARKCORNER}. + +@item @code{length(}[@var{string}]@code{)} +@cindexawkfunc{length} +@cindex string length +@cindex length of string Return the number of characters in @var{string}. If @var{string} is a number, the length of the digit string representing that number is returned. For example, @code{length("abcde")} is five. By -contrast, @code{length(15 * 35)} works out to three. In this example, 15 * 35 = -525, and 525 is then converted to the string @code{"525"}, which has +contrast, @code{length(15 * 35)} works out to three. In this example, +@iftex +@math{15 @cdot 35 = 525}, +@end iftex +@ifnottex +@ifnotdocbook +15 * 35 = 525, +@end ifnotdocbook +@end ifnottex +@docbook +15 ⋅ 35 = 525, @c +@end docbook +and 525 is then converted to the string @code{"525"}, which has three characters. +@cindex length of input record +@cindex input record, length of If no argument is supplied, @code{length()} returns the length of @code{$0}. @c @cindex historical features @@ -14469,6 +17324,8 @@ warning about this. @cindex common extensions, @code{length()} applied to an array @cindex extensions, common@comma{} @code{length()} applied to an array @cindex differences between @command{gawk} and @command{awk} +@cindex number of array elements +@cindex array, number of elements With @command{gawk} and several other @command{awk} implementations, when given an array argument, the @code{length()} function returns the number of elements in the array. @value{COMMONEXT} @@ -14481,18 +17338,20 @@ If @option{--lint} is provided on the command line If @option{--posix} is supplied, using an array argument is a fatal error (@pxref{Arrays}). -@item match(@var{string}, @var{regexp} @r{[}, @var{array}@r{]}) -@cindex @code{match()} function +@item @code{match(@var{string}, @var{regexp}} [@code{, @var{array}}]@code{)} +@cindexawkfunc{match} +@cindex string, regular expression match +@cindex match regexp in string Search @var{string} for the longest, leftmost substring matched by the regular expression, -@var{regexp} and return the character position, or @dfn{index}, +@var{regexp} and return the character position (index) at which that substring begins (one, if it starts at the beginning of @var{string}). If no match is found, return zero. The @var{regexp} argument may be either a regexp constant -(@code{/@dots{}/}) or a string constant (@code{"@dots{}"}). +(@code{/}@dots{}@code{/}) or a string constant (@code{"}@dots{}@code{"}). In the latter case, the string is treated as a regexp to be matched. -@xref{Computed Regexps}, for a +@DBXREF{Computed Regexps} for a discussion of the difference between the two forms, and the implications for writing your program correctly. @@ -14505,8 +17364,8 @@ for @code{match()}, the order is the same as for the @samp{~} operator: @cindex @code{RSTART} variable, @code{match()} function and @cindex @code{RLENGTH} variable, @code{match()} function and @cindex @code{match()} function, @code{RSTART}/@code{RLENGTH} variables -The @code{match()} function sets the built-in variable @code{RSTART} to -the index. It also sets the built-in variable @code{RLENGTH} to the +The @code{match()} function sets the predefined variable @code{RSTART} to +the index. It also sets the predefined variable @code{RLENGTH} to the length in characters of the matched substring. If no match is found, @code{RSTART} is set to zero, and @code{RLENGTH} to @minus{}1. @@ -14515,13 +17374,12 @@ For example: @example @c file eg/misc/findpat.awk @{ - if ($1 == "FIND") - regex = $2 - else @{ - where = match($0, regex) - if (where != 0) - print "Match of", regex, "found at", - where, "in", $0 + if ($1 == "FIND") + regex = $2 + else @{ + where = match($0, regex) + if (where != 0) + print "Match of", regex, "found at", where, "in", $0 @} @} @c endfile @@ -14586,7 +17444,7 @@ $ @kbd{echo foooobazbarrrrr |} @end example There may not be subscripts for the start and index for every parenthesized -subexpression, since they may not all have matched text; thus they +subexpression, because they may not all have matched text; thus they should be tested for with the @code{in} operator (@pxref{Reference to Elements}). @@ -14596,8 +17454,9 @@ The @var{array} argument to @code{match()} is a (@pxref{Options}), using a third argument is a fatal error. -@item patsplit(@var{string}, @var{array} @r{[}, @var{fieldpat} @r{[}, @var{seps} @r{]} @r{]}) # -@cindex @code{patsplit()} function +@item @code{patsplit(@var{string}, @var{array}} [@code{, @var{fieldpat}} [@code{, @var{seps}} ] ]@code{) #} +@cindexgawkfunc{patsplit} +@cindex split string into array Divide @var{string} into pieces defined by @var{fieldpat} and store the pieces in @var{array} and the separator strings in the @@ -14616,38 +17475,31 @@ Any leading separator will be in @code{@var{seps}[0]}. The @code{patsplit()} function splits strings into pieces in a manner similar to the way input lines are split into fields using @code{FPAT} -(@pxref{Splitting By Content}. +(@pxref{Splitting By Content}). Before splitting the string, @code{patsplit()} deletes any previously existing elements in the arrays @var{array} and @var{seps}. -@cindex troubleshooting, @code{patsplit()} function -The @code{patsplit()} function is a -@command{gawk} extension. In compatibility mode -(@pxref{Options}), -it is not available. - -@item split(@var{string}, @var{array} @r{[}, @var{fieldsep} @r{[}, @var{seps} @r{]} @r{]}) -@cindex @code{split()} function +@item @code{split(@var{string}, @var{array}} [@code{, @var{fieldsep}} [@code{, @var{seps}} ] ]@code{)} +@cindexawkfunc{split} Divide @var{string} into pieces separated by @var{fieldsep} and store the pieces in @var{array} and the separator strings in the @var{seps} array. The first piece is stored in @code{@var{array}[1]}, the second piece in @code{@var{array}[2]}, and so forth. The string value of the third argument, @var{fieldsep}, is a regexp describing where to split @var{string} (much as @code{FS} can -be a regexp describing where to split input records; -@pxref{Regexp Field Splitting}). +be a regexp describing where to split input records). If @var{fieldsep} is omitted, the value of @code{FS} is used. @code{split()} returns the number of elements created. -@var{seps} is a @command{gawk} extension with @code{@var{seps}[@var{i}]} +@var{seps} is a @command{gawk} extension with @code{@var{seps}[@var{i}]} being the separator string -between @code{@var{array}[@var{i}]} and @code{@var{array}[@var{i}+1]}. +between @code{@var{array}[@var{i}]} and @code{@var{array}[@var{i}+1]}. If @var{fieldsep} is a single -space then any leading whitespace goes into @code{@var{seps}[0]} and +space then any leading whitespace goes into @code{@var{seps}[0]} and any trailing -whitespace goes into @code{@var{seps}[@var{n}]} where @var{n} is the -return value of -@code{split()} (that is, the number of elements in @var{array}). +whitespace goes into @code{@var{seps}[@var{n}]} where @var{n} is the +return value of +@code{split()} (i.e., the number of elements in @var{array}). The @code{split()} function splits strings into pieces in a manner similar to the way input lines are split into fields. For example: @@ -14657,7 +17509,7 @@ split("cul-de-sac", a, "-", seps) @end example @noindent -@cindex strings, splitting +@cindex strings splitting, example splits the string @samp{cul-de-sac} into three fields using @samp{-} as the separator. It sets the contents of the array @code{a} as follows: @@ -14683,7 +17535,7 @@ As with input field-splitting, when the value of @var{fieldsep} is the elements of @var{array} but not in @var{seps}, and the elements are separated by runs of whitespace. -Also as with input field-splitting, if @var{fieldsep} is the null string, each +Also, as with input field-splitting, if @var{fieldsep} is the null string, each individual character in the string is split into its own array element. @value{COMMONEXT} @@ -14697,7 +17549,7 @@ the third argument to be a regexp constant (@code{/abc/}) as well as a string. @value{DARKCORNER} The POSIX standard allows this as well. -@xref{Computed Regexps}, for a +@DBXREF{Computed Regexps} for a discussion of the difference between using a string constant or a regexp constant, and the implications for writing your program correctly. @@ -14712,8 +17564,11 @@ If @var{string} does not match @var{fieldsep} at all (but is not null), @var{array} has one element only. The value of that element is the original @var{string}. -@item sprintf(@var{format}, @var{expression1}, @dots{}) -@cindex @code{sprintf()} function +In POSIX mode (@pxref{Options}), the fourth argument is not allowed. + +@item @code{sprintf(@var{format}, @var{expression1}, @dots{})} +@cindexawkfunc{sprintf} +@cindex formatting strings Return (without printing) the string that @code{printf} would have printed out with the same arguments (@pxref{Printf}). @@ -14726,8 +17581,9 @@ pival = sprintf("pi = %.2f (approx.)", 22/7) @noindent assigns the string @w{@samp{pi = 3.14 (approx.)}} to the variable @code{pival}. -@cindex @code{strtonum()} function (@command{gawk}) -@item strtonum(@var{str}) # +@cindexgawkfunc{strtonum} +@cindex convert string to number +@item @code{strtonum(@var{str}) #} Examine @var{str} and return its numeric value. If @var{str} begins with a leading @samp{0}, @code{strtonum()} assumes that @var{str} is an octal number. If @var{str} begins with a leading @samp{0x} or @@ -14744,17 +17600,14 @@ Using the @code{strtonum()} function is @emph{not} the same as adding zero to a string value; the automatic coercion of strings to numbers works only for decimal data, not for octal or hexadecimal.@footnote{Unless you use the @option{--non-decimal-data} option, which isn't recommended. -@xref{Nondecimal Data}, for more information.} +@DBXREF{Nondecimal Data} for more information.} Note also that @code{strtonum()} uses the current locale's decimal point for recognizing numbers (@pxref{Locales}). -@cindex differences in @command{awk} and @command{gawk}, @code{strtonum()} function (@command{gawk}) -@code{strtonum()} is a @command{gawk} extension; it is not available -in compatibility mode (@pxref{Options}). - -@item sub(@var{regexp}, @var{replacement} @r{[}, @var{target}@r{]}) -@cindex @code{sub()} function +@item @code{sub(@var{regexp}, @var{replacement}} [@code{, @var{target}}]@code{)} +@cindexawkfunc{sub} +@cindex replace in string Search @var{target}, which is treated as a string, for the leftmost, longest substring matched by the regular expression @var{regexp}. Modify the entire string @@ -14763,9 +17616,9 @@ The modified string becomes the new value of @var{target}. Return the number of substitutions made (zero or one). The @var{regexp} argument may be either a regexp constant -(@code{/@dots{}/}) or a string constant (@code{"@dots{}"}). +(@code{/}@dots{}@code{/}) or a string constant (@code{"}@dots{}@code{"}). In the latter case, the string is treated as a regexp to be matched. -@xref{Computed Regexps}, for a +@DBXREF{Computed Regexps} for a discussion of the difference between the two forms, and the implications for writing your program correctly. @@ -14853,8 +17706,9 @@ will not run. Finally, if the @var{regexp} is not a regexp constant, it is converted into a string, and then the value of that string is treated as the regexp to match. -@item substr(@var{string}, @var{start} @r{[}, @var{length}@r{]}) -@cindex @code{substr()} function +@item @code{substr(@var{string}, @var{start}} [@code{, @var{length}} ]@code{)} +@cindexawkfunc{substr} +@cindex substring Return a @var{length}-character-long substring of @var{string}, starting at character number @var{start}. The first character of a string is character number one.@footnote{This is different from @@ -14868,9 +17722,10 @@ suffix is also returned if @var{length} is greater than the number of characters remaining in the string, counting from character @var{start}. +@cindex Brian Kernighan's @command{awk} If @var{start} is less than one, @code{substr()} treats it as if it was one. (POSIX doesn't specify what to do in this case: -Brian Kernighan's @command{awk} acts this way, and therefore @command{gawk} +BWK @command{awk} acts this way, and therefore @command{gawk} does too.) If @var{start} is greater than the number of characters in the string, @code{substr()} returns the null string. @@ -14910,24 +17765,79 @@ string = substr(string, 1, 2) "CDE" substr(string, 6) @end example @cindex case sensitivity, converting case -@cindex converting, case -@item tolower(@var{string}) -@cindex @code{tolower()} function +@cindex strings, converting letter case +@item @code{tolower(@var{string})} +@cindexawkfunc{tolower} +@cindex convert string to lower case Return a copy of @var{string}, with each uppercase character in the string replaced with its corresponding lowercase character. Nonalphabetic characters are left unchanged. For example, @code{tolower("MiXeD cAsE 123")} returns @code{"mixed case 123"}. -@item toupper(@var{string}) -@cindex @code{toupper()} function +@item @code{toupper(@var{string})} +@cindexawkfunc{toupper} +@cindex convert string to upper case Return a copy of @var{string}, with each lowercase character in the string replaced with its corresponding uppercase character. Nonalphabetic characters are left unchanged. For example, @code{toupper("MiXeD cAsE 123")} returns @code{"MIXED CASE 123"}. @end table +@cindex sidebar, Matching the Null String +@ifdocbook +@docbook +<sidebar><title>Matching the Null String</title> +@end docbook + +@cindex matching, null strings +@cindex null strings, matching +@cindex @code{*} (asterisk), @code{*} operator, null strings@comma{} matching +@cindex asterisk (@code{*}), @code{*} operator, null strings@comma{} matching + +In @command{awk}, the @samp{*} operator can match the null string. +This is particularly important for the @code{sub()}, @code{gsub()}, +and @code{gensub()} functions. For example: + +@example +$ @kbd{echo abc | awk '@{ gsub(/m*/, "X"); print @}'} +@print{} XaXbXcX +@end example + +@noindent +Although this makes a certain amount of sense, it can be surprising. + +@docbook +</sidebar> +@end docbook +@end ifdocbook + +@ifnotdocbook +@cartouche +@center @b{Matching the Null String} + + +@cindex matching, null strings +@cindex null strings, matching +@cindex @code{*} (asterisk), @code{*} operator, null strings@comma{} matching +@cindex asterisk (@code{*}), @code{*} operator, null strings@comma{} matching + +In @command{awk}, the @samp{*} operator can match the null string. +This is particularly important for the @code{sub()}, @code{gsub()}, +and @code{gensub()} functions. For example: + +@example +$ @kbd{echo abc | awk '@{ gsub(/m*/, "X"); print @}'} +@print{} XaXbXcX +@end example + +@noindent +Although this makes a certain amount of sense, it can be surprising. +@end cartouche +@end ifnotdocbook + + @node Gory Details -@subsubsection More About @samp{\} and @samp{&} with @code{sub()}, @code{gsub()}, and @code{gensub()} +@subsubsection More about @samp{\} and @samp{&} with @code{sub()}, @code{gsub()}, and @code{gensub()} @cindex escape processing, @code{gsub()}/@code{gensub()}/@code{sub()} functions @cindex @code{sub()} function, escape processing @@ -14937,23 +17847,30 @@ Nonalphabetic characters are left unchanged. For example, @cindex backslash (@code{\}), @code{gsub()}/@code{gensub()}/@code{sub()} functions and @cindex @code{&} (ampersand), @code{gsub()}/@code{gensub()}/@code{sub()} functions and @cindex ampersand (@code{&}), @code{gsub()}/@code{gensub()}/@code{sub()} functions and + +@quotation CAUTION +This subsubsection has been reported to cause headaches. +You might want to skip it upon first reading. +@end quotation + When using @code{sub()}, @code{gsub()}, or @code{gensub()}, and trying to get literal backslashes and ampersands into the replacement text, you need to remember that there are several levels of @dfn{escape processing} going on. First, there is the @dfn{lexical} level, which is when @command{awk} reads your program -and builds an internal copy of it that can be executed. +and builds an internal copy of it to execute. Then there is the runtime level, which is when @command{awk} actually scans the replacement string to determine what to generate. +@cindex Brian Kernighan's @command{awk} At both levels, @command{awk} looks for a defined set of characters that can come after a backslash. At the lexical level, it looks for the escape sequences listed in @ref{Escape Sequences}. Thus, for every @samp{\} that @command{awk} processes at the runtime level, you must type two backslashes at the lexical level. When a character that is not valid for an escape sequence follows the -@samp{\}, Brian Kernighan's @command{awk} and @command{gawk} both simply remove the initial +@samp{\}, BWK @command{awk} and @command{gawk} both simply remove the initial @samp{\} and put the next character into the string. Thus, for example, @code{"a\qb"} is treated as @code{"aqb"}. @@ -14967,36 +17884,37 @@ through unchanged. This is illustrated in @ref{table-sub-escapes}. @c Thank to Karl Berry for help with the TeX stuff. @float Table,table-sub-escapes -@caption{Historical Escape Sequence Processing for @code{sub()} and @code{gsub()}} +@caption{Historical escape sequence processing for @code{sub()} and @code{gsub()}} @tex \vbox{\bigskip -% This table has lots of &'s and \'s, so unspecialize them. +% We need more characters for escape and tab ... +\catcode`_ = 0 +\catcode`! = 4 +% ... since this table has lots of &'s and \'s, so we unspecialize them. \catcode`\& = \other \catcode`\\ = \other -% But then we need character for escape and tab. -@catcode`! = 4 -@halign{@hfil#!@qquad@hfil#!@qquad#@hfil@cr - You type!@code{sub()} sees!@code{sub()} generates@cr -@hrulefill!@hrulefill!@hrulefill@cr - @code{\&}! @code{&}!the matched text@cr - @code{\\&}! @code{\&}!a literal @samp{&}@cr - @code{\\\&}! @code{\&}!a literal @samp{&}@cr -@code{\\\\&}! @code{\\&}!a literal @samp{\&}@cr -@code{\\\\\&}! @code{\\&}!a literal @samp{\&}@cr -@code{\\\\\\&}! @code{\\\&}!a literal @samp{\\&}@cr - @code{\\q}! @code{\q}!a literal @samp{\q}@cr +_halign{_hfil#!_qquad_hfil#!_qquad#_hfil_cr + You type!@code{sub()} sees!@code{sub()} generates_cr +_hrulefill!_hrulefill!_hrulefill_cr + @code{\&}! @code{&}!The matched text_cr + @code{\\&}! @code{\&}!A literal @samp{&}_cr + @code{\\\&}! @code{\&}!A literal @samp{&}_cr + @code{\\\\&}! @code{\\&}!A literal @samp{\&}_cr + @code{\\\\\&}! @code{\\&}!A literal @samp{\&}_cr +@code{\\\\\\&}! @code{\\\&}!A literal @samp{\\&}_cr + @code{\\q}! @code{\q}!A literal @samp{\q}_cr } -@bigskip} +_bigskip} @end tex @ifdocbook @multitable @columnfractions .20 .20 .60 @headitem You type @tab @code{sub()} sees @tab @code{sub()} generates -@item @code{\&} @tab @code{&} @tab the matched text -@item @code{\\&} @tab @code{\&} @tab a literal @samp{&} -@item @code{\\\&} @tab @code{\&} @tab a literal @samp{&} -@item @code{\\\\&} @tab @code{\\&} @tab a literal @samp{\&} -@item @code{\\\\\&} @tab @code{\\&} @tab a literal @samp{\&} -@item @code{\\\\\\&} @tab @code{\\\&} @tab a literal @samp{\\&} -@item @code{\\q} @tab @code{\q} @tab a literal @samp{\q} +@item @code{\&} @tab @code{&} @tab The matched text +@item @code{\\&} @tab @code{\&} @tab A literal @samp{&} +@item @code{\\\&} @tab @code{\&} @tab A literal @samp{&} +@item @code{\\\\&} @tab @code{\\&} @tab A literal @samp{\&} +@item @code{\\\\\&} @tab @code{\\&} @tab A literal @samp{\&} +@item @code{\\\\\\&} @tab @code{\\\&} @tab A literal @samp{\\&} +@item @code{\\q} @tab @code{\q} @tab A literal @samp{\q} @end multitable @end ifdocbook @ifnottex @@ -15004,13 +17922,13 @@ through unchanged. This is illustrated in @ref{table-sub-escapes}. @display You type @code{sub()} sees @code{sub()} generates -------- ---------- --------------- - @code{\&} @code{&} the matched text - @code{\\&} @code{\&} a literal @samp{&} - @code{\\\&} @code{\&} a literal @samp{&} - @code{\\\\&} @code{\\&} a literal @samp{\&} - @code{\\\\\&} @code{\\&} a literal @samp{\&} -@code{\\\\\\&} @code{\\\&} a literal @samp{\\&} - @code{\\q} @code{\q} a literal @samp{\q} + @code{\&} @code{&} The matched text + @code{\\&} @code{\&} A literal @samp{&} + @code{\\\&} @code{\&} A literal @samp{&} + @code{\\\\&} @code{\\&} A literal @samp{\&} + @code{\\\\\&} @code{\\&} A literal @samp{\&} +@code{\\\\\\&} @code{\\\&} A literal @samp{\\&} + @code{\\q} @code{\q} A literal @samp{\q} @end display @end ifnotdocbook @end ifnottex @@ -15026,109 +17944,44 @@ case of even numbers of backslashes entered at the lexical level.) The problem with the historical approach is that there is no way to get a literal @samp{\} followed by the matched text. -@c @cindex @command{awk} language, POSIX version -@cindex POSIX @command{awk}, functions and, @code{gsub()}/@code{sub()} -The 1992 POSIX standard attempted to fix this problem. That standard -says that @code{sub()} and @code{gsub()} look for either a @samp{\} or an @samp{&} -after the @samp{\}. If either one follows a @samp{\}, that character is -output literally. The interpretation of @samp{\} and @samp{&} then becomes -as shown in @ref{table-sub-posix-92}. - -@float Table,table-sub-posix-92 -@caption{1992 POSIX Rules for sub and gsub Escape Sequence Processing} -@c thanks to Karl Berry for formatting this table -@tex -\vbox{\bigskip -% This table has lots of &'s and \'s, so unspecialize them. -\catcode`\& = \other \catcode`\\ = \other -% But then we need character for escape and tab. -@catcode`! = 4 -@halign{@hfil#!@qquad@hfil#!@qquad#@hfil@cr - You type!@code{sub()} sees!@code{sub()} generates@cr -@hrulefill!@hrulefill!@hrulefill@cr - @code{&}! @code{&}!the matched text@cr - @code{\\&}! @code{\&}!a literal @samp{&}@cr -@code{\\\\&}! @code{\\&}!a literal @samp{\}, then the matched text@cr -@code{\\\\\\&}! @code{\\\&}!a literal @samp{\&}@cr -} -@bigskip} -@end tex -@ifdocbook -@multitable @columnfractions .20 .20 .60 -@headitem You type @tab @code{sub()} sees @tab @code{sub()} generates -@item @code{&} @tab @code{&} @tab the matched text -@item @code{\\&} @tab @code{\&} @tab a literal @samp{&} -@item @code{\\\\&} @tab @code{\\&} @tab a literal @samp{\}, then the matched text -@item @code{\\\\\\&} @tab @code{\\\&} @tab a literal @samp{\&} -@end multitable -@end ifdocbook -@ifnottex -@ifnotdocbook -@display - You type @code{sub()} sees @code{sub()} generates - -------- ---------- --------------- - @code{&} @code{&} the matched text - @code{\\&} @code{\&} a literal @samp{&} - @code{\\\\&} @code{\\&} a literal @samp{\}, then the matched text -@code{\\\\\\&} @code{\\\&} a literal @samp{\&} -@end display -@end ifnotdocbook -@end ifnottex -@end float +Several editions of the POSIX standard attempted to fix this problem +but weren't successful. The details are irrelevant at this point in time. -@noindent -This appears to solve the problem. -Unfortunately, the phrasing of the standard is unusual. It -says, in effect, that @samp{\} turns off the special meaning of any -following character, but for anything other than @samp{\} and @samp{&}, -such special meaning is undefined. This wording leads to two problems: - -@itemize @bullet -@item -Backslashes must now be doubled in the @var{replacement} string, breaking -historical @command{awk} programs. - -@item -To make sure that an @command{awk} program is portable, @emph{every} character -in the @var{replacement} string must be preceded with a -backslash.@footnote{This consequence was certainly unintended.} -@c I can say that, 'cause I was involved in making this change -@end itemize - -Because of the problems just listed, -in 1996, the @command{gawk} maintainer submitted +At one point, the @command{gawk} maintainer submitted proposed text for a revised standard that reverts to rules that correspond more closely to the original existing practice. The proposed rules have special cases that make it possible -to produce a @samp{\} preceding the matched text. This is shown in +to produce a @samp{\} preceding the matched text. +This is shown in @ref{table-sub-proposed}. @float Table,table-sub-proposed -@caption{Proposed rules for sub and backslash} +@caption{GNU @command{awk} rules for @code{sub()} and backslash} @tex \vbox{\bigskip -% This table has lots of &'s and \'s, so unspecialize them. +% We need more characters for escape and tab ... +\catcode`_ = 0 +\catcode`! = 4 +% ... since this table has lots of &'s and \'s, so we unspecialize them. \catcode`\& = \other \catcode`\\ = \other -% But then we need character for escape and tab. -@catcode`! = 4 -@halign{@hfil#!@qquad@hfil#!@qquad#@hfil@cr - You type!@code{sub()} sees!@code{sub()} generates@cr -@hrulefill!@hrulefill!@hrulefill@cr -@code{\\\\\\&}! @code{\\\&}!a literal @samp{\&}@cr -@code{\\\\&}! @code{\\&}!a literal @samp{\}, followed by the matched text@cr - @code{\\&}! @code{\&}!a literal @samp{&}@cr - @code{\\q}! @code{\q}!a literal @samp{\q}@cr - @code{\\\\}! @code{\\}!@code{\\}@cr +_halign{_hfil#!_qquad_hfil#!_qquad#_hfil_cr + You type!@code{sub()} sees!@code{sub()} generates_cr +_hrulefill!_hrulefill!_hrulefill_cr +@code{\\\\\\&}! @code{\\\&}!A literal @samp{\&}_cr +@code{\\\\&}! @code{\\&}!A literal @samp{\}, followed by the matched text_cr + @code{\\&}! @code{\&}!A literal @samp{&}_cr + @code{\\q}! @code{\q}!A literal @samp{\q}_cr + @code{\\\\}! @code{\\}!@code{\\}_cr } -@bigskip} +_bigskip} @end tex @ifdocbook @multitable @columnfractions .20 .20 .60 @headitem You type @tab @code{sub()} sees @tab @code{sub()} generates -@item @code{\\\\\\&} @tab @code{\\\&} @tab a literal @samp{\&} -@item @code{\\\\&} @tab @code{\\&} @tab a literal @samp{\}, followed by the matched text -@item @code{\\&} @tab @code{\&} @tab a literal @samp{&} -@item @code{\\q} @tab @code{\q} @tab a literal @samp{\q} +@item @code{\\\\\\&} @tab @code{\\\&} @tab A literal @samp{\&} +@item @code{\\\\&} @tab @code{\\&} @tab A literal @samp{\}, followed by the matched text +@item @code{\\&} @tab @code{\&} @tab A literal @samp{&} +@item @code{\\q} @tab @code{\q} @tab A literal @samp{\q} @item @code{\\\\} @tab @code{\\} @tab @code{\\} @end multitable @end ifdocbook @@ -15137,10 +17990,10 @@ to produce a @samp{\} preceding the matched text. This is shown in @display You type @code{sub()} sees @code{sub()} generates -------- ---------- --------------- -@code{\\\\\\&} @code{\\\&} a literal @samp{\&} - @code{\\\\&} @code{\\&} a literal @samp{\}, followed by the matched text - @code{\\&} @code{\&} a literal @samp{&} - @code{\\q} @code{\q} a literal @samp{\q} +@code{\\\\\\&} @code{\\\&} A literal @samp{\&} + @code{\\\\&} @code{\\&} A literal @samp{\}, followed by the matched text + @code{\\&} @code{\&} A literal @samp{&} + @code{\\q} @code{\q} A literal @samp{\q} @code{\\\\} @code{\\} @code{\\} @end display @end ifnotdocbook @@ -15153,13 +18006,13 @@ there was only one. However, as in the historical case, any @samp{\} that is not part of one of these three sequences is not special and appears in the output literally. -@command{gawk} 3.0 and 3.1 follow these proposed POSIX rules for @code{sub()} and -@code{gsub()}. -@c As much as we think it's a lousy idea. You win some, you lose some. Sigh. -The POSIX standard took much longer to be revised than was expected in 1996. -The 2001 standard does not follow the above rules. Instead, the rules -there are somewhat simpler. The results are similar except for one case. +@command{gawk} 3.0 and 3.1 follow these rules for @code{sub()} and +@code{gsub()}. The POSIX standard took much longer to be revised than +was expected. In addition, the @command{gawk} maintainer's proposal was +lost during the standardization process. The final rules are +somewhat simpler. The results are similar except for one case. +@cindex POSIX @command{awk}, functions and, @code{gsub()}/@code{sub()} The POSIX rules state that @samp{\&} in the replacement string produces a literal @samp{&}, @samp{\\} produces a literal @samp{\}, and @samp{\} followed by anything else is not special; the @samp{\} is placed straight into the output. @@ -15169,28 +18022,29 @@ These rules are presented in @ref{table-posix-sub}. @caption{POSIX rules for @code{sub()} and @code{gsub()}} @tex \vbox{\bigskip -% This table has lots of &'s and \'s, so unspecialize them. +% We need more characters for escape and tab ... +\catcode`_ = 0 +\catcode`! = 4 +% ... since this table has lots of &'s and \'s, so we unspecialize them. \catcode`\& = \other \catcode`\\ = \other -% But then we need character for escape and tab. -@catcode`! = 4 -@halign{@hfil#!@qquad@hfil#!@qquad#@hfil@cr - You type!@code{sub()} sees!@code{sub()} generates@cr -@hrulefill!@hrulefill!@hrulefill@cr -@code{\\\\\\&}! @code{\\\&}!a literal @samp{\&}@cr -@code{\\\\&}! @code{\\&}!a literal @samp{\}, followed by the matched text@cr - @code{\\&}! @code{\&}!a literal @samp{&}@cr - @code{\\q}! @code{\q}!a literal @samp{\q}@cr - @code{\\\\}! @code{\\}!@code{\}@cr +_halign{_hfil#!_qquad_hfil#!_qquad#_hfil_cr + You type!@code{sub()} sees!@code{sub()} generates_cr +_hrulefill!_hrulefill!_hrulefill_cr +@code{\\\\\\&}! @code{\\\&}!A literal @samp{\&}_cr +@code{\\\\&}! @code{\\&}!A literal @samp{\}, followed by the matched text_cr + @code{\\&}! @code{\&}!A literal @samp{&}_cr + @code{\\q}! @code{\q}!A literal @samp{\q}_cr + @code{\\\\}! @code{\\}!@code{\}_cr } -@bigskip} +_bigskip} @end tex @ifdocbook @multitable @columnfractions .20 .20 .60 @headitem You type @tab @code{sub()} sees @tab @code{sub()} generates -@item @code{\\\\\\&} @tab @code{\\\&} @tab a literal @samp{\&} -@item @code{\\\\&} @tab @code{\\&} @tab a literal @samp{\}, followed by the matched text -@item @code{\\&} @tab @code{\&} @tab a literal @samp{&} -@item @code{\\q} @tab @code{\q} @tab a literal @samp{\q} +@item @code{\\\\\\&} @tab @code{\\\&} @tab A literal @samp{\&} +@item @code{\\\\&} @tab @code{\\&} @tab A literal @samp{\}, followed by the matched text +@item @code{\\&} @tab @code{\&} @tab A literal @samp{&} +@item @code{\\q} @tab @code{\q} @tab A literal @samp{\q} @item @code{\\\\} @tab @code{\\} @tab @code{\} @end multitable @end ifdocbook @@ -15199,10 +18053,10 @@ These rules are presented in @ref{table-posix-sub}. @display You type @code{sub()} sees @code{sub()} generates -------- ---------- --------------- -@code{\\\\\\&} @code{\\\&} a literal @samp{\&} - @code{\\\\&} @code{\\&} a literal @samp{\}, followed by the matched text - @code{\\&} @code{\&} a literal @samp{&} - @code{\\q} @code{\q} a literal @samp{\q} +@code{\\\\\\&} @code{\\\&} A literal @samp{\&} + @code{\\\\&} @code{\\&} A literal @samp{\}, followed by the matched text + @code{\\&} @code{\&} A literal @samp{&} + @code{\\q} @code{\q} A literal @samp{\q} @code{\\\\} @code{\\} @code{\} @end display @end ifnotdocbook @@ -15214,12 +18068,12 @@ is seen as @samp{\\} and produces @samp{\} instead of @samp{\\}. Starting with @value{PVERSION} 3.1.4, @command{gawk} followed the POSIX rules when @option{--posix} is specified (@pxref{Options}). Otherwise, -it continued to follow the 1996 proposed rules, since +it continued to follow the proposed rules, as that had been its behavior for many years. -When @value{PVERSION} 4.0.0, was released, the @command{gawk} maintainer +When @value{PVERSION} 4.0.0 was released, the @command{gawk} maintainer made the POSIX rules the default, breaking well over a decade's worth -of backwards compatibility.@footnote{This was rather naive of him, despite +of backward compatibility.@footnote{This was rather naive of him, despite there being a note in this section indicating that the next major version would move to the POSIX rules.} Needless to say, this was a bad idea, and as of @value{PVERSION} 4.0.1, @command{gawk} resumed its historical @@ -15234,34 +18088,35 @@ appears in the generated text and the @samp{\} does not, as shown in @ref{table-gensub-escapes}. @float Table,table-gensub-escapes -@caption{Escape Sequence Processing for @code{gensub()}} +@caption{Escape sequence processing for @code{gensub()}} @tex \vbox{\bigskip -% This table has lots of &'s and \'s, so unspecialize them. +% We need more characters for escape and tab ... +\catcode`_ = 0 +\catcode`! = 4 +% ... since this table has lots of &'s and \'s, so we unspecialize them. \catcode`\& = \other \catcode`\\ = \other -% But then we need character for escape and tab. -@catcode`! = 4 -@halign{@hfil#!@qquad@hfil#!@qquad#@hfil@cr - You type!@code{gensub()} sees!@code{gensub()} generates@cr -@hrulefill!@hrulefill!@hrulefill@cr - @code{&}! @code{&}!the matched text@cr - @code{\\&}! @code{\&}!a literal @samp{&}@cr - @code{\\\\}! @code{\\}!a literal @samp{\}@cr - @code{\\\\&}! @code{\\&}!a literal @samp{\}, then the matched text@cr -@code{\\\\\\&}! @code{\\\&}!a literal @samp{\&}@cr - @code{\\q}! @code{\q}!a literal @samp{q}@cr +_halign{_hfil#!_qquad_hfil#!_qquad#_hfil_cr + You type!@code{gensub()} sees!@code{gensub()} generates_cr +_hrulefill!_hrulefill!_hrulefill_cr + @code{&}! @code{&}!The matched text_cr + @code{\\&}! @code{\&}!A literal @samp{&}_cr + @code{\\\\}! @code{\\}!A literal @samp{\}_cr + @code{\\\\&}! @code{\\&}!A literal @samp{\}, then the matched text_cr +@code{\\\\\\&}! @code{\\\&}!A literal @samp{\&}_cr + @code{\\q}! @code{\q}!A literal @samp{q}_cr } -@bigskip} +_bigskip} @end tex @ifdocbook @multitable @columnfractions .20 .20 .60 @headitem You type @tab @code{gensub()} sees @tab @code{gensub()} generates -@item @code{&} @tab @code{&} @tab the matched text -@item @code{\\&} @tab @code{\&} @tab a literal @samp{&} -@item @code{\\\\} @tab @code{\\} @tab a literal @samp{\} -@item @code{\\\\&} @tab @code{\\&} @tab a literal @samp{\}, then the matched text -@item @code{\\\\\\&} @tab @code{\\\&} @tab a literal @samp{\&} -@item @code{\\q} @tab @code{\q} @tab a literal @samp{q} +@item @code{&} @tab @code{&} @tab The matched text +@item @code{\\&} @tab @code{\&} @tab A literal @samp{&} +@item @code{\\\\} @tab @code{\\} @tab A literal @samp{\} +@item @code{\\\\&} @tab @code{\\&} @tab A literal @samp{\}, then the matched text +@item @code{\\\\\\&} @tab @code{\\\&} @tab A literal @samp{\&} +@item @code{\\q} @tab @code{\q} @tab A literal @samp{q} @end multitable @end ifdocbook @ifnottex @@ -15269,12 +18124,12 @@ as shown in @ref{table-gensub-escapes}. @display You type @code{gensub()} sees @code{gensub()} generates -------- ------------- ------------------ - @code{&} @code{&} the matched text - @code{\\&} @code{\&} a literal @samp{&} - @code{\\\\} @code{\\} a literal @samp{\} - @code{\\\\&} @code{\\&} a literal @samp{\}, then the matched text -@code{\\\\\\&} @code{\\\&} a literal @samp{\&} - @code{\\q} @code{\q} a literal @samp{q} + @code{&} @code{&} The matched text + @code{\\&} @code{\&} A literal @samp{&} + @code{\\\\} @code{\\} A literal @samp{\} + @code{\\\\&} @code{\\&} A literal @samp{\}, then the matched text +@code{\\\\\\&} @code{\\\&} A literal @samp{\&} + @code{\\q} @code{\q} A literal @samp{q} @end display @end ifnotdocbook @end ifnottex @@ -15285,40 +18140,22 @@ and the special cases for @code{sub()} and @code{gsub()}, we recommend the use of @command{gawk} and @code{gensub()} when you have to do substitutions. -@c fakenode --- for prepinfo -@subheading Advanced Notes: Matching the Null String -@cindex advanced features, null strings@comma{} matching -@cindex matching, null strings -@cindex null strings, matching -@cindex @code{*} (asterisk), @code{*} operator, null strings@comma{} matching -@cindex asterisk (@code{*}), @code{*} operator, null strings@comma{} matching - -In @command{awk}, the @samp{*} operator can match the null string. -This is particularly important for the @code{sub()}, @code{gsub()}, -and @code{gensub()} functions. For example: - -@example -$ @kbd{echo abc | awk '@{ gsub(/m*/, "X"); print @}'} -@print{} XaXbXcX -@end example - -@noindent -Although this makes a certain amount of sense, it can be surprising. - @node I/O Functions @subsection Input/Output Functions +@cindex input/output functions The following functions relate to input/output (I/O). Optional parameters are enclosed in square brackets ([ ]): -@table @code -@item close(@var{filename} @r{[}, @var{how}@r{]}) -@cindex @code{close()} function +@table @asis +@item @code{close(}@var{filename} [@code{,} @var{how}]@code{)} +@cindexawkfunc{close} @cindex files, closing +@cindex close file or coprocess Close the file @var{filename} for input or output. Alternatively, the argument may be a shell command that was used for creating a coprocess, or for redirecting to or from a pipe; then the coprocess or pipe is closed. -@xref{Close Files And Pipes}, +@DBXREF{Close Files And Pipes} for more information. When closing a coprocess, it is occasionally useful to first close @@ -15330,46 +18167,59 @@ not matter. @xref{Two-way I/O}, which discusses this feature in more detail and gives an example. -@item fflush(@r{[}@var{filename}@r{]}) -@cindex @code{fflush()} function -@cindex common extensions, @code{fflush()} function -@cindex extensions, common@comma{} @code{fflush()} function +Note that the second argument to @code{close()} is a @command{gawk} +extension; it is not available in compatibility mode (@pxref{Options}). + +@item @code{fflush(}[@var{filename}]@code{)} +@cindexawkfunc{fflush} +@cindex flush buffered output Flush any buffered output associated with @var{filename}, which is either a file opened for writing or a shell command for redirecting output to -a pipe or coprocess. @value{COMMONEXT}. +a pipe or coprocess. -@cindex portability, @code{fflush()} function and @cindex buffers, flushing @cindex output, buffering -Many utility programs @dfn{buffer} their output; i.e., they save information +Many utility programs @dfn{buffer} their output (i.e., they save information to write to a disk file or the screen in memory until there is enough -for it to be worthwhile to send the data to the output device. +for it to be worthwhile to send the data to the output device). This is often more efficient than writing every little bit of information as soon as it is ready. However, sometimes -it is necessary to force a program to @dfn{flush} its buffers; that is, -write the information to its destination, even if a buffer is not full. +it is necessary to force a program to @dfn{flush} its buffers (i.e., +write the information to its destination, even if a buffer is not full). This is the purpose of the @code{fflush()} function---@command{gawk} also buffers its output and the @code{fflush()} function forces @command{gawk} to flush its buffers. -@code{fflush()} was added to Brian Kernighan's -version of @command{awk} in 1994; it is not part of the POSIX standard and is -not available if @option{--posix} has been specified on the -command line (@pxref{Options}). +@cindex extensions, common@comma{} @code{fflush()} function +@cindex Brian Kernighan's @command{awk} +Brian Kernighan added @code{fflush()} to his @command{awk} in April +1992. For two decades, it was a common extension. In December +2012, it was accepted for inclusion into the POSIX standard. +See @uref{http://austingroupbugs.net/view.php?id=634, the Austin Group website}. -@cindex @command{gawk}, @code{fflush()} function in -@command{gawk} extends the @code{fflush()} function in two ways. The first -is to allow no argument at all. In this case, the buffer for the -standard output is flushed. The second is to allow the null string -(@w{@code{""}}) as the argument. In this case, the buffers for -@emph{all} open output files and pipes are flushed. -Brian Kernighan's @command{awk} also supports these extensions. +POSIX standardizes @code{fflush()} as follows: if there +is no argument, or if the argument is the null string (@w{@code{""}}), +then @command{awk} flushes the buffers for @emph{all} open output files +and pipes. + +@quotation NOTE +Prior to @value{PVERSION} 4.0.2, @command{gawk} +would flush only the standard output if there was no argument, +and flush all output files and pipes if the argument was the null +string. This was changed in order to be compatible with Brian +Kernighan's @command{awk}, in the hope that standardizing this +feature in POSIX would then be easier (which indeed helped). + +With @command{gawk}, +you can use @samp{fflush("/dev/stdout")} if you wish to flush +only the standard output. +@end quotation @c @cindex automatic warnings @c @cindex warnings, automatic @cindex troubleshooting, @code{fflush()} function @code{fflush()} returns zero if the buffer is successfully flushed; -otherwise, it returns @minus{}1. +otherwise, it returns non-zero. (@command{gawk} returns @minus{}1.) In the case where all buffers are flushed, the return value is zero only if all buffers were flushed successfully. Otherwise, it is @minus{}1, and @command{gawk} warns about the problem @var{filename}. @@ -15379,8 +18229,109 @@ a file or pipe that was opened for reading (such as with @code{getline}), or if @var{filename} is not an open file, pipe, or coprocess. In such a case, @code{fflush()} returns @minus{}1, as well. -@item system(@var{command}) -@cindex @code{system()} function +@cindex sidebar, Interactive Versus Noninteractive Buffering +@ifdocbook +@docbook +<sidebar><title>Interactive Versus Noninteractive Buffering</title> +@end docbook + +@cindex buffering, interactive vs.@: noninteractive + +As a side point, buffering issues can be even more confusing, depending +upon whether your program is @dfn{interactive} (i.e., communicating +with a user sitting at a keyboard).@footnote{A program is interactive +if the standard output is connected to a terminal device. On modern +systems, this means your keyboard and screen.} + +@c Thanks to Walter.Mecky@dresdnerbank.de for this example, and for +@c motivating me to write this section. +Interactive programs generally @dfn{line buffer} their output (i.e., they +write out every line). Noninteractive programs wait until they have +a full buffer, which may be many lines of output. +Here is an example of the difference: + +@example +$ @kbd{awk '@{ print $1 + $2 @}'} +@kbd{1 1} +@print{} 2 +@kbd{2 3} +@print{} 5 +@kbd{Ctrl-d} +@end example + +@noindent +Each line of output is printed immediately. Compare that behavior +with this example: + +@example +$ @kbd{awk '@{ print $1 + $2 @}' | cat} +@kbd{1 1} +@kbd{2 3} +@kbd{Ctrl-d} +@print{} 2 +@print{} 5 +@end example + +@noindent +Here, no output is printed until after the @kbd{Ctrl-d} is typed, because +it is all buffered and sent down the pipe to @command{cat} in one shot. + +@docbook +</sidebar> +@end docbook +@end ifdocbook + +@ifnotdocbook +@cartouche +@center @b{Interactive Versus Noninteractive Buffering} + + +@cindex buffering, interactive vs.@: noninteractive + +As a side point, buffering issues can be even more confusing, depending +upon whether your program is @dfn{interactive} (i.e., communicating +with a user sitting at a keyboard).@footnote{A program is interactive +if the standard output is connected to a terminal device. On modern +systems, this means your keyboard and screen.} + +@c Thanks to Walter.Mecky@dresdnerbank.de for this example, and for +@c motivating me to write this section. +Interactive programs generally @dfn{line buffer} their output (i.e., they +write out every line). Noninteractive programs wait until they have +a full buffer, which may be many lines of output. +Here is an example of the difference: + +@example +$ @kbd{awk '@{ print $1 + $2 @}'} +@kbd{1 1} +@print{} 2 +@kbd{2 3} +@print{} 5 +@kbd{Ctrl-d} +@end example + +@noindent +Each line of output is printed immediately. Compare that behavior +with this example: + +@example +$ @kbd{awk '@{ print $1 + $2 @}' | cat} +@kbd{1 1} +@kbd{2 3} +@kbd{Ctrl-d} +@print{} 2 +@print{} 5 +@end example + +@noindent +Here, no output is printed until after the @kbd{Ctrl-d} is typed, because +it is all buffered and sent down the pipe to @command{cat} in one shot. +@end cartouche +@end ifnotdocbook + +@item @code{system(@var{command})} +@cindexawkfunc{system} +@cindex invoke shell command @cindex interacting with other programs Execute the operating-system command @var{command} and then return to the @command{awk} program. @@ -15411,7 +18362,7 @@ close("/bin/sh") @noindent @cindex troubleshooting, @code{system()} function -@cindex @code{--sandbox} option, disabling @code{system()} function +@cindex @option{--sandbox} option, disabling @code{system()} function However, if your @command{awk} program is interactive, @code{system()} is useful for running large self-contained programs, such as a shell or an editor. @@ -15425,59 +18376,83 @@ When @option{--sandbox} is specified, the @code{system()} function is disabled @end table -@c fakenode --- for prepinfo -@subheading Advanced Notes: Interactive Versus Noninteractive Buffering -@cindex advanced features, buffering -@cindex buffering, interactive vs.@: noninteractive +@cindex sidebar, Controlling Output Buffering with @code{system()} +@ifdocbook +@docbook +<sidebar><title>Controlling Output Buffering with @code{system()}</title> +@end docbook -As a side point, buffering issues can be even more confusing, depending -upon whether your program is @dfn{interactive}, i.e., communicating -with a user sitting at a keyboard.@footnote{A program is interactive -if the standard output is connected to a terminal device. On modern -systems, this means your keyboard and screen.} +@cindex buffers, flushing +@cindex buffering, input/output +@cindex output, buffering -@c Thanks to Walter.Mecky@dresdnerbank.de for this example, and for -@c motivating me to write this section. -Interactive programs generally @dfn{line buffer} their output; i.e., they -write out every line. Noninteractive programs wait until they have -a full buffer, which may be many lines of output. -Here is an example of the difference: +The @code{fflush()} function provides explicit control over output buffering for +individual files and pipes. However, its use is not portable to many older +@command{awk} implementations. An alternative method to flush output +buffers is to call @code{system()} with a null string as its argument: @example -$ @kbd{awk '@{ print $1 + $2 @}'} -@kbd{1 1} -@print{} 2 -@kbd{2 3} -@print{} 5 -@kbd{@value{CTL}-d} +system("") # flush output @end example @noindent -Each line of output is printed immediately. Compare that behavior -with this example: +@command{gawk} treats this use of the @code{system()} function as a special +case and is smart enough not to run a shell (or other command +interpreter) with the empty command. Therefore, with @command{gawk}, this +idiom is not only useful, it is also efficient. Although this method should work +with other @command{awk} implementations, it does not necessarily avoid +starting an unnecessary shell. (Other implementations may only +flush the buffer associated with the standard output and not necessarily +all buffered output.) + +If you think about what a programmer expects, it makes sense that +@code{system()} should flush any pending output. The following program: @example -$ @kbd{awk '@{ print $1 + $2 @}' | cat} -@kbd{1 1} -@kbd{2 3} -@kbd{@value{CTL}-d} -@print{} 2 -@print{} 5 +BEGIN @{ + print "first print" + system("echo system echo") + print "second print" +@} @end example @noindent -Here, no output is printed until after the @kbd{@value{CTL}-d} is typed, because -it is all buffered and sent down the pipe to @command{cat} in one shot. +must print: + +@example +first print +system echo +second print +@end example + +@noindent +and not: + +@example +system echo +first print +second print +@end example + +If @command{awk} did not flush its buffers before calling @code{system()}, +you would see the latter (undesirable) output. + +@docbook +</sidebar> +@end docbook +@end ifdocbook + +@ifnotdocbook +@cartouche +@center @b{Controlling Output Buffering with @code{system()}} + -@c fakenode --- for prepinfo -@subheading Advanced Notes: Controlling Output Buffering with @code{system()} -@cindex advanced features, buffering @cindex buffers, flushing @cindex buffering, input/output @cindex output, buffering The @code{fflush()} function provides explicit control over output buffering for -individual files and pipes. However, its use is not portable to many other +individual files and pipes. However, its use is not portable to many older @command{awk} implementations. An alternative method to flush output buffers is to call @code{system()} with a null string as its argument: @@ -15489,7 +18464,7 @@ system("") # flush output @command{gawk} treats this use of the @code{system()} function as a special case and is smart enough not to run a shell (or other command interpreter) with the empty command. Therefore, with @command{gawk}, this -idiom is not only useful, it is also efficient. While this method should work +idiom is not only useful, it is also efficient. Although this method should work with other @command{awk} implementations, it does not necessarily avoid starting an unnecessary shell. (Other implementations may only flush the buffer associated with the standard output and not necessarily @@ -15526,17 +18501,16 @@ second print If @command{awk} did not flush its buffers before calling @code{system()}, you would see the latter (undesirable) output. +@end cartouche +@end ifnotdocbook @node Time Functions @subsection Time Functions +@cindex time functions -@c STARTOFRANGE tst @cindex timestamps -@c STARTOFRANGE logftst @cindex log files, timestamps in -@c STARTOFRANGE filogtst @cindex files, log@comma{} timestamps in -@c STARTOFRANGE gawtst @cindex @command{gawk}, timestamps @cindex POSIX @command{awk}, timestamps and @code{awk} programs are commonly used to process log files @@ -15545,10 +18519,26 @@ particular log record was written. Many programs log their timestamp in the form returned by the @code{time()} system call, which is the number of seconds since a particular epoch. On POSIX-compliant systems, it is the number of seconds since -1970-01-01 00:00:00 UTC, not counting leap seconds.@footnote{@xref{Glossary}, -especially the entries ``Epoch'' and ``UTC.''} +1970-01-01 00:00:00 UTC, not counting leap +@ifclear FOR_PRINT +seconds.@footnote{@xref{Glossary}, especially the entries ``Epoch'' and ``UTC.''} +@end ifclear +@ifset FOR_PRINT +seconds. +@end ifset All known POSIX-compliant systems support timestamps from 0 through -@math{2^{31} - 1}, which is sufficient to represent times through +@iftex +@math{2^{31} - 1}, +@end iftex +@ifnottex +@ifnotdocbook +2^31 - 1, +@end ifnotdocbook +@end ifnottex +@docbook +2<superscript>31</superscript> − 1, @c +@end docbook +which is sufficient to represent times through 2038-01-19 03:14:07 UTC. Many systems support a wider range of timestamps, including negative timestamps that represent times before the epoch. @@ -15558,15 +18548,18 @@ epoch. In order to make it easier to process such log files and to produce useful reports, @command{gawk} provides the following functions for working with timestamps. They are @command{gawk} extensions; they are -not specified in the POSIX standard, nor are they in any other known -version of @command{awk}.@footnote{The GNU @command{date} utility can +not specified in the POSIX standard.@footnote{The GNU @command{date} utility can also do many of the things described here. Its use may be preferable for simple time-related operations in shell scripts.} +However, recent versions +of @command{mawk} (@pxref{Other Versions}) also support these functions. Optional parameters are enclosed in square brackets ([ ]): -@table @code -@item mktime(@var{datespec}) -@cindex @code{mktime()} function (@command{gawk}) +@c @asis for docbook +@table @asis +@item @code{mktime(@var{datespec})} +@cindexgawkfunc{mktime} +@cindex generate time values Turn @var{datespec} into a timestamp in the same form as is returned by @code{systime()}. It is similar to the function of the same name in ISO C. The argument, @var{datespec}, is a string of the form @@ -15594,9 +18587,9 @@ is out of range, @code{mktime()} returns @minus{}1. @cindex @command{gawk}, @code{PROCINFO} array in @cindex @code{PROCINFO} array -@item strftime(@r{[}@var{format} @r{[}, @var{timestamp} @r{[}, @var{utc-flag}@r{]]]}) -@c STARTOFRANGE strf -@cindex @code{strftime()} function (@command{gawk}) +@item @code{strftime(}[@var{format} [@code{,} @var{timestamp} [@code{,} @var{utc-flag}] ] ]@code{)} +@cindexgawkfunc{strftime} +@cindex format time string Format the time specified by @var{timestamp} based on the contents of the @var{format} string and return the result. It is similar to the function of the same name in ISO C. @@ -15606,18 +18599,19 @@ Mean Time). Otherwise, the value is formatted for the local time zone. The @var{timestamp} is in the same format as the value returned by the @code{systime()} function. If no @var{timestamp} argument is supplied, @command{gawk} uses the current time of day as the timestamp. -If no @var{format} argument is supplied, @code{strftime()} uses +Without a @var{format} argument, @code{strftime()} uses the value of @code{PROCINFO["strftime"]} as the format string (@pxref{Built-in Variables}). The default string value is @code{@w{"%a %b %e %H:%M:%S %Z %Y"}}. This format string produces output that is equivalent to that of the @command{date} utility. You can assign a new value to @code{PROCINFO["strftime"]} to -change the default format. +change the default format; see the following list for the various format directives. -@item systime() -@cindex @code{systime()} function (@command{gawk}) +@item @code{systime()} +@cindexgawkfunc{systime} @cindex timestamps +@cindex current system time Return the current time as the number of seconds since the system epoch. On POSIX systems, this is the number of seconds since 1970-01-01 00:00:00 UTC, not counting leap seconds. @@ -15689,10 +18683,10 @@ This is the ISO 8601 date format. @item %g The year modulo 100 of the ISO 8601 week number, as a decimal number (00--99). -For example, January 1, 1993 is in week 53 of 1992. Thus, the year -of its ISO 8601 week number is 1992, even though its year is 1993. -Similarly, December 31, 1973 is in week 1 of 1974. Thus, the year -of its ISO week number is 1974, even though its year is 1973. +For example, January 1, 2012, is in week 53 of 2011. Thus, the year +of its ISO 8601 week number is 2011, even though its year is 2012. +Similarly, December 31, 2012, is in week 1 of 2013. Thus, the year +of its ISO week number is 2013, even though its year is 2012. @item %G The full year of the ISO week number, as a decimal number. @@ -15773,7 +18767,7 @@ The locale's ``appropriate'' time representation. The year modulo 100 as a decimal number (00--99). @item %Y -The full year as a decimal number (e.g., 2011). +The full year as a decimal number (e.g., 2015). @c @cindex RFC 822 @c @cindex RFC 1036 @@ -15787,7 +18781,7 @@ no time zone is determinable. @item %Ec %EC %Ex %EX %Ey %EY %Od %Oe %OH @itemx %OI %Om %OM %OS %Ou %OU %OV %Ow %OW %Oy -``Alternate representations'' for the specifications +``Alternative representations'' for the specifications that use only the second letter (@samp{%c}, @samp{%C}, and so on).@footnote{If you don't understand any of this, don't worry about it; these facilities are meant to make it easier to ``internationalize'' @@ -15800,24 +18794,13 @@ Other internationalization features are described in A literal @samp{%}. @end table -If a conversion specifier is not one of the above, the behavior is +If a conversion specifier is not one of those just listed, the behavior is undefined.@footnote{This is because ISO C leaves the behavior of the C version of @code{strftime()} undefined and @command{gawk} uses the system's version of @code{strftime()} if it's there. Typically, the conversion specifier either does not appear in the returned string or appears literally.} -@c @cindex locale, definition of -Informally, a @dfn{locale} is the geographic place in which a program -is meant to run. For example, a common way to abbreviate the date -September 4, 2012 in the United States is ``9/4/12.'' -In many countries in Europe, however, it is abbreviated ``4.9.12.'' -Thus, the @samp{%x} specification in a @code{"US"} locale might produce -@samp{9/4/12}, while in a @code{"EUROPE"} locale, it might produce -@samp{4.9.12}. The ISO C standard defines a default @code{"C"} -locale, which is an environment that is typical of what many C programmers -are used to. - For systems that are not yet fully standards-compliant, @command{gawk} supplies a copy of @code{strftime()} from the GNU C Library. @@ -15838,11 +18821,11 @@ Single-digit numbers are padded with a space. @ignore @item %N The ``Emperor/Era'' name. -Equivalent to @code{%C}. +Equivalent to @samp{%C}. @item %o The ``Emperor/Era'' year. -Equivalent to @code{%y}. +Equivalent to @samp{%y}. @end ignore @item %s @@ -15853,9 +18836,8 @@ The time as a decimal timestamp in seconds since the epoch. The date in VMS format (e.g., @samp{20-JUN-1991}). @end ignore @end table -@c ENDOFRANGE strf -Additionally, the alternate representations are recognized but their +Additionally, the alternative representations are recognized but their normal representations are used. @cindex @code{date} utility, POSIX @@ -15869,8 +18851,8 @@ interprets the current time according to the format specifiers in the string. For example: @example -$ date '+Today is %A, %B %d, %Y.' -@print{} Today is Wednesday, March 30, 2011. +$ @kbd{date '+Today is %A, %B %d, %Y.'} +@print{} Today is Monday, September 22, 2014. @end example Here is the @command{gawk} version of the @command{date} utility. @@ -15890,7 +18872,7 @@ case $1 in esac gawk 'BEGIN @{ - format = "%a %b %e %H:%M:%S %Z %Y" + format = PROCINFO["strftime"] exitval = 0 if (ARGC > 2) @@ -15904,26 +18886,18 @@ gawk 'BEGIN @{ exit exitval @}' "$@@" @end example -@c ENDOFRANGE tst -@c ENDOFRANGE logftst -@c ENDOFRANGE filogtst -@c ENDOFRANGE gawtst @node Bitwise Functions @subsection Bit-Manipulation Functions -@c STARTOFRANGE bit +@cindex bit-manipulation functions @cindex bitwise, operations -@c STARTOFRANGE and @cindex AND bitwise operation -@c STARTOFRANGE oro @cindex OR bitwise operation -@c STARTOFRANGE xor @cindex XOR bitwise operation -@c STARTOFRANGE opbit @cindex operations, bitwise @quotation -@i{I can explain it for you, but I can't understand it for you.}@* -Anonymous +@i{I can explain it for you, but I can't understand it for you.} +@author Anonymous @end quotation Many languages provide the ability to perform @dfn{bitwise} operations @@ -15932,8 +18906,10 @@ each successive pair of bits in the operands. Three common operations are bitwise AND, OR, and XOR. The operations are described in @ref{table-bitwise-ops}. +@c 11/2014: Postprocessing turns the docbook informaltable +@c into a table. Hurray for scripting! @float Table,table-bitwise-ops -@caption{Bitwise Operations} +@caption{Bitwise operations} @ifnottex @ifnotdocbook @display @@ -15977,9 +18953,7 @@ Operands | 0 | 1 | 0 | 1 | 0 | 1 @end tex @docbook -<!-- FIXME: Fix ID and add xref in text. --> -<table id="table-bitwise-ops"> -<title>Bitwise Operations</title> +<informaltable> <tgroup cols="7" colsep="1"> <colspec colname="c1"/> @@ -16039,7 +19013,7 @@ Operands | 0 | 1 | 0 | 1 | 0 | 1 </tbody> </tgroup> -</table> +</informaltable> @end docbook @end float @@ -16063,42 +19037,47 @@ For example, if you have a bit string @samp{10111001} and you shift it right by three bits, you end up with @samp{00010111}.@footnote{This example shows that 0's come in on the left side. For @command{gawk}, this is always true, but in some languages, it's possible to have the left side -fill with 1's. Caveat emptor.} +fill with 1's.} @c Purposely decided to use 0's and 1's here. 2/2001. -If you start over -again with @samp{10111001} and shift it left by three bits, you end up -with @samp{11001000}. -@command{gawk} provides built-in functions that implement the -bitwise operations just described. They are: +If you start over again with @samp{10111001} and shift it left by three +bits, you end up with @samp{11001000}. The following list describes +@command{gawk}'s built-in functions that implement the bitwise operations. +Optional parameters are enclosed in square brackets ([ ]): @cindex @command{gawk}, bitwise operations in @table @code -@cindex @code{and()} function (@command{gawk}) -@item and(@var{v1}, @var{v2}) -Return the bitwise AND of the values provided by @var{v1} and @var{v2}. - -@cindex @code{compl()} function (@command{gawk}) -@item compl(@var{val}) +@cindexgawkfunc{and} +@cindex bitwise AND +@item @code{and(}@var{v1}@code{,} @var{v2} [@code{,} @dots{}]@code{)} +Return the bitwise AND of the arguments. There must be at least two. + +@cindexgawkfunc{compl} +@cindex bitwise complement +@item @code{compl(@var{val})} Return the bitwise complement of @var{val}. -@cindex @code{lshift()} function (@command{gawk}) -@item lshift(@var{val}, @var{count}) +@cindexgawkfunc{lshift} +@cindex left shift +@item @code{lshift(@var{val}, @var{count})} Return the value of @var{val}, shifted left by @var{count} bits. -@cindex @code{or()} function (@command{gawk}) -@item or(@var{v1}, @var{v2}) -Return the bitwise OR of the values provided by @var{v1} and @var{v2}. +@cindexgawkfunc{or} +@cindex bitwise OR +@item @code{or(}@var{v1}@code{,} @var{v2} [@code{,} @dots{}]@code{)} +Return the bitwise OR of the arguments. There must be at least two. -@cindex @code{rshift()} function (@command{gawk}) -@item rshift(@var{val}, @var{count}) +@cindexgawkfunc{rshift} +@cindex right shift +@item @code{rshift(@var{val}, @var{count})} Return the value of @var{val}, shifted right by @var{count} bits. -@cindex @code{xor()} function (@command{gawk}) -@item xor(@var{v1}, @var{v2}) -Return the bitwise XOR of the values provided by @var{v1} and @var{v2}. +@cindexgawkfunc{xor} +@cindex bitwise XOR +@item @code{xor(}@var{v1}@code{,} @var{v2} [@code{,} @dots{}]@code{)} +Return the bitwise XOR of the arguments. There must be at least two. @end table -For all of these functions, first the double precision floating-point value is +For all of these functions, first the double-precision floating-point value is converted to the widest C unsigned integer type, then the bitwise operation is performed. If the result cannot be represented exactly as a C @code{double}, leading nonzero bits are removed one by one until it can be represented @@ -16185,6 +19164,7 @@ $ @kbd{gawk -f testbits.awk} @cindex strings, converting @cindex numbers, converting @cindex converting, numbers to strings +@cindex number as string of bits The @code{bits2str()} function turns a binary number into a string. The number @code{1} represents a binary value where the rightmost bit is set to 1. Using this mask, @@ -16196,7 +19176,7 @@ Otherwise, a @code{"0"} is added. The value is then shifted right by one bit and the loop continues until there are no more 1 bits. -If the initial value is zero it returns a simple @code{"0"}. +If the initial value is zero, it returns a simple @code{"0"}. Otherwise, at the end, it pads the value with zeros to represent multiples of 8-bit quantities. This is typical in modern computers. @@ -16205,30 +19185,42 @@ decimal and octal values for the same numbers (@pxref{Nondecimal-numbers}), and then demonstrates the results of the @code{compl()}, @code{lshift()}, and @code{rshift()} functions. -@c ENDOFRANGE bit -@c ENDOFRANGE and -@c ENDOFRANGE oro -@c ENDOFRANGE xor -@c ENDOFRANGE opbit @node Type Functions @subsection Getting Type Information @command{gawk} provides a single function that lets you distinguish an array from a scalar variable. This is necessary for writing code -that traverses every element of a true multidimensional array +that traverses every element of an array of arrays (@pxref{Arrays of Arrays}). @table @code -@cindex @code{isarray()} function (@command{gawk}) +@cindexgawkfunc{isarray} +@cindex scalar or array @item isarray(@var{x}) Return a true value if @var{x} is an array. Otherwise return false. @end table +@code{isarray()} is meant for use in two circumstances. The first is when +traversing a multidimensional array: you can test if an element is itself +an array or not. The second is inside the body of a user-defined function +(not discussed yet; @pxref{User-defined}), to test if a parameter is an +array or not. + +@quotation NOTE +Using @code{isarray()} at the global level to test +variables makes no sense. Because you are the one writing the program, you +are supposed to know if your variables are arrays or not. And in fact, +due to the way @command{gawk} works, if you pass the name of a variable +that has not been previously used to @code{isarray()}, @command{gawk} +ends up turning it into a scalar. +@end quotation + @node I18N Functions @subsection String-Translation Functions @cindex @command{gawk}, string-translation functions @cindex functions, string-translation +@cindex string-translation functions @cindex internationalization @cindex @command{awk} programs, internationalizing @@ -16239,9 +19231,10 @@ The descriptions here are purposely brief. for the full story. Optional parameters are enclosed in square brackets ([ ]): -@table @code -@cindex @code{bindtextdomain()} function (@command{gawk}) -@item bindtextdomain(@var{directory} @r{[}, @var{domain}@r{]}) +@table @asis +@cindexgawkfunc{bindtextdomain} +@cindex set directory of message catalogs +@item @code{bindtextdomain(@var{directory}} [@code{,} @var{domain}]@code{)} Set the directory in which @command{gawk} will look for message translation files, in case they will not or cannot be placed in the ``standard'' locations @@ -16253,15 +19246,16 @@ If @var{directory} is the null string (@code{""}), then @code{bindtextdomain()} returns the current binding for the given @var{domain}. -@cindex @code{dcgettext()} function (@command{gawk}) -@item dcgettext(@var{string} @r{[}, @var{domain} @r{[}, @var{category}@r{]]}) +@cindexgawkfunc{dcgettext} +@cindex translate string +@item @code{dcgettext(@var{string}} [@code{,} @var{domain} [@code{,} @var{category}] ]@code{)} Return the translation of @var{string} in text domain @var{domain} for locale category @var{category}. The default value for @var{domain} is the current value of @code{TEXTDOMAIN}. The default value for @var{category} is @code{"LC_MESSAGES"}. -@cindex @code{dcngettext()} function (@command{gawk}) -@item dcngettext(@var{string1}, @var{string2}, @var{number} @r{[}, @var{domain} @r{[}, @var{category}@r{]]}) +@cindexgawkfunc{dcngettext} +@item @code{dcngettext(@var{string1}, @var{string2}, @var{number}} [@code{,} @var{domain} [@code{,} @var{category}] ]@code{)} Return the plural form used for @var{number} of the translation of @var{string1} and @var{string2} in text domain @var{domain} for locale category @var{category}. @var{string1} is the @@ -16270,20 +19264,16 @@ variant of the same message. The default value for @var{domain} is the current value of @code{TEXTDOMAIN}. The default value for @var{category} is @code{"LC_MESSAGES"}. @end table -@c ENDOFRANGE funcbi -@c ENDOFRANGE bifunc @node User-defined @section User-Defined Functions -@c STARTOFRANGE udfunc -@cindex user-defined, functions -@c STARTOFRANGE funcud +@cindex user-defined functions @cindex functions, user-defined Complicated @command{awk} programs can often be simplified by defining your own functions. User-defined functions can be called just like built-in ones (@pxref{Function Calls}), but it is up to you to define -them, i.e., to tell @command{awk} what they should do. +them (i.e., to tell @command{awk} what they should do). @menu * Definition Syntax:: How to write definitions and what they mean. @@ -16297,7 +19287,12 @@ them, i.e., to tell @command{awk} what they should do. @node Definition Syntax @subsection Function Definition Syntax -@c STARTOFRANGE fdef +@quotation +@i{It's entirely fair to say that the @command{awk} syntax for local +variable definitions is appallingly awful.} +@author Brian Kernighan +@end quotation + @cindex functions, defining Definitions of functions can appear anywhere between the rules of an @command{awk} program. Thus, the general form of an @command{awk} program is @@ -16309,12 +19304,12 @@ entire program before starting to execute any of it. The definition of a function named @var{name} looks like this: -@example -function @var{name}(@r{[}@var{parameter-list}@r{]}) -@{ +@display +@code{function} @var{name}@code{(}[@var{parameter-list}]@code{)} +@code{@{} @var{body-of-function} -@} -@end example +@code{@}} +@end display @cindex names, functions @cindex functions, names of @@ -16323,20 +19318,28 @@ function @var{name}(@r{[}@var{parameter-list}@r{]}) Here, @var{name} is the name of the function to define. A valid function name is like a valid variable name: a sequence of letters, digits, and underscores that doesn't start with a digit. +Here too, only the 52 upper- and lowercase English letters may +be used in a function name. Within a single @command{awk} program, any particular name can only be used as a variable, array, or function. @var{parameter-list} is an optional list of the function's arguments and local variable names, separated by commas. When the function is called, the argument names are used to hold the argument values given in -the call. The local variables are initialized to the empty string. +the call. + A function cannot have two parameters with the same name, nor may it have a parameter with the same name as the function itself. +In addition, according to the POSIX standard, function parameters +cannot have the same name as one of the special predefined variables +(@pxref{Built-in Variables}). Not all versions of @command{awk} enforce +this restriction. -In addition, according to the POSIX standard, function parameters cannot have the same -name as one of the special built-in variables -(@pxref{Built-in Variables}. Not all versions of @command{awk} -enforce this restriction. +Local variables act like the empty string if referenced where a string +value is required, and like zero if referenced where a numeric value +is required. This is the same as regular variables that have never been +assigned a value. (There is more to understand about local variables; +@pxref{Dynamic Typing}.) The @var{body-of-function} consists of @command{awk} statements. It is the most important part of the definition, because it says what the function @@ -16363,6 +19366,7 @@ conventional to place some extra space between the arguments and the local variables, in order to document how your function is supposed to be used. @cindex variables, shadowing +@cindex shadowing of variable values During execution of the function body, the arguments and local variable values hide, or @dfn{shadow}, any variables of the same names used in the rest of the program. The shadowed variables are not accessible in the @@ -16383,7 +19387,7 @@ function. When this happens, we say the function is @dfn{recursive}. The act of a function calling itself is called @dfn{recursion}. All the built-in functions return a value to their caller. -User-defined functions can do also, using the @code{return} statement, +User-defined functions can do so also, using the @code{return} statement, which is described in detail in @ref{Return Statement}. Many of the subsequent examples in this @value{SECTION} use the @code{return} statement. @@ -16407,13 +19411,13 @@ func foo() @{ a = sqrt($1) ; print a @} @end example @noindent -Instead it defines a rule that, for each record, concatenates the value +Instead, it defines a rule that, for each record, concatenates the value of the variable @samp{func} with the return value of the function @samp{foo}. If the resulting string is non-null, the action is executed. This is probably not what is desired. (@command{awk} accepts this input as syntactically valid, because functions may be used before they are defined in @command{awk} programs.@footnote{This program won't actually run, -since @code{foo()} is undefined.}) +because @code{foo()} is undefined.}) @cindex portability, functions@comma{} defining To ensure that your @command{awk} programs are portable, always use the @@ -16421,6 +19425,7 @@ keyword @code{function} when defining a function. @node Function Example @subsection Function Definition Examples +@cindex function definition example Here is an example of a user-defined function, called @code{myprint()}, that takes a number and prints it in a specific format: @@ -16458,13 +19463,14 @@ this program, using our function to format the results, prints: 21.2 @end example -This function deletes all the elements in an array: +This function deletes all the elements in an array (recall that the +extra whitespace signifies the start of the local variable list): @example function delarray(a, i) @{ for (i in a) - delete a[i] + delete a[i] @} @end example @@ -16475,22 +19481,24 @@ Instead of having to repeat this loop everywhere that you need to clear out an array, your program can just call @code{delarray}. (This guarantees portability. The use of @samp{delete @var{array}} to delete -the contents of an entire array is a nonstandard extension.) +the contents of an entire array is a relatively recent@footnote{Late in 2012.} +addition to the POSIX standard.) The following is an example of a recursive function. It takes a string as an input parameter and returns the string in backwards order. Recursive functions must always have a test that stops the recursion. -In this case, the recursion terminates when the starting position -is zero, i.e., when there are no more characters left in the string. +In this case, the recursion terminates when the input string is +already empty: +@c 8/2014: Thanks to Mike Brennan for the improved formulation @cindex @code{rev()} user-defined function @example -function rev(str, start) +function rev(str) @{ - if (start == 0) + if (str == "") return "" - return (substr(str, start, 1) rev(str, start - 1)) + return (rev(substr(str, 2)) substr(str, 1, 1)) @} @end example @@ -16499,11 +19507,11 @@ this way: @example $ @kbd{echo "Don't Panic!" |} -> @kbd{gawk --source '@{ print rev($0, length($0)) @}' -f rev.awk} +> @kbd{gawk -e '@{ print rev($0) @}' -f rev.awk} @print{} !cinaP t'noD @end example -The C @code{ctime()} function takes a timestamp and returns it in a string, +The C @code{ctime()} function takes a timestamp and returns it as a string, formatted in a well-known fashion. The following example uses the built-in @code{strftime()} function (@pxref{Time Functions}) @@ -16519,19 +19527,26 @@ to create an @command{awk} version of @code{ctime()}: function ctime(ts, format) @{ format = "%a %b %e %H:%M:%S %Z %Y" + if (ts == 0) ts = systime() # use current time as default return strftime(format, ts) @} @c endfile @end example -@c ENDOFRANGE fdef + +You might think that @code{ctime()} could use @code{PROCINFO["strftime"]} +for its format string. That would be a mistake, because @code{ctime()} is +supposed to return the time formatted in a standard fashion, and user-level +code could have changed @code{PROCINFO["strftime"]}. @node Function Caveats @subsection Calling User-Defined Functions -@c STARTOFRANGE fudc -This section describes how to call a user-defined function. +@cindex functions, user-defined, calling +@dfn{Calling a function} means causing the function to run and do its job. +A function call is an expression and its value is the value returned by +the function. @menu * Calling A Function:: Don't use spaces. @@ -16540,12 +19555,7 @@ This section describes how to call a user-defined function. @end menu @node Calling A Function -@subsubsection Writing A Function Call - -@cindex functions, user-defined, calling -@dfn{Calling a function} means causing the function to run and do its job. -A function call is an expression and its value is the value returned by -the function. +@subsubsection Writing a Function Call A function call consists of the function name followed by the arguments in parentheses. @command{awk} expressions are what you write in the @@ -16560,7 +19570,7 @@ foo(x y, "lose", 4 * z) @quotation CAUTION Whitespace characters (spaces and TABs) are not allowed -between the function name and the open-parenthesis of the argument list. +between the function name and the opening parenthesis of the argument list. If you write whitespace by mistake, @command{awk} might think that you mean to concatenate a variable with an expression in parentheses. However, it notices that you used a function name and not a variable name, and reports @@ -16570,9 +19580,10 @@ an error. @node Variable Scope @subsubsection Controlling Variable Scope -@cindex local variables -@cindex variables, local -There is no way to make a variable local to a @code{@{ @dots{} @}} block in +@cindex local variables, in a function +@cindex variables, local to a function +Unlike many languages, +there is no way to make a variable local to a @code{@{} @dots{} @code{@}} block in @command{awk}, but you can make a variable local to a function. It is good practice to do so whenever a variable is needed only in that function. @@ -16599,7 +19610,7 @@ function foo(j) print "foo's i=" i @} -BEGIN @{ +BEGIN @{ i = 10 print "top's i=" i foo(0) @@ -16622,13 +19633,13 @@ top's i=3 @end example If you want @code{i} to be local to both @code{foo()} and @code{bar()} do as -follows (the extra-space before @code{i} is a coding convention to +follows (the extra space before @code{i} is a coding convention to indicate that @code{i} is a local variable, not an argument): @example function bar( i) @{ - for (i = 0; i < 3; i++) + for (i = 0; i < 3; i++) print "bar's i=" i @} @@ -16640,10 +19651,10 @@ function foo(j, i) print "foo's i=" i @} -BEGIN @{ +BEGIN @{ i = 10 print "top's i=" i - foo(0) + foo(0) print "top's i=" i @} @end example @@ -16660,22 +19671,58 @@ foo's i=1 top's i=10 @end example +Besides scalar values (strings and numbers), you may also have +local arrays. By using a parameter name as an array, @command{awk} +treats it as an array, and it is local to the function. +In addition, recursive calls create new arrays. +Consider this example: + +@example +function some_func(p1, a) +@{ + if (p1++ > 3) + return + + a[p1] = p1 + + some_func(p1) + + printf("At level %d, index %d %s found in a\n", + p1, (p1 - 1), (p1 - 1) in a ? "is" : "is not") + printf("At level %d, index %d %s found in a\n", + p1, p1, p1 in a ? "is" : "is not") + print "" +@} + +BEGIN @{ + some_func(1) +@} +@end example + +When run, this program produces the following output: + +@example +At level 4, index 3 is not found in a +At level 4, index 4 is found in a + +At level 3, index 2 is not found in a +At level 3, index 3 is found in a + +At level 2, index 1 is not found in a +At level 2, index 2 is found in a +@end example + @node Pass By Value/Reference -@subsubsection Passing Function Arguments By Value Or By Reference +@subsubsection Passing Function Arguments by Value Or by Reference In @command{awk}, when you declare a function, there is no way to declare explicitly whether the arguments are passed @dfn{by value} or @dfn{by reference}. -Instead the passing convention is determined at runtime when +Instead, the passing convention is determined at runtime when the function is called according to the following rule: - -@itemize -@item -If the argument is an array variable, then it is passed by reference, -@item -Otherwise the argument is passed by value. -@end itemize +if the argument is an array variable, then it is passed by reference. +Otherwise, the argument is passed by value. @cindex call by value Passing an argument by value means that when a function is called, it @@ -16744,7 +19791,7 @@ BEGIN @{ @noindent prints @samp{a[1] = 1, a[2] = two, a[3] = 3}, because -@code{changeit} stores @code{"two"} in the second element of @code{a}. +@code{changeit()} stores @code{"two"} in the second element of @code{a}. @end quotation @cindex undefined functions @@ -16776,11 +19823,17 @@ If @option{--lint} is specified @cindex portability, @code{next} statement in user-defined functions Some @command{awk} implementations generate a runtime -error if you use the @code{next} statement -(@pxref{Next Statement}) +error if you use either the @code{next} statement +or the @code{nextfile} statement +(@pxref{Next Statement}, and +@ifdocbook +@ref{Nextfile Statement}) +@end ifdocbook +@ifnotdocbook +@pxref{Nextfile Statement}) +@end ifnotdocbook inside a user-defined function. @command{gawk} does not have this limitation. -@c ENDOFRANGE fudc @node Return Statement @subsection The @code{return} Statement @@ -16792,14 +19845,14 @@ This statement returns control to the calling part of the @command{awk} program. can also be used to return a value for use in the rest of the @command{awk} program. It looks like this: -@example -return @r{[}@var{expression}@r{]} -@end example +@display +@code{return} [@var{expression}] +@end display The @var{expression} part is optional. Due most likely to an oversight, POSIX does not define what the return value is if you omit the @var{expression}. Technically speaking, this -make the returned value undefined, and therefore, unpredictable. +makes the returned value undefined, and therefore, unpredictable. In practice, though, all versions of @command{awk} simply return the null string, which acts like zero if used in a numeric context. @@ -16833,8 +19886,8 @@ function maxelt(vec, i, ret) @noindent You call @code{maxelt()} with one argument, which is an array name. The local variables @code{i} and @code{ret} are not intended to be arguments; -while there is nothing to stop you from passing more than one argument -to @code{maxelt()}, the results would be strange. The extra space before +there is nothing to stop you from passing more than one argument +to @code{maxelt()} but the results would be strange. The extra space before @code{i} in the function parameter list indicates that @code{i} and @code{ret} are local variables. You should follow this convention when defining functions. @@ -16901,9 +19954,13 @@ BEGIN @{ @} @end example +In this example, the first call to @code{foo()} generates +a fatal error, so @command{awk} will not report the second +error. If you comment out that call, though, then @command{awk} +does report the second error. + Usually, such things aren't a big issue, but it's worth being aware of them. -@c ENDOFRANGE udfunc @node Indirect Calls @section Indirect Function Calls @@ -16914,7 +19971,7 @@ being aware of them. @cindex pointers to functions @cindex differences in @command{awk} and @command{gawk}, indirect function calls -This section describes a @command{gawk}-specific extension. +This section describes an advanced, @command{gawk}-specific extension. Often, you may wish to defer the choice of function to call until runtime. For example, you may have different kinds of records, each of which @@ -16960,20 +20017,23 @@ To process the data, you might write initially: @noindent This style of programming works, but can be awkward. With @dfn{indirect} function calls, you tell @command{gawk} to use the @emph{value} of a -variable as the name of the function to call. +variable as the @emph{name} of the function to call. +@cindex @code{@@}-notation for indirect function calls +@cindex indirect function calls, @code{@@}-notation +@cindex function calls, indirect, @code{@@}-notation for The syntax is similar to that of a regular function call: an identifier -immediately followed by a left parenthesis, any arguments, and then -a closing right parenthesis, with the addition of a leading @samp{@@} +immediately followed by an opening parenthesis, any arguments, and then +a closing parenthesis, with the addition of a leading @samp{@@} character: @example the_func = "sum" -result = @@the_func() # calls the `sum' function +result = @@the_func() # calls the sum() function @end example Here is a full program that processes the previously shown data, -using indirect function calls. +using indirect function calls: @example @c file eg/prog/indirectcall.awk @@ -17014,12 +20074,11 @@ function sum(first, last, ret, i) These two functions expect to work on fields; thus the parameters @code{first} and @code{last} indicate where in the fields to start and end. -Otherwise they perform the expected computations and are not unusual. +Otherwise they perform the expected computations and are not unusual: @example @c file eg/prog/indirectcall.awk # For each record, print the class name and the requested statistics - @{ class_name = $1 gsub(/_/, " ", class_name) # Replace _ with spaces @@ -17060,11 +20119,11 @@ $ @kbd{gawk -f indirectcall.awk class_data1} @print{} Biology 101: @print{} sum: <352.8> @print{} average: <88.2> -@print{} +@print{} @print{} Chemistry 305: @print{} sum: <356.4> @print{} average: <89.1> -@print{} +@print{} @print{} English 401: @print{} sum: <376.1> @print{} average: <94.025> @@ -17090,8 +20149,9 @@ We can do something similar using @command{gawk}, like this: @ignore @c file eg/lib/quicksort.awk # -# Arnold Robbins, arnold@skeeve.com, Public Domain +# Arnold Robbins, arnold@@skeeve.com, Public Domain # January 2009 + @c endfile @end ignore @@ -17124,7 +20184,7 @@ function quicksort(data, left, right, less_than, i, last) # quicksort_swap --- helper function for quicksort, should really be inline -function quicksort_swap(data, i, j, temp) +function quicksort_swap(data, i, j, temp) @{ temp = data[i] data[i] = data[j] @@ -17164,7 +20224,7 @@ or equal to), which yields data sorted in descending order. Next comes a sorting function. It is parameterized with the starting and ending field numbers and the comparison function. It builds an array with -the data and calls @code{quicksort} appropriately, and then formats the +the data and calls @code{quicksort()} appropriately, and then formats the results as a single string: @example @@ -17185,7 +20245,7 @@ function do_sort(first, last, compare, data, i, retval) retval = data[1] for (i = 2; i in data; i++) retval = retval " " data[i] - + return retval @} @c endfile @@ -17212,7 +20272,7 @@ function rsort(first, last) @c endfile @end example -Here is an extended version of the data file: +Here is an extended version of the @value{DF}: @example @c file eg/data/class_data2 @@ -17231,13 +20291,13 @@ $ @kbd{gawk -f quicksort.awk -f indirectcall.awk class_data2} @print{} average: <88.2> @print{} sort: <78.5 87.0 92.4 94.9> @print{} rsort: <94.9 92.4 87.0 78.5> -@print{} +@print{} @print{} Chemistry 305: @print{} sum: <356.4> @print{} average: <89.1> @print{} sort: <75.2 88.2 94.7 98.3> @print{} rsort: <98.3 94.7 88.2 75.2> -@print{} +@print{} @print{} English 401: @print{} sum: <376.1> @print{} average: <94.025> @@ -17245,2082 +20305,232 @@ $ @kbd{gawk -f quicksort.awk -f indirectcall.awk class_data2} @print{} rsort: <100.0 95.6 93.4 87.1> @end example -Remember that you must supply a leading @samp{@@} in front of an indirect function call. - -Unfortunately, indirect function calls cannot be used with the built-in functions. However, -you can generally write ``wrapper'' functions which call the built-in ones, and those can -be called indirectly. (Other than, perhaps, the mathematical functions, there is not a lot -of reason to try to call the built-in functions indirectly.) - -@command{gawk} does its best to make indirect function calls efficient. -For example, in the following case: - -@example -for (i = 1; i <= n; i++) - @@the_func() -@end example - -@noindent -@code{gawk} will look up the actual function to call only once. - -@c ENDOFRANGE funcud - -@node Internationalization -@chapter Internationalization with @command{gawk} - -Once upon a time, computer makers -wrote software that worked only in English. -Eventually, hardware and software vendors noticed that if their -systems worked in the native languages of non-English-speaking -countries, they were able to sell more systems. -As a result, internationalization and localization -of programs and software systems became a common practice. - -@c STARTOFRANGE inloc -@cindex internationalization, localization -@cindex @command{gawk}, internationalization and, See internationalization -@cindex internationalization, localization, @command{gawk} and -For many years, the ability to provide internationalization -was largely restricted to programs written in C and C++. -This @value{CHAPTER} describes the underlying library @command{gawk} -uses for internationalization, as well as how -@command{gawk} makes internationalization -features available at the @command{awk} program level. -Having internationalization available at the @command{awk} level -gives software developers additional flexibility---they are no -longer forced to write in C or C++ when internationalization is -a requirement. - -@menu -* I18N and L10N:: Internationalization and Localization. -* Explaining gettext:: How GNU @code{gettext} works. -* Programmer i18n:: Features for the programmer. -* Translator i18n:: Features for the translator. -* I18N Example:: A simple i18n example. -* Gawk I18N:: @command{gawk} is also internationalized. -@end menu - -@node I18N and L10N -@section Internationalization and Localization - -@cindex internationalization -@cindex localization, See internationalization@comma{} localization -@cindex localization -@dfn{Internationalization} means writing (or modifying) a program once, -in such a way that it can use multiple languages without requiring -further source-code changes. -@dfn{Localization} means providing the data necessary for an -internationalized program to work in a particular language. -Most typically, these terms refer to features such as the language -used for printing error messages, the language used to read -responses, and information related to how numerical and -monetary values are printed and read. - -@node Explaining gettext -@section GNU @code{gettext} - -@cindex internationalizing a program -@c STARTOFRANGE gettex -@cindex @code{gettext} library -The facilities in GNU @code{gettext} focus on messages; strings printed -by a program, either directly or via formatting with @code{printf} or -@code{sprintf()}.@footnote{For some operating systems, the @command{gawk} -port doesn't support GNU @code{gettext}. -Therefore, these features are not available -if you are using one of those operating systems. Sorry.} - -@cindex portability, @code{gettext} library and -When using GNU @code{gettext}, each application has its own -@dfn{text domain}. This is a unique name, such as @samp{kpilot} or @samp{gawk}, -that identifies the application. -A complete application may have multiple components---programs written -in C or C++, as well as scripts written in @command{sh} or @command{awk}. -All of the components use the same text domain. - -To make the discussion concrete, assume we're writing an application -named @command{guide}. Internationalization consists of the -following steps, in this order: - -@enumerate -@item -The programmer goes -through the source for all of @command{guide}'s components -and marks each string that is a candidate for translation. -For example, @code{"`-F': option required"} is a good candidate for translation. -A table with strings of option names is not (e.g., @command{gawk}'s -@option{--profile} option should remain the same, no matter what the local -language). - -@cindex @code{textdomain()} function (C library) -@item -The programmer indicates the application's text domain -(@code{"guide"}) to the @code{gettext} library, -by calling the @code{textdomain()} function. - -@cindex @code{.pot} files -@cindex files, @code{.pot} -@cindex portable object template files -@cindex files, portable object template -@item -Messages from the application are extracted from the source code and -collected into a portable object template file (@file{guide.pot}), -which lists the strings and their translations. -The translations are initially empty. -The original (usually English) messages serve as the key for -lookup of the translations. - -@cindex @code{.po} files -@cindex files, @code{.po} -@cindex portable object files -@cindex files, portable object -@item -For each language with a translator, @file{guide.pot} -is copied to a portable object file (@code{.po}) -and translations are created and shipped with the application. -For example, there might be a @file{fr.po} for a French translation. - -@cindex @code{.mo} files -@cindex files, @code{.mo} -@cindex message object files -@cindex files, message object -@item -Each language's @file{.po} file is converted into a binary -message object (@file{.mo}) file. -A message object file contains the original messages and their -translations in a binary format that allows fast lookup of translations -at runtime. - -@item -When @command{guide} is built and installed, the binary translation files -are installed in a standard place. - -@cindex @code{bindtextdomain()} function (C library) -@item -For testing and development, it is possible to tell @code{gettext} -to use @file{.mo} files in a different directory than the standard -one by using the @code{bindtextdomain()} function. - -@cindex @code{.mo} files, specifying directory of -@cindex files, @code{.mo}, specifying directory of -@cindex message object files, specifying directory of -@cindex files, message object, specifying directory of -@item -At runtime, @command{guide} looks up each string via a call -to @code{gettext()}. The returned string is the translated string -if available, or the original string if not. - -@item -If necessary, it is possible to access messages from a different -text domain than the one belonging to the application, without -having to switch the application's default text domain back -and forth. -@end enumerate - -@cindex @code{gettext()} function (C library) -In C (or C++), the string marking and dynamic translation lookup -are accomplished by wrapping each string in a call to @code{gettext()}: - -@example -printf("%s", gettext("Don't Panic!\n")); -@end example - -The tools that extract messages from source code pull out all -strings enclosed in calls to @code{gettext()}. - -@cindex @code{_} (underscore), @code{_} C macro -@cindex underscore (@code{_}), @code{_} C macro -The GNU @code{gettext} developers, recognizing that typing -@samp{gettext(@dots{})} over and over again is both painful and ugly to look -at, use the macro @samp{_} (an underscore) to make things easier: - -@example -/* In the standard header file: */ -#define _(str) gettext(str) - -/* In the program text: */ -printf("%s", _("Don't Panic!\n")); -@end example - -@cindex internationalization, localization, locale categories -@cindex @code{gettext} library, locale categories -@cindex locale categories -@noindent -This reduces the typing overhead to just three extra characters per string -and is considerably easier to read as well. - -There are locale @dfn{categories} -for different types of locale-related information. -The defined locale categories that @code{gettext} knows about are: - -@table @code -@cindex @code{LC_MESSAGES} locale category -@item LC_MESSAGES -Text messages. This is the default category for @code{gettext} -operations, but it is possible to supply a different one explicitly, -if necessary. (It is almost never necessary to supply a different category.) - -@cindex sorting characters in different languages -@cindex @code{LC_COLLATE} locale category -@item LC_COLLATE -Text-collation information; i.e., how different characters -and/or groups of characters sort in a given language. - -@cindex @code{LC_CTYPE} locale category -@item LC_CTYPE -Character-type information (alphabetic, digit, upper- or lowercase, and -so on). -This information is accessed via the -POSIX character classes in regular expressions, -such as @code{/[[:alnum:]]/} -(@pxref{Regexp Operators}). - -@cindex monetary information, localization -@cindex currency symbols, localization -@cindex @code{LC_MONETARY} locale category -@item LC_MONETARY -Monetary information, such as the currency symbol, and whether the -symbol goes before or after a number. - -@cindex @code{LC_NUMERIC} locale category -@item LC_NUMERIC -Numeric information, such as which characters to use for the decimal -point and the thousands separator.@footnote{Americans -use a comma every three decimal places and a period for the decimal -point, while many Europeans do exactly the opposite: -1,234.56 versus 1.234,56.