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       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

       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:

       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
                             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.


       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


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