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diff --git a/doc/gawk.info b/doc/gawk.info index b92d1b87..cf827935 100644 --- a/doc/gawk.info +++ b/doc/gawk.info @@ -1,4 +1,4 @@ -This is gawk.info, produced by makeinfo version 4.8 from gawk.texi. +This is gawk.info, produced by makeinfo version 4.13 from gawk.texi. INFO-DIR-SECTION Text creation and manipulation START-INFO-DIR-ENTRY @@ -9,31 +9,27 @@ START-INFO-DIR-ENTRY * awk: (gawk)Invoking gawk. Text scanning and processing. END-INFO-DIR-ENTRY - Copyright (C) 1989, 1991, 1992, 1993, 1996, 1997, 1998, 1999, 2000, -2001, 2002, 2003, 2004, 2005, 2007, 2009, 2010, 2011 Free Software -Foundation, Inc. + Copyright (C) 1989, 1991, 1992, 1993, 1996-2005, 2007, 2009-2015 +Free Software Foundation, Inc. - This is Edition 4 of `GAWK: Effective AWK Programming: A User's -Guide for GNU Awk', for the 4.0.0 (or later) version of the GNU + This is Edition 4.1 of `GAWK: Effective AWK Programming: A User's +Guide for GNU Awk', for the 4.1.2 (or later) version of the GNU 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 -"GNU Free Documentation License". +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. A copy of the license is included in the section +entitled "GNU Free Documentation License". - a. "A GNU Manual" - - b. "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." + a. The FSF's Back-Cover Text is: "You have the freedom to copy and + modify this GNU manual." -File: gawk.info, Node: Top, Next: Foreword, Up: (dir) +File: gawk.info, Node: Top, Next: Foreword3, Up: (dir) General Introduction ******************** @@ -41,33 +37,30 @@ General Introduction This file documents `awk', a program that you can use to select particular records in a file and perform operations upon them. - Copyright (C) 1989, 1991, 1992, 1993, 1996, 1997, 1998, 1999, 2000, -2001, 2002, 2003, 2004, 2005, 2007, 2009, 2010, 2011 Free Software -Foundation, Inc. + Copyright (C) 1989, 1991, 1992, 1993, 1996-2005, 2007, 2009-2015 +Free Software Foundation, Inc. - This is Edition 4 of `GAWK: Effective AWK Programming: A User's -Guide for GNU Awk', for the 4.0.0 (or later) version of the GNU + This is Edition 4.1 of `GAWK: Effective AWK Programming: A User's +Guide for GNU Awk', for the 4.1.2 (or later) version of the GNU 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 -"GNU Free Documentation License". - - a. "A GNU Manual" +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. A copy of the license is included in the section +entitled "GNU Free Documentation License". - b. "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." + a. The FSF's Back-Cover Text is: "You have the freedom to copy and + modify this GNU manual." * Menu: -* Foreword:: Some nice words about this +* Foreword3:: Some nice words about this Info file. +* Foreword4:: More nice words. * Preface:: What this Info file is about; brief history and acknowledgments. * Getting Started:: A basic introduction to using @@ -87,20 +80,24 @@ texts being (a) (see below), and with the Back-Cover Texts being (b) * Arrays:: The description and use of arrays. Also includes array-oriented control statements. * Functions:: Built-in and user-defined functions. -* Internationalization:: Getting `gawk' to speak your - language. -* Advanced Features:: Stuff for advanced users, specific to - `gawk'. * Library Functions:: A Library of `awk' Functions. * Sample Programs:: Many `awk' programs with complete explanations. -* Debugger:: The `dgawk' debugger. +* Advanced Features:: Stuff for advanced users, specific to + `gawk'. +* Internationalization:: Getting `gawk' to speak your + language. +* Debugger:: The `gawk' debugger. +* Arbitrary Precision Arithmetic:: Arbitrary precision arithmetic with + `gawk'. +* Dynamic Extensions:: Adding new built-in functions to + `gawk'. * Language History:: The evolution of the `awk' language. * Installation:: Installing `gawk' under various operating systems. -* Notes:: Notes about `gawk' extensions and - possible future work. +* Notes:: Notes about adding things to `gawk' + and possible future work. * Basic Concepts:: A very quick introduction to programming concepts. * Glossary:: An explanation of some unfamiliar terms. @@ -109,478 +106,609 @@ texts being (a) (see below), and with the Back-Cover Texts being (b) * GNU Free Documentation License:: The license for this Info file. * Index:: Concept and Variable Index. -* History:: The history of `gawk' and - `awk'. -* Names:: What name to use to find `awk'. -* This Manual:: Using this Info file. Includes - sample input files that you can use. -* Conventions:: Typographical Conventions. -* Manual History:: Brief history of the GNU project and - this Info file. -* How To Contribute:: Helping to save the world. -* Acknowledgments:: Acknowledgments. -* Running gawk:: How to run `gawk' programs; - includes command-line syntax. -* One-shot:: Running a short throwaway `awk' - program. -* Read Terminal:: Using no input files (input from - terminal instead). -* Long:: Putting permanent `awk' - programs in files. -* Executable Scripts:: Making self-contained `awk' - programs. -* Comments:: Adding documentation to `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 - `awk' programs illustrated in - this Info file. -* 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 `awk'. -* When:: When to use `gawk' and when to - use other things. -* Command Line:: How to run `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 - `gawk' uses. -* AWKPATH Variable:: Searching directories for `awk' - programs. -* Other Environment Variables:: The environment variables. -* Exit Status:: `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 `[...]'. -* 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 `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 `getline' - function. -* Plain Getline:: Using `getline' with no arguments. -* Getline/Variable:: Using `getline' into a variable. -* Getline/File:: Using `getline' from a file. -* Getline/Variable/File:: Using `getline' into a variable - from a file. -* Getline/Pipe:: Using `getline' from a pipe. -* Getline/Variable/Pipe:: Using `getline' into a variable - from a pipe. -* Getline/Coprocess:: Using `getline' from a coprocess. -* Getline/Variable/Coprocess:: Using `getline' into a variable - from a coprocess. -* Getline Notes:: Important things to know about - `getline'. -* Getline Summary:: Summary of `getline' Variants. -* Command line directories:: What happens if you put a directory on - the command line. -* Print:: The `print' statement. -* Print Examples:: Simple examples of `print' - statements. -* Output Separators:: The output separators and how to change - them. -* OFMT:: Controlling Numeric Output With - `print'. -* Printf:: The `printf' statement. -* Basic Printf:: Syntax of the `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 - `gawk'. `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:: `gawk''s operators. -* Arithmetic Ops:: Arithmetic operations (`+', - `-', 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 `<', 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 `||' (``or''), - `&&' (``and'') and `!' - (``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 - `awk'. -* Action Overview:: What goes into an action. -* Statements:: Describes the various control - statements in detail. -* If Statement:: Conditionally execute some - `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 `awk'. -* Built-in Variables:: Summarizes the built-in variables. -* User-modified:: Built-in variables that you change to - control `awk'. -* Auto-set:: Built-in variables where `awk' - gives you information. -* ARGC and ARGV:: Ways to use `ARGC' and - `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 `for' - statement. It loops through the indices - of an array's existing elements. -* Delete:: The `delete' statement removes an - element from an array. -* Numeric Array Subscripts:: How to use numbers as subscripts in - `awk'. -* Uninitialized Subscripts:: Using Uninitialized variables as - subscripts. -* Multi-dimensional:: Emulating multidimensional arrays in - `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 `int()', `sin()' - and `rand()'. -* String Functions:: Functions for string manipulation, such - as `split()', `match()' and - `sprintf()'. -* Gory Details:: More than you want to know about - `\' and `&' with - `sub()', `gsub()', and - `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 `gettext' works. -* Programmer i18n:: Features for the programmer. -* Translator i18n:: Features for the translator. -* String Extraction:: Extracting marked strings. -* Printf Ordering:: Rearranging `printf' arguments. -* I18N Portability:: `awk'-level portability issues. -* I18N Example:: A simple i18n example. -* Gawk I18N:: `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 `asort()' and - `asorti()'. -* Two-way I/O:: Two-way communications with another - process. -* TCP/IP Networking:: Using `gawk' for network - programming. -* Profiling:: Profiling your `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 - `strtonum()' function. -* Assert Function:: A function for assertions in - `awk' programs. -* Round Function:: A function for rounding if - `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 `cut' utility. -* Egrep Program:: The `egrep' utility. -* Id Program:: The `id' utility. -* Split Program:: The `split' utility. -* Tee Program:: The `tee' utility. -* Uniq Program:: The `uniq' utility. -* Wc Program:: The `wc' utility. -* Miscellaneous Programs:: Some interesting `awk' - programs. -* Dupword Program:: Finding duplicated words in a document. -* Alarm Program:: An alarm clock. -* Translate Program:: A program similar to the `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 `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 `dgawk'. -* Debugging Concepts:: Debugging In General. -* Debugging Terms:: Additional Debugging Concepts. -* Awk Debugging:: Awk Debugging. -* Sample dgawk session:: Sample `dgawk' session. -* dgawk invocation:: `dgawk' Invocation. -* Finding The Bug:: Finding The Bug. -* List of Debugger Commands:: Main `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 `awk'. -* POSIX/GNU:: The extensions in `gawk' not in - POSIX `awk'. -* Common Extensions:: Common Extensions Summary. -* Ranges and Locales:: How locales used to affect regexp - ranges. -* Contributors:: The major contributors to - `gawk'. -* Gawk Distribution:: What is in the `gawk' - distribution. -* Getting:: How to get the distribution. -* Extracting:: How to extract the distribution. -* Distribution contents:: What is in the distribution. -* Unix Installation:: Installing `gawk' under various - versions of Unix. -* Quick Installation:: Compiling `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 `gawk' - on MS-DOS and OS/2. -* PC Binary Installation:: Installing a prepared distribution. -* PC Compiling:: Compiling `gawk' for MS-DOS, - Windows32, and OS/2. -* PC Testing:: Testing `gawk' on PC systems. -* PC Using:: Running `gawk' on MS-DOS, - Windows32 and OS/2. -* Cygwin:: Building and running `gawk' for - Cygwin. -* MSYS:: Using `gawk' In The MSYS - Environment. -* VMS Installation:: Installing `gawk' on VMS. -* VMS Compilation:: How to compile `gawk' under - VMS. -* VMS Installation Details:: How to install `gawk' under - VMS. -* VMS Running:: How to run `gawk' under VMS. -* VMS Old Gawk:: An old version comes with some VMS - systems. -* Bugs:: Reporting Problems and Bugs. -* Other Versions:: Other freely available `awk' - implementations. -* Compatibility Mode:: How to disable certain `gawk' - extensions. -* Additions:: Making Additions To `gawk'. -* Accessing The Source:: Accessing the Git repository. -* Adding Code:: Adding code to the main body of - `gawk'. -* New Ports:: Porting `gawk' to a new - operating system. -* Dynamic Extensions:: Adding new built-in functions to - `gawk'. -* Internals:: A brief look at some `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. - - To Miriam, for making me complete. - - To Chana, for the joy you bring us. - - To Rivka, for the exponential increase. - - To Nachum, for the added dimension. - - To Malka, for the new beginning. - -File: gawk.info, Node: Foreword, Next: Preface, Prev: Top, Up: Top - -Foreword -******** +* History:: The history of `gawk' and + `awk'. +* Names:: What name to use to find + `awk'. +* This Manual:: Using this Info file. Includes + sample input files that you can use. +* Conventions:: Typographical Conventions. +* Manual History:: Brief history of the GNU project and + this Info file. +* How To Contribute:: Helping to save the world. +* Acknowledgments:: Acknowledgments. +* Running gawk:: How to run `gawk' programs; + includes command-line syntax. +* One-shot:: Running a short throwaway + `awk' program. +* Read Terminal:: Using no input files (input from the + keyboard instead). +* Long:: Putting permanent `awk' + programs in files. +* Executable Scripts:: Making self-contained `awk' + programs. +* Comments:: Adding documentation to `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 + `awk' programs illustrated in + this Info file. +* 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 `awk'. +* When:: When to use `gawk' and when to + use other things. +* Intro Summary:: Summary of the introduction. +* Command Line:: How to run `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 + `gawk' uses. +* AWKPATH Variable:: Searching directories for + `awk' programs. +* AWKLIBPATH Variable:: Searching directories for + `awk' shared libraries. +* Other Environment Variables:: The environment variables. +* Exit Status:: `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 `[...]'. +* 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 `awk' splits + records. +* gawk split records:: How `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 `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 `getline' + function. +* Plain Getline:: Using `getline' with no + arguments. +* Getline/Variable:: Using `getline' into a variable. +* Getline/File:: Using `getline' from a file. +* Getline/Variable/File:: Using `getline' into a variable + from a file. +* Getline/Pipe:: Using `getline' from a pipe. +* Getline/Variable/Pipe:: Using `getline' into a variable + from a pipe. +* Getline/Coprocess:: Using `getline' from a coprocess. +* Getline/Variable/Coprocess:: Using `getline' into a variable + from a coprocess. +* Getline Notes:: Important things to know about + `getline'. +* Getline Summary:: Summary of `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 `print' statement. +* Print Examples:: Simple examples of `print' + statements. +* Output Separators:: The output separators and how to + change them. +* OFMT:: Controlling Numeric Output With + `print'. +* Printf:: The `printf' statement. +* Basic Printf:: Syntax of the `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 + `gawk'. `gawk' allows + access to inherited file descriptors. +* Other Inherited Files:: Accessing other open files with + `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 `awk' Converts Between + Strings And Numbers. +* Locale influences conversions:: How the locale may affect conversions. +* All Operators:: `gawk''s operators. +* Arithmetic Ops:: Arithmetic operations (`+', + `-', 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 `<', 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 `||' (``or''), + `&&' (``and'') and `!' + (``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 + `awk'. +* Action Overview:: What goes into an action. +* Statements:: Describes the various control + statements in detail. +* If Statement:: Conditionally execute some + `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 `awk'. +* Built-in Variables:: Summarizes the predefined variables. +* User-modified:: Built-in variables that you change to + control `awk'. +* Auto-set:: Built-in variables where `awk' + gives you information. +* ARGC and ARGV:: Ways to use `ARGC' and + `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 `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 + `awk'. +* Uninitialized Subscripts:: Using Uninitialized variables as + subscripts. +* Delete:: The `delete' statement removes an + element from an array. +* Multidimensional:: Emulating multidimensional arrays in + `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 `int()', `sin()' + and `rand()'. +* String Functions:: Functions for string manipulation, + such as `split()', `match()' + and `sprintf()'. +* Gory Details:: More than you want to know about + `\' and `&' with + `sub()', `gsub()', and + `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 + `strtonum()' function. +* Assert Function:: A function for assertions in + `awk' programs. +* Round Function:: A function for rounding if + `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 `cut' utility. +* Egrep Program:: The `egrep' utility. +* Id Program:: The `id' utility. +* Split Program:: The `split' utility. +* Tee Program:: The `tee' utility. +* Uniq Program:: The `uniq' utility. +* Wc Program:: The `wc' utility. +* Miscellaneous Programs:: Some interesting `awk' + programs. +* Dupword Program:: Finding duplicated words in a + document. +* Alarm Program:: An alarm clock. +* Translate Program:: A program similar to the `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 `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 `asort()' and + `asorti()'. +* Two-way I/O:: Two-way communications with another + process. +* TCP/IP Networking:: Using `gawk' for network + programming. +* Profiling:: Profiling your `awk' programs. +* Advanced Features Summary:: Summary of advanced features. +* I18N and L10N:: Internationalization and Localization. +* Explaining gettext:: How GNU `gettext' works. +* Programmer i18n:: Features for the programmer. +* Translator i18n:: Features for the translator. +* String Extraction:: Extracting marked strings. +* Printf Ordering:: Rearranging `printf' arguments. +* I18N Portability:: `awk'-level portability + issues. +* I18N Example:: A simple i18n example. +* Gawk I18N:: `gawk' is also + internationalized. +* I18N Summary:: Summary of I18N stuff. +* Debugging:: Introduction to `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 `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 `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 + `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 `ERRNO':: Functions for updating `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 + `gawk''s invocation. +* Extension API Boilerplate:: Boilerplate code for using the API. +* Finding Extensions:: How `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 + `gawk'. +* Extension Sample File Functions:: The file functions sample. +* Extension Sample Fnmatch:: An interface to `fnmatch()'. +* Extension Sample Fork:: An interface to `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 `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 `gettimeofday()' + and `sleep()'. +* Extension Sample API Tests:: Tests for the API. +* gawkextlib:: The `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 `awk'. +* POSIX/GNU:: The extensions in `gawk' not + in POSIX `awk'. +* Feature History:: The history of the features in + `gawk'. +* Common Extensions:: Common Extensions Summary. +* Ranges and Locales:: How locales used to affect regexp + ranges. +* Contributors:: The major contributors to + `gawk'. +* History summary:: History summary. +* Gawk Distribution:: What is in the `gawk' + distribution. +* Getting:: How to get the distribution. +* Extracting:: How to extract the distribution. +* Distribution contents:: What is in the distribution. +* Unix Installation:: Installing `gawk' under + various versions of Unix. +* Quick Installation:: Compiling `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 + `gawk' on MS-DOS and OS/2. +* PC Binary Installation:: Installing a prepared distribution. +* PC Compiling:: Compiling `gawk' for MS-DOS, + Windows32, and OS/2. +* PC Testing:: Testing `gawk' on PC systems. +* PC Using:: Running `gawk' on MS-DOS, + Windows32 and OS/2. +* Cygwin:: Building and running `gawk' + for Cygwin. +* MSYS:: Using `gawk' In The MSYS + Environment. +* VMS Installation:: Installing `gawk' on VMS. +* VMS Compilation:: How to compile `gawk' under + VMS. +* VMS Dynamic Extensions:: Compiling `gawk' dynamic + extensions on VMS. +* VMS Installation Details:: How to install `gawk' under + VMS. +* VMS Running:: How to run `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 `awk' + implementations. +* Installation summary:: Summary of installation. +* Compatibility Mode:: How to disable certain `gawk' + extensions. +* Additions:: Making Additions To `gawk'. +* Accessing The Source:: Accessing the Git repository. +* Adding Code:: Adding code to the main body of + `gawk'. +* New Ports:: Porting `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. + + To my parents, for their love, and for the wonderful example they +set for me. + + To my wife Miriam, for making me complete. Thank you for building +your life together with me. + + To our children Chana, Rivka, Nachum and Malka, for enrichening our +lives in innumerable ways. + + +File: gawk.info, Node: Foreword3, Next: Foreword4, Prev: Top, Up: Top + +Foreword to the Third Edition +***************************** Arnold Robbins and I are good friends. We were introduced in 1990 by circumstances--and our favorite programming language, AWK. 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 I was `root' and the one-and-only user. That -day, I began the transition from statistician to Unix programmer. +later, it was running, and I was `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, `The AWK Programming Language', Addison-Wesley, 1988. -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 hand at programming in -AWK. +on Unix, I found the gray AWK book, a.k.a. Alfred V. Aho, Brian W. +Kernighan, and Peter J. Weinberger's `The AWK Programming Language' +(Addison-Wesley, 1988). `awk''s simple programming paradigm--find a +pattern in the input and then perform an action--often reduced complex +or tedious data manipulations to a few lines of code. I was excited to +try my hand at programming in AWK. Alas, the `awk' on my computer was a limited version of the -language described in the AWK book. I discovered that my computer had -"old `awk'" and the AWK book described "new `awk'." I learned that -this was typical; the old version refused to step aside or relinquish -its name. If a system had a new `awk', it was invariably called -`nawk', and few systems had it. The best way to get a new `awk' was to -`ftp' the source code for `gawk' from `prep.ai.mit.edu'. `gawk' was a +language described in the gray book. I discovered that my computer had +"old `awk'" and the book described "new `awk'." I learned that this +was typical; the old version refused to step aside or relinquish its +name. If a system had a new `awk', it was invariably called `nawk', +and few systems had it. The best way to get a new `awk' was to `ftp' +the source code for `gawk' from `prep.ai.mit.edu'. `gawk' was a version of new `awk' written by David Trueman and Arnold, and available under the GNU General Public License. @@ -591,14 +719,15 @@ almost any system; my wife uses `gawk' on her VMS box.) My Unix system started out unplugged from the wall; it certainly was not plugged into a network. So, oblivious to the existence of `gawk' and the Unix community in general, and desiring a new `awk', I wrote my -own, called `mawk'. Before I was finished I knew about `gawk', but it +own, called `mawk'. Before I was finished, I knew about `gawk', but it was too late to stop, so I eventually posted to a `comp.sources' newsgroup. A few days after my posting, I got a friendly email from Arnold introducing himself. He suggested we share design and algorithms and attached a draft of the POSIX standard so that I could update `mawk' to -support language extensions added after publication of the AWK book. +support language extensions added after publication of `The AWK +Programming Language'. Frankly, if our roles had been reversed, I would not have been so open and we probably would have never met. I'm glad we did meet. He @@ -612,17 +741,17 @@ a definitive reference to the AWK language as defined by the 1987 Bell Laboratories release and codified in the 1992 POSIX Utilities 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, and -associative arrays. Those looking for something new can try out +practical programs that emphasize the power of AWK's basic idioms: +data-driven control flow, pattern matching with regular expressions, +and associative arrays. Those looking for something new can try out `gawk''s interface to network protocols via special `/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 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. +in C. 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. The new `pgawk' (profiling `gawk'), produces program execution counts. I recently experimented with an algorithm that for n lines of @@ -637,32 +766,67 @@ want to learn how, then read this book. Michael Brennan Author of `mawk' - March, 2001 + March 2001 + + +File: gawk.info, Node: Foreword4, Next: Preface, Prev: Foreword3, Up: Top + +Foreword to the Fourth Edition +****************************** + +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 `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 `gawk' +module loads the C/C++ module as a dynamic plug-in. *note 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. + + Michael Brennan + Author of `mawk' + October 2014 -File: gawk.info, Node: Preface, Next: Getting Started, Prev: Foreword, Up: Top +File: gawk.info, Node: Preface, Next: Getting Started, Prev: Foreword4, Up: Top Preface ******* 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 `awk'. The `awk' -utility interprets a special-purpose programming language that makes it -easy to handle simple data-reformatting jobs. +may need to make changes wherever certain patterns appear, but leave the +rest of the file alone. Such jobs are often easy with `awk'. The +`awk' utility interprets a special-purpose programming language that +makes it easy to handle simple data-reformatting jobs. The GNU implementation of `awk' is called `gawk'; if you invoke it -with the proper options or environment variables (*note Options::), it -is fully compatible with the POSIX(1) specification of the `awk' -language and with the Unix version of `awk' maintained by Brian -Kernighan. This means that all properly written `awk' programs should -work with `gawk'. Thus, we usually don't distinguish between `gawk' -and other `awk' implementations. +with the proper options or environment variables, it is fully +compatible with the POSIX(1) specification of the `awk' language and +with the Unix version of `awk' maintained by Brian Kernighan. This +means that all properly written `awk' programs should work with `gawk'. +So most of the time, we don't distinguish between `gawk' and other +`awk' implementations. - Using `awk' allows you to: + Using `awk' you can: * Manage small, personal databases @@ -670,7 +834,7 @@ and other `awk' implementations. * Validate data - * Produce indexes and perform other document preparation tasks + * Produce indexes and perform other document-preparation tasks * Experiment with algorithms that you can adapt later to other computer languages @@ -683,6 +847,10 @@ and other `awk' implementations. * Perform simple network communications + * Profile and debug `awk' programs + + * Extend the language with functions written in C or C++ + This Info file teaches you about the `awk' language and how you can use it effectively. You should already be familiar with basic system commands, such as `cat' and `ls',(2) as well as basic shell facilities, @@ -691,13 +859,11 @@ such as input/output (I/O) redirection and pipes. Implementations of the `awk' language are available for many different computing environments. This Info file, while describing the `awk' language in general, also describes the particular implementation -of `awk' called `gawk' (which stands for "GNU awk"). `gawk' runs on a -broad range of Unix systems, ranging from Intel(R)-architecture -PC-based computers up through large-scale systems, such as Crays. -`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 `gawk' was once ported are no longer supported and the code for -those systems has been removed.) +of `awk' called `gawk' (which stands for "GNU `awk'"). `gawk' runs on +a broad range of Unix systems, ranging from Intel-architecture PC-based +computers up through large-scale systems. `gawk' has also been ported +to Mac OS X, Microsoft Windows (all versions) and OS/2 PCs, and +OpenVMS.(3) * Menu: @@ -714,33 +880,36 @@ those systems has been removed.) ---------- Footnotes ---------- - (1) The 2008 POSIX standard can be found online at + (1) The 2008 POSIX standard is accessible online at `http://www.opengroup.org/onlinepubs/9699919799/'. - (2) These commands are available on POSIX-compliant systems, as well -as on traditional Unix-based systems. If you are using some other + (2) 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. + (3) Some other, obsolete systems to which `gawk' was once ported are +no longer supported and the code for those systems has been removed. + File: gawk.info, Node: History, Next: Names, Up: Preface History of `awk' and `gawk' =========================== - Recipe For A Programming Language + Recipe for a Programming Language 1 part `egrep' 1 part `snobol' 2 parts `ed' 3 parts C - Blend all parts well using `lex' and `yacc'. Document minimally - and release. + Blend all parts well using `lex' and `yacc'. Document minimally and +release. - After eight years, add another part `egrep' and two more parts C. - Document very well and release. + After eight years, add another part `egrep' and two more parts C. +Document very well and release. - The name `awk' comes from the initials of its designers: Alfred V. -Aho, Peter J. Weinberger and Brian W. Kernighan. The original version +The name `awk' comes from the initials of its designers: Alfred V. +Aho, Peter J. Weinberger, and Brian W. Kernighan. The original version of `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 streams, and computed regular @@ -749,18 +918,18 @@ V Release 3.1 (1987). 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 `awk' in the POSIX Command Language and Utilities standard further clarified the language. -Both the `gawk' designers and the original Bell Laboratories `awk' -designers provided feedback for the POSIX specification. - - Paul Rubin wrote the GNU implementation, `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 `gawk' for compatibility -with the newer `awk'. Circa 1994, I became the primary maintainer. -Current development focuses on bug fixes, performance improvements, -standards compliance, and occasionally, new features. - - In May of 1997, Ju"rgen Kahrs felt the need for network access from +Both the `gawk' designers and the original `awk' designers at Bell +Laboratories provided feedback for the POSIX specification. + + Paul Rubin wrote `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 `gawk' for compatibility with the newer `awk'. +Circa 1994, I became the primary maintainer. Current development +focuses on bug fixes, performance improvements, standards compliance, +and, occasionally, new features. + + In May 1997, Ju"rgen Kahrs felt the need for network access from `awk', and with a little help from me, set about adding features to do this for `gawk'. At that time, he also wrote the bulk of `TCP/IP Internetworking with `gawk'' (a separate document, available as part of @@ -769,9 +938,9 @@ the `gawk' distribution). His code finally became part of the main John Haque rewrote the `gawk' internals, in the process providing an `awk'-level debugger. This version became available as `gawk' version -4.0, in 2011. +4.0 in 2011. - *Note Contributors::, for a complete list of those who made + *Note Contributors::, for a full list of those who have made important contributions to `gawk'. @@ -781,23 +950,20 @@ A Rose by Any Other Name ======================== The `awk' language has evolved over the years. Full details are -provided in *Note Language History::. The language described in this -Info file is often referred to as "new `awk'" (`nawk'). - - Because of this, there are systems with multiple versions of `awk'. -Some systems have an `awk' utility that implements the original version -of the `awk' language and a `nawk' utility for the new version. Others -have an `oawk' version for the "old `awk'" language and plain `awk' for -the new one. Still others only have one version, which is usually the -new one.(1) - - All in all, this makes it difficult for you to know which version of -`awk' you should run when writing your programs. The best advice we -can give here is to check your local documentation. Look for `awk', -`oawk', and `nawk', as well as for `gawk'. It is likely that you -already have some version of new `awk' on your system, which is what -you should use when running your programs. (Of course, if you're -reading this Info file, chances are good that you have `gawk'!) +provided in *note Language History::. The language described in this +Info file is often referred to as "new `awk'." By analogy, the +original version of `awk' is referred to as "old `awk'." + + Today, on most systems, when you run the `awk' utility you get some +version of new `awk'.(1) If your system's standard `awk' is the old +one, you will see something like this if you try the test program: + + $ awk 1 /dev/null + error--> awk: syntax error near line 1 + error--> awk: bailing out near line 1 + +In this case, you should find a version of new `awk', or just install +`gawk'! Throughout this Info file, whenever we refer to a language feature that should be available in any complete implementation of POSIX `awk', @@ -806,7 +972,9 @@ specific to the GNU implementation, we use the term `gawk'. ---------- Footnotes ---------- - (1) Often, these systems use `gawk' for their `awk' implementation! + (1) Only Solaris systems still use an old `awk' for the default +`awk' utility. A more modern `awk' lives in `/usr/xpg6/bin' on these +systems. File: gawk.info, Node: This Manual, Next: Conventions, Prev: Names, Up: Preface @@ -826,96 +994,132 @@ programming language. in the POSIX standard. It does so in the context of the `gawk' implementation. While doing so, it also attempts to describe important differences between `gawk' and other `awk' implementations.(1) Finally, -any `gawk' features that are not in the POSIX standard for `awk' are -noted. +it notes any `gawk' features that are not in the POSIX standard for +`awk'. - There are subsections labeled as *Advanced Notes* scattered -throughout the Info file. 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." + There are sidebars scattered throughout the Info file. 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 "sidebar." Most of the time, the examples use complete `awk' programs. Some of the more advanced sections show only the part of the `awk' program that -illustrates the concept currently being described. +illustrates the concept being described. + + Although this Info file is aimed principally at people who have not +been exposed to `awk', there is a lot of information here that even the +`awk' expert should find useful. In particular, the description of +POSIX `awk' and the example programs in *note Library Functions::, and +in *note Sample Programs::, should be of interest. + + This Info file is split into several parts, as follows: + + * Part I describes the `awk' language and the `gawk' program in + detail. It starts with the basics, and continues through all of + the features of `awk'. It contains the following chapters: + + - *note Getting Started::, provides the essentials you need to + know to begin using `awk'. + + - *note Invoking Gawk::, describes how to run `gawk', the + meaning of its command-line options, and how it finds `awk' + program source files. + + - *note Regexp::, introduces regular expressions in general, + and in particular the flavors supported by POSIX `awk' and + `gawk'. + + - *note Reading Files::, describes how `awk' reads your data. + It introduces the concepts of records and fields, as well as + the `getline' command. I/O redirection is first described + here. Network I/O is also briefly introduced here. + + - *note Printing::, describes how `awk' programs can produce + output with `print' and `printf'. - While this Info file is aimed principally at people who have not been -exposed to `awk', there is a lot of information here that even the `awk' -expert should find useful. In particular, the description of POSIX -`awk' and the example programs in *Note Library Functions::, and in -*Note Sample Programs::, should be of interest. + - *note Expressions::, describes expressions, which are the + basic building blocks for getting most things done in a + program. - *Note Getting Started::, provides the essentials you need to know to -begin using `awk'. + - *note Patterns and Actions::, describes how to write patterns + for matching records, actions for doing something when a + record is matched, and the predefined variables `awk' and + `gawk' use. - *Note Invoking Gawk::, describes how to run `gawk', the meaning of -its command-line options, and how it finds `awk' program source files. + - *note Arrays::, covers `awk''s one-and-only data structure: + the associative array. Deleting array elements and whole + arrays is described, as well as sorting arrays in `gawk'. + The major node also describes how `gawk' provides arrays of + arrays. - *Note Regexp::, introduces regular expressions in general, and in -particular the flavors supported by POSIX `awk' and `gawk'. + - *note Functions::, describes the built-in functions `awk' and + `gawk' provide, as well as how to define your own functions. + It also discusses how `gawk' lets you call functions + indirectly. - *Note Reading Files::, describes how `awk' reads your data. It -introduces the concepts of records and fields, as well as the `getline' -command. I/O redirection is first described here. Network I/O is also -briefly introduced here. + * Part II shows how to use `awk' and `gawk' for problem solving. + There is lots of code here for you to read and learn from. This + part contains the following chapters: - *Note Printing::, describes how `awk' programs can produce output -with `print' and `printf'. + - *note Library Functions::, provides a number of functions + meant to be used from main `awk' programs. - *Note Expressions::, describes expressions, which are the basic -building blocks for getting most things done in a program. + - *note Sample Programs::, provides many sample `awk' programs. - *Note 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 `awk' and `gawk' use. + Reading these two chapters allows you to see `awk' solving real + problems. - *Note Arrays::, covers `awk''s one-and-only data structure: -associative arrays. Deleting array elements and whole arrays is also -described, as well as sorting arrays in `gawk'. It also describes how -`gawk' provides arrays of arrays. + * Part III focuses on features specific to `gawk'. It contains the + following chapters: - *Note Functions::, describes the built-in functions `awk' and `gawk' -provide, as well as how to define your own functions. + - *note Advanced Features::, describes a number of advanced + features. Of particular note are the abilities to control + the order of array traversal, have two-way communications + with another process, perform TCP/IP networking, and profile + your `awk' programs. - *Note Internationalization::, describes special features in `gawk' -for translating program messages into different languages at runtime. + - *note Internationalization::, describes special features for + translating program messages into different languages at + runtime. - *Note Advanced Features::, describes a number of `gawk'-specific -advanced features. Of particular note are the abilities to have -two-way communications with another process, perform TCP/IP networking, -and profile your `awk' programs. + - *note Debugger::, describes the `gawk' debugger. - *Note Library Functions::, and *Note Sample Programs::, provide many -sample `awk' programs. Reading them allows you to see `awk' solving -real problems. + - *note Arbitrary Precision Arithmetic::, describes advanced + arithmetic facilities. - *Note Debugger::, describes the `awk' debugger, `dgawk'. + - *note Dynamic Extensions::, describes how to add new + variables and functions to `gawk' by writing extensions in C + or C++. - *Note Language History::, describes how the `awk' language has -evolved since its first release to present. It also describes how -`gawk' has acquired features over time. + * Part IV provides the appendices, the Glossary, and two licenses + that cover the `gawk' source code and this Info file, respectively. + It contains the following appendices: - *Note Installation::, describes how to get `gawk', how to compile it -on POSIX-compatible systems, and how to compile and use it on different -non-POSIX systems. It also describes how to report bugs in `gawk' and -where to get other freely available `awk' implementations. + - *note Language History::, describes how the `awk' language + has evolved since its first release to the present. It also + describes how `gawk' has acquired features over time. - *Note Notes::, describes how to disable `gawk''s extensions, as well -as how to contribute new code to `gawk', how to write extension -libraries, and some possible future directions for `gawk' development. + - *note Installation::, describes how to get `gawk', how to + compile it on POSIX-compatible systems, and how to compile + and use it on different non-POSIX systems. It also describes + how to report bugs in `gawk' and where to get other freely + available `awk' implementations. - *Note 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. + - *note Notes::, describes how to disable `gawk''s extensions, + as well as how to contribute new code to `gawk', and some + possible future directions for `gawk' development. - The *Note 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. + - *note Basic Concepts::, provides some very cursory background + material for those who are completely unfamiliar with + computer programming. - *Note Copying::, and *Note GNU Free Documentation License::, present -the licenses that cover the `gawk' source code and this Info file, -respectively. + The *note Glossary::, defines most, if not all, of the + significant terms used throughout the Info file. If you find + terms that you aren't familiar with, try looking them up here. + + - *note Copying::, and *note GNU Free Documentation License::, + present the licenses that cover the `gawk' source code and + this Info file, respectively. ---------- Footnotes ---------- @@ -928,18 +1132,18 @@ File: gawk.info, Node: Conventions, Next: Manual History, Prev: This Manual, Typographical Conventions ========================= -This Info file is written in Texinfo (http://texinfo.org), the GNU -documentation formatting language. A single Texinfo source file is -used to produce both the printed and online versions of the -documentation. This minor node briefly documents the typographical -conventions used in Texinfo. +This Info file is written in Texinfo +(http://www.gnu.org/software/texinfo/), the GNU documentation +formatting language. A single Texinfo source file is used to produce +both the printed and online versions of the documentation. This minor +node briefly documents the typographical conventions used in Texinfo. - Examples you would type at the command-line are preceded by the + Examples you would type at the command line are preceded by the common shell primary and secondary prompts, `$' and `>'. Input that you type is shown `like this'. Output from the command is preceded by the glyph "-|". This typically represents the command's standard -output. Error messages, and other output on the command's standard -error, are preceded by the glyph "error-->". For example: +output. Error messages and other output on the command's standard +error are preceded by the glyph "error-->". For example: $ echo hi on stdout -| hi on stdout @@ -951,23 +1155,27 @@ particular, there are special characters called "control characters." These are characters that you type by holding down both the `CONTROL' key and another key, at the same time. For example, a `Ctrl-d' is typed by first pressing and holding the `CONTROL' key, next pressing the `d' -key and finally releasing both keys. +key, and finally releasing both keys. + + For the sake of brevity, throughout this Info file, we refer to +Brian Kernighan's version of `awk' as "BWK `awk'." (*Note Other +Versions::, for information on his and other versions.) Dark Corners -............ +------------ - Dark corners are basically fractal -- no matter how much you - illuminate, there's always a smaller but darker one. - Brian Kernighan + Dark corners are basically fractal--no matter how much you + illuminate, there's always a smaller but darker one. -- Brian + Kernighan Until the POSIX standard (and `GAWK: Effective AWK Programming'), many features of `awk' were either poorly documented or not documented at all. Descriptions of such features (often called "dark corners") -are noted in this Info file with "(d.c.)". They also appear in the +are noted in this Info file with "(d.c.)." They also appear in the index under the heading "dark corner." - 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. Extensions to the standard `awk' language that are supported by more than one `awk' implementation are marked "(c.e.)," and listed in the @@ -986,13 +1194,13 @@ editor. GNU Emacs is the most widely used version of Emacs today. The GNU(1) 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 for +POSIX-compliant computing environment. The FSF uses the GNU General +Public License (GPL) to ensure that its software's source code is +always available to the end user. A copy of the GPL is included for your reference (*note Copying::). The GPL applies to the C language source code for `gawk'. To find out more about the FSF and the GNU Project online, see the GNU Project's home page (http://www.gnu.org). -This Info file may also be read from their web site +This Info file may also be read from GNU's website (http://www.gnu.org/software/gawk/manual/). A shell, an editor (Emacs), highly portable optimizing C, C++, and @@ -1003,45 +1211,40 @@ released but remains in an early stage of development. Until the GNU operating system is more fully developed, you should consider using GNU/Linux, a freely distributable, Unix-like operating -system for Intel(R), Power Architecture, Sun SPARC, IBM S/390, and other +system for Intel, Power Architecture, Sun SPARC, IBM S/390, and other systems.(2) 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 `gawk' for their versions of `awk'. NetBSD -(http://www.netbsd.org), FreeBSD (http://www.freebsd.org), and OpenBSD -(http://www.openbsd.org) are three of the most popular ones, but there -are others.) - - The Info file itself has gone through a number of previous editions. + The Info file itself has gone through multiple previous editions. Paul Rubin wrote the very first draft of `The GAWK Manual'; it was -around 40 pages in size. Diane Close and Richard Stallman improved it, -yielding a version that was around 90 pages long and barely described -the original, "old" version of `awk'. +around 40 pages long. Diane Close and Richard Stallman improved it, +yielding a version that was around 90 pages and barely described the +original, "old" version of `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.X). In 1996, Edition 1.0 was released with `gawk' 3.0.0. The FSF +0.X). In 1996, edition 1.0 was released with `gawk' 3.0.0. The FSF published the first two editions under the title `The GNU Awk User's Guide'. 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 *Note Debugger::. +For FSF edition 4.0, the content was thoroughly reviewed and updated. +All references to `gawk' versions prior to 4.0 were removed. Of +significant note for that edition was the addition of *note Debugger::. - `GAWK: Effective AWK Programming' will undoubtedly continue to -evolve. An electronic version comes with the `gawk' distribution from -the FSF. If you find an error in this Info file, please report it! -*Note Bugs::, for information on submitting problem reports -electronically. + For FSF edition 4.1, the content has been reorganized into parts, +and the major new additions are *note Arbitrary Precision Arithmetic::, +and *note Dynamic Extensions::. + + This Info file will undoubtedly continue to evolve. If you find an +error in the Info file, please report it! *Note Bugs::, for +information on submitting problem reports electronically. ---------- Footnotes ---------- - (1) GNU stands for "GNU's not Unix." + (1) GNU stands for "GNU's Not Unix." - (2) The terminology "GNU/Linux" is explained in the *Note Glossary::. + (2) The terminology "GNU/Linux" is explained in the *note Glossary::. File: gawk.info, Node: How To Contribute, Next: Acknowledgments, Prev: Manual History, Up: Preface @@ -1062,13 +1265,13 @@ something more broad, I acquired the `awk.info' domain. 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 `awk'-related web site--`http://awk.info'--and did a very nice job. + Late in 2008, a volunteer took on the task of setting up an +`awk'-related website--`http://awk.info'--and did a very nice job. If you have written an interesting `awk' program, or have written a `gawk' extension that you would like to share with the rest of the world, please see `http://awk.info/?contribute' for how to contribute -it to the web site. +it to the website. File: gawk.info, Node: Acknowledgments, Prev: How To Contribute, Up: Preface @@ -1083,7 +1286,7 @@ acknowledgments: 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 `A Supplemental - Document for `awk'' by John W. Pierce of the Chemistry Department + Document for AWK' by John W. Pierce of the Chemistry Department at UC San Diego, pinpointed several issues relevant both to `awk' implementation and to this manual, that would otherwise have escaped us. @@ -1096,7 +1299,7 @@ GNU Project. acknowledgements: The following people (in alphabetical order) provided helpful - comments on various versions of this book, Rick Adams, Dr. Nelson + comments on various versions of this book: Rick Adams, Dr. Nelson H.F. Beebe, Karl Berry, Dr. Michael Brennan, Rich Burridge, Claire Cloutier, Diane Close, Scott Deifik, Christopher ("Topher") Eliot, Jeffrey Friedl, Dr. Darrel Hankerson, Michal Jaegermann, Dr. @@ -1105,7 +1308,7 @@ acknowledgements: Robert J. Chassell provided much valuable advice on the use of Texinfo. He also deserves special thanks for convincing me _not_ - to title this Info file `How To Gawk Politely'. Karl Berry helped + to title this Info file `How to Gawk Politely'. Karl Berry helped significantly with the TeX part of Texinfo. I would like to thank Marshall and Elaine Hartholz of Seattle and @@ -1126,30 +1329,43 @@ acknowledgements: Ulrich Drepper, provided invaluable help and feedback for the design of the internationalization features. - Chuck Toporek, Mary Sheehan, and Claire Coutier of O'Reilly & + Chuck Toporek, Mary Sheehan, and Claire Cloutier of O'Reilly & Associates contributed significant editorial help for this Info file for the 3.1 release of `gawk'. - Dr. Nelson Beebe, Andreas Buening, Antonio Colombo, Stephen Davies, -Scott Deifik, John H. DuBois III, Darrel Hankerson, Michal Jaegermann, -Ju"rgen Kahrs, Dave Pitts, Stepan Kasal, Pat Rankin, Andrew Schorr, -Corinna Vinschen, Anders Wallin, and Eli Zaretskii (in alphabetical -order) make up the current `gawk' "crack portability team." Without -their hard work and help, `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 `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 -*Note Debugger::. - - I would like to thank Brian Kernighan for invaluable assistance -during the testing and debugging of `gawk', and for ongoing help and -advice in clarifying numerous points about the language. We could not -have done nearly as good a job on either `gawk' or its documentation -without his help. + Dr. Nelson Beebe, Andreas Buening, Dr. Manuel Collado, Antonio +Colombo, Stephen Davies, Scott Deifik, Akim Demaille, Darrel Hankerson, +Michal Jaegermann, Ju"rgen Kahrs, Stepan Kasal, John Malmberg, Dave +Pitts, Chet Ramey, Pat Rankin, Andrew Schorr, Corinna Vinschen, and Eli +Zaretskii (in alphabetical order) make up the current `gawk' "crack +portability team." Without their hard work and help, `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. *Note Contributors::, for the full list. + + Thanks to Michael Brennan for the Forewords. + + Thanks to Patrice Dumas for the new `makeinfo' program. Thanks to +Karl Berry, who continues to work to keep the Texinfo markup language +sane. + + Robert P.J. Day, Michael Brennan, and Brian Kernighan kindly acted as +reviewers for the 2015 edition of this Info file. 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 `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 `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... I must thank my wonderful wife, Miriam, for her patience through the many versions of this project, for her proofreading, and for sharing me @@ -1159,12 +1375,6 @@ 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. - -Arnold Robbins -Nof Ayalon -ISRAEL -March, 2011 - File: gawk.info, Node: Getting Started, Next: Invoking Gawk, Prev: Preface, Up: Top @@ -1174,28 +1384,28 @@ File: gawk.info, Node: Getting Started, Next: Invoking Gawk, Prev: Preface, The basic function of `awk' is to search files for lines (or other units of text) that contain certain patterns. When a line matches one of the patterns, `awk' performs specified actions on that line. `awk' -keeps processing input lines in this way until it reaches the end of -the input files. +continues to process input lines in this way until it reaches the end +of the input files. Programs in `awk' are different from programs in most other -languages, because `awk' programs are "data-driven"; that is, you -describe the data you want to work with and then what to do when you -find it. Most other languages are "procedural"; you have to describe, -in great detail, every step the program is to take. When working with +languages, because `awk' programs are "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 "procedural"; you have to describe, in great +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, `awk' programs are often refreshingly easy to read and write. When you run `awk', you specify an `awk' "program" that tells `awk' -what to do. The program consists of a series of "rules". (It may also +what to do. The program consists of a series of "rules" (it may also contain "function definitions", an advanced feature that we will ignore -for now. *Note User-defined::.) Each rule specifies one pattern to +for now; *note 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 `awk' program looks -like this: + Syntactically, a rule consists of a "pattern" followed by an +"action". The action is enclosed in braces to separate it from the +pattern. Newlines usually separate rules. Therefore, an `awk' program +looks like this: PATTERN { ACTION } PATTERN { ACTION } @@ -1216,6 +1426,7 @@ like this: * Other Features:: Other Features of `awk'. * When:: When to use `gawk' and when to use other things. +* Intro Summary:: Summary of the introduction. File: gawk.info, Node: Running gawk, Next: Sample Data Files, Up: Getting Started @@ -1241,7 +1452,7 @@ variations of each. * One-shot:: Running a short throwaway `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 `awk' programs in files. @@ -1262,7 +1473,7 @@ program as the first argument of the `awk' command, like this: awk 'PROGRAM' INPUT-FILE1 INPUT-FILE2 ... -where PROGRAM consists of a series of PATTERNS and ACTIONS, as +where PROGRAM consists of a series of patterns and actions, as described earlier. This command format instructs the "shell", or command interpreter, @@ -1277,7 +1488,8 @@ programs from shell scripts, because it avoids the need for a separate file for the `awk' program. A self-contained shell script is more reliable because there are no other files to misplace. - *Note Very Simple::, presents several short, self-contained programs. + Later in this chapter, in *note Very Simple::, we'll see examples of +several short, self-contained programs. File: gawk.info, Node: Read Terminal, Next: Long, Prev: One-shot, Up: Running gawk @@ -1291,27 +1503,35 @@ following command line: awk 'PROGRAM' `awk' applies the PROGRAM to the "standard input", which usually means -whatever you type on the terminal. This continues until you indicate -end-of-file by typing `Ctrl-d'. (On other operating systems, the +whatever you type on the keyboard. This continues until you indicate +end-of-file by typing `Ctrl-d'. (On non-POSIX operating systems, the end-of-file character may be different. For example, on OS/2, it is `Ctrl-z'.) As an example, the following program prints a friendly piece of advice (from Douglas Adams's `The Hitchhiker's Guide to the Galaxy'), to keep you from worrying about the complexities of computer -programming(1) (`BEGIN' is a feature we haven't discussed yet): +programming: - $ awk "BEGIN { print \"Don't Panic!\" }" + $ awk 'BEGIN { print "Don\47t Panic!" }' -| Don't Panic! - This program does not read any input. The `\' 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.(2) + `awk' executes statements associated with `BEGIN' before reading any +input. If there are no other statements in your program, as is the +case here, `awk' just stops, instead of trying to read input it doesn't +know how to process. The `\47' is a magic way (explained later) of +getting a single quote into the program, without having to engage in +ugly shell quoting tricks. + + NOTE: If you use Bash as your shell, you should execute the + command `set +H' before running this program interactively, to + disable the C shell-style command history, which treats `!' as a + special character. We recommend putting this command into your + personal startup file. This next simple `awk' program emulates the `cat' utility; it copies whatever you type on the keyboard to its standard output (why this -works is explained shortly). +works is explained shortly): $ awk '{ print }' Now is the time for all good men @@ -1324,32 +1544,21 @@ works is explained shortly). -| What, me worry? Ctrl-d - ---------- Footnotes ---------- - - (1) If you use Bash as your shell, you should execute the command -`set +H' before running this program interactively, to disable the C -shell-style command history, which treats `!' as a special character. -We recommend putting this command into your personal startup file. - - (2) 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. - File: gawk.info, Node: Long, Next: Executable Scripts, Prev: Read Terminal, Up: Running gawk 1.1.3 Running Long Programs --------------------------- -Sometimes your `awk' programs can be very long. In this case, it is -more convenient to put the program into a separate file. In order to -tell `awk' to use that file for its program, you type: +Sometimes `awk' programs are very long. In these cases, it is more +convenient to put the program into a separate file. In order to tell +`awk' to use that file for its program, you type: awk -f SOURCE-FILE INPUT-FILE1 INPUT-FILE2 ... The `-f' instructs the `awk' utility to get the `awk' program from -the file SOURCE-FILE. Any file name can be used for SOURCE-FILE. For -example, you could put the program: +the file SOURCE-FILE (*note Options::). Any file name can be used for +SOURCE-FILE. For example, you could put the program: BEGIN { print "Don't Panic!" } @@ -1359,19 +1568,20 @@ into the file `advice'. Then this command: does the same thing as this one: - awk "BEGIN { print \"Don't Panic!\" }" + awk 'BEGIN { print "Don\47t Panic!" }' This was explained earlier (*note Read Terminal::). Note that you don't usually need single quotes around the file name that you specify with `-f', because most file names don't contain any of the shell's special characters. Notice that in `advice', the `awk' program did not have single quotes around it. The quotes are only needed for programs -that are provided on the `awk' command line. +that are provided on the `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 `\47'.) - If you want to clearly identify your `awk' program files as such, -you can add the extension `.awk' to the file name. This doesn't affect -the execution of the `awk' program but it does make "housekeeping" -easier. + If you want to clearly identify an `awk' program file as such, you +can add the extension `.awk' to the file name. This doesn't affect the +execution of the `awk' program but it does make "housekeeping" easier. File: gawk.info, Node: Executable Scripts, Next: Comments, Prev: Long, Up: Running gawk @@ -1389,8 +1599,8 @@ like this: BEGIN { print "Don't Panic!" } After making this file executable (with the `chmod' utility), simply -type `advice' at the shell and the system arranges to run `awk'(2) as -if you had typed `awk -f advice': +type `advice' at the shell and the system arranges to run `awk' as if +you had typed `awk -f advice': $ chmod +x advice $ advice @@ -1404,11 +1614,27 @@ at the shell.) program that users can invoke without their having to know that the program is written in `awk'. -Advanced Notes: Portability Issues with `#!' --------------------------------------------- + Understanding `#!' + + `awk' is an "interpreted" language. This means that the `awk' +utility reads your program and then processes your data according to +the instructions in your program. (This is different from a "compiled" +language such as C, where your program is first compiled into machine +code that is executed directly by your system's processor.) The `awk' +utility is thus termed an "interpreter". Many modern languages are +interpreted. + + The line beginning with `#!' lists the full file name 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 file name +of the `awk' program. The rest of the argument list contains either +options to `awk', or data files, or both. (Note that on many systems +`awk' may be found in `/usr/bin' instead of in `/bin'.) -Some systems limit the length of the interpreter name to 32 characters. -Often, this can be dealt with by using a symbolic link. + 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 `#!' line after the path to `awk'. It does not work. The operating system treats the rest @@ -1424,16 +1650,8 @@ the name of your script (`advice'). (d.c.) Don't rely on the value of ---------- Footnotes ---------- - (1) The `#!' mechanism works on GNU/Linux systems, BSD-based systems -and commercial Unix systems. - - (2) The line beginning with `#!' lists the full file name 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 file name -of the `awk' program. The rest of the argument list contains either -options to `awk', or data files, or both. + (1) The `#!' mechanism works on GNU/Linux systems, BSD-based +systems, and commercial Unix systems. File: gawk.info, Node: Comments, Next: Quoting, Prev: Executable Scripts, Up: Running gawk @@ -1447,13 +1665,13 @@ Comments 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 `awk' language, a comment starts with the sharp sign + In the `awk' language, a comment starts with the number sign character (`#') and continues to the end of the line. The `#' does not have to be the first character on the line. The `awk' language ignores -the rest of a line following a sharp sign. For example, we could have +the rest of a line following a number sign. For example, we could have put the following into `advice': - # 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!" } @@ -1462,17 +1680,17 @@ 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. - CAUTION: As mentioned in *Note One-shot::, you can enclose small - to medium programs in single quotes, in order to keep your shell - scripts self-contained. When doing so, _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 quote for - the entire program. As a result, usually the shell prints a - message about mismatched quotes, and if `awk' actually runs, it - will probably print strange messages about syntax errors. For - example, look at the following: - - $ awk '{ print "hello" } # let's be cute' + CAUTION: As mentioned in *note One-shot::, you can enclose short + to medium-sized programs in single quotes, in order to keep your + shell scripts self-contained. When doing so, _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 + quote for the entire program. As a result, usually the shell + prints a message about mismatched quotes, and if `awk' actually + runs, it will probably print strange messages about syntax errors. + For example, look at the following: + + $ awk 'BEGIN { print "hello" } # let's be cute' > The shell sees that the first two quotes match, and that a new @@ -1486,20 +1704,20 @@ at a later time. error--> source line number 1 Putting a backslash before the single quote in `let's' wouldn't - help, since backslashes are not special inside single quotes. The - next node describes the shell's quoting rules. + help, because backslashes are not special inside single quotes. + The next node describes the shell's quoting rules. File: gawk.info, Node: Quoting, Prev: Comments, Up: Running gawk -1.1.6 Shell-Quoting Issues +1.1.6 Shell Quoting Issues -------------------------- * Menu: * DOS Quoting:: Quoting in Windows Batch Files. - For short to medium length `awk' programs, it is most convenient to + For short to medium-length `awk' programs, it is most convenient to enter the program on the `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 the shell prompt, or @@ -1512,6 +1730,23 @@ 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. + Before diving into the rules, we introduce a concept that appears +throughout this Info file, which is that of the "null", or empty, +string. + + The null string is character data that has no value. In other +words, it is empty. It is written in `awk' programs like this: `""'. +In the shell, it can be written using single or double quotes: `""' or +`'''. Although the null string has no characters in it, it does exist. +For example, consider this command: + + $ echo "" + +Here, the `echo' utility receives a single argument, even though that +argument has no characters in it. In the rest of this Info file, we use +the terms "null string" and "empty string" interchangeably. Now, on to +the quoting rules: + * Quoted items can be concatenated with nonquoted items as well as with other quoted items. The shell turns everything into one argument for the command. @@ -1524,20 +1759,23 @@ Shell). If you use the C shell, you're on your own. quotes. The shell does no interpretation of the quoted text, passing it on verbatim to the command. It is _impossible_ to embed a single quote inside single-quoted text. Refer back to - *Note Comments::, for an example of what happens if you try. + *note Comments::, for an example of what happens if you try. * 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 + Because certain characters within double-quoted text are processed by the shell, they must be "escaped" within the text. Of note are the characters `$', ``', `\', and `"', all of which must be preceded by a backslash within double-quoted text if they are to be passed on literally to the program. (The leading backslash is - stripped first.) Thus, the example seen in *Note Read Terminal::, - is applicable: + stripped first.) Thus, the example seen in *note Read Terminal::: + + awk 'BEGIN { print "Don\47t Panic!" }' + + could instead be written this way: $ awk "BEGIN { print \"Don't Panic!\" }" -| Don't Panic! @@ -1545,9 +1783,9 @@ Shell). If you use the C shell, you're on your own. Note that the single quote is not special within double quotes. * Null strings are removed when they occur as part of a non-null - command-line argument, while explicit non-null objects are kept. - For example, to specify that the field separator `FS' should be - set to the null string, use: + command-line argument, while explicit null objects are kept. For + example, to specify that the field separator `FS' should be set to + the null string, use: awk -F "" 'PROGRAM' FILES # correct @@ -1555,10 +1793,10 @@ Shell). If you use the C shell, you're on your own. awk -F"" 'PROGRAM' FILES # wrong! - In the second case, `awk' will attempt to use the text of the - program as the value of `FS', and the first file name as the text - of the program! This results in syntax errors at best, and - confusing behavior at worst. + In the second case, `awk' attempts to use the text of the program + as the value of `FS', and the first file name as the text of the + program! This results in syntax errors at best, and confusing + behavior at worst. Mixing single and double quotes is difficult. You have to resort to shell quoting tricks, like this: @@ -1567,7 +1805,7 @@ shell quoting tricks, like this: -| Here is a single quote <'> This program consists of three concatenated quoted strings. The first -and the third are single-quoted, the second is double-quoted. +and the third are single-quoted, and the second is double-quoted. This can be "simplified" to: @@ -1594,8 +1832,7 @@ like so: $ awk 'BEGIN { print "Here is a double quote <\42>" }' -| Here is a double quote <"> -This works nicely, except that you should comment clearly what the -escapes mean. +This works nicely, but you should comment clearly what the escapes mean. A fourth option is to use command-line variable assignment, like this: @@ -1603,9 +1840,12 @@ this: $ awk -v sq="'" 'BEGIN { print "Here is a single quote <" sq ">" }' -| Here is a single quote <'> + (Here, the two string constants and the value of `sq' are +concatenated into a single string that is printed by `print'.) + If you really need both single and double quotes in your `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. +shell won't be part of the picture and you can say what you mean. File: gawk.info, Node: DOS Quoting, Up: Quoting @@ -1632,37 +1872,38 @@ File: gawk.info, Node: Sample Data Files, Next: Very Simple, Prev: Running ga =============================== Many of the examples in this Info file take their input from two sample -data files. The first, `BBS-list', represents a list of computer -bulletin board systems together with information about those systems. +data files. The first, `mail-list', represents a list of peoples' names +together with their email addresses and information about those people. The second data file, called `inventory-shipped', contains information about monthly shipments. In both files, each line is considered to be one "record". - In the data 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 `A' in the -last column means the board operates 24 hours a day. A `B' in the last -column means the board only operates on evening and weekend hours. A -`C' means the board operates only on weekends: - - 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 + In `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 +`A' in the last column means that the person is an acquaintance. An +`F' in the last column means that the person is a friend. An `R' means +that the person is a relative: + + 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 The data file `inventory-shipped' represents information about shipments during the year. Each record contains the month, the number 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. +and the first four months of the current year. An empty line separates +the data for the two years: Jan 13 25 15 115 Feb 15 32 24 226 @@ -1682,18 +1923,8 @@ and the first four months of the current year. Mar 24 75 70 495 Apr 21 70 74 514 - 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 `M-x write-region' to copy -text from the Info file into a file for use with `awk' (*Note -Miscellaneous File Operations: (emacs)Misc File Ops, for more -information). Using this information, create your own `BBS-list' and -`inventory-shipped' files and practice what you learn in this Info file. - - If you are using the stand-alone version of Info, see *Note Extract -Program::, for an `awk' program that extracts these data files from -`gawk.texi', the Texinfo source file for this Info file. + The sample files are included in the `gawk' distribution, in the +directory `awklib/eg/data'. File: gawk.info, Node: Very Simple, Next: Two Rules, Prev: Sample Data Files, Up: Getting Started @@ -1702,32 +1933,32 @@ File: gawk.info, Node: Very Simple, Next: Two Rules, Prev: Sample Data Files, ======================== The following command runs a simple `awk' program that searches the -input file `BBS-list' for the character string `foo' (a grouping of +input file `mail-list' for the character string `li' (a grouping of characters is usually called a "string"; the term "string" is based on -similar usage in English, such as "a string of pearls," or "a string of +similar usage in English, such as "a string of pearls" or "a string of cars in a train"): - awk '/foo/ { print $0 }' BBS-list + awk '/li/ { print $0 }' mail-list -When lines containing `foo' are found, they are printed because +When lines containing `li' are found, they are printed because `print $0' means print the current line. (Just `print' by itself means the same thing, so we could have written that instead.) - You will notice that slashes (`/') surround the string `foo' in the -`awk' program. The slashes indicate that `foo' is the pattern to -search for. This type of pattern is called a "regular expression", -which is covered in more detail later (*note Regexp::). The pattern is -allowed to match parts of words. There are single quotes around the -`awk' program so that the shell won't interpret any of it as special -shell characters. + You will notice that slashes (`/') surround the string `li' in the +`awk' program. The slashes indicate that `li' is the pattern to search +for. This type of pattern is called a "regular expression", which is +covered in more detail later (*note Regexp::). The pattern is allowed +to match parts of words. There are single quotes around the `awk' +program so that the shell won't interpret any of it as special shell +characters. Here is what this program prints: - $ awk '/foo/ { print $0 }' BBS-list - -| fooey 555-1234 2400/1200/300 B - -| foot 555-6699 1200/300 B - -| macfoo 555-6480 1200/300 A - -| sabafoo 555-2127 1200/300 C + $ awk '/li/ { print $0 }' mail-list + -| Amelia 555-5553 amelia.zodiacusque@gmail.com F + -| Broderick 555-0542 broderick.aliquotiens@yahoo.com R + -| Julie 555-6699 julie.perscrutabor@skeeve.com F + -| Samuel 555-3430 samuel.lanceolis@shu.edu A In an `awk' rule, either the pattern or the action can be omitted, but not both. If the pattern is omitted, then the action is performed @@ -1735,43 +1966,48 @@ for _every_ input line. If the action is omitted, the default action is to print all lines that match the pattern. Thus, we could leave out the action (the `print' statement and the -curly braces) in the previous example and the result would be the same: -`awk' prints all lines matching the pattern `foo'. By comparison, -omitting the `print' statement but retaining the curly braces makes an -empty action that does nothing (i.e., no lines are printed). - - Many practical `awk' programs are just a line or two. 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 Info file to become an `awk' -expert!) Most of the examples use a data file named `data'. This is -just a placeholder; if you use these programs yourself, substitute your -own file names for `data'. For future reference, note that there is -often more than one way to do things in `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: +braces) in the previous example and the result would be the same: `awk' +prints all lines matching the pattern `li'. By comparison, omitting +the `print' statement but retaining the braces makes an empty action +that does nothing (i.e., no lines are printed). + + Many practical `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 you'll need to read the rest of the Info file to +become an `awk' expert!) Most of the examples use a data file named +`data'. This is just a placeholder; if you use these programs +yourself, substitute your own file names for `data'. For future +reference, note that there is often more than one way to do things in +`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: + + * Print every line that is longer than 80 characters: + + awk 'length($0) > 80' data + + The sole rule has a relational expression as its pattern and has no + action--so it uses the default action, printing the record. * Print the length of the longest input line: awk '{ if (length($0) > max) max = length($0) } END { print max }' data - * Print every line that is longer than 80 characters: - - awk 'length($0) > 80' data - - 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 `END' executes after all input has been + read; it's the other side of the coin to `BEGIN'. * Print the length of the longest line in `data': - 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 }' - The input is processed by the `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 `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. * Print every line that has at least one field: @@ -1789,7 +2025,7 @@ different ways to do the same things shown here: * Print the total number of bytes used by FILES: ls -l FILES | awk '{ x += $5 } - END { print "total bytes: " x }' + END { print "total bytes: " x }' * Print the total number of kilobytes used by FILES: @@ -1808,8 +2044,8 @@ different ways to do the same things shown here: awk 'NR % 2 == 0' data - If you use the expression `NR % 2 == 1' instead, the program would - print the odd-numbered lines. + If you used the expression `NR % 2 == 1' instead, the program + would print the odd-numbered lines. File: gawk.info, Node: Two Rules, Next: More Complex, Prev: Very Simple, Up: Getting Started @@ -1818,14 +2054,13 @@ File: gawk.info, Node: Two Rules, Next: More Complex, Prev: Very Simple, Up: ============================= The `awk' utility reads the input files one line at a time. For each -line, `awk' tries the patterns of each of the rules. If several -patterns match, then several actions are run in the order in which they -appear in the `awk' program. If no patterns match, then no actions are -run. +line, `awk' tries the patterns of each rule. If several patterns +match, then several actions execute in the order in which they appear +in the `awk' program. If no patterns match, then no actions run. After processing all the rules that match the line (and perhaps there are none), `awk' reads the next line. (However, *note Next -Statement::, and also *note Nextfile Statement::). This continues +Statement::, and also *note Nextfile Statement::.) This continues until the program reaches the end of the file. For example, the following `awk' program contains two rules: @@ -1842,25 +2077,19 @@ the string `21'. If a line contains both strings, it is printed twice, once by each rule. This is what happens if we run this program on our two sample data -files, `BBS-list' and `inventory-shipped': +files, `mail-list' and `inventory-shipped': $ awk '/12/ { print $0 } - > /21/ { print $0 }' BBS-list inventory-shipped - -| 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 - -| 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 - -| sabafoo 555-2127 1200/300 C + > /21/ { print $0 }' mail-list inventory-shipped + -| Anthony 555-3412 anthony.asserturo@hotmail.com A + -| Camilla 555-2912 camilla.infusarum@skynet.be R + -| Fabius 555-1234 fabius.undevicesimus@ucb.edu F + -| Jean-Paul 555-2127 jeanpaul.campanorum@nyu.edu R + -| Jean-Paul 555-2127 jeanpaul.campanorum@nyu.edu R -| Jan 21 36 64 620 -| Apr 21 70 74 514 -Note how the line beginning with `sabafoo' in `BBS-list' was printed +Note how the line beginning with `Jean-Paul' in `mail-list' was printed twice, once for each rule. @@ -1875,8 +2104,8 @@ summarize, select, and rearrange the output of another utility. It uses features that haven't been covered yet, so don't worry if you don't understand all the details: - LC_ALL=C ls -l | awk '$6 == "Nov" { sum += $5 } - END { print sum }' + ls -l | awk '$6 == "Nov" { sum += $5 } + END { print sum }' This command prints the total number of bytes in all the files in the current directory that were last modified in November (of any year). @@ -1895,20 +2124,20 @@ date the file was last modified. Its output looks like this: 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 sixth, seventh, and eighth fields contain the month, day, and time, +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 file name.(1) +contains the file name. The `$6 == "Nov"' in our `awk' program is an expression that tests whether the sixth field of the output from `ls -l' matches the string -`Nov'. Each time a line has the string `Nov' for its sixth field, the -action `sum += $5' is performed. This adds the fifth field (the file's -size) to the variable `sum'. As a result, when `awk' has finished -reading all the input lines, `sum' is the total of the sizes of the -files whose lines matched the pattern. (This works because `awk' -variables are automatically initialized to zero.) +`Nov'. Each time a line has the string `Nov' for its sixth field, +`awk' performs the action `sum += $5'. This adds the fifth field (the +file's size) to the variable `sum'. As a result, when `awk' has +finished reading all the input lines, `sum' is the total of the sizes +of the files whose lines matched the pattern. (This works because +`awk' variables are automatically initialized to zero.) After the last line of output from `ls' has been processed, the `END' rule executes and prints the value of `sum'. In this example, @@ -1921,11 +2150,6 @@ displays your output. By manipulating fields and using `print' statements, you can produce some very useful and impressive-looking reports. - ---------- Footnotes ---------- - - (1) The `LC_ALL=C' is needed to produce this traditional-style -output from `ls'. - File: gawk.info, Node: Statements/Lines, Next: Other Features, Prev: More Complex, Up: Getting Started @@ -1936,7 +2160,7 @@ Most often, each line in an `awk' program is a separate statement or separate rule, like this: awk '/12/ { print $0 } - /21/ { print $0 }' BBS-list inventory-shipped + /21/ { print $0 }' mail-list inventory-shipped However, `gawk' ignores newlines after any of the following symbols and keywords: @@ -1960,24 +2184,24 @@ We have generally not used backslash continuation in our sample programs. `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 presented throughout the -Info file. Backslash continuation is most useful when your `awk' -program is in a separate source file instead of entered from the -command line. You should also note that many `awk' implementations are -more particular about where you may use backslash continuation. For -example, they may not allow you to split a string constant using -backslash continuation. Thus, for maximum portability of your `awk' -programs, it is best not to split your lines in the middle of a regular -expression or a string. +most statements short in the programs presented throughout the Info +file. Backslash continuation is most useful when your `awk' program is +in a separate source file instead of entered from the command line. +You should also note that many `awk' implementations are more +particular about where you may use backslash continuation. For example, +they may not allow you to split a string constant using backslash +continuation. Thus, for maximum portability of your `awk' programs, it +is best not to split your lines in the middle of a regular expression +or a string. CAUTION: _Backslash continuation does not work as described with the C shell._ It works for `awk' programs in files and for one-shot programs, _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 a newline. Note also that when using the C - shell, _every_ newline in your `awk' program must be escaped with - a backslash. To illustrate: + behaves differently! There you must use two backslashes in a row, + followed by a newline. Note also that when using the C shell, + _every_ newline in your `awk' program must be escaped with a + backslash. To illustrate: % awk 'BEGIN { \ ? print \\ @@ -2010,7 +2234,7 @@ comment, it ignores _everything_ on the rest of the line. For example: > BEGIN rule > }' error--> gawk: cmd. line:2: BEGIN rule - error--> gawk: cmd. line:2: ^ parse error + error--> gawk: cmd. line:2: ^ syntax error In this case, it looks like the backslash would continue the comment onto the next line. However, the backslash-newline combination is never @@ -2033,7 +2257,7 @@ minor node could also be written this way: ---------- Footnotes ---------- (1) The `?' and `:' referred to here is the three-operand -conditional expression described in *Note Conditional Exp::. Splitting +conditional expression described in *note Conditional Exp::. Splitting lines after `?' and `:' is a minor `gawk' extension; if `--posix' is specified (*note Options::), then this extension is disabled. @@ -2054,12 +2278,13 @@ built-in functions for working with timestamps, performing bit manipulation, for runtime string translation (internationalization), determining the type of a variable, and array sorting. - As we develop our presentation of the `awk' language, we introduce -most of the variables and many of the functions. They are described -systematically in *Note Built-in Variables::, and *Note Built-in::. + As we develop our presentation of the `awk' language, we will +introduce most of the variables and many of the functions. They are +described systematically in *note Built-in Variables::, and in *note +Built-in::. -File: gawk.info, Node: When, Prev: Other Features, Up: Getting Started +File: gawk.info, Node: When, Next: Intro Summary, Prev: Other Features, Up: Getting Started 1.8 When to Use `awk' ===================== @@ -2082,21 +2307,46 @@ edit-compile-test-debug cycle of software development. Complex programs have been written in `awk', including a complete retargetable assembler for eight-bit microprocessors (*note Glossary::, for more information), and a microcode assembler for a special-purpose -Prolog computer. While the original `awk''s capabilities were strained -by tasks of such complexity, modern versions are more capable. Even -Brian Kernighan's version of `awk' has fewer predefined limits, and -those that it has are much larger than they used to be. +Prolog computer. The original `awk''s capabilities were strained by +tasks of such complexity, but modern versions are more capable. If you find yourself writing `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 `awk' programs, but they are easier -to maintain and usually run more efficiently. +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.(1) + + ---------- Footnotes ---------- + + (1) Other popular scripting languages include Ruby and Perl. + + +File: gawk.info, Node: Intro Summary, Prev: When, Up: Getting Started + +1.9 Summary +=========== + + * Programs in `awk' consist of PATTERN-ACTION pairs. + + * An ACTION without a PATTERN always runs. The default ACTION for a + pattern without one is `{ print $0 }'. + + * Use either `awk 'PROGRAM' FILES' or `awk -f PROGRAM-FILE FILES' to + run `awk'. + + * You may use the special `#!' header line to create `awk' programs + that are directly executable. + + * Comments in `awk' programs start with `#' and continue to the end + of the same line. + + * Be aware of quoting issues when writing `awk' programs as part of + a larger shell script (or MS-Windows batch file). + + * You may use backslash continuation to continue a source line. + Lines are automatically continued after a comma, open brace, + question mark, colon, `||', `&&', `do', and `else'. File: gawk.info, Node: Invoking Gawk, Next: Regexp, Prev: Getting Started, Up: Top @@ -2104,12 +2354,12 @@ File: gawk.info, Node: Invoking Gawk, Next: Regexp, Prev: Getting Started, U 2 Running `awk' and `gawk' ************************** -This major node covers how to run awk, both POSIX-standard and +This major node covers how to run `awk', both POSIX-standard and `gawk'-specific command-line options, and what `awk' and `gawk' do with -non-option arguments. It then proceeds to cover how `gawk' searches -for source files, reading standard input along with other files, -`gawk''s environment variables, `gawk''s exit status, using include -files, and obsolete and undocumented options and/or features. +nonoption arguments. It then proceeds to cover how `gawk' searches for +source files, reading standard input along with other files, `gawk''s +environment variables, `gawk''s exit status, using include files, and +obsolete and undocumented options and/or features. Many of the options and features described here are discussed in more detail later in the Info file; feel free to skip over things in @@ -2125,8 +2375,10 @@ this major node that don't interest you right now. * Environment Variables:: The environment variables `gawk' uses. * Exit Status:: `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. File: gawk.info, Node: Command Line, Next: Options, Up: Invoking Gawk @@ -2138,11 +2390,11 @@ There are two ways to run `awk'--with an explicit program or with one or more program files. Here are templates for both of them; items enclosed in [...] in these templates are optional: - awk [OPTIONS] -f progfile [`--'] FILE ... - awk [OPTIONS] [`--'] 'PROGRAM' FILE ... + `awk' [OPTIONS] `-f' PROGFILE [`--'] FILE ... + `awk' [OPTIONS] [`--'] `'PROGRAM'' FILE ... - Besides traditional one-letter POSIX-style options, `gawk' also -supports GNU long options. + In addition to traditional one-letter POSIX-style options, `gawk' +also supports GNU long options. It is possible to invoke `awk' with an empty program: @@ -2161,8 +2413,8 @@ File: gawk.info, Node: Options, Next: Other Arguments, Prev: Command Line, U 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 (`=') and the +uniquely identified. If the option takes an argument, either the +keyword is immediately followed by an equals sign (`=') 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 last value that counts. @@ -2177,10 +2429,10 @@ The following list describes options mandated by the POSIX standard: `-f SOURCE-FILE' `--file SOURCE-FILE' - Read `awk' program source from SOURCE-FILE instead of in the first - non-option argument. This option may be given multiple times; the - `awk' program consists of the concatenation the contents of each - specified SOURCE-FILE. + Read the `awk' program source from SOURCE-FILE instead of in the + first nonoption argument. This option may be given multiple + times; the `awk' program consists of the concatenation of the + contents of each specified SOURCE-FILE. `-v VAR=VAL' `--assign VAR=VAL' @@ -2195,7 +2447,7 @@ The following list describes options mandated by the POSIX standard: CAUTION: Using `-v' to set the values of the built-in variables may lead to surprising results. `awk' will reset the values of those variables as it needs to, possibly - ignoring any predefined value you may have given. + ignoring any initial value you may have given. `-W GAWK-OPT' Provide an implementation-specific option. This is the POSIX @@ -2214,38 +2466,41 @@ The following list describes options mandated by the POSIX standard: This is useful if you have file names that start with `-', or in shell scripts, if you have file names that will be specified by the user that could start with `-'. It is also useful for passing - options on to the `awk' program; see *Note Getopt Function::. + options on to the `awk' program; see *note Getopt Function::. The following list describes `gawk'-specific options: `-b' `--characters-as-bytes' Cause `gawk' to treat all input data as single-byte characters. + In addition, all output written with `print' or `printf' is + treated as single-byte characters. + Normally, `gawk' follows the POSIX standard and attempts to process - its input data according to the current locale. 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 `gawk': "hands off my data!". + its input data according to the current locale (*note 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 `gawk', "Hands off my data!" `-c' `--traditional' Specify "compatibility mode", in which the GNU extensions to the - `awk' language are disabled, so that `gawk' behaves just like - Brian Kernighan's version `awk'. *Note POSIX/GNU::, which - summarizes the extensions. Also see *Note Compatibility Mode::. + `awk' language are disabled, so that `gawk' behaves just like BWK + `awk'. *Note POSIX/GNU::, which summarizes the extensions. Also + see *note Compatibility Mode::. `-C' `--copyright' Print the short version of the General Public License and then exit. -`-d[FILE]' -`--dump-variables[=FILE]' +`-d'[FILE] +`--dump-variables'[`='FILE] Print a sorted list of global variables, their types, and final - values to FILE. If no FILE is provided, print this list to the - file named `awkvars.out' in the current directory. No space is - allowed between the `-d' and FILE, if FILE is supplied. + values to FILE. If no FILE is provided, print this list to a file + named `awkvars.out' in the current directory. No space is allowed + between the `-d' and FILE, if FILE is supplied. Having a list of all global variables is a good way to look for typographical errors in your programs. You would also use this @@ -2255,16 +2510,25 @@ The following list describes options mandated by the POSIX standard: particularly easy mistake to make with simple variable names like `i', `j', etc.) -`-e PROGRAM-TEXT' -`--source PROGRAM-TEXT' +`-D'[FILE] +`--debug'[`='FILE] + Enable debugging of `awk' programs (*note Debugging::). By + default, the debugger reads commands interactively from the + keyboard (standard input). The optional 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 `-D' + and FILE, if FILE is supplied. + +`-e' PROGRAM-TEXT +`--source' PROGRAM-TEXT Provide program source code in the PROGRAM-TEXT. This option allows you to mix source code in files with source code that you enter on the command line. This is particularly useful when you have library functions that you want to use from your command-line programs (*note AWKPATH Variable::). -`-E FILE' -`--exec FILE' +`-E' FILE +`--exec' FILE Similar to `-f', read `awk' program text from FILE. There are two differences from `-f': @@ -2277,8 +2541,8 @@ The following list describes options mandated by the POSIX standard: 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 `awk' source code (via `--source') to the - CGI application. This option should be used with `#!' scripts + options, assignments, or `awk' source code (via `-e') to the CGI + application.(1) This option should be used with `#!' scripts (*note Executable Scripts::), like so: #! /usr/local/bin/gawk -E @@ -2287,24 +2551,51 @@ The following list describes options mandated by the POSIX standard: `-g' `--gen-pot' - Analyze the source program and generate a GNU `gettext' Portable - Object Template file on standard output for all string constants + Analyze the source program and generate a GNU `gettext' portable + object template file on standard output for all string constants that have been marked for translation. *Note Internationalization::, for information about this option. `-h' `--help' - Print a "usage" message summarizing the short and long style + Print a "usage" message summarizing the short- and long-style options that `gawk' accepts and then exit. -`-L [value]' -`--lint[=value]' +`-i' SOURCE-FILE +`--include' SOURCE-FILE + Read an `awk' source library from SOURCE-FILE. This option is + completely equivalent to using the `@include' directive inside + your program. It is very similar to the `-f' option, but there + are two important differences. First, when `-i' is used, the + program source is not loaded if it has been previously loaded, + whereas with `-f', `gawk' always loads the file. Second, because + this option is intended to be used with code libraries, `gawk' + does not recognize such files as constituting main program input. + Thus, after processing an `-i' argument, `gawk' still expects to + find the main source code via the `-f' option or on the command + line. + +`-l' EXT +`--load' EXT + Load a dynamic extension named EXT. Extensions are stored as + system shared libraries. This option searches for the library + using the `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 `dl_load()'. An + alternative is to use the `@load' keyword inside the program to + load a shared library. This advanced feature is described in + detail in *note Dynamic Extensions::. + +`-L'[VALUE] +`--lint'[`='VALUE] Warn about constructs that are dubious or nonportable to other - `awk' implementations. Some warnings are issued when `gawk' first - reads your program. Others are issued at runtime, as your program - executes. With an optional argument of `fatal', lint warnings - become fatal errors. This may be drastic, but its use will - certainly encourage the development of cleaner `awk' programs. + `awk' implementations. No space is allowed between the `-L' and + VALUE, if VALUE is supplied. Some warnings are issued when `gawk' + first reads your program. Others are issued at runtime, as your + program executes. With an optional argument of `fatal', lint + warnings become fatal errors. This may be drastic, but its use + will certainly encourage the development of cleaner `awk' programs. With an optional argument of `invalid', only warnings about things that are actually invalid are issued. (This is not fully implemented yet.) @@ -2316,38 +2607,54 @@ The following list describes options mandated by the POSIX standard: inappropriate construct. As `awk' programs are usually short, doing so is not burdensome. +`-M' +`--bignum' + Force arbitrary-precision arithmetic on numbers. This option has + no effect if `gawk' is not compiled to use the GNU MPFR and MP + libraries (*note Arbitrary Precision Arithmetic::). + `-n' `--non-decimal-data' Enable automatic interpretation of octal and hexadecimal values in input data (*note Nondecimal Data::). CAUTION: This option can severely break old programs. Use - with care. + with care. Also note that this option may disappear in a + future version of `gawk'. `-N' `--use-lc-numeric' Force the use of the locale's decimal point character when parsing numeric input data (*note Locales::). +`-o'[FILE] +`--pretty-print'[`='FILE] + Enable pretty-printing of `awk' programs. By default, the output + program is created in a file named `awkprof.out' (*note + Profiling::). The optional FILE argument allows you to specify a + different file name for the output. No space is allowed between + the `-o' and FILE, if FILE is supplied. + + NOTE: In the past, this option would also execute your + program. This is no longer the case. + `-O' `--optimize' Enable some optimizations on the internal representation of the - program. At the moment this includes just simple constant - folding. The `gawk' maintainer hopes to add more optimizations - over time. + program. At the moment, this includes just simple constant + folding. -`-p[FILE]' -`--profile[=FILE]' +`-p'[FILE] +`--profile'[`='FILE] Enable profiling of `awk' programs (*note Profiling::). By default, profiles are created in a file named `awkprof.out'. The optional FILE argument allows you to specify a different file name for the profile file. No space is allowed between the `-p' and FILE, if FILE is supplied. - When run with `gawk', the profile is just a "pretty printed" - version of the program. When run with `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. `-P' `--posix' @@ -2363,7 +2670,7 @@ The following list describes options mandated by the POSIX standard: * Newlines are not allowed after `?' or `:' (*note Conditional Exp::). - * Specifying `-Ft' on the command-line does not set the value + * Specifying `-Ft' on the command line does not set the value of `FS' to be a single TAB character (*note Field Separators::). @@ -2371,20 +2678,15 @@ The following list describes options mandated by the POSIX standard: data (*note Locales::). If you supply both `--traditional' and `--posix' on the command - line, `--posix' takes precedence. `gawk' also issues a warning if - both options are supplied. + line, `--posix' takes precedence. `gawk' issues a warning if both + options are supplied. `-r' `--re-interval' Allow interval expressions (*note Regexp Operators::) in regexps. This is now `gawk''s default behavior. Nevertheless, this option - remains both for backward compatibility, and for use in - combination with the `--traditional' option. - -`-R FILE' -`--command=FILE' - `dgawk' only. Read `dgawk' debugger options and commands from - FILE. *Note Dgawk Info::, for more information. + remains (both for backward compatibility and for use in + combination with `--traditional'). `-S' `--sandbox' @@ -2420,44 +2722,43 @@ it is, `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 `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. (As mentioned in -*Note Definition Syntax::, function names must be unique.) +having to be included in each individual program. The `-i' option is +similar in this regard. (As mentioned in *note Definition Syntax::, +function names must be unique.) With standard `awk', library functions can still be used, even if -the program is entered at the terminal, by specifying `-f /dev/tty'. +the program is entered at the keyboard, by specifying `-f /dev/tty'. After typing your program, type `Ctrl-d' (the end-of-file character) to terminate it. (You may also use `-f -' to read program source from the -standard input but then you will not be able to also use the standard +standard 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 `awk' mechanisms to mix -source file and command-line `awk' programs, `gawk' provides the -`--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 (*note AWKPATH Variable::). The `--source' -option may also be used multiple times on the command line. - - If no `-f' or `--source' option is specified, then `gawk' uses the -first non-option command-line argument as the text of the program -source code. +source file and command-line `awk' programs, `gawk' provides the `-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 (*note AWKPATH Variable::). As with `-f', the `-e' and `-i' +options may also be used multiple times on the command line. + + If no `-f' or `-e' option is specified, then `gawk' uses the first +nonoption command-line argument as the text of the program source code. If the environment variable `POSIXLY_CORRECT' exists, then `gawk' -behaves in strict POSIX mode, exactly as if you had supplied the -`--posix' command-line option. Many GNU programs look for this -environment variable to suppress extensions that conflict with POSIX, -but `gawk' behaves differently: it suppresses all extensions, even -those that do not conflict with POSIX, and behaves in strict POSIX -mode. If `--lint' is supplied on the command line and `gawk' turns on -POSIX mode because of `POSIXLY_CORRECT', then it issues a warning -message indicating that POSIX mode is in effect. You would typically -set this variable in your shell's startup file. For a -Bourne-compatible shell (such as Bash), you would add these lines to -the `.profile' file in your home directory: +behaves in strict POSIX mode, exactly as if you had supplied `--posix'. +Many GNU programs look for this environment variable to suppress +extensions that conflict with POSIX, but `gawk' behaves differently: it +suppresses all extensions, even those that do not conflict with POSIX, +and behaves in strict POSIX mode. If `--lint' is supplied on the +command line and `gawk' turns on POSIX mode because of +`POSIXLY_CORRECT', then it issues a warning message indicating that +POSIX mode is in effect. You would typically set this variable in your +shell's startup file. For a Bourne-compatible shell (such as Bash), +you would add these lines to the `.profile' file in your home directory: POSIXLY_CORRECT=true export POSIXLY_CORRECT - For a C shell-compatible shell,(1) you would add this line to the + For a C shell-compatible shell,(2) you would add this line to the `.login' file in your home directory: setenv POSIXLY_CORRECT true @@ -2468,7 +2769,12 @@ environments. ---------- Footnotes ---------- - (1) Not recommended. + (1) For more detail, please see Section 4.4 of RFC 3875 +(http://www.ietf.org/rfc/rfc3875). Also see the explanatory note sent +to the `gawk' bug mailing list +(http://lists.gnu.org/archive/html/bug-gawk/2014-11/msg00022.html). + + (2) Not recommended. File: gawk.info, Node: Other Arguments, Next: Naming Standard Input, Prev: Options, Up: Invoking Gawk @@ -2479,15 +2785,22 @@ File: gawk.info, Node: Other Arguments, Next: Naming Standard Input, Prev: Op 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 `VAR=VALUE', assigns the value VALUE to the -variable VAR--it does not specify a file at all. (See *Note Assignment -Options::.) +variable VAR--it does not specify a file at all. (See *note Assignment +Options::.) In the following example, COUNT=1 is a variable assignment, +not a file name: - All these arguments are made available to your `awk' program in the -`ARGV' array (*note Built-in Variables::). Command-line options and -the program text (if present) are omitted from `ARGV'. All other -arguments, including variable assignments, are included. As each -element of `ARGV' is processed, `gawk' sets the variable `ARGIND' to -the index in `ARGV' of the current element. + awk -f program.awk file1 count=1 file2 + + All the command-line arguments are made available to your `awk' +program in the `ARGV' array (*note Built-in Variables::). Command-line +options and the program text (if present) are omitted from `ARGV'. All +other arguments, including variable assignments, are included. As +each element of `ARGV' is processed, `gawk' sets `ARGIND' to the index +in `ARGV' of the current element. + + Changing `ARGC' and `ARGV' in your `awk' program lets you control +how `awk' processes the input files; this is described in more detail +in *note ARGC and ARGV::. The distinction between file name arguments and variable-assignment arguments is made when `awk' is about to open the next input file. At @@ -2504,18 +2817,18 @@ begins scanning the argument list. The variable values given on the command line are processed for escape sequences (*note Escape Sequences::). (d.c.) - In some earlier implementations of `awk', when a variable assignment -occurred before any file names, the assignment would happen _before_ -the `BEGIN' rule was executed. `awk''s behavior was thus inconsistent; -some command-line assignments were available inside the `BEGIN' rule, -while others were not. Unfortunately, some applications came to depend -upon this "feature." When `awk' was changed to be more consistent, the -`-v' option was added to accommodate applications that depended upon -the old behavior. + In some very early implementations of `awk', when a variable +assignment occurred before any file names, the assignment would happen +_before_ the `BEGIN' rule was executed. `awk''s behavior was thus +inconsistent; some command-line assignments were available inside the +`BEGIN' rule, while others were not. Unfortunately, some applications +came to depend upon this "feature." When `awk' was changed to be more +consistent, the `-v' option was added to accommodate applications that +depended upon the old behavior. The variable assignment feature is most useful for assigning to variables such as `RS', `OFS', and `ORS', which control input and -output formats before scanning the data files. It is also useful for +output formats, before scanning the data files. It is also useful for controlling state if multiple passes are needed over a data file. For example: @@ -2550,7 +2863,7 @@ with `getline' (*note Getline/File::). In addition, `gawk' allows you to specify the special file name `/dev/stdin', both on the command line and with `getline'. Some other versions of `awk' also support this, but it is not standard. (Some -operating systems provide a `/dev/stdin' file in the file system, +operating systems provide a `/dev/stdin' file in the filesystem; however, `gawk' always processes this file name itself.) @@ -2565,102 +2878,157 @@ A number of environment variables influence how `gawk' behaves. * AWKPATH Variable:: Searching directories for `awk' programs. +* AWKLIBPATH Variable:: Searching directories for `awk' shared + libraries. * Other Environment Variables:: The environment variables. -File: gawk.info, Node: AWKPATH Variable, Next: Other Environment Variables, Up: Environment Variables +File: gawk.info, Node: AWKPATH Variable, Next: AWKLIBPATH Variable, Up: Environment Variables 2.5.1 The `AWKPATH' Environment Variable ---------------------------------------- The previous minor node described how `awk' program files can be named -on the command-line with the `-f' option. In most `awk' -implementations, you must supply a precise path name for each program -file, unless the file is in the current directory. But in `gawk', if -the file name supplied to the `-f' option does not contain a `/', then -`gawk' searches a list of directories (called the "search path"), one -by one, looking for a file with the specified name. +on the command line with the `-f' option. In most `awk' +implementations, you must supply a precise pathname for each program +file, unless the file is in the current directory. But with `gawk', if +the file name supplied to the `-f' or `-i' options does not contain a +directory separator `/', then `gawk' searches a list of directories +(called the "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. `gawk' gets its search path from the `AWKPATH' environment -variable. If that variable does not exist, `gawk' uses a default path, -`.:/usr/local/share/awk'.(1) - - The search path feature is particularly useful for building libraries -of useful `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 file name. Otherwise, the full file name -would have to be typed for each file. - - By using both the `--source' and `-f' options, your command-line -`awk' programs can use facilities in `awk' library files (*note Library -Functions::). Path searching is not done if `gawk' is in compatibility -mode. This is true for both `--traditional' and `--posix'. *Note -Options::. +colons.(1) `gawk' gets its search path from the `AWKPATH' environment +variable. If that variable does not exist, or if it has an empty value, +`gawk' uses a default path (described shortly). + + The search path feature is particularly helpful for building +libraries of useful `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 file name. Otherwise, you would have to type +the full file name for each file. + + By using the `-i' or `-f' options, your command-line `awk' programs +can use facilities in `awk' library files (*note Library Functions::). +Path searching is not done if `gawk' is in compatibility mode. This is +true for both `--traditional' and `--posix'. *Note Options::. + + If the source code file is not found after the initial search, the +path is searched again after adding the suffix `.awk' to the file name. + + `gawk''s path search mechanism is similar to the shell's. (See `The +Bourne-Again SHell manual' (http://www.gnu.org/software/bash/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 [`::'].) NOTE: To include the current directory in the path, either place - `.' 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 (`::').) This - path search mechanism is similar to the shell's. - - However, `gawk' always looks in the current directory _before_ - searching `AWKPATH', so there is no real reason to include the - current directory in the search path. - - If `AWKPATH' is not defined in the environment, `gawk' places its -default search path into `ENVIRON["AWKPATH"]'. This makes it easy to -determine the actual search path that `gawk' will use from within an -`awk' program. + `.' as an entry in the path or write a null entry in the path. - While you can change `ENVIRON["AWKPATH"]' within your `awk' program, -this has no effect on the running program's behavior. This makes -sense: the `AWKPATH' environment variable is used to find the program -source files. Once your program is running, all the files have been -found, and `gawk' no longer needs to use `AWKPATH'. + Different past versions of `gawk' would also look explicitly in + the current directory, either before or after the path search. As + of version 4.1.2, this no longer happens; if you wish to look in + the current directory, you must include `.' either as a separate + entry or as a null entry in the search path. + + The default value for `AWKPATH' is `.:/usr/local/share/awk'.(2) +Since `.' is included at the beginning, `gawk' searches first in the +current directory and then in `/usr/local/share/awk'. In practice, +this means that you will rarely need to change the value of `AWKPATH'. + + *Note Shell Startup Files::, for information on functions that help +to manipulate the `AWKPATH' variable. + + `gawk' places the value of the search path that it used into +`ENVIRON["AWKPATH"]'. This provides access to the actual search path +value from within an `awk' program. + + Although you can change `ENVIRON["AWKPATH"]' within your `awk' +program, this has no effect on the running program's behavior. This +makes sense: the `AWKPATH' environment variable is used to find the +program source files. Once your program is running, all the files have +been found, and `gawk' no longer needs to use `AWKPATH'. ---------- Footnotes ---------- - (1) Your version of `gawk' may use a different directory; it will + (1) Semicolons on MS-Windows and MS-DOS. + + (2) Your version of `gawk' may use a different directory; it will depend upon how `gawk' was built and installed. The actual directory is the value of `$(datadir)' generated when `gawk' was configured. You probably don't need to worry about this, though. -File: gawk.info, Node: Other Environment Variables, Prev: AWKPATH Variable, Up: Environment Variables +File: gawk.info, Node: AWKLIBPATH Variable, Next: Other Environment Variables, Prev: AWKPATH Variable, Up: Environment Variables -2.5.2 Other Environment Variables +2.5.2 The `AWKLIBPATH' Environment Variable +------------------------------------------- + +The `AWKLIBPATH' environment variable is similar to the `AWKPATH' +variable, but it is used to search for loadable extensions (stored as +system shared libraries) specified with the `-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 `.so' is used. +The search path specified is also used for extensions loaded via the +`@load' keyword (*note Loading Shared Libraries::). + + If `AWKLIBPATH' does not exist in the environment, or if it has an +empty value, `gawk' uses a default path; this is typically +`/usr/local/lib/gawk', although it can vary depending upon how `gawk' +was built. + + *Note Shell Startup Files::, for information on functions that help +to manipulate the `AWKLIBPATH' variable. + + `gawk' places the value of the search path that it used into +`ENVIRON["AWKLIBPATH"]'. This provides access to the actual search path +value from within an `awk' program. + + +File: gawk.info, Node: Other Environment Variables, Prev: AWKLIBPATH Variable, Up: Environment Variables + +2.5.3 Other Environment Variables --------------------------------- A number of other environment variables affect `gawk''s behavior, but they are more specialized. Those in the following list are meant to be -used by regular users. +used by regular users: -`POSIXLY_CORRECT' - Causes `gawk' to switch POSIX compatibility mode, disabling all - traditional and GNU extensions. *Note Options::. +`GAWK_MSEC_SLEEP' + Specifies the interval between connection retries, in + milliseconds. On systems that do not support the `usleep()' system + call, the value is rounded up to an integral number of seconds. + +`GAWK_READ_TIMEOUT' + Specifies the time, in milliseconds, for `gawk' to wait for input + before returning with an error. *Note Read Timeout::. `GAWK_SOCK_RETRIES' - Controls the number of time `gawk' will attempt to retry a two-way + Controls the number of times `gawk' attempts to retry a two-way TCP/IP (socket) connection before giving up. *Note TCP/IP Networking::. -`GAWK_MSEC_SLEEP' - Specifies the interval between connection retries, in - milliseconds. On systems that do not support the `usleep()' system - call, the value is rounded up to an integral number of seconds. +`POSIXLY_CORRECT' + Causes `gawk' to switch to POSIX-compatibility mode, disabling all + traditional and GNU extensions. *Note Options::. The environment variables in the following list are meant for use by the `gawk' developers for testing and tuning. They are subject to change. The variables are: -`AVG_CHAIN_MAX' - The average number of items `gawk' will maintain on a hash chain - for managing arrays. +`AWKBUFSIZE' + This variable only affects `gawk' on POSIX-compliant systems. + With a value of `exact', `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 `gawk' uses that number as the + size of the buffer to allocate. (When this variable is not set, + `gawk' uses the smaller of the file's size and the "default" + blocksize, which is usually the filesystem's I/O blocksize.) `AWK_HASH' - If this variable exists with a value of `gst', `gawk' will switch - to using the hash function from GNU Smalltalk for managing arrays. + If this variable exists with a value of `gst', `gawk' switches to + using the hash function from GNU Smalltalk for managing arrays. This function may be marginally faster than the standard function. `AWKREADFUNC' @@ -2669,6 +3037,13 @@ change. The variables are: debugging problems on filesystems on non-POSIX operating systems where I/O is performed in records, not in blocks. +`GAWK_MSG_SRC' + If this variable exists, `gawk' includes the file name and line + number within the `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. + `GAWK_NO_DFA' If this variable exists, `gawk' does not use the DFA regexp matcher for "does it match" kinds of tests. This can cause `gawk' to be @@ -2681,9 +3056,17 @@ change. The variables are: This specifies the amount by which `gawk' should grow its internal evaluation stack, when needed. +`INT_CHAIN_MAX' + This specifies intended maximum number of items `gawk' will + maintain on a hash chain for managing arrays indexed by integers. + +`STR_CHAIN_MAX' + This specifies intended maximum number of items `gawk' will + maintain on a hash chain for managing arrays indexed by strings. + `TIDYMEM' If this variable exists, `gawk' uses the `mtrace()' library calls - from GNU LIBC to help track down possible memory leaks. + from the GNU C library to help track down possible memory leaks. File: gawk.info, Node: Exit Status, Next: Include Files, Prev: Environment Variables, Up: Invoking Gawk @@ -2700,13 +3083,13 @@ with the value of the C constant `EXIT_SUCCESS'. This is usually zero. If an error occurs, `gawk' exits with the value of the C constant `EXIT_FAILURE'. This is usually one. - If `gawk' exits because of a fatal error, the exit status is 2. On -non-POSIX systems, this value may be mapped to `EXIT_FAILURE'. + If `gawk' exits because of a fatal error, the exit status is two. +On non-POSIX systems, this value may be mapped to `EXIT_FAILURE'. -File: gawk.info, Node: Include Files, Next: Obsolete, Prev: Exit Status, Up: Invoking Gawk +File: gawk.info, Node: Include Files, Next: Loading Shared Libraries, Prev: Exit Status, Up: Invoking Gawk -2.7 Including Other Files Into Your Program +2.7 Including Other Files into Your Program =========================================== This minor node describes a feature that is specific to `gawk'. @@ -2715,10 +3098,11 @@ This minor node describes a feature that is specific to `gawk'. files. This gives you the ability to split large `awk' source files into smaller, more manageable pieces, and also lets you reuse common `awk' code from various `awk' scripts. In other words, you can group -together `awk' functions, used to carry out specific tasks, into -external files. These files can be used just like function libraries, -using the `@include' keyword in conjunction with the `AWKPATH' -environment variable. +together `awk' functions used to carry out specific tasks into external +files. These files can be used just like function libraries, using the +`@include' keyword in conjunction with the `AWKPATH' environment +variable. Note that source files may also be included using the `-i' +option. Let's see an example. We'll start with two (trivial) `awk' scripts, namely `test1' and `test2'. Here is the `test1' script: @@ -2737,17 +3121,17 @@ and here is `test2': Running `gawk' with `test2' produces the following result: $ gawk -f test2 - -| This is file test1. - -| This is file test2. + -| This is script test1. + -| This is script test2. - `gawk' runs the `test2' script which includes `test1' using the -`@include' keyword. So, to include external `awk' source files you just -use `@include' followed by the name of the file to be included, + `gawk' runs the `test2' script, which includes `test1' using the +`@include' keyword. So, to include external `awk' source files, you +just use `@include' followed by the name of the file to be included, enclosed in double quotes. NOTE: Keep in mind that this is a language construct and the file name cannot be a string variable, but rather just a literal string - in double quotes. + constant in double quotes. The files to be included may be nested; e.g., given a third script, namely `test3': @@ -2760,31 +3144,31 @@ namely `test3': Running `gawk' with the `test3' script produces the following results: $ gawk -f test3 - -| This is file test1. - -| This is file test2. - -| This is file test3. + -| This is script test1. + -| This is script test2. + -| This is script test3. The file name can, of course, be a pathname. For example: @include "../io_funcs" -or: +and: @include "/usr/awklib/network" -are valid. The `AWKPATH' environment variable can be of great value -when using `@include'. The same rules for the use of the `AWKPATH' -variable in command-line file searches (*note AWKPATH Variable::) apply -to `@include' also. +are both valid. The `AWKPATH' environment variable can be of great +value when using `@include'. The same rules for the use of the +`AWKPATH' variable in command-line file searches (*note AWKPATH +Variable::) apply to `@include' also. This is very helpful in constructing `gawk' function libraries. If -you have a large script with useful, general purpose `awk' functions, +you have a large script with useful, general-purpose `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 `AWKPATH' +special directory. You can then include those "libraries," either by +using the full pathnames of the files, or by setting the `AWKPATH' environment variable accordingly and then using `@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 +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. @@ -2795,38 +3179,116 @@ reducing the need for writing complex and tedious command lines. In particular, `@include' is very useful for writing CGI scripts to be run from web pages. - As mentioned in *Note AWKPATH Variable::, the current directory is -always searched first for source files, before searching in `AWKPATH', -and this also applies to files named with `@include'. + As mentioned in *note AWKPATH Variable::, the current directory is +always searched first for source files, before searching in `AWKPATH'; +this also applies to files named with `@include'. + + +File: gawk.info, Node: Loading Shared Libraries, Next: Obsolete, Prev: Include Files, Up: Invoking Gawk + +2.8 Loading Dynamic Extensions into Your Program +================================================ + +This minor node describes a feature that is specific to `gawk'. + + The `@load' keyword can be used to read external `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 `awk' language. +The `AWKLIBPATH' variable is used to search for the extension. Using +`@load' is completely equivalent to using the `-l' command-line option. + + If the extension is not initially found in `AWKLIBPATH', another +search is conducted after appending the platform's default shared +library suffix to the file name. For example, on GNU/Linux systems, +the suffix `.so' is used: + + $ gawk '@load "ordchr"; BEGIN {print chr(65)}' + -| A + +This is equivalent to the following example: + + $ gawk -lordchr 'BEGIN {print chr(65)}' + -| A + +For command-line usage, the `-l' option is more convenient, but `@load' +is useful for embedding inside an `awk' source file that requires +access to an extension. + + *note Dynamic Extensions::, describes how to write extensions (in C +or C++) that can be loaded with either `@load' or the `-l' option. It +also describes the `ordchr' extension. -File: gawk.info, Node: Obsolete, Next: Undocumented, Prev: Include Files, Up: Invoking Gawk +File: gawk.info, Node: Obsolete, Next: Undocumented, Prev: Loading Shared Libraries, Up: Invoking Gawk -2.8 Obsolete Options and/or Features +2.9 Obsolete Options and/or Features ==================================== This minor node describes features and/or command-line options from -previous releases of `gawk' that are either not available in the -current version or that are still supported but deprecated (meaning that +previous releases of `gawk' that either are not available in the +current version or are still supported but deprecated (meaning that they will _not_ be in the next release). The process-related special files `/dev/pid', `/dev/ppid', `/dev/pgrpid', and `/dev/user' were deprecated in `gawk' 3.1, but still worked. As of version 4.0, they are no longer interpreted specially by -`gawk'. (Use `PROCINFO' instead; see *Note Auto-set::.) +`gawk'. (Use `PROCINFO' instead; see *note Auto-set::.) -File: gawk.info, Node: Undocumented, Prev: Obsolete, Up: Invoking Gawk +File: gawk.info, Node: Undocumented, Next: Invoking Summary, Prev: Obsolete, Up: Invoking Gawk -2.9 Undocumented Options and Features -===================================== +2.10 Undocumented Options and Features +====================================== - Use the Source, Luke! - Obi-Wan + Use the Source, Luke! -- Obi-Wan This minor node intentionally left blank. +File: gawk.info, Node: Invoking Summary, Prev: Undocumented, Up: Invoking Gawk + +2.11 Summary +============ + + * Use either `awk 'PROGRAM' FILES' or `awk -f PROGRAM-FILE FILES' to + run `awk'. + + * The three standard options for all versions of `awk' are `-f', + `-F', and `-v'. `gawk' supplies these and many others, as well as + corresponding GNU-style long options. + + * Nonoption command-line arguments are usually treated as file names, + unless they have the form `VAR=VALUE', in which case they are + taken as variable assignments to be performed at that point in + processing the input. + + * All nonoption command-line arguments, excluding the program text, + are placed in the `ARGV' array. Adjusting `ARGC' and `ARGV' + affects how `awk' processes input. + + * You can use a single minus sign (`-') to refer to standard input + on the command line. `gawk' also lets you use the special file + name `/dev/stdin'. + + * `gawk' pays attention to a number of environment variables. + `AWKPATH', `AWKLIBPATH', and `POSIXLY_CORRECT' are the most + important ones. + + * `gawk''s exit status conveys information to the program that + invoked it. Use the `exit' statement from within an `awk' program + to set the exit status. + + * `gawk' allows you to include other `awk' source files into your + program using the `@include' statement and/or the `-i' and `-f' + command-line options. + + * `gawk' allows you to load additional functions written in C or C++ + using the `@load' statement and/or the `-l' option. (This + advanced feature is described later, in *note Dynamic + Extensions::.) + + File: gawk.info, Node: Regexp, Next: Reading Files, Prev: Invoking Gawk, Up: Top 3 Regular Expressions @@ -2840,8 +3302,8 @@ strings. Because regular expressions are such a fundamental part of 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 `foo' matches any string containing `foo'. Therefore, the -pattern `/foo/' matches any input record containing the three +the regexp `foo' matches any string containing `foo'. Thus, the +pattern `/foo/' matches any input record containing the three adjacent characters `foo' _anywhere_ in the record. Other kinds of regexps let you specify more complicated classes of strings. @@ -2851,10 +3313,11 @@ you specify more complicated classes of strings. * Escape Sequences:: How to write nonprinting characters. * Regexp Operators:: Regular Expression Operators. * Bracket Expressions:: What can go between `[...]'. -* 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. File: gawk.info, Node: Regexp Usage, Next: Escape Sequences, Up: Regexp @@ -2866,27 +3329,27 @@ 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 `foo' anywhere in -it: +second field of each record where the string `li' appears anywhere in +the record: - $ awk '/foo/ { print $2 }' BBS-list - -| 555-1234 + $ awk '/li/ { print $2 }' mail-list + -| 555-5553 + -| 555-0542 -| 555-6699 - -| 555-6480 - -| 555-2127 + -| 555-3430 Regular expressions can also be used in matching expressions. These expressions allow you to specify the string to match against; it need not be the entire current input record. The two operators `~' and `!~' perform regular expression comparisons. Expressions using these operators can be used as patterns, or in `if', `while', `for', and `do' -statements. (*Note Statements::.) For example: +statements. (*Note Statements::.) For example, the following is true +if the expression EXP (taken as a string) matches REGEXP: EXP ~ /REGEXP/ -is true if the expression EXP (taken as a string) matches REGEXP. The -following example matches, or selects, all input records with the -uppercase letter `J' somewhere in the first field: +This example matches, or selects, all input records with the uppercase +letter `J' somewhere in the first field: $ awk '$1 ~ /J/' inventory-shipped -| Jan 13 25 15 115 @@ -2940,20 +3403,20 @@ string or regexp. Thus, the string whose contents are the two characters `"' and `\' must be written `"\"\\"'. Other escape sequences represent unprintable characters such as TAB -or newline. While there is nothing to stop you from entering most +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 all the escape sequences used in `awk' and -what they represent. Unless noted otherwise, all these escape sequences -apply to both string constants and regexp constants: + The following list presents all the escape sequences used in `awk' +and what they represent. Unless noted otherwise, all these escape +sequences apply to both string constants and regexp constants: `\\' A literal backslash, `\'. `\a' - The "alert" character, `Ctrl-g', ASCII code 7 (BEL). (This - usually makes some sort of audible noise.) + The "alert" character, `Ctrl-g', ASCII code 7 (BEL). (This often + makes some sort of audible noise.) `\b' Backspace, `Ctrl-h', ASCII code 8 (BS). @@ -2971,7 +3434,7 @@ apply to both string constants and regexp constants: Horizontal TAB, `Ctrl-i', ASCII code 9 (HT). `\v' - Vertical tab, `Ctrl-k', ASCII code 11 (VT). + Vertical TAB, `Ctrl-k', ASCII code 11 (VT). `\NNN' The octal value NNN, where NNN stands for 1 to 3 digits between @@ -2980,77 +3443,84 @@ apply to both string constants and regexp constants: `\xHH...' The hexadecimal value HH, where HH stands for a sequence of - hexadecimal digits (`0'-`9', and either `A'-`F' or `a'-`f'). Like - the same construct in ISO C, the escape sequence continues until - the first nonhexadecimal digit is seen. (c.e.) However, using - more than two hexadecimal digits produces undefined results. (The - `\x' escape sequence is not allowed in POSIX `awk'.) + hexadecimal digits (`0'-`9', and either `A'-`F' or `a'-`f'). A + maximum of two digts are allowed after the `\x'. Any further + hexadecimal digits are treated as simple letters or numbers. + (c.e.) (The `\x' escape sequence is not allowed in POSIX awk.) + + CAUTION: In ISO C, the escape sequence continues until the + first nonhexadecimal digit is seen. For many years, `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 version *FIXME:* + 4.3.0, only two digits are processed. `\/' 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, in order to + contains a slash (such as `/.*:\/home\/[[:alnum:]]+:.*/'; the + `[[:alnum:]]' notation is discussed in *note 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 `awk' to keep processing the rest of the regexp. `\"' 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, in order to tell `awk' to keep processing the rest of the - string. + that contains a double quote (such as `"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 + `awk' to keep processing the rest of the string. In `gawk', a number of additional two-character sequences that begin with a backslash have special meaning in regexps. *Note GNU Regexp Operators::. In a regexp, a backslash before any character that is not in the -previous list and not listed in *Note GNU Regexp Operators::, means +previous list and not listed in *note GNU Regexp Operators::, means that the next character should be taken literally, even if it would normally be a regexp operator. For example, `/a\+b/' matches the three characters `a+b'. For complete portability, do not use a backslash before any -character not shown in the previous list. +character not shown in the previous list or that is not an operator. - To summarize: - - * 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 `awk' reads your program. - - * `gawk' processes both regexp constants and dynamic regexps (*note - Computed Regexps::), for the special operators listed in *Note GNU - Regexp Operators::. + Backslash Before Regular Characters - * A backslash before any other character means to treat that - character literally. - -Advanced Notes: Backslash Before Regular Characters ---------------------------------------------------- - -If you place a backslash in a string constant before something that is -not one of the characters previously listed, POSIX `awk' purposely + If you place a backslash in a string constant before something that +is not one of the characters previously listed, POSIX `awk' purposely leaves what happens as undefined. There are two choices: Strip the backslash out - This is what Brian Kernighan's `awk' and `gawk' both do. For - example, `"a\qc"' is the same as `"aqc"'. (Because this is such - an easy bug both to introduce and to miss, `gawk' warns you about - it.) Consider `FS = "[ \t]+\|[ \t]+"' to use vertical bars - surrounded by whitespace as the field separator. There should be - two backslashes in the string: `FS = "[ \t]+\\|[ \t]+"'.) + This is what BWK `awk' and `gawk' both do. For example, `"a\qc"' + is the same as `"aqc"'. (Because this is such an easy bug both to + introduce and to miss, `gawk' warns you about it.) Consider `FS = + "[ \t]+\|[ \t]+"' to use vertical bars surrounded by whitespace as + the field separator. There should be two backslashes in the + string: `FS = "[ \t]+\\|[ \t]+"'.) Leave the backslash alone Some other `awk' implementations do this. In such implementations, typing `"a\qc"' is the same as typing `"a\\qc"'. -Advanced Notes: Escape Sequences for Metacharacters ---------------------------------------------------- + To summarize: + + * 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 `awk' reads your program. + + * `gawk' processes both regexp constants and dynamic regexps (*note + Computed Regexps::), for the special operators listed in *note GNU + Regexp Operators::. + + * A backslash before any other character means to treat that + character literally. + + Escape Sequences for Metacharacters -Suppose you use an octal or hexadecimal escape to represent a regexp -metacharacter. (See *Note Regexp Operators::.) Does `awk' treat the + Suppose you use an octal or hexadecimal escape to represent a regexp +metacharacter. (See *note Regexp Operators::.) Does `awk' treat the character as a literal character or as a regexp operator? Historically, such characters were taken literally. (d.c.) @@ -3070,40 +3540,41 @@ You can combine regular expressions with special characters, called "regular expression operators" or "metacharacters", to increase the power and versatility of regular expressions. - The escape sequences described in *Note Escape Sequences::, are + The escape sequences described in *note Escape Sequences::, are valid inside a regexp. They are introduced by a `\' 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: `\' - This is used to suppress the special meaning of a character when - matching. For example, `\$' matches the character `$'. + This suppresses the special meaning of a character when matching. + For example, `\$' matches the character `$'. `^' - This matches the beginning of a string. For example, `^@chapter' - matches `@chapter' at the beginning of a string and can be used to - identify chapter beginnings in Texinfo source files. The `^' is - known as an "anchor", because it anchors the pattern to match only - at the beginning of the string. + This matches the beginning of a string. `^@chapter' matches + `@chapter' at the beginning of a string, for example, and can be + used to identify chapter beginnings in Texinfo source files. The + `^' is known as an "anchor", because it anchors the pattern to + match only at the beginning of the string. It is important to realize that `^' does not match the beginning of - a line embedded in a string. The condition is not true in the - following example: + a line (the point right after a `\n' newline character) embedded + in a string. The condition is not true in the following example: if ("line1\nLINE 2" ~ /^L/) ... `$' This is similar to `^', but it matches only at the end of a string. For example, `p$' matches a record that ends with a `p'. The `$' - is an anchor and does not match the end of a line embedded in a - string. The condition in the following example is not true: + is an anchor and does not match the end of a line (the point right + before a `\n' newline character) embedded in a string. The + condition in the following example is not true: if ("line1\nLINE 2" ~ /1$/) ... -`. (period)' +`.' (period) This matches any single character, _including_ the newline character. For example, `.P' matches any single character followed by a `P' in a string. Using concatenation, we can make a @@ -3115,15 +3586,15 @@ sequences and that are not listed in the table stand for themselves: Otherwise, NUL is just another character. Other versions of `awk' may not be able to match the NUL character. -`[...]' +`['...`]' This is called a "bracket expression".(1) It matches any _one_ of the characters that are enclosed in the square brackets. For example, `[MVX]' matches any one of the characters `M', `V', or `X' in a string. A full discussion of what can be inside the - square brackets of a bracket expression is given in *Note Bracket + square brackets of a bracket expression is given in *note Bracket Expressions::. -`[^ ...]' +`[^'...`]' This is a "complemented bracket expression". The first character after the `[' _must_ be a `^'. It matches any characters _except_ those in the square brackets. For example, `[^awk]' matches any @@ -3132,14 +3603,15 @@ sequences and that are not listed in the table stand for themselves: `|' This is the "alternation operator" and it is used to specify alternatives. The `|' has the lowest precedence of all the regular - expression operators. For example, `^P|[[:digit:]]' matches any - string that matches either `^P' or `[[:digit:]]'. This means it - matches any string that starts with `P' or contains a digit. + expression operators. For example, `^P|[aeiouy]' matches any + string that matches either `^P' or `[aeiouy]'. This means it + matches any string that starts with `P' or contains (anywhere + within it) a lowercase English vowel. The alternation applies to the largest possible regexps on either side. -`(...)' +`('...`)' Parentheses are used for grouping in regular expressions, as in arithmetic. They can be used to concatenate regular expressions containing the alternation operator, `|'. For example, @@ -3154,31 +3626,29 @@ sequences and that are not listed in the table stand for themselves: matches of one `p' followed by any number of `h's. This also matches just `p' if no `h's are present. - The `*' repeats the _smallest_ possible preceding expression. - (Use parentheses if you want to repeat a larger expression.) It - finds as many repetitions as possible. For example, `awk - '/\(c[ad][ad]*r x\)/ { print }' sample' prints every record in - `sample' containing a string of the form `(car x)', `(cdr x)', - `(cadr x)', and so on. Notice the escaping of the parentheses by - preceding them with backslashes. + There are two subtle points to understand about how `*' works. + First, the `*' applies only to the single preceding regular + expression component (e.g., in `ph*', it applies just to the `h'). + To cause `*' to apply to a larger subexpression, use parentheses: + `(ph)*' matches `ph', `phph', `phphph', and so on. + + Second, `*' finds as many repetitions as possible. If the text to + be matched is `phhhhhhhhhhhhhhooey', `ph*' matches all of the `h's. `+' This symbol is similar to `*', except that the preceding expression must be matched at least once. This means that `wh+y' would match `why' and `whhy', but not `wy', whereas `wh*y' would - match all three of these strings. The following is a simpler way - of writing the last `*' example: - - awk '/\(c[ad]+r x\)/ { print }' sample + match all three. `?' This symbol is similar to `*', except that the preceding expression can be matched either once or not at all. For example, `fe?d' matches `fed' and `fd', but nothing else. -`{N}' -`{N,}' -`{N,M}' +`{'N`}' +`{'N`,}' +`{'N`,'M`}' One or two numbers inside braces denote an "interval expression". If there is one number in the braces, the preceding regexp is repeated N times. If there are two numbers separated by a comma, @@ -3190,10 +3660,10 @@ sequences and that are not listed in the table stand for themselves: Matches `whhhy', but not `why' or `whhhhy'. `wh{3,5}y' - Matches `whhhy', `whhhhy', or `whhhhhy', only. + Matches `whhhy', `whhhhy', or `whhhhhy' only. `wh{2,}y' - Matches `whhy' or `whhhy', and so on. + Matches `whhy', `whhhy', and so on. Interval expressions were not traditionally available in `awk'. They were added as part of the POSIX standard to make `awk' and @@ -3212,6 +3682,10 @@ sequences and that are not listed in the table stand for themselves: constants are valid and work the way you want them to, using any version of `awk'.