} - -@cindex @code{LC_RESPONSE} locale category -@item LC_RESPONSE -Response information, such as how ``yes'' and ``no'' appear in the -local language, and possibly other information as well. - -@cindex time, localization and -@cindex dates, information related to@comma{} localization -@cindex @code{LC_TIME} locale category -@item LC_TIME -Time- and date-related information, such as 12- or 24-hour clock, month printed -before or after the day in a date, local month abbreviations, and so on. - -@cindex @code{LC_ALL} locale category -@item LC_ALL -All of the above. (Not too useful in the context of @code{gettext}.) -@end table -@c ENDOFRANGE gettex - -@node Programmer i18n -@section Internationalizing @command{awk} Programs -@c STARTOFRANGE inap -@cindex @command{awk} programs, internationalizing - -@command{gawk} provides the following variables and functions for -internationalization: - -@table @code -@cindex @code{TEXTDOMAIN} variable -@item TEXTDOMAIN -This variable indicates the application's text domain. -For compatibility with GNU @code{gettext}, the default -value is @code{"messages"}. - -@cindex internationalization, localization, marked strings -@cindex strings, for localization -@item _"your message here" -String constants marked with a leading underscore -are candidates for translation at runtime. -String constants without a leading underscore are not translated. - -@cindex @code{dcgettext()} function (@command{gawk}) -@item dcgettext(@var{string} @r{[}, @var{domain} @r{[}, @var{category}@r{]]}) -Return the translation of @var{string} in -text domain @var{domain} for locale category @var{category}. -The default value for @var{domain} is the current value of @code{TEXTDOMAIN}. -The default value for @var{category} is @code{"LC_MESSAGES"}. - -If you supply a value for @var{category}, it must be a string equal to -one of the known locale categories described in -@ifnotinfo -the previous @value{SECTION}. -@end ifnotinfo -@ifinfo -@ref{Explaining gettext}. -@end ifinfo -You must also supply a text domain. Use @code{TEXTDOMAIN} if -you want to use the current domain. - -@quotation CAUTION -The order of arguments to the @command{awk} version -of the @code{dcgettext()} function is purposely different from the order for -the C version. The @command{awk} version's order was -chosen to be simple and to allow for reasonable @command{awk}-style -default arguments. -@end quotation - -@cindex @code{dcngettext()} function (@command{gawk}) -@item dcngettext(@var{string1}, @var{string2}, @var{number} @r{[}, @var{domain} @r{[}, @var{category}@r{]]}) -Return the plural form used for @var{number} of the -translation of @var{string1} and @var{string2} in text domain -@var{domain} for locale category @var{category}. @var{string1} is the -English singular variant of a message, and @var{string2} the English plural -variant of the same message. -The default value for @var{domain} is the current value of @code{TEXTDOMAIN}. -The default value for @var{category} is @code{"LC_MESSAGES"}. - -The same remarks about argument order as for the @code{dcgettext()} function apply. - -@cindex @code{.mo} files, specifying directory of -@cindex files, @code{.mo}, specifying directory of -@cindex message object files, specifying directory of -@cindex files, message object, specifying directory of -@cindex @code{bindtextdomain()} function (@command{gawk}) -@item bindtextdomain(@var{directory} @r{[}, @var{domain}@r{]}) -Change the directory in which -@code{gettext} looks for @file{.mo} files, in case they -will not or cannot be placed in the standard locations -(e.g., during testing). -Return the directory in which @var{domain} is ``bound.'' - -The default @var{domain} is the value of @code{TEXTDOMAIN}. -If @var{directory} is the null string (@code{""}), then -@code{bindtextdomain()} returns the current binding for the -given @var{domain}. -@end table - -To use these facilities in your @command{awk} program, follow the steps -outlined in -@ifnotinfo -the previous @value{SECTION}, -@end ifnotinfo -@ifinfo -@ref{Explaining gettext}, -@end ifinfo -like so: - -@enumerate -@cindex @code{BEGIN} pattern, @code{TEXTDOMAIN} variable and -@cindex @code{TEXTDOMAIN} variable, @code{BEGIN} pattern and -@item -Set the variable @code{TEXTDOMAIN} to the text domain of -your program. This is best done in a @code{BEGIN} rule -(@pxref{BEGIN/END}), -or it can also be done via the @option{-v} command-line -option (@pxref{Options}): - -@example -BEGIN @{ - TEXTDOMAIN = "guide" - @dots{} -@} -@end example - -@cindex @code{_} (underscore), translatable string -@cindex underscore (@code{_}), translatable string -@item -Mark all translatable strings with a leading underscore (@samp{_}) -character. It @emph{must} be adjacent to the opening -quote of the string. For example: +Another example where indirect functions calls are useful can be found in +processing arrays. @DBREF{Walking Arrays} presented a simple function +for ``walking'' an array of arrays. That function simply printed the +name and value of each scalar array element. However, it is easy to +generalize that function, by passing in the name of a function to call +when walking an array. The modified function looks like this: @example -print _"hello, world" -x = _"you goofed" -printf(_"Number of users is %d\n", nusers) -@end example - -@item -If you are creating strings dynamically, you can -still translate them, using the @code{dcgettext()} -built-in function: - -@example -message = nusers " users logged in" -message = dcgettext(message, "adminprog") -print message -@end example - -Here, the call to @code{dcgettext()} supplies a different -text domain (@code{"adminprog"}) in which to find the -message, but it uses the default @code{"LC_MESSAGES"} category. - -@cindex @code{LC_MESSAGES} locale category, @code{bindtextdomain()} function (@command{gawk}) -@item -During development, you might want to put the @file{.mo} -file in a private directory for testing. This is done -with the @code{bindtextdomain()} built-in function: - -@example -BEGIN @{ - TEXTDOMAIN = "guide" # our text domain - if (Testing) @{ - # where to find our files - bindtextdomain("testdir") - # joe is in charge of adminprog - bindtextdomain("../joe/testdir", "adminprog") - @} - @dots{} -@} -@end example - -@end enumerate - -@xref{I18N Example}, -for an example program showing the steps to create -and use translations from @command{awk}. - -@node Translator i18n -@section Translating @command{awk} Programs - -@cindex @code{.po} files -@cindex files, @code{.po} -@cindex portable object files -@cindex files, portable object -Once a program's translatable strings have been marked, they must -be extracted to create the initial @file{.po} file. -As part of translation, it is often helpful to rearrange the order -in which arguments to @code{printf} are output. - -@command{gawk}'s @option{--gen-pot} command-line option extracts -the messages and is discussed next. -After that, @code{printf}'s ability to -rearrange the order for @code{printf} arguments at runtime -is covered. - -@menu -* String Extraction:: Extracting marked strings. -* Printf Ordering:: Rearranging @code{printf} arguments. -* I18N Portability:: @command{awk}-level portability issues. -@end menu - -@node String Extraction -@subsection Extracting Marked Strings -@cindex strings, extracting -@cindex marked strings@comma{} extracting -@cindex @code{--gen-pot} option -@cindex command-line options, string extraction -@cindex string extraction (internationalization) -@cindex marked string extraction (internationalization) -@cindex extraction, of marked strings (internationalization) - -@cindex @code{--gen-pot} option -Once your @command{awk} program is working, and all the strings have -been marked and you've set (and perhaps bound) the text domain, -it is time to produce translations. -First, use the @option{--gen-pot} command-line option to create -the initial @file{.pot} file: - -@example -$ @kbd{gawk --gen-pot -f guide.awk > guide.pot} -@end example - -@cindex @code{xgettext} utility -When run with @option{--gen-pot}, @command{gawk} does not execute your -program. Instead, it parses it as usual and prints all marked strings -to standard output in the format of a GNU @code{gettext} Portable Object -file. Also included in the output are any constant strings that -appear as the first argument to @code{dcgettext()} or as the first and -second argument to @code{dcngettext()}.@footnote{The -@command{xgettext} utility that comes with GNU -@code{gettext} can handle @file{.awk} files.} -@xref{I18N Example}, -for the full list of steps to go through to create and test -translations for @command{guide}. - -@node Printf Ordering -@subsection Rearranging @code{printf} Arguments - -@cindex @code{printf} statement, positional specifiers -@cindex positional specifiers, @code{printf} statement -Format strings for @code{printf} and @code{sprintf()} -(@pxref{Printf}) -present a special problem for translation. -Consider the following:@footnote{This example is borrowed -from the GNU @code{gettext} manual.} - -@c line broken here only for smallbook format -@example -printf(_"String `%s' has %d characters\n", - string, length(string))) -@end example - -A possible German translation for this might be: - -@example -"%d Zeichen lang ist die Zeichenkette `%s'\n" -@end example - -The problem should be obvious: the order of the format -specifications is different from the original! -Even though @code{gettext()} can return the translated string -at runtime, -it cannot change the argument order in the call to @code{printf}. - -To solve this problem, @code{printf} format specifiers may have -an additional optional element, which we call a @dfn{positional specifier}. -For example: - -@example -"%2$d Zeichen lang ist die Zeichenkette `%1$s'\n" -@end example - -Here, the positional specifier consists of an integer count, which indicates which -argument to use, and a @samp{$}. Counts are one-based, and the -format string itself is @emph{not} included. Thus, in the following -example, @samp{string} is the first argument and @samp{length(string)} is the second: - -@example -$ @kbd{gawk 'BEGIN @{} -> @kbd{string = "Dont Panic"} -> @kbd{printf _"%2$d characters live in \"%1$s\"\n",} -> @kbd{string, length(string)} -> @kbd{@}'} -@print{} 10 characters live in "Dont Panic" -@end example - -If present, positional specifiers come first in the format specification, -before the flags, the field width, and/or the precision. - -Positional specifiers can be used with the dynamic field width and -precision capability: - -@example -$ @kbd{gawk 'BEGIN @{} -> @kbd{printf("%*.*s\n", 10, 20, "hello")} -> @kbd{printf("%3$*2$.*1$s\n", 20, 10, "hello")} -> @kbd{@}'} -@print{} hello -@print{} hello -@end example - -@quotation NOTE -When using @samp{*} with a positional specifier, the @samp{*} -comes first, then the integer position, and then the @samp{$}. -This is somewhat counterintuitive. -@end quotation - -@cindex @code{printf} statement, positional specifiers, mixing with regular formats -@cindex positional specifiers, @code{printf} statement, mixing with regular formats -@cindex format specifiers, mixing regular with positional specifiers -@command{gawk} does not allow you to mix regular format specifiers -and those with positional specifiers in the same string: - -@example -$ @kbd{gawk 'BEGIN @{ printf _"%d %3$s\n", 1, 2, "hi" @}'} -@error{} gawk: cmd. line:1: fatal: must use `count$' on all formats or none -@end example - -@quotation NOTE -There are some pathological cases that @command{gawk} may fail to -diagnose. In such cases, the output may not be what you expect. -It's still a bad idea to try mixing them, even if @command{gawk} -doesn't detect it. -@end quotation - -Although positional specifiers can be used directly in @command{awk} programs, -their primary purpose is to help in producing correct translations of -format strings into languages different from the one in which the program -is first written. - -@node I18N Portability -@subsection @command{awk} Portability Issues - -@cindex portability, internationalization and -@cindex internationalization, localization, portability and -@command{gawk}'s internationalization features were purposely chosen to -have as little impact as possible on the portability of @command{awk} -programs that use them to other versions of @command{awk}. -Consider this program: - -@example -BEGIN @{ - TEXTDOMAIN = "guide" - if (Test_Guide) # set with -v - bindtextdomain("/test/guide/messages") - print _"don't panic!" -@} -@end example - -@noindent -As written, it won't work on other versions of @command{awk}. -However, it is actually almost portable, requiring very little -change: - -@itemize @bullet -@cindex @code{TEXTDOMAIN} variable, portability and -@item -Assignments to @code{TEXTDOMAIN} won't have any effect, -since @code{TEXTDOMAIN} is not special in other @command{awk} implementations. - -@item -Non-GNU versions of @command{awk} treat marked strings -as the concatenation of a variable named @code{_} with the string -following it.@footnote{This is good fodder for an ``Obfuscated -@command{awk}'' contest.} Typically, the variable @code{_} has -the null string (@code{""}) as its value, leaving the original string constant as -the result. - -@item -By defining ``dummy'' functions to replace @code{dcgettext()}, @code{dcngettext()} -and @code{bindtextdomain()}, the @command{awk} program can be made to run, but -all the messages are output in the original language. -For example: - -@cindex @code{bindtextdomain()} function (@command{gawk}), portability and -@cindex @code{dcgettext()} function (@command{gawk}), portability and -@cindex @code{dcngettext()} function (@command{gawk}), portability and -@example -@c file eg/lib/libintl.awk -function bindtextdomain(dir, domain) -@{ - return dir -@} - -function dcgettext(string, domain, category) -@{ - return string -@} - -function dcngettext(string1, string2, number, domain, category) +@c file eg/lib/processarray.awk +function process_array(arr, name, process, do_arrays, i, new_name) @{ - return (number == 1 ? string1 : string2) -@} -@c endfile -@end example - -@item -The use of positional specifications in @code{printf} or -@code{sprintf()} is @emph{not} portable. -To support @code{gettext()} at the C level, many systems' C versions of -@code{sprintf()} do support positional specifiers. But it works only if -enough arguments are supplied in the function call. Many versions of -@command{awk} pass @code{printf} formats and arguments unchanged to the -underlying C library version of @code{sprintf()}, but only one format and -argument at a time. What happens if a positional specification is -used is anybody's guess. -However, since the positional specifications are primarily for use in -@emph{translated} format strings, and since non-GNU @command{awk}s never -retrieve the translated string, this should not be a problem in practice. -@end itemize -@c ENDOFRANGE inap - -@node I18N Example -@section A Simple Internationalization Example - -Now let's look at a step-by-step example of how to internationalize and -localize a simple @command{awk} program, using @file{guide.awk} as our -original source: - -@example -@c file eg/prog/guide.awk -BEGIN @{ - TEXTDOMAIN = "guide" - bindtextdomain(".") # for testing - print _"Don't Panic" - print _"The Answer Is", 42 - print "Pardon me, Zaphod who?" + for (i in arr) @{ + new_name = (name "[" i "]") + if (isarray(arr[i])) @{ + if (do_arrays) + @@process(new_name, arr[i]) + process_array(arr[i], new_name, process, do_arrays) + @} else + @@process(new_name, arr[i]) + @} @} @c endfile @end example -@noindent -Run @samp{gawk --gen-pot} to create the @file{.pot} file: - -@example -$ @kbd{gawk --gen-pot -f guide.awk > guide.pot} -@end example - -@noindent -This produces: - -@example -@c file eg/data/guide.po -#: guide.awk:4 -msgid "Don't Panic" -msgstr "" - -#: guide.awk:5 -msgid "The Answer Is" -msgstr "" - -@c endfile -@end example - -This original portable object template file is saved and reused for each language -into which the application is translated. The @code{msgid} -is the original string and the @code{msgstr} is the translation. - -@quotation NOTE -Strings not marked with a leading underscore do not -appear in the @file{guide.pot} file. -@end quotation - -Next, the messages must be translated. -Here is a translation to a hypothetical dialect of English, -called ``Mellow'':@footnote{Perhaps it would be better if it were -called ``Hippy.'' Ah, well.} - -@example -@group -$ cp guide.pot guide-mellow.po -@var{Add translations to} guide-mellow.po @dots{} -@end group -@end example - -@noindent -Following are the translations: - -@example -@c file eg/data/guide-mellow.po -#: guide.awk:4 -msgid "Don't Panic" -msgstr "Hey man, relax!" - -#: guide.awk:5 -msgid "The Answer Is" -msgstr "Like, the scoop is" - -@c endfile -@end example - -@cindex Linux -@cindex GNU/Linux -The next step is to make the directory to hold the binary message object -file and then to create the @file{guide.mo} file. -The directory layout shown here is standard for GNU @code{gettext} on -GNU/Linux systems. Other versions of @code{gettext} may use a different -layout: - -@example -$ @kbd{mkdir en_US en_US/LC_MESSAGES} -@end example - -@cindex @code{.po} files, converting to @code{.mo} -@cindex files, @code{.po}, converting to @code{.mo} -@cindex @code{.mo} files, converting from @code{.po} -@cindex files, @code{.mo}, converting from @code{.po} -@cindex portable object files, converting to message object files -@cindex files, portable object, converting to message object files -@cindex message object files, converting from portable object files -@cindex files, message object, converting from portable object files -@cindex @command{msgfmt} utility -The @command{msgfmt} utility does the conversion from human-readable -@file{.po} file to machine-readable @file{.mo} file. -By default, @command{msgfmt} creates a file named @file{messages}. -This file must be renamed and placed in the proper directory so that -@command{gawk} can find it: - -@example -$ @kbd{msgfmt guide-mellow.po} -$ @kbd{mv messages en_US/LC_MESSAGES/guide.mo} -@end example - -Finally, we run the program to test it: - -@example -$ @kbd{gawk -f guide.awk} -@print{} Hey man, relax! -@print{} Like, the scoop is 42 -@print{} Pardon me, Zaphod who? -@end example - -If the three replacement functions for @code{dcgettext()}, @code{dcngettext()} -and @code{bindtextdomain()} -(@pxref{I18N Portability}) -are in a file named @file{libintl.awk}, -then we can run @file{guide.awk} unchanged as follows: - -@example -$ @kbd{gawk --posix -f guide.awk -f libintl.awk} -@print{} Don't Panic -@print{} The Answer Is 42 -@print{} Pardon me, Zaphod who? -@end example - -@node Gawk I18N -@section @command{gawk} Can Speak Your Language - -@command{gawk} itself has been internationalized -using the GNU @code{gettext} package. -(GNU @code{gettext} is described in -complete detail in -@ifinfo -@inforef{Top, , GNU @code{gettext} utilities, gettext, GNU gettext tools}.) -@end ifinfo -@ifnotinfo -@cite{GNU gettext tools}.) -@end ifnotinfo -As of this writing, the latest version of GNU @code{gettext} is -@uref{ftp://ftp.gnu.org/gnu/gettext/gettext-0.18.1.tar.gz, @value{PVERSION} 0.18.1}. - -If a translation of @command{gawk}'s messages exists, -then @command{gawk} produces usage messages, warnings, -and fatal errors in the local language. -@c ENDOFRANGE inloc - -@node Advanced Features -@chapter Advanced Features of @command{gawk} -@cindex advanced features, network connections, See Also networks, connections -@c STARTOFRANGE gawadv -@cindex @command{gawk}, features, advanced -@c STARTOFRANGE advgaw -@cindex advanced features, @command{gawk} -@ignore -Contributed by: Peter Langston <pud!psl@bellcore.bellcore.com> - - Found in Steve English's "signature" line: - -"Write documentation as if whoever reads it is a violent psychopath -who knows where you live." -@end ignore -@quotation -@i{Write documentation as if whoever reads it is -a violent psychopath who knows where you live.}@* -Steve English, as quoted by Peter Langston -@end quotation - -This @value{CHAPTER} discusses advanced features in @command{gawk}. -It's a bit of a ``grab bag'' of items that are otherwise unrelated -to each other. -First, a command-line option allows @command{gawk} to recognize -nondecimal numbers in input data, not just in @command{awk} -programs. -Then, @command{gawk}'s special features for sorting arrays are presented. -Next, two-way I/O, discussed briefly in earlier parts of this -@value{DOCUMENT}, is described in full detail, along with the basics -of TCP/IP networking. Finally, @command{gawk} -can @dfn{profile} an @command{awk} program, making it possible to tune -it for performance. - -@ref{Dynamic Extensions}, -discusses the ability to dynamically add new built-in functions to -@command{gawk}. As this feature is still immature and likely to change, -its description is relegated to an appendix. - -@menu -* Nondecimal Data:: Allowing nondecimal input data. -* Array Sorting:: Facilities for controlling array traversal and - sorting arrays. -* Two-way I/O:: Two-way communications with another process. -* TCP/IP Networking:: Using @command{gawk} for network programming. -* Profiling:: Profiling your @command{awk} programs. -@end menu - -@node Nondecimal Data -@section Allowing Nondecimal Input Data -@cindex @code{--non-decimal-data} option -@cindex advanced features, @command{gawk}, nondecimal input data -@cindex input, data@comma{} nondecimal -@cindex constants, nondecimal - -If you run @command{gawk} with the @option{--non-decimal-data} option, -you can have nondecimal constants in your input data: - -@c line break here for small book format -@example -$ @kbd{echo 0123 123 0x123 |} -> @kbd{gawk --non-decimal-data '@{ printf "%d, %d, %d\n",} -> @kbd{$1, $2, $3 @}'} -@print{} 83, 123, 291 -@end example - -For this feature to work, write your program so that -@command{gawk} treats your data as numeric: - -@example -$ @kbd{echo 0123 123 0x123 | gawk '@{ print $1, $2, $3 @}'} -@print{} 0123 123 0x123 -@end example - -@noindent -The @code{print} statement treats its expressions as strings. -Although the fields can act as numbers when necessary, -they are still strings, so @code{print} does not try to treat them -numerically. You may need to add zero to a field to force it to -be treated as a number. For example: - -@example -$ @kbd{echo 0123 123 0x123 | gawk --non-decimal-data '} -> @kbd{@{ print $1, $2, $3} -> @kbd{print $1 + 0, $2 + 0, $3 + 0 @}'} -@print{} 0123 123 0x123 -@print{} 83 123 291 -@end example - -Because it is common to have decimal data with leading zeros, and because -using this facility could lead to surprising results, the default is to leave it -disabled. If you want it, you must explicitly request it. - -@cindex programming conventions, @code{--non-decimal-data} option -@cindex @code{--non-decimal-data} option, @code{strtonum()} function and -@cindex @code{strtonum()} function (@command{gawk}), @code{--non-decimal-data} option and -@quotation CAUTION -@emph{Use of this option is not recommended.} -It can break old programs very badly. -Instead, use the @code{strtonum()} function to convert your data -(@pxref{Nondecimal-numbers}). -This makes your programs easier to write and easier to read, and -leads to less surprising results. -@end quotation - -@node Array Sorting -@section Controlling Array Traversal and Array Sorting - -@command{gawk} lets you control the order in which @samp{for (i in array)} loops -will traverse an array. - -In addition, two built-in functions, @code{asort()} and @code{asorti()}, -let you sort arrays based on the array values and indices, respectively. -These two functions also provide control over the sorting criteria used -to order the elements during sorting. - -@menu -* Controlling Array Traversal:: How to use PROCINFO["sorted_in"]. -* Array Sorting Functions:: How to use @code{asort()} and @code{asorti()}. -@end menu - -@node Controlling Array Traversal -@subsection Controlling Array Traversal - -By default, the order in which a @samp{for (i in array)} loop -scans an array is not defined; it is generally based upon -the internal implementation of arrays inside @command{awk}. - -Often, though, it is desirable to be able to loop over the elements -in a particular order that you, the programmer, choose. @command{gawk} -lets you do this; this @value{SUBSECTION} describes how. - -@menu -* Controlling Scanning With A Function:: Using a function to control scanning. -* Controlling Scanning:: Controlling the order in which arrays - are scanned. -@end menu - -@node Controlling Scanning With A Function -@subsubsection Array Scanning Using A User-defined Function - -The value of @code{PROCINFO["sorted_in"]} can be a function name. -This lets you traverse an array based on any custom criterion. -The array elements are ordered according to the return value of this -function. The comparison function should be defined with at least -four arguments: - -@example -function comp_func(i1, v1, i2, v2) -@{ - @var{compare elements 1 and 2 in some fashion} - @var{return < 0; 0; or > 0} -@} -@end example - -Here, @var{i1} and @var{i2} are the indices, and @var{v1} and @var{v2} -are the corresponding values of the two elements being compared. -Either @var{v1} or @var{v2}, or both, can be arrays if the array being -traversed contains subarrays as values. The three possible return values -are interpreted this way: +The arguments are as follows: @table @code -@item comp_func(i1, v1, i2, v2) < 0 -Index @var{i1} comes before index @var{i2} during loop traversal. +@item arr +The array. -@item comp_func(i1, v1, i2, v2) == 0 -Indices @var{i1} and @var{i2} -come together but the relative order with respect to each other is undefined. +@item name +The name of the array (a string). -@item comp_func(i1, v1, i2, v2) > 0 -Index @var{i1} comes after index @var{i2} during loop traversal. -@end table +@item process +The name of the function to call. -Our first comparison function can be used to scan an array in -numerical order of the indices: - -@example -function cmp_num_idx(i1, v1, i2, v2) -@{ - # numerical index comparison, ascending order - return (i1 - i2) -@} -@end example - -Our second function traverses an array based on the string order of -the element values rather than by indices: - -@example -function cmp_str_val(i1, v1, i2, v2) -@{ - # string value comparison, ascending order - v1 = v1 "" - v2 = v2 "" - if (v1 < v2) - return -1 - return (v1 != v2) -@} -@end example +@item do_arrays +If this is true, the function can handle elements that are subarrays. +@end table -The third -comparison function makes all numbers, and numeric strings without -any leading or trailing spaces, come out first during loop traversal: +If subarrays are to be processed, that is done before walking them further. -@example -function cmp_num_str_val(i1, v1, i2, v2, n1, n2) -@{ - # numbers before string value comparison, ascending order - n1 = v1 + 0 - n2 = v2 + 0 - if (n1 == v1) - return (n2 == v2) ? (n1 - n2) : -1 - else if (n2 == v2) - return 1 - return (v1 < v2) ? -1 : (v1 != v2) -@} -@end example - -Here is a main program to demonstrate how @command{gawk} -behaves using each of the previous functions: +When run with the following scaffolding, the function produces the same +results as does the earlier @code{walk_array()} function: @example BEGIN @{ - data["one"] = 10 - data["two"] = 20 - data[10] = "one" - data[100] = 100 - data[20] = "two" - - f[1] = "cmp_num_idx" - f[2] = "cmp_str_val" - f[3] = "cmp_num_str_val" - for (i = 1; i <= 3; i++) @{ - printf("Sort function: %s\n", f[i]) - PROCINFO["sorted_in"] = f[i] - for (j in data) - printf("\tdata[%s] = %s\n", j, data[j]) - print "" - @} -@} -@end example - -Here are the results when the program is run: -@page - -@example -$ @kbd{gawk -f compdemo.awk} -@print{} Sort function: cmp_num_idx @ii{Sort by numeric index} -@print{} data[two] = 20 -@print{} data[one] = 10 @ii{Both strings are numerically zero} -@print{} data[10] = one -@print{} data[20] = two -@print{} data[100] = 100 -@print{} -@print{} Sort function: cmp_str_val @ii{Sort by element values as strings} -@print{} data[one] = 10 -@print{} data[100] = 100 @ii{String 100 is less than string 20} -@print{} data[two] = 20 -@print{} data[10] = one -@print{} data[20] = two -@print{} -@print{} Sort function: cmp_num_str_val @ii{Sort all numbers before all strings} -@print{} data[one] = 10 -@print{} data[two] = 20 -@print{} data[100] = 100 -@print{} data[10] = one -@print{} data[20] = two -@end example - -Consider sorting the entries of a GNU/Linux system password file -according to login names. The following program sorts records -by a specific field position and can be used for this purpose: - -@example -# sort.awk --- simple program to sort by field position -# field position is specified by the global variable POS - -function cmp_field(i1, v1, i2, v2) -@{ - # comparison by value, as string, and ascending order - return v1[POS] < v2[POS] ? -1 : (v1[POS] != v2[POS]) -@} - -@{ - for (i = 1; i <= NF; i++) - a[NR][i] = $i -@} - -END @{ - PROCINFO["sorted_in"] = "cmp_field" - if (POS < 1 || POS > NF) - POS = 1 - for (i in a) @{ - for (j = 1; j <= NF; j++) - printf("%s%c", a[i][j], j < NF ? ":" : "") - print "" - @} -@} -@end example - -The first field in each entry of the password file is the user's login name, -and the fields are seperated by colons. -Each record defines a subarray (@pxref{Arrays of Arrays}), -with each field as an element in the subarray. -Running the program produces the -following output: - -@example -$ @kbd{gawk -vPOS=1 -F: -f sort.awk /etc/passwd} -@print{} adm:x:3:4:adm:/var/adm:/sbin/nologin -@print{} apache:x:48:48:Apache:/var/www:/sbin/nologin -@print{} avahi:x:70:70:Avahi daemon:/:/sbin/nologin -@dots{} -@end example - -The comparison should normally always return the same value when given a -specific pair of array elements as its arguments. If inconsistent -results are returned then the order is undefined. This behavior can be -exploited to introduce random order into otherwise seemingly -ordered data: - -@example -function cmp_randomize(i1, v1, i2, v2) -@{ - # random order - return (2 - 4 * rand()) -@} -@end example - -As mentioned above, the order of the indices is arbitrary if two -elements compare equal. This is usually not a problem, but letting -the tied elements come out in arbitrary order can be an issue, especially -when comparing item values. The partial ordering of the equal elements -may change during the next loop traversal, if other elements are added or -removed from the array. One way to resolve ties when comparing elements -with otherwise equal values is to include the indices in the comparison -rules. Note that doing this may make the loop traversal less efficient, -so consider it only if necessary. The following comparison functions -force a deterministic order, and are based on the fact that the -indices of two elements are never equal: + a[1] = 1 + a[2][1] = 21 + a[2][2] = 22 + a[3] = 3 + a[4][1][1] = 411 + a[4][2] = 42 -@example -function cmp_numeric(i1, v1, i2, v2) -@{ - # numerical value (and index) comparison, descending order - return (v1 != v2) ? (v2 - v1) : (i2 - i1) + process_array(a, "a", "do_print", 0) @} -function cmp_string(i1, v1, i2, v2) +function do_print(name, element) @{ - # string value (and index) comparison, descending order - v1 = v1 i1 - v2 = v2 i2 - return (v1 > v2) ? -1 : (v1 != v2) + printf "%s = %s\n", name, element @} @end example -@c Avoid using the term ``stable'' when describing the unpredictable behavior -@c if two items compare equal. Usually, the goal of a "stable algorithm" -@c is to maintain the original order of the items, which is a meaningless -@c concept for a list constructed from a hash. - -A custom comparison function can often simplify ordered loop -traversal, and the sky is really the limit when it comes to -designing such a function. - -When string comparisons are made during a sort, either for element -values where one or both aren't numbers, or for element indices -handled as strings, the value of @code{IGNORECASE} -(@pxref{Built-in Variables}) controls whether -the comparisons treat corresponding uppercase and lowercase letters as -equivalent or distinct. - -Another point to keep in mind is that in the case of subarrays -the element values can themselves be arrays; a production comparison -function should use the @code{isarray()} function -(@pxref{Type Functions}), -to check for this, and choose a defined sorting order for subarrays. - -All sorting based on @code{PROCINFO["sorted_in"]} -is disabled in POSIX mode, -since the @code{PROCINFO} array is not special in that case. - -As a side note, sorting the array indices before traversing -the array has been reported to add 15% to 20% overhead to the -execution time of @command{awk} programs. For this reason, -sorted array traversal is not the default. - -@c The @command{gawk} -@c maintainers believe that only the people who wish to use a -@c feature should have to pay for it. - -@node Controlling Scanning -@subsubsection Controlling Array Scanning Order - -As described in -@iftex -the previous subsubsection, -@end iftex -@ifnottex -@ref{Controlling Scanning With A Function}, -@end ifnottex -you can provide the name of a function as the value of -@code{PROCINFO["sorted_in"]} to specify custom sorting criteria. - -Often, though, you may wish to do something simple, such as -``sort based on comparing the indices in ascending order,'' -or ``sort based on comparing the values in descending order.'' -Having to write a simple comparison function for this purpose -for use in all of your programs becomes tedious. -For the common simple cases, @command{gawk} provides -the option of supplying special names that do the requested -sorting for you. -You can think of them as ``predefined'' sorting functions, -if you like, although the names purposely include characters -that are not valid in real @command{awk} function names. - -The following special values are available: - -@table @code -@item "@@ind_str_asc" -Order by indices compared as strings; this is the most basic sort. -(Internally, array indices are always strings, so with @samp{a[2*5] = 1} -the index is @code{"10"} rather than numeric 10.) - -@item "@@ind_num_asc" -Order by indices but force them to be treated as numbers in the process. -Any index with a non-numeric value will end up positioned as if it were zero. - -@item "@@val_type_asc" -Order by element values rather than indices. -Ordering is by the type assigned to the element -(@pxref{Typing and Comparison}). -All numeric values come before all string values, -which in turn come before all subarrays. - -@item "@@val_str_asc" -Order by element values rather than by indices. Scalar values are -compared as strings. Subarrays, if present, come out last. - -@item "@@val_num_asc" -Order by element values rather than by indices. Scalar values are -compared as numbers. Subarrays, if present, come out last. -When numeric values are equal, the string values are used to provide -an ordering: this guarantees consistent results across different -versions of the C @code{qsort()} function.@footnote{When two elements -compare as equal, the C @code{qsort()} function does not guarantee -that they will maintain their original relative order after sorting. -Using the string value to provide a unique ordering when the numeric -values are equal ensures that @command{gawk} behaves consistently -across different environments.} - -@item "@@ind_str_desc" -Reverse order from the most basic sort. - -@item "@@ind_num_desc" -Numeric indices ordered from high to low. - -@item "@@val_type_desc" -Element values, based on type, in descending order. - -@item "@@val_str_desc" -Element values, treated as strings, ordered from high to low. -Subarrays, if present, come out first. - -@item "@@val_num_desc" -Element values, treated as numbers, ordered from high to low. -Subarrays, if present, come out first. - -@item "@@unsorted" -Array elements are processed in arbitrary order, which is the normal -@command{awk} behavior. You can also get the normal behavior by just -deleting the @code{"sorted_in"} element from the @code{PROCINFO} array, -if it previously had a value assigned to it. -@end table - -The array traversal order is determined before the @code{for} loop -starts to run. Changing @code{PROCINFO["sorted_in"]} in the loop body -will not affect the loop. - -For example: - -@example -$ @kbd{gawk 'BEGIN @{} -> @kbd{ a[4] = 4} -> @kbd{ a[3] = 3} -> @kbd{ for (i in a)} -> @kbd{ print i, a[i]} -> @kbd{@}'} -@print{} 4 4 -@print{} 3 3 -$ @kbd{gawk 'BEGIN @{} -> @kbd{ PROCINFO["sorted_in"] = "@@ind_str_asc"} -> @kbd{ a[4] = 4} -> @kbd{ a[3] = 3} -> @kbd{ for (i in a)} -> @kbd{ print i, a[i]} -> @kbd{@}'} -@print{} 3 3 -@print{} 4 4 -@end example - -When sorting an array by element values, if a value happens to be -a subarray then it is considered to be greater than any string or -numeric value, regardless of what the subarray itself contains, -and all subarrays are treated as being equal to each other. Their -order relative to each other is determined by their index strings. - -@node Array Sorting Functions -@subsection Sorting Array Values and Indices with @command{gawk} - -@cindex arrays, sorting -@cindex @code{asort()} function (@command{gawk}) -@cindex @code{asort()} function (@command{gawk}), arrays@comma{} sorting -@cindex sort function, arrays, sorting -In most @command{awk} implementations, sorting an array requires -writing a @code{sort} function. -While this can be educational for exploring different sorting algorithms, -usually that's not the point of the program. -@command{gawk} provides the built-in @code{asort()} -and @code{asorti()} functions -(@pxref{String Functions}) -for sorting arrays. For example: - -@example -@var{populate the array} data -n = asort(data) -for (i = 1; i <= n; i++) - @var{do something with} data[i] -@end example +Remember that you must supply a leading @samp{@@} in front of an indirect function call. -After the call to @code{asort()}, the array @code{data} is indexed from 1 -to some number @var{n}, the total number of elements in @code{data}. -(This count is @code{asort()}'s return value.) -@code{data[1]} @value{LEQ} @code{data[2]} @value{LEQ} @code{data[3]}, and so on. -The array elements are compared as strings. +Starting with @value{PVERSION} 4.1.2 of @command{gawk}, indirect function +calls may also be used with built-in functions and with extension functions +(@pxref{Dynamic Extensions}). The only thing you cannot do is pass a regular +expression constant to a built-in function through an indirect function +call.@footnote{This may change in a future version; recheck the documentation that +comes with your version of @command{gawk} to see if it has.} -@cindex side effects, @code{asort()} function -An important side effect of calling @code{asort()} is that -@emph{the array's original indices are irrevocably lost}. -As this isn't always desirable, @code{asort()} accepts a -second argument: +@command{gawk} does its best to make indirect function calls efficient. +For example, in the following case: @example -@var{populate the array} source -n = asort(source, dest) for (i = 1; i <= n; i++) - @var{do something with} dest[i] -@end example - -In this case, @command{gawk} copies the @code{source} array into the -@code{dest} array and then sorts @code{dest}, destroying its indices. -However, the @code{source} array is not affected. - -@code{asort()} accepts a third string argument -to control comparison of array elements. -As with @code{PROCINFO["sorted_in"]}, this argument may be the -name of a user-defined function, or one of the predefined names -that @command{gawk} provides -(@pxref{Controlling Scanning With A Function}). - -@quotation NOTE -In all cases, the sorted element values consist of the original -array's element values. The ability to control comparison merely -affects the way in which they are sorted. -@end quotation - -Often, what's needed is to sort on the values of the @emph{indices} -instead of the values of the elements. -To do that, use the -@code{asorti()} function. The interface is identical to that of -@code{asort()}, except that the index values are used for sorting, and -become the values of the result array: - -@example -@{ source[$0] = some_func($0) @} - -END @{ - n = asorti(source, dest) - for (i = 1; i <= n; i++) @{ - @ii{Work with sorted indices directly:} - @var{do something with} dest[i] - @dots{} - @ii{Access original array via sorted indices:} - @var{do something with} source[dest[i]] - @} -@} -@end example - -Similar to @code{asort()}, -in all cases, the sorted element values consist of the original -array's indices. The ability to control comparison merely -affects the way in which they are sorted. - -Sorting the array by replacing the indices provides maximal flexibility. -To traverse the elements in decreasing order, use a loop that goes from -@var{n} down to 1, either over the elements or over the indices.@footnote{You -may also use one of the predefined sorting names that sorts in -decreasing order.} - -@cindex reference counting, sorting arrays -Copying array indices and elements isn't expensive in terms of memory. -Internally, @command{gawk} maintains @dfn{reference counts} to data. -For example, when @code{asort()} copies the first array to the second one, -there is only one copy of the original array elements' data, even though -both arrays use the values. - -@c Document It And Call It A Feature. Sigh. -@cindex @command{gawk}, @code{IGNORECASE} variable in -@cindex @code{IGNORECASE} variable -@cindex arrays, sorting, @code{IGNORECASE} variable and -@cindex @code{IGNORECASE} variable, array sorting and -Because @code{IGNORECASE} affects string comparisons, the value -of @code{IGNORECASE} also affects sorting for both @code{asort()} and @code{asorti()}. -Note also that the locale's sorting order does @emph{not} -come into play; comparisons are based on character values only.@footnote{This -is true because locale-based comparison occurs only when in POSIX -compatibility mode, and since @code{asort()} and @code{asorti()} are -@command{gawk} extensions, they are not available in that case.} -Caveat Emptor. - -@node Two-way I/O -@section Two-Way Communications with Another Process -@cindex Brennan, Michael -@cindex programmers, attractiveness of -@smallexample -@c Path: cssun.mathcs.emory.edu!gatech!newsxfer3.itd.umich.edu!news-peer.sprintlink.net!news-sea-19.sprintlink.net!news-in-west.sprintlink.net!news.sprintlink.net!Sprint!204.94.52.5!news.whidbey.com!brennan -From: brennan@@whidbey.com (Mike Brennan) -Newsgroups: comp.lang.awk -Subject: Re: Learn the SECRET to Attract Women Easily -Date: 4 Aug 1997 17:34:46 GMT -@c Organization: WhidbeyNet -@c Lines: 12 -Message-ID: <5s53rm$eca@@news.whidbey.com> -@c References: <5s20dn$2e1@chronicle.concentric.net> -@c Reply-To: brennan@whidbey.com -@c NNTP-Posting-Host: asn202.whidbey.com -@c X-Newsreader: slrn (0.9.4.1 UNIX) -@c Xref: cssun.mathcs.emory.edu comp.lang.awk:5403 - -On 3 Aug 1997 13:17:43 GMT, Want More Dates??? -<tracy78@@kilgrona.com> wrote: ->Learn the SECRET to Attract Women Easily -> ->The SCENT(tm) Pheromone Sex Attractant For Men to Attract Women - -The scent of awk programmers is a lot more attractive to women than -the scent of perl programmers. --- -Mike Brennan -@c brennan@@whidbey.com -@end smallexample - -@cindex advanced features, @command{gawk}, processes@comma{} communicating with -@cindex processes, two-way communications with -It is often useful to be able to -send data to a separate program for -processing and then read the result. This can always be -done with temporary files: - -@example -# Write the data for processing -tempfile = ("mydata." PROCINFO["pid"]) -while (@var{not done with data}) - print @var{data} | ("subprogram > " tempfile) -close("subprogram > " tempfile) - -# Read the results, remove tempfile when done -while ((getline newdata < tempfile) > 0) - @var{process} newdata @var{appropriately} -close(tempfile) -system("rm " tempfile) -@end example - -@noindent -This works, but not elegantly. Among other things, it requires that -the program be run in a directory that cannot be shared among users; -for example, @file{/tmp} will not do, as another user might happen -to be using a temporary file with the same name. - -@cindex coprocesses -@cindex input/output, two-way -@cindex @code{|} (vertical bar), @code{|&} operator (I/O) -@cindex vertical bar (@code{|}), @code{|&} operator (I/O) -@cindex @command{csh} utility, @code{|&} operator, comparison with -However, with @command{gawk}, it is possible to -open a @emph{two-way} pipe to another process. The second process is -termed a @dfn{coprocess}, since it runs in parallel with @command{gawk}. -The two-way connection is created using the @samp{|&} operator -(borrowed from the Korn shell, @command{ksh}):@footnote{This is very -different from the same operator in the C shell.} - -@example -do @{ - print @var{data} |& "subprogram" - "subprogram" |& getline results -@} while (@var{data left to process}) -close("subprogram") -@end example - -The first time an I/O operation is executed using the @samp{|&} -operator, @command{gawk} creates a two-way pipeline to a child process -that runs the other program. Output created with @code{print} -or @code{printf} is written to the program's standard input, and -output from the program's standard output can be read by the @command{gawk} -program using @code{getline}. -As is the case with processes started by @samp{|}, the subprogram -can be any program, or pipeline of programs, that can be started by -the shell. - -There are some cautionary items to be aware of: - -@itemize @bullet -@item -As the code inside @command{gawk} currently stands, the coprocess's -standard error goes to the same place that the parent @command{gawk}'s -standard error goes. It is not possible to read the child's -standard error separately. - -@cindex deadlocks -@cindex buffering, input/output -@cindex @code{getline} command, deadlock and -@item -I/O buffering may be a problem. @command{gawk} automatically -flushes all output down the pipe to the coprocess. -However, if the coprocess does not flush its output, -@command{gawk} may hang when doing a @code{getline} in order to read -the coprocess's results. This could lead to a situation -known as @dfn{deadlock}, where each process is waiting for the -other one to do something. -@end itemize - -@cindex @code{close()} function, two-way pipes and -It is possible to close just one end of the two-way pipe to -a coprocess, by supplying a second argument to the @code{close()} -function of either @code{"to"} or @code{"from"} -(@pxref{Close Files And Pipes}). -These strings tell @command{gawk} to close the end of the pipe -that sends data to the coprocess or the end that reads from it, -respectively. - -@cindex @command{sort} utility, coprocesses and -This is particularly necessary in order to use -the system @command{sort} utility as part of a coprocess; -@command{sort} must read @emph{all} of its input -data before it can produce any output. -The @command{sort} program does not receive an end-of-file indication -until @command{gawk} closes the write end of the pipe. - -When you have finished writing data to the @command{sort} -utility, you can close the @code{"to"} end of the pipe, and -then start reading sorted data via @code{getline}. -For example: - -@example -BEGIN @{ - command = "LC_ALL=C sort" - n = split("abcdefghijklmnopqrstuvwxyz", a, "") - - for (i = n; i > 0; i--) - print a[i] |& command - close(command, "to") - - while ((command |& getline line) > 0) - print "got", line - close(command) -@} -@end example - -This program writes the letters of the alphabet in reverse order, one -per line, down the two-way pipe to @command{sort}. It then closes the -write end of the pipe, so that @command{sort} receives an end-of-file -indication. This causes @command{sort} to sort the data and write the -sorted data back to the @command{gawk} program. Once all of the data -has been read, @command{gawk} terminates the coprocess and exits. - -As a side note, the assignment @samp{LC_ALL=C} in the @command{sort} -command ensures traditional Unix (ASCII) sorting from @command{sort}. - -@cindex @command{gawk}, @code{PROCINFO} array in -@cindex @code{PROCINFO} array -You may also use pseudo-ttys (ptys) for -two-way communication instead of pipes, if your system supports them. -This is done on a per-command basis, by setting a special element -in the @code{PROCINFO} array -(@pxref{Auto-set}), -like so: - -@example -command = "sort -nr" # command, save in convenience variable -PROCINFO[command, "pty"] = 1 # update PROCINFO -print @dots{} |& command # start two-way pipe -@dots{} -@end example - -@noindent -Using ptys avoids the buffer deadlock issues described earlier, at some -loss in performance. If your system does not have ptys, or if all the -system's ptys are in use, @command{gawk} automatically falls back to -using regular pipes. - -@node TCP/IP Networking -@section Using @command{gawk} for Network Programming -@cindex advanced features, @command{gawk}, network programming -@cindex networks, programming -@c STARTOFRANGE tcpip -@cindex TCP/IP -@cindex @code{/inet/@dots{}} special files (@command{gawk}) -@cindex files, @code{/inet/@dots{}} (@command{gawk}) -@cindex @code{/inet4/@dots{}} special files (@command{gawk}) -@cindex files, @code{/inet4/@dots{}} (@command{gawk}) -@cindex @code{/inet6/@dots{}} special files (@command{gawk}) -@cindex files, @code{/inet6/@dots{}} (@command{gawk}) -@cindex @code{EMISTERED} -@quotation -@code{EMISTERED}:@* -@ @ @ @ @i{A host is a host from coast to coast,@* -@ @ @ @ and no-one can talk to host that's close,@* -@ @ @ @ unless the host that isn't close@* -@ @ @ @ is busy hung or dead.} -@end quotation - -In addition to being able to open a two-way pipeline to a coprocess -on the same system -(@pxref{Two-way I/O}), -it is possible to make a two-way connection to -another process on another system across an IP network connection. - -You can think of this as just a @emph{very long} two-way pipeline to -a coprocess. -The way @command{gawk} decides that you want to use TCP/IP networking is -by recognizing special @value{FN}s that begin with one of @samp{/inet/}, -@samp{/inet4/} or @samp{/inet6}. - -The full syntax of the special @value{FN} is -@file{/@var{net-type}/@var{protocol}/@var{local-port}/@var{remote-host}/@var{remote-port}}. -The components are: - -@table @var -@item net-type -Specifies the kind of Internet connection to make. -Use @samp{/inet4/} to force IPv4, and -@samp{/inet6/} to force IPv6. -Plain @samp{/inet/} (which used to be the only option) uses -the system default, most likely IPv4. - -@item protocol -The protocol to use over IP. This must be either @samp{tcp}, or -@samp{udp}, for a TCP or UDP IP connection, -respectively. The use of TCP is recommended for most applications. - -@item local-port -@cindex @code{getaddrinfo()} function (C library) -The local TCP or UDP port number to use. Use a port number of @samp{0} -when you want the system to pick a port. This is what you should do -when writing a TCP or UDP client. -You may also use a well-known service name, such as @samp{smtp} -or @samp{http}, in which case @command{gawk} attempts to determine -the predefined port number using the C @code{getaddrinfo()} function. - -@item remote-host -The IP address or fully-qualified domain name of the Internet -host to which you want to connect. - -@item remote-port -The TCP or UDP port number to use on the given @var{remote-host}. -Again, use @samp{0} if you don't care, or else a well-known -service name. -@end table - -@cindex @command{gawk}, @code{ERRNO} variable in -@cindex @code{ERRNO} variable -@quotation NOTE -Failure in opening a two-way socket will result in a non-fatal error -being returned to the calling code. The value of @code{ERRNO} indicates -the error (@pxref{Auto-set}). -@end quotation - -Consider the following very simple example: - -@example -BEGIN @{ - Service = "/inet/tcp/0/localhost/daytime" - Service |& getline - print $0 - close(Service) -@} -@end example - -This program reads the current date and time from the local system's -TCP @samp{daytime} server. -It then prints the results and closes the connection. - -Because this topic is extensive, the use of @command{gawk} for -TCP/IP programming is documented separately. -@ifinfo -See -@inforef{Top, , General Introduction, gawkinet, TCP/IP Internetworking with @command{gawk}}, -@end ifinfo -@ifnotinfo -See @cite{TCP/IP Internetworking with @command{gawk}}, -which comes as part of the @command{gawk} distribution, -@end ifnotinfo -for a much more complete introduction and discussion, as well as -extensive examples. - -@c ENDOFRANGE tcpip - -@node Profiling -@section Profiling Your @command{awk} Programs -@c STARTOFRANGE awkp -@cindex @command{awk} programs, profiling -@c STARTOFRANGE proawk -@cindex profiling @command{awk} programs -@c STARTOFRANGE pgawk -@cindex @command{pgawk} program -@cindex profiling @command{gawk}, See @command{pgawk} program - -You may produce execution -traces of your @command{awk} programs. -This is done with a specially compiled version of @command{gawk}, -called @command{pgawk} (``profiling @command{gawk}''). - -@cindex @code{awkprof.out} file -@cindex files, @code{awkprof.out} -@cindex @command{pgawk} program, @code{awkprof.out} file -@command{pgawk} is identical in every way to @command{gawk}, except that when -it has finished running, it creates a profile of your program in a file -named @file{awkprof.out}. -Because it is profiling, it also executes up to 45% slower than -@command{gawk} normally does. - -@cindex @code{--profile} option -As shown in the following example, -the @option{--profile} option can be used to change the name of the file -where @command{pgawk} will write the profile: - -@example -pgawk --profile=myprog.prof -f myprog.awk data1 data2 + @@the_func() @end example @noindent -In the above example, @command{pgawk} places the profile in -@file{myprog.prof} instead of in @file{awkprof.out}. - -Here is a sample -session showing a simple @command{awk} program, its input data, and the -results from running @command{pgawk}. First, the @command{awk} program: - -@example -BEGIN @{ print "First BEGIN rule" @} +@code{gawk} looks up the actual function to call only once. -END @{ print "First END rule" @} - -/foo/ @{ - print "matched /foo/, gosh" - for (i = 1; i <= 3; i++) - sing() -@} +@node Functions Summary +@section Summary -@{ - if (/foo/) - print "if is true" - else - print "else is true" -@} - -BEGIN @{ print "Second BEGIN rule" @} - -END @{ print "Second END rule" @} - -function sing( dummy) -@{ - print "I gotta be me!" -@} -@end example - -Following is the input data: - -@example -foo -bar -baz -foo -junk -@end example - -Here is the @file{awkprof.out} that results from running @command{pgawk} -on this program and data (this example also illustrates that @command{awk} -programmers sometimes have to work late): - -@cindex @code{BEGIN} pattern, @command{pgawk} program -@cindex @code{END} pattern, @command{pgawk} program -@example - # gawk profile, created Sun Aug 13 00:00:15 2000 - - # BEGIN block(s) - - BEGIN @{ - 1 print "First BEGIN rule" - 1 print "Second BEGIN rule" - @} - - # Rule(s) - - 5 /foo/ @{ # 2 - 2 print "matched /foo/, gosh" - 6 for (i = 1; i <= 3; i++) @{ - 6 sing() - @} - @} - - 5 @{ - 5 if (/foo/) @{ # 2 - 2 print "if is true" - 3 @} else @{ - 3 print "else is true" - @} - @} - - # END block(s) - - END @{ - 1 print "First END rule" - 1 print "Second END rule" - @} - - # Functions, listed alphabetically - - 6 function sing(dummy) - @{ - 6 print "I gotta be me!" - @} -@end example - -This example illustrates many of the basic features of profiling output. -They are as follows: - -@itemize @bullet +@itemize @value{BULLET} @item -The program is printed in the order @code{BEGIN} rule, -@code{BEGINFILE} rule, -pattern/action rules, -@code{ENDFILE} rule, @code{END} rule and functions, listed -alphabetically. -Multiple @code{BEGIN} and @code{END} rules are merged together, -as are multiple @code{BEGINFILE} and @code{ENDFILE} rules. +@command{awk} provides built-in functions and lets you define your own +functions. -@cindex patterns, counts @item -Pattern-action rules have two counts. -The first count, to the left of the rule, shows how many times -the rule's pattern was @emph{tested}. -The second count, to the right of the rule's opening left brace -in a comment, -shows how many times the rule's action was @emph{executed}. -The difference between the two indicates how many times the rule's -pattern evaluated to false. +POSIX @command{awk} provides three kinds of built-in functions: numeric, +string, and I/O. @command{gawk} provides functions that sort arrays, work +with values representing time, do bit manipulation, determine variable +type (array versus scalar), and internationalize and localize programs. +@command{gawk} also provides several extensions to some of standard +functions, typically in the form of additional arguments. @item -Similarly, -the count for an @code{if}-@code{else} statement shows how many times -the condition was tested. -To the right of the opening left brace for the @code{if}'s body -is a count showing how many times the condition was true. -The count for the @code{else} -indicates how many times the test failed. +Functions accept zero or more arguments and return a value. The +expressions that provide the argument values are completely evaluated +before the function is called. Order of evaluation is not defined. +The return value can be ignored. -@cindex loops, count for header @item -The count for a loop header (such as @code{for} -or @code{while}) shows how many times the loop test was executed. -(Because of this, you can't just look at the count on the first -statement in a rule to determine how many times the rule was executed. -If the first statement is a loop, the count is misleading.) +The handling of backslash in @code{sub()} and @code{gsub()} is not simple. +It is more straightforward in @command{gawk}'s @code{gensub()} function, +but that function still requires care in its use. -@cindex functions, user-defined, counts -@cindex user-defined, functions, counts @item -For user-defined functions, the count next to the @code{function} -keyword indicates how many times the function was called. -The counts next to the statements in the body show how many times -those statements were executed. +User-defined functions provide important capabilities but come with +some syntactic inelegancies. In a function call, there cannot be any +space between the function name and the opening left parenthesis of the +argument list. Also, there is no provision for local variables, so the +convention is to add extra parameters, and to separate them visually +from the real parameters by extra whitespace. -@cindex @code{@{@}} (braces), @command{pgawk} program -@cindex braces (@code{@{@}}), @command{pgawk} program @item -The layout uses ``K&R'' style with TABs. -Braces are used everywhere, even when -the body of an @code{if}, @code{else}, or loop is only a single statement. +User-defined functions may call other user-defined (and built-in) +functions and may call themselves recursively. Function parameters +``hide'' any global variables of the same names. +You cannot use the name of a reserved variable (such as @code{ARGC}) +as the name of a parameter in user-defined functions. -@cindex @code{()} (parentheses), @command{pgawk} program -@cindex parentheses @code{()}, @command{pgawk} program @item -Parentheses are used only where needed, as indicated by the structure -of the program and the precedence rules. -@c extra verbiage here satisfies the copyeditor. ugh. -For example, @samp{(3 + 5) * 4} means add three plus five, then multiply -the total by four. However, @samp{3 + 5 * 4} has no parentheses, and -means @samp{3 + (5 * 4)}. +Scalar values are passed to user-defined functions by value. Array +parameters are passed by reference; any changes made by the function to +array parameters are thus visible after the function has returned. -@ignore @item -All string concatenations are parenthesized too. -(This could be made a bit smarter.) -@end ignore +Use the @code{return} statement to return from a user-defined function. +An optional expression becomes the function's return value. Only scalar +values may be returned by a function. @item -Parentheses are used around the arguments to @code{print} -and @code{printf} only when -the @code{print} or @code{printf} statement is followed by a redirection. -Similarly, if -the target of a redirection isn't a scalar, it gets parenthesized. +If a variable that has never been used is passed to a user-defined +function, how that function treats the variable can set its nature: +either scalar or array. @item -@command{pgawk} supplies leading comments in -front of the @code{BEGIN} and @code{END} rules, -the pattern/action rules, and the functions. +@command{gawk} provides indirect function calls using a special syntax. +By setting a variable to the name of a function, you can +determine at runtime what function will be called at that point in the +program. This is equivalent to function pointers in C and C++. @end itemize -The profiled version of your program may not look exactly like what you -typed when you wrote it. This is because @command{pgawk} creates the -profiled version by ``pretty printing'' its internal representation of -the program. The advantage to this is that @command{pgawk} can produce -a standard representation. The disadvantage is that all source-code -comments are lost, as are the distinctions among multiple @code{BEGIN}, -@code{END}, @code{BEGINFILE}, and @code{ENDFILE} rules. Also, things such as: - -@example -/foo/ -@end example - -@noindent -come out as: - -@example -/foo/ @{ - print $0 -@} -@end example - -@noindent -which is correct, but possibly surprising. - -@cindex profiling @command{awk} programs, dynamically -@cindex @command{pgawk} program, dynamic profiling -Besides creating profiles when a program has completed, -@command{pgawk} can produce a profile while it is running. -This is useful if your @command{awk} program goes into an -infinite loop and you want to see what has been executed. -To use this feature, run @command{pgawk} in the background: - -@example -$ @kbd{pgawk -f myprog &} -[1] 13992 -@end example - -@cindex @command{kill} command@comma{} dynamic profiling -@cindex @code{USR1} signal -@cindex @code{SIGUSR1} signal -@cindex signals, @code{USR1}/@code{SIGUSR1} -@noindent -The shell prints a job number and process ID number; in this case, 13992. -Use the @command{kill} command to send the @code{USR1} signal -to @command{pgawk}: - -@example -$ @kbd{kill -USR1 13992} -@end example - -@noindent -As usual, the profiled version of the program is written to -@file{awkprof.out}, or to a different file if you use the @option{--profile} -option. - -Along with the regular profile, as shown earlier, the profile -includes a trace of any active functions: - -@example -# Function Call Stack: - -# 3. baz -# 2. bar -# 1. foo -# -- main -- -@end example -You may send @command{pgawk} the @code{USR1} signal as many times as you like. -Each time, the profile and function call trace are appended to the output -profile file. +@ifnotinfo +@part @value{PART2}Problem Solving with @command{awk} +@end ifnotinfo -@cindex @code{HUP} signal -@cindex @code{SIGHUP} signal -@cindex signals, @code{HUP}/@code{SIGHUP} -If you use the @code{HUP} signal instead of the @code{USR1} signal, -@command{pgawk} produces the profile and the function call trace and then exits. +@ifdocbook +Part II shows how to use @command{awk} and @command{gawk} for problem solving. +There is lots of code here for you to read and learn from. +It contains the following chapters: -@cindex @code{INT} signal (MS-Windows) -@cindex @code{SIGINT} signal (MS-Windows) -@cindex signals, @code{INT}/@code{SIGINT} (MS-Windows) -@cindex @code{QUIT} signal (MS-Windows) -@cindex @code{SIGQUIT} signal (MS-Windows) -@cindex signals, @code{QUIT}/@code{SIGQUIT} (MS-Windows) -When @command{pgawk} runs on MS-Windows systems, it uses the -@code{INT} and @code{QUIT} signals for producing the profile and, in -the case of the @code{INT} signal, @command{pgawk} exits. This is -because these systems don't support the @command{kill} command, so the -only signals you can deliver to a program are those generated by the -keyboard. The @code{INT} signal is generated by the -@kbd{@value{CTL}-@key{C}} or @kbd{@value{CTL}-@key{BREAK}} key, while the -@code{QUIT} signal is generated by the @kbd{@value{CTL}-@key{\}} key. +@itemize @value{BULLET} +@item +@ref{Library Functions} -Finally, regular @command{gawk} also accepts the @option{--profile} option. -When called this way, @command{gawk} ``pretty prints'' the program into -@file{awkprof.out}, without any execution counts. -@c ENDOFRANGE advgaw -@c ENDOFRANGE gawadv -@c ENDOFRANGE pgawk -@c ENDOFRANGE awkp -@c ENDOFRANGE proawk +@item +@ref{Sample Programs} +@end itemize +@end ifdocbook @node Library Functions @chapter A Library of @command{awk} Functions -@c STARTOFRANGE libf @cindex libraries of @command{awk} functions -@c STARTOFRANGE flib @cindex functions, library -@c STARTOFRANGE fudlib @cindex functions, user-defined, library of -@ref{User-defined}, describes how to write +@DBREF{User-defined} describes how to write your own @command{awk} functions. Writing functions is important, because it allows you to encapsulate algorithms and program tasks in a single place. It simplifies programming, making program development more manageable, and making programs more readable. -One valuable way to learn a new programming language is to @emph{read} -programs in that language. To that end, this @value{CHAPTER} -and @ref{Sample Programs}, -provide a good-sized body of code for you to read, -and hopefully, to learn from. +@cindex Kernighan, Brian +@cindex Plauger, P.J.@: +In their seminal 1976 book, @cite{Software Tools},@footnote{Sadly, over 35 +years later, many of the lessons taught by this book have yet to be +learned by a vast number of practicing programmers.} Brian Kernighan +and P.J.@: Plauger wrote: + +@quotation +Good Programming is not learned from generalities, but by seeing how +significant programs can be made clean, easy to read, easy to maintain and +modify, human-engineered, efficient and reliable, by the application of +common sense and good programming practices. Careful study and imitation +of good programs leads to better writing. +@end quotation + +In fact, they felt this idea was so important that they placed this +statement on the cover of their book. Because we believe strongly +that their statement is correct, this @value{CHAPTER} and @ref{Sample +Programs}, provide a good-sized body of code for you to read and, we hope, +to learn from. -@c 2e: USE TEXINFO-2 FUNCTION DEFINITION STUFF!!!!!!!!!!!!! This @value{CHAPTER} presents a library of useful @command{awk} functions. Many of the sample programs presented later in this @value{DOCUMENT} use these functions. The functions are presented here in a progression from simple to complex. @cindex Texinfo -@ref{Extract Program}, +@DBREF{Extract Program} presents a program that you can use to extract the source code for these example library functions and programs from the Texinfo source for this @value{DOCUMENT}. (This has already been done as part of the @command{gawk} distribution.) +@ifclear FOR_PRINT If you have written one or more useful, general-purpose @command{awk} functions and would like to contribute them to the @command{awk} user community, see @ref{How To Contribute}, for more information. +@end ifclear @cindex portability, example programs The programs in this @value{CHAPTER} and in @ref{Sample Programs}, -freely use features that are @command{gawk}-specific. +freely use @command{gawk}-specific features. Rewriting these programs for different implementations of @command{awk} -is pretty straightforward. +is pretty straightforward: -@itemize @bullet +@itemize @value{BULLET} @item Diagnostic error messages are sent to @file{/dev/stderr}. Use @samp{| "cat 1>&2"} instead of @samp{> "/dev/stderr"} if your system @@ -19364,6 +20574,8 @@ comparisons use only lowercase letters. * Passwd Functions:: Functions for getting user information. * Group Functions:: Functions for getting group information. * Walking Arrays:: A function to walk arrays of arrays. +* Library Functions Summary:: Summary of library functions. +* Library Exercises:: Exercises. @end menu @node Library Names @@ -19386,7 +20598,7 @@ Library functions often need to have global variables that they can use to preserve state information between calls to the function---for example, @code{getopt()}'s variable @code{_opti} (@pxref{Getopt Function}). -Such variables are called @dfn{private}, since the only functions that need to +Such variables are called @dfn{private}, as the only functions that need to use them are the ones in the library. When writing a library function, you should try to choose names for your @@ -19406,12 +20618,12 @@ with the user's program. @cindex underscore (@code{_}), in names of private variables In addition, several of the library functions use a prefix that helps indicate what function or set of functions use the variables---for example, -@code{_pw_byname} in the user database routines +@code{_pw_byname()} in the user database routines (@pxref{Passwd Functions}). -This convention is recommended, since it even further decreases the +This convention is recommended, as it even further decreases the chance of inadvertent conflict among variable names. Note that this convention is used equally well for variable names and for private -function names.@footnote{While all the library routines could have +function names.@footnote{Although all the library routines could have been rewritten to use this convention, this was not done, in order to show how our own @command{awk} programming style has evolved and to provide some basis for this discussion.} @@ -19423,9 +20635,9 @@ example, @code{getopt()}'s @code{Opterr} and @code{Optind} variables (@pxref{Getopt Function}). The leading capital letter indicates that it is global, while the fact that the variable name is not all capital letters indicates that the variable is -not one of @command{awk}'s built-in variables, such as @code{FS}. +not one of @command{awk}'s predefined variables, such as @code{FS}. -@cindex @code{--dump-variables} option +@cindex @option{--dump-variables} option, using for library functions It is also important that @emph{all} variables in library functions that do not need to save state are, in fact, declared local.@footnote{@command{gawk}'s @option{--dump-variables} command-line @@ -19437,8 +20649,9 @@ are very difficult to track down: function lib_func(x, y, l1, l2) @{ @dots{} - @var{use variable} some_var # some_var should be local - @dots{} # but is not by oversight + # some_var should be local but by oversight is not + @var{use variable} some_var + @dots{} @} @end example @@ -19450,7 +20663,7 @@ A different convention, common in the Tcl community, is to use a single associative array to hold the values needed by the library function(s), or ``package.'' This significantly decreases the number of actual global names in use. For example, the functions described in -@ref{Passwd Functions}, +@DBREF{Passwd Functions} might have used array elements @code{@w{PW_data["inited"]}}, @code{@w{PW_data["total"]}}, @code{@w{PW_data["count"]}}, and @code{@w{PW_data["awklib"]}}, instead of @code{@w{_pw_inited}}, @code{@w{_pw_awklib}}, @code{@w{_pw_total}}, @@ -19477,11 +20690,13 @@ programming use. * Ordinal Functions:: Functions for using characters as numbers and vice versa. * Join Function:: A function to join an array into a string. -* Gettimeofday Function:: A function to get formatted times. +* Getlocaltime Function:: A function to get formatted times. +* Readfile Function:: A function to read an entire file at once. +* Shell Quoting:: A function to quote strings for the shell. @end menu @node Strtonum Function -@subsection Converting Strings To Numbers +@subsection Converting Strings to Numbers The @code{strtonum()} function (@pxref{String Functions}) is a @command{gawk} extension. The following function @@ -19497,11 +20712,12 @@ provides an implementation for other versions of @command{awk}: # # Arnold Robbins, arnold@@skeeve.com, Public Domain # February, 2004 +# Revised June, 2014 @c endfile @end ignore @c file eg/lib/strtonum.awk -function mystrtonum(str, ret, chars, n, i, k, c) +function mystrtonum(str, ret, n, i, k, c) @{ if (str ~ /^0[0-7]*$/) @{ # octal @@ -19509,12 +20725,13 @@ function mystrtonum(str, ret, chars, n, i, k, c) ret = 0 for (i = 1; i <= n; i++) @{ c = substr(str, i, 1) - if ((k = index("01234567", c)) > 0) - k-- # adjust for 1-basing in awk + # index() returns 0 if c not in string, + # includes c == "0" + k = index("1234567", c) ret = ret * 8 + k @} - @} else if (str ~ /^0[xX][[:xdigit:]]+/) @{ + @} else if (str ~ /^0[xX][[:xdigit:]]+$/) @{ # hexadecimal str = substr(str, 3) # lop off leading 0x n = length(str) @@ -19522,10 +20739,9 @@ function mystrtonum(str, ret, chars, n, i, k, c) for (i = 1; i <= n; i++) @{ c = substr(str, i, 1) c = tolower(c) - if ((k = index("0123456789", c)) > 0) - k-- # adjust for 1-basing in awk - else if ((k = index("abcdef", c)) > 0) - k += 9 + # index() returns 0 if c not in string, + # includes c == "0" + k = index("123456789abcdef", c) ret = ret * 16 + k @} @@ -19547,8 +20763,8 @@ function mystrtonum(str, ret, chars, n, i, k, c) # a[5] = "123.45" # a[6] = "1.e3" # a[7] = "1.32" -# a[7] = "1.32E2" -# +# a[8] = "1.32E2" +# # for (i = 1; i in a; i++) # print a[i], strtonum(a[i]), mystrtonum(a[i]) # @} @@ -19558,9 +20774,12 @@ function mystrtonum(str, ret, chars, n, i, k, c) The function first looks for C-style octal numbers (base 8). If the input string matches a regular expression describing octal numbers, then @code{mystrtonum()} loops through each character in the -string. It sets @code{k} to the index in @code{"01234567"} of the current -octal digit. Since the return value is one-based, the @samp{k--} -adjusts @code{k} so it can be used in computing the return value. +string. It sets @code{k} to the index in @code{"1234567"} of the current +octal digit. +The return value will either be the same number as the digit, or zero +if the character is not there, which will be true for a @samp{0}. +This is safe, because the regexp test in the @code{if} ensures that +only octal values are converted. Similar logic applies to the code that checks for and converts a hexadecimal value, which starts with @samp{0x} or @samp{0X}. @@ -19579,13 +20798,9 @@ be tested with @command{gawk} and the results compared to the built-in @node Assert Function @subsection Assertions -@c STARTOFRANGE asse @cindex assertions -@c STARTOFRANGE assef @cindex @code{assert()} function (C library) -@c STARTOFRANGE libfass @cindex libraries of @command{awk} functions, assertions -@c STARTOFRANGE flibass @cindex functions, library, assertions @cindex @command{awk} programs, lengthy, assertions When writing large programs, it is often useful to know @@ -19593,7 +20808,7 @@ that a condition or set of conditions is true. Before proceeding with a particular computation, you make a statement about what you believe to be the case. Such a statement is known as an @dfn{assertion}. The C language provides an @code{<assert.h>} header file -and corresponding @code{assert()} macro that the programmer can use to make +and corresponding @code{assert()} macro that a programmer can use to make assertions. If an assertion fails, the @code{assert()} macro arranges to print a diagnostic message describing the condition that should have been true but was not, and then it kills the program. In C, using @@ -19701,10 +20916,6 @@ most likely causing the program to hang as it waits for input. There is a simple workaround to this: make sure that such a @code{BEGIN} rule always ends with an @code{exit} statement. -@c ENDOFRANGE asse -@c ENDOFRANGE assef -@c ENDOFRANGE flibass -@c ENDOFRANGE libfass @node Round Function @subsection Rounding Numbers @@ -19719,9 +20930,9 @@ with an @code{exit} statement. The way @code{printf} and @code{sprintf()} (@pxref{Printf}) perform rounding often depends upon the system's C @code{sprintf()} -subroutine. On many machines, @code{sprintf()} rounding is ``unbiased,'' -which means it doesn't always round a trailing @samp{.5} up, contrary -to naive expectations. In unbiased rounding, @samp{.5} rounds to even, +subroutine. On many machines, @code{sprintf()} rounding is @dfn{unbiased}, +which means it doesn't always round a trailing .5 up, contrary +to naive expectations. In unbiased rounding, .5 rounds to even, rather than always up, so 1.5 rounds to 2 but 4.5 rounds to 4. This means that if you are using a format that does rounding (e.g., @code{"%.0f"}), you should check what your system does. The following function does @@ -19770,7 +20981,7 @@ function round(x, ival, aval, fraction) @c don't include test harness in the file that gets installed # test harness -@{ print $0, round($0) @} +# @{ print $0, round($0) @} @end example @node Cliff Random Function @@ -19837,6 +21048,7 @@ reason to build them into the @command{awk} interpreter: @cindex @code{ord()} user-defined function @cindex @code{chr()} user-defined function +@cindex @code{_ord_init()} user-defined function @example @c file eg/lib/ord.awk # ord.awk --- do ord and chr @@ -19883,8 +21095,9 @@ function _ord_init( low, high, i, t) @cindex character sets (machine character encodings) @cindex ASCII @cindex EBCDIC +@cindex Unicode @cindex mark parity -Some explanation of the numbers used by @code{chr} is worthwhile. +Some explanation of the numbers used by @code{_ord_init()} is worthwhile. The most prominent character set in use today is ASCII.@footnote{This is changing; many systems use Unicode, a very large character set that includes ASCII as a subset. On systems with full Unicode support, @@ -19895,7 +21108,7 @@ Although an defines characters that use the values from 0 to 127.@footnote{ASCII has been extended in many countries to use the values from 128 to 255 for country-specific characters. If your system uses these extensions, -you can simplify @code{_ord_init} to loop from 0 to 255.} +you can simplify @code{_ord_init()} to loop from 0 to 255.} In the now distant past, at least one minicomputer manufacturer @c Pr1me, blech @@ -19904,7 +21117,7 @@ is always 1. This means that on those systems, characters have numeric values from 128 to 255. Finally, large mainframe systems use the EBCDIC character set, which uses all 256 values. -While there are other character sets in use on some older systems, +There are other character sets in use on some older systems, but they are not really worth worrying about: @example @@ -19924,8 +21137,7 @@ function chr(c) @c endfile #### test code #### -# BEGIN \ -# @{ +# BEGIN @{ # for (;;) @{ # printf("enter a character: ") # if (getline var <= 0) @@ -19959,7 +21171,7 @@ Good function design is important; this function needs to be general but it should also have a reasonable default behavior. It is called with an array as well as the beginning and ending indices of the elements in the array to be merged. This assumes that the array indices are numeric---a reasonable -assumption since the array was likely created with @code{split()} +assumption, as the array was likely created with @code{split()} (@pxref{String Functions}): @cindex @code{join()} user-defined function @@ -20002,7 +21214,7 @@ be nice if @command{awk} had an assignment operator for concatenation. The lack of an explicit operator for concatenation makes string operations more difficult than they really need to be.} -@node Gettimeofday Function +@node Getlocaltime Function @subsection Managing the Time of Day @cindex libraries of @command{awk} functions, managing, time @@ -20010,20 +21222,20 @@ more difficult than they really need to be.} @cindex timestamps, formatted @cindex time, managing The @code{systime()} and @code{strftime()} functions described in -@ref{Time Functions}, +@DBREF{Time Functions} provide the minimum functionality necessary for dealing with the time of day -in human readable form. While @code{strftime()} is extensive, the control +in human-readable form. Although @code{strftime()} is extensive, the control formats are not necessarily easy to remember or intuitively obvious when reading a program. -The following function, @code{gettimeofday()}, populates a user-supplied array +The following function, @code{getlocaltime()}, populates a user-supplied array with preformatted time information. It returns a string with the current time formatted in the same way as the @command{date} utility: -@cindex @code{gettimeofday()} user-defined function +@cindex @code{getlocaltime()} user-defined function @example @c file eg/lib/gettime.awk -# gettimeofday.awk --- get the time of day in a usable format +# getlocaltime.awk --- get the time of day in a usable format @c endfile @ignore @c file eg/lib/gettime.awk @@ -20056,7 +21268,7 @@ time formatted in the same way as the @command{date} utility: # time["weeknum"] -- week number, Sunday first day # time["altweeknum"] -- week number, Monday first day -function gettimeofday(time, ret, now, i) +function getlocaltime(time, ret, now, i) @{ # get time once, avoids unnecessary system calls now = systime() @@ -20096,21 +21308,174 @@ function gettimeofday(time, ret, now, i) The string indices are easier to use and read than the various formats required by @code{strftime()}. The @code{alarm} program presented in -@ref{Alarm Program}, +@DBREF{Alarm Program} uses this function. -A more general design for the @code{gettimeofday()} function would have +A more general design for the @code{getlocaltime()} function would have allowed the user to supply an optional timestamp value to use instead of the current time. +@node Readfile Function +@subsection Reading a Whole File At Once + +Often, it is convenient to have the entire contents of a file available +in memory as a single string. A straightforward but naive way to +do that might be as follows: + +@example +function readfile(file, tmp, contents) +@{ + if ((getline tmp < file) < 0) + return + + contents = tmp + while (getline tmp < file) > 0) + contents = contents RT tmp + + close(file) + return contents +@} +@end example + +This function reads from @code{file} one record at a time, building +up the full contents of the file in the local variable @code{contents}. +It works, but is not necessarily efficient. + +The following function, based on a suggestion by Denis Shirokov, +reads the entire contents of the named file in one shot: + +@cindex @code{readfile()} user-defined function +@example +@c file eg/lib/readfile.awk +# readfile.awk --- read an entire file at once +@c endfile +@ignore +@c file eg/lib/readfile.awk +# +# Original idea by Denis Shirokov, cosmogen@@gmail.com, April 2013 +# +@c endfile +@end ignore +@c file eg/lib/readfile.awk + +function readfile(file, tmp, save_rs) +@{ + save_rs = RS + RS = "^$" + getline tmp < file + close(file) + RS = save_rs + + return tmp +@} +@c endfile +@end example + +It works by setting @code{RS} to @samp{^$}, a regular expression that +will never match if the file has contents. @command{gawk} reads data from +the file into @code{tmp} attempting to match @code{RS}. The match fails +after each read, but fails quickly, such that @command{gawk} fills +@code{tmp} with the entire contents of the file. +(@DBXREF{Records} for information on @code{RT} and @code{RS}.) + +In the case that @code{file} is empty, the return value is the null +string. Thus calling code may use something like: + +@example +contents = readfile("/some/path") +if (length(contents) == 0) + # file was empty @dots{} +@end example + +This tests the result to see if it is empty or not. An equivalent +test would be @samp{contents == ""}. + +@xref{Extension Sample Readfile}, for an extension function that +also reads an entire file into memory. + +@node Shell Quoting +@subsection Quoting Strings to Pass to the Shell + +@c included by permission +@ignore +Date: Sun, 27 Jul 2014 17:16:16 -0700 +Message-ID: <CAKuGj+iCF_obaCLDUX60aSAgbfocFVtguG39GyeoNxTFby5sqQ@mail.gmail.com> +Subject: Useful awk function +From: Mike Brennan <mike@madronabluff.com> +To: Arnold Robbins <arnold@skeeve.com> +@end ignore + +Michael Brennan offers the following programming pattern, +which he uses frequently: + +@example +#! /bin/sh + +awkp=' + @dots{} + ' + +@var{input_program} | awk "$awkp" | /bin/sh +@end example + +For example, a program of his named @command{flac-edit} has this form: + +@example +$ @kbd{flac-edit -song="Whoope! That's Great" file.flac} +@end example + +It generates the following output, which is to be piped to +the shell (@file{/bin/sh}): + +@example +chmod +w file.flac +metaflac --remove-tag=TITLE file.flac +LANG=en_US.88591 metaflac --set-tag=TITLE='Whoope! That'"'"'s Great' file.flac +chmod -w file.flac +@end example + +Note the need for shell quoting. The function @code{shell_quote()} +does it. @code{SINGLE} is the one-character string @code{"'"} and +@code{QSINGLE} is the three-character string @code{"\"'\""}: + +@example +@c file eg/lib/shellquote.awk +# shell_quote --- quote an argument for passing to the shell +@c endfile +@ignore +@c file eg/lib/shellquote.awk +# +# Michael Brennan +# brennan@@madronabluff.com +# September 2014 +@c endfile +@end ignore +@c file eg/lib/shellquote.awk + +function shell_quote(s, # parameter + SINGLE, QSINGLE, i, X, n, ret) # locals +@{ + if (s == "") + return "\"\"" + + SINGLE = "\x27" # single quote + QSINGLE = "\"\x27\"" + n = split(s, X, SINGLE) + + ret = SINGLE X[1] SINGLE + for (i = 2; i <= n; i++) + ret = ret QSINGLE SINGLE X[i] SINGLE + + return ret +@} +@c endfile +@end example + @node Data File Management @section @value{DDF} Management -@c STARTOFRANGE dataf @cindex files, managing -@c STARTOFRANGE libfdataf -@cindex libraries of @command{awk} functions, managing, @value{DF}s -@c STARTOFRANGE flibdataf -@cindex functions, library, managing @value{DF}s +@cindex libraries of @command{awk} functions, managing, data files +@cindex functions, library, managing data files This @value{SECTION} presents functions that are useful for managing command-line @value{DF}s. @@ -20125,9 +21490,9 @@ command-line @value{DF}s. @node Filetrans Function @subsection Noting @value{DDF} Boundaries -@cindex files, managing, @value{DF} boundaries +@cindex files, managing, data file boundaries @cindex files, initialization and cleanup -The @code{BEGIN} and @code{END} rules are each executed exactly once at +The @code{BEGIN} and @code{END} rules are each executed exactly once, at the beginning and end of your @command{awk} program, respectively (@pxref{BEGIN/END}). We (the @command{gawk} authors) once had a user who mistakenly thought that the @@ -20159,15 +21524,14 @@ Besides solving the problem in only nine(!) lines of code, it does so @c # Arnold Robbins, arnold@@skeeve.com, Public Domain @c # January 1992 -FILENAME != _oldfilename \ -@{ +FILENAME != _oldfilename @{ if (_oldfilename != "") endfile(_oldfilename) _oldfilename = FILENAME beginfile(FILENAME) @} -END @{ endfile(FILENAME) @} +END @{ endfile(FILENAME) @} @end example This file must be loaded before the user's ``main'' program, so that the @@ -20200,7 +21564,7 @@ The following version solves the problem: @example @c file eg/lib/ftrans.awk -# ftrans.awk --- handle data file transitions +# ftrans.awk --- handle datafile transitions # # user supplies beginfile() and endfile() functions @c endfile @@ -20220,16 +21584,43 @@ FNR == 1 @{ beginfile(FILENAME) @} -END @{ endfile(_filename_) @} +END @{ endfile(_filename_) @} @c endfile @end example -@ref{Wc Program}, +@DBREF{Wc Program} shows how this library function can be used and how it simplifies writing the main program. -@c fakenode --- for prepinfo -@subheading Advanced Notes: So Why Does @command{gawk} have @code{BEGINFILE} and @code{ENDFILE}? +@cindex sidebar, So Why Does @command{gawk} Have @code{BEGINFILE} and @code{ENDFILE}? +@ifdocbook +@docbook +<sidebar><title>So Why Does @command{gawk} Have @code{BEGINFILE} and @code{ENDFILE}?</title> +@end docbook + + +You are probably wondering, if @code{beginfile()} and @code{endfile()} +functions can do the job, why does @command{gawk} have +@code{BEGINFILE} and @code{ENDFILE} patterns (@pxref{BEGINFILE/ENDFILE})? + +Good question. Normally, if @command{awk} cannot open a file, this +causes an immediate fatal error. In this case, there is no way for a +user-defined function to deal with the problem, as the mechanism for +calling it relies on the file being open and at the first record. Thus, +the main reason for @code{BEGINFILE} is to give you a ``hook'' to catch +files that cannot be processed. @code{ENDFILE} exists for symmetry, +and because it provides an easy way to do per-file cleanup processing. + +@docbook +</sidebar> +@end docbook +@end ifdocbook + +@ifnotdocbook +@cartouche +@center @b{So Why Does @command{gawk} Have @code{BEGINFILE} and @code{ENDFILE}?} + + You are probably wondering, if @code{beginfile()} and @code{endfile()} functions can do the job, why does @command{gawk} have @@ -20237,11 +21628,13 @@ functions can do the job, why does @command{gawk} have Good question. Normally, if @command{awk} cannot open a file, this causes an immediate fatal error. In this case, there is no way for a -user-defined function to deal with the problem, since the mechanism for +user-defined function to deal with the problem, as the mechanism for calling it relies on the file being open and at the first record. Thus, the main reason for @code{BEGINFILE} is to give you a ``hook'' to catch files that cannot be processed. @code{ENDFILE} exists for symmetry, and because it provides an easy way to do per-file cleanup processing. +@end cartouche +@end ifnotdocbook @node Rewind Function @subsection Rereading the Current File @@ -20290,34 +21683,26 @@ function rewind( i) @c endfile @end example -This code relies on the @code{ARGIND} variable -(@pxref{Auto-set}), -which is specific to @command{gawk}. -If you are not using -@command{gawk}, you can use ideas presented in -@ifnotinfo -the previous @value{SECTION} -@end ifnotinfo -@ifinfo -@ref{Filetrans Function}, -@end ifinfo -to either update @code{ARGIND} on your own -or modify this code as appropriate. - -The @code{rewind()} function also relies on the @code{nextfile} keyword -(@pxref{Nextfile Statement}). +The @code{rewind()} function relies on the @code{ARGIND} variable +(@pxref{Auto-set}), which is specific to @command{gawk}. It also +relies on the @code{nextfile} keyword (@pxref{Nextfile Statement}). +Because of this, you should not call it from an @code{ENDFILE} rule. +(This isn't necessary anyway, because @command{gawk} goes to the next +file as soon as an @code{ENDFILE} rule finishes!) @node File Checking @subsection Checking for Readable @value{DDF}s -@cindex troubleshooting, readable @value{DF}s -@cindex readable @value{DF}s@comma{} checking +@cindex troubleshooting, readable data files +@cindex readable data files@comma{} checking @cindex files, skipping Normally, if you give @command{awk} a @value{DF} that isn't readable, -it stops with a fatal error. There are times when you -might want to just ignore such files and keep going. You can -do this by prepending the following program to your @command{awk} -program: +it stops with a fatal error. There are times when you might want to +just ignore such files and keep going.@footnote{The @code{BEGINFILE} +special pattern (@pxref{BEGINFILE/ENDFILE}) provides an alternative +mechanism for dealing with files that can't be opened. However, the +code here provides a portable solution.} You can do this by prepending +the following program to your @command{awk} program: @cindex @code{readable.awk} program @example @@ -20336,7 +21721,7 @@ program: BEGIN @{ for (i = 1; i < ARGC; i++) @{ - if (ARGV[i] ~ /^[[:alpha:]_][[:alnum:]_]*=.*/ \ + if (ARGV[i] ~ /^[a-zA-Z_][a-zA-Z0-9_]*=.*/ \ || ARGV[i] == "-" || ARGV[i] == "/dev/stdin") continue # assignment or standard input else if ((getline junk < ARGV[i]) < 0) # unreadable @@ -20351,14 +21736,19 @@ BEGIN @{ @cindex troubleshooting, @code{getline} function This works, because the @code{getline} won't be fatal. Removing the element from @code{ARGV} with @code{delete} -skips the file (since it's no longer in the list). +skips the file (because it's no longer in the list). See also @ref{ARGC and ARGV}. +Because @command{awk} variable names only allow the English letters, +the regular expression check purposely does not use character classes +such as @samp{[:alpha:]} and @samp{[:alnum:]} +(@pxref{Bracket Expressions}) + @node Empty Files -@subsection Checking For Zero-length Files +@subsection Checking for Zero-length Files All known @command{awk} implementations silently skip over zero-length files. -This is a by-product of @command{awk}'s implicit +This is a by-product of @command{awk}'s implicit read-a-record-and-match-against-the-rules loop: when @command{awk} tries to read a record from an empty file, it immediately receives an end of file indication, closes the file, and proceeds on to the next @@ -20417,46 +21807,6 @@ the end of the command-line arguments. Note that the test in the condition of the @code{for} loop uses the @samp{<=} operator, not @samp{<}. -As an exercise, you might consider whether this same problem can -be solved without relying on @command{gawk}'s @code{ARGIND} variable. - -As a second exercise, revise this code to handle the case where -an intervening value in @code{ARGV} is a variable assignment. - -@ignore -# zerofile2.awk --- same thing, portably - -BEGIN @{ - ARGIND = Argind = 0 - for (i = 1; i < ARGC; i++) - Fnames[ARGV[i]]++ - -@} -FNR == 1 @{ - while (ARGV[ARGIND] != FILENAME) - ARGIND++ - Seen[FILENAME]++ - if (Seen[FILENAME] == Fnames[FILENAME]) - do - ARGIND++ - while (ARGV[ARGIND] != FILENAME) -@} -ARGIND > Argind + 1 @{ - for (Argind++; Argind < ARGIND; Argind++) - zerofile(ARGV[Argind], Argind) -@} -ARGIND != Argind @{ - Argind = ARGIND -@} -END @{ - if (ARGIND < ARGC - 1) - ARGIND = ARGC - 1 - if (ARGIND > Argind) - for (Argind++; Argind <= ARGIND; Argind++) - zerofile(ARGV[Argind], Argind) -@} -@end ignore - @node Ignoring Assigns @subsection Treating Assignments as @value{FFN}s @@ -20465,7 +21815,7 @@ END @{ Occasionally, you might not want @command{awk} to process command-line variable assignments (@pxref{Assignment Options}). -In particular, if you have a @value{FN} that contain an @samp{=} character, +In particular, if you have a @value{FN} that contains an @samp{=} character, @command{awk} treats the @value{FN} as an assignment, and does not process it. Some users have suggested an additional command-line option for @command{gawk} @@ -20490,7 +21840,7 @@ a library file does the trick: function disable_assigns(argc, argv, i) @{ for (i = 1; i < argc; i++) - if (argv[i] ~ /^[[:alpha:]_][[:alnum:]_]*=.*/) + if (argv[i] ~ /^[a-zA-Z_][a-zA-Z0-9_]*=.*/) argv[i] = ("./" argv[i]) @} @@ -20516,30 +21866,22 @@ The use of @code{No_command_assign} allows you to disable command-line assignments at invocation time, by giving the variable a true value. When not set, it is initially zero (i.e., false), so the command-line arguments are left alone. -@c ENDOFRANGE dataf -@c ENDOFRANGE flibdataf -@c ENDOFRANGE libfdataf @node Getopt Function @section Processing Command-Line Options -@c STARTOFRANGE libfclo @cindex libraries of @command{awk} functions, command-line options -@c STARTOFRANGE flibclo @cindex functions, library, command-line options -@c STARTOFRANGE clop @cindex command-line options, processing -@c STARTOFRANGE oclp @cindex options, command-line, processing -@c STARTOFRANGE clibf @cindex functions, library, C library @cindex arguments, processing -Most utilities on POSIX compatible systems take options on +Most utilities on POSIX-compatible systems take options on the command line that can be used to change the way a program behaves. @command{awk} is an example of such a program (@pxref{Options}). -Often, options take @dfn{arguments}; i.e., data that the program needs to -correctly obey the command-line option. For example, @command{awk}'s +Often, options take @dfn{arguments} (i.e., data that the program needs to +correctly obey the command-line option). For example, @command{awk}'s @option{-F} option requires a string to use as the field separator. The first occurrence on the command line of either @option{--} or a string that does not begin with @samp{-} ends the options. @@ -20594,7 +21936,6 @@ application might want to print its own error message.) @item optopt The letter representing the command-line option. -@c While not usually documented, most versions supply this variable. @end table The following C fragment shows how @code{getopt()} might process command-line @@ -20644,8 +21985,7 @@ necessary for accessing individual characters (@pxref{String Functions}).@footnote{This function was written before @command{gawk} acquired the ability to split strings into single characters using @code{""} as the separator. -We have left it alone, since using @code{substr()} is more portable.} -@c FIXME: could use split(str, a, "") to do it more easily. +We have left it alone, as using @code{substr()} is more portable.} The discussion that follows walks through the code a bit at a time: @@ -20677,7 +22017,7 @@ The discussion that follows walks through the code a bit at a time: # <c> a character representing the current option # Private Data: -# _opti -- index in multi-flag option, e.g., -abc +# _opti -- index in multiflag option, e.g., -abc @c endfile @end example @@ -20733,8 +22073,7 @@ it is not an option, and it ends option processing. Continuing on: i = index(options, thisopt) if (i == 0) @{ if (Opterr) - printf("%c -- invalid option\n", - thisopt) > "/dev/stderr" + printf("%c -- invalid option\n", thisopt) > "/dev/stderr" if (_opti >= length(argv[Optind])) @{ Optind++ _opti = 0 @@ -20814,9 +22153,9 @@ next element in @code{argv}. If neither condition is true, then only on the next call to @code{getopt()}. The @code{BEGIN} rule initializes both @code{Opterr} and @code{Optind} to one. -@code{Opterr} is set to one, since the default behavior is for @code{getopt()} +@code{Opterr} is set to one, because the default behavior is for @code{getopt()} to print a diagnostic message upon seeing an invalid option. @code{Optind} -is set to one, since there's no reason to look at the program name, which is +is set to one, because there's no reason to look at the program name, which is in @code{ARGV[0]}: @example @@ -20828,7 +22167,7 @@ BEGIN @{ # test program if (_getopt_test) @{ while ((_go_c = getopt(ARGC, ARGV, "ab:cd")) != -1) - printf("c = <%c>, optarg = <%s>\n", + printf("c = <%c>, Optarg = <%s>\n", _go_c, Optarg) printf("non-option arguments:\n") for (; Optind < ARGC; Optind++) @@ -20844,52 +22183,55 @@ result of two sample runs of the test program: @example $ @kbd{awk -f getopt.awk -v _getopt_test=1 -- -a -cbARG bax -x} -@print{} c = <a>, optarg = <> -@print{} c = <c>, optarg = <> -@print{} c = <b>, optarg = <ARG> +@print{} c = <a>, Optarg = <> +@print{} c = <c>, Optarg = <> +@print{} c = <b>, Optarg = <ARG> @print{} non-option arguments: @print{} ARGV[3] = <bax> @print{} ARGV[4] = <-x> $ @kbd{awk -f getopt.awk -v _getopt_test=1 -- -a -x -- xyz abc} -@print{} c = <a>, optarg = <> +@print{} c = <a>, Optarg = <> @error{} x -- invalid option -@print{} c = <?>, optarg = <> +@print{} c = <?>, Optarg = <> @print{} non-option arguments: @print{} ARGV[4] = <xyz> @print{} ARGV[5] = <abc> @end example -In both runs, -the first @option{--} terminates the arguments to @command{awk}, so that it does -not try to interpret the @option{-a}, etc., as its own options. +In both runs, the first @option{--} terminates the arguments to +@command{awk}, so that it does not try to interpret the @option{-a}, +etc., as its own options. @quotation NOTE -After @code{getopt()} is through, it is the responsibility of the user level -code to -clear out all the elements of @code{ARGV} from 1 to @code{Optind}, -so that @command{awk} does not try to process the command-line options -as @value{FN}s. +After @code{getopt()} is through, +user-level code must clear out all the elements of @code{ARGV} from 1 +to @code{Optind}, so that @command{awk} does not try to process the +command-line options as @value{FN}s. @end quotation +Using @samp{#!} with the @option{-E} option may help avoid +conflicts between your program's options and @command{gawk}'s options, +as @option{-E} causes @command{gawk} to abandon processing of +further options +(@DBPXREF{Executable Scripts} and +@ifnotdocbook +@pxref{Options}). +@end ifnotdocbook +@ifdocbook +@ref{Options}). +@end ifdocbook + Several of the sample programs presented in @ref{Sample Programs}, use @code{getopt()} to process their arguments. -@c ENDOFRANGE libfclo -@c ENDOFRANGE flibclo -@c ENDOFRANGE clop -@c ENDOFRANGE oclp @node Passwd Functions @section Reading the User Database -@c STARTOFRANGE libfudata @cindex libraries of @command{awk} functions, user database, reading -@c STARTOFRANGE flibudata -@cindex functions, library, user database, reading -@c STARTOFRANGE udatar +@cindex functions, library, user database@comma{} reading @cindex user database@comma{} reading -@c STARTOFRANGE dataur @cindex database, users@comma{} reading @cindex @code{PROCINFO} array The @code{PROCINFO} array @@ -20900,7 +22242,7 @@ However, because these are numbers, they do not provide very useful information to the average user. There needs to be some way to find the user information associated with the user and group ID numbers. This @value{SECTION} presents a suite of functions for retrieving information from the -user database. @xref{Group Functions}, +user database. @DBXREF{Group Functions} for a similar suite that retrieves information from the group database. @cindex @code{getpwent()} function (C library) @@ -20919,7 +22261,7 @@ The ``password'' comes from the original user database file, encrypted passwords (hence the name). @cindex @command{pwcat} program -While an @command{awk} program could simply read @file{/etc/passwd} +Although an @command{awk} program could simply read @file{/etc/passwd} directly, this file may not contain complete information about the system's set of users.