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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old library is now obsolete and is no longer maintained.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_PATTERN_INFO(3) DragonFly Library Functions Manual
NAME
PCRE2 - Perl-compatible regular expressions (revised API)
SYNOPSIS
#include <pcre2.h>
int pcre2_pattern_info(const pcre2_code *code, uint32_t what,
void *where);
DESCRIPTION
This function returns information about a compiled pattern. Its
arguments are:
code Pointer to a compiled regular expression pattern
what What information is required
where Where to put the information
The recognized values for the what argument, and the information they
request are as follows:
PCRE2_INFO_ALLOPTIONS Final options after compiling
PCRE2_INFO_ARGOPTIONS Options passed to pcre2_compile()
PCRE2_INFO_BACKREFMAX Number of highest backreference
PCRE2_INFO_BSR What \R matches:
PCRE2_BSR_UNICODE: Unicode line endings
PCRE2_BSR_ANYCRLF: CR, LF, or CRLF only
PCRE2_INFO_CAPTURECOUNT Number of capturing subpatterns
PCRE2_INFO_DEPTHLIMIT Backtracking depth limit if set,
otherwise PCRE2_ERROR_UNSET
PCRE2_INFO_EXTRAOPTIONS Extra options that were passed in the
compile context
PCRE2_INFO_FIRSTBITMAP Bitmap of first code units, or NULL
PCRE2_INFO_FIRSTCODETYPE Type of start-of-match information
0 nothing set
1 first code unit is set
2 start of string or after newline
PCRE2_INFO_FIRSTCODEUNIT First code unit when type is 1
PCRE2_INFO_FRAMESIZE Size of backtracking frame
PCRE2_INFO_HASBACKSLASHC Return 1 if pattern contains \C
PCRE2_INFO_HASCRORLF Return 1 if explicit CR or LF matches
exist in the pattern
PCRE2_INFO_HEAPLIMIT Heap memory limit if set,
otherwise PCRE2_ERROR_UNSET
PCRE2_INFO_JCHANGED Return 1 if (?J) or (?-J) was used
PCRE2_INFO_JITSIZE Size of JIT compiled code, or 0
PCRE2_INFO_LASTCODETYPE Type of must-be-present information
0 nothing set
1 code unit is set
PCRE2_INFO_LASTCODEUNIT Last code unit when type is 1
PCRE2_INFO_MATCHEMPTY 1 if the pattern can match an
empty string, 0 otherwise
PCRE2_INFO_MATCHLIMIT Match limit if set,
otherwise PCRE2_ERROR_UNSET
PCRE2_INFO_MAXLOOKBEHIND Length (in characters) of the longest
lookbehind assertion
PCRE2_INFO_MINLENGTH Lower bound length of matching strings
PCRE2_INFO_NAMECOUNT Number of named subpatterns
PCRE2_INFO_NAMEENTRYSIZE Size of name table entries
PCRE2_INFO_NAMETABLE Pointer to name table
PCRE2_CONFIG_NEWLINE Code for the newline sequence:
PCRE2_NEWLINE_CR
PCRE2_NEWLINE_LF
PCRE2_NEWLINE_CRLF
PCRE2_NEWLINE_ANY
PCRE2_NEWLINE_ANYCRLF
PCRE2_NEWLINE_NUL
PCRE2_INFO_RECURSIONLIMIT Obsolete synonym for PCRE2_INFO_DEPTHLIMIT
PCRE2_INFO_SIZE Size of compiled pattern
If where is NULL, the function returns the amount of memory needed for
the requested information, in bytes. Otherwise, the where argument must
point to an unsigned 32-bit integer (uint32_t variable), except for the
following what values, when it must point to a variable of the type
shown:
PCRE2_INFO_FIRSTBITMAP const uint8_t *
PCRE2_INFO_JITSIZE size_t
PCRE2_INFO_NAMETABLE PCRE2_SPTR
PCRE2_INFO_SIZE size_t
The yield of the function is zero on success or:
PCRE2_ERROR_NULL the argument code is NULL
PCRE2_ERROR_BADMAGIC the "magic number" was not found
PCRE2_ERROR_BADOPTION the value of what is invalid
PCRE2_ERROR_BADMODE the pattern was compiled in the wrong mode
PCRE2_ERROR_UNSET the requested information is not set
There is a complete description of the PCRE2 native API in the pcre2api
page and a description of the POSIX API in the pcre2posix page.
PCRE2 10.33 14 February 2019 PCRE2_PATTERN_INFO(3)