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Line 8 pcretest commands.	Line 8 pcretest commands.
-----------------------------------------------------------------------------	-----------------------------------------------------------------------------


PCRE(3) PCRE(3)	PCRE(3) Library Functions Manual PCRE(3)



NAME	NAME
PCRE - Perl-compatible regular expressions	PCRE - Perl-compatible regular expressions


INTRODUCTION	INTRODUCTION

The PCRE library is a set of functions that implement regular expres-	The PCRE library is a set of functions that implement regular expres-
Line 25 INTRODUCTION	Line 25 INTRODUCTION
items, and there is an option for requesting some minor changes that	items, and there is an option for requesting some minor changes that
give better JavaScript compatibility.	give better JavaScript compatibility.

	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.

	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.

	The three libraries contain identical sets of functions, except that
	the names in the 16-bit library start with pcre16_ instead of pcre_,
	and the names in the 32-bit library start with pcre32_ instead of
	pcre_. To avoid over-complication and reduce the documentation mainte-
	nance load, most of the documentation describes the 8-bit library, with
	the differences for the 16-bit and 32-bit libraries described sepa-
	rately in the pcre16 and pcre32 pages. References to functions or
	structures of the form pcre[16\|32]_xxx should be read as meaning
	"pcre_xxx when using the 8-bit library, pcre16_xxx when using the
	16-bit library, or pcre32_xxx when using the 32-bit library".

The current implementation of PCRE corresponds approximately with Perl	The current implementation of PCRE corresponds approximately with Perl
5.12, including support for UTF-8 encoded strings and Unicode general	5.12, including support for UTF-8/16/32 encoded strings and Unicode
category properties. However, UTF-8 and Unicode support has to be	general category properties. However, UTF-8/16/32 and Unicode support
explicitly enabled; it is not the default. The Unicode tables corre-	has to be explicitly enabled; it is not the default. The Unicode tables
spond to Unicode release 6.0.0.	correspond to Unicode release 6.3.0.

In addition to the Perl-compatible matching function, PCRE contains an	In addition to the Perl-compatible matching function, PCRE contains an
alternative function that matches the same compiled patterns in a dif-	alternative function that matches the same compiled patterns in a dif-
Line 39 INTRODUCTION	Line 63 INTRODUCTION

PCRE is written in C and released as a C library. A number of people	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,	have written wrappers and interfaces of various kinds. In particular,
Google Inc. have provided a comprehensive C++ wrapper. This is now	Google Inc. have provided a comprehensive C++ wrapper for the 8-bit
included as part of the PCRE distribution. The pcrecpp page has details	library. This is now included as part of the PCRE distribution. The
of this interface. Other people's contributions can be found in the	pcrecpp page has details of this interface. Other people's contribu-
Contrib directory at the primary FTP site, which is:	tions can be found in the Contrib directory at the primary FTP site,
	which is:

ftp://ftp.csx.cam.ac.uk/pub/software/programming/pcre	ftp://ftp.csx.cam.ac.uk/pub/software/programming/pcre

Details of exactly which Perl regular expression features are and are	Details of exactly which Perl regular expression features are and are
not supported by PCRE are given in separate documents. See the pcrepat-	not supported by PCRE are given in separate documents. See the pcrepat-
tern and pcrecompat pages. There is a syntax summary in the pcresyntax	tern and pcrecompat pages. There is a syntax summary in the pcresyntax
page.	page.

Some features of PCRE can be included, excluded, or changed when the	Some features of PCRE can be included, excluded, or changed when the
library is built. The pcre_config() function makes it possible for a	library is built. The pcre_config() function makes it possible for a
client to discover which features are available. The features them-	client to discover which features are available. The features them-
selves are described in the pcrebuild page. Documentation about build-	selves are described in the pcrebuild page. Documentation about build-
ing PCRE for various operating systems can be found in the README and	ing PCRE for various operating systems can be found in the README and
NON-UNIX-USE files in the source distribution.	NON-AUTOTOOLS_BUILD files in the source distribution.

The library contains a number of undocumented internal functions and	The libraries contains a number of undocumented internal functions and
data tables that are used by more than one of the exported external	data tables that are used by more than one of the exported external
functions, but which are not intended for use by external callers.	functions, but which are not intended for use by external callers.
Their names all begin with "_pcre_", which hopefully will not provoke	Their names all begin with "_pcre_" or "_pcre16_" or "_pcre32_", which
any name clashes. In some environments, it is possible to control which	hopefully will not provoke any name clashes. In some environments, it
external symbols are exported when a shared library is built, and in	is possible to control which external symbols are exported when a
these cases the undocumented symbols are not exported.	shared library is built, and in these cases the undocumented symbols
	are not exported.


	SECURITY CONSIDERATIONS

	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 valid-
	ity. If the data string is very long, such a check might use suffi-
	ciently many resources as to cause your application to lose perfor-
	mance.

	One way of guarding against this possibility is to use the
	pcre_fullinfo() 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.

	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.

	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 pro-
	vides some protection against this: see the PCRE_EXTRA_MATCH_LIMIT fea-
	ture in the pcreapi page.


USER DOCUMENTATION	USER DOCUMENTATION

The user documentation for PCRE comprises a number of different sec-	The user documentation for PCRE comprises a number of different sec-
tions. In the "man" format, each of these is a separate "man page". In	tions. 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.	the HTML format, each is a separate page, linked from the index page.
In the plain text format, all the sections, except the pcredemo sec-	In the plain text format, all the sections, except the pcredemo sec-
tion, are concatenated, for ease of searching. The sections are as fol-	tion, are concatenated, for ease of searching. The sections are as fol-
lows:	lows:

pcre this document	pcre this document
pcre-config show PCRE installation configuration information	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	pcreapi details of PCRE's native C API
pcrebuild options for building PCRE	pcrebuild building PCRE
pcrecallout details of the callout feature	pcrecallout details of the callout feature
pcrecompat discussion of Perl compatibility	pcrecompat discussion of Perl compatibility
pcrecpp details of the C++ wrapper	pcrecpp details of the C++ wrapper for the 8-bit library
pcredemo a demonstration C program that uses PCRE	pcredemo a demonstration C program that uses PCRE
pcregrep description of the pcregrep command	pcregrep description of the pcregrep command (8-bit only)
pcrejit discussion of the just-in-time optimization support	pcrejit discussion of the just-in-time optimization support
pcrelimits details of size and other limits	pcrelimits details of size and other limits
pcrematching discussion of the two matching algorithms	pcrematching discussion of the two matching algorithms
Line 92 USER DOCUMENTATION	Line 152 USER DOCUMENTATION
pcrepattern syntax and semantics of supported	pcrepattern syntax and semantics of supported
regular expressions	regular expressions
pcreperform discussion of performance issues	pcreperform discussion of performance issues
pcreposix the POSIX-compatible C API	pcreposix the POSIX-compatible C API for the 8-bit library
pcreprecompile details of saving and re-using precompiled patterns	pcreprecompile details of saving and re-using precompiled patterns
pcresample discussion of the pcredemo program	pcresample discussion of the pcredemo program
pcrestack discussion of stack usage	pcrestack discussion of stack usage
pcresyntax quick syntax reference	pcresyntax quick syntax reference
pcretest description of the pcretest testing command	pcretest description of the pcretest testing command
pcreunicode discussion of Unicode and UTF-8 support	pcreunicode discussion of Unicode and UTF-8/16/32 support

In addition, in the "man" and HTML formats, there is a short page for	In addition, in the "man" and HTML formats, there is a short page for
each C library function, listing its arguments and results.	each C library function, listing its arguments and results.


Line 110 AUTHOR	Line 170 AUTHOR
University Computing Service	University Computing Service
Cambridge CB2 3QH, England.	Cambridge CB2 3QH, England.

Putting an actual email address here seems to have been a spam magnet,	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,	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.	followed by the two digits 10, at the domain cam.ac.uk.


REVISION	REVISION

Last updated: 24 August 2011	Last updated: 13 May 2013
Copyright (c) 1997-2011 University of Cambridge.	Copyright (c) 1997-2013 University of Cambridge.
------------------------------------------------------------------------------	------------------------------------------------------------------------------


PCREBUILD(3) PCREBUILD(3)	PCRE(3) Library Functions Manual PCRE(3)



NAME	NAME
PCRE - Perl-compatible regular expressions	PCRE - Perl-compatible regular expressions

	#include <pcre.h>


	PCRE 16-BIT API BASIC FUNCTIONS

	pcre16 *pcre16_compile(PCRE_SPTR16 pattern, int options,
	const char *errptr, int erroffset,
	const unsigned char *tableptr);

	pcre16 *pcre16_compile2(PCRE_SPTR16 pattern, int options,
	int *errorcodeptr,
	const char *errptr, int erroffset,
	const unsigned char *tableptr);

	pcre16_extra pcre16_study(const pcre16 code, int options,
	const char **errptr);

	void pcre16_free_study(pcre16_extra *extra);

	int pcre16_exec(const pcre16 code, const pcre16_extra extra,
	PCRE_SPTR16 subject, int length, int startoffset,
	int options, int *ovector, int ovecsize);

	int pcre16_dfa_exec(const pcre16 code, const pcre16_extra extra,
	PCRE_SPTR16 subject, int length, int startoffset,
	int options, int *ovector, int ovecsize,
	int *workspace, int wscount);


	PCRE 16-BIT API STRING EXTRACTION FUNCTIONS

	int pcre16_copy_named_substring(const pcre16 *code,
	PCRE_SPTR16 subject, int *ovector,
	int stringcount, PCRE_SPTR16 stringname,
	PCRE_UCHAR16 *buffer, int buffersize);

	int pcre16_copy_substring(PCRE_SPTR16 subject, int *ovector,
	int stringcount, int stringnumber, PCRE_UCHAR16 *buffer,
	int buffersize);

	int pcre16_get_named_substring(const pcre16 *code,
	PCRE_SPTR16 subject, int *ovector,
	int stringcount, PCRE_SPTR16 stringname,
	PCRE_SPTR16 *stringptr);

	int pcre16_get_stringnumber(const pcre16 *code,
	PCRE_SPTR16 name);

	int pcre16_get_stringtable_entries(const pcre16 *code,
	PCRE_SPTR16 name, PCRE_UCHAR16 first, PCRE_UCHAR16 last);

	int pcre16_get_substring(PCRE_SPTR16 subject, int *ovector,
	int stringcount, int stringnumber,
	PCRE_SPTR16 *stringptr);

	int pcre16_get_substring_list(PCRE_SPTR16 subject,
	int ovector, int stringcount, PCRE_SPTR16 *listptr);

	void pcre16_free_substring(PCRE_SPTR16 stringptr);

	void pcre16_free_substring_list(PCRE_SPTR16 *stringptr);


	PCRE 16-BIT API AUXILIARY FUNCTIONS

	pcre16_jit_stack *pcre16_jit_stack_alloc(int startsize, int maxsize);

	void pcre16_jit_stack_free(pcre16_jit_stack *stack);

	void pcre16_assign_jit_stack(pcre16_extra *extra,
	pcre16_jit_callback callback, void *data);

	const unsigned char *pcre16_maketables(void);

	int pcre16_fullinfo(const pcre16 code, const pcre16_extra extra,
	int what, void *where);

	int pcre16_refcount(pcre16 *code, int adjust);

	int pcre16_config(int what, void *where);

	const char *pcre16_version(void);

	int pcre16_pattern_to_host_byte_order(pcre16 *code,
	pcre16_extra extra, const unsigned char tables);


	PCRE 16-BIT API INDIRECTED FUNCTIONS

	void (pcre16_malloc)(size_t);

	void (pcre16_free)(void );

	void (pcre16_stack_malloc)(size_t);

	void (pcre16_stack_free)(void );

	int (pcre16_callout)(pcre16_callout_block );


	PCRE 16-BIT API 16-BIT-ONLY FUNCTION

	int pcre16_utf16_to_host_byte_order(PCRE_UCHAR16 *output,
	PCRE_SPTR16 input, int length, int *byte_order,
	int keep_boms);


	THE PCRE 16-BIT LIBRARY

	Starting with release 8.30, it is possible to compile a PCRE library
	that supports 16-bit character strings, including UTF-16 strings, as
	well as or instead of the original 8-bit library. The majority of the
	work to make this possible was done by Zoltan Herczeg. The two
	libraries contain identical sets of functions, used in exactly the same
	way. Only the names of the functions and the data types of their argu-
	ments and results are different. To avoid over-complication and reduce
	the documentation maintenance load, most of the PCRE documentation
	describes the 8-bit library, with only occasional references to the
	16-bit library. This page describes what is different when you use the
	16-bit library.

	WARNING: A single application can be linked with both libraries, but
	you must take care when processing any particular pattern to use func-
	tions from just one library. For example, if you want to study a pat-
	tern that was compiled with pcre16_compile(), you must do so with
	pcre16_study(), not pcre_study(), and you must free the study data with
	pcre16_free_study().


	THE HEADER FILE

	There is only one header file, pcre.h. It contains prototypes for all
	the functions in all libraries, as well as definitions of flags, struc-
	tures, error codes, etc.


	THE LIBRARY NAME

	In Unix-like systems, the 16-bit library is called libpcre16, and can
	normally be accesss by adding -lpcre16 to the command for linking an
	application that uses PCRE.


	STRING TYPES

	In the 8-bit library, strings are passed to PCRE library functions as
	vectors of bytes with the C type "char *". In the 16-bit library,
	strings are passed as vectors of unsigned 16-bit quantities. The macro
	PCRE_UCHAR16 specifies an appropriate data type, and PCRE_SPTR16 is
	defined as "const PCRE_UCHAR16 *". In very many environments, "short
	int" is a 16-bit data type. When PCRE is built, it defines PCRE_UCHAR16
	as "unsigned short int", but checks that it really is a 16-bit data
	type. If it is not, the build fails with an error message telling the
	maintainer to modify the definition appropriately.


	STRUCTURE TYPES

	The types of the opaque structures that are used for compiled 16-bit
	patterns and JIT stacks are pcre16 and pcre16_jit_stack respectively.
	The type of the user-accessible structure that is returned by
	pcre16_study() is pcre16_extra, and the type of the structure that is
	used for passing data to a callout function is pcre16_callout_block.
	These structures contain the same fields, with the same names, as their
	8-bit counterparts. The only difference is that pointers to character
	strings are 16-bit instead of 8-bit types.


	16-BIT FUNCTIONS

	For every function in the 8-bit library there is a corresponding func-
	tion in the 16-bit library with a name that starts with pcre16_ instead
	of pcre_. The prototypes are listed above. In addition, there is one
	extra function, pcre16_utf16_to_host_byte_order(). This is a utility
	function that converts a UTF-16 character string to host byte order if
	necessary. The other 16-bit functions expect the strings they are
	passed to be in host byte order.

	The input and output arguments of pcre16_utf16_to_host_byte_order() may
	point to the same address, that is, conversion in place is supported.
	The output buffer must be at least as long as the input.

	The length argument specifies the number of 16-bit data units in the
	input string; a negative value specifies a zero-terminated string.

	If byte_order is NULL, it is assumed that the string starts off in host
	byte order. This may be changed by byte-order marks (BOMs) anywhere in
	the string (commonly as the first character).

	If byte_order is not NULL, a non-zero value of the integer to which it
	points means that the input starts off in host byte order, otherwise
	the opposite order is assumed. Again, BOMs in the string can change
	this. The final byte order is passed back at the end of processing.

	If keep_boms is not zero, byte-order mark characters (0xfeff) are
	copied into the output string. Otherwise they are discarded.

	The result of the function is the number of 16-bit units placed into
	the output buffer, including the zero terminator if the string was
	zero-terminated.


	SUBJECT STRING OFFSETS

	The lengths and starting offsets of subject strings must be specified
	in 16-bit data units, and the offsets within subject strings that are
	returned by the matching functions are in also 16-bit units rather than
	bytes.


	NAMED SUBPATTERNS

	The name-to-number translation table that is maintained for named sub-
	patterns uses 16-bit characters. The pcre16_get_stringtable_entries()
	function returns the length of each entry in the table as the number of
	16-bit data units.


	OPTION NAMES

	There are two new general option names, PCRE_UTF16 and
	PCRE_NO_UTF16_CHECK, which correspond to PCRE_UTF8 and
	PCRE_NO_UTF8_CHECK in the 8-bit library. In fact, these new options
	define the same bits in the options word. There is a discussion about
	the validity of UTF-16 strings in the pcreunicode page.

	For the pcre16_config() function there is an option PCRE_CONFIG_UTF16
	that returns 1 if UTF-16 support is configured, otherwise 0. If this
	option is given to pcre_config() or pcre32_config(), or if the
	PCRE_CONFIG_UTF8 or PCRE_CONFIG_UTF32 option is given to pcre16_con-
	fig(), the result is the PCRE_ERROR_BADOPTION error.


	CHARACTER CODES

	In 16-bit mode, when PCRE_UTF16 is not set, character values are
	treated in the same way as in 8-bit, non UTF-8 mode, except, of course,
	that they can range from 0 to 0xffff instead of 0 to 0xff. Character
	types for characters less than 0xff can therefore be influenced by the
	locale in the same way as before. Characters greater than 0xff have
	only one case, and no "type" (such as letter or digit).

	In UTF-16 mode, the character code is Unicode, in the range 0 to
	0x10ffff, with the exception of values in the range 0xd800 to 0xdfff
	because those are "surrogate" values that are used in pairs to encode
	values greater than 0xffff.

	A UTF-16 string can indicate its endianness by special code knows as a
	byte-order mark (BOM). The PCRE functions do not handle this, expecting
	strings to be in host byte order. A utility function called
	pcre16_utf16_to_host_byte_order() is provided to help with this (see
	above).


	ERROR NAMES

	The errors PCRE_ERROR_BADUTF16_OFFSET and PCRE_ERROR_SHORTUTF16 corre-
	spond to their 8-bit counterparts. The error PCRE_ERROR_BADMODE is
	given when a compiled pattern is passed to a function that processes
	patterns in the other mode, for example, if a pattern compiled with
	pcre_compile() is passed to pcre16_exec().

	There are new error codes whose names begin with PCRE_UTF16_ERR for
	invalid UTF-16 strings, corresponding to the PCRE_UTF8_ERR codes for
	UTF-8 strings that are described in the section entitled "Reason codes
	for invalid UTF-8 strings" in the main pcreapi page. The UTF-16 errors
	are:

	PCRE_UTF16_ERR1 Missing low surrogate at end of string
	PCRE_UTF16_ERR2 Invalid low surrogate follows high surrogate
	PCRE_UTF16_ERR3 Isolated low surrogate
	PCRE_UTF16_ERR4 Non-character


	ERROR TEXTS

	If there is an error while compiling a pattern, the error text that is
	passed back by pcre16_compile() or pcre16_compile2() is still an 8-bit
	character string, zero-terminated.


	CALLOUTS

	The subject and mark fields in the callout block that is passed to a
	callout function point to 16-bit vectors.


	TESTING

	The pcretest program continues to operate with 8-bit input and output
	files, but it can be used for testing the 16-bit library. If it is run
	with the command line option -16, patterns and subject strings are con-
	verted from 8-bit to 16-bit before being passed to PCRE, and the 16-bit
	library functions are used instead of the 8-bit ones. Returned 16-bit
	strings are converted to 8-bit for output. If both the 8-bit and the
	32-bit libraries were not compiled, pcretest defaults to 16-bit and the
	-16 option is ignored.

	When PCRE is being built, the RunTest script that is called by "make
	check" uses the pcretest -C option to discover which of the 8-bit,
	16-bit and 32-bit libraries has been built, and runs the tests appro-
	priately.


	NOT SUPPORTED IN 16-BIT MODE

	Not all the features of the 8-bit library are available with the 16-bit
	library. The C++ and POSIX wrapper functions support only the 8-bit
	library, and the pcregrep program is at present 8-bit only.


	AUTHOR

	Philip Hazel
	University Computing Service
	Cambridge CB2 3QH, England.


	REVISION

	Last updated: 12 May 2013
	Copyright (c) 1997-2013 University of Cambridge.
	------------------------------------------------------------------------------


	PCRE(3) Library Functions Manual PCRE(3)



	NAME
	PCRE - Perl-compatible regular expressions

	#include <pcre.h>


	PCRE 32-BIT API BASIC FUNCTIONS

	pcre32 *pcre32_compile(PCRE_SPTR32 pattern, int options,
	const char *errptr, int erroffset,
	const unsigned char *tableptr);

	pcre32 *pcre32_compile2(PCRE_SPTR32 pattern, int options,
	int *errorcodeptr,
	const unsigned char *tableptr);

	pcre32_extra pcre32_study(const pcre32 code, int options,
	const char **errptr);

	void pcre32_free_study(pcre32_extra *extra);

	int pcre32_exec(const pcre32 code, const pcre32_extra extra,
	PCRE_SPTR32 subject, int length, int startoffset,
	int options, int *ovector, int ovecsize);

	int pcre32_dfa_exec(const pcre32 code, const pcre32_extra extra,
	PCRE_SPTR32 subject, int length, int startoffset,
	int options, int *ovector, int ovecsize,
	int *workspace, int wscount);


	PCRE 32-BIT API STRING EXTRACTION FUNCTIONS

	int pcre32_copy_named_substring(const pcre32 *code,
	PCRE_SPTR32 subject, int *ovector,
	int stringcount, PCRE_SPTR32 stringname,
	PCRE_UCHAR32 *buffer, int buffersize);

	int pcre32_copy_substring(PCRE_SPTR32 subject, int *ovector,
	int stringcount, int stringnumber, PCRE_UCHAR32 *buffer,
	int buffersize);

	int pcre32_get_named_substring(const pcre32 *code,
	PCRE_SPTR32 subject, int *ovector,
	int stringcount, PCRE_SPTR32 stringname,
	PCRE_SPTR32 *stringptr);

	int pcre32_get_stringnumber(const pcre32 *code,
	PCRE_SPTR32 name);

	int pcre32_get_stringtable_entries(const pcre32 *code,
	PCRE_SPTR32 name, PCRE_UCHAR32 first, PCRE_UCHAR32 last);

	int pcre32_get_substring(PCRE_SPTR32 subject, int *ovector,
	int stringcount, int stringnumber,
	PCRE_SPTR32 *stringptr);

	int pcre32_get_substring_list(PCRE_SPTR32 subject,
	int ovector, int stringcount, PCRE_SPTR32 *listptr);

	void pcre32_free_substring(PCRE_SPTR32 stringptr);

	void pcre32_free_substring_list(PCRE_SPTR32 *stringptr);


	PCRE 32-BIT API AUXILIARY FUNCTIONS

	pcre32_jit_stack *pcre32_jit_stack_alloc(int startsize, int maxsize);

	void pcre32_jit_stack_free(pcre32_jit_stack *stack);

	void pcre32_assign_jit_stack(pcre32_extra *extra,
	pcre32_jit_callback callback, void *data);

	const unsigned char *pcre32_maketables(void);

	int pcre32_fullinfo(const pcre32 code, const pcre32_extra extra,
	int what, void *where);

	int pcre32_refcount(pcre32 *code, int adjust);

	int pcre32_config(int what, void *where);

	const char *pcre32_version(void);

	int pcre32_pattern_to_host_byte_order(pcre32 *code,
	pcre32_extra extra, const unsigned char tables);


	PCRE 32-BIT API INDIRECTED FUNCTIONS

	void (pcre32_malloc)(size_t);

	void (pcre32_free)(void );

	void (pcre32_stack_malloc)(size_t);

	void (pcre32_stack_free)(void );

	int (pcre32_callout)(pcre32_callout_block );


	PCRE 32-BIT API 32-BIT-ONLY FUNCTION

	int pcre32_utf32_to_host_byte_order(PCRE_UCHAR32 *output,
	PCRE_SPTR32 input, int length, int *byte_order,
	int keep_boms);


	THE PCRE 32-BIT LIBRARY

	Starting with release 8.32, it is possible to compile a PCRE library
	that supports 32-bit character strings, including UTF-32 strings, as
	well as or instead of the original 8-bit library. This work was done by
	Christian Persch, based on the work done by Zoltan Herczeg for the
	16-bit library. All three libraries contain identical sets of func-
	tions, used in exactly the same way. Only the names of the functions
	and the data types of their arguments and results are different. To
	avoid over-complication and reduce the documentation maintenance load,
	most of the PCRE documentation describes the 8-bit library, with only
	occasional references to the 16-bit and 32-bit libraries. This page
	describes what is different when you use the 32-bit library.

	WARNING: A single application can be linked with all or any of the
	three libraries, but you must take care when processing any particular
	pattern to use functions from just one library. For example, if you
	want to study a pattern that was compiled with pcre32_compile(), you
	must do so with pcre32_study(), not pcre_study(), and you must free the
	study data with pcre32_free_study().


	THE HEADER FILE

	There is only one header file, pcre.h. It contains prototypes for all
	the functions in all libraries, as well as definitions of flags, struc-
	tures, error codes, etc.


	THE LIBRARY NAME

	In Unix-like systems, the 32-bit library is called libpcre32, and can
	normally be accesss by adding -lpcre32 to the command for linking an
	application that uses PCRE.


	STRING TYPES

	In the 8-bit library, strings are passed to PCRE library functions as
	vectors of bytes with the C type "char *". In the 32-bit library,
	strings are passed as vectors of unsigned 32-bit quantities. The macro
	PCRE_UCHAR32 specifies an appropriate data type, and PCRE_SPTR32 is
	defined as "const PCRE_UCHAR32 *". In very many environments, "unsigned
	int" is a 32-bit data type. When PCRE is built, it defines PCRE_UCHAR32
	as "unsigned int", but checks that it really is a 32-bit data type. If
	it is not, the build fails with an error message telling the maintainer
	to modify the definition appropriately.


	STRUCTURE TYPES

	The types of the opaque structures that are used for compiled 32-bit
	patterns and JIT stacks are pcre32 and pcre32_jit_stack respectively.
	The type of the user-accessible structure that is returned by
	pcre32_study() is pcre32_extra, and the type of the structure that is
	used for passing data to a callout function is pcre32_callout_block.
	These structures contain the same fields, with the same names, as their
	8-bit counterparts. The only difference is that pointers to character
	strings are 32-bit instead of 8-bit types.


	32-BIT FUNCTIONS

	For every function in the 8-bit library there is a corresponding func-
	tion in the 32-bit library with a name that starts with pcre32_ instead
	of pcre_. The prototypes are listed above. In addition, there is one
	extra function, pcre32_utf32_to_host_byte_order(). This is a utility
	function that converts a UTF-32 character string to host byte order if
	necessary. The other 32-bit functions expect the strings they are
	passed to be in host byte order.

	The input and output arguments of pcre32_utf32_to_host_byte_order() may
	point to the same address, that is, conversion in place is supported.
	The output buffer must be at least as long as the input.

	The length argument specifies the number of 32-bit data units in the
	input string; a negative value specifies a zero-terminated string.

	If byte_order is NULL, it is assumed that the string starts off in host
	byte order. This may be changed by byte-order marks (BOMs) anywhere in
	the string (commonly as the first character).

	If byte_order is not NULL, a non-zero value of the integer to which it
	points means that the input starts off in host byte order, otherwise
	the opposite order is assumed. Again, BOMs in the string can change
	this. The final byte order is passed back at the end of processing.

	If keep_boms is not zero, byte-order mark characters (0xfeff) are
	copied into the output string. Otherwise they are discarded.

	The result of the function is the number of 32-bit units placed into
	the output buffer, including the zero terminator if the string was
	zero-terminated.


	SUBJECT STRING OFFSETS

	The lengths and starting offsets of subject strings must be specified
	in 32-bit data units, and the offsets within subject strings that are
	returned by the matching functions are in also 32-bit units rather than
	bytes.


	NAMED SUBPATTERNS

	The name-to-number translation table that is maintained for named sub-
	patterns uses 32-bit characters. The pcre32_get_stringtable_entries()
	function returns the length of each entry in the table as the number of
	32-bit data units.


	OPTION NAMES

	There are two new general option names, PCRE_UTF32 and
	PCRE_NO_UTF32_CHECK, which correspond to PCRE_UTF8 and
	PCRE_NO_UTF8_CHECK in the 8-bit library. In fact, these new options
	define the same bits in the options word. There is a discussion about
	the validity of UTF-32 strings in the pcreunicode page.

	For the pcre32_config() function there is an option PCRE_CONFIG_UTF32
	that returns 1 if UTF-32 support is configured, otherwise 0. If this
	option is given to pcre_config() or pcre16_config(), or if the
	PCRE_CONFIG_UTF8 or PCRE_CONFIG_UTF16 option is given to pcre32_con-
	fig(), the result is the PCRE_ERROR_BADOPTION error.


	CHARACTER CODES

	In 32-bit mode, when PCRE_UTF32 is not set, character values are
	treated in the same way as in 8-bit, non UTF-8 mode, except, of course,
	that they can range from 0 to 0x7fffffff instead of 0 to 0xff. Charac-
	ter types for characters less than 0xff can therefore be influenced by
	the locale in the same way as before. Characters greater than 0xff
	have only one case, and no "type" (such as letter or digit).

	In UTF-32 mode, the character code is Unicode, in the range 0 to
	0x10ffff, with the exception of values in the range 0xd800 to 0xdfff
	because those are "surrogate" values that are ill-formed in UTF-32.

	A UTF-32 string can indicate its endianness by special code knows as a
	byte-order mark (BOM). The PCRE functions do not handle this, expecting
	strings to be in host byte order. A utility function called
	pcre32_utf32_to_host_byte_order() is provided to help with this (see
	above).


	ERROR NAMES

	The error PCRE_ERROR_BADUTF32 corresponds to its 8-bit counterpart.
	The error PCRE_ERROR_BADMODE is given when a compiled pattern is passed
	to a function that processes patterns in the other mode, for example,
	if a pattern compiled with pcre_compile() is passed to pcre32_exec().

	There are new error codes whose names begin with PCRE_UTF32_ERR for
	invalid UTF-32 strings, corresponding to the PCRE_UTF8_ERR codes for
	UTF-8 strings that are described in the section entitled "Reason codes
	for invalid UTF-8 strings" in the main pcreapi page. The UTF-32 errors
	are:

	PCRE_UTF32_ERR1 Surrogate character (range from 0xd800 to 0xdfff)
	PCRE_UTF32_ERR2 Non-character
	PCRE_UTF32_ERR3 Character > 0x10ffff


	ERROR TEXTS

	If there is an error while compiling a pattern, the error text that is
	passed back by pcre32_compile() or pcre32_compile2() is still an 8-bit
	character string, zero-terminated.


	CALLOUTS

	The subject and mark fields in the callout block that is passed to a
	callout function point to 32-bit vectors.


	TESTING

	The pcretest program continues to operate with 8-bit input and output
	files, but it can be used for testing the 32-bit library. If it is run
	with the command line option -32, patterns and subject strings are con-
	verted from 8-bit to 32-bit before being passed to PCRE, and the 32-bit
	library functions are used instead of the 8-bit ones. Returned 32-bit
	strings are converted to 8-bit for output. If both the 8-bit and the
	16-bit libraries were not compiled, pcretest defaults to 32-bit and the
	-32 option is ignored.

	When PCRE is being built, the RunTest script that is called by "make
	check" uses the pcretest -C option to discover which of the 8-bit,
	16-bit and 32-bit libraries has been built, and runs the tests appro-
	priately.


	NOT SUPPORTED IN 32-BIT MODE

	Not all the features of the 8-bit library are available with the 32-bit
	library. The C++ and POSIX wrapper functions support only the 8-bit
	library, and the pcregrep program is at present 8-bit only.


	AUTHOR

	Philip Hazel
	University Computing Service
	Cambridge CB2 3QH, England.


	REVISION

	Last updated: 12 May 2013
	Copyright (c) 1997-2013 University of Cambridge.
	------------------------------------------------------------------------------


	PCREBUILD(3) Library Functions Manual PCREBUILD(3)



	NAME
	PCRE - Perl-compatible regular expressions

	BUILDING PCRE

	PCRE is distributed with a configure script that can be used to build
	the library in Unix-like environments using the applications known as
	Autotools. Also in the distribution are files to support building
	using CMake instead of configure. The text file README contains general
	information about building with Autotools (some of which is repeated
	below), and also has some comments about building on various operating
	systems. There is a lot more information about building PCRE without
	using Autotools (including information about using CMake and building
	"by hand") in the text file called NON-AUTOTOOLS-BUILD. You should
	consult this file as well as the README file if you are building in a
	non-Unix-like environment.


PCRE BUILD-TIME OPTIONS	PCRE BUILD-TIME OPTIONS

This document describes the optional features of PCRE that can be	The rest of this document describes the optional features of PCRE that
selected when the library is compiled. It assumes use of the configure	can be selected when the library is compiled. It assumes use of the
script, where the optional features are selected or deselected by pro-	configure script, where the optional features are selected or dese-
viding options to configure before running the make command. However,	lected by providing options to configure before running the make com-
the same options can be selected in both Unix-like and non-Unix-like	mand. However, the same options can be selected in both Unix-like and
environments using the GUI facility of cmake-gui if you are using CMake	non-Unix-like environments using the GUI facility of cmake-gui if you
instead of configure to build PCRE.	are using CMake instead of configure to build PCRE.

There is a lot more information about building PCRE in non-Unix-like	If you are not using Autotools or CMake, option selection can be done
environments in the file called NON_UNIX_USE, which is part of the PCRE	by editing the config.h file, or by passing parameter settings to the
distribution. You should consult this file as well as the README file	compiler, as described in NON-AUTOTOOLS-BUILD.
if you are building in a non-Unix-like environment.

The complete list of options for configure (which includes the standard	The complete list of options for configure (which includes the standard
ones such as the selection of the installation directory) can be	ones such as the selection of the installation directory) can be
obtained by running	obtained by running

./configure --help	./configure --help

The following sections include descriptions of options whose names	The following sections include descriptions of options whos The following sections include descriptions of options whos
begin with --enable or --disable. These settings specify changes to the	begin with --enable or --disable. These settings specify changes to the
defaults for the configure command. Because of the way that configure	defaults for the configure command. Because of the way that configure
works, --enable and --disable always come in pairs, so the complemen-	works, --enable and --disable always come in pairs, so the complemen-
tary option always exists as well, but as it specifies the default, it	tary option always exists as well, but as it specifies the default, it
is not described.	is not described.


	BUILDING 8-BIT, 16-BIT AND 32-BIT LIBRARIES

	By default, a library called libpcre is built, containing functions
	that take string arguments contained in vectors of bytes, either as
	single-byte characters, or interpreted as UTF-8 strings. You can also
	build a separate library, called libpcre16, in which strings are con-
	tained in vectors of 16-bit data units and interpreted either as sin-
	gle-unit characters or UTF-16 strings, by adding

	--enable-pcre16

	to the configure command. You can also build yet another separate
	library, called libpcre32, in which strings are contained in vectors of
	32-bit data units and interpreted either as single-unit characters or
	UTF-32 strings, by adding

	--enable-pcre32

	to the configure command. If you do not want the 8-bit library, add

	--disable-pcre8

	as well. At least one of the three libraries must be built. Note that
	the C++ and POSIX wrappers are for the 8-bit library only, and that
	pcregrep is an 8-bit program. None of these are built if you select
	only the 16-bit or 32-bit libraries.


BUILDING SHARED AND STATIC LIBRARIES	BUILDING SHARED AND STATIC LIBRARIES

The PCRE building process uses libtool to build both shared and static	The Autotools PCRE building process uses libtool to build both shared
Unix libraries by default. You can suppress one of these by adding one	and static libraries by default. You can suppress one of these by
of	adding one of

--disable-shared	--disable-shared
--disable-static	--disable-static
Line 172 BUILDING SHARED AND STATIC LIBRARIES	Line 934 BUILDING SHARED AND STATIC LIBRARIES

C++ SUPPORT	C++ SUPPORT

By default, the configure script will search for a C++ compiler and C++	By default, if the 8-bit library is being built, the configure script
header files. If it finds them, it automatically builds the C++ wrapper	will search for a C++ compiler and C++ header files. If it finds them,
library for PCRE. You can disable this by adding	it automatically builds the C++ wrapper library (which supports only
	8-bit strings). You can disable this by adding

--disable-cpp	--disable-cpp

to the configure command.	to the configure command.


UTF-8 SUPPORT	UTF-8, UTF-16 AND UTF-32 SUPPORT

To build PCRE with support for UTF-8 Unicode character strings, add	To build PCRE with support for UTF Unicode character strings, add

--enable-utf8	--enable-utf

to the configure command. Of itself, this does not make PCRE treat	to the configure command. This setting applies to all three libraries,
strings as UTF-8. As well as compiling PCRE with this option, you also	adding support for UTF-8 to the 8-bit library, support for UTF-16 to
have have to set the PCRE_UTF8 option when you call the pcre_compile()	the 16-bit library, and support for UTF-32 to the to the 32-bit
or pcre_compile2() functions.	library. There are no separate options for enabling UTF-8, UTF-16 and
	UTF-32 independently because that would allow ridiculous settings such
	as requesting UTF-16 support while building only the 8-bit library. It
	is not possible to build one library with UTF support and another with-
	out in the same configuration. (For backwards compatibility, --enable-
	utf8 is a synonym of --enable-utf.)

If you set --enable-utf8 when compiling in an EBCDIC environment, PCRE	Of itself, this setting does not make PCRE treat strings as UTF-8,
expects its input to be either ASCII or UTF-8 (depending on the runtime	UTF-16 or UTF-32. As well as compiling PCRE with this option, you also
option). It is not possible to support both EBCDIC and UTF-8 codes in	have have to set the PCRE_UTF8, PCRE_UTF16 or PCRE_UTF32 option (as
the same version of the library. Consequently, --enable-utf8 and	appropriate) when you call one of the pattern compiling functions.

	If you set --enable-utf when compiling in an EBCDIC environment, PCRE
	expects its input to be either ASCII or UTF-8 (depending on the run-
	time option). It is not possible to support both EBCDIC and UTF-8 codes
	in the same version of the library. Consequently, --enable-utf and
--enable-ebcdic are mutually exclusive.	--enable-ebcdic are mutually exclusive.


UNICODE CHARACTER PROPERTY SUPPORT	UNICODE CHARACTER PROPERTY SUPPORT

UTF-8 support allows PCRE to process character values greater than 255	UTF support allows the libraries to process character codepoints up to
in the strings that it handles. On its own, however, it does not pro-	0x10ffff in the strings that they handle. On its own, however, it does
vide any facilities for accessing the properties of such characters. If	not provide any facilities for accessing the properties of such charac-
you want to be able to use the pattern escapes \P, \p, and \X, which	ters. If you want to be able to use the pattern escapes \P, \p, and \X,
refer to Unicode character properties, you must add	which refer to Unicode character properties, you must add

--enable-unicode-properties	--enable-unicode-properties

to the configure command. This implies UTF-8 support, even if you have	to the configure command. This implies UTF support, even if yo to the configure command. This implies UTF support, even if yo
not explicitly requested it.	not explicitly requested it.

Including Unicode property support adds around 30K of tables to the	Including Unicode property support adds around 30K of tables to the
PCRE library. Only the general category properties such as Lu and Nd	PCRE library. Only the general category properties such as Lu and Nd
are supported. Details are given in the pcrepattern documentation.	are supported. Details are given in the pcrepattern documentation.


Line 223 JUST-IN-TIME COMPILER SUPPORT	Line 996 JUST-IN-TIME COMPILER SUPPORT

--enable-jit	--enable-jit

This support is available only for certain hardware architectures. If	This support is available only for certain hardware architectures. If
this option is set for an unsupported architecture, a compile time	this option is set for an unsupported architecture, a compile time
error occurs. See the pcrejit documentation for a discussion of JIT	error occurs. See the pcrejit documentation for a discussion of JIT
usage. When JIT support is enabled, pcregrep automatically makes use of	usage. When JIT support is enabled, pcregrep automatically makes use of
it, unless you add	it, unless you add

Line 236 JUST-IN-TIME COMPILER SUPPORT	Line 1009 JUST-IN-TIME COMPILER SUPPORT

CODE VALUE OF NEWLINE	CODE VALUE OF NEWLINE

By default, PCRE interprets the linefeed (LF) character as indicating	By default, PCRE interprets the linefeed (LF) character as indicating
the end of a line. This is the normal newline character on Unix-like	the end of a line. This is the normal newline character on Unix-like
systems. You can compile PCRE to use carriage return (CR) instead, by	systems. You can compile PCRE to use carriage return (CR) instead, by
adding	adding

--enable-newline-is-cr	--enable-newline-is-cr

to the configure command. There is also a --enable-newline-is-lf	to the configure command. There is also a --enable-newline-is-lf
option, which explicitly specifies linefeed as the newline character.	option, which explicitly specifies linefeed as the newline character.

Alternatively, you can specify that line endings are to be indicated by	Alternatively, you can specify that line endings are to be indicated by
Line 255 CODE VALUE OF NEWLINE	Line 1028 CODE VALUE OF NEWLINE

--enable-newline-is-anycrlf	--enable-newline-is-anycrlf

which causes PCRE to recognize any of the three sequences CR, LF, or	which causes PCRE to recognize any of the three sequences CR, LF, or
CRLF as indicating a line ending. Finally, a fifth option, specified by	CRLF as indicating a line ending. Finally, a fifth option, specified by

--enable-newline-is-any	--enable-newline-is-any

causes PCRE to recognize any Unicode newline sequence.	causes PCRE to recognize any Unicode newline sequence.

Whatever line ending convention is selected when PCRE is built can be	Whatever line ending convention is selected when PCRE is built can be
overridden when the library functions are called. At build time it is	overridden when the library functions are called. At build time it is
conventional to use the standard for your operating system.	conventional to use the standard for your operating system.


WHAT \R MATCHES	WHAT \R MATCHES

By default, the sequence \R in a pattern matches any Unicode newline	By default, the sequence \R in a pattern matches any Unicode newline
sequence, whatever has been selected as the line ending sequence. If	sequence, whatever has been selected as the line ending sequence. If
you specify	you specify

--enable-bsr-anycrlf	--enable-bsr-anycrlf

the default is changed so that \R matches only CR, LF, or CRLF. What-	the default is changed so that \R matches only CR, LF, or CRLF. What-
ever is selected when PCRE is built can be overridden when the library	ever is selected when PCRE is built can be overridden when the library
functions are called.	functions are called.


POSIX MALLOC USAGE	POSIX MALLOC USAGE

When PCRE is called through the POSIX interface (see the pcreposix doc-	When the 8-bit library is called through the POSIX interface (see the
umentation), additional working storage is required for holding the	pcreposix documentation), additional working storage is required for
pointers to capturing substrings, because PCRE requires three integers	holding the pointers to capturing substrings, because PCRE requires
per substring, whereas the POSIX interface provides only two. If the	three integers per substring, whereas the POSIX interface provides only
number of expected substrings is small, the wrapper function uses space	two. If the number of expected substrings is small, the wrapper func-
on the stack, because this is faster than using malloc() for each call.	tion uses space on the stack, because this is faster than using mal-
The default threshold above which the stack is no longer used is 10; it	loc() for each call. The default threshold above which the stack is no
can be changed by adding a setting such as	longer used is 10; it can be changed by adding a setting such as

--with-posix-malloc-threshold=20	--with-posix-malloc-threshold=20

Line 298 POSIX MALLOC USAGE	Line 1071 POSIX MALLOC USAGE

HANDLING VERY LARGE PATTERNS	HANDLING VERY LARGE PATTERNS

Within a compiled pattern, offset values are used to point from one	Within a compiled pattern, offset values are used to point from one
part to another (for example, from an opening parenthesis to an alter-	part to another (for example, from an opening parenthesis to an alter-
nation metacharacter). By default, two-byte values are used for these	nation metacharacter). By default, in the 8-bit and 16-bit libraries,
offsets, leading to a maximum size for a compiled pattern of around	two-byte values are used for these offsets, leading to a maximum size
64K. This is sufficient to handle all but the most gigantic patterns.	for a compiled pattern of around 64K. This is sufficient to handle all
Nevertheless, some people do want to process truyl enormous patterns,	but the most gigantic patterns. Nevertheless, some people do want to
so it is possible to compile PCRE to use three-byte or four-byte off-	process truly enormous patterns, so it is possible to compile PCRE to
sets by adding a setting such as	use three-byte or four-byte offsets by adding a setting such as

--with-link-size=3	--with-link-size=3

to the configure command. The value given must be 2, 3, or 4. Using	to the configure command. The value given must be 2, 3, or 4. For the
longer offsets slows down the operation of PCRE because it has to load	16-bit library, a value of 3 is rounded up to 4. In these libraries,
additional bytes when handling them.	using longer offsets slows down the operation of PCRE because it has to
	load additional data when handling them. For the 32-bit library the
	value is always 4 and cannot be overridden; the value of --with-link-
	size is ignored.


AVOIDING EXCESSIVE STACK USAGE	AVOIDING EXCESSIVE STACK USAGE
Line 385 CREATING CHARACTER TABLES AT BUILD TIME	Line 1161 CREATING CHARACTER TABLES AT BUILD TIME
to the configure command, the distributed tables are no longer used.	to the configure command, the distributed tables are no longer used.
Instead, a program called dftables is compiled and run. This outputs	Instead, a program called dftables is compiled and run. This outputs
the source for new set of tables, created in the default locale of your	the source for new set of tables, created in the default locale of your
C runtime system. (This method of replacing the tables does not work if	C run-time system. (This method of replacing the tables does not work
you are cross compiling, because dftables is run on the local host. If	if you are cross compiling, because dftables is run on the local host.
you need to create alternative tables when cross compiling, you will	If you need to create alternative tables when cross compiling, you will
have to do so "by hand".)	have to do so "by hand".)


Line 403 USING EBCDIC CODE	Line 1179 USING EBCDIC CODE
to the configure command. This setting implies --enable-rebuild-charta-	to the configure command. This setting implies --enable-rebuild-charta-
bles. You should only use it if you know that you are in an EBCDIC	bles. You should only use it if you know that you are in an EBCDIC
environment (for example, an IBM mainframe operating system). The	environment (for example, an IBM mainframe operating system). The
--enable-ebcdic option is incompatible with --enable-utf8.	--enable-ebcdic option is incompatible with --enable-utf.

	The EBCDIC character that corresponds to an ASCII LF is assumed to have
	the value 0x15 by default. However, in some EBCDIC environments, 0x25
	is used. In such an environment you should use

	--enable-ebcdic-nl25

	as well as, or instead of, --enable-ebcdic. The EBCDIC character for CR
	has the same value as in ASCII, namely, 0x0d. Whichever of 0x15 and
	0x25 is not chosen as LF is made to correspond to the Unicode NEL char-
	acter (which, in Unicode, is 0x85).

	The options that select newline behaviour, such as --enable-newline-is-
	cr, and equivalent run-time options, refer to these character values in
	an EBCDIC environment.


PCREGREP OPTIONS FOR COMPRESSED FILE SUPPORT	PCREGREP OPTIONS FOR COMPRESSED FILE SUPPORT

By default, pcregrep reads all files as plain text. You can build it so	By default, pcregrep reads all files as plain text. You can build it so
Line 416 PCREGREP OPTIONS FOR COMPRESSED FILE SUPPORT	Line 1207 PCREGREP OPTIONS FOR COMPRESSED FILE SUPPORT
--enable-pcregrep-libbz2	--enable-pcregrep-libbz2

to the configure command. These options naturally require that the rel-	to the configure command. These options naturally require that the rel-
evant libraries are installed on your system. Configuration will fail	evant libraries are installed on your system. Configuration will fail
if they are not.	if they are not.


PCREGREP BUFFER SIZE	PCREGREP BUFFER SIZE

pcregrep uses an internal buffer to hold a "window" on the file it is	pcregrep uses an internal buffer to hold a "window" on the file it is
scanning, in order to be able to output "before" and "after" lines when	scanning, in order to be able to output "before" and "after" lines when
it finds a match. The size of the buffer is controlled by a parameter	it finds a match. The size of the buffer is controlled by a parameter
whose default value is 20K. The buffer itself is three times this size,	whose default value is 20K. The buffer itself is three times this size,
but because of the way it is used for holding "before" lines, the long-	but because of the way it is used for holding "before" lines, the long-
est line that is guaranteed to be processable is the parameter size.	est line that is guaranteed to be processable is the paramete est line that is guaranteed to be processable is the paramete
You can change the default parameter value by adding, for example,	You can change the default parameter value by adding, for example,

--with-pcregrep-bufsize=50K	--with-pcregrep-bufsize=50K
Line 442 PCRETEST OPTION FOR LIBREADLINE SUPPORT	Line 1233 PCRETEST OPTION FOR LIBREADLINE SUPPORT

--enable-pcretest-libreadline	--enable-pcretest-libreadline

to the configure command, pcretest is linked with the libreadline	to the configure command, pcretest is linked with the libreadline
library, and when its input is from a terminal, it reads it using the	library, and when its input is from a terminal, it reads it using the
readline() function. This provides line-editing and history facilities.	readline() function. This provides line-editing and history facilities.
Note that libreadline is GPL-licensed, so if you distribute a binary of	Note that libreadline is GPL-licensed, so if you distribute a binary of
pcretest linked in this way, there may be licensing issues.	pcretest linked in this way, there may be licensing issues.

Setting this option causes the -lreadline option to be added to the	Setting this option causes the -lreadline option to be added to the
pcretest build. In many operating environments with a sytem-installed	pcretest build. In many operating environments with a sytem-installed
libreadline this is sufficient. However, in some environments (e.g. if	libreadline this is sufficient. However, in some environments (e.g. if
an unmodified distribution version of readline is in use), some extra	an unmodified distribution version of readline is in use), some extra
configuration may be necessary. The INSTALL file for libreadline says	configuration may be necessary. The INSTALL file for libreadline says
this:	this:

"Readline uses the termcap functions, but does not link with the	"Readline uses the termcap functions, but does not link with the
termcap or curses library itself, allowing applications which link	termcap or curses library itself, allowing applications which link
with readline the to choose an appropriate library."	with readline the to choose an appropriate library."

If your environment has not been set up so that an appropriate library	If your environment has not been set up so that an appropriate library
is automatically included, you may need to add something like	is automatically included, you may need to add something like

LIBS="-ncurses"	LIBS="-ncurses"
Line 467 PCRETEST OPTION FOR LIBREADLINE SUPPORT	Line 1258 PCRETEST OPTION FOR LIBREADLINE SUPPORT
immediately before the configure command.	immediately before the configure command.


	DEBUGGING WITH VALGRIND SUPPORT

	By adding the

	--enable-valgrind

	option to to the configure command, PCRE will use valgrind annotations
	to mark certain memory regions as unaddressable. This allows it to
	detect invalid memory accesses, and is mostly useful for debugging PCRE
	itself.


	CODE COVERAGE REPORTING

	If your C compiler is gcc, you can build a version of PCRE that can
	generate a code coverage report for its test suite. To enable this, you
	must install lcov version 1.6 or above. Then specify

	--enable-coverage

	to the configure command and build PCRE in the usual way.

	Note that using ccache (a caching C compiler) is incompatible with code
	coverage reporting. If you have configured ccache to run automatically
	on your system, you must set the environment variable

	CCACHE_DISABLE=1

	before running make to build PCRE, so that ccache is not used.

	When --enable-coverage is used, the following addition targets are
	added to the Makefile:

	make coverage

	This creates a fresh coverage report for the PCRE test suite. It is
	equivalent to running "make coverage-reset", "make coverage-baseline",
	"make check", and then "make coverage-report".

	make coverage-reset

	This zeroes the coverage counters, but does nothing else.

	make coverage-baseline

	This captures baseline coverage information.

	make coverage-report

	This creates the coverage report.

	make coverage-clean-report

	This removes the generated coverage report without cleaning the cover-
	age data itself.

	make coverage-clean-data

	This removes the captured coverage data without removing the coverage
	files created at compile time (*.gcno).

	make coverage-clean

	This cleans all coverage data including the generated coverage report.
	For more information about code coverage, see the gcov and lcov docu-
	mentation.


SEE ALSO	SEE ALSO

pcreapi(3), pcre_config(3).	pcreapi(3), pcre16, pcre32, pcre_config(3).


AUTHOR	AUTHOR
Line 481 AUTHOR	Line 1340 AUTHOR

REVISION	REVISION

Last updated: 06 September 2011	Last updated: 12 May 2013
Copyright (c) 1997-2011 University of Cambridge.	Copyright (c) 1997-2013 University of Cambridge.
------------------------------------------------------------------------------	------------------------------------------------------------------------------


PCREMATCHING(3) PCREMATCHING(3)	PCREMATCHING(3) Library Functions Manual PCREMATCHING(3)



NAME	NAME
PCRE - Perl-compatible regular expressions	PCRE - Perl-compatible regular expressions


PCRE MATCHING ALGORITHMS	PCRE MATCHING ALGORITHMS

This document describes the two different algorithms that are available	This document describes the two different algorithms that are available
in PCRE for matching a compiled regular expression against a given sub-	in PCRE for matching a compiled regular expression against a given sub-
ject string. The "standard" algorithm is the one provided by the	ject string. The "standard" algorithm is the one provided by the
pcre_exec() function. This works in the same was as Perl's matching	pcre_exec(), pcre16_exec() and pcre32_exec() functions. These work in
function, and provides a Perl-compatible matching operation.	the same as as Perl's matching function, and provide a Perl-compatible
	matching operation. The just-in-time (JIT) optimization that is
	described in the pcrejit documentation is compatible with these func-
	tions.

An alternative algorithm is provided by the pcre_dfa_exec() function;	An alternative algorithm is provided by the pcre_dfa_exec(),
this operates in a different way, and is not Perl-compatible. It has	pcre16_dfa_exec() and pcre32_dfa_exec() functions; they operate in a
advantages and disadvantages compared with the standard algorithm, and	different way, and are not Perl-compatible. This alternative has advan-
these are described below.	tages and disadvantages compared with the standard algorithm, and these
	are described below.

When there is only one possible way in which a given subject string can	When there is only one possible way in which a given subject string can
match a pattern, the two algorithms give the same answer. A difference	match a pattern, the two algorithms give the same answer. A difference
Line 594 THE ALTERNATIVE MATCHING ALGORITHM	Line 1457 THE ALTERNATIVE MATCHING ALGORITHM
at the fifth character of the subject. The algorithm does not automati-	at the fifth character of the subject. The algorithm does not automati-
cally move on to find matches that start at later positions.	cally move on to find matches that start at later positions.

	PCRE's "auto-possessification" optimization usually applies to charac-
	ter repeats at the end of a pattern (as well as internally). For exam-
	ple, the pattern "a\d+" is compiled as if it were "a\d++" because there
	is no point even considering the possibility of backtracking into the
	repeated digits. For DFA matching, this means that only one possible
	match is found. If you really do want multiple matches in such cases,
	either use an ungreedy repeat ("a\d+?") or set the PCRE_NO_AUTO_POSSESS
	option when compiling.

There are a number of features of PCRE regular expressions that are not	There are a number of features of PCRE regular expressions that are not
supported by the alternative matching algorithm. They are as follows:	supported by the alternative matching algorithm. They are as follows:

1. Because the algorithm finds all possible matches, the greedy or	1. Because the algorithm finds all possible matches, the greedy or
ungreedy nature of repetition quantifiers is not relevant. Greedy and	ungreedy nature of repetition quantifiers is not relevant. Greedy and
ungreedy quantifiers are treated in exactly the same way. However, pos-	ungreedy quantifiers are treated in exactly the same way. However, pos-
sessive quantifiers can make a difference when what follows could also	sessive quantifiers can make a difference when what follows could also
match what is quantified, for example in a pattern like this:	match what is quantified, for example in a pattern like this:

^a++\w!	^a++\w!

This pattern matches "aaab!" but not "aaa!", which would be matched by	This pattern matches "aaab!" but not "aaa!", which would be matched by
a non-possessive quantifier. Similarly, if an atomic group is present,	a non-possessive quantifier. Similarly, if an atomic group is present,
it is matched as if it were a standalone pattern at the current point,	it is matched as if it were a standalone pattern at the current point,
and the longest match is then "locked in" for the rest of the overall	and the longest match is then "locked in" for the rest of the overall
pattern.	pattern.

2. When dealing with multiple paths through the tree simultaneously, it	2. When dealing with multiple paths through the tree simultaneously, it
is not straightforward to keep track of captured substrings for the	is not straightforward to keep track of captured substrings for the
different matching possibilities, and PCRE's implementation of this	different matching possibilities, and PCRE's implementation of this
algorithm does not attempt to do this. This means that no captured sub-	algorithm does not attempt to do this. This means that no captured sub-
strings are available.	strings are available.

3. Because no substrings are captured, back references within the pat-	3. Because no substrings are captured, back references within the pat-
tern are not supported, and cause errors if encountered.	tern are not supported, and cause errors if encountered.

4. For the same reason, conditional expressions that use a backrefer-	4. For the same reason, conditional expressions that use a backrefer-
ence as the condition or test for a specific group recursion are not	ence as the condition or test for a specific group recursion are not
supported.	supported.

5. Because many paths through the tree may be active, the \K escape	5. Because many paths through the tree may be active, the \K escape
sequence, which resets the start of the match when encountered (but may	sequence, which resets the start of the match when encountered (but may
be on some paths and not on others), is not supported. It causes an	be on some paths and not on others), is not supported. It causes an
error if encountered.	error if encountered.

6. Callouts are supported, but the value of the capture_top field is	6. Callouts are supported, but the value of the capture_t 6. Callouts are supported, but the value of the capture_t
always 1, and the value of the capture_last field is always -1.	always 1, and the value of the capture_last field is always -1.

7. The \C escape sequence, which (in the standard algorithm) matches a	7. The \C escape sequence, which (in the standard algorithm) always
single byte, even in UTF-8 mode, is not supported in UTF-8 mode,	matches a single data unit, even in UTF-8, UTF-16 or UTF-32 modes, is
because the alternative algorithm moves through the subject string one	not supported in these modes, because the alternative algorithm moves
character at a time, for all active paths through the tree.	through the subject string one character (not data unit) at a time, for
	all active paths through the tree.

8. Except for (FAIL), the backtracking control verbs such as (PRUNE)	8. Except for (FAIL), the backtracking control verbs such as (PRUNE)
are not supported. (*FAIL) is supported, and behaves like a failing	are not supported. (*FAIL) is supported, and behaves like a failing
Line 653 ADVANTAGES OF THE ALTERNATIVE ALGORITHM	Line 1526 ADVANTAGES OF THE ALTERNATIVE ALGORITHM
things with callouts.	things with callouts.

2. Because the alternative algorithm scans the subject string just	2. Because the alternative algorithm scans the subject string just
once, and never needs to backtrack, it is possible to pass very long	once, and never needs to backtrack (except for lookbehinds), it is pos-
subject strings to the matching function in several pieces, checking	sible to pass very long subject strings to the matching function in
for partial matching each time. Although it is possible to do multi-	several pieces, checking for partial matching each time. Although it is
segment matching using the standard algorithm (pcre_exec()), by retain-	possible to do multi-segment matching using the standard algorithm by
ing partially matched substrings, it is more complicated. The pcrepar-	retaining partially matched substrings, it is more complicated. The
tial documentation gives details of partial matching and discusses	pcrepartial documentation gives details of partial matching and dis-
multi-segment matching.	cusses multi-segment matching.


DISADVANTAGES OF THE ALTERNATIVE ALGORITHM	DISADVANTAGES OF THE ALTERNATIVE ALGORITHM
Line 685 AUTHOR	Line 1558 AUTHOR

REVISION	REVISION

Last updated: 19 November 2011	Last updated: 12 November 2013
Copyright (c) 1997-2010 University of Cambridge.	Copyright (c) 1997-2012 University of Cambridge.
------------------------------------------------------------------------------	------------------------------------------------------------------------------


PCREAPI(3) PCREAPI(3)	PCREAPI(3) Library Functions Manual PCREAPI(3)



NAME	NAME
PCRE - Perl-compatible regular expressions	PCRE - Perl-compatible regular expressions

	#include <pcre.h>


PCRE NATIVE API BASIC FUNCTIONS	PCRE NATIVE API BASIC FUNCTIONS

#include <pcre.h>

pcre pcre_compile(const char pattern, int options,	pcre pcre_compile(const char pattern, int options,
const char *errptr, int erroffset,	const char *errptr, int erroffset,
const unsigned char *tableptr);	const unsigned char *tableptr);
Line 719 PCRE NATIVE API BASIC FUNCTIONS	Line 1593 PCRE NATIVE API BASIC FUNCTIONS
const char *subject, int length, int startoffset,	const char *subject, int length, int startoffset,
int options, int *ovector, int ovecsize);	int options, int *ovector, int ovecsize);


PCRE NATIVE API AUXILIARY FUNCTIONS

pcre_jit_stack *pcre_jit_stack_alloc(int startsize, int maxsize);

void pcre_jit_stack_free(pcre_jit_stack *stack);

void pcre_assign_jit_stack(pcre_extra *extra,
pcre_jit_callback callback, void *data);

int pcre_dfa_exec(const pcre code, const pcre_extra extra,	int pcre_dfa_exec(const pcre code, const pcre_extra extra,
const char *subject, int length, int startoffset,	const char *subject, int length, int startoffset,
int options, int *ovector, int ovecsize,	int options, int *ovector, int ovecsize,
int *workspace, int wscount);	int *workspace, int wscount);


	PCRE NATIVE API STRING EXTRACTION FUNCTIONS

int pcre_copy_named_substring(const pcre *code,	int pcre_copy_named_substring(const pcre *code,
const char subject, int ovector,	const char subject, int ovector,
int stringcount, const char *stringname,	int stringcount, const char *stringname,
Line 765 PCRE NATIVE API AUXILIARY FUNCTIONS	Line 1632 PCRE NATIVE API AUXILIARY FUNCTIONS

void pcre_free_substring_list(const char **stringptr);	void pcre_free_substring_list(const char **stringptr);


	PCRE NATIVE API AUXILIARY FUNCTIONS

	int pcre_jit_exec(const pcre code, const pcre_extra extra,
	const char *subject, int length, int startoffset,
	int options, int *ovector, int ovecsize,
	pcre_jit_stack *jstack);

	pcre_jit_stack *pcre_jit_stack_alloc(int startsize, int maxsize);

	void pcre_jit_stack_free(pcre_jit_stack *stack);

	void pcre_assign_jit_stack(pcre_extra *extra,
	pcre_jit_callback callback, void *data);

const unsigned char *pcre_maketables(void);	const unsigned char *pcre_maketables(void);

int pcre_fullinfo(const pcre code, const pcre_extra extra,	int pcre_fullinfo(const pcre code, const pcre_extra extra,
int what, void *where);	int what, void *where);

int pcre_info(const pcre code, int optptr, int *firstcharptr);

int pcre_refcount(pcre *code, int adjust);	int pcre_refcount(pcre *code, int adjust);

int pcre_config(int what, void *where);	int pcre_config(int what, void *where);

char *pcre_version(void);	const char *pcre_version(void);

	int pcre_pattern_to_host_byte_order(pcre *code,
	pcre_extra extra, const unsigned char tables);


PCRE NATIVE API INDIRECTED FUNCTIONS	PCRE NATIVE API INDIRECTED FUNCTIONS

void (pcre_malloc)(size_t);	void (pcre_malloc)(size_t);
Line 792 PCRE NATIVE API INDIRECTED FUNCTIONS	Line 1675 PCRE NATIVE API INDIRECTED FUNCTIONS
int (pcre_callout)(pcre_callout_block );	int (pcre_callout)(pcre_callout_block );


	PCRE 8-BIT, 16-BIT, AND 32-BIT LIBRARIES

	As well as support for 8-bit character strings, PCRE also supports
	16-bit strings (from release 8.30) and 32-bit strings (from release
	8.32), by means of two additional libraries. They can be built as well
	as, or instead of, the 8-bit library. To avoid too much complication,
	this document describes the 8-bit versions of the functions, with only
	occasional references to the 16-bit and 32-bit libraries.