@footnote{It is often the case that password information is stored in a network database.} To be sure you are able to @@ -20931,14 +22273,12 @@ no more entries, it returns @code{NULL}, the null pointer. When this happens, the C program should call @code{endpwent()} to close the database. Following is @command{pwcat}, a C program that ``cats'' the password database: -@c Use old style function header for portability to old systems (SunOS, HP/UX). - @example @c file eg/lib/pwcat.c /* * pwcat.c * - * Generate a printable version of the password database + * Generate a printable version of the password database. */ @c endfile @ignore @@ -21016,12 +22356,12 @@ The user's encrypted password. This may not be available on some systems. @item User-ID The user's numeric user ID number. -(On some systems it's a C @code{long}, and not an @code{int}. Thus +(On some systems, it's a C @code{long}, and not an @code{int}. Thus we cast it to @code{long} for all cases.) @item Group-ID The user's numeric group ID number. -(Similar comments about @code{long} vs.@: @code{int} apply here.) +(Similar comments about @code{long} versus @code{int} apply here.) @item Full name The user's full name, and perhaps other information associated with the @@ -21043,7 +22383,7 @@ A few lines representative of @command{pwcat}'s output are as follows: @cindex Robbins, Miriam @example $ @kbd{pwcat} -@print{} root:3Ov02d5VaUPB6:0:1:Operator:/:/bin/sh +@print{} root:x:0:1:Operator:/:/bin/sh @print{} nobody:*:65534:65534::/: @print{} daemon:*:1:1::/: @print{} sys:*:2:2::/:/bin/csh @@ -21118,33 +22458,29 @@ The @code{BEGIN} rule sets a private variable to the directory where routine, we have chosen to put it in @file{/usr/local/libexec/awk}; however, you might want it to be in a different directory on your system. -The function @code{_pw_init()} keeps three copies of the user information -in three associative arrays. The arrays are indexed by username +The function @code{_pw_init()} fills three copies of the user information +into three associative arrays. The arrays are indexed by username (@code{_pw_byname}), by user ID number (@code{_pw_byuid}), and by order of occurrence (@code{_pw_bycount}). -The variable @code{_pw_inited} is used for efficiency, since @code{_pw_init()} +The variable @code{_pw_inited} is used for efficiency, as @code{_pw_init()} needs to be called only once. +@cindex @code{PROCINFO} array, testing the field splitting @cindex @code{getline} command, @code{_pw_init()} function Because this function uses @code{getline} to read information from @command{pwcat}, it first saves the values of @code{FS}, @code{RS}, and @code{$0}. It notes in the variable @code{using_fw} whether field splitting with @code{FIELDWIDTHS} is in effect or not. -Doing so is necessary, since these functions could be called +Doing so is necessary, as these functions could be called from anywhere within a user's program, and the user may have his -or her -own way of splitting records and fields. - -@cindex @code{PROCINFO} array -The @code{using_fw} variable checks @code{PROCINFO["FS"]}, which -is @code{"FIELDWIDTHS"} if field splitting is being done with -@code{FIELDWIDTHS}. This makes it possible to restore the correct +or her own way of splitting records and fields. +This makes it possible to restore the correct field-splitting mechanism later. The test can only be true for @command{gawk}. It is false if using @code{FS} or @code{FPAT}, or on some other @command{awk} implementation. The code that checks for using @code{FPAT}, using @code{using_fpat} -and @code{PROCINFO["FS"]} is similar. +and @code{PROCINFO["FS"]}, is similar. The main part of the function uses a loop to read database lines, split the line into fields, and then store the line into each array as necessary. @@ -21174,10 +22510,9 @@ function getpwnam(name) @end example @cindex @code{getpwuid()} function (C library) -Similarly, -the @code{getpwuid} function takes a user ID number argument. If that -user number is in the database, it returns the appropriate line. Otherwise, it -returns the null string: +Similarly, the @code{getpwuid()} function takes a user ID number +argument. If that user number is in the database, it returns the +appropriate line. Otherwise, it returns the null string: @cindex @code{getpwuid()} user-defined function @example @@ -21238,28 +22573,20 @@ In turn, calling @code{_pw_init()} is not too expensive, because the once. If you are worried about squeezing every last cycle out of your @command{awk} program, the check of @code{_pw_inited} could be moved out of @code{_pw_init()} and duplicated in all the other functions. In practice, -this is not necessary, since most @command{awk} programs are I/O-bound, +this is not necessary, as most @command{awk} programs are I/O-bound, and such a change would clutter up the code. -The @command{id} program in @ref{Id Program}, +The @command{id} program in @DBREF{Id Program} uses these functions. -@c ENDOFRANGE libfudata -@c ENDOFRANGE flibudata -@c ENDOFRANGE udatar -@c ENDOFRANGE dataur @node Group Functions @section Reading the Group Database -@c STARTOFRANGE libfgdata @cindex libraries of @command{awk} functions, group database, reading -@c STARTOFRANGE flibgdata -@cindex functions, library, group database, reading -@c STARTOFRANGE gdatar +@cindex functions, library, group database@comma{} reading @cindex group database, reading -@c STARTOFRANGE datagr @cindex database, group, reading -@cindex @code{PROCINFO} array +@cindex @code{PROCINFO} array, and group membership @cindex @code{getgrent()} function (C library) @cindex @code{getgrent()} user-defined function @cindex groups@comma{} information about @@ -21267,7 +22594,7 @@ uses these functions. @cindex group file @cindex files, group Much of the discussion presented in -@ref{Passwd Functions}, +@DBREF{Passwd Functions} applies to the group database as well. Although there has traditionally been a well-known file (@file{/etc/group}) in a well-known format, the POSIX standard only provides a set of C library routines @@ -21285,7 +22612,7 @@ is as follows: /* * grcat.c * - * Generate a printable version of the group database + * Generate a printable version of the group database. */ @c endfile @ignore @@ -21372,12 +22699,12 @@ it is usually empty or set to @samp{*}. @item Group ID Number The group's numeric group ID number; -this number must be unique within the file. +the association of name to number must be unique within the file. (On some systems it's a C @code{long}, and not an @code{int}. Thus we cast it to @code{long} for all cases.) @item Group Member List -A comma-separated list of user names. These users are members of the group. +A comma-separated list of usernames. These users are members of the group. Modern Unix systems allow users to be members of several groups simultaneously. If your system does, then there are elements @code{"group1"} through @code{"group@var{N}"} in @code{PROCINFO} @@ -21420,8 +22747,7 @@ There are several, modeled after the C library functions of the same names: @c line break on _gr_init for smallbook @c file eg/lib/groupawk.in -BEGIN \ -@{ +BEGIN @{ # Change to suit your system _gr_awklib = "/usr/local/libexec/awk/" @} @@ -21454,8 +22780,7 @@ function _gr_init( oldfs, oldrs, olddol0, grcat, n = split($4, a, "[ \t]*,[ \t]*") for (i = 1; i <= n; i++) if (a[i] in _gr_groupsbyuser) - _gr_groupsbyuser[a[i]] = \ - _gr_groupsbyuser[a[i]] " " $1 + _gr_groupsbyuser[a[i]] = gr_groupsbyuser[a[i]] " " $1 else _gr_groupsbyuser[a[i]] = $1 @@ -21494,7 +22819,7 @@ is being used, and to restore the appropriate field splitting mechanism. The group information is stored is several associative arrays. The arrays are indexed by group name (@code{@w{_gr_byname}}), by group ID number (@code{@w{_gr_bygid}}), and by position in the database (@code{@w{_gr_bycount}}). -There is an additional array indexed by user name (@code{@w{_gr_groupsbyuser}}), +There is an additional array indexed by username (@code{@w{_gr_groupsbyuser}}), which is a space-separated list of groups to which each user belongs. Unlike the user database, it is possible to have multiple records in the @@ -21502,16 +22827,16 @@ database for the same group. This is common when a group has a large number of members. A pair of such entries might look like the following: @example -tvpeople:*:101:johnny,jay,arsenio +tvpeople:*:101:johny,jay,arsenio tvpeople:*:101:david,conan,tom,joan @end example For this reason, @code{_gr_init()} looks to see if a group name or -group ID number is already seen. If it is, then the user names are -simply concatenated onto the previous list of users. (There is actually a +group ID number is already seen. If it is, the usernames are +simply concatenated onto the previous list of users.@footnote{There is actually a subtle problem with the code just presented. Suppose that the first time there were no names. This code adds the names with -a leading comma. It also doesn't check that there is a @code{$4}.) +a leading comma. It also doesn't check that there is a @code{$4}.} Finally, @code{_gr_init()} closes the pipeline to @command{grcat}, restores @code{FS} (and @code{FIELDWIDTHS} or @code{FPAT} if necessary), @code{RS}, and @code{$0}, @@ -21553,7 +22878,7 @@ function getgrgid(gid) @cindex @code{getgruser()} function (C library) The @code{getgruser()} function does not have a C counterpart. It takes a -user name and returns the list of groups that have the user as a member: +username and returns the list of groups that have the user as a member: @cindex @code{getgruser()} function, user-defined @example @@ -21582,7 +22907,6 @@ function getgrent() @} @c endfile @end example -@c ENDOFRANGE clibf @cindex @code{endgrent()} function (C library) The @code{endgrent()} function resets @code{_gr_count} to zero so that @code{getgrent()} can @@ -21607,13 +22931,13 @@ Most of the work is in scanning the database and building the various associative arrays. The functions that the user calls are themselves very simple, relying on @command{awk}'s associative arrays to do work. -The @command{id} program in @ref{Id Program}, +The @command{id} program in @DBREF{Id Program} uses these functions. @node Walking Arrays @section Traversing Arrays of Arrays -@ref{Arrays of Arrays}, described how @command{gawk} +@DBREF{Arrays of Arrays} described how @command{gawk} provides arrays of arrays. In particular, any element of an array may be either a scalar, or another array. The @code{isarray()} function (@pxref{Type Functions}) @@ -21663,32 +22987,139 @@ When run, the program produces the following output: @example $ @kbd{gawk -f walk_array.awk} -@print{} a[4][1][1] = 411 -@print{} a[4][2] = 42 @print{} a[1] = 1 @print{} a[2][1] = 21 @print{} a[2][2] = 22 @print{} a[3] = 3 +@print{} a[4][1][1] = 411 +@print{} a[4][2] = 42 @end example -@c ENDOFRANGE libfgdata -@c ENDOFRANGE flibgdata -@c ENDOFRANGE gdatar -@c ENDOFRANGE libf -@c ENDOFRANGE flib -@c ENDOFRANGE fudlib -@c ENDOFRANGE datagr + +@node Library Functions Summary +@section Summary + +@itemize @value{BULLET} +@item +Reading programs is an excellent way to learn Good Programming. +The functions and programs provided in this @value{CHAPTER} and the next +are intended to serve that purpose. + +@item +When writing general-purpose library functions, put some thought into how +to name any global variables so that they won't conflict with variables +from a user's program. + +@item +The functions presented here fit into the following categories: + +@c nested list +@table @asis +@item General problems +Number-to-string conversion, assertions, rounding, random number +generation, converting characters to numbers, joining strings, getting +easily usable time-of-day information, and reading a whole file in +one shot. + +@item Managing @value{DF}s +Noting @value{DF} boundaries, rereading the current file, checking for +readable files, checking for zero-length files, and treating assignments +as @value{FN}s. + +@item Processing command-line options +An @command{awk} version of the standard C @code{getopt()} function. + +@item Reading the user and group databases +Two sets of routines that parallel the C library versions. + +@item Traversing arrays of arrays +A simple function to traverse an array of arrays to any depth. +@end table +@c end nested list + +@end itemize + +@c EXCLUDE START +@node Library Exercises +@section Exercises + +@enumerate +@item +In @ref{Empty Files}, we presented the @file{zerofile.awk} program, +which made use of @command{gawk}'s @code{ARGIND} variable. Can this +problem be solved without relying on @code{ARGIND}? If so, how? + +@ignore +# zerofile2.awk --- same thing, portably + +BEGIN @{ + ARGIND = Argind = 0 + for (i = 1; i < ARGC; i++) + Fnames[ARGV[i]]++ + +@} +FNR == 1 @{ + while (ARGV[ARGIND] != FILENAME) + ARGIND++ + Seen[FILENAME]++ + if (Seen[FILENAME] == Fnames[FILENAME]) + do + ARGIND++ + while (ARGV[ARGIND] != FILENAME) +@} +ARGIND > Argind + 1 @{ + for (Argind++; Argind < ARGIND; Argind++) + zerofile(ARGV[Argind], Argind) +@} +ARGIND != Argind @{ + Argind = ARGIND +@} +END @{ + if (ARGIND < ARGC - 1) + ARGIND = ARGC - 1 + if (ARGIND > Argind) + for (Argind++; Argind <= ARGIND; Argind++) + zerofile(ARGV[Argind], Argind) +@} +@end ignore + +@item +As a related challenge, revise that code to handle the case where +an intervening value in @code{ARGV} is a variable assignment. + +@item +@DBREF{Walking Arrays} presented a function that walked a multidimensional +array to print it out. However, walking an array and processing +each element is a general-purpose operation. Generalize the +@code{walk_array()} function by adding an additional parameter named +@code{process}. + +Then, inside the loop, instead of printing the array element's index and +value, use the indirect function call syntax (@pxref{Indirect Calls}) +on @code{process}, passing it the index and the value. + +When calling @code{walk_array()}, you would pass the name of a +user-defined function that expects to receive an index and a value, +and then processes the element. + +Test your new version by printing the array; you should end up with +output identical to that of the original version. + +@end enumerate +@c EXCLUDE END + @node Sample Programs @chapter Practical @command{awk} Programs -@c STARTOFRANGE awkpex @cindex @command{awk} programs, examples of +@c FULLXREF ON @ref{Library Functions}, presents the idea that reading programs in a language contributes to learning that language. This @value{CHAPTER} continues that theme, presenting a potpourri of @command{awk} programs for your reading enjoyment. +@c FULLXREF OFF @ifnotinfo There are three sections. The first describes how to run the programs presented @@ -21715,6 +23146,8 @@ Many of these programs use library functions presented in * Running Examples:: How to run these examples. * Clones:: Clones of common utilities. * Miscellaneous Programs:: Some interesting @command{awk} programs. +* Programs Summary:: Summary of programs. +* Programs Exercises:: Exercises. @end menu @node Running Examples @@ -21747,7 +23180,6 @@ cut.awk -- -c1-8 myfiles > results @node Clones @section Reinventing Wheels for Fun and Profit -@c STARTOFRANGE posimawk @cindex POSIX, programs@comma{} implementing in @command{awk} This @value{SECTION} presents a number of POSIX utilities implemented in @@ -21775,14 +23207,11 @@ The programs are presented in alphabetical order. @end menu @node Cut Program -@subsection Cutting out Fields and Columns +@subsection Cutting Out Fields and Columns @cindex @command{cut} utility -@c STARTOFRANGE cut @cindex @command{cut} utility -@c STARTOFRANGE ficut @cindex fields, cutting -@c STARTOFRANGE colcut @cindex columns, cutting The @command{cut} utility selects, or ``cuts,'' characters or fields from its standard input and sends them to its standard output. @@ -21853,28 +23282,16 @@ supplied: # Requires getopt() and join() library functions @group -function usage( e1, e2) +function usage() @{ - e1 = "usage: cut [-f list] [-d c] [-s] [files...]" - e2 = "usage: cut [-c list] [files...]" - print e1 > "/dev/stderr" - print e2 > "/dev/stderr" + print("usage: cut [-f list] [-d c] [-s] [files...]") > "/dev/stderr" + print("usage: cut [-c list] [files...]") > "/dev/stderr" exit 1 @} @end group @c endfile @end example -@noindent -The variables @code{e1} and @code{e2} are used so that the function -fits nicely on the -@ifnotinfo -page. -@end ifnotinfo -@ifnottex -screen. -@end ifnottex - @cindex @code{BEGIN} pattern, running @command{awk} programs and @cindex @code{FS} variable, running @command{awk} programs and Next comes a @code{BEGIN} rule that parses the command-line options. @@ -21889,8 +23306,7 @@ string: @example @c file eg/prog/cut.awk -BEGIN \ -@{ +BEGIN @{ FS = "\t" # default OFS = FS while ((c = getopt(ARGC, ARGV, "sf:c:d:")) != -1) @{ @@ -21903,7 +23319,7 @@ BEGIN \ OFS = "" @} else if (c == "d") @{ if (length(Optarg) > 1) @{ - printf("Using first character of %s" \ + printf("cut: using first character of %s" \ " for delimiter\n", Optarg) > "/dev/stderr" Optarg = substr(Optarg, 1, 1) @} @@ -21912,7 +23328,7 @@ BEGIN \ if (FS == " ") # defeat awk semantics FS = "[ ]" @} else if (c == "s") - suppress++ + suppress = 1 else usage() @} @@ -21984,7 +23400,7 @@ function set_fieldlist( n, m, i, j, k, f, g) m = split(f[i], g, "-") @group if (m != 2 || g[1] >= g[2]) @{ - printf("bad field list: %s\n", + printf("cut: bad field list: %s\n", f[i]) > "/dev/stderr" exit 1 @} @@ -22021,7 +23437,7 @@ complete field list, including filler fields: @example @c file eg/prog/cut.awk -function set_charlist( field, i, j, f, g, t, +function set_charlist( field, i, j, f, g, n, m, t, filler, last, len) @{ field = 1 # count total fields @@ -22031,7 +23447,7 @@ function set_charlist( field, i, j, f, g, t, if (index(f[i], "-") != 0) @{ # range m = split(f[i], g, "-") if (m != 2 || g[1] >= g[2]) @{ - printf("bad character list: %s\n", + printf("cut: bad character list: %s\n", f[i]) > "/dev/stderr" exit 1 @} @@ -22065,7 +23481,7 @@ function set_charlist( field, i, j, f, g, t, @c endfile @end example -Next is the rule that actually processes the data. If the @option{-s} option +Next is the rule that processes the data. If the @option{-s} option is given, then @code{suppress} is true. The first @code{if} statement makes sure that the input record does have the field separator. If @command{cut} is processing fields, @code{suppress} is true, and the field @@ -22081,7 +23497,7 @@ written out between the fields: @example @c file eg/prog/cut.awk @{ - if (by_fields && suppress && index($0, FS) != 0) + if (by_fields && suppress && index($0, FS) == 0) next for (i = 1; i <= nfields; i++) @{ @@ -22097,26 +23513,19 @@ written out between the fields: @end example This version of @command{cut} relies on @command{gawk}'s @code{FIELDWIDTHS} -variable to do the character-based cutting. While it is possible in +variable to do the character-based cutting. It is possible in other @command{awk} implementations to use @code{substr()} -(@pxref{String Functions}), +(@pxref{String Functions}), but it is also extremely painful. The @code{FIELDWIDTHS} variable supplies an elegant solution to the problem of picking the input line apart by characters. -@c ENDOFRANGE cut -@c ENDOFRANGE ficut -@c ENDOFRANGE colcut -@c Exercise: Rewrite using split with "". @node Egrep Program @subsection Searching for Regular Expressions in Files -@c STARTOFRANGE regexps @cindex regular expressions, searching for -@c STARTOFRANGE sfregexp @cindex searching, files for regular expressions -@c STARTOFRANGE fsregexp @cindex files, searching for regular expressions @cindex @command{egrep} utility The @command{egrep} utility searches files for patterns. It uses regular @@ -22124,9 +23533,9 @@ expressions that are almost identical to those available in @command{awk} (@pxref{Regexp}). You invoke it as follows: -@example -egrep @r{[} @var{options} @r{]} '@var{pattern}' @var{files} @dots{} -@end example +@display +@command{egrep} [@var{options}] @code{'@var{pattern}'} @var{files} @dots{} +@end display The @var{pattern} is a regular expression. In typical usage, the regular expression is quoted to prevent the shell from expanding any of the @@ -22170,7 +23579,7 @@ and the file transition library program The program begins with a descriptive comment and then a @code{BEGIN} rule that processes the command-line arguments with @code{getopt()}. The @option{-i} (ignore case) option is particularly easy with @command{gawk}; we just use the -@code{IGNORECASE} built-in variable +@code{IGNORECASE} predefined variable (@pxref{Built-in Variables}): @cindex @code{egrep.awk} program @@ -22244,7 +23653,7 @@ matched lines in the output: @c endfile @end example -The last two lines are commented out, since they are not needed in +The last two lines are commented out, as they are not needed in @command{gawk}. They should be uncommented if you have to use another version of @command{awk}. @@ -22254,9 +23663,7 @@ into lowercase if the @option{-i} option is specified.@footnote{It also introduces a subtle bug; if a match happens, we output the translated line, not the original.} The rule is -commented out since it is not necessary with @command{gawk}: - -@c Exercise: Fix this, w/array and new line as key to original line +commented out as it is not necessary with @command{gawk}: @example @c file eg/prog/egrep.awk @@ -22308,6 +23715,11 @@ function endfile(file) @c endfile @end example +The @code{BEGINFILE} and @code{ENDFILE} special patterns +(@pxref{BEGINFILE/ENDFILE}) could be used, but then the program would be +@command{gawk}-specific. Additionally, this example was written before +@command{gawk} acquired @code{BEGINFILE} and @code{ENDFILE}. + The following rule does most of the work of matching lines. The variable @code{matches} is true if the line matched the pattern. If the user wants lines that did not match, the sense of @code{matches} is inverted @@ -22362,11 +23774,8 @@ there are no matches, the exit status is one; otherwise it is zero: @example @c file eg/prog/egrep.awk -END \ -@{ - if (total == 0) - exit 1 - exit 0 +END @{ + exit (total == 0) @} @c endfile @end example @@ -22376,36 +23785,18 @@ and then exits: @example @c file eg/prog/egrep.awk -function usage( e) +function usage() @{ - e = "Usage: egrep [-csvil] [-e pat] [files ...]" - e = e "\n\tegrep [-csvil] pat [files ...]" - print e > "/dev/stderr" + print("Usage: egrep [-csvil] [-e pat] [files ...]") > "/dev/stderr" + print("\n\tegrep [-csvil] pat [files ...]") > "/dev/stderr" exit 1 @} @c endfile @end example -The variable @code{e} is used so that the function fits nicely -on the printed page. - -@cindex @code{END} pattern, backslash continuation and -@cindex @code{\} (backslash), continuing lines and -@cindex backslash (@code{\}), continuing lines and -Just a note on programming style: you may have noticed that the @code{END} -rule uses backslash continuation, with the open brace on a line by -itself. This is so that it more closely resembles the way functions -are written. Many of the examples -in this @value{CHAPTER} -use this style. You can decide for yourself if you like writing -your @code{BEGIN} and @code{END} rules this way -or not. -@c ENDOFRANGE regexps -@c ENDOFRANGE sfregexp -@c ENDOFRANGE fsregexp @node Id Program -@subsection Printing out User Information +@subsection Printing Out User Information @cindex printing, user information @cindex users, information about, printing @@ -22418,10 +23809,10 @@ corresponding user and group names. The output might look like this: @example $ @kbd{id} -@print{} uid=500(arnold) gid=500(arnold) groups=6(disk),7(lp),19(floppy) +@print{} uid=1000(arnold) gid=1000(arnold) groups=1000(arnold),4(adm),7(lp),27(sudo) @end example -@cindex @code{PROCINFO} array +@cindex @code{PROCINFO} array, and user and group ID numbers This information is part of what is provided by @command{gawk}'s @code{PROCINFO} array (@pxref{Built-in Variables}). However, the @command{id} utility provides a more palatable output than just @@ -22454,6 +23845,8 @@ numbers: # Arnold Robbins, arnold@@skeeve.com, Public Domain # May 1993 # Revised February 1996 +# Revised May 2014 +# Revised September 2014 @c endfile @end ignore @@ -22463,8 +23856,7 @@ numbers: # egid=5(blat) groups=9(nine),2(two),1(one) @group -BEGIN \ -@{ +BEGIN @{ uid = PROCINFO["uid"] euid = PROCINFO["euid"] gid = PROCINFO["gid"] @@ -22473,34 +23865,22 @@ BEGIN \ printf("uid=%d", uid) pw = getpwuid(uid) - if (pw != "") @{ - split(pw, a, ":") - printf("(%s)", a[1]) - @} + pr_first_field(pw) if (euid != uid) @{ printf(" euid=%d", euid) pw = getpwuid(euid) - if (pw != "") @{ - split(pw, a, ":") - printf("(%s)", a[1]) - @} + pr_first_field(pw) @} printf(" gid=%d", gid) pw = getgrgid(gid) - if (pw != "") @{ - split(pw, a, ":") - printf("(%s)", a[1]) - @} + pr_first_field(pw) if (egid != gid) @{ printf(" egid=%d", egid) pw = getgrgid(egid) - if (pw != "") @{ - split(pw, a, ":") - printf("(%s)", a[1]) - @} + pr_first_field(pw) @} for (i = 1; ("group" i) in PROCINFO; i++) @{ @@ -22509,49 +23889,51 @@ BEGIN \ group = PROCINFO["group" i] printf("%d", group) pw = getgrgid(group) - if (pw != "") @{ - split(pw, a, ":") - printf("(%s)", a[1]) - @} + pr_first_field(pw) if (("group" (i+1)) in PROCINFO) printf(",") @} print "" @} + +function pr_first_field(str, a) +@{ + if (str != "") @{ + split(str, a, ":") + printf("(%s)", a[1]) + @} +@} @c endfile @end example -@cindex @code{in} operator The test in the @code{for} loop is worth noting. Any supplementary groups in the @code{PROCINFO} array have the indices @code{"group1"} through @code{"group@var{N}"} for some -@var{N}, i.e., the total number of supplementary groups. +@var{N} (i.e., the total number of supplementary groups). However, we don't know in advance how many of these groups there are. This loop works by starting at one, concatenating the value with @code{"group"}, and then using @code{in} to see if that value is -in the array. Eventually, @code{i} is incremented past +in the array (@pxref{Reference to Elements}). Eventually, @code{i} is incremented past the last group in the array and the loop exits. The loop is also correct if there are @emph{no} supplementary groups; then the condition is false the first time it's tested, and the loop body never executes. -@c exercise!!! -@ignore -The POSIX version of @command{id} takes arguments that control which -information is printed. Modify this version to accept the same -arguments and perform in the same way. -@end ignore +The @code{pr_first_field()} function simply isolates out some +code that is used repeatedly, making the whole program +shorter and cleaner. In particular, moving the check for +the empty string into this function saves several lines of code. + @node Split Program @subsection Splitting a Large File into Pieces @c FIXME: One day, update to current POSIX version of split -@c STARTOFRANGE filspl @cindex files, splitting @cindex @code{split} utility The @command{split} program splits large text files into smaller pieces. @@ -22559,16 +23941,16 @@ Usage is as follows:@footnote{This is the traditional usage. The POSIX usage is different, but not relevant for what the program aims to demonstrate.} -@example -split @r{[}-@var{count}@r{]} file @r{[} @var{prefix} @r{]} -@end example +@display +@command{split} [@code{-@var{count}}] [@var{file}] [@var{prefix}] +@end display By default, the output files are named @file{xaa}, @file{xab}, and so on. Each file has -1000 lines in it, with the likely exception of the last file. To change the +1,000 lines in it, with the likely exception of the last file. To change the number of lines in each file, supply a number on the command line -preceded with a minus; e.g., @samp{-500} for files with 500 lines in them -instead of 1000. To change the name of the output files to something like +preceded with a minus (e.g., @samp{-500} for files with 500 lines in them +instead of 1,000). To change the name of the output files to something like @file{myfileaa}, @file{myfileab}, and so on, supply an additional argument that specifies the @value{FN} prefix. @@ -22580,7 +23962,7 @@ The program first sets its defaults, and then tests to make sure there are not too many arguments. It then looks at each argument in turn. The first argument could be a minus sign followed by a number. If it is, this happens to look like a negative number, so it is made positive, and that is the -count of lines. The data @value{FN} is skipped over and the final argument +count of lines. The @value{DF} name is skipped over and the final argument is used as the prefix for the output @value{FN}s: @cindex @code{split.awk} program @@ -22595,11 +23977,12 @@ is used as the prefix for the output @value{FN}s: # # Arnold Robbins, arnold@@skeeve.com, Public Domain # May 1993 +# Revised slightly, May 2014 @c endfile @end ignore @c file eg/prog/split.awk -# usage: split [-num] [file] [outname] +# usage: split [-count] [file] [outname] BEGIN @{ outfile = "x" # default @@ -22608,14 +23991,14 @@ BEGIN @{ usage() i = 1 - if (ARGV[i] ~ /^-[[:digit:]]+$/) @{ + if (i in ARGV && ARGV[i] ~ /^-[[:digit:]]+$/) @{ count = -ARGV[i] ARGV[i] = "" i++ @} # test argv in case reading from stdin instead of file if (i in ARGV) - i++ # skip data file name + i++ # skip datafile name if (i in ARGV) @{ outfile = ARGV[i] ARGV[i] = "" @@ -22662,40 +24045,30 @@ moves to the next letter in the alphabet and @code{s2} starts over again at @c endfile @end example -@c Exercise: do this with just awk builtin functions, index("abc..."), substr, etc. - @noindent The @code{usage()} function simply prints an error message and exits: @example @c file eg/prog/split.awk -function usage( e) +function usage() @{ - e = "usage: split [-num] [file] [outname]" - print e > "/dev/stderr" + print("usage: split [-num] [file] [outname]") > "/dev/stderr" exit 1 @} @c endfile @end example -@noindent -The variable @code{e} is used so that the function -fits nicely on the -@ifinfo -screen. -@end ifinfo -@ifnotinfo -page. -@end ifnotinfo - This program is a bit sloppy; it relies on @command{awk} to automatically close the last file instead of doing it in an @code{END} rule. It also assumes that letters are contiguous in the character set, which isn't true for EBCDIC systems. -@c Exercise: Fix these problems. -@c BFD... -@c ENDOFRANGE filspl +@ifset FOR_PRINT +You might want to consider how to eliminate the use of +@code{ord()} and @code{chr()}; this can be done in such a +way as to solve the EBCDIC issue as well. +@end ifset + @node Tee Program @subsection Duplicating Output into Multiple Files @@ -22707,17 +24080,17 @@ The @code{tee} program is known as a ``pipe fitting.'' @code{tee} copies its standard input to its standard output and also duplicates it to the files named on the command line. Its usage is as follows: -@example -tee @r{[}-a@r{]} file @dots{} -@end example +@display +@command{tee} [@option{-a}] @var{file} @dots{} +@end display The @option{-a} option tells @code{tee} to append to the named files, instead of truncating them and starting over. The @code{BEGIN} rule first makes a copy of all the command-line arguments into an array named @code{copy}. -@code{ARGV[0]} is not copied, since it is not needed. -@code{tee} cannot use @code{ARGV} directly, since @command{awk} attempts to +@code{ARGV[0]} is not needed, so it is not copied. +@code{tee} cannot use @code{ARGV} directly, because @command{awk} attempts to process each @value{FN} in @code{ARGV} as input data. @cindex flag variables @@ -22746,8 +24119,7 @@ Finally, @command{awk} is forced to read the standard input by setting @c endfile @end ignore @c file eg/prog/tee.awk -BEGIN \ -@{ +BEGIN @{ for (i = 1; i < ARGC; i++) copy[i] = ARGV[i] @@ -22767,7 +24139,7 @@ BEGIN \ @c endfile @end example -The following single rule does all the work. Since there is no pattern, it is +The following single rule does all the work. Because there is no pattern, it is executed for each line of input. The body of the rule simply prints the line into each file on the command line, and then to the standard output: @@ -22798,7 +24170,7 @@ for (i in copy) @end example @noindent -This is more concise but it is also less efficient. The @samp{if} is +This is more concise, but it is also less efficient. The @samp{if} is tested for each record and for each output file. By duplicating the loop body, the @samp{if} is only tested once for each input record. If there are @var{N} input records and @var{M} output files, the first method only @@ -22809,8 +24181,7 @@ Finally, the @code{END} rule cleans up by closing all the output files: @example @c file eg/prog/tee.awk -END \ -@{ +END @{ for (i in copy) close(copy[i]) @} @@ -22822,9 +24193,7 @@ END \ @c FIXME: One day, update to current POSIX version of uniq -@c STARTOFRANGE prunt @cindex printing, unduplicated lines of text -@c STARTOFRANGE tpul @cindex text@comma{} printing, unduplicated lines of @cindex @command{uniq} utility The @command{uniq} utility reads sorted lines of data on its standard @@ -22832,18 +24201,18 @@ input, and by default removes duplicate lines. In other words, it only prints unique lines---hence the name. @command{uniq} has a number of options. The usage is as follows: -@example -uniq @r{[}-udc @r{[}-@var{n}@r{]]} @r{[}+@var{n}@r{]} @r{[} @var{input file} @r{[} @var{output file} @r{]]} -@end example +@display +@command{uniq} [@option{-udc} [@code{-@var{n}}]] [@code{+@var{n}}] [@var{inputfile} [@var{outputfile}]] +@end display The options for @command{uniq} are: @table @code @item -d -Print only repeated lines. +Print only repeated (duplicated) lines. @item -u -Print only nonrepeated lines. +Print only nonrepeated (unique) lines. @item -c Count lines. This option overrides @option{-d} and @option{-u}. Both repeated @@ -22858,11 +24227,11 @@ by runs of spaces and/or TABs. Skip @var{n} characters before comparing lines. Any fields specified with @samp{-@var{n}} are skipped first. -@item @var{input file} +@item @var{inputfile} Data is read from the input file named on the command line, instead of from the standard input. -@item @var{output file} +@item @var{outputfile} The generated output is sent to the named output file, instead of to the standard output. @end table @@ -22912,10 +24281,9 @@ standard output, @file{/dev/stdout}: @end ignore @c file eg/prog/uniq.awk -function usage( e) +function usage() @{ - e = "Usage: uniq [-udc [-n]] [+n] [ in [ out ]]" - print e > "/dev/stderr" + print("Usage: uniq [-udc [-n]] [+n] [ in [ out ]]") > "/dev/stderr" exit 1 @} @@ -22925,8 +24293,7 @@ function usage( e) # -n skip n fields # +n skip n characters, skip fields first -BEGIN \ -@{ +BEGIN @{ count = 1 outputfile = "/dev/stdout" opts = "udc0:1:2:3:4:5:6:7:8:9:" @@ -22938,7 +24305,7 @@ BEGIN \ else if (c == "c") do_count++ else if (index("0123456789", c) != 0) @{ - # getopt requires args to options + # getopt() requires args to options # this messes us up for things like -5 if (Optarg ~ /^[[:digit:]]+$/) fcount = (c Optarg) + 0 @@ -22970,22 +24337,20 @@ BEGIN \ @end example The following function, @code{are_equal()}, compares the current line, -@code{$0}, to the -previous line, @code{last}. It handles skipping fields and characters. -If no field count and no character count are specified, @code{are_equal()} -simply returns one or zero depending upon the result of a simple string -comparison of @code{last} and @code{$0}. Otherwise, things get more -complicated. -If fields have to be skipped, each line is broken into an array using -@code{split()} -(@pxref{String Functions}); -the desired fields are then joined back into a line using @code{join()}. -The joined lines are stored in @code{clast} and @code{cline}. -If no fields are skipped, @code{clast} and @code{cline} are set to -@code{last} and @code{$0}, respectively. -Finally, if characters are skipped, @code{substr()} is used to strip off the -leading @code{charcount} characters in @code{clast} and @code{cline}. The -two strings are then compared and @code{are_equal()} returns the result: +@code{$0}, to the previous line, @code{last}. It handles skipping fields +and characters. If no field count and no character count are specified, +@code{are_equal()} returns one or zero depending upon the result of a +simple string comparison of @code{last} and @code{$0}. + +Otherwise, things get more complicated. If fields have to be skipped, +each line is broken into an array using @code{split()} (@pxref{String +Functions}); the desired fields are then joined back into a line +using @code{join()}. The joined lines are stored in @code{clast} and +@code{cline}. If no fields are skipped, @code{clast} and @code{cline} +are set to @code{last} and @code{$0}, respectively. Finally, if +characters are skipped, @code{substr()} is used to strip off the leading +@code{charcount} characters in @code{clast} and @code{cline}. The two +strings are then compared and @code{are_equal()} returns the result: @example @c file eg/prog/uniq.awk @@ -23021,10 +24386,10 @@ The second rule does the work. The variable @code{equal} is one or zero, depending upon the results of @code{are_equal()}'s comparison. If @command{uniq} is counting repeated lines, and the lines are equal, then it increments the @code{count} variable. Otherwise, it prints the line and resets @code{count}, -since the two lines are not equal. +because the two lines are not equal. If @command{uniq} is not counting, and if the lines are equal, @code{count} is incremented. -Nothing is printed, since the point is to remove duplicates. +Nothing is printed, as the point is to remove duplicates. Otherwise, if @command{uniq} is counting repeated lines and more than one line is seen, or if @command{uniq} is counting nonrepeated lines and only one line is seen, then the line is printed, and @code{count} @@ -23075,35 +24440,51 @@ END @{ @} @c endfile @end example -@c ENDOFRANGE prunt -@c ENDOFRANGE tpul + +@c FIXME: Include this? +@ignore +This program does not follow our recommended convention of naming +global variables with a leading capital letter. Doing that would +make the program a little easier to follow. +@end ignore + +@ifset FOR_PRINT +The logic for choosing which lines to print represents a @dfn{state +machine}, which is ``a device that can be in one of a set number of stable +conditions depending on its previous condition and on the present values +of its inputs.''@footnote{This is the definition returned from entering +@code{define: state machine} into Google.} +Brian Kernighan suggests that +``an alternative approach to state machines is to just read +the input into an array, then use indexing. It's almost always +easier code, and for most inputs where you would use this, just +as fast.'' Consider how to rewrite the logic to follow this +suggestion. +@end ifset + + @node Wc Program @subsection Counting Things @c FIXME: One day, update to current POSIX version of wc -@c STARTOFRANGE count @cindex counting -@c STARTOFRANGE infco @cindex input files, counting elements in -@c STARTOFRANGE woco @cindex words, counting -@c STARTOFRANGE chco @cindex characters, counting -@c STARTOFRANGE lico @cindex lines, counting @cindex @command{wc} utility The @command{wc} (word count) utility counts lines, words, and characters in one or more input files. Its usage is as follows: -@example -wc @r{[}-lwc@r{]} @r{[} @var{files} @dots{} @r{]} -@end example +@display +@command{wc} [@option{-lwc}] [@var{files} @dots{}] +@end display If no files are specified on the command line, @command{wc} reads its standard input. If there are multiple files, it also prints total counts for all -the files. The options and their meanings are shown in the following list: +the files. The options and their meanings are as follows: @table @code @item -l @@ -23120,7 +24501,7 @@ Count only characters. @end table Implementing @command{wc} in @command{awk} is particularly elegant, -since @command{awk} does a lot of the work for us; it splits lines into +because @command{awk} does a lot of the work for us; it splits lines into words (i.e., fields) and counts them, it counts lines (i.e., records), and it can easily tell us how long a line is. @@ -23199,18 +24580,10 @@ function beginfile(file) @c endfile @end example -The @code{endfile()} function adds the current file's numbers to the running -totals of lines, words, and characters.@footnote{@command{wc} can't just use the value of -@code{FNR} in @code{endfile()}. If you examine -the code in -@ref{Filetrans Function}, -you will see that -@code{FNR} has already been reset by the time -@code{endfile()} is called.} It then prints out those numbers -for the file that was just read. It relies on @code{beginfile()} to reset the -numbers for the following @value{DF}: -@c FIXME: ONE DAY: make the above footnote an exercise, -@c instead of giving away the answer. +The @code{endfile()} function adds the current file's numbers to the +running totals of lines, words, and characters. It then prints out those +numbers for the file that was just read. It relies on @code{beginfile()} +to reset the numbers for the following @value{DF}: @example @c file eg/prog/wc.awk @@ -23233,7 +24606,7 @@ function endfile(file) @end example There is one rule that is executed for each line. It adds the length of -the record, plus one, to @code{chars}.@footnote{Since @command{gawk} +the record, plus one, to @code{chars}.@footnote{Because @command{gawk} understands multibyte locales, this code counts characters, not bytes.} Adding one plus the record length is needed because the newline character separating records (the value @@ -23270,12 +24643,6 @@ END @{ @} @c endfile @end example -@c ENDOFRANGE count -@c ENDOFRANGE infco -@c ENDOFRANGE lico -@c ENDOFRANGE woco -@c ENDOFRANGE chco -@c ENDOFRANGE posimawk @node Miscellaneous Programs @section A Grab Bag of @command{awk} Programs @@ -23376,13 +24743,37 @@ word, comparing it to the previous one: @cindex insomnia, cure for @cindex Robbins, Arnold @quotation -@i{Nothing cures insomnia like a ringing alarm clock.}@* -Arnold Robbins +@i{Nothing cures insomnia like a ringing alarm clock.} +@author Arnold Robbins +@end quotation +@cindex Quanstrom, Erik +@ignore +Date: Sat, 15 Feb 2014 16:47:09 -0500 +Subject: Re: 9atom install question +Message-ID: <l2jcvx6j6mey60xnrkb0hhob.1392500829294@email.android.com> +From: Erik Quanstrom <quanstro@quanstro.net> +To: Aharon Robbins <arnold@skeeve.com> + +yes. + +- erik + +Aharon Robbins <arnold@skeeve.com> wrote: + +>> sleep is for web developers. +> +>Can I quote you, in the gawk manual? +> +>Thanks, +> +>Arnold +@end ignore +@quotation +@i{Sleep is for web developers.} +@author Erik Quanstrom @end quotation -@c STARTOFRANGE tialarm @cindex time, alarm clock example program -@c STARTOFRANGE alaex @cindex alarm clock example program The following program is a simple ``alarm clock'' program. You give it a time of day and an optional message. At the specified time, @@ -23390,8 +24781,8 @@ it prints the message on the standard output. In addition, you can give it the number of times to repeat the message as well as a delay between repetitions. -This program uses the @code{gettimeofday()} function from -@ref{Gettimeofday Function}. +This program uses the @code{getlocaltime()} function from +@ref{Getlocaltime Function}. All the work is done in the @code{BEGIN} rule. The first part is argument checking and setting of defaults: the delay, the count, and the message to @@ -23410,7 +24801,7 @@ Here is the program: @c file eg/prog/alarm.awk # alarm.awk --- set an alarm # -# Requires gettimeofday() library function +# Requires getlocaltime() library function @c endfile @ignore @c file eg/prog/alarm.awk @@ -23424,8 +24815,7 @@ Here is the program: @c file eg/prog/alarm.awk # usage: alarm time [ "message" [ count [ delay ] ] ] -BEGIN \ -@{ +BEGIN @{ # Initial argument sanity checking usage1 = "usage: alarm time ['message' [count [delay]]]" usage2 = sprintf("\t(%s) time ::= hh:mm", ARGV[1]) @@ -23482,7 +24872,7 @@ is how long to wait before setting off the alarm: minute = atime[2] + 0 # force numeric # get current broken down time - gettimeofday(now) + getlocaltime(now) # if time given is 12-hour hours and it's after that # hour, e.g., `alarm 5:30' at 9 a.m. means 5:30 p.m., @@ -23500,7 +24890,7 @@ is how long to wait before setting off the alarm: # how long to sleep for naptime = target - current if (naptime <= 0) @{ - print "time is in the past!" > "/dev/stderr" + print "alarm: time is in the past!" > "/dev/stderr" exit 1 @} @c endfile @@ -23535,13 +24925,10 @@ seconds are necessary: @} @c endfile @end example -@c ENDOFRANGE tialarm -@c ENDOFRANGE alaex @node Translate Program @subsection Transliterating Characters -@c STARTOFRANGE chtra @cindex characters, transliterating @cindex @command{tr} utility The system @command{tr} utility transliterates characters. For example, it is @@ -23552,24 +24939,21 @@ often used to map uppercase letters into lowercase for further processing: @end example @command{tr} requires two lists of characters.@footnote{On some older -systems, -@ifset ORA -including Solaris, -@end ifset -@command{tr} may require that the lists be written as -range expressions enclosed in square brackets (@samp{[a-z]}) and quoted, -to prevent the shell from attempting a @value{FN} expansion. This is -not a feature.} When processing the input, the first character in the -first list is replaced with the first character in the second list, -the second character in the first list is replaced with the second -character in the second list, and so on. If there are more characters -in the ``from'' list than in the ``to'' list, the last character of the -``to'' list is used for the remaining characters in the ``from'' list. - -Some time ago, +systems, including Solaris, the system version of @command{tr} may require +that the lists be written as range expressions enclosed in square brackets +(@samp{[a-z]}) and quoted, to prevent the shell from attempting a +@value{FN} expansion. This is not a feature.} When processing the input, the +first character in the first list is replaced with the first character +in the second list, the second character in the first list is replaced +with the second character in the second list, and so on. If there are +more characters in the ``from'' list than in the ``to'' list, the last +character of the ``to'' list is used for the remaining characters in the +``from'' list. + +Once upon a time, @c early or mid-1989! -a user proposed that a transliteration function should -be added to @command{gawk}. +a user proposed adding a transliteration function +to @command{gawk}. @c Wishing to avoid gratuitous new features, @c at least theoretically The following program was written to @@ -23577,16 +24961,12 @@ prove that character transliteration could be done with a user-level function. This program is not as complete as the system @command{tr} utility but it does most of the job. -The @command{translate} program demonstrates one of the few weaknesses -of standard @command{awk}: dealing with individual characters is very -painful, requiring repeated use of the @code{substr()}, @code{index()}, -and @code{gsub()} built-in functions -(@pxref{String Functions}).@footnote{This -program was written before @command{gawk} acquired the ability to -split each character in a string into separate array elements.} -@c Exercise: How might you use this new feature to simplify the program? -There are two functions. The first, @code{stranslate()}, takes three -arguments: +The @command{translate} program was written long before @command{gawk} +acquired the ability to split each character in a string into separate +array elements. Thus, it makes repeated use of the @code{substr()}, +@code{index()}, and @code{gsub()} built-in functions (@pxref{String +Functions}). There are two functions. The first, @code{stranslate()}, +takes three arguments: @table @code @item from @@ -23605,7 +24985,7 @@ loop goes through @code{from}, one character at a time. For each character in @code{from}, if the character appears in @code{target}, it is replaced with the corresponding @code{to} character. -The @code{translate()} function simply calls @code{stranslate()} using @code{$0} +The @code{translate()} function calls @code{stranslate()} using @code{$0} as the target. The main program sets two global variables, @code{FROM} and @code{TO}, from the command line, and then changes @code{ARGV} so that @command{awk} reads from the standard input. @@ -23677,29 +25057,31 @@ BEGIN @{ @c endfile @end example -While it is possible to do character transliteration in a user-level -function, it is not necessarily efficient, and we (the @command{gawk} -authors) started to consider adding a built-in function. However, -shortly after writing this program, we learned that the System V Release 4 -@command{awk} had added the @code{toupper()} and @code{tolower()} functions -(@pxref{String Functions}). -These functions handle the vast majority of the -cases where character transliteration is necessary, and so we chose to -simply add those functions to @command{gawk} as well and then leave well -enough alone. +It is possible to do character transliteration in a user-level +function, but it is not necessarily efficient, and we (the @command{gawk} +developers) started to consider adding a built-in function. However, +shortly after writing this program, we learned that Brian Kernighan +had added the @code{toupper()} and @code{tolower()} functions to his +@command{awk} (@pxref{String Functions}). These functions handle the +vast majority of the cases where character transliteration is necessary, +and so we chose to simply add those functions to @command{gawk} as well +and then leave well enough alone. An obvious improvement to this program would be to set up the @code{t_ar} array only once, in a @code{BEGIN} rule. However, this assumes that the ``from'' and ``to'' lists will never change throughout the lifetime of the program. -@c ENDOFRANGE chtra + +Another obvious improvement is to enable the use of ranges, +such as @samp{a-z}, as allowed by the @command{tr} utility. +Look at the code for @file{cut.awk} (@pxref{Cut Program}) +for inspiration. + @node Labels Program @subsection Printing Mailing Labels -@c STARTOFRANGE prml @cindex printing, mailing labels -@c STARTOFRANGE mlprint @cindex mailing labels@comma{} printing Here is a ``real world''@footnote{``Real world'' is defined as ``a program actually used to get something done.''} @@ -23717,13 +25099,24 @@ the @code{line} array and printing the page when 20 labels have been read. The @code{BEGIN} rule simply sets @code{RS} to the empty string, so that @command{awk} splits records at blank lines (@pxref{Records}). -It sets @code{MAXLINES} to 100, since 100 is the maximum number -of lines on the page (20 * 5 = 100). +It sets @code{MAXLINES} to 100, because 100 is the maximum number +of lines on the page +@iftex +(@math{20 @cdot 5 = 100}). +@end iftex +@ifnottex +@ifnotdocbook +(20 * 5 = 100). +@end ifnotdocbook +@end ifnottex +@docbook +(20 ⋅ 5 = 100). @c +@end docbook Most of the work is done in the @code{printpage()} function. The label lines are stored sequentially in the @code{line} array. But they have to print horizontally; @code{line[1]} next to @code{line[6]}, -@code{line[2]} next to @code{line[7]}, and so on. Two loops are used to +@code{line[2]} next to @code{line[7]}, and so on. Two loops accomplish this. The outer loop, controlled by @code{i}, steps through every 10 lines of data; this is each row of labels. The inner loop, controlled by @code{j}, goes through the lines within the row. @@ -23811,24 +25204,20 @@ function printpage( i, j) Count++ @} -END \ -@{ +END @{ printpage() @} @c endfile @end example -@c ENDOFRANGE prml -@c ENDOFRANGE mlprint @node Word Sorting @subsection Generating Word-Usage Counts -@c STARTOFRANGE worus @cindex words, usage counts@comma{} generating When working with large amounts of text, it can be interesting to know how often different words appear. For example, an author may overuse -certain words, in which case she might wish to find synonyms to substitute +certain words, in which case he or she might wish to find synonyms to substitute for words that appear too often. This @value{SUBSECTION} develops a program for counting words and presenting the frequency information in a useful format. @@ -23836,7 +25225,7 @@ in a useful format. At first glance, a program like this would seem to do the job: @example -# Print list of word frequencies +# wordfreq-first-try.awk --- print list of word frequencies @{ for (i = 1; i <= NF; i++) @@ -23858,13 +25247,13 @@ it prints the counts. This program has several problems that prevent it from being useful on real text files: -@itemize @bullet +@itemize @value{BULLET} @item The @command{awk} language considers upper- and lowercase characters to be distinct. Therefore, ``bartender'' and ``Bartender'' are not treated -as the same word. This is undesirable, since in normal text, words -are capitalized if they begin sentences, and a frequency analyzer should not -be sensitive to capitalization. +as the same word. This is undesirable, because words are capitalized +if they begin sentences in normal text, and a frequency analyzer should +not be sensitive to capitalization. @item Words are detected using the @command{awk} convention that fields are @@ -23905,6 +25294,10 @@ END @{ @} @end example +The regexp @code{/[^[:alnum:]_[:blank:]]/} might have been written +@code{/[[:punct:]]/}, but then underscores would also be removed, +and we want to keep them. + Assuming we have saved this program in a file named @file{wordfreq.awk}, and that the data is in @file{file1}, the following pipeline: @@ -23945,12 +25338,10 @@ This way of sorting must be used on systems that do not have true pipes at the command-line (or batch-file) level. See the general operating system documentation for more information on how to use the @command{sort} program. -@c ENDOFRANGE worus @node History Sorting @subsection Removing Duplicates from Unsorted Text -@c STARTOFRANGE lidu @cindex lines, duplicate@comma{} removing The @command{uniq} program (@pxref{Uniq Program}), @@ -24014,16 +25405,14 @@ information. For example, using the following @code{print} statement in the print data[lines[i]], lines[i] @end example +@noindent This works because @code{data[$0]} is incremented each time a line is seen. -@c ENDOFRANGE lidu @node Extract Program @subsection Extracting Programs from Texinfo Source Files -@c STARTOFRANGE texse @cindex Texinfo, extracting programs from source files -@c STARTOFRANGE fitex @cindex files, Texinfo@comma{} extracting programs from @ifnotinfo Both this chapter and the previous chapter @@ -24036,29 +25425,30 @@ The nodes and @ref{Sample Programs}, are the top level nodes for a large number of @command{awk} programs. @end ifinfo -If you want to experiment with these programs, it is tedious to have to type +If you want to experiment with these programs, it is tedious to type them in by hand. Here we present a program that can extract parts of a Texinfo input file into separate files. @cindex Texinfo -This @value{DOCUMENT} is written in @uref{http://texinfo.org, Texinfo}, +This @value{DOCUMENT} is written in @uref{http://www.gnu.org/software/texinfo/, Texinfo}, the GNU project's document formatting language. A single Texinfo source file can be used to produce both -printed and online documentation. +printed documentation, with @TeX{}, and online documentation. @ifnotinfo -Texinfo is fully documented in the book +(Texinfo is fully documented in the book @cite{Texinfo---The GNU Documentation Format}, -available from the Free Software Foundation. +available from the Free Software Foundation, +and also available @uref{http://www.gnu.org/software/texinfo/manual/texinfo/, online}.) @end ifnotinfo @ifinfo -The Texinfo language is described fully, starting with -@inforef{Top, , Texinfo, texinfo,Texinfo---The GNU Documentation Format}. +(The Texinfo language is described fully, starting with +@inforef{Top, , Texinfo, texinfo,Texinfo---The GNU Documentation Format}.) @end ifinfo For our purposes, it is enough to know three things about Texinfo input files: -@itemize @bullet +@itemize @value{BULLET} @item The ``at'' symbol (@samp{@@}) is special in Texinfo, much as the backslash (@samp{\}) is in C @@ -24092,7 +25482,7 @@ Lines containing @samp{@@group} and @samp{@@end group} are simply removed. (@pxref{Join Function}). The example programs in the online Texinfo source for @cite{@value{TITLE}} -(@file{gawk.texi}) have all been bracketed inside @samp{file} and +(@file{gawktexi.in}) have all been bracketed inside @samp{file} and @samp{endfile} lines. The @command{gawk} distribution uses a copy of @file{extract.awk} to extract the sample programs and install many of them in a standard directory where @command{gawk} can find them. @@ -24113,7 +25503,7 @@ It also prints some final advice: @@example @@c file examples/messages.awk -END @@@{ print "Always avoid bored archeologists!" @@@} +END @@@{ print "Always avoid bored archaeologists!" @@@} @@c end file @@end example @dots{} @@ -24129,8 +25519,7 @@ exits with a zero exit status, signifying OK: @cindex @code{extract.awk} program @example @c file eg/prog/extract.awk -# extract.awk --- extract files and run programs -# from texinfo files +# extract.awk --- extract files and run programs from texinfo files @c endfile @ignore @c file eg/prog/extract.awk @@ -24144,10 +25533,9 @@ exits with a zero exit status, signifying OK: BEGIN @{ IGNORECASE = 1 @} -/^@@c(omment)?[ \t]+system/ \ -@{ +/^@@c(omment)?[ \t]+system/ @{ if (NF < 3) @{ - e = (FILENAME ":" FNR) + e = ("extract: " FILENAME ":" FNR) e = (e ": badly formed `system' line") print e > "/dev/stderr" next @@ -24156,7 +25544,7 @@ BEGIN @{ IGNORECASE = 1 @} $2 = "" stat = system($0) if (stat != 0) @{ - e = (FILENAME ":" FNR) + e = ("extract: " FILENAME ":" FNR) e = (e ": warning: system returned " stat) print e > "/dev/stderr" @} @@ -24166,13 +25554,7 @@ BEGIN @{ IGNORECASE = 1 @} @noindent The variable @code{e} is used so that the rule -fits nicely on the -@ifnotinfo -page. -@end ifnotinfo -@ifnottex -screen. -@end ifnottex +fits nicely on the @value{PAGE}. The second rule handles moving data into files. It verifies that a @value{FN} is given in the directive. If the file named is not the @@ -24199,20 +25581,18 @@ the array @code{a}, using the @code{split()} function The @samp{@@} symbol is used as the separator character. Each element of @code{a} that is empty indicates two successive @samp{@@} symbols in the original line. For each two empty elements (@samp{@@@@} in -the original file), we have to add a single @samp{@@} symbol back -in.@footnote{This program was written before @command{gawk} had the -@code{gensub()} function. Consider how you might use it to simplify the code.} +the original file), we have to add a single @samp{@@} symbol back in. When the processing of the array is finished, @code{join()} is called with the -value of @code{SUBSEP}, to rejoin the pieces back into a single +value of @code{SUBSEP} (@pxref{Multidimensional}), +to rejoin the pieces back into a single line. That line is then printed to the output file: @example @c file eg/prog/extract.awk -/^@@c(omment)?[ \t]+file/ \ -@{ +/^@@c(omment)?[ \t]+file/ @{ if (NF != 3) @{ - e = (FILENAME ":" FNR ": badly formed `file' line") + e = ("extract: " FILENAME ":" FNR ": badly formed `file' line") print e > "/dev/stderr" next @} @@ -24257,21 +25637,20 @@ subsequent output is appended to the file (@pxref{Redirection}). This makes it easy to mix program text and explanatory prose for the same sample source file (as has been done here!) without any hassle. The file is -only closed when a new data @value{FN} is encountered or at the end of the +only closed when a new @value{DF} name is encountered or at the end of the input file. Finally, the function @code{@w{unexpected_eof()}} prints an appropriate error message and then exits. The @code{END} rule handles the final cleanup, closing the open file: -@c function lb put on same line for page breaking. sigh @example @c file eg/prog/extract.awk @group function unexpected_eof() @{ - printf("%s:%d: unexpected EOF or error\n", - FILENAME, FNR) > "/dev/stderr" + printf("extract: %s:%d: unexpected EOF or error\n", + FILENAME, FNR) > "/dev/stderr" exit 1 @} @end group @@ -24282,8 +25661,6 @@ END @{ @} @c endfile @end example -@c ENDOFRANGE texse -@c ENDOFRANGE fitex @node Simple Sed @subsection A Simple Stream Editor @@ -24294,22 +25671,22 @@ The @command{sed} utility is a stream editor, a program that reads a stream of data, makes changes to it, and passes it on. It is often used to make global changes to a large file or to a stream of data generated by a pipeline of commands. -While @command{sed} is a complicated program in its own right, its most common +Although @command{sed} is a complicated program in its own right, its most common use is to perform global substitutions in the middle of a pipeline: @example -command1 < orig.data | sed 's/old/new/g' | command2 > result +@var{command1} < orig.data | sed 's/old/new/g' | @var{command2} > result @end example Here, @samp{s/old/new/g} tells @command{sed} to look for the regexp @samp{old} on each input line and globally replace it with the text -@samp{new}, i.e., all the occurrences on a line. This is similar to +@samp{new} (i.e., all the occurrences on a line). This is similar to @command{awk}'s @code{gsub()} function (@pxref{String Functions}). The following program, @file{awksed.awk}, accepts at least two command-line arguments: the pattern to look for and the text to replace it with. Any -additional arguments are treated as data @value{FN}s to process. If none +additional arguments are treated as @value{DF} names to process. If none are provided, the standard input is used: @cindex Brennan, Michael @@ -24386,36 +25763,14 @@ not treated as @value{FN}s (@pxref{ARGC and ARGV}). The @code{usage()} function prints an error message and exits. -Finally, the single rule handles the printing scheme outlined above, +Finally, the single rule handles the printing scheme outlined earlier, using @code{print} or @code{printf} as appropriate, depending upon the value of @code{RT}. -@ignore -Exercise, compare the performance of this version with the more -straightforward: - -BEGIN { - pat = ARGV[1] - repl = ARGV[2] - ARGV[1] = ARGV[2] = "" -} - -{ gsub(pat, repl); print } - -Exercise: what are the advantages and disadvantages of this version versus sed? - Advantage: egrep regexps - speed (?) - Disadvantage: no & in replacement text - -Others? -@end ignore - @node Igawk Program @subsection An Easy Way to Use Library Functions -@c STARTOFRANGE libfex @cindex libraries of @command{awk} functions, example program for using -@c STARTOFRANGE flibex @cindex functions, library, example program for using In @ref{Include Files}, we saw how @command{gawk} provides a built-in file-inclusion capability. However, this is a @command{gawk} extension. @@ -24449,8 +25804,8 @@ BEGIN @{ The following program, @file{igawk.sh}, provides this service. It simulates @command{gawk}'s searching of the @env{AWKPATH} variable -and also allows @dfn{nested} includes; i.e., a file that is included -with @samp{@@include} can contain further @samp{@@include} statements. +and also allows @dfn{nested} includes (i.e., a file that is included +with @code{@@include} can contain further @code{@@include} statements). @command{igawk} makes an effort to only include files once, so that nested includes don't accidentally include a library function twice. @@ -24476,24 +25831,24 @@ a shell variable that will be expanded. There are two cases: @enumerate a @item -Literal text, provided with @option{--source} or @option{--source=}. This +Literal text, provided with @option{-e} or @option{--source}. This text is just appended directly. @item -Source @value{FN}s, provided with @option{-f}. We use a neat trick and append -@samp{@@include @var{filename}} to the shell variable's contents. Since the file-inclusion -program works the way @command{gawk} does, this gets the text -of the file included into the program at the correct point. +Source @value{FN}s, provided with @option{-f}. We use a neat trick and +append @samp{@@include @var{filename}} to the shell variable's contents. +Because the file-inclusion program works the way @command{gawk} does, this +gets the text of the file included in the program at the correct point. @end enumerate @item Run an @command{awk} program (naturally) over the shell variable's contents to expand -@samp{@@include} statements. The expanded program is placed in a second +@code{@@include} statements. The expanded program is placed in a second shell variable. @item Run the expanded program with @command{gawk} and any other original command-line -arguments that the user supplied (such as the data @value{FN}s). +arguments that the user supplied (such as the @value{DF} names). @end enumerate This program uses shell variables extensively: for storing command-line arguments, @@ -24508,24 +25863,25 @@ argument is @samp{debug}. The next part loops through all the command-line arguments. There are several cases of interest: -@table @code -@item -- +@c @asis for docbook +@table @asis +@item @option{--} This ends the arguments to @command{igawk}. Anything else should be passed on to the user's @command{awk} program without being evaluated. -@item -W +@item @option{-W} This indicates that the next option is specific to @command{gawk}. To make argument processing easier, the @option{-W} is appended to the front of the remaining arguments and the loop continues. (This is an @command{sh} programming trick. Don't worry about it if you are not familiar with @command{sh}.) -@item -v@r{,} -F +@item @option{-v}, @option{-F} These are saved and passed on to @command{gawk}. -@item -f@r{,} --file@r{,} --file=@r{,} -Wfile= +@item @option{-f}, @option{--file}, @option{--file=}, @option{-Wfile=} The @value{FN} is appended to the shell variable @code{program} with an -@samp{@@include} statement. +@code{@@include} statement. The @command{expr} utility is used to remove the leading option part of the argument (e.g., @samp{--file=}). (Typical @command{sh} usage would be to use the @command{echo} and @command{sed} @@ -24533,10 +25889,10 @@ utilities to do this work. Unfortunately, some versions of @command{echo} evalu escape sequences in their arguments, possibly mangling the program text. Using @command{expr} avoids this problem.) -@item --source@r{,} --source=@r{,} -Wsource= +@item @option{--source}, @option{--source=}, @option{-Wsource=} The source text is appended to @code{program}. -@item --version@r{,} -Wversion +@item @option{--version}, @option{-Wversion} @command{igawk} prints its version number, runs @samp{gawk --version} to get the @command{gawk} version information, and then exits. @end table @@ -24547,6 +25903,7 @@ should be the @command{awk} program. If there are no command-line arguments left, @command{igawk} prints an error message and exits. Otherwise, the first argument is appended to @code{program}. In any case, after the arguments have been processed, +the shell variable @code{program} contains the complete text of the original @command{awk} program. @@ -24643,14 +26000,14 @@ fi @c endfile @end example -The @command{awk} program to process @samp{@@include} directives +The @command{awk} program to process @code{@@include} directives is stored in the shell variable @code{expand_prog}. Doing this keeps the shell script readable. The @command{awk} program reads through the user's program, one line at a time, using @code{getline} (@pxref{Getline}). The input -@value{FN}s and @samp{@@include} statements are managed using a stack. -As each @samp{@@include} is encountered, the current @value{FN} is -``pushed'' onto the stack and the file named in the @samp{@@include} +@value{FN}s and @code{@@include} statements are managed using a stack. +As each @code{@@include} is encountered, the current @value{FN} is +``pushed'' onto the stack and the file named in the @code{@@include} directive becomes the current @value{FN}. As each file is finished, the stack is ``popped,'' and the previous input file becomes the current input file again. The process is started by making the original file @@ -24668,8 +26025,8 @@ the path, and an attempt is made to open the generated @value{FN}. The only way to test if a file can be read in @command{awk} is to go ahead and try to read it with @code{getline}; this is what @code{pathto()} does.@footnote{On some very old versions of @command{awk}, the test -@samp{getline junk < t} can loop forever if the file exists but is empty. -Caveat emptor.} If the file can be read, it is closed and the @value{FN} +@samp{getline junk < t} can loop forever if the file exists but is empty.} +If the file can be read, it is closed and the @value{FN} is returned: @ignore @@ -24724,10 +26081,10 @@ BEGIN @{ @c endfile @end example -The stack is initialized with @code{ARGV[1]}, which will be @file{/dev/stdin}. +The stack is initialized with @code{ARGV[1]}, which will be @code{"/dev/stdin"}. The main loop comes next. Input lines are read in succession. Lines that -do not start with @samp{@@include} are printed verbatim. -If the line does start with @samp{@@include}, the @value{FN} is in @code{$2}. +do not start with @code{@@include} are printed verbatim. +If the line does start with @code{@@include}, the @value{FN} is in @code{$2}. @code{pathto()} is called to generate the full path. If it cannot, then the program prints an error message and continues. @@ -24755,7 +26112,7 @@ the program is done: fpath = pathto($2) @group if (fpath == "") @{ - printf("igawk:%s:%d: cannot find %s\n", + printf("igawk: %s:%d: cannot find %s\n", input[stackptr], FNR, $2) > "/dev/stderr" continue @} @@ -24779,9 +26136,10 @@ EOF @c endfile @end example -The shell construct @samp{@var{command} << @var{marker}} is called a @dfn{here document}. -Everything in the shell script up to the @var{marker} is fed to @var{command} as input. -The shell processes the contents of the here document for variable and command substitution +The shell construct @samp{@var{command} << @var{marker}} is called +a @dfn{here document}. Everything in the shell script up to the +@var{marker} is fed to @var{command} as input. The shell processes +the contents of the here document for variable and command substitution (and possibly other things as well, depending upon the shell). The shell construct @samp{$(@dots{})} is called @dfn{command substitution}. @@ -24795,15 +26153,17 @@ It's done in these steps: @enumerate @item -Run @command{gawk} with the @samp{@@include}-processing program (the -value of the @code{expand_prog} shell variable) on standard input. +Run @command{gawk} with the @code{@@include}-processing program (the +value of the @code{expand_prog} shell variable) reading standard input. @item -Standard input is the contents of the user's program, from the shell variable @code{program}. -Its contents are fed to @command{gawk} via a here document. +Standard input is the contents of the user's program, +from the shell variable @code{program}. +Feed its contents to @command{gawk} via a here document. @item -The results of this processing are saved in the shell variable @code{processed_program} by using command substitution. +Save the results of this processing in the shell variable +@code{processed_program} by using command substitution. @end enumerate The last step is to call @command{gawk} with the expanded program, @@ -24819,7 +26179,7 @@ The program should exit without reading any @value{DF}s. However, suppose that an included library file defines an @code{END} rule of its own. In this case, @command{gawk} will hang, reading standard input. In order to avoid this, @file{/dev/null} is explicitly added to the -command-line. Reading from @file{/dev/null} always returns an immediate +command line. Reading from @file{/dev/null} always returns an immediate end of file indication. @c Hmm. Add /dev/null if $# is 0? Still messes up ARGV. Sigh. @@ -24834,27 +26194,25 @@ eval gawk $opts -- '"$processed_program"' '"$@@"' The @command{eval} command is a shell construct that reruns the shell's parsing process. This keeps things properly quoted. -This version of @command{igawk} represents my fifth version of this program. +This version of @command{igawk} represents the fifth version of this program. There are four key simplifications that make the program work better: -@itemize @bullet +@itemize @value{BULLET} @item -Using @samp{@@include} even for the files named with @option{-f} makes building +Using @code{@@include} even for the files named with @option{-f} makes building the initial collected @command{awk} program much simpler; all the -@samp{@@include} processing can be done once. +@code{@@include} processing can be done once. @item Not trying to save the line read with @code{getline} in the @code{pathto()} function when testing for the file's accessibility for use with the main program simplifies things considerably. -@c what problem does this engender though - exercise -@c answer, reading from "-" or /dev/stdin @item Using a @code{getline} loop in the @code{BEGIN} rule does it all in one place. It is not necessary to call out to a separate loop for processing -nested @samp{@@include} statements. +nested @code{@@include} statements. @item Instead of saving the expanded program in a temporary file, putting it in a shell variable @@ -24871,68 +26229,32 @@ in C or C++, and it is frequently easier to do certain kinds of string and argument manipulation using the shell than it is in @command{awk}. Finally, @command{igawk} shows that it is not always necessary to add new -features to a program; they can often be layered on top. -@ignore -With @command{igawk}, -there is no real reason to build @samp{@@include} processing into -@command{gawk} itself. -@end ignore - -@cindex search paths -@cindex search paths, for source files -@cindex source files@comma{} search path for -@cindex files, source@comma{} search path for -@cindex directories, searching -As an additional example of this, consider the idea of having two -files in a directory in the search path: - -@table @file -@item default.awk -This file contains a set of default library functions, such -as @code{getopt()} and @code{assert()}. - -@item site.awk -This file contains library functions that are specific to a site or -installation; i.e., locally developed functions. -Having a separate file allows @file{default.awk} to change with -new @command{gawk} releases, without requiring the system administrator to -update it each time by adding the local functions. -@end table - -One user -@c Karl Berry, karl@ileaf.com, 10/95 -suggested that @command{gawk} be modified to automatically read these files -upon startup. Instead, it would be very simple to modify @command{igawk} -to do this. Since @command{igawk} can process nested @samp{@@include} -directives, @file{default.awk} could simply contain @samp{@@include} -statements for the desired library functions. +features to a program; they can often be layered on top.@footnote{@command{gawk} +does @code{@@include} processing itself in order to support the use +of @command{awk} programs as Web CGI scripts.} -@c Exercise: make this change -@c ENDOFRANGE libfex -@c ENDOFRANGE flibex -@c ENDOFRANGE awkpex @node Anagram Program -@subsection Finding Anagrams From A Dictionary +@subsection Finding Anagrams from a Dictionary +@cindex anagrams, finding An interesting programming challenge is to search for @dfn{anagrams} in a word list (such as @file{/usr/share/dict/words} on many GNU/Linux systems). One word is an anagram of another if both words contain the same letters -(for example, ``babbling'' and ``blabbing''). +(e.g., ``babbling'' and ``blabbing''). -An elegant algorithm is presented in Column 2, Problem C of -Jon Bentley's @cite{Programming Pearls}, second edition. -The idea is to give words that are anagrams a common signature, -sort all the words together by their signature, and then print them. -Dr.@: Bentley observes that taking the letters in each word and -sorting them produces that common signature. +Column 2, Problem C, of Jon Bentley's @cite{Programming Pearls}, Second +Edition, presents an elegant algorithm. The idea is to give words that +are anagrams a common signature, sort all the words together by their +signature, and then print them. Dr.@: Bentley observes that taking the +letters in each word and sorting them produces that common signature. The following program uses arrays of arrays to bring together words with the same signature and array sorting to print the words -in sorted order. +in sorted order: @cindex @code{anagram.awk} program @example @@ -25003,7 +26325,7 @@ function word2key(word, a, i, n, result) Finally, the @code{END} rule traverses the array and prints out the anagram lists. It sends the output -to the system @command{sort} command, since otherwise +to the system @command{sort} command because otherwise the anagrams would appear in arbitrary order: @example @@ -25031,20 +26353,23 @@ Here is some partial output when the program is run: @example $ @kbd{gawk -f anagram.awk /usr/share/dict/words | grep '^b'} @dots{} -babbled blabbed -babbler blabber brabble -babblers blabbers brabbles -babbling blabbing -babbly blabby -babel bable -babels beslab -babery yabber +babbled blabbed +babbler blabber brabble +babblers blabbers brabbles +babbling blabbing +babbly blabby +babel bable +babels beslab +babery yabber @dots{} @end example + @node Signature Program -@subsection And Now For Something Completely Different +@subsection And Now for Something Completely Different +@cindex signature program +@cindex Brini, Davide The following program was written by Davide Brini @c (@email{dave_br@@gmx.com}) and is published on @uref{http://backreference.org/2011/02/03/obfuscated-awk/, @@ -25069,7 +26394,10 @@ X*(X-x)-o*o,(x+X)*o*o+o,x*(X-x)-O-O,x-O+(O+o+X+x)*(o+O),X*X-X*(x-O)-x+O, O+X*(o*(o+O)+O),+x+O+X*o,x*(x-o),(o+X+x)*o*o-(x-O-O),O+(X-x)*(X+O),x-O@}' @end example -We leave it to you to determine what the program does. +@cindex Johansen, Chris +We leave it to you to determine what the program does. (If you are +truly desperate to understand it, see Chris Johansen's explanation, +which is embedded in the Texinfo source file for this @value{DOCUMENT}.) @ignore To: "Arnold Robbins" <arnold@skeeve.com> @@ -25078,28 +26406,28 @@ Subject: The GNU Awk User's Guide, Section 13.3.11 From: "Chris Johansen" <johansen@main.nc.us> Message-ID: <op.v0iw6wlv7finx3@asusodin.thrudvang.lan> -Arnold, you don't know me, but we have a tenuous connection. My wife is +Arnold, you don't know me, but we have a tenuous connection. My wife is Barbara A. Field, FAIA, GIT '65 (B. Arch.). -I have had a couple of paper copies of "Effective Awk Programming" for -years, and now I'm going through a Kindle version of "The GNU Awk User's -Guide" again. When I got to section 13.3.11, I reformatted and lightly +I have had a couple of paper copies of "Effective Awk Programming" for +years, and now I'm going through a Kindle version of "The GNU Awk User's +Guide" again. When I got to section 13.3.11, I reformatted and lightly commented Davide Brin's signature script to understand its workings. -It occurs to me that this might have pedagogical value as an example -(although imperfect) of the value of whitespace and comments, and a -starting point for that discussion. It certainly helped _me_ understand -what's going on. You are welcome to it, as-is or modified (subject to +It occurs to me that this might have pedagogical value as an example +(although imperfect) of the value of whitespace and comments, and a +starting point for that discussion. It certainly helped _me_ understand +what's going on. You are welcome to it, as-is or modified (subject to Davide's constraints, of course, which I think I have met). -If I were to include it in a future edition, I would put it at some -distance from section 13.3.11, say, as a note or an appendix, so as not to +If I were to include it in a future edition, I would put it at some +distance from section 13.3.11, say, as a note or an appendix, so as not to be a "spoiler" to the puzzle. Best regards, --- +-- Chris Johansen {johansen at main dot nc dot us} - . . . collapsing the probability wave function, sending ripples of + . . . collapsing the probability wave function, sending ripples of certainty through the space-time continuum. @@ -25108,7 +26436,7 @@ certainty through the space-time continuum. # From "13.3.11 And Now For Something Completely Different" # http://www.gnu.org/software/gawk/manual/html_node/Signature-Program.html#Signature-Program -# Copyright © 2008 Davide Brini +# Copyright © 2008 Davide Brini # Copying and distribution of the code published in this page, with # or without modification, are permitted in any medium without @@ -25149,58 +26477,2317 @@ BEGIN { } @end ignore -@c The original text for this chapter was contributed by Efraim Yawitz. -@c FIXME: Add more indexing. +@node Programs Summary +@section Summary + +@itemize @value{BULLET} +@item +The programs provided in this @value{CHAPTER} +continue on the theme that reading programs is an excellent way to learn +Good Programming. + +@item +Using @samp{#!} to make @command{awk} programs directly runnable makes +them easier to use. Otherwise, invoke the program using @samp{awk +-f @dots{}}. + +@item +Reimplementing standard POSIX programs in @command{awk} is a pleasant +exercise; @command{awk}'s expressive power lets you write such programs +in relatively few lines of code, yet they are functionally complete +and usable. + +@item +One of standard @command{awk}'s weaknesses is working with individual +characters. The ability to use @code{split()} with the empty string as +the separator can considerably simplify such tasks. + +@item +The library functions from @ref{Library Functions}, proved their +usefulness for a number of real (if small) programs. + +@item +Besides reinventing POSIX wheels, other programs solved a selection of +interesting problems, such as finding duplicates words in text, printing +mailing labels, and finding anagrams. + +@end itemize + +@c EXCLUDE START +@node Programs Exercises +@section Exercises + +@enumerate +@item +Rewrite @file{cut.awk} (@pxref{Cut Program}) +using @code{split()} with @code{""} as the separator. + +@item +In @ref{Egrep Program}, we mentioned that @samp{egrep -i} could be +simulated in versions of @command{awk} without @code{IGNORECASE} by +using @code{tolower()} on the line and the pattern. In a footnote there, +we also mentioned that this solution has a bug: the translated line is +output, and not the original one. Fix this problem. +@c Exercise: Fix this, w/array and new line as key to original line + +@item +The POSIX version of @command{id} takes options that control which +information is printed. Modify the @command{awk} version +(@pxref{Id Program}) to accept the same arguments and perform in the +same way. + +@item +The @code{split.awk} program (@pxref{Split Program}) assumes +that letters are contiguous in the character set, +which isn't true for EBCDIC systems. +Fix this problem. +(Hint: Consider a different way to work through the alphabet, +without relying on @code{ord()} and @code{chr()}.) + +@item +In @file{uniq.awk} (@pxref{Uniq Program}, the +logic for choosing which lines to print represents a @dfn{state +machine}, which is ``a device that can be in one of a set number of stable +conditions depending on its previous condition and on the present values +of its inputs.''@footnote{This is the definition returned from entering +@code{define: state machine} into Google.} +Brian Kernighan suggests that +``an alternative approach to state machines is to just read +the input into an array, then use indexing. It's almost always +easier code, and for most inputs where you would use this, just +as fast.'' Rewrite the logic to follow this +suggestion. + + +@item +Why can't the @file{wc.awk} program (@pxref{Wc Program}) just +use the value of @code{FNR} in @code{endfile()}? +Hint: Examine the code in @ref{Filetrans Function}. + +@ignore +@command{wc} can't just use the value of @code{FNR} in +@code{endfile()}. If you examine the code in @ref{Filetrans Function}, +you will see that @code{FNR} has already been reset by the time +@code{endfile()} is called. +@end ignore + +@item +Manipulation of individual characters in the @command{translate} program +(@pxref{Translate Program}) is painful using standard @command{awk} +functions. Given that @command{gawk} can split strings into individual +characters using @code{""} as the separator, how might you use this +feature to simplify the program? + +@item +The @file{extract.awk} program (@pxref{Extract Program}) was written +before @command{gawk} had the @code{gensub()} function. Use it +to simplify the code. + +@item +Compare the performance of the @file{awksed.awk} program +(@pxref{Simple Sed}) with the more straightforward: + +@example +BEGIN @{ + pat = ARGV[1] + repl = ARGV[2] + ARGV[1] = ARGV[2] = "" +@} + +@{ gsub(pat, repl); print @} +@end example + +@item +What are the advantages and disadvantages of @file{awksed.awk} versus +the real @command{sed} utility? + +@ignore + Advantage: egrep regexps + speed (?) + Disadvantage: no & in replacement text + +Others? +@end ignore + +@item +In @ref{Igawk Program}, we mentioned that not trying to save the line +read with @code{getline} in the @code{pathto()} function when testing +for the file's accessibility for use with the main program simplifies +things considerably. What problem does this engender though? +@c answer, reading from "-" or /dev/stdin + +@cindex search paths +@cindex search paths, for source files +@cindex source files@comma{} search path for +@cindex files, source@comma{} search path for +@cindex directories, searching +@item +As an additional example of the idea that it is not always necessary to +add new features to a program, consider the idea of having two files in +a directory in the search path: + +@table @file +@item default.awk +This file contains a set of default library functions, such +as @code{getopt()} and @code{assert()}. + +@item site.awk +This file contains library functions that are specific to a site or +installation; i.e., locally developed functions. +Having a separate file allows @file{default.awk} to change with +new @command{gawk} releases, without requiring the system administrator to +update it each time by adding the local functions. +@end table + +One user +@c Karl Berry, karl@ileaf.com, 10/95 +suggested that @command{gawk} be modified to automatically read these files +upon startup. Instead, it would be very simple to modify @command{igawk} +to do this. Since @command{igawk} can process nested @code{@@include} +directives, @file{default.awk} could simply contain @code{@@include} +statements for the desired library functions. +Make this change. + +@item +Modify @file{anagram.awk} (@pxref{Anagram Program}), to avoid +the use of the external @command{sort} utility. + +@end enumerate +@c EXCLUDE END + +@ifnotinfo +@part @value{PART3}Moving Beyond Standard @command{awk} with @command{gawk} +@end ifnotinfo + +@ifdocbook +Part III focuses on features specific to @command{gawk}. +It contains the following chapters: + +@itemize @value{BULLET} +@item +@ref{Advanced Features} + +@item +@ref{Internationalization} + +@item +@ref{Debugger} + +@item +@ref{Arbitrary Precision Arithmetic} + +@item +@ref{Dynamic Extensions} +@end itemize +@end ifdocbook + +@node Advanced Features +@chapter Advanced Features of @command{gawk} +@cindex @command{gawk}, features, advanced +@cindex advanced features, @command{gawk} +@ignore +Contributed by: Peter Langston <pud!psl@bellcore.bellcore.com> + + Found in Steve English's "signature" line: + +"Write documentation as if whoever reads it is a violent psychopath +who knows where you live." +@end ignore +@cindex Langston, Peter +@cindex English, Steve +@quotation +@i{Write documentation as if whoever reads it is +a violent psychopath who knows where you live.} +@author Steve English, as quoted by Peter Langston +@end quotation + +This @value{CHAPTER} discusses advanced features in @command{gawk}. +It's a bit of a ``grab bag'' of items that are otherwise unrelated +to each other. +First, a command-line option allows @command{gawk} to recognize +nondecimal numbers in input data, not just in @command{awk} +programs. +Then, @command{gawk}'s special features for sorting arrays are presented. +Next, two-way I/O, discussed briefly in earlier parts of this +@value{DOCUMENT}, is described in full detail, along with the basics +of TCP/IP networking. Finally, @command{gawk} +can @dfn{profile} an @command{awk} program, making it possible to tune +it for performance. + +@c FULLXREF ON +A number of advanced features require separate @value{CHAPTER}s of their +own: + +@itemize @value{BULLET} +@item +@ref{Internationalization}, discusses how to internationalize +your @command{awk} programs, so that they can speak multiple +national languages. + +@item +@ref{Debugger}, describes @command{gawk}'s built-in command-line +debugger for debugging @command{awk} programs. + +@item +@ref{Arbitrary Precision Arithmetic}, describes how you can use +@command{gawk} to perform arbitrary-precision arithmetic. + +@item +@ref{Dynamic Extensions}, +discusses the ability to dynamically add new built-in functions to +@command{gawk}. +@end itemize +@c FULLXREF OFF + +@menu +* Nondecimal Data:: Allowing nondecimal input data. +* Array Sorting:: Facilities for controlling array traversal and + sorting arrays. +* Two-way I/O:: Two-way communications with another process. +* TCP/IP Networking:: Using @command{gawk} for network programming. +* Profiling:: Profiling your @command{awk} programs. +* Advanced Features Summary:: Summary of advanced features. +@end menu + +@node Nondecimal Data +@section Allowing Nondecimal Input Data +@cindex @option{--non-decimal-data} option +@cindex advanced features, nondecimal input data +@cindex input, data@comma{} nondecimal +@cindex constants, nondecimal + +If you run @command{gawk} with the @option{--non-decimal-data} option, +you can have nondecimal values in your input data: + +@example +$ @kbd{echo 0123 123 0x123 |} +> @kbd{gawk --non-decimal-data '@{ printf "%d, %d, %d\n", $1, $2, $3 @}'} +@print{} 83, 123, 291 +@end example + +For this feature to work, write your program so that +@command{gawk} treats your data as numeric: + +@example +$ @kbd{echo 0123 123 0x123 | gawk '@{ print $1, $2, $3 @}'} +@print{} 0123 123 0x123 +@end example + +@noindent +The @code{print} statement treats its expressions as strings. +Although the fields can act as numbers when necessary, +they are still strings, so @code{print} does not try to treat them +numerically. You need to add zero to a field to force it to +be treated as a number. For example: + +@example +$ @kbd{echo 0123 123 0x123 | gawk --non-decimal-data '} +> @kbd{@{ print $1, $2, $3} +> @kbd{print $1 + 0, $2 + 0, $3 + 0 @}'} +@print{} 0123 123 0x123 +@print{} 83 123 291 +@end example + +Because it is common to have decimal data with leading zeros, and because +using this facility could lead to surprising results, the default is to leave it +disabled. If you want it, you must explicitly request it. + +@cindex programming conventions, @code{--non-decimal-data} option +@cindex @option{--non-decimal-data} option, @code{strtonum()} function and +@cindex @code{strtonum()} function (@command{gawk}), @code{--non-decimal-data} option and +@quotation CAUTION +@emph{Use of this option is not recommended.} +It can break old programs very badly. +Instead, use the @code{strtonum()} function to convert your data +(@pxref{String Functions}). +This makes your programs easier to write and easier to read, and +leads to less surprising results. + +This option may disappear in a future version of @command{gawk}. +@end quotation + +@node Array Sorting +@section Controlling Array Traversal and Array Sorting + +@command{gawk} lets you control the order in which a @samp{for (i in array)} +loop traverses an array. + +In addition, two built-in functions, @code{asort()} and @code{asorti()}, +let you sort arrays based on the array values and indices, respectively. +These two functions also provide control over the sorting criteria used +to order the elements during sorting. + +@menu +* Controlling Array Traversal:: How to use PROCINFO["sorted_in"]. +* Array Sorting Functions:: How to use @code{asort()} and @code{asorti()}. +@end menu + +@node Controlling Array Traversal +@subsection Controlling Array Traversal + +By default, the order in which a @samp{for (i in array)} loop +scans an array is not defined; it is generally based upon +the internal implementation of arrays inside @command{awk}. + +Often, though, it is desirable to be able to loop over the elements +in a particular order that you, the programmer, choose. @command{gawk} +lets you do this. + +@DBREF{Controlling Scanning} describes how you can assign special, +predefined values to @code{PROCINFO["sorted_in"]} in order to +control the order in which @command{gawk} traverses an array +during a @code{for} loop. + +In addition, the value of @code{PROCINFO["sorted_in"]} can be a +function name.@footnote{This is why the predefined sorting orders +start with an @samp{@@} character, which cannot be part of an identifier.