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version 1.1.1.3, 2012/10/09 09:19:17	version 1.1.1.4, 2013/07/22 08:25:56
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 32 INTRODUCTION	Line 32 INTRODUCTION
either one or both to be built. The majority of the work to make this	either one or both to be built. The majority of the work to make this
possible was done by Zoltan Herczeg.	possible was done by Zoltan Herczeg.

The two libraries contain identical sets of functions, except that the	Starting with release 8.32 it is possible to compile a third separate
names in the 16-bit library start with pcre16_ instead of pcre_. To	PCRE library that supports 32-bit character strings (including UTF-32
avoid over-complication and reduce the documentation maintenance load,	strings). The build process allows any combination of the 8-, 16- and
most of the documentation describes the 8-bit library, with the differ-	32-bit libraries. The work to make this possible was done by Christian
ences for the 16-bit library described separately in the pcre16 page.	Persch.
References to functions or structures of the form pcre[16]_xxx should
be read as meaning "pcre_xxx when using the 8-bit library and
pcre16_xxx when using the 16-bit library".

	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-8/16 encoded strings and Unicode gen-	5.12, including support for UTF-8/16/32 encoded strings and Unicode
eral category properties. However, UTF-8/16 and Unicode support has to	general category properties. However, UTF-8/16/32 and Unicode support
be 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 6.2.0.

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 73 INTRODUCTION	Line 81 INTRODUCTION
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 libraries 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_" or "_pcre16_", which hopefully will	Their names all begin with "_pcre_" or "_pcre16_" or "_pcre32_", which
not provoke any name clashes. In some environments, it is possible to	hopefully will not provoke any name clashes. In some environments, it
control which external symbols are exported when a shared library is	is possible to control which external symbols are exported when a
built, and in 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-
Line 94 USER DOCUMENTATION	Line 135 USER DOCUMENTATION
lows:	lows:

pcre this document	pcre this document
pcre16 details of the 16-bit library
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 for the 8-bit library	pcrecpp details of the C++ wrapper for the 8-bit library
Line 116 USER DOCUMENTATION	Line 158 USER DOCUMENTATION
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-8/16 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 8-bit C library function, listing its arguments and results.	each C library function, listing its arguments and results.


AUTHOR	AUTHOR
Line 135 AUTHOR	Line 177 AUTHOR

REVISION	REVISION

Last updated: 10 January 2012	Last updated: 13 May 2013
Copyright (c) 1997-2012 University of Cambridge.	Copyright (c) 1997-2013 University of Cambridge.
------------------------------------------------------------------------------	------------------------------------------------------------------------------


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



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

Line 278 THE PCRE 16-BIT LIBRARY	Line 321 THE PCRE 16-BIT LIBRARY
THE HEADER FILE	THE HEADER FILE

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


THE LIBRARY NAME	THE LIBRARY NAME
Line 297 STRING TYPES	Line 340 STRING TYPES
PCRE_UCHAR16 specifies an appropriate data type, and PCRE_SPTR16 is	PCRE_UCHAR16 specifies an appropriate data type, and PCRE_SPTR16 is
defined as "const PCRE_UCHAR16 *". In very many environments, "short	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	int" is a 16-bit data type. When PCRE is built, it defines PCRE_UCHAR16
as "short int", but checks that it really is a 16-bit data type. If it	as "unsigned short int", but checks that it really is a 16-bit data
is not, the build fails with an error message telling the maintainer to	type. If it is not, the build fails with an error message telling the
modify the definition appropriately.	maintainer to modify the definition appropriately.


STRUCTURE TYPES	STRUCTURE TYPES
Line 350 STRUCTURE TYPES	Line 393 STRUCTURE TYPES

SUBJECT STRING OFFSETS	SUBJECT STRING OFFSETS

The offsets within subject strings that are returned by the matching	The lengths and starting offsets of subject strings must be specified
functions are in 16-bit units rather than bytes.	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	NAMED SUBPATTERNS
Line 372 OPTION NAMES	Line 417 OPTION NAMES

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


CHARACTER CODES	CHARACTER CODES

In 16-bit mode, when PCRE_UTF16 is not set, character values are	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,	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	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	types for characters less than 0xff can therefore be influenced by the
locale in the same way as before. Characters greater than 0xff have	locale in the same way as before. Characters greater than 0xff have
only one case, and no "type" (such as letter or digit).	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	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	0x10ffff, with the exception of values in the range 0xd800 to 0xdfff
because those are "surrogate" values that are used in pairs to encode	because those are "surrogate" values that are used in pairs to encode
values greater than 0xffff.	values greater than 0xffff.

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


ERROR NAMES	ERROR NAMES

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

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

PCRE_UTF16_ERR1 Missing low surrogate at end of string	PCRE_UTF16_ERR1 Missing low surrogate at end of string
PCRE_UTF16_ERR2 Invalid low surrogate follows high surrogate	PCRE_UTF16_ERR2 Invalid low surrogate follows high surrogate
PCRE_UTF16_ERR3 Isolated low surrogate	PCRE_UTF16_ERR3 Isolated low surrogate
PCRE_UTF16_ERR4 Invalid character 0xfffe	PCRE_UTF16_ERR4 Non-character


ERROR TEXTS	ERROR TEXTS

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


CALLOUTS	CALLOUTS

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


TESTING	TESTING

The pcretest program continues to operate with 8-bit input and output	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	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-	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	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	library functions are used instead of the 8-bit ones. Returned 16-bit
strings are converted to 8-bit for output. If the 8-bit library was not	strings are converted to 8-bit for output. If both the 8-bit and the
compiled, pcretest defaults to 16-bit and the -16 option is ignored.	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	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 and	check" uses the pcretest -C option to discover which of the 8-bit,
16-bit libraries has been built, and runs the tests appropriately.	16-bit and 32-bit libraries has been built, and runs the tests appro-
	priately.


NOT SUPPORTED IN 16-BIT MODE	NOT SUPPORTED IN 16-BIT MODE

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


Line 461 AUTHOR	Line 509 AUTHOR

REVISION	REVISION

Last updated: 14 April 2012	Last updated: 12 May 2013
Copyright (c) 1997-2012 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 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 char *errptr, int erroffset,
	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 and 16-BIT LIBRARIES	BUILDING 8-BIT, 16-BIT AND 32-BIT LIBRARIES

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

--enable-pcre16	--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	to the configure command. If you do not want the 8-bit library, add

--disable-pcre8	--disable-pcre8

as well. At least one of the two libraries must be built. Note that the	as well. At least one of the three libraries must be built. Note that
C++ and POSIX wrappers are for the 8-bit library only, and that pcre-	the C++ and POSIX wrappers are for the 8-bit library only, and that
grep is an 8-bit program. None of these are built if you select only	pcregrep is an 8-bit program. None of these are built if you select
the 16-bit library.	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 547 C++ SUPPORT	Line 945 C++ SUPPORT
to the configure command.	to the configure command.


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

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

--enable-utf	--enable-utf

to the configure command. This setting applies to both libraries,	to the configure command. This setting applies to all three libraries,
adding support for UTF-8 to the 8-bit library and support for UTF-16 to	adding support for UTF-8 to the 8-bit library, support for UTF-16 to
the 16-bit library. There are no separate options for enabling UTF-8	the 16-bit library, and support for UTF-32 to the to the 32-bit
and UTF-16 independently because that would allow ridiculous settings	library. There are no separate options for enabling UTF-8, UTF-16 and
such as requesting UTF-16 support while building only the 8-bit	UTF-32 independently because that would allow ridiculous settings such
library. It is not possible to build one library with UTF support and	as requesting UTF-16 support while building only the 8-bit library. It
the other without in the same configuration. (For backwards compatibil-	is not possible to build one library with UTF support and another with-
ity, --enable-utf8 is a synonym of --enable-utf.)	out in the same configuration. (For backwards compatibility, --enable-
	utf8 is a synonym of --enable-utf.)

Of itself, this setting does not make PCRE treat strings as UTF-8 or	Of itself, this setting does not make PCRE treat strings as UTF-8,
UTF-16. As well as compiling PCRE with this option, you also have have	UTF-16 or UTF-32. As well as compiling PCRE with this option, you also
to set the PCRE_UTF8 or PCRE_UTF16 option when you call one of the pat-	have have to set the PCRE_UTF8, PCRE_UTF16 or PCRE_UTF32 option (as
tern compiling functions.	appropriate) when you call one of the pattern compiling functions.

If you set --enable-utf when compiling in an EBCDIC environment, PCRE	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-	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	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	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 support allows the libraries to process character codepoints up to	UTF support allows the libraries to process character codepoints up to
0x10ffff in the strings that they handle. On its own, however, it does	0x10ffff in the strings that they handle. On its own, however, it does
not provide any facilities for accessing the properties of such charac-	not provide any facilities for accessing the properties of such charac-
ters. If you want to be able to use the pattern escapes \P, \p, and \X,	ters. If you want to be able to use the pattern escapes \P, \p, and \X,
which 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 support, even if you have	to the configu to the configure command. This implies UTF support, even if you have
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 598 JUST-IN-TIME COMPILER SUPPORT	Line 997 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 611 JUST-IN-TIME COMPILER SUPPORT	Line 1010 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 630 CODE VALUE OF NEWLINE	Line 1029 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 the 8-bit library is called through the POSIX interface (see the	When the 8-bit library is called through the POSIX interface (see the
pcreposix documentation), additional working storage is required for	pcreposix documentation), additional working storage is required for
holding the pointers to capturing substrings, because PCRE requires	holding the pointers to capturing substrings, because PCRE requires
three integers per substring, whereas the POSIX interface provides only	three integers per substring, whereas the POSIX interface provides only
two. If the number of expected substrings is small, the wrapper func-	two. If the number of expected substrings is small, the wrapper func-
tion uses space on the stack, because this is faster than using mal-	tion uses space on the stack, because this is faster than using mal-
loc() for each call. The default threshold above which the stack is no	loc() for each call. The default threshold above which the stack is no
longer used is 10; it 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 673 POSIX MALLOC USAGE	Line 1072 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 truly 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. For the	to the configure command. The value given must be 2, 3, or 4. For the
16-bit library, a value of 3 is rounded up to 4. Using longer offsets	16-bit library, a value of 3 is rounded up to 4. In these libraries,
slows down the operation of PCRE because it has to load additional data	using longer offsets slows down the operation of PCRE because it has to
when handling them.	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

When matching with the pcre_exec() function, PCRE implements backtrack-	When matching with the pcre_exec() function, PCRE implements backtrack-
ing by making recursive calls to an internal function called match().	ing by making recursive calls to an internal function called match().
In environments where the size of the stack is limited, this can se-	In environments where the size of the stack is limited, this can se-
verely limit PCRE's operation. (The Unix environment does not usually	verely limit PCRE's operation. (The Unix environment does not usually
suffer from this problem, but it may sometimes be necessary to increase	suffer from this problem, but it may sometimes be necessary to increase
the maximum stack size. There is a discussion in the pcrestack docu-	the maximum stack size. There is a discussion in the pcrestack docu-
mentation.) An alternative approach to recursion that uses memory from	mentation.) An alternative approach to recursion that uses memory from
the heap to remember data, instead of using recursive function calls,	the heap to remember data, instead of using recursive function calls,
has been implemented to work round the problem of limited stack size.	has been implemented to work round the problem of limited stack size.
If you want to build a version of PCRE that works this way, add	If you want to build a version of PCRE that works this way, add

--disable-stack-for-recursion	--disable-stack-for-recursion

to the configure command. With this configuration, PCRE will use the	to the configure command. With this configuration, PCRE will use the
pcre_stack_malloc and pcre_stack_free variables to call memory manage-	pcre_stack_malloc and pcre_stack_free variables to call memory manage-
ment functions. By default these point to malloc() and free(), but you	ment functions. By default these point to malloc() and free(), but you
can replace the pointers so that your own functions are used instead.	can replace the pointers so that your own functions are used instead.

Separate functions are provided rather than using pcre_malloc and	Separate functions are provided rather than using pcre_malloc and
pcre_free because the usage is very predictable: the block sizes	pcre_free because the usage is very predictable: the block sizes
requested are always the same, and the blocks are always freed in	requested are always the same, and the blocks are always freed in
reverse order. A calling program might be able to implement optimized	reverse order. A calling program might be able to implement optimized
functions that perform better than malloc() and free(). PCRE runs	functions that perform better than malloc() and free(). PCRE runs
noticeably more slowly when built in this way. This option affects only	noticeably more slowly when built in this way. This option affects only
the pcre_exec() function; it is not relevant for pcre_dfa_exec().	the pcre_exec() function; it is not relevant for pcre_dfa_exec().


LIMITING PCRE RESOURCE USAGE	LIMITING PCRE RESOURCE USAGE

Internally, PCRE has a function called match(), which it calls repeat-	Internally, PCRE has a function called match(), which it calls repeat-
edly (sometimes recursively) when matching a pattern with the	edly (sometimes recursively) when matching a pattern with the
pcre_exec() function. By controlling the maximum number of times this	pcre_exec() function. By controlling the maximum number of times this
function may be called during a single matching operation, a limit can	function may be called during a single matching operation, a limit can
be placed on the resources used by a single call to pcre_exec(). The	be placed on the resources used by a single call to pcre_exec(). The
limit can be changed at run time, as described in the pcreapi documen-	limit can be changed at run time, as described in the pcreapi documen-
tation. The default is 10 million, but this can be changed by adding a	tation. The default is 10 million, but this can be changed by adding a
setting such as	setting such as

--with-match-limit=500000	--with-match-limit=500000

to the configure command. This setting has no effect on the	to the configure command. This setting has no effect on the
pcre_dfa_exec() matching function.	pcre_dfa_exec() matching function.

In some environments it is desirable to limit the depth of recursive	In some environments it is desirable to limit In some environments it is desirable to limit the depth of recursive
calls of match() more strictly than the total number of calls, in order	calls of match() more strictly than the total number of calls, in order
to restrict the maximum amount of stack (or heap, if --disable-stack-	to restrict the maximum amount of stack (or heap, if --disable-stack-
for-recursion is specified) that is used. A second limit controls this;	for-recursion is specified) that is used. A second limit controls this;
it defaults to the value that is set for --with-match-limit, which	it defaults to the value that is set for --with-match-limit, which
imposes no additional constraints. However, you can set a lower limit	imposes no additional constraints. However, you can set a lower limit
by adding, for example,	by adding, for example,

--with-match-limit-recursion=10000	--with-match-limit-recursion=10000

to the configure command. This value can also be overridden at run	to the configure command. This valu to the configure command. This valu
time.	time.


CREATING CHARACTER TABLES AT BUILD TIME	CREATING CHARACTER TABLES AT BUILD TIME

PCRE uses fixed tables for processing characters whose code values are	PCRE uses fixed tables for processing characters whose code values are
less than 256. By default, PCRE is built with a set of tables that are	less than 256. By default, PCRE is built with a set of tables that are
distributed in the file pcre_chartables.c.dist. These tables are for	distributed in the file pcre_chartables.c.dist. These tables are for
ASCII codes only. If you add	ASCII codes only. If you add

--enable-rebuild-chartables	--enable-rebuild-chartables

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 run-time system. (This method of replacing the tables does not work	C run-time system. (This method of replacing the tables does not work
if you are cross compiling, because dftables is run on the local host.	if you are cross compiling, because dftables is run on the local host.
If 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".)


USING EBCDIC CODE	USING EBCDIC CODE

PCRE assumes by default that it will run in an environment where the	PCRE assumes by default that it will run in an environment where the
character code is ASCII (or Unicode, which is a superset of ASCII).	character code is ASCII (or Unicode, which is a superset of ASCII).
This is the case for most computer operating systems. PCRE can, how-	This is the case for most computer operating systems. PCRE can, how-
ever, be compiled to run in an EBCDIC environment by adding	ever, be compiled to run in an EBCDIC environment by adding

--enable-ebcdic	--enable-ebcdic

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-utf.	--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 843 PCRETEST OPTION FOR LIBREADLINE SUPPORT	Line 1259 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), pcre16, pcre_config(3).	pcreapi(3), pcre16, pcre32, pcre_config(3).


AUTHOR	AUTHOR
Line 857 AUTHOR	Line 1341 AUTHOR

REVISION	REVISION

Last updated: 07 January 2012	Last updated: 12 May 2013
Copyright (c) 1997-2012 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() and pcre16_exec() functions. These work in the same was as	pcre_exec(), pcre16_exec() and pcre32_exec() functions. These work in
Perl's matching function, and provide a Perl-compatible matching opera-	the same as as Perl's matching function, and provide a Perl-compatible
tion. The just-in-time (JIT) optimization that is described in the	matching operation. The just-in-time (JIT) optimization that is
pcrejit documentation is compatible with these functions.	described in the pcrejit documentation is compatible with these func-
	tions.

An alternative algorithm is provided by the pcre_dfa_exec() and	An alternative algorithm is provided by the pcre_dfa_exec(),
pcre16_dfa_exec() functions; they operate in a different way, and are	pcre16_dfa_exec() and pcre32_dfa_exec() functions; they operate in a
not Perl-compatible. This alternative has advantages and disadvantages	different way, and are not Perl-compatible. This alternative has advan-
compared with the standard algorithm, and 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 1011 THE ALTERNATIVE MATCHING ALGORITHM	Line 1497 THE ALTERNATIVE MATCHING ALGORITHM
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) always	7. The \C escape sequence, which (in the standard algorithm) always
matches a single data unit, even in UTF-8 or UTF-16 modes, is not sup-	matches a single data unit, even in UTF-8, UTF-16 or UTF-32 modes, is
ported in these modes, because the alternative algorithm moves through	not supported in these modes, because the alternative algorithm moves
the subject string one character (not data unit) at a time, for all	through the subject string one character (not data unit) at a time, for
active paths through the tree.	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 1069 REVISION	Line 1555 REVISION
------------------------------------------------------------------------------	------------------------------------------------------------------------------


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



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

Line 1140 PCRE NATIVE API STRING EXTRACTION FUNCTIONS	Line 1627 PCRE NATIVE API STRING EXTRACTION FUNCTIONS

PCRE NATIVE API AUXILIARY FUNCTIONS	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);	pcre_jit_stack *pcre_jit_stack_alloc(int startsize, int maxsize);

void pcre_jit_stack_free(pcre_jit_stack *stack);	void pcre_jit_stack_free(pcre_jit_stack *stack);
Line 1175 PCRE NATIVE API INDIRECTED FUNCTIONS	Line 1667 PCRE NATIVE API INDIRECTED FUNCTIONS
int (pcre_callout)(pcre_callout_block );	int (pcre_callout)(pcre_callout_block );


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

From release 8.30, PCRE can be compiled as a library for handling	As well as support for 8-bit character strings, PCRE also supports
16-bit character strings as well as, or instead of, the original	16-bit strings (from release 8.30) and 32-bit strings (from release
library that handles 8-bit character strings. To avoid too much compli-	8.32), by means of two additional libraries. They can be built as well
cation, this document describes the 8-bit versions of the functions,	as, or instead of, the 8-bit library. To avoid too much complication,
with only occasional references to the 16-bit library.	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 functions operate in the same way as their 8-bit counter-	The 16-bit and 32-bit functions operate in the same way as their 8-bit
parts; they just use different data types for their arguments and	counterparts; they just use different data types for their arguments
results, and their names start with pcre16_ instead of pcre_. For every	and results, and their names start with pcre16_ or pcre32_ instead of
option that has UTF8 in its name (for example, PCRE_UTF8), there is a	pcre_. For every option that has UTF8 in its name (for example,
corresponding 16-bit name with UTF8 replaced by UTF16. This facility is	PCRE_UTF8), there are corresponding 16-bit and 32-bit names with UTF8
in fact just cosmetic; the 16-bit option names define the same bit val-	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.	ues.

References to bytes and UTF-8 in this document should be read as refer-	References to bytes and UTF-8 in this document should be read as refer-
ences to 16-bit data quantities and UTF-16 when using the 16-bit	ences to 16-bit data units and UTF-16 when using the 16-bit library, or
library, unless specified otherwise. More details of the specific dif-	32-bit data units and UTF-32 when using the 32-bit library, unless
ferences for the 16-bit library are given in the pcre16 page.	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 (for the 8-bit library only) that cor-	are also some wrapper functions (for the 8-bit library only) that cor-
respond to the POSIX regular expression API, but they do not give	respond to the POSIX regular expression API, but they do not give
access to all the functionality. They are described in the pcreposix	access to all the functionality. They are described in the pcreposix
documentation. Both of these APIs define a set of C function calls. A	documentation. Both of these APIs define a set of C function calls. A
C++ wrapper (again for the 8-bit library only) is also distributed with	C++ wrapper (again for the 8-bit library only) is also distributed with
PCRE. It is documented in the pcrecpp page.	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-like systems the (8-bit) library itself is called	pcre.h, and on Unix-like systems the (8-bit) library itself is called
libpcre. It can normally be accessed by adding -lpcre to the command	libpcre. It can normally be accessed by adding -lpcre to the command
for linking an application that uses PCRE. The header file defines the	for linking an application that uses PCRE. The header file defines the
macros PCRE_MAJOR and PCRE_MINOR to contain the major and minor release	macros PCRE_MAJOR and PCRE_MINOR to contain the major and minor release
numbers 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 1384 CHECKING BUILD-TIME OPTIONS	Line 1882 CHECKING BUILD-TIME OPTIONS
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. If this option is given to the	able; otherwise it is set to zero. This value should normally be given
16-bit version of this function, pcre16_config(), the result is	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_ERROR_BADOPTION.

PCRE_CONFIG_UTF16	PCRE_CONFIG_UTF16

The output is an integer that is set to one if UTF-16 support is avail-	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	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 16-bit version of this function, pcre16_config(). If it is given
to the 8-bit version of this function, the result is PCRE_ERROR_BADOP-	to the 8-bit or 32-bit version of this function, the result is to the 8-bit or 32-bit version of this function, the result is
TION.	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
character properties is available; otherwise it is set to zero.	character properties is available; otherwise it is set to zero.

PCRE_CONFIG_JIT	PCRE_CONFIG_JIT
Line 1408 CHECKING BUILD-TIME OPTIONS	Line 1915 CHECKING BUILD-TIME OPTIONS

PCRE_CONFIG_JITTARGET	PCRE_CONFIG_JITTARGET

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

The output is an integer whose value indicates what character sequences	The output is an integer whose value indicates what character sequences
the \R escape sequence matches by default. A value of 0 means that \R	the \R escape sequence matches by default. A value of 0 means that \R
matches any Unicode line ending sequence; a value of 1 means that \R	matches any Unicode line ending sequence; a value of 1 means that \R
matches only CR, LF, or CRLF. The default can be overridden when a pat-	matches only CR, LF, or CRLF. The default can be overridden when a pat-
tern is compiled or matched.	tern is compiled or matched.

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

PCRE_CONFIG_POSIX_MALLOC_THRESHOLD	PCRE_CONFIG_POSIX_MALLOC_THRESHOLD

Line 1520 COMPILING A PATTERN	Line 2030 COMPILING A PATTERN
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
	failing character.

Some errors are not detected until the whole pattern has been scanned;	Some errors are not detected until the whole pattern has been scanned;
in these cases, the offset passed back is the length of the pattern.	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.	Note that the offset is in data units, not characters, even in a UTF
It may sometimes point into the middle of a UTF-8 character.	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
Line 1698 COMPILING A PATTERN	Line 2210 COMPILING A PATTERN

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
newlines in the subject string, respectively, as well as at the very	newlines in the subject string, respectively, as well as at the very
start and end. This is equivalent to Perl's /m option, and it can be	start and end. This is equivalent to Perl's /m option, and it can be
changed within a pattern by a (?m) option setting. If there are no new-	changed within a pattern by a (?m) option setting. If there are no new-
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
Line 1726 COMPILING A PATTERN	Line 2250 COMPILING A PATTERN
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 (form feed,
U+000C), NEL (next line, U+0085), LS (line separator, U+2028), and PS
(paragraph separator, U+2029). For the 8-bit library, the last two are
recognized only in UTF-8 mode.

The newline setting in the options word uses three bits that are	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
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
more than one newline option, the combination may or may not be sensi-	more than one newline option, the combination may or may not be sensi-
ble. For example, PCRE_NEWLINE_CR with PCRE_NEWLINE_LF is equivalent to	ble. For example, PCRE_NEWLINE_CR with PCRE_NEWLINE_LF is equivalent to
PCRE_NEWLINE_CRLF, but other combinations may yield unused numbers and	PCRE_NEWLINE_CRLF, but other combinations may yield unused numbers and
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 white space	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
in patterns are treated as literal data.	in patterns are treated as literal data.

The newline option that is set at compile time becomes the default that	The newline option that is set at compile time becomes the default that
Line 1753 COMPILING A PATTERN	Line 2286 COMPILING A PATTERN
PCRE_NO_AUTO_CAPTURE	PCRE_NO_AUTO_CAPTURE

If this option is set, it disables the use of numbered capturing paren-	If this option is set, it disables the use of numbered capturing paren-
theses in the pattern. Any opening parenthesis that is not followed by	theses in the pattern. Any opening parenthesis that is not followed by
? behaves as if it were followed by ?: but named parentheses can still	? behaves as if it were followed by ?: but named parentheses can still
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_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

Line 1803 COMPILING A PATTERN	Line 2337 COMPILING A PATTERN
effect of passing an invalid UTF-8 string as a pattern is undefined. It	effect of passing an invalid UTF-8 string as a pattern is undefined. It
may cause your program to crash. Note that this option can also be	may cause your program to crash. Note that this option can also be
passed to pcre_exec() and pcre_dfa_exec(), to suppress the validity	passed to pcre_exec() and pcre_dfa_exec(), to suppress the 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
Line 1811 COMPILATION ERROR CODES	Line 2347 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. Note that error messages are always 8-bit	both compiling functions. Note that error messages are always 8-bit
ASCII strings, even in 16-bit mode. As PCRE has developed, some error	ASCII strings, even in 16-bit or 32-bit mode. As PCRE has developed,
codes have fallen out of use. To avoid confusion, they have not been	some error codes have fallen out of use. To avoid confusion, they have
re-used.	not been re-used.