(2) + Finally, when `{' and `}' appear in regexp constants in a way that + cannot be interpreted as an interval expression (such as + `/q{a}/'), then they stand for themselves. + In regular expressions, the `*', `+', and `?' operators, as well as the braces `{' and `}', have the highest precedence, followed by concatenation, and finally by `|'. As in arithmetic, parentheses can @@ -3235,19 +3709,19 @@ list". regexp operator or function. -File: gawk.info, Node: Bracket Expressions, Next: GNU Regexp Operators, Prev: Regexp Operators, Up: Regexp +File: gawk.info, Node: Bracket Expressions, Next: Leftmost Longest, Prev: Regexp Operators, Up: Regexp 3.4 Using Bracket Expressions ============================= -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 "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, `[0-9]' is equivalent to `[0123456789]'. -(See *Note Ranges and Locales::, for an explanation of how the POSIX +(See *note Ranges and Locales::, for an explanation of how the POSIX standard and `gawk' have changed over time. This is mainly of historical interest.) @@ -3256,10 +3730,12 @@ expression, put a `\' in front of it. For example: [d\]] -matches either `d' or `]'. +matches either `d' or `]'. Additionally, if you place `]' right after +the opening `[', the closing bracket is treated as one of the +characters to be matched. - This treatment of `\' in bracket expressions is compatible with -other `awk' implementations and is also mandated by POSIX. The regular + The treatment of `\' in bracket expressions is compatible with other +`awk' implementations and is also mandated by POSIX. The regular expressions in `awk' are a superset of the POSIX specification for Extended Regular Expressions (EREs). POSIX EREs are based on the regular expressions accepted by the traditional `egrep' utility. @@ -3273,29 +3749,29 @@ differs between the United States and France. A character class is only valid in a regexp _inside_ the brackets of a bracket expression. Character classes consist of `[:', a keyword -denoting the class, and `:]'. *Note table-char-classes:: lists the +denoting the class, and `:]'. *note table-char-classes:: lists the character classes defined by the POSIX standard. Class Meaning -------------------------------------------------------------------------- -`[:alnum:]' Alphanumeric characters. -`[:alpha:]' Alphabetic characters. -`[:blank:]' Space and TAB characters. -`[:cntrl:]' Control characters. -`[:digit:]' Numeric characters. -`[:graph:]' Characters that are both printable and visible. (A space is - printable but not visible, whereas an `a' is both.) -`[:lower:]' Lowercase alphabetic characters. +`[:alnum:]' Alphanumeric characters +`[:alpha:]' Alphabetic characters +`[:blank:]' Space and TAB characters +`[:cntrl:]' Control characters +`[:digit:]' Numeric characters +`[:graph:]' Characters that are both printable and visible (a space is + printable but not visible, whereas an `a' is both) +`[:lower:]' Lowercase alphabetic characters `[:print:]' Printable characters (characters that are not control - characters). + characters) `[:punct:]' Punctuation characters (characters that are not letters, - digits, control characters, or space characters). + digits, control characters, or space characters) `[:space:]' Space characters (such as space, TAB, and formfeed, to name - a few). -`[:upper:]' Uppercase alphabetic characters. -`[:xdigit:]'Characters that are hexadecimal digits. + a few) +`[:upper:]' Uppercase alphabetic characters +`[:xdigit:]'Characters that are hexadecimal digits -Table 3.1: POSIX Character Classes +Table 3.1: POSIX character classes For example, before the POSIX standard, you had to write `/[A-Za-z0-9]/' to match alphanumeric characters. If your character @@ -3303,6 +3779,14 @@ set had other alphabetic characters in it, this would not match them. With the POSIX character classes, you can write `/[[:alnum:]]/' to match the alphabetic and numeric characters in your character set. + Some utilities that match regular expressions provide a nonstandard +`[:ascii:]' character class; `awk' does not. However, you can simulate +such a construct using `[\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 +(`[^\x00-\x7F]') to match any single-byte characters that are not in +the ASCII range. + Two additional special sequences can appear in bracket expressions. These apply to non-ASCII character sets, which can have single symbols (called "collating elements") that are represented with more than one @@ -3330,9 +3814,119 @@ Equivalence classes classes. -File: gawk.info, Node: GNU Regexp Operators, Next: Case-sensitivity, Prev: Bracket Expressions, Up: Regexp +File: gawk.info, Node: Leftmost Longest, Next: Computed Regexps, Prev: Bracket Expressions, Up: Regexp + +3.5 How Much Text Matches? +========================== + +Consider the following: + + echo aaaabcd | awk '{ sub(/a+/, "<A>"); print }' + + This example uses the `sub()' function to make a change to the input +record. (`sub()' replaces the first instance of any text matched by +the first argument with the string provided as the second argument; +*note String Functions::). Here, the regexp `/a+/' indicates "one or +more `a' characters," and the replacement text is `<A>'. + + The input contains four `a' characters. `awk' (and POSIX) regular +expressions always match the leftmost, _longest_ sequence of input +characters that can match. Thus, all four `a' characters are replaced +with `<A>' in this example: + + $ echo aaaabcd | awk '{ sub(/a+/, "<A>"); print }' + -| <A>bcd + + For simple match/no-match tests, this is not so important. But when +doing text matching and substitutions with the `match()', `sub()', +`gsub()', and `gensub()' functions, it is very important. *Note String +Functions::, for more information on these functions. Understanding +this principle is also important for regexp-based record and field +splitting (*note Records::, and also *note Field Separators::). + + +File: gawk.info, Node: Computed Regexps, Next: GNU Regexp Operators, Prev: Leftmost Longest, Up: Regexp + +3.6 Using Dynamic Regexps +========================= + +The righthand side of a `~' or `!~' 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 "dynamic regexp" or a "computed +regexp": + + BEGIN { digits_regexp = "[[:digit:]]+" } + $0 ~ digits_regexp { print } + +This sets `digits_regexp' to a regexp that describes one or more digits, +and tests whether the input record matches this regexp. + + NOTE: When using the `~' and `!~' 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 _twice_: the first time when `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 + `digits_regexp', shown previously), not just string 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, `/\*/' is a regexp constant for a literal `*'. Only +one backslash is needed. To do the same thing with a string, you have +to type `"\\*"'. The first backslash escapes the second one so that +the string actually contains the two characters `\' and `*'. + + 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: + + * 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. + + * It is more efficient to use regexp constants. `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, `awk' must first convert the string into this internal + form and then perform the pattern matching. + + * Using regexp constants is better form; it shows clearly that you + intend a regexp match. + + Using `\n' in Bracket Expressions of Dynamic Regexps + + Some older versions of `awk' do not allow the newline character to +be used inside a bracket expression for a dynamic regexp: + + $ awk '$0 ~ "[ \t\n]"' + error--> awk: newline in character class [ + error--> ]... + error--> source line number 1 + error--> context is + error--> $0 ~ "[ >>> \t\n]" <<< + + But a newline in a regexp constant works with no problem: + + $ awk '$0 ~ /[ \t\n]/' + here is a sample line + -| here is a sample line + Ctrl-d + + `gawk' does not have this problem, and it isn't likely to occur +often in practice, but it's worth noting for future reference. + + +File: gawk.info, Node: GNU Regexp Operators, Next: Case-sensitivity, Prev: Computed Regexps, Up: Regexp -3.5 `gawk'-Specific Regexp Operators +3.7 `gawk'-Specific Regexp Operators ==================================== GNU software that deals with regular expressions provides a number of @@ -3378,9 +3972,9 @@ letters, digits, or underscores (`_'): not match `dirty rat'. `\B' is essentially the opposite of `\y'. There are two other operators that work on buffers. In Emacs, a -"buffer" is, naturally, an Emacs buffer. For other programs, `gawk''s -regexp library routines consider the entire string to match as the -buffer. The operators are: +"buffer" is, naturally, an Emacs buffer. Other GNU programs, including +`gawk', consider the entire string to match as the buffer. The +operators are: `\`' Matches the empty string at the beginning of a buffer (string). @@ -3404,21 +3998,20 @@ GNU `\b' appears to be the lesser of two evils. No options In the default case, `gawk' provides all the facilities of POSIX - regexps and the GNU regexp operators described in *Note Regexp + regexps and the GNU regexp operators described in *note Regexp Operators::. `--posix' - Only POSIX regexps are supported; the GNU operators are not special - (e.g., `\w' matches a literal `w'). Interval expressions are - allowed. + Match only POSIX regexps; the GNU operators are not special (e.g., + `\w' matches a literal `w'). Interval expressions are allowed. `--traditional' - Traditional Unix `awk' regexps are matched. The GNU operators are - not special, and interval expressions are not available. The - POSIX character classes (`[[:alnum:]]', etc.) are supported, as - Brian Kernighan's `awk' does support them. Characters described - by octal and hexadecimal escape sequences are treated literally, - even if they represent regexp metacharacters. + Match traditional Unix `awk' regexps. The GNU operators are not + special, and interval expressions are not available. Because BWK + `awk' supports them, the POSIX character classes (`[[:alnum:]]', + etc.) are available. Characters described by octal and + hexadecimal escape sequences are treated literally, even if they + represent regexp metacharacters. `--re-interval' Allow interval expressions in regexps, if `--traditional' has been @@ -3426,9 +4019,9 @@ No options default. -File: gawk.info, Node: Case-sensitivity, Next: Leftmost Longest, Prev: GNU Regexp Operators, Up: Regexp +File: gawk.info, Node: Case-sensitivity, Next: Regexp Summary, Prev: GNU Regexp Operators, Up: Regexp -3.6 Case Sensitivity in Matching +3.8 Case Sensitivity in Matching ================================ Case is normally significant in regular expressions, both when matching @@ -3454,10 +4047,11 @@ works in any POSIX-compliant `awk'. Another method, specific to `gawk', is to set the variable `IGNORECASE' to a nonzero value (*note Built-in Variables::). When `IGNORECASE' is not zero, _all_ regexp and string operations ignore -case. Changing the value of `IGNORECASE' dynamically controls the -case-sensitivity of the program as it runs. Case is significant by -default because `IGNORECASE' (like most variables) is initialized to -zero: +case. + + Changing the value of `IGNORECASE' dynamically controls the case +sensitivity of the program as it runs. Case is significant by default +because `IGNORECASE' (like most variables) is initialized to zero: x = "aB" if (x ~ /ab/) ... # this test will fail @@ -3465,20 +4059,17 @@ zero: IGNORECASE = 1 if (x ~ /ab/) ... # now it will succeed - In general, you cannot use `IGNORECASE' to make certain rules -case-insensitive and other rules case-sensitive, because there is no + In general, you cannot use `IGNORECASE' to make certain rules case +insensitive and other rules case sensitive, as there is no straightforward way to set `IGNORECASE' just for the pattern of a particular rule.(1) To do this, use either bracket expressions or `tolower()'. However, one thing you can do with `IGNORECASE' only is -dynamically turn case-sensitivity on or off for all the rules at once. +dynamically turn case sensitivity on or off for all the rules at once. `IGNORECASE' can be set on the command line or in a `BEGIN' rule (*note Other Arguments::; also *note Using BEGIN/END::). Setting -`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 -`IGNORECASE'. +`IGNORECASE' from the command line is a way to make a program case +insensitive without having to edit it. In multibyte locales, the equivalences between upper- and lowercase characters are tested based on the wide-character values of the @@ -3502,113 +4093,42 @@ obscure and we don't recommend it. means that `gawk' does the right thing. -File: gawk.info, Node: Leftmost Longest, Next: Computed Regexps, Prev: Case-sensitivity, Up: Regexp - -3.7 How Much Text Matches? -========================== - -Consider the following: - - echo aaaabcd | awk '{ sub(/a+/, "<A>"); print }' - - This example uses the `sub()' function (which we haven't discussed -yet; *note String Functions::) to make a change to the input record. -Here, the regexp `/a+/' indicates "one or more `a' characters," and the -replacement text is `<A>'. - - The input contains four `a' characters. `awk' (and POSIX) regular -expressions always match the leftmost, _longest_ sequence of input -characters that can match. Thus, all four `a' characters are replaced -with `<A>' in this example: - - $ echo aaaabcd | awk '{ sub(/a+/, "<A>"); print }' - -| <A>bcd - - For simple match/no-match tests, this is not so important. But when -doing text matching and substitutions with the `match()', `sub()', -`gsub()', and `gensub()' functions, it is very important. *Note String -Functions::, for more information on these functions. Understanding -this principle is also important for regexp-based record and field -splitting (*note Records::, and also *note Field Separators::). - - -File: gawk.info, Node: Computed Regexps, Prev: Leftmost Longest, Up: Regexp - -3.8 Using Dynamic Regexps -========================= - -The righthand side of a `~' or `!~' 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 "dynamic regexp": - - BEGIN { digits_regexp = "[[:digit:]]+" } - $0 ~ digits_regexp { print } - -This sets `digits_regexp' to a regexp that describes one or more digits, -and tests whether the input record matches this regexp. - - NOTE: When using the `~' and `!~' 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 _twice_: the first time when `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 - `digits_regexp', shown previously), not just string 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. +File: gawk.info, Node: Regexp Summary, Prev: Case-sensitivity, Up: Regexp - For example, `/\*/' is a regexp constant for a literal `*'. Only -one backslash is needed. To do the same thing with a string, you have -to type `"\\*"'. The first backslash escapes the second one so that -the string actually contains the two characters `\' and `*'. +3.9 Summary +=========== - 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: + * Regular expressions describe sets of strings to be matched. In + `awk', regular expression constants are written enclosed between + slashes: `/'...`/'. - * 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 `~' and `!~' operators. - * It is more efficient to use regexp constants. `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, `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. - * Using regexp constants is better form; it shows clearly that you - intend a regexp match. - -Advanced Notes: Using `\n' in Bracket Expressions of Dynamic Regexps --------------------------------------------------------------------- + * Regexp operators provide grouping, alternation, and repetition. -Some commercial versions of `awk' do not allow the newline character to -be used inside a bracket expression for a dynamic regexp: + * 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. - $ awk '$0 ~ "[ \t\n]"' - error--> awk: newline in character class [ - error--> ]... - error--> source line number 1 - error--> context is - error--> >>> <<< + * 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. - But a newline in a regexp constant works with no problem: + * Matching expressions may use dynamic regexps (i.e., string values + treated as regular expressions). - $ awk '$0 ~ /[ \t\n]/' - here is a sample line - -| here is a sample line - Ctrl-d + * `gawk''s `IGNORECASE' variable lets you control the case + sensitivity of regexp matching. In other `awk' versions, use + `tolower()' or `toupper()'. - `gawk' does not have this problem, and it isn't likely to occur -often in practice, but it's worth noting for future reference. File: gawk.info, Node: Reading Files, Next: Printing, Prev: Regexp, Up: Top @@ -3621,8 +4141,8 @@ standard input (by default, this is the keyboard, but often it is a pipe from another command) or from files whose names you specify on the `awk' command line. If you specify input files, `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 -`FILENAME' (*note Built-in Variables::). +The name of the current input file can be found in the predefined +variable `FILENAME' (*note Built-in Variables::). The input is read in units called "records", and is processed by the rules of your program one record at a time. By default, each record is @@ -3644,11 +4164,14 @@ have to be named on the `awk' command line (*note Getline::). * 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 `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. File: gawk.info, Node: Records, Next: Fields, Up: Reading Files @@ -3656,97 +4179,129 @@ File: gawk.info, Node: Records, Next: Fields, Up: Reading Files 4.1 How Input Is Split into Records =================================== -The `awk' utility divides the input for your `awk' program into records -and fields. `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 `FNR'. It is reset to zero when a new file is -started. Another built-in variable, `NR', records the total number of -input records read so far from all data files. It starts at zero, but -is never automatically reset to zero. +`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 `FNR', which is reset to zero every time a new file is started. +Another predefined variable, `NR', records the total number of input +records read so far from all data files. It starts at zero, but is +never automatically reset to zero. + +* Menu: + +* awk split records:: How standard `awk' splits records. +* gawk split records:: How `gawk' splits records. + + +File: gawk.info, Node: awk split records, Next: gawk split records, Up: Records + +4.1.1 Record Splitting with Standard `awk' +------------------------------------------ - Records are separated by a character called the "record separator". -By default, the record separator is the newline character. This is why +Records are separated by a character called the "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 `RS'. +predefined variable `RS'. Like any other variable, the value of `RS' can be changed in the `awk' program with the assignment operator, `=' (*note Assignment Ops::). The new record-separator character should be enclosed in -quotation marks, which indicate a string constant. Often the right +quotation marks, 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 `BEGIN' pattern (*note BEGIN/END::). For example: - awk 'BEGIN { RS = "/" } - { print $0 }' BBS-list - -changes the value of `RS' to `"/"', 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 rule -in the `awk' program (the action with no pattern) prints each record. -Because each `print' statement adds a newline at the end of its output, -this `awk' program copies the input with each slash changed to a -newline. Here are the results of running the program on `BBS-list': - - $ awk 'BEGIN { RS = "/" } - > { print $0 }' 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 + awk 'BEGIN { RS = "u" } + { print $0 }' mail-list + +changes the value of `RS' to `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 `awk' program (the action with no pattern) prints +each record. Because each `print' statement adds a newline at the end +of its output, this `awk' program copies the input with each `u' +changed to a newline. Here are the results of running the program on +`mail-list': + + $ awk 'BEGIN { RS = "u" } + > { print $0 }' mail-list + -| Amelia 555-5553 amelia.zodiac + -| sq + -| e@gmail.com F + -| Anthony 555-3412 anthony.assert + -| ro@hotmail.com A + -| Becky 555-7685 becky.algebrar + -| m@gmail.com A + -| Bill 555-1675 bill.drowning@hotmail.com A + -| Broderick 555-0542 broderick.aliq + -| otiens@yahoo.com R + -| Camilla 555-2912 camilla.inf + -| sar + -| m@skynet.be R + -| Fabi + -| s 555-1234 fabi + -| s. + -| ndevicesim + -| s@ + -| cb.ed + -| F + -| J + -| lie 555-6699 j + -| lie.perscr + -| tabor@skeeve.com F + -| Martin 555-6480 martin.codicib + -| s@hotmail.com A + -| Sam + -| el 555-3430 sam + -| el.lanceolis@sh + -| .ed + -| A + -| Jean-Pa + -| l 555-2127 jeanpa + -| l.campanor + -| m@ny + -| .ed + -| R -| -Note that the entry for the `camelot' BBS is not split. In the -original data file (*note Sample Data Files::), the line looks like -this: +Note that the entry for the name `Bill' is not split. In the original +data file (*note Sample Data Files::), the line looks like this: - camelot 555-0542 300 C + Bill 555-1675 bill.drowning@hotmail.com A -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 `core' BBS; the newline +It contains no `u' so there is no reason to split the record, unlike +the others which have one or more occurrences of the `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 data file, not the one added by `awk' when it printed the record! Another way to change the record separator is on the command line, using the variable-assignment feature (*note Other Arguments::): - awk '{ print $0 }' RS="/" BBS-list + awk '{ print $0 }' RS="u" mail-list -This sets `RS' to `/' before processing `BBS-list'. +This sets `RS' to `u' before processing `mail-list'. - Using an unusual character such as `/' for the record separator -produces correct behavior in the vast majority of cases. However, the -following (extreme) pipeline prints a surprising `1': + Using an alphabetic character such as `u' for the record separator +is highly likely to produce strange results. Using an unusual +character such as `/' is more likely to produce correct behavior in the +majority of cases, but there are no guarantees. The moral is: Know Your +Data. - $ echo | awk 'BEGIN { RS = "a" } ; { print NF }' + When using regular characters as the record separator, there is one +unusual case that occurs when `gawk' is being fully POSIX-compliant +(*note Options::). Then, the following (extreme) pipeline prints a +surprising `1': + + $ echo | gawk --posix 'BEGIN { RS = "a" } ; { print NF }' -| 1 There is one field, consisting of a newline. The value of the built-in variable `NF' is the number of fields in the current record. +(In the normal case, `gawk' treats the newline as whitespace, printing +`0' as the result. Most other versions of `awk' also act this way.) 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 @@ -3765,16 +4320,22 @@ affected. After the end of the record has been determined, `gawk' sets the variable `RT' to the text in the input that matched `RS'. - When using `gawk', the value of `RS' is not limited to a -one-character string. It can be any regular expression (*note -Regexp::). (c.e.) In general, each record ends at the next string that -matches the regular expression; the next record starts at the end of -the matching string. This general rule is actually at work in the -usual case, where `RS' contains just a newline: a record ends at the -beginning of the next matching string (the next newline in the input), -and the following record starts just after the end of this string (at -the first character of the following line). The newline, because it -matches `RS', is not part of either record. + +File: gawk.info, Node: gawk split records, Prev: awk split records, Up: Records + +4.1.2 Record Splitting with `gawk' +---------------------------------- + +When using `gawk', the value of `RS' is not limited to a one-character +string. It can be any regular expression (*note Regexp::). (c.e.) In +general, each record ends at the next string that matches the regular +expression; the next record starts at the end of the matching string. +This general rule is actually at work in the usual case, where `RS' +contains just a newline: a record ends at the beginning of the next +matching string (the next newline in the input), and the following +record starts just after the end of this string (at the first character +of the following line). The newline, because it matches `RS', is not +part of either record. When `RS' is a single character, `RT' contains the same single character. However, when `RS' is a regular expression, `RT' contains @@ -3790,19 +4351,19 @@ trailing whitespace: $ echo record 1 AAAA record 2 BBBB record 3 | > gawk 'BEGIN { RS = "\n|( *[[:upper:]]+ *)" } - > { print "Record =", $0, "and RT =", RT }' - -| Record = record 1 and RT = AAAA - -| Record = record 2 and RT = BBBB - -| Record = record 3 and RT = - -| + > { print "Record =", $0,"and RT = [" RT "]" }' + -| Record = record 1 and RT = [ AAAA ] + -| Record = record 2 and RT = [ BBBB ] + -| Record = record 3 and RT = [ + -| ] -The final line of output has an extra blank line. This is because the -value of `RT' is a newline, and the `print' statement supplies its own -terminating newline. *Note Simple Sed::, for a more useful example of -`RS' as a regexp and `RT'. +The square brackets delineate the contents of `RT', letting you see the +leading and trailing whitespace. The final value of `RT' is a newline. +*Note Simple Sed::, for a more useful example of `RS' as a regexp and +`RT'. If you set `RS' to a regular expression that allows optional -trailing text, such as `RS = "abc(XYZ)?"' it is possible, due to +trailing text, such as `RS = "abc(XYZ)?"', it is possible, due to implementation constraints, that `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. `gawk' @@ -3814,18 +4375,17 @@ that this will never happen. the beginning and end of a _line_. As a result, something like `RS = "^[[:upper:]]"' can only match at the beginning of a file. This is because `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 `RS'. + that happens to contain newline characters. It is thus best to + avoid anchor metacharacters in the value of `RS'. The use of `RS' as a regular expression and the `RT' variable are `gawk' extensions; they are not available in compatibility mode (*note Options::). In compatibility mode, only the first character of the -value of `RS' is used to determine the end of the record. +value of `RS' determines the end of the record. -Advanced Notes: `RS = "\0"' Is Not Portable -------------------------------------------- + `RS = "\0"' Is Not Portable -There are times when you might want to treat an entire data file as a + There are times when you might want to treat an entire data file as a single record. The only way to make this happen is to give `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 @@ -3838,17 +4398,24 @@ use for `RS' in this case: BEGIN { RS = "\0" } # whole file becomes one record? `gawk' in fact accepts this, and uses the NUL character for the -record separator. However, this usage is _not_ portable to other `awk' -implementations. +record separator. This works for certain special files, such as +`/proc/environ' on GNU/Linux systems, where the NUL character is in +fact the record separator. However, this usage is _not_ portable to +most other `awk' implementations. - All other `awk' implementations(1) store strings internally as -C-style strings. C strings use the NUL character as the string + Almost all other `awk' implementations(1) store strings internally +as C-style strings. C strings use the NUL character as the string terminator. In effect, this means that `RS = "\0"' is the same as `RS = ""'. (d.c.) - 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. + It happens that recent versions of `mawk' can use the NUL character +as a record separator. However, this is a special case: `mawk' does not +allow embedded NUL characters in strings. (This may change in a future +version of `mawk'.) + + *Note Readfile Function::, for an interesting way to read whole +files. If you are using `gawk', see *note Extension Sample Readfile::, +for another option. ---------- Footnotes ---------- @@ -3864,8 +4431,8 @@ When `awk' reads an input record, the record is automatically "parsed" or separated by the `awk' utility into chunks called "fields". By default, fields are separated by "whitespace", like words in a line. Whitespace in `awk' means any string of one or more spaces, TABs, or -newlines;(1) other characters, such as formfeed, vertical tab, etc., -that are considered whitespace by other languages, are _not_ considered +newlines;(1) other characters that are considered whitespace by other +languages (such as formfeed, vertical tab, etc.) are _not_ considered whitespace by `awk'. The purpose of fields is to make it more convenient for you to refer @@ -3873,12 +4440,12 @@ to these pieces of the record. You don't have to use them--you can operate on the whole record if you want--but fields are what make simple `awk' programs so powerful. - A dollar-sign (`$') is used to refer to a field in an `awk' program, + You use a dollar-sign (`$') to refer to a field in an `awk' program, followed by the number of the field you want. Thus, `$1' refers to the first field, `$2' to the second, and so on. (Unlike the Unix shells, -the field numbers are not limited to single digits. `$127' is the one -hundred twenty-seventh field in the record.) For example, suppose the -following is a line of input: +the field numbers are not limited to single digits. `$127' is the +127th field in the record.) For example, suppose the following is a +line of input: This seems like a pretty nice example. @@ -3887,7 +4454,7 @@ Here the first field, or `$1', is `This', the second field, or `$2', is Because there is no space between the `e' and the `.', the period is considered part of the seventh field. - `NF' is a built-in variable whose value is the number of fields in + `NF' is a predefined variable whose value is the number of fields in the current record. `awk' automatically updates the value of `NF' each time it reads a record. No matter how many fields there are, the last field in a record can be represented by `$NF'. So, `$NF' is the same @@ -3896,29 +4463,26 @@ the last one (such as `$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 `$0', which looks like a reference to the "zero-th" -field, is a special case: it represents the whole input record when you -are not interested in specific fields. Here are some more examples: - - $ awk '$1 ~ /foo/ { print $0 }' BBS-list - -| fooey 555-1234 2400/1200/300 B - -| foot 555-6699 1200/300 B - -| macfoo 555-6480 1200/300 A - -| sabafoo 555-2127 1200/300 C - -This example prints each record in the file `BBS-list' whose first -field contains the string `foo'. The operator `~' is called a -"matching operator" (*note Regexp Usage::); it tests whether a string -(here, the field `$1') matches a given regular expression. - - By contrast, the following example looks for `foo' in _the entire -record_ and prints the first field and the last field for each matching -input record: - - $ awk '/foo/ { print $1, $NF }' BBS-list - -| fooey B - -| foot B - -| macfoo A - -| sabafoo C +field, is a special case: it represents the whole input record. Use it +when you are not interested in specific fields. Here are some more +examples: + + $ awk '$1 ~ /li/ { print $0 }' mail-list + -| Amelia 555-5553 amelia.zodiacusque@gmail.com F + -| Julie 555-6699 julie.perscrutabor@skeeve.com F + +This example prints each record in the file `mail-list' whose first +field contains the string `li'. + + By contrast, the following example looks for `li' in _the entire +record_ and prints the first and last fields for each matching input +record: + + $ awk '/li/ { print $1, $NF }' mail-list + -| Amelia F + -| Broderick R + -| Julie F + -| Samuel A ---------- Footnotes ---------- @@ -3931,31 +4495,31 @@ File: gawk.info, Node: Nonconstant Fields, Next: Changing Fields, Prev: Field 4.3 Nonconstant Field Numbers ============================= -The number of a field does not need to be a constant. Any expression in -the `awk' language can be used after a `$' 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. Consider -this example: +A field number need not be a constant. Any expression in the `awk' +language can be used after a `$' 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. Consider this +example: awk '{ print $NR }' Recall that `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 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: +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: - awk '{ print $(2*2) }' BBS-list + awk '{ print $(2*2) }' mail-list `awk' evaluates the expression `(2*2)' and uses its value as the number of the field to print. The `*' sign represents multiplication, so the expression `2*2' evaluates to four. The parentheses are used so that the multiplication is done before the `$' 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 `BBS-list'. (All of the `awk' -operators are listed, in order of decreasing precedence, in *Note +necessary whenever there is a binary operator(1) in the field-number +expression. This example, then, prints the type of relationship (the +fourth field) for every line of the file `mail-list'. (All of the +`awk' operators are listed, in order of decreasing precedence, in *note Precedence::.) If the field number you compute is zero, you get the entire record. @@ -3965,11 +4529,17 @@ not allowed; trying to reference one usually terminates the program. negative field number. `gawk' notices this and terminates your program. Other `awk' implementations may behave differently.) - As mentioned in *Note Fields::, `awk' stores the current record's + As mentioned in *note Fields::, `awk' stores the current record's number of fields in the built-in variable `NF' (also *note Built-in -Variables::). The expression `$NF' is not a special feature--it is the -direct consequence of evaluating `NF' and using its value as a field -number. +Variables::). Thus, the expression `$NF' is not a special feature--it +is the direct consequence of evaluating `NF' and using its value as a +field number. + + ---------- Footnotes ---------- + + (1) A "binary operator", such as `*' for multiplication, is one that +takes two operands. The distinction is required, because `awk' also has +unary (one-operand) and ternary (three-operand) operators. File: gawk.info, Node: Changing Fields, Next: Field Separators, Prev: Nonconstant Fields, Up: Reading Files @@ -3996,11 +4566,11 @@ three minus ten: `$3 - 10'. (*Note Arithmetic Ops::.) 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 `$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 then -becomes field three. *Note Conversion::. + For this to work, the text in `$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 then becomes field three. +*Note Conversion::. When the value of a field is changed (as perceived by `awk'), the text of the input record is recalculated to contain the new field where @@ -4014,8 +4584,8 @@ subtracted from the second field of each line: -| Mar 5 24 34 228 ... - It is also possible to also assign contents to fields that are out -of range. For example: + It is also possible to assign contents to fields that are out of +range. For example: $ awk '{ $6 = ($5 + $4 + $3 + $2) > print $6 }' inventory-shipped @@ -4065,7 +4635,7 @@ even when you assign the empty string to a field. For example: -| a::c:d -| 4 -The field is still there; it just has an empty value, denoted by the +The field is still there; it just has an empty value, delimited by the two colons between `a' and `c'. This example shows what happens if you create a new field: @@ -4082,12 +4652,12 @@ value six. value of `NF' and recomputes `$0'. (d.c.) Here is an example: $ echo a b c d e f | awk '{ print "NF =", NF; - > NF = 3; print $0 }' + > NF = 3; print $0 }' -| NF = 6 -| a b c CAUTION: Some versions of `awk' don't rebuild `$0' when `NF' is - decremented. Caveat emptor. + decremented. Finally, there are times when it is convenient to force `awk' to rebuild the entire record, using the current value of the fields and @@ -4096,8 +4666,8 @@ rebuild the entire record, using the current value of the fields and $1 = $1 # force record to be reconstituted print $0 # or whatever else with $0 -This forces `awk' rebuild the record. It does help to add a comment, -as we've shown here. +This forces `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 `$0' and the fields. Any assignment to `$0' causes the record to be reparsed into @@ -4105,19 +4675,18 @@ fields using the _current_ value of `FS'. This also applies to any built-in function that updates `$0', such as `sub()' and `gsub()' (*note String Functions::). -Advanced Notes: Understanding `$0' ----------------------------------- + Understanding `$0' -It is important to remember that `$0' is the _full_ record, exactly as -it was read from the input. This includes any leading or trailing + It is important to remember that `$0' is the _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 in -a record simply by setting `FS' and `OFS', and then expecting a plain + It is a common error to try to change the field separators in a +record simply by setting `FS' and `OFS', and then expecting a plain `print' or `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 `$1 = $1', as described earlier. @@ -4132,7 +4701,8 @@ File: gawk.info, Node: Field Separators, Next: Constant Size, Prev: Changing * 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 `FS' from the command-line. +* Command Line Field Separator:: Setting `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. The "field separator", which is either a single character or a @@ -4150,13 +4720,13 @@ the following line: is split into three fields: `m', `*g', and `*gai*pan'. Note the leading spaces in the values of the second and third fields. - The field separator is represented by the built-in variable `FS'. + The field separator is represented by the predefined variable `FS'. Shell programmers take note: `awk' does _not_ use the name `IFS' that is used by the POSIX-compliant shells (such as the Unix Bourne shell, `sh', or Bash). The value of `FS' can be changed in the `awk' program with the -assignment operator, `=' (*note Assignment Ops::). Often the right +assignment operator, `=' (*note Assignment Ops::). 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 `BEGIN' pattern (*note @@ -4251,7 +4821,7 @@ letter): > { print $2 }' -| a -In this case, the first field is "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 `$0' is recomputed. For instance, study this pipeline: @@ -4263,25 +4833,24 @@ play whenever `$0' is recomputed. For instance, study this pipeline: The first `print' statement prints the record as it was read, with leading whitespace intact. The assignment to `$2' rebuilds `$0' by concatenating `$1' through `$NF' together, separated by the value of -`OFS'. Because the leading whitespace was ignored when finding `$1', -it is not part of the new `$0'. Finally, the last `print' statement -prints the new `$0'. +`OFS' (which is a space by default). Because the leading whitespace +was ignored when finding `$1', it is not part of the new `$0'. +Finally, the last `print' statement prints the new `$0'. There is an additional subtlety to be aware of when using regular -expressions for field splitting. It is not well-specified in the POSIX +expressions for field splitting. It is not well specified in the POSIX standard, or anywhere else, what `^' means when splitting fields. Does the `^' match only at the beginning of the entire record? Or is each field separator a new string? It turns out that different `awk' versions answer this question differently, and you should not rely on any specific behavior in your programs. (d.c.) - As a point of information, Brian Kernighan's `awk' allows `^' to -match only at the beginning of the record. `gawk' also works this way. -For example: + As a point of information, BWK `awk' allows `^' to match only at the +beginning of the record. `gawk' also works this way. For example: $ echo 'xxAA xxBxx C' | > gawk -F '(^x+)|( +)' '{ for (i = 1; i <= NF; i++) - > printf "-->%s<--\n", $i }' + > printf "-->%s<--\n", $i }' -| --><-- -| -->AA<-- -| -->xxBxx<-- @@ -4314,7 +4883,7 @@ Options::), if `FS' is the null string, then `gawk' also behaves this way. -File: gawk.info, Node: Command Line Field Separator, Next: Field Splitting Summary, Prev: Single Character Fields, Up: Field Separators +File: gawk.info, Node: Command Line Field Separator, Next: Full Line Fields, Prev: Single Character Fields, Up: Field Separators 4.5.4 Setting `FS' from the Command Line ---------------------------------------- @@ -4326,13 +4895,10 @@ For example: sets `FS' to the `,' character. Notice that the option uses an uppercase `F' instead of a lowercase `f'. The latter option (`-f') -specifies a file containing an `awk' program. Case is significant in -command-line options: the `-F' and `-f' options have nothing to do with -each other. You can use both options at the same time to set the `FS' -variable _and_ get an `awk' program from a file. +specifies a file containing an `awk' program. The value used for the argument to `-F' is processed in exactly the -same way as assignments to the built-in variable `FS'. Any special +same way as assignments to the predefined variable `FS'. Any special characters in the field separator must be escaped appropriately. For example, to use a `\' as the field separator on the command line, you would have to type: @@ -4350,60 +4916,101 @@ argument to `-F' is `t', then `FS' is set to the TAB character. If you type `-F\t' at the shell, without any quotes, the `\' gets deleted, so `awk' figures that you really want your fields to be separated with TABs and not `t's. Use `-v FS="t"' or `-F"[t]"' on the command line if -you really do want to separate your fields with `t's. +you really do want to separate your fields with `t's. Use `-F '\t'' +when not in compatibility mode to specify that TABs separate fields. - As an example, let's use an `awk' program file called `baud.awk' -that contains the pattern `/300/' and the action `print $1': + As an example, let's use an `awk' program file called `edu.awk' that +contains the pattern `/edu/' and the action `print $1': - /300/ { print $1 } + /edu/ { print $1 } Let's also set `FS' to be the `-' character and run the program on -the file `BBS-list'. The following command prints a list of the names -of the bulletin boards that operate at 300 baud and the first three +the 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: - $ awk -F- -f baud.awk BBS-list - -| aardvark 555 - -| alpo - -| barfly 555 - -| bites 555 - -| camelot 555 - -| core 555 - -| fooey 555 - -| foot 555 - -| macfoo 555 - -| sdace 555 - -| sabafoo 555 - -Note the second line of output. The second line in the original file + $ awk -F- -f edu.awk mail-list + -| Fabius 555 + -| Samuel 555 + -| Jean + +Note the third line of output. The third line in the original file looked like this: - alpo-net 555-3412 2400/1200/300 A + Jean-Paul 555-2127 jeanpaul.campanorum@nyu.edu R - The `-' as part of the system's name was used as the field + The `-' as part of the person's name was used as the field separator, instead of the `-' in the phone number that was originally intended. This demonstrates why you have to be careful in choosing your field and record separators. 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: +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 `x' in the second field.) A +password file entry might look like this: - arnold:xyzzy:2076:10:Arnold Robbins:/home/arnold:/bin/bash + arnold:x:2076:10:Arnold Robbins:/home/arnold:/bin/bash 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: + + awk -F: '$5 == ""' /etc/passwd + + +File: gawk.info, Node: Full Line Fields, Next: Field Splitting Summary, Prev: Command Line Field Separator, Up: Field Separators + +4.5.5 Making the Full Line Be a Single Field +-------------------------------------------- + +Occasionally, it's useful to treat the whole input line as a single +field. This can be done easily and portably simply by setting `FS' to +`"\n"' (a newline):(1) + + awk -F'\n' 'PROGRAM' FILES ... + +When you do this, `$1' is the same as `$0'. - awk -F: '$2 == ""' /etc/passwd + Changing `FS' Does Not Affect the Fields + + According to the POSIX standard, `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 `FS' after a +record is read, the value of the fields (i.e., how they were split) +should reflect the old value of `FS', not the new one. + + However, many older implementations of `awk' do not work this way. +Instead, they defer splitting the fields until a field is actually +referenced. The fields are split using the _current_ value of `FS'! +(d.c.) This behavior can be difficult to diagnose. The following +example illustrates the difference between the two methods. (The +`sed'(2) command prints just the first line of `/etc/passwd'.) + + sed 1q /etc/passwd | awk '{ FS = ":" ; print $1 }' + +which usually prints: + + root + +on an incorrect implementation of `awk', while `gawk' prints the full +first line of the file, something like: + + root:x:0:0:Root:/: + + ---------- Footnotes ---------- + + (1) Thanks to Andrew Schorr for this tip. + + (2) The `sed' utility is a "stream editor." Its behavior is also +defined by the POSIX standard. -File: gawk.info, Node: Field Splitting Summary, Prev: Command Line Field Separator, Up: Field Separators +File: gawk.info, Node: Field Splitting Summary, Prev: Full Line Fields, Up: Field Separators -4.5.5 Field-Splitting Summary +4.5.6 Field-Splitting Summary ----------------------------- It is important to remember that when you assign a string constant as @@ -4415,7 +5022,7 @@ occurrences of any two characters." If instead you want fields to be separated by a literal period followed by any single character, use `FS = "\\.."'. - The following table summarizes how fields are split, based on the + The following list summarizes how fields are split, based on the value of `FS' (`==' means "is equal to"): `FS == " "' @@ -4435,40 +5042,12 @@ value of `FS' (`==' means "is equal to"): `FS == ""' Each individual character in the record becomes a separate field. - (This is a `gawk' extension; it is not specified by the POSIX + (This is a common extension; it is not specified by the POSIX standard.) -Advanced Notes: Changing `FS' Does Not Affect the Fields --------------------------------------------------------- - -According to the POSIX standard, `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 `FS' after a record is read, -the value of the fields (i.e., how they were split) should reflect the -old value of `FS', not the new one. + `FS' and `IGNORECASE' - However, many older implementations of `awk' do not work this way. -Instead, they defer splitting the fields until a field is actually -referenced. The fields are split using the _current_ value of `FS'! -(d.c.) This behavior can be difficult to diagnose. The following -example illustrates the difference between the two methods. (The -`sed'(1) command prints just the first line of `/etc/passwd'.) - - sed 1q /etc/passwd | awk '{ FS = ":" ; print $1 }' - -which usually prints: - - root - -on an incorrect implementation of `awk', while `gawk' prints something -like: - - root:nSijPlPhZZwgE:0:0:Root:/: - -Advanced Notes: `FS' and `IGNORECASE' -------------------------------------- - -The `IGNORECASE' variable (*note User-modified::) affects field + The `IGNORECASE' variable (*note User-modified::) affects field splitting _only_ when the value of `FS' is a regexp. It has no effect when `FS' is a single character, even if that character is a letter. Thus, in the following code: @@ -4480,28 +5059,23 @@ Thus, in the following code: The output is `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., `FS = "[c]"'. In this case, `IGNORECASE' will take +for you (e.g., `FS = "[c]"'). In this case, `IGNORECASE' will take effect. - ---------- Footnotes ---------- - - (1) The `sed' utility is a "stream editor." Its behavior is also -defined by the POSIX standard. - File: gawk.info, Node: Constant Size, Next: Splitting By Content, Prev: Field Separators, Up: Reading Files 4.6 Reading Fixed-Width Data ============================ -(This minor node discusses an advanced feature of `awk'. If you are a -novice `awk' user, you might want to skip it on the first reading.) +This minor node discusses an advanced feature of `gawk'. If you are a +novice `awk' user, you might want to skip it on the first reading. -`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. + `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 _empty fields are just @@ -4531,17 +5105,14 @@ use of `FIELDWIDTHS': brent ttyp0 26Jun91 4:46 26:46 4:41 bash dave ttyq4 26Jun9115days 46 46 wnewmail - The following program takes the above input, converts the idle time -to number of seconds, and prints out the first two fields and the + 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: - NOTE: This program uses a number of `awk' features that haven't - been introduced yet. - 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 ~ /:/) { @@ -4554,6 +5125,9 @@ calculated idle time: print $1, $2, idle } + NOTE: The preceding program uses a number of `awk' features that + haven't been introduced yet. + Running the program on the data produces the following results: hzuo ttyV0 0 @@ -4597,26 +5171,25 @@ of such a function). File: gawk.info, Node: Splitting By Content, Next: Multiple Line, Prev: Constant Size, Up: Reading Files -4.7 Defining Fields By Content +4.7 Defining Fields by Content ============================== -(This minor node discusses an advanced feature of `awk'. If you are a -novice `awk' user, you might want to skip it on the first reading.) +This minor node discusses an advanced feature of `gawk'. If you are a +novice `awk' user, you might want to skip it on the first reading. -Normally, when using `FS', `gawk' defines the fields as the parts of + Normally, when using `FS', `gawk' defines the fields as the parts of the record that occur in between each field separator. In other words, `FS' defines what a field _is not_, instead of what a field _is_. 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 "comma separated value" + The most notorious such case is so-called "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 _embedded_ comma. While there is no formal standard -specification for CSV data(1), in such cases, most programs embed the -field in double quotes. So we might have data like this: +contains an _embedded_ comma. In such cases, most programs embed the +field in double quotes.(1) So we might have data like this: Robbins,Arnold,"1234 A Pretty Street, NE",MyTown,MyState,12345-6789,USA @@ -4624,7 +5197,7 @@ field in double quotes. So we might have data like this: value of `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 + 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 (*note Regexp::), we would have @@ -4671,15 +5244,17 @@ would be to remove the quotes when they occur, with something like this: As with `FS', the `IGNORECASE' variable (*note User-modified::) affects field splitting with `FPAT'. - Similar to `FIELDWIDTHS', the value of `PROCINFO["FS"]' will be -`"FPAT"' if content-based field splitting is being used. + Assigning a value to `FPAT' overrides field splitting with `FS' and +with `FIELDWIDTHS'. Similar to `FIELDWIDTHS', the value of +`PROCINFO["FS"]' will be `"FPAT"' if content-based field splitting is +being used. NOTE: Some programs export CSV data that contains embedded newlines between the double quotes. `gawk' provides no way to - deal with this. Since there is no formal specification for CSV - data, there isn't much more to be done; the `FPAT' mechanism + deal with this. Even though a formal specification for CSV data + exists, there isn't much more to be done; the `FPAT' mechanism provides an elegant solution for the majority of cases, and the - `gawk' maintainer is satisfied with that. + `gawk' developers are satisfied with that. As written, the regexp used for `FPAT' requires that each field have a least one character. A straightforward modification (changing @@ -4690,9 +5265,16 @@ changed the first `+' to `*') allows fields to be empty: Finally, the `patsplit()' function makes the same functionality available for splitting regular strings (*note String Functions::). + To recap, `gawk' provides three independent methods to split input +records into fields. `gawk' uses whichever mechanism was last chosen +based on which of the three variables--`FS', `FIELDWIDTHS', and +`FPAT'--was last assigned to. + ---------- Footnotes ---------- - (1) At least, we don't know of one. + (1) The CSV format lacked a formal standard definition for many +years. RFC 4180 (http://www.ietf.org/rfc/rfc4180.txt) standardizes the +most common practices. File: gawk.info, Node: Multiple Line, Next: Getline, Prev: Splitting By Content, Up: Reading Files @@ -4729,8 +5311,8 @@ doesn't start until the first nonblank line that follows--no matter how many blank lines appear in a row, they are considered one record separator. - There is an important difference between `RS = ""' and `RS = -"\n\n+"'. In the first case, leading newlines in the input data file + However, there is an important difference between `RS = ""' and `RS += "\n\n+"'. In the first case, leading newlines in the input data file 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. (d.c.) @@ -4798,8 +5380,8 @@ A simple program to process this file is as follows: -| ... - *Note Labels Program::, for a more realistic program that deals with -address lists. The following table summarizes how records are split, + *Note Labels Program::, for a more realistic program dealing with +address lists. The following list summarizes how records are split, based on the value of `RS'. (`==' means "is equal to.") `RS == "\n"' @@ -4823,9 +5405,10 @@ based on the value of `RS'. (`==' means "is equal to.") records. (This is a `gawk' extension; it is not specified by the POSIX standard.) - In all cases, `gawk' sets `RT' to the input text that matched the -value specified by `RS'. But if the input file ended without any text -that matches `RS', then `gawk' sets `RT' to the null string. + If not in compatibility mode (*note Options::), `gawk' sets `RT' to +the input text that matched the value specified by `RS'. But if the +input file ended without any text that matches `RS', then `gawk' sets +`RT' to the null string. ---------- Footnotes ---------- @@ -4834,13 +5417,13 @@ feature of `RS' does not apply. It does apply to the default field separator of a single space: `FS = " "'. -File: gawk.info, Node: Getline, Next: Command line directories, Prev: Multiple Line, Up: Reading Files +File: gawk.info, Node: Getline, Next: Read Timeout, Prev: Multiple Line, Up: Reading Files 4.9 Explicit Input with `getline' ================================= So far we have been getting our input data from `awk''s main input -stream--either the standard input (usually your terminal, sometimes the +stream--either the standard input (usually your keyboard, sometimes the output from another program) or from the files specified on the command line. The `awk' language has a special built-in command called `getline' that can be used to read input under your explicit control. @@ -4852,8 +5435,8 @@ yet. Therefore, come back and study the `getline' command _after_ you have reviewed the rest of this Info file and have a good knowledge of how `awk' works. - The `getline' command returns one if it finds a record and zero if -it encounters the end of the file. If there is some error in getting a + The `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 `getline' returns -1. In this case, `gawk' sets the variable `ERRNO' to a string describing the error that occurred. @@ -4862,7 +5445,7 @@ describing the error that occurred. represents a shell command. NOTE: When `--sandbox' is specified (*note Options::), reading - lines from files, pipes and coprocesses is disabled. + lines from files, pipes, and coprocesses is disabled. * Menu: @@ -4892,38 +5475,48 @@ input record and split it up into fields. This is useful if you've finished processing the current record, but want to do some special processing on the next record _right now_. For 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 } This `awk' program deletes C-style comments (`/* ... */') from the -input. By replacing the `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.) - - This form of the `getline' command sets `NF', `NR', `FNR', and the -value of `$0'. +input. It uses a number of features we haven't covered yet, including +string concatenation (*note Concatenation::) and the `index()' and +`substr()' built-in functions (*note String Functions::). By replacing +the `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.) + + This form of the `getline' command sets `NF', `NR', `FNR', `RT', and +the value of `$0'. NOTE: The new value of `$0' is used to test the patterns of any subsequent rules. The original value of `$0' that triggered the @@ -4968,10 +5561,10 @@ and produces these results: phore free - The `getline' command used in this way sets only the variables `NR' -and `FNR' (and of course, VAR). The record is not split into fields, -so the values of the fields (including `$0') and the value of `NF' do -not change. + The `getline' command used in this way sets only the variables `NR', +`FNR', and `RT' (and of course, VAR). The record is not split into +fields, so the values of the fields (including `$0') and the value of +`NF' do not change. File: gawk.info, Node: Getline/File, Next: Getline/Variable/File, Prev: Getline/Variable, Up: Getline @@ -4997,14 +5590,14 @@ with a value equal to 10 in the current input file: Because the main input stream is not used, the values of `NR' and `FNR' are not changed. However, the record it reads is split into fields in the normal manner, so the values of `$0' and the other fields -are changed, resulting in a new value of `NF'. +are changed, resulting in a new value of `NF'. `RT' is also set. According to POSIX, `getline < EXPRESSION' is ambiguous if EXPRESSION contains unparenthesized operators other than `$'; for example, `getline < dir "/" file' is ambiguous because the -concatenation operator is not parenthesized. You should write it as -`getline < (dir "/" file)' if you want your program to be portable to -all `awk' implementations. +concatenation operator (not discussed yet; *note Concatenation::) is +not parenthesized. You should write it as `getline < (dir "/" file)' if +you want your program to be portable to all `awk' implementations. File: gawk.info, Node: Getline/Variable/File, Next: Getline/Pipe, Prev: Getline/File, Up: Getline @@ -5013,10 +5606,10 @@ File: gawk.info, Node: Getline/Variable/File, Next: Getline/Pipe, Prev: Getli ------------------------------------------------- Use `getline VAR < FILE' to read input from the file FILE, and put it -in the variable VAR. As above, FILE is a string-valued expression that -specifies the file from which to read. +in the variable VAR. As earlier, FILE is a string-valued expression +that specifies the file from which to read. - In this version of `getline', none of the built-in variables are + In this version of `getline', none of the predefined variables are changed and the record is not split into fields. The only variable changed is VAR.(1) For example, the following program copies all the input files to the output, except for records that say @@ -5056,7 +5649,10 @@ File: gawk.info, Node: Getline/Pipe, Next: Getline/Variable/Pipe, Prev: Getli 4.9.5 Using `getline' from a Pipe --------------------------------- -The output of a command can also be piped into `getline', using + Omniscience has much to recommend it. Failing that, attention to + details would be useful. -- Brian Kernighan + + The output of a command can also be piped into `getline', using `COMMAND | getline'. In this case, the string COMMAND is run as a shell command and its output is piped into `awk' to be used as input. This form of `getline' reads one record at a time from the pipe. For @@ -5094,13 +5690,13 @@ the program might produce: bill ttyp1 Jul 13 14:23 (murphy:0) bletch -Notice that this program ran the command `who' and printed the previous -result. (If you try this program yourself, you will of course get -different results, depending upon who is logged in on your system.) +Notice that this program ran the 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 `getline' splits the record into fields, sets the value of `NF', and recomputes the value of `$0'. The values of `NR' -and `FNR' are not changed. +and `FNR' are not changed. `RT' is set. According to POSIX, `EXPRESSION | getline' is ambiguous if EXPRESSION contains unparenthesized operators other than `$'--for @@ -5112,10 +5708,10 @@ all `awk' implementations. NOTE: Unfortunately, `gawk' has not been consistent in its treatment of a construct like `"echo " "date" | getline'. Most versions, including the current version, treat it at as `("echo " - "date") | getline'. (This how Brian Kernighan's `awk' behaves.) - Some versions changed and treated it as `"echo " ("date" | - getline)'. (This is how `mawk' behaves.) In short, _always_ use - explicit parentheses, and then you won't have to worry. + "date") | getline'. (This is also how BWK `awk' behaves.) Some + versions changed and treated it as `"echo " ("date" | getline)'. + (This is how `mawk' behaves.) In short, _always_ use explicit + parentheses, and then you won't have to worry. File: gawk.info, Node: Getline/Variable/Pipe, Next: Getline/Coprocess, Prev: Getline/Pipe, Up: Getline @@ -5134,8 +5730,8 @@ following program reads the current date and time into the variable print "Report printed on " current_time } - In this version of `getline', none of the built-in variables are -changed and the record is not split into fields. + In this version of `getline', none of the predefined variables are +changed and the record is not split into fields. However, `RT' is set. According to POSIX, `EXPRESSION | getline VAR' is ambiguous if EXPRESSION contains unparenthesized operators other than `$'; for @@ -5168,7 +5764,7 @@ which sends a query to `db_server' and then reads the results. The values of `NR' and `FNR' are not changed, because the main input stream is not used. However, the record is split into fields in the normal manner, thus changing the values of `$0', of the other fields, -and of `NF'. +and of `NF' and `RT'. Coprocesses are an advanced feature. They are discussed here only because this is the minor node on `getline'. *Note Two-way I/O::, @@ -5184,9 +5780,9 @@ When you use `COMMAND |& getline VAR', the output from the coprocess COMMAND is sent through a two-way pipe to `getline' and into the variable VAR. - In this version of `getline', none of the built-in variables are + In this version of `getline', none of the predefined variables are changed and the record is not split into fields. The only variable -changed is VAR. +changed is VAR. However, `RT' is set. Coprocesses are an advanced feature. They are discussed here only because this is the minor node on `getline'. *Note Two-way I/O::, @@ -5206,10 +5802,10 @@ in mind: testing the new record against every pattern. However, the new record is tested against any subsequent rules. - * Many `awk' implementations limit the number of pipelines that an - `awk' program may have open to just one. In `gawk', there is no - such limit. You can open as many pipelines (and coprocesses) as - the underlying operating system permits. + * Some very old `awk' implementations limit the number of pipelines + that an `awk' program may have open to just one. In `gawk', there + is no such limit. You can open as many pipelines (and + coprocesses) as the underlying operating system permits. * An interesting side effect occurs if you use `getline' without a redirection inside a `BEGIN' rule. Because an unredirected @@ -5217,62 +5813,276 @@ in mind: `getline' command causes `awk' to set the value of `FILENAME'. Normally, `FILENAME' does not have a value inside `BEGIN' rules, because you have not yet started to process the command-line data - files. (d.c.) (*Note BEGIN/END::, also *note Auto-set::.) + files. (d.c.) (See *note BEGIN/END::; also *note Auto-set::.) * Using `FILENAME' with `getline' (`getline < FILENAME') is likely to be a source for confusion. `awk' opens a separate input stream from the current input file. However, by not using a variable, - `$0' and `NR' are still updated. If you're doing this, it's + `$0' and `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. - * *Note Getline Summary::, presents a table summarizing the + * *note Getline Summary::, presents a table summarizing the `getline' variants and which variables they can affect. It is worth noting that those variants which do not use redirection can cause `FILENAME' to be updated if they cause `awk' to start reading a new input file. + * If the variable being assigned is an expression with side effects, + different versions of `awk' behave differently upon encountering + end-of-file. Some versions don't evaluate the expression; many + versions (including `gawk') do. Here is an example, due to Duncan + Moore: + + BEGIN { + system("echo 1 > f") + while ((getline a[++c] < "f") > 0) { } + print c + } + + Here, the side effect is the `++c'. Is `c' incremented if end of + file is encountered, before the element in `a' is assigned? + + `gawk' treats `getline' like a function call, and evaluates the + expression `a[++c]' before attempting to read from `f'. However, + some versions of `awk' only evaluate the expression once they know + that there is a string value to be assigned. + File: gawk.info, Node: Getline Summary, Prev: Getline Notes, Up: Getline 4.9.10 Summary of `getline' Variants ------------------------------------ -*Note table-getline-variants:: summarizes the eight variants of -`getline', listing which built-in variables are set by each one, and -whether the variant is standard or a `gawk' extension. +*note table-getline-variants:: summarizes the eight variants of +`getline', listing which predefined variables are set by each one, and +whether the variant is standard or a `gawk' extension. Note: for each +variant, `gawk' sets the `RT' predefined variable. -Variant Effect Standard / - Extension +Variant Effect `awk' / `gawk' ------------------------------------------------------------------------- -`getline' Sets `$0', `NF', `FNR', Standard - and `NR' -`getline' VAR Sets VAR, `FNR', and `NR' Standard -`getline <' FILE Sets `$0' and `NF' Standard -`getline VAR < FILE' Sets VAR Standard -COMMAND `| getline' Sets `$0' and `NF' Standard -COMMAND `| getline' VAR Sets VAR Standard -COMMAND `|& getline' Sets `$0' and `NF' Extension -COMMAND `|& getline' Sets VAR Extension +`getline' Sets `$0', `NF', `FNR', `awk' + `NR', and `RT' +`getline' VAR Sets VAR, `FNR', `NR', and `awk' + `RT' +`getline <' FILE Sets `$0', `NF', and `RT' `awk' +`getline VAR < FILE' Sets VAR and `RT' `awk' +COMMAND `| getline' Sets `$0', `NF', and `RT' `awk' +COMMAND `| getline' VAR Sets VAR and `RT' `awk' +COMMAND `|& getline' Sets `$0', `NF', and `RT' `gawk' +COMMAND `|& getline' Sets VAR and `RT' `gawk' VAR -Table 4.1: getline Variants and What They Set +Table 4.1: `getline' variants and what they set -File: gawk.info, Node: Command line directories, Prev: Getline, Up: Reading Files +File: gawk.info, Node: Read Timeout, Next: Command-line directories, Prev: Getline, Up: Reading Files + +4.10 Reading Input with a Timeout +================================= -4.10 Directories On The Command Line +This minor node describes a feature that is specific to `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 `PROCINFO' array (*note Auto-set::): + + PROCINFO["input_name", "READ_TIMEOUT"] = TIMEOUT IN MILLISECONDS + + When set, this causes `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: + + Service = "/inet/tcp/0/localhost/daytime" + PROCINFO[Service, "READ_TIMEOUT"] = 100 + if ((Service |& getline) > 0) + print $0 + else if (ERRNO != "") + print ERRNO + + Here is how to read interactively from the user(1) without waiting +for more than five seconds: + + PROCINFO["/dev/stdin", "READ_TIMEOUT"] = 5000 + while ((getline < "/dev/stdin") > 0) + print $0 + + `gawk' terminates the read operation if input does not arrive after +waiting for the timeout period, returns failure and sets `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: + + $ gawk 'BEGIN { PROCINFO["-", "READ_TIMEOUT"] = 5000 } + > { print "You entered: " $0 }' + gawk + -| You entered: gawk + + In this case, failure to respond within five seconds results in the +following error message: + + error--> gawk: cmd. line:2: (FILENAME=- FNR=1) fatal: error reading input file `-': Connection timed out + + 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: + + PROCINFO[Service, "READ_TIMEOUT"] = 1000 + while ((Service |& getline) > 0) { + print $0 + PROCINFO[Service, "READ_TIMEOUT"] -= 100 + } + + NOTE: You should not assume that the read operation will block + exactly after the tenth record has been printed. It is possible + that `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. + + If the `PROCINFO' element is not present and the `GAWK_READ_TIMEOUT' +environment variable exists, `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. + + `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 `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. + + ---------- Footnotes ---------- + + (1) This assumes that standard input is the keyboard. + + +File: gawk.info, Node: Command-line directories, Next: Input Summary, Prev: Read Timeout, Up: Reading Files + +4.11 Directories on the Command Line ==================================== According to the POSIX standard, files named on the `awk' command line -must be text files. It is a fatal error if they are not. Most -versions of `awk' treat a directory on the command line as a fatal -error. +must be text files; it is a fatal error if they are not. Most versions +of `awk' treat a directory on the command line as a fatal error. By default, `gawk' produces a warning for a directory on the command -line, but otherwise ignores it. If either of the `--posix' or -`--traditional' options is given, then `gawk' reverts to treating a -directory on the command line as a fatal error. +line, but otherwise ignores it. This makes it easier to use shell +wildcards with your `awk' program: + + $ gawk -f whizprog.awk * Directories could kill this program + + If either of the `--posix' or `--traditional' options is given, then +`gawk' reverts to treating a directory on the command line as a fatal +error. + + *Note Extension Sample Readdir::, for a way to treat directories as +usable data from an `awk' program. + + +File: gawk.info, Node: Input Summary, Next: Input Exercises, Prev: Command-line directories, Up: Reading Files + +4.12 Summary +============ + + * Input is split into records based on the value of `RS'. The + possibilities are as follows: + + Value of `RS' Records are split on `awk' / `gawk' + ... + ---------------------------------------------------------------------- + Any single That character `awk' + character + The empty string Runs of two or more `awk' + (`""') newlines + A regexp Text that matches the `gawk' + regexp + + * `FNR' indicates how many records have been read from the current + input file; `NR' indicates how many records have been read in + total. + + * `gawk' sets `RT' to the text matched by `RS'. + + * After splitting the input into records, `awk' further splits the + record into individual fields, named `$1', `$2', and so on. `$0' + is the whole record, and `NF' indicates how many fields there are. + The default way to split fields is between whitespace characters. + + * Fields may be referenced using a variable, as in `$NF'. Fields + may also be assigned values, which causes the value of `$0' to be + recomputed when it is later referenced. Assigning to a field with + a number greater than `NF' creates the field and rebuilds the + record, using `OFS' to separate the fields. Incrementing `NF' + does the same thing. Decrementing `NF' throws away fields and + rebuilds the record. + + * Field splitting is more complicated than record splitting: + + Field separator value Fields are split ... `awk' / + `gawk' + ---------------------------------------------------------------------- + `FS == " "' On runs of whitespace `awk' + `FS == ANY SINGLE On that character `awk' + CHARACTER' + `FS == REGEXP' On text matching the regexp `awk' + `FS == ""' Each individual character is `gawk' + a separate field + `FIELDWIDTHS == LIST OF Based on character position `gawk' + COLUMNS' + `FPAT == REGEXP' On the text surrounding text `gawk' + matching the regexp + + * Using `FS = "\n"' causes the entire record to be a single field + (assuming that newlines separate records). + + * `FS' may be set from the command line using the `-F' option. This + can also be done using command-line variable assignment. + + * Use `PROCINFO["FS"]' to see how fields are being split. + + * Use `getline' in its various forms to read additional records, + from the default input stream, from a file, or from a pipe or + coprocess. + + * Use `PROCINFO[FILE, "READ_TIMEOUT"]' to cause reads to timeout for + FILE. + + * Directories on the command line are fatal for standard `awk'; + `gawk' ignores them if not in POSIX mode. + + + +File: gawk.info, Node: Input Exercises, Prev: Input Summary, Up: Reading Files + +4.13 Exercises +============== + + 1. Using the `FIELDWIDTHS' variable (*note 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. + + 2. *note Plain Getline::, presented a program to remove C-style + comments (`/* ... */') 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? + File: gawk.info, Node: Printing, Next: Expressions, Prev: Reading Files, Up: Top @@ -5286,7 +6096,7 @@ and the `printf' statement for fancier formatting. The `print' statement is not limited when computing _which_ values to print. However, with two exceptions, you cannot specify _how_ to print them--how many columns, whether to use exponential notation or not, and -so on. (For the exceptions, *note Output Separators::, and *Note +so on. (For the exceptions, *note Output Separators::, and *note OFMT::.) For printing with specifications, you need the `printf' statement (*note Printf::). @@ -5304,10 +6114,13 @@ function. * Printf:: The `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 `gawk'. `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. File: gawk.info, Node: Print, Next: Print Examples, Up: Printing @@ -5315,10 +6128,10 @@ File: gawk.info, Node: Print, Next: Print Examples, Up: Printing 5.1 The `print' Statement ========================= -The `print' statement is used for producing output with simple, -standardized formatting. 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: +Use the `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: print ITEM1, ITEM2, ... @@ -5333,11 +6146,15 @@ Numeric values are converted to strings and then printed. The simple statement `print' with no items is equivalent to `print $0': it prints the entire current record. To print a blank line, use -`print ""', where `""' is the empty string. To print a fixed piece of -text, use a string constant, such as `"Don't Panic"', as one item. If -you forget to use the double-quote characters, your text is taken as an -`awk' expression, and you will probably get an error. Keep in mind -that a space is printed between any two items. +`print ""'. To print a fixed piece of text, use a string constant, +such as `"Don't Panic"', as one item. If you forget to use the +double-quote characters, your text is taken as an `awk' expression, and +you will probably get an error. Keep in mind that a space is printed +between any two items. + + Note that the `print' statement is a statement and not an +expression--you can't use it in the pattern part of a PATTERN-ACTION +statement, for example. File: gawk.info, Node: Print Examples, Next: Output Separators, Prev: Print, Up: Printing @@ -5385,8 +6202,8 @@ Here is the same program, without the comma: To someone unfamiliar with the `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 -(`$1') and green crates shipped (`$2'). We do this using the `BEGIN' -pattern (*note BEGIN/END::) so that the headings are only printed once: +(`$1') and green crates shipped (`$2'). We do this using a `BEGIN' +rule (*note BEGIN/END::) so that the headings are only printed once: awk 'BEGIN { print "Month Crates" print "----- ------" } @@ -5429,15 +6246,16 @@ As mentioned previously, a `print' statement contains a list 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 "output field separator" by setting the built-in variable `OFS'. -The initial value of this variable is the string `" "'--that is, a -single space. +the "output field separator" by setting the predefined variable `OFS'. +The initial value of this variable is the string `" "' (i.e., a single +space). The output from an entire `print' statement is called an "output record". Each `print' statement outputs one output record, and then outputs a string called the "output record separator" (or `ORS'). The -initial value of `ORS' is the string `"\n"'; i.e., a newline character. -Thus, each `print' statement normally makes a separate line. +initial value of `ORS' is the string `"\n"' (i.e., a newline +character). Thus, each `print' statement normally makes a separate +line. In order to change how output fields and records are separated, assign new values to the variables `OFS' and `ORS'. The usual place to @@ -5449,13 +6267,29 @@ prints the first and second fields of each input record, separated by a semicolon, with a blank line added after each newline: $ awk 'BEGIN { OFS = ";"; ORS = "\n\n" } - > { print $1, $2 }' BBS-list - -| aardvark;555-5553 + > { print $1, $2 }' mail-list + -| Amelia;555-5553 -| - -| alpo-net;555-3412 + -| Anthony;555-3412 + -| + -| Becky;555-7685 + -| + -| Bill;555-1675 + -| + -| Broderick;555-0542 + -| + -| Camilla;555-2912 + -| + -| Fabius;555-1234 + -| + -| Julie;555-6699 + -| + -| Martin;555-6480 + -| + -| Samuel;555-3430 + -| + -| Jean-Paul;555-2127 -| - -| barfly;555-7685 - ... If the value of `ORS' does not contain a newline, the program's output runs together on a single line. @@ -5473,14 +6307,14 @@ that string. `awk' uses the `sprintf()' function to do this conversion `sprintf()' function accepts a "format specification" that tells it how to format numbers (or strings), and that there are a number of different ways in which numbers can be formatted. The different format -specifications are discussed more fully in *Note Control Letters::. +specifications are discussed more fully in *note Control Letters::. - The built-in variable `OFMT' contains the default format -specification that `print' uses with `sprintf()' when it wants to -convert a number to a string for printing. The default value of `OFMT' -is `"%.6g"'. The way `print' prints numbers can be changed by -supplying different format specifications as the value of `OFMT', as -shown in the following example: + The predefined variable `OFMT' contains the format specification +that `print' uses with `sprintf()' when it wants to convert a number to +a string for printing. The default value of `OFMT' is `"%.6g"'. The +way `print' prints numbers can be changed by supplying a different +format specification for the value of `OFMT', as shown in the following +example: $ awk 'BEGIN { > OFMT = "%.0f" # print numbers as integers (rounds) @@ -5502,8 +6336,6 @@ by `print', use `printf'. With `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 "format string", that -controls how and where to print the other arguments. * Menu: @@ -5522,10 +6354,10 @@ A simple `printf' statement looks like this: printf FORMAT, ITEM1, ITEM2, ... -The entire list of arguments may optionally be enclosed in parentheses. -The parentheses are necessary if any of the item expressions use the -`>' relational operator; otherwise, it can be confused with an output -redirection (*note Redirection::). +As for `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 `>' relational operator; otherwise, it can be +confused with an output redirection (*note Redirection::). The difference between `printf' and `print' is the FORMAT argument. This is an expression whose value is taken as a string; it specifies @@ -5546,12 +6378,12 @@ statements. For example: $ awk 'BEGIN { > ORS = "\nOUCH!\n"; OFS = "+" - > msg = "Dont Panic!" + > msg = "Don\47t Panic!" > printf "%s\n", msg > }' - -| Dont Panic! + -| Don't Panic! -Here, neither the `+' nor the `OUCH' appear in the output message. +Here, neither the `+' nor the `OUCH!' appear in the output message. File: gawk.info, Node: Control Letters, Next: Format Modifiers, Prev: Basic Printf, Up: Printf @@ -5567,9 +6399,9 @@ print. The rest of the format specifier is made up of optional width. Here is a list of the format-control letters: `%c' - Print a number as an ASCII character; thus, `printf "%c", 65' - outputs the letter `A'. The output for a string value is the first - character of the string. + Print a number as a character; thus, `printf "%c", 65' outputs the + letter `A'. The output for a string value is the first character + of the string. NOTE: The POSIX standard says the first character of a string is printed. In locales with multibyte characters, `gawk' @@ -5577,17 +6409,19 @@ width. Here is a list of the format-control letters: valid wide character and then to print the multibyte encoding of that character. Similarly, when printing a numeric value, `gawk' allows the value to be within the numeric range of - values that can be held in a wide character. + values that can be held in a wide character. If the + conversion to multibyte encoding fails, `gawk' uses the low + eight bits of the value as the character to print. Other `awk' versions generally restrict themselves to printing the first byte of a string or to numeric values within the range of a single byte (0-255). -`%d, %i' +`%d', `%i' Print a decimal integer. The two control letters are equivalent. (The `%i' specification is for compatibility with ISO C.) -`%e, %E' +`%e', `%E' Print a number in scientific (exponential) notation; for example: printf "%4.3e\n", 1950 @@ -5606,10 +6440,11 @@ width. Here is a list of the format-control letters: of which follow the decimal point. (The `4.3' represents two modifiers, discussed in the next node.) - On systems supporting IEEE 754 floating point format, values + On systems supporting IEEE 754 floating-point format, values representing negative infinity are formatted as `-inf' or - `-infinity', and positive infinity as `inf' and `infinity'. The - special "not a number" value formats as `-nan' or `nan'. + `-infinity', and positive infinity as `inf' or `infinity'. The + special "not a number" value formats as `-nan' or `nan' (*note + Math Definitions::). `%F' Like `%f' but the infinity and "not a number" values are spelled @@ -5618,7 +6453,7 @@ width. Here is a list of the format-control letters: The `%F' format is a POSIX extension to ISO C; not all systems support it. On those that don't, `gawk' uses `%f' instead. -`%g, %G' +`%g', `%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, `%G' uses `E' instead of `e'. @@ -5631,10 +6466,10 @@ width. Here is a list of the format-control letters: `%u' Print an unsigned decimal integer. (This format is of marginal - use, because all numbers in `awk' are floating-point; it is + use, because all numbers in `awk' are floating point; it is provided primarily for compatibility with C.) -`%x, %X' +`%x', `%X' Print an unsigned hexadecimal integer; `%X' uses the letters `A' through `F' instead of `a' through `f' (*note Nondecimal-numbers::). @@ -5659,7 +6494,7 @@ File: gawk.info, Node: Format Modifiers, Next: Printf Examples, Prev: Control A format specification can also include "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 `%' and the format-control letter. -We will use the bullet symbol "*" in the following examples to represent +We use the bullet symbol "*" in the following examples to represent spaces in the output. Here are the possible modifiers, in the order in which they may appear: @@ -5679,10 +6514,9 @@ which they may appear: At first glance, this feature doesn't seem to be of much use. It is in fact a `gawk' extension, intended for use in translating messages at runtime. *Note Printf Ordering::, which describes how - and why to use positional specifiers. For now, we will not use - them. + and why to use positional specifiers. For now, we ignore them. -`-' +`- (Minus)' The minus sign, used before the width modifier (see later on in this list), says to left-justify the argument within its specified width. Normally, the argument is printed right-justified in the @@ -5703,21 +6537,21 @@ which they may appear: space modifier. `#' - Use an "alternate form" for certain control letters. For `%o', + Use an "alternative form" for certain control letters. For `%o', supply a leading zero. For `%x' and `%X', supply a leading `0x' or `0X' for a nonzero result. For `%e', `%E', `%f', and `%F', the result always contains a decimal point. For `%g' and `%G', trailing zeros are not removed from the result. `0' - A leading `0' (zero) acts as a flag that indicates 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 value to print. + A leading `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 value to print. `'' A single quote or apostrophe character is a POSIX extension to ISO - C. It indicates that the integer part of a floating point value, + C. 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: @@ -5730,12 +6564,12 @@ which they may appear: -| 1,234,567 Results in US English UTF locale For more information about locales and internationalization issues, - see *Note Locales::. + see *note Locales::. NOTE: The `'' flag is a nice feature, but its use complicates things: it becomes difficult to use it in command-line programs. For information on appropriate quoting tricks, see - *Note Quoting::. + *note Quoting::. `WIDTH' This is a number specifying the desired minimum width of a field. @@ -5782,10 +6616,10 @@ which they may appear: prints `foob'. - The C library `printf''s dynamic WIDTH and PREC capability (for -example, `"%*.*s"') is supported. Instead of supplying explicit WIDTH -and/or PREC values in the format string, they are passed in the -argument list. For example: + The C library `printf''s dynamic WIDTH and PREC capability (e.g., +`"%*.*s"') is supported. Instead of supplying explicit WIDTH and/or +PREC values in the format string, they are passed in the argument list. +For example: w = 5 p = 3 @@ -5809,11 +6643,12 @@ string, like so: This is not particularly easy to read but it does work. - C programmers may be used to supplying additional `l', `L', and `h' -modifiers in `printf' format strings. These are not valid in `awk'. -Most `awk' implementations silently ignore them. If `--lint' is -provided on the command line (*note Options::), `gawk' warns about -their use. If `--posix' is supplied, their use is a fatal error. + C programmers may be used to supplying additional modifiers (`h', +`j', `l', `L', `t', and `z') in `printf' format strings. These are not +valid in `awk'. Most `awk' implementations silently ignore them. If +`--lint' is provided on the command line (*note Options::), `gawk' +warns about their use. If `--posix' is supplied, their use is a fatal +error. File: gawk.info, Node: Printf Examples, Prev: Format Modifiers, Up: Printf @@ -5824,25 +6659,25 @@ File: gawk.info, Node: Printf Examples, Prev: Format Modifiers, Up: Printf The following simple example shows how to use `printf' to make an aligned table: - awk '{ printf "%-10s %s\n", $1, $2 }' BBS-list + awk '{ printf "%-10s %s\n", $1, $2 }' mail-list -This command prints the names of the bulletin boards (`$1') in the file -`BBS-list' as a string of 10 characters that are left-justified. It +This command prints the names of the people (`$1') in the file +`mail-list' as a string of 10 characters that are left-justified. It also prints the phone numbers (`$2') next on the line. This produces an aligned two-column table of names and phone numbers, as shown here: - $ awk '{ printf "%-10s %s\n", $1, $2 }' BBS-list - -| aardvark 555-5553 - -| alpo-net 555-3412 - -| barfly 555-7685 - -| bites 555-1675 - -| camelot 555-0542 - -| core 555-2912 - -| fooey 555-1234 - -| foot 555-6699 - -| macfoo 555-6480 - -| sdace 555-3430 - -| sabafoo 555-2127 + $ awk '{ printf "%-10s %s\n", $1, $2 }' mail-list + -| Amelia 555-5553 + -| Anthony 555-3412 + -| Becky 555-7685 + -| Bill 555-1675 + -| Broderick 555-0542 + -| Camilla 555-2912 + -| Fabius 555-1234 + -| Julie 555-6699 + -| Martin 555-6480 + -| Samuel 555-3430 + -| Jean-Paul 555-2127 In this case, the phone numbers had to be printed as strings because the numbers are separated by a dash. Printing the phone numbers as @@ -5854,20 +6689,21 @@ 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 `BEGIN' pattern (*note +tops of the columns. This is done using a `BEGIN' rule (*note BEGIN/END::) so that the headers are only printed once, at the beginning of the `awk' program: awk 'BEGIN { print "Name Number" print "---- ------" } - { printf "%-10s %s\n", $1, $2 }' BBS-list + { printf "%-10s %s\n", $1, $2 }' mail-list - The above example mixes `print' and `printf' statements in the same -program. Using just `printf' statements can produce the same results: + The preceding example mixes `print' and `printf' statements in the +same program. Using just `printf' statements can produce the same +results: 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 Printing each column heading with the same format specification used for the column elements ensures that the headings are aligned just like @@ -5879,15 +6715,10 @@ be 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 - - At this point, it would be a worthwhile exercise to use the `printf' -statement to line up the headings and table data for the -`inventory-shipped' example that was covered earlier in the minor node -on the `print' statement (*note Print::). + { printf format, $1, $2 }' mail-list -File: gawk.info, Node: Redirection, Next: Special Files, Prev: Printf, Up: Printing +File: gawk.info, Node: Redirection, Next: Special FD, Prev: Printf, Up: Printing 5.6 Redirecting Output of `print' and `printf' ============================================== @@ -5897,7 +6728,7 @@ output, usually the screen. Both `print' and `printf' can also send their output to other places. This is called "redirection". NOTE: When `--sandbox' is specified (*note Options::), redirecting - output to files and pipes is disabled. + output to files, pipes and coprocesses is disabled. A redirection appears after the `print' or `printf' statement. Redirections in `awk' are written just like redirections in shell @@ -5905,7 +6736,7 @@ commands, except that they are written inside the `awk' program. 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 `print' statement, but they +to a coprocess. We show them all for the `print' statement, but they work identically for `printf': `print ITEMS > OUTPUT-FILE' @@ -5919,19 +6750,19 @@ work identically for `printf': the same OUTPUT-FILE do not erase OUTPUT-FILE, but append to it. (This is different from how you use redirections in shell scripts.) If OUTPUT-FILE does not exist, it is created. For example, here - is how an `awk' program can write a list of BBS names to one file - named `name-list', and a list of phone numbers to another file + is how an `awk' program can write a list of peoples' names to one + file named `name-list', and a list of phone numbers to another file named `phone-list': $ awk '{ print $2 > "phone-list" - > print $1 > "name-list" }' BBS-list + > print $1 > "name-list" }' mail-list $ cat phone-list -| 555-5553 -| 555-3412 ... $ cat name-list - -| aardvark - -| alpo-net + -| Amelia + -| Anthony ... Each output file contains one name or number per line. @@ -5952,12 +6783,12 @@ work identically for `printf': The redirection argument COMMAND is actually an `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 + one unsorted list of peoples' names, and one list sorted in reverse alphabetical order: awk '{ print $1 > "names.unsorted" command = "sort -r > names.sorted" - print $1 | command }' BBS-list + print $1 | command }' mail-list The unsorted list is written with an ordinary redirection, while the sorted list is written by piping through the `sort' utility. @@ -5968,16 +6799,10 @@ work identically for `printf': maintenance: 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) - The message is built using string concatenation and saved in the - variable `m'. It's then sent down the pipeline to the `mail' - program. (The parentheses group the items to concatenate--see - *Note Concatenation::.) - The `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. *Note Close Files And Pipes::, for more information. @@ -5986,7 +6811,7 @@ work identically for `printf': FILE or 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) `awk' requires - that the string value be spelled identically every time. + that the string value be written identically every time. `print ITEMS |& COMMAND' This redirection prints the items to the input of COMMAND. The @@ -6015,7 +6840,7 @@ a file, and then to use `>>' for subsequent output: This is indeed how redirections must be used from the shell. But in `awk', it isn't necessary. In this kind of case, a program should use -`>' for all the `print' statements, since the output file is only +`>' for all the `print' statements, because the output file is only opened once. (It happens that if you mix `>' and `>>' 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 of your @@ -6026,14 +6851,13 @@ an `awk' program may have open to just one! In `gawk', there is no such limit. `gawk' allows a program to open as many pipelines as the underlying operating system permits. -Advanced Notes: Piping into `sh' --------------------------------- + Piping into `sh' -A particularly powerful way to use redirection is to build command lines -and pipe them into the shell, `sh'. For example, suppose you have a -list of files brought over from a system where all the file names are -stored in uppercase, and you wish to rename them to have names in all -lowercase. The following program is both simple and efficient: + A particularly powerful way to use redirection is to build command +lines and pipe them into the shell, `sh'. For example, suppose you +have a list of files brought over from a system where all the file names +are stored in uppercase, and you wish to rename them to have names in +all lowercase. The following program is both simple and efficient: { printf("mv %s %s\n", $0, tolower($0)) | "sh" } @@ -6044,67 +6868,56 @@ uppercase characters converted to lowercase (*note String Functions::). The program builds up a list of command lines, using the `mv' utility to rename the files. It then sends the list to the shell for execution. - -File: gawk.info, Node: Special Files, Next: Close Files And Pipes, Prev: Redirection, Up: Printing - -5.7 Special File Names in `gawk' -================================ - -`gawk' provides a number of special file names that it interprets -internally. These file names provide access to standard file -descriptors and TCP/IP networking. - -* Menu: - -* Special FD:: Special files for I/O. -* Special Network:: Special files for network communications. -* Special Caveats:: Things to watch out for. + *Note Shell Quoting::, for a function that can help in generating +command lines to be fed to the shell. -File: gawk.info, Node: Special FD, Next: Special Network, Up: Special Files +File: gawk.info, Node: Special FD, Next: Special Files, Prev: Redirection, Up: Printing -5.7.1 Special Files for Standard Descriptors --------------------------------------------- +5.7 Special Files for Standard Pre-Opened Data Streams +====================================================== Running programs conventionally have three input and output streams already available to them for reading and writing. These are known as the "standard input", "standard output", and "standard error output". -These streams are, by default, connected to your keyboard and screen, -but they are often redirected with the shell, via the `<', `<<', `>', -`>>', `>&', and `|' operators. Standard error is typically used for -writing error messages; the reason there are two separate streams, +These open streams (and any other open file or pipe) are often referred +to by the technical term "file descriptors". + + These streams are, by default, connected to your keyboard and +screen, but they are often redirected with the shell, via the `<', `<<', +`>', `>>', `>&', and `|' operators. Standard error is typically used +for writing error messages; the reason there are two separate streams, standard output and standard error, is so that they can be redirected separately. - In other implementations of `awk', the only way to write an error -message to standard error in an `awk' program is as follows: + In traditional implementations of `awk', the only way to write an +error message to standard error in an `awk' program is as follows: print "Serious error detected!" | "cat 1>&2" This works by opening a pipeline to a shell command that can access the standard error stream that it inherits from the `awk' process. This is -far from elegant, and it is also inefficient, because it requires a -separate process. So people writing `awk' programs often don't do -this. Instead, they send the error messages to the screen, like this: +far from elegant, and it also requires a separate process. So people +writing `awk' programs often don't do this. Instead, they send the +error messages to the screen, like this: print "Serious error detected!" > "/dev/tty" (`/dev/tty' is a special file supplied by the operating system that is connected to your keyboard and screen. It represents the "terminal,"(1) which on modern systems is a keyboard and screen, not a serial console.) -This usually 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 `awk' is -run from a background job, it may not have a terminal at all. Then +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 `awk' +is run from a background job, it may not have a terminal at all. Then opening `/dev/tty' fails. - `gawk' provides special file names for accessing the three standard -streams. (c.e.). It also provides syntax for accessing any other -inherited open files. If the file name matches one of these special -names when `gawk' redirects input or output, then it directly uses the -stream that the file name stands for. These special file names work -for all operating systems that `gawk' has been ported to, not just -those that are POSIX-compliant: + `gawk', BWK `awk', and `mawk' provide special file names for +accessing the three standard streams. If the file name matches one of +these special names when `gawk' (or one of the others) redirects input +or output, then it directly uses the descriptor that the file name +stands for. These special file names work for all operating systems +that `gawk' has been ported to, not just those that are POSIX-compliant: `/dev/stdin' The standard input (file descriptor 0). @@ -6115,16 +6928,8 @@ those that are POSIX-compliant: `/dev/stderr' The standard error output (file descriptor 2). -`/dev/fd/N' - The file associated with file descriptor N. Such a file must be - opened by the program initiating the `awk' execution (typically - the shell). Unless special pains are taken in the shell from which - `gawk' is invoked, only descriptors 0, 1, and 2 are available. - - The file names `/dev/stdin', `/dev/stdout', and `/dev/stderr' are -aliases for `/dev/fd/0', `/dev/fd/1', and `/dev/fd/2', respectively. -However, they are more self-explanatory. The proper way to write an -error message in a `gawk' program is to use `/dev/stderr', like this: + With these facilities, the proper way to write an error message then +becomes: print "Serious error detected!" > "/dev/stderr" @@ -6132,21 +6937,60 @@ error message in a `gawk' program is to use `/dev/stderr', like this: redirection, the value must be a string. It is a common error to omit the quotes, which leads to confusing results. - Finally, using the `close()' function on a file name of the form -`"/dev/fd/N"', for file descriptor numbers above two, will actually -close the given file descriptor. - - The `/dev/stdin', `/dev/stdout', and `/dev/stderr' special files are -also recognized internally by several other versions of `awk'. + `gawk' does not treat these file names as special when in +POSIX-compatibility mode. However, because BWK `awk' supports them, +`gawk' does support them even when invoked with the `--traditional' +option (*note Options::). ---------- Footnotes ---------- (1) The "tty" in `/dev/tty' stands for "Teletype," a serial terminal. -File: gawk.info, Node: Special Network, Next: Special Caveats, Prev: Special FD, Up: Special Files +File: gawk.info, Node: Special Files, Next: Close Files And Pipes, Prev: Special FD, Up: Printing + +5.8 Special File Names in `gawk' +================================ + +Besides access to standard input, standard output, and standard error, +`gawk' provides access to any open file descriptor. Additionally, +there are special file names reserved for TCP/IP networking. + +* Menu: -5.7.2 Special Files for Network Communications +* Other Inherited Files:: Accessing other open files with + `gawk'. +* Special Network:: Special files for network communications. +* Special Caveats:: Things to watch out for. + + +File: gawk.info, Node: Other Inherited Files, Next: Special Network, Up: Special Files + +5.8.1 Accessing Other Open Files With `gawk' +-------------------------------------------- + +Besides the `/dev/stdin', `/dev/stdout', and `/dev/stderr' special file +names mentioned earlier, `gawk' provides syntax for accessing any other +inherited open file: + +`/dev/fd/N' + The file associated with file descriptor N. Such a file must be + opened by the program initiating the `awk' execution (typically + the shell). Unless special pains are taken in the shell from which + `gawk' is invoked, only descriptors 0, 1, and 2 are available. + + The file names `/dev/stdin', `/dev/stdout', and `/dev/stderr' are +essentially aliases for `/dev/fd/0', `/dev/fd/1', and `/dev/fd/2', +respectively. However, those names are more self-explanatory. + + Note that using `close()' on a file name of the form `"/dev/fd/N"', +for file descriptor numbers above two, does actually close the given +file descriptor. + + +File: gawk.info, Node: Special Network, Next: Special Caveats, Prev: Other Inherited Files, Up: Special Files + +5.8.2 Special Files for Network Communications ---------------------------------------------- `gawk' programs can open a two-way TCP/IP connection, acting as either @@ -6155,25 +6999,29 @@ form: `/NET-TYPE/PROTOCOL/LOCAL-PORT/REMOTE-HOST/REMOTE-PORT' - The NET-TYPE is one of `inet', `inet4' or `inet6'. The PROTOCOL is + The NET-TYPE is one of `inet', `inet4', or `inet6'. The PROTOCOL is one of `tcp' or `udp', and the other fields represent the other essential pieces of information for making a networking connection. These file names are used with the `|&' operator for communicating with a coprocess (*note Two-way I/O::). This is an advanced feature, mentioned here only for completeness. Full discussion is delayed until -*Note TCP/IP Networking::. +*note TCP/IP Networking::. File: gawk.info, Node: Special Caveats, Prev: Special Network, Up: Special Files -5.7.3 Special File Name Caveats +5.8.3 Special File Name Caveats ------------------------------- -Here is a list of things to bear in mind when using the special file -names that `gawk' provides: +Here are some things to bear in mind when using the special file names +that `gawk' provides: - * Recognition of these special file names is disabled if `gawk' is in - compatibility mode (*note Options::). + * Recognition of the file names for the three standard pre-opened + files is disabled only in POSIX mode. + + * Recognition of the other special file names is disabled if `gawk' + is in compatibility mode (either `--traditional' or `--posix'; + *note Options::). * `gawk' _always_ interprets these special file names. For example, using `/dev/fd/4' for output actually writes on file descriptor 4, @@ -6184,9 +7032,9 @@ names that `gawk' provides: behavior. -File: gawk.info, Node: Close Files And Pipes, Prev: Special Files, Up: Printing +File: gawk.info, Node: Close Files And Pipes, Next: Output Summary, Prev: Special Files, Up: Printing -5.8 Closing Input and Output Redirections +5.9 Closing Input and Output Redirections ========================================= If the same file name or the same shell command is used with `getline' @@ -6292,14 +7140,17 @@ end-of-file return status from `getline'), the child process is not terminated;(1) more importantly, the file descriptor for the pipe is not closed and released until `close()' is called or `awk' exits. - `close()' will silently do nothing if given an argument that does -not represent a file, pipe or coprocess that was opened with a -redirection. + `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, `gawk' sets `ERRNO' to a string indicating the +error. Note also that `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 `awk' -silently does nothing. +It is, more likely, a close of a file that was never opened with a +redirection, so `awk' silently does nothing, except return a negative +value. When using the `|&' operator to communicate with a coprocess, it is occasionally useful to be able to close one end of the two-way pipe @@ -6308,15 +7159,14 @@ to `close()'. As in any other call to `close()', 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 `"to"' or `"from"'. Case does not matter. As this is an advanced -feature, a more complete discussion is delayed until *Note Two-way -I/O::, which discusses it in more detail and gives an example. +feature, discussion is delayed until *note Two-way I/O::, which +describes it in more detail and gives an example. -Advanced Notes: Using `close()''s Return Value ----------------------------------------------- + Using `close()''s Return Value -In many versions of Unix `awk', the `close()' function is actually a -statement. It is a syntax error to try and use the return value from -`close()': (d.c.) + In many older versions of Unix `awk', the `close()' function is +actually a statement. (d.c.) It is a syntax error to try and use the +return value from `close()': command = "..." command | getline info @@ -6325,8 +7175,8 @@ statement. It is a syntax error to try and use the return value from `gawk' treats `close()' as a function. The return value is -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, `gawk' sets the built-in variable `ERRNO' to a string describing -the problem. +cases, `gawk' sets the predefined variable `ERRNO' to a string +describing the problem. In `gawk', when closing a pipe or coprocess (input or output), the return value is the exit status of the command.(2) Otherwise, it is the @@ -6351,6 +7201,56 @@ call. See the system manual pages for information on how to decode this value. +File: gawk.info, Node: Output Summary, Next: Output Exercises, Prev: Close Files And Pipes, Up: Printing + +5.10 Summary +============ + + * The `print' statement prints comma-separated expressions. Each + expression is separated by the value of `OFS' and terminated by + the value of `ORS'. `OFMT' provides the conversion format for + numeric values for the `print' statement. + + * The `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. + + * Output from both `print' and `printf' may be redirected to files, + pipes, and coprocesses. + + * `gawk' provides special file names for access to standard input, + output, and error, and for network communications. + + * Use `close()' to close open file, pipe, and coprocess redirections. + For coprocesses, it is possible to close only one direction of the + communications. + + + +File: gawk.info, Node: Output Exercises, Prev: Output Summary, Up: Printing + +5.11 Exercises +============== + + 1. Rewrite the program: + + awk 'BEGIN { print "Month Crates" + print "----- ------" } + { print $1, " ", $2 }' inventory-shipped + + from *note Output Separators::, by using a new value of `OFS'. + + 2. Use the `printf' statement to line up the headings and table data + for the `inventory-shipped' example that was covered in *note + Print::. + + 3. What happens if you forget the double quotes when redirecting + output, as follows: + + BEGIN { print "Serious error detected!" > /dev/stderr } + + + File: gawk.info, Node: Expressions, Next: Patterns and Actions, Prev: Printing, Up: Top 6 Expressions @@ -6376,12 +7276,13 @@ operators. * Function Calls:: A function call is an expression. * Precedence:: How various operators nest. * Locales:: How the locale affects things. +* Expressions Summary:: Expressions summary. File: gawk.info, Node: Values, Next: All Operators, Up: Expressions -6.1 Constants, Variables and Conversions -======================================== +6.1 Constants, Variables, and Conversions +========================================= Expressions are built up from values and the operations performed upon them. This minor node describes the elementary objects which provide @@ -6407,7 +7308,7 @@ 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. +forms, but are internally stored in an identical manner. * Menu: @@ -6431,7 +7332,7 @@ the same value: 1050e-1 A string constant consists of a sequence of characters enclosed in -double-quotation marks. For example: +double quotation marks. For example: "parrot" @@ -6444,8 +7345,9 @@ codes. ---------- Footnotes ---------- (1) 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. +uses double-precision floating-point numbers. On most modern systems, +these are in IEEE 754 standard format. *Note Arbitrary Precision +Arithmetic::, for much more information. File: gawk.info, Node: Nondecimal-numbers, Next: Regexp Constants, Prev: Scalar Constants, Up: Constants @@ -6453,17 +7355,17 @@ File: gawk.info, Node: Nondecimal-numbers, Next: Regexp Constants, Prev: Scal 6.1.1.2 Octal and Hexadecimal Numbers ..................................... -In `awk', all numbers are in decimal; i.e., base 10. Many other +In `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. Just as `11', in decimal, is 1 -times 10 plus 1, so `11', in octal, is 1 times 8, plus 1. This equals 9 -in decimal. In hexadecimal, there are 16 digits. Since the everyday -decimal number system only has ten digits (`0'-`9'), the letters `a' -through `f' are used to represent the rest. (Case in the letters is -usually irrelevant; hexadecimal `a' and `A' have the same value.) -Thus, `11', in hexadecimal, is 1 times 16 plus 1, which equals 17 in -decimal. +1, 2, 3, 4, 5, 6, 7, 10, 11, 12, and so on. Just as `11', in decimal, +is 1 times 10 plus 1, so `11', in octal, is 1 times 8, plus 1. This +equals 9 in decimal. In hexadecimal, there are 16 digits. Because the +everyday decimal number system only has ten digits (`0'-`9'), the +letters `a' through `f' are used to represent the rest. (Case in the +letters is usually irrelevant; hexadecimal `a' and `A' have the same +value.) Thus, `11', in hexadecimal, is 1 times 16 plus 1, which equals +17 in decimal. Just by looking at plain `11', you can't tell what base it's in. So, in C, C++, and other languages derived from C, there is a special @@ -6497,11 +7399,11 @@ option; *note Nondecimal Data::.) If you have octal or hexadecimal data, you can use the `strtonum()' function (*note String Functions::) 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 *Note Bitwise Functions::, for more +manipulation functions; see *note Bitwise Functions::, for more information. Unlike some early C implementations, `8' and `9' are not valid in -octal constants; e.g., `gawk' treats `018' as decimal 18: +octal constants. For example, `gawk' treats `018' as decimal 18: $ gawk 'BEGIN { print "021 is", 021 ; print 018 }' -| 021 is 17 @@ -6511,10 +7413,9 @@ octal constants; e.g., `gawk' treats `018' as decimal 18: If `gawk' is in compatibility mode (*note Options::), they are not available. -Advanced Notes: A Constant's Base Does Not Affect Its Value ------------------------------------------------------------ + A Constant's Base Does Not Affect Its Value -Once a numeric constant has been converted internally into a number, + Once a numeric constant has been converted internally into a number, `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: @@ -6531,8 +7432,9 @@ File: gawk.info, Node: Regexp Constants, Prev: Nondecimal-numbers, Up: Consta A regexp constant is a regular expression description enclosed in slashes, such as `/^beginning and end$/'. Most regexps used in `awk' programs are constant, but the `~' and `!~' matching operators can also -match computed or dynamic regexps (which are just ordinary strings or -variables that contain a regexp). +match computed or dynamic regexps (which are typically just ordinary +strings or variables that contain a regexp, but could be a more complex +expression). File: gawk.info, Node: Using Constant Regexps, Next: Variables, Prev: Constants, Up: Values @@ -6544,8 +7446,8 @@ When used on the righthand side of the `~' or `!~' operators, a regexp constant merely stands for the regexp that is to be matched. However, regexp constants (such as `/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., `($0 ~ /foo/)' (d.c.) *Note Expression -Patterns::. This means that the following two code segments: +it appeared in a pattern (i.e., `($0 ~ /foo/)'). (d.c.) *Note +Expression Patterns::. This means that the following two code segments: if ($0 ~ /barfly/ || $0 ~ /camelot/) print "found" @@ -6557,7 +7459,7 @@ and: 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 intended: +its author probably intended: # Note that /foo/ is on the left of the ~ if (/foo/ ~ $1) print "found foo" @@ -6579,13 +7481,14 @@ the contents of the current input record. Constant regular expressions are also used as the first argument for the `gensub()', `sub()', and `gsub()' functions, as the second argument -of the `match()' function, and as the third argument of the -`patsplit()' function (*note String Functions::). Modern +of the `match()' function, and as the third argument of the `split()' +and `patsplit()' functions (*note String Functions::). Modern implementations of `awk', including `gawk', allow the third argument of `split()' to be a regexp constant, but some older implementations do -not. (d.c.) This can lead to confusion when attempting to use regexp -constants as arguments to user-defined functions (*note User-defined::). -For example: +not. (d.c.) 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 (*note +User-defined::). For example: function mysub(pat, repl, str, global) { @@ -6604,12 +7507,12 @@ For example: } In this example, the programmer wants to pass a regexp constant to -the user-defined function `mysub', which in turn passes it on to either -`sub()' or `gsub()'. However, what really happens is that the `pat' -parameter is either one or zero, depending upon whether or not `$0' -matches `/hi/'. `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 this way is probably not what was intended. +the user-defined function `mysub()', which in turn passes it on to +either `sub()' or `gsub()'. However, what really happens is that the +`pat' parameter is either one or zero, depending upon whether or not +`$0' matches `/hi/'. `gawk' issues a warning when it sees a regexp +constant used as a parameter to a user-defined function, because +passing a truth value in this way is probably not what was intended. File: gawk.info, Node: Variables, Next: Conversion, Prev: Using Constant Regexps, Up: Values @@ -6625,7 +7528,7 @@ on the `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. @@ -6638,31 +7541,34 @@ File: gawk.info, Node: Using Variables, Next: Assignment Options, Up: Variabl 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; -`a' and `A' are distinct variables. +it may not begin with a digit. Here, a "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; `a' and `A' are distinct +variables. A variable name is a valid expression by itself; it represents the variable's current value. Variables are given new values with "assignment operators", "increment operators", and "decrement operators". *Note Assignment Ops::. In addition, the `sub()' and `gsub()' functions can change a variable's value, and the `match()', -`patsplit()' and `split()' functions can change the contents of their +`split()', and `patsplit()' functions can change the contents of their array parameters. *Note String Functions::. A few variables have special built-in meanings, such as `FS' (the field separator), and `NF' (the number of fields in the current input -record). *Note Built-in Variables::, for a list of the built-in -variables. These built-in variables can be used and assigned just like -all other variables, but their values are also used or changed -automatically by `awk'. All built-in variables' names are entirely +record). *Note 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 `awk'. All predefined variables' names are entirely uppercase. Variables in `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 `awk', which is what you would do in C and -in most other traditional languages. +initialize a variable in `awk', which is what you would do in C and in +most other traditional languages. File: gawk.info, Node: Assignment Options, Prev: Using Variables, Up: Variables @@ -6690,16 +7596,16 @@ 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: - awk '{ print $n }' n=4 inventory-shipped n=2 BBS-list + awk '{ print $n }' n=4 inventory-shipped n=2 mail-list prints the value of field number `n' for all input records. Before the first file is read, the command line sets the variable `n' equal to four. This causes the fourth field to be printed in lines from `inventory-shipped'. After the first file has finished, but before the second file is started, `n' is set to two, so that the second field is -printed in lines from `BBS-list': +printed in lines from `mail-list': - $ awk '{ print $n }' n=4 inventory-shipped n=2 BBS-list + $ awk '{ print $n }' n=4 inventory-shipped n=2 mail-list -| 15 -| 24 ... @@ -6718,6 +7624,22 @@ File: gawk.info, Node: Conversion, Prev: Variables, Up: Values 6.1.4 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 minor +node discusses this important facet of `awk'. + +* Menu: + +* Strings And Numbers:: How `awk' Converts Between Strings And + Numbers. +* Locale influences conversions:: How the locale may affect conversions. + + +File: gawk.info, Node: Strings And Numbers, Next: Locale influences conversions, Up: Conversion + +6.1.4.1 How `awk' Converts Between Strings and Numbers +...................................................... + Strings are converted to numbers and numbers are converted to strings, if the context of the `awk' program demands it. For example, if the value of either `foo' or `bar' in the expression `foo + bar' happens to @@ -6738,15 +7660,15 @@ string, concatenate that number with the empty string, `""'. 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: `"2.5"' converts to 2.5, `"1e3"' converts to -1000, and `"25fix"' has a numeric value of 25. Strings that can't be +1,000, and `"25fix"' has a numeric value of 25. Strings that can't be interpreted as valid numbers convert to zero. The exact manner in which numbers are converted into strings is -controlled by the `awk' built-in variable `CONVFMT' (*note Built-in +controlled by the `awk' predefined variable `CONVFMT' (*note Built-in Variables::). Numbers are converted using the `sprintf()' function with `CONVFMT' as the format specifier (*note String Functions::). - `CONVFMT''s default value is `"%.6g"', which prints a value with at + `CONVFMT''s default value is `"%.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, 17 digits is usually enough to capture a floating-point number's value @@ -6767,61 +7689,74 @@ value of `CONVFMT' may be. Given the following code fragment: `b' has the value `"12"', not `"12.00"'. (d.c.) + Pre-POSIX `awk' Used `OFMT' for String Conversion + Prior to the POSIX standard, `awk' used the value of `OFMT' for converting numbers to strings. `OFMT' specifies the output format to use when printing numbers with `print'. `CONVFMT' was introduced in order to separate the semantics of conversion from the semantics of printing. Both `CONVFMT' and `OFMT' have the same default value: `"%.6g"'. In the vast majority of cases, old `awk' programs do not -change their behavior. However, these semantics for `OFMT' are -something to keep in mind if you must port your new-style program to -older implementations of `awk'. We recommend that instead of changing -your programs, just port `gawk' itself. *Note Print::, for more -information on the `print' statement. - - And, once again, where you are can matter when it comes to converting -between numbers and strings. In *Note Locales::, we mentioned that the -local character set and language (the locale) can affect how `gawk' -matches characters. The locale also affects numeric formats. In -particular, for `awk' programs, it affects the decimal point character. -The `"C"' locale, and most English-language locales, use the period -character (`.') as the decimal point. However, many (if not most) -European and non-English locales use the comma (`,') as the decimal -point character. +change their behavior. *Note Print::, for more information on the +`print' statement. + + ---------- Footnotes ---------- + + (1) Pathological cases can require up to 752 digits (!), but we +doubt that you need to worry about this. + + +File: gawk.info, Node: Locale influences conversions, Prev: Strings And Numbers, Up: Conversion + +6.1.4.2 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 "locale"--can +affect numeric formats. In particular, for `awk' programs, it affects +the decimal point character and the thousands-separator character. The +`"C"' locale, and most English-language locales, use the period +character (`.') as the decimal point and don't have a thousands +separator. However, many (if not most) European and non-English +locales use the comma (`,') as the decimal point character. European +locales often use either a space or a period as the thousands +separator, if they have one. The POSIX standard says that `awk' always uses the period as the decimal point when reading the `awk' program source code, and for command-line variable assignments (*note Other Arguments::). However, when interpreting input data, for `print' and `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: +number-to-string conversion, the local decimal point character is used. +(d.c.) 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: + $ export POSIXLY_CORRECT=1 Force POSIX behavior $ gawk 'BEGIN { printf "%g\n", 3.1415927 }' -| 3.14159 - $ LC_ALL=en_DK gawk 'BEGIN { printf "%g\n", 3.1415927 }' + $ LC_ALL=en_DK.utf-8 gawk 'BEGIN { printf "%g\n", 3.1415927 }' -| 3,14159 $ echo 4,321 | gawk '{ print $1 + 1 }' -| 5 - $ echo 4,321 | LC_ALL=en_DK gawk '{ print $1 + 1 }' + $ echo 4,321 | LC_ALL=en_DK.utf-8 gawk '{ print $1 + 1 }' -| 5,321 -The `en_DK' locale is for English in Denmark, where the comma acts as -the decimal point separator. In the normal `"C"' locale, `gawk' treats -`4,321' as `4', while in the Danish locale, it's treated as the full -number, 4.321. +The `en_DK.utf-8' locale is for English in Denmark, where the comma +acts as the decimal point separator. In the normal `"C"' locale, `gawk' +treats `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 `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 `--use-lc-numeric' option (*note Options::) to force `gawk' to use the locale's decimal point character. (`gawk' also uses the locale's decimal point character when in POSIX mode, either via `--posix', or the `POSIXLY_CORRECT' -environment variable.) +environment variable, as shown previously.) - *Note table-locale-affects:: describes the cases in which the + *note 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. @@ -6832,22 +7767,17 @@ Feature Default `--posix' or `--use-lc-numeric' Input Use period Use locale `strtonum()'Use period Use locale -Table 6.1: Locale Decimal Point versus A Period +Table 6.1: Locale decimal point versus a period - 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 `gawk' converts some special string values to numbers. The details are -presented in *Note POSIX Floating Point Problems::. - - ---------- Footnotes ---------- - - (1) Pathological cases can require up to 752 digits (!), but we -doubt that you need to worry about this. +presented in *note POSIX Floating Point Problems::. File: gawk.info, Node: All Operators, Next: Truth Values and Conditions, Prev: Values, Up: Expressions -6.2 Operators: Doing Something With Values +6.2 Operators: Doing Something with Values ========================================== This minor node introduces the "operators" which make use of the values @@ -6891,17 +7821,17 @@ scores: The following list provides the arithmetic operators in `awk', in order from the highest precedence to the lowest: +`X ^ Y' +`X ** Y' + Exponentiation; X raised to the Y power. `2 ^ 3' has the value + eight; the character sequence `**' is equivalent to `^'. (c.e.) + `- X' Negation. `+ X' Unary plus; the expression is converted to a number. -`X ^ Y' -`X ** Y' - Exponentiation; X raised to the Y power. `2 ^ 3' has the value - eight; the character sequence `**' is equivalent to `^'. (c.e.) - `X * Y' Multiplication. @@ -6909,9 +7839,9 @@ order from the highest precedence to the lowest: Division; because all numbers in `awk' are floating-point numbers, the result is _not_ rounded to an integer--`3 / 4' has the value 0.75. (It is a common mistake, especially for C - programmers, to forget that _all_ numbers in `awk' are - floating-point, and that division of integer-looking constants - produces a real number, not an integer.) + programmers, to forget that _all_ numbers in `awk' are floating + point, and that division of integer-looking constants produces a + real number, not an integer.) `X % Y' Remainder; further discussion is provided in the text, just after @@ -6952,29 +7882,28 @@ File: gawk.info, Node: Concatenation, Next: Assignment Ops, Prev: Arithmetic 6.2.2 String Concatenation -------------------------- - It seemed like a good idea at the time. - Brian Kernighan + It seemed like a good idea at the time. -- Brian Kernighan There is only one string operation: concatenation. It does not have a specific operator to represent it. Instead, concatenation is performed by writing expressions next to one another, with no operator. For example: - $ awk '{ print "Field number one: " $1 }' BBS-list - -| Field number one: aardvark - -| Field number one: alpo-net + $ awk '{ print "Field number one: " $1 }' mail-list + -| Field number one: Amelia + -| Field number one: Anthony ... Without the space in the string constant after the `:', the line runs together. For example: - $ awk '{ print "Field number one:" $1 }' BBS-list - -| Field number one:aardvark - -| Field number one:alpo-net + $ awk '{ print "Field number one:" $1 }' mail-list + -| Field number one:Amelia + -| Field number one:Anthony ... Because string concatenation does not have an explicit operator, it -is often necessary to insure that it happens at the right time by using +is 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 `file' and `name': @@ -7000,9 +7929,9 @@ example: print (a " " (a = "panic")) } -It is not defined whether the assignment to `a' happens before or after -the value of `a' is retrieved for producing the concatenated value. -The result could be either `don't panic', or `panic panic'. +It is not defined whether the second assignment to `a' happens before +or after the value of `a' is retrieved for producing the concatenated +value. The result could be either `don't panic', or `panic panic'. The precedence of concatenation, when mixed with other operators, is often counter-intuitive. Consider this example: @@ -7026,13 +7955,14 @@ Otherwise, it's parsed as follows: => -12 (-24) => -12-24 - As mentioned earlier, when doing concatenation, _parenthesize_. -Otherwise, you're never quite sure what you'll get. + As mentioned earlier, when mixing concatenation with other +operators, _parenthesize_. Otherwise, you're never quite sure what +you'll get. ---------- Footnotes ---------- - (1) It happens that Brian Kernighan's `awk', `gawk' and `mawk' all -"get it right," but you should not rely on this. + (1) It happens that BWK `awk', `gawk' and `mawk' all "get it right," +but you should not rely on this. File: gawk.info, Node: Assignment Ops, Next: Increment Ops, Prev: Concatenation, Up: All Operators @@ -7075,9 +8005,9 @@ that the assignment stores in the specified variable, field, or array element. (Such values are called "rvalues".) It is important to note that variables do _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 -`foo' has a numeric value at first, and a string value later on: +A variable's type is simply the type of whatever value was last assigned +to it. In the following program fragment, the variable `foo' has a +numeric value at first, and a string value later on: foo = 1 print foo @@ -7148,43 +8078,43 @@ righthand expression. For example: The indices of `bar' are practically guaranteed to be different, because `rand()' returns different values each time it is called. (Arrays and the `rand()' function haven't been covered yet. *Note Arrays::, and -see *Note Numeric Functions::, for more information). This example +*note Numeric Functions::, for more information). This example illustrates an important fact about assignment operators: the lefthand -expression is only evaluated _once_. It is up to the implementation as -to which expression is evaluated first, the lefthand or the righthand. -Consider this example: +expression is only evaluated _once_. + + It is up to the implementation as to which expression is evaluated +first, the lefthand or the righthand. Consider this example: i = 1 a[i += 2] = i + 1 The value of `a[3]' could be either two or four. - *Note table-assign-ops:: lists the arithmetic assignment operators. + *note table-assign-ops:: lists the arithmetic assignment operators. In each case, the righthand operand is an expression whose value is converted to a number. Operator Effect -------------------------------------------------------------------------- -LVALUE `+=' INCREMENT Adds INCREMENT to the value of LVALUE. -LVALUE `-=' DECREMENT Subtracts DECREMENT from the value of LVALUE. -LVALUE `*=' Multiplies the value of LVALUE by COEFFICIENT. +LVALUE `+=' INCREMENT Add INCREMENT to the value of LVALUE +LVALUE `-=' DECREMENT Subtract DECREMENT from the value of LVALUE +LVALUE `*=' Multiply the value of LVALUE by COEFFICIENT COEFFICIENT -LVALUE `/=' DIVISOR Divides the value of LVALUE by DIVISOR. -LVALUE `%=' MODULUS Sets LVALUE to its remainder by MODULUS. +LVALUE `/=' DIVISOR Divide the value of LVALUE by DIVISOR +LVALUE `%=' MODULUS Set LVALUE to its remainder by MODULUS LVALUE `^=' POWER -LVALUE `**=' POWER Raises LVALUE to the power POWER. (c.e.) +LVALUE `**=' POWER Raise LVALUE to the power POWER (c.e.) -Table 6.2: Arithmetic Assignment Operators +Table 6.2: Arithmetic assignment operators NOTE: Only the `^=' operator is specified by POSIX. For maximum portability, do not use the `**=' operator. -Advanced Notes: Syntactic Ambiguities Between `/=' and Regular Expressions --------------------------------------------------------------------------- + Syntactic Ambiguities Between `/=' and Regular Expressions -There is a syntactic ambiguity between the `/=' assignment operator and -regexp constants whose first character is an `='. (d.c.) This is most -notable in commercial `awk' versions. For example: + There is a syntactic ambiguity between the `/=' assignment operator +and regexp constants whose first character is an `='. (d.c.) This is +most notable in some commercial `awk' versions. For example: $ awk /==/ /dev/null error--> awk: syntax error at source line 1 @@ -7196,8 +8126,7 @@ A workaround is: awk '/[=]=/' /dev/null - `gawk' does not have this problem, nor do the other freely available -versions described in *Note Other Versions::. + `gawk' does not have this problem; BWK `awk' and `mawk' also do not. File: gawk.info, Node: Increment Ops, Prev: Assignment Ops, Up: All Operators @@ -7212,20 +8141,20 @@ they are convenient abbreviations for very common operations. The operator used for adding one is written `++'. It can be used to increment a variable either before or after taking its value. To -pre-increment a variable `v', write `++v'. This adds one to the value -of `v'--that new value is also the value of the expression. (The +"pre-increment" a variable `v', write `++v'. This adds one to the +value of `v'--that new value is also the value of the expression. (The assignment expression `v += 1' is completely equivalent.) Writing the -`++' after the variable specifies 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 _old_ value. Thus, if -`foo' has the value four, then the expression `foo++' has the value +`++' after the variable specifies "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 _old_ value. Thus, +if `foo' has the value four, then the expression `foo++' has the value four, but it changes the value of `foo' to five. In other words, the operator returns the old value of the variable, but with the side effect of incrementing it. The post-increment `foo++' is nearly the same as writing `(foo += 1) - 1'. It is not perfectly equivalent because all numbers in `awk' are -floating-point--in floating-point, `foo + 1 - 1' does not necessarily +floating point--in floating point, `foo + 1 - 1' does not necessarily equal `foo'. But the difference is minute as long as you stick to numbers that are fairly small (less than 10e12). @@ -7257,12 +8186,10 @@ is a summary of increment and decrement expressions: of the expression. (This expression is like `LVALUE++', but instead of adding, it subtracts.) -Advanced Notes: Operator Evaluation Order ------------------------------------------ + Operator Evaluation Order Doctor, doctor! It hurts when I do this! - So don't do that! - Groucho Marx + So don't do that! -- Groucho Marx What happens for something like the following? @@ -7291,8 +8218,8 @@ File: gawk.info, Node: Truth Values and Conditions, Next: Function Calls, Pre 6.3 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 minor node describes how `awk' defines "true" and "false" and how values are compared. @@ -7343,8 +8270,8 @@ File: gawk.info, Node: Typing and Comparison, Next: Boolean Ops, Prev: Truth 6.3.2 Variable Typing and Comparison Expressions ------------------------------------------------ - The Guide is definitive. Reality is frequently inaccurate. - The Hitchhiker's Guide to the Galaxy + The Guide is definitive. Reality is frequently inaccurate. -- + Douglas Adams, `The Hitchhiker's Guide to the Galaxy' Unlike other programming languages, `awk' variables do not have a fixed type. Instead, they can be either a number or a string, depending @@ -7360,17 +8287,14 @@ are typed, and how `awk' compares variables. File: gawk.info, Node: Variable Typing, Next: Comparison Operators, Up: Typing and Comparison -6.3.2.1 String Type Versus Numeric Type +6.3.2.1 String Type versus Numeric Type ....................................... -The 1992 POSIX standard introduced the concept of a "numeric string", -which is simply a string that looks like a number--for example, -`" +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:(1) +The POSIX standard introduced the concept of a "numeric string", which +is simply a string that looks like a number--for example, `" +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. Variable typing follows these rules: * A numeric constant or the result of a numeric operation has the NUMERIC attribute. @@ -7379,9 +8303,9 @@ the standard has been fixed, and variable typing follows these rules:(1) STRING attribute. * Fields, `getline' input, `FILENAME', `ARGV' elements, `ENVIRON' - elements, and the elements of an array created by `patsplit()', - `split()' and `match()' that are numeric strings have the STRNUM - attribute. Otherwise, they have the STRING attribute. + elements, and the elements of an array created by `match()', + `split()', and `patsplit()' that are numeric strings have the + STRNUM attribute. Otherwise, they have the STRING attribute. Uninitialized variables also have the STRNUM attribute. * Attributes propagate across assignments but are not changed by any @@ -7416,7 +8340,7 @@ operands, according to the following symmetric matrix: user input--should be treated as numeric, even though it is actually made of characters and is therefore also a string. Thus, for example, the string constant `" +3.14"', when it appears in program source code, -is a string--even though it looks numeric--and is _never_ treated as +is a string--even though it looks numeric--and is _never_ treated as a number for comparison purposes. In short, when one operand is a "pure" string, such as a string @@ -7427,33 +8351,27 @@ comparison is performed. characters, and so is first and foremost of STRING type; input strings that look numeric are additionally given the STRNUM attribute. Thus, the six-character input string ` +3.14' receives the STRNUM attribute. -In contrast, the eight-character literal `" +3.14"' appearing in -program text is a string constant. The following examples print `1' -when the comparison between the two different constants is true, `0' -otherwise: +In contrast, the eight characters `" +3.14"' appearing in program text +comprise a string constant. The following examples print `1' when the +comparison between the two different constants is true, `0' otherwise: - $ echo ' +3.14' | gawk '{ print $0 == " +3.14" }' True + $ echo ' +3.14' | awk '{ print($0 == " +3.14") }' True -| 1 - $ echo ' +3.14' | gawk '{ print $0 == "+3.14" }' False + $ echo ' +3.14' | awk '{ print($0 == "+3.14") }' False -| 0 - $ echo ' +3.14' | gawk '{ print $0 == "3.14" }' False + $ echo ' +3.14' | awk '{ print($0 == "3.14") }' False -| 0 - $ echo ' +3.14' | gawk '{ print $0 == 3.14 }' True + $ echo ' +3.14' | awk '{ print($0 == 3.14) }' True -| 1 - $ echo ' +3.14' | gawk '{ print $1 == " +3.14" }' False + $ echo ' +3.14' | awk '{ print($1 == " +3.14") }' False -| 0 - $ echo ' +3.14' | gawk '{ print $1 == "+3.14" }' True + $ echo ' +3.14' | awk '{ print($1 == "+3.14") }' True -| 1 - $ echo ' +3.14' | gawk '{ print $1 == "3.14" }' False + $ echo ' +3.14' | awk '{ print($1 == "3.14") }' False -| 0 - $ echo ' +3.14' | gawk '{ print $1 == 3.14 }' True + $ echo ' +3.14' | awk '{ print($1 == 3.14) }' True -| 1 - ---------- Footnotes ---------- - - (1) `gawk' has followed these rules for many years, and it is -gratifying that the POSIX standard is also now correct. - File: gawk.info, Node: Comparison Operators, Next: POSIX String Comparison, Prev: Variable Typing, Up: Typing and Comparison @@ -7462,24 +8380,24 @@ File: gawk.info, Node: Comparison Operators, Next: POSIX String Comparison, P "Comparison expressions" compare strings or numbers for relationships such as equality. They are written using "relational operators", which -are a superset of those in C. *Note table-relational-ops:: describes +are a superset of those in C. *note table-relational-ops:: describes them. Expression Result -------------------------------------------------------------------------- -X `<' Y True if X is less than Y. -X `<=' Y True if X is less than or equal to Y. -X `>' Y True if X is greater than Y. -X `>=' Y True if X is greater than or equal to Y. -X `==' Y True if X is equal to Y. -X `!=' Y True if X is not equal to Y. -X `~' Y True if the string X matches the regexp denoted by Y. +X `<' Y True if X is less than Y +X `<=' Y True if X is less than or equal to Y +X `>' Y True if X is greater than Y +X `>=' Y True if X is greater than or equal to Y +X `==' Y True if X is equal to Y +X `!