} +This lets you traverse an array based on any custom criterion. +The array elements are ordered according to the return value of this +function. The comparison function should be defined with at least +four arguments: + +@example +function comp_func(i1, v1, i2, v2) +@{ + @var{compare elements 1 and 2 in some fashion} + @var{return < 0; 0; or > 0} +@} +@end example + +Here, @var{i1} and @var{i2} are the indices, and @var{v1} and @var{v2} +are the corresponding values of the two elements being compared. +Either @var{v1} or @var{v2}, or both, can be arrays if the array being +traversed contains subarrays as values. +(@DBXREF{Arrays of Arrays} for more information about subarrays.) +The three possible return values are interpreted as follows: + +@table @code +@item comp_func(i1, v1, i2, v2) < 0 +Index @var{i1} comes before index @var{i2} during loop traversal. + +@item comp_func(i1, v1, i2, v2) == 0 +Indices @var{i1} and @var{i2} +come together but the relative order with respect to each other is undefined. + +@item comp_func(i1, v1, i2, v2) > 0 +Index @var{i1} comes after index @var{i2} during loop traversal. +@end table + +Our first comparison function can be used to scan an array in +numerical order of the indices: + +@example +function cmp_num_idx(i1, v1, i2, v2) +@{ + # numerical index comparison, ascending order + return (i1 - i2) +@} +@end example + +Our second function traverses an array based on the string order of +the element values rather than by indices: + +@example +function cmp_str_val(i1, v1, i2, v2) +@{ + # string value comparison, ascending order + v1 = v1 "" + v2 = v2 "" + if (v1 < v2) + return -1 + return (v1 != v2) +@} +@end example + +The third +comparison function makes all numbers, and numeric strings without +any leading or trailing spaces, come out first during loop traversal: + +@example +function cmp_num_str_val(i1, v1, i2, v2, n1, n2) +@{ + # numbers before string value comparison, ascending order + n1 = v1 + 0 + n2 = v2 + 0 + if (n1 == v1) + return (n2 == v2) ? (n1 - n2) : -1 + else if (n2 == v2) + return 1 + return (v1 < v2) ? -1 : (v1 != v2) +@} +@end example + +Here is a main program to demonstrate how @command{gawk} +behaves using each of the previous functions: + +@example +BEGIN @{ + data["one"] = 10 + data["two"] = 20 + data[10] = "one" + data[100] = 100 + data[20] = "two" + + f[1] = "cmp_num_idx" + f[2] = "cmp_str_val" + f[3] = "cmp_num_str_val" + for (i = 1; i <= 3; i++) @{ + printf("Sort function: %s\n", f[i]) + PROCINFO["sorted_in"] = f[i] + for (j in data) + printf("\tdata[%s] = %s\n", j, data[j]) + print "" + @} +@} +@end example + +Here are the results when the program is run: + +@example +$ @kbd{gawk -f compdemo.awk} +@print{} Sort function: cmp_num_idx @ii{Sort by numeric index} +@print{} data[two] = 20 +@print{} data[one] = 10 @ii{Both strings are numerically zero} +@print{} data[10] = one +@print{} data[20] = two +@print{} data[100] = 100 +@print{} +@print{} Sort function: cmp_str_val @ii{Sort by element values as strings} +@print{} data[one] = 10 +@print{} data[100] = 100 @ii{String 100 is less than string 20} +@print{} data[two] = 20 +@print{} data[10] = one +@print{} data[20] = two +@print{} +@print{} Sort function: cmp_num_str_val @ii{Sort all numeric values before all strings} +@print{} data[one] = 10 +@print{} data[two] = 20 +@print{} data[100] = 100 +@print{} data[10] = one +@print{} data[20] = two +@end example + +Consider sorting the entries of a GNU/Linux system password file +according to login name. The following program sorts records +by a specific field position and can be used for this purpose: + +@example +# passwd-sort.awk --- simple program to sort by field position +# field position is specified by the global variable POS + +function cmp_field(i1, v1, i2, v2) +@{ + # comparison by value, as string, and ascending order + return v1[POS] < v2[POS] ? -1 : (v1[POS] != v2[POS]) +@} + +@{ + for (i = 1; i <= NF; i++) + a[NR][i] = $i +@} + +END @{ + PROCINFO["sorted_in"] = "cmp_field" + if (POS < 1 || POS > NF) + POS = 1 + for (i in a) @{ + for (j = 1; j <= NF; j++) + printf("%s%c", a[i][j], j < NF ? ":" : "") + print "" + @} +@} +@end example + +The first field in each entry of the password file is the user's login name, +and the fields are separated by colons. +Each record defines a subarray, +with each field as an element in the subarray. +Running the program produces the +following output: + +@example +$ @kbd{gawk -v POS=1 -F: -f sort.awk /etc/passwd} +@print{} adm:x:3:4:adm:/var/adm:/sbin/nologin +@print{} apache:x:48:48:Apache:/var/www:/sbin/nologin +@print{} avahi:x:70:70:Avahi daemon:/:/sbin/nologin +@dots{} +@end example + +The comparison should normally always return the same value when given a +specific pair of array elements as its arguments. If inconsistent +results are returned, then the order is undefined. This behavior can be +exploited to introduce random order into otherwise seemingly +ordered data: + +@example +function cmp_randomize(i1, v1, i2, v2) +@{ + # random order (caution: this may never terminate!) + return (2 - 4 * rand()) +@} +@end example + +As already mentioned, the order of the indices is arbitrary if two +elements compare equal. This is usually not a problem, but letting +the tied elements come out in arbitrary order can be an issue, especially +when comparing item values. The partial ordering of the equal elements +may change the next time the array is traversed, if other elements are added or +removed from the array. One way to resolve ties when comparing elements +with otherwise equal values is to include the indices in the comparison +rules. Note that doing this may make the loop traversal less efficient, +so consider it only if necessary. The following comparison functions +force a deterministic order, and are based on the fact that the +(string) indices of two elements are never equal: + +@example +function cmp_numeric(i1, v1, i2, v2) +@{ + # numerical value (and index) comparison, descending order + return (v1 != v2) ? (v2 - v1) : (i2 - i1) +@} + +function cmp_string(i1, v1, i2, v2) +@{ + # string value (and index) comparison, descending order + v1 = v1 i1 + v2 = v2 i2 + return (v1 > v2) ? -1 : (v1 != v2) +@} +@end example + +@c Avoid using the term ``stable'' when describing the unpredictable behavior +@c if two items compare equal. Usually, the goal of a "stable algorithm" +@c is to maintain the original order of the items, which is a meaningless +@c concept for a list constructed from a hash. + +A custom comparison function can often simplify ordered loop +traversal, and the sky is really the limit when it comes to +designing such a function. + +When string comparisons are made during a sort, either for element +values where one or both aren't numbers, or for element indices +handled as strings, the value of @code{IGNORECASE} +(@pxref{Built-in Variables}) controls whether +the comparisons treat corresponding upper- and lowercase letters as +equivalent or distinct. + +Another point to keep in mind is that in the case of subarrays, +the element values can themselves be arrays; a production comparison +function should use the @code{isarray()} function +(@pxref{Type Functions}), +to check for this, and choose a defined sorting order for subarrays. + +All sorting based on @code{PROCINFO["sorted_in"]} +is disabled in POSIX mode, +because the @code{PROCINFO} array is not special in that case. + +As a side note, sorting the array indices before traversing +the array has been reported to add 15% to 20% overhead to the +execution time of @command{awk} programs. For this reason, +sorted array traversal is not the default. + +@c The @command{gawk} +@c maintainers believe that only the people who wish to use a +@c feature should have to pay for it. + +@node Array Sorting Functions +@subsection Sorting Array Values and Indices with @command{gawk} + +@cindex arrays, sorting +@cindexgawkfunc{asort} +@cindex @code{asort()} function (@command{gawk}), arrays@comma{} sorting +@cindexgawkfunc{asorti} +@cindex @code{asorti()} function (@command{gawk}), arrays@comma{} sorting +@cindex sort function, arrays, sorting +In most @command{awk} implementations, sorting an array requires writing +a @code{sort()} function. This can be educational for exploring +different sorting algorithms, but usually that's not the point of the program. +@command{gawk} provides the built-in @code{asort()} and @code{asorti()} +functions (@pxref{String Functions}) for sorting arrays. For example: + +@example +@var{populate the array} data +n = asort(data) +for (i = 1; i <= n; i++) + @var{do something with} data[i] +@end example + +After the call to @code{asort()}, the array @code{data} is indexed from 1 +to some number @var{n}, the total number of elements in @code{data}. +(This count is @code{asort()}'s return value.) +@code{data[1]} @value{LEQ} @code{data[2]} @value{LEQ} @code{data[3]}, and so on. +The default comparison is based on the type of the elements +(@pxref{Typing and Comparison}). +All numeric values come before all string values, +which in turn come before all subarrays. + +@cindex side effects, @code{asort()} function +An important side effect of calling @code{asort()} is that +@emph{the array's original indices are irrevocably lost}. +As this isn't always desirable, @code{asort()} accepts a +second argument: + +@example +@var{populate the array} source +n = asort(source, dest) +for (i = 1; i <= n; i++) + @var{do something with} dest[i] +@end example + +In this case, @command{gawk} copies the @code{source} array into the +@code{dest} array and then sorts @code{dest}, destroying its indices. +However, the @code{source} array is not affected. + +Often, what's needed is to sort on the values of the @emph{indices} +instead of the values of the elements. To do that, use the +@code{asorti()} function. The interface and behavior are identical to +that of @code{asort()}, except that the index values are used for sorting, +and become the values of the result array: + +@example +@{ source[$0] = some_func($0) @} + +END @{ + n = asorti(source, dest) + for (i = 1; i <= n; i++) @{ + @ii{Work with sorted indices directly:} + @var{do something with} dest[i] + @dots{} + @ii{Access original array via sorted indices:} + @var{do something with} source[dest[i]] + @} +@} +@end example + +So far, so good. Now it starts to get interesting. Both @code{asort()} +and @code{asorti()} accept a third string argument to control comparison +of array elements. When we introduced @code{asort()} and @code{asorti()} +in @ref{String Functions}, we ignored this third argument; however, +now is the time to describe how this argument affects these two functions. + +Basically, the third argument specifies how the array is to be sorted. +There are two possibilities. As with @code{PROCINFO["sorted_in"]}, +this argument may be one of the predefined names that @command{gawk} +provides (@pxref{Controlling Scanning}), or it may be the name of a +user-defined function (@pxref{Controlling Array Traversal}). + +In the latter case, @emph{the function can compare elements in any way +it chooses}, taking into account just the indices, just the values, +or both. This is extremely powerful. + +Once the array is sorted, @code{asort()} takes the @emph{values} in +their final order, and uses them to fill in the result array, whereas +@code{asorti()} takes the @emph{indices} in their final order, and uses +them to fill in the result array. + +@cindex reference counting, sorting arrays +@quotation NOTE +Copying array indices and elements isn't expensive in terms of memory. +Internally, @command{gawk} maintains @dfn{reference counts} to data. +For example, when @code{asort()} copies the first array to the second one, +there is only one copy of the original array elements' data, even though +both arrays use the values. +@end quotation + +@c Document It And Call It A Feature. Sigh. +@cindex @command{gawk}, @code{IGNORECASE} variable in +@cindex arrays, sorting, and @code{IGNORECASE} variable +@cindex @code{IGNORECASE} variable, and array sorting functions +Because @code{IGNORECASE} affects string comparisons, the value +of @code{IGNORECASE} also affects sorting for both @code{asort()} and @code{asorti()}. +Note also that the locale's sorting order does @emph{not} +come into play; comparisons are based on character values only.@footnote{This +is true because locale-based comparison occurs only when in +POSIX-compatibility mode, and because @code{asort()} and @code{asorti()} are +@command{gawk} extensions, they are not available in that case.} + +@node Two-way I/O +@section Two-Way Communications with Another Process + +@c 8/2014. Neither Mike nor BWK saw this as relevant. Commenting it out. +@ignore +@cindex Brennan, Michael +@cindex programmers, attractiveness of +@smallexample +@c Path: cssun.mathcs.emory.edu!gatech!newsxfer3.itd.umich.edu!news-peer.sprintlink.net!news-sea-19.sprintlink.net!news-in-west.sprintlink.net!news.sprintlink.net!Sprint!204.94.52.5!news.whidbey.com!brennan +From: brennan@@whidbey.com (Mike Brennan) +Newsgroups: comp.lang.awk +Subject: Re: Learn the SECRET to Attract Women Easily +Date: 4 Aug 1997 17:34:46 GMT +@c Organization: WhidbeyNet +@c Lines: 12 +Message-ID: <5s53rm$eca@@news.whidbey.com> +@c References: <5s20dn$2e1@chronicle.concentric.net> +@c Reply-To: brennan@whidbey.com +@c NNTP-Posting-Host: asn202.whidbey.com +@c X-Newsreader: slrn (0.9.4.1 UNIX) +@c Xref: cssun.mathcs.emory.edu comp.lang.awk:5403 + +On 3 Aug 1997 13:17:43 GMT, Want More Dates??? +<tracy78@@kilgrona.com> wrote: +>Learn the SECRET to Attract Women Easily +> +>The SCENT(tm) Pheromone Sex Attractant For Men to Attract Women + +The scent of awk programmers is a lot more attractive to women than +the scent of perl programmers. +-- +Mike Brennan +@c brennan@@whidbey.com +@end smallexample +@end ignore + +@cindex advanced features, processes@comma{} communicating with +@cindex processes, two-way communications with +It is often useful to be able to +send data to a separate program for +processing and then read the result. This can always be +done with temporary files: + +@example +# Write the data for processing +tempfile = ("mydata." PROCINFO["pid"]) +while (@var{not done with data}) + print @var{data} | ("subprogram > " tempfile) +close("subprogram > " tempfile) + +# Read the results, remove tempfile when done +while ((getline newdata < tempfile) > 0) + @var{process} newdata @var{appropriately} +close(tempfile) +system("rm " tempfile) +@end example + +@noindent +This works, but not elegantly. Among other things, it requires that +the program be run in a directory that cannot be shared among users; +for example, @file{/tmp} will not do, as another user might happen +to be using a temporary file with the same name.@footnote{Michael +Brennan suggests the use of @command{rand()} to generate unique +@value{FN}s. This is a valid point; nevertheless, temporary files +remain more difficult to use than two-way pipes.} @c 8/2014 + +@cindex coprocesses +@cindex input/output, two-way +@cindex @code{|} (vertical bar), @code{|&} operator (I/O) +@cindex vertical bar (@code{|}), @code{|&} operator (I/O) +@cindex @command{csh} utility, @code{|&} operator, comparison with +However, with @command{gawk}, it is possible to +open a @emph{two-way} pipe to another process. The second process is +termed a @dfn{coprocess}, as it runs in parallel with @command{gawk}. +The two-way connection is created using the @samp{|&} operator +(borrowed from the Korn shell, @command{ksh}):@footnote{This is very +different from the same operator in the C shell and in Bash.} + +@example +do @{ + print @var{data} |& "subprogram" + "subprogram" |& getline results +@} while (@var{data left to process}) +close("subprogram") +@end example + +The first time an I/O operation is executed using the @samp{|&} +operator, @command{gawk} creates a two-way pipeline to a child process +that runs the other program. Output created with @code{print} +or @code{printf} is written to the program's standard input, and +output from the program's standard output can be read by the @command{gawk} +program using @code{getline}. +As is the case with processes started by @samp{|}, the subprogram +can be any program, or pipeline of programs, that can be started by +the shell. + +There are some cautionary items to be aware of: + +@itemize @value{BULLET} +@item +As the code inside @command{gawk} currently stands, the coprocess's +standard error goes to the same place that the parent @command{gawk}'s +standard error goes. It is not possible to read the child's +standard error separately. + +@cindex deadlocks +@cindex buffering, input/output +@cindex @code{getline} command, deadlock and +@item +I/O buffering may be a problem. @command{gawk} automatically +flushes all output down the pipe to the coprocess. +However, if the coprocess does not flush its output, +@command{gawk} may hang when doing a @code{getline} in order to read +the coprocess's results. This could lead to a situation +known as @dfn{deadlock}, where each process is waiting for the +other one to do something. +@end itemize + +@cindex @code{close()} function, two-way pipes and +It is possible to close just one end of the two-way pipe to +a coprocess, by supplying a second argument to the @code{close()} +function of either @code{"to"} or @code{"from"} +(@pxref{Close Files And Pipes}). +These strings tell @command{gawk} to close the end of the pipe +that sends data to the coprocess or the end that reads from it, +respectively. + +@cindex @command{sort} utility, coprocesses and +This is particularly necessary in order to use +the system @command{sort} utility as part of a coprocess; +@command{sort} must read @emph{all} of its input +data before it can produce any output. +The @command{sort} program does not receive an end-of-file indication +until @command{gawk} closes the write end of the pipe. + +When you have finished writing data to the @command{sort} +utility, you can close the @code{"to"} end of the pipe, and +then start reading sorted data via @code{getline}. +For example: + +@example +BEGIN @{ + command = "LC_ALL=C sort" + n = split("abcdefghijklmnopqrstuvwxyz", a, "") + + for (i = n; i > 0; i--) + print a[i] |& command + close(command, "to") + + while ((command |& getline line) > 0) + print "got", line + close(command) +@} +@end example + +This program writes the letters of the alphabet in reverse order, one +per line, down the two-way pipe to @command{sort}. It then closes the +write end of the pipe, so that @command{sort} receives an end-of-file +indication. This causes @command{sort} to sort the data and write the +sorted data back to the @command{gawk} program. Once all of the data +has been read, @command{gawk} terminates the coprocess and exits. + +As a side note, the assignment @samp{LC_ALL=C} in the @command{sort} +command ensures traditional Unix (ASCII) sorting from @command{sort}. +This is not strictly necessary here, but it's good to know how to do this. + +@cindex @command{gawk}, @code{PROCINFO} array in +@cindex @code{PROCINFO} array, and communications via ptys +You may also use pseudo-ttys (ptys) for +two-way communication instead of pipes, if your system supports them. +This is done on a per-command basis, by setting a special element +in the @code{PROCINFO} array +(@pxref{Auto-set}), +like so: + +@example +command = "sort -nr" # command, save in convenience variable +PROCINFO[command, "pty"] = 1 # update PROCINFO +print @dots{} |& command # start two-way pipe +@dots{} +@end example + +@noindent +Using ptys usually avoids the buffer deadlock issues described earlier, at some +loss in performance. If your system does not have ptys, or if all the +system's ptys are in use, @command{gawk} automatically falls back to +using regular pipes. + +@node TCP/IP Networking +@section Using @command{gawk} for Network Programming +@cindex advanced features, network programming +@cindex networks, programming +@cindex TCP/IP +@cindex @code{/inet/@dots{}} special files (@command{gawk}) +@cindex files, @code{/inet/@dots{}} (@command{gawk}) +@cindex @code{/inet4/@dots{}} special files (@command{gawk}) +@cindex files, @code{/inet4/@dots{}} (@command{gawk}) +@cindex @code{/inet6/@dots{}} special files (@command{gawk}) +@cindex files, @code{/inet6/@dots{}} (@command{gawk}) +@cindex @code{EMISTERED} +@ifnotdocbook +@quotation +@code{EMRED}:@* +@ @ @ @ @i{A host is a host from coast to coast,@* +@ @ @ @ and nobody talks to a host that's close,@* +@ @ @ @ unless the host that isn't close@* +@ @ @ @ is busy, hung, or dead.} +@author Mike O'Brien (aka Mr.@: Protocol) +@end quotation +@end ifnotdocbook + +@docbook +<blockquote> +<attribution>Mike O'Brien (aka Mr. Protocol)</attribution> +<literallayout class="normal"><literal>EMISTERED</literal>: + <emphasis>A host is a host from coast to coast,</emphasis> + <emphasis>and no-one can talk to host that's close,</emphasis> + <emphasis>unless the host that isn't close</emphasis> + <emphasis>is busy, hung, or dead.</emphasis></literallayout> +</blockquote> +@end docbook + +In addition to being able to open a two-way pipeline to a coprocess +on the same system +(@pxref{Two-way I/O}), +it is possible to make a two-way connection to +another process on another system across an IP network connection. + +You can think of this as just a @emph{very long} two-way pipeline to +a coprocess. +The way @command{gawk} decides that you want to use TCP/IP networking is +by recognizing special @value{FN}s that begin with one of @samp{/inet/}, +@samp{/inet4/}, or @samp{/inet6/}. + +The full syntax of the special @value{FN} is +@file{/@var{net-type}/@var{protocol}/@var{local-port}/@var{remote-host}/@var{remote-port}}. +The components are: + +@table @var +@item net-type +Specifies the kind of Internet connection to make. +Use @samp{/inet4/} to force IPv4, and +@samp{/inet6/} to force IPv6. +Plain @samp{/inet/} (which used to be the only option) uses +the system default, most likely IPv4. + +@item protocol +The protocol to use over IP. This must be either @samp{tcp}, or +@samp{udp}, for a TCP or UDP IP connection, +respectively. TCP should be used for most applications. + +@item local-port +@cindex @code{getaddrinfo()} function (C library) +The local TCP or UDP port number to use. Use a port number of @samp{0} +when you want the system to pick a port. This is what you should do +when writing a TCP or UDP client. +You may also use a well-known service name, such as @samp{smtp} +or @samp{http}, in which case @command{gawk} attempts to determine +the predefined port number using the C @code{getaddrinfo()} function. + +@item remote-host +The IP address or fully qualified domain name of the Internet +host to which you want to connect. + +@item remote-port +The TCP or UDP port number to use on the given @var{remote-host}. +Again, use @samp{0} if you don't care, or else a well-known +service name. +@end table + +@cindex @command{gawk}, @code{ERRNO} variable in +@cindex @code{ERRNO} variable +@quotation NOTE +Failure in opening a two-way socket will result in a non-fatal error +being returned to the calling code. The value of @code{ERRNO} indicates +the error (@pxref{Auto-set}). +@end quotation + +Consider the following very simple example: + +@example +BEGIN @{ + Service = "/inet/tcp/0/localhost/daytime" + Service |& getline + print $0 + close(Service) +@} +@end example + +This program reads the current date and time from the local system's +TCP @samp{daytime} server. +It then prints the results and closes the connection. + +Because this topic is extensive, the use of @command{gawk} for +TCP/IP programming is documented separately. +@ifinfo +See +@inforef{Top, , General Introduction, gawkinet, TCP/IP Internetworking with @command{gawk}}, +@end ifinfo +@ifnotinfo +See +@uref{http://www.gnu.org/software/gawk/manual/gawkinet/, +@cite{TCP/IP Internetworking with @command{gawk}}}, +which comes as part of the @command{gawk} distribution, +@end ifnotinfo +for a much more complete introduction and discussion, as well as +extensive examples. + + +@node Profiling +@section Profiling Your @command{awk} Programs +@cindex @command{awk} programs, profiling +@cindex profiling @command{awk} programs +@cindex @code{awkprof.out} file +@cindex files, @code{awkprof.out} + +You may produce execution traces of your @command{awk} programs. +This is done by passing the option @option{--profile} to @command{gawk}. +When @command{gawk} has finished running, it creates a profile of your program in a file +named @file{awkprof.out}. Because it is profiling, it also executes up to 45% slower than +@command{gawk} normally does. + +@cindex @option{--profile} option +As shown in the following example, +the @option{--profile} option can be used to change the name of the file +where @command{gawk} will write the profile: + +@example +gawk --profile=myprog.prof -f myprog.awk data1 data2 +@end example + +@noindent +In the preceding example, @command{gawk} places the profile in +@file{myprog.prof} instead of in @file{awkprof.out}. + +Here is a sample session showing a simple @command{awk} program, +its input data, and the results from running @command{gawk} with the +@option{--profile} option. First, the @command{awk} program: + +@example +BEGIN @{ print "First BEGIN rule" @} + +END @{ print "First END rule" @} + +/foo/ @{ + print "matched /foo/, gosh" + for (i = 1; i <= 3; i++) + sing() +@} + +@{ + if (/foo/) + print "if is true" + else + print "else is true" +@} + +BEGIN @{ print "Second BEGIN rule" @} + +END @{ print "Second END rule" @} + +function sing( dummy) +@{ + print "I gotta be me!" +@} +@end example + +Following is the input data: + +@example +foo +bar +baz +foo +junk +@end example + +Here is the @file{awkprof.out} that results from running the +@command{gawk} profiler on this program and data. (This example also +illustrates that @command{awk} programmers sometimes get up very early +in the morning to work.) + +@cindex @code{BEGIN} pattern, and profiling +@cindex @code{END} pattern, and profiling +@example + # gawk profile, created Mon Sep 29 05:16:21 2014 + + # BEGIN rule(s) + + BEGIN @{ + 1 print "First BEGIN rule" + @} + + BEGIN @{ + 1 print "Second BEGIN rule" + @} + + # Rule(s) + + 5 /foo/ @{ # 2 + 2 print "matched /foo/, gosh" + 6 for (i = 1; i <= 3; i++) @{ + 6 sing() + @} + @} + + 5 @{ + 5 if (/foo/) @{ # 2 + 2 print "if is true" + 3 @} else @{ + 3 print "else is true" + @} + @} + + # END rule(s) + + END @{ + 1 print "First END rule" + @} + + END @{ + 1 print "Second END rule" + @} + + + # Functions, listed alphabetically + + 6 function sing(dummy) + @{ + 6 print "I gotta be me!" + @} +@end example + +This example illustrates many of the basic features of profiling output. +They are as follows: + +@itemize @value{BULLET} +@item +The program is printed in the order @code{BEGIN} rules, +@code{BEGINFILE} rules, +pattern/action rules, +@code{ENDFILE} rules, @code{END} rules and functions, listed +alphabetically. +Multiple @code{BEGIN} and @code{END} rules retain their +separate identities, as do +multiple @code{BEGINFILE} and @code{ENDFILE} rules. + +@cindex patterns, counts, in a profile +@item +Pattern-action rules have two counts. +The first count, to the left of the rule, shows how many times +the rule's pattern was @emph{tested}. +The second count, to the right of the rule's opening left brace +in a comment, +shows how many times the rule's action was @emph{executed}. +The difference between the two indicates how many times the rule's +pattern evaluated to false. + +@item +Similarly, +the count for an @code{if}-@code{else} statement shows how many times +the condition was tested. +To the right of the opening left brace for the @code{if}'s body +is a count showing how many times the condition was true. +The count for the @code{else} +indicates how many times the test failed. + +@cindex loops, count for header, in a profile +@item +The count for a loop header (such as @code{for} +or @code{while}) shows how many times the loop test was executed. +(Because of this, you can't just look at the count on the first +statement in a rule to determine how many times the rule was executed. +If the first statement is a loop, the count is misleading.) + +@cindex functions, user-defined, counts, in a profile +@cindex user-defined, functions, counts, in a profile +@item +For user-defined functions, the count next to the @code{function} +keyword indicates how many times the function was called. +The counts next to the statements in the body show how many times +those statements were executed. + +@cindex @code{@{@}} (braces) +@cindex braces (@code{@{@}}) +@item +The layout uses ``K&R'' style with TABs. +Braces are used everywhere, even when +the body of an @code{if}, @code{else}, or loop is only a single statement. + +@cindex @code{()} (parentheses), in a profile +@cindex parentheses @code{()}, in a profile +@item +Parentheses are used only where needed, as indicated by the structure +of the program and the precedence rules. +For example, @samp{(3 + 5) * 4} means add three and five, then multiply +the total by four. However, @samp{3 + 5 * 4} has no parentheses, and +means @samp{3 + (5 * 4)}. + +@ignore +@item +All string concatenations are parenthesized too. +(This could be made a bit smarter.) +@end ignore + +@item +Parentheses are used around the arguments to @code{print} +and @code{printf} only when +the @code{print} or @code{printf} statement is followed by a redirection. +Similarly, if +the target of a redirection isn't a scalar, it gets parenthesized. + +@item +@command{gawk} supplies leading comments in +front of the @code{BEGIN} and @code{END} rules, +the @code{BEGINFILE} and @code{ENDFILE} rules, +the pattern/action rules, and the functions. + +@end itemize + +The profiled version of your program may not look exactly like what you +typed when you wrote it. This is because @command{gawk} creates the +profiled version by ``pretty printing'' its internal representation of +the program. The advantage to this is that @command{gawk} can produce +a standard representation. +Also, things such as: + +@example +/foo/ +@end example + +@noindent +come out as: + +@example +/foo/ @{ + print $0 +@} +@end example + +@noindent +which is correct, but possibly unexpected. + +@cindex profiling @command{awk} programs, dynamically +@cindex @command{gawk} program, dynamic profiling +@cindex dynamic profiling +Besides creating profiles when a program has completed, +@command{gawk} can produce a profile while it is running. +This is useful if your @command{awk} program goes into an +infinite loop and you want to see what has been executed. +To use this feature, run @command{gawk} with the @option{--profile} +option in the background: + +@example +$ @kbd{gawk --profile -f myprog &} +[1] 13992 +@end example + +@cindex @command{kill} command@comma{} dynamic profiling +@cindex @code{USR1} signal, for dynamic profiling +@cindex @code{SIGUSR1} signal, for dynamic profiling +@cindex signals, @code{USR1}/@code{SIGUSR1}, for profiling +@noindent +The shell prints a job number and process ID number; in this case, 13992. +Use the @command{kill} command to send the @code{USR1} signal +to @command{gawk}: + +@example +$ @kbd{kill -USR1 13992} +@end example + +@noindent +As usual, the profiled version of the program is written to +@file{awkprof.out}, or to a different file if one was specified with +the @option{--profile} option. + +Along with the regular profile, as shown earlier, the profile file +includes a trace of any active functions: + +@example +# Function Call Stack: + +# 3. baz +# 2. bar +# 1. foo +# -- main -- +@end example + +You may send @command{gawk} the @code{USR1} signal as many times as you like. +Each time, the profile and function call trace are appended to the output +profile file. + +@cindex @code{HUP} signal, for dynamic profiling +@cindex @code{SIGHUP} signal, for dynamic profiling +@cindex signals, @code{HUP}/@code{SIGHUP}, for profiling +If you use the @code{HUP} signal instead of the @code{USR1} signal, +@command{gawk} produces the profile and the function call trace and then exits. + +@cindex @code{INT} signal (MS-Windows) +@cindex @code{SIGINT} signal (MS-Windows) +@cindex signals, @code{INT}/@code{SIGINT} (MS-Windows) +@cindex @code{QUIT} signal (MS-Windows) +@cindex @code{SIGQUIT} signal (MS-Windows) +@cindex signals, @code{QUIT}/@code{SIGQUIT} (MS-Windows) +When @command{gawk} runs on MS-Windows systems, it uses the +@code{INT} and @code{QUIT} signals for producing the profile and, in +the case of the @code{INT} signal, @command{gawk} exits. This is +because these systems don't support the @command{kill} command, so the +only signals you can deliver to a program are those generated by the +keyboard. The @code{INT} signal is generated by the +@kbd{Ctrl-@key{C}} or @kbd{Ctrl-@key{BREAK}} key, while the +@code{QUIT} signal is generated by the @kbd{Ctrl-@key{\}} key. + +Finally, @command{gawk} also accepts another option, @option{--pretty-print}. +When called this way, @command{gawk} ``pretty prints'' the program into +@file{awkprof.out}, without any execution counts. + +@quotation NOTE +Once upon a time, the @option{--pretty-print} option would also run +your program. This is is no longer the case. +@end quotation + +There is a significant difference between the output created when +profiling, and that created when pretty-printing. Pretty-printed output +preserves the original comments that were in the program, although their +placement may not correspond exactly to their original locations in the +source code. + +However, as a deliberate design decision, profiling output @emph{omits} +the original program's comments. This allows you to focus on the +execution count data and helps you avoid the temptation to use the +profiler for pretty-printing. + +Additionally, pretty-printed output does not have the leading indentation +that the profiling output does. This makes it easy to pretty-print your +code once development is completed, and then use the result as the final +version of your program. + +@node Advanced Features Summary +@section Summary + +@itemize @value{BULLET} +@item +The @option{--non-decimal-data} option causes @command{gawk} to treat +octal- and hexadecimal-looking input data as octal and hexadecimal. +This option should be used with caution or not at all; use of @code{strtonum()} +is preferable. +Note that this option may disappear in a future version of @command{gawk}. + +@item +You can take over complete control of sorting in @samp{for (@var{indx} in @var{array})} +array traversal by setting @code{PROCINFO["sorted_in"]} to the name of a user-defined +function that does the comparison of array elements based on index and value. + +@item +Similarly, you can supply the name of a user-defined comparison function as the +third argument to either @code{asort()} or @command{asorti()} to control how +those functions sort arrays. Or you may provide one of the predefined control +strings that work for @code{PROCINFO["sorted_in"]}. + +@item +You can use the @samp{|&} operator to create a two-way pipe to a coprocess. +You read from the coprocess with @code{getline} and write to it with @code{print} +or @code{printf}. Use @code{close()} to close off the coprocess completely, or +optionally, close off one side of the two-way communications. + +@item +By using special @value{FN}s with the @samp{|&} operator, you can open a +TCP/IP (or UDP/IP) connection to remote hosts in the Internet. @command{gawk} +supports both IPv4 and IPv6. + +@item +You can generate statement count profiles of your program. This can help you +determine which parts of your program may be taking the most time and let +you tune them more easily. Sending the @code{USR1} signal while profiling causes +@command{gawk} to dump the profile and keep going, including a function call stack. + +@item +You can also just ``pretty print'' the program. This currently also runs +the program, but that will change in the next major release. + +@end itemize + + +@node Internationalization +@chapter Internationalization with @command{gawk} + +Once upon a time, computer makers +wrote software that worked only in English. +Eventually, hardware and software vendors noticed that if their +systems worked in the native languages of non-English-speaking +countries, they were able to sell more systems. +As a result, internationalization and localization +of programs and software systems became a common practice. + +@cindex internationalization, localization +@cindex @command{gawk}, internationalization and, See internationalization +@cindex internationalization, localization, @command{gawk} and +For many years, the ability to provide internationalization +was largely restricted to programs written in C and C++. +This @value{CHAPTER} describes the underlying library @command{gawk} +uses for internationalization, as well as how +@command{gawk} makes internationalization +features available at the @command{awk} program level. +Having internationalization available at the @command{awk} level +gives software developers additional flexibility---they are no +longer forced to write in C or C++ when internationalization is +a requirement. + +@menu +* I18N and L10N:: Internationalization and Localization. +* Explaining gettext:: How GNU @command{gettext} works. +* Programmer i18n:: Features for the programmer. +* Translator i18n:: Features for the translator. +* I18N Example:: A simple i18n example. +* Gawk I18N:: @command{gawk} is also internationalized. +* I18N Summary:: Summary of I18N stuff. +@end menu + +@node I18N and L10N +@section Internationalization and Localization + +@cindex internationalization +@cindex localization, See internationalization@comma{} localization +@cindex localization +@dfn{Internationalization} means writing (or modifying) a program once, +in such a way that it can use multiple languages without requiring +further source-code changes. +@dfn{Localization} means providing the data necessary for an +internationalized program to work in a particular language. +Most typically, these terms refer to features such as the language +used for printing error messages, the language used to read +responses, and information related to how numerical and +monetary values are printed and read. + +@node Explaining gettext +@section GNU @command{gettext} + +@cindex internationalizing a program +@cindex @command{gettext} library +@command{gawk} uses GNU @command{gettext} to provide its internationalization +features. +The facilities in GNU @command{gettext} focus on messages; strings printed +by a program, either directly or via formatting with @code{printf} or +@code{sprintf()}.@footnote{For some operating systems, the @command{gawk} +port doesn't support GNU @command{gettext}. +Therefore, these features are not available +if you are using one of those operating systems. Sorry.} + +@cindex portability, @command{gettext} library and +When using GNU @command{gettext}, each application has its own +@dfn{text domain}. This is a unique name, such as @samp{kpilot} or @samp{gawk}, +that identifies the application. +A complete application may have multiple components---programs written +in C or C++, as well as scripts written in @command{sh} or @command{awk}. +All of the components use the same text domain. + +To make the discussion concrete, assume we're writing an application +named @command{guide}. Internationalization consists of the +following steps, in this order: + +@enumerate +@item +The programmer reviews the source for all of @command{guide}'s components +and marks each string that is a candidate for translation. +For example, @code{"`-F': option required"} is a good candidate for translation. +A table with strings of option names is not (e.g., @command{gawk}'s +@option{--profile} option should remain the same, no matter what the local +language). + +@cindex @code{textdomain()} function (C library) +@item +The programmer indicates the application's text domain +(@command{"guide"}) to the @command{gettext} library, +by calling the @code{textdomain()} function. + +@cindex @code{.pot} files +@cindex files, @code{.pot} +@cindex portable object template files +@cindex files, portable object template +@item +Messages from the application are extracted from the source code and +collected into a portable object template file (@file{guide.pot}), +which lists the strings and their translations. +The translations are initially empty. +The original (usually English) messages serve as the key for +lookup of the translations. + +@cindex @code{.po} files +@cindex files, @code{.po} +@cindex portable object files +@cindex files, portable object +@item +For each language with a translator, @file{guide.pot} +is copied to a portable object file (@code{.po}) +and translations are created and shipped with the application. +For example, there might be a @file{fr.po} for a French translation. + +@cindex @code{.gmo} files +@cindex files, @code{.gmo} +@cindex message object files +@cindex files, message object +@item +Each language's @file{.po} file is converted into a binary +message object (@file{.gmo}) file. +A message object file contains the original messages and their +translations in a binary format that allows fast lookup of translations +at runtime. + +@item +When @command{guide} is built and installed, the binary translation files +are installed in a standard place. + +@cindex @code{bindtextdomain()} function (C library) +@item +For testing and development, it is possible to tell @command{gettext} +to use @file{.gmo} files in a different directory than the standard +one by using the @code{bindtextdomain()} function. + +@cindex @code{.gmo} files, specifying directory of +@cindex files, @code{.gmo}, specifying directory of +@cindex message object files, specifying directory of +@cindex files, message object, specifying directory of +@item +At runtime, @command{guide} looks up each string via a call +to @code{gettext()}. The returned string is the translated string +if available, or the original string if not. + +@item +If necessary, it is possible to access messages from a different +text domain than the one belonging to the application, without +having to switch the application's default text domain back +and forth. +@end enumerate + +@cindex @code{gettext()} function (C library) +In C (or C++), the string marking and dynamic translation lookup +are accomplished by wrapping each string in a call to @code{gettext()}: + +@example +printf("%s", gettext("Don't Panic!\n")); +@end example + +The tools that extract messages from source code pull out all +strings enclosed in calls to @code{gettext()}. + +@cindex @code{_} (underscore), C macro +@cindex underscore (@code{_}), C macro +The GNU @command{gettext} developers, recognizing that typing +@samp{gettext(@dots{})} over and over again is both painful and ugly to look +at, use the macro @samp{_} (an underscore) to make things easier: + +@example +/* In the standard header file: */ +#define _(str) gettext(str) + +/* In the program text: */ +printf("%s", _("Don't Panic!\n")); +@end example + +@cindex internationalization, localization, locale categories +@cindex @command{gettext} library, locale categories +@cindex locale categories +@noindent +This reduces the typing overhead to just three extra characters per string +and is considerably easier to read as well. + +There are locale @dfn{categories} +for different types of locale-related information. +The defined locale categories that @command{gettext} knows about are: + +@table @code +@cindex @code{LC_MESSAGES} locale category +@item LC_MESSAGES +Text messages. This is the default category for @command{gettext} +operations, but it is possible to supply a different one explicitly, +if necessary. (It is almost never necessary to supply a different category.) + +@cindex sorting characters in different languages +@cindex @code{LC_COLLATE} locale category +@item LC_COLLATE +Text-collation information (i.e., how different characters +and/or groups of characters sort in a given language). + +@cindex @code{LC_CTYPE} locale category +@item LC_CTYPE +Character-type information (alphabetic, digit, upper- or lowercase, and +so on) as well as character encoding. +@ignore +In June 2001 Bruno Haible wrote: +- Description of LC_CTYPE: It determines both + 1. character encoding, + 2. character type information. + (For example, in both KOI8-R and ISO-8859-5 the character type information + is the same - cyrillic letters could as 'alpha' - but the encoding is + different.) +@end ignore +This information is accessed via the +POSIX character classes in regular expressions, +such as @code{/[[:alnum:]]/} +(@pxref{Bracket Expressions}). + +@cindex monetary information, localization +@cindex currency symbols, localization +@cindex @code{LC_MONETARY} locale category +@item LC_MONETARY +Monetary information, such as the currency symbol, and whether the +symbol goes before or after a number. + +@cindex @code{LC_NUMERIC} locale category +@item LC_NUMERIC +Numeric information, such as which characters to use for the decimal +point and the thousands separator.@footnote{Americans +use a comma every three decimal places and a period for the decimal +point, while many Europeans do exactly the opposite: +1,234.56 versus 1.234,56.} + +@cindex time, localization and +@cindex dates, information related to@comma{} localization +@cindex @code{LC_TIME} locale category +@item LC_TIME +Time- and date-related information, such as 12- or 24-hour clock, month printed +before or after the day in a date, local month abbreviations, and so on. + +@cindex @code{LC_ALL} locale category +@item LC_ALL +All of the above. (Not too useful in the context of @command{gettext}.) +@end table + +@node Programmer i18n +@section Internationalizing @command{awk} Programs +@cindex @command{awk} programs, internationalizing + +@command{gawk} provides the following variables and functions for +internationalization: + +@table @code +@cindex @code{TEXTDOMAIN} variable +@item TEXTDOMAIN +This variable indicates the application's text domain. +For compatibility with GNU @command{gettext}, the default +value is @code{"messages"}. + +@cindex internationalization, localization, marked strings +@cindex strings, for localization +@item _"your message here" +String constants marked with a leading underscore +are candidates for translation at runtime. +String constants without a leading underscore are not translated. + +@cindexgawkfunc{dcgettext} +@item @code{dcgettext(@var{string}} [@code{,} @var{domain} [@code{,} @var{category}]]@code{)} +Return the translation of @var{string} in +text domain @var{domain} for locale category @var{category}. +The default value for @var{domain} is the current value of @code{TEXTDOMAIN}. +The default value for @var{category} is @code{"LC_MESSAGES"}. + +If you supply a value for @var{category}, it must be a string equal to +one of the known locale categories described in +@ifnotinfo +the previous @value{SECTION}. +@end ifnotinfo +@ifinfo +@ref{Explaining gettext}. +@end ifinfo +You must also supply a text domain. Use @code{TEXTDOMAIN} if +you want to use the current domain. + +@quotation CAUTION +The order of arguments to the @command{awk} version +of the @code{dcgettext()} function is purposely different from the order for +the C version. The @command{awk} version's order was +chosen to be simple and to allow for reasonable @command{awk}-style +default arguments. +@end quotation + +@cindexgawkfunc{dcngettext} +@item @code{dcngettext(@var{string1}, @var{string2}, @var{number}} [@code{,} @var{domain} [@code{,} @var{category}]]@code{)} +Return the plural form used for @var{number} of the +translation of @var{string1} and @var{string2} in text domain +@var{domain} for locale category @var{category}. @var{string1} is the +English singular variant of a message, and @var{string2} is the English plural +variant of the same message. +The default value for @var{domain} is the current value of @code{TEXTDOMAIN}. +The default value for @var{category} is @code{"LC_MESSAGES"}. + +The same remarks about argument order as for the @code{dcgettext()} function apply. + +@cindex @code{.gmo} files, specifying directory of +@cindex files, @code{.gmo}, specifying directory of +@cindex message object files, specifying directory of +@cindex files, message object, specifying directory of +@cindexgawkfunc{bindtextdomain} +@item @code{bindtextdomain(@var{directory}} [@code{,} @var{domain} ]@code{)} +Change the directory in which +@command{gettext} looks for @file{.gmo} files, in case they +will not or cannot be placed in the standard locations +(e.g., during testing). +Return the directory in which @var{domain} is ``bound.'' + +The default @var{domain} is the value of @code{TEXTDOMAIN}. +If @var{directory} is the null string (@code{""}), then +@code{bindtextdomain()} returns the current binding for the +given @var{domain}. +@end table + +To use these facilities in your @command{awk} program, follow the steps +outlined in +@ifnotinfo +the previous @value{SECTION}, +@end ifnotinfo +@ifinfo +@ref{Explaining gettext}, +@end ifinfo +like so: + +@enumerate +@cindex @code{BEGIN} pattern, @code{TEXTDOMAIN} variable and +@cindex @code{TEXTDOMAIN} variable, @code{BEGIN} pattern and +@item +Set the variable @code{TEXTDOMAIN} to the text domain of +your program. This is best done in a @code{BEGIN} rule +(@pxref{BEGIN/END}), +or it can also be done via the @option{-v} command-line +option (@pxref{Options}): + +@example +BEGIN @{ + TEXTDOMAIN = "guide" + @dots{} +@} +@end example + +@cindex @code{_} (underscore), translatable string +@cindex underscore (@code{_}), translatable string +@item +Mark all translatable strings with a leading underscore (@samp{_}) +character. It @emph{must} be adjacent to the opening +quote of the string. For example: + +@example +print _"hello, world" +x = _"you goofed" +printf(_"Number of users is %d\n", nusers) +@end example + +@item +If you are creating strings dynamically, you can +still translate them, using the @code{dcgettext()} +built-in function:@footnote{Thanks to Bruno Haible for this +example.} + +@example +if (groggy) + message = dcgettext("%d customers disturbing me\n", "adminprog") +else + message = dcgettext("enjoying %d customers\n", "adminprog") +printf(message, ncustomers) +@end example + +Here, the call to @code{dcgettext()} supplies a different +text domain (@code{"adminprog"}) in which to find the +message, but it uses the default @code{"LC_MESSAGES"} category. + +The previous example only works if @code{ncustomers} is greater than one. +This example would be better done with @code{dcngettext()}: + +@example +if (groggy) + message = dcngettext("%d customer disturbing me\n", + "%d customers disturbing me\n", "adminprog") +else + message = dcngettext("enjoying %d customer\n", + "enjoying %d customers\n", "adminprog") +printf(message, ncustomers) +@end example + + +@cindex @code{LC_MESSAGES} locale category, @code{bindtextdomain()} function (@command{gawk}) +@item +During development, you might want to put the @file{.gmo} +file in a private directory for testing. This is done +with the @code{bindtextdomain()} built-in function: + +@example +BEGIN @{ + TEXTDOMAIN = "guide" # our text domain + if (Testing) @{ + # where to find our files + bindtextdomain("testdir") + # joe is in charge of adminprog + bindtextdomain("../joe/testdir", "adminprog") + @} + @dots{} +@} +@end example + +@end enumerate + +@DBXREF{I18N Example} +for an example program showing the steps to create +and use translations from @command{awk}. + +@node Translator i18n +@section Translating @command{awk} Programs + +@cindex @code{.po} files +@cindex files, @code{.po} +@cindex portable object files +@cindex files, portable object +Once a program's translatable strings have been marked, they must +be extracted to create the initial @file{.pot} file. +As part of translation, it is often helpful to rearrange the order +in which arguments to @code{printf} are output. + +@command{gawk}'s @option{--gen-pot} command-line option extracts +the messages and is discussed next. +After that, @code{printf}'s ability to +rearrange the order for @code{printf} arguments at runtime +is covered. + +@menu +* String Extraction:: Extracting marked strings. +* Printf Ordering:: Rearranging @code{printf} arguments. +* I18N Portability:: @command{awk}-level portability issues. +@end menu + +@node String Extraction +@subsection Extracting Marked Strings +@cindex strings, extracting +@cindex marked strings@comma{} extracting +@cindex @option{--gen-pot} option +@cindex command-line options, string extraction +@cindex string extraction (internationalization) +@cindex marked string extraction (internationalization) +@cindex extraction, of marked strings (internationalization) + +@cindex @option{--gen-pot} option +Once your @command{awk} program is working, and all the strings have +been marked and you've set (and perhaps bound) the text domain, +it is time to produce translations. +First, use the @option{--gen-pot} command-line option to create +the initial @file{.pot} file: + +@example +gawk --gen-pot -f guide.awk > guide.pot +@end example + +@cindex @code{xgettext} utility +When run with @option{--gen-pot}, @command{gawk} does not execute your +program. Instead, it parses it as usual and prints all marked strings +to standard output in the format of a GNU @command{gettext} Portable Object +file. Also included in the output are any constant strings that +appear as the first argument to @code{dcgettext()} or as the first and +second argument to @code{dcngettext()}.@footnote{The +@command{xgettext} utility that comes with GNU +@command{gettext} can handle @file{.awk} files.} +You should distribute the generated @file{.pot} file with +your @command{awk} program; translators will eventually use it +to provide you translations that you can also then distribute. +@DBXREF{I18N Example} +for the full list of steps to go through to create and test +translations for @command{guide}. + +@node Printf Ordering +@subsection Rearranging @code{printf} Arguments + +@cindex @code{printf} statement, positional specifiers +@cindex positional specifiers, @code{printf} statement +Format strings for @code{printf} and @code{sprintf()} +(@pxref{Printf}) +present a special problem for translation. +Consider the following:@footnote{This example is borrowed +from the GNU @command{gettext} manual.} + +@example +printf(_"String `%s' has %d characters\n", + string, length(string))) +@end example + +A possible German translation for this might be: + +@example +"%d Zeichen lang ist die Zeichenkette `%s'\n" +@end example + +The problem should be obvious: the order of the format +specifications is different from the original! +Even though @code{gettext()} can return the translated string +at runtime, +it cannot change the argument order in the call to @code{printf}. + +To solve this problem, @code{printf} format specifiers may have +an additional optional element, which we call a @dfn{positional specifier}. +For example: + +@example +"%2$d Zeichen lang ist die Zeichenkette `%1$s'\n" +@end example + +Here, the positional specifier consists of an integer count, which indicates which +argument to use, and a @samp{$}. Counts are one-based, and the +format string itself is @emph{not} included. Thus, in the following +example, @samp{string} is the first argument and @samp{length(string)} is the second: + +@example +$ @kbd{gawk 'BEGIN @{} +> @kbd{string = "Don\47t Panic"} +> @kbd{printf "%2$d characters live in \"%1$s\"\n",} +> @kbd{string, length(string)} +> @kbd{@}'} +@print{} 11 characters live in "Don't Panic" +@end example + +If present, positional specifiers come first in the format specification, +before the flags, the field width, and/or the precision. + +Positional specifiers can be used with the dynamic field width and +precision capability: + +@example +$ @kbd{gawk 'BEGIN @{} +> @kbd{printf("%*.*s\n", 10, 20, "hello")} +> @kbd{printf("%3$*2$.*1$s\n", 20, 10, "hello")} +> @kbd{@}'} +@print{} hello +@print{} hello +@end example + +@quotation NOTE +When using @samp{*} with a positional specifier, the @samp{*} +comes first, then the integer position, and then the @samp{$}. +This is somewhat counterintuitive. +@end quotation + +@cindex @code{printf} statement, positional specifiers, mixing with regular formats +@cindex positional specifiers, @code{printf} statement, mixing with regular formats +@cindex format specifiers, mixing regular with positional specifiers +@command{gawk} does not allow you to mix regular format specifiers +and those with positional specifiers in the same string: + +@example +$ @kbd{gawk 'BEGIN @{ printf "%d %3$s\n", 1, 2, "hi" @}'} +@error{} gawk: cmd. line:1: fatal: must use `count$' on all formats or none +@end example + +@quotation NOTE +There are some pathological cases that @command{gawk} may fail to +diagnose. In such cases, the output may not be what you expect. +It's still a bad idea to try mixing them, even if @command{gawk} +doesn't detect it. +@end quotation + +Although positional specifiers can be used directly in @command{awk} programs, +their primary purpose is to help in producing correct translations of +format strings into languages different from the one in which the program +is first written. + +@node I18N Portability +@subsection @command{awk} Portability Issues + +@cindex portability, internationalization and +@cindex internationalization, localization, portability and +@command{gawk}'s internationalization features were purposely chosen to +have as little impact as possible on the portability of @command{awk} +programs that use them to other versions of @command{awk}. +Consider this program: + +@example +BEGIN @{ + TEXTDOMAIN = "guide" + if (Test_Guide) # set with -v + bindtextdomain("/test/guide/messages") + print _"don't panic!" +@} +@end example + +@noindent +As written, it won't work on other versions of @command{awk}. +However, it is actually almost portable, requiring very little +change: + +@itemize @value{BULLET} +@cindex @code{TEXTDOMAIN} variable, portability and +@item +Assignments to @code{TEXTDOMAIN} won't have any effect, +because @code{TEXTDOMAIN} is not special in other @command{awk} implementations. + +@item +Non-GNU versions of @command{awk} treat marked strings +as the concatenation of a variable named @code{_} with the string +following it.@footnote{This is good fodder for an ``Obfuscated +@command{awk}'' contest.} Typically, the variable @code{_} has +the null string (@code{""}) as its value, leaving the original string constant as +the result. + +@item +By defining ``dummy'' functions to replace @code{dcgettext()}, @code{dcngettext()} +and @code{bindtextdomain()}, the @command{awk} program can be made to run, but +all the messages are output in the original language. +For example: + +@cindex @code{bindtextdomain()} function (@command{gawk}), portability and +@cindex @code{dcgettext()} function (@command{gawk}), portability and +@cindex @code{dcngettext()} function (@command{gawk}), portability and +@example +@c file eg/lib/libintl.awk +function bindtextdomain(dir, domain) +@{ + return dir +@} + +function dcgettext(string, domain, category) +@{ + return string +@} + +function dcngettext(string1, string2, number, domain, category) +@{ + return (number == 1 ? string1 : string2) +@} +@c endfile +@end example + +@item +The use of positional specifications in @code{printf} or +@code{sprintf()} is @emph{not} portable. +To support @code{gettext()} at the C level, many systems' C versions of +@code{sprintf()} do support positional specifiers. But it works only if +enough arguments are supplied in the function call. Many versions of +@command{awk} pass @code{printf} formats and arguments unchanged to the +underlying C library version of @code{sprintf()}, but only one format and +argument at a time. What happens if a positional specification is +used is anybody's guess. +However, because the positional specifications are primarily for use in +@emph{translated} format strings, and because non-GNU @command{awk}s never +retrieve the translated string, this should not be a problem in practice. +@end itemize + +@node I18N Example +@section A Simple Internationalization Example + +Now let's look at a step-by-step example of how to internationalize and +localize a simple @command{awk} program, using @file{guide.awk} as our +original source: + +@example +@c file eg/prog/guide.awk +BEGIN @{ + TEXTDOMAIN = "guide" + bindtextdomain(".") # for testing + print _"Don't Panic" + print _"The Answer Is", 42 + print "Pardon me, Zaphod who?" +@} +@c endfile +@end example + +@noindent +Run @samp{gawk --gen-pot} to create the @file{.pot} file: + +@example +$ @kbd{gawk --gen-pot -f guide.awk > guide.pot} +@end example + +@noindent +This produces: + +@example +@c file eg/data/guide.po +#: guide.awk:4 +msgid "Don't Panic" +msgstr "" + +#: guide.awk:5 +msgid "The Answer Is" +msgstr "" + +@c endfile +@end example + +This original portable object template file is saved and reused for each language +into which the application is translated. The @code{msgid} +is the original string and the @code{msgstr} is the translation. + +@quotation NOTE +Strings not marked with a leading underscore do not +appear in the @file{guide.pot} file. +@end quotation + +Next, the messages must be translated. +Here is a translation to a hypothetical dialect of English, +called ``Mellow'':@footnote{Perhaps it would be better if it were +called ``Hippy.'' Ah, well.} + +@example +@group +$ @kbd{cp guide.pot guide-mellow.po} +@var{Add translations to} guide-mellow.po @dots{} +@end group +@end example + +@noindent +Following are the translations: + +@example +@c file eg/data/guide-mellow.po +#: guide.awk:4 +msgid "Don't Panic" +msgstr "Hey man, relax!" + +#: guide.awk:5 +msgid "The Answer Is" +msgstr "Like, the scoop is" + +@c endfile +@end example + +@cindex Linux +@cindex GNU/Linux +The next step is to make the directory to hold the binary message object +file and then to create the @file{guide.mo} file. +We pretend that our file is to be used in the @code{en_US.UTF-8} locale, +because we have to use a locale name known to the C @command{gettext} routines. +The directory layout shown here is standard for GNU @command{gettext} on +GNU/Linux systems. Other versions of @command{gettext} may use a different +layout: + +@example +$ @kbd{mkdir en_US.UTF-8 en_US.UTF-8/LC_MESSAGES} +@end example + +@cindex @code{.po} files, converting to @code{.mo} +@cindex files, @code{.po}, converting to @code{.mo} +@cindex @code{.mo} files, converting from @code{.po} +@cindex files, @code{.mo}, converting from @code{.po} +@cindex portable object files, converting to message object files +@cindex files, portable object, converting to message object files +@cindex message object files, converting from portable object files +@cindex files, message object, converting from portable object files +@cindex @command{msgfmt} utility +The @command{msgfmt} utility does the conversion from human-readable +@file{.po} file to machine-readable @file{.mo} file. +By default, @command{msgfmt} creates a file named @file{messages}. +This file must be renamed and placed in the proper directory (using +the @option{-o} option) so that @command{gawk} can find it: + +@example +$ @kbd{msgfmt guide-mellow.po -o en_US.UTF-8/LC_MESSAGES/guide.mo} +@end example + +Finally, we run the program to test it: + +@example +$ @kbd{gawk -f guide.awk} +@print{} Hey man, relax! +@print{} Like, the scoop is 42 +@print{} Pardon me, Zaphod who? +@end example + +If the three replacement functions for @code{dcgettext()}, @code{dcngettext()}, +and @code{bindtextdomain()} +(@pxref{I18N Portability}) +are in a file named @file{libintl.awk}, +then we can run @file{guide.awk} unchanged as follows: + +@example +$ @kbd{gawk --posix -f guide.awk -f libintl.awk} +@print{} Don't Panic +@print{} The Answer Is 42 +@print{} Pardon me, Zaphod who? +@end example + +@node Gawk I18N +@section @command{gawk} Can Speak Your Language + +@command{gawk} itself has been internationalized +using the GNU @command{gettext} package. +(GNU @command{gettext} is described in +complete detail in +@ifinfo +@inforef{Top, , GNU @command{gettext} utilities, gettext, GNU gettext tools}.) +@end ifinfo +@ifnotinfo +@uref{http://www.gnu.org/software/gettext/manual/, +@cite{GNU gettext tools}}.) +@end ifnotinfo +As of this writing, the latest version of GNU @command{gettext} is +@uref{ftp://ftp.gnu.org/gnu/gettext/gettext-0.19.4.tar.gz, +@value{PVERSION} 0.19.4}. + +If a translation of @command{gawk}'s messages exists, +then @command{gawk} produces usage messages, warnings, +and fatal errors in the local language. + +@node I18N Summary +@section Summary + +@itemize @value{BULLET} +@item +Internationalization means writing a program such that it can use multiple +languages without requiring source-code changes. Localization means +providing the data necessary for an internationalized program to work +in a particular language. + +@item +@command{gawk} uses GNU @command{gettext} to let you internationalize +and localize @command{awk} programs. A program's text domain identifies +the program for grouping all messages and other data together. + +@item +You mark a program's strings for translation by preceding them with +an underscore. Once that is done, the strings are extracted into a +@file{.pot} file. This file is copied for each language into a @file{.po} +file, and the @file{.po} files are compiled into @file{.gmo} files for +use at runtime. + +@item +You can use position specifications with @code{sprintf()} and +@code{printf} to rearrange the placement of argument values in formatted +strings and output. This is useful for the translations of format +control strings. + +@item +The internationalization features have been designed so that they +can be easily worked around in a standard @command{awk}. + +@item +@command{gawk} itself has been internationalized and ships with +a number of translations for its messages. + +@end itemize + @node Debugger -@chapter @command{dgawk}: The @command{awk} Debugger -@cindex @command{dgawk} +@chapter Debugging @command{awk} Programs +@cindex debugging @command{awk} programs + +@c The original text for this chapter was contributed by Efraim Yawitz. +@c FIXME: Add more indexing. It would be nice if computer programs worked perfectly the first time they were run, but in real life, this rarely happens for programs of any complexity. Thus, most programming languages have facilities available for ``debugging'' programs, and now @command{awk} is no exception. -The @command{dgawk} debugger is purposely modeled after +The @command{gawk} debugger is purposely modeled after @uref{http://www.gnu.org/software/gdb/, the GNU Debugger (GDB)} command-line debugger. If you are familiar with GDB, learning -@command{dgawk} is easy. +how to use @command{gawk} for debugging your program is easy. @menu -* Debugging:: Introduction to @command{dgawk}. -* Sample dgawk session:: Sample @command{dgawk} session. -* List of Debugger Commands:: Main @command{dgawk} Commands. -* Readline Support:: Readline Support. -* Dgawk Limitations:: Limitations and future plans. +* Debugging:: Introduction to @command{gawk} debugger. +* Sample Debugging Session:: Sample debugging session. +* List of Debugger Commands:: Main debugger commands. +* Readline Support:: Readline support. +* Limitations:: Limitations and future plans. +* Debugging Summary:: Debugging summary. @end menu @node Debugging -@section Introduction to @command{dgawk} +@section Introduction to the @command{gawk} Debugger This @value{SECTION} introduces debugging in general and begins the discussion of debugging in @command{gawk}. @menu -* Debugging Concepts:: Debugging In General. +* Debugging Concepts:: Debugging in General. * Debugging Terms:: Additional Debugging Concepts. * Awk Debugging:: Awk Debugging. @end menu @node Debugging Concepts -@subsection Debugging In General +@subsection Debugging in General (If you have used debuggers in other languages, you may want to skip -ahead to the next section on the specific features of the @command{awk} +ahead to the next section on the specific features of the @command{gawk} debugger.) -Of course, a debugging program cannot remove bugs for you, since it has -no way of knowing what you or your users consider a ``bug'' and what is a +Of course, a debugging program cannot remove bugs for you, because it has +no way of knowing what you or your users consider a ``bug'' versus a ``feature.'' (Sometimes, we humans have a hard time with this ourselves.) In that case, what can you expect from such a tool? The answer to that depends on the language being debugged, but in general, you can expect at least the following: -@itemize @bullet +@itemize @value{BULLET} @item The ability to watch a program execute its instructions one by one, giving you, the programmer, the opportunity to think about what is happening @@ -25215,7 +28802,7 @@ having to change your source files. @item The chance to see the values of data in the program at any point in execution, and also to change that data on the fly, to see how that -affects what happens afterwards. (This often includes the ability +affects what happens afterward. (This often includes the ability to look at internal data structures besides the variables you actually defined in your code.) @@ -25230,16 +28817,16 @@ is going wrong (or, for that matter, to better comprehend a perfectly functional program that you or someone else wrote). @node Debugging Terms -@subsection Additional Debugging Concepts +@subsection Debugging Concepts Before diving in to the details, we need to introduce several -important concepts that apply to just about all debuggers, including -@command{dgawk}. +important concepts that apply to just about all debuggers. The following list defines terms used throughout the rest of -this @value{CHAPTER}. +this @value{CHAPTER}: @table @dfn -@item Stack Frame +@cindex stack frame +@item Stack frame Programs generally call functions during the course of their execution. One function can call another, or a function can call itself (recursion). You can view the chain of called functions (main program calls A, which @@ -25253,13 +28840,14 @@ that contains the function's parameters, local variables, and return value, as well as any other ``bookkeeping'' information needed to manage the call stack. This data area is termed a @dfn{stack frame}. -@command{gawk} also follows this model, and @command{dgawk} gives you +@command{gawk} also follows this model, and gives you access to the call stack and to each stack frame. You can see the call stack, as well as from where each function on the stack was invoked. Commands that print the call stack print information about each stack frame (as detailed later on). @item Breakpoint +@cindex breakpoint During debugging, you often wish to let the program run until it reaches a certain point, and then continue execution from there one statement (or instruction) at a time. The way to do this is to set @@ -25269,10 +28857,11 @@ take over control of the program's execution. You can add and remove as many breakpoints as you like. @item Watchpoint +@cindex watchpoint A watchpoint is similar to a breakpoint. The difference is that breakpoints are oriented around the code: stop when a certain point in the code is reached. A watchpoint, however, specifies that program execution -should stop when a @emph{data value} is changed. This is useful, since +should stop when a @emph{data value} is changed. This is useful, as sometimes it happens that a variable receives an erroneous value, and it's hard to track down where this happens just by looking at the code. By using a watchpoint, you can stop whenever a variable is assigned to, @@ -25286,60 +28875,65 @@ Debugging an @command{awk} program has some specific aspects that are not shared with other programming languages. First of all, the fact that @command{awk} programs usually take input -line-by-line from a file or files and operate on those lines using specific +line by line from a file or files and operate on those lines using specific rules makes it especially useful to organize viewing the execution of the program in terms of these rules. As we will see, each @command{awk} rule is treated almost like a function call, with its own specific block of instructions. -In addition, since @command{awk} is by design a very concise language, +In addition, because @command{awk} is by design a very concise language, it is easy to lose sight of everything that is going on ``inside'' each line of @command{awk} code. The debugger provides the opportunity to look at the individual primitive instructions carried out by the higher-level @command{awk} commands. -@node Sample dgawk session -@section Sample @command{dgawk} session +@node Sample Debugging Session +@section Sample Debugging Session +@cindex sample debugging session -In order to illustrate the use of @command{dgawk}, let's look at a sample +In order to illustrate the use of @command{gawk} as a debugger, let's look at a sample debugging session. We will use the @command{awk} implementation of the POSIX @command{uniq} command described earlier (@pxref{Uniq Program}) as our example. @menu -* dgawk invocation:: @command{dgawk} Invocation. -* Finding The Bug:: Finding The Bug. +* Debugger Invocation:: How to Start the Debugger. +* Finding The Bug:: Finding the Bug. @end menu -@node dgawk invocation -@subsection @command{dgawk} Invocation +@node Debugger Invocation +@subsection How to Start the Debugger +@cindex starting the debugger +@cindex debugger, how to start -Starting @command{dgawk} is exactly like running @command{awk}. The -file(s) containing the program and any supporting code are given on the -command line as arguments to one or more @option{-f} options. -(@command{dgawk} is not designed to debug command-line -programs, only programs contained in files.) In our case, -we call @command{dgawk} like this: +Starting the debugger is almost exactly like running @command{gawk} normally, +except you have to pass an additional option @option{--debug}, or the +corresponding short option @option{-D}. The file(s) containing the +program and any supporting code are given on the command line as arguments +to one or more @option{-f} options. (@command{gawk} is not designed +to debug command-line programs, only programs contained in files.) +In our case, we invoke the debugger like this: @example -$ @kbd{dgawk -f getopt.awk -f join.awk -f uniq.awk inputfile} +$ @kbd{gawk -D -f getopt.awk -f join.awk -f uniq.awk -1 inputfile} @end example @noindent where both @file{getopt.awk} and @file{uniq.awk} are in @env{$AWKPATH}. (Experienced users of GDB or similar debuggers should note that this syntax is slightly different from what they are used to. -With @command{dgawk}, the arguments for running the program are given +With the @command{gawk} debugger, you give the arguments for running the program in the command line to the debugger rather than as part of the @code{run} command at the debugger prompt.) +The @option{-1} is an option to @file{uniq.awk}. Instead of immediately running the program on @file{inputfile}, as -@command{gawk} would ordinarily do, @command{dgawk} merely loads all +@command{gawk} would ordinarily do, the debugger merely loads all the program source files, compiles them internally, and then gives us a prompt: @example -dgawk> +gawk> @end example @noindent @@ -25347,7 +28941,7 @@ from which we can issue commands to the debugger. At this point, no code has been executed. @node Finding The Bug -@subsection Finding The Bug +@subsection Finding the Bug Let's say that we are having a problem using (a faulty version of) @file{uniq.awk} in the ``field-skipping'' mode, and it doesn't seem to be @@ -25383,8 +28977,8 @@ a breakpoint in @file{uniq.awk} is at the beginning of the function the breakpoint, use the @code{b} (breakpoint) command: @example -dgawk> @kbd{b are_equal} -@print{} Breakpoint 1 set at file `awklib/eg/prog/uniq.awk', line 64 +gawk> @kbd{b are_equal} +@print{} Breakpoint 1 set at file `awklib/eg/prog/uniq.awk', line 63 @end example The debugger tells us the file and line number where the breakpoint is. @@ -25392,29 +28986,29 @@ Now type @samp{r} or @samp{run} and the program runs until it hits the breakpoint for the first time: @example -dgawk> @kbd{r} +gawk> @kbd{r} @print{} Starting program: @print{} Stopping in Rule ... @print{} Breakpoint 1, are_equal(n, m, clast, cline, alast, aline) - at `awklib/eg/prog/uniq.awk':64 -@print{} 64 if (fcount == 0 && charcount == 0) -dgawk> + at `awklib/eg/prog/uniq.awk':63 +@print{} 63 if (fcount == 0 && charcount == 0) +gawk> @end example Now we can look at what's going on inside our program. First of all, let's see how we got to where we are. At the prompt, we type @samp{bt} -(short for ``backtrace''), and @command{dgawk} responds with a +(short for ``backtrace''), and the debugger responds with a listing of the current stack frames: @example -dgawk> @kbd{bt} +gawk> @kbd{bt} @print{} #0 are_equal(n, m, clast, cline, alast, aline) - at `awklib/eg/prog/uniq.awk':69 -@print{} #1 in main() at `awklib/eg/prog/uniq.awk':89 + at `awklib/eg/prog/uniq.awk':68 +@print{} #1 in main() at `awklib/eg/prog/uniq.awk':88 @end example This tells us that @code{are_equal()} was called by the main program at -line 89 of @file{uniq.awk}. (This is not a big surprise, since this +line 88 of @file{uniq.awk}. (This is not a big surprise, because this is the only call to @code{are_equal()} in the program, but in more complex programs, knowing who called a function and with what parameters can be the key to finding the source of the problem.) @@ -25422,37 +29016,37 @@ the key to finding the source of the problem.) Now that we're in @code{are_equal()}, we can start looking at the values of some variables. Let's say we type @samp{p n} (@code{p} is short for ``print''). We would expect to see the value of -@code{n}, a parameter to @code{are_equal()}. Actually, @command{dgawk} +@code{n}, a parameter to @code{are_equal()}. Actually, the debugger gives us: @example -dgawk> @kbd{p n} +gawk> @kbd{p n} @print{} n = untyped variable @end example @noindent -In this case, @code{n} is an uninitialized local variable, since the +In this case, @code{n} is an uninitialized local variable, because the function was called without arguments (@pxref{Function Calls}). A more useful variable to display might be the current record: @example -dgawk> @kbd{p $0} -@print{} $0 = string ("gawk is a wonderful program!") +gawk> @kbd{p $0} +@print{} $0 = "gawk is a wonderful program!" @end example @noindent -This might be a bit puzzling at first since this is the second line of -our test input above. Let's look at @code{NR}: +This might be a bit puzzling at first, as this is the second line of +our test input. Let's look at @code{NR}: @example -dgawk> @kbd{p NR} -@print{} NR = number (2) +gawk> @kbd{p NR} +@print{} NR = 2 @end example @noindent So we can see that @code{are_equal()} was only called for the second record -of the file. Of course, this is because our program contained a rule for +of the file. Of course, this is because our program contains a rule for @samp{NR == 1}: @example @@ -25465,8 +29059,8 @@ NR == 1 @{ OK, let's just check that that rule worked correctly: @example -dgawk> @kbd{p last} -@print{} last = string ("awk is a wonderful program!") +gawk> @kbd{p last} +@print{} last = "awk is a wonderful program!" @end example Everything we have done so far has verified that the program has worked as @@ -25476,41 +29070,35 @@ be inside this function. To investigate further, we must begin @samp{n} (for ``next''): @example -dgawk> @kbd{n} -@print{} 67 if (fcount > 0) @{ +gawk> @kbd{n} +@print{} 66 if (fcount > 0) @{ @end example -This tells us that @command{gawk} is now ready to execute line 67, which +This tells us that @command{gawk} is now ready to execute line 66, which decides whether to give the lines the special ``field skipping'' treatment -indicated by the @option{-f} command-line option. (Notice that we skipped -from where we were before at line 64 to here, since the condition in line 64 - -@example -if (fcount == 0 && charcount == 0) -@end example - -@noindent -was false.) +indicated by the @option{-1} command-line option. (Notice that we skipped +from where we were before at line 63 to here, because the condition in line 63 +@samp{if (fcount == 0 && charcount == 0)} was false.) Continuing to step, we now get to the splitting of the current and last records: @example -dgawk> @kbd{n} -@print{} 68 n = split(last, alast) -dgawk> @kbd{n} -@print{} 69 m = split($0, aline) +gawk> @kbd{n} +@print{} 67 n = split(last, alast) +gawk> @kbd{n} +@print{} 68 m = split($0, aline) @end example At this point, we should be curious to see what our records were split into, so we try to look: @example -dgawk> @kbd{p n m alast aline} -@print{} n = number (5) -@print{} m = number (5) +gawk> @kbd{p n m alast aline} +@print{} n = 5 +@print{} m = untyped variable @print{} alast = array, 5 elements -@print{} aline = array, 5 elements +@print{} aline = untyped variable @end example @noindent @@ -25518,14 +29106,16 @@ dgawk> @kbd{p n m alast aline} @command{awk}'s @code{print} statement.) This is kind of disappointing, though. All we found out is that there -are five elements in each of our arrays. Useful enough (we now know that +are five elements in @code{alast}; @code{m} and @code{aline} don't have +values because we are at line 68 but haven't executed it yet. +This information is useful enough (we now know that none of the words were accidentally left out), but what if we want to see inside the array? The first choice would be to use subscripts: @example -dgawk> @kbd{p alast[0]} +gawk> @kbd{p alast[0]} @print{} "0" not in array `alast' @end example @@ -25533,31 +29123,31 @@ dgawk> @kbd{p alast[0]} Oops! @example -dgawk> @kbd{p alast[1]} -@print{} alast["1"] = string ("awk") +gawk> @kbd{p alast[1]} +@print{} alast["1"] = "awk" @end example This would be kind of slow for a 100-member array, though, so -@command{dgawk} provides a shortcut (reminiscent of another language +@command{gawk} provides a shortcut (reminiscent of another language not to be mentioned): @example -dgawk> @kbd{p @@alast} -@print{} alast["1"] = string ("awk") -@print{} alast["2"] = string ("is") -@print{} alast["3"] = string ("a") -@print{} alast["4"] = string ("wonderful") -@print{} alast["5"] = string ("program!") +gawk> @kbd{p @@alast} +@print{} alast["1"] = "awk" +@print{} alast["2"] = "is" +@print{} alast["3"] = "a" +@print{} alast["4"] = "wonderful" +@print{} alast["5"] = "program!" @end example It looks like we got this far OK. Let's take another step or two: @example -dgawk> @kbd{n} -@print{} 70 clast = join(alast, fcount, n) -dgawk> @kbd{n} -@print{} 71 cline = join(aline, fcount, m) +gawk> @kbd{n} +@print{} 69 clast = join(alast, fcount, n) +gawk> @kbd{n} +@print{} 70 cline = join(aline, fcount, m) @end example Well, here we are at our error (sorry to spoil the suspense). What we @@ -25566,19 +29156,19 @@ the virtual record to compare, and if the first field was numbered zero, this would work. Let's look at what we've got: @example -dgawk> @kbd{p cline clast} -@print{} cline = string ("gawk is a wonderful program!") -@print{} clast = string ("awk is a wonderful program!") +gawk> @kbd{p cline clast} +@print{} cline = "gawk is a wonderful program!" +@print{} clast = "awk is a wonderful program!" @end example Hey, those look pretty familiar! They're just our original, unaltered, input records. A little thinking (the human brain is still the best debugging tool), and we realize that we were off by one! -We get out of @command{dgawk}: +We get out of the debugger: @example -dgawk> @kbd{q} +gawk> @kbd{q} @print{} The program is running. Exit anyway (y/n)? @kbd{y} @end example @@ -25594,12 +29184,12 @@ cline = join(aline, fcount+1, m) and problem solved! @node List of Debugger Commands -@section Main @command{dgawk} Commands +@section Main Debugger Commands -The @command{dgawk} command set can be divided into the +The @command{gawk} debugger command set can be divided into the following categories: -@itemize @bullet{} +@itemize @value{BULLET} @item Breakpoint control @@ -25623,28 +29213,29 @@ Miscellaneous Each of these are discussed in the following subsections. In the following descriptions, commands which may be abbreviated show the abbreviation on a second description line. -A @command{dgawk} command name may also be truncated if that partial -name is unambiguous. @command{dgawk} has the built-in capability to -automatically repeat the previous command when just hitting @key{Enter}. -This works for the commands @code{list}, @code{next}, @code{nexti}, @code{step}, @code{stepi} -and @code{continue} executed without any argument. +A debugger command name may also be truncated if that partial +name is unambiguous. The debugger has the built-in capability to +automatically repeat the previous command just by hitting @key{Enter}. +This works for the commands @code{list}, @code{next}, @code{nexti}, +@code{step}, @code{stepi}, and @code{continue} executed without any +argument. @menu -* Breakpoint Control:: Control of breakpoints. -* Dgawk Execution Control:: Control of execution. -* Viewing And Changing Data:: Viewing and changing data. -* Dgawk Stack:: Dealing with the stack. -* Dgawk Info:: Obtaining information about the program and - the debugger state. -* Miscellaneous Dgawk Commands:: Miscellaneous Commands. +* Breakpoint Control:: Control of Breakpoints. +* Debugger Execution Control:: Control of Execution. +* Viewing And Changing Data:: Viewing and Changing Data. +* Execution Stack:: Dealing with the Stack. +* Debugger Info:: Obtaining Information about the Program and + the Debugger State. +* Miscellaneous Debugger Commands:: Miscellaneous Commands. @end menu @node Breakpoint Control -@subsection Control Of Breakpoints +@subsection Control of Breakpoints -As we saw above, the first thing you probably want to do in a debugging -session is to get your breakpoints set up, since otherwise your program -will just run as if it was not under the debugger. The commands for +As we saw earlier, the first thing you probably want to do in a debugging +session is to get your breakpoints set up, because your program +will otherwise just run as if it was not under the debugger. The commands for controlling breakpoints are: @table @asis @@ -25652,21 +29243,24 @@ controlling breakpoints are: @cindex debugger commands, @code{break} @cindex @code{break} debugger command @cindex @code{b} debugger command (alias for @code{break}) +@cindex set breakpoint +@cindex breakpoint, setting @item @code{break} [[@var{filename}@code{:}]@var{n} | @var{function}] [@code{"@var{expression}"}] @itemx @code{b} [[@var{filename}@code{:}]@var{n} | @var{function}] [@code{"@var{expression}"}] Without any argument, set a breakpoint at the next instruction to be executed in the selected stack frame. Arguments can be one of the following: +@c @asis for docbook @c nested table -@table @var -@item n +@table @asis +@item @var{n} Set a breakpoint at line number @var{n} in the current source file. -@item filename@code{:}n +@item @var{filename}@code{:}@var{n} Set a breakpoint at line number @var{n} in source file @var{filename}. -@item function +@item @var{function} Set a breakpoint at entry to (the first instruction of) function @var{function}. @end table @@ -25675,13 +29269,15 @@ Each breakpoint is assigned a number which can be used to delete it from the breakpoint list using the @code{delete} command. With a breakpoint, you may also supply a condition. This is an -@command{awk} expression (enclosed in double quotes) that @command{dgawk} +@command{awk} expression (enclosed in double quotes) that the debugger evaluates whenever the breakpoint is reached. If the condition is true, -then @command{dgawk} stops execution and prompts for a command. Otherwise, -@command{dgawk} continues executing the program. +then the debugger stops execution and prompts for a command. Otherwise, +it continues executing the program. @cindex debugger commands, @code{clear} @cindex @code{clear} debugger command +@cindex delete breakpoint at location +@cindex breakpoint at location, how to delete @item @code{clear} [[@var{filename}@code{:}]@var{n} | @var{function}] Without any argument, delete any breakpoint at the next instruction to be executed in the selected stack frame. If the program stops at @@ -25689,32 +29285,36 @@ a breakpoint, this deletes that breakpoint so that the program does not stop at that location again. Arguments can be one of the following: @c nested table -@table @var -@item n +@table @asis +@item @var{n} Delete breakpoint(s) set at line number @var{n} in the current source file. -@item filename@code{:}n +@item @var{filename}@code{:}@var{n} Delete breakpoint(s) set at line number @var{n} in source file @var{filename}. -@item function +@item @var{function} Delete breakpoint(s) set at entry to function @var{function}. @end table @cindex debugger commands, @code{condition} @cindex @code{condition} debugger command +@cindex breakpoint condition @item @code{condition} @var{n} @code{"@var{expression}"} Add a condition to existing breakpoint or watchpoint @var{n}. The -condition is an @command{awk} expression that @command{dgawk} evaluates +condition is an @command{awk} expression @emph{enclosed in double quotes} +that the debugger evaluates whenever the breakpoint or watchpoint is reached. If the condition is true, then -@command{dgawk} stops execution and prompts for a command. Otherwise, -@command{dgawk} continues executing the program. If the condition expression is -not specified, any existing condition is removed; i.e., the breakpoint or -watchpoint is made unconditional. +the debugger stops execution and prompts for a command. Otherwise, +the debugger continues executing the program. If the condition expression is +not specified, any existing condition is removed (i.e., the breakpoint or +watchpoint is made unconditional). @cindex debugger commands, @code{d} (@code{delete}) @cindex debugger commands, @code{delete} @cindex @code{delete} debugger command @cindex @code{d} debugger command (alias for @code{delete}) +@cindex delete breakpoint by number +@cindex breakpoint, delete by number @item @code{delete} [@var{n1 n2} @dots{}] [@var{n}--@var{m}] @itemx @code{d} [@var{n1 n2} @dots{}] [@var{n}--@var{m}] Delete specified breakpoints or a range of breakpoints. Deletes @@ -25722,6 +29322,8 @@ all defined breakpoints if no argument is supplied. @cindex debugger commands, @code{disable} @cindex @code{disable} debugger command +@cindex disable breakpoint +@cindex breakpoint, how to disable or enable @item @code{disable} [@var{n1 n2} @dots{} | @var{n}--@var{m}] Disable specified breakpoints or a range of breakpoints. Without any argument, disables all breakpoints. @@ -25730,6 +29332,7 @@ any argument, disables all breakpoints. @cindex debugger commands, @code{enable} @cindex @code{enable} debugger command @cindex @code{e} debugger command (alias for @code{enable}) +@cindex enable breakpoint @item @code{enable} [@code{del} | @code{once}] [@var{n1 n2} @dots{}] [@var{n}--@var{m}] @itemx @code{e} [@code{del} | @code{once}] [@var{n1 n2} @dots{}] [@var{n}--@var{m}] Enable specified breakpoints or a range of breakpoints. Without @@ -25749,6 +29352,7 @@ the program stops at the breakpoint. @cindex debugger commands, @code{ignore} @cindex @code{ignore} debugger command +@cindex ignore breakpoint @item @code{ignore} @var{n} @var{count} Ignore breakpoint number @var{n} the next @var{count} times it is hit. @@ -25757,13 +29361,14 @@ hit. @cindex debugger commands, @code{tbreak} @cindex @code{tbreak} debugger command @cindex @code{t} debugger command (alias for @code{tbreak}) +@cindex temporary breakpoint @item @code{tbreak} [[@var{filename}@code{:}]@var{n} | @var{function}] @itemx @code{t} [[@var{filename}@code{:}]@var{n} | @var{function}] Set a temporary breakpoint (enabled for only one stop). The arguments are the same as for @code{break}. @end table -@node Dgawk Execution Control +@node Debugger Execution Control @subsection Control of Execution Now that your breakpoints are ready, you can start running the program @@ -25777,6 +29382,8 @@ execution of the program than we saw in our earlier example: @cindex @code{silent} debugger command @cindex debugger commands, @code{end} @cindex @code{end} debugger command +@cindex breakpoint commands +@cindex commands to execute at breakpoint @item @code{commands} [@var{n}] @itemx @code{silent} @itemx @dots{} @@ -25792,18 +29399,19 @@ in the list that resumes execution (e.g., @code{continue}) terminates the list For example: @example -dgawk> @kbd{commands} +gawk> @kbd{commands} > @kbd{silent} > @kbd{printf "A silent breakpoint; i = %d\n", i} > @kbd{info locals} > @kbd{set i = 10} > @kbd{continue} > @kbd{end} -dgawk> +gawk> @end example @cindex debugger commands, @code{c} (@code{continue}) @cindex debugger commands, @code{continue} +@cindex continue program, in debugger @item @code{continue} [@var{count}] @itemx @code{c} [@var{count}] Resume program execution. If continued from a breakpoint and @var{count} is @@ -25820,6 +29428,7 @@ Print the returned value. @cindex debugger commands, @code{next} @cindex @code{next} debugger command @cindex @code{n} debugger command (alias for @code{next}) +@cindex single-step execution, in the debugger @item @code{next} [@var{count}] @itemx @code{n} [@var{count}] Continue execution to the next source line, stepping over function calls. @@ -25839,7 +29448,7 @@ Execute one (or @var{count}) instruction(s), stepping over function calls. @item @code{return} [@var{value}] Cancel execution of a function call. If @var{value} (either a string or a number) is specified, it is used as the function's return value. If used in a -frame other than the innermost one (the currently executing function, i.e., +frame other than the innermost one (the currently executing function; i.e., frame number 0), discard all inner frames in addition to the selected one, and the caller of that frame becomes the innermost frame. @@ -25849,7 +29458,7 @@ and the caller of that frame becomes the innermost frame. @cindex @code{r} debugger command (alias for @code{run}) @item @code{run} @itemx @code{r} -Start/restart execution of the program. When restarting, @command{dgawk} +Start/restart execution of the program. When restarting, the debugger retains the current breakpoints, watchpoints, command history, automatic display variables, and debugger options. @@ -25872,7 +29481,7 @@ stopping, unless it encounters a breakpoint or watchpoint. @itemx @code{si} [@var{count}] Execute one (or @var{count}) instruction(s), stepping inside function calls. (For illustration of what is meant by an ``instruction'' in @command{gawk}, -see the output shown under @code{dump} in @ref{Miscellaneous Dgawk Commands}.) +see the output shown under @code{dump} in @ref{Miscellaneous Debugger Commands}.) @cindex debugger commands, @code{u} (@code{until}) @cindex debugger commands, @code{until} @@ -25881,7 +29490,7 @@ see the output shown under @code{dump} in @ref{Miscellaneous Dgawk Commands}.) @item @code{until} [[@var{filename}@code{:}]@var{n} | @var{function}] @itemx @code{u} [[@var{filename}@code{:}]@var{n} | @var{function}] Without any argument, continue execution until a line past the current -line in current stack frame is reached. With an argument, +line in the current stack frame is reached. With an argument, continue execution until the specified location is reached, or the current stack frame returns. @end table @@ -25900,12 +29509,12 @@ The value of the variable or field is displayed each time the program stops. Each variable added to the list is identified by a unique number: @example -dgawk> @kbd{display x} +gawk> @kbd{display x} @print{} 10: x = 1 @end example @noindent -displays the assigned item number, the variable name and its current value. +This displays the assigned item number, the variable name, and its current value. If the display variable refers to a function parameter, it is silently deleted from the list as soon as the execution reaches a context where no such variable of the given name exists. @@ -25914,6 +29523,7 @@ items on the list. @cindex debugger commands, @code{eval} @cindex @code{eval} debugger command +@cindex evaluate expressions, in debugger @item @code{eval "@var{awk statements}"} Evaluate @var{awk statements} in the context of the running program. You can do anything that an @command{awk} program would do: assign @@ -25931,19 +29541,20 @@ parameters defined by the program. @cindex debugger commands, @code{print} @cindex @code{print} debugger command @cindex @code{p} debugger command (alias for @code{print}) +@cindex print variables, in debugger @item @code{print} @var{var1}[@code{,} @var{var2} @dots{}] @itemx @code{p} @var{var1}[@code{,} @var{var2} @dots{}] Print the value of a @command{gawk} variable or field. Fields must be referenced by constants: @example -dgawk> @kbd{print $3} +gawk> @kbd{print $3} @end example @noindent This prints the third field in the input record (if the specified field does not exist, it prints @samp{Null field}). A variable can be an array element, with -the subscripts being constant values. To print the contents of an array, +the subscripts being constant string values. To print the contents of an array, prefix the name of the array with the @samp{@@} symbol: @example @@ -25964,48 +29575,52 @@ No newline is printed unless one is specified. @cindex debugger commands, @code{set} @cindex @code{set} debugger command +@cindex assign values to variables, in debugger @item @code{set} @var{var}@code{=}@var{value} Assign a constant (number or string) value to an @command{awk} variable or field. -String values must be enclosed between double quotes (@code{"@dots{}"}). +String values must be enclosed between double quotes (@code{"}@dots{}@code{"}). You can also set special @command{awk} variables, such as @code{FS}, -@code{NF}, @code{NR}, etc. +@code{NF}, @code{NR}, and son on. @cindex debugger commands, @code{w} (@code{watch}) @cindex debugger commands, @code{watch} @cindex @code{watch} debugger command @cindex @code{w} debugger command (alias for @code{watch}) +@cindex set watchpoint @item @code{watch} @var{var} | @code{$}@var{n} [@code{"@var{expression}"}] @itemx @code{w} @var{var} | @code{$}@var{n} [@code{"@var{expression}"}] Add variable @var{var} (or field @code{$@var{n}}) to the watch list. -@command{dgawk} then stops whenever +The debugger then stops whenever the value of the variable or field changes. Each watched item is assigned a number which can be used to delete it from the watch list using the @code{unwatch} command. With a watchpoint, you may also supply a condition. This is an -@command{awk} expression (enclosed in double quotes) that @command{dgawk} +@command{awk} expression (enclosed in double quotes) that the debugger evaluates whenever the watchpoint is reached. If the condition is true, -then @command{dgawk} stops execution and prompts for a command. Otherwise, -@command{dgawk} continues executing the program. +then the debugger stops execution and prompts for a command. Otherwise, +@command{gawk} continues executing the program. @cindex debugger commands, @code{undisplay} @cindex @code{undisplay} debugger command +@cindex stop automatic display, in debugger @item @code{undisplay} [@var{n}] Remove item number @var{n} (or all items, if no argument) from the automatic display list. @cindex debugger commands, @code{unwatch} @cindex @code{unwatch} debugger command +@cindex delete watchpoint @item @code{unwatch} [@var{n}] Remove item number @var{n} (or all items, if no argument) from the watch list. @end table -@node Dgawk Stack -@subsection Dealing With The Stack +@node Execution Stack +@subsection Working with the Stack Whenever you run a program which contains any function calls, @command{gawk} maintains a stack of all of the function calls leading up @@ -26016,14 +29631,22 @@ functions which called the one you are in. The commands for doing this are: @table @asis @cindex debugger commands, @code{bt} (@code{backtrace}) @cindex debugger commands, @code{backtrace} +@cindex debugger commands, @code{where} (@code{backtrace}) @cindex @code{backtrace} debugger command @cindex @code{bt} debugger command (alias for @code{backtrace}) +@cindex @code{where} debugger command +@cindex @code{where} debugger command (alias for @code{backtrace}) +@cindex call stack, display in debugger +@cindex traceback, display in debugger @item @code{backtrace} [@var{count}] @itemx @code{bt} [@var{count}] +@itemx @code{where} [@var{count}] Print a backtrace of all function calls (stack frames), or innermost @var{count} frames if @var{count} > 0. Print the outermost @var{count} frames if @var{count} < 0. The backtrace displays the name and arguments to each function, the source @value{FN}, and the line number. +The alias @code{where} for @code{backtrace} is provided for longtime +GDB users who may be used to that command. @cindex debugger commands, @code{down} @cindex @code{down} debugger command @@ -26037,10 +29660,11 @@ Then select and print the frame. @cindex @code{f} debugger command (alias for @code{frame}) @item @code{frame} [@var{n}] @itemx @code{f} [@var{n}] -Select and print (frame number, function and argument names, source file, -and the source line) stack frame @var{n}. Frame 0 is the currently executing, -or @dfn{innermost}, frame (function call), frame 1 is the frame that called the -innermost one. The highest numbered frame is the one for the main program. +Select and print stack frame @var{n}. Frame 0 is the currently executing, +or @dfn{innermost}, frame (function call), frame 1 is the frame that +called the innermost one. The highest numbered frame is the one for the +main program. The printed information consists of the frame number, +function and argument names, source file, and the source line. @cindex debugger commands, @code{up} @cindex @code{up} debugger command @@ -26049,12 +29673,12 @@ Move @var{count} (default 1) frames up the stack toward the outermost frame. Then select and print the frame. @end table -@node Dgawk Info -@subsection Obtaining Information About The Program and The Debugger State +@node Debugger Info +@subsection Obtaining Information About the Program and the Debugger State Besides looking at the values of variables, there is often a need to get other sorts of information about the state of your program and of the -debugging environment itself. @command{dgawk} has one command which +debugging environment itself. The @command{gawk} debugger has one command which provides this information, appropriately called @code{info}. @code{info} is used with one of a number of arguments that tell it exactly what you want to know: @@ -26071,39 +29695,49 @@ The value for @var{what} should be one of the following: @c nested table @table @code @item args -Arguments of the selected frame. +@cindex show function arguments, in debugger +List arguments of the selected frame. @item break +@cindex show breakpoints List all currently set breakpoints. @item display +@cindex automatic displays, in debugger List all items in the automatic display list. @item frame -Description of the selected stack frame. +@cindex describe call stack frame, in debugger +Give a description of the selected stack frame. @item functions -List all function definitions including source file names and +@cindex list function definitions, in debugger +List all function definitions including source @value{FN}s and line numbers. @item locals -Local variables of the selected frame. +@cindex show local variables, in debugger +List local variables of the selected frame. @item source -The name of the current source file. Each time the program stops, the +@cindex show name of current source file, in debugger +Print the name of the current source file. Each time the program stops, the current source file is the file containing the current instruction. -When @command{dgawk} first starts, the current source file is the first file +When the debugger first starts, the current source file is the first file included via the @option{-f} option. The @samp{list @var{filename}:@var{lineno}} command can be used at any time to change the current source. @item sources +@cindex show all source files, in debugger List all program sources. @item variables +@cindex list all global variables, in debugger List all global variables. @item watch +@cindex show watchpoints List all items in the watch list. @end table @end table @@ -26117,6 +29751,8 @@ from a file. The commands are: @cindex debugger commands, @code{option} @cindex @code{option} debugger command @cindex @code{o} debugger command (alias for @code{option}) +@cindex display debugger options +@cindex debugger options @item @code{option} [@var{name}[@code{=}@var{value}]] @itemx @code{o} [@var{name}[@code{=}@var{value}]] Without an argument, display the available