0 no error	0 no error
1 \ at end of pattern	1 \ at end of pattern
Line 1877 COMPILATION ERROR CODES	Line 2413 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 1896 COMPILATION ERROR CODES	Line 2432 COMPILATION ERROR CODES
74 invalid UTF-16 string (specifically UTF-16)	74 invalid UTF-16 string (specifically UTF-16)
75 name is too long in (MARK), (PRUNE), (SKIP), or (THEN)	75 name is too long in (MARK), (PRUNE), (SKIP), or (THEN)
76 character value in \u.... sequence is too large	76 character value in \u.... sequence is too large
	77 invalid UTF-32 string (specifically UTF-32)

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 1920 STUDYING A PATTERN	Line 2457 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 are	The second argument of pcre_study() contains option bits. There are
three options:	three further options in addition to PCRE_STUDY_EXTRA_NEEDED:

PCRE_STUDY_JIT_COMPILE	PCRE_STUDY_JIT_COMPILE
PCRE_STUDY_JIT_PARTIAL_HARD_COMPILE	PCRE_STUDY_JIT_PARTIAL_HARD_COMPILE
Line 1935 STUDYING A PATTERN	Line 2476 STUDYING A PATTERN
the pattern is further compiled into machine code that executes much	the pattern is further compiled into machine code that executes much
faster than the pcre_exec() interpretive matching function. If the	faster than the pcre_exec() interpretive matching function. If the
just-in-time compiler is not available, these options are ignored. All	just-in-time compiler is not available, these options are ignored. All
other bits in the options argument must be zero.	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-
Line 1979 STUDYING A PATTERN	Line 2520 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. (In 16-bit mode, the bitmap is used for 16-bit	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.)	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(),
and the information is also used by the JIT compiler. The optimiza-	and the information is also used by the JIT compiler. The optimiza-
tions can be disabled by setting the PCRE_NO_START_OPTIMIZE option when	tions can be disabled by setting the PCRE_NO_START_OPTIMIZE option.
calling pcre_exec() or pcre_dfa_exec(), but if this is done, JIT execu-	You might want to do this if your pattern contains callouts or (*MARK)
tion is also disabled. You might want to do this if your pattern con-	and you want to make use of these facilities in cases where matching
tains callouts or (*MARK) and you want to make use of these facilities	fails.
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 value. When running in UTF-8 mode, this applies only to
characters with codes less than 128. By default, higher-valued codes	characters with codes less than 128. By default, higher-valued codes
never match escapes such as \w or \d, but they can be tested with \p if	never match escapes such as \w or \d, but they can be tested with \p if
PCRE is built with Unicode character property support. Alternatively,	PCRE is built with Unicode character property support. Alternatively,
the PCRE_UCP option can be set at compile time; this causes \w and	the PCRE_UCP option can be set at compile time; this causes \w and
friends to use Unicode property support instead of built-in tables. The	friends to use Unicode property support instead of built-in tables. The
use of locales with Unicode is discouraged. If you are handling charac-	use of locales with Unicode is discouraged. If you are handling charac-
ters with codes greater than 128, you should either use UTF-8 and Uni-	ters with codes greater than 128, you should either use UTF-8 and Uni-
code, or use locales, but not try to mix the two.	code, 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-
acters. However, when PCRE is built, it is possible to cause the inter-	acters. However, when PCRE is built, it is possible to cause the inter-
nal tables to be rebuilt in the default "C" locale of the local system,	nal tables to be rebuilt in the default "C" locale of the local system,
which may cause them to be different.	which may cause them to be different.

The internal tables can always be overridden by tables supplied by the	The internal tables can always be overridden by tables supplied by the
application that calls PCRE. These may be created in a different locale	application that calls PCRE. These may be created in a different locale
from the default. As more and more applications change to using Uni-	from the default. As more and more applications change to using Uni-
code, the need for this locale support is expected to die away.	code, the need for this locale support is expected to die away.

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() or pcre_exec() as often as necessary. For
example, to build and use tables that are appropriate for the French	example, to build and use tables that are appropriate for the French
locale (where accented characters with values greater than 128 are	locale (where accented characters with values greater than 128 are
treated as letters), the following code could be used:	treated as letters), the following code could be used:

setlocale(LC_CTYPE, "fr_FR");	setlocale(LC_CTYPE, "fr_FR");
tables = pcre_maketables();	tables = pcre_maketables();
re = pcre_compile(..., tables);	re = pcre_compile(..., tables);

The locale name "fr_FR" is used on Linux and other Unix-like systems;	The locale name "fr_FR" is used on Linux and other Unix-like systems;
if you are using Windows, the name for the French locale is "french".	if you are using Windows, the name for the French locale is "french".

When pcre_maketables() runs, the tables are built in memory that is	When pcre_maketables() runs, the tables are built in memory that is
obtained via pcre_malloc. It is the caller's responsibility to ensure	obtained via pcre_malloc. It is the caller's responsibility to ensure
that the memory containing the tables remains available for as long as	that the memory containing the tables remains available for as long as
it is needed.	it is needed.

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 normally also by pcre_exec(). Thus, by default, 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 compiled 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(). Although not intended for this
purpose, this facility could be used to match a pattern in a different	purpose, this facility could be used to match a pattern in a different
locale from the one in which it was compiled. Passing table pointers at	locale from the one in which it was compiled. Passing table pointers at
run time is discussed below in the section on matching a pattern.	run time is discussed below in the section on matching a pattern.

Line 2063 INFORMATION ABOUT A PATTERN	Line 2611 INFORMATION ABOUT A PATTERN
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);

The pcre_fullinfo() function returns information about a compiled pat-	The pcre_fullinfo() function returns information about a compiled pat-
tern. It replaces the pcre_info() function, which was removed from the	tern. It replaces the pcre_info() function, which was removed from the
library at version 8.30, after more than 10 years of obsolescence.	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
the pattern was not studied. The third argument specifies which piece	the pattern was not studied. The third argument specifies which piece
of information is required, and the fourth argument is a pointer to a	of information is required, and the fourth argument is a pointer to a
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
Line 2080 INFORMATION ABOUT A PATTERN	Line 2628 INFORMATION ABOUT A PATTERN
PCRE_ERROR_BADENDIANNESS the pattern was compiled with different	PCRE_ERROR_BADENDIANNESS the pattern was compiled with different
endianness	endianness
PCRE_ERROR_BADOPTION the value of what was invalid	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. The endi-	an simple check against passing an arbitrary memory pointer. The endi-
anness error can occur if a compiled pattern is saved and reloaded on a	anness error can occur if a compiled pattern is saved and reloaded on a
different host. Here is a typical call of pcre_fullinfo(), to obtain	different host. Here is a typical call of pcre_fullinfo(), to obtain
the length of the compiled pattern:	the length of the compiled pattern:

int rc;	int rc;
Line 2095 INFORMATION ABOUT A PATTERN	Line 2644 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 data unit of any matched string, for	Return information about the first data unit of any matched string, for
a non-anchored pattern. (The name of this option refers to the 8-bit	a non-anchored pattern. (The name of this option refers to the 8-bit
library, where data units are bytes.) The fourth argument should point	library, where data units are bytes.) The fourth argument should point
to an int variable.	to an int variable.

If there is a fixed first value, for example, the letter "c" from a	If there is a fixed first value, for example, the letter "c" from a
pattern such as (cat\|cow\|coyote), its value is returned. In the 8-bit	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	library, the value is always less than 256. In the 16-bit library the
value can be up to 0xffff.	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	If there is no fixed first value, and if either

Line 2141 INFORMATION ABOUT A PATTERN	Line 2691 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 values for the first data unit	256-bit table indicating a fixed set of values for the first data unit
in any matching string, a pointer to the table is returned. Otherwise	in any matching string, a pointer to the table is returned. Otherwise
NULL is returned. The fourth argument should point to an unsigned char	NULL is returned. The fourth argument should point to an unsigned char
* variable.	* 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 one of the JIT options, and	Return 1 if the pattern was studied with one of the JIT options, and
just-in-time compiling was successful. The fourth argument should point	just-in-time compiling was successful. The fourth argument should point
to an int variable. A return value of 0 means that JIT support is not	to an int variable. A return value of 0 means that JIT support is not
available in this version of PCRE, or that the pattern was not studied	available in this version of PCRE, or that the pattern was not studied
with a JIT option, or that the JIT compiler could not handle this par-	with a JIT option, or that the JIT compiler could not handle this par-
ticular pattern. See the pcrejit documentation for details of what can	ticular pattern. See the pcrejit documentation 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 a JIT option, return the	If the pattern was successfully studied with a JIT option, return the
size of the JIT compiled code, otherwise return zero. The fourth argu-	size of the JIT compiled code, otherwise return zero. The fourth argu-
ment 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 data unit that must exist in	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	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 value, -1 is returned. For anchored patterns, a last literal	is no such value, -1 is returned. For anchored patterns, a last literal
value 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 the character, this value
	is deprecated; instead the PCRE_INFO_REQUIREDCHARFLAGS and
	PCRE_INFO_REQUIREDCHAR values should be used.

	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	PCRE_INFO_MAXLOOKBEHIND

Return the number of characters (NB not bytes) in the longest lookbe-	Return the number of characters (NB not data units) in the longest
hind assertion in the pattern. Note that the simple assertions \b and	lookbehind assertion in the pattern. This information is useful when
\B require a one-character lookbehind. This information is useful when	doing multi-segment matching using the partial matching facilities.
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, which in UTF-8 mode	value is -1. The value is a number of characters, which in UTF mode may
may be different from the number of bytes. The fourth argument should	be different from the number of data units. The fourth argument should
point to an int variable. A non-negative value is a lower bound to the	point to an int variable. A non-negative value is a lower bound to the
length of any matching string. There may not be any strings of that	length of any matching string. There may not be any strings of that
length that do actually match, but every string that does match is at	length that do actually match, but every string that does match is at
least that long.	least that long.

PCRE_INFO_NAMECOUNT	PCRE_INFO_NAMECOUNT
PCRE_INFO_NAMEENTRYSIZE	PCRE_INFO_NAMEENTRYSIZE
PCRE_INFO_NAMETABLE	PCRE_INFO_NAMETABLE

PCRE supports the use of named as well as numbered capturing parenthe-	PCRE supports the use of named as well as numbered capturing parenthe-
ses. The names are just an additional way of identifying the parenthe-	ses. The names are just an additional way of identifying the parenthe-
ses, which still acquire numbers. Several convenience functions such as	ses, which still acquire numbers. Several convenience functions such as
pcre_get_named_substring() are provided for extracting captured sub-	pcre_get_named_substring() are provided for extracting captured sub-
strings by name. It is also possible to extract the data directly, by	strings by name. It is also possible to extract the data directly, by
first converting the name to a number in order to access the correct	first converting the name to a number in order to access the correct
pointers in the output vector (described with pcre_exec() below). To do	pointers in the output vector (described with pcre_exec() below). To do
the conversion, you need to use the name-to-number map, which is	the conversion, you need to use the name-to-num the conversion, you need to use the name-to-number map, which is
described by these three values.	described by these three values.

The map consists of a number of fixed-size entries. PCRE_INFO_NAMECOUNT	The map consists of a number of fixed-size entries. PCRE_INFO_NAMECOUNT
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. This is a pointer to char in	a pointer to the first entry of the table. This is a pointer to char in
the 8-bit library, where the first two bytes of each entry are the num-	the 8-bit library, where the first two bytes of each entry are the num-
ber of the capturing parenthesis, most significant byte first. In the	ber of the capturing parenthesis, most significant byte first. In the
16-bit library, the pointer points to 16-bit data units, the first of	16-bit library, the pointer points to 16-bit data units, the first of
which contains the parenthesis number. The rest of the entry is the	which contains the parenthesis number. In the 32-bit library, the
corresponding name, zero terminated.	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. Duplicate names may appear if (?\|
is used to create multiple groups with the same number, as described in	is used to create multiple groups with the same number, as described in
the section on duplicate subpattern numbers in the pcrepattern page.	the section on duplicate subpattern numbers in the pcrepattern page.
Duplicate names for subpatterns with different numbers are permitted	Duplicate names for subpatterns with different numbers are permitted
only if PCRE_DUPNAMES is set. In all cases of duplicate names, they	only if PCRE_DUPNAMES is set. In all cases of duplicate names, they
appear in the table in the order in which they were found in the pat-	appear in the table in the order in which they were found in the pat-
tern. In the absence of (?\| this is the order of increasing number;	tern. In the absence of (?\| this is the order of increasing number;
when (?\| is used this is not necessarily the case because later subpat-	when (?\| is used this is not necessarily the case because later subpat-
terns may have lower numbers.	terns may have lower numbers.

As a simple example of the name/number table, consider the following	As a simple example of the name/number tab As a simple example of the name/number table, consider the following
pattern after compilation by the 8-bit library (assume PCRE_EXTENDED is	pattern after compilation by the 8-bit library (assume PCRE_EXTENDED is
set, so white space - including newlines - 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 2258 INFORMATION ABOUT A PATTERN	Line 2833 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 2294 INFORMATION ABOUT A PATTERN	Line 2869 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 in bytes (for both libraries).	Return the size of the compiled pattern in bytes (for all three
The fourth argument should point to a size_t variable. This value does	libraries). The fourth argument should point to a size_t variable. This
not include the size of the pcre structure that is returned by	value does not include the size of the pcre structure that is returned
pcre_compile(). The value that is passed as the argument to pcre_mal-	by pcre_compile(). The value that is passed as the argument to
loc() when pcre_compile() is getting memory in which to place the com-	pcre_malloc() when pcre_compile() is getting memory in which to place
piled data is the value returned by this option plus the size of the	the compiled data is the value returned by this option plus the size of
pcre structure. Studying a compiled pattern, with or without JIT, does	the pcre structure. Studying a compiled pattern, with or without JIT,
not alter the value returned by this option.	does not alter the value returned by this option.

PCRE_INFO_STUDYSIZE	PCRE_INFO_STUDYSIZE

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

	PCRE_INFO_FIRSTCHARACTERFLAGS

	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.

	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.

	If there is no fixed first value, and if either

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

	(b) every branch of the pattern starts with ".*" and PCRE_DOTALL is not
	set (if it were set, the pattern would be anchored),

	2 is returned, indicating that the pattern matches only at the start of
	a subject string or after any newline within the string. Otherwise 0 is
	returned. For anchored patterns, 0 is returned.

	PCRE_INFO_FIRSTCHARACTER

	Return the fixed first character value, if PCRE_INFO_FIRSTCHARACTER-
	FLAGS returned 1; otherwise returns 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.

	If there is no fixed first value, and if either

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

	(b) every branch of the pattern starts with ".*" and PCRE_DOTALL is not
	set (if it were set, the pattern would be anchored),

	-1 is returned, indicating that the pattern matches only at the start
	of a subject string or after any newline within the string. Otherwise
	-2 is returned. For anchored patterns, -2 is returned.

	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);
Line 2398 MATCHING A PATTERN: THE TRADITIONAL FUNCTION	Line 3046 MATCHING A PATTERN: THE TRADITIONAL FUNCTION
In the 16-bit version of this structure, the mark field has type	In the 16-bit version of this structure, the mark field has type
"PCRE_UCHAR16 **".	"PCRE_UCHAR16 **".

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

PCRE_EXTRA_CALLOUT_DATA	PCRE_EXTRA_CALLOUT_DATA
Line 2409 MATCHING A PATTERN: THE TRADITIONAL FUNCTION	Line 3060 MATCHING A PATTERN: THE TRADITIONAL FUNCTION
PCRE_EXTRA_STUDY_DATA	PCRE_EXTRA_STUDY_DATA
PCRE_EXTRA_TABLES	PCRE_EXTRA_TABLES

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
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 a JIT option, the way that the matching is executed is entirely	with a JIT option, the way that the matching is executed is entirely
different. However, there is still the possibility of runaway matching	different. However, there is still the possibility of runaway matching
that goes on for a very long time, and so the match_limit value is also	that goes on for a very long time, and so the match_limit value is also
used in this case (but in a different way) to limit how long the match-	used in this case (but in a different way) to limit how long the match-
ing 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 2461 MATCHING A PATTERN: THE TRADITIONAL FUNCTION	Line 3121 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 used to pass a character tables pointer to
pcre_exec(); this overrides the value that is stored with the compiled	pcre_exec(); this overrides the value that is stored with the compiled
pattern. A non-NULL value is stored with the compiled pattern only if	pattern. A non-NULL value is stored with the compiled pattern only if
custom tables were supplied to pcre_compile() via its tableptr argu-	custom tables were supplied to pcre_compile() via its tableptr argu-
ment. If NULL is passed to pcre_exec() using this mechanism, it forces	ment. If NULL is passed to pcre_exec() using this mechanism, it forces
PCRE's internal tables to be used. This facility is helpful when re-	PCRE's internal tables to be used. This facility is helpful when re-
using patterns that have been saved after compiling with an external	using patterns that have been saved after compiling with an external
set of tables, because the external tables might be at a different	set of tables, because the external tables might be at a different
address when pcre_exec() is called. See the pcreprecompile documenta-	address when pcre_exec() is called. See the pcreprecompile documenta-
tion for a discussion of saving compiled patterns for later use.	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	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-	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	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-	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	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	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.	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	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,	field is set to NULL. For details of the backtracking control verbs,
see the section entitled "Backtracking control" in the pcrepattern doc-	see the section entitled "Backtracking control" in the pcrepattern doc-
umentation.	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_HARD, and	PCRE_NO_START_OPTIMIZE, PCRE_NO_UTF8_CHECK, PCRE_PARTIAL_HARD, and
PCRE_PARTIAL_SOFT.	PCRE_PARTIAL_SOFT.

If the pattern was successfully studied with one of the just-in-time	If the pattern was successfully studied with one of the just-in-time
(JIT) compile options, 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,	PCRE_NO_UTF8_CHECK, PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY,
PCRE_NOTEMPTY_ATSTART, PCRE_PARTIAL_HARD, and PCRE_PARTIAL_SOFT. If an	PCRE_NOTEMPTY_ATSTART, PCRE_PARTIAL_HARD, and PCRE_PARTIAL_SOFT. If an
unsupported option is used, JIT execution is disabled and the normal	unsupported option is used, JIT execution is disabled 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 2523 MATCHING A PATTERN: THE TRADITIONAL FUNCTION	Line 3192 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. The use of	compile time, it cannot be unset at matching time. The use of
PCRE_NO_START_OPTIMIZE disables JIT execution; when it is set, matching	PCRE_NO_START_OPTIMIZE at matching time (that is, passing it to
is always done using interpretively.	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 2711 MATCHING A PATTERN: THE TRADITIONAL FUNCTION	Line 3381 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
nor 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 2862 MATCHING A PATTERN: THE TRADITIONAL FUNCTION	Line 3539 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 2871 MATCHING A PATTERN: THE TRADITIONAL FUNCTION	Line 3548 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 2956 MATCHING A PATTERN: THE TRADITIONAL FUNCTION	Line 3633 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 2970 MATCHING A PATTERN: THE TRADITIONAL FUNCTION	Line 3647 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	This error is returned when a pattern that was successfully studied
using a JIT compile option is being matched, but the memory available	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	for the just-in-time processing stack is not large enough. See the
pcrejit documentation for more details.	pcrejit documentation for more details.

PCRE_ERROR_BADMODE (-28)	PCRE_ERROR_BADMODE (-28)

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

PCRE_ERROR_BADENDIANNESS (-29)	PCRE_ERROR_BADENDIANNESS (-29)

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

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

	This error is returned when a pattern that was successfully studied
	using a JIT compile option is being matched, but the matching mode
	(partial or complete match) does not correspond to any JIT compilation
	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.

	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	This section applies only to the 8-bit library. The corresponding
information for the 16-bit library is given in the pcre16 page.	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
Line 3083 MATCHING A PATTERN: THE TRADITIONAL FUNCTION	Line 3775 MATCHING A PATTERN: THE TRADITIONAL FUNCTION
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 3097 EXTRACTING CAPTURED SUBSTRINGS BY NUMBER	Line 3796 EXTRACTING CAPTURED SUBSTRINGS BY NUMBER
int pcre_get_substring_list(const char *subject,	int pcre_get_substring_list(const char *subject,
int ovector, int stringcount, const char **listptr);	int ovector, int stringcount, const char **listptr);

Captured substrings can be accessed directly by using the offsets	Captured substrings can be accessed directly by using the offsets
returned by pcre_exec() in ovector. For convenience, the functions	returned by pcre_exec() in ovector. For convenience, the functions
pcre_copy_substring(), pcre_get_substring(), and pcre_get_sub-	pcre_copy_substring(), pcre_get_substring(), and pcre_get_sub-
string_list() are provided for extracting captured substrings as new,	string_list() are provided for extracting captured substrings as new,
separate, zero-terminated strings. These functions identify substrings	separate, zero-terminated strings. These functions identify substrings
by number. The next section describes functions for extracting named	by number. The next section describes functions for extracting named
substrings.	substrings.

A substring that contains a binary zero is correctly extracted and has	A substring that contains a binary zero is correctly extracted and has
a further zero added on the end, but the result is not, of course, a C	a further zero added on the end, but the result is not, of course, a C
string. However, you can process such a string by referring to the	string. However, you can process such a string by referring to the
length that is returned by pcre_copy_substring() and pcre_get_sub-	length that is returned by pcre_copy_substring() and pcre_get_sub-
string(). Unfortunately, the interface to pcre_get_substring_list() is	string(). Unfortunately, the interface to pcre_get_substring_list() is
not adequate for handling strings containing binary zeros, because the	not adequate for handling strings containing binary zeros, because the
end of the final string is not independently indicated.	end of the final string is not independently indicated.

The first three arguments are the same for all three of these func-	The first three arguments are the same for all three of these func-
tions: subject is the subject string that has just been successfully	tions: subject is the subject string that has just been successfully
matched, ovector is a pointer to the vector of integer offsets that was	matched, ovector is a pointer to the vector of integer offsets that was
passed to pcre_exec(), and stringcount is the number of substrings that	passed to pcre_exec(), and stringcount is the number of substrings that
were captured by the match, including the substring that matched the	were captured by the match, including the substring that matched the
entire regular expression. This is the value returned by pcre_exec() if	entire regular expression. This is the value returned by pcre_exec() if
it is greater than zero. If pcre_exec() returned zero, indicating that	it is greater than zero. If pcre_exec() returned zero, indicating that
it ran out of space in ovector, the value passed as stringcount should	it ran out of space in ovector, the value passed as stringcount should
be the number of elements in the vector divided by three.	be the number of elements in the vector divided by three.

The functions pcre_copy_substring() and pcre_get_substring() extract a	The functions pcre_copy_substring() and pcre_get_substring() extract a
single substring, whose number is given as stringnumber. A value of	single substring, whose number is given as stringnumber. A value of
zero extracts the substring that matched the entire pattern, whereas	zero extracts the substring that matched the entire pattern, whereas
higher values extract the captured substrings. For pcre_copy_sub-	higher values extract the captured substrings. For pcre_copy_sub-
string(), the string is placed in buffer, whose length is given by	string(), the string is placed in buffer, whose length is given by
buffersize, while for pcre_get_substring() a new block of memory is	buffersize, while for pcre_get_substring() a new block of memory is
obtained via pcre_malloc, and its address is returned via stringptr.	obtained via pcre_malloc, and its address is returned via stringptr.
The yield of the function is the length of the string, not including	The yield of the function is the length of the string, not including
the terminating zero, or one of these error codes:	the terminating zero, or one of these error codes:

PCRE_ERROR_NOMEMORY (-6)	PCRE_ERROR_NOMEMORY (-6)

The buffer was too small for pcre_copy_substring(), or the attempt to	The buffer was too small for pcre_copy_substring(), or t The buffer was too small for pcre_copy_substring(), or the attempt to
get memory failed for pcre_get_substring().	get memory failed for pcre_get_substring().

PCRE_ERROR_NOSUBSTRING (-7)	PCRE_ERROR_NOSUBSTRING (-7)

There is no substring whose number is stringnumber.	There is no substring whose number is stringnumber.

The pcre_get_substring_list() function extracts all available sub-	The pcre_get_substring_list() function extracts all available sub-
strings and builds a list of pointers to them. All this is done in a	strings and builds a list of pointers to them. All this is done in a
single block of memory that is obtained via pcre_malloc. The address of	single block of memory that is obtained via pcre_malloc. The address of
the memory block is returned via listptr, which is also the start of	the memory block is returned via listptr, which is also the start of
the list of string pointers. The end of the list is marked by a NULL	the list of string pointers. The end of the list is marked by a NULL
pointer. The yield of the function is zero if all went well, or the	pointer. The yield of the function is zero if all went well, or the
error code	error code

PCRE_ERROR_NOMEMORY (-6)	PCRE_ERROR_NOMEMORY (-6)

if the attempt to get the memory block failed.	if the attempt to get the memory block failed.

When any of these functions encounter a substring that is unset, which	When any of these functions encounter a substring that is unset, which
can happen when capturing subpattern number n+1 matches some part of	can happen when capturing subpattern number n+1 matches some part of
the subject, but subpattern n has not been used at all, they return an	the subject, but subpattern n has not been used at all, they return an
empty string. This can be distinguished from a genuine zero-length sub-	empty string. This can be distinguished from a genuine zero-length sub-
string by inspecting the appropriate offset in ovector, which is nega-	string by inspecting the appropriate offset in ovector, which is nega-
tive for unset substrings.	tive for unset substrings.

The two convenience functions pcre_free_substring() and pcre_free_sub-	The two convenience functions pcre_free_substring() and pcre_free_sub-
string_list() can be used to free the memory returned by a previous	string_list() can be used to free the memory returned by a previous
call of pcre_get_substring() or pcre_get_substring_list(), respec-	call of pcre_get_substring() or pcre_get_substring_list(), respec-
tively. They do nothing more than call the function pointed to by	tively. They do nothing more than call the function pointed to by
pcre_free, which of course could be called directly from a C program.	pcre_free, which of course could be called directly from a C program.
However, PCRE is used in some situations where it is linked via a spe-	However, PCRE is used in some situations where it is linked via a spe-
cial interface to another programming language that cannot use	cial interface to another programming language that cannot use
pcre_free directly; it is for these cases that the functions are pro-	pcre_free directly; it is for these cases that the functions are pro-
vided.	vided.