	The 16-bit and 32-bit functions operate in the same way as their 8-bit
	counterparts; they just use different data types for their arguments
	and results, and their names start with pcre16_ or pcre32_ instead of
	pcre_. For every option that has UTF8 in its name (for example,
	PCRE_UTF8), there are corresponding 16-bit and 32-bit names with UTF8
	replaced by UTF16 or UTF32, respectively. This facility is in fact just
	cosmetic; the 16-bit and 32-bit option names define the same bit val-
	ues.

	References to bytes and UTF-8 in this document should be read as refer-
	ences to 16-bit data units and UTF-16 when using the 16-bit library, or
	32-bit data units and UTF-32 when using the 32-bit library, unless
	specified otherwise. More details of the specific differences for the
	16-bit and 32-bit libraries are given in the pcre16 and pcre32 pages.


PCRE API OVERVIEW	PCRE API OVERVIEW

PCRE has its own native API, which is described in this document. There	PCRE has its own native API, which is described in this document. There
are also some wrapper functions that correspond to the POSIX regular	are also some wrapper functions (for the 8-bit library only) that cor-
expression API, but they do not give access to all the functionality.	respond to the POSIX regular expression API, but they do not give
They are described in the pcreposix documentation. Both of these APIs	access to all the functionality. They are described in the pcreposix
define a set of C function calls. A C++ wrapper is also distributed	documentation. Both of these APIs define a set of C function calls. A
with PCRE. It is documented in the pcrecpp page.	C++ wrapper (again for the 8-bit library only) is also distributed with
	PCRE. It is documented in the pcrecpp page.

The native API C function prototypes are defined in the header file	The native API C function prototypes are defined in the header file
pcre.h, and on Unix systems the library itself is called libpcre. It	pcre.h, and on Unix-like systems the (8-bit) library itself is called
can normally be accessed by adding -lpcre to the command for linking an	libpcre. It can normally be accessed by adding -lpcre to the command
application that uses PCRE. The header file defines the macros	for linking an application that uses PCRE. The header file defines the
PCRE_MAJOR and PCRE_MINOR to contain the major and minor release num-	macros PCRE_MAJOR and PCRE_MINOR to contain the major and minor release
bers for the library. Applications can use these to include support	numbers for the library. Applications can use these to include support
for different releases of PCRE.	for different releases of PCRE.

In a Windows environment, if you want to statically link an application	In a Windows environment, if you want to statically link an application
program against a non-dll pcre.a file, you must define PCRE_STATIC	program against a non-dll pcre.a file, you must define PCRE_STATIC
before including pcre.h or pcrecpp.h, because otherwise the pcre_mal-	before including pcre.h or pcrecpp.h, because otherwise the pcre_mal-
loc() and pcre_free() exported functions will be declared	loc() and pcre_free() exported functions will be declared
__declspec(dllimport), with unwanted results.	__declspec(dllimport), with unwanted results.

The functions pcre_compile(), pcre_compile2(), pcre_study(), and	The functions pcre_compile(), pcre_compile2(), pcre_study(), and
pcre_exec() are used for compiling and matching regular expressions in	pcre_exec() are used for compiling and matching regular expressions in
a Perl-compatible manner. A sample program that demonstrates the sim-	a Perl-compatible manner. A sample program that demonstrates the sim-
plest way of using them is provided in the file called pcredemo.c in	plest way of using them is provided in the file called pcredemo.c in
the PCRE source distribution. A listing of this program is given in the	the PCRE source distribution. A listing of this program is given in the
pcredemo documentation, and the pcresample documentation describes how	pcredemo documentation, and the pcresample documentation describes how
to compile and run it.	to compile and run it.

Just-in-time compiler support is an optional feature of PCRE that can	Just-in-time compiler support is an optional feature of PCRE that can
be built in appropriate hardware environments. It greatly speeds up the	be built in appropriate hardware environments. It greatly speeds up the
matching performance of many patterns. Simple programs can easily	matching performance of many patterns. Simple programs can easily
request that it be used if available, by setting an option that is	request that it be used if available, by setting an option that is
ignored when it is not relevant. More complicated programs might need	ignored when it is not relevant. More complicated programs might need
to make use of the functions pcre_jit_stack_alloc(),	to make use of the functions pcre_jit_stack_alloc(),
pcre_jit_stack_free(), and pcre_assign_jit_stack() in order to control	pcre_jit_stack_free(), and pcre_assign_jit_stack() in order to control
the JIT code's memory usage. These functions are discussed in the	the JIT code's memory usage.
pcrejit documentation.

	From release 8.32 there is also a direct interface for JIT execution,
	which gives improved performance. The JIT-specific functions are dis-
	cussed in the pcrejit documentation.

A second matching function, pcre_dfa_exec(), which is not Perl-compati-	A second matching function, pcre_dfa_exec(), which is not Perl-compati-
ble, is also provided. This uses a different algorithm for the match-	ble, is also provided. This uses a different algorithm for the match-
ing. The alternative algorithm finds all possible matches (at a given	ing. The alternative algorithm finds all possible matches (at a given
Line 865 PCRE API OVERVIEW	Line 1777 PCRE API OVERVIEW
built are used.	built are used.

The function pcre_fullinfo() is used to find out information about a	The function pcre_fullinfo() is used to find out information about a
compiled pattern; pcre_info() is an obsolete version that returns only	compiled pattern. The function pcre_version() returns a pointer to a
some of the available information, but is retained for backwards com-	string containing the version of PCRE and its date of release.
patibility. The function pcre_version() returns a pointer to a string
containing the version of PCRE and its date of release.

The function pcre_refcount() maintains a reference count in a data	The function pcre_refcount() maintains a reference count in a data
block containing a compiled pattern. This is provided for the benefit	block containing a compiled pattern. This is provided for the benefit
Line 907 NEWLINES	Line 1817 NEWLINES
feed) character, the two-character sequence CRLF, any of the three pre-	feed) character, the two-character sequence CRLF, any of the three pre-
ceding, or any Unicode newline sequence. The Unicode newline sequences	ceding, or any Unicode newline sequence. The Unicode newline sequences
are the three just mentioned, plus the single characters VT (vertical	are the three just mentioned, plus the single characters VT (vertical
tab, U+000B), FF (formfeed, U+000C), NEL (next line, U+0085), LS (line	tab, U+000B), FF (form feed, U+000C), NEL (next line, U+0085), LS (line
separator, U+2028), and PS (paragraph separator, U+2029).	separator, U+2028), and PS (paragraph separator, U+2029).

Each of the first three conventions is used by at least one operating	Each of the first three conventions is used by at least one operating
Line 955 SAVING PRECOMPILED PATTERNS FOR LATER USE	Line 1865 SAVING PRECOMPILED PATTERNS FOR LATER USE
The compiled form of a regular expression can be saved and re-used at a	The compiled form of a regular expression can be saved and re-used at a
later time, possibly by a different program, and even on a host other	later time, possibly by a different program, and even on a host other
than the one on which it was compiled. Details are given in the	than the one on which it was compiled. Details are given in the
pcreprecompile documentation. However, compiling a regular expression	pcreprecompile documentation, which includes a description of the
with one version of PCRE for use with a different version is not guar-	pcre_pattern_to_host_byte_order() function. However, compiling a regu-
anteed to work and may cause crashes.	lar expression with one version of PCRE for use with a different ver-
	sion is not guaranteed to work and may cause crashes.


CHECKING BUILD-TIME OPTIONS	CHECKING BUILD-TIME OPTIONS

int pcre_config(int what, void *where);	int pcre_config(int what, void *where);

The function pcre_config() makes it possible for a PCRE client to dis-	The function pcre_config() makes it possible for a PCRE client to dis-
cover which optional features have been compiled into the PCRE library.	cover which optional features have been compiled into the PCRE library.
The pcrebuild documentation has more details about these optional fea-	The pcrebuild documentation has more details about these optional fea-
tures.	tures.

The first argument for pcre_config() is an integer, specifying which	The first argument for pcre_config() is an integer, specifyin The first argument for pcre_config() is an integer, specifyin
information is required; the second argument is a pointer to a variable	information is required; the second argument is a pointer to a variable
into which the information is placed. The following information is	into which the information is placed. The returned value is zero on
	success, or the negative error code PCRE_ERROR_BADOPTION if the value
	in the first argument is not recognized. The following information is
available:	available:

PCRE_CONFIG_UTF8	PCRE_CONFIG_UTF8

The output is an integer that is set to one if UTF-8 support is avail-	The output is an integer that is set to one if UTF-8 support is avail-
able; otherwise it is set to zero.	able; otherwise it is set to zero. This value should normally be given
	to the 8-bit version of this function, pcre_config(). If it is given to
	the 16-bit or 32-bit version of this function, the result is
	PCRE_ERROR_BADOPTION.

	PCRE_CONFIG_UTF16

	The output is an integer that is set to one if UTF-16 support is avail-
	able; otherwise it is set to zero. This value should normally be given
	to the 16-bit version of this function, pcre16_config(). If it is given
	to the 8-bit or 32-bit version of this function, the result is
	PCRE_ERROR_BADOPTION.

	PCRE_CONFIG_UTF32

	The output is an integer that is set to one if UTF-32 support is avail-
	able; otherwise it is set to zero. This value should normally be given
	to the 32-bit version of this function, pcre32_config(). If it is given
	to the 8-bit or 16-bit version of this function, the result is
	PCRE_ERROR_BADOPTION.

PCRE_CONFIG_UNICODE_PROPERTIES	PCRE_CONFIG_UNICODE_PROPERTIES

The output is an integer that is set to one if support for Unicode	The output is an integer that is set to one if support for Unicode
Line 989 CHECKING BUILD-TIME OPTIONS	Line 1921 CHECKING BUILD-TIME OPTIONS
The output is an integer that is set to one if support for just-in-time	The output is an integer that is set to one if support for just-in-time
compiling is available; otherwise it is set to zero.	compiling is available; otherwise it is set to zero.

	PCRE_CONFIG_JITTARGET

	The output is a pointer to a zero-terminated "const char *" string. If
	JIT support is available, the string contains the name of the architec-
	ture for which the JIT compiler is configured, for example "x86 32bit
	(little endian + unaligned)". If JIT support is not available, the
	result is NULL.

PCRE_CONFIG_NEWLINE	PCRE_CONFIG_NEWLINE

The output is an integer whose value specifies the default character	The output is an integer whose value specifies the default character
sequence that is recognized as meaning "newline". The four values that	sequence that is recognized as meaning "newline". The values that are
are supported are: 10 for LF, 13 for CR, 3338 for CRLF, -2 for ANYCRLF,	supported in ASCII/Unicode environments are: 10 for LF, 13 for CR, 3338
and -1 for ANY. Though they are derived from ASCII, the same values	for CRLF, -2 for ANYCRLF, and -1 for ANY. In EBCDIC environments, CR,
are returned in EBCDIC environments. The default should normally corre-	ANYCRLF, and ANY yield the same values. However, the value for LF is
	normally 21, though some EBCDIC environments use 37. The corresponding
	values for CRLF are 3349 and 3365. The default should normally corre-
spond to the standard sequence for your operating system.	spond to the standard sequence for your operating system.

PCRE_CONFIG_BSR	PCRE_CONFIG_BSR
Line 1009 CHECKING BUILD-TIME OPTIONS	Line 1951 CHECKING BUILD-TIME OPTIONS
PCRE_CONFIG_LINK_SIZE	PCRE_CONFIG_LINK_SIZE

The output is an integer that contains the number of bytes used for	The output is an integer that contains the number of bytes used for
internal linkage in compiled regular expressions. The value is 2, 3, or	internal linkage in compiled regular expressions. For the 8-bit
4. Larger values allow larger regular expressions to be compiled, at	library, the value can be 2, 3, or 4. For the 16-bit library, the value
the expense of slower matching. The default value of 2 is sufficient	is either 2 or 4 and is still a number of bytes. For the 32-bit
for all but the most massive patterns, since it allows the compiled	library, the value is either 2 or 4 and is still a number of bytes. The
pattern to be up to 64K in size.	default value of 2 is sufficient for all but the most massive patterns,
	since it allows the compiled pattern to be up to 64K in size. Larger
	values allow larger regular expressions to be compiled, at the expense
	of slower matching.

PCRE_CONFIG_POSIX_MALLOC_THRESHOLD	PCRE_CONFIG_POSIX_MALLOC_THRESHOLD

The output is an integer that contains the threshold above which the	The output is an integer that contains the threshold above which the
POSIX interface uses malloc() for output vectors. Further details are	POSIX interface uses malloc() for output vectors. Further details are
given in the pcreposix documentation.	given in the pcreposix documentation.

	PCRE_CONFIG_PARENS_LIMIT

	The output is a long integer that gives the maximum depth of nesting of
	parentheses (of any kind) in a pattern. This limit is imposed to cap
	the amount of system stack used when a pattern is compiled. It is spec-
	ified when PCRE is built; the default is 250.

PCRE_CONFIG_MATCH_LIMIT	PCRE_CONFIG_MATCH_LIMIT

The output is a long integer that gives the default limit for the num-	The output is a long integer that gives the default limit for the num-
Line 1085 COMPILING A PATTERN	Line 2037 COMPILING A PATTERN
different parts of the pattern, the contents of the options argument	different parts of the pattern, the contents of the options argument
specifies their settings at the start of compilation and execution. The	specifies their settings at the start of compilation and execution. The
PCRE_ANCHORED, PCRE_BSR_xxx, PCRE_NEWLINE_xxx, PCRE_NO_UTF8_CHECK, and	PCRE_ANCHORED, PCRE_BSR_xxx, PCRE_NEWLINE_xxx, PCRE_NO_UTF8_CHECK, and
PCRE_NO_START_OPT options can be set at the time of matching as well as	PCRE_NO_START_OPTIMIZE options can be set at the time of matching as
at compile time.	well as at compile time.

If errptr is NULL, pcre_compile() returns NULL immediately. Otherwise,	If errptr is NULL, pcre_compile() returns NULL immediately. Otherwise,
if compilation of a pattern fails, pcre_compile() returns NULL, and	if compilation of a pattern fails, pcre_compile() returns NULL, and
sets the variable pointed to by errptr to point to a textual error mes-	sets the variable pointed to by errptr to point to a textual error mes-
sage. This is a static string that is part of the library. You must not	sage. This is a static string that is part of the library. You must not
try to free it. Normally, the offset from the start of the pattern to	try to free it. Normally, the offset from the start of the pattern to
the byte that was being processed when the error was discovered is	the data unit that was being processed when the error was discovered is
placed in the variable pointed to by erroffset, which must not be NULL	placed in the variable pointed to by erroffset, which must not be NULL
(if it is, an immediate error is given). However, for an invalid UTF-8	(if it is, an immediate error is given). However, for an invalid UTF-8
string, the offset is that of the first byte of the failing character.	or UTF-16 string, the offset is that of the first data unit of the
Also, some errors are not detected until checks are carried out when	failing character.
the whole pattern has been scanned; in these cases the offset passed
back is the length of the pattern.

Note that the offset is in bytes, not characters, even in UTF-8 mode.	Some errors are not detected until the whole pattern has been scanned;
It may sometimes point into the middle of a UTF-8 character.	in these cases, the offset passed back is the length of the pattern.
	Note that the offset is in data units, not characters, even in a UTF
	mode. It may sometimes point into the middle of a UTF-8 or UTF-16 char-
	acter.

If pcre_compile2() is used instead of pcre_compile(), and the error-	If pcre_compile2() is used instead of pcre_compile(), and the error-
codeptr argument is not NULL, a non-zero error code number is returned	codeptr argument is not NULL, a non-zero error code number is returned
via this argument in the event of an error. This is in addition to the	via this argument in the event of an error. This is in addition to the
textual error message. Error codes and messages are listed below.	textual error message. Error codes and messages are listed below.

If the final argument, tableptr, is NULL, PCRE uses a default set of	If the final argument, tableptr, is NULL, PCRE uses a default set of
character tables that are built when PCRE is compiled, using the	character tables that are built when PCRE is compiled, using the
default C locale. Otherwise, tableptr must be an address that is the	default C locale. Otherwise, tableptr must be an address that is the
result of a call to pcre_maketables(). This value is stored with the	result of a call to pcre_maketables(). This value is stored with the
compiled pattern, and used again by pcre_exec(), unless another table	compiled pattern, and used again by pcre_exec() and pcre_dfa_exec()
pointer is passed to it. For more discussion, see the section on locale	when the pattern is matched. For more discussion, see the section on
support below.	locale support below.

This code fragment shows a typical straightforward call to pcre_com-	This code fragment shows a typical straightforward call to pcre_com-
pile():	pile():

pcre *re;	pcre *re;
Line 1130 COMPILING A PATTERN	Line 2083 COMPILING A PATTERN
&erroffset, /* for error offset */	&erroffset, /* for error offset */
NULL); /* use default character tables */	NULL); /* use default character tables */

The following names for option bits are defined in the pcre.h header	The following names for option bits are defined in the pcre.h header
file:	file:

PCRE_ANCHORED	PCRE_ANCHORED

If this bit is set, the pattern is forced to be "anchored", that is, it	If this bit is set, the pattern is forced to be "anchored", that is, it
is constrained to match only at the first matching point in the string	is constrained to match only at the first matching point in the string
that is being searched (the "subject string"). This effect can also be	that is being searched (the "subject string"). This effect can also be
achieved by appropriate constructs in the pattern itself, which is the	achieved by appropriate constructs in the pattern itself, which is the
only way to do it in Perl.	only way to do it in Perl.

PCRE_AUTO_CALLOUT	PCRE_AUTO_CALLOUT

If this bit is set, pcre_compile() automatically inserts callout items,	If this bit is set, pcre_compile() automatically inserts callout items,
all with number 255, before each pattern item. For discussion of the	all with number 255, before each pattern item. For discussion of the
callout facility, see the pcrecallout documentation.	callout facility, see the pcrecallout documentation.

PCRE_BSR_ANYCRLF	PCRE_BSR_ANYCRLF
PCRE_BSR_UNICODE	PCRE_BSR_UNICODE

These options (which are mutually exclusive) control what the \R escape	These options (which are mutually exclusive) control what the \R escape
sequence matches. The choice is either to match only CR, LF, or CRLF,	sequence matches. The choice is either to match only CR, LF, or CRLF,
or to match any Unicode newline sequence. The default is specified when	or to match any Unicode newline sequence. The default is specified when
PCRE is built. It can be overridden from within the pattern, or by set-	PCRE is built. It can be overridden from within the pattern, or by set-
ting an option when a compiled pattern is matched.	ting an option when a compiled pattern is matched.

PCRE_CASELESS	PCRE_CASELESS

If this bit is set, letters in the pattern match both upper and lower	If this bit is set, letters in the pattern match both upper and lower
case letters. It is equivalent to Perl's /i option, and it can be	case letters. It is equivalent to Perl's /i option, and it can be
changed within a pattern by a (?i) option setting. In UTF-8 mode, PCRE	changed within a pattern by a (?i) option setting. In UTF-8 mode, PCRE
always understands the concept of case for characters whose values are	always understands the concept of case for characters whose values are
less than 128, so caseless matching is always possible. For characters	less than 128, so caseless matching is always possible. For characters
with higher values, the concept of case is supported if PCRE is com-	with higher values, the concept of case is supported if PCRE is com-
piled with Unicode property support, but not otherwise. If you want to	piled with Unicode property support, but not otherwise. If you want to
use caseless matching for characters 128 and above, you must ensure	use caseless matching for characters 128 and above, you must ensure
that PCRE is compiled with Unicode property support as well as with	that PCRE is compiled with Unicode property support as well as with
UTF-8 support.	UTF-8 support.

PCRE_DOLLAR_ENDONLY	PCRE_DOLLAR_ENDONLY

If this bit is set, a dollar metacharacter in the pattern matches only	If this bit is set, a dollar metacharacter in the pattern matches only
at the end of the subject string. Without this option, a dollar also	at the end of the subject string. Without this option, a dollar also
matches immediately before a newline at the end of the string (but not	matches immediately before a newline at the end of the string (but not
before any other newlines). The PCRE_DOLLAR_ENDONLY option is ignored	before any other newlines). The PCRE_DOLLAR_ENDONLY option is ignored
if PCRE_MULTILINE is set. There is no equivalent to this option in	if PCRE_MULTILINE is set. There is no equivalent to this option in
Perl, and no way to set it within a pattern.	Perl, and no way to set it within a pattern.

PCRE_DOTALL	PCRE_DOTALL

If this bit is set, a dot metacharacter in the pattern matches a char-	If this bit is set, a dot metacharacter in the pattern matches a char-
acter of any value, including one that indicates a newline. However, it	acter of any value, including one that indicates a newline. However, it
only ever matches one character, even if newlines are coded as CRLF.	only ever matches one character, even if newlines are coded as CRLF.
Without this option, a dot does not match when the current position is	Without this option, a dot does not match when the current position is
at a newline. This option is equivalent to Perl's /s option, and it can	at a newline. This option is equivalent to Perl's /s option, and it can
be changed within a pattern by a (?s) option setting. A negative class	be changed within a pattern by a (?s) option setting. A negative class
such as [^a] always matches newline characters, independent of the set-	such as [^a] always matches newline characters, independent of the set-
ting of this option.	ting of this option.

PCRE_DUPNAMES	PCRE_DUPNAMES

If this bit is set, names used to identify capturing subpatterns need	If this bit is set, names used to identify capturing subpatterns need
not be unique. This can be helpful for certain types of pattern when it	not be unique. This can be helpful for certain types of pattern when it
is known that only one instance of the named subpattern can ever be	is known that only one instance of the named subpattern can ever be
matched. There are more details of named subpatterns below; see also	matched. There are more details of named subpatterns below; see also
the pcrepattern documentation.	the pcrepattern documentation.

PCRE_EXTENDED	PCRE_EXTENDED

If this bit is set, whitespace data characters in the pattern are	If this bit is set, most white space characters in the pattern are
totally ignored except when escaped or inside a character class. White-	totally ignored except when escaped or inside a character class. How-
space does not include the VT character (code 11). In addition, charac-	ever, white space is not allowed within sequences such as (?> that
ters between an unescaped # outside a character class and the next new-	introduce various parenthesized subpatterns, nor within a numerical
line, inclusive, are also ignored. This is equivalent to Perl's /x	quantifier such as {1,3}. However, ignorable white space is permitted
option, and it can be changed within a pattern by a (?x) option set-	between an item and a following quantifier and between a quantifier and
ting.	a following + that indicates possessiveness.

Which characters are interpreted as newlines is controlled by the	White space did not used to include the VT character (code 11), because
options passed to pcre_compile() or by a special sequence at the start	Perl did not treat this character as white space. However, Perl changed
of the pattern, as described in the section entitled "Newline conven-	at release 5.18, so PCRE followed at release 8.34, and VT is now
	treated as white space.

	PCRE_EXTENDED also causes characters between an unescaped # outside a
	character class and the next newline, inclusive, to be ignored.
	PCRE_EXTENDED is equivalent to Perl's /x option, and it can be changed
	within a pattern by a (?x) option setting.

	Which characters are interpreted as newlines is controlled by the
	options passed to pcre_compile() or by a special sequence at the start
	of the pattern, as described in the section entitled "Newline conven-
tions" in the pcrepattern documentation. Note that the end of this type	tions" in the pcrepattern documentation. Note that the end of this type
of comment is a literal newline sequence in the pattern; escape	of comment is a literal newline sequence in the pattern; escape
sequences that happen to represent a newline do not count.	sequences that happen to represent a newline do not count.

This option makes it possible to include comments inside complicated	This option makes it possible to include comments inside complicated
patterns. Note, however, that this applies only to data characters.	patterns. Note, however, that this applies only to data characters.
Whitespace characters may never appear within special character	White space characters may never appear within special character
sequences in a pattern, for example within the sequence (?( that intro-	sequences in a pattern, for example within the sequence (?( that intro-
duces a conditional subpattern.	duces a conditional subpattern.

PCRE_EXTRA	PCRE_EXTRA

This option was invented in order to turn on additional functionality	This option was invented in order to turn on additional functionality
of PCRE that is incompatible with Perl, but it is currently of very	of PCRE that is incompatible with Perl, but it is currently of very
little use. When set, any backslash in a pattern that is followed by a	little use. When set, any backslash in a pattern that is followed by a
letter that has no special meaning causes an error, thus reserving	letter that has no special meaning causes an error, thus reserving
these combinations for future expansion. By default, as in Perl, a	these combinations for future expansion. By default, as in Perl, a
backslash followed by a letter with no special meaning is treated as a	backslash followed by a letter with no special meaning is treated as a
literal. (Perl can, however, be persuaded to give an error for this, by	literal. (Perl can, however, be persuaded to give an error for this, by
running it with the -w option.) There are at present no other features	running it with the -w option.) There are at present no other features
controlled by this option. It can also be set by a (?X) option setting	controlled by this option. It can also be set by a (?X) option setting
within a pattern.	within a pattern.

PCRE_FIRSTLINE	PCRE_FIRSTLINE

If this option is set, an unanchored pattern is required to match	If this option is set, an unanchored pattern is required to match
before or at the first newline in the subject string, though the	before or at the first newline in the subject string, though the
matched text may continue over the newline.	matched text may continue over the newline.

PCRE_JAVASCRIPT_COMPAT	PCRE_JAVASCRIPT_COMPAT

If this option is set, PCRE's behaviour is changed in some ways so that	If this option is set, PCRE's behaviour is changed in some ways so that
it is compatible with JavaScript rather than Perl. The changes are as	it is compatible with JavaScript rather than Perl. The changes are as
follows:	follows:

(1) A lone closing square bracket in a pattern causes a compile-time	(1) A lone closing square bracket in a pattern causes a compile-time
error, because this is illegal in JavaScript (by default it is treated	error, because this is illegal in JavaScript (by default it is treated
as a data character). Thus, the pattern AB]CD becomes illegal when this	as a data character). Thus, the pattern AB]CD becomes illegal when this
option is set.	option is set.

(2) At run time, a back reference to an unset subpattern group matches	(2) At run time, a back reference to an unset subpattern group matches
an empty string (by default this causes the current matching alterna-	an empty string (by default this causes the current matching alterna-
tive to fail). A pattern such as (\1)(a) succeeds when this option is	tive to fail). A pattern such as (\1)(a) succeeds when this option is
set (assuming it can find an "a" in the subject), whereas it fails by	set (assuming it can find an "a" in the subject), whereas it fails by
default, for Perl compatibility.	default, for Perl compatibility.

(3) \U matches an upper case "U" character; by default \U causes a com-	(3) \U matches an upper case "U" character; by default \U causes a com-
pile time error (Perl uses \U to upper case subsequent characters).	pile time error (Perl uses \U to upper case subsequent characters).

(4) \u matches a lower case "u" character unless it is followed by four	(4) \u matches a lower case "u" character unless it is followed by four
hexadecimal digits, in which case the hexadecimal number defines the	hexadecimal digits, in which case the hexadecimal number defines the
code point to match. By default, \u causes a compile time error (Perl	code point to match. By default, \u causes a compile time error (Perl
uses it to upper case the following character).	uses it to upper case the following character).

(5) \x matches a lower case "x" character unless it is followed by two	(5) \x matches a lower case "x" character unless it is followed by two
hexadecimal digits, in which case the hexadecimal number defines the	hexadecimal digits, in which case the hexadecimal number defines the
code point to match. By default, as in Perl, a hexadecimal number is	code point to match. By default, as in Perl, a hexadecimal number is
always expected after \x, but it may have zero, one, or two digits (so,	always expected after \x, but it may have zero, one, or two digits (so,
for example, \xz matches a binary zero character followed by z).	for example, \xz matches a binary zero character followed by z).

PCRE_MULTILINE	PCRE_MULTILINE

By default, PCRE treats the subject string as consisting of a single	By default, for the purposes of matching "start of line" and "end of
line of characters (even if it actually contains newlines). The "start	line", PCRE treats the subject string as consisting of a single line of
of line" metacharacter (^) matches only at the start of the string,	characters, even if it actually contains newlines. The "start of line"
while the "end of line" metacharacter ($) matches only at the end of	metacharacter (^) matches only at the start of the string, and the "end
the string, or before a terminating newline (unless PCRE_DOLLAR_ENDONLY	of line" metacharacter ($) matches only at the end of the string, or
is set). This is the same as Perl.	before a terminating newline (except when PCRE_DOLLAR_ENDONLY is set).
	Note, however, that unless PCRE_DOTALL is set, the "any character"
	metacharacter (.) does not match at a newline. This behaviour (for ^,
	$, and dot) is the same as Perl.

When PCRE_MULTILINE it is set, the "start of line" and "end of line"	When PCRE_MULTILINE it is set, the "start of line" and "end of line"
constructs match immediately following or immediately before internal	constructs match immediately following or immediately before internal
Line 1287 COMPILING A PATTERN	Line 2253 COMPILING A PATTERN
lines in a subject string, or no occurrences of ^ or $ in a pattern,	lines in a subject string, or no occurrences of ^ or $ in a pattern,
setting PCRE_MULTILINE has no effect.	setting PCRE_MULTILINE has no effect.

	PCRE_NEVER_UTF

	This option locks out interpretation of the pattern as UTF-8 (or UTF-16
	or UTF-32 in the 16-bit and 32-bit libraries). In particular, it pre-
	vents the creator of the pattern from switching to UTF interpretation
	by starting the pattern with (*UTF). This may be useful in applications
	that process patterns from external sources. The combination of
	PCRE_UTF8 and PCRE_NEVER_UTF also causes an error.

PCRE_NEWLINE_CR	PCRE_NEWLINE_CR
PCRE_NEWLINE_LF	PCRE_NEWLINE_LF
PCRE_NEWLINE_CRLF	PCRE_NEWLINE_CRLF
PCRE_NEWLINE_ANYCRLF	PCRE_NEWLINE_ANYCRLF
PCRE_NEWLINE_ANY	PCRE_NEWLINE_ANY

These options override the default newline definition that was chosen	These options override the default newline definition that was chosen
when PCRE was built. Setting the first or the second specifies that a	when PCRE was built. Setting the first or the second specifies that a
newline is indicated by a single character (CR or LF, respectively).	newline is indicated by a single character (CR or LF, respectively).
Setting PCRE_NEWLINE_CRLF specifies that a newline is indicated by the	Setting PCRE_NEWLINE_CRLF specifies that a newline is indicated by the
two-character CRLF sequence. Setting PCRE_NEWLINE_ANYCRLF specifies	two-character CRLF sequence. Setting PCRE_NEWLINE_ANYCRLF specifies
that any of the three preceding sequences should be recognized. Setting	that any of the three preceding sequences should be recognized. Setting
PCRE_NEWLINE_ANY specifies that any Unicode newline sequence should be	PCRE_NEWLINE_ANY specifies that any Unicode newline sequence should be
recognized. The Unicode newline sequences are the three just mentioned,	recognized.
plus the single characters VT (vertical tab, U+000B), FF (formfeed,
U+000C), NEL (next line, U+0085), LS (line separator, U+2028), and PS
(paragraph separator, U+2029). The last two are recognized only in
UTF-8 mode.

	In an ASCII/Unicode environment, the Unicode newline sequences are the
	three just mentioned, plus the single characters VT (vertical tab,
	U+000B), FF (form feed, U+000C), NEL (next line, U+0085), LS (line sep-
	arator, U+2028), and PS (paragraph separator, U+2029). For the 8-bit
	library, the last two are recognized only in UTF-8 mode.

	When PCRE is compiled to run in an EBCDIC (mainframe) environment, the
	code for CR is 0x0d, the same as ASCII. However, the character code for
	LF is normally 0x15, though in some EBCDIC environments 0x25 is used.
	Whichever of these is not LF is made to correspond to Unicode's NEL
	character. EBCDIC codes are all less than 256. For more details, see
	the pcrebuild documentation.

The newline setting in the options word uses three bits that are	The newline setting in the options word uses three bits that are
treated as a number, giving eight possibilities. Currently only six are	treated as a number, giving eight possibilities. Currently only six are
used (default plus the five values above). This means that if you set	used (default plus the five values above). This means that if you set
Line 1315 COMPILING A PATTERN	Line 2299 COMPILING A PATTERN
cause an error.	cause an error.

The only time that a line break in a pattern is specially recognized	The only time that a line break in a pattern is specially recognized
when compiling is when PCRE_EXTENDED is set. CR and LF are whitespace	when compiling is when PCRE_EXTENDED is set. CR and LF are white space
characters, and so are ignored in this mode. Also, an unescaped # out-	characters, and so are ignored in this mode. Also, an unescaped # out-
side a character class indicates a comment that lasts until after the	side a character class indicates a comment that lasts until after the
next line break sequence. In other circumstances, line break sequences	next line break sequence. In other circumstances, line break sequences
Line 1332 COMPILING A PATTERN	Line 2316 COMPILING A PATTERN
be used for capturing (and they acquire numbers in the usual way).	be used for capturing (and they acquire numbers in the usual way).
There is no equivalent of this option in Perl.	There is no equivalent of this option in Perl.

NO_START_OPTIMIZE	PCRE_NO_AUTO_POSSESS

	If this option is set, it disables "auto-possessification". This is an
	optimization that, for example, turns a+b into a++b in order to avoid
	backtracks into a+ that can never be successful. However, if callouts
	are in use, auto-possessification means that some of them are never
	taken. You can set this option if you want the matching functions to do
	a full unoptimized search and run all the callouts, but it is mainly
	provided for testing purposes.

	PCRE_NO_START_OPTIMIZE

This is an option that acts at matching time; that is, it is really an	This is an option that acts at matching time; that is, it is really an
option for pcre_exec() or pcre_dfa_exec(). If it is set at compile	option for pcre_exec() or pcre_dfa_exec(). If it is set at compile
time, it is remembered with the compiled pattern and assumed at match-	time, it is remembered with the compiled pattern and assumed at match-
ing time. For details see the discussion of PCRE_NO_START_OPTIMIZE	ing time. This is necessary if you want to use JIT execution, because
below.	the JIT compiler needs to know whether or not this option is set. For
	details see the discussion of PCRE_NO_START_OPTIMIZE below.

PCRE_UCP	PCRE_UCP

This option changes the way PCRE processes \B, \b, \D, \d, \S, \s, \W,	This option changes the way PCRE processes \B, \b, \D, \d, \S, \s, \W,
\w, and some of the POSIX character classes. By default, only ASCII	\w, and some of the POSIX character classes. By default, only ASCII
characters are recognized, but if PCRE_UCP is set, Unicode properties	characters are recognized, but if PCRE_UCP is set, Unicode properties
are used instead to classify characters. More details are given in the	are used instead to classify characters. More details are given in the
section on generic character types in the pcrepattern page. If you set	section on generic character types in the pcrepattern page. If you set
PCRE_UCP, matching one of the items it affects takes much longer. The	PCRE_UCP, matching one of the items it affects takes much longer. The
option is available only if PCRE has been compiled with Unicode prop-	option is available only if PCRE has been compiled with Unicode prop-
erty support.	erty support.

PCRE_UNGREEDY	PCRE_UNGREEDY

This option inverts the "greediness" of the quantifiers so that they	This option inverts the "greediness" of the quantifiers so that they
are not greedy by default, but become greedy if followed by "?". It is	are not greedy by default, but become greedy if followed by "?". It is
not compatible with Perl. It can also be set by a (?U) option setting	not compatible with Perl. It can also be set by a (?U) option setting
within the pattern.	within the pattern.

PCRE_UTF8	PCRE_UTF8

This option causes PCRE to regard both the pattern and the subject as	This option causes PCRE to regard both the pattern and the subject as
strings of UTF-8 characters instead of single-byte character strings.	strings of UTF-8 characters instead of single-byte strings. However, it
However, it is available only when PCRE is built to include UTF-8 sup-	is available only when PCRE is built to include UTF support. If not,
port. If not, the use of this option provokes an error. Details of how	the use of this option provokes an error. Details of how this option
this option changes the behaviour of PCRE are given in the pcreunicode	changes the behaviour of PCRE are given in the pcreunicode page.
page.

PCRE_NO_UTF8_CHECK	PCRE_NO_UTF8_CHECK

When PCRE_UTF8 is set, the validity of the pattern as a UTF-8 string is	When PCRE_UTF8 is set, the validity of the pattern as a UTF-8 string is
automatically checked. There is a discussion about the validity of	automatically checked. There is a discussion about the validity of
UTF-8 strings in the main pcre page. If an invalid UTF-8 sequence of	UTF-8 strings in the pcreunicode page. If an invalid UTF-8 sequence is
bytes is found, pcre_compile() returns an error. If you already know	found, pcre_compile() returns an error. If you already know that your
that your pattern is valid, and you want to skip this check for perfor-	pattern is valid, and you want to skip this check for performance rea-
mance reasons, you can set the PCRE_NO_UTF8_CHECK option. When it is	sons, you can set the PCRE_NO_UTF8_CHECK option. When it is set, the
set, the effect of passing an invalid UTF-8 string as a pattern is	effect of passing an invalid UTF-8 string as a pattern is undefined. It
undefined. It may cause your program to crash. Note that this option	may cause your program to crash or loop. Note that this option can also
can also be passed to pcre_exec() and pcre_dfa_exec(), to suppress the	be passed to pcre_exec() and pcre_dfa_exec(), to suppress the validity
UTF-8 validity checking of subject strings.	checking of subject strings only. If the same string is being matched
	many times, the option can be safely set for the second and subsequent
	matchings to improve performance.


COMPILATION ERROR CODES	COMPILATION ERROR CODES

The following table lists the error codes than may be returned by	The following table lists the error codes than may be returned by
pcre_compile2(), along with the error messages that may be returned by	pcre_compile2(), along with the error messages that may be returned by
both compiling functions. As PCRE has developed, some error codes have	both compiling functions. Note that error messages are always 8-bit
fallen out of use. To avoid confusion, they have not been re-used.	ASCII strings, even in 16-bit or 32-bit mode. As PCRE has developed,
	some error codes have fallen out of use. To avoid confusion, they have
	not been re-used.

0 no error	0 no error
1 \ at end of pattern	1 \ at end of pattern
Line 1420 COMPILATION ERROR CODES	Line 2418 COMPILATION ERROR CODES
29 (?R or (?[+-]digits must be followed by )	29 (?R or (?[+-]digits must be followed by )
30 unknown POSIX class name	30 unknown POSIX class name
31 POSIX collating elements are not supported	31 POSIX collating elements are not supported
32 this version of PCRE is not compiled with PCRE_UTF8 support	32 this version of PCRE is compiled without UTF support
33 [this code is not in use]	33 [this code is not in use]
34 character value in \x{...} sequence is too large	34 character value in \x{} or \o{} is too large
35 invalid condition (?(0)	35 invalid condition (?(0)
36 \C not allowed in lookbehind assertion	36 \C not allowed in lookbehind assertion
37 PCRE does not support \L, \l, \N{name}, \U, or \u	37 PCRE does not support \L, \l, \N{name}, \U, or \u
Line 1432 COMPILATION ERROR CODES	Line 2430 COMPILATION ERROR CODES
41 unrecognized character after (?P	41 unrecognized character after (?P
42 syntax error in subpattern name (missing terminator)	42 syntax error in subpattern name (missing terminator)
43 two named subpatterns have the same name	43 two named subpatterns have the same name
44 invalid UTF-8 string	44 invalid UTF-8 string (specifically UTF-8)
45 support for \P, \p, and \X has not been compiled	45 support for \P, \p, and \X has not been compiled
46 malformed \P or \p sequence	46 malformed \P or \p sequence
47 unknown property name after \P or \p	47 unknown property name after \P or \p
48 subpattern name is too long (maximum 32 characters)	48 subpattern name is too long (maximum 32 characters)
49 too many named subpatterns (maximum 10000)	49 too many named subpatterns (maximum 10000)
50 [this code is not in use]	50 [this code is not in use]
51 octal value is greater than \377 (not in UTF-8 mode)	51 octal value is greater than \377 in 8-bit non-UTF-8 mode
52 internal error: overran compiling workspace	52 internal error: overran compiling workspace
53 internal error: previously-checked referenced subpattern	53 internal error: previously-checked referenced subpattern
not found	not found
Line 1450 COMPILATION ERROR CODES	Line 2448 COMPILATION ERROR CODES
name/number or by a plain number	name/number or by a plain number
58 a numbered reference must not be zero	58 a numbered reference must not be zero
59 an argument is not allowed for (ACCEPT), (FAIL), or (*COMMIT)	59 an argument is not allowed for (ACCEPT), (FAIL), or (*COMMIT)
60 (*VERB) not recognized	60 (*VERB) not recognized or malformed
61 number is too big	61 number is too big
62 subpattern name expected	62 subpattern name expected
63 digit expected after (?+	63 digit expected after (?+
Line 1458 COMPILATION ERROR CODES	Line 2456 COMPILATION ERROR CODES
65 different names for subpatterns of the same number are	65 different names for subpatterns of the same number are
not allowed	not allowed
66 (*MARK) must have an argument	66 (*MARK) must have an argument
67 this version of PCRE is not compiled with PCRE_UCP support	67 this version of PCRE is not compiled with Unicode property
	support
68 \c must be followed by an ASCII character	68 \c must be followed by an ASCII character
69 \k is not followed by a braced, angle-bracketed, or quoted name	69 \k is not followed by a braced, angle-bracketed, or quoted name
	70 internal error: unknown opcode in find_fixedlength()
	71 \N is not supported in a class
	72 too many forward references
	73 disallowed Unicode code point (>= 0xd800 && <= 0xdfff)
	74 invalid UTF-16 string (specifically UTF-16)
	75 name is too long in (MARK), (PRUNE), (SKIP), or (THEN)
	76 character value in \u.... sequence is too large
	77 invalid UTF-32 string (specifically UTF-32)
	78 setting UTF is disabled by the application
	79 non-hex character in \x{} (closing brace missing?)
	80 non-octal character in \o{} (closing brace missing?)
	81 missing opening brace after \o
	82 parentheses are too deeply nested
	83 invalid range in character class

The numbers 32 and 10000 in errors 48 and 49 are defaults; different	The numbers 32 and 10000 in errors 48 and 49 are defaults; different
values may be used if the limits were changed when PCRE was built.	values may be used if the limits were changed when PCRE was built.
Line 1468 COMPILATION ERROR CODES	Line 2481 COMPILATION ERROR CODES

STUDYING A PATTERN	STUDYING A PATTERN

pcre_extra pcre_study(const pcre code, int options	pcre_extra pcre_study(const pcre code, int options,
const char **errptr);	const char **errptr);

If a compiled pattern is going to be used several times, it is worth	If a compiled pattern is going to be used several times, it is worth
Line 1485 STUDYING A PATTERN	Line 2498 STUDYING A PATTERN
passed; these are described below in the section on matching a pattern.	passed; these are described below in the section on matching a pattern.

If studying the pattern does not produce any useful information,	If studying the pattern does not produce any useful information,
pcre_study() returns NULL. In that circumstance, if the calling program	pcre_study() returns NULL by default. In that circumstance, if the
wants to pass any of the other fields to pcre_exec() or	calling program wants to pass any of the other fields to pcre_exec() or
pcre_dfa_exec(), it must set up its own pcre_extra block.	pcre_dfa_exec(), it must set up its own pcre_extra block. However, if
	pcre_study() is called with the PCRE_STUDY_EXTRA_NEEDED option, it
	returns a pcre_extra block even if studying did not find any additional
	information. It may still return NULL, however, if an error occurs in
	pcre_study().

The second argument of pcre_study() contains option bits. There is only	The second argument of pcre_study() contains option bits. There are
one option: PCRE_STUDY_JIT_COMPILE. If this is set, and the just-in-	three further options in addition to PCRE_STUDY_EXTRA_NEEDED:
time compiler is available, the pattern is further compiled into
machine code that executes much faster than the pcre_exec() matching
function. If the just-in-time compiler is not available, this option is
ignored. All other bits in the options argument must be zero.

	PCRE_STUDY_JIT_COMPILE
	PCRE_STUDY_JIT_PARTIAL_HARD_COMPILE
	PCRE_STUDY_JIT_PARTIAL_SOFT_COMPILE

	If any of these are set, and the just-in-time compiler is available,
	the pattern is further compiled into machine code that executes much
	faster than the pcre_exec() interpretive matching function. If the
	just-in-time compiler is not available, these options are ignored. All
	undefined bits in the options argument must be zero.

JIT compilation is a heavyweight optimization. It can take some time	JIT compilation is a heavyweight optimization. It can take some time
for patterns to be analyzed, and for one-off matches and simple pat-	for patterns to be analyzed, and for one-off matches and simple pat-
terns the benefit of faster execution might be offset by a much slower	terns the benefit of faster execution might be offset by a much slower
Line 1515 STUDYING A PATTERN	Line 2538 STUDYING A PATTERN
the study data by calling pcre_free_study(). This function was added to	the study data by calling pcre_free_study(). This function was added to
the API for release 8.20. For earlier versions, the memory could be	the API for release 8.20. For earlier versions, the memory could be
freed with pcre_free(), just like the pattern itself. This will still	freed with pcre_free(), just like the pattern itself. This will still
work in cases where PCRE_STUDY_JIT_COMPILE is not used, but it is	work in cases where JIT optimization is not used, but it is advisable
advisable to change to the new function when convenient.	to change to the new function when convenient.

This is a typical way in which pcre_study() is used (except that in a	This is a typical way in which pcre_study() is used (except that in a
real application there should be tests for errors):	real application there should be tests for errors):
Line 1538 STUDYING A PATTERN	Line 2561 STUDYING A PATTERN
Studying a pattern does two things: first, a lower bound for the length	Studying a pattern does two things: first, a lower bound for the length
of subject string that is needed to match the pattern is computed. This	of subject string that is needed to match the pattern is computed. This
does not mean that there are any strings of that length that match, but	does not mean that there are any strings of that length that match, but
it does guarantee that no shorter strings match. The value is used by	it does guarantee that no shorter strings match. The value is used to
pcre_exec() and pcre_dfa_exec() to avoid wasting time by trying to	avoid wasting time by trying to match strings that are shorter than the
match strings that are shorter than the lower bound. You can find out	lower bound. You can find out the value in a calling program via the
the value in a calling program via the pcre_fullinfo() function.	pcre_fullinfo() function.

Studying a pattern is also useful for non-anchored patterns that do not	Studying a pattern is also useful for non-anchored patterns that do not
have a single fixed starting character. A bitmap of possible starting	have a single fixed starting character. A bitmap of possible starting
bytes is created. This speeds up finding a position in the subject at	bytes is created. This speeds up finding a position in the subject at
which to start matching.	which to start matching. (In 16-bit mode, the bitmap is used for 16-bit
	values less than 256. In 32-bit mode, the bitmap is used for 32-bit
	values less than 256.)

These two optimizations apply to both pcre_exec() and pcre_dfa_exec().	These two optimizations apply to both pcre_exec() and pcre_dfa_exec(),
However, they are not used by pcre_exec() if pcre_study() is called	and the information is also used by the JIT compiler. The optimiza-
with the PCRE_STUDY_JIT_COMPILE option, and just-in-time compiling is	tions can be disabled by setting the PCRE_NO_START_OPTIMIZE option.
successful. The optimizations can be disabled by setting the	You might want to do this if your pattern contains callouts or (*MARK)
PCRE_NO_START_OPTIMIZE option when calling pcre_exec() or	and you want to make use of these facilities in cases where matching
pcre_dfa_exec(). You might want to do this if your pattern contains	fails.
callouts or (*MARK) (which cannot be handled by the JIT compiler), and
you want to make use of these facilities in cases where matching fails.
See the discussion of PCRE_NO_START_OPTIMIZE below.

	PCRE_NO_START_OPTIMIZE can be specified at either compile time or exe-
	cution time. However, if PCRE_NO_START_OPTIMIZE is passed to
	pcre_exec(), (that is, after any JIT compilation has happened) JIT exe-
	cution is disabled. For JIT execution to work with PCRE_NO_START_OPTI-
	MIZE, the option must be set at compile time.

	There is a longer discussion of PCRE_NO_START_OPTIMIZE below.


LOCALE SUPPORT	LOCALE SUPPORT

PCRE handles caseless matching, and determines whether characters are	PCRE handles caseless matching, and determines whether characters are
letters, digits, or whatever, by reference to a set of tables, indexed	letters, digits, or whatever, by reference to a set of tables, indexed
by character value. When running in UTF-8 mode, this applies only to	by character code point. When running in UTF-8 mode, or in the 16- or
characters with codes less than 128. By default, higher-valued codes	32-bit libraries, this applies only to characters with code points less
never match escapes such as \w or \d, but they can be tested with \p if	than 256. By default, higher-valued code points never match escapes
PCRE is built with Unicode character property support. Alternatively,	such as \w or \d. However, if PCRE is built with Unicode property sup-
the PCRE_UCP option can be set at compile time; this causes \w and	port, all characters can be tested with \p and \P, or, alternatively,
friends to use Unicode property support instead of built-in tables. The	the PCRE_UCP option can be set when a pattern is compiled; this causes
use of locales with Unicode is discouraged. If you are handling charac-	\w and friends to use Unicode property support instead of the built-in
ters with codes greater than 128, you should either use UTF-8 and Uni-	tables.
code, or use locales, but not try to mix the two.

	The use of locales with Unicode is discouraged. If you are handling
	characters with code points greater than 128, you should either use
	Unicode support, or use locales, but not try to mix the two.

PCRE contains an internal set of tables that are used when the final	PCRE contains an internal set of tables that are used when the final
argument of pcre_compile() is NULL. These are sufficient for many	argument of pcre_compile() is NULL. These are sufficient for many
applications. Normally, the internal tables recognize only ASCII char-	applications. Normally, the internal tables recognize only ASCII char-
Line 1587 LOCALE SUPPORT	Line 2620 LOCALE SUPPORT

External tables are built by calling the pcre_maketables() function,	External tables are built by calling the pcre_maketables() function,
which has no arguments, in the relevant locale. The result can then be	which has no arguments, in the relevant locale. The result can then be
passed to pcre_compile() or pcre_exec() as often as necessary. For	passed to pcre_compile() as often as necessary. For example, to build
example, to build and use tables that are appropriate for the French	and use tables that are appropriate for the French locale (where
locale (where accented characters with values greater than 128 are	accented characters with values greater than 128 are treated as let-
treated as letters), the following code could be used:	ters), the following code could be used:

setlocale(LC_CTYPE, "fr_FR");	setlocale(LC_CTYPE, "fr_FR");
tables = pcre_maketables();	tables = pcre_maketables();
Line 1606 LOCALE SUPPORT	Line 2639 LOCALE SUPPORT

The pointer that is passed to pcre_compile() is saved with the compiled	The pointer that is passed to pcre_compile() is saved with the compiled
pattern, and the same tables are used via this pointer by pcre_study()	pattern, and the same tables are used via this pointer by pcre_study()
and normally also by pcre_exec(). Thus, by default, for any single pat-	and also by pcre_exec() and pcre_dfa_exec(). Thus, for any single pat-
tern, compilation, studying and matching all happen in the same locale,	tern, compilation, studying and matching all happen in the same locale,
but different patterns can be compiled in different locales.	but different patterns can be processed in different locales.

It is possible to pass a table pointer or NULL (indicating the use of	It is possible to pass a table pointer or NULL (indicating the use of
the internal tables) to pcre_exec(). Although not intended for this	the internal tables) to pcre_exec() or pcre_dfa_exec() (see the discus-
purpose, this facility could be used to match a pattern in a different	sion below in the section on matching a pattern). This facility is pro-
locale from the one in which it was compiled. Passing table pointers at	vided for use with pre-compiled patterns that have been saved and
run time is discussed below in the section on matching a pattern.	reloaded. Character tables are not saved with patterns, so if a non-
	standard table was used at compile time, it must be provided again when
	the reloaded pattern is matched. Attempting to use this facility to
	match a pattern in a different locale from the one in which it was com-
	piled is likely to lead to anomalous (usually incorrect) results.


INFORMATION ABOUT A PATTERN	INFORMATION ABOUT A PATTERN
Line 1623 INFORMATION ABOUT A PATTERN	Line 2660 INFORMATION ABOUT A PATTERN
int what, void *where);	int what, void *where);

The pcre_fullinfo() function returns information about a compiled pat-	The pcre_fullinfo() function returns information about a compiled pat-
tern. It replaces the obsolete pcre_info() function, which is neverthe-	tern. It replaces the pcre_info() function, which was removed from the
less retained for backwards compability (and is documented below).	library at version 8.30, after more than 10 years of obsolescence.

The first argument for pcre_fullinfo() is a pointer to the compiled	The first argument for pcre_fullinfo() is a pointer to the compiled
pattern. The second argument is the result of pcre_study(), or NULL if	pattern. The second argument is the result of pcre_study(), or NULL if
Line 1633 INFORMATION ABOUT A PATTERN	Line 2670 INFORMATION ABOUT A PATTERN
variable to receive the data. The yield of the function is zero for	variable to receive the data. The yield of the function is zero for
success, or one of the following negative numbers:	success, or one of the following negative numbers:

PCRE_ERROR_NULL the argument code was NULL	PCRE_ERROR_NULL the argument code was NULL
the argument where was NULL	the argument where was NULL
PCRE_ERROR_BADMAGIC the "magic number" was not found	PCRE_ERROR_BADMAGIC the "magic number" was not found
PCRE_ERROR_BADOPTION the value of what was invalid	PCRE_ERROR_BADENDIANNESS the pattern was compiled with different
	endianness
	PCRE_ERROR_BADOPTION the value of what was invalid
	PCRE_ERROR_UNSET the requested field is not set

The "magic number" is placed at the start of each compiled pattern as	The "magic number" is placed at the start of each compiled pattern as
an simple check against passing an arbitrary memory pointer. Here is a	an simple check against passing an arbitrary memory pointer. The endi-
typical call of pcre_fullinfo(), to obtain the length of the compiled	anness error can occur if a compiled pattern is saved and reloaded on a
pattern:	different host. Here is a typical call of pcre_fullinfo(), to obtain
	the length of the compiled pattern:

int rc;	int rc;
size_t length;	size_t length;
Line 1651 INFORMATION ABOUT A PATTERN	Line 2692 INFORMATION ABOUT A PATTERN
PCRE_INFO_SIZE, /* what is required */	PCRE_INFO_SIZE, /* what is required */
&length); /* where to put the data */	&length); /* where to put the data */

The possible values for the third argument are defined in pcre.h, and	The possible values for the third argument are defined The possible values for the third argument are defined in pcre.h, and
are as follows:	are as follows:

PCRE_INFO_BACKREFMAX	PCRE_INFO_BACKREFMAX

Return the number of the highest back reference in the pattern. The	Return the number of the highest back reference in the pattern. The
fourth argument should point to an int variable. Zero is returned if	fourth argument should point to an int variable. Zero is returned if
there are no back references.	there are no back references.

PCRE_INFO_CAPTURECOUNT	PCRE_INFO_CAPTURECOUNT

Return the number of capturing subpatterns in the pattern. The fourth	Return the number of capturing subpatterns in the pattern. The fourth
argument should point to an int variable.	argument should point to an int variable.

PCRE_INFO_DEFAULT_TABLES	PCRE_INFO_DEFAULT_TABLES

Return a pointer to the internal default character tables within PCRE.	Return a pointer to the internal default character tables within PCRE.
The fourth argument should point to an unsigned char * variable. This	The fourth argument should point to an unsigned char * variable. This
information call is provided for internal use by the pcre_study() func-	information call is provided for internal use by the pcre_study() func-
tion. External callers can cause PCRE to use its internal tables by	tion. External callers can cause PCRE to use its internal tables by
passing a NULL table pointer.	passing a NULL table pointer.

PCRE_INFO_FIRSTBYTE	PCRE_INFO_FIRSTBYTE

Return information about the first byte of any matched string, for a	Return information about the first data unit of any matched string, for
non-anchored pattern. The fourth argument should point to an int vari-	a non-anchored pattern. (The name of this option refers to the 8-bit
able. (This option used to be called PCRE_INFO_FIRSTCHAR; the old name	library, where data units are bytes.) The fourth argument should point
is still recognized for backwards compatibility.)	to an int variable.

If there is a fixed first byte, for example, from a pattern such as	If there is a fixed first value, for example, the letter "c" from a
(cat\|cow\|coyote), its value is returned. Otherwise, if either	pattern such as (cat\|cow\|coyote), its value is returned. In the 8-bit
	library, the value is always less than 256. In the 16-bit library the
	value can be up to 0xffff. In the 32-bit library the value can be up to
	0x10ffff.

	If there is no fixed first value, and if either

(a) the pattern was compiled with the PCRE_MULTILINE option, and every	(a) the pattern was compiled with the PCRE_MULTILINE option, and every
branch starts with "^", or	branch starts with "^", or

Line 1693 INFORMATION ABOUT A PATTERN	Line 2739 INFORMATION ABOUT A PATTERN
of a subject string or after any newline within the string. Otherwise	of a subject string or after any newline within the string. Otherwise
-2 is returned. For anchored patterns, -2 is returned.	-2 is returned. For anchored patterns, -2 is returned.

	Since for the 32-bit library using the non-UTF-32 mode, this function
	is unable to return the full 32-bit range of the character, this value
	is deprecated; instead the PCRE_INFO_FIRSTCHARACTERFLAGS and
	PCRE_INFO_FIRSTCHARACTER values should be used.

PCRE_INFO_FIRSTTABLE	PCRE_INFO_FIRSTTABLE

If the pattern was studied, and this resulted in the construction of a	If the pattern was studied, and this resulted in the construction of a
256-bit table indicating a fixed set of bytes for the first byte in any	256-bit table indicating a fixed set of values for the first data unit
matching string, a pointer to the table is returned. Otherwise NULL is	in any matching string, a pointer to the table is returned. Otherwise
returned. The fourth argument should point to an unsigned char * vari-	NULL is returned. The fourth argument should point to an unsigned char
able.	* variable.

PCRE_INFO_HASCRORLF	PCRE_INFO_HASCRORLF

Return 1 if the pattern contains any explicit matches for CR or LF	Return 1 if the pattern contains any explicit matches for CR or LF
characters, otherwise 0. The fourth argument should point to an int	characters, otherwise 0. The fourth argument should point to an int
variable. An explicit match is either a literal CR or LF character, or	variable. An explicit match is either a literal CR or LF character, or
\r or \n.	\r or \n.

PCRE_INFO_JCHANGED	PCRE_INFO_JCHANGED

Return 1 if the (?J) or (?-J) option setting is used in the pattern,	Return 1 if the (?J) or (?-J) option setting is used in the pattern,
otherwise 0. The fourth argument should point to an int variable. (?J)	otherwise 0. The fourth argument should point to an int variable. (?J)
and (?-J) set and unset the local PCRE_DUPNAMES option, respectively.	and (?-J) set and unset the local PCRE_DUPNAMES option, respectively.

PCRE_INFO_JIT	PCRE_INFO_JIT

Return 1 if the pattern was studied with the PCRE_STUDY_JIT_COMPILE	Return 1 if the pattern was studied with one of the JIT options, and
option, and just-in-time compiling was successful. The fourth argument	just-in-time compiling was successful. The fourth argument should point
should point to an int variable. A return value of 0 means that JIT	to an int variable. A return value of 0 means that JIT support is not
support is not available in this version of PCRE, or that the pattern	available in this version of PCRE, or that the pattern was not studied
was not studied with the PCRE_STUDY_JIT_COMPILE option, or that the JIT	with a JIT option, or that the JIT compiler could not handle this par-
compiler could not handle this particular pattern. See the pcrejit doc-	ticular pattern. See the pcrejit documentation for details of what can
umentation for details of what can and cannot be handled.	and cannot be handled.

PCRE_INFO_JITSIZE	PCRE_INFO_JITSIZE

If the pattern was successfully studied with the PCRE_STUDY_JIT_COMPILE	If the pattern was successfully studied with a JIT option, return the
option, return the size of the JIT compiled code, otherwise return	size of the JIT compiled code, otherwise return zero. The fourth argu-
zero. The fourth argument should point to a size_t variable.	ment should point to a size_t variable.

PCRE_INFO_LASTLITERAL	PCRE_INFO_LASTLITERAL

Return the value of the rightmost literal byte that must exist in any	Return the value of the rightmost literal data unit that must exist in
matched string, other than at its start, if such a byte has been	any matched string, other than at its start, if such a value has been
recorded. The fourth argument should point to an int variable. If there	recorded. The fourth argument should point to an int variable. If there
is no such byte, -1 is returned. For anchored patterns, a last literal	is no such value, -1 is returned. For anchored patterns, a last literal
byte is recorded only if it follows something of variable length. For	value is recorded only if it follows something of variable length. For
example, for the pattern /^a\d+z\d+/ the returned value is "z", but for	example, for the pattern /^a\d+z\d+/ the returned value is "z", but for
/^a\dz\d/ the returned value is -1.	/^a\dz\d/ the returned value is -1.

	Since for the 32-bit library using the non-UTF-32 mode, this function
	is unable to return the full 32-bit range of characters, this value is
	deprecated; instead the PCRE_INFO_REQUIREDCHARFLAGS and
	PCRE_INFO_REQUIREDCHAR values should be used.

	PCRE_INFO_MATCH_EMPTY

	Return 1 if the pattern can match an empty string, otherwise 0. The
	fourth argument should point to an int variable.

	PCRE_INFO_MATCHLIMIT

	If the pattern set a match limit by including an item of the form
	(*LIMIT_MATCH=nnnn) at the start, the value is returned. The fourth
	argument should point to an unsigned 32-bit integer. If no such value
	has been set, the call to pcre_fullinfo() returns the error
	PCRE_ERROR_UNSET.

	PCRE_INFO_MAXLOOKBEHIND

	Return the number of characters (NB not data units) in the longest
	lookbehind assertion in the pattern. This information is useful when
	doing multi-segment matching using the partial matching facilities.
	Note that the simple assertions \b and \B require a one-character look-
	behind. \A also registers a one-character lookbehind, though it does
	not actually inspect the previous character. This is to ensure that at
	least one character from the old segment is retained when a new segment
	is processed. Otherwise, if there are no lookbehinds in the pattern, \A
	might match incorrectly at the start of a new segment.