debugger options @@ -26126,32 +29762,40 @@ a new value to the named option. The available options are: @c nested table -@table @code -@item history_size -The maximum number of lines to keep in the history file @file{./.dgawk_history}. +@c asis for docbook +@table @asis +@item @code{history_size} +@cindex debugger history size +The maximum number of lines to keep in the history file @file{./.gawk_history}. The default is 100. -@item listsize +@item @code{listsize} +@cindex debugger default list amount The number of lines that @code{list} prints. The default is 15. -@item outfile +@item @code{outfile} +@cindex redirect @command{gawk} output, in debugger Send @command{gawk} output to a file; debugger output still goes to standard output. An empty string (@code{""}) resets output to standard output. -@item prompt -The debugger prompt. The default is @samp{@w{dgawk> }}. +@item @code{prompt} +@cindex debugger prompt +The debugger prompt. The default is @samp{@w{gawk> }}. -@item save_history @r{[}on @r{|} off@r{]} -Save command history to file @file{./.dgawk_history}. +@item @code{save_history} [@code{on} | @code{off}] +@cindex debugger history file +Save command history to file @file{./.gawk_history}. The default is @code{on}. -@item save_options @r{[}on @r{|} off@r{]} -Save current options to file @file{./.dgawkrc} upon exit. +@item @code{save_options} [@code{on} | @code{off}] +@cindex save debugger options +Save current options to file @file{./.gawkrc} upon exit. The default is @code{on}. Options are read back in to the next session upon startup. -@item trace @r{[}on @r{|} off@r{]} +@item @code{trace} [@code{on} | @code{off}] +@cindex instruction tracing, in debugger Turn instruction tracing on or off. The default is @code{off}. @end table @@ -26160,6 +29804,7 @@ Save the commands from the current session to the given @value{FN}, so that they can be replayed using the @command{source} command. @item @code{source} @var{filename} +@cindex debugger, read commands from a file Run command(s) from a file; an error in any command does not terminate execution of subsequent commands. Comments (lines starting with @samp{#}) are allowed in a command file. @@ -26167,16 +29812,16 @@ Empty lines are ignored; they do @emph{not} repeat the last command. You can't restart the program by having more than one @code{run} command in the file. Also, the list of commands may include additional -@code{source} commands; however, @command{dgawk} will not source the +@code{source} commands; however, the @command{gawk} debugger will not source the same file more than once in order to avoid infinite recursion. In addition to, or instead of the @code{source} command, you can use -the @option{-R @var{file}} or @option{--command=@var{file}} command-line +the @option{-D @var{file}} or @option{--debug=@var{file}} command-line options to execute commands from a file non-interactively -(@pxref{Options}. +(@pxref{Options}). @end table -@node Miscellaneous Dgawk Commands +@node Miscellaneous Debugger Commands @subsection Miscellaneous Commands There are a few more commands which do not fit into the @@ -26193,57 +29838,56 @@ commands in a program. This can be very enlightening, as the following partial dump of Davide Brini's obfuscated code (@pxref{Signature Program}) demonstrates: +@c FIXME: This will need updating if num-handler branch is ever merged in. @smallexample -dgawk> @kbd{dump} +gawk> @kbd{dump} @print{} # BEGIN @print{} -@print{} [ 2:0x89faef4] Op_rule : [in_rule = BEGIN] [source_file = brini.awk] -@print{} [ 3:0x89fa428] Op_push_i : "~" [PERM|STRING|STRCUR] -@print{} [ 3:0x89fa464] Op_push_i : "~" [PERM|STRING|STRCUR] -@print{} [ 3:0x89fa450] Op_match : -@print{} [ 3:0x89fa3ec] Op_store_var : O [do_reference = FALSE] -@print{} [ 4:0x89fa48c] Op_push_i : "==" [PERM|STRING|STRCUR] -@print{} [ 4:0x89fa4c8] Op_push_i : "==" [PERM|STRING|STRCUR] -@print{} [ 4:0x89fa4b4] Op_equal : -@print{} [ 4:0x89fa400] Op_store_var : o [do_reference = FALSE] -@print{} [ 5:0x89fa4f0] Op_push : o -@print{} [ 5:0x89fa4dc] Op_plus_i : 0 [PERM|NUMCUR|NUMBER] -@print{} [ 5:0x89fa414] Op_push_lhs : o [do_reference = TRUE] -@print{} [ 5:0x89fa4a0] Op_assign_plus : -@print{} [ :0x89fa478] Op_pop : -@print{} [ 6:0x89fa540] Op_push : O -@print{} [ 6:0x89fa554] Op_push_i : "" [PERM|STRING|STRCUR] -@print{} [ :0x89fa5a4] Op_no_op : -@print{} [ 6:0x89fa590] Op_push : O -@print{} [ :0x89fa5b8] Op_concat : [expr_count = 3] [concat_flag = 0] -@print{} [ 6:0x89fa518] Op_store_var : x [do_reference = FALSE] -@print{} [ 7:0x89fa504] Op_push_loop : [target_continue = 0x89fa568] [target_break = 0x89fa680] -@print{} [ 7:0x89fa568] Op_push_lhs : X [do_reference = TRUE] -@print{} [ 7:0x89fa52c] Op_postincrement : -@print{} [ 7:0x89fa5e0] Op_push : x -@print{} [ 7:0x89fa61c] Op_push : o -@print{} [ 7:0x89fa5f4] Op_plus : -@print{} [ 7:0x89fa644] Op_push : o -@print{} [ 7:0x89fa630] Op_plus : -@print{} [ 7:0x89fa5cc] Op_leq : -@print{} [ :0x89fa57c] Op_jmp_false : [target_jmp = 0x89fa680] -@print{} [ 7:0x89fa694] Op_push_i : "%c" [PERM|STRING|STRCUR] -@print{} [ :0x89fa6d0] Op_no_op : -@print{} [ 7:0x89fa608] Op_assign_concat : c -@print{} [ :0x89fa6a8] Op_jmp : [target_jmp = 0x89fa568] -@print{} [ :0x89fa680] Op_pop_loop : -@print{} +@print{} [ 1:0xfcd340] Op_rule : [in_rule = BEGIN] [source_file = brini.awk] +@print{} [ 1:0xfcc240] Op_push_i : "~" [MALLOC|STRING|STRCUR] +@print{} [ 1:0xfcc2a0] Op_push_i : "~" [MALLOC|STRING|STRCUR] +@print{} [ 1:0xfcc280] Op_match : +@print{} [ 1:0xfcc1e0] Op_store_var : O +@print{} [ 1:0xfcc2e0] Op_push_i : "==" [MALLOC|STRING|STRCUR] +@print{} [ 1:0xfcc340] Op_push_i : "==" [MALLOC|STRING|STRCUR] +@print{} [ 1:0xfcc320] Op_equal : +@print{} [ 1:0xfcc200] Op_store_var : o +@print{} [ 1:0xfcc380] Op_push : o +@print{} [ 1:0xfcc360] Op_plus_i : 0 [MALLOC|NUMCUR|NUMBER] +@print{} [ 1:0xfcc220] Op_push_lhs : o [do_reference = true] +@print{} [ 1:0xfcc300] Op_assign_plus : +@print{} [ :0xfcc2c0] Op_pop : +@print{} [ 1:0xfcc400] Op_push : O +@print{} [ 1:0xfcc420] Op_push_i : "" [MALLOC|STRING|STRCUR] +@print{} [ :0xfcc4a0] Op_no_op : +@print{} [ 1:0xfcc480] Op_push : O +@print{} [ :0xfcc4c0] Op_concat : [expr_count = 3] [concat_flag = 0] +@print{} [ 1:0xfcc3c0] Op_store_var : x +@print{} [ 1:0xfcc440] Op_push_lhs : X [do_reference = true] +@print{} [ 1:0xfcc3a0] Op_postincrement : +@print{} [ 1:0xfcc4e0] Op_push : x +@print{} [ 1:0xfcc540] Op_push : o +@print{} [ 1:0xfcc500] Op_plus : +@print{} [ 1:0xfcc580] Op_push : o +@print{} [ 1:0xfcc560] Op_plus : +@print{} [ 1:0xfcc460] Op_leq : +@print{} [ :0xfcc5c0] Op_jmp_false : [target_jmp = 0xfcc5e0] +@print{} [ 1:0xfcc600] Op_push_i : "%c" [MALLOC|STRING|STRCUR] +@print{} [ :0xfcc660] Op_no_op : +@print{} [ 1:0xfcc520] Op_assign_concat : c +@print{} [ :0xfcc620] Op_jmp : [target_jmp = 0xfcc440] +@print{} @dots{} -@print{} -@print{} [ 8:0x89fa658] Op_K_printf : [expr_count = 17] [redir_type = ""] -@print{} [ :0x89fa374] Op_no_op : -@print{} [ :0x89fa3d8] Op_atexit : -@print{} [ :0x89fa6bc] Op_stop : -@print{} [ :0x89fa39c] Op_no_op : -@print{} [ :0x89fa3b0] Op_after_beginfile : -@print{} [ :0x89fa388] Op_no_op : -@print{} [ :0x89fa3c4] Op_after_endfile : -dgawk> +@print{} +@print{} [ 2:0xfcc5a0] Op_K_printf : [expr_count = 17] [redir_type = ""] +@print{} [ :0xfcc140] Op_no_op : +@print{} [ :0xfcc1c0] Op_atexit : +@print{} [ :0xfcc640] Op_stop : +@print{} [ :0xfcc180] Op_no_op : +@print{} [ :0xfcd150] Op_after_beginfile : +@print{} [ :0xfcc160] Op_no_op : +@print{} [ :0xfcc1a0] Op_after_endfile : +gawk> @end smallexample @cindex debugger commands, @code{h} (@code{help}) @@ -26252,7 +29896,7 @@ dgawk> @cindex @code{h} debugger command (alias for @code{help}) @item @code{help} @itemx @code{h} -Print a list of all of the @command{dgawk} commands with a short +Print a list of all of the @command{gawk} debugger commands with a short summary of their usage. @samp{help @var{command}} prints the information about the command @var{command}. @@ -26260,15 +29904,15 @@ about the command @var{command}. @cindex debugger commands, @code{list} @cindex @code{list} debugger command @cindex @code{l} debugger command (alias for @code{list}) -@item @code{list} [@code{-} | @code{+} | @var{n} | @var{filename@code{:}n} | @var{n}--@var{m} | @var{function}] -@itemx @code{l} [@code{-} | @code{+} | @var{n} | @var{filename@code{:}n} | @var{n}--@var{m} | @var{function}] +@item @code{list} [@code{-} | @code{+} | @var{n} | @var{filename}@code{:}@var{n} | @var{n}--@var{m} | @var{function}] +@itemx @code{l} [@code{-} | @code{+} | @var{n} | @var{filename}@code{:}@var{n} | @var{n}--@var{m} | @var{function}] Print the specified lines (default 15) from the current source file or the file named @var{filename}. The possible arguments to @code{list} are as follows: @c nested table @table @asis -@item @code{-} +@item @code{-} (Minus) Print lines before the lines last printed. @item @code{+} @@ -26281,7 +29925,7 @@ Print lines centered around line number @var{n}. @item @var{n}--@var{m} Print lines from @var{n} to @var{m}. -@item @var{filename@code{:}n} +@item @var{filename}@code{:}@var{n} Print lines centered around line number @var{n} in source file @var{filename}. This command may change the current source file. @@ -26294,17 +29938,18 @@ function @var{function}. This command may change the current source file. @cindex debugger commands, @code{quit} @cindex @code{quit} debugger command @cindex @code{q} debugger command (alias for @code{quit}) +@cindex exit the debugger @item @code{quit} @itemx @code{q} Exit the debugger. Debugging is great fun, but sometimes we all have to tend to other obligations in life, and sometimes we find the bug, -and are free to go on to the next one! As we saw above, if you are -running a program, @command{dgawk} warns you if you accidentally type +and are free to go on to the next one! As we saw earlier, if you are +running a program, the debugger warns you if you accidentally type @samp{q} or @samp{quit}, to make sure you really want to quit. @cindex debugger commands, @code{trace} @cindex @code{trace} debugger command -@item @code{trace} @code{on} @r{|} @code{off} +@item @code{trace} [@code{on} | @code{off}] Turn on or off a continuous printing of instructions which are about to be executed, along with printing the @command{awk} line which they implement. The default is @code{off}. @@ -26317,10 +29962,14 @@ fairly self-explanatory, and using @code{stepi} and @code{nexti} while @node Readline Support @section Readline Support +@cindex command completion, in debugger +@cindex history expansion, in debugger -If @command{dgawk} is compiled with the @code{readline} library, you -can take advantage of that library's command completion and history expansion -features. The following types of completion are available: +If @command{gawk} is compiled with +@uref{http://cnswww.cns.cwru.edu/php/chet/readline/readline.html, +the @code{readline} library}, you can take advantage of that library's +command completion and history expansion features. The following types +of completion are available: @table @asis @item Command completion @@ -26350,29 +29999,32 @@ and @end table -@node Dgawk Limitations -@section Limitations and Future Plans +@node Limitations +@section Limitations -We hope you find @command{dgawk} useful and enjoyable to work with, +We hope you find the @command{gawk} debugger useful and enjoyable to work with, but as with any program, especially in its early releases, it still has some limitations. A few which are worth being aware of are: -@itemize @bullet{} +@itemize @value{BULLET} @item -At this point, @command{dgawk} does not give a detailed explanation of +At this point, the debugger does not give a detailed explanation of what you did wrong when you type in something it doesn't like. Rather, it just responds @samp{syntax error}. When you do figure out what your mistake was, though, you'll feel like a real guru. @item -If you perused the dump of opcodes in @ref{Miscellaneous Dgawk Commands}, +@c NOTE: no comma after the ref{} on purpose, due to following +@c parenthetical remark. +If you perused the dump of opcodes in @ref{Miscellaneous Debugger Commands} (or if you are already familiar with @command{gawk} internals), you will realize that much of the internal manipulation of data in @command{gawk}, as in many interpreters, is done on a stack. -@code{Op_push}, @code{Op_pop}, etc., are the ``bread and butter'' of -most @command{gawk} code. Unfortunately, as of now, @command{dgawk} -does not allow you to examine the stack's contents. +@code{Op_push}, @code{Op_pop}, and the like, are the ``bread and butter'' of +most @command{gawk} code. +Unfortunately, as of now, the @command{gawk} +debugger does not allow you to examine the stack's contents. That is, the intermediate results of expression evaluation are on the stack, but cannot be printed. Rather, only variables which are defined in the program can be printed. Of course, a workaround for @@ -26382,78 +30034,5231 @@ change back to obscure, perhaps more optimal code later. @item There is no way to look ``inside'' the process of compiling regular expressions to see if you got it right. As an @command{awk} -programmer, you are expected to know what @code{/[^[:alnum:][:blank:]]/} -means. +programmer, you are expected to know the meaning of +@code{/[^[:alnum:][:blank:]]/}. @item -@command{dgawk} is designed to be used by running a program (with all its -parameters) on the command line, as described in @ref{dgawk invocation}. +The @command{gawk} debugger is designed to be used by running a program (with all its +parameters) on the command line, as described in @ref{Debugger Invocation}. There is no way (as of now) to attach or ``break in'' to a running program. This seems reasonable for a language which is used mainly for quickly executing, short programs. @item -@command{dgawk} only accepts source supplied with the @option{-f} option. +The @command{gawk} debugger only accepts source supplied with the @option{-f} option. @end itemize +@ignore Look forward to a future release when these and other missing features may be added, and of course feel free to try to add them yourself! +@end ignore -@ignore -@c Try this +@node Debugging Summary +@section Summary + +@itemize @value{BULLET} +@item +Programs rarely work correctly the first time. Finding bugs +is @dfn{debugging} and a program that helps you find bugs is a +@dfn{debugger}. @command{gawk} has a built-in debugger that works very +similarly to the GNU Debugger, GDB. + +@item +Debuggers let you step through your program one statement at a time, +examine and change variable and array values, and do a number of other +things that let you understand what your program is actually doing (as +opposed to what it is supposed to do). + +@item +Like most debuggers, the @command{gawk} debugger works in terms of stack +frames, and lets you set both breakpoints (stop at a point in the code) +and watchpoints (stop when a data value changes). + +@item +The debugger command set is fairly complete, providing control over +breakpoints, execution, viewing and changing data, working with the stack, +getting information, and other tasks. + +@item +If the @code{readline} library is available when @command{gawk} is +compiled, it is used by the debugger to provide command-line history +and editing. + +@end itemize + +@node Arbitrary Precision Arithmetic +@chapter Arithmetic and Arbitrary-Precision Arithmetic with @command{gawk} +@cindex arbitrary precision +@cindex multiple precision +@cindex infinite precision +@cindex floating-point, numbers@comma{} arbitrary precision + +This @value{CHAPTER} introduces some basic concepts relating to +how computers do arithmetic and defines some important terms. +It then proceeds to describe floating-point arithmetic, +which is what @command{awk} uses for all its computations, including a +discussion of arbitrary-precision floating-point arithmetic, which is +a feature available only in @command{gawk}. It continues on to present +arbitrary-precision integers, and concludes with a description of some +points where @command{gawk} and the POSIX standard are not quite in +agreement. + +@quotation NOTE +Most users of @command{gawk} can safely skip this chapter. +But if you want to do scientific calculations with @command{gawk}, +this is the place to be. +@end quotation + +@menu +* Computer Arithmetic:: A quick intro to computer math. +* Math Definitions:: Defining terms used. +* MPFR features:: The MPFR features in @command{gawk}. +* FP Math Caution:: Things to know. +* Arbitrary Precision Integers:: Arbitrary Precision Integer Arithmetic with + @command{gawk}. +* POSIX Floating Point Problems:: Standards Versus Existing Practice. +* Floating point summary:: Summary of floating point discussion. +@end menu + +@node Computer Arithmetic +@section A General Description of Computer Arithmetic + +Until now, we have worked with data as either numbers or +strings. Ultimately, however, computers represent everything in terms +of @dfn{binary digits}, or @dfn{bits}. A decimal digit can take on any +of 10 values: zero through nine. A binary digit can take on any of two +values, zero or one. Using binary, computers (and computer software) +can represent and manipulate numerical and character data. In general, +the more bits you can use to represent a particular thing, the greater +the range of possible values it can take on. + +Modern computers support at least two, and often more, ways to do +arithmetic. Each kind of arithmetic uses a different representation +(organization of the bits) for the numbers. The kinds of arithmetic +that interest us are: + +@table @asis +@item Decimal arithmetic +This is the kind of arithmetic you learned in elementary school, using +paper and pencil (and/or a calculator). In theory, numbers can have an +arbitrary number of digits on either side (or both sides) of the decimal +point, and the results of a computation are always exact. + +Some modern system can do decimal arithmetic in hardware, but usually you +need a special software library to provide access to these instructions. +There are also libraries that do decimal arithmetic entirely in software. + +Despite the fact that some users expect @command{gawk} to be performing +decimal arithmetic,@footnote{We don't know why they expect this, but +they do.} it does not do so. + +@item Integer arithmetic +In school, integer values were referred to as ``whole'' numbers---that +is, numbers without any fractional part, such as 1, 42, or @minus{}17. +The advantage to integer numbers is that they represent values exactly. +The disadvantage is that their range is limited. + +@cindex unsigned integers +@cindex integers, unsigned +In computers, integer values come in two flavors: @dfn{signed} and +@dfn{unsigned}. Signed values may be negative or positive, whereas +unsigned values are always positive (i.e., greater than or equal +to zero). + +In computer systems, integer arithmetic is exact, but the possible +range of values is limited. Integer arithmetic is generally faster than +floating-point arithmetic. + +@item Floating-point arithmetic +Floating-point numbers represent what were called in school ``real'' +numbers (i.e., those that have a fractional part, such as 3.1415927). +The advantage to floating-point numbers is that they can represent a +much larger range of values than can integers. The disadvantage is that +there are numbers that they cannot represent exactly. + +Modern systems support floating-point arithmetic in hardware, with a +limited range of values. There are software libraries that allow +the use of arbitrary-precision floating-point calculations. + +POSIX @command{awk} uses @dfn{double-precision} floating-point numbers, which +can hold more digits than @dfn{single-precision} floating-point numbers. +@command{gawk} has facilities for performing arbitrary-precision +floating-point arithmetic, which we describe in more detail shortly. +@end table + +Computers work with integer and floating-point values of different +ranges. Integer values are usually either 32 or 64 bits in size. +Single-precision floating-point values occupy 32 bits, whereas double-precision +floating-point values occupy 64 bits. Floating-point values are always +signed. The possible ranges of values are shown in @ref{table-numeric-ranges}. + +@float Table,table-numeric-ranges +@caption{Value ranges for different numeric representations} +@multitable @columnfractions .34 .33 .33 +@headitem Numeric representation @tab Minimum value @tab Maximum value +@item 32-bit signed integer @tab @minus{}2,147,483,648 @tab 2,147,483,647 +@item 32-bit unsigned integer @tab 0 @tab 4,294,967,295 +@item 64-bit signed integer @tab @minus{}9,223,372,036,854,775,808 @tab 9,223,372,036,854,775,807 +@item 64-bit unsigned integer @tab 0 @tab 18,446,744,073,709,551,615 +@item Single-precision floating point (approximate) @tab @code{1.175494e-38} @tab @code{3.402823e+38} +@item Double-precision floating point (approximate) @tab @code{2.225074e-308} @tab @code{1.797693e+308} +@end multitable +@end float + +@node Math Definitions +@section Other Stuff to Know + +The rest of this @value{CHAPTER} uses a number of terms. Here are some +informal definitions that should help you work your way through the material +here. + +@table @dfn +@item Accuracy +A floating-point calculation's accuracy is how close it comes +to the real (paper and pencil) value. + +@item Error +The difference between what the result of a computation ``should be'' +and what it actually is. It is best to minimize error as much +as possible. + +@item Exponent +The order of magnitude of a value; +some number of bits in a floating-point value store the exponent. + +@item Inf +A special value representing infinity. Operations involving another +number and infinity produce infinity. + +@item NaN +``Not A Number.''@footnote{Thanks to Michael Brennan for this description, +which we have paraphrased, and for the examples.} A special value that +results from attempting a calculation that has no answer as a real number. +In such a case, programs can either receive a floating-point exception, +or get @code{NaN} back as the result. The IEEE 754 standard recommends +that systems return @code{NaN}. Some examples: + +@table @code +@item sqrt(-1) +This makes sense in the range of complex numbers, but not in the +range of real numbers, so the result is @code{NaN}. + +@item log(-8) +@minus{}8 is out of the domain of @code{log()}, so the result is @code{NaN}. +@end table + +@item Normalized +How the significand (see later in this list) is usually stored. The +value is adjusted so that the first bit is one, and then that leading +one is assumed instead of physically stored. This provides one +extra bit of precision. + +@item Precision +The number of bits used to represent a floating-point number. +The more bits, the more digits you can represent. +Binary and decimal precisions are related approximately, according to the +formula: + +@display @iftex -@page -@headings off -@majorheading III@ @ @ Appendixes -Part III provides the appendixes, the Glossary, and two licenses that cover -the @command{gawk} source code and this @value{DOCUMENT}, respectively. -It contains the following appendixes: +@math{prec = 3.322 @cdot dps} +@end iftex +@ifnottex +@ifnotdocbook +@var{prec} = 3.322 * @var{dps} +@end ifnotdocbook +@end ifnottex +@docbook +<emphasis>prec</emphasis> = 3.322 ⋅ <emphasis>dps</emphasis> @c +@end docbook +@end display + +@noindent +Here, @var{prec} denotes the binary precision +(measured in bits) and @var{dps} (short for decimal places) +is the decimal digits. + +@item Rounding mode +How numbers are rounded up or down when necessary. +More details are provided later. + +@item Significand +A floating-point value consists the significand multiplied by 10 +to the power of the exponent. For example, in @code{1.2345e67}, +the significand is @code{1.2345}. + +@item Stability +From @uref{http://en.wikipedia.org/wiki/Numerical_stability, +the Wikipedia article on numerical stability}: +``Calculations that can be proven not to magnify approximation errors +are called @dfn{numerically stable}.'' +@end table + +See @uref{http://en.wikipedia.org/wiki/Accuracy_and_precision, +the Wikipedia article on accuracy and precision} for more information +on some of those terms. + +On modern systems, floating-point hardware uses the representation and +operations defined by the IEEE 754 standard. +Three of the standard IEEE 754 types are 32-bit single precision, +64-bit double precision, and 128-bit quadruple precision. +The standard also specifies extended precision formats +to allow greater precisions and larger exponent ranges. +(@command{awk} uses only the 64-bit double-precision format.) + +@ref{table-ieee-formats} lists the precision and exponent +field values for the basic IEEE 754 binary formats: + +@float Table,table-ieee-formats +@caption{Basic IEEE format values} +@multitable @columnfractions .20 .20 .20 .20 .20 +@headitem Name @tab Total bits @tab Precision @tab Minimum exponent @tab Maximum exponent +@item Single @tab 32 @tab 24 @tab @minus{}126 @tab +127 +@item Double @tab 64 @tab 53 @tab @minus{}1022 @tab +1023 +@item Quadruple @tab 128 @tab 113 @tab @minus{}16382 @tab +16383 +@end multitable +@end float + +@quotation NOTE +The precision numbers include the implied leading one that gives them +one extra bit of significand. +@end quotation + +@node MPFR features +@section Arbitrary-Precision Arithmetic Features in @command{gawk} + +By default, @command{gawk} uses the double-precision floating-point values +supplied by the hardware of the system it runs on. However, if it was +compiled to do so, @command{gawk} uses the @uref{http://www.mpfr.org, +GNU MPFR} and @uref{http://gmplib.org, GNU MP} (GMP) libraries for +arbitrary-precision arithmetic on numbers. You can see if MPFR support +is available like so: + +@example +$ @kbd{gawk --version} +@print{} GNU Awk 4.1.2, API: 1.1 (GNU MPFR 3.1.0-p3, GNU MP 5.0.2) +@print{} Copyright (C) 1989, 1991-2015 Free Software Foundation. +@dots{} +@end example + +@noindent +(You may see different version numbers than what's shown here. That's OK; +what's important is to see that GNU MPFR and GNU MP are listed in +the output.) + +Additionally, there are a few elements available in the @code{PROCINFO} +array to provide information about the MPFR and GMP libraries +(@pxref{Auto-set}). + +The MPFR library provides precise control over precisions and rounding +modes, and gives correctly rounded, reproducible, platform-independent +results. With the @option{-M} command-line option, +all floating-point arithmetic operators and numeric functions +can yield results to any desired precision level supported by MPFR. + +Two predefined variables, @code{PREC} and @code{ROUNDMODE}, +provide control over the working precision and the rounding mode. +The precision and the rounding mode are set globally for every operation +to follow. +@DBXREF{Setting precision} and @DBREF{Setting the rounding mode} +for more information. + +@node FP Math Caution +@section Floating-Point Arithmetic: Caveat Emptor! + +@quotation +@i{Math class is tough!} +@author Teen Talk Barbie, July 1992 +@end quotation + +This @value{SECTION} provides a high level overview of the issues +involved when doing lots of floating-point arithmetic.@footnote{There +is a very nice @uref{http://www.validlab.com/goldberg/paper.pdf, +paper on floating-point arithmetic} by David Goldberg, ``What Every +Computer Scientist Should Know About Floating-point Arithmetic,'' +@cite{ACM Computing Surveys} @strong{23}, 1 (1991-03), 5-48. This is +worth reading if you are interested in the details, but it does require +a background in computer science.} +The discussion applies to both hardware and arbitrary-precision +floating-point arithmetic. + +@quotation CAUTION +The material here is purposely general. If you need to do serious +computer arithmetic, you should do some research first, and not +rely just on what we tell you. +@end quotation + +@menu +* Inexactness of computations:: Floating point math is not exact. +* Getting Accuracy:: Getting more accuracy takes some work. +* Try To Round:: Add digits and round. +* Setting precision:: How to set the precision. +* Setting the rounding mode:: How to set the rounding mode. +@end menu + +@node Inexactness of computations +@subsection Floating-Point Arithmetic Is Not Exact + +Binary floating-point representations and arithmetic are inexact. +Simple values like 0.1 cannot be precisely represented using +binary floating-point numbers, and the limited precision of +floating-point numbers means that slight changes in +the order of operations or the precision of intermediate storage +can change the result. To make matters worse, with arbitrary-precision +floating-point arithmetic, you can set the precision before starting a +computation, but then you cannot be sure of the number of significant +decimal places in the final result. + +@menu +* Inexact representation:: Numbers are not exactly represented. +* Comparing FP Values:: How to compare floating point values. +* Errors accumulate:: Errors get bigger as they go. +@end menu + +@node Inexact representation +@subsubsection Many Numbers Cannot Be Represented Exactly + +So, before you start to write any code, you should think +about what you really want and what's really happening. Consider the +two numbers in the following example: + +@example +x = 0.875 # 1/2 + 1/4 + 1/8 +y = 0.425 +@end example + +Unlike the number in @code{y}, the number stored in @code{x} +is exactly representable +in binary because it can be written as a finite sum of one or +more fractions whose denominators are all powers of two. +When @command{gawk} reads a floating-point number from +program source, it automatically rounds that number to whatever +precision your machine supports. If you try to print the numeric +content of a variable using an output format string of @code{"%.17g"}, +it may not produce the same number as you assigned to it: + +@example +$ @kbd{gawk 'BEGIN @{ x = 0.875; y = 0.425} +> @kbd{ printf("%0.17g, %0.17g\n", x, y) @}'} +@print{} 0.875, 0.42499999999999999 +@end example + +Often the error is so small you do not even notice it, and if you do, +you can always specify how much precision you would like in your output. +Usually this is a format string like @code{"%.15g"}, which when +used in the previous example, produces an output identical to the input. + +@node Comparing FP Values +@subsubsection Be Careful Comparing Values + +Because the underlying representation can be a little bit off from the exact value, +comparing floating-point values to see if they are exactly equal is generally a bad idea. +Here is an example where it does not work like you would expect: + +@example +$ @kbd{gawk 'BEGIN @{ print (0.1 + 12.2 == 12.3) @}'} +@print{} 0 +@end example + +The general wisdom when comparing floating-point values is to see if +they are within some small range of each other (called a @dfn{delta}, +or @dfn{tolerance}). +You have to decide how small a delta is important to you. Code to do +this looks something like the following: + +@example +delta = 0.00001 # for example +difference = abs(a) - abs(b) # subtract the two values +if (difference < delta) + # all ok +else + # not ok +@end example + +@noindent +(We assume that you have a simple absolute value function named +@code{abs()} defined elsewhere in your program.) + +@node Errors accumulate +@subsubsection Errors Accumulate + +The loss of accuracy during a single computation with floating-point +numbers usually isn't enough to worry about. However, if you compute a +value which is the result of a sequence of floating-point operations, +the error can accumulate and greatly affect the computation itself. +Here is an attempt to compute the value of @value{PI} using one of its +many series representations: + +@example +BEGIN @{ + x = 1.0 / sqrt(3.0) + n = 6 + for (i = 1; i < 30; i++) @{ + n = n * 2.0 + x = (sqrt(x * x + 1) - 1) / x + printf("%.15f\n", n * x) + @} +@} +@end example + +When run, the early errors propagate through later computations, +causing the loop to terminate prematurely after attempting to divide by zero: + +@example +$ @kbd{gawk -f pi.awk} +@print{} 3.215390309173475 +@print{} 3.159659942097510 +@print{} 3.146086215131467 +@print{} 3.142714599645573 +@dots{} +@print{} 3.224515243534819 +@print{} 2.791117213058638 +@print{} 0.000000000000000 +@error{} gawk: pi.awk:6: fatal: division by zero attempted +@end example + +Here is an additional example where the inaccuracies in internal representations +yield an unexpected result: + +@example +$ @kbd{gawk 'BEGIN @{} +> @kbd{for (d = 1.1; d <= 1.5; d += 0.1) # loop five times (?)} +> @kbd{i++} +> @kbd{print i} +> @kbd{@}'} +@print{} 4 +@end example + +@node Getting Accuracy +@subsection Getting the Accuracy You Need + +Can arbitrary-precision arithmetic give exact results? There are +no easy answers. The standard rules of algebra often do not apply +when using floating-point arithmetic. +Among other things, the distributive and associative laws +do not hold completely, and order of operation may be important +for your computation. Rounding error, cumulative precision loss +and underflow are often troublesome. + +When @command{gawk} tests the expressions @samp{0.1 + 12.2} and +@samp{12.3} for equality using the machine double-precision arithmetic, +it decides that they are not equal! (@xref{Comparing FP Values}.) +You can get the result you want by increasing the precision; 56 bits in +this case does the job: -@itemize @bullet +@example +$ @kbd{gawk -M -v PREC=56 'BEGIN @{ print (0.1 + 12.2 == 12.3) @}'} +@print{} 1 +@end example + +If adding more bits is good, perhaps adding even more bits of +precision is better? +Here is what happens if we use an even larger value of @code{PREC}: + +@example +$ @kbd{gawk -M -v PREC=201 'BEGIN @{ print (0.1 + 12.2 == 12.3) @}'} +@print{} 0 +@end example + +This is not a bug in @command{gawk} or in the MPFR library. +It is easy to forget that the finite number of bits used to store the value +is often just an approximation after proper rounding. +The test for equality succeeds if and only if @emph{all} bits in the two operands +are exactly the same. Because this is not necessarily true after floating-point +computations with a particular precision and effective rounding mode, +a straight test for equality may not work. Instead, compare the +two numbers to see if they are within the desirable delta of each other. + +In applications where 15 or fewer decimal places suffice, +hardware double-precision arithmetic can be adequate, and is usually much faster. +But you need to keep in mind that every floating-point operation +can suffer a new rounding error with catastrophic consequences, as illustrated +by our earlier attempt to compute the value of @value{PI}. +Extra precision can greatly enhance the stability and the accuracy +of your computation in such cases. + +Repeated addition is not necessarily equivalent to multiplication +in floating-point arithmetic. In the example in +@ref{Errors accumulate}: + +@example +$ @kbd{gawk 'BEGIN @{} +> @kbd{for (d = 1.1; d <= 1.5; d += 0.1) # loop five times (?)} +> @kbd{i++} +> @kbd{print i} +> @kbd{@}'} +@print{} 4 +@end example + +@noindent +you may or may not succeed in getting the correct result by choosing +an arbitrarily large value for @code{PREC}. Reformulation of +the problem at hand is often the correct approach in such situations. + +@node Try To Round +@subsection Try a Few Extra Bits of Precision and Rounding + +Instead of arbitrary-precision floating-point arithmetic, +often all you need is an adjustment of your logic +or a different order for the operations in your calculation. +The stability and the accuracy of the computation of @value{PI} +in the earlier example can be enhanced by using the following +simple algebraic transformation: + +@example +(sqrt(x * x + 1) - 1) / x @equiv{} x / (sqrt(x * x + 1) + 1) +@end example + +@noindent +After making this change, the program converges to +@value{PI} in under 30 iterations: + +@example +$ @kbd{gawk -f pi2.awk} +@print{} 3.215390309173473 +@print{} 3.159659942097501 +@print{} 3.146086215131436 +@print{} 3.142714599645370 +@print{} 3.141873049979825 +@dots{} +@print{} 3.141592653589797 +@print{} 3.141592653589797 +@end example + +@node Setting precision +@subsection Setting the Precision + +@command{gawk} uses a global working precision; it does not keep track of +the precision or accuracy of individual numbers. Performing an arithmetic +operation or calling a built-in function rounds the result to the current +working precision. The default working precision is 53 bits, which you can +modify using the predefined variable @code{PREC}. You can also set the +value to one of the predefined case-insensitive strings +shown in @ref{table-predefined-precision-strings}, +to emulate an IEEE 754 binary format. + +@float Table,table-predefined-precision-strings +@caption{Predefined precision strings for @code{PREC}} +@multitable {@code{"double"}} {12345678901234567890123456789012345} +@headitem @code{PREC} @tab IEEE 754 Binary Format +@item @code{"half"} @tab 16-bit half-precision +@item @code{"single"} @tab Basic 32-bit single precision +@item @code{"double"} @tab Basic 64-bit double precision +@item @code{"quad"} @tab Basic 128-bit quadruple precision +@item @code{"oct"} @tab 256-bit octuple precision +@end multitable +@end float + +The following example illustrates the effects of changing precision +on arithmetic operations: + +@example +$ @kbd{gawk -M -v PREC=100 'BEGIN @{ x = 1.0e-400; print x + 0} +> @kbd{PREC = "double"; print x + 0 @}'} +@print{} 1e-400 +@print{} 0 +@end example + +@quotation CAUTION +Be wary of floating-point constants! When reading a floating-point +constant from program source code, @command{gawk} uses the default +precision (that of a C @code{double}), unless overridden by an assignment +to the special variable @code{PREC} on the command line, to store it +internally as an MPFR number. Changing the precision using @code{PREC} +in the program text does @emph{not} change the precision of a constant. + +If you need to represent a floating-point constant at a higher precision +than the default and cannot use a command-line assignment to @code{PREC}, +you should either specify the constant as a string, or as a rational +number, whenever possible. The following example illustrates the +differences among various ways to print a floating-point constant: +@end quotation + +@example +$ @kbd{gawk -M 'BEGIN @{ PREC = 113; printf("%0.25f\n", 0.1) @}'} +@print{} 0.1000000000000000055511151 +$ @kbd{gawk -M -v PREC=113 'BEGIN @{ printf("%0.25f\n", 0.1) @}'} +@print{} 0.1000000000000000000000000 +$ @kbd{gawk -M 'BEGIN @{ PREC = 113; printf("%0.25f\n", "0.1") @}'} +@print{} 0.1000000000000000000000000 +$ @kbd{gawk -M 'BEGIN @{ PREC = 113; printf("%0.25f\n", 1/10) @}'} +@print{} 0.1000000000000000000000000 +@end example + +@node Setting the rounding mode +@subsection Setting the Rounding Mode + +The @code{ROUNDMODE} variable provides +program level control over the rounding mode. +The correspondence between @code{ROUNDMODE} and the IEEE +rounding modes is shown in @ref{table-gawk-rounding-modes}. + +@float Table,table-gawk-rounding-modes +@caption{@command{gawk} rounding modes} +@multitable @columnfractions .45 .30 .25 +@headitem Rounding Mode @tab IEEE Name @tab @code{ROUNDMODE} +@item Round to nearest, ties to even @tab @code{roundTiesToEven} @tab @code{"N"} or @code{"n"} +@item Round toward plus Infinity @tab @code{roundTowardPositive} @tab @code{"U"} or @code{"u"} +@item Round toward negative Infinity @tab @code{roundTowardNegative} @tab @code{"D"} or @code{"d"} +@item Round toward zero @tab @code{roundTowardZero} @tab @code{"Z"} or @code{"z"} +@item Round to nearest, ties away from zero @tab @code{roundTiesToAway} @tab @code{"A"} or @code{"a"} +@end multitable +@end float + +@code{ROUNDMODE} has the default value @code{"N"}, which +selects the IEEE 754 rounding mode @code{roundTiesToEven}. +In @ref{table-gawk-rounding-modes}, the value @code{"A"} selects +@code{roundTiesToAway}. This is only available if your version of the +MPFR library supports it; otherwise, setting @code{ROUNDMODE} to @code{"A"} +has no effect. + +The default mode @code{roundTiesToEven} is the most preferred, +but the least intuitive. This method does the obvious thing for most values, +by rounding them up or down to the nearest digit. +For example, rounding 1.132 to two digits yields 1.13, +and rounding 1.157 yields 1.16. + +However, when it comes to rounding a value that is exactly halfway between, +things do not work the way you probably learned in school. +In this case, the number is rounded to the nearest even digit. +So rounding 0.125 to two digits rounds down to 0.12, +but rounding 0.6875 to three digits rounds up to 0.688. +You probably have already encountered this rounding mode when +using @code{printf} to format floating-point numbers. +For example: + +@example +BEGIN @{ + x = -4.5 + for (i = 1; i < 10; i++) @{ + x += 1.0 + printf("%4.1f => %2.0f\n", x, x) + @} +@} +@end example + +@noindent +produces the following output when run on the author's system:@footnote{It +is possible for the output to be completely different if the +C library in your system does not use the IEEE 754 even-rounding +rule to round halfway cases for @code{printf}.} + +@example +-3.5 => -4 +-2.5 => -2 +-1.5 => -2 +-0.5 => 0 + 0.5 => 0 + 1.5 => 2 + 2.5 => 2 + 3.5 => 4 + 4.5 => 4 +@end example + +The theory behind @code{roundTiesToEven} is that it more or less evenly +distributes upward and downward rounds of exact halves, which might +cause any accumulating round-off error to cancel itself out. This is the +default rounding mode for IEEE 754 computing functions and operators. + +The other rounding modes are rarely used. Round toward positive infinity +(@code{roundTowardPositive}) and round toward negative infinity +(@code{roundTowardNegative}) are often used to implement interval +arithmetic, where you adjust the rounding mode to calculate upper and +lower bounds for the range of output. The @code{roundTowardZero} mode can +be used for converting floating-point numbers to integers. The rounding +mode @code{roundTiesToAway} rounds the result to the nearest number and +selects the number with the larger magnitude if a tie occurs. + +Some numerical analysts will tell you that your choice of rounding +style has tremendous impact on the final outcome, and advise you to +wait until final output for any rounding. Instead, you can often avoid +round-off error problems by setting the precision initially to some +value sufficiently larger than the final desired precision, so that +the accumulation of round-off error does not influence the outcome. +If you suspect that results from your computation are sensitive to +accumulation of round-off error, look for a significant difference in +output when you change the rounding mode to be sure. + +@node Arbitrary Precision Integers +@section Arbitrary-Precision Integer Arithmetic with @command{gawk} +@cindex integers, arbitrary precision +@cindex arbitrary precision integers + +When given the @option{-M} option, +@command{gawk} performs all integer arithmetic using GMP arbitrary-precision +integers. Any number that looks like an integer in a source +or @value{DF} is stored as an arbitrary-precision integer. The size +of the integer is limited only by the available memory. For example, +the following computes +@iftex +@math{5^{4^{3^{2}}}}, +@end iftex +@ifnottex +@ifnotdocbook +5^4^3^2, +@end ifnotdocbook +@end ifnottex +@docbook +5<superscript>4<superscript>3<superscript>2</superscript></superscript></superscript>, @c +@end docbook +the result of which is beyond the +limits of ordinary hardware double-precision floating-point values: + +@example +$ @kbd{gawk -M 'BEGIN @{} +> @kbd{x = 5^4^3^2} +> @kbd{print "number of digits =", length(x)} +> @kbd{print substr(x, 1, 20), "...", substr(x, length(x) - 19, 20)} +> @kbd{@}'} +@print{} number of digits = 183231 +@print{} 62060698786608744707 ... 92256259918212890625 +@end example + +If instead you were to compute the same value using arbitrary-precision +floating-point values, the precision needed for correct output (using +the formula +@iftex +@math{prec = 3.322 @cdot dps}), +would be @math{3.322 @cdot 183231}, +@end iftex +@ifnottex +@ifnotdocbook +@samp{prec = 3.322 * dps}), +would be 3.322 x 183231, +@end ifnotdocbook +@end ifnottex +@docbook +<emphasis>prec</emphasis> = 3.322 ⋅ <emphasis>dps</emphasis>), +would be +<emphasis>prec</emphasis> = 3.322 ⋅ 183231, @c +@end docbook +or 608693. + +The result from an arithmetic operation with an integer and a floating-point value +is a floating-point value with a precision equal to the working precision. +The following program calculates the eighth term in +Sylvester's sequence@footnote{Weisstein, Eric W. +@cite{Sylvester's Sequence}. From MathWorld---A Wolfram Web Resource +@w{(@url{http://mathworld.wolfram.com/SylvestersSequence.html}).}} +using a recurrence: + +@example +$ @kbd{gawk -M 'BEGIN @{} +> @kbd{s = 2.0} +> @kbd{for (i = 1; i <= 7; i++)} +> @kbd{s = s * (s - 1) + 1} +> @kbd{print s} +> @kbd{@}'} +@print{} 113423713055421845118910464 +@end example + +The output differs from the actual number, 113,423,713,055,421,844,361,000,443, +because the default precision of 53 bits is not enough to represent the +floating-point results exactly. You can either increase the precision +(100 bits is enough in this case), or replace the floating-point constant +@samp{2.0} with an integer, to perform all computations using integer +arithmetic to get the correct output. + +Sometimes @command{gawk} must implicitly convert an arbitrary-precision +integer into an arbitrary-precision floating-point value. This is +primarily because the MPFR library does not always provide the relevant +interface to process arbitrary-precision integers or mixed-mode numbers +as needed by an operation or function. In such a case, the precision is +set to the minimum value necessary for exact conversion, and the working +precision is not used for this purpose. If this is not what you need or +want, you can employ a subterfuge, and convert the integer to floating +point first, like this: + +@example +gawk -M 'BEGIN @{ n = 13; print (n + 0.0) % 2.0 @}' +@end example + +You can avoid this issue altogether by specifying the number as a floating-point value +to begin with: + +@example +gawk -M 'BEGIN @{ n = 13.0; print n % 2.0 @}' +@end example + +Note that for this particular example, it is likely best +to just use the following: + +@example +gawk -M 'BEGIN @{ n = 13; print n % 2 @}' +@end example + +When dividing two arbitrary precision integers with either +@samp{/} or @samp{%}, the result is typically an arbitrary +precision floating point value (unless the denominator evenly +divides into the numerator). In order to do integer division +or remainder with arbitrary precision integers, use the built-in +@code{div()} function (@pxref{Numeric Functions}). + +You can simulate the @code{div()} function in standard @command{awk} +using this user-defined function: + +@example +@c file eg/lib/div.awk +# div --- do integer division + +@c endfile +@ignore +@c file eg/lib/div.awk +# +# Arnold Robbins, arnold@@skeeve.com, Public Domain +# July, 2014 + +@c endfile + +@end ignore +@c file eg/lib/div.awk +function div(numerator, denominator, result) +@{ + split("", result) + + numerator = int(numerator) + denominator = int(denominator) + result["quotient"] = int(numerator / denominator) + result["remainder"] = int(numerator % denominator) + + return 0.0 +@} +@c endfile +@end example + +The following example program, contributed by Katie Wasserman, +uses @code{div()} to +compute the digits of @value{PI} to as many places as you +choose to set: + +@example +@c file eg/prog/pi.awk +# pi.awk --- compute the digits of pi +@c endfile +@c endfile +@ignore +@c file eg/prog/pi.awk +# +# Katie Wasserman, katie@@wass.net +# August 2014 +@c endfile +@end ignore +@c file eg/prog/pi.awk + +BEGIN @{ + digits = 100000 + two = 2 * 10 ^ digits + pi = two + for (m = digits * 4; m > 0; --m) @{ + d = m * 2 + 1 + x = pi * m + div(x, d, result) + pi = result["quotient"] + pi = pi + two + @} + print pi +@} +@c endfile +@end example + +@ignore +Date: Wed, 20 Aug 2014 10:19:11 -0400 +To: arnold@skeeve.com +From: Katherine Wasserman <katie@wass.net> +Subject: Re: computation of digits of pi? + +Arnold, + +>The program that you sent to compute the digits of pi using div(). Is +>that some standard algorithm that every math student knows? If so, +>what's it called? + +It's not that well known but it's not that obscure either + +It's Euler's modification to Newton's method for calculating pi. + +Take a look at lines (23) - (25) here: http://mathworld.wolfram.com/PiFormulas.htm + +The algorithm I wrote simply expands the multiply by 2 and works from the innermost expression outwards. I used this to program HP calculators because it's quite easy to modify for tiny memory devices with smallish word sizes. + +http://www.hpmuseum.org/cgi-sys/cgiwrap/hpmuseum/articles.cgi?read=899 + +-Katie +@end ignore + +When asked about the algorithm used, Katie replied: + +@quotation +It's not that well known but it's not that obscure either. +It's Euler's modification to Newton's method for calculating pi. +Take a look at lines (23) - (25) here: @uref{http://mathworld.wolfram.com/PiFormulas.htm}. + +The algorithm I wrote simply expands the multiply by 2 and works from +the innermost expression outwards. I used this to program HP calculators +because it's quite easy to modify for tiny memory devices with smallish +word sizes. See +@uref{http://www.hpmuseum.org/cgi-sys/cgiwrap/hpmuseum/articles.cgi?read=899}. +@end quotation + +@node POSIX Floating Point Problems +@section Standards Versus Existing Practice + +Historically, @command{awk} has converted any non-numeric looking string +to the numeric value zero, when required. Furthermore, the original +definition of the language and the original POSIX standards specified that +@command{awk} only understands decimal numbers (base 10), and not octal +(base 8) or hexadecimal numbers (base 16). + +Changes in the language of the +2001 and 2004 POSIX standards can be interpreted to imply that @command{awk} +should support additional features. These features are: + +@itemize @value{BULLET} @item -@ref{Language History}. +Interpretation of floating-point data values specified in hexadecimal +notation (e.g., @code{0xDEADBEEF}). (Note: data values, @emph{not} +source code constants.) @item -@ref{Installation}. +Support for the special IEEE 754 floating-point values ``Not A Number'' +(NaN), positive Infinity (``inf''), and negative Infinity (``@minus{}inf''). +In particular, the format for these values is as specified by the ISO 1999 +C standard, which ignores case and can allow implementation-dependent additional +characters after the @samp{nan} and allow either @samp{inf} or @samp{infinity}. +@end itemize +The first problem is that both of these are clear changes to historical +practice: + +@itemize @value{BULLET} @item -@ref{Notes}. +The @command{gawk} maintainer feels that supporting hexadecimal +floating-point values, in particular, is ugly, and was never intended by the +original designers to be part of the language. @item -@ref{Basic Concepts}. +Allowing completely alphabetic strings to have valid numeric +values is also a very severe departure from historical practice. +@end itemize + +The second problem is that the @code{gawk} maintainer feels that this +interpretation of the standard, which requires a certain amount of +``language lawyering'' to arrive at in the first place, was not even +intended by the standard developers. In other words, ``we see how you +got where you are, but we don't think that that's where you want to be.'' + +Recognizing these issues, but attempting to provide compatibility +with the earlier versions of the standard, +the 2008 POSIX standard added explicit wording to allow, but not require, +that @command{awk} support hexadecimal floating-point values and +special values for ``Not A Number'' and infinity. +Although the @command{gawk} maintainer continues to feel that +providing those features is inadvisable, +nevertheless, on systems that support IEEE floating point, it seems +reasonable to provide @emph{some} way to support NaN and Infinity values. +The solution implemented in @command{gawk} is as follows: + +@itemize @value{BULLET} @item -@ref{Glossary}. +With the @option{--posix} command-line option, @command{gawk} becomes +``hands off.'' String values are passed directly to the system library's +@code{strtod()} function, and if it successfully returns a numeric value, +that is what's used.@footnote{You asked for it, you got it.} +By definition, the results are not portable across +different systems. They are also a little surprising: + +@example +$ @kbd{echo nanny | gawk --posix '@{ print $1 + 0 @}'} +@print{} nan +$ @kbd{echo 0xDeadBeef | gawk --posix '@{ print $1 + 0 @}'} +@print{} 3735928559 +@end example @item -@ref{Copying}. +Without @option{--posix}, @command{gawk} interprets the four strings +@samp{+inf}, +@samp{-inf}, +@samp{+nan}, +and +@samp{-nan} +specially, producing the corresponding special numeric values. +The leading sign acts a signal to @command{gawk} (and the user) +that the value is really numeric. Hexadecimal floating point is +not supported (unless you also use @option{--non-decimal-data}, +which is @emph{not} recommended). For example: + +@example +$ @kbd{echo nanny | gawk '@{ print $1 + 0 @}'} +@print{} 0 +$ @kbd{echo +nan | gawk '@{ print $1 + 0 @}'} +@print{} nan +$ @kbd{echo 0xDeadBeef | gawk '@{ print $1 + 0 @}'} +@print{} 0 +@end example + +@command{gawk} ignores case in the four special values. +Thus @samp{+nan} and @samp{+NaN} are the same. +@end itemize +@node Floating point summary +@section Summary + +@itemize @value{BULLET} +@item +Most computer arithmetic is done using either integers or floating-point +values. Standard @command{awk} uses double-precision +floating-point values. + +@item +In the early 1990s, Barbie mistakenly said ``Math class is tough!'' +Although math isn't tough, floating-point arithmetic isn't the same +as pencil and paper math, and care must be taken: + +@c nested list +@itemize @value{MINUS} @item -@ref{GNU Free Documentation License}. +Not all numbers can be represented exactly. + +@item +Comparing values should use a delta, instead of being done directly +with @samp{==} and @samp{!=}. + +@item +Errors accumulate. + +@item +Operations are not always truly associative or distributive. @end itemize -@page -@evenheading @thispage@ @ @ @strong{@value{TITLE}} @| @| -@oddheading @| @| @strong{@thischapter}@ @ @ @thispage -@end iftex +@item +Increasing the accuracy can help, but it is not a panacea. + +@item +Often, increasing the accuracy and then rounding to the desired +number of digits produces reasonable results. + +@item +Use @option{-M} (or @option{--bignum}) to enable MPFR +arithmetic. Use @code{PREC} to set the precision in bits, and +@code{ROUNDMODE} to set the IEEE 754 rounding mode. + +@item +With @option{-M}, @command{gawk} performs +arbitrary-precision integer arithmetic using the GMP library. +This is faster and more space efficient than using MPFR for +the same calculations. + +@item +There are several ``dark corners'' with respect to floating-point +numbers where @command{gawk} disagrees with the POSIX standard. +It pays to be aware of them. + +@item +Overall, there is no need to be unduly suspicious about the results from +floating-point arithmetic. The lesson to remember is that floating-point +arithmetic is always more complex than arithmetic using pencil and +paper. In order to take advantage of the power of computer floating point, +you need to know its limitations and work within them. For most casual +use of floating-point arithmetic, you will often get the expected result +if you simply round the display of your final results to the correct number +of significant decimal digits. + +@item +As general advice, avoid presenting numerical data in a manner that +implies better precision than is actually the case. + +@end itemize + +@node Dynamic Extensions +@chapter Writing Extensions for @command{gawk} +@cindex dynamically loaded extensions + +It is possible to add new functions written in C or C++ to @command{gawk} using +dynamically loaded libraries. This facility is available on systems +that support the C @code{dlopen()} and @code{dlsym()} +functions. This @value{CHAPTER} describes how to create extensions +using code written in C or C++. + +If you don't know anything about C programming, you can safely skip this +@value{CHAPTER}, although you may wish to review the documentation on the +extensions that come with @command{gawk} (@pxref{Extension Samples}), +and the information on the @code{gawkextlib} project (@pxref{gawkextlib}). +The sample extensions are automatically built and installed when +@command{gawk} is. + +@quotation NOTE +When @option{--sandbox} is specified, extensions are disabled +(@pxref{Options}). +@end quotation + +@menu +* Extension Intro:: What is an extension. +* Plugin License:: A note about licensing. +* Extension Mechanism Outline:: An outline of how it works. +* Extension API Description:: A full description of the API. +* Finding Extensions:: How @command{gawk} finds compiled extensions. +* Extension Example:: Example C code for an extension. +* Extension Samples:: The sample extensions that ship with + @code{gawk}. +* gawkextlib:: The @code{gawkextlib} project. +* Extension summary:: Extension summary. +* Extension Exercises:: Exercises. +@end menu + +@node Extension Intro +@section Introduction + +@cindex plug-in +An @dfn{extension} (sometimes called a @dfn{plug-in}) is a piece of +external compiled code that @command{gawk} can load at runtime to +provide additional functionality, over and above the built-in capabilities +described in the rest of this @value{DOCUMENT}. + +Extensions are useful because they allow you (of course) to extend +@command{gawk}'s functionality. For example, they can provide access to +system calls (such as @code{chdir()} to change directory) and to other +C library routines that could be of use. As with most software, +``the sky is the limit;'' if you can imagine something that you might +want to do and can write in C or C++, you can write an extension to do it! + +Extensions are written in C or C++, using the @dfn{application programming +interface} (API) defined for this purpose by the @command{gawk} +developers. The rest of this @value{CHAPTER} explains +the facilities that the API provides and how to use +them, and presents a small example extension. In addition, it documents +the sample extensions included in the @command{gawk} distribution, +and describes the @code{gawkextlib} project. +@ifclear FOR_PRINT +@xref{Extension Design}, for a discussion of the extension mechanism +goals and design. +@end ifclear +@ifset FOR_PRINT +See @uref{http://www.gnu.org/software/gawk/manual/html_node/Extension-Design.html} +for a discussion of the extension mechanism +goals and design. +@end ifset + +@node Plugin License +@section Extension Licensing + +Every dynamic extension must be distributed under a license that is +compatible with the GNU GPL (@pxref{Copying}). + +In order for the extension to tell @command{gawk} that it is +properly licensed, the extension must define the global symbol +@code{plugin_is_GPL_compatible}. If this symbol does not exist, +@command{gawk} emits a fatal error and exits when it tries to load +your extension. + +The declared type of the symbol should be @code{int}. It does not need +to be in any allocated section, though. The code merely asserts that +the symbol exists in the global scope. Something like this is enough: + +@example +int plugin_is_GPL_compatible; +@end example + +@node Extension Mechanism Outline +@section How It Works at a High Level + +Communication between +@command{gawk} and an extension is two-way. First, when an extension +is loaded, @command{gawk} passes it a pointer to a @code{struct} whose fields are +function pointers. +@ifnotdocbook +This is shown in @ref{figure-load-extension}. +@end ifnotdocbook +@ifdocbook +This is shown in @inlineraw{docbook, <xref linkend="figure-load-extension"/>}. +@end ifdocbook + +@ifnotdocbook +@float Figure,figure-load-extension +@caption{Loading the extension} +@c FIXME: One day, it should not be necessary to have two cases, +@c but rather just the one without the "txt" final argument. +@c This applies to the other figures as well. +@ifinfo +@center @image{api-figure1, , , Loading the extension, txt} +@end ifinfo +@ifnotinfo +@center @image{api-figure1, , , Loading the extension} +@end ifnotinfo +@end float +@end ifnotdocbook + +@docbook +<figure id="figure-load-extension" float="0"> +<title>Loading the extension</title> +<mediaobject> +<imageobject role="web"><imagedata fileref="api-figure1.png" format="PNG"/></imageobject> +</mediaobject> +</figure> +@end docbook + +The extension can call functions inside @command{gawk} through these +function pointers, at runtime, without needing (link-time) access +to @command{gawk}'s symbols. One of these function pointers is to a +function for ``registering'' new functions. +@ifnotdocbook +This is shown in @ref{figure-register-new-function}. +@end ifnotdocbook +@ifdocbook +This is shown in @inlineraw{docbook, <xref linkend="figure-register-new-function"/>}. +@end ifdocbook + +@ifnotdocbook +@float Figure,figure-register-new-function +@caption{Registering a new function} +@ifinfo +@center @image{api-figure2, , , Registering a new Function, txt} +@end ifinfo +@ifnotinfo +@center @image{api-figure2, , , Registering a new Function} +@end ifnotinfo +@end float +@end ifnotdocbook + +@docbook +<figure id="figure-register-new-function" float="0"> +<title>Registering a new function</title> +<mediaobject> +<imageobject role="web"><imagedata fileref="api-figure2.png" format="PNG"/></imageobject> +</mediaobject> +</figure> +@end docbook + +In the other direction, the extension registers its new functions +with @command{gawk} by passing function pointers to the functions that +provide the new feature (@code{do_chdir()}, for example). @command{gawk} +associates the function pointer with a name and can then call it, using a +defined calling convention. +@ifnotdocbook +This is shown in @ref{figure-call-new-function}. +@end ifnotdocbook +@ifdocbook +This is shown in @inlineraw{docbook, <xref linkend="figure-call-new-function"/>}. +@end ifdocbook + +@ifnotdocbook +@float Figure,figure-call-new-function +@caption{Calling the new function} +@ifinfo +@center @image{api-figure3, , , Calling the new function, txt} +@end ifinfo +@ifnotinfo +@center @image{api-figure3, , , Calling the new function} +@end ifnotinfo +@end float +@end ifnotdocbook + +@docbook +<figure id="figure-call-new-function" float="0"> +<title>Calling the new function</title> +<mediaobject> +<imageobject role="web"><imagedata fileref="api-figure3.png" format="PNG"/></imageobject> +</mediaobject> +</figure> +@end docbook + +The @code{do_@var{xxx}()} function, in turn, then uses the function +pointers in the API @code{struct} to do its work, such as updating +variables or arrays, printing messages, setting @code{ERRNO}, and so on. + +Convenience macros make calling through the function pointers look +like regular function calls so that extension code is quite readable +and understandable. + +Although all of this sounds somewhat complicated, the result is that +extension code is quite straightforward to write and to read. You can +see this in the sample extension @file{filefuncs.c} (@pxref{Extension +Example}) and also in the @file{testext.c} code for testing the APIs. + +Some other bits and pieces: + +@itemize @value{BULLET} +@item +The API provides access to @command{gawk}'s @code{do_@var{xxx}} values, +reflecting command-line options, like @code{do_lint}, @code{do_profiling} +and so on (@pxref{Extension API Variables}). +These are informational: an extension cannot affect their values +inside @command{gawk}. In addition, attempting to assign to them +produces a compile-time error. + +@item +The API also provides major and minor version numbers, so that an +extension can check if the @command{gawk} it is loaded with supports the +facilities it was compiled with. (Version mismatches ``shouldn't'' +happen, but we all know how @emph{that} goes.) +@DBXREF{Extension Versioning} for details. +@end itemize + +@node Extension API Description +@section API Description +@cindex extension API + +C or C++ code for an extension must include the header file +@file{gawkapi.h}, which declares the functions and defines the data +types used to communicate with @command{gawk}. +This (rather large) @value{SECTION} describes the API in detail. + +@menu +* Extension API Functions Introduction:: Introduction to the API functions. +* General Data Types:: The data types. +* Memory Allocation Functions:: Functions for allocating memory. +* Constructor Functions:: Functions for creating values. +* Registration Functions:: Functions to register things with + @command{gawk}. +* Printing Messages:: Functions for printing messages. +* Updating @code{ERRNO}:: Functions for updating @code{ERRNO}. +* Requesting Values:: How to get a value. +* Accessing Parameters:: Functions for accessing parameters. +* Symbol Table Access:: Functions for accessing global + variables. +* Array Manipulation:: Functions for working with arrays. +* Extension API Variables:: Variables provided by the API. +* Extension API Boilerplate:: Boilerplate code for using the API. +@end menu + +@node Extension API Functions Introduction +@subsection Introduction + +Access to facilities within @command{gawk} are made available +by calling through function pointers passed into your extension. + +API function pointers are provided for the following kinds of operations: + +@itemize @value{BULLET} +@item +Allocating, reallocating, and releasing memory. + +@item +Registration functions. You may register: + +@c nested list +@itemize @value{MINUS} +@item +Extension functions +@item +Exit callbacks +@item +A version string +@item +Input parsers +@item +Output wrappers +@item +Two-way processors +@end itemize + +All of these are discussed in detail, later in this @value{CHAPTER}. + +@item +Printing fatal, warning, and ``lint'' warning messages. + +@item +Updating @code{ERRNO}, or unsetting it. + +@item +Accessing parameters, including converting an undefined parameter into +an array. + +@item +Symbol table access: retrieving a global variable, creating one, +or changing one. + +@item +Creating and releasing cached values; this provides an +efficient way to use values for multiple variables and +can be a big performance win. + +@item +Manipulating arrays: + +@itemize @value{MINUS} +@item +Retrieving, adding, deleting, and modifying elements + +@item +Getting the count of elements in an array + +@item +Creating a new array + +@item +Clearing an array + +@item +Flattening an array for easy C style looping over all its indices and elements +@end itemize +@end itemize + +Some points about using the API: + +@itemize @value{BULLET} +@item +The following types, macros, and/or functions are referenced +in @file{gawkapi.h}. For correct use, you must therefore include the +corresponding standard header file @emph{before} including @file{gawkapi.h}: + +@multitable {@code{memset()}, @code{memcpy()}} {@code{<sys/types.h>}} +@headitem C Entity @tab Header File +@item @code{EOF} @tab @code{<stdio.h>} +@item Values for @code{errno} @tab @code{<errno.h>} +@item @code{FILE} @tab @code{<stdio.h>} +@item @code{NULL} @tab @code{<stddef.h>} +@item @code{memcpy()} @tab @code{<string.h>} +@item @code{memset()} @tab @code{<string.h>} +@item @code{size_t} @tab @code{<sys/types.h>} +@item @code{struct stat} @tab @code{<sys/stat.h>} +@end multitable + +Due to portability concerns, especially to systems that are not +fully standards-compliant, it is your responsibility +to include the correct files in the correct way. This requirement +is necessary in order to keep @file{gawkapi.h} clean, instead of becoming +a portability hodge-podge as can be seen in some parts of +the @command{gawk} source code. + +@item +The @file{gawkapi.h} file may be included more than once without ill effect. +Doing so, however, is poor coding practice. + +@item +Although the API only uses ISO C 90 features, there is an exception; the +``constructor'' functions use the @code{inline} keyword. If your compiler +does not support this keyword, you should either place +@samp{-Dinline=''} on your command line, or use the GNU Autotools and include a +@file{config.h} file in your extensions. + +@item +All pointers filled in by @command{gawk} point to memory +managed by @command{gawk} and should be treated by the extension as +read-only. Memory for @emph{all} strings passed into @command{gawk} +from the extension @emph{must} come from calling one of +@code{gawk_malloc()}, @code{gawk_calloc()} or @code{gawk_realloc()}, +and is managed by @command{gawk} from then on. + +@item +The API defines several simple @code{struct}s that map values as seen +from @command{awk}. A value can be a @code{double}, a string, or an +array (as in multidimensional arrays, or when creating a new array). +String values maintain both pointer and length, because embedded @sc{nul} +characters are allowed. + +@quotation NOTE +By intent, strings are maintained using the current multibyte encoding (as +defined by @env{LC_@var{xxx}} environment variables) and not using wide +characters. This matches how @command{gawk} stores strings internally +and also how characters are likely to be input and output from files. +@end quotation + +@item +When retrieving a value (such as a parameter or that of a global variable +or array element), the extension requests a specific type (number, string, +scalar, value cookie, array, or ``undefined''). When the request is +``undefined,'' the returned value will have the real underlying type. + +However, if the request and actual type don't match, the access function +returns ``false'' and fills in the type of the actual value that is there, +so that the extension can, e.g., print an error message +(such as ``scalar passed where array expected''). + +@c This is documented in the header file and needs some expanding upon. +@c The table there should be presented here +@end itemize + +You may call the API functions by using the function pointers +directly, but the interface is not so pretty. To make extension code look +more like regular code, the @file{gawkapi.h} header file defines several +macros that you should use in your code. This @value{SECTION} presents +the macros as if they were functions. + +@node General Data Types +@subsection General-Purpose Data Types + +@cindex Robbins, Arnold +@cindex Ramey, Chet +@quotation +@i{I have a true love/hate relationship with unions.} +@author Arnold Robbins +@end quotation + +@quotation +@i{That's the thing about unions: the compiler will arrange things so they +can accommodate both love and hate.} +@author Chet Ramey +@end quotation + +The extension API defines a number of simple types and structures for +general-purpose use. Additional, more specialized, data structures are +introduced in subsequent @value{SECTION}s, together with the functions +that use them. + +@table @code +@item typedef void *awk_ext_id_t; +A value of this type is received from @command{gawk} when an extension is loaded. +That value must then be passed back to @command{gawk} as the first parameter of +each API function. + +@item #define awk_const @dots{} +This macro expands to @samp{const} when compiling an extension, +and to nothing when compiling @command{gawk} itself. This makes +certain fields in the API data structures unwritable from extension code, +while allowing @command{gawk} to use them as it needs to. + +@item typedef enum awk_bool @{ +@itemx @ @ @ @ awk_false = 0, +@itemx @ @ @ @ awk_true +@itemx @} awk_bool_t; +A simple boolean type. + +@item typedef struct awk_string @{ +@itemx @ @ @ @ char *str;@ @ @ @ @ @ /* data */ +@itemx @ @ @ @ size_t len;@ @ @ @ @ /* length thereof, in chars */ +@itemx @} awk_string_t; +This represents a mutable string. @command{gawk} +owns the memory pointed to if it supplied +the value. Otherwise, it takes ownership of the memory pointed to. +@emph{Such memory must come from calling one of the +@code{gawk_malloc()}, @code{gawk_calloc()}, or +@code{gawk_realloc()} functions!} + +As mentioned earlier, strings are maintained using the current +multibyte encoding. + +@item typedef enum @{ +@itemx @ @ @ @ AWK_UNDEFINED, +@itemx @ @ @ @ AWK_NUMBER, +@itemx @ @ @ @ AWK_STRING, +@itemx @ @ @ @ AWK_ARRAY, +@itemx @ @ @ @ AWK_SCALAR,@ @ @ @ @ @ @ @ @ /* opaque access to a variable */ +@itemx @ @ @ @ AWK_VALUE_COOKIE@ @ @ @ /* for updating a previously created value */ +@itemx @} awk_valtype_t; +This @code{enum} indicates the type of a value. +It is used in the following @code{struct}. + +@item typedef struct awk_value @{ +@itemx @ @ @ @ awk_valtype_t val_type; +@itemx @ @ @ @ union @{ +@itemx @ @ @ @ @ @ @ @ awk_string_t@ @ @ @ @ @ @ s; +@itemx @ @ @ @ @ @ @ @ double@ @ @ @ @ @ @ @ @ @ @ @ @ d; +@itemx @ @ @ @ @ @ @ @ awk_array_t@ @ @ @ @ @ @ @ a; +@itemx @ @ @ @ @ @ @ @ awk_scalar_t@ @ @ @ @ @ @ scl; +@itemx @ @ @ @ @ @ @ @ awk_value_cookie_t@ vc; +@itemx @ @ @ @ @} u; +@itemx @} awk_value_t; +An ``@command{awk} value.'' +The @code{val_type} member indicates what kind of value the +@code{union} holds, and each member is of the appropriate type. + +@item #define str_value@ @ @ @ @ @ u.s +@itemx #define num_value@ @ @ @ @ @ u.d +@itemx #define array_cookie@ @ @ u.a +@itemx #define scalar_cookie@ @ u.scl +@itemx #define value_cookie@ @ @ u.vc +These macros make accessing the fields of the @code{awk_value_t} more +readable. + +@item typedef void *awk_scalar_t; +Scalars can be represented as an opaque type. These values are obtained +from @command{gawk} and then passed back into it. This is discussed +in a general fashion in the text following this list, and in more detail in +@ref{Symbol table by cookie}. + +@item typedef void *awk_value_cookie_t; +A ``value cookie'' is an opaque type representing a cached value. +This is also discussed in a general fashion in the text following this list, +and in more detail in @ref{Cached values}. + +@end table + +Scalar values in @command{awk} are either numbers or strings. The +@code{awk_value_t} struct represents values. The @code{val_type} member +indicates what is in the @code{union}. + +Representing numbers is easy---the API uses a C @code{double}. Strings +require more work. Because @command{gawk} allows embedded @sc{nul} bytes +in string values, a string must be represented as a pair containing a +data-pointer and length. This is the @code{awk_string_t} type. + +Identifiers (i.e., the names of global variables) can be associated +with either scalar values or with arrays. In addition, @command{gawk} +provides true arrays of arrays, where any given array element can +itself be an array. Discussion of arrays is delayed until +@ref{Array Manipulation}. + +The various macros listed earlier make it easier to use the elements +of the @code{union} as if they were fields in a @code{struct}; this +is a common coding practice in C. Such code is easier to write and to +read, but it remains @emph{your} responsibility to make sure that +the @code{val_type} member correctly reflects the type of the value in +the @code{awk_value_t}. + +Conceptually, the first three members of the @code{union} (number, string, +and array) are all that is needed for working with @command{awk} values. +However, because the API provides routines for accessing and changing +the value of global scalar variables only by using the variable's name, +there is a performance penalty: @command{gawk} must find the variable +each time it is accessed and changed. This turns out to be a real issue, +not just a theoretical one. + +Thus, if you know that your extension will spend considerable time +reading and/or changing the value of one or more scalar variables, you +can obtain a @dfn{scalar cookie}@footnote{See +@uref{http://catb.org/jargon/html/C/cookie.html, the ``cookie'' entry in the Jargon file} for a +definition of @dfn{cookie}, and @uref{http://catb.org/jargon/html/M/magic-cookie.html, +the ``magic cookie'' entry in the Jargon file} for a nice example. +@ifclear FOR_PRINT +See also the entry for ``Cookie'' in the @ref{Glossary}. +@end ifclear +} +object for that variable, and then use +the cookie for getting the variable's value or for changing the variable's +value. +This is the @code{awk_scalar_t} type and @code{scalar_cookie} macro. +Given a scalar cookie, @command{gawk} can directly retrieve or +modify the value, as required, without having to find it first. + +The @code{awk_value_cookie_t} type and @code{value_cookie} macro are similar. +If you know that you wish to +use the same numeric or string @emph{value} for one or more variables, +you can create the value once, retaining a @dfn{value cookie} for it, +and then pass in that value cookie whenever you wish to set the value of a +variable. This saves both storage space within the running @command{gawk} +process as well as the time needed to create the value. + +@node Memory Allocation Functions +@subsection Memory Allocation Functions and Convenience Macros +@cindex allocating memory for extensions +@cindex extensions, allocating memory + +The API provides a number of @dfn{memory allocation} functions for +allocating memory that can be passed to @command{gawk}, as well as a number of +convenience macros. +This @value{SUBSECTION} presents them all as function prototypes, in +the way that extension code would use them: + +@table @code +@item void *gawk_malloc(size_t size); +Call the correct version of @code{malloc()} to allocate storage that may +be passed to @command{gawk}. + +@item void *gawk_calloc(size_t nmemb, size_t size); +Call the correct version of @code{calloc()} to allocate storage that may +be passed to @command{gawk}. + +@item void *gawk_realloc(void *ptr, size_t size); +Call the correct version of @code{realloc()} to allocate storage that may +be passed to @command{gawk}. + +@item void gawk_free(void *ptr); +Call the correct version of @code{free()} to release storage that was +allocated with @code{gawk_malloc()}, @code{gawk_calloc()} or @code{gawk_realloc()}. +@end table + +The API has to provide these functions because it is possible +for an extension to be compiled and linked against a different +version of the C library than was used for the @command{gawk} +executable.@footnote{This is more common on MS-Windows systems, but +can happen on Unix-like systems as well.} If @command{gawk} were +to use its version of @code{free()} when the memory came from an +unrelated version of @code{malloc()}, unexpected behavior would +likely result. + +Two convenience macros may be used for allocating storage +from @code{gawk_malloc()} and +@code{gawk_realloc()}. If the allocation fails, they cause @command{gawk} +to exit with a fatal error message. They should be used as if they were +procedure calls that do not return a value. + +@table @code +@item #define emalloc(pointer, type, size, message) @dots{} +The arguments to this macro are as follows: + +@c nested table +@table @code +@item pointer +The pointer variable to point at the allocated storage. + +@item type +The type of the pointer variable. This is used to create a cast for +the call to @code{gawk_malloc()}. + +@item size +The total number of bytes to be allocated. + +@item message +A message to be prefixed to the fatal error message. Typically this is the name +of the function using the macro. +@end table + +@noindent +For example, you might allocate a string value like so: + +@example +awk_value_t result; +char *message; +const char greet[] = "Don't Panic!"; + +emalloc(message, char *, sizeof(greet), "myfunc"); +strcpy(message, greet); +make_malloced_string(message, strlen(message), & result); +@end example + +@item #define erealloc(pointer, type, size, message) @dots{} +This is like @code{emalloc()}, but it calls @code{gawk_realloc()}, +instead of @code{gawk_malloc()}. +The arguments are the same as for the @code{emalloc()} macro. +@end table + +@node Constructor Functions +@subsection Constructor Functions + +The API provides a number of @dfn{constructor} functions for creating +string and numeric values, as well as a number of convenience macros. +This @value{SUBSECTION} presents them all as function prototypes, in +the way that extension code would use them: + +@table @code +@item static inline awk_value_t * +@itemx make_const_string(const char *string, size_t length, awk_value_t *result) +This function creates a string value in the @code{awk_value_t} variable +pointed to by @code{result}. It expects @code{string} to be a C string constant +(or other string data), and automatically creates a @emph{copy} of the data +for storage in @code{result}. It returns @code{result}. + +@item static inline awk_value_t * +@itemx make_malloced_string(const char *string, size_t length, awk_value_t *result) +This function creates a string value in the @code{awk_value_t} variable +pointed to by @code{result}. It expects @code{string} to be a @samp{char *} +value pointing to data previously obtained from @code{gawk_malloc()}, @code{gawk_calloc()} or @code{gawk_realloc()}. The idea here +is that the data is passed directly to @command{gawk}, which assumes +responsibility for it. It returns @code{result}. + +@item static inline awk_value_t * +@itemx make_null_string(awk_value_t *result) +This specialized function creates a null string (the ``undefined'' value) +in the @code{awk_value_t} variable pointed to by @code{result}. +It returns @code{result}. + +@item static inline awk_value_t * +@itemx make_number(double num, awk_value_t *result) +This function simply creates a numeric value in the @code{awk_value_t} variable +pointed to by @code{result}. +@end table + +@node Registration Functions +@subsection Registration Functions +@cindex register extension +@cindex extension registration + +This @value{SECTION} describes the API functions for +registering parts of your extension with @command{gawk}. + +@menu +* Extension Functions:: Registering extension functions. +* Exit Callback Functions:: Registering an exit callback. +* Extension Version String:: Registering a version string. +* Input Parsers:: Registering an input parser. +* Output Wrappers:: Registering an output wrapper. +* Two-way processors:: Registering a two-way processor. +@end menu + +@node Extension Functions +@subsubsection Registering An Extension Function + +Extension functions are described by the following record: + +@example +typedef struct awk_ext_func @{ +@ @ @ @ const char *name; +@ @ @ @ awk_value_t *(*function)(int num_actual_args, awk_value_t *result); +@ @ @ @ size_t num_expected_args; +@} awk_ext_func_t; +@end example + +The fields are: + +@table @code +@item const char *name; +The name of the new function. +@command{awk} level code calls the function by this name. +This is a regular C string. + +Function names must obey the rules for @command{awk} +identifiers. That is, they must begin with either an English letter +or an underscore, which may be followed by any number of +letters, digits, and underscores. +Letter case in function names is significant. + +@item awk_value_t *(*function)(int num_actual_args, awk_value_t *result); +This is a pointer to the C function that provides the extension's +functionality. +The function must fill in @code{*result} with either a number +or a string. @command{gawk} takes ownership of any string memory. +As mentioned earlier, string memory @strong{must} come from one of +@code{gawk_malloc()}, @code{gawk_calloc()}, or @code{gawk_realloc()}. + +The @code{num_actual_args} argument tells the C function how many +actual parameters were passed from the calling @command{awk} code. + +The function must return the value of @code{result}. +This is for the convenience of the calling code inside @command{gawk}. + +@item size_t num_expected_args; +This is the number of arguments the function expects to receive. +Each extension function may decide what to do if the number of +arguments isn't what it expected. As with real @command{awk} functions, it +is likely OK to ignore extra arguments. +@end table + +Once you have a record representing your extension function, you register +it with @command{gawk} using this API function: + +@table @code +@item awk_bool_t add_ext_func(const char *namespace, const awk_ext_func_t *func); +This function returns true upon success, false otherwise. +The @code{namespace} parameter is currently not used; you should pass in an +empty string (@code{""}). The @code{func} pointer is the address of a +@code{struct} representing your function, as just described. +@end table + +@node Exit Callback Functions +@subsubsection Registering An Exit Callback Function + +An @dfn{exit callback} function is a function that +@command{gawk} calls before it exits. +Such functions are useful if you have general ``cleanup'' tasks +that should be performed in your extension (such as closing database +connections or other resource deallocations). +You can register such +a function with @command{gawk} using the following function: + +@table @code +@item void awk_atexit(void (*funcp)(void *data, int exit_status), +@itemx @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ void *arg0); +The parameters are: + +@c nested table +@table @code +@item funcp +A pointer to the function to be called before @command{gawk} exits. The @code{data} +parameter will be the original value of @code{arg0}. +The @code{exit_status} parameter is the exit status value that +@command{gawk} intends to pass to the @code{exit()} system call. + +@item arg0 +A pointer to private data which @command{gawk} saves in order to pass to +the function pointed to by @code{funcp}. +@end table +@end table + +Exit callback functions are called in last-in-first-out (LIFO) +order---that is, in the reverse order in which they are registered with +@command{gawk}. + +@node Extension Version String +@subsubsection Registering An Extension Version String + +You can register a version string which indicates the name and +version of your extension, with @command{gawk}, as follows: + +@table @code +@item void register_ext_version(const char *version); +Register the string pointed to by @code{version} with @command{gawk}. +Note that @command{gawk} does @emph{not} copy the @code{version} string, so +it should not be changed. +@end table + +@command{gawk} prints all registered extension version strings when it +is invoked with the @option{--version} option. + +@node Input Parsers +@subsubsection Customized Input Parsers +@cindex customized input parser + +By default, @command{gawk} reads text files as its input. It uses the value +of @code{RS} to find the end of the record, and then uses @code{FS} +(or @code{FIELDWIDTHS} or @code{FPAT}) to split it into fields (@pxref{Reading Files}). +Additionally, it sets the value of @code{RT} (@pxref{Built-in Variables}). + +If you want, you can provide your own custom input parser. An input +parser's job is to return a record to the @command{gawk} record processing +code, along with indicators for the value and length of the data to be +used for @code{RT}, if any. + +To provide an input parser, you must first provide two functions +(where @var{XXX} is a prefix name for your extension): + +@table @code +@item awk_bool_t @var{XXX}_can_take_file(const awk_input_buf_t *iobuf); +This function examines the information available in @code{iobuf} +(which we discuss shortly). Based on the information there, it +decides if the input parser should be used for this file. +If so, it should return true. Otherwise, it should return false. +It should not change any state (variable values, etc.) within @command{gawk}. + +@item awk_bool_t @var{XXX}_take_control_of(awk_input_buf_t *iobuf); +When @command{gawk} decides to hand control of the file over to the +input parser, it calls this function. This function in turn must fill +in certain fields in the @code{awk_input_buf_t} structure, and ensure +that certain conditions are true. It should then return true. If an +error of some kind occurs, it should not fill in any fields, and should +return false; then @command{gawk} will not use the input parser. +The details are presented shortly. +@end table + +Your extension should package these functions inside an +@code{awk_input_parser_t}, which looks like this: + +@example +typedef struct awk_input_parser @{ + const char *name; /* name of parser */ + awk_bool_t (*can_take_file)(const awk_input_buf_t *iobuf); + awk_bool_t (*take_control_of)(awk_input_buf_t *iobuf); + awk_const struct awk_input_parser *awk_const next; /* for gawk */ +@} awk_input_parser_t; +@end example + +The fields are: + +@table @code +@item const char *name; +The name of the input parser. This is a regular C string. + +@item awk_bool_t (*can_take_file)(const awk_input_buf_t *iobuf); +A pointer to your @code{@var{XXX}_can_take_file()} function. + +@item awk_bool_t (*take_control_of)(awk_input_buf_t *iobuf); +A pointer to your @code{@var{XXX}_take_control_of()} function. + +@item awk_const struct input_parser *awk_const next; +This is for use by @command{gawk}; +therefore it is marked @code{awk_const} so that the extension cannot +modify it. +@end table + +The steps are as follows: + +@enumerate +@item +Create a @code{static awk_input_parser_t} variable and initialize it +appropriately. + +@item +When your extension is loaded, register your input parser with +@command{gawk} using the @code{register_input_parser()} API function +(described next). +@end enumerate + +An @code{awk_input_buf_t} looks like this: + +@example +typedef struct awk_input @{ + const char *name; /* filename */ + int fd; /* file descriptor */ +#define INVALID_HANDLE (-1) + void *opaque; /* private data for input parsers */ + int (*get_record)(char **out, struct awk_input *iobuf, + int *errcode, char **rt_start, size_t *rt_len); + ssize_t (*read_func)(); + void (*close_func)(struct awk_input *iobuf); + struct stat sbuf; /* stat buf */ +@} awk_input_buf_t; +@end example + +The fields can be divided into two categories: those for use (initially, +at least) by @code{@var{XXX}_can_take_file()}, and those for use by +@code{@var{XXX}_take_control_of()}. The first group of fields and their uses +are as follows: + +@table @code +@item const char *name; +The name of the file. + +@item int fd; +A file descriptor for the file. If @command{gawk} was able to +open the file, then @code{fd} will @emph{not} be equal to +@code{INVALID_HANDLE}. Otherwise, it will. + +@item struct stat sbuf; +If the file descriptor is valid, then @command{gawk} will have filled +in this structure via a call to the @code{fstat()} system call. +@end table + +The @code{@var{XXX}_can_take_file()} function should examine these +fields and decide if the input parser should be used for the file. +The decision can be made based upon @command{gawk} state (the value +of a variable defined previously by the extension and set by +@command{awk} code), the name of the +file, whether or not the file descriptor is valid, the information +in the @code{struct stat}, or any combination of these factors. + +Once @code{@var{XXX}_can_take_file()} has returned true, and +@command{gawk} has decided to use your input parser, it calls +@code{@var{XXX}_take_control_of()}. That function then fills one of +either the @code{get_record} field or the @code{read_func} field in +the @code{awk_input_buf_t}. It must also ensure that @code{fd} is @emph{not} +set to @code{INVALID_HANDLE}. The following list describes the fields that +may be filled by @code{@var{XXX}_take_control_of()}: + +@table @code +@item void *opaque; +This is used to hold any state information needed by the input parser +for this file. It is ``opaque'' to @command{gawk}. The input parser +is not required to use this pointer. + +@item int@ (*get_record)(char@ **out, +@itemx @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ struct@ awk_input *iobuf, +@itemx @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ int *errcode, +@itemx @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ char **rt_start, +@itemx @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ size_t *rt_len); +This function pointer should point to a function that creates the input +records. Said function is the core of the input parser. Its behavior +is described in the text following this list. + +@item ssize_t (*read_func)(); +This function pointer should point to function that has the +same behavior as the standard POSIX @code{read()} system call. +It is an alternative to the @code{get_record} pointer. Its behavior +is also described in the text following this list. + +@item void (*close_func)(struct awk_input *iobuf); +This function pointer should point to a function that does +the ``tear down.'' It should release any resources allocated by +@code{@var{XXX}_take_control_of()}. It may also close the file. If it +does so, it should set the @code{fd} field to @code{INVALID_HANDLE}. + +If @code{fd} is still not @code{INVALID_HANDLE} after the call to this +function, @command{gawk} calls the regular @code{close()} system call. + +Having a ``tear down'' function is optional. If your input parser does +not need it, do not set this field. Then, @command{gawk} calls the +regular @code{close()} system call on the file descriptor, so it should +be valid. +@end table + +The @code{@var{XXX}_get_record()} function does the work of creating +input records. The parameters are as follows: + +@table @code +@item char **out +This is a pointer to a @code{char *} variable which is set to point +to the record. @command{gawk} makes its own copy of the data, so +the extension must manage this storage. + +@item struct awk_input *iobuf +This is the @code{awk_input_buf_t} for the file. The fields should be +used for reading data (@code{fd}) and for managing private state +(@code{opaque}), if any. + +@item int *errcode +If an error occurs, @code{*errcode} should be set to an appropriate +code from @code{<errno.h>}. + +@item char **rt_start +@itemx size_t *rt_len +If the concept of a ``record terminator'' makes sense, then +@code{*rt_start} should be set to point to the data to be used for +@code{RT}, and @code{*rt_len} should be set to the length of the +data. Otherwise, @code{*rt_len} should be set to zero. +@code{gawk} makes its own copy of this data, so the +extension must manage this storage. +@end table + +The return value is the length of the buffer pointed to by +@code{*out}, or @code{EOF} if end-of-file was reached or an +error occurred. + +It is guaranteed that @code{errcode} is a valid pointer, so there is no +need to test for a @code{NULL} value. @command{gawk} sets @code{*errcode} +to zero, so there is no need to set it unless an error occurs. + +If an error does occur, the function should return @code{EOF} and set +@code{*errcode} to a value greater than zero. In that case, if @code{*errcode} +does not equal zero, @command{gawk} automatically updates +the @code{ERRNO} variable based on the value of @code{*errcode}. +(In general, setting @samp{*errcode = errno} should do the right thing.) + +As an alternative to supplying a function that returns an input record, +you may instead supply a function that simply reads bytes, and let +@command{gawk} parse the data into records. If you do so, the data +should be returned in the multibyte encoding of the current locale. +Such a function should follow the same behavior as the @code{read()} +system call, and you fill in the @code{read_func} pointer with its +address in the @code{awk_input_buf_t} structure. + +By default, @command{gawk} sets the @code{read_func} pointer to +point to the @code{read()} system call. So your extension need not +set this field explicitly. + +@quotation NOTE +You must choose one method or the other: either a function that +returns a record, or one that returns raw data. In particular, +if you supply a function to get a record, @command{gawk} will +call it, and never call the raw read function. +@end quotation + +@command{gawk} ships with a sample extension that reads directories, +returning records for each entry in the directory (@pxref{Extension +Sample Readdir}). You may wish to use that code as a guide for writing +your own input parser. + +When writing an input parser, you should think about (and document) +how it is expected to interact with @command{awk} code. You may want +it to always be called, and take effect as appropriate (as the +@code{readdir} extension does). Or you may want it to take effect +based upon the value of an @code{awk} variable, as the XML extension +from the @code{gawkextlib} project does (@pxref{gawkextlib}). +In the latter case, code in a @code{BEGINFILE} section +can look at @code{FILENAME} and @code{ERRNO} to decide whether or +not to activate an input parser (@pxref{BEGINFILE/ENDFILE}). + +You register your input parser with the following function: + +@table @code +@item void register_input_parser(awk_input_parser_t *input_parser); +Register the input parser pointed to by @code{input_parser} with +@command{gawk}. +@end table + +@node Output Wrappers +@subsubsection Customized Output Wrappers +@cindex customized output wrapper + +@cindex output wrapper +An @dfn{output wrapper} is the mirror image of an input parser. +It allows an extension to take over the output to a file opened +with the @samp{>} or @samp{>>} I/O redirection operators (@pxref{Redirection}). + +The output wrapper is very similar to the input parser structure: + +@example +typedef struct awk_output_wrapper @{ + const char *name; /* name of the wrapper */ + awk_bool_t (*can_take_file)(const awk_output_buf_t *outbuf); + awk_bool_t (*take_control_of)(awk_output_buf_t *outbuf); + awk_const struct awk_output_wrapper *awk_const next; /* for gawk */ +@} awk_output_wrapper_t; +@end example + +The members are as follows: + +@table @code +@item const char *name; +This is the name of the output wrapper. + +@item awk_bool_t (*can_take_file)(const awk_output_buf_t *outbuf); +This points to a function that examines the information in +the @code{awk_output_buf_t} structure pointed to by @code{outbuf}. +It should return true if the output wrapper wants to take over the +file, and false otherwise. It should not change any state (variable +values, etc.) within @command{gawk}. + +@item awk_bool_t (*take_control_of)(awk_output_buf_t *outbuf); +The function pointed to by this field is called when @command{gawk} +decides to let the output wrapper take control of the file. It should +fill in appropriate members of the @code{awk_output_buf_t} structure, +as described next, and return true if successful, false otherwise. + +@item awk_const struct output_wrapper *awk_const next; +This is for use by @command{gawk}; +therefore it is marked @code{awk_const} so that the extension cannot +modify it. +@end table + +The @code{awk_output_buf_t} structure looks like this: + +@example +typedef struct awk_output_buf @{ + const char *name; /* name of output file */ + const char *mode; /* mode argument to fopen */ + FILE *fp; /* stdio file pointer */ + awk_bool_t redirected; /* true if a wrapper is active */ + void *opaque; /* for use by output wrapper */ + size_t (*gawk_fwrite)(const void *buf, size_t size, size_t count, + FILE *fp, void *opaque); + int (*gawk_fflush)(FILE *fp, void *opaque); + int (*gawk_ferror)(FILE *fp, void *opaque); + int (*gawk_fclose)(FILE *fp, void *opaque); +@} awk_output_buf_t; +@end example + +Here too, your extension will define @code{@var{XXX}_can_take_file()} +and @code{@var{XXX}_take_control_of()} functions that examine and update +data members in the @code{awk_output_buf_t}. +The data members are as follows: + +@table @code +@item const char *name; +The name of the output file. + +@item const char *mode; +The mode string (as would be used in the second argument to @code{fopen()}) +with which the file was opened. + +@item FILE *fp; +The @code{FILE} pointer from @code{<stdio.h>}. @command{gawk} opens the file +before attempting to find an output wrapper. + +@item awk_bool_t redirected; +This field must be set to true by the @code{@var{XXX}_take_control_of()} function. + +@item void *opaque; +This pointer is opaque to @command{gawk}. The extension should use it to store +a pointer to any private data associated with the file. + +@item size_t (*gawk_fwrite)(const void *buf, size_t size, size_t count, +@itemx @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ FILE *fp, void *opaque); +@itemx int (*gawk_fflush)(FILE *fp, void *opaque); +@itemx int (*gawk_ferror)(FILE *fp, void *opaque); +@itemx int (*gawk_fclose)(FILE *fp, void *opaque); +These pointers should be set to point to functions that perform +the equivalent function as the @code{<stdio.h>} functions do, if appropriate. +@command{gawk} uses these function pointers for all output. +@command{gawk} initializes the pointers to point to internal, ``pass through'' +functions that just call the regular @code{<stdio.h>} functions, so an +extension only needs to redefine those functions that are appropriate for +what it does. +@end table + +The @code{@var{XXX}_can_take_file()} function should make a decision based +upon the @code{name} and @code{mode} fields, and any additional state +(such as @command{awk} variable values) that is appropriate. + +When @command{gawk} calls @code{@var{XXX}_take_control_of()}, that function should fill +in the other fields, as appropriate, except for @code{fp}, which it should just +use normally. + +You register your output wrapper with the following function: + +@table @code +@item void register_output_wrapper(awk_output_wrapper_t *output_wrapper); +Register the output wrapper pointed to by @code{output_wrapper} with +@command{gawk}. +@end table + +@node Two-way processors +@subsubsection Customized Two-way Processors +@cindex customized two-way processor + +A @dfn{two-way processor} combines an input parser and an output wrapper for +two-way I/O with the @samp{|&} operator (@pxref{Redirection}). It makes identical +use of the @code{awk_input_parser_t} and @code{awk_output_buf_t} structures +as described earlier. + +A two-way processor is represented by the following structure: + +@example +typedef struct awk_two_way_processor @{ + const char *name; /* name of the two-way processor */ + awk_bool_t (*can_take_two_way)(const char *name); + awk_bool_t (*take_control_of)(const char *name, + awk_input_buf_t *inbuf, + awk_output_buf_t *outbuf); + awk_const struct awk_two_way_processor *awk_const next; /* for gawk */ +@} awk_two_way_processor_t; +@end example + +The fields are as follows: + +@table @code +@item const char *name; +The name of the two-way processor. + +@item awk_bool_t (*can_take_two_way)(const char *name); +This function returns true if it wants to take over two-way I/O for this @value{FN}. +It should not change any state (variable +values, etc.) within @command{gawk}. + +@item awk_bool_t (*take_control_of)(const char *name, +@itemx @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ awk_input_buf_t *inbuf, +@itemx @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ awk_output_buf_t *outbuf); +This function should fill in the @code{awk_input_buf_t} and +@code{awk_outut_buf_t} structures pointed to by @code{inbuf} and +@code{outbuf}, respectively. These structures were described earlier. + +@item awk_const struct two_way_processor *awk_const next; +This is for use by @command{gawk}; +therefore it is marked @code{awk_const} so that the extension cannot +modify it. +@end table + +As with the input parser and output processor, you provide +``yes I can take this'' and ``take over for this'' functions, +@code{@var{XXX}_can_take_two_way()} and @code{@var{XXX}_take_control_of()}. + +You register your two-way processor with the following function: + +@table @code +@item void register_two_way_processor(awk_two_way_processor_t *two_way_processor); +Register the two-way processor pointed to by @code{two_way_processor} with +@command{gawk}. +@end table + +@node Printing Messages +@subsection Printing Messages +@cindex printing messages from extensions +@cindex messages from extensions + +You can print different kinds of warning messages from your +extension, as described here. Note that for these functions, +you must pass in the extension id received from @command{gawk} +when the extension was loaded:@footnote{Because the API uses only ISO C 90 +features, it cannot make use of the ISO C 99 variadic macro feature to hide +that parameter. More's the pity.