=' Y True if X is not equal to Y +X `~' Y True if the string X matches the regexp denoted by Y X `!~' Y True if the string X does not match the regexp - denoted by Y. + denoted by Y SUBSCRIPT `in' True if the array ARRAY has an element with the -ARRAY subscript SUBSCRIPT. +ARRAY subscript SUBSCRIPT -Table 6.3: Relational Operators +Table 6.3: Relational operators Comparison expressions have the value one if true and zero if false. When comparing operands of mixed types, numeric operands are converted @@ -7504,29 +8422,29 @@ Unless `b' happens to be zero or the null string, the `if' 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. - The following table of expressions illustrates the kind of comparison -`gawk' performs, as well as what the result of the comparison is: + The following list of expressions illustrates the kinds of +comparisons `awk' performs, as well as what the result of each +comparison is: `1.5 <= 2.0' - numeric comparison (true) + Numeric comparison (true) `"abc" >= "xyz"' - string comparison (false) + String comparison (false) `1.5 != " +2"' - string comparison (true) + String comparison (true) `"1e2" < "3"' - string comparison (true) + String comparison (true) `a = 2; b = "2"' `a == b' - string comparison (true) + String comparison (true) `a = 2; b = " +2"' - `a == b' - string comparison (false) + String comparison (false) In this example: @@ -7553,13 +8471,13 @@ has the value one if `x' contains `foo', such as `"Oh, what a fool am I!"'. The righthand operand of the `~' and `!~' operators may be either a -regexp constant (`/.../') or an ordinary expression. In the latter +regexp constant (`/'...`/') or an ordinary expression. In the latter case, the value of the expression as a string is used as a dynamic regexp (*note Regexp Usage::; also *note Computed Regexps::). - In modern implementations of `awk', a constant regular expression in -slashes by itself is also an expression. The regexp `/REGEXP/' is an -abbreviation for the following comparison expression: + A constant regular expression in slashes by itself is also an +expression. `/REGEXP/' is an abbreviation for the following comparison +expression: $0 ~ /REGEXP/ @@ -7570,13 +8488,14 @@ Constant Regexps::, where this is discussed in more detail. File: gawk.info, Node: POSIX String Comparison, Prev: Comparison Operators, Up: Typing and Comparison -6.3.2.3 String Comparison With POSIX Rules +6.3.2.3 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 from the -results obtained when doing straight character-by-character -comparison.(1) +the locale's "collating order". This is the order in which characters +sort, as defined by the locale (for more discussion, *note Locales::). +This order is usually very different from the results obtained when +doing straight character-by-character comparison.(1) Because this behavior differs considerably from existing practice, `gawk' only implements it when in POSIX mode (*note Options::). Here @@ -7620,9 +8539,9 @@ Boolean operators are: `BOOLEAN1 && BOOLEAN2' True if both BOOLEAN1 and BOOLEAN2 are true. For example, the following statement prints the current input record if it contains - both `2400' and `foo': + both `edu' and `li': - if ($0 ~ /2400/ && $0 ~ /foo/) print + if ($0 ~ /edu/ && $0 ~ /li/) print The subexpression BOOLEAN2 is evaluated only if BOOLEAN1 is true. This can make a difference when BOOLEAN2 contains expressions that @@ -7633,13 +8552,15 @@ Boolean operators are: `BOOLEAN1 || BOOLEAN2' True if at least one of BOOLEAN1 or BOOLEAN2 is true. For example, the following statement prints all records in the input - that contain _either_ `2400' or `foo' or both: + that contain _either_ `edu' or `li': - if ($0 ~ /2400/ || $0 ~ /foo/) print + if ($0 ~ /edu/ || $0 ~ /li/) print The subexpression BOOLEAN2 is evaluated only if BOOLEAN1 is false. - This can make a difference when BOOLEAN2 contains expressions - that have side effects. + This can make a difference when BOOLEAN2 contains expressions that + have side effects. (Thus, this test never really distinguishes + records that contain both `edu' and `li'--as soon as `edu' is + matched, the full test succeeds.) `! BOOLEAN' True if BOOLEAN is false. For example, the following program @@ -7647,18 +8568,18 @@ Boolean operators are: variable is not defined: BEGIN { if (! ("HOME" in ENVIRON)) - print "no home!" } + print "no home!" } - (The `in' operator is described in *Note Reference to Elements::.) + (The `in' operator is described in *note Reference to Elements::.) The `&&' and `||' operators are called "short-circuit" operators because of the way they work. Evaluation of the full expression is "short-circuited" if the result can be determined part way through its evaluation. - Statements that use `&&' or `||' 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 (*note + Statements that end with `&&' or `||' 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 (*note Statements/Lines::). The actual value of an expression using the `!' operator is either @@ -7669,7 +8590,7 @@ following program is one way to print lines in between special bracketing lines: $1 == "START" { interested = ! interested; next } - interested == 1 { print } + interested { print } $1 == "END" { interested = ! interested; next } The variable `interested', as with all `awk' variables, starts out @@ -7679,7 +8600,15 @@ using `!'. The next rule prints lines as long as `interested' is true. When a line is seen whose first field is `END', `interested' is toggled back to false.(1) - NOTE: The `next' statement is discussed in *Note Next Statement::. + Most commonly, the `!' operator is used in the conditions of `if' +and `while' statements, where it often makes more sense to phrase the +logic in the negative: + + if (! SOME CONDITION || SOME OTHER CONDITION) { + ... DO WHATEVER PROCESSING ... + } + + NOTE: The `next' statement is discussed in *note Next Statement::. `next' tells `awk' to skip the rest of the rules, get the next record, and start processing the rules over again at the top. The reason it's there is to avoid printing the bracketing `START' and @@ -7728,7 +8657,7 @@ not. *Note Arrays::, for more information about arrays. continued simply by putting a newline after either character. However, putting a newline in front of either character does not work without using backslash continuation (*note Statements/Lines::). If `--posix' -is specified (*note Options::), then this extension is disabled. +is specified (*note Options::), this extension is disabled. File: gawk.info, Node: Function Calls, Next: Precedence, Prev: Truth Values and Conditions, Up: Expressions @@ -7745,6 +8674,8 @@ available in every `awk' program. The `sqrt()' function is one of these. *Note Built-in::, for a list of built-in functions and their descriptions. In addition, you can define functions for use in your program. *Note User-defined::, for instructions on how to do this. +Finally, `gawk' lets you write functions in C or C++ that may be called +from your program (*note Dynamic Extensions::). The way to use a function is with a "function call" expression, which consists of the function name followed immediately by a list of @@ -7759,7 +8690,7 @@ examples show function calls with and without arguments: rand() no arguments CAUTION: Do not put any space between the function name and the - open-parenthesis! A user-defined function name looks just like + 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. With built-in functions, space before the @@ -7776,19 +8707,21 @@ the number of which to take the square root: If those arguments are not supplied, the functions use a reasonable default value. *Note 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 (*note -User-defined::). +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 (*note User-defined::). As an advanced feature, `gawk' provides indirect function calls, which is a way to choose the function to call at runtime, instead of when you write the source code to your program. We defer discussion of -this feature until later; see *Note Indirect Calls::. +this feature until later; see *note Indirect 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 `sqrt(ARGUMENT)' is the square root of 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 "return value", which is computed by the function based on +the arguments you give it. In this example, the return value of +`sqrt(ARGUMENT)' is the square root of ARGUMENT. The following program +reads numbers, one number per line, and prints the square root of each +one: $ awk '{ print "The square root of", $1, "is", sqrt($1) }' 1 @@ -7858,10 +8791,10 @@ violates the precedence rules; for example, `$$0++--' is not a valid expression because the first `$' has higher precedence than the `++'; to avoid the problem the expression can be rewritten as `$($0++)--'. - This table presents `awk''s operators, in order of highest to lowest + This list presents `awk''s operators, in order of highest to lowest precedence: -`(...)' +`('...`)' Grouping. `$' @@ -7882,7 +8815,7 @@ precedence: `+ -' Addition, subtraction. -`String Concatenation' +String concatenation There is no special symbol for concatenation. The operands are simply written side by side (*note Concatenation::). @@ -7897,9 +8830,9 @@ precedence: 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, - `print foo > a ? b : c'), result in syntax errors. The correct - way to write this statement is `print foo > (a ? b : c)'. + precedence without parentheses. Such combinations (e.g., `print + foo > a ? b : c'), result in syntax errors. The correct way to + write this statement is `print foo > (a ? b : c)'. `~ !~' Matching, nonmatching. @@ -7923,16 +8856,18 @@ precedence: POSIX. For maximum portability, do not use them. -File: gawk.info, Node: Locales, Prev: Precedence, Up: Expressions +File: gawk.info, Node: Locales, Next: Expressions Summary, Prev: Precedence, Up: Expressions -6.6 Where You Are Makes A Difference +6.6 Where You Are Makes a Difference ==================================== Modern systems support the notion of "locales": a way to tell the -system about the local character set and language. +system about the local character set and language. The ISO C standard +defines a default `"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 -(*note 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 (*note Ranges and Locales::). Locales can affect record splitting. For the normal case of `RS = "\n"', the locale is largely irrelevant. For other single-character @@ -7941,13 +8876,77 @@ much better performance when reading records. Otherwise, `gawk' has to make several function calls, _per input character_, to find the record terminator. + Locales can affect how dates and times are formatted (*note 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 `%x' +specification in a `"US"' locale might produce `9/4/15', while in a +`"EUROPE"' locale, it might produce `4.9.15'. + According to POSIX, string comparison is also affected by locales -(similar to regular expressions). The details are presented in *Note +(similar to regular expressions). The details are presented in *note POSIX String Comparison::. Finally, the locale affects the value of the decimal point character used when `gawk' parses input data. This is discussed in detail in -*Note Conversion::. +*note Conversion::. + + +File: gawk.info, Node: Expressions Summary, Prev: Locales, Up: Expressions + +6.7 Summary +=========== + + * 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. + + * `awk' supplies three kinds of constants: numeric, string, and + regexp. `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 `/foo/' has + the same meaning as `$0 ~ /foo/'. + + * Variables hold values between uses in computations. A number of + built-in variables provide information to your `awk' program, and + a number of others let you control how `awk' behaves. + + * Numbers are automatically converted to strings, and strings to + numbers, as needed by `awk'. Numeric values are converted as if + they were formatted with `sprintf()' using the format in `CONVFMT'. + Locales can influence the conversions. + + * `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 `?:' operator provides an "if-else" test within + expressions. + + * Assignment operators provide convenient shorthands for common + arithmetic operations. + + * In `awk', a value is considered to be true if it is non-zero _or_ + non-null. Otherwise, the value is false. + + * 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). + + * 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. `awk' provides built-in + and user-defined functions; this is described in *note Functions::. + + * Operator precedence specifies the order in which operations are + performed, unless explicitly overridden by parentheses. `awk''s + operator precedence is compatible with that of C. + + * Locales can affect the format of data as output by an `awk' + program, and occasionally the format for data read as input. + File: gawk.info, Node: Patterns and Actions, Next: Arrays, Prev: Expressions, Up: Top @@ -7958,7 +8957,7 @@ File: gawk.info, Node: Patterns and Actions, Next: Arrays, Prev: Expressions, As you have already seen, each `awk' statement consists of a pattern with an associated action. This major node describes how you build patterns and actions, what kinds of things you can do within actions, -and `awk''s built-in variables. +and `awk''s predefined variables. The pattern-action rules and the statements available for use within actions form the core of `awk' programming. In a sense, everything @@ -7972,7 +8971,8 @@ top of. Now it's time to start 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. File: gawk.info, Node: Pattern Overview, Next: Using Shell Variables, Up: Patterns and Actions @@ -8001,10 +9001,10 @@ summary of the types of `awk' patterns: A single expression. It matches when its value is nonzero (if a number) or non-null (if a string). (*Note Expression Patterns::.) -`PAT1, PAT2' - A pair of patterns separated by a comma, specifying a range of +`BEGPAT, ENDPAT' + A pair of patterns separated by a comma, specifying a "range" of records. The range includes both the initial record that matches - PAT1 and the final record that matches PAT2. (*Note Ranges::.) + BEGPAT and the final record that matches ENDPAT. (*Note Ranges::.) `BEGIN' `END' @@ -8013,8 +9013,8 @@ summary of the types of `awk' patterns: `BEGINFILE' `ENDFILE' - Special patterns for you to supply startup or cleanup actions to - done on a per file basis. (*Note BEGINFILE/ENDFILE::.) + Special patterns for you to supply startup or cleanup actions to be + done on a per-file basis. (*Note BEGINFILE/ENDFILE::.) `EMPTY' The empty pattern matches every input record. (*Note Empty::.) @@ -8048,73 +9048,69 @@ otherwise, it depends on only what has happened so far in the execution of the `awk' program. Comparison expressions, using the comparison operators described in -*Note Typing and Comparison::, are a very common kind of pattern. +*note Typing and Comparison::, are a very common kind of pattern. Regexp matching and nonmatching are also very common expressions. The left operand of the `~' and `!~' operators is a string. The right operand is either a constant regular expression enclosed in slashes (`/REGEXP/'), or any expression whose string value is used as a dynamic regular expression (*note Computed Regexps::). The following example prints the second field of each input record whose first field is -precisely `foo': +precisely `li': - $ awk '$1 == "foo" { print $2 }' BBS-list + $ awk '$1 == "li" { print $2 }' mail-list -(There is no output, because there is no BBS site with the exact name -`foo'.) Contrast this with the following regular expression match, -which accepts any record with a first field that contains `foo': +(There is no output, because there is no person with the exact name +`li'.) Contrast this with the following regular expression match, which +accepts any record with a first field that contains `li': - $ awk '$1 ~ /foo/ { print $2 }' BBS-list - -| 555-1234 + $ awk '$1 ~ /li/ { print $2 }' mail-list + -| 555-5553 -| 555-6699 - -| 555-6480 - -| 555-2127 - A regexp constant as a pattern is also a special case of an -expression pattern. The expression `/foo/' has the value one if `foo' -appears in the current input record. Thus, as a pattern, `/foo/' -matches any record containing `foo'. + pattern. The expression `/li/' has the value one if `li' appears in +the current input record. Thus, as a pattern, `/li/' matches any record +containing `li'. 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 -`BBS-list' that contain both `2400' and `foo': - - $ awk '/2400/ && /foo/' BBS-list - -| fooey 555-1234 2400/1200/300 B - - The following command prints all records in `BBS-list' that contain -_either_ `2400' or `foo' (or both, of course): - - $ awk '/2400/ || /foo/' BBS-list - -| alpo-net 555-3412 2400/1200/300 A - -| bites 555-1675 2400/1200/300 A - -| 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 - - The following command prints all records in `BBS-list' that do _not_ -contain the string `foo': - - $ awk '! /foo/' 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 - -| sdace 555-3430 2400/1200/300 A +`mail-list' that contain both `edu' and `li': + + $ awk '/edu/ && /li/' mail-list + -| Samuel 555-3430 samuel.lanceolis@shu.edu A + + The following command prints all records in `mail-list' that contain +_either_ `edu' or `li' (or both, of course): + + $ awk '/edu/ || /li/' mail-list + -| Amelia 555-5553 amelia.zodiacusque@gmail.com F + -| Broderick 555-0542 broderick.aliquotiens@yahoo.com R + -| Fabius 555-1234 fabius.undevicesimus@ucb.edu F + -| Julie 555-6699 julie.perscrutabor@skeeve.com F + -| Samuel 555-3430 samuel.lanceolis@shu.edu A + -| Jean-Paul 555-2127 jeanpaul.campanorum@nyu.edu R + + The following command prints all records in `mail-list' that do +_not_ contain the string `li': + + $ awk '! /li/' mail-list + -| Anthony 555-3412 anthony.asserturo@hotmail.com A + -| Becky 555-7685 becky.algebrarum@gmail.com A + -| Bill 555-1675 bill.drowning@hotmail.com A + -| Camilla 555-2912 camilla.infusarum@skynet.be R + -| Fabius 555-1234 fabius.undevicesimus@ucb.edu F + -| Martin 555-6480 martin.codicibus@hotmail.com A + -| Jean-Paul 555-2127 jeanpaul.campanorum@nyu.edu R The subexpressions of a Boolean operator in a pattern can be constant regular expressions, comparisons, or any other `awk' expressions. Range patterns are not expressions, so they cannot appear inside Boolean patterns. Likewise, the special patterns `BEGIN', `END', -`BEGINFILE' and `ENDFILE', which never match any input record, are not +`BEGINFILE', and `ENDFILE', which never match any input record, are not expressions and cannot appear inside Boolean patterns. The precedence of the different operators which can appear in -patterns is described in *Note Precedence::. +patterns is described in *note Precedence::. File: gawk.info, Node: Ranges, Next: BEGIN/END, Prev: Expression Patterns, Up: Pattern Overview @@ -8137,7 +9133,7 @@ record. When a record matches BEGPAT, the range pattern is "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 ENDPAT against every input -record; when this succeeds, the range pattern is turned off again for +record; when this succeeds, the range pattern is "turned off" again for the following record. Then the range pattern goes back to checking BEGPAT against each record. @@ -8181,6 +9177,10 @@ worked around; range patterns do not combine with other patterns: error--> gawk: cmd. line:1: (/1/,/2/) || /Yes/ error--> gawk: cmd. line:1: ^ syntax error + 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. +(d.c.) + File: gawk.info, Node: BEGIN/END, Next: BEGINFILE/ENDFILE, Prev: Ranges, Up: Pattern Overview @@ -8192,8 +9192,7 @@ All the patterns described so far are for matching input records. The and cleanup actions for `awk' programs. `BEGIN' and `END' rules must have actions; there is no default action for these rules because there is no current record when they run. `BEGIN' and `END' rules are often -referred to as "`BEGIN' and `END' blocks" by long-time `awk' -programmers. +referred to as "`BEGIN' and `END' blocks" by longtime `awk' programmers. * Menu: @@ -8211,19 +9210,19 @@ read. Likewise, an `END' rule is executed once only, after all the input is read. For example: $ awk ' - > BEGIN { print "Analysis of \"foo\"" } - > /foo/ { ++n } - > END { print "\"foo\" appears", n, "times." }' BBS-list - -| Analysis of "foo" - -| "foo" appears 4 times. - - This program finds the number of records in the input file `BBS-list' -that contain the string `foo'. The `BEGIN' rule prints a title for the -report. There is no need to use the `BEGIN' rule to initialize the -counter `n' to zero, since `awk' does this automatically (*note -Variables::). The second rule increments the variable `n' every time a -record containing the pattern `foo' is read. The `END' rule prints the -value of `n' at the end of the run. + > BEGIN { print "Analysis of \"li\"" } + > /li/ { ++n } + > END { print "\"li\" appears in", n, "records." }' mail-list + -| Analysis of "li" + -| "li" appears in 4 records. + + This program finds the number of records in the input file +`mail-list' that contain the string `li'. The `BEGIN' rule prints a +title for the report. There is no need to use the `BEGIN' rule to +initialize the counter `n' to zero, as `awk' does this automatically +(*note Variables::). The second rule increments the variable `n' every +time a record containing the pattern `li' is read. The `END' rule +prints the value of `n' at the end of the run. The special patterns `BEGIN' and `END' cannot be used in ranges or with Boolean operators (indeed, they cannot be used with any operators). @@ -8265,10 +9264,10 @@ File: gawk.info, Node: I/O And BEGIN/END, Prev: Using BEGIN/END, Up: BEGIN/EN 7.1.4.2 Input/Output from `BEGIN' and `END' Rules ................................................. -There are several (sometimes subtle) points to remember when doing I/O -from a `BEGIN' or `END' rule. The first has to do with the value of -`$0' in a `BEGIN' rule. Because `BEGIN' rules are executed before any -input is read, there simply is no input record, and therefore no +There are several (sometimes subtle) points to be aware of when doing +I/O from a `BEGIN' or `END' rule. The first has to do with the value +of `$0' in a `BEGIN' rule. Because `BEGIN' rules are executed before +any input is read, there simply is no input record, and therefore no fields, when executing `BEGIN' rules. References to `$0' and the fields yield a null string or zero, depending upon the context. One way to give `$0' a real value is to execute a `getline' command without a @@ -8281,27 +9280,27 @@ and `NF' were _undefined_ inside an `END' rule. The POSIX standard specifies that `NF' is available in an `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 `$0' is also preserved, -although logically one would think that it should be. In fact, `gawk' -does preserve the value of `$0' for use in `END' rules. Be aware, -however, that Brian Kernighan's `awk', and possibly other -implementations, do not. +although logically one would think that it should be. In fact, all of +BWK `awk', `mawk', and `gawk' preserve the value of `$0' for use in +`END' rules. Be aware, however, that some other implementations and +many older versions of Unix `awk' do not. The third point follows from the first two. The meaning of `print' inside a `BEGIN' or `END' rule is the same as always: `print $0'. If -`$0' is the null string, then this prints an empty record. Many long -time `awk' programmers use an unadorned `print' in `BEGIN' and `END' -rules, to mean `print ""', relying on `$0' being null. Although one -might generally get away with this in `BEGIN' rules, it is a very bad -idea in `END' rules, at least in `gawk'. It is also poor style, since -if an empty line is needed in the output, the program should print one -explicitly. +`$0' is the null string, then this prints an empty record. Many +longtime `awk' programmers use an unadorned `print' in `BEGIN' and +`END' rules, to mean `print ""', relying on `$0' being null. Although +one might generally get away with this in `BEGIN' rules, it is a very +bad idea in `END' rules, at least in `gawk'. It is also poor style, +because if an empty line is needed in the output, the program should +print one explicitly. Finally, the `next' and `nextfile' statements are not allowed in a `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 `END' rule, since all -the input has been read. (*Note Next Statement::, and see *Note -Nextfile Statement::.) +Similarly, those statements are not valid in an `END' rule, because all +the input has been read. (*Note Next Statement::, and *note Nextfile +Statement::,.) File: gawk.info, Node: BEGINFILE/ENDFILE, Next: Empty, Prev: BEGIN/END, Up: Pattern Overview @@ -8321,8 +9320,8 @@ program are merged, in the order they are read by `gawk', and all reads the first record from a file. `FILENAME' is set to the name of the current file, and `FNR' is set to zero. - The `BEGINFILE' rule provides you the opportunity for two tasks that -would otherwise be difficult or impossible to perform: + The `BEGINFILE' rule provides you the opportunity to accomplish two +tasks that would otherwise be difficult or impossible to perform: * 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 @@ -8336,10 +9335,10 @@ would otherwise be difficult or impossible to perform: entirely. Otherwise, `gawk' exits with the usual fatal error. * If you have written extensions that modify the record handling (by - inserting an "open hook"), you can invoke them at this point, - before `gawk' has started processing the file. (This is a _very_ - advanced feature, currently used only by the XMLgawk project - (http://xmlgawk.sourceforge.net).) + inserting an "input parser," *note Input Parsers::), you can invoke + them at this point, before `gawk' has started processing the file. + (This is a _very_ advanced feature, currently used only by the + `gawkextlib' project (http://gawkextlib.sourceforge.net).) The `ENDFILE' rule is called when `gawk' has finished processing the last record in an input file. For the last input file, it will be @@ -8353,12 +9352,12 @@ makes it possible to catch and process I/O errors at the level of the `awk' program. The `next' statement (*note Next Statement::) is not allowed inside -either a `BEGINFILE' or and `ENDFILE' rule. The `nextfile' statement -(*note Nextfile Statement::) is allowed only inside a `BEGINFILE' rule, -but not inside an `ENDFILE' rule. +either a `BEGINFILE' or an `ENDFILE' rule. The `nextfile' statement is +allowed only inside a `BEGINFILE' rule, but not inside an `ENDFILE' +rule. The `getline' statement (*note Getline::) is restricted inside both -`BEGINFILE' and `ENDFILE'. Only the `getline VARIABLE < FILE' form is +`BEGINFILE' and `ENDFILE': only redirected forms of `getline' are allowed. `BEGINFILE' and `ENDFILE' are `gawk' extensions. In most other @@ -8374,7 +9373,7 @@ File: gawk.info, Node: Empty, Prev: BEGINFILE/ENDFILE, Up: Pattern Overview An empty (i.e., nonexistent) pattern is considered to match _every_ input record. For example, the program: - awk '{ print $1 }' BBS-list + awk '{ print $1 }' mail-list prints the first field of every record. @@ -8390,19 +9389,19 @@ hold a pattern that the `awk' program searches for. There are two ways to get the value of the shell variable into the body of the `awk' program. - The most common method is to use shell quoting to substitute the -variable's value into the program inside the script. For example, in -the following program: + A common method is to use shell quoting to substitute the variable's +value into the program inside the script. For example, consider the +following program: printf "Enter search pattern: " read pattern awk "/$pattern/ "'{ nmatches++ } END { print nmatches, "found" }' /path/to/data -the `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 `pattern' shell -variable inside the quotes. The second part is single-quoted. +The `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 `pattern' shell variable +inside the quotes. 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 @@ -8411,7 +9410,7 @@ quotes when reading the program. A better method is to use `awk''s variable assignment feature (*note Assignment Options::) to assign the shell variable's value to an `awk' -variable's value. Then use dynamic regexps to match the pattern (*note +variable. Then use dynamic regexps to match the pattern (*note Computed Regexps::). The following shows how to redo the previous example using this technique: @@ -8424,10 +9423,10 @@ Now, the `awk' program is just one single-quoted string. The assignment `-v pat="$pattern"' still requires double quotes, in case there is whitespace in the value of `$pattern'. The `awk' variable `pat' could be named `pattern' too, but that would be more confusing. -Using a variable also provides more flexibility, since 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. +Using a variable also 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. File: gawk.info, Node: Action Overview, Next: Statements, Prev: Using Shell Variables, Up: Patterns and Actions @@ -8442,19 +9441,19 @@ which (but not both) may be omitted. The purpose of the "action" is to tell `awk' what to do once a match for the pattern is found. Thus, in outline, an `awk' program generally looks like this: - [PATTERN] { ACTION } - PATTERN [{ ACTION }] + [PATTERN] `{ ACTION }' + PATTERN [`{ ACTION }'] ... - function NAME(ARGS) { ... } + `function NAME(ARGS) { ... }' ... An action consists of one or more `awk' "statements", enclosed in -curly braces (`{...}'). 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 contains only one -statement, or if it contains no statements at all. However, if you -omit the action entirely, omit the curly braces as well. An omitted -action is equivalent to `{ print $0 }': +braces (`{...}'). Each statement specifies one thing to do. The +statements are separated by newlines or semicolons. 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 braces as well. An omitted action is +equivalent to `{ print $0 }': /foo/ { } match `foo', do nothing -- empty action /foo/ match `foo', print the record -- omitted action @@ -8473,13 +9472,13 @@ Control statements well as a few special ones (*note Statements::). 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 `if', `while', `do', or `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 + `if', `while', `do', or `for' statement. Input statements Use the `getline' command (*note Getline::). Also supplied in - `awk' are the `next' statement (*note Next Statement::), and the + `awk' are the `next' statement (*note Next Statement::) and the `nextfile' statement (*note Nextfile Statement::). Output statements @@ -8504,7 +9503,7 @@ statements contain other statements. For example, the `if' statement contains another statement that may or may not be executed. The contained statement is called the "body". To include more than one statement in the body, group them into a single "compound statement" -with curly braces, separating them with newlines or semicolons. +with braces, separating them with newlines or semicolons. * Menu: @@ -8533,7 +9532,7 @@ File: gawk.info, Node: If Statement, Next: While Statement, Up: Statements The `if'-`else' statement is `awk''s decision-making statement. It looks like this: - if (CONDITION) THEN-BODY [else ELSE-BODY] + `if (CONDITION) THEN-BODY' [`else ELSE-BODY'] The CONDITION is an expression that controls what the rest of the statement does. If the CONDITION is true, THEN-BODY is executed; @@ -8547,13 +9546,13 @@ following: else print "x is odd" - In this example, if the expression `x % 2 == 0' is true (that is, if + In this example, if the expression `x % 2 == 0' is true (i.e., if the value of `x' is evenly divisible by two), then the first `print' statement is executed; otherwise, the second `print' statement is executed. If the `else' keyword appears on the same line as THEN-BODY and THEN-BODY is not a compound statement (i.e., not surrounded by -curly braces), then a semicolon must separate THEN-BODY from the `else'. -To illustrate this, the previous example can be rewritten as: +braces), then a semicolon must separate THEN-BODY from the `else'. To +illustrate this, the previous example can be rewritten as: if (x % 2 == 0) print "x is even"; else print "x is odd" @@ -8583,18 +9582,18 @@ thing the `while' statement does is test the CONDITION. If the CONDITION is true, it executes the statement BODY. (The CONDITION is true when the value is not zero and not a null string.) After BODY has been executed, CONDITION is tested again, and if it is still true, BODY -is executed again. This process repeats until the CONDITION is no -longer true. If the CONDITION is initially false, the body of the loop -is never executed and `awk' continues with the statement following the -loop. This example prints the first three fields of each record, one -per line: - - awk '{ - i = 1 - while (i <= 3) { - print $i - i++ - } +executes again. This process repeats until the CONDITION is no longer +true. If the CONDITION is initially false, the body of the loop never +executes and `awk' continues with the statement following the loop. +This example prints the first three fields of each record, one per line: + + awk ' + { + i = 1 + while (i <= 3) { + print $i + i++ + } }' inventory-shipped The body of this loop is a compound statement enclosed in braces, @@ -8606,7 +9605,7 @@ increments the value of `i' and the loop repeats. The loop terminates when `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 +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. @@ -8625,27 +9624,27 @@ the CONDITION is true. It looks like this: BODY while (CONDITION) - Even if the CONDITION is false at the start, the BODY is executed at + Even if the CONDITION is false at the start, the BODY executes at least once (and only once, unless executing BODY makes CONDITION true). Contrast this with the corresponding `while' statement: while (CONDITION) - BODY + BODY This statement does not execute BODY even once if the CONDITION is false to begin with. The following is an example of a `do' statement: { - i = 1 - do { - print $0 - i++ - } while (i <= 10) + i = 1 + do { + print $0 + i++ + } while (i <= 10) } This program prints each input record 10 times. However, it isn't a -very realistic example, since in this case an ordinary `while' would do -just as well. This situation reflects actual experience; only +very realistic example, because in this case an ordinary `while' would +do just as well. This situation reflects actual experience; only occasionally is there a real use for a `do' statement. @@ -8669,9 +9668,10 @@ INCREMENT. Typically, INITIALIZATION sets a variable to either zero or one, INCREMENT adds one to it, and CONDITION compares it against the desired number of iterations. For example: - awk '{ - for (i = 1; i <= 3; i++) - print $i + awk ' + { + for (i = 1; i <= 3; i++) + print $i }' inventory-shipped This prints the first three fields of each input record, with one field @@ -8695,7 +9695,7 @@ whatsoever. For example, the following statement prints all the powers of two between 1 and 100: for (i = 1; i <= 100; i *= 2) - print i + print i If there is nothing to be done, any of the three expressions in the parentheses following the `for' keyword may be omitted. Thus, @@ -8723,7 +9723,7 @@ natural to think of. Counting the number of iterations is 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. - There is an alternate version of the `for' loop, for iterating over + There is an alternative version of the `for' loop, for iterating over all the indices of an array: for (i in array) @@ -8738,9 +9738,12 @@ File: gawk.info, Node: Switch Statement, Next: Break Statement, Prev: For Sta 7.4.5 The `switch' Statement ---------------------------- -The `switch' statement allows the evaluation of an expression and the -execution of statements based on a `case' match. Case statements are -checked for a match in the order they are defined. If no suitable +This minor node describes a `gawk'-specific feature. If `gawk' is in +compatibility mode (*note Options::), it is not available. + + The `switch' statement allows the evaluation of an expression and +the execution of statements based on a `case' match. Case statements +are checked for a match in the order they are defined. If no suitable `case' is found, the `default' section is executed, if supplied. Each `case' contains a single constant, be it numeric, string, or @@ -8763,32 +9766,36 @@ match to a given case is made, the case statement bodies execute until a `break', `continue', `next', `nextfile' or `exit' is encountered, or the end of the `switch' statement itself. For 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 + } } - Note that if none of the statements specified above halt execution -of a matched `case' statement, execution falls through to the next -`case' until execution halts. In the above example, for any case value -starting with `2' followed by one or more digits, the `print' statement -is executed and then falls through into the `default' section, -executing its `print' statement. In turn, the -1 case will also be -executed since the `default' does not halt execution. - - This `switch' statement is a `gawk' extension. If `gawk' is in -compatibility mode (*note Options::), it is not available. + Note that if none of the statements specified here halt execution of +a matched `case' statement, execution falls through to the next `case' +until execution halts. In this example, the `case' for `"?"' falls +through to the `default' case, which is to call a function named +`usage()'. (The `getopt()' function being called here is described in +*note Getopt Function::.) File: gawk.info, Node: Break Statement, Next: Continue Statement, Prev: Switch Statement, Up: Statements @@ -8802,15 +9809,15 @@ divisor of any integer, and also identifies prime numbers: # 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 } When the remainder is zero in the first `if' statement, `awk' @@ -8825,28 +9832,28 @@ Statement::.) # 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 + } } - } } The `break' statement is also used to break out of the `switch' -statement. This is discussed in *Note Switch Statement::. +statement. This is discussed in *note Switch Statement::. The `break' statement has no meaning when used outside the body of a loop or `switch'. However, although it was never documented, historical implementations of `awk' treated the `break' statement outside of a loop as if it were a `next' statement (*note Next -Statement::). (d.c.) Recent versions of Brian Kernighan's `awk' no -longer allow this usage, nor does `gawk'. +Statement::). (d.c.) Recent versions of BWK `awk' no longer allow +this usage, nor does `gawk'. File: gawk.info, Node: Continue Statement, Next: Next Statement, Prev: Break Statement, Up: Statements @@ -8889,14 +9896,15 @@ the previous example with the following `while' loop: print "" } -This program loops forever once `x' reaches 5. +This program loops forever once `x' reaches 5, because the increment +(`x++') is never reached. The `continue' statement has no special meaning with respect to the -`switch' statement, nor does it any meaning when used outside the body -of a loop. Historical versions of `awk' treated a `continue' statement -outside a loop the same way they treated a `break' statement outside a -loop: as if it were a `next' statement (*note Next Statement::). -(d.c.) Recent versions of Brian Kernighan's `awk' no longer work this +`switch' statement, nor does it have any meaning when used outside the +body of a loop. Historical versions of `awk' treated a `continue' +statement outside a loop the same way they treated a `break' statement +outside a loop: as if it were a `next' statement (*note Next +Statement::). (d.c.) Recent versions of BWK `awk' no longer work this way, nor does `gawk'. @@ -8928,15 +9936,14 @@ complicating the rest of the program, write a "weed out" rule near the beginning, in the following manner: 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 } Because of the `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 -*Note Special Files::. +error output stream, as error messages should be. For more detail, see +*note Special Files::. If the `next' statement causes the end of the input to be reached, then the code in any `END' rules is executed. *Note BEGIN/END::. @@ -8946,62 +9953,65 @@ rules. *Note BEGINFILE/ENDFILE::. According to the POSIX standard, the behavior is undefined if the `next' statement is used in a `BEGIN' or `END' rule. `gawk' treats it -as a syntax error. Although POSIX permits it, some other `awk' -implementations don't allow the `next' statement inside function bodies -(*note User-defined::). Just as with any other `next' statement, a -`next' statement inside a function body reads the next record and -starts processing it with the first rule in the program. +as a syntax error. Although POSIX does not disallow it, most other +`awk' implementations don't allow the `next' statement inside function +bodies (*note User-defined::). Just as with any other `next' +statement, a `next' statement inside a function body reads the next +record and starts processing it with the first rule in the program. File: gawk.info, Node: Nextfile Statement, Next: Exit Statement, Prev: Next Statement, Up: Statements -7.4.9 Using `gawk''s `nextfile' Statement ------------------------------------------ +7.4.9 The `nextfile' Statement +------------------------------ -`gawk' provides the `nextfile' statement, which is similar to the -`next' statement. (c.e.) However, instead of abandoning processing of -the current record, the `nextfile' statement instructs `gawk' to stop -processing the current data file. - - The `nextfile' statement is a `gawk' extension. In most other `awk' -implementations, or if `gawk' is in compatibility mode (*note -Options::), `nextfile' is not special. - - Upon execution of the `nextfile' statement, any `ENDFILE' rules are -executed except in the case as mentioned below, `FILENAME' is updated -to the name of the next data file listed on the command line, `FNR' is -reset to one, `ARGIND' is incremented, any `BEGINFILE' rules are -executed, and processing starts over with the first rule in the program. -(`ARGIND' hasn't been introduced yet. *Note Built-in Variables::.) If -the `nextfile' statement causes the end of the input to be reached, -then the code in any `END' rules is executed. An exception to this is -when the `nextfile' is invoked during execution of any statement in an -`END' rule; In this case, it causes the program to stop immediately. +The `nextfile' statement is similar to the `next' statement. However, +instead of abandoning processing of the current record, the `nextfile' +statement instructs `awk' to stop processing the current data file. + + Upon execution of the `nextfile' statement, `FILENAME' is updated to +the name of the next data file listed on the command line, `FNR' is +reset to one, and processing starts over with the first rule in the +program. If the `nextfile' statement causes the end of the input to be +reached, then the code in any `END' rules is executed. An exception to +this is when `nextfile' is invoked during execution of any statement in +an `END' rule; in this case, it causes the program to stop immediately. *Note BEGIN/END::. The `nextfile' statement is useful when there are many data files to process but it isn't necessary to process every record in every file. -Normally, in order to move on to the next data file, a program has to -continue scanning the unwanted records. The `nextfile' statement -accomplishes this much more efficiently. +Without `nextfile', in order to move on to the next data file, a program +would have to continue scanning the unwanted records. The `nextfile' +statement accomplishes this much more efficiently. + + In `gawk', execution of `nextfile' causes additional things to +happen: any `ENDFILE' rules are executed if `gawk' is not currently in +an `END' or `BEGINFILE' rule, `ARGIND' is incremented, and any +`BEGINFILE' rules are executed. (`ARGIND' hasn't been introduced yet. +*Note Built-in Variables::.) - In addition, `nextfile' is useful inside a `BEGINFILE' rule to skip + With `gawk', `nextfile' is useful inside a `BEGINFILE' rule to skip over a file that would otherwise cause `gawk' to exit with a fatal error. In this case, `ENDFILE' rules are not executed. *Note BEGINFILE/ENDFILE::. - While one might think that `close(FILENAME)' would accomplish the + Although it might seem that `close(FILENAME)' would accomplish the same as `nextfile', this isn't true. `close()' is reserved for closing files, pipes, and coprocesses that are opened with redirections. It is not related to the main processing that `awk' does with the files listed in `ARGV'. - The current version of the Brian Kernighan's `awk' (*note Other -Versions::) also supports `nextfile'. However, it doesn't allow the -`nextfile' statement inside function bodies (*note User-defined::). -`gawk' does; a `nextfile' inside a function body reads the next record -and starts processing it with the first rule in the program, just as -any other `nextfile' statement. + NOTE: For many years, `nextfile' was a common extension. In + September 2012, it was accepted for inclusion into the POSIX + standard. See the Austin Group website + (http://austingroupbugs.net/view.php?id=607). + + The current version of BWK `awk', and `mawk' also support +`nextfile'. However, they don't allow the `nextfile' statement inside +function bodies (*note User-defined::). `gawk' does; a `nextfile' +inside a function body reads the next record and starts processing it +with the first rule in the program, just as any other `nextfile' +statement. File: gawk.info, Node: Exit Statement, Prev: Nextfile Statement, Up: Statements @@ -9013,7 +10023,7 @@ The `exit' statement causes `awk' to immediately stop executing the current rule and to stop processing input; any remaining input is ignored. The `exit' statement is written as follows: - exit [RETURN CODE] + `exit' [RETURN CODE] When an `exit' statement is executed from a `BEGIN' rule, the program stops processing everything immediately. No input records are @@ -9025,8 +10035,8 @@ stop immediately. An `exit' statement that is not part of a `BEGIN' or `END' rule stops the execution of any further automatic rules for the current record, skips reading any remaining input records, and executes the -`END' rule if there is one. Any `ENDFILE' rules are also skipped; they -are not executed. +`END' rule if there is one. `gawk' also skips any `ENDFILE' rules; +they do not execute. In such a case, if you don't want the `END' rule to do its job, set a variable to nonzero before the `exit' statement and check that @@ -9047,12 +10057,12 @@ with a nonzero status. An `awk' program can do this using an `exit' statement with a nonzero argument, as shown in the following 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") } NOTE: For full portability, exit values should be between zero and @@ -9061,10 +10071,10 @@ statement with a nonzero argument, as shown in the following example: systems. -File: gawk.info, Node: Built-in Variables, Prev: Statements, Up: Patterns and Actions +File: gawk.info, Node: Built-in Variables, Next: Pattern Action Summary, Prev: Statements, Up: Patterns and Actions -7.5 Built-in Variables -====================== +7.5 Predefined Variables +======================== Most `awk' variables are available to use for your own purposes; they never change unless your program assigns values to them, and they never @@ -9074,9 +10084,9 @@ of these automatically, so that they enable you to tell `awk' how to do certain things. Others are set automatically by `awk', so that they carry information from the internal workings of `awk' to your program. - This minor node documents all the built-in variables of `gawk', most -of which are also documented in the chapters describing their areas of -activity. + This minor node documents all of `gawk''s predefined variables, most +of which are also documented in the major nodes describing their areas +of activity. * Menu: @@ -9089,12 +10099,17 @@ activity. File: gawk.info, Node: User-modified, Next: Auto-set, Up: Built-in Variables -7.5.1 Built-in Variables That Control `awk' +7.5.1 Built-In Variables That Control `awk' ------------------------------------------- The following is an alphabetical list of variables that you can change -to control how `awk' does certain things. The variables that are -specific to `gawk' are marked with a pound sign (`#'). +to control how `awk' does certain things. + + The variables that are specific to `gawk' are marked with a pound +sign (`#'). These variables are `gawk' extensions. In other `awk' +implementations or if `gawk' is in compatibility mode (*note +Options::), they are not special. (Any exceptions are noted in the +description of each variable.) `BINMODE #' On non-POSIX systems, this variable specifies use of binary mode @@ -9107,14 +10122,11 @@ specific to `gawk' are marked with a pound sign (`#'). string value of `"rw"' or `"wr"' indicates that all files should use binary I/O. Any other string value is treated the same as `"rw"', but causes `gawk' to generate a warning message. - `BINMODE' is described in more detail in *Note PC Using::. + `BINMODE' is described in more detail in *note PC Using::. `mawk' + (*note Other Versions::), also supports this variable, but only + using numeric values. - This variable is a `gawk' extension. In other `awk' - implementations (except `mawk', *note Other Versions::), or if - `gawk' is in compatibility mode (*note Options::), it is not - special. - -`CONVFMT' +``CONVFMT'' This string controls conversion of numbers to strings (*note Conversion::). It works by being passed, in effect, as the first argument to the `sprintf()' function (*note String Functions::). @@ -9122,29 +10134,21 @@ specific to `gawk' are marked with a pound sign (`#'). POSIX standard. `FIELDWIDTHS #' - This is a space-separated list of columns that tells `gawk' how to - split input with fixed columnar boundaries. Assigning a value to + A space-separated list of columns that tells `gawk' how to split + input with fixed columnar boundaries. Assigning a value to `FIELDWIDTHS' overrides the use of `FS' and `FPAT' for field splitting. *Note Constant Size::, for more information. - If `gawk' is in compatibility mode (*note Options::), then - `FIELDWIDTHS' has no special meaning, and field-splitting - operations occur based exclusively on the value of `FS'. - `FPAT #' - This is a regular expression (as a string) that tells `gawk' to - create the fields based on text that matches the regular - expression. Assigning a value to `FPAT' overrides the use of `FS' - and `FIELDWIDTHS' for field splitting. *Note Splitting By - Content::, for more information. - - If `gawk' is in compatibility mode (*note Options::), then `FPAT' - has no special meaning, and field-splitting operations occur based - exclusively on the value of `FS'. + A regular expression (as a string) that tells `gawk' to create the + fields based on text that matches the regular expression. + Assigning a value to `FPAT' overrides the use of `FS' and + `FIELDWIDTHS' for field splitting. *Note Splitting By Content::, + for more information. `FS' - This is the input field separator (*note Field Separators::). The - value is a single-character string or a multi-character regular + The input field separator (*note 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 (`""'), then each character in the record becomes a separate field. (This behavior @@ -9180,13 +10184,9 @@ specific to `gawk' are marked with a pound sign (`#'). splitting when using a single-character field separator. *Note Case-sensitivity::. - If `gawk' is in compatibility mode (*note Options::), then - `IGNORECASE' has no special meaning. Thus, string and regexp - operations are always case-sensitive. - `LINT #' When this variable is true (nonzero or non-null), `gawk' behaves - as if the `--lint' command-line option is in effect. (*note + as if the `--lint' command-line option is in effect (*note Options::). With a value of `"fatal"', lint warnings become fatal errors. With a value of `"invalid"', only warnings about things that are actually invalid are issued. (This is not fully @@ -9202,13 +10202,12 @@ specific to `gawk' are marked with a pound sign (`#'). execution is independent of the flavor of `awk' being executed. `OFMT' - This string controls conversion of numbers to strings (*note - Conversion::) for printing with the `print' statement. It works - by being passed as the first argument to the `sprintf()' function - (*note String Functions::). Its default value is `"%.6g"'. - Earlier versions of `awk' also used `OFMT' to specify the format - for converting numbers to strings in general expressions; this is - now done by `CONVFMT'. + Controls conversion of numbers to strings (*note Conversion::) for + printing with the `print' statement. It works by being passed as + the first argument to the `sprintf()' function (*note String + Functions::). Its default value is `"%.6g"'. Earlier versions of + `awk' used `OFMT' to specify the format for converting numbers to + strings in general expressions; this is now done by `CONVFMT'. `OFS' This is the output field separator (*note Output Separators::). @@ -9216,40 +10215,45 @@ specific to `gawk' are marked with a pound sign (`#'). Its default value is `" "', a string consisting of a single space. `ORS' - This is the output record separator. It is output at the end of - every `print' statement. Its default value is `"\n"', the newline + The output record separator. It is output at the end of every + `print' statement. Its default value is `"\n"', the newline character. (*Note Output Separators::.) -`RS' - This is `awk''s 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 runs of - blank lines. If it is a regexp, records are separated by matches - of the regexp in the input text. (*Note Records::.) +`PREC #' + The working precision of arbitrary-precision floating-point + numbers, 53 bits by default (*note Setting precision::). + +`ROUNDMODE #' + The rounding mode to use for arbitrary-precision arithmetic on + numbers, by default `"N"' (`roundTiesToEven' in the IEEE 754 + standard; *note Setting the rounding mode::). + +``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 runs of blank lines. + If it is a regexp, records are separated by matches of the regexp + in the input text. (*Note Records::.) The ability for `RS' to be a regular expression is a `gawk' extension. In most other `awk' implementations, or if `gawk' is in compatibility mode (*note Options::), just the first character of `RS''s value is used. -`SUBSEP' - This is the subscript separator. It has the default value of - `"\034"' and is used to separate the parts of the indices of a - multidimensional array. Thus, the expression `foo["A", "B"]' - really accesses `foo["A\034B"]' (*note Multi-dimensional::). +``SUBSEP'' + The subscript separator. It has the default value of `"\034"' and + is used to separate the parts of the indices of a multidimensional + array. Thus, the expression `foo["A", "B"]' really accesses + `foo["A\034B"]' (*note Multidimensional::). `TEXTDOMAIN #' - This variable is used for internationalization of programs at the - `awk' level. It sets the default text domain for specially marked - string constants in the source text, as well as for the - `dcgettext()', `dcngettext()' and `bindtextdomain()' functions - (*note Internationalization::). The default value of `TEXTDOMAIN' - is `"messages"'. - - This variable is a `gawk' extension. In other `awk' - implementations, or if `gawk' is in compatibility mode (*note - Options::), it is not special. + Used for internationalization of programs at the `awk' level. It + sets the default text domain for specially marked string constants + in the source text, as well as for the `dcgettext()', + `dcngettext()', and `bindtextdomain()' functions (*note + Internationalization::). The default value of `TEXTDOMAIN' is + `"messages"'. ---------- Footnotes ---------- @@ -9258,15 +10262,19 @@ specific to `gawk' are marked with a pound sign (`#'). File: gawk.info, Node: Auto-set, Next: ARGC and ARGV, Prev: User-modified, Up: Built-in Variables -7.5.2 Built-in Variables That Convey Information +7.5.2 Built-In Variables That Convey Information ------------------------------------------------ The following is an alphabetical list of variables that `awk' sets automatically on certain occasions in order to provide information to -your program. The variables that are specific to `gawk' are marked -with a pound sign (`#'). +your program. + + The variables that are specific to `gawk' are marked with a pound +sign (`#'). These variables are `gawk' extensions. In other `awk' +implementations or if `gawk' is in compatibility mode (*note +Options::), they are not special: -`ARGC, ARGV' +`ARGC', `ARGV' The command-line arguments available to `awk' programs are stored in an array called `ARGV'. `ARGC' is the number of command-line arguments present. *Note Other Arguments::. Unlike most `awk' @@ -9276,13 +10284,13 @@ with a pound sign (`#'). $ awk 'BEGIN { > for (i = 0; i < ARGC; i++) > print ARGV[i] - > }' inventory-shipped BBS-list + > }' inventory-shipped mail-list -| awk -| inventory-shipped - -| BBS-list + -| mail-list `ARGV[0]' contains `awk', `ARGV[1]' contains `inventory-shipped', - and `ARGV[2]' contains `BBS-list'. The value of `ARGC' is three, + and `ARGV[2]' contains `mail-list'. The value of `ARGC' is three, one more than the index of the last element in `ARGV', because the elements are numbered from zero. @@ -9308,28 +10316,40 @@ with a pound sign (`#'). the command line. While you can change the value of `ARGIND' within your `awk' - program, `gawk' automatically sets it to a new value when the next - file is opened. - - This variable is a `gawk' extension. In other `awk' - implementations, or if `gawk' is in compatibility mode (*note - Options::), it is not special. + program, `gawk' automatically sets it to a new value when it opens + the next file. `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, `ENVIRON["HOME"]' might be `/home/arnold'. Changing this - array does not affect the environment passed on to any programs - that `awk' may spawn via redirection or the `system()' function. + example, `ENVIRON["HOME"]' might be `/home/arnold'. + + For POSIX `awk', changing this array does not affect the + environment passed on to any programs that `awk' may spawn via + redirection or the `system()' function. + + However, beginning with version 4.2, if not in POSIX compatibility + mode, `gawk' does update its own environment when `ENVIRON' is + changed, thus changing the environment seen by programs that it + creates. You should therefore be especially careful if you modify + `ENVIRON["PATH"]"', which is the search path for finding + executable programs. + + This can also affect the running `gawk' program, since some of the + built-in functions may pay attention to certain environment + variables. The most notable instance of this is `mktime()' (*note + Time Functions::), which pays attention the value of the `TZ' + environment variable on many systems. Some operating systems may not have environment variables. On such systems, the `ENVIRON' array is empty (except for - `ENVIRON["AWKPATH"]', *note AWKPATH Variable::). + `ENVIRON["AWKPATH"]' and `ENVIRON["AWKLIBPATH"]'; *note AWKPATH + Variable::, and *note AWKLIBPATH Variable::). `ERRNO #' - If a system error occurs during a redirection for `getline', - during a read for `getline', or during a `close()' operation, then + If a system error occurs during a redirection for `getline', during + a read for `getline', or during a `close()' operation, then `ERRNO' contains a string describing the error. In addition, `gawk' clears `ERRNO' before opening each @@ -9343,24 +10363,20 @@ with a pound sign (`#'). `getline' returning -1. You are, of course, free to clear it yourself before doing an I/O operation. - This variable is a `gawk' extension. In other `awk' - implementations, or if `gawk' is in compatibility mode (*note - Options::), it is not special. - `FILENAME' - The name of the file that `awk' is currently reading. When no - data files are listed on the command line, `awk' reads from the - standard input and `FILENAME' is set to `"-"'. `FILENAME' is - changed each time a new file is read (*note Reading Files::). - Inside a `BEGIN' rule, the value of `FILENAME' is `""', since - there are no input files being processed yet.(1) (d.c.) Note, - though, that using `getline' (*note Getline::) inside a `BEGIN' - rule can give `FILENAME' a value. + The name of the current input file. When no data files are listed + on the command line, `awk' reads from the standard input and + `FILENAME' is set to `"-"'. `FILENAME' changes each time a new + file is read (*note Reading Files::). Inside a `BEGIN' rule, the + value of `FILENAME' is `""', because there are no input files + being processed yet.(1) (d.c.) Note, though, that using `getline' + (*note Getline::) inside a `BEGIN' rule can give `FILENAME' a + value. `FNR' - The current record number in the current file. `FNR' is - incremented each time a new record is read (*note Records::). It - is reinitialized to zero each time a new input file is started. + The current record number in the current file. `awk' increments + `FNR' each time it reads a new record (*note Records::). `awk' + resets `FNR' to zero each time it starts a new input file. `NF' The number of fields in the current input record. `NF' is set @@ -9373,10 +10389,19 @@ with a pound sign (`#'). create or remove fields from the current record. *Note Changing Fields::. +`FUNCTAB #' + An array whose indices and corresponding values are the names of + all the built-in, user-defined, and extension functions in the + program. + + NOTE: Attempting to use the `delete' statement with the + `FUNCTAB' array causes a fatal error. Any attempt to assign + to an element of `FUNCTAB' also causes a fatal error. + `NR' The number of input records `awk' has processed since the - beginning of the program's execution (*note Records::). `NR' is - incremented each time a new record is read. + beginning of the program's execution (*note Records::). `awk' + increments `NR' each time it reads a new record. `PROCINFO #' The elements of this array provide access to information about the @@ -9395,6 +10420,38 @@ with a pound sign (`#'). effect, or `"FPAT"' if field matching with `FPAT' is in effect. + `PROCINFO["identifiers"]' + A subarray, indexed by the names of all identifiers used in + the text of the AWK program. An "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: + + `"array"' + The identifier is an array. + + `"builtin"' + The identifier is a built-in function. + + `"extension"' + The identifier is an extension function loaded via + `@load' or `-l'. + + `"scalar"' + The identifier is a scalar. + + `"untyped"' + The identifier is untyped (could be used as a scalar or + array, `gawk' doesn't know yet). + + `"user"' + The identifier is a user-defined function. + + The values indicate what `gawk' knows about the identifiers + after it has finished parsing the program; they are _not_ + updated while the program runs. + `PROCINFO["gid"]' The value of the `getgid()' system call. @@ -9409,9 +10466,9 @@ with a pound sign (`#'). `PROCINFO["sorted_in"]' If this element exists in `PROCINFO', its value controls the - order in which array indices will be processed by `for (index - in array) ...' loops. Since this is an advanced feature, we - defer the full description until later; see *Note Scanning an + order in which array indices will be processed by `for (INDX + in ARRAY)' loops. This is an advanced feature, so we defer + the full description until later; see *note Scanning an Array::. `PROCINFO["strftime"]' @@ -9425,18 +10482,48 @@ with a pound sign (`#'). `PROCINFO["version"]' The version of `gawk'. + The following additional elements in the array are available to + provide information about the MPFR and GMP libraries if your + version of `gawk' supports arbitrary-precision arithmetic (*note + Arbitrary Precision Arithmetic::): + + `PROCINFO["mpfr_version"]' + The version of the GNU MPFR library. + + `PROCINFO["gmp_version"]' + The version of the GNU MP library. + + `PROCINFO["prec_max"]' + The maximum precision supported by MPFR. + + `PROCINFO["prec_min"]' + The minimum precision required by MPFR. + + The following additional elements in the array are available to + provide information about the version of the extension API, if + your version of `gawk' supports dynamic loading of extension + functions (*note Dynamic Extensions::): + + `PROCINFO["api_major"]' + The major version of the extension API. + + `PROCINFO["api_minor"]' + The minor version of the extension API. + On some systems, there may be elements in the array, `"group1"' through `"groupN"' for some N. N is the number of supplementary groups that the process has. Use the `in' operator to test for these elements (*note Reference to Elements::). - The `PROCINFO' array is also used to cause coprocesses to - communicate over pseudo-ttys instead of through two-way pipes; - this is discussed further in *Note Two-way I/O::. + The `PROCINFO' array has the following additional uses: + + * It may be used to provide a timeout when reading from any + open input file, pipe, or coprocess. *Note Read Timeout::, + for more information. - This array is a `gawk' extension. In other `awk' implementations, - or if `gawk' is in compatibility mode (*note Options::), it is not - special. + * It may be used to cause coprocesses to communicate over + pseudo-ttys instead of through two-way pipes; this is + discussed further in *note Two-way I/O::. `RLENGTH' The length of the substring matched by the `match()' function @@ -9452,21 +10539,59 @@ with a pound sign (`#'). match was found. `RT #' - This is set each time a record is read. It contains the input text - that matched the text denoted by `RS', the record separator. + The input text that matched the text denoted by `RS', the record + separator. It is set every time a record is read. - This variable is a `gawk' extension. In other `awk' - implementations, or if `gawk' is in compatibility mode (*note - Options::), it is not special. +`SYMTAB #' + An array whose indices are the names of all defined global + variables and arrays in the program. `SYMTAB' makes `gawk''s + symbol table visible to the `awk' programmer. It is built as + `gawk' parses the program and is complete before the program + starts to run. -Advanced Notes: Changing `NR' and `FNR' ---------------------------------------- + The array may be used for indirect access to read or write the + value of a variable: -`awk' increments `NR' and `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. (d.c.) The following example shows -this: + foo = 5 + SYMTAB["foo"] = 4 + print foo # prints 4 + + The `isarray()' function (*note Type Functions::) may be used to + test if an element in `SYMTAB' is an array. Also, you may not use + the `delete' statement with the `SYMTAB' array. + + You may use an index for `SYMTAB' that is not a predefined + identifier: + + SYMTAB["xxx"] = 5 + print SYMTAB["xxx"] + + This works as expected: in this case `SYMTAB' acts just like a + regular array. The only difference is that you can't then delete + `SYMTAB["xxx"]'. + + The `SYMTAB' array is more interesting than it looks. Andrew Schorr + points out that it effectively gives `awk' data pointers. Consider + his example: + + # Indirect multiply of any variable by amount, return result + + function multiply(variable, amount) + { + return SYMTAB[variable] *= amount + } + + NOTE: In order to avoid severe time-travel paradoxes,(2) + neither `FUNCTAB' nor `SYMTAB' are available as elements + within the `SYMTAB' array. + + Changing `NR' and `FNR' + + `awk' increments `NR' and `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. (d.c.) The following example +shows this: $ echo '1 > 2 @@ -9488,25 +10613,27 @@ file by resetting `NR' to zero when `FILENAME' changed. to `"-"', even if there were data files to be processed. This behavior was incorrect and should not be relied upon in your programs. + (2) Not to mention difficult implementation issues. + File: gawk.info, Node: ARGC and ARGV, Prev: Auto-set, Up: Built-in Variables 7.5.3 Using `ARGC' and `ARGV' ----------------------------- -*Note Auto-set::, presented the following program describing the +*note Auto-set::, presented the following program describing the information contained in `ARGC' and `ARGV': $ awk 'BEGIN { > for (i = 0; i < ARGC; i++) > print ARGV[i] - > }' inventory-shipped BBS-list + > }' inventory-shipped mail-list -| awk -| inventory-shipped - -| BBS-list + -| mail-list In this example, `ARGV[0]' contains `awk', `ARGV[1]' contains -`inventory-shipped', and `ARGV[2]' contains `BBS-list'. Notice that +`inventory-shipped', and `ARGV[2]' contains `mail-list'. Notice that the `awk' program is not entered in `ARGV'. The other command-line options, with their arguments, are also not entered. This includes variable assignments done with the `-v' option (*note Options::). @@ -9549,10 +10676,18 @@ string. Another option is to use the `delete' statement to remove elements from `ARGV' (*note Delete::). All of these actions are typically done in the `BEGIN' rule, before -actual processing of the input begins. *Note Split Program::, and see -*Note Tee Program::, for examples of each way of removing elements from -`ARGV'. The following fragment processes `ARGV' in order to examine, -and then remove, command-line options: +actual processing of the input begins. *Note Split Program::, and +*note Tee Program::, for examples of each way of removing elements from +`ARGV'. + + To actually get options into an `awk' program, end the `awk' options +with `--' and then supply the `awk' program's options, in the following +manner: + + awk -f myprog.awk -- -v -q file1 file2 ... + + The following fragment processes `ARGV' in order to examine, and +then remove, the previously mentioned command-line options: BEGIN { for (i = 1; i < ARGC; i++) { @@ -9570,24 +10705,79 @@ and then remove, command-line options: } } - To actually get the options into the `awk' program, end the `awk' -options with `--' and then supply the `awk' program's options, in the -following manner: + Ending the `awk' options with `--' isn't necessary in `gawk'. Unless +`--posix' has been specified, `gawk' silently puts any unrecognized +options into `ARGV' for the `awk' program to deal with. As soon as it +sees an unknown option, `gawk' stops looking for other options that it +might otherwise recognize. The previous command line with `gawk' would +be: - awk -f myprog -- -v -q file1 file2 ... - - This is not necessary in `gawk'. Unless `--posix' has been -specified, `gawk' silently puts any unrecognized options into `ARGV' -for the `awk' program to deal with. As soon as it sees an unknown -option, `gawk' stops looking for other options that it might otherwise -recognize. The previous example with `gawk' would be: - - gawk -f myprog -q -v file1 file2 ... + gawk -f myprog.awk -q -v file1 file2 ... Because `-q' is not a valid `gawk' option, it and the following `-v' are passed on to the `awk' program. (*Note Getopt Function::, for an `awk' library function that parses command-line options.) + When designing your program, you should choose options that don't +conflict with `gawk''s, because it will process any options that it +accepts before passing the rest of the command line on to your program. +Using `#!' with the `-E' option may help (*Note Executable Scripts::, +and *note Options::,). + + +File: gawk.info, Node: Pattern Action Summary, Prev: Built-in Variables, Up: Patterns and Actions + +7.6 Summary +=========== + + * Pattern-action pairs make up the basic elements of an `awk' + program. Patterns are either normal expressions, range + expressions, regexp constants, one of the special keywords + `BEGIN', `END', `BEGINFILE', `ENDFILE', or empty. The action + executes if the current record matches the pattern. Empty + (missing) patterns match all records. + + * I/O from `BEGIN' and `END' rules have certain constraints. This + is also true, only more so, for `BEGINFILE' and `ENDFILE' rules. + The latter two give you "hooks" into `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). + + * Shell variables can be used in `awk' programs by careful use of + shell quoting. It is easier to pass a shell variable into `awk' + by using the `-v' option and an `awk' variable. + + * 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. + + * The control statements in `awk' are `if'-`else', `while', `for', + and `do'-`while'. `gawk' adds the `switch' statement. There are + two flavors of `for' statement: one for performing general + looping, and the other for iterating through an array. + + * `break' and `continue' let you exit early or start the next + iteration of a loop (or get out of a `switch'). + + * `next' and `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. + + * The `exit' statement terminates your program. When executed from + an action (or function body) it transfers control to the `END' + statements. From an `END' statement body, it exits immediately. + You may pass an optional numeric value to be used as `awk''s exit + status. + + * Some predefined variables provide control over `awk', mainly for + I/O. Other variables convey information from `awk' to your + program. + + * `ARGC' and `ARGV' make the command-line arguments available to + your program. Manipulating them from a `BEGIN' rule lets you + control how `awk' will process the provided data files. + + File: gawk.info, Node: Arrays, Next: Functions, Prev: Patterns and Actions, Up: Top @@ -9604,27 +10794,23 @@ remove array elements. It also describes how `awk' simulates multidimensional arrays, as well as some of the less obvious points about array usage. The major node moves on to discuss `gawk''s facility for sorting arrays, and ends with a brief description of `gawk''s -ability to support true multidimensional arrays. - - `awk' maintains a single set of names that may be used for naming -variables, arrays, and functions (*note User-defined::). Thus, you -cannot have a variable and an array with the same name in the same -`awk' program. +ability to support true arrays of arrays. * Menu: * Array Basics:: The basics of arrays. -* Delete:: The `delete' statement removes an element - from an array. * Numeric Array Subscripts:: How to use numbers as subscripts in `awk'. * Uninitialized Subscripts:: Using Uninitialized variables as subscripts. -* Multi-dimensional:: Emulating multidimensional arrays in +* Delete:: The `delete' statement removes an element + from an array. +* Multidimensional:: Emulating multidimensional arrays in `awk'. * Arrays of Arrays:: True multidimensional arrays. +* Arrays Summary:: Summary of arrays. -File: gawk.info, Node: Array Basics, Next: Delete, Up: Arrays +File: gawk.info, Node: Array Basics, Next: Numeric Array Subscripts, Up: Arrays 8.1 The Basics of Arrays ======================== @@ -9641,6 +10827,8 @@ one at a time, and traversing all of the elements in an array. * Scanning an Array:: A variation of the `for' statement. It loops through the indices of an array's existing elements. +* Controlling Scanning:: Controlling the order in which arrays are + scanned. File: gawk.info, Node: Array Intro, Next: Reference to Elements, Up: Array Basics @@ -9649,8 +10837,7 @@ File: gawk.info, Node: Array Intro, Next: Reference to Elements, Up: Array Ba ---------------------------- Doing linear scans over an associative array is like trying to - club someone to death with a loaded Uzi. - Larry Wall + club someone to death with a loaded Uzi. -- Larry Wall The `awk' language provides one-dimensional arrays for storing groups of related strings or numbers. Every `awk' array must have a @@ -9662,8 +10849,8 @@ program. Arrays in `awk' superficially resemble arrays in other programming languages, but there are fundamental differences. In `awk', it isn't necessary to specify the size of an array before starting to use it. -Additionally, any number or string in `awk', not just consecutive -integers, may be used as an array index. +Additionally, any number or string, not just consecutive integers, may +be used as an array index. In most other languages, arrays must be "declared" before use, including a specification of how many elements or components they @@ -9681,19 +10868,20 @@ declared.) A contiguous array of four elements might look like the following example, conceptually, if the element values are 8, `"foo"', `""', and -30: +30 as shown in *note figure-array-elements::: - +---------+---------+--------+---------+ - | 8 | "foo" | "" | 30 | Value - +---------+---------+--------+---------+ - 0 1 2 3 Index ++---------+---------+--------+---------+ +| 8 | "foo" | "" | 30 | @r{Value} ++---------+---------+--------+---------+ + 0 1 2 3 @r{Index} +Figure 8.1: A contiguous array 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. Arrays in `awk' are different--they are "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: Index 3 Value 30 @@ -9701,7 +10889,8 @@ array element value: Index 0 Value 8 Index 2 Value "" -The pairs are shown in jumbled order because their order is irrelevant. +The pairs are shown in jumbled order because their order is +irrelevant.(1) 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 @@ -9729,10 +10918,11 @@ from English to French: 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 *Note Numeric Array -Subscripts::. Here, the number `1' isn't double-quoted, since `awk' -automatically converts it to a string. +numbers and strings as indices. (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 *note Numeric +Array Subscripts::.) Here, the number `1' isn't double quoted, because +`awk' automatically converts it to a string. The value of `IGNORECASE' has no effect upon array subscripting. The identical string value used to store an array element must be used @@ -9743,6 +10933,11 @@ starting at one. (*Note String Functions::.) `awk''s arrays are efficient--the time to access an element is independent of the number of elements in the array. + ---------- Footnotes ---------- + + (1) The ordering will vary among `awk' implementations, which +typically use hash tables to store array elements and values. + File: gawk.info, Node: Reference to Elements, Next: Assigning Elements, Prev: Array Intro, Up: Array Basics @@ -9777,18 +10972,20 @@ been assigned any value as well as elements that have been deleted # Check if "foo" exists in a: Incorrect! if (a["foo"] != "") ... - This is incorrect, since this will _create_ `a["foo"]' if it - didn't exist before! + This is incorrect for two reasons. First, it _creates_ `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. To determine whether an element exists in an array at a certain index, use the following expression: - IND in ARRAY + INDX in ARRAY -This expression tests whether the particular index IND exists, without +This expression tests whether the particular index INDX exists, without the side effect of creating that element if it is not present. The -expression has the value one (true) if `ARRAY[IND]' exists and zero -(false) if it does not exist. For example, this statement tests +expression has the value one (true) if `ARRAY[INDX]' exists and zero +(false) if it does not exist. (We use INDX here, because `index' is +the name of a built-in function.) For example, this statement tests whether the array `frequencies' contains the index `2': if (2 in frequencies) @@ -9832,14 +11029,14 @@ encountering repeated numbers, gaps, or lines that don't begin with a number: { - 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] } The first rule keeps track of the largest line number seen so far; @@ -9867,13 +11064,13 @@ overrides the others. Gaps in the line numbers can be handled with an easy improvement to the program's `END' rule, as follows: 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] } -File: gawk.info, Node: Scanning an Array, Prev: Array Example, Up: Array Basics +File: gawk.info, Node: Scanning an Array, Next: Controlling Scanning, Prev: Array Example, Up: Array Basics 8.1.5 Scanning All Elements of an Array --------------------------------------- @@ -9887,7 +11084,7 @@ lowest index up to the highest. This technique won't do the job in has a special kind of `for' statement for scanning an array: for (VAR in ARRAY) - BODY + BODY This loop executes BODY once for each index in ARRAY that the program has previously used, with the variable VAR set to that index. @@ -9922,105 +11119,202 @@ built-in function `length()'. The order in which elements of the array are accessed by this statement is determined by the internal arrangement of the array -elements within `awk' and normally cannot be controlled or changed. -This can lead to problems if new elements are added to ARRAY by -statements in the loop body; it is not predictable whether the `for' +elements within `awk' and in standard `awk' cannot be controlled or +changed. This can lead to problems if new elements are added to ARRAY +by statements in the loop body; it is not predictable whether the `for' loop will reach them. Similarly, changing VAR inside the loop may produce strange results. It is best to avoid such things. - As an extension, `gawk' makes it possible for you to loop over the -elements of an array in order, based on the value of -`PROCINFO["sorted_in"]' (*note Auto-set::). This is an advanced -feature, so discussion of it is delayed until *Note Controlling Array -Traversal::. + As a point of information, `gawk' sets up the list of elements to be +iterated over before the loop starts, and does not change it. But not +all `awk' versions do so. Consider this program, named `loopcheck.awk': - In addition, `gawk' provides built-in functions for sorting arrays; -see *Note Array Sorting Functions::. + BEGIN { + a["here"] = "here" + a["is"] = "is" + a["a"] = "a" + a["loop"] = "loop" + for (i in a) { + j++ + a[j] = j + print i + } + } + + Here is what happens when run with `gawk' (and `mawk'): + + $ gawk -f loopcheck.awk + -| here + -| loop + -| a + -| is + + Contrast this to BWK `awk': + + $ nawk -f loopcheck.awk + -| loop + -| here + -| is + -| a + -| 1 -File: gawk.info, Node: Delete, Next: Numeric Array Subscripts, Prev: Array Basics, Up: Arrays +File: gawk.info, Node: Controlling Scanning, Prev: Scanning an Array, Up: Array Basics -8.2 The `delete' Statement -========================== +8.1.6 Using Predefined Array Scanning Orders with `gawk' +-------------------------------------------------------- -To remove an individual element of an array, use the `delete' statement: +This node describes a feature that is specific to `gawk'. - delete ARRAY[INDEX-EXPRESSION] + By default, when a `for' loop traverses an array, the order is +undefined, meaning that the `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 +`awk' to the next. - 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: + 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." +`gawk' provides two mechanisms which give you this control. - for (i in frequencies) - delete frequencies[i] + * Set `PROCINFO["sorted_in"]' to one of a set of predefined values. + We describe this now. -This example removes all the elements from the array `frequencies'. -Once an element is deleted, a subsequent `for' statement to scan the -array does not report that element and the `in' operator to check for -the presence of that element returns zero (i.e., false): + * Set `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 *note Array Sorting::. - delete foo[4] - if (4 in foo) - print "This will never be printed" + The following special values for `PROCINFO["sorted_in"]' are +available: - It is important to note that deleting an element is _not_ the same -as assigning it a null value (the empty string, `""'). For example: +`"@unsorted"' + Array elements are processed in arbitrary order, which is the + default `awk' behavior. - foo[4] = "" - if (4 in foo) - print "This is printed, even though foo[4] is empty" +`"@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 `a[2*5] = 1' the index is `"10"' rather than + numeric 10.) - It is not an error to delete an element that does not exist. -However, if `--lint' is provided on the command line (*note Options::), -`gawk' issues a warning message when an element that is not in the -array is deleted. +`"@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. - All the elements of an array may be deleted with a single statement -(c.e.) by leaving off the subscript in the `delete' statement, as -follows: +`"@val_type_asc"' + Order by element values in ascending order (rather than by + indices). Ordering is by the type assigned to the element (*note + Typing and Comparison::). All numeric values come before all + string values, which in turn come before all subarrays. + (Subarrays have not been described yet; *note Arrays of Arrays::.) - delete ARRAY +`"@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. - This ability is a `gawk' extension; it is not available in -compatibility mode (*note Options::). +`"@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 `qsort()' function,(1) + which `gawk' uses internally to perform the sorting. - Using this version of the `delete' statement is about three times -more efficient than the equivalent loop that deletes each element one -at a time. +`"@ind_str_desc"' + String indices ordered from high to low. - The following statement provides a portable but nonobvious way to -clear out an array:(1) +`"@ind_num_desc"' + Numeric indices ordered from high to low. - split("", array) +`"@val_type_desc"' + Element values, based on type, ordered from high to low. + Subarrays, if present, come out first. - The `split()' function (*note 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. +`"@val_str_desc"' + Element values, treated as strings, ordered from high to low. + Subarrays, if present, come out first. + +`"@val_num_desc"' + Element values, treated as numbers, ordered from high to low. + Subarrays, if present, come out first. - 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: + The array traversal order is determined before the `for' loop starts +to run. Changing `PROCINFO["sorted_in"]' in the loop body does not +affect the loop. For example: - a[1] = 3 - delete a - a = 3 + $ gawk ' + > BEGIN { + > a[4] = 4 + > a[3] = 3 + > for (i in a) + > print i, a[i] + > }' + -| 4 4 + -| 3 3 + $ gawk ' + > BEGIN { + > PROCINFO["sorted_in"] = "@ind_str_asc" + > a[4] = 4 + > a[3] = 3 + > for (i in a) + > print i, a[i] + > }' + -| 3 3 + -| 4 4 + + 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. + + Here are some additional things to bear in mind about sorted array +traversal: + + * The value of `PROCINFO["sorted_in"]' is global. That is, it affects + all array traversal `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: + + ... + if ("sorted_in" in PROCINFO) { + save_sorted = PROCINFO["sorted_in"] + PROCINFO["sorted_in"] = "@val_str_desc" # or whatever + } + ... + if (save_sorted) + PROCINFO["sorted_in"] = save_sorted + + * As already mentioned, the default array traversal order is + represented by `"@unsorted"'. You can also get the default + behavior by assigning the null string to `PROCINFO["sorted_in"]' + or by just deleting the `"sorted_in"' element from the `PROCINFO' + array with the `delete' statement. (The `delete' statement hasn't + been described yet; *note Delete::.) + + In addition, `gawk' provides built-in functions for sorting arrays; +see *note Array Sorting Functions::. ---------- Footnotes ---------- - (1) Thanks to Michael Brennan for pointing this out. + (1) When two elements compare as equal, the C `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 `gawk' behaves +consistently across different environments. -File: gawk.info, Node: Numeric Array Subscripts, Next: Uninitialized Subscripts, Prev: Delete, Up: Arrays +File: gawk.info, Node: Numeric Array Subscripts, Next: Uninitialized Subscripts, Prev: Array Basics, Up: Arrays -8.3 Using Numbers to Subscript Arrays +8.2 Using Numbers to Subscript Arrays ===================================== An important aspect to remember about arrays is that _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 -(*note Conversion::). This means that the value of the built-in +(*note Conversion::). This means that the value of the predefined variable `CONVFMT' can affect how your program accesses elements of an array. For example: @@ -10039,13 +11333,13 @@ string value `"12.153"' (using the default conversion value of assigned the value one. The program then changes the value of `CONVFMT'. The test `(xyz in data)' generates a new string value from `xyz'--this time `"12.15"'--because the value of `CONVFMT' only allows -two significant digits. This test fails, since `"12.15"' is different -from `"12.153"'. +two significant digits. This test fails, because `"12.15"' is +different from `"12.153"'. According to the rules for conversions (*note Conversion::), integer -values are always converted to strings as integers, no matter what the -value of `CONVFMT' may happen to be. So the usual case of the -following works: +values always convert to strings as integers, no matter what the value +of `CONVFMT' may happen to be. So the usual case of the following +works: for (i = 1; i <= maxsub; i++) do something with array[i] @@ -10058,14 +11352,14 @@ example, that `array[17]', `array[021]', and `array[0x11]' all refer to the same element! As with many things in `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 +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. -File: gawk.info, Node: Uninitialized Subscripts, Next: Multi-dimensional, Prev: Numeric Array Subscripts, Up: Arrays +File: gawk.info, Node: Uninitialized Subscripts, Next: Delete, Prev: Numeric Array Subscripts, Up: Arrays -8.4 Using Uninitialized Variables as Subscripts +8.3 Using Uninitialized Variables as Subscripts =============================================== Suppose it's necessary to write a program to print the input data in @@ -10076,13 +11370,13 @@ might look like this: > line 2 > line 3' | awk '{ l[lines] = $0; ++lines } > END { - > for (i = lines-1; i >= 0; --i) + > for (i = lines - 1; i >= 0; i--) > print l[i] > }' -| line 3 -| line 2 - Unfortunately, the very first line of input data did not come out in + 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 @@ -10097,7 +11391,7 @@ following version of the program works correctly: { l[lines++] = $0 } END { - for (i = lines - 1; i >= 0; --i) + for (i = lines - 1; i >= 0; i--) print l[i] } @@ -10111,19 +11405,98 @@ string as a subscript if `--lint' is provided on the command line (*note Options::). -File: gawk.info, Node: Multi-dimensional, Next: Arrays of Arrays, Prev: Uninitialized Subscripts, Up: Arrays +File: gawk.info, Node: Delete, Next: Multidimensional, Prev: Uninitialized Subscripts, Up: Arrays + +8.4 The `delete' Statement +========================== + +To remove an individual element of an array, use the `delete' statement: + + delete ARRAY[INDEX-EXPRESSION] + + 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: + + for (i in frequencies) + delete frequencies[i] + +This example removes all the elements from the array `frequencies'. +Once an element is deleted, a subsequent `for' statement to scan the +array does not report that element and the `in' operator to check for +the presence of that element returns zero (i.e., false): + + delete foo[4] + if (4 in foo) + print "This will never be printed" + + It is important to note that deleting an element is _not_ the same +as assigning it a null value (the empty string, `""'). For example: + + foo[4] = "" + if (4 in foo) + print "This is printed, even though foo[4] is empty" + + It is not an error to delete an element that does not exist. +However, if `--lint' is provided on the command line (*note Options::), +`gawk' issues a warning message when an element that is not in the +array is deleted. + + All the elements of an array may be deleted with a single statement +by leaving off the subscript in the `delete' statement, as follows: + + delete ARRAY + + Using this version of the `delete' statement is about three times +more efficient than the equivalent loop that deletes each element one +at a time. + + This form of the `delete' statement is also supported by BWK `awk' +and `mawk', as well as by a number of other implementations. + + NOTE: For many years, using `delete' without a subscript was a + common extension. In September 2012, it was accepted for + inclusion into the POSIX standard. See the Austin Group website + (http://austingroupbugs.net/view.php?id=544). + + The following statement provides a portable but nonobvious way to +clear out an array:(1) + + split("", array) + + The `split()' function (*note 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. + + 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: + + a[1] = 3 + delete a + a = 3 + + ---------- Footnotes ---------- + + (1) Thanks to Michael Brennan for pointing this out. + + +File: gawk.info, Node: Multidimensional, Next: Arrays of Arrays, Prev: Delete, Up: Arrays 8.5 Multidimensional Arrays =========================== * Menu: -* Multi-scanning:: Scanning multidimensional arrays. +* Multiscanning:: Scanning multidimensional arrays. - A multidimensional array is an array in which an element is + A "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 languages, including `awk') to refer to an element of a +(in many languages, including `awk') to refer to an element of a two-dimensional array named `grid' is with `grid[X,Y]'. Multidimensional arrays are supported in `awk' through concatenation @@ -10155,13 +11528,14 @@ stored as `foo["a@b@c"]'. To test whether a particular index sequence exists in a multidimensional array, use the same operator (`in') that is used for -single dimensional arrays. Write the whole sequence of indices in +single-dimensional arrays. Write the whole sequence of indices in parentheses, separated by commas, as the left operand: - (SUBSCRIPT1, SUBSCRIPT2, ...) in ARRAY + if ((SUBSCRIPT1, SUBSCRIPT2, ...) in ARRAY) + ... - The following example treats its input as a two-dimensional array of -fields; it rotates this array 90 degrees clockwise and prints the + 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: { @@ -10197,13 +11571,13 @@ the program produces the following output: 3 2 1 6 -File: gawk.info, Node: Multi-scanning, Up: Multi-dimensional +File: gawk.info, Node: Multiscanning, Up: Multidimensional 8.5.1 Scanning Multidimensional Arrays -------------------------------------- There is no special `for' statement for scanning a "multidimensional" -array. There cannot be one, because, in truth, there are no +array. There cannot be one, because, in truth, `awk' does not have multidimensional arrays or elements--there is only a multidimensional _way of accessing_ an array. @@ -10223,7 +11597,7 @@ in the array, and splits it into the individual indices by breaking it apart where the value of `SUBSEP' appears. The individual indices then become the elements of the array `separate'. - Thus, if a value is previously stored in `array[1, "foo"]'; then an + Thus, if a value is previously stored in `array[1, "foo"]', then an element with index `"1\034foo"' exists in `array'. (Recall that the default value of `SUBSEP' is the character with code 034.) Sooner or later, the `for' statement finds that index and does an iteration with @@ -10237,13 +11611,14 @@ The result is to set `separate[1]' to `"1"' and `separate[2]' to recovered. -File: gawk.info, Node: Arrays of Arrays, Prev: Multi-dimensional, Up: Arrays +File: gawk.info, Node: Arrays of Arrays, Next: Arrays Summary, Prev: Multidimensional, Up: Arrays 8.6 Arrays of Arrays ==================== -`gawk' supports arrays of arrays. Elements of a subarray are referred -to by their own indices enclosed in square brackets, just like the +`gawk' goes beyond standard `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 `1' of the main array `a': @@ -10254,20 +11629,21 @@ two-element subarray at index `1' of the main array `a': 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 `awk' expression, including scalars -separated by commas (that is, a regular `awk' simulated -multidimensional subscript). So the following is valid in `gawk': +separated by commas (i.e., a regular `awk' simulated multidimensional +subscript). So the following is valid in `gawk': 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 `4' of the main array `a': +can be non-rectangular, or jagged in structure. You can assign a scalar +value to the index `4' of the main array `a', even though `a[1]' is +itself an array and not a scalar: a[4] = "An element in a jagged array" - The terms "dimension", "row" and "column" are meaningless when + The terms "dimension", "row", and "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 type of any element that has already been assigned cannot @@ -10324,6 +11700,8 @@ an array element is itself an array: print array[i][j] } } + else + print array[i] } If the structure of a jagged array of arrays is known in advance, @@ -10340,8 +11718,8 @@ the following code prints the elements of our main array `a': } } -*Note Walking Arrays::, for a user-defined function that will "walk" an -arbitrarily-dimensioned array of arrays. +*Note 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 `""', the null string. This has one important implication when @@ -10358,7 +11736,55 @@ by creating an arbitrary index: -| a -File: gawk.info, Node: Functions, Next: Internationalization, Prev: Arrays, Up: Top +File: gawk.info, Node: Arrays Summary, Prev: Arrays of Arrays, Up: Arrays + +8.7 Summary +=========== + + * Standard `awk' provides one-dimensional associative arrays (arrays + indexed by string values). All arrays are associative; numeric + indices are converted automatically to strings. + + * Array elements are referenced as `ARRAY[INDX]'. Referencing an + element creates it if it did not exist previously. + + * The proper way to see if an array has an element with a given index + is to use the `in' operator: `INDX in ARRAY'. + + * Use `for (INDX in ARRAY) ...' to scan through all the individual + elements of an array. In the body of the loop, INDX takes on the + value of each element's index in turn. + + * The order in which a `for (INDX in ARRAY)' loop traverses an array + is undefined in POSIX `awk' and varies among implementations. + `gawk' lets you control the order by assigning special predefined + values to `PROCINFO["sorted_in"]'. + + * Use `delete ARRAY[INDX]' to delete an individual element. To + delete all of the elements in an array, use `delete 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 `awk'. + + * Standard `awk' simulates multidimensional arrays by separating + subscript values with a comma. The values are concatenated into a + single string, separated by the value of `SUBSEP'. The fact that + such a subscript was created in this way is not retained; thus + changing `SUBSEP' may have unexpected consequences. You can use + `(SUB1, SUB2, ...) in ARRAY' to see if such a multidimensional + subscript exists in ARRAY. + + * `gawk' provides true arrays of arrays. You use a separate set of + square brackets for each dimension in such an array: + `data[row][col]', for example. Array elements may thus be either + scalar values (number or string) or another array. + + * Use the `isarray()' built-in function to determine if an array + element is itself a subarray. + + + +File: gawk.info, Node: Functions, Next: Library Functions, Prev: Arrays, Up: Top 9 Functions *********** @@ -10366,7 +11792,8 @@ File: gawk.info, Node: Functions, Next: Internationalization, Prev: Arrays, This major node describes `awk''s built-in functions, which fall into three categories: numeric, string, and I/O. `gawk' provides additional groups of functions to work with values that represent time, do bit -manipulation, sort arrays, and internationalize and localize programs. +manipulation, sort arrays, provide type information, and +internationalize and localize programs. Besides the built-in functions, `awk' has provisions for writing new functions that the rest of a program can use. The second half of this @@ -10377,11 +11804,12 @@ major node describes these "user-defined" functions. * 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. File: gawk.info, Node: Built-in, Next: User-defined, Up: Functions -9.1 Built-in Functions +9.1 Built-In Functions ====================== "Built-in" functions are always available for your `awk' program to @@ -10406,7 +11834,7 @@ for your convenience. File: gawk.info, Node: Calling Built-in, Next: Numeric Functions, Up: Built-in -9.1.1 Calling Built-in Functions +9.1.1 Calling Built-In Functions -------------------------------- To call one of `awk''s built-in functions, write the name of the @@ -10414,7 +11842,7 @@ function followed by arguments in parentheses. For example, `atan2(y + z, 1)' is a call to the function `atan2()' and has two arguments. Whitespace is ignored between the built-in function name and the -open parenthesis, but nonetheless it is good practice to avoid using +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. @@ -10440,7 +11868,7 @@ undefined. Thus, avoid writing programs that assume that parameters are evaluated from left to right or from right to left. For example: i = 5 - j = atan2(i++, i *= 2) + j = atan2(++i, i *= 2) If the order of evaluation is left to right, then `i' first becomes 6, and then 12, and `atan2()' is called with the two arguments 6 and @@ -10458,11 +11886,27 @@ with numbers. Optional parameters are enclosed in square brackets ([ ]): `atan2(Y, X)' - Return the arctangent of `Y / X' in radians. + Return the arctangent of `Y / X' in radians. You can use `pi = + atan2(0, -1)' to retrieve the value of pi. `cos(X)' Return the cosine of X, with X in radians. +`div(NUMERATOR, DENOMINATOR, RESULT)' + Perform integer division, similar to the standard C function of the + same name. First, truncate `numerator' and `denominator' towards + zero, creating integer values. Clear the `result' array, and then + set `result["quotient"]' to the result of `numerator / + denominator', truncated towards zero to an integer, and set + `result["remainder"]' to the result of `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 (*note + Arbitrary Precision Integers::). + + This function is a `gawk' extension. It is not available in + compatibility mode (*note Options::). + `exp(X)' Return the exponential of X (`e ^ X') or report an error if X is out of range. The range of values X can have depends on your @@ -10470,14 +11914,13 @@ brackets ([ ]): `int(X)' Return the nearest integer to X, located between X and zero and - truncated toward zero. - - For example, `int(3)' is 3, `int(3.9)' is 3, `int(-3.9)' is -3, - and `int(-3)' is -3 as well. + truncated toward zero. For example, `int(3)' is 3, `int(3.9)' is + 3, `int(-3.9)' is -3, and `int(-3)' is -3 as well. `log(X)' Return the natural logarithm of X, if X is positive; otherwise, - report an error. + return `NaN' ("not a number") on IEEE 754 systems. Additionally, + `gawk' prints a warning message when `x' is negative. `rand()' Return a random number. The values of `rand()' are uniformly @@ -10488,8 +11931,9 @@ brackets ([ ]): user-defined function that can be used to obtain a random non-negative integer less than N: - function randint(n) { - return int(n * rand()) + function randint(n) + { + return int(n * rand()) } The multiplication produces a random number greater than zero and @@ -10506,8 +11950,7 @@ brackets ([ ]): # 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)) } CAUTION: In most `awk' implementations, including `gawk', @@ -10527,7 +11970,7 @@ brackets ([ ]): Return the positive square root of X. `gawk' prints a warning message if X is negative. Thus, `sqrt(4)' is 2. -`srand([X])' +`srand('[X]`)' Set the starting point, or seed, for generating random numbers to the value X. @@ -10548,6 +11991,9 @@ brackets ([ ]): 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 `awk' + implementations. + ---------- Footnotes ---------- (1) The C version of `rand()' on many Unix systems is known to @@ -10560,7 +12006,7 @@ numbers. (2) `mawk' uses a different seed each time. (3) Computer-generated random numbers really are not truly random. -They are technically known as "pseudorandom." This means that while +They are technically known as "pseudorandom." This means 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. @@ -10571,20 +12017,32 @@ File: gawk.info, Node: String Functions, Next: I/O Functions, Prev: Numeric F ----------------------------------- The functions in this minor node look at or change the text of one or -more strings. `gawk' understands locales (*note Locales::), and does -all string processing in terms of _characters_, not _bytes_. This -distinction is particularly important to understand for locales where -one character may be represented by multiple bytes. Thus, for example, -`length()' returns the number of characters in a string, and not the -number of bytes used to represent those characters, Similarly, -`index()' works with character indices, and not byte indices. +more strings. + + `gawk' understands locales (*note Locales::), and does all string +processing in terms of _characters_, not _bytes_. This distinction is +particularly important to understand for locales where one character +may be represented by multiple bytes. Thus, for example, `length()' +returns the number of characters in a string, and not the number of +bytes used to represent those characters. Similarly, `index()' works +with character indices, and not byte indices. + + 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. In the following list, optional parameters are enclosed in square brackets ([ ]). Several functions perform string substitution; the full discussion is provided in the description of the `sub()' function, -which comes towards the end since the list is presented in alphabetic -order. Those functions that are specific to `gawk' are marked with a -pound sign (`#'): +which comes toward the end, because the list is presented +alphabetically. + + Those functions that are specific to `gawk' are marked with a pound +sign (`#'). They are not available in compatibility mode (*note +Options::): * Menu: @@ -10592,27 +12050,29 @@ pound sign (`#'): `&' with `sub()', `gsub()', and `gensub()'. -`asort(SOURCE [, DEST [, HOW ] ]) #' - Return the number of elements in the array SOURCE. `gawk' sorts - the contents of SOURCE and replaces the indices of the sorted - values of SOURCE with sequential integers starting with one. If - the optional array DEST is specified, then SOURCE is duplicated - into DEST. DEST is then sorted, leaving the indices of SOURCE - unchanged. The optional third argument HOW is a string which - controls the rule for comparing values, and the sort direction. A - single space is required between the comparison mode, `string' or - `number', and the direction specification, `ascending' or - `descending'. You can omit direction and/or mode in which case it - will default to `ascending' and `string', respectively. An empty - string "" is the same as the default `"ascending string"' for the - value of HOW. If the `source' array contains subarrays as values, - they will come out last(first) in the `dest' array for - `ascending'(`descending') order specification. The value of - `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. *Note Array Sorting Functions::, - for more information. +`asort('SOURCE [`,' DEST [`,' HOW ] ]`) #' +`asorti('SOURCE [`,' DEST [`,' HOW ] ]`) #' + These two functions are similar in behavior, so they are described + together. + + NOTE: The following description ignores the third argument, + 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 + *note Array Sorting Functions::, for the full story.) + + Both functions return the number of elements in the array SOURCE. + For `asort()', `gawk' sorts the values of SOURCE and replaces the + indices of the sorted values of SOURCE with sequential integers + starting with one. If the optional array DEST is specified, then + SOURCE is duplicated into DEST. DEST is then sorted, leaving the + indices of SOURCE unchanged. + + When comparing strings, `IGNORECASE' affects the sorting (*note + Array Sorting Functions::). If the SOURCE array contains + subarrays as values (*note Arrays of Arrays::), they will come + last, after all scalar values. Subarrays are _not_ recursively + sorted. For example, if the contents of `a' are as follows: @@ -10630,26 +12090,16 @@ pound sign (`#'): a[2] = "de" a[3] = "sac" - In order to reverse the direction of the sorted results in the - above example, `asort()' can be called with three arguments as - follows: - - asort(a, a, "descending") - - The `asort()' function is described in more detail in *Note Array - Sorting Functions::. `asort()' is a `gawk' extension; it is not - available in compatibility mode (*note Options::). + The `asorti()' function works similarly to `asort()', however, the + _indices_ are sorted, instead of the values. Thus, in the previous + example, starting with the same initial set of indices and values + in `a', calling `asorti(a)' would yield: -`asorti(SOURCE [, DEST [, HOW ] ]) #' - Return the number of elements in the array SOURCE. It works - similarly to `asort()', however, the _indices_ are sorted, instead - of the values. (Here too, `IGNORECASE' affects the sorting.) + a[1] = "first" + a[2] = "last" + a[3] = "middle" - The `asorti()' function is described in more detail in *Note Array - Sorting Functions::. `asorti()' is a `gawk' extension; it is not - available in compatibility mode (*note Options::). - -`gensub(REGEXP, REPLACEMENT, HOW [, TARGET]) #' +`gensub(REGEXP, REPLACEMENT, HOW' [`, TARGET']`) #' Search the target string TARGET for matches of the regular expression REGEXP. If HOW is a string beginning with `g' or `G' (short for "global"), then replace all matches of REGEXP with @@ -10658,7 +12108,7 @@ pound sign (`#'): `$0'. It returns the modified string as the result of the function and the original target string is _not_ changed. - `gensub()' is a general substitution function. It's purpose is to + `gensub()' is a general substitution function. Its purpose is to provide more features than the standard `sub()' and `gsub()' functions. @@ -10699,10 +12149,7 @@ pound sign (`#'): If REGEXP does not match TARGET, `gensub()''s return value is the original unchanged value of TARGET. - `gensub()' is a `gawk' extension; it is not available in - compatibility mode (*note Options::). - -`gsub(REGEXP, REPLACEMENT [, TARGET])' +`gsub(REGEXP, REPLACEMENT' [`, TARGET']`)' Search TARGET for _all_ of the longest, leftmost, _nonoverlapping_ matching substrings it can find and replace them with REPLACEMENT. The `g' in `gsub()' stands for "global," which means replace @@ -10726,10 +12173,14 @@ pound sign (`#'): $ awk 'BEGIN { print index("peanut", "an") }' -| 3 - If FIND is not found, `index()' returns zero. (Remember that - string indices in `awk' start at one.) + If FIND is not found, `index()' returns zero. -`length([STRING])' + With BWK `awk' and `gawk', it is a fatal error to use a regexp + constant for FIND. Other implementations allow it, simply + treating the regexp constant as an expression meaning `$0 ~ + /regexp/'. (d.c.). + +`length('[STRING]`)' Return the number of characters in STRING. If STRING is a number, the length of the digit string representing that number is returned. For example, `length("abcde")' is five. By contrast, @@ -10769,14 +12220,14 @@ pound sign (`#'): array argument is not portable. If `--posix' is supplied, using an array argument is a fatal error (*note Arrays::). -`match(STRING, REGEXP [, ARRAY])' +`match(STRING, REGEXP' [`, ARRAY']`)' Search STRING for the longest, leftmost substring matched by the - regular expression, REGEXP and return the character position, or - "index", at which that substring begins (one, if it starts at the + regular expression, REGEXP and return the character position + (index) at which that substring begins (one, if it starts at the beginning of STRING). If no match is found, return zero. - The REGEXP argument may be either a regexp constant (`/.../') or a - string constant (`"..."'). In the latter case, the string is + The REGEXP argument may be either a regexp constant (`/'...`/') or + a string constant (`"'...`"'). In the latter case, the string is treated as a regexp to be matched. *Note Computed Regexps::, for a discussion of the difference between the two forms, and the implications for writing your program correctly. @@ -10787,21 +12238,20 @@ pound sign (`#'): `match()', the order is the same as for the `~' operator: `STRING ~ REGEXP'. - The `match()' function sets the built-in variable `RSTART' to the - index. It also sets the built-in variable `RLENGTH' to the length - in characters of the matched substring. If no match is found, - `RSTART' is set to zero, and `RLENGTH' to -1. + The `match()' function sets the predefined variable `RSTART' to + the index. It also sets the predefined variable `RLENGTH' to the + length in characters of the matched substring. If no match is + found, `RSTART' is set to zero, and `RLENGTH' to -1. For example: { - 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 } } @@ -10848,7 +12298,7 @@ pound sign (`#'): -| 9 7 There may not be subscripts for the start and index for every - parenthesized subexpression, since they may not all have matched + parenthesized subexpression, because they may not all have matched text; thus they should be tested for with the `in' operator (*note Reference to Elements::). @@ -10856,7 +12306,7 @@ pound sign (`#'): compatibility mode (*note Options::), using a third argument is a fatal error. -`patsplit(STRING, ARRAY [, FIELDPAT [, SEPS ] ]) #' +`patsplit(STRING, ARRAY' [`, FIELDPAT' [`, SEPS' ] ]`) #' Divide STRING into pieces defined by FIELDPAT and store the pieces in ARRAY and the separator strings in the SEPS array. The first piece is stored in `ARRAY[1]', the second piece in `ARRAY[2]', and @@ -10870,29 +12320,25 @@ pound sign (`#'): The `patsplit()' function splits strings into pieces in a manner similar to the way input lines are split into fields using `FPAT' - (*note Splitting By Content::. + (*note Splitting By Content::). Before splitting the string, `patsplit()' deletes any previously existing elements in the arrays ARRAY and SEPS. - The `patsplit()' function is a `gawk' extension. In compatibility - mode (*note Options::), it is not available. - -`split(STRING, ARRAY [, FIELDSEP [, SEPS ] ])' +`split(STRING, ARRAY' [`, FIELDSEP' [`, SEPS' ] ]`)' Divide STRING into pieces separated by FIELDSEP and store the pieces in ARRAY and the separator strings in the SEPS array. The first piece is stored in `ARRAY[1]', the second piece in `ARRAY[2]', and so forth. The string value of the third argument, FIELDSEP, is a regexp describing where to split STRING (much as - `FS' can be a regexp describing where to split input records; - *note Regexp Field Splitting::). If FIELDSEP is omitted, the - value of `FS' is used. `split()' returns the number of elements - created. SEPS is a `gawk' extension with `SEPS[I]' being the - separator string between `ARRAY[I]' and `ARRAY[I+1]'. If FIELDSEP - is a single space then any leading whitespace goes into `SEPS[0]' - and any trailing whitespace goes into `SEPS[N]' where N is the - return value of `split()' (that is, the number of elements in - ARRAY). + `FS' can be a regexp describing where to split input records). If + FIELDSEP is omitted, the value of `FS' is used. `split()' returns + the number of elements created. SEPS is a `gawk' extension with + `SEPS[I]' being the separator string between `ARRAY[I]' and + `ARRAY[I+1]'. If FIELDSEP is a single space then any leading + whitespace goes into `SEPS[0]' and any trailing whitespace goes + into `SEPS[N]' where N is the return value of `split()' (i.e., the + number of elements in ARRAY). The `split()' function splits strings into pieces in a manner similar to the way input lines are split into fields. For example: @@ -10916,7 +12362,7 @@ pound sign (`#'): As with input field-splitting, when the value of FIELDSEP is `" "', leading and trailing whitespace is ignored in values assigned to the elements of ARRAY but not in SEPS, and the elements - are separated by runs of whitespace. Also as with input + are separated by runs of whitespace. Also, as with input field-splitting, if FIELDSEP is the null string, each individual character in the string is split into its own array element. (c.e.) @@ -10943,6 +12389,9 @@ pound sign (`#'): has one element only. The value of that element is the original STRING. + In POSIX mode (*note Options::), the fourth argument is not + allowed. + `sprintf(FORMAT, EXPRESSION1, ...)' Return (without printing) the string that `printf' would have printed out with the same arguments (*note Printf::). For example: @@ -10968,18 +12417,15 @@ pound sign (`#'): Note also that `strtonum()' uses the current locale's decimal point for recognizing numbers (*note Locales::). - `strtonum()' is a `gawk' extension; it is not available in - compatibility mode (*note Options::). - -`sub(REGEXP, REPLACEMENT [, TARGET])' +`sub(REGEXP, REPLACEMENT' [`, TARGET']`)' Search TARGET, which is treated as a string, for the leftmost, longest substring matched by the regular expression REGEXP. Modify the entire string by replacing the matched text with REPLACEMENT. The modified string becomes the new value of TARGET. Return the number of substitutions made (zero or one). - The REGEXP argument may be either a regexp constant (`/.../') or a - string constant (`"..."'). In the latter case, the string is + The REGEXP argument may be either a regexp constant (`/'...`/') or + a string constant (`"'...`"'). In the latter case, the string is treated as a regexp to be matched. *Note Computed Regexps::, for a discussion of the difference between the two forms, and the implications for writing your program correctly. @@ -11044,7 +12490,7 @@ pound sign (`#'): into a string, and then the value of that string is treated as the regexp to match. -`substr(STRING, START [, LENGTH])' +`substr(STRING, START' [`, LENGTH' ]`)' Return a LENGTH-character-long substring of STRING, starting at character number START. The first character of a string is character number one.(3) For example, `substr("washington", 5, 3)' @@ -11057,11 +12503,11 @@ pound sign (`#'): remaining in the string, counting from character START. If START is less than one, `substr()' treats it as if it was one. - (POSIX doesn't specify what to do in this case: Brian Kernighan's - `awk' acts this way, and therefore `gawk' does too.) If START is - greater than the number of characters in the string, `substr()' - returns the null string. Similarly, if LENGTH is present but less - than or equal to zero, the null string is returned. + (POSIX doesn't specify what to do in this case: BWK `awk' acts + this way, and therefore `gawk' does too.) If START is greater + than the number of characters in the string, `substr()' returns + the null string. Similarly, if LENGTH is present but less than or + equal to zero, the null string is returned. The string returned by `substr()' _cannot_ be assigned. Thus, it is a mistake to attempt to change a portion of a string, as shown @@ -11098,6 +12544,17 @@ pound sign (`#'): Nonalphabetic characters are left unchanged. For example, `toupper("MiXeD cAsE 123")' returns `"MIXED CASE 123"'. + Matching the Null String + + In `awk', the `*' operator can match the null string. This is +particularly important for the `sub()', `gsub()', and `gensub()' +functions. For example: + + $ echo abc | awk '{ gsub(/m*/, "X"); print }' + -| XaXbXcX + +Although this makes a certain amount of sense, it can be surprising. + ---------- Footnotes ---------- (1) Unless you use the `--non-decimal-data' option, which isn't @@ -11114,26 +12571,30 @@ is number zero. File: gawk.info, Node: Gory Details, Up: String Functions -9.1.3.1 More About `\' and `&' with `sub()', `gsub()', and `gensub()' +9.1.3.1 More about `\' and `&' with `sub()', `gsub()', and `gensub()' ..................................................................... -When using `sub()', `gsub()', or `gensub()', and trying to get literal -backslashes and ampersands into the replacement text, you need to -remember that there are several levels of "escape processing" going on. + CAUTION: This subsubsection has been reported to cause headaches. + You might want to skip it upon first reading. + + When using `sub()', `gsub()', or `gensub()', and trying to get +literal backslashes and ampersands into the replacement text, you need +to remember that there are several levels of "escape processing" going +on. First, there is the "lexical" level, which is when `awk' reads your -program and builds an internal copy of it that can be executed. Then -there is the runtime level, which is when `awk' actually scans the -replacement string to determine what to generate. +program and builds an internal copy of it to execute. Then there is +the runtime level, which is when `awk' actually scans the replacement +string to determine what to generate. At both levels, `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 *Note Escape Sequences::. Thus, for every `\' that +sequences listed in *note Escape Sequences::. Thus, for every `\' that `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 `\', Brian Kernighan's `awk' and `gawk' both -simply remove the initial `\' and put the next character into the -string. Thus, for example, `"a\qb"' is treated as `"aqb"'. +sequence follows the `\', BWK `awk' and `gawk' both simply remove the +initial `\' and put the next character into the string. Thus, for +example, `"a\qb"' is treated as `"aqb"'. At the runtime level, the various functions handle sequences of `\' and `&' differently. The situation is (sadly) somewhat complex. @@ -11141,19 +12602,20 @@ Historically, the `sub()' and `gsub()' functions treated the two character sequence `\&' specially; this sequence was replaced in the generated text with a single `&'. Any other `\' within the REPLACEMENT string that did not precede an `&' was passed through unchanged. This -is illustrated in *Note table-sub-escapes::. +is illustrated in *note table-sub-escapes::. You type `sub()' sees `sub()' generates ------- --------- -------------- - `\&' `&' the matched text - `\\&' `\&' a literal `&' - `\\\&' `\&' a literal `&' - `\\\\&' `\\&' a literal `\&' - `\\\\\&' `\\&' a literal `\&' - `\\\\\\&' `\\\&' a literal `\\&' - `\\q' `\q' a literal `\q' + `\&' `&' The matched text + `\\&' `\&' A literal `&' + `\\\&' `\&' A literal `&' + `\\\\&' `\\&' A literal `\&' + `\\\\\&' `\\&' A literal `\&' + `\\\\\\&' `\\\&' A literal `\\&' + `\\q' `\q' A literal `\q' -Table 9.1: Historical Escape Sequence Processing for `sub()' and `gsub()' +Table 9.1: Historical escape sequence processing for `sub()' and +`gsub()' This table shows both the lexical-level processing, where an odd number of backslashes becomes an even number at the runtime level, as well as @@ -11164,49 +12626,25 @@ backslashes entered at the lexical level.) The problem with the historical approach is that there is no way to get a literal `\' followed by the matched text. - The 1992 POSIX standard attempted to fix this problem. That standard -says that `sub()' and `gsub()' look for either a `\' or an `&' after -the `\'. If either one follows a `\', that character is output -literally. The interpretation of `\' and `&' then becomes as shown in -*Note table-sub-posix-92::. + Several editions of the POSIX standard attempted to fix this problem +but weren't successful. The details are irrelevant at this point in +time. - You type `sub()' sees `sub()' generates - ------- --------- -------------- - `&' `&' the matched text - `\\&' `\&' a literal `&' - `\\\\&' `\\&' a literal `\', then the matched text - `\\\\\\&' `\\\&' a literal `\&' - -Table 9.2: 1992 POSIX Rules for sub and gsub Escape Sequence Processing - -This appears to solve the problem. Unfortunately, the phrasing of the -standard is unusual. It says, in effect, that `\' turns off the special -meaning of any following character, but for anything other than `\' and -`&', such special meaning is undefined. This wording leads to two -problems: - - * Backslashes must now be doubled in the REPLACEMENT string, breaking - historical `awk' programs. - - * To make sure that an `awk' program is portable, _every_ character - in the REPLACEMENT string must be preceded with a backslash.(1) - - Because of the problems just listed, in 1996, the `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 -`\' preceding the matched text. This is shown in *Note -table-sub-proposed::. + At one point, the `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 `\' preceding the matched text. +This is shown in *note table-sub-proposed::. You type `sub()' sees `sub()' generates ------- --------- -------------- - `\\\\\\&' `\\\&' a literal `\&' - `\\\\&' `\\&' a literal `\', followed by the matched text - `\\&' `\&' a literal `&' - `\\q' `\q' a literal `\q' + `\\\\\\&' `\\\&' A literal `\&' + `\\\\&' `\\&' A literal `\', followed by the matched text + `\\&' `\&' A literal `&' + `\\q' `\q' A literal `\q' `\\\\' `\\' `\\' -Table 9.3: Proposed rules for sub and backslash +Table 9.2: GNU `awk' rules for `sub()' and backslash In a nutshell, at the runtime level, there are now three special sequences of characters (`\\\&', `\\&' and `\&') whereas historically @@ -11214,39 +12652,38 @@ there was only one. However, as in the historical case, any `\' that is not part of one of these three sequences is not special and appears in the output literally. - `gawk' 3.0 and 3.1 follow these proposed POSIX rules for `sub()' and -`gsub()'. 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. + `gawk' 3.0 and 3.1 follow these rules for `sub()' and `gsub()'. The +POSIX standard took much longer to be revised than was expected. In +addition, the `gawk' maintainer's proposal was lost during the +standardization process. The final rules are somewhat simpler. The +results are similar except for one case. The POSIX rules state that `\&' in the replacement string produces a literal `&', `\\' produces a literal `\', and `\' followed by anything else is not special; the `\' is placed straight into the output. These -rules are presented in *Note table-posix-sub::. +rules are presented in *note table-posix-sub::. You type `sub()' sees `sub()' generates ------- --------- -------------- - `\\\\\\&' `\\\&' a literal `\&' - `\\\\&' `\\&' a literal `\', followed by the matched text - `\\&' `\&' a literal `&' - `\\q' `\q' a literal `\q' + `\\\\\\&' `\\\&' A literal `\&' + `\\\\&' `\\&' A literal `\', followed by the matched text + `\\&' `\&' A literal `&' + `\\q' `\q' A literal `\q' `\\\\' `\\' `\' -Table 9.4: POSIX rules for `sub()' and `gsub()' +Table 9.3: POSIX rules for `sub()' and `gsub()' The only case where the difference is noticeable is the last one: `\\\\' is seen as `\\' and produces `\' instead of `\\'. Starting with version 3.1.4, `gawk' followed the POSIX rules when `--posix' is specified (*note Options::). Otherwise, it continued to -follow the 1996 proposed rules, since that had been its behavior for -many years. +follow the proposed rules, as that had been its behavior for many years. - When version 4.0.0, was released, the `gawk' maintainer made the + When version 4.0.0 was released, the `gawk' maintainer made the POSIX rules the default, breaking well over a decade's worth of -backwards compatibility.(2) Needless to say, this was a bad idea, and -as of version 4.0.1, `gawk' resumed its historical behavior, and only +backward compatibility.(1) Needless to say, this was a bad idea, and as +of version 4.0.1, `gawk' resumed its historical behavior, and only follows the POSIX rules when `--posix' is given. The rules for `gensub()' are considerably simpler. At the runtime @@ -11254,40 +12691,26 @@ level, whenever `gawk' sees a `\', if the following character is a digit, then the text that matched the corresponding parenthesized subexpression is placed in the generated output. Otherwise, no matter what character follows the `\', it appears in the generated text and -the `\' does not, as shown in *Note table-gensub-escapes::. +the `\' does not, as shown in *note table-gensub-escapes::. You type `gensub()' sees `gensub()' generates ------- ------------ ----------------- - `&' `&' the matched text - `\\&' `\&' a literal `&' - `\\\\' `\\' a literal `\' - `\\\\&' `\\&' a literal `\', then the matched text - `\\\\\\&' `\\\&' a literal `\&' - `\\q' `\q' a literal `q' + `&' `&' The matched text + `\\&' `\&' A literal `&' + `\\\\' `\\' A literal `\' + `\\\\&' `\\&' A literal `\', then the matched text + `\\\\\\&' `\\\&' A literal `\&' + `\\q' `\q' A literal `q' -Table 9.5: Escape Sequence Processing for `gensub()' +Table 9.4: Escape sequence processing for `gensub()' Because of the complexity of the lexical and runtime level processing and the special cases for `sub()' and `gsub()', we recommend the use of `gawk' and `gensub()' when you have to do substitutions. -Advanced Notes: Matching the Null String ----------------------------------------- - -In `awk', the `*' operator can match the null string. This is -particularly important for the `sub()', `gsub()', and `gensub()' -functions. For example: - - $ echo abc | awk '{ gsub(/m*/, "X"); print }' - -| XaXbXcX - -Although this makes a certain amount of sense, it can be surprising. - ---------- Footnotes ---------- - (1) This consequence was certainly unintended. - - (2) This was rather naive of him, despite there being a note in this + (1) 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. @@ -11300,7 +12723,7 @@ File: gawk.info, Node: I/O Functions, Next: Time Functions, Prev: String Func The following functions relate to input/output (I/O). Optional parameters are enclosed in square brackets ([ ]): -`close(FILENAME [, HOW])' +`close('FILENAME [`,' HOW]`)' Close the file 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 @@ -11315,44 +12738,87 @@ parameters are enclosed in square brackets ([ ]): not matter. *Note Two-way I/O::, which discusses this feature in more detail and gives an example. -`fflush([FILENAME])' + Note that the second argument to `close()' is a `gawk' extension; + it is not available in compatibility mode (*note Options::). + +`fflush('[FILENAME]`)' Flush any buffered output associated with FILENAME, which is either a file opened for writing or a shell command for - redirecting output to a pipe or coprocess. (c.e.). + redirecting output to a pipe or coprocess. - Many utility programs "buffer" their output; i.e., they save + Many utility programs "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. This is often more efficient than writing every + 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 "flush" its - buffers; that is, write the information to its destination, even - if a buffer is not full. This is the purpose of the `fflush()' + buffers (i.e., write the information to its destination, even if a + buffer is not full). This is the purpose of the `fflush()' function--`gawk' also buffers its output and the `fflush()' function forces `gawk' to flush its buffers. - `fflush()' was added to Brian Kernighan's version of `awk' in - 1994; it is not part of the POSIX standard and is not available if - `--posix' has been specified on the command line (*note Options::). + Brian Kernighan added `fflush()' to his `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 the Austin + Group website (http://austingroupbugs.net/view.php?id=634). + + POSIX standardizes `fflush()' as follows: if there is no argument, + or if the argument is the null string (`""'), then `awk' flushes + the buffers for _all_ open output files and pipes. + + NOTE: Prior to version 4.0.2, `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 `awk', in the hope that standardizing this + feature in POSIX would then be easier (which indeed helped). - `gawk' extends the `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 - (`""') as the argument. In this case, the buffers for _all_ open - output files and pipes are flushed. Brian Kernighan's `awk' also - supports these extensions. + With `gawk', you can use `fflush("/dev/stdout")' if you wish + to flush only the standard output. `fflush()' returns zero if the buffer is successfully flushed; - otherwise, it returns -1. In the case where all buffers are - flushed, the return value is zero only if all buffers were flushed - successfully. Otherwise, it is -1, and `gawk' warns about the - problem FILENAME. + otherwise, it returns non-zero. (`gawk' returns -1.) In the case + where all buffers are flushed, the return value is zero only if + all buffers were flushed successfully. Otherwise, it is -1, and + `gawk' warns about the problem FILENAME. `gawk' also issues a warning message if you attempt to flush a file or pipe that was opened for reading (such as with `getline'), or if FILENAME is not an open file, pipe, or coprocess. In such a case, `fflush()' returns -1, as well. + Interactive Versus Noninteractive Buffering + + As a side point, buffering issues can be even more confusing, + depending upon whether your program is "interactive" (i.e., + communicating with a user sitting at a keyboard).(1) + + Interactive programs generally "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: + + $ awk '{ print $1 + $2 }' + 1 1 + -| 2 + 2 3 + -| 5 + Ctrl-d + + Each line of output is printed immediately. Compare that behavior + with this example: + + $ awk '{ print $1 + $2 }' | cat + 1 1 + 2 3 + Ctrl-d + -| 2 + -| 5 + + Here, no output is printed until after the `Ctrl-d' is typed, + because it is all buffered and sent down the pipe to `cat' in one + shot. + `system(COMMAND)' Execute the operating-system command COMMAND and then return to the `awk' program. Return COMMAND's exit status. @@ -11386,53 +12852,21 @@ parameters are enclosed in square brackets ([ ]): is disabled (*note Options::). -Advanced Notes: Interactive Versus Noninteractive Buffering ------------------------------------------------------------ - -As a side point, buffering issues can be even more confusing, depending -upon whether your program is "interactive", i.e., communicating with a -user sitting at a keyboard.(1) - - Interactive programs generally "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: - - $ awk '{ print $1 + $2 }' - 1 1 - -| 2 - 2 3 - -| 5 - Ctrl-d - -Each line of output is printed immediately. Compare that behavior with -this example: - - $ awk '{ print $1 + $2 }' | cat - 1 1 - 2 3 - Ctrl-d - -| 2 - -| 5 - -Here, no output is printed until after the `Ctrl-d' is typed, because -it is all buffered and sent down the pipe to `cat' in one shot. + Controlling Output Buffering with `system()' -Advanced Notes: Controlling Output Buffering with `system()' ------------------------------------------------------------- - -The `fflush()' function provides explicit control over output buffering -for individual files and pipes. However, its use is not portable to -many other `awk' implementations. An alternative method to flush output -buffers is to call `system()' with a null string as its argument: + The `fflush()' function provides explicit control over output +buffering for individual files and pipes. However, its use is not +portable to many older `awk' implementations. An alternative method to +flush output buffers is to call `system()' with a null string as its +argument: system("") # flush output `gawk' treats this use of the `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 `gawk', this idiom is not only -useful, it is also efficient. While this method should work with other -`awk' implementations, it does not necessarily avoid starting an +useful, it is also efficient. Although this method should work with +other `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.) @@ -11487,8 +12921,9 @@ timestamps that represent times before the epoch. In order to make it easier to process such log files and to produce useful reports, `gawk' provides the following functions for working with timestamps. They are `gawk' extensions; they are not specified in -the POSIX standard, nor are they in any other known version of `awk'.(2) -Optional parameters are enclosed in square brackets ([ ]): +the POSIX standard.(2) However, recent versions of `mawk' (*note Other +Versions::) also support these functions. Optional parameters are +enclosed in square brackets ([ ]): `mktime(DATESPEC)' Turn DATESPEC into a timestamp in the same form as is returned by @@ -11513,7 +12948,7 @@ Optional parameters are enclosed in square brackets ([ ]): If DATESPEC does not contain enough elements or if the resulting time is out of range, `mktime()' returns -1. -`strftime([FORMAT [, TIMESTAMP [, UTC-FLAG]]])' +`strftime('[FORMAT [`,' TIMESTAMP [`,' UTC-FLAG] ] ]`)' Format the time specified by TIMESTAMP based on the contents of the FORMAT string and return the result. It is similar to the function of the same name in ISO C. If UTC-FLAG is present and is @@ -11522,13 +12957,14 @@ Optional parameters are enclosed in square brackets ([ ]): Otherwise, the value is formatted for the local time zone. The TIMESTAMP is in the same format as the value returned by the `systime()' function. If no TIMESTAMP argument is supplied, - `gawk' uses the current time of day as the timestamp. If no - FORMAT argument is supplied, `strftime()' uses the value of + `gawk' uses the current time of day as the timestamp. Without a + FORMAT argument, `strftime()' uses the value of `PROCINFO["strftime"]' as the format string (*note Built-in Variables::). The default string value is `"%a %b %e %H:%M:%S %Z %Y"'. This format string produces output that is equivalent to that of the `date' utility. You can assign - a new value to `PROCINFO["strftime"]' to change the default format. + a new value to `PROCINFO["strftime"]' to change the default + format; see the following list for the various format directives. `systime()' Return the current time as the number of seconds since the system @@ -11592,11 +13028,11 @@ the following date format specifications: `%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. + number (00-99). 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. `%G' The full year of the ISO week number, as a decimal number. @@ -11676,7 +13112,7 @@ the following date format specifications: The year modulo 100 as a decimal number (00-99). `%Y' - The full year as a decimal number (e.g., 2011). + The full year as a decimal number (e.g., 2015). `%z' The timezone offset in a +HHMM format (e.g., the format necessary @@ -11688,24 +13124,15 @@ the following date format specifications: `%Ec %EC %Ex %EX %Ey %EY %Od %Oe %OH' `%OI %Om %OM %OS %Ou %OU %OV %Ow %OW %Oy' - "Alternate representations" for the specifications that use only + "Alternative representations" for the specifications that use only the second letter (`%c', `%C', and so on).(5) (These facilitate compliance with the POSIX `date' utility.) `%%' A literal `%'. - If a conversion specifier is not one of the above, the behavior is -undefined.(6) - - Informally, a "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 `%x' -specification in a `"US"' locale might produce `9/4/12', while in a -`"EUROPE"' locale, it might produce `4.9.12'. The ISO C standard -defines a default `"C"' locale, which is an environment that is typical -of what many C programmers are used to. + If a conversion specifier is not one of those just listed, the +behavior is undefined.(6) For systems that are not yet fully standards-compliant, `gawk' supplies a copy of `strftime()' from the GNU C Library. It supports @@ -11725,8 +13152,8 @@ format specifications are available: The time as a decimal timestamp in seconds since the epoch. - Additionally, the alternate representations are recognized but their -normal representations are used. + Additionally, the alternative representations are recognized but +their normal representations are used. The following example is an `awk' implementation of the POSIX `date' utility. Normally, the `date' utility prints the current date and time @@ -11736,7 +13163,7 @@ to the standard output and interprets the current time according to the format specifiers in the string. For example: $ date '+Today is %A, %B %d, %Y.' - -| Today is Wednesday, March 30, 2011. + -| Today is Monday, September 22, 2014. Here is the `gawk' version of the `date' utility. It has a shell "wrapper" to handle the `-u' option, which requires that `date' run as @@ -11753,7 +13180,7 @@ if the time zone is set to UTC: esac gawk 'BEGIN { - format = "%a %b %e %H:%M:%S %Z %Y" + format = PROCINFO["strftime"] exitval = 0 if (ARGC > 2) @@ -11783,7 +13210,7 @@ supports all of the conversions listed here. (5) If you don't understand any of this, don't worry about it; these facilities are meant to make it easier to "internationalize" programs. -Other internationalization features are described in *Note +Other internationalization features are described in *note Internationalization::. (6) This is because ISO C leaves the behavior of the C version of @@ -11797,13 +13224,13 @@ File: gawk.info, Node: Bitwise Functions, Next: Type Functions, Prev: Time Fu 9.1.6 Bit-Manipulation Functions -------------------------------- - I can explain it for you, but I can't understand it for you. + I can explain it for you, but I can't understand it for you. -- Anonymous Many languages provide the ability to perform "bitwise" operations on two integer numbers. In other words, the operation is performed on each successive pair of bits in the operands. Three common operations -are bitwise AND, OR, and XOR. The operations are described in *Note +are bitwise AND, OR, and XOR. The operations are described in *note table-bitwise-ops::. Bit Operator @@ -11814,7 +13241,7 @@ table-bitwise-ops::. 