path: root/README

README file for PCRE (Perl-compatible regular expressions)
----------------------------------------------------------

*******************************************************************************
*           IMPORTANT FOR THOSE UPGRADING FROM VERSIONS BEFORE 2.00           *
*                                                                             *
* Please note that there has been a change in the API such that a larger      *
* ovector is required at matching time, to provide some additional workspace. *
* The new man page has details. This change was necessary in order to support *
* some of the new functionality in Perl 5.005.                                *
*                                                                             *
*           IMPORTANT FOR THOSE UPGRADING FROM VERSION 2.00                   *
*                                                                             *
* Another (I hope this is the last!) change has been made to the API for the  *
* pcre_compile() function. An additional argument has been added to make it   *
* possible to pass over a pointer to character tables built in the current    *
* locale by pcre_maketables(). To use the default tables, this new arguement  *
* should be passed as NULL.                                                   *
*******************************************************************************

The distribution should contain the following files:

  ChangeLog         log of changes to the code
  Makefile          for building PCRE
  README            this file
  RunTest           a shell script for running tests
  Tech.Notes        notes on the encoding
  pcre.3            man page for the functions
  pcreposix.3       man page for the POSIX wrapper API
  dftables.c        auxiliary program for building chartables.c
  maketables.c      )
  study.c           ) source of
  pcre.c            )   the functions
  pcreposix.c       )
  pcre.h            header for the external API
  pcreposix.h       header for the external POSIX wrapper API
  internal.h        header for internal use
  pcretest.c        test program
  pgrep.1           man page for pgrep
  pgrep.c           source of a grep utility that uses PCRE
  perltest          Perl test program
  testinput         test data, compatible with Perl 5.004 and 5.005
  testinput2        test data for error messages and non-Perl things
  testinput3        test data, compatible with Perl 5.005
  testinput4        test data for locale-specific tests
  testoutput        test results corresponding to testinput
  testoutput2       test results corresponding to testinput2
  testoutput3       test results corresponding to testinput3
  testoutput4       test results corresponding to testinput4

To build PCRE, edit Makefile for your system (it is a fairly simple make file,
and there are some comments at the top) and then run it. It builds two
libraries called libpcre.a and libpcreposix.a, a test program called pcretest,
and the pgrep command.

To test PCRE, run the RunTest script in the pcre directory. This runs pcretest
on each of the testinput files in turn, and compares the output with the
contents of the corresponding testoutput file. A file called testtry is used to
hold the output from pcretest (which is documented below).

To run pcretest on just one of the test files, give its number as an argument
to RunTest, for example:

  RunTest 3

The first and third test files can also be fed directly into the perltest
program to check that Perl gives the same results. The third file requires the
additional features of release 5.005, which is why it is kept separate from the
main test input, which needs only Perl 5.004. In the long run, when 5.005 is
widespread, these two test files may get amalgamated.

The second set of tests check pcre_info(), pcre_study(), error detection and
run-time flags that are specific to PCRE, as well as the POSIX wrapper API.

The fourth set of tests checks pcre_maketables(), the facility for building a
set of character tables for a specific locale and using them instead of the
default tables. The tests make use of the "fr" (French) locale. Before running
the test, the script checks for the presence of this locale by running the
"locale" command. If that command fails, or if it doesn't include "fr" in the
list of available locales, the fourth test cannot be run, and a comment is
output to say why. If running this test produces instances of the error

  ** Failed to set locale "fr"

in the comparison output, it means that locale is not available on your system,
despite being listed by "locale". This does not mean that PCRE is broken.

To install PCRE, copy libpcre.a to any suitable library directory (e.g.
/usr/local/lib), pcre.h to any suitable include directory (e.g.
/usr/local/include), and pcre.3 to any suitable man directory (e.g.
/usr/local/man/man3).

To install the pgrep command, copy it to any suitable binary directory, (e.g.
/usr/local/bin) and pgrep.1 to any suitable man directory (e.g.
/usr/local/man/man1).

PCRE has its own native API, but a set of "wrapper" functions that are based on
the POSIX API are also supplied in the library libpcreposix.a. Note that this
just provides a POSIX calling interface to PCRE: the regular expressions
themselves still follow Perl syntax and semantics. The header file
for the POSIX-style functions is called pcreposix.h. The official POSIX name is
regex.h, but I didn't want to risk possible problems with existing files of
that name by distributing it that way. To use it with an existing program that
uses the POSIX API, it will have to be renamed or pointed at by a link.


Character tables
----------------

PCRE uses four tables for manipulating and identifying characters. The final
argument of the pcre_compile() function is a pointer to a block of memory
containing the concatenated tables. A call to pcre_maketables() is used to
generate a set of tables in the current locale. However, if the final argument
is passed as NULL, a set of default tables that is built into the binary is
used.

The source file called chartables.c contains the default set of tables. This is
not supplied in the distribution, but is built by the program dftables
(compiled from dftables.c), which uses the ANSI C character handling functions
such as isalnum(), isalpha(), isupper(), islower(), etc. to build the table
sources. This means that the default C locale set your system will control the
contents of the tables. You can change the default tables by editing
chartables.c and then re-building PCRE. If you do this, you should probably
also edit Makefile to ensure that the file doesn't ever get re-generated.

The first two 256-byte tables provide lower casing and case flipping functions,
respectively. The next table consists of three 32-byte bit maps which identify
digits, "word" characters, and white space, respectively. These are used when
building 32-byte bit maps that represent character classes.

The final 256-byte table has bits indicating various character types, as
follows:

    1   white space character
    2   letter
    4   decimal digit
    8   hexadecimal digit
   16   alphanumeric or '_'
  128   regular expression metacharacter or binary zero

You should not alter the set of characters that contain the 128 bit, as that
will cause PCRE to malfunction.