} + +@table @code +@item void fatal(awk_ext_id_t id, const char *format, ...); +Print a message and then cause @command{gawk} to exit immediately. + +@item void warning(awk_ext_id_t id, const char *format, ...); +Print a warning message. + +@item void lintwarn(awk_ext_id_t id, const char *format, ...); +Print a ``lint warning.'' Normally this is the same as printing a +warning message, but if @command{gawk} was invoked with @samp{--lint=fatal}, +then lint warnings become fatal error messages. +@end table + +All of these functions are otherwise like the C @code{printf()} +family of functions, where the @code{format} parameter is a string +with literal characters and formatting codes intermixed. + +@node Updating @code{ERRNO} +@subsection Updating @code{ERRNO} + +The following functions allow you to update the @code{ERRNO} +variable: + +@table @code +@item void update_ERRNO_int(int errno_val); +Set @code{ERRNO} to the string equivalent of the error code +in @code{errno_val}. The value should be one of the defined +error codes in @code{<errno.h>}, and @command{gawk} turns it +into a (possibly translated) string using the C @code{strerror()} function. + +@item void update_ERRNO_string(const char *string); +Set @code{ERRNO} directly to the string value of @code{ERRNO}. +@command{gawk} makes a copy of the value of @code{string}. + +@item void unset_ERRNO(void); +Unset @code{ERRNO}. +@end table + +@node Requesting Values +@subsection Requesting Values + +All of the functions that return values from @command{gawk} +work in the same way. You pass in an @code{awk_valtype_t} value +to indicate what kind of value you expect. If the actual value +matches what you requested, the function returns true and fills +in the @code{awk_value_t} result. +Otherwise, the function returns false, and the @code{val_type} +member indicates the type of the actual value. You may then +print an error message, or reissue the request for the actual +value type, as appropriate. This behavior is summarized in +@ref{table-value-types-returned}. + +@float Table,table-value-types-returned +@caption{API value types returned} +@docbook +<informaltable> +<tgroup cols="6"> + <colspec colwidth="16.6*"/> + <colspec colwidth="16.6*"/> + <colspec colwidth="19.8*" colname="c3"/> + <colspec colwidth="15*" colname="c4"/> + <colspec colwidth="15*" colname="c5"/> + <colspec colwidth="16.6*" colname="c6"/> + <spanspec spanname="hspan" namest="c3" nameend="c6" align="center"/> + <thead> + <row><entry></entry><entry spanname="hspan"><para>Type of Actual Value</para></entry></row> + <row> + <entry></entry> + <entry></entry> + <entry><para>String</para></entry> + <entry><para>Number</para></entry> + <entry><para>Array</para></entry> + <entry><para>Undefined</para></entry> + </row> + </thead> + <tbody> + <row> + <entry></entry> + <entry><para><emphasis role="bold">String</emphasis></para></entry> + <entry><para>String</para></entry> + <entry><para>String</para></entry> + <entry><para>false</para></entry> + <entry><para>false</para></entry> + </row> + <row> + <entry></entry> + <entry><para><emphasis role="bold">Number</emphasis></para></entry> + <entry><para>Number if can be converted, else false</para></entry> + <entry><para>Number</para></entry> + <entry><para>false</para></entry> + <entry><para>false</para></entry> + </row> + <row> + <entry><para><emphasis role="bold">Type</emphasis></para></entry> + <entry><para><emphasis role="bold">Array</emphasis></para></entry> + <entry><para>false</para></entry> + <entry><para>false</para></entry> + <entry><para>Array</para></entry> + <entry><para>false</para></entry> + </row> + <row> + <entry><para><emphasis role="bold">Requested</emphasis></para></entry> + <entry><para><emphasis role="bold">Scalar</emphasis></para></entry> + <entry><para>Scalar</para></entry> + <entry><para>Scalar</para></entry> + <entry><para>false</para></entry> + <entry><para>false</para></entry> + </row> + <row> + <entry></entry> + <entry><para><emphasis role="bold">Undefined</emphasis></para></entry> + <entry><para>String</para></entry> + <entry><para>Number</para></entry> + <entry><para>Array</para></entry> + <entry><para>Undefined</para></entry> + </row> + <row> + <entry></entry> + <entry><para><emphasis role="bold">Value Cookie</emphasis></para></entry> + <entry><para>false</para></entry> + <entry><para>false</para></entry> + <entry><para>false</para> + </entry><entry><para>false</para></entry> + </row> + </tbody> +</tgroup> +</informaltable> +@end docbook + +@ifnotplaintext +@ifnotdocbook +@multitable @columnfractions .50 .50 +@headitem @tab Type of Actual Value +@end multitable +@c 10/2014: Thanks to Karl Berry for this bit to reduce the space: +@tex +\vglue-1.1\baselineskip +@end tex +@multitable @columnfractions .166 .166 .198 .15 .15 .166 +@headitem @tab @tab String @tab Number @tab Array @tab Undefined +@item @tab @b{String} @tab String @tab String @tab false @tab false +@item @tab @b{Number} @tab Number if can be converted, else false @tab Number @tab false @tab false +@item @b{Type} @tab @b{Array} @tab false @tab false @tab Array @tab false +@item @b{Requested} @tab @b{Scalar} @tab Scalar @tab Scalar @tab false @tab false +@item @tab @b{Undefined} @tab String @tab Number @tab Array @tab Undefined +@item @tab @b{Value Cookie} @tab false @tab false @tab false @tab false +@end multitable +@end ifnotdocbook +@end ifnotplaintext +@ifplaintext +@example + +-------------------------------------------------+ + | Type of Actual Value: | + +------------+------------+-----------+-----------+ + | String | Number | Array | Undefined | ++-----------+-----------+------------+------------+-----------+-----------+ +| | String | String | String | false | false | +| |-----------+------------+------------+-----------+-----------+ +| | Number | Number if | Number | false | false | +| | | can be | | | | +| | | converted, | | | | +| | | else false | | | | +| |-----------+------------+------------+-----------+-----------+ +| Type | Array | false | false | Array | false | +| Requested |-----------+------------+------------+-----------+-----------+ +| | Scalar | Scalar | Scalar | false | false | +| |-----------+------------+------------+-----------+-----------+ +| | Undefined | String | Number | Array | Undefined | +| |-----------+------------+------------+-----------+-----------+ +| | Value | false | false | false | false | +| | Cookie | | | | | ++-----------+-----------+------------+------------+-----------+-----------+ +@end example +@end ifplaintext +@end float + +@node Accessing Parameters +@subsection Accessing and Updating Parameters + +Two functions give you access to the arguments (parameters) +passed to your extension function. They are: + +@table @code +@item awk_bool_t get_argument(size_t count, +@itemx @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ awk_valtype_t wanted, +@itemx @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ awk_value_t *result); +Fill in the @code{awk_value_t} structure pointed to by @code{result} +with the @code{count}'th argument. Return true if the actual +type matches @code{wanted}, false otherwise. In the latter +case, @code{result@w{->}val_type} indicates the actual type +(@pxref{table-value-types-returned}). Counts are zero based---the first +argument is numbered zero, the second one, and so on. @code{wanted} +indicates the type of value expected. + +@item awk_bool_t set_argument(size_t count, awk_array_t array); +Convert a parameter that was undefined into an array; this provides +call-by-reference for arrays. Return false if @code{count} is too big, +or if the argument's type is not undefined. @DBXREF{Array Manipulation} +for more information on creating arrays. +@end table + +@node Symbol Table Access +@subsection Symbol Table Access +@cindex accessing global variables from extensions + +Two sets of routines provide access to global variables, and one set +allows you to create and release cached values. + +@menu +* Symbol table by name:: Accessing variables by name. +* Symbol table by cookie:: Accessing variables by ``cookie''. +* Cached values:: Creating and using cached values. +@end menu + +@node Symbol table by name +@subsubsection Variable Access and Update by Name + +The following routines provide the ability to access and update +global @command{awk}-level variables by name. In compiler terminology, +identifiers of different kinds are termed @dfn{symbols}, thus the ``sym'' +in the routines' names. The data structure which stores information +about symbols is termed a @dfn{symbol table}. + +@table @code +@item awk_bool_t sym_lookup(const char *name, +@itemx @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ awk_valtype_t wanted, +@itemx @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ awk_value_t *result); +Fill in the @code{awk_value_t} structure pointed to by @code{result} +with the value of the variable named by the string @code{name}, which is +a regular C string. @code{wanted} indicates the type of value expected. +Return true if the actual type matches @code{wanted}, false otherwise. +In the latter case, @code{result->val_type} indicates the actual type +(@pxref{table-value-types-returned}). + +@item awk_bool_t sym_update(const char *name, awk_value_t *value); +Update the variable named by the string @code{name}, which is a regular +C string. The variable is added to @command{gawk}'s symbol table +if it is not there. Return true if everything worked, false otherwise. + +Changing types (scalar to array or vice versa) of an existing variable +is @emph{not} allowed, nor may this routine be used to update an array. +This routine cannot be used to update any of the predefined +variables (such as @code{ARGC} or @code{NF}). +@end table + +An extension can look up the value of @command{gawk}'s special variables. +However, with the exception of the @code{PROCINFO} array, an extension +cannot change any of those variables. + +@quotation CAUTION +It is possible for the lookup of @code{PROCINFO} to fail. This happens if +the @command{awk} program being run does not reference @code{PROCINFO}; +in this case, @command{gawk} doesn't bother to create the array and +populate it. +@end quotation + +@node Symbol table by cookie +@subsubsection Variable Access and Update by Cookie + +A @dfn{scalar cookie} is an opaque handle that provides access +to a global variable or array. It is an optimization that +avoids looking up variables in @command{gawk}'s symbol table every time +access is needed. This was discussed earlier in @ref{General Data Types}. + +The following functions let you work with scalar cookies: + +@table @code +@item awk_bool_t sym_lookup_scalar(awk_scalar_t cookie, +@itemx @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ awk_valtype_t wanted, +@itemx @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ awk_value_t *result); +Retrieve the current value of a scalar cookie. +Once you have obtained a scalar cookie using @code{sym_lookup()}, you can +use this function to get its value more efficiently. +Return false if the value cannot be retrieved. + +@item awk_bool_t sym_update_scalar(awk_scalar_t cookie, awk_value_t *value); +Update the value associated with a scalar cookie. Return false if +the new value is not of type @code{AWK_STRING} or @code{AWK_NUMBER}. +Here too, the predefined variables may not be updated. +@end table + +It is not obvious at first glance how to work with scalar cookies or +what their @i{raison d'@^etre} really is. In theory, the @code{sym_lookup()} +and @code{sym_update()} routines are all you really need to work with +variables. For example, you might have code that looks up the value of +a variable, evaluates a condition, and then possibly changes the value +of the variable based on the result of that evaluation, like so: + +@example +/* do_magic --- do something really great */ + +static awk_value_t * +do_magic(int nargs, awk_value_t *result) +@{ + awk_value_t value; + + if ( sym_lookup("MAGIC_VAR", AWK_NUMBER, & value) + && some_condition(value.num_value)) @{ + value.num_value += 42; + sym_update("MAGIC_VAR", & value); + @} + + return make_number(0.0, result); +@} +@end example + +@noindent +This code looks (and is) simple and straightforward. So what's the problem? + +Well, consider what happens if @command{awk}-level code associated +with your extension calls the @code{magic()} function (implemented in +C by @code{do_magic()}), once per record, while processing hundreds +of thousands or millions of records. The @code{MAGIC_VAR} variable is +looked up in the symbol table once or twice per function call! + +The symbol table lookup is really pure overhead; it is considerably +more efficient to get a cookie that represents the variable, and use +that to get the variable's value and update it as needed.@footnote{The +difference is measurable and quite real. Trust us.} + +Thus, the way to use cookies is as follows. First, install +your extension's variable in @command{gawk}'s symbol table using +@code{sym_update()}, as usual. Then get a scalar cookie for the variable +using @code{sym_lookup()}: + +@example +static awk_scalar_t magic_var_cookie; /* cookie for MAGIC_VAR */ + +static void +my_extension_init() +@{ + awk_value_t value; + + /* install initial value */ + sym_update("MAGIC_VAR", make_number(42.0, & value)); + + /* get the cookie */ + sym_lookup("MAGIC_VAR", AWK_SCALAR, & value); + + /* save the cookie */ + magic_var_cookie = value.scalar_cookie; + @dots{} +@} +@end example + +Next, use the routines in this section for retrieving and updating +the value through the cookie. Thus, @code{do_magic()} now becomes +something like this: + +@example +/* do_magic --- do something really great */ + +static awk_value_t * +do_magic(int nargs, awk_value_t *result) +@{ + awk_value_t value; + + if ( sym_lookup_scalar(magic_var_cookie, AWK_NUMBER, & value) + && some_condition(value.num_value)) @{ + value.num_value += 42; + sym_update_scalar(magic_var_cookie, & value); + @} + @dots{} + + return make_number(0.0, result); +@} +@end example + +@quotation NOTE +The previous code omitted error checking for +presentation purposes. Your extension code should be more robust +and carefully check the return values from the API functions. +@end quotation + +@node Cached values +@subsubsection Creating and Using Cached Values + +The routines in this section allow you to create and release +cached values. As with scalar cookies, in theory, cached values +are not necessary. You can create numbers and strings using +the functions in @ref{Constructor Functions}. You can then +assign those values to variables using @code{sym_update()} +or @code{sym_update_scalar()}, as you like. + +However, you can understand the point of cached values if you remember that +@emph{every} string value's storage @emph{must} come from @code{gawk_malloc()}, +@code{gawk_calloc()}, or @code{gawk_realloc()}. +If you have 20 variables, all of which have the same string value, you +must create 20 identical copies of the string.@footnote{Numeric values +are clearly less problematic, requiring only a C @code{double} to store.} + +It is clearly more efficient, if possible, to create a value once, and +then tell @command{gawk} to reuse the value for multiple variables. That +is what the routines in this section let you do. The functions are as follows: + +@table @code +@item awk_bool_t create_value(awk_value_t *value, awk_value_cookie_t *result); +Create a cached string or numeric value from @code{value} for +efficient later assignment. Only values of type @code{AWK_NUMBER} +and @code{AWK_STRING} are allowed. Any other type is rejected. +@code{AWK_UNDEFINED} could be allowed, but doing so would result in +inferior performance. + +@item awk_bool_t release_value(awk_value_cookie_t vc); +Release the memory associated with a value cookie obtained +from @code{create_value()}. +@end table + +You use value cookies in a fashion similar to the way you use scalar cookies. +In the extension initialization routine, you create the value cookie: + +@example +static awk_value_cookie_t answer_cookie; /* static value cookie */ + +static void +my_extension_init() +@{ + awk_value_t value; + char *long_string; + size_t long_string_len; + + /* code from earlier */ + @dots{} + /* @dots{} fill in long_string and long_string_len @dots{} */ + make_malloced_string(long_string, long_string_len, & value); + create_value(& value, & answer_cookie); /* create cookie */ + @dots{} +@} +@end example + +Once the value is created, you can use it as the value of any number +of variables: + +@example +static awk_value_t * +do_magic(int nargs, awk_value_t *result) +@{ + awk_value_t new_value; + + @dots{} /* as earlier */ + + value.val_type = AWK_VALUE_COOKIE; + value.value_cookie = answer_cookie; + sym_update("VAR1", & value); + sym_update("VAR2", & value); + @dots{} + sym_update("VAR100", & value); + @dots{} +@} +@end example + +@noindent +Using value cookies in this way saves considerable storage, as all of +@code{VAR1} through @code{VAR100} share the same value. + +You might be wondering, ``Is this sharing problematic? +What happens if @command{awk} code assigns a new value to @code{VAR1}, +are all the others changed too?'' + +That's a great question. The answer is that no, it's not a problem. +Internally, @command{gawk} uses @dfn{reference-counted strings}. This means +that many variables can share the same string value, and @command{gawk} +keeps track of the usage. When a variable's value changes, @command{gawk} +simply decrements the reference count on the old value and updates +the variable to use the new value. + +Finally, as part of your cleanup action (@pxref{Exit Callback Functions}) +you should release any cached values that you created, using +@code{release_value()}. + +@node Array Manipulation +@subsection Array Manipulation +@cindex array manipulation in extensions + +The primary data structure@footnote{OK, the only data structure.} in @command{awk} +is the associative array (@pxref{Arrays}). +Extensions need to be able to manipulate @command{awk} arrays. +The API provides a number of data structures for working with arrays, +functions for working with individual elements, and functions for +working with arrays as a whole. This includes the ability to +``flatten'' an array so that it is easy for C code to traverse +every element in an array. The array data structures integrate +nicely with the data structures for values to make it easy to +both work with and create true arrays of arrays (@pxref{General Data Types}). + +@menu +* Array Data Types:: Data types for working with arrays. +* Array Functions:: Functions for working with arrays. +* Flattening Arrays:: How to flatten arrays. +* Creating Arrays:: How to create and populate arrays. +@end menu + +@node Array Data Types +@subsubsection Array Data Types + +The data types associated with arrays are as follows: + +@table @code +@item typedef void *awk_array_t; +If you request the value of an array variable, you get back an +@code{awk_array_t} value. This value is opaque@footnote{It is also +a ``cookie,'' but the @command{gawk} developers did not wish to overuse this +term.} to the extension; it uniquely identifies the array but can +only be used by passing it into API functions or receiving it from API +functions. This is very similar to way @samp{FILE *} values are used +with the @code{<stdio.h>} library routines. + +@item typedef struct awk_element @{ +@itemx @ @ @ @ /* convenience linked list pointer, not used by gawk */ +@itemx @ @ @ @ struct awk_element *next; +@itemx @ @ @ @ enum @{ +@itemx @ @ @ @ @ @ @ @ AWK_ELEMENT_DEFAULT = 0,@ @ /* set by gawk */ +@itemx @ @ @ @ @ @ @ @ AWK_ELEMENT_DELETE = 1@ @ @ @ /* set by extension */ +@itemx @ @ @ @ @} flags; +@itemx @ @ @ @ awk_value_t index; +@itemx @ @ @ @ awk_value_t value; +@itemx @} awk_element_t; +The @code{awk_element_t} is a ``flattened'' +array element. @command{awk} produces an array of these +inside the @code{awk_flat_array_t} (see the next item). +Individual elements may be marked for deletion. New elements must be added +individually, one at a time, using the separate API for that purpose. +The fields are as follows: + +@c nested table +@table @code +@item struct awk_element *next; +This pointer is for the convenience of extension writers. It allows +an extension to create a linked list of new elements that can then be +added to an array in a loop that traverses the list. + +@item enum @{ @dots{} @} flags; +A set of flag values that convey information between the extension +and @command{gawk}. Currently there is only one: @code{AWK_ELEMENT_DELETE}. +Setting it causes @command{gawk} to delete the +element from the original array upon release of the flattened array. + +@item index +@itemx value +The index and value of the element, respectively. +@emph{All} memory pointed to by @code{index} and @code{value} belongs to @command{gawk}. +@end table + +@item typedef struct awk_flat_array @{ +@itemx @ @ @ @ awk_const void *awk_const opaque1;@ @ @ @ /* for use by gawk */ +@itemx @ @ @ @ awk_const void *awk_const opaque2;@ @ @ @ /* for use by gawk */ +@itemx @ @ @ @ awk_const size_t count;@ @ @ @ @ /* how many elements */ +@itemx @ @ @ @ awk_element_t elements[1];@ @ /* will be extended */ +@itemx @} awk_flat_array_t; +This is a flattened array. When an extension gets one of these +from @command{gawk}, the @code{elements} array is of actual +size @code{count}. +The @code{opaque1} and @code{opaque2} pointers are for use by @command{gawk}; +therefore they are marked @code{awk_const} so that the extension cannot +modify them. +@end table + +@node Array Functions +@subsubsection Array Functions + +The following functions relate to individual array elements. + +@table @code +@item awk_bool_t get_element_count(awk_array_t a_cookie, size_t *count); +For the array represented by @code{a_cookie}, place in @code{*count} +the number of elements it contains. A subarray counts as a single element. +Return false if there is an error. + +@item awk_bool_t get_array_element(awk_array_t a_cookie, +@itemx @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ const awk_value_t *const index, +@itemx @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ awk_valtype_t wanted, +@itemx @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ awk_value_t *result); +For the array represented by @code{a_cookie}, return in @code{*result} +the value of the element whose index is @code{index}. +@code{wanted} specifies the type of value you wish to retrieve. +Return false if @code{wanted} does not match the actual type or if +@code{index} is not in the array (@pxref{table-value-types-returned}). + +The value for @code{index} can be numeric, in which case @command{gawk} +converts it to a string. Using non-integral values is possible, but +requires that you understand how such values are converted to strings +(@pxref{Conversion}); thus using integral values is safest. + +As with @emph{all} strings passed into @code{gawk} from an extension, +the string value of @code{index} must come from @code{gawk_malloc()}, +@code{gawk_calloc()} or @code{gawk_realloc()}, and +@command{gawk} releases the storage. + +@item awk_bool_t set_array_element(awk_array_t a_cookie, +@itemx @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ const@ awk_value_t *const index, +@itemx @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ const@ awk_value_t *const value); +In the array represented by @code{a_cookie}, create or modify +the element whose index is given by @code{index}. +The @code{ARGV} and @code{ENVIRON} arrays may not be changed, +although the @code{PROCINFO} array can be. + +@item awk_bool_t set_array_element_by_elem(awk_array_t a_cookie, +@itemx @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ awk_element_t element); +Like @code{set_array_element()}, but take the @code{index} and @code{value} +from @code{element}. This is a convenience macro. + +@item awk_bool_t del_array_element(awk_array_t a_cookie, +@itemx @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ const awk_value_t* const index); +Remove the element with the given index from the array +represented by @code{a_cookie}. +Return true if the element was removed, or false if the element did +not exist in the array. +@end table + +The following functions relate to arrays as a whole: + +@table @code +@item awk_array_t create_array(void); +Create a new array to which elements may be added. +@DBXREF{Creating Arrays} for a discussion of how to +create a new array and add elements to it. + +@item awk_bool_t clear_array(awk_array_t a_cookie); +Clear the array represented by @code{a_cookie}. +Return false if there was some kind of problem, true otherwise. +The array remains an array, but after calling this function, it +has no elements. This is equivalent to using the @code{delete} +statement (@pxref{Delete}). + +@item awk_bool_t flatten_array(awk_array_t a_cookie, awk_flat_array_t **data); +For the array represented by @code{a_cookie}, create an @code{awk_flat_array_t} +structure and fill it in. Set the pointer whose address is passed as @code{data} +to point to this structure. +Return true upon success, or false otherwise. +@ifset FOR_PRINT +See the next section +@end ifset +@ifclear FOR_PRINT +@xref{Flattening Arrays}, +@end ifclear +for a discussion of how to +flatten an array and work with it. + +@item awk_bool_t release_flattened_array(awk_array_t a_cookie, +@itemx @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ awk_flat_array_t *data); +When done with a flattened array, release the storage using this function. +You must pass in both the original array cookie, and the address of +the created @code{awk_flat_array_t} structure. +The function returns true upon success, false otherwise. +@end table + +@node Flattening Arrays +@subsubsection Working With All The Elements of an Array + +To @dfn{flatten} an array is to create a structure that +represents the full array in a fashion that makes it easy +for C code to traverse the entire array. Test code +in @file{extension/testext.c} does this, and also serves +as a nice example showing how to use the APIs. + +We walk through that part of the code one step at a time. +First, the @command{gawk} script that drives the test extension: + +@example +@@load "testext" +BEGIN @{ + n = split("blacky rusty sophie raincloud lucky", pets) + printf("pets has %d elements\n", length(pets)) + ret = dump_array_and_delete("pets", "3") + printf("dump_array_and_delete(pets) returned %d\n", ret) + if ("3" in pets) + printf("dump_array_and_delete() did NOT remove index \"3\"!\n") + else + printf("dump_array_and_delete() did remove index \"3\"!\n") + print "" +@} +@end example + +@noindent +This code creates an array with @code{split()} (@pxref{String Functions}) +and then calls @code{dump_array_and_delete()}. That function looks up +the array whose name is passed as the first argument, and +deletes the element at the index passed in the second argument. +The @command{awk} code then prints the return value and checks if the element +was indeed deleted. Here is the C code that implements +@code{dump_array_and_delete()}. It has been edited slightly for +presentation. + +The first part declares variables, sets up the default +return value in @code{result}, and checks that the function +was called with the correct number of arguments: + +@example +static awk_value_t * +dump_array_and_delete(int nargs, awk_value_t *result) +@{ + awk_value_t value, value2, value3; + awk_flat_array_t *flat_array; + size_t count; + char *name; + int i; + + assert(result != NULL); + make_number(0.0, result); + + if (nargs != 2) @{ + printf("dump_array_and_delete: nargs not right " + "(%d should be 2)\n", nargs); + goto out; + @} +@end example + +The function then proceeds in steps, as follows. First, retrieve +the name of the array, passed as the first argument. Then +retrieve the array itself. If either operation fails, print +error messages and return: + +@example + /* get argument named array as flat array and print it */ + if (get_argument(0, AWK_STRING, & value)) @{ + name = value.str_value.str; + if (sym_lookup(name, AWK_ARRAY, & value2)) + printf("dump_array_and_delete: sym_lookup of %s passed\n", + name); + else @{ + printf("dump_array_and_delete: sym_lookup of %s failed\n", + name); + goto out; + @} + @} else @{ + printf("dump_array_and_delete: get_argument(0) failed\n"); + goto out; + @} +@end example + +For testing purposes and to make sure that the C code sees +the same number of elements as the @command{awk} code, +the second step is to get the count of elements in the array +and print it: + +@example + if (! get_element_count(value2.array_cookie, & count)) @{ + printf("dump_array_and_delete: get_element_count failed\n"); + goto out; + @} + + printf("dump_array_and_delete: incoming size is %lu\n", + (unsigned long) count); +@end example + +The third step is to actually flatten the array, and then +to double check that the count in the @code{awk_flat_array_t} +is the same as the count just retrieved: + +@example + if (! flatten_array(value2.array_cookie, & flat_array)) @{ + printf("dump_array_and_delete: could not flatten array\n"); + goto out; + @} + + if (flat_array->count != count) @{ + printf("dump_array_and_delete: flat_array->count (%lu)" + " != count (%lu)\n", + (unsigned long) flat_array->count, + (unsigned long) count); + goto out; + @} +@end example + +The fourth step is to retrieve the index of the element +to be deleted, which was passed as the second argument. +Remember that argument counts passed to @code{get_argument()} +are zero-based, thus the second argument is numbered one: + +@example + if (! get_argument(1, AWK_STRING, & value3)) @{ + printf("dump_array_and_delete: get_argument(1) failed\n"); + goto out; + @} +@end example + +The fifth step is where the ``real work'' is done. The function +loops over every element in the array, printing the index and +element values. In addition, upon finding the element with the +index that is supposed to be deleted, the function sets the +@code{AWK_ELEMENT_DELETE} bit in the @code{flags} field +of the element. When the array is released, @command{gawk} +traverses the flattened array, and deletes any elements which +have this flag bit set: + +@example + for (i = 0; i < flat_array->count; i++) @{ + printf("\t%s[\"%.*s\"] = %s\n", + name, + (int) flat_array->elements[i].index.str_value.len, + flat_array->elements[i].index.str_value.str, + valrep2str(& flat_array->elements[i].value)); + + if (strcmp(value3.str_value.str, + flat_array->elements[i].index.str_value.str) == 0) @{ + flat_array->elements[i].flags |= AWK_ELEMENT_DELETE; + printf("dump_array_and_delete: marking element \"%s\" " + "for deletion\n", + flat_array->elements[i].index.str_value.str); + @} + @} +@end example + +The sixth step is to release the flattened array. This tells +@command{gawk} that the extension is no longer using the array, +and that it should delete any elements marked for deletion. +@command{gawk} also frees any storage that was allocated, +so you should not use the pointer (@code{flat_array} in this +code) once you have called @code{release_flattened_array()}: + +@example + if (! release_flattened_array(value2.array_cookie, flat_array)) @{ + printf("dump_array_and_delete: could not release flattened array\n"); + goto out; + @} +@end example + +Finally, because everything was successful, the function sets the +return value to success, and returns: + +@example + make_number(1.0, result); +out: + return result; +@} +@end example + +Here is the output from running this part of the test: + +@example +pets has 5 elements +dump_array_and_delete: sym_lookup of pets passed +dump_array_and_delete: incoming size is 5 + pets["1"] = "blacky" + pets["2"] = "rusty" + pets["3"] = "sophie" +dump_array_and_delete: marking element "3" for deletion + pets["4"] = "raincloud" + pets["5"] = "lucky" +dump_array_and_delete(pets) returned 1 +dump_array_and_delete() did remove index "3"! +@end example + +@node Creating Arrays +@subsubsection How To Create and Populate Arrays + +Besides working with arrays created by @command{awk} code, you can +create arrays and populate them as you see fit, and then @command{awk} +code can access them and manipulate them. + +There are two important points about creating arrays from extension code: + +@itemize @value{BULLET} +@item +You must install a new array into @command{gawk}'s symbol +table immediately upon creating it. Once you have done so, +you can then populate the array. + +@ignore +Strictly speaking, this is required only +for arrays that will have subarrays as elements; however it is +a good idea to always do this. This restriction may be relaxed +in a subsequent revision of the API. +@end ignore + +Similarly, if installing a new array as a subarray of an existing array, +you must add the new array to its parent before adding any elements to it. + +Thus, the correct way to build an array is to work ``top down.'' Create +the array, and immediately install it in @command{gawk}'s symbol table +using @code{sym_update()}, or install it as an element in a previously +existing array using @code{set_array_element()}. We show example code shortly. + +@item +Due to @command{gawk} internals, after using @code{sym_update()} to install an array +into @command{gawk}, you have to retrieve the array cookie from the value +passed in to @command{sym_update()} before doing anything else with it, like so: + +@example +awk_value_t value; +awk_array_t new_array; + +new_array = create_array(); +val.val_type = AWK_ARRAY; +val.array_cookie = new_array; + +/* install array in the symbol table */ +sym_update("array", & val); + +new_array = val.array_cookie; /* YOU MUST DO THIS */ +@end example + +If installing an array as a subarray, you must also retrieve the value +of the array cookie after the call to @code{set_element()}. +@end itemize + +The following C code is a simple test extension to create an array +with two regular elements and with a subarray. The leading @code{#include} +directives and boilerplate variable declarations +(@pxref{Extension API Boilerplate}) +are omitted for brevity. +The first step is to create a new array and then install it +in the symbol table: + +@example +@ignore +#ifdef HAVE_CONFIG_H +#include <config.h> +#endif + +#include <stdio.h> +#include <assert.h> +#include <errno.h> +#include <stdlib.h> +#include <string.h> +#include <unistd.h> + +#include <sys/types.h> +#include <sys/stat.h> + +#include "gawkapi.h" + +static const gawk_api_t *api; /* for convenience macros to work */ +static awk_ext_id_t *ext_id; +static const char *ext_version = "testarray extension: version 1.0"; + +int plugin_is_GPL_compatible; + +@end ignore +/* create_new_array --- create a named array */ + +static void +create_new_array() +@{ + awk_array_t a_cookie; + awk_array_t subarray; + awk_value_t index, value; + + a_cookie = create_array(); + value.val_type = AWK_ARRAY; + value.array_cookie = a_cookie; + + if (! sym_update("new_array", & value)) + printf("create_new_array: sym_update(\"new_array\") failed!\n"); + a_cookie = value.array_cookie; +@end example + +@noindent +Note how @code{a_cookie} is reset from the @code{array_cookie} field in +the @code{value} structure. + +The second step is to install two regular values into @code{new_array}: + +@example + (void) make_const_string("hello", 5, & index); + (void) make_const_string("world", 5, & value); + if (! set_array_element(a_cookie, & index, & value)) @{ + printf("fill_in_array: set_array_element failed\n"); + return; + @} + + (void) make_const_string("answer", 6, & index); + (void) make_number(42.0, & value); + if (! set_array_element(a_cookie, & index, & value)) @{ + printf("fill_in_array: set_array_element failed\n"); + return; + @} +@end example + +The third step is to create the subarray and install it: + +@example + (void) make_const_string("subarray", 8, & index); + subarray = create_array(); + value.val_type = AWK_ARRAY; + value.array_cookie = subarray; + if (! set_array_element(a_cookie, & index, & value)) @{ + printf("fill_in_array: set_array_element failed\n"); + return; + @} + subarray = value.array_cookie; +@end example + +The final step is to populate the subarray with its own element: + +@example + (void) make_const_string("foo", 3, & index); + (void) make_const_string("bar", 3, & value); + if (! set_array_element(subarray, & index, & value)) @{ + printf("fill_in_array: set_array_element failed\n"); + return; + @} +@} +@ignore +static awk_ext_func_t func_table[] = @{ + @{ NULL, NULL, 0 @} +@}; + +/* init_testarray --- additional initialization function */ + +static awk_bool_t init_testarray(void) +@{ + create_new_array(); + + return awk_true; +@} + +static awk_bool_t (*init_func)(void) = init_testarray; + +dl_load_func(func_table, testarray, "") +@end ignore +@end example + +Here is a sample script that loads the extension +and then dumps the array: + +@example +@@load "subarray" + +function dumparray(name, array, i) +@{ + for (i in array) + if (isarray(array[i])) + dumparray(name "[\"" i "\"]", array[i]) + else + printf("%s[\"%s\"] = %s\n", name, i, array[i]) +@} + +BEGIN @{ + dumparray("new_array", new_array); +@} +@end example + +Here is the result of running the script: + +@example +$ @kbd{AWKLIBPATH=$PWD ./gawk -f subarray.awk} +@print{} new_array["subarray"]["foo"] = bar +@print{} new_array["hello"] = world +@print{} new_array["answer"] = 42 +@end example + +@noindent +(@DBXREF{Finding Extensions} for more information on the +@env{AWKLIBPATH} environment variable.) + +@node Extension API Variables +@subsection API Variables + +The API provides two sets of variables. The first provides information +about the version of the API (both with which the extension was compiled, +and with which @command{gawk} was compiled). The second provides +information about how @command{gawk} was invoked. + +@menu +* Extension Versioning:: API Version information. +* Extension API Informational Variables:: Variables providing information about + @command{gawk}'s invocation. +@end menu + +@node Extension Versioning +@subsubsection API Version Constants and Variables +@cindex API version +@cindex extension API version + +The API provides both a ``major'' and a ``minor'' version number. +The API versions are available at compile time as constants: + +@table @code +@item GAWK_API_MAJOR_VERSION +The major version of the API. + +@item GAWK_API_MINOR_VERSION +The minor version of the API. +@end table + +The minor version increases when new functions are added to the API. Such +new functions are always added to the end of the API @code{struct}. + +The major version increases (and the minor version is reset to zero) if any +of the data types change size or member order, or if any of the existing +functions change signature. + +It could happen that an extension may be compiled against one version +of the API but loaded by a version of @command{gawk} using a different +version. For this reason, the major and minor API versions of the +running @command{gawk} are included in the API @code{struct} as read-only +constant integers: + +@table @code +@item api->major_version +The major version of the running @command{gawk}. + +@item api->minor_version +The minor version of the running @command{gawk}. +@end table + +It is up to the extension to decide if there are API incompatibilities. +Typically a check like this is enough: + +@example +if (api->major_version != GAWK_API_MAJOR_VERSION + || api->minor_version < GAWK_API_MINOR_VERSION) @{ + fprintf(stderr, "foo_extension: version mismatch with gawk!\n"); + fprintf(stderr, "\tmy version (%d, %d), gawk version (%d, %d)\n", + GAWK_API_MAJOR_VERSION, GAWK_API_MINOR_VERSION, + api->major_version, api->minor_version); + exit(1); +@} +@end example + +Such code is included in the boilerplate @code{dl_load_func()} macro +provided in @file{gawkapi.h} (discussed later, in +@ref{Extension API Boilerplate}). + +@node Extension API Informational Variables +@subsubsection Informational Variables +@cindex API informational variables +@cindex extension API informational variables + +The API provides access to several variables that describe +whether the corresponding command-line options were enabled when +@command{gawk} was invoked. The variables are: + +@table @code +@item do_debug +This variable is true if @command{gawk} was invoked with @option{--debug} option. + +@item do_lint +This variable is true if @command{gawk} was invoked with @option{--lint} option. + +@item do_mpfr +This variable is true if @command{gawk} was invoked with @option{--bignum} option. + +@item do_profile +This variable is true if @command{gawk} was invoked with @option{--profile} option. + +@item do_sandbox +This variable is true if @command{gawk} was invoked with @option{--sandbox} option. + +@item do_traditional +This variable is true if @command{gawk} was invoked with @option{--traditional} option. +@end table + +The value of @code{do_lint} can change if @command{awk} code +modifies the @code{LINT} predefined variable (@pxref{Built-in Variables}). +The others should not change during execution. + +@node Extension API Boilerplate +@subsection Boilerplate Code + +As mentioned earlier (@pxref{Extension Mechanism Outline}), the function +definitions as presented are really macros. To use these macros, your +extension must provide a small amount of boilerplate code (variables and +functions) toward the top of your source file, using predefined names +as described here. The boilerplate needed is also provided in comments +in the @file{gawkapi.h} header file: + +@example +/* Boiler plate code: */ +int plugin_is_GPL_compatible; + +static gawk_api_t *const api; +static awk_ext_id_t ext_id; +static const char *ext_version = NULL; /* or @dots{} = "some string" */ + +static awk_ext_func_t func_table[] = @{ + @{ "name", do_name, 1 @}, + /* @dots{} */ +@}; + +/* EITHER: */ + +static awk_bool_t (*init_func)(void) = NULL; + +/* OR: */ + +static awk_bool_t +init_my_extension(void) +@{ + @dots{} +@} + +static awk_bool_t (*init_func)(void) = init_my_extension; + +dl_load_func(func_table, some_name, "name_space_in_quotes") +@end example + +These variables and functions are as follows: + +@table @code +@item int plugin_is_GPL_compatible; +This asserts that the extension is compatible with +@ifclear FOR_PRINT +the GNU GPL (@pxref{Copying}). +@end ifclear +@ifset FOR_PRINT +the GNU GPL. +@end ifset +If your extension does not have this, @command{gawk} +will not load it (@pxref{Plugin License}). + +@item static gawk_api_t *const api; +This global @code{static} variable should be set to point to +the @code{gawk_api_t} pointer that @command{gawk} passes to your +@code{dl_load()} function. This variable is used by all of the macros. + +@item static awk_ext_id_t ext_id; +This global static variable should be set to the @code{awk_ext_id_t} +value that @command{gawk} passes to your @code{dl_load()} function. +This variable is used by all of the macros. + +@item static const char *ext_version = NULL; /* or @dots{} = "some string" */ +This global @code{static} variable should be set either +to @code{NULL}, or to point to a string giving the name and version of +your extension. + +@item static awk_ext_func_t func_table[] = @{ @dots{} @}; +This is an array of one or more @code{awk_ext_func_t} structures +as described earlier (@pxref{Extension Functions}). +It can then be looped over for multiple calls to +@code{add_ext_func()}. + +@c Use @var{OR} for docbook +@item static awk_bool_t (*init_func)(void) = NULL; +@itemx @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @var{OR} +@itemx static awk_bool_t init_my_extension(void) @{ @dots{} @} +@itemx static awk_bool_t (*init_func)(void) = init_my_extension; +If you need to do some initialization work, you should define a +function that does it (creates variables, opens files, etc.) +and then define the @code{init_func} pointer to point to your +function. +The function should return @code{awk_false} upon failure, or @code{awk_true} +if everything goes well. + +If you don't need to do any initialization, define the pointer and +initialize it to @code{NULL}. + +@item dl_load_func(func_table, some_name, "name_space_in_quotes") +This macro expands to a @code{dl_load()} function that performs +all the necessary initializations. +@end table + +The point of all the variables and arrays is to let the +@code{dl_load()} function (from the @code{dl_load_func()} +macro) do all the standard work. It does the following: + +@enumerate 1 +@item +Check the API versions. If the extension major version does not match +@command{gawk}'s, or if the extension minor version is greater than +@command{gawk}'s, it prints a fatal error message and exits. + +@item +Load the functions defined in @code{func_table}. +If any of them fails to load, it prints a warning message but +continues on. + +@item +If the @code{init_func} pointer is not @code{NULL}, call the +function it points to. If it returns @code{awk_false}, print a +warning message. + +@item +If @code{ext_version} is not @code{NULL}, register +the version string with @command{gawk}. +@end enumerate + +@node Finding Extensions +@section How @command{gawk} Finds Extensions +@cindex extension search path +@cindex finding extensions + +Compiled extensions have to be installed in a directory where +@command{gawk} can find them. If @command{gawk} is configured and +built in the default fashion, the directory in which to find +extensions is @file{/usr/local/lib/gawk}. You can also specify a search +path with a list of directories to search for compiled extensions. +@DBXREF{AWKLIBPATH Variable} for more information. + +@node Extension Example +@section Example: Some File Functions +@cindex extension example + +@quotation +@i{No matter where you go, there you are.} +@author Buckaroo Banzai +@end quotation + +@c It's enough to show chdir and stat, no need for fts + +Two useful functions that are not in @command{awk} are @code{chdir()} (so +that an @command{awk} program can change its directory) and @code{stat()} +(so that an @command{awk} program can gather information about a file). +In order to illustrate the API in action, this @value{SECTION} implements +these functions for @command{gawk} in an extension. + +@menu +* Internal File Description:: What the new functions will do. +* Internal File Ops:: The code for internal file operations. +* Using Internal File Ops:: How to use an external extension. +@end menu + +@node Internal File Description +@subsection Using @code{chdir()} and @code{stat()} + +This @value{SECTION} shows how to use the new functions at +the @command{awk} level once they've been integrated into the +running @command{gawk} interpreter. Using @code{chdir()} is very +straightforward. It takes one argument, the new directory to change to: + +@example +@@load "filefuncs" +@dots{} +newdir = "/home/arnold/funstuff" +ret = chdir(newdir) +if (ret < 0) @{ + printf("could not change to %s: %s\n", newdir, ERRNO) > "/dev/stderr" + exit 1 +@} +@dots{} +@end example + +The return value is negative if the @code{chdir()} failed, and +@code{ERRNO} (@pxref{Built-in Variables}) is set to a string indicating +the error. + +Using @code{stat()} is a bit more complicated. The C @code{stat()} +function fills in a structure that has a fair amount of information. +The right way to model this in @command{awk} is to fill in an associative +array with the appropriate information: + +@c broke printf for page breaking +@example +file = "/home/arnold/.profile" +ret = stat(file, fdata) +if (ret < 0) @{ + printf("could not stat %s: %s\n", + file, ERRNO) > "/dev/stderr" + exit 1 +@} +printf("size of %s is %d bytes\n", file, fdata["size"]) +@end example + +The @code{stat()} function always clears the data array, even if +the @code{stat()} fails. It fills in the following elements: + +@table @code +@item "name" +The name of the file that was @code{stat()}'ed. + +@item "dev" +@itemx "ino" +The file's device and inode numbers, respectively. + +@item "mode" +The file's mode, as a numeric value. This includes both the file's +type and its permissions. + +@item "nlink" +The number of hard links (directory entries) the file has. + +@item "uid" +@itemx "gid" +The numeric user and group ID numbers of the file's owner. + +@item "size" +The size in bytes of the file. + +@item "blocks" +The number of disk blocks the file actually occupies. This may not +be a function of the file's size if the file has holes. + +@item "atime" +@itemx "mtime" +@itemx "ctime" +The file's last access, modification, and inode update times, +respectively. These are numeric timestamps, suitable for formatting +with @code{strftime()} +(@pxref{Time Functions}). + +@item "pmode" +The file's ``printable mode.'' This is a string representation of +the file's type and permissions, such as is produced by +@samp{ls -l}---for example, @code{"drwxr-xr-x"}. + +@item "type" +A printable string representation of the file's type. The value +is one of the following: + +@table @code +@item "blockdev" +@itemx "chardev" +The file is a block or character device (``special file''). + +@ignore +@item "door" +The file is a Solaris ``door'' (special file used for +interprocess communications). +@end ignore + +@item "directory" +The file is a directory. + +@item "fifo" +The file is a named-pipe (also known as a FIFO). + +@item "file" +The file is just a regular file. + +@item "socket" +The file is an @code{AF_UNIX} (``Unix domain'') socket in the +filesystem. + +@item "symlink" +The file is a symbolic link. +@end table + +@c 5/2013: Thanks to Corinna Vinschen for this information. +@item "devbsize" +The size of a block for the element indexed by @code{"blocks"}. +This information is derived from either the @code{DEV_BSIZE} +constant defined in @code{<sys/param.h>} on most systems, +or the @code{S_BLKSIZE} constant in @code{<sys/stat.h>} on BSD systems. +For some other systems, @dfn{a priori} knowledge is used to provide +a value. Where no value can be determined, it defaults to 512. +@end table + +Several additional elements may be present depending upon the operating +system and the type of the file. You can test for them in your @command{awk} +program by using the @code{in} operator +(@pxref{Reference to Elements}): + +@table @code +@item "blksize" +The preferred block size for I/O to the file. This field is not +present on all POSIX-like systems in the C @code{stat} structure. + +@item "linkval" +If the file is a symbolic link, this element is the name of the +file the link points to (i.e., the value of the link). + +@item "rdev" +@itemx "major" +@itemx "minor" +If the file is a block or character device file, then these values +represent the numeric device number and the major and minor components +of that number, respectively. +@end table + +@node Internal File Ops +@subsection C Code for @code{chdir()} and @code{stat()} + +Here is the C code for these extensions.@footnote{This version is +edited slightly for presentation. See @file{extension/filefuncs.c} +in the @command{gawk} distribution for the complete version.} + +The file includes a number of standard header files, and then includes +the @file{gawkapi.h} header file which provides the API definitions. +Those are followed by the necessary variable declarations +to make use of the API macros and boilerplate code +(@pxref{Extension API Boilerplate}): + +@example +#ifdef HAVE_CONFIG_H +#include <config.h> +#endif + +#include <stdio.h> +#include <assert.h> +#include <errno.h> +#include <stdlib.h> +#include <string.h> +#include <unistd.h> + +#include <sys/types.h> +#include <sys/stat.h> + +#include "gawkapi.h" + +#include "gettext.h" +#define _(msgid) gettext(msgid) +#define N_(msgid) msgid + +#include "gawkfts.h" +#include "stack.h" + +static const gawk_api_t *api; /* for convenience macros to work */ +static awk_ext_id_t *ext_id; +static awk_bool_t init_filefuncs(void); +static awk_bool_t (*init_func)(void) = init_filefuncs; +static const char *ext_version = "filefuncs extension: version 1.0"; + +int plugin_is_GPL_compatible; +@end example + +@cindex programming conventions, @command{gawk} extensions +By convention, for an @command{awk} function @code{foo()}, the C function +that implements it is called @code{do_foo()}. The function should have +two arguments: the first is an @code{int} usually called @code{nargs}, +that represents the number of actual arguments for the function. +The second is a pointer to an @code{awk_value_t}, usually named +@code{result}: + +@example +/* do_chdir --- provide dynamically loaded chdir() function for gawk */ + +static awk_value_t * +do_chdir(int nargs, awk_value_t *result) +@{ + awk_value_t newdir; + int ret = -1; + + assert(result != NULL); + + if (do_lint && nargs != 1) + lintwarn(ext_id, + _("chdir: called with incorrect number of arguments, " + "expecting 1")); +@end example + +The @code{newdir} +variable represents the new directory to change to, which is retrieved +with @code{get_argument()}. Note that the first argument is +numbered zero. + +If the argument is retrieved successfully, the function calls the +@code{chdir()} system call. If the @code{chdir()} fails, @code{ERRNO} +is updated: + +@example + if (get_argument(0, AWK_STRING, & newdir)) @{ + ret = chdir(newdir.str_value.str); + if (ret < 0) + update_ERRNO_int(errno); + @} +@end example + +Finally, the function returns the return value to the @command{awk} level: + +@example + return make_number(ret, result); +@} +@end example + +The @code{stat()} extension is more involved. First comes a function +that turns a numeric mode into a printable representation +(e.g., 644 becomes @samp{-rw-r--r--}). This is omitted here for brevity: + +@example +/* format_mode --- turn a stat mode field into something readable */ + +static char * +format_mode(unsigned long fmode) +@{ + @dots{} +@} +@end example + +Next comes a function for reading symbolic links, which is also +omitted here for brevity: + +@example +/* read_symlink --- read a symbolic link into an allocated buffer. + @dots{} */ + +static char * +read_symlink(const char *fname, size_t bufsize, ssize_t *linksize) +@{ + @dots{} +@} +@end example + +Two helper functions simplify entering values in the +array that will contain the result of the @code{stat()}: + +@example +/* array_set --- set an array element */ + +static void +array_set(awk_array_t array, const char *sub, awk_value_t *value) +@{ + awk_value_t index; + + set_array_element(array, + make_const_string(sub, strlen(sub), & index), + value); + +@} + +/* array_set_numeric --- set an array element with a number */ + +static void +array_set_numeric(awk_array_t array, const char *sub, double num) +@{ + awk_value_t tmp; + + array_set(array, sub, make_number(num, & tmp)); +@} +@end example + +The following function does most of the work to fill in +the @code{awk_array_t} result array with values obtained +from a valid @code{struct stat}. It is done in a separate function +to support the @code{stat()} function for @command{gawk} and also +to support the @code{fts()} extension which is included in +the same file but whose code is not shown here +(@pxref{Extension Sample File Functions}). + +The first part of the function is variable declarations, +including a table to map file types to strings: + +@example +/* fill_stat_array --- do the work to fill an array with stat info */ + +static int +fill_stat_array(const char *name, awk_array_t array, struct stat *sbuf) +@{ + char *pmode; /* printable mode */ + const char *type = "unknown"; + awk_value_t tmp; + static struct ftype_map @{ + unsigned int mask; + const char *type; + @} ftype_map[] = @{ + @{ S_IFREG, "file" @}, + @{ S_IFBLK, "blockdev" @}, + @{ S_IFCHR, "chardev" @}, + @{ S_IFDIR, "directory" @}, +#ifdef S_IFSOCK + @{ S_IFSOCK, "socket" @}, +#endif +#ifdef S_IFIFO + @{ S_IFIFO, "fifo" @}, +#endif +#ifdef S_IFLNK + @{ S_IFLNK, "symlink" @}, +#endif +#ifdef S_IFDOOR /* Solaris weirdness */ + @{ S_IFDOOR, "door" @}, +#endif /* S_IFDOOR */ + @}; + int j, k; +@end example + +The destination array is cleared, and then code fills in +various elements based on values in the @code{struct stat}: + +@example + /* empty out the array */ + clear_array(array); + + /* fill in the array */ + array_set(array, "name", make_const_string(name, strlen(name), + & tmp)); + array_set_numeric(array, "dev", sbuf->st_dev); + array_set_numeric(array, "ino", sbuf->st_ino); + array_set_numeric(array, "mode", sbuf->st_mode); + array_set_numeric(array, "nlink", sbuf->st_nlink); + array_set_numeric(array, "uid", sbuf->st_uid); + array_set_numeric(array, "gid", sbuf->st_gid); + array_set_numeric(array, "size", sbuf->st_size); + array_set_numeric(array, "blocks", sbuf->st_blocks); + array_set_numeric(array, "atime", sbuf->st_atime); + array_set_numeric(array, "mtime", sbuf->st_mtime); + array_set_numeric(array, "ctime", sbuf->st_ctime); + + /* for block and character devices, add rdev, + major and minor numbers */ + if (S_ISBLK(sbuf->st_mode) || S_ISCHR(sbuf->st_mode)) @{ + array_set_numeric(array, "rdev", sbuf->st_rdev); + array_set_numeric(array, "major", major(sbuf->st_rdev)); + array_set_numeric(array, "minor", minor(sbuf->st_rdev)); + @} +@end example + +@noindent +The latter part of the function makes selective additions +to the destination array, depending upon the availability of +certain members and/or the type of the file. It then returns zero, +for success: + +@example +#ifdef HAVE_STRUCT_STAT_ST_BLKSIZE + array_set_numeric(array, "blksize", sbuf->st_blksize); +#endif /* HAVE_STRUCT_STAT_ST_BLKSIZE */ + + pmode = format_mode(sbuf->st_mode); + array_set(array, "pmode", make_const_string(pmode, strlen(pmode), + & tmp)); + + /* for symbolic links, add a linkval field */ + if (S_ISLNK(sbuf->st_mode)) @{ + char *buf; + ssize_t linksize; + + if ((buf = read_symlink(name, sbuf->st_size, + & linksize)) != NULL) + array_set(array, "linkval", + make_malloced_string(buf, linksize, & tmp)); + else + warning(ext_id, _("stat: unable to read symbolic link `%s'"), + name); + @} + + /* add a type field */ + type = "unknown"; /* shouldn't happen */ + for (j = 0, k = sizeof(ftype_map)/sizeof(ftype_map[0]); j < k; j++) @{ + if ((sbuf->st_mode & S_IFMT) == ftype_map[j].mask) @{ + type = ftype_map[j].type; + break; + @} + @} + + array_set(array, "type", make_const_string(type, strlen(type), & tmp)); + + return 0; +@} +@end example + +The third argument to @code{stat()} was not discussed previously. This +argument is optional. If present, it causes @code{do_stat()} to use +the @code{stat()} system call instead of the @code{lstat()} system +call. This is done by using a function pointer: @code{statfunc}. +@code{statfunc} is initialized to point to @code{lstat()} (instead +of @code{stat()}) to get the file information, in case the file is a +symbolic link. However, if there were three arguments, @code{statfunc} +is set point to @code{stat()}, instead. + +Here is the @code{do_stat()} function, which starts with +variable declarations and argument checking: + +@ignore +Changed message for page breaking. Used to be: + "stat: called with incorrect number of arguments (%d), should be 2", @end ignore +@example +/* do_stat --- provide a stat() function for gawk */ + +static awk_value_t * +do_stat(int nargs, awk_value_t *result) +@{ + awk_value_t file_param, array_param; + char *name; + awk_array_t array; + int ret; + struct stat sbuf; + /* default is lstat() */ + int (*statfunc)(const char *path, struct stat *sbuf) = lstat; + + assert(result != NULL); + + if (nargs != 2 && nargs != 3) @{ + if (do_lint) + lintwarn(ext_id, + _("stat: called with wrong number of arguments")); + return make_number(-1, result); + @} +@end example + +Then comes the actual work. First, the function gets the arguments. +Next, it gets the information for the file. If the called function +(@code{lstat()} or @code{stat()}) returns an error, the code sets +@code{ERRNO} and returns: + +@example + /* file is first arg, array to hold results is second */ + if ( ! get_argument(0, AWK_STRING, & file_param) + || ! get_argument(1, AWK_ARRAY, & array_param)) @{ + warning(ext_id, _("stat: bad parameters")); + return make_number(-1, result); + @} + + if (nargs == 3) @{ + statfunc = stat; + @} + + name = file_param.str_value.str; + array = array_param.array_cookie; + + /* always empty out the array */ + clear_array(array); + + /* stat the file, if error, set ERRNO and return */ + ret = statfunc(name, & sbuf); + if (ret < 0) @{ + update_ERRNO_int(errno); + return make_number(ret, result); + @} +@end example + +The tedious work is done by @code{fill_stat_array()}, shown +earlier. When done, the function returns the result from @code{fill_stat_array()}: + +@example + ret = fill_stat_array(name, array, & sbuf); + + return make_number(ret, result); +@} +@end example + +Finally, it's necessary to provide the ``glue'' that loads the +new function(s) into @command{gawk}. + +The @code{filefuncs} extension also provides an @code{fts()} +function, which we omit here. For its sake there is an initialization +function: + +@example +/* init_filefuncs --- initialization routine */ + +static awk_bool_t +init_filefuncs(void) +@{ + @dots{} +@} +@end example + +We are almost done. We need an array of @code{awk_ext_func_t} +structures for loading each function into @command{gawk}: + +@example +static awk_ext_func_t func_table[] = @{ + @{ "chdir", do_chdir, 1 @}, + @{ "stat", do_stat, 2 @}, +#ifndef __MINGW32__ + @{ "fts", do_fts, 3 @}, +#endif +@}; +@end example + +Each extension must have a routine named @code{dl_load()} to load +everything that needs to be loaded. It is simplest to use the +@code{dl_load_func()} macro in @code{gawkapi.h}: + +@example +/* define the dl_load() function using the boilerplate macro */ + +dl_load_func(func_table, filefuncs, "") +@end example + +And that's it! + +@node Using Internal File Ops +@subsection Integrating the Extensions + +@cindex @command{gawk}, interpreter@comma{} adding code to +Now that the code is written, it must be possible to add it at +runtime to the running @command{gawk} interpreter. First, the +code must be compiled. Assuming that the functions are in +a file named @file{filefuncs.c}, and @var{idir} is the location +of the @file{gawkapi.h} header file, +the following steps@footnote{In practice, you would probably want to +use the GNU Autotools (Automake, Autoconf, Libtool, and @command{gettext}) to +configure and build your libraries. Instructions for doing so are beyond +the scope of this @value{DOCUMENT}. @DBXREF{gawkextlib} for Internet links to +the tools.} create a GNU/Linux shared library: + +@example +$ @kbd{gcc -fPIC -shared -DHAVE_CONFIG_H -c -O -g -I@var{idir} filefuncs.c} +$ @kbd{gcc -o filefuncs.so -shared filefuncs.o} +@end example + +Once the library exists, it is loaded by using the @code{@@load} keyword: + +@example +# file testff.awk +@@load "filefuncs" + +BEGIN @{ + "pwd" | getline curdir # save current directory + close("pwd") + + chdir("/tmp") + system("pwd") # test it + chdir(curdir) # go back + + print "Info for testff.awk" + ret = stat("testff.awk", data) + print "ret =", ret + for (i in data) + printf "data[\"%s\"] = %s\n", i, data[i] + print "testff.awk modified:", + strftime("%m %d %Y %H:%M:%S", data["mtime"]) + + print "\nInfo for JUNK" + ret = stat("JUNK", data) + print "ret =", ret + for (i in data) + printf "data[\"%s\"] = %s\n", i, data[i] + print "JUNK modified:", strftime("%m %d %Y %H:%M:%S", data["mtime"]) +@} +@end example + +The @env{AWKLIBPATH} environment variable tells +@command{gawk} where to find extensions (@pxref{Finding Extensions}). +We set it to the current directory and run the program: + +@example +$ @kbd{AWKLIBPATH=$PWD gawk -f testff.awk} +@print{} /tmp +@print{} Info for testff.awk +@print{} ret = 0 +@print{} data["blksize"] = 4096 +@print{} data["devbsize"] = 512 +@print{} data["mtime"] = 1412004710 +@print{} data["mode"] = 33204 +@print{} data["type"] = file +@print{} data["dev"] = 2053 +@print{} data["gid"] = 1000 +@print{} data["ino"] = 10358899 +@print{} data["ctime"] = 1412004710 +@print{} data["blocks"] = 8 +@print{} data["nlink"] = 1 +@print{} data["name"] = testff.awk +@print{} data["atime"] = 1412004716 +@print{} data["pmode"] = -rw-rw-r-- +@print{} data["size"] = 666 +@print{} data["uid"] = 1000 +@print{} testff.awk modified: 09 29 2014 18:31:50 +@print{} +@print{} Info for JUNK +@print{} ret = -1 +@print{} JUNK modified: 01 01 1970 02:00:00 +@end example + +@node Extension Samples +@section The Sample Extensions in the @command{gawk} Distribution +@cindex extensions distributed with @command{gawk} + +This @value{SECTION} provides brief overviews of the sample extensions +that come in the @command{gawk} distribution. Some of them are intended +for production use (e.g., the @code{filefuncs}, @code{readdir} and +@code{inplace} extensions). Others mainly provide example code that +shows how to use the extension API. + +@menu +* Extension Sample File Functions:: The file functions sample. +* Extension Sample Fnmatch:: An interface to @code{fnmatch()}. +* Extension Sample Fork:: An interface to @code{fork()} and other + process functions. +* Extension Sample Inplace:: Enabling in-place file editing. +* Extension Sample Ord:: Character to value to character + conversions. +* Extension Sample Readdir:: An interface to @code{readdir()}. +* Extension Sample Revout:: Reversing output sample output wrapper. +* Extension Sample Rev2way:: Reversing data sample two-way processor. +* Extension Sample Read write array:: Serializing an array to a file. +* Extension Sample Readfile:: Reading an entire file into a string. +* Extension Sample Time:: An interface to @code{gettimeofday()} + and @code{sleep()}. +* Extension Sample API Tests:: Tests for the API. +@end menu + +@node Extension Sample File Functions +@subsection File-Related Functions + +The @code{filefuncs} extension provides three different functions, as follows. +The usage is: + +@table @asis +@item @code{@@load "filefuncs"} +This is how you load the extension. + +@cindex @code{chdir()} extension function +@item @code{result = chdir("/some/directory")} +The @code{chdir()} function is a direct hook to the @code{chdir()} +system call to change the current directory. It returns zero +upon success or less than zero upon error. In the latter case, it updates +@code{ERRNO}. + +@cindex @code{stat()} extension function +@item @code{result = stat("/some/path", statdata} [@code{, follow}]@code{)} +The @code{stat()} function provides a hook into the +@code{stat()} system call. +It returns zero upon success or less than zero upon error. +In the latter case, it updates @code{ERRNO}. + +By default, it uses the @code{lstat()} system call. However, if passed +a third argument, it uses @code{stat()} instead. + +In all cases, it clears the @code{statdata} array. +When the call is successful, @code{stat()} fills the @code{statdata} +array with information retrieved from the filesystem, as follows: + +@multitable @columnfractions .15 .50 .20 +@headitem Subscript @tab Field in @code{struct stat} @tab File type +@item @code{"name"} @tab The @value{FN} @tab All +@item @code{"dev"} @tab @code{st_dev} @tab All +@item @code{"ino"} @tab @code{st_ino} @tab All +@item @code{"mode"} @tab @code{st_mode} @tab All +@item @code{"nlink"} @tab @code{st_nlink} @tab All +@item @code{"uid"} @tab @code{st_uid} @tab All +@item @code{"gid"} @tab @code{st_gid} @tab All +@item @code{"size"} @tab @code{st_size} @tab All +@item @code{"atime"} @tab @code{st_atime} @tab All +@item @code{"mtime"} @tab @code{st_mtime} @tab All +@item @code{"ctime"} @tab @code{st_ctime} @tab All +@item @code{"rdev"} @tab @code{st_rdev} @tab Device files +@item @code{"major"} @tab @code{st_major} @tab Device files +@item @code{"minor"} @tab @code{st_minor} @tab Device files +@item @code{"blksize"} @tab @code{st_blksize} @tab All +@item @code{"pmode"} @tab A human-readable version of the mode value, such as printed by +@command{ls}. For example, @code{"-rwxr-xr-x"} @tab All +@item @code{"linkval"} @tab The value of the symbolic link @tab Symbolic links +@item @code{"type"} @tab The type of the file as a string. One of +@code{"file"}, +@code{"blockdev"}, +@code{"chardev"}, +@code{"directory"}, +@code{"socket"}, +@code{"fifo"}, +@code{"symlink"}, +@code{"door"}, +or +@code{"unknown"}. +Not all systems support all file types. @tab All +@end multitable + +@cindex @code{fts()} extension function +@item @code{flags = or(FTS_PHYSICAL, ...)} +@itemx @code{result = fts(pathlist, flags, filedata)} +Walk the file trees provided in @code{pathlist} and fill in the +@code{filedata} array as described next. @code{flags} is the bitwise +OR of several predefined values, also described in a moment. +Return zero if there were no errors, otherwise return @minus{}1. +@end table + +The @code{fts()} function provides a hook to the C library @code{fts()} +routines for traversing file hierarchies. Instead of returning data +about one file at a time in a stream, it fills in a multidimensional +array with data about each file and directory encountered in the requested +hierarchies. + +The arguments are as follows: + +@table @code +@item pathlist +An array of @value{FN}s. The element values are used; the index values are ignored. + +@item flags +This should be the bitwise OR of one or more of the following +predefined constant flag values. At least one of +@code{FTS_LOGICAL} or @code{FTS_PHYSICAL} must be provided; otherwise +@code{fts()} returns an error value and sets @code{ERRNO}. +The flags are: + +@c nested table +@table @code +@item FTS_LOGICAL +Do a ``logical'' file traversal, where the information returned for +a symbolic link refers to the linked-to file, and not to the symbolic +link itself. This flag is mutually exclusive with @code{FTS_PHYSICAL}. + +@item FTS_PHYSICAL +Do a ``physical'' file traversal, where the information returned for a +symbolic link refers to the symbolic link itself. This flag is mutually +exclusive with @code{FTS_LOGICAL}. + +@item FTS_NOCHDIR +As a performance optimization, the C library @code{fts()} routines +change directory as they traverse a file hierarchy. This flag disables +that optimization. + +@item FTS_COMFOLLOW +Immediately follow a symbolic link named in @code{pathlist}, +whether or not @code{FTS_LOGICAL} is set. + +@item FTS_SEEDOT +By default, the C library @code{fts()} routines do not return entries for +@file{.} (dot) and @file{..} (dot-dot). This option causes entries for +dot-dot to also be included. (The extension always includes an entry +for dot; more on this in a moment.) + +@item FTS_XDEV +During a traversal, do not cross onto a different mounted filesystem. +@end table + +@item filedata +The @code{filedata} array is first cleared. Then, @code{fts()} creates +an element in @code{filedata} for every element in @code{pathlist}. +The index is the name of the directory or file given in @code{pathlist}. +The element for this index is itself an array. There are two cases: + +@c nested table +@table @emph +@item The path is a file +In this case, the array contains two or three elements: + +@c doubly nested table +@table @code +@item "path" +The full path to this file, starting from the ``root'' that was given +in the @code{pathlist} array. + +@item "stat" +This element is itself an array, containing the same information as provided +by the @code{stat()} function described earlier for its +@code{statdata} argument. The element may not be present if +the @code{stat()} system call for the file failed. + +@item "error" +If some kind of error was encountered, the array will also +contain an element named @code{"error"}, which is a string describing the error. +@end table + +@item The path is a directory +In this case, the array contains one element for each entry in the +directory. If an entry is a file, that element is the same as for files, just +described. If the entry is a directory, that element is (recursively) +an array describing the subdirectory. If @code{FTS_SEEDOT} was provided +in the flags, then there will also be an element named @code{".."}. This +element will be an array containing the data as provided by @code{stat()}. + +In addition, there will be an element whose index is @code{"."}. +This element is an array containing the same two or three elements as +for a file: @code{"path"}, @code{"stat"}, and @code{"error"}. +@end table +@end table + +The @code{fts()} function returns zero if there were no errors. +Otherwise it returns @minus{}1. + +@quotation NOTE +The @code{fts()} extension does not exactly mimic the +interface of the C library @code{fts()} routines, choosing instead to +provide an interface that is based on associative arrays, which is +more comfortable to use from an @command{awk} program. This includes the +lack of a comparison function, because @command{gawk} already provides +powerful array sorting facilities. Although an @code{fts_read()}-like +interface could have been provided, this felt less natural than simply +creating a multidimensional array to represent the file hierarchy and +its information. +@end quotation + +See @file{test/fts.awk} in the @command{gawk} distribution for an example +use of the @code{fts()} extension function. + +@node Extension Sample Fnmatch +@subsection Interface to @code{fnmatch()} + +This extension provides an interface to the C library +@code{fnmatch()} function. The usage is: + +@table @code +@item @@load "fnmatch" +This is how you load the extension. + +@cindex @code{fnmatch()} extension function +@item result = fnmatch(pattern, string, flags) +The return value is zero on success, @code{FNM_NOMATCH} +if the string did not match the pattern, or +a different nonzero value if an error occurred. +@end table + +In addition to the @code{fnmatch()} function, the @code{fnmatch} extension +adds one constant (@code{FNM_NOMATCH}), and an array of flag values +named @code{FNM}. + +The arguments to @code{fnmatch()} are: + +@table @code +@item pattern +The @value{FN} wildcard to match. + +@item string +The @value{FN} string. + +@item flag +Either zero, or the bitwise OR of one or more of the +flags in the @code{FNM} array. +@end table + +The flags are as follows: + +@multitable @columnfractions .25 .75 +@headitem Array element @tab Corresponding flag defined by @code{fnmatch()} +@item @code{FNM["CASEFOLD"]} @tab @code{FNM_CASEFOLD} +@item @code{FNM["FILE_NAME"]} @tab @code{FNM_FILE_NAME} +@item @code{FNM["LEADING_DIR"]} @tab @code{FNM_LEADING_DIR} +@item @code{FNM["NOESCAPE"]} @tab @code{FNM_NOESCAPE} +@item @code{FNM["PATHNAME"]} @tab @code{FNM_PATHNAME} +@item @code{FNM["PERIOD"]} @tab @code{FNM_PERIOD} +@end multitable + +Here is an example: + +@example +@@load "fnmatch" +@dots{} +flags = or(FNM["PERIOD"], FNM["NOESCAPE"]) +if (fnmatch("*.a", "foo.c", flags) == FNM_NOMATCH) + print "no match" +@end example + +@node Extension Sample Fork +@subsection Interface to @code{fork()}, @code{wait()}, and @code{waitpid()} + +The @code{fork} extension adds three functions, as follows: + +@table @code +@item @@load "fork" +This is how you load the extension. + +@cindex @code{fork()} extension function +@item pid = fork() +This function creates a new process. The return value is zero in the +child and the process-ID number of the child in the parent, or @minus{}1 +upon error. In the latter case, @code{ERRNO} indicates the problem. +In the child, @code{PROCINFO["pid"]} and @code{PROCINFO["ppid"]} are +updated to reflect the correct values. + +@cindex @code{waitpid()} extension function +@item ret = waitpid(pid) +This function takes a numeric argument, which is the process-ID to +wait for. The return value is that of the +@code{waitpid()} system call. + +@cindex @code{wait()} extension function +@item ret = wait() +This function waits for the first child to die. +The return value is that of the +@code{wait()} system call. +@end table + +There is no corresponding @code{exec()} function. + +Here is an example: + +@example +@@load "fork" +@dots{} +if ((pid = fork()) == 0) + print "hello from the child" +else + print "hello from the parent" +@end example + +@node Extension Sample Inplace +@subsection Enabling In-Place File Editing + +@cindex @code{inplace} extension +The @code{inplace} extension emulates GNU @command{sed}'s @option{-i} option +which performs ``in place'' editing of each input file. +It uses the bundled @file{inplace.awk} include file to invoke the extension +properly: + +@example +@c file eg/lib/inplace.awk +@group +# inplace --- load and invoke the inplace extension. + +@@load "inplace" + +# Please set INPLACE_SUFFIX to make a backup copy. For example, you may +# want to set INPLACE_SUFFIX to .bak on the command line or in a BEGIN rule. + +BEGINFILE @{ + inplace_begin(FILENAME, INPLACE_SUFFIX) +@} + +ENDFILE @{ + inplace_end(FILENAME, INPLACE_SUFFIX) +@} +@end group +@c endfile +@end example + +For each regular file that is processed, the extension redirects +standard output to a temporary file configured to have the same owner +and permissions as the original. After the file has been processed, +the extension restores standard output to its original destination. +If @code{INPLACE_SUFFIX} is not an empty string, the original file is +linked to a backup @value{FN} created by appending that suffix. Finally, +the temporary file is renamed to the original @value{FN}. + +If any error occurs, the extension issues a fatal error to terminate +processing immediately without damaging the original file. + +Here are some simple examples: + +@example +$ @kbd{gawk -i inplace '@{ gsub(/foo/, "bar") @}; @{ print @}' file1 file2 file3} +@end example + +To keep a backup copy of the original files, try this: + +@example +$ @kbd{gawk -i inplace -v INPLACE_SUFFIX=.bak '@{ gsub(/foo/, "bar") @}} +> @kbd{@{ print @}' file1 file2 file3} +@end example + +@node Extension Sample Ord +@subsection Character and Numeric values: @code{ord()} and @code{chr()} + +The @code{ordchr} extension adds two functions, named +@code{ord()} and @code{chr()}, as follows: + +@table @code +@item @@load "ordchr" +This is how you load the extension. + +@cindex @code{ord()} extension function +@item number = ord(string) +Return the numeric value of the first character in @code{string}. + +@cindex @code{chr()} extension function +@item char = chr(number) +Return a string whose first character is that represented by @code{number}. +@end table + +These functions are inspired by the Pascal language functions +of the same name. Here is an example: + +@example +@@load "ordchr" +@dots{} +printf("The numeric value of 'A' is %d\n", ord("A")) +printf("The string value of 65 is %s\n", chr(65)) +@end example + +@node Extension Sample Readdir +@subsection Reading Directories + +The @code{readdir} extension adds an input parser for directories. +The usage is as follows: + +@cindex @code{readdir} extension +@example +@@load "readdir" +@end example + +When this extension is in use, instead of skipping directories named +on the command line (or with @code{getline}), +they are read, with each entry returned as a record. + +The record consists of three fields. The first two are the inode number and the +@value{FN}, separated by a forward slash character. +On systems where the directory entry contains the file type, the record +has a third field (also separated by a slash) which is a single letter +indicating the type of the file. The letters and their corresponding file +types are shown in @ref{table-readdir-file-types}. + +@float Table,table-readdir-file-types +@caption{File types returned by the @code{readdir} extension} +@multitable @columnfractions .1 .9 +@headitem Letter @tab File Type +@item @code{b} @tab Block device +@item @code{c} @tab Character device +@item @code{d} @tab Directory +@item @code{f} @tab Regular file +@item @code{l} @tab Symbolic link +@item @code{p} @tab Named pipe (FIFO) +@item @code{s} @tab Socket +@item @code{u} @tab Anything else (unknown) +@end multitable +@end float + +On systems without the file type information, the third field is always +@samp{u}. + +@quotation NOTE +On GNU/Linux systems, there are filesystems that don't support the +@code{d_type} entry (see the @i{readdir}(3) manual page), and so the file +type is always @samp{u}. You can use the @code{filefuncs} extension to call +@code{stat()} in order to get correct type information. +@end quotation + +Here is an example: + +@example +@@load "readdir" +@dots{} +BEGIN @{ FS = "/" @} +@{ print "file name is", $2 @} +@end example + +@node Extension Sample Revout +@subsection Reversing Output + +The @code{revoutput} extension adds a simple output wrapper that reverses +the characters in each output line. Its main purpose is to show how to +write an output wrapper, although it may be mildly amusing for the unwary. +Here is an example: + +@cindex @code{revoutput} extension +@example +@@load "revoutput" + +BEGIN @{ + REVOUT = 1 + print "don't panic" > "/dev/stdout" +@} +@end example + +The output from this program is: +@samp{cinap t'nod}. + +@node Extension Sample Rev2way +@subsection Two-Way I/O Example + +The @code{revtwoway} extension adds a simple two-way processor that +reverses the characters in each line sent to it for reading back by +the @command{awk} program. Its main purpose is to show how to write +a two-way processor, although it may also be mildly amusing. +The following example shows how to use it: + +@cindex @code{revtwoway} extension +@example +@@load "revtwoway" + +BEGIN @{ + cmd = "/magic/mirror" + print "don't panic" |& cmd + cmd |& getline result + print result + close(cmd) +@} +@end example + +The output from this program +@ifnotinfo +also is: +@end ifnotinfo +@ifinfo +is: +@end ifinfo +@samp{cinap t'nod}. + +@node Extension Sample Read write array +@subsection Dumping and Restoring an Array + +The @code{rwarray} extension adds two functions, +named @code{writea()} and @code{reada()}, as follows: + +@table @code +@item @@load "rwarray" +This is how you load the extension. + +@cindex @code{writea()} extension function +@item ret = writea(file, array) +This function takes a string argument, which is the name of the file +to which to dump the array, and the array itself as the second argument. +@code{writea()} understands arrays of arrays. It returns one on +success, or zero upon failure. + +@cindex @code{reada()} extension function +@item ret = reada(file, array) +@code{reada()} is the inverse of @code{writea()}; +it reads the file named as its first argument, filling in +the array named as the second argument. It clears the array first. +Here too, the return value is one on success and zero upon failure. +@end table + +The array created by @code{reada()} is identical to that written by +@code{writea()} in the sense that the contents are the same. However, +due to implementation issues, the array traversal order of the re-created +array is likely to be different from that of the original array. As array +traversal order in @command{awk} is by default undefined, this is (technically) +not a problem. If you need to guarantee a particular traversal +order, use the array sorting features in @command{gawk} to do so +(@pxref{Array Sorting}). + +The file contains binary data. All integral values are written in network +byte order. However, double-precision floating-point values are written +as native binary data. Thus, arrays containing only string data can +theoretically be dumped on systems with one byte order and restored on +systems with a different one, but this has not been tried. + +Here is an example: + +@example +@@load "rwarray" +@dots{} +ret = writea("arraydump.bin", array) +@dots{} +ret = reada("arraydump.bin", array) +@end example + +@node Extension Sample Readfile +@subsection Reading an Entire File + +The @code{readfile} extension adds a single function +named @code{readfile()}, and an input parser: + +@table @code +@item @@load "readfile" +This is how you load the extension. + +@cindex @code{readfile()} extension function +@item result = readfile("/some/path") +The argument is the name of the file to read. The return value is a +string containing the entire contents of the requested file. Upon error, +the function returns the empty string and sets @code{ERRNO}. + +@item BEGIN @{ PROCINFO["readfile"] = 1 @} +In addition, the extension adds an input parser that is activated if +@code{PROCINFO["readfile"]} exists. +When activated, each input file is returned in its entirety as @code{$0}. +@code{RT} is set to the null string. +@end table + +Here is an example: + +@example +@@load "readfile" +@dots{} +contents = readfile("/path/to/file"); +if (contents == "" && ERRNO != "") @{ + print("problem reading file", ERRNO) > "/dev/stderr" + ... +@} +@end example + +@node Extension Sample Time +@subsection Extension Time Functions + +The @code{time} extension adds two functions, named @code{gettimeofday()} +and @code{sleep()}, as follows: + +@table @code +@item @@load "time" +This is how you load the extension. + +@cindex @code{gettimeofday()} extension function +@item the_time = gettimeofday() +Return the time in seconds that has elapsed since 1970-01-01 UTC as a +floating-point value. If the time is unavailable on this platform, return +@minus{}1 and set @code{ERRNO}. The returned time should have sub-second +precision, but the actual precision may vary based on the platform. +If the standard C @code{gettimeofday()} system call is available on this +platform, then it simply returns the value. Otherwise, if on MS-Windows, +it tries to use @code{GetSystemTimeAsFileTime()}. + +@cindex @code{sleep()} extension function +@item result = sleep(@var{seconds}) +Attempt to sleep for @var{seconds} seconds. If @var{seconds} is negative, +or the attempt to sleep fails, return @minus{}1 and set @code{ERRNO}. +Otherwise, return zero after sleeping for the indicated amount of time. +Note that @var{seconds} may be a floating-point (non-integral) value. +Implementation details: depending on platform availability, this function +tries to use @code{nanosleep()} or @code{select()} to implement the delay. +@end table + +@node Extension Sample API Tests +@subsection API Tests +@cindex @code{testext} extension + +The @code{testext} extension exercises parts of the extension API that +are not tested by the other samples. The @file{extension/testext.c} +file contains both the C code for the extension and @command{awk} +test code inside C comments that run the tests. The testing framework +extracts the @command{awk} code and runs the tests. See the source file +for more information. + +@node gawkextlib +@section The @code{gawkextlib} Project +@cindex @code{gawkextlib} +@cindex extensions, where to find + +@cindex @code{gawkextlib} project +The @uref{http://sourceforge.net/projects/gawkextlib/, @code{gawkextlib}} +project provides a number of @command{gawk} extensions, including one for +processing XML files. This is the evolution of the original @command{xgawk} +(XML @command{gawk}) project. + +As of this writing, there are six extensions: + +@itemize @value{BULLET} +@item +GD graphics library extension + +@item +PDF extension + +@item +PostgreSQL extension + +@item +MPFR library extension +(this provides access to a number of MPFR functions which @command{gawk}'s +native MPFR support does not) + +@item +Redis extension + +@item +XML parser extension, using the @uref{http://expat.sourceforge.net, Expat} +XML parsing library +@end itemize + +@cindex @command{git} utility +You can check out the code for the @code{gawkextlib} project +using the @uref{http://git-scm.com, Git} distributed source +code control system. The command is as follows: + +@example +git clone git://git.code.sf.net/p/gawkextlib/code gawkextlib-code +@end example + +@cindex Expat XML parser library +You will need to have the @uref{http://expat.sourceforge.net, Expat} +XML parser library installed in order to build and use the XML extension. + +In addition, you must have the GNU Autotools installed +(@uref{http://www.gnu.org/software/autoconf, Autoconf}, +@uref{http://www.gnu.org/software/automake, Automake}, +@uref{http://www.gnu.org/software/libtool, Libtool}, +and +@uref{http://www.gnu.org/software/gettext, GNU @command{gettext}}). + +The simple recipe for building and testing @code{gawkextlib} is as follows. +First, build and install @command{gawk}: + +@example +cd .../path/to/gawk/code +./configure --prefix=/tmp/newgawk @ii{Install in /tmp/newgawk for now} +make && make check @ii{Build and check that all is OK} +make install @ii{Install gawk} +@end example + +Next, build @code{gawkextlib} and test it: + +@example +cd .../path/to/gawkextlib-code +./update-autotools @ii{Generate configure, etc.} + @ii{You may have to run this command twice} +./configure --with-gawk=/tmp/newgawk @ii{Configure, point at ``installed'' gawk} +make && make check @ii{Build and check that all is OK} +make install @ii{Install the extensions} +@end example + +If you have installed @command{gawk} in the standard way, then you +will likely not need the @option{--with-gawk} option when configuring +@code{gawkextlib}. You may also need to use the @command{sudo} utility +to install both @command{gawk} and @code{gawkextlib}, depending upon +how your system works. + +If you write an extension that you wish to share with other +@command{gawk} users, consider doing so through the +@code{gawkextlib} project. +See the project's website for more information. + +@node Extension summary +@section Summary + +@itemize @value{BULLET} +@item +You can write extensions (sometimes called plug-ins) for @command{gawk} +in C or C++ using the application programming interface (API) defined +by the @command{gawk} developers. + +@item +Extensions must have a license compatible with the GNU General Public +License (GPL), and they must assert that fact by declaring a variable +named @code{plugin_is_GPL_compatible}. + +@item +Communication between @command{gawk} and an extension is two-way. +@command{gawk} passes a @code{struct} to the extension which contains +various data fields and function pointers. The extension can then call +into @command{gawk} via the supplied function pointers to accomplish +certain tasks. + +@item +One of these tasks is to ``register'' the name and implementation of +new @command{awk}-level functions with @command{gawk}. The implementation +takes the form of a C function pointer with a defined signature. +By convention, implementation functions are named @code{do_@var{XXXX}()} +for some @command{awk}-level function @code{@var{XXXX}()}. + +@item +The API is defined in a header file named @file{gawkpi.h}. You must include +a number of standard header files @emph{before} including it in your source file. + +@item +API function pointers are provided for the following kinds of operations: + +@itemize @value{BULLET} +@item +Allocating, reallocating, and releasing memory + +@item +Registration functions (you may register +extension functions, +exit callbacks, +a version string, +input parsers, +output wrappers, +and two-way processors) + +@item +Printing fatal, warning, and ``lint'' warning messages + +@item +Updating @code{ERRNO}, or unsetting it + +@item +Accessing parameters, including converting an undefined parameter into +an array + +@item +Symbol table access (retrieving a global variable, creating one, +or changing one) + +@item +Creating and releasing cached values; this provides an +efficient way to use values for multiple variables and +can be a big performance win + +@item +Manipulating arrays +(retrieving, adding, deleting, and modifying elements; +getting the count of elements in an array; +creating a new array; +clearing an array; +and +flattening an array for easy C style looping over all its indices and elements) +@end itemize + +@item +The API defines a number of standard data types for representing +@command{awk} values, array elements, and arrays. + +@item +The API provide convenience functions for constructing values. +It also provides memory management functions to ensure compatibility +between memory allocated by @command{gawk} and memory allocated by an +extension. + +@item +@emph{All} memory passed from @command{gawk} to an extension must be +treated as read-only by the extension. + +@item +@emph{All} memory passed from an extension to @command{gawk} must come from +the API's memory allocation functions. @command{gawk} takes responsibility for +the memory and releases it when appropriate. + +@item +The API provides information about the running version of @command{gawk} so +that an extension can make sure it is compatible with the @command{gawk} +that loaded it. + +@item +It is easiest to start a new extension by copying the boilerplate code +described in this @value{CHAPTER}. Macros in the @file{gawkapi.h} header +file make this easier to do. + +@item +The @command{gawk} distribution includes a number of small but useful +sample extensions. The @code{gawkextlib} project includes several more, +larger, extensions. If you wish to write an extension and contribute it +to the community of @command{gawk} users, the @code{gawkextlib} project +is the place to do so. + +@end itemize + +@c EXCLUDE START +@node Extension Exercises +@section Exercises + +@enumerate +@item +Add functions to implement system calls such as @code{chown()}, +@code{chmod()}, and @code{umask()} to the file operations extension +presented in @ref{Internal File Ops}. + +@item +(Hard.) +How would you provide namespaces in @command{gawk}, so that the +names of functions in different extensions don't conflict with each other? +If you come up with a really good scheme, contact the @command{gawk} +maintainer to tell him about it. + +@item +Write a wrapper script that provides an interface similar to +@samp{sed -i} for the ``inplace'' extension presented in +@ref{Extension Sample Inplace}. + +@end enumerate +@c EXCLUDE END + +@ifnotinfo +@part @value{PART4}Appendices +@end ifnotinfo + +@ifdocbook + +@ifclear FOR_PRINT +Part IV contains the appendices (including the two licenses that cover +the @command{gawk} source code and this @value{DOCUMENT}, respectively) +and the Glossary: +@end ifclear + +@ifset FOR_PRINT +Part IV contains three appendices, the last of which is the license that +covers the @command{gawk} source code: +@end ifset + +@itemize @value{BULLET} +@item +@ref{Language History} + +@item +@ref{Installation} + +@ifclear FOR_PRINT +@item +@ref{Notes} + +@item +@ref{Basic Concepts} + +@item +@ref{Glossary} +@end ifclear + +@item +@ref{Copying} + +@ifclear FOR_PRINT +@item +@ref{GNU Free Documentation License} +@end ifclear +@end itemize +@end ifdocbook @node Language History @appendix The Evolution of the @command{awk} Language -This @value{DOCUMENT} describes the GNU implementation of @command{awk}, which follows -the POSIX specification. -Many long-time @command{awk} users learned @command{awk} programming -with the original @command{awk} implementation in Version 7 Unix. -(This implementation was the basis for @command{awk} in Berkeley Unix, -through 4.3-Reno. Subsequent versions of Berkeley Unix, and some systems -derived from 4.4BSD-Lite, use various versions of @command{gawk} -for their @command{awk}.) -This @value{CHAPTER} briefly describes the -evolution of the @command{awk} language, with cross-references to other parts -of the @value{DOCUMENT} where you can find more information. - -@c FIXME: Try to determine whether it was 3.1 or 3.2 that had new awk. +This @value{DOCUMENT} describes the GNU implementation of @command{awk}, +which follows the POSIX specification. Many longtime @command{awk} +users learned @command{awk} programming with the original @command{awk} +implementation in Version 7 Unix. (This implementation was the basis for +@command{awk} in Berkeley Unix, through 4.3-Reno. Subsequent versions +of Berkeley Unix, and, for a while, some systems derived from 4.4BSD-Lite, used various +versions of @command{gawk} for their @command{awk}.) This @value{CHAPTER} +briefly describes the evolution of the @command{awk} language, with +cross-references to other parts of the @value{DOCUMENT} where you can +find more information. + +@ifset FOR_PRINT +To save space, we have omitted +information on the history of features in @command{gawk} from this +edition. You can find it in the +@uref{http://www.gnu.org/software/gawk/manual/html_node/Feature-History.html, +online documentation}. +@end ifset @menu * V7/SVR3.1:: The major changes between V7 and System V @@ -26465,16 +35270,16 @@ of the @value{DOCUMENT} where you can find more information. @command{awk}. * POSIX/GNU:: The extensions in @command{gawk} not in POSIX @command{awk}. +* Feature History:: The history of the features in @command{gawk}. * Common Extensions:: Common Extensions Summary. * Ranges and Locales:: How locales used to affect regexp ranges. * Contributors:: The major contributors to @command{gawk}. +* History summary:: History summary. @end menu @node V7/SVR3.1 @appendixsec Major Changes Between V7 and SVR3.1 -@c STARTOFRANGE gawkv @cindex @command{awk}, versions of -@c STARTOFRANGE gawkv1 @cindex @command{awk}, versions of, changes between V7 and SVR3.1 The @command{awk} language evolved considerably between the release of @@ -26482,7 +35287,7 @@ Version 7 Unix (1978) and the new version that was first made generally availabl System V Release 3.1 (1987). This @value{SECTION} summarizes the changes, with cross-references to further details: -@itemize @bullet +@itemize @value{BULLET} @item The requirement for @samp{;} to separate rules on a line (@pxref{Statements/Lines}). @@ -26512,7 +35317,7 @@ The built-in functions @code{close()} and @code{system()} @item The @code{ARGC}, @code{ARGV}, @code{FNR}, @code{RLENGTH}, @code{RSTART}, -and @code{SUBSEP} built-in variables (@pxref{Built-in Variables}). +and @code{SUBSEP} predefined variables (@pxref{Built-in Variables}). @item Assignable @code{$0} (@pxref{Changing Fields}). @@ -26543,14 +35348,11 @@ of @code{FS}. @item Dynamic regexps as operands of the @samp{~} and @samp{!