Line 3187 EXTRACTING CAPTURED SUBSTRINGS BY NAME	Line 3886 EXTRACTING CAPTURED SUBSTRINGS BY NAME
int stringcount, const char *stringname,	int stringcount, const char *stringname,
const char **stringptr);	const char **stringptr);

To extract a substring by name, you first have to find associated num-	To extract a substring by name, you first have to find associated num-
ber. For example, for this pattern	ber. For example, for this pattern

(a+)b(?<xxx>\d+)...	(a+)b(?<xxx>\d+)...
Line 3196 EXTRACTING CAPTURED SUBSTRINGS BY NAME	Line 3895 EXTRACTING CAPTURED SUBSTRINGS BY NAME
be unique (PCRE_DUPNAMES was not set), you can find the number from the	be unique (PCRE_DUPNAMES was not set), you can find the number from the
name by calling pcre_get_stringnumber(). The first argument is the com-	name by calling pcre_get_stringnumber(). The first argument is the com-
piled pattern, and the second is the name. The yield of the function is	piled pattern, and the second is the name. The yield of the function is
the subpattern number, or PCRE_ERROR_NOSUBSTRING (-7) if there is no	the subpattern number, or PCRE_ERROR_NOSUBSTRING (-7) if there is no
subpattern of that name.	subpattern of that name.

Given the number, you can extract the substring directly, or use one of	Given the number, you can extract the substring directly, or use one of
the functions described in the previous section. For convenience, there	the functions described in the previous section. For convenience, there
are also two functions that do the whole job.	are also two functions that do the whole job.

Most of the arguments of pcre_copy_named_substring() and	Most of the arguments of pcre_copy_named_substring() and
pcre_get_named_substring() are the same as those for the similarly	pcre_get_named_substring() are the same as those for the similarly
named functions that extract by number. As these are described in the	named functions that extract by number. As these are described in the
previous section, they are not re-described here. There are just two	previous section, they are not re-described here. There are just two
differences:	differences:

First, instead of a substring number, a substring name is given. Sec-	First, instead of a substring number, a substring name is given. Sec-
ond, there is an extra argument, given at the start, which is a pointer	ond, there is an extra argument, given at the start, which is a pointer
to the compiled pattern. This is needed in order to gain access to the	to the compiled pattern. This is needed in order to gain access to the
name-to-number translation table.	name-to-number translation table.

These functions call pcre_get_stringnumber(), and if it succeeds, they	These functions call pcre_get_stringnumber(), and if it succeeds, they
then call pcre_copy_substring() or pcre_get_substring(), as appropri-	then call pcre_copy_substring() or pcre_get_substring(), as appropri-
ate. NOTE: If PCRE_DUPNAMES is set and there are duplicate names, the	ate. NOTE: If PCRE_DUPNAMES is set and there are duplicate names, the
behaviour may not be what you want (see the next section).	behaviour may not be what you want (see the next section).

Warning: If the pattern uses the (?\| feature to set up multiple subpat-	Warning: If the pattern uses the (?\| feature to set up multiple subpat-
terns with the same number, as described in the section on duplicate	terns with the same number, as described in the section on duplicate
subpattern numbers in the pcrepattern page, you cannot use names to	subpattern numbers in the pcrepattern page, you cannot use names to
distinguish the different subpatterns, because names are not included	distinguish the different subpatterns, because names are not included
in the compiled code. The matching process uses only numbers. For this	in the compiled code. The matching process uses only numbers. For this
reason, the use of different names for subpatterns of the same number	reason, the use of different names for subpatterns of the same number
causes an error at compile time.	causes an error at compile time.


Line 3233 DUPLICATE SUBPATTERN NAMES	Line 3932 DUPLICATE SUBPATTERN NAMES
int pcre_get_stringtable_entries(const pcre *code,	int pcre_get_stringtable_entries(const pcre *code,
const char name, char first, char *last);	const char name, char first, char *last);

When a pattern is compiled with the PCRE_DUPNAMES option, names for	When a pattern is compiled with the PCRE_DUPNAMES option, names for
subpatterns are not required to be unique. (Duplicate names are always	subpatterns are not required to be unique. (Duplicate names are always
allowed for subpatterns with the same number, created by using the (?\|	allowed for subpatterns with the same number, created by using the (?\|
feature. Indeed, if such subpatterns are named, they are required to	feature. Indeed, if such subpatterns are named, they are required to
use the same names.)	use the same names.)

Normally, patterns with duplicate names are such that in any one match,	Normally, patterns with duplicate names are such that in any one match,
only one of the named subpatterns participates. An example is shown in	only one of the named subpatterns participates. An example is shown in
the pcrepattern documentation.	the pcrepattern documentation.

When duplicates are present, pcre_copy_named_substring() and	When duplicates are present, pcre_copy_named_substring() and
pcre_get_named_substring() return the first substring corresponding to	pcre_get_named_substring() return the first substring corresponding to
the given name that is set. If none are set, PCRE_ERROR_NOSUBSTRING	the given name that is set. If none are set, PCRE_ERROR_NOSUBSTRING
(-7) is returned; no data is returned. The pcre_get_stringnumber()	(-7) is returned; no data is returned. The pcre_get_stringnumber()
function returns one of the numbers that are associated with the name,	function returns one of the numbers that are associated with the name,
but it is not defined which it is.	but it is not defined which it is.

If you want to get full details of all captured substrings for a given	If you want to get full details of all captured substrings for a given
name, you must use the pcre_get_stringtable_entries() function. The	name, you must use the pcre_get_stringtable_entries() function. The
first argument is the compiled pattern, and the second is the name. The	first argument is the compiled pattern, and the second is the name. The
third and fourth are pointers to variables which are updated by the	third and fourth are pointers to variables which are updated by the
function. After it has run, they point to the first and last entries in	function. After it has run, they point to the first and last entries in
the name-to-number table for the given name. The function itself	the name-to-number table for the given name. The function itself
returns the length of each entry, or PCRE_ERROR_NOSUBSTRING (-7) if	returns the length of each entry, or PCRE_ERROR_NOSUBSTRING (-7) if
there are none. The format of the table is described above in the sec-	there are none. The format of the table is described above in the sec-
tion entitled Information about a pattern above. Given all the rele-	tion entitled Information about a pattern above. Given all the rele-
vant entries for the name, you can extract each of their numbers, and	vant entries for the name, you can extract each of their numbers, and
hence the captured data, if any.	hence the captured data, if any.


FINDING ALL POSSIBLE MATCHES	FINDING ALL POSSIBLE MATCHES

The traditional matching function uses a similar algorithm to Perl,	The traditional matching function uses a similar algorithm to Perl,
which stops when it finds the first match, starting at a given point in	which stops when it finds the first match, starting at a given point in
the subject. If you want to find all possible matches, or the longest	the subject. If you want to find all possible matches, or the longest
possible match, consider using the alternative matching function (see	possible match, consider using the alternative matching function (see
below) instead. If you cannot use the alternative function, but still	below) instead. If you cannot use the alternative function, but still
need to find all possible matches, you can kludge it up by making use	need to find all possible matches, you can kludge it up by making use
of the callout facility, which is described in the pcrecallout documen-	of the callout facility, which is described in the pcrecallout documen-
tation.	tation.

What you have to do is to insert a callout right at the end of the pat-	What you have to do is to insert a callout right at the end of the pat-
tern. When your callout function is called, extract and save the cur-	tern. When your callout function is called, extract and save the cur-
rent matched substring. Then return 1, which forces pcre_exec() to	rent matched substring. Then return 1, which forces pcre_exec() to
backtrack and try other alternatives. Ultimately, when it runs out of	backtrack and try other alternatives. Ultimately, when it runs out of
matches, pcre_exec() will yield PCRE_ERROR_NOMATCH.	matches, pcre_exec() will yield PCRE_ERROR_NOMATCH.


OBTAINING AN ESTIMATE OF STACK USAGE	OBTAINING AN ESTIMATE OF STACK USAGE

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

Normally, if its first argument is NULL, pcre_exec() immediately	Normally, if its first argument is NULL, pcre_exec() immediately
returns the negative error code PCRE_ERROR_NULL, but with this special	returns the negative error code PCRE_ERROR_NULL, but with this special
combination of arguments, it returns instead a negative number whose	combination of arguments, it returns instead a negative number whose
absolute value is the approximate stack frame size in bytes. (A nega-	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.)	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	The value is approximate because in some cases, recursive calls to
pcre_exec() occur when there are one or two additional variables on the	pcre_exec() occur when there are one or two additional variables on the
stack.	stack.

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


Line 3313 MATCHING A PATTERN: THE ALTERNATIVE FUNCTION	Line 4012 MATCHING A PATTERN: THE ALTERNATIVE FUNCTION
int options, int *ovector, int ovecsize,	int options, int *ovector, int ovecsize,
int *workspace, int wscount);	int *workspace, int wscount);

The function pcre_dfa_exec() is called to match a subject string	The function pcre_dfa_exec() is called to match a subject string
against a compiled pattern, using a matching algorithm that scans the	against a compiled pattern, using a matching algorithm that scans the
subject string just once, and does not backtrack. This has different	subject string just once, and does not backtrack. This has different
characteristics to the normal algorithm, and is not compatible with	characteristics to the normal algorithm, and is not compatible with
Perl. Some of the features of PCRE patterns are not supported. Never-	Perl. Some of the features of PCRE patterns are not supported. Never-
theless, there are times when this kind of matching can be useful. For	theless, there are times when this kind of matching can be useful. For
a discussion of the two matching algorithms, and a list of features	a discussion of the two matching algorithms, and a list of features
that pcre_dfa_exec() does not support, see the pcrematching documenta-	that pcre_dfa_exec() does not support, see the pcrematching documenta-
tion.	tion.

The arguments for the pcre_dfa_exec() function are the same as for	The arguments for the pcre_dfa_exec() fun The arguments for the pcre_dfa_exec() fun
pcre_exec(), plus two extras. The ovector argument is used in a differ-	pcre_exec(), plus two extras. The ovector argument is used in a differ-
ent way, and this is described below. The other common arguments are	ent way, and this is described below. The other common arguments are
used in the same way as for pcre_exec(), so their description is not	used in the same way as for pcre_exec(), so their description is not
repeated here.	repeated here.

The two additional arguments provide workspace for the function. The	The two additional arguments provide workspace for the function. The
workspace vector should contain at least 20 elements. It is used for	workspace vector should contain at least 20 elements. It is used for
keeping track of multiple paths through the pattern tree. More	keeping track of multiple paths through the pattern tree. More
workspace will be needed for patterns and subjects where there are a	workspace will be needed for patterns and subjects where there are a
lot of potential matches.	lot of potential matches.

Here is an example of a simple call to pcre_dfa_exec():	Here is an example of a simple call to pcre_dfa_exec():
Line 3354 MATCHING A PATTERN: THE ALTERNATIVE FUNCTION	Line 4053 MATCHING A PATTERN: THE ALTERNATIVE FUNCTION

Option bits for pcre_dfa_exec()	Option bits for pcre_dfa_exec()

The unused bits of the options argument for pcre_dfa_exec() must be	The unused bits of the options argument for pcre_dfa_exec() must be
zero. The only bits that may be set are PCRE_ANCHORED, PCRE_NEW-	zero. The only bits that may be set are PCRE_ANCHORED, PCRE_NEW-
LINE_xxx, PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY,	LINE_xxx, PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY,
PCRE_NOTEMPTY_ATSTART, PCRE_NO_UTF8_CHECK, PCRE_BSR_ANYCRLF,	PCRE_NOTEMPTY_ATSTART, PCRE_NO_UTF8_CHECK, PCRE_BSR_ANYCRLF,
PCRE_BSR_UNICODE, PCRE_NO_START_OPTIMIZE, PCRE_PARTIAL_HARD, PCRE_PAR-	PCRE_BSR_UNICODE, PCRE_NO_START_OPTIMIZE, PCRE_PARTIAL_HARD, PCRE_PAR-
TIAL_SOFT, PCRE_DFA_SHORTEST, and PCRE_DFA_RESTART. All but the last	TIAL_SOFT, PCRE_DFA_SHORTEST, and PCRE_DFA_RESTART. All but the last
four of these are exactly the same as for pcre_exec(), so their	four of these are exactly the same as for pcre_exec(), so their
description is not repeated here.	description is not repeated here.

PCRE_PARTIAL_HARD	PCRE_PARTIAL_HARD
PCRE_PARTIAL_SOFT	PCRE_PARTIAL_SOFT

These have the same general effect as they do for pcre_exec(), but the	These have the same general effect as they do for pcre_exec(), but the
details are slightly different. When PCRE_PARTIAL_HARD is set for	details are slightly different. When PCRE_PARTIAL_HARD is set for
pcre_dfa_exec(), it returns PCRE_ERROR_PARTIAL if the end of the sub-	pcre_dfa_exec(), it returns PCRE_ERROR_PARTIAL if the end of the sub-
ject is reached and there is still at least one matching possibility	ject is reached and there is still at least one matching possibility
that requires additional characters. This happens even if some complete	that requires additional characters. This happens even if some complete
matches have also been found. When PCRE_PARTIAL_SOFT is set, the return	matches have also been found. When PCRE_PARTIAL_SOFT is set, the return
code PCRE_ERROR_NOMATCH is converted into PCRE_ERROR_PARTIAL if the end	code PCRE_ERROR_NOMATCH is converted into PCRE_ERROR_PARTIAL if the end
of the subject is reached, there have been no complete matches, but	of the subject is reached, there have been no complete matches, but
there is still at least one matching possibility. The portion of the	there is still at least one matching possibility. The portion of the
string that was inspected when the longest partial match was found is	string that was inspected when the longest partial match was found is
set as the first matching string in both cases. There is a more	set as the first matching string in both cases. There is a more
detailed discussion of partial and multi-segment matching, with exam-	detailed discussion of partial and multi-segment matching, with exam-
ples, in the pcrepartial documentation.	ples, in the pcrepartial documentation.

PCRE_DFA_SHORTEST	PCRE_DFA_SHORTEST

Setting the PCRE_DFA_SHORTEST option causes the matching algorithm to	Setting the PCRE_DFA_SHORTEST option causes the matching algorithm to
stop as soon as it has found one match. Because of the way the alterna-	stop as soon as it has found one match. Because of the way the alterna-
tive algorithm works, this is necessarily the shortest possible match	tive algorithm works, this is necessarily the shortest possible match
at the first possible matching point in the subject string.	at the first possible matching point in the subject string.

PCRE_DFA_RESTART	PCRE_DFA_RESTART

When pcre_dfa_exec() returns a partial match, it is possible to call it	When pcre_dfa_exec() returns a partial match, it is possible to call it
again, with additional subject characters, and have it continue with	again, with additional subject characters, and have it continue with
the same match. The PCRE_DFA_RESTART option requests this action; when	the same match. The PCRE_DFA_RESTART option requests this action; when
it is set, the workspace and wscount options must reference the same	it is set, the workspace and wscount options must reference the same
vector as before because data about the match so far is left in them	vector as before because data about the match so far is left in them
after a partial match. There is more discussion of this facility in the	after a partial match. There is more discussion of this facility in the
pcrepartial documentation.	pcrepartial documentation.

Successful returns from pcre_dfa_exec()	Successful returns from pcre_dfa_exec()

When pcre_dfa_exec() succeeds, it may have matched more than one sub-	When pcre_dfa_exec() succeeds, it may have matched more than one sub-
string in the subject. Note, however, that all the matches from one run	string in the subject. Note, however, that all the matches from one run
of the function start at the same point in the subject. The shorter	of the function start at the same point in the subject. The shorter
matches are all initial substrings of the longer matches. For example,	matches are all initial substrings of the longer matches. For example,
if the pattern	if the pattern

<.*>	<.*>
Line 3417 MATCHING A PATTERN: THE ALTERNATIVE FUNCTION	Line 4116 MATCHING A PATTERN: THE ALTERNATIVE FUNCTION
<something> <something else>	<something> <something else>
<something> <something else> <something further>	<something> <something else> <something further>

On success, the yield of the function is a number greater than zero,	On success, the yield of the function is a number greater than zero,
which is the number of matched substrings. The substrings themselves	which is the number of matched substrings. The substrings themselves
are returned in ovector. Each string uses two elements; the first is	are returned in ovector. Each string uses two elements; the first is
the offset to the start, and the second is the offset to the end. In	the offset to the start, and the second is the offset to the end. In
fact, all the strings have the same start offset. (Space could have	fact, all the strings have the same start offset. (Space could have
been saved by giving this only once, but it was decided to retain some	been saved by giving this only once, but it was decided to retain some
compatibility with the way pcre_exec() returns data, even though the	compatibility with the way pcre_exec() returns data, even though the
meaning of the strings is different.)	meaning of the strings is different.)

The strings are returned in reverse order of length; that is, the long-	The strings are returned in reverse order of length; that is, the long-
est matching string is given first. If there were too many matches to	est matching string is given first. If there were too many matches to
fit into ovector, the yield of the function is zero, and the vector is	fit into ovector, the yield of the function is zero, and the vector is
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.

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)	PCRE_ERROR_DFA_BADRESTART (-30)

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


SEE ALSO	SEE ALSO

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


AUTHOR	AUTHOR
Line 3494 AUTHOR	Line 4193 AUTHOR

REVISION	REVISION

Last updated: 17 June 2012	Last updated: 12 May 2013
Copyright (c) 1997-2012 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 (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 (pcre16_callout for	its entry point in the global variable pcre_callout (pcre16_callout for
the 16-bit library). By default, this variable contains NULL, which	the 16-bit library, pcre32_callout for the 32-bit library). By default,
disables all calling out.	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
Line 3539 PCRE CALLOUTS	Line 4245 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 command has an option that sets automatic call-
	outs; when it is used, the output indicates how the pattern is matched.
	This is useful information when you are trying to optimize the perfor-
	mance 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
Line 3577 MISSING CALLOUTS	Line 4289 MISSING CALLOUTS
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 or pcre16_callout is called (if it is	tion defined by pcre_callout or pcre[16\|32]_callout is called (if it is
set). This applies to both normal and DFA matching. The only argument	set). This applies to both normal and DFA matching. The only argument
to the callout function is a pointer to a pcre_callout or pcre16_call-	to the callout function is a pointer to a pcre_callout or
out block. These structures 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; (8-bit version)	const char *subject; (8-bit version)
PCRE_SPTR16 subject; (16-bit version)	PCRE_SPTR16 subject; (16-bit version)
	PCRE_SPTR32 subject; (32-bit version)
int subject_length;	int subject_length;
int start_match;	int start_match;
int current_position;	int current_position;
Line 3597 THE CALLOUT INTERFACE	Line 4311 THE CALLOUT INTERFACE
int next_item_length;	int next_item_length;
const unsigned char *mark; (8-bit version)	const unsigned char *mark; (8-bit version)
const PCRE_UCHAR16 *mark; (16-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
version number will change again in future if additional fields are	version number will change again in future if additional fields are
added, but the intention is never to remove any of the existing fields.	added, but the intention is never to remove any of the existing fields.

The callout_number field contains the number of the callout, as com-	The callout_number field contains the number of the callout, as com-
piled into the pattern (that is, the number after ?C for manual call-	piled into the pattern (that is, the number after ?C for manual call-
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 the matching function. When pcre_exec() or	passed by the caller to the matching function. When pcre_exec() or
pcre16_exec() is used, the contents can be inspected, in order to	pcre[16\|32]_exec() is used, the contents can be inspected, in order to
extract substrings that have been matched so far, in the same way as	extract substrings that have been matched so far, in the same way as
for extracting substrings after a match has completed. For the DFA	for extracting substrings after a match has completed. For the DFA
matching functions, 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 the matching function.	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
sequence \K has been encountered, this value is changed to reflect the	sequence \K has been encountered, this value is changed to reflect the
modified starting point. If the pattern is not anchored, the callout	modified starting point. If the pattern is not anchored, the callout
function may be called several times from the same point in the pattern	function may be called several times from the same point in the pattern
for different starting points in the subject.	for different starting points in the subject.

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() or pcre16_exec() is used, the capture_top field	When the pcre_exec() or pcre[16\|32]_exec() is used, the capture_top
contains one more than the number of the highest numbered captured sub-	field contains one more than the number of the highest numbered cap-
string so far. If no substrings have been captured, the value of cap-	tured substring so far. If no substrings have been captured, the value
ture_top is one. This is always the case when the DFA functions are	of capture_top is one. This is always the case when the DFA functions
used, because they do 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 for the DFA matching functions.	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 a matching	The callout_data field contains a value that is passed to a matching
function specifically so that it can be passed back in callouts. It is	function specifically so that it can be passed back in callouts. It is
passed in the callout_data field of a pcre_extra or pcre16_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
callout block is NULL. There is a description of the pcre_extra struc-	in a callout block is NULL. There is a description of the pcre_extra
ture in the pcreapi documentation.	structure in the pcreapi documentation.

The pattern_position field is present from version 1 of the callout	The pattern_position field is present from version 1 of the callout
structure. It contains the offset to the next item to be matched in the	structure. It contains the offset to the next item to be matched in the
Line 3660 THE CALLOUT INTERFACE	Line 4378 THE CALLOUT INTERFACE
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 callout structure. In	The mark field is present from version 2 of the callout structure. In
callouts from pcre_exec() or pcre16_exec() it contains a pointer to the	callouts from pcre_exec() or pcre[16\|32]_exec() it contains a pointer
zero-terminated name of the most recently passed (MARK), (PRUNE), or	to the zero-terminated name of the most recently passed (*MARK),
(*THEN) item in the match, or NULL if no such items have been passed.	(PRUNE), or (THEN) item in the match, or NULL if no such items have
Instances of (PRUNE) or (THEN) without a name do not obliterate a	been passed. Instances of (PRUNE) or (THEN) without a name do not
previous (*MARK). In callouts from the DFA matching functions this	obliterate a previous (*MARK). In callouts from the DFA matching func-
field always contains NULL.	tions this field always contains NULL.


RETURN VALUES	RETURN VALUES
Line 3693 AUTHOR	Line 4411 AUTHOR

REVISION	REVISION

Last updated: 08 Janurary 2012	Last updated: 03 March 2013
Copyright (c) 1997-2012 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
Line 3723 DIFFERENCES BETWEEN PCRE AND PERL	Line 4441 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 3752 DIFFERENCES BETWEEN PCRE AND PERL	Line 4468 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 3770 DIFFERENCES BETWEEN PCRE AND PERL	Line 4481 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 any of the backtracking control verbs are used in an assertion	10. If any of the backtracking control verbs are used in a subpattern
or in a subpattern that is called as a subroutine (whether or not	that is called as a subroutine (whether or not recursively), their
recursively), their effect is confined to that subpattern; it does not	effect is confined to that subpattern; it does not extend to the sur-
extend to the surrounding pattern. This is not always the case in Perl.	rounding pattern. This is not always the case in Perl. In particular,
In particular, if (*THEN) is present in a group that is called as a	if (*THEN) is present in a group that is called as a subroutine, its
subroutine, its action is limited to that group, even if the group does	action is limited to that group, even if the group does not contain any
not contain any \| characters. There is one exception to this: the name	\| characters. Note that such subpatterns are processed as anchored at
from a (MARK), (PRUNE), or (*THEN) that is encountered in a success-	the point where they are tested.
ful 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.

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 white space between ( and ? but PCRE never	modifier is set, Perl allows white space between ( and ? but PCRE never
does, even if the PCRE_EXTENDED option is set.	does, even if the PCRE_EXTENDED option is set.

15. PCRE provides some extensions to the Perl regular expression facil-	16. 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.

	17. 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 3858 DIFFERENCES BETWEEN PCRE AND PERL	Line 4582 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 functions (pcre_dfa_exec() and	(k) The alternative matching functions (pcre_dfa_exec(),
pcre16_dfa_exec()) match in a different way and are not Perl-compati-	pcre16_dfa_exec() and pcre32_dfa_exec(),) match in a different way and
ble.	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
Line 3876 AUTHOR	Line 4600 AUTHOR

REVISION	REVISION

Last updated: 01 June 2012	Last updated: 19 March 2013
Copyright (c) 1997-2012 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 3905 PCRE REGULAR EXPRESSION DETAILS	Line 4629 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 strings in the original	However, there is now also support for UTF-8 strings in the original
library, and a second library that supports 16-bit and UTF-16 character	library, an extra library that supports 16-bit and UTF-16 character
	strings, and a third library that supports 32-bit and UTF-32 character
strings. To use these features, PCRE must be built to include appropri-	strings. To use these features, PCRE must be built to include appropri-
ate support. When using UTF strings you must either call the compiling	ate support. When using UTF strings you must either call the compiling
function with the PCRE_UTF8 or PCRE_UTF16 option, or the pattern must	function with the PCRE_UTF8, PCRE_UTF16, or PCRE_UTF32 option, or the
start with one of these special sequences:	pattern must start with one of these special sequences:

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

Starting a pattern with such a sequence is equivalent to setting the	(*UTF) is a generic sequence that can be used with any of the
relevant option. This feature is not Perl-compatible. How setting a UTF	libraries. Starting a pattern with such a sequence is equivalent to
mode affects pattern matching is mentioned in several places below.	setting the relevant option. How setting a UTF mode affects pattern
There is also a summary of features in the pcreunicode page.	matching is mentioned in several places below. There is also a summary
	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) or (UTF16) 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.

	Unicode property support

	Another special sequence that may appear at the start of a pattern is

(*UCP)	(*UCP)

This has the same effect as setting the PCRE_UCP option: it causes	This has the same effect as setting the PCRE_UCP option: it causes
Line 3931 PCRE REGULAR EXPRESSION DETAILS	Line 4688 PCRE REGULAR EXPRESSION DETAILS
character types, instead of recognizing only characters with codes less	character types, instead of recognizing only characters with codes less
than 128 via a lookup table.	than 128 via a lookup table.

	Disabling start-up optimizations

If a pattern starts with (*NO_START_OPT), it has the same effect as	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	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-	time.
cerned with the handling of newlines; they are described below.

The remainder of this document discusses the patterns that are sup-	Newline conventions
ported by PCRE when one its main matching functions, pcre_exec()
(8-bit) or pcre16_exec() (16-bit), is used. PCRE also has alternative
matching functions, pcre_dfa_exec() and pcre16_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 pcrematch-
ing page.

	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 3966 NEWLINE CONVENTIONS	Line 4713 NEWLINE CONVENTIONS
(*ANY) all Unicode newline sequences	(*ANY) all Unicode newline sequences

These override the default and the options given to the compiling func-	These override the default and the options given to the compiling func-
tion. For example, on a Unix system where LF is the default newline	tion. For example, on a Unix system where LF is the default 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 by the caller of pcre_exec() for
	it to have any effect. In other words, the pattern writer can lower the
	limit set by the programmer, but not raise it. 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
string from left to right. Most characters stand for themselves in a	string from left to right. Most characters stand for themselves in a
pattern, and match the corresponding characters in the subject. As a	pattern, and match the corresponding characters in the subject. As a
trivial example, the pattern	trivial example, the pattern

The quick brown fox	The quick brown fox

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 a UTF 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 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
pattern by the use of metacharacters, which do not stand for themselves	pattern by the use of metacharacters, which do not stand for themselves
but instead are interpreted in some special way.	but instead are interpreted in some special way.