0 | 0 0 | 0 1 | 0 1 1 | 0 1 | 1 1 | 1 0 -Table 9.6: Bitwise Operations +Table 9.5: Bitwise operations As you can see, the result of an AND operation is 1 only when _both_ bits are 1. The result of an OR operation is 1 if _either_ bit is 1. @@ -11825,30 +13252,33 @@ a given value. Finally, two other common operations are to shift the bits left or right. For example, if you have a bit string `10111001' and you shift -it right by three bits, you end up with `00010111'.(1) If you start over -again with `10111001' and shift it left by three bits, you end up with -`11001000'. `gawk' provides built-in functions that implement the -bitwise operations just described. They are: +it right by three bits, you end up with `00010111'.(1) If you start +over again with `10111001' and shift it left by three bits, you end up +with `11001000'. The following list describes `gawk''s built-in +functions that implement the bitwise operations. Optional parameters +are enclosed in square brackets ([ ]): -`and(V1, V2)' - Return the bitwise AND of the values provided by V1 and V2. +``and('V1`,' V2 [`,' ...]`)'' + Return the bitwise AND of the arguments. There must be at least + two. -`compl(VAL)' +``compl(VAL)'' Return the bitwise complement of VAL. -`lshift(VAL, COUNT)' +``lshift(VAL, COUNT)'' Return the value of VAL, shifted left by COUNT bits. -`or(V1, V2)' - Return the bitwise OR of the values provided by V1 and V2. +``or('V1`,' V2 [`,' ...]`)'' + Return the bitwise OR of the arguments. There must be at least two. -`rshift(VAL, COUNT)' +``rshift(VAL, COUNT)'' Return the value of VAL, shifted right by COUNT bits. -`xor(V1, V2)' - Return the bitwise XOR of the values provided by V1 and V2. +``xor('V1`,' V2 [`,' ...]`)'' + Return the bitwise XOR of the arguments. There must be at least + two. - For all of these functions, first the double precision + 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 `double', leading nonzero bits are removed @@ -11906,7 +13336,7 @@ or not. If so, a `"1"' is concatenated onto the front of the string. Otherwise, a `"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 `"0"'. Otherwise, + If the initial value is zero, it returns a simple `"0"'. Otherwise, at the end, it pads the value with zeros to represent multiples of 8-bit quantities. This is typical in modern computers. @@ -11919,7 +13349,7 @@ Nondecimal-numbers::), and then demonstrates the results of the (1) This example shows that 0's come in on the left side. For `gawk', this is always true, but in some languages, it's possible to -have the left side fill with 1's. Caveat emptor. +have the left side fill with 1's. File: gawk.info, Node: Type Functions, Next: I18N Functions, Prev: Bitwise Functions, Up: Built-in @@ -11929,12 +13359,25 @@ File: gawk.info, Node: Type Functions, Next: I18N Functions, Prev: Bitwise Fu `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 (*note Arrays -of Arrays::). +traverses every element of an array of arrays (*note Arrays of +Arrays::). `isarray(X)' Return a true value if X is an array. Otherwise return false. + `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; *note User-defined::), to +test if a parameter is an array or not. + + NOTE: Using `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 `gawk' works, if you pass the name of a + variable that has not been previously used to `isarray()', `gawk' + ends up turning it into a scalar. + File: gawk.info, Node: I18N Functions, Prev: Type Functions, Up: Built-in @@ -11947,7 +13390,7 @@ descriptions here are purposely brief. *Note Internationalization::, for the full story. Optional parameters are enclosed in square brackets ([ ]): -`bindtextdomain(DIRECTORY [, DOMAIN])' +`bindtextdomain(DIRECTORY' [`,' DOMAIN]`)' Set the directory in which `gawk' will look for message translation files, in case they will not or cannot be placed in the "standard" locations (e.g., during testing). It returns the @@ -11957,13 +13400,13 @@ brackets ([ ]): the null string (`""'), then `bindtextdomain()' returns the current binding for the given DOMAIN. -`dcgettext(STRING [, DOMAIN [, CATEGORY]])' +`dcgettext(STRING' [`,' DOMAIN [`,' CATEGORY] ]`)' Return the translation of STRING in text domain DOMAIN for locale category CATEGORY. The default value for DOMAIN is the current value of `TEXTDOMAIN'. The default value for CATEGORY is `"LC_MESSAGES"'. -`dcngettext(STRING1, STRING2, NUMBER [, DOMAIN [, CATEGORY]])' +`dcngettext(STRING1, STRING2, NUMBER' [`,' DOMAIN [`,' CATEGORY] ]`)' Return the plural form used for NUMBER of the translation of STRING1 and STRING2 in text domain DOMAIN for locale category CATEGORY. STRING1 is the English singular variant of a message, @@ -11979,8 +13422,8 @@ File: gawk.info, Node: User-defined, Next: Indirect Calls, Prev: Built-in, U Complicated `awk' programs can often be simplified by defining your own functions. User-defined functions can be called just like built-in -ones (*note Function Calls::), but it is up to you to define them, -i.e., to tell `awk' what they should do. +ones (*note Function Calls::), but it is up to you to define them +(i.e., to tell `awk' what they should do). * Menu: @@ -11997,7 +13440,10 @@ File: gawk.info, Node: Definition Syntax, Next: Function Example, Up: User-de 9.2.1 Function Definition Syntax -------------------------------- -Definitions of functions can appear anywhere between the rules of an + It's entirely fair to say that the `awk' syntax for local variable + definitions is appallingly awful. -- Brian Kernighan + + Definitions of functions can appear anywhere between the rules of an `awk' program. Thus, the general form of an `awk' program is extended to include sequences of rules _and_ user-defined function definitions. There is no need to put the definition of a function before all uses of @@ -12006,29 +13452,36 @@ starting to execute any of it. The definition of a function named NAME looks like this: - function NAME([PARAMETER-LIST]) - { + `function' NAME`('[PARAMETER-LIST]`)' + `{' BODY-OF-FUNCTION - } + `}' Here, 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. Within a single `awk' -program, any particular name can only be used as a variable, array, or -function. +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 `awk' program, any particular name can only be used as +a variable, array, or function. 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. A -function cannot have two parameters with the same name, nor may it have -a parameter with the same name as the function itself. +call. - In addition, according to the POSIX standard, function parameters -cannot have the same name as one of the special built-in variables -(*note Built-in Variables::. Not all versions of `awk' enforce this + 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 (*note +Built-in Variables::). Not all versions of `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; *note Dynamic Typing::.) + The BODY-OF-FUNCTION consists of `awk' statements. It is the most important part of the definition, because it says what the function should actually _do_. The argument names exist to give the body a way @@ -12070,8 +13523,8 @@ function. When this happens, we say the function is "recursive". The act of a function calling itself is called "recursion". All the built-in functions return a value to their caller. -User-defined functions can do also, using the `return' statement, which -is described in detail in *Note Return Statement::. Many of the +User-defined functions can do so also, using the `return' statement, +which is described in detail in *note Return Statement::. Many of the subsequent examples in this minor node use the `return' statement. In many `awk' implementations, including `gawk', the keyword @@ -12083,7 +13536,7 @@ function: func foo() { a = sqrt($1) ; print a } -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 `func' with the return value of the function `foo'. If the resulting string is non-null, the action is executed. This is probably not what is desired. (`awk' accepts this input as @@ -12095,7 +13548,7 @@ keyword `function' when defining a function. ---------- Footnotes ---------- - (1) This program won't actually run, since `foo()' is undefined. + (1) This program won't actually run, because `foo()' is undefined. File: gawk.info, Node: Function Example, Next: Function Caveats, Prev: Definition Syntax, Up: User-defined @@ -12128,12 +13581,13 @@ this program, using our function to format the results, prints: 5.6 21.2 - 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): function delarray(a, i) { for (i in a) - delete a[i] + delete a[i] } When working with arrays, it is often necessary to delete all the @@ -12141,30 +13595,31 @@ elements in an array and start over with a new list of elements (*note Delete::). Instead of having to repeat this loop everywhere that you need to clear out an array, your program can just call `delarray'. (This guarantees portability. The use of `delete ARRAY' to delete the -contents of an entire array is a nonstandard extension.) +contents of an entire array is a relatively recent(1) 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: - 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)) } If this function is in a file named `rev.awk', it can be tested this way: $ echo "Don't Panic!" | - > gawk --source '{ print rev($0, length($0)) }' -f rev.awk + > gawk -e '{ print rev($0) }' -f rev.awk -| !cinaP t'noD - The C `ctime()' function takes a timestamp and returns it in a + The C `ctime()' function takes a timestamp and returns it as a string, formatted in a well-known fashion. The following example uses the built-in `strftime()' function (*note Time Functions::) to create an `awk' version of `ctime()': @@ -12176,18 +13631,30 @@ an `awk' version of `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) } + You might think that `ctime()' could use `PROCINFO["strftime"]' for +its format string. That would be a mistake, because `ctime()' is +supposed to return the time formatted in a standard fashion, and +user-level code could have changed `PROCINFO["strftime"]'. + + ---------- Footnotes ---------- + + (1) Late in 2012. + File: gawk.info, Node: Function Caveats, Next: Return Statement, Prev: Function Example, Up: User-defined 9.2.3 Calling User-Defined Functions ------------------------------------ -This section describes how to call a user-defined function. +"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: @@ -12198,27 +13665,23 @@ This section describes how to call a user-defined function. File: gawk.info, Node: Calling A Function, Next: Variable Scope, Up: Function Caveats -9.2.3.1 Writing A Function Call +9.2.3.1 Writing a Function Call ............................... -"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. - - A function call consists of the function name followed by the -arguments in parentheses. `awk' expressions are what you write in the -call for the arguments. Each time the call is executed, these -expressions are evaluated, and the values become the actual arguments. -For example, here is a call to `foo()' with three arguments (the first -being a string concatenation): +A function call consists of the function name followed by the arguments +in parentheses. `awk' expressions are what you write in the call for +the arguments. Each time the call is executed, these expressions are +evaluated, and the values become the actual arguments. For example, +here is a call to `foo()' with three arguments (the first being a +string concatenation): foo(x y, "lose", 4 * z) CAUTION: Whitespace characters (spaces and TABs) are not allowed - between the function name and the open-parenthesis of the argument - list. If you write whitespace by mistake, `awk' might think that - you mean to concatenate a variable with an expression in - parentheses. However, it notices that you used a function name + between the function name and the opening parenthesis of the + argument list. If you write whitespace by mistake, `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 an error. @@ -12227,9 +13690,10 @@ File: gawk.info, Node: Variable Scope, Next: Pass By Value/Reference, Prev: C 9.2.3.2 Controlling Variable Scope .................................. -There is no way to make a variable local to a `{ ... }' block in `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. +Unlike many languages, there is no way to make a variable local to a +`{' ... `}' block in `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. To make a variable local to a function, simply declare the variable as an argument after the actual function arguments (*note Definition @@ -12270,7 +13734,7 @@ variable instance: top's i=3 If you want `i' to be local to both `foo()' and `bar()' do as -follows (the extra-space before `i' is a coding convention to indicate +follows (the extra space before `i' is a coding convention to indicate that `i' is a local variable, not an argument): function bar( i) @@ -12304,23 +13768,56 @@ that `i' is a local variable, not an argument): foo's i=1 top's i=10 + Besides scalar values (strings and numbers), you may also have local +arrays. By using a parameter name as an array, `awk' treats it as an +array, and it is local to the function. In addition, recursive calls +create new arrays. Consider this 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) + } + + When run, this program produces the following output: + + 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 + File: gawk.info, Node: Pass By Value/Reference, Prev: Variable Scope, Up: Function Caveats -9.2.3.3 Passing Function Arguments By Value Or By Reference +9.2.3.3 Passing Function Arguments by Value Or by Reference ........................................................... In `awk', when you declare a function, there is no way to declare explicitly whether the arguments are passed "by value" or "by reference". - Instead the passing convention is determined at runtime when the -function is called according to the following rule: - - * If the argument is an array variable, then it is passed by - reference, - - * Otherwise the argument is passed by value. + Instead, the passing convention is determined at runtime when the +function is called according to the following rule: if the argument is +an array variable, then it is passed by reference. Otherwise, the +argument is passed by value. Passing an argument by value means that when a function is called, it is given a _copy_ of the value of this argument. The caller may use a @@ -12372,8 +13869,8 @@ function _are_ visible outside that function. a[1], a[2], a[3] } - prints `a[1] = 1, a[2] = two, a[3] = 3', because `changeit' stores - `"two"' in the second element of `a'. + prints `a[1] = 1, a[2] = two, a[3] = 3', because `changeit()' + stores `"two"' in the second element of `a'. Some `awk' implementations allow you to call a function that has not been defined. They only report a problem at runtime when the program @@ -12395,8 +13892,9 @@ problem if a program calls an undefined function. If `--lint' is specified (*note Options::), `gawk' reports calls to undefined functions. - Some `awk' implementations generate a runtime error if you use the -`next' statement (*note Next Statement::) inside a user-defined + Some `awk' implementations generate a runtime error if you use +either the `next' statement or the `nextfile' statement (*note Next +Statement::, and *note Nextfile Statement::) inside a user-defined function. `gawk' does not have this limitation. @@ -12411,11 +13909,11 @@ control to the calling part of the `awk' program. It can also be used to return a value for use in the rest of the `awk' program. It looks like this: - return [EXPRESSION] + `return' [EXPRESSION] The EXPRESSION part is optional. Due most likely to an oversight, POSIX does not define what the return value is if you omit the -EXPRESSION. Technically speaking, this make the returned value +EXPRESSION. Technically speaking, this makes the returned value undefined, and therefore, unpredictable. In practice, though, all versions of `awk' simply return the null string, which acts like zero if used in a numeric context. @@ -12445,11 +13943,12 @@ a value for the largest number among the elements of an array: } You call `maxelt()' with one argument, which is an array name. The -local variables `i' and `ret' are not intended to be arguments; while -there is nothing to stop you from passing more than one argument to -`maxelt()', the results would be strange. The extra space before `i' -in the function parameter list indicates that `i' and `ret' are local -variables. You should follow this convention when defining functions. +local variables `i' and `ret' are not intended to be arguments; there +is nothing to stop you from passing more than one argument to +`maxelt()' but the results would be strange. The extra space before +`i' in the function parameter list indicates that `i' and `ret' are +local variables. You should follow this convention when defining +functions. The following program uses the `maxelt()' function. It loads an array, calls `maxelt()', and then reports the maximum number in that @@ -12508,16 +14007,20 @@ Here is an annotated sample program: x = 1 # now not allowed, runtime error } + In this example, the first call to `foo()' generates a fatal error, +so `awk' will not report the second error. If you comment out that +call, though, then `awk' does report the second error. + Usually, such things aren't a big issue, but it's worth being aware of them. -File: gawk.info, Node: Indirect Calls, Prev: User-defined, Up: Functions +File: gawk.info, Node: Indirect Calls, Next: Functions Summary, Prev: User-defined, Up: Functions 9.3 Indirect Function Calls =========================== -This section describes a `gawk'-specific extension. +This section describes an advanced, `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 @@ -12556,18 +14059,18 @@ your test scores: This style of programming works, but can be awkward. With "indirect" function calls, you tell `gawk' to use the _value_ of a variable as the -name of the function to call. +_name_ of the function to call. 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 `@' -character: +identifier immediately followed by an opening parenthesis, any +arguments, and then a closing parenthesis, with the addition of a +leading `@' character: the_func = "sum" - result = @the_func() # calls the `sum' function + result = @the_func() # calls the sum() function Here is a full program that processes the previously shown data, -using indirect function calls. +using indirect function calls: # indirectcall.awk --- Demonstrate indirect function calls @@ -12595,10 +14098,9 @@ using indirect function calls. These two functions expect to work on fields; thus the parameters `first' and `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: # For each record, print the class name and the requested statistics - { class_name = $1 gsub(/_/, " ", class_name) # Replace _ with spaces @@ -12679,7 +14181,7 @@ mechanism allows you to sort arbitrary data in an arbitrary fashion. # 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] @@ -12715,8 +14217,8 @@ 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 `quicksort' appropriately, and -then formats the results as a single string: +builds an array with the data and calls `quicksort()' appropriately, +and then formats the results as a single string: # do_sort --- sort the data according to `compare' # and return it as a string @@ -12782,1602 +14284,189 @@ names of the two comparison functions: -| sort: <87.1 93.4 95.6 100.0> -| rsort: <100.0 95.6 93.4 87.1> - Remember that you must supply a leading `@' 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.) - - `gawk' does its best to make indirect function calls efficient. For -example, in the following case: - - for (i = 1; i <= n; i++) - @the_func() - -`gawk' will look up the actual function to call only once. - - -File: gawk.info, Node: Internationalization, Next: Advanced Features, Prev: Functions, Up: Top - -10 Internationalization with `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. - - For many years, the ability to provide internationalization was -largely restricted to programs written in C and C++. This major node -describes the underlying library `gawk' uses for internationalization, -as well as how `gawk' makes internationalization features available at -the `awk' program level. Having internationalization available at the -`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 `gettext' works. -* Programmer i18n:: Features for the programmer. -* Translator i18n:: Features for the translator. -* I18N Example:: A simple i18n example. -* Gawk I18N:: `gawk' is also internationalized. - - -File: gawk.info, Node: I18N and L10N, Next: Explaining gettext, Up: Internationalization - -10.1 Internationalization and Localization -========================================== - -"Internationalization" means writing (or modifying) a program once, in -such a way that it can use multiple languages without requiring further -source-code changes. "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. - - -File: gawk.info, Node: Explaining gettext, Next: Programmer i18n, Prev: I18N and L10N, Up: Internationalization - -10.2 GNU `gettext' -================== - -The facilities in GNU `gettext' focus on messages; strings printed by a -program, either directly or via formatting with `printf' or -`sprintf()'.(1) - - When using GNU `gettext', each application has its own "text -domain". This is a unique name, such as `kpilot' or `gawk', that -identifies the application. A complete application may have multiple -components--programs written in C or C++, as well as scripts written in -`sh' or `awk'. All of the components use the same text domain. - - To make the discussion concrete, assume we're writing an application -named `guide'. Internationalization consists of the following steps, -in this order: - - 1. The programmer goes through the source for all of `guide''s - components and marks each string that is a candidate for - translation. For example, `"`-F': option required"' is a good - candidate for translation. A table with strings of option names - is not (e.g., `gawk''s `--profile' option should remain the same, - no matter what the local language). - - 2. The programmer indicates the application's text domain (`"guide"') - to the `gettext' library, by calling the `textdomain()' function. - - 3. Messages from the application are extracted from the source code - and collected into a portable object template 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. - - 4. For each language with a translator, `guide.pot' is copied to a - portable object file (`.po') and translations are created and - shipped with the application. For example, there might be a - `fr.po' for a French translation. - - 5. Each language's `.po' file is converted into a binary message - object (`.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. - - 6. When `guide' is built and installed, the binary translation files - are installed in a standard place. - - 7. For testing and development, it is possible to tell `gettext' to - use `.mo' files in a different directory than the standard one by - using the `bindtextdomain()' function. - - 8. At runtime, `guide' looks up each string via a call to - `gettext()'. The returned string is the translated string if - available, or the original string if not. - - 9. 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. - - In C (or C++), the string marking and dynamic translation lookup are -accomplished by wrapping each string in a call to `gettext()': - - printf("%s", gettext("Don't Panic!\n")); - - The tools that extract messages from source code pull out all -strings enclosed in calls to `gettext()'. - - The GNU `gettext' developers, recognizing that typing `gettext(...)' -over and over again is both painful and ugly to look at, use the macro -`_' (an underscore) to make things easier: - - /* In the standard header file: */ - #define _(str) gettext(str) - - /* In the program text: */ - printf("%s", _("Don't Panic!\n")); - -This reduces the typing overhead to just three extra characters per -string and is considerably easier to read as well. - - There are locale "categories" for different types of locale-related -information. The defined locale categories that `gettext' knows about -are: - -`LC_MESSAGES' - Text messages. This is the default category for `gettext' - operations, but it is possible to supply a different one - explicitly, if necessary. (It is almost never necessary to supply - a different category.) - -`LC_COLLATE' - Text-collation information; i.e., how different characters and/or - groups of characters sort in a given language. - -`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 `/[[:alnum:]]/' - (*note Regexp Operators::). - -`LC_MONETARY' - Monetary information, such as the currency symbol, and whether the - symbol goes before or after a number. - -`LC_NUMERIC' - Numeric information, such as which characters to use for the - decimal point and the thousands separator.(2) - -`LC_RESPONSE' - Response information, such as how "yes" and "no" appear in the - local language, and possibly other information as well. - -`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. - -`LC_ALL' - All of the above. (Not too useful in the context of `gettext'.) - - ---------- Footnotes ---------- - - (1) For some operating systems, the `gawk' port doesn't support GNU -`gettext'. Therefore, these features are not available if you are -using one of those operating systems. Sorry. - - (2) 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. - - -File: gawk.info, Node: Programmer i18n, Next: Translator i18n, Prev: Explaining gettext, Up: Internationalization - -10.3 Internationalizing `awk' Programs -====================================== - -`gawk' provides the following variables and functions for -internationalization: - -`TEXTDOMAIN' - This variable indicates the application's text domain. For - compatibility with GNU `gettext', the default value is - `"messages"'. - -`_"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. - -`dcgettext(STRING [, DOMAIN [, CATEGORY]])' - Return the translation of STRING in text domain DOMAIN for locale - category CATEGORY. The default value for DOMAIN is the current - value of `TEXTDOMAIN'. The default value for CATEGORY is - `"LC_MESSAGES"'. - - If you supply a value for CATEGORY, it must be a string equal to - one of the known locale categories described in *Note Explaining - gettext::. You must also supply a text domain. Use `TEXTDOMAIN' - if you want to use the current domain. - - CAUTION: The order of arguments to the `awk' version of the - `dcgettext()' function is purposely different from the order - for the C version. The `awk' version's order was chosen to - be simple and to allow for reasonable `awk'-style default - arguments. - -`dcngettext(STRING1, STRING2, NUMBER [, DOMAIN [, CATEGORY]])' - Return the plural form used for NUMBER of the translation of - STRING1 and STRING2 in text domain DOMAIN for locale category - CATEGORY. STRING1 is the English singular variant of a message, - and STRING2 the English plural variant of the same message. The - default value for DOMAIN is the current value of `TEXTDOMAIN'. - The default value for CATEGORY is `"LC_MESSAGES"'. - - The same remarks about argument order as for the `dcgettext()' - function apply. - -`bindtextdomain(DIRECTORY [, DOMAIN])' - Change the directory in which `gettext' looks for `.mo' files, in - case they will not or cannot be placed in the standard locations - (e.g., during testing). Return the directory in which DOMAIN is - "bound." - - The default DOMAIN is the value of `TEXTDOMAIN'. If DIRECTORY is - the null string (`""'), then `bindtextdomain()' returns the - current binding for the given DOMAIN. - - To use these facilities in your `awk' program, follow the steps -outlined in *Note Explaining gettext::, like so: - - 1. Set the variable `TEXTDOMAIN' to the text domain of your program. - This is best done in a `BEGIN' rule (*note BEGIN/END::), or it can - also be done via the `-v' command-line option (*note Options::): - - BEGIN { - TEXTDOMAIN = "guide" - ... - } - - 2. Mark all translatable strings with a leading underscore (`_') - character. It _must_ be adjacent to the opening quote of the - string. For example: - - print _"hello, world" - x = _"you goofed" - printf(_"Number of users is %d\n", nusers) - - 3. If you are creating strings dynamically, you can still translate - them, using the `dcgettext()' built-in function: - - message = nusers " users logged in" - message = dcgettext(message, "adminprog") - print message - - Here, the call to `dcgettext()' supplies a different text domain - (`"adminprog"') in which to find the message, but it uses the - default `"LC_MESSAGES"' category. - - 4. During development, you might want to put the `.mo' file in a - private directory for testing. This is done with the - `bindtextdomain()' built-in function: - - 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") - } - ... - } - - - *Note I18N Example::, for an example program showing the steps to -create and use translations from `awk'. - - -File: gawk.info, Node: Translator i18n, Next: I18N Example, Prev: Programmer i18n, Up: Internationalization - -10.4 Translating `awk' Programs -=============================== - -Once a program's translatable strings have been marked, they must be -extracted to create the initial `.po' file. As part of translation, it -is often helpful to rearrange the order in which arguments to `printf' -are output. - - `gawk''s `--gen-pot' command-line option extracts the messages and -is discussed next. After that, `printf''s ability to rearrange the -order for `printf' arguments at runtime is covered. - -* Menu: - -* String Extraction:: Extracting marked strings. -* Printf Ordering:: Rearranging `printf' arguments. -* I18N Portability:: `awk'-level portability issues. - - -File: gawk.info, Node: String Extraction, Next: Printf Ordering, Up: Translator i18n - -10.4.1 Extracting Marked Strings --------------------------------- - -Once your `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 `--gen-pot' command-line -option to create the initial `.pot' file: - - $ gawk --gen-pot -f guide.awk > guide.pot - - When run with `--gen-pot', `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 `gettext' Portable Object file. -Also included in the output are any constant strings that appear as the -first argument to `dcgettext()' or as the first and second argument to -`dcngettext()'.(1) *Note I18N Example::, for the full list of steps to -go through to create and test translations for `guide'. - - ---------- Footnotes ---------- - - (1) The `xgettext' utility that comes with GNU `gettext' can handle -`.awk' files. - - -File: gawk.info, Node: Printf Ordering, Next: I18N Portability, Prev: String Extraction, Up: Translator i18n - -10.4.2 Rearranging `printf' Arguments -------------------------------------- - -Format strings for `printf' and `sprintf()' (*note Printf::) present a -special problem for translation. Consider the following:(1) - - printf(_"String `%s' has %d characters\n", - string, length(string))) - - A possible German translation for this might be: - - "%d Zeichen lang ist die Zeichenkette `%s'\n" - - The problem should be obvious: the order of the format -specifications is different from the original! Even though `gettext()' -can return the translated string at runtime, it cannot change the -argument order in the call to `printf'. - - To solve this problem, `printf' format specifiers may have an -additional optional element, which we call a "positional specifier". -For example: - - "%2$d Zeichen lang ist die Zeichenkette `%1$s'\n" - - Here, the positional specifier consists of an integer count, which -indicates which argument to use, and a `$'. Counts are one-based, and -the format string itself is _not_ included. Thus, in the following -example, `string' is the first argument and `length(string)' is the -second: - - $ gawk 'BEGIN { - > string = "Dont Panic" - > printf _"%2$d characters live in \"%1$s\"\n", - > string, length(string) - > }' - -| 10 characters live in "Dont Panic" - - 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: - - $ gawk 'BEGIN { - > printf("%*.*s\n", 10, 20, "hello") - > printf("%3$*2$.*1$s\n", 20, 10, "hello") - > }' - -| hello - -| hello - - NOTE: When using `*' with a positional specifier, the `*' comes - first, then the integer position, and then the `$'. This is - somewhat counterintuitive. - - `gawk' does not allow you to mix regular format specifiers and those -with positional specifiers in the same string: - - $ gawk 'BEGIN { printf _"%d %3$s\n", 1, 2, "hi" }' - error--> gawk: cmd. line:1: fatal: must use `count$' on all formats or none - - NOTE: There are some pathological cases that `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 `gawk' doesn't - detect it. - - Although positional specifiers can be used directly in `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. - - ---------- Footnotes ---------- - - (1) This example is borrowed from the GNU `gettext' manual. - - -File: gawk.info, Node: I18N Portability, Prev: Printf Ordering, Up: Translator i18n - -10.4.3 `awk' Portability Issues -------------------------------- - -`gawk''s internationalization features were purposely chosen to have as -little impact as possible on the portability of `awk' programs that use -them to other versions of `awk'. Consider this program: - - BEGIN { - TEXTDOMAIN = "guide" - if (Test_Guide) # set with -v - bindtextdomain("/test/guide/messages") - print _"don't panic!" - } - -As written, it won't work on other versions of `awk'. However, it is -actually almost portable, requiring very little change: - - * Assignments to `TEXTDOMAIN' won't have any effect, since - `TEXTDOMAIN' is not special in other `awk' implementations. - - * Non-GNU versions of `awk' treat marked strings as the - concatenation of a variable named `_' with the string following - it.(1) Typically, the variable `_' has the null string (`""') as - its value, leaving the original string constant as the result. - - * By defining "dummy" functions to replace `dcgettext()', - `dcngettext()' and `bindtextdomain()', the `awk' program can be - made to run, but all the messages are output in the original - language. For example: - - 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) - } - - * The use of positional specifications in `printf' or `sprintf()' is - _not_ portable. To support `gettext()' at the C level, many - systems' C versions of `sprintf()' do support positional - specifiers. But it works only if enough arguments are supplied in - the function call. Many versions of `awk' pass `printf' formats - and arguments unchanged to the underlying C library version of - `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 _translated_ format strings, and since non-GNU `awk's never - retrieve the translated string, this should not be a problem in - practice. - - ---------- Footnotes ---------- - - (1) This is good fodder for an "Obfuscated `awk'" contest. - - -File: gawk.info, Node: I18N Example, Next: Gawk I18N, Prev: Translator i18n, Up: Internationalization - -10.5 A Simple Internationalization Example -========================================== - -Now let's look at a step-by-step example of how to internationalize and -localize a simple `awk' program, using `guide.awk' as our original -source: - - BEGIN { - TEXTDOMAIN = "guide" - bindtextdomain(".") # for testing - print _"Don't Panic" - print _"The Answer Is", 42 - print "Pardon me, Zaphod who?" - } - -Run `gawk --gen-pot' to create the `.pot' file: - - $ gawk --gen-pot -f guide.awk > guide.pot - -This produces: - - #: guide.awk:4 - msgid "Don't Panic" - msgstr "" - - #: guide.awk:5 - msgid "The Answer Is" - msgstr "" - - This original portable object template file is saved and reused for -each language into which the application is translated. The `msgid' is -the original string and the `msgstr' is the translation. - - NOTE: Strings not marked with a leading underscore do not appear - in the `guide.pot' file. - - Next, the messages must be translated. Here is a translation to a -hypothetical dialect of English, called "Mellow":(1) - - $ cp guide.pot guide-mellow.po - ADD TRANSLATIONS TO guide-mellow.po ... - -Following are the translations: - - #: guide.awk:4 - msgid "Don't Panic" - msgstr "Hey man, relax!" - - #: guide.awk:5 - msgid "The Answer Is" - msgstr "Like, the scoop is" - - The next step is to make the directory to hold the binary message -object file and then to create the `guide.mo' file. The directory -layout shown here is standard for GNU `gettext' on GNU/Linux systems. -Other versions of `gettext' may use a different layout: - - $ mkdir en_US en_US/LC_MESSAGES - - The `msgfmt' utility does the conversion from human-readable `.po' -file to machine-readable `.mo' file. By default, `msgfmt' creates a -file named `messages'. This file must be renamed and placed in the -proper directory so that `gawk' can find it: - - $ msgfmt guide-mellow.po - $ mv messages en_US/LC_MESSAGES/guide.mo - - Finally, we run the program to test it: - - $ gawk -f guide.awk - -| Hey man, relax! - -| Like, the scoop is 42 - -| Pardon me, Zaphod who? - - If the three replacement functions for `dcgettext()', `dcngettext()' -and `bindtextdomain()' (*note I18N Portability::) are in a file named -`libintl.awk', then we can run `guide.awk' unchanged as follows: - - $ gawk --posix -f guide.awk -f libintl.awk - -| Don't Panic - -| The Answer Is 42 - -| Pardon me, Zaphod who? - - ---------- Footnotes ---------- - - (1) Perhaps it would be better if it were called "Hippy." Ah, well. - - -File: gawk.info, Node: Gawk I18N, Prev: I18N Example, Up: Internationalization - -10.6 `gawk' Can Speak Your Language -=================================== - -`gawk' itself has been internationalized using the GNU `gettext' -package. (GNU `gettext' is described in complete detail in *note (GNU -`gettext' utilities)Top:: gettext, GNU gettext tools.) As of this -writing, the latest version of GNU `gettext' is version 0.18.1 -(ftp://ftp.gnu.org/gnu/gettext/gettext-0.18.1.tar.gz). - - If a translation of `gawk''s messages exists, then `gawk' produces -usage messages, warnings, and fatal errors in the local language. - - -File: gawk.info, Node: Advanced Features, Next: Library Functions, Prev: Internationalization, Up: Top - -11 Advanced Features of `gawk' -****************************** - - Write documentation as if whoever reads it is a violent psychopath - who knows where you live. - Steve English, as quoted by Peter Langston - - This major node discusses advanced features in `gawk'. It's a bit -of a "grab bag" of items that are otherwise unrelated to each other. -First, a command-line option allows `gawk' to recognize nondecimal -numbers in input data, not just in `awk' programs. Then, `gawk''s -special features for sorting arrays are presented. Next, two-way I/O, -discussed briefly in earlier parts of this Info file, is described in -full detail, along with the basics of TCP/IP networking. Finally, -`gawk' can "profile" an `awk' program, making it possible to tune it -for performance. - - *Note Dynamic Extensions::, discusses the ability to dynamically add -new built-in functions to `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 `gawk' for network programming. -* Profiling:: Profiling your `awk' programs. - - -File: gawk.info, Node: Nondecimal Data, Next: Array Sorting, Up: Advanced Features - -11.1 Allowing Nondecimal Input Data -=================================== - -If you run `gawk' with the `--non-decimal-data' option, you can have -nondecimal constants in your input data: - - $ echo 0123 123 0x123 | - > gawk --non-decimal-data '{ printf "%d, %d, %d\n", - > $1, $2, $3 }' - -| 83, 123, 291 - - For this feature to work, write your program so that `gawk' treats -your data as numeric: - - $ echo 0123 123 0x123 | gawk '{ print $1, $2, $3 }' - -| 0123 123 0x123 - -The `print' statement treats its expressions as strings. Although the -fields can act as numbers when necessary, they are still strings, so -`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: - - $ echo 0123 123 0x123 | gawk --non-decimal-data ' - > { print $1, $2, $3 - > print $1 + 0, $2 + 0, $3 + 0 }' - -| 0123 123 0x123 - -| 83 123 291 - - 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. - - CAUTION: _Use of this option is not recommended._ It can break old - programs very badly. Instead, use the `strtonum()' function to - convert your data (*note Nondecimal-numbers::). This makes your - programs easier to write and easier to read, and leads to less - surprising results. - - -File: gawk.info, Node: Array Sorting, Next: Two-way I/O, Prev: Nondecimal Data, Up: Advanced Features - -11.2 Controlling Array Traversal and Array Sorting -================================================== - -`gawk' lets you control the order in which `for (i in array)' loops -will traverse an array. - - In addition, two built-in functions, `asort()' and `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 `asort()' and `asorti()'. - - -File: gawk.info, Node: Controlling Array Traversal, Next: Array Sorting Functions, Up: Array Sorting - -11.2.1 Controlling Array Traversal ----------------------------------- - -By default, the order in which a `for (i in array)' loop scans an array -is not defined; it is generally based upon the internal implementation -of arrays inside `awk'. - - Often, though, it is desirable to be able to loop over the elements -in a particular order that you, the programmer, choose. `gawk' lets -you do this; this node describes how. - -* Menu: - -* Controlling Scanning With A Function:: Using a function to control scanning. -* Controlling Scanning:: Controlling the order in which arrays - are scanned. - - -File: gawk.info, Node: Controlling Scanning With A Function, Next: Controlling Scanning, Up: Controlling Array Traversal - -11.2.1.1 Array Scanning Using A User-defined Function -..................................................... - -The value of `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: - - function comp_func(i1, v1, i2, v2) - { - COMPARE ELEMENTS 1 AND 2 IN SOME FASHION - RETURN < 0; 0; OR > 0 - } - - Here, I1 and I2 are the indices, and V1 and V2 are the corresponding -values of the two elements being compared. Either V1 or V2, or both, -can be arrays if the array being traversed contains subarrays as -values. The three possible return values are interpreted this way: - -`comp_func(i1, v1, i2, v2) < 0' - Index I1 comes before index I2 during loop traversal. - -`comp_func(i1, v1, i2, v2) == 0' - Indices I1 and I2 come together but the relative order with - respect to each other is undefined. - -`comp_func(i1, v1, i2, v2) > 0' - Index I1 comes after index I2 during loop traversal. - - Our first comparison function can be used to scan an array in -numerical order of the indices: - - function cmp_num_idx(i1, v1, i2, v2) - { - # numerical index comparison, ascending order - return (i1 - i2) - } - - Our second function traverses an array based on the string order of -the element values rather than by indices: - - 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) - } - - The third comparison function makes all numbers, and numeric strings -without any leading or trailing spaces, come out first during loop -traversal: + Another example where indirect functions calls are useful can be +found in processing arrays. *note 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: - function cmp_num_str_val(i1, v1, i2, v2, n1, n2) + function process_array(arr, name, process, do_arrays, i, new_name) { - # 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) - } - - Here is a main program to demonstrate how `gawk' behaves using each -of the previous functions: - - 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 "" + 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]) } } - Here are the results when the program is run: - - $ gawk -f compdemo.awk - -| Sort function: cmp_num_idx Sort by numeric index - -| data[two] = 20 - -| data[one] = 10 Both strings are numerically zero - -| data[10] = one - -| data[20] = two - -| data[100] = 100 - -| - -| Sort function: cmp_str_val Sort by element values as strings - -| data[one] = 10 - -| data[100] = 100 String 100 is less than string 20 - -| data[two] = 20 - -| data[10] = one - -| data[20] = two - -| - -| Sort function: cmp_num_str_val Sort all numbers before all strings - -| data[one] = 10 - -| data[two] = 20 - -| data[100] = 100 - -| data[10] = one - -| data[20] = two + The arguments are as follows: - 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: +`arr' + The array. - # sort.awk --- simple program to sort by field position - # field position is specified by the global variable POS +`name' + The name of the array (a string). - 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 "" - } - } - - 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 (*note Arrays of Arrays::), with each field as an -element in the subarray. Running the program produces the following -output: +`process' + The name of the function to call. - $ gawk -vPOS=1 -F: -f sort.awk /etc/passwd - -| adm:x:3:4:adm:/var/adm:/sbin/nologin - -| apache:x:48:48:Apache:/var/www:/sbin/nologin - -| avahi:x:70:70:Avahi daemon:/:/sbin/nologin - ... +`do_arrays' + If this is true, the function can handle elements that are + subarrays. - 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: + If subarrays are to be processed, that is done before walking them +further. - function cmp_randomize(i1, v1, i2, v2) - { - # random order - return (2 - 4 * rand()) - } + When run with the following scaffolding, the function produces the +same results as does the earlier `walk_array()' function: - 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: + BEGIN { + a[1] = 1 + a[2][1] = 21 + a[2][2] = 22 + a[3] = 3 + a[4][1][1] = 411 + a[4][2] = 42 - 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 } - 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 `IGNORECASE' (*note 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 `isarray()' function (*note Type Functions::), -to check for this, and choose a defined sorting order for subarrays. - - All sorting based on `PROCINFO["sorted_in"]' is disabled in POSIX -mode, since the `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 `awk' programs. For this reason, sorted array traversal is not -the default. - - -File: gawk.info, Node: Controlling Scanning, Prev: Controlling Scanning With A Function, Up: Controlling Array Traversal - -11.2.1.2 Controlling Array Scanning Order -......................................... - -As described in *Note Controlling Scanning With A Function::, you can -provide the name of a function as the value of `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, `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 `awk' function names. - - The following special values are available: - -`"@ind_str_asc"' - Order by indices compared as strings; this is the most basic sort. - (Internally, array indices are always strings, so with `a[2*5] = 1' - the index is `"10"' rather than numeric 10.) - -`"@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. - -`"@val_type_asc"' - Order by element values rather than indices. Ordering is by the - type assigned to the element (*note Typing and Comparison::). All - numeric values come before all string values, which in turn come - before all subarrays. - -`"@val_str_asc"' - Order by element values rather than by indices. Scalar values are - compared as strings. Subarrays, if present, come out last. - -`"@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 `qsort()' function.(1) - -`"@ind_str_desc"' - Reverse order from the most basic sort. - -`"@ind_num_desc"' - Numeric indices ordered from high to low. - -`"@val_type_desc"' - Element values, based on type, in descending order. - -`"@val_str_desc"' - Element values, treated as strings, ordered from high to low. - Subarrays, if present, come out first. - -`"@val_num_desc"' - Element values, treated as numbers, ordered from high to low. - Subarrays, if present, come out first. - -`"@unsorted"' - Array elements are processed in arbitrary order, which is the - normal `awk' behavior. You can also get the normal behavior by just - deleting the `"sorted_in"' element from the `PROCINFO' array, if - it previously had a value assigned to it. - - The array traversal order is determined before the `for' loop starts -to run. Changing `PROCINFO["sorted_in"]' in the loop body will not -affect the loop. - - For example: - - $ gawk 'BEGIN { - > a[4] = 4 - > a[3] = 3 - > for (i in a) - > print i, a[i] - > }' - -| 4 4 - -| 3 3 - $ gawk 'BEGIN { - > PROCINFO["sorted_in"] = "@ind_str_asc" - > a[4] = 4 - > a[3] = 3 - > for (i in a) - > print i, a[i] - > }' - -| 3 3 - -| 4 4 - - 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. - - ---------- Footnotes ---------- - - (1) When two elements compare as equal, the C `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 `gawk' behaves -consistently across different environments. - - -File: gawk.info, Node: Array Sorting Functions, Prev: Controlling Array Traversal, Up: Array Sorting - -11.2.2 Sorting Array Values and Indices with `gawk' ---------------------------------------------------- - -In most `awk' implementations, sorting an array requires writing a -`sort' function. While this can be educational for exploring different -sorting algorithms, usually that's not the point of the program. -`gawk' provides the built-in `asort()' and `asorti()' functions (*note -String Functions::) for sorting arrays. For example: - - POPULATE THE ARRAY data - n = asort(data) - for (i = 1; i <= n; i++) - DO SOMETHING WITH data[i] + Remember that you must supply a leading `@' in front of an indirect +function call. - After the call to `asort()', the array `data' is indexed from 1 to -some number N, the total number of elements in `data'. (This count is -`asort()''s return value.) `data[1]' <= `data[2]' <= `data[3]', and so -on. The array elements are compared as strings. + Starting with version 4.1.2 of `gawk', indirect function calls may +also be used with built-in functions and with extension functions +(*note Dynamic Extensions::). The only thing you cannot do is pass a +regular expression constant to a built-in function through an indirect +function call.(1) - An important side effect of calling `asort()' is that _the array's -original indices are irrevocably lost_. As this isn't always -desirable, `asort()' accepts a second argument: + `gawk' does its best to make indirect function calls efficient. For +example, in the following case: - POPULATE THE ARRAY source - n = asort(source, dest) for (i = 1; i <= n; i++) - DO SOMETHING WITH dest[i] - - In this case, `gawk' copies the `source' array into the `dest' array -and then sorts `dest', destroying its indices. However, the `source' -array is not affected. - - `asort()' accepts a third string argument to control comparison of -array elements. As with `PROCINFO["sorted_in"]', this argument may be -the name of a user-defined function, or one of the predefined names -that `gawk' provides (*note Controlling Scanning With A Function::). - - 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. - - Often, what's needed is to sort on the values of the _indices_ -instead of the values of the elements. To do that, use the `asorti()' -function. The interface is identical to that of `asort()', except that -the index values are used for sorting, and become the values of the -result array: - - { source[$0] = some_func($0) } - - END { - n = asorti(source, dest) - for (i = 1; i <= n; i++) { - Work with sorted indices directly: - DO SOMETHING WITH dest[i] - ... - Access original array via sorted indices: - DO SOMETHING WITH source[dest[i]] - } - } - - Similar to `asort()', in all cases, the sorted element values -consist of the original array's indices. The ability to control -comparison merely affects the way in which they are sorted. - - Sorting the array by replacing the indices provides maximal -flexibility. To traverse the elements in decreasing order, use a loop -that goes from N down to 1, either over the elements or over the -indices.(1) - - Copying array indices and elements isn't expensive in terms of -memory. Internally, `gawk' maintains "reference counts" to data. For -example, when `asort()' copies the first array to the second one, there -is only one copy of the original array elements' data, even though both -arrays use the values. - - Because `IGNORECASE' affects string comparisons, the value of -`IGNORECASE' also affects sorting for both `asort()' and `asorti()'. -Note also that the locale's sorting order does _not_ come into play; -comparisons are based on character values only.(2) Caveat Emptor. - - ---------- Footnotes ---------- - - (1) You may also use one of the predefined sorting names that sorts -in decreasing order. - - (2) This is true because locale-based comparison occurs only when in -POSIX compatibility mode, and since `asort()' and `asorti()' are `gawk' -extensions, they are not available in that case. - - -File: gawk.info, Node: Two-way I/O, Next: TCP/IP Networking, Prev: Array Sorting, Up: Advanced Features - -11.3 Two-Way Communications with Another Process -================================================ - - From: brennan@whidbey.com (Mike Brennan) - Newsgroups: comp.lang.awk - Subject: Re: Learn the SECRET to Attract Women Easily - Date: 4 Aug 1997 17:34:46 GMT - Message-ID: <5s53rm$eca@news.whidbey.com> - - 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 - - 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: - - # Write the data for processing - tempfile = ("mydata." PROCINFO["pid"]) - while (NOT DONE WITH DATA) - print DATA | ("subprogram > " tempfile) - close("subprogram > " tempfile) - - # Read the results, remove tempfile when done - while ((getline newdata < tempfile) > 0) - PROCESS newdata APPROPRIATELY - close(tempfile) - system("rm " tempfile) - -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, `/tmp' will not do, as another user might happen to be -using a temporary file with the same name. - - However, with `gawk', it is possible to open a _two-way_ pipe to -another process. The second process is termed a "coprocess", since it -runs in parallel with `gawk'. The two-way connection is created using -the `|&' operator (borrowed from the Korn shell, `ksh'):(1) - - do { - print DATA |& "subprogram" - "subprogram" |& getline results - } while (DATA LEFT TO PROCESS) - close("subprogram") - - The first time an I/O operation is executed using the `|&' operator, -`gawk' creates a two-way pipeline to a child process that runs the -other program. Output created with `print' or `printf' is written to -the program's standard input, and output from the program's standard -output can be read by the `gawk' program using `getline'. As is the -case with processes started by `|', 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: - - * As the code inside `gawk' currently stands, the coprocess's - standard error goes to the same place that the parent `gawk''s - standard error goes. It is not possible to read the child's - standard error separately. - - * I/O buffering may be a problem. `gawk' automatically flushes all - output down the pipe to the coprocess. However, if the coprocess - does not flush its output, `gawk' may hang when doing a `getline' - in order to read the coprocess's results. This could lead to a - situation known as "deadlock", where each process is waiting for - the other one to do something. - - It is possible to close just one end of the two-way pipe to a -coprocess, by supplying a second argument to the `close()' function of -either `"to"' or `"from"' (*note Close Files And Pipes::). These -strings tell `gawk' to close the end of the pipe that sends data to the -coprocess or the end that reads from it, respectively. - - This is particularly necessary in order to use the system `sort' -utility as part of a coprocess; `sort' must read _all_ of its input -data before it can produce any output. The `sort' program does not -receive an end-of-file indication until `gawk' closes the write end of -the pipe. - - When you have finished writing data to the `sort' utility, you can -close the `"to"' end of the pipe, and then start reading sorted data -via `getline'. For 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) - } - - This program writes the letters of the alphabet in reverse order, one -per line, down the two-way pipe to `sort'. It then closes the write -end of the pipe, so that `sort' receives an end-of-file indication. -This causes `sort' to sort the data and write the sorted data back to -the `gawk' program. Once all of the data has been read, `gawk' -terminates the coprocess and exits. - - As a side note, the assignment `LC_ALL=C' in the `sort' command -ensures traditional Unix (ASCII) sorting from `sort'. - - 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 `PROCINFO' array -(*note Auto-set::), like so: - - command = "sort -nr" # command, save in convenience variable - PROCINFO[command, "pty"] = 1 # update PROCINFO - print ... |& command # start two-way pipe - ... + @the_func() -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, `gawk' automatically falls back to using -regular pipes. +`gawk' looks up the actual function to call only once. ---------- Footnotes ---------- - (1) This is very different from the same operator in the C shell. - - -File: gawk.info, Node: TCP/IP Networking, Next: Profiling, Prev: Two-way I/O, Up: Advanced Features - -11.4 Using `gawk' for Network Programming -========================================= - - `EMISTERED': - 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. - - In addition to being able to open a two-way pipeline to a coprocess -on the same system (*note 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 _very long_ two-way pipeline to a -coprocess. The way `gawk' decides that you want to use TCP/IP -networking is by recognizing special file names that begin with one of -`/inet/', `/inet4/' or `/inet6'. - - The full syntax of the special file name is -`/NET-TYPE/PROTOCOL/LOCAL-PORT/REMOTE-HOST/REMOTE-PORT'. The -components are: - -NET-TYPE - Specifies the kind of Internet connection to make. Use `/inet4/' - to force IPv4, and `/inet6/' to force IPv6. Plain `/inet/' (which - used to be the only option) uses the system default, most likely - IPv4. - -PROTOCOL - The protocol to use over IP. This must be either `tcp', or `udp', - for a TCP or UDP IP connection, respectively. The use of TCP is - recommended for most applications. - -LOCAL-PORT - The local TCP or UDP port number to use. Use a port number of `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 `smtp' or `http', in which case `gawk' - attempts to determine the predefined port number using the C - `getaddrinfo()' function. - -REMOTE-HOST - The IP address or fully-qualified domain name of the Internet host - to which you want to connect. - -REMOTE-PORT - The TCP or UDP port number to use on the given REMOTE-HOST. - Again, use `0' if you don't care, or else a well-known service - name. - - NOTE: Failure in opening a two-way socket will result in a - non-fatal error being returned to the calling code. The value of - `ERRNO' indicates the error (*note Auto-set::). - - Consider the following very simple example: - - BEGIN { - Service = "/inet/tcp/0/localhost/daytime" - Service |& getline - print $0 - close(Service) - } - - This program reads the current date and time from the local system's -TCP `daytime' server. It then prints the results and closes the -connection. - - Because this topic is extensive, the use of `gawk' for TCP/IP -programming is documented separately. See *note (General -Introduction)Top:: gawkinet, TCP/IP Internetworking with `gawk', for a -much more complete introduction and discussion, as well as extensive -examples. + (1) This may change in a future version; recheck the documentation +that comes with your version of `gawk' to see if it has. -File: gawk.info, Node: Profiling, Prev: TCP/IP Networking, Up: Advanced Features - -11.5 Profiling Your `awk' Programs -================================== - -You may produce execution traces of your `awk' programs. This is done -with a specially compiled version of `gawk', called `pgawk' ("profiling -`gawk'"). - - `pgawk' is identical in every way to `gawk', except that when it has -finished running, it creates a profile of your program in a file named -`awkprof.out'. Because it is profiling, it also executes up to 45% -slower than `gawk' normally does. - - As shown in the following example, the `--profile' option can be -used to change the name of the file where `pgawk' will write the -profile: - - pgawk --profile=myprog.prof -f myprog.awk data1 data2 - -In the above example, `pgawk' places the profile in `myprog.prof' -instead of in `awkprof.out'. - - Here is a sample session showing a simple `awk' program, its input -data, and the results from running `pgawk'. First, the `awk' program: - - 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!" - } - - Following is the input data: - - foo - bar - baz - foo - junk - - Here is the `awkprof.out' that results from running `pgawk' on this -program and data (this example also illustrates that `awk' programmers -sometimes have to work late): - - # 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!" - } - - This example illustrates many of the basic features of profiling -output. They are as follows: - - * The program is printed in the order `BEGIN' rule, `BEGINFILE' rule, - pattern/action rules, `ENDFILE' rule, `END' rule and functions, - listed alphabetically. Multiple `BEGIN' and `END' rules are - merged together, as are multiple `BEGINFILE' and `ENDFILE' rules. - - * Pattern-action rules have two counts. The first count, to the - left of the rule, shows how many times the rule's pattern was - _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 _executed_. The difference between the two indicates how many - times the rule's pattern evaluated to false. - - * Similarly, the count for an `if'-`else' statement shows how many - times the condition was tested. To the right of the opening left - brace for the `if''s body is a count showing how many times the - condition was true. The count for the `else' indicates how many - times the test failed. - - * The count for a loop header (such as `for' or `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.) - - * For user-defined functions, the count next to the `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. - - * The layout uses "K&R" style with TABs. Braces are used - everywhere, even when the body of an `if', `else', or loop is only - a single statement. - - * Parentheses are used only where needed, as indicated by the - structure of the program and the precedence rules. For example, - `(3 + 5) * 4' means add three plus five, then multiply the total - by four. However, `3 + 5 * 4' has no parentheses, and means `3 + - (5 * 4)'. +File: gawk.info, Node: Functions Summary, Prev: Indirect Calls, Up: Functions - * Parentheses are used around the arguments to `print' and `printf' - only when the `print' or `printf' statement is followed by a - redirection. Similarly, if the target of a redirection isn't a - scalar, it gets parenthesized. - - * `pgawk' supplies leading comments in front of the `BEGIN' and - `END' rules, the pattern/action rules, and the functions. - - - The profiled version of your program may not look exactly like what -you typed when you wrote it. This is because `pgawk' creates the -profiled version by "pretty printing" its internal representation of -the program. The advantage to this is that `pgawk' can produce a -standard representation. The disadvantage is that all source-code -comments are lost, as are the distinctions among multiple `BEGIN', -`END', `BEGINFILE', and `ENDFILE' rules. Also, things such as: - - /foo/ - -come out as: - - /foo/ { - print $0 - } - -which is correct, but possibly surprising. - - Besides creating profiles when a program has completed, `pgawk' can -produce a profile while it is running. This is useful if your `awk' -program goes into an infinite loop and you want to see what has been -executed. To use this feature, run `pgawk' in the background: +9.4 Summary +=========== - $ pgawk -f myprog & - [1] 13992 + * `awk' provides built-in functions and lets you define your own + functions. -The shell prints a job number and process ID number; in this case, -13992. Use the `kill' command to send the `USR1' signal to `pgawk': + * POSIX `awk' provides three kinds of built-in functions: numeric, + string, and I/O. `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. `gawk' also provides several extensions to + some of standard functions, typically in the form of additional + arguments. - $ kill -USR1 13992 + * 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. -As usual, the profiled version of the program is written to -`awkprof.out', or to a different file if you use the `--profile' option. + * The handling of backslash in `sub()' and `gsub()' is not simple. + It is more straightforward in `gawk''s `gensub()' function, but + that function still requires care in its use. - Along with the regular profile, as shown earlier, the profile -includes a trace of any active functions: + * 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. - # Function Call Stack: + * 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 `ARGC') as the name of a + parameter in user-defined functions. - # 3. baz - # 2. bar - # 1. foo - # -- main -- + * 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. - You may send `pgawk' the `USR1' signal as many times as you like. -Each time, the profile and function call trace are appended to the -output profile file. + * Use the `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. - If you use the `HUP' signal instead of the `USR1' signal, `pgawk' -produces the profile and the function call trace and then exits. + * 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. - When `pgawk' runs on MS-Windows systems, it uses the `INT' and -`QUIT' signals for producing the profile and, in the case of the `INT' -signal, `pgawk' exits. This is because these systems don't support the -`kill' command, so the only signals you can deliver to a program are -those generated by the keyboard. The `INT' signal is generated by the -`Ctrl-<C>' or `Ctrl-<BREAK>' key, while the `QUIT' signal is generated -by the `Ctrl-<\>' key. + * `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++. - Finally, regular `gawk' also accepts the `--profile' option. When -called this way, `gawk' "pretty prints" the program into `awkprof.out', -without any execution counts. -File: gawk.info, Node: Library Functions, Next: Sample Programs, Prev: Advanced Features, Up: Top +File: gawk.info, Node: Library Functions, Next: Sample Programs, Prev: Functions, Up: Top -12 A Library of `awk' Functions +10 A Library of `awk' Functions ******************************* -*Note User-defined::, describes how to write your own `awk' functions. +*note User-defined::, describes how to write your own `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 _read_ -programs in that language. To that end, this major node and *Note -Sample Programs::, provide a good-sized body of code for you to read, -and hopefully, to learn from. + In their seminal 1976 book, `Software Tools',(1) Brian Kernighan and +P.J. Plauger wrote: + + 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. + + 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 major node and *note Sample +Programs::, provide a good-sized body of code for you to read and, we +hope, to learn from. This major node presents a library of useful `awk' functions. Many of the sample programs presented later in this Info file use these functions. The functions are presented here in a progression from simple to complex. - *Note Extract Program::, presents a program that you can use to + *note 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 Info file. (This has already been done as part of the `gawk' distribution.) If you have written one or more useful, general-purpose `awk' functions and would like to contribute them to the `awk' user -community, see *Note How To Contribute::, for more information. +community, see *note How To Contribute::, for more information. - The programs in this major node and in *Note Sample Programs::, -freely use features that are `gawk'-specific. Rewriting these programs -for different implementations of `awk' is pretty straightforward. + The programs in this major node and in *note Sample Programs::, +freely use `gawk'-specific features. Rewriting these programs for +different implementations of `awk' is pretty straightforward: * Diagnostic error messages are sent to `/dev/stderr'. Use `| "cat 1>&2"' instead of `> "/dev/stderr"' if your system does not have a @@ -14388,7 +14477,7 @@ for different implementations of `awk' is pretty straightforward. * Finally, some of the programs choose to ignore upper- and lowercase distinctions in their input. They do so by assigning one to - `IGNORECASE'. You can achieve almost the same effect(1) by adding + `IGNORECASE'. You can achieve almost the same effect(2) by adding the following rule to the beginning of the program: # ignore case @@ -14409,17 +14498,22 @@ for different implementations of `awk' is pretty straightforward. * 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. ---------- Footnotes ---------- - (1) The effects are not identical. Output of the transformed record + (1) 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. + + (2) The effects are not identical. Output of the transformed record will be in all lowercase, while `IGNORECASE' preserves the original contents of the input record. File: gawk.info, Node: Library Names, Next: General Functions, Up: Library Functions -12.1 Naming Library Function Global Variables +10.1 Naming Library Function Global Variables ============================================= Due to the way the `awk' language evolved, variables are either @@ -14430,8 +14524,8 @@ specific function). There is no intermediate state analogous to Library functions often need to have global variables that they can use to preserve state information between calls to the function--for example, `getopt()''s variable `_opti' (*note Getopt Function::). Such -variables are called "private", since the only functions that need to -use them are the ones in the library. +variables are called "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 private variables that will not conflict with any variables used by @@ -14447,8 +14541,8 @@ will be accidentally shared with the user's program. In addition, several of the library functions use a prefix that helps indicate what function or set of functions use the variables--for -example, `_pw_byname' in the user database routines (*note Passwd -Functions::). This convention is recommended, since it even further +example, `_pw_byname()' in the user database routines (*note Passwd +Functions::). 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.(1) @@ -14459,7 +14553,7 @@ to start that variable's name with a capital letter--for example, `getopt()''s `Opterr' and `Optind' variables (*note 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 `awk''s built-in variables, such as `FS'. +variable is not one of `awk''s predefined variables, such as `FS'. It is also important that _all_ variables in library functions that do not need to save state are, in fact, declared local.(2) If this is @@ -14469,15 +14563,16 @@ program, leading to bugs that are very difficult to track down: function lib_func(x, y, l1, l2) { ... - USE VARIABLE some_var # some_var should be local - ... # but is not by oversight + # some_var should be local but by oversight is not + USE VARIABLE some_var + ... } 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 -*Note Passwd Functions::, might have used array elements +*note Passwd Functions::, might have used array elements `PW_data["inited"]', `PW_data["total"]', `PW_data["count"]', and `PW_data["awklib"]', instead of `_pw_inited', `_pw_awklib', `_pw_total', and `_pw_count'. @@ -14488,9 +14583,9 @@ merely recommend that you do so. ---------- Footnotes ---------- - (1) While all the library routines could have been rewritten to use -this convention, this was not done, in order to show how our own `awk' -programming style has evolved and to provide some basis for this + (1) Although all the library routines could have been rewritten to +use this convention, this was not done, in order to show how our own +`awk' programming style has evolved and to provide some basis for this discussion. (2) `gawk''s `--dump-variables' command-line option is useful for @@ -14499,7 +14594,7 @@ verifying this. File: gawk.info, Node: General Functions, Next: Data File Management, Prev: Library Names, Up: Library Functions -12.2 General Programming +10.2 General Programming ======================== This minor node presents a number of functions that are of general @@ -14517,12 +14612,14 @@ 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. File: gawk.info, Node: Strtonum Function, Next: Assert Function, Up: General Functions -12.2.1 Converting Strings To Numbers +10.2.1 Converting Strings to Numbers ------------------------------------ The `strtonum()' function (*note String Functions::) is a `gawk' @@ -14531,7 +14628,7 @@ versions of `awk': # mystrtonum --- convert string to number - function mystrtonum(str, ret, chars, n, i, k, c) + function mystrtonum(str, ret, n, i, k, c) { if (str ~ /^0[0-7]*$/) { # octal @@ -14539,12 +14636,13 @@ versions of `awk': ret = 0 for (i = 1; i <= n; i++) { c = substr(str, i, 1) - if ((k = index("01234567", c)) > 0) - k-- # adjust for 1-basing in awk + # index() returns 0 if c not in string, + # includes c == "0" + k = index("1234567", c) ret = ret * 8 + k } - } else if (str ~ /^0[xX][[:xdigit:]]+/) { + } else if (str ~ /^0[xX][[:xdigit:]]+$/) { # hexadecimal str = substr(str, 3) # lop off leading 0x n = length(str) @@ -14552,10 +14650,9 @@ versions of `awk': 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 } @@ -14577,7 +14674,7 @@ versions of `awk': # 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]) @@ -14586,9 +14683,11 @@ versions of `awk': The function first looks for C-style octal numbers (base 8). If the input string matches a regular expression describing octal numbers, then `mystrtonum()' loops through each character in the string. It -sets `k' to the index in `"01234567"' of the current octal digit. -Since the return value is one-based, the `k--' adjusts `k' so it can be -used in computing the return value. +sets `k' to the index in `"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 `0'. This is +safe, because the regexp test in the `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 `0x' or `0X'. The use of @@ -14606,7 +14705,7 @@ be tested with `gawk' and the results compared to the built-in File: gawk.info, Node: Assert Function, Next: Round Function, Prev: Strtonum Function, Up: General Functions -12.2.2 Assertions +10.2.2 Assertions ----------------- When writing large programs, it is often useful to know that a @@ -14614,7 +14713,7 @@ 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 "assertion". The C language provides an `<assert.h>' header file and corresponding -`assert()' macro that the programmer can use to make assertions. If an +`assert()' macro that a programmer can use to make assertions. If an assertion fails, the `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 `assert()' looks this: @@ -14692,14 +14791,14 @@ rule always ends with an `exit' statement. File: gawk.info, Node: Round Function, Next: Cliff Random Function, Prev: Assert Function, Up: General Functions -12.2.3 Rounding Numbers +10.2.3 Rounding Numbers ----------------------- The way `printf' and `sprintf()' (*note Printf::) perform rounding often depends upon the system's C `sprintf()' subroutine. On many -machines, `sprintf()' rounding is "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 +machines, `sprintf()' rounding is "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., `"%.0f"'), you should check what your system does. The following function does traditional rounding; it @@ -14733,12 +14832,12 @@ might be useful if your `awk''s `printf' does unbiased rounding: } # test harness - { print $0, round($0) } + # { print $0, round($0) } File: gawk.info, Node: Cliff Random Function, Next: Ordinal Functions, Prev: Round Function, Up: General Functions -12.2.4 The Cliff Random Number Generator +10.2.4 The Cliff Random Number Generator ---------------------------------------- The Cliff random number generator @@ -14767,7 +14866,7 @@ might try using this function instead. File: gawk.info, Node: Ordinal Functions, Next: Join Function, Prev: Cliff Random Function, Up: General Functions -12.2.5 Translating Between Characters and Numbers +10.2.5 Translating Between Characters and Numbers ------------------------------------------------- One commercial implementation of `awk' supplies a built-in function, @@ -14809,16 +14908,16 @@ corresponding character. Both functions are written very nicely in } } - Some explanation of the numbers used by `chr' is worthwhile. The -most prominent character set in use today is ASCII.(1) Although an + Some explanation of the numbers used by `_ord_init()' is worthwhile. +The most prominent character set in use today is ASCII.(1) Although an 8-bit byte can hold 256 distinct values (from 0 to 255), ASCII only defines characters that use the values from 0 to 127.(2) In the now distant past, at least one minicomputer manufacturer used ASCII, but with mark parity, meaning that the leftmost bit in the byte 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, they are not really worth +character set, which uses all 256 values. There are other character +sets in use on some older systems, but they are not really worth worrying about: function ord(str, c) @@ -14835,8 +14934,7 @@ worrying about: } #### test code #### - # BEGIN \ - # { + # BEGIN { # for (;;) { # printf("enter a character: ") # if (getline var <= 0) @@ -14860,12 +14958,12 @@ tests such as used here prohibitively expensive. (2) 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 `_ord_init' to loop from 0 to 255. +extensions, you can simplify `_ord_init()' to loop from 0 to 255. -File: gawk.info, Node: Join Function, Next: Gettimeofday Function, Prev: Ordinal Functions, Up: General Functions +File: gawk.info, Node: Join Function, Next: Getlocaltime Function, Prev: Ordinal Functions, Up: General Functions -12.2.6 Merging an Array into a String +10.2.6 Merging an Array into a String ------------------------------------- When doing string processing, it is often useful to be able to join all @@ -14877,7 +14975,7 @@ application programs (*note Sample Programs::). 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 +indices are numeric--a reasonable assumption, as the array was likely created with `split()' (*note String Functions::): # join.awk --- join an array into a string @@ -14910,22 +15008,22 @@ concatenation. The lack of an explicit operator for concatenation makes string operations more difficult than they really need to be. -File: gawk.info, Node: Gettimeofday Function, Prev: Join Function, Up: General Functions +File: gawk.info, Node: Getlocaltime Function, Next: Readfile Function, Prev: Join Function, Up: General Functions -12.2.7 Managing the Time of Day +10.2.7 Managing the Time of Day ------------------------------- -The `systime()' and `strftime()' functions described in *Note Time +The `systime()' and `strftime()' functions described in *note Time Functions::, provide the minimum functionality necessary for dealing -with the time of day in human readable form. While `strftime()' is +with the time of day in human-readable form. Although `strftime()' is extensive, the control formats are not necessarily easy to remember or intuitively obvious when reading a program. - The following function, `gettimeofday()', populates a user-supplied + The following function, `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 `date' utility: - # gettimeofday.awk --- get the time of day in a usable format + # getlocaltime.awk --- get the time of day in a usable format # Returns a string in the format of output of date(1) # Populates the array argument time with individual values: @@ -14949,7 +15047,7 @@ current time formatted in the same way as the `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() @@ -14987,14 +15085,129 @@ current time formatted in the same way as the `date' utility: The string indices are easier to use and read than the various formats required by `strftime()'. The `alarm' program presented in -*Note Alarm Program::, uses this function. A more general design for -the `gettimeofday()' function would have allowed the user to supply an +*note Alarm Program::, uses this function. A more general design for +the `getlocaltime()' function would have allowed the user to supply an optional timestamp value to use instead of the current time. +File: gawk.info, Node: Readfile Function, Next: Shell Quoting, Prev: Getlocaltime Function, Up: General Functions + +10.2.8 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: + + 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 + } + + This function reads from `file' one record at a time, building up +the full contents of the file in the local variable `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: + + # readfile.awk --- read an entire file at once + + function readfile(file, tmp, save_rs) + { + save_rs = RS + RS = "^$" + getline tmp < file + close(file) + RS = save_rs + + return tmp + } + + It works by setting `RS' to `^$', a regular expression that will +never match if the file has contents. `gawk' reads data from the file +into `tmp' attempting to match `RS'. The match fails after each read, +but fails quickly, such that `gawk' fills `tmp' with the entire +contents of the file. (*Note Records::, for information on `RT' and +`RS'.) + + In the case that `file' is empty, the return value is the null +string. Thus calling code may use something like: + + contents = readfile("/some/path") + if (length(contents) == 0) + # file was empty ... + + This tests the result to see if it is empty or not. An equivalent +test would be `contents == ""'. + + *Note Extension Sample Readfile::, for an extension function that +also reads an entire file into memory. + + +File: gawk.info, Node: Shell Quoting, Prev: Readfile Function, Up: General Functions + +10.2.9 Quoting Strings to Pass to the Shell +------------------------------------------- + +Michael Brennan offers the following programming pattern, which he uses +frequently: + + #! /bin/sh + + awkp=' + ... + ' + + INPUT_PROGRAM | awk "$awkp" | /bin/sh + + For example, a program of his named `flac-edit' has this form: + + $ flac-edit -song="Whoope! That's Great" file.flac + + It generates the following output, which is to be piped to the shell +(`/bin/sh'): + + 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 + + Note the need for shell quoting. The function `shell_quote()' does +it. `SINGLE' is the one-character string `"'"' and `QSINGLE' is the +three-character string `"\"'\""': + + # shell_quote --- quote an argument for passing to the shell + + 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 + } + + File: gawk.info, Node: Data File Management, Next: Getopt Function, Prev: General Functions, Up: Library Functions -12.3 Data File Management +10.3 Data File Management ========================= This minor node presents functions that are useful for managing @@ -15011,10 +15224,10 @@ command-line data files. File: gawk.info, Node: Filetrans Function, Next: Rewind Function, Up: Data File Management -12.3.1 Noting Data File Boundaries +10.3.1 Noting Data File Boundaries ---------------------------------- -The `BEGIN' and `END' rules are each executed exactly once at the +The `BEGIN' and `END' rules are each executed exactly once, at the beginning and end of your `awk' program, respectively (*note BEGIN/END::). We (the `gawk' authors) once had a user who mistakenly thought that the `BEGIN' rule is executed at the beginning of each data @@ -15040,15 +15253,14 @@ does so _portably_; this works with any implementation of `awk': # that each take the name of the file being started or # finished, respectively. - FILENAME != _oldfilename \ - { + FILENAME != _oldfilename { if (_oldfilename != "") endfile(_oldfilename) _oldfilename = FILENAME beginfile(FILENAME) } - END { endfile(FILENAME) } + END { endfile(FILENAME) } This file must be loaded before the user's "main" program, so that the rule it supplies is executed first. @@ -15075,7 +15287,7 @@ again the value of multiple `BEGIN' and `END' rules should be clear. pass and at the beginning of the second pass. The following version solves the problem: - # ftrans.awk --- handle data file transitions + # ftrans.awk --- handle datafile transitions # # user supplies beginfile() and endfile() functions @@ -15086,21 +15298,20 @@ solves the problem: beginfile(FILENAME) } - END { endfile(_filename_) } + END { endfile(_filename_) } - *Note Wc Program::, shows how this library function can be used and + *note Wc Program::, shows how this library function can be used and how it simplifies writing the main program. -Advanced Notes: So Why Does `gawk' have `BEGINFILE' and `ENDFILE'? ------------------------------------------------------------------- + So Why Does `gawk' Have `BEGINFILE' and `ENDFILE'? -You are probably wondering, if `beginfile()' and `endfile()' functions -can do the job, why does `gawk' have `BEGINFILE' and `ENDFILE' patterns -(*note BEGINFILE/ENDFILE::)? + You are probably wondering, if `beginfile()' and `endfile()' +functions can do the job, why does `gawk' have `BEGINFILE' and +`ENDFILE' patterns (*note BEGINFILE/ENDFILE::)? Good question. Normally, if `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 `BEGINFILE' is to give you a "hook" to catch files that cannot be processed. `ENDFILE' exists for symmetry, and because @@ -15109,7 +15320,7 @@ it provides an easy way to do per-file cleanup processing. File: gawk.info, Node: Rewind Function, Next: File Checking, Prev: Filetrans Function, Up: Data File Management -12.3.2 Rereading the Current File +10.3.2 Rereading the Current File --------------------------------- Another request for a new built-in function was for a `rewind()' @@ -15140,30 +15351,29 @@ over with it from the top. For lack of a better name, we'll call it nextfile } - This code relies on the `ARGIND' variable (*note Auto-set::), which -is specific to `gawk'. If you are not using `gawk', you can use ideas -presented in *Note Filetrans Function::, to either update `ARGIND' on -your own or modify this code as appropriate. - - The `rewind()' function also relies on the `nextfile' keyword (*note -Nextfile Statement::). + The `rewind()' function relies on the `ARGIND' variable (*note +Auto-set::), which is specific to `gawk'. It also relies on the +`nextfile' keyword (*note Nextfile Statement::). Because of this, you +should not call it from an `ENDFILE' rule. (This isn't necessary +anyway, because `gawk' goes to the next file as soon as an `ENDFILE' +rule finishes!) File: gawk.info, Node: File Checking, Next: Empty Files, Prev: Rewind Function, Up: Data File Management -12.3.3 Checking for Readable Data Files +10.3.3 Checking for Readable Data Files --------------------------------------- Normally, if you give `awk' a data file 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 `awk' program: +such files and keep going.(1) You can do this by prepending the +following program to your `awk' program: # readable.awk --- library file to skip over unreadable files 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 @@ -15174,13 +15384,23 @@ program to your `awk' program: } This works, because the `getline' won't be fatal. Removing the -element from `ARGV' with `delete' skips the file (since it's no longer -in the list). See also *Note ARGC and ARGV::. +element from `ARGV' with `delete' skips the file (because it's no +longer in the list). See also *note ARGC and ARGV::. + + Because `awk' variable names only allow the English letters, the +regular expression check purposely does not use character classes such +as `[:alpha:]' and `[:alnum:]' (*note Bracket Expressions::) + + ---------- Footnotes ---------- + + (1) The `BEGINFILE' special pattern (*note BEGINFILE/ENDFILE::) +provides an alternative mechanism for dealing with files that can't be +opened. However, the code here provides a portable solution. File: gawk.info, Node: Empty Files, Next: Ignoring Assigns, Prev: File Checking, Up: Data File Management -12.3.4 Checking For Zero-length Files +10.3.4 Checking for Zero-length Files ------------------------------------- All known `awk' implementations silently skip over zero-length files. @@ -15193,7 +15413,7 @@ program code. Using `gawk''s `ARGIND' variable (*note Built-in Variables::), it is possible to detect when an empty data file has been skipped. Similar -to the library file presented in *Note Filetrans Function::, the +to the library file presented in *note Filetrans Function::, the following library file calls a function named `zerofile()' that the user must provide. The arguments passed are the file name and the position in `ARGV' where it was found: @@ -15228,21 +15448,15 @@ normal case. end of the command-line arguments. Note that the test in the condition of the `for' loop uses the `<=' operator, not `<'. - As an exercise, you might consider whether this same problem can be -solved without relying on `gawk''s `ARGIND' variable. - - As a second exercise, revise this code to handle the case where an -intervening value in `ARGV' is a variable assignment. - File: gawk.info, Node: Ignoring Assigns, Prev: Empty Files, Up: Data File Management -12.3.5 Treating Assignments as File Names +10.3.5 Treating Assignments as File Names ----------------------------------------- Occasionally, you might not want `awk' to process command-line variable assignments (*note Assignment Options::). In particular, if you have a -file name that contain an `=' character, `awk' treats the file name as +file name that contains an `=' character, `awk' treats the file name as an assignment, and does not process it. Some users have suggested an additional command-line option for @@ -15255,7 +15469,7 @@ programming with 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]) } @@ -15280,14 +15494,14 @@ arguments are left alone. File: gawk.info, Node: Getopt Function, Next: Passwd Functions, Prev: Data File Management, Up: Library Functions -12.4 Processing Command-Line Options +10.4 Processing Command-Line Options ==================================== -Most utilities on POSIX compatible systems take options on the command +Most utilities on POSIX-compatible systems take options on the command line that can be used to change the way a program behaves. `awk' is an example of such a program (*note Options::). Often, options take -"arguments"; i.e., data that the program needs to correctly obey the -command-line option. For example, `awk''s `-F' option requires a +"arguments" (i.e., data that the program needs to correctly obey the +command-line option). For example, `awk''s `-F' option requires a string to use as the field separator. The first occurrence on the command line of either `--' or a string that does not begin with `-' ends the options. @@ -15399,7 +15613,7 @@ characters (*note String Functions::).(1) # <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 The function starts out with comments presenting a list of the global variables it uses, what the return values are, what they mean, @@ -15443,8 +15657,7 @@ 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 @@ -15513,10 +15726,10 @@ next element in `argv'. If neither condition is true, then only on the next call to `getopt()'. The `BEGIN' rule initializes both `Opterr' and `Optind' to one. -`Opterr' is set to one, since the default behavior is for `getopt()' to -print a diagnostic message upon seeing an invalid option. `Optind' is -set to one, since there's no reason to look at the program name, which -is in `ARGV[0]': +`Opterr' is set to one, because the default behavior is for `getopt()' +to print a diagnostic message upon seeing an invalid option. `Optind' +is set to one, because there's no reason to look at the program name, +which is in `ARGV[0]': BEGIN { Opterr = 1 # default is to diagnose @@ -15525,7 +15738,7 @@ is in `ARGV[0]': # 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++) @@ -15538,17 +15751,17 @@ is in `ARGV[0]': result of two sample runs of the test program: $ awk -f getopt.awk -v _getopt_test=1 -- -a -cbARG bax -x - -| c = <a>, optarg = <> - -| c = <c>, optarg = <> - -| c = <b>, optarg = <ARG> + -| c = <a>, Optarg = <> + -| c = <c>, Optarg = <> + -| c = <b>, Optarg = <ARG> -| non-option arguments: -| ARGV[3] = <bax> -| ARGV[4] = <-x> $ awk -f getopt.awk -v _getopt_test=1 -- -a -x -- xyz abc - -| c = <a>, optarg = <> + -| c = <a>, Optarg = <> error--> x -- invalid option - -| c = <?>, optarg = <> + -| c = <?>, Optarg = <> -| non-option arguments: -| ARGV[4] = <xyz> -| ARGV[5] = <abc> @@ -15556,24 +15769,28 @@ result of two sample runs of the test program: In both runs, the first `--' terminates the arguments to `awk', so that it does not try to interpret the `-a', etc., as its own options. - NOTE: After `getopt()' is through, it is the responsibility of the - user level code to clear out all the elements of `ARGV' from 1 to - `Optind', so that `awk' does not try to process the command-line - options as file names. + NOTE: After `getopt()' is through, user-level code must clear out + all the elements of `ARGV' from 1 to `Optind', so that `awk' does + not try to process the command-line options as file names. + + Using `#!' with the `-E' option may help avoid conflicts between +your program's options and `gawk''s options, as `-E' causes `gawk' to +abandon processing of further options (*note Executable Scripts::, and +*note Options::). - Several of the sample programs presented in *Note Sample Programs::, + Several of the sample programs presented in *note Sample Programs::, use `getopt()' to process their arguments. ---------- Footnotes ---------- (1) This function was written before `gawk' acquired the ability to split strings into single characters using `""' as the separator. We -have left it alone, since using `substr()' is more portable. +have left it alone, as using `substr()' is more portable. File: gawk.info, Node: Passwd Functions, Next: Group Functions, Prev: Getopt Function, Up: Library Functions -12.5 Reading the User Database +10.5 Reading the User Database ============================== The `PROCINFO' array (*note Built-in Variables::) provides access to @@ -15593,7 +15810,7 @@ function is `getpwent()', for "get password entry." The "password" comes from the original user database file, `/etc/passwd', which stores user information, along with the encrypted passwords (hence the name). - While an `awk' program could simply read `/etc/passwd' directly, + Although an `awk' program could simply read `/etc/passwd' directly, this file may not contain complete information about the system's set of users.(1) To be sure you are able to produce a readable and complete version of the user database, it is necessary to write a small C @@ -15607,7 +15824,7 @@ that "cats" the password database: /* * pwcat.c * - * Generate a printable version of the password database + * Generate a printable version of the password database. */ #include <stdio.h> #include <pwd.h> @@ -15638,13 +15855,13 @@ Encrypted password systems. User-ID - The user's numeric user ID number. (On some systems it's a C + The user's numeric user ID number. (On some systems, it's a C `long', and not an `int'. Thus we cast it to `long' for all cases.) Group-ID The user's numeric group ID number. (Similar comments about - `long' vs. `int' apply here.) + `long' versus `int' apply here.) Full name The user's full name, and perhaps other information associated @@ -15661,7 +15878,7 @@ Login shell A few lines representative of `pwcat''s output are as follows: $ pwcat - -| root:3Ov02d5VaUPB6:0:1:Operator:/:/bin/sh + -| root:x:0:1:Operator:/:/bin/sh -| nobody:*:65534:65534::/: -| daemon:*:1:1::/: -| sys:*:2:2::/:/bin/csh @@ -15718,27 +15935,24 @@ corresponding to the C functions of the same names: routine, we have chosen to put it in `/usr/local/libexec/awk'; however, you might want it to be in a different directory on your system. - The function `_pw_init()' keeps three copies of the user information -in three associative arrays. The arrays are indexed by username + The function `_pw_init()' fills three copies of the user information +into three associative arrays. The arrays are indexed by username (`_pw_byname'), by user ID number (`_pw_byuid'), and by order of occurrence (`_pw_bycount'). The variable `_pw_inited' is used for -efficiency, since `_pw_init()' needs to be called only once. +efficiency, as `_pw_init()' needs to be called only once. Because this function uses `getline' to read information from `pwcat', it first saves the values of `FS', `RS', and `$0'. It notes in the variable `using_fw' whether field splitting with `FIELDWIDTHS' -is in effect or not. Doing so is necessary, since 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. - - The `using_fw' variable checks `PROCINFO["FS"]', which is -`"FIELDWIDTHS"' if field splitting is being done with `FIELDWIDTHS'. -This makes it possible to restore the correct field-splitting mechanism -later. The test can only be true for `gawk'. It is false if using -`FS' or `FPAT', or on some other `awk' implementation. +is in effect or not. 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. This makes it +possible to restore the correct field-splitting mechanism later. The +test can only be true for `gawk'. It is false if using `FS' or `FPAT', +or on some other `awk' implementation. The code that checks for using `FPAT', using `using_fpat' and -`PROCINFO["FS"]' is similar. +`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 @@ -15758,9 +15972,9 @@ create the element with the null string as its value: return _pw_byname[name] } - Similarly, the `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 `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: function getpwuid(uid) { @@ -15803,10 +16017,10 @@ simplifies the code but runs an extra process that may never be needed.) once. If you are worried about squeezing every last cycle out of your `awk' program, the check of `_pw_inited' could be moved out of `_pw_init()' and duplicated in all the other functions. In practice, -this is not necessary, since most `awk' programs are I/O-bound, and -such a change would clutter up the code. +this is not necessary, as most `awk' programs are I/O-bound, and such a +change would clutter up the code. - The `id' program in *Note Id Program::, uses these functions. + The `id' program in *note Id Program::, uses these functions. ---------- Footnotes ---------- @@ -15816,10 +16030,10 @@ network database. File: gawk.info, Node: Group Functions, Next: Walking Arrays, Prev: Passwd Functions, Up: Library Functions -12.6 Reading the Group Database +10.6 Reading the Group Database =============================== -Much of the discussion presented in *Note Passwd Functions::, applies +Much of the discussion presented in *note Passwd Functions::, applies to the group database as well. Although there has traditionally been a well-known file (`/etc/group') in a well-known format, the POSIX standard only provides a set of C library routines (`<grp.h>' and @@ -15832,7 +16046,7 @@ group database, is as follows: /* * grcat.c * - * Generate a printable version of the group database + * Generate a printable version of the group database. */ #include <stdio.h> #include <grp.h> @@ -15868,12 +16082,13 @@ Group Password used; it is usually empty or set to `*'. Group ID Number - The group's numeric group ID number; this number must be unique - within the file. (On some systems it's a C `long', and not an - `int'. Thus we cast it to `long' for all cases.) + The group's numeric group ID number; the association of name to + number must be unique within the file. (On some systems it's a C + `long', and not an `int'. Thus we cast it to `long' for all + cases.) Group Member List - A comma-separated list of user names. These users are members of + 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 `"group1"' through `"groupN"' in `PROCINFO' for those @@ -15897,8 +16112,7 @@ the same names: # group.awk --- functions for dealing with the group file - BEGIN \ - { + BEGIN { # Change to suit your system _gr_awklib = "/usr/local/libexec/awk/" } @@ -15931,8 +16145,7 @@ the same names: 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 @@ -15966,7 +16179,7 @@ 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 (`_gr_byname'), by group ID number (`_gr_bygid'), and by position in the database (`_gr_bycount'). There -is an additional array indexed by user name (`_gr_groupsbyuser'), which +is an additional array indexed by username (`_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 @@ -15974,15 +16187,12 @@ the 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: - tvpeople:*:101:johnny,jay,arsenio + tvpeople:*:101:johny,jay,arsenio tvpeople:*:101:david,conan,tom,joan For this reason, `_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 -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 `$4'.) +ID number is already seen. If it is, the usernames are simply +concatenated onto the previous list of users.(1) Finally, `_gr_init()' closes the pipeline to `grcat', restores `FS' (and `FIELDWIDTHS' or `FPAT' if necessary), `RS', and `$0', initializes @@ -16009,7 +16219,7 @@ looks up the information associated with that group ID: } The `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: function getgruser(user) { @@ -16045,15 +16255,21 @@ body of `_gr_init()' into a `BEGIN' rule). associative arrays. The functions that the user calls are themselves very simple, relying on `awk''s associative arrays to do work. - The `id' program in *Note Id Program::, uses these functions. + The `id' program in *note Id Program::, uses these functions. + + ---------- Footnotes ---------- + + (1) 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 `$4'. -File: gawk.info, Node: Walking Arrays, Prev: Group Functions, Up: Library Functions +File: gawk.info, Node: Walking Arrays, Next: Library Functions Summary, Prev: Group Functions, Up: Library Functions -12.7 Traversing Arrays of Arrays +10.7 Traversing Arrays of Arrays ================================ -*Note Arrays of Arrays::, described how `gawk' provides arrays of +*note Arrays of Arrays::, described how `gawk' provides arrays of arrays. In particular, any element of an array may be either a scalar, or another array. The `isarray()' function (*note Type Functions::) lets you distinguish an array from a scalar. The following function, @@ -16091,25 +16307,93 @@ value. Here is a main program to demonstrate: When run, the program produces the following output: $ gawk -f walk_array.awk - -| a[4][1][1] = 411 - -| a[4][2] = 42 -| a[1] = 1 -| a[2][1] = 21 -| a[2][2] = 22 -| a[3] = 3 + -| a[4][1][1] = 411 + -| a[4][2] = 42 + + +File: gawk.info, Node: Library Functions Summary, Next: Library Exercises, Prev: Walking Arrays, Up: Library Functions + +10.8 Summary +============ + + * Reading programs is an excellent way to learn Good Programming. + The functions and programs provided in this major node and the next + are intended to serve that purpose. + + * 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. + + * The functions presented here fit into the following categories: + + 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. + + Managing data files + Noting data file boundaries, rereading the current file, + checking for readable files, checking for zero-length files, + and treating assignments as file names. + + Processing command-line options + An `awk' version of the standard C `getopt()' function. + + Reading the user and group databases + Two sets of routines that parallel the C library versions. + + Traversing arrays of arrays + A simple function to traverse an array of arrays to any depth. + + + +File: gawk.info, Node: Library Exercises, Prev: Library Functions Summary, Up: Library Functions + +10.9 Exercises +============== + + 1. In *note Empty Files::, we presented the `zerofile.awk' program, + which made use of `gawk''s `ARGIND' variable. Can this problem be + solved without relying on `ARGIND'? If so, how? + + 2. As a related challenge, revise that code to handle the case where + an intervening value in `ARGV' is a variable assignment. + + 3. *note 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 `walk_array()' function by adding an additional + parameter named `process'. + + Then, inside the loop, instead of printing the array element's + index and value, use the indirect function call syntax (*note + Indirect Calls::) on `process', passing it the index and the value. + + When calling `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. + -File: gawk.info, Node: Sample Programs, Next: Debugger, Prev: Library Functions, Up: Top +File: gawk.info, Node: Sample Programs, Next: Advanced Features, Prev: Library Functions, Up: Top -13 Practical `awk' Programs +11 Practical `awk' Programs *************************** -*Note Library Functions::, presents the idea that reading programs in a +*note Library Functions::, presents the idea that reading programs in a language contributes to learning that language. This major node continues that theme, presenting a potpourri of `awk' programs for your reading enjoyment. - Many of these programs use library functions presented in *Note + Many of these programs use library functions presented in *note Library Functions::. * Menu: @@ -16117,11 +16401,13 @@ Library Functions::. * Running Examples:: How to run these examples. * Clones:: Clones of common utilities. * Miscellaneous Programs:: Some interesting `awk' programs. +* Programs Summary:: Summary of programs. +* Programs Exercises:: Exercises. File: gawk.info, Node: Running Examples, Next: Clones, Up: Sample Programs -13.1 Running the Example Programs +11.1 Running the Example Programs ================================= To run a given program, you would typically do something like this: @@ -16144,7 +16430,7 @@ OPTIONS are any command-line options for the program that start with a File: gawk.info, Node: Clones, Next: Miscellaneous Programs, Prev: Running Examples, Up: Sample Programs -13.2 Reinventing Wheels for Fun and Profit +11.2 Reinventing Wheels for Fun and Profit ========================================== This minor node presents a number of POSIX utilities implemented in @@ -16174,7 +16460,7 @@ programming for "real world" tasks. File: gawk.info, Node: Cut Program, Next: Egrep Program, Up: Clones -13.2.1 Cutting out Fields and Columns +11.2.1 Cutting Out Fields and Columns ------------------------------------- The `cut' utility selects, or "cuts," characters or fields from its @@ -16227,18 +16513,13 @@ supplied: # # Requires getopt() and join() library functions - 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 } -The variables `e1' and `e2' are used so that the function fits nicely -on the screen. - Next comes a `BEGIN' rule that parses the command-line options. It sets `FS' to a single TAB character, because that is `cut''s default field separator. The rule then sets the output field separator to be the @@ -16248,8 +16529,7 @@ through the command-line options. Exactly one of the variables should be done by fields or by characters, respectively. When cutting by characters, the output field separator is set to the null string: - BEGIN \ - { + BEGIN { FS = "\t" # default OFS = FS while ((c = getopt(ARGC, ARGV, "sf:c:d:")) != -1) { @@ -16262,7 +16542,7 @@ by characters, the output field separator is set to the null string: 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) } @@ -16271,7 +16551,7 @@ by characters, the output field separator is set to the null string: if (FS == " ") # defeat awk semantics FS = "[ ]" } else if (c == "s") - suppress++ + suppress = 1 else usage() } @@ -16284,7 +16564,7 @@ by characters, the output field separator is set to the null string: Using a single space (`" "') for the value of `FS' is incorrect--`awk' would separate fields with runs of spaces, TABs, and/or newlines, and we want them to be separated with individual spaces. Also remember -that after `getopt()' is through (as described in *Note Getopt +that after `getopt()' is through (as described in *note Getopt Function::), we have to clear out all the elements of `ARGV' from 1 to `Optind', so that `awk' does not try to process the command-line options as file names. @@ -16329,7 +16609,7 @@ splitting: if (index(f[i], "-") != 0) { # a range m = split(f[i], g, "-") 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 } @@ -16357,7 +16637,7 @@ fields to print are `$1', `$3', and `$5'. The intermediate fields are the fields to print, and `t' tracks the complete field list, including filler fields: - 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 @@ -16367,7 +16647,7 @@ filler fields: 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 } @@ -16397,10 +16677,10 @@ filler fields: nfields = j - 1 } - Next is the rule that actually processes the data. If the `-s' -option is given, then `suppress' is true. The first `if' statement -makes sure that the input record does have the field separator. If -`cut' is processing fields, `suppress' is true, and the field separator + Next is the rule that processes the data. If the `-s' option is +given, then `suppress' is true. The first `if' statement makes sure +that the input record does have the field separator. If `cut' is +processing fields, `suppress' is true, and the field separator character is not in the record, then the record is skipped. If the record is valid, then `gawk' has split the data into fields, @@ -16411,7 +16691,7 @@ the next field also has data, then the separator character is written out between the fields: { - if (by_fields && suppress && index($0, FS) != 0) + if (by_fields && suppress && index($0, FS) == 0) next for (i = 1; i <= nfields; i++) { @@ -16425,22 +16705,22 @@ out between the fields: } This version of `cut' relies on `gawk''s `FIELDWIDTHS' variable to -do the character-based cutting. While it is possible in other `awk' -implementations to use `substr()' (*note String Functions::), it is +do the character-based cutting. It is possible in other `awk' +implementations to use `substr()' (*note String Functions::), but it is also extremely painful. The `FIELDWIDTHS' variable supplies an elegant solution to the problem of picking the input line apart by characters. File: gawk.info, Node: Egrep Program, Next: Id Program, Prev: Cut Program, Up: Clones -13.2.2 Searching for Regular Expressions in Files +11.2.2 Searching for Regular Expressions in Files ------------------------------------------------- The `egrep' utility searches files for patterns. It uses regular expressions that are almost identical to those available in `awk' (*note Regexp::). You invoke it as follows: - egrep [ OPTIONS ] 'PATTERN' FILES ... + `egrep' [OPTIONS] `'PATTERN'' FILES ... The PATTERN is a regular expression. In typical usage, the regular expression is quoted to prevent the shell from expanding any of the @@ -16482,7 +16762,7 @@ Function::). The program begins with a descriptive comment and then a `BEGIN' rule that processes the command-line arguments with `getopt()'. The `-i' (ignore case) option is particularly easy with `gawk'; we just use the -`IGNORECASE' built-in variable (*note Built-in Variables::): +`IGNORECASE' predefined variable (*note Built-in Variables::): # egrep.awk --- simulate egrep in awk # @@ -16537,14 +16817,14 @@ the matched lines in the output: # pattern = tolower(pattern) } - 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 `gawk'. They should be uncommented if you have to use another version of `awk'. The next set of lines should be uncommented if you are not using `gawk'. This rule translates all the characters in the input line into lowercase if the `-i' option is specified.(1) The rule is commented out -since it is not necessary with `gawk': +as it is not necessary with `gawk': #{ # if (IGNORECASE) @@ -16584,6 +16864,11 @@ know the total number of lines that matched the pattern: total += fcount } + The `BEGINFILE' and `ENDFILE' special patterns (*note +BEGINFILE/ENDFILE::) could be used, but then the program would be +`gawk'-specific. Additionally, this example was written before `gawk' +acquired `BEGINFILE' and `ENDFILE'. + The following rule does most of the work of matching lines. The variable `matches' is true if the line matched the pattern. If the user wants lines that did not match, the sense of `matches' is inverted @@ -16629,34 +16914,20 @@ line is printed, with a leading file name and colon if necessary: The `END' rule takes care of producing the correct exit status. If there are no matches, the exit status is one; otherwise it is zero: - END \ - { - if (total == 0) - exit 1 - exit 0 + END { + exit (total == 0) } The `usage()' function prints a usage message in case of invalid options, and then exits: - 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 } - The variable `e' is used so that the function fits nicely on the -printed page. - - Just a note on programming style: you may have noticed that the `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 major node use this style. -You can decide for yourself if you like writing your `BEGIN' and `END' -rules this way or not. - ---------- Footnotes ---------- (1) It also introduces a subtle bug; if a match happens, we output @@ -16665,7 +16936,7 @@ the translated line, not the original. File: gawk.info, Node: Id Program, Next: Split Program, Prev: Egrep Program, Up: Clones -13.2.3 Printing out User Information +11.2.3 Printing Out User Information ------------------------------------ The `id' utility lists a user's real and effective user ID numbers, @@ -16675,7 +16946,7 @@ different from the real ones. If possible, `id' also supplies the corresponding user and group names. The output might look like this: $ id - -| uid=500(arnold) gid=500(arnold) groups=6(disk),7(lp),19(floppy) + -| uid=1000(arnold) gid=1000(arnold) groups=1000(arnold),4(adm),7(lp),27(sudo) This information is part of what is provided by `gawk''s `PROCINFO' array (*note Built-in Variables::). However, the `id' utility provides @@ -16699,8 +16970,7 @@ and the group numbers: # uid=12(foo) euid=34(bar) gid=3(baz) \ # egid=5(blat) groups=9(nine),2(two),1(one) - BEGIN \ - { + BEGIN { uid = PROCINFO["uid"] euid = PROCINFO["euid"] gid = PROCINFO["gid"] @@ -16708,34 +16978,22 @@ and the group numbers: 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++) { @@ -16744,10 +17002,7 @@ and the group numbers: 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(",") } @@ -16755,41 +17010,54 @@ and the group numbers: print "" } + function pr_first_field(str, a) + { + if (str != "") { + split(str, a, ":") + printf("(%s)", a[1]) + } + } + The test in the `for' loop is worth noting. Any supplementary groups in the `PROCINFO' array have the indices `"group1"' through -`"groupN"' for some N, i.e., the total number of supplementary groups. +`"groupN"' for some 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 -`"group"', and then using `in' to see if that value is in the array. -Eventually, `i' is incremented past the last group in the array and the -loop exits. +`"group"', and then using `in' to see if that value is in the array +(*note Reference to Elements::). Eventually, `i' is incremented past +the last group in the array and the loop exits. The loop is also correct if there are _no_ supplementary groups; then the condition is false the first time it's tested, and the loop body never executes. + The `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. + File: gawk.info, Node: Split Program, Next: Tee Program, Prev: Id Program, Up: Clones -13.2.4 Splitting a Large File into Pieces +11.2.4 Splitting a Large File into Pieces ----------------------------------------- The `split' program splits large text files into smaller pieces. Usage is as follows:(1) - split [-COUNT] file [ PREFIX ] + `split' [`-COUNT'] [FILE] [PREFIX] By default, the output files are named `xaa', `xab', and so on. Each -file has 1000 lines in it, with the likely exception of the last file. +file has 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., `-500' for files with 500 -lines in them instead of 1000. To change the name of the output files -to something like `myfileaa', `myfileab', and so on, supply an +command line preceded with a minus (e.g., `-500' for files with 500 +lines in them instead of 1,000). To change the name of the output +files to something like `myfileaa', `myfileab', and so on, supply an additional argument that specifies the file name prefix. Here is a version of `split' in `awk'. It uses the `ord()' and -`chr()' functions presented in *Note Ordinal Functions::. +`chr()' functions presented in *note Ordinal Functions::. 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 @@ -16802,7 +17070,7 @@ output file names: # split.awk --- do split in awk # # Requires ord() and chr() library functions - # usage: split [-num] [file] [outname] + # usage: split [-count] [file] [outname] BEGIN { outfile = "x" # default @@ -16811,14 +17079,14 @@ output file names: 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] = "" @@ -16858,15 +17126,12 @@ moves to the next letter in the alphabet and `s2' starts over again at The `usage()' function simply prints an error message and exits: - 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 } -The variable `e' is used so that the function fits nicely on the screen. - This program is a bit sloppy; it relies on `awk' to automatically close the last file instead of doing it in an `END' rule. It also assumes that letters are contiguous in the character set, which isn't @@ -16880,21 +17145,21 @@ not relevant for what the program aims to demonstrate. File: gawk.info, Node: Tee Program, Next: Uniq Program, Prev: Split Program, Up: Clones -13.2.5 Duplicating Output into Multiple Files +11.2.5 Duplicating Output into Multiple Files --------------------------------------------- The `tee' program is known as a "pipe fitting." `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: - tee [-a] file ... + `tee' [`-a'] FILE ... The `-a' option tells `tee' to append to the named files, instead of truncating them and starting over. The `BEGIN' rule first makes a copy of all the command-line arguments -into an array named `copy'. `ARGV[0]' is not copied, since it is not -needed. `tee' cannot use `ARGV' directly, since `awk' attempts to +into an array named `copy'. `ARGV[0]' is not needed, so it is not +copied. `tee' cannot use `ARGV' directly, because `awk' attempts to process each file name in `ARGV' as input data. If the first argument is `-a', then the flag variable `append' is @@ -16908,8 +17173,7 @@ input by setting `ARGV[1]' to `"-"' and `ARGC' to two: # Copy standard input to all named output files. # Append content if -a option is supplied. # - BEGIN \ - { + BEGIN { for (i = 1; i < ARGC; i++) copy[i] = ARGV[i] @@ -16927,7 +17191,7 @@ input by setting `ARGV[1]' to `"-"' and `ARGC' to two: ARGC = 2 } - The following single rule does all the work. Since there is no + 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: @@ -16951,16 +17215,16 @@ It is also possible to write the loop this way: else print > copy[i] -This is more concise but it is also less efficient. The `if' is tested -for each record and for each output file. By duplicating the loop -body, the `if' is only tested once for each input record. If there are -N input records and M output files, the first method only executes N -`if' statements, while the second executes N`*'M `if' statements. +This is more concise, but it is also less efficient. The `if' is +tested for each record and for each output file. By duplicating the +loop body, the `if' is only tested once for each input record. If +there are N input records and M output files, the first method only +executes N `if' statements, while the second executes N`*'M `if' +statements. Finally, the `END' rule cleans up by closing all the output files: - END \ - { + END { for (i in copy) close(copy[i]) } @@ -16968,7 +17232,7 @@ N input records and M output files, the first method only executes N File: gawk.info, Node: Uniq Program, Next: Wc Program, Prev: Tee Program, Up: Clones -13.2.6 Printing Nonduplicated Lines of Text +11.2.6 Printing Nonduplicated Lines of Text ------------------------------------------- The `uniq' utility reads sorted lines of data on its standard input, @@ -16976,15 +17240,15 @@ and by default removes duplicate lines. In other words, it only prints unique lines--hence the name. `uniq' has a number of options. The usage is as follows: - uniq [-udc [-N]] [+N] [ INPUT FILE [ OUTPUT FILE ]] + `uniq' [`-udc' [`-N']] [`+N'] [INPUTFILE [OUTPUTFILE]] The options for `uniq' are: `-d' - Print only repeated lines. + Print only repeated (duplicated) lines. `-u' - Print only nonrepeated lines. + Print only nonrepeated (unique) lines. `-c' Count lines. This option overrides `-d' and `-u'. Both repeated @@ -16999,11 +17263,11 @@ usage is as follows: Skip N characters before comparing lines. Any fields specified with `-N' are skipped first. -`INPUT FILE' +`INPUTFILE' Data is read from the input file named on the command line, instead of from the standard input. -`OUTPUT FILE' +`OUTPUTFILE' The generated output is sent to the named output file, instead of to the standard output. @@ -17034,10 +17298,9 @@ standard output, `/dev/stdout': # # Requires getopt() and join() library functions - 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 } @@ -17047,8 +17310,7 @@ standard output, `/dev/stdout': # -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:" @@ -17060,7 +17322,7 @@ standard output, `/dev/stdout': 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 @@ -17092,16 +17354,18 @@ standard output, `/dev/stdout': The following function, `are_equal()', compares the current line, `$0', to the previous line, `last'. It handles skipping fields and characters. If no field count and no character count are specified, -`are_equal()' simply returns one or zero depending upon the result of a -simple string comparison of `last' and `$0'. Otherwise, things get more -complicated. If fields have to be skipped, each line is broken into an -array using `split()' (*note String Functions::); the desired fields -are then joined back into a line using `join()'. The joined lines are -stored in `clast' and `cline'. If no fields are skipped, `clast' and -`cline' are set to `last' and `$0', respectively. Finally, if -characters are skipped, `substr()' is used to strip off the leading -`charcount' characters in `clast' and `cline'. The two strings are -then compared and `are_equal()' returns the result: +`are_equal()' returns one or zero depending upon the result of a simple +string comparison of `last' and `$0'. + + Otherwise, things get more complicated. If fields have to be +skipped, each line is broken into an array using `split()' (*note +String Functions::); the desired fields are then joined back into a line +using `join()'. The joined lines are stored in `clast' and `cline'. +If no fields are skipped, `clast' and `cline' are set to `last' and +`$0', respectively. Finally, if characters are skipped, `substr()' is +used to strip off the leading `charcount' characters in `clast' and +`cline'. The two strings are then compared and `are_equal()' returns +the result: function are_equal( n, m, clast, cline, alast, aline) { @@ -17134,13 +17398,13 @@ to. depending upon the results of `are_equal()''s comparison. If `uniq' is counting repeated lines, and the lines are equal, then it increments the `count' variable. Otherwise, it prints the line and resets `count', -since the two lines are not equal. +because the two lines are not equal. If `uniq' is not counting, and if the lines are equal, `count' is -incremented. Nothing is printed, since the point is to remove -duplicates. Otherwise, if `uniq' is counting repeated lines and more -than one line is seen, or if `uniq' is counting nonrepeated lines and -only one line is seen, then the line is printed, and `count' is reset. +incremented. Nothing is printed, as the point is to remove duplicates. +Otherwise, if `uniq' is counting repeated lines and more than one line +is seen, or if `uniq' is counting nonrepeated lines and only one line +is seen, then the line is printed, and `count' is reset. Finally, similar logic is used in the `END' rule to print the final line of input data: @@ -17187,18 +17451,18 @@ line of input data: File: gawk.info, Node: Wc Program, Prev: Uniq Program, Up: Clones -13.2.7 Counting Things +11.2.7 Counting Things ---------------------- The `wc' (word count) utility counts lines, words, and characters in one or more input files. Its usage is as follows: - wc [-lwc] [ FILES ... ] + `wc' [`-lwc'] [FILES ...] If no files are specified on the command line, `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: +counts for all the files. The options and their meanings are as +follows: `-l' Count only lines. @@ -17212,10 +17476,10 @@ the following list: `-c' Count only characters. - Implementing `wc' in `awk' is particularly elegant, since `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. + Implementing `wc' in `awk' is particularly elegant, because `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. This program uses the `getopt()' library function (*note Getopt Function::) and the file-transition functions (*note Filetrans @@ -17273,7 +17537,7 @@ lines, words, and characters to zero, and saves the current file name in } The `endfile()' function adds the current file's numbers to the -running totals of lines, words, and characters.(1) It then prints out +running totals of lines, words, and characters. It then prints out those numbers for the file that was just read. It relies on `beginfile()' to reset the numbers for the following data file: @@ -17292,7 +17556,7 @@ those numbers for the file that was just read. It relies on } There is one rule that is executed for each line. It adds the length -of the record, plus one, to `chars'.(2) Adding one plus the record +of the record, plus one, to `chars'.(1) Adding one plus the record length is needed because the newline character separating records (the value of `RS') is not part of the record itself, and thus not included in its length. Next, `lines' is incremented for each line read, and @@ -17322,17 +17586,13 @@ in its length. Next, `lines' is incremented for each line read, and ---------- Footnotes ---------- - (1) `wc' can't just use the value of `FNR' in `endfile()'. If you -examine the code in *Note Filetrans Function::, you will see that `FNR' -has already been reset by the time `endfile()' is called. - - (2) Since `gawk' understands multibyte locales, this code counts + (1) Because `gawk' understands multibyte locales, this code counts characters, not bytes. -File: gawk.info, Node: Miscellaneous Programs, Prev: Clones, Up: Sample Programs +File: gawk.info, Node: Miscellaneous Programs, Next: Programs Summary, Prev: Clones, Up: Sample Programs -13.3 A Grab Bag of `awk' Programs +11.3 A Grab Bag of `awk' Programs ================================= This minor node is a large "grab bag" of miscellaneous programs. We @@ -17359,7 +17619,7 @@ hope you find them both interesting and enjoyable. File: gawk.info, Node: Dupword Program, Next: Alarm Program, Up: Miscellaneous Programs -13.3.1 Finding Duplicated Words in a Document +11.3.1 Finding Duplicated Words in a Document --------------------------------------------- A common error when writing large amounts of prose is to accidentally @@ -17407,11 +17667,13 @@ word, comparing it to the previous one: File: gawk.info, Node: Alarm Program, Next: Translate Program, Prev: Dupword Program, Up: Miscellaneous Programs -13.3.2 An Alarm Clock Program +11.3.2 An Alarm Clock Program ----------------------------- - Nothing cures insomnia like a ringing alarm clock. - Arnold Robbins + Nothing cures insomnia like a ringing alarm clock. -- Arnold + Robbins + + Sleep is for web developers. -- Erik Quanstrom The following program is a simple "alarm clock" program. You give it a time of day and an optional message. At the specified time, it @@ -17419,8 +17681,8 @@ 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 `gettimeofday()' function from *Note -Gettimeofday Function::. + This program uses the `getlocaltime()' function from *note +Getlocaltime Function::. All the work is done in the `BEGIN' rule. The first part is argument checking and setting of defaults: the delay, the count, and the message @@ -17435,11 +17697,10 @@ Statement::), but the processing could be done with a series of # alarm.awk --- set an alarm # - # Requires gettimeofday() library function + # Requires getlocaltime() library function # 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]) @@ -17491,7 +17752,7 @@ 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., @@ -17509,7 +17770,7 @@ 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 } @@ -17540,7 +17801,7 @@ necessary: File: gawk.info, Node: Translate Program, Next: Labels Program, Prev: Alarm Program, Up: Miscellaneous Programs -13.3.3 Transliterating Characters +11.3.3 Transliterating Characters --------------------------------- The system `tr' utility transliterates characters. For example, it is @@ -17557,17 +17818,17 @@ 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, a user proposed that a transliteration function should -be added to `gawk'. The following program was written to prove that -character transliteration could be done with a user-level function. -This program is not as complete as the system `tr' utility but it does -most of the job. + Once upon a time, a user proposed adding a transliteration function +to `gawk'. The following program was written to prove that character +transliteration could be done with a user-level function. This program +is not as complete as the system `tr' utility but it does most of the +job. - The `translate' program demonstrates one of the few weaknesses of -standard `awk': dealing with individual characters is very painful, -requiring repeated use of the `substr()', `index()', and `gsub()' -built-in functions (*note String Functions::).(2) There are two -functions. The first, `stranslate()', takes three arguments: + The `translate' program was written long before `gawk' acquired the +ability to split each character in a string into separate array +elements. Thus, it makes repeated use of the `substr()', `index()', +and `gsub()' built-in functions (*note String Functions::). There are +two functions. The first, `stranslate()', takes three arguments: `from' A list of characters from which to translate. @@ -17584,10 +17845,10 @@ simple loop goes through `from', one character at a time. For each character in `from', if the character appears in `target', it is replaced with the corresponding `to' character. - The `translate()' function simply calls `stranslate()' using `$0' as -the target. The main program sets two global variables, `FROM' and -`TO', from the command line, and then changes `ARGV' so that `awk' -reads from the standard input. + The `translate()' function calls `stranslate()' using `$0' as the +target. The main program sets two global variables, `FROM' and `TO', +from the command line, and then changes `ARGV' so that `awk' reads from +the standard input. Finally, the processing rule simply calls `translate()' for each record: @@ -17639,34 +17900,36 @@ record: print } - While it is possible to do character transliteration in a user-level -function, it is not necessarily efficient, and we (the `gawk' authors) -started to consider adding a built-in function. However, shortly after -writing this program, we learned that the System V Release 4 `awk' had -added the `toupper()' and `tolower()' functions (*note 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 `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 `gawk' +developers) started to consider adding a built-in function. However, +shortly after writing this program, we learned that Brian Kernighan had +added the `toupper()' and `tolower()' functions to his `awk' (*note +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 `gawk' as well and then leave well enough +alone. An obvious improvement to this program would be to set up the `t_ar' array only once, in a `BEGIN' rule. However, this assumes that the "from" and "to" lists will never change throughout the lifetime of the program. - ---------- Footnotes ---------- + Another obvious improvement is to enable the use of ranges, such as +`a-z', as allowed by the `tr' utility. Look at the code for `cut.awk' +(*note Cut Program::) for inspiration. - (1) On some older systems, `tr' may require that the lists be -written as range expressions enclosed in square brackets (`[a-z]') and -quoted, to prevent the shell from attempting a file name expansion. -This is not a feature. + ---------- Footnotes ---------- - (2) This program was written before `gawk' acquired the ability to -split each character in a string into separate array elements. + (1) On some older systems, including Solaris, the system version of +`tr' may require that the lists be written as range expressions +enclosed in square brackets (`[a-z]') and quoted, to prevent the shell +from attempting a file name expansion. This is not a feature. File: gawk.info, Node: Labels Program, Next: Word Sorting, Prev: Translate Program, Up: Miscellaneous Programs -13.3.4 Printing Mailing Labels +11.3.4 Printing Mailing Labels ------------------------------ Here is a "real world"(1) program. This script reads lists of names and @@ -17682,18 +17945,18 @@ been read. The `BEGIN' rule simply sets `RS' to the empty string, so that `awk' splits records at blank lines (*note Records::). It sets `MAXLINES' to -100, since 100 is the maximum number of lines on the page (20 * 5 = +100, because 100 is the maximum number of lines on the page (20 * 5 = 100). Most of the work is done in the `printpage()' function. The label lines are stored sequentially in the `line' array. But they have to print horizontally; `line[1]' next to `line[6]', `line[2]' next to -`line[7]', and so on. Two loops are used to accomplish this. The -outer loop, controlled by `i', steps through every 10 lines of data; -this is each row of labels. The inner loop, controlled by `j', goes -through the lines within the row. As `j' goes from 0 to 4, `i+j' is -the `j'-th line in the row, and `i+j+5' is the entry next to it. The -output ends up looking something like this: +`line[7]', and so on. Two loops accomplish this. The outer loop, +controlled by `i', steps through every 10 lines of data; this is each +row of labels. The inner loop, controlled by `j', goes through the +lines within the row. As `j' goes from 0 to 4, `i+j' is the `j'-th +line in the row, and `i+j+5' is the entry next to it. The output ends +up looking something like this: line 1 line 6 line 2 line 7 @@ -17760,8 +18023,7 @@ not have been an even multiple of 20 labels in the data: Count++ } - END \ - { + END { printpage() } @@ -17773,19 +18035,19 @@ something done." File: gawk.info, Node: Word Sorting, Next: History Sorting, Prev: Labels Program, Up: Miscellaneous Programs -13.3.5 Generating Word-Usage Counts +11.3.5 Generating Word-Usage Counts ----------------------------------- 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 +certain words, in which case he or she might wish to find synonyms to substitute for words that appear too often. This node develops a program for counting words and presenting the frequency information in a useful format. At first glance, a program like this would seem to do the job: - # Print list of word frequencies + # wordfreq-first-try.awk --- print list of word frequencies { for (i = 1; i <= NF; i++) @@ -17807,9 +18069,9 @@ on real text files: * The `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. * Words are detected using the `awk' convention that fields are separated just by whitespace. Other characters in the input @@ -17841,6 +18103,10 @@ script. Here is the new version of the program: printf "%s\t%d\n", word, freq[word] } + The regexp `/[^[:alnum:]_[:blank:]]/' might have been written +`/[[:punct:]]/', but then underscores would also be removed, and we +want to keep them. + Assuming we have saved this program in a file named `wordfreq.awk', and that the data is in `file1', the following pipeline: @@ -17877,7 +18143,7 @@ operating system documentation for more information on how to use the File: gawk.info, Node: History Sorting, Next: Extract Program, Prev: Word Sorting, Up: Miscellaneous Programs -13.3.6 Removing Duplicates from Unsorted Text +11.3.6 Removing Duplicates from Unsorted Text --------------------------------------------- The `uniq' program (*note Uniq Program::), removes duplicate lines from @@ -17918,26 +18184,26 @@ information. For example, using the following `print' statement in the print data[lines[i]], lines[i] - This works because `data[$0]' is incremented each time a line is -seen. +This works because `data[$0]' is incremented each time a line is seen. File: gawk.info, Node: Extract Program, Next: Simple Sed, Prev: History Sorting, Up: Miscellaneous Programs -13.3.7 Extracting Programs from Texinfo Source Files +11.3.7 Extracting Programs from Texinfo Source Files ---------------------------------------------------- -The nodes *Note Library Functions::, and *Note Sample Programs::, are +The nodes *note Library Functions::, and *note Sample Programs::, are the top level nodes for a large number of `awk' programs. If you want -to experiment with these programs, it is tedious to have to type them -in by hand. Here we present a program that can extract parts of a -Texinfo input file into separate files. +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. -This Info file is written in Texinfo (http://texinfo.org), the GNU -project's document formatting language. A single Texinfo source file -can be used to produce both printed and online documentation. The -Texinfo language is described fully, starting with *note (Texinfo)Top:: -texinfo,Texinfo--The GNU Documentation Format. +This Info file is written in Texinfo +(http://www.gnu.org/software/texinfo/), the GNU project's document +formatting language. A single Texinfo source file can be used to +produce both printed documentation, with TeX, and online documentation. +(The Texinfo language is described fully, starting with *note +(Texinfo)Top:: texinfo,Texinfo--The GNU Documentation Format.) For our purposes, it is enough to know three things about Texinfo input files: @@ -17967,11 +18233,11 @@ are simply removed. `extract.awk' uses the `join()' library function (*note Join Function::). The example programs in the online Texinfo source for `GAWK: -Effective AWK Programming' (`gawk.texi') have all been bracketed inside -`file' and `endfile' lines. The `gawk' distribution uses a copy of -`extract.awk' to extract the sample programs and install many of them -in a standard directory where `gawk' can find them. The Texinfo file -looks something like this: +Effective AWK Programming' (`gawktexi.in') have all been bracketed +inside `file' and `endfile' lines. The `gawk' distribution uses a copy +of `extract.awk' to extract the sample programs and install many of +them in a standard directory where `gawk' can find them. The Texinfo +file looks something like this: ... This program has a @code{BEGIN} rule, @@ -17987,7 +18253,7 @@ looks something like this: @example @c file examples/messages.awk - END @{ print "Always avoid bored archeologists!" @} + END @{ print "Always avoid bored archaeologists!" @} @c end file @end example ... @@ -17999,15 +18265,13 @@ upper- and lowercase letters in the directives won't matter. given (`NF' is at least three) and also checking that the command exits with a zero exit status, signifying OK: - # extract.awk --- extract files and run programs - # from texinfo files + # extract.awk --- extract files and run programs from texinfo files 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 @@ -18016,7 +18280,7 @@ with a zero exit status, signifying OK: $2 = "" stat = system($0) if (stat != 0) { - e = (FILENAME ":" FNR) + e = ("extract: " FILENAME ":" FNR) e = (e ": warning: system returned " stat) print e > "/dev/stderr" } @@ -18046,16 +18310,16 @@ function (*note String Functions::). The `@' symbol is used as the separator character. Each element of `a' that is empty indicates two successive `@' symbols in the original line. For each two empty elements (`@@' in the original file), we have to add a single `@' -symbol back in.