PCRE(3)PCRE(3)NAME
PCRE - Perl-compatible regular expressions
INTRODUCTION
The PCRE library is a set of functions that implement regular expres‐
sion 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 syn‐
tax, 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 differ‐
ences 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 gen‐
eral category properties. However, UTF-8/16 and Unicode support has to
be explicitly enabled; it is not the default. The Unicode tables corre‐
spond 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 dif‐
ferent 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 contribu‐
tions 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 pcrepat‐
tern 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 them‐
selves are described in the pcrebuild page. Documentation about build‐
ing 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 sec‐
tions. 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 sec‐
tion, are concatenated, for ease of searching. The sections are as fol‐
lows:
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.
PCRE 8.30 10 January 2012 PCRE(3)