There are two different sets of metacharacters: those that are recog-	There are two different sets of metacharacters: those that are recog-
nized anywhere in the pattern except within square brackets, and those	nized anywhere in the pattern except within square brackets, and those
that are recognized within square brackets. Outside square brackets,	that are recognized within square brackets. Outside square brackets,
the metacharacters are as follows:	the metacharacters are as follows:

\ general escape character with several uses	\ general escape character with several uses
Line 4031 CHARACTERS AND METACHARACTERS	Line 4806 CHARACTERS AND METACHARACTERS
also "possessive quantifier"	also "possessive quantifier"
{ start min/max quantifier	{ start min/max quantifier

Part of a pattern that is in square brackets is called a "character	Part of a pattern that is in square brackets is called a "character
class". In a character class the only metacharacters are:	class". In a character class the only metacharacters are:

\ general escape character	\ general escape character
Line 4048 BACKSLASH	Line 4823 BACKSLASH

The backslash character has several uses. Firstly, if it is followed by	The backslash character has several uses. Firstly, if it is followed by
a character that is not a number or a letter, it takes away any special	a character that is not a number or a letter, it takes away any special
meaning that character may have. This use of backslash as an escape	meaning that character may have. This use of backslash as an escape
character applies both inside and outside character classes.	character applies both inside and outside character classes.

For example, if you want to match a * character, you write \* in the	For example, if you want to match a * character, you write \* in the
pattern. This escaping action applies whether or not the following	pattern. This escaping action applies whether or not the following
character would otherwise be interpreted as a metacharacter, so it is	character would otherwise be interpreted as a metacharacter, so it is
always safe to precede a non-alphanumeric with backslash to specify	always safe to precede a non-alphanumeric with backslash to specify
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 a UTF 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, white space in	If a pattern is compiled with the PCRE_EXTENDED option, white space in
the pattern (other than in a character class) and characters between a	the pattern (other than in a character class) and characters between a
# outside a character class and the next newline are ignored. An escap-	# outside a character class and the next newline are ignored. An escap-
ing backslash can be used to include a white space or # character as	ing backslash can be used to include a white space or # character as
part of the pattern.	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-
ent from Perl in that $ and @ are handled as literals in \Q...\E	ent from Perl in that $ and @ are handled as literals in \Q...\E
sequences in PCRE, whereas in Perl, $ and @ cause variable interpola-	sequences in PCRE, whereas in Perl, $ and @ cause variable interpola-
tion. Note the following examples:	tion. Note the following examples:

Pattern PCRE matches Perl matches	Pattern PCRE matches Perl matches
Line 4081 BACKSLASH	Line 4856 BACKSLASH
\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. An isolated \E that is not preceded by \Q is ignored. If \Q	classes. An isolated \E that is not preceded by \Q is ignored. If \Q
is not followed by \E later in the pattern, the literal interpretation	is not followed by \E later in the pattern, the literal interpretation
continues to the end of the pattern (that is, \E is assumed at the	continues to the end of the pattern (that is, \E is assumed at the
end). If the isolated \Q is inside a character class, this causes an	end). If the isolated \Q is inside a character class, this causes an
error, because the character class is not terminated.	error, because the character class is not terminated.

Non-printing characters	Non-printing characters

A second use of backslash provides a way of encoding non-printing char-	A second use of backslash provides a way of encoding non-printing char-
acters in patterns in a visible manner. There is no restriction on the	acters in patterns in a visible manner. There is no restriction on the
appearance of non-printing characters, apart from the binary zero that	appearance of non-printing characters, apart from the binary zero that
terminates a pattern, but when a pattern is being prepared by text	terminates a pattern, but when a pattern is being prepared by text
editing, it is often easier to use one of the following escape	editing, it is often easier to use one of the following escape
sequences than the binary character it represents:	sequences than the binary character it represents:

\a alarm, that is, the BEL character (hex 07)	\a alarm, that is, the BEL character (hex 07)
Line 4109 BACKSLASH	Line 4884 BACKSLASH
\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
	hex 7B (; is 3B). If the data item (byte or 16-bit value) following \c
has a value greater than 127, a compile-time error occurs. This locks	has a value greater than 127, a compile-time error occurs. This locks
out non-ASCII characters in all modes. (When PCRE is compiled in EBCDIC	out non-ASCII characters in all modes.
mode, all byte values are valid. A lower case letter is converted to
upper case, and then the 0xc0 bits are flipped.)

	The \c facility was designed for use with ASCII characters, but with
	the extension to Unicode it is even less useful than it once was. It
	is, however, recognized when PCRE is compiled in EBCDIC mode, where
	data items are always bytes. In this mode, all values are valid after
	\c. If the next character is a lower case letter, it is converted to
	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.

By default, after \x, from zero to two hexadecimal digits are read	By default, after \x, from zero to two hexadecimal digits are read
(letters can be in upper or lower case). Any number of hexadecimal dig-	(letters can be in upper or lower case). Any number of hexadecimal dig-
its may appear between \x{ and }, but the character code is constrained	its may appear between \x{ and }, but the character code is constrained
Line 4127 BACKSLASH	Line 4911 BACKSLASH
8-bit UTF-8 mode less than 0x10ffff and a valid codepoint	8-bit UTF-8 mode less than 0x10ffff and a valid codepoint
16-bit non-UTF mode less than 0x10000	16-bit non-UTF mode less than 0x10000
16-bit UTF-16 mode less than 0x10ffff and a valid codepoint	16-bit UTF-16 mode less than 0x10ffff and a valid codepoint
	32-bit non-UTF mode less than 0x80000000
	32-bit UTF-32 mode less than 0x10ffff and a valid codepoint

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

If characters other than hexadecimal digits appear between \x{ and },	If characters other than hexadecimal digits appear between \x{ and },
or if there is no terminating }, this form of escape is not recognized.	or if there is no terminating }, this form of escape is not recognized.
Line 4172 BACKSLASH	Line 4958 BACKSLASH
value of the character is constrained in the same way as characters	value of the character is constrained in the same way as characters
specified in hexadecimal. For example:	specified in hexadecimal. For 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 4292 BACKSLASH	Line 5078 BACKSLASH
codepoints, whether or not PCRE_UCP is set. The horizontal space char-	codepoints, whether or not PCRE_UCP is set. The horizontal space char-
acters are:	acters 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 4314 BACKSLASH	Line 5100 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 Form feed	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

Line 4367 BACKSLASH	Line 5153 BACKSLASH

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

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

Unicode character properties	Unicode character properties

Line 4382 BACKSLASH	Line 5168 BACKSLASH

\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 4485 BACKSLASH	Line 5271 BACKSLASH
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 Unicode strings and	U+D800 to U+DFFF. Such characters are not valid in Unicode strings and
so cannot be tested by PCRE, unless UTF validity checking has been	so cannot be tested by PCRE, unless UTF validity checking has been
turned off (see the discussion of PCRE_NO_UTF8_CHECK and	turned off (see the discussion of PCRE_NO_UTF8_CHECK,
PCRE_NO_UTF16_CHECK in the pcreapi page). Perl does not support the Cs	PCRE_NO_UTF16_CHECK and PCRE_NO_UTF32_CHECK in the pcreapi page). Perl
property.	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
Line 4498 BACKSLASH	Line 5284 BACKSLASH
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} alw For example, \p{Lu} alw
	different from the behaviour of current versions of Perl.

	Matching characters by Unicode property is not fast, because PCRE has
	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	The \X escape matches any number of Unicode characters that form an
extended Unicode sequence. \X is equivalent to	"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 8-bit 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 or by starting the pat-
tern 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 and POSIX character classes to use Unicode
to use Unicode properties. PCRE uses these non-standard, non-Perl prop-	properties. PCRE uses these non-standard, non-Perl properties inter-
erties internally when PCRE_UCP is set. They are:	nally when PCRE_UCP is set. However, 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,
form feed, 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, except that vertical tab
is excluded. Xwd matches the same characters as Xan, plus underscore.	is excluded. 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 4580 BACKSLASH	Line 5405 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 a	string if the first or last character matches \w, respectively. In a
UTF 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 4710 MATCHING A SINGLE DATA UNIT	Line 5540 MATCHING A SINGLE DATA UNIT

Outside a character class, the escape sequence \C matches any one data	Outside a character class, the escape sequence \C matches any one data
unit, whether or not a UTF mode is set. In the 8-bit library, one data	unit, whether or not a UTF mode is set. In the 8-bit library, one data
unit is one byte; in the 16-bit library it is a 16-bit unit. Unlike a	unit is one byte; in the 16-bit library it is a 16-bit unit; in the
dot, \C always matches line-ending characters. The feature is provided	32-bit library it is a 32-bit unit. Unlike a dot, \C always matches
in Perl in order to match individual bytes in UTF-8 mode, but it is	line-ending characters. The feature is provided in Perl in order to
unclear how it can usefully be used. Because \C breaks up characters	match individual bytes in UTF-8 mode, but it is unclear how it can use-
into individual data units, matching one unit with \C in a UTF mode	fully be used. Because \C breaks up characters into individual data
means that the rest of the string may start with a malformed UTF char-	units, matching one unit with \C in a UTF mode means that the rest of
acter. This has undefined results, because PCRE assumes that it is	the string may start with a malformed UTF character. This has undefined
dealing with valid UTF strings (and by default it checks this at the	results, because PCRE assumes that it is dealing with valid UTF strings
start of processing unless the PCRE_NO_UTF8_CHECK or	(and by default it checks this at the start of processing unless the
PCRE_NO_UTF16_CHECK option is used).	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 a UTF 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. However, one way of	In general, the \C escape sequence is best avoided. However, one way of
using it that avoids the problem of malformed UTF characters is to use	using it that avoids the problem of malformed UTF characters is to use
a lookahead to check the length of the next character, as in this pat-	a lookahead to check the length of the next character, as in this pat-
tern, which could be used with a UTF-8 string (ignore white space and	tern, which could be used with a UTF-8 string (ignore white space and
line breaks):	line breaks):

(?\| (?=[\x00-\x7f])(\C) \|	(?\| (?=[\x00-\x7f])(\C) \|
Line 4736 MATCHING A SINGLE DATA UNIT	Line 5567 MATCHING A SINGLE DATA UNIT
(?=[\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 4750 SQUARE BRACKETS AND CHARACTER CLASSES	Line 5581 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 a UTF	A character class matches a single character in the subject. In a UTF
mode, the character may be more than one data unit long. A matched	mode, the character may be more than one data unit long. A matched
character must be in the set of characters defined by the class, unless	character must be in the set of characters defined by the class, unless
the first character in the class definition is a circumflex, in which	the first character in the class definition is a circumflex, in which
case the subject character must not be in the set defined by the class.	case the subject character must not be in the set defined by the class.
If a circumflex is actually required as a member of the class, ensure	If a circumflex is actually required as a member of the class If a circumflex is actually required as a member of the class
it is 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 (UTF-16) mode, characters with values greater than 255	In UTF-8 (UTF-16, UTF-32) mode, characters with values greater than 255
(0xffff) can be included in a class as a literal string of data units,	(0xffff) can be included in a class as a literal string of data units,
or by using the \x{ escaping 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 a UTF 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 a UTF 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 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.

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.

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]. Ranges can include any characters that are valid for the	[\000-\037]. Ranges can include any characters that are valid for the
current mode.	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 a non-UTF 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 modes, 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 modes, 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
meaning inside a character class; it matches the backspace character.	meaning inside a character class; it matches the backspace character.
The sequences \B, \N, \R, and \X are not special inside a character	The sequences \B, \N, \R, and \X are not special inside a character
class. Like any other unrecognized escape sequences, they are treated	class. Like any other unrecognized escape sequences, they are treated
as the literal characters "B", "N", "R", and "X" by default, but cause	as the literal characters "B", "N", "R", and "X" by default, but cause
an error if the PCRE_EXTRA option is set.	an error if the PCRE_EXTRA option is set.

A circumflex can conveniently be used with the upper case character	A circumflex can conveniently be used with the upper case character
types to specify a more restricted set of characters than the matching	types to specify a more restricted set of characters than the matching
lower case type. For example, the class [^\W_] matches any letter or	lower case type. For example, the class [^\W_] matches any letter or
digit, but not underscore, whereas [\w] includes underscore. A positive	digit, but not underscore, whereas [\w] includes underscore. A positive
character class should be read as "something OR something OR ..." and a	character class should be read as "something OR something OR ..." and a
negative class as "NOT something AND NOT something AND NOT ...".	negative class as "NOT something AND NOT something AND NOT ...".

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 - see the
next section), and the terminating closing square bracket. However,	next section), and the terminating closing square bracket. However,
escaping other non-alphanumeric characters does no harm.	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 4875 POSIX CHARACTER CLASSES	Line 5706 POSIX CHARACTER CLASSES
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 "space" characters are HT (9), LF (10), VT (11), FF (12), CR (13),
and space (32). Notice that this list includes the VT character (code	and space (32). Notice that this list includes the VT character (code
11). This makes "space" different to \s, which does not include VT (for	11). This makes "space" different to \s, which does not include VT (for
Perl compatibility).	Perl compatibility).

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
by a ^ character after the colon. For example,	by a ^ character after the colon. For example,

[12[:^digit:]]	[12[:^digit:]]

matches "1", "2", or any non-digit. PCRE (and Perl) also recognize the	matches "1", "2", or any non-digit. PCRE (and Perl) also recognize the
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 modes, characters with values greater than 128 do	By default, in UTF modes, characters with values greater than 128 do
not match any of the POSIX character classes. However, if the PCRE_UCP	not match any of the POSIX character classes. However, if the PCRE_UCP
option is passed to pcre_compile(), some of the classes are changed so	option is passed to pcre_compile(), some of the classes are changed so
that Unicode character properties are used. This is achieved by replac-	that Unicode character properties are used. This is achieved by replac-
ing the POSIX classes by other sequences, as follows:	ing the POSIX classes by other sequences, as follows:

Line 4905 POSIX CHARACTER CLASSES	Line 5736 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. The other
POSIX classes are unchanged, and match only characters with code points	POSIX classes are unchanged, and match only characters with code points
less than 128.	less than 128.


VERTICAL BAR	VERTICAL BAR

Vertical bar characters are used to separate alternative patterns. For	Vertical bar characters are used to separate alternative patterns. For
example, the pattern	example, the pattern

gilbert\|sullivan	gilbert\|sullivan

matches either "gilbert" or "sullivan". Any number of alternatives may	matches either "gilbert" or "sullivan". Any number of alternatives may
appear, and an empty alternative is permitted (matching the empty	appear, and an empty alternative is permitted (matching the empty
string). The matching process tries each alternative in turn, from left	string). The matching process tries each alternative in turn, from left
to right, and the first one that succeeds is used. If the alternatives	to right, and the first one that succeeds is used. If the alternatives
are within a subpattern (defined below), "succeeds" means matching the	are within a subpattern (defined below), "succeeds" means matching the
rest of the main pattern as well as the alternative in the subpattern.	rest of the main pattern as well as the alternative in the subpattern.


INTERNAL OPTION SETTING	INTERNAL OPTION SETTING

The settings of the PCRE_CASELESS, PCRE_MULTILINE, PCRE_DOTALL, and	The settings of the PCRE_CASELESS, PCRE_MULTILINE, PCRE_DOTALL, and
PCRE_EXTENDED options (which are Perl-compatible) can be changed from	PCRE_EXTENDED options (which are Perl-compatible) can be changed from
within the pattern by a sequence of Perl option letters enclosed	within the pattern by a sequence of Perl option letters enclosed
between "(?" and ")". The option letters are	between "(?" and ")". The option letters are

i for PCRE_CASELESS	i for PCRE_CASELESS
Line 4939 INTERNAL OPTION SETTING	Line 5770 INTERNAL OPTION SETTING

For example, (?im) sets caseless, multiline matching. It is also possi-	For example, (?im) sets caseless, multiline matching. It is also possi-
ble to unset these options by preceding the letter with a hyphen, and a	ble to unset these options by preceding the letter with a hyphen, and a
combined setting and unsetting such as (?im-sx), which sets PCRE_CASE-	combined setting and unsetting such as (?im-sx), which sets PCRE_CASE-
LESS and PCRE_MULTILINE while unsetting PCRE_DOTALL and PCRE_EXTENDED,	LESS and PCRE_MULTILINE while unsetting PCRE_DOTALL and PCRE_EXTENDED,
is also permitted. If a letter appears both before and after the	is also permitted. If a letter appears both before and after the
hyphen, the option is unset.	hyphen, the option is unset.

The PCRE-specific options PCRE_DUPNAMES, PCRE_UNGREEDY, and PCRE_EXTRA	The PCRE-specific options PCRE_DUPNAMES, PCRE_UNGREEDY, and PCRE_EXTRA
can be changed in the same way as the Perl-compatible options by using	can be changed in the same way as the Perl-compatible options by using
the characters J, U and X respectively.	the characters J, U and X respectively.

When one of these option changes occurs at top level (that is, not	When one of these option changes occurs at top level (that is, not
inside subpattern parentheses), the change applies to the remainder of	inside subpattern parentheses), the change applies to the remainder of
the pattern that follows. If the change is placed right at the start of	the pattern that follows. If the change is placed right at the start of
a pattern, PCRE extracts it into the global options (and it will there-	a pattern, PCRE extracts it into the global options (and it will there-
fore show up in data extracted by the pcre_fullinfo() function).	fore show up in data extracted by the pcre_fullinfo() function).

An option change within a subpattern (see below for a description of	An option change within a subpattern (see below for a description of
subpatterns) affects only that part of the subpattern that follows it,	subpatterns) affects only that part of the subpattern that follows it,
so	so

(a(?i)b)c	(a(?i)b)c

matches abc and aBc and no other strings (assuming PCRE_CASELESS is not	matches abc and aBc and no other strings (assuming PCRE_CASELESS is not
used). By this means, options can be made to have different settings	used). By this means, options can be made to have different settings
in different parts of the pattern. Any changes made in one alternative	in different parts of the pattern. Any changes made in one alternative
do carry on into subsequent branches within the same subpattern. For	do carry on into subsequent branches within the same subpattern. For
example,	example,

(a(?i)b\|c)	(a(?i)b\|c)

matches "ab", "aB", "c", and "C", even though when matching "C" the	matches "ab", "aB", "c", and "C", even though when matching "C" the
first branch is abandoned before the option setting. This is because	first branch is abandoned before the option setting. This is because
the effects of option settings happen at compile time. There would be	the effects of option settings happen at compile time. There would be
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 compiling or matching functions are called. In	application when the compiling or matching functions are called. In
some cases the pattern can contain special leading sequences such as	some cases the pattern can contain special leading sequences such as
(*CRLF) to override what the application has set or what has been	(*CRLF) to override what the application has set or what has been
defaulted. Details are given in the section entitled "Newline	defaulted. Details are given in the section entitled "Newline
sequences" above. There are also the (UTF8), (UTF16), and (*UCP)	sequences" above. There are also the (UTF8), (UTF16),(*UTF32), and
leading sequences that can be used to set UTF and Unicode property	(*UCP) leading sequences that can be used to set UTF and Unicode prop-
modes; they are equivalent to setting the PCRE_UTF8, PCRE_UTF16, and	erty modes; they are equivalent to setting the PCRE_UTF8, PCRE_UTF16,
the PCRE_UCP options, respectively.	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 5196 REPETITION	Line 6030 REPETITION
In UTF modes, quantifiers apply to characters rather than to individual	In UTF modes, quantifiers apply to characters rather than to individual
data units. Thus, for example, \x{100}{2} matches two characters, each	data units. Thus, for example, \x{100}{2} matches two characters, each
of which is represented by a two-byte sequence in a UTF-8 string. Simi-	of which is represented by a two-byte sequence in a UTF-8 string. Simi-
larly, \X{3} matches three Unicode extended sequences, each of which	larly, \X{3} matches three Unicode extended grapheme clusters, each of
may be several data units long (and they may be of different lengths).	which may be several data units long (and they may be of different
	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-
ful for subpatterns that are referenced as subroutines from elsewhere	ful for subpatterns that are referenced as subroutin ful for subpatterns that are referenced as subroutines from elsewhere
in the pattern (but see also the section entitled "Defining subpatterns	in the pattern (but see also the section entitled "Defining subpatterns
for use by reference only" below). Items other than subpatterns that	for use by reference only" below). Items other than subpattern for use by reference only" below). Items other than subpattern
have a {0} quantifier are omitted from the compiled pattern.	have a {0} quantifier are omitted from the compiled pattern.

For convenience, the three most common quantifiers have single-charac-	For convenience, the three most common quantifiers have single-charac-
ter abbreviations:	ter abbreviations:

* is equivalent to {0,}	* is equivalent to {0,}
+ is equivalent to {1,}	+ is equivalent to {1,}
? is equivalent to {0,1}	? is equivalent to {0,1}

It is possible to construct infinite loops by following a subpattern	It is possible to construct infinite loops It is possible to construct infinite loops by following a subpattern
that can match no characters with a quantifier that has no upper limit,	that can match no characters with a quantifier that has no upper limit,
for example:	for example:

(a?)*	(a?)*

Earlier versions of Perl and PCRE used to give an error at compile time	Earlier versions of Perl and PCRE used to give an error at compile time
for such patterns. However, because there are cases where this can be	for such patterns. However, because there are cases where this can be
useful, such patterns are now accepted, but if any repetition of the	useful, such patterns are now accepted, but if any repetition of the
subpattern does in fact match no characters, the loop is forcibly bro-	subpattern does in fact match no characters, the loop is forcibly bro-
ken.	ken.

By default, the quantifiers are "greedy", that is, they match as much	By default, the quantifiers are "greedy", that is, they match as much
as possible (up to the maximum number of permitted times), without	as possible (up to the maximum number of permitted times), without
causing the rest of the pattern to fail. The classic example of where	causing the rest of the pattern to fail. The classic example of where
this gives problems is in trying to match comments in C programs. These	this gives problems is in trying to match comments in C programs. These
appear between /* and / and within the comment, individual and /	appear between /* and / and within the comment, individual and /
characters may appear. An attempt to match C comments by applying the	characters may appear. An attempt to match C comments by applying the
pattern	pattern

/\.\*/	/\.\*/
Line 5239 REPETITION	Line 6074 REPETITION

/* first comment / not comment / second comment */	/* first comment / not comment / second comment */

fails, because it matches the entire string owing to the greediness of	fails, because it matches the entire string owing to the greediness of
the .* item.	the .* item.

However, if a quantifier is followed by a question mark, it ceases to	However, if a quantifier is followed by a question mark, it ceases to
be greedy, and instead matches the minimum number of times possible, so	be greedy, and instead matches the minimum number of times possible, so
the pattern	the pattern

/\.?\*/	/\.?\*/

does the right thing with the C comments. The meaning of the various	does the right thing with the C comments. The meaning of the various
quantifiers is not otherwise changed, just the preferred number of	quantifiers is not otherwise changed, just the preferred number of
matches. Do not confuse this use of question mark with its use as a	matches. Do not confuse this use of question mark with its use as a
quantifier in its own right. Because it has two uses, it can sometimes	quantifier in its own right. Because it has two uses, it can sometimes
appear doubled, as in	appear doubled, as in

\d??\d	\d??\d
Line 5259 REPETITION	Line 6094 REPETITION
which matches one digit by preference, but can match two if that is the	which matches one digit by preference, but can match two if that is the
only way the rest of the pattern matches.	only way the rest of the pattern matches.

If the PCRE_UNGREEDY option is set (an option that is not available in	If the PCRE_UNGREEDY option is set (an option that is not available in
Perl), the quantifiers are not greedy by default, but individual ones	Perl), the quantifiers are not greedy by default, but individual ones
can be made greedy by following them with a question mark. In other	can be made greedy by following them with a question mark. In other
words, it inverts the default behaviour.	words, it inverts the default behaviour.

When a parenthesized subpattern is quantified with a minimum repeat	When a parenthesized subpattern is quantified with a minimum repeat
count that is greater than 1 or with a limited maximum, more memory is	count that is greater than 1 or with a limited maximum, more memory is
required for the compiled pattern, in proportion to the size of the	required for the compiled pattern, in proportion to the size of the
minimum or maximum.	minimum or maximum.

If a pattern starts with .* or .{0,} and the PCRE_DOTALL option (equiv-	If a pattern starts with .* or .{0,} and the PCRE_DOTALL option (equiv-
alent to Perl's /s) is set, thus allowing the dot to match newlines,	alent to Perl's /s) is set, thus allowing the dot to match newlines,
the pattern is implicitly anchored, because whatever follows will be	the pattern is implicitly anchored, because whatever follows will be
tried against every character position in the subject string, so there	tried against every character position in the subject string, so there
is no point in retrying the overall match at any position after the	is no point in retrying the overall match at any position after the
first. PCRE normally treats such a pattern as though it were preceded	first. PCRE normally treats such a pattern as though it were preceded
by \A.	by \A.

In cases where it is known that the subject string contains no new-	In cases where it is known that the subject string contains no new-
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:

(.*)abc\1	(.*)abc\1

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

Line 5545 ASSERTIONS	Line 6389 ASSERTIONS
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
side effect of capturing parentheses may occasionally be useful. In	side effect of capturing parentheses may occasionally be useful. In
practice, there only three cases:	practice, there only three cases:

(1) If the quantifier is {0}, the assertion is never obeyed during	(1) If the quantifier is {0}, the assertion is never obeyed during
matching. However, it may contain internal capturing parenthesized	matching. However, it may contain internal capturing parenthesized
groups that are called from elsewhere via the subroutine mechanism.	groups that are called from elsewhere via the subroutine mechanism.

(2) If quantifier is {0,n} where n is greater than zero, it is treated	(2) If quantifier is {0,n} where n is greater than zero, it is treated
as if it were {0,1}. At run time, the rest of the pattern match is	as if it were {0,1}. At run time, the rest of the pattern match is
tried with and without the assertion, the order depending on the greed-	tried with and without the assertion, the order depending on the greed-
iness of the quantifier.	iness of the quantifier.

(3) If the minimum repetition is greater than zero, the quantifier is	(3) If the minimum repetition is greater than zero, the quantifier is
ignored. The assertion is obeyed just once when encountered during	ignored. The assertion is obeyed just once when encountered during
matching.	matching.