(1) +symbol back in. When the processing of the array is finished, `join()' is called -with the value of `SUBSEP', to rejoin the pieces back into a single -line. That line is then printed to the output file: +with the value of `SUBSEP' (*note Multidimensional::), to rejoin the +pieces back into a single line. That line is then printed to the +output file: - /^@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 } @@ -18106,8 +18370,8 @@ closing the open file: 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 } @@ -18116,29 +18380,24 @@ closing the open file: close(curfile) } - ---------- Footnotes ---------- - - (1) This program was written before `gawk' had the `gensub()' -function. Consider how you might use it to simplify the code. - File: gawk.info, Node: Simple Sed, Next: Igawk Program, Prev: Extract Program, Up: Miscellaneous Programs -13.3.8 A Simple Stream Editor +11.3.8 A Simple Stream Editor ----------------------------- The `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 `sed' is a complicated program in its own -right, its most common use is to perform global substitutions in the -middle of a pipeline: +pipeline of commands. Although `sed' is a complicated program in its +own right, its most common use is to perform global substitutions in +the middle of a pipeline: - command1 < orig.data | sed 's/old/new/g' | command2 > result + COMMAND1 < orig.data | sed 's/old/new/g' | COMMAND2 > result Here, `s/old/new/g' tells `sed' to look for the regexp `old' on each -input line and globally replace it with the text `new', i.e., all the -occurrences on a line. This is similar to `awk''s `gsub()' function +input line and globally replace it with the text `new' (i.e., all the +occurrences on a line). This is similar to `awk''s `gsub()' function (*note String Functions::). The following program, `awksed.awk', accepts at least two @@ -18199,16 +18458,16 @@ arguments and calling `usage()' if there is a problem. Then it sets (*note ARGC and ARGV::). The `usage()' function prints an error message and exits. Finally, -the single rule handles the printing scheme outlined above, using +the single rule handles the printing scheme outlined earlier, using `print' or `printf' as appropriate, depending upon the value of `RT'. File: gawk.info, Node: Igawk Program, Next: Anagram Program, Prev: Simple Sed, Up: Miscellaneous Programs -13.3.9 An Easy Way to Use Library Functions +11.3.9 An Easy Way to Use Library Functions ------------------------------------------- -In *Note Include Files::, we saw how `gawk' provides a built-in +In *note Include Files::, we saw how `gawk' provides a built-in file-inclusion capability. However, this is a `gawk' extension. This minor node provides the motivation for making file inclusion available for standard `awk', and shows how to do it using a combination of shell @@ -18237,10 +18496,10 @@ to be able to write programs in the following manner: The following program, `igawk.sh', provides this service. It simulates `gawk''s searching of the `AWKPATH' variable and also allows -"nested" includes; i.e., a file that is included with `@include' can -contain further `@include' statements. `igawk' makes an effort to only -include files once, so that nested includes don't accidentally include -a library function twice. +"nested" includes (i.e., a file that is included with `@include' can +contain further `@include' statements). `igawk' makes an effort to +only include files once, so that nested includes don't accidentally +include a library function twice. `igawk' should behave just like `gawk' externally. This means it should accept all of `gawk''s command-line arguments, including the @@ -18256,13 +18515,13 @@ language.(1) It works as follows: 2. For any arguments that do represent `awk' text, put the arguments into a shell variable that will be expanded. There are two cases: - a. Literal text, provided with `--source' or `--source='. This - text is just appended directly. + a. Literal text, provided with `-e' or `--source'. This text is + just appended directly. b. Source file names, provided with `-f'. We use a neat trick and append `@include FILENAME' to the shell variable's - contents. Since the file-inclusion program works the way - `gawk' does, this gets the text of the file included into the + contents. Because the file-inclusion program works the way + `gawk' does, this gets the text of the file included in the program at the correct point. 3. Run an `awk' program (naturally) over the shell variable's @@ -18297,10 +18556,10 @@ are several cases of interest: programming trick. Don't worry about it if you are not familiar with `sh'.) -`-v, -F' +`-v', `-F' These are saved and passed on to `gawk'. -`-f, --file, --file=, -Wfile=' +`-f', `--file', `--file=', `-Wfile=' The file name is appended to the shell variable `program' with an `@include' statement. The `expr' utility is used to remove the leading option part of the argument (e.g., `--file='). (Typical @@ -18309,10 +18568,10 @@ are several cases of interest: sequences in their arguments, possibly mangling the program text. Using `expr' avoids this problem.) -`--source, --source=, -Wsource=' +`--source', `--source=', `-Wsource=' The source text is appended to `program'. -`--version, -Wversion' +`--version', `-Wversion' `igawk' prints its version number, runs `gawk --version' to get the `gawk' version information, and then exits. @@ -18321,8 +18580,8 @@ arguments are supplied, then the first nonoption argument should be the `awk' program. If there are no command-line arguments left, `igawk' prints an error message and exits. Otherwise, the first argument is appended to `program'. In any case, after the arguments have been -processed, `program' contains the complete text of the original `awk' -program. +processed, the shell variable `program' contains the complete text of +the original `awk' program. The program is as follows: @@ -18458,12 +18717,12 @@ which represents the current directory: pathlist[i] = "." } - The stack is initialized with `ARGV[1]', which will be `/dev/stdin'. -The main loop comes next. Input lines are read in succession. Lines -that do not start with `@include' are printed verbatim. If the line -does start with `@include', the file name is in `$2'. `pathto()' is -called to generate the full path. If it cannot, then the program -prints an error message and continues. + The stack is initialized with `ARGV[1]', which will be +`"/dev/stdin"'. The main loop comes next. Input lines are read in +succession. Lines that do not start with `@include' are printed +verbatim. If the line does start with `@include', the file name is in +`$2'. `pathto()' is called to generate the full path. If it cannot, +then the program prints an error message and continues. The next thing to check is if the file is included already. The `processed' array is indexed by the full file name of each included @@ -18486,7 +18745,7 @@ zero, the program is done: } fpath = pathto($2) 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 } @@ -18522,13 +18781,13 @@ is saved as a single string, even if the results contain whitespace. It's done in these steps: 1. Run `gawk' with the `@include'-processing program (the value of - the `expand_prog' shell variable) on standard input. + the `expand_prog' shell variable) reading standard input. 2. Standard input is the contents of the user's program, from the - shell variable `program'. Its contents are fed to `gawk' via a - here document. + shell variable `program'. Feed its contents to `gawk' via a here + document. - 3. The results of this processing are saved in the shell variable + 3. Save the results of this processing in the shell variable `processed_program' by using command substitution. The last step is to call `gawk' with the expanded program, along @@ -18540,7 +18799,7 @@ supplied. The `eval' command is a shell construct that reruns the shell's parsing process. This keeps things properly quoted. - This version of `igawk' represents my fifth version of this program. + This version of `igawk' represents the fifth version of this program. There are four key simplifications that make the program work better: * Using `@include' even for the files named with `-f' makes building @@ -18568,27 +18827,7 @@ and it is frequently easier to do certain kinds of string and argument manipulation using the shell than it is in `awk'. Finally, `igawk' shows that it is not always necessary to add new -features to a program; they can often be layered on top. - - As an additional example of this, consider the idea of having two -files in a directory in the search path: - -`default.awk' - This file contains a set of default library functions, such as - `getopt()' and `assert()'. - -`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 `default.awk' to change with new `gawk' - releases, without requiring the system administrator to update it - each time by adding the local functions. - - One user suggested that `gawk' be modified to automatically read -these files upon startup. Instead, it would be very simple to modify -`igawk' to do this. Since `igawk' can process nested `@include' -directives, `default.awk' could simply contain `@include' statements -for the desired library functions. +features to a program; they can often be layered on top.(3) ---------- Footnotes ---------- @@ -18597,29 +18836,31 @@ book. We provide some minimal explanations, but see a good shell programming book if you wish to understand things in more depth. (2) On some very old versions of `awk', the test `getline junk < t' -can loop forever if the file exists but is empty. Caveat emptor. +can loop forever if the file exists but is empty. + + (3) `gawk' does `@include' processing itself in order to support the +use of `awk' programs as Web CGI scripts. File: gawk.info, Node: Anagram Program, Next: Signature Program, Prev: Igawk Program, Up: Miscellaneous Programs -13.3.10 Finding Anagrams From A Dictionary +11.3.10 Finding Anagrams from a Dictionary ------------------------------------------ An interesting programming challenge is to search for "anagrams" in a word list (such as `/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 `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 `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. +order: # anagram.awk --- An implementation of the anagram finding algorithm # from Jon Bentley's "Programming Pearls", 2nd edition. @@ -18656,8 +18897,8 @@ back together: } Finally, the `END' rule traverses the array and prints out the -anagram lists. It sends the output to the system `sort' command, since -otherwise the anagrams would appear in arbitrary order: +anagram lists. It sends the output to the system `sort' command +because otherwise the anagrams would appear in arbitrary order: END { sort = "sort" @@ -18692,7 +18933,7 @@ otherwise the anagrams would appear in arbitrary order: File: gawk.info, Node: Signature Program, Prev: Anagram Program, Up: Miscellaneous Programs -13.3.11 And Now For Something Completely Different +11.3.11 And Now for Something Completely Different -------------------------------------------------- The following program was written by Davide Brini and is published on @@ -18714,59 +18955,1753 @@ supplies the following copyright terms: 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}' - We leave it to you to determine what the program does. + 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 Info file.) + + +File: gawk.info, Node: Programs Summary, Next: Programs Exercises, Prev: Miscellaneous Programs, Up: Sample Programs + +11.4 Summary +============ + + * The programs provided in this major node continue on the theme + that reading programs is an excellent way to learn Good + Programming. + + * Using `#!' to make `awk' programs directly runnable makes them + easier to use. Otherwise, invoke the program using `awk -f ...'. + + * Reimplementing standard POSIX programs in `awk' is a pleasant + exercise; `awk''s expressive power lets you write such programs in + relatively few lines of code, yet they are functionally complete + and usable. + + * One of standard `awk''s weaknesses is working with individual + characters. The ability to use `split()' with the empty string as + the separator can considerably simplify such tasks. + + * The library functions from *note Library Functions::, proved their + usefulness for a number of real (if small) programs. + + * 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. + + + +File: gawk.info, Node: Programs Exercises, Prev: Programs Summary, Up: Sample Programs + +11.5 Exercises +============== + + 1. Rewrite `cut.awk' (*note Cut Program::) using `split()' with `""' + as the separator. + + 2. In *note Egrep Program::, we mentioned that `egrep -i' could be + simulated in versions of `awk' without `IGNORECASE' by using + `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. + + 3. The POSIX version of `id' takes options that control which + information is printed. Modify the `awk' version (*note Id + Program::) to accept the same arguments and perform in the same + way. + + 4. The `split.awk' program (*note 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 `ord()' and + `chr()'.) + + 5. In `uniq.awk' (*note Uniq Program::, the logic for choosing which + lines to print represents a "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."(1) 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. + + 6. Why can't the `wc.awk' program (*note Wc Program::) just use the + value of `FNR' in `endfile()'? Hint: Examine the code in *note + Filetrans Function::. + + 7. Manipulation of individual characters in the `translate' program + (*note Translate Program::) is painful using standard `awk' + functions. Given that `gawk' can split strings into individual + characters using `""' as the separator, how might you use this + feature to simplify the program? + + 8. The `extract.awk' program (*note Extract Program::) was written + before `gawk' had the `gensub()' function. Use it to simplify the + code. + + 9. Compare the performance of the `awksed.awk' program (*note Simple + Sed::) with the more straightforward: + + BEGIN { + pat = ARGV[1] + repl = ARGV[2] + ARGV[1] = ARGV[2] = "" + } + + { gsub(pat, repl); print } + + 10. What are the advantages and disadvantages of `awksed.awk' versus + the real `sed' utility? + + 11. In *note Igawk Program::, we mentioned that not trying to save the + line read with `getline' in the `pathto()' function when testing + for the file's accessibility for use with the main program + simplifies things considerably. What problem does this engender + though? + + 12. 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: + + `default.awk' + This file contains a set of default library functions, such + as `getopt()' and `assert()'. + + `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 `default.awk' to change with + new `gawk' releases, without requiring the system + administrator to update it each time by adding the local + functions. + + One user suggested that `gawk' be modified to automatically read + these files upon startup. Instead, it would be very simple to + modify `igawk' to do this. Since `igawk' can process nested + `@include' directives, `default.awk' could simply contain + `@include' statements for the desired library functions. Make + this change. + + 13. Modify `anagram.awk' (*note Anagram Program::), to avoid the use + of the external `sort' utility. + + + ---------- Footnotes ---------- + + (1) This is the definition returned from entering `define: state +machine' into Google. -File: gawk.info, Node: Debugger, Next: Language History, Prev: Sample Programs, Up: Top +File: gawk.info, Node: Advanced Features, Next: Internationalization, Prev: Sample Programs, Up: Top -14 `dgawk': The `awk' Debugger +12 Advanced Features of `gawk' ****************************** + Write documentation as if whoever reads it is a violent psychopath + who knows where you live. -- Steve English, as quoted by Peter + Langston + + This major node discusses advanced features in `gawk'. It's a bit +of a "grab bag" of items that are otherwise unrelated to each other. +First, a command-line option allows `gawk' to recognize nondecimal +numbers in input data, not just in `awk' programs. Then, `gawk''s +special features for sorting arrays are presented. Next, two-way I/O, +discussed briefly in earlier parts of this Info file, is described in +full detail, along with the basics of TCP/IP networking. Finally, +`gawk' can "profile" an `awk' program, making it possible to tune it +for performance. + + A number of advanced features require separate major nodes of their +own: + + * *note Internationalization::, discusses how to internationalize + your `awk' programs, so that they can speak multiple national + languages. + + * *note Debugger::, describes `gawk''s built-in command-line + debugger for debugging `awk' programs. + + * *note Arbitrary Precision Arithmetic::, describes how you can use + `gawk' to perform arbitrary-precision arithmetic. + + * *note Dynamic Extensions::, discusses the ability to dynamically + add new built-in functions to `gawk'. + +* 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 `gawk' for network programming. +* Profiling:: Profiling your `awk' programs. +* Advanced Features Summary:: Summary of advanced features. + + +File: gawk.info, Node: Nondecimal Data, Next: Array Sorting, Up: Advanced Features + +12.1 Allowing Nondecimal Input Data +=================================== + +If you run `gawk' with the `--non-decimal-data' option, you can have +nondecimal values in your input data: + + $ echo 0123 123 0x123 | + > gawk --non-decimal-data '{ printf "%d, %d, %d\n", $1, $2, $3 }' + -| 83, 123, 291 + + For this feature to work, write your program so that `gawk' treats +your data as numeric: + + $ echo 0123 123 0x123 | gawk '{ print $1, $2, $3 }' + -| 0123 123 0x123 + +The `print' statement treats its expressions as strings. Although the +fields can act as numbers when necessary, they are still strings, so +`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: + + $ echo 0123 123 0x123 | gawk --non-decimal-data ' + > { print $1, $2, $3 + > print $1 + 0, $2 + 0, $3 + 0 }' + -| 0123 123 0x123 + -| 83 123 291 + + 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. + + CAUTION: _Use of this option is not recommended._ It can break old + programs very badly. Instead, use the `strtonum()' function to + convert your data (*note 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 `gawk'. + + +File: gawk.info, Node: Array Sorting, Next: Two-way I/O, Prev: Nondecimal Data, Up: Advanced Features + +12.2 Controlling Array Traversal and Array Sorting +================================================== + +`gawk' lets you control the order in which a `for (i in array)' loop +traverses an array. + + In addition, two built-in functions, `asort()' and `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 `asort()' and `asorti()'. + + +File: gawk.info, Node: Controlling Array Traversal, Next: Array Sorting Functions, Up: Array Sorting + +12.2.1 Controlling Array Traversal +---------------------------------- + +By default, the order in which a `for (i in array)' loop scans an array +is not defined; it is generally based upon the internal implementation +of arrays inside `awk'. + + Often, though, it is desirable to be able to loop over the elements +in a particular order that you, the programmer, choose. `gawk' lets +you do this. + + *note Controlling Scanning::, describes how you can assign special, +predefined values to `PROCINFO["sorted_in"]' in order to control the +order in which `gawk' traverses an array during a `for' loop. + + In addition, the value of `PROCINFO["sorted_in"]' can be a function +name.(1) 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: + + function comp_func(i1, v1, i2, v2) + { + COMPARE ELEMENTS 1 AND 2 IN SOME FASHION + RETURN < 0; 0; OR > 0 + } + + Here, I1 and I2 are the indices, and V1 and V2 are the corresponding +values of the two elements being compared. Either V1 or V2, or both, +can be arrays if the array being traversed contains subarrays as values. +(*Note Arrays of Arrays::, for more information about subarrays.) The +three possible return values are interpreted as follows: + +`comp_func(i1, v1, i2, v2) < 0' + Index I1 comes before index I2 during loop traversal. + +`comp_func(i1, v1, i2, v2) == 0' + Indices I1 and I2 come together but the relative order with + respect to each other is undefined. + +`comp_func(i1, v1, i2, v2) > 0' + Index I1 comes after index I2 during loop traversal. + + Our first comparison function can be used to scan an array in +numerical order of the indices: + + function cmp_num_idx(i1, v1, i2, v2) + { + # numerical index comparison, ascending order + return (i1 - i2) + } + + Our second function traverses an array based on the string order of +the element values rather than by indices: + + 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) + } + + The third comparison function makes all numbers, and numeric strings +without any leading or trailing spaces, come out first during loop +traversal: + + 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) + } + + Here is a main program to demonstrate how `gawk' behaves using each +of the previous functions: + + 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 "" + } + } + + Here are the results when the program is run: + + $ gawk -f compdemo.awk + -| Sort function: cmp_num_idx Sort by numeric index + -| data[two] = 20 + -| data[one] = 10 Both strings are numerically zero + -| data[10] = one + -| data[20] = two + -| data[100] = 100 + -| + -| Sort function: cmp_str_val Sort by element values as strings + -| data[one] = 10 + -| data[100] = 100 String 100 is less than string 20 + -| data[two] = 20 + -| data[10] = one + -| data[20] = two + -| + -| Sort function: cmp_num_str_val Sort all numeric values before all strings + -| data[one] = 10 + -| data[two] = 20 + -| data[100] = 100 + -| data[10] = one + -| data[20] = two + + 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: + + # 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 "" + } + } + + 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: + + $ gawk -v POS=1 -F: -f sort.awk /etc/passwd + -| adm:x:3:4:adm:/var/adm:/sbin/nologin + -| apache:x:48:48:Apache:/var/www:/sbin/nologin + -| avahi:x:70:70:Avahi daemon:/:/sbin/nologin + ... + + 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: + + function cmp_randomize(i1, v1, i2, v2) + { + # random order (caution: this may never terminate!) + return (2 - 4 * rand()) + } + + 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: + + 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) + } + + 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 `IGNORECASE' (*note 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 `isarray()' function (*note Type Functions::), +to check for this, and choose a defined sorting order for subarrays. + + All sorting based on `PROCINFO["sorted_in"]' is disabled in POSIX +mode, because the `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 `awk' programs. For this reason, sorted array traversal is not +the default. + + ---------- Footnotes ---------- + + (1) This is why the predefined sorting orders start with an `@' +character, which cannot be part of an identifier. + + +File: gawk.info, Node: Array Sorting Functions, Prev: Controlling Array Traversal, Up: Array Sorting + +12.2.2 Sorting Array Values and Indices with `gawk' +--------------------------------------------------- + +In most `awk' implementations, sorting an array requires writing a +`sort()' function. This can be educational for exploring different +sorting algorithms, but usually that's not the point of the program. +`gawk' provides the built-in `asort()' and `asorti()' functions (*note +String Functions::) for sorting arrays. For example: + + POPULATE THE ARRAY data + n = asort(data) + for (i = 1; i <= n; i++) + DO SOMETHING WITH data[i] + + After the call to `asort()', the array `data' is indexed from 1 to +some number N, the total number of elements in `data'. (This count is +`asort()''s return value.) `data[1]' <= `data[2]' <= `data[3]', and so +on. The default comparison is based on the type of the elements (*note +Typing and Comparison::). All numeric values come before all string +values, which in turn come before all subarrays. + + An important side effect of calling `asort()' is that _the array's +original indices are irrevocably lost_. As this isn't always +desirable, `asort()' accepts a second argument: + + POPULATE THE ARRAY source + n = asort(source, dest) + for (i = 1; i <= n; i++) + DO SOMETHING WITH dest[i] + + In this case, `gawk' copies the `source' array into the `dest' array +and then sorts `dest', destroying its indices. However, the `source' +array is not affected. + + Often, what's needed is to sort on the values of the _indices_ +instead of the values of the elements. To do that, use the `asorti()' +function. The interface and behavior are identical to that of +`asort()', except that the index values are used for sorting, and +become the values of the result array: + + { source[$0] = some_func($0) } + + END { + n = asorti(source, dest) + for (i = 1; i <= n; i++) { + Work with sorted indices directly: + DO SOMETHING WITH dest[i] + ... + Access original array via sorted indices: + DO SOMETHING WITH source[dest[i]] + } + } + + So far, so good. Now it starts to get interesting. Both `asort()' +and `asorti()' accept a third string argument to control comparison of +array elements. When we introduced `asort()' and `asorti()' in *note +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 `PROCINFO["sorted_in"]', +this argument may be one of the predefined names that `gawk' provides +(*note Controlling Scanning::), or it may be the name of a user-defined +function (*note Controlling Array Traversal::). + + In the latter case, _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, `asort()' takes the _values_ in their +final order, and uses them to fill in the result array, whereas +`asorti()' takes the _indices_ in their final order, and uses them to +fill in the result array. + + NOTE: Copying array indices and elements isn't expensive in terms + of memory. Internally, `gawk' maintains "reference counts" to + data. For example, when `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. + + Because `IGNORECASE' affects string comparisons, the value of +`IGNORECASE' also affects sorting for both `asort()' and `asorti()'. +Note also that the locale's sorting order does _not_ come into play; +comparisons are based on character values only.(1) + + ---------- Footnotes ---------- + + (1) This is true because locale-based comparison occurs only when in +POSIX-compatibility mode, and because `asort()' and `asorti()' are +`gawk' extensions, they are not available in that case. + + +File: gawk.info, Node: Two-way I/O, Next: TCP/IP Networking, Prev: Array Sorting, Up: Advanced Features + +12.3 Two-Way Communications with Another Process +================================================ + +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: + + # Write the data for processing + tempfile = ("mydata." PROCINFO["pid"]) + while (NOT DONE WITH DATA) + print DATA | ("subprogram > " tempfile) + close("subprogram > " tempfile) + + # Read the results, remove tempfile when done + while ((getline newdata < tempfile) > 0) + PROCESS newdata APPROPRIATELY + close(tempfile) + system("rm " tempfile) + +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, `/tmp' will not do, as another user might happen to be +using a temporary file with the same name.(1) However, with `gawk', it +is possible to open a _two-way_ pipe to another process. The second +process is termed a "coprocess", as it runs in parallel with `gawk'. +The two-way connection is created using the `|&' operator (borrowed +from the Korn shell, `ksh'):(2) + + do { + print DATA |& "subprogram" + "subprogram" |& getline results + } while (DATA LEFT TO PROCESS) + close("subprogram") + + The first time an I/O operation is executed using the `|&' operator, +`gawk' creates a two-way pipeline to a child process that runs the +other program. Output created with `print' or `printf' is written to +the program's standard input, and output from the program's standard +output can be read by the `gawk' program using `getline'. As is the +case with processes started by `|', 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: + + * As the code inside `gawk' currently stands, the coprocess's + standard error goes to the same place that the parent `gawk''s + standard error goes. It is not possible to read the child's + standard error separately. + + * I/O buffering may be a problem. `gawk' automatically flushes all + output down the pipe to the coprocess. However, if the coprocess + does not flush its output, `gawk' may hang when doing a `getline' + in order to read the coprocess's results. This could lead to a + situation known as "deadlock", where each process is waiting for + the other one to do something. + + It is possible to close just one end of the two-way pipe to a +coprocess, by supplying a second argument to the `close()' function of +either `"to"' or `"from"' (*note Close Files And Pipes::). These +strings tell `gawk' to close the end of the pipe that sends data to the +coprocess or the end that reads from it, respectively. + + This is particularly necessary in order to use the system `sort' +utility as part of a coprocess; `sort' must read _all_ of its input +data before it can produce any output. The `sort' program does not +receive an end-of-file indication until `gawk' closes the write end of +the pipe. + + When you have finished writing data to the `sort' utility, you can +close the `"to"' end of the pipe, and then start reading sorted data +via `getline'. For 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) + } + + This program writes the letters of the alphabet in reverse order, one +per line, down the two-way pipe to `sort'. It then closes the write +end of the pipe, so that `sort' receives an end-of-file indication. +This causes `sort' to sort the data and write the sorted data back to +the `gawk' program. Once all of the data has been read, `gawk' +terminates the coprocess and exits. + + As a side note, the assignment `LC_ALL=C' in the `sort' command +ensures traditional Unix (ASCII) sorting from `sort'. This is not +strictly necessary here, but it's good to know how to do this. + + 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 `PROCINFO' array +(*note Auto-set::), like so: + + command = "sort -nr" # command, save in convenience variable + PROCINFO[command, "pty"] = 1 # update PROCINFO + print ... |& command # start two-way pipe + ... + +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, `gawk' automatically falls back to +using regular pipes. + + ---------- Footnotes ---------- + + (1) Michael Brennan suggests the use of `rand()' to generate unique +file names. This is a valid point; nevertheless, temporary files remain +more difficult to use than two-way pipes. + + (2) This is very different from the same operator in the C shell and +in Bash. + + +File: gawk.info, Node: TCP/IP Networking, Next: Profiling, Prev: Two-way I/O, Up: Advanced Features + +12.4 Using `gawk' for Network Programming +========================================= + + `EMRED': + 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. -- Mike O'Brien (aka Mr. Protocol) + +In addition to being able to open a two-way pipeline to a coprocess on +the same system (*note 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 _very long_ two-way pipeline to a +coprocess. The way `gawk' decides that you want to use TCP/IP +networking is by recognizing special file names that begin with one of +`/inet/', `/inet4/', or `/inet6/'. + + The full syntax of the special file name is +`/NET-TYPE/PROTOCOL/LOCAL-PORT/REMOTE-HOST/REMOTE-PORT'. The +components are: + +NET-TYPE + Specifies the kind of Internet connection to make. Use `/inet4/' + to force IPv4, and `/inet6/' to force IPv6. Plain `/inet/' (which + used to be the only option) uses the system default, most likely + IPv4. + +PROTOCOL + The protocol to use over IP. This must be either `tcp', or `udp', + for a TCP or UDP IP connection, respectively. TCP should be used + for most applications. + +LOCAL-PORT + The local TCP or UDP port number to use. Use a port number of `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 `smtp' or `http', in which case `gawk' + attempts to determine the predefined port number using the C + `getaddrinfo()' function. + +REMOTE-HOST + The IP address or fully qualified domain name of the Internet host + to which you want to connect. + +REMOTE-PORT + The TCP or UDP port number to use on the given REMOTE-HOST. + Again, use `0' if you don't care, or else a well-known service + name. + + NOTE: Failure in opening a two-way socket will result in a + non-fatal error being returned to the calling code. The value of + `ERRNO' indicates the error (*note Auto-set::). + + Consider the following very simple example: + + BEGIN { + Service = "/inet/tcp/0/localhost/daytime" + Service |& getline + print $0 + close(Service) + } + + This program reads the current date and time from the local system's +TCP `daytime' server. It then prints the results and closes the +connection. + + Because this topic is extensive, the use of `gawk' for TCP/IP +programming is documented separately. See *note (General +Introduction)Top:: gawkinet, TCP/IP Internetworking with `gawk', for a +much more complete introduction and discussion, as well as extensive +examples. + + +File: gawk.info, Node: Profiling, Next: Advanced Features Summary, Prev: TCP/IP Networking, Up: Advanced Features + +12.5 Profiling Your `awk' Programs +================================== + +You may produce execution traces of your `awk' programs. This is done +by passing the option `--profile' to `gawk'. When `gawk' has finished +running, it creates a profile of your program in a file named +`awkprof.out'. Because it is profiling, it also executes up to 45% +slower than `gawk' normally does. + + As shown in the following example, the `--profile' option can be +used to change the name of the file where `gawk' will write the profile: + + gawk --profile=myprog.prof -f myprog.awk data1 data2 + +In the preceding example, `gawk' places the profile in `myprog.prof' +instead of in `awkprof.out'. + + Here is a sample session showing a simple `awk' program, its input +data, and the results from running `gawk' with the `--profile' option. +First, the `awk' program: + + 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!" + } + + Following is the input data: + + foo + bar + baz + foo + junk + + Here is the `awkprof.out' that results from running the `gawk' +profiler on this program and data. (This example also illustrates that +`awk' programmers sometimes get up very early in the morning to work.) + + # 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!" + } + + This example illustrates many of the basic features of profiling +output. They are as follows: + + * The program is printed in the order `BEGIN' rules, `BEGINFILE' + rules, pattern/action rules, `ENDFILE' rules, `END' rules and + functions, listed alphabetically. Multiple `BEGIN' and `END' + rules retain their separate identities, as do multiple `BEGINFILE' + and `ENDFILE' rules. + + * Pattern-action rules have two counts. The first count, to the + left of the rule, shows how many times the rule's pattern was + _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 _executed_. The difference between the two indicates how many + times the rule's pattern evaluated to false. + + * Similarly, the count for an `if'-`else' statement shows how many + times the condition was tested. To the right of the opening left + brace for the `if''s body is a count showing how many times the + condition was true. The count for the `else' indicates how many + times the test failed. + + * The count for a loop header (such as `for' or `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.) + + * For user-defined functions, the count next to the `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. + + * The layout uses "K&R" style with TABs. Braces are used + everywhere, even when the body of an `if', `else', or loop is only + a single statement. + + * Parentheses are used only where needed, as indicated by the + structure of the program and the precedence rules. For example, + `(3 + 5) * 4' means add three and five, then multiply the total by + four. However, `3 + 5 * 4' has no parentheses, and means `3 + (5 + * 4)'. + + * Parentheses are used around the arguments to `print' and `printf' + only when the `print' or `printf' statement is followed by a + redirection. Similarly, if the target of a redirection isn't a + scalar, it gets parenthesized. + + * `gawk' supplies leading comments in front of the `BEGIN' and `END' + rules, the `BEGINFILE' and `ENDFILE' rules, the pattern/action + rules, and the functions. + + + The profiled version of your program may not look exactly like what +you typed when you wrote it. This is because `gawk' creates the +profiled version by "pretty printing" its internal representation of +the program. The advantage to this is that `gawk' can produce a +standard representation. Also, things such as: + + /foo/ + +come out as: + + /foo/ { + print $0 + } + +which is correct, but possibly unexpected. + + Besides creating profiles when a program has completed, `gawk' can +produce a profile while it is running. This is useful if your `awk' +program goes into an infinite loop and you want to see what has been +executed. To use this feature, run `gawk' with the `--profile' option +in the background: + + $ gawk --profile -f myprog & + [1] 13992 + +The shell prints a job number and process ID number; in this case, +13992. Use the `kill' command to send the `USR1' signal to `gawk': + + $ kill -USR1 13992 + +As usual, the profiled version of the program is written to +`awkprof.out', or to a different file if one was specified with the +`--profile' option. + + Along with the regular profile, as shown earlier, the profile file +includes a trace of any active functions: + + # Function Call Stack: + + # 3. baz + # 2. bar + # 1. foo + # -- main -- + + You may send `gawk' the `USR1' signal as many times as you like. +Each time, the profile and function call trace are appended to the +output profile file. + + If you use the `HUP' signal instead of the `USR1' signal, `gawk' +produces the profile and the function call trace and then exits. + + When `gawk' runs on MS-Windows systems, it uses the `INT' and `QUIT' +signals for producing the profile and, in the case of the `INT' signal, +`gawk' exits. This is because these systems don't support the `kill' +command, so the only signals you can deliver to a program are those +generated by the keyboard. The `INT' signal is generated by the +`Ctrl-<C>' or `Ctrl-<BREAK>' key, while the `QUIT' signal is generated +by the `Ctrl-<\>' key. + + Finally, `gawk' also accepts another option, `--pretty-print'. When +called this way, `gawk' "pretty prints" the program into `awkprof.out', +without any execution counts. + + NOTE: Once upon a time, the `--pretty-print' option would also run + your program. This is is no longer the case. + + 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 _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. + + +File: gawk.info, Node: Advanced Features Summary, Prev: Profiling, Up: Advanced Features + +12.6 Summary +============ + + * The `--non-decimal-data' option causes `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 + `strtonum()' is preferable. Note that this option may disappear + in a future version of `gawk'. + + * You can take over complete control of sorting in `for (INDX in + ARRAY)' array traversal by setting `PROCINFO["sorted_in"]' to the + name of a user-defined function that does the comparison of array + elements based on index and value. + + * Similarly, you can supply the name of a user-defined comparison + function as the third argument to either `asort()' or `asorti()' + to control how those functions sort arrays. Or you may provide one + of the predefined control strings that work for + `PROCINFO["sorted_in"]'. + + * You can use the `|&' operator to create a two-way pipe to a + coprocess. You read from the coprocess with `getline' and write + to it with `print' or `printf'. Use `close()' to close off the + coprocess completely, or optionally, close off one side of the + two-way communications. + + * By using special file names with the `|&' operator, you can open a + TCP/IP (or UDP/IP) connection to remote hosts in the Internet. + `gawk' supports both IPv4 and IPv6. + + * 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 + `USR1' signal while profiling causes `gawk' to dump the profile + and keep going, including a function call stack. + + * You can also just "pretty print" the program. This currently also + runs the program, but that will change in the next major release. + + + +File: gawk.info, Node: Internationalization, Next: Debugger, Prev: Advanced Features, Up: Top + +13 Internationalization with `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. + + For many years, the ability to provide internationalization was +largely restricted to programs written in C and C++. This major node +describes the underlying library `gawk' uses for internationalization, +as well as how `gawk' makes internationalization features available at +the `awk' program level. Having internationalization available at the +`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 `gettext' works. +* Programmer i18n:: Features for the programmer. +* Translator i18n:: Features for the translator. +* I18N Example:: A simple i18n example. +* Gawk I18N:: `gawk' is also internationalized. +* I18N Summary:: Summary of I18N stuff. + + +File: gawk.info, Node: I18N and L10N, Next: Explaining gettext, Up: Internationalization + +13.1 Internationalization and Localization +========================================== + +"Internationalization" means writing (or modifying) a program once, in +such a way that it can use multiple languages without requiring further +source-code changes. "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. + + +File: gawk.info, Node: Explaining gettext, Next: Programmer i18n, Prev: I18N and L10N, Up: Internationalization + +13.2 GNU `gettext' +================== + +`gawk' uses GNU `gettext' to provide its internationalization features. +The facilities in GNU `gettext' focus on messages; strings printed by a +program, either directly or via formatting with `printf' or +`sprintf()'.(1) + + When using GNU `gettext', each application has its own "text +domain". This is a unique name, such as `kpilot' or `gawk', that +identifies the application. A complete application may have multiple +components--programs written in C or C++, as well as scripts written in +`sh' or `awk'. All of the components use the same text domain. + + To make the discussion concrete, assume we're writing an application +named `guide'. Internationalization consists of the following steps, +in this order: + + 1. The programmer reviews the source for all of `guide''s components + and marks each string that is a candidate for translation. For + example, `"`-F': option required"' is a good candidate for + translation. A table with strings of option names is not (e.g., + `gawk''s `--profile' option should remain the same, no matter what + the local language). + + 2. The programmer indicates the application's text domain (`"guide"') + to the `gettext' library, by calling the `textdomain()' function. + + 3. Messages from the application are extracted from the source code + and collected into a portable object template 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. + + 4. For each language with a translator, `guide.pot' is copied to a + portable object file (`.po') and translations are created and + shipped with the application. For example, there might be a + `fr.po' for a French translation. + + 5. Each language's `.po' file is converted into a binary message + object (`.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. + + 6. When `guide' is built and installed, the binary translation files + are installed in a standard place. + + 7. For testing and development, it is possible to tell `gettext' to + use `.gmo' files in a different directory than the standard one by + using the `bindtextdomain()' function. + + 8. At runtime, `guide' looks up each string via a call to + `gettext()'. The returned string is the translated string if + available, or the original string if not. + + 9. 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. + + In C (or C++), the string marking and dynamic translation lookup are +accomplished by wrapping each string in a call to `gettext()': + + printf("%s", gettext("Don't Panic!\n")); + + The tools that extract messages from source code pull out all +strings enclosed in calls to `gettext()'. + + The GNU `gettext' developers, recognizing that typing `gettext(...)' +over and over again is both painful and ugly to look at, use the macro +`_' (an underscore) to make things easier: + + /* In the standard header file: */ + #define _(str) gettext(str) + + /* In the program text: */ + printf("%s", _("Don't Panic!\n")); + +This reduces the typing overhead to just three extra characters per +string and is considerably easier to read as well. + + There are locale "categories" for different types of locale-related +information. The defined locale categories that `gettext' knows about +are: + +`LC_MESSAGES' + Text messages. This is the default category for `gettext' + operations, but it is possible to supply a different one + explicitly, if necessary. (It is almost never necessary to supply + a different category.) + +`LC_COLLATE' + Text-collation information (i.e., how different characters and/or + groups of characters sort in a given language). + +`LC_CTYPE' + Character-type information (alphabetic, digit, upper- or + lowercase, and so on) as well as character encoding. This + information is accessed via the POSIX character classes in regular + expressions, such as `/[[:alnum:]]/' (*note Bracket Expressions::). + +`LC_MONETARY' + Monetary information, such as the currency symbol, and whether the + symbol goes before or after a number. + +`LC_NUMERIC' + Numeric information, such as which characters to use for the + decimal point and the thousands separator.(2) + +`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. + +`LC_ALL' + All of the above. (Not too useful in the context of `gettext'.) + + ---------- Footnotes ---------- + + (1) For some operating systems, the `gawk' port doesn't support GNU +`gettext'. Therefore, these features are not available if you are +using one of those operating systems. Sorry. + + (2) 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. + + +File: gawk.info, Node: Programmer i18n, Next: Translator i18n, Prev: Explaining gettext, Up: Internationalization + +13.3 Internationalizing `awk' Programs +====================================== + +`gawk' provides the following variables and functions for +internationalization: + +`TEXTDOMAIN' + This variable indicates the application's text domain. For + compatibility with GNU `gettext', the default value is + `"messages"'. + +`_"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. + +``dcgettext(STRING' [`,' DOMAIN [`,' CATEGORY]]`)'' + Return the translation of STRING in text domain DOMAIN for locale + category CATEGORY. The default value for DOMAIN is the current + value of `TEXTDOMAIN'. The default value for CATEGORY is + `"LC_MESSAGES"'. + + If you supply a value for CATEGORY, it must be a string equal to + one of the known locale categories described in *note Explaining + gettext::. You must also supply a text domain. Use `TEXTDOMAIN' + if you want to use the current domain. + + CAUTION: The order of arguments to the `awk' version of the + `dcgettext()' function is purposely different from the order + for the C version. The `awk' version's order was chosen to + be simple and to allow for reasonable `awk'-style default + arguments. + +``dcngettext(STRING1, STRING2, NUMBER' [`,' DOMAIN [`,' CATEGORY]]`)'' + Return the plural form used for NUMBER of the translation of + STRING1 and STRING2 in text domain DOMAIN for locale category + CATEGORY. STRING1 is the English singular variant of a message, + and STRING2 is the English plural variant of the same message. + The default value for DOMAIN is the current value of `TEXTDOMAIN'. + The default value for CATEGORY is `"LC_MESSAGES"'. + + The same remarks about argument order as for the `dcgettext()' + function apply. + +``bindtextdomain(DIRECTORY' [`,' DOMAIN ]`)'' + Change the directory in which `gettext' looks for `.gmo' files, in + case they will not or cannot be placed in the standard locations + (e.g., during testing). Return the directory in which DOMAIN is + "bound." + + The default DOMAIN is the value of `TEXTDOMAIN'. If DIRECTORY is + the null string (`""'), then `bindtextdomain()' returns the + current binding for the given DOMAIN. + + To use these facilities in your `awk' program, follow the steps +outlined in *note Explaining gettext::, like so: + + 1. Set the variable `TEXTDOMAIN' to the text domain of your program. + This is best done in a `BEGIN' rule (*note BEGIN/END::), or it can + also be done via the `-v' command-line option (*note Options::): + + BEGIN { + TEXTDOMAIN = "guide" + ... + } + + 2. Mark all translatable strings with a leading underscore (`_') + character. It _must_ be adjacent to the opening quote of the + string. For example: + + print _"hello, world" + x = _"you goofed" + printf(_"Number of users is %d\n", nusers) + + 3. If you are creating strings dynamically, you can still translate + them, using the `dcgettext()' built-in function:(1) + + if (groggy) + message = dcgettext("%d customers disturbing me\n", "adminprog") + else + message = dcgettext("enjoying %d customers\n", "adminprog") + printf(message, ncustomers) + + Here, the call to `dcgettext()' supplies a different text domain + (`"adminprog"') in which to find the message, but it uses the + default `"LC_MESSAGES"' category. + + The previous example only works if `ncustomers' is greater than + one. This example would be better done with `dcngettext()': + + 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) + + 4. During development, you might want to put the `.gmo' file in a + private directory for testing. This is done with the + `bindtextdomain()' built-in function: + + 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") + } + ... + } + + + *Note I18N Example::, for an example program showing the steps to +create and use translations from `awk'. + + ---------- Footnotes ---------- + + (1) Thanks to Bruno Haible for this example. + + +File: gawk.info, Node: Translator i18n, Next: I18N Example, Prev: Programmer i18n, Up: Internationalization + +13.4 Translating `awk' Programs +=============================== + +Once a program's translatable strings have been marked, they must be +extracted to create the initial `.pot' file. As part of translation, +it is often helpful to rearrange the order in which arguments to +`printf' are output. + + `gawk''s `--gen-pot' command-line option extracts the messages and +is discussed next. After that, `printf''s ability to rearrange the +order for `printf' arguments at runtime is covered. + +* Menu: + +* String Extraction:: Extracting marked strings. +* Printf Ordering:: Rearranging `printf' arguments. +* I18N Portability:: `awk'-level portability issues. + + +File: gawk.info, Node: String Extraction, Next: Printf Ordering, Up: Translator i18n + +13.4.1 Extracting Marked Strings +-------------------------------- + +Once your `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 `--gen-pot' command-line +option to create the initial `.pot' file: + + gawk --gen-pot -f guide.awk > guide.pot + + When run with `--gen-pot', `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 `gettext' Portable Object file. +Also included in the output are any constant strings that appear as the +first argument to `dcgettext()' or as the first and second argument to +`dcngettext()'.(1) You should distribute the generated `.pot' file with +your `awk' program; translators will eventually use it to provide you +translations that you can also then distribute. *Note I18N Example::, +for the full list of steps to go through to create and test +translations for `guide'. + + ---------- Footnotes ---------- + + (1) The `xgettext' utility that comes with GNU `gettext' can handle +`.awk' files. + + +File: gawk.info, Node: Printf Ordering, Next: I18N Portability, Prev: String Extraction, Up: Translator i18n + +13.4.2 Rearranging `printf' Arguments +------------------------------------- + +Format strings for `printf' and `sprintf()' (*note Printf::) present a +special problem for translation. Consider the following:(1) + + printf(_"String `%s' has %d characters\n", + string, length(string))) + + A possible German translation for this might be: + + "%d Zeichen lang ist die Zeichenkette `%s'\n" + + The problem should be obvious: the order of the format +specifications is different from the original! Even though `gettext()' +can return the translated string at runtime, it cannot change the +argument order in the call to `printf'. + + To solve this problem, `printf' format specifiers may have an +additional optional element, which we call a "positional specifier". +For example: + + "%2$d Zeichen lang ist die Zeichenkette `%1$s'\n" + + Here, the positional specifier consists of an integer count, which +indicates which argument to use, and a `$'. Counts are one-based, and +the format string itself is _not_ included. Thus, in the following +example, `string' is the first argument and `length(string)' is the +second: + + $ gawk 'BEGIN { + > string = "Don\47t Panic" + > printf "%2$d characters live in \"%1$s\"\n", + > string, length(string) + > }' + -| 11 characters live in "Don't Panic" + + 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: + + $ gawk 'BEGIN { + > printf("%*.*s\n", 10, 20, "hello") + > printf("%3$*2$.*1$s\n", 20, 10, "hello") + > }' + -| hello + -| hello + + NOTE: When using `*' with a positional specifier, the `*' comes + first, then the integer position, and then the `$'. This is + somewhat counterintuitive. + + `gawk' does not allow you to mix regular format specifiers and those +with positional specifiers in the same string: + + $ gawk 'BEGIN { printf "%d %3$s\n", 1, 2, "hi" }' + error--> gawk: cmd. line:1: fatal: must use `count$' on all formats or none + + NOTE: There are some pathological cases that `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 `gawk' doesn't + detect it. + + Although positional specifiers can be used directly in `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. + + ---------- Footnotes ---------- + + (1) This example is borrowed from the GNU `gettext' manual. + + +File: gawk.info, Node: I18N Portability, Prev: Printf Ordering, Up: Translator i18n + +13.4.3 `awk' Portability Issues +------------------------------- + +`gawk''s internationalization features were purposely chosen to have as +little impact as possible on the portability of `awk' programs that use +them to other versions of `awk'. Consider this program: + + BEGIN { + TEXTDOMAIN = "guide" + if (Test_Guide) # set with -v + bindtextdomain("/test/guide/messages") + print _"don't panic!" + } + +As written, it won't work on other versions of `awk'. However, it is +actually almost portable, requiring very little change: + + * Assignments to `TEXTDOMAIN' won't have any effect, because + `TEXTDOMAIN' is not special in other `awk' implementations. + + * Non-GNU versions of `awk' treat marked strings as the + concatenation of a variable named `_' with the string following + it.(1) Typically, the variable `_' has the null string (`""') as + its value, leaving the original string constant as the result. + + * By defining "dummy" functions to replace `dcgettext()', + `dcngettext()' and `bindtextdomain()', the `awk' program can be + made to run, but all the messages are output in the original + language. For example: + + 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) + } + + * The use of positional specifications in `printf' or `sprintf()' is + _not_ portable. To support `gettext()' at the C level, many + systems' C versions of `sprintf()' do support positional + specifiers. But it works only if enough arguments are supplied in + the function call. Many versions of `awk' pass `printf' formats + and arguments unchanged to the underlying C library version of + `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 _translated_ format strings, and because non-GNU `awk's + never retrieve the translated string, this should not be a problem + in practice. + + ---------- Footnotes ---------- + + (1) This is good fodder for an "Obfuscated `awk'" contest. + + +File: gawk.info, Node: I18N Example, Next: Gawk I18N, Prev: Translator i18n, Up: Internationalization + +13.5 A Simple Internationalization Example +========================================== + +Now let's look at a step-by-step example of how to internationalize and +localize a simple `awk' program, using `guide.awk' as our original +source: + + BEGIN { + TEXTDOMAIN = "guide" + bindtextdomain(".") # for testing + print _"Don't Panic" + print _"The Answer Is", 42 + print "Pardon me, Zaphod who?" + } + +Run `gawk --gen-pot' to create the `.pot' file: + + $ gawk --gen-pot -f guide.awk > guide.pot + +This produces: + + #: guide.awk:4 + msgid "Don't Panic" + msgstr "" + + #: guide.awk:5 + msgid "The Answer Is" + msgstr "" + + This original portable object template file is saved and reused for +each language into which the application is translated. The `msgid' is +the original string and the `msgstr' is the translation. + + NOTE: Strings not marked with a leading underscore do not appear + in the `guide.pot' file. + + Next, the messages must be translated. Here is a translation to a +hypothetical dialect of English, called "Mellow":(1) + + $ cp guide.pot guide-mellow.po + ADD TRANSLATIONS TO guide-mellow.po ... + +Following are the translations: + + #: guide.awk:4 + msgid "Don't Panic" + msgstr "Hey man, relax!" + + #: guide.awk:5 + msgid "The Answer Is" + msgstr "Like, the scoop is" + + The next step is to make the directory to hold the binary message +object file and then to create the `guide.mo' file. We pretend that +our file is to be used in the `en_US.UTF-8' locale, because we have to +use a locale name known to the C `gettext' routines. The directory +layout shown here is standard for GNU `gettext' on GNU/Linux systems. +Other versions of `gettext' may use a different layout: + + $ mkdir en_US.UTF-8 en_US.UTF-8/LC_MESSAGES + + The `msgfmt' utility does the conversion from human-readable `.po' +file to machine-readable `.mo' file. By default, `msgfmt' creates a +file named `messages'. This file must be renamed and placed in the +proper directory (using the `-o' option) so that `gawk' can find it: + + $ msgfmt guide-mellow.po -o en_US.UTF-8/LC_MESSAGES/guide.mo + + Finally, we run the program to test it: + + $ gawk -f guide.awk + -| Hey man, relax! + -| Like, the scoop is 42 + -| Pardon me, Zaphod who? + + If the three replacement functions for `dcgettext()', `dcngettext()', +and `bindtextdomain()' (*note I18N Portability::) are in a file named +`libintl.awk', then we can run `guide.awk' unchanged as follows: + + $ gawk --posix -f guide.awk -f libintl.awk + -| Don't Panic + -| The Answer Is 42 + -| Pardon me, Zaphod who? + + ---------- Footnotes ---------- + + (1) Perhaps it would be better if it were called "Hippy." Ah, well. + + +File: gawk.info, Node: Gawk I18N, Next: I18N Summary, Prev: I18N Example, Up: Internationalization + +13.6 `gawk' Can Speak Your Language +=================================== + +`gawk' itself has been internationalized using the GNU `gettext' +package. (GNU `gettext' is described in complete detail in *note (GNU +`gettext' utilities)Top:: gettext, GNU gettext tools.) As of this +writing, the latest version of GNU `gettext' is version 0.19.4 +(ftp://ftp.gnu.org/gnu/gettext/gettext-0.19.4.tar.gz). + + If a translation of `gawk''s messages exists, then `gawk' produces +usage messages, warnings, and fatal errors in the local language. + + +File: gawk.info, Node: I18N Summary, Prev: Gawk I18N, Up: Internationalization + +13.7 Summary +============ + + * 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. + + * `gawk' uses GNU `gettext' to let you internationalize and localize + `awk' programs. A program's text domain identifies the program + for grouping all messages and other data together. + + * You mark a program's strings for translation by preceding them with + an underscore. Once that is done, the strings are extracted into a + `.pot' file. This file is copied for each language into a `.po' + file, and the `.po' files are compiled into `.gmo' files for use + at runtime. + + * You can use position specifications with `sprintf()' and `printf' + to rearrange the placement of argument values in formatted strings + and output. This is useful for the translations of format control + strings. + + * The internationalization features have been designed so that they + can be easily worked around in a standard `awk'. + + * `gawk' itself has been internationalized and ships with a number + of translations for its messages. + + + +File: gawk.info, Node: Debugger, Next: Arbitrary Precision Arithmetic, Prev: Internationalization, Up: Top + +14 Debugging `awk' Programs +*************************** + 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 `awk' is no exception. - The `dgawk' debugger is purposely modeled after the GNU Debugger + The `gawk' debugger is purposely modeled after the GNU Debugger (GDB) (http://www.gnu.org/software/gdb/) command-line debugger. If you -are familiar with GDB, learning `dgawk' is easy. +are familiar with GDB, learning how to use `gawk' for debugging your +program is easy. * Menu: -* Debugging:: Introduction to `dgawk'. -* Sample dgawk session:: Sample `dgawk' session. -* List of Debugger Commands:: Main `dgawk' Commands. -* Readline Support:: Readline Support. -* Dgawk Limitations:: Limitations and future plans. +* Debugging:: Introduction to `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. -File: gawk.info, Node: Debugging, Next: Sample dgawk session, Up: Debugger +File: gawk.info, Node: Debugging, Next: Sample Debugging Session, Up: Debugger -14.1 Introduction to `dgawk' -============================ +14.1 Introduction to the `gawk' Debugger +======================================== This minor node introduces debugging in general and begins the discussion of debugging in `gawk'. * Menu: -* Debugging Concepts:: Debugging In General. +* Debugging Concepts:: Debugging in General. * Debugging Terms:: Additional Debugging Concepts. * Awk Debugging:: Awk Debugging. File: gawk.info, Node: Debugging Concepts, Next: Debugging Terms, Up: Debugging -14.1.1 Debugging In General +14.1.1 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 `awk' +ahead to the next section on the specific features of the `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 "feature." (Sometimes, we humans have a hard time with this + 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: @@ -18782,7 +20717,7 @@ you can expect at least the following: * 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.) @@ -18797,15 +20732,14 @@ functional program that you or someone else wrote). File: gawk.info, Node: Debugging Terms, Next: Awk Debugging, Prev: Debugging Concepts, Up: Debugging -14.1.2 Additional Debugging Concepts ------------------------------------- +14.1.2 Debugging Concepts +------------------------- Before diving in to the details, we need to introduce several important -concepts that apply to just about all debuggers, including `dgawk'. -The following list defines terms used throughout the rest of this -major node. +concepts that apply to just about all debuggers. The following list +defines terms used throughout the rest of this major node: -"Stack Frame" +"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 @@ -18821,11 +20755,11 @@ major node. needed to manage the call stack. This data area is termed a "stack frame". - `gawk' also follows this model, and `dgawk' 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). + `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). "Breakpoint" During debugging, you often wish to let the program run until it @@ -18841,11 +20775,11 @@ major node. 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 _data value_ is changed. - This is useful, since 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, and usually find - the errant code quite quickly. + 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, and usually find the errant + code quite quickly. File: gawk.info, Node: Awk Debugging, Prev: Debugging Terms, Up: Debugging @@ -18856,68 +20790,71 @@ File: gawk.info, Node: Awk Debugging, Prev: Debugging Terms, Up: Debugging Debugging an `awk' program has some specific aspects that are not shared with other programming languages. - First of all, the fact that `awk' programs usually take input -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 -`awk' rule is treated almost like a function call, with its own -specific block of instructions. + First of all, the fact that `awk' programs usually take input 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 `awk' rule +is treated almost like a function call, with its own specific block of +instructions. - In addition, since `awk' is by design a very concise language, it is -easy to lose sight of everything that is going on "inside" each line of -`awk' code. The debugger provides the opportunity to look at the + In addition, because `awk' is by design a very concise language, it +is easy to lose sight of everything that is going on "inside" each line +of `awk' code. The debugger provides the opportunity to look at the individual primitive instructions carried out by the higher-level `awk' commands. -File: gawk.info, Node: Sample dgawk session, Next: List of Debugger Commands, Prev: Debugging, Up: Debugger +File: gawk.info, Node: Sample Debugging Session, Next: List of Debugger Commands, Prev: Debugging, Up: Debugger -14.2 Sample `dgawk' session -=========================== +14.2 Sample Debugging Session +============================= -In order to illustrate the use of `dgawk', let's look at a sample -debugging session. We will use the `awk' implementation of the POSIX -`uniq' command described earlier (*note Uniq Program::) as our example. +In order to illustrate the use of `gawk' as a debugger, let's look at a +sample debugging session. We will use the `awk' implementation of the +POSIX `uniq' command described earlier (*note Uniq Program::) as our +example. * Menu: -* dgawk invocation:: `dgawk' Invocation. -* Finding The Bug:: Finding The Bug. +* Debugger Invocation:: How to Start the Debugger. +* Finding The Bug:: Finding the Bug. -File: gawk.info, Node: dgawk invocation, Next: Finding The Bug, Up: Sample dgawk session +File: gawk.info, Node: Debugger Invocation, Next: Finding The Bug, Up: Sample Debugging Session -14.2.1 `dgawk' Invocation -------------------------- +14.2.1 How to Start the Debugger +-------------------------------- -Starting `dgawk' is exactly like running `awk'. The file(s) containing -the program and any supporting code are given on the command line as -arguments to one or more `-f' options. (`dgawk' is not designed to -debug command-line programs, only programs contained in files.) In our -case, we call `dgawk' like this: +Starting the debugger is almost exactly like running `gawk' normally, +except you have to pass an additional option `--debug', or the +corresponding short option `-D'. The file(s) containing the program +and any supporting code are given on the command line as arguments to +one or more `-f' options. (`gawk' is not designed to debug command-line +programs, only programs contained in files.) In our case, we invoke +the debugger like this: - $ dgawk -f getopt.awk -f join.awk -f uniq.awk inputfile + $ gawk -D -f getopt.awk -f join.awk -f uniq.awk -1 inputfile where both `getopt.awk' and `uniq.awk' are in `$AWKPATH'. (Experienced users of GDB or similar debuggers should note that this syntax is -slightly different from what they are used to. With `dgawk', the -arguments for running the program are given in the command line to the -debugger rather than as part of the `run' command at the debugger -prompt.) +slightly different from what they are used to. With the `gawk' +debugger, you give the arguments for running the program in the command +line to the debugger rather than as part of the `run' command at the +debugger prompt.) The `-1' is an option to `uniq.awk'. Instead of immediately running the program on `inputfile', as `gawk' -would ordinarily do, `dgawk' merely loads all the program source files, -compiles them internally, and then gives us a prompt: +would ordinarily do, the debugger merely loads all the program source +files, compiles them internally, and then gives us a prompt: - dgawk> + gawk> from which we can issue commands to the debugger. At this point, no code has been executed. -File: gawk.info, Node: Finding The Bug, Prev: dgawk invocation, Up: Sample dgawk session +File: gawk.info, Node: Finding The Bug, Prev: Debugger Invocation, Up: Sample Debugging Session -14.2.2 Finding The Bug +14.2.2 Finding the Bug ---------------------- Let's say that we are having a problem using (a faulty version of) @@ -18947,62 +20884,62 @@ for a breakpoint in `uniq.awk' is at the beginning of the function `are_equal()', which compares the current line with the previous one. To set the breakpoint, use the `b' (breakpoint) command: - dgawk> b are_equal - -| Breakpoint 1 set at file `awklib/eg/prog/uniq.awk', line 64 + gawk> b are_equal + -| Breakpoint 1 set at file `awklib/eg/prog/uniq.awk', line 63 The debugger tells us the file and line number where the breakpoint is. Now type `r' or `run' and the program runs until it hits the breakpoint for the first time: - dgawk> r + gawk> r -| Starting program: -| Stopping in Rule ... -| Breakpoint 1, are_equal(n, m, clast, cline, alast, aline) - at `awklib/eg/prog/uniq.awk':64 - -| 64 if (fcount == 0 && charcount == 0) - dgawk> + at `awklib/eg/prog/uniq.awk':63 + -| 63 if (fcount == 0 && charcount == 0) + gawk> 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 `bt' -(short for "backtrace"), and `dgawk' responds with a listing of the -current stack frames: +(short for "backtrace"), and the debugger responds with a listing of +the current stack frames: - dgawk> bt + gawk> bt -| #0 are_equal(n, m, clast, cline, alast, aline) - at `awklib/eg/prog/uniq.awk':69 - -| #1 in main() at `awklib/eg/prog/uniq.awk':89 + at `awklib/eg/prog/uniq.awk':68 + -| #1 in main() at `awklib/eg/prog/uniq.awk':88 This tells us that `are_equal()' was called by the main program at -line 89 of `uniq.awk'. (This is not a big surprise, since this is the -only call to `are_equal()' in the program, but in more complex +line 88 of `uniq.awk'. (This is not a big surprise, because this is +the only call to `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.) Now that we're in `are_equal()', we can start looking at the values of some variables. Let's say we type `p n' (`p' is short for "print"). We would expect to see the value of `n', a parameter to `are_equal()'. -Actually, `dgawk' gives us: +Actually, the debugger gives us: - dgawk> p n + gawk> p n -| n = untyped variable -In this case, `n' is an uninitialized local variable, since the +In this case, `n' is an uninitialized local variable, because the function was called without arguments (*note Function Calls::). A more useful variable to display might be the current record: - dgawk> p $0 - -| $0 = string ("gawk is a wonderful program!") + gawk> p $0 + -| $0 = "gawk is a wonderful program!" -This might be a bit puzzling at first since this is the second line of -our test input above. Let's look at `NR': +This might be a bit puzzling at first, as this is the second line of +our test input. Let's look at `NR': - dgawk> p NR - -| NR = number (2) + gawk> p NR + -| NR = 2 So we can see that `are_equal()' was only called for the second record -of the file. Of course, this is because our program contained a rule -for `NR == 1': +of the file. Of course, this is because our program contains a rule for +`NR == 1': NR == 1 { last = $0 @@ -19011,8 +20948,8 @@ for `NR == 1': OK, let's just check that that rule worked correctly: - dgawk> p last - -| last = string ("awk is a wonderful program!") + gawk> p last + -| last = "awk is a wonderful program!" Everything we have done so far has verified that the program has worked as planned, up to and including the call to `are_equal()', so @@ -19020,88 +20957,85 @@ the problem must be inside this function. To investigate further, we must begin "stepping through" the lines of `are_equal()'. We start by typing `n' (for "next"): - dgawk> n - -| 67 if (fcount > 0) { + gawk> n + -| 66 if (fcount > 0) { - This tells us that `gawk' is now ready to execute line 67, which + This tells us that `gawk' is now ready to execute line 66, which decides whether to give the lines the special "field skipping" treatment -indicated by the `-f' command-line option. (Notice that we skipped -from where we were before at line 64 to here, since the condition in -line 64 - - if (fcount == 0 && charcount == 0) - -was false.) +indicated by the `-1' command-line option. (Notice that we skipped +from where we were before at line 63 to here, because the condition in +line 63 `if (fcount == 0 && charcount == 0)' was false.) Continuing to step, we now get to the splitting of the current and last records: - dgawk> n - -| 68 n = split(last, alast) - dgawk> n - -| 69 m = split($0, aline) + gawk> n + -| 67 n = split(last, alast) + gawk> n + -| 68 m = split($0, aline) At this point, we should be curious to see what our records were split into, so we try to look: - dgawk> p n m alast aline - -| n = number (5) - -| m = number (5) + gawk> p n m alast aline + -| n = 5 + -| m = untyped variable -| alast = array, 5 elements - -| aline = array, 5 elements + -| aline = untyped variable (The `p' command can take more than one argument, similar to `awk''s `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 none of the words were accidentally left out), but what if we -want to see inside the array? +there are five elements in `alast'; `m' and `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: - dgawk> p alast[0] + gawk> p alast[0] -| "0" not in array `alast' Oops! - dgawk> p alast[1] - -| alast["1"] = string ("awk") + gawk> p alast[1] + -| alast["1"] = "awk" - This would be kind of slow for a 100-member array, though, so -`dgawk' provides a shortcut (reminiscent of another language not to be + This would be kind of slow for a 100-member array, though, so `gawk' +provides a shortcut (reminiscent of another language not to be mentioned): - dgawk> p @alast - -| alast["1"] = string ("awk") - -| alast["2"] = string ("is") - -| alast["3"] = string ("a") - -| alast["4"] = string ("wonderful") - -| alast["5"] = string ("program!") + gawk> p @alast + -| alast["1"] = "awk" + -| alast["2"] = "is" + -| alast["3"] = "a" + -| alast["4"] = "wonderful" + -| alast["5"] = "program!" It looks like we got this far OK. Let's take another step or two: - dgawk> n - -| 70 clast = join(alast, fcount, n) - dgawk> n - -| 71 cline = join(aline, fcount, m) + gawk> n + -| 69 clast = join(alast, fcount, n) + gawk> n + -| 70 cline = join(aline, fcount, m) Well, here we are at our error (sorry to spoil the suspense). What we had in mind was to join the fields starting from the second one to make the virtual record to compare, and if the first field was numbered zero, this would work. Let's look at what we've got: - dgawk> p cline clast - -| cline = string ("gawk is a wonderful program!") - -| clast = string ("awk is a wonderful program!") + gawk> p cline clast + -| cline = "gawk is a wonderful program!" + -| clast = "awk is a wonderful program!" 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 `dgawk': + We get out of the debugger: - dgawk> q + gawk> q -| The program is running. Exit anyway (y/n)? y Then we get into an editor: @@ -19112,12 +21046,13 @@ Then we get into an editor: and problem solved! -File: gawk.info, Node: List of Debugger Commands, Next: Readline Support, Prev: Sample dgawk session, Up: Debugger +File: gawk.info, Node: List of Debugger Commands, Next: Readline Support, Prev: Sample Debugging Session, Up: Debugger -14.3 Main `dgawk' Commands -========================== +14.3 Main Debugger Commands +=========================== -The `dgawk' command set can be divided into the following categories: +The `gawk' debugger command set can be divided into the following +categories: * Breakpoint control @@ -19133,32 +21068,32 @@ The `dgawk' command set can be divided into the following categories: 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 `dgawk' command name may -also be truncated if that partial name is unambiguous. `dgawk' has the -built-in capability to automatically repeat the previous command when -just hitting <Enter>. This works for the commands `list', `next', -`nexti', `step', `stepi' and `continue' executed without any argument. +abbreviation on a second description line. 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 <Enter>. This works for the commands `list', `next', +`nexti', `step', `stepi', and `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. -File: gawk.info, Node: Breakpoint Control, Next: Dgawk Execution Control, Up: List of Debugger Commands +File: gawk.info, Node: Breakpoint Control, Next: Debugger Execution Control, Up: List of Debugger Commands -14.3.1 Control Of Breakpoints +14.3.1 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 -controlling breakpoints are: +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: `break' [[FILENAME`:']N | FUNCTION] [`"EXPRESSION"'] `b' [[FILENAME`:']N | FUNCTION] [`"EXPRESSION"'] @@ -19180,10 +21115,10 @@ controlling breakpoints are: it from the breakpoint list using the `delete' command. With a breakpoint, you may also supply a condition. This is an - `awk' expression (enclosed in double quotes) that `dgawk' + `awk' expression (enclosed in double quotes) that the debugger evaluates whenever the breakpoint is reached. If the condition is - true, then `dgawk' stops execution and prompts for a command. - Otherwise, `dgawk' continues executing the program. + true, then the debugger stops execution and prompts for a command. + Otherwise, it continues executing the program. `clear' [[FILENAME`:']N | FUNCTION] Without any argument, delete any breakpoint at the next instruction @@ -19205,12 +21140,13 @@ controlling breakpoints are: `condition' N `"EXPRESSION"' Add a condition to existing breakpoint or watchpoint N. The - condition is an `awk' expression that `dgawk' evaluates whenever - the breakpoint or watchpoint is reached. If the condition is true, - then `dgawk' stops execution and prompts for a command. Otherwise, - `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. + condition is an `awk' expression _enclosed in double quotes_ that + the debugger evaluates whenever the breakpoint or watchpoint is + reached. If the condition is true, then 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). `delete' [N1 N2 ...] [N-M] `d' [N1 N2 ...] [N-M] @@ -19244,7 +21180,7 @@ controlling breakpoints are: arguments are the same as for `break'. -File: gawk.info, Node: Dgawk Execution Control, Next: Viewing And Changing Data, Prev: Breakpoint Control, Up: List of Debugger Commands +File: gawk.info, Node: Debugger Execution Control, Next: Viewing And Changing Data, Prev: Breakpoint Control, Up: List of Debugger Commands 14.3.2 Control of Execution --------------------------- @@ -19267,14 +21203,14 @@ execution of the program than we saw in our earlier example: `continue') terminates the list (an implicit `end'), and subsequent commands are ignored. For example: - dgawk> commands + gawk> commands > silent > printf "A silent breakpoint; i = %d\n", i > info locals > set i = 10 > continue > end - dgawk> + gawk> `continue' [COUNT] `c' [COUNT] @@ -19301,15 +21237,15 @@ execution of the program than we saw in our earlier example: Cancel execution of a function call. If 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 number 0), discard all inner + 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. `run' `r' - Start/restart execution of the program. When restarting, `dgawk' - retains the current breakpoints, watchpoints, command history, - automatic display variables, and debugger options. + Start/restart execution of the program. When restarting, the + debugger retains the current breakpoints, watchpoints, command + history, automatic display variables, and debugger options. `step' [COUNT] `s' [COUNT] @@ -19323,18 +21259,18 @@ execution of the program than we saw in our earlier example: `si' [COUNT] Execute one (or COUNT) instruction(s), stepping inside function calls. (For illustration of what is meant by an "instruction" in - `gawk', see the output shown under `dump' in *Note Miscellaneous - Dgawk Commands::.) + `gawk', see the output shown under `dump' in *note Miscellaneous + Debugger Commands::.) `until' [[FILENAME`:']N | FUNCTION] `u' [[FILENAME`:']N | FUNCTION] Without any argument, continue execution until a line past the - current line in current stack frame is reached. With an argument, - continue execution until the specified location is reached, or the - current stack frame returns. + current 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. -File: gawk.info, Node: Viewing And Changing Data, Next: Dgawk Stack, Prev: Dgawk Execution Control, Up: List of Debugger Commands +File: gawk.info, Node: Viewing And Changing Data, Next: Execution Stack, Prev: Debugger Execution Control, Up: List of Debugger Commands 14.3.3 Viewing and Changing Data -------------------------------- @@ -19346,10 +21282,10 @@ The commands for viewing and changing variables inside of `gawk' are: of the variable or field is displayed each time the program stops. Each variable added to the list is identified by a unique number: - dgawk> display x + gawk> display x -| 10: x = 1 - displays the assigned item number, the variable name and its + 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 @@ -19374,13 +21310,13 @@ AWK STATEMENTS Print the value of a `gawk' variable or field. Fields must be referenced by constants: - dgawk> print $3 + gawk> print $3 This prints the third field in the input record (if the specified field does not exist, it prints `Null field'). A variable can be - an array element, with the subscripts being constant values. To - print the contents of an array, prefix the name of the array with - the `@' symbol: + an array element, with the subscripts being constant string + values. To print the contents of an array, prefix the name of the + array with the `@' symbol: gawk> print @a @@ -19395,23 +21331,23 @@ AWK STATEMENTS `set' VAR`='VALUE Assign a constant (number or string) value to an `awk' variable or field. String values must be enclosed between double quotes - (`"..."'). + (`"'...`"'). You can also set special `awk' variables, such as `FS', `NF', - `NR', etc. + `NR', and son on. `watch' VAR | `$'N [`"EXPRESSION"'] `w' VAR | `$'N [`"EXPRESSION"'] - Add variable VAR (or field `$N') to the watch list. `dgawk' 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 `unwatch' command. + Add variable VAR (or field `$N') to the watch list. 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 `unwatch' command. With a watchpoint, you may also supply a condition. This is an - `awk' expression (enclosed in double quotes) that `dgawk' + `awk' expression (enclosed in double quotes) that the debugger evaluates whenever the watchpoint is reached. If the condition is - true, then `dgawk' stops execution and prompts for a command. - Otherwise, `dgawk' continues executing the program. + true, then the debugger stops execution and prompts for a command. + Otherwise, `gawk' continues executing the program. `undisplay' [N] Remove item number N (or all items, if no argument) from the @@ -19423,9 +21359,9 @@ AWK STATEMENTS -File: gawk.info, Node: Dgawk Stack, Next: Dgawk Info, Prev: Viewing And Changing Data, Up: List of Debugger Commands +File: gawk.info, Node: Execution Stack, Next: Debugger Info, Prev: Viewing And Changing Data, Up: List of Debugger Commands -14.3.4 Dealing With The Stack +14.3.4 Working with the Stack ----------------------------- Whenever you run a program which contains any function calls, `gawk' @@ -19437,11 +21373,13 @@ are: `backtrace' [COUNT] `bt' [COUNT] +`where' [COUNT] Print a backtrace of all function calls (stack frames), or innermost COUNT frames if COUNT > 0. Print the outermost COUNT frames if COUNT < 0. The backtrace displays the name and arguments to each function, the source file name, and the line - number. + number. The alias `where' for `backtrace' is provided for longtime + GDB users who may be used to that command. `down' [COUNT] Move COUNT (default 1) frames down the stack toward the innermost @@ -19449,34 +21387,36 @@ are: `frame' [N] `f' [N] - Select and print (frame number, function and argument names, - source file, and the source line) stack frame N. Frame 0 is the - currently executing, or "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 N. Frame 0 is the currently + executing, or "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. `up' [COUNT] Move COUNT (default 1) frames up the stack toward the outermost frame. Then select and print the frame. -File: gawk.info, Node: Dgawk Info, Next: Miscellaneous Dgawk Commands, Prev: Dgawk Stack, Up: List of Debugger Commands +File: gawk.info, Node: Debugger Info, Next: Miscellaneous Debugger Commands, Prev: Execution Stack, Up: List of Debugger Commands -14.3.5 Obtaining Information About The Program and The Debugger State +14.3.5 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. `dgawk' has one command which provides -this information, appropriately called `info'. `info' is used with one -of a number of arguments that tell it exactly what you want to know: +debugging environment itself. The `gawk' debugger has one command which +provides this information, appropriately called `info'. `info' is used +with one of a number of arguments that tell it exactly what you want to +know: `info' WHAT `i' WHAT The value for WHAT should be one of the following: `args' - Arguments of the selected frame. + List arguments of the selected frame. `break' List all currently set breakpoints. @@ -19485,22 +21425,22 @@ of a number of arguments that tell it exactly what you want to know: List all items in the automatic display list. `frame' - Description of the selected stack frame. + Give a description of the selected stack frame. `functions' List all function definitions including source file names and line numbers. `locals' - Local variables of the selected frame. + List local variables of the selected frame. `source' - The name of the current source file. Each time the program - stops, the current source file is the file containing the - current instruction. When `dgawk' first starts, the current - source file is the first file included via the `-f' option. - The `list FILENAME:LINENO' command can be used at any time to - change the current source. + 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 the debugger first starts, the + current source file is the first file included via the `-f' + option. The `list FILENAME:LINENO' command can be used at any + time to change the current source. `sources' List all program sources. @@ -19524,7 +21464,7 @@ from a file. The commands are: `history_size' The maximum number of lines to keep in the history file - `./.dgawk_history'. The default is 100. + `./.gawk_history'. The default is 100. `listsize' The number of lines that `list' prints. The default is 15. @@ -19535,18 +21475,18 @@ from a file. The commands are: standard output. `prompt' - The debugger prompt. The default is `dgawk> '. + The debugger prompt. The default is `gawk> '. - `save_history [on | off]' - Save command history to file `./.dgawk_history'. The default + `save_history' [`on' | `off'] + Save command history to file `./.gawk_history'. The default is `on'. - `save_options [on | off]' - Save current options to file `./.dgawkrc' upon exit. The + `save_options' [`on' | `off'] + Save current options to file `./.gawkrc' upon exit. The default is `on'. Options are read back in to the next session upon startup. - `trace [on | off]' + `trace' [`on' | `off'] Turn instruction tracing on or off. The default is `off'. `save' FILENAME @@ -19560,15 +21500,15 @@ from a file. The commands are: ignored; they do _not_ repeat the last command. You can't restart the program by having more than one `run' command in the file. Also, the list of commands may include additional `source' - commands; however, `dgawk' will not source the same file more than - once in order to avoid infinite recursion. + commands; however, the `gawk' debugger will not source the same + file more than once in order to avoid infinite recursion. In addition to, or instead of the `source' command, you can use - the `-R FILE' or `--command=FILE' command-line options to execute - commands from a file non-interactively (*note Options::. + the `-D FILE' or `--debug=FILE' command-line options to execute + commands from a file non-interactively (*note Options::). -File: gawk.info, Node: Miscellaneous Dgawk Commands, Prev: Dgawk Info, Up: List of Debugger Commands +File: gawk.info, Node: Miscellaneous Debugger Commands, Prev: Debugger Info, Up: List of Debugger Commands 14.3.6 Miscellaneous Commands ----------------------------- @@ -19584,62 +21524,60 @@ categories, as follows: partial dump of Davide Brini's obfuscated code (*note Signature Program::) demonstrates: - dgawk> dump + gawk> dump -| # BEGIN -| - -| [ 2:0x89faef4] Op_rule : [in_rule = BEGIN] [source_file = brini.awk] - -| [ 3:0x89fa428] Op_push_i : "~" [PERM|STRING|STRCUR] - -| [ 3:0x89fa464] Op_push_i : "~" [PERM|STRING|STRCUR] - -| [ 3:0x89fa450] Op_match : - -| [ 3:0x89fa3ec] Op_store_var : O [do_reference = FALSE] - -| [ 4:0x89fa48c] Op_push_i : "==" [PERM|STRING|STRCUR] - -| [ 4:0x89fa4c8] Op_push_i : "==" [PERM|STRING|STRCUR] - -| [ 4:0x89fa4b4] Op_equal : - -| [ 4:0x89fa400] Op_store_var : o [do_reference = FALSE] - -| [ 5:0x89fa4f0] Op_push : o - -| [ 5:0x89fa4dc] Op_plus_i : 0 [PERM|NUMCUR|NUMBER] - -| [ 5:0x89fa414] Op_push_lhs : o [do_reference = TRUE] - -| [ 5:0x89fa4a0] Op_assign_plus : - -| [ :0x89fa478] Op_pop : - -| [ 6:0x89fa540] Op_push : O - -| [ 6:0x89fa554] Op_push_i : "" [PERM|STRING|STRCUR] - -| [ :0x89fa5a4] Op_no_op : - -| [ 6:0x89fa590] Op_push : O - -| [ :0x89fa5b8] Op_concat : [expr_count = 3] [concat_flag = 0] - -| [ 6:0x89fa518] Op_store_var : x [do_reference = FALSE] - -| [ 7:0x89fa504] Op_push_loop : [target_continue = 0x89fa568] [target_break = 0x89fa680] - -| [ 7:0x89fa568] Op_push_lhs : X [do_reference = TRUE] - -| [ 7:0x89fa52c] Op_postincrement : - -| [ 7:0x89fa5e0] Op_push : x - -| [ 7:0x89fa61c] Op_push : o - -| [ 7:0x89fa5f4] Op_plus : - -| [ 7:0x89fa644] Op_push : o - -| [ 7:0x89fa630] Op_plus : - -| [ 7:0x89fa5cc] Op_leq : - -| [ :0x89fa57c] Op_jmp_false : [target_jmp = 0x89fa680] - -| [ 7:0x89fa694] Op_push_i : "%c" [PERM|STRING|STRCUR] - -| [ :0x89fa6d0] Op_no_op : - -| [ 7:0x89fa608] Op_assign_concat : c - -| [ :0x89fa6a8] Op_jmp : [target_jmp = 0x89fa568] - -| [ :0x89fa680] Op_pop_loop : + -| [ 1:0xfcd340] Op_rule : [in_rule = BEGIN] [source_file = brini.awk] + -| [ 1:0xfcc240] Op_push_i : "~" [MALLOC|STRING|STRCUR] + -| [ 1:0xfcc2a0] Op_push_i : "~" [MALLOC|STRING|STRCUR] + -| [ 1:0xfcc280] Op_match : + -| [ 1:0xfcc1e0] Op_store_var : O + -| [ 1:0xfcc2e0] Op_push_i : "==" [MALLOC|STRING|STRCUR] + -| [ 1:0xfcc340] Op_push_i : "==" [MALLOC|STRING|STRCUR] + -| [ 1:0xfcc320] Op_equal : + -| [ 1:0xfcc200] Op_store_var : o + -| [ 1:0xfcc380] Op_push : o + -| [ 1:0xfcc360] Op_plus_i : 0 [MALLOC|NUMCUR|NUMBER] + -| [ 1:0xfcc220] Op_push_lhs : o [do_reference = true] + -| [ 1:0xfcc300] Op_assign_plus : + -| [ :0xfcc2c0] Op_pop : + -| [ 1:0xfcc400] Op_push : O + -| [ 1:0xfcc420] Op_push_i : "" [MALLOC|STRING|STRCUR] + -| [ :0xfcc4a0] Op_no_op : + -| [ 1:0xfcc480] Op_push : O + -| [ :0xfcc4c0] Op_concat : [expr_count = 3] [concat_flag = 0] + -| [ 1:0xfcc3c0] Op_store_var : x + -| [ 1:0xfcc440] Op_push_lhs : X [do_reference = true] + -| [ 1:0xfcc3a0] Op_postincrement : + -| [ 1:0xfcc4e0] Op_push : x + -| [ 1:0xfcc540] Op_push : o + -| [ 1:0xfcc500] Op_plus : + -| [ 1:0xfcc580] Op_push : o + -| [ 1:0xfcc560] Op_plus : + -| [ 1:0xfcc460] Op_leq : + -| [ :0xfcc5c0] Op_jmp_false : [target_jmp = 0xfcc5e0] + -| [ 1:0xfcc600] Op_push_i : "%c" [MALLOC|STRING|STRCUR] + -| [ :0xfcc660] Op_no_op : + -| [ 1:0xfcc520] Op_assign_concat : c + -| [ :0xfcc620] Op_jmp : [target_jmp = 0xfcc440] -| ... -| - -| [ 8:0x89fa658] Op_K_printf : [expr_count = 17] [redir_type = ""] - -| [ :0x89fa374] Op_no_op : - -| [ :0x89fa3d8] Op_atexit : - -| [ :0x89fa6bc] Op_stop : - -| [ :0x89fa39c] Op_no_op : - -| [ :0x89fa3b0] Op_after_beginfile : - -| [ :0x89fa388] Op_no_op : - -| [ :0x89fa3c4] Op_after_endfile : - dgawk> + -| [ 2:0xfcc5a0] Op_K_printf : [expr_count = 17] [redir_type = ""] + -| [ :0xfcc140] Op_no_op : + -| [ :0xfcc1c0] Op_atexit : + -| [ :0xfcc640] Op_stop : + -| [ :0xfcc180] Op_no_op : + -| [ :0xfcd150] Op_after_beginfile : + -| [ :0xfcc160] Op_no_op : + -| [ :0xfcc1a0] Op_after_endfile : + gawk> `help' `h' - Print a list of all of the `dgawk' commands with a short summary - of their usage. `help COMMAND' prints the information about the - command COMMAND. + Print a list of all of the `gawk' debugger commands with a short + summary of their usage. `help COMMAND' prints the information + about the command COMMAND. `list' [`-' | `+' | N | FILENAME`:'N | N-M | FUNCTION] `l' [`-' | `+' | N | FILENAME`:'N | N-M | FUNCTION] @@ -19647,7 +21585,7 @@ categories, as follows: or the file named FILENAME. The possible arguments to `list' are as follows: - `-' + `-' (Minus) Print lines before the lines last printed. `+' @@ -19672,12 +21610,12 @@ categories, as follows: `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, `dgawk' warns you if you - accidentally type `q' or `quit', to make sure you really want to - quit. + the bug, 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 `q' or `quit', to make sure you really want + to quit. -`trace' `on' | `off' +`trace' [`on' | `off'] Turn on or off a continuous printing of instructions which are about to be executed, along with printing the `awk' line which they implement. The default is `off'. @@ -19688,14 +21626,15 @@ categories, as follows: -File: gawk.info, Node: Readline Support, Next: Dgawk Limitations, Prev: List of Debugger Commands, Up: Debugger +File: gawk.info, Node: Readline Support, Next: Limitations, Prev: List of Debugger Commands, Up: Debugger 14.4 Readline Support ===================== -If `dgawk' is compiled with the `readline' library, you can take -advantage of that library's command completion and history expansion -features. The following types of completion are available: +If `gawk' is compiled with the `readline' library +(http://cnswww.cns.cwru.edu/php/chet/readline/readline.html), you can +take advantage of that library's command completion and history +expansion features. The following types of completion are available: Command completion Command names. @@ -19715,66 +21654,4550 @@ Variable name completion -File: gawk.info, Node: Dgawk Limitations, Prev: Readline Support, Up: Debugger +File: gawk.info, Node: Limitations, Next: Debugging Summary, Prev: Readline Support, Up: Debugger -14.5 Limitations and Future Plans -================================= +14.5 Limitations +================ -We hope you find `dgawk' 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: +We hope you find the `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: - * At this point, `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 `syntax error'. When you do figure out what your mistake was, though, you'll feel like a real guru. - * If you perused the dump of opcodes in *Note Miscellaneous Dgawk - Commands::, (or if you are already familiar with `gawk' internals), + * If you perused the dump of opcodes in *note Miscellaneous Debugger + Commands:: (or if you are already familiar with `gawk' internals), you will realize that much of the internal manipulation of data in `gawk', as in many interpreters, is done on a stack. `Op_push', - `Op_pop', etc., are the "bread and butter" of most `gawk' code. - Unfortunately, as of now, `dgawk' does not allow you to examine - the stack's contents. + `Op_pop', and the like, are the "bread and butter" of most `gawk' + code. - 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 this is to use more explicit variables at the - debugging stage and then change back to obscure, perhaps more - optimal code later. + Unfortunately, as of now, the `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 this is to use more + explicit variables at the debugging stage and then change back to + obscure, perhaps more optimal code later. * There is no way to look "inside" the process of compiling regular expressions to see if you got it right. As an `awk' programmer, - you are expected to know what `/[^[:alnum:][:blank:]]/' means. + you are expected to know the meaning of `/[^[:alnum:][:blank:]]/'. + + * The `gawk' debugger is designed to be used by running a program + (with all its parameters) on the command line, as described in + *note 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. + + * The `gawk' debugger only accepts source supplied with the `-f' + option. + + +File: gawk.info, Node: Debugging Summary, Prev: Limitations, Up: Debugger + +14.6 Summary +============ + + * Programs rarely work correctly the first time. Finding bugs is + "debugging" and a program that helps you find bugs is a + "debugger". `gawk' has a built-in debugger that works very + similarly to the GNU Debugger, GDB. + + * 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). + + * Like most debuggers, the `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). + + * 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. + + * If the `readline' library is available when `gawk' is compiled, it + is used by the debugger to provide command-line history and + editing. + + + +File: gawk.info, Node: Arbitrary Precision Arithmetic, Next: Dynamic Extensions, Prev: Debugger, Up: Top + +15 Arithmetic and Arbitrary-Precision Arithmetic with `gawk' +************************************************************ + +This major node 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 `awk' +uses for all its computations, including a discussion of +arbitrary-precision floating-point arithmetic, which is a feature +available only in `gawk'. It continues on to present +arbitrary-precision integers, and concludes with a description of some +points where `gawk' and the POSIX standard are not quite in agreement. + + NOTE: Most users of `gawk' can safely skip this chapter. But if + you want to do scientific calculations with `gawk', this is the + place to be. + +* Menu: + +* Computer Arithmetic:: A quick intro to computer math. +* Math Definitions:: Defining terms used. +* MPFR features:: The MPFR features in `gawk'. +* FP Math Caution:: Things to know. +* Arbitrary Precision Integers:: Arbitrary Precision Integer Arithmetic with + `gawk'. +* POSIX Floating Point Problems:: Standards Versus Existing Practice. +* Floating point summary:: Summary of floating point discussion. + + +File: gawk.info, Node: Computer Arithmetic, Next: Math Definitions, Up: Arbitrary Precision Arithmetic + +15.1 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 "binary +digits", or "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: + +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 `gawk' to be performing + decimal arithmetic,(1) it does not do so. + +Integer arithmetic + In school, integer values were referred to as "whole" numbers--that + is, numbers without any fractional part, such as 1, 42, or -17. + The advantage to integer numbers is that they represent values + exactly. The disadvantage is that their range is limited. + + In computers, integer values come in two flavors: "signed" and + "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. + +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 `awk' uses "double-precision" floating-point numbers, which + can hold more digits than "single-precision" floating-point + numbers. `gawk' has facilities for performing arbitrary-precision + floating-point arithmetic, which we describe in more detail + shortly. + + 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 +*note table-numeric-ranges::. + +Numeric representation Minimum value Maximum value +--------------------------------------------------------------------------- +32-bit signed integer -2,147,483,648 2,147,483,647 +32-bit unsigned integer 0 4,294,967,295 +64-bit signed integer -9,223,372,036,854,775,8089,223,372,036,854,775,807 +64-bit unsigned integer 0 18,446,744,073,709,551,615 +Single-precision `1.175494e-38' `3.402823e+38' +floating point +(approximate) +Double-precision `2.225074e-308' `1.797693e+308' +floating point +(approximate) + +Table 15.1: Value ranges for different numeric representations + + ---------- Footnotes ---------- + + (1) We don't know why they expect this, but they do. + + +File: gawk.info, Node: Math Definitions, Next: MPFR features, Prev: Computer Arithmetic, Up: Arbitrary Precision Arithmetic + +15.2 Other Stuff to Know +======================== + +The rest of this major node uses a number of terms. Here are some +informal definitions that should help you work your way through the +material here. + +"Accuracy" + A floating-point calculation's accuracy is how close it comes to + the real (paper and pencil) value. + +"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. + +"Exponent" + The order of magnitude of a value; some number of bits in a + floating-point value store the exponent. + +"Inf" + A special value representing infinity. Operations involving another + number and infinity produce infinity. + +"NaN" + "Not A Number."(1) 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 + `NaN' back as the result. The IEEE 754 standard recommends that + systems return `NaN'. Some examples: + + `sqrt(-1)' + This makes sense in the range of complex numbers, but not in + the range of real numbers, so the result is `NaN'. + + `log(-8)' + -8 is out of the domain of `log()', so the result is `NaN'. + +"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. + +"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: + + PREC = 3.322 * DPS + + Here, PREC denotes the binary precision (measured in bits) and DPS + (short for decimal places) is the decimal digits. + +"Rounding mode" + How numbers are rounded up or down when necessary. More details + are provided later. + +"Significand" + A floating-point value consists the significand multiplied by 10 + to the power of the exponent. For example, in `1.2345e67', the + significand is `1.2345'. + +"Stability" + From the Wikipedia article on numerical stability + (http://en.wikipedia.org/wiki/Numerical_stability): "Calculations + that can be proven not to magnify approximation errors are called + "numerically stable"." + + See the Wikipedia article on accuracy and precision +(http://en.wikipedia.org/wiki/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. (`awk' uses only the 64-bit double-precision format.) + + *note table-ieee-formats:: lists the precision and exponent field +values for the basic IEEE 754 binary formats: + +Name Total bits Precision Minimum Maximum + exponent exponent +--------------------------------------------------------------------------- +Single 32 24 -126 +127 +Double 64 53 -1022 +1023 +Quadruple 128 113 -16382 +16383 + +Table 15.2: Basic IEEE format values + + NOTE: The precision numbers include the implied leading one that + gives them one extra bit of significand. + + ---------- Footnotes ---------- + + (1) Thanks to Michael Brennan for this description, which we have +paraphrased, and for the examples. + + +File: gawk.info, Node: MPFR features, Next: FP Math Caution, Prev: Math Definitions, Up: Arbitrary Precision Arithmetic + +15.3 Arbitrary-Precision Arithmetic Features in `gawk' +====================================================== + +By default, `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, `gawk' uses the GNU MPFR (http://www.mpfr.org) and +GNU MP (http://gmplib.org) (GMP) libraries for arbitrary-precision +arithmetic on numbers. You can see if MPFR support is available like +so: + + $ gawk --version + -| GNU Awk 4.1.2, API: 1.1 (GNU MPFR 3.1.0-p3, GNU MP 5.0.2) + -| Copyright (C) 1989, 1991-2015 Free Software Foundation. + ... + +(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 `PROCINFO' +array to provide information about the MPFR and GMP libraries (*note +Auto-set::). + + The MPFR library provides precise control over precisions and +rounding modes, and gives correctly rounded, reproducible, +platform-independent results. With the `-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, `PREC' and `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. +*Note Setting precision::, and *note Setting the rounding mode::, for +more information. + + +File: gawk.info, Node: FP Math Caution, Next: Arbitrary Precision Integers, Prev: MPFR features, Up: Arbitrary Precision Arithmetic + +15.4 Floating-Point Arithmetic: Caveat Emptor! +============================================== + + Math class is tough! -- Teen Talk Barbie, July 1992 + + This minor node provides a high level overview of the issues +involved when doing lots of floating-point arithmetic.(1) The +discussion applies to both hardware and arbitrary-precision +floating-point arithmetic. + + 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. + +* 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. + + ---------- Footnotes ---------- + + (1) There is a very nice paper on floating-point arithmetic +(http://www.validlab.com/goldberg/paper.pdf) by David Goldberg, "What +Every Computer Scientist Should Know About Floating-point Arithmetic," +`ACM Computing Surveys' *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. + + +File: gawk.info, Node: Inexactness of computations, Next: Getting Accuracy, Up: FP Math Caution + +15.4.1 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. + + +File: gawk.info, Node: Inexact representation, Next: Comparing FP Values, Up: Inexactness of computations + +15.4.1.1 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: + + x = 0.875 # 1/2 + 1/4 + 1/8 + y = 0.425 + + Unlike the number in `y', the number stored in `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 +`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 `"%.17g"', it may not produce the same +number as you assigned to it: + + $ gawk 'BEGIN { x = 0.875; y = 0.425 + > printf("%0.17g, %0.17g\n", x, y) }' + -| 0.875, 0.42499999999999999 + + 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 `"%.15g"', which when used in the +previous example, produces an output identical to the input. + + +File: gawk.info, Node: Comparing FP Values, Next: Errors accumulate, Prev: Inexact representation, Up: Inexactness of computations + +15.4.1.2 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: + + $ gawk 'BEGIN { print (0.1 + 12.2 == 12.3) }' + -| 0 + + The general wisdom when comparing floating-point values is to see if +they are within some small range of each other (called a "delta", or +"tolerance"). You have to decide how small a delta is important to +you. Code to do this looks something like the following: + + delta = 0.00001 # for example + difference = abs(a) - abs(b) # subtract the two values + if (difference < delta) + # all ok + else + # not ok + +(We assume that you have a simple absolute value function named `abs()' +defined elsewhere in your program.) + + +File: gawk.info, Node: Errors accumulate, Prev: Comparing FP Values, Up: Inexactness of computations + +15.4.1.3 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 pi using one of its many +series representations: + + 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) + } + } + + When run, the early errors propagate through later computations, +causing the loop to terminate prematurely after attempting to divide by +zero: + + $ gawk -f pi.awk + -| 3.215390309173475 + -| 3.159659942097510 + -| 3.146086215131467 + -| 3.142714599645573 + ... + -| 3.224515243534819 + -| 2.791117213058638 + -| 0.000000000000000 + error--> gawk: pi.awk:6: fatal: division by zero attempted + + Here is an additional example where the inaccuracies in internal +representations yield an unexpected result: + + $ gawk 'BEGIN { + > for (d = 1.1; d <= 1.5; d += 0.1) # loop five times (?) + > i++ + > print i + > }' + -| 4 + + +File: gawk.info, Node: Getting Accuracy, Next: Try To Round, Prev: Inexactness of computations, Up: FP Math Caution + +15.4.2 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 `gawk' tests the expressions `0.1 + 12.2' and `12.3' for +equality using the machine double-precision arithmetic, it decides that +they are not equal! (*Note Comparing FP Values::.) You can get the +result you want by increasing the precision; 56 bits in this case does +the job: + + $ gawk -M -v PREC=56 'BEGIN { print (0.1 + 12.2 == 12.3) }' + -| 1 + + 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 `PREC': + + $ gawk -M -v PREC=201 'BEGIN { print (0.1 + 12.2 == 12.3) }' + -| 0 + + This is not a bug in `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 _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 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 *note Errors accumulate::: + + $ gawk 'BEGIN { + > for (d = 1.1; d <= 1.5; d += 0.1) # loop five times (?) + > i++ + > print i + > }' + -| 4 + +you may or may not succeed in getting the correct result by choosing an +arbitrarily large value for `PREC'. Reformulation of the problem at +hand is often the correct approach in such situations. + + +File: gawk.info, Node: Try To Round, Next: Setting precision, Prev: Getting Accuracy, Up: FP Math Caution + +15.4.3 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 pi in the earlier example can be enhanced by using the +following simple algebraic transformation: + + (sqrt(x * x + 1) - 1) / x == x / (sqrt(x * x + 1) + 1) + +After making this change, the program converges to pi in under 30 +iterations: + + $ gawk -f pi2.awk + -| 3.215390309173473 + -| 3.159659942097501 + -| 3.146086215131436 + -| 3.142714599645370 + -| 3.141873049979825 + ... + -| 3.141592653589797 + -| 3.141592653589797 + + +File: gawk.info, Node: Setting precision, Next: Setting the rounding mode, Prev: Try To Round, Up: FP Math Caution + +15.4.4 Setting the Precision +---------------------------- + +`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 `PREC'. You can also +set the value to one of the predefined case-insensitive strings shown +in *note table-predefined-precision-strings::, to emulate an IEEE 754 +binary format. + +`PREC' IEEE 754 Binary Format +--------------------------------------------------- +`"half"' 16-bit half-precision +`"single"' Basic 32-bit single precision +`"double"' Basic 64-bit double precision +`"quad"' Basic 128-bit quadruple precision +`"oct"' 256-bit octuple precision + +Table 15.3: Predefined precision strings for `PREC' + + The following example illustrates the effects of changing precision +on arithmetic operations: + + $ gawk -M -v PREC=100 'BEGIN { x = 1.0e-400; print x + 0 + > PREC = "double"; print x + 0 }' + -| 1e-400 + -| 0 + + CAUTION: Be wary of floating-point constants! When reading a + floating-point constant from program source code, `gawk' uses the + default precision (that of a C `double'), unless overridden by an + assignment to the special variable `PREC' on the command line, to + store it internally as an MPFR number. Changing the precision + using `PREC' in the program text does _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 `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: + + $ gawk -M 'BEGIN { PREC = 113; printf("%0.25f\n", 0.1) }' + -| 0.1000000000000000055511151 + $ gawk -M -v PREC=113 'BEGIN { printf("%0.25f\n", 0.1) }' + -| 0.1000000000000000000000000 + $ gawk -M 'BEGIN { PREC = 113; printf("%0.25f\n", "0.1") }' + -| 0.1000000000000000000000000 + $ gawk -M 'BEGIN { PREC = 113; printf("%0.25f\n", 1/10) }' + -| 0.1000000000000000000000000 + + +File: gawk.info, Node: Setting the rounding mode, Prev: Setting precision, Up: FP Math Caution + +15.4.5 Setting the Rounding Mode +-------------------------------- + +The `ROUNDMODE' variable provides program level control over the +rounding mode. The correspondence between `ROUNDMODE' and the IEEE +rounding modes is shown in *note table-gawk-rounding-modes::. + +Rounding Mode IEEE Name `ROUNDMODE' +--------------------------------------------------------------------------- +Round to nearest, ties to even `roundTiesToEven' `"N"' or `"n"' +Round toward plus Infinity `roundTowardPositive' `"U"' or `"u"' +Round toward negative Infinity `roundTowardNegative' `"D"' or `"d"' +Round toward zero `roundTowardZero' `"Z"' or `"z"' +Round to nearest, ties away `roundTiesToAway' `"A"' or `"a"' +from zero + +Table 15.4: `gawk' rounding modes + + `ROUNDMODE' has the default value `"N"', which selects the IEEE 754 +rounding mode `roundTiesToEven'. In *note Table 15.4: +table-gawk-rounding-modes, the value `"A"' selects `roundTiesToAway'. +This is only available if your version of the MPFR library supports it; +otherwise, setting `ROUNDMODE' to `"A"' has no effect. + + The default mode `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 `printf' to format +floating-point numbers. For example: + + BEGIN { + x = -4.5 + for (i = 1; i < 10; i++) { + x += 1.0 + printf("%4.1f => %2.0f\n", x, x) + } + } + +produces the following output when run on the author's system:(1) + + -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 + + The theory behind `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 (`roundTowardPositive') and round toward negative infinity +(`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 `roundTowardZero' mode can be +used for converting floating-point numbers to integers. The rounding +mode `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. + + ---------- Footnotes ---------- + + (1) 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 `printf'. + + +File: gawk.info, Node: Arbitrary Precision Integers, Next: POSIX Floating Point Problems, Prev: FP Math Caution, Up: Arbitrary Precision Arithmetic + +15.5 Arbitrary-Precision Integer Arithmetic with `gawk' +======================================================= + +When given the `-M' option, `gawk' performs all integer arithmetic +using GMP arbitrary-precision integers. Any number that looks like an +integer in a source or data file is stored as an arbitrary-precision +integer. The size of the integer is limited only by the available +memory. For example, the following computes 5^4^3^2, the result of +which is beyond the limits of ordinary hardware double-precision +floating-point values: + + $ gawk -M 'BEGIN { + > x = 5^4^3^2 + > print "number of digits =", length(x) + > print substr(x, 1, 20), "...", substr(x, length(x) - 19, 20) + > }' + -| number of digits = 183231 + -| 62060698786608744707 ... 92256259918212890625 + + If instead you were to compute the same value using +arbitrary-precision floating-point values, the precision needed for +correct output (using the formula `prec = 3.322 * dps'), would be 3.322 +x 183231, 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(1) using a recurrence: + + $ gawk -M 'BEGIN { + > s = 2.0 + > for (i = 1; i <= 7; i++) + > s = s * (s - 1) + 1 + > print s + > }' + -| 113423713055421845118910464 + + 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 `2.0' with an integer, to +perform all computations using integer arithmetic to get the correct +output. + + Sometimes `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: + + gawk -M 'BEGIN { n = 13; print (n + 0.0) % 2.0 }' + + You can avoid this issue altogether by specifying the number as a +floating-point value to begin with: + + gawk -M 'BEGIN { n = 13.0; print n % 2.0 }' + + Note that for this particular example, it is likely best to just use +the following: + + gawk -M 'BEGIN { n = 13; print n % 2 }' + + When dividing two arbitrary precision integers with either `/' or +`%', 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 `div()' function (*note Numeric Functions::). + + You can simulate the `div()' function in standard `awk' using this +user-defined function: + + # div --- do integer division + + 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 + } + + The following example program, contributed by Katie Wasserman, uses +`div()' to compute the digits of pi to as many places as you choose to +set: + + # pi.awk --- compute the digits of pi + + 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 + } + + When asked about the algorithm used, Katie replied: + + 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. See + `http://www.hpmuseum.org/cgi-sys/cgiwrap/hpmuseum/articles.cgi?read=899'. + + ---------- Footnotes ---------- + + (1) Weisstein, Eric W. `Sylvester's Sequence'. From MathWorld--A +Wolfram Web Resource +(`http://mathworld.wolfram.com/SylvestersSequence.html'). + + +File: gawk.info, Node: POSIX Floating Point Problems, Next: Floating point summary, Prev: Arbitrary Precision Integers, Up: Arbitrary Precision Arithmetic + +15.6 Standards Versus Existing Practice +======================================= + +Historically, `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 `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 `awk' should support additional features. +These features are: + + * Interpretation of floating-point data values specified in + hexadecimal notation (e.g., `0xDEADBEEF'). (Note: data values, + _not_ source code constants.) + + * Support for the special IEEE 754 floating-point values "Not A + Number" (NaN), positive Infinity ("inf"), and negative Infinity + ("-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 + `nan' and allow either `inf' or `infinity'. + + The first problem is that both of these are clear changes to +historical practice: + + * The `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. + + * Allowing completely alphabetic strings to have valid numeric + values is also a very severe departure from historical practice. + + The second problem is that the `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 `awk' support +hexadecimal floating-point values and special values for "Not A Number" +and infinity. + + Although the `gawk' maintainer continues to feel that providing +those features is inadvisable, nevertheless, on systems that support +IEEE floating point, it seems reasonable to provide _some_ way to +support NaN and Infinity values. The solution implemented in `gawk' is +as follows: + + * With the `--posix' command-line option, `gawk' becomes "hands + off." String values are passed directly to the system library's + `strtod()' function, and if it successfully returns a numeric + value, that is what's used.(1) By definition, the results are not + portable across different systems. They are also a little + surprising: + + $ echo nanny | gawk --posix '{ print $1 + 0 }' + -| nan + $ echo 0xDeadBeef | gawk --posix '{ print $1 + 0 }' + -| 3735928559 + + * Without `--posix', `gawk' interprets the four strings `+inf', + `-inf', `+nan', and `-nan' specially, producing the corresponding + special numeric values. The leading sign acts a signal to `gawk' + (and the user) that the value is really numeric. Hexadecimal + floating point is not supported (unless you also use + `--non-decimal-data', which is _not_ recommended). For example: + + $ echo nanny | gawk '{ print $1 + 0 }' + -| 0 + $ echo +nan | gawk '{ print $1 + 0 }' + -| nan + $ echo 0xDeadBeef | gawk '{ print $1 + 0 }' + -| 0 + + `gawk' ignores case in the four special values. Thus `+nan' and + `+NaN' are the same. + + ---------- Footnotes ---------- + + (1) You asked for it, you got it. + + +File: gawk.info, Node: Floating point summary, Prev: POSIX Floating Point Problems, Up: Arbitrary Precision Arithmetic + +15.7 Summary +============ + + * Most computer arithmetic is done using either integers or + floating-point values. Standard `awk' uses double-precision + floating-point values. + + * 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: + + - Not all numbers can be represented exactly. + + - Comparing values should use a delta, instead of being done + directly with `==' and `!='. + + - Errors accumulate. + + - Operations are not always truly associative or distributive. + + * Increasing the accuracy can help, but it is not a panacea. + + * Often, increasing the accuracy and then rounding to the desired + number of digits produces reasonable results. + + * Use `-M' (or `--bignum') to enable MPFR arithmetic. Use `PREC' to + set the precision in bits, and `ROUNDMODE' to set the IEEE 754 + rounding mode. + + * With `-M', `gawk' performs arbitrary-precision integer arithmetic + using the GMP library. This is faster and more space efficient + than using MPFR for the same calculations. + + * There are several "dark corners" with respect to floating-point + numbers where `gawk' disagrees with the POSIX standard. It pays + to be aware of them. + + * 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. + + * As general advice, avoid presenting numerical data in a manner that + implies better precision than is actually the case. + + + +File: gawk.info, Node: Dynamic Extensions, Next: Language History, Prev: Arbitrary Precision Arithmetic, Up: Top + +16 Writing Extensions for `gawk' +******************************** + +It is possible to add new functions written in C or C++ to `gawk' using +dynamically loaded libraries. This facility is available on systems +that support the C `dlopen()' and `dlsym()' functions. This major node +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 major node, although you may wish to review the documentation on +the extensions that come with `gawk' (*note Extension Samples::), and +the information on the `gawkextlib' project (*note gawkextlib::). The +sample extensions are automatically built and installed when `gawk' is. + + NOTE: When `--sandbox' is specified, extensions are disabled + (*note Options::). + +* 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 `gawk' finds compiled extensions. +* Extension Example:: Example C code for an extension. +* Extension Samples:: The sample extensions that ship with + `gawk'. +* gawkextlib:: The `gawkextlib' project. +* Extension summary:: Extension summary. +* Extension Exercises:: Exercises. + + +File: gawk.info, Node: Extension Intro, Next: Plugin License, Up: Dynamic Extensions + +16.1 Introduction +================= + +An "extension" (sometimes called a "plug-in") is a piece of external +compiled code that `gawk' can load at runtime to provide additional +functionality, over and above the built-in capabilities described in +the rest of this Info file. + + Extensions are useful because they allow you (of course) to extend +`gawk''s functionality. For example, they can provide access to system +calls (such as `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 "application +programming interface" (API) defined for this purpose by the `gawk' +developers. The rest of this major node 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 `gawk' distribution, and describes the `gawkextlib' project. *Note +Extension Design::, for a discussion of the extension mechanism goals +and design. + + +File: gawk.info, Node: Plugin License, Next: Extension Mechanism Outline, Prev: Extension Intro, Up: Dynamic Extensions + +16.2 Extension Licensing +======================== + +Every dynamic extension must be distributed under a license that is +compatible with the GNU GPL (*note Copying::). + + In order for the extension to tell `gawk' that it is properly +licensed, the extension must define the global symbol +`plugin_is_GPL_compatible'. If this symbol does not exist, `gawk' +emits a fatal error and exits when it tries to load your extension. + + The declared type of the symbol should be `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: + + int plugin_is_GPL_compatible; + + +File: gawk.info, Node: Extension Mechanism Outline, Next: Extension API Description, Prev: Plugin License, Up: Dynamic Extensions + +16.3 How It Works at a High Level +================================= + +Communication between `gawk' and an extension is two-way. First, when +an extension is loaded, `gawk' passes it a pointer to a `struct' whose +fields are function pointers. This is shown in *note +figure-load-extension::. + + API + Struct + +---+ + | | + +---+ + +---------------| | + | +---+ dl_load(api_p, id); + | | | ___________________ + | +---+ | + | +---------| | __________________ | + | | +---+ || + | | | | || + | | +---+ || + | | +---| | || + | | | +---+ \ || / + | | | \ / + v v v \/ ++-------+-+---+-+---+-+------------------+--------------------+ +| |x| |x| |x| |OOOOOOOOOOOOOOOOOOOO| +| |x| |x| |x| |OOOOOOOOOOOOOOOOOOOO| +| |x| |x| |x| |OOOOOOOOOOOOOOOOOOOO| ++-------+-+---+-+---+-+------------------+--------------------+ + + gawk Main Program Address Space Extension +Figure 16.1: Loading the extension + + The extension can call functions inside `gawk' through these +function pointers, at runtime, without needing (link-time) access to +`gawk''s symbols. One of these function pointers is to a function for +"registering" new functions. This is shown in *note +figure-register-new-function::. + + register_ext_func({ "chdir", do_chdir, 1 }); + + +--------------------------------------------+ + | | + V | ++-------+-+---+-+---+-+------------------+--------------+-+---+ +| |x| |x| |x| |OOOOOOOOOOOOOO|X|OOO| +| |x| |x| |x| |OOOOOOOOOOOOOO|X|OOO| +| |x| |x| |x| |OOOOOOOOOOOOOO|X|OOO| ++-------+-+---+-+---+-+------------------+--------------+-+---+ + + gawk Main Program Address Space Extension +Figure 16.2: Registering a new function + + In the other direction, the extension registers its new functions +with `gawk' by passing function pointers to the functions that provide +the new feature (`do_chdir()', for example). `gawk' associates the +function pointer with a name and can then call it, using a defined +calling convention. This is shown in *note figure-call-new-function::. + + BEGIN { + chdir("/path") (*fnptr)(1); + } + +--------------------------------------------+ + | | + | V ++-------+-+---+-+---+-+------------------+--------------+-+---+ +| |x| |x| |x| |OOOOOOOOOOOOOO|X|OOO| +| |x| |x| |x| |OOOOOOOOOOOOOO|X|OOO| +| |x| |x| |x| |OOOOOOOOOOOOOO|X|OOO| ++-------+-+---+-+---+-+------------------+--------------+-+---+ + + gawk Main Program Address Space Extension +Figure 16.3: Calling the new function + + The `do_XXX()' function, in turn, then uses the function pointers in +the API `struct' to do its work, such as updating variables or arrays, +printing messages, setting `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 `filefuncs.c' (*note Extension +Example::) and also in the `testext.c' code for testing the APIs. + + Some other bits and pieces: + + * The API provides access to `gawk''s `do_XXX' values, reflecting + command-line options, like `do_lint', `do_profiling' and so on + (*note Extension API Variables::). These are informational: an + extension cannot affect their values inside `gawk'. In addition, + attempting to assign to them produces a compile-time error. + + * The API also provides major and minor version numbers, so that an + extension can check if the `gawk' it is loaded with supports the + facilities it was compiled with. (Version mismatches "shouldn't" + happen, but we all know how _that_ goes.) *Note Extension + Versioning::, for details. + + +File: gawk.info, Node: Extension API Description, Next: Finding Extensions, Prev: Extension Mechanism Outline, Up: Dynamic Extensions + +16.4 API Description +==================== + +C or C++ code for an extension must include the header file +`gawkapi.h', which declares the functions and defines the data types +used to communicate with `gawk'. This (rather large) minor node +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 + `gawk'. +* Printing Messages:: Functions for printing messages. +* Updating `ERRNO':: Functions for updating `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. + + +File: gawk.info, Node: Extension API Functions Introduction, Next: General Data Types, Up: Extension API Description + +16.4.1 Introduction +------------------- + +Access to facilities within `gawk' are made available by calling +through function pointers passed into your extension. + + API function pointers are provided for the following kinds of +operations: + + * Allocating, reallocating, and releasing memory. + + * Registration functions. You may register: + + - Extension functions + + - Exit callbacks + + - A version string + + - Input parsers + + - Output wrappers + + - Two-way processors + + All of these are discussed in detail, later in this major node. + + * Printing fatal, warning, and "lint" warning messages. + + * Updating `ERRNO', or unsetting it. + + * Accessing parameters, including converting an undefined parameter + into an array. + + * Symbol table access: retrieving a global variable, creating one, + or changing one. + + * Creating and releasing cached values; this provides an efficient + way to use values for multiple variables and can be a big + performance win. + + * Manipulating arrays: + + - Retrieving, adding, deleting, and modifying elements + + - Getting the count of elements in an array + + - Creating a new array + + - Clearing an array + + - Flattening an array for easy C style looping over all its + indices and elements + + Some points about using the API: + + * The following types, macros, and/or functions are referenced in + `gawkapi.h'. For correct use, you must therefore include the + corresponding standard header file _before_ including `gawkapi.h': + + C Entity Header File + ------------------------------------------- + `EOF' `<stdio.h>' + Values for `errno' `<errno.h>' + `FILE' `<stdio.h>' + `NULL' `<stddef.h>' + `memcpy()' `<string.h>' + `memset()' `<string.h>' + `size_t' `<sys/types.h>' + `struct stat' `<sys/stat.h>' + + 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 `gawkapi.h' clean, instead of becoming + a portability hodge-podge as can be seen in some parts of the + `gawk' source code. + + * The `gawkapi.h' file may be included more than once without ill + effect. Doing so, however, is poor coding practice. + + * Although the API only uses ISO C 90 features, there is an + exception; the "constructor" functions use the `inline' keyword. + If your compiler does not support this keyword, you should either + place `-Dinline=''' on your command line, or use the GNU Autotools + and include a `config.h' file in your extensions. + + * All pointers filled in by `gawk' point to memory managed by `gawk' + and should be treated by the extension as read-only. Memory for + _all_ strings passed into `gawk' from the extension _must_ come + from calling one of `gawk_malloc()', `gawk_calloc()' or + `gawk_realloc()', and is managed by `gawk' from then on. + + * The API defines several simple `struct's that map values as seen + from `awk'. A value can be a `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 NUL + characters are allowed. + + NOTE: By intent, strings are maintained using the current + multibyte encoding (as defined by `LC_XXX' environment + variables) and not using wide characters. This matches how + `gawk' stores strings internally and also how characters are + likely to be input and output from files. + + * 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"). + + + 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 `gawkapi.h' header file defines several +macros that you should use in your code. This minor node presents the +macros as if they were functions. + + +File: gawk.info, Node: General Data Types, Next: Memory Allocation Functions, Prev: Extension API Functions Introduction, Up: Extension API Description + +16.4.2 General-Purpose Data Types +--------------------------------- + + I have a true love/hate relationship with unions. -- Arnold + Robbins + + That's the thing about unions: the compiler will arrange things so + they can accommodate both love and hate. -- Chet Ramey + + The extension API defines a number of simple types and structures for +general-purpose use. Additional, more specialized, data structures are +introduced in subsequent minor nodes, together with the functions that +use them. + +`typedef void *awk_ext_id_t;' + A value of this type is received from `gawk' when an extension is + loaded. That value must then be passed back to `gawk' as the + first parameter of each API function. + +`#define awk_const ...' + This macro expands to `const' when compiling an extension, and to + nothing when compiling `gawk' itself. This makes certain fields + in the API data structures unwritable from extension code, while + allowing `gawk' to use them as it needs to. + +`typedef enum awk_bool {' +` awk_false = 0,' +` awk_true' +`} awk_bool_t;' + A simple boolean type. + +`typedef struct awk_string {' +` char *str; /* data */' +` size_t len; /* length thereof, in chars */' +`} awk_string_t;' + This represents a mutable string. `gawk' owns the memory pointed + to if it supplied the value. Otherwise, it takes ownership of the + memory pointed to. _Such memory must come from calling one of the + `gawk_malloc()', `gawk_calloc()', or `gawk_realloc()' functions!_ + + As mentioned earlier, strings are maintained using the current + multibyte encoding. + +`typedef enum {' +` AWK_UNDEFINED,' +` AWK_NUMBER,' +` AWK_STRING,' +` AWK_ARRAY,' +` AWK_SCALAR, /* opaque access to a variable */' +` AWK_VALUE_COOKIE /* for updating a previously created value */' +`} awk_valtype_t;' + This `enum' indicates the type of a value. It is used in the + following `struct'. + +`typedef struct awk_value {' +` awk_valtype_t val_type;' +` union {' +` awk_string_t s;' +` double d;' +` awk_array_t a;' +` awk_scalar_t scl;' +` awk_value_cookie_t vc;' +` } u;' +`} awk_value_t;' + An "`awk' value." The `val_type' member indicates what kind of + value the `union' holds, and each member is of the appropriate + type. + +`#define str_value u.s' +`#define num_value u.d' +`#define array_cookie u.a' +`#define scalar_cookie u.scl' +`#define value_cookie u.vc' + These macros make accessing the fields of the `awk_value_t' more + readable. + +`typedef void *awk_scalar_t;' + Scalars can be represented as an opaque type. These values are + obtained from `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 *note Symbol table by cookie::. + +`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 *note Cached values::. + + + Scalar values in `awk' are either numbers or strings. The +`awk_value_t' struct represents values. The `val_type' member +indicates what is in the `union'. + + Representing numbers is easy--the API uses a C `double'. Strings +require more work. Because `gawk' allows embedded NUL bytes in string +values, a string must be represented as a pair containing a +data-pointer and length. This is the `awk_string_t' type. + + Identifiers (i.e., the names of global variables) can be associated +with either scalar values or with arrays. In addition, `gawk' provides +true arrays of arrays, where any given array element can itself be an +array. Discussion of arrays is delayed until *note Array +Manipulation::. + + The various macros listed earlier make it easier to use the elements +of the `union' as if they were fields in a `struct'; this is a common +coding practice in C. Such code is easier to write and to read, but it +remains _your_ responsibility to make sure that the `val_type' member +correctly reflects the type of the value in the `awk_value_t'. + + Conceptually, the first three members of the `union' (number, string, +and array) are all that is needed for working with `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: `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 "scalar cookie"(1) 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 `awk_scalar_t' type and `scalar_cookie' +macro. Given a scalar cookie, `gawk' can directly retrieve or modify +the value, as required, without having to find it first. + + The `awk_value_cookie_t' type and `value_cookie' macro are similar. +If you know that you wish to use the same numeric or string _value_ for +one or more variables, you can create the value once, retaining a +"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 `gawk' process as well as the time needed to create +the value. + + ---------- Footnotes ---------- + + (1) See the "cookie" entry in the Jargon file +(http://catb.org/jargon/html/C/cookie.html) for a definition of +"cookie", and the "magic cookie" entry in the Jargon file +(http://catb.org/jargon/html/M/magic-cookie.html) for a nice example. +See also the entry for "Cookie" in the *note Glossary::. + + +File: gawk.info, Node: Memory Allocation Functions, Next: Constructor Functions, Prev: General Data Types, Up: Extension API Description + +16.4.3 Memory Allocation Functions and Convenience Macros +--------------------------------------------------------- - * `dgawk' is designed to be used by running a program (with all its - parameters) on the command line, as described in *Note dgawk - 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. +The API provides a number of "memory allocation" functions for +allocating memory that can be passed to `gawk', as well as a number of +convenience macros. This node presents them all as function +prototypes, in the way that extension code would use them: - * `dgawk' only accepts source supplied with the `-f' option. +`void *gawk_malloc(size_t size);' + Call the correct version of `malloc()' to allocate storage that may + be passed to `gawk'. - 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! +`void *gawk_calloc(size_t nmemb, size_t size);' + Call the correct version of `calloc()' to allocate storage that may + be passed to `gawk'. + +`void *gawk_realloc(void *ptr, size_t size);' + Call the correct version of `realloc()' to allocate storage that + may be passed to `gawk'. + +`void gawk_free(void *ptr);' + Call the correct version of `free()' to release storage that was + allocated with `gawk_malloc()', `gawk_calloc()' or + `gawk_realloc()'. + + 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 `gawk' executable.(1) If `gawk' were to +use its version of `free()' when the memory came from an unrelated +version of `malloc()', unexpected behavior would likely result. + + Two convenience macros may be used for allocating storage from +`gawk_malloc()' and `gawk_realloc()'. If the allocation fails, they +cause `gawk' to exit with a fatal error message. They should be used +as if they were procedure calls that do not return a value. + +`#define emalloc(pointer, type, size, message) ...' + The arguments to this macro are as follows: + + `pointer' + The pointer variable to point at the allocated storage. + + `type' + The type of the pointer variable. This is used to create a + cast for the call to `gawk_malloc()'. + + `size' + The total number of bytes to be allocated. + + `message' + A message to be prefixed to the fatal error message. + Typically this is the name of the function using the macro. + + For example, you might allocate a string value like so: + + 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); + +`#define erealloc(pointer, type, size, message) ...' + This is like `emalloc()', but it calls `gawk_realloc()', instead + of `gawk_malloc()'. The arguments are the same as for the + `emalloc()' macro. + + ---------- Footnotes ---------- + + (1) This is more common on MS-Windows systems, but can happen on +Unix-like systems as well. + + +File: gawk.info, Node: Constructor Functions, Next: Registration Functions, Prev: Memory Allocation Functions, Up: Extension API Description + +16.4.4 Constructor Functions +---------------------------- + +The API provides a number of "constructor" functions for creating +string and numeric values, as well as a number of convenience macros. +This node presents them all as function prototypes, in the way that +extension code would use them: + +`static inline awk_value_t *' +`make_const_string(const char *string, size_t length, awk_value_t *result)' + This function creates a string value in the `awk_value_t' variable + pointed to by `result'. It expects `string' to be a C string + constant (or other string data), and automatically creates a + _copy_ of the data for storage in `result'. It returns `result'. + +`static inline awk_value_t *' +`make_malloced_string(const char *string, size_t length, awk_value_t *result)' + This function creates a string value in the `awk_value_t' variable + pointed to by `result'. It expects `string' to be a `char *' value + pointing to data previously obtained from `gawk_malloc()', + `gawk_calloc()' or `gawk_realloc()'. The idea here is that the + data is passed directly to `gawk', which assumes responsibility + for it. It returns `result'. + +`static inline awk_value_t *' +`make_null_string(awk_value_t *result)' + This specialized function creates a null string (the "undefined" + value) in the `awk_value_t' variable pointed to by `result'. It + returns `result'. + +`static inline awk_value_t *' +`make_number(double num, awk_value_t *result)' + This function simply creates a numeric value in the `awk_value_t' + variable pointed to by `result'. + + +File: gawk.info, Node: Registration Functions, Next: Printing Messages, Prev: Constructor Functions, Up: Extension API Description + +16.4.5 Registration Functions +----------------------------- + +This minor node describes the API functions for registering parts of +your extension with `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. + + +File: gawk.info, Node: Extension Functions, Next: Exit Callback Functions, Up: Registration Functions + +16.4.5.1 Registering An Extension Function +.......................................... + +Extension functions are described by the following record: + + 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; + + The fields are: + +`const char *name;' + The name of the new function. `awk' level code calls the function + by this name. This is a regular C string. + + Function names must obey the rules for `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. + +`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 `*result' with either a + number or a string. `gawk' takes ownership of any string memory. + As mentioned earlier, string memory *must* come from one of + `gawk_malloc()', `gawk_calloc()', or `gawk_realloc()'. + + The `num_actual_args' argument tells the C function how many + actual parameters were passed from the calling `awk' code. + + The function must return the value of `result'. This is for the + convenience of the calling code inside `gawk'. + +`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 `awk' functions, it + is likely OK to ignore extra arguments. + + Once you have a record representing your extension function, you +register it with `gawk' using this API function: + +`awk_bool_t add_ext_func(const char *namespace, const awk_ext_func_t *func);' + This function returns true upon success, false otherwise. The + `namespace' parameter is currently not used; you should pass in an + empty string (`""'). The `func' pointer is the address of a + `struct' representing your function, as just described. + + +File: gawk.info, Node: Exit Callback Functions, Next: Extension Version String, Prev: Extension Functions, Up: Registration Functions + +16.4.5.2 Registering An Exit Callback Function +.............................................. + +An "exit callback" function is a function that `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 `gawk' using the following function: + +`void awk_atexit(void (*funcp)(void *data, int exit_status),' +` void *arg0);' + The parameters are: + + `funcp' + A pointer to the function to be called before `gawk' exits. + The `data' parameter will be the original value of `arg0'. + The `exit_status' parameter is the exit status value that + `gawk' intends to pass to the `exit()' system call. + + `arg0' + A pointer to private data which `gawk' saves in order to pass + to the function pointed to by `funcp'. + + Exit callback functions are called in last-in-first-out (LIFO) +order--that is, in the reverse order in which they are registered with +`gawk'. + + +File: gawk.info, Node: Extension Version String, Next: Input Parsers, Prev: Exit Callback Functions, Up: Registration Functions + +16.4.5.3 Registering An Extension Version String +................................................ + +You can register a version string which indicates the name and version +of your extension, with `gawk', as follows: + +`void register_ext_version(const char *version);' + Register the string pointed to by `version' with `gawk'. Note + that `gawk' does _not_ copy the `version' string, so it should not + be changed. + + `gawk' prints all registered extension version strings when it is +invoked with the `--version' option. + + +File: gawk.info, Node: Input Parsers, Next: Output Wrappers, Prev: Extension Version String, Up: Registration Functions + +16.4.5.4 Customized Input Parsers +................................. + +By default, `gawk' reads text files as its input. It uses the value of +`RS' to find the end of the record, and then uses `FS' (or +`FIELDWIDTHS' or `FPAT') to split it into fields (*note Reading +Files::). Additionally, it sets the value of `RT' (*note 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 `gawk' record processing +code, along with indicators for the value and length of the data to be +used for `RT', if any. + + To provide an input parser, you must first provide two functions +(where XXX is a prefix name for your extension): + +`awk_bool_t XXX_can_take_file(const awk_input_buf_t *iobuf);' + This function examines the information available in `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 `gawk'. + +`awk_bool_t XXX_take_control_of(awk_input_buf_t *iobuf);' + When `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 `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 `gawk' will not use the input parser. + The details are presented shortly. + + Your extension should package these functions inside an +`awk_input_parser_t', which looks like this: + + 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; + + The fields are: + +`const char *name;' + The name of the input parser. This is a regular C string. + +`awk_bool_t (*can_take_file)(const awk_input_buf_t *iobuf);' + A pointer to your `XXX_can_take_file()' function. + +`awk_bool_t (*take_control_of)(awk_input_buf_t *iobuf);' + A pointer to your `XXX_take_control_of()' function. + +`awk_const struct input_parser *awk_const next;' + This is for use by `gawk'; therefore it is marked `awk_const' so + that the extension cannot modify it. + + The steps are as follows: + + 1. Create a `static awk_input_parser_t' variable and initialize it + appropriately. + + 2. When your extension is loaded, register your input parser with + `gawk' using the `register_input_parser()' API function (described + next). + + An `awk_input_buf_t' looks like this: + + 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; + + The fields can be divided into two categories: those for use +(initially, at least) by `XXX_can_take_file()', and those for use by +`XXX_take_control_of()'. The first group of fields and their uses are +as follows: + +`const char *name;' + The name of the file. + +`int fd;' + A file descriptor for the file. If `gawk' was able to open the + file, then `fd' will _not_ be equal to `INVALID_HANDLE'. + Otherwise, it will. + +`struct stat sbuf;' + If the file descriptor is valid, then `gawk' will have filled in + this structure via a call to the `fstat()' system call. + + The `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 `gawk' state (the value of a variable defined +previously by the extension and set by `awk' code), the name of the +file, whether or not the file descriptor is valid, the information in +the `struct stat', or any combination of these factors. + + Once `XXX_can_take_file()' has returned true, and `gawk' has decided +to use your input parser, it calls `XXX_take_control_of()'. That +function then fills one of either the `get_record' field or the +`read_func' field in the `awk_input_buf_t'. It must also ensure that +`fd' is _not_ set to `INVALID_HANDLE'. The following list describes +the fields that may be filled by `XXX_take_control_of()': + +`void *opaque;' + This is used to hold any state information needed by the input + parser for this file. It is "opaque" to `gawk'. The input parser + is not required to use this pointer. + +`int (*get_record)(char **out,' +` struct awk_input *iobuf,' +` int *errcode,' +` char **rt_start,' +` 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. + +`ssize_t (*read_func)();' + This function pointer should point to function that has the same + behavior as the standard POSIX `read()' system call. It is an + alternative to the `get_record' pointer. Its behavior is also + described in the text following this list. + +`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 + `XXX_take_control_of()'. It may also close the file. If it does + so, it should set the `fd' field to `INVALID_HANDLE'. + + If `fd' is still not `INVALID_HANDLE' after the call to this + function, `gawk' calls the regular `close()' system call. + + Having a "tear down" function is optional. If your input parser + does not need it, do not set this field. Then, `gawk' calls the + regular `close()' system call on the file descriptor, so it should + be valid. + + The `XXX_get_record()' function does the work of creating input +records. The parameters are as follows: + +`char **out' + This is a pointer to a `char *' variable which is set to point to + the record. `gawk' makes its own copy of the data, so the + extension must manage this storage. + +`struct awk_input *iobuf' + This is the `awk_input_buf_t' for the file. The fields should be + used for reading data (`fd') and for managing private state + (`opaque'), if any. + +`int *errcode' + If an error occurs, `*errcode' should be set to an appropriate + code from `<errno.h>'. + +`char **rt_start' +`size_t *rt_len' + If the concept of a "record terminator" makes sense, then + `*rt_start' should be set to point to the data to be used for + `RT', and `*rt_len' should be set to the length of the data. + Otherwise, `*rt_len' should be set to zero. `gawk' makes its own + copy of this data, so the extension must manage this storage. + + The return value is the length of the buffer pointed to by `*out', +or `EOF' if end-of-file was reached or an error occurred. + + It is guaranteed that `errcode' is a valid pointer, so there is no +need to test for a `NULL' value. `gawk' sets `*errcode' to zero, so +there is no need to set it unless an error occurs. + + If an error does occur, the function should return `EOF' and set +`*errcode' to a value greater than zero. In that case, if `*errcode' +does not equal zero, `gawk' automatically updates the `ERRNO' variable +based on the value of `*errcode'. (In general, setting `*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 `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 `read()' system call, +and you fill in the `read_func' pointer with its address in the +`awk_input_buf_t' structure. + + By default, `gawk' sets the `read_func' pointer to point to the +`read()' system call. So your extension need not set this field +explicitly. + + 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, `gawk' will + call it, and never call the raw read function. + + `gawk' ships with a sample extension that reads directories, +returning records for each entry in the directory (*note 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 `awk' code. You may want it to +always be called, and take effect as appropriate (as the `readdir' +extension does). Or you may want it to take effect based upon the +value of an `awk' variable, as the XML extension from the `gawkextlib' +project does (*note gawkextlib::). In the latter case, code in a +`BEGINFILE' section can look at `FILENAME' and `ERRNO' to decide +whether or not to activate an input parser (*note BEGINFILE/ENDFILE::). + + You register your input parser with the following function: + +`void register_input_parser(awk_input_parser_t *input_parser);' + Register the input parser pointed to by `input_parser' with `gawk'. + + +File: gawk.info, Node: Output Wrappers, Next: Two-way processors, Prev: Input Parsers, Up: Registration Functions + +16.4.5.5 Customized Output Wrappers +................................... + +An "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 `>' or +`>>' I/O redirection operators (*note Redirection::). + + The output wrapper is very similar to the input parser structure: + + 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; + + The members are as follows: + +`const char *name;' + This is the name of the output wrapper. + +`awk_bool_t (*can_take_file)(const awk_output_buf_t *outbuf);' + This points to a function that examines the information in the + `awk_output_buf_t' structure pointed to by `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 `gawk'. + +`awk_bool_t (*take_control_of)(awk_output_buf_t *outbuf);' + The function pointed to by this field is called when `gawk' + decides to let the output wrapper take control of the file. It + should fill in appropriate members of the `awk_output_buf_t' + structure, as described next, and return true if successful, false + otherwise. + +`awk_const struct output_wrapper *awk_const next;' + This is for use by `gawk'; therefore it is marked `awk_const' so + that the extension cannot modify it. + + The `awk_output_buf_t' structure looks like this: + + 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; + + Here too, your extension will define `XXX_can_take_file()' and +`XXX_take_control_of()' functions that examine and update data members +in the `awk_output_buf_t'. The data members are as follows: + +`const char *name;' + The name of the output file. + +`const char *mode;' + The mode string (as would be used in the second argument to + `fopen()') with which the file was opened. + +`FILE *fp;' + The `FILE' pointer from `<stdio.h>'. `gawk' opens the file before + attempting to find an output wrapper. + +`awk_bool_t redirected;' + This field must be set to true by the `XXX_take_control_of()' + function. + +`void *opaque;' + This pointer is opaque to `gawk'. The extension should use it to + store a pointer to any private data associated with the file. + +`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);' + These pointers should be set to point to functions that perform + the equivalent function as the `<stdio.h>' functions do, if + appropriate. `gawk' uses these function pointers for all output. + `gawk' initializes the pointers to point to internal, "pass + through" functions that just call the regular `<stdio.h>' + functions, so an extension only needs to redefine those functions + that are appropriate for what it does. + + The `XXX_can_take_file()' function should make a decision based upon +the `name' and `mode' fields, and any additional state (such as `awk' +variable values) that is appropriate. + + When `gawk' calls `XXX_take_control_of()', that function should fill +in the other fields, as appropriate, except for `fp', which it should +just use normally. + + You register your output wrapper with the following function: + +`void register_output_wrapper(awk_output_wrapper_t *output_wrapper);' + Register the output wrapper pointed to by `output_wrapper' with + `gawk'. + + +File: gawk.info, Node: Two-way processors, Prev: Output Wrappers, Up: Registration Functions + +16.4.5.6 Customized Two-way Processors +...................................... + +A "two-way processor" combines an input parser and an output wrapper for +two-way I/O with the `|&' operator (*note Redirection::). It makes +identical use of the `awk_input_parser_t' and `awk_output_buf_t' +structures as described earlier. + + A two-way processor is represented by the following structure: + + 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; + + The fields are as follows: + +`const char *name;' + The name of the two-way processor. + +`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 file name. It should not change any state (variable + values, etc.) within `gawk'. + +`awk_bool_t (*take_control_of)(const char *name,' +` awk_input_buf_t *inbuf,' +` awk_output_buf_t *outbuf);' + This function should fill in the `awk_input_buf_t' and + `awk_outut_buf_t' structures pointed to by `inbuf' and `outbuf', + respectively. These structures were described earlier. + +`awk_const struct two_way_processor *awk_const next;' + This is for use by `gawk'; therefore it is marked `awk_const' so + that the extension cannot modify it. + + As with the input parser and output processor, you provide "yes I +can take this" and "take over for this" functions, +`XXX_can_take_two_way()' and `XXX_take_control_of()'. + + You register your two-way processor with the following function: + +`void register_two_way_processor(awk_two_way_processor_t *two_way_processor);' + Register the two-way processor pointed to by `two_way_processor' + with `gawk'. + + +File: gawk.info, Node: Printing Messages, Next: Updating `ERRNO', Prev: Registration Functions, Up: Extension API Description + +16.4.6 Printing Messages +------------------------ + +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 `gawk' when the extension was loaded:(1) + +`void fatal(awk_ext_id_t id, const char *format, ...);' + Print a message and then cause `gawk' to exit immediately. + +`void warning(awk_ext_id_t id, const char *format, ...);' + Print a warning message. + +`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 `gawk' was invoked with `--lint=fatal', + then lint warnings become fatal error messages. + + All of these functions are otherwise like the C `printf()' family of +functions, where the `format' parameter is a string with literal +characters and formatting codes intermixed. + + ---------- Footnotes ---------- + + (1) 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. + + +File: gawk.info, Node: Updating `ERRNO', Next: Requesting Values, Prev: Printing Messages, Up: Extension API Description + +16.4.7 Updating `ERRNO' +----------------------- + +The following functions allow you to update the `ERRNO' variable: + +`void update_ERRNO_int(int errno_val);' + Set `ERRNO' to the string equivalent of the error code in + `errno_val'. The value should be one of the defined error codes in + `<errno.h>', and `gawk' turns it into a (possibly translated) + string using the C `strerror()' function. + +`void update_ERRNO_string(const char *string);' + Set `ERRNO' directly to the string value of `ERRNO'. `gawk' makes + a copy of the value of `string'. + +`void unset_ERRNO(void);' + Unset `ERRNO'. + + +File: gawk.info, Node: Requesting Values, Next: Accessing Parameters, Prev: Updating `ERRNO', Up: Extension API Description + +16.4.8 Requesting Values +------------------------ + +All of the functions that return values from `gawk' work in the same +way. You pass in an `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 `awk_value_t' result. +Otherwise, the function returns false, and the `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 *note +table-value-types-returned::. + + Type of Actual Value +-------------------------------------------------------------------------- + + String Number Array Undefined +------------------------------------------------------------------------------ + String String String false false + Number Number if can Number false false + 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 + +Table 16.1: API value types returned + + +File: gawk.info, Node: Accessing Parameters, Next: Symbol Table Access, Prev: Requesting Values, Up: Extension API Description + +16.4.9 Accessing and Updating Parameters +---------------------------------------- + +Two functions give you access to the arguments (parameters) passed to +your extension function. They are: + +`awk_bool_t get_argument(size_t count,' +` awk_valtype_t wanted,' +` awk_value_t *result);' + Fill in the `awk_value_t' structure pointed to by `result' with + the `count''th argument. Return true if the actual type matches + `wanted', false otherwise. In the latter case, `result->val_type' + indicates the actual type (*note Table 16.1: + table-value-types-returned.). Counts are zero based--the first + argument is numbered zero, the second one, and so on. `wanted' + indicates the type of value expected. + +`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 `count' is too big, + or if the argument's type is not undefined. *Note Array + Manipulation::, for more information on creating arrays. + + +File: gawk.info, Node: Symbol Table Access, Next: Array Manipulation, Prev: Accessing Parameters, Up: Extension API Description + +16.4.10 Symbol Table Access +--------------------------- + +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. + + +File: gawk.info, Node: Symbol table by name, Next: Symbol table by cookie, Up: Symbol Table Access + +16.4.10.1 Variable Access and Update by Name +............................................ + +The following routines provide the ability to access and update global +`awk'-level variables by name. In compiler terminology, identifiers of +different kinds are termed "symbols", thus the "sym" in the routines' +names. The data structure which stores information about symbols is +termed a "symbol table". + +`awk_bool_t sym_lookup(const char *name,' +` awk_valtype_t wanted,' +` awk_value_t *result);' + Fill in the `awk_value_t' structure pointed to by `result' with + the value of the variable named by the string `name', which is a + regular C string. `wanted' indicates the type of value expected. + Return true if the actual type matches `wanted', false otherwise. + In the latter case, `result->val_type' indicates the actual type + (*note Table 16.1: table-value-types-returned.). + +`awk_bool_t sym_update(const char *name, awk_value_t *value);' + Update the variable named by the string `name', which is a regular + C string. The variable is added to `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 _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 `ARGC' or `NF'). + + An extension can look up the value of `gawk''s special variables. +However, with the exception of the `PROCINFO' array, an extension +cannot change any of those variables. + + CAUTION: It is possible for the lookup of `PROCINFO' to fail. This + happens if the `awk' program being run does not reference + `PROCINFO'; in this case, `gawk' doesn't bother to create the + array and populate it. + + +File: gawk.info, Node: Symbol table by cookie, Next: Cached values, Prev: Symbol table by name, Up: Symbol Table Access + +16.4.10.2 Variable Access and Update by Cookie +.............................................. + +A "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 `gawk''s symbol table every time access is needed. This +was discussed earlier in *note General Data Types::. + + The following functions let you work with scalar cookies: + +`awk_bool_t sym_lookup_scalar(awk_scalar_t cookie,' +` awk_valtype_t wanted,' +` awk_value_t *result);' + Retrieve the current value of a scalar cookie. Once you have + obtained a scalar cookie using `sym_lookup()', you can use this + function to get its value more efficiently. Return false if the + value cannot be retrieved. + +`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 `AWK_STRING' or `AWK_NUMBER'. Here + too, the predefined variables may not be updated. + + It is not obvious at first glance how to work with scalar cookies or +what their raison d'e^tre really is. In theory, the `sym_lookup()' and +`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: + + /* 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); + } + +This code looks (and is) simple and straightforward. So what's the +problem? + + Well, consider what happens if `awk'-level code associated with your +extension calls the `magic()' function (implemented in C by +`do_magic()'), once per record, while processing hundreds of thousands +or millions of records. The `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.(1) + + Thus, the way to use cookies is as follows. First, install your +extension's variable in `gawk''s symbol table using `sym_update()', as +usual. Then get a scalar cookie for the variable using `sym_lookup()': + + 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; + ... + } + + Next, use the routines in this section for retrieving and updating +the value through the cookie. Thus, `do_magic()' now becomes something +like this: + + /* 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); + } + ... + + return make_number(0.0, result); + } + + 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. + + ---------- Footnotes ---------- + + (1) The difference is measurable and quite real. Trust us. + + +File: gawk.info, Node: Cached values, Prev: Symbol table by cookie, Up: Symbol Table Access + +16.4.10.3 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 +*note Constructor Functions::. You can then assign those values to +variables using `sym_update()' or `sym_update_scalar()', as you like. + + However, you can understand the point of cached values if you +remember that _every_ string value's storage _must_ come from +`gawk_malloc()', `gawk_calloc()', or `gawk_realloc()'. If you have 20 +variables, all of which have the same string value, you must create 20 +identical copies of the string.(1) + + It is clearly more efficient, if possible, to create a value once, +and then tell `gawk' to reuse the value for multiple variables. That is +what the routines in this section let you do. The functions are as +follows: + +`awk_bool_t create_value(awk_value_t *value, awk_value_cookie_t *result);' + Create a cached string or numeric value from `value' for efficient + later assignment. Only values of type `AWK_NUMBER' and + `AWK_STRING' are allowed. Any other type is rejected. + `AWK_UNDEFINED' could be allowed, but doing so would result in + inferior performance. + +`awk_bool_t release_value(awk_value_cookie_t vc);' + Release the memory associated with a value cookie obtained from + `create_value()'. + + 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: + + 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 */ + ... + /* ... fill in long_string and long_string_len ... */ + make_malloced_string(long_string, long_string_len, & value); + create_value(& value, & answer_cookie); /* create cookie */ + ... + } + + Once the value is created, you can use it as the value of any number +of variables: + + static awk_value_t * + do_magic(int nargs, awk_value_t *result) + { + awk_value_t new_value; + + ... /* as earlier */ + + value.val_type = AWK_VALUE_COOKIE; + value.value_cookie = answer_cookie; + sym_update("VAR1", & value); + sym_update("VAR2", & value); + ... + sym_update("VAR100", & value); + ... + } + +Using value cookies in this way saves considerable storage, as all of +`VAR1' through `VAR100' share the same value. + + You might be wondering, "Is this sharing problematic? What happens +if `awk' code assigns a new value to `VAR1', are all the others changed +too?" + + That's a great question. The answer is that no, it's not a problem. +Internally, `gawk' uses "reference-counted strings". This means that +many variables can share the same string value, and `gawk' keeps track +of the usage. When a variable's value changes, `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 (*note Exit Callback +Functions::) you should release any cached values that you created, +using `release_value()'. + + ---------- Footnotes ---------- + + (1) Numeric values are clearly less problematic, requiring only a C +`double' to store. + + +File: gawk.info, Node: Array Manipulation, Next: Extension API Variables, Prev: Symbol Table Access, Up: Extension API Description + +16.4.11 Array Manipulation +-------------------------- + +The primary data structure(1) in `awk' is the associative array (*note +Arrays::). Extensions need to be able to manipulate `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 (*note 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. + + ---------- Footnotes ---------- + + (1) OK, the only data structure. + + +File: gawk.info, Node: Array Data Types, Next: Array Functions, Up: Array Manipulation + +16.4.11.1 Array Data Types +.......................... + +The data types associated with arrays are as follows: + +`typedef void *awk_array_t;' + If you request the value of an array variable, you get back an + `awk_array_t' value. This value is opaque(1) 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 `FILE *' values are used with the `<stdio.h>' + library routines. + +`typedef struct awk_element {' +` /* convenience linked list pointer, not used by gawk */' +` struct awk_element *next;' +` enum {' +` AWK_ELEMENT_DEFAULT = 0, /* set by gawk */' +` AWK_ELEMENT_DELETE = 1 /* set by extension */' +` } flags;' +` awk_value_t index;' +` awk_value_t value;' +`} awk_element_t;' + The `awk_element_t' is a "flattened" array element. `awk' produces + an array of these inside the `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: + + `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. + + `enum { ... } flags;' + A set of flag values that convey information between the + extension and `gawk'. Currently there is only one: + `AWK_ELEMENT_DELETE'. Setting it causes `gawk' to delete the + element from the original array upon release of the flattened + array. + + `index' + `value' + The index and value of the element, respectively. _All_ + memory pointed to by `index' and `value' belongs to `gawk'. + +`typedef struct awk_flat_array {' +` awk_const void *awk_const opaque1; /* for use by gawk */' +` awk_const void *awk_const opaque2; /* for use by gawk */' +` awk_const size_t count; /* how many elements */' +` awk_element_t elements[1]; /* will be extended */' +`} awk_flat_array_t;' + This is a flattened array. When an extension gets one of these + from `gawk', the `elements' array is of actual size `count'. The + `opaque1' and `opaque2' pointers are for use by `gawk'; therefore + they are marked `awk_const' so that the extension cannot modify + them. + + ---------- Footnotes ---------- + + (1) It is also a "cookie," but the `gawk' developers did not wish to +overuse this term. + + +File: gawk.info, Node: Array Functions, Next: Flattening Arrays, Prev: Array Data Types, Up: Array Manipulation + +16.4.11.2 Array Functions +......................... + +The following functions relate to individual array elements. + +`awk_bool_t get_element_count(awk_array_t a_cookie, size_t *count);' + For the array represented by `a_cookie', place in `*count' the + number of elements it contains. A subarray counts as a single + element. Return false if there is an error. + +`awk_bool_t get_array_element(awk_array_t a_cookie,' +` const awk_value_t *const index,' +` awk_valtype_t wanted,' +` awk_value_t *result);' + For the array represented by `a_cookie', return in `*result' the + value of the element whose index is `index'. `wanted' specifies + the type of value you wish to retrieve. Return false if `wanted' + does not match the actual type or if `index' is not in the array + (*note Table 16.1: table-value-types-returned.). + + The value for `index' can be numeric, in which case `gawk' + converts it to a string. Using non-integral values is possible, but + requires that you understand how such values are converted to + strings (*note Conversion::); thus using integral values is safest. + + As with _all_ strings passed into `gawk' from an extension, the + string value of `index' must come from `gawk_malloc()', + `gawk_calloc()' or `gawk_realloc()', and `gawk' releases the + storage. + +`awk_bool_t set_array_element(awk_array_t a_cookie,' +` const awk_value_t *const index,' +` const awk_value_t *const value);' + In the array represented by `a_cookie', create or modify the + element whose index is given by `index'. The `ARGV' and `ENVIRON' + arrays may not be changed, although the `PROCINFO' array can be. + +`awk_bool_t set_array_element_by_elem(awk_array_t a_cookie,' +` awk_element_t element);' + Like `set_array_element()', but take the `index' and `value' from + `element'. This is a convenience macro. + +`awk_bool_t del_array_element(awk_array_t a_cookie,' +` const awk_value_t* const index);' + Remove the element with the given index from the array represented + by `a_cookie'. Return true if the element was removed, or false + if the element did not exist in the array. + + The following functions relate to arrays as a whole: + +`awk_array_t create_array(void);' + Create a new array to which elements may be added. *Note Creating + Arrays::, for a discussion of how to create a new array and add + elements to it. + +`awk_bool_t clear_array(awk_array_t a_cookie);' + Clear the array represented by `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 `delete' statement (*note Delete::). + +`awk_bool_t flatten_array(awk_array_t a_cookie, awk_flat_array_t **data);' + For the array represented by `a_cookie', create an + `awk_flat_array_t' structure and fill it in. Set the pointer whose + address is passed as `data' to point to this structure. Return + true upon success, or false otherwise. *Note Flattening Arrays::, + for a discussion of how to flatten an array and work with it. + +`awk_bool_t release_flattened_array(awk_array_t a_cookie,' +` 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 `awk_flat_array_t' structure. The + function returns true upon success, false otherwise. + + +File: gawk.info, Node: Flattening Arrays, Next: Creating Arrays, Prev: Array Functions, Up: Array Manipulation + +16.4.11.3 Working With All The Elements of an Array +................................................... + +To "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 `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 `gawk' script that drives the test extension: + + @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 "" + } + +This code creates an array with `split()' (*note String Functions::) +and then calls `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 `awk' code +then prints the return value and checks if the element was indeed +deleted. Here is the C code that implements `dump_array_and_delete()'. +It has been edited slightly for presentation. + + The first part declares variables, sets up the default return value +in `result', and checks that the function was called with the correct +number of arguments: + + 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; + } + + 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: + + /* 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; + } + + For testing purposes and to make sure that the C code sees the same +number of elements as the `awk' code, the second step is to get the +count of elements in the array and print it: + + 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); + + The third step is to actually flatten the array, and then to double +check that the count in the `awk_flat_array_t' is the same as the count +just retrieved: + + 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; + } + + 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 `get_argument()' are zero-based, thus the +second argument is numbered one: + + if (! get_argument(1, AWK_STRING, & value3)) { + printf("dump_array_and_delete: get_argument(1) failed\n"); + goto out; + } + + 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 `AWK_ELEMENT_DELETE' bit in the +`flags' field of the element. When the array is released, `gawk' +traverses the flattened array, and deletes any elements which have this +flag bit set: + + 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); + } + } + + The sixth step is to release the flattened array. This tells `gawk' +that the extension is no longer using the array, and that it should +delete any elements marked for deletion. `gawk' also frees any storage +that was allocated, so you should not use the pointer (`flat_array' in +this code) once you have called `release_flattened_array()': + + if (! release_flattened_array(value2.array_cookie, flat_array)) { + printf("dump_array_and_delete: could not release flattened array\n"); + goto out; + } + + Finally, because everything was successful, the function sets the +return value to success, and returns: + + make_number(1.0, result); + out: + return result; + } + + Here is the output from running this part of the test: + + 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"! + + +File: gawk.info, Node: Creating Arrays, Prev: Flattening Arrays, Up: Array Manipulation + +16.4.11.4 How To Create and Populate Arrays +........................................... + +Besides working with arrays created by `awk' code, you can create +arrays and populate them as you see fit, and then `awk' code can access +them and manipulate them. + + There are two important points about creating arrays from extension +code: + + * You must install a new array into `gawk''s symbol table + immediately upon creating it. Once you have done so, you can then + populate the array. + + 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 `gawk''s symbol + table using `sym_update()', or install it as an element in a + previously existing array using `set_array_element()'. We show + example code shortly. + + * Due to `gawk' internals, after using `sym_update()' to install an + array into `gawk', you have to retrieve the array cookie from the + value passed in to `sym_update()' before doing anything else with + it, like so: + + 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 */ + + If installing an array as a subarray, you must also retrieve the + value of the array cookie after the call to `set_element()'. + + The following C code is a simple test extension to create an array +with two regular elements and with a subarray. The leading `#include' +directives and boilerplate variable declarations (*note Extension API +Boilerplate::) are omitted for brevity. The first step is to create a +new array and then install it in the symbol table: + + /* 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; + +Note how `a_cookie' is reset from the `array_cookie' field in the +`value' structure. + + The second step is to install two regular values into `new_array': + + (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; + } + + The third step is to create the subarray and install it: + + (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; + + The final step is to populate the subarray with its own element: + + (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; + } + } + + Here is a sample script that loads the extension and then dumps the +array: + + @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); + } + + Here is the result of running the script: + + $ AWKLIBPATH=$PWD ./gawk -f subarray.awk + -| new_array["subarray"]["foo"] = bar + -| new_array["hello"] = world + -| new_array["answer"] = 42 + +(*Note Finding Extensions::, for more information on the `AWKLIBPATH' +environment variable.) + + +File: gawk.info, Node: Extension API Variables, Next: Extension API Boilerplate, Prev: Array Manipulation, Up: Extension API Description + +16.4.12 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 `gawk' was compiled). The second provides +information about how `gawk' was invoked. + +* Menu: + +* Extension Versioning:: API Version information. +* Extension API Informational Variables:: Variables providing information about + `gawk''s invocation. + + +File: gawk.info, Node: Extension Versioning, Next: Extension API Informational Variables, Up: Extension API Variables + +16.4.12.1 API Version Constants and Variables +............................................. + +The API provides both a "major" and a "minor" version number. The API +versions are available at compile time as constants: + +`GAWK_API_MAJOR_VERSION' + The major version of the API. + +`GAWK_API_MINOR_VERSION' + The minor version of the API. + + The minor version increases when new functions are added to the API. +Such new functions are always added to the end of the API `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 `gawk' using a different version. +For this reason, the major and minor API versions of the running `gawk' +are included in the API `struct' as read-only constant integers: + +`api->major_version' + The major version of the running `gawk'. + +`api->minor_version' + The minor version of the running `gawk'. + + It is up to the extension to decide if there are API +incompatibilities. Typically a check like this is enough: + + 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); + } + + Such code is included in the boilerplate `dl_load_func()' macro +provided in `gawkapi.h' (discussed later, in *note Extension API +Boilerplate::). + + +File: gawk.info, Node: Extension API Informational Variables, Prev: Extension Versioning, Up: Extension API Variables + +16.4.12.2 Informational Variables +................................. + +The API provides access to several variables that describe whether the +corresponding command-line options were enabled when `gawk' was +invoked. The variables are: + +`do_debug' + This variable is true if `gawk' was invoked with `--debug' option. + +`do_lint' + This variable is true if `gawk' was invoked with `--lint' option. + +`do_mpfr' + This variable is true if `gawk' was invoked with `--bignum' option. + +`do_profile' + This variable is true if `gawk' was invoked with `--profile' + option. + +`do_sandbox' + This variable is true if `gawk' was invoked with `--sandbox' + option. + +`do_traditional' + This variable is true if `gawk' was invoked with `--traditional' + option. + + The value of `do_lint' can change if `awk' code modifies the `LINT' +predefined variable (*note Built-in Variables::). The others should +not change during execution. -File: gawk.info, Node: Language History, Next: Installation, Prev: Debugger, Up: Top +File: gawk.info, Node: Extension API Boilerplate, Prev: Extension API Variables, Up: Extension API Description + +16.4.13 Boilerplate Code +------------------------ + +As mentioned earlier (*note 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 `gawkapi.h' header file: + + /* 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 ... = "some string" */ + + static awk_ext_func_t func_table[] = { + { "name", do_name, 1 }, + /* ... */ + }; + + /* EITHER: */ + + static awk_bool_t (*init_func)(void) = NULL; + + /* OR: */ + + static awk_bool_t + init_my_extension(void) + { + ... + } + + static awk_bool_t (*init_func)(void) = init_my_extension; + + dl_load_func(func_table, some_name, "name_space_in_quotes") + + These variables and functions are as follows: + +`int plugin_is_GPL_compatible;' + This asserts that the extension is compatible with the GNU GPL + (*note Copying::). If your extension does not have this, `gawk' + will not load it (*note Plugin License::). + +`static gawk_api_t *const api;' + This global `static' variable should be set to point to the + `gawk_api_t' pointer that `gawk' passes to your `dl_load()' + function. This variable is used by all of the macros. + +`static awk_ext_id_t ext_id;' + This global static variable should be set to the `awk_ext_id_t' + value that `gawk' passes to your `dl_load()' function. This + variable is used by all of the macros. + +`static const char *ext_version = NULL; /* or ... = "some string" */' + This global `static' variable should be set either to `NULL', or + to point to a string giving the name and version of your extension. + +`static awk_ext_func_t func_table[] = { ... };' + This is an array of one or more `awk_ext_func_t' structures as + described earlier (*note Extension Functions::). It can then be + looped over for multiple calls to `add_ext_func()'. + +`static awk_bool_t (*init_func)(void) = NULL;' +` OR' +`static awk_bool_t init_my_extension(void) { ... }' +`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 `init_func' pointer to point to your function. + The function should return `awk_false' upon failure, or `awk_true' + if everything goes well. + + If you don't need to do any initialization, define the pointer and + initialize it to `NULL'. + +`dl_load_func(func_table, some_name, "name_space_in_quotes")' + This macro expands to a `dl_load()' function that performs all the + necessary initializations. + + The point of all the variables and arrays is to let the `dl_load()' +function (from the `dl_load_func()' macro) do all the standard work. It +does the following: + + 1. Check the API versions. If the extension major version does not + match `gawk''s, or if the extension minor version is greater than + `gawk''s, it prints a fatal error message and exits. + + 2. Load the functions defined in `func_table'. If any of them fails + to load, it prints a warning message but continues on. + + 3. If the `init_func' pointer is not `NULL', call the function it + points to. If it returns `awk_false', print a warning message. + + 4. If `ext_version' is not `NULL', register the version string with + `gawk'. + + +File: gawk.info, Node: Finding Extensions, Next: Extension Example, Prev: Extension API Description, Up: Dynamic Extensions + +16.5 How `gawk' Finds Extensions +================================ + +Compiled extensions have to be installed in a directory where `gawk' +can find them. If `gawk' is configured and built in the default +fashion, the directory in which to find extensions is +`/usr/local/lib/gawk'. You can also specify a search path with a list +of directories to search for compiled extensions. *Note AWKLIBPATH +Variable::, for more information. + + +File: gawk.info, Node: Extension Example, Next: Extension Samples, Prev: Finding Extensions, Up: Dynamic Extensions + +16.6 Example: Some File Functions +================================= + + No matter where you go, there you are. -- Buckaroo Banzai + + Two useful functions that are not in `awk' are `chdir()' (so that an +`awk' program can change its directory) and `stat()' (so that an `awk' +program can gather information about a file). In order to illustrate +the API in action, this minor node implements these functions for +`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. + + +File: gawk.info, Node: Internal File Description, Next: Internal File Ops, Up: Extension Example + +16.6.1 Using `chdir()' and `stat()' +----------------------------------- + +This minor node shows how to use the new functions at the `awk' level +once they've been integrated into the running `gawk' interpreter. +Using `chdir()' is very straightforward. It takes one argument, the new +directory to change to: + + @load "filefuncs" + ... + newdir = "/home/arnold/funstuff" + ret = chdir(newdir) + if (ret < 0) { + printf("could not change to %s: %s\n", newdir, ERRNO) > "/dev/stderr" + exit 1 + } + ... + + The return value is negative if the `chdir()' failed, and `ERRNO' +(*note Built-in Variables::) is set to a string indicating the error. + + Using `stat()' is a bit more complicated. The C `stat()' function +fills in a structure that has a fair amount of information. The right +way to model this in `awk' is to fill in an associative array with the +appropriate information: + + 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"]) + + The `stat()' function always clears the data array, even if the +`stat()' fails. It fills in the following elements: + +`"name"' + The name of the file that was `stat()''ed. + +`"dev"' +`"ino"' + The file's device and inode numbers, respectively. + +`"mode"' + The file's mode, as a numeric value. This includes both the file's + type and its permissions. + +`"nlink"' + The number of hard links (directory entries) the file has. + +`"uid"' +`"gid"' + The numeric user and group ID numbers of the file's owner. + +`"size"' + The size in bytes of the file. + +`"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. + +`"atime"' +`"mtime"' +`"ctime"' + The file's last access, modification, and inode update times, + respectively. These are numeric timestamps, suitable for + formatting with `strftime()' (*note Time Functions::). + +`"pmode"' + The file's "printable mode." This is a string representation of + the file's type and permissions, such as is produced by `ls + -l'--for example, `"drwxr-xr-x"'. + +`"type"' + A printable string representation of the file's type. The value + is one of the following: + + `"blockdev"' + `"chardev"' + The file is a block or character device ("special file"). + + `"directory"' + The file is a directory. + + `"fifo"' + The file is a named-pipe (also known as a FIFO). + + `"file"' + The file is just a regular file. + + `"socket"' + The file is an `AF_UNIX' ("Unix domain") socket in the + filesystem. + + `"symlink"' + The file is a symbolic link. + +`"devbsize"' + The size of a block for the element indexed by `"blocks"'. This + information is derived from either the `DEV_BSIZE' constant + defined in `<sys/param.h>' on most systems, or the `S_BLKSIZE' + constant in `<sys/stat.h>' on BSD systems. For some other + systems, "a priori" knowledge is used to provide a value. Where no + value can be determined, it defaults to 512. + + Several additional elements may be present depending upon the +operating system and the type of the file. You can test for them in +your `awk' program by using the `in' operator (*note Reference to +Elements::): + +`"blksize"' + The preferred block size for I/O to the file. This field is not + present on all POSIX-like systems in the C `stat' structure. + +`"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). + +`"rdev"' +`"major"' +`"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. + + +File: gawk.info, Node: Internal File Ops, Next: Using Internal File Ops, Prev: Internal File Description, Up: Extension Example + +16.6.2 C Code for `chdir()' and `stat()' +---------------------------------------- + +Here is the C code for these extensions.(1) + + The file includes a number of standard header files, and then +includes the `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 (*note Extension API +Boilerplate::): + + #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; + + By convention, for an `awk' function `foo()', the C function that +implements it is called `do_foo()'. The function should have two +arguments: the first is an `int' usually called `nargs', that +represents the number of actual arguments for the function. The second +is a pointer to an `awk_value_t', usually named `result': + + /* 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")); + + The `newdir' variable represents the new directory to change to, +which is retrieved with `get_argument()'. Note that the first argument +is numbered zero. + + If the argument is retrieved successfully, the function calls the +`chdir()' system call. If the `chdir()' fails, `ERRNO' is updated: + + if (get_argument(0, AWK_STRING, & newdir)) { + ret = chdir(newdir.str_value.str); + if (ret < 0) + update_ERRNO_int(errno); + } + + Finally, the function returns the return value to the `awk' level: + + return make_number(ret, result); + } + + The `stat()' extension is more involved. First comes a function +that turns a numeric mode into a printable representation (e.g., 644 +becomes `-rw-r--r--'). This is omitted here for brevity: + + /* format_mode --- turn a stat mode field into something readable */ + + static char * + format_mode(unsigned long fmode) + { + ... + } + + Next comes a function for reading symbolic links, which is also +omitted here for brevity: + + /* read_symlink --- read a symbolic link into an allocated buffer. + ... */ + + static char * + read_symlink(const char *fname, size_t bufsize, ssize_t *linksize) + { + ... + } + + Two helper functions simplify entering values in the array that will +contain the result of the `stat()': + + /* 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)); + } + + The following function does most of the work to fill in the +`awk_array_t' result array with values obtained from a valid `struct +stat'. It is done in a separate function to support the `stat()' +function for `gawk' and also to support the `fts()' extension which is +included in the same file but whose code is not shown here (*note +Extension Sample File Functions::). + + The first part of the function is variable declarations, including a +table to map file types to strings: + + /* 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; + + The destination array is cleared, and then code fills in various +elements based on values in the `struct stat': + + /* 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)); + } + +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: + + #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; + } + + The third argument to `stat()' was not discussed previously. This +argument is optional. If present, it causes `do_stat()' to use the +`stat()' system call instead of the `lstat()' system call. This is +done by using a function pointer: `statfunc'. `statfunc' is +initialized to point to `lstat()' (instead of `stat()') to get the file +information, in case the file is a symbolic link. However, if there +were three arguments, `statfunc' is set point to `stat()', instead. + + Here is the `do_stat()' function, which starts with variable +declarations and argument checking: + + /* 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); + } + + Then comes the actual work. First, the function gets the arguments. +Next, it gets the information for the file. If the called function +(`lstat()' or `stat()') returns an error, the code sets `ERRNO' and +returns: + + /* 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); + } + + The tedious work is done by `fill_stat_array()', shown earlier. +When done, the function returns the result from `fill_stat_array()': + + ret = fill_stat_array(name, array, & sbuf); + + return make_number(ret, result); + } + + Finally, it's necessary to provide the "glue" that loads the new +function(s) into `gawk'. + + The `filefuncs' extension also provides an `fts()' function, which +we omit here. For its sake there is an initialization function: + + /* init_filefuncs --- initialization routine */ + + static awk_bool_t + init_filefuncs(void) + { + ... + } + + We are almost done. We need an array of `awk_ext_func_t' structures +for loading each function into `gawk': + + static awk_ext_func_t func_table[] = { + { "chdir", do_chdir, 1 }, + { "stat", do_stat, 2 }, + #ifndef __MINGW32__ + { "fts", do_fts, 3 }, + #endif + }; + + Each extension must have a routine named `dl_load()' to load +everything that needs to be loaded. It is simplest to use the +`dl_load_func()' macro in `gawkapi.h': + + /* define the dl_load() function using the boilerplate macro */ + + dl_load_func(func_table, filefuncs, "") + + And that's it! + + ---------- Footnotes ---------- + + (1) This version is edited slightly for presentation. See +`extension/filefuncs.c' in the `gawk' distribution for the complete +version. + + +File: gawk.info, Node: Using Internal File Ops, Prev: Internal File Ops, Up: Extension Example + +16.6.3 Integrating the Extensions +--------------------------------- + +Now that the code is written, it must be possible to add it at runtime +to the running `gawk' interpreter. First, the code must be compiled. +Assuming that the functions are in a file named `filefuncs.c', and IDIR +is the location of the `gawkapi.h' header file, the following steps(1) +create a GNU/Linux shared library: + + $ gcc -fPIC -shared -DHAVE_CONFIG_H -c -O -g -IIDIR filefuncs.c + $ gcc -o filefuncs.so -shared filefuncs.o + + Once the library exists, it is loaded by using the `@load' keyword: + + # 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"]) + } + + The `AWKLIBPATH' environment variable tells `gawk' where to find +extensions (*note Finding Extensions::). We set it to the current +directory and run the program: + + $ AWKLIBPATH=$PWD gawk -f testff.awk + -| /tmp + -| Info for testff.awk + -| ret = 0 + -| data["blksize"] = 4096 + -| data["devbsize"] = 512 + -| data["mtime"] = 1412004710 + -| data["mode"] = 33204 + -| data["type"] = file + -| data["dev"] = 2053 + -| data["gid"] = 1000 + -| data["ino"] = 10358899 + -| data["ctime"] = 1412004710 + -| data["blocks"] = 8 + -| data["nlink"] = 1 + -| data["name"] = testff.awk + -| data["atime"] = 1412004716 + -| data["pmode"] = -rw-rw-r-- + -| data["size"] = 666 + -| data["uid"] = 1000 + -| testff.awk modified: 09 29 2014 18:31:50 + -| + -| Info for JUNK + -| ret = -1 + -| JUNK modified: 01 01 1970 02:00:00 + + ---------- Footnotes ---------- + + (1) In practice, you would probably want to use the GNU Autotools +(Automake, Autoconf, Libtool, and `gettext') to configure and build +your libraries. Instructions for doing so are beyond the scope of this +Info file. *Note gawkextlib::, for Internet links to the tools. + + +File: gawk.info, Node: Extension Samples, Next: gawkextlib, Prev: Extension Example, Up: Dynamic Extensions + +16.7 The Sample Extensions in the `gawk' Distribution +===================================================== + +This minor node provides brief overviews of the sample extensions that +come in the `gawk' distribution. Some of them are intended for +production use (e.g., the `filefuncs', `readdir' and `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 `fnmatch()'. +* Extension Sample Fork:: An interface to `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 `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 `gettimeofday()' + and `sleep()'. +* Extension Sample API Tests:: Tests for the API. + + +File: gawk.info, Node: Extension Sample File Functions, Next: Extension Sample Fnmatch, Up: Extension Samples + +16.7.1 File-Related Functions +----------------------------- + +The `filefuncs' extension provides three different functions, as +follows. The usage is: + +`@load "filefuncs"' + This is how you load the extension. + +`result = chdir("/some/directory")' + The `chdir()' function is a direct hook to the `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 `ERRNO'. + +`result = stat("/some/path", statdata' [`, follow']`)' + The `stat()' function provides a hook into the `stat()' system + call. It returns zero upon success or less than zero upon error. + In the latter case, it updates `ERRNO'. + + By default, it uses the `lstat()' system call. However, if passed + a third argument, it uses `stat()' instead. + + In all cases, it clears the `statdata' array. When the call is + successful, `stat()' fills the `statdata' array with information + retrieved from the filesystem, as follows: + + Subscript Field in `struct stat' File type + ------------------------------------------------------------ + `"name"' The file name All + `"dev"' `st_dev' All + `"ino"' `st_ino' All + `"mode"' `st_mode' All + `"nlink"' `st_nlink' All + `"uid"' `st_uid' All + `"gid"' `st_gid' All + `"size"' `st_size' All + `"atime"' `st_atime' All + `"mtime"' `st_mtime' All + `"ctime"' `st_ctime' All + `"rdev"' `st_rdev' Device files + `"major"' `st_major' Device files + `"minor"' `st_minor' Device files + `"blksize"'`st_blksize' All + `"pmode"' A human-readable version of the All + mode value, such as printed by + `ls'. For example, + `"-rwxr-xr-x"' + `"linkval"'The value of the symbolic link Symbolic + links + `"type"' The type of the file as a string. All + One of `"file"', `"blockdev"', + `"chardev"', `"directory"', + `"socket"', `"fifo"', `"symlink"', + `"door"', or `"unknown"'. Not + all systems support all file + types. + +`flags = or(FTS_PHYSICAL, ...)' +`result = fts(pathlist, flags, filedata)' + Walk the file trees provided in `pathlist' and fill in the + `filedata' array as described next. `flags' is the bitwise OR of + several predefined values, also described in a moment. Return + zero if there were no errors, otherwise return -1. + + The `fts()' function provides a hook to the C library `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: + +`pathlist' + An array of file names. The element values are used; the index + values are ignored. + +`flags' + This should be the bitwise OR of one or more of the following + predefined constant flag values. At least one of `FTS_LOGICAL' or + `FTS_PHYSICAL' must be provided; otherwise `fts()' returns an + error value and sets `ERRNO'. The flags are: + + `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 `FTS_PHYSICAL'. + + `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 `FTS_LOGICAL'. + + `FTS_NOCHDIR' + As a performance optimization, the C library `fts()' routines + change directory as they traverse a file hierarchy. This + flag disables that optimization. + + `FTS_COMFOLLOW' + Immediately follow a symbolic link named in `pathlist', + whether or not `FTS_LOGICAL' is set. + + `FTS_SEEDOT' + By default, the C library `fts()' routines do not return + entries for `.' (dot) and `..' (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.) + + `FTS_XDEV' + During a traversal, do not cross onto a different mounted + filesystem. + +`filedata' + The `filedata' array is first cleared. Then, `fts()' creates an + element in `filedata' for every element in `pathlist'. The index + is the name of the directory or file given in `pathlist'. The + element for this index is itself an array. There are two cases: + + _The path is a file_ + In this case, the array contains two or three elements: + + `"path"' + The full path to this file, starting from the "root" + that was given in the `pathlist' array. + + `"stat"' + This element is itself an array, containing the same + information as provided by the `stat()' function + described earlier for its `statdata' argument. The + element may not be present if the `stat()' system call + for the file failed. + + `"error"' + If some kind of error was encountered, the array will + also contain an element named `"error"', which is a + string describing the error. + + _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 `FTS_SEEDOT' was provided in the flags, + then there will also be an element named `".."'. This + element will be an array containing the data as provided by + `stat()'. + + In addition, there will be an element whose index is `"."'. + This element is an array containing the same two or three + elements as for a file: `"path"', `"stat"', and `"error"'. + + The `fts()' function returns zero if there were no errors. +Otherwise it returns -1. + + NOTE: The `fts()' extension does not exactly mimic the interface + of the C library `fts()' routines, choosing instead to provide an + interface that is based on associative arrays, which is more + comfortable to use from an `awk' program. This includes the lack + of a comparison function, because `gawk' already provides powerful + array sorting facilities. Although an `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. + + See `test/fts.awk' in the `gawk' distribution for an example use of +the `fts()' extension function. + + +File: gawk.info, Node: Extension Sample Fnmatch, Next: Extension Sample Fork, Prev: Extension Sample File Functions, Up: Extension Samples + +16.7.2 Interface to `fnmatch()' +------------------------------- + +This extension provides an interface to the C library `fnmatch()' +function. The usage is: + +`@load "fnmatch"' + This is how you load the extension. + +`result = fnmatch(pattern, string, flags)' + The return value is zero on success, `FNM_NOMATCH' if the string + did not match the pattern, or a different nonzero value if an + error occurred. + + In addition to the `fnmatch()' function, the `fnmatch' extension +adds one constant (`FNM_NOMATCH'), and an array of flag values named +`FNM'. + + The arguments to `fnmatch()' are: + +`pattern' + The file name wildcard to match. + +`string' + The file name string. + +`flag' + Either zero, or the bitwise OR of one or more of the flags in the + `FNM' array. + + The flags are as follows: + +Array element Corresponding flag defined by `fnmatch()' +-------------------------------------------------------------------------- +`FNM["CASEFOLD"]' `FNM_CASEFOLD' +`FNM["FILE_NAME"]' `FNM_FILE_NAME' +`FNM["LEADING_DIR"]'`FNM_LEADING_DIR' +`FNM["NOESCAPE"]' `FNM_NOESCAPE' +`FNM["PATHNAME"]' `FNM_PATHNAME' +`FNM["PERIOD"]' `FNM_PERIOD' + + Here is an example: + + @load "fnmatch" + ... + flags = or(FNM["PERIOD"], FNM["NOESCAPE"]) + if (fnmatch("*.a", "foo.c", flags) == FNM_NOMATCH) + print "no match" + + +File: gawk.info, Node: Extension Sample Fork, Next: Extension Sample Inplace, Prev: Extension Sample Fnmatch, Up: Extension Samples + +16.7.3 Interface to `fork()', `wait()', and `waitpid()' +------------------------------------------------------- + +The `fork' extension adds three functions, as follows: + +`@load "fork"' + This is how you load the extension. + +`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 + -1 upon error. In the latter case, `ERRNO' indicates the problem. + In the child, `PROCINFO["pid"]' and `PROCINFO["ppid"]' are updated + to reflect the correct values. + +`ret = waitpid(pid)' + This function takes a numeric argument, which is the process-ID to + wait for. The return value is that of the `waitpid()' system call. + +`ret = wait()' + This function waits for the first child to die. The return value + is that of the `wait()' system call. + + There is no corresponding `exec()' function. + + Here is an example: + + @load "fork" + ... + if ((pid = fork()) == 0) + print "hello from the child" + else + print "hello from the parent" + + +File: gawk.info, Node: Extension Sample Inplace, Next: Extension Sample Ord, Prev: Extension Sample Fork, Up: Extension Samples + +16.7.4 Enabling In-Place File Editing +------------------------------------- + +The `inplace' extension emulates GNU `sed''s `-i' option which performs +"in place" editing of each input file. It uses the bundled +`inplace.awk' include file to invoke the extension properly: + + # 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) + } + + 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 +`INPLACE_SUFFIX' is not an empty string, the original file is linked to +a backup file name created by appending that suffix. Finally, the +temporary file is renamed to the original file name. + + If any error occurs, the extension issues a fatal error to terminate +processing immediately without damaging the original file. + + Here are some simple examples: + + $ gawk -i inplace '{ gsub(/foo/, "bar") }; { print }' file1 file2 file3 + + To keep a backup copy of the original files, try this: + + $ gawk -i inplace -v INPLACE_SUFFIX=.bak '{ gsub(/foo/, "bar") } + > { print }' file1 file2 file3 + + +File: gawk.info, Node: Extension Sample Ord, Next: Extension Sample Readdir, Prev: Extension Sample Inplace, Up: Extension Samples + +16.7.5 Character and Numeric values: `ord()' and `chr()' +-------------------------------------------------------- + +The `ordchr' extension adds two functions, named `ord()' and `chr()', +as follows: + +`@load "ordchr"' + This is how you load the extension. + +`number = ord(string)' + Return the numeric value of the first character in `string'. + +`char = chr(number)' + Return a string whose first character is that represented by + `number'. + + These functions are inspired by the Pascal language functions of the +same name. Here is an example: + + @load "ordchr" + ... + printf("The numeric value of 'A' is %d\n", ord("A")) + printf("The string value of 65 is %s\n", chr(65)) + + +File: gawk.info, Node: Extension Sample Readdir, Next: Extension Sample Revout, Prev: Extension Sample Ord, Up: Extension Samples + +16.7.6 Reading Directories +-------------------------- + +The `readdir' extension adds an input parser for directories. The +usage is as follows: + + @load "readdir" + + When this extension is in use, instead of skipping directories named +on the command line (or with `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 file name, 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 *note table-readdir-file-types::. + +Letter File Type +-------------------------------------------------------------------------- +`b' Block device +`c' Character device +`d' Directory +`f' Regular file +`l' Symbolic link +`p' Named pipe (FIFO) +`s' Socket +`u' Anything else (unknown) + +Table 16.2: File types returned by the `readdir' extension + + On systems without the file type information, the third field is +always `u'. + + NOTE: On GNU/Linux systems, there are filesystems that don't + support the `d_type' entry (see the readdir(3) manual page), and + so the file type is always `u'. You can use the `filefuncs' + extension to call `stat()' in order to get correct type + information. + + Here is an example: + + @load "readdir" + ... + BEGIN { FS = "/" } + { print "file name is", $2 } + + +File: gawk.info, Node: Extension Sample Revout, Next: Extension Sample Rev2way, Prev: Extension Sample Readdir, Up: Extension Samples + +16.7.7 Reversing Output +----------------------- + +The `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: + + @load "revoutput" + + BEGIN { + REVOUT = 1 + print "don't panic" > "/dev/stdout" + } + + The output from this program is: `cinap t'nod'. + + +File: gawk.info, Node: Extension Sample Rev2way, Next: Extension Sample Read write array, Prev: Extension Sample Revout, Up: Extension Samples + +16.7.8 Two-Way I/O Example +-------------------------- + +The `revtwoway' extension adds a simple two-way processor that reverses +the characters in each line sent to it for reading back by the `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: + + @load "revtwoway" + + BEGIN { + cmd = "/magic/mirror" + print "don't panic" |& cmd + cmd |& getline result + print result + close(cmd) + } + + The output from this program is: `cinap t'nod'. + + +File: gawk.info, Node: Extension Sample Read write array, Next: Extension Sample Readfile, Prev: Extension Sample Rev2way, Up: Extension Samples + +16.7.9 Dumping and Restoring an Array +------------------------------------- + +The `rwarray' extension adds two functions, named `writea()' and +`reada()', as follows: + +`@load "rwarray"' + This is how you load the extension. + +`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. `writea()' understands arrays of arrays. It + returns one on success, or zero upon failure. + +`ret = reada(file, array)' + `reada()' is the inverse of `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. + + The array created by `reada()' is identical to that written by +`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 `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 `gawk' to do so +(*note 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: + + @load "rwarray" + ... + ret = writea("arraydump.bin", array) + ... + ret = reada("arraydump.bin", array) + + +File: gawk.info, Node: Extension Sample Readfile, Next: Extension Sample Time, Prev: Extension Sample Read write array, Up: Extension Samples + +16.7.10 Reading an Entire File +------------------------------ + +The `readfile' extension adds a single function named `readfile()', and +an input parser: + +`@load "readfile"' + This is how you load the extension. + +`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 `ERRNO'. + +`BEGIN { PROCINFO["readfile"] = 1 }' + In addition, the extension adds an input parser that is activated + if `PROCINFO["readfile"]' exists. When activated, each input file + is returned in its entirety as `$0'. `RT' is set to the null + string. + + Here is an example: + + @load "readfile" + ... + contents = readfile("/path/to/file"); + if (contents == "" && ERRNO != "") { + print("problem reading file", ERRNO) > "/dev/stderr" + ... + } + + +File: gawk.info, Node: Extension Sample Time, Next: Extension Sample API Tests, Prev: Extension Sample Readfile, Up: Extension Samples + +16.7.11 Extension Time Functions +-------------------------------- + +The `time' extension adds two functions, named `gettimeofday()' and +`sleep()', as follows: + +`@load "time"' + This is how you load the extension. + +`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 -1 and set `ERRNO'. The returned time should + have sub-second precision, but the actual precision may vary based + on the platform. If the standard C `gettimeofday()' system call + is available on this platform, then it simply returns the value. + Otherwise, if on MS-Windows, it tries to use + `GetSystemTimeAsFileTime()'. + +`result = sleep(SECONDS)' + Attempt to sleep for SECONDS seconds. If SECONDS is negative, or + the attempt to sleep fails, return -1 and set `ERRNO'. Otherwise, + return zero after sleeping for the indicated amount of time. Note + that SECONDS may be a floating-point (non-integral) value. + Implementation details: depending on platform availability, this + function tries to use `nanosleep()' or `select()' to implement the + delay. + + +File: gawk.info, Node: Extension Sample API Tests, Prev: Extension Sample Time, Up: Extension Samples + +16.7.12 API Tests +----------------- + +The `testext' extension exercises parts of the extension API that are +not tested by the other samples. The `extension/testext.c' file +contains both the C code for the extension and `awk' test code inside C +comments that run the tests. The testing framework extracts the `awk' +code and runs the tests. See the source file for more information. + + +File: gawk.info, Node: gawkextlib, Next: Extension summary, Prev: Extension Samples, Up: Dynamic Extensions + +16.8 The `gawkextlib' Project +============================= + +The `gawkextlib' (http://sourceforge.net/projects/gawkextlib/) project +provides a number of `gawk' extensions, including one for processing +XML files. This is the evolution of the original `xgawk' (XML `gawk') +project. + + As of this writing, there are six extensions: + + * GD graphics library extension + + * PDF extension + + * PostgreSQL extension + + * MPFR library extension (this provides access to a number of MPFR + functions which `gawk''s native MPFR support does not) + + * Redis extension + + * XML parser extension, using the Expat + (http://expat.sourceforge.net) XML parsing library + + You can check out the code for the `gawkextlib' project using the +Git (http://git-scm.com) distributed source code control system. The +command is as follows: + + git clone git://git.code.sf.net/p/gawkextlib/code gawkextlib-code + + You will need to have the Expat (http://expat.sourceforge.net) XML +parser library installed in order to build and use the XML extension. + + In addition, you must have the GNU Autotools installed (Autoconf +(http://www.gnu.org/software/autoconf), Automake +(http://www.gnu.org/software/automake), Libtool +(http://www.gnu.org/software/libtool), and GNU `gettext' +(http://www.gnu.org/software/gettext)). + + The simple recipe for building and testing `gawkextlib' is as +follows. First, build and install `gawk': + + cd .../path/to/gawk/code + ./configure --prefix=/tmp/newgawk Install in /tmp/newgawk for now + make && make check Build and check that all is OK + make install Install gawk + + Next, build `gawkextlib' and test it: + + cd .../path/to/gawkextlib-code + ./update-autotools Generate configure, etc. + You may have to run this command twice + ./configure --with-gawk=/tmp/newgawk Configure, point at "installed" gawk + make && make check Build and check that all is OK + make install Install the extensions + + If you have installed `gawk' in the standard way, then you will +likely not need the `--with-gawk' option when configuring `gawkextlib'. +You may also need to use the `sudo' utility to install both `gawk' and +`gawkextlib', depending upon how your system works. + + If you write an extension that you wish to share with other `gawk' +users, consider doing so through the `gawkextlib' project. See the +project's website for more information. + + +File: gawk.info, Node: Extension summary, Next: Extension Exercises, Prev: gawkextlib, Up: Dynamic Extensions + +16.9 Summary +============ + + * You can write extensions (sometimes called plug-ins) for `gawk' in + C or C++ using the application programming interface (API) defined + by the `gawk' developers. + + * Extensions must have a license compatible with the GNU General + Public License (GPL), and they must assert that fact by declaring + a variable named `plugin_is_GPL_compatible'. + + * Communication between `gawk' and an extension is two-way. `gawk' + passes a `struct' to the extension which contains various data + fields and function pointers. The extension can then call into + `gawk' via the supplied function pointers to accomplish certain + tasks. + + * One of these tasks is to "register" the name and implementation of + new `awk'-level functions with `gawk'. The implementation takes + the form of a C function pointer with a defined signature. By + convention, implementation functions are named `do_XXXX()' for + some `awk'-level function `XXXX()'. + + * The API is defined in a header file named `gawkpi.h'. You must + include a number of standard header files _before_ including it in + your source file. + + * API function pointers are provided for the following kinds of + operations: + + * Allocating, reallocating, and releasing memory + + * Registration functions (you may register extension functions, + exit callbacks, a version string, input parsers, output + wrappers, and two-way processors) + + * Printing fatal, warning, and "lint" warning messages + + * Updating `ERRNO', or unsetting it + + * Accessing parameters, including converting an undefined + parameter into an array + + * Symbol table access (retrieving a global variable, creating + one, or changing one) + + * Creating and releasing cached values; this provides an + efficient way to use values for multiple variables and can be + a big performance win + + * 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) + + * The API defines a number of standard data types for representing + `awk' values, array elements, and arrays. + + * The API provide convenience functions for constructing values. It + also provides memory management functions to ensure compatibility + between memory allocated by `gawk' and memory allocated by an + extension. + + * _All_ memory passed from `gawk' to an extension must be treated as + read-only by the extension. + + * _All_ memory passed from an extension to `gawk' must come from the + API's memory allocation functions. `gawk' takes responsibility for + the memory and releases it when appropriate. + + * The API provides information about the running version of `gawk' so + that an extension can make sure it is compatible with the `gawk' + that loaded it. + + * It is easiest to start a new extension by copying the boilerplate + code described in this major node. Macros in the `gawkapi.h' + header file make this easier to do. + + * The `gawk' distribution includes a number of small but useful + sample extensions. The `gawkextlib' project includes several more, + larger, extensions. If you wish to write an extension and + contribute it to the community of `gawk' users, the `gawkextlib' + project is the place to do so. + + + +File: gawk.info, Node: Extension Exercises, Prev: Extension summary, Up: Dynamic Extensions + +16.10 Exercises +=============== + + 1. Add functions to implement system calls such as `chown()', + `chmod()', and `umask()' to the file operations extension + presented in *note Internal File Ops::. + + 2. (Hard.) How would you provide namespaces in `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 + `gawk' maintainer to tell him about it. + + 3. Write a wrapper script that provides an interface similar to `sed + -i' for the "inplace" extension presented in *note Extension + Sample Inplace::. + + + +File: gawk.info, Node: Language History, Next: Installation, Prev: Dynamic Extensions, Up: Top Appendix A The Evolution of the `awk' Language ********************************************** This Info file describes the GNU implementation of `awk', which follows -the POSIX specification. Many long-time `awk' users learned `awk' +the POSIX specification. Many longtime `awk' users learned `awk' programming with the original `awk' implementation in Version 7 Unix. (This implementation was the basis for `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 `gawk' for their -`awk'.) This major node briefly describes the evolution of the `awk' -language, with cross-references to other parts of the Info file where -you can find more information. +4.3-Reno. Subsequent versions of Berkeley Unix, and, for a while, some +systems derived from 4.4BSD-Lite, used various versions of `gawk' for +their `awk'.) This major node briefly describes the evolution of the +`awk' language, with cross-references to other parts of the Info file +where you can find more information. * Menu: @@ -19787,9 +26210,11 @@ you can find more information. `awk'. * POSIX/GNU:: The extensions in `gawk' not in POSIX `awk'. +* Feature History:: The history of the features in `gawk'. * Common Extensions:: Common Extensions Summary. * Ranges and Locales:: How locales used to affect regexp ranges. * Contributors:: The major contributors to `gawk'. +* History summary:: History summary. File: gawk.info, Node: V7/SVR3.1, Next: SVR4, Up: Language History @@ -19822,7 +26247,7 @@ the changes, with cross-references to further details: Functions::). * The `ARGC', `ARGV', `FNR', `RLENGTH', `RSTART', and `SUBSEP' - built-in variables (*note Built-in Variables::). + predefined variables (*note Built-in Variables::). * Assignable `$0' (*note Changing Fields::). @@ -19843,18 +26268,16 @@ the changes, with cross-references to further details: Functions::), rather than using only the first character of `FS'. * Dynamic regexps as operands of the `~' and `!~' operators (*note - Regexp Usage::). + Computed Regexps::). * The escape sequences `\b', `\f', and `\r' (*note Escape - Sequences::). (Some vendors have updated their old versions of - `awk' to recognize `\b', `\f', and `\r', but this is not something - you can rely on.) + Sequences::). * Redirection of input for the `getline' function (*note Getline::). * Multiple `BEGIN' and `END' rules (*note BEGIN/END::). - * Multidimensional arrays (*note Multi-dimensional::). + * Multidimensional arrays (*note Multidimensional::). File: gawk.info, Node: SVR4, Next: POSIX, Prev: V7/SVR3.1, Up: Language History @@ -19872,7 +26295,7 @@ The System V Release 4 (1989) version of Unix `awk' added these features * The `-v' option for assigning variables before program execution begins (*note Options::). - * The `--' option for terminating command-line options. + * The `--' signal for terminating command-line options. * The `\a', `\v', and `\x' escape sequences (*note Escape Sequences::). @@ -19887,8 +26310,8 @@ The System V Release 4 (1989) version of Unix `awk' added these features `printf' function (*note Control Letters::). * The ability to dynamically pass the field width and precision - (`"%*.*d"') in the argument list of the `printf' function (*note - Control Letters::). + (`"%*.*d"') in the argument list of `printf' and `sprintf()' + (*note Control Letters::). * The use of regexp constants, such as `/foo/', as expressions, where they are equivalent to using the matching operator, as in `$0 ~ @@ -19915,12 +26338,24 @@ introduced the following changes into the language: * The concept of a numeric string and tighter comparison rules to go with it (*note Typing and Comparison::). - * The use of built-in variables as function parameter names is - forbidden (*note Definition Syntax::. + * The use of predefined variables as function parameter names is + forbidden (*note Definition Syntax::). * More complete documentation of many of the previously undocumented features of the language. + In 2012, a number of extensions that had been commonly available for +many years were finally added to POSIX. They are: + + * The `fflush()' built-in function for flushing buffered output + (*note I/O Functions::). + + * The `nextfile' statement (*note Nextfile Statement::). + + * The ability to delete all of an array at once with `delete ARRAY' + (*note Delete::). + + *Note Common Extensions::, for a list of common extensions not permitted by the POSIX standard. @@ -19937,9 +26372,9 @@ Brian Kernighan has made his version available via his home page (*note Other Versions::). This minor node describes common extensions that originally appeared -in his version of `awk'. +in his version of `awk': - * The `**' and `**=' operators (*note Arithmetic Ops:: and *Note + * The `**' and `**=' operators (*note Arithmetic Ops:: and *note Assignment Ops::). * The use of `func' as an abbreviation for `function' (*note @@ -19953,7 +26388,7 @@ in his version of `awk'. available in his `awk'. -File: gawk.info, Node: POSIX/GNU, Next: Common Extensions, Prev: BTL, Up: Language History +File: gawk.info, Node: POSIX/GNU, Next: Feature History, Prev: BTL, Up: Language History A.5 Extensions in `gawk' Not in POSIX `awk' =========================================== @@ -19966,7 +26401,7 @@ can all be disabled with either the `--traditional' or `--posix' options node summarizes the additional features over POSIX `awk' that are in the current version of `gawk'. - * Additional built-in variables: + * Additional predefined variables: - The `ARGIND' `BINMODE', `ERRNO', `FIELDWIDTHS', `FPAT', `IGNORECASE', `LINT', `PROCINFO', `RT', and `TEXTDOMAIN' @@ -19979,7 +26414,7 @@ the current version of `gawk'. - The `/inet', `/inet4', and `/inet6' special files for TCP/IP networking using `|&' to specify which version of the IP - protocol to use. (*note TCP/IP Networking::). + protocol to use (*note TCP/IP Networking::). * Changes and/or additions to the language: @@ -20001,18 +26436,13 @@ the current version of `gawk'. - Indirect function calls (*note Indirect Calls::). - Directories on the command line produce a warning and are - skipped (*note Command line directories::). + skipped (*note Command-line directories::). * New keywords: - - The `BEGINFILE' and `ENDFILE' special patterns. (*note + - The `BEGINFILE' and `ENDFILE' special patterns (*note BEGINFILE/ENDFILE::). - - The ability to delete all of an array at once with `delete - ARRAY' (*note Delete::). - - - The `nextfile' statement (*note Nextfile Statement::). - - The `switch' statement (*note Switch Statement::). * Changes to standard `awk' functions: @@ -20021,7 +26451,7 @@ the current version of `gawk'. one end of a two-way pipe to a coprocess (*note Two-way I/O::). - - POSIX compliance for `gsub()' and `sub()'. + - POSIX compliance for `gsub()' and `sub()' with `--posix'. - The `length()' function accepts an array argument and returns the number of elements in the array (*note String @@ -20035,44 +26465,50 @@ the current version of `gawk'. translations easier (*note Printf Ordering::). - The `split()' function's additional optional fourth argument - which is an array to hold the text of the field separators. + which is an array to hold the text of the field separators (*note String Functions::). * Additional functions only in `gawk': - - The `and()', `compl()', `lshift()', `or()', `rshift()', and - `xor()' functions for bit manipulation (*note Bitwise - Functions::). + - The `gensub()', `patsplit()', and `strtonum()' functions for + more powerful text manipulation (*note String Functions::). - The `asort()' and `asorti()' functions for sorting arrays (*note Array Sorting::). - - The `bindtextdomain()', `dcgettext()' and `dcngettext()' - functions for internationalization (*note Programmer i18n::). - - - The `extension()' built-in function and the ability to add - new functions dynamically (*note Dynamic Extensions::). + - The `mktime()', `systime()', and `strftime()' functions for + working with timestamps (*note Time Functions::). - - The `fflush()' function from Brian Kernighan's version of - `awk' (*note I/O Functions::). + - The `and()', `compl()', `lshift()', `or()', `rshift()', and + `xor()' functions for bit manipulation (*note Bitwise + Functions::). - - The `gensub()', `patsplit()', and `strtonum()' functions for - more powerful text manipulation (*note String Functions::). + - The `isarray()' function to check if a variable is an array + or not (*note Type Functions::). - - The `mktime()', `systime()', and `strftime()' functions for - working with timestamps (*note Time Functions::). + - The `bindtextdomain()', `dcgettext()' and `dcngettext()' + functions for internationalization (*note Programmer i18n::). * Changes and/or additions in the command-line options: - The `AWKPATH' environment variable for specifying a path search for the `-f' command-line option (*note Options::). - - The ability to use GNU-style long-named options that start - with `--' and the `--characters-as-bytes', `--compat', - `--dump-variables', `--exec', `--gen-pot', `--lint', - `--lint-old', `--non-decimal-data', `--posix', `--profile', - `--re-interval', `--sandbox', `--source', `--traditional', and - `--use-lc-numeric' options (*note Options::). + - The `AWKLIBPATH' environment variable for specifying a path + search for the `-l' command-line option (*note Options::). + + - The `-b', `-c', `-C', `-d', `-D', `-e', `-E', `-g', `-h', + `-i', `-l', `-L', `-M', `-n', `-N', `-o', `-O', `-p', `-P', + `-r', `-S', `-t', and `-V' short options. Also, the ability + to use GNU-style long-named options that start with `--' and + the `--assign', `--bignum', `--characters-as-bytes', + `--copyright', `--debug', `--dump-variables', `--exec', + `--field-separator', `--file', `--gen-pot', `--help', + `--include', `--lint', `--lint-old', `--load', + `--non-decimal-data', `--optimize', `--posix', + `--pretty-print', `--profile', `--re-interval', `--sandbox', + `--source', `--traditional', `--use-lc-numeric', and + `--version' long options (*note Options::). * Support for the following obsolete systems was removed from the code and the documentation for `gawk' version 4.0: @@ -20099,38 +26535,433 @@ the current version of `gawk'. - Prestandard VAX C compiler for VAX/VMS + - GCC for VAX and Alpha has not been tested for a while. + + + * Support for the following obsolete systems was removed from the + code for `gawk' version 4.1: + + - Ultrix + + * Support for MirBSD was removed at `gawk' version 4.2. + + + +File: gawk.info, Node: Feature History, Next: Common Extensions, Prev: POSIX/GNU, Up: Language History + +A.6 History of `gawk' Features +============================== + +This minor node describes the features in `gawk' over and above those +in POSIX `awk', in the order they were added to `gawk'. + + Version 2.10 of `gawk' introduced the following features: + + * The `AWKPATH' environment variable for specifying a path search for + the `-f' command-line option (*note Options::). + + * The `IGNORECASE' variable and its effects (*note + Case-sensitivity::). + + * The `/dev/stdin', `/dev/stdout', `/dev/stderr' and `/dev/fd/N' + special file names (*note Special Files::). + + Version 2.13 of `gawk' introduced the following features: + + * The `FIELDWIDTHS' variable and its effects (*note Constant Size::). + + * The `systime()' and `strftime()' built-in functions for obtaining + and printing timestamps (*note Time Functions::). + + * Additional command-line options (*note Options::): + + - The `-W lint' option to provide error and portability checking + for both the source code and at runtime. + + - The `-W compat' option to turn off the GNU extensions. + + - The `-W posix' option for full POSIX compliance. + + Version 2.14 of `gawk' introduced the following feature: + + * The `next file' statement for skipping to the next data file + (*note Nextfile Statement::). + + Version 2.15 of `gawk' introduced the following features: + + * New variables (*note Built-in Variables::): + + - `ARGIND', which tracks the movement of `FILENAME' through + `ARGV'. + + - `ERRNO', which contains the system error message when + `getline' returns -1 or `close()' fails. + + * The `/dev/pid', `/dev/ppid', `/dev/pgrpid', and `/dev/user' + special file names. These have since been removed. + + * The ability to delete all of an array at once with `delete ARRAY' + (*note Delete::). + + * Command-line option changes (*note Options::): + + - The ability to use GNU-style long-named options that start + with `--'. + + - The `--source' option for mixing command-line and library-file + source code. + + Version 3.0 of `gawk' introduced the following features: + + * New or changed variables: + + - `IGNORECASE' changed, now applying to string comparison as + well as regexp operations (*note Case-sensitivity::). + + - `RT', which contains the input text that matched `RS' (*note + Records::). + + * Full support for both POSIX and GNU regexps (*note Regexp::). + + * The `gensub()' function for more powerful text manipulation (*note + String Functions::). + + * The `strftime()' function acquired a default time format, allowing + it to be called with no arguments (*note Time Functions::). + + * The ability for `FS' and for the third argument to `split()' to be + null strings (*note Single Character Fields::). + + * The ability for `RS' to be a regexp (*note Records::). + + * The `next file' statement became `nextfile' (*note Nextfile + Statement::). + + * The `fflush()' function from BWK `awk' (then at Bell Laboratories; + *note I/O Functions::). + + * New command-line options: + + - The `--lint-old' option to warn about constructs that are not + available in the original Version 7 Unix version of `awk' + (*note V7/SVR3.1::). + + - The `-m' option from BWK `awk'. (Brian was still at Bell + Laboratories at the time.) This was later removed from both + his `awk' and from `gawk'. + + - The `--re-interval' option to provide interval expressions in + regexps (*note Regexp Operators::). + + - The `--traditional' option was added as a better name for + `--compat' (*note Options::). + + * The use of GNU Autoconf to control the configuration process + (*note Quick Installation::). + + * Amiga support. This has since been removed. + + + Version 3.1 of `gawk' introduced the following features: + + * New variables (*note Built-in Variables::): + + - `BINMODE', for non-POSIX systems, which allows binary I/O for + input and/or output files (*note PC Using::). + + - `LINT', which dynamically controls lint warnings. + + - `PROCINFO', an array for providing process-related + information. + + - `TEXTDOMAIN', for setting an application's + internationalization text domain (*note + Internationalization::). + + * The ability to use octal and hexadecimal constants in `awk' + program source code (*note Nondecimal-numbers::). + + * The `|&' operator for two-way I/O to a coprocess (*note Two-way + I/O::). + + * The `/inet' special files for TCP/IP networking using `|&' (*note + TCP/IP Networking::). + + * The optional second argument to `close()' that allows closing one + end of a two-way pipe to a coprocess (*note Two-way I/O::). + + * The optional third argument to the `match()' function for + capturing text-matching subexpressions within a regexp (*note + String Functions::). + + * Positional specifiers in `printf' formats for making translations + easier (*note Printf Ordering::). + + * A number of new built-in functions: + + - The `asort()' and `asorti()' functions for sorting arrays + (*note Array Sorting::). + + - The `bindtextdomain()', `dcgettext()' and `dcngettext()' + functions for internationalization (*note Programmer i18n::). + + - The `extension()' function and the ability to add new + built-in functions dynamically (*note Dynamic Extensions::). + + - The `mktime()' function for creating timestamps (*note Time + Functions::). + + - The `and()', `or()', `xor()', `compl()', `lshift()', + `rshift()', and `strtonum()' functions (*note Bitwise + Functions::). + + * The support for `next file' as two words was removed completely + (*note Nextfile Statement::). + + * Additional command-line options (*note Options::): + + - The `--dump-variables' option to print a list of all global + variables. + + - The `--exec' option, for use in CGI scripts. + + - The `--gen-po' command-line option and the use of a leading + underscore to mark strings that should be translated (*note + String Extraction::). + + - The `--non-decimal-data' option to allow non-decimal input + data (*note Nondecimal Data::). + + - The `--profile' option and `pgawk', the profiling version of + `gawk', for producing execution profiles of `awk' programs + (*note Profiling::). + + - The `--use-lc-numeric' option to force `gawk' to use the + locale's decimal point for parsing input data (*note + Conversion::). + + * The use of GNU Automake to help in standardizing the configuration + process (*note Quick Installation::). + + * The use of GNU `gettext' for `gawk''s own message output (*note + Gawk I18N::). + + * BeOS support. This was later removed. + + * Tandem support. This was later removed. + + * The Atari port became officially unsupported and was later removed + entirely. + + * The source code changed to use ISO C standard-style function + definitions. + + * POSIX compliance for `sub()' and `gsub()' (*note Gory Details::). + + * The `length()' function was extended to accept an array argument + and return the number of elements in the array (*note String + Functions::). + + * The `strftime()' function acquired a third argument to enable + printing times as UTC (*note Time Functions::). + + Version 4.0 of `gawk' introduced the following features: + + * Variable additions: + + - `FPAT', which allows you to specify a regexp that matches the + fields, instead of matching the field separator (*note + Splitting By Content::). + + - If `PROCINFO["sorted_in"]' exists, `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 (*note Controlling + Scanning::). + + - `PROCINFO["strftime"]', which holds the default format for + `strftime()' (*note Time Functions::). + + * The special files `/dev/pid', `/dev/ppid', `/dev/pgrpid' and + `/dev/user' were removed. + + * Support for IPv6 was added via the `/inet6' special file. + `/inet4' forces IPv4 and `/inet' chooses the system default, which + is probably IPv4 (*note TCP/IP Networking::). + + * The use of `\s' and `\S' escape sequences in regular expressions + (*note GNU Regexp Operators::). + + * Interval expressions became part of default regular expressions + (*note Regexp Operators::). + + * POSIX character classes work even with `--traditional' (*note + Regexp Operators::). + + * `break' and `continue' became invalid outside a loop, even with + `--traditional' (*note Break Statement::, and also see *note + Continue Statement::). + + * `fflush()', `nextfile', and `delete ARRAY' are allowed if + `--posix' or `--traditional', since they are all now part of POSIX. + + * An optional third argument to `asort()' and `asorti()', specifying + how to sort (*note String Functions::). + + * The behavior of `fflush()' changed to match BWK `awk' and for + POSIX; now both `fflush()' and `fflush("")' flush all open output + redirections (*note I/O Functions::). + + * The `isarray()' function which distinguishes if an item is an array + or not, to make it possible to traverse arrays of arrays (*note + Type Functions::). + + * The `patsplit()' function which gives the same capability as + `FPAT', for splitting (*note String Functions::). + + * An optional fourth argument to the `split()' function, which is an + array to hold the values of the separators (*note String + Functions::). + + * Arrays of arrays (*note Arrays of Arrays::). + + * The `BEGINFILE' and `ENDFILE' special patterns (*note + BEGINFILE/ENDFILE::). + + * Indirect function calls (*note Indirect Calls::). + + * `switch' / `case' are enabled by default (*note Switch + Statement::). + + * Command-line option changes (*note Options::): + + - The `-b' and `--characters-as-bytes' options which prevent + `gawk' from treating input as a multibyte string. + + - The redundant `--compat', `--copyleft', and `--usage' long + options were removed. + + - The `--gen-po' option was finally renamed to the correct + `--gen-pot'. + + - The `--sandbox' option which disables certain features. + + - All long options acquired corresponding short options, for + use in `#!' scripts. + + * Directories named on the command line now produce a warning, not a + fatal error, unless `--posix' or `--traditional' are used (*note + Command-line directories::). + + * The `gawk' internals were rewritten, bringing the `dgawk' debugger + and possibly improved performance (*note Debugger::). + + * Per the GNU Coding Standards, dynamic extensions must now define a + global symbol indicating that they are GPL-compatible (*note + Plugin License::). + + * In POSIX mode, string comparisons use `strcoll()' / `wcscoll()' + (*note POSIX String Comparison::). + + * The option for raw sockets was removed, since it was never + implemented (*note TCP/IP Networking::). + + * Ranges of the form `[d-h]' are treated as if they were in the C + locale, no matter what kind of regexp is being used, and even if + `--posix' (*note Ranges and Locales::). + + * Support was removed for the following systems: + + - Atari + + - Amiga + + - BeOS + + - Cray + + - MIPS RiscOS + + - MS-DOS with Microsoft Compiler + + - MS-Windows with Microsoft Compiler + + - NeXT + + - SunOS 3.x, Sun 386 (Road Runner) + + - Tandem (non-POSIX) + + - Prestandard VAX C compiler for VAX/VMS + + Version 4.1 of `gawk' introduced the following features: + + * Three new arrays: `SYMTAB', `FUNCTAB', and + `PROCINFO["identifiers"]' (*note Auto-set::). + + * The three executables `gawk', `pgawk', and `dgawk', were merged + into one, named just `gawk'. As a result the command-line options + changed. + + * Command-line option changes (*note Options::): + + - The `-D' option invokes the debugger. + + - The `-i' and `--include' options load `awk' library files. + + - The `-l' and `--load' options load compiled dynamic + extensions. + + - The `-M' and `--bignum' options enable MPFR. + + - The `-o' option only does pretty-printing. + + - The `-p' option is used for profiling. + + - The `-R' option was removed. + + * Support for high precision arithmetic with MPFR. (*note Arbitrary + Precision Arithmetic::). + + * The `and()', `or()' and `xor()' functions changed to allow any + number of arguments, with a minimum of two (*note Bitwise + Functions::). + + * The dynamic extension interface was completely redone (*note + Dynamic Extensions::). -File: gawk.info, Node: Common Extensions, Next: Ranges and Locales, Prev: POSIX/GNU, Up: Language History +File: gawk.info, Node: Common Extensions, Next: Ranges and Locales, Prev: Feature History, Up: Language History -A.6 Common Extensions Summary +A.7 Common Extensions Summary ============================= -This minor node summarizes the common extensions supported by `gawk', -Brian Kernighan's `awk', and `mawk', the three most widely-used freely -available versions of `awk' (*note Other Versions::). - -Feature BWK Awk Mawk GNU Awk --------------------------------------------------------- -`\x' Escape sequence X X X -`RS' as regexp X X -`FS' as null string X X X -`/dev/stdin' special file X X -`/dev/stdout' special file X X X -`/dev/stderr' special file X X X -`**' and `**=' operators X X -`func' keyword X X -`nextfile' statement X X X -`delete' without subscript X X X -`length()' of an array X X -`fflush()' function X X X -`BINMODE' variable X X +The following table summarizes the common extensions supported by +`gawk', Brian Kernighan's `awk', and `mawk', the three most widely used +freely available versions of `awk' (*note Other Versions::). + +Feature BWK Awk Mawk GNU Awk Now standard +----------------------------------------------------------------------- +`\x' Escape sequence X X X +`FS' as null string X X X +`/dev/stdin' special file X X X +`/dev/stdout' special file X X X +`/dev/stderr' special file X X X +`delete' without subscript X X X X +`fflush()' function X X X X +`length()' of an array X X X +`nextfile' statement X X X X +`**' and `**=' operators X X +`func' keyword X X +`BINMODE' variable X X +`RS' as regexp X X +Time-related functions X X File: gawk.info, Node: Ranges and Locales, Next: Contributors, Prev: Common Extensions, Up: Language History -A.7 Regexp Ranges and Locales: A Long Sad Story +A.8 Regexp Ranges and Locales: A Long Sad Story =============================================== This minor node describes the confusing history of ranges within @@ -20143,20 +26974,20 @@ 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, `[a-z]' matched all the lowercase letters, and only the lowercase -letters, since the numeric values for the letters from `a' through `z' -were contigous. (On an EBCDIC system, the range `[a-z]' includes +letters, as the numeric values for the letters from `a' through `z' +were contiguous. (On an EBCDIC system, the range `[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 `[a-z]', and that -`[A-Z]' was the the "correct" way to match uppercase letters. And -indeed, this was true. +`[A-Z]' was the "correct" way to match uppercase letters. And indeed, +this was true.(1) - The 1993 POSIX standard introduced the idea of locales (*note -Locales::). Since many locales include other letters besides the plain -twenty-six letters of the American English alphabet, the POSIX standard -added character classes (*note Bracket Expressions::) as a way to match + The 1992 POSIX standard introduced the idea of locales (*note +Locales::). Because many locales include other letters besides the +plain 26 letters of the English alphabet, the POSIX standard added +character classes (*note Bracket Expressions::) as a way to match different kinds of characters besides the traditional ones in the ASCII character set. @@ -20166,16 +26997,16 @@ like `[a-dx-z]' is still equivalent to `[abcdxyz]', as in ASCII. But outside those locales, the ordering was defined to be based on "collation order". - In many locales, `A' and `a' are both less than `B'. In other -words, these locales sort characters in dictionary order, and -`[a-dx-z]' is typically not equivalent to `[abcdxyz]'; instead it might -be equivalent to `[aBbCcdXxYyz]', for example. + What does that mean? In many locales, `A' and `a' are both less +than `B'. In other words, these locales sort characters in dictionary +order, and `[a-dx-z]' is typically not equivalent to `[abcdxyz]'; +instead it might be equivalent to `[ABCXYabcdxyz]', for example. - This point needs to be emphasized: Much literature teaches that you + This point needs to be emphasized: much literature teaches that you should use `[a-z]' to match a lowercase character. But on systems with -non-ASCII locales, this also matched all of the uppercase characters -except `Z'! This was a continuous cause of confusion, even well into -the twenty-first century. +non-ASCII locales, this also matches all of the uppercase characters +except `A' or `Z'! This was a continuous cause of confusion, even well +into the twenty-first century. To demonstrate these issues, the following example uses the `sub()' function, which does text replacement (*note String Functions::). Here, @@ -20184,9 +27015,9 @@ the intent is to remove trailing uppercase characters: $ echo something1234abc | gawk-3.1.8 '{ sub("[A-Z]*$", ""); print }' -| something1234a -This output is unexpected, since the `bc' at the end of -`something1234abc' should not normally match `[A-Z]*'. This result is -due to the locale setting (and thus you may not see it on your system). +This output is unexpected, as the `bc' at the end of `something1234abc' +should not normally match `[A-Z]*'. This result is due to the locale +setting (and thus you may not see it on your system). Similar considerations apply to other ranges. For example, `["-/]' is perfectly valid in ASCII, but is not valid in many Unicode locales, @@ -20203,37 +27034,43 @@ like "why does `[A-Z]' match lowercase letters?!?" This situation existed for close to 10 years, if not more, and the `gawk' maintainer grew weary of trying to explain that `gawk' was being -nicely standards-compliant, and that the issue was in the user's +nicely standards compliant, and that the issue was in the user's locale. During the development of version 4.0, he modified `gawk' to always treat ranges in the original, pre-POSIX fashion, unless -`--posix' was used (*note Options::). +`--posix' was used (*note Options::).(2) Fortunately, shortly before the final release of `gawk' 4.0, the maintainer learned that the 2008 standard had changed the definition of ranges, such that outside the `"C"' and `"POSIX"' locales, the meaning -of range expressions was _undefined_.(1) +of range expressions was _undefined_.(3) By using this lovely technical term, the standard gives license to implementors to implement ranges in whatever way they choose. The `gawk' maintainer chose to apply the pre-POSIX meaning in all cases: -the default regexp matching; with `--traditional', and with `--posix'; +the default regexp matching; with `--traditional' and with `--posix'; in all cases, `gawk' remains POSIX compliant. ---------- Footnotes ---------- - (1) See the standard + (1) And Life was good. + + (2) 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." + + (3) See the standard (http://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap09.html#tag_09_03_05) and its rationale (http://pubs.opengroup.org/onlinepubs/9699919799/xrat/V4_xbd_chap09.html#tag_21_09_03_05). -File: gawk.info, Node: Contributors, Prev: Ranges and Locales, Up: Language History +File: gawk.info, Node: Contributors, Next: History summary, Prev: Ranges and Locales, Up: Language History -A.8 Major Contributors to `gawk' +A.9 Major Contributors to `gawk' ================================ - Always give credit where credit is due. - Anonymous + Always give credit where credit is due. -- Anonymous This minor node names the major contributors to `gawk' and/or this Info file, in approximate chronological order: @@ -20274,8 +27111,8 @@ Info file, in approximate chronological order: * 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 `gawk' works on non-32-bit systems. + to provide portability checking, and has done a lot of work to + make sure `gawk' works on non-32-bit systems. * Fred Fish provided the port to Amiga systems and its documentation. (With Fred's sad passing, this is no longer supported.) @@ -20294,7 +27131,8 @@ Info file, in approximate chronological order: various PC platforms. * Christos Zoulas provided the `extension()' built-in function for - dynamically adding new modules. + dynamically adding new functions. (This was obsoleted at `gawk' + 4.1.) * Ju"rgen Kahrs contributed the initial version of the TCP/IP networking code and documentation, and motivated the inclusion of @@ -20327,18 +27165,86 @@ Info file, in approximate chronological order: statements. * Patrick T.J. McPhee contributed the code for dynamic loading in - Windows32 environments. (This is no longer supported) + Windows32 environments. (This is no longer supported.) + + * Anders Wallin helped keep the VMS port going for several years. + + * Assaf Gordon contributed the code to implement the `--sandbox' + option. + + * John Haque made the following contributions: + + - The modifications to convert `gawk' into a byte-code + interpreter, including the debugger. + + - The addition of true arrays of arrays. + + - The additional modifications for support of + arbitrary-precision arithmetic. + + - The initial text of *note Arbitrary Precision Arithmetic::. + + - The work to merge the three versions of `gawk' into one, for + the 4.1 release. - * John Haque reworked the `gawk' internals to use a byte-code engine, - providing the `dgawk' debugger for `awk' programs. + - Improved array internals for arrays indexed by integers. - * Efraim Yawitz contributed the original text for *Note Debugger::. + - The improved array sorting features were driven by John + together with Pat Rankin. + + * Panos Papadopoulos contributed the original text for *note Include + Files::. + + * Efraim Yawitz contributed the original text for *note Debugger::. + + * The development of the extension API first released with `gawk' + 4.1 was driven primarily by Arnold Robbins and Andrew Schorr, with + notable contributions from the rest of the development team. + + * John Malmberg contributed significant improvements to the OpenVMS + port and the related documentation. + + * Antonio Giovanni Colombo rewrote a number of examples in the early + chapters that were severely dated, for which I am incredibly + grateful. * Arnold Robbins has been working on `gawk' since 1988, at first helping David Trueman, and as the primary maintainer since around 1994. +File: gawk.info, Node: History summary, Prev: Contributors, Up: Language History + +A.10 Summary +============ + + * The `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. + + * Brian Kernighan's `awk' provides a small number of extensions that + are implemented in common with other versions of `awk'. + + * `gawk' provides a large number of extensions over POSIX `awk'. + They can be disabled with either the `--traditional' or `--posix' + options. + + * The interaction of POSIX locales and regexp matching in `gawk' has + been confusing over the years. Today, `gawk' implements Rational + Range Interpretation, where ranges of the form `[a-z]' match + _only_ the characters numerically between `a' through `z' in the + machine's native character set. Usually this is ASCII but it can + be EBCDIC on IBM S/390 systems. + + * Many people have contributed to `gawk' development over the years. + We hope that the list provided in this major node is complete and + gives the appropriate credit where credit is due. + + + File: gawk.info, Node: Installation, Next: Notes, Prev: Language History, Up: Top Appendix B Installing `gawk' @@ -20347,8 +27253,8 @@ Appendix B Installing `gawk' This appendix provides instructions for installing `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. *Note Bugs::, for the electronic mail addresses of the -people who did the respective ports. +contributed. *Note Bugs::, for the email addresses of the people who +maintain the respective ports. * Menu: @@ -20359,6 +27265,7 @@ people who did the respective ports. * Bugs:: Reporting Problems and Bugs. * Other Versions:: Other freely available `awk' implementations. +* Installation summary:: Summary of installation. File: gawk.info, Node: Gawk Distribution, Next: Unix Installation, Up: Installation @@ -20381,7 +27288,7 @@ File: gawk.info, Node: Getting, Next: Extracting, Up: Gawk Distribution B.1.1 Getting the `gawk' Distribution ------------------------------------- -There are three ways to get GNU software: +There are two ways to get GNU software: * Copy it from someone else who already has it. @@ -20390,10 +27297,10 @@ There are three ways to get GNU software: supported. If you have the `wget' program, you can use a command like the following: - wget http://ftp.gnu.org/gnu/gawk/gawk-4.0.0.tar.gz + wget http://ftp.gnu.org/gnu/gawk/gawk-4.1.2.tar.gz The GNU software archive is mirrored around the world. The -up-to-date list of mirror sites is available from the main FSF web site +up-to-date list of mirror sites is available from the main FSF website (http://www.gnu.org/order/ftp.html). Try to use one of the mirrors; they will be less busy, and you can usually find one closer to your site. @@ -20409,26 +27316,25 @@ compression programs: `gzip', `bzip2', and `xz'. For simplicity, the rest of these instructions assume you are using the one compressed with the GNU Zip program, `gzip'. - Once you have the distribution (for example, `gawk-4.0.0.tar.gz'), -use `gzip' to expand the file and then use `tar' to extract it. You -can use the following pipeline to produce the `gawk' distribution: + Once you have the distribution (e.g., `gawk-4.1.2.tar.gz'), use +`gzip' to expand the file and then use `tar' to extract it. You can +use the following pipeline to produce the `gawk' distribution: - # Under System V, add 'o' to the tar options - gzip -d -c gawk-4.0.0.tar.gz | tar -xvpf - + gzip -d -c gawk-4.1.2.tar.gz | tar -xvpf - On a system with GNU `tar', you can let `tar' do the decompression for you: - tar -xvpzf gawk-4.0.0.tar.gz + tar -xvpzf gawk-4.1.2.tar.gz -Extracting the archive creates a directory named `gawk-4.0.0' in the +Extracting the archive creates a directory named `gawk-4.1.2' in the current directory. The distribution file name is of the form `gawk-V.R.P.tar.gz'. The V represents the major version of `gawk', the R represents the current release of version V, and the P represents a "patch level", meaning that minor bugs have been fixed in the release. The current patch -level is 0, but when retrieving distributions, you should get the +level is 2, but when retrieving distributions, you should get the version with the highest version, release, and patch level. (Note, however, that patch levels greater than or equal to 70 denote "beta" or nonproduction software; you might not want to retrieve such a version @@ -20450,6 +27356,13 @@ to different non-Unix operating systems: Various `.c', `.y', and `.h' files The actual `gawk' source code. +`ABOUT-NLS' + Information about GNU `gettext' and translations. + +`AUTHORS' + A file with some information about the authorship of `gawk'. It + exists only to satisfy the pedants at the Free Software Foundation. + `README' `README_d/README.*' Descriptive files: `README' for `gawk' under Unix and the rest for @@ -20475,16 +27388,6 @@ Various `.c', `.y', and `.h' files `COPYING' The GNU General Public License. -`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. - -`LIMITATIONS' - A list of those factors that limit `gawk''s performance. Most of - these depend on the hardware or operating system software and are - not limits in `gawk' itself. - `POSIX.STD' A description of behaviors in the POSIX standard for `awk' which are left undefined, or where `gawk' may not comply fully, as well @@ -20492,8 +27395,9 @@ Various `.c', `.y', and `.h' files does not. `doc/awkforai.txt' - A short article describing why `gawk' is a good language for - Artificial Intelligence (AI) programming. + Pointers to the original draft of a short article describing why + `gawk' is a good language for artificial intelligence (AI) + programming. `doc/bc_notes' A brief description of `gawk''s "byte code" internals. @@ -20515,11 +27419,18 @@ Various `.c', `.y', and `.h' files The `troff' source for a manual page describing `gawk'. This is distributed for the convenience of Unix users. -`doc/gawk.texi' +`doc/gawktexi.in' +`doc/sidebar.awk' The Texinfo source file for this Info file. It should be - processed with TeX (via `texi2dvi' or `texi2pdf') to produce a - printed document, and with `makeinfo' to produce an Info or HTML - file. + processed by `doc/sidebar.awk' before processing with `texi2dvi' + or `texi2pdf' to produce a printed document, and with `makeinfo' + to produce an Info or HTML file. The `Makefile' takes care of + this processing and produces printable output via `texi2dvi' or + `texi2pdf'. + +`doc/gawk.texi' + The file produced after processing `gawktexi.in' with + `sidebar.awk'. `doc/gawk.info' The generated Info file for this Info file. @@ -20536,7 +27447,9 @@ Various `.c', `.y', and `.h' files `doc/igawk.1' The `troff' source for a manual page describing the `igawk' - program presented in *Note Igawk Program::. + program presented in *note Igawk Program::. (Since `gawk' can do + its own `@include' processing, neither `igawk' nor `igawk.1' are + installed.) `doc/Makefile.in' The input file used during the configuration process to generate @@ -20544,20 +27457,26 @@ Various `.c', `.y', and `.h' files `Makefile.am' `*/Makefile.am' - Files used by the GNU `automake' software for generating the - `Makefile.in' files used by `autoconf' and `configure'. + Files used by the GNU Automake software for generating the + `Makefile.in' files used by Autoconf and `configure'. `Makefile.in' `aclocal.m4' +`bisonfix.awk' +`config.guess' `configh.in' `configure.ac' `configure' `custom.h' +`depcomp' +`install-sh' `missing_d/*' +`mkinstalldirs' `m4/*' - These files and subdirectories are used when configuring `gawk' - for various Unix systems. They are explained in *Note Unix - Installation::. + These files and subdirectories are used when configuring and + compiling `gawk' for various Unix systems. Most of them are + explained in *note Unix Installation::. The rest are there to + support the main infrastructure. `po/*' The `po' library contains message translations. @@ -20571,12 +27490,23 @@ Various `.c', `.y', and `.h' files programs from the Texinfo source file for this Info file. It also contains a `Makefile.in' file, which `configure' uses to generate a `Makefile'. `Makefile.am' is used by GNU Automake to create - `Makefile.in'. The library functions from *Note Library - Functions::, and the `igawk' program from *Note Igawk Program::, - are included as ready-to-use files in the `gawk' distribution. - They are installed as part of the installation process. The rest - of the programs in this Info file are available in appropriate - subdirectories of `awklib/eg'. + `Makefile.in'. The library functions from *note Library + Functions::, are included as ready-to-use files in the `gawk' + distribution. They are installed as part of the installation + process. The rest of the programs in this Info file are available + in appropriate subdirectories of `awklib/eg'. + +`extension/*' + The source code, manual pages, and infrastructure files for the + sample extensions included with `gawk'. *Note Dynamic + Extensions::, for more information. + +`extras/*' + Additional non-essential files. Currently, this directory + contains some shell startup files to be installed in + `/etc/profile.d' to aid in manipulating the `AWKPATH' and + `AWKLIBPATH' environment variables. *Note Shell Startup Files::, + for more information. `posix/*' Files needed for building `gawk' on POSIX-compliant systems. @@ -20586,8 +27516,8 @@ Various `.c', `.y', and `.h' files PC Installation::, for details). `vms/*' - Files needed for building `gawk' under VMS (*note VMS - Installation::, for details). + Files needed for building `gawk' under Vax/VMS and OpenVMS (*note + VMS Installation::, for details). `test/*' A test suite for `gawk'. You can use `make check' from the @@ -20598,7 +27528,7 @@ Various `.c', `.y', and `.h' files File: gawk.info, Node: Unix Installation, Next: Non-Unix Installation, Prev: Gawk Distribution, Up: Installation -B.2 Compiling and Installing `gawk' on Unix-like Systems +B.2 Compiling and Installing `gawk' on Unix-Like Systems ======================================================== Usually, you can compile and install `gawk' by typing only two @@ -20608,13 +27538,14 @@ configure `gawk' for your system yourself. * Menu: * Quick Installation:: Compiling `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. -File: gawk.info, Node: Quick Installation, Next: Additional Configuration Options, Up: Unix Installation +File: gawk.info, Node: Quick Installation, Next: Shell Startup Files, Up: Unix Installation -B.2.1 Compiling `gawk' for Unix-like Systems +B.2.1 Compiling `gawk' for Unix-Like Systems -------------------------------------------- The normal installation steps should work on all modern commercial @@ -20622,12 +27553,12 @@ Unix-derived systems, GNU/Linux, BSD-based systems, and the Cygwin environment for MS-Windows. After you have extracted the `gawk' distribution, `cd' to -`gawk-4.0.0'. Like most GNU software, `gawk' is configured -automatically for your system by running the `configure' program. This -program is a Bourne shell script that is generated automatically using -GNU `autoconf'. (The `autoconf' software is described fully starting -with *note (Autoconf)Top:: autoconf,Autoconf--Generating Automatic -Configuration Scripts.) +`gawk-4.1.2'. As with most GNU software, you configure `gawk' for your +system by running the `configure' program. This program is a Bourne +shell script that is generated automatically using GNU Autoconf. (The +Autoconf software is described fully starting with *note +(Autoconf)Top:: autoconf,Autoconf--Generating Automatic Configuration +Scripts.) To configure `gawk', simply run `configure': @@ -20657,18 +27588,65 @@ That's all there is to it! To verify that `gawk' is working properly, run `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 `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 (*note -Bugs::). +failure is not described there, send in a bug report (*note Bugs::). + + Of course, once you've built `gawk', it is likely that you will wish +to install it. To do so, you need to run the command `make install', +as a user with the appropriate permissions. How to do this varies by +system, but on many systems you can use the `sudo' command to do so. +The command then becomes `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 `sudo' command. -File: gawk.info, Node: Additional Configuration Options, Next: Configuration Philosophy, Prev: Quick Installation, Up: Unix Installation +File: gawk.info, Node: Shell Startup Files, Next: Additional Configuration Options, Prev: Quick Installation, Up: Unix Installation + +B.2.2 Shell Startup Files +------------------------- + +The distribution contains shell startup files `gawk.sh' and `gawk.csh' +containing functions to aid in manipulating the `AWKPATH' and +`AWKLIBPATH' environment variables. On a Fedora system, these files +should be installed in `/etc/profile.d'; on other platforms, the +appropriate location may be different. + +`gawkpath_default' + Reset the `AWKPATH' environment variable to its default value. + +`gawkpath_prepend' + Add the argument to the front of the `AWKPATH' environment + variable. + +`gawkpath_append' + Add the argument to the end of the `AWKPATH' environment variable. + +`gawklibpath_default' + Reset the `AWKLIBPATH' environment variable to its default value. + +`gawklibpath_prepend' + Add the argument to the front of the `AWKLIBPATH' environment + variable. + +`gawklibpath_append' + Add the argument to the end of the `AWKLIBPATH' environment + variable. + -B.2.2 Additional Configuration Options + +File: gawk.info, Node: Additional Configuration Options, Next: Configuration Philosophy, Prev: Shell Startup Files, Up: Unix Installation + +B.2.3 Additional Configuration Options -------------------------------------- There are several additional options you may use on the `configure' command line when compiling `gawk' from scratch, including: +`--disable-extensions' + Disable configuring and building the sample extensions in the + `extension' directory. This is useful for cross-compiling. The + default action is to dynamically check if the extensions can be + configured and compiled. + `--disable-lint' Disable all lint checking within `gawk'. The `--lint' and `--lint-old' options (*note Options::) are accepted, but silently @@ -20676,8 +27654,8 @@ command line when compiling `gawk' from scratch, including: User-modified::) has no effect on the running `awk' program. When used with GCC's automatic dead-code-elimination, this option - cuts almost 200K bytes off the size of the `gawk' executable on - GNU/Linux x86 systems. Results on other systems and with other + cuts almost 23K bytes off the size of the `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. @@ -20690,16 +27668,16 @@ command line when compiling `gawk' from scratch, including: improvement. `--with-whiny-user-strftime' - Force use of the included version of the `strftime()' function for - deficient systems. + Force use of the included version of the C `strftime()' function + for deficient systems. Use the command `./configure --help' to see the full list of options -that `configure' supplies. +supplied by `configure'. File: gawk.info, Node: Configuration Philosophy, Prev: Additional Configuration Options, Up: Unix Installation -B.2.3 The Configuration Process +B.2.4 The Configuration Process ------------------------------- This minor node is of interest only if you know something about using @@ -20723,21 +27701,21 @@ are: what header files are available, so that 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 `st_blksize' -element in the `stat' structure. In this case, `HAVE_ST_BLKSIZE' is -undefined. +element in the `stat' structure. In this case, +`HAVE_STRUCT_STAT_ST_BLKSIZE' is undefined. It is possible for your C compiler to lie to `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 `custom.h'. Use an +available. To get around this, edit the `custom.h' file. Use an `#ifdef' that is appropriate for your system, and either `#define' any constants that `configure' should have defined but didn't, or `#undef' -any constants that `configure' defined and should not have. `custom.h' -is automatically included by `config.h'. +any constants that `configure' defined and should not have. The +`custom.h' file is automatically included by the `config.h' file. It is also possible that the `configure' program generated by -`autoconf' will not work on your system in some other fashion. If you -do have a problem, the file `configure.ac' is the input for `autoconf'. -You may be able to change this file and generate a new version of +Autoconf will not work on your system in some other fashion. If you do +have a problem, the `configure.ac' file is the input for Autoconf. You +may be able to change this file and generate a new version of `configure' that works on your system (*note Bugs::, for information on how to report problems in configuring `gawk'). The same mechanism may be used to send in updates to `configure.ac' and/or `custom.h'. @@ -20763,16 +27741,16 @@ File: gawk.info, Node: PC Installation, Next: VMS Installation, Up: Non-Unix B.3.1 Installation on PC Operating Systems ------------------------------------------ -This minor node covers installation and usage of `gawk' on x86 machines -running MS-DOS, any version of MS-Windows, or OS/2. In this minor -node, the term "Windows32" refers to any of Microsoft -Windows-95/98/ME/NT/2000/XP/Vista/7. +This minor node covers installation and usage of `gawk' on Intel +architecture machines running MS-DOS, any version of MS-Windows, or +OS/2. In this minor node, the term "Windows32" 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 `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 `README_d/README.pc' in the + 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 `gawk'. The varying capabilities of +Microsoft Windows 3.1 and Windows32 can add to the confusion. For an +overview of the considerations, refer to `README_d/README.pc' in the distribution. * Menu: @@ -20832,13 +27810,13 @@ B.3.1.2 Compiling `gawk' for PC Operating Systems ................................................. `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 -`README_d/README.pc' in the `gawk' distribution contains additional -notes, and `pc/Makefile' contains important information on compilation -options. +development tools from DJ Delorie (DJGPP: MS-DOS only), MinGW +(Windows32) or Eberhard Mattes (EMX: MS-DOS, Windows32 and OS/2). The +file `README_d/README.pc' in the `gawk' distribution contains +additional notes, and `pc/Makefile' contains important information on +compilation options. - To build `gawk' for MS-DOS and Windows32, copy the files in the `pc' +To build `gawk' for MS-DOS and Windows32, copy the files in the `pc' directory (_except_ for `ChangeLog') to the directory with the rest of the `gawk' sources, then invoke `make' with the appropriate target name as an argument to build `gawk'. The `Makefile' copied from the `pc' @@ -20851,7 +27829,7 @@ MS-DOS and Windows32 versions. A list of targets is printed if the `gawk' using the DJGPP tools, enter `make djgpp'. (The DJGPP tools needed for the build may be found at `ftp://ftp.delorie.com/pub/djgpp/current/v2gnu/'.) To build a native -MS-Windows binary of `gawk', type `make mingw32'. +MS-Windows binary of `gawk' using the MinGW tools, type `make mingw32'. The 32 bit EMX version of `gawk' works "out of the box" under OS/2. However, it is highly recommended to use GCC 2.95.3 for the compilation. @@ -20898,7 +27876,12 @@ other set of (self-consistent) environment variables and compiler flags. NOTE: Ancient OS/2 ports of GNU `make' are not able to handle the Makefiles of this package. If you encounter any problems with `make', try GNU Make 3.79.1 or later versions. You should find - the latest version on `ftp://hobbes.nmsu.edu/pub/os2/'. + the latest version on `ftp://hobbes.nmsu.edu/pub/os2/'.(1) + + ---------- Footnotes ---------- + + (1) As of November 2014, this site is still there, but the author +could not find a package for GNU Make. File: gawk.info, Node: PC Testing, Next: PC Using, Prev: PC Compiling, Up: PC Installation @@ -20931,20 +27914,19 @@ File: gawk.info, Node: PC Using, Next: Cygwin, Prev: PC Testing, Up: PC Inst B.3.1.4 Using `gawk' on PC Operating Systems ............................................ -With the exception of the Cygwin environment, the `|&' operator and -TCP/IP networking (*note TCP/IP Networking::) are not supported for -MS-DOS or MS-Windows. EMX (OS/2 only) does support at least the `|&' -operator. +Under MS-DOS and MS-Windows, the Cygwin and MinGW environments support +both the `|&' operator and TCP/IP networking (*note TCP/IP +Networking::). EMX (OS/2 only) supports at least the `|&' operator. The MS-DOS and MS-Windows versions of `gawk' search for program -files as described in *Note AWKPATH Variable::. However, semicolons +files as described in *note AWKPATH Variable::. However, semicolons (rather than colons) separate elements in the `AWKPATH' variable. If -`AWKPATH' is not set or is empty, then the default search path for -MS-Windows and MS-DOS versions is `".;c:/lib/awk;c:/gnu/lib/awk"'. +`AWKPATH' is not set or is empty, then the default search path is +`.;c:/lib/awk;c:/gnu/lib/awk'. The search path for OS/2 (32 bit, EMX) is determined by the prefix directory (most likely `/usr' or `c:/usr') that has been specified as -an option of the `configure' script like it is the case for the Unix +an option of the `configure' script as is the case for the Unix versions. If `c:/usr' is the prefix directory then the default search path contains `.' and `c:/usr/share/awk'. Additionally, to support binary distributions of `gawk' for OS/2 systems whose drive `c:' might @@ -20952,7 +27934,7 @@ not support long file names or might not exist at all, there is a special environment variable. If `UNIXROOT' specifies a drive then this specific drive is also searched for program files. E.g., if `UNIXROOT' is set to `e:' the complete default search path is -`".;c:/usr/share/awk;e:/usr/share/awk"'. +`.;c:/usr/share/awk;e:/usr/share/awk'. An `sh'-like shell (as opposed to `command.com' under MS-DOS or `cmd.exe' under MS-Windows or OS/2) may be useful for `awk' programming. @@ -20960,15 +27942,14 @@ The DJGPP collection of tools includes an MS-DOS port of Bash, and several shells are available for OS/2, including `ksh'. Under MS-Windows, OS/2 and MS-DOS, `gawk' (and many other text -programs) silently translate end-of-line `"\r\n"' to `"\n"' on input -and `"\n"' to `"\r\n"' on output. A special `BINMODE' variable -(c.e.) allows control over these translations and is interpreted as -follows: +programs) silently translate end-of-line `\r\n' to `\n' on input and +`\n' to `\r\n' on output. A special `BINMODE' variable (c.e.) allows +control over these translations and is interpreted as follows: - * If `BINMODE' is `"r"', or one, then binary mode is set on read + * If `BINMODE' is `"r"' or one, then binary mode is set on read (i.e., no translations on reads). - * If `BINMODE' is `"w"', or two, then binary mode is set on write + * If `BINMODE' is `"w"' or two, then binary mode is set on write (i.e., no translations on writes). * If `BINMODE' is `"rw"' or `"wr"' or three, binary mode is set for @@ -20989,11 +27970,11 @@ and cannot be changed mid-stream. Versions::). `mawk' and `gawk' handle `BINMODE' similarly; however, `mawk' adds a `-W BINMODE=N' option and an environment variable that can set `BINMODE', `RS', and `ORS'. The files `binmode[1-3].awk' -(under `gnu/lib/awk' in some of the prepared distributions) have been -chosen to match `mawk''s `-W BINMODE=N' option. These can be changed -or discarded; in particular, the setting of `RS' giving the fewest -"surprises" is open to debate. `mawk' uses `RS = "\r\n"' if binary -mode is set on read, which is appropriate for files with the +(under `gnu/lib/awk' in some of the prepared binary distributions) have +been chosen to match `mawk''s `-W BINMODE=N' option. These can be +changed or discarded; in particular, the setting of `RS' giving the +fewest "surprises" is open to debate. `mawk' uses `RS = "\r\n"' if +binary mode is set on read, which is appropriate for files with the MS-DOS-style end-of-line. To illustrate, the following examples set binary mode on writes for @@ -21010,7 +27991,7 @@ These give the same result as the `-W BINMODE=2' option in `mawk'. The following changes the record separator to `"\r\n"' and sets binary mode on reads, but does not affect the mode on standard input: - gawk -v RS="\r\n" --source "BEGIN { BINMODE = 1 }" ... + gawk -v RS="\r\n" -e "BEGIN { BINMODE = 1 }" ... or: @@ -21027,24 +28008,20 @@ B.3.1.5 Using `gawk' In The Cygwin Environment `gawk' can be built and used "out of the box" under MS-Windows if you are using the Cygwin environment (http://www.cygwin.com). This -environment provides an excellent simulation of Unix, 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 +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: - tar -xvpzf gawk-4.0.0.tar.gz - cd gawk-4.0.0 + tar -xvpzf gawk-4.1.2.tar.gz + cd gawk-4.1.2 ./configure - make + make && make check When compared to GNU/Linux on the same system, the `configure' step on Cygwin takes considerably longer. However, it does finish, and then the `make' proceeds as usual. - NOTE: The `|&' operator and TCP/IP networking (*note TCP/IP - Networking::) are fully supported in the Cygwin environment. This - is not true for any other environment on MS-Windows. - File: gawk.info, Node: MSYS, Prev: Cygwin, Up: PC Installation @@ -21057,13 +28034,13 @@ use the `BINMODE' variable. This can cause problems with other Unix-like components that have been ported to MS-Windows that expect `gawk' to do automatic -translation of `"\r\n"', since it won't. Caveat Emptor! +translation of `"\r\n"', because it won't. File: gawk.info, Node: VMS Installation, Prev: PC Installation, Up: Non-Unix Installation -B.3.2 How to Compile and Install `gawk' on VMS ----------------------------------------------- +B.3.2 Compiling and Installing `gawk' on Vax/VMS and OpenVMS +------------------------------------------------------------ This node describes how to compile and install `gawk' under VMS. The older designation "VMS" is used throughout to refer to OpenVMS. @@ -21071,51 +28048,118 @@ older designation "VMS" is used throughout to refer to OpenVMS. * Menu: * VMS Compilation:: How to compile `gawk' under VMS. +* VMS Dynamic Extensions:: Compiling `gawk' dynamic extensions on + VMS. * VMS Installation Details:: How to install `gawk' under VMS. * VMS Running:: How to run `gawk' under VMS. +* VMS GNV:: The VMS GNV Project. * VMS Old Gawk:: An old version comes with some VMS systems. -File: gawk.info, Node: VMS Compilation, Next: VMS Installation Details, Up: VMS Installation +File: gawk.info, Node: VMS Compilation, Next: VMS Dynamic Extensions, Up: VMS Installation B.3.2.1 Compiling `gawk' on VMS ............................... To compile `gawk' under VMS, there is a `DCL' command procedure that issues all the necessary `CC' and `LINK' commands. There is also a -`Makefile' for use with the `MMS' utility. From the source directory, -use either: +`Makefile' for use with the `MMS' and `MMK' utilities. From the source +directory, use either: + + $ @[.vms]vmsbuild.com - $ @[.VMS]VMSBUILD.COM +or: + + $ MMS/DESCRIPTION=[.vms]descrip.mms gawk or: - $ MMS/DESCRIPTION=[.VMS]DESCRIP.MMS GAWK + $ MMK/DESCRIPTION=[.vms]descrip.mms gawk + + `MMK' is an open source, free, near-clone of `MMS' and can better +handle ODS-5 volumes with upper- and lowercase file names. `MMK' is +available from `https://github.com/endlesssoftware/mmk'. - Older versions of `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 `VMSBUILD.COM' and `DESCRIP.MMS' -contain some obsolete support for the older compilers but are set up to -use DEC C by default. + With ODS-5 volumes and extended parsing enabled, the case of the +target parameter may need to be exact. - `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.(1) + `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.(1) + + *Note VMS GNV::, for information on building `gawk' as a PCSI kit +that is compatible with the GNV product. ---------- Footnotes ---------- (1) The IA64 architecture is also known as "Itanium." -File: gawk.info, Node: VMS Installation Details, Next: VMS Running, Prev: VMS Compilation, Up: VMS Installation +File: gawk.info, Node: VMS Dynamic Extensions, Next: VMS Installation Details, Prev: VMS Compilation, Up: VMS Installation + +B.3.2.2 Compiling `gawk' Dynamic Extensions on VMS +.................................................. + +The extensions that have been ported to VMS can be built using one of +the following commands: + + $ MMS/DESCRIPTION=[.vms]descrip.mms extensions + +or: + + $ MMK/DESCRIPTION=[.vms]descrip.mms extensions + + `gawk' uses `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 `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. -B.3.2.2 Installing `gawk' on VMS + For Alpha and Itanium: + + /name=(as_is,short) + /float=ieee/ieee_mode=denorm_results + + For VAX: + + /name=(as_is,short) + + Compile time macros need to be defined before the first VMS-supplied +header file is included, as follows: + + #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 + + If you are writing your own extensions to run on VMS, you must +supply these definitions yourself. The `config.h' file created when +building `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. + + +File: gawk.info, Node: VMS Installation Details, Next: VMS Running, Prev: VMS Dynamic Extensions, Up: VMS Installation + +B.3.2.3 Installing `gawk' on VMS ................................ -To install `gawk', all you need is a "foreign" command, which is a -`DCL' symbol whose value begins with a dollar sign. For example: +To use `gawk', all you need is a "foreign" command, which is a `DCL' +symbol whose value begins with a dollar sign. For example: - $ GAWK :== $disk1:[gnubin]GAWK + $ GAWK :== $disk1:[gnubin]gawk Substitute the actual location of `gawk.exe' for `$disk1:[gnubin]'. The symbol should be placed in the `login.com' of any user who wants to run @@ -21123,9 +28167,27 @@ symbol should be placed in the `login.com' of any user who wants to run Alternatively, the symbol may be placed in the system-wide `sylogin.com' procedure, which allows all users to run `gawk'. - Optionally, the help entry can be loaded into a VMS help library: + If your `gawk' was installed by a PCSI kit into the `GNV$GNU:' +directory tree, the program will be known as +`GNV$GNU:[bin]gnv$gawk.exe' and the help file will be +`GNV$GNU:[vms_help]gawk.hlp'. + + The PCSI kit also installs a `GNV$GNU:[vms_bin]gawk_verb.cld' file +which can be used to add `gawk' and `awk' as DCL commands. + + For just the current process you can use: - $ LIBRARY/HELP SYS$HELP:HELPLIB [.VMS]GAWK.HLP + $ set command gnv$gnu:[vms_bin]gawk_verb.cld + + Or the system manager can use `GNV$GNU:[vms_bin]gawk_verb.cld' to +add the `gawk' and `awk' to the system wide `DCLTABLES'. + + The DCL syntax is documented in the `gawk.hlp' file. + + Optionally, the `gawk.hlp' entry can be loaded into a VMS help +library: + + $ LIBRARY/HELP sys$help:helplib [.vms]gawk.hlp (You may want to substitute a site-specific help library rather than the standard VMS library `HELPLIB'.) After loading the help text, the @@ -21142,14 +28204,14 @@ has no device or directory path information in it, `gawk' looks in the current directory first, then in the directory specified by the translation of `AWK_LIBRARY' if the file is not found. If, after searching in both directories, the file still is not found, `gawk' -appends the suffix `.awk' to the filename and retries the file search. +appends the suffix `.awk' to the file name and retries the file search. If `AWK_LIBRARY' has no definition, a default value of `SYS$LIBRARY:' is used for it. -File: gawk.info, Node: VMS Running, Next: VMS Old Gawk, Prev: VMS Installation Details, Up: VMS Installation +File: gawk.info, Node: VMS Running, Next: VMS GNV, Prev: VMS Installation Details, Up: VMS Installation -B.3.2.3 Running `gawk' on VMS +B.3.2.4 Running `gawk' on VMS ............................. Command-line parsing and quoting conventions are significantly different @@ -21168,12 +28230,40 @@ Note that uppercase and mixed-case text must be quoted. The VMS port of `gawk' includes a `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 -becomes ambiguous. To work around this, the normally optional `--' -flag is required to force Unix-style parsing rather than `DCL' parsing. -If any other dash-type options (or multiple parameters such as data -files to process) are present, there is no ambiguity and `--' can be -omitted. +single parameter (as in the quoted string program), the command becomes +ambiguous. To work around this, the normally optional `--' flag is +required to force Unix-style parsing rather than `DCL' parsing. If any +other dash-type options (or multiple parameters such as data files to +process) are present, there is no ambiguity and `--' can be omitted. + + The `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 `exit' value. A +failure is indicated by 1 and VMS sets the `ERROR' status. A fatal +error is indicated by 2 and VMS sets the `FATAL' status. All other +values will have the `SUCCESS' status. The exit value is encoded to +comply with VMS coding standards and will have the `C_FACILITY_NO' of +`0x350000' with the constant `0xA000' added to the number shifted over +by 3 bits to make room for the severity codes. + + To extract the actual `gawk' exit code from the VMS status use: + + unix_status = (vms_status .and. &x7f8) / 8 + +A C program that uses `exec()' to call `gawk' will get the original +Unix-style exit value. + + Older versions of `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. + + VAX/VMS floating point uses unbiased rounding. *Note Round +Function::. + + VMS reports time values in GMT unless one of the `SYS$TIMEZONE_RULE' +or `TZ' logical names is set. Older versions of VMS, such as VAX/VMS +7.3 do not set these logical names. The default search path, when looking for `awk' program files specified by the `-f' option, is `"SYS$DISK:[],AWK_LIBRARY:"'. The @@ -21183,9 +28273,27 @@ When defining it, the value should be quoted so that it retains a single translation and not a multitranslation `RMS' searchlist. -File: gawk.info, Node: VMS Old Gawk, Prev: VMS Running, Up: VMS Installation +File: gawk.info, Node: VMS GNV, Next: VMS Old Gawk, Prev: VMS Running, Up: VMS Installation + +B.3.2.5 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 `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 +`https://sourceforge.net/p/gnv/wiki/InstallingGNVPackages/'. + + The normal build procedure for `gawk' produces a program that is +suitable for use with GNV. + + The file `vms/gawk_build_steps.txt' in the distribution documents +the procedure for building a VMS PCSI kit that is compatible with GNV. + + +File: gawk.info, Node: VMS Old Gawk, Prev: VMS GNV, Up: VMS Installation -B.3.2.4 Some VMS Systems Have An Old Version of `gawk' +B.3.2.6 Some VMS Systems Have An Old Version of `gawk' ...................................................... Some versions of VMS have an old version of `gawk'. To access it, @@ -21202,15 +28310,15 @@ File: gawk.info, Node: Bugs, Next: Other Versions, Prev: Non-Unix Installatio B.4 Reporting Problems and Bugs =============================== - There is nothing more dangerous than a bored archeologist. - The Hitchhiker's Guide to the Galaxy + There is nothing more dangerous than a bored archaeologist. -- + Douglas Adams, `The Hitchhiker's Guide to the Galaxy' If you have problems with `gawk' or think that you have found a bug, -please report it to the developers; we cannot promise to do anything -but we might well want to fix it. +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! @@ -21223,75 +28331,76 @@ compile `gawk', and the exact results `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 `gawk' you are using. You can -get this information with the command `gawk --version'. + Make sure to include the version number of `gawk' you are using. +You can get this information with the command `gawk --version'. - Once you have a precise problem, send email to <bug-gawk@gnu.org>. + Once you have a precise problem description, send email to +<bug-gawk@gnu.org>. - Using this address automatically sends a copy of your mail to me. -If necessary, I can be reached directly at <arnold@skeeve.com>. The -bug reporting address is preferred since the email list is archived at -the GNU Project. _All email should be in English, since that is my -native language._ + The `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. _All email must be in English. This is +the only language understood in common by all the maintainers._ CAUTION: Do _not_ try to report bugs in `gawk' by posting to the - Usenet/Internet newsgroup `comp.lang.awk'. While the `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. Really. + Usenet/Internet newsgroup `comp.lang.awk'. The `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. 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, - _please_ also send a copy to <bug-gawk@gnu.org>. + report a bug using your distribution's bug reporting system, you + should also send a copy to <bug-gawk@gnu.org>. - This is for two reasons. First, while some distributions forward - bug reports "upstream" to the GNU mailing list, many don't, so - there is a good chance that the `gawk' maintainer 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. + 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 `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 organizations. 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. +just obscure 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 `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 `README' file in the -`gawk' distribution. Information in the `README' file should be -considered authoritative if it conflicts with this Info file. + If you find bugs in one of the non-Unix ports of `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 `README' +file in the `gawk' distribution. Information in the `README' file +should be considered authoritative if it conflicts with this Info file. - The people maintaining the non-Unix ports of `gawk' are as follows: + The people maintaining the various `gawk' ports are: +Unix and POSIX systems Arnold Robbins, <arnold@skeeve.com>. MS-DOS with DJGPP Scott Deifik, <scottd.mail@sbcglobal.net>. -MS-Windows with MINGW Eli Zaretskii, <eliz@gnu.org>. +MS-Windows with MinGW Eli Zaretskii, <eliz@gnu.org>. OS/2 Andreas Buening, <andreas.buening@nexgo.de>. -VMS Pat Rankin, <r.pat.rankin@gmail.com> +VMS John Malmberg, <wb8tyw@qsl.net>. z/OS (OS/390) Dave Pitts, <dpitts@cozx.com>. - If your bug is also reproducible under Unix, please send a copy of -your report to the <bug-gawk@gnu.org> email list as well. + If your bug is also reproducible under Unix, send a copy of your +report to the <bug-gawk@gnu.org> email list as well. -File: gawk.info, Node: Other Versions, Prev: Bugs, Up: Installation +File: gawk.info, Node: Other Versions, Next: Installation summary, Prev: Bugs, Up: Installation B.5 Other Freely Available `awk' Implementations ================================================ It's kind of fun to put comments like this in your awk code. - `// Do C++ comments work? answer: yes! of course' - Michael Brennan + `// Do C++ comments work? answer: yes! of course' -- Michael + Brennan - There are a number of other freely available `awk' implementations. +There are a number of other freely available `awk' implementations. This minor node briefly describes where to get them: Unix `awk' Brian Kernighan, one of the original designers of Unix `awk', has made his implementation of `awk' freely available. You can - retrieve this version via the World Wide Web from his home page + retrieve this version via his home page (http://www.cs.princeton.edu/~bwk). It is available in several archive formats: @@ -21304,12 +28413,25 @@ Unix `awk' Zip file `http://www.cs.princeton.edu/~bwk/btl.mirror/awk.zip' + You can also retrieve it from Git Hub: + + git clone git://github.com/onetrueawk/awk bwkawk + + This command creates a copy of the Git (http://git-scm.com) + repository in a directory named `bwkawk'. If you leave that + argument off the `git' command line, the repository copy is + created in a directory named `awk'. + This version requires an ISO C (1990 standard) compiler; the C compiler from GCC (the GNU Compiler Collection) works quite nicely. *Note Common Extensions::, for a list of extensions in this `awk' that are not in POSIX `awk'. + As a side note, Dan Bornstein has created a Git repository tracking + all the versions of BWK `awk' that he could find. It's available + at `git://github.com/danfuzz/one-true-awk'. + `mawk' Michael Brennan wrote an independent implementation of `awk', called `mawk'. It is available under the GPL (*note Copying::), @@ -21321,8 +28443,8 @@ Unix `awk' In 2009, Thomas Dickey took on `mawk' maintenance. Basic information is available on the project's web page - (http://www.invisible-island.net/mawk/mawk.html). The download - URL is `http://invisible-island.net/datafiles/release/mawk.tar.gz'. + (http://www.invisible-island.net/mawk). The download URL is + `http://invisible-island.net/datafiles/release/mawk.tar.gz'. Once you have it, `gunzip' may be used to decompress this file. Installation is similar to `gawk''s (*note Unix Installation::). @@ -21345,11 +28467,12 @@ Unix `awk' since approximately 2003. `pawk' - Nelson H.F. Beebe at the University of Utah has modified Brian - Kernighan's `awk' to provide timing and profiling information. It - is different from `pgawk' (*note Profiling::), in that it uses - CPU-based profiling, not line-count profiling. You may find it at - either `ftp://ftp.math.utah.edu/pub/pawk/pawk-20030606.tar.gz' or + Nelson H.F. Beebe at the University of Utah has modified BWK `awk' + to provide timing and profiling information. It is different from + `gawk' with the `--profile' option (*note Profiling::), in that it + uses CPU-based profiling, not line-count profiling. You may find + it at either + `ftp://ftp.math.utah.edu/pub/pawk/pawk-20030606.tar.gz' or `http://www.math.utah.edu/pub/pawk/pawk-20030606.tar.gz'. Busybox Awk @@ -21362,14 +28485,21 @@ Busybox Awk (http://busybox.net). The OpenSolaris POSIX `awk' - The version of `awk' in `/usr/xpg4/bin' on Solaris is more-or-less - POSIX-compliant. It is based on the `awk' from Mortice Kern - Systems for PCs. The source code can be downloaded from the - OpenSolaris web site (http://www.opensolaris.org). This author - was able to make it 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. + The versions of `awk' in `/usr/xpg4/bin' and `/usr/xpg6/bin' on + Solaris are more-or-less POSIX-compliant. They are based on the + `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. + + The source code used to be available from the OpenSolaris website. + However, that project was ended and the website shut down. + Fortunately, the Illumos project + (http://wiki.illumos.org/display/illumos/illumos+Home) makes this + implementation available. You can view the files one at a time + from + `https://github.com/joyent/illumos-joyent/blob/master/usr/src/cmd/awk_xpg4'. `jawk' This is an interpreter for `awk' written in Java. It claims to be @@ -21380,10 +28510,16 @@ The OpenSolaris POSIX `awk' Libmawk This is an embeddable `awk' interpreter derived from `mawk'. For - more information see `http://repo.hu/projects/libmawk/'. + more information, see `http://repo.hu/projects/libmawk/'. + +`pawk' + This is a Python module that claims to bring `awk'-like features + to Python. See `https://github.com/alecthomas/pawk' for more + information. (This is not related to Nelson Beebe's modified + version of BWK `awk', described earlier.) QSE Awk - This is an embeddable `awk' interpreter. For more information see + This is an embeddable `awk' interpreter. For more information, see `http://code.google.com/p/qse/' and `http://awk.info/?tools/qse'. `QTawk' @@ -21393,12 +28529,42 @@ QSE Awk `http://www.quiktrim.org/QTawk.html' for more information, including the manual and a download link. -`xgawk' - XML `gawk'. This is a fork of the `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 `gawk' - code base. For more information, see the XMLgawk project web site - (http://xmlgawk.sourceforge.net). + The project may also be frozen; no new code changes have been made + since approximately 2008. + +Other versions + See also the "Versions and implementations" section of the + Wikipedia article + (http://en.wikipedia.org/wiki/Awk_language#Versions_and_implementations) + for information on additional versions. + + + +File: gawk.info, Node: Installation summary, Prev: Other Versions, Up: Installation + +B.6 Summary +=========== + + * The `gawk' distribution is available from GNU project's main + distribution site, `ftp.gnu.org'. The canonical build recipe is: + + wget http://ftp.gnu.org/gnu/gawk/gawk-4.1.2.tar.gz + tar -xvpzf gawk-4.1.2.tar.gz + cd gawk-4.1.2 + ./configure && make && make check + + * `gawk' may be built on non-POSIX systems as well. The currently + supported systems are MS-Windows using DJGPP, MSYS, MinGW and + Cygwin, OS/2 using EMX, and both Vax/VMS and OpenVMS. + Instructions for each system are included in this major node. + + * Bug reports should be sent via email to <bug-gawk@gnu.org>. Bug + reports should be in English, and should include the version of + `gawk', how it was compiled, and a short program and data file + which demonstrate the problem. + + * There are a number of other freely available `awk' + implementations. Many are POSIX compliant; others are less so. @@ -21416,9 +28582,11 @@ and maintainers of `gawk'. Everything in it applies specifically to * Compatibility Mode:: How to disable certain `gawk' extensions. * Additions:: Making Additions To `gawk'. -* Dynamic Extensions:: Adding new built-in functions to - `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. File: gawk.info, Node: Compatibility Mode, Next: Additions, Up: Notes @@ -21436,7 +28604,7 @@ one more option available on the command line: `-Y' `--parsedebug' - Prints out the parse stack information as the program is being + Print out the parse stack information as the program is being parsed. This option is intended only for serious `gawk' developers and not @@ -21444,7 +28612,7 @@ for the casual user. It probably has not even been compiled into your version of `gawk', since it slows down execution. -File: gawk.info, Node: Additions, Next: Dynamic Extensions, Prev: Compatibility Mode, Up: Notes +File: gawk.info, Node: Additions, Next: Future Extensions, Prev: Compatibility Mode, Up: Notes C.2 Making Additions to `gawk' ============================== @@ -21464,6 +28632,8 @@ as well as any considerations you should bear in mind. `gawk'. * New Ports:: Porting `gawk' to a new operating system. +* Derived Files:: Why derived files are kept in the Git + repository. File: gawk.info, Node: Accessing The Source, Next: Adding Code, Up: Additions @@ -21471,7 +28641,7 @@ File: gawk.info, Node: Accessing The Source, Next: Adding Code, Up: Additions C.2.1 Accessing The `gawk' Git Repository ----------------------------------------- -As `gawk' is Free Software, the source code is always available. *Note +As `gawk' is Free Software, the source code is always available. *note Gawk Distribution::, describes how to get and build the formal, released versions of `gawk'. @@ -21479,26 +28649,25 @@ released versions of `gawk'. changes, you will probably wish to work with the development version. To do so, you will need to access the `gawk' source code repository. The code is maintained using the Git distributed version control system -(http://git-scm.com/). You will need to install it if your system +(http://git-scm.com). You will need to install it if your system doesn't have it. Once you have done so, use the command: git clone git://git.savannah.gnu.org/gawk.git -This will clone the `gawk' repository. If you are behind a firewall -that will not allow you to use the Git native protocol, you can still -access the repository using: +This clones the `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: git clone http://git.savannah.gnu.org/r/gawk.git Once you have made changes, you can use `git diff' to produce a -patch, and send that to the `gawk' maintainer; see *Note 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: +patch, and send that to the `gawk' maintainer; see *note Bugs::, for +how to do that. - cvs -d:pserver:anonymous@pserver.git.sv.gnu.org:/gawk.git co -d gawk master + 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. File: gawk.info, Node: Adding Code, Next: New Ports, Prev: Accessing The Source, Up: Additions @@ -21509,12 +28678,12 @@ C.2.2 Adding New Features You are free to add any new features you like to `gawk'. However, if you want your changes to be incorporated into the `gawk' distribution, there are several steps that you need to take in order to make it -possible to include your changes: +possible to include them: 1. Before building the new feature into `gawk' itself, consider - writing it as an extension module (*note Dynamic Extensions::). - If that's not possible, continue with the rest of the steps in - this list. + writing it as an extension (*note Dynamic Extensions::). If + that's not possible, continue with the rest of the steps in this + list. 2. Be prepared to sign the appropriate paperwork. In order for the FSF to distribute your changes, you must either place those @@ -21526,17 +28695,17 @@ possible to include your changes: 3. Get the latest version. It is much easier for me to integrate changes if they are relative to the most recent distributed - version of `gawk'. If your version of `gawk' is very old, I may - not be able to integrate them at all. (*Note Getting::, for - information on getting the latest version of `gawk'.) + version of `gawk', or better yet, relative to the latest code in + the Git repository. If your version of `gawk' is very old, I may + not be able to integrate your changes at all. (*Note Getting::, + for information on getting the latest version of `gawk'.) 4. See *note (Version)Top:: standards, GNU Coding Standards. This document describes how GNU software should be written. If you haven't read it, please do so, preferably _before_ starting to modify `gawk'. (The `GNU Coding Standards' are available from the - GNU Project's web site - (http://www.gnu.org/prep/standards_toc.html). Texinfo, Info, and - DVI versions are also available.) + GNU Project's website (http://www.gnu.org/prep/standards_toc.html). + Texinfo, Info, and DVI versions are also available.) 5. Use the `gawk' coding style. The C code for `gawk' follows the instructions in the `GNU Coding Standards', with minor exceptions. @@ -21575,9 +28744,9 @@ possible to include your changes: of `switch' statements, instead of just the plain pointer or character value. - * Use the `TRUE', `FALSE' and `NULL' symbolic constants and the - character constant `'\0'' where appropriate, instead of `1' - and `0'. + * Use `true' and `false' for `bool' values, the `NULL' symbolic + constant for pointer values, and the character constant + `'\0'' where appropriate, instead of `1' and `0'. * Provide one-line descriptive comments for each function. @@ -21613,9 +28782,10 @@ possible to include your changes: 7. Submit changes as unified diffs. Use `diff -u -r -N' to compare the original `gawk' source tree with your version. I recommend - using the GNU version of `diff'. Send the output produced by - either run of `diff' to me when you submit your changes. (*Note - Bugs::, for the electronic mail information.) + using the GNU version of `diff', or best of all, `git diff' or + `git format-patch'. Send the output produced by `diff' to me when + you submit your changes. (*Note Bugs::, for the electronic mail + information.) Using this format makes it easy for me to apply your changes to the master version of the `gawk' source code (using `patch'). If I @@ -21624,7 +28794,8 @@ possible to include your changes: 8. Include an entry for the `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. + making it easier for me to accept patches. It is simplest if you + just make this part of your diff. 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 @@ -21632,7 +28803,7 @@ isn't possible for me to do that with a minimum of extra work, then I probably will not. -File: gawk.info, Node: New Ports, Prev: Adding Code, Up: Additions +File: gawk.info, Node: New Ports, Next: Derived Files, Prev: Adding Code, Up: Additions C.2.3 Porting `gawk' to a New Operating System ---------------------------------------------- @@ -21640,7 +28811,7 @@ C.2.3 Porting `gawk' to a New Operating System If you want to port `gawk' to a new operating system, there are several steps: - 1. Follow the guidelines in *Note Adding Code::, concerning coding + 1. Follow the guidelines in *note Adding Code::, concerning coding style, submission of diffs, and so on. 2. Be prepared to sign the appropriate paperwork. In order for the @@ -21665,18 +28836,24 @@ steps: 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 `dfa.c', `dfa.h', `getopt1.c', `getopt.c', `getopt.h', - `install-sh', `mkinstalldirs', `regcomp.c', `regex.c', - `regexec.c', `regexex.c', `regex.h', `regex_internal.c', and - `regex_internal.h'. - - 5. Be willing to continue to maintain the port. Non-Unix operating + are `dfa.c', `dfa.h', `getopt.c', `getopt.h', `getopt1.c', + `getopt_int.h', `gettext.h', `regcomp.c', `regex.c', `regex.h', + `regex_internal.c', `regex_internal.h', and `regexec.c'. + + 5. A number of other files are provided by the GNU Autotools + (Autoconf, Automake, and GNU `gettext'). You should not change + them either, unless it is for a very good reason. The files are + `ABOUT-NLS', `config.guess', `config.rpath', `config.sub', + `depcomp', `INSTALL', `install-sh', `missing', `mkinstalldirs', + `xalloc.h', and `ylwrap'. + + 6. 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 `gawk' on their systems. If noone volunteers to - maintain a port, it becomes unsupported and it may be necessary to - remove it from the distribution. + to compile and run `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. - 6. Supply an appropriate `gawkmisc.???' file. Each port has its own + 7. Supply an appropriate `gawkmisc.???' file. Each port has its own `gawkmisc.???' that implements certain operating system specific functions. This is cleaner than a plethora of `#ifdef's scattered throughout the code. The `gawkmisc.c' in the main source @@ -21692,7 +28869,7 @@ steps: (Currently, this is only an issue for the PC operating system ports.) - 7. Supply a `Makefile' as well as any other C source and header files + 8. Supply a `Makefile' as well as any other C source and header files that are necessary for your operating system. All your code should be in a separate subdirectory, with a name that is the same as, or reminiscent of, either your operating system or the @@ -21702,7 +28879,7 @@ steps: avoid using names for your files that duplicate the names of files in the main source directory. - 8. Update the documentation. Please write a section (or sections) + 9. Update the documentation. Please write a section (or sections) for this Info file describing the installation and compilation steps needed to compile and/or install `gawk' for your system. @@ -21714,681 +28891,479 @@ code that is already there. style and brace layout that suits your taste. -File: gawk.info, Node: Dynamic Extensions, Next: Future Extensions, Prev: Additions, Up: Notes +File: gawk.info, Node: Derived Files, Prev: New Ports, Up: Additions -C.3 Adding New Built-in Functions to `gawk' -=========================================== +C.2.4 Why Generated Files Are Kept In Git +----------------------------------------- - Danger Will Robinson! Danger!! - Warning! Warning! - The Robot +If you look at the `gawk' source in the Git repository, you will notice +that it includes files that are automatically generated by GNU +infrastructure tools, such as `Makefile.in' from Automake and even +`configure' from Autoconf. - It is possible to add new built-in functions to `gawk' using -dynamically loaded libraries. This facility is available on systems -(such as GNU/Linux) that support the C `dlopen()' and `dlsym()' -functions. This minor node describes how to write and use dynamically -loaded extensions for `gawk'. Experience with programming in C or C++ -is necessary when reading this minor node. + 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. - CAUTION: The facilities described in this minor node are very much - subject to change in a future `gawk' release. Be aware that you - may have to re-do everything, at some future time. + However, there are several reasons why the `gawk' maintainer likes +to have everything in the repository. - If you have written your own dynamic extensions, be sure to - recompile them for each new `gawk' release. There is no guarantee - of binary compatibility between different releases, nor will there - ever be such a guarantee. + 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. - NOTE: When `--sandbox' is specified, extensions are disabled - (*note Options::. + As an extreme example, if you ever even think about trying to +compile, oh, say, the V7 `awk', you will discover that not only do you +have to bootstrap the V7 `yacc' to do so, but you also need the V7 +`lex'. And the latter is pretty much impossible to bring up on a +modern GNU/Linux system.(1) -* Menu: + (Or, let's say `gawk' 1.2 required `bison' whatever-it-was in 1989 +and that there was no `awkgram.c' file in the repository. Is there a +guarantee that we could find that `bison' version? Or that _it_ would +build?) -* Internals:: A brief look at some `gawk' internals. -* Plugin License:: A note about licensing. -* Sample Library:: A example of new functions. + If the repository has all the generated files, then it's easy to +just check them out and build. (Or _easier_, depending upon how far +back we go.) - -File: gawk.info, Node: Internals, Next: Plugin License, Up: Dynamic Extensions + 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 `gawk' developer(s), or the user who just wants to check out a +version and try it out? -C.3.1 A Minimal Introduction to `gawk' Internals ------------------------------------------------- + The `gawk' maintainer wants it to be possible for any interested +`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.(2) That is the point of the +`bootstrap.sh' file. It touches the various other files in the right +order such that -The truth is that `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 `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 `awk.h', -`builtin.c', and `eval.c'. Reading `awkgram.y' in order to see how the -parse tree is built would also be of use. - - With the disclaimers out of the way, the following types, structure -members, functions, and macros are declared in `awk.h' and are of use -when writing extensions. The next minor node shows how they are used: - -`AWKNUM' - An `AWKNUM' is the internal type of `awk' floating-point numbers. - Typically, it is a C `double'. - -`NODE' - Just about everything is done using objects of type `NODE'. These - contain both strings and numbers, as well as variables and arrays. - -`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 `gawk' function. - -`void force_string(NODE *n)' - This macro guarantees that a `NODE''s string value is current. It - may end up calling an internal `gawk' function. It also - guarantees that the string is zero-terminated. - -`void force_wstring(NODE *n)' - Similarly, this macro guarantees that a `NODE''s wide-string value - is current. It may end up calling an internal `gawk' function. - It also guarantees that the wide string is zero-terminated. - -`nargs' - Inside an extension function, this is the actual number of - parameters passed to the current function. - -`n->stptr' -`n->stlen' - The data and length of a `NODE''s string value, respectively. The - string is _not_ guaranteed to be zero-terminated. If you need to - pass the string value to a C library function, save the value in - `n->stptr[n->stlen]', assign `'\0'' to it, call the routine, and - then restore the value. - -`n->wstptr' -`n->wstlen' - The data and length of a `NODE''s wide-string value, respectively. - Use `force_wstring()' to make sure these values are current. - -`n->type' - The type of the `NODE'. This is a C `enum'. Values should be one - of `Node_var', `Node_var_new', or `Node_var_array' for function - parameters. - -`n->vname' - The "variable name" of a node. This is not of much use inside - externally written extensions. - -`void assoc_clear(NODE *n)' - Clears the associative array pointed to by `n'. Make sure that - `n->type == Node_var_array' first. - -`NODE **assoc_lookup(NODE *symbol, NODE *subs)' - Finds, and installs if necessary, array elements. `symbol' is the - array, `subs' is the subscript. This is usually a value created - with `make_string()' (see below). - -`NODE *make_string(char *s, size_t len)' - Take a C string and turn it into a pointer to a `NODE' that can be - stored appropriately. This is permanent storage; understanding of - `gawk' memory management is helpful. - -`NODE *make_number(AWKNUM val)' - Take an `AWKNUM' and turn it into a pointer to a `NODE' that can - be stored appropriately. This is permanent storage; understanding - of `gawk' memory management is helpful. - -`NODE *dupnode(NODE *n)' - Duplicate a node. In most cases, this increments an internal - reference count instead of actually duplicating the entire `NODE'; - understanding of `gawk' memory management is helpful. - -`void unref(NODE *n)' - This macro releases the memory associated with a `NODE' allocated - with `make_string()' or `make_number()'. Understanding of `gawk' - memory management is helpful. - -`void make_builtin(const char *name, NODE *(*func)(NODE *), int count)' - Register a C function pointed to by `func' as new built-in - function `name'. `name' is a regular C string. `count' is the - maximum number of arguments that the function takes. The function - should be written in the following manner: - - /* do_xxx --- do xxx function for gawk */ - - NODE * - do_xxx(int nargs) - { - ... - } + # The canonical incantation for building GNU software: + ./bootstrap.sh && ./configure && make -`NODE *get_argument(int i)' - This function is called from within a C extension function to get - the `i'-th argument from the function call. The first argument is - argument zero. - -`NODE *get_actual_argument(int i,' -` int optional, int wantarray);' - This function retrieves a particular argument `i'. `wantarray' is - `TRUE' if the argument should be an array, `FALSE' otherwise. If - `optional' is `TRUE', the argument need not have been supplied. - If it wasn't, the return value is `NULL'. It is a fatal error if - `optional' is `TRUE' but the argument was not provided. - -`get_scalar_argument(i, opt)' - This is a convenience macro that calls `get_actual_argument()'. - -`get_array_argument(i, opt)' - This is a convenience macro that calls `get_actual_argument()'. - -`void update_ERRNO(void)' - This function is called from within a C extension function to set - the value of `gawk''s `ERRNO' variable, based on the current value - of the C `errno' global variable. It is provided as a convenience. - -`void update_ERRNO_saved(int errno_saved)' - This function is called from within a C extension function to set - the value of `gawk''s `ERRNO' variable, based on the error value - provided as the argument. It is provided as a convenience. - -`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 `NODE' containing the newly created variable. This - function is used to implement the builtin `ENVIRON' and `PROCINFO' - arrays, so you can refer to them for examples. - -`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 - `IOBUF' structure in `iop_alloc()'. After creating the new - `IOBUF', `iop_alloc()' will call (in reverse order of - registration, so the last function registered is called first) - each open hook until one returns non-`NULL'. If any hook returns - a non-`NULL' value, that value is assigned to the `IOBUF''s - `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 `IOBUF''s - `get_record' method to indicate that future input records should - be retrieved by calling that method instead of using the standard - `gawk' input processing. - - And the function will also probably want to set the `IOBUF''s - `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 `IOBUF' - structure where the `fd' field is set to `INVALID_HANDLE', meaning - that `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 `awk.h' and in `io.c'. - - 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: - - NODE *the_arg; - - /* assume need 3rd arg, 0-based */ - the_arg = get_array_argument(2, FALSE); - - Again, you should spend time studying the `gawk' internals; don't -just blindly copy this code. - - -File: gawk.info, Node: Plugin License, Next: Sample Library, Prev: Internals, Up: Dynamic Extensions - -C.3.2 Extension Licensing -------------------------- +will _just work_. -Every dynamic extension should define the global symbol -`plugin_is_GPL_compatible' to assert that it has been licensed under a -GPL-compatible license. If this symbol does not exist, `gawk' will -emit a fatal error and exit. + This is extremely important for the `master' and `gawk-X.Y-stable' +branches. - The declared type of the symbol should be `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: + Further, the `gawk' maintainer would argue that it's also important +for the `gawk' developers. When he tried to check out the `xgawk' +branch(3) to build it, he couldn't. (No `ltmain.sh' file, and he had no +idea how to create it, and that was not the only problem.) - int plugin_is_GPL_compatible; + He felt _extremely_ frustrated. With respect to that branch, the +maintainer is no different than Jane User who wants to try to build +`gawk-4.1-stable' or `master' from the repository. - -File: gawk.info, Node: Sample Library, Prev: Plugin License, Up: Dynamic Extensions + Thus, the maintainer thinks that it's not just important, but +critical, that for any given branch, the above incantation _just works_. -C.3.3 Example: Directory and File Operation Built-ins ------------------------------------------------------ + A third reason to have all the files is that without them, using `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 `configure' and +so on; it was really painful. When the repository is self-contained, +using `git bisect' in it is very easy. -Two useful functions that are not in `awk' are `chdir()' (so that an -`awk' program can change its directory) and `stat()' (so that an `awk' -program can gather information about a file). This minor node -implements these functions for `gawk' in an external extension library. + What are some of the consequences and/or actions to take? -* Menu: + 1. We don't mind that there are differing files in the different + branches as a result of different versions of the autotools. -* 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. + A. It's the maintainer's job to merge them and he will deal with + it. - -File: gawk.info, Node: Internal File Description, Next: Internal File Ops, Up: Sample Library + B. He is really good at `git diff x y > /tmp/diff1 ; gvim + /tmp/diff1' to remove the diffs that aren't of interest in + order to review code. -C.3.3.1 Using `chdir()' and `stat()' -.................................... + 2. 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, `bison', and GNU `gettext'. -This minor node shows how to use the new functions at the `awk' level -once they've been integrated into the running `gawk' interpreter. -Using `chdir()' is very straightforward. It takes one argument, the new -directory to change to: + Installing from source is quite easy. It's how the maintainer + worked for years (and still works). He had `/usr/local/bin' at + the front of his `PATH' and just did: - ... - newdir = "/home/arnold/funstuff" - ret = chdir(newdir) - if (ret < 0) { - printf("could not change to %s: %s\n", - newdir, ERRNO) > "/dev/stderr" - exit 1 - } - ... + wget http://ftp.gnu.org/gnu/PACKAGE/PACKAGE-X.Y.Z.tar.gz + tar -xpzvf PACKAGE-X.Y.Z.tar.gz + cd PACKAGE-X.Y.Z + ./configure && make && make check + make install # as root - The return value is negative if the `chdir' failed, and `ERRNO' -(*note Built-in Variables::) is set to a string indicating the error. - Using `stat()' is a bit more complicated. The C `stat()' function -fills in a structure that has a fair amount of information. The right -way to model this in `awk' is to fill in an associative array with the -appropriate information: + Most of the above was originally written by the maintainer to other +`gawk' developers. It raised the objection from one of the developers +"... that anybody pulling down the source from Git is not an end user." - 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"]) + However, this is not true. There are "power `awk' users" who can +build `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. - The `stat()' function always clears the data array, even if the -`stat()' fails. It fills in the following elements: + It was then suggested that there be a `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. -`"name"' - The name of the file that was `stat()''ed. + Fortunately, the Git server can meet this need. For any given branch +named BRANCHNAME, use: -`"dev"' -`"ino"' - The file's device and inode numbers, respectively. + wget http://git.savannah.gnu.org/cgit/gawk.git/snapshot/gawk-BRANCHNAME.tar.gz -`"mode"' - The file's mode, as a numeric value. This includes both the file's - type and its permissions. +to retrieve a snapshot of the given branch. -`"nlink"' - The number of hard links (directory entries) the file has. + ---------- Footnotes ---------- -`"uid"' -`"gid"' - The numeric user and group ID numbers of the file's owner. + (1) We tried. It was painful. -`"size"' - The size in bytes of the file. + (2) 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. -`"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. + Starting with the latest tarball was no picnic either. The +maintainers had dropped `.gz' and `.bz2' files and only distribute +`.tar.xz' files. It was necessary to bootstrap `xz' first! -`"atime"' -`"mtime"' -`"ctime"' - The file's last access, modification, and inode update times, - respectively. These are numeric timestamps, suitable for - formatting with `strftime()' (*note Built-in::). + (3) A branch (since removed) created by one of the other developers +that did not include the generated files. -`"pmode"' - The file's "printable mode." This is a string representation of - the file's type and permissions, such as what is produced by `ls - -l'--for example, `"drwxr-xr-x"'. + +File: gawk.info, Node: Future Extensions, Next: Implementation Limitations, Prev: Additions, Up: Notes -`"type"' - A printable string representation of the file's type. The value - is one of the following: +C.3 Probable Future Extensions +============================== - `"blockdev"' - `"chardev"' - The file is a block or character device ("special file"). + AWK is a language similar to PERL, only considerably more elegant. + -- Arnold Robbins - `"directory"' - The file is a directory. + Hey! -- Larry Wall - `"fifo"' - The file is a named-pipe (also known as a FIFO). + The `TODO' file in the `master' branch of the `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. *Note Additions::, if you are interested in tackling any of +the projects listed there. - `"file"' - The file is just a regular file. + +File: gawk.info, Node: Implementation Limitations, Next: Extension Design, Prev: Future Extensions, Up: Notes - `"socket"' - The file is an `AF_UNIX' ("Unix domain") socket in the - filesystem. +C.4 Some Limitations of the Implementation +========================================== - `"symlink"' - The file is a symbolic link. +This following table describes limits of `gawk' on a Unix-like system +(although it is variable even then). Other systems may have different +limits. - Several additional elements may be present depending upon the -operating system and the type of the file. You can test for them in -your `awk' program by using the `in' operator (*note Reference to -Elements::): +Item Limit +-------------------------------------------------------------------------- +Characters in a character 2^(number of bits per byte) +class +Length of input record `MAX_INT' +Length of output record Unlimited +Length of source line Unlimited +Number of fields in a record `MAX_LONG' +Number of file redirections Unlimited +Number of input records in `MAX_LONG' +one file +Number of input records `MAX_LONG' +total +Number of pipe redirections min(number of processes per user, number + of open files) +Numeric values Double-precision floating point (if not + using MPFR) +Size of a field `MAX_INT' +Size of a literal string `MAX_INT' +Size of a printf string `MAX_INT' + + +File: gawk.info, Node: Extension Design, Next: Old Extension Mechanism, Prev: Implementation Limitations, Up: Notes + +C.5 Extension API Design +======================== -`"blksize"' - The preferred block size for I/O to the file. This field is not - present on all POSIX-like systems in the C `stat' structure. +This minor node documents the design of the extension API, including a +discussion of some of the history and problems that needed to be solved. -`"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). + The first version of extensions for `gawk' was developed in the +mid-1990s and released with `gawk' 3.1 in the late 1990s. The basic +mechanisms and design remained unchanged for close to 15 years, until +2012. -`"rdev"' -`"major"' -`"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. + The old extension mechanism used data types and functions from +`gawk' itself, with a "clever hack" to install extension functions. - -File: gawk.info, Node: Internal File Ops, Next: Using Internal File Ops, Prev: Internal File Description, Up: Sample Library + `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. -C.3.3.2 C Code for `chdir()' and `stat()' -......................................... +* Menu: -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:(1) +* 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. - #include "awk.h" + +File: gawk.info, Node: Old Extension Problems, Next: Extension New Mechanism Goals, Up: Extension Design - #include <sys/sysmacros.h> +C.5.1 Problems With The Old Mechanism +------------------------------------- - int plugin_is_GPL_compatible; +The old extension mechanism had several problems: - /* do_chdir --- provide dynamically loaded chdir() builtin for gawk */ + * It depended heavily upon `gawk' internals. Any time the `NODE' + structure(1) changed, an extension would have to be recompiled. + Furthermore, to really write extensions required understanding + something about `gawk''s internal functions. There was some + documentation in this Info file, but it was quite minimal. - static NODE * - do_chdir(int nargs) - { - NODE *newdir; - int ret = -1; + * Being able to call into `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 `gawk', even though + MS-Windows supports dynamic loading of shared objects. - if (do_lint && nargs != 1) - lintwarn("chdir: called with incorrect number of arguments"); + * The API would change occasionally as `gawk' changed; no + compatibility between versions was ever offered or planned for. - newdir = get_scalar_argument(0, FALSE); + Despite the drawbacks, the `xgawk' project developers forked `gawk' +and developed several significant extensions. They also enhanced +`gawk''s facilities relating to file inclusion and shared object access. - The file includes the `"awk.h"' header file for definitions for the -`gawk' internals. It includes `<sys/sysmacros.h>' for access to the -`major()' and `minor'() macros. + A new API was desired for a long time, but only in 2012 did the +`gawk' maintainer and the `xgawk' developers finally start working on +it together. More information about the `xgawk' project is provided in +*note gawkextlib::. - By convention, for an `awk' function `foo', the function that -implements it is called `do_foo'. The function should take a `int' -argument, usually called `nargs', that represents the number of defined -arguments for the function. The `newdir' variable represents the new -directory to change to, retrieved with `get_scalar_argument()'. Note -that the first argument is numbered zero. + ---------- Footnotes ---------- - This code actually accomplishes the `chdir()'. It first forces the -argument to be a string and passes the string value to the `chdir()' -system call. If the `chdir()' fails, `ERRNO' is updated. + (1) A critical central data structure inside `gawk'. - (void) force_string(newdir); - ret = chdir(newdir->stptr); - if (ret < 0) - update_ERRNO(); + +File: gawk.info, Node: Extension New Mechanism Goals, Next: Extension Other Design Decisions, Prev: Old Extension Problems, Up: Extension Design - Finally, the function returns the return value to the `awk' level: +C.5.2 Goals For A New Mechanism +------------------------------- - return make_number((AWKNUM) ret); - } +Some goals for the new API were: - The `stat()' built-in is more involved. First comes a function that -turns a numeric mode into a printable representation (e.g., 644 becomes -`-rw-r--r--'). This is omitted here for brevity: + * The API should be independent of `gawk' internals. Changes in + `gawk' internals should not be visible to the writer of an + extension function. - /* format_mode --- turn a stat mode field into something readable */ + * The API should provide _binary_ compatibility across `gawk' + releases as long as the API itself does not change. - static char * - format_mode(unsigned long fmode) - { - ... - } + * The API should enable extensions written in C or C++ to have + roughly the same "appearance" to `awk'-level code as `awk' + functions do. This means that extensions should have: - Next comes the `do_stat()' function. It starts with variable -declarations and argument checking: + - The ability to access function parameters. - /* do_stat --- provide a stat() function for gawk */ + - The ability to turn an undefined parameter into an array + (call by reference). - static NODE * - do_stat(int nargs) - { - NODE *file, *array, *tmp; - struct stat sbuf; - int ret; - NODE **aptr; - char *pmode; /* printable mode */ - char *type = "unknown"; + - The ability to create, access and update global variables. - if (do_lint && nargs > 2) - lintwarn("stat: called with too many arguments"); + - 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. - Then comes the actual work. First, the function gets the arguments. -Then, it always clears the array. The code use `lstat()' (instead of -`stat()') to get the file information, in case the file is a symbolic -link. If there's an error, it sets `ERRNO' and returns: + - The ability to create arrays (including `gawk''s true arrays + of arrays). - /* file is first arg, array to hold results is second */ - file = get_scalar_argument(0, FALSE); - array = get_array_argument(1, FALSE); + Some additional important goals were: - /* empty out the array */ - assoc_clear(array); + * 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 `#ifdef __cplusplus' and + `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 `gawk' is a C program. As of this + writing, this has not been tested.) - /* 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); - } + * The API mechanism should not require access to `gawk''s symbols(1) + by the compile-time or dynamic linker, in order to enable creation + of extensions that also work on MS-Windows. - 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: + During development, it became clear that there were other features +that should be available to extensions, which were also subsequently +provided: - /* fill in the array */ - aptr = assoc_lookup(array, tmp = make_string("name", 4)); - *aptr = dupnode(file); - unref(tmp); + * Extensions should have the ability to hook into `gawk''s I/O + redirection mechanism. In particular, the `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. - aptr = assoc_lookup(array, tmp = make_string("mode", 4)); - *aptr = make_number((AWKNUM) sbuf.st_mode); - unref(tmp); + * An extension should be able to provide a "call back" function to + perform cleanup actions when `gawk' exits. - aptr = assoc_lookup(array, tmp = make_string("pmode", 5)); - pmode = format_mode(sbuf.st_mode); - *aptr = make_string(pmode, strlen(pmode)); - unref(tmp); + * An extension should be able to provide a version string so that + `gawk''s `--version' option can provide information about + extensions as well. - When done, return the `lstat()' return value: + The requirement to avoid access to `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 `gawk' code into a library, with the `gawk' +utility a small C `main()' function linked against the library. - return make_number((AWKNUM) ret); - } + This seemed like the tail wagging the dog, complicating build and +installation and making a simple copy of the `gawk' executable from one +system to another (or one place to another on the same system!) into a +chancy operation. - Finally, it's necessary to provide the "glue" that loads the new -function(s) into `gawk'. By convention, each library has a routine -named `dlload()' that does the job: + Pat Rankin suggested the solution that was adopted. *Note Extension +Mechanism Outline::, for the details. - /* dlload --- load new builtins in this library */ + ---------- Footnotes ---------- - NODE * - dlload(NODE *tree, void *dl) - { - make_builtin("chdir", do_chdir, 1); - make_builtin("stat", do_stat, 2); - return make_number((AWKNUM) 0); - } + (1) The "symbols" are the variables and functions defined inside +`gawk'. Access to these symbols by code external to `gawk' loaded +dynamically at runtime is problematic on MS-Windows. - And that's it! As an exercise, consider adding functions to -implement system calls such as `chown()', `chmod()', and `umask()'. + +File: gawk.info, Node: Extension Other Design Decisions, Next: Extension Future Growth, Prev: Extension New Mechanism Goals, Up: Extension Design - ---------- Footnotes ---------- +C.5.3 Other Design Decisions +---------------------------- - (1) This version is edited slightly for presentation. See -`extension/filefuncs.c' in the `gawk' distribution for the complete -version. +As an arbitrary design decision, extensions can read the values of +predefined variables and arrays (such as `ARGV' and `FS'), but cannot +change them, with the exception of `PROCINFO'. - -File: gawk.info, Node: Using Internal File Ops, Prev: Internal File Ops, Up: Sample Library + The reason for this is to prevent an extension function from +affecting the flow of an `awk' program outside its control. While a +real `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 `awk', and not mess with `FS' or +`ARGC' and `ARGV'. -C.3.3.3 Integrating the Extensions -.................................. + In addition, it becomes easy to start down a slippery slope. How +much access to `gawk' facilities do extensions need? Do they need +`getline'? What about calling `gsub()' or compiling regular +expressions? What about calling into `awk' functions? (_That_ would be +messy.) -Now that the code is written, it must be possible to add it at runtime -to the running `gawk' interpreter. First, the code must be compiled. -Assuming that the functions are in a file named `filefuncs.c', and IDIR -is the location of the `gawk' include files, the following steps create -a GNU/Linux shared library: + In order to avoid these issues, the `gawk' developers chose to start +with the simplest, most basic features that are still truly useful. - $ gcc -fPIC -shared -DHAVE_CONFIG_H -c -O -g -IIDIR filefuncs.c - $ ld -o filefuncs.so -shared filefuncs.o + Another decision is that although `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 `awk' semantics. (In fact, arrays indexed internally by +integers are so transparent that they aren't even documented!) - Once the library exists, it is loaded by calling the `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 `gawk'. It -returns the value returned by the initialization function within the -shared library: + Additionally, all functions in the API check that their pointer +input parameters are not `NULL'. If they are, they return an error. +(It is a good idea for extension code to verify that pointers received +from `gawk' are not `NULL'. Such a thing should not happen, but the +`gawk' developers are only human, and they have been known to +occasionally make mistakes.) - # file testff.awk - BEGIN { - extension("./filefuncs.so", "dlload") + With time, the API will undoubtedly evolve; the `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. - chdir(".") # no-op + +File: gawk.info, Node: Extension Future Growth, Prev: Extension Other Design Decisions, Up: Extension Design - 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"]) +C.5.4 Room For Future Growth +---------------------------- - 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"]) - } +The API can later be expanded, in two ways: - Here are the results of running the program: + * `gawk' passes an "extension id" into the extension when it first + loads the extension. The extension then passes this id back to + `gawk' with each function call. This mechanism allows `gawk' to + identify the extension calling into it, should it need to know. - $ gawk -f testff.awk - -| Info for testff.awk - -| ret = 0 - -| data["size"] = 607 - -| data["ino"] = 14945891 - -| data["name"] = testff.awk - -| data["pmode"] = -rw-rw-r-- - -| data["nlink"] = 1 - -| data["atime"] = 1293993369 - -| data["mtime"] = 1288520752 - -| data["mode"] = 33204 - -| data["blksize"] = 4096 - -| data["dev"] = 2054 - -| data["type"] = file - -| data["gid"] = 500 - -| data["uid"] = 500 - -| data["blocks"] = 8 - -| data["ctime"] = 1290113572 - -| testff.awk modified: 10 31 10 12:25:52 - -| - -| Info for JUNK - -| ret = -1 - -| JUNK modified: 01 01 70 02:00:00 + * Similarly, the extension passes a "name space" into `gawk' when it + registers each extension function. This accommodates a possible + future mechanism for grouping extension functions and possibly + avoiding name conflicts. + + Of course, as of this writing, no decisions have been made with +respect to any of the above. -File: gawk.info, Node: Future Extensions, Prev: Dynamic Extensions, Up: Notes +File: gawk.info, Node: Old Extension Mechanism, Next: Notes summary, Prev: Extension Design, Up: Notes -C.4 Probable Future Extensions -============================== +C.6 Compatibility For Old Extensions +==================================== - AWK is a language similar to PERL, only considerably more elegant. - Arnold Robbins +*note Dynamic Extensions::, describes the supported API and mechanisms +for writing extensions for `gawk'. This API was introduced in version +4.1. However, for many years `gawk' provided an extension mechanism +that required knowledge of `gawk' internals and that was not as well +designed. - Hey! - Larry Wall + In order to provide a transition period, `gawk' version 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. - This minor node briefly lists extensions and possible improvements -that indicate the directions we are currently considering for `gawk'. -The file `FUTURES' in the `gawk' distribution lists these extensions as -well. + Briefly, original-style extensions should be compiled by including +the `awk.h' header file in the extension source code. Additionally, you +must define the identifier `GAWK' when building (use `-DGAWK' with +Unix-style compilers). Otherwise, the definitions in `gawkapi.h' will +cause conflicts with those in `awk.h' and your extension will not +compile. - Following is a list of probable future changes visible at the `awk' -language level: + Just as in previous versions, you load an old-style extension with +the `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 `dl_load()' C routine. -Loadable module interface - It is not clear that the `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. + Because original-style and new-style extensions use different +initialization routines (`dl_load()' versus `dlload()'), they may safely +be installed in the same directory (to be found by `AWKLIBPATH') +without conflict. -`RECLEN' variable for fixed-length records - Along with `FIELDWIDTHS', this would speed up the processing of - fixed-length records. `PROCINFO["RS"]' would be `"RS"' or - `"RECLEN"', depending upon which kind of record processing is in - effect. + The `gawk' development team strongly recommends that you convert any +old extensions that you may have to use the new API described in *note +Dynamic Extensions::. -Databases - It may be possible to map a GDBM/NDBM/SDBM file into an `awk' - array. + +File: gawk.info, Node: Notes summary, Prev: Old Extension Mechanism, Up: Notes -More `lint' warnings - There are more things that could be checked for portability. +C.7 Summary +=========== + + * `gawk''s extensions can be disabled with either the + `--traditional' option or with the `--posix' option. The + `--parsedebug' option is available if `gawk' is compiled with + `-DDEBUG'. - Following is a list of probable improvements that will make `gawk''s -source code easier to work with: + * The source code for `gawk' is maintained in a publicly accessible + Git repository. Anyone may check it out and view the source. -Loadable module mechanics - The current extension mechanism works (*note 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 `libtool' - package provides a number of features that would make using - loadable modules much easier. `gawk' should be changed to use - `libtool'. + * Contributions to `gawk' are welcome. Following the steps outlined + in this major node 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. -Loadable module internals - The API to its internals that `gawk' "exports" should be revised. - Too many things are needlessly exposed. A new API should be - designed and implemented to make module writing easier. + * `gawk' has some limits--generally those that are imposed by the + machine architecture. -Better array subscript management - `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. + * The extension API design was intended to solve a number of problems + with the previous extension mechanism, enable features needed by + the `xgawk' project, and provide binary compatibility going + forward. - Finally, the programs in the test suite could use documenting in -this Info file. + * The previous extension mechanism is still supported in version 4.1 + of `gawk', but it _will_ be removed in the next major release. - *Note Additions::, if you are interested in tackling any of these -projects. File: gawk.info, Node: Basic Concepts, Next: Glossary, Prev: Notes, Up: Top @@ -22407,7 +29382,6 @@ introductory texts that you should refer to instead.) * 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. File: gawk.info, Node: Basic High Level, Next: Basic Data Typing, Up: Basic Concepts @@ -22416,12 +29390,13 @@ D.1 What a Program Does ======================= At the most basic level, the job of a program is to process some input -data and produce results. +data and produce results. See *note figure-general-flow::. - _______ - +------+ / \ +---------+ - | Data | -----> < Program > -----> | Results | - +------+ \_______/ +---------+ + _______ ++------+ / \ +---------+ +| Data | -----> < Program > -----> | Results | ++------+ \_______/ +---------+ +Figure D.1: General Program Flow The "program" in the figure can be either a compiled program(1) (such as `ls'), or it may be "interpreted". In the latter case, a @@ -22429,19 +29404,20 @@ machine-executable program such as `awk' reads your program, and then uses the instructions in your program to process the data. When you write a program, it usually consists of the following, very -basic set of steps: - - ______ - +----------------+ / More \ No +----------+ - | Initialization | -------> < Data > -------> | Clean Up | - +----------------+ ^ \ ? / +----------+ - | +--+-+ - | | Yes - | | - | V - | +---------+ - +-----+ Process | - +---------+ +basic set of steps, as shown in *note figure-process-flow::: + + ______ ++----------------+ / More \ No +----------+ +| Initialization | -------> < Data > -------> | Clean Up | ++----------------+ ^ \ ? / +----------+ + | +--+-+ + | | Yes + | | + | V + | +---------+ + +-----+ Process | + +---------+ +Figure D.2: Basic Program Steps Initialization These are the things you do before actually starting to process @@ -22506,7 +29482,7 @@ such as C, C++, or Ada, and then translated, or "compiled", into a form that the computer can execute directly. -File: gawk.info, Node: Basic Data Typing, Next: Floating Point Issues, Prev: Basic High Level, Up: Basic Concepts +File: gawk.info, Node: Basic Data Typing, Prev: Basic High Level, Up: Basic Concepts D.2 Data Values in a Computer ============================= @@ -22526,34 +29502,10 @@ characters that comprise them. Individual variables, as well as numeric and string variables, are referred to as "scalar" values. Groups of values, such as arrays, are not scalars. - Within computers, there are two kinds of numeric values: "integers" -and "floating-point". In school, integer values were referred to as -"whole" numbers--that is, numbers without any fractional part, such as -1, 42, or -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 -2,147,483,648 to 2,147,483,647. However, -many systems now support a range from -9,223,372,036,854,775,808 to -9,223,372,036,854,775,807. - - Integer values come in two flavors: "signed" and "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. - - 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. `awk' uses "double precision" -floating-point numbers, which can hold more digits than "single -precision" floating-point numbers. Floating-point issues are discussed -more fully in *Note Floating Point Issues::. - - At the very lowest level, computers store values as groups of binary -digits, or "bits". Modern computers group bits into groups of eight, -called "bytes". Advanced applications sometimes have to manipulate -bits directly, and `gawk' provides functions for doing so. + *note 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. While you are probably used to the idea of a number without a value (i.e., zero), it takes a bit more getting used to the idea of @@ -22564,15 +29516,19 @@ like this: `""'. 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.) +(Remember grade school? 42 = 4 x 10 + 2.) There are other number bases though. Computers commonly use base 2 or "binary", base 8 or "octal", and base 16 or "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. Octal and hexadecimal are discussed more in *Note -Nondecimal-numbers::. +represents (1 x 8) + (0 x 4) + (1 x 2) + (0 x 1), or decimal 10. Octal +and hexadecimal are discussed more in *note Nondecimal-numbers::. + + At the very lowest level, computers store values as groups of binary +digits, or "bits". Modern computers group bits into groups of eight, +called "bytes". Advanced applications sometimes have to manipulate +bits directly, and `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 @@ -22591,218 +29547,6 @@ In 1999, a revised ISO C standard was approved and released. Where it makes sense, POSIX `awk' is compatible with 1999 ISO C. -File: gawk.info, Node: Floating Point Issues, Prev: Basic Data Typing, Up: Basic Concepts - -D.3 Floating-Point Number Caveats -================================= - -As mentioned earlier, floating-point numbers represent what are called -"real" numbers, i.e., those that have a fractional part. `awk' uses -double precision floating-point numbers to represent all numeric -values. This minor node describes some of the issues involved in using -floating-point numbers. - - There is a very nice paper on floating-point arithmetic -(http://www.validlab.com/goldberg/paper.pdf) by David Goldberg, "What -Every Computer Scientist Should Know About Floating-point Arithmetic," -`ACM Computing Surveys' *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. - - -File: gawk.info, Node: String Conversion Precision, Next: Unexpected Results, Up: Floating Point Issues - -D.3.1 The String Value Can Lie ------------------------------- - -Internally, `awk' keeps both the numeric value (double precision -floating-point) and the string value for a variable. Separately, `awk' -keeps track of what type the variable has (*note 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 (`values.awk') illustrates this: - - { - 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 - } - -This program shows the full value of the sum of `$1' and `$2' using -`printf', and then prints the string values obtained from both -automatic conversion (via `CONVFMT') and from printing (via `OFMT'). - - Here is what happens when the program is run: - - $ echo 3.654321 1.2345678 | awk -f values.awk - -| sum = 4.8888888 - -| a = <4.88889> - -| sum = 4.88889 - - This makes it clear that the full numeric value is different from -what the default string representations show. - - `CONVFMT''s default value is `"%.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.(1) - - ---------- Footnotes ---------- - - (1) Pathological cases can require up to 752 digits (!), but we -doubt that you need to worry about this. - - -File: gawk.info, Node: Unexpected Results, Next: POSIX Floating Point Problems, Prev: String Conversion Precision, Up: Floating Point Issues - -D.3.2 Floating Point Numbers Are Not Abstract 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: - - $ awk '{ printf("%010d\n", $1 * 100) }' - 515.79 - -| 0000051579 - 515.80 - -| 0000051579 - 515.81 - -| 0000051580 - 515.82 - -| 0000051582 - Ctrl-d - -This shows that some values can be represented exactly, whereas others -are only approximated. This is not a "bug" in `awk', but simply an -artifact of how computers represent numbers. - - 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: - - $ gawk 'BEGIN { mz = -0 ; pz = 0 - > printf "-0 = %g, +0 = %g, (-0 == +0) -> %d\n", mz, pz, mz == pz - > printf "mz == 0 -> %d, pz == 0 -> %d\n", mz == 0, pz == 0 - > }' - -| -0 = -0, +0 = 0, (-0 == +0) -> 1 - -| mz == 0 -> 1, pz == 0 -> 1 - - 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. - - -File: gawk.info, Node: POSIX Floating Point Problems, Prev: Unexpected Results, Up: Floating Point Issues - -D.3.3 Standards Versus Existing Practice ----------------------------------------- - -Historically, `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 `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 `awk' should support additional features. -These features are: - - * Interpretation of floating point data values specified in - hexadecimal notation (`0xDEADBEEF'). (Note: data values, _not_ - source code constants.) - - * Support for the special IEEE 754 floating point values "Not A - Number" (NaN), positive Infinity ("inf") and negative Infinity - ("-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 `nan' and - allow either `inf' or `infinity'. - - The first problem is that both of these are clear changes to -historical practice: - - * The `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. - - * Allowing completely alphabetic strings to have valid numeric - values is also a very severe departure from historical practice. - - The second problem is that the `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 `awk' support hexadecimal floating point values and -special values for "Not A Number" and infinity. - - Although the `gawk' maintainer continues to feel that providing -those features is inadvisable, nevertheless, on systems that support -IEEE floating point, it seems reasonable to provide _some_ way to -support NaN and Infinity values. The solution implemented in `gawk' is -as follows: - - * With the `--posix' command-line option, `gawk' becomes "hands - off." String values are passed directly to the system library's - `strtod()' function, and if it successfully returns a numeric - value, that is what's used.(1) By definition, the results are not - portable across different systems. They are also a little - surprising: - - $ echo nanny | gawk --posix '{ print $1 + 0 }' - -| nan - $ echo 0xDeadBeef | gawk --posix '{ print $1 + 0 }' - -| 3735928559 - - * Without `--posix', `gawk' interprets the four strings `+inf', - `-inf', `+nan', and `-nan' specially, producing the corresponding - special numeric values. The leading sign acts a signal to `gawk' - (and the user) that the value is really numeric. Hexadecimal - floating point is not supported (unless you also use - `--non-decimal-data', which is _not_ recommended). For example: - - $ echo nanny | gawk '{ print $1 + 0 }' - -| 0 - $ echo +nan | gawk '{ print $1 + 0 }' - -| nan - $ echo 0xDeadBeef | gawk '{ print $1 + 0 }' - -| 0 - - `gawk' does ignore case in the four special values. Thus `+nan' - and `+NaN' are the same. - - ---------- Footnotes ---------- - - (1) You asked for it, you got it. - - File: gawk.info, Node: Glossary, Next: Copying, Prev: Basic Concepts, Up: Top Glossary @@ -22811,8 +29555,12 @@ Glossary Action A series of `awk' statements attached to a rule. If the rule's pattern matches an input record, `awk' executes the rule's action. - Actions are always enclosed in curly braces. (*Note Action - Overview::.) + Actions are always enclosed in braces. (*Note Action Overview::.) + +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. Amazing `awk' Assembler Henry Spencer at the University of Toronto wrote a retargetable @@ -22822,11 +29570,6 @@ Amazing `awk' Assembler been better written in another language. You can get it from `http://awk.info/?awk100/aaa'. -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. - Amazingly Workable Formatter (`awf') Henry Spencer at the University of Toronto wrote a formatter that accepts a large subset of the `nroff -ms' and `nroff -man' @@ -22878,9 +29621,6 @@ Bash The GNU version of the standard shell (the Bourne-Again SHell). See also "Bourne Shell." -BBS - See "Bulletin Board System." - Bit Short for "Binary Digit." All values in computer memory ultimately reduce to binary digits: values that are either zero or @@ -22888,7 +29628,7 @@ Bit floating-point numbers, character data, addresses of other memory objects, or other data. `awk' lets you work with floating-point numbers and strings. `gawk' lets you manipulate bit values with - the built-in functions described in *Note Bitwise Functions::. + the built-in functions described in *note Bitwise Functions::. Computers are often defined by how many bits they use to represent integer values. Typical systems are 32-bit systems, but 64-bit @@ -22901,9 +29641,13 @@ Boolean Expression Bourne Shell The standard shell (`/bin/sh') on Unix and Unix-like systems, - originally written by Steven R. Bourne. Many shells (Bash, `ksh', - `pdksh', `zsh') are generally upwardly compatible with the Bourne - shell. + originally written by Steven R. Bourne at Bell Laboratories. Many + shells (Bash, `ksh', `pdksh', `zsh') are generally upwardly + compatible with the Bourne shell. + +Braces + The characters `{' and `}'. Braces are used in `awk' for + delimiting actions, compound statements, and function bodies. Built-in Function The `awk' language provides built-in functions that perform various @@ -22923,14 +29667,6 @@ Built-in Variable them affects `awk''s running environment. (*Note Built-in Variables::.) -Braces - See "Curly Braces." - -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. - C The system programming language that most GNU software is written in. The `awk' programming language has C-like syntax, and this @@ -22950,8 +29686,8 @@ Character Set ASCII (American Standard Code for Information Interchange). Many European countries use an extension of ASCII known as ISO-8859-1 (ISO Latin-1). The Unicode character set (http://www.unicode.org) - is becoming increasingly popular and standard, and is particularly - widely used on GNU/Linux systems. + is increasingly popular and standard, and is particularly widely + used on GNU/Linux systems. CHEM A preprocessor for `pic' that reads descriptions of molecules and @@ -22959,9 +29695,11 @@ CHEM Brian Kernighan and Jon Bentley, and is available from `http://netlib.sandia.gov/netlib/typesetting/chem.gz'. -Coprocess - A subordinate program with which two-way communications is - possible. +Comparison Expression + A relation that is either true or false, such as `a < b'. + Comparison expressions are used in `if', `while', `do', and `for' + statements, and in patterns to select which input records to + process. (*Note Typing and Comparison::.) Compiler A program that translates human-readable source code into @@ -22985,15 +29723,16 @@ Conditional Expression otherwise the value is EXPR3. In either case, only one of EXPR2 and EXPR3 is evaluated. (*Note Conditional Exp::.) -Comparison Expression - A relation that is either true or false, such as `a < b'. - Comparison expressions are used in `if', `while', `do', and `for' - statements, and in patterns to select which input records to - process. (*Note Typing and Comparison::.) +Cookie + A peculiar goodie, token, saying or remembrance produced by or + presented to a program. (With thanks to Professor Doug McIlroy.) + +Coprocess + A subordinate program with which two-way communications is + possible. Curly Braces - The characters `{' and `}'. Curly braces are used in `awk' for - delimiting actions, compound statements, and function bodies. + See "Braces." Dark Corner An area in the language where specifications often were (or still @@ -23032,15 +29771,15 @@ Dynamic Regular Expression `"foo"', but it may also be an expression whose value can vary. (*Note Computed Regexps::.) +Empty String + See "Null String." + Environment - A collection of strings, of the form NAME`='VAL, that each program + A collection of strings, of the form `NAME=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 `HOME' and `PATH'. -Empty String - See "Null String." - Epoch The date used as the "beginning of time" for timestamps. Time values in most systems are represented as seconds since the epoch, @@ -23066,12 +29805,12 @@ FDL Field When `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 `FS'). Such pieces are + change by setting the predefined variable `FS'). Such pieces are called fields. If the pieces are of fixed length, you can use the built-in variable `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 `FPAT' to do so. - (*Note Field Separators::, *Note Constant Size::, and *Note + separator, you can use the predefined variable `FPAT' to do so. + (*Note Field Separators::, *note Constant Size::, and *note Splitting By Content::.) Flag @@ -23084,31 +29823,31 @@ Floating-Point Number See also "Double Precision" and "Single Precision." Format - Format strings are used to control the appearance of output in the - `strftime()' and `sprintf()' functions, and are used in the - `printf' statement as well. Also, data conversions from numbers - to strings are controlled by the format strings contained in the - built-in variables `CONVFMT' and `OFMT'. (*Note Control Letters::.) + Format strings control the appearance of output in the + `strftime()' and `sprintf()' functions, and in the `printf' + statement as well. Also, data conversions from numbers to strings + are controlled by the format strings contained in the predefined + variables `CONVFMT' and `OFMT'. (*Note Control Letters::.) Free Documentation License This document describes the terms under which this Info file is published and may be copied. (*Note GNU Free Documentation License::.) -Function - A specialized group of statements used to encapsulate general or - program-specific tasks. `awk' has a number of built-in functions, - and also allows you to define your own. (*Note Functions::.) - -FSF - See "Free Software Foundation." - Free Software Foundation A nonprofit organization dedicated 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. +FSF + See "Free Software Foundation." + +Function + A specialized group of statements used to encapsulate general or + program-specific tasks. `awk' has a number of built-in functions, + and also allows you to define your own. (*Note Functions::.) + `gawk' The GNU implementation of `awk'. @@ -23143,8 +29882,8 @@ Hexadecimal Base 16 notation, where the digits are `0'-`9' and `A'-`F', with `A' representing 10, `B' representing 11, and so on, up to `F' for 15. Hexadecimal numbers are written in C using a leading `0x', to - indicate their base. Thus, `0x12' is 18 (1 times 16 plus 2). - *Note Nondecimal-numbers::. + indicate their base. Thus, `0x12' is 18 ((1 x 16) + 2). *Note + Nondecimal-numbers::. I/O Abbreviation for "Input/Output," the act of moving data into and/or @@ -23175,12 +29914,16 @@ Interval Expression originally available in `awk' programs. ISO - The International Standards Organization. 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 Info file refers to Standard C as "ISO C" throughout. + 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 Info file refers to Standard C as + "ISO C" throughout. See the ISO website + (http://www.iso.org/iso/home/about.htm) for more information about + the name of the organization and its language-independent + three-letter acronym. Java A modern programming language originally developed by Sun @@ -23197,19 +29940,19 @@ Keyword `gawk''s keywords are: `BEGIN', `BEGINFILE', `END', `ENDFILE', `break', `case', `continue', `default' `delete', `do...while', `else', `exit', `for...in', `for', `function', `func', `if', - `nextfile', `next', `switch', and `while'. + `next', `nextfile', `switch', and `while'. Lesser General Public License This document describes the terms under which binary library archives or shared objects, and their source code may be distributed. -Linux - See "GNU/Linux." - LGPL See "Lesser General Public License." +Linux + See "GNU/Linux." + Localization The process of providing the data necessary for an internationalized program to work in a particular language. @@ -23253,11 +29996,7 @@ Number Octal Base-eight notation, where the digits are `0'-`7'. Octal numbers are written in C using a leading `0', to indicate their base. - Thus, `013' is 11 (one times 8 plus 3). *Note - Nondecimal-numbers::. - -P1003.1, P1003.2 - See "POSIX." + Thus, `013' is 11 ((1 x 8) + 3). *Note Nondecimal-numbers::. Pattern Patterns tell `awk' which input records are interesting to which @@ -23269,6 +30008,11 @@ Pattern the input record against a regular expression. (*Note Pattern Overview::.) +PEBKAC + An acronym describing what is possibly the most frequent source of + computer usage problems. (Problem Exists Between Keyboard And + Chair.) + POSIX The name for a series of standards that specify a Portable Operating System interface. The "IX" denotes the Unix heritage of @@ -23293,9 +30037,9 @@ Range (of input lines) specify single lines. (*Note Pattern Overview::.) 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. + When a function calls itself, either directly or indirectly. If + this is clear, stop, and proceed to the next entry. Otherwise, + refer to the entry for "recursion." Redirection Redirection means performing input from something other than the @@ -23306,7 +30050,7 @@ Redirection `|', and `|&' operators. You can redirect the output of the `print' and `printf' statements to a file or a system command, using the `>', `>>', `|', and `|&' operators. (*Note Getline::, - and *Note Redirection::.) + and *note Redirection::.) Regexp See "Regular Expression." @@ -23347,13 +30091,13 @@ Search Path source files. In the shell, a list of directories to search for executable programs. +`sed' + See "Stream Editor." + Seed The initial value, or starting point, for a sequence of random numbers. -`sed' - See "Stream Editor." - Shell The command interpreter for Unix and POSIX-compliant systems. The shell works both interactively, and as a programming language for @@ -23376,8 +30120,8 @@ Single Precision 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 `awk' to store numeric values. It is - the C type `float'. + some ancient versions of `awk' to store numeric values. It is the + C type `float'. Space The character generated by hitting the space bar on the keyboard. @@ -23411,7 +30155,7 @@ Text Domain Timestamp A value in the "seconds since the epoch" format used by Unix and POSIX systems. Used for the `gawk' functions `mktime()', - `strftime()', and `systime()'. See also "Epoch" and "UTC." + `strftime()', and `systime()'. See also "Epoch," "GMT," and "UTC." Unix A computer operating system originally developed in the early @@ -23440,7 +30184,6 @@ GNU General Public License ************************** Version 3, 29 June 2007 - Copyright (C) 2007 Free Software Foundation, Inc. `http://fsf.org/' Everyone is permitted to copy and distribute verbatim copies of this @@ -24163,7 +30906,6 @@ GNU Free Documentation License ****************************** Version 1.3, 3 November 2008 - Copyright (C) 2000, 2001, 2002, 2007, 2008 Free Software Foundation, Inc. `http://fsf.org/' @@ -24651,8 +31393,8 @@ Index * Menu: -* ! (exclamation point), ! operator: Boolean Ops. (line 67) -* ! (exclamation point), ! operator <1>: Egrep Program. (line 170) +* ! (exclamation point), ! operator: Boolean Ops. (line 69) +* ! (exclamation point), ! operator <1>: Egrep Program. (line 175) * ! (exclamation point), ! operator <2>: Ranges. (line 48) * ! (exclamation point), ! operator: Precedence. (line 52) * ! (exclamation point), != operator <1>: Precedence. (line 65) @@ -24664,163 +31406,170 @@ Index * ! (exclamation point), !~ operator <3>: Comparison Operators. (line 11) * ! (exclamation point), !~ operator <4>: Regexp Constants. (line 6) -* ! (exclamation point), !~ operator <5>: Computed Regexps. (line 6) -* ! (exclamation point), !~ operator <6>: Case-sensitivity. (line 26) +* ! (exclamation point), !~ operator <5>: Case-sensitivity. (line 26) +* ! (exclamation point), !~ operator <6>: Computed Regexps. (line 6) * ! (exclamation point), !~ operator: Regexp Usage. (line 19) -* " (double quote) <1>: Quoting. (line 37) -* " (double quote): Read Terminal. (line 25) -* " (double quote), regexp constants: Computed Regexps. (line 28) +* " (double quote), in regexp constants: Computed Regexps. (line 29) +* " (double quote), in shell commands: Quoting. (line 54) * # (number sign), #! (executable scripts): Executable Scripts. (line 6) -* # (number sign), #! (executable scripts), portability issues with: Executable Scripts. - (line 6) * # (number sign), commenting: Comments. (line 6) -* $ (dollar sign): Regexp Operators. (line 35) * $ (dollar sign), $ field operator <1>: Precedence. (line 43) * $ (dollar sign), $ field operator: Fields. (line 19) * $ (dollar sign), incrementing fields and arrays: Increment Ops. (line 30) +* $ (dollar sign), regexp operator: Regexp Operators. (line 35) * % (percent sign), % operator: Precedence. (line 55) * % (percent sign), %= operator <1>: Precedence. (line 95) -* % (percent sign), %= operator: Assignment Ops. (line 129) +* % (percent sign), %= operator: Assignment Ops. (line 130) * & (ampersand), && operator <1>: Precedence. (line 86) -* & (ampersand), && operator: Boolean Ops. (line 57) +* & (ampersand), && operator: Boolean Ops. (line 59) * & (ampersand), gsub()/gensub()/sub() functions and: Gory Details. (line 6) -* ' (single quote) <1>: Quoting. (line 31) -* ' (single quote) <2>: Long. (line 33) * ' (single quote): One-shot. (line 15) +* ' (single quote) in gawk command lines: Long. (line 35) +* ' (single quote), in shell commands: Quoting. (line 48) * ' (single quote), vs. apostrophe: Comments. (line 27) -* ' (single quote), with double quotes: Quoting. (line 53) -* () (parentheses): Regexp Operators. (line 79) -* () (parentheses), pgawk program: Profiling. (line 141) +* ' (single quote), with double quotes: Quoting. (line 73) +* () (parentheses), in a profile: Profiling. (line 146) +* () (parentheses), regexp operator: Regexp Operators. (line 81) * * (asterisk), * operator, as multiplication operator: Precedence. (line 55) * * (asterisk), * operator, as regexp operator: Regexp Operators. - (line 87) -* * (asterisk), * operator, null strings, matching: Gory Details. - (line 163) + (line 89) +* * (asterisk), * operator, null strings, matching: String Functions. + (line 536) * * (asterisk), ** operator <1>: Precedence. (line 49) * * (asterisk), ** operator: Arithmetic Ops. (line 81) * * (asterisk), **= operator <1>: Precedence. (line 95) -* * (asterisk), **= operator: Assignment Ops. (line 129) +* * (asterisk), **= operator: Assignment Ops. (line 130) * * (asterisk), *= operator <1>: Precedence. (line 95) -* * (asterisk), *= operator: Assignment Ops. (line 129) -* + (plus sign): Regexp Operators. (line 102) +* * (asterisk), *= operator: Assignment Ops. (line 130) * + (plus sign), + operator: Precedence. (line 52) -* + (plus sign), ++ (decrement/increment operators): Increment Ops. - (line 11) * + (plus sign), ++ operator <1>: Precedence. (line 46) -* + (plus sign), ++ operator: Increment Ops. (line 40) +* + (plus sign), ++ operator: Increment Ops. (line 11) * + (plus sign), += operator <1>: Precedence. (line 95) * + (plus sign), += operator: Assignment Ops. (line 82) +* + (plus sign), regexp operator: Regexp Operators. (line 105) * , (comma), in range patterns: Ranges. (line 6) * - (hyphen), - operator: Precedence. (line 52) -* - (hyphen), -- (decrement/increment) operator: Precedence. (line 46) +* - (hyphen), -- operator <1>: Precedence. (line 46) * - (hyphen), -- operator: Increment Ops. (line 48) * - (hyphen), -= operator <1>: Precedence. (line 95) -* - (hyphen), -= operator: Assignment Ops. (line 129) +* - (hyphen), -= operator: Assignment Ops. (line 130) * - (hyphen), filenames beginning with: Options. (line 59) * - (hyphen), in bracket expressions: Bracket Expressions. (line 17) * --assign option: Options. (line 32) -* --c option: Options. (line 78) +* --bignum option: Options. (line 205) * --characters-as-bytes option: Options. (line 68) -* --command option: Options. (line 231) -* --copyright option: Options. (line 85) -* --disable-lint configuration option: Additional Configuration Options. +* --copyright option: Options. (line 88) +* --debug option: Options. (line 108) +* --disable-extensions configuration option: Additional Configuration Options. (line 9) +* --disable-lint configuration option: Additional Configuration Options. + (line 15) * --disable-nls configuration option: Additional Configuration Options. - (line 24) -* --dump-variables option <1>: Library Names. (line 45) -* --dump-variables option: Options. (line 90) -* --exec option: Options. (line 113) + (line 30) +* --dump-variables option: Options. (line 93) +* --dump-variables option, using for library functions: Library Names. + (line 45) +* --exec option: Options. (line 125) * --field-separator option: Options. (line 21) * --file option: Options. (line 25) * --gen-pot option <1>: String Extraction. (line 6) -* --gen-pot option: Options. (line 135) -* --help option: Options. (line 142) -* --L option: Options. (line 245) -* --lint option <1>: Options. (line 147) +* --gen-pot option: Options. (line 147) +* --help option: Options. (line 154) +* --include option: Options. (line 159) +* --lint option <1>: Options. (line 185) * --lint option: Command Line. (line 20) -* --lint-old option: Options. (line 245) +* --lint-old option: Options. (line 295) +* --load option: Options. (line 173) * --non-decimal-data option <1>: Nondecimal Data. (line 6) -* --non-decimal-data option: Options. (line 166) +* --non-decimal-data option: Options. (line 211) * --non-decimal-data option, strtonum() function and: Nondecimal Data. - (line 36) -* --optimize option: Options. (line 179) -* --posix option: Options. (line 199) -* --posix option, --traditional option and: Options. (line 218) -* --profile option <1>: Profiling. (line 15) -* --profile option: Options. (line 186) -* --re-interval option: Options. (line 224) -* --sandbox option: Options. (line 236) + (line 35) +* --optimize option: Options. (line 236) +* --posix option: Options. (line 254) +* --posix option, --traditional option and: Options. (line 273) +* --pretty-print option: Options. (line 225) +* --profile option <1>: Profiling. (line 12) +* --profile option: Options. (line 242) +* --re-interval option: Options. (line 279) +* --sandbox option: Options. (line 286) * --sandbox option, disabling system() function: I/O Functions. - (line 85) + (line 128) * --sandbox option, input redirection with getline: Getline. (line 19) * --sandbox option, output redirection with print, printf: Redirection. (line 6) -* --source option: Options. (line 105) -* --traditional option: Options. (line 78) -* --traditional option, --posix option and: Options. (line 218) -* --use-lc-numeric option: Options. (line 174) -* --version option: Options. (line 250) +* --source option: Options. (line 117) +* --traditional option: Options. (line 81) +* --traditional option, --posix option and: Options. (line 273) +* --use-lc-numeric option: Options. (line 220) +* --version option: Options. (line 300) * --with-whiny-user-strftime configuration option: Additional Configuration Options. - (line 29) + (line 35) * -b option: Options. (line 68) -* -C option: Options. (line 85) -* -d option: Options. (line 90) -* -E option: Options. (line 113) -* -e option: Options. (line 105) -* -F option: Command Line Field Separator. - (line 6) +* -C option: Options. (line 88) +* -c option: Options. (line 81) +* -D option: Options. (line 108) +* -d option: Options. (line 93) +* -e option: Options. (line 336) +* -E option: Options. (line 125) +* -e option: Options. (line 117) * -f option: Options. (line 25) * -F option: Options. (line 21) * -f option: Long. (line 12) -* -F option, -Ft sets FS to TAB: Options. (line 258) -* -f option, on command line: Options. (line 263) -* -g option: Options. (line 135) -* -h option: Options. (line 142) -* -l option: Options. (line 147) -* -N option: Options. (line 174) -* -n option: Options. (line 166) -* -O option: Options. (line 179) -* -P option: Options. (line 199) -* -p option: Options. (line 186) -* -R option: Options. (line 231) -* -r option: Options. (line 224) -* -S option: Options. (line 236) -* -V option: Options. (line 250) +* -F option, -Ft sets FS to TAB: Options. (line 308) +* -F option, command-line: Command Line Field Separator. + (line 6) +* -f option, multiple uses: Options. (line 313) +* -g option: Options. (line 147) +* -h option: Options. (line 154) +* -i option: Options. (line 159) +* -L option: Options. (line 295) +* -l option: Options. (line 173) +* -M option: Options. (line 205) +* -N option: Options. (line 220) +* -n option: Options. (line 211) +* -O option: Options. (line 236) +* -o option: Options. (line 225) +* -P option: Options. (line 254) +* -p option: Options. (line 242) +* -r option: Options. (line 279) +* -S option: Options. (line 286) +* -v option: Assignment Options. (line 12) +* -V option: Options. (line 300) * -v option: Options. (line 32) -* -v option, variables, assigning: Assignment Options. (line 12) * -W option: Options. (line 46) -* . (period): Regexp Operators. (line 43) -* .mo files: Explaining gettext. (line 41) -* .mo files, converting from .po: I18N Example. (line 62) -* .mo files, specifying directory of <1>: Programmer i18n. (line 47) -* .mo files, specifying directory of: Explaining gettext. (line 53) +* . (period), regexp operator: Regexp Operators. (line 44) +* .gmo files: Explaining gettext. (line 42) +* .gmo files, specifying directory of <1>: Programmer i18n. (line 47) +* .gmo files, specifying directory of: Explaining gettext. (line 54) +* .mo files, converting from .po: I18N Example. (line 64) * .po files <1>: Translator i18n. (line 6) -* .po files: Explaining gettext. (line 36) -* .po files, converting to .mo: I18N Example. (line 62) -* .pot files: Explaining gettext. (line 30) -* / (forward slash): Regexp. (line 10) +* .po files: Explaining gettext. (line 37) +* .po files, converting to .mo: I18N Example. (line 64) +* .pot files: Explaining gettext. (line 31) +* / (forward slash) to enclose regular expressions: Regexp. (line 10) * / (forward slash), / operator: Precedence. (line 55) * / (forward slash), /= operator <1>: Precedence. (line 95) -* / (forward slash), /= operator: Assignment Ops. (line 129) +* / (forward slash), /= operator: Assignment Ops. (line 130) * / (forward slash), /= operator, vs. /=.../ regexp constant: Assignment Ops. (line 148) * / (forward slash), patterns and: Expression Patterns. (line 24) * /= operator vs. /=.../ regexp constant: Assignment Ops. (line 148) -* /dev/... special files (gawk): Special FD. (line 46) -* /dev/fd/N special files: Special FD. (line 46) +* /dev/... special files: Special FD. (line 48) +* /dev/fd/N special files (gawk): Special FD. (line 48) * /inet/... special files (gawk): TCP/IP Networking. (line 6) * /inet4/... special files (gawk): TCP/IP Networking. (line 6) * /inet6/... special files (gawk): TCP/IP Networking. (line 6) -* ; (semicolon): Statements/Lines. (line 91) -* ; (semicolon), AWKPATH variable and: PC Using. (line 11) +* ; (semicolon), AWKPATH variable and: PC Using. (line 10) * ; (semicolon), separating statements in actions <1>: Statements. (line 10) -* ; (semicolon), separating statements in actions: Action Overview. +* ; (semicolon), separating statements in actions <2>: Action Overview. (line 19) +* ; (semicolon), separating statements in actions: Statements/Lines. + (line 91) * < (left angle bracket), < operator <1>: Precedence. (line 65) * < (left angle bracket), < operator: Comparison Operators. (line 11) @@ -24841,19 +31590,20 @@ Index (line 11) * > (right angle bracket), >> operator (I/O) <1>: Precedence. (line 65) * > (right angle bracket), >> operator (I/O): Redirection. (line 50) -* ? (question mark) regexp operator <1>: GNU Regexp Operators. - (line 59) -* ? (question mark) regexp operator: Regexp Operators. (line 111) * ? (question mark), ?: operator: Precedence. (line 92) -* [] (square brackets): Regexp Operators. (line 55) -* \ (backslash) <1>: Regexp Operators. (line 18) -* \ (backslash) <2>: Quoting. (line 31) -* \ (backslash) <3>: Comments. (line 50) -* \ (backslash): Read Terminal. (line 25) -* \ (backslash), \" escape sequence: Escape Sequences. (line 76) +* ? (question mark), regexp operator <1>: GNU Regexp Operators. + (line 59) +* ? (question mark), regexp operator: Regexp Operators. (line 111) +* @-notation for indirect function calls: Indirect Calls. (line 47) +* @include directive: Include Files. (line 8) +* @load directive: Loading Shared Libraries. + (line 8) +* [] (square brackets), regexp operator: Regexp Operators. (line 56) +* \ (backslash): Comments. (line 50) +* \ (backslash), \" escape sequence: Escape Sequences. (line 85) * \ (backslash), \' operator (gawk): GNU Regexp Operators. (line 56) -* \ (backslash), \/ escape sequence: Escape Sequences. (line 69) +* \ (backslash), \/ escape sequence: Escape Sequences. (line 76) * \ (backslash), \< operator (gawk): GNU Regexp Operators. (line 30) * \ (backslash), \> operator (gawk): GNU Regexp Operators. @@ -24881,9 +31631,8 @@ Index * \ (backslash), \x escape sequence: Escape Sequences. (line 61) * \ (backslash), \y operator (gawk): GNU Regexp Operators. (line 38) -* \ (backslash), as field separators: Command Line Field Separator. - (line 27) -* \ (backslash), continuing lines and <1>: Egrep Program. (line 220) +* \ (backslash), as field separator: Command Line Field Separator. + (line 24) * \ (backslash), continuing lines and: Statements/Lines. (line 19) * \ (backslash), continuing lines and, comments and: Statements/Lines. (line 76) @@ -24894,162 +31643,179 @@ Index * \ (backslash), in bracket expressions: Bracket Expressions. (line 17) * \ (backslash), in escape sequences: Escape Sequences. (line 6) * \ (backslash), in escape sequences, POSIX and: Escape Sequences. - (line 113) -* \ (backslash), regexp constants: Computed Regexps. (line 28) -* ^ (caret) <1>: GNU Regexp Operators. - (line 59) -* ^ (caret): Regexp Operators. (line 22) + (line 108) +* \ (backslash), in regexp constants: Computed Regexps. (line 29) +* \ (backslash), in shell commands: Quoting. (line 48) +* \ (backslash), regexp operator: Regexp Operators. (line 18) * ^ (caret), ^ operator: Precedence. (line 49) * ^ (caret), ^= operator <1>: Precedence. (line 95) -* ^ (caret), ^= operator: Assignment Ops. (line 129) +* ^ (caret), ^= operator: Assignment Ops. (line 130) * ^ (caret), in bracket expressions: Bracket Expressions. (line 17) -* ^, in FS: Regexp Field Splitting. +* ^ (caret), in FS: Regexp Field Splitting. + (line 59) +* ^ (caret), regexp operator <1>: GNU Regexp Operators. (line 59) -* _ (underscore), _ C macro: Explaining gettext. (line 70) +* ^ (caret), regexp operator: Regexp Operators. (line 22) +* _ (underscore), C macro: Explaining gettext. (line 71) * _ (underscore), in names of private variables: Library Names. (line 29) * _ (underscore), translatable string: Programmer i18n. (line 69) -* _gr_init() user-defined function: Group Functions. (line 82) +* _gr_init() user-defined function: Group Functions. (line 83) +* _ord_init() user-defined function: Ordinal Functions. (line 16) * _pw_init() user-defined function: Passwd Functions. (line 105) * accessing fields: Fields. (line 6) +* accessing global variables from extensions: Symbol Table Access. + (line 6) * account information <1>: Group Functions. (line 6) * account information: Passwd Functions. (line 16) * actions: Action Overview. (line 6) * actions, control statements in: Statements. (line 6) * actions, default: Very Simple. (line 34) * actions, empty: Very Simple. (line 39) -* Ada programming language: Glossary. (line 20) +* Ada programming language: Glossary. (line 11) * adding, features to gawk: Adding Code. (line 6) * adding, fields: Changing Fields. (line 53) -* adding, functions to gawk: Dynamic Extensions. (line 10) -* advanced features, buffering: I/O Functions. (line 98) -* advanced features, close() function: Close Files And Pipes. - (line 131) -* advanced features, constants, values of: Nondecimal-numbers. - (line 67) -* advanced features, data files as single record: Records. (line 175) -* advanced features, fixed-width data: Constant Size. (line 9) -* advanced features, FNR/NR variables: Auto-set. (line 207) +* advanced features, fixed-width data: Constant Size. (line 6) * advanced features, gawk: Advanced Features. (line 6) -* advanced features, gawk, network programming: TCP/IP Networking. - (line 6) -* advanced features, gawk, nondecimal input data: Nondecimal Data. +* advanced features, network programming: TCP/IP Networking. (line 6) +* advanced features, nondecimal input data: Nondecimal Data. (line 6) +* advanced features, processes, communicating with: Two-way I/O. (line 6) -* advanced features, gawk, processes, communicating with: Two-way I/O. - (line 23) -* advanced features, network connections, See Also networks, connections: Advanced Features. - (line 6) -* advanced features, null strings, matching: Gory Details. (line 163) -* advanced features, operators, precedence: Increment Ops. (line 61) -* advanced features, piping into sh: Redirection. (line 143) -* advanced features, regexp constants: Assignment Ops. (line 148) * advanced features, specifying field content: Splitting By Content. (line 9) -* Aho, Alfred <1>: Contributors. (line 12) +* Aho, Alfred <1>: Contributors. (line 11) * Aho, Alfred: History. (line 17) -* alarm clock example program: Alarm Program. (line 9) -* alarm.awk program: Alarm Program. (line 29) -* algorithms: Basic High Level. (line 66) -* Alpha (DEC): Manual History. (line 28) -* amazing awk assembler (aaa): Glossary. (line 12) -* amazingly workable formatter (awf): Glossary. (line 25) +* alarm clock example program: Alarm Program. (line 11) +* alarm.awk program: Alarm Program. (line 31) +* algorithms: Basic High Level. (line 68) +* allocating memory for extensions: Memory Allocation Functions. + (line 6) +* amazing awk assembler (aaa): Glossary. (line 16) +* amazingly workable formatter (awf): Glossary. (line 24) * ambiguity, syntactic: /= operator vs. /=.../ regexp constant: Assignment Ops. (line 148) * ampersand (&), && operator <1>: Precedence. (line 86) -* ampersand (&), && operator: Boolean Ops. (line 57) +* ampersand (&), && operator: Boolean Ops. (line 59) * ampersand (&), gsub()/gensub()/sub() functions and: Gory Details. (line 6) -* anagram.awk program: Anagram Program. (line 22) +* anagram.awk program: Anagram Program. (line 21) +* anagrams, finding: Anagram Program. (line 6) +* and: Bitwise Functions. (line 40) * AND bitwise operation: Bitwise Functions. (line 6) * and Boolean-logic operator: Boolean Ops. (line 6) -* and() function (gawk): Bitwise Functions. (line 39) -* ANSI: Glossary. (line 35) -* archeologists: Bugs. (line 6) -* ARGC/ARGV variables <1>: ARGC and ARGV. (line 6) -* ARGC/ARGV variables: Auto-set. (line 11) +* ANSI: Glossary. (line 34) +* API informational variables: Extension API Informational Variables. + (line 6) +* API version: Extension Versioning. + (line 6) +* arbitrary precision: Arbitrary Precision Arithmetic. + (line 6) +* arbitrary precision integers: Arbitrary Precision Integers. + (line 6) +* archaeologists: Bugs. (line 6) +* arctangent: Numeric Functions. (line 11) +* ARGC/ARGV variables: Auto-set. (line 15) * ARGC/ARGV variables, command-line arguments: Other Arguments. - (line 12) -* ARGC/ARGV variables, portability and: Executable Scripts. (line 43) -* ARGIND variable: Auto-set. (line 40) -* ARGIND variable, command-line arguments: Other Arguments. (line 12) + (line 15) +* ARGC/ARGV variables, how to use: ARGC and ARGV. (line 6) +* ARGC/ARGV variables, portability and: Executable Scripts. (line 59) +* ARGIND variable: Auto-set. (line 44) +* ARGIND variable, command-line arguments: Other Arguments. (line 15) * arguments, command-line <1>: ARGC and ARGV. (line 6) -* arguments, command-line <2>: Auto-set. (line 11) +* arguments, command-line <2>: Auto-set. (line 15) * arguments, command-line: Other Arguments. (line 6) * arguments, command-line, invoking awk: Command Line. (line 6) -* arguments, in function calls: Function Calls. (line 16) +* arguments, in function calls: Function Calls. (line 18) * arguments, processing: Getopt Function. (line 6) -* arguments, retrieving: Internals. (line 111) +* ARGV array, indexing into: Other Arguments. (line 15) * arithmetic operators: Arithmetic Ops. (line 6) +* array manipulation in extensions: Array Manipulation. (line 6) +* array members: Reference to Elements. + (line 6) +* array scanning order, controlling: Controlling Scanning. + (line 14) +* array, number of elements: String Functions. (line 201) * arrays: Arrays. (line 6) +* arrays of arrays: Arrays of Arrays. (line 6) +* arrays, an example of using: Array Example. (line 6) +* arrays, and IGNORECASE variable: Array Intro. (line 94) * arrays, as parameters to functions: Pass By Value/Reference. - (line 47) + (line 44) * arrays, associative: Array Intro. (line 50) -* arrays, associative, clearing: Internals. (line 68) -* arrays, associative, library functions and: Library Names. (line 57) +* arrays, associative, library functions and: Library Names. (line 58) * arrays, deleting entire contents: Delete. (line 39) -* arrays, elements, assigning: Assigning Elements. (line 6) +* arrays, elements that don't exist: Reference to Elements. + (line 23) +* arrays, elements, assigning values: Assigning Elements. (line 6) * arrays, elements, deleting: Delete. (line 6) -* arrays, elements, installing: Internals. (line 72) -* arrays, elements, order of: Scanning an Array. (line 48) -* arrays, elements, referencing: Reference to Elements. - (line 6) -* arrays, elements, retrieving number of: String Functions. (line 29) +* arrays, elements, order of access by in operator: Scanning an Array. + (line 48) +* arrays, elements, retrieving number of: String Functions. (line 42) * arrays, for statement and: Scanning an Array. (line 20) -* arrays, IGNORECASE variable and: Array Intro. (line 92) * arrays, indexing: Array Intro. (line 50) * arrays, merging into strings: Join Function. (line 6) -* arrays, multidimensional: Multi-dimensional. (line 10) -* arrays, multidimensional, scanning: Multi-scanning. (line 11) -* arrays, names of: Arrays. (line 18) +* arrays, multidimensional: Multidimensional. (line 10) +* arrays, multidimensional, scanning: Multiscanning. (line 11) +* arrays, numeric subscripts: Numeric Array Subscripts. + (line 6) +* arrays, referencing elements: Reference to Elements. + (line 6) * arrays, scanning: Scanning an Array. (line 6) * arrays, sorting: Array Sorting Functions. (line 6) -* arrays, sorting, IGNORECASE variable and: Array Sorting Functions. - (line 78) -* arrays, sparse: Array Intro. (line 71) -* arrays, subscripts: Numeric Array Subscripts. - (line 6) +* arrays, sorting, and IGNORECASE variable: Array Sorting Functions. + (line 83) +* arrays, sparse: Array Intro. (line 72) * arrays, subscripts, uninitialized variables as: Uninitialized Subscripts. (line 6) +* arrays, unassigned elements: Reference to Elements. + (line 18) * artificial intelligence, gawk and: Distribution contents. - (line 55) -* ASCII <1>: Glossary. (line 141) + (line 52) +* ASCII <1>: Glossary. (line 133) * ASCII: Ordinal Functions. (line 45) -* asort() function (gawk) <1>: Array Sorting Functions. +* asort <1>: Array Sorting Functions. (line 6) -* asort() function (gawk): String Functions. (line 29) +* asort: String Functions. (line 42) * asort() function (gawk), arrays, sorting: Array Sorting Functions. (line 6) -* asorti() function (gawk): String Functions. (line 77) +* asorti <1>: Array Sorting Functions. + (line 6) +* asorti: String Functions. (line 42) +* asorti() function (gawk), arrays, sorting: Array Sorting Functions. + (line 6) * assert() function (C library): Assert Function. (line 6) * assert() user-defined function: Assert Function. (line 28) * assertions: Assert Function. (line 6) +* assign values to variables, in debugger: Viewing And Changing Data. + (line 59) * assignment operators: Assignment Ops. (line 6) * assignment operators, evaluation order: Assignment Ops. (line 111) * assignment operators, lvalues/rvalues: Assignment Ops. (line 32) * assignments as filenames: Ignoring Assigns. (line 6) -* assoc_clear() internal function: Internals. (line 68) -* assoc_lookup() internal function: Internals. (line 72) * associative arrays: Array Intro. (line 50) * asterisk (*), * operator, as multiplication operator: Precedence. (line 55) * asterisk (*), * operator, as regexp operator: Regexp Operators. - (line 87) -* asterisk (*), * operator, null strings, matching: Gory Details. - (line 163) + (line 89) +* asterisk (*), * operator, null strings, matching: String Functions. + (line 536) * asterisk (*), ** operator <1>: Precedence. (line 49) * asterisk (*), ** operator: Arithmetic Ops. (line 81) * asterisk (*), **= operator <1>: Precedence. (line 95) -* asterisk (*), **= operator: Assignment Ops. (line 129) +* asterisk (*), **= operator: Assignment Ops. (line 130) * asterisk (*), *= operator <1>: Precedence. (line 95) -* asterisk (*), *= operator: Assignment Ops. (line 129) -* atan2() function: Numeric Functions. (line 11) -* awf (amazingly workable formatter) program: Glossary. (line 25) -* awk language, POSIX version: Assignment Ops. (line 136) +* asterisk (*), *= operator: Assignment Ops. (line 130) +* atan2: Numeric Functions. (line 11) +* automatic displays, in debugger: Debugger Info. (line 24) +* awf (amazingly workable formatter) program: Glossary. (line 24) +* awk debugging, enabling: Options. (line 108) +* awk language, POSIX version: Assignment Ops. (line 137) +* awk profiling, enabling: Options. (line 242) * awk programs <1>: Two Rules. (line 6) * awk programs <2>: Executable Scripts. (line 6) * awk programs: Getting Started. (line 12) -* awk programs, complex: When. (line 29) +* awk programs, complex: When. (line 27) * awk programs, documenting <1>: Library Names. (line 6) * awk programs, documenting: Comments. (line 6) * awk programs, examples of: Sample Programs. (line 6) @@ -25061,7 +31827,6 @@ Index * awk programs, location of: Options. (line 25) * awk programs, one-line examples: Very Simple. (line 45) * awk programs, profiling: Profiling. (line 6) -* awk programs, profiling, enabling: Options. (line 186) * awk programs, running <1>: Long. (line 6) * awk programs, running: Running gawk. (line 6) * awk programs, running, from shell scripts: One-shot. (line 22) @@ -25070,25 +31835,24 @@ Index (line 6) * awk, function of: Getting Started. (line 6) * awk, gawk and <1>: This Manual. (line 14) -* awk, gawk and: Preface. (line 23) +* awk, gawk and: Preface. (line 21) * awk, history of: History. (line 17) -* awk, implementation issues, pipes: Redirection. (line 135) +* awk, implementation issues, pipes: Redirection. (line 129) * awk, implementations: Other Versions. (line 6) * awk, implementations, limits: Getline Notes. (line 14) * awk, invoking: Command Line. (line 6) * awk, new vs. old: Names. (line 6) -* awk, new vs. old, OFMT variable: Conversion. (line 55) -* awk, POSIX and: Preface. (line 23) -* awk, POSIX and, See Also POSIX awk: Preface. (line 23) +* awk, new vs. old, OFMT variable: Strings And Numbers. (line 57) +* awk, POSIX and: Preface. (line 21) +* awk, POSIX and, See Also POSIX awk: Preface. (line 21) * awk, regexp constants and: Comparison Operators. (line 103) -* awk, See Also gawk: Preface. (line 36) +* awk, See Also gawk: Preface. (line 34) * awk, terms describing: This Manual. (line 6) * awk, uses for <1>: When. (line 6) * awk, uses for <2>: Getting Started. (line 12) -* awk, uses for: Preface. (line 23) -* awk, versions of <1>: V7/SVR3.1. (line 6) -* awk, versions of: Names. (line 10) +* awk, uses for: Preface. (line 21) +* awk, versions of: V7/SVR3.1. (line 6) * awk, versions of, changes between SVR3.1 and SVR4: SVR4. (line 6) * awk, versions of, changes between SVR4 and POSIX awk: POSIX. (line 6) @@ -25096,23 +31860,19 @@ Index * awk, versions of, See Also Brian Kernighan's awk <1>: Other Versions. (line 13) * awk, versions of, See Also Brian Kernighan's awk: BTL. (line 6) -* awk.h file (internal): Internals. (line 15) -* awka compiler for awk: Other Versions. (line 55) -* AWKNUM internal type: Internals. (line 19) -* AWKPATH environment variable <1>: PC Using. (line 11) +* awka compiler for awk: Other Versions. (line 68) +* AWKLIBPATH environment variable: AWKLIBPATH Variable. (line 6) +* AWKPATH environment variable <1>: PC Using. (line 10) * AWKPATH environment variable: AWKPATH Variable. (line 6) -* awkprof.out file: Profiling. (line 10) +* awkprof.out file: Profiling. (line 6) * awksed.awk program: Simple Sed. (line 25) -* awkvars.out file: Options. (line 90) +* awkvars.out file: Options. (line 93) * b debugger command (alias for break): Breakpoint Control. (line 11) -* backslash (\) <1>: Regexp Operators. (line 18) -* backslash (\) <2>: Quoting. (line 31) -* backslash (\) <3>: Comments. (line 50) -* backslash (\): Read Terminal. (line 25) -* backslash (\), \" escape sequence: Escape Sequences. (line 76) +* backslash (\): Comments. (line 50) +* backslash (\), \" escape sequence: Escape Sequences. (line 85) * backslash (\), \' operator (gawk): GNU Regexp Operators. (line 56) -* backslash (\), \/ escape sequence: Escape Sequences. (line 69) +* backslash (\), \/ escape sequence: Escape Sequences. (line 76) * backslash (\), \< operator (gawk): GNU Regexp Operators. (line 30) * backslash (\), \> operator (gawk): GNU Regexp Operators. @@ -25140,9 +31900,8 @@ Index * backslash (\), \x escape sequence: Escape Sequences. (line 61) * backslash (\), \y operator (gawk): GNU Regexp Operators. (line 38) -* backslash (\), as field separators: Command Line Field Separator. - (line 27) -* backslash (\), continuing lines and <1>: Egrep Program. (line 220) +* backslash (\), as field separator: Command Line Field Separator. + (line 24) * backslash (\), continuing lines and: Statements/Lines. (line 19) * backslash (\), continuing lines and, comments and: Statements/Lines. (line 76) @@ -25153,198 +31912,238 @@ Index * backslash (\), in bracket expressions: Bracket Expressions. (line 17) * backslash (\), in escape sequences: Escape Sequences. (line 6) * backslash (\), in escape sequences, POSIX and: Escape Sequences. - (line 113) -* backslash (\), regexp constants: Computed Regexps. (line 28) -* backtrace debugger command: Dgawk Stack. (line 13) -* BBS-list file: Sample Data Files. (line 6) -* Beebe, Nelson <1>: Other Versions. (line 69) -* Beebe, Nelson: Acknowledgments. (line 60) -* BEGIN pattern <1>: BEGIN/END. (line 6) -* BEGIN pattern <2>: Field Separators. (line 44) -* BEGIN pattern: Records. (line 29) + (line 108) +* backslash (\), in regexp constants: Computed Regexps. (line 29) +* backslash (\), in shell commands: Quoting. (line 48) +* backslash (\), regexp operator: Regexp Operators. (line 18) +* backtrace debugger command: Execution Stack. (line 13) +* Beebe, Nelson H.F. <1>: Other Versions. (line 82) +* Beebe, Nelson H.F.: Acknowledgments. (line 60) +* BEGIN pattern <1>: Using BEGIN/END. (line 6) +* BEGIN pattern <2>: BEGIN/END. (line 6) +* BEGIN pattern: Field Separators. (line 45) +* BEGIN pattern, and profiling: Profiling. (line 62) * BEGIN pattern, assert() user-defined function and: Assert Function. (line 83) -* BEGIN pattern, Boolean patterns and: Expression Patterns. (line 73) +* BEGIN pattern, Boolean patterns and: Expression Patterns. (line 69) * BEGIN pattern, exit statement and: Exit Statement. (line 12) * BEGIN pattern, getline and: Getline Notes. (line 19) * BEGIN pattern, headings, adding: Print Examples. (line 43) * BEGIN pattern, next/nextfile statements and <1>: Next Statement. - (line 45) + (line 44) * BEGIN pattern, next/nextfile statements and: I/O And BEGIN/END. (line 37) * BEGIN pattern, OFS/ORS variables, assigning values to: Output Separators. - (line 20) + (line 21) * BEGIN pattern, operators and: Using BEGIN/END. (line 17) -* BEGIN pattern, pgawk program: Profiling. (line 65) * BEGIN pattern, print statement and: I/O And BEGIN/END. (line 16) * BEGIN pattern, pwcat program: Passwd Functions. (line 143) -* BEGIN pattern, running awk programs and: Cut Program. (line 68) +* BEGIN pattern, running awk programs and: Cut Program. (line 63) * BEGIN pattern, TEXTDOMAIN variable and: Programmer i18n. (line 60) * BEGINFILE pattern: BEGINFILE/ENDFILE. (line 6) * BEGINFILE pattern, Boolean patterns and: Expression Patterns. - (line 73) -* beginfile() user-defined function: Filetrans Function. (line 62) + (line 69) +* beginfile() user-defined function: Filetrans Function. (line 61) +* Bentley, Jon: Glossary. (line 143) * Benzinger, Michael: Contributors. (line 97) +* Berry, Karl <1>: Ranges and Locales. (line 74) * Berry, Karl: Acknowledgments. (line 33) -* binary input/output: User-modified. (line 10) -* bindtextdomain() function (C library): Explaining gettext. (line 49) -* bindtextdomain() function (gawk) <1>: Programmer i18n. (line 47) -* bindtextdomain() function (gawk): I18N Functions. (line 12) +* binary input/output: User-modified. (line 15) +* bindtextdomain <1>: Programmer i18n. (line 47) +* bindtextdomain: I18N Functions. (line 12) +* bindtextdomain() function (C library): Explaining gettext. (line 50) * bindtextdomain() function (gawk), portability and: I18N Portability. (line 33) -* BINMODE variable <1>: PC Using. (line 34) -* BINMODE variable: User-modified. (line 10) -* bits2str() user-defined function: Bitwise Functions. (line 68) +* BINMODE variable <1>: PC Using. (line 33) +* BINMODE variable: User-modified. (line 15) +* bit-manipulation functions: Bitwise Functions. (line 6) +* bits2str() user-defined function: Bitwise Functions. (line 71) +* bitwise AND: Bitwise Functions. (line 40) +* bitwise complement: Bitwise Functions. (line 44) +* bitwise OR: Bitwise Functions. (line 50) +* bitwise XOR: Bitwise Functions. (line 56) * bitwise, complement: Bitwise Functions. (line 25) * bitwise, operations: Bitwise Functions. (line 6) * bitwise, shift: Bitwise Functions. (line 32) * body, in actions: Statements. (line 10) * body, in loops: While Statement. (line 14) * Boolean expressions: Boolean Ops. (line 6) -* Boolean expressions, as patterns: Expression Patterns. (line 41) +* Boolean expressions, as patterns: Expression Patterns. (line 38) * Boolean operators, See Boolean expressions: Boolean Ops. (line 6) * Bourne shell, quoting rules for: Quoting. (line 18) +* braces ({}): Profiling. (line 142) * braces ({}), actions and: Action Overview. (line 19) -* braces ({}), pgawk program: Profiling. (line 137) * braces ({}), statements, grouping: Statements. (line 10) * bracket expressions <1>: Bracket Expressions. (line 6) -* bracket expressions: Regexp Operators. (line 55) +* bracket expressions: Regexp Operators. (line 56) * bracket expressions, character classes: Bracket Expressions. - (line 30) + (line 32) * bracket expressions, collating elements: Bracket Expressions. - (line 69) + (line 79) * bracket expressions, collating symbols: Bracket Expressions. - (line 76) -* bracket expressions, complemented: Regexp Operators. (line 63) + (line 86) +* bracket expressions, complemented: Regexp Operators. (line 64) * bracket expressions, equivalence classes: Bracket Expressions. - (line 82) -* bracket expressions, non-ASCII: Bracket Expressions. (line 69) + (line 92) +* bracket expressions, non-ASCII: Bracket Expressions. (line 79) * bracket expressions, range expressions: Bracket Expressions. (line 6) * break debugger command: Breakpoint Control. (line 11) * break statement: Break Statement. (line 6) +* breakpoint: Debugging Terms. (line 33) +* breakpoint at location, how to delete: Breakpoint Control. (line 36) +* breakpoint commands: Debugger Execution Control. + (line 10) +* breakpoint condition: Breakpoint Control. (line 54) +* breakpoint, delete by number: Breakpoint Control. (line 64) +* breakpoint, how to disable or enable: Breakpoint Control. (line 69) +* breakpoint, setting: Breakpoint Control. (line 11) * Brennan, Michael <1>: Other Versions. (line 6) * Brennan, Michael <2>: Simple Sed. (line 25) -* Brennan, Michael <3>: Two-way I/O. (line 6) -* Brennan, Michael: Delete. (line 52) -* Brian Kernighan's awk, extensions <1>: Other Versions. (line 13) +* Brennan, Michael <3>: Delete. (line 56) +* Brennan, Michael <4>: Acknowledgments. (line 78) +* Brennan, Michael <5>: Foreword4. (line 33) +* Brennan, Michael: Foreword3. (line 84) +* Brian Kernighan's awk <1>: I/O Functions. (line 43) +* Brian Kernighan's awk <2>: Gory Details. (line 19) +* Brian Kernighan's awk <3>: String Functions. (line 492) +* Brian Kernighan's awk <4>: Delete. (line 51) +* Brian Kernighan's awk <5>: Nextfile Statement. (line 47) +* Brian Kernighan's awk <6>: Continue Statement. (line 44) +* Brian Kernighan's awk <7>: Break Statement. (line 51) +* Brian Kernighan's awk <8>: I/O And BEGIN/END. (line 16) +* Brian Kernighan's awk <9>: Concatenation. (line 36) +* Brian Kernighan's awk <10>: Getline/Pipe. (line 62) +* Brian Kernighan's awk <11>: Regexp Field Splitting. + (line 67) +* Brian Kernighan's awk <12>: GNU Regexp Operators. + (line 82) +* Brian Kernighan's awk <13>: Escape Sequences. (line 112) +* Brian Kernighan's awk: When. (line 21) * Brian Kernighan's awk, extensions: BTL. (line 6) +* Brian Kernighan's awk, source code: Other Versions. (line 13) +* Brini, Davide: Signature Program. (line 6) +* Brink, Jeroen: DOS Quoting. (line 10) * Broder, Alan J.: Contributors. (line 88) * Brown, Martin: Contributors. (line 82) * BSD-based operating systems: Glossary. (line 611) -* bt debugger command (alias for backtrace): Dgawk Stack. (line 13) -* Buening, Andreas <1>: Bugs. (line 71) +* bt debugger command (alias for backtrace): Execution Stack. (line 13) +* Buening, Andreas <1>: Bugs. (line 70) * Buening, Andreas <2>: Contributors. (line 92) * Buening, Andreas: Acknowledgments. (line 60) -* buffering, input/output <1>: Two-way I/O. (line 70) -* buffering, input/output: I/O Functions. (line 130) -* buffering, interactive vs. noninteractive: I/O Functions. (line 98) -* buffers, flushing: I/O Functions. (line 29) +* buffering, input/output <1>: Two-way I/O. (line 52) +* buffering, input/output: I/O Functions. (line 140) +* buffering, interactive vs. noninteractive: I/O Functions. (line 75) +* buffers, flushing: I/O Functions. (line 32) * buffers, operators for: GNU Regexp Operators. (line 48) * bug reports, email address, bug-gawk@gnu.org: Bugs. (line 30) * bug-gawk@gnu.org bug reporting address: Bugs. (line 30) * built-in functions: Functions. (line 6) * built-in functions, evaluation order: Calling Built-in. (line 30) -* built-in variables: Built-in Variables. (line 6) -* built-in variables, -v option, setting with: Options. (line 40) -* built-in variables, conveying information: Auto-set. (line 6) -* built-in variables, user-modifiable: User-modified. (line 6) -* Busybox Awk: Other Versions. (line 78) +* Busybox Awk: Other Versions. (line 92) +* c.e., See common extensions: Conventions. (line 51) * call by reference: Pass By Value/Reference. - (line 47) + (line 44) * call by value: Pass By Value/Reference. - (line 18) -* caret (^) <1>: GNU Regexp Operators. - (line 59) -* caret (^): Regexp Operators. (line 22) + (line 15) +* call stack, display in debugger: Execution Stack. (line 13) * caret (^), ^ operator: Precedence. (line 49) * caret (^), ^= operator <1>: Precedence. (line 95) -* caret (^), ^= operator: Assignment Ops. (line 129) +* caret (^), ^= operator: Assignment Ops. (line 130) * caret (^), in bracket expressions: Bracket Expressions. (line 17) +* caret (^), regexp operator <1>: GNU Regexp Operators. + (line 59) +* caret (^), regexp operator: Regexp Operators. (line 22) * case keyword: Switch Statement. (line 6) -* case sensitivity, array indices and: Array Intro. (line 92) +* case sensitivity, and regexps: User-modified. (line 76) +* case sensitivity, and string comparisons: User-modified. (line 76) +* case sensitivity, array indices and: Array Intro. (line 94) * case sensitivity, converting case: String Functions. (line 522) -* case sensitivity, example programs: Library Functions. (line 42) +* case sensitivity, example programs: Library Functions. (line 53) * case sensitivity, gawk: Case-sensitivity. (line 26) -* case sensitivity, regexps and <1>: User-modified. (line 82) * case sensitivity, regexps and: Case-sensitivity. (line 6) -* case sensitivity, string comparisons and: User-modified. (line 82) -* CGI, awk scripts for: Options. (line 113) -* character lists, See bracket expressions: Regexp Operators. (line 55) -* character sets (machine character encodings) <1>: Glossary. (line 141) +* CGI, awk scripts for: Options. (line 125) +* character classes, See bracket expressions: Regexp Operators. + (line 56) +* character lists in regular expression: Bracket Expressions. (line 6) +* character lists, See bracket expressions: Regexp Operators. (line 56) +* character sets (machine character encodings) <1>: Glossary. (line 133) * character sets (machine character encodings): Ordinal Functions. (line 45) * character sets, See Also bracket expressions: Regexp Operators. - (line 55) + (line 56) * characters, counting: Wc Program. (line 6) * characters, transliterating: Translate Program. (line 6) * characters, values of as numbers: Ordinal Functions. (line 6) * Chassell, Robert J.: Acknowledgments. (line 33) -* chdir() function, implementing in gawk: Sample Library. (line 6) -* chem utility: Glossary. (line 151) +* chdir() extension function: Extension Sample File Functions. + (line 12) +* chem utility: Glossary. (line 143) +* chr() extension function: Extension Sample Ord. + (line 15) * chr() user-defined function: Ordinal Functions. (line 16) * clear debugger command: Breakpoint Control. (line 36) * Cliff random numbers: Cliff Random Function. (line 6) * cliff_rand() user-defined function: Cliff Random Function. (line 12) -* close() function <1>: I/O Functions. (line 10) -* close() function <2>: Close Files And Pipes. +* close <1>: I/O Functions. (line 10) +* close: Close Files And Pipes. (line 18) -* close() function <3>: Getline/Pipe. (line 24) -* close() function: Getline/Variable/File. - (line 30) -* close() function, return values: Close Files And Pipes. - (line 131) -* close() function, two-way pipes and: Two-way I/O. (line 77) -* Close, Diane <1>: Contributors. (line 21) -* Close, Diane: Manual History. (line 41) -* close_func() input method: Internals. (line 151) -* collating elements: Bracket Expressions. (line 69) -* collating symbols: Bracket Expressions. (line 76) +* close file or coprocess: I/O Functions. (line 10) +* close() function, portability: Close Files And Pipes. + (line 81) +* close() function, return value: Close Files And Pipes. + (line 133) +* close() function, two-way pipes and: Two-way I/O. (line 59) +* Close, Diane <1>: Contributors. (line 20) +* Close, Diane: Manual History. (line 34) +* Collado, Manuel: Acknowledgments. (line 60) +* collating elements: Bracket Expressions. (line 79) +* collating symbols: Bracket Expressions. (line 86) +* Colombo, Antonio <1>: Contributors. (line 140) * Colombo, Antonio: Acknowledgments. (line 60) * columns, aligning: Print Examples. (line 70) * columns, cutting: Cut Program. (line 6) * comma (,), in range patterns: Ranges. (line 6) +* command completion, in debugger: Readline Support. (line 6) * command line, arguments <1>: ARGC and ARGV. (line 6) -* command line, arguments <2>: Auto-set. (line 11) +* command line, arguments <2>: Auto-set. (line 15) * command line, arguments: Other Arguments. (line 6) -* command line, directories on: Command line directories. +* command line, directories on: Command-line directories. (line 6) * command line, formats: Running gawk. (line 12) * command line, FS on, setting: Command Line Field Separator. (line 6) * command line, invoking awk from: Command Line. (line 6) -* command line, options <1>: Command Line Field Separator. - (line 6) -* command line, options <2>: Options. (line 6) -* command line, options: Long. (line 12) +* command line, option -f: Long. (line 12) +* command line, options: Options. (line 6) * command line, options, end of: Options. (line 54) * command line, variables, assigning on: Assignment Options. (line 6) * command-line options, processing: Getopt Function. (line 6) * command-line options, string extraction: String Extraction. (line 6) -* commands debugger command: Dgawk Execution Control. +* commands debugger command: Debugger Execution Control. + (line 10) +* commands to execute at breakpoint: Debugger Execution Control. (line 10) * commenting: Comments. (line 6) * commenting, backslash continuation and: Statements/Lines. (line 76) -* common extensions, ** operator: Arithmetic Ops. (line 36) -* common extensions, **= operator: Assignment Ops. (line 136) -* common extensions, /dev/stderr special file: Special FD. (line 46) -* common extensions, /dev/stdin special file: Special FD. (line 46) -* common extensions, /dev/stdout special file: Special FD. (line 46) +* common extensions, ** operator: Arithmetic Ops. (line 30) +* common extensions, **= operator: Assignment Ops. (line 137) +* common extensions, /dev/stderr special file: Special FD. (line 48) +* common extensions, /dev/stdin special file: Special FD. (line 48) +* common extensions, /dev/stdout special file: Special FD. (line 48) * common extensions, \x escape sequence: Escape Sequences. (line 61) -* common extensions, BINMODE variable: PC Using. (line 34) +* common extensions, BINMODE variable: PC Using. (line 33) * common extensions, delete to delete entire arrays: Delete. (line 39) -* common extensions, fflush() function: I/O Functions. (line 25) -* common extensions, func keyword: Definition Syntax. (line 83) +* common extensions, func keyword: Definition Syntax. (line 93) * common extensions, length() applied to an array: String Functions. - (line 196) -* common extensions, nextfile statement: Nextfile Statement. (line 6) -* common extensions, RS as a regexp: Records. (line 115) + (line 201) +* common extensions, RS as a regexp: gawk split records. (line 6) * common extensions, single character fields: Single Character Fields. (line 6) -* comp.lang.awk newsgroup: Bugs. (line 38) +* comp.lang.awk newsgroup: Bugs. (line 39) * comparison expressions: Typing and Comparison. (line 9) * comparison expressions, as patterns: Expression Patterns. (line 14) @@ -25356,93 +32155,113 @@ Index (line 60) * compatibility mode (gawk), octal numbers: Nondecimal-numbers. (line 60) -* compatibility mode (gawk), specifying: Options. (line 78) -* compiled programs <1>: Glossary. (line 161) -* compiled programs: Basic High Level. (line 14) +* compatibility mode (gawk), specifying: Options. (line 81) +* compiled programs <1>: Glossary. (line 155) +* compiled programs: Basic High Level. (line 15) * compiling gawk for Cygwin: Cygwin. (line 6) * compiling gawk for MS-DOS and MS-Windows: PC Compiling. (line 13) * compiling gawk for VMS: VMS Compilation. (line 6) * compiling gawk with EMX for OS/2: PC Compiling. (line 28) -* compl() function (gawk): Bitwise Functions. (line 42) +* compl: Bitwise Functions. (line 44) * complement, bitwise: Bitwise Functions. (line 25) * compound statements, control statements and: Statements. (line 10) -* concatenating: Concatenation. (line 9) +* concatenating: Concatenation. (line 8) * condition debugger command: Breakpoint Control. (line 54) * conditional expressions: Conditional Exp. (line 6) -* configuration option, --disable-lint: Additional Configuration Options. +* configuration option, --disable-extensions: Additional Configuration Options. (line 9) +* configuration option, --disable-lint: Additional Configuration Options. + (line 15) * configuration option, --disable-nls: Additional Configuration Options. - (line 24) + (line 30) * configuration option, --with-whiny-user-strftime: Additional Configuration Options. - (line 29) + (line 35) * configuration options, gawk: Additional Configuration Options. (line 6) +* constant regexps: Regexp Usage. (line 57) * constants, nondecimal: Nondecimal Data. (line 6) +* constants, numeric: Scalar Constants. (line 6) * constants, types of: Constants. (line 6) +* continue program, in debugger: Debugger Execution Control. + (line 33) * continue statement: Continue Statement. (line 6) * control statements: Statements. (line 6) -* converting, case: String Functions. (line 522) -* converting, dates to timestamps: Time Functions. (line 74) -* converting, during subscripting: Numeric Array Subscripts. +* controlling array scanning order: Controlling Scanning. + (line 14) +* convert string to lower case: String Functions. (line 523) +* convert string to number: String Functions. (line 390) +* convert string to upper case: String Functions. (line 529) +* converting integer array subscripts: Numeric Array Subscripts. (line 31) -* converting, numbers to strings <1>: Bitwise Functions. (line 107) -* converting, numbers to strings: Conversion. (line 6) -* converting, strings to numbers <1>: Bitwise Functions. (line 107) -* converting, strings to numbers: Conversion. (line 6) -* CONVFMT variable <1>: User-modified. (line 28) -* CONVFMT variable: Conversion. (line 29) -* CONVFMT variable, array subscripts and: Numeric Array Subscripts. +* converting, dates to timestamps: Time Functions. (line 76) +* converting, numbers to strings <1>: Bitwise Functions. (line 110) +* converting, numbers to strings: Strings And Numbers. (line 6) +* converting, strings to numbers <1>: Bitwise Functions. (line 110) +* converting, strings to numbers: Strings And Numbers. (line 6) +* CONVFMT variable <1>: User-modified. (line 30) +* CONVFMT variable: Strings And Numbers. (line 29) +* CONVFMT variable, and array subscripts: Numeric Array Subscripts. (line 6) -* coprocesses <1>: Two-way I/O. (line 44) -* coprocesses: Redirection. (line 102) +* cookie: Glossary. (line 177) +* coprocesses <1>: Two-way I/O. (line 25) +* coprocesses: Redirection. (line 96) * coprocesses, closing: Close Files And Pipes. (line 6) * coprocesses, getline from: Getline/Coprocess. (line 6) -* cos() function: Numeric Functions. (line 14) +* cos: Numeric Functions. (line 15) +* cosine: Numeric Functions. (line 15) * counting: Wc Program. (line 6) * csh utility: Statements/Lines. (line 44) -* csh utility, POSIXLY_CORRECT environment variable: Options. (line 305) -* csh utility, |& operator, comparison with: Two-way I/O. (line 44) -* ctime() user-defined function: Function Example. (line 72) -* currency symbols, localization: Explaining gettext. (line 103) +* csh utility, POSIXLY_CORRECT environment variable: Options. (line 354) +* csh utility, |& operator, comparison with: Two-way I/O. (line 25) +* ctime() user-defined function: Function Example. (line 74) +* currency symbols, localization: Explaining gettext. (line 104) +* current system time: Time Functions. (line 66) * custom.h file: Configuration Philosophy. (line 30) +* customized input parser: Input Parsers. (line 6) +* customized output wrapper: Output Wrappers. (line 6) +* customized two-way processor: Two-way processors. (line 6) * cut utility: Cut Program. (line 6) * cut.awk program: Cut Program. (line 45) -* d debugger command (alias for delete): Breakpoint Control. (line 63) -* d.c., See dark corner: Conventions. (line 38) -* dark corner <1>: Glossary. (line 193) -* dark corner <2>: Truth Values. (line 24) -* dark corner <3>: Assignment Ops. (line 148) -* dark corner: Conventions. (line 38) +* d debugger command (alias for delete): Breakpoint Control. (line 64) +* d.c., See dark corner: Conventions. (line 42) +* dark corner <1>: Glossary. (line 188) +* dark corner: Conventions. (line 42) +* dark corner, "0" is actually true: Truth Values. (line 24) +* dark corner, /= operator vs. /=.../ regexp constant: Assignment Ops. + (line 148) * dark corner, ^, in FS: Regexp Field Splitting. (line 59) * dark corner, array subscripts: Uninitialized Subscripts. (line 43) * dark corner, break statement: Break Statement. (line 51) * dark corner, close() function: Close Files And Pipes. - (line 131) + (line 133) * dark corner, command-line arguments: Assignment Options. (line 43) -* dark corner, continue statement: Continue Statement. (line 43) -* dark corner, CONVFMT variable: Conversion. (line 40) -* dark corner, escape sequences: Other Arguments. (line 31) +* dark corner, continue statement: Continue Statement. (line 44) +* dark corner, CONVFMT variable: Strings And Numbers. (line 40) +* dark corner, escape sequences: Other Arguments. (line 38) * dark corner, escape sequences, for metacharacters: Escape Sequences. - (line 136) + (line 143) * dark corner, exit statement: Exit Statement. (line 30) -* dark corner, field separators: Field Splitting Summary. - (line 47) -* dark corner, FILENAME variable <1>: Auto-set. (line 92) +* dark corner, field separators: Full Line Fields. (line 22) +* dark corner, FILENAME variable <1>: Auto-set. (line 104) * dark corner, FILENAME variable: Getline Notes. (line 19) -* dark corner, FNR/NR variables: Auto-set. (line 207) +* dark corner, FNR/NR variables: Auto-set. (line 328) * dark corner, format-control characters: Control Letters. (line 18) * dark corner, FS as null string: Single Character Fields. (line 20) -* dark corner, input files: Records. (line 98) +* dark corner, input files: awk split records. (line 111) * dark corner, invoking awk: Command Line. (line 16) -* dark corner, length() function: String Functions. (line 182) +* dark corner, length() function: String Functions. (line 187) +* dark corner, locale's decimal point character: Locale influences conversions. + (line 17) * dark corner, multiline records: Multiple Line. (line 35) * dark corner, NF variable, decrementing: Changing Fields. (line 107) * dark corner, OFMT variable: OFMT. (line 27) +* dark corner, regexp as second argument to index(): String Functions. + (line 165) * dark corner, regexp constants: Using Constant Regexps. (line 6) * dark corner, regexp constants, /= operator and: Assignment Ops. @@ -25450,301 +32269,339 @@ Index * dark corner, regexp constants, as arguments to user-defined functions: Using Constant Regexps. (line 43) * dark corner, split() function: String Functions. (line 361) -* dark corner, strings, storing: Records. (line 191) -* dark corner, value of ARGV[0]: Auto-set. (line 35) -* data, fixed-width: Constant Size. (line 9) -* data-driven languages: Basic High Level. (line 83) +* dark corner, strings, storing: gawk split records. (line 83) +* dark corner, value of ARGV[0]: Auto-set. (line 39) +* data, fixed-width: Constant Size. (line 6) +* data-driven languages: Basic High Level. (line 85) * database, group, reading: Group Functions. (line 6) * database, users, reading: Passwd Functions. (line 6) * date utility, GNU: Time Functions. (line 17) -* date utility, POSIX: Time Functions. (line 261) -* dates, converting to timestamps: Time Functions. (line 74) +* date utility, POSIX: Time Functions. (line 254) +* dates, converting to timestamps: Time Functions. (line 76) * dates, information related to, localization: Explaining gettext. - (line 115) + (line 112) * Davies, Stephen <1>: Contributors. (line 74) * Davies, Stephen: Acknowledgments. (line 60) -* dcgettext() function (gawk) <1>: Programmer i18n. (line 19) -* dcgettext() function (gawk): I18N Functions. (line 22) +* Day, Robert P.J.: Acknowledgments. (line 78) +* dcgettext <1>: Programmer i18n. (line 19) +* dcgettext: I18N Functions. (line 22) * dcgettext() function (gawk), portability and: I18N Portability. (line 33) -* dcngettext() function (gawk) <1>: Programmer i18n. (line 36) -* dcngettext() function (gawk): I18N Functions. (line 28) +* dcngettext <1>: Programmer i18n. (line 36) +* dcngettext: I18N Functions. (line 28) * dcngettext() function (gawk), portability and: I18N Portability. (line 33) -* deadlocks: Two-way I/O. (line 70) +* deadlocks: Two-way I/O. (line 52) * debugger commands, b (break): Breakpoint Control. (line 11) -* debugger commands, backtrace: Dgawk Stack. (line 13) +* debugger commands, backtrace: Execution Stack. (line 13) * debugger commands, break: Breakpoint Control. (line 11) -* debugger commands, bt (backtrace): Dgawk Stack. (line 13) -* debugger commands, c (continue): Dgawk Execution Control. +* debugger commands, bt (backtrace): Execution Stack. (line 13) +* debugger commands, c (continue): Debugger Execution Control. (line 33) * debugger commands, clear: Breakpoint Control. (line 36) -* debugger commands, commands: Dgawk Execution Control. +* debugger commands, commands: Debugger Execution Control. (line 10) * debugger commands, condition: Breakpoint Control. (line 54) -* debugger commands, continue: Dgawk Execution Control. +* debugger commands, continue: Debugger Execution Control. (line 33) -* debugger commands, d (delete): Breakpoint Control. (line 63) -* debugger commands, delete: Breakpoint Control. (line 63) -* debugger commands, disable: Breakpoint Control. (line 68) +* debugger commands, d (delete): Breakpoint Control. (line 64) +* debugger commands, delete: Breakpoint Control. (line 64) +* debugger commands, disable: Breakpoint Control. (line 69) * debugger commands, display: Viewing And Changing Data. (line 8) -* debugger commands, down: Dgawk Stack. (line 21) -* debugger commands, dump: Miscellaneous Dgawk Commands. +* debugger commands, down: Execution Stack. (line 23) +* debugger commands, dump: Miscellaneous Debugger Commands. (line 9) -* debugger commands, e (enable): Breakpoint Control. (line 72) -* debugger commands, enable: Breakpoint Control. (line 72) -* debugger commands, end: Dgawk Execution Control. +* debugger commands, e (enable): Breakpoint Control. (line 73) +* debugger commands, enable: Breakpoint Control. (line 73) +* debugger commands, end: Debugger Execution Control. (line 10) * debugger commands, eval: Viewing And Changing Data. (line 23) -* debugger commands, f (frame): Dgawk Stack. (line 25) -* debugger commands, finish: Dgawk Execution Control. +* debugger commands, f (frame): Execution Stack. (line 27) +* debugger commands, finish: Debugger Execution Control. (line 39) -* debugger commands, frame: Dgawk Stack. (line 25) -* debugger commands, h (help): Miscellaneous Dgawk Commands. - (line 68) -* debugger commands, help: Miscellaneous Dgawk Commands. - (line 68) -* debugger commands, i (info): Dgawk Info. (line 12) -* debugger commands, ignore: Breakpoint Control. (line 86) -* debugger commands, info: Dgawk Info. (line 12) -* debugger commands, l (list): Miscellaneous Dgawk Commands. - (line 74) -* debugger commands, list: Miscellaneous Dgawk Commands. - (line 74) -* debugger commands, n (next): Dgawk Execution Control. +* debugger commands, frame: Execution Stack. (line 27) +* debugger commands, h (help): Miscellaneous Debugger Commands. + (line 66) +* debugger commands, help: Miscellaneous Debugger Commands. + (line 66) +* debugger commands, i (info): Debugger Info. (line 13) +* debugger commands, ignore: Breakpoint Control. (line 87) +* debugger commands, info: Debugger Info. (line 13) +* debugger commands, l (list): Miscellaneous Debugger Commands. + (line 72) +* debugger commands, list: Miscellaneous Debugger Commands. + (line 72) +* debugger commands, n (next): Debugger Execution Control. (line 43) -* debugger commands, next: Dgawk Execution Control. +* debugger commands, next: Debugger Execution Control. (line 43) -* debugger commands, nexti: Dgawk Execution Control. +* debugger commands, nexti: Debugger Execution Control. (line 49) -* debugger commands, ni (nexti): Dgawk Execution Control. +* debugger commands, ni (nexti): Debugger Execution Control. (line 49) -* debugger commands, o (option): Dgawk Info. (line 56) -* debugger commands, option: Dgawk Info. (line 56) +* debugger commands, o (option): Debugger Info. (line 57) +* debugger commands, option: Debugger Info. (line 57) * debugger commands, p (print): Viewing And Changing Data. (line 36) * debugger commands, print: Viewing And Changing Data. (line 36) * debugger commands, printf: Viewing And Changing Data. (line 54) -* debugger commands, q (quit): Miscellaneous Dgawk Commands. - (line 101) -* debugger commands, quit: Miscellaneous Dgawk Commands. - (line 101) -* debugger commands, r (run): Dgawk Execution Control. +* debugger commands, q (quit): Miscellaneous Debugger Commands. + (line 99) +* debugger commands, quit: Miscellaneous Debugger Commands. + (line 99) +* debugger commands, r (run): Debugger Execution Control. (line 62) -* debugger commands, return: Dgawk Execution Control. +* debugger commands, return: Debugger Execution Control. (line 54) -* debugger commands, run: Dgawk Execution Control. +* debugger commands, run: Debugger Execution Control. (line 62) -* debugger commands, s (step): Dgawk Execution Control. +* debugger commands, s (step): Debugger Execution Control. (line 68) * debugger commands, set: Viewing And Changing Data. (line 59) -* debugger commands, si (stepi): Dgawk Execution Control. +* debugger commands, si (stepi): Debugger Execution Control. (line 76) -* debugger commands, silent: Dgawk Execution Control. +* debugger commands, silent: Debugger Execution Control. (line 10) -* debugger commands, step: Dgawk Execution Control. +* debugger commands, step: Debugger Execution Control. (line 68) -* debugger commands, stepi: Dgawk Execution Control. +* debugger commands, stepi: Debugger Execution Control. (line 76) -* debugger commands, t (tbreak): Breakpoint Control. (line 89) -* debugger commands, tbreak: Breakpoint Control. (line 89) -* debugger commands, trace: Miscellaneous Dgawk Commands. - (line 110) -* debugger commands, u (until): Dgawk Execution Control. +* debugger commands, t (tbreak): Breakpoint Control. (line 90) +* debugger commands, tbreak: Breakpoint Control. (line 90) +* debugger commands, trace: Miscellaneous Debugger Commands. + (line 108) +* debugger commands, u (until): Debugger Execution Control. (line 83) * debugger commands, undisplay: Viewing And Changing Data. (line 80) -* debugger commands, until: Dgawk Execution Control. +* debugger commands, until: Debugger Execution Control. (line 83) * debugger commands, unwatch: Viewing And Changing Data. (line 84) -* debugger commands, up: Dgawk Stack. (line 33) +* debugger commands, up: Execution Stack. (line 36) * debugger commands, w (watch): Viewing And Changing Data. (line 67) * debugger commands, watch: Viewing And Changing Data. (line 67) +* debugger commands, where (backtrace): Execution Stack. (line 13) +* debugger default list amount: Debugger Info. (line 69) +* debugger history file: Debugger Info. (line 80) +* debugger history size: Debugger Info. (line 65) +* debugger options: Debugger Info. (line 57) +* debugger prompt: Debugger Info. (line 77) +* debugger, how to start: Debugger Invocation. (line 6) +* debugger, read commands from a file: Debugger Info. (line 96) +* debugging awk programs: Debugger. (line 6) * debugging gawk, bug reports: Bugs. (line 9) -* decimal point character, locale specific: Options. (line 215) +* decimal point character, locale specific: Options. (line 270) * decrement operators: Increment Ops. (line 35) * default keyword: Switch Statement. (line 6) * Deifik, Scott <1>: Bugs. (line 70) -* Deifik, Scott <2>: Contributors. (line 54) +* Deifik, Scott <2>: Contributors. (line 53) * Deifik, Scott: Acknowledgments. (line 60) -* delete debugger command: Breakpoint Control. (line 63) +* delete ARRAY: Delete. (line 39) +* delete breakpoint at location: Breakpoint Control. (line 36) +* delete breakpoint by number: Breakpoint Control. (line 64) +* delete debugger command: Breakpoint Control. (line 64) * delete statement: Delete. (line 6) +* delete watchpoint: Viewing And Changing Data. + (line 84) * deleting elements in arrays: Delete. (line 6) * deleting entire arrays: Delete. (line 39) -* dgawk: Debugger. (line 6) -* differences between gawk and awk: String Functions. (line 196) +* Demaille, Akim: Acknowledgments. (line 60) +* describe call stack frame, in debugger: Debugger Info. (line 27) +* differences between gawk and awk: String Functions. (line 201) * differences in awk and gawk, ARGC/ARGV variables: ARGC and ARGV. - (line 88) -* differences in awk and gawk, ARGIND variable: Auto-set. (line 40) + (line 90) +* differences in awk and gawk, ARGIND variable: Auto-set. (line 44) * differences in awk and gawk, array elements, deleting: Delete. (line 39) +* differences in awk and gawk, AWKLIBPATH environment variable: AWKLIBPATH Variable. + (line 6) * differences in awk and gawk, AWKPATH environment variable: AWKPATH Variable. (line 6) * differences in awk and gawk, BEGIN/END patterns: I/O And BEGIN/END. (line 16) +* differences in awk and gawk, BEGINFILE/ENDFILE patterns: BEGINFILE/ENDFILE. + (line 6) * differences in awk and gawk, BINMODE variable <1>: PC Using. - (line 34) + (line 33) * differences in awk and gawk, BINMODE variable: User-modified. - (line 23) + (line 15) * differences in awk and gawk, close() function: Close Files And Pipes. (line 81) -* differences in awk and gawk, ERRNO variable: Auto-set. (line 72) -* differences in awk and gawk, error messages: Special FD. (line 16) +* differences in awk and gawk, command-line directories: Command-line directories. + (line 6) +* differences in awk and gawk, ERRNO variable: Auto-set. (line 88) +* differences in awk and gawk, error messages: Special FD. (line 19) * differences in awk and gawk, FIELDWIDTHS variable: User-modified. - (line 35) -* differences in awk and gawk, FPAT variable: User-modified. (line 45) + (line 37) +* differences in awk and gawk, FPAT variable: User-modified. (line 43) +* differences in awk and gawk, FUNCTAB variable: Auto-set. (line 130) * differences in awk and gawk, function arguments (gawk): Calling Built-in. (line 16) * differences in awk and gawk, getline command: Getline. (line 19) * differences in awk and gawk, IGNORECASE variable: User-modified. - (line 82) + (line 76) * differences in awk and gawk, implementation limitations <1>: Redirection. - (line 135) + (line 129) * differences in awk and gawk, implementation limitations: Getline Notes. (line 14) * differences in awk and gawk, indirect function calls: Indirect Calls. (line 6) * differences in awk and gawk, input/output operators <1>: Redirection. - (line 102) + (line 96) * differences in awk and gawk, input/output operators: Getline/Coprocess. (line 6) * differences in awk and gawk, line continuations: Conditional Exp. (line 34) -* differences in awk and gawk, LINT variable: User-modified. (line 98) +* differences in awk and gawk, LINT variable: User-modified. (line 88) * differences in awk and gawk, match() function: String Functions. - (line 259) -* differences in awk and gawk, next/nextfile statements: Nextfile Statement. - (line 6) + (line 263) * differences in awk and gawk, print/printf statements: Format Modifiers. (line 13) -* differences in awk and gawk, PROCINFO array: Auto-set. (line 123) -* differences in awk and gawk, record separators: Records. (line 112) +* differences in awk and gawk, PROCINFO array: Auto-set. (line 144) +* differences in awk and gawk, read timeouts: Read Timeout. (line 6) +* differences in awk and gawk, record separators: awk split records. + (line 125) * differences in awk and gawk, regexp constants: Using Constant Regexps. (line 43) * differences in awk and gawk, regular expressions: Case-sensitivity. (line 26) -* differences in awk and gawk, RS/RT variables: Records. (line 167) -* differences in awk and gawk, RT variable: Auto-set. (line 196) +* differences in awk and gawk, RS/RT variables: gawk split records. + (line 58) +* differences in awk and gawk, RT variable: Auto-set. (line 279) * differences in awk and gawk, single-character fields: Single Character Fields. (line 6) * differences in awk and gawk, split() function: String Functions. (line 349) * differences in awk and gawk, strings: Scalar Constants. (line 20) -* differences in awk and gawk, strings, storing: Records. (line 187) -* differences in awk and gawk, strtonum() function (gawk): String Functions. - (line 404) +* differences in awk and gawk, strings, storing: gawk split records. + (line 77) +* differences in awk and gawk, SYMTAB variable: Auto-set. (line 283) * differences in awk and gawk, TEXTDOMAIN variable: User-modified. - (line 153) + (line 151) * differences in awk and gawk, trunc-mod operation: Arithmetic Ops. (line 66) -* directories, changing: Sample Library. (line 6) -* directories, command line: Command line directories. +* directories, command-line: Command-line directories. + (line 6) +* directories, searching: Programs Exercises. (line 70) +* directories, searching for loadable extensions: AWKLIBPATH Variable. (line 6) -* directories, searching <1>: Igawk Program. (line 368) -* directories, searching: AWKPATH Variable. (line 6) -* disable debugger command: Breakpoint Control. (line 68) +* directories, searching for source files: AWKPATH Variable. (line 6) +* disable breakpoint: Breakpoint Control. (line 69) +* disable debugger command: Breakpoint Control. (line 69) * display debugger command: Viewing And Changing Data. (line 8) +* display debugger options: Debugger Info. (line 57) +* div: Numeric Functions. (line 18) * division: Arithmetic Ops. (line 44) -* do-while statement <1>: Do Statement. (line 6) -* do-while statement: Regexp Usage. (line 19) +* do-while statement: Do Statement. (line 6) +* do-while statement, use of regexps in: Regexp Usage. (line 19) * documentation, of awk programs: Library Names. (line 6) * documentation, online: Manual History. (line 11) * documents, searching: Dupword Program. (line 6) -* dollar sign ($): Regexp Operators. (line 35) * dollar sign ($), $ field operator <1>: Precedence. (line 43) * dollar sign ($), $ field operator: Fields. (line 19) * dollar sign ($), incrementing fields and arrays: Increment Ops. (line 30) -* double precision floating-point: Basic Data Typing. (line 36) -* double quote (") <1>: Quoting. (line 37) -* double quote ("): Read Terminal. (line 25) -* double quote ("), regexp constants: Computed Regexps. (line 28) -* down debugger command: Dgawk Stack. (line 21) +* dollar sign ($), regexp operator: Regexp Operators. (line 35) +* double quote ("), in regexp constants: Computed Regexps. (line 29) +* double quote ("), in shell commands: Quoting. (line 54) +* down debugger command: Execution Stack. (line 23) * Drepper, Ulrich: Acknowledgments. (line 52) -* DuBois, John: Acknowledgments. (line 60) -* dump debugger command: Miscellaneous Dgawk Commands. +* Duman, Patrice: Acknowledgments. (line 74) +* dump all variables of a program: Options. (line 93) +* dump debugger command: Miscellaneous Debugger Commands. (line 9) -* dupnode() internal function: Internals. (line 87) * dupword.awk program: Dupword Program. (line 31) -* e debugger command (alias for enable): Breakpoint Control. (line 72) +* dynamic profiling: Profiling. (line 178) +* dynamically loaded extensions: Dynamic Extensions. (line 6) +* e debugger command (alias for enable): Breakpoint Control. (line 73) * EBCDIC: Ordinal Functions. (line 45) +* effective group ID of gawk user: Auto-set. (line 149) +* effective user ID of gawk user: Auto-set. (line 153) * egrep utility <1>: Egrep Program. (line 6) -* egrep utility: Bracket Expressions. (line 24) +* egrep utility: Bracket Expressions. (line 26) * egrep.awk program: Egrep Program. (line 54) -* elements in arrays: Reference to Elements. - (line 6) -* elements in arrays, assigning: Assigning Elements. (line 6) +* elements in arrays, assigning values: Assigning Elements. (line 6) * elements in arrays, deleting: Delete. (line 6) -* elements in arrays, order of: Scanning an Array. (line 48) +* elements in arrays, order of access by in operator: Scanning an Array. + (line 48) * elements in arrays, scanning: Scanning an Array. (line 6) +* elements of arrays: Reference to Elements. + (line 6) * email address for bug reports, bug-gawk@gnu.org: Bugs. (line 30) * EMISTERED: TCP/IP Networking. (line 6) +* empty array elements: Reference to Elements. + (line 18) * empty pattern: Empty. (line 6) +* empty strings: awk split records. (line 115) * empty strings, See null strings: Regexp Field Splitting. (line 43) -* enable debugger command: Breakpoint Control. (line 72) -* end debugger command: Dgawk Execution Control. +* enable breakpoint: Breakpoint Control. (line 73) +* enable debugger command: Breakpoint Control. (line 73) +* end debugger command: Debugger Execution Control. (line 10) +* END pattern <1>: Using BEGIN/END. (line 6) * END pattern: BEGIN/END. (line 6) +* END pattern, and profiling: Profiling. (line 62) * END pattern, assert() user-defined function and: Assert Function. (line 75) -* END pattern, backslash continuation and: Egrep Program. (line 220) -* END pattern, Boolean patterns and: Expression Patterns. (line 73) +* END pattern, Boolean patterns and: Expression Patterns. (line 69) * END pattern, exit statement and: Exit Statement. (line 12) * END pattern, next/nextfile statements and <1>: Next Statement. - (line 45) + (line 44) * END pattern, next/nextfile statements and: I/O And BEGIN/END. (line 37) * END pattern, operators and: Using BEGIN/END. (line 17) -* END pattern, pgawk program: Profiling. (line 65) * END pattern, print statement and: I/O And BEGIN/END. (line 16) * ENDFILE pattern: BEGINFILE/ENDFILE. (line 6) -* ENDFILE pattern, Boolean patterns and: Expression Patterns. (line 73) -* endfile() user-defined function: Filetrans Function. (line 62) -* endgrent() function (C library): Group Functions. (line 215) -* endgrent() user-defined function: Group Functions. (line 218) -* endpwent() function (C library): Passwd Functions. (line 210) -* endpwent() user-defined function: Passwd Functions. (line 213) -* ENVIRON array <1>: Internals. (line 140) +* ENDFILE pattern, Boolean patterns and: Expression Patterns. (line 69) +* endfile() user-defined function: Filetrans Function. (line 61) +* endgrent() function (C library): Group Functions. (line 211) +* endgrent() user-defined function: Group Functions. (line 214) +* endpwent() function (C library): Passwd Functions. (line 207) +* endpwent() user-defined function: Passwd Functions. (line 210) +* English, Steve: Advanced Features. (line 6) * ENVIRON array: Auto-set. (line 60) -* environment variables: Auto-set. (line 60) -* epoch, definition of: Glossary. (line 239) +* environment variables used by gawk: Environment Variables. + (line 6) +* environment variables, in ENVIRON array: Auto-set. (line 60) +* epoch, definition of: Glossary. (line 234) * equals sign (=), = operator: Assignment Ops. (line 6) * equals sign (=), == operator <1>: Precedence. (line 65) * equals sign (=), == operator: Comparison Operators. (line 11) -* EREs (Extended Regular Expressions): Bracket Expressions. (line 24) -* ERRNO variable <1>: Internals. (line 130) -* ERRNO variable <2>: TCP/IP Networking. (line 54) -* ERRNO variable <3>: Auto-set. (line 72) -* ERRNO variable <4>: BEGINFILE/ENDFILE. (line 26) -* ERRNO variable <5>: Close Files And Pipes. - (line 139) -* ERRNO variable: Getline. (line 19) -* error handling: Special FD. (line 16) -* error handling, ERRNO variable and: Auto-set. (line 72) +* EREs (Extended Regular Expressions): Bracket Expressions. (line 26) +* ERRNO variable <1>: TCP/IP Networking. (line 54) +* ERRNO variable: Auto-set. (line 88) +* ERRNO variable, with BEGINFILE pattern: BEGINFILE/ENDFILE. (line 26) +* ERRNO variable, with close() function: Close Files And Pipes. + (line 141) +* ERRNO variable, with getline command: Getline. (line 19) +* error handling: Special FD. (line 19) +* error handling, ERRNO variable and: Auto-set. (line 88) * error output: Special FD. (line 6) * escape processing, gsub()/gensub()/sub() functions: Gory Details. (line 6) -* escape sequences: Escape Sequences. (line 6) +* escape sequences, in strings: Escape Sequences. (line 6) * eval debugger command: Viewing And Changing Data. (line 23) -* evaluation order: Increment Ops. (line 61) -* evaluation order, concatenation: Concatenation. (line 42) +* evaluate expressions, in debugger: Viewing And Changing Data. + (line 23) +* evaluation order: Increment Ops. (line 60) +* evaluation order, concatenation: Concatenation. (line 41) * evaluation order, functions: Calling Built-in. (line 30) * examining fields: Fields. (line 6) -* exclamation point (!), ! operator <1>: Egrep Program. (line 170) +* exclamation point (!), ! operator <1>: Egrep Program. (line 175) * exclamation point (!), ! operator <2>: Precedence. (line 52) -* exclamation point (!), ! operator: Boolean Ops. (line 67) +* exclamation point (!), ! operator: Boolean Ops. (line 69) * exclamation point (!), != operator <1>: Precedence. (line 65) * exclamation point (!), != operator: Comparison Operators. (line 11) @@ -25754,13 +32611,18 @@ Index * exclamation point (!), !