~} operators -(@pxref{Regexp Usage}). +(@pxref{Computed Regexps}). @item The escape sequences @samp{\b}, @samp{\f}, and @samp{\r} (@pxref{Escape Sequences}). -(Some vendors have updated their old versions of @command{awk} to -recognize @samp{\b}, @samp{\f}, and @samp{\r}, but this is not -something you can rely on.) @item Redirection of input for the @code{getline} function @@ -26562,9 +35364,8 @@ Multiple @code{BEGIN} and @code{END} rules @item Multidimensional arrays -(@pxref{Multi-dimensional}). +(@pxref{Multidimensional}). @end itemize -@c ENDOFRANGE gawkv1 @node SVR4 @appendixsec Changes Between SVR3.1 and SVR4 @@ -26573,7 +35374,7 @@ Multidimensional arrays The System V Release 4 (1989) version of Unix @command{awk} added these features (some of which originated in @command{gawk}): -@itemize @bullet +@itemize @value{BULLET} @item The @code{ENVIRON} array (@pxref{Built-in Variables}). @c gawk and MKS awk @@ -26589,7 +35390,7 @@ The @option{-v} option for assigning variables before program execution begins @c GNU, Bell Laboratories & MKS together @item -The @option{--} option for terminating command-line options. +The @option{--} signal for terminating command-line options. @item The @samp{\a}, @samp{\v}, and @samp{\x} escape sequences @@ -26612,7 +35413,7 @@ A cleaner specification for the @samp{%c} format-control letter in the @item The ability to dynamically pass the field width and precision (@code{"%*.*d"}) -in the argument list of the @code{printf} function +in the argument list of @code{printf} and @code{sprintf()} (@pxref{Control Letters}). @item @@ -26633,7 +35434,7 @@ Processing of escape sequences inside command-line variable assignments The POSIX Command Language and Utilities standard for @command{awk} (1992) introduced the following changes into the language: -@itemize @bullet +@itemize @value{BULLET} @item The use of @option{-W} for implementation-specific options (@pxref{Options}). @@ -26647,21 +35448,38 @@ The concept of a numeric string and tighter comparison rules to go with it (@pxref{Typing and Comparison}). @item -The use of built-in variables as function parameter names is forbidden -(@pxref{Definition Syntax}. +The use of predefined variables as function parameter names is forbidden +(@pxref{Definition Syntax}). @item More complete documentation of many of the previously undocumented features of the language. @end itemize -@xref{Common Extensions}, for a list of common extensions +In 2012, a number of extensions that had been commonly available for +many years were finally added to POSIX. They are: + +@itemize @value{BULLET} +@item +The @code{fflush()} built-in function for flushing buffered output +(@pxref{I/O Functions}). + +@item +The @code{nextfile} statement +(@pxref{Nextfile Statement}). + +@item +The ability to delete all of an array at once with @samp{delete @var{array}} +(@pxref{Delete}). + +@end itemize + +@DBXREF{Common Extensions} for a list of common extensions not permitted by the POSIX standard. The 2008 POSIX standard can be found online at @url{http://www.opengroup.org/onlinepubs/9699919799/}. -@c ENDOFRANGE gawkv @node BTL @appendixsec Extensions in Brian Kernighan's @command{awk} @@ -26675,9 +35493,9 @@ has made his version available via his home page (@pxref{Other Versions}). This @value{SECTION} describes common extensions that -originally appeared in his version of @command{awk}. +originally appeared in his version of @command{awk}: -@itemize @bullet +@itemize @value{BULLET} @item The @samp{**} and @samp{**=} operators (@pxref{Arithmetic Ops} @@ -26695,23 +35513,20 @@ The @code{fflush()} built-in function for flushing buffered output @ignore @item The @code{SYMTAB} array, that allows access to @command{awk}'s internal symbol -table. This feature is not documented, largely because +table. This feature was never documented for his @command{awk}, largely because it is somewhat shakily implemented. For instance, you cannot access arrays or array elements through it. @end ignore @end itemize -@xref{Common Extensions}, for a full list of the extensions +@DBXREF{Common Extensions} for a full list of the extensions available in his @command{awk}. @node POSIX/GNU @appendixsec Extensions in @command{gawk} Not in POSIX @command{awk} -@c STARTOFRANGE fripls @cindex compatibility mode (@command{gawk}), extensions -@c STARTOFRANGE exgnot @cindex extensions, in @command{gawk}, not in POSIX @command{awk} -@c STARTOFRANGE posnot @cindex POSIX, @command{gawk} extensions not included in The GNU implementation, @command{gawk}, adds a large number of features. They can all be disabled with either the @option{--traditional} or @@ -26722,12 +35537,12 @@ A number of features have come and gone over the years. This @value{SECTION} summarizes the additional features over POSIX @command{awk} that are in the current version of @command{gawk}. -@itemize @bullet +@itemize @value{BULLET} @item -Additional built-in variables: +Additional predefined variables: -@itemize @minus +@itemize @value{MINUS} @item The @code{ARGIND} @@ -26748,7 +35563,7 @@ variables @item Special files in I/O redirections: -@itemize @minus{} +@itemize @value{MINUS} @item The @file{/dev/stdin}, @file{/dev/stdout}, @file{/dev/stderr} and @file{/dev/fd/@var{N}} special @value{FN}s @@ -26757,14 +35572,14 @@ The @file{/dev/stdin}, @file{/dev/stdout}, @file{/dev/stderr} and @item The @file{/inet}, @file{/inet4}, and @samp{/inet6} special files for TCP/IP networking using @samp{|&} to specify which version of the -IP protocol to use. +IP protocol to use (@pxref{TCP/IP Networking}). @end itemize @item Changes and/or additions to the language: -@itemize @minus{} +@itemize @value{MINUS} @item The @samp{\x} escape sequence (@pxref{Escape Sequences}). @@ -26797,26 +35612,18 @@ Indirect function calls @item Directories on the command line produce a warning and are skipped -(@pxref{Command line directories}). +(@pxref{Command-line directories}). @end itemize @item New keywords: -@itemize @minus{} +@itemize @value{MINUS} @item -The @code{BEGINFILE} and @code{ENDFILE} special patterns. +The @code{BEGINFILE} and @code{ENDFILE} special patterns (@pxref{BEGINFILE/ENDFILE}). @item -The ability to delete all of an array at once with @samp{delete @var{array}} -(@pxref{Delete}). - -@item -The @code{nextfile} statement -(@pxref{Nextfile Statement}). - -@item The @code{switch} statement (@pxref{Switch Statement}). @end itemize @@ -26824,14 +35631,14 @@ The @code{switch} statement @item Changes to standard @command{awk} functions: -@itemize @minus +@itemize @value{MINUS} @item The optional second argument to @code{close()} that allows closing one end of a two-way pipe to a coprocess (@pxref{Two-way I/O}). @item -POSIX compliance for @code{gsub()} and @code{sub()}. +POSIX compliance for @code{gsub()} and @code{sub()} with @option{--posix}. @item The @code{length()} function accepts an array argument @@ -26850,14 +35657,28 @@ making translations easier @item The @code{split()} function's additional optional fourth -argument which is an array to hold the text of the field separators. +argument which is an array to hold the text of the field separators (@pxref{String Functions}). @end itemize @item Additional functions only in @command{gawk}: -@itemize @minus +@itemize @value{MINUS} +@item +The @code{gensub()}, @code{patsplit()}, and @code{strtonum()} functions +for more powerful text manipulation +(@pxref{String Functions}). + +@item +The @code{asort()} and @code{asorti()} functions for sorting arrays +(@pxref{Array Sorting}). + +@item +The @code{mktime()}, @code{systime()}, and @code{strftime()} +functions for working with timestamps +(@pxref{Time Functions}). + @item The @code{and()}, @@ -26869,71 +35690,92 @@ and @code{xor()} functions for bit manipulation (@pxref{Bitwise Functions}). +@c In 4.1, and(), or() and xor() grew the ability to take > 2 arguments @item -The @code{asort()} and @code{asorti()} functions for sorting arrays -(@pxref{Array Sorting}). +The @code{isarray()} function to check if a variable is an array or not +(@pxref{Type Functions}). @item The @code{bindtextdomain()}, @code{dcgettext()} and @code{dcngettext()} functions for internationalization (@pxref{Programmer i18n}). - -@item -The @code{extension()} built-in function and the ability to add -new functions dynamically -(@pxref{Dynamic Extensions}). - -@item -The @code{fflush()} function from Brian Kernighan's -version of @command{awk} -(@pxref{I/O Functions}). - -@item -The @code{gensub()}, @code{patsplit()}, and @code{strtonum()} functions -for more powerful text manipulation -(@pxref{String Functions}). - -@item -The @code{mktime()}, @code{systime()}, and @code{strftime()} -functions for working with timestamps -(@pxref{Time Functions}). @end itemize - @item Changes and/or additions in the command-line options: -@itemize @minus +@itemize @value{MINUS} @item The @env{AWKPATH} environment variable for specifying a path search for the @option{-f} command-line option (@pxref{Options}). @item -The ability to use GNU-style long-named options that start with @option{--} +The @env{AWKLIBPATH} environment variable for specifying a path search for +the @option{-l} command-line option +(@pxref{Options}). + +@item +The +@option{-b}, +@option{-c}, +@option{-C}, +@option{-d}, +@option{-D}, +@option{-e}, +@option{-E}, +@option{-g}, +@option{-h}, +@option{-i}, +@option{-l}, +@option{-L}, +@option{-M}, +@option{-n}, +@option{-N}, +@option{-o}, +@option{-O}, +@option{-p}, +@option{-P}, +@option{-r}, +@option{-S}, +@option{-t}, +and +@option{-V} +short options. Also, the +ability to use GNU-style long-named options that start with @option{--} and the +@option{--assign}, +@option{--bignum}, @option{--characters-as-bytes}, -@option{--compat}, +@option{--copyright}, +@option{--debug}, @option{--dump-variables}, @option{--exec}, +@option{--field-separator}, +@option{--file}, @option{--gen-pot}, +@option{--help}, +@option{--include}, @option{--lint}, @option{--lint-old}, +@option{--load}, @option{--non-decimal-data}, +@option{--optimize}, @option{--posix}, +@option{--pretty-print}, @option{--profile}, @option{--re-interval}, @option{--sandbox}, @option{--source}, @option{--traditional}, +@option{--use-lc-numeric}, and -@option{--use-lc-numeric} -options +@option{--version} +long options (@pxref{Options}). @end itemize - @c new ports @item @@ -26941,7 +35783,7 @@ Support for the following obsolete systems was removed from the code and the documentation for @command{gawk} @value{PVERSION} 4.0: @c nested table -@itemize @minus +@itemize @value{MINUS} @item Amiga @@ -26975,39 +35817,668 @@ Tandem (non-POSIX) @item Prestandard VAX C compiler for VAX/VMS +@item +GCC for VAX and Alpha has not been tested for a while. + +@end itemize + +@item +Support for the following obsolete systems was removed from the code +for @command{gawk} @value{PVERSION} 4.1: + +@c nested table +@itemize @value{MINUS} +@item +Ultrix @end itemize +@item +@c FIXME: Verify the version here. +Support for MirBSD was removed at @command{gawk} @value{PVERSION} 4.2. + @end itemize @c XXX ADD MORE STUFF HERE -@c ENDOFRANGE fripls -@c ENDOFRANGE exgnot -@c ENDOFRANGE posnot + +@c This does not need to be in the formal book. +@ifclear FOR_PRINT +@node Feature History +@appendixsec History of @command{gawk} Features + +@ignore +See the thread: +https://groups.google.com/forum/#!topic/comp.lang.awk/SAUiRuff30c +This motivated me to add this section. +@end ignore + +@ignore +I've tried to follow this general order, esp.@: for the 3.0 and 3.1 sections: + variables + special files + language changes (e.g., hex constants) + differences in standard awk functions + new gawk functions + new keywords + new command-line options + behavioral changes + new ports +Within each category, be alphabetical. +@end ignore + +This @value{SECTION} describes the features in @command{gawk} +over and above those in POSIX @command{awk}, +in the order they were added to @command{gawk}. + +Version 2.10 of @command{gawk} introduced the following features: + +@itemize @value{BULLET} +@item +The @env{AWKPATH} environment variable for specifying a path search for +the @option{-f} command-line option +(@pxref{Options}). + +@item +The @code{IGNORECASE} variable and its effects +(@pxref{Case-sensitivity}). + +@item +The @file{/dev/stdin}, @file{/dev/stdout}, @file{/dev/stderr} and +@file{/dev/fd/@var{N}} special @value{FN}s +(@pxref{Special Files}). +@end itemize + +Version 2.13 of @command{gawk} introduced the following features: + +@itemize @value{BULLET} +@item +The @code{FIELDWIDTHS} variable and its effects +(@pxref{Constant Size}). + +@item +The @code{systime()} and @code{strftime()} built-in functions for obtaining +and printing timestamps +(@pxref{Time Functions}). + +@item +Additional command-line options +(@pxref{Options}): + +@itemize @value{MINUS} +@item +The @option{-W lint} option to provide error and portability checking +for both the source code and at runtime. + +@item +The @option{-W compat} option to turn off the GNU extensions. + +@item +The @option{-W posix} option for full POSIX compliance. +@end itemize +@end itemize + +Version 2.14 of @command{gawk} introduced the following feature: + +@itemize @value{BULLET} +@item +The @code{next file} statement for skipping to the next @value{DF} +(@pxref{Nextfile Statement}). +@end itemize + +Version 2.15 of @command{gawk} introduced the following features: + +@itemize @value{BULLET} +@item +New variables (@pxref{Built-in Variables}): + +@itemize @value{MINUS} +@item +@code{ARGIND}, which tracks the movement of @code{FILENAME} +through @code{ARGV}. + +@item +@code{ERRNO}, which contains the system error message when +@code{getline} returns @minus{}1 or @code{close()} fails. +@end itemize + +@item +The @file{/dev/pid}, @file{/dev/ppid}, @file{/dev/pgrpid}, and +@file{/dev/user} special @value{FN}s. These have since been removed. + +@item +The ability to delete all of an array at once with @samp{delete @var{array}} +(@pxref{Delete}). + +@item +Command-line option changes +(@pxref{Options}): + +@itemize @value{MINUS} +@item +The ability to use GNU-style long-named options that start with @option{--}. + +@item +The @option{--source} option for mixing command-line and library-file +source code. +@end itemize +@end itemize + +Version 3.0 of @command{gawk} introduced the following features: + +@itemize @value{BULLET} +@item +New or changed variables: + +@itemize @value{MINUS} +@item +@code{IGNORECASE} changed, now applying to string comparison as well +as regexp operations +(@pxref{Case-sensitivity}). + +@item +@code{RT}, which contains the input text that matched @code{RS} +(@pxref{Records}). +@end itemize + +@item +Full support for both POSIX and GNU regexps +(@pxref{Regexp}). + +@item +The @code{gensub()} function for more powerful text manipulation +(@pxref{String Functions}). + +@item +The @code{strftime()} function acquired a default time format, +allowing it to be called with no arguments +(@pxref{Time Functions}). + +@item +The ability for @code{FS} and for the third +argument to @code{split()} to be null strings +(@pxref{Single Character Fields}). + +@item +The ability for @code{RS} to be a regexp +(@pxref{Records}). + +@item +The @code{next file} statement became @code{nextfile} +(@pxref{Nextfile Statement}). + +@item +The @code{fflush()} function from +BWK @command{awk} +(then at Bell Laboratories; +@pxref{I/O Functions}). + +@item +New command-line options: + +@itemize @value{MINUS} +@item +The @option{--lint-old} option to +warn about constructs that are not available in +the original Version 7 Unix version of @command{awk} +(@pxref{V7/SVR3.1}). + +@item +The @option{-m} option from BWK @command{awk}. (Brian was +still at Bell Laboratories at the time.) This was later removed from +both his @command{awk} and from @command{gawk}. + +@item +The @option{--re-interval} option to provide interval expressions in regexps +(@pxref{Regexp Operators}). + +@item +The @option{--traditional} option was added as a better name for +@option{--compat} (@pxref{Options}). +@end itemize + +@item +The use of GNU Autoconf to control the configuration process +(@pxref{Quick Installation}). + +@item +Amiga support. +This has since been removed. + +@end itemize + +Version 3.1 of @command{gawk} introduced the following features: + +@itemize @value{BULLET} +@item +New variables +(@pxref{Built-in Variables}): + +@itemize @value{MINUS} +@item +@code{BINMODE}, for non-POSIX systems, +which allows binary I/O for input and/or output files +(@pxref{PC Using}). + +@item +@code{LINT}, which dynamically controls lint warnings. + +@item +@code{PROCINFO}, an array for providing process-related information. + +@item +@code{TEXTDOMAIN}, for setting an application's internationalization text domain +(@pxref{Internationalization}). +@end itemize + +@item +The ability to use octal and hexadecimal constants in @command{awk} +program source code +(@pxref{Nondecimal-numbers}). + +@item +The @samp{|&} operator for two-way I/O to a coprocess +(@pxref{Two-way I/O}). + +@item +The @file{/inet} special files for TCP/IP networking using @samp{|&} +(@pxref{TCP/IP Networking}). + +@item +The optional second argument to @code{close()} that allows closing one end +of a two-way pipe to a coprocess +(@pxref{Two-way I/O}). + +@item +The optional third argument to the @code{match()} function +for capturing text-matching subexpressions within a regexp +(@pxref{String Functions}). + +@item +Positional specifiers in @code{printf} formats for +making translations easier +(@pxref{Printf Ordering}). + +@item +A number of new built-in functions: + +@itemize @value{MINUS} +@item +The @code{asort()} and @code{asorti()} functions for sorting arrays +(@pxref{Array Sorting}). + +@item +The @code{bindtextdomain()}, @code{dcgettext()} and @code{dcngettext()} functions +for internationalization +(@pxref{Programmer i18n}). + +@item +The @code{extension()} function and the ability to add +new built-in functions dynamically +(@pxref{Dynamic Extensions}). + +@item +The @code{mktime()} function for creating timestamps +(@pxref{Time Functions}). + +@item +The @code{and()}, @code{or()}, @code{xor()}, @code{compl()}, +@code{lshift()}, @code{rshift()}, and @code{strtonum()} functions +(@pxref{Bitwise Functions}). +@end itemize + +@item +@cindex @code{next file} statement +The support for @samp{next file} as two words was removed completely +(@pxref{Nextfile Statement}). + +@item +Additional command-line options +(@pxref{Options}): + +@itemize @value{MINUS} +@item +The @option{--dump-variables} option to print a list of all global variables. + +@item +The @option{--exec} option, for use in CGI scripts. + +@item +The @option{--gen-po} command-line option and the use of a leading +underscore to mark strings that should be translated +(@pxref{String Extraction}). + +@item +The @option{--non-decimal-data} option to allow non-decimal +input data +(@pxref{Nondecimal Data}). + +@item +The @option{--profile} option and @command{pgawk}, the +profiling version of @command{gawk}, for producing execution +profiles of @command{awk} programs +(@pxref{Profiling}). + +@item +The @option{--use-lc-numeric} option to force @command{gawk} +to use the locale's decimal point for parsing input data +(@pxref{Conversion}). +@end itemize + +@item +The use of GNU Automake to help in standardizing the configuration process +(@pxref{Quick Installation}). + +@item +The use of GNU @command{gettext} for @command{gawk}'s own message output +(@pxref{Gawk I18N}). + +@item +BeOS support. This was later removed. + +@item +Tandem support. This was later removed. + +@item +The Atari port became officially unsupported and was +later removed entirely. + +@item +The source code changed to use ISO C standard-style function definitions. + +@item +POSIX compliance for @code{sub()} and @code{gsub()} +(@pxref{Gory Details}). + +@item +The @code{length()} function was extended to accept an array argument +and return the number of elements in the array +(@pxref{String Functions}). + +@item +The @code{strftime()} function acquired a third argument to +enable printing times as UTC +(@pxref{Time Functions}). +@end itemize + +Version 4.0 of @command{gawk} introduced the following features: + +@itemize @value{BULLET} + +@item +Variable additions: + +@itemize @value{MINUS} +@item +@code{FPAT}, which allows you to specify a regexp that matches +the fields, instead of matching the field separator +(@pxref{Splitting By Content}). + +@item +If @code{PROCINFO["sorted_in"]} exists, @samp{for(iggy in foo)} loops sort the +indices before looping over them. The value of this element +provides control over how the indices are sorted before the loop +traversal starts +(@pxref{Controlling Scanning}). + +@item +@code{PROCINFO["strftime"]}, which holds +the default format for @code{strftime()} +(@pxref{Time Functions}). +@end itemize + +@item +The special files @file{/dev/pid}, @file{/dev/ppid}, @file{/dev/pgrpid} +and @file{/dev/user} were removed. + +@item +Support for IPv6 was added via the @file{/inet6} special file. +@file{/inet4} forces IPv4 and @file{/inet} chooses the system +default, which is probably IPv4 +(@pxref{TCP/IP Networking}). + +@item +The use of @samp{\s} and @samp{\S} escape sequences in regular expressions +(@pxref{GNU Regexp Operators}). + +@item +Interval expressions became part of default regular expressions +(@pxref{Regexp Operators}). + +@item +POSIX character classes work even with @option{--traditional} +(@pxref{Regexp Operators}). + +@item +@code{break} and @code{continue} became invalid outside a loop, +even with @option{--traditional} +(@pxref{Break Statement}, and also see +@ref{Continue Statement}). + +@item +@code{fflush()}, @code{nextfile}, and @samp{delete @var{array}} +are allowed if @option{--posix} or @option{--traditional}, since they +are all now part of POSIX. + +@item +An optional third argument to +@code{asort()} and @code{asorti()}, specifying how to sort +(@pxref{String Functions}). + +@item +The behavior of @code{fflush()} changed to match BWK @command{awk} +and for POSIX; now both @samp{fflush()} and @samp{fflush("")} +flush all open output redirections +(@pxref{I/O Functions}). + +@item +The @code{isarray()} +function which distinguishes if an item is an array +or not, to make it possible to traverse arrays of arrays +(@pxref{Type Functions}). + +@item +The @code{patsplit()} +function which gives the same capability as @code{FPAT}, for splitting +(@pxref{String Functions}). + +@item +An optional fourth argument to the @code{split()} function, +which is an array to hold the values of the separators +(@pxref{String Functions}). + +@item +Arrays of arrays +(@pxref{Arrays of Arrays}). + +@item +The @code{BEGINFILE} and @code{ENDFILE} special patterns +(@pxref{BEGINFILE/ENDFILE}). + +@item +Indirect function calls +(@pxref{Indirect Calls}). + +@item +@code{switch} / @code{case} are enabled by default +(@pxref{Switch Statement}). + +@item +Command-line option changes +(@pxref{Options}): + +@itemize @value{MINUS} +@item +The @option{-b} and @option{--characters-as-bytes} options +which prevent @command{gawk} from treating input as a multibyte string. + +@item +The redundant @option{--compat}, @option{--copyleft}, and @option{--usage} +long options were removed. + +@item +The @option{--gen-po} option was finally renamed to the correct @option{--gen-pot}. + +@item +The @option{--sandbox} option which disables certain features. + +@item +All long options acquired corresponding short options, for use in @samp{#!} scripts. +@end itemize + +@item +Directories named on the command line now produce a warning, not a fatal +error, unless @option{--posix} or @option{--traditional} are used +(@pxref{Command-line directories}). + +@item +The @command{gawk} internals were rewritten, bringing the @command{dgawk} +debugger and possibly improved performance +(@pxref{Debugger}). + +@item +Per the GNU Coding Standards, dynamic extensions must now define +a global symbol indicating that they are GPL-compatible +(@pxref{Plugin License}). + +@item +In POSIX mode, string comparisons use @code{strcoll()} / @code{wcscoll()} +(@pxref{POSIX String Comparison}). + +@item +The option for raw sockets was removed, since it was never implemented +(@pxref{TCP/IP Networking}). + +@item +Ranges of the form @samp{[d-h]} are treated as if they were in the +C locale, no matter what kind of regexp is being used, and even if +@option{--posix} +(@pxref{Ranges and Locales}). + +@item +Support was removed for the following systems: + +@itemize @value{MINUS} +@item +Atari + +@item +Amiga + +@item +BeOS + +@item +Cray + +@item +MIPS RiscOS + +@item +MS-DOS with Microsoft Compiler + +@item +MS-Windows with Microsoft Compiler + +@item +NeXT + +@item +SunOS 3.x, Sun 386 (Road Runner) + +@item +Tandem (non-POSIX) + +@item +Prestandard VAX C compiler for VAX/VMS +@end itemize +@end itemize + +Version 4.1 of @command{gawk} introduced the following features: + +@itemize @value{BULLET} + +@item +Three new arrays: +@code{SYMTAB}, @code{FUNCTAB}, and @code{PROCINFO["identifiers"]} +(@pxref{Auto-set}). + +@item +The three executables @command{gawk}, @command{pgawk}, and @command{dgawk}, were merged into +one, named just @command{gawk}. As a result the command-line options changed. + +@item +Command-line option changes +(@pxref{Options}): + +@itemize @value{MINUS} +@item +The @option{-D} option invokes the debugger. + +@item +The @option{-i} and @option{--include} options +load @command{awk} library files. + +@item +The @option{-l} and @option{--load} options load compiled dynamic extensions. + +@item +The @option{-M} and @option{--bignum} options enable MPFR. + +@item +The @option{-o} option only does pretty-printing. + +@item +The @option{-p} option is used for profiling. + +@item +The @option{-R} option was removed. +@end itemize + +@item +Support for high precision arithmetic with MPFR. +(@pxref{Arbitrary Precision Arithmetic}). + +@item +The @code{and()}, @code{or()} and @code{xor()} functions +changed to allow any number of arguments, +with a minimum of two +(@pxref{Bitwise Functions}). + +@item +The dynamic extension interface was completely redone +(@pxref{Dynamic Extensions}). + +@end itemize + +@c XXX ADD MORE STUFF HERE +@end ifclear @node Common Extensions @appendixsec Common Extensions Summary -This @value{SECTION} summarizes the common extensions supported +@cindex extensions, Brian Kernighan's @command{awk} +@cindex extensions, @command{mawk} +The following table summarizes the common extensions supported by @command{gawk}, Brian Kernighan's @command{awk}, and @command{mawk}, -the three most widely-used freely available versions of @command{awk} +the three most widely used freely available versions of @command{awk} (@pxref{Other Versions}). -@multitable {@file{/dev/stderr} special file} {BWK Awk} {Mawk} {GNU Awk} -@headitem Feature @tab BWK Awk @tab Mawk @tab GNU Awk -@item @samp{\x} Escape sequence @tab X @tab X @tab X -@item @code{RS} as regexp @tab @tab X @tab X -@item @code{FS} as null string @tab X @tab X @tab X -@item @file{/dev/stdin} special file @tab X @tab @tab X -@item @file{/dev/stdout} special file @tab X @tab X @tab X -@item @file{/dev/stderr} special file @tab X @tab X @tab X -@item @code{**} and @code{**=} operators @tab X @tab @tab X -@item @code{func} keyword @tab X @tab @tab X -@item @code{nextfile} statement @tab X @tab X @tab X -@item @code{delete} without subscript @tab X @tab X @tab X -@item @code{length()} of an array @tab X @tab @tab X -@item @code{fflush()} function @tab X @tab X @tab X -@item @code{BINMODE} variable @tab @tab X @tab X +@multitable {@file{/dev/stderr} special file} {BWK Awk} {Mawk} {GNU Awk} {Now standard} +@headitem Feature @tab BWK Awk @tab Mawk @tab GNU Awk @tab Now standard +@item @samp{\x} Escape sequence @tab X @tab X @tab X @tab +@item @code{FS} as null string @tab X @tab X @tab X @tab +@item @file{/dev/stdin} special file @tab X @tab X @tab X @tab +@item @file{/dev/stdout} special file @tab X @tab X @tab X @tab +@item @file{/dev/stderr} special file @tab X @tab X @tab X @tab +@item @code{delete} without subscript @tab X @tab X @tab X @tab X +@item @code{fflush()} function @tab X @tab X @tab X @tab X +@item @code{length()} of an array @tab X @tab X @tab X @tab +@item @code{nextfile} statement @tab X @tab X @tab X @tab X +@item @code{**} and @code{**=} operators @tab X @tab @tab X @tab +@item @code{func} keyword @tab X @tab @tab X @tab +@item @code{BINMODE} variable @tab @tab X @tab X @tab +@item @code{RS} as regexp @tab @tab X @tab X @tab +@item Time-related functions @tab @tab X @tab X @tab @end multitable @node Ranges and Locales @@ -27022,20 +36493,20 @@ character ranges (such as @samp{[a-z]}) to match any character between the first character in the range and the last character in the range, inclusive. Ordering was based on the numeric value of each character in the machine's native character set. Thus, on ASCII-based systems, -@code{[a-z]} matched all the lowercase letters, and only the lowercase -letters, since the numeric values for the letters from @samp{a} through -@samp{z} were contigous. (On an EBCDIC system, the range @samp{[a-z]} +@samp{[a-z]} matched all the lowercase letters, and only the lowercase +letters, as the numeric values for the letters from @samp{a} through +@samp{z} were contiguous. (On an EBCDIC system, the range @samp{[a-z]} includes additional, non-alphabetic characters as well.) Almost all introductory Unix literature explained range expressions as working in this fashion, and in particular, would teach that the ``correct'' way to match lowercase letters was with @samp{[a-z]}, and -that @samp{[A-Z]} was the the ``correct'' way to match uppercase letters. -And indeed, this was true. +that @samp{[A-Z]} was the ``correct'' way to match uppercase letters. +And indeed, this was true.@footnote{And Life was good.} -The 1993 POSIX standard introduced the idea of locales (@pxref{Locales}). -Since many locales include other letters besides the plain twenty-six -letters of the American English alphabet, the POSIX standard added +The 1992 POSIX standard introduced the idea of locales (@pxref{Locales}). +Because many locales include other letters besides the plain 26 +letters of the English alphabet, the POSIX standard added character classes (@pxref{Bracket Expressions}) as a way to match different kinds of characters besides the traditional ones in the ASCII character set. @@ -27046,15 +36517,16 @@ In the @code{"C"} and @code{"POSIX"} locales, a range expression like But outside those locales, the ordering was defined to be based on @dfn{collation order}. +What does that mean? In many locales, @samp{A} and @samp{a} are both less than @samp{B}. In other words, these locales sort characters in dictionary order, and @samp{[a-dx-z]} is typically not equivalent to @samp{[abcdxyz]}; -instead it might be equivalent to @samp{[aBbCcdXxYyz]}, for example. +instead it might be equivalent to @samp{[ABCXYabcdxyz]}, for example. -This point needs to be emphasized: Much literature teaches that you should +This point needs to be emphasized: much literature teaches that you should use @samp{[a-z]} to match a lowercase character. But on systems with -non-ASCII locales, this also matched all of the uppercase characters -except @samp{Z}! This was a continuous cause of confusion, even well +non-ASCII locales, this also matches all of the uppercase characters +except @samp{A} or @samp{Z}! This was a continuous cause of confusion, even well into the twenty-first century. To demonstrate these issues, the following example uses the @code{sub()} @@ -27067,14 +36539,15 @@ $ @kbd{echo something1234abc | gawk-3.1.8 '@{ sub("[A-Z]*$", ""); print @}'} @end example @noindent -This output is unexpected, since the @samp{bc} at the end of +This output is unexpected, as the @samp{bc} at the end of @samp{something1234abc} should not normally match @samp{[A-Z]*}. This result is due to the locale setting (and thus you may not see it on your system). +@cindex Unicode Similar considerations apply to other ranges. For example, @samp{["-/]} is perfectly valid in ASCII, but is not valid in many Unicode locales, -such as @samp{en_US.UTF-8}. +such as @code{en_US.UTF-8}. Early versions of @command{gawk} used regexp matching code that was not locale aware, so ranges had their traditional interpretation. @@ -27083,20 +36556,24 @@ When @command{gawk} switched to using locale-aware regexp matchers, the problems began; especially as both GNU/Linux and commercial Unix vendors started implementing non-ASCII locales, @emph{and making them the default}. Perhaps the most frequently asked question became something -like ``why does @code{[A-Z]} match lowercase letters?!?'' +like ``why does @samp{[A-Z]} match lowercase letters?!?'' +@cindex Berry, Karl This situation existed for close to 10 years, if not more, and the @command{gawk} maintainer grew weary of trying to explain that -@command{gawk} was being nicely standards-compliant, and that the issue -was in the user's locale. During the development of version 4.0, +@command{gawk} was being nicely standards compliant, and that the issue +was in the user's locale. During the development of @value{PVERSION} 4.0, he modified @command{gawk} to always treat ranges in the original, -pre-POSIX fashion, unless @option{--posix} was used (@pxref{Options}). +pre-POSIX fashion, unless @option{--posix} was used (@pxref{Options}).@footnote{And +thus was born the Campaign for Rational Range Interpretation (or +RRI). A number of GNU tools have either implemented this change, +or will soon. Thanks to Karl Berry for coining the phrase ``Rational +Range Interpretation.''} Fortunately, shortly before the final release of @command{gawk} 4.0, the maintainer learned that the 2008 standard had changed the definition of ranges, such that outside the @code{"C"} and @code{"POSIX"} -locales, the meaning of range expressions was -@emph{undefined}.@footnote{See +locales, the meaning of range expressions was @emph{undefined}.@footnote{See @uref{http://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap09.html#tag_09_03_05, the standard} and @uref{http://pubs.opengroup.org/onlinepubs/9699919799/xrat/V4_xbd_chap09.html#tag_21_09_03_05, its rationale}.} @@ -27104,21 +36581,21 @@ and By using this lovely technical term, the standard gives license to implementors to implement ranges in whatever way they choose. The @command{gawk} maintainer chose to apply the pre-POSIX meaning in all -cases: the default regexp matching; with @option{--traditional}, and with +cases: the default regexp matching; with @option{--traditional} and with @option{--posix}; in all cases, @command{gawk} remains POSIX compliant. @node Contributors @appendixsec Major Contributors to @command{gawk} @cindex @command{gawk}, list of contributors to @quotation -@i{Always give credit where credit is due.}@* -Anonymous +@i{Always give credit where credit is due.} +@author Anonymous @end quotation This @value{SECTION} names the major contributors to @command{gawk} and/or this @value{DOCUMENT}, in approximate chronological order: -@itemize @bullet +@itemize @value{BULLET} @item @cindex Aho, Alfred @cindex Weinberger, Peter @@ -27198,8 +36675,8 @@ provided the initial port to OS/2 and its documentation. Michal Jaegermann provided the port to Atari systems and its documentation. (This port is no longer supported.) -He continues to provide portability checking with DEC Alpha -systems, and has done a lot of work to make sure @command{gawk} +He continues to provide portability checking, +and has done a lot of work to make sure @command{gawk} works on non-32-bit systems. @item @@ -27238,7 +36715,8 @@ the various PC platforms. @cindex Zoulas, Christos Christos Zoulas provided the @code{extension()} -built-in function for dynamically adding new modules. +built-in function for dynamically adding new functions. +(This was obsoleted at @command{gawk} 4.1.) @item @cindex Kahrs, J@"urgen @@ -27269,7 +36747,7 @@ provided the port to BeOS and its documentation. @cindex Peters, Arno Arno Peters did the initial work to convert @command{gawk} to use -GNU Automake and GNU @code{gettext}. +GNU Automake and GNU @command{gettext}. @item @cindex Broder, Alan J.@: @@ -27296,40 +36774,128 @@ Michael Benzinger contributed the initial code for @code{switch} statements. @cindex McPhee, Patrick Patrick T.J.@: McPhee contributed the code for dynamic loading in Windows32 environments. -(This is no longer supported) +(This is no longer supported.) + +@item +@cindex Wallin, Anders +Anders Wallin helped keep the VMS port going for several years. + +@item +@cindex Gordon, Assaf +Assaf Gordon contributed the code to implement the +@option{--sandbox} option. @item @cindex Haque, John -John Haque -reworked the @command{gawk} internals to use a byte-code engine, -providing the @command{dgawk} debugger for @command{awk} programs. +John Haque made the following contributions: + +@itemize @value{MINUS} +@item +The modifications to convert @command{gawk} +into a byte-code interpreter, including the debugger. + +@item +The addition of true arrays of arrays. + +@item +The additional modifications for support of arbitrary-precision arithmetic. + +@item +The initial text of +@ref{Arbitrary Precision Arithmetic}. + +@item +The work to merge the three versions of @command{gawk} +into one, for the 4.1 release. + +@item +Improved array internals for arrays indexed by integers. + +@item +The improved array sorting features were driven by John together +with Pat Rankin. +@end itemize + +@cindex Papadopoulos, Panos +@item +Panos Papadopoulos contributed the original text for @ref{Include Files}. @item @cindex Yawitz, Efraim Efraim Yawitz contributed the original text for @ref{Debugger}. @item +@cindex Schorr, Andrew +The development of the extension API first released with +@command{gawk} 4.1 was driven primarily by +Arnold Robbins and Andrew Schorr, with notable contributions from +the rest of the development team. + +@cindex Malmberg, John E. +@item +John Malmberg contributed significant improvements to the +OpenVMS port and the related documentation. + +@item +@cindex Colombo, Antonio +Antonio Giovanni Colombo rewrote a number of examples in the early +chapters that were severely dated, for which I am incredibly grateful. + +@item @cindex Robbins, Arnold Arnold Robbins has been working on @command{gawk} since 1988, at first helping David Trueman, and as the primary maintainer since around 1994. @end itemize +@node History summary +@appendixsec Summary + +@itemize @value{BULLET} +@item +The @command{awk} language has evolved over time. The first release +was with V7 Unix circa 1978. In 1987, for System V Release 3.1, +major additions, including user-defined functions, were made to the language. +Additional changes were made for System V Release 4, in 1989. +Since then, further minor changes happen under the auspices of the +POSIX standard. + +@item +Brian Kernighan's @command{awk} provides a small number of extensions +that are implemented in common with other versions of @command{awk}. + +@item +@command{gawk} provides a large number of extensions over POSIX @command{awk}. +They can be disabled with either the @option{--traditional} or @option{--posix} +options. + +@item +The interaction of POSIX locales and regexp matching in @command{gawk} has been confusing over +the years. Today, @command{gawk} implements Rational Range Interpretation, where +ranges of the form @samp{[a-z]} match @emph{only} the characters numerically between +@samp{a} through @samp{z} in the machine's native character set. Usually this is ASCII +but it can be EBCDIC on IBM S/390 systems. + +@item +Many people have contributed to @command{gawk} development over the years. +We hope that the list provided in this @value{CHAPTER} is complete and gives +the appropriate credit where credit is due. + +@end itemize + @node Installation @appendix Installing @command{gawk} @c last two commas are part of see also -@cindex operating systems, See Also GNU/Linux, PC operating systems, Unix -@c STARTOFRANGE gligawk +@cindex operating systems, See Also GNU/Linux@comma{} PC operating systems@comma{} Unix @cindex @command{gawk}, installing -@c STARTOFRANGE ingawk @cindex installing @command{gawk} This appendix provides instructions for installing @command{gawk} on the various platforms that are supported by the developers. The primary developer supports GNU/Linux (and Unix), whereas the other ports are contributed. -@xref{Bugs}, -for the electronic mail addresses of the people who did +@DBXREF{Bugs} +for the email addresses of the people who maintain the respective ports. @menu @@ -27340,6 +36906,7 @@ the respective ports. * Bugs:: Reporting Problems and Bugs. * Other Versions:: Other freely available @command{awk} implementations. +* Installation summary:: Summary of installation. @end menu @node Gawk Distribution @@ -27359,9 +36926,9 @@ subdirectories. @node Getting @appendixsubsec Getting the @command{gawk} Distribution @cindex @command{gawk}, source code@comma{} obtaining -There are three ways to get GNU software: +There are two ways to get GNU software: -@itemize @bullet +@itemize @value{BULLET} @item Copy it from someone else who already has it. @@ -27382,7 +36949,7 @@ wget http://ftp.gnu.org/gnu/gawk/gawk-@value{VERSION}.@value{PATCHLEVEL}.tar.gz The GNU software archive is mirrored around the world. The up-to-date list of mirror sites is available from -@uref{http://www.gnu.org/order/ftp.html, the main FSF web site}. +@uref{http://www.gnu.org/order/ftp.html, the main FSF website}. Try to use one of the mirrors; they will be less busy, and you can usually find one closer to your site. @@ -27393,14 +36960,13 @@ different compression programs: @command{gzip}, @command{bzip2}, and @command{xz}. For simplicity, the rest of these instructions assume you are using the one compressed with the GNU Zip program, @code{gzip}. -Once you have the distribution (for example, +Once you have the distribution (e.g., @file{gawk-@value{VERSION}.@value{PATCHLEVEL}.tar.gz}), use @code{gzip} to expand the file and then use @code{tar} to extract it. You can use the following pipeline to produce the @command{gawk} distribution: @example -# Under System V, add 'o' to the tar options gzip -d -c gawk-@value{VERSION}.@value{PATCHLEVEL}.tar.gz | tar -xvpf - @end example @@ -27432,7 +36998,6 @@ a local expert. @node Distribution contents @appendixsubsec Contents of the @command{gawk} Distribution -@c STARTOFRANGE gawdis @cindex @command{gawk}, distribution The @command{gawk} distribution has a number of C source files, @@ -27448,6 +37013,13 @@ The actual @command{gawk} source code. @end table @table @file +@item ABOUT-NLS +Information about GNU @command{gettext} and translations. + +@item AUTHORS +A file with some information about the authorship of @command{gawk}. +It exists only to satisfy the pedants at the Free Software Foundation. + @item README @itemx README_d/README.* Descriptive files: @file{README} for @command{gawk} under Unix and the @@ -27471,16 +37043,6 @@ An older list of changes to @command{gawk}. @item COPYING The GNU General Public License. -@item FUTURES -A brief list of features and changes being contemplated for future -releases, with some indication of the time frame for the feature, based -on its difficulty. - -@item LIMITATIONS -A list of those factors that limit @command{gawk}'s performance. -Most of these depend on the hardware or operating system software and -are not limits in @command{gawk} itself. - @item POSIX.STD A description of behaviors in the POSIX standard for @command{awk} which are left undefined, or where @command{gawk} may not comply fully, as well @@ -27488,8 +37050,9 @@ as a list of things that the POSIX standard should describe but does not. @cindex artificial intelligence@comma{} @command{gawk} and @item doc/awkforai.txt -A short article describing why @command{gawk} is a good language for -Artificial Intelligence (AI) programming. +Pointers to the original draft of +a short article describing why @command{gawk} is a good language for +artificial intelligence (AI) programming. @item doc/bc_notes A brief description of @command{gawk}'s ``byte code'' internals. @@ -27512,12 +37075,19 @@ The @command{troff} source for a manual page describing @command{gawk}. This is distributed for the convenience of Unix users. @cindex Texinfo -@item doc/gawk.texi +@item doc/gawktexi.in +@itemx doc/sidebar.awk The Texinfo source file for this @value{DOCUMENT}. -It should be processed with @TeX{} -(via @command{texi2dvi} or @command{texi2pdf}) +It should be processed by @file{doc/sidebar.awk} +before processing with @command{texi2dvi} or @command{texi2pdf} to produce a printed document, and with @command{makeinfo} to produce an Info or HTML file. +The @file{Makefile} takes care of this processing and produces +printable output via @command{texi2dvi} or @command{texi2pdf}. + +@item doc/gawk.texi +The file produced after processing @file{gawktexi.in} +with @file{sidebar.awk}. @item doc/gawk.info The generated Info file for this @value{DOCUMENT}. @@ -27543,6 +37113,8 @@ The generated Info file for The @command{troff} source for a manual page describing the @command{igawk} program presented in @ref{Igawk Program}. +(Since @command{gawk} can do its own @code{@@include} processing, +neither @command{igawk} nor @file{igawk.1} are installed.) @item doc/Makefile.in The input file used during the configuration process to generate the @@ -27550,21 +37122,27 @@ actual @file{Makefile} for creating the documentation. @item Makefile.am @itemx */Makefile.am -Files used by the GNU @command{automake} software for generating -the @file{Makefile.in} files used by @command{autoconf} and +Files used by the GNU Automake software for generating +the @file{Makefile.in} files used by Autoconf and @command{configure}. @item Makefile.in @itemx aclocal.m4 +@itemx bisonfix.awk +@itemx config.guess @itemx configh.in @itemx configure.ac @itemx configure @itemx custom.h +@itemx depcomp +@itemx install-sh @itemx missing_d/* +@itemx mkinstalldirs @itemx m4/* -These files and subdirectories are used when configuring @command{gawk} -for various Unix systems. They are explained in -@ref{Unix Installation}. +These files and subdirectories are used when configuring and compiling +@command{gawk} for various Unix systems. Most of them are explained +in @ref{Unix Installation}. The rest are there to support the main +infrastructure. @item po/* The @file{po} library contains message translations. @@ -27581,23 +37159,35 @@ source file for this @value{DOCUMENT}. It also contains a @file{Makefile.in} fil @file{Makefile.am} is used by GNU Automake to create @file{Makefile.in}. The library functions from @ref{Library Functions}, -and the @command{igawk} program from -@ref{Igawk Program}, are included as ready-to-use files in the @command{gawk} distribution. They are installed as part of the installation process. The rest of the programs in this @value{DOCUMENT} are available in appropriate subdirectories of @file{awklib/eg}. +@item extension/* +The source code, manual pages, and infrastructure files for +the sample extensions included with @command{gawk}. +@xref{Dynamic Extensions}, for more information. + +@item extras/* +Additional non-essential files. Currently, this directory contains some shell +startup files to be installed in @file{/etc/profile.d} to aid in manipulating +the @env{AWKPATH} and @env{AWKLIBPATH} environment variables. +@xref{Shell Startup Files}, for more information. + @item posix/* Files needed for building @command{gawk} on POSIX-compliant systems. @item pc/* -Files needed for building @command{gawk} under MS-Windows and OS/2 -(@pxref{PC Installation}, for details). +Files needed for building @command{gawk} under MS-Windows +@ifclear FOR_PRINT +and OS/2 +@end ifclear +(@DBPXREF{PC Installation} for details). @item vms/* -Files needed for building @command{gawk} under VMS -(@pxref{VMS Installation}, for details). +Files needed for building @command{gawk} under Vax/VMS and OpenVMS +(@DBPXREF{VMS Installation} for details). @item test/* A test suite for @@ -27606,10 +37196,9 @@ directory to run your version of @command{gawk} against the test suite. If @command{gawk} successfully passes @samp{make check}, then you can be confident of a successful port. @end table -@c ENDOFRANGE gawdis @node Unix Installation -@appendixsec Compiling and Installing @command{gawk} on Unix-like Systems +@appendixsec Compiling and Installing @command{gawk} on Unix-Like Systems Usually, you can compile and install @command{gawk} by typing only two commands. However, if you use an unusual system, you may need @@ -27617,33 +37206,33 @@ to configure @command{gawk} for your system yourself. @menu * Quick Installation:: Compiling @command{gawk} under Unix. +* Shell Startup Files:: Shell convenience functions. * Additional Configuration Options:: Other compile-time options. * Configuration Philosophy:: How it's all supposed to work. @end menu @node Quick Installation -@appendixsubsec Compiling @command{gawk} for Unix-like Systems +@appendixsubsec Compiling @command{gawk} for Unix-Like Systems The normal installation steps should work on all modern commercial Unix-derived systems, GNU/Linux, BSD-based systems, and the Cygwin environment for MS-Windows. After you have extracted the @command{gawk} distribution, @command{cd} -to @file{gawk-@value{VERSION}.@value{PATCHLEVEL}}. Like most GNU software, -@command{gawk} is configured -automatically for your system by running the @command{configure} program. -This program is a Bourne shell script that is generated automatically using -GNU @command{autoconf}. +to @file{gawk-@value{VERSION}.@value{PATCHLEVEL}}. As with most GNU +software, you configure @command{gawk} for your system by running the +@command{configure} program. This program is a Bourne shell script that +is generated automatically using GNU Autoconf. @ifnotinfo -(The @command{autoconf} software is +(The Autoconf software is described fully in @cite{Autoconf---Generating Automatic Configuration Scripts}, which can be found online at @uref{http://www.gnu.org/software/autoconf/manual/index.html, -the Free Software Foundation's web site}.) +the Free Software Foundation's website}.) @end ifnotinfo @ifinfo -(The @command{autoconf} software is described fully starting with +(The Autoconf software is described fully starting with @inforef{Top, , Autoconf, autoconf,Autoconf---Generating Automatic Configuration Scripts}.) @end ifinfo @@ -27687,7 +37276,54 @@ run @samp{make check}. All of the tests should succeed. If these steps do not work, or if any of the tests fail, check the files in the @file{README_d} directory to see if you've found a known problem. If the failure is not described there, -please send in a bug report (@pxref{Bugs}). +send in a bug report (@pxref{Bugs}). + +Of course, once you've built @command{gawk}, it is likely that you will +wish to install it. To do so, you need to run the command @samp{make +install}, as a user with the appropriate permissions. How to do this +varies by system, but on many systems you can use the @command{sudo} +command to do so. The command then becomes @samp{sudo make install}. It +is likely that you will be asked for your password, and you will have +to have been set up previously as a user who is allowed to run the +@command{sudo} command. + +@node Shell Startup Files +@appendixsubsec Shell Startup Files + +The distribution contains shell startup files @file{gawk.sh} and +@file{gawk.csh} containing functions to aid in manipulating +the @env{AWKPATH} and @env{AWKLIBPATH} environment variables. +On a Fedora system, these files should be installed in @file{/etc/profile.d}; +on other platforms, the appropriate location may be different. + +@table @command + +@cindex @command{gawkpath_default} shell function +@item gawkpath_default +Reset the @env{AWKPATH} environment variable to its default value. + +@cindex @command{gawkpath_prepend} shell function +@item gawkpath_prepend +Add the argument to the front of the @env{AWKPATH} environment variable. + +@cindex @command{gawkpath_append} shell function +@item gawkpath_append +Add the argument to the end of the @env{AWKPATH} environment variable. + +@cindex @command{gawklibpath_default} shell function +@item gawklibpath_default +Reset the @env{AWKLIBPATH} environment variable to its default value. + +@cindex @command{gawklibpath_prepend} shell function +@item gawklibpath_prepend +Add the argument to the front of the @env{AWKLIBPATH} environment variable. + +@cindex @command{gawklibpath_append} shell function +@item gawklibpath_append +Add the argument to the end of the @env{AWKLIBPATH} environment variable. + +@end table + @node Additional Configuration Options @appendixsubsec Additional Configuration Options @@ -27699,7 +37335,15 @@ command line when compiling @command{gawk} from scratch, including: @table @code -@cindex @code{--disable-lint} configuration option +@cindex @option{--disable-extensions} configuration option +@cindex configuration option, @code{--disable-extensions} +@item --disable-extensions +Disable configuring and building the sample extensions in the +@file{extension} directory. This is useful for cross-compiling. +The default action is to dynamically check if the extensions +can be configured and compiled. + +@cindex @option{--disable-lint} configuration option @cindex configuration option, @code{--disable-lint} @item --disable-lint Disable all lint checking within @code{gawk}. The @@ -27711,30 +37355,30 @@ Similarly, setting the @code{LINT} variable has no effect on the running @command{awk} program. When used with GCC's automatic dead-code-elimination, this option -cuts almost 200K bytes off the size of the @command{gawk} -executable on GNU/Linux x86 systems. Results on other systems and +cuts almost 23K bytes off the size of the @command{gawk} +executable on GNU/Linux x86_64 systems. Results on other systems and with other compilers are likely to vary. Using this option may bring you some slight performance improvement. Using this option will cause some of the tests in the test suite to fail. This option may be removed at a later date. -@cindex @code{--disable-nls} configuration option +@cindex @option{--disable-nls} configuration option @cindex configuration option, @code{--disable-nls} @item --disable-nls Disable all message-translation facilities. This is usually not desirable, but it may bring you some slight performance improvement. -@cindex @code{--with-whiny-user-strftime} configuration option +@cindex @option{--with-whiny-user-strftime} configuration option @cindex configuration option, @code{--with-whiny-user-strftime} @item --with-whiny-user-strftime -Force use of the included version of the @code{strftime()} +Force use of the included version of the C @code{strftime()} function for deficient systems. @end table Use the command @samp{./configure --help} to see the full list of -options that @command{configure} supplies. +options supplied by @command{configure}. @node Configuration Philosophy @appendixsubsec The Configuration Process @@ -27763,24 +37407,24 @@ they can be correctly included, what (supposedly) standard functions are actually available in your C libraries, and various miscellaneous facts about your operating system. For example, there may not be an @code{st_blksize} element in the @code{stat} structure. In this case, -@samp{HAVE_ST_BLKSIZE} is undefined. +@samp{HAVE_STRUCT_STAT_ST_BLKSIZE} is undefined. @cindex @code{custom.h} file It is possible for your C compiler to lie to @command{configure}. It may do so by not exiting with an error when a library function is not -available. To get around this, edit the file @file{custom.h}. +available. To get around this, edit the @file{custom.h} file. Use an @samp{#ifdef} that is appropriate for your system, and either @code{#define} any constants that @command{configure} should have defined but didn't, or @code{#undef} any constants that @command{configure} defined and -should not have. @file{custom.h} is automatically included by -@file{config.h}. +should not have. The @file{custom.h} file is automatically included by +the @file{config.h} file. It is also possible that the @command{configure} program generated by -@command{autoconf} will not work on your system in some other fashion. -If you do have a problem, the file @file{configure.ac} is the input for -@command{autoconf}. You may be able to change this file and generate a +Autoconf will not work on your system in some other fashion. +If you do have a problem, the @file{configure.ac} file is the input for +Autoconf. You may be able to change this file and generate a new version of @command{configure} that works on your system -(@pxref{Bugs}, +(@DBPXREF{Bugs} for information on how to report problems in configuring @command{gawk}). The same mechanism may be used to send in updates to @file{configure.ac} and/or @file{custom.h}. @@ -27805,17 +37449,23 @@ various non-Unix systems. @cindex PC operating systems@comma{} @command{gawk} on, installing @cindex operating systems, PC@comma{} @command{gawk} on, installing -This @value{SECTION} covers installation and usage of @command{gawk} on x86 machines +This @value{SECTION} covers installation and usage of @command{gawk} +on Intel architecture machines +@ifclear FOR_PRINT running MS-DOS, any version of MS-Windows, or OS/2. +@end ifclear +@ifset FOR_PRINT +running MS-DOS and any version of MS-Windows. +@end ifset In this @value{SECTION}, the term ``Windows32'' -refers to any of Microsoft Windows-95/98/ME/NT/2000/XP/Vista/7. +refers to any of Microsoft Windows-95/98/ME/NT/2000/XP/Vista/7/8. -The limitations of MS-DOS (and MS-DOS shells under Windows32 or OS/2) has meant -that various ``DOS extenders'' are often used with programs such as -@command{gawk}. The varying capabilities of Microsoft Windows 3.1 -and Windows32 can add to the confusion. For an overview of the -considerations, please refer to @file{README_d/README.pc} in the -distribution. +The limitations of MS-DOS (and MS-DOS shells under the other operating +systems) has meant that various ``DOS extenders'' are often used with +programs such as @command{gawk}. The varying capabilities of Microsoft +Windows 3.1 and Windows32 can add to the confusion. For an overview +of the considerations, refer to @file{README_d/README.pc} in +the distribution. @menu * PC Binary Installation:: Installing a prepared distribution. @@ -27829,6 +37479,7 @@ distribution. * MSYS:: Using @command{gawk} In The MSYS Environment. @end menu +@ifclear FOR_PRINT @node PC Binary Installation @appendixsubsubsec Installing a Prepared Distribution for PC Systems @@ -27867,13 +37518,21 @@ install-info --info-dir=x:/usr/info x:/usr/info/gawkinet.info The binary distribution may contain a separate file containing additional or more detailed installation instructions. +@end ifclear @node PC Compiling @appendixsubsubsec Compiling @command{gawk} for PC Operating Systems +@ifclear FOR_PRINT @command{gawk} can be compiled for MS-DOS, Windows32, and OS/2 using the GNU -development tools from DJ Delorie (DJGPP: MS-DOS only) or Eberhard -Mattes (EMX: MS-DOS, Windows32 and OS/2). The file +development tools from DJ Delorie (DJGPP: MS-DOS only), MinGW (Windows32) or Eberhard +Mattes (EMX: MS-DOS, Windows32 and OS/2). +@end ifclear +@ifset FOR_PRINT +@command{gawk} can be compiled for MS-DOS and Windows32 using the GNU +development tools from DJ Delorie (DJGPP: MS-DOS only) or MinGW (Windows32). +@end ifset +The file @file{README_d/README.pc} in the @command{gawk} distribution contains additional notes, and @file{pc/Makefile} contains important information on compilation options. @@ -27893,8 +37552,10 @@ MS-DOS and Windows32 versions. A list of targets is printed if the build @command{gawk} using the DJGPP tools, enter @samp{make djgpp}. (The DJGPP tools needed for the build may be found at @uref{ftp://ftp.delorie.com/pub/djgpp/current/v2gnu/}.) To build a -native MS-Windows binary of @command{gawk}, type @samp{make mingw32}. +native MS-Windows binary of @command{gawk} using the MinGW tools, +type @samp{make mingw32}. +@ifclear FOR_PRINT @cindex compiling @command{gawk} with EMX for OS/2 The 32 bit EMX version of @command{gawk} works ``out of the box'' under OS/2. However, it is highly recommended to use GCC 2.95.3 for the compilation. @@ -27929,7 +37590,7 @@ and @option{--libexecdir=c:/usr/lib}. @end ignore @ignore -The internal @code{gettext} library tends to be problematic. It is therefore recommended +The internal @command{gettext} library tends to be problematic. It is therefore recommended to use either an external one (@option{--without-included-gettext}) or to disable NLS entirely (@option{--disable-nls}). @end ignore @@ -27966,8 +37627,11 @@ Ancient OS/2 ports of GNU @command{make} are not able to handle the Makefiles of this package. If you encounter any problems with @command{make}, try GNU Make 3.79.1 or later versions. You should find the latest version on -@uref{ftp://hobbes.nmsu.edu/pub/os2/}. +@uref{ftp://hobbes.nmsu.edu/pub/os2/}.@footnote{As of November 2014, +this site is still there, but the author could not find a package +for GNU Make.} @end quotation +@end ifclear @node PC Testing @appendixsubsubsec Testing @command{gawk} on PC Operating Systems @@ -27979,6 +37643,7 @@ be converted so that they have the usual MS-DOS-style end-of-line markers. Alternatively, run @command{make check CMP="diff -a"} to use GNU @command{diff} in text mode instead of @command{cmp} to compare the resulting files. +@ifclear FOR_PRINT Most of the tests work properly with Stewartson's shell along with the companion utilities or appropriate GNU utilities. However, some editing of @@ -27991,71 +37656,82 @@ On OS/2 the @code{pid} test fails because @code{spawnl()} is used instead of @code{fork()}/@code{execl()} to start child processes. Also the @code{mbfw1} and @code{mbprintf1} tests fail because the needed multibyte functionality is not available. - +@end ifclear @node PC Using @appendixsubsubsec Using @command{gawk} on PC Operating Systems -@c STARTOFRANGE opgawx @cindex operating systems, PC, @command{gawk} on -@c STARTOFRANGE pcgawon @cindex PC operating systems, @command{gawk} on -With the exception of the Cygwin environment, -the @samp{|&} operator and TCP/IP networking -(@pxref{TCP/IP Networking}) -are not supported for MS-DOS or MS-Windows. EMX (OS/2 only) does support -at least the @samp{|&} operator. +Under MS-DOS and MS-Windows, the Cygwin and MinGW environments support +both the @samp{|&} operator and TCP/IP networking +(@pxref{TCP/IP Networking}). +@ifclear FOR_PRINT +EMX (OS/2 only) supports at least the @samp{|&} operator. +@end ifclear @cindex search paths @cindex search paths, for source files -@cindex @command{gawk}, OS/2 version of @cindex @command{gawk}, MS-DOS version of @cindex @command{gawk}, MS-Windows version of -@cindex @code{;} (semicolon), @code{AWKPATH} variable and -@cindex semicolon (@code{;}), @code{AWKPATH} variable and -@cindex @code{AWKPATH} environment variable +@cindex @code{;} (semicolon), @env{AWKPATH} variable and +@cindex semicolon (@code{;}), @env{AWKPATH} variable and +@cindex @env{AWKPATH} environment variable The MS-DOS and MS-Windows versions of @command{gawk} search for program files as described in @ref{AWKPATH Variable}. However, semicolons (rather than colons) separate elements in the @env{AWKPATH} variable. If @env{AWKPATH} is not set or is empty, then the default -search path for MS-Windows and MS-DOS versions is -@code{@w{".;c:/lib/awk;c:/gnu/lib/awk"}}. +search path is @samp{@w{.;c:/lib/awk;c:/gnu/lib/awk}}. +@ifclear FOR_PRINT +@cindex @command{gawk}, OS/2 version of @cindex @code{UNIXROOT} variable, on OS/2 systems The search path for OS/2 (32 bit, EMX) is determined by the prefix directory (most likely @file{/usr} or @file{c:/usr}) that has been specified as an option of -the @command{configure} script like it is the case for the Unix versions. +the @command{configure} script as is the case for the Unix versions. If @file{c:/usr} is the prefix directory then the default search path contains @file{.} and @file{c:/usr/share/awk}. Additionally, to support binary distributions of @command{gawk} for OS/2 -systems whose drive @samp{c:} might not support long file names or might not exist +systems whose drive @samp{c:} might not support long @value{FN}s or might not exist at all, there is a special environment variable. If @env{UNIXROOT} specifies a drive then this specific drive is also searched for program files. E.g., if @env{UNIXROOT} is set to @file{e:} the complete default search path is -@code{@w{".;c:/usr/share/awk;e:/usr/share/awk"}}. +@samp{@w{.;c:/usr/share/awk;e:/usr/share/awk}}. An @command{sh}-like shell (as opposed to @command{command.com} under MS-DOS or @command{cmd.exe} under MS-Windows or OS/2) may be useful for @command{awk} programming. The DJGPP collection of tools includes an MS-DOS port of Bash, and several shells are available for OS/2, including @command{ksh}. +@end ifclear +@ifset FOR_PRINT +An @command{sh}-like shell (as opposed to @command{command.com} under MS-DOS +or @command{cmd.exe} under MS-Windows) may be useful for @command{awk} programming. +The DJGPP collection of tools includes an MS-DOS port of Bash. +@end ifset @cindex common extensions, @code{BINMODE} variable @cindex extensions, common@comma{} @code{BINMODE} variable @cindex differences in @command{awk} and @command{gawk}, @code{BINMODE} variable @cindex @code{BINMODE} variable -Under MS-Windows, OS/2 and MS-DOS, @command{gawk} (and many other text programs) silently -translate end-of-line @code{"\r\n"} to @code{"\n"} on input and @code{"\n"} -to @code{"\r\n"} on output. A special @code{BINMODE} variable @value{COMMONEXT} +@ifclear FOR_PRINT +Under MS-Windows, OS/2 and MS-DOS, +@end ifclear +@ifset FOR_PRINT +Under MS-Windows and MS-DOS, +@end ifset +@command{gawk} (and many other text programs) silently +translate end-of-line @samp{\r\n} to @samp{\n} on input and @samp{\n} +to @samp{\r\n} on output. A special @code{BINMODE} variable @value{COMMONEXT} allows control over these translations and is interpreted as follows: -@itemize @bullet +@itemize @value{BULLET} @item -If @code{BINMODE} is @code{"r"}, or one, +If @code{BINMODE} is @code{"r"} or one, then binary mode is set on read (i.e., no translations on reads). @item -If @code{BINMODE} is @code{"w"}, or two, +If @code{BINMODE} is @code{"w"} or two, then binary mode is set on write (i.e., no translations on writes). @@ -28086,7 +37762,7 @@ The name @code{BINMODE} was chosen to match @command{mawk} @command{mawk} adds a @samp{-W BINMODE=@var{N}} option and an environment variable that can set @code{BINMODE}, @code{RS}, and @code{ORS}. The files @file{binmode[1-3].awk} (under @file{gnu/lib/awk} in some of the -prepared distributions) have been chosen to match @command{mawk}'s @samp{-W +prepared binary distributions) have been chosen to match @command{mawk}'s @samp{-W BINMODE=@var{N}} option. These can be changed or discarded; in particular, the setting of @code{RS} giving the fewest ``surprises'' is open to debate. @command{mawk} uses @samp{RS = "\r\n"} if binary mode is set on read, which is @@ -28114,7 +37790,7 @@ The following changes the record separator to @code{"\r\n"} and sets binary mode on reads, but does not affect the mode on standard input: @example -gawk -v RS="\r\n" --source "BEGIN @{ BINMODE = 1 @}" @dots{} +gawk -v RS="\r\n" -e "BEGIN @{ BINMODE = 1 @}" @dots{} @end example @noindent @@ -28134,7 +37810,7 @@ moved into the @code{BEGIN} rule. @command{gawk} can be built and used ``out of the box'' under MS-Windows if you are using the @uref{http://www.cygwin.com, Cygwin environment}. -This environment provides an excellent simulation of Unix, using the +This environment provides an excellent simulation of GNU/Linux, using the GNU tools, such as Bash, the GNU Compiler Collection (GCC), GNU Make, and other GNU programs. Compilation and installation for Cygwin is the same as for a Unix system: @@ -28143,20 +37819,13 @@ same as for a Unix system: tar -xvpzf gawk-@value{VERSION}.@value{PATCHLEVEL}.tar.gz cd gawk-@value{VERSION}.@value{PATCHLEVEL} ./configure -make +make && make check @end example When compared to GNU/Linux on the same system, the @samp{configure} step on Cygwin takes considerably longer. However, it does finish, and then the @samp{make} proceeds as usual. -@quotation NOTE -The @samp{|&} operator and TCP/IP networking -(@pxref{TCP/IP Networking}) -are fully supported in the Cygwin environment. This is not true -for any other environment on MS-Windows. -@end quotation - @node MSYS @appendixsubsubsec Using @command{gawk} In The MSYS Environment @@ -28166,10 +37835,10 @@ need to use the @code{BINMODE} variable. This can cause problems with other Unix-like components that have been ported to MS-Windows that expect @command{gawk} to do automatic -translation of @code{"\r\n"}, since it won't. Caveat Emptor! +translation of @code{"\r\n"}, because it won't. @node VMS Installation -@appendixsubsec How to Compile and Install @command{gawk} on VMS +@appendixsubsec Compiling and Installing @command{gawk} on Vax/VMS and OpenVMS @c based on material from Pat Rankin <rankin@eql.caltech.edu> @c now rankin@pactechdata.com @@ -28182,8 +37851,11 @@ The older designation ``VMS'' is used throughout to refer to OpenVMS. @menu * VMS Compilation:: How to compile @command{gawk} under VMS. +* VMS Dynamic Extensions:: Compiling @command{gawk} dynamic extensions on + VMS. * VMS Installation Details:: How to install @command{gawk} under VMS. * VMS Running:: How to run @command{gawk} under VMS. +* VMS GNV:: The VMS GNV Project. * VMS Old Gawk:: An old version comes with some VMS systems. @end menu @@ -28191,41 +37863,115 @@ The older designation ``VMS'' is used throughout to refer to OpenVMS. @appendixsubsubsec Compiling @command{gawk} on VMS @cindex compiling @command{gawk} for VMS -To compile @command{gawk} under VMS, there is a @code{DCL} command procedure that -issues all the necessary @code{CC} and @code{LINK} commands. There is -also a @file{Makefile} for use with the @code{MMS} utility. From the source -directory, use either: +To compile @command{gawk} under VMS, there is a @code{DCL} command procedure +that issues all the necessary @code{CC} and @code{LINK} commands. There is +also a @file{Makefile} for use with the @code{MMS} and @code{MMK} utilities. +From the source directory, use either: + +@example +$ @kbd{@@[.vms]vmsbuild.com} +@end example + +@noindent +or: + +@example +$ @kbd{MMS/DESCRIPTION=[.vms]descrip.mms gawk} +@end example + +@noindent +or: + +@example +$ @kbd{MMK/DESCRIPTION=[.vms]descrip.mms gawk} +@end example + +@command{MMK} is an open source, free, near-clone of @command{MMS} and +can better handle ODS-5 volumes with upper- and lowercase @value{FN}s. +@command{MMK} is available from @uref{https://github.com/endlesssoftware/mmk}. + +With ODS-5 volumes and extended parsing enabled, the case of the target +parameter may need to be exact. + +@command{gawk} has been tested under VAX/VMS 7.3 and Alpha/VMS 7.3-1 +using Compaq C V6.4, and Alpha/VMS 7.3, Alpha/VMS 7.3-2, and IA64/VMS 8.3. +The most recent builds used HP C V7.3 on Alpha VMS 8.3 and both +Alpha and IA64 VMS 8.4 used HP C 7.3.@footnote{The IA64 architecture +is also known as ``Itanium.''} + +@DBXREF{VMS GNV} for information on building +@command{gawk} as a PCSI kit that is compatible with the GNV product. + +@node VMS Dynamic Extensions +@appendixsubsubsec Compiling @command{gawk} Dynamic Extensions on VMS + +The extensions that have been ported to VMS can be built using one of +the following commands: @example -$ @kbd{@@[.VMS]VMSBUILD.COM} +$ @kbd{MMS/DESCRIPTION=[.vms]descrip.mms extensions} @end example @noindent or: @example -$ @kbd{MMS/DESCRIPTION=[.VMS]DESCRIP.MMS GAWK} +$ @kbd{MMK/DESCRIPTION=[.vms]descrip.mms extensions} +@end example + +@command{gawk} uses @code{AWKLIBPATH} as either an environment variable +or a logical name to find the dynamic extensions. + +Dynamic extensions need to be compiled with the same compiler options for +floating-point, pointer size, and symbol name handling as were used +to compile @command{gawk} itself. +Alpha and Itanium should use IEEE floating point. The pointer size is 32 bits, +and the symbol name handling should be exact case with CRC shortening for +symbols longer than 32 bits. + +For Alpha and Itanium: + +@example +/name=(as_is,short) +/float=ieee/ieee_mode=denorm_results +@end example + +For VAX: + +@example +/name=(as_is,short) @end example -Older versions of @command{gawk} could be built with VAX C or -GNU C on VAX/VMS, as well as with DEC C, but that is no longer -supported. DEC C (also briefly known as ``Compaq C'' and now known -as ``HP C,'' but referred to here as ``DEC C'') is required. Both -@code{VMSBUILD.COM} and @code{DESCRIP.MMS} contain some obsolete support -for the older compilers but are set up to use DEC C by default. +Compile time macros need to be defined before the first VMS-supplied +header file is included, as follows: -@command{gawk} has been tested under Alpha/VMS 7.3-1 using Compaq C V6.4, -and on Alpha/VMS 7.3, Alpha/VMS 7.3-2, and IA64/VMS 8.3.@footnote{The IA64 -architecture is also known as ``Itanium.''} +@example +#if (__CRTL_VER >= 70200000) && !defined (__VAX) +#define _LARGEFILE 1 +#endif + +#ifndef __VAX +#ifdef __CRTL_VER +#if __CRTL_VER >= 80200000 +#define _USE_STD_STAT 1 +#endif +#endif +#endif +@end example + +If you are writing your own extensions to run on VMS, you must supply these +definitions yourself. The @file{config.h} file created when building @command{gawk} +on VMS does this for you; if instead you use that file or a similar one, then you +must remember to include it before any VMS-supplied header files. @node VMS Installation Details @appendixsubsubsec Installing @command{gawk} on VMS -To install @command{gawk}, all you need is a ``foreign'' command, which is -a @code{DCL} symbol whose value begins with a dollar sign. For example: +To use @command{gawk}, all you need is a ``foreign'' command, which is a +@code{DCL} symbol whose value begins with a dollar sign. For example: @example -$ @kbd{GAWK :== $disk1:[gnubin]GAWK} +$ @kbd{GAWK :== $disk1:[gnubin]gawk} @end example @noindent @@ -28237,10 +37983,29 @@ Alternatively, the symbol may be placed in the system-wide @file{sylogin.com} procedure, which allows all users to run @command{gawk}. -Optionally, the help entry can be loaded into a VMS help library: +If your @command{gawk} was installed by a PCSI kit into the +@file{GNV$GNU:} directory tree, the program will be known as +@file{GNV$GNU:[bin]gnv$gawk.exe} and the help file will be +@file{GNV$GNU:[vms_help]gawk.hlp}. + +The PCSI kit also installs a @file{GNV$GNU:[vms_bin]gawk_verb.cld} file +which can be used to add @command{gawk} and @command{awk} as DCL commands. + +For just the current process you can use: @example -$ @kbd{LIBRARY/HELP SYS$HELP:HELPLIB [.VMS]GAWK.HLP} +$ @kbd{set command gnv$gnu:[vms_bin]gawk_verb.cld} +@end example + +Or the system manager can use @file{GNV$GNU:[vms_bin]gawk_verb.cld} to +add the @command{gawk} and @command{awk} to the system wide @samp{DCLTABLES}. + +The DCL syntax is documented in the @file{gawk.hlp} file. + +Optionally, the @file{gawk.hlp} entry can be loaded into a VMS help library: + +@example +$ @kbd{LIBRARY/HELP sys$help:helplib [.vms]gawk.hlp} @end example @noindent @@ -28262,7 +38027,7 @@ for @command{awk} program files. For the @option{-f} option, if the specified looks in the current directory first, then in the directory specified by the translation of @samp{AWK_LIBRARY} if the file is not found. If, after searching in both directories, the file still is not found, -@command{gawk} appends the suffix @samp{.awk} to the filename and retries +@command{gawk} appends the suffix @samp{.awk} to the @value{FN} and retries the file search. If @samp{AWK_LIBRARY} has no definition, a default value of @samp{SYS$LIBRARY:} is used for it. @@ -28288,12 +38053,45 @@ Note that uppercase and mixed-case text must be quoted. The VMS port of @command{gawk} includes a @code{DCL}-style interface in addition to the original shell-style interface (see the help entry for details). One side effect of dual command-line parsing is that if there is only a -single parameter (as in the quoted string program above), the command +single parameter (as in the quoted string program), the command becomes ambiguous. To work around this, the normally optional @option{--} flag is required to force Unix-style parsing rather than @code{DCL} parsing. If any other dash-type options (or multiple parameters such as @value{DF}s to process) are present, there is no ambiguity and @option{--} can be omitted. +@cindex exit status, of VMS +The @code{exit} value is a Unix-style value and is encoded into a VMS exit +status value when the program exits. + +The VMS severity bits will be set based on the @code{exit} value. +A failure is indicated by 1 and VMS sets the @code{ERROR} status. +A fatal error is indicated by 2 and VMS sets the @code{FATAL} status. +All other values will have the @code{SUCCESS} status. The exit value is +encoded to comply with VMS coding standards and will have the +@code{C_FACILITY_NO} of @code{0x350000} with the constant @code{0xA000} +added to the number shifted over by 3 bits to make room for the severity codes. + +To extract the actual @command{gawk} exit code from the VMS status use: + +@example +unix_status = (vms_status .and. &x7f8) / 8 +@end example + +@noindent +A C program that uses @code{exec()} to call @command{gawk} will get the original +Unix-style exit value. + +Older versions of @command{gawk} for VMS treated a Unix exit code 0 as 1, a failure +as 2, a fatal error as 4, and passed all the other numbers through. +This violated the VMS exit status coding requirements. + +@cindex floating-point, VAX/VMS +VAX/VMS floating point uses unbiased rounding. @xref{Round Function}. + +VMS reports time values in GMT unless one of the @code{SYS$TIMEZONE_RULE} +or @code{TZ} logical names is set. Older versions of VMS, such as VAX/VMS +7.3 do not set these logical names. + @c @cindex directory search @c @cindex path, search @cindex search paths @@ -28305,6 +38103,21 @@ of @env{AWKPATH} is a comma-separated list of directory specifications. When defining it, the value should be quoted so that it retains a single translation and not a multitranslation @code{RMS} searchlist. +@node VMS GNV +@appendixsubsubsec The VMS GNV Project + +The VMS GNV package provides a build environment similar to POSIX with ports +of a collection of open source tools. The @command{gawk} found in the GNV +base kit is an older port. Currently the GNV project is being reorganized +to supply individual PCSI packages for each component. +See @w{@uref{https://sourceforge.net/p/gnv/wiki/InstallingGNVPackages/}.} + +The normal build procedure for @command{gawk} produces a program that +is suitable for use with GNV. + +The file @file{vms/gawk_build_steps.txt} in the distribution documents +the procedure for building a VMS PCSI kit that is compatible with GNV. + @ignore @c The VMS POSIX product, also known as POSIX for OpenVMS, is long defunct @c and building gawk for it has not been tested in many years, but these @@ -28355,28 +38168,24 @@ $ @kbd{gawk :== $sys$common:[syshlp.examples.tcpip.snmp]gawk.exe} This is apparently @value{PVERSION} 2.15.6, which is extremely old. We recommend compiling and using the current version. -@c ENDOFRANGE opgawx -@c ENDOFRANGE pcgawon @node Bugs @appendixsec Reporting Problems and Bugs -@cindex archeologists +@cindex archaeologists @quotation -@i{There is nothing more dangerous than a bored archeologist.}@* -The Hitchhiker's Guide to the Galaxy +@i{There is nothing more dangerous than a bored archaeologist.} +@author Douglas Adams, @cite{The Hitchhiker's Guide to the Galaxy} @end quotation @c the radio show, not the book. :-) -@c STARTOFRANGE dbugg @cindex debugging @command{gawk}, bug reports -@c STARTOFRANGE tblgawb @cindex troubleshooting, @command{gawk}, bug reports If you have problems with @command{gawk} or think that you have found a bug, -please report it to the developers; we cannot promise to do anything +report it to the developers; we cannot promise to do anything but we might well want to fix it. -Before reporting a bug, make sure you have actually found a real bug. -Carefully reread the documentation and see if it really says you can do +Before reporting a bug, make sure you have really found a genuine bug. +Carefully reread the documentation and see if it says you can do what you're trying to do. If it's not clear whether you should be able to do something or not, report that too; it's a bug in the documentation! @@ -28388,86 +38197,87 @@ the compiler you used to compile @command{gawk}, and the exact results @command{gawk} gave you. Also say what you expected to occur; this helps us decide whether the problem is really in the documentation. -Please include the version number of @command{gawk} you are using. +Make sure to include the version number of @command{gawk} you are using. You can get this information with the command @samp{gawk --version}. @cindex @code{bug-gawk@@gnu.org} bug reporting address @cindex email address for bug reports, @code{bug-gawk@@gnu.org} @cindex bug reports, email address, @code{bug-gawk@@gnu.org} -Once you have a precise problem, send email to +Once you have a precise problem description, send email to @EMAIL{bug-gawk@@gnu.org,bug-gawk at gnu dot org}. -@cindex Robbins, Arnold -Using this address automatically sends a copy of your -mail to me. If necessary, I can be reached directly at -@EMAIL{arnold@@skeeve.com,arnold at skeeve dot com}. -The bug reporting address is preferred since the +The @command{gawk} maintainers subscribe to this address and +thus they will receive your bug report. +Although you can send mail to the maintainers directly, +the bug reporting address is preferred because the email list is archived at the GNU Project. -@emph{All email should be in English, since that is my native language.} +@emph{All email must be in English. This is the only language +understood in common by all the maintainers.} @cindex @code{comp.lang.awk} newsgroup @quotation CAUTION Do @emph{not} try to report bugs in @command{gawk} by posting to the Usenet/Internet newsgroup @code{comp.lang.awk}. -While the @command{gawk} developers do occasionally read this newsgroup, -there is no guarantee that we will see your posting. The steps described -above are the official recognized ways for reporting bugs. +The @command{gawk} developers do occasionally read this newsgroup, +but there is no guarantee that we will see your posting. The steps described +here are the only officially recognized way for reporting bugs. Really. @end quotation @quotation NOTE Many distributions of GNU/Linux and the various BSD-based operating systems have their own bug reporting systems. If you report a bug using your distribution's -bug reporting system, @emph{please} also send a copy to +bug reporting system, you should also send a copy to @EMAIL{bug-gawk@@gnu.org,bug-gawk at gnu dot org}. -This is for two reasons. First, while some distributions forward +This is for two reasons. First, although some distributions forward bug reports ``upstream'' to the GNU mailing list, many don't, so there is a good -chance that the @command{gawk} maintainer won't even see the bug report! Second, +chance that the @command{gawk} maintainers won't even see the bug report! Second, mail to the GNU list is archived, and having everything at the GNU project -keeps things self-contained and not dependant on other web sites. +keeps things self-contained and not dependant on other organizations. @end quotation Non-bug suggestions are always welcome as well. If you have questions about things that are unclear in the documentation or are just obscure -features, ask me; I will try to help you out, although I -may not have the time to fix the problem. You can send me electronic -mail at the Internet address noted previously. +features, ask on the bug list; we will try to help you out if we can. -If you find bugs in one of the non-Unix ports of @command{gawk}, please send -an electronic mail message to the person who maintains that port. They -are named in the following list, as well as in the @file{README} file in the @command{gawk} -distribution. Information in the @file{README} file should be considered -authoritative if it conflicts with this @value{DOCUMENT}. +If you find bugs in one of the non-Unix ports of @command{gawk}, +send an email to the bug list, with a copy to the +person who maintains that port. They are named in the following list, +as well as in the @file{README} file in the @command{gawk} distribution. +Information in the @file{README} file should be considered authoritative +if it conflicts with this @value{DOCUMENT}. -The people maintaining the non-Unix ports of @command{gawk} are -as follows: +The people maintaining the various @command{gawk} ports are: -@multitable {MS-Windows with MINGW} {123456789012345678901234567890123456789001234567890} +@c put the index entries outside the table, for docbook +@cindex Buening, Andreas @cindex Deifik, Scott +@cindex Malmberg, John +@cindex Pitts, Dave +@cindex Robbins, Arnold +@cindex Zaretskii, Eli +@multitable {MS-Windows with MinGW} {123456789012345678901234567890123456789001234567890} +@item Unix and POSIX systems @tab Arnold Robbins, @EMAIL{arnold@@skeeve.com,arnold at skeeve dot com}. + @item MS-DOS with DJGPP @tab Scott Deifik, @EMAIL{scottd.mail@@sbcglobal.net,scottd dot mail at sbcglobal dot net}. -@cindex Zaretskii, Eli -@item MS-Windows with MINGW @tab Eli Zaretskii, @EMAIL{eliz@@gnu.org,eliz at gnu dot org}. +@item MS-Windows with MinGW @tab Eli Zaretskii, @EMAIL{eliz@@gnu.org,eliz at gnu dot org}. -@cindex Buening, Andreas +@c Leave this in the print version on purpose. +@c OS/2 is not mentioned anywhere else in the print version though. @item OS/2 @tab Andreas Buening, @EMAIL{andreas.buening@@nexgo.de,andreas dot buening at nexgo dot de}. -@cindex Rankin, Pat -@item VMS @tab Pat Rankin, @EMAIL{r.pat.rankin@@gmail.com,r.pat.rankin at gmail.com} +@item VMS @tab John Malmberg, @EMAIL{wb8tyw@@qsl.net,wb8tyw at qsl.net}. -@cindex Pitts, Dave @item z/OS (OS/390) @tab Dave Pitts, @EMAIL{dpitts@@cozx.com,dpitts at cozx dot com}. @end multitable -If your bug is also reproducible under Unix, please send a copy of your +If your bug is also reproducible under Unix, send a copy of your report to the @EMAIL{bug-gawk@@gnu.org,bug-gawk at gnu dot org} email list as well. -@c ENDOFRANGE dbugg -@c ENDOFRANGE tblgawb @node Other Versions @appendixsec Other Freely Available @command{awk} Implementations -@c STARTOFRANGE awkim @cindex @command{awk}, implementations @ignore From: emory!amc.com!brennan (Michael Brennan) @@ -28477,11 +38287,20 @@ Date: Wed, 4 Sep 1996 08:11:48 -0700 (PDT) @end ignore @cindex Brennan, Michael +@ifnotdocbook @quotation @i{It's kind of fun to put comments like this in your awk code.}@* -@ @ @ @ @ @ @code{// Do C++ comments work? answer: yes! of course}@* -Michael Brennan +@ @ @ @ @ @ @code{// Do C++ comments work? answer: yes! of course} +@author Michael Brennan @end quotation +@end ifnotdocbook + +@docbook +<blockquote><attribution>Michael Brennan</attribution> +<literallayout><emphasis>It's kind of fun to put comments like this in your awk code.</emphasis> + <literal>// Do C++ comments work? answer: yes! of course</literal></literallayout> +</blockquote> +@end docbook There are a number of other freely available @command{awk} implementations. This @value{SECTION} briefly describes where to get them: @@ -28490,13 +38309,12 @@ This @value{SECTION} briefly describes where to get them: @cindex Kernighan, Brian @cindex source code, Brian Kernighan's @command{awk} @cindex @command{awk}, versions of, See Also Brian Kernighan's @command{awk} -@cindex extensions, Brian Kernighan's @command{awk} -@cindex Brian Kernighan's @command{awk}, extensions +@cindex Brian Kernighan's @command{awk}, source code @item Unix @command{awk} Brian Kernighan, one of the original designers of Unix @command{awk}, has made his implementation of @command{awk} freely available. -You can retrieve this version via the World Wide Web from +You can retrieve this version via @uref{http://www.cs.princeton.edu/~bwk, his home page}. It is available in several archive formats: @@ -28511,21 +38329,41 @@ It is available in several archive formats: @uref{http://www.cs.princeton.edu/~bwk/btl.mirror/awk.zip} @end table -This version requires an ISO C (1990 standard) compiler; -the C compiler from -GCC (the GNU Compiler Collection) -works quite nicely. +@cindex @command{git} utility +You can also retrieve it from Git Hub: -@xref{Common Extensions}, +@example +git clone git://github.com/onetrueawk/awk bwkawk +@end example + +@noindent +This command creates a copy of the @uref{http://git-scm.com, Git} +repository in a directory named @file{bwkawk}. If you leave that argument +off the @command{git} command line, the repository copy is created in a +directory named @file{awk}. + +This version requires an ISO C (1990 standard) compiler; the C compiler +from GCC (the GNU Compiler Collection) works quite nicely. + +@DBXREF{Common Extensions} for a list of extensions in this @command{awk} that are not in POSIX @command{awk}. +As a side note, Dan Bornstein has created a Git repository tracking +all the versions of BWK @command{awk} that he could find. It's +available at @uref{git://github.com/danfuzz/one-true-awk}. + @cindex Brennan, Michael -@cindex @command{mawk} program +@cindex @command{mawk} utility @cindex source code, @command{mawk} @item @command{mawk} Michael Brennan wrote an independent implementation of @command{awk}, -called @command{mawk}. It is available under the GPL -(@pxref{Copying}), +called @command{mawk}. It is available under the +@ifclear FOR_PRINT +GPL (@pxref{Copying}), +@end ifclear +@ifset FOR_PRINT +GPL, +@end ifset just as @command{gawk} is. The original distribution site for the @command{mawk} source code @@ -28534,7 +38372,7 @@ no longer has it. A copy is available at In 2009, Thomas Dickey took on @command{mawk} maintenance. Basic information is available on -@uref{http://www.invisible-island.net/mawk/mawk.html, the project's web page}. +@uref{http://www.invisible-island.net/mawk, the project's web page}. The download URL is @url{http://invisible-island.net/datafiles/release/mawk.tar.gz}. @@ -28543,7 +38381,7 @@ Once you have it, is similar to @command{gawk}'s (@pxref{Unix Installation}). -@xref{Common Extensions}, +@DBXREF{Common Extensions} for a list of extensions in @command{mawk} that are not in POSIX @command{awk}. @cindex Sumner, Andrew @@ -28566,13 +38404,13 @@ To get @command{awka}, go to @url{http://sourceforge.net/projects/awka}. The project seems to be frozen; no new code changes have been made since approximately 2003. -@cindex Beebe, Nelson +@cindex Beebe, Nelson H.F.@: @cindex @command{pawk} (profiling version of Brian Kernighan's @command{awk}) @cindex source code, @command{pawk} @item @command{pawk} Nelson H.F.@: Beebe at the University of Utah has modified -Brian Kernighan's @command{awk} to provide timing and profiling information. -It is different from @command{pgawk} +BWK @command{awk} to provide timing and profiling information. +It is different from @command{gawk} with the @option{--profile} option (@pxref{Profiling}), in that it uses CPU-based profiling, not line-count profiling. You may find it at either @@ -28594,16 +38432,23 @@ information, see the @uref{http://busybox.net, project's home page}. @cindex Solaris, POSIX-compliant @command{awk} @cindex source code, Solaris @command{awk} @item The OpenSolaris POSIX @command{awk} -The version of @command{awk} in @file{/usr/xpg4/bin} on Solaris is -more-or-less -POSIX-compliant. It is based on the @command{awk} from Mortice Kern -Systems for PCs. The source code can be downloaded from -the @uref{http://www.opensolaris.org, OpenSolaris web site}. -This author was able to make it compile and work under GNU/Linux +The versions of @command{awk} in @file{/usr/xpg4/bin} and +@file{/usr/xpg6/bin} on Solaris are more-or-less POSIX-compliant. +They are based on the @command{awk} from Mortice Kern Systems for PCs. +We were able to make this code compile and work under GNU/Linux with 1--2 hours of work. Making it more generally portable (using GNU Autoconf and/or Automake) would take more work, and this has not been done, at least to our knowledge. +@cindex Illumos +@cindex Illumos, POSIX-compliant @command{awk} +@cindex source code, Illumos @command{awk} +The source code used to be available from the OpenSolaris website. +However, that project was ended and the website shut down. Fortunately, the +@uref{http://wiki.illumos.org/display/illumos/illumos+Home, Illumos project} +makes this implementation available. You can view the files one at a time from +@uref{https://github.com/joyent/illumos-joyent/blob/master/usr/src/cmd/awk_xpg4}. + @cindex @command{jawk} @cindex Java implementation of @command{awk} @cindex source code, @command{jawk} @@ -28618,13 +38463,21 @@ from POSIX @command{awk}. More information is available on the @cindex libmawk @cindex source code, libmawk This is an embeddable @command{awk} interpreter derived from -@command{mawk}. For more information see +@command{mawk}. For more information, see @uref{http://repo.hu/projects/libmawk/}. +@item @code{pawk} +@cindex source code, @command{pawk} (Python version) +@cindex @code{pawk}, @command{awk}-like facilities for Python +This is a Python module that claims to bring @command{awk}-like +features to Python. See @uref{https://github.com/alecthomas/pawk} +for more information. (This is not related to Nelson Beebe's +modified version of BWK @command{awk}, described earlier.) + @item @w{QSE Awk} @cindex QSE Awk @cindex source code, QSE Awk -This is an embeddable @command{awk} interpreter. For more information +This is an embeddable @command{awk} interpreter. For more information, see @uref{http://code.google.com/p/qse/} and @uref{http://awk.info/?tools/qse}. @item @command{QTawk} @@ -28636,27 +38489,57 @@ under the GPL. It has a large number of extensions over standard See @uref{http://www.quiktrim.org/QTawk.html} for more information, including the manual and a download link. -@item @command{xgawk} -@cindex @command{xgawk} -@cindex source code, @command{xgawk} -XML @command{gawk}. -This is a fork of the @command{gawk} 3.1.6 source base -to support processing XML files. It has a number of -interesting extensions which should one day be integrated -into the main @command{gawk} code base. -For more information, see -@uref{http://xmlgawk.sourceforge.net, the XMLgawk project web site}. +The project may also be frozen; no new code changes have been made +since approximately 2008. + +@item Other versions +See also the ``Versions and implementations'' section of the +@uref{http://en.wikipedia.org/wiki/Awk_language#Versions_and_implementations, +Wikipedia article} for information on additional versions. @end table -@c ENDOFRANGE gligawk -@c ENDOFRANGE ingawk -@c ENDOFRANGE awkim +@node Installation summary +@appendixsec Summary + +@itemize @value{BULLET} +@item +The @command{gawk} distribution is available from GNU project's main +distribution site, @code{ftp.gnu.org}. The canonical build recipe is: + +@example +wget http://ftp.gnu.org/gnu/gawk/gawk-@value{VERSION}.