PCRE — Perl-compatible regular expressions
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(3) 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(3) 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(3) 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(3) and pcrecompat(3) pages. There is a syntax summary in the pcresyntax(3) page.
Some features of PCRE can be included, excluded, or
changed when the library is built. The pcre_config()(3) function makes
it possible for a client to discover which features are
available. The features themselves are described in the
pcrebuild(3) 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.
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:
this document
details of the 16-bit library
show PCRE installation configuration information
details of PCRE's native C API
options for building PCRE
details of the callout feature
discussion of Perl compatibility
details of the C++ wrapper for the 8-bit library
a demonstration C program that uses PCRE
description of the pcregrep command (8-bit only)
discussion of the just-in-time optimization support
details of size and other limits
discussion of the two matching algorithms
details of the partial matching facility
syntax and semantics of supported regular expressions
discussion of performance issues
the POSIX-compatible C API for the 8-bit library
details of saving and re-using precompiled patterns
discussion of the pcredemo program
discussion of stack usage
quick syntax reference
description of the pcretest testing command
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.
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.
Last updated: 10 January 2012 Copyright (c) 1997-2012 University of Cambridge.
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This manual page is taken from the PCRE library, which is distributed under the BSD license. |