| <html> |
| <head> |
| <title>pcre specification</title> |
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| <body bgcolor="#FFFFFF" text="#00005A" link="#0066FF" alink="#3399FF" vlink="#2222BB"> |
| <h1>pcre man page</h1> |
| <p> |
| Return to the <a href="index.html">PCRE index page</a>. |
| </p> |
| <p> |
| This page is part of the PCRE HTML documentation. It was generated automatically |
| from the original man page. If there is any nonsense in it, please consult the |
| man page, in case the conversion went wrong. |
| <br> |
| <ul> |
| <li><a name="TOC1" href="#SEC1">INTRODUCTION</a> |
| <li><a name="TOC2" href="#SEC2">SECURITY CONSIDERATIONS</a> |
| <li><a name="TOC3" href="#SEC3">USER DOCUMENTATION</a> |
| <li><a name="TOC4" href="#SEC4">AUTHOR</a> |
| <li><a name="TOC5" href="#SEC5">REVISION</a> |
| </ul> |
| <br><a name="SEC1" href="#TOC1">INTRODUCTION</a><br> |
| <P> |
| 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. |
| </P> |
| <P> |
| 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. |
| </P> |
| <P> |
| Starting with release 8.32 it is possible to compile a third separate PCRE |
| library that supports 32-bit character strings (including UTF-32 strings). The |
| build process allows any combination of the 8-, 16- and 32-bit libraries. The |
| work to make this possible was done by Christian Persch. |
| </P> |
| <P> |
| The three libraries contain identical sets of functions, except that the names |
| in the 16-bit library start with <b>pcre16_</b> instead of <b>pcre_</b>, and the |
| names in the 32-bit library start with <b>pcre32_</b> instead of <b>pcre_</b>. 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 and 32-bit libraries described separately in the |
| <a href="pcre16.html"><b>pcre16</b></a> |
| and |
| <a href="pcre32.html"><b>pcre32</b></a> |
| pages. References to functions or structures of the form <i>pcre[16|32]_xxx</i> |
| should be read as meaning "<i>pcre_xxx</i> when using the 8-bit library, |
| <i>pcre16_xxx</i> when using the 16-bit library, or <i>pcre32_xxx</i> when using |
| the 32-bit library". |
| </P> |
| <P> |
| The current implementation of PCRE corresponds approximately with Perl 5.12, |
| including support for UTF-8/16/32 encoded strings and Unicode general category |
| properties. However, UTF-8/16/32 and Unicode support has to be explicitly |
| enabled; it is not the default. The Unicode tables correspond to Unicode |
| release 6.3.0. |
| </P> |
| <P> |
| 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 |
| <a href="pcrematching.html"><b>pcrematching</b></a> |
| page. |
| </P> |
| <P> |
| 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 |
| <a href="pcrecpp.html"><b>pcrecpp</b></a> |
| page has details of this interface. Other people's contributions can be found |
| in the <i>Contrib</i> directory at the primary FTP site, which is: |
| <a href="ftp://ftp.csx.cam.ac.uk/pub/software/programming/pcre">ftp://ftp.csx.cam.ac.uk/pub/software/programming/pcre</a> |
| </P> |
| <P> |
| Details of exactly which Perl regular expression features are and are not |
| supported by PCRE are given in separate documents. See the |
| <a href="pcrepattern.html"><b>pcrepattern</b></a> |
| and |
| <a href="pcrecompat.html"><b>pcrecompat</b></a> |
| pages. There is a syntax summary in the |
| <a href="pcresyntax.html"><b>pcresyntax</b></a> |
| page. |
| </P> |
| <P> |
| Some features of PCRE can be included, excluded, or changed when the library is |
| built. The |
| <a href="pcre_config.html"><b>pcre_config()</b></a> |
| function makes it possible for a client to discover which features are |
| available. The features themselves are described in the |
| <a href="pcrebuild.html"><b>pcrebuild</b></a> |
| page. Documentation about building PCRE for various operating systems can be |
| found in the |
| <a href="README.txt"><b>README</b></a> |
| and |
| <a href="NON-AUTOTOOLS-BUILD.txt"><b>NON-AUTOTOOLS_BUILD</b></a> |
| files in the source distribution. |
| </P> |
| <P> |
| 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_" or "_pcre32_", 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. |
| </P> |
| <br><a name="SEC2" href="#TOC1">SECURITY CONSIDERATIONS</a><br> |
| <P> |
| If you are using PCRE in a non-UTF application that permits users to supply |
| arbitrary patterns for compilation, you should be aware of a feature that |
| allows users to turn on UTF support from within a pattern, provided that PCRE |
| was built with UTF support. For example, an 8-bit pattern that begins with |
| "(*UTF8)" or "(*UTF)" turns on UTF-8 mode, which interprets patterns and |
| subjects as strings of UTF-8 characters instead of individual 8-bit characters. |
| This causes both the pattern and any data against which it is matched to be |
| checked for UTF-8 validity. If the data string is very long, such a check might |
| use sufficiently many resources as to cause your application to lose |
| performance. |
| </P> |
| <P> |
| One way of guarding against this possibility is to use the |
| <b>pcre_fullinfo()</b> function to check the compiled pattern's options for UTF. |
| Alternatively, from release 8.33, you can set the PCRE_NEVER_UTF option at |
| compile time. This causes an compile time error if a pattern contains a |
| UTF-setting sequence. |
| </P> |
| <P> |
| If your application is one that supports UTF, be aware that validity checking |
| can take time. If the same data string is to be matched many times, you can use |
| the PCRE_NO_UTF[8|16|32]_CHECK option for the second and subsequent matches to |
| save redundant checks. |
| </P> |
| <P> |
| Another way that performance can be hit is by running a pattern that has a very |
| large search tree against a string that will never match. Nested unlimited |
| repeats in a pattern are a common example. PCRE provides some protection |
| against this: see the PCRE_EXTRA_MATCH_LIMIT feature in the |
| <a href="pcreapi.html"><b>pcreapi</b></a> |
| page. |
| </P> |
| <br><a name="SEC3" href="#TOC1">USER DOCUMENTATION</a><br> |
| <P> |
| 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, |
| the descriptions of the <b>pcregrep</b> and <b>pcretest</b> programs are in files |
| called <b>pcregrep.txt</b> and <b>pcretest.txt</b>, respectively. The remaining |
| sections, except for the <b>pcredemo</b> section (which is a program listing), |
| are concatenated in <b>pcre.txt</b>, for ease of searching. The sections are as |
| follows: |
| <pre> |
| pcre this document |
| pcre-config show PCRE installation configuration information |
| pcre16 details of the 16-bit library |
| pcre32 details of the 32-bit library |
| pcreapi details of PCRE's native C API |
| pcrebuild 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 <b>pcregrep</b> 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 <b>pcretest</b> testing command |
| pcreunicode discussion of Unicode and UTF-8/16/32 support |
| </pre> |
| In the "man" and HTML formats, there is also a short page for each C library |
| function, listing its arguments and results. |
| </P> |
| <br><a name="SEC4" href="#TOC1">AUTHOR</a><br> |
| <P> |
| Philip Hazel |
| <br> |
| University Computing Service |
| <br> |
| Cambridge CB2 3QH, England. |
| <br> |
| </P> |
| <P> |
| 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. |
| </P> |
| <br><a name="SEC5" href="#TOC1">REVISION</a><br> |
| <P> |
| Last updated: 08 January 2014 |
| <br> |
| Copyright © 1997-2014 University of Cambridge. |
| <br> |
| <p> |
| Return to the <a href="index.html">PCRE index page</a>. |
| </p> |