dist2/doc/pcre2posix.3 - platform/external/pcre - Gitiles

 .TH PCRE2POSIX 3 "31 January 2016" "PCRE2 10.22"
 .SH NAME
 PCRE2 - Perl-compatible regular expressions (revised API)
 .SH "SYNOPSIS"
 .rs
 .sp
 .B #include <pcre2posix.h>
 .PP
 .nf
 .B int regcomp(regex_t *\fIpreg\fP, const char *\fIpattern\fP,
 .B "     int \fIcflags\fP);"
 .sp
 .B int regexec(const regex_t *\fIpreg\fP, const char *\fIstring\fP,
 .B "     size_t \fInmatch\fP, regmatch_t \fIpmatch\fP[], int \fIeflags\fP);"
 .sp
 .B "size_t regerror(int \fIerrcode\fP, const regex_t *\fIpreg\fP,"
 .B "     char *\fIerrbuf\fP, size_t \fIerrbuf_size\fP);"
 .sp
 .B void regfree(regex_t *\fIpreg\fP);
 .fi
 .
 .SH DESCRIPTION
 .rs
 .sp
 This set of functions provides a POSIX-style API for the PCRE2 regular
 expression 8-bit library. See the
 .\" HREF
 \fBpcre2api\fP
 .\"
 documentation for a description of PCRE2's native API, which contains much
 additional functionality. There are no POSIX-style wrappers for PCRE2's 16-bit
 and 32-bit libraries.
 .P
 The functions described here are just wrapper functions that ultimately call
 the PCRE2 native API. Their prototypes are defined in the \fBpcre2posix.h\fP
 header file, and on Unix systems the library itself is called
 \fBlibpcre2-posix.a\fP, so can be accessed by adding \fB-lpcre2-posix\fP to the
 command for linking an application that uses them. Because the POSIX functions
 call the native ones, it is also necessary to add \fB-lpcre2-8\fP.
 .P
 Those POSIX option bits that can reasonably be mapped to PCRE2 native options
 have been implemented. In addition, the option REG_EXTENDED is 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 easier to slot in PCRE2 as a
 replacement library. Other POSIX options are not even defined.
 .P
 There are also some options that are not defined by POSIX. These have been
 added at the request of users who want to make use of certain PCRE2-specific
 features via the POSIX calling interface.
 .P
 When PCRE2 is called via these functions, it is only the API that is POSIX-like
 in style. The syntax and semantics of the regular expressions themselves are
 still those of Perl, subject to the setting of various PCRE2 options, as
 described below. "POSIX-like in style" means that the API approximates to the
 POSIX definition; it is not fully POSIX-compatible, and in multi-unit encoding
 domains it is probably even less compatible.
 .P
 The header for these functions is supplied as \fBpcre2posix.h\fP to avoid any
 potential clash with other POSIX libraries. It can, of course, be renamed or
 aliased as \fBregex.h\fP, which is the "correct" name. It provides two
 structure types, \fIregex_t\fP for compiled internal forms, and
 \fIregmatch_t\fP for returning captured substrings. It also defines some
 constants whose names start with "REG_"; these are used for setting options and
 identifying error codes.
 .
 .
 .SH "COMPILING A PATTERN"
 .rs
 .sp
 The function \fBregcomp()\fP is called to compile a pattern into an
 internal form. The pattern is a C string terminated by a binary zero, and
 is passed in the argument \fIpattern\fP. The \fIpreg\fP argument is a pointer
 to a \fBregex_t\fP structure that is used as a base for storing information
 about the compiled regular expression.
 .P
 The argument \fIcflags\fP is either zero, or contains one or more of the bits
 defined by the following macros:
 .sp
   REG_DOTALL
 .sp
 The PCRE2_DOTALL option is set when the regular expression is passed for
 compilation to the native function. Note that REG_DOTALL is not part of the
 POSIX standard.
 .sp
   REG_ICASE
 .sp
 The PCRE2_CASELESS option is set when the regular expression is passed for
 compilation to the native function.
 .sp
   REG_NEWLINE
 .sp
 The PCRE2_MULTILINE option is set when the regular expression is passed for
 compilation to the native function. Note that this does \fInot\fP mimic the
 defined POSIX behaviour for REG_NEWLINE (see the following section).
 .sp
   REG_NOSUB
 .sp
 When a pattern that is compiled with this flag is passed to \fBregexec()\fP for
 matching, the \fInmatch\fP and \fIpmatch\fP arguments are ignored, and no
 captured strings are returned. Versions of the PCRE library prior to 10.22 used
 to set the PCRE2_NO_AUTO_CAPTURE compile option, but this no longer happens
 because it disables the use of back references.