Lookahead assertions	Lookahead assertions
Line 5572 ASSERTIONS	Line 6417 ASSERTIONS

\w+(?=;)	\w+(?=;)

matches a word followed by a semicolon, but does not include the semi-	matches a word followed by a semicolon, but does not include the semi-
colon in the match, and	colon in the match, and

foo(?!bar)	foo(?!bar)

matches any occurrence of "foo" that is not followed by "bar". Note	matches any occurrence of "foo" that is not followed by "bar". Note
that the apparently similar pattern	that the apparently similar pattern

(?!foo)bar	(?!foo)bar

does not find an occurrence of "bar" that is preceded by something	does not find an occurrence of "bar" that is preceded by something
other than "foo"; it finds any occurrence of "bar" whatsoever, because	other than "foo"; it finds any occurrence of "bar" whatsoever, because
the assertion (?!foo) is always true when the next three characters are	the assertion (?!foo) is always true when the next three characters are
"bar". A lookbehind assertion is needed to achieve the other effect.	"bar". A lookbehind assertion is needed to achieve the other effect.

If you want to force a matching failure at some point in a pattern, the	If you want to force a matching failure at some point in a pattern, the
most convenient way to do it is with (?!) because an empty string	most convenient way to do it is with (?!) because an empty string
always matches, so an assertion that requires there not to be an empty	always matches, so an assertion that requires there not to be an empty
string must always fail. The backtracking control verb (FAIL) or (F)	string must always fail. The backtracking control verb (FAIL) or (F)
is a synonym for (?!).	is a synonym for (?!).

Lookbehind assertions	Lookbehind assertions

Lookbehind assertions start with (?<= for positive assertions and (?<!	Lookbehind assertions start with (?<= for positive assertions and (?<!
for negative assertions. For example,	for negative assertions. For example,

(?<!foo)bar	(?<!foo)bar

does find an occurrence of "bar" that is not preceded by "foo". The	does find an occurrence of "bar" that is not preceded by "foo". The
contents of a lookbehind assertion are restricted such that all the	contents of a lookbehind assertion are restricted such that all the
strings it matches must have a fixed length. However, if there are sev-	strings it matches must have a fixed length. However, if there are sev-
eral top-level alternatives, they do not all have to have the same	eral top-level alternatives, they do not all have to have the same
fixed length. Thus	fixed length. Thus

(?<=bullock\|donkey)	(?<=bullock\|donkey)
Line 5612 ASSERTIONS	Line 6457 ASSERTIONS

(?<!dogs?\|cats?)	(?<!dogs?\|cats?)

causes an error at compile time. Branches that match different length	causes an error at compile time. Branches that match different length
strings are permitted only at the top level of a lookbehind assertion.	strings are permitted only at the top level of a lookbehind assertion.
This is an extension compared with Perl, which requires all branches to	This is an extension compared with Perl, which requires all branches to
match the same length of string. An assertion such as	match the same length of string. An assertion such as

(?<=ab(c\|de))	(?<=ab(c\|de))

is not permitted, because its single top-level branch can match two	is not permitted, because its single top-l is not permitted, because its single top-l
different lengths, but it is acceptable to PCRE if rewritten to use two	different lengths, but it is acceptable to PCRE if rewritten to use two
top-level branches:	top-level branches:

(?<=abc\|abde)	(?<=abc\|abde)

In some cases, the escape sequence \K (see above) can be used instead	In some cases, the escape sequence \K (see above) can In some cases, the escape sequence \K (see above) can be used instead
of a lookbehind assertion to get round the fixed-length restriction.	of a lookbehind assertion to get round the fixed-length restriction.

The implementation of lookbehind assertions is, for each alternative,	The implementation of lookbehind assertions is, for each alternative,
to temporarily move the current position back by the fixed length and	to temporarily move the current position back by the fixed length and
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 a UTF 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 data unit even in a UTF 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 data	hind. The \X and \R escapes, which can match different numbers of data
units, 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.
Recursion, however, is not supported.	Recursion, however, is not supported.

Possessive quantifiers can be used in conjunction with lookbehind	Possessive quantifiers can be used in conjunction with lookbehind
assertions to specify efficient matching of fixed-length strings at the	assertions to specify efficient matching of fixed-length strings at the
end of subject strings. Consider a simple pattern such as	end of subject strings. Consider a simple pattern such as

abcd$	abcd$

when applied to a long string that does not match. Because matching	when applied to a long string that does not match. Because matching
proceeds from left to right, PCRE will look for each "a" in the subject	proceeds from left to right, PCRE will look for each "a" in the subject
and then see if what follows matches the rest of the pattern. If the	and then see if what follows matches the rest of and then see if what follows matches the rest of the pattern. If the
pattern is specified as	pattern is specified as

^.*abcd$	^.*abcd$

the initial .* matches the entire string at first, but when this fails	the initial .* matches the entire string at first, but when this fails
(because there is no following "a"), it backtracks to match all but the	(because there is no following "a"), it backtracks to match all but the
last character, then all but the last two characters, and so on. Once	last character, then all but the last two characters, and so on. Once
again the search for "a" covers the entire string, from right to left,	again the search for "a" covers the entire string, from right to left,
so we are no better off. However, if the pattern is written as	so we are no better off. However, if the pattern is written as

^.*+(?<=abcd)	^.*+(?<=abcd)

there can be no backtracking for the .*+ item; it can match only the	there can be no backtracking for the .*+ item; it can match only the
entire string. The subsequent lookbehind assertion does a single test	entire string. The subsequent lookbehind assertion does a single test
on the last four characters. If it fails, the match fails immediately.	on the last four characters. If it fails, the match fails immediately.
For long strings, this approach makes a significant difference to the	For long strings, this approach makes a significant difference to the
processing time.	processing time.

Using multiple assertions	Using multiple assertions
Line 5676 ASSERTIONS	Line 6521 ASSERTIONS

(?<=\d{3})(?<!999)foo	(?<=\d{3})(?<!999)foo

matches "foo" preceded by three digits that are not "999". Notice that	matches "foo" preceded by three digits that are not "999". Notice that
each of the assertions is applied independently at the same point in	each of the assertions is applied independently at the same point in
the subject string. First there is a check that the previous three	the subject string. First there is a check that the previous three
characters are all digits, and then there is a check that the same	characters are all digits, and then there is a check that the same
three characters are not "999". This pattern does not match "foo" pre-	three characters are not "999". This pattern does not match "foo" pre-
ceded by six characters, the first of which are digits and the last	ceded by six characters, the first of which are digits and the last
three of which are not "999". For example, it doesn't match "123abc-	three of which are not "999". For example, it doesn't match "123abc-
foo". A pattern to do that is	foo". A pattern to do that is

(?<=\d{3}...)(?<!999)foo	(?<=\d{3}...)(?<!999)foo

This time the first assertion looks at the preceding six characters,	This time the first assertion looks at the preceding six characters,
checking that the first three are digits, and then the second assertion	checking that the first three are digits, and then the second assertion
checks that the preceding three characters are not "999".	checks that the preceding three characters are not "999".

Line 5695 ASSERTIONS	Line 6540 ASSERTIONS

(?<=(?<!foo)bar)baz	(?<=(?<!foo)bar)baz

matches an occurrence of "baz" that is preceded by "bar" which in turn	matches an occurrence of "baz" that is preceded by "bar" which in turn
is not preceded by "foo", while	is not preceded by "foo", while

(?<=\d{3}(?!999)...)foo	(?<=\d{3}(?!999)...)foo

is another pattern that matches "foo" preceded by three digits and any	is another pattern that matches "foo" preceded by three digits and any
three characters that are not "999".	three characters that are not "999".


CONDITIONAL SUBPATTERNS	CONDITIONAL SUBPATTERNS

It is possible to cause the matching process to obey a subpattern con-	It is possible to cause the matching process to obey a subpattern con-
ditionally or to choose between two alternative subpatterns, depending	ditionally or to choose between two alternative subpatterns, depending
on the result of an assertion, or whether a specific capturing subpat-	on the result of an assertion, or whether a specific capturing subpat-
tern has already been matched. The two possible forms of conditional	tern has already been matched. The two possible forms of conditional
subpattern are:	subpattern are:

(?(condition)yes-pattern)	(?(condition)yes-pattern)
(?(condition)yes-pattern\|no-pattern)	(?(condition)yes-pattern\|no-pattern)

If the condition is satisfied, the yes-pattern is used; otherwise the	If the condition is satisfied, the yes-pattern is used; otherwise the
no-pattern (if present) is used. If there are more than two alterna-	no-pattern (if present) is used. If there are more than two alterna-
tives in the subpattern, a compile-time error occurs. Each of the two	tives in the subpattern, a compile-time error occurs. Each of the two
alternatives may itself contain nested subpatterns of any form, includ-	alternatives may itself contain nested subpatterns of any form, includ-
ing conditional subpatterns; the restriction to two alternatives	ing conditional subpatterns; the restriction to two alternatives
applies only at the level of the condition. This pattern fragment is an	applies only at the level of the condition. This pattern fragment is an
Line 5726 CONDITIONAL SUBPATTERNS	Line 6571 CONDITIONAL SUBPATTERNS
(?(1) (A\|B\|C) \| (D \| (?(2)E\|F) \| E) )	(?(1) (A\|B\|C) \| (D \| (?(2)E\|F) \| E) )


There are four kinds of condition: references to subpatterns, refer-	There are four kinds of condition: references to subpatterns, refer-
ences to recursion, a pseudo-condition called DEFINE, and assertions.	ences to recursion, a pseudo-condition called DEFINE, and assertions.

Checking for a used subpattern by number	Checking for a used subpattern by number

If the text between the parentheses consists of a sequence of digits,	If the text between the parentheses consists of a sequence of digits,
the condition is true if a capturing subpattern of that number has pre-	the condition is true if a capturing subpattern of that number has pre-
viously matched. If there is more than one capturing subpattern with	viously matched. If there is more than one capturing subpattern with
the same number (see the earlier section about duplicate subpattern	the same number (see the earlier section about duplicate subpattern
numbers), the condition is true if any of them have matched. An alter-	numbers), the condition is true if any of them have matched. An alter-
native notation is to precede the digits with a plus or minus sign. In	native notation is to precede the digits with a plus or minus sign. In
this case, the subpattern number is relative rather than absolute. The	this case, the subpattern number is relative rather than absolute. The
most recently opened parentheses can be referenced by (?(-1), the next	most recently opened parentheses can be referenced by (?(-1), the next
most recent by (?(-2), and so on. Inside loops it can also make sense	most recent by (?(-2), and so on. Inside loops it can also make sense
to refer to subsequent groups. The next parentheses to be opened can be	to refer to subsequent groups. The next parentheses to be opened can be
referenced as (?(+1), and so on. (The value zero in any of these forms	referenced as (?(+1), and so on. (The value zero in any of these forms
is not used; it provokes a compile-time error.)	is not used; it provokes a compile-time error.)

Consider the following pattern, which contains non-significant white	Consider the following pattern, which contains non-significant white
space to make it more readable (assume the PCRE_EXTENDED option) and to	space to make it more readable (assume the PCRE_EXTENDED option) and to
divide it into three parts for ease of discussion:	divide it into three parts for ease of discussion:

( \( )? [^()]+ (?(1) \) )	( \( )? [^()]+ (?(1) \) )

The first part matches an optional opening parenthesis, and if that	The first part matches an optional opening parenthes The first part matches an optional opening parenthes
character is present, sets it as the first captured substring. The sec-	character is present, sets it as the first captured substring. The sec-
ond part matches one or more characters that are not parentheses. The	ond part matches one or more characters that are not parentheses. The
third part is a conditional subpattern that tests whether or not the	third part is a conditional subpattern that tests whether or not the
first set of parentheses matched. If they did, that is, if subject	first set of parentheses matched. If they did, that is, if subject
started with an opening parenthesis, the condition is true, and so the	started with an opening parenthesis, the condition is true, and so the
yes-pattern is executed and a closing parenthesis is required. Other-	yes-pattern is executed and a closing parenthesis is required. Other-
wise, since no-pattern is not present, the subpattern matches nothing.	wise, since no-pattern is not present, the subpattern matches nothing.
In other words, this pattern matches a sequence of non-parentheses,	In other words, this pattern matches a sequence of non-parentheses,
optionally enclosed in parentheses.	optionally enclosed in parentheses.

If you were embedding this pattern in a larger one, you could use a	If you were embedding this pattern in a larger one, you could use a
relative reference:	relative reference:

...other stuff... ( \( )? [^()]+ (?(-1) \) ) ...	...other stuff... ( \( )? [^()]+ (?(-1) \) ) ...

This makes the fragment independent of the parentheses in the larger	This makes the fragment independent of the parentheses in the larger
pattern.	pattern.

Checking for a used subpattern by name	Checking for a used subpattern by name

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. However, there is a possible ambiguity with this syn-
tax, because subpattern names may consist entirely of digits. PCRE	tax, because subpattern names may consist entirely of digits. PCRE
looks first for a named subpattern; if it cannot find one and the name	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-	consists entirely of digits, PCRE looks for a subpattern of that num-
ber, which must be greater than zero. Using subpattern names that con-	ber, which must be greater than zero. Using subpattern names that con-
sist entirely of digits is not recommended.	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 5800 CONDITIONAL SUBPATTERNS	Line 6645 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 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 white space 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 5853 COMMENTS	Line 6698 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
a compiling function or by a special sequence at the start of the pat-	a compiling function or by a special sequence at the start of the pat-
tern, as described in the section entitled "Newline conventions" above.	tern, as described in the section entitled "Newline conventions" above.
Note that the end of this type of comment is a literal newline sequence	Note that the end of this type of comment is a literal newline sequence
in the pattern; escape sequences that happen to represent a newline do	in the pattern; escape sequences that happen to represent a newline do
not count. For example, consider this pattern when PCRE_EXTENDED is	not count. For example, consider this pattern when PCRE_EXTENDED is
set, 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 5897 RECURSIVE PATTERNS	Line 6742 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 not want to recurse
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 t 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 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 pattern has to
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 6102 SUBPATTERNS AS SUBROUTINES	Line 6947 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 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 (8-bit library) or pcre16_callout (16-bit library). By	pcre_callout (8-bit library) or pcre[16\|32]_callout (16-bit or 32-bit
default, this variable contains NULL, which disables 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 6173 CALLOUTS	Line 7019 CALLOUTS

If the PCRE_AUTO_CALLOUT flag is passed to a compiling function, call-	If the PCRE_AUTO_CALLOUT flag is passed to a compiling function, call-
outs are automatically installed before each item in the pattern. They	outs are automatically installed before each item in the pattern. They
are all numbered 255.	are all number 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:

	(?(?C9)(?=a)abc\|def)

	Note that this applies only to assertion conditions, not to other types
	of condition.

During matching, when PCRE reaches a callout point, the external func-	During matching, when PCRE reaches a callout point, the external func-
tion is called. It is provided with the number of the callout, the	tion is called. It is provided with the number of the callout, the
position in the pattern, and, optionally, one item of data originally	position in the pattern, and, optionally, one item of data originally
Line 6187 CALLOUTS	Line 7041 CALLOUTS
BACKTRACKING CONTROL	BACKTRACKING CONTROL

Perl 5.10 introduced a number of "Special Backtracking Control Verbs",	Perl 5.10 introduced a number of "Special Backtracking Control Verbs",
which are described in the Perl documentation as "experimental and sub-	which are still described in the Perl documentation as "experimental
ject to change or removal in a future version of Perl". It goes on to	and subject to change or removal in a future version of Perl". It goes
say: "Their usage in production code should be noted to avoid problems	on to say: "Their usage in production code should be noted to avoid
during upgrades." The same remarks apply to the PCRE features described	problems during upgrades." The same remarks apply to the PCRE features
in this section.	described in this section.

Since these verbs are specifically related to backtracking, most of	The new verbs make use of what was previously invalid syntax: an open-
them can be used only when the pattern is to be matched using one of
the traditional matching functions, which use a backtracking algorithm.
With the exception of (*FAIL), which behaves like a failing negative
assertion, they cause an error if encountered by a DFA matching func-
tion.

If any of these verbs are used in an assertion or in a subpattern that
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 and
assertions is different in some cases.

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.
The maximum length of name is 255 in the 8-bit library and 65535 in the	The maximum length of name is 255 in the 8-bit library and 65535 in the
16-bit library. If the name is empty, that is, if the closing parenthe-	16-bit and 32-bit libraries. If the name is empty, that is, if the
sis immediately follows the colon, the effect is as if the colon were	closing parenthesis immediately follows the colon, the effect is as if
not there. Any number of these verbs may occur in a pattern.	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	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	There is more discussion of this option in the section entitled "Option
bits for pcre_exec()" in the pcreapi documentation.	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.

Verbs that act immediately	Verbs that act immediately

The following verbs act as soon as they are encountered. They may not	The following verbs act as soon as they are encountered. They may not
be followed by a name.	be followed by a name.

(*ACCEPT)	(*ACCEPT)

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-
tured by the outer parentheses.	tured by the outer parentheses.

(FAIL) or (F)	(FAIL) or (F)

This verb causes a matching failure, forcing backtracking to occur. It	This verb causes a matching failure, forcing backtracking to occur. It
is equivalent to (?!) but easier to read. The Perl documentation notes	is equivalent to (?!) but easier to read. The Perl documentation notes
that it is probably useful only when combined with (?{}) or (??{}).	that it is probably useful only when combined with (?{}) or (??{}).
Those are, of course, Perl features that are not present in PCRE. The	Those are, of course, Perl features that are not present in PCRE. The
nearest equivalent is the callout feature, as for example in this pat-	nearest equivalent is the callout feature, as for example in this pat-
tern:	tern:

a+(?C)(*FAIL)	a+(?C)(*FAIL)

A match with the string "aaaa" always fails, but the callout is taken	A match with the string "aaaa" always fails, but the callout is taken
before each backtrack happens (in this example, 10 times).	before each backtrack happens (in this example, 10 times).

Recording which path was taken	Recording which path was taken

There is one verb whose main purpose is to track how a match was	There is one verb whose main purpose is to track how a match was
arrived at, though it also has a secondary use in conjunction with	arrived at, though it also has a secondary use in conjunction with
advancing the match starting point (see (*SKIP) below).	advancing the match starting point (see (*SKIP) below).

(MARK:NAME) or (:NAME)	(MARK:NAME) or (:NAME)

A name is always required with this verb. There may be as many	A name is always required with this verb. There may be as many
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 as described in the section	(PRUNE:NAME), or (THEN:NAME) on the matching path is passed back to
entitled "Extra data for pcre_exec()" in the pcreapi documentation.	the caller as described in the section entitled "Extra data for
Here is an example of pcretest output, where the /K modifier requests	pcre_exec()" in the pcreapi documentation. Here is an example of
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 6299 BACKTRACKING CONTROL	Line 7153 BACKTRACKING CONTROL
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" in the subject. Subsequent	match attempt that started at the letter "X" in the subject. Subsequent
match attempts starting at "P" and then with an empty string do not get	match attempts starting at "P" and then with an empty string do not get
as far as the (*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	If you are interested in (*MARK) values after failed matches, you
should probably set the PCRE_NO_START_OPTIMIZE option (see above) to	should probably set the PCRE_NO_START_OPTIMIZE option (see above) to
ensure that the match is always attempted.	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

This matches "xxaab" but not "aacaab". It can be thought of as a kind	This matches "xxaab" but not "aacaab". It can be thought of as a kind
of dynamic anchor, or "I've started, so I must finish." The name of the	of dynamic anchor, or "I've started, so I must finish." The name of the
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.

	If there is more than one backtracking verb in a pattern, a different
	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	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	anchor, unless PCRE's start-of-match optimizations are turned off, as
shown in this pcretest example:	shown in this pcretest example:
Line 6369 BACKTRACKING CONTROL	Line 7233 BACKTRACKING CONTROL
(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
the pattern is unanchored, the "bumpalong" advance is not to the next	the pattern is unanchored, the "bumpalong" advance is not to the next
character, but to the position in the subject where (*SKIP) was encoun-	character, but to the position in the subject where (*SKIP) was encoun-
tered. (*SKIP) signifies that whatever text was matched leading up to	tered. (*SKIP) signifies that whatever text was matched leading up to
it cannot be part of a successful match. Consider:	it cannot be part of a successful match. Consider:

a+(*SKIP)b	a+(*SKIP)b

If the subject is "aaaac...", after the first match attempt fails	If the subject is "aaaac...", after the first match attempt fails
(starting at the first character in the string), the starting point	(starting at the first character in the string), the starting point
skips on to start the next attempt at "c". Note that a possessive quan-	skips on to start the next attempt at "c". Note that a possessive quan-
tifer does not have the same effect as this example; although it would	tifer does not have the same effect as this example; although it would
suppress backtracking during the first match attempt, the second	suppress backtracking during the first match attempt, the second
attempt would start at the second character instead of skipping on to	attempt would start at the second character instead of skipping on to
"c".	"c".

(*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
Line 6444 BACKTRACKING CONTROL	Line 7322 BACKTRACKING CONTROL
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:
Line 6468 BACKTRACKING CONTROL	Line 7346 BACKTRACKING CONTROL
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)
	cases 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).	pcre16(3), pcre32(3).


AUTHOR	AUTHOR
Line 6495 AUTHOR	Line 7435 AUTHOR

REVISION	REVISION

Last updated: 17 June 2012	Last updated: 26 April 2013
Copyright (c) 1997-2012 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-
Line 6553 CHARACTER TYPES	Line 7493 CHARACTER TYPES
\V a character that is not a vertical white space 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	In PCRE, by default, \d, \D, \s, \S, \w, and \W recognize only ASCII
characters, even in a UTF mode. However, this can be changed by setting	characters, even in a UTF mode. However, this can be changed by setting
Line 6613 PCRE SPECIAL CATEGORY PROPERTIES FOR \p and \P	Line 7553 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, 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


Line 6744 OPTION SETTING	Line 7686 OPTION SETTING
The following are recognized only at the start of a pattern or after	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: 8-bit library (PCRE_UTF8)	(*UTF8) set UTF-8 mode: 8-bit library (PCRE_UTF8)
(*UTF16) set UTF-16 mode: 16-bit library (PCRE_UTF16)	(*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)


Line 6835 BACKTRACKING CONTROL	Line 7781 BACKTRACKING CONTROL
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_...), (UTF8), (UTF16) 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 6873 AUTHOR	Line 7819 AUTHOR

REVISION	REVISION

Last updated: 10 January 2012	Last updated: 26 April 2013
Copyright (c) 1997-2012 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, UTF-16, 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.

From Release 8.30, in addition to its previous UTF-8 support, PCRE also
supports UTF-16 by means of a separate 16-bit library. This can be
built as well as, or instead of, the 8-bit library.


UTF-8 SUPPORT	UTF-8 SUPPORT

In order process UTF-8 strings, you must build PCRE's 8-bit library	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	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	the PCRE_UTF8 option flag, or the pattern must start with the sequence
(*UTF8). When either of these is the case, both the pattern and any	(UTF8) or (UTF). When either of these is the case, both the pattern
subject strings that are matched against it are treated as UTF-8	and any subject strings that are matched against it are treated as
strings instead of strings of 1-byte characters.	UTF-8 strings instead of strings of individual 1-byte characters.


UTF-16 SUPPORT	UTF-16 AND UTF-32 SUPPORT

In order process UTF-16 strings, you must build PCRE's 16-bit library	In order process UTF-16 or UTF-32 strings, you must build PCRE's 16-bit
with UTF support, and, in addition, you must call pcre16_compile() with	or 32-bit library with UTF support, and, in addition, you must call
the PCRE_UTF16 option flag, or the pattern must start with the sequence	pcre16_compile() or pcre32_compile() with the PCRE_UTF16 or PCRE_UTF32
(*UTF16). When either of these is the case, both the pattern and any	option flag, as appropriate. Alternatively, the pattern must start with
subject strings that are matched against it are treated as UTF-16	the sequence (UTF16), (UTF32), as appropriate, or (*UTF), which can
strings instead of strings of 16-bit characters.	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	UTF SUPPORT OVERHEAD

If you compile PCRE with UTF support, but do not use it at run time,	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	the library will be a bit bigger, but the additional run time overhead
is limited to testing the PCRE_UTF8/16 flag occasionally, so should not	is limited to testing the PCRE_UTF[8\|16\|32] flag occasionally, so
be very big.	should not be very big.


UNICODE PROPERTY SUPPORT	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 support), the escape sequences \p{..}, \P{..}, and \X can be used.	UTF support), the escape sequences \p{..}, \P{..}, and \X can be used.
The available properties that can be tested are limited to the general	The available properties that can be tested are limited to the general
category properties such as Lu for an upper case letter or Nd for a	category properties such as Lu for an upper case letter or Nd for a
decimal number, the Unicode script names such as Arabic or Han, and the	decimal number, the Unicode script names such as Arabic or Han, and the
derived properties Any and L&. A full list is given in the pcrepattern	derived properties Any and L&. Full lists is given in the pcrepattern
documentation. Only the short names for properties are supported. For	and pcresyntax documentation. Only the short names for properties are
example, \p{L} matches a letter. Its Perl synonym, \p{Letter}, is not	supported. For example, \p{L} matches a letter. Its Perl synonym,
supported. Furthermore, in Perl, many properties may optionally be	\p{Letter}, is not supported. Furthermore, in Perl, many properties
prefixed by "Is", for compatibility with Perl 5.6. PCRE does not sup-	may optionally be prefixed by "Is", for compatibility with Perl 5.6.
port this.	PCRE does not support this.

Validity of UTF-8 strings	Validity of UTF-8 strings

When you set the PCRE_UTF8 flag, the byte strings passed as patterns	When you set the PCRE_UTF8 flag, the byte strings passed as patterns
and subjects are (by default) checked for validity on entry to the rel-	and subjects are (by default) checked for validity on entry to the rel-
evant functions. The entire string is checked before any other process-	evant functions. The entire string is checked before any other process-
ing takes place. From release 7.3 of PCRE, the check is according the	ing takes place. From release 7.3 of PCRE, the check is according the
rules of RFC 3629, which are themselves derived from the Unicode speci-	rules of RFC 3629, which are themselves derived from the Unicode speci-
fication. Earlier releases of PCRE followed the rules of RFC 2279,	fication. Earlier releases of PCRE followed the rules of RFC 2279,
which allows the full range of 31-bit values (0 to 0x7FFFFFFF). The	which allows the full range of 31-bit values (0 to 0x7FFFFFFF). The
current check allows only values in the range U+0 to U+10FFFF, exclud-	current check allows only values in the range U+0 to U+10FFFF, exclud-
ing U+D800 to U+DFFF.	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 "Surrogate Area" of Unicode. They are	Characters in the "Surrogate Area" of Unicode are reserved for use by
reserved for use by UTF-16, where they are used in pairs to encode	UTF-16, where they are used in pairs to encode codepoints with values
codepoints with values greater than 0xFFFF. The code points that are	greater than 0xFFFF. The code points that are encoded by UTF-16 pairs
encoded by UTF-16 pairs are available independently in the UTF-8 encod-	are available independently in the UTF-8 and UTF-32 encodings. (In
ing. (In other words, the whole surrogate thing is a fudge for UTF-16	other words, the whole surrogate thing is a fudge for UTF-16 which
which unfortunately messes up UTF-8.)	unfortunately messes up UTF-8 and UTF-32.)

