214 lines
9.6 KiB
HTML
214 lines
9.6 KiB
HTML
<html>
|
|
<head>
|
|
<title>pcre2 specification</title>
|
|
</head>
|
|
<body bgcolor="#FFFFFF" text="#00005A" link="#0066FF" alink="#3399FF" vlink="#2222BB">
|
|
<h1>pcre2 man page</h1>
|
|
<p>
|
|
Return to the <a href="index.html">PCRE2 index page</a>.
|
|
</p>
|
|
<p>
|
|
This page is part of the PCRE2 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>
|
|
PCRE2 is the name used for a revised API for the PCRE library, which is a set
|
|
of functions, written in C, that implement regular expression pattern matching
|
|
using the same syntax and semantics as Perl, with just a few differences. After
|
|
nearly two decades, the limitations of the original API were making development
|
|
increasingly difficult. The new API is more extensible, and it was simplified
|
|
by abolishing the separate "study" optimizing function; in PCRE2, patterns are
|
|
automatically optimized where possible. Since forking from PCRE1, the code has
|
|
been extensively refactored and new features introduced.
|
|
</P>
|
|
<P>
|
|
As well as Perl-style regular expression patterns, some features that appeared
|
|
in Python and the original PCRE before they appeared in Perl are available
|
|
using the Python syntax. There is also some support for one or two .NET and
|
|
Oniguruma syntax items, and there are options for requesting some minor changes
|
|
that give better ECMAScript (aka JavaScript) compatibility.
|
|
</P>
|
|
<P>
|
|
The source code for PCRE2 can be compiled to support strings of 8-bit, 16-bit,
|
|
or 32-bit code units, which means that up to three separate libraries may be
|
|
installed, one for each code unit size. The size of code unit is not related to
|
|
the bit size of the underlying hardware. In a 64-bit environment that also
|
|
supports 32-bit applications, versions of PCRE2 that are compiled in both
|
|
64-bit and 32-bit modes may be needed.
|
|
</P>
|
|
<P>
|
|
The original work to extend PCRE to 16-bit and 32-bit code units was done by
|
|
Zoltan Herczeg and Christian Persch, respectively. In all three cases, strings
|
|
can be interpreted either as one character per code unit, or as UTF-encoded
|
|
Unicode, with support for Unicode general category properties. Unicode support
|
|
is optional at build time (but is the default). However, processing strings as
|
|
UTF code units must be enabled explicitly at run time. The version of Unicode
|
|
in use can be discovered by running
|
|
<pre>
|
|
pcre2test -C
|
|
</PRE>
|
|
</P>
|
|
<P>
|
|
The three libraries contain identical sets of functions, with names ending in
|
|
_8, _16, or _32, respectively (for example, <b>pcre2_compile_8()</b>). However,
|
|
by defining PCRE2_CODE_UNIT_WIDTH to be 8, 16, or 32, a program that uses just
|
|
one code unit width can be written using generic names such as
|
|
<b>pcre2_compile()</b>, and the documentation is written assuming that this is
|
|
the case.
|
|
</P>
|
|
<P>
|
|
In addition to the Perl-compatible matching function, PCRE2 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="pcre2matching.html"><b>pcre2matching</b></a>
|
|
page.
|
|
</P>
|
|
<P>
|
|
Details of exactly which Perl regular expression features are and are not
|
|
supported by PCRE2 are given in separate documents. See the
|
|
<a href="pcre2pattern.html"><b>pcre2pattern</b></a>
|
|
and
|
|
<a href="pcre2compat.html"><b>pcre2compat</b></a>
|
|
pages. There is a syntax summary in the
|
|
<a href="pcre2syntax.html"><b>pcre2syntax</b></a>
|
|
page.