 .sp
   REG_UCP
 .sp
 The PCRE2_UCP option is set when the regular expression is passed for
 compilation to the native function. This causes PCRE2 to use Unicode properties
 when matchine \ed, \ew, etc., instead of just recognizing ASCII values. Note
 that REG_UCP is not part of the POSIX standard.
 .sp
   REG_UNGREEDY
 .sp
 The PCRE2_UNGREEDY option is set when the regular expression is passed for
 compilation to the native function. Note that REG_UNGREEDY is not part of the
 POSIX standard.
 .sp
   REG_UTF
 .sp
 The PCRE2_UTF option is set when the regular expression is passed for
 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. Note that REG_UTF
 is not part of the POSIX standard.
 .P
 In the absence of these flags, no options are passed to the native function.
 This means the the regex is compiled with PCRE2 default semantics. In
 particular, the way it handles newline characters in the subject string is the
 Perl way, not the POSIX way. Note that setting PCRE2_MULTILINE has only
 \fIsome\fP of the effects specified for REG_NEWLINE. It does not affect the way
 newlines are matched by the dot metacharacter (they are not) or by a negative
 class such as [^a] (they are).
 .P
 The yield of \fBregcomp()\fP is zero on success, and non-zero otherwise. The
 \fIpreg\fP structure is filled in on success, and one member of the structure
 is public: \fIre_nsub\fP contains the number of capturing subpatterns in
 the regular expression. Various error codes are defined in the header file.
 .P
 NOTE: If the yield of \fBregcomp()\fP is non-zero, you must not attempt to
 use the contents of the \fIpreg\fP structure. If, for example, you pass it to
 \fBregexec()\fP, the result is undefined and your program is likely to crash.
 .
 .
 .SH "MATCHING NEWLINE CHARACTERS"
 .rs
 .sp
 This area is not simple, because POSIX and Perl take different views of things.
 It is not possible to get PCRE2 to obey POSIX semantics, but then PCRE2 was
 never intended to be a POSIX engine. The following table lists the different
 possibilities for matching newline characters in Perl and PCRE2:
 .sp
                           Default   Change with
 .sp
   . matches newline          no     PCRE2_DOTALL
   newline matches [^a]       yes    not changeable
   $ matches \en at end        yes    PCRE2_DOLLAR_ENDONLY
   $ matches \en in middle     no     PCRE2_MULTILINE
   ^ matches \en in middle     no     PCRE2_MULTILINE
 .sp
 This is the equivalent table for a POSIX-compatible pattern matcher:
 .sp
                           Default   Change with
 .sp
   . matches newline          yes    REG_NEWLINE
   newline matches [^a]       yes    REG_NEWLINE
   $ matches \en at end        no     REG_NEWLINE
   $ matches \en in middle     no     REG_NEWLINE
   ^ matches \en in middle     no     REG_NEWLINE
 .sp
 This behaviour is not what happens when PCRE2 is called via its POSIX
 API. By default, PCRE2's behaviour is the same as Perl's, except that there is
 no equivalent for PCRE2_DOLLAR_ENDONLY in Perl. In both PCRE2 and Perl, there
 is no way to stop newline from matching [^a].
 .P
 Default POSIX newline handling can be obtained by setting PCRE2_DOTALL and
 PCRE2_DOLLAR_ENDONLY when calling \fBpcre2_compile()\fP directly, but there is
 no way to make PCRE2 behave exactly as for the REG_NEWLINE action. When using
 the POSIX API, passing REG_NEWLINE to PCRE2's \fBregcomp()\fP function
 causes PCRE2_MULTILINE to be passed to \fBpcre2_compile()\fP, and REG_DOTALL
 passes PCRE2_DOTALL. There is no way to pass PCRE2_DOLLAR_ENDONLY.
 .
 .
 .SH "MATCHING A PATTERN"
 .rs
 .sp
 The function \fBregexec()\fP is called to match a compiled pattern \fIpreg\fP
 against a given \fIstring\fP, which is by default terminated by a zero byte
 (but see REG_STARTEND below), subject to the options in \fIeflags\fP. These can
 be:
 .sp
   REG_NOTBOL
 .sp
 The PCRE2_NOTBOL option is set when calling the underlying PCRE2 matching
 function.