PCRE_INFO_MINLENGTH	PCRE_INFO_MINLENGTH

If the pattern was studied and a minimum length for matching subject	If the pattern was studied and a minimum length for matching subject
strings was computed, its value is returned. Otherwise the returned	strings was computed, its value is returned. Otherwise the returned
value is -1. The value is a number of characters, not bytes (this may	value is -1. The value is a number of characters, which in UTF mode may
be relevant in UTF-8 mode). The fourth argument should point to an int	be different from the number of data units. The fourth argument should
variable. A non-negative value is a lower bound to the length of any	point to an int variable. A non-negative value is a lower bound to the
matching string. There may not be any strings of that length that do	length of any matching string. There may not be any strings of that
actually match, but every string that does match is at least that long.	length that do actually match, but every string that does match is at
	least that long.

PCRE_INFO_NAMECOUNT	PCRE_INFO_NAMECOUNT
PCRE_INFO_NAMEENTRYSIZE	PCRE_INFO_NAMEENTRYSIZE
Line 1768 INFORMATION ABOUT A PATTERN	Line 2850 INFORMATION ABOUT A PATTERN
gives the number of entries, and PCRE_INFO_NAMEENTRYSIZE gives the size	gives the number of entries, and PCRE_INFO_NAMEENTRYSIZE gives the size
of each entry; both of these return an int value. The entry size	of each entry; both of these return an int value. The entry size
depends on the length of the longest name. PCRE_INFO_NAMETABLE returns	depends on the length of the longest name. PCRE_INFO_NAMETABLE returns
a pointer to the first entry of the table (a pointer to char). The	a pointer to the first entry of the table. This is a pointer to char in
first two bytes of each entry are the number of the capturing parenthe-	the 8-bit library, where the first two bytes of each entry are the num-
sis, most significant byte first. The rest of the entry is the corre-	ber of the capturing parenthesis, most significant byte first. In the
sponding name, zero terminated.	16-bit library, the pointer points to 16-bit data units, the first of
	which contains the parenthesis number. In the 32-bit library, the
	pointer points to 32-bit data units, the first of which contains the
	parenthesis number. The rest of the entry is the corresponding name,
	zero terminated.

The names are in alphabetical order. Duplicate names may appear if (?\|	The names are in alphabetical order. If (?\| is used to create multiple
is used to create multiple groups with the same number, as described in	groups with the same number, as described in the section on duplicate
the section on duplicate subpattern numbers in the pcrepattern page.	subpattern numbers in the pcrepattern page, the groups may be given the
Duplicate names for subpatterns with different numbers are permitted	same name, but there is only one entry in the table. Different names
only if PCRE_DUPNAMES is set. In all cases of duplicate names, they	for groups of the same number are not permitted. Duplicate names for
appear in the table in the order in which they were found in the pat-	subpatterns with different numbers are permitted, but only if PCRE_DUP-
tern. In the absence of (?\| this is the order of increasing number;	NAMES is set. They appear in the table in the order in which they were
when (?\| is used this is not necessarily the case because later subpat-	found in the pattern. In the absence of (?\| this is the order of
terns may have lower numbers.	increasing number; when (?\| is used this is not necessarily the case
	because later subpatterns may have lower numbers.

As a simple example of the name/number table, consider the following	As a simple example of the name/number table, consider the following
pattern (assume PCRE_EXTENDED is set, so white space - including new-	pattern after compilation by the 8-bit library (assume PCRE_EXTENDED is
lines - is ignored):	set, so white space - including newlines - is ignored):

(?<date> (?<year>(\d\d)?\d\d) -	(?<date> (?<year>(\d\d)?\d\d) -
(?<month>\d\d) - (?<day>\d\d) )	(?<month>\d\d) - (?<day>\d\d) )

There are four named subpatterns, so the table has four entries, and	There are four named subpatterns, so the table has four entries, and
each entry in the table is eight bytes long. The table is as follows,	each entry in the table is eight bytes long. The table is as follows,
with non-printing bytes shows in hexadecimal, and undefined bytes shown	with non-printing bytes shows in hexadecimal, and undefined bytes shown
as ??:	as ??:

Line 1800 INFORMATION ABOUT A PATTERN	Line 2887 INFORMATION ABOUT A PATTERN
00 04 m o n t h 00	00 04 m o n t h 00
00 02 y e a r 00 ??	00 02 y e a r 00 ??

When writing code to extract data from named subpatterns using the	When writing code to extract data from named subpatterns using the
name-to-number map, remember that the length of the entries is likely	name-to-number map, remember that the length of the entries is likely
to be different for each compiled pattern.	to be different for each compiled pattern.

PCRE_INFO_OKPARTIAL	PCRE_INFO_OKPARTIAL

Return 1 if the pattern can be used for partial matching with	Return 1 if the pattern can be used for partial matching with
pcre_exec(), otherwise 0. The fourth argument should point to an int	pcre_exec(), otherwise 0. The fourth argument should point to an int
variable. From release 8.00, this always returns 1, because the	variable. From release 8.00, this always returns 1, because the
restrictions that previously applied to partial matching have been	restrictions that previously applied to partial matching have been
lifted. The pcrepartial documentation gives details of partial match-	lifted. The pcrepartial documentation gives details of partial match-
ing.	ing.

PCRE_INFO_OPTIONS	PCRE_INFO_OPTIONS

Return a copy of the options with which the pattern was compiled. The	Return a copy of the options with which the pattern was compiled. The
fourth argument should point to an unsigned long int variable. These	fourth argument should point to an unsigned long int variable. These
option bits are those specified in the call to pcre_compile(), modified	option bits are those specified in the call to pcre_compile(), modified
by any top-level option settings at the start of the pattern itself. In	by any top-level option settings at the start of the pattern itself. In
other words, they are the options that will be in force when matching	other words, they are the options that will be in force when matching
starts. For example, if the pattern /(?im)abc(?-i)d/ is compiled with	starts. For example, if the pattern /(?im)abc(?-i)d/ is compiled with
the PCRE_EXTENDED option, the result is PCRE_CASELESS, PCRE_MULTILINE,	the PCRE_EXTENDED option, the result is PCRE_CASELESS, PCRE_MULTILINE,
and PCRE_EXTENDED.	and PCRE_EXTENDED.

A pattern is automatically anchored by PCRE if all of its top-level	A pattern is automatically anchored by PCRE if all of its top-level
alternatives begin with one of the following:	alternatives begin with one of the following:

^ unless PCRE_MULTILINE is set	^ unless PCRE_MULTILINE is set
Line 1836 INFORMATION ABOUT A PATTERN	Line 2923 INFORMATION ABOUT A PATTERN
For such patterns, the PCRE_ANCHORED bit is set in the options returned	For such patterns, the PCRE_ANCHORED bit is set in the options returned
by pcre_fullinfo().	by pcre_fullinfo().

	PCRE_INFO_RECURSIONLIMIT

	If the pattern set a recursion limit by including an item of the form
	(*LIMIT_RECURSION=nnnn) at the start, the value is returned. The fourth
	argument should point to an unsigned 32-bit integer. If no such value
	has been set, the call to pcre_fullinfo() returns the error
	PCRE_ERROR_UNSET.

PCRE_INFO_SIZE	PCRE_INFO_SIZE

Return the size of the compiled pattern. The fourth argument should	Return the size of the compiled pattern in bytes (for all three
point to a size_t variable. This value does not include the size of the	libraries). The fourth argument should point to a size_t variable. This
pcre structure that is returned by pcre_compile(). The value that is	value does not include the size of the pcre structure that is returned
passed as the argument to pcre_malloc() when pcre_compile() is getting	by pcre_compile(). The value that is passed as the argument to
memory in which to place the compiled data is the value returned by	pcre_malloc() when pcre_compile() is getting memory in which to place
this option plus the size of the pcre structure. Studying a compiled	the compiled data is the value returned by this option plus the size of
pattern, with or without JIT, does not alter the value returned by this	the pcre structure. Studying a compiled pattern, with or without JIT,
option.	does not alter the value returned by this option.

PCRE_INFO_STUDYSIZE	PCRE_INFO_STUDYSIZE

Return the size of the data block pointed to by the study_data field in	Return the size in bytes (for all three libraries) of the data block
a pcre_extra block. If pcre_extra is NULL, or there is no study data,	pointed to by the study_data field in a pcre_extra block. If pcre_extra
zero is returned. The fourth argument should point to a size_t vari-	is NULL, or there is no study data, zero is returned. The fourth argu-
able. The study_data field is set by pcre_study() to record informa-	ment should point to a size_t variable. The study_data field is set by
tion that will speed up matching (see the section entitled "Studying a	pcre_study() to record information that will speed up matching (see the
pattern" above). The format of the study_data block is private, but its	section entitled "Studying a pattern" above). The format of the
length is made available via this option so that it can be saved and	study_data block is private, but its length is made available via this
restored (see the pcreprecompile documentation for details).	option so that it can be saved and restored (see the pcreprecompile
	documentation for details).

	PCRE_INFO_FIRSTCHARACTERFLAGS

OBSOLETE INFO FUNCTION	Return information about the first data unit of any matched string, for
	a non-anchored pattern. The fourth argument should point to an int
	variable.

int pcre_info(const pcre code, int optptr, int *firstcharptr);	If there is a fixed first value, for example, the letter "c" from a
	pattern such as (cat\|cow\|coyote), 1 is returned, and the character
	value can be retrieved using PCRE_INFO_FIRSTCHARACTER.

The pcre_info() function is now obsolete because its interface is too	If there is no fixed first value, and if either
restrictive to return all the available data about a compiled pattern.
New programs should use pcre_fullinfo() instead. The yield of
pcre_info() is the number of capturing subpatterns, or one of the fol-
lowing negative numbers:

PCRE_ERROR_NULL the argument code was NULL	(a) the pattern was compiled with the PCRE_MULTILINE option, and every
PCRE_ERROR_BADMAGIC the "magic number" was not found	branch starts with "^", or

If the optptr argument is not NULL, a copy of the options with which	(b) every branch of the pattern starts with ".*" and PCRE_DOTALL is not
the pattern was compiled is placed in the integer it points to (see	set (if it were set, the pattern would be anchored),
PCRE_INFO_OPTIONS above).

If the pattern is not anchored and the firstcharptr argument is not	2 is returned, indicating that the pattern matches only at the start of
NULL, it is used to pass back information about the first character of	a subject string or after any newline within the string. Otherwise 0 is
any matched string (see PCRE_INFO_FIRSTBYTE above).	returned. For anchored patterns, 0 is returned.

	PCRE_INFO_FIRSTCHARACTER

	Return the fixed first character value in the situation where
	PCRE_INFO_FIRSTCHARACTERFLAGS returns 1; otherwise return 0. The fourth
	argument should point to an uint_t variable.

	In the 8-bit library, the value is always less than 256. In the 16-bit
	library the value can be up to 0xffff. In the 32-bit library in UTF-32
	mode the value can be up to 0x10ffff, and up to 0xffffffff when not
	using UTF-32 mode.

	PCRE_INFO_REQUIREDCHARFLAGS

	Returns 1 if there is a rightmost literal data unit that must exist in
	any matched string, other than at its start. The fourth argument should
	point to an int variable. If there is no such value, 0 is returned. If
	returning 1, the character value itself can be retrieved using
	PCRE_INFO_REQUIREDCHAR.

	For anchored patterns, a last literal value is recorded only if it fol-
	lows something of variable length. For example, for the pattern
	/^a\d+z\d+/ the returned value 1 (with "z" returned from
	PCRE_INFO_REQUIREDCHAR), but for /^a\dz\d/ the returned value is 0.

	PCRE_INFO_REQUIREDCHAR

	Return the value of the rightmost literal data unit that must exist in
	any matched string, other than at its start, if such a value has been
	recorded. The fourth argument should point to an uint32_t variable. If
	there is no such value, 0 is returned.


REFERENCE COUNTS	REFERENCE COUNTS

int pcre_refcount(pcre *code, int adjust);	int pcre_refcount(pcre *code, int adjust);

The pcre_refcount() function is used to maintain a reference count in	The pcre_refcount() function is used to maintain a reference count in
the data block that contains a compiled pattern. It is provided for the	the data block that contains a compiled pattern. It is provided for the
benefit of applications that operate in an object-oriented manner,	benefit of applications that operate in an object-oriented manner,
where different parts of the application may be using the same compiled	where different parts of the application may be using the same compiled
pattern, but you want to free the block when they are all done.	pattern, but you want to free the block when they are all done.

When a pattern is compiled, the reference count field is initialized to	When a pattern is compiled, the reference count field is initialized to
zero. It is changed only by calling this function, whose action is to	zero. It is changed only by calling this function, whose action is to
add the adjust value (which may be positive or negative) to it. The	add the adjust value (which may be positive or negative) to it. The
yield of the function is the new value. However, the value of the count	yield of the function is the new value. However, the value of the count
is constrained to lie between 0 and 65535, inclusive. If the new value	is constrained to lie between 0 and 65535, inclusive. If the new value
is outside these limits, it is forced to the appropriate limit value.	is outside these limits, it is forced to the appropriate limit value.

Except when it is zero, the reference count is not correctly preserved	Except when it is zero, the reference count is not correctly preserved
if a pattern is compiled on one host and then transferred to a host	if a pattern is compiled on one host and then transferred to a host
whose byte-order is different. (This seems a highly unlikely scenario.)	whose byte-order is different. (This seems a highly unlikely scenario.)


Line 1909 MATCHING A PATTERN: THE TRADITIONAL FUNCTION	Line 3036 MATCHING A PATTERN: THE TRADITIONAL FUNCTION
const char *subject, int length, int startoffset,	const char *subject, int length, int startoffset,
int options, int *ovector, int ovecsize);	int options, int *ovector, int ovecsize);

The function pcre_exec() is called to match a subject string against a	The function pcre_exec() is called to match a subject string against a
compiled pattern, which is passed in the code argument. If the pattern	compiled pattern, which is passed in the code argument. If the pattern
was studied, the result of the study should be passed in the extra	was studied, the result of the study should be passed in the extra
argument. You can call pcre_exec() with the same code and extra argu-	argument. You can call pcre_exec() with the same code and extra argu-
ments as many times as you like, in order to match different subject	ments as many times as you like, in order to match different subject
strings with the same pattern.	strings with the same pattern.

This function is the main matching facility of the library, and it	This function is the main matching facility of the library, and it
operates in a Perl-like manner. For specialist use there is also an	operates in a Perl-like manner. For specialist use there is also an
alternative matching function, which is described below in the section	alternative matching function, which is described below in the section
about the pcre_dfa_exec() function.	about the pcre_dfa_exec() function.

In most applications, the pattern will have been compiled (and option-	In most applications, the pattern will have been compiled (and option-
ally studied) in the same process that calls pcre_exec(). However, it	ally studied) in the same process that calls pcre_exec(). However, it
is possible to save compiled patterns and study data, and then use them	is possible to save compiled patterns and study data, and then use them
later in different processes, possibly even on different hosts. For a	later in different processes, possibly even on different hosts. For a
discussion about this, see the pcreprecompile documentation.	discussion about this, see the pcreprecompile documentation.

Here is an example of a simple call to pcre_exec():	Here is an example of a simple call to pcre_exec():
Line 1943 MATCHING A PATTERN: THE TRADITIONAL FUNCTION	Line 3070 MATCHING A PATTERN: THE TRADITIONAL FUNCTION

Extra data for pcre_exec()	Extra data for pcre_exec()

If the extra argument is not NULL, it must point to a pcre_extra data	If the extra argument is not NULL, it must point to a pcre_extra data
block. The pcre_study() function returns such a block (when it doesn't	block. The pcre_study() function returns such a block (when it doesn't
return NULL), but you can also create one for yourself, and pass addi-	return NULL), but you can also create one for yourself, and pass addi-
tional information in it. The pcre_extra block contains the following	tional information in it. The pcre_extra block contains the following
fields (not necessarily in this order):	fields (not necessarily in this order):

unsigned long int flags;	unsigned long int flags;
Line 1958 MATCHING A PATTERN: THE TRADITIONAL FUNCTION	Line 3085 MATCHING A PATTERN: THE TRADITIONAL FUNCTION
const unsigned char *tables;	const unsigned char *tables;
unsigned char **mark;	unsigned char **mark;

The flags field is a bitmap that specifies which of the other fields	In the 16-bit version of this structure, In the 16-bit version of this structure, the mark field has type
are set. The flag bits are:	"PCRE_UCHAR16 **".

PCRE_EXTRA_STUDY_DATA	In the 32-bit version of this structure, the mark field has type
	"PCRE_UCHAR32 **".

	The flags field is used to specify which of the other fields are set.
	The flag bits are:

	PCRE_EXTRA_CALLOUT_DATA
PCRE_EXTRA_EXECUTABLE_JIT	PCRE_EXTRA_EXECUTABLE_JIT
	PCRE_EXTRA_MARK
PCRE_EXTRA_MATCH_LIMIT	PCRE_EXTRA_MATCH_LIMIT
PCRE_EXTRA_MATCH_LIMIT_RECURSION	PCRE_EXTRA_MATCH_LIMIT_RECURSION
PCRE_EXTRA_CALLOUT_DATA	PCRE_EXTRA_STUDY_DATA
PCRE_EXTRA_TABLES	PCRE_EXTRA_TABLES
PCRE_EXTRA_MARK

Other flag bits should be set to zero. The study_data field and some-	Other flag bits should be set to zero. The study_data field and some-
times the executable_jit field are set in the pcre_extra block that is	times the executable_jit field are set in the pcre_extra block that is
returned by pcre_study(), together with the appropriate flag bits. You	returned by pcre_study(), together with the appropriate flag bits. You
should not set these yourself, but you may add to the block by setting	should not set these yourself, but you may add to the block by setting
the other fields and their corresponding flag bits.	other fields and their corresponding flag bits.

The match_limit field provides a means of preventing PCRE from using up	The match_limit field provides a means of preventing PCRE from using up
a vast amount of resources when running patterns that are not going to	a vast amount of resources when running patterns that are not going to
match, but which have a very large number of possibilities in their	match, but which have a very large number of possibilities in their
search trees. The classic example is a pattern that uses nested unlim-	search trees. The classic example is a pattern that uses nested unlim-
ited repeats.	ited repeats.

Internally, pcre_exec() uses a function called match(), which it calls	Internally, pcre_exec() uses a function called match(), which it calls
repeatedly (sometimes recursively). The limit set by match_limit is	repeatedly (sometimes recursively). The limit set by match_limit is
imposed on the number of times this function is called during a match,	imposed on the number of times this function is called during a match,
which has the effect of limiting the amount of backtracking that can	which has the effect of limiting the amount of backtracking that can
take place. For patterns that are not anchored, the count restarts from	take place. For patterns that are not anchored, the count restarts from
zero for each position in the subject string.	zero for each position in the subject string.

When pcre_exec() is called with a pattern that was successfully studied	When pcre_exec() is called with a pattern that was successfully studied
with the PCRE_STUDY_JIT_COMPILE option, the way that the matching is	with a JIT option, the way that the matching is executed is entirely
executed is entirely different. However, there is still the possibility	different. However, there is still the possibility of runaway matching
of runaway matching that goes on for a very long time, and so the	that goes on for a very long time, and so the match_limit value is also
match_limit value is also used in this case (but in a different way) to	used in this case (but in a different way) to limit how long the match-
limit how long the matching can continue.	ing can continue.

The default value for the limit can be set when PCRE is built; the	The default value for the limit can be set when PCRE is built; the
default default is 10 million, which handles all but the most extreme	default default is 10 million, which handles all but the most extreme
cases. You can override the default by suppling pcre_exec() with a	cases. You can override the default by suppling pcre_exec() with a
pcre_extra block in which match_limit is set, and	pcre_extra block in which match_limit is set, and
PCRE_EXTRA_MATCH_LIMIT is set in the flags field. If the limit is	PCRE_EXTRA_MATCH_LIMIT is set in the flags field. If the limit is
exceeded, pcre_exec() returns PCRE_ERROR_MATCHLIMIT.	exceeded, pcre_exec() returns PCRE_ERROR_MATCHLIMIT.

	A value for the match limit may also be supplied by an item at the
	start of a pattern of the form

	(*LIMIT_MATCH=d)

	where d is a decimal number. However, such a setting is ignored unless
	d is less than the limit set by the caller of pcre_exec() or, if no
	such limit is set, less than the default.

The match_limit_recursion field is similar to match_limit, but instead	The match_limit_recursion field is similar to match_limit, but instead
of limiting the total number of times that match() is called, it limits	of limiting the total number of times that match() is called, it limits
the depth of recursion. The recursion depth is a smaller number than	the depth of recursion. The recursion depth is a smaller number than
Line 2011 MATCHING A PATTERN: THE TRADITIONAL FUNCTION	Line 3153 MATCHING A PATTERN: THE TRADITIONAL FUNCTION
Limiting the recursion depth limits the amount of machine stack that	Limiting the recursion depth limits the amount of machine stack that
can be used, or, when PCRE has been compiled to use memory on the heap	can be used, or, when PCRE has been compiled to use memory on the heap
instead of the stack, the amount of heap memory that can be used. This	instead of the stack, the amount of heap memory that can be used. This
limit is not relevant, and is ignored, if the pattern was successfully	limit is not relevant, and is ignored, when matching is done using JIT
studied with PCRE_STUDY_JIT_COMPILE.	compiled code.

The default value for match_limit_recursion can be set when PCRE is	The default value for match_limit_recursion can be set when PCRE is
built; the default default is the same value as the default for	built; the default default is the same value as the default for
Line 2021 MATCHING A PATTERN: THE TRADITIONAL FUNCTION	Line 3163 MATCHING A PATTERN: THE TRADITIONAL FUNCTION
PCRE_EXTRA_MATCH_LIMIT_RECURSION is set in the flags field. If the	PCRE_EXTRA_MATCH_LIMIT_RECURSION is set in the flags field. If the
limit is exceeded, pcre_exec() returns PCRE_ERROR_RECURSIONLIMIT.	limit is exceeded, pcre_exec() returns PCRE_ERROR_RECURSIONLIMIT.

The callout_data field is used in conjunction with the "callout" fea-	A value for the recursion limit may also be supplied by an item at the
	start of a pattern of the form

	(*LIMIT_RECURSION=d)

	where d is a decimal number. However, such a setting is ignored unless
	d is less than the limit set by the caller of pcre_exec() or, if no
	such limit is set, less than the default.

	The callout_data field is used in conjunction with the "callout" fea-
ture, and is described in the pcrecallout documentation.	ture, and is described in the pcrecallout documentation.

The tables field is used to pass a character tables pointer to	The tables field is provided for use with patterns that have been pre-
pcre_exec(); this overrides the value that is stored with the compiled	compiled using custom character tables, saved to disc or elsewhere, and
pattern. A non-NULL value is stored with the compiled pattern only if	then reloaded, because the tables that were used to compile a pattern
custom tables were supplied to pcre_compile() via its tableptr argu-	are not saved with it. See the pcreprecompile documentation for a dis-
ment. If NULL is passed to pcre_exec() using this mechanism, it forces	cussion of saving compiled patterns for later use. If NULL is passed
PCRE's internal tables to be used. This facility is helpful when re-	using this mechanism, it forces PCRE's internal tables to be used.
using patterns that have been saved after compiling with an external
set of tables, because the external tables might be at a different
address when pcre_exec() is called. See the pcreprecompile documenta-
tion for a discussion of saving compiled patterns for later use.

If PCRE_EXTRA_MARK is set in the flags field, the mark field must be	Warning: The tables that pcre_exec() uses must be the same as those
set to point to a char * variable. If the pattern contains any back-	that were used when the pattern was compiled. If this is not the case,
tracking control verbs such as (*MARK:NAME), and the execution ends up	the behaviour of pcre_exec() is undefined. Therefore, when a pattern is
with a name to pass back, a pointer to the name string (zero termi-	compiled and matched in the same process, this field should never be
nated) is placed in the variable pointed to by the mark field. The	set. In this (the most common) case, the correct table pointer is auto-
names are within the compiled pattern; if you wish to retain such a	matically passed with the compiled pattern from pcre_compile() to
name you must copy it before freeing the memory of a compiled pattern.	pcre_exec().
If there is no name to pass back, the variable pointed to by the mark
field set to NULL. For details of the backtracking control verbs, see
the section entitled "Backtracking control" in the pcrepattern documen-
tation.

	If PCRE_EXTRA_MARK is set in the flags field, the mark field must be
	set to point to a suitable variable. If the pattern contains any back-
	tracking control verbs such as (*MARK:NAME), and the execution ends up
	with a name to pass back, a pointer to the name string (zero termi-
	nated) is placed in the variable pointed to by the mark field. The
	names are within the compiled pattern; if you wish to retain such a
	name you must copy it before freeing the memory of a compiled pattern.
	If there is no name to pass back, the variable pointed to by the mark
	field is set to NULL. For details of the backtracking control verbs,
	see the section entitled "Backtracking control" in the pcrepattern doc-
	umentation.

Option bits for pcre_exec()	Option bits for pcre_exec()

The unused bits of the options argument for pcre_exec() must be zero.	The unused bits of the options argument for pcre_exec() must be zero.
The only bits that may be set are PCRE_ANCHORED, PCRE_NEWLINE_xxx,	The only bits that may be set are PCRE_ANCHORED, PCRE_NEWLINE_xxx,
PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, PCRE_NOTEMPTY_ATSTART,	PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, PCRE_NOTEMPTY_ATSTART,
PCRE_NO_START_OPTIMIZE, PCRE_NO_UTF8_CHECK, PCRE_PARTIAL_SOFT, and	PCRE_NO_START_OPTIMIZE, PCRE_NO_UTF8_CHECK, PCRE_PARTIAL_HARD, and
PCRE_PARTIAL_HARD.	PCRE_PARTIAL_SOFT.

If the pattern was successfully studied with the PCRE_STUDY_JIT_COMPILE	If the pattern was successfully studied with one of the just-in-time
option, the only supported options for JIT execution are	(JIT) compile options, the only supported options for JIT execution are
PCRE_NO_UTF8_CHECK, PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, and	PCRE_NO_UTF8_CHECK, PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY,
PCRE_NOTEMPTY_ATSTART. Note in particular that partial matching is not	PCRE_NOTEMPTY_ATSTART, PCRE_PARTIAL_HARD, and PCRE_PARTIAL_SOFT. If an
supported. If an unsupported option is used, JIT execution is disabled	unsupported option is used, JIT execution is disabled and the normal
and the normal interpretive code in pcre_exec() is run.	interpretive code in pcre_exec() is run.

PCRE_ANCHORED	PCRE_ANCHORED

The PCRE_ANCHORED option limits pcre_exec() to matching at the first	The PCRE_ANCHORED option limits pcre_exec() to matching at the first
matching position. If a pattern was compiled with PCRE_ANCHORED, or	matching position. If a pattern was compiled with PCRE_ANCHORED, or
turned out to be anchored by virtue of its contents, it cannot be made	turned out to be anchored by virtue of its contents, it cannot be made
unachored at matching time.	unachored at matching time.

PCRE_BSR_ANYCRLF	PCRE_BSR_ANYCRLF
PCRE_BSR_UNICODE	PCRE_BSR_UNICODE

These options (which are mutually exclusive) control what the \R escape	These options (which are mutually exclusive) control what the \R escape
sequence matches. The choice is either to match only CR, LF, or CRLF,	sequence matches. The choice is either to match only CR, LF, or CRLF,
or to match any Unicode newline sequence. These options override the	or to match any Unicode newline sequence. These options override the
choice that was made or defaulted when the pattern was compiled.	choice that was made or defaulted when the pattern was compiled.

PCRE_NEWLINE_CR	PCRE_NEWLINE_CR
Line 2083 MATCHING A PATTERN: THE TRADITIONAL FUNCTION	Line 3238 MATCHING A PATTERN: THE TRADITIONAL FUNCTION
PCRE_NEWLINE_ANYCRLF	PCRE_NEWLINE_ANYCRLF
PCRE_NEWLINE_ANY	PCRE_NEWLINE_ANY

These options override the newline definition that was chosen or	These options override the newline definition that was chosen or
defaulted when the pattern was compiled. For details, see the descrip-	defaulted when the pattern was compiled. For details, see the descrip-
tion of pcre_compile() above. During matching, the newline choice	tion of pcre_compile() above. During matching, the newline choice
affects the behaviour of the dot, circumflex, and dollar metacharac-	affects the behaviour of the dot, circumflex, and dollar metacharac-
ters. It may also alter the way the match position is advanced after a	ters. It may also alter the way the match position is advanced after a
match failure for an unanchored pattern.	match failure for an unanchored pattern.

When PCRE_NEWLINE_CRLF, PCRE_NEWLINE_ANYCRLF, or PCRE_NEWLINE_ANY is	When PCRE_NEWLINE_CRLF, PCRE_NEWLINE_ANYCRLF, or PCRE_NEWLINE_ANY is
set, and a match attempt for an unanchored pattern fails when the cur-	set, and a match attempt for an unanchored pattern fails when the cur-
rent position is at a CRLF sequence, and the pattern contains no	rent position is at a CRLF sequence, and the pattern contains no
explicit matches for CR or LF characters, the match position is	explicit matches for CR or LF characters, the match position is
advanced by two characters instead of one, in other words, to after the	advanced by two characters instead of one, in other words, to after the
CRLF.	CRLF.

The above rule is a compromise that makes the most common cases work as	The above rule is a compromise that makes the most common cases work as
expected. For example, if the pattern is .+A (and the PCRE_DOTALL	expected. For example, if the pattern is .+A (and the PCRE_DOTALL
option is not set), it does not match the string "\r\nA" because, after	option is not set), it does not match the string "\r\nA" because, after
failing at the start, it skips both the CR and the LF before retrying.	failing at the start, it skips both the CR and the LF before retrying.
However, the pattern [\r\n]A does match that string, because it con-	However, the pattern [\r\n]A does match that string, because it con-
tains an explicit CR or LF reference, and so advances only by one char-	tains an explicit CR or LF reference, and so advances only by one char-
acter after the first failure.	acter after the first failure.

An explicit match for CR of LF is either a literal appearance of one of	An explicit match for CR of LF is either a literal appearance of one of
those characters, or one of the \r or \n escape sequences. Implicit	those characters, or one of the \r or \n escape sequences. Implicit
matches such as [^X] do not count, nor does \s (which includes CR and	matches such as [^X] do not count, nor does \s (which includes CR and
LF in the characters that it matches).	LF in the characters that it matches).

Notwithstanding the above, anomalous effects may still occur when CRLF	Notwithstanding the above, anomalous effects may still occur when CRLF
is a valid newline sequence and explicit \r or \n escapes appear in the	is a valid newline sequence and explicit \r or \n escapes appear in the
pattern.	pattern.

PCRE_NOTBOL	PCRE_NOTBOL

This option specifies that first character of the subject string is not	This option specifies that first character of the subject string is not
the beginning of a line, so the circumflex metacharacter should not	the beginning of a line, so the circumflex metacharacter should not
match before it. Setting this without PCRE_MULTILINE (at compile time)	match before it. Setting this without PCRE_MULTILINE (at compile time)
causes circumflex never to match. This option affects only the behav-	causes circumflex never to match. This option affects only the behav-
iour of the circumflex metacharacter. It does not affect \A.	iour of the circumflex metacharacter. It does not affect \A.

PCRE_NOTEOL	PCRE_NOTEOL

This option specifies that the end of the subject string is not the end	This option specifies that the end of the subject string is not the end
of a line, so the dollar metacharacter should not match it nor (except	of a line, so the dollar metacharacter should not match it nor (except
in multiline mode) a newline immediately before it. Setting this with-	in multiline mode) a newline immediately before it. Setting this with-
out PCRE_MULTILINE (at compile time) causes dollar never to match. This	out PCRE_MULTILINE (at compile time) causes dollar never to match. This
option affects only the behaviour of the dollar metacharacter. It does	option affects only the behaviour of the dollar metacharacter. It does
not affect \Z or \z.	not affect \Z or \z.

PCRE_NOTEMPTY	PCRE_NOTEMPTY

An empty string is not considered to be a valid match if this option is	An empty string is not considered to be a valid match if this option is
set. If there are alternatives in the pattern, they are tried. If all	set. If there are alternatives in the pattern, they are tried. If all
the alternatives match the empty string, the entire match fails. For	the alternatives match the empty string, the entire match fails. For
example, if the pattern	example, if the pattern

a?b?	a?b?

is applied to a string not beginning with "a" or "b", it matches an	is applied to a string not beginning with "a" or "b", it matches an
empty string at the start of the subject. With PCRE_NOTEMPTY set, this	empty string at the start of the subject. With PCRE_NOTEMPTY set, this
match is not valid, so PCRE searches further into the string for occur-	match is not valid, so PCRE searches further into the string for occur-
rences of "a" or "b".	rences of "a" or "b".

PCRE_NOTEMPTY_ATSTART	PCRE_NOTEMPTY_ATSTART

This is like PCRE_NOTEMPTY, except that an empty string match that is	This is like PCRE_NOTEMPTY, except that an empty string match that is
not at the start of the subject is permitted. If the pattern is	not at the start of the subject is permitted. If the pattern is
anchored, such a match can occur only if the pattern contains \K.	anchored, such a match can occur only if the pattern contains \K.

Perl has no direct equivalent of PCRE_NOTEMPTY or	Perl has no direct equivalent of PCRE_NOTEMPTY or
PCRE_NOTEMPTY_ATSTART, but it does make a special case of a pattern	PCRE_NOTEMPTY_ATSTART, but it does make a special case of a pattern
match of the empty string within its split() function, and when using	match of the empty string within its split() function, and when using
the /g modifier. It is possible to emulate Perl's behaviour after	the /g modifier. It is possible to emulate Perl's behaviour after
matching a null string by first trying the match again at the same off-	matching a null string by first trying the match again at the same off-
set with PCRE_NOTEMPTY_ATSTART and PCRE_ANCHORED, and then if that	set with PCRE_NOTEMPTY_ATSTART and PCRE_ANCHORED, and then if that
fails, by advancing the starting offset (see below) and trying an ordi-	fails, by advancing the starting offset (see below) and trying an ordi-
nary match again. There is some code that demonstrates how to do this	nary match again. There is some code that demonstrates how to do this
in the pcredemo sample program. In the most general case, you have to	in the pcredemo sample program. In the most general case, you have to
check to see if the newline convention recognizes CRLF as a newline,	check to see if the newline convention recognizes CRLF as a newline,
and if so, and the current character is CR followed by LF, advance the	and if so, and the current character is CR followed by LF, advance the
starting offset by two characters instead of one.	starting offset by two characters instead of one.

PCRE_NO_START_OPTIMIZE	PCRE_NO_START_OPTIMIZE

There are a number of optimizations that pcre_exec() uses at the start	There are a number of optimizations that pcre_exec() uses at the start
of a match, in order to speed up the process. For example, if it is	of a match, in order to speed up the process. For example, if it is
known that an unanchored match must start with a specific character, it	known that an unanchored match must start with a specific character, it
searches the subject for that character, and fails immediately if it	searches the subject for that character, and fails immediately if it
cannot find it, without actually running the main matching function.	cannot find it, without actually running the main matching function.
This means that a special item such as (*COMMIT) at the start of a pat-	This means that a special item such as (*COMMIT) at the start of a pat-
tern is not considered until after a suitable starting point for the	tern is not considered until after a suitable starting point for the
match has been found. When callouts or (*MARK) items are in use, these	match has been found. Also, when callouts or (*MARK) items are in use,
"start-up" optimizations can cause them to be skipped if the pattern is	these "start-up" optimizations can cause them to be skipped if the pat-
never actually used. The start-up optimizations are in effect a pre-	tern is never actually used. The start-up optimizations are in effect a
scan of the subject that takes place before the pattern is run.	pre-scan of the subject that takes place before the pattern is run.

The PCRE_NO_START_OPTIMIZE option disables the start-up optimizations,	The PCRE_NO_START_OPTIMIZE option disables the start-up optimizations,
possibly causing performance to suffer, but ensuring that in cases	possibly causing performance to suffer, but ensuring that in cases
where the result is "no match", the callouts do occur, and that items	where the result is "no match", the callouts do occur, and that items
such as (COMMIT) and (MARK) are considered at every possible starting	such as (COMMIT) and (MARK) are considered at every possible starting
position in the subject string. If PCRE_NO_START_OPTIMIZE is set at	position in the subject string. If PCRE_NO_START_OPTIMIZE is set at
compile time, it cannot be unset at matching time.	compile time, it cannot be unset at matching time. The use of
	PCRE_NO_START_OPTIMIZE at matching time (that is, passing it to
	pcre_exec()) disables JIT execution; in this situation, matching is
	always done using interpretively.

Setting PCRE_NO_START_OPTIMIZE can change the outcome of a matching	Setting PCRE_NO_START_OPTIMIZE can change the outcome of a matching
operation. Consider the pattern	operation. Consider the pattern
Line 2217 MATCHING A PATTERN: THE TRADITIONAL FUNCTION	Line 3375 MATCHING A PATTERN: THE TRADITIONAL FUNCTION

When PCRE_UTF8 is set at compile time, the validity of the subject as a	When PCRE_UTF8 is set at compile time, the validity of the subject as a
UTF-8 string is automatically checked when pcre_exec() is subsequently	UTF-8 string is automatically checked when pcre_exec() is subsequently
called. The value of startoffset is also checked to ensure that it	called. The entire string is checked before any other processing takes
points to the start of a UTF-8 character. There is a discussion about	place. The value of startoffset is also checked to ensure that it
the validity of UTF-8 strings in the section on UTF-8 support in the	points to the start of a UTF-8 character. There is a discussion about
main pcre page. If an invalid UTF-8 sequence of bytes is found,	the validity of UTF-8 strings in the pcreunicode page. If an invalid
pcre_exec() returns the error PCRE_ERROR_BADUTF8 or, if PCRE_PAR-	sequence of bytes is found, pcre_exec() returns the error
TIAL_HARD is set and the problem is a truncated UTF-8 character at the	PCRE_ERROR_BADUTF8 or, if PCRE_PARTIAL_HARD is set and the problem is a
end of the subject, PCRE_ERROR_SHORTUTF8. In both cases, information	truncated character at the end of the subject, PCRE_ERROR_SHORTUTF8. In
about the precise nature of the error may also be returned (see the	both cases, information about the precise nature of the error may also
descriptions of these errors in the section entitled Error return val-	be returned (see the descriptions of these errors in the section enti-
ues from pcre_exec() below). If startoffset contains a value that does	tled Error return values from pcre_exec() below). If startoffset con-
not point to the start of a UTF-8 character (or to the end of the sub-	tains a value that does not point to the start of a UTF-8 character (or
ject), PCRE_ERROR_BADUTF8_OFFSET is returned.	to the end of the subject), PCRE_ERROR_BADUTF8_OFFSET is returned.

If you already know that your subject is valid, and you want to skip	If you already know that your subject is valid, and you want to skip
these checks for performance reasons, you can set the	these checks for performance reasons, you can set the
Line 2236 MATCHING A PATTERN: THE TRADITIONAL FUNCTION	Line 3394 MATCHING A PATTERN: THE TRADITIONAL FUNCTION
do this for the second and subsequent calls to pcre_exec() if you are	do this for the second and subsequent calls to pcre_exec() if you are
making repeated calls to find all the matches in a single subject	making repeated calls to find all the matches in a single subject
string. However, you should be sure that the value of startoffset	string. However, you should be sure that the value of startoffset
points to the start of a UTF-8 character (or the end of the subject).	points to the start of a character (or the end of the subject). When
When PCRE_NO_UTF8_CHECK is set, the effect of passing an invalid UTF-8	PCRE_NO_UTF8_CHECK is set, the effect of passing an invalid string as a
string as a subject or an invalid value of startoffset is undefined.	subject or an invalid value of startoffset is undefined. Your program
Your program may crash.	may crash or loop.

PCRE_PARTIAL_HARD	PCRE_PARTIAL_HARD
PCRE_PARTIAL_SOFT	PCRE_PARTIAL_SOFT
Line 2269 MATCHING A PATTERN: THE TRADITIONAL FUNCTION	Line 3427 MATCHING A PATTERN: THE TRADITIONAL FUNCTION
The string to be matched by pcre_exec()	The string to be matched by pcre_exec()

The subject string is passed to pcre_exec() as a pointer in subject, a	The subject string is passed to pcre_exec() as a pointer in subject, a
length (in bytes) in length, and a starting byte offset in startoffset.	length in length, and a starting offset in startoffset. The units for
If this is negative or greater than the length of the subject,	length and startoffset are bytes for the 8-bit library, 16-bit data
	items for the 16-bit library, and 32-bit data items for the 32-bit
	library.

	If startoffset is negative or greater than the length of the subject,
pcre_exec() returns PCRE_ERROR_BADOFFSET. When the starting offset is	pcre_exec() returns PCRE_ERROR_BADOFFSET. When the starting offset is
zero, the search for a match starts at the beginning of the subject,	zero, the search for a match starts at the beginning of the subject,
and this is by far the most common case. In UTF-8 mode, the byte offset	and this is by far the most common case. In UTF-8 or UTF-16 mode, the
must point to the start of a UTF-8 character (or the end of the sub-	offset must point to the start of a character, or the end of the sub-
ject). Unlike the pattern string, the subject may contain binary zero	ject (in UTF-32 mode, one data unit equals one character, so all off-
bytes.	sets are valid). Unlike the pattern string, the subject may contain
	binary zeroes.

A non-zero starting offset is useful when searching for another match	A non-zero starting offset is useful when searching for another match
in the same subject by calling pcre_exec() again after a previous suc-	in the same subject by calling pcre_exec() again after a previous suc-
cess. Setting startoffset differs from just passing over a shortened	cess. Setting startoffset differs from just passing over a shortened
string and setting PCRE_NOTBOL in the case of a pattern that begins	string and setting PCRE_NOTBOL in the case of a pattern that begins
with any kind of lookbehind. For example, consider the pattern	with any kind of lookbehind. For example, consider the pattern

\Biss\B	\Biss\B

which finds occurrences of "iss" in the middle of words. (\B matches	which finds occurrences of "iss" in the middle of words. (\B matches
only if the current position in the subject is not a word boundary.)	only if the current position in the subject is not a word boundary.)
When applied to the string "Mississipi" the first call to pcre_exec()	When applied to the string "Mississipi" the first call to pcre_exec()
finds the first occurrence. If pcre_exec() is called again with just	finds the first occurrence. If pcre_exec() is called again with just
the remainder of the subject, namely "issipi", it does not match,	the remainder of the subject, namely "issipi", it does not match,
because \B is always false at the start of the subject, which is deemed	because \B is always false at the start of the subject, which is deemed
to be a word boundary. However, if pcre_exec() is passed the entire	to be a w to be a word boundary. However, if pcre_exec() is passed the entire
string again, but with startoffset set to 4, it finds the second occur-	string again, but with startoffset set to 4, it finds the second occur-
rence of "iss" because it is able to look behind the starting point to	rence of "iss" because it is able to look behind the starting point to
discover that it is preceded by a letter.	discover that it is preceded by a letter.

Finding all the matches in a subject is tricky when the pattern can	Finding all the matches in a subject is tricky when the pattern can
match an empty string. It is possible to emulate Perl's /g behaviour by	match an empty string. It is possible to emulate Perl's /g behaviour by
first trying the match again at the same offset, with the	first trying the match again at the same offset, with the
PCRE_NOTEMPTY_ATSTART and PCRE_ANCHORED options, and then if that	PCRE_NOTEMPTY_ATSTART and PCRE_ANCHORED options, and then if that
fails, advancing the starting offset and trying an ordinary match	fails, advancing the starting offset and trying an ordinary match
again. There is some code that demonstrates how to do this in the pcre-	again. There is some code that demonstrates how to do this in the pcre-
demo sample program. In the most general case, you have to check to see	demo sample program. In the most general case, you have to check to see
if the newline convention recognizes CRLF as a newline, and if so, and	if the newline convention recognizes CRLF as a newline, and if so, and
the current character is CR followed by LF, advance the starting offset	the current character is CR followed by LF, advance the starting offset
by two characters instead of one.	by two characters instead of one.

If a non-zero starting offset is passed when the pattern is anchored,	If a non-zero starting offset is passed when the pattern is anchored,
one attempt to match at the given offset is made. This can only succeed	one attempt to match at the given offset is made. This can only succeed
if the pattern does not require the match to be at the start of the	if the pattern d if the pattern d
subject.	subject.

How pcre_exec() returns captured substrings	How pcre_exec() returns captured substrings

In general, a pattern matches a certain portion of the subject, and in	In general, a pattern matches a certain portion of the subject, and in
addition, further substrings from the subject may be picked out by	addition, further substrings from the subject may be picked out by
parts of the pattern. Following the usage in Jeffrey Friedl's book,	parts of the pattern. Following the usage in Jeffrey Friedl's book,
this is called "capturing" in what follows, and the phrase "capturing	this is called "capturing" in what follows, and the phrase "capturing
subpattern" is used for a fragment of a pattern that picks out a sub-	subpattern" is used for a fragment of a pattern that picks out a sub-
string. PCRE supports several other kinds of parenthesized subpattern	string. PCRE supports several other kinds of parenthesized subpattern
that do not cause substrings to be captured.	that do not cause substrings to be captured.

Captured substrings are returned to the caller via a vector of integers	Captured substrings are returned to the caller via a vector of integers
whose address is passed in ovector. The number of elements in the vec-	whose address is passed in ovector. The number of elements in the vec-
tor is passed in ovecsize, which must be a non-negative number. Note:	tor is passed in ovecsize, which must be a non-negative number. Note:
this argument is NOT the size of ovector in bytes.	this argument is NOT the size of ovector in bytes.

The first two-thirds of the vector is used to pass back captured sub-	The first two-thirds of the vector is used to pass back captured sub-
strings, each substring using a pair of integers. The remaining third	strings, each substring using a pair of integers. The remaining third
of the vector is used as workspace by pcre_exec() while matching cap-	of the vector is used as workspace by pcre_exec() while matching cap-
turing subpatterns, and is not available for passing back information.	turing subpatterns, and is not available for passing back information.
The number passed in ovecsize should always be a multiple of three. If	The number passed in ovecsize should always be a multiple of three. If
it is not, it is rounded down.	it is not, it is rounded down.

When a match is successful, information about captured substrings is	When a match is successful, information about captured substrings is
returned in pairs of integers, starting at the beginning of ovector,	returned in pairs of integers, starting at the beginning of ovector,
and continuing up to two-thirds of its length at the most. The first	and continuing up to two-thirds of its length at the most. The first
element of each pair is set to the byte offset of the first character	element of each pair is set to the offset of the first character in a
in a substring, and the second is set to the byte offset of the first	substring, and the second is set to the offset of the first character
character after the end of a substring. Note: these values are always	after the end of a substring. These values are always data unit off-
byte offsets, even in UTF-8 mode. They are not character counts.	sets, even in UTF mode. They are byte offsets in the 8-bit library,
	16-bit data item offsets in the 16-bit library, and 32-bit data item
	offsets in the 32-bit library. Note: they are not character counts.

The first pair of integers, ovector[0] and ovector[1], identify the	The first pair of integers, ovector[0] and ovector[1], identify the
portion of the subject string matched by the entire pattern. The next	portion of the subject string matched by the entire pattern. The next
pair is used for the first capturing subpattern, and so on. The value	pair is used for the first capturing subpattern, and so on. The value
returned by pcre_exec() is one more than the highest numbered pair that	returned by pcre_exec() is one more than the highest numbered pair that
has been set. For example, if two substrings have been captured, the	has been set. For example, if two substrings have been captured, the
returned value is 3. If there are no capturing subpatterns, the return	returned value is 3. If there are no capturing subpatterns, the return
value from a successful match is 1, indicating that just the first pair	value from a successful match is 1, indicating that just the first pair
of offsets has been set.	of offsets has been set.

If a capturing subpattern is matched repeatedly, it is the last portion	If a capturing subpattern is matched repeatedly, it is the last portion
of the string that it matched that is returned.	of the string that it matched that is returned.

If the vector is too small to hold all the captured substring offsets,	If the vector is too small to hold all the captured substring offsets,
it is used as far as possible (up to two-thirds of its length), and the	it is used as far as possible (up to two-thirds of its length), and the
function returns a value of zero. If neither the actual string matched	function returns a value of zero. If neither the actual string matched
not any captured substrings are of interest, pcre_exec() may be called	nor any captured substrings are of interest, pcre_exec() may be called
with ovector passed as NULL and ovecsize as zero. However, if the pat-	with ovector passed as NULL and ovecsize as zero. However, if the pat-
tern contains back references and the ovector is not big enough to	tern contains back references and the ovector is not big enough to
remember the related substrings, PCRE has to get additional memory for	remember the related substrings, PCRE has to get additional memory for
use during matching. Thus it is usually advisable to supply an ovector	use during matching. Thus it is usually advisable to supply an ovector
of reasonable size.	of reasonable size.

There are some cases where zero is returned (indicating vector over-	There are some cases where zero is returned (indicating vector over-
flow) when in fact the vector is exactly the right size for the final	flow) when in fact the vector is exactly the right size for the final
match. For example, consider the pattern	match. For example, consider the pattern

(a)(?:(b)c\|bd)	(a)(?:(b)c\|bd)

If a vector of 6 elements (allowing for only 1 captured substring) is	If a vector of 6 elements (allowing for only 1 captured substring) is
given with subject string "abd", pcre_exec() will try to set the second	given with subject string "abd", pcre_exec() will try to set the second
captured string, thereby recording a vector overflow, before failing to	captured string, thereby recording a vector overflow, before failing to
match "c" and backing up to try the second alternative. The zero	match "c" and backing up to try the second alternative. The zero
return, however, does correctly indicate that the maximum number of	return, however, does correctly indicate that the maximum number of
slots (namely 2) have been filled. In similar cases where there is tem-	slots (namely 2) have been filled. In similar cases where there is tem-
porary overflow, but the final number of used slots is actually less	porary overflow, but the final number of used slots is actually less
than the maximum, a non-zero value is returned.	than the maximum, a non-zero value is returned.

The pcre_fullinfo() function can be used to find out how many capturing	The pcre_fullinfo() function can be used to find out how many capturing
subpatterns there are in a compiled pattern. The smallest size for	subpatterns there are in a compiled pattern. The smallest size for
ovector that will allow for n captured substrings, in addition to the	ovector that will allow for n captured substrings, in addition to the
offsets of the substring matched by the whole pattern, is (n+1)*3.	offsets of the substring matched by the whole pattern, is (n+1)*3.

It is possible for capturing subpattern number n+1 to match some part	It is possible for capturing subpattern number n+1 to match some part
of the subject when subpattern n has not been used at all. For example,	of the subject when subpattern n has not been used at all. For example,
if the string "abc" is matched against the pattern (a\|(z))(bc) the	if the string "abc" is matched against the pattern (a\|(z))(bc) the
return from the function is 4, and subpatterns 1 and 3 are matched, but	return from the function is 4, and subpatterns 1 and 3 are matched, but
2 is not. When this happens, both values in the offset pairs corre-	2 is not. When this happens, both values in the offset pairs corre-
sponding to unused subpatterns are set to -1.	sponding to unused subpatterns are set to -1.

Offset values that correspond to unused subpatterns at the end of the	Offset values that correspond to unused subpatterns at the end of the
expression are also set to -1. For example, if the string "abc" is	expression are also set to -1. For example, if the string "abc" is
matched against the pattern (abc)(x(yz)?)? subpatterns 2 and 3 are not	matched against the pattern (abc)(x(yz)?)? subpatterns 2 and 3 are not
matched. The return from the function is 2, because the highest used	matched. The return from the function is 2, because the highest used
capturing subpattern number is 1, and the offsets for for the second	capturing subpattern number is 1, and the offsets for for the second
and third capturing subpatterns (assuming the vector is large enough,	and third capturing subpatterns (assuming the vector is large enough,
of course) are set to -1.	of course) are set to -1.

Note: Elements in the first two-thirds of ovector that do not corre-	Note: Elements in the first two-thirds of ovector that do not corre-
spond to capturing parentheses in the pattern are never changed. That	spond to capturing parentheses in the pattern are never changed. That
is, if a pattern contains n capturing parentheses, no more than ovec-	is, if a pattern contains n capturing parentheses, no more than ovec-
tor[0] to ovector[2n+1] are set by pcre_exec(). The other elements (in	tor[0] to ovector[2n+1] are set by pcre_exec(). The other elements (in
the first two-thirds) retain whatever values they previously had.	the first two-thirds) retain whatever values they previously had.

Some convenience functions are provided for extracting the captured	Some convenience functions are provided for extracting the captured
substrings as separate strings. These are described below.	substrings as separate strings. These are described below.

Error return values from pcre_exec()	Error return values from pcre_exec()

If pcre_exec() fails, it returns a negative number. The following are	If pcre_exec() fails, it returns a negative number. The following are
defined in the header file:	defined in the header file:

PCRE_ERROR_NOMATCH (-1)	PCRE_ERROR_NOMATCH (-1)
Line 2420 MATCHING A PATTERN: THE TRADITIONAL FUNCTION	Line 3585 MATCHING A PATTERN: THE TRADITIONAL FUNCTION

PCRE_ERROR_NULL (-2)	PCRE_ERROR_NULL (-2)

Either code or subject was passed as NULL, or ovector was NULL and	Either code or subject was passed as NULL, or ovector was NULL and
ovecsize was not zero.	ovecsize was not zero.

PCRE_ERROR_BADOPTION (-3)	PCRE_ERROR_BADOPTION (-3)
Line 2429 MATCHING A PATTERN: THE TRADITIONAL FUNCTION	Line 3594 MATCHING A PATTERN: THE TRADITIONAL FUNCTION

PCRE_ERROR_BADMAGIC (-4)	PCRE_ERROR_BADMAGIC (-4)

PCRE stores a 4-byte "magic number" at the start of the compiled code,	PCRE stores a 4-byte "magic number" at the start of the compiled code,
to catch the case when it is passed a junk pointer and to detect when a	to catch the case when it is passed a junk pointer and to detect when a
pattern that was compiled in an environment of one endianness is run in	pattern that was compiled in an environment of one endianness is run in
an environment with the other endianness. This is the error that PCRE	an environment with the other endianness. This is the err an environment with the other endianness. This is the error that PCRE
gives when the magic number is not present.	gives when the magic number is not present.

PCRE_ERROR_UNKNOWN_OPCODE (-5)	PCRE_ERROR_UNKNOWN_OPCODE (-5)

While running the pattern match, an unknown item was encountered in the	While running the pattern match, an unknown item was encountered in the
compiled pattern. This error could be caused by a bug in PCRE or by	compiled pattern. This error could be caused by a bug in PCRE or by
overwriting of the compiled pattern.	overwriting of the compiled pattern.

PCRE_ERROR_NOMEMORY (-6)	PCRE_ERROR_NOMEMORY (-6)

If a pattern contains back references, but the ovector that is passed	If a pattern contains back references, but the ovector that is passed
to pcre_exec() is not big enough to remember the referenced substrings,	to pcre_exec() is not big enough to remember the referenced substrings,
PCRE gets a block of memory at the start of matching to use for this	PCRE gets a block of memory at the start of matching to use for this
purpose. If the call via pcre_malloc() fails, this error is given. The	purpose. If the call via pcre_malloc() fails, this error is given. The
memory is automatically freed at the end of matching.	memory is automatically freed at the end of matching.

This error is also given if pcre_stack_malloc() fails in pcre_exec().	This error is also given if pcre_stack_malloc() fails in pcre_exec().
This can happen only when PCRE has been compiled with --disable-stack-	This can happen only when PCRE has been compiled with --disable-stack-
for-recursion.	for-recursion.

PCRE_ERROR_NOSUBSTRING (-7)	PCRE_ERROR_NOSUBSTRING (-7)

This error is used by the pcre_copy_substring(), pcre_get_substring(),	This error is used by the pcre_copy_substring(), pcre_get_substring(),
and pcre_get_substring_list() functions (see below). It is never	and pcre_get_substring_list() functions (see below). It is never
returned by pcre_exec().	returned by pcre_exec().

PCRE_ERROR_MATCHLIMIT (-8)	PCRE_ERROR_MATCHLIMIT (-8)

The backtracking limit, as specified by the match_limit field in a	The backtracking limit, as specified by the match_limit field in a
pcre_extra structure (or defaulted) was reached. See the description	pcre_extra structure (or defaulted) was reached. See the description
above.	above.

PCRE_ERROR_CALLOUT (-9)	PCRE_ERROR_CALLOUT (-9)

This error is never generated by pcre_exec() itself. It is provided for	This error is never generated by pcre_exec() itself. It is provided for
use by callout functions that want to yield a distinctive error code.	use by callout functions that want to yield a distinctive error code.
See the pcrecallout documentation for details.	See the pcrecallout documentation for details.

PCRE_ERROR_BADUTF8 (-10)	PCRE_ERROR_BADUTF8 (-10)

A string that contains an invalid UTF-8 byte sequence was passed as a	A string that contains an invalid UTF-8 byte sequence was passed as a
subject, and the PCRE_NO_UTF8_CHECK option was not set. If the size of	subject, and the PCRE_NO_UTF8_CHECK option was not set. If the size of
the output vector (ovecsize) is at least 2, the byte offset to the	the output vector (ovecsize) is at least 2, the byte offset to the
start of the the invalid UTF-8 character is placed in the first ele-	start of the the invalid UTF-8 character is placed in the first ele-
ment, and a reason code is placed in the second element. The reason	ment, and a reason code is placed in the second element. The reason
codes are listed in the following section. For backward compatibility,	codes are listed in the following section. For backward compatibility,
if PCRE_PARTIAL_HARD is set and the problem is a truncated UTF-8 char-	if PCRE_PARTIAL_HARD is set and the problem is a truncated UTF-8 char-
acter at the end of the subject (reason codes 1 to 5),	acter at the end of the subject (reason codes 1 to 5),
PCRE_ERROR_SHORTUTF8 is returned instead of PCRE_ERROR_BADUTF8.	PCRE_ERROR_SHORTUTF8 is returned instead of PCRE_ERROR_BADUTF8.

PCRE_ERROR_BADUTF8_OFFSET (-11)	PCRE_ERROR_BADUTF8_OFFSET (-11)

The UTF-8 byte sequence that was passed as a subject was checked and	The UTF-8 byte sequence that was passed as a subject was checked and
found to be valid (the PCRE_NO_UTF8_CHECK option was not set), but the	found to be valid (the PCRE_NO_UTF8_CHECK option was not set), but the
value of startoffset did not point to the beginning of a UTF-8 charac-	value of startoffset did not point to the beginning of a UTF-8 charac-
ter or the end of the subject.	ter or the end of the subject.

PCRE_ERROR_PARTIAL (-12)	PCRE_ERROR_PARTIAL (-12)

The subject string did not match, but it did match partially. See the	The subject string did not match, but it did match partiall The subject string did not match, but it did match partially. See the
pcrepartial documentation for details of partial matching.	pcrepartial documentation for details of partial matching.

PCRE_ERROR_BADPARTIAL (-13)	PCRE_ERROR_BADPARTIAL (-13)

This code is no longer in use. It was formerly returned when the	This code is no longer in use. It was formerly returned when the
PCRE_PARTIAL option was used with a compiled pattern containing items	PCRE_PARTIAL option was used with a compiled pattern containing items
that were not supported for partial matching. From release 8.00	that were not supported for partial matching. From release 8.00
onwards, there are no restrictions on partial matching.	onwards, there are no restrictions on partial matching.

PCRE_ERROR_INTERNAL (-14)	PCRE_ERROR_INTERNAL (-14)

An unexpected internal error has occurred. This error could be caused	An unexpected internal error has occurred. This error could be caused
by a bug in PCRE or by overwriting of the compiled pattern.	by a bug in PCRE or by overwriting of the compiled pattern.

PCRE_ERROR_BADCOUNT (-15)	PCRE_ERROR_BADCOUNT (-15)
Line 2514 MATCHING A PATTERN: THE TRADITIONAL FUNCTION	Line 3679 MATCHING A PATTERN: THE TRADITIONAL FUNCTION
PCRE_ERROR_RECURSIONLIMIT (-21)	PCRE_ERROR_RECURSIONLIMIT (-21)

The internal recursion limit, as specified by the match_limit_recursion	The internal recursion limit, as specified by the match_limit_recursion
field in a pcre_extra structure (or defaulted) was reached. See the	field in a pcre_extra structure (or defaulted) was reached. See the
description above.	description above.

PCRE_ERROR_BADNEWLINE (-23)	PCRE_ERROR_BADNEWLINE (-23)
Line 2528 MATCHING A PATTERN: THE TRADITIONAL FUNCTION	Line 3693 MATCHING A PATTERN: THE TRADITIONAL FUNCTION

PCRE_ERROR_SHORTUTF8 (-25)	PCRE_ERROR_SHORTUTF8 (-25)

This error is returned instead of PCRE_ERROR_BADUTF8 when the subject	This error is returned instead of PCRE_ERROR_BADUTF8 when the subject
string ends with a truncated UTF-8 character and the PCRE_PARTIAL_HARD	string ends with a truncated UTF-8 character and the PCRE_PARTIAL_HARD
option is set. Information about the failure is returned as for	option is set. Information about the failure is returned as for
PCRE_ERROR_BADUTF8. It is in fact sufficient to detect this case, but	PCRE_ERROR_BADUTF8. It is in fact sufficient to detect this case, but
this special error code for PCRE_PARTIAL_HARD precedes the implementa-	this special error code for PCRE_PARTIAL_HARD precedes the implementa-
tion of returned information; it is retained for backwards compatibil-	tion of returned information; it is retained for backwards compatibil-
ity.	ity.

PCRE_ERROR_RECURSELOOP (-26)	PCRE_ERROR_RECURSELOOP (-26)

This error is returned when pcre_exec() detects a recursion loop within	This error is returned when pcre_exec() detects a recursion loop within
the pattern. Specifically, it means that either the whole pattern or a	the pattern. Specifically, it means that either the whole pattern or a
subpattern has been called recursively for the second time at the same	subpattern has been called recursively for the second time at the same
position in the subject string. Some simple patterns that might do this	position in the subject string. Some simple patterns that might do this
are detected and faulted at compile time, but more complicated cases,	are detected and faulted at compile time, but more complicate are detected and faulted at compile time, but more complicate
in particular mutual recursions between two different subpatterns, can-	in particular mutual recursions between two different subpatterns, can-
not be detected until run time.	not be detected until run time.

PCRE_ERROR_JIT_STACKLIMIT (-27)	PCRE_ERROR_JIT_STACKLIMIT (-27)

	This error is returned when a pattern that was successfully studied
	using a JIT compile option is being matched, but the memory available
	for the just-in-time processing stack is not large enough. See the
	pcrejit documentation for more details.

	PCRE_ERROR_BADMODE (-28)

	This error is given if a pattern that was compiled by the 8-bit library
	is passed to a 16-bit or 32-bit library function, or vice versa.

