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PCRESAMPLE(3)						     Library Functions Manual						     PCRESAMPLE(3)

PCRE - Perl-compatible regular expressions PCRE SAMPLE PROGRAM
A simple, complete demonstration program, to get you started with using PCRE, is supplied in the file pcredemo.c in the PCRE distribution. A listing of this program is given in the pcredemo documentation. If you do not have a copy of the PCRE distribution, you can save this listing to re-create pcredemo.c. The program compiles the regular expression that is its first argument, and matches it against the subject string in its second argument. No PCRE options are set, and default character tables are used. If matching succeeds, the program outputs the portion of the subject that matched, together with the contents of any captured substrings. If the -g option is given on the command line, the program then goes on to check for further matches of the same regular expression in the same subject string. The logic is a little bit tricky because of the possibility of matching an empty string. Comments in the code explain what is going on. If PCRE is installed in the standard include and library directories for your operating system, you should be able to compile the demon- stration program using this command: gcc -o pcredemo pcredemo.c -lpcre If PCRE is installed elsewhere, you may need to add additional options to the command line. For example, on a Unix-like system that has PCRE installed in /usr/local, you can compile the demonstration program using a command like this: gcc -o pcredemo -I/usr/local/include pcredemo.c -L/usr/local/lib -lpcre In a Windows environment, if you want to statically link the program against a non-dll pcre.a file, you must uncomment the line that defines PCRE_STATIC before including pcre.h, because otherwise the pcre_malloc() and pcre_free() exported functions will be declared __declspec(dllimport), with unwanted results. Once you have compiled and linked the demonstration program, you can run simple tests like this: ./pcredemo 'cat|dog' 'the cat sat on the mat' ./pcredemo -g 'cat|dog' 'the dog sat on the cat' Note that there is a much more comprehensive test program, called pcretest, which supports many more facilities for testing regular expres- sions and the PCRE library. The pcredemo program is provided as a simple coding example. If you try to run pcredemo when PCRE is not installed in the standard library directory, you may get an error like this on some operating systems (e.g. Solaris): a.out: fatal: open failed: No such file or directory This is caused by the way shared library support works on those systems. You need to add -R/usr/local/lib (for example) to the compile command to get round this problem. AUTHOR
Philip Hazel University Computing Service Cambridge CB2 3QH, England. REVISION
Last updated: 17 November 2010 Copyright (c) 1997-2010 University of Cambridge. PCRESAMPLE(3)

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PCRE(3)                                                      Library Functions Manual                                                      PCRE(3)