@value{PATCHLEVEL}.tar.gz +tar -xvpzf gawk-@value{VERSION}.@value{PATCHLEVEL}.tar.gz +cd gawk-@value{VERSION}.@value{PATCHLEVEL} +./configure && make && make check +@end example + +@item +@command{gawk} may be built on non-POSIX systems as well. The currently +supported systems are MS-Windows using DJGPP, MSYS, MinGW and Cygwin, +@ifclear FOR_PRINT +OS/2 using EMX, +@end ifclear +and both Vax/VMS and OpenVMS. +Instructions for each system are included in this @value{CHAPTER}. + +@item +Bug reports should be sent via email to @email{bug-gawk@@gnu.org}. +Bug reports should be in English, and should include the version of @command{gawk}, +how it was compiled, and a short program and @value{DF} which demonstrate +the problem. + +@item +There are a number of other freely available @command{awk} +implementations. Many are POSIX compliant; others are less so. + +@end itemize + + +@ifclear FOR_PRINT @node Notes @appendix Implementation Notes -@c STARTOFRANGE gawii @cindex @command{gawk}, implementation issues -@c STARTOFRANGE impis @cindex implementation issues, @command{gawk} This appendix contains information mainly of interest to implementers and @@ -28667,9 +38550,11 @@ maintainers of @command{gawk}. Everything in it applies specifically to * Compatibility Mode:: How to disable certain @command{gawk} extensions. * Additions:: Making Additions To @command{gawk}. -* Dynamic Extensions:: Adding new built-in functions to - @command{gawk}. * Future Extensions:: New features that may be implemented one day. +* Implementation Limitations:: Some limitations of the implementation. +* Extension Design:: Design notes about the extension API. +* Old Extension Mechanism:: Some compatibility for old extensions. +* Notes summary:: Summary of implementation notes. @end menu @node Compatibility Mode @@ -28690,7 +38575,7 @@ is one more option available on the command line: @table @code @item -Y @itemx --parsedebug -Prints out the parse stack information as the program is being parsed. +Print out the parse stack information as the program is being parsed. @end table This option is intended only for serious @command{gawk} developers @@ -28714,20 +38599,23 @@ as well as any considerations you should bear in mind. @command{gawk}. * New Ports:: Porting @command{gawk} to a new operating system. +* Derived Files:: Why derived files are kept in the Git + repository. @end menu @node Accessing The Source @appendixsubsec Accessing The @command{gawk} Git Repository As @command{gawk} is Free Software, the source code is always available. -@ref{Gawk Distribution}, describes how to get and build the formal, +@DBREF{Gawk Distribution} describes how to get and build the formal, released versions of @command{gawk}. +@cindex @command{git} utility However, if you want to modify @command{gawk} and contribute back your changes, you will probably wish to work with the development version. To do so, you will need to access the @command{gawk} source code repository. The code is maintained using the -@uref{http://git-scm.com/, Git distributed version control system}. +@uref{http://git-scm.com, Git distributed version control system}. You will need to install it if your system doesn't have it. Once you have done so, use the command: @@ -28736,8 +38624,8 @@ git clone git://git.savannah.gnu.org/gawk.git @end example @noindent -This will clone the @command{gawk} repository. If you are behind a -firewall that will not allow you to use the Git native protocol, you +This clones the @command{gawk} repository. If you are behind a +firewall that does not allow you to use the Git native protocol, you can still access the repository using: @example @@ -28745,35 +38633,29 @@ git clone http://git.savannah.gnu.org/r/gawk.git @end example Once you have made changes, you can use @samp{git diff} to produce a -patch, and send that to the @command{gawk} maintainer; see @ref{Bugs} +patch, and send that to the @command{gawk} maintainer; see @ref{Bugs}, for how to do that. -Finally, if you cannot install Git (e.g., if it hasn't been ported -yet to your operating system), you can use the Git--CVS gateway -to check out a copy using CVS, as follows: - -@example -cvs -d:pserver:anonymous@@pserver.git.sv.gnu.org:/gawk.git co -d gawk master -@end example +Once upon a time there was Git--CVS gateway for use by people who could +not install Git. However, this gateway no longer works, so you may have +better luck using a more modern version control system like Bazaar, +that has a Git plug-in for working with Git repositories. @node Adding Code @appendixsubsec Adding New Features -@c STARTOFRANGE adfgaw @cindex adding, features to @command{gawk} -@c STARTOFRANGE fadgaw @cindex features, adding to @command{gawk} -@c STARTOFRANGE gawadf @cindex @command{gawk}, features, adding You are free to add any new features you like to @command{gawk}. However, if you want your changes to be incorporated into the @command{gawk} distribution, there are several steps that you need to take in order to -make it possible to include your changes: +make it possible to include them: @enumerate 1 @item Before building the new feature into @command{gawk} itself, -consider writing it as an extension module +consider writing it as an extension (@pxref{Dynamic Extensions}). If that's not possible, continue with the rest of the steps in this list. @@ -28790,14 +38672,15 @@ or @EMAIL{assign@@gnu.org,assign at gnu dot org}. @item Get the latest version. It is much easier for me to integrate changes if they are relative to -the most recent distributed version of @command{gawk}. If your version of -@command{gawk} is very old, I may not be able to integrate them at all. +the most recent distributed version of @command{gawk}, or better yet, +relative to the latest code in the Git repository. If your version of +@command{gawk} is very old, I may not be able to integrate your changes at all. (@xref{Getting}, for information on getting the latest version of @command{gawk}.) @item @ifnotinfo -Follow the @cite{GNU Coding Standards}. +Follow the @uref{http://www.gnu.org/prep/standards/, @cite{GNU Coding Standards}}. @end ifnotinfo @ifinfo See @inforef{Top, , Version, standards, GNU Coding Standards}. @@ -28806,7 +38689,7 @@ This document describes how GNU software should be written. If you haven't read it, please do so, preferably @emph{before} starting to modify @command{gawk}. (The @cite{GNU Coding Standards} are available from the GNU Project's -@uref{http://www.gnu.org/prep/standards_toc.html, web site}. +@uref{http://www.gnu.org/prep/standards_toc.html, website}. Texinfo, Info, and DVI versions are also available.) @cindex @command{gawk}, coding style in @@ -28818,7 +38701,7 @@ using the traditional ``K&R'' style, particularly as regards to the placement of braces and the use of TABs. In brief, the coding rules for @command{gawk} are as follows: -@itemize @bullet +@itemize @value{BULLET} @item Use ANSI/ISO style (prototype) function headers when defining functions. @@ -28857,7 +38740,8 @@ of @code{switch} statements, instead of just the plain pointer or character value. @item -Use the @code{TRUE}, @code{FALSE} and @code{NULL} symbolic constants +Use @code{true} and @code{false} for @code{bool} values, +the @code{NULL} symbolic constant for pointer values, and the character constant @code{'\0'} where appropriate, instead of @code{1} and @code{0}. @@ -28900,12 +38784,14 @@ If possible, please update the @command{man} page as well. You will also have to sign paperwork for your documentation changes. +@cindex @command{git} utility @item Submit changes as unified diffs. Use @samp{diff -u -r -N} to compare the original @command{gawk} source tree with your version. -I recommend using the GNU version of @command{diff}. -Send the output produced by either run of @command{diff} to me when you +I recommend using the GNU version of @command{diff}, or best of all, +@samp{git diff} or @samp{git format-patch}. +Send the output produced by @command{diff} to me when you submit your changes. (@xref{Bugs}, for the electronic mail information.) @@ -28919,15 +38805,13 @@ not do so, particularly if there are lots of changes. Include an entry for the @file{ChangeLog} file with your submission. This helps further minimize the amount of work I have to do, making it easier for me to accept patches. +It is simplest if you just make this part of your diff. @end enumerate Although this sounds like a lot of work, please remember that while you may write the new code, I have to maintain it and support it. If it isn't possible for me to do that with a minimum of extra work, then I probably will not. -@c ENDOFRANGE adfgaw -@c ENDOFRANGE gawadf -@c ENDOFRANGE fadgaw @node New Ports @appendixsubsec Porting @command{gawk} to a New Operating System @@ -28954,11 +38838,9 @@ Be prepared to sign the appropriate paperwork. In order for the FSF to distribute your code, you must either place your code in the public domain and submit a signed statement to that effect, or assign the copyright in your code to the FSF. -@ifinfo Both of these actions are easy to do and @emph{many} people have done so already. If you have questions, please contact me, or @email{gnu@@gnu.org}. -@end ifinfo @item When doing a port, bear in mind that your code must coexist peacefully @@ -28978,15 +38860,44 @@ A number of the files that come with @command{gawk} are maintained by other people. Thus, you should not change them unless it is for a very good reason; i.e., changes are not out of the question, but changes to these files are scrutinized extra carefully. -The files are @file{dfa.c}, @file{dfa.h}, @file{getopt1.c}, @file{getopt.c}, -@file{getopt.h}, @file{install-sh}, @file{mkinstalldirs}, @file{regcomp.c}, -@file{regex.c}, @file{regexec.c}, @file{regexex.c}, @file{regex.h}, -@file{regex_internal.c}, and @file{regex_internal.h}. +The files are +@file{dfa.c}, +@file{dfa.h}, +@file{getopt.c}, +@file{getopt.h}, +@file{getopt1.c}, +@file{getopt_int.h}, +@file{gettext.h}, +@file{regcomp.c}, +@file{regex.c}, +@file{regex.h}, +@file{regex_internal.c}, +@file{regex_internal.h}, +and +@file{regexec.c}. + +@item +A number of other files are provided by the GNU +Autotools (Autoconf, Automake, and GNU @command{gettext}). +You should not change them either, unless it is for a very +good reason. The files are +@file{ABOUT-NLS}, +@file{config.guess}, +@file{config.rpath}, +@file{config.sub}, +@file{depcomp}, +@file{INSTALL}, +@file{install-sh}, +@file{missing}, +@file{mkinstalldirs}, +@file{xalloc.h}, +and +@file{ylwrap}. @item Be willing to continue to maintain the port. Non-Unix operating systems are supported by volunteers who maintain -the code needed to compile and run @command{gawk} on their systems. If noone +the code needed to compile and run @command{gawk} on their systems. If no-one volunteers to maintain a port, it becomes unsupported and it may be necessary to remove it from the distribution. @@ -29031,789 +38942,197 @@ operating systems' code that is already there. In the code that you supply and maintain, feel free to use a coding style and brace layout that suits your taste. -@node Dynamic Extensions -@appendixsec Adding New Built-in Functions to @command{gawk} -@cindex Robinson, Will -@cindex robot, the -@cindex Lost In Space -@quotation -@i{Danger Will Robinson! Danger!!@* -Warning! Warning!}@* -The Robot -@end quotation +@node Derived Files +@appendixsubsec Why Generated Files Are Kept In Git -@c STARTOFRANGE gladfgaw -@cindex @command{gawk}, functions, adding -@c STARTOFRANGE adfugaw -@cindex adding, functions to @command{gawk} -@c STARTOFRANGE fubadgaw -@cindex functions, built-in, adding to @command{gawk} -It is possible to add new built-in -functions to @command{gawk} using dynamically loaded libraries. This -facility is available on systems (such as GNU/Linux) that support -the C @code{dlopen()} and @code{dlsym()} functions. -This @value{SECTION} describes how to write and use dynamically -loaded extensions for @command{gawk}. -Experience with programming in -C or C++ is necessary when reading this @value{SECTION}. +@cindex Git, use of for @command{gawk} source code +@c From emails written March 22, 2012, to the gawk developers list. -@quotation CAUTION -The facilities described in this @value{SECTION} -are very much subject to change in a future @command{gawk} release. -Be aware that you may have to re-do everything, -at some future time. - -If you have written your own dynamic extensions, -be sure to recompile them for each new @command{gawk} release. -There is no guarantee of binary compatibility between different -releases, nor will there ever be such a guarantee. -@end quotation +If you look at the @command{gawk} source in the Git +repository, you will notice that it includes files that are automatically +generated by GNU infrastructure tools, such as @file{Makefile.in} from +Automake and even @file{configure} from Autoconf. -@quotation NOTE -When @option{--sandbox} is specified, extensions are disabled -(@pxref{Options}. -@end quotation +This is different from many Free Software projects that do not store +the derived files, because that keeps the repository less cluttered, +and it is easier to see the substantive changes when comparing versions +and trying to understand what changed between commits. -@menu -* Internals:: A brief look at some @command{gawk} internals. -* Plugin License:: A note about licensing. -* Sample Library:: A example of new functions. -@end menu +However, there are several reasons why the @command{gawk} maintainer +likes to have everything in the repository. -@node Internals -@appendixsubsec A Minimal Introduction to @command{gawk} Internals -@c STARTOFRANGE gawint -@cindex @command{gawk}, internals - -The truth is that @command{gawk} was not designed for simple extensibility. -The facilities for adding functions using shared libraries work, but -are something of a ``bag on the side.'' Thus, this tour is -brief and simplistic; would-be @command{gawk} hackers are encouraged to -spend some time reading the source code before trying to write -extensions based on the material presented here. Of particular note -are the files @file{awk.h}, @file{builtin.c}, and @file{eval.c}. -Reading @file{awkgram.y} in order to see how the parse tree is built -would also be of use. - -@cindex @code{awk.h} file (internal) -With the disclaimers out of the way, the following types, structure -members, functions, and macros are declared in @file{awk.h} and are of -use when writing extensions. The next @value{SECTION} -shows how they are used: +First, because it is then easy to reproduce any given version completely, +without relying upon the availability of (older, likely obsolete, and +maybe even impossible to find) other tools. -@table @code -@cindex floating-point, numbers, @code{AWKNUM} internal type -@cindex numbers, floating-point, @code{AWKNUM} internal type -@cindex @code{AWKNUM} internal type -@cindex internal type, @code{AWKNUM} -@item AWKNUM -An @code{AWKNUM} is the internal type of @command{awk} -floating-point numbers. Typically, it is a C @code{double}. - -@cindex @code{NODE} internal type -@cindex internal type, @code{NODE} -@cindex strings, @code{NODE} internal type -@cindex numbers, @code{NODE} internal type -@item NODE -Just about everything is done using objects of type @code{NODE}. -These contain both strings and numbers, as well as variables and arrays. - -@cindex @code{force_number()} internal function -@cindex internal function, @code{force_number()} -@cindex numeric, values -@item AWKNUM force_number(NODE *n) -This macro forces a value to be numeric. It returns the actual -numeric value contained in the node. -It may end up calling an internal @command{gawk} function. - -@cindex @code{force_string()} internal function -@cindex internal function, @code{force_string()} -@item void force_string(NODE *n) -This macro guarantees that a @code{NODE}'s string value is current. -It may end up calling an internal @command{gawk} function. -It also guarantees that the string is zero-terminated. - -@cindex @code{force_wstring()} internal function -@cindex internal function, @code{force_wstring()} -@item void force_wstring(NODE *n) -Similarly, this -macro guarantees that a @code{NODE}'s wide-string value is current. -It may end up calling an internal @command{gawk} function. -It also guarantees that the wide string is zero-terminated. - -@cindex parameters@comma{} number of -@cindex @code{nargs} internal variable -@cindex internal variable, @code{nargs} -@item nargs -Inside an extension function, this is the actual number of -parameters passed to the current function. - -@cindex @code{stptr} internal variable -@cindex internal variable, @code{stptr} -@cindex @code{stlen} internal variable -@cindex internal variable, @code{stlen} -@item n->stptr -@itemx n->stlen -The data and length of a @code{NODE}'s string value, respectively. -The string is @emph{not} guaranteed to be zero-terminated. -If you need to pass the string value to a C library function, save -the value in @code{n->stptr[n->stlen]}, assign @code{'\0'} to it, -call the routine, and then restore the value. - -@cindex @code{wstptr} internal variable -@cindex internal variable, @code{wstptr} -@cindex @code{wstlen} internal variable -@cindex internal variable, @code{wstlen} -@item n->wstptr -@itemx n->wstlen -The data and length of a @code{NODE}'s wide-string value, respectively. -Use @code{force_wstring()} to make sure these values are current. - -@cindex @code{type} internal variable -@cindex internal variable, @code{type} -@item n->type -The type of the @code{NODE}. This is a C @code{enum}. Values should -be one of @code{Node_var}, @code{Node_var_new}, or @code{Node_var_array} -for function parameters. - -@cindex @code{vname} internal variable -@cindex internal variable, @code{vname} -@item n->vname -The ``variable name'' of a node. This is not of much use inside -externally written extensions. - -@cindex arrays, associative, clearing -@cindex @code{assoc_clear()} internal function -@cindex internal function, @code{assoc_clear()} -@item void assoc_clear(NODE *n) -Clears the associative array pointed to by @code{n}. -Make sure that @samp{n->type == Node_var_array} first. - -@cindex arrays, elements, installing -@cindex @code{assoc_lookup()} internal function -@cindex internal function, @code{assoc_lookup()} -@item NODE **assoc_lookup(NODE *symbol, NODE *subs) -Finds, and installs if necessary, array elements. -@code{symbol} is the array, @code{subs} is the subscript. -This is usually a value created with @code{make_string()} (see below). - -@cindex strings -@cindex @code{make_string()} internal function -@cindex internal function, @code{make_string()} -@item NODE *make_string(char *s, size_t len) -Take a C string and turn it into a pointer to a @code{NODE} that -can be stored appropriately. This is permanent storage; understanding -of @command{gawk} memory management is helpful. - -@cindex numbers -@cindex @code{make_number()} internal function -@cindex internal function, @code{make_number()} -@item NODE *make_number(AWKNUM val) -Take an @code{AWKNUM} and turn it into a pointer to a @code{NODE} that -can be stored appropriately. This is permanent storage; understanding -of @command{gawk} memory management is helpful. - - -@cindex nodes@comma{} duplicating -@cindex @code{dupnode()} internal function -@cindex internal function, @code{dupnode()} -@item NODE *dupnode(NODE *n) -Duplicate a node. In most cases, this increments an internal -reference count instead of actually duplicating the entire @code{NODE}; -understanding of @command{gawk} memory management is helpful. - -@cindex memory, releasing -@cindex @code{unref()} internal function -@cindex internal function, @code{unref()} -@item void unref(NODE *n) -This macro releases the memory associated with a @code{NODE} -allocated with @code{make_string()} or @code{make_number()}. -Understanding of @command{gawk} memory management is helpful. - -@cindex @code{make_builtin()} internal function -@cindex internal function, @code{make_builtin()} -@item void make_builtin(const char *name, NODE *(*func)(NODE *), int count) -Register a C function pointed to by @code{func} as new built-in -function @code{name}. @code{name} is a regular C string. @code{count} -is the maximum number of arguments that the function takes. -The function should be written in the following manner: - -@example -/* do_xxx --- do xxx function for gawk */ - -NODE * -do_xxx(int nargs) -@{ - @dots{} -@} -@end example - -@cindex arguments, retrieving -@cindex @code{get_argument()} internal function -@cindex internal function, @code{get_argument()} -@item NODE *get_argument(int i) -This function is called from within a C extension function to get -the @code{i}-th argument from the function call. -The first argument is argument zero. - -@cindex @code{get_actual_argument()} internal function -@cindex internal function, @code{get_actual_argument()} -@item NODE *get_actual_argument(int i, -@itemx @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ int@ optional,@ int@ wantarray); -This function retrieves a particular argument @code{i}. @code{wantarray} is @code{TRUE} -if the argument should be an array, @code{FALSE} otherwise. If @code{optional} is -@code{TRUE}, the argument need not have been supplied. If it wasn't, the return -value is @code{NULL}. It is a fatal error if @code{optional} is @code{TRUE} but -the argument was not provided. - -@cindex @code{get_scalar_argument()} internal macro -@cindex internal macro, @code{get_scalar_argument()} -@item get_scalar_argument(i, opt) -This is a convenience macro that calls @code{get_actual_argument()}. - -@cindex @code{get_array_argument()} internal macro -@cindex internal macro, @code{get_array_argument()} -@item get_array_argument(i, opt) -This is a convenience macro that calls @code{get_actual_argument()}. - -@cindex functions, return values@comma{} setting - -@cindex @code{ERRNO} variable -@cindex @code{update_ERRNO()} internal function -@cindex internal function, @code{update_ERRNO()} -@item void update_ERRNO(void) -This function is called from within a C extension function to set -the value of @command{gawk}'s @code{ERRNO} variable, based on the current -value of the C @code{errno} global variable. -It is provided as a convenience. - -@cindex @code{ERRNO} variable -@cindex @code{update_ERRNO_saved()} internal function -@cindex internal function, @code{update_ERRNO_saved()} -@item void update_ERRNO_saved(int errno_saved) -This function is called from within a C extension function to set -the value of @command{gawk}'s @code{ERRNO} variable, based on the error -value provided as the argument. -It is provided as a convenience. - -@cindex @code{ENVIRON} array -@cindex @code{PROCINFO} array -@cindex @code{register_deferred_variable()} internal function -@cindex internal function, @code{register_deferred_variable()} -@item void register_deferred_variable(const char *name, NODE *(*load_func)(void)) -This function is called to register a function to be called when a -reference to an undefined variable with the given name is encountered. -The callback function will never be called if the variable exists already, -so, unless the calling code is running at program startup, it should first -check whether a variable of the given name already exists. -The argument function must return a pointer to a @code{NODE} containing the -newly created variable. This function is used to implement the builtin -@code{ENVIRON} and @code{PROCINFO} arrays, so you can refer to them -for examples. - -@cindex @code{IOBUF} internal structure -@cindex internal structure, @code{IOBUF} -@cindex @code{iop_alloc()} internal function -@cindex internal function, @code{iop_alloc()} -@cindex @code{get_record()} input method -@cindex @code{close_func}() input method -@cindex @code{INVALID_HANDLE} internal constant -@cindex internal constant, @code{INVALID_HANDLE} -@cindex XML (eXtensible Markup Language) -@cindex eXtensible Markup Language (XML) -@cindex @code{register_open_hook()} internal function -@cindex internal function, @code{register_open_hook()} -@item void register_open_hook(void *(*open_func)(IOBUF *)) -This function is called to register a function to be called whenever -a new data file is opened, leading to the creation of an @code{IOBUF} -structure in @code{iop_alloc()}. After creating the new @code{IOBUF}, -@code{iop_alloc()} will call (in reverse order of registration, so the last -function registered is called first) each open hook until one returns -non-@code{NULL}. If any hook returns a non-@code{NULL} value, that value is assigned -to the @code{IOBUF}'s @code{opaque} field (which will presumably point -to a structure containing additional state associated with the input -processing), and no further open hooks are called. - -The function called will most likely want to set the @code{IOBUF}'s -@code{get_record} method to indicate that future input records should -be retrieved by calling that method instead of using the standard -@command{gawk} input processing. - -And the function will also probably want to set the @code{IOBUF}'s -@code{close_func} method to be called when the file is closed to clean -up any state associated with the input. - -Finally, hook functions should be prepared to receive an @code{IOBUF} -structure where the @code{fd} field is set to @code{INVALID_HANDLE}, -meaning that @command{gawk} was not able to open the file itself. In -this case, the hook function must be able to successfully open the file -and place a valid file descriptor there. - -Currently, for example, the hook function facility is used to implement -the XML parser shared library extension. For more info, please look in -@file{awk.h} and in @file{io.c}. -@end table - -An argument that is supposed to be an array needs to be handled with -some extra code, in case the array being passed in is actually -from a function parameter. - -The following boilerplate code shows how to do this: - -@example -NODE *the_arg; - -/* assume need 3rd arg, 0-based */ -the_arg = get_array_argument(2, FALSE); -@end example - -Again, you should spend time studying the @command{gawk} internals; -don't just blindly copy this code. -@c ENDOFRANGE gawint - -@node Plugin License -@appendixsubsec Extension Licensing - -Every dynamic extension should define the global symbol -@code{plugin_is_GPL_compatible} to assert that it has been licensed under -a GPL-compatible license. If this symbol does not exist, @command{gawk} -will emit a fatal error and exit. - -The declared type of the symbol should be @code{int}. It does not need -to be in any allocated section, though. The code merely asserts that -the symbol exists in the global scope. Something like this is enough: - -@example -int plugin_is_GPL_compatible; -@end example - -@node Sample Library -@appendixsubsec Example: Directory and File Operation Built-ins -@c STARTOFRANGE chdirg -@cindex @code{chdir()} function@comma{} implementing in @command{gawk} -@c STARTOFRANGE statg -@cindex @code{stat()} function@comma{} implementing in @command{gawk} -@c STARTOFRANGE filre -@cindex files, information about@comma{} retrieving -@c STARTOFRANGE dirch -@cindex directories, changing - -Two useful functions that are not in @command{awk} are @code{chdir()} -(so that an @command{awk} program can change its directory) and -@code{stat()} (so that an @command{awk} program can gather information about -a file). -This @value{SECTION} implements these functions for @command{gawk} in an -external extension library. - -@menu -* Internal File Description:: What the new functions will do. -* Internal File Ops:: The code for internal file operations. -* Using Internal File Ops:: How to use an external extension. -@end menu +As an extreme example, if you ever even think about trying to compile, +oh, say, the V7 @command{awk}, you will discover that not only do you +have to bootstrap the V7 @command{yacc} to do so, but you also need the +V7 @command{lex}. And the latter is pretty much impossible to bring up +on a modern GNU/Linux system.@footnote{We tried. It was painful.} -@node Internal File Description -@appendixsubsubsec Using @code{chdir()} and @code{stat()} +(Or, let's say @command{gawk} 1.2 required @command{bison} whatever-it-was +in 1989 and that there was no @file{awkgram.c} file in the repository. Is +there a guarantee that we could find that @command{bison} version? Or that +@emph{it} would build?) -This @value{SECTION} shows how to use the new functions at the @command{awk} -level once they've been integrated into the running @command{gawk} -interpreter. -Using @code{chdir()} is very straightforward. It takes one argument, -the new directory to change to: +If the repository has all the generated files, then it's easy to just check +them out and build. (Or @emph{easier}, depending upon how far back we go.) -@example -@dots{} -newdir = "/home/arnold/funstuff" -ret = chdir(newdir) -if (ret < 0) @{ - printf("could not change to %s: %s\n", - newdir, ERRNO) > "/dev/stderr" - exit 1 -@} -@dots{} -@end example +And that brings us to the second (and stronger) reason why all the files +really need to be in Git. It boils down to who do you cater +to---the @command{gawk} developer(s), or the user who just wants to check +out a version and try it out? -The return value is negative if the @code{chdir} failed, -and @code{ERRNO} -(@pxref{Built-in Variables}) -is set to a string indicating the error. +The @command{gawk} maintainer +wants it to be possible for any interested @command{awk} user in the +world to just clone the repository, check out the branch of interest and +build it. Without their having to have the correct version(s) of the +autotools.@footnote{There is one GNU program that is (in our opinion) +severely difficult to bootstrap from the Git repository. For +example, on the author's old (but still working) PowerPC Macintosh with +Mac OS X 10.5, it was necessary to bootstrap a ton of software, starting +with Git itself, in order to try to work with the latest code. +It's not pleasant, and especially on older systems, it's a big waste +of time. -Using @code{stat()} is a bit more complicated. -The C @code{stat()} function fills in a structure that has a fair -amount of information. -The right way to model this in @command{awk} is to fill in an associative -array with the appropriate information: +Starting with the latest tarball was no picnic either. The maintainers +had dropped @file{.gz} and @file{.bz2} files and only distribute +@file{.tar.xz} files. It was necessary to bootstrap @command{xz} first!} +That is the point of the @file{bootstrap.sh} file. It touches the +various other files in the right order such that -@c broke printf for page breaking @example -file = "/home/arnold/.profile" -fdata[1] = "x" # force `fdata' to be an array -ret = stat(file, fdata) -if (ret < 0) @{ - printf("could not stat %s: %s\n", - file, ERRNO) > "/dev/stderr" - exit 1 -@} -printf("size of %s is %d bytes\n", file, fdata["size"]) +# The canonical incantation for building GNU software: +./bootstrap.sh && ./configure && make @end example -The @code{stat()} function always clears the data array, even if -the @code{stat()} fails. It fills in the following elements: +@noindent +will @emph{just work}. -@table @code -@item "name" -The name of the file that was @code{stat()}'ed. +This is extremely important for the @code{master} and +@code{gawk-@var{X}.@var{Y}-stable} branches. -@item "dev" -@itemx "ino" -The file's device and inode numbers, respectively. +Further, the @command{gawk} maintainer would argue that it's also +important for the @command{gawk} developers. When he tried to check out +the @code{xgawk} branch@footnote{A branch (since removed) created by one of the other +developers that did not include the generated files.} to build it, he +couldn't. (No @file{ltmain.sh} file, and he had no idea how to create it, +and that was not the only problem.) -@item "mode" -The file's mode, as a numeric value. This includes both the file's -type and its permissions. +He felt @emph{extremely} frustrated. With respect to that branch, +the maintainer is no different than Jane User who wants to try to build +@code{gawk-4.1-stable} or @code{master} from the repository. -@item "nlink" -The number of hard links (directory entries) the file has. +Thus, the maintainer thinks that it's not just important, but critical, +that for any given branch, the above incantation @emph{just works}. -@item "uid" -@itemx "gid" -The numeric user and group ID numbers of the file's owner. +@c Added 9/2014: +A third reason to have all the files is that without them, using @samp{git +bisect} to try to find the commit that introduced a bug is exceedingly +difficult. The maintainer tried to do that on another project that +requires running bootstrapping scripts just to create @command{configure} +and so on; it was really painful. When the repository is self-contained, +using @command{git bisect} in it is very easy. -@item "size" -The size in bytes of the file. +@c So - that's my reasoning and philosophy. -@item "blocks" -The number of disk blocks the file actually occupies. This may not -be a function of the file's size if the file has holes. +What are some of the consequences and/or actions to take? -@item "atime" -@itemx "mtime" -@itemx "ctime" -The file's last access, modification, and inode update times, -respectively. These are numeric timestamps, suitable for formatting -with @code{strftime()} -(@pxref{Built-in}). +@enumerate 1 +@item +We don't mind that there are differing files in the different branches +as a result of different versions of the autotools. -@item "pmode" -The file's ``printable mode.'' This is a string representation of -the file's type and permissions, such as what is produced by -@samp{ls -l}---for example, @code{"drwxr-xr-x"}. +@enumerate A +@item +It's the maintainer's job to merge them and he will deal with it. -@item "type" -A printable string representation of the file's type. The value -is one of the following: +@item +He is really good at @samp{git diff x y > /tmp/diff1 ; gvim /tmp/diff1} to +remove the diffs that aren't of interest in order to review code. +@end enumerate -@table @code -@item "blockdev" -@itemx "chardev" -The file is a block or character device (``special file''). +@item +It would certainly help if everyone used the same versions of the GNU tools +as he does, which in general are the latest released versions of +Automake, +Autoconf, +@command{bison}, +and +GNU @command{gettext}. @ignore -@item "door" -The file is a Solaris ``door'' (special file used for -interprocess communications). +If it would help if I sent out an ``I just upgraded to version x.y +of tool Z'' kind of message to this list, I can do that. Up until +now it hasn't been a real issue since I'm the only one who's been +dorking with the configuration machinery. @end ignore -@item "directory" -The file is a directory. +@c @enumerate A +@c @item +Installing from source is quite easy. It's how the maintainer worked for years +(and still works). +He had @file{/usr/local/bin} at the front of his @env{PATH} and just did: -@item "fifo" -The file is a named-pipe (also known as a FIFO). - -@item "file" -The file is just a regular file. - -@item "socket" -The file is an @code{AF_UNIX} (``Unix domain'') socket in the -filesystem. - -@item "symlink" -The file is a symbolic link. -@end table -@end table - -Several additional elements may be present depending upon the operating -system and the type of the file. You can test for them in your @command{awk} -program by using the @code{in} operator -(@pxref{Reference to Elements}): - -@table @code -@item "blksize" -The preferred block size for I/O to the file. This field is not -present on all POSIX-like systems in the C @code{stat} structure. - -@item "linkval" -If the file is a symbolic link, this element is the name of the -file the link points to (i.e., the value of the link). - -@item "rdev" -@itemx "major" -@itemx "minor" -If the file is a block or character device file, then these values -represent the numeric device number and the major and minor components -of that number, respectively. -@end table - -@node Internal File Ops -@appendixsubsubsec C Code for @code{chdir()} and @code{stat()} - -Here is the C code for these extensions. They were written for -GNU/Linux. The code needs some more work for complete portability -to other POSIX-compliant systems:@footnote{This version is edited -slightly for presentation. See -@file{extension/filefuncs.c} in the @command{gawk} distribution -for the complete version.} - -@c break line for page breaking @example -#include "awk.h" - -#include <sys/sysmacros.h> - -int plugin_is_GPL_compatible; - -/* do_chdir --- provide dynamically loaded chdir() builtin for gawk */ - -static NODE * -do_chdir(int nargs) -@{ - NODE *newdir; - int ret = -1; - - if (do_lint && nargs != 1) - lintwarn("chdir: called with incorrect number of arguments"); - - newdir = get_scalar_argument(0, FALSE); -@end example - -The file includes the @code{"awk.h"} header file for definitions -for the @command{gawk} internals. It includes @code{<sys/sysmacros.h>} -for access to the @code{major()} and @code{minor}() macros. - -@cindex programming conventions, @command{gawk} internals -By convention, for an @command{awk} function @code{foo}, the function that -implements it is called @samp{do_foo}. The function should take -a @samp{int} argument, usually called @code{nargs}, that -represents the number of defined arguments for the function. The @code{newdir} -variable represents the new directory to change to, retrieved -with @code{get_scalar_argument()}. Note that the first argument is -numbered zero. - -This code actually accomplishes the @code{chdir()}. It first forces -the argument to be a string and passes the string value to the -@code{chdir()} system call. If the @code{chdir()} fails, @code{ERRNO} -is updated. - -@example - (void) force_string(newdir); - ret = chdir(newdir->stptr); - if (ret < 0) - update_ERRNO(); -@end example - -Finally, the function returns the return value to the @command{awk} level: - -@example - return make_number((AWKNUM) ret); -@} +wget http://ftp.gnu.org/gnu/@var{package}/@var{package}-@var{x}.@var{y}.@var{z}.tar.gz +tar -xpzvf @var{package}-@var{x}.@var{y}.@var{z}.tar.gz +cd @var{package}-@var{x}.@var{y}.@var{z} +./configure && make && make check +make install # as root @end example -The @code{stat()} built-in is more involved. First comes a function -that turns a numeric mode into a printable representation -(e.g., 644 becomes @samp{-rw-r--r--}). This is omitted here for brevity: - -@c break line for page breaking -@example -/* format_mode --- turn a stat mode field into something readable */ - -static char * -format_mode(unsigned long fmode) -@{ - @dots{} -@} -@end example - -Next comes the @code{do_stat()} function. It starts with -variable declarations and argument checking: - +@c @item @ignore -Changed message for page breaking. Used to be: - "stat: called with incorrect number of arguments (%d), should be 2", +These days the maintainer uses Ubuntu 12.04 which is medium current, but +he is already doing the above for Automake, Autoconf, and @command{bison}. @end ignore -@example -/* do_stat --- provide a stat() function for gawk */ - -static NODE * -do_stat(int nargs) -@{ - NODE *file, *array, *tmp; - struct stat sbuf; - int ret; - NODE **aptr; - char *pmode; /* printable mode */ - char *type = "unknown"; - - if (do_lint && nargs > 2) - lintwarn("stat: called with too many arguments"); -@end example - -Then comes the actual work. First, the function gets the arguments. -Then, it always clears the array. -The code use @code{lstat()} (instead of @code{stat()}) -to get the file information, -in case the file is a symbolic link. -If there's an error, it sets @code{ERRNO} and returns: - -@c comment made multiline for page breaking -@example - /* file is first arg, array to hold results is second */ - file = get_scalar_argument(0, FALSE); - array = get_array_argument(1, FALSE); - - /* empty out the array */ - assoc_clear(array); - - /* lstat the file, if error, set ERRNO and return */ - (void) force_string(file); - ret = lstat(file->stptr, & sbuf); - if (ret < 0) @{ - update_ERRNO(); - return make_number((AWKNUM) ret); - @} -@end example - -Now comes the tedious part: filling in the array. Only a few of the -calls are shown here, since they all follow the same pattern: - -@example - /* fill in the array */ - aptr = assoc_lookup(array, tmp = make_string("name", 4)); - *aptr = dupnode(file); - unref(tmp); - - aptr = assoc_lookup(array, tmp = make_string("mode", 4)); - *aptr = make_number((AWKNUM) sbuf.st_mode); - unref(tmp); - - aptr = assoc_lookup(array, tmp = make_string("pmode", 5)); - pmode = format_mode(sbuf.st_mode); - *aptr = make_string(pmode, strlen(pmode)); - unref(tmp); -@end example - -When done, return the @code{lstat()} return value: - -@example - - return make_number((AWKNUM) ret); -@} -@end example - -@cindex programming conventions, @command{gawk} internals -Finally, it's necessary to provide the ``glue'' that loads the -new function(s) into @command{gawk}. By convention, each library has -a routine named @code{dlload()} that does the job: - -@example -/* dlload --- load new builtins in this library */ -NODE * -dlload(NODE *tree, void *dl) -@{ - make_builtin("chdir", do_chdir, 1); - make_builtin("stat", do_stat, 2); - return make_number((AWKNUM) 0); -@} -@end example +@ignore +(C. Rant: Recent Linux versions with GNOME 3 really suck. What + are all those people thinking? Fedora 15 was such a bust it drove + me to Ubuntu, but Ubuntu 11.04 and 11.10 are totally unusable from + a UI perspective. Bleah.) +@end ignore +@c @end enumerate -And that's it! As an exercise, consider adding functions to -implement system calls such as @code{chown()}, @code{chmod()}, -and @code{umask()}. +@ignore +@item +If someone still feels really strongly about all this, then perhaps they +can have two branches, one for their development with just the clean +changes, and one that is buildable (xgawk and xgawk-buildable, maybe). +Or, as I suggested in another mail, make commits in pairs, the first with +the "real" changes and the second with "everything else needed for + building". +@end ignore +@end enumerate -@node Using Internal File Ops -@appendixsubsubsec Integrating the Extensions +Most of the above was originally written by the maintainer to other +@command{gawk} developers. It raised the objection from one of +the developers ``@dots{} that anybody pulling down the source from +Git is not an end user.'' -@cindex @command{gawk}, interpreter@comma{} adding code to -Now that the code is written, it must be possible to add it at -runtime to the running @command{gawk} interpreter. First, the -code must be compiled. Assuming that the functions are in -a file named @file{filefuncs.c}, and @var{idir} is the location -of the @command{gawk} include files, -the following steps create -a GNU/Linux shared library: +However, this is not true. There are ``power @command{awk} users'' +who can build @command{gawk} (using the magic incantation shown previously) +but who can't program in C. Thus, the major branches should be +kept buildable all the time. -@example -$ @kbd{gcc -fPIC -shared -DHAVE_CONFIG_H -c -O -g -I@var{idir} filefuncs.c} -$ @kbd{ld -o filefuncs.so -shared filefuncs.o} -@end example +It was then suggested that there be a @command{cron} job to create +nightly tarballs of ``the source.'' Here, the problem is that there +are source trees, corresponding to the various branches! So, +nightly tarballs aren't the answer, especially as the repository can go +for weeks without significant change being introduced. -@cindex @code{extension()} function (@command{gawk}) -Once the library exists, it is loaded by calling the @code{extension()} -built-in function. -This function takes two arguments: the name of the -library to load and the name of a function to call when the library -is first loaded. This function adds the new functions to @command{gawk}. -It returns the value returned by the initialization function -within the shared library: +Fortunately, the Git server can meet this need. For any given +branch named @var{branchname}, use: @example -# file testff.awk -BEGIN @{ - extension("./filefuncs.so", "dlload") - - chdir(".") # no-op - - data[1] = 1 # force `data' to be an array - print "Info for testff.awk" - ret = stat("testff.awk", data) - print "ret =", ret - for (i in data) - printf "data[\"%s\"] = %s\n", i, data[i] - print "testff.awk modified:", - strftime("%m %d %y %H:%M:%S", data["mtime"]) - - print "\nInfo for JUNK" - ret = stat("JUNK", data) - print "ret =", ret - for (i in data) - printf "data[\"%s\"] = %s\n", i, data[i] - print "JUNK modified:", strftime("%m %d %y %H:%M:%S", data["mtime"]) -@} +wget http://git.savannah.gnu.org/cgit/gawk.git/snapshot/gawk-@var{branchname}.tar.gz @end example -Here are the results of running the program: - -@example -$ @kbd{gawk -f testff.awk} -@print{} Info for testff.awk -@print{} ret = 0 -@print{} data["size"] = 607 -@print{} data["ino"] = 14945891 -@print{} data["name"] = testff.awk -@print{} data["pmode"] = -rw-rw-r-- -@print{} data["nlink"] = 1 -@print{} data["atime"] = 1293993369 -@print{} data["mtime"] = 1288520752 -@print{} data["mode"] = 33204 -@print{} data["blksize"] = 4096 -@print{} data["dev"] = 2054 -@print{} data["type"] = file -@print{} data["gid"] = 500 -@print{} data["uid"] = 500 -@print{} data["blocks"] = 8 -@print{} data["ctime"] = 1290113572 -@print{} testff.awk modified: 10 31 10 12:25:52 -@print{} -@print{} Info for JUNK -@print{} ret = -1 -@print{} JUNK modified: 01 01 70 02:00:00 -@end example -@c ENDOFRANGE filre -@c ENDOFRANGE dirch -@c ENDOFRANGE statg -@c ENDOFRANGE chdirg -@c ENDOFRANGE gladfgaw -@c ENDOFRANGE adfugaw -@c ENDOFRANGE fubadgaw +@noindent +to retrieve a snapshot of the given branch. @node Future Extensions @appendixsec Probable Future Extensions @@ -29855,80 +39174,349 @@ Larry @cindex Wall, Larry @cindex Robbins, Arnold @quotation -@i{AWK is a language similar to PERL, only considerably more elegant.}@* -Arnold Robbins +@i{AWK is a language similar to PERL, only considerably more elegant.} +@author Arnold Robbins +@end quotation -@i{Hey!}@* -Larry Wall +@quotation +@i{Hey!} +@author Larry Wall @end quotation -This @value{SECTION} briefly lists extensions and possible improvements -that indicate the directions we are -currently considering for @command{gawk}. The file @file{FUTURES} in the -@command{gawk} distribution lists these extensions as well. +The @file{TODO} file in the @code{master} branch of the @command{gawk} +Git repository lists possible future enhancements. Some of these relate +to the source code, and others to possible new features. Please see +that file for the list. +@xref{Additions}, +if you are interested in tackling any of the projects listed there. + +@node Implementation Limitations +@appendixsec Some Limitations of the Implementation + +This following table describes limits of @command{gawk} on a Unix-like +system (although it is variable even then). Other systems may have +different limits. + +@multitable @columnfractions .40 .60 +@headitem Item @tab Limit +@item Characters in a character class @tab 2^(number of bits per byte) +@item Length of input record @tab @code{MAX_INT} +@item Length of output record @tab Unlimited +@item Length of source line @tab Unlimited +@item Number of fields in a record @tab @code{MAX_LONG} +@item Number of file redirections @tab Unlimited +@item Number of input records in one file @tab @code{MAX_LONG} +@item Number of input records total @tab @code{MAX_LONG} +@item Number of pipe redirections @tab min(number of processes per user, number of open files) +@item Numeric values @tab Double-precision floating point (if not using MPFR) +@item Size of a field @tab @code{MAX_INT} +@item Size of a literal string @tab @code{MAX_INT} +@item Size of a printf string @tab @code{MAX_INT} +@end multitable -Following is a list of probable future changes visible at the -@command{awk} language level: +@node Extension Design +@appendixsec Extension API Design -@c these are ordered by likelihood -@table @asis -@item Loadable module interface -It is not clear that the @command{awk}-level interface to the -modules facility is as good as it should be. The interface needs to be -redesigned, particularly taking namespace issues into account, as -well as possibly including issues such as library search path order -and versioning. - -@item @code{RECLEN} variable for fixed-length records -Along with @code{FIELDWIDTHS}, this would speed up the processing of -fixed-length records. -@code{PROCINFO["RS"]} would be @code{"RS"} or @code{"RECLEN"}, -depending upon which kind of record processing is in effect. - -@item Databases -It may be possible to map a GDBM/NDBM/SDBM file into an @command{awk} array. - -@item More @code{lint} warnings -There are more things that could be checked for portability. -@end table +This @value{SECTION} documents the design of the extension API, +including a discussion of some of the history and problems that needed +to be solved. -Following is a list of probable improvements that will make @command{gawk}'s -source code easier to work with: +The first version of extensions for @command{gawk} was developed in +the mid-1990s and released with @command{gawk} 3.1 in the late 1990s. +The basic mechanisms and design remained unchanged for close to 15 years, +until 2012. -@table @asis -@item Loadable module mechanics -The current extension mechanism works -(@pxref{Dynamic Extensions}), -but is rather primitive. It requires a fair amount of manual work -to create and integrate a loadable module. -Nor is the current mechanism as portable as might be desired. -The GNU @command{libtool} package provides a number of features that -would make using loadable modules much easier. -@command{gawk} should be changed to use @command{libtool}. - -@item Loadable module internals -The API to its internals that @command{gawk} ``exports'' should be revised. -Too many things are needlessly exposed. A new API should be designed -and implemented to make module writing easier. - -@item Better array subscript management -@command{gawk}'s management of array subscript storage could use revamping, -so that using the same value to index multiple arrays only -stores one copy of the index value. -@end table +The old extension mechanism used data types and functions from +@command{gawk} itself, with a ``clever hack'' to install extension +functions. -Finally, -the programs in the test suite could use documenting in this @value{DOCUMENT}. +@command{gawk} included some sample extensions, of which a few were +really useful. However, it was clear from the outset that the extension +mechanism was bolted onto the side and was not really well thought out. + +@menu +* Old Extension Problems:: Problems with the old mechanism. +* Extension New Mechanism Goals:: Goals for the new mechanism. +* Extension Other Design Decisions:: Some other design decisions. +* Extension Future Growth:: Some room for future growth. +@end menu + +@node Old Extension Problems +@appendixsubsec Problems With The Old Mechanism + +The old extension mechanism had several problems: + +@itemize @value{BULLET} +@item +It depended heavily upon @command{gawk} internals. Any time the +@code{NODE} structure@footnote{A critical central data structure +inside @command{gawk}.} changed, an extension would have to be +recompiled. Furthermore, to really write extensions required understanding +something about @command{gawk}'s internal functions. There was some +documentation in this @value{DOCUMENT}, but it was quite minimal. + +@item +Being able to call into @command{gawk} from an extension required linker +facilities that are common on Unix-derived systems but that did +not work on MS-Windows systems; users wanting extensions on MS-Windows +had to statically link them into @command{gawk}, even though MS-Windows supports +dynamic loading of shared objects. + +@item +The API would change occasionally as @command{gawk} changed; no compatibility +between versions was ever offered or planned for. +@end itemize + +Despite the drawbacks, the @command{xgawk} project developers forked +@command{gawk} and developed several significant extensions. They also +enhanced @command{gawk}'s facilities relating to file inclusion and +shared object access. + +A new API was desired for a long time, but only in 2012 did the +@command{gawk} maintainer and the @command{xgawk} developers finally +start working on it together. More information about the @command{xgawk} +project is provided in @ref{gawkextlib}. + +@node Extension New Mechanism Goals +@appendixsubsec Goals For A New Mechanism + +Some goals for the new API were: + +@itemize @value{BULLET} +@item +The API should be independent of @command{gawk} internals. Changes in +@command{gawk} internals should not be visible to the writer of an +extension function. + +@item +The API should provide @emph{binary} compatibility across @command{gawk} +releases as long as the API itself does not change. + +@item +The API should enable extensions written in C or C++ to have roughly the +same ``appearance'' to @command{awk}-level code as @command{awk} +functions do. This means that extensions should have: + +@itemize @value{MINUS} +@item +The ability to access function parameters. + +@item +The ability to turn an undefined parameter into an array (call by reference). + +@item +The ability to create, access and update global variables. + +@item +Easy access to all the elements of an array at once (``array flattening'') +in order to loop over all the element in an easy fashion for C code. + +@item +The ability to create arrays (including @command{gawk}'s true +arrays of arrays). +@end itemize +@end itemize + +Some additional important goals were: + +@itemize @value{BULLET} +@item +The API should use only features in ISO C 90, so that extensions +can be written using the widest range of C and C++ compilers. The header +should include the appropriate @samp{#ifdef __cplusplus} and @samp{extern "C"} +magic so that a C++ compiler could be used. (If using C++, the runtime +system has to be smart enough to call any constructors and destructors, +as @command{gawk} is a C program. As of this writing, this has not been +tested.) + +@item +The API mechanism should not require access to @command{gawk}'s +symbols@footnote{The @dfn{symbols} are the variables and functions +defined inside @command{gawk}. Access to these symbols by code +external to @command{gawk} loaded dynamically at runtime is +problematic on MS-Windows.} by the compile-time or dynamic linker, +in order to enable creation of extensions that also work on MS-Windows. +@end itemize + +During development, it became clear that there were other features +that should be available to extensions, which were also subsequently +provided: + +@itemize @value{BULLET} +@item +Extensions should have the ability to hook into @command{gawk}'s +I/O redirection mechanism. In particular, the @command{xgawk} +developers provided a so-called ``open hook'' to take over reading +records. During development, this was generalized to allow +extensions to hook into input processing, output processing, and +two-way I/O. + +@item +An extension should be able to provide a ``call back'' function +to perform cleanup actions when @command{gawk} exits. + +@item +An extension should be able to provide a version string so that +@command{gawk}'s @option{--version} option can provide information +about extensions as well. +@end itemize + +The requirement to avoid access to @command{gawk}'s symbols is, at first +glance, a difficult one to meet. + +One design, apparently used by Perl and Ruby and maybe others, would +be to make the mainline @command{gawk} code into a library, with the +@command{gawk} utility a small C @code{main()} function linked against +the library. + +This seemed like the tail wagging the dog, complicating build and +installation and making a simple copy of the @command{gawk} executable +from one system to another (or one place to another on the same +system!) into a chancy operation. + +Pat Rankin suggested the solution that was adopted. +@xref{Extension Mechanism Outline}, for the details. + +@node Extension Other Design Decisions +@appendixsubsec Other Design Decisions + +As an arbitrary design decision, extensions can read the values of +predefined variables and arrays (such as @code{ARGV} and @code{FS}), but cannot +change them, with the exception of @code{PROCINFO}. + +The reason for this is to prevent an extension function from affecting +the flow of an @command{awk} program outside its control. While a real +@command{awk} function can do what it likes, that is at the discretion +of the programmer. An extension function should provide a service or +make a C API available for use within @command{awk}, and not mess with +@code{FS} or @code{ARGC} and @code{ARGV}. + +In addition, it becomes easy to start down a slippery slope. How +much access to @command{gawk} facilities do extensions need? +Do they need @code{getline}? What about calling @code{gsub()} or +compiling regular expressions? What about calling into @command{awk} +functions? (@emph{That} would be messy.) + +In order to avoid these issues, the @command{gawk} developers chose +to start with the simplest, most basic features that are still truly useful. + +Another decision is that although @command{gawk} provides nice things like +MPFR, and arrays indexed internally by integers, these features are not +being brought out to the API in order to keep things simple and close to +traditional @command{awk} semantics. (In fact, arrays indexed internally +by integers are so transparent that they aren't even documented!) + +Additionally, all functions in the API check that their pointer +input parameters are not @code{NULL}. If they are, they return an error. +(It is a good idea for extension code to verify that +pointers received from @command{gawk} are not @code{NULL}. +Such a thing should not happen, but the @command{gawk} developers +are only human, and they have been known to occasionally make +mistakes.) + +With time, the API will undoubtedly evolve; the @command{gawk} developers +expect this to be driven by user needs. For now, the current API seems +to provide a minimal yet powerful set of features for creating extensions. + +@node Extension Future Growth +@appendixsubsec Room For Future Growth + +The API can later be expanded, in two ways: + +@itemize @value{BULLET} +@item +@command{gawk} passes an ``extension id'' into the extension when it +first loads the extension. The extension then passes this id back +to @command{gawk} with each function call. This mechanism allows +@command{gawk} to identify the extension calling into it, should it need +to know. + +@item +Similarly, the extension passes a ``name space'' into @command{gawk} +when it registers each extension function. This accommodates a possible future +mechanism for grouping extension functions and possibly avoiding name +conflicts. +@end itemize + +Of course, as of this writing, no decisions have been made with respect +to any of the above. + +@node Old Extension Mechanism +@appendixsec Compatibility For Old Extensions + +@ref{Dynamic Extensions}, describes the supported API and mechanisms +for writing extensions for @command{gawk}. This API was introduced +in @value{PVERSION} 4.1. However, for many years @command{gawk} +provided an extension mechanism that required knowledge of @command{gawk} +internals and that was not as well designed. + +In order to provide a transition period, @command{gawk} @value{PVERSION} 4.1 +continues to support the original extension mechanism. +This will be true for the life of exactly one major release. This support +will be withdrawn, and removed from the source code, at the next major +release. + +Briefly, original-style extensions should be compiled by including the +@file{awk.h} header file in the extension source code. Additionally, +you must define the identifier @samp{GAWK} when building (use +@samp{-DGAWK} with Unix-style compilers). Otherwise, the definitions +in @file{gawkapi.h} will cause conflicts with those in @file{awk.h} +and your extension will not compile. + +Just as in previous versions, you load an old-style extension with the +@code{extension()} built-in function (which is not otherwise documented). +This function in turn finds and loads the shared object file containing +the extension and calls its @code{dl_load()} C routine. + +Because original-style and new-style extensions use different initialization +routines (@code{dl_load()} versus @code{dlload()}), they may safely +be installed in the same directory (to be found by @env{AWKLIBPATH}) +without conflict. + +The @command{gawk} development team strongly recommends that you +convert any old extensions that you may have to use the new API +described in @ref{Dynamic Extensions}. + +@node Notes summary +@appendixsec Summary + +@itemize @value{BULLET} +@item +@command{gawk}'s extensions can be disabled with either the +@option{--traditional} option or with the @option{--posix} option. +The @option{--parsedebug} option is available if @command{gawk} is +compiled with @samp{-DDEBUG}. + +@item +The source code for @command{gawk} is maintained in a publicly +accessible Git repository. Anyone may check it out and view the source. + +@item +Contributions to @command{gawk} are welcome. Following the steps +outlined in this @value{CHAPTER} will make it easier to integrate +your contributions into the code base. +This applies both to new feature contributions and to ports to +additional operating systems. + +@item +@command{gawk} has some limits---generally those that are imposed by +the machine architecture. + +@item +The extension API design was intended to solve a number of problems +with the previous extension mechanism, enable features needed by +the @code{xgawk} project, and provide binary compatibility going forward. + +@item +The previous extension mechanism is still supported in @value{PVERSION} 4.1 +of @command{gawk}, but it @emph{will} be removed in the next major release. + +@end itemize -@xref{Additions}, -if you are interested in tackling any of these projects. -@c ENDOFRANGE impis -@c ENDOFRANGE gawii @node Basic Concepts @appendix Basic Programming Concepts @cindex programming, concepts -@c STARTOFRANGE procon @cindex programming, concepts This @value{APPENDIX} attempts to define some of the basic concepts @@ -29942,7 +39530,6 @@ other introductory texts that you should refer to instead.) @menu * Basic High Level:: The high level view. * Basic Data Typing:: A very quick intro to data types. -* Floating Point Issues:: Stuff to know about floating-point numbers. @end menu @node Basic High Level @@ -29951,18 +39538,33 @@ other introductory texts that you should refer to instead.) @cindex processing data At the most basic level, the job of a program is to process some input data and produce results. +@ifnotdocbook +See @ref{figure-general-flow}. +@end ifnotdocbook +@ifdocbook +See @inlineraw{docbook, <xref linkend="figure-general-flow"/>}. +@end ifdocbook -@iftex -@image{general-program} -@end iftex -@ifnottex -@example - _______ -+------+ / \ +---------+ -| Data | -----> < Program > -----> | Results | -+------+ \_______/ +---------+ -@end example -@end ifnottex +@ifnotdocbook +@float Figure,figure-general-flow +@caption{General Program Flow} +@ifinfo +@center @image{general-program, , , General program flow, txt} +@end ifinfo +@ifnotinfo +@center @image{general-program, , , General program flow} +@end ifnotinfo +@end float +@end ifnotdocbook + +@docbook +<figure id="figure-general-flow" float="0"> +<title>General Program Flow</title> +<mediaobject> +<imageobject role="web"><imagedata fileref="general-program.png" format="PNG"/></imageobject> +</mediaobject> +</figure> +@end docbook @cindex compiled programs @cindex interpreted programs @@ -29978,26 +39580,34 @@ instructions in your program to process the data. @cindex programming, basic steps When you write a program, it usually consists -of the following, very basic set of steps: +of the following, very basic set of steps, +@ifnotdocbook +as shown in @ref{figure-process-flow}: +@end ifnotdocbook +@ifdocbook +as shown in @inlineraw{docbook, <xref linkend="figure-process-flow"/>}: +@end ifdocbook -@iftex -@image{process-flow} -@end iftex -@ifnottex -@example - ______ -+----------------+ / More \ No +----------+ -| Initialization | -------> < Data > -------> | Clean Up | -+----------------+ ^ \ ? / +----------+ - | +--+-+ - | | Yes - | | - | V - | +---------+ - +-----+ Process | - +---------+ -@end example -@end ifnottex +@ifnotdocbook +@float Figure,figure-process-flow +@caption{Basic Program Steps} +@ifinfo +@center @image{process-flow, , , Basic Program Stages, txt} +@end ifinfo +@ifnotinfo +@center @image{process-flow, , , Basic Program Stages} +@end ifnotinfo +@end float +@end ifnotdocbook + +@docbook +<figure id="figure-process-flow" float="0"> +<title>Basic Program Stages</title> +<mediaobject> +<imageobject role="web"><imagedata fileref="process-flow.png" format="PNG"/></imageobject> +</mediaobject> +</figure> +@end docbook @table @asis @item Initialization @@ -30093,47 +39703,10 @@ Individual variables, as well as numeric and string variables, are referred to as @dfn{scalar} values. Groups of values, such as arrays, are not scalars. -@cindex integers -@cindex floating-point, numbers -@cindex numbers, floating-point -Within computers, there are two kinds of numeric values: @dfn{integers} -and @dfn{floating-point}. -In school, integer values were referred to as ``whole'' numbers---that is, -numbers without any fractional part, such as 1, 42, or @minus{}17. -The advantage to integer numbers is that they represent values exactly. -The disadvantage is that their range is limited. On most systems, -this range is @minus{}2,147,483,648 to 2,147,483,647. -However, many systems now support a range from -@minus{}9,223,372,036,854,775,808 to 9,223,372,036,854,775,807. - -@cindex unsigned integers -@cindex integers, unsigned -Integer values come in two flavors: @dfn{signed} and @dfn{unsigned}. -Signed values may be negative or positive, with the range of values just -described. -Unsigned values are always positive. On most systems, -the range is from 0 to 4,294,967,295. -However, many systems now support a range from -0 to 18,446,744,073,709,551,615. - -@cindex double precision floating-point -@cindex single precision floating-point -Floating-point numbers represent what are called ``real'' numbers; i.e., -those that do have a fractional part, such as 3.1415927. -The advantage to floating-point numbers is that they -can represent a much larger range of values. -The disadvantage is that there are numbers that they cannot represent -exactly. -@command{awk} uses @dfn{double precision} floating-point numbers, which -can hold more digits than @dfn{single precision} -floating-point numbers. -Floating-point issues are discussed more fully in -@ref{Floating Point Issues}. - -At the very lowest level, computers store values as groups of binary digits, -or @dfn{bits}. Modern computers group bits into groups of eight, called @dfn{bytes}. -Advanced applications sometimes have to manipulate bits directly, -and @command{gawk} provides functions for doing so. +@ref{Computer Arithmetic}, provided a basic introduction to numeric +types (integer and floating-point) and how they are used in a computer. +Please review that information, including a number of caveats that +were presented. @cindex null strings While you are probably used to the idea of a number without a value (i.e., zero), @@ -30146,17 +39719,22 @@ like this: @code{""}. Humans are used to working in decimal; i.e., base 10. In base 10, numbers go from 0 to 9, and then ``roll over'' into the next -column. (Remember grade school? 42 is 4 times 10 plus 2.) +column. (Remember grade school? 42 = 4 x 10 + 2.) There are other number bases though. Computers commonly use base 2 or @dfn{binary}, base 8 or @dfn{octal}, and base 16 or @dfn{hexadecimal}. In binary, each column represents two times the value in the column to its right. Each column may contain either a 0 or a 1. -Thus, binary 1010 represents 1 times 8, plus 0 times 4, plus 1 times 2, -plus 0 times 1, or decimal 10. +Thus, binary 1010 represents (1 x 8) + (0 x 4) + (1 x 2) ++ (0 x 1), or decimal 10. Octal and hexadecimal are discussed more in @ref{Nondecimal-numbers}. +At the very lowest level, computers store values as groups of binary digits, +or @dfn{bits}. Modern computers group bits into groups of eight, called @dfn{bytes}. +Advanced applications sometimes have to manipulate bits directly, +and @command{gawk} provides functions for doing so. + Programs are written in programming languages. Hundreds, if not thousands, of programming languages exist. One of the most popular is the C programming language. @@ -30176,240 +39754,6 @@ standard for C. This standard became an ISO standard in 1990. In 1999, a revised ISO C standard was approved and released. Where it makes sense, POSIX @command{awk} is compatible with 1999 ISO C. -@node Floating Point Issues -@appendixsec Floating-Point Number Caveats - -As mentioned earlier, floating-point numbers represent what are called -``real'' numbers, i.e., those that have a fractional part. @command{awk} -uses double precision floating-point numbers to represent all -numeric values. This @value{SECTION} describes some of the issues -involved in using floating-point numbers. - -There is a very nice -@uref{http://www.validlab.com/goldberg/paper.pdf, paper on floating-point arithmetic} -by David Goldberg, -``What Every Computer Scientist Should Know About Floating-point Arithmetic,'' -@cite{ACM Computing Surveys} @strong{23}, 1 (1991-03), 5-48. -This is worth reading if you are interested in the details, -but it does require a background in computer science. - -@menu -* String Conversion Precision:: The String Value Can Lie. -* Unexpected Results:: Floating Point Numbers Are Not Abstract - Numbers. -* POSIX Floating Point Problems:: Standards Versus Existing Practice. -@end menu - -@node String Conversion Precision -@appendixsubsec The String Value Can Lie - -Internally, @command{awk} keeps both the numeric value -(double precision floating-point) and the string value for a variable. -Separately, @command{awk} keeps -track of what type the variable has -(@pxref{Typing and Comparison}), -which plays a role in how variables are used in comparisons. - -It is important to note that the string value for a number may not -reflect the full value (all the digits) that the numeric value -actually contains. -The following program (@file{values.awk}) illustrates this: - -@example -@{ - sum = $1 + $2 - # see it for what it is - printf("sum = %.12g\n", sum) - # use CONVFMT - a = "<" sum ">" - print "a =", a - # use OFMT - print "sum =", sum -@} -@end example - -@noindent -This program shows the full value of the sum of @code{$1} and @code{$2} -using @code{printf}, and then prints the string values obtained -from both automatic conversion (via @code{CONVFMT}) and -from printing (via @code{OFMT}). - -Here is what happens when the program is run: - -@example -$ @kbd{echo 3.654321 1.2345678 | awk -f values.awk} -@print{} sum = 4.8888888 -@print{} a = <4.88889> -@print{} sum = 4.88889 -@end example - -This makes it clear that the full numeric value is different from -what the default string representations show. - -@code{CONVFMT}'s default value is @code{"%.6g"}, which yields a value with -at least six significant digits. For some applications, you might want to -change it to specify more precision. -On most modern machines, most of the time, -17 digits is enough to capture a floating-point number's -value exactly.@footnote{Pathological cases can require up to -752 digits (!), but we doubt that you need to worry about this.} - -@node Unexpected Results -@appendixsubsec Floating Point Numbers Are Not Abstract Numbers - -@cindex floating-point, numbers -Unlike numbers in the abstract sense (such as what you studied in high school -or college math), numbers stored in computers are limited in certain ways. -They cannot represent an infinite number of digits, nor can they always -represent things exactly. -In particular, -floating-point numbers cannot -always represent values exactly. Here is an example: - -@example -$ @kbd{awk '@{ printf("%010d\n", $1 * 100) @}'} -515.79 -@print{} 0000051579 -515.80 -@print{} 0000051579 -515.81 -@print{} 0000051580 -515.82 -@print{} 0000051582 -@kbd{@value{CTL}-d} -@end example - -@noindent -This shows that some values can be represented exactly, -whereas others are only approximated. This is not a ``bug'' -in @command{awk}, but simply an artifact of how computers -represent numbers. - -@cindex negative zero -@cindex positive zero -@cindex zero@comma{} negative vs.@: positive -Another peculiarity of floating-point numbers on modern systems -is that they often have more than one representation for the number zero! -In particular, it is possible to represent ``minus zero'' as well as -regular, or ``positive'' zero. - -This example shows that negative and positive zero are distinct values -when stored internally, but that they are in fact equal to each other, -as well as to ``regular'' zero: - -@example -$ @kbd{gawk 'BEGIN @{ mz = -0 ; pz = 0} -> @kbd{printf "-0 = %g, +0 = %g, (-0 == +0) -> %d\n", mz, pz, mz == pz} -> @kbd{printf "mz == 0 -> %d, pz == 0 -> %d\n", mz == 0, pz == 0} -> @kbd{@}'} -@print{} -0 = -0, +0 = 0, (-0 == +0) -> 1 -@print{} mz == 0 -> 1, pz == 0 -> 1 -@end example - -It helps to keep this in mind should you process numeric data -that contains negative zero values; the fact that the zero is negative -is noted and can affect comparisons. - -@node POSIX Floating Point Problems -@appendixsubsec Standards Versus Existing Practice - -Historically, @command{awk} has converted any non-numeric looking string -to the numeric value zero, when required. Furthermore, the original -definition of the language and the original POSIX standards specified that -@command{awk} only understands decimal numbers (base 10), and not octal -(base 8) or hexadecimal numbers (base 16). - -Changes in the language of the -2001 and 2004 POSIX standard can be interpreted to imply that @command{awk} -should support additional features. These features are: - -@itemize @bullet -@item -Interpretation of floating point data values specified in hexadecimal -notation (@samp{0xDEADBEEF}). (Note: data values, @emph{not} -source code constants.) - -@item -Support for the special IEEE 754 floating point values ``Not A Number'' -(NaN), positive Infinity (``inf'') and negative Infinity (``@minus{}inf''). -In particular, the format for these values is as specified by the ISO 1999 -C standard, which ignores case and can allow machine-dependent additional -characters after the @samp{nan} and allow either @samp{inf} or @samp{infinity}. -@end itemize - -The first problem is that both of these are clear changes to historical -practice: - -@itemize @bullet -@item -The @command{gawk} maintainer feels that supporting hexadecimal floating -point values, in particular, is ugly, and was never intended by the -original designers to be part of the language. - -@item -Allowing completely alphabetic strings to have valid numeric -values is also a very severe departure from historical practice. -@end itemize - -The second problem is that the @code{gawk} maintainer feels that this -interpretation of the standard, which requires a certain amount of -``language lawyering'' to arrive at in the first place, was not even -intended by the standard developers. In other words, ``we see how you -got where you are, but we don't think that that's where you want to be.'' - -The 2008 POSIX standard added explicit wording to allow, but not require, -that @command{awk} support hexadecimal floating point values and -special values for ``Not A Number'' and infinity. - -Although the @command{gawk} maintainer continues to feel that -providing those features is inadvisable, -nevertheless, on systems that support IEEE floating point, it seems -reasonable to provide @emph{some} way to support NaN and Infinity values. -The solution implemented in @command{gawk} is as follows: - -@itemize @bullet -@item -With the @option{--posix} command-line option, @command{gawk} becomes -``hands off.'' String values are passed directly to the system library's -@code{strtod()} function, and if it successfully returns a numeric value, -that is what's used.@footnote{You asked for it, you got it.} -By definition, the results are not portable across -different systems. They are also a little surprising: - -@example -$ @kbd{echo nanny | gawk --posix '@{ print $1 + 0 @}'} -@print{} nan -$ @kbd{echo 0xDeadBeef | gawk --posix '@{ print $1 + 0 @}'} -@print{} 3735928559 -@end example - -@item -Without @option{--posix}, @command{gawk} interprets the four strings -@samp{+inf}, -@samp{-inf}, -@samp{+nan}, -and -@samp{-nan} -specially, producing the corresponding special numeric values. -The leading sign acts a signal to @command{gawk} (and the user) -that the value is really numeric. Hexadecimal floating point is -not supported (unless you also use @option{--non-decimal-data}, -which is @emph{not} recommended). For example: - -@example -$ @kbd{echo nanny | gawk '@{ print $1 + 0 @}'} -@print{} 0 -$ @kbd{echo +nan | gawk '@{ print $1 + 0 @}'} -@print{} nan -$ @kbd{echo 0xDeadBeef | gawk '@{ print $1 + 0 @}'} -@print{} 0 -@end example - -@command{gawk} does ignore case in the four special values. -Thus @samp{+nan} and @samp{+NaN} are the same. -@end itemize - -@c ENDOFRANGE procon @node Glossary @unnumbered Glossary @@ -30418,9 +39762,16 @@ Thus @samp{+nan} and @samp{+NaN} are the same. @item Action A series of @command{awk} statements attached to a rule. If the rule's pattern matches an input record, @command{awk} executes the -rule's action. Actions are always enclosed in curly braces. +rule's action. Actions are always enclosed in braces. (@xref{Action Overview}.) +@cindex Ada programming language +@cindex programming languages, Ada +@item Ada +A programming language originally defined by the U.S.@: Department of +Defense for embedded programming. It was designed to enforce good +Software Engineering practices. + @cindex Spencer, Henry @cindex @command{sed} utility @cindex amazing @command{awk} assembler (@command{aaa}) @@ -30432,13 +39783,6 @@ microcomputers. It is a good example of a program that would have been better written in another language. You can get it from @uref{http://awk.info/?awk100/aaa}. -@cindex Ada programming language -@cindex Programming languages, Ada -@item Ada -A programming language originally defined by the U.S.@: Department of -Defense for embedded programming. It was designed to enforce good -Software Engineering practices. - @cindex amazingly workable formatter (@command{awf}) @cindex @command{awf} (amazingly workable formatter) program @item Amazingly Workable Formatter (@command{awf}) @@ -30501,9 +39845,6 @@ The GNU version of the standard shell @end ifinfo See also ``Bourne Shell.'' -@item BBS -See ``Bulletin Board System.'' - @item Bit Short for ``Binary Digit.'' All values in computer memory ultimately reduce to binary digits: values @@ -30526,10 +39867,15 @@ Named after the English mathematician Boole. See also ``Logical Expression.'' @item Bourne Shell The standard shell (@file{/bin/sh}) on Unix and Unix-like systems, -originally written by Steven R.@: Bourne. +originally written by Steven R.@: Bourne at Bell Laboratories. Many shells (Bash, @command{ksh}, @command{pdksh}, @command{zsh}) are generally upwardly compatible with the Bourne shell. +@item Braces +The characters @samp{@{} and @samp{@}}. Braces are used in +@command{awk} for delimiting actions, compound statements, and function +bodies. + @item Built-in Function The @command{awk} language provides built-in functions that perform various numerical, I/O-related, and string computations. Examples are @@ -30575,14 +39921,6 @@ are the variables that have special meaning to @command{gawk}. Changing some of them affects @command{awk}'s running environment. (@xref{Built-in Variables}.) -@item Braces -See ``Curly Braces.'' - -@item Bulletin Board System -A computer system allowing users to log in and read and/or leave messages -for other users of the system, much like leaving paper notes on a bulletin -board. - @item C The system programming language that most GNU software is written in. The @command{awk} programming language has C-like syntax, and this @value{DOCUMENT} @@ -30606,9 +39944,11 @@ or place. The most common character set in use today is ASCII (American Standard Code for Information Interchange). Many European countries use an extension of ASCII known as ISO-8859-1 (ISO Latin-1). The @uref{http://www.unicode.org, Unicode character set} is -becoming increasingly popular and standard, and is particularly +increasingly popular and standard, and is particularly widely used on GNU/Linux systems. +@cindex Kernighan, Brian +@cindex Bentley, Jon @cindex @command{chem} utility @item CHEM A preprocessor for @command{pic} that reads descriptions of molecules @@ -30617,8 +39957,12 @@ It was written in @command{awk} by Brian Kernighan and Jon Bentley, and is available from @uref{http://netlib.sandia.gov/netlib/typesetting/chem.gz}. -@item Coprocess -A subordinate program with which two-way communications is possible. +@item Comparison Expression +A relation that is either true or false, such as @samp{a < b}. +Comparison expressions are used in @code{if}, @code{while}, @code{do}, +and @code{for} +statements, and in patterns to select which input records to process. +(@xref{Typing and Comparison}.) @cindex compiled programs @item Compiler @@ -30646,17 +39990,56 @@ expression is the value of @var{expr2}; otherwise the value is @var{expr3}. In either case, only one of @var{expr2} and @var{expr3} is evaluated. (@xref{Conditional Exp}.) -@item Comparison Expression -A relation that is either true or false, such as @samp{a < b}. -Comparison expressions are used in @code{if}, @code{while}, @code{do}, -and @code{for} -statements, and in patterns to select which input records to process. -(@xref{Typing and Comparison}.) +@cindex McIlroy, Doug +@cindex cookie +@item Cookie +A peculiar goodie, token, saying or remembrance +produced by or presented to a program. (With thanks to Professor Doug McIlroy.) +@ignore +From: Doug McIlroy <doug@cs.dartmouth.edu> +Date: Sat, 13 Oct 2012 19:55:25 -0400 +To: arnold@skeeve.com +Subject: Re: origin of the term "cookie"? + +I believe the term "cookie", for a more or less inscrutable +saying or crumb of information, was injected into Unix +jargon by Bob Morris, who used the word quite frequently. +It had no fixed meaning as it now does in browsers. + +The word had been around long before it was recognized in +the 8th edition glossary (earlier editions had no glossary): + +cookie a peculiar goodie, token, saying or remembrance +returned by or presented to a program. [I would say that +"returned by" would better read "produced by", and assume +responsibility for the inexactitude.] + +Doug McIlroy + +From: Doug McIlroy <doug@cs.dartmouth.edu> +Date: Sun, 14 Oct 2012 10:08:43 -0400 +To: arnold@skeeve.com +Subject: Re: origin of the term "cookie"? + +> Can I forward your email to Eric Raymond, for possible addition to the +> Jargon File? + +Sure. I might add that I don't know how "cookie" entered Morris's +vocabulary. Certainly "values of beta give rise to dom!" (see google) +was an early, if not the earliest Unix cookie. The fact that it was +found lying around on a model 37 teletype (which had Greek beta in +its type box) suggests that maybe it was seen to be like milk and +cookies laid out for Santa Claus. Morris was wont to make such +connections. + +Doug +@end ignore + +@item Coprocess +A subordinate program with which two-way communications is possible. @item Curly Braces -The characters @samp{@{} and @samp{@}}. Curly braces are used in -@command{awk} for delimiting actions, compound statements, and function -bodies. +See ``Braces.'' @cindex dark corner @item Dark Corner @@ -30700,15 +40083,15 @@ ordinary expression. It could be a string constant, such as @code{"foo"}, but it may also be an expression whose value can vary. (@xref{Computed Regexps}.) +@item Empty String +See ``Null String.'' + @item Environment -A collection of strings, of the form @var{name@code{=}val}, that each +A collection of strings, of the form @samp{@var{name}=@var{val}}, that each program has available to it. Users generally place values into the environment in order to provide information to various programs. Typical examples are the environment variables @env{HOME} and @env{PATH}. -@item Empty String -See ``Null String.'' - @cindex epoch, definition of @item Epoch The date used as the ``beginning of time'' for timestamps. @@ -30735,11 +40118,11 @@ See ``Free Documentation License.'' @item Field When @command{awk} reads an input record, it splits the record into pieces separated by whitespace (or by a separator regexp that you can -change by setting the built-in variable @code{FS}). Such pieces are +change by setting the predefined variable @code{FS}). Such pieces are called fields. If the pieces are of fixed length, you can use the built-in variable @code{FIELDWIDTHS} to describe their lengths. If you wish to specify the contents of fields instead of the field -separator, you can use the built-in variable @code{FPAT} to do so. +separator, you can use the predefined variable @code{FPAT} to do so. (@xref{Field Separators}, @ref{Constant Size}, and @@ -30755,25 +40138,16 @@ this is just a number that can have a fractional part. See also ``Double Precision'' and ``Single Precision.'' @item Format -Format strings are used to control the appearance of output in the -@code{strftime()} and @code{sprintf()} functions, and are used in the +Format strings control the appearance of output in the +@code{strftime()} and @code{sprintf()} functions, and in the @code{printf} statement as well. Also, data conversions from numbers to strings -are controlled by the format strings contained in the built-in variables +are controlled by the format strings contained in the predefined variables @code{CONVFMT} and @code{OFMT}. (@xref{Control Letters}.) @item Free Documentation License This document describes the terms under which this @value{DOCUMENT} is published and may be copied. (@xref{GNU Free Documentation License}.) -@item Function -A specialized group of statements used to encapsulate general -or program-specific tasks. @command{awk} has a number of built-in -functions, and also allows you to define your own. -(@xref{Functions}.) - -@item FSF -See ``Free Software Foundation.'' - @cindex FSF (Free Software Foundation) @cindex Free Software Foundation (FSF) @cindex Stallman, Richard @@ -30783,6 +40157,15 @@ to the production and distribution of freely distributable software. It was founded by Richard M.@: Stallman, the author of the original Emacs editor. GNU Emacs is the most widely used version of Emacs today. +@item FSF +See ``Free Software Foundation.'' + +@item Function +A specialized group of statements used to encapsulate general +or program-specific tasks. @command{awk} has a number of built-in +functions, and also allows you to define your own. +(@xref{Functions}.) + @item @command{gawk} The GNU implementation of @command{awk}. @@ -30825,7 +40208,7 @@ Base 16 notation, where the digits are @code{0}--@code{9} and @code{A}--@code{F}, with @samp{A} representing 10, @samp{B} representing 11, and so on, up to @samp{F} for 15. Hexadecimal numbers are written in C using a leading @samp{0x}, -to indicate their base. Thus, @code{0x12} is 18 (1 times 16 plus 2). +to indicate their base. Thus, @code{0x12} is 18 ((1 x 16) + 2). @xref{Nondecimal-numbers}. @item I/O @@ -30859,15 +40242,18 @@ in @command{awk} programs. @cindex ISO @item ISO -The International Standards Organization. +The International Organization for Standardization. This organization produces international standards for many things, including programming languages, such as C and C++. In the computer arena, important standards like those for C, C++, and POSIX become both American national and ISO international standards simultaneously. This @value{DOCUMENT} refers to Standard C as ``ISO C'' throughout. +See @uref{http://www.iso.org/iso/home/about.htm, the ISO website} for more +information about the name of the organization and its language-independent +three-letter acronym. @cindex Java programming language -@cindex Programming languages, Java +@cindex programming languages, Java @item Java A modern programming language originally developed by Sun Microsystems (now Oracle) supporting Object-Oriented programming. Although usually @@ -30896,8 +40282,8 @@ meaning. Keywords are reserved and may not be used as variable names. @code{function}, @code{func}, @code{if}, -@code{nextfile}, @code{next}, +@code{nextfile}, @code{switch}, and @code{while}. @@ -30910,12 +40296,12 @@ This document describes the terms under which binary library archives or shared objects, and their source code may be distributed. -@item Linux -See ``GNU/Linux.'' - @item LGPL See ``Lesser General Public License.'' +@item Linux +See ``GNU/Linux.'' + @item Localization The process of providing the data necessary for an internationalized program to work in a particular language. @@ -30958,14 +40344,9 @@ Ancient @command{awk} implementations used single precision floating-point. @item Octal Base-eight notation, where the digits are @code{0}--@code{7}. Octal numbers are written in C using a leading @samp{0}, -to indicate their base. Thus, @code{013} is 11 (one times 8 plus 3). +to indicate their base. Thus, @code{013} is 11 ((1 x 8) + 3). @xref{Nondecimal-numbers}. -@cindex P1003.1 POSIX standard -@cindex P1003.2 POSIX standard -@item P1003.1, P1003.2 -See ``POSIX.'' - @item Pattern Patterns tell @command{awk} which input records are interesting to which rules. @@ -30975,9 +40356,13 @@ tested. If the condition is satisfied, the pattern is said to @dfn{match} the input record. A typical pattern might compare the input record against a regular expression. (@xref{Pattern Overview}.) +@item PEBKAC +An acronym describing what is possibly the most frequent +source of computer usage problems. (Problem Exists Between +Keyboard And Chair.) + @item POSIX The name for a series of standards -@c being developed by the IEEE that specify a Portable Operating System interface. The ``IX'' denotes the Unix heritage of these standards. The main standard of interest for @command{awk} users is @@ -31002,8 +40387,8 @@ specify single lines. (@xref{Pattern Overview}.) @item Recursion When a function calls itself, either directly or indirectly. -As long as this is not clear, refer to the entry for ``recursion.'' If this is clear, stop, and proceed to the next entry. +Otherwise, refer to the entry for ``recursion.'' @item Redirection Redirection means performing input from something other than the standard input @@ -31054,12 +40439,12 @@ Regular variables are scalars; arrays and functions are not. In @command{gawk}, a list of directories to search for @command{awk} program source files. In the shell, a list of directories to search for executable programs. -@item Seed -The initial value, or starting point, for a sequence of random numbers. - @item @command{sed} See ``Stream Editor.'' +@item Seed +The initial value, or starting point, for a sequence of random numbers. + @item Shell The command interpreter for Unix and POSIX-compliant systems. The shell works both interactively, and as a programming language @@ -31082,7 +40467,7 @@ expressions, and function calls have side effects. An internal representation of numbers that can have fractional parts. Single precision numbers keep track of fewer digits than do double precision numbers, but operations on them are sometimes less expensive in terms of CPU time. -This is the type used by some very old versions of @command{awk} to store +This is the type used by some ancient versions of @command{awk} to store numeric values. It is the C type @code{float}. @item Space @@ -31119,7 +40504,7 @@ into the local language. A value in the ``seconds since the epoch'' format used by Unix and POSIX systems. Used for the @command{gawk} functions @code{mktime()}, @code{strftime()}, and @code{systime()}. -See also ``Epoch'' and ``UTC.'' +See also ``Epoch,'' ``GMT,'' and ``UTC.'' @cindex Linux @cindex GNU/Linux @@ -31148,13 +40533,20 @@ A sequence of space, TAB, or newline characters occurring inside an input record or a string. @end table +@end ifclear + @c The GNU General Public License. @node Copying @unnumbered GNU General Public License +@ifnotdocbook @center Version 3, 29 June 2007 +@end ifnotdocbook +@docbook +<subtitle>Version 3, 29 June 2007</subtitle> +@end docbook @c This file is intended to be included within another document, -@c hence no sectioning command or @node. +@c hence no sectioning command or @node. @display Copyright @copyright{} 2007 Free Software Foundation, Inc. @url{http://fsf.org/} @@ -31376,7 +40768,7 @@ terms of section 4, provided that you also meet all of these conditions: @enumerate a -@item +@item The work must carry prominent notices stating that you modified it, and giving a relevant date. @@ -31826,7 +41218,7 @@ state the exclusion of warranty; and each file should have at least the ``copyright'' line and a pointer to where the full notice is found. @smallexample -@var{one line to give the program's name and a brief idea of what it does.} +@var{one line to give the program's name and a brief idea of what it does.} Copyright (C) @var{year} @var{name of author} This program is free software: you can redistribute it and/or modify @@ -31849,7 +41241,7 @@ If the program does terminal interaction, make it output a short notice like this when it starts in an interactive mode: @smallexample -@var{program} Copyright (C) @var{year} @var{name of author} +@var{program} Copyright (C) @var{year} @var{name of author} This program comes with ABSOLUTELY NO WARRANTY; for details type @samp{show w}. This is free software, and you are welcome to redistribute it under certain conditions; type @samp{show c} for details. @@ -31872,14 +41264,21 @@ applications with the library. If this is what you want to do, use the GNU Lesser General Public License instead of this License. But first, please read @url{http://www.gnu.org/philosophy/why-not-lgpl.html}. - +@ifclear FOR_PRINT @c The GNU Free Documentation License. @node GNU Free Documentation License @unnumbered GNU Free Documentation License +@ifnotdocbook +@center Version 1.3, 3 November 2008 +@end ifnotdocbook + +@docbook +<subtitle>Version 1.3, 3 November 2008</subtitle> +@end docbook + @cindex FDL (Free Documentation License) @cindex Free Documentation License (FDL) @cindex GNU Free Documentation License -@center Version 1.3, 3 November 2008 @c This file is intended to be included within another document, @c hence no sectioning command or @node. @@ -32380,12 +41779,12 @@ recommend releasing these examples in parallel under your choice of free software license, such as the GNU General Public License, to permit their use in free software. -@c Local Variables: -@c ispell-local-pdict: "ispell-dict" -@c End: +@end ifclear +@ifnotdocbook @node Index @unnumbered Index +@end ifnotdocbook @printindex cp @bye @@ -32398,9 +41797,6 @@ Unresolved Issues: of how to use them. It would be useful to perhaps have a "programming style" section of the manual that would include this and other tips. -2. The default AWKPATH search path should be configurable via `configure' - The default and how this changes needs to be documented. - Consistency issues: /.../ regexps are in @code, not @samp ".." strings are in @code, not @samp @@ -32424,16 +41820,18 @@ Consistency issues: Use --foo, not -Wfoo when describing long options Use "Bell Laboratories", but not "Bell Labs". Use "behavior" instead of "behaviour". + Use "coprocess" instead of "co-process". Use "zeros" instead of "zeroes". Use "nonzero" not "non-zero". Use "runtime" not "run time" or "run-time". - Use "command-line" not "command line". + Use "command-line" as an adjective and "command line" as a noun. Use "online" not "on-line". Use "whitespace" not "white space". Use "Input/Output", not "input/output". Also "I/O", not "i/o". Use "lefthand"/"righthand", not "left-hand"/"right-hand". Use "workaround", not "work-around". Use "startup"/"cleanup", not "start-up"/"clean-up" + Use "filesystem", not "file system" Use @code{do}, and not @code{do}-@code{while}, except where actually discussing the do-while. Use "versus" in text and "vs." in index entries @@ -32448,8 +41846,6 @@ Consistency issues: The numbers zero through ten should be spelled out, except when talking about file descriptor numbers. > 10 and < 0, it's ok to use numbers. - In tables, put command-line options in @code, while in the text, - put them in @option. For most cases, do NOT put a comma before "and", "or" or "but". But exercise taste with this rule. Don't show the awk command with a program in quotes when it's @@ -32473,6 +41869,7 @@ Consistency issues: Use MS-Windows not MS Windows Use MS-DOS not MS-DOS Use an empty set of parentheses after built-in and awk function names. + Use "multiFOO" without a hyphen. Date: Wed, 13 Apr 94 15:20:52 -0400 From: rms@gnu.org (Richard Stallman) @@ -32495,14 +41892,37 @@ ORA uses filename, thus the macro. Suggestions: ------------ -Enhance FIELDWIDTHS with some way to indicate "the rest of the record". -E.g., a length of 0 or -1 or something. May be "n"? -Make FIELDWIDTHS be an array? +Better sidebars can almost sort of be done with: + + @ifdocbook + @macro @sidebar{title, content} + @inlinefmt{docbook, <sidebar><title>} + \title\ + @inlinefmt{docbook, </title>} + \content\ + @inlinefmt{docbook, </sidebar>} + @end macro + @end ifdocbook + + + @ifnotdocbook + @macro @sidebar{title, content} + @cartouche + @center @b{\title\} + + \content\ + @end cartouche + @end macro + @end ifnotdocbook + +But to use it you have to say + + @sidebar{Title Here, + @include file-with-content + } + +which sorta sucks. -% Next edition: -% 1. Talk about common extensions, those in nawk, gawk, mawk -% 2. Use @code{foo} for variables and @code{foo()} for functions -% 3. Standardize the error messages from the functions and programs -% in Chapters 12 and 13. -% 4. Nuke the BBS stuff and use something that won't be obsolete +TODO: +Check that all dark corners are indexed properly. |