	PCRE_ERROR_BADENDIANNESS (-29)

	This error is given if a pattern that was compiled and saved is
	reloaded on a host with different endianness. The utility function
	pcre_pattern_to_host_byte_order() can be used to convert such a pattern
	so that it runs on the new host.

	PCRE_ERROR_JIT_BADOPTION

This error is returned when a pattern that was successfully studied	This error is returned when a pattern that was successfully studied
using the PCRE_STUDY_JIT_COMPILE option is being matched, but the mem-	using a JIT compile option is being matched, but the matching mode
ory available for the just-in-time processing stack is not large	(partial or complete match) does not correspond to any JIT compilation
enough. See the pcrejit documentation for more details.	mode. When the JIT fast path function is used, this error may be also
	given for invalid options. See the pcrejit documentation for more
	details.

Error numbers -16 to -20 and -22 are not used by pcre_exec().	PCRE_ERROR_BADLENGTH (-32)

	This error is given if pcre_exec() is called with a negative value for
	the length argument.

	Error numbers -16 to -20, -22, and 30 are not used by pcre_exec().

Reason codes for invalid UTF-8 strings	Reason codes for invalid UTF-8 strings

	This section applies only to the 8-bit library. The corresponding
	information for the 16-bit and 32-bit libraries is given in the pcre16
	and pcre32 pages.

When pcre_exec() returns either PCRE_ERROR_BADUTF8 or PCRE_ERROR_SHORT-	When pcre_exec() returns either PCRE_ERROR_BADUTF8 or PCRE_ERROR_SHORT-
UTF8, and the size of the output vector (ovecsize) is at least 2, the	UTF8, and the size of the output vector (ovecsize) is at least 2, the
offset of the start of the invalid UTF-8 character is placed in the	offset of the start of the invalid UTF-8 character is placed in the
first output vector element (ovector[0]) and a reason code is placed in	first output vector element (ovector[0]) and a reason code is placed in
the second element (ovector[1]). The reason codes are given names in	the second element (ovector[1]). The reason codes are given names in
the pcre.h header file:	the pcre.h header file:

PCRE_UTF8_ERR1	PCRE_UTF8_ERR1
Line 2570 MATCHING A PATTERN: THE TRADITIONAL FUNCTION	Line 3765 MATCHING A PATTERN: THE TRADITIONAL FUNCTION
PCRE_UTF8_ERR4	PCRE_UTF8_ERR4
PCRE_UTF8_ERR5	PCRE_UTF8_ERR5

The string ends with a truncated UTF-8 character; the code specifies	The string ends with a truncated UTF-8 character; the code specifies
how many bytes are missing (1 to 5). Although RFC 3629 restricts UTF-8	how many bytes are missing (1 to 5). Although RFC 3629 restricts UTF-8
characters to be no longer than 4 bytes, the encoding scheme (origi-	characters to be no longer than 4 bytes, the encoding scheme (origi-
nally defined by RFC 2279) allows for up to 6 bytes, and this is	nally defined by RFC 2279) allows for up to 6 bytes, and this is
checked first; hence the possibility of 4 or 5 missing bytes.	checked first; hence the possibility of 4 or 5 missing bytes.

PCRE_UTF8_ERR6	PCRE_UTF8_ERR6
Line 2583 MATCHING A PATTERN: THE TRADITIONAL FUNCTION	Line 3778 MATCHING A PATTERN: THE TRADITIONAL FUNCTION
PCRE_UTF8_ERR10	PCRE_UTF8_ERR10

The two most significant bits of the 2nd, 3rd, 4th, 5th, or 6th byte of	The two most significant bits of the 2nd, 3rd, 4th, 5th, or 6th byte of
the character do not have the binary value 0b10 (that is, either the	the character do not have the binary value 0b10 (that is, either the
most significant bit is 0, or the next bit is 1).	most significant bit is 0, or the next bit is 1).

PCRE_UTF8_ERR11	PCRE_UTF8_ERR11
PCRE_UTF8_ERR12	PCRE_UTF8_ERR12

A character that is valid by the RFC 2279 rules is either 5 or 6 bytes	A character that is valid by the RFC 2279 rules is either 5 or 6 bytes
long; these code points are excluded by RFC 3629.	long; these code points are excluded by RFC 3629.

PCRE_UTF8_ERR13	PCRE_UTF8_ERR13

A 4-byte character has a value greater than 0x10fff; these code points	A 4-byte character has a value greater than 0x10fff; these code points
are excluded by RFC 3629.	are excluded by RFC 3629.

PCRE_UTF8_ERR14	PCRE_UTF8_ERR14

A 3-byte character has a value in the range 0xd800 to 0xdfff; this	A 3-byte character has a value i A 3-byte character has a value i
range of code points are reserved by RFC 3629 for use with UTF-16, and	range of code points are reserved by RFC 3629 for use with UTF-16, and
so are excluded from UTF-8.	so are excluded from UTF-8.

PCRE_UTF8_ERR15	PCRE_UTF8_ERR15
Line 2609 MATCHING A PATTERN: THE TRADITIONAL FUNCTION	Line 3804 MATCHING A PATTERN: THE TRADITIONAL FUNCTION
PCRE_UTF8_ERR18	PCRE_UTF8_ERR18
PCRE_UTF8_ERR19	PCRE_UTF8_ERR19

A 2-, 3-, 4-, 5-, or 6-byte character is "overlong", that is, it codes	A 2-, 3-, 4-, 5-, or 6-byte character is "overlong", that is, it codes
for a value that can be represented by fewer bytes, which is invalid.	for a value that can be represented by fewer bytes, which is invalid.
For example, the two bytes 0xc0, 0xae give the value 0x2e, whose cor-	For example, the two bytes 0xc0, 0xae give the value 0x2e, whose cor-
rect coding uses just one byte.	rect coding uses just one byte.

PCRE_UTF8_ERR20	PCRE_UTF8_ERR20

The two most significant bits of the first byte of a character have the	The two most significant bits of the first byte of a character have the
binary value 0b10 (that is, the most significant bit is 1 and the sec-	binary value 0b10 (that is, the most significant bit is 1 and the sec-
ond is 0). Such a byte can only validly occur as the second or subse-	ond is 0). Such a byte can only validly occur as the second or subse-
quent byte of a multi-byte character.	quent byte of a multi-byte character.

PCRE_UTF8_ERR21	PCRE_UTF8_ERR21

The first byte of a character has the value 0xfe or 0xff. These values	The first byte of a character has the value 0xfe or 0xff. These values
can never occur in a valid UTF-8 string.	can never occur in a valid UTF-8 string.

	PCRE_UTF8_ERR22

	This error code was formerly used when the presence of a so-called
	"non-character" caused an error. Unicode corrigendum #9 makes it clear
	that such characters should not cause a string to be rejected, and so
	this code is no longer in use and is never returned.


EXTRACTING CAPTURED SUBSTRINGS BY NUMBER	EXTRACTING CAPTURED SUBSTRINGS BY NUMBER

int pcre_copy_substring(const char subject, int ovector,	int pcre_copy_substring(const char subject, int ovector,
Line 2824 FINDING ALL POSSIBLE MATCHES	Line 4026 FINDING ALL POSSIBLE MATCHES
matches, pcre_exec() will yield PCRE_ERROR_NOMATCH.	matches, pcre_exec() will yield PCRE_ERROR_NOMATCH.


	OBTAINING AN ESTIMATE OF STACK USAGE

	Matching certain patterns using pcre_exec() can use a lot of process
	stack, which in certain environments can be rather limited in size.
	Some users find it helpful to have an estimate of the amount of stack
	that is used by pcre_exec(), to help them set recursion limits, as
	described in the pcrestack documentation. The estimate that is output
	by pcretest when called with the -m and -C options is obtained by call-
	ing pcre_exec with the values NULL, NULL, NULL, -999, and -999 for its
	first five arguments.

	Normally, if its first argument is NULL, pcre_exec() immediately
	returns the negative error code PCRE_ERROR_NULL, but with this special
	combination of arguments, it returns instead a negative number whose
	absolute value is the approximate stack frame size in bytes. (A nega-
	tive number is used so that it is clear that no match has happened.)
	The value is approximate because in some cases, recursive calls to
	pcre_exec() occur when there are one or two additional variables on the
	stack.

	If PCRE has been compiled to use the heap instead of the stack for
	recursion, the value returned is the size of each block that is
	obtained from the heap.


MATCHING A PATTERN: THE ALTERNATIVE FUNCTION	MATCHING A PATTERN: THE ALTERNATIVE FUNCTION

int pcre_dfa_exec(const pcre code, const pcre_extra extra,	int pcre_dfa_exec(const pcre code, const pcre_extra extra,
Line 2950 MATCHING A PATTERN: THE ALTERNATIVE FUNCTION	Line 4177 MATCHING A PATTERN: THE ALTERNATIVE FUNCTION
filled with the longest matches. Unlike pcre_exec(), pcre_dfa_exec()	filled with the longest matches. Unlike pcre_exec(), pcre_dfa_exec()
can use the entire ovector for returning matched strings.	can use the entire ovector for returning matched strings.

	NOTE: PCRE's "auto-possessification" optimization usually applies to
	character repeats at the end of a pattern (as well as internally). For
	example, the pattern "a\d+" is compiled as if it were "a\d++" because
	there is no point even considering the possibility of backtracking into
	the repeated digits. For DFA matching, this means that only one possi-
	ble match is found. If you really do want multiple matches in such
	cases, either use an ungreedy repeat ("a\d+?") or set the
	PCRE_NO_AUTO_POSSESS option when compiling.

Error returns from pcre_dfa_exec()	Error returns from pcre_dfa_exec()

The pcre_dfa_exec() function returns a negative number when it fails.	The pcre_dfa_exec() function returns a negative number when it fails.
Many of the errors are the same as for pcre_exec(), and these are	Many of the errors are the same as for pcre_exec(), and these are
described above. There are in addition the following errors that are	described above. There are in addition the following errors that are
specific to pcre_dfa_exec():	specific to pcre_dfa_exec():

PCRE_ERROR_DFA_UITEM (-16)	PCRE_ERROR_DFA_UITEM (-16)

This return is given if pcre_dfa_exec() encounters an item in the pat-	This return is given if pcre_dfa_exec() encounters an item in the pat-
tern that it does not support, for instance, the use of \C or a back	tern that it does not support, for instance, the use of \C or a back
reference.	reference.

PCRE_ERROR_DFA_UCOND (-17)	PCRE_ERROR_DFA_UCOND (-17)

This return is given if pcre_dfa_exec() encounters a condition item	This return is given if pcre_dfa_exec() encounters a condition item
that uses a back reference for the condition, or a test for recursion	that uses a back reference for the condition, or a test for recursion
in a specific group. These are not supported.	in a specific group. These are not supported.

PCRE_ERROR_DFA_UMLIMIT (-18)	PCRE_ERROR_DFA_UMLIMIT (-18)

This return is given if pcre_dfa_exec() is called with an extra block	This return is given if pcre_dfa_exec() is called with an extra block
that contains a setting of the match_limit or match_limit_recursion	that contains a setting of the match_limit or match_limit_recursion
fields. This is not supported (these fields are meaningless for DFA	fields. This is not supported (these fields are meaningless for DFA
matching).	matching).

PCRE_ERROR_DFA_WSSIZE (-19)	PCRE_ERROR_DFA_WSSIZE (-19)

This return is given if pcre_dfa_exec() runs out of space in the	This return is given if pcre_dfa_exec() runs out of space in the
workspace vector.	workspace vector.

PCRE_ERROR_DFA_RECURSE (-20)	PCRE_ERROR_DFA_RECURSE (-20)

When a recursive subpattern is processed, the matching function calls	When a recursive subpattern is processed, the matching function calls
itself recursively, using private vectors for ovector and workspace.	itself recursively, using private vectors for ovector and workspace.
This error is given if the output vector is not large enough. This	This error is given if the output vector is not large enough. This
should be extremely rare, as a vector of size 1000 is used.	should be extremely rare, as a vector of size 1000 is used.

	PCRE_ERROR_DFA_BADRESTART (-30)

	When pcre_dfa_exec() is called with the PCRE_DFA_RESTART option, some
	plausibility checks are made on the contents of the workspace, which
	should contain data about the previous partial match. If any of these
	checks fail, this error is given.


SEE ALSO	SEE ALSO

pcrebuild(3), pcrecallout(3), pcrecpp(3)(3), pcrematching(3), pcrepar-	pcre16(3), pcre32(3), pcrebuild(3), pcrecallout(3), pcrecpp(3)(3),
tial(3), pcreposix(3), pcreprecompile(3), pcresample(3), pcrestack(3).	pcrematching(3), pcrepartial(3), pcreposix(3), pcreprecompile(3), pcre-
	sample(3), pcrestack(3).


AUTHOR	AUTHOR
Line 3004 AUTHOR	Line 4248 AUTHOR

REVISION	REVISION

Last updated: 02 December 2011	Last updated: 12 November 2013
Copyright (c) 1997-2011 University of Cambridge.	Copyright (c) 1997-2013 University of Cambridge.
------------------------------------------------------------------------------	------------------------------------------------------------------------------


PCRECALLOUT(3) PCRECALLOUT(3)	PCRECALLOUT(3) Library Functions Manual PCRECALLOUT(3)



NAME	NAME
PCRE - Perl-compatible regular expressions	PCRE - Perl-compatible regular expressions

	SYNOPSIS

PCRE CALLOUTS	#include <pcre.h>

int (pcre_callout)(pcre_callout_block );	int (pcre_callout)(pcre_callout_block );

	int (pcre16_callout)(pcre16_callout_block );

	int (pcre32_callout)(pcre32_callout_block );


	DESCRIPTION

PCRE provides a feature called "callout", which is a means of temporar-	PCRE provides a feature called "callout", which is a means of temporar-
ily passing control to the caller of PCRE in the middle of pattern	ily passing control to the caller of PCRE in the middle of pattern
matching. The caller of PCRE provides an external function by putting	matching. The caller of PCRE provides an external function by putting
its entry point in the global variable pcre_callout. By default, this	its entry point in the global variable pcre_callout (pcre16_callout for
variable contains NULL, which disables all calling out.	the 16-bit library, pcre32_callout for the 32-bit library). By default,
	this variable contains NULL, which disables all calling out.

Within a regular expression, (?C) indicates the points at which the	Within a regular expression, (?C) indicates the points at which the
external function is to be called. Different callout points can be	external function is to be called. Different callout points can be
identified by putting a number less than 256 after the letter C. The	identified by putting a number less than 256 after the letter C. The
default value is zero. For example, this pattern has two callout	default value is zero. For example, this pattern has two callout
points:	points:

(?C1)abc(?C2)def	(?C1)abc(?C2)def

If the PCRE_AUTO_CALLOUT option bit is set when pcre_compile() or	If the PCRE_AUTO_CALLOUT option bit is set when a pattern is compiled,
pcre_compile2() is called, PCRE automatically inserts callouts, all	PCRE automatically inserts callouts, all with number 255, before each
with number 255, before each item in the pattern. For example, if	item in the pattern. For example, if PCRE_AUTO_CALLOUT is used with the
PCRE_AUTO_CALLOUT is used with the pattern	pattern

A(\d{2}\|--)	A(\d{2}\|--)

Line 3045 PCRE CALLOUTS	Line 4299 PCRE CALLOUTS

(?C255)A(?C255)((?C255)\d{2}(?C255)\|(?C255)-(?C255)-(?C255))(?C255)	(?C255)A(?C255)((?C255)\d{2}(?C255)\|(?C255)-(?C255)-(?C255))(?C255)

Notice that there is a callout before and after each parenthesis and	Notice that there is a callout before and after each parenthesis and
alternation bar. Automatic callouts can be used for tracking the	alternation bar. If the pattern contains a conditional group whose con-
progress of pattern matching. The pcretest command has an option that	dition is an assertion, an automatic callout is inserted immediately
sets automatic callouts; when it is used, the output indicates how the	before the condition. Such a callout may also be inserted explicitly,
pattern is matched. This is useful information when you are trying to	for example:
optimize the performance of a particular pattern.

The use of callouts in a pattern makes it ineligible for optimization	(?(?C9)(?=a)ab\|de)
by the just-in-time compiler. Studying such a pattern with the
PCRE_STUDY_JIT_COMPILE option always fails.

	This applies only to assertion conditions (because they are themselves
	independent groups).

	Automatic callouts can be used for tracking the progress of pattern
	matching. The pcretest program has a pattern qualifier (/C) that sets
	automatic callouts; when it is used, the output indicates how the pat-
	tern is being matched. This is useful information when you are trying
	to optimize the performance of a particular pattern.


MISSING CALLOUTS	MISSING CALLOUTS

You should be aware that, because of optimizations in the way PCRE	You should be aware that, because of optimizations in the way PCRE com-
matches patterns by default, callouts sometimes do not happen. For	piles and matches patterns, callouts sometimes do not happen exactly as
example, if the pattern is	you might expect.

	At compile time, PCRE "auto-possessifies" repeated items when it knows
	that what follows cannot be part of the repeat. For example, a+[bc] is
	compiled as if it were a++[bc]. The pcretest output when this pattern
	is anchored and then applied with automatic callouts to the string
	"aaaa" is:

	--->aaaa
	+0 ^ ^
	+1 ^ a+
	+3 ^ ^ [bc]
	No match

	This indicates that when matching [bc] fails, there is no backtracking
	into a+ and therefore the callouts that would be taken for the back-
	tracks do not occur. You can disable the auto-possessify feature by
	passing PCRE_NO_AUTO_POSSESS to pcre_compile(), or starting the pattern
	with (*NO_AUTO_POSSESS). If this is done in pcretest (using the /O
	qualifier), the output changes to this:

	--->aaaa
	+0 ^ ^
	+1 ^ a+
	+3 ^ ^ [bc]
	+3 ^ ^ [bc]
	+3 ^ ^ [bc]
	+3 ^^ [bc]
	No match

	This time, when matching [bc] fails, the matcher backtracks into a+ and
	tries again, repeatedly, until a+ itself fails.

	Other optimizations that provide fast "no match" results also affect
	callouts. For example, if the pattern is

ab(?C4)cd	ab(?C4)cd

PCRE knows that any matching string must contain the letter "d". If the	PCRE knows that any matching string must contain the letter "d". If the
Line 3076 MISSING CALLOUTS	Line 4370 MISSING CALLOUTS
patterns, if it has been scanned far enough.	patterns, if it has been scanned far enough.

You can disable these optimizations by passing the PCRE_NO_START_OPTI-	You can disable these optimizations by passing the PCRE_NO_START_OPTI-
MIZE option to pcre_compile(), pcre_exec(), or pcre_dfa_exec(), or by	MIZE option to the matching function, or by starting the pattern with
starting the pattern with (*NO_START_OPT). This slows down the matching	(*NO_START_OPT). This slows down the matching process, but does ensure
process, but does ensure that callouts such as the example above are	that callouts such as the example above are obeyed.
obeyed.


THE CALLOUT INTERFACE	THE CALLOUT INTERFACE

During matching, when PCRE reaches a callout point, the external func-	During matching, when PCRE reaches a callout point, the external func-
tion defined by pcre_callout is called (if it is set). This applies to	tion defined by pcre_callout or pcre[16\|32]_callout is called (if it is
both the pcre_exec() and the pcre_dfa_exec() matching functions. The	set). This applies to both normal and DFA matching. The only argument
only argument to the callout function is a pointer to a pcre_callout	to the callout function is a pointer to a pcre_callout or
block. This structure contains the following fields:	pcre[16\|32]_callout block. These structures contains the following
	fields:

int version;	int version;
int callout_number;	int callout_number;
int *offset_vector;	int *offset_vector;
const char *subject;	const char *subject; (8-bit version)
int subject_length;	PCRE_SPTR16 subject; (16-bit version)
int start_match;	PCRE_SPTR32 subject; (32-bit version)
int current_position;	int subject_length;
int capture_top;	int start_match;
int capture_last;	int current_position;
void *callout_data;	int capture_top;
int pattern_position;	int capture_last;
int next_item_length;
const unsigned char *mark;	int pattern_position;
	int next_item_length;
	const unsigned char *mark; (8-bit version)
	const PCRE_UCHAR16 *mark; (16-bit version)
	const PCRE_UCHAR32 *mark; (32-bit version)

The version field is an integer containing the version number of the	The version field is an integer containing the version number of the
block format. The initial version was 0; the current version is 2. The	block format. The initial version was 0; the current version is 2. The
Line 3114 THE CALLOUT INTERFACE	Line 4412 THE CALLOUT INTERFACE
outs, and 255 for automatically generated callouts).	outs, and 255 for automatically generated callouts).

The offset_vector field is a pointer to the vector of offsets that was	The offset_vector field is a pointer to the vector of offsets that was
passed by the caller to pcre_exec() or pcre_dfa_exec(). When	passed by the caller to the matching function. When pcre_exec() or
pcre_exec() is used, the contents can be inspected in order to extract	pcre[16\|32]_exec() is used, the contents can be inspected, in order to
substrings that have been matched so far, in the same way as for	extract substrings that have been matched so far, in the same way as
extracting substrings after a match has completed. For pcre_dfa_exec()	for extracting substrings after a match has completed. For the DFA
this field is not useful.	matching functions, this field is not useful.

The subject and subject_length fields contain copies of the values that	The subject and subject_length fields contain copies of the values that
were passed to pcre_exec().	were passed to the matching function.

The start_match field normally contains the offset within the subject	The start_match field normally contains the offset within the subject
at which the current match attempt started. However, if the escape	at which the current match attempt started. However, if the escape
Line 3133 THE CALLOUT INTERFACE	Line 4431 THE CALLOUT INTERFACE
The current_position field contains the offset within the subject of	The current_position field contains the offset within the subject of
the current match pointer.	the current match pointer.

When the pcre_exec() function is used, the capture_top field contains	When the pcre_exec() or pcre[16\|32]_exec() is used, the capture_top
one more than the number of the highest numbered captured substring so	field contains one more than the number of the highest numbered cap-
far. If no substrings have been captured, the value of capture_top is	tured substring so far. If no substrings have been captured, the value
one. This is always the case when pcre_dfa_exec() is used, because it	of capture_top is one. This is always the case when the DFA functions
does not support captured substrings.	are used, because they do not support captured substrings.

The capture_last field contains the number of the most recently cap-	The capture_last field contains the number of the most recently cap-
tured substring. If no substrings have been captured, its value is -1.	tured substring. However, when a recursion exits, the value reverts to
This is always the case when pcre_dfa_exec() is used.	what it was outside the recursion, as do the values of all captured
	substrings. If no substrings have been captured, the value of cap-
	ture_last is -1. This is always the case for the DFA matching func-
	tions.

The callout_data field contains a value that is passed to pcre_exec()	The callout_data field contains a value that is passed to a matching
or pcre_dfa_exec() specifically so that it can be passed back in call-	function specifically so that it can be passed back in callouts. It is
outs. It is passed in the pcre_callout field of the pcre_extra data	passed in the callout_data field of a pcre_extra or pcre[16\|32]_extra
structure. If no such data was passed, the value of callout_data in a	data structure. If no such data was passed, the value of callout_data
pcre_callout block is NULL. There is a description of the pcre_extra	in a callout block is NULL. There is a description of the pcre_extra
structure in the pcreapi documentation.	structure in the pcreapi documentation.

The pattern_position field is present from version 1 of the pcre_call-	The pattern_position field is present from version 1 of the callout
out structure. It contains the offset to the next item to be matched in	structure. It contains the offset to the next item to be matched in the
the pattern string.	pattern string.

The next_item_length field is present from version 1 of the pcre_call-	The next_item_length field is present from version 1 of the callout
out structure. It contains the length of the next item to be matched in	structure. It contains the length of the next item to be matched in the
the pattern string. When the callout immediately precedes an alterna-	pattern string. When the callout immediately precedes an alternation
tion bar, a closing parenthesis, or the end of the pattern, the length	bar, a closing parenthesis, or the end of the pattern, the length is
is zero. When the callout precedes an opening parenthesis, the length	zero. When the callout precedes an opening parenthesis, the length is
is that of the entire subpattern.	that of the entire subpattern.

The pattern_position and next_item_length fields are intended to help	The pattern_position and next_item_length fields are intended to help
in distinguishing between different automatic callouts, which all have	in distinguishing between different automatic callouts, which all have
the same callout number. However, they are set for all callouts.	the same callout number. However, they are set for all callouts.

The mark field is present from version 2 of the pcre_callout structure.	The mark field is present from version 2 of the callout structure. In
In callouts from pcre_exec() it contains a pointer to the zero-termi-	callouts from pcre_exec() or pcre[16\|32]_exec() it contains a pointer
nated name of the most recently passed (MARK), (PRUNE), or (*THEN)	to the zero-terminated name of the most recently passed (*MARK),
item in the match, or NULL if no such items have been passed. Instances	(PRUNE), or (THEN) item in the match, or NULL if no such items have
of (PRUNE) or (THEN) without a name do not obliterate a previous	been passed. Instances of (PRUNE) or (THEN) without a name do not
(*MARK). In callouts from pcre_dfa_exec() this field always contains	obliterate a previous (*MARK). In callouts from the DFA matching func-
NULL.	tions this field always contains NULL.


RETURN VALUES	RETURN VALUES

The external callout function returns an integer to PCRE. If the value	The external callout function returns an integer to PCRE. If the value
is zero, matching proceeds as normal. If the value is greater than	is zero, matching proceeds as normal. If the value is greater than
zero, matching fails at the current point, but the testing of other	zero, matching fails at the current point, but the testing of other
matching possibilities goes ahead, just as if a lookahead assertion had	matching possibilities goes ahead, just as if a lookahead assertion had
failed. If the value is less than zero, the match is abandoned, and	failed. If the value is less than zero, the match is abandoned, the
pcre_exec() or pcre_dfa_exec() returns the negative value.	matching function returns the negative value.

Negative values should normally be chosen from the set of	Negative values should normally be chosen from the set of
PCRE_ERROR_xxx values. In particular, PCRE_ERROR_NOMATCH forces a stan-	PCRE_ERROR_xxx values. In particular, PCRE_ERROR_NOMATCH forces a stan-
dard "no match" failure. The error number PCRE_ERROR_CALLOUT is	dard "no match" failure. The error number PCRE_ERROR_CALLOUT is
reserved for use by callout functions; it will never be used by PCRE	reserved for use by callout functions; it will never be used by PCRE
itself.	itself.


Line 3199 AUTHOR	Line 4500 AUTHOR

REVISION	REVISION

Last updated: 30 November 2011	Last updated: 12 November 2013
Copyright (c) 1997-2011 University of Cambridge.	Copyright (c) 1997-2013 University of Cambridge.
------------------------------------------------------------------------------	------------------------------------------------------------------------------


PCRECOMPAT(3) PCRECOMPAT(3)	PCRECOMPAT(3) Library Functions Manual PCRECOMPAT(3)



NAME	NAME
PCRE - Perl-compatible regular expressions	PCRE - Perl-compatible regular expressions


DIFFERENCES BETWEEN PCRE AND PERL	DIFFERENCES BETWEEN PCRE AND PERL

This document describes the differences in the ways that PCRE and Perl	This document describes the differences in the ways that PCRE and Perl
handle regular expressions. The differences described here are with	handle regular expressions. The differences described here are with
respect to Perl versions 5.10 and above.	respect to Perl versions 5.10 and above.

1. PCRE has only a subset of Perl's UTF-8 and Unicode support. Details	1. PCRE has only a subset of Perl's Unicode support. Details of what it
of what it does have are given in the pcreunicode page.	does have are given in the pcreunicode page.

2. PCRE allows repeat quantifiers only on parenthesized assertions, but	2. PCRE allows repeat quantifiers only on parenthesized assertions, but
they do not mean what you might think. For example, (?!a){3} does not	they do not mean what you might think. For example, (?!a){3} does not
Line 3229 DIFFERENCES BETWEEN PCRE AND PERL	Line 4530 DIFFERENCES BETWEEN PCRE AND PERL

3. Capturing subpatterns that occur inside negative lookahead asser-	3. Capturing subpatterns that occur inside negative lookahead asser-
tions are counted, but their entries in the offsets vector are never	tions are counted, but their entries in the offsets vector are never
set. Perl sets its numerical variables from any such patterns that are	set. Perl sometimes (but not always) sets its numerical variables from
matched before the assertion fails to match something (thereby succeed-	inside negative assertions.
ing), but only if the negative lookahead assertion contains just one
branch.

4. Though binary zero characters are supported in the subject string,	4. Though binary zero characters are supported in the subject string,
they are not allowed in a pattern string because it is passed as a nor-	they are not allowed in a pattern string because it is passed as a nor-
Line 3258 DIFFERENCES BETWEEN PCRE AND PERL	Line 4557 DIFFERENCES BETWEEN PCRE AND PERL
tion of Unicode characters, there is no need to implement the somewhat	tion of Unicode characters, there is no need to implement the somewhat
messy concept of surrogates."	messy concept of surrogates."

7. PCRE implements a simpler version of \X than Perl, which changed to	7. PCRE does support the \Q...\E escape for quoting substrings. Charac-
make \X match what Unicode calls an "extended grapheme cluster". This	ters in between are treated as literals. This is slightly different
is more complicated than an extended Unicode sequence, which is what	from Perl in that $ and @ are also handled as literals inside the
PCRE matches.	quotes. In Perl, they cause variable interpolation (but of course PCRE

8. PCRE does support the \Q...\E escape for quoting substrings. Charac-
ters in between are treated as literals. This is slightly different
from Perl in that $ and @ are also handled as literals inside the
quotes. In Perl, they cause variable interpolation (but of course PCRE
does not have variables). Note the following examples:	does not have variables). Note the following examples:

Pattern PCRE matches Perl matches	Pattern PCRE matches Perl matches
Line 3276 DIFFERENCES BETWEEN PCRE AND PERL	Line 4570 DIFFERENCES BETWEEN PCRE AND PERL
\Qabc\$xyz\E abc\$xyz abc\$xyz	\Qabc\$xyz\E abc\$xyz abc\$xyz
\Qabc\E\$\Qxyz\E abc$xyz abc$xyz	\Qabc\E\$\Qxyz\E abc$xyz abc$xyz

The \Q...\E sequence is recognized both inside and outside character	The \Q...\E sequence is recognized both inside and outside character
classes.	classes.

9. Fairly obviously, PCRE does not support the (?{code}) and (??{code})	8. Fairly obviously, PCRE does not support the (?{code}) and (??{code})
constructions. However, there is support for recursive patterns. This	constructions. However, there is support for recursive patterns. This
is not available in Perl 5.8, but it is in Perl 5.10. Also, the PCRE	is not available in Perl 5.8, but it is in Perl 5.10. Also, the PCRE
"callout" feature allows an external function to be called during pat-	"callout" feature allows an external function to be called during pat-
tern matching. See the pcrecallout documentation for details.	tern matching. See the pcrecallout documentation for details.

10. Subpatterns that are called as subroutines (whether or not recur-	9. Subpatterns that are called as subroutines (whether or not recur-
sively) are always treated as atomic groups in PCRE. This is like	sively) are always treated as atomic groups in PCRE. This is like
Python, but unlike Perl. Captured values that are set outside a sub-	Python, but unlike Perl. Captured values that are set outside a sub-
routine call can be reference from inside in PCRE, but not in Perl.	routine call can be reference from inside in PCRE, but not in Perl.
There is a discussion that explains these differences in more detail in	There is a discussion that explains these differences in more detail in
the section on recursion differences from Perl in the pcrepattern page.	the section on recursion differences from Perl in the pcrepattern page.

11. If (*THEN) is present in a group that is called as a subroutine,	10. If any of the backtracking control verbs are used in a subpattern
its action is limited to that group, even if the group does not contain	that is called as a subroutine (whether or not recursively), their
any \| characters.	effect is confined to that subpattern; it does not extend to the sur-
	rounding pattern. This is not always the case in Perl. In particular,
	if (*THEN) is present in a group that is called as a subroutine, its
	action is limited to that group, even if the group does not contain any
	\| characters. Note that such subpatterns are processed as anchored at
	the point where they are tested.

12. There are some differences that are concerned with the settings of	11. If a pattern contains more than one backtracking control verb, the
captured strings when part of a pattern is repeated. For example,	first one that is backtracked onto acts. For example, in the pattern
matching "aba" against the pattern /^(a(b)?)+$/ in Perl leaves $2	A(COMMIT)B(PRUNE)C a failure in B triggers (*COMMIT), but a failure
	in C triggers (*PRUNE). Perl's behaviour is more complex; in many cases
	it is the same as PCRE, but there are examples where it differs.

	12. Most backtracking verbs in assertions have their normal actions.
	They are not confined to the assertion.

	13. There are some differences that are concerned with the settings of
	captured strings when part of a pattern is repeated. For example,
	matching "aba" against the pattern /^(a(b)?)+$/ in Perl leaves $2
unset, but in PCRE it is set to "b".	unset, but in PCRE it is set to "b".

13. PCRE's handling of duplicate subpattern numbers and duplicate sub-	14. PCRE's handling of duplicate subpattern numbers and duplicate sub-
pattern names is not as general as Perl's. This is a consequence of the	pattern names is not as general as Perl's. This is a consequence of the
fact the PCRE works internally just with numbers, using an external ta-	fact the PCRE works internally just with numbers, using an external ta-
ble to translate between numbers and names. In particular, a pattern	ble to translate between numbers and names. In particular, a pattern
such as (?\|(?<a>A)\|(?<b)B), where the two capturing parentheses have	such as (?\|(?<a>A)\|(?<b)B), where the two capturing parentheses have
the same number but different names, is not supported, and causes an	the same number but different names, is not supported, and causes an
error at compile time. If it were allowed, it would not be possible to	error at compile time. If it were allowed, it would not be possible to
distinguish which parentheses matched, because both names map to cap-	distinguish which parentheses matched, because both names map to cap-
turing subpattern number 1. To avoid this confusing situation, an error	turing subpattern number 1. To avoid this confusing situation, an error
is given at compile time.	is given at compile time.

14. Perl recognizes comments in some places that PCRE does not, for	15. Perl recognizes comments in some places that PCRE does not, for
example, between the ( and ? at the start of a subpattern. If the /x	example, between the ( and ? at the start of a subpattern. If the /x
modifier is set, Perl allows whitespace between ( and ? but PCRE never	modifier is set, Perl allows white space between ( and ? (though cur-
does, even if the PCRE_EXTENDED option is set.	rent Perls warn that this is deprecated) but PCRE never does, even if
	the PCRE_EXTENDED option is set.

15. PCRE provides some extensions to the Perl regular expression facil-	16. Perl, when in warning mode, gives warnings for character classes
	such as [A-\d] or [a-[:digit:]]. It then treats the hyphens as liter-
	als. PCRE has no warning features, so it gives an error in these cases
	because they are almost certainly user mistakes.

	17. In PCRE, the upper/lower case character properties Lu and Ll are
	not affected when case-independent matching is specified. For example,
	\p{Lu} always matches an upper case letter. I think Perl has changed in
	this respect; in the release at the time of writing (5.16), \p{Lu} and
	\p{Ll} match all letters, regardless of case, when case independence is
	specified.

	18. PCRE provides some extensions to the Perl regular expression facil-
ities. Perl 5.10 includes new features that are not in earlier ver-	ities. Perl 5.10 includes new features that are not in earlier ver-
sions of Perl, some of which (such as named parentheses) have been in	sions of Perl, some of which (such as named parentheses) have been in
PCRE for some time. This list is with respect to Perl 5.10:	PCRE for some time. This list is with respect to Perl 5.10:
Line 3356 DIFFERENCES BETWEEN PCRE AND PERL	Line 4677 DIFFERENCES BETWEEN PCRE AND PERL
even on different hosts that have the other endianness. However, this	even on different hosts that have the other endianness. However, this
does not apply to optimized data created by the just-in-time compiler.	does not apply to optimized data created by the just-in-time compiler.

(k) The alternative matching function (pcre_dfa_exec()) matches in a	(k) The alternative matching functions (pcre_dfa_exec(),
different way and is not Perl-compatible.	pcre16_dfa_exec() and pcre32_dfa_exec(),) match in a different way and
	are not Perl-compatible.

(l) PCRE recognizes some special sequences such as (*CR) at the start	(l) PCRE recognizes some special sequences such as (*CR) at the start
of a pattern that set overall options that cannot be changed within the	of a pattern that set overall options that cannot be changed within the
pattern.	pattern.

Line 3373 AUTHOR	Line 4695 AUTHOR

REVISION	REVISION

Last updated: 14 November 2011	Last updated: 10 November 2013
Copyright (c) 1997-2011 University of Cambridge.	Copyright (c) 1997-2013 University of Cambridge.
------------------------------------------------------------------------------	------------------------------------------------------------------------------


PCREPATTERN(3) PCREPATTERN(3)	PCREPATTERN(3) Library Functions Manual PCREPATTERN(3)



NAME	NAME
PCRE - Perl-compatible regular expressions	PCRE - Perl-compatible regular expressions


PCRE REGULAR EXPRESSION DETAILS	PCRE REGULAR EXPRESSION DETAILS

The syntax and semantics of the regular expressions that are supported	The syntax and semantics of the regular expressions that are supported
Line 3402 PCRE REGULAR EXPRESSION DETAILS	Line 4724 PCRE REGULAR EXPRESSION DETAILS
great detail. This description of PCRE's regular expressions is	great detail. This description of PCRE's regular expressions is
intended as reference material.	intended as reference material.

	This document discusses the patterns that are supported by PCRE when
	one its main matching functions, pcre_exec() (8-bit) or
	pcre[16\|32]_exec() (16- or 32-bit), is used. PCRE also has alternative
	matching functions, pcre_dfa_exec() and pcre[16\|32_dfa_exec(), which
	match using a different algorithm that is not Perl-compatible. Some of
	the features discussed below are not available when DFA matching is
	used. The advantages and disadvantages of the alternative functions,
	and how they differ from the normal functions, are discussed in the
	pcrematching page.


	SPECIAL START-OF-PATTERN ITEMS

	A number of options that can be passed to pcre_compile() can also be
	set by special items at the start of a pattern. These are not Perl-com-
	patible, but are provided to make these options accessible to pattern
	writers who are not able to change the program that processes the pat-
	tern. Any number of these items may appear, but they must all be
	together right at the start of the pattern string, and the letters must
	be in upper case.

	UTF support

The original operation of PCRE was on strings of one-byte characters.	The original operation of PCRE was on strings of one-byte characters.
However, there is now also support for UTF-8 character strings. To use	However, there is now also support for UTF-8 strings in the original
this, PCRE must be built to include UTF-8 support, and you must call	library, an extra library that supports 16-bit and UTF-16 character
pcre_compile() or pcre_compile2() with the PCRE_UTF8 option. There is	strings, and a third library that supports 32-bit and UTF-32 character
also a special sequence that can be given at the start of a pattern:	strings. To use these features, PCRE must be built to include appropri-
	ate support. When using UTF strings you must either call the compiling
	function with the PCRE_UTF8, PCRE_UTF16, or PCRE_UTF32 option, or the
	pattern must start with one of these special sequences:

(*UTF8)	(*UTF8)
	(*UTF16)
	(*UTF32)
	(*UTF)

Starting a pattern with this sequence is equivalent to setting the	(*UTF) is a generic sequence that can be used with any of the
PCRE_UTF8 option. This feature is not Perl-compatible. How setting	libraries. Starting a pattern with such a sequence is equivalent to
UTF-8 mode affects pattern matching is mentioned in several places	setting the relevant option. How setting a UTF mode affects pattern
below. There is also a summary of UTF-8 features in the pcreunicode	matching is mentioned in several places below. There is also a summary
page.	of features in the pcreunicode page.

Another special sequence that may appear at the start of a pattern or	Some applications that allow their users to supply patterns may wish to
in combination with (*UTF8) is:	restrict them to non-UTF data for security reasons. If the
	PCRE_NEVER_UTF option is set at compile time, (*UTF) etc. are not
	allowed, and their appearance causes an error.

(*UCP)	Unicode property support

This has the same effect as setting the PCRE_UCP option: it causes	Another special sequence that may appear at the start of a pattern is
sequences such as \d and \w to use Unicode properties to determine	(*UCP). This has the same effect as setting the PCRE_UCP option: it
character types, instead of recognizing only characters with codes less	causes sequences such as \d and \w to use Unicode properties to deter-
than 128 via a lookup table.	mine character types, instead of recognizing only characters with codes
	less than 128 via a lookup table.

If a pattern starts with (*NO_START_OPT), it has the same effect as	Disabling auto-possessification
setting the PCRE_NO_START_OPTIMIZE option either at compile or matching
time. There are also some more of these special sequences that are con-
cerned with the handling of newlines; they are described below.

The remainder of this document discusses the patterns that are sup-	If a pattern starts with (*NO_AUTO_POSSESS), it has the same effect as
ported by PCRE when its main matching function, pcre_exec(), is used.	setting the PCRE_NO_AUTO_POSSESS option at compile time. This stops
From release 6.0, PCRE offers a second matching function,	PCRE from making quantifiers possessive when what follows cannot match
pcre_dfa_exec(), which matches using a different algorithm that is not	the repeated item. For example, by default a+b is treated as a++b. For
Perl-compatible. Some of the features discussed below are not available	more details, see the pcreapi documentation.
when pcre_dfa_exec() is used. The advantages and disadvantages of the
alternative function, and how it differs from the normal function, are
discussed in the pcrematching page.

	Disabling start-up optimizations

NEWLINE CONVENTIONS	If a pattern starts with (*NO_START_OPT), it has the same effect as
	setting the PCRE_NO_START_OPTIMIZE option either at compile or matching
	time. This disables several optimizations for quickly reaching "no
	match" results. For more details, see the pcreapi documentation.

PCRE supports five different conventions for indicating line breaks in	Newline conventions
strings: a single CR (carriage return) character, a single LF (line-
	PCRE supports five different conventions for indicating line breaks in
	strings: a single CR (carriage return) character, a single LF (line-
feed) character, the two-character sequence CRLF, any of the three pre-	feed) character, the two-character sequence CRLF, any of the three pre-
ceding, or any Unicode newline sequence. The pcreapi page has further	ceding, or any Unicode newline sequence. The pcreapi page has further
discussion about newlines, and shows how to set the newline convention	discussion about newlines, and shows how to set the newline convention
in the options arguments for the compiling and matching functions.	in the options arguments for the compiling and matching functions.

It is also possible to specify a newline convention by starting a pat-	It is also possible to specify a newline convention by starting a pat-
tern string with one of the following five sequences:	tern string with one of the following five sequences:

(*CR) carriage return	(*CR) carriage return
Line 3459 NEWLINE CONVENTIONS	Line 4813 NEWLINE CONVENTIONS
(*ANYCRLF) any of the three above	(*ANYCRLF) any of the three above
(*ANY) all Unicode newline sequences	(*ANY) all Unicode newline sequences

These override the default and the options given to pcre_compile() or	These override the default and the options given to the compiling func-
pcre_compile2(). For example, on a Unix system where LF is the default	tion. For example, on a Unix system where LF is the default newline
newline sequence, the pattern	sequence, the pattern

(*CR)a.b	(*CR)a.b

changes the convention to CR. That pattern matches "a\nb" because LF is	changes the convention to CR. That pattern matches "a\nb" because LF is
no longer a newline. Note that these special settings, which are not	no longer a newline. If more than one of these settings is present, the
Perl-compatible, are recognized only at the very start of a pattern,	last one is used.
and that they must be in upper case. If more than one of them is
present, the last one is used.

The newline convention affects the interpretation of the dot metachar-	The newline convention affects where the circumflex and dollar asser-
acter when PCRE_DOTALL is not set, and also the behaviour of \N. How-	tions are true. It also affects the interpretation of the dot metachar-
ever, it does not affect what the \R escape sequence matches. By	acter when PCRE_DOTALL is not set, and the behaviour of \N. However, it
default, this is any Unicode newline sequence, for Perl compatibility.	does not affect what the \R escape sequence matches. By default, this
However, this can be changed; see the description of \R in the section	is any Unicode newline sequence, for Perl compatibility. However, this
entitled "Newline sequences" below. A change of \R setting can be com-	can be changed; see the description of \R in the section entitled "New-
bined with a change of newline convention.	line sequences" below. A change of \R setting can be combined with a
	change of newline convention.

	Setting match and recursion limits

	The caller of pcre_exec() can set a limit on the number of times the
	internal match() function is called and on the maximum depth of recur-
	sive calls. These facilities are provided to catch runaway matches that
	are provoked by patterns with huge matching trees (a typical example is
	a pattern with nested unlimited repeats) and to avoid running out of
	system stack by too much recursion. When one of these limits is
	reached, pcre_exec() gives an error return. The limits can also be set
	by items at the start of the pattern of the form

	(*LIMIT_MATCH=d)
	(*LIMIT_RECURSION=d)

	where d is any number of decimal digits. However, the value of the set-
	ting must be less than the value set (or defaulted) by the caller of
	pcre_exec() for it to have any effect. In other words, the pattern
	writer can lower the limits set by the programmer, but not raise them.
	If there is more than one setting of one of these limits, the lower
	value is used.


	EBCDIC CHARACTER CODES

	PCRE can be compiled to run in an environment that uses EBCDIC as its
	character code rather than ASCII or Unicode (typically a mainframe sys-
	tem). In the sections below, character code values are ASCII or Uni-
	code; in an EBCDIC environment these characters may have different code
	values, and there are no code points greater than 255.


CHARACTERS AND METACHARACTERS	CHARACTERS AND METACHARACTERS

A regular expression is a pattern that is matched against a subject	A regular expression is a pattern that is matched against a subject
Line 3491 CHARACTERS AND METACHARACTERS	Line 4874 CHARACTERS AND METACHARACTERS

matches a portion of a subject string that is identical to itself. When	matches a portion of a subject string that is identical to itself. When
caseless matching is specified (the PCRE_CASELESS option), letters are	caseless matching is specified (the PCRE_CASELESS option), letters are
matched independently of case. In UTF-8 mode, PCRE always understands	matched independently of case. In a UTF mode, PCRE always understands
the concept of case for characters whose values are less than 128, so	the concept of case for characters whose values are less than 128, so
caseless matching is always possible. For characters with higher val-	caseless matching is always possible. For characters with higher val-
ues, the concept of case is supported if PCRE is compiled with Unicode	ues, the concept of case is supported if PCRE is compiled with Unicode
property support, but not otherwise. If you want to use caseless	property support, but not otherwise. If you want to use caseless
matching for characters 128 and above, you must ensure that PCRE is	matching for characters 128 and above, you must ensure that PCRE is
compiled with Unicode property support as well as with UTF-8 support.	compiled with Unicode property support as well as with UTF support.

The power of regular expressions comes from the ability to include	The power of regular expressions comes from the ability to include
alternatives and repetitions in the pattern. These are encoded in the	alternatives and repetitions in the pattern. These are encoded in the
Line 3552 BACKSLASH	Line 4935 BACKSLASH
that it stands for itself. In particular, if you want to match a back-	that it stands for itself. In particular, if you want to match a back-
slash, you write \\.	slash, you write \\.

In UTF-8 mode, only ASCII numbers and letters have any special meaning	In a UTF mode, only ASCII numbers and letters have any special meaning
after a backslash. All other characters (in particular, those whose	after a backslash. All other characters (in particular, those whose
codepoints are greater than 127) are treated as literals.	codepoints are greater than 127) are treated as literals.

If a pattern is compiled with the PCRE_EXTENDED option, whitespace in	If a pattern is compiled with the PCRE_EXTENDED option, most white
the pattern (other than in a character class) and characters between a	space in the pattern (other than in a character class), and characters
# outside a character class and the next newline are ignored. An escap-	between a # outside a character class and the next newline, inclusive,
ing backslash can be used to include a whitespace or # character as	are ignored. An escaping backslash can be used to include a white space
part of the pattern.	or # character as part of the pattern.

If you want to remove the special meaning from a sequence of charac-	If you want to remove the special meaning from a sequence of charac-
ters, you can do so by putting them between \Q and \E. This is differ-	ters, you can do so by putting them between \Q and \E. This is differ-
Line 3594 BACKSLASH	Line 4977 BACKSLASH
\a alarm, that is, the BEL character (hex 07)	\a alarm, that is, the BEL character (hex 07)
\cx "control-x", where x is any ASCII character	\cx "control-x", where x is any ASCII character
\e escape (hex 1B)	\e escape (hex 1B)
\f formfeed (hex 0C)	\f form feed (hex 0C)
\n linefeed (hex 0A)	\n linefeed (hex 0A)
\r carriage return (hex 0D)	\r carriage return (hex 0D)
\t tab (hex 09)	\t tab (hex 09)
	\0dd character with octal code 0dd
\ddd character with octal code ddd, or back reference	\ddd character with octal code ddd, or back reference
	\o{ddd..} character with octal code ddd..
\xhh character with hex code hh	\xhh character with hex code hh
\x{hhh..} character with hex code hhh.. (non-JavaScript mode)	\x{hhh..} character with hex code hhh.. (non-JavaScript mode)
\uhhhh character with hex code hhhh (JavaScript mode only)	\uhhhh character with hex code hhhh (JavaScript mode only)

The precise effect of \cx is as follows: if x is a lower case letter,	The precise effect of \cx on ASCII characters is as follows: if x is a
it is converted to upper case. Then bit 6 of the character (hex 40) is	lower case letter, it is converted to upper case. Then bit 6 of the
inverted. Thus \cz becomes hex 1A (z is 7A), but \c{ becomes hex 3B ({	character (hex 40) is inverted. Thus \cA to \cZ become hex 01 to hex 1A
is 7B), while \c; becomes hex 7B (; is 3B). If the byte following \c	(A is 41, Z is 5A), but \c{ becomes hex 3B ({ is 7B), and \c; becomes
has a value greater than 127, a compile-time error occurs. This locks	hex 7B (; is 3B). If the data item (byte or 16-bit value) following \c
out non-ASCII characters in both byte mode and UTF-8 mode. (When PCRE	has a value greater than 127, a compile-time error occurs. This locks
is compiled in EBCDIC mode, all byte values are valid. A lower case	out non-ASCII characters in all modes.
letter is converted to upper case, and then the 0xc0 bits are flipped.)

By default, after \x, from zero to two hexadecimal digits are read	The \c facility was designed for use with ASCII characters, but with
(letters can be in upper or lower case). Any number of hexadecimal dig-	the extension to Unicode it is even less useful than it once was. It
its may appear between \x{ and }, but the value of the character code	is, however, recognized when PCRE is compiled in EBCDIC mode, where
must be less than 256 in non-UTF-8 mode, and less than 2**31 in UTF-8	data items are always bytes. In this mode, all values are valid after
mode. That is, the maximum value in hexadecimal is 7FFFFFFF. Note that	\c. If the next character is a lower case letter, it is converted to
this is bigger than the largest Unicode code point, which is 10FFFF.	upper case. Then the 0xc0 bits of the byte are inverted. Thus \cA
	becomes hex 01, as in ASCII (A is C1), but because the EBCDIC letters
	are disjoint, \cZ becomes hex 29 (Z is E9), and other characters also
	generate different values.

If characters other than hexadecimal digits appear between \x{ and },
or if there is no terminating }, this form of escape is not recognized.
Instead, the initial \x will be interpreted as a basic hexadecimal
escape, with no following digits, giving a character whose value is
zero.

If the PCRE_JAVASCRIPT_COMPAT option is set, the interpretation of \x
is as just described only when it is followed by two hexadecimal dig-
its. Otherwise, it matches a literal "x" character. In JavaScript
mode, support for code points greater than 256 is provided by \u, which
must be followed by four hexadecimal digits; otherwise it matches a
literal "u" character.

Characters whose value is less than 256 can be defined by either of the
two syntaxes for \x (or by \u in JavaScript mode). There is no differ-
ence in the way they are handled. For example, \xdc is exactly the same
as \x{dc} (or \u00dc in JavaScript mode).

After \0 up to two further octal digits are read. If there are fewer	After \0 up to two further octal digits are read. If there are fewer
than two digits, just those that are present are used. Thus the	than two digits, just those that are present are used. Thus the
sequence \0\x\07 specifies two binary zeros followed by a BEL character	sequence \0\x\07 specifies two binary zeros followed by a BEL character
(code value 7). Make sure you supply two digits after the initial zero	(code value 7). Make sure you supply two digits after the initial zero
if the pattern character that follows is itself an octal digit.	if the pattern character that follows is itself an octal digit.

	The escape \o must be followed by a sequence of octal digits, enclosed
	in braces. An error occurs if this is not the case. This escape is a
	recent addition to Perl; it provides way of specifying character code
	points as octal numbers greater than 0777, and it also allows octal
	numbers and back references to be unambiguously specified.

	For greater clarity and unambiguity, it is best to avoid following \ by
	a digit greater than zero. Instead, use \o{} or \x{} to specify charac-
	ter numbers, and \g{} to specify back references. The following para-
	graphs describe the old, ambiguous syntax.

The handling of a backslash followed by a digit other than 0 is compli-	The handling of a backslash followed by a digit other than 0 is compli-
cated. Outside a character class, PCRE reads it and any following dig-	cated, and Perl has changed in recent releases, causing PCRE also to
its as a decimal number. If the number is less than 10, or if there	change. Outside a character class, PCRE reads the digit and any follow-
have been at least that many previous capturing left parentheses in the	ing digits as a decimal number. If the number is less than 8, or if
expression, the entire sequence is taken as a back reference. A	there have been at least that many previous capturing left parentheses
	in the expression, the entire sequence is taken as a back reference. A
description of how this works is given later, following the discussion	description of how this works is given later, following the discussion
of parenthesized subpatterns.	of parenthesized subpatterns.

Inside a character class, or if the decimal number is greater than 9	Inside a character class, or if the decimal number following \ is
and there have not been that many capturing subpatterns, PCRE re-reads	greater than 7 and there have not been that many capturing subpatterns,
up to three octal digits following the backslash, and uses them to gen-	PCRE handles \8 and \9 as the literal characters "8" and "9", and oth-
erate a data character. Any subsequent digits stand for themselves. In	erwise re-reads up to three octal digits following the backslash, using
non-UTF-8 mode, the value of a character specified in octal must be	them to generate a data character. Any subsequent digits stand for
less than \400. In UTF-8 mode, values up to \777 are permitted. For	themselves. For example:
example:

\040 is another way of writing a space	\040 is another way of writing an ASCII space
\40 is the same, provided there are fewer than 40	\40 is the same, provided there are fewer than 40
previous capturing subpatterns	previous capturing subpatterns
\7 is always a back reference	\7 is always a back reference
Line 3670 BACKSLASH	Line 5050 BACKSLASH
\113 might be a back reference, otherwise the	\113 might be a back reference, otherwise the
character with octal code 113	character with octal code 113
\377 might be a back reference, otherwise	\377 might be a back reference, otherwise
the byte consisting entirely of 1 bits	the value 255 (decimal)
\81 is either a back reference, or a binary zero	\81 is either a back reference, or the two
followed by the two characters "8" and "1"	characters "8" and "1"

Note that octal values of 100 or greater must not be introduced by a	Note that octal values of 100 or greater that are specified using this
leading zero, because no more than three octal digits are ever read.	syntax must not be introduced by a leading zero, because no more than
	three octal digits are ever read.

	By default, after \x that is not followed by {, from zero to two hexa-
	decimal digits are read (letters can be in upper or lower case). Any
	number of hexadecimal digits may appear between \x{ and }. If a charac-
	ter other than a hexadecimal digit appears between \x{ and }, or if
	there is no terminating }, an error occurs.

	If the PCRE_JAVASCRIPT_COMPAT option is set, the interpretation of \x
	is as just described only when it is followed by two hexadecimal dig-
	its. Otherwise, it matches a literal "x" character. In JavaScript
	mode, support for code points greater than 256 is provided by \u, which
	must be followed by four hexadecimal digits; otherwise it matches a
	literal "u" character.

	Characters whose value is less than 256 can be defined by either of the
	two syntaxes for \x (or by \u in JavaScript mode). There is no differ-
	ence in the way they are handled. For example, \xdc is exactly the same
	as \x{dc} (or \u00dc in JavaScript mode).

	Constraints on character values

	Characters that are specified using octal or hexadecimal numbers are
	limited to certain values, as follows:

	8-bit non-UTF mode less than 0x100
	8-bit UTF-8 mode less than 0x10ffff and a valid codepoint
	16-bit non-UTF mode less than 0x10000
	16-bit UTF-16 mode less than 0x10ffff and a valid codepoint
	32-bit non-UTF mode less than 0x100000000
	32-bit UTF-32 mode less than 0x10ffff and a valid codepoint

	Invalid Unicode codepoints are the range 0xd800 to 0xdfff (the so-
	called "surrogate" codepoints), and 0xffef.

	Escape sequences in character classes

All the sequences that define a single character value can be used both	All the sequences that define a single character value can be used both
inside and outside character classes. In addition, inside a character	inside and outside character classes. In addition, inside a character
class, \b is interpreted as the backspace character (hex 08).	class, \b is interpreted as the backspace character (hex 08).
Line 3718 BACKSLASH	Line 5134 BACKSLASH

\d any decimal digit	\d any decimal digit
\D any character that is not a decimal digit	\D any character that is not a decimal digit
\h any horizontal whitespace character	\h any horizontal white space character
\H any character that is not a horizontal whitespace character	\H any character that is not a horizontal white space character
\s any whitespace character	\s any white space character
\S any character that is not a whitespace character	\S any character that is not a white space character
\v any vertical whitespace character	\v any vertical white space character
\V any character that is not a vertical whitespace character	\V any character that is not a vertical white space character
\w any "word" character	\w any "word" character
\W any "non-word" character	\W any "non-word" character

Line 3740 BACKSLASH	Line 5156 BACKSLASH
the subject string, all of them fail, because there is no character to	the subject string, all of them fail, because there is no character to
match.	match.

For compatibility with Perl, \s does not match the VT character (code	For compatibility with Perl, \s did not used to match the VT character
11). This makes it different from the the POSIX "space" class. The \s	(code 11), which made it different from the the POSIX "space" class.
characters are HT (9), LF (10), FF (12), CR (13), and space (32). If	However, Perl added VT at release 5.18, and PCRE followed suit at
"use locale;" is included in a Perl script, \s may match the VT charac-	release 8.34. The default \s characters are now HT (9), LF (10), VT
ter. In PCRE, it never does.	(11), FF (12), CR (13), and space (32), which are defined as white
	space in the "C" locale. This list may vary if locale-specific matching
	is taking place. For example, in some locales the "non-breaking space"
	character (\xA0) is recognized as white space, and in others the VT
	character is not.

A "word" character is an underscore or any character that is a letter	A "word" character is an underscore or any character that is a letter
or digit. By default, the definition of letters and digits is con-	or digit. By default, the definition of letters and digits is con-
trolled by PCRE's low-valued character tables, and may vary if locale-	trolled by PCRE's low-valued character tables, and may vary if locale-
specific matching is taking place (see "Locale support" in the pcreapi	specific matching is taking place (see "Locale support" in the pcreapi
page). For example, in a French locale such as "fr_FR" in Unix-like	page). For example, in a French locale such as "fr_FR" in Unix-like
systems, or "french" in Windows, some character codes greater than 128	systems, or "french" in Windows, some character codes greater than 127
are used for accented letters, and these are then matched by \w. The	are used for accented letters, and these are then matched by \w. The
use of locales with Unicode is discouraged.	use of locales with Unicode is discouraged.

By default, in UTF-8 mode, characters with values greater than 128	By default, characters whose code points are greater than 127 never
never match \d, \s, or \w, and always match \D, \S, and \W. These	match \d, \s, or \w, and always match \D, \S, and \W, although this may
sequences retain their original meanings from before UTF-8 support was	vary for characters in the range 128-255 when locale-specific matching
available, mainly for efficiency reasons. However, if PCRE is compiled	is happening. These escape sequences retain their original meanings
with Unicode property support, and the PCRE_UCP option is set, the be-	from before Unicode support was available, mainly for efficiency rea-
haviour is changed so that Unicode properties are used to determine	sons. If PCRE is compiled with Unicode property support, and the
character types, as follows:	PCRE_UCP option is set, the behaviour is changed so that Unicode prop-
	erties are used to determine character types, as follows:

\d any character that \p{Nd} matches (decimal digit)	\d any character that matches \p{Nd} (decimal digit)
\s any character that \p{Z} matches, plus HT, LF, FF, CR	\s any character that matches \p{Z} or \h or \v
\w any character that \p{L} or \p{N} matches, plus underscore	\w any character that matches \p{L} or \p{N}, plus underscore

The upper case escapes match the inverse sets of characters. Note that	The upper case escapes match the inverse sets of characters. Note that
\d matches only decimal digits, whereas \w matches any Unicode digit,	\d matches only decimal digits, whereas \w matches any Unicode digit,
as well as any Unicode letter, and underscore. Note also that PCRE_UCP	as well as any Unicode letter, and underscore. Note also that PCRE_UCP
affects \b, and \B because they are defined in terms of \w and \W.	affects \b, and \B because they are defined in terms of \w and \W.
Matching these sequences is noticeably slower when PCRE_UCP is set.	Matching these sequences is noticeably slower when PCRE_UCP is set.

The sequences \h, \H, \v, and \V are features that were added to Perl	The sequences \h, \H, \v, and \V are features that were added to Perl
at release 5.10. In contrast to the other sequences, which match only	at release 5.10. In contrast to the other sequences, which match only
ASCII characters by default, these always match certain high-valued	ASCII characters by default, these always match certain high-valued
codepoints in UTF-8 mode, whether or not PCRE_UCP is set. The horizon-	code points, whether or not PCRE_UCP is set. The horizontal space char-
tal space characters are:

U+0009 Horizontal tab	U+0009 Horizontal tab (HT)
U+0020 Space	U+0020 Space
U+00A0 Non-break space	U+00A0 Non-break space
U+1680 Ogham space mark	U+1680 Ogham space mark
Line 3801 BACKSLASH	Line 5222 BACKSLASH

The vertical space characters are:	The vertical space characters are:

U+000A Linefeed	U+000A Linefeed (LF)
U+000B Vertical tab	U+000B Vertical tab (VT)
U+000C Formfeed	U+000C Form feed (FF)
U+000D Carriage return	U+000D Carriage return (CR)
U+0085 Next line	U+0085 Next line (NEL)
U+2028 Line separator	U+2028 Line separator
U+2029 Paragraph separator	U+2029 Paragraph separator

	In 8-bit, non-UTF-8 mode, only the characters with codepoints less than
	256 are relevant.