PCRE - Perl-compatible regular expressions (original API) PLEASE TAKE NOTE
This document relates to PCRE releases that use the original API, with library names libpcre, libpcre16, and libpcre32. January 2015 saw the first release of a new API, known as PCRE2, with release numbers starting at 10.00 and library names libpcre2-8, libpcre2-16, and libpcre2-32. The old libraries (now called PCRE1) are still being maintained for bug fixes, but there will be no new development. New projects are advised to use the new PCRE2 libraries. INTRODUCTION
The PCRE library is a set of functions that implement regular expression pattern matching using the same syntax and semantics as Perl, with just a few differences. Some features that appeared in Python and PCRE before they appeared in Perl are also available using the Python syntax, there is some support for one or two .NET and Oniguruma syntax items, and there is an option for requesting some minor changes that give better JavaScript compatibility. Starting with release 8.30, it is possible to compile two separate PCRE libraries: the original, which supports 8-bit character strings (including UTF-8 strings), and a second library that supports 16-bit character strings (including UTF-16 strings). The build process allows either one or both to be built. The majority of the work to make this possible was done by Zoltan Herczeg. Starting with release 8.32 it is possible to compile a third separate PCRE library that supports 32-bit character strings (including UTF-32 strings). The build process allows any combination of the 8-, 16- and 32-bit libraries. The work to make this possible was done by Chris- tian Persch. The three libraries contain identical sets of functions, except that the names in the 16-bit library start with pcre16_ instead of pcre_, and the names in the 32-bit library start with pcre32_ instead of pcre_. To avoid over-complication and reduce the documentation mainte- nance load, most of the documentation describes the 8-bit library, with the differences for the 16-bit and 32-bit libraries described sepa- rately in the pcre16 and pcre32 pages. References to functions or structures of the form pcre[16|32]_xxx should be read as meaning "pcre_xxx when using the 8-bit library, pcre16_xxx when using the 16-bit library, or pcre32_xxx when using the 32-bit library". The current implementation of PCRE corresponds approximately with Perl 5.12, including support for UTF-8/16/32 encoded strings and Unicode general category properties. However, UTF-8/16/32 and Unicode support has to be explicitly enabled; it is not the default. The Unicode tables correspond to Unicode release 6.3.0. In addition to the Perl-compatible matching function, PCRE contains an alternative function that matches the same compiled patterns in a different way. In certain circumstances, the alternative function has some advantages. For a discussion of the two matching algorithms, see the pcrematching page. PCRE is written in C and released as a C library. A number of people have written wrappers and interfaces of various kinds. In particular, Google Inc. have provided a comprehensive C++ wrapper for the 8-bit library. This is now included as part of the PCRE distribution. The pcrecpp page has details of this interface. Other people's contributions can be found in the Contrib directory at the primary FTP site, which is: Details of exactly which Perl regular expression features are and are not supported by PCRE are given in separate documents. See the pcrepattern and pcrecompat pages. There is a syntax summary in the pcresyntax page. Some features of PCRE can be included, excluded, or changed when the library is built. The pcre_config() function makes it possible for a client to discover which features are available. The features themselves are described in the pcrebuild page. Documentation about building PCRE for various operating systems can be found in the README and NON-AUTOTOOLS_BUILD files in the source distribution. The libraries contains a number of undocumented internal functions and data tables that are used by more than one of the exported external functions, but which are not intended for use by external callers. Their names all begin with "_pcre_" or "_pcre16_" or "_pcre32_", which hopefully will not provoke any name clashes. In some environments, it is possible to control which external symbols are exported when a shared library is built, and in these cases the undocumented symbols are not exported. SECURITY CONSIDERATIONS
If you are using PCRE in a non-UTF application that permits users to supply arbitrary patterns for compilation, you should be aware of a feature that allows users to turn on UTF support from within a pattern, provided that PCRE was built with UTF support. For example, an 8-bit pattern that begins with "(*UTF8)" or "(*UTF)" turns on UTF-8 mode, which interprets patterns and subjects as strings of UTF-8 char- acters instead of individual 8-bit characters. This causes both the pattern and any data against which it is matched to be checked for UTF-8 validity. If the data string is very long, such a check might use sufficiently many resources as to cause your application to lose performance. One way of guarding against this possibility is to use the pcre_fullinfo() function to check the compiled pattern's options for UTF. Alternatively, from release 8.33, you can set the PCRE_NEVER_UTF option at compile time. This causes an compile time error if a pattern contains a UTF-setting sequence. If your application is one that supports UTF, be aware that validity checking can take time. If the same data string is to be matched many times, you can use the PCRE_NO_UTF[8|16|32]_CHECK option for the second and subsequent matches to save redundant checks. Another way that performance can be hit is by running a pattern that has a very large search tree against a string that will never match. Nested unlimited repeats in a pattern are a common example. PCRE provides some protection against this: see the PCRE_EXTRA_MATCH_LIMIT fea- ture in the pcreapi page. USER DOCUMENTATION
The user documentation for PCRE comprises a number of different sections. In the "man" format, each of these is a separate "man page". In the HTML format, each is a separate page, linked from the index page. In the plain text format, the descriptions of the pcregrep and pcretest programs are in files called pcregrep.txt and pcretest.txt, respectively. The remaining sections, except for the pcredemo section (which is a program listing), are concatenated in pcre.txt, for ease of searching. The sections are as follows: pcre this document pcre-config show PCRE installation configuration information pcre16 details of the 16-bit library pcre32 details of the 32-bit library pcreapi details of PCRE's native C API pcrebuild building PCRE pcrecallout details of the callout feature pcrecompat discussion of Perl compatibility pcrecpp details of the C++ wrapper for the 8-bit library pcredemo a demonstration C program that uses PCRE pcregrep description of the pcregrep command (8-bit only) pcrejit discussion of the just-in-time optimization support pcrelimits details of size and other limits pcrematching discussion of the two matching algorithms pcrepartial details of the partial matching facility pcrepattern syntax and semantics of supported regular expressions pcreperform discussion of performance issues pcreposix the POSIX-compatible C API for the 8-bit library pcreprecompile details of saving and re-using precompiled patterns pcresample discussion of the pcredemo program pcrestack discussion of stack usage pcresyntax quick syntax reference pcretest description of the pcretest testing command pcreunicode discussion of Unicode and UTF-8/16/32 support In the "man" and HTML formats, there is also a short page for each C library function, listing its arguments and results. AUTHOR
Philip Hazel University Computing Service Cambridge CB2 3QH, England. Putting an actual email address here seems to have been a spam magnet, so I've taken it away. If you want to email me, use my two initials, followed by the two digits 10, at the domain REVISION
Last updated: 10 February 2015 Copyright (c) 1997-2015 University of Cambridge. PCRE 8.37 10 February 2015 PCRE(3)
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