PCRE(3)

NAME
PCRE - Perl-compatible regular expressions

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.

The two libraries contain identical sets of functions, except that the names in the 16-bit library start with pcre16_ instead of pcre_. To avoid over-complication and reduce the documentation maintenance load, most of the documentation describes the 8-bit library, with the differences for the 16-bit library described separately in the pcre16 page. References to functions or structures of the form pcre[16]_xxx should be read as meaning "pcre_xxx when using the 8-bit library and pcre16_xxx when using the 16-bit library".

The current implementation of PCRE corresponds approximately with Perl 5.12, including support for UTF-8/16 encoded strings and Unicode general category properties. However, UTF-8/16 and Unicode support has to be explicitly enabled; it is not the default. The Unicode tables correspond to Unicode release 6.0.0.

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:

ftp://ftp.csx.cam.ac.uk/pub/software/programming/pcre

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-UNIX-USE 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_", 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.

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, all the sections, except the pcredemo section, are concatenated, for ease of searching. The sections are as follows:

  pcre this document
  pcre16 details of the 16-bit library
  pcre-config show PCRE installation configuration information
  pcreapi details of PCRE's native C API
  pcrebuild options for 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 support

In addition, in the "man" and HTML formats, there is a short page for each 8-bit 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 cam.ac.uk.

REVISION

Last updated: 10 January 2012
Copyright (c) 1997-2012 University of Cambridge.