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 run-time 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, for example in the case of a long subject string that is being	mance, for example in the case of a long subject string that is being
scanned repeatedly with different patterns. If you set the	scanned repeatedly. If you set the PCRE_NO_UTF8_CHECK flag at compile
PCRE_NO_UTF8_CHECK flag at compile time or at run time, PCRE assumes	time or at run time, PCRE assumes that the pattern or subject it is
that the pattern or subject it is given (respectively) contains only	given (respectively) contains only valid UTF-8 codes. In this case, it
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()	this option to pcre_exec() or 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.

Validity of UTF-16 strings	Validity of UTF-16 strings

When you set the PCRE_UTF16 flag, the strings of 16-bit data units that	When you set the PCRE_UTF16 flag, the strings of 16-bit data units that
are passed as patterns and subjects are (by default) checked for valid-	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	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	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.	the surrogate range must be used in pairs in the correct manner.

If an invalid UTF-16 string is passed to PCRE, an error return is	If an invalid UTF-16 string is passed to PCRE, an error return is
given. At compile time, the only additional information is the offset	given. At compile time, the only additional information is the offset
to the first data unit of the failing character. The run-time functions	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	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.

	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_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.

	Validity of UTF-32 strings

	When you set the PCRE_UTF32 flag, the strings of 32-bit data units that
	are passed as patterns and subjects are (by default) checked for valid-
	ity on entry to the relevant functions. This check allows only values
	in the range U+0 to U+10FFFF, excluding the surrogate area U+D800 to
	U+DFFF.

	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	well as a more detailed reason code if the caller has provided memory
in which to do this.	in which to do 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_UTF16_CHECK flag at compile time or at	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-	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	tively) contains only valid UTF-32 sequences. In this case, it does not
diagnose an invalid UTF-16 string.	diagnose an invalid UTF-32 string. However, if an invalid string is
	passed, the result is undefined.

General comments about UTF modes	General comments about UTF modes

1. Codepoints less than 256 can be specified by either braced or	1. Codepoints less than 256 can be specified in patterns by either
unbraced hexadecimal escape sequences (for example, \x{b3} or \xb3).	braced or unbraced hexadecimal escape sequences (for example, \x{b3} or
Larger values have to use braced sequences.	\xb3). Larger values have to use braced sequences.

2. Octal numbers up to \777 are recognized, and in UTF-8 mode, they	2. Octal numbers up to \777 are recognized, and in UT 2. Octal numbers up to \777 are recognized, and in UT
match two-byte characters for values greater than \177.	match two-byte characters for values greater than \177.

3. Repeat quantifiers apply to complete UTF characters, not to individ-	3. Repeat quantifiers apply to complete UTF characters, not to individ-
ual data units, for example: \x{100}{3}.	ual data units, for example: \x{100}{3}.

4. The dot metacharacter matches one UTF character instead of a single	4. The dot metacharacter matches one UTF character instead of a single
data unit.	data unit.

5. The escape sequence \C can be used to match a single byte in UTF-8	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, but its use can lead	mode, or a single 16-bit data unit in UTF-16 mode, or a single 32-bit
to some strange effects because it breaks up multi-unit characters (see	data unit in UTF-32 mode, but its use can lead to some strange effects
the description of \C in the pcrepattern documentation). The use of \C	because it breaks up multi-unit characters (see the description of \C
is not supported in the alternative matching function	in the pcrepattern documentation). The use of \C is not supported in
pcre[16]_dfa_exec(), nor is it supported in UTF mode by the JIT opti-	the alternative matching function pcre[16\|32]_dfa_exec(), nor is it
mization of pcre[16]_exec(). If JIT optimization is requested for a UTF	supported in UTF mode by the JIT optimization of pcre[16\|32]_exec(). If
pattern that contains \C, it will not succeed, and so the matching will	JIT optimization is requested for a UTF pattern that contains \C, it
be carried out by the normal interpretive function.	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	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
Line 7056 UNICODE PROPERTY SUPPORT	Line 8022 UNICODE PROPERTY SUPPORT

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 7074 AUTHOR	Line 8038 AUTHOR

REVISION	REVISION

Last updated: 14 April 2012	Last updated: 27 February 2013
Copyright (c) 1997-2012 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
Line 7103 PCRE JUST-IN-TIME COMPILER SUPPORT	Line 8067 PCRE JUST-IN-TIME COMPILER SUPPORT
used. The code for this support was written by Zoltan Herczeg.	used. The code for this support was written by Zoltan Herczeg.


8-BIT and 16-BIT SUPPORT	8-BIT, 16-BIT AND 32-BIT SUPPORT

JIT support is available for both the 8-bit and 16-bit PCRE libraries.	JIT support is available for all of the 8-bit, 16-bit and 32-bit PCRE
To keep this documentation simple, only the 8-bit interface is	libraries. To keep this documentation simple, only the 8-bit interface
described in what follows. If you are using the 16-bit library, substi-	is described in what follows. If you are using the 16-bit library, sub-
tute the 16-bit functions and 16-bit structures (for example,	stitute the 16-bit functions and 16-bit structures (for example,
pcre16_jit_stack instead of pcre_jit_stack).	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
Line 7123 AVAILABILITY OF JIT SUPPORT	Line 8089 AVAILABILITY OF JIT SUPPORT
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	Power PC 32-bit and 64-bit
	SPARC 32-bit (experimental)

If --enable-jit is set on an unsupported platform, compilation fails.	If --enable-jit is set on an unsupported platform, compilation fails.

Line 7130 AVAILABILITY OF JIT SUPPORT	Line 8097 AVAILABILITY OF JIT SUPPORT
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 interpretive	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 7149 SIMPLE USE OF JIT	Line 8118 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 7168 SIMPLE USE OF JIT	Line 8138 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	PCRE_STUDY_JIT_COMPILE requests the JIT compiler to generate code for
complete matches. If you want to run partial matches using the	complete matches. If you want to run partial matches using the
PCRE_PARTIAL_HARD or PCRE_PARTIAL_SOFT options of pcre_exec(), you	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	should set one or both of the following options in addition to, or
instead of, PCRE_STUDY_JIT_COMPILE when you call pcre_study():	instead of, PCRE_STUDY_JIT_COMPILE when you call pcre_study():

PCRE_STUDY_JIT_PARTIAL_HARD_COMPILE	PCRE_STUDY_JIT_PARTIAL_HARD_COMPILE
PCRE_STUDY_JIT_PARTIAL_SOFT_COMPILE	PCRE_STUDY_JIT_PARTIAL_SOFT_COMPILE

The JIT compiler generates different optimized code for each of the	The JIT compiler generates different optimized code for each of the
three modes (normal, soft partial, hard partial). When pcre_exec() is	three modes (normal, soft partial, hard partial). When pcre_exec() is
called, the appropriate code is run if it is available. Otherwise, the	called, the appropriate code is run if it is available. Otherwise, the
pattern is matched using interpretive code.	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 etc. are	If JIT support is not available, PCRE_STUDY_JIT_COMPILE etc. are
ignored, and no JIT data is created. Otherwise, the compiled pattern is	ignored, and no JIT data is created. Otherwise, the compiled pattern is
passed to the JIT compiler, which turns it into machine code that exe-	passed to the JIT compiler, which turns it into machine code that exe-
cutes much faster than the normal interpretive code. When pcre_exec()	cutes much faster than the normal interpretive code. When pcre_exec()
is passed a pcre_extra block containing a pointer to JIT code of the	is passed a pcre_extra block containing a pointer to JIT code of the
appropriate mode (normal or hard/soft partial), it obeys that code	appropriate mode (normal or hard/soft partial), it obeys that code
instead of running the interpreter. The result is identical, but the	instead of running the interpreter. The result is identical, but the
compiled JIT code runs much faster.	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. If you want to know whether JIT was	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	actually used for a particular match, you should arrange for a JIT
callback function to be set up as described in the section entitled	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	"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	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	code is about to be obeyed. If the execution options are not right for
JIT execution, the callback function is not obeyed.	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 etc., or the JIT compiler was not able to	with PCRE_STUDY_JIT_COMPILE etc., or the JIT compiler was not able to
handle 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
Line 7220 SIMPLE USE OF JIT	Line 8190 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_NO_UTF16_CHECK, PCRE_NOTBOL, PCRE_NOTEOL,	PCRE_NO_UTF8_CHECK, PCRE_NO_UTF16_CHECK, PCRE_NO_UTF32_CHECK, PCRE_NOT-
PCRE_NOTEMPTY, PCRE_NOTEMPTY_ATSTART, PCRE_PARTIAL_HARD, and PCRE_PAR-	BOL, PCRE_NOTEOL, PCRE_NOTEMPTY, PCRE_NOTEMPTY_ATSTART, PCRE_PAR-
TIAL_SOFT.	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
(*PRUNE) )
(*SKIP) ) backtracking control verbs
(*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 of studying a patter The extra argument must be the result of studying a patter
PCRE_STUDY_JIT_COMPILE etc. 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:

Line 7313 CONTROLLING THE JIT STACK	Line 8277 CONTROLLING THE JIT STACK
return value must be a valid JIT stack, the result of calling	return value must be a valid JIT stack, the result of calling
pcre_jit_stack_alloc().	pcre_jit_stack_alloc().

A callback function is obeyed whenever JIT code is about to be run; it	A callback function is obeyed whenever JIT code is about to be run; it
is not obeyed when pcre_exec() is called with options that are incom-	is not obeyed when pcre_exec() is called with options that are incom-
patible for JIT execution. A callback function can therefore be used to	patible for JIT execution. A callback function can therefore be used to
determine whether a match operation was executed by JIT or by the	determine whether a match operation was executed by JIT or by the
interpreter.	interpreter.

You may safely use the same JIT stack for more than one pattern (either	You may safely use the same JIT stack for more than one pattern (either
by assigning directly or by callback), as long as the patterns are all	by assigning directly or by callback), as long as the patterns are all
matched sequentially in the same thread. In a multithread application,	matched sequentially in the same thread. In a multithread application,
if you do not specify a JIT stack, or if you assign or pass back NULL	if you do not specify a JIT stack, or if you assign or pass back NULL
from a callback, that is thread-safe, because each thread has its own	from a callback, that is thread-safe, because each thread has its own
machine stack. However, if you assign or pass back a non-NULL JIT	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	stack, this must be a different stack for each thread so that the
application is thread-safe.	application is thread-safe.

Strictly speaking, even more is allowed. You can assign the same non-	Strictly speaking, even more is allowed. You can assign the same non-
NULL stack to any number of patterns as long as they are not used for	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	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	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,	in the callback to wait until the stack is available for use. However,
this is an inefficient solution, and not recommended.	this is an inefficient solution, and not recommended.

This is a suggestion for how a multithreaded program that needs to set	This is a suggestion for how a multithreaded program that needs to set
up non-default JIT stacks might operate:	up non-default JIT stacks might operate:

During thread initalization	During thread initalization
Line 7347 CONTROLLING THE JIT STACK	Line 8311 CONTROLLING THE JIT STACK
Use a one-line callback function	Use a one-line callback function
return thread_local_var	return thread_local_var

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 etc.	result of a successful study with PCRE_STUDY_JIT_COMPILE etc.


Line 7357 JIT STACK FAQ	Line 8321 JIT STACK FAQ

(1) Why do we need JIT stacks?	(1) Why do we need JIT stacks?

PCRE (and JIT) is a recursive, depth-first engine, so it needs a stack	PCRE (and JIT) is a recursive, depth-first engine, so it needs a stack
where the local data of the current node is pushed before checking its	where the local data of the current node is pushed before checking its
child nodes. Allocating real machine stack on some platforms is diffi-	child nodes. Allocating real machine stack on some platforms is diffi-
cult. For example, the stack chain needs to be updated every time if we	cult. For example, the stack chain needs to be updated every time if we
extend the stack on PowerPC. Although it is possible, its updating	extend the stack on PowerPC. Although it is possible, its updating
time overhead decreases performance. So we do the recursion in memory.	time overhead decreases performance. So we do the recursion in memory.

(2) Why don't we simply allocate blocks of memory with malloc()?	(2) Why don't we simply allocate blocks of memory with malloc()?

Modern operating systems have a nice feature: they can reserve an	Modern operating systems have a nice feature: they can reserve an
address space instead of allocating memory. We can safely allocate mem-	address space instead of allocating memory. We can safely allocate mem-
ory pages inside this address space, so the stack could grow without	ory pages inside this address space, so the stack could grow without
moving memory data (this is important because of pointers). Thus we can	moving memory data (this is important because of pointers). Thus we can
allocate 1M address space, and use only a single memory page (usually	allocate 1M address space, and use only a single memory page (usually
4K) if that is enough. However, we can still grow up to 1M anytime if	4K) if that is enough. However, we can still grow up to 1M anytime if
needed.	needed.

(3) Who "owns" a JIT stack?	(3) Who "owns" a JIT stack?

The owner of the stack is the user program, not the JIT studied pattern	The owner of the stack is the user program, not the JIT studied pattern
or anything else. The user program must ensure that if a stack is used	or anything else. The user program must ensure that if a stack is used
by pcre_exec(), (that is, it is assigned to the pattern currently run-	by pcre_exec(), (that is, it is assigned to the pattern currently run-
ning), that stack must not be used by any other threads (to avoid over-	ning), that stack must not be used by any other threads (to avoid over-
writing the same memory area). The best practice for multithreaded pro-	writing the same memory area). The best practice for multithreaded pro-
grams is to allocate a stack for each thread, and return this stack	grams is to allocate a stack for each thread, and return this stack
through the JIT callback function.	through the JIT callback function.

(4) When should a JIT stack be freed?	(4) When should a JIT stack be freed?

You can free a JIT stack at any time, as long as it will not be used by	You can free a JIT stack at any time, as long as it will not be used by
pcre_exec() again. When you assign the stack to a pattern, only a	pcre_exec() again. When you assign the stack to a pattern, only a
pointer is set. There is no reference counting or any other magic. You	pointer is set. There is no reference counting or any other magic. You
can free the patterns and stacks in any order, anytime. Just do not	can free the patterns and stacks in any order, anytime. Just do not
call pcre_exec() with a pattern pointing to an already freed stack, as	call pcre_exec() with a pattern pointing to an already freed stack, as
that will cause SEGFAULT. (Also, do not free a stack currently used by	that will cause SEGFAULT. (Also, do not free a stack currently used by
pcre_exec() in another thread). You can also replace the stack for a	pcre_exec() in another thread). You can also replace the stack for a
pattern at any time. You can even free the previous stack before	pattern at any time. You can even free the previous stack before
assigning a replacement.	assigning a replacement.

(5) Should I allocate/free a stack every time before/after calling	(5) Should I allocate/free a stack every time before/after calling
pcre_exec()?	pcre_exec()?

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
until the stack is freed?	until the stack is freed?

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.

(7) This is too much of a headache. Isn't there any better solution for	(7) This is too much of a headache. Isn't there any better solution for
JIT stack handling?	JIT stack handling?

No, thanks to Windows. If POSIX threads were used everywhere, we could	No, thanks to Windows. If POSIX threads were used everywhere, we could
throw out this complicated API.	throw out this complicated API.


EXAMPLE CODE	EXAMPLE CODE

This is a single-threaded example that specifies a JIT stack without	This is a single-threaded example that specifies a JIT stack without
using a callback.	using a callback.

int rc;	int rc;
Line 7445 EXAMPLE CODE	Line 8409 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 7459 AUTHOR	Line 8451 AUTHOR

REVISION	REVISION

Last updated: 04 May 2012	Last updated: 17 March 2013
Copyright (c) 1997-2012 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 a match-	In normal use of PCRE, if the subject string that is passed to a match-
Line 7504 PARTIAL MATCHING IN PCRE	Line 8496 PARTIAL MATCHING IN PCRE
precedence.	precedence.

If you want to use partial matching with just-in-time optimized code,	If you want to use partial matching with just-in-time optimized code,
you must call pcre_study() or pcre16_study() with one or both of these	you must call pcre_study(), pcre16_study() or pcre32_study() with one
options:	or both of these options:

PCRE_STUDY_JIT_PARTIAL_SOFT_COMPILE	PCRE_STUDY_JIT_PARTIAL_SOFT_COMPILE
PCRE_STUDY_JIT_PARTIAL_HARD_COMPILE	PCRE_STUDY_JIT_PARTIAL_HARD_COMPILE
Line 7524 PARTIAL MATCHING IN PCRE	Line 8516 PARTIAL MATCHING IN PCRE
abled for partial matching.	abled for partial matching.


PARTIAL MATCHING USING pcre_exec() OR pcre16_exec()	PARTIAL MATCHING USING pcre_exec() OR pcre[16\|32]_exec()

A partial match occurs during a call to pcre_exec() or pcre16_exec()	A partial match occurs during a call to pcre_exec() or
when the end of the subject string is reached successfully, but match-	pcre[16\|32]_exec() when the end of the subject string is reached suc-
ing cannot continue because more characters are needed. However, at	cessfully, but matching cannot continue because more characters are
least one character in the subject must have been inspected. This char-	needed. However, at least one character in the subject must have been
acter need not form part of the final matched string; lookbehind asser-	inspected. This character need not form part of the final matched
tions and the \K escape sequence provide ways of inspecting characters	string; lookbehind assertions and the \K escape sequence provide ways
before the start of a matched substring. The requirement for inspecting	of inspecting characters before the start of a matched substring. The
at least one character exists because an empty string can always be	requirement for inspecting at least one character exists because an
matched; without such a restriction there would always be a partial	empty string can always be matched; without such a restriction there
match of an empty string 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 a partial	If there are at least two slots in the offsets vector when a partial
match is returned, the first slot is set to the offset of the earliest	match is returned, the first slot is set to the offset of the earliest
character that was inspected. For convenience, the second offset points	character that was inspected. For convenience, the second offset points
to the end of the subject so that a substring can easily be identified.	to the end of the subject 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() OR pcre16_exec()	PCRE_PARTIAL_SOFT WITH pcre_exec() OR pcre[16\|32]_exec()

If PCRE_PARTIAL_SOFT is set when pcre_exec() or pcre16_exec() identi-	If PCRE_PARTIAL_SOFT is set when pcre_exec() or pcre[16\|32]_exec()
fies a partial match, the partial match is remembered, but matching	identifies a partial match, the partial match is remembered, but match-
continues as normal, and other alternatives in the pattern are tried.	ing continues as normal, and other alternatives in the pattern are
If no complete match can be found, PCRE_ERROR_PARTIAL is returned	tried. If no complete match can be found, PCRE_ERROR_PARTIAL is
instead of 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() OR pcre16_exec()	PCRE_PARTIAL_HARD WITH pcre_exec() OR pcre[16\|32]_exec()

If PCRE_PARTIAL_HARD is set for pcre_exec() or pcre16_exec(),	If PCRE_PARTIAL_HARD is set for pcre_exec() or pcre[16\|32]_exec(),
PCRE_ERROR_PARTIAL is returned as soon as a partial match is found,	PCRE_ERROR_PARTIAL is returned as soon as a partial match is found,
without continuing to search for possible complete matches. This option	without continuing to search for possible complete matches. This option
is "hard" because it prefers an earlier partial match over a later com-	is "hard" because it prefers an earlier partial match over a later com-
plete match. For this reason, the assumption is made that the end of	plete match. For this reason, the assumption is made that the end of
the supplied subject string may not be the true end of the available	the supplied subject string may not be the true end of the available
data, and so, if \z, \Z, \b, \B, or $ are encountered at the end of the	data, and so, if \z, \Z, \b, \B, or $ are encountered at the end of the
subject, the result is PCRE_ERROR_PARTIAL, provided that at least one	subject, the result is PCRE_ERROR_PARTIAL, provided that at least one
character in the subject has been inspected.	character in the subject has been inspected.

Setting PCRE_PARTIAL_HARD also affects the way UTF-8 and UTF-16 subject	Setting PCRE_PARTIAL_HARD also affects the way UTF-8 and UTF-16 subject
strings are checked for validity. Normally, an invalid sequence causes	strings are checked for validity. Normally, an invalid sequence causes
the error PCRE_ERROR_BADUTF8 or PCRE_ERROR_BADUTF16. However, in the	the error PCRE_ERROR_BADUTF8 or PCRE_ERROR_BADUTF16. However, in the
special case of a truncated character at the end of the subject,	special case of a truncated character at the end of the subject,
PCRE_ERROR_SHORTUTF8 or PCRE_ERROR_SHORTUTF16 is returned when	PCRE_ERROR_SHORTUTF8 or PCRE_ERROR_SHORTUTF16 is returned when
PCRE_PARTIAL_HARD is set.	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 that is	In this case the result is always a complete match because that is
found first, and matching never continues after finding a complete	found first, and matching never continues after finding a complete
match. It might be easier to follow this explanation by thinking of the	match. It might be easier to follow this explanation by thinking of the
two patterns 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", because it will always	The second pattern will never match "dogsbody", because it will always
find the shorter match first.	find the shorter match first.


PARTIAL MATCHING USING pcre_dfa_exec() OR pcre16_dfa_exec()	PARTIAL MATCHING USING pcre_dfa_exec() OR pcre[16\|32]_dfa_exec()

The DFA functions move along the subject string character by character,	The DFA functions move along the subject string character by character,
without backtracking, searching for all possible matches simultane-	without backtracking, searching for all possible matches simultane-
ously. If the end of the subject is reached before the end of the pat-	ously. If the end of the subject is reached before the end of the pat-
tern, there is the possibility of a partial match, again provided that	tern, there is the possibility of a partial match, again provided 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 the DFA functions always search 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, their	there is no difference between greedy and ungreedy repetition, their
behaviour is different from the standard functions when PCRE_PAR-	behaviour is different from the standard functions when PCRE_PAR-
TIAL_HARD is set. Consider the string "dog" matched against the	TIAL_HARD is set. Consider the string "dog" matched against the
ungreedy pattern shown above:	ungreedy pattern shown above:

/dog(sbody)??/	/dog(sbody)??/

Whereas the standard functions stop as soon as they find the complete	Whereas the standard functions stop as soon as they find the complete
match for "dog", the DFA functions also find the partial match for	match for "dog", the DFA functions also find the partial match for
"dogsbody", and so return 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, normal matching carries on, and \b matches at the end of the	However, normal matching carries on, and \b matches at the end of the
subject when the last character is a letter, so a complete match is	subject when the last character is a letter, so a complete match is
found. The result, therefore, is not PCRE_ERROR_PARTIAL. Using	found. The result, therefore, is not PCRE_ERROR_PARTIAL. Using
PCRE_PARTIAL_HARD in this case does yield PCRE_ERROR_PARTIAL, because	PCRE_PARTIAL_HARD in this case does yield PCRE_ERROR_PARTIAL, because
then the partial match takes precedence.	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 can be requested for any pat-	longer apply, and partial matching with can be requested for any pat-
tern.	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
not conform to the restrictions, pcre_exec() returned the error code	not conform to the restrictions, pcre_exec() returned the error code
PCRE_ERROR_BADPARTIAL (-13). This error code is no longer in use. The	PCRE_ERROR_BADPARTIAL (-13). This error code is no longer in use. The
PCRE_INFO_OKPARTIAL call to pcre_fullinfo() to find out if a compiled	PCRE_INFO_OKPARTIAL call to pcre_fullinfo() to find out if a compiled
pattern can be used for partial matching now always returns 1.	pattern can be used for partial matching now always returns 1.


EXAMPLE OF PARTIAL MATCHING USING PCRETEST	EXAMPLE OF PARTIAL MATCHING USING PCRETEST

If the escape sequence \P is present in a pcretest data line, the	If the escape sequence \P is present in a pcretest data line, the
PCRE_PARTIAL_SOFT option is used for the match. Here is a run of	PCRE_PARTIAL_SOFT option is used for the match. Here is a run of
pcretest that uses the date example quoted above:	pcretest that uses the date example quoted above:

re> /^\d?\d(jan\|feb\|mar\|apr\|may\|jun\|jul\|aug\|sep\|oct\|nov\|dec)\d\d$/	re> /^\d?\d(jan\|feb\|mar\|apr\|may\|jun\|jul\|aug\|sep\|oct\|nov\|dec)\d\d$/
Line 7713 EXAMPLE OF PARTIAL MATCHING USING PCRETEST	Line 8710 EXAMPLE OF PARTIAL MATCHING USING PCRETEST
data> j\P	data> j\P
No match	No match

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 if DFA matching 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() OR pcre16_dfa_exec()	MULTI-SEGMENT MATCHING WITH pcre_dfa_exec() OR pcre[16\|32]_dfa_exec()

When a partial match has been found using a DFA matching function, it	When a partial match has been found using a DFA matching function, it
is possible to continue the match by providing additional subject data	is possible to continue the match by providing additional subject data
and calling the function 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 the DFA matching function):	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$/	re> /^\d?\d(jan\|feb\|mar\|apr\|may\|jun\|jul\|aug\|sep\|oct\|nov\|dec)\d\d$/
Line 7739 MULTI-SEGMENT MATCHING WITH pcre_dfa_exec() OR pcre16_	Line 8736 MULTI-SEGMENT MATCHING WITH pcre_dfa_exec() OR pcre16_
data> n05\R\D	data> n05\R\D
0: n05	0: n05

The first call has "23ja" as the subject, and requests partial match-	The first call has "23ja" as the subject, and requests partial match-
ing; the second call has "n05" as the subject for the continued	ing; the second call has "n05" as the subject for the continued
(restarted) match. Notice that when the match is complete, only the	(restarted) match. Notice that when the match is complete, only the
last part is shown; PCRE does not retain the previously partially-	last part is shown; PCRE does not retain the previously partially-
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.

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 the DFA	This facility can be used to pass very long subject strings to the DFA
matching functions.	matching functions.