Newline sequences	Newline sequences

Outside a character class, by default, the escape sequence \R matches	Outside a character class, by default, the escape sequence \R matches
any Unicode newline sequence. In non-UTF-8 mode \R is equivalent to the	any Unicode newline sequence. In 8-bit non-UTF-8 mode \R is equivalent any Unicode newline sequence. In 8-bit non-UTF-8 mode \R is equivalent
following:	to the following:

(?>\r\n\|\n\|\x0b\|\f\|\r\|\x85)	(?>\r\n\|\n\|\x0b\|\f\|\r\|\x85)

This is an example of an "atomic group", details of which are given	This is an example of an "atomic group", details of which are given
below. This particular group matches either the two-character sequence	below. This particular group matches either the two-character sequence
CR followed by LF, or one of the single characters LF (linefeed,	CR followed by LF, or one of the single characters LF (linefeed,
U+000A), VT (vertical tab, U+000B), FF (formfeed, U+000C), CR (carriage	U+000A), VT (vertical tab, U+000B), FF (form feed, U+000C), CR (car-
return, U+000D), or NEL (next line, U+0085). The two-character sequence	riage return, U+000D), or NEL (next line, U+0085). The two-character
is treated as a single unit that cannot be split.	sequence is treated as a single unit that cannot be split.

In UTF-8 mode, two additional characters whose codepoints are greater	In other modes, two additional characters whose codepoints are greater
than 255 are added: LS (line separator, U+2028) and PS (paragraph sepa-	than 255 are added: LS (line separator, U+2028) and PS (paragraph sepa-
rator, U+2029). Unicode character property support is not needed for	rator, U+2029). Unicode character property support is not needed for
these characters to be recognized.	these characters to be recognized.
Line 3841 BACKSLASH	Line 5265 BACKSLASH
(*BSR_ANYCRLF) CR, LF, or CRLF only	(*BSR_ANYCRLF) CR, LF, or CRLF only
(*BSR_UNICODE) any Unicode newline sequence	(*BSR_UNICODE) any Unicode newline sequence

These override the default and the options given to pcre_compile() or	These override the default and the options given to the compiling func-
pcre_compile2(), but they can be overridden by options given to	tion, but they can themselves be overridden by options given to a
pcre_exec() or pcre_dfa_exec(). Note that these special settings, which	matching function. Note that these special settings, which are not
are not Perl-compatible, are recognized only at the very start of a	Perl-compatible, are recognized only at the very start of a pattern,
pattern, and that they must be in upper case. If more than one of them	and that they must be in upper case. If more than one of them is
is present, the last one is used. They can be combined with a change of	present, the last one is used. They can be combined with a change of
newline convention; for example, a pattern can start with:	newline convention; for example, a pattern can start with:

(ANY)(BSR_ANYCRLF)	(ANY)(BSR_ANYCRLF)

They can also be combined with the (UTF8) or (UCP) special sequences.	They can also be combined with the (UTF8), (UTF16), (UTF32), (UTF)
Inside a character class, \R is treated as an unrecognized escape	or (*UCP) special sequences. Inside a character class, \R is treated as
sequence, and so matches the letter "R" by default, but causes an error	an unrecognized escape sequence, and so matches the letter "R" by
if PCRE_EXTRA is set.	default, but causes an error if PCRE_EXTRA is set.

Unicode character properties	Unicode character properties

When PCRE is built with Unicode character property support, three addi-	When PCRE is built with Unicode character property support, three addi-
tional escape sequences that match characters with specific properties	tional escape sequences that match characters with specific properties
are available. When not in UTF-8 mode, these sequences are of course	are available. When in 8-bit non-UTF-8 mode, these sequences are of
limited to testing characters whose codepoints are less than 256, but	course limited to testing characters whose codepoints are less than
they do work in this mode. The extra escape sequences are:	256, but they do work in this mode. The extra escape sequences are:

\p{xx} a character with the xx property	\p{xx} a character with the xx property
\P{xx} a character without the xx property	\P{xx} a character without the xx property
\X an extended Unicode sequence	\X a Unicode extended grapheme cluster

The property names represented by xx above are limited to the Unicode	The property names represented by xx above are limited to the Unicode
script names, the general category properties, "Any", which matches any	script names, the general category properties, "Any", which matches any
Line 3885 BACKSLASH	Line 5309 BACKSLASH
Those that are not part of an identified script are lumped together as	Those that are not part of an identified script are lumped together as
"Common". The current list of scripts is:	"Common". The current list of scripts is:

Arabic, Armenian, Avestan, Balinese, Bamum, Bengali, Bopomofo, Braille,	Arabic, Armenian, Avestan, Balinese, Bamum, Batak, Bengali, Bopomofo,
Buginese, Buhid, Canadian_Aboriginal, Carian, Cham, Cherokee, Common,	Brahmi, Braille, Buginese, Buhid, Canadian_Aboriginal, Carian, Chakma,
Coptic, Cuneiform, Cypriot, Cyrillic, Deseret, Devanagari, Egyp-	Cham, Cherokee, Common, Coptic, Cuneiform, Cypriot, Cyrillic, Deseret,
tian_Hieroglyphs, Ethiopic, Georgian, Glagolitic, Gothic, Greek,	Devanagari, Egyptian_Hieroglyphs, Ethiopic, Georgian, Glagolitic,
Gujarati, Gurmukhi, Han, Hangul, Hanunoo, Hebrew, Hiragana, Impe-	Gothic, Greek, Gujarati, Gurmukhi, Han, Hangul, Hanunoo, Hebrew, Hira-
rial_Aramaic, Inherited, Inscriptional_Pahlavi, Inscriptional_Parthian,	gana, Imperial_Aramaic, Inherited, Inscriptional_Pahlavi, Inscrip-
Javanese, Kaithi, Kannada, Katakana, Kayah_Li, Kharoshthi, Khmer, Lao,	tional_Parthian, Javanese, Kaithi, Kannada, Katakana, Kayah_Li,
Latin, Lepcha, Limbu, Linear_B, Lisu, Lycian, Lydian, Malayalam,	Kharoshthi, Khmer, Lao, Latin, Lepcha, Limbu, Linear_B, Lisu, Lycian,
Meetei_Mayek, Mongolian, Myanmar, New_Tai_Lue, Nko, Ogham, Old_Italic,	Lydian, Malayalam, Mandaic, Meetei_Mayek, Meroitic_Cursive,
Old_Persian, Old_South_Arabian, Old_Turkic, Ol_Chiki, Oriya, Osmanya,	Meroitic_Hieroglyphs, Miao, Mongolian, Myanmar, New_Tai_Lue, Nko,
Phags_Pa, Phoenician, Rejang, Runic, Samaritan, Saurashtra, Shavian,	Ogham, Old_Italic, Old_Persian, Old_South_Arabian, Old_Turkic,
Sinhala, Sundanese, Syloti_Nagri, Syriac, Tagalog, Tagbanwa, Tai_Le,	Ol_Chiki, Oriya, Osmanya, Phags_Pa, Phoenician, Rejang, Runic, Samari-
Tai_Tham, Tai_Viet, Tamil, Telugu, Thaana, Thai, Tibetan, Tifinagh,	tan, Saurashtra, Sharada, Shavian, Sinhala, Sora_Sompeng, Sundanese,
Ugaritic, Vai, Yi.	Syloti_Nagri, Syriac, Tagalog, Tagbanwa, Tai_Le, Tai_Tham, Tai_Viet,
	Takri, Tamil, Telugu, Thaana, Thai, Tibetan, Tifinagh, Ugaritic, Vai,
	Yi.

Each character has exactly one Unicode general category property, spec-	Each character has exactly one Unicode general category property, spec-
ified by a two-letter abbreviation. For compatibility with Perl, nega-	ified by a two-letter abbreviation. For compatibility with Perl, nega-
Line 3965 BACKSLASH	Line 5391 BACKSLASH
classified as a modifier or "other".	classified as a modifier or "other".

The Cs (Surrogate) property applies only to characters in the range	The Cs (Surrogate) property applies only to characters in the range
U+D800 to U+DFFF. Such characters are not valid in UTF-8 strings (see	U+D800 to U+DFFF. Such characters are not valid in Unicode strings and
RFC 3629) and so cannot be tested by PCRE, unless UTF-8 validity check-	so cannot be tested by PCRE, unless UTF validity checking has been
ing has been turned off (see the discussion of PCRE_NO_UTF8_CHECK in	turned off (see the discussion of PCRE_NO_UTF8_CHECK,
the pcreapi page). Perl does not support the Cs property.	PCRE_NO_UTF16_CHECK and PCRE_NO_UTF32_CHECK in the pcreapi page). Perl
	does not support the Cs property.

The long synonyms for property names that Perl supports (such as	The long synonyms for property names that Perl supports (such as
\p{Letter}) are not supported by PCRE, nor is it permitted to prefix	\p{Letter}) are not supported by PCRE, nor is it permitted to prefix
any of these properties with "Is".	any of these properties with "Is".

No character that is in the Unicode table has the Cn (unassigned) prop-	No character that is in the Unicode table has the Cn (unassigned) prop-
erty. Instead, this property is assumed for any code point that is not	erty. Instead, this property is assumed for any code point that is not
in the Unicode table.	in the Unicode table.

Specifying caseless matching does not affect these escape sequences.	Specifying caseless matching does not affect these escape sequences.
For example, \p{Lu} always matches only upper case letters.	For example, \p{Lu} always matches only upper case letters. This is
	different from the behaviour of current versions of Perl.

The \X escape matches any number of Unicode characters that form an	Matching characters by Unicode property is not fast, because PCRE has
extended Unicode sequence. \X is equivalent to	to do a multistage table lookup in order to find a character's prop-
	erty. That is why the traditional escape sequences such as \d and \w do
	not use Unicode properties in PCRE by default, though you can make them
	do so by setting the PCRE_UCP option or by starting the pattern with
	(*UCP).

	Extended grapheme clusters

	The \X escape matches any number of Unicode characters that form an
	"extended grapheme cluster", and treats the sequence as an atomic group
	(see below). Up to and including release 8.31, PCRE matched an ear-
	lier, simpler definition that was equivalent to

(?>\PM\pM*)	(?>\PM\pM*)

That is, it matches a character without the "mark" property, followed	That is, it matched a character without the "mark" property, followed
by zero or more characters with the "mark" property, and treats the	by zero or more characters with the "mark" property. Characters with
sequence as an atomic group (see below). Characters with the "mark"	the "mark" property are typically non-spacing accents that affect the
property are typically accents that affect the preceding character.	preceding character.
None of them have codepoints less than 256, so in non-UTF-8 mode \X
matches any one character.

Note that recent versions of Perl have changed \X to match what Unicode	This simple definition was extended in Unicode to include more compli-
calls an "extended grapheme cluster", which has a more complicated def-	cated kinds of composite character by giving each character a grapheme
inition.	breaking property, and creating rules that use these properties to
	define the boundaries of extended grapheme clusters. In releases of
	PCRE later than 8.31, \X matches one of these clusters.

Matching characters by Unicode property is not fast, because PCRE has	\X always matches at least one character. Then it decides whether to
to search a structure that contains data for over fifteen thousand	add additional characters according to the following rules for ending a
characters. That is why the traditional escape sequences such as \d and	cluster:
\w do not use Unicode properties in PCRE by default, though you can
make them do so by setting the PCRE_UCP option for pcre_compile() or by
starting the pattern with (*UCP).

	1. End at the end of the subject string.

	2. Do not end between CR and LF; otherwise end after any control char-
	acter.

	3. Do not break Hangul (a Korean script) syllable sequences. Hangul
	characters are of five types: L, V, T, LV, and LVT. An L character may
	be followed by an L, V, LV, or LVT character; an LV or V character may
	be followed by a V or T character; an LVT or T character may be follwed
	only by a T character.

	4. Do not end before extending characters or spacing marks. Characters
	with the "mark" property always have the "extend" grapheme breaking
	property.

	5. Do not end after prepend characters.

	6. Otherwise, end the cluster.

PCRE's additional properties	PCRE's additional properties

As well as the standard Unicode properties described in the previous	As well as the standard Unicode properties described above, PCRE sup-
section, PCRE supports four more that make it possible to convert tra-	ports four more that make it possible to convert traditional escape
ditional escape sequences such as \w and \s and POSIX character classes	sequences such as \w and \s to use Unicode properties. PCRE uses these
to use Unicode properties. PCRE uses these non-standard, non-Perl prop-	non-standard, non-Perl properties internally when PCRE_UCP is set. How-
erties internally when PCRE_UCP is set. They are:	ever, they may also be used explicitly. These properties are:

Xan Any alphanumeric character	Xan Any alphanumeric character
Xps Any POSIX space character	Xps Any POSIX space character
Xsp Any Perl space character	Xsp Any Perl space character
Xwd Any Perl "word" character	Xwd Any Perl "word" character

Xan matches characters that have either the L (letter) or the N (num-	Xan matches characters that have either the L (letter) or the N (num-
ber) property. Xps matches the characters tab, linefeed, vertical tab,	ber) property. Xps matches the characters tab, linefeed, vertical tab,
formfeed, or carriage return, and any other character that has the Z	form feed, or carriage return, and any other character that has the Z
(separator) property. Xsp is the same as Xps, except that vertical tab	(separator) property. Xsp is the same as Xps; it used to exclude ver-
is excluded. Xwd matches the same characters as Xan, plus underscore.	tical tab, for Perl compatibility, but Perl changed, and so PCRE fol-
	lowed at release 8.34. Xwd matches the same characters as Xan, plus
	underscore.

	There is another non-standard property, Xuc, which matches any charac-
	ter that can be represented by a Universal Character Name in C++ and
	other programming languages. These are the characters $, @, ` (grave
	accent), and all characters with Unicode code points greater than or
	equal to U+00A0, except for the surrogates U+D800 to U+DFFF. Note that
	most base (ASCII) characters are excluded. (Universal Character Names
	are of the form \uHHHH or \UHHHHHHHH where H is a hexadecimal digit.
	Note that the Xuc property does not match these sequences but the char-
	acters that they represent.)

Resetting the match start	Resetting the match start

The escape sequence \K causes any previously matched characters not to	The escape sequence \K causes any previously matched characters not to
be included in the final matched sequence. For example, the pattern:	be included in the final matched sequence. For example, the pattern:

foo\Kbar	foo\Kbar

matches "foobar", but reports that it has matched "bar". This feature	matches "foobar", but reports that it has matched "bar". This feature
is similar to a lookbehind assertion (described below). However, in	is similar to a lookbehind assertion (described below). However, in
this case, the part of the subject before the real match does not have	this case, the part of the subject before the real match does not have
to be of fixed length, as lookbehind assertions do. The use of \K does	to be of fixed length, as lookbehind assertions do. The use of \K does
not interfere with the setting of captured substrings. For example,	not interfere with the setting of captured substrings. For example,
when the pattern	when the pattern

(foo)\Kbar	(foo)\Kbar

matches "foobar", the first substring is still set to "foo".	matches "foobar", the first substring is still set to "foo".

Perl documents that the use of \K within assertions is "not well	Perl documents that the use of \K within assertions is "not well
defined". In PCRE, \K is acted upon when it occurs inside positive	defined". In PCRE, \K is acted upon when it occurs inside positive
assertions, but is ignored in negative assertions.	assertions, but is ignored in negative assertions.

Simple assertions	Simple assertions

The final use of backslash is for certain simple assertions. An asser-	The final use of backslash is for certain simple assertions. An asser-
tion specifies a condition that has to be met at a particular point in	tion specifies a condition that has to be met at a particular point in
a match, without consuming any characters from the subject string. The	a match, without consuming any characters from the subject string. The
use of subpatterns for more complicated assertions is described below.	use of subpatterns for more complicated assertions is described below.
The backslashed assertions are:	The backslashed assertions are:

\b matches at a word boundary	\b matches at a word boundary
Line 4061 BACKSLASH	Line 5528 BACKSLASH
\z matches only at the end of the subject	\z matches only at the end of the subject
\G matches at the first matching position in the subject	\G matches at the first matching position in the subject

Inside a character class, \b has a different meaning; it matches the	Inside a character class, \b has a different meaning; it matches the
backspace character. If any other of these assertions appears in a	backspace character. If any other of these assertions appears in a
character class, by default it matches the corresponding literal char-	character class, by default it matches the corresponding literal char-
acter (for example, \B matches the letter B). However, if the	acter (for example, \B matches the letter B). However, if the
PCRE_EXTRA option is set, an "invalid escape sequence" error is gener-	PCRE_EXTRA option is set, an "invalid escape sequence" error is gener-
ated instead.	ated instead.

A word boundary is a position in the subject string where the current	A word boundary is a position in the subject string where the current
character and the previous character do not both match \w or \W (i.e.	character and the previous character do not both match \w or \W (i.e.
one matches \w and the other matches \W), or the start or end of the	one matches \w and the other matches \W), or the start or end of the
string if the first or last character matches \w, respectively. In	string if the first or last character matches \w, respectively. In a
UTF-8 mode, the meanings of \w and \W can be changed by setting the	UTF mode, the meanings of \w and \W can be changed by setting the
PCRE_UCP option. When this is done, it also affects \b and \B. Neither	PCRE_UCP option. When this is done, it also affects \b and \B. Neither
PCRE nor Perl has a separate "start of word" or "end of word" metase-	PCRE nor Perl has a separate "start of word" or "end of word" metase-
quence. However, whatever follows \b normally determines which it is.	quence. However, whatever follows \b normally determines which it is.
For example, the fragment \ba matches "a" at the start of a word.	For example, the fragment \ba matches "a" at the start of a word.

The \A, \Z, and \z assertions differ from the traditional circumflex	The \A, \Z, and \z assertions differ from the traditional circumflex
and dollar (described in the next section) in that they only ever match	and dollar (described in the next section) in that they only ever match
at the very start and end of the subject string, whatever options are	at the very start and end of the subject string, whatever options are
set. Thus, they are independent of multiline mode. These three asser-	set. Thus, they are independent of multiline mode. These three asser-
tions are not affected by the PCRE_NOTBOL or PCRE_NOTEOL options, which	tions are not affected by the PCRE_NOTBOL or PCRE_NOTEOL options, which
affect only the behaviour of the circumflex and dollar metacharacters.	affect only the behaviour of the circumflex and dollar metacharacters.
However, if the startoffset argument of pcre_exec() is non-zero, indi-	However, if the startoffset argument of pcre_exec() is non-zero, indi-
cating that matching is to start at a point other than the beginning of	cating that matching is to start at a point other than the beginning of
the subject, \A can never match. The difference between \Z and \z is	the subject, \A can never match. The difference between \Z and \z is
that \Z matches before a newline at the end of the string as well as at	that \Z matches before a newline at the end of the string as well as at
the very end, whereas \z matches only at the end.	the very end, whereas \z matches only at the end.

The \G assertion is true only when the current matching position is at	The \G assertion is true only when the current matching position is at
the start point of the match, as specified by the startoffset argument	the start point of the match, as specified by the startoffset argument
of pcre_exec(). It differs from \A when the value of startoffset is	of pcre_exec(). It differs from \A when the value of startoffset is
non-zero. By calling pcre_exec() multiple times with appropriate argu-	non-zero. By calling pcre_exec() multiple times with appropriate argu-
ments, you can mimic Perl's /g option, and it is in this kind of imple-	ments, you can mimic Perl's /g option, and it is in this kind of imple-
mentation where \G can be useful.	mentation where \G can be useful.

Note, however, that PCRE's interpretation of \G, as the start of the	Note, however, that PCRE's interpretation of \G, as the start of the
current match, is subtly different from Perl's, which defines it as the	current match, is subtly different from Perl's, which defines it as the
end of the previous match. In Perl, these can be different when the	end of the previous match. In Perl, these can be different when the
previously matched string was empty. Because PCRE does just one match	previously matched string was empty. Because PCRE does just one match
at a time, it cannot reproduce this behaviour.	at a time, it cannot reproduce this behaviour.

If all the alternatives of a pattern begin with \G, the expression is	If all the alternatives of a pattern begin with \G, t If all the alternatives of a pattern begin with \G, the expression is
anchored to the starting match position, and the "anchored" flag is set	anchored to the starting match position, and the "anchored" flag is set
in the compiled regular expression.	in the compiled regular expression.


CIRCUMFLEX AND DOLLAR	CIRCUMFLEX AND DOLLAR

	The circumflex and dollar metacharacters are zero-width assertions.
	That is, they test for a particular condition being true without con-
	suming any characters from the subject string.

Outside a character class, in the default matching mode, the circumflex	Outside a character class, in the default matching mode, the circumflex
character is an assertion that is true only if the current matching	character is an assertion that is true only if the current matching
point is at the start of the subject string. If the startoffset argu-	point is at the start of the subject string. If the startoffset argu-
ment of pcre_exec() is non-zero, circumflex can never match if the	ment of pcre_exec() is non-zero, circumflex can never match if the
PCRE_MULTILINE option is unset. Inside a character class, circumflex	PCRE_MULTILINE option is unset. Inside a character class, circumflex
has an entirely different meaning (see below).	has an entirely different meaning (see below).

Circumflex need not be the first character of the pattern if a number	Circumflex need not be the first character of the pattern if a number
of alternatives are involved, but it should be the first thing in each	of alternatives are involved, but it should be the first thing in each
alternative in which it appears if the pattern is ever to match that	alternative in which it appears if the pattern is ever to match that
branch. If all possible alternatives start with a circumflex, that is,	branch. If all possible alternatives start with a circumflex, that is,
if the pattern is constrained to match only at the start of the sub-	if the pattern is constrained to match only at the start of the sub-
ject, it is said to be an "anchored" pattern. (There are also other	ject, it is said to be an "anchored" pattern. (There are also other
constructs that can cause a pattern to be anchored.)	constructs that can cause a pattern to be anchored.)

A dollar character is an assertion that is true only if the current	The dollar character is an assertion that is true only if the current
matching point is at the end of the subject string, or immediately	matching point is at the end of the subject string, or immediately
before a newline at the end of the string (by default). Dollar need not	before a newline at the end of the string (by default). Note, however,
be the last character of the pattern if a number of alternatives are	that it does not actually match the newline. Dollar need not be the
involved, but it should be the last item in any branch in which it	last character of the pattern if a number of alternatives are involved,
appears. Dollar has no special meaning in a character class.	but it should be the last item in any branch in which it appears. Dol-
	lar has no special meaning in a character class.

The meaning of dollar can be changed so that it matches only at the	The meaning of dollar can be changed so that it matches only at the
very end of the string, by setting the PCRE_DOLLAR_ENDONLY option at	very end of the string, by setting the PCRE_DOLLAR_ENDONLY option at
Line 4163 FULL STOP (PERIOD, DOT) AND \N	Line 5635 FULL STOP (PERIOD, DOT) AND \N

Outside a character class, a dot in the pattern matches any one charac-	Outside a character class, a dot in the pattern matches any one charac-
ter in the subject string except (by default) a character that signi-	ter in the subject string except (by default) a character that signi-
fies the end of a line. In UTF-8 mode, the matched character may be	fies the end of a line.
more than one byte long.

When a line ending is defined as a single character, dot never matches	When a line ending is defined as a single character, dot never matches
that character; when the two-character sequence CRLF is used, dot does	that character; when the two-character sequence CRLF is used, dot does
not match CR if it is immediately followed by LF, but otherwise it	not match CR if it is immediately followed by LF, but otherwise it
matches all characters (including isolated CRs and LFs). When any Uni-	matches all characters (including isolated CRs and LFs). When any Uni-
code line endings are being recognized, dot does not match CR or LF or	code line endings are being recognized, dot does not match CR or LF or
any of the other line ending characters.	any of the other line ending characters.

The behaviour of dot with regard to newlines can be changed. If the	The behaviour of dot with regard to newlines can be changed. If the
PCRE_DOTALL option is set, a dot matches any one character, without	PCRE_DOTALL option is set, a dot matches any one character, without
exception. If the two-character sequence CRLF is present in the subject	exception. If the two-character sequence CRLF is present in the subject
string, it takes two dots to match it.	string, it takes two dots to match it.

The handling of dot is entirely independent of the handling of circum-	The handling of dot is entirely independent of the handling of circum-
flex and dollar, the only relationship being that they both involve	flex and dollar, the only relationship being that they both involve
newlines. Dot has no special meaning in a character class.	newlines. Dot has no special meaning in a character class.

The escape sequence \N behaves like a dot, except that it is not	The escape sequence \N behaves like a dot, except that it is not
affected by the PCRE_DOTALL option. In other words, it matches any	affected by the PCRE_DOTALL option. In other words, it matches any
character except one that signifies the end of a line. Perl also uses	character except one that signifies the end of a line. Perl also uses
\N to match characters by name; PCRE does not support this.	\N to match characters by name; PCRE does not support this.


MATCHING A SINGLE BYTE	MATCHING A SINGLE DATA UNIT

Outside a character class, the escape sequence \C matches any one byte,	Outside a character class, the escape sequence \C matches any one data
both in and out of UTF-8 mode. Unlike a dot, it always matches line-	unit, whether or not a UTF mode is set. In the 8-bit library, one data
ending characters. The feature is provided in Perl in order to match	unit is one byte; in the 16-bit library it is a 16-bit unit; in the
individual bytes in UTF-8 mode, but it is unclear how it can usefully	32-bit library it is a 32-bit unit. Unlike a dot, \C always matches
be used. Because \C breaks up characters into individual bytes, match-	line-ending characters. The feature is provided in Perl in order to
ing one byte with \C in UTF-8 mode means that the rest of the string	match individual bytes in UTF-8 mode, but it is unclear how it can use-
may start with a malformed UTF-8 character. This has undefined results,	fully be used. Because \C breaks up characters into individual data
because PCRE assumes that it is dealing with valid UTF-8 strings (and	units, matching one unit with \C in a UTF mode means that the rest of
by default it checks this at the start of processing unless the	the string may start with a malformed UTF character. This has undefined
PCRE_NO_UTF8_CHECK option is used).	results, because PCRE assumes that it is dealing with valid UTF strings
	(and by default it checks this at the start of processing unless the
	PCRE_NO_UTF8_CHECK, PCRE_NO_UTF16_CHECK or PCRE_NO_UTF32_CHECK option
	is used).

PCRE does not allow \C to appear in lookbehind assertions (described	PCRE does not allow \C to appear in lookbehind assertions (described
below) in UTF-8 mode, because this would make it impossible to calcu-	below) in a UTF mode, because this would make it impossible to calcu-
late the length of the lookbehind.	late the length of the lookbehind.

In general, the \C escape sequence is best avoided in UTF-8 mode. How-	In general, the \C escape sequence is best avoided. However, one way of
ever, one way of using it that avoids the problem of malformed UTF-8	using it that avoids the problem of malformed UTF characters is to use
characters is to use a lookahead to check the length of the next char-	a lookahead to check the length of the next character, as in this pat-
acter, as in this pattern (ignore white space and line breaks):	tern, which could be used with a UTF-8 string (ignore white space and
	line breaks):

(?\| (?=[\x00-\x7f])(\C) \|	(?\| (?=[\x00-\x7f])(\C) \|
(?=[\x80-\x{7ff}])(\C)(\C) \|	(?=[\x80-\x{7ff}])(\C)(\C) \|
(?=[\x{800}-\x{ffff}])(\C)(\C)(\C) \|	(?=[\x{800}-\x{ffff}])(\C)(\C)(\C) \|
(?=[\x{10000}-\x{1fffff}])(\C)(\C)(\C)(\C))	(?=[\x{10000}-\x{1fffff}])(\C)(\C)(\C)(\C))

A group that starts with (?\| resets the capturing parentheses numbers	A group that starts with (?\| resets the capturing parentheses numbers
in each alternative (see "Duplicate Subpattern Numbers" below). The	in each alternative (see "Duplicate Subpattern Numbers" below). The
assertions at the start of each branch check the next UTF-8 character	assertions at the start of each branch check the next UTF-8 character
for values whose encoding uses 1, 2, 3, or 4 bytes, respectively. The	for values whose encoding uses 1, 2, 3, or 4 bytes, respectively. The
character's individual bytes are then captured by the appropriate num-	character's individual bytes are then captured by the appropriate num-
ber of groups.	ber of groups.


Line 4229 SQUARE BRACKETS AND CHARACTER CLASSES	Line 5704 SQUARE BRACKETS AND CHARACTER CLASSES
closing square bracket. A closing square bracket on its own is not spe-	closing square bracket. A closing square bracket on its own is not spe-
cial by default. However, if the PCRE_JAVASCRIPT_COMPAT option is set,	cial by default. However, if the PCRE_JAVASCRIPT_COMPAT option is set,
a lone closing square bracket causes a compile-time error. If a closing	a lone closing square bracket causes a compile-time error. If a closing
square bracket is required as a member of the class, it should be the	square bracket is required as a member of the class, it should be the
first data character in the class (after an initial circumflex, if	first data character in the class (after an initial circumflex, if
present) or escaped with a backslash.	present) or escaped with a backslash.

A character class matches a single character in the subject. In UTF-8	A character class matches a single character in the subject. In a UTF
mode, the character may be more than one byte long. A matched character	mode, the character may be more than one data unit long. A matched
must be in the set of characters defined by the class, unless the first	character must be in the set of characters defined by the class, unless
character in the class definition is a circumflex, in which case the	the first character in the class definition is a circumflex, in which
subject character must not be in the set defined by the class. If a	case the subject character must not be in the set defined by the class.
circumflex is actually required as a member of the class, ensure it is	If a circumflex is actually required as a member of the class, ensure
not the first character, or escape it with a backslash.	it is not the first character, or escape it with a backslash.

For example, the character class [aeiou] matches any lower case vowel,	For example, the character class [aeiou] matches any lower case vowel,
while [^aeiou] matches any character that is not a lower case vowel.	while [^aeiou] matches any character that is not a lower case vowel.
Note that a circumflex is just a convenient notation for specifying the	Note that a circumflex is just a convenient notation for specifying the
characters that are in the class by enumerating those that are not. A	characters that are in the class by enumerating those that are not. A
class that starts with a circumflex is not an assertion; it still con-	class that starts with a circumflex is not an assertion; it still con-
sumes a character from the subject string, and therefore it fails if	sumes a character from the subject string, and therefore it fails if
the current pointer is at the end of the string.	the current pointer is at the end of the string.

In UTF-8 mode, characters with values greater than 255 can be included	In UTF-8 (UTF-16, UTF-32) mode, characters with values greater than 255
in a class as a literal string of bytes, or by using the \x{ escaping	(0xffff) can be included in a class as a literal string of data units,
mechanism.	or by using the \x{ escaping mechanism.

When caseless matching is set, any letters in a class represent both	When caseless matching is set, any letters in a class represent both
their upper case and lower case versions, so for example, a caseless	their upper case and lower case versions, so for example, a caseless
[aeiou] matches "A" as well as "a", and a caseless [^aeiou] does not	[aeiou] matches "A" as well as "a", and a caseless [^aeiou] does not
match "A", whereas a caseful version would. In UTF-8 mode, PCRE always	match "A", whereas a caseful version would. In a UTF mode, PCRE always
understands the concept of case for characters whose values are less	understands the concept of case for characters whose values are less
than 128, so caseless matching is always possible. For characters with	than 128, so caseless matching is always possible. For characters with
higher values, the concept of case is supported if PCRE is compiled	higher values, the concept of case is supported if PCRE is compiled
with Unicode property support, but not otherwise. If you want to use	with Unicode property support, but not otherwise. If you want to use
caseless matching in UTF8-mode for characters 128 and above, you must	caseless matching in a UTF mode for characters 128 and above, you must
ensure that PCRE is compiled with Unicode property support as well as	ensure that PCRE is compiled with Unicode property support as well as
with UTF-8 support.	with UTF support.

Characters that might indicate line breaks are never treated in any	Characters that might indicate line breaks are never treated in any
special way when matching character classes, whatever line-ending	special way when matching character classes, whatever line-ending
sequence is in use, and whatever setting of the PCRE_DOTALL and	sequence is in use, and whatever setting of the PCRE_DOTALL and
PCRE_MULTILINE options is used. A class such as [^a] always matches one	PCRE_MULTILINE options is used. A class such as [^a] always matches one
of these characters.	of these characters.

The minus (hyphen) character can be used to specify a range of charac-	The minus (hyphen) character can be used to specify a range of charac-
ters in a character class. For example, [d-m] matches any letter	ters in a character class. For example, [d-m] matches any letter
between d and m, inclusive. If a minus character is required in a	between d and m, inclusive. If a minus character is required in a
class, it must be escaped with a backslash or appear in a position	class, it must be escaped with a backslash or appear in a position
where it cannot be interpreted as indicating a range, typically as the	where it cannot be interpreted as indicating a range, typically as the
first or last character in the class.	first or last character in the class, or immediately after a range. For
	example, [b-d-z] matches letters in the range b to d, a hyphen charac-
	ter, or z.

It is not possible to have the literal character "]" as the end charac-	It is not possible to have the literal character "]" as the end charac-
ter of a range. A pattern such as [W-]46] is interpreted as a class of	ter of a range. A pattern such as [W-]46] is interpreted as a class of
two characters ("W" and "-") followed by a literal string "46]", so it	two characters ("W" and "-") followed by a literal string "46]", so it
would match "W46]" or "-46]". However, if the "]" is escaped with a	would match "W46]" or "-46]". However, if the "]" is escaped with a
backslash it is interpreted as the end of range, so [W-\]46] is inter-	backslash it is interpreted as the end of range, so [W-\]46] is inter-
preted as a class containing a range followed by two other characters.	preted as a class containing a range followed by two other characters.
The octal or hexadecimal representation of "]" can also be used to end	The octal or hexadecimal representation of "]" can also be used to end
a range.	a range.

	An error is generated if a POSIX character class (see below) or an
	escape sequence other than one that defines a single character appears
	at a point where a range ending character is expected. For example,
	[z-\xff] is valid, but [A-\d] and [A-[:digit:]] are not.

Ranges operate in the collating sequence of character values. They can	Ranges operate in the collating sequence of character values. They can
also be used for characters specified numerically, for example	also be used for characters specified numerically, for example
[\000-\037]. In UTF-8 mode, ranges can include characters whose values	[\000-\037]. Ranges can include any characters that are valid for the
are greater than 255, for example [\x{100}-\x{2ff}].	current mode.

If a range that includes letters is used when caseless matching is set,	If a range that includes letters is used when caseless matching is set,
it matches the letters in either case. For example, [W-c] is equivalent	it matches the letters in either case. For example, [W-c] is equivalent
to [][\\^_`wxyzabc], matched caselessly, and in non-UTF-8 mode, if	to [][\\^_`wxyzabc], matched caselessly, and in a non-UTF mode, if
character tables for a French locale are in use, [\xc8-\xcb] matches	character tables for a French locale are in use, [\xc8-\xcb] matches
accented E characters in both cases. In UTF-8 mode, PCRE supports the	accented E characters in both cases. In UTF modes, PCRE supports the
concept of case for characters with values greater than 128 only when	concept of case for characters with values greater than 128 only when
it is compiled with Unicode property support.	it is compiled with Unicode property support.

The character escape sequences \d, \D, \h, \H, \p, \P, \s, \S, \v, \V,	The character escape sequences \d, \D, \h, \H, \p, \P, \s, \S, \v, \V,
\w, and \W may appear in a character class, and add the characters that	\w, and \W may appear in a character class, and add the characters that
they match to the class. For example, [\dABCDEF] matches any hexadeci-	they match to the class. For example, [\dABCDEF] matches any hexadeci-
mal digit. In UTF-8 mode, the PCRE_UCP option affects the meanings of	mal digit. In UTF modes, the PCRE_UCP option affects the meanings of
\d, \s, \w and their upper case partners, just as it does when they	\d, \s, \w and their upper case partners, just as it does when they
appear outside a character class, as described in the section entitled	appear outside a character class, as described in the section entitled
"Generic character types" above. The escape sequence \b has a different	"Generic character types" above. The escape sequence \b has a different
Line 4323 SQUARE BRACKETS AND CHARACTER CLASSES	Line 5805 SQUARE BRACKETS AND CHARACTER CLASSES
The only metacharacters that are recognized in character classes are	The only metacharacters that are recognized in character classes are
backslash, hyphen (only where it can be interpreted as specifying a	backslash, hyphen (only where it can be interpreted as specifying a
range), circumflex (only at the start), opening square bracket (only	range), circumflex (only at the start), opening square bracket (only
when it can be interpreted as introducing a POSIX class name - see the	when it can be interpreted as introducing a POSIX class name, or for a
next section), and the terminating closing square bracket. However,	special compatibility feature - see the next two sections), and the
escaping other non-alphanumeric characters does no harm.	terminating closing square bracket. However, escaping other non-
	alphanumeric characters does no harm.


POSIX CHARACTER CLASSES	POSIX CHARACTER CLASSES

Perl supports the POSIX notation for character classes. This uses names	Perl supports the POSIX notation for character classes. This uses names
enclosed by [: and :] within the enclosing square brackets. PCRE also	enclosed by [: and :] within the enclosing square brackets. PCRE also
supports this notation. For example,	supports this notation. For example,

[01[:alpha:]%]	[01[:alpha:]%]
Line 4349 POSIX CHARACTER CLASSES	Line 5832 POSIX CHARACTER CLASSES
lower lower case letters	lower lower case letters
print printing characters, including space	print printing characters, including space
punct printing characters, excluding letters and digits and space	punct printing characters, excluding letters and digits and space
space white space (not quite the same as \s)	space white space (the same as \s from PCRE 8.34)
upper upper case letters	upper upper case letters
word "word" characters (same as \w)	word "word" characters (same as \w)
xdigit hexadecimal digits	xdigit hexadecimal digits

The "space" characters are HT (9), LF (10), VT (11), FF (12), CR (13),	The default "space" characters are HT (9), LF (10), VT (11), FF (12),
and space (32). Notice that this list includes the VT character (code	CR (13), and space (32). If locale-specific matching is taking place,
11). This makes "space" different to \s, which does not include VT (for	the list of space characters may be different; there may be fewer or
Perl compatibility).	more of them. "Space" used to be different to \s, which did not include
	VT, for Perl compatibility. However, Perl changed at release 5.18, and
	PCRE followed at release 8.34. "Space" and \s now match the same set
	of characters.

The name "word" is a Perl extension, and "blank" is a GNU extension	The name "word" is a Perl extension, and "blank" is a GNU extension
from Perl 5.8. Another Perl extension is negation, which is indicated	from Perl 5.8. Another Perl extension is negation, which is indicated
Line 4369 POSIX CHARACTER CLASSES	Line 5855 POSIX CHARACTER CLASSES
POSIX syntax [.ch.] and [=ch=] where "ch" is a "collating element", but	POSIX syntax [.ch.] and [=ch=] where "ch" is a "collating element", but
these are not supported, and an error is given if they are encountered.	these are not supported, and an error is given if they are encountered.

By default, in UTF-8 mode, characters with values greater than 128 do	By default, characters with values greater than 128 do not match any of
not match any of the POSIX character classes. However, if the PCRE_UCP	the POSIX character classes. However, if the PCRE_UCP option is passed
option is passed to pcre_compile(), some of the classes are changed so	to pcre_compile(), some of the classes are changed so that Unicode
that Unicode character properties are used. This is achieved by replac-	character properties are used. This is achieved by replacing certain
ing the POSIX classes by other sequences, as follows:	POSIX classes by other sequences, as follows:

[:alnum:] becomes \p{Xan}	[:alnum:] becomes \p{Xan}
[:alpha:] becomes \p{L}	[:alpha:] becomes \p{L}
Line 4384 POSIX CHARACTER CLASSES	Line 5870 POSIX CHARACTER CLASSES
[:upper:] becomes \p{Lu}	[:upper:] becomes \p{Lu}
[:word:] becomes \p{Xwd}	[:word:] becomes \p{Xwd}

Negated versions, such as [:^alpha:] use \P instead of \p. The other	Negated versions, such as [:^alpha:] use \P instead of \p. Three other
POSIX classes are unchanged, and match only characters with code points	POSIX classes are handled specially in UCP mode:
less than 128.

	[:graph:] This matches characters that have glyphs that mark the page
	when printed. In Unicode property terms, it matches all char-
	acters with the L, M, N, P, S, or Cf properties, except for:

	U+061C Arabic Letter Mark
	U+180E Mongolian Vowel Separator
	U+2066 - U+2069 Various "isolate"s


	[:print:] This matches the same characters as [:graph:] plus space
	characters that are not controls, that is, characters with
	the Zs property.

	[:punct:] This matches all characters that have the Unicode P (punctua-
	tion) property, plus those characters whose code points are
	less than 128 that have the S (Symbol) property.

	The other POSIX classes are unchanged, and match only characters with
	code points less than 128.


	COMPATIBILITY FEATURE FOR WORD BOUNDARIES

	In the POSIX.2 compliant library that was included in 4.4BSD Unix, the
	ugly syntax [[:<:]] and [[:>:]] is used for matching "start of word"
	and "end of word". PCRE treats these items as follows:

	[[:<:]] is converted to \b(?=\w)
	[[:>:]] is converted to \b(?<=\w)

	Only these exact character sequences are recognized. A sequence such as
	[a[:<:]b] provokes error for an unrecognized POSIX class name. This
	support is not compatible with Perl. It is provided to help migrations
	from other environments, and is best not used in any new patterns. Note
	that \b matches at the start and the end of a word (see "Simple asser-
	tions" above), and in a Perl-style pattern the preceding or following
	character normally shows which is wanted, without the need for the
	assertions that are used above in order to give exactly the POSIX be-
	haviour.


VERTICAL BAR	VERTICAL BAR

Vertical bar characters are used to separate alternative patterns. For	Vertical bar characters are used to separate alternative patterns. For
Line 4453 INTERNAL OPTION SETTING	Line 5978 INTERNAL OPTION SETTING
some very weird behaviour otherwise.	some very weird behaviour otherwise.

Note: There are other PCRE-specific options that can be set by the	Note: There are other PCRE-specific options that can be set by the
application when the compile or match functions are called. In some	application when the compiling or matching functions are called. In
cases the pattern can contain special leading sequences such as (*CRLF)	some cases the pattern can contain special leading sequences such as
to override what the application has set or what has been defaulted.	(*CRLF) to override what the application has set or what has been
Details are given in the section entitled "Newline sequences" above.	defaulted. Details are given in the section entitled "Newline
There are also the (UTF8) and (UCP) leading sequences that can be	sequences" above. There are also the (UTF8), (UTF16),(*UTF32), and
used to set UTF-8 and Unicode property modes; they are equivalent to	(*UCP) leading sequences that can be used to set UTF and Unicode prop-
setting the PCRE_UTF8 and the PCRE_UCP options, respectively.	erty modes; they are equivalent to setting the PCRE_UTF8, PCRE_UTF16,
	PCRE_UTF32 and the PCRE_UCP options, respectively. The (*UTF) sequence
	is a generic version that can be used with any of the libraries. How-
	ever, the application can set the PCRE_NEVER_UTF option, which locks
	out the use of the (*UTF) sequences.


SUBPATTERNS	SUBPATTERNS
Line 4477 SUBPATTERNS	Line 6006 SUBPATTERNS
2. It sets up the subpattern as a capturing subpattern. This means	2. It sets up the subpattern as a capturing subpattern. This means
that, when the whole pattern matches, that portion of the subject	that, when the whole pattern matches, that portion of the subject
string that matched the subpattern is passed back to the caller via the	string that matched the subpattern is passed back to the caller via the
ovector argument of pcre_exec(). Opening parentheses are counted from	ovector argument of the matching function. (This applies only to the
left to right (starting from 1) to obtain numbers for the capturing	traditional matching functions; the DFA matching functions do not sup-
subpatterns. For example, if the string "the red king" is matched	port capturing.)
against the pattern

	Opening parentheses are counted from left to right (starting from 1) to
	obtain numbers for the capturing subpatterns. For example, if the
	string "the red king" is matched against the pattern

the ((red\|white) (king\|queen))	the ((red\|white) (king\|queen))

the captured substrings are "red king", "red", and "king", and are num-	the captured substrings are "red king", "red", and "king", and are num-
bered 1, 2, and 3, respectively.	bered 1, 2, and 3, respectively.

The fact that plain parentheses fulfil two functions is not always	The fact that plain parentheses fulfil two functions is not always
helpful. There are often times when a grouping subpattern is required	helpful. There are often times when a grouping subpattern is required
without a capturing requirement. If an opening parenthesis is followed	without a capturing requirement. If an opening parenthesis is followed
by a question mark and a colon, the subpattern does not do any captur-	by a question mark and a colon, the subpattern does not do any captur-
ing, and is not counted when computing the number of any subsequent	ing, and is not counted when computing the number of any subsequent
capturing subpatterns. For example, if the string "the white queen" is	capturing subpatterns. For example, if the string "the white queen" is
matched against the pattern	matched against the pattern

the ((?:red\|white) (king\|queen))	the ((?:red\|white) (king\|queen))
Line 4500 SUBPATTERNS	Line 6032 SUBPATTERNS
the captured substrings are "white queen" and "queen", and are numbered	the captured substrings are "white queen" and "queen", and are numbered
1 and 2. The maximum number of capturing subpatterns is 65535.	1 and 2. The maximum number of capturing subpatterns is 65535.

As a convenient shorthand, if any option settings are required at the	As a convenient shorthand, if any option settings are required at the
start of a non-capturing subpattern, the option letters may appear	start of a non-capturing subpattern, the option letters may appear
between the "?" and the ":". Thus the two patterns	between the "?" and the ":". Thus the two patterns

(?i:saturday\|sunday)	(?i:saturday\|sunday)
(?:(?i)saturday\|sunday)	(?:(?i)saturday\|sunday)

match exactly the same set of strings. Because alternative branches are	match exactly the same set of strings. Because alternative branches are
tried from left to right, and options are not reset until the end of	tried from left to right, and options are not reset until the end of
the subpattern is reached, an option setting in one branch does affect	the subpattern is reached, an option setting in one branch does affect
subsequent branches, so the above patterns match "SUNDAY" as well as	subsequent branches, so the above patterns match "SUNDAY" as well as
"Saturday".	"Saturday".


DUPLICATE SUBPATTERN NUMBERS	DUPLICATE SUBPATTERN NUMBERS

Perl 5.10 introduced a feature whereby each alternative in a subpattern	Perl 5.10 introduced a feature whereby each alternative in a subpattern
uses the same numbers for its capturing parentheses. Such a subpattern	uses the same numbers for its capturing parentheses. Such a subpattern
starts with (?\| and is itself a non-capturing subpattern. For example,	starts with (?\| and is itself a non-capturing subpattern. For example,
consider this pattern:	consider this pattern:

(?\|(Sat)ur\|(Sun))day	(?\|(Sat)ur\|(Sun))day

Because the two alternatives are inside a (?\| group, both sets of cap-	Because the two alternatives are inside a (?\| group, both sets of cap-
turing parentheses are numbered one. Thus, when the pattern matches,	turing parentheses are numbered one. Thus, when the pattern matches,
you can look at captured substring number one, whichever alternative	you can look at captured substring number one, whichever alternative
matched. This construct is useful when you want to capture part, but	matched. This construct is useful when you want to capture part, but
not all, of one of a number of alternatives. Inside a (?\| group, paren-	not all, of one of a number of alternatives. Inside a (?\| group, paren-
theses are numbered as usual, but the number is reset at the start of	theses are numbered as usual, but the number is reset at the start of
each branch. The numbers of any capturing parentheses that follow the	each branch. The numbers of any capturing parentheses that follow the
subpattern start after the highest number used in any branch. The fol-	subpattern start after the highest number used in any branch. The fol-
lowing example is taken from the Perl documentation. The numbers under-	lowing example is taken from the Perl documentation. The numbers under-
neath show in which buffer the captured content will be stored.	neath show in which buffer the captured content will be stored.

Line 4538 DUPLICATE SUBPATTERN NUMBERS	Line 6070 DUPLICATE SUBPATTERN NUMBERS
/ ( a ) (?\| x ( y ) z \| (p (q) r) \| (t) u (v) ) ( z ) /x	/ ( a ) (?\| x ( y ) z \| (p (q) r) \| (t) u (v) ) ( z ) /x
# 1 2 2 3 2 3 4	# 1 2 2 3 2 3 4

A back reference to a numbered subpattern uses the most recent value	A back reference to a numbered subpattern uses the most recent value
that is set for that number by any subpattern. The following pattern	that is set for that number by any subpattern. The following pattern
matches "abcabc" or "defdef":	matches "abcabc" or "defdef":

/(?\|(abc)\|(def))\1/	/(?\|(abc)\|(def))\1/

In contrast, a subroutine call to a numbered subpattern always refers	In contrast, a subroutine call to a numbered subpattern always refers
to the first one in the pattern with the given number. The following	to the first one in the pattern with the given number. The following
pattern matches "abcabc" or "defabc":	pattern matches "abcabc" or "defabc":

/(?\|(abc)\|(def))(?1)/	/(?\|(abc)\|(def))(?1)/

If a condition test for a subpattern's having matched refers to a non-	If a condition test for a subpattern's having matched refers to a non-
unique number, the test is true if any of the subpatterns of that num-	unique number, the test is true if any of the subpatterns of that num-
ber have matched.	ber have matched.

An alternative approach to using this "branch reset" feature is to use	An alternative approach to using this "branch reset" feature is to use
duplicate named subpatterns, as described in the next section.	duplicate named subpatterns, as described in the next section.


NAMED SUBPATTERNS	NAMED SUBPATTERNS

Identifying capturing parentheses by number is simple, but it can be	Identifying capturing parentheses by number is simple, but it can be
very hard to keep track of the numbers in complicated regular expres-	very hard to keep track of the numbers in complicated regular expres-
sions. Furthermore, if an expression is modified, the numbers may	sions. Furthermore, if an expression is modified, the numbers may
change. To help with this difficulty, PCRE supports the naming of sub-	change. To help with this difficulty, PCRE supports the naming of sub-
patterns. This feature was not added to Perl until release 5.10. Python	patterns. This feature was not added to Perl until release 5.10. Python
had the feature earlier, and PCRE introduced it at release 4.0, using	had the feature earlier, and PCRE introduced it at release 4.0, using
the Python syntax. PCRE now supports both the Perl and the Python syn-	the Python syntax. PCRE now supports both the Perl and the Python syn-
tax. Perl allows identically numbered subpatterns to have different	tax. Perl allows identically numbered subpatterns to have different
names, but PCRE does not.	names, but PCRE does not.

In PCRE, a subpattern can be named in one of three ways: (?<name>...)	In PCRE, a subpattern can be named in one of three ways: (?<name>...)
or (?'name'...) as in Perl, or (?P<name>...) as in Python. References	or (?'name'...) as in Perl, or (?P<name>...) as in Python. References
to capturing parentheses from other parts of the pattern, such as back	to capturing parentheses from other parts of the pattern, such as back
references, recursion, and conditions, can be made by name as well as	references, recursion, and conditions, can be made by name as well as
by number.	by number.

Names consist of up to 32 alphanumeric characters and underscores.	Names consist of up to 32 alphanumeric characters and underscores, but
Named capturing parentheses are still allocated numbers as well as	must start with a non-digit. Named capturing parentheses are still
names, exactly as if the names were not present. The PCRE API provides	allocated numbers as well as names, exactly as if the names were not
function calls for extracting the name-to-number translation table from	present. The PCRE API provides function calls for extracting the name-
a compiled pattern. There is also a convenience function for extracting	to-number translation table from a compiled pattern. There is also a
a captured substring by name.	convenience function for extracting a captured substring by name.

By default, a name must be unique within a pattern, but it is possible	By default, a name must be unique within a pattern, but it is possible
to relax this constraint by setting the PCRE_DUPNAMES option at compile	to relax this constraint by setting the PCRE_DUPNAMES option at compile
time. (Duplicate names are also always permitted for subpatterns with	time. (Duplicate names are also always permitted for subpatterns with
the same number, set up as described in the previous section.) Dupli-	the same number, set up as described in the previous section.) Dupli-
cate names can be useful for patterns where only one instance of the	cate names can be useful for patterns where only one instance of the
named parentheses can match. Suppose you want to match the name of a	named parentheses can match. Suppose you want to match the name of a
weekday, either as a 3-letter abbreviation or as the full name, and in	weekday, either as a 3-letter abbreviation or as the full name, and in
both cases you want to extract the abbreviation. This pattern (ignoring	both cases you want to extract the abbreviation. This pattern (ignoring
the line breaks) does the job:	the line breaks) does the job:

Line 4599 NAMED SUBPATTERNS	Line 6131 NAMED SUBPATTERNS
(?<DN>Thu)(?:rsday)?\|	(?<DN>Thu)(?:rsday)?\|
(?<DN>Sat)(?:urday)?	(?<DN>Sat)(?:urday)?

There are five capturing substrings, but only one is ever set after a	There are five capturing substrings, but only one is ever set after a
match. (An alternative way of solving this problem is to use a "branch	match. (An alternative way of solving this problem is to use a "branch
reset" subpattern, as described in the previous section.)	reset" subpattern, as described in the previous section.)

The convenience function for extracting the data by name returns the	The convenience function for extracting the data by name returns the
substring for the first (and in this example, the only) subpattern of	substring for the first (and in this example, the only) subpattern of
that name that matched. This saves searching to find which numbered	that name that matched. This saves searching to find which numbered
subpattern it was.	subpattern it was.

If you make a back reference to a non-unique named subpattern from	If you make a back reference to a non-unique named subpattern from
elsewhere in the pattern, the one that corresponds to the first occur-	elsewhere in the pattern, the subpatterns to which the name refers are
rence of the name is used. In the absence of duplicate numbers (see the	checked in the order in which they appear in the overall pattern. The
previous section) this is the one with the lowest number. If you use a	first one that is set is used for the reference. For example, this pat-
named reference in a condition test (see the section about conditions	tern matches both "foofoo" and "barbar" but not "foobar" or "barfoo":
below), either to check whether a subpattern has matched, or to check
for recursion, all subpatterns with the same name are tested. If the
condition is true for any one of them, the overall condition is true.
This is the same behaviour as testing by number. For further details of
the interfaces for handling named subpatterns, see the pcreapi documen-
tation.

	(?:(?<n>foo)\|(?<n>bar))\k<n>


	If you make a subroutine call to a non-unique named subpattern, the one
	that corresponds to the first occurrence of the name is used. In the
	absence of duplicate numbers (see the previous section) this is the one
	with the lowest number.

	If you use a named reference in a condition test (see the section about
	conditions below), either to check whether a subpattern has matched, or
	to check for recursion, all subpatterns with the same name are tested.
	If the condition is true for any one of them, the overall condition is
	true. This is the same behaviour as testing by number. For further
	details of the interfaces for handling named subpatterns, see the
	pcreapi documentation.

Warning: You cannot use different names to distinguish between two sub-	Warning: You cannot use different names to distinguish between two sub-
patterns with the same number because PCRE uses only the numbers when	patterns with the same number because PCRE uses only the numbers when
matching. For this reason, an error is given at compile time if differ-	matching. For this reason, an error is given at compile time if differ-
ent names are given to subpatterns with the same number. However, you	ent names are given to subpatterns with the same number. However, you
can give the same name to subpatterns with the same number, even when	can always give the same name to subpatterns with the same number, even
PCRE_DUPNAMES is not set.	when PCRE_DUPNAMES is not set.


REPETITION	REPETITION
Line 4636 REPETITION	Line 6178 REPETITION
a literal data character	a literal data character
the dot metacharacter	the dot metacharacter
the \C escape sequence	the \C escape sequence
the \X escape sequence (in UTF-8 mode with Unicode properties)	the \X escape sequence
the \R escape sequence	the \R escape sequence
an escape such as \d or \pL that matches a single character	an escape such as \d or \pL that matches a single character
a character class	a character class
Line 4668 REPETITION	Line 6210 REPETITION
the syntax of a quantifier, is taken as a literal character. For exam-	the syntax of a quantifier, is taken as a literal character. For exam-
ple, {,6} is not a quantifier, but a literal string of four characters.	ple, {,6} is not a quantifier, but a literal string of four characters.

In UTF-8 mode, quantifiers apply to UTF-8 characters rather than to	In UTF modes, quantifiers apply to characters rather than to individual
individual bytes. Thus, for example, \x{100}{2} matches two UTF-8 char-	data units. Thus, for example, \x{100}{2} matches two characters, each
acters, each of which is represented by a two-byte sequence. Similarly,	of which is represented by a two-byte sequence in a UTF-8 string. Simi-
when Unicode property support is available, \X{3} matches three Unicode	larly, \X{3} matches three Unicode extended grapheme clusters, each of
extended sequences, each of which may be several bytes long (and they	which may be several data units long (and they may be of different
may be of different lengths).	lengths).

The quantifier {0} is permitted, causing the expression to behave as if	The quantifier {0} is permitted, causing the expression to behave as if
the previous item and the quantifier were not present. This may be use-	the previous item and the quantifier were not present. This may be use-
Line 4757 REPETITION	Line 6299 REPETITION
lines, it is worth setting PCRE_DOTALL in order to obtain this opti-	lines, it is worth setting PCRE_DOTALL in order to obtain this opti-
mization, or alternatively using ^ to indicate anchoring explicitly.	mization, or alternatively using ^ to indicate anchoring explicitly.

However, there is one situation where the optimization cannot be used.	However, there are some cases where the optimization cannot be used.
When .* is inside capturing parentheses that are the subject of a back	When .* is inside capturing parentheses that are the subject of a back
reference elsewhere in the pattern, a match at the start may fail where	reference elsewhere in the pattern, a match at the start may fail where
a later one succeeds. Consider, for example:	a later one succeeds. Consider, for example:
Line 4767 REPETITION	Line 6309 REPETITION
If the subject is "xyz123abc123" the match point is the fourth charac-	If the subject is "xyz123abc123" the match point is the fourth charac-
ter. For this reason, such a pattern is not implicitly anchored.	ter. For this reason, such a pattern is not implicitly anchored.

	Another case where implicit anchoring is not applied is when the lead-
	ing .* is inside an atomic group. Once again, a match at the start may
	fail where a later one succeeds. Consider this pattern:

	(?>.*?a)b

	It matches "ab" in the subject "aab". The use of the backtracking con-
	trol verbs (PRUNE) and (SKIP) also disable this optimization.

When a capturing subpattern is repeated, the value captured is the sub-	When a capturing subpattern is repeated, the value captured is the sub-
string that matched the final iteration. For example, after	string that matched the final iteration. For example, after

(tweedle[dume]{3}\s*)+	(tweedle[dume]{3}\s*)+

has matched "tweedledum tweedledee" the value of the captured substring	has matched "tweedledum tweedledee" the value of the captured substring
is "tweedledee". However, if there are nested capturing subpatterns,	is "tweedledee". However, if there are nested capturing subpatterns,
the corresponding captured values may have been set in previous itera-	the corresponding captured values may have been set in previous itera-
tions. For example, after	tions. For example, after

/(a\|(b))+/	/(a\|(b))+/
Line 4784 REPETITION	Line 6335 REPETITION

ATOMIC GROUPING AND POSSESSIVE QUANTIFIERS	ATOMIC GROUPING AND POSSESSIVE QUANTIFIERS

With both maximizing ("greedy") and minimizing ("ungreedy" or "lazy")	With both maximizing ("greedy") and minimizing ("ungreedy" or "lazy")
repetition, failure of what follows normally causes the repeated item	repetition, failure of what follows normally causes the repeated item
to be re-evaluated to see if a different number of repeats allows the	to be re-evaluated to see if a different number of repeats allows the
rest of the pattern to match. Sometimes it is useful to prevent this,	rest of the pattern to match. Sometimes it is useful to prevent this,
either to change the nature of the match, or to cause it fail earlier	either to change the nature of the match, or to cause it fail earlier
than it otherwise might, when the author of the pattern knows there is	than it otherwise might, when the author of the pattern knows there is
no point in carrying on.	no point in carrying on.

Consider, for example, the pattern \d+foo when applied to the subject	Consider, for example, the pattern \d+foo when applied to the subject
line	line

123456bar	123456bar

After matching all 6 digits and then failing to match "foo", the normal	After matching all 6 digits and then failing to match "foo", the normal
action of the matcher is to try again with only 5 digits matching the	action of the matcher is to try again with only 5 digits matching the
\d+ item, and then with 4, and so on, before ultimately failing.	\d+ item, and then with 4, and so on, before ultimately failing.
"Atomic grouping" (a term taken from Jeffrey Friedl's book) provides	"Atomic grouping" (a term taken from Jeffrey Friedl's book) provides
the means for specifying that once a subpattern has matched, it is not	the means for specifying that once a subpattern has matched, it is not
to be re-evaluated in this way.	to be re-evaluated in this way.

If we use atomic grouping for the previous example, the matcher gives	If we use atomic grouping for the previous example, the matcher gives
up immediately on failing to match "foo" the first time. The notation	up immediately on failing to match "foo" the first time. The notation
is a kind of special parenthesis, starting with (?> as in this example:	is a kind of special parenthesis, starting with (?> as in this example:

(?>\d+)foo	(?>\d+)foo

This kind of parenthesis "locks up" the part of the pattern it con-	This kind of parenthesis "locks up" the part of the pattern it con-
tains once it has matched, and a failure further into the pattern is	tains once it has matched, and a failure further into the pattern is
prevented from backtracking into it. Backtracking past it to previous	prevented from backtracking into it. Backtracking past it to previous
items, however, works as normal.	items, however, works as normal.

An alternative description is that a subpattern of this type matches	An alternative description is that a subpattern of this type matches
the string of characters that an identical standalone pattern would	the string of characters that an identical standalone pattern would
match, if anchored at the current point in the subject string.	match, if anchored at the current point in the subject string.

Atomic grouping subpatterns are not capturing subpatterns. Simple cases	Atomic grouping subpatterns are not capturing subpatterns. Simple cases
such as the above example can be thought of as a maximizing repeat that	such as the above example can be thought of as a maximizing repeat that
must swallow everything it can. So, while both \d+ and \d+? are pre-	must swallow everything it can. So, while both \d+ and \d+? are pre-
pared to adjust the number of digits they match in order to make the	pared to adjust the number of digits they match in order to make the
rest of the pattern match, (?>\d+) can only match an entire sequence of	rest of the pattern match, (?>\d+) can only match an entire sequence of
digits.	digits.

Atomic groups in general can of course contain arbitrarily complicated	Atomic groups in general can of course contain arbitrarily complicated
subpatterns, and can be nested. However, when the subpattern for an	subpatterns, and can be nested. However, when the subpattern for an
atomic group is just a single repeated item, as in the example above, a	atomic group is just a single repeated item, as in the example above, a
simpler notation, called a "possessive quantifier" can be used. This	simpler notation, called a "possessive quantifier" can be used. This
consists of an additional + character following a quantifier. Using	consists of an additional + character following a quantifier. Using
this notation, the previous example can be rewritten as	this notation, the previous example can be rewritten as

\d++foo	\d++foo
Line 4840 ATOMIC GROUPING AND POSSESSIVE QUANTIFIERS	Line 6391 ATOMIC GROUPING AND POSSESSIVE QUANTIFIERS

(abc\|xyz){2,3}+	(abc\|xyz){2,3}+

Possessive quantifiers are always greedy; the setting of the	Possessive quantifiers are always greedy; the setting of the
PCRE_UNGREEDY option is ignored. They are a convenient notation for the	PCRE_UNGREEDY option is ignored. They are a convenient notation for the
simpler forms of atomic group. However, there is no difference in the	simpler forms of atomic group. However, there is no difference in the
meaning of a possessive quantifier and the equivalent atomic group,	meaning of a possessive quantifier and the equivalent atomic group,
though there may be a performance difference; possessive quantifiers	though there may be a performance difference; possessive quantifiers
should be slightly faster.	should be slightly faster.

