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PCRE2(3) DragonFly Library Functions Manual PCRE2(3)
NAME
PCRE2 - Perl-compatible regular expressions (revised API)
INTRODUCTION
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. The
old library is now obsolete and is no longer maintained.
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.
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.
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
pcre2test -C
The three libraries contain identical sets of functions, with names
ending in _8, _16, or _32, respectively (for example,
pcre2_compile_8()). 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 pcre2_compile(), and the documentation is
written assuming that this is the case.
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 pcre2matching page.
Details of exactly which Perl regular expression features are and are
not supported by PCRE2 are given in separate documents. See the
pcre2pattern and pcre2compat pages. There is a syntax summary in the
pcre2syntax page.
Some features of PCRE2 can be included, excluded, or changed when the
library is built. The pcre2_config() function makes it possible for a
client to discover which features are available. The features
themselves are described in the pcre2build page. Documentation about
building PCRE2 for various operating systems can be found in the README
and NON-AUTOTOOLS_BUILD 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 "_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.
SECURITY CONSIDERATIONS
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.
One way of guarding against this possibility is to use the
pcre2_pattern_info() function to check the compiled pattern's options
for PCRE2_UTF. Alternatively, you can set the PCRE2_NEVER_UTF option
when calling pcre2_compile(). This causes a compile time error if the
pattern contains a UTF-setting sequence.
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.
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.
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.
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 pcre2_set_match_limit()
function in the pcre2api page. There is a similar function called
pcre2_set_depth_limit() that can be used to restrict the amount of
memory that is used.
USER DOCUMENTATION
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 pcre2grep and
pcre2test programs are in files called pcre2grep.txt and pcre2test.txt,
respectively. The remaining sections, except for the pcre2demo section
(which is a program listing), and the short pages for individual
functions, are concatenated in pcre2.txt, for ease of searching. The
sections are as follows:
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 pcre2grep 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 pcre2test command
pcre2unicode discussion of Unicode and UTF support
In the "man" and HTML formats, there is also a short page for each C
library function, listing its arguments and results.
AUTHOR
Philip Hazel
Retired from University Computing Service
Cambridge, England.
Putting an actual email address here is a spam magnet. If you want to
email me, use my two names separated by a dot at gmail.com.
REVISION
Last updated: 27 August 2021
Copyright (c) 1997-2021 University of Cambridge.
PCRE2 10.38 27 August 2021 PCRE2(3)
PCRE2_COMPILE(3) DragonFly Library Functions Manual PCRE2_COMPILE(3)
NAME
PCRE2 - Perl-compatible regular expressions (revised API)
SYNOPSIS
#include <pcre2.h>
pcre2_code *pcre2_compile(PCRE2_SPTR pattern, PCRE2_SIZE length,
uint32_t options, int *errorcode, PCRE2_SIZE *erroroffset,
pcre2_compile_context *ccontext);
DESCRIPTION
This function compiles a regular expression pattern into an internal
form. Its arguments are:
pattern A string containing expression to be compiled
length The length of the string or PCRE2_ZERO_TERMINATED
options Option bits
errorcode Where to put an error code
erroffset Where to put an error offset
ccontext Pointer to a compile context or NULL
The length of the pattern and any error offset that is returned are in
code units, not characters. A compile context is needed only if you
want to provide custom memory allocation functions, or to provide an
external function for system stack size checking, or to change one or
more of these parameters:
What \R matches (Unicode newlines, or CR, LF, CRLF only);
PCRE2's character tables;
The newline character sequence;
The compile time nested parentheses limit;
The maximum pattern length (in code units) that is allowed.
The additional options bits (see pcre2_set_compile_extra_options())
The option bits are:
PCRE2_ANCHORED Force pattern anchoring
PCRE2_ALLOW_EMPTY_CLASS Allow empty classes
PCRE2_ALT_BSUX Alternative handling of \u, \U, and \x
PCRE2_ALT_CIRCUMFLEX Alternative handling of ^ in multiline mode
PCRE2_ALT_VERBNAMES Process backslashes in verb names
PCRE2_AUTO_CALLOUT Compile automatic callouts
PCRE2_CASELESS Do caseless matching
PCRE2_DOLLAR_ENDONLY $ not to match newline at end
PCRE2_DOTALL . matches anything including NL
PCRE2_DUPNAMES Allow duplicate names for subpatterns
PCRE2_ENDANCHORED Pattern can match only at end of subject
PCRE2_EXTENDED Ignore white space and # comments
PCRE2_FIRSTLINE Force matching to be before newline
PCRE2_LITERAL Pattern characters are all literal
PCRE2_MATCH_INVALID_UTF Enable support for matching invalid UTF
PCRE2_MATCH_UNSET_BACKREF Match unset backreferences
PCRE2_MULTILINE ^ and $ match newlines within data
PCRE2_NEVER_BACKSLASH_C Lock out the use of \C in patterns
PCRE2_NEVER_UCP Lock out PCRE2_UCP, e.g. via (*UCP)
PCRE2_NEVER_UTF Lock out PCRE2_UTF, e.g. via (*UTF)
PCRE2_NO_AUTO_CAPTURE Disable numbered capturing paren-
theses (named ones available)
PCRE2_NO_AUTO_POSSESS Disable auto-possessification
PCRE2_NO_DOTSTAR_ANCHOR Disable automatic anchoring for .*
PCRE2_NO_START_OPTIMIZE Disable match-time start optimizations
PCRE2_NO_UTF_CHECK Do not check the pattern for UTF validity
(only relevant if PCRE2_UTF is set)
PCRE2_UCP Use Unicode properties for \d, \w, etc.
PCRE2_UNGREEDY Invert greediness of quantifiers
PCRE2_USE_OFFSET_LIMIT Enable offset limit for unanchored matching
PCRE2_UTF Treat pattern and subjects as UTF strings
PCRE2 must be built with Unicode support (the default) in order to use
PCRE2_UTF, PCRE2_UCP and related options.
Additional options may be set in the compile context via the
pcre2_set_compile_extra_options function.
The yield of this function is a pointer to a private data structure
that contains the compiled pattern, or NULL if an error was detected.
There is a complete description of the PCRE2 native API, with more
detail on each option, in the pcre2api page, and a description of the
POSIX API in the pcre2posix page.
PCRE2 10.34 23 May 2019 PCRE2_COMPILE(3)