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_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:
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.
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
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.
Philip Hazel University Computing Service Cambridge CB2 3QH, England.
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Last updated: 10 January 2012 Copyright (c) 1997-2012 University of Cambridge.