The possessive quantifier syntax is an extension to the Perl 5.8 syn-	The possessive quantifier syntax is an extension to the Perl 5.8 syn-
tax. Jeffrey Friedl originated the idea (and the name) in the first	tax. Jeffrey Friedl originated the idea (and the name) in the first
edition of his book. Mike McCloskey liked it, so implemented it when he	edition of his book. Mike McCloskey liked it, so implemented it when he
built Sun's Java package, and PCRE copied it from there. It ultimately	built Sun's Java package, and PCRE copied it from there. It ultimately
found its way into Perl at release 5.10.	found its way into Perl at release 5.10.

PCRE has an optimization that automatically "possessifies" certain sim-	PCRE has an optimization that automatically "possessifies" certain sim-
ple pattern constructs. For example, the sequence A+B is treated as	ple pattern constructs. For example, the sequence A+B is treated as
A++B because there is no point in backtracking into a sequence of A's	A++B because there is no point in backtracking into a sequence of A's
when B must follow.	when B must follow.

When a pattern contains an unlimited repeat inside a subpattern that	When a pattern contains an unlimited repeat inside a subpattern that
can itself be repeated an unlimited number of times, the use of an	can itself be repeated an unlimited number of times, the use of an
atomic group is the only way to avoid some failing matches taking a	atomic group is the only way to avoid some failing matches taking a
very long time indeed. The pattern	very long time indeed. The pattern

(\D+\|<\d+>)*[!?]	(\D+\|<\d+>)*[!?]

matches an unlimited number of substrings that either consist of non-	matches an unlimited number of substrings that either consist of non-
digits, or digits enclosed in <>, followed by either ! or ?. When it	digits, or digits enclosed in <>, followed by either ! or ?. When it
matches, it runs quickly. However, if it is applied to	matches, it runs quickly. However, if it is applied to

aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa	aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa

it takes a long time before reporting failure. This is because the	it takes a long time before reporting failure. This is because the
string can be divided between the internal \D+ repeat and the external	string can be divided between the internal \D+ repeat and the external
* repeat in a large number of ways, and all have to be tried. (The	* repeat in a large number of ways, and all have to be tried. (The
example uses [!?] rather than a single character at the end, because	example uses [!?] rather than a single character at the end, because
both PCRE and Perl have an optimization that allows for fast failure	both PCRE and Perl have an optimization that allows for fast failure
when a single character is used. They remember the last single charac-	when a single character is used. They remember the last single charac-
ter that is required for a match, and fail early if it is not present	ter that is required for a match, and fail early if it is not present
in the string.) If the pattern is changed so that it uses an atomic	in the string.) If the pattern is changed so that it uses an atomic
group, like this:	group, like this:

((?>\D+)\|<\d+>)*[!?]	((?>\D+)\|<\d+>)*[!?]
Line 4890 BACK REFERENCES	Line 6441 BACK REFERENCES

Outside a character class, a backslash followed by a digit greater than	Outside a character class, a backslash followed by a digit greater than
0 (and possibly further digits) is a back reference to a capturing sub-	0 (and possibly further digits) is a back reference to a capturing sub-
pattern earlier (that is, to its left) in the pattern, provided there	pattern earlier (that is, to its left) in the pattern, provided there
have been that many previous capturing left parentheses.	have been that many previous capturing left parentheses.

However, if the decimal number following the backslash is less than 10,	However, if the decimal number following the backslash is less than 10,
it is always taken as a back reference, and causes an error only if	it is always taken as a back reference, and causes an error only if
there are not that many capturing left parentheses in the entire pat-	there are not that many capturing left parentheses in the entire pat-
tern. In other words, the parentheses that are referenced need not be	tern. In other words, the parentheses that are referenced need not be
to the left of the reference for numbers less than 10. A "forward back	to the left of the reference for numbers less than 10. A "forward back
reference" of this type can make sense when a repetition is involved	reference" of this type can make sense when a repetition is involved
and the subpattern to the right has participated in an earlier itera-	and the subpattern to the right has participated in an earlier itera-
tion.	tion.

It is not possible to have a numerical "forward back reference" to a	It is not possible to have a numerical "forward back reference" to a
subpattern whose number is 10 or more using this syntax because a	subpattern whose number is 10 or more using this syntax because a
sequence such as \50 is interpreted as a character defined in octal.	sequence such as \50 is interpreted as a character defined in octal.
See the subsection entitled "Non-printing characters" above for further	See the subsection entitled "Non-printing characters" above for further
details of the handling of digits following a backslash. There is no	details of the handling of digits following a backslash. There is no
such problem when named parentheses are used. A back reference to any	such problem when named parentheses are used. A back reference to any
subpattern is possible using named parentheses (see below).	subpattern is possible using named parentheses (see below).

Another way of avoiding the ambiguity inherent in the use of digits	Another way of avoiding the ambiguity inherent in the use of digits
following a backslash is to use the \g escape sequence. This escape	following a backslash is to use the \g escape sequence. This escape
must be followed by an unsigned number or a negative number, optionally	must be followed by an unsigned number or a negative number, optionally
enclosed in braces. These examples are all identical:	enclosed in braces. These examples are all identical:

Line 4919 BACK REFERENCES	Line 6470 BACK REFERENCES
(ring), \g1	(ring), \g1
(ring), \g{1}	(ring), \g{1}

An unsigned number specifies an absolute reference without the ambigu-	An unsigned number specifies an absolute reference without the ambigu-
ity that is present in the older syntax. It is also useful when literal	ity that is present in the older syntax. It is also useful when literal
digits follow the reference. A negative number is a relative reference.	digits follow the reference. A negative number is a relative reference.
Consider this example:	Consider this example:
Line 4928 BACK REFERENCES	Line 6479 BACK REFERENCES

The sequence \g{-1} is a reference to the most recently started captur-	The sequence \g{-1} is a reference to the most recently started captur-
ing subpattern before \g, that is, is it equivalent to \2 in this exam-	ing subpattern before \g, that is, is it equivalent to \2 in this exam-
ple. Similarly, \g{-2} would be equivalent to \1. The use of relative	ple. Similarly, \g{-2} would be equivalent to \1. The use of relative
references can be helpful in long patterns, and also in patterns that	references can be helpful in long patterns, and also in patterns that
are created by joining together fragments that contain references	are created by joining together fragments that contain references
within themselves.	within themselves.

A back reference matches whatever actually matched the capturing sub-	A back reference matches whatever actually matched the capturing sub-
pattern in the current subject string, rather than anything matching	pattern in the current subject string, rather than anything matching
the subpattern itself (see "Subpatterns as subroutines" below for a way	the subpattern itself (see "Subpatterns as subroutines" below for a way
of doing that). So the pattern	of doing that). So the pattern

(sens\|respons)e and \1ibility	(sens\|respons)e and \1ibility

matches "sense and sensibility" and "response and responsibility", but	matches "sense and sensibility" and "response and responsibility", but
not "sense and responsibility". If caseful matching is in force at the	not "sense and responsibility". If caseful matching is in force at the
time of the back reference, the case of letters is relevant. For exam-	time of the back reference, the case of letters is relevant. For exam-
ple,	ple,

((?i)rah)\s+\1	((?i)rah)\s+\1

matches "rah rah" and "RAH RAH", but not "RAH rah", even though the	matches "rah rah" and "RAH RAH", but not "RAH rah", even though the
original capturing subpattern is matched caselessly.	original capturing subpattern is matched caselessly.

There are several different ways of writing back references to named	There are several different ways of writing back references to named
subpatterns. The .NET syntax \k{name} and the Perl syntax \k<name> or	subpatterns. The .NET syntax \k{name} and the Perl syntax \k<name> or
\k'name' are supported, as is the Python syntax (?P=name). Perl 5.10's	\k'name' are supported, as is the Python syntax (?P=name). Perl 5.10's
unified back reference syntax, in which \g can be used for both numeric	unified back reference syntax, in which \g can be used for both numeric
and named references, is also supported. We could rewrite the above	and named references, is also supported and named references, is also supported. We could rewrite the above
example in any of the following ways:	example in any of the following ways:

(?<p1>(?i)rah)\s+\k<p1>	(?<p1>(?i)rah)\s+\k<p1>
Line 4962 BACK REFERENCES	Line 6513 BACK REFERENCES
(?P<p1>(?i)rah)\s+(?P=p1)	(?P<p1>(?i)rah)\s+(?P=p1)
(?<p1>(?i)rah)\s+\g{p1}	(?<p1>(?i)rah)\s+\g{p1}

A subpattern that is referenced by name may appear in the pattern	A subpattern that is referenced by name may appear in the pattern
before or after the reference.	before or after the reference.

There may be more than one back reference to the same subpattern. If a	There may be more than one back reference to the same subpattern. If a
subpattern has not actually been used in a particular match, any back	subpattern has not actually been used in a particular match, any back
references to it always fail by default. For example, the pattern	references to it always fail by default. For example, the pattern

(a\|(bc))\2	(a\|(bc))\2

always fails if it starts to match "a" rather than "bc". However, if	always fails if it starts to match "a" rather than "bc". However, if
the PCRE_JAVASCRIPT_COMPAT option is set at compile time, a back refer-	the PCRE_JAVASCRIPT_COMPAT option is set at compile time, a back refer-
ence to an unset value matches an empty string.	ence to an unset value matches an empty string.

Because there may be many capturing parentheses in a pattern, all dig-	Because there may be many capturing parentheses in a pattern, all dig-
its following a backslash are taken as part of a potential back refer-	its following a backslash are taken as part of a potential back refer-
ence number. If the pattern continues with a digit character, some	ence number. If the pattern continues with a digit character, some
delimiter must be used to terminate the back reference. If the	delimiter must be used to terminate the back reference. If the
PCRE_EXTENDED option is set, this can be whitespace. Otherwise, the \g{	PCRE_EXTENDED option is set, this can be white space. Otherwise, the
syntax or an empty comment (see "Comments" below) can be used.	\g{ syntax or an empty comment (see "Comments" below) can be used.

Recursive back references	Recursive back references

A back reference that occurs inside the parentheses to which it refers	A back reference that occurs inside the parentheses to which it refers
fails when the subpattern is first used, so, for example, (a\1) never	fails when the subpattern is first used, so, for example, (a\1) never
matches. However, such references can be useful inside repeated sub-	matches. However, such references can be useful inside repeated sub-
patterns. For example, the pattern	patterns. For example, the pattern

(a\|b\1)+	(a\|b\1)+

matches any number of "a"s and also "aba", "ababbaa" etc. At each iter-	matches any number of "a"s and also "aba", "ababbaa" etc. At each iter-
ation of the subpattern, the back reference matches the character	ation of the subpattern, the back reference matches the character
string corresponding to the previous iteration. In order for this to	string corresponding to the previous iteration. In order for this to
work, the pattern must be such that the first iteration does not need	work, the pattern must be such that the first iteration does not need
to match the back reference. This can be done using alternation, as in	to match the back reference. This can be done using alternation, as in
the example above, or by a quantifier with a minimum of zero.	the example above, or by a quantifier with a minimum of zero.

Back references of this type cause the group that they reference to be	Back references of this type cause the group that they reference to be
treated as an atomic group. Once the whole group has been matched, a	treated as an atomic group. Once the whole group has been matched, a
subsequent matching failure cannot cause backtracking into the middle	subsequent matching failure cannot cause backtracking into the middle
of the group.	of the group.


ASSERTIONS	ASSERTIONS

An assertion is a test on the characters following or preceding the	An assertion is a test on the characters following or preceding the
current matching point that does not actually consume any characters.	current matching point that does not actually consume any characters.
The simple assertions coded as \b, \B, \A, \G, \Z, \z, ^ and $ are	The simple assertions coded as \b, \B, \A, \G, \Z, \z, ^ and $ are
described above.	described above.

More complicated assertions are coded as subpatterns. There are two	More complicated assertions are coded as subpatterns. There are two
kinds: those that look ahead of the current position in the subject	kinds: those that look ahead of the current position in the subject
string, and those that look behind it. An assertion subpattern is	string, and those that look behind it. An assertion subpattern is
matched in the normal way, except that it does not cause the current	matched in the normal way, except that it does not cause the current
matching position to be changed.	matching position to be changed.

Assertion subpatterns are not capturing subpatterns. If such an asser-	Assertion subpatterns are not capturing subpatterns. If such an asser-
tion contains capturing subpatterns within it, these are counted for	tion contains capturing subpatterns within it, these are counted for
the purposes of numbering the capturing subpatterns in the whole pat-	the purposes of numbering the capturing subpatterns in the whole pat-
tern. However, substring capturing is carried out only for positive	tern. However, substring capturing is carried out only for positive
assertions, because it does not make sense for negative assertions.	assertions. (Perl sometimes, but not always, does do capturing in nega-
	tive assertions.)

For compatibility with Perl, assertion subpatterns may be repeated;	For compatibility with Perl, assertion subpatterns may be repeated;
though it makes no sense to assert the same thing several times, the	though it makes no sense to assert the same thing several times, the
Line 5109 ASSERTIONS	Line 6661 ASSERTIONS
then try to match. If there are insufficient characters before the cur-	then try to match. If there are insufficient characters before the cur-
rent position, the assertion fails.	rent position, the assertion fails.

In UTF-8 mode, PCRE does not allow the \C escape (which matches a sin-	In a UTF mode, PCRE does not allow the \C escape (which matches a sin-
gle byte, even in UTF-8 mode) to appear in lookbehind assertions,	gle data unit even in a UTF mode) to appear in lookbehind assertions,
because it makes it impossible to calculate the length of the lookbe-	because it makes it impossible to calculate the length of the lookbe-
hind. The \X and \R escapes, which can match different numbers of	hind. The \X and \R escapes, which can match different numbers of data
bytes, are also not permitted.	units, are also not permitted.

"Subroutine" calls (see below) such as (?2) or (?&X) are permitted in	"Subroutine" calls (see below) such as (?2) or (?&X) are permitted in
lookbehinds, as long as the subpattern matches a fixed-length string.	lookbehinds, as long as the subpattern matches a fixed-length string.
Line 5250 CONDITIONAL SUBPATTERNS	Line 6802 CONDITIONAL SUBPATTERNS
Perl uses the syntax (?(<name>)...) or (?('name')...) to test for a	Perl uses the syntax (?(<name>)...) or (?('name')...) to test for a
used subpattern by name. For compatibility with earlier versions of	used subpattern by name. For compatibility with earlier versions of
PCRE, which had this facility before Perl, the syntax (?(name)...) is	PCRE, which had this facility before Perl, the syntax (?(name)...) is
also recognized. However, there is a possible ambiguity with this syn-	also recognized.
tax, because subpattern names may consist entirely of digits. PCRE
looks first for a named subpattern; if it cannot find one and the name
consists entirely of digits, PCRE looks for a subpattern of that num-
ber, which must be greater than zero. Using subpattern names that con-
sist entirely of digits is not recommended.

Rewriting the above example to use a named subpattern gives this:	Rewriting the above example to use a named subpattern gives this:

(?<OPEN> $ )? [^()]+ (?(<OPEN>) $ )	(?<OPEN> $ )? [^()]+ (?(<OPEN>) $ )

If the name used in a condition of this kind is a duplicate, the test	If the name used in a condition of this kind is a duplicate, the test
is applied to all subpatterns of the same name, and is true if any one	is applied to all subpatterns of the same name, and is true if any one
of them has matched.	of them has matched.

Checking for pattern recursion	Checking for pattern recursion

If the condition is the string (R), and there is no subpattern with the	If the condition is the string (R), and there is no subpattern with the
name R, the condition is true if a recursive call to the whole pattern	name R, the condition is true if a recursive call to the whole pattern
or any subpattern has been made. If digits or a name preceded by amper-	or any subpattern has been made. If digits or a name preceded by amper-
sand follow the letter R, for example:	sand follow the letter R, for example:

Line 5276 CONDITIONAL SUBPATTERNS	Line 6823 CONDITIONAL SUBPATTERNS

the condition is true if the most recent recursion is into a subpattern	the condition is true if the most recent recursion is into a subpattern
whose number or name is given. This condition does not check the entire	whose number or name is given. This condition does not check the entire
recursion stack. If the name used in a condition of this kind is a	recursion stack. If the name used in a condition of this kind is a
duplicate, the test is applied to all subpatterns of the same name, and	duplicate, the test is applied to all subpatterns of the same name, and
is true if any one of them is the most recent recursion.	is true if any one of them is the most recent recursion.

At "top level", all these recursion test conditions are false. The	At "top level", all these recursion test conditions are false. The
syntax for recursive patterns is described below.	syntax for recursive patterns is described below.

Defining subpatterns for use by reference only	Defining subpatterns for use by reference only

If the condition is the string (DEFINE), and there is no subpattern	If the condition is the string (DEFINE), and there is no subpattern
with the name DEFINE, the condition is always false. In this case,	with the name DEFINE, the condition is always false. In this case,
there may be only one alternative in the subpattern. It is always	there may be only one alternative in the subpattern. It is always
skipped if control reaches this point in the pattern; the idea of	skipped if control reaches this point in the pattern; the idea of
DEFINE is that it can be used to define subroutines that can be refer-	DEFINE is that it can be used to define subroutines that can be refer-
enced from elsewhere. (The use of subroutines is described below.) For	enced from elsewhere. (The use of subroutines is described below.) For
example, a pattern to match an IPv4 address such as "192.168.23.245"	example, a pattern to match an IPv4 address such as "192.168.23.245"
could be written like this (ignore whitespace and line breaks):	could be written like this (ignore white space and line breaks):

(?(DEFINE) (?<byte> 2[0-4]\d \| 25[0-5] \| 1\d\d \| [1-9]?\d) )	(?(DEFINE) (?<byte> 2[0-4]\d \| 25[0-5] \| 1\d\d \| [1-9]?\d) )
\b (?&byte) (\.(?&byte)){3} \b	\b (?&byte) (\.(?&byte)){3} \b

The first part of the pattern is a DEFINE group inside which a another	The first part of the pattern is a DEFINE group inside which a another
group named "byte" is defined. This matches an individual component of	group named "byte" is defined. This matches an individual component of
an IPv4 address (a number less than 256). When matching takes place,	an IPv4 address (a number less than 256). When matching takes place,
this part of the pattern is skipped because DEFINE acts like a false	this part of the pattern is skipped because DEFINE acts like a false
condition. The rest of the pattern uses references to the named group	condition. The rest of the pattern uses references to the named group
to match the four dot-separated components of an IPv4 address, insist-	to match the four dot-separated components of an IPv4 address, insist-
ing on a word boundary at each end.	ing on a word boundary at each end.

Assertion conditions	Assertion conditions

If the condition is not in any of the above formats, it must be an	If the condition is not in any of the above formats, it must be an
assertion. This may be a positive or negative lookahead or lookbehind	assertion. This may be a positive or negative lookahead or lookbehind
assertion. Consider this pattern, again containing non-significant	assertion. Consider this pattern, again containing non-significant
white space, and with the two alternatives on the second line:	white space, and with the two alternatives on the second line:

(?(?=[^a-z]*[a-z])	(?(?=[^a-z]*[a-z])
\d{2}-[a-z]{3}-\d{2} \| \d{2}-\d{2}-\d{2} )	\d{2}-[a-z]{3}-\d{2} \| \d{2}-\d{2}-\d{2} )

The condition is a positive lookahead assertion that matches an	The condition is a positive lookahead assertion that matches an
optional sequence of non-letters followed by a letter. In other words,	optional sequence of non-letters followed by a letter. In other words,
it tests for the presence of at least one letter in the subject. If a	it tests for the presence of at least one letter in the subject. If a
letter is found, the subject is matched against the first alternative;	letter is found, the subject is matched against the first alternative;
otherwise it is matched against the second. This pattern matches	otherwise it is matched against the second. This pattern matches
strings in one of the two forms dd-aaa-dd or dd-dd-dd, where aaa are	strings in one of the two forms dd-aaa-dd or dd-dd-dd, where aaa are
letters and dd are digits.	letters and dd are digits.


Line 5329 COMMENTS	Line 6876 COMMENTS
There are two ways of including comments in patterns that are processed	There are two ways of including comments in patterns that are processed
by PCRE. In both cases, the start of the comment must not be in a char-	by PCRE. In both cases, the start of the comment must not be in a char-
acter class, nor in the middle of any other sequence of related charac-	acter class, nor in the middle of any other sequence of related charac-
ters such as (?: or a subpattern name or number. The characters that	ters such as (?: or a subpattern name or number. The characters that
make up a comment play no part in the pattern matching.	make up a comment play no part in the pattern matching.

The sequence (?# marks the start of a comment that continues up to the	The sequence (?# marks the start of a comment that continues up to the
next closing parenthesis. Nested parentheses are not permitted. If the	next closing parenthesis. Nested parentheses are not permitted. If the
PCRE_EXTENDED option is set, an unescaped # character also introduces a	PCRE_EXTENDED option is set, an unescaped # character also introduces a
comment, which in this case continues to immediately after the next	comment, which in this case continues to immediately after the next
newline character or character sequence in the pattern. Which charac-	newline character or character sequence in the pattern. Which charac-
ters are interpreted as newlines is controlled by the options passed to	ters are interpreted as newlines is controlled by the options passed to
pcre_compile() or by a special sequence at the start of the pattern, as	a compiling function or by a special sequence at the start of the pat-
described in the section entitled "Newline conventions" above. Note	tern, as described in the section entitled "Newline conventions" above.
that the end of this type of comment is a literal newline sequence in	Note that the end of this type of comment is a literal newline sequence
the pattern; escape sequences that happen to represent a newline do not	in the pattern; escape sequences that happen to represent a newline do
count. For example, consider this pattern when PCRE_EXTENDED is set,	not count. For example, consider this pattern when PCRE_EXTENDED is
and the default newline convention is in force:	set, and the default newline convention is in force:

abc #comment \n still comment	abc #comment \n still comment

On encountering the # character, pcre_compile() skips along, looking	On encountering the # character, pcre_compile() skips along, looking
for a newline in the pattern. The sequence \n is still literal at this	for a newline in the pattern. The sequence \n is still literal at this
stage, so it does not terminate the comment. Only an actual character	stage, so it does not terminate the comment. Only an actual character
with the code value 0x0a (the default newline) does so.	with the code value 0x0a (the default newline) does so.


RECURSIVE PATTERNS	RECURSIVE PATTERNS

Consider the problem of matching a string in parentheses, allowing for	Consider the problem of matching a string in parentheses, allowing for
unlimited nested parentheses. Without the use of recursion, the best	unlimited nested parentheses. Without the use of recursion, the best
that can be done is to use a pattern that matches up to some fixed	that can be done is to use a pattern that matches up to some fixed
depth of nesting. It is not possible to handle an arbitrary nesting	depth of nesting. It is not possible to handle an arbitrary nesting
depth.	depth.

For some time, Perl has provided a facility that allows regular expres-	For some time, Perl has provided a facility that allows regular expres-
sions to recurse (amongst other things). It does this by interpolating	sions to recurse (amongst other things). It does this by interpolating
Perl code in the expression at run time, and the code can refer to the	Perl code in the expression at run time, and the code can refer to the
expression itself. A Perl pattern using code interpolation to solve the	expression itself. A Perl pattern using code interpolation to solve the
parentheses problem can be created like this:	parentheses problem can be created like this:

Line 5373 RECURSIVE PATTERNS	Line 6920 RECURSIVE PATTERNS
refers recursively to the pattern in which it appears.	refers recursively to the pattern in which it appears.

Obviously, PCRE cannot support the interpolation of Perl code. Instead,	Obviously, PCRE cannot support the interpolation of Perl code. Instead,
it supports special syntax for recursion of the entire pattern, and	it supports special syntax for recursion of the entire pattern, and
also for individual subpattern recursion. After its introduction in	also for individual subpattern recursion. After its introduction in
PCRE and Python, this kind of recursion was subsequently introduced	PCRE and Python, this kind of recursion was subsequently introduced
into Perl at release 5.10.	into Perl at release 5.10.

A special item that consists of (? followed by a number greater than	A special item that consists of (? followed by a number greater than
zero and a closing parenthesis is a recursive subroutine call of the	zero and a closing parenthesis is a recursive subroutine call of the
subpattern of the given number, provided that it occurs inside that	subpattern of the given number, provided that it occurs inside that
subpattern. (If not, it is a non-recursive subroutine call, which is	subpattern. (If not, it is a non-recursive subroutine call, which is
described in the next section.) The special item (?R) or (?0) is a	described in the next section.) The special item (?R) or (?0) is a
recursive call of the entire regular expression.	recursive call of the entire regular expression.

This PCRE pattern solves the nested parentheses problem (assume the	This PCRE pattern solves the nested parentheses problem (assume the
PCRE_EXTENDED option is set so that white space is ignored):	PCRE_EXTENDED option is set so that white space is ignored):

$ ( [^()]++ \| (?R) )* $	$ ( [^()]++ \| (?R) )* $

First it matches an opening parenthesis. Then it matches any number of	First it matches an opening parenthesis. Then it matches any number of
substrings which can either be a sequence of non-parentheses, or a	substrings which can either be a sequence of non-parentheses, or a
recursive match of the pattern itself (that is, a correctly parenthe-	recursive match of the pattern itself (that is, a correctly parenthe-
sized substring). Finally there is a closing parenthesis. Note the use	sized substring). Finally there is a closing parenthesis. Note the use
of a possessive quantifier to avoid backtracking into sequences of non-	of a possessive quantifier to avoid backtracking into sequences of non-
parentheses.	parentheses.

If this were part of a larger pattern, you would not want to recurse	If this were part of a larger pattern, you would If this were part of a larger pattern, you would
the entire pattern, so instead you could use this:	the entire pattern, so instead you could use this:

( $ ( [^()]++ \| (?1) )* $ )	( $ ( [^()]++ \| (?1) )* $ )

We have put the pattern into parentheses, and caused the recursion to	We have put the pattern into parentheses, and caused the recursion to
refer to them instead of the whole pattern.	refer to them instead of the whole pattern.

In a larger pattern, keeping track of parenthesis numbers can be	In a larger pattern, keeping track of parenthesis numbers can be
tricky. This is made easier by the use of relative references. Instead	tricky. This is made easier by the use of relative references. Instead
of (?1) in the pattern above you can write (?-2) to refer to the second	of (?1) in the pattern above you can write (?-2) to refer to the second
most recently opened parentheses preceding the recursion. In other	most recently opened parentheses preceding the recursion. In other
words, a negative number counts capturing parentheses leftwards from	words, a negative number counts capturing parentheses leftwards from
the point at which it is encountered.	the point at which it is encountered.

It is also possible to refer to subsequently opened parentheses, by	It is also possible to refer to subsequently opened parentheses, by
writing references such as (?+2). However, these cannot be recursive	writing references such as (?+2). However, these cannot be recursive
because the reference is not inside the parentheses that are refer-	because the reference is not inside the parentheses that are refer-
enced. They are always non-recursive subroutine calls, as described in	enced. They are always non-recursive subroutine calls, as described in
the next section.	the next section.

An alternative approach is to use named parentheses instead. The Perl	An alternative approach is to use named parentheses instead. The Perl
syntax for this is (?&name); PCRE's earlier syntax (?P>name) is also	syntax for this is (?&name); PCRE's earlier syntax (?P>name) is also
supported. We could rewrite the above example as follows:	supported. We could rewrite the above example as follows:

(?<pn> $ ( [^()]++ \| (?&pn) )* $ )	(?<pn> $ ( [^()]++ \| (?&pn) )* $ )

If there is more than one subpattern with the same name, the earliest	If there is more than one subpattern with the same name, the earliest
one is used.	one is used.

This particular example pattern that we have been looking at contains	This particular example pattern that we have been looking at contains
nested unlimited repeats, and so the use of a possessive quantifier for	nested unlimited repeats, and so the use of a possessive quantifier for
matching strings of non-parentheses is important when applying the pat-	matching strings of non-parentheses is important when applying the pat-
tern to strings that do not match. For example, when this pattern is	tern to strings that do not match. For example, when this pattern is
applied to	applied to

(aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa()	(aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa()

it yields "no match" quickly. However, if a possessive quantifier is	it yields "no match" quickly. However, if a possessive quantifier is
not used, the match runs for a very long time indeed because there are	not used, the match runs for a very long time indeed because there are
so many different ways the + and * repeats can carve up the subject,	so many different ways the + and * repeats can carve up the subject,
and all have to be tested before failure can be reported.	and all have to be tested before failure can be reported.

At the end of a match, the values of capturing parentheses are those	At the end of a match, the values of capturing parentheses are those
from the outermost level. If you want to obtain intermediate values, a	from the outermost level. If you want to obtain intermediate values, a
callout function can be used (see below and the pcrecallout documenta-	callout function can be used (see below and the pcrecallout documenta-
tion). If the pattern above is matched against	tion). If the pattern above is matched against

(ab(cd)ef)	(ab(cd)ef)

the value for the inner capturing parentheses (numbered 2) is "ef",	the value for the inner capturing parentheses (numbered 2) is "ef",
which is the last value taken on at the top level. If a capturing sub-	which is the last value taken on at the top level. If a capturing sub-
pattern is not matched at the top level, its final captured value is	pattern is not matched at the top level, its final captured value is
unset, even if it was (temporarily) set at a deeper level during the	unset, even if it was (temporarily) set at a deeper level during the
matching process.	matching process.

If there are more than 15 capturing parentheses in a pattern, PCRE has	If there are more than 15 capturing parentheses in a pattern, PCRE has
to obtain extra memory to store data during a recursion, which it does	to obtain extra memory to store data during a recursion, which it does
by using pcre_malloc, freeing it via pcre_free afterwards. If no memory	by using pcre_malloc, freeing it via pcre_free afterwards. If no memory
can be obtained, the match fails with the PCRE_ERROR_NOMEMORY error.	can be obtained, the match fails with the PCRE_ERROR_NOMEMORY error.

Do not confuse the (?R) item with the condition (R), which tests for	Do not confuse the (?R) item with the condition (R), which tests for
recursion. Consider this pattern, which matches text in angle brack-	recursion. Consider this pattern, which matches text in angle brack-
ets, allowing for arbitrary nesting. Only digits are allowed in nested	ets, allowing for arbitrary nesting. Only digits are allowed in nested
brackets (that is, when recursing), whereas any characters are permit-	brackets (that is, when recursing), whereas any characters are permit-
ted at the outer level.	ted at the outer level.

< (?: (?(R) \d++ \| [^<>]+) \| (?R)) >	< (?: (?(R) \d++ \| [^<>]+) \| (?R)) >

In this pattern, (?(R) is the start of a conditional subpattern, with	In this pattern, (?(R) is the start of a conditional subpattern, with
two different alternatives for the recursive and non-recursive cases.	two different alternatives for the recursive and non-recursive cases.
The (?R) item is the actual recursive call.	The (?R) item is the actual recursive call.

Differences in recursion processing between PCRE and Perl	Differences in recursion processing between PCRE and Perl

Recursion processing in PCRE differs from Perl in two important ways.	Recursion processing in PCRE differs from Perl in two important ways.
In PCRE (like Python, but unlike Perl), a recursive subpattern call is	In PCRE (like Python, but unlike Perl), a recursive subpattern call is
always treated as an atomic group. That is, once it has matched some of	always treated as an atomic group. That is, once it has matched some of
the subject string, it is never re-entered, even if it contains untried	the subject string, it is never re-entered, even if it contains untried
alternatives and there is a subsequent matching failure. This can be	alternatives and there is a subsequent matching failure. This can be
illustrated by the following pattern, which purports to match a palin-	illustrated by the following pattern, which purports to match a palin-
dromic string that contains an odd number of characters (for example,	dromic string that contains an odd number of characters (for example,
"a", "aba", "abcba", "abcdcba"):	"a", "aba", "abcba", "abcdcba"):

^(.\|(.)(?1)\2)$	^(.\|(.)(?1)\2)$

The idea is that it either matches a single character, or two identical	The idea is that it either matches a single character, or two identical
characters surrounding a sub-palindrome. In Perl, this pattern works;	characters surrounding a sub-palindrome. In Perl, this pattern works;
in PCRE it does not if the pattern is longer than three characters.	in PCRE it does not if the pattern is longer than three characters.
Consider the subject string "abcba":	Consider the subject string "abcba":

At the top level, the first character is matched, but as it is not at	At the top level, the first character is matched, but as it is not at
the end of the string, the first alternative fails; the second alterna-	the end of the string, the first alternative fails; the second alterna-
tive is taken and the recursion kicks in. The recursive call to subpat-	tive is taken and the recursion kicks in. The recursive call to subpat-
tern 1 successfully matches the next character ("b"). (Note that the	tern 1 successfully matches the next character ("b"). (Note that the
beginning and end of line tests are not part of the recursion).	beginning and end of line tests are not part of the recursion).

Back at the top level, the next character ("c") is compared with what	Back at the top level, the next character ("c") is compared with what
subpattern 2 matched, which was "a". This fails. Because the recursion	subpattern 2 matched, which was "a". This fails. Because the recursion
is treated as an atomic group, there are now no backtracking points,	is treated as an atomic group, there are now no backtracking points,
and so the entire match fails. (Perl is able, at this point, to re-	and so the entire match fails. (Perl is able, at this point, to re-
enter the recursion and try the second alternative.) However, if the	enter the recursion and try the second alternative.) However, if the
pattern is written with the alternatives in the other order, things are	pattern is written with the alternatives in the other order, things are
different:	different:

^((.)(?1)\2\|.)$	^((.)(?1)\2\|.)$

This time, the recursing alternative is tried first, and continues to	This time, the recursing alternative is tried first, and continues to
recurse until it runs out of characters, at which point the recursion	recurse until it runs out of characters, at which point the recursion
fails. But this time we do have another alternative to try at the	fails. But this time we do have another alternative to try at the
higher level. That is the big difference: in the previous case the	higher level. That is the big difference: in the previous case the
remaining alternative is at a deeper recursion level, which PCRE cannot	remaining alternative is at a deeper recursion level, which PCRE cannot
use.	use.

To change the pattern so that it matches all palindromic strings, not	To change the pattern so that it matches all palindromic strings, not
just those with an odd number of characters, it is tempting to change	just those with an odd number of characters, it is tempting to change
the pattern to this:	the pattern to this:

^((.)(?1)\2\|.?)$	^((.)(?1)\2\|.?)$

Again, this works in Perl, but not in PCRE, and for the same reason.	Again, this works in Perl, but not in PCRE, and for the same reason.
When a deeper recursion has matched a single character, it cannot be	When a deeper recursion has matched a single character, it cannot be
entered again in order to match an empty string. The solution is to	entered again in order to match an empty string. The solution is to
separate the two cases, and write out the odd and even cases as alter-	separate the two cases, and write out the odd and even cases as alter-
natives at the higher level:	natives at the higher level:

^(?:((.)(?1)\2\|)\|((.)(?3)\4\|.))	^(?:((.)(?1)\2\|)\|((.)(?3)\4\|.))

If you want to match typical palindromic phrases, the pattern has to	If you want to match typical palindromic phrases, the patte If you want to match typical palindromic phrases, the patte
ignore all non-word characters, which can be done like this:	ignore all non-word characters, which can be done like this:

^\W+(?:((.)\W+(?1)\W+\2\|)\|((.)\W+(?3)\W+\4\|\W+.\W+))\W+$	^\W+(?:((.)\W+(?1)\W+\2\|)\|((.)\W+(?3)\W+\4\|\W+.\W+))\W+$

If run with the PCRE_CASELESS option, this pattern matches phrases such	If run with the PCRE_CASELESS option, this pattern matches phrases such
as "A man, a plan, a canal: Panama!" and it works well in both PCRE and	as "A man, a plan, a canal: Panama!" and it works well in both PCRE and
Perl. Note the use of the possessive quantifier *+ to avoid backtrack-	Perl. Note the use of the possessive quantifier *+ to avoid backtrack-
ing into sequences of non-word characters. Without this, PCRE takes a	ing into sequences of non-word characters. Without this, PCRE takes a
great deal longer (ten times or more) to match typical phrases, and	great deal longer (ten times or more) to match typical phrases, and
Perl takes so long that you think it has gone into a loop.	Perl takes so long that you think it has gone into a loop.

WARNING: The palindrome-matching patterns above work only if the sub-	WARNING: The palindrome-matching patterns above work only if the sub-
ject string does not start with a palindrome that is shorter than the	ject string does not start with a palindrome that is shorter than the
entire string. For example, although "abcba" is correctly matched, if	entire string. For example, although "abcba" is correctly matched, if
the subject is "ababa", PCRE finds the palindrome "aba" at the start,	the subject is "ababa", PCRE finds the palindrome "aba" at the start,
then fails at top level because the end of the string does not follow.	then fails at top level because the end of the string does not follow.
Once again, it cannot jump back into the recursion to try other alter-	Once again, it cannot jump back into the recursion to try other alter-
natives, so the entire match fails.	natives, so the entire match fails.

The second way in which PCRE and Perl differ in their recursion pro-	The second way in which PCRE and Perl differ in their recursion pro-
cessing is in the handling of captured values. In Perl, when a subpat-	cessing is in the handling of captured values. In Perl, when a subpat-
tern is called recursively or as a subpattern (see the next section),	tern is called recursively or as a subpattern (see the next section),
it has no access to any values that were captured outside the recur-	it has no access to any values that were captured outside the recur-
sion, whereas in PCRE these values can be referenced. Consider this	sion, whereas in PCRE these values can be referenced. Consider this
pattern:	pattern:

^(.)(\1\|a(?2))	^(.)(\1\|a(?2))

In PCRE, this pattern matches "bab". The first capturing parentheses	In PCRE, this pattern matches "bab". The first capturing parentheses
match "b", then in the second group, when the back reference \1 fails	match "b", then in the second group, when the back reference \1 fails
to match "b", the second alternative matches "a" and then recurses. In	to match "b", the second alternative matches "a" and then recurses. In
the recursion, \1 does now match "b" and so the whole match succeeds.	the recursion, \1 does now match "b" and so the whole match succeeds.
In Perl, the pattern fails to match because inside the recursive call	In Perl, the pattern fails to match because inside the recursive call
\1 cannot access the externally set value.	\1 cannot access the externally set value.


SUBPATTERNS AS SUBROUTINES	SUBPATTERNS AS SUBROUTINES

If the syntax for a recursive subpattern call (either by number or by	If the syntax for a recursive subpattern call (either by number or by
name) is used outside the parentheses to which it refers, it operates	name) is used outside the parentheses to which it refers, it operates
like a subroutine in a programming language. The called subpattern may	like a subroutine in a programming language. The called subpattern may
be defined before or after the reference. A numbered reference can be	be defined before or after the reference. A numbered reference can be
absolute or relative, as in these examples:	absolute or relative, as in these examples:

(...(absolute)...)...(?2)...	(...(absolute)...)...(?2)...
Line 5578 SUBPATTERNS AS SUBROUTINES	Line 7125 SUBPATTERNS AS SUBROUTINES

(sens\|respons)e and \1ibility	(sens\|respons)e and \1ibility

matches "sense and sensibility" and "response and responsibility", but	matches "sense and sensibility" and "response and responsibility", but
not "sense and responsibility". If instead the pattern	not "sense and responsibility". If instead the pattern

(sens\|respons)e and (?1)ibility	(sens\|respons)e and (?1)ibility

is used, it does match "sense and responsibility" as well as the other	is used, it does match "sense and responsibility" as well as the other
two strings. Another example is given in the discussion of DEFINE	two strings. Another example is given in the discussion of DEFINE
above.	above.

All subroutine calls, whether recursive or not, are always treated as	All subroutine calls, whether recursive or not, are always treated as
atomic groups. That is, once a subroutine has matched some of the sub-	atomic groups. That is, once a subroutine has matched some of the sub-
ject string, it is never re-entered, even if it contains untried alter-	ject string, it is never re-entered, even if it contains untried alter-
natives and there is a subsequent matching failure. Any capturing	natives and there is a subsequent matching failure. Any capturing
parentheses that are set during the subroutine call revert to their	parentheses that are set during the subroutine call revert to their
previous values afterwards.	previous values afterwards.

Processing options such as case-independence are fixed when a subpat-	Processing options such as case-independence are fixed when a subpat-
tern is defined, so if it is used as a subroutine, such options cannot	tern is defined, so if it is used as a subroutine, such options cannot
be changed for different calls. For example, consider this pattern:	be changed for different calls. For example, consider this pattern:

(abc)(?i:(?-1))	(abc)(?i:(?-1))

It matches "abcabc". It does not match "abcABC" because the change of	It matches "abcabc". It does not match "abcABC" because t It matches "abcabc". It does not match "abcABC" because the change of
processing option does not affect the called subpattern.	processing option does not affect the called subpattern.


ONIGURUMA SUBROUTINE SYNTAX	ONIGURUMA SUBROUTINE SYNTAX

For compatibility with Oniguruma, the non-Perl syntax \g followed by a	For compatibility with Oniguruma, the non-Perl syntax \g followed by a
name or a number enclosed either in angle brackets or single quotes, is	name or a number enclosed either in angle brackets or single quotes, is
an alternative syntax for referencing a subpattern as a subroutine,	an alternative syntax for referencing a subpattern as a subroutine,
possibly recursively. Here are two of the examples used above, rewrit-	possibly recursively. Here are two of the examples used above, rewrit-
ten using this syntax:	ten using this syntax:

(?<pn> $ ( (?>[^()]+) \| \g<pn> )* $ )	(?<pn> $ ( (?>[^()]+) \| \g<pn> )* $ )
(sens\|respons)e and \g'1'ibility	(sens\|respons)e and \g'1'ibility

PCRE supports an extension to Oniguruma: if a number is preceded by a	PCRE supports an extension to Oniguruma: if a number is preceded by a
plus or a minus sign it is taken as a relative reference. For example:	plus or a minus sign it is taken as a relative reference. For example:

(abc)(?i:\g<-1>)	(abc)(?i:\g<-1>)

Note that \g{...} (Perl syntax) and \g<...> (Oniguruma syntax) are not	Note that \g{...} (Perl syntax) and \g<...> (Oniguruma syntax) are not
synonymous. The former is a back reference; the latter is a subroutine	synonymous. The former is a back reference; the latter is a subroutine
call.	call.


CALLOUTS	CALLOUTS

Perl has a feature whereby using the sequence (?{...}) causes arbitrary	Perl has a feature whereby using the sequence (?{...}) causes arbitrary
Perl code to be obeyed in the middle of matching a regular expression.	Perl code to be obeyed in the middle of matching a regular expression.
This makes it possible, amongst other things, to extract different sub-	This makes it possible, amongst other things, to extract different sub-
strings that match the same pair of parentheses when there is a repeti-	strings that match the same pair of parentheses when there is a repeti-
tion.	tion.

PCRE provides a similar feature, but of course it cannot obey arbitrary	PCRE provides a similar feature, but of course it cannot obey arbitrary
Perl code. The feature is called "callout". The caller of PCRE provides	Perl code. The feature is called "callout". The caller of PCRE provides
an external function by putting its entry point in the global variable	an external function by putting its entry point in the global variable
pcre_callout. By default, this variable contains NULL, which disables	pcre_callout (8-bit library) or pcre[16\|32]_callout (16-bit or 32-bit
all calling out.	library). By default, this variable contains NULL, which disables all
	calling out.

Within a regular expression, (?C) indicates the points at which the	Within a regular expression, (?C) indicates the points at which the
external function is to be called. If you want to identify different	external function is to be called. If you want to identify different
Line 5647 CALLOUTS	Line 7195 CALLOUTS

(?C1)abc(?C2)def	(?C1)abc(?C2)def

If the PCRE_AUTO_CALLOUT flag is passed to pcre_compile(), callouts are	If the PCRE_AUTO_CALLOUT flag is passed to a compiling function, call-
automatically installed before each item in the pattern. They are all	outs are automatically installed before each item in the pattern. They
numbered 255.	are all numbered 255. If there is a conditional group in the pattern
	whose condition is an assertion, an additional callout is inserted just
	before the condition. An explicit callout may also be set at this posi-
	tion, as in this example:

During matching, when PCRE reaches a callout point (and pcre_callout is	(?(?C9)(?=a)abc\|def)
set), the external function is called. It is provided with the number
of the callout, the position in the pattern, and, optionally, one item
of data originally supplied by the caller of pcre_exec(). The callout
function may cause matching to proceed, to backtrack, or to fail alto-
gether. A complete description of the interface to the callout function
is given in the pcrecallout documentation.

	Note that this applies only to assertion conditions, not to other types
	of condition.

BACKTRACKING CONTROL	During matching, when PCRE reaches a callout point, the external func-
	tion is called. It is provided with the number of the callout, the
	position in the pattern, and, optionally, one item of data originally
	supplied by the caller of the matching function. The callout function
	may cause matching to proceed, to backtrack, or to fail altogether.

Perl 5.10 introduced a number of "Special Backtracking Control Verbs",	By default, PCRE implements a number of optimizations at compile time
which are described in the Perl documentation as "experimental and sub-	and matching time, and one side-effect is that sometimes callouts are
ject to change or removal in a future version of Perl". It goes on to	skipped. If you need all possible callouts to happen, you need to set
say: "Their usage in production code should be noted to avoid problems	options that disable the relevant optimizations. More details, and a
during upgrades." The same remarks apply to the PCRE features described	complete description of the interface to the callout function, are
in this section.	given in the pcrecallout documentation.

Since these verbs are specifically related to backtracking, most of
them can be used only when the pattern is to be matched using
pcre_exec(), which uses a backtracking algorithm. With the exception of
(*FAIL), which behaves like a failing negative assertion, they cause an
error if encountered by pcre_dfa_exec().

If any of these verbs are used in an assertion or in a subpattern that	BACKTRACKING CONTROL
is called as a subroutine (whether or not recursively), their effect is
confined to that subpattern; it does not extend to the surrounding pat-
tern, with one exception: the name from a (MARK), (PRUNE), or (*THEN)
that is encountered in a successful positive assertion is passed back
when a match succeeds (compare capturing parentheses in assertions).
Note that such subpatterns are processed as anchored at the point where
they are tested. Note also that Perl's treatment of subroutines is dif-
ferent in some cases.

The new verbs make use of what was previously invalid syntax: an open-	Perl 5.10 introduced a number of "Special Backtracking Control Verbs",
	which are still described in the Perl documentation as "experimental
	and subject to change or removal in a future version of Perl". It goes
	on to say: "Their usage in production code should be noted to avoid
	problems during upgrades." The same remarks apply to the PCRE features
	described in this section.

	The new verbs make use of what was previously invalid syntax: an open-
ing parenthesis followed by an asterisk. They are generally of the form	ing parenthesis followed by an asterisk. They are generally of the form
(VERB) or (VERB:NAME). Some may take either form, with differing be-	(VERB) or (VERB:NAME). Some may take either form, possibly behaving
haviour, depending on whether or not an argument is present. A name is	differently depending on whether or not a name is present. A name is
any sequence of characters that does not include a closing parenthesis.	any sequence of characters that does not include a closing parenthesis.
If the name is empty, that is, if the closing parenthesis immediately	The maximum length of name is 255 in the 8-bit library and 65535 in the
follows the colon, the effect is as if the colon were not there. Any	16-bit and 32-bit libraries. If the name is empty, that is, if the
number of these verbs may occur in a pattern.	closing parenthesis immediately follows the colon, the effect is as if
	the colon were not there. Any number of these verbs may occur in a
	pattern.

	Since these verbs are specifically related to backtracking, most of
	them can be used only when the pattern is to be matched using one of
	the traditional matching functions, because these use a backtracking
	algorithm. With the exception of (*FAIL), which behaves like a failing
	negative assertion, the backtracking control verbs cause an error if
	encountered by a DFA matching function.

	The behaviour of these verbs in repeated groups, assertions, and in
	subpatterns called as subroutines (whether or not recursively) is docu-
	mented below.

	Optimizations that affect backtracking verbs

PCRE contains some optimizations that are used to speed up matching by	PCRE contains some optimizations that are used to speed up matching by
running some checks at the start of each match attempt. For example, it	running some checks at the start of each match attempt. For example, it
may know the minimum length of matching subject, or that a particular	may know the minimum length of matching subject, or that a particular
character must be present. When one of these optimizations suppresses	character must be present. When one of these optimizations bypasses the
the running of a match, any included backtracking verbs will not, of	running of a match, any included backtracking verbs will not, of
course, be processed. You can suppress the start-of-match optimizations	course, be processed. You can suppress the start-of-match optimizations
by setting the PCRE_NO_START_OPTIMIZE option when calling pcre_com-	by setting the PCRE_NO_START_OPTIMIZE option when calling pcre_com-
pile() or pcre_exec(), or by starting the pattern with (*NO_START_OPT).	pile() or pcre_exec(), or by starting the pattern with (*NO_START_OPT).
	There is more discussion of this option in the section entitled "Option
	bits for pcre_exec()" in the pcreapi documentation.

Experiments with Perl suggest that it too has similar optimizations,	Experiments with Perl suggest that it too has similar optimizations,
sometimes leading to anomalous results.	sometimes leading to anomalous results.
Line 5716 BACKTRACKING CONTROL	Line 7278 BACKTRACKING CONTROL
This verb causes the match to end successfully, skipping the remainder	This verb causes the match to end successfully, skipping the remainder
of the pattern. However, when it is inside a subpattern that is called	of the pattern. However, when it is inside a subpattern that is called
as a subroutine, only that subpattern is ended successfully. Matching	as a subroutine, only that subpattern is ended successfully. Matching
then continues at the outer level. If (*ACCEPT) is inside capturing	then continues at the outer level. If (*ACCEPT) in triggered in a posi-
parentheses, the data so far is captured. For example:	tive assertion, the assertion succeeds; in a negative assertion, the
	assertion fails.

	If (*ACCEPT) is inside capturing parentheses, the data so far is cap-
	tured. For example:

A((?:A\|B(*ACCEPT)\|C)D)	A((?:A\|B(*ACCEPT)\|C)D)

This matches "AB", "AAD", or "ACD"; when it matches "AB", "B" is cap-	This matches "AB", "AAD", or "ACD"; when it matches "AB", "B" is cap-
Line 5750 BACKTRACKING CONTROL	Line 7316 BACKTRACKING CONTROL
instances of (*MARK) as you like in a pattern, and their names do not	instances of (*MARK) as you like in a pattern, and their names do not
have to be unique.	have to be unique.

When a match succeeds, the name of the last-encountered (*MARK) on the	When a match succeeds, the name of the last-encountered (*MARK:NAME),
matching path is passed back to the caller via the pcre_extra data	(PRUNE:NAME), or (THEN:NAME) on the matching path is passed back to
structure, as described in the section on pcre_extra in the pcreapi	the caller as described in the section entitled "Extra data for
documentation. Here is an example of pcretest output, where the /K mod-	pcre_exec()" in the pcreapi documentation. Here is an example of
ifier requests the retrieval and outputting of (*MARK) data:	pcretest output, where the /K modifier requests the retrieval and out-
	putting of (*MARK) data:

re> /X(MARK:A)Y\|X(MARK:B)Z/K	re> /X(MARK:A)Y\|X(MARK:B)Z/K
data> XY	data> XY
Line 5765 BACKTRACKING CONTROL	Line 7332 BACKTRACKING CONTROL
MK: B	MK: B

The (*MARK) name is tagged with "MK:" in this output, and in this exam-	The (*MARK) name is tagged with "MK:" in this output, and in this exam-
ple it indicates which of the two alternatives matched. This is a more	ple it indicates which of the two alternatives matched. This is a more
efficient way of obtaining this information than putting each alterna-	efficient way of obtaining this information than putting each alterna-
tive in its own capturing parentheses.	tive in its own capturing parentheses.

If (*MARK) is encountered in a positive assertion, its name is recorded	If a verb with a name is encountered in a positive assertion that is
and passed back if it is the last-encountered. This does not happen for	true, the name is recorded and passed back if it is the last-encoun-
negative assertions.	tered. This does not happen for negative assertions or failing positive
	assertions.

After a partial match or a failed match, the name of the last encoun-	After a partial match or a failed match, the last encountered name in
tered (*MARK) in the entire match process is returned. For example:	the entire match process is returned. For example:

re> /X(MARK:A)Y\|X(MARK:B)Z/K	re> /X(MARK:A)Y\|X(MARK:B)Z/K
data> XP	data> XP
No match, mark = B	No match, mark = B

Note that in this unanchored example the mark is retained from the	Note that in this unanchored example the mark is retained from the
match attempt that started at the letter "X". Subsequent match attempts	match attempt that started at the letter "X" in the subject. Subsequent
starting at "P" and then with an empty string do not get as far as the	match attempts starting at "P" and then with an empty string do not get
(*MARK) item, but nevertheless do not reset it.	as far as the (*MARK) item, but nevertheless do not reset it.

	If you are interested in (*MARK) values after failed matches, you
	should probably set the PCRE_NO_START_OPTIMIZE option (see above) to
	ensure that the match is always attempted.

Verbs that act after backtracking	Verbs that act after backtracking

The following verbs do nothing when they are encountered. Matching con-	The following verbs do nothing when they are encountered. Matching con-
tinues with what follows, but if there is no subsequent match, causing	tinues with what follows, but if there is no subsequent match, causing
a backtrack to the verb, a failure is forced. That is, backtracking	a backtrack to the verb, a failure is forced. That is, backtracking
cannot pass to the left of the verb. However, when one of these verbs	cannot pass to the left of the verb. However, when one of these verbs
appears inside an atomic group, its effect is confined to that group,	appears inside an atomic group or an assertion that is true, its effect
because once the group has been matched, there is never any backtrack-	is confined to that group, because once the group has been matched,
ing into it. In this situation, backtracking can "jump back" to the	there is never any backtracking into it. In this situation, backtrack-
left of the entire atomic group. (Remember also, as stated above, that	ing can "jump back" to the left of the entire atomic group or asser-
this localization also applies in subroutine calls and assertions.)	tion. (Remember also, as stated above, that this localization also
	applies in subroutine calls.)

These verbs differ in exactly what kind of failure occurs when back-	These verbs differ in exactly what kind of failure occurs when back-
tracking reaches them.	tracking reaches them. The behaviour described below is what happens
	when the verb is not in a subroutine or an assertion. Subsequent sec-
	tions cover these special cases.

(*COMMIT)	(*COMMIT)

This verb, which may not be followed by a name, causes the whole match	This verb, which may not be followed by a name, causes the whole match
to fail outright if the rest of the pattern does not match. Even if the	to fail outright if there is a later matching failure that causes back-
pattern is unanchored, no further attempts to find a match by advancing	tracking to reach it. Even if the pattern is unanchored, no further
the starting point take place. Once (*COMMIT) has been passed,	attempts to find a match by advancing the starting point take place. If
pcre_exec() is committed to finding a match at the current starting	(*COMMIT) is the only backtracking verb that is encountered, once it
point, or not at all. For example:	has been passed pcre_exec() is committed to finding a match at the cur-
	rent starting point, or not at all. For example:

a+(*COMMIT)b	a+(*COMMIT)b

Line 5816 BACKTRACKING CONTROL	Line 7392 BACKTRACKING CONTROL
most recently passed (MARK) in the path is passed back when (COMMIT)	most recently passed (MARK) in the path is passed back when (COMMIT)
forces a match failure.	forces a match failure.

Note that (*COMMIT) at the start of a pattern is not the same as an	If there is more than one backtracking verb in a pattern, a different
anchor, unless PCRE's start-of-match optimizations are turned off, as	one that follows (COMMIT) may be triggered first, so merely one that follows (COMMIT) may be triggered first, so merely passing
	(*COMMIT) during a match does not always guarantee that a match must be
	at this starting point.

	Note that (*COMMIT) at the start of a pattern is not the same as an
	anchor, unless PCRE's start-of-match optimizations are turned off, as
shown in this pcretest example:	shown in this pcretest example:

re> /(*COMMIT)abc/	re> /(*COMMIT)abc/
Line 5826 BACKTRACKING CONTROL	Line 7407 BACKTRACKING CONTROL
xyzabc\Y	xyzabc\Y
No match	No match

PCRE knows that any match must start with "a", so the optimization	PCRE knows that any match must start with "a", so the optimization
skips along the subject to "a" before running the first match attempt,	skips along the subject to "a" before running the first match attempt,
which succeeds. When the optimization is disabled by the \Y escape in	which succeeds. When the optimization is disabled by the \Y escape in
the second subject, the match starts at "x" and so the (*COMMIT) causes	the second subject, the match starts at "x" and so the (*COMMIT) causes
it to fail without trying any other starting points.	it to fail without trying any other starting points.

(PRUNE) or (PRUNE:NAME)	(PRUNE) or (PRUNE:NAME)

This verb causes the match to fail at the current starting position in	This verb causes the match to fail at the current starting position in
the subject if the rest of the pattern does not match. If the pattern	the subject if there is a later matching failure that causes backtrack-
is unanchored, the normal "bumpalong" advance to the next starting	ing to reach it. If the pattern is unanchored, the normal "bumpalong"
character then happens. Backtracking can occur as usual to the left of	advance to the next starting character then happens. Backtracking can
(*PRUNE), before it is reached, or when matching to the right of	occur as usual to the left of (*PRUNE), before it is reached, or when
(*PRUNE), but if there is no match to the right, backtracking cannot	matching to the right of (*PRUNE), but if there is no match to the
cross (PRUNE). In simple cases, the use of (PRUNE) is just an alter-	right, backtracking cannot cross (*PRUNE). In simple cases, the use of
native to an atomic group or possessive quantifier, but there are some	(*PRUNE) is just an alternative to an atomic group or possessive quan-
uses of (*PRUNE) that cannot be expressed in any other way. The behav-	tifier, but there are some uses of (*PRUNE) that cannot be expressed in
iour of (PRUNE:NAME) is the same as (MARK:NAME)(*PRUNE). In an	any other way. In an anchored pattern (*PRUNE) has the same effect as
anchored pattern (PRUNE) has the same effect as (COMMIT).	(*COMMIT).

	The behaviour of (*PRUNE:NAME) is the not the same as
	(MARK:NAME)(PRUNE). It is like (*MARK:NAME) in that the name is
	remembered for passing back to the caller. However, (*SKIP:NAME)
	searches only for names set with (*MARK).

(*SKIP)	(*SKIP)

This verb, when given without a name, is like (*PRUNE), except that if	This verb, when given without a name, is like (*PRUNE), except that if
Line 5866 BACKTRACKING CONTROL	Line 7452 BACKTRACKING CONTROL

(*SKIP:NAME)	(*SKIP:NAME)

When (*SKIP) has an associated name, its behaviour is modified. If the	When (*SKIP) has an associated name, its behaviour is modified. When it
following pattern fails to match, the previous path through the pattern	is triggered, the previous path through the pattern is searched for the
is searched for the most recent (*MARK) that has the same name. If one	most recent (*MARK) that has the same name. If one is found, the
is found, the "bumpalong" advance is to the subject position that cor-	"bumpalong" advance is to the subject position that corresponds to that
responds to that (MARK) instead of to where (SKIP) was encountered.	(MARK) instead of to where (SKIP) was encountered. If no (*MARK) with
If no (MARK) with a matching name is found, the (SKIP) is ignored.	a matching name is found, the (*SKIP) is ignored.

	Note that (SKIP:NAME) searches only for names set by (MARK:NAME). It
	ignores names that are set by (PRUNE:NAME) or (THEN:NAME).

(THEN) or (THEN:NAME)	(THEN) or (THEN:NAME)

This verb causes a skip to the next innermost alternative if the rest	This verb causes a skip to the next innermost alternative when back-
of the pattern does not match. That is, it cancels pending backtrack-	tracking reaches it. That is, it cancels any further backtracking
ing, but only within the current alternative. Its name comes from the	within the current alternative. Its name comes from the observation
observation that it can be used for a pattern-based if-then-else block:	that it can be used for a pattern-based if-then-else block:

( COND1 (THEN) FOO \| COND2 (THEN) BAR \| COND3 (*THEN) BAZ ) ...	( COND1 (THEN) FOO \| COND2 (THEN) BAR \| COND3 (*THEN) BAZ ) ...

If the COND1 pattern matches, FOO is tried (and possibly further items	If the COND1 pattern matches, FOO is tried (and possibly further items
after the end of the group if FOO succeeds); on failure, the matcher	after the end of the group if FOO succeeds); on failure, the matcher
skips to the second alternative and tries COND2, without backtracking	skips to the second alternative and tries COND2, without backtracking
into COND1. The behaviour of (*THEN:NAME) is exactly the same as	into COND1. If that succeeds and BAR fails, COND3 is tried. If subse-
(MARK:NAME)(THEN). If (*THEN) is not inside an alternation, it acts	quently BAZ fails, there are no more alternatives, so there is a back-
like (*PRUNE).	track to whatever came before the entire group. If (*THEN) is not
	inside an alternation, it acts like (*PRUNE).

Note that a subpattern that does not contain a \| character is just a	The behaviour of (*THEN:NAME) is the not the same as
part of the enclosing alternative; it is not a nested alternation with	(MARK:NAME)(THEN). It is like (*MARK:NAME) in that the name is
only one alternative. The effect of (*THEN) extends beyond such a sub-	remembered for passing back to the caller. However, (*SKIP:NAME)
pattern to the enclosing alternative. Consider this pattern, where A,	searches only for names set with (*MARK).
B, etc. are complex pattern fragments that do not contain any \| charac-
ters at this level:

	A subpattern that does not contain a \| character is just a part of the
	enclosing alternative; it is not a nested alternation with only one
	alternative. The effect of (*THEN) extends beyond such a subpattern to
	the enclosing alternative. Consider this pattern, where A, B, etc. are
	complex pattern fragments that do not contain any \| characters at this
	level:

A (B(*THEN)C) \| D	A (B(*THEN)C) \| D

If A and B are matched, but there is a failure in C, matching does not	If A and B are matched, but there is a failure in C, matching does not
backtrack into A; instead it moves to the next alternative, that is, D.	backtrack into A; instead it moves to the next alternative, that is, D.
However, if the subpattern containing (*THEN) is given an alternative,	However, if the subpattern containing (*THEN) is given an alternative,
it behaves differently:	it behaves differently:

A (B(THEN)C \| (FAIL)) \| D	A (B(THEN)C \| (FAIL)) \| D

The effect of (*THEN) is now confined to the inner subpattern. After a	The effect of (*THEN) is now confined to the inner subpattern. After a
failure in C, matching moves to (*FAIL), which causes the whole subpat-	failure in C, matching moves to (*FAIL), which causes the whole subpat-
tern to fail because there are no more alternatives to try. In this	tern to fail because there are no more alternatives to try. In this
case, matching does now backtrack into A.	case, matching does now backtrack into A.