The pcretest program
--------------------

This program is intended for testing PCRE, but it can also be used for
experimenting with regular expressions.

If it is given two filename arguments, it reads from the first and writes to
the second. If it is given only one filename argument, it reads from that file
and writes to stdout. Otherwise, it reads from stdin and writes to stdout, and
prompts for each line of input.

The program handles any number of sets of input on a single input file. Each
set starts with a regular expression, and continues with any number of data
lines to be matched against the pattern. An empty line signals the end of the
set. The regular expressions are given enclosed in any non-alphameric
delimiters, for example

  /(a|bc)x+yz/

and may be followed by i, m, s, or x to set the PCRE_CASELESS, PCRE_MULTILINE,
PCRE_DOTALL, or PCRE_EXTENDED options, respectively. These options have the
same effect as they do in Perl.

There are also some upper case options that do not match Perl options: /A, /E,
and /X set PCRE_ANCHORED, PCRE_DOLLAR_ENDONLY, and PCRE_EXTRA respectively.

The /L option must be followed directly by the name of a locale, for example,

  /pattern/Lfr

For this reason, it must be the last option letter. The given locale is set,
pcre_maketables() is called to build a set of character tables for the locale,
and this is then passed to pcre_compile() when compiling the regular
expression. Without an /L option, NULL is passed as the tables pointer; that
is, /L applies only to the expression on which it appears.

The /I option requests that pcretest output information about the compiled
expression (whether it is anchored, has a fixed first character, and so on). It
does this by calling pcre_info() after compiling an expression, and outputting
the information it gets back. If the pattern is studied, the results of that
are also output.

The /D option is a PCRE debugging feature, which also assumes /I. It causes the
internal form of compiled regular expressions to be output after compilation.

The /S option causes pcre_study() to be called after the expression has been
compiled, and the results used when the expression is matched.

Finally, the /P option causes pcretest to call PCRE via the POSIX wrapper API
rather than its native API. When this is done, all other options except /i and
/m are ignored. REG_ICASE is set if /i is present, and REG_NEWLINE is set if /m
is present. The wrapper functions force PCRE_DOLLAR_ENDONLY always, and
PCRE_DOTALL unless REG_NEWLINE is set.

A regular expression can extend over several lines of input; the newlines are
included in it. See the testinput files for many examples.

Before each data line is passed to pcre_exec(), leading and trailing whitespace
is removed, and it is then scanned for \ escapes. The following are recognized:

  \a     alarm (= BEL)
  \b     backspace
  \e     escape
  \f     formfeed
  \n     newline
  \r     carriage return
  \t     tab
  \v     vertical tab
  \nnn   octal character (up to 3 octal digits)
  \xhh   hexadecimal character (up to 2 hex digits)

  \A     pass the PCRE_ANCHORED option to pcre_exec()
  \B     pass the PCRE_NOTBOL option to pcre_exec()
  \Odd   set the size of the output vector passed to pcre_exec() to dd
           (any number of decimal digits)
  \Z     pass the PCRE_NOTEOL option to pcre_exec()

A backslash followed by anything else just escapes the anything else. If the
very last character is a backslash, it is ignored. This gives a way of passing
an empty line as data, since a real empty line terminates the data input.

If /P was present on the regex, causing the POSIX wrapper API to be used, only
\B, and \Z have any effect, causing REG_NOTBOL and REG_NOTEOL to be passed to
regexec() respectively.

When a match succeeds, pcretest outputs the list of identified substrings that
pcre_exec() returns, starting with number 0 for the string that matched the
whole pattern. Here is an example of an interactive pcretest run.

  $ pcretest
  Testing Perl-Compatible Regular Expressions
  PCRE version 0.90 08-Sep-1997

    re> /^abc(\d+)/
  data> abc123
    0: abc123
    1: 123
  data> xyz
  No match

Note that while patterns can be continued over several lines (a plain ">"
prompt is used for continuations), data lines may not. However newlines can be
included in data by means of the \n escape.

If the -p option is given to pcretest, it is equivalent to adding /P to each
regular expression: the POSIX wrapper API is used to call PCRE. None of the
following flags has any effect in this case.

If the option -d is given to pcretest, it is equivalent to adding /D to each
regular expression: the internal form is output after compilation.

If the option -i is given to pcretest, it is equivalent to adding /I to each
regular expression: information about the compiled pattern is given after
compilation.

If the option -s is given to pcretest, it outputs the size of each compiled
pattern after it has been compiled.

If the -t option is given, each compile, study, and match is run 10000 times
while being timed, and the resulting time per compile or match is output in
milliseconds. Do not set -t with -s, because you will then get the size output
10000 times and the timing will be distorted. If you want to change the number
of repetitions used for timing, edit the definition of LOOPREPEAT at the top of
pcretest.c



The perltest program
--------------------

The perltest program tests Perl's regular expressions; it has the same
specification as pcretest, and so can be given identical input, except that
input patterns can be followed only by Perl's lower case options. The contents
of testinput and testinput3 meet this condition.

The data lines are processed as Perl strings, so if they contain $ or @
characters, these have to be escaped. For this reason, all such characters in
the testinput file are escaped so that it can be used for perltest as well as
for pcretest, and the special upper case options such as /A that pcretest
recognizes are not used in this file. The output should be identical, apart
from the initial identifying banner.

The testinput2 and testinput4 files are not suitable for feeding to Perltest,
since they do make use of the special upper case options and escapes that
pcretest uses to test some features of PCRE. The first of these files also
contains malformed regular expressions, in order to check that PCRE diagnoses
them correctly.

Philip Hazel <ph10@cam.ac.uk>
January 1999