|
|
</P>
|
|
<P>
|
|
Some features of PCRE2 can be included, excluded, or changed when the library
|
|
is built. The
|
|
<a href="pcre2_config.html"><b>pcre2_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="pcre2build.html"><b>pcre2build</b></a>
|
|
page. Documentation about building PCRE2 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
|
|
"_pcre2", 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 PCRE2 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. For example, an
|
|
8-bit pattern that begins with "(*UTF)" turns on UTF-8 mode, which interprets
|
|
patterns and subjects as strings of UTF-8 code units 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>pcre2_pattern_info()</b> function to check the compiled pattern's options for
|
|
PCRE2_UTF. Alternatively, you can set the PCRE2_NEVER_UTF option when calling
|
|
<b>pcre2_compile()</b>. This causes a compile time error if the pattern contains
|
|
a UTF-setting sequence.
|
|
</P>
|
|
<P>
|
|
The use of Unicode properties for character types such as \d can also be
|
|
enabled from within the pattern, by specifying "(*UCP)". This feature can be
|
|
disallowed by setting the PCRE2_NEVER_UCP option.
|
|
</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 PCRE2_NO_UTF_CHECK option for the second and subsequent matches to avoid
|
|
running redundant checks.
|
|
</P>
|
|
<P>
|
|
The use of the \C escape sequence in a UTF-8 or UTF-16 pattern can lead to
|
|
problems, because it may leave the current matching point in the middle of a
|
|
multi-code-unit character. The PCRE2_NEVER_BACKSLASH_C option can be used by an
|
|
application to lock out the use of \C, causing a compile-time error if it is
|
|
encountered. It is also possible to build PCRE2 with the use of \C permanently
|
|
disabled.
|
|
</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. PCRE2 provides some protection
|
|
against this: see the <b>pcre2_set_match_limit()</b> function in the
|
|
<a href="pcre2api.html"><b>pcre2api</b></a>
|
|
page. There is a similar function called <b>pcre2_set_depth_limit()</b> that can
|
|
be used to restrict the amount of memory that is used.
|
|
</P>
|
|
<br><a name="SEC3" href="#TOC1">USER DOCUMENTATION</a><br>
|
|
<P>
|
|
The user documentation for PCRE2 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>pcre2grep</b> and <b>pcre2test</b> programs are in
|
|
files called <b>pcre2grep.txt</b> and <b>pcre2test.txt</b>, respectively. The
|
|
remaining sections, except for the <b>pcre2demo</b> section (which is a program
|
|
listing), and the short pages for individual functions, are concatenated in
|
|
<b>pcre2.txt</b>, for ease of searching. The sections are as follows:
|
|
<pre>
|
|
pcre2 this document
|
|
pcre2-config show PCRE2 installation configuration information
|
|
pcre2api details of PCRE2's native C API
|
|
pcre2build building PCRE2
|
|
pcre2callout details of the pattern callout feature
|
|
pcre2compat discussion of Perl compatibility
|
|
pcre2convert details of pattern conversion functions
|
|
pcre2demo a demonstration C program that uses PCRE2
|
|
pcre2grep description of the <b>pcre2grep</b> command (8-bit only)
|
|
pcre2jit discussion of just-in-time optimization support
|
|
pcre2limits details of size and other limits
|
|
pcre2matching discussion of the two matching algorithms
|
|
pcre2partial details of the partial matching facility
|
|
pcre2pattern syntax and semantics of supported regular expression patterns
|
|
pcre2perform discussion of performance issues
|
|
pcre2posix the POSIX-compatible C API for the 8-bit library
|
|
pcre2sample discussion of the pcre2demo program
|
|
pcre2serialize details of pattern serialization
|
|
pcre2syntax quick syntax reference
|
|
pcre2test description of the <b>pcre2test</b> command
|
|
pcre2unicode discussion of Unicode and UTF 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, England.
|
|
<br>
|
|
</P>
|
|
<P>
|
|
Putting an actual email address here is a spam magnet. 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: 28 April 2021
|
|
<br>
|
|
Copyright © 1997-2021 University of Cambridge.
|
|
<br>
|
|
<p>
|
|
Return to the <a href="index.html">PCRE2 index page</a>.
|
|
</p>
|