Note also that a conditional subpattern is not considered as having two	Note that a conditional subpattern is not considered as having two
alternatives, because only one is ever used. In other words, the \|	alternatives, because only one is ever used. In other words, the \|
character in a conditional subpattern has a different meaning. Ignoring	character in a conditional subpattern has a different meaning. Ignoring
white space, consider:	white space, consider:

^.? (?(?=a) a \| b(THEN)c )	^.? (?(?=a) a \| b(THEN)c )

If the subject is "ba", this pattern does not match. Because .*? is	If the subject is "ba", this pattern does not match. Because .*? is
ungreedy, it initially matches zero characters. The condition (?=a)	ungreedy, it initially matches zero characters. The condition (?=a)
then fails, the character "b" is matched, but "c" is not. At this	then fails, the character "b" is matched, but "c" is not. At this
point, matching does not backtrack to .*? as might perhaps be expected	point, matching does not backtrack to .*? as might perhaps be expected
from the presence of the \| character. The conditional subpattern is	from the presence of the \| character. The conditional subpattern is
part of the single alternative that comprises the whole pattern, and so	part of the single alternative that comprises the whole pattern, and so
the match fails. (If there was a backtrack into .*?, allowing it to	the match fails. (If there was a backtrack into .*?, allowing it to
match "b", the match would succeed.)	match "b", the match would succeed.)

The verbs just described provide four different "strengths" of control	The verbs just described provide four different "strengths" of control
when subsequent matching fails. (*THEN) is the weakest, carrying on the	when subsequent matching fails. (*THEN) is the weakest, carrying on the
match at the next alternative. (*PRUNE) comes next, failing the match	match at the next alternative. (*PRUNE) comes next, failing the match
at the current starting position, but allowing an advance to the next	at the current starting position, but allowing an advance to the next
character (for an unanchored pattern). (*SKIP) is similar, except that	character (for an unanchored pattern). (*SKIP) is similar, except that
the advance may be more than one character. (*COMMIT) is the strongest,	the advance may be more than one character. (*COMMIT) is the strongest,
causing the entire match to fail.	causing the entire match to fail.

If more than one such verb is present in a pattern, the "strongest" one	More than one backtracking verb
wins. For example, consider this pattern, where A, B, etc. are complex
pattern fragments:

(A(COMMIT)B(THEN)C\|D)	If more than one backtracking verb is present in a pattern, the one
	that is backtracked onto first acts. For example, consider this pat-
	tern, where A, B, etc. are complex pattern fragments:

Once A has matched, PCRE is committed to this match, at the current	(A(COMMIT)B(THEN)C\|ABD)
starting position. If subsequently B matches, but C does not, the nor-
mal (*THEN) action of trying the next alternative (that is, D) does not
happen because (*COMMIT) overrides.

	If A matches but B fails, the backtrack to (*COMMIT) causes the entire
	match to fail. However, if A and B match, but C fails, the backtrack to
	(*THEN) causes the next alternative (ABD) to be tried. This behaviour
	is consistent, but is not always the same as Perl's. It means that if
	two or more backtracking verbs appear in succession, all the the last
	of them has no effect. Consider this example:

	...(COMMIT)(PRUNE)...

	If there is a matching failure to the right, backtracking onto (*PRUNE)
	causes it to be triggered, and its action is taken. There can never be
	a backtrack onto (*COMMIT).

	Backtracking verbs in repeated groups

	PCRE differs from Perl in its handling of backtracking verbs in
	repeated groups. For example, consider:

	/(a(*COMMIT)b)+ac/

	If the subject is "abac", Perl matches, but PCRE fails because the
	(*COMMIT) in the second repeat of the group acts.

	Backtracking verbs in assertions

	(*FAIL) in an assertion has its normal effect: it forces an immediate
	backtrack.

	(*ACCEPT) in a positive assertion causes the assertion to succeed with-
	out any further processing. In a negative assertion, (*ACCEPT) causes
	the assertion to fail without any further processing.

	The other backtracking verbs are not treated specially if they appear
	in a positive assertion. In particular, (*THEN) skips to the next
	alternative in the innermost enclosing group that has alternations,
	whether or not this is within the assertion.

	Negative assertions are, however, different, in order to ensure that
	changing a positive assertion into a negative assertion changes its
	result. Backtracking into (COMMIT), (SKIP), or (*PRUNE) causes a neg-
	ative assertion to be true, without considering any further alternative
	branches in the assertion. Backtracking into (*THEN) causes it to skip
	to the next enclosing alternative within the assertion (the normal be-
	haviour), but if the assertion does not have such an alternative,
	(THEN) behaves like (PRUNE).

	Backtracking verbs in subroutines

	These behaviours occur whether or not the subpattern is called recur-
	sively. Perl's treatment of subroutines is different in some cases.

	(*FAIL) in a subpattern called as a subroutine has its normal effect:
	it forces an immediate backtrack.

	(*ACCEPT) in a subpattern called as a subroutine causes the subroutine
	match to succeed without any further processing. Matching then contin-
	ues after the subroutine call.

	(COMMIT), (SKIP), and (*PRUNE) in a subpattern called as a subroutine
	cause the subroutine match to fail.

	(*THEN) skips to the next alternative in the innermost enclosing group
	within the subpattern that has alternatives. If there is no such group
	within the subpattern, (*THEN) causes the subroutine match to fail.


SEE ALSO	SEE ALSO

pcreapi(3), pcrecallout(3), pcrematching(3), pcresyntax(3), pcre(3).	pcreapi(3), pcrecallout(3), pcrematching(3), pcresyntax(3), pcre(3),
	pcre16(3), pcre32(3).


AUTHOR	AUTHOR
Line 5960 AUTHOR	Line 7618 AUTHOR

REVISION	REVISION

Last updated: 29 November 2011	Last updated: 03 December 2013
Copyright (c) 1997-2011 University of Cambridge.	Copyright (c) 1997-2013 University of Cambridge.
------------------------------------------------------------------------------	------------------------------------------------------------------------------


PCRESYNTAX(3) PCRESYNTAX(3)	PCRESYNTAX(3) Library Functions Manual PCRESYNTAX(3)



NAME	NAME
PCRE - Perl-compatible regular expressions	PCRE - Perl-compatible regular expressions


PCRE REGULAR EXPRESSION SYNTAX SUMMARY	PCRE REGULAR EXPRESSION SYNTAX SUMMARY

The full syntax and semantics of the regular expressions that are sup-	The full syntax and semantics of the regular expressions that are sup-
ported by PCRE are described in the pcrepattern documentation. This	ported by PCRE are described in the pcrepattern documentation. This
document contains just a quick-reference summary of the syntax.	document contains a quick-reference summary of the syntax.


QUOTING	QUOTING
Line 5990 CHARACTERS	Line 7648 CHARACTERS
\a alarm, that is, the BEL character (hex 07)	\a alarm, that is, the BEL character (hex 07)
\cx "control-x", where x is any ASCII character	\cx "control-x", where x is any ASCII character
\e escape (hex 1B)	\e escape (hex 1B)
\f formfeed (hex 0C)	\f form feed (hex 0C)
\n newline (hex 0A)	\n newline (hex 0A)
\r carriage return (hex 0D)	\r carriage return (hex 0D)
\t tab (hex 09)	\t tab (hex 09)
	\0dd character with octal code 0dd
\ddd character with octal code ddd, or backreference	\ddd character with octal code ddd, or backreference
	\o{ddd..} character with octal code ddd..
\xhh character with hex code hh	\xhh character with hex code hh
\x{hhh..} character with hex code hhh..	\x{hhh..} character with hex code hhh..

	Note that \0dd is always an octal code, and that \8 and \9 are the lit-
	eral characters "8" and "9".


CHARACTER TYPES	CHARACTER TYPES

. any character except newline;	. any character except newline;
in dotall mode, any character whatsoever	in dotall mode, any character whatsoever
\C one byte, even in UTF-8 mode (best avoided)	\C one data unit, even in UTF mode (best avoided)
\d a decimal digit	\d a decimal digit
\D a character that is not a decimal digit	\D a character that is not a decimal digit
\h a horizontal whitespace character	\h a horizontal white space character
\H a character that is not a horizontal whitespace character	\H a character that is not a horizontal white space character
\N a character that is not a newline	\N a character that is not a newline
\p{xx} a character with the xx property	\p{xx} a character with the xx property
\P{xx} a character without the xx property	\P{xx} a character without the xx property
\R a newline sequence	\R a newline sequence
\s a whitespace character	\s a white space character
\S a character that is not a whitespace character	\S a character that is not a white space character
\v a vertical whitespace character	\v a vertical white space character
\V a character that is not a vertical whitespace character	\V a character that is not a vertical white space character
\w a "word" character	\w a "word" character
\W a "non-word" character	\W a "non-word" character
\X an extended Unicode sequence	\X a Unicode extended grapheme cluster

In PCRE, by default, \d, \D, \s, \S, \w, and \W recognize only ASCII	By default, \d, \s, and \w match only ASCII characters, even in UTF-8
characters, even in UTF-8 mode. However, this can be changed by setting	mode or in the 16- bit and 32-bit libraries. However, if locale-spe-
the PCRE_UCP option.	cific matching is happening, \s and \w may also match characters with
	code points in the range 128-255. If the PCRE_UCP option is set, the
	behaviour of these escape sequences is changed to use Unicode proper-
	ties and they match many more characters.


GENERAL CATEGORY PROPERTIES FOR \p and \P	GENERAL CATEGORY PROPERTIES FOR \p and \P
Line 6077 PCRE SPECIAL CATEGORY PROPERTIES FOR \p and \P	Line 7743 PCRE SPECIAL CATEGORY PROPERTIES FOR \p and \P

Xan Alphanumeric: union of properties L and N	Xan Alphanumeric: union of properties L and N
Xps POSIX space: property Z or tab, NL, VT, FF, CR	Xps POSIX space: property Z or tab, NL, VT, FF, CR
Xsp Perl space: property Z or tab, NL, FF, CR	Xsp Perl space: property Z or tab, NL, VT, FF, CR
	Xuc Univerally-named character: one that can be
	represented by a Universal Character Name
Xwd Perl word: property Xan or underscore	Xwd Perl word: property Xan or underscore

	Perl and POSIX space are now the same. Perl added VT to its space char-
	acter set at release 5.18 and PCRE changed at release 8.34.


SCRIPT NAMES FOR \p AND \P	SCRIPT NAMES FOR \p AND \P

Arabic, Armenian, Avestan, Balinese, Bamum, Bengali, Bopomofo, Braille,	Arabic, Armenian, Avestan, Balinese, Bamum, Batak, Bengali, Bopomofo,
Buginese, Buhid, Canadian_Aboriginal, Carian, Cham, Cherokee, Common,	Brahmi, Braille, Buginese, Buhid, Canadian_Aboriginal, Carian, Chakma,
Coptic, Cuneiform, Cypriot, Cyrillic, Deseret, Devanagari, Egyp-	Cham, Cherokee, Common, Coptic, Cuneiform, Cypriot, Cyrillic, Deseret,
tian_Hieroglyphs, Ethiopic, Georgian, Glagolitic, Gothic, Greek,	Devanagari, Egyptian_Hieroglyphs, Ethiopic, Georgian, Glagolitic,
Gujarati, Gurmukhi, Han, Hangul, Hanunoo, Hebrew, Hiragana, Impe-	Gothic, Greek, Gujarati, Gurmukhi, Han, Hangul, Hanunoo, Hebrew, Hira-
rial_Aramaic, Inherited, Inscriptional_Pahlavi, Inscriptional_Parthian,	gana, Imperial_Aramaic, Inherited, Inscriptional_Pahlavi, Inscrip-
Javanese, Kaithi, Kannada, Katakana, Kayah_Li, Kharoshthi, Khmer, Lao,	tional_Parthian, Javanese, Kaithi, Kannada, Katakana, Kayah_Li,
Latin, Lepcha, Limbu, Linear_B, Lisu, Lycian, Lydian, Malayalam,	Kharoshthi, Khmer, Lao, Latin, Lepcha, Limbu, Linear_B, Lisu, Lycian,
Meetei_Mayek, Mongolian, Myanmar, New_Tai_Lue, Nko, Ogham, Old_Italic,	Lydian, Malayalam, Mandaic, Meetei_Mayek, Meroitic_Cursive,
Old_Persian, Old_South_Arabian, Old_Turkic, Ol_Chiki, Oriya, Osmanya,	Meroitic_Hieroglyphs, Miao, Mongolian, Myanmar, New_Tai_Lue, Nko,
Phags_Pa, Phoenician, Rejang, Runic, Samaritan, Saurashtra, Shavian,	Ogham, Old_Italic, Old_Persian, Old_South_Arabian, Old_Turkic,
Sinhala, Sundanese, Syloti_Nagri, Syriac, Tagalog, Tagbanwa, Tai_Le,	Ol_Chiki, Oriya, Osmanya, Phags_Pa, Phoenician, Rejang, Runic, Samari-
Tai_Tham, Tai_Viet, Tamil, Telugu, Thaana, Thai, Tibetan, Tifinagh,	tan, Saurashtra, Sharada, Shavian, Sinhala, Sora_Sompeng, Sundanese,
Ugaritic, Vai, Yi.	Syloti_Nagri, Syriac, Tagalog, Tagbanwa, Tai_Le, Tai_Tham, Tai_Viet,
	Takri, Tamil, Telugu, Thaana, Thai, Tibetan, Tifinagh, Ugaritic, Vai,
	Yi.


CHARACTER CLASSES	CHARACTER CLASSES
Line 6117 CHARACTER CLASSES	Line 7790 CHARACTER CLASSES
lower lower case letter	lower lower case letter
print printing, including space	print printing, including space
punct printing, excluding alphanumeric	punct printing, excluding alphanumeric
space whitespace	space white space
upper upper case letter	upper upper case letter
word same as \w	word same as \w
xdigit hexadecimal digit	xdigit hexadecimal digit

In PCRE, POSIX character set names recognize only ASCII characters by	In PCRE, POSIX character set names recognize only ASCII characters by
default, but some of them use Unicode properties if PCRE_UCP is set.	default, but some of them use Unicode properties if PCRE_UCP is set.
You can use \Q...\E inside a character class.	You can use \Q...\E inside a character class.


Line 6204 OPTION SETTING	Line 7877 OPTION SETTING
(?x) extended (ignore white space)	(?x) extended (ignore white space)
(?-...) unset option(s)	(?-...) unset option(s)

The following are recognized only at the start of a pattern or after	The following are recognized only at the start o The following are recognized only at the start of a pattern or after
one of the newline-setting options with similar syntax:	one of the newline-setting options with similar syntax:

	(*LIMIT_MATCH=d) set the match limit to d (decimal number)
	(*LIMIT_RECURSION=d) set the recursion limit to d (decimal number)
(*NO_START_OPT) no start-match optimization (PCRE_NO_START_OPTIMIZE)	(*NO_START_OPT) no start-match optimization (PCRE_NO_START_OPTIMIZE)
(*UTF8) set UTF-8 mode (PCRE_UTF8)	(*UTF8) set UTF-8 mode: 8-bit library (PCRE_UTF8)
	(*UTF16) set UTF-16 mode: 16-bit library (PCRE_UTF16)
	(*UTF32) set UTF-32 mode: 32-bit library (PCRE_UTF32)
	(*UTF) set appropriate UTF mode for the library in use
(*UCP) set PCRE_UCP (use Unicode properties for \d etc)	(*UCP) set PCRE_UCP (use Unicode properties for \d etc)

	Note that LIMIT_MATCH and LIMIT_RECURSION can only reduce the value of
	the limits set by the caller of pcre_exec(), not increase them.


LOOKAHEAD AND LOOKBEHIND ASSERTIONS	LOOKAHEAD AND LOOKBEHIND ASSERTIONS

(?=...) positive look ahead	(?=...) positive look ahead
Line 6277 BACKTRACKING CONTROL	Line 7958 BACKTRACKING CONTROL

(*ACCEPT) force successful match	(*ACCEPT) force successful match
(FAIL) force backtrack; synonym (F)	(FAIL) force backtrack; synonym (F)
	(MARK:NAME) set name to be passed back; synonym (:NAME)

The following act only when a subsequent match failure causes a back-	The following act only when a subsequent match failure causes a back-
track to reach them. They all force a match failure, but they differ in	track to reach them. They all force a match failure, but they differ in
Line 6285 BACKTRACKING CONTROL	Line 7967 BACKTRACKING CONTROL

(*COMMIT) overall failure, no advance of starting point	(*COMMIT) overall failure, no advance of starting point
(*PRUNE) advance to next starting character	(*PRUNE) advance to next starting character
(*SKIP) advance start to current matching position	(PRUNE:NAME) equivalent to (MARK:NAME)(*PRUNE)
	(*SKIP) advance to current matching position
	(*SKIP:NAME) advance to position corresponding to an earlier
	(MARK:NAME); if not found, the (SKIP) is ignored
(*THEN) local failure, backtrack to next alternation	(*THEN) local failure, backtrack to next alternation
	(THEN:NAME) equivalent to (MARK:NAME)(*THEN)


NEWLINE CONVENTIONS	NEWLINE CONVENTIONS

These are recognized only at the very start of the pattern or after a	These are recognized only at the very start of the pattern or after a
(BSR_...) or (UTF8) or (*UCP) option.	(BSR_...), (UTF8), (UTF16), (UTF32) or (*UCP) option.

(*CR) carriage return only	(*CR) carriage return only
(*LF) linefeed only	(*LF) linefeed only
Line 6304 NEWLINE CONVENTIONS	Line 7990 NEWLINE CONVENTIONS
WHAT \R MATCHES	WHAT \R MATCHES

These are recognized only at the very start of the pattern or after a	These are recognized only at the very start of the pattern or after a
(*...) option that sets the newline convention or UTF-8 or UCP mode.	(*...) option that sets the newline convention or a UTF or UCP mode.

(*BSR_ANYCRLF) CR, LF, or CRLF	(*BSR_ANYCRLF) CR, LF, or CRLF
(*BSR_UNICODE) any Unicode newline sequence	(*BSR_UNICODE) any Unicode newline sequence
Line 6330 AUTHOR	Line 8016 AUTHOR

REVISION	REVISION

Last updated: 21 November 2010	Last updated: 12 November 2013
Copyright (c) 1997-2010 University of Cambridge.	Copyright (c) 1997-2013 University of Cambridge.
------------------------------------------------------------------------------	------------------------------------------------------------------------------


PCREUNICODE(3) PCREUNICODE(3)	PCREUNICODE(3) Library Functions Manual PCREUNICODE(3)



NAME	NAME
PCRE - Perl-compatible regular expressions	PCRE - Perl-compatible regular expressions

	UTF-8, UTF-16, UTF-32, AND UNICODE PROPERTY SUPPORT

UTF-8 AND UNICODE PROPERTY SUPPORT	As well as UTF-8 support, PCRE also supports UTF-16 (from release 8.30)
	and UTF-32 (from release 8.32), by means of two additional libraries.
	They can be built as well as, or instead of, the 8-bit library.

In order process UTF-8 strings, you must build PCRE to include UTF-8
support in the code, and, in addition, you must call pcre_compile()	UTF-8 SUPPORT
with the PCRE_UTF8 option flag, or the pattern must start with the
sequence (*UTF8). When either of these is the case, both the pattern	In order process UTF-8 strings, you must build PCRE's 8-bit library
	with UTF support, and, in addition, you must call pcre_compile() with
	the PCRE_UTF8 option flag, or the pattern must start with the sequence
	(UTF8) or (UTF). When either of these is the case, both the pattern
and any subject strings that are matched against it are treated as	and any subject strings that are matched against it are treated as
UTF-8 strings instead of strings of 1-byte characters. PCRE does not	UTF-8 strings instead of strings of individual 1-byte characters.
support any other formats (in particular, it does not support UTF-16).

If you compile PCRE with UTF-8 support, but do not use it at run time,
the library will be a bit bigger, but the additional run time overhead
is limited to testing the PCRE_UTF8 flag occasionally, so should not be
very big.

	UTF-16 AND UTF-32 SUPPORT

	In order process UTF-16 or UTF-32 strings, you must build PCRE's 16-bit
	or 32-bit library with UTF support, and, in addition, you must call
	pcre16_compile() or pcre32_compile() with the PCRE_UTF16 or PCRE_UTF32
	option flag, as appropriate. Alternatively, the pattern must start with
	the sequence (UTF16), (UTF32), as appropriate, or (*UTF), which can
	be used with either library. When UTF mode is set, both the pattern and
	any subject strings that are matched against it are treated as UTF-16
	or UTF-32 strings instead of strings of individual 16-bit or 32-bit
	characters.


	UTF SUPPORT OVERHEAD

	If you compile PCRE with UTF support, but do not use it at run time,
	the library will be a bit bigger, but the additional run time overhead
	is limited to testing the PCRE_UTF[8\|16\|32] flag occasionally, so
	should not be very big.


	UNICODE PROPERTY SUPPORT

If PCRE is built with Unicode character property support (which implies	If PCRE is built with Unicode character property support (which implies
UTF-8 support), the escape sequences \p{..}, \P{..}, and \X are sup-	UTF support), the escape sequences \p{..}, \P{..}, and \X can be used.
ported. The available properties that can be tested are limited to the	The available properties that can be tested are limited to the general
general category properties such as Lu for an upper case letter or Nd	category properties such as Lu for an upper case letter or Nd for a
for a decimal number, the Unicode script names such as Arabic or Han,	decimal number, the Unicode script names such as Arabic or Han, and the
and the derived properties Any and L&. A full list is given in the	derived properties Any and L&. Full lists is given in the pcrepattern
pcrepattern documentation. Only the short names for properties are sup-	and pcresyntax documentation. Only the short names for properties are
ported. For example, \p{L} matches a letter. Its Perl synonym, \p{Let-	supported. For example, \p{L} matches a letter. Its Perl synonym,
ter}, is not supported. Furthermore, in Perl, many properties may	\p{Letter}, is not supported. Furthermore, in Perl, many properties
optionally be prefixed by "Is", for compatibility with Perl 5.6. PCRE	may optionally be prefixed by "Is", for compatibility with Perl 5.6.
does not support this.	PCRE does not support this.

Validity of UTF-8 strings	Validity of UTF-8 strings

When you set the PCRE_UTF8 flag, the strings passed as patterns and	When you set the PCRE_UTF8 flag, the byte strings passed as patterns
subjects are (by default) checked for validity on entry to the relevant	and subjects are (by default) checked for validity on entry to the rel-
functions. From release 7.3 of PCRE, the check is according the rules	evant functions. The entire string is checked before any other process-
of RFC 3629, which are themselves derived from the Unicode specifica-	ing takes place. From release 7.3 of PCRE, the check is according the
tion. Earlier releases of PCRE followed the rules of RFC 2279, which	rules of RFC 3629, which are themselves derived from the Unicode speci-
allows the full range of 31-bit values (0 to 0x7FFFFFFF). The current	fication. Earlier releases of PCRE followed the rules of RFC 2279,
check allows only values in the range U+0 to U+10FFFF, excluding U+D800	which allows the full range of 31-bit values (0 to 0x7FFFFFFF). The
to U+DFFF.	current check allows only values in the range U+0 to U+10FFFF, exclud-
	ing the surrogate area. (From release 8.33 the so-called "non-charac-
	ter" code points are no longer excluded because Unicode corrigendum #9
	makes it clear that they should not be.)

The excluded code points are the "Low Surrogate Area" of Unicode, of	Characters in the "Surrogate Area" of Unicode are reserved for use by
which the Unicode Standard says this: "The Low Surrogate Area does not	UTF-16, where they are used in pairs to encode codepoints with values
contain any character assignments, consequently no character code	greater than 0xFFFF. The code points that are encoded by UTF-16 pairs
charts or namelists are provided for this area. Surrogates are reserved	are available independently in the UTF-8 and UTF-32 encodings. (In
for use with UTF-16 and then must be used in pairs." The code points	other words, the whole surrogate thing is a fudge for UTF-16 which
that are encoded by UTF-16 pairs are available as independent code	unfortunately messes up UTF-8 and UTF-32.)
points in the UTF-8 encoding. (In other words, the whole surrogate
thing is a fudge for UTF-16 which unfortunately messes up UTF-8.)

If an invalid UTF-8 string is passed to PCRE, an error return is given.	If an invalid UTF-8 string is passed to PCRE, an error return is given.
At compile time, the only additional information is the offset to the	At compile time, the only additional information is the offset to the
first byte of the failing character. The runtime functions pcre_exec()	first byte of the failing character. The run-time functions pcre_exec()
and pcre_dfa_exec() also pass back this information, as well as a more	and pcre_dfa_exec() also pass back this information, as well as a more
detailed reason code if the caller has provided memory in which to do	detailed reason code if the caller has provided memory in which to do
this.	this.

In some situations, you may already know that your strings are valid,	In some situations, you may already know that your strings are valid,
and therefore want to skip these checks in order to improve perfor-	and therefore want to skip these checks in order to improve perfor-
mance. If you set the PCRE_NO_UTF8_CHECK flag at compile time or at run	mance, for example in the case of a long subject string that is being
time, PCRE assumes that the pattern or subject it is given (respec-	scanned repeatedly. If you set the PCRE_NO_UTF8_CHECK flag at compile
tively) contains only valid UTF-8 codes. In this case, it does not	time or at run time, PCRE assumes that the pattern or subject it is
diagnose an invalid UTF-8 string.	given (respectively) contains only valid UTF-8 codes. In this case, it
	does not diagnose an invalid UTF-8 string.

If you pass an invalid UTF-8 string when PCRE_NO_UTF8_CHECK is set,	Note that passing PCRE_NO_UTF8_CHECK to pcre_compile() just disables
what happens depends on why the string is invalid. If the string con-	the check for the pattern; it does not also apply to subject strings.
forms to the "old" definition of UTF-8 (RFC 2279), it is processed as a	If you want to disable the check for a subject string you must pass
string of characters in the range 0 to 0x7FFFFFFF by pcre_dfa_exec()
and the interpreted version of pcre_exec(). In other words, apart from
the initial validity test, these functions (when in UTF-8 mode) handle
strings according to the more liberal rules of RFC 2279. However, the
just-in-time (JIT) optimization for pcre_exec() supports only RFC 3629.
If you are using JIT optimization, or if the string does not even con-
form to RFC 2279, the result is undefined. Your program may crash.

If you want to process strings of values in the full range 0 to	If you pass an invalid UTF-8 string when PCRE_NO_UTF8_CHECK is set, the
0x7FFFFFFF, encoded in a UTF-8-like manner as per the old RFC, you can	result is undefined and your program may crash.
set PCRE_NO_UTF8_CHECK to bypass the more restrictive test. However, in
this situation, you will have to apply your own validity check, and
avoid the use of JIT optimization.

General comments about UTF-8 mode	Validity of UTF-16 strings

1. An unbraced hexadecimal escape sequence (such as \xb3) matches a	When you set the PCRE_UTF16 flag, the strings of 16-bit data units that
two-byte UTF-8 character if the value is greater than 127.	are passed as patterns and subjects are (by default) checked for valid-
	ity on entry to the relevant functions. Values other than those in the
	surrogate range U+D800 to U+DFFF are independent code points. Values in
	the surrogate range must be used in pairs in the correct manner.

2. Octal numbers up to \777 are recognized, and match two-byte UTF-8	If an invalid UTF-16 string is passed to PCRE, an error return is
characters for values greater than \177.	given. At compile time, the only additional information is the offset
	to the first data unit of the failing character. The run-time functions
	pcre16_exec() and pcre16_dfa_exec() also pass back this information, as
	well as a more detailed reason code if the caller has provided memory
	in which to do this.

3. Repeat quantifiers apply to complete UTF-8 characters, not to indi-	In some situations, you may already know that your strings are valid,
vidual bytes, for example: \x{100}{3}.	and therefore want to skip these checks in order to improve perfor-
	mance. If you set the PCRE_NO_UTF16_CHECK flag at compile time or at
	run time, PCRE assumes that the pattern or subject it is given (respec-
	tively) contains only valid UTF-16 sequences. In this case, it does not
	diagnose an invalid UTF-16 string. However, if an invalid string is
	passed, the result is undefined.

4. The dot metacharacter matches one UTF-8 character instead of a sin-	Validity of UTF-32 strings
gle byte.

5. The escape sequence \C can be used to match a single byte in UTF-8	When you set the PCRE_UTF32 flag, the strings of 32-bit data units that
mode, but its use can lead to some strange effects because it breaks up	are passed as patterns and subjects are (by default) checked for valid-
multibyte characters (see the description of \C in the pcrepattern doc-	ity on entry to the relevant functions. This check allows only values
umentation). The use of \C is not supported in the alternative matching	in the range U+0 to U+10FFFF, excluding the surrogate area U+D800 to
function pcre_dfa_exec(), nor is it supported in UTF-8 mode by the JIT	U+DFFF.
optimization of pcre_exec(). If JIT optimization is requested for a
UTF-8 pattern that contains \C, it will not succeed, and so the match-
ing will be carried out by the normal interpretive function.

6. The character escapes \b, \B, \d, \D, \s, \S, \w, and \W correctly	If an invalid UTF-32 string is passed to PCRE, an error return is
	given. At compile time, the only additional information is the offset
	to the first data unit of the failing character. The run-time functions
	pcre32_exec() and pcre32_dfa_exec() also pass back this information, as
	well as a more detailed reason code if the caller has provided memory
	in which to do this.

	In some situations, you may already know that your strings are valid,
	and therefore want to skip these checks in order to improve perfor-
	mance. If you set the PCRE_NO_UTF32_CHECK flag at compile time or at
	run time, PCRE assumes that the pattern or subject it is given (respec-
	tively) contains only valid UTF-32 sequences. In this case, it does not
	diagnose an invalid UTF-32 string. However, if an invalid string is
	passed, the result is undefined.

	General comments about UTF modes

	1. Codepoints less than 256 can be specified in patterns by either
	braced or unbraced hexadecimal escape sequences (for example, \x{b3} or
	\xb3). Larger values have to use braced sequences.

	2. Octal numbers up to \777 are recognized, and in UTF-8 mode they
	match two-byte characters for values greater than \177.

	3. Repeat quantifiers apply to complete UTF characters, not to individ-
	ual data units, for example: \x{100}{3}.

	4. The dot metacharacter matches one UTF character instead of a single
	data unit.

	5. The escape sequence \C can be used to match a single byte in UTF-8
	mode, or a single 16-bit data unit in UTF-16 mode, or a single 32-bit
	data unit in UTF-32 mode, but its use can lead to some strange effects
	because it breaks up multi-unit characters (see the description of \C
	in the pcrepattern documentation). The use of \C is not supported in
	the alternative matching function pcre[16\|32]_dfa_exec(), nor is it
	supported in UTF mode by the JIT optimization of pcre[16\|32]_exec(). If
	JIT optimization is requested for a UTF pattern that contains \C, it
	will not succeed, and so the matching will be carried out by the normal
	interpretive function.

	6. The character escapes \b, \B, \d, \D, \s, \S, \w, and \W correctly
test characters of any code value, but, by default, the characters that	test characters of any code value, but, by default, the characters that
PCRE recognizes as digits, spaces, or word characters remain the same	PCRE recognizes as digits, spaces, or word characters remain the same
set as before, all with values less than 256. This remains true even	set as in non-UTF mode, all with values less than 256. This remains
when PCRE is built to include Unicode property support, because to do	true even when PCRE is built to include Unicode property support,
otherwise would slow down PCRE in many common cases. Note in particular	because to do otherwise would slow down PCRE in many common cases. Note
that this applies to \b and \B, because they are defined in terms of \w	in particular that this applies to \b and \B, because they are defined
and \W. If you really want to test for a wider sense of, say, "digit",	in terms of \w and \W. If you really want to test for a wider sense of,
you can use explicit Unicode property tests such as \p{Nd}. Alterna-	say, "digit", you can use explicit Unicode property tests such as
tively, if you set the PCRE_UCP option, the way that the character	\p{Nd}. Alternatively, if you set the PCRE_UCP option, the way that the
escapes work is changed so that Unicode properties are used to deter-	character escapes work is changed so that Unicode properties are used
mine which characters match. There are more details in the section on	to determine which characters match. There are more details in the sec-
generic character types in the pcrepattern documentation.	tion on generic character types in the pcrepattern documentation.

7. Similarly, characters that match the POSIX named character classes	7. Similarly, characters that match the POSIX named characte 7. Similarly, characters that match the POSIX named characte
are all low-valued characters, unless the PCRE_UCP option is set.	are all low-valued characters, unless the PCRE_UCP option is set.

8. However, the horizontal and vertical whitespace matching escapes	8. However, the horizontal and vertical white space matching escapes
(\h, \H, \v, and \V) do match all the appropriate Unicode characters,	(\h, \H, \v, and \V) do match all the appropriate Unicode characters,
whether or not PCRE_UCP is set.	whether or not PCRE_UCP is set.

9. Case-insensitive matching applies only to characters whose values	9. Case-insensitive matching applies only to characters whose values
are less than 128, unless PCRE is built with Unicode property support.	are less than 128, unless PCRE is built with Unicode property support.
Even when Unicode property support is available, PCRE still uses its	A few Unicode characters such as Greek sigma have more than two code-
own character tables when checking the case of low-valued characters,	points that are case-equivalent. Up to and including PCRE release 8.31,
so as not to degrade performance. The Unicode property information is	only one-to-one case mappings were supported, but later releases (with
used only for characters with higher values. Furthermore, PCRE supports	Unicode property support) do treat as case-equivalent all versions of
case-insensitive matching only when there is a one-to-one mapping	characters such as Greek sigma.
between a letter's cases. There are a small number of many-to-one map-
pings in Unicode; these are not supported by PCRE.


AUTHOR	AUTHOR
Line 6484 AUTHOR	Line 8235 AUTHOR

REVISION	REVISION

Last updated: 19 October 2011	Last updated: 27 February 2013
Copyright (c) 1997-2011 University of Cambridge.	Copyright (c) 1997-2013 University of Cambridge.
------------------------------------------------------------------------------	------------------------------------------------------------------------------


PCREJIT(3) PCREJIT(3)	PCREJIT(3) Library Functions Manual PCREJIT(3)



NAME	NAME
PCRE - Perl-compatible regular expressions	PCRE - Perl-compatible regular expressions


PCRE JUST-IN-TIME COMPILER SUPPORT	PCRE JUST-IN-TIME COMPILER SUPPORT

Just-in-time compiling is a heavyweight optimization that can greatly	Just-in-time compiling is a heavyweight optimization that can greatly
speed up pattern matching. However, it comes at the cost of extra pro-	speed up pattern matching. However, it comes at the cost of extra pro-
cessing before the match is performed. Therefore, it is of most benefit	cessing before the match is performed. Therefore, it is of most benefit
when the same pattern is going to be matched many times. This does not	when the same pattern is going to be matched many times. This does not
necessarily mean many calls of pcre_exec(); if the pattern is not	necessarily mean many calls of a matching function; if the pattern is
anchored, matching attempts may take place many times at various posi-	not anchored, matching attempts may take place many times at various
tions in the subject, even for a single call to pcre_exec(). If the	positions in the subject, even for a single call. Therefore, if the
subject string is very long, it may still pay to use JIT for one-off	subject string is very long, it may still pay to use JIT for one-off
matches.	matches.

JIT support applies only to the traditional matching function,	JIT support applies only to the traditional Perl-compatible matching
pcre_exec(). It does not apply when pcre_dfa_exec() is being used. The	function. It does not apply when the DFA matching function is being
code for this support was written by Zoltan Herczeg.	used. The code for this support was written by Zoltan Herczeg.


	8-BIT, 16-BIT AND 32-BIT SUPPORT

	JIT support is available for all of the 8-bit, 16-bit and 32-bit PCRE
	libraries. To keep this documentation simple, only the 8-bit interface
	is described in what follows. If you are using the 16-bit library, sub-
	stitute the 16-bit functions and 16-bit structures (for example,
	pcre16_jit_stack instead of pcre_jit_stack). If you are using the
	32-bit library, substitute the 32-bit functions and 32-bit structures
	(for example, pcre32_jit_stack instead of pcre_jit_stack).


AVAILABILITY OF JIT SUPPORT	AVAILABILITY OF JIT SUPPORT

JIT support is an optional feature of PCRE. The "configure" option	JIT support is an optional feature of PCRE. The "configure" option
Line 6523 AVAILABILITY OF JIT SUPPORT	Line 8285 AVAILABILITY OF JIT SUPPORT
ARM v5, v7, and Thumb2	ARM v5, v7, and Thumb2
Intel x86 32-bit and 64-bit	Intel x86 32-bit and 64-bit
MIPS 32-bit	MIPS 32-bit
Power PC 32-bit and 64-bit (experimental)	Power PC 32-bit and 64-bit
	SPARC 32-bit (experimental)

The Power PC support is designated as experimental because it has not	If --enable-jit is set on an unsupported platform, compilation fails.
been fully tested. If --enable-jit is set on an unsupported platform,
compilation fails.

A program that is linked with PCRE 8.20 or later can tell if JIT sup-	A program that is linked with PCRE 8.20 or later can tell if JIT sup-
port is available by calling pcre_config() with the PCRE_CONFIG_JIT	port is available by calling pcre_config() with the PCRE_CONFIG_JIT
option. The result is 1 when JIT is available, and 0 otherwise. How-	option. The result is 1 when JIT is available, and 0 otherwise. How-
ever, a simple program does not need to check this in order to use JIT.	ever, a simple program does not need to check this in order to use JIT.
The API is implemented in a way that falls back to the ordinary PCRE	The normal API is implemented in a way that falls back to the interpre-
code if JIT is not available.	tive code if JIT is not available. For programs that need the best pos-
	sible performance, there is also a "fast path" API that is JIT-spe-
	cific.

If your program may sometimes be linked with versions of PCRE that are	If your program may sometimes be linked with versions of PCRE that are
older than 8.20, but you want to use JIT when it is available, you can	older than 8.20, but you want to use JIT when it is available, you can
Line 6552 SIMPLE USE OF JIT	Line 8315 SIMPLE USE OF JIT
pcre_exec().	pcre_exec().

(2) Use pcre_free_study() to free the pcre_extra block when it is	(2) Use pcre_free_study() to free the pcre_extra block when it is
no longer needed instead of just freeing it yourself. This	no longer needed, instead of just freeing it yourself. This
ensures that any JIT data is also freed.	ensures that
	any JIT data is also freed.

For a program that may be linked with pre-8.20 versions of PCRE, you	For a program that may be linked with pre-8.20 versions of PCRE, you
can insert	can insert

#ifndef PCRE_STUDY_JIT_COMPILE	#ifndef PCRE_STUDY_JIT_COMPILE
#define PCRE_STUDY_JIT_COMPILE 0	#define PCRE_STUDY_JIT_COMPILE 0
#endif	#endif

so that no option is passed to pcre_study(), and then use something	so that no opt so that no option is passed to pcre_study(), and then use something
like this to free the study data:	like this to free the study data:

#ifdef PCRE_CONFIG_JIT	#ifdef PCRE_CONFIG_JIT
Line 6571 SIMPLE USE OF JIT	Line 8335 SIMPLE USE OF JIT
pcre_free(study_ptr);	pcre_free(study_ptr);
#endif	#endif

	PCRE_STUDY_JIT_COMPILE requests the JIT compiler to generate code for
	complete matches. If you want to run partial matches using the
	PCRE_PARTIAL_HARD or PCRE_PARTIAL_SOFT options of pcre_exec(), you
	should set one or both of the following options in addition to, or
	instead of, PCRE_STUDY_JIT_COMPILE when you call pcre_study():

	PCRE_STUDY_JIT_PARTIAL_HARD_COMPILE
	PCRE_STUDY_JIT_PARTIAL_SOFT_COMPILE

	The JIT compiler generates different optimized code for each of the
	three modes (normal, soft partial, hard partial). When pcre_exec() is
	called, the appropriate code is run if it is available. Otherwise, the
	pattern is matched using interpretive code.

In some circumstances you may need to call additional functions. These	In some circumstances you may need to call additional functions. These
are described in the section entitled "Controlling the JIT stack"	are described in the section entitled "Controlling the JIT stack"
below.	below.

If JIT support is not available, PCRE_STUDY_JIT_COMPILE is ignored, and	If JIT support is not available, PCRE_STUDY_JIT_COMPILE etc. are
no JIT data is set up. Otherwise, the compiled pattern is passed to the	ignored, and no JIT data is created. Otherwise, the compiled pattern is
JIT compiler, which turns it into machine code that executes much	passed to the JIT compiler, which turns it into machine code that exe-
faster than the normal interpretive code. When pcre_exec() is passed a	cutes much faster than the normal interpretive code. When pcre_exec()
pcre_extra block containing a pointer to JIT code, it obeys that	is passed a pcre_extra block containing a pointer to JIT code of the
instead of the normal code. The result is identical, but the code runs	appropriate mode (normal or hard/soft partial), it obeys that code
much faster.	instead of running the interpreter. The result is identical, but the
	compiled JIT code runs much faster.

There are some pcre_exec() options that are not supported for JIT exe-	There are some pcre_exec() options that are not supported for JIT exe-
cution. There are also some pattern items that JIT cannot handle.	cution. There are also some pattern items that JIT cannot handle.
Details are given below. In both cases, execution automatically falls	Details are given below. In both cases, execution automatically falls
back to the interpretive code.	back to the interpretive code. If you want to know whether JIT was
	actually used for a particular match, you should arrange for a JIT
	callback function to be set up as described in the section entitled
	"Controlling the JIT stack" below, even if you do not need to supply a
	non-default JIT stack. Such a callback function is called whenever JIT
	code is about to be obeyed. If the execution options are not right for
	JIT execution, the callback function is not obeyed.

If the JIT compiler finds an unsupported item, no JIT data is gener-	If the JIT compiler finds an unsupported item, no JIT data is gener-
ated. You can find out if JIT execution is available after studying a	ated. You can find out if JIT execution is available after studying a
pattern by calling pcre_fullinfo() with the PCRE_INFO_JIT option. A	pattern by calling pcre_fullinfo() with the PCRE_INFO_JIT option. A
result of 1 means that JIT compilation was successful. A result of 0	result of 1 means that JIT compilation was successful. A result of 0
means that JIT support is not available, or the pattern was not studied	means that JIT support is not available, or the pattern was not studied
with PCRE_STUDY_JIT_COMPILE, or the JIT compiler was not able to handle	with PCRE_STUDY_JIT_COMPILE etc., or the JIT compiler was not able to
the pattern.	handle the pattern.

Once a pattern has been studied, with or without JIT, it can be used as	Once a pattern has been studied, with or without JIT, it can be used as
many times as you like for matching different subject strings.	many times as you like for matching different subject strings.
Line 6602 SIMPLE USE OF JIT	Line 8387 SIMPLE USE OF JIT

UNSUPPORTED OPTIONS AND PATTERN ITEMS	UNSUPPORTED OPTIONS AND PATTERN ITEMS

The only pcre_exec() options that are supported for JIT execution are	The only pcre_exec() options that are supported for JIT execution are
PCRE_NO_UTF8_CHECK, PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, and	PCRE_NO_UTF8_CHECK, PCRE_NO_UTF16_CHECK, PCRE_NO_UTF32_CHECK, PCRE_NOT-
PCRE_NOTEMPTY_ATSTART. Note in particular that partial matching is not	BOL, PCRE_NOTEOL, PCRE_NOTEMPTY, PCRE_NOTEMPTY_ATSTART, PCRE_PAR-
supported.	TIAL_HARD, and PCRE_PARTIAL_SOFT.

The unsupported pattern items are:	The only unsupported pattern items are \C (match a single data unit)
	when running in a UTF mode, and a callout immediately before an asser-
	tion condition in a conditional group.

\C match a single byte; not supported in UTF-8 mode
(?Cn) callouts
(*COMMIT) )
(*MARK) )
(*PRUNE) ) the backtracking control verbs
(*SKIP) )
(*THEN) )

Support for some of these may be added in future.


RETURN VALUES FROM JIT EXECUTION	RETURN VALUES FROM JIT EXECUTION

When a pattern is matched using JIT execution, the return values are	When a pattern is matched using JIT execution, the return values are
the same as those given by the interpretive pcre_exec() code, with the	the same as those given by the interpretive pcre_exec() code, with the
addition of one new error code: PCRE_ERROR_JIT_STACKLIMIT. This means	addition of one new error code: PCRE_ERROR_JIT_STACKLIMIT. This means
that the memory used for the JIT stack was insufficient. See "Control-	that the memory used for the JIT stack was insufficient. See "Control-
ling the JIT stack" below for a discussion of JIT stack usage. For com-	ling the JIT stack" below for a discussion of JIT stack usage. For com-
patibility with the interpretive pcre_exec() code, no more than two-	patibility with the interpretive pcre_exec() code, no more than two-
thirds of the ovector argument is used for passing back captured sub-	thirds of the ovector argument is used for passing back captured sub-
strings.	strings.

The error code PCRE_ERROR_MATCHLIMIT is returned by the JIT code if	The error code PCRE_ERROR_MATCHLIMIT is returned by the JIT code if
searching a very large pattern tree goes on for too long, as it is in	searching a very large pattern tree goes on for too long, as it is in
the same circumstance when JIT is not used, but the details of exactly	the same circumstance when JIT is not used, but the details of exactly
what is counted are not the same. The PCRE_ERROR_RECURSIONLIMIT error	what is counted are not the same. The PCRE_ERROR_RECURSIONLIMIT error
code is never returned by JIT execution.	code is never returned by JIT execution.


SAVING AND RESTORING COMPILED PATTERNS	SAVING AND RESTORING COMPILED PATTERNS

The code that is generated by the JIT compiler is architecture-spe-	The code that is generated by the JIT compiler is architecture-spe-
cific, and is also position dependent. For those reasons it cannot be	cific, and is also position dependent. For those reasons it cannot be
saved (in a file or database) and restored later like the bytecode and	saved (in a file or database) and restored later like the bytecode and
other data of a compiled pattern. Saving and restoring compiled pat-	other data of a compiled pattern. Saving and restoring compiled pat-
terns is not something many people do. More detail about this facility	terns is not something many people do. More detail about this facility
is given in the pcreprecompile documentation. It should be possible to	is given in the pcreprecompile documentation. It should be possible to
run pcre_study() on a saved and restored pattern, and thereby recreate	run pcre_study() on a saved and restored pattern, and thereby recreate
the JIT data, but because JIT compilation uses significant resources,	the JIT data, but because JIT compilation uses significant resources,
it is probably not worth doing this; you might as well recompile the	it is probably not worth doing this; you might as well recompile the
original pattern.	original pattern.


CONTROLLING THE JIT STACK	CONTROLLING THE JIT STACK

When the compiled JIT code runs, it needs a block of memory to use as a	When the compiled JIT code runs, it needs a block of memory to use as a
stack. By default, it uses 32K on the machine stack. However, some	stack. By default, it uses 32K on the machine stack. However, some
large or complicated patterns need more than this. The error	large or complicated patterns need more than this. The error
PCRE_ERROR_JIT_STACKLIMIT is given when there is not enough stack.	PCRE_ERROR_JIT_STACKLIMIT is given when there is not enough stack.
Three functions are provided for managing blocks of memory for use as	Three functions are provided for managing blocks of memory for use as
JIT stacks. There is further discussion about the use of JIT stacks in	JIT stacks. There is further discussion about the use of JIT stacks in
the section entitled "JIT stack FAQ" below.	the section entitled "JIT stack FAQ" below.

The pcre_jit_stack_alloc() function creates a JIT stack. Its arguments	The pcre_jit_stack_alloc() function creates a JIT stack. Its arguments
are a starting size and a maximum size, and it returns a pointer to an	are a starting size and a maximum size, and it returns a pointer to an
opaque structure of type pcre_jit_stack, or NULL if there is an error.	opaque structure of type pcre_jit_stack, or NULL if there is an error.
The pcre_jit_stack_free() function can be used to free a stack that is	The pcre_jit_stack_free() function can be used to free a stack that is
no longer needed. (For the technically minded: the address space is	no longer needed. (For the technically minded: the address space is
allocated by mmap or VirtualAlloc.)	allocated by mmap or VirtualAlloc.)

JIT uses far less memory for recursion than the interpretive code, and	JIT uses far less memory for recursion than the interpretive code, and
a maximum stack size of 512K to 1M should be more than enough for any	a maximum stack size of 512K to 1M should be more than enough for any
pattern.	pattern.

The pcre_assign_jit_stack() function specifies which stack JIT code	The pcre_assign_jit_stack() function specifies which stack JIT code
should use. Its arguments are as follows:	should use. Its arguments are as follows:

pcre_extra *extra	pcre_extra *extra
pcre_jit_callback callback	pcre_jit_callback callback
void *data	void *data

The extra argument must be the result of studying a pattern with	The extra argument must be the result The extra argument must be the result
PCRE_STUDY_JIT_COMPILE. There are three cases for the values of the	PCRE_STUDY_JIT_COMPILE etc. There are three cases for the values of the
other two options:	other two options:

(1) If callback is NULL and data is NULL, an internal 32K block	(1) If callback is NULL and data is NULL, an internal 32K block
Line 6690 CONTROLLING THE JIT STACK	Line 8467 CONTROLLING THE JIT STACK
(2) If callback is NULL and data is not NULL, data must be	(2) If callback is NULL and data is not NULL, data must be
a valid JIT stack, the result of calling pcre_jit_stack_alloc().	a valid JIT stack, the result of calling pcre_jit_stack_alloc().

(3) If callback not NULL, it must point to a function that is called	(3) If callback is not NULL, it must point to a function that is
with data as an argument at the start of matching, in order to	called with data as an argument at the start of matching, in
set up a JIT stack. If the result is NULL, the internal 32K stack	order to set up a JIT stack. If the return from the callback
is used; otherwise the return value must be a valid JIT stack,	function is NULL, the internal 32K stack is used; otherwise the
the result of calling pcre_jit_stack_alloc().	return value must be a valid JIT stack, the result of calling
	pcre_jit_stack_alloc().

You may safely assign the same JIT stack to more than one pattern, as	A callback function is obeyed whenever JIT code is about to be run; it
long as they are all matched sequentially in the same thread. In a mul-	is not obeyed when pcre_exec() is called with options that are incom-
tithread application, each thread must use its own JIT stack.	patible for JIT execution. A callback function can therefore be used to
	determine whether a match operation was executed by JIT or by the
	interpreter.

Strictly speaking, even more is allowed. You can assign the same stack	You may safely use the same JIT stack for more than one pattern (either
to any number of patterns as long as they are not used for matching by	by assigning directly or by callback), as long as the patterns are all
multiple threads at the same time. For example, you can assign the same	matched sequentially in the same thread. In a multithread application,
stack to all compiled patterns, and use a global mutex in the callback	if you do not specify a JIT stack, or if you assign or pass back NULL
to wait until the stack is available for use. However, this is an inef-	from a callback, that is thread-safe, because each thread has its own
ficient solution, and not recommended.	machine stack. However, if you assign or pass back a non-NULL JIT
	stack, this must be a different stack for each thread so that the
	application is thread-safe.

This is a suggestion for how a typical multithreaded program might	Strictly speaking, even more is allowed. You can assign the same non-
operate:	NULL stack to any number of patterns as long as they are not used for
	matching by multiple threads at the same time. For example, you can
	assign the same stack to all compiled patterns, and use a global mutex
	in the callback to wait until the stack is available for use. However,
	this is an inefficient solution, and not recommended.

	This is a suggestion for how a multithreaded program that needs to set
	up non-default JIT stacks might operate:

During thread initalization	During thread initalization
thread_local_var = pcre_jit_stack_alloc(...)	thread_local_var = pcre_jit_stack_alloc(...)

Line 6722 CONTROLLING THE JIT STACK	Line 8511 CONTROLLING THE JIT STACK
All the functions described in this section do nothing if JIT is not	All the functions described in this section do nothing if JIT is not
available, and pcre_assign_jit_stack() does nothing unless the extra	available, and pcre_assign_jit_stack() does nothing unless the extra
argument is non-NULL and points to a pcre_extra block that is the	argument is non-NULL and points to a pcre_extra block that is the
result of a successful study with PCRE_STUDY_JIT_COMPILE.	result of a successful study with PCRE_STUDY_JIT_COMPILE etc.


JIT STACK FAQ	JIT STACK FAQ
Line 6773 JIT STACK FAQ	Line 8562 JIT STACK FAQ

No, because this is too costly in terms of resources. However, you	No, because this is too costly in terms of resources. However, you
could implement some clever idea which release the stack if it is not	could implement some clever idea which release the stack if it is not
used in let's say two minutes. The JIT callback can help to achive this	used in let's say two minutes. The JIT callback can help to achieve
without keeping a list of the currently JIT studied patterns.	this without keeping a list of the currently JIT studied patterns.

(6) OK, the stack is for long term memory allocation. But what happens	(6) OK, the stack is for long term memory allocation. But what happens
if a pattern causes stack overflow with a stack of 1M? Is that 1M kept	if a pattern causes stack overflow with a stack of 1M? Is that 1M kept
Line 6782 JIT STACK FAQ	Line 8571 JIT STACK FAQ

Especially on embedded sytems, it might be a good idea to release mem-	Especially on embedded sytems, it might be a good idea to release mem-
ory sometimes without freeing the stack. There is no API for this at	ory sometimes without freeing the stack. There is no API for this at
the moment. Probably a function call which returns with the currently	the moment. Probably a function call which returns with the currently
allocated memory for any stack and another which allows releasing mem-	allocated memory for any stack and another which allows releasing mem-
ory (shrinking the stack) would be a good idea if someone needs this.	ory (shrinking the stack) would be a good idea if someone needs this.

Line 6817 EXAMPLE CODE	Line 8606 EXAMPLE CODE
pcre_jit_stack_free(jit_stack);	pcre_jit_stack_free(jit_stack);


	JIT FAST PATH API

	Because the API described above falls back to interpreted execution
	when JIT is not available, it is convenient for programs that are writ-
	ten for general use in many environments. However, calling JIT via
	pcre_exec() does have a performance impact. Programs that are written
	for use where JIT is known to be available, and which need the best
	possible performance, can instead use a "fast path" API to call JIT
	execution directly instead of calling pcre_exec() (obviously only for
	patterns that have been successfully studied by JIT).

	The fast path function is called pcre_jit_exec(), and it takes exactly
	the same arguments as pcre_exec(), plus one additional argument that
	must point to a JIT stack. The JIT stack arrangements described above
	do not apply. The return values are the same as for pcre_exec().

	When you call pcre_exec(), as well as testing for invalid options, a
	number of other sanity checks are performed on the arguments. For exam-
	ple, if the subject pointer is NULL, or its length is negative, an
	immediate error is given. Also, unless PCRE_NO_UTF[8\|16\|32] is set, a
	UTF subject string is tested for validity. In the interests of speed,
	these checks do not happen on the JIT fast path, and if invalid data is
	passed, the result is undefined.

	Bypassing the sanity checks and the pcre_exec() wrapping can give
	speedups of more than 10%.


SEE ALSO	SEE ALSO

pcreapi(3)	pcreapi(3)
Line 6831 AUTHOR	Line 8648 AUTHOR

REVISION	REVISION

Last updated: 26 November 2011	Last updated: 17 March 2013
Copyright (c) 1997-2011 University of Cambridge.	Copyright (c) 1997-2013 University of Cambridge.
------------------------------------------------------------------------------	------------------------------------------------------------------------------


PCREPARTIAL(3) PCREPARTIAL(3)	PCREPARTIAL(3) Library Functions Manual PCREPARTIAL(3)



NAME	NAME
PCRE - Perl-compatible regular expressions	PCRE - Perl-compatible regular expressions


PARTIAL MATCHING IN PCRE	PARTIAL MATCHING IN PCRE

In normal use of PCRE, if the subject string that is passed to	In normal use of PCRE, if the subject string that is passed to a match-
pcre_exec() or pcre_dfa_exec() matches as far as it goes, but is too	ing function matches as far as it goes, but is too short to match the
short to match the entire pattern, PCRE_ERROR_NOMATCH is returned.	entire pattern, PCRE_ERROR_NOMATCH is returned. There are circumstances
There are circumstances where it might be helpful to distinguish this	where it might be helpful to distinguish this case from other cases in
case from other cases in which there is no match.	which there is no match.

Consider, for example, an application where a human is required to type	Consider, for example, an application where a human is required to type
in data for a field with specific formatting requirements. An example	in data for a field with specific formatting requirements. An example
Line 6867 PARTIAL MATCHING IN PCRE	Line 8684 PARTIAL MATCHING IN PCRE
available at once.	available at once.

PCRE supports partial matching by means of the PCRE_PARTIAL_SOFT and	PCRE supports partial matching by means of the PCRE_PARTIAL_SOFT and
PCRE_PARTIAL_HARD options, which can be set when calling pcre_exec() or	PCRE_PARTIAL_HARD options, which can be set when calling any of the
pcre_dfa_exec(). For backwards compatibility, PCRE_PARTIAL is a synonym	matching functions. For backwards compatibility, PCRE_PARTIAL is a syn-
for PCRE_PARTIAL_SOFT. The essential difference between the two options	onym for PCRE_PARTIAL_SOFT. The essential difference between the two
is whether or not a partial match is preferred to an alternative com-	options is whether or not a partial match is preferred to an alterna-
plete match, though the details differ between the two matching func-	tive complete match, though the details differ between the two types of
tions. If both options are set, PCRE_PARTIAL_HARD takes precedence.	matching function. If both options are set, PCRE_PARTIAL_HARD takes
	precedence.

Setting a partial matching option for pcre_exec() disables the use of	If you want to use partial matching with just-in-time optimized code,
any just-in-time code that was set up by calling pcre_study() with the	you must call pcre_study(), pcre16_study() or pcre32_study() with one
PCRE_STUDY_JIT_COMPILE option. It also disables two of PCRE's standard	or both of these options:
optimizations. PCRE remembers the last literal byte in a pattern, and
abandons matching immediately if such a byte is not present in the sub-	PCRE_STUDY_JIT_PARTIAL_SOFT_COMPILE
ject string. This optimization cannot be used for a subject string that	PCRE_STUDY_JIT_PARTIAL_HARD_COMPILE
might match only partially. If the pattern was studied, PCRE knows the
minimum length of a matching string, and does not bother to run the	PCRE_STUDY_JIT_COMPILE should also be set if you are going to run non-
matching function on shorter strings. This optimization is also dis-	partial matches on the same pattern. If the appropriate JIT study mode
	has not been set for a match, the interpretive matching code is used.

	Setting a partial matching option disables two of PCRE's standard opti-
	mizations. PCRE remembers the last literal data unit in a pattern, and
	abandons matching immediately if it is not present in the subject
	string. This optimization cannot be used for a subject string that
	might match only partially. If the pattern was studied, PCRE knows the
	minimum length of a matching string, and does not bother to run the
	matching function on shorter strings. This optimization is also dis-
abled for partial matching.	abled for partial matching.


PARTIAL MATCHING USING pcre_exec()	PARTIAL MATCHING USING pcre_exec() OR pcre[16\|32]_exec()

A partial match occurs during a call to pcre_exec() when the end of the	A partial match occurs during a call to pcre_exec() or
subject string is reached successfully, but matching cannot continue	pcre[16\|32]_exec() when the end of the subject string is reached suc-
because more characters are needed. However, at least one character in	cessfully, but matching cannot continue because more characters are
the subject must have been inspected. This character need not form part	needed. However, at least one character in the subject must have been
of the final matched string; lookbehind assertions and the \K escape	inspected. This character need not form part of the final matched
sequence provide ways of inspecting characters before the start of a	string; lookbehind assertions and the \K escape sequence provide ways
matched substring. The requirement for inspecting at least one charac-	of inspecting characters before the start of a matched substring. The
ter exists because an empty string can always be matched; without such	requirement for inspecting at least one character exists because an
a restriction there would always be a partial match of an empty string	empty string can always be matched; without such a restriction there
at the end of the subject.	would always be a partial match of an empty string at the end of the
	subject.

If there are at least two slots in the offsets vector when pcre_exec()	If there are at least two slots in the offsets vector when a partial
returns with a partial match, the first slot is set to the offset of	match is returned, the first slot is set to the offset of the earliest
the earliest character that was inspected when the partial match was	character that was inspected. For convenience, the second offset points
found. For convenience, the second offset points to the end of the sub-	to the end of the subject so that a substring can easily be identified.
ject so that a substring can easily be identified.	If there are at least three slots in the offsets vector, the third slot
	is set to the offset of the character where matching started.

For the majority of patterns, the first offset identifies the start of	For the majority of patterns, the contents of the first and third slots
the partially matched string. However, for patterns that contain look-	will be the same. However, for patterns that contain lookbehind asser-
behind assertions, or \K, or begin with \b or \B, earlier characters	tions, or begin with \b or \B, characters before the one where matching
have been inspected while carrying out the match. For example:	started may have been inspected while carrying out the match. For exam-
	ple, consider this pattern:

/(?<=abc)123/	/(?<=abc)123/

This pattern matches "123", but only if it is preceded by "abc". If the	This pattern matches "123", but only if it is preceded by "abc". If the
subject string is "xyzabc12", the offsets after a partial match are for	subject string is "xyzabc12", the first two offsets after a partial
the substring "abc12", because all these characters are needed if	match are for the substring "abc12", because all these characters were
another match is tried with extra characters added to the subject.	inspected. However, the third offset is set to 6, because that is the
	offset where matching began.

What happens when a partial match is identified depends on which of the	What happens when a partial match is identified depends on which of the
two partial matching options are set.	two partial matching options are set.

PCRE_PARTIAL_SOFT with pcre_exec()	PCRE_PARTIAL_SOFT WITH pcre_exec() OR pcre[16\|32]_exec()

If PCRE_PARTIAL_SOFT is set when pcre_exec() identifies a partial	If PCRE_PARTIAL_SOFT is set when pcre_exec() or pcre[16\|32]_exec()
match, the partial match is remembered, but matching continues as nor-	identifies a partial match, the partial match is remembered, but match-
mal, and other alternatives in the pattern are tried. If no complete	ing continues as normal, and other alternatives in the pattern are
match can be found, pcre_exec() returns PCRE_ERROR_PARTIAL instead of	tried. If no complete match can be found, PCRE_ERROR_PARTIAL is
PCRE_ERROR_NOMATCH.	returned instead of PCRE_ERROR_NOMATCH.

This option is "soft" because it prefers a complete match over a par-	This option is "soft" because it prefers a complete match over a par-
tial match. All the various matching items in a pattern behave as if	tial match. All the various matching items in a pattern behave as if
the subject string is potentially complete. For example, \z, \Z, and $	the subject string is potentially complete. For example, \z, \Z, and $
match at the end of the subject, as normal, and for \b and \B the end	match at the end of the subject, as normal, and for \b and \B the end
of the subject is treated as a non-alphanumeric.	of the subject is treated as a non-alphanumeric.

If there is more than one partial match, the first one that was found	If there is more than one partial match, the first one that was found
provides the data that is returned. Consider this pattern:	provides the data that is returned. Consider this pattern:

/123\w+X\|dogY/	/123\w+X\|dogY/

If this is matched against the subject string "abc123dog", both alter-	If this is matched against the subject string "abc123dog", both alter-
natives fail to match, but the end of the subject is reached during	natives fail to match, but the end of the subject is reached during
matching, so PCRE_ERROR_PARTIAL is returned. The offsets are set to 3	matching, so PCRE_ERROR_PARTIAL is returned. The offsets are set to 3
and 9, identifying "123dog" as the first partial match that was found.	and 9, identifying "123dog" as the first partial match that was found.
(In this example, there are two partial matches, because "dog" on its	(In this example, there are two partial matches, because "dog" on its
own partially matches the second alternative.)	own partially matches the second alternative.)