~ operator <3>: Comparison Operators. (line 11) * exclamation point (!), !~ operator <4>: Regexp Constants. (line 6) -* exclamation point (!), !~ operator <5>: Computed Regexps. (line 6) -* exclamation point (!), !~ operator <6>: Case-sensitivity. (line 26) +* exclamation point (!), !~ operator <5>: Case-sensitivity. (line 26) +* exclamation point (!), !~ operator <6>: Computed Regexps. (line 6) * exclamation point (!), !~ operator: Regexp Usage. (line 19) * exit statement: Exit Statement. (line 6) * exit status, of gawk: Exit Status. (line 6) -* exp() function: Numeric Functions. (line 17) -* expand utility: Very Simple. (line 69) +* exit status, of VMS: VMS Running. (line 28) +* exit the debugger: Miscellaneous Debugger Commands. + (line 99) +* exp: Numeric Functions. (line 33) +* expand utility: Very Simple. (line 73) +* Expat XML parser library: gawkextlib. (line 33) +* exponent: Numeric Functions. (line 33) * expressions: Expressions. (line 6) * expressions, as patterns: Expression Patterns. (line 6) * expressions, assignment: Assignment Ops. (line 6) @@ -25771,63 +32633,75 @@ Index * expressions, matching, See comparison expressions: Typing and Comparison. (line 9) * expressions, selecting: Conditional Exp. (line 6) -* Extended Regular Expressions (EREs): Bracket Expressions. (line 24) -* eXtensible Markup Language (XML): Internals. (line 151) -* extension() function (gawk): Using Internal File Ops. - (line 15) -* extensions, Brian Kernighan's awk <1>: Other Versions. (line 13) +* Extended Regular Expressions (EREs): Bracket Expressions. (line 26) +* extension API: Extension API Description. + (line 6) +* extension API informational variables: Extension API Informational Variables. + (line 6) +* extension API version: Extension Versioning. + (line 6) +* extension API, version number: Auto-set. (line 246) +* extension example: Extension Example. (line 6) +* extension registration: Registration Functions. + (line 6) +* extension search path: Finding Extensions. (line 6) +* extensions distributed with gawk: Extension Samples. (line 6) +* extensions, allocating memory: Memory Allocation Functions. + (line 6) +* extensions, Brian Kernighan's awk <1>: Common Extensions. (line 6) * extensions, Brian Kernighan's awk: BTL. (line 6) -* extensions, common, ** operator: Arithmetic Ops. (line 36) -* extensions, common, **= operator: Assignment Ops. (line 136) -* extensions, common, /dev/stderr special file: Special FD. (line 46) -* extensions, common, /dev/stdin special file: Special FD. (line 46) -* extensions, common, /dev/stdout special file: Special FD. (line 46) +* extensions, common, ** operator: Arithmetic Ops. (line 30) +* extensions, common, **= operator: Assignment Ops. (line 137) +* extensions, common, /dev/stderr special file: Special FD. (line 48) +* extensions, common, /dev/stdin special file: Special FD. (line 48) +* extensions, common, /dev/stdout special file: Special FD. (line 48) * extensions, common, \x escape sequence: Escape Sequences. (line 61) -* extensions, common, BINMODE variable: PC Using. (line 34) +* extensions, common, BINMODE variable: PC Using. (line 33) * extensions, common, delete to delete entire arrays: Delete. (line 39) -* extensions, common, fflush() function: I/O Functions. (line 25) -* extensions, common, func keyword: Definition Syntax. (line 83) +* extensions, common, fflush() function: I/O Functions. (line 43) +* extensions, common, func keyword: Definition Syntax. (line 93) * extensions, common, length() applied to an array: String Functions. - (line 196) -* extensions, common, nextfile statement: Nextfile Statement. (line 6) -* extensions, common, RS as a regexp: Records. (line 115) + (line 201) +* extensions, common, RS as a regexp: gawk split records. (line 6) * extensions, common, single character fields: Single Character Fields. (line 6) * extensions, in gawk, not in POSIX awk: POSIX/GNU. (line 6) -* extract.awk program: Extract Program. (line 78) +* extensions, loading, @load directive: Loading Shared Libraries. + (line 8) +* extensions, mawk: Common Extensions. (line 6) +* extensions, where to find: gawkextlib. (line 6) +* extract.awk program: Extract Program. (line 79) * extraction, of marked strings (internationalization): String Extraction. (line 6) -* f debugger command (alias for frame): Dgawk Stack. (line 25) +* f debugger command (alias for frame): Execution Stack. (line 27) * false, logical: Truth Values. (line 6) * FDL (Free Documentation License): GNU Free Documentation License. - (line 6) + (line 7) * features, adding to gawk: Adding Code. (line 6) -* features, advanced, See advanced features: Obsolete. (line 6) * features, deprecated: Obsolete. (line 6) * features, undocumented: Undocumented. (line 6) -* Fenlason, Jay <1>: Contributors. (line 19) +* Fenlason, Jay <1>: Contributors. (line 18) * Fenlason, Jay: History. (line 30) -* fflush() function: I/O Functions. (line 25) +* fflush: I/O Functions. (line 28) * field numbers: Nonconstant Fields. (line 6) * field operator $: Fields. (line 19) * field operators, dollar sign as: Fields. (line 19) -* field separators <1>: User-modified. (line 56) -* field separators: Field Separators. (line 14) -* field separators, choice of: Field Separators. (line 50) -* field separators, FIELDWIDTHS variable and: User-modified. (line 35) -* field separators, FPAT variable and: User-modified. (line 45) -* field separators, in multiline records: Multiple Line. (line 41) -* field separators, on command line: Command Line Field Separator. +* field separator, in multiline records: Multiple Line. (line 41) +* field separator, on command line: Command Line Field Separator. (line 6) -* field separators, POSIX and <1>: Field Splitting Summary. - (line 41) +* field separator, POSIX and: Full Line Fields. (line 16) +* field separators <1>: User-modified. (line 50) +* field separators: Field Separators. (line 15) +* field separators, choice of: Field Separators. (line 51) +* field separators, FIELDWIDTHS variable and: User-modified. (line 37) +* field separators, FPAT variable and: User-modified. (line 43) * field separators, POSIX and: Fields. (line 6) * field separators, regular expressions as <1>: Regexp Field Splitting. (line 6) -* field separators, regular expressions as: Field Separators. (line 50) +* field separators, regular expressions as: Field Separators. (line 51) * field separators, See Also OFS: Changing Fields. (line 64) -* field separators, spaces as: Cut Program. (line 109) -* fields <1>: Basic High Level. (line 71) +* field separators, spaces as: Cut Program. (line 103) +* fields <1>: Basic High Level. (line 73) * fields <2>: Fields. (line 6) * fields: Reading Files. (line 14) * fields, adding: Changing Fields. (line 53) @@ -25837,141 +32711,151 @@ Index * fields, number of: Fields. (line 33) * fields, numbers: Nonconstant Fields. (line 6) * fields, printing: Print Examples. (line 21) -* fields, separating: Field Separators. (line 14) +* fields, separating: Field Separators. (line 15) * fields, single-character: Single Character Fields. (line 6) -* FIELDWIDTHS variable <1>: User-modified. (line 35) +* FIELDWIDTHS variable <1>: User-modified. (line 37) * FIELDWIDTHS variable: Constant Size. (line 22) * file descriptors: Special FD. (line 6) -* file names, distinguishing: Auto-set. (line 52) +* file inclusion, @include directive: Include Files. (line 8) +* file names, distinguishing: Auto-set. (line 56) * file names, in compatibility mode: Special Caveats. (line 9) -* file names, standard streams in gawk: Special FD. (line 46) -* FILENAME variable <1>: Auto-set. (line 92) +* file names, standard streams in gawk: Special FD. (line 48) +* FILENAME variable <1>: Auto-set. (line 104) * FILENAME variable: Reading Files. (line 6) * FILENAME variable, getline, setting with: Getline Notes. (line 19) * filenames, assignments as: Ignoring Assigns. (line 6) -* files, .mo: Explaining gettext. (line 41) -* files, .mo, converting from .po: I18N Example. (line 62) -* files, .mo, specifying directory of <1>: Programmer i18n. (line 47) -* files, .mo, specifying directory of: Explaining gettext. (line 53) +* files, .gmo: Explaining gettext. (line 42) +* files, .gmo, specifying directory of <1>: Programmer i18n. (line 47) +* files, .gmo, specifying directory of: Explaining gettext. (line 54) +* files, .mo, converting from .po: I18N Example. (line 64) * files, .po <1>: Translator i18n. (line 6) -* files, .po: Explaining gettext. (line 36) -* files, .po, converting to .mo: I18N Example. (line 62) -* files, .pot: Explaining gettext. (line 30) -* files, /dev/... special files: Special FD. (line 46) +* files, .po: Explaining gettext. (line 37) +* files, .po, converting to .mo: I18N Example. (line 64) +* files, .pot: Explaining gettext. (line 31) +* files, /dev/... special files: Special FD. (line 48) * files, /inet/... (gawk): TCP/IP Networking. (line 6) * files, /inet4/... (gawk): TCP/IP Networking. (line 6) * files, /inet6/... (gawk): TCP/IP Networking. (line 6) -* files, as single records: Records. (line 196) * files, awk programs in: Long. (line 6) -* files, awkprof.out: Profiling. (line 10) -* files, awkvars.out: Options. (line 90) +* files, awkprof.out: Profiling. (line 6) +* files, awkvars.out: Options. (line 93) * files, closing: I/O Functions. (line 10) * files, descriptors, See file descriptors: Special FD. (line 6) * files, group: Group Functions. (line 6) -* files, information about, retrieving: Sample Library. (line 6) * files, initialization and cleanup: Filetrans Function. (line 6) * files, input, See input files: Read Terminal. (line 17) * files, log, timestamps in: Time Functions. (line 6) * files, managing: Data File Management. (line 6) * files, managing, data file boundaries: Filetrans Function. (line 6) -* files, message object: Explaining gettext. (line 41) +* files, message object: Explaining gettext. (line 42) * files, message object, converting from portable object files: I18N Example. - (line 62) + (line 64) * files, message object, specifying directory of <1>: Programmer i18n. (line 47) * files, message object, specifying directory of: Explaining gettext. - (line 53) -* files, multiple passes over: Other Arguments. (line 49) + (line 54) +* files, multiple passes over: Other Arguments. (line 56) * files, multiple, duplicating output into: Tee Program. (line 6) * files, output, See output files: Close Files And Pipes. (line 6) * files, password: Passwd Functions. (line 16) * files, portable object <1>: Translator i18n. (line 6) -* files, portable object: Explaining gettext. (line 36) -* files, portable object template: Explaining gettext. (line 30) +* files, portable object: Explaining gettext. (line 37) +* files, portable object template: Explaining gettext. (line 31) * files, portable object, converting to message object files: I18N Example. - (line 62) -* files, portable object, generating: Options. (line 135) -* files, processing, ARGIND variable and: Auto-set. (line 47) + (line 64) +* files, portable object, generating: Options. (line 147) +* files, processing, ARGIND variable and: Auto-set. (line 51) * files, reading: Rewind Function. (line 6) * files, reading, multiline records: Multiple Line. (line 6) * files, searching for regular expressions: Egrep Program. (line 6) * files, skipping: File Checking. (line 6) -* files, source, search path for: Igawk Program. (line 368) +* files, source, search path for: Programs Exercises. (line 70) * files, splitting: Split Program. (line 6) * files, Texinfo, extracting programs from: Extract Program. (line 6) -* finish debugger command: Dgawk Execution Control. +* find substring in string: String Functions. (line 156) +* finding extensions: Finding Extensions. (line 6) +* finish debugger command: Debugger Execution Control. (line 39) -* Fish, Fred: Contributors. (line 51) -* fixed-width data: Constant Size. (line 9) +* Fish, Fred: Contributors. (line 50) +* fixed-width data: Constant Size. (line 6) * flag variables <1>: Tee Program. (line 20) -* flag variables: Boolean Ops. (line 67) -* floating-point, numbers <1>: Unexpected Results. (line 6) -* floating-point, numbers: Basic Data Typing. (line 21) -* floating-point, numbers, AWKNUM internal type: Internals. (line 19) -* FNR variable <1>: Auto-set. (line 102) +* flag variables: Boolean Ops. (line 69) +* floating-point, numbers, arbitrary precision: Arbitrary Precision Arithmetic. + (line 6) +* floating-point, VAX/VMS: VMS Running. (line 50) +* flush buffered output: I/O Functions. (line 28) +* fnmatch() extension function: Extension Sample Fnmatch. + (line 12) +* FNR variable <1>: Auto-set. (line 114) * FNR variable: Records. (line 6) -* FNR variable, changing: Auto-set. (line 207) +* FNR variable, changing: Auto-set. (line 328) * for statement: For Statement. (line 6) -* for statement, in arrays: Scanning an Array. (line 20) -* force_number() internal function: Internals. (line 27) -* force_string() internal function: Internals. (line 32) -* force_wstring() internal function: Internals. (line 37) +* for statement, looping over arrays: Scanning an Array. (line 20) +* fork() extension function: Extension Sample Fork. + (line 11) +* format specifiers: Basic Printf. (line 15) * format specifiers, mixing regular with positional specifiers: Printf Ordering. (line 57) * format specifiers, printf statement: Control Letters. (line 6) * format specifiers, strftime() function (gawk): Time Functions. - (line 87) -* format strings: Basic Printf. (line 15) + (line 89) +* format time string: Time Functions. (line 48) * formats, numeric output: OFMT. (line 6) * formatting output: Printf. (line 6) -* forward slash (/): Regexp. (line 10) +* formatting strings: String Functions. (line 383) +* forward slash (/) to enclose regular expressions: Regexp. (line 10) * forward slash (/), / operator: Precedence. (line 55) * forward slash (/), /= operator <1>: Precedence. (line 95) -* forward slash (/), /= operator: Assignment Ops. (line 129) +* forward slash (/), /= operator: Assignment Ops. (line 130) * forward slash (/), /= operator, vs. /=.../ regexp constant: Assignment Ops. (line 148) * forward slash (/), patterns and: Expression Patterns. (line 24) -* FPAT variable <1>: User-modified. (line 45) +* FPAT variable <1>: User-modified. (line 43) * FPAT variable: Splitting By Content. - (line 26) -* frame debugger command: Dgawk Stack. (line 25) + (line 25) +* frame debugger command: Execution Stack. (line 27) * Free Documentation License (FDL): GNU Free Documentation License. - (line 6) -* Free Software Foundation (FSF) <1>: Glossary. (line 301) + (line 7) +* Free Software Foundation (FSF) <1>: Glossary. (line 288) * Free Software Foundation (FSF) <2>: Getting. (line 10) * Free Software Foundation (FSF): Manual History. (line 6) * FreeBSD: Glossary. (line 611) -* FS variable <1>: User-modified. (line 56) -* FS variable: Field Separators. (line 14) +* FS variable <1>: User-modified. (line 50) +* FS variable: Field Separators. (line 15) * FS variable, --field-separator option and: Options. (line 21) * FS variable, as null string: Single Character Fields. (line 20) -* FS variable, as TAB character: Options. (line 211) -* FS variable, changing value of: Field Separators. (line 34) -* FS variable, running awk programs and: Cut Program. (line 68) +* FS variable, as TAB character: Options. (line 266) +* FS variable, changing value of: Field Separators. (line 35) +* FS variable, running awk programs and: Cut Program. (line 63) * FS variable, setting from command line: Command Line Field Separator. (line 6) * FS, containing ^: Regexp Field Splitting. (line 59) -* FSF (Free Software Foundation) <1>: Glossary. (line 301) +* FS, in multiline records: Multiple Line. (line 41) +* FSF (Free Software Foundation) <1>: Glossary. (line 288) * FSF (Free Software Foundation) <2>: Getting. (line 10) * FSF (Free Software Foundation): Manual History. (line 6) +* fts() extension function: Extension Sample File Functions. + (line 61) +* FUNCTAB array: Auto-set. (line 130) * function calls: Function Calls. (line 6) * function calls, indirect: Indirect Calls. (line 6) +* function calls, indirect, @-notation for: Indirect Calls. (line 47) +* function definition example: Function Example. (line 6) * function pointers: Indirect Calls. (line 6) * functions, arrays as parameters to: Pass By Value/Reference. - (line 47) + (line 44) * functions, built-in <1>: Functions. (line 6) * functions, built-in: Function Calls. (line 10) -* functions, built-in, adding to gawk: Dynamic Extensions. (line 10) * functions, built-in, evaluation order: Calling Built-in. (line 30) -* functions, defining: Definition Syntax. (line 6) +* functions, defining: Definition Syntax. (line 9) * functions, library: Library Functions. (line 6) * functions, library, assertions: Assert Function. (line 6) -* functions, library, associative arrays and: Library Names. (line 57) +* functions, library, associative arrays and: Library Names. (line 58) * functions, library, C library: Getopt Function. (line 6) * functions, library, character values as numbers: Ordinal Functions. (line 6) @@ -25984,259 +32868,278 @@ Index (line 6) * functions, library, managing data files: Data File Management. (line 6) -* functions, library, managing time: Gettimeofday Function. +* functions, library, managing time: Getlocaltime Function. (line 6) * functions, library, merging arrays into strings: Join Function. (line 6) * functions, library, rounding numbers: Round Function. (line 6) * functions, library, user database, reading: Passwd Functions. (line 6) -* functions, names of <1>: Definition Syntax. (line 20) -* functions, names of: Arrays. (line 18) -* functions, recursive: Definition Syntax. (line 73) -* functions, return values, setting: Internals. (line 130) +* functions, names of: Definition Syntax. (line 23) +* functions, recursive: Definition Syntax. (line 83) * functions, string-translation: I18N Functions. (line 6) * functions, undefined: Pass By Value/Reference. - (line 71) + (line 68) * functions, user-defined: User-defined. (line 6) -* functions, user-defined, calling: Calling A Function. (line 6) -* functions, user-defined, counts: Profiling. (line 132) +* functions, user-defined, calling: Function Caveats. (line 6) +* functions, user-defined, counts, in a profile: Profiling. (line 137) * functions, user-defined, library of: Library Functions. (line 6) * functions, user-defined, next/nextfile statements and <1>: Nextfile Statement. - (line 44) + (line 47) * functions, user-defined, next/nextfile statements and: Next Statement. - (line 45) -* G-d: Acknowledgments. (line 81) -* Garfinkle, Scott: Contributors. (line 35) -* gawk, ARGIND variable in: Other Arguments. (line 12) + (line 44) +* G-d: Acknowledgments. (line 94) +* Garfinkle, Scott: Contributors. (line 34) +* gawk program, dynamic profiling: Profiling. (line 178) +* gawk version: Auto-set. (line 221) +* gawk, ARGIND variable in: Other Arguments. (line 15) * gawk, awk and <1>: This Manual. (line 14) -* gawk, awk and: Preface. (line 23) -* gawk, bitwise operations in: Bitwise Functions. (line 39) +* gawk, awk and: Preface. (line 21) +* gawk, bitwise operations in: Bitwise Functions. (line 40) * gawk, break statement in: Break Statement. (line 51) -* gawk, built-in variables and: Built-in Variables. (line 14) -* gawk, character classes and: Bracket Expressions. (line 90) +* gawk, character classes and: Bracket Expressions. (line 100) * gawk, coding style in: Adding Code. (line 38) -* gawk, command-line options: GNU Regexp Operators. +* gawk, command-line options, and regular expressions: GNU Regexp Operators. (line 70) -* gawk, comparison operators and: Comparison Operators. - (line 50) * gawk, configuring: Configuration Philosophy. (line 6) * gawk, configuring, options: Additional Configuration Options. (line 6) -* gawk, continue statement in: Continue Statement. (line 43) +* gawk, continue statement in: Continue Statement. (line 44) * gawk, distribution: Distribution contents. (line 6) * gawk, ERRNO variable in <1>: TCP/IP Networking. (line 54) -* gawk, ERRNO variable in <2>: Auto-set. (line 72) +* gawk, ERRNO variable in <2>: Auto-set. (line 88) * gawk, ERRNO variable in <3>: BEGINFILE/ENDFILE. (line 26) * gawk, ERRNO variable in <4>: Close Files And Pipes. - (line 139) + (line 141) * gawk, ERRNO variable in: Getline. (line 19) -* gawk, escape sequences: Escape Sequences. (line 125) -* gawk, extensions, disabling: Options. (line 199) +* gawk, escape sequences: Escape Sequences. (line 120) +* gawk, extensions, disabling: Options. (line 254) * gawk, features, adding: Adding Code. (line 6) * gawk, features, advanced: Advanced Features. (line 6) -* gawk, fflush() function in: I/O Functions. (line 44) -* gawk, field separators and: User-modified. (line 77) -* gawk, FIELDWIDTHS variable in <1>: User-modified. (line 35) +* gawk, field separators and: User-modified. (line 71) +* gawk, FIELDWIDTHS variable in <1>: User-modified. (line 37) * gawk, FIELDWIDTHS variable in: Constant Size. (line 22) * gawk, file names in: Special Files. (line 6) * gawk, format-control characters: Control Letters. (line 18) -* gawk, FPAT variable in <1>: User-modified. (line 45) +* gawk, FPAT variable in <1>: User-modified. (line 43) * gawk, FPAT variable in: Splitting By Content. - (line 26) + (line 25) +* gawk, FUNCTAB array in: Auto-set. (line 130) * gawk, function arguments and: Calling Built-in. (line 16) -* gawk, functions, adding: Dynamic Extensions. (line 10) * gawk, hexadecimal numbers and: Nondecimal-numbers. (line 42) * gawk, IGNORECASE variable in <1>: Array Sorting Functions. - (line 78) -* gawk, IGNORECASE variable in <2>: String Functions. (line 29) -* gawk, IGNORECASE variable in <3>: Array Intro. (line 92) -* gawk, IGNORECASE variable in <4>: User-modified. (line 82) + (line 83) +* gawk, IGNORECASE variable in <2>: String Functions. (line 58) +* gawk, IGNORECASE variable in <3>: Array Intro. (line 94) +* gawk, IGNORECASE variable in <4>: User-modified. (line 76) * gawk, IGNORECASE variable in: Case-sensitivity. (line 26) * gawk, implementation issues: Notes. (line 6) * gawk, implementation issues, debugging: Compatibility Mode. (line 6) * gawk, implementation issues, downward compatibility: Compatibility Mode. (line 6) * gawk, implementation issues, limits: Getline Notes. (line 14) -* gawk, implementation issues, pipes: Redirection. (line 135) +* gawk, implementation issues, pipes: Redirection. (line 129) * gawk, installing: Installation. (line 6) -* gawk, internals: Internals. (line 6) * gawk, internationalization and, See internationalization: Internationalization. (line 13) * gawk, interpreter, adding code to: Using Internal File Ops. (line 6) * gawk, interval expressions and: Regexp Operators. (line 139) * gawk, line continuation in: Conditional Exp. (line 34) -* gawk, LINT variable in: User-modified. (line 98) +* gawk, LINT variable in: User-modified. (line 88) * gawk, list of contributors to: Contributors. (line 6) -* gawk, MS-DOS version of: PC Using. (line 11) -* gawk, MS-Windows version of: PC Using. (line 11) +* gawk, MS-DOS version of: PC Using. (line 10) +* gawk, MS-Windows version of: PC Using. (line 10) * gawk, newlines in: Statements/Lines. (line 12) * gawk, octal numbers and: Nondecimal-numbers. (line 42) -* gawk, OS/2 version of: PC Using. (line 11) -* gawk, PROCINFO array in <1>: Two-way I/O. (line 116) -* gawk, PROCINFO array in <2>: Time Functions. (line 46) -* gawk, PROCINFO array in: Auto-set. (line 123) +* gawk, OS/2 version of: PC Using. (line 16) +* gawk, predefined variables and: Built-in Variables. (line 14) +* gawk, PROCINFO array in <1>: Two-way I/O. (line 99) +* gawk, PROCINFO array in <2>: Time Functions. (line 47) +* gawk, PROCINFO array in: Auto-set. (line 144) * gawk, regexp constants and: Using Constant Regexps. (line 28) * gawk, regular expressions, case sensitivity: Case-sensitivity. (line 26) * gawk, regular expressions, operators: GNU Regexp Operators. (line 6) -* gawk, regular expressions, precedence: Regexp Operators. (line 157) -* gawk, RT variable in <1>: Auto-set. (line 196) -* gawk, RT variable in <2>: Getline/Variable/File. - (line 10) -* gawk, RT variable in <3>: Multiple Line. (line 129) -* gawk, RT variable in: Records. (line 112) -* gawk, See Also awk: Preface. (line 36) +* gawk, regular expressions, precedence: Regexp Operators. (line 161) +* gawk, RT variable in <1>: Auto-set. (line 279) +* gawk, RT variable in <2>: Multiple Line. (line 129) +* gawk, RT variable in: awk split records. (line 125) +* gawk, See Also awk: Preface. (line 34) * gawk, source code, obtaining: Getting. (line 6) * gawk, splitting fields and: Constant Size. (line 87) * gawk, string-translation functions: I18N Functions. (line 6) -* gawk, TEXTDOMAIN variable in: User-modified. (line 153) +* gawk, SYMTAB array in: Auto-set. (line 283) +* gawk, TEXTDOMAIN variable in: User-modified. (line 151) * gawk, timestamps: Time Functions. (line 6) -* gawk, uses for: Preface. (line 36) -* gawk, versions of, information about, printing: Options. (line 250) +* gawk, uses for: Preface. (line 34) +* gawk, versions of, information about, printing: Options. (line 300) * gawk, VMS version of: VMS Installation. (line 6) * gawk, word-boundary operator: GNU Regexp Operators. (line 63) -* General Public License (GPL): Glossary. (line 310) +* gawkextlib: gawkextlib. (line 6) +* gawkextlib project: gawkextlib. (line 6) +* gawklibpath_append shell function: Shell Startup Files. (line 29) +* gawklibpath_default shell function: Shell Startup Files. (line 22) +* gawklibpath_prepend shell function: Shell Startup Files. (line 25) +* gawkpath_append shell function: Shell Startup Files. (line 19) +* gawkpath_default shell function: Shell Startup Files. (line 12) +* gawkpath_prepend shell function: Shell Startup Files. (line 15) +* General Public License (GPL): Glossary. (line 305) * General Public License, See GPL: Manual History. (line 11) -* gensub() function (gawk) <1>: String Functions. (line 86) -* gensub() function (gawk): Using Constant Regexps. +* generate time values: Time Functions. (line 25) +* gensub <1>: String Functions. (line 90) +* gensub: Using Constant Regexps. (line 43) * gensub() function (gawk), escape processing: Gory Details. (line 6) -* get_actual_argument() internal function: Internals. (line 116) -* get_argument() internal function: Internals. (line 111) -* get_array_argument() internal macro: Internals. (line 127) -* get_record() input method: Internals. (line 151) -* get_scalar_argument() internal macro: Internals. (line 124) * getaddrinfo() function (C library): TCP/IP Networking. (line 38) * getgrent() function (C library): Group Functions. (line 6) * getgrent() user-defined function: Group Functions. (line 6) -* getgrgid() function (C library): Group Functions. (line 186) -* getgrgid() user-defined function: Group Functions. (line 189) -* getgrnam() function (C library): Group Functions. (line 175) -* getgrnam() user-defined function: Group Functions. (line 180) -* getgruser() function (C library): Group Functions. (line 195) -* getgruser() function, user-defined: Group Functions. (line 198) +* getgrgid() function (C library): Group Functions. (line 182) +* getgrgid() user-defined function: Group Functions. (line 185) +* getgrnam() function (C library): Group Functions. (line 171) +* getgrnam() user-defined function: Group Functions. (line 176) +* getgruser() function (C library): Group Functions. (line 191) +* getgruser() function, user-defined: Group Functions. (line 194) * getline command: Reading Files. (line 20) * getline command, _gr_init() user-defined function: Group Functions. - (line 82) + (line 83) * getline command, _pw_init() function: Passwd Functions. (line 154) * getline command, coprocesses, using from <1>: Close Files And Pipes. (line 6) * getline command, coprocesses, using from: Getline/Coprocess. (line 6) -* getline command, deadlock and: Two-way I/O. (line 70) +* getline command, deadlock and: Two-way I/O. (line 52) * getline command, explicit input with: Getline. (line 6) * getline command, FILENAME variable and: Getline Notes. (line 19) * getline command, return values: Getline. (line 19) * getline command, variants: Getline Summary. (line 6) +* getline from a file: Getline/File. (line 6) +* getline into a variable: Getline/Variable. (line 6) * getline statement, BEGINFILE/ENDFILE patterns and: BEGINFILE/ENDFILE. (line 54) +* getlocaltime() user-defined function: Getlocaltime Function. + (line 16) * getopt() function (C library): Getopt Function. (line 15) * getopt() user-defined function: Getopt Function. (line 108) * getpwent() function (C library): Passwd Functions. (line 16) * getpwent() user-defined function: Passwd Functions. (line 16) -* getpwnam() function (C library): Passwd Functions. (line 177) -* getpwnam() user-defined function: Passwd Functions. (line 182) -* getpwuid() function (C library): Passwd Functions. (line 188) -* getpwuid() user-defined function: Passwd Functions. (line 192) +* getpwnam() function (C library): Passwd Functions. (line 174) +* getpwnam() user-defined function: Passwd Functions. (line 179) +* getpwuid() function (C library): Passwd Functions. (line 185) +* getpwuid() user-defined function: Passwd Functions. (line 189) * gettext library: Explaining gettext. (line 6) -* gettext library, locale categories: Explaining gettext. (line 80) -* gettext() function (C library): Explaining gettext. (line 62) -* gettimeofday() user-defined function: Gettimeofday Function. - (line 16) +* gettext library, locale categories: Explaining gettext. (line 81) +* gettext() function (C library): Explaining gettext. (line 63) +* gettimeofday() extension function: Extension Sample Time. + (line 12) +* git utility <1>: Adding Code. (line 111) +* git utility <2>: Accessing The Source. + (line 10) +* git utility <3>: Other Versions. (line 29) +* git utility: gawkextlib. (line 27) +* Git, use of for gawk source code: Derived Files. (line 6) * GNITS mailing list: Acknowledgments. (line 52) -* GNU awk, See gawk: Preface. (line 49) +* GNU awk, See gawk: Preface. (line 51) * GNU Free Documentation License: GNU Free Documentation License. - (line 6) -* GNU General Public License: Glossary. (line 310) -* GNU Lesser General Public License: Glossary. (line 397) + (line 7) +* GNU General Public License: Glossary. (line 305) +* GNU Lesser General Public License: Glossary. (line 396) * GNU long options <1>: Options. (line 6) * GNU long options: Command Line. (line 13) -* GNU long options, printing list of: Options. (line 142) -* GNU Project <1>: Glossary. (line 319) +* GNU long options, printing list of: Options. (line 154) +* GNU Project <1>: Glossary. (line 314) * GNU Project: Manual History. (line 11) * GNU/Linux <1>: Glossary. (line 611) * GNU/Linux <2>: I18N Example. (line 55) * GNU/Linux: Manual History. (line 28) -* GPL (General Public License) <1>: Glossary. (line 310) +* Gordon, Assaf: Contributors. (line 105) +* GPL (General Public License) <1>: Glossary. (line 305) * GPL (General Public License): Manual History. (line 11) -* GPL (General Public License), printing: Options. (line 85) +* GPL (General Public License), printing: Options. (line 88) * grcat program: Group Functions. (line 16) -* Grigera, Juan: Contributors. (line 58) +* Grigera, Juan: Contributors. (line 57) * group database, reading: Group Functions. (line 6) * group file: Group Functions. (line 6) +* group ID of gawk user: Auto-set. (line 194) * groups, information about: Group Functions. (line 6) -* gsub() function <1>: String Functions. (line 139) -* gsub() function: Using Constant Regexps. +* gsub <1>: String Functions. (line 140) +* gsub: Using Constant Regexps. (line 43) * gsub() function, arguments of: String Functions. (line 462) * gsub() function, escape processing: Gory Details. (line 6) -* h debugger command (alias for help): Miscellaneous Dgawk Commands. - (line 68) -* Hankerson, Darrel <1>: Contributors. (line 61) +* h debugger command (alias for help): Miscellaneous Debugger Commands. + (line 66) +* Hankerson, Darrel <1>: Contributors. (line 60) * Hankerson, Darrel: Acknowledgments. (line 60) -* Haque, John <1>: Contributors. (line 103) -* Haque, John: Acknowledgments. (line 60) +* Haque, John: Contributors. (line 108) * Hartholz, Elaine: Acknowledgments. (line 38) * Hartholz, Marshall: Acknowledgments. (line 38) * Hasegawa, Isamu: Contributors. (line 94) -* help debugger command: Miscellaneous Dgawk Commands. - (line 68) +* help debugger command: Miscellaneous Debugger Commands. + (line 66) * hexadecimal numbers: Nondecimal-numbers. (line 6) -* hexadecimal values, enabling interpretation of: Options. (line 166) +* hexadecimal values, enabling interpretation of: Options. (line 211) +* history expansion, in debugger: Readline Support. (line 6) * histsort.awk program: History Sorting. (line 25) * Hughes, Phil: Acknowledgments. (line 43) -* HUP signal: Profiling. (line 204) +* HUP signal, for dynamic profiling: Profiling. (line 210) * hyphen (-), - operator: Precedence. (line 52) -* hyphen (-), -- (decrement/increment) operators: Precedence. (line 46) +* hyphen (-), -- operator <1>: Precedence. (line 46) * hyphen (-), -- operator: Increment Ops. (line 48) * hyphen (-), -= operator <1>: Precedence. (line 95) -* hyphen (-), -= operator: Assignment Ops. (line 129) +* hyphen (-), -= operator: Assignment Ops. (line 130) * hyphen (-), filenames beginning with: Options. (line 59) * hyphen (-), in bracket expressions: Bracket Expressions. (line 17) -* i debugger command (alias for info): Dgawk Info. (line 12) +* i debugger command (alias for info): Debugger Info. (line 13) * id utility: Id Program. (line 6) * id.awk program: Id Program. (line 30) -* if statement <1>: If Statement. (line 6) -* if statement: Regexp Usage. (line 19) +* if statement: If Statement. (line 6) * if statement, actions, changing: Ranges. (line 25) +* if statement, use of regexps in: Regexp Usage. (line 19) * igawk.sh program: Igawk Program. (line 124) -* ignore debugger command: Breakpoint Control. (line 86) -* IGNORECASE variable <1>: Array Sorting Functions. - (line 78) -* IGNORECASE variable <2>: String Functions. (line 29) -* IGNORECASE variable <3>: Array Intro. (line 92) -* IGNORECASE variable <4>: User-modified. (line 82) -* IGNORECASE variable: Case-sensitivity. (line 26) -* IGNORECASE variable, array sorting and: Array Sorting Functions. - (line 78) -* IGNORECASE variable, array subscripts and: Array Intro. (line 92) +* ignore breakpoint: Breakpoint Control. (line 87) +* ignore debugger command: Breakpoint Control. (line 87) +* IGNORECASE variable: User-modified. (line 76) +* IGNORECASE variable, and array indices: Array Intro. (line 94) +* IGNORECASE variable, and array sorting functions: Array Sorting Functions. + (line 83) * IGNORECASE variable, in example programs: Library Functions. - (line 42) + (line 53) +* IGNORECASE variable, with ~ and !~ operators: Case-sensitivity. + (line 26) +* Illumos: Other Versions. (line 109) +* Illumos, POSIX-compliant awk: Other Versions. (line 109) * implementation issues, gawk: Notes. (line 6) * implementation issues, gawk, debugging: Compatibility Mode. (line 6) -* implementation issues, gawk, limits <1>: Redirection. (line 135) +* implementation issues, gawk, limits <1>: Redirection. (line 129) * implementation issues, gawk, limits: Getline Notes. (line 14) -* in operator <1>: Id Program. (line 93) -* in operator <2>: For Statement. (line 75) -* in operator <3>: Precedence. (line 83) +* in operator <1>: For Statement. (line 76) +* in operator <2>: Precedence. (line 83) * in operator: Comparison Operators. (line 11) -* in operator, arrays and <1>: Scanning an Array. (line 17) -* in operator, arrays and: Reference to Elements. - (line 37) +* in operator, index existence in multidimensional arrays: Multidimensional. + (line 43) +* in operator, order of array access: Scanning an Array. (line 48) +* in operator, testing if array element exists: Reference to Elements. + (line 38) +* in operator, use in loops: Scanning an Array. (line 17) +* including files, @include directive: Include Files. (line 8) * increment operators: Increment Ops. (line 6) -* index() function: String Functions. (line 155) +* index: String Functions. (line 156) * indexing arrays: Array Intro. (line 50) * indirect function calls: Indirect Calls. (line 6) -* info debugger command: Dgawk Info. (line 12) +* indirect function calls, @-notation: Indirect Calls. (line 47) +* infinite precision: Arbitrary Precision Arithmetic. + (line 6) +* info debugger command: Debugger Info. (line 13) * initialization, automatic: More Complex. (line 38) +* inplace extension: Extension Sample Inplace. + (line 6) * input files: Reading Files. (line 6) * input files, closing: Close Files And Pipes. (line 6) @@ -26244,8 +33147,9 @@ Index * input files, examples: Sample Data Files. (line 6) * input files, reading: Reading Files. (line 6) * input files, running awk without: Read Terminal. (line 6) -* input files, variable assignments and: Other Arguments. (line 19) -* input pipeline: Getline/Pipe. (line 6) +* input files, variable assignments and: Other Arguments. (line 26) +* input pipeline: Getline/Pipe. (line 9) +* input record, length of: String Functions. (line 178) * input redirection: Getline/File. (line 6) * input, data, nondecimal: Nondecimal Data. (line 6) * input, explicit: Getline. (line 6) @@ -26254,111 +33158,88 @@ Index * input, splitting into records: Records. (line 6) * input, standard <1>: Special FD. (line 6) * input, standard: Read Terminal. (line 6) -* input/output, binary: User-modified. (line 10) +* input/output functions: I/O Functions. (line 6) +* input/output, binary: User-modified. (line 15) * input/output, from BEGIN and END: I/O And BEGIN/END. (line 6) -* input/output, two-way: Two-way I/O. (line 44) +* input/output, two-way: Two-way I/O. (line 25) * insomnia, cure for: Alarm Program. (line 6) * installation, VMS: VMS Installation. (line 6) * installing gawk: Installation. (line 6) -* INT signal (MS-Windows): Profiling. (line 207) -* int() function: Numeric Functions. (line 22) -* integers: Basic Data Typing. (line 21) -* integers, unsigned: Basic Data Typing. (line 30) -* interacting with other programs: I/O Functions. (line 63) -* internal constant, INVALID_HANDLE: Internals. (line 151) -* internal function, assoc_clear(): Internals. (line 68) -* internal function, assoc_lookup(): Internals. (line 72) -* internal function, dupnode(): Internals. (line 87) -* internal function, force_number(): Internals. (line 27) -* internal function, force_string(): Internals. (line 32) -* internal function, force_wstring(): Internals. (line 37) -* internal function, get_actual_argument(): Internals. (line 116) -* internal function, get_argument(): Internals. (line 111) -* internal function, iop_alloc(): Internals. (line 151) -* internal function, make_builtin(): Internals. (line 97) -* internal function, make_number(): Internals. (line 82) -* internal function, make_string(): Internals. (line 77) -* internal function, register_deferred_variable(): Internals. (line 140) -* internal function, register_open_hook(): Internals. (line 151) -* internal function, unref(): Internals. (line 92) -* internal function, update_ERRNO(): Internals. (line 130) -* internal function, update_ERRNO_saved(): Internals. (line 135) -* internal macro, get_array_argument(): Internals. (line 127) -* internal macro, get_scalar_argument(): Internals. (line 124) -* internal structure, IOBUF: Internals. (line 151) -* internal type, AWKNUM: Internals. (line 19) -* internal type, NODE: Internals. (line 23) -* internal variable, nargs: Internals. (line 42) -* internal variable, stlen: Internals. (line 46) -* internal variable, stptr: Internals. (line 46) -* internal variable, type: Internals. (line 59) -* internal variable, vname: Internals. (line 64) -* internal variable, wstlen: Internals. (line 54) -* internal variable, wstptr: Internals. (line 54) +* instruction tracing, in debugger: Debugger Info. (line 89) +* int: Numeric Functions. (line 38) +* INT signal (MS-Windows): Profiling. (line 213) +* integer array indices: Numeric Array Subscripts. + (line 31) +* integers, arbitrary precision: Arbitrary Precision Integers. + (line 6) +* integers, unsigned: Computer Arithmetic. (line 41) +* interacting with other programs: I/O Functions. (line 106) * internationalization <1>: I18N and L10N. (line 6) * internationalization: I18N Functions. (line 6) * internationalization, localization <1>: Internationalization. (line 13) -* internationalization, localization: User-modified. (line 153) +* internationalization, localization: User-modified. (line 151) * internationalization, localization, character classes: Bracket Expressions. - (line 90) + (line 100) * internationalization, localization, gawk and: Internationalization. (line 13) * internationalization, localization, locale categories: Explaining gettext. - (line 80) + (line 81) * internationalization, localization, marked strings: Programmer i18n. (line 14) * internationalization, localization, portability and: I18N Portability. (line 6) * internationalizing a program: Explaining gettext. (line 6) -* interpreted programs <1>: Glossary. (line 361) -* interpreted programs: Basic High Level. (line 14) -* interval expressions: Regexp Operators. (line 116) -* INVALID_HANDLE internal constant: Internals. (line 151) +* interpreted programs <1>: Glossary. (line 356) +* interpreted programs: Basic High Level. (line 15) +* interval expressions, regexp operator: Regexp Operators. (line 116) * inventory-shipped file: Sample Data Files. (line 32) -* IOBUF internal structure: Internals. (line 151) -* iop_alloc() internal function: Internals. (line 151) -* isarray() function (gawk): Type Functions. (line 11) -* ISO: Glossary. (line 372) -* ISO 8859-1: Glossary. (line 141) -* ISO Latin-1: Glossary. (line 141) +* invoke shell command: I/O Functions. (line 106) +* isarray: Type Functions. (line 11) +* ISO: Glossary. (line 367) +* ISO 8859-1: Glossary. (line 133) +* ISO Latin-1: Glossary. (line 133) * Jacobs, Andrew: Passwd Functions. (line 90) -* Jaegermann, Michal <1>: Contributors. (line 46) +* Jaegermann, Michal <1>: Contributors. (line 45) * Jaegermann, Michal: Acknowledgments. (line 60) -* Java implementation of awk: Other Versions. (line 96) -* Java programming language: Glossary. (line 380) -* jawk: Other Versions. (line 96) +* Java implementation of awk: Other Versions. (line 117) +* Java programming language: Glossary. (line 379) +* jawk: Other Versions. (line 117) * Jedi knights: Undocumented. (line 6) +* Johansen, Chris: Signature Program. (line 25) * join() user-defined function: Join Function. (line 18) * Kahrs, Ju"rgen <1>: Contributors. (line 70) * Kahrs, Ju"rgen: Acknowledgments. (line 60) * Kasal, Stepan: Acknowledgments. (line 60) * Kenobi, Obi-Wan: Undocumented. (line 6) -* Kernighan, Brian <1>: Basic Data Typing. (line 74) -* Kernighan, Brian <2>: Other Versions. (line 13) -* Kernighan, Brian <3>: Contributors. (line 12) -* Kernighan, Brian <4>: BTL. (line 6) -* Kernighan, Brian <5>: Concatenation. (line 6) -* Kernighan, Brian <6>: Acknowledgments. (line 75) -* Kernighan, Brian <7>: Conventions. (line 34) +* Kernighan, Brian <1>: Glossary. (line 143) +* Kernighan, Brian <2>: Basic Data Typing. (line 54) +* Kernighan, Brian <3>: Other Versions. (line 13) +* Kernighan, Brian <4>: Contributors. (line 11) +* Kernighan, Brian <5>: BTL. (line 6) +* Kernighan, Brian <6>: Library Functions. (line 12) +* Kernighan, Brian <7>: Concatenation. (line 6) +* Kernighan, Brian <8>: Getline/Pipe. (line 6) +* Kernighan, Brian <9>: Acknowledgments. (line 78) +* Kernighan, Brian <10>: Conventions. (line 38) * Kernighan, Brian: History. (line 17) -* kill command, dynamic profiling: Profiling. (line 182) +* kill command, dynamic profiling: Profiling. (line 187) * Knights, jedi: Undocumented. (line 6) -* Kwok, Conrad: Contributors. (line 35) -* l debugger command (alias for list): Miscellaneous Dgawk Commands. - (line 74) +* Kwok, Conrad: Contributors. (line 34) +* l debugger command (alias for list): Miscellaneous Debugger Commands. + (line 72) * labels.awk program: Labels Program. (line 51) -* languages, data-driven: Basic High Level. (line 83) -* LC_ALL locale category: Explaining gettext. (line 120) -* LC_COLLATE locale category: Explaining gettext. (line 93) -* LC_CTYPE locale category: Explaining gettext. (line 97) -* LC_MESSAGES locale category: Explaining gettext. (line 87) +* Langston, Peter: Advanced Features. (line 6) +* languages, data-driven: Basic High Level. (line 85) +* LC_ALL locale category: Explaining gettext. (line 117) +* LC_COLLATE locale category: Explaining gettext. (line 94) +* LC_CTYPE locale category: Explaining gettext. (line 98) +* LC_MESSAGES locale category: Explaining gettext. (line 88) * LC_MESSAGES locale category, bindtextdomain() function (gawk): Programmer i18n. - (line 88) -* LC_MONETARY locale category: Explaining gettext. (line 103) -* LC_NUMERIC locale category: Explaining gettext. (line 107) -* LC_RESPONSE locale category: Explaining gettext. (line 111) -* LC_TIME locale category: Explaining gettext. (line 115) + (line 101) +* LC_MONETARY locale category: Explaining gettext. (line 104) +* LC_NUMERIC locale category: Explaining gettext. (line 108) +* LC_TIME locale category: Explaining gettext. (line 112) * left angle bracket (<), < operator <1>: Precedence. (line 65) * left angle bracket (<), < operator: Comparison Operators. (line 11) @@ -26366,16 +33247,19 @@ Index * left angle bracket (<), <= operator <1>: Precedence. (line 65) * left angle bracket (<), <= operator: Comparison Operators. (line 11) +* left shift: Bitwise Functions. (line 47) * left shift, bitwise: Bitwise Functions. (line 32) * leftmost longest match: Multiple Line. (line 26) -* length() function: String Functions. (line 166) -* Lesser General Public License (LGPL): Glossary. (line 397) -* LGPL (Lesser General Public License): Glossary. (line 397) -* libmawk: Other Versions. (line 104) +* length: String Functions. (line 171) +* length of input record: String Functions. (line 178) +* length of string: String Functions. (line 171) +* Lesser General Public License (LGPL): Glossary. (line 396) +* LGPL (Lesser General Public License): Glossary. (line 396) +* libmawk: Other Versions. (line 125) * libraries of awk functions: Library Functions. (line 6) * libraries of awk functions, assertions: Assert Function. (line 6) * libraries of awk functions, associative arrays and: Library Names. - (line 57) + (line 58) * libraries of awk functions, character values as numbers: Ordinal Functions. (line 6) * libraries of awk functions, command-line options: Getopt Function. @@ -26386,7 +33270,7 @@ Index (line 6) * libraries of awk functions, managing, data files: Data File Management. (line 6) -* libraries of awk functions, managing, time: Gettimeofday Function. +* libraries of awk functions, managing, time: Getlocaltime Function. (line 6) * libraries of awk functions, merging arrays into strings: Join Function. (line 6) @@ -26395,7 +33279,7 @@ Index * libraries of awk functions, user database, reading: Passwd Functions. (line 6) * line breaks: Statements/Lines. (line 6) -* line continuations: Boolean Ops. (line 62) +* line continuations: Boolean Ops. (line 64) * line continuations, gawk: Conditional Exp. (line 34) * line continuations, in print statement: Print Examples. (line 76) * line continuations, with C shell: More Complex. (line 30) @@ -26404,182 +33288,197 @@ Index * lines, duplicate, removing: History Sorting. (line 6) * lines, matching ranges of: Ranges. (line 6) * lines, skipping between markers: Ranges. (line 43) -* lint checking: User-modified. (line 98) +* lint checking: User-modified. (line 88) * lint checking, array elements: Delete. (line 34) * lint checking, array subscripts: Uninitialized Subscripts. (line 43) * lint checking, empty programs: Command Line. (line 16) -* lint checking, issuing warnings: Options. (line 147) +* lint checking, issuing warnings: Options. (line 185) * lint checking, POSIXLY_CORRECT environment variable: Options. - (line 289) + (line 339) * lint checking, undefined functions: Pass By Value/Reference. - (line 88) -* LINT variable: User-modified. (line 98) + (line 85) +* LINT variable: User-modified. (line 88) * Linux <1>: Glossary. (line 611) * Linux <2>: I18N Example. (line 55) * Linux: Manual History. (line 28) -* list debugger command: Miscellaneous Dgawk Commands. - (line 74) -* local variables: Variable Scope. (line 6) -* locale categories: Explaining gettext. (line 80) -* locale decimal point character: Options. (line 215) +* list all global variables, in debugger: Debugger Info. (line 48) +* list debugger command: Miscellaneous Debugger Commands. + (line 72) +* list function definitions, in debugger: Debugger Info. (line 30) +* loading extensions, @load directive: Loading Shared Libraries. + (line 8) +* loading, extensions: Options. (line 173) +* local variables, in a function: Variable Scope. (line 6) +* locale categories: Explaining gettext. (line 81) +* locale decimal point character: Options. (line 270) * locale, definition of: Locales. (line 6) * localization: I18N and L10N. (line 6) * localization, See internationalization, localization: I18N and L10N. (line 6) +* log: Numeric Functions. (line 43) * log files, timestamps in: Time Functions. (line 6) -* log() function: Numeric Functions. (line 29) +* logarithm: Numeric Functions. (line 43) * logical false/true: Truth Values. (line 6) * logical operators, See Boolean expressions: Boolean Ops. (line 6) * login information: Passwd Functions. (line 16) * long options: Command Line. (line 13) * loops: While Statement. (line 6) -* loops, continue statements and: For Statement. (line 64) -* loops, count for header: Profiling. (line 126) +* loops, break statement and: Break Statement. (line 6) +* loops, continue statements and: For Statement. (line 65) +* loops, count for header, in a profile: Profiling. (line 131) +* loops, do-while: Do Statement. (line 6) * loops, exiting: Break Statement. (line 6) +* loops, for, array scanning: Scanning an Array. (line 6) +* loops, for, iterative: For Statement. (line 6) * loops, See Also while statement: While Statement. (line 6) -* Lost In Space: Dynamic Extensions. (line 6) +* loops, while: While Statement. (line 6) * ls utility: More Complex. (line 15) -* lshift() function (gawk): Bitwise Functions. (line 45) +* lshift: Bitwise Functions. (line 47) * lvalues/rvalues: Assignment Ops. (line 32) +* mail-list file: Sample Data Files. (line 6) * mailing labels, printing: Labels Program. (line 6) * mailing list, GNITS: Acknowledgments. (line 52) -* make_builtin() internal function: Internals. (line 97) -* make_number() internal function: Internals. (line 82) -* make_string() internal function: Internals. (line 77) +* Malmberg, John <1>: Bugs. (line 70) +* Malmberg, John: Acknowledgments. (line 60) +* Malmberg, John E.: Contributors. (line 137) * mark parity: Ordinal Functions. (line 45) * marked string extraction (internationalization): String Extraction. (line 6) * marked strings, extracting: String Extraction. (line 6) -* Marx, Groucho: Increment Ops. (line 61) -* match() function: String Functions. (line 206) +* Marx, Groucho: Increment Ops. (line 60) +* match: String Functions. (line 211) +* match regexp in string: String Functions. (line 211) * match() function, RSTART/RLENGTH variables: String Functions. - (line 223) + (line 228) * matching, expressions, See comparison expressions: Typing and Comparison. (line 9) * matching, leftmost longest: Multiple Line. (line 26) -* matching, null strings: Gory Details. (line 163) -* mawk program: Other Versions. (line 35) +* matching, null strings: String Functions. (line 536) +* mawk utility <1>: Other Versions. (line 48) +* mawk utility <2>: Nextfile Statement. (line 47) +* mawk utility <3>: Concatenation. (line 36) +* mawk utility <4>: Getline/Pipe. (line 62) +* mawk utility: Escape Sequences. (line 120) +* maximum precision supported by MPFR library: Auto-set. (line 235) +* McIlroy, Doug: Glossary. (line 177) * McPhee, Patrick: Contributors. (line 100) -* memory, releasing: Internals. (line 92) -* message object files: Explaining gettext. (line 41) +* message object files: Explaining gettext. (line 42) * message object files, converting from portable object files: I18N Example. - (line 62) + (line 64) * message object files, specifying directory of <1>: Programmer i18n. (line 47) * message object files, specifying directory of: Explaining gettext. - (line 53) -* metacharacters, escape sequences for: Escape Sequences. (line 132) -* mktime() function (gawk): Time Functions. (line 24) + (line 54) +* messages from extensions: Printing Messages. (line 6) +* metacharacters in regular expressions: Regexp Operators. (line 6) +* metacharacters, escape sequences for: Escape Sequences. (line 139) +* minimum precision supported by MPFR library: Auto-set. (line 238) +* mktime: Time Functions. (line 25) * modifiers, in format specifiers: Format Modifiers. (line 6) -* monetary information, localization: Explaining gettext. (line 103) -* msgfmt utility: I18N Example. (line 62) -* n debugger command (alias for next): Dgawk Execution Control. +* monetary information, localization: Explaining gettext. (line 104) +* Moore, Duncan: Getline Notes. (line 40) +* msgfmt utility: I18N Example. (line 64) +* multiple precision: Arbitrary Precision Arithmetic. + (line 6) +* multiple-line records: Multiple Line. (line 6) +* n debugger command (alias for next): Debugger Execution Control. (line 43) -* names, arrays/variables <1>: Library Names. (line 6) -* names, arrays/variables: Arrays. (line 18) +* names, arrays/variables: Library Names. (line 6) * names, functions <1>: Library Names. (line 6) -* names, functions: Definition Syntax. (line 20) -* namespace issues <1>: Library Names. (line 6) -* namespace issues: Arrays. (line 18) -* namespace issues, functions: Definition Syntax. (line 20) -* nargs internal variable: Internals. (line 42) -* nawk utility: Names. (line 17) -* negative zero: Unexpected Results. (line 28) +* names, functions: Definition Syntax. (line 23) +* namespace issues: Library Names. (line 6) +* namespace issues, functions: Definition Syntax. (line 23) * NetBSD: Glossary. (line 611) * networks, programming: TCP/IP Networking. (line 6) * networks, support for: Special Network. (line 6) -* newlines <1>: Boolean Ops. (line 67) -* newlines <2>: Options. (line 205) +* newlines <1>: Boolean Ops. (line 69) +* newlines <2>: Options. (line 260) * newlines: Statements/Lines. (line 6) * newlines, as field separators: Default Field Splitting. (line 6) -* newlines, as record separators: Records. (line 20) +* newlines, as record separators: awk split records. (line 12) * newlines, in dynamic regexps: Computed Regexps. (line 59) * newlines, in regexp constants: Computed Regexps. (line 69) * newlines, printing: Print Examples. (line 12) * newlines, separating statements in actions <1>: Statements. (line 10) * newlines, separating statements in actions: Action Overview. (line 19) -* next debugger command: Dgawk Execution Control. +* next debugger command: Debugger Execution Control. (line 43) +* next file statement: Feature History. (line 169) * next statement <1>: Next Statement. (line 6) -* next statement: Boolean Ops. (line 85) +* next statement: Boolean Ops. (line 95) * next statement, BEGIN/END patterns and: I/O And BEGIN/END. (line 37) * next statement, BEGINFILE/ENDFILE patterns and: BEGINFILE/ENDFILE. (line 49) -* next statement, user-defined functions and: Next Statement. (line 45) +* next statement, user-defined functions and: Next Statement. (line 44) * nextfile statement: Nextfile Statement. (line 6) * nextfile statement, BEGIN/END patterns and: I/O And BEGIN/END. (line 37) * nextfile statement, BEGINFILE/ENDFILE patterns and: BEGINFILE/ENDFILE. (line 26) * nextfile statement, user-defined functions and: Nextfile Statement. - (line 44) -* nexti debugger command: Dgawk Execution Control. + (line 47) +* nexti debugger command: Debugger Execution Control. (line 49) -* NF variable <1>: Auto-set. (line 107) +* NF variable <1>: Auto-set. (line 119) * NF variable: Fields. (line 33) * NF variable, decrementing: Changing Fields. (line 107) -* ni debugger command (alias for nexti): Dgawk Execution Control. +* ni debugger command (alias for nexti): Debugger Execution Control. (line 49) * noassign.awk program: Ignoring Assigns. (line 15) -* NODE internal type: Internals. (line 23) -* nodes, duplicating: Internals. (line 87) +* non-existent array elements: Reference to Elements. + (line 23) * not Boolean-logic operator: Boolean Ops. (line 6) -* NR variable <1>: Auto-set. (line 118) +* NR variable <1>: Auto-set. (line 139) * NR variable: Records. (line 6) -* NR variable, changing: Auto-set. (line 207) -* null strings <1>: Basic Data Typing. (line 50) +* NR variable, changing: Auto-set. (line 328) +* null strings <1>: Basic Data Typing. (line 26) * null strings <2>: Truth Values. (line 6) * null strings <3>: Regexp Field Splitting. (line 43) -* null strings: Records. (line 102) -* null strings, array elements and: Delete. (line 27) +* null strings: awk split records. (line 115) +* null strings in gawk arguments, quoting and: Quoting. (line 82) +* null strings, and deleting array elements: Delete. (line 27) * null strings, as array subscripts: Uninitialized Subscripts. (line 43) -* null strings, converting numbers to strings: Conversion. (line 21) -* null strings, matching: Gory Details. (line 163) -* null strings, quoting and: Quoting. (line 62) +* null strings, converting numbers to strings: Strings And Numbers. + (line 21) +* null strings, matching: String Functions. (line 536) +* number as string of bits: Bitwise Functions. (line 110) +* number of array elements: String Functions. (line 201) * number sign (#), #! (executable scripts): Executable Scripts. (line 6) -* number sign (#), #! (executable scripts), portability issues with: Executable Scripts. - (line 6) * number sign (#), commenting: Comments. (line 6) -* numbers: Internals. (line 82) * numbers, as array subscripts: Numeric Array Subscripts. (line 6) * numbers, as values of characters: Ordinal Functions. (line 6) * numbers, Cliff random: Cliff Random Function. (line 6) -* numbers, converting <1>: Bitwise Functions. (line 107) -* numbers, converting: Conversion. (line 6) -* numbers, converting, to strings: User-modified. (line 28) -* numbers, floating-point: Basic Data Typing. (line 21) -* numbers, floating-point, AWKNUM internal type: Internals. (line 19) +* numbers, converting <1>: Bitwise Functions. (line 110) +* numbers, converting: Strings And Numbers. (line 6) +* numbers, converting, to strings: User-modified. (line 30) * numbers, hexadecimal: Nondecimal-numbers. (line 6) -* numbers, NODE internal type: Internals. (line 23) * numbers, octal: Nondecimal-numbers. (line 6) -* numbers, random: Numeric Functions. (line 63) * numbers, rounding: Round Function. (line 6) -* numeric, constants: Scalar Constants. (line 6) +* numeric constants: Scalar Constants. (line 6) +* numeric functions: Numeric Functions. (line 6) * numeric, output format: OFMT. (line 6) * numeric, strings: Variable Typing. (line 6) -* numeric, values: Internals. (line 27) -* o debugger command (alias for option): Dgawk Info. (line 56) -* oawk utility: Names. (line 17) +* o debugger command (alias for option): Debugger Info. (line 57) * obsolete features: Obsolete. (line 6) * octal numbers: Nondecimal-numbers. (line 6) -* octal values, enabling interpretation of: Options. (line 166) -* OFMT variable <1>: User-modified. (line 115) -* OFMT variable <2>: Conversion. (line 55) +* octal values, enabling interpretation of: Options. (line 211) +* OFMT variable <1>: User-modified. (line 105) +* OFMT variable <2>: Strings And Numbers. (line 57) * OFMT variable: OFMT. (line 15) * OFMT variable, POSIX awk and: OFMT. (line 27) -* OFS variable <1>: User-modified. (line 124) +* OFS variable <1>: User-modified. (line 113) * OFS variable <2>: Output Separators. (line 6) * OFS variable: Changing Fields. (line 64) * OpenBSD: Glossary. (line 611) -* OpenSolaris: Other Versions. (line 86) +* OpenSolaris: Other Versions. (line 100) * operating systems, BSD-based: Manual History. (line 28) * operating systems, PC, gawk on: PC Using. (line 6) * operating systems, PC, gawk on, installing: PC Installation. @@ -26598,44 +33497,44 @@ Index * operators, input/output <1>: Precedence. (line 65) * operators, input/output <2>: Redirection. (line 22) * operators, input/output <3>: Getline/Coprocess. (line 6) -* operators, input/output <4>: Getline/Pipe. (line 6) +* operators, input/output <4>: Getline/Pipe. (line 9) * operators, input/output: Getline/File. (line 6) * operators, logical, See Boolean expressions: Boolean Ops. (line 6) * operators, precedence <1>: Precedence. (line 6) -* operators, precedence: Increment Ops. (line 61) +* operators, precedence: Increment Ops. (line 60) * operators, relational, See operators, comparison: Typing and Comparison. (line 9) -* operators, short-circuit: Boolean Ops. (line 57) -* operators, string: Concatenation. (line 9) +* operators, short-circuit: Boolean Ops. (line 59) +* operators, string: Concatenation. (line 8) * operators, string-matching: Regexp Usage. (line 19) * operators, string-matching, for buffers: GNU Regexp Operators. (line 48) * operators, word-boundary (gawk): GNU Regexp Operators. (line 63) -* option debugger command: Dgawk Info. (line 56) -* options, command-line <1>: Command Line Field Separator. - (line 6) -* options, command-line <2>: Options. (line 6) -* options, command-line: Long. (line 12) +* option debugger command: Debugger Info. (line 57) +* options, command-line: Options. (line 6) * options, command-line, end of: Options. (line 54) * options, command-line, invoking awk: Command Line. (line 6) * options, command-line, processing: Getopt Function. (line 6) * options, deprecated: Obsolete. (line 6) * options, long <1>: Options. (line 6) * options, long: Command Line. (line 13) -* options, printing list of: Options. (line 142) +* options, printing list of: Options. (line 154) +* or: Bitwise Functions. (line 50) * OR bitwise operation: Bitwise Functions. (line 6) * or Boolean-logic operator: Boolean Ops. (line 6) -* or() function (gawk): Bitwise Functions. (line 48) +* ord() extension function: Extension Sample Ord. + (line 12) * ord() user-defined function: Ordinal Functions. (line 16) -* order of evaluation, concatenation: Concatenation. (line 42) -* ORS variable <1>: User-modified. (line 129) -* ORS variable: Output Separators. (line 20) +* order of evaluation, concatenation: Concatenation. (line 41) +* ORS variable <1>: User-modified. (line 118) +* ORS variable: Output Separators. (line 21) * output field separator, See OFS variable: Changing Fields. (line 64) * output record separator, See ORS variable: Output Separators. - (line 20) + (line 21) * output redirection: Redirection. (line 6) -* output, buffering: I/O Functions. (line 29) +* output wrapper: Output Wrappers. (line 6) +* output, buffering: I/O Functions. (line 32) * output, duplicating into files: Tee Program. (line 6) * output, files, closing: Close Files And Pipes. (line 6) @@ -26643,139 +33542,139 @@ Index * output, formatted: Printf. (line 6) * output, pipes: Redirection. (line 57) * output, printing, See printing: Printing. (line 6) -* output, records: Output Separators. (line 20) +* output, records: Output Separators. (line 21) * output, standard: Special FD. (line 6) * p debugger command (alias for print): Viewing And Changing Data. (line 36) -* P1003.1 POSIX standard: Glossary. (line 454) -* P1003.2 POSIX standard: Glossary. (line 454) -* parameters, number of: Internals. (line 42) -* parentheses (): Regexp Operators. (line 79) -* parentheses (), pgawk program: Profiling. (line 141) +* Papadopoulos, Panos: Contributors. (line 128) +* parent process ID of gawk process: Auto-set. (line 203) +* parentheses (), in a profile: Profiling. (line 146) +* parentheses (), regexp operator: Regexp Operators. (line 81) * password file: Passwd Functions. (line 16) -* patsplit() function: String Functions. (line 293) +* patsplit: String Functions. (line 297) * patterns: Patterns and Actions. (line 6) * patterns, comparison expressions as: Expression Patterns. (line 14) -* patterns, counts: Profiling. (line 113) +* patterns, counts, in a profile: Profiling. (line 118) * patterns, default: Very Simple. (line 34) * patterns, empty: Empty. (line 6) * patterns, expressions as: Regexp Patterns. (line 6) * patterns, ranges in: Ranges. (line 6) -* patterns, regexp constants as: Expression Patterns. (line 36) +* patterns, regexp constants as: Expression Patterns. (line 34) * patterns, types of: Pattern Overview. (line 15) * pawk (profiling version of Brian Kernighan's awk): Other Versions. - (line 69) + (line 82) +* pawk, awk-like facilities for Python: Other Versions. (line 129) * PC operating systems, gawk on: PC Using. (line 6) * PC operating systems, gawk on, installing: PC Installation. (line 6) * percent sign (%), % operator: Precedence. (line 55) * percent sign (%), %= operator <1>: Precedence. (line 95) -* percent sign (%), %= operator: Assignment Ops. (line 129) -* period (.): Regexp Operators. (line 43) +* percent sign (%), %= operator: Assignment Ops. (line 130) +* period (.), regexp operator: Regexp Operators. (line 44) * Perl: Future Extensions. (line 6) * Peters, Arno: Contributors. (line 85) -* Peterson, Hal: Contributors. (line 40) -* pgawk program: Profiling. (line 6) -* pgawk program, awkprof.out file: Profiling. (line 10) -* pgawk program, dynamic profiling: Profiling. (line 174) -* pipes, closing: Close Files And Pipes. +* Peterson, Hal: Contributors. (line 39) +* pipe, closing: Close Files And Pipes. (line 6) -* pipes, input: Getline/Pipe. (line 6) -* pipes, output: Redirection. (line 57) -* Pitts, Dave <1>: Bugs. (line 73) +* pipe, input: Getline/Pipe. (line 9) +* pipe, output: Redirection. (line 57) +* Pitts, Dave <1>: Bugs. (line 70) * Pitts, Dave: Acknowledgments. (line 60) -* plus sign (+): Regexp Operators. (line 102) +* Plauger, P.J.: Library Functions. (line 12) +* plug-in: Extension Intro. (line 6) * plus sign (+), + operator: Precedence. (line 52) -* plus sign (+), ++ (decrement/increment operators): Increment Ops. - (line 11) * plus sign (+), ++ operator <1>: Precedence. (line 46) -* plus sign (+), ++ operator: Increment Ops. (line 40) +* plus sign (+), ++ operator: Increment Ops. (line 11) * plus sign (+), += operator <1>: Precedence. (line 95) * plus sign (+), += operator: Assignment Ops. (line 82) +* plus sign (+), regexp operator: Regexp Operators. (line 105) * pointers to functions: Indirect Calls. (line 6) -* portability: Escape Sequences. (line 94) -* portability, #! (executable scripts): Executable Scripts. (line 34) +* portability: Escape Sequences. (line 103) +* portability, #! (executable scripts): Executable Scripts. (line 33) * portability, ** operator and: Arithmetic Ops. (line 81) -* portability, **= operator and: Assignment Ops. (line 142) -* portability, ARGV variable: Executable Scripts. (line 43) +* portability, **= operator and: Assignment Ops. (line 143) +* portability, ARGV variable: Executable Scripts. (line 59) * portability, backslash continuation and: Statements/Lines. (line 30) * portability, backslash in escape sequences: Escape Sequences. - (line 113) + (line 108) * portability, close() function and: Close Files And Pipes. (line 81) -* portability, data files as single record: Records. (line 175) -* portability, deleting array elements: Delete. (line 52) -* portability, example programs: Library Functions. (line 31) -* portability, fflush() function and: I/O Functions. (line 29) -* portability, functions, defining: Definition Syntax. (line 99) +* portability, data files as single record: gawk split records. + (line 65) +* portability, deleting array elements: Delete. (line 56) +* portability, example programs: Library Functions. (line 42) +* portability, functions, defining: Definition Syntax. (line 109) * portability, gawk: New Ports. (line 6) -* portability, gettext library and: Explaining gettext. (line 10) +* portability, gettext library and: Explaining gettext. (line 11) * portability, internationalization and: I18N Portability. (line 6) -* portability, length() function: String Functions. (line 175) -* portability, new awk vs. old awk: Conversion. (line 55) +* portability, length() function: String Functions. (line 180) +* portability, new awk vs. old awk: Strings And Numbers. (line 57) * portability, next statement in user-defined functions: Pass By Value/Reference. - (line 91) + (line 88) * portability, NF variable, decrementing: Changing Fields. (line 115) -* portability, operators: Increment Ops. (line 61) +* portability, operators: Increment Ops. (line 60) * portability, operators, not in POSIX awk: Precedence. (line 98) -* portability, POSIXLY_CORRECT environment variable: Options. (line 310) +* portability, POSIXLY_CORRECT environment variable: Options. (line 359) * portability, substr() function: String Functions. (line 512) * portable object files <1>: Translator i18n. (line 6) -* portable object files: Explaining gettext. (line 36) +* portable object files: Explaining gettext. (line 37) * portable object files, converting to message object files: I18N Example. - (line 62) -* portable object files, generating: Options. (line 135) -* portable object template files: Explaining gettext. (line 30) + (line 64) +* portable object files, generating: Options. (line 147) +* portable object template files: Explaining gettext. (line 31) * porting gawk: New Ports. (line 6) * positional specifiers, printf statement <1>: Printf Ordering. (line 6) * positional specifiers, printf statement: Format Modifiers. (line 13) * positional specifiers, printf statement, mixing with regular formats: Printf Ordering. (line 57) -* positive zero: Unexpected Results. (line 28) -* POSIX awk <1>: Assignment Ops. (line 136) +* POSIX awk <1>: Assignment Ops. (line 137) * POSIX awk: This Manual. (line 14) * POSIX awk, ** operator and: Precedence. (line 98) -* POSIX awk, **= operator and: Assignment Ops. (line 142) +* POSIX awk, **= operator and: Assignment Ops. (line 143) * POSIX awk, < operator and: Getline/File. (line 26) -* POSIX awk, arithmetic operators and: Arithmetic Ops. (line 36) +* POSIX awk, arithmetic operators and: Arithmetic Ops. (line 30) * POSIX awk, backslashes in string constants: Escape Sequences. - (line 113) + (line 108) * POSIX awk, BEGIN/END patterns: I/O And BEGIN/END. (line 16) -* POSIX awk, bracket expressions and: Bracket Expressions. (line 24) +* POSIX awk, bracket expressions and: Bracket Expressions. (line 26) * POSIX awk, bracket expressions and, character classes: Bracket Expressions. - (line 30) + (line 32) * POSIX awk, break statement and: Break Statement. (line 51) * POSIX awk, changes in awk versions: POSIX. (line 6) -* POSIX awk, continue statement and: Continue Statement. (line 43) -* POSIX awk, CONVFMT variable and: User-modified. (line 28) -* POSIX awk, date utility and: Time Functions. (line 261) -* POSIX awk, field separators and <1>: Field Splitting Summary. - (line 41) +* POSIX awk, continue statement and: Continue Statement. (line 44) +* POSIX awk, CONVFMT variable and: User-modified. (line 30) +* POSIX awk, date utility and: Time Functions. (line 254) +* POSIX awk, field separators and <1>: Full Line Fields. (line 16) * POSIX awk, field separators and: Fields. (line 6) -* POSIX awk, FS variable and: User-modified. (line 66) -* POSIX awk, function keyword in: Definition Syntax. (line 83) -* POSIX awk, functions and, gsub()/sub(): Gory Details. (line 53) -* POSIX awk, functions and, length(): String Functions. (line 175) +* POSIX awk, FS variable and: User-modified. (line 60) +* POSIX awk, function keyword in: Definition Syntax. (line 93) +* POSIX awk, functions and, gsub()/sub(): Gory Details. (line 90) +* POSIX awk, functions and, length(): String Functions. (line 180) * POSIX awk, GNU long options and: Options. (line 15) * POSIX awk, interval expressions in: Regexp Operators. (line 135) -* POSIX awk, next/nextfile statements and: Next Statement. (line 45) +* POSIX awk, next/nextfile statements and: Next Statement. (line 44) * POSIX awk, numeric strings and: Variable Typing. (line 6) -* POSIX awk, OFMT variable and <1>: Conversion. (line 55) +* POSIX awk, OFMT variable and <1>: Strings And Numbers. (line 57) * POSIX awk, OFMT variable and: OFMT. (line 27) -* POSIX awk, period (.), using: Regexp Operators. (line 50) -* POSIX awk, printf format strings and: Format Modifiers. (line 159) -* POSIX awk, regular expressions and: Regexp Operators. (line 157) +* POSIX awk, period (.), using: Regexp Operators. (line 51) +* POSIX awk, printf format strings and: Format Modifiers. (line 158) +* POSIX awk, regular expressions and: Regexp Operators. (line 161) * POSIX awk, timestamps and: Time Functions. (line 6) -* POSIX awk, | I/O operator and: Getline/Pipe. (line 52) -* POSIX mode: Options. (line 199) -* POSIX, awk and: Preface. (line 23) +* POSIX awk, | I/O operator and: Getline/Pipe. (line 55) +* POSIX mode: Options. (line 254) +* POSIX, awk and: Preface. (line 21) * POSIX, gawk extensions not included in: POSIX/GNU. (line 6) * POSIX, programs, implementing in awk: Clones. (line 6) -* POSIXLY_CORRECT environment variable: Options. (line 289) +* POSIXLY_CORRECT environment variable: Options. (line 339) +* PREC variable: User-modified. (line 123) * precedence <1>: Precedence. (line 6) -* precedence: Increment Ops. (line 61) -* precedence, regexp operators: Regexp Operators. (line 152) +* precedence: Increment Ops. (line 60) +* precedence, regexp operators: Regexp Operators. (line 156) +* predefined variables: Built-in Variables. (line 6) +* predefined variables, -v option, setting with: Options. (line 40) +* predefined variables, conveying information: Auto-set. (line 6) +* predefined variables, user-modifiable: User-modified. (line 6) * print debugger command: Viewing And Changing Data. (line 36) * print statement: Printing. (line 16) @@ -26783,10 +33682,12 @@ Index * print statement, commas, omitting: Print Examples. (line 31) * print statement, I/O operators in: Precedence. (line 71) * print statement, line continuations and: Print Examples. (line 76) -* print statement, OFMT variable and: User-modified. (line 124) +* print statement, OFMT variable and: User-modified. (line 113) * print statement, See Also redirection, of output: Redirection. (line 17) * print statement, sprintf() function and: Round Function. (line 6) +* print variables, in debugger: Viewing And Changing Data. + (line 36) * printf debugger command: Viewing And Changing Data. (line 54) * printf statement <1>: Printf. (line 6) @@ -26806,120 +33707,138 @@ Index * printf statement, sprintf() function and: Round Function. (line 6) * printf statement, syntax of: Basic Printf. (line 6) * printing: Printing. (line 6) -* printing, list of options: Options. (line 142) +* printing messages from extensions: Printing Messages. (line 6) +* printing, list of options: Options. (line 154) * printing, mailing labels: Labels Program. (line 6) * printing, unduplicated lines of text: Uniq Program. (line 6) * printing, user information: Id Program. (line 6) * private variables: Library Names. (line 11) -* processes, two-way communications with: Two-way I/O. (line 23) +* process group idIDof gawk process: Auto-set. (line 197) +* process ID of gawk process: Auto-set. (line 200) +* processes, two-way communications with: Two-way I/O. (line 6) * processing data: Basic High Level. (line 6) -* PROCINFO array <1>: Internals. (line 140) -* PROCINFO array <2>: Id Program. (line 15) -* PROCINFO array <3>: Group Functions. (line 6) -* PROCINFO array <4>: Passwd Functions. (line 6) -* PROCINFO array <5>: Two-way I/O. (line 116) -* PROCINFO array <6>: Time Functions. (line 46) -* PROCINFO array <7>: Auto-set. (line 123) -* PROCINFO array: Obsolete. (line 11) +* PROCINFO array <1>: Passwd Functions. (line 6) +* PROCINFO array <2>: Time Functions. (line 47) +* PROCINFO array: Auto-set. (line 144) +* PROCINFO array, and communications via ptys: Two-way I/O. (line 99) +* PROCINFO array, and group membership: Group Functions. (line 6) +* PROCINFO array, and user and group ID numbers: Id Program. (line 15) +* PROCINFO array, testing the field splitting: Passwd Functions. + (line 154) +* PROCINFO array, uses: Auto-set. (line 256) +* PROCINFO, values of sorted_in: Controlling Scanning. + (line 26) * profiling awk programs: Profiling. (line 6) -* profiling awk programs, dynamically: Profiling. (line 174) -* profiling gawk, See pgawk program: Profiling. (line 6) +* profiling awk programs, dynamically: Profiling. (line 178) +* program identifiers: Auto-set. (line 162) * program, definition of: Getting Started. (line 21) -* programmers, attractiveness of: Two-way I/O. (line 6) * programming conventions, --non-decimal-data option: Nondecimal Data. - (line 36) -* programming conventions, ARGC/ARGV variables: Auto-set. (line 31) + (line 35) +* programming conventions, ARGC/ARGV variables: Auto-set. (line 35) * programming conventions, exit statement: Exit Statement. (line 38) * programming conventions, function parameters: Return Statement. (line 45) * programming conventions, functions, calling: Calling Built-in. (line 10) * programming conventions, functions, writing: Definition Syntax. - (line 55) -* programming conventions, gawk internals: Internal File Ops. (line 33) + (line 65) +* programming conventions, gawk extensions: Internal File Ops. + (line 45) * programming conventions, private variable names: Library Names. (line 23) * programming language, recipe for: History. (line 6) -* Programming languages, Ada: Glossary. (line 20) +* programming languages, Ada: Glossary. (line 11) * programming languages, data-driven vs. procedural: Getting Started. (line 12) -* Programming languages, Java: Glossary. (line 380) -* programming, basic steps: Basic High Level. (line 19) +* programming languages, Java: Glossary. (line 379) +* programming, basic steps: Basic High Level. (line 20) * programming, concepts: Basic Concepts. (line 6) * pwcat program: Passwd Functions. (line 23) -* q debugger command (alias for quit): Miscellaneous Dgawk Commands. - (line 101) -* QSE Awk: Other Versions. (line 108) -* question mark (?) regexp operator <1>: GNU Regexp Operators. - (line 59) -* question mark (?) regexp operator: Regexp Operators. (line 111) +* q debugger command (alias for quit): Miscellaneous Debugger Commands. + (line 99) +* QSE Awk: Other Versions. (line 135) +* Quanstrom, Erik: Alarm Program. (line 8) * question mark (?), ?: operator: Precedence. (line 92) -* QuikTrim Awk: Other Versions. (line 112) -* quit debugger command: Miscellaneous Dgawk Commands. - (line 101) -* QUIT signal (MS-Windows): Profiling. (line 207) -* quoting <1>: Comments. (line 27) -* quoting <2>: Long. (line 26) -* quoting: Read Terminal. (line 25) -* quoting, rules for: Quoting. (line 6) -* quoting, tricks for: Quoting. (line 71) -* r debugger command (alias for run): Dgawk Execution Control. +* question mark (?), regexp operator <1>: GNU Regexp Operators. + (line 59) +* question mark (?), regexp operator: Regexp Operators. (line 111) +* QuikTrim Awk: Other Versions. (line 139) +* quit debugger command: Miscellaneous Debugger Commands. + (line 99) +* QUIT signal (MS-Windows): Profiling. (line 213) +* quoting in gawk command lines: Long. (line 26) +* quoting in gawk command lines, tricks for: Quoting. (line 91) +* quoting, for small awk programs: Comments. (line 27) +* r debugger command (alias for run): Debugger Execution Control. (line 62) * Rakitzis, Byron: History Sorting. (line 25) -* rand() function: Numeric Functions. (line 33) +* Ramey, Chet <1>: General Data Types. (line 6) +* Ramey, Chet: Acknowledgments. (line 60) +* rand: Numeric Functions. (line 48) * random numbers, Cliff: Cliff Random Function. (line 6) * random numbers, rand()/srand() functions: Numeric Functions. - (line 33) -* random numbers, seed of: Numeric Functions. (line 63) + (line 48) +* random numbers, seed of: Numeric Functions. (line 78) * range expressions (regexps): Bracket Expressions. (line 6) * range patterns: Ranges. (line 6) -* Rankin, Pat <1>: Bugs. (line 72) -* Rankin, Pat <2>: Contributors. (line 38) -* Rankin, Pat <3>: Assignment Ops. (line 100) +* range patterns, line continuation and: Ranges. (line 65) +* Rankin, Pat <1>: Contributors. (line 37) +* Rankin, Pat <2>: Assignment Ops. (line 100) * Rankin, Pat: Acknowledgments. (line 60) +* reada() extension function: Extension Sample Read write array. + (line 18) * readable data files, checking: File Checking. (line 6) * readable.awk program: File Checking. (line 11) +* readdir extension: Extension Sample Readdir. + (line 9) +* readfile() extension function: Extension Sample Readfile. + (line 12) +* readfile() user-defined function: Readfile Function. (line 30) +* reading input files: Reading Files. (line 6) * recipe for a programming language: History. (line 6) -* record separators <1>: User-modified. (line 134) -* record separators: Records. (line 14) -* record separators, changing: Records. (line 81) -* record separators, regular expressions as: Records. (line 112) +* record separators <1>: User-modified. (line 132) +* record separators: awk split records. (line 6) +* record separators, changing: awk split records. (line 85) +* record separators, regular expressions as: awk split records. + (line 125) * record separators, with multiline records: Multiple Line. (line 10) -* records <1>: Basic High Level. (line 71) +* records <1>: Basic High Level. (line 73) * records: Reading Files. (line 14) * records, multiline: Multiple Line. (line 6) * records, printing: Print. (line 22) * records, splitting input into: Records. (line 6) -* records, terminating: Records. (line 112) -* records, treating files as: Records. (line 196) -* recursive functions: Definition Syntax. (line 73) +* records, terminating: awk split records. (line 125) +* records, treating files as: gawk split records. (line 93) +* recursive functions: Definition Syntax. (line 83) +* redirect gawk output, in debugger: Debugger Info. (line 72) * redirection of input: Getline/File. (line 6) * redirection of output: Redirection. (line 6) * reference counting, sorting arrays: Array Sorting Functions. - (line 72) + (line 77) +* regexp: Regexp. (line 6) * regexp constants <1>: Comparison Operators. (line 103) * regexp constants <2>: Regexp Constants. (line 6) * regexp constants: Regexp Usage. (line 57) * regexp constants, /=.../, /= operator and: Assignment Ops. (line 148) -* regexp constants, as patterns: Expression Patterns. (line 36) +* regexp constants, as patterns: Expression Patterns. (line 34) * regexp constants, in gawk: Using Constant Regexps. (line 28) -* regexp constants, slashes vs. quotes: Computed Regexps. (line 28) -* regexp constants, vs. string constants: Computed Regexps. (line 38) -* regexp, See regular expressions: Regexp. (line 6) -* register_deferred_variable() internal function: Internals. (line 140) -* register_open_hook() internal function: Internals. (line 151) +* regexp constants, slashes vs. quotes: Computed Regexps. (line 29) +* regexp constants, vs. string constants: Computed Regexps. (line 39) +* register extension: Registration Functions. + (line 6) * regular expressions: Regexp. (line 6) -* regular expressions as field separators: Field Separators. (line 50) +* regular expressions as field separators: Field Separators. (line 51) * regular expressions, anchors in: Regexp Operators. (line 22) * regular expressions, as field separators: Regexp Field Splitting. (line 6) * regular expressions, as patterns <1>: Regexp Patterns. (line 6) * regular expressions, as patterns: Regexp Usage. (line 6) -* regular expressions, as record separators: Records. (line 112) -* regular expressions, case sensitivity <1>: User-modified. (line 82) +* regular expressions, as record separators: awk split records. + (line 125) +* regular expressions, case sensitivity <1>: User-modified. (line 76) * regular expressions, case sensitivity: Case-sensitivity. (line 6) * regular expressions, computed: Computed Regexps. (line 6) * regular expressions, constants, See regexp constants: Regexp Usage. @@ -26929,7 +33848,7 @@ Index (line 59) * regular expressions, gawk, command-line options: GNU Regexp Operators. (line 70) -* regular expressions, interval expressions and: Options. (line 224) +* regular expressions, interval expressions and: Options. (line 279) * regular expressions, leftmost longest match: Leftmost Longest. (line 6) * regular expressions, operators <1>: Regexp Operators. (line 6) @@ -26941,16 +33860,21 @@ Index * regular expressions, operators, gawk: GNU Regexp Operators. (line 6) * regular expressions, operators, precedence of: Regexp Operators. - (line 152) + (line 156) * regular expressions, searching for: Egrep Program. (line 6) * relational operators, See comparison operators: Typing and Comparison. (line 9) -* return debugger command: Dgawk Execution Control. +* replace in string: String Functions. (line 408) +* return debugger command: Debugger Execution Control. (line 54) * return statement, user-defined functions: Return Statement. (line 6) -* return values, close() function: Close Files And Pipes. - (line 131) -* rev() user-defined function: Function Example. (line 52) +* return value, close() function: Close Files And Pipes. + (line 133) +* rev() user-defined function: Function Example. (line 54) +* revoutput extension: Extension Sample Revout. + (line 11) +* revtwoway extension: Extension Sample Rev2way. + (line 12) * rewind() user-defined function: Rewind Function. (line 16) * right angle bracket (>), > operator <1>: Precedence. (line 65) * right angle bracket (>), > operator: Comparison Operators. @@ -26961,249 +33885,327 @@ Index (line 11) * right angle bracket (>), >> operator (I/O) <1>: Precedence. (line 65) * right angle bracket (>), >> operator (I/O): Redirection. (line 50) +* right shift: Bitwise Functions. (line 53) * right shift, bitwise: Bitwise Functions. (line 32) -* Ritchie, Dennis: Basic Data Typing. (line 74) -* RLENGTH variable: Auto-set. (line 183) -* RLENGTH variable, match() function and: String Functions. (line 223) +* Ritchie, Dennis: Basic Data Typing. (line 54) +* RLENGTH variable: Auto-set. (line 266) +* RLENGTH variable, match() function and: String Functions. (line 228) * Robbins, Arnold <1>: Future Extensions. (line 6) -* Robbins, Arnold <2>: Bugs. (line 32) -* Robbins, Arnold <3>: Contributors. (line 108) -* Robbins, Arnold <4>: Alarm Program. (line 6) -* Robbins, Arnold <5>: Passwd Functions. (line 90) -* Robbins, Arnold <6>: Getline/Pipe. (line 36) +* Robbins, Arnold <2>: Bugs. (line 70) +* Robbins, Arnold <3>: Contributors. (line 144) +* Robbins, Arnold <4>: General Data Types. (line 6) +* Robbins, Arnold <5>: Alarm Program. (line 6) +* Robbins, Arnold <6>: Passwd Functions. (line 90) +* Robbins, Arnold <7>: Getline/Pipe. (line 39) * Robbins, Arnold: Command Line Field Separator. - (line 80) -* Robbins, Bill: Getline/Pipe. (line 36) -* Robbins, Harry: Acknowledgments. (line 81) -* Robbins, Jean: Acknowledgments. (line 81) + (line 71) +* Robbins, Bill: Getline/Pipe. (line 39) +* Robbins, Harry: Acknowledgments. (line 94) +* Robbins, Jean: Acknowledgments. (line 94) * Robbins, Miriam <1>: Passwd Functions. (line 90) -* Robbins, Miriam <2>: Getline/Pipe. (line 36) -* Robbins, Miriam: Acknowledgments. (line 81) -* Robinson, Will: Dynamic Extensions. (line 6) -* robot, the: Dynamic Extensions. (line 6) -* Rommel, Kai Uwe: Contributors. (line 43) +* Robbins, Miriam <2>: Getline/Pipe. (line 39) +* Robbins, Miriam: Acknowledgments. (line 94) +* Rommel, Kai Uwe: Contributors. (line 42) +* round to nearest integer: Numeric Functions. (line 38) * round() user-defined function: Round Function. (line 16) * rounding numbers: Round Function. (line 6) -* RS variable <1>: User-modified. (line 134) -* RS variable: Records. (line 20) +* ROUNDMODE variable: User-modified. (line 127) +* RS variable <1>: User-modified. (line 132) +* RS variable: awk split records. (line 12) * RS variable, multiline records and: Multiple Line. (line 17) -* rshift() function (gawk): Bitwise Functions. (line 51) -* RSTART variable: Auto-set. (line 189) -* RSTART variable, match() function and: String Functions. (line 223) -* RT variable <1>: Auto-set. (line 196) -* RT variable <2>: Getline/Variable/File. - (line 10) -* RT variable <3>: Multiple Line. (line 129) -* RT variable: Records. (line 112) -* Rubin, Paul <1>: Contributors. (line 16) +* rshift: Bitwise Functions. (line 53) +* RSTART variable: Auto-set. (line 272) +* RSTART variable, match() function and: String Functions. (line 228) +* RT variable <1>: Auto-set. (line 279) +* RT variable <2>: Multiple Line. (line 129) +* RT variable: awk split records. (line 125) +* Rubin, Paul <1>: Contributors. (line 15) * Rubin, Paul: History. (line 30) * rule, definition of: Getting Started. (line 21) -* run debugger command: Dgawk Execution Control. +* run debugger command: Debugger Execution Control. (line 62) * rvalues/lvalues: Assignment Ops. (line 32) -* s debugger command (alias for step): Dgawk Execution Control. +* s debugger command (alias for step): Debugger Execution Control. (line 68) -* sandbox mode: Options. (line 236) +* sample debugging session: Sample Debugging Session. + (line 6) +* sandbox mode: Options. (line 286) +* save debugger options: Debugger Info. (line 84) +* scalar or array: Type Functions. (line 11) * scalar values: Basic Data Typing. (line 13) +* scanning arrays: Scanning an Array. (line 6) +* scanning multidimensional arrays: Multiscanning. (line 11) +* Schorr, Andrew <1>: Contributors. (line 133) +* Schorr, Andrew <2>: Auto-set. (line 311) * Schorr, Andrew: Acknowledgments. (line 60) * Schreiber, Bert: Acknowledgments. (line 38) * Schreiber, Rita: Acknowledgments. (line 38) -* search paths <1>: VMS Running. (line 29) -* search paths <2>: PC Using. (line 11) -* search paths <3>: Igawk Program. (line 368) -* search paths: AWKPATH Variable. (line 6) -* search paths, for source files <1>: VMS Running. (line 29) -* search paths, for source files <2>: PC Using. (line 11) -* search paths, for source files <3>: Igawk Program. (line 368) +* search and replace in strings: String Functions. (line 90) +* search in string: String Functions. (line 156) +* search paths <1>: VMS Running. (line 57) +* search paths <2>: PC Using. (line 10) +* search paths: Programs Exercises. (line 70) +* search paths, for loadable extensions: AWKLIBPATH Variable. (line 6) +* search paths, for source files <1>: VMS Running. (line 57) +* search paths, for source files <2>: PC Using. (line 10) +* search paths, for source files <3>: Programs Exercises. (line 70) * search paths, for source files: AWKPATH Variable. (line 6) -* searching: String Functions. (line 155) * searching, files for regular expressions: Egrep Program. (line 6) * searching, for words: Dupword Program. (line 6) -* sed utility <1>: Glossary. (line 12) +* sed utility <1>: Glossary. (line 16) * sed utility <2>: Simple Sed. (line 6) -* sed utility: Field Splitting Summary. - (line 47) -* semicolon (;): Statements/Lines. (line 91) -* semicolon (;), AWKPATH variable and: PC Using. (line 11) +* sed utility: Full Line Fields. (line 22) +* seeding random number generator: Numeric Functions. (line 78) +* semicolon (;), AWKPATH variable and: PC Using. (line 10) * semicolon (;), separating statements in actions <1>: Statements. (line 10) -* semicolon (;), separating statements in actions: Action Overview. +* semicolon (;), separating statements in actions <2>: Action Overview. (line 19) -* separators, field: User-modified. (line 56) -* separators, field, FIELDWIDTHS variable and: User-modified. (line 35) -* separators, field, FPAT variable and: User-modified. (line 45) +* semicolon (;), separating statements in actions: Statements/Lines. + (line 91) +* separators, field: User-modified. (line 50) +* separators, field, FIELDWIDTHS variable and: User-modified. (line 37) +* separators, field, FPAT variable and: User-modified. (line 43) * separators, field, POSIX and: Fields. (line 6) -* separators, for records <1>: User-modified. (line 134) -* separators, for records: Records. (line 14) -* separators, for records, regular expressions as: Records. (line 112) +* separators, for records <1>: User-modified. (line 132) +* separators, for records: awk split records. (line 6) +* separators, for records, regular expressions as: awk split records. + (line 125) * separators, for statements in actions: Action Overview. (line 19) -* separators, subscript: User-modified. (line 147) +* separators, subscript: User-modified. (line 145) +* set breakpoint: Breakpoint Control. (line 11) * set debugger command: Viewing And Changing Data. (line 59) -* shells, piping commands into: Redirection. (line 143) +* set directory of message catalogs: I18N Functions. (line 12) +* set watchpoint: Viewing And Changing Data. + (line 67) +* shadowing of variable values: Definition Syntax. (line 71) +* shell quoting, rules for: Quoting. (line 6) +* shells, piping commands into: Redirection. (line 136) * shells, quoting: Using Shell Variables. (line 12) * shells, quoting, rules for: Quoting. (line 18) * shells, scripts: One-shot. (line 22) +* shells, sea: Undocumented. (line 8) * shells, variables: Using Shell Variables. (line 6) * shift, bitwise: Bitwise Functions. (line 32) -* short-circuit operators: Boolean Ops. (line 57) -* si debugger command (alias for stepi): Dgawk Execution Control. +* short-circuit operators: Boolean Ops. (line 59) +* show all source files, in debugger: Debugger Info. (line 45) +* show breakpoints: Debugger Info. (line 21) +* show function arguments, in debugger: Debugger Info. (line 18) +* show local variables, in debugger: Debugger Info. (line 34) +* show name of current source file, in debugger: Debugger Info. + (line 37) +* show watchpoints: Debugger Info. (line 51) +* si debugger command (alias for stepi): Debugger Execution Control. (line 76) * side effects <1>: Increment Ops. (line 11) -* side effects: Concatenation. (line 42) +* side effects: Concatenation. (line 41) * side effects, array indexing: Reference to Elements. - (line 42) + (line 43) * side effects, asort() function: Array Sorting Functions. - (line 22) + (line 24) * side effects, assignment expressions: Assignment Ops. (line 23) * side effects, Boolean operators: Boolean Ops. (line 30) * side effects, conditional expressions: Conditional Exp. (line 22) * side effects, decrement/increment operators: Increment Ops. (line 11) * side effects, FILENAME variable: Getline Notes. (line 19) -* side effects, function calls: Function Calls. (line 54) +* side effects, function calls: Function Calls. (line 57) * side effects, statements: Action Overview. (line 32) -* SIGHUP signal: Profiling. (line 204) -* SIGINT signal (MS-Windows): Profiling. (line 207) -* signals, HUP/SIGHUP: Profiling. (line 204) -* signals, INT/SIGINT (MS-Windows): Profiling. (line 207) -* signals, QUIT/SIGQUIT (MS-Windows): Profiling. (line 207) -* signals, USR1/SIGUSR1: Profiling. (line 182) -* SIGQUIT signal (MS-Windows): Profiling. (line 207) -* SIGUSR1 signal: Profiling. (line 182) -* silent debugger command: Dgawk Execution Control. +* sidebar, A Constant's Base Does Not Affect Its Value: Nondecimal-numbers. + (line 64) +* sidebar, Backslash Before Regular Characters: Escape Sequences. + (line 106) +* sidebar, Changing FS Does Not Affect the Fields: Full Line Fields. + (line 14) +* sidebar, Changing NR and FNR: Auto-set. (line 326) +* sidebar, Controlling Output Buffering with system(): I/O Functions. + (line 138) +* sidebar, Escape Sequences for Metacharacters: Escape Sequences. + (line 137) +* sidebar, FS and IGNORECASE: Field Splitting Summary. + (line 38) +* sidebar, Interactive Versus Noninteractive Buffering: I/O Functions. + (line 73) +* sidebar, Matching the Null String: String Functions. (line 534) +* sidebar, Operator Evaluation Order: Increment Ops. (line 58) +* sidebar, Piping into sh: Redirection. (line 134) +* sidebar, Pre-POSIX awk Used OFMT for String Conversion: Strings And Numbers. + (line 55) +* sidebar, Recipe for a Programming Language: History. (line 6) +* sidebar, RS = "\0" Is Not Portable: gawk split records. (line 63) +* sidebar, So Why Does gawk Have BEGINFILE and ENDFILE?: Filetrans Function. + (line 82) +* sidebar, Syntactic Ambiguities Between /= and Regular Expressions: Assignment Ops. + (line 146) +* sidebar, Understanding #!: Executable Scripts. (line 31) +* sidebar, Understanding $0: Changing Fields. (line 134) +* sidebar, Using \n in Bracket Expressions of Dynamic Regexps: Computed Regexps. + (line 57) +* sidebar, Using close()'s Return Value: Close Files And Pipes. + (line 131) +* SIGHUP signal, for dynamic profiling: Profiling. (line 210) +* SIGINT signal (MS-Windows): Profiling. (line 213) +* signals, HUP/SIGHUP, for profiling: Profiling. (line 210) +* signals, INT/SIGINT (MS-Windows): Profiling. (line 213) +* signals, QUIT/SIGQUIT (MS-Windows): Profiling. (line 213) +* signals, USR1/SIGUSR1, for profiling: Profiling. (line 187) +* signature program: Signature Program. (line 6) +* SIGQUIT signal (MS-Windows): Profiling. (line 213) +* SIGUSR1 signal, for dynamic profiling: Profiling. (line 187) +* silent debugger command: Debugger Execution Control. (line 10) -* sin() function: Numeric Functions. (line 74) -* single precision floating-point: Basic Data Typing. (line 36) -* single quote (') <1>: Quoting. (line 31) -* single quote (') <2>: Long. (line 33) +* sin: Numeric Functions. (line 89) +* sine: Numeric Functions. (line 89) * single quote ('): One-shot. (line 15) +* single quote (') in gawk command lines: Long. (line 35) +* single quote ('), in shell commands: Quoting. (line 48) * single quote ('), vs. apostrophe: Comments. (line 27) -* single quote ('), with double quotes: Quoting. (line 53) +* single quote ('), with double quotes: Quoting. (line 73) * single-character fields: Single Character Fields. (line 6) +* single-step execution, in the debugger: Debugger Execution Control. + (line 43) * Skywalker, Luke: Undocumented. (line 6) -* sleep utility: Alarm Program. (line 109) -* Solaris, POSIX-compliant awk: Other Versions. (line 86) +* sleep utility: Alarm Program. (line 110) +* sleep() extension function: Extension Sample Time. + (line 22) +* Solaris, POSIX-compliant awk: Other Versions. (line 100) +* sort array: String Functions. (line 42) +* sort array indices: String Functions. (line 42) * sort function, arrays, sorting: Array Sorting Functions. (line 6) * sort utility: Word Sorting. (line 50) -* sort utility, coprocesses and: Two-way I/O. (line 83) +* sort utility, coprocesses and: Two-way I/O. (line 65) * sorting characters in different languages: Explaining gettext. - (line 93) -* source code, awka: Other Versions. (line 55) + (line 94) +* source code, awka: Other Versions. (line 68) * source code, Brian Kernighan's awk: Other Versions. (line 13) -* source code, Busybox Awk: Other Versions. (line 78) +* source code, Busybox Awk: Other Versions. (line 92) * source code, gawk: Gawk Distribution. (line 6) -* source code, jawk: Other Versions. (line 96) -* source code, libmawk: Other Versions. (line 104) -* source code, mawk: Other Versions. (line 35) -* source code, mixing: Options. (line 105) -* source code, pawk: Other Versions. (line 69) -* source code, QSE Awk: Other Versions. (line 108) -* source code, QuikTrim Awk: Other Versions. (line 112) -* source code, Solaris awk: Other Versions. (line 86) -* source code, xgawk: Other Versions. (line 119) -* source files, search path for: Igawk Program. (line 368) -* sparse arrays: Array Intro. (line 71) -* Spencer, Henry: Glossary. (line 12) +* source code, Illumos awk: Other Versions. (line 109) +* source code, jawk: Other Versions. (line 117) +* source code, libmawk: Other Versions. (line 125) +* source code, mawk: Other Versions. (line 48) +* source code, mixing: Options. (line 117) +* source code, pawk: Other Versions. (line 82) +* source code, pawk (Python version): Other Versions. (line 129) +* source code, QSE Awk: Other Versions. (line 135) +* source code, QuikTrim Awk: Other Versions. (line 139) +* source code, Solaris awk: Other Versions. (line 100) +* source files, search path for: Programs Exercises. (line 70) +* sparse arrays: Array Intro. (line 72) +* Spencer, Henry: Glossary. (line 16) +* split: String Functions. (line 316) +* split string into array: String Functions. (line 297) * split utility: Split Program. (line 6) -* split() function: String Functions. (line 315) -* split() function, array elements, deleting: Delete. (line 57) +* split() function, array elements, deleting: Delete. (line 61) * split.awk program: Split Program. (line 30) -* sprintf() function <1>: String Functions. (line 380) -* sprintf() function: OFMT. (line 15) -* sprintf() function, OFMT variable and: User-modified. (line 124) +* sprintf <1>: String Functions. (line 383) +* sprintf: OFMT. (line 15) +* sprintf() function, OFMT variable and: User-modified. (line 113) * sprintf() function, print/printf statements and: Round Function. (line 6) -* sqrt() function: Numeric Functions. (line 77) -* square brackets ([]): Regexp Operators. (line 55) -* srand() function: Numeric Functions. (line 81) -* Stallman, Richard <1>: Glossary. (line 301) -* Stallman, Richard <2>: Contributors. (line 24) +* sqrt: Numeric Functions. (line 92) +* square brackets ([]), regexp operator: Regexp Operators. (line 56) +* square root: Numeric Functions. (line 92) +* srand: Numeric Functions. (line 96) +* stack frame: Debugging Terms. (line 10) +* Stallman, Richard <1>: Glossary. (line 288) +* Stallman, Richard <2>: Contributors. (line 23) * Stallman, Richard <3>: Acknowledgments. (line 18) * Stallman, Richard: Manual History. (line 6) * standard error: Special FD. (line 6) * standard input <1>: Special FD. (line 6) * standard input: Read Terminal. (line 6) * standard output: Special FD. (line 6) -* stat() function, implementing in gawk: Sample Library. (line 6) +* starting the debugger: Debugger Invocation. (line 6) +* stat() extension function: Extension Sample File Functions. + (line 18) * statements, compound, control statements and: Statements. (line 10) * statements, control, in actions: Statements. (line 6) * statements, multiple: Statements/Lines. (line 91) -* step debugger command: Dgawk Execution Control. +* step debugger command: Debugger Execution Control. (line 68) -* stepi debugger command: Dgawk Execution Control. +* stepi debugger command: Debugger Execution Control. (line 76) -* stlen internal variable: Internals. (line 46) -* stptr internal variable: Internals. (line 46) +* stop automatic display, in debugger: Viewing And Changing Data. + (line 80) * stream editors <1>: Simple Sed. (line 6) -* stream editors: Field Splitting Summary. - (line 47) -* strftime() function (gawk): Time Functions. (line 47) +* stream editors: Full Line Fields. (line 22) +* strftime: Time Functions. (line 48) * string constants: Scalar Constants. (line 15) -* string constants, vs. regexp constants: Computed Regexps. (line 38) +* string constants, vs. regexp constants: Computed Regexps. (line 39) * string extraction (internationalization): String Extraction. (line 6) -* string operators: Concatenation. (line 9) +* string length: String Functions. (line 171) +* string operators: Concatenation. (line 8) +* string, regular expression match: String Functions. (line 211) +* string-manipulation functions: String Functions. (line 6) * string-matching operators: Regexp Usage. (line 19) -* strings: Internals. (line 77) -* strings, converting <1>: Bitwise Functions. (line 107) -* strings, converting: Conversion. (line 6) -* strings, converting, numbers to: User-modified. (line 28) -* strings, empty, See null strings: Records. (line 102) +* string-translation functions: I18N Functions. (line 6) +* strings splitting, example: String Functions. (line 335) +* strings, converting <1>: Bitwise Functions. (line 110) +* strings, converting: Strings And Numbers. (line 6) +* strings, converting letter case: String Functions. (line 522) +* strings, converting, numbers to: User-modified. (line 30) +* strings, empty, See null strings: awk split records. (line 115) * strings, extracting: String Extraction. (line 6) * strings, for localization: Programmer i18n. (line 14) -* strings, length of: Scalar Constants. (line 20) +* strings, length limitations: Scalar Constants. (line 20) * strings, merging arrays into: Join Function. (line 6) -* strings, NODE internal type: Internals. (line 23) * strings, null: Regexp Field Splitting. (line 43) * strings, numeric: Variable Typing. (line 6) -* strings, splitting: String Functions. (line 335) -* strtonum() function (gawk): String Functions. (line 387) +* strtonum: String Functions. (line 390) * strtonum() function (gawk), --non-decimal-data option and: Nondecimal Data. - (line 36) -* sub() function <1>: String Functions. (line 408) -* sub() function: Using Constant Regexps. + (line 35) +* sub <1>: String Functions. (line 408) +* sub: Using Constant Regexps. (line 43) * sub() function, arguments of: String Functions. (line 462) * sub() function, escape processing: Gory Details. (line 6) -* subscript separators: User-modified. (line 147) -* subscripts in arrays, multidimensional: Multi-dimensional. (line 10) -* subscripts in arrays, multidimensional, scanning: Multi-scanning. +* subscript separators: User-modified. (line 145) +* subscripts in arrays, multidimensional: Multidimensional. (line 10) +* subscripts in arrays, multidimensional, scanning: Multiscanning. (line 11) * subscripts in arrays, numbers as: Numeric Array Subscripts. (line 6) * subscripts in arrays, uninitialized variables as: Uninitialized Subscripts. (line 6) -* SUBSEP variable: User-modified. (line 147) -* SUBSEP variable, multidimensional arrays: Multi-dimensional. +* SUBSEP variable: User-modified. (line 145) +* SUBSEP variable, and multidimensional arrays: Multidimensional. (line 16) -* substr() function: String Functions. (line 481) -* Sumner, Andrew: Other Versions. (line 55) +* substitute in string: String Functions. (line 90) +* substr: String Functions. (line 481) +* substring: String Functions. (line 481) +* Sumner, Andrew: Other Versions. (line 68) +* supplementary groups of gawk process: Auto-set. (line 251) * switch statement: Switch Statement. (line 6) +* SYMTAB array: Auto-set. (line 283) * syntactic ambiguity: /= operator vs. /=.../ regexp constant: Assignment Ops. (line 148) -* system() function: I/O Functions. (line 63) -* systime() function (gawk): Time Functions. (line 64) -* t debugger command (alias for tbreak): Breakpoint Control. (line 89) -* tbreak debugger command: Breakpoint Control. (line 89) -* Tcl: Library Names. (line 57) +* system: I/O Functions. (line 106) +* systime: Time Functions. (line 66) +* t debugger command (alias for tbreak): Breakpoint Control. (line 90) +* tbreak debugger command: Breakpoint Control. (line 90) +* Tcl: Library Names. (line 58) * TCP/IP: TCP/IP Networking. (line 6) * TCP/IP, support for: Special Network. (line 6) * tee utility: Tee Program. (line 6) * tee.awk program: Tee Program. (line 26) -* terminating records: Records. (line 112) -* testbits.awk program: Bitwise Functions. (line 68) +* temporary breakpoint: Breakpoint Control. (line 90) +* terminating records: awk split records. (line 125) +* testbits.awk program: Bitwise Functions. (line 71) +* testext extension: Extension Sample API Tests. + (line 6) * Texinfo <1>: Adding Code. (line 99) * Texinfo <2>: Distribution contents. - (line 79) + (line 77) * Texinfo <3>: Extract Program. (line 12) * Texinfo <4>: Dupword Program. (line 17) -* Texinfo <5>: Library Functions. (line 22) -* Texinfo <6>: Sample Data Files. (line 66) +* Texinfo <5>: Library Functions. (line 33) * Texinfo: Conventions. (line 6) * Texinfo, chapter beginnings in files: Regexp Operators. (line 22) * Texinfo, extracting programs from source files: Extract Program. @@ -27211,128 +34213,130 @@ Index * text, printing: Print. (line 22) * text, printing, unduplicated lines of: Uniq Program. (line 6) * TEXTDOMAIN variable <1>: Programmer i18n. (line 9) -* TEXTDOMAIN variable: User-modified. (line 153) +* TEXTDOMAIN variable: User-modified. (line 151) * TEXTDOMAIN variable, BEGIN pattern and: Programmer i18n. (line 60) * TEXTDOMAIN variable, portability and: I18N Portability. (line 20) -* textdomain() function (C library): Explaining gettext. (line 27) +* textdomain() function (C library): Explaining gettext. (line 28) * tilde (~), ~ operator <1>: Expression Patterns. (line 24) * tilde (~), ~ operator <2>: Precedence. (line 80) * tilde (~), ~ operator <3>: Comparison Operators. (line 11) * tilde (~), ~ operator <4>: Regexp Constants. (line 6) -* tilde (~), ~ operator <5>: Computed Regexps. (line 6) -* tilde (~), ~ operator <6>: Case-sensitivity. (line 26) +* tilde (~), ~ operator <5>: Case-sensitivity. (line 26) +* tilde (~), ~ operator <6>: Computed Regexps. (line 6) * tilde (~), ~ operator: Regexp Usage. (line 19) -* time, alarm clock example program: Alarm Program. (line 9) -* time, localization and: Explaining gettext. (line 115) -* time, managing: Gettimeofday Function. +* time functions: Time Functions. (line 6) +* time, alarm clock example program: Alarm Program. (line 11) +* time, localization and: Explaining gettext. (line 112) +* time, managing: Getlocaltime Function. (line 6) * time, retrieving: Time Functions. (line 17) +* timeout, reading input: Read Timeout. (line 6) * timestamps: Time Functions. (line 6) -* timestamps, converting dates to: Time Functions. (line 74) -* timestamps, formatted: Gettimeofday Function. +* timestamps, converting dates to: Time Functions. (line 76) +* timestamps, formatted: Getlocaltime Function. (line 6) -* tolower() function: String Functions. (line 523) -* toupper() function: String Functions. (line 529) +* tolower: String Functions. (line 523) +* toupper: String Functions. (line 529) * tr utility: Translate Program. (line 6) -* trace debugger command: Miscellaneous Dgawk Commands. - (line 110) +* trace debugger command: Miscellaneous Debugger Commands. + (line 108) +* traceback, display in debugger: Execution Stack. (line 13) +* translate string: I18N Functions. (line 22) * translate.awk program: Translate Program. (line 55) -* troubleshooting, --non-decimal-data option: Options. (line 166) +* treating files, as single records: gawk split records. (line 93) +* troubleshooting, --non-decimal-data option: Options. (line 211) * troubleshooting, == operator: Comparison Operators. (line 37) -* troubleshooting, awk uses FS not IFS: Field Separators. (line 29) +* troubleshooting, awk uses FS not IFS: Field Separators. (line 30) * troubleshooting, backslash before nonspecial character: Escape Sequences. - (line 113) + (line 108) * troubleshooting, division: Arithmetic Ops. (line 44) * troubleshooting, fatal errors, field widths, specifying: Constant Size. (line 22) * troubleshooting, fatal errors, printf format strings: Format Modifiers. - (line 159) -* troubleshooting, fflush() function: I/O Functions. (line 51) -* troubleshooting, function call syntax: Function Calls. (line 28) + (line 158) +* troubleshooting, fflush() function: I/O Functions. (line 62) +* troubleshooting, function call syntax: Function Calls. (line 30) * troubleshooting, gawk: Compatibility Mode. (line 6) * troubleshooting, gawk, bug reports: Bugs. (line 9) * troubleshooting, gawk, fatal errors, function arguments: Calling Built-in. (line 16) * troubleshooting, getline function: File Checking. (line 25) * troubleshooting, gsub()/sub() functions: String Functions. (line 472) -* troubleshooting, match() function: String Functions. (line 288) -* troubleshooting, patsplit() function: String Functions. (line 311) +* troubleshooting, match() function: String Functions. (line 292) * troubleshooting, print statement, omitting commas: Print Examples. (line 31) -* troubleshooting, printing: Redirection. (line 118) -* troubleshooting, quotes with file names: Special FD. (line 68) +* troubleshooting, printing: Redirection. (line 112) +* troubleshooting, quotes with file names: Special FD. (line 62) * troubleshooting, readable data files: File Checking. (line 6) * troubleshooting, regexp constants vs. string constants: Computed Regexps. - (line 38) -* troubleshooting, string concatenation: Concatenation. (line 27) + (line 39) +* troubleshooting, string concatenation: Concatenation. (line 26) * troubleshooting, substr() function: String Functions. (line 499) -* troubleshooting, system() function: I/O Functions. (line 85) +* troubleshooting, system() function: I/O Functions. (line 128) * troubleshooting, typographical errors, global variables: Options. - (line 95) + (line 98) * true, logical: Truth Values. (line 6) -* Trueman, David <1>: Contributors. (line 31) +* Trueman, David <1>: Contributors. (line 30) * Trueman, David <2>: Acknowledgments. (line 47) * Trueman, David: History. (line 30) * trunc-mod operation: Arithmetic Ops. (line 66) * truth values: Truth Values. (line 6) -* type conversion: Conversion. (line 21) -* type internal variable: Internals. (line 59) -* u debugger command (alias for until): Dgawk Execution Control. +* type conversion: Strings And Numbers. (line 21) +* u debugger command (alias for until): Debugger Execution Control. (line 83) +* unassigned array elements: Reference to Elements. + (line 18) * undefined functions: Pass By Value/Reference. - (line 71) -* underscore (_), _ C macro: Explaining gettext. (line 70) + (line 68) +* underscore (_), C macro: Explaining gettext. (line 71) * underscore (_), in names of private variables: Library Names. (line 29) * underscore (_), translatable string: Programmer i18n. (line 69) * undisplay debugger command: Viewing And Changing Data. (line 80) * undocumented features: Undocumented. (line 6) -* Unicode: Glossary. (line 141) +* Unicode <1>: Glossary. (line 133) +* Unicode <2>: Ranges and Locales. (line 61) +* Unicode: Ordinal Functions. (line 45) * uninitialized variables, as array subscripts: Uninitialized Subscripts. (line 6) * uniq utility: Uniq Program. (line 6) * uniq.awk program: Uniq Program. (line 65) * Unix: Glossary. (line 611) * Unix awk, backslashes in escape sequences: Escape Sequences. - (line 125) + (line 120) * Unix awk, close() function and: Close Files And Pipes. - (line 131) + (line 133) * Unix awk, password files, field separators and: Command Line Field Separator. - (line 72) + (line 62) * Unix, awk scripts and: Executable Scripts. (line 6) -* UNIXROOT variable, on OS/2 systems: PC Using. (line 17) -* unref() internal function: Internals. (line 92) -* unsigned integers: Basic Data Typing. (line 30) -* until debugger command: Dgawk Execution Control. +* UNIXROOT variable, on OS/2 systems: PC Using. (line 16) +* unsigned integers: Computer Arithmetic. (line 41) +* until debugger command: Debugger Execution Control. (line 83) * unwatch debugger command: Viewing And Changing Data. (line 84) -* up debugger command: Dgawk Stack. (line 33) -* update_ERRNO() internal function: Internals. (line 130) -* update_ERRNO_saved() internal function: Internals. (line 135) +* up debugger command: Execution Stack. (line 36) * user database, reading: Passwd Functions. (line 6) -* user-defined, functions: User-defined. (line 6) -* user-defined, functions, counts: Profiling. (line 132) +* user-defined functions: User-defined. (line 6) +* user-defined, functions, counts, in a profile: Profiling. (line 137) * user-defined, variables: Variables. (line 6) * user-modifiable variables: User-modified. (line 6) * users, information about, printing: Id Program. (line 6) * users, information about, retrieving: Passwd Functions. (line 16) -* USR1 signal: Profiling. (line 182) +* USR1 signal, for dynamic profiling: Profiling. (line 187) * values, numeric: Basic Data Typing. (line 13) * values, string: Basic Data Typing. (line 13) +* variable assignments and input files: Other Arguments. (line 26) * variable typing: Typing and Comparison. (line 9) * variables <1>: Basic Data Typing. (line 6) * variables: Other Features. (line 6) * variables, assigning on command line: Assignment Options. (line 6) -* variables, built-in <1>: Built-in Variables. (line 6) -* variables, built-in: Using Variables. (line 20) -* variables, built-in, -v option, setting with: Options. (line 40) -* variables, built-in, conveying information: Auto-set. (line 6) -* variables, flag: Boolean Ops. (line 67) +* variables, built-in: Using Variables. (line 23) +* variables, flag: Boolean Ops. (line 69) * variables, getline command into, using <1>: Getline/Variable/Coprocess. (line 6) * variables, getline command into, using <2>: Getline/Variable/Pipe. @@ -27341,52 +34345,65 @@ Index (line 6) * variables, getline command into, using: Getline/Variable. (line 6) * variables, global, for library functions: Library Names. (line 11) -* variables, global, printing list of: Options. (line 90) -* variables, initializing: Using Variables. (line 20) -* variables, local: Variable Scope. (line 6) -* variables, names of: Arrays. (line 18) +* variables, global, printing list of: Options. (line 93) +* variables, initializing: Using Variables. (line 23) +* variables, local to a function: Variable Scope. (line 6) +* variables, predefined: Built-in Variables. (line 6) +* variables, predefined -v option, setting with: Options. (line 40) +* variables, predefined conveying information: Auto-set. (line 6) * variables, private: Library Names. (line 11) * variables, setting: Options. (line 32) -* variables, shadowing: Definition Syntax. (line 61) +* variables, shadowing: Definition Syntax. (line 71) * variables, types of: Assignment Ops. (line 40) * variables, types of, comparison expressions and: Typing and Comparison. (line 9) * variables, uninitialized, as array subscripts: Uninitialized Subscripts. (line 6) * variables, user-defined: Variables. (line 6) -* vertical bar (|): Regexp Operators. (line 69) +* version of gawk: Auto-set. (line 221) +* version of gawk extension API: Auto-set. (line 246) +* version of GNU MP library: Auto-set. (line 232) +* version of GNU MPFR library: Auto-set. (line 228) +* vertical bar (|): Regexp Operators. (line 70) * vertical bar (|), | operator (I/O) <1>: Precedence. (line 65) -* vertical bar (|), | operator (I/O): Getline/Pipe. (line 6) -* vertical bar (|), |& operator (I/O) <1>: Two-way I/O. (line 44) +* vertical bar (|), | operator (I/O): Getline/Pipe. (line 9) +* vertical bar (|), |& operator (I/O) <1>: Two-way I/O. (line 25) * vertical bar (|), |& operator (I/O) <2>: Precedence. (line 65) * vertical bar (|), |& operator (I/O): Getline/Coprocess. (line 6) * vertical bar (|), || operator <1>: Precedence. (line 89) -* vertical bar (|), || operator: Boolean Ops. (line 57) +* vertical bar (|), || operator: Boolean Ops. (line 59) * Vinschen, Corinna: Acknowledgments. (line 60) -* vname internal variable: Internals. (line 64) * w debugger command (alias for watch): Viewing And Changing Data. (line 67) * w utility: Constant Size. (line 22) +* wait() extension function: Extension Sample Fork. + (line 22) +* waitpid() extension function: Extension Sample Fork. + (line 18) * walk_array() user-defined function: Walking Arrays. (line 14) * Wall, Larry <1>: Future Extensions. (line 6) * Wall, Larry: Array Intro. (line 6) -* Wallin, Anders: Acknowledgments. (line 60) -* warnings, issuing: Options. (line 147) +* Wallin, Anders: Contributors. (line 103) +* warnings, issuing: Options. (line 185) * watch debugger command: Viewing And Changing Data. (line 67) +* watchpoint: Debugging Terms. (line 42) * wc utility: Wc Program. (line 6) * wc.awk program: Wc Program. (line 46) -* Weinberger, Peter <1>: Contributors. (line 12) +* Weinberger, Peter <1>: Contributors. (line 11) * Weinberger, Peter: History. (line 17) -* while statement <1>: While Statement. (line 6) -* while statement: Regexp Usage. (line 19) +* where debugger command: Execution Stack. (line 13) +* where debugger command (alias for backtrace): Execution Stack. + (line 13) +* while statement: While Statement. (line 6) +* while statement, use of regexps in: Regexp Usage. (line 19) * whitespace, as field separators: Default Field Splitting. (line 6) * whitespace, functions, calling: Calling Built-in. (line 10) -* whitespace, newlines as: Options. (line 205) -* Williams, Kent: Contributors. (line 35) +* whitespace, newlines as: Options. (line 260) +* Williams, Kent: Contributors. (line 34) * Woehlke, Matthew: Contributors. (line 79) -* Woods, John: Contributors. (line 28) +* Woods, John: Contributors. (line 27) * word boundaries, matching: GNU Regexp Operators. (line 38) * word, regexp definition of: GNU Regexp Operators. @@ -27397,869 +34414,599 @@ Index * words, counting: Wc Program. (line 6) * words, duplicate, searching for: Dupword Program. (line 6) * words, usage counts, generating: Word Sorting. (line 6) -* wstlen internal variable: Internals. (line 54) -* wstptr internal variable: Internals. (line 54) -* xgawk: Other Versions. (line 119) +* writea() extension function: Extension Sample Read write array. + (line 12) * xgettext utility: String Extraction. (line 13) -* XML (eXtensible Markup Language): Internals. (line 151) +* xor: Bitwise Functions. (line 56) * XOR bitwise operation: Bitwise Functions. (line 6) -* xor() function (gawk): Bitwise Functions. (line 54) -* Yawitz, Efraim: Contributors. (line 106) +* Yawitz, Efraim: Contributors. (line 131) * Zaretskii, Eli <1>: Bugs. (line 70) -* Zaretskii, Eli <2>: Contributors. (line 56) +* Zaretskii, Eli <2>: Contributors. (line 55) * Zaretskii, Eli: Acknowledgments. (line 60) -* zero, negative vs. positive: Unexpected Results. (line 28) * zerofile.awk program: Empty Files. (line 21) -* Zoulas, Christos: Contributors. (line 67) +* Zoulas, Christos: Contributors. (line 66) +* {} (braces): Profiling. (line 142) * {} (braces), actions and: Action Overview. (line 19) -* {} (braces), pgawk program: Profiling. (line 137) * {} (braces), statements, grouping: Statements. (line 10) -* | (vertical bar): Regexp Operators. (line 69) +* | (vertical bar): Regexp Operators. (line 70) * | (vertical bar), | operator (I/O) <1>: Precedence. (line 65) * | (vertical bar), | operator (I/O) <2>: Redirection. (line 57) -* | (vertical bar), | operator (I/O): Getline/Pipe. (line 6) -* | (vertical bar), |& operator (I/O) <1>: Two-way I/O. (line 44) +* | (vertical bar), | operator (I/O): Getline/Pipe. (line 9) +* | (vertical bar), |& operator (I/O) <1>: Two-way I/O. (line 25) * | (vertical bar), |& operator (I/O) <2>: Precedence. (line 65) -* | (vertical bar), |& operator (I/O) <3>: Redirection. (line 102) +* | (vertical bar), |& operator (I/O) <3>: Redirection. (line 96) * | (vertical bar), |& operator (I/O): Getline/Coprocess. (line 6) * | (vertical bar), |& operator (I/O), pipes, closing: Close Files And Pipes. - (line 118) + (line 121) * | (vertical bar), || operator <1>: Precedence. (line 89) -* | (vertical bar), || operator: Boolean Ops. (line 57) +* | (vertical bar), || operator: Boolean Ops. (line 59) * ~ (tilde), ~ operator <1>: Expression Patterns. (line 24) * ~ (tilde), ~ operator <2>: Precedence. (line 80) * ~ (tilde), ~ operator <3>: Comparison Operators. (line 11) * ~ (tilde), ~ operator <4>: Regexp Constants. (line 6) -* ~ (tilde), ~ operator <5>: Computed Regexps. (line 6) -* ~ (tilde), ~ operator <6>: Case-sensitivity. (line 26) +* ~ (tilde), ~ operator <5>: Case-sensitivity. (line 26) +* ~ (tilde), ~ operator <6>: Computed Regexps. (line 6) * ~ (tilde), ~ operator: Regexp Usage. 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+Node: Old Extension Mechanism1178389 +Node: Notes summary1180151 +Node: Basic Concepts1181337 +Node: Basic High Level1182018 +Ref: figure-general-flow1182290 +Ref: figure-process-flow1182889 +Ref: Basic High Level-Footnote-11186118 +Node: Basic Data Typing1186303 +Node: Glossary1189631 +Node: Copying1214789 +Node: GNU Free Documentation License1252345 +Node: Index1277481 End Tag Table |