MULTI-SEGMENT MATCHING WITH pcre_exec() OR pcre16_exec()	MULTI-SEGMENT MATCHING WITH pcre_exec() OR pcre[16\|32]_exec()

From release 8.00, the standard matching functions can also be used to	From release 8.00, the standard matching functions can also be used to
do multi-segment matching. Unlike the DFA functions, it is not possible	do multi-segment matching. Unlike the DFA functions, it is not possible
to restart the previous match with a new segment of data. Instead, new	to restart the previous match with a new segment of data. Instead, new
data must be added to the previous subject string, and the entire match	data must be added to the previous subject string, and the entire match
re-run, starting from the point where the partial match occurred. Ear-	re-run, starting from the point where the partial match occurred. Ear-
lier data can be discarded.	lier data can be discarded.

It is best to use PCRE_PARTIAL_HARD in this situation, because it does	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	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	\z, \Z, \b, \B, and $. Consider an unanchored pattern that matches
dates:	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 the matching function	add on text from the next segment, and call the matching function
again. Unlike the DFA matching functions, the entire matching string	again. Unlike the DFA matching functions, the entire matching string
must always be available, and the complete matching process occurs for	must always be available, and the complete matching process occurs for
each call, so more memory 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 includes	with \b or \B, the string that is returned for a partial match includes
characters that precede the partially matched string itself, because	characters that precede the start of what would be returned for a com-
these must be retained when adding on more characters for a subsequent	plete match, because it contains all the characters that were inspected
matching attempt. However, in some cases you may need to retain even	during the partial match.
earlier characters, as discussed in the next section.


ISSUES WITH MULTI-SEGMENT MATCHING	ISSUES WITH MULTI-SEGMENT MATCHING
Line 7800 ISSUES WITH MULTI-SEGMENT MATCHING	Line 8796 ISSUES WITH MULTI-SEGMENT MATCHING
hind assertion later in the pattern could require even earlier charac-	hind assertion later in the pattern could require even earlier charac-
ters to be inspected. You can handle this case by using the	ters to be inspected. You can handle this case by using the
PCRE_INFO_MAXLOOKBEHIND option of the pcre_fullinfo() or	PCRE_INFO_MAXLOOKBEHIND option of the pcre_fullinfo() or
pcre16_fullinfo() functions to obtain the length of the largest lookbe-	pcre[16\|32]_fullinfo() functions to obtain the length of the longest
hind in the pattern. This length is given in characters, not bytes. If	lookbehind in the pattern. This length is given in characters, not
you always retain at least that many characters before the partially	bytes. If you always retain at least that many characters before the
matched string, all should be well. (Of course, near the start of the	partially matched string, all should be well. (Of course, near the
subject, fewer characters may be present; in that case all characters	start of the subject, fewer characters may be present; in that case all
should be retained.)	characters should be retained.)

3. Because a partial match must always contain at least one character,	From release 8.33, there is a more accurate way of deciding which char-
what might be considered a partial match of an empty string actually	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:	gives a "no match" result. For example:

re> /c(?<=abc)x/	re> /c(?<=abc)x/
Line 7816 ISSUES WITH MULTI-SEGMENT MATCHING	Line 8833 ISSUES WITH MULTI-SEGMENT MATCHING
No match	No match

If the next segment begins "cx", a match should be found, but this will	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	only happen if characters from the previous segment are retained. For
this reason, a "no match" result should be interpreted as "partial	this reason, a "no match" result should be interpreted as "partial
match of an empty string" when the pattern contains lookbehinds.	match of an empty string" when the pattern contains lookbehinds.

4. Matching a subject string that is split into multiple segments may	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
arises if the pattern ends with \b or \B. Another kind of difference	arises if the pattern ends with \b or \B. Another kind of difference
may occur when there are multiple matching possibilities, because (for	may occur when there are multiple matching possibilities, because (for
PCRE_PARTIAL_SOFT) a partial match result is given only when there are	PCRE_PARTIAL_SOFT) a partial match result is given only when there are
no completed matches. This means that as soon as the shortest match has	no completed matches. This means that as soon as the shortest match has
been found, continuation to a new subject segment is no longer possi-	been found, continuation to a new subject segment is no longer possi-
ble. Consider again this pcretest example:	ble. Consider again this pcretest example:

re> /dog(sbody)?/	re> /dog(sbody)?/
Line 7842 ISSUES WITH MULTI-SEGMENT MATCHING	Line 8859 ISSUES WITH MULTI-SEGMENT MATCHING
0: dogsbody	0: dogsbody
1: dog	1: dog

The first data line passes the string "dogsb" to a standard matching	The first data line passes the string "dogsb" to a standard matching
function, setting the PCRE_PARTIAL_SOFT option. Although the string is	function, setting the PCRE_PARTIAL_SOFT option. Although the string is
a partial match for "dogsbody", the result is not PCRE_ERROR_PARTIAL,	a partial match for "dogsbody", the result is not PCRE_ERROR_PARTIAL,
because the shorter string "dog" is a complete match. Similarly, when	because the shorter string "dog" is a complete match. Similarly, when
the subject is presented to a DFA matching function in several parts	the subject is presented to a DFA matching function in several parts
("do" and "gsb" being the first two) the match stops when "dog" has	("do" and "gsb" being the first two) the match stops when "dog" has
been found, and it is not possible to continue. On the other hand, if	been found, and it is not possible to continue. On the other hand, if
"dogsbody" is presented as a single string, a DFA matching function	"dogsbody" is presented as a single string, a DFA matching function
finds both matches.	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 7865 ISSUES WITH MULTI-SEGMENT MATCHING	Line 8882 ISSUES WITH MULTI-SEGMENT MATCHING
Partial match: gsb	Partial match: gsb

5. 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. For example, consider this pattern:	PCRE_DFA_RESTART is used. For example, consider this pattern:

1234\|3789	1234\|3789

If the first part of the subject is "ABC123", a partial match of the	If the first part of the subject is "ABC123", a partial match of the
first alternative is found at offset 3. There is no partial match for	first alternative is found at offset 3. There is no partial match for
the second alternative, because such a match does not start at the same	the second alternative, because such a match does not start at the same
point in the subject string. Attempting to continue with the string	point in the subject string. Attempting to continue with the string
"7890" does not yield a match because only those alternatives that	"7890" does not yield a match because only those alternatives that
match at one point in the subject are remembered. The problem arises	match at one point in the subject are remembered. The problem arises
because the start of the second alternative matches within the first	because the start of the second alternative matches within the first
alternative. There is no problem with anchored patterns or patterns	alternative. There is no problem with anchored patterns or patterns
such as:	such as:

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 a standard matching function is used, because the	not a problem if a standard matching function is used, because the
entire match has to be rerun each time:	entire match has to be rerun each time:

re> /1234\|3789/	re> /1234\|3789/
Line 7893 ISSUES WITH MULTI-SEGMENT MATCHING	Line 8910 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 the DFA matching func-	running the entire match can also be used with the DFA matching func-
tions. Another possibility is to work with two buffers. If a partial	tions. Another possibility is to work with two buffers. If a partial
match at offset n in the first buffer is followed by "no match" when	match at offset n in the first buffer is followed by "no match" when
PCRE_DFA_RESTART is used on the second buffer, you can then try a new	PCRE_DFA_RESTART is used on the second buffer, you can then try a new
match starting at offset n+1 in the first buffer.	match starting at offset n+1 in the first buffer.


Line 7909 AUTHOR	Line 8926 AUTHOR

REVISION	REVISION

Last updated: 24 February 2012	Last updated: 20 February 2013
Copyright (c) 1997-2012 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 7934 SAVING AND RE-USING PRECOMPILED PCRE PATTERNS	Line 8951 SAVING AND RE-USING PRECOMPILED PCRE PATTERNS

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. If the two hosts have different endianness	ent host and run them there. If the two hosts have different endianness
(byte order), you should run the pcre[16]_pattern_to_host_byte_order()	(byte order), you should run the pcre[16\|32]_pat-
function on the new host before trying to match the pattern. The match-	tern_to_host_byte_order() function on the new host before trying to
ing functions return PCRE_ERROR_BADENDIANNESS if they detect a pattern	match the pattern. The matching functions return PCRE_ERROR_BADENDIAN-
with the wrong endianness.	NESS if they detect a pattern with the wrong endianness.

Compiling regular expressions with one version of PCRE for use with a	Compiling regular expressions with one version of PCRE for use with a
different version is not guaranteed to work and may cause crashes, and	different version is not guaranteed to work and may cause crashes, and
Line 7947 SAVING AND RE-USING PRECOMPILED PCRE PATTERNS	Line 8964 SAVING AND RE-USING PRECOMPILED PCRE PATTERNS

SAVING A COMPILED PATTERN	SAVING A COMPILED PATTERN

The value returned by pcre[16]_compile() points to a single block of	The value returned by pcre[16\|32]_compile() points to a single block of
memory that holds the compiled pattern and associated data. You can	memory that holds the compiled pattern and associated data. You can
find the length of this block in bytes by calling pcre[16]_fullinfo()	find the length of this block in bytes by calling
with an argument of PCRE_INFO_SIZE. You can then save the data in any	pcre[16\|32]_fullinfo() with an argument of PCRE_INFO_SIZE. You can then
appropriate manner. Here is sample code for the 8-bit library that com-	save the data in any appropriate manner. Here is sample code for the
piles a pattern and writes it to a file. It assumes that the variable	8-bit library that compiles a pattern and writes it to a file. It
fd refers to a file that is open for 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 7988 SAVING A COMPILED PATTERN	Line 9005 SAVING A COMPILED PATTERN
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,	ronment. When studying generates additional information,
pcre[16]_study() returns a pointer to a pcre[16]_extra data block. Its	pcre[16\|32]_study() returns a pointer to a pcre[16\|32]_extra data
format is defined in the section on matching a pattern in the pcreapi	block. Its format is defined in the section on matching a pattern in
documentation. The study_data field points to the binary study data,	the pcreapi documentation. The study_data field points to the binary
and this is what you must save (not the pcre[16]_extra block itself).	study data, and this is what you must save (not the pcre[16\|32]_extra
The length of the study data can be obtained by calling	block itself). The length of the study data can be obtained by calling
pcre[16]_fullinfo() with an argument of PCRE_INFO_STUDYSIZE. Remember	pcre[16\|32]_fullinfo() with an argument of PCRE_INFO_STUDYSIZE. Remem-
to check that pcre[16]_study() did return a non-NULL value before try-	ber to check that pcre[16\|32]_study() did return a non-NULL value
ing to save the study data.	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, called pcre[16]_pattern_to_host_byte_order() if nec-	into main memory, called pcre[16\|32]_pattern_to_host_byte_order() if
essary, you pass its pointer to pcre[16]_exec() or pcre[16]_dfa_exec()	necessary, you pass its pointer to pcre[16\|32]_exec() or
in the usual way.	pcre[16\|32]_dfa_exec() in the usual way.

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[16]_compile()), you	pattern was compiled (the tableptr argument of pcre[16\|32]_compile()),
must now pass a similar pointer to pcre[16]_exec() or	you must now pass a similar pointer to pcre[16\|32]_exec() or
pcre[16]_dfa_exec(), because the value saved with the compiled pattern	pcre[16\|32]_dfa_exec(), because the value saved with the compiled pat-
will obviously be nonsense. A field in a pcre[16]_extra() block is used	tern will obviously be nonsense. A field in a pcre[16\|32]_extra() block
to pass this data, as described in the section on matching a pattern in	is used to pass this data, as described in the section on matching a
the pcreapi documentation.	pattern in the pcreapi documentation.

If you did not provide custom character tables when the pattern was	If you did not provide custom character tables when the pattern was
compiled, the pointer in the compiled pattern is NULL, which causes the	compiled, the pointer in the compiled pattern is NULL, which causes the
Line 8019 RE-USING A PRECOMPILED PATTERN	Line 9036 RE-USING A PRECOMPILED PATTERN
to take any special action at run time in this case.	to 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 saved study data with the compiled pattern, you need to create
your own pcre[16]_extra data block and set the study_data field to	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	point to the reloaded study data. You must also set the
PCRE_EXTRA_STUDY_DATA bit in the flags field to indicate that study	PCRE_EXTRA_STUDY_DATA bit in the flags field to indicate that study
data is present. Then pass the pcre[16]_extra block to the matching	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	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	optimization, that data cannot be saved, and so is lost by a
save/restore cycle.	save/restore cycle.
Line 8044 AUTHOR	Line 9061 AUTHOR

REVISION	REVISION

Last updated: 10 January 2012	Last updated: 24 June 2012
Copyright (c) 1997-2012 University of Cambridge.	Copyright (c) 1997-2012 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 8115 COMPILED PATTERN MEMORY USAGE	Line 9132 COMPILED PATTERN MEMORY USAGE

STACK USAGE AT RUN TIME	STACK USAGE AT RUN TIME

When pcre_exec() or pcre16_exec() is used for matching, certain kinds	When pcre_exec() or pcre[16\|32]_exec() is used for matching, certain
of pattern can cause it to use large amounts of the process stack. In	kinds of pattern can cause it to use large amounts of the process
some environments the default process stack is quite small, and if it	stack. In some environments the default process stack is quite small,
runs out the result is often SIGSEGV. This issue is probably the most	and if it runs out the result is often SIGSEGV. This issue is probably
frequently raised problem with PCRE. Rewriting your pattern can often	the most frequently raised problem with PCRE. Rewriting your pattern
help. The pcrestack documentation discusses this issue in detail.	can often help. The pcrestack documentation discusses this issue in
	detail.


PROCESSING TIME	PROCESSING TIME

Certain items in regular expression patterns are processed more effi-	Certain items in regular expression patterns are processed more effi-
ciently than others. It is more efficient to use a character class like	ciently than others. It is more efficient to use a character class like
[aeiou] than a set of single-character alternatives such as	[aeiou] than a set of single-character alternatives such as
(a\|e\|i\|o\|u). In general, the simplest construction that provides the	(a\|e\|i\|o\|u). In general, the simplest construction that provides the
required behaviour is usually the most efficient. Jeffrey Friedl's book	required behaviour is usually the most efficient. Jeffrey Friedl's book
contains a lot of useful general discussion about optimizing regular	contains a lot of useful general discussion about optimizing regular
expressions for efficient performance. This document contains a few	expressions for efficient performance. This document contains a few
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,
Line 8214 AUTHOR	Line 9231 AUTHOR

REVISION	REVISION

Last updated: 09 January 2012	Last updated: 25 August 2012
Copyright (c) 1997-2012 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 OF POSIX API	SYNOPSIS OF POSIX API

#include <pcreposix.h>	#include <pcreposix.h>
Line 8247 DESCRIPTION	Line 9264 DESCRIPTION
This set of functions provides a POSIX-style API for the PCRE regular	This set of functions provides a POSIX-style API for the PCRE regular
expression 8-bit library. See the pcreapi documentation for a descrip-	expression 8-bit library. See the pcreapi documentation for a descrip-
tion of PCRE's native API, which contains much additional functional-	tion of PCRE's native API, which contains much additional functional-
ity. There is no POSIX-style wrapper for PCRE's 16-bit library.	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
pcreposix.h header file, and on Unix systems the library itself is	pcreposix.h header file, and on Unix systems the library itself is
called pcreposix.a, so can be accessed by adding -lpcreposix to the	called pcreposix.a, so can be accessed by adding -lpcreposix to the
command for linking an application that uses them. Because the POSIX	command for linking an application that uses them. Because the POSIX
functions call the native ones, it is also necessary to add -lpcre.	functions call the native ones, it is also necessary to add -lpcre.

I have implemented only those POSIX option bits that can be reasonably	I have implemented only those POSIX option bits that can be reasonably
mapped to PCRE native options. In addition, the option REG_EXTENDED is	mapped to PCRE native options. In addition, the option REG_EXTENDED is
defined with the value zero. This has no effect, but since programs	defined with the value zero. This has no effect, but since programs
that are written to the POSIX interface often use it, this makes it	that are written to the POSIX interface often use it, this makes it
easier to slot in PCRE as a replacement library. Other POSIX options	easier to slot in PCRE as a replacement library. Other POSIX options
are not even defined.	are not even defined.

There are also some other options that are not defined by POSIX. These	There are also some other options that are not defined by POSIX. These
have been added at the request of users who want to make use of certain	have been added at the request of users who want to make use of certain
PCRE-specific features via the POSIX calling interface.	PCRE-specific features via the POSIX calling interface.

When PCRE is called via these functions, it is only the API that is	When PCRE is called via these functions, it is only the API that is
POSIX-like in style. The syntax and semantics of the regular expres-	POSIX-like in style. The syntax and semantics of the regular expres-
sions themselves are still those of Perl, subject to the setting of	sions themselves are still those of Perl, subject to the setting of
various PCRE options, as described below. "POSIX-like in style" means	various PCRE options, as described below. "POSIX-like in style" means
that the API approximates to the POSIX definition; it is not fully	that the API approximates to the POSIX definition; it is not fully
POSIX-compatible, and in multi-byte encoding domains it is probably	POSIX-compatible, and in multi-byte encoding domains it is probably
even less compatible.	even less compatible.

The header for these functions is supplied as pcreposix.h to avoid any	The header for these functions is supplied as pcreposix.h to avoid any
potential clash with other POSIX libraries. It can, of course, be	potential clash with other POSIX libraries. It can, of course, be
renamed or aliased as regex.h, which is the "correct" name. It provides	renamed or aliased as regex.h, which is the "correct" name. It provides
two structure types, regex_t for compiled internal forms, and reg-	two structure types, regex_t for compiled internal forms, and reg-
match_t for returning captured substrings. It also defines some con-	match_t for returning captured substrings. It also defines some con-
stants whose names start with "REG_"; these are used for setting	stants whose names start with "REG_"; these are used for setting
options and identifying error codes.	options and identifying error codes.


COMPILING A PATTERN	COMPILING A PATTERN

The function regcomp() is called to compile a pattern into an internal	The function regcomp() is called to compile a pattern into an internal
form. The pattern is a C string terminated by a binary zero, and is	form. The pattern is a C string terminated by a binary zero, and is
passed in the argument pattern. The preg argument is a pointer to a	passed in the argument pattern. The preg argument is a pointer to a
regex_t structure that is used as a base for storing information about	regex_t structure that is used as a base for storing information about
the compiled regular expression.	the compiled regular expression.

The argument cflags is either zero, or contains one or more of the bits	The argument cflags is either zero, or contains one or more of the bits
Line 8303 COMPILING A PATTERN	Line 9321 COMPILING A PATTERN

REG_ICASE	REG_ICASE

The PCRE_CASELESS option is set when the regular expression is passed	The PCRE_CASELESS option is set when the regular expression is passed
for compilation to the native function.	for compilation to the native function.

REG_NEWLINE	REG_NEWLINE

The PCRE_MULTILINE option is set when the regular expression is passed	The PCRE_MULTILINE option is set when the regular expression is passed
for compilation to the native function. Note that this does not mimic	for compilation to the native function. Note that this does not mimic
the defined POSIX behaviour for REG_NEWLINE (see the following sec-	the defined POSIX behaviour for REG_NEWLINE (see the following sec-
tion).	tion).

REG_NOSUB	REG_NOSUB

The PCRE_NO_AUTO_CAPTURE option is set when the regular expression is	The PCRE_NO_AUTO_CAPTURE option is set when the regular expression is
passed for compilation to the native function. In addition, when a pat-	passed for compilation to the native function. In addition, when a pat-
tern that is compiled with this flag is passed to regexec() for match-	tern that is compiled with this flag is passed to regexec() for match-
ing, the nmatch and pmatch arguments are ignored, and no captured	ing, the nmatch and pmatch arguments are ignored, and no captured
strings are returned.	strings are returned.

REG_UCP	REG_UCP

The PCRE_UCP option is set when the regular expression is passed for	The PCRE_UCP option is set when the regular expression is passed for
compilation to the native function. This causes PCRE to use Unicode	compilation to the native function. This causes PCRE to use Unicode
properties when matchine \d, \w, etc., instead of just recognizing	properties when matchine \d, \w, etc., instead of just recognizing
ASCII values. Note that REG_UTF8 is not part of the POSIX standard.	ASCII values. Note that REG_UTF8 is not part of the POSIX standard.

REG_UNGREEDY	REG_UNGREEDY

The PCRE_UNGREEDY option is set when the regular expression is passed	The PCRE_UNGREEDY option is set when the regular expression is passed
for compilation to the native function. Note that REG_UNGREEDY is not	for compilation to the native function. Note that REG_UNGREEDY is not
part of the POSIX standard.	part of the POSIX standard.

REG_UTF8	REG_UTF8

The PCRE_UTF8 option is set when the regular expression is passed for	The PCRE_UTF8 option is set when the regular expression is passed for
compilation to the native function. This causes the pattern itself and	compilation to the native function. This causes the pattern itself and
all data strings used for matching it to be treated as UTF-8 strings.	all data strings used for matching it to be treated as UTF-8 strings.
Note that REG_UTF8 is not part of the POSIX standard.	Note that REG_UTF8 is not part of the POSIX standard.

In the absence of these flags, no options are passed to the native	In the absence of these flags, no options are passed to the native
function. This means the the regex is compiled with PCRE default	function. This means the the regex is compiled with PCRE default
semantics. In particular, the way it handles newline characters in the	semantics. In particular, the way it handles newline characters in the
subject string is the Perl way, not the POSIX way. Note that setting	subject string is the Perl way, not the POSIX way. Note that setting
PCRE_MULTILINE has only some of the effects specified for REG_NEWLINE.	PCRE_MULTILINE has only some of the effects specified for REG_NEWLINE.
It does not affect the way newlines are matched by . (they are not) or	It does not affect the way newlines are matched by . (they are not) or
by a negative class such as [^a] (they are).	by a negative class such as [^a] (they are).

The yield of regcomp() is zero on success, and non-zero otherwise. The	The yield of regcomp() is zero on success, and non-zero otherwise. The
preg structure is filled in on success, and one member of the structure	preg structure is filled in on success, and one member of the structure
is public: re_nsub contains the number of capturing subpatterns in the	is public: re_nsub contains the number of capturing subpatterns in the
regular expression. Various error codes are defined in the header file.	regular expression. Various error codes are defined in the header file.

NOTE: If the yield of regcomp() is non-zero, you must not attempt to	NOTE: If the yield of regcomp() is non-zero, you must not attempt to
use the contents of the preg structure. If, for example, you pass it to	use the contents of the preg structure. If, for example, you pass it to
regexec(), the result is undefined and your program is likely to crash.	regexec(), the result is undefined and your program is likely to crash.

Line 8362 COMPILING A PATTERN	Line 9380 COMPILING A PATTERN
MATCHING NEWLINE CHARACTERS	MATCHING NEWLINE CHARACTERS

This area is not simple, because POSIX and Perl take different views of	This area is not simple, because POSIX and Perl take different views of
things. It is not possible to get PCRE to obey POSIX semantics, but	things. It is not possible to get PCRE to obey POSIX semantics, but
then PCRE was never intended to be a POSIX engine. The following table	then PCRE was never intended to be a POSIX engine. The following table
lists the different possibilities for matching newline characters in	lists the different possibilities for matching newline characters in
PCRE:	PCRE:

Default Change with	Default Change with
Line 8386 MATCHING NEWLINE CHARACTERS	Line 9404 MATCHING NEWLINE CHARACTERS
^ matches \n in middle no REG_NEWLINE	^ matches \n in middle no REG_NEWLINE

PCRE's behaviour is the same as Perl's, except that there is no equiva-	PCRE's behaviour is the same as Perl's, except that there is no equiva-
lent for PCRE_DOLLAR_ENDONLY in Perl. In both PCRE and Perl, there is	lent for PCRE_DOLLAR_ENDONLY in Perl. In both PCRE and Perl, there is
no way to stop newline from matching [^a].	no way to stop newline from matching [^a].

The default POSIX newline handling can be obtained by setting	The default POSIX newline handling can be obtained by setting
PCRE_DOTALL and PCRE_DOLLAR_ENDONLY, but there is no way to make PCRE	PCRE_DOTALL and PCRE_DOLLAR_ENDONLY, but there is no way to make PCRE
behave exactly as for the REG_NEWLINE action.	behave exactly as for the REG_NEWLINE action.


MATCHING A PATTERN	MATCHING A PATTERN

The function regexec() is called to match a compiled pattern preg	The function regexec() is called to match a compiled pattern preg
against a given string, which is by default terminated by a zero byte	against a given string, which is by default terminated by a zero byte
(but see REG_STARTEND below), subject to the options in eflags. These	(but see REG_STARTEND below), subject to the options in eflags. These
can be:	can be:

REG_NOTBOL	REG_NOTBOL
Line 8420 MATCHING A PATTERN	Line 9438 MATCHING A PATTERN

REG_STARTEND	REG_STARTEND

The string is considered to start at string + pmatch[0].rm_so and to	The string is considered to start at string + pmatch[0].rm_so and to
have a terminating NUL located at string + pmatch[0].rm_eo (there need	have a terminating NUL located at string + pmatch[0].rm_eo (there need
not actually be a NUL at that location), regardless of the value of	not actually be a NUL at that location), regardless of the value of
nmatch. This is a BSD extension, compatible with but not specified by	nmatch. This is a BSD extension, compatible with but not specified by
IEEE Standard 1003.2 (POSIX.2), and should be used with caution in	IEEE Standard 1003.2 (POSIX.2), and should be used with caution in
software intended to be portable to other systems. Note that a non-zero	software intended to be portable to other systems. Note that a non-zero
rm_so does not imply REG_NOTBOL; REG_STARTEND affects only the location	rm_so does not imply REG_NOTBOL; REG_STARTEND affects only the location
of the string, not how it is matched.	of the string, not how it is matched.

If the pattern was compiled with the REG_NOSUB flag, no data about any	If the pattern was compiled with the REG_NOSUB flag, no data about any
matched strings is returned. The nmatch and pmatch arguments of	matched strings is returned. The nmatch and pmatch arguments of
regexec() are ignored.	regexec() are ignored.