 .sp
   REG_NOTEMPTY
 .sp
 The PCRE2_NOTEMPTY option is set when calling the underlying PCRE2 matching
 function. Note that REG_NOTEMPTY is not part of the POSIX standard. However,
 setting this option can give more POSIX-like behaviour in some situations.
 .sp
   REG_NOTEOL
 .sp
 The PCRE2_NOTEOL option is set when calling the underlying PCRE2 matching
 function.
 .sp
   REG_STARTEND
 .sp
 The string is considered to start at \fIstring\fP + \fIpmatch[0].rm_so\fP and
 to have a terminating NUL located at \fIstring\fP + \fIpmatch[0].rm_eo\fP
 (there need not actually be a NUL at that location), regardless of the value of
 \fInmatch\fP. This is a BSD extension, compatible with but not specified by
 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 \fIrm_so\fP does
 not imply REG_NOTBOL; REG_STARTEND affects only the location of the string, not
 how it is matched. Setting REG_STARTEND and passing \fIpmatch\fP as NULL are
 mutually exclusive; the error REG_INVARG is returned.
 .P
 If the pattern was compiled with the REG_NOSUB flag, no data about any matched
 strings is returned. The \fInmatch\fP and \fIpmatch\fP arguments of
 \fBregexec()\fP are ignored (except possibly as input for REG_STARTEND).
 .P
 The value of \fInmatch\fP may be zero, and the value \fIpmatch\fP may be NULL
 (unless REG_STARTEND is set); in both these cases no data about any matched
 strings is returned.
 .P
 Otherwise, the portion of the string that was matched, and also any captured
 substrings, are returned via the \fIpmatch\fP argument, which points to an
 array of \fInmatch\fP structures of type \fIregmatch_t\fP, containing the
 members \fIrm_so\fP and \fIrm_eo\fP. These contain the byte offset to the first
 character of each substring and the offset to the first character after the end
 of each substring, respectively. The 0th element of the vector relates to the
 entire portion of \fIstring\fP that was matched; subsequent elements relate to
 the capturing subpatterns of the regular expression. Unused entries in the
 array have both structure members set to -1.
 .P
 A successful match yields a zero return; various error codes are defined in the
 header file, of which REG_NOMATCH is the "expected" failure code.
 .
 .
 .SH "ERROR MESSAGES"
 .rs
 .sp
 The \fBregerror()\fP function maps a non-zero errorcode from either
 \fBregcomp()\fP or \fBregexec()\fP to a printable message. If \fIpreg\fP is not
 NULL, the error should have arisen from the use of that structure. A message
 terminated by a binary zero is placed in \fIerrbuf\fP. If the buffer is too
 short, only the first \fIerrbuf_size\fP - 1 characters of the error message are
 used. The yield of the function is the size of buffer needed to hold the whole
 message, including the terminating zero. This value is greater than
 \fIerrbuf_size\fP if the message was truncated.
 .
 .
 .SH MEMORY USAGE
 .rs
 .sp
 Compiling a regular expression causes memory to be allocated and associated
 with the \fIpreg\fP structure. The function \fBregfree()\fP frees all such
 memory, after which \fIpreg\fP may no longer be used as a compiled expression.
 .
 .
 .SH AUTHOR
 .rs
 .sp
 .nf
 Philip Hazel
 University Computing Service
 Cambridge, England.
 .fi
 .
 .
 .SH REVISION
 .rs
 .sp
 .nf
 Last updated: 31 January 2016
 Copyright (c) 1997-2016 University of Cambridge.
 .fi
	.TH PCRE2POSIX 3 "31 January 2016" "PCRE2 10.22"
	.SH NAME
	PCRE2 - Perl-compatible regular expressions (revised API)
	.SH "SYNOPSIS"
	.rs
	.sp
	.B #include <pcre2posix.h>
	.PP
	.nf
	.B int regcomp(regex_t \fIpreg\fP, const char \fIpattern\fP,
	.B " int \fIcflags\fP);"
	.sp
	.B int regexec(const regex_t \fIpreg\fP, const char \fIstring\fP,
	.B " size_t \fInmatch\fP, regmatch_t \fIpmatch\fP[], int \fIeflags\fP);"
	.sp
	.B "size_t regerror(int \fIerrcode\fP, const regex_t *\fIpreg\fP,"
	.B " char *\fIerrbuf\fP, size_t \fIerrbuf_size\fP);"
	.sp
	.B void regfree(regex_t *\fIpreg\fP);
	.fi
	.
	.SH DESCRIPