| .TH PCRE 3 "08 January 2014" "PCRE 8.35" |
| .SH NAME |
| PCRE - Perl-compatible regular expressions |
| .SH INTRODUCTION |
| .rs |
| .sp |
| 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 |
| 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 |
| 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 |
| The three libraries contain identical sets of functions, except that the names |
| in the 16-bit library start with \fBpcre16_\fP instead of \fBpcre_\fP, and the |
| names in the 32-bit library start with \fBpcre32_\fP instead of \fBpcre_\fP. 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 |
| .\" HREF |
| \fBpcre16\fP |
| and |
| .\" HREF |
| \fBpcre32\fP |
| .\" |
| pages. References to functions or structures of the form \fIpcre[16|32]_xxx\fP |
| should be read as meaning "\fIpcre_xxx\fP when using the 8-bit library, |
| \fIpcre16_xxx\fP when using the 16-bit library, or \fIpcre32_xxx\fP when using |
| the 32-bit library". |
| .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 |
| 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 |
| .\" HREF |
| \fBpcrematching\fP |
| .\" |
| page. |
| .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 |
| .\" HREF |
| \fBpcrecpp\fP |
| .\" |
| page has details of this interface. Other people's contributions can be found |
| in the \fIContrib\fP directory at the primary FTP site, which is: |
| .sp |
| .\" HTML <a href="ftp://ftp.csx.cam.ac.uk/pub/software/programming/pcre"> |
| .\" </a> |
| ftp://ftp.csx.cam.ac.uk/pub/software/programming/pcre |
| .\" |
| .P |
| Details of exactly which Perl regular expression features are and are not |
| supported by PCRE are given in separate documents. See the |
| .\" HREF |
| \fBpcrepattern\fP |
| .\" |
| and |
| .\" HREF |
| \fBpcrecompat\fP |
| .\" |
| pages. There is a syntax summary in the |
| .\" HREF |
| \fBpcresyntax\fP |
| .\" |
| page. |
| .P |
| Some features of PCRE can be included, excluded, or changed when the library is |
| built. The |
| .\" HREF |
| \fBpcre_config()\fP |
| .\" |
| function makes it possible for a client to discover which features are |
| available. The features themselves are described in the |
| .\" HREF |
| \fBpcrebuild\fP |
| .\" |
| page. Documentation about building PCRE for various operating systems can be |
| found in the |
| .\" HTML <a href="README.txt"> |
| .\" </a> |
| \fBREADME\fP |
| .\" |
| and |
| .\" HTML <a href="NON-AUTOTOOLS-BUILD.txt"> |
| .\" </a> |
| \fBNON-AUTOTOOLS_BUILD\fP |
| .\" |
| files in the source distribution. |
| .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. |
| . |
| . |
| .SH "SECURITY CONSIDERATIONS" |
| .rs |
| .sp |
| 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 |
| One way of guarding against this possibility is to use the |
| \fBpcre_fullinfo()\fP 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 |
| 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 |
| 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 |
| .\" HREF |
| \fBpcreapi\fP |
| .\" |
| page. |
| . |
| . |
| .SH "USER DOCUMENTATION" |
| .rs |
| .sp |
| 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 \fBpcregrep\fP and \fBpcretest\fP programs are in files |
| called \fBpcregrep.txt\fP and \fBpcretest.txt\fP, respectively. The remaining |
| sections, except for the \fBpcredemo\fP section (which is a program listing), |
| are concatenated in \fBpcre.txt\fP, for ease of searching. The sections are as |
| follows: |
| .sp |
| 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 \fBpcregrep\fP 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 |
| .\" JOIN |
| 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 \fBpcretest\fP testing command |
| pcreunicode discussion of Unicode and UTF-8/16/32 support |
| .sp |
| In the "man" and HTML formats, there is also a short page for each C library |
| function, listing its arguments and results. |
| . |
| . |
| .SH AUTHOR |
| .rs |
| .sp |
| .nf |
| Philip Hazel |
| University Computing Service |
| Cambridge CB2 3QH, England. |
| .fi |
| .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. |
| . |
| . |
| .SH REVISION |
| .rs |
| .sp |
| .nf |
| Last updated: 08 January 2014 |
| Copyright (c) 1997-2014 University of Cambridge. |
| .fi |