PCRE_PARTIAL_HARD with pcre_exec()	PCRE_PARTIAL_HARD WITH pcre_exec() OR pcre[16\|32]_exec()

If PCRE_PARTIAL_HARD is set for pcre_exec(), it returns PCRE_ERROR_PAR-	If PCRE_PARTIAL_HARD is set for pcre_exec() or pcre[16\|32]_exec(),
TIAL as soon as a partial match is found, without continuing to search	PCRE_ERROR_PARTIAL is returned as soon as a partial match is found,
for possible complete matches. This option is "hard" because it prefers	without continuing to search for possible complete matches. This option
an earlier partial match over a later complete match. For this reason,	is "hard" because it prefers an earlier partial match over a later com-
the assumption is made that the end of the supplied subject string may	plete match. For this reason, the assumption is made that the end of
not be the true end of the available data, and so, if \z, \Z, \b, \B,	the supplied subject string may not be the true end of the available
or $ are encountered at the end of the subject, the result is	data, and so, if \z, \Z, \b, \B, or $ are encountered at the end of the
PCRE_ERROR_PARTIAL.	subject, the result is PCRE_ERROR_PARTIAL, provided that at least one
	character in the subject has been inspected.

Setting PCRE_PARTIAL_HARD also affects the way pcre_exec() checks UTF-8	Setting PCRE_PARTIAL_HARD also affects the way UTF-8 and UTF-16 subject
subject strings for validity. Normally, an invalid UTF-8 sequence	strings are checked for validity. Normally, an invalid sequence causes
causes the error PCRE_ERROR_BADUTF8. However, in the special case of a	the error PCRE_ERROR_BADUTF8 or PCRE_ERROR_BADUTF16. However, in the
truncated UTF-8 character at the end of the subject, PCRE_ERROR_SHORT-	special case of a truncated character at the end of the subject,
UTF8 is returned when PCRE_PARTIAL_HARD is set.	PCRE_ERROR_SHORTUTF8 or PCRE_ERROR_SHORTUTF16 is returned when
	PCRE_PARTIAL_HARD is set.

Comparing hard and soft partial matching	Comparing hard and soft partial matching

The difference between the two partial matching options can be illus-	The difference between the two partial matching options can be illus-
trated by a pattern such as:	trated by a pattern such as:

/dog(sbody)?/	/dog(sbody)?/

This matches either "dog" or "dogsbody", greedily (that is, it prefers	This matches either "dog" or "dogsbody", greedily (that is, it prefers
the longer string if possible). If it is matched against the string	the longer string if possible). If it is matched against the string
"dog" with PCRE_PARTIAL_SOFT, it yields a complete match for "dog".	"dog" with PCRE_PARTIAL_SOFT, it yields a complete match for "dog".
However, if PCRE_PARTIAL_HARD is set, the result is PCRE_ERROR_PARTIAL.	However, if PCRE_PARTIAL_HARD is set, the result is PCRE_ERROR_PARTIAL.
On the other hand, if the pattern is made ungreedy the result is dif-	On the other hand, if the pattern is made ungreedy the result is dif-
ferent:	ferent:

/dog(sbody)??/	/dog(sbody)??/

In this case the result is always a complete match because pcre_exec()	In this case the result is always a complete match because that is
finds that first, and it never continues after finding a match. It	found first, and matching never continues after finding a complete
might be easier to follow this explanation by thinking of the two pat-	match. It might be easier to follow this explanation by thinking of the
terns like this:	two patterns like this:

/dog(sbody)?/ is the same as /dogsbody\|dog/	/dog(sbody)?/ is the same as /dogsbody\|dog/
/dog(sbody)??/ is the same as /dog\|dogsbody/	/dog(sbody)??/ is the same as /dog\|dogsbody/

The second pattern will never match "dogsbody" when pcre_exec() is	The second pattern will never match "dogsbody", because it will always
used, because it will always find the shorter match first.	find the shorter match first.


PARTIAL MATCHING USING pcre_dfa_exec()	PARTIAL MATCHING USING pcre_dfa_exec() OR pcre[16\|32]_dfa_exec()

The pcre_dfa_exec() function moves along the subject string character	The DFA functions move along the subject string character by character,
by character, without backtracking, searching for all possible matches	without backtracking, searching for all possible matches simultane-
simultaneously. If the end of the subject is reached before the end of	ously. If the end of the subject is reached before the end of the pat-
the pattern, there is the possibility of a partial match, again pro-	tern, there is the possibility of a partial match, again provided that
vided that at least one character has been inspected.	at least one character has been inspected.

When PCRE_PARTIAL_SOFT is set, PCRE_ERROR_PARTIAL is returned only if	When PCRE_PARTIAL_SOFT is set, PCRE_ERROR_PARTIAL is returned only if
there have been no complete matches. Otherwise, the complete matches	there have been no complete matches. Otherwise, the complete matches
are returned. However, if PCRE_PARTIAL_HARD is set, a partial match	are returned. However, if PCRE_PARTIAL_HARD is set, a partial match
takes precedence over any complete matches. The portion of the string	takes precedence over any complete matches. The portion of the string
that was inspected when the longest partial match was found is set as	that was inspected when the longest partial match was found is set as
the first matching string, provided there are at least two slots in the	the first matching string, provided there are at least two slots in the
offsets vector.	offsets vector.

Because pcre_dfa_exec() always searches for all possible matches, and	Because the DFA functions always search for all possible matches, and
there is no difference between greedy and ungreedy repetition, its be-	there is no difference between greedy and ungreedy repetition, their
haviour is different from pcre_exec when PCRE_PARTIAL_HARD is set. Con-	behaviour is different from the standard functions when PCRE_PAR-
sider the string "dog" matched against the ungreedy pattern shown	TIAL_HARD is set. Consider the string "dog" matched against the
above:	ungreedy pattern shown above:

/dog(sbody)??/	/dog(sbody)??/

Whereas pcre_exec() stops as soon as it finds the complete match for	Whereas the standard functions stop as soon as they find the complete
"dog", pcre_dfa_exec() also finds the partial match for "dogsbody", and	match for "dog", the DFA functions also find the partial match for
so returns that when PCRE_PARTIAL_HARD is set.	"dogsbody", and so return that when PCRE_PARTIAL_HARD is set.


PARTIAL MATCHING AND WORD BOUNDARIES	PARTIAL MATCHING AND WORD BOUNDARIES

If a pattern ends with one of sequences \b or \B, which test for word	If a pattern ends with one of sequences \b or \B, which test for word
boundaries, partial matching with PCRE_PARTIAL_SOFT can give counter-	boundaries, partial matching with PCRE_PARTIAL_SOFT can give counter-
intuitive results. Consider this pattern:	intuitive results. Consider this pattern:

/\bcat\b/	/\bcat\b/

This matches "cat", provided there is a word boundary at either end. If	This matches "cat", provided there is a word boundary at either end. If
the subject string is "the cat", the comparison of the final "t" with a	the subject string is "the cat", the comparison of the final "t" with a
following character cannot take place, so a partial match is found.	following character cannot take place, so a partial match is found.
However, pcre_exec() carries on with normal matching, which matches \b	However, normal matching carries on, and \b matches at the end of the
at the end of the subject when the last character is a letter, thus	subject when the last character is a letter, so a complete match is
finding a complete match. The result, therefore, is not PCRE_ERROR_PAR-	found. The result, therefore, is not PCRE_ERROR_PARTIAL. Using
TIAL. The same thing happens with pcre_dfa_exec(), because it also	PCRE_PARTIAL_HARD in this case does yield PCRE_ERROR_PARTIAL, because
finds the complete match.	then the partial match takes precedence.

Using PCRE_PARTIAL_HARD in this case does yield PCRE_ERROR_PARTIAL,
because then the partial match takes precedence.


FORMERLY RESTRICTED PATTERNS	FORMERLY RESTRICTED PATTERNS

For releases of PCRE prior to 8.00, because of the way certain internal	For releases of PCRE prior to 8.00, because of the way certain internal
optimizations were implemented in the pcre_exec() function, the	optimizations were implemented in the pcre_exec() function, the
PCRE_PARTIAL option (predecessor of PCRE_PARTIAL_SOFT) could not be	PCRE_PARTIAL option (predecessor of PCRE_PARTIAL_SOFT) could not be
used with all patterns. From release 8.00 onwards, the restrictions no	used with all patterns. From release 8.00 onwards, the restrictions no
longer apply, and partial matching with pcre_exec() can be requested	longer apply, and partial matching with can be requested for any pat-
for any pattern.	tern.

Items that were formerly restricted were repeated single characters and	Items that were formerly restricted were repeated single characters and
repeated metasequences. If PCRE_PARTIAL was set for a pattern that did	repeated metasequences. If PCRE_PARTIAL was set for a pattern that did
Line 7080 EXAMPLE OF PARTIAL MATCHING USING PCRETEST	Line 8910 EXAMPLE OF PARTIAL MATCHING USING PCRETEST
The first data string is matched completely, so pcretest shows the	The first data string is matched completely, so pcretest shows the
matched substrings. The remaining four strings do not match the com-	matched substrings. The remaining four strings do not match the com-
plete pattern, but the first two are partial matches. Similar output is	plete pattern, but the first two are partial matches. Similar output is
obtained when pcre_dfa_exec() is used.	obtained if DFA matching is used.

If the escape sequence \P is present more than once in a pcretest data	If the escape sequence \P is present more than once in a pcretest data
line, the PCRE_PARTIAL_HARD option is set for the match.	line, the PCRE_PARTIAL_HARD option is set for the match.


MULTI-SEGMENT MATCHING WITH pcre_dfa_exec()	MULTI-SEGMENT MATCHING WITH pcre_dfa_exec() OR pcre[16\|32]_dfa_exec()

When a partial match has been found using pcre_dfa_exec(), it is possi-	When a partial match has been found using a DFA matching function, it
ble to continue the match by providing additional subject data and	is possible to continue the match by providing additional subject data
calling pcre_dfa_exec() again with the same compiled regular expres-	and calling the function again with the same compiled regular expres-
sion, this time setting the PCRE_DFA_RESTART option. You must pass the	sion, this time setting the PCRE_DFA_RESTART option. You must pass the
same working space as before, because this is where details of the pre-	same working space as before, because this is where details of the pre-
vious partial match are stored. Here is an example using pcretest,	vious partial match are stored. Here is an example using pcretest,
using the \R escape sequence to set the PCRE_DFA_RESTART option (\D	using the \R escape sequence to set the PCRE_DFA_RESTART option (\D
specifies the use of pcre_dfa_exec()):	specifies the use of the DFA matching function):

re> /^\d?\d(jan\|feb\|mar\|apr\|may\|jun\|jul\|aug\|sep\|oct\|nov\|dec)\d\d$/	re> /^\d?\d(jan\|feb\|mar\|apr\|may\|jun\|jul\|aug\|sep\|oct\|nov\|dec)\d\d$/
data> 23ja\P\D	data> 23ja\P\D
Line 7110 MULTI-SEGMENT MATCHING WITH pcre_dfa_exec()	Line 8940 MULTI-SEGMENT MATCHING WITH pcre_dfa_exec()
matched string. It is up to the calling program to do that if it needs	matched string. It is up to the calling program to do that if it needs
to.	to.

	That means that, for an unanchored pattern, if a continued match fails,
	it is not possible to try again at a new starting point. All this
	facility is capable of doing is continuing with the previous match
	attempt. In the previous example, if the second set of data is "ug23"
	the result is no match, even though there would be a match for "aug23"
	if the entire string were given at once. Depending on the application,
	this may or may not be what you want. The only way to allow for start-
	ing again at the next character is to retain the matched part of the
	subject and try a new complete match.

You can set the PCRE_PARTIAL_SOFT or PCRE_PARTIAL_HARD options with	You can set the PCRE_PARTIAL_SOFT or PCRE_PARTIAL_HARD options with
PCRE_DFA_RESTART to continue partial matching over multiple segments.	PCRE_DFA_RESTART to continue partial matching over multiple segments.
This facility can be used to pass very long subject strings to	This facility can be used to pass very long subject strings to the DFA
pcre_dfa_exec().	matching functions.


MULTI-SEGMENT MATCHING WITH pcre_exec()	MULTI-SEGMENT MATCHING WITH pcre_exec() OR pcre[16\|32]_exec()

From release 8.00, pcre_exec() can also be used to do multi-segment	From release 8.00, the standard matching functions can also be used to
matching. Unlike pcre_dfa_exec(), it is not possible to restart the	do multi-segment matching. Unlike the DFA functions, it is not possible
previous match with a new segment of data. Instead, new data must be	to restart the previous match with a new segment of data. Instead, new
added to the previous subject string, and the entire match re-run,	data must be added to the previous subject string, and the entire match
starting from the point where the partial match occurred. Earlier data	re-run, starting from the point where the partial match occurred. Ear-
can be discarded. It is best to use PCRE_PARTIAL_HARD in this situa-	lier data can be discarded.
tion, because it does not treat the end of a segment as the end of the
subject when matching \z, \Z, \b, \B, and $. Consider an unanchored
pattern that matches dates:

	It is best to use PCRE_PARTIAL_HARD in this situation, because it does
	not treat the end of a segment as the end of the subject when matching
	\z, \Z, \b, \B, and $. Consider an unanchored pattern that matches
	dates:

re> /\d?\d(jan\|feb\|mar\|apr\|may\|jun\|jul\|aug\|sep\|oct\|nov\|dec)\d\d/	re> /\d?\d(jan\|feb\|mar\|apr\|may\|jun\|jul\|aug\|sep\|oct\|nov\|dec)\d\d/
data> The date is 23ja\P\P	data> The date is 23ja\P\P
Partial match: 23ja	Partial match: 23ja

At this stage, an application could discard the text preceding "23ja",	At this stage, an application could discard the text preceding "23ja",
add on text from the next segment, and call pcre_exec() again. Unlike	add on text from the next segment, and call the matching function
pcre_dfa_exec(), the entire matching string must always be available,	again. Unlike the DFA matching functions, the entire matching string
and the complete matching process occurs for each call, so more memory	must always be available, and the complete matching process occurs for
and more processing time is needed.	each call, so more memory and more processing time is needed.

Note: If the pattern contains lookbehind assertions, or \K, or starts	Note: If the pattern contains lookbehind assertions, or \K, or starts
with \b or \B, the string that is returned for a partial match will	with \b or \B, the string that is returned for a partial match includes
include characters that precede the partially matched string itself,	characters that precede the start of what would be returned for a com-
because these must be retained when adding on more characters for a	plete match, because it contains all the characters that were inspected
subsequent matching attempt.	during the partial match.


ISSUES WITH MULTI-SEGMENT MATCHING	ISSUES WITH MULTI-SEGMENT MATCHING
Line 7156 ISSUES WITH MULTI-SEGMENT MATCHING	Line 8998 ISSUES WITH MULTI-SEGMENT MATCHING
option, but in practice when doing multi-segment matching you should be	option, but in practice when doing multi-segment matching you should be
using PCRE_PARTIAL_HARD, which includes the effect of PCRE_NOTEOL.	using PCRE_PARTIAL_HARD, which includes the effect of PCRE_NOTEOL.

2. Lookbehind assertions at the start of a pattern are catered for in	2. Lookbehind assertions that have already been obeyed are catered for
the offsets that are returned for a partial match. However, in theory,	in the offsets that are returned for a partial match. However a lookbe-
a lookbehind assertion later in the pattern could require even earlier	hind assertion later in the pattern could require even earlier charac-
characters to be inspected, and it might not have been reached when a	ters to be inspected. You can handle this case by using the
partial match occurs. This is probably an extremely unlikely case; you	PCRE_INFO_MAXLOOKBEHIND option of the pcre_fullinfo() or
could guard against it to a certain extent by always including extra	pcre[16\|32]_fullinfo() functions to obtain the length of the longest
characters at the start.	lookbehind in the pattern. This length is given in characters, not
	bytes. If you always retain at least that many characters before the
	partially matched string, all should be well. (Of course, near the
	start of the subject, fewer characters may be present; in that case all
	characters should be retained.)

3. Matching a subject string that is split into multiple segments may	From release 8.33, there is a more accurate way of deciding which char-
	acters to retain. Instead of subtracting the length of the longest
	lookbehind from the earliest inspected character (offsets[0]), the
	match start position (offsets[2]) should be used, and the next match
	attempt started at the offsets[2] character by setting the startoffset
	argument of pcre_exec() or pcre_dfa_exec().

	For example, if the pattern "(?<=123)abc" is partially matched against
	the string "xx123a", the three offset values returned are 2, 6, and 5.
	This indicates that the matching process that gave a partial match
	started at offset 5, but the characters "123a" were all inspected. The
	maximum lookbehind for that pattern is 3, so taking that away from 5
	shows that we need only keep "123a", and the next match attempt can be
	started at offset 3 (that is, at "a") when further characters have been
	added. When the match start is not the earliest inspected character,
	pcretest shows it explicitly:

	re> "(?<=123)abc"
	data> xx123a\P\P
	Partial match at offset 5: 123a

	3. Because a partial match must always contain at least one character,
	what might be considered a partial match of an empty string actually
	gives a "no match" result. For example:

	re> /c(?<=abc)x/
	data> ab\P
	No match

	If the next segment begins "cx", a match should be found, but this will
	only happen if characters from the previous segment are retained. For
	this reason, a "no match" result should be interpreted as "partial
	match of an empty string" when the pattern contains lookbehinds.

	4. Matching a subject string that is split into multiple segments may
not always produce exactly the same result as matching over one single	not always produce exactly the same result as matching over one single
long string, especially when PCRE_PARTIAL_SOFT is used. The section	long string, especially when PCRE_PARTIAL_SOFT is used. The section
"Partial Matching and Word Boundaries" above describes an issue that	"Partial Matching and Word Boundaries" above describes an issue that
Line 7186 ISSUES WITH MULTI-SEGMENT MATCHING	Line 9066 ISSUES WITH MULTI-SEGMENT MATCHING
0: dogsbody	0: dogsbody
1: dog	1: dog

The first data line passes the string "dogsb" to pcre_exec(), setting	The first data line passes the string "dogsb" to a standard matching
the PCRE_PARTIAL_SOFT option. Although the string is a partial match	function, setting the PCRE_PARTIAL_SOFT option. Although the string is
for "dogsbody", the result is not PCRE_ERROR_PARTIAL, because the	a partial match for "dogsbody", the result is not PCRE_ERROR_PARTIAL,
shorter string "dog" is a complete match. Similarly, when the subject	because the shorter string "dog" is a complete match. Similarly, when
is presented to pcre_dfa_exec() in several parts ("do" and "gsb" being	the subject is presented to a DFA matching function in several parts
the first two) the match stops when "dog" has been found, and it is not	("do" and "gsb" being the first two) the match stops when "dog" has
possible to continue. On the other hand, if "dogsbody" is presented as	been found, and it is not possible to continue. On the other hand, if
a single string, pcre_dfa_exec() finds both matches.	"dogsbody" is presented as a single string, a DFA matching function
	finds both matches.

Because of these problems, it is best to use PCRE_PARTIAL_HARD when	Because of these problems, it is best to use PCRE_PARTIAL_HARD when
matching multi-segment data. The example above then behaves differ-	matching multi-segment data. The example above then behaves differ-
ently:	ently:

re> /dog(sbody)?/	re> /dog(sbody)?/
Line 7207 ISSUES WITH MULTI-SEGMENT MATCHING	Line 9088 ISSUES WITH MULTI-SEGMENT MATCHING
data> gsb\R\P\P\D	data> gsb\R\P\P\D
Partial match: gsb	Partial match: gsb

4. Patterns that contain alternatives at the top level which do not all	5. Patterns that contain alternatives at the top level which do not all
start with the same pattern item may not work as expected when	start with the same pattern item may not work as expected when
PCRE_DFA_RESTART is used with pcre_dfa_exec(). For example, consider	PCRE_DFA_RESTART is used. For example, consider this pattern:
this pattern:

1234\|3789	1234\|3789

Line 7227 ISSUES WITH MULTI-SEGMENT MATCHING	Line 9107 ISSUES WITH MULTI-SEGMENT MATCHING
1234\|ABCD	1234\|ABCD

where no string can be a partial match for both alternatives. This is	where no string can be a partial match for both alternatives. This is
not a problem if pcre_exec() is used, because the entire match has to	not a problem if a standard matching function is used, because the
be rerun each time:	entire match has to be rerun each time:

re> /1234\|3789/	re> /1234\|3789/
data> ABC123\P\P	data> ABC123\P\P
Line 7237 ISSUES WITH MULTI-SEGMENT MATCHING	Line 9117 ISSUES WITH MULTI-SEGMENT MATCHING
0: 3789	0: 3789

Of course, instead of using PCRE_DFA_RESTART, the same technique of re-	Of course, instead of using PCRE_DFA_RESTART, the same technique of re-
running the entire match can also be used with pcre_dfa_exec(). Another	running the entire match can also be used with the DFA matching func-
possibility is to work with two buffers. If a partial match at offset n	tions. Another possibility is to work with two buffers. If a partial
in the first buffer is followed by "no match" when PCRE_DFA_RESTART is	match at offset n in the first buffer is followed by "no match" when
used on the second buffer, you can then try a new match starting at	PCRE_DFA_RESTART is used on the second buffer, you can then try a new
offset n+1 in the first buffer.	match starting at offset n+1 in the first buffer.


AUTHOR	AUTHOR
Line 7253 AUTHOR	Line 9133 AUTHOR

REVISION	REVISION

Last updated: 26 August 2011	Last updated: 02 July 2013
Copyright (c) 1997-2011 University of Cambridge.	Copyright (c) 1997-2013 University of Cambridge.
------------------------------------------------------------------------------	------------------------------------------------------------------------------


PCREPRECOMPILE(3) PCREPRECOMPILE(3)	PCREPRECOMPILE(3) Library Functions Manual PCREPRECOMPILE(3)



NAME	NAME
PCRE - Perl-compatible regular expressions	PCRE - Perl-compatible regular expressions


SAVING AND RE-USING PRECOMPILED PCRE PATTERNS	SAVING AND RE-USING PRECOMPILED PCRE PATTERNS

If you are running an application that uses a large number of regular	If you are running an application that uses a large number of regular
Line 7273 SAVING AND RE-USING PRECOMPILED PCRE PATTERNS	Line 9153 SAVING AND RE-USING PRECOMPILED PCRE PATTERNS
run. If you are not using any private character tables (see the	run. If you are not using any private character tables (see the
pcre_maketables() documentation), this is relatively straightforward.	pcre_maketables() documentation), this is relatively straightforward.
If you are using private tables, it is a little bit more complicated.	If you are using private tables, it is a little bit more complicated.
However, if you are using the just-in-time optimization feature of	However, if you are using the just-in-time optimization feature, it is
pcre_study(), it is not possible to save and reload the JIT data.	not possible to save and reload the JIT data.

If you save compiled patterns to a file, you can copy them to a differ-	If you save compiled patterns to a file, you can copy them to a differ-
ent host and run them there. This works even if the new host has the	ent host and run them there. If the two hosts have different endianness
opposite endianness to the one on which the patterns were compiled.	(byte order), you should run the pcre[16\|32]_pat-
There may be a small performance penalty, but it should be insignifi-	tern_to_host_byte_order() function on the new host before trying to
cant. However, compiling regular expressions with one version of PCRE	match the pattern. The matching functions return PCRE_ERROR_BADENDIAN-
for use with a different version is not guaranteed to work and may	NESS if they detect a pattern with the wrong endianness.
cause crashes, and saving and restoring a compiled pattern loses any
JIT optimization data.

	Compiling regular expressions with one version of PCRE for use with a
	different version is not guaranteed to work and may cause crashes, and
	saving and restoring a compiled pattern loses any JIT optimization
	data.


SAVING A COMPILED PATTERN	SAVING A COMPILED PATTERN

The value returned by pcre_compile() points to a single block of memory	The value returned by pcre[16\|32]_compile() points to a single block of
that holds the compiled pattern and associated data. You can find the	memory that holds the compiled pattern and associated data. You can
length of this block in bytes by calling pcre_fullinfo() with an argu-	find the length of this block in bytes by calling
ment of PCRE_INFO_SIZE. You can then save the data in any appropriate	pcre[16\|32]_fullinfo() with an argument of PCRE_INFO_SIZE. You can then
manner. Here is sample code that compiles a pattern and writes it to a	save the data in any appropriate manner. Here is sample code for the
file. It assumes that the variable fd refers to a file that is open for	8-bit library that compiles a pattern and writes it to a file. It
output:	assumes that the variable fd refers to a file that is open for output:

int erroroffset, rc, size;	int erroroffset, rc, size;
char *error;	char *error;
Line 7307 SAVING A COMPILED PATTERN	Line 9190 SAVING A COMPILED PATTERN
rc = fwrite(re, 1, size, fd);	rc = fwrite(re, 1, size, fd);
if (rc != size) { ... handle errors ... }	if (rc != size) { ... handle errors ... }

In this example, the bytes that comprise the compiled pattern are	In this example, the bytes that comprise the compiled pattern are
copied exactly. Note that this is binary data that may contain any of	copied exactly. Note that this is binary data that may contain any of
the 256 possible byte values. On systems that make a distinction	the 256 possible byte values. On systems that make a distinction
between binary and non-binary data, be sure that the file is opened for	between binary and non-binary data, be sure that the file is opened for
binary output.	binary output.

If you want to write more than one pattern to a file, you will have to	If you want to write more than one pattern to a file, you will have to
devise a way of separating them. For binary data, preceding each pat-	devise a way of separating them. For binary data, preceding each pat-
tern with its length is probably the most straightforward approach.	tern with its length is probably the most straightforward approach.
Another possibility is to write out the data in hexadecimal instead of	Another possibility is to write out the data in hexadecimal instead of
binary, one pattern to a line.	binary, one pattern to a line.

Saving compiled patterns in a file is only one possible way of storing	Saving compiled patterns in a file is only one possible way of storing
them for later use. They could equally well be saved in a database, or	them for later use. They could equally well be saved in a database, or
in the memory of some daemon process that passes them via sockets to	in the memory of some daemon process that passes them via sockets to
the processes that want them.	the processes that want them.

If the pattern has been studied, it is also possible to save the normal	If the pattern has been studied, it is also possible to save the normal
study data in a similar way to the compiled pattern itself. However, if	study data in a similar way to the compiled pattern itself. However, if
the PCRE_STUDY_JIT_COMPILE was used, the just-in-time data that is cre-	the PCRE_STUDY_JIT_COMPILE was used, the just-in-time data that is cre-
ated cannot be saved because it is too dependent on the current envi-	ated cannot be saved because it is too dependent on the current envi-
ronment. When studying generates additional information, pcre_study()	ronment. When studying generates additional information,
returns a pointer to a pcre_extra data block. Its format is defined in	pcre[16\|32]_study() returns a pointer to a pcre[16\|32]_extra data
the section on matching a pattern in the pcreapi documentation. The	block. Its format is defined in the section on matching a pattern in
study_data field points to the binary study data, and this is what you	the pcreapi documentation. The study_data field points to the binary
must save (not the pcre_extra block itself). The length of the study	study data, and this is what you must save (not the pcre[16\|32]_extra
data can be obtained by calling pcre_fullinfo() with an argument of	block itself). The length of the study data can be obtained by calling
PCRE_INFO_STUDYSIZE. Remember to check that pcre_study() did return a	pcre[16\|32]_fullinfo() with an argument of PCRE_INFO_STUDYSIZE. Remem-
non-NULL value before trying to save the study data.	ber to check that pcre[16\|32]_study() did return a non-NULL value
	before trying to save the study data.


RE-USING A PRECOMPILED PATTERN	RE-USING A PRECOMPILED PATTERN

Re-using a precompiled pattern is straightforward. Having reloaded it	Re-using a precompiled pattern is straightforward. Having reloaded it
into main memory, you pass its pointer to pcre_exec() or	into main memory, called pcre[16\|32]_pattern_to_host_byte_order() if
pcre_dfa_exec() in the usual way. This should work even on another	necessary, you pass its pointer to pcre[16\|32]_exec() or
host, and even if that host has the opposite endianness to the one	pcre[16\|32]_dfa_exec() in the usual way.
where the pattern was compiled.

However, if you passed a pointer to custom character tables when the	However, if you passed a pointer to custom character tables when the
pattern was compiled (the tableptr argument of pcre_compile()), you	pattern was compiled (the tableptr argument of pcre[16\|32]_compile()),
must now pass a similar pointer to pcre_exec() or pcre_dfa_exec(),	you must now pass a similar pointer to pcre[16\|32]_exec() or
because the value saved with the compiled pattern will obviously be	pcre[16\|32]_dfa_exec(), because the value saved with the compiled pat-
nonsense. A field in a pcre_extra() block is used to pass this data, as	tern will obviously be nonsense. A field in a pcre[16\|32]_extra() block
described in the section on matching a pattern in the pcreapi documen-	is used to pass this data, as described in the section on matching a
tation.	pattern in the pcreapi documentation.

If you did not provide custom character tables when the pattern was	Warning: The tables that pcre_exec() and pcre_dfa_exec() use must be
compiled, the pointer in the compiled pattern is NULL, which causes	the same as those that were used when the pattern was compiled. If this
pcre_exec() to use PCRE's internal tables. Thus, you do not need to	is not the case, the behaviour is undefined.
take any special action at run time in this case.

If you saved study data with the compiled pattern, you need to create	If you did not provide custom character tables when the pattern was
your own pcre_extra data block and set the study_data field to point to	compiled, the pointer in the compiled pattern is NULL, which causes the
the reloaded study data. You must also set the PCRE_EXTRA_STUDY_DATA	matching functions to use PCRE's internal tables. Thus, you do not need
bit in the flags field to indicate that study data is present. Then	to take any special action at run time in this case.
pass the pcre_extra block to pcre_exec() or pcre_dfa_exec() in the
usual way. If the pattern was studied for just-in-time optimization,
that data cannot be saved, and so is lost by a save/restore cycle.

	If you saved study data with the compiled pattern, you need to create
	your own pcre[16\|32]_extra data block and set the study_data field to
	point to the reloaded study data. You must also set the
	PCRE_EXTRA_STUDY_DATA bit in the flags field to indicate that study
	data is present. Then pass the pcre[16\|32]_extra block to the matching
	function in the usual way. If the pattern was studied for just-in-time
	optimization, that data cannot be saved, and so is lost by a
	save/restore cycle.


COMPATIBILITY WITH DIFFERENT PCRE RELEASES	COMPATIBILITY WITH DIFFERENT PCRE RELEASES

In general, it is safest to recompile all saved patterns when you	In general, it is safest to recompile all saved patterns when you
Line 7384 AUTHOR	Line 9272 AUTHOR

REVISION	REVISION

Last updated: 26 August 2011	Last updated: 12 November 2013
Copyright (c) 1997-2011 University of Cambridge.	Copyright (c) 1997-2013 University of Cambridge.
------------------------------------------------------------------------------	------------------------------------------------------------------------------


PCREPERFORM(3) PCREPERFORM(3)	PCREPERFORM(3) Library Functions Manual PCREPERFORM(3)



NAME	NAME
PCRE - Perl-compatible regular expressions	PCRE - Perl-compatible regular expressions


PCRE PERFORMANCE	PCRE PERFORMANCE

Two aspects of performance are discussed below: memory usage and pro-	Two aspects of performance are discussed below: memory usage and pro-
Line 7405 PCRE PERFORMANCE	Line 9293 PCRE PERFORMANCE

COMPILED PATTERN MEMORY USAGE	COMPILED PATTERN MEMORY USAGE

Patterns are compiled by PCRE into a reasonably efficient byte code, so	Patterns are compiled by PCRE into a reasonably efficient interpretive
that most simple patterns do not use much memory. However, there is one	code, so that most simple patterns do not use much memory. However,
case where the memory usage of a compiled pattern can be unexpectedly	there is one case where the memory usage of a compiled pattern can be
large. If a parenthesized subpattern has a quantifier with a minimum	unexpectedly large. If a parenthesized subpattern has a quantifier with
greater than 1 and/or a limited maximum, the whole subpattern is	a minimum greater than 1 and/or a limited maximum, the whole subpattern
repeated in the compiled code. For example, the pattern	is repeated in the compiled code. For example, the pattern

(abc\|def){2,4}	(abc\|def){2,4}

Line 7428 COMPILED PATTERN MEMORY USAGE	Line 9316 COMPILED PATTERN MEMORY USAGE

((ab){1,1000}c){1,3}	((ab){1,1000}c){1,3}

uses 51K bytes when compiled. When PCRE is compiled with its default	uses 51K bytes when compiled using the 8-bit library. When PCRE is com-
internal pointer size of two bytes, the size limit on a compiled pat-	piled with its default internal pointer size of two bytes, the size
tern is 64K, and this is reached with the above pattern if the outer	limit on a compiled pattern is 64K data units, and this is reached with
repetition is increased from 3 to 4. PCRE can be compiled to use larger	the above pattern if the outer repetition is increased from 3 to 4.
internal pointers and thus handle larger compiled patterns, but it is	PCRE can be compiled to use larger internal pointers and thus handle
better to try to rewrite your pattern to use less memory if you can.	larger compiled patterns, but it is better to try to rewrite your pat-
	tern to use less memory if you can.

One way of reducing the memory usage for such patterns is to make use	One way of reducing the memory usage for such patterns is to make use
of PCRE's "subroutine" facility. Re-writing the above pattern as	of PCRE's "subroutine" facility. Re-writing the above pattern as

((ab)(?2){0,999}c)(?1){0,2}	((ab)(?2){0,999}c)(?1){0,2}

reduces the memory requirements to 18K, and indeed it remains under 20K	reduces the memory requirements to 18K, and indeed it remains under 20K
even with the outer repetition increased to 100. However, this pattern	even with the outer repetition increased to 100. However, this pattern
is not exactly equivalent, because the "subroutine" calls are treated	is not exactly equivalent, because the "subroutine" calls are treated
as atomic groups into which there can be no backtracking if there is a	as atomic groups into which there can be no backtracking if there is a
subsequent matching failure. Therefore, PCRE cannot do this kind of	subsequent matching failure. Therefore, PCRE cannot do this kind of
rewriting automatically. Furthermore, there is a noticeable loss of	rewriting automatically. Furthermore, there is a noticeable loss of
speed when executing the modified pattern. Nevertheless, if the atomic	speed when executing the modified pattern. Nevertheless, if the atomic
grouping is not a problem and the loss of speed is acceptable, this	grouping is not a problem and the loss of speed is acceptable, this
kind of rewriting will allow you to process patterns that PCRE cannot	kind of rewriting will allow you to process patterns that PCRE cannot
otherwise handle.	otherwise handle.


STACK USAGE AT RUN TIME	STACK USAGE AT RUN TIME

When pcre_exec() is used for matching, certain kinds of pattern can	When pcre_exec() or pcre[16\|32]_exec() is used for matching, certain
cause it to use large amounts of the process stack. In some environ-	kinds of pattern can cause it to use large amounts of the process
ments the default process stack is quite small, and if it runs out the	stack. In some environments the default process stack is quite small,
result is often SIGSEGV. This issue is probably the most frequently	and if it runs out the result is often SIGSEGV. This issue is probably
raised problem with PCRE. Rewriting your pattern can often help. The	the most frequently raised problem with PCRE. Rewriting your pattern
pcrestack documentation discusses this issue in detail.	can often help. The pcrestack documentation discusses this issue in
	detail.


PROCESSING TIME	PROCESSING TIME
Line 7474 PROCESSING TIME	Line 9364 PROCESSING TIME
observations about PCRE.	observations about PCRE.

Using Unicode character properties (the \p, \P, and \X escapes) is	Using Unicode character properties (the \p, \P, and \X escapes) is
slow, because PCRE has to scan a structure that contains data for over	slow, because PCRE has to use a multi-stage table lookup whenever it
fifteen thousand characters whenever it needs a character's property.	needs a character's property. If you can find an alternative pattern
If you can find an alternative pattern that does not use character	that does not use character properties, it will probably be faster.
properties, it will probably be faster.

By default, the escape sequences \b, \d, \s, and \w, and the POSIX	By default, the escape sequences \b, \d, \s, and \w, and the POSIX
character classes such as [:alpha:] do not use Unicode properties,	character classes such as [:alpha:] do not use Unicode properties,
partly for backwards compatibility, and partly for performance reasons.	partly for backwards compatibility, and partly for performance reasons.
However, you can set PCRE_UCP if you want Unicode character properties	However, you can set PCRE_UCP if you want Unicode character properties
to be used. This can double the matching time for items such as \d,	to be used. This can double the matching time for items such as \d,
when matched with pcre_exec(); the performance loss is less with	when matched with a traditional matching function; the performance loss
pcre_dfa_exec(), and in both cases there is not much difference for \b.	is less with a DFA matching function, and in both cases there is not
	much difference for \b.

When a pattern begins with .* not in parentheses, or in parentheses	When a pattern begins with .* not in parentheses, or in parentheses
that are not the subject of a backreference, and the PCRE_DOTALL option	that are not the subject of a backreference, and the PCRE_DOTALL option
Line 7552 AUTHOR	Line 9442 AUTHOR

REVISION	REVISION

Last updated: 16 May 2010	Last updated: 25 August 2012
Copyright (c) 1997-2010 University of Cambridge.	Copyright (c) 1997-2012 University of Cambridge.
------------------------------------------------------------------------------	------------------------------------------------------------------------------


PCREPOSIX(3) PCREPOSIX(3)	PCREPOSIX(3) Library Functions Manual PCREPOSIX(3)



NAME	NAME
PCRE - Perl-compatible regular expressions.	PCRE - Perl-compatible regular expressions.

	SYNOPSIS

SYNOPSIS OF POSIX API

#include <pcreposix.h>	#include <pcreposix.h>

int regcomp(regex_t preg, const char pattern,	int regcomp(regex_t preg, const char pattern,
Line 7573 SYNOPSIS OF POSIX API	Line 9463 SYNOPSIS OF POSIX API

int regexec(regex_t preg, const char string,	int regexec(regex_t preg, const char string,
size_t nmatch, regmatch_t pmatch[], int eflags);	size_t nmatch, regmatch_t pmatch[], int eflags);
	size_t regerror(int errcode, const regex_t *preg,
size_t regerror(int errcode, const regex_t *preg,
char *errbuf, size_t errbuf_size);	char *errbuf, size_t errbuf_size);

void regfree(regex_t *preg);	void regfree(regex_t *preg);
Line 7582 SYNOPSIS OF POSIX API	Line 9471 SYNOPSIS OF POSIX API

DESCRIPTION	DESCRIPTION

This set of functions provides a POSIX-style API to the PCRE regular	This set of functions provides a POSIX-style API for the PCRE regular
expression package. See the pcreapi documentation for a description of	expression 8-bit library. See the pcreapi documentation for a descrip-
PCRE's native API, which contains much additional functionality.	tion of PCRE's native API, which contains much additional functional-
	ity. There is no POSIX-style wrapper for PCRE's 16-bit and 32-bit
	library.

The functions described here are just wrapper functions that ultimately	The functions described here are just wrapper functions that ultimately
call the PCRE native API. Their prototypes are defined in the	call the PCRE native API. Their prototypes are defined in the
Line 7815 AUTHOR	Line 9706 AUTHOR

REVISION	REVISION

Last updated: 16 May 2010	Last updated: 09 January 2012
Copyright (c) 1997-2010 University of Cambridge.	Copyright (c) 1997-2012 University of Cambridge.
------------------------------------------------------------------------------	------------------------------------------------------------------------------


PCRECPP(3) PCRECPP(3)	PCRECPP(3) Library Functions Manual PCRECPP(3)



NAME	NAME
PCRE - Perl-compatible regular expressions.	PCRE - Perl-compatible regular expressions.


SYNOPSIS OF C++ WRAPPER	SYNOPSIS OF C++ WRAPPER

#include <pcrecpp.h>	#include <pcrecpp.h>
Line 7837 DESCRIPTION	Line 9728 DESCRIPTION
The C++ wrapper for PCRE was provided by Google Inc. Some additional	The C++ wrapper for PCRE was provided by Google Inc. Some additional
functionality was added by Giuseppe Maxia. This brief man page was con-	functionality was added by Giuseppe Maxia. This brief man page was con-
structed from the notes in the pcrecpp.h file, which should be con-	structed from the notes in the pcrecpp.h file, which should be con-
sulted for further details.	sulted for further details. Note that the C++ wrapper supports only the
	original 8-bit PCRE library. There is no 16-bit or 32-bit support at
	present.


MATCHING INTERFACE	MATCHING INTERFACE
Line 7995 PASSING MODIFIERS TO THE REGULAR EXPRESSION ENGINE	Line 9888 PASSING MODIFIERS TO THE REGULAR EXPRESSION ENGINE
PCRE_DOTALL dot matches newlines /s	PCRE_DOTALL dot matches newlines /s
PCRE_DOLLAR_ENDONLY $ matches only at end N/A	PCRE_DOLLAR_ENDONLY $ matches only at end N/A
PCRE_EXTRA strict escape parsing N/A	PCRE_EXTRA strict escape parsing N/A
PCRE_EXTENDED ignore whitespaces /x	PCRE_EXTENDED ignore white spaces /x
PCRE_UTF8 handles UTF8 chars built-in	PCRE_UTF8 handles UTF8 chars built-in
PCRE_UNGREEDY reverses * and *? N/A	PCRE_UNGREEDY reverses * and *? N/A
PCRE_NO_AUTO_CAPTURE disables capturing parens N/A (*)	PCRE_NO_AUTO_CAPTURE disables capturing parens N/A (*)
Line 8157 AUTHOR	Line 10050 AUTHOR

REVISION	REVISION

Last updated: 17 March 2009	Last updated: 08 January 2012
Minor typo fixed: 25 July 2011
------------------------------------------------------------------------------	------------------------------------------------------------------------------


PCRESAMPLE(3) PCRESAMPLE(3)	PCRESAMPLE(3) Library Functions Manual PCRESAMPLE(3)



NAME	NAME
PCRE - Perl-compatible regular expressions	PCRE - Perl-compatible regular expressions


PCRE SAMPLE PROGRAM	PCRE SAMPLE PROGRAM

A simple, complete demonstration program, to get you started with using	A simple, complete demonstration program, to get you started with using
Line 8177 PCRE SAMPLE PROGRAM	Line 10069 PCRE SAMPLE PROGRAM
do not have a copy of the PCRE distribution, you can save this listing	do not have a copy of the PCRE distribution, you can save this listing
to re-create pcredemo.c.	to re-create pcredemo.c.

The program compiles the regular expression that is its first argument,	The demonstration program, which uses the original PCRE 8-bit library,
and matches it against the subject string in its second argument. No	compiles the regular expression that is its first argument, and matches
PCRE options are set, and default character tables are used. If match-	it against the subject string in its second argument. No PCRE options
ing succeeds, the program outputs the portion of the subject that	are set, and default character tables are used. If matching succeeds,
matched, together with the contents of any captured substrings.	the program outputs the portion of the subject that matched, together
	with the contents of any captured substrings.

If the -g option is given on the command line, the program then goes on	If the -g option is given on the command line, the program then goes on
to check for further matches of the same regular expression in the same	to check for further matches of the same regular expression in the same
subject string. The logic is a little bit tricky because of the possi-	subject string. The logic is a little bit tricky because of the possi-
bility of matching an empty string. Comments in the code explain what	bility of matching an empty string. Comments in the code explain what
is going on.	is going on.

If PCRE is installed in the standard include and library directories	If PCRE is installed in the standard include and library directories
for your operating system, you should be able to compile the demonstra-	for your operating system, you should be able to compile the demonstra-
tion program using this command:	tion program using this command:

gcc -o pcredemo pcredemo.c -lpcre	gcc -o pcredemo pcredemo.c -lpcre

If PCRE is installed elsewhere, you may need to add additional options	If PCRE is installed elsewhere, you may need to add additional options
to the command line. For example, on a Unix-like system that has PCRE	to the command line. For example, on a Unix-like system that has PCRE
installed in /usr/local, you can compile the demonstration program	installed in /usr/local, you can compile the demonstration program
using a command like this:	using a command like this:

gcc -o pcredemo -I/usr/local/include pcredemo.c \	gcc -o pcredemo -I/usr/local/include pcredemo.c \
-L/usr/local/lib -lpcre	-L/usr/local/lib -lpcre

In a Windows environment, if you want to statically link the program	In a Windows environment, if you want to statica In a Windows environment, if you want to statically link the program
against a non-dll pcre.a file, you must uncomment the line that defines	against a non-dll pcre.a file, you must uncomment the line that defines
PCRE_STATIC before including pcre.h, because otherwise the pcre_mal-	PCRE_STATIC before including pcre.h, because otherwise the pcre_mal-
loc() and pcre_free() exported functions will be declared	loc() and pcre_free() exported functions will be declared
__declspec(dllimport), with unwanted results.	__declspec(dllimport), with unwanted results.

Once you have compiled and linked the demonstration program, you can	Once you have compiled and linked the demonstration program, you can
run simple tests like this:	run simple tests like this:

./pcredemo 'cat\|dog' 'the cat sat on the mat'	./pcredemo 'cat\|dog' 'the cat sat on the mat'
./pcredemo -g 'cat\|dog' 'the dog sat on the cat'	./pcredemo -g 'cat\|dog' 'the dog sat on the cat'

Note that there is a much more comprehensive test program, called	Note that there is a much more comprehensive test program, called
pcretest, which supports many more facilities for testing regular	pcretest, which supports many more facilities for testing regular
expressions and the PCRE library. The pcredemo program is provided as a	expressions and both PCRE libraries. The pcredemo program is provided
simple coding example.	as a simple coding example.

If you try to run pcredemo when PCRE is not installed in the standard	If you try to run pcredemo when PCRE is not installed in the standard
library directory, you may get an error like this on some operating	library directory, you may get an error like this on some operating
systems (e.g. Solaris):	systems (e.g. Solaris):

ld.so.1: a.out: fatal: libpcre.so.0: open failed: No such file or	ld.so.1: a.out: fatal: libpcre.so.0: open failed: No such file or
directory	directory

This is caused by the way shared library support works on those sys-	This is caused by the way shared library support works on those sys-
tems. You need to add	tems. You need to add

-R/usr/local/lib	-R/usr/local/lib
Line 8244 AUTHOR	Line 10137 AUTHOR

REVISION	REVISION

Last updated: 17 November 2010	Last updated: 10 January 2012
Copyright (c) 1997-2010 University of Cambridge.	Copyright (c) 1997-2012 University of Cambridge.
------------------------------------------------------------------------------	------------------------------------------------------------------------------
PCRELIMITS(3) PCRELIMITS(3)	PCRELIMITS(3) Library Functions Manual PCRELIMITS(3)



NAME	NAME
PCRE - Perl-compatible regular expressions	PCRE - Perl-compatible regular expressions


SIZE AND OTHER LIMITATIONS	SIZE AND OTHER LIMITATIONS

There are some size limitations in PCRE but it is hoped that they will	There are some size limitations in PCRE but it is hoped that they will
never in practice be relevant.	never in practice be relevant.

The maximum length of a compiled pattern is 65539 (sic) bytes if PCRE	The maximum length of a compiled pattern is approximately 64K data
is compiled with the default internal linkage size of 2. If you want to	units (bytes for the 8-bit library, 16-bit units for the 16-bit
process regular expressions that are truly enormous, you can compile	library, and 32-bit units for the 32-bit library) if PCRE is compiled
PCRE with an internal linkage size of 3 or 4 (see the README file in	with the default internal linkage size, which is 2 bytes for the 8-bit
the source distribution and the pcrebuild documentation for details).	and 16-bit libraries, and 4 bytes for the 32-bit library. If you want
In these cases the limit is substantially larger. However, the speed	to process regular expressions that are truly enormous, you can compile
of execution is slower.	PCRE with an internal linkage size of 3 or 4 (when building the 16-bit
	or 32-bit library, 3 is rounded up to 4). See the README file in the
	source distribution and the pcrebuild documentation for details. In
	these cases the limit is substantially larger. However, the speed of
	execution is slower.

All values in repeating quantifiers must be less than 65536.	All values in repeating quantifiers must be less than 65536.

There is no limit to the number of parenthesized subpatterns, but there	There is no limit to the number of parenthesized subpatterns, but there
can be no more than 65535 capturing subpatterns.	can be no more than 65535 capturing subpatterns. There is, however, a
	limit to the depth of nesting of parenthesized subpatterns of all
	kinds. This is imposed in order to limit the amount of system stack
	used at compile time. The limit can be specified when PCRE is built;
	the default is 250.

There is a limit to the number of forward references to subsequent sub-	There is a limit to the number of forward references to subsequent sub-
patterns of around 200,000. Repeated forward references with fixed	patterns of around 200,000. Repeated forward references with fixed
Line 8281 SIZE AND OTHER LIMITATIONS	Line 10182 SIZE AND OTHER LIMITATIONS
The maximum length of name for a named subpattern is 32 characters, and	The maximum length of name for a named subpattern is 32 characters, and
the maximum number of named subpatterns is 10000.	the maximum number of named subpatterns is 10000.

	The maximum length of a name in a (MARK), (PRUNE), (*SKIP), or
	(*THEN) verb is 255 for the 8-bit library and 65535 for the 16-bit and
	32-bit libraries.

The maximum length of a subject string is the largest positive number	The maximum length of a subject string is the largest positive number
that an integer variable can hold. However, when using the traditional	that an integer variable can hold. However, when using the traditional
matching function, PCRE uses recursion to handle subpatterns and indef-	matching function, PCRE uses recursion to handle subpatterns and indef-
Line 8298 AUTHOR	Line 10203 AUTHOR

REVISION	REVISION

Last updated: 30 November 2011	Last updated: 05 November 2013
Copyright (c) 1997-2011 University of Cambridge.	Copyright (c) 1997-2013 University of Cambridge.
------------------------------------------------------------------------------	------------------------------------------------------------------------------


PCRESTACK(3) PCRESTACK(3)	PCRESTACK(3) Library Functions Manual PCRESTACK(3)



NAME	NAME
PCRE - Perl-compatible regular expressions	PCRE - Perl-compatible regular expressions


PCRE DISCUSSION OF STACK USAGE	PCRE DISCUSSION OF STACK USAGE

When you call pcre_exec(), it makes use of an internal function called	When you call pcre[16\|32]_exec(), it makes use of an internal function
match(). This calls itself recursively at branch points in the pattern,	called match(). This calls itself recursively at branch points in the
in order to remember the state of the match so that it can back up and	pattern, in order to remember the state of the match so that it can
try a different alternative if the first one fails. As matching pro-	back up and try a different alternative if the first one fails. As
ceeds deeper and deeper into the tree of possibilities, the recursion	matching proceeds deeper and deeper into the tree of possibilities, the
depth increases. The match() function is also called in other circum-	recursion depth increases. The match() function is also called in other
stances, for example, whenever a parenthesized sub-pattern is entered,	circumstances, for example, whenever a parenthesized sub-pattern is
and in certain cases of repetition.	entered, and in certain cases of repetition.

Not all calls of match() increase the recursion depth; for an item such	Not all calls of match() increase the recursion depth; for an item such
as a* it may be called several times at the same level, after matching	as a* it may be called several times at the same level, after matching
Line 8328 PCRE DISCUSSION OF STACK USAGE	Line 10233 PCRE DISCUSSION OF STACK USAGE
result of the current call (a "tail recursion"), the function is just	result of the current call (a "tail recursion"), the function is just
restarted instead.	restarted instead.

The above comments apply when pcre_exec() is run in its normal inter-	The above comments apply when pcre[16\|32]_exec() is run in its normal
pretive manner. If the pattern was studied with the PCRE_STUDY_JIT_COM-	interpretive manner. If the pattern was studied with the
PILE option, and just-in-time compiling was successful, and the options	PCRE_STUDY_JIT_COMPILE option, and just-in-time compiling was success-
passed to pcre_exec() were not incompatible, the matching process uses	ful, and the options passed to pcre[16\|32]_exec() were not incompati-
the JIT-compiled code instead of the match() function. In this case,	ble, the matching process uses the JIT-compiled code instead of the
the memory requirements are handled entirely differently. See the pcre-	match() function. In this case, the memory requirements are handled
jit documentation for details.	entirely differently. See the pcrejit documentation for details.

The pcre_dfa_exec() function operates in an entirely different way, and	The pcre[16\|32]_dfa_exec() function operates in an entirely different
uses recursion only when there is a regular expression recursion or	way, and uses recursion only when there is a regular expression recur-
subroutine call in the pattern. This includes the processing of asser-	sion or subroutine call in the pattern. This includes the processing of
tion and "once-only" subpatterns, which are handled like subroutine	assertion and "once-only" subpatterns, which are handled like subrou-
calls. Normally, these are never very deep, and the limit on the com-	tine calls. Normally, these are never very deep, and the limit on the
plexity of pcre_dfa_exec() is controlled by the amount of workspace it	complexity of pcre[16\|32]_dfa_exec() is controlled by the amount of
is given. However, it is possible to write patterns with runaway infi-	workspace it is given. However, it is possible to write patterns with
nite recursions; such patterns will cause pcre_dfa_exec() to run out of	runaway infinite recursions; such patterns will cause
stack. At present, there is no protection against this.	pcre[16\|32]_dfa_exec() to run out of stack. At present, there is no
	protection against this.

The comments that follow do NOT apply to pcre_dfa_exec(); they are rel-	The comments that follow do NOT apply to pcre[16\|32]_dfa_exec(); they
evant only for pcre_exec() without the JIT optimization.	are relevant only for pcre[16\|32]_exec() without the JIT optimization.

Reducing pcre_exec()'s stack usage	Reducing pcre[16\|32]_exec()'s stack usage

Each time that match() is actually called recursively, it uses memory	Each time that match() is actually called recursively, it uses memory
from the process stack. For certain kinds of pattern and data, very	from the process stack. For certain kinds of pattern and data, very
large amounts of stack may be needed, despite the recognition of "tail	large amounts of stack may be needed, despite the recognition of "tail
recursion". You can often reduce the amount of recursion, and there-	recursion". You can often reduce the amount of recursion, and there-
fore the amount of stack used, by modifying the pattern that is being	fore the amount of stack used, by modifying the pattern that is being
matched. Consider, for example, this pattern:	matched. Consider, for example, this pattern:

([^<]\|<(?!inet))+	([^<]\|<(?!inet))+

It matches from wherever it starts until it encounters "<inet" or the	It matches from wherever it starts until it encounters "<inet" or the
end of the data, and is the kind of pattern that might be used when	end of the data, and is the kind of pattern that might be used when
processing an XML file. Each iteration of the outer parentheses matches	processing an XML file. Each iteration of the outer parentheses matches
either one character that is not "<" or a "<" that is not followed by	either one character that is not "<" or a "<" that is not followed by
"inet". However, each time a parenthesis is processed, a recursion	"inet". However, each time a parenthesis is processed, a recursion
occurs, so this formulation uses a stack frame for each matched charac-	occurs, so this formulation uses a stack frame for each matched charac-
ter. For a long string, a lot of stack is required. Consider now this	ter. For a long string, a lot of stack is required. Consider now this
rewritten pattern, which matches exactly the same strings:	rewritten pattern, which matches exactly the same strings:

([^<]++\|<(?!inet))+	([^<]++\|<(?!inet))+

This uses very much less stack, because runs of characters that do not	This uses very much less stack, because runs of characters that do not
contain "<" are "swallowed" in one item inside the parentheses. Recur-	contain "<" are "swallowed" in one item inside the parentheses. Recur-
sion happens only when a "<" character that is not followed by "inet"	sion happens only when a "<" character that is not followed by "inet"
is encountered (and we assume this is relatively rare). A possessive	is encountered (and we assume this is relatively rare). A possessive
quantifier is used to stop any backtracking into the runs of non-"<"	quantifier is used to stop any backtracking into the runs of non-"<"
characters, but that is not related to stack usage.	characters, but that is not related to stack usage.

This example shows that one way of avoiding stack problems when match-	This example shows that one way of avoiding stack problems when match-
ing long subject strings is to write repeated parenthesized subpatterns	ing long subject strings is to write repeated parenthesized subpatterns
to match more than one character whenever possible.	to match more than one character whenever possible.

Compiling PCRE to use heap instead of stack for pcre_exec()	Compiling PCRE to use heap instead of stack for pcre[16\|32]_exec()

In environments where stack memory is constrained, you might want to	In environments where stack memory is constrained, you might want to
compile PCRE to use heap memory instead of stack for remembering back-	compile PCRE to use heap memory instead of stack for remembering back-
up points when pcre_exec() is running. This makes it run a lot more	up points when pcre[16\|32]_exec() is running. This makes it run a lot
slowly, however. Details of how to do this are given in the pcrebuild	more slowly, however. Details of how to do this are given in the pcre-
documentation. When built in this way, instead of using the stack, PCRE	build documentation. When built in this way, instead of using the
obtains and frees memory by calling the functions that are pointed to	stack, PCRE obtains and frees memory by calling the functions that are
by the pcre_stack_malloc and pcre_stack_free variables. By default,	pointed to by the pcre[16\|32]_stack_malloc and pcre[16\|32]_stack_free
these point to malloc() and free(), but you can replace the pointers to	variables. By default, these point to malloc() and free(), but you can
cause PCRE to use your own functions. Since the block sizes are always	replace the pointers to cause PCRE to use your own functions. Since the
the same, and are always freed in reverse order, it may be possible to	block sizes are always the same, and are always freed in reverse order,
implement customized memory handlers that are more efficient than the	it may be possible to implement customized memory handlers that are
standard functions.	more efficient than the standard functions.

Limiting pcre_exec()'s stack usage	Limiting pcre[16\|32]_exec()'s stack usage

You can set limits on the number of times that match() is called, both	You can set limits on the number of times that match() is called, both
in total and recursively. If a limit is exceeded, pcre_exec() returns	in total and recursively. If a limit is exceeded, pcre[16\|32]_exec()
an error code. Setting suitable limits should prevent it from running	returns an error code. Setting suitable limits should prevent it from
out of stack. The default values of the limits are very large, and	running out of stack. The default values of the limits are very large,
unlikely ever to operate. They can be changed when PCRE is built, and	and unlikely ever to operate. They can be changed when PCRE is built,
they can also be set when pcre_exec() is called. For details of these	and they can also be set when pcre[16\|32]_exec() is called. For details
interfaces, see the pcrebuild documentation and the section on extra	of these interfaces, see the pcrebuild documentation and the section on
data for pcre_exec() in the pcreapi documentation.	extra data for pcre[16\|32]_exec() in the pcreapi documentation.

As a very rough rule of thumb, you should reckon on about 500 bytes per	As a very rough rule of thumb, you should reckon on about 500 bytes per
recursion. Thus, if you want to limit your stack usage to 8Mb, you	recursion. Thus, if you want to limit your stack usage to 8Mb, you
should set the limit at 16000 recursions. A 64Mb stack, on the other	should set the limit at 16000 recursions. A 64Mb stack, on the other
hand, can support around 128000 recursions.	hand, can support around 128000 recursions.

In Unix-like environments, the pcretest test program has a command line	In Unix-like environments, the pcretest test program has a command line
option (-S) that can be used to increase the size of its stack. As long	option (-S) that can be used to increase the size of its stack. As long
as the stack is large enough, another option (-M) can be used to find	as the stack is large enough, another option (-M) can be used to find
the smallest limits that allow a particular pattern to match a given	the smallest limits that allow a particular pattern to match a given
subject string. This is done by calling pcre_exec() repeatedly with	subject string. This is done by calling pcre[16\|32]_exec() repeatedly
different limits.	with different limits.

	Obtaining an estimate of stack usage

	The actual amount of stack used per recursion can vary quite a lot,
	depending on the compiler that was used to build PCRE and the optimiza-
	tion or debugging options that were set for it. The rule of thumb value
	of 500 bytes mentioned above may be larger or smaller than what is
	actually needed. A better approximation can be obtained by running this
	command:

	pcretest -m -C

	The -C option causes pcretest to output information about the options
	with which PCRE was compiled. When -m is also given (before -C), infor-
	mation about stack use is given in a line like this:

	Match recursion uses stack: approximate frame size = 640 bytes

	The value is approximate because some recursions need a bit more (up to
	perhaps 16 more bytes).

	If the above command is given when PCRE is compiled to use the heap
	instead of the stack for recursion, the value that is output is the
	size of each block that is obtained from the heap.

Changing stack size in Unix-like systems	Changing stack size in Unix-like systems

In Unix-like environments, there is not often a problem with the stack	In Unix-like environments, there is not often a problem with the stack
unless very long strings are involved, though the default limit on	unless very long strings are involved, though the default limit on
stack size varies from system to system. Values from 8Mb to 64Mb are	stack size varies from system to system. Values from 8Mb to 64Mb are
common. You can find your default limit by running the command:	common. You can find your default limit by running the command:

ulimit -s	ulimit -s

Unfortunately, the effect of running out of stack is often SIGSEGV,	Unfortunately, the effect of running out of stack is often SIGSEGV,
though sometimes a more explicit error message is given. You can nor-	though sometimes a more explicit error message is given. You can nor-
mally increase the limit on stack size by code such as this:	mally increase the limit on stack size by code such as this:

struct rlimit rlim;	struct rlimit rlim;
Line 8438 PCRE DISCUSSION OF STACK USAGE	Line 10368 PCRE DISCUSSION OF STACK USAGE
rlim.rlim_cur = 10010241024;	rlim.rlim_cur = 10010241024;
setrlimit(RLIMIT_STACK, &rlim);	setrlimit(RLIMIT_STACK, &rlim);

This reads the current limits (soft and hard) using getrlimit(), then	This reads the current limits (soft and hard) using getrlimit(), then
attempts to increase the soft limit to 100Mb using setrlimit(). You	attempts to increase the soft limit to 100Mb using setrlimit(). You
must do this before calling pcre_exec().	must do this before calling pcre[16\|32]_exec().

Changing stack size in Mac OS X	Changing stack size in Mac OS X

Using setrlimit(), as described above, should also work on Mac OS X. It	Using setrlimit(), as described above, should also work on Mac OS X. It
is also possible to set a stack size when linking a program. There is a	is also possible to set a stack size when linking a program. There is a
discussion about stack sizes in Mac OS X at this web site:	discussion about stack sizes in Mac OS X at this web site:
http://developer.apple.com/qa/qa2005/qa1419.html.	http://developer.apple.com/qa/qa2005/qa1419.html.


Line 8459 AUTHOR	Line 10389 AUTHOR

REVISION	REVISION

Last updated: 26 August 2011	Last updated: 24 June 2012
Copyright (c) 1997-2011 University of Cambridge.	Copyright (c) 1997-2012 University of Cambridge.
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