203 lines
8.1 KiB
Groff
203 lines
8.1 KiB
Groff
.TH PCRE 3 "11 November 2012" "PCRE 8.32"
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.SH NAME
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PCRE - Perl-compatible regular expressions
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.SH INTRODUCTION
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.rs
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.sp
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The PCRE library is a set of functions that implement regular expression
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pattern matching using the same syntax and semantics as Perl, with just a few
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differences. Some features that appeared in Python and PCRE before they
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appeared in Perl are also available using the Python syntax, there is some
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support for one or two .NET and Oniguruma syntax items, and there is an option
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for requesting some minor changes that give better JavaScript compatibility.
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.P
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Starting with release 8.30, it is possible to compile two separate PCRE
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libraries: the original, which supports 8-bit character strings (including
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UTF-8 strings), and a second library that supports 16-bit character strings
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(including UTF-16 strings). The build process allows either one or both to be
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built. The majority of the work to make this possible was done by Zoltan
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Herczeg.
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.P
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Starting with release 8.32 it is possible to compile a third separate PCRE
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library, which supports 32-bit character strings (including
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UTF-32 strings). The build process allows any set of the 8-, 16- and 32-bit
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libraries. The work to make this possible was done by Christian Persch.
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.P
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The three libraries contain identical sets of functions, except that the names
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in the 16-bit library start with \fBpcre16_\fP instead of \fBpcre_\fP, and the
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names in the 32-bit library start with \fBpcre32_\fP instead of \fBpcre_\fP. To
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avoid over-complication and reduce the documentation maintenance load, most of
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the documentation describes the 8-bit library, with the differences for the
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16-bit and 32-bit libraries described separately in the
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.\" HREF
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\fBpcre16\fP
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and
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.\" HREF
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\fBpcre32\fP
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.\"
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pages. References to functions or structures of the form \fIpcre[16|32]_xxx\fP
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should be read as meaning "\fIpcre_xxx\fP when using the 8-bit library,
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\fIpcre16_xxx\fP when using the 16-bit library, or \fIpcre32_xxx\fP when using
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the 32-bit library".
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.P
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The current implementation of PCRE corresponds approximately with Perl 5.12,
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including support for UTF-8/16/32 encoded strings and Unicode general category
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properties. However, UTF-8/16/32 and Unicode support has to be explicitly
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enabled; it is not the default. The Unicode tables correspond to Unicode
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release 6.2.0.
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.P
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In addition to the Perl-compatible matching function, PCRE contains an
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alternative function that matches the same compiled patterns in a different
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way. In certain circumstances, the alternative function has some advantages.
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For a discussion of the two matching algorithms, see the
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.\" HREF
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\fBpcrematching\fP
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.\"
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page.
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.P
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PCRE is written in C and released as a C library. A number of people have
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written wrappers and interfaces of various kinds. In particular, Google Inc.
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have provided a comprehensive C++ wrapper for the 8-bit library. This is now
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included as part of the PCRE distribution. The
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.\" HREF
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\fBpcrecpp\fP
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.\"
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page has details of this interface. Other people's contributions can be found
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in the \fIContrib\fP directory at the primary FTP site, which is:
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.sp
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.\" HTML <a href="ftp://ftp.csx.cam.ac.uk/pub/software/programming/pcre">
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.\" </a>
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ftp://ftp.csx.cam.ac.uk/pub/software/programming/pcre
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.P
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Details of exactly which Perl regular expression features are and are not
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supported by PCRE are given in separate documents. See the
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.\" HREF
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\fBpcrepattern\fP
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.\"
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and
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.\" HREF
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\fBpcrecompat\fP
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.\"
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pages. There is a syntax summary in the
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.\" HREF
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\fBpcresyntax\fP
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.\"
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page.
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.P
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Some features of PCRE can be included, excluded, or changed when the library is
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built. The
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.\" HREF
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\fBpcre_config()\fP
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.\"
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function makes it possible for a client to discover which features are
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available. The features themselves are described in the
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.\" HREF
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\fBpcrebuild\fP
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.\"
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page. Documentation about building PCRE for various operating systems can be
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found in the \fBREADME\fP and \fBNON-AUTOTOOLS_BUILD\fP files in the source
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distribution.