If the value of nmatch is zero, or if the value pmatch is NULL, no data	If the value of nmatch is zero, or if the value pmatch is NULL, no data
Line 8438 MATCHING A PATTERN	Line 9456 MATCHING A PATTERN

Otherwise,the portion of the string that was matched, and also any cap-	Otherwise,the portion of the string that was matched, and also any cap-
tured substrings, are returned via the pmatch argument, which points to	tured substrings, are returned via the pmatch argument, which points to
an array of nmatch structures of type regmatch_t, containing the mem-	an array of nmatch structures of type regmatch_t, containing the mem-
bers rm_so and rm_eo. These contain the offset to the first character	bers rm_so and rm_eo. These contain the offset to the first character
of each substring and the offset to the first character after the end	of each substring and the offset to the first character after the end
of each substring, respectively. The 0th element of the vector relates	of each substring, respectively. The 0th element of the vector relates
to the entire portion of string that was matched; subsequent elements	to the entire portion of string that was matched; subsequent elements
relate to the capturing subpatterns of the regular expression. Unused	relate to the capturing subpatterns of the regular expression. Unused
entries in the array have both structure members set to -1.	entries in the array have both structure members set to -1.

A successful match yields a zero return; various error codes are	A successful match yields a zero return; various error codes are
defined in the header file, of which REG_NOMATCH is the "expected"	defined in the header file, of which REG_NOMATCH is the "expected"
failure code.	failure code.


ERROR MESSAGES	ERROR MESSAGES

The regerror() function maps a non-zero errorcode from either regcomp()	The regerror() function maps a non-zero errorcode from either regcomp()
or regexec() to a printable message. If preg is not NULL, the error	or regexec() to a printable message. If preg is not NULL, the error
should have arisen from the use of that structure. A message terminated	should have arisen from the use of that structure. A message terminated
by a binary zero is placed in errbuf. The length of the message,	by a binary zero is placed in errbuf. The length of the message,
including the zero, is limited to errbuf_size. The yield of the func-	including the zero, is limited to errbuf_size. The yield of the func-
tion is the size of buffer needed to hold the whole message.	tion is the size of buffer needed to hold the whole message.


MEMORY USAGE	MEMORY USAGE

Compiling a regular expression causes memory to be allocated and asso-	Compiling a regular expression causes memory to be allocated and asso-
ciated with the preg structure. The function regfree() frees all such	ciated with the preg structure. The function regfree() frees all such
memory, after which preg may no longer be used as a compiled expres-	memory, after which preg may no longer be used as a compiled expres-
sion.	sion.


Line 8483 REVISION	Line 9501 REVISION
------------------------------------------------------------------------------	------------------------------------------------------------------------------


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 8501 DESCRIPTION	Line 9519 DESCRIPTION
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. Note that the C++ wrapper supports only the	sulted for further details. Note that the C++ wrapper supports only the
original 8-bit PCRE library. There is no 16-bit support at present.	original 8-bit PCRE library. There is no 16-bit or 32-bit support at
	present.


MATCHING INTERFACE	MATCHING INTERFACE

The "FullMatch" operation checks that supplied text matches a supplied	The "FullMatch" operation checks that supplied text matches a supplied
pattern exactly. If pointer arguments are supplied, it copies matched	pattern exactly. If pointer arguments are supplied, it copies matched
sub-strings that match sub-patterns into them.	sub-strings that match sub-patterns into them.

Example: successful match	Example: successful match
Line 8521 MATCHING INTERFACE	Line 9540 MATCHING INTERFACE
Example: creating a temporary RE object:	Example: creating a temporary RE object:
pcrecpp::RE("h.*o").FullMatch("hello");	pcrecpp::RE("h.*o").FullMatch("hello");

You can pass in a "const char*" or a "string" for "text". The examples	You can pass in a "const char*" or a "string" for "text". The examples
below tend to use a const char*. You can, as in the different examples	below tend to use a const char*. You can, as in the different examples
above, store the RE object explicitly in a variable or use a temporary	above, store the RE object explicitly in a variable or use a temporary
RE object. The examples below use one mode or the other arbitrarily.	RE object. The examples below use one mode or the other arbitrarily.
Either could correctly be used for any of these examples.	Either could correctly be used for any of these examples.

You must supply extra pointer arguments to extract matched subpieces.	You must supply extra pointer arguments to extract matched subpieces.
Line 8550 MATCHING INTERFACE	Line 9569 MATCHING INTERFACE
Example: fails because string cannot be stored in integer	Example: fails because string cannot be stored in integer
!pcrecpp::RE("(.*)").FullMatch("ruby", &i);	!pcrecpp::RE("(.*)").FullMatch("ruby", &i);

The provided pointer arguments can be pointers to any scalar numeric	The provided pointer arguments can be pointers to any scalar numeric
type, or one of:	type, or one of:

string (matched piece is copied to string)	string (matched piece is copied to string)
Line 8558 MATCHING INTERFACE	Line 9577 MATCHING INTERFACE
T (where "bool T::ParseFrom(const char*, int)" exists)	T (where "bool T::ParseFrom(const char*, int)" exists)
NULL (the corresponding matched sub-pattern is not copied)	NULL (the corresponding matched sub-pattern is not copied)

The function returns true iff all of the following conditions are sat-	The function returns true iff all of the following conditions are sat-
isfied:	isfied:

a. "text" matches "pattern" exactly;	a. "text" matches "pattern" exactly;
Line 8573 MATCHING INTERFACE	Line 9592 MATCHING INTERFACE
number of sub-patterns, "i"th captured sub-pattern is	number of sub-patterns, "i"th captured sub-pattern is
ignored.	ignored.

CAVEAT: An optional sub-pattern that does not exist in the matched	CAVEAT: An optional sub-pattern that does not exist in the matched
string is assigned the empty string. Therefore, the following will	string is assigned the empty string. Therefore, the following will
return false (because the empty string is not a valid number):	return false (because the empty string is not a valid number):

int number;	int number;
pcrecpp::RE::FullMatch("abc", "[a-z]+(\\d+)?", &number);	pcrecpp::RE::FullMatch("abc", "[a-z]+(\\d+)?", &number);

The matching interface supports at most 16 arguments per call. If you	The matching interface supports at most 16 arguments per call. If you
need more, consider using the more general interface	need more, consider using the more general interface
pcrecpp::RE::DoMatch. See pcrecpp.h for the signature for DoMatch.	pcrecpp::RE::DoMatch. See pcrecpp.h for the signature for DoMatch.

NOTE: Do not use no_arg, which is used internally to mark the end of a	NOTE: Do not use no_arg, which is used internally to mark the end of a
list of optional arguments, as a placeholder for missing arguments, as	list of optional arguments, as a placeholder for missing arguments, as
this can lead to segfaults.	this can lead to segfaults.


QUOTING METACHARACTERS	QUOTING METACHARACTERS

You can use the "QuoteMeta" operation to insert backslashes before all	You can use the "QuoteMeta" operation to insert backslashes before all
potentially meaningful characters in a string. The returned string,	potentially meaningful characters in a string. The returned string,
used as a regular expression, will exactly match the original string.	used as a regular expression, will exactly match the original string.

Example:	Example:
string quoted = RE::QuoteMeta(unquoted);	string quoted = RE::QuoteMeta(unquoted);

Note that it's legal to escape a character even if it has no special	Note that it's legal to escape a character even if it has no special
meaning in a regular expression -- so this function does that. (This	meaning in a regular expression -- so this function does that. (This
also makes it identical to the perl function of the same name; see	also makes it identical to the perl function of the same name; see
"perldoc -f quotemeta".) For example, "1.5-2.0?" becomes	"perldoc -f quotemeta".) For example, "1.5-2.0?" becomes
"1\.5\-2\.0\?".	"1\.5\-2\.0\?".


PARTIAL MATCHES	PARTIAL MATCHES

You can use the "PartialMatch" operation when you want the pattern to	You can use the "PartialMatch" operation when you want the pattern to
match any substring of the text.	match any substring of the text.

Example: simple search for a string:	Example: simple search for a string:
Line 8622 PARTIAL MATCHES	Line 9641 PARTIAL MATCHES

UTF-8 AND THE MATCHING INTERFACE	UTF-8 AND THE MATCHING INTERFACE

By default, pattern and text are plain text, one byte per character.	By default, pattern and text are plain text, one byte per character.
The UTF8 flag, passed to the constructor, causes both pattern and	The UTF8 flag, passed to the constructor, causes both pattern and
string to be treated as UTF-8 text, still a byte stream but potentially	string to be treated as UTF-8 text, still a byte stream but potentially
multiple bytes per character. In practice, the text is likelier to be	multiple bytes per character. In practice, the text is likelier to be
UTF-8 than the pattern, but the match returned may depend on the UTF8	UTF-8 than the pattern, but the match returned may depend on the UTF8
flag, so always use it when matching UTF8 text. For example, "." will	flag, so always use it when matching UTF8 text. For example, "." will
match one byte normally but with UTF8 set may match up to three bytes	match one byte normally but with UTF8 set may match up to three bytes
of a multi-byte character.	of a multi-byte character.

Example:	Example:
Line 8647 UTF-8 AND THE MATCHING INTERFACE	Line 9666 UTF-8 AND THE MATCHING INTERFACE

PASSING MODIFIERS TO THE REGULAR EXPRESSION ENGINE	PASSING MODIFIERS TO THE REGULAR EXPRESSION ENGINE

PCRE defines some modifiers to change the behavior of the regular	PCRE defines some modifiers to change the behavior of the regular
expression engine. The C++ wrapper defines an auxiliary class,	expression engine. The C++ wrapper defines an auxiliary class,
RE_Options, as a vehicle to pass such modifiers to a RE class. Cur-	RE_Options, as a vehicle to pass such modifiers to a RE class. Cur-
rently, the following modifiers are supported:	rently, the following modifiers are supported:

modifier description Perl corresponding	modifier description Perl corresponding
Line 8664 PASSING MODIFIERS TO THE REGULAR EXPRESSION ENGINE	Line 9683 PASSING MODIFIERS TO THE REGULAR EXPRESSION ENGINE
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 (*)

(*) Both Perl and PCRE allow non capturing parentheses by means of the	(*) Both Perl and PCRE allow non capturing parentheses by means of the
"?:" modifier within the pattern itself. e.g. (?:ab\|cd) does not cap-	"?:" modifier within the pattern itself. e.g. (?:ab\|cd) does not cap-
ture, while (ab\|cd) does.	ture, while (ab\|cd) does.

For a full account on how each modifier works, please check the PCRE	For a full account on how each modifier works, please check the PCRE
API reference page.	API reference page.

For each modifier, there are two member functions whose name is made	For each modifier, there are two member functions whose name is made
out of the modifier in lowercase, without the "PCRE_" prefix. For	out of the modifier in lowercase, without the "PCRE_" prefix. For
instance, PCRE_CASELESS is handled by	instance, PCRE_CASELESS is handled by

bool caseless()	bool caseless()
Line 8682 PASSING MODIFIERS TO THE REGULAR EXPRESSION ENGINE	Line 9701 PASSING MODIFIERS TO THE REGULAR EXPRESSION ENGINE
RE_Options & set_caseless(bool)	RE_Options & set_caseless(bool)

which sets or unsets the modifier. Moreover, PCRE_EXTRA_MATCH_LIMIT can	which sets or unsets the modifier. Moreover, PCRE_EXTRA_MATCH_LIMIT can
be accessed through the set_match_limit() and match_limit() member	be accessed through the set_match_limit() and match_limit() member
functions. Setting match_limit to a non-zero value will limit the exe-	functions. Setting match_limit to a non-zero value will limit the exe-
cution of pcre to keep it from doing bad things like blowing the stack	cution of pcre to keep it from doing bad things like blowing the stack
or taking an eternity to return a result. A value of 5000 is good	or taking an eternity to return a result. A value of 5000 is good
enough to stop stack blowup in a 2MB thread stack. Setting match_limit	enough to stop stack blowup in a 2MB thread stack. Setting match_limit
to zero disables match limiting. Alternatively, you can call	to zero disables match limiting. Alternatively, you can call
match_limit_recursion() which uses PCRE_EXTRA_MATCH_LIMIT_RECURSION to	match_limit_recursion() which uses PCRE_EXTRA_MATCH_LIMIT_RECURSION to
limit how much PCRE recurses. match_limit() limits the number of	limit how much PCRE recurses. match_limit() limits the number of
matches PCRE does; match_limit_recursion() limits the depth of internal	matches PCRE does; match_limit_recursion() limits the depth of internal
recursion, and therefore the amount of stack that is used.	recursion, and therefore the amount of stack that is used.

Normally, to pass one or more modifiers to a RE class, you declare a	Normally, to pass one or more modifiers to a RE class, you declare a
RE_Options object, set the appropriate options, and pass this object to	RE_Options object, set the appropriate options, and pass this object to
a RE constructor. Example:	a RE constructor. Example:

Line 8702 PASSING MODIFIERS TO THE REGULAR EXPRESSION ENGINE	Line 9721 PASSING MODIFIERS TO THE REGULAR EXPRESSION ENGINE
if (RE("HELLO", opt).PartialMatch("hello world")) ...	if (RE("HELLO", opt).PartialMatch("hello world")) ...

RE_options has two constructors. The default constructor takes no argu-	RE_options has two constructors. The default constructor takes no argu-
ments and creates a set of flags that are off by default. The optional	ments and creates a set of flags that are off by default. The optional
parameter option_flags is to facilitate transfer of legacy code from C	parameter option_flags is to facilitate transfer of legacy code from C
programs. This lets you do	programs. This lets you do

RE(pattern,	RE(pattern,
Line 8717 PASSING MODIFIERS TO THE REGULAR EXPRESSION ENGINE	Line 9736 PASSING MODIFIERS TO THE REGULAR EXPRESSION ENGINE

If you are going to pass one of the most used modifiers, there are some	If you are going to pass one of the most used modifiers, there are some
convenience functions that return a RE_Options class with the appropri-	convenience functions that return a RE_Options class with the appropri-
ate modifier already set: CASELESS(), UTF8(), MULTILINE(), DOTALL(),	ate modifier already set: CASELESS(), UTF8(), MULTILINE() ate modifier already set: CASELESS(), UTF8(), MULTILINE()
and EXTENDED().	and EXTENDED().

If you need to set several options at once, and you don't want to go	If you need to set several options at once, and you don't want to go
through the pains of declaring a RE_Options object and setting several	through the pains of declaring a RE_Options object and setting several
options, there is a parallel method that give you such ability on the	options, there is a parallel method that give you such ability on the
fly. You can concatenate several set_xxxxx() member functions, since	fly. You can concatenate several set_xxxxx() member functions, since
each of them returns a reference to its class object. For example, to	each of them returns a reference to its class object. For example, to
pass PCRE_CASELESS, PCRE_EXTENDED, and PCRE_MULTILINE to a RE with one	pass PCRE_CASELESS, PCRE_EXTENDED, and PCRE_MULTILINE to a RE with one
statement, you may write:	statement, you may write:

RE(" ^ xyz \\s+ .* blah$",	RE(" ^ xyz \\s+ .* blah$",
Line 8737 PASSING MODIFIERS TO THE REGULAR EXPRESSION ENGINE	Line 9756 PASSING MODIFIERS TO THE REGULAR EXPRESSION ENGINE

SCANNING TEXT INCREMENTALLY	SCANNING TEXT INCREMENTALLY

The "Consume" operation may be useful if you want to repeatedly match	The "Consume" operation may be useful if you want to repeatedly match
regular expressions at the front of a string and skip over them as they	regular expressions at the front of a string and skip over them as they
match. This requires use of the "StringPiece" type, which represents a	match. This requires use of the "StringPiece" type, which represents a
sub-range of a real string. Like RE, StringPiece is defined in the	sub-range of a real string. Like RE, StringPiece is defined in the
pcrecpp namespace.	pcrecpp namespace.

Example: read lines of the form "var = value" from a string.	Example: read lines of the form "var = value" from a string.
Line 8754 SCANNING TEXT INCREMENTALLY	Line 9773 SCANNING TEXT INCREMENTALLY
...;	...;
}	}

Each successful call to "Consume" will set "var/value", and also	Each successful call to "Consume" will set "var/value", and also
advance "input" so it points past the matched text.	advance "input" so it points past the matched text.

The "FindAndConsume" operation is similar to "Consume" but does not	The "FindAndConsume" operation is similar to "Consume" but does not
anchor your match at the beginning of the string. For example, you	anchor your match at the beginning of the string. For example, you
could extract all words from a string by repeatedly calling	could extract all words from a string by repeatedly calling

pcrecpp::RE("(\\w+)").FindAndConsume(&input, &word)	pcrecpp::RE("(\\w+)").FindAndConsume(&input, &word)
Line 8767 SCANNING TEXT INCREMENTALLY	Line 9786 SCANNING TEXT INCREMENTALLY
PARSING HEX/OCTAL/C-RADIX NUMBERS	PARSING HEX/OCTAL/C-RADIX NUMBERS

By default, if you pass a pointer to a numeric value, the corresponding	By default, if you pass a pointer to a numeric value, the corresponding
text is interpreted as a base-10 number. You can instead wrap the	text is interpreted as a base-10 number. You can instead wrap the
pointer with a call to one of the operators Hex(), Octal(), or CRadix()	pointer with a call to one of the operators Hex(), Octal(), or CRadix()
to interpret the text in another base. The CRadix operator interprets	to interpret the text in another base. The CRadix operator interprets
C-style "0" (base-8) and "0x" (base-16) prefixes, but defaults to	C-style "0" (base-8) and "0x" (base-16) prefixes, but defaults to
base-10.	base-10.

Example:	Example:
Line 8785 PARSING HEX/OCTAL/C-RADIX NUMBERS	Line 9804 PARSING HEX/OCTAL/C-RADIX NUMBERS

REPLACING PARTS OF STRINGS	REPLACING PARTS OF STRINGS

You can replace the first match of "pattern" in "str" with "rewrite".	You can replace the first match of "pattern" in "str" with "rewrite".
Within "rewrite", backslash-escaped digits (\1 to \9) can be used to	Within "rewrite", backslash-escaped digits (\1 to \9) can be used to
insert text matching corresponding parenthesized group from the pat-	insert text matching corresponding parenthesized group from the pat-
tern. \0 in "rewrite" refers to the entire matching text. For example:	tern. \0 in "rewrite" refers to the entire matching text. For example:

string s = "yabba dabba doo";	string s = "yabba dabba doo";
pcrecpp::RE("b+").Replace("d", &s);	pcrecpp::RE("b+").Replace("d", &s);

will leave "s" containing "yada dabba doo". The result is true if the	will leave "s" containing "yada dabba doo". The result is true if the
pattern matches and a replacement occurs, false otherwise.	pattern matches and a replacement occurs, false otherwise.

GlobalReplace is like Replace except that it replaces all occurrences	GlobalReplace is like Replace except that it replaces all occurrences
of the pattern in the string with the rewrite. Replacements are not	of the pattern in the string with the rewrite. Replacements are not
subject to re-matching. For example:	subject to re-matching. For example:

string s = "yabba dabba doo";	string s = "yabba dabba doo";
pcrecpp::RE("b+").GlobalReplace("d", &s);	pcrecpp::RE("b+").GlobalReplace("d", &s);

will leave "s" containing "yada dada doo". It returns the number of	will leave "s" containing "yada dada doo". It returns the number of
replacements made.	replacements made.

Extract is like Replace, except that if the pattern matches, "rewrite"	Extract is like Replace, except that if the pattern matches, "rewrite"
is copied into "out" (an additional argument) with substitutions. The	is copied into "out" (an additional argument) with substitutions. The
non-matching portions of "text" are ignored. Returns true iff a match	non-matching portions of "text" are ignored. Returns true iff a match
occurred and the extraction happened successfully; if no match occurs,	occurred and the extraction happened successfully; if no match occurs,
the string is left unaffected.	the string is left unaffected.

Line 8825 REVISION	Line 9844 REVISION
------------------------------------------------------------------------------	------------------------------------------------------------------------------


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 8911 REVISION	Line 9930 REVISION
Last updated: 10 January 2012	Last updated: 10 January 2012
Copyright (c) 1997-2012 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 approximately 64K data	The maximum length of a compiled pattern is approximately 64K data
units (bytes for the 8-bit library, 16-bit units for the 16-bit	units (bytes for the 8-bit library, 32-bit units for the 32-bit
library) if PCRE is compiled with the default internal linkage size of	library, and 32-bit units for the 32-bit library) if PCRE is compiled
2 bytes. If you want to process regular expressions that are truly	with the default internal linkage size of 2 bytes. If you want to
enormous, you can compile PCRE with an internal linkage size of 3 or 4	process regular expressions that are truly enormous, you can compile
(when building the 16-bit library, 3 is rounded up to 4). See the	PCRE with an internal linkage size of 3 or 4 (when building the 16-bit
README file in the source distribution and the pcrebuild documentation	or 32-bit library, 3 is rounded up to 4). See the README file in the
for details. In these cases the limit is substantially larger. How-	source distribution and the pcrebuild documentation for details. In
ever, the speed of execution is slower.	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.

Line 8939 SIZE AND OTHER LIMITATIONS	Line 9959 SIZE AND OTHER LIMITATIONS
can be no more than 65535 capturing subpatterns.	can be no more than 65535 capturing subpatterns.

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
upper limits, for example, (?2){0,100} when subpattern number 2 is to	upper limits, for example, (?2){0,100} when subpattern number 2 is to
the right, are included in the count. There is no limit to the number	the right, are included in the count. There is no limit to the number
of backward references.	of backward references.

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	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	(*THEN) verb is 255 for the 8-bit library and 65535 for the 16-bit and
library.	32-bit library.

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-
inite repetition. This means that the available stack space may limit	inite repetition. This means that the available stack space may limit
the size of a subject string that can be processed by certain patterns.	the size of a subject string that can be processed by certain patterns.
For a discussion of stack issues, see the pcrestack documentation.	For a discussion of stack issues, see the pcrestack documentation.

Line 8973 REVISION	Line 9993 REVISION
------------------------------------------------------------------------------	------------------------------------------------------------------------------


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[16]_exec(), it makes use of an internal function	When you call pcre[16\|32]_exec(), it makes use of an internal function
called match(). This calls itself recursively at branch points in the	called match(). This calls itself recursively at branch points in the
pattern, in order to remember the state of the match so that it can	pattern, in order to remember the state of the match so that it can
back up and try a different alternative if the first one fails. As	back up and try a different alternative if the first one fails. As
Line 8998 PCRE DISCUSSION OF STACK USAGE	Line 10018 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[16]_exec() is run in its normal	The above comments apply when pcre[16\|32]_exec() is run in its normal
interpretive manner. If the pattern was studied with the	interpretive manner. If the pattern was studied with the
PCRE_STUDY_JIT_COMPILE option, and just-in-time compiling was success-	PCRE_STUDY_JIT_COMPILE option, and just-in-time compiling was success-
ful, and the options passed to pcre[16]_exec() were not incompatible,	ful, and the options passed to pcre[16\|32]_exec() were not incompati-
the matching process uses the JIT-compiled code instead of the match()	ble, the matching process uses the JIT-compiled code instead of the
function. In this case, the memory requirements are handled entirely	match() function. In this case, the memory requirements are handled
differently. See the pcrejit documentation for details.	entirely differently. See the pcrejit documentation for details.

The pcre[16]_dfa_exec() function operates in an entirely different way,	The pcre[16\|32]_dfa_exec() function operates in an entirely different
and 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[16]_dfa_exec() is controlled by the amount of workspace	complexity of pcre[16\|32]_dfa_exec() is controlled by the amount of
it is given. However, it is possible to write patterns with runaway	workspace it is given. However, it is possible to write patterns with
infinite recursions; such patterns will cause pcre[16]_dfa_exec() to	runaway infinite recursions; such patterns will cause
run out of 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[16]_dfa_exec(); they are	The comments that follow do NOT apply to pcre[16\|32]_dfa_exec(); they
relevant only for pcre[16]_exec() without the JIT optimization.	are relevant only for pcre[16\|32]_exec() without the JIT optimization.

Reducing pcre[16]_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[16]_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[16]_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[16]_stack_malloc and pcre[16]_stack_free variables. By	pointed to by the pcre[16\|32]_stack_malloc and pcre[16\|32]_stack_free
default, these point to malloc() and free(), but you can replace the	variables. By default, these point to malloc() and free(), but you can
pointers to cause PCRE to use your own functions. Since the block sizes	replace the pointers to cause PCRE to use your own functions. Since the
are always the same, and are always freed in reverse order, it may be	block sizes are always the same, and are always freed in reverse order,
possible to implement customized memory handlers that are more effi-	it may be possible to implement customized memory handlers that are
cient than the standard functions.	more efficient than the standard functions.

Limiting pcre[16]_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[16]_exec()	in total and recursively. If a limit is exceeded, pcre[16\|32]_exec()
returns an error code. Setting suitable limits should prevent it from	returns an error code. Setting suitable limits should prevent it from
running out of stack. The default values of the limits are very large,	running out of stack. The default values of the limits are very large,
and unlikely ever to operate. They can be changed when PCRE is built,	and unlikely ever to operate. They can be changed when PCRE is built,
and they can also be set when pcre[16]_exec() is called. For details of	and they can also be set when pcre[16\|32]_exec() is called. For details
these interfaces, see the pcrebuild documentation and the section on	of these interfaces, see the pcrebuild documentation and the section on
extra data for pcre[16]_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[16]_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	Obtaining an estimate of stack usage

The actual amount of stack used per recursion can vary quite a lot,	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-	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	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	of 500 bytes mentioned above may be larger or smal of 500 bytes mentioned above may be larger or smal
actually needed. A better approximation can be obtained by running this	actually needed. A better approximation can be obtained by running this
command:	command:

pcretest -m -C	pcretest -m -C

The -C option causes pcretest to output information about the options	The -C option causes pcretest to output information about the options
with which PCRE was compiled. When -m is also given (before -C), infor-	with which PCRE was compiled. When -m is also given (before -C), infor-
mation about stack use is given in a line like this:	mation about stack use is given in a line like this:

Line 9110 PCRE DISCUSSION OF STACK USAGE	Line 10131 PCRE DISCUSSION OF STACK USAGE
The value is approximate because some recursions need a bit more (up to	The value is approximate because some recursions need a bit more (up to
perhaps 16 more bytes).	perhaps 16 more bytes).

If the above command is given when PCRE is compiled to use the heap	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	instead of the stack for recursion, the value that is output is the
size of each block that is obtained from the heap.	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 9132 PCRE DISCUSSION OF STACK USAGE	Line 10153 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[16]_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 9153 AUTHOR	Line 10174 AUTHOR

REVISION	REVISION

Last updated: 21 January 2012	Last updated: 24 June 2012
Copyright (c) 1997-2012 University of Cambridge.	Copyright (c) 1997-2012 University of Cambridge.
------------------------------------------------------------------------------	------------------------------------------------------------------------------

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