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.P
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The libraries contains a number of undocumented internal functions and data
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tables that are used by more than one of the exported external functions, but
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which are not intended for use by external callers. Their names all begin with
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"_pcre_" or "_pcre16_" or "_pcre32_", which hopefully will not provoke any name
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clashes. In some environments, it is possible to control which external symbols
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are exported when a shared library is built, and in these cases the
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undocumented symbols are not exported.
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.
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.
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.SH "SECURITY CONSIDERATIONS"
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.rs
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.sp
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If you are using PCRE in a non-UTF application that permits users to supply
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arbitrary patterns for compilation, you should be aware of a feature that
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allows users to turn on UTF support from within a pattern, provided that PCRE
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was built with UTF support. For example, an 8-bit pattern that begins with
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"(*UTF8)" or "(*UTF)" turns on UTF-8 mode, which interprets patterns and
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subjects as strings of UTF-8 characters instead of individual 8-bit characters.
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This causes both the pattern and any data against which it is matched to be
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checked for UTF-8 validity. If the data string is very long, such a check might
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use sufficiently many resources as to cause your application to lose
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performance.
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.P
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The best way of guarding against this possibility is to use the
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\fBpcre_fullinfo()\fP function to check the compiled pattern's options for UTF.
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.P
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If your application is one that supports UTF, be aware that validity checking
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can take time. If the same data string is to be matched many times, you can use
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the PCRE_NO_UTF[8|16|32]_CHECK option for the second and subsequent matches to
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save redundant checks.
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.P
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Another way that performance can be hit is by running a pattern that has a very
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large search tree against a string that will never match. Nested unlimited
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repeats in a pattern are a common example. PCRE provides some protection
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against this: see the PCRE_EXTRA_MATCH_LIMIT feature in the
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.\" HREF
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\fBpcreapi\fP
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.\"
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page.
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.
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.
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.SH "USER DOCUMENTATION"
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.rs
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.sp
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The user documentation for PCRE comprises a number of different sections. In
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the "man" format, each of these is a separate "man page". In the HTML format,
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each is a separate page, linked from the index page. In the plain text format,
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all the sections, except the \fBpcredemo\fP section, are concatenated, for ease
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of searching. The sections are as follows:
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.sp
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pcre this document
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pcre16 details of the 16-bit library
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pcre32 details of the 32-bit library
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pcre-config show PCRE installation configuration information
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pcreapi details of PCRE's native C API
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pcrebuild options for building PCRE
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pcrecallout details of the callout feature
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pcrecompat discussion of Perl compatibility
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pcrecpp details of the C++ wrapper for the 8-bit library
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pcredemo a demonstration C program that uses PCRE
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pcregrep description of the \fBpcregrep\fP command (8-bit only)
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pcrejit discussion of the just-in-time optimization support
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pcrelimits details of size and other limits
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pcrematching discussion of the two matching algorithms
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pcrepartial details of the partial matching facility
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.\" JOIN
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pcrepattern syntax and semantics of supported
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regular expressions
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pcreperform discussion of performance issues
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pcreposix the POSIX-compatible C API for the 8-bit library
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pcreprecompile details of saving and re-using precompiled patterns
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pcresample discussion of the pcredemo program
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pcrestack discussion of stack usage
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pcresyntax quick syntax reference
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pcretest description of the \fBpcretest\fP testing command
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pcreunicode discussion of Unicode and UTF-8/16/32 support
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.sp
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In addition, in the "man" and HTML formats, there is a short page for each
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C library function, listing its arguments and results.
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.
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.
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.SH AUTHOR
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.rs
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.sp
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.nf
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Philip Hazel
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University Computing Service
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Cambridge CB2 3QH, England.
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.fi
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.P
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Putting an actual email address here seems to have been a spam magnet, so I've
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taken it away. If you want to email me, use my two initials, followed by the
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two digits 10, at the domain cam.ac.uk.
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.
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.
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.SH REVISION
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.rs
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.sp
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.nf
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Last updated: 11 November 2012
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Copyright (c) 1997-2012 University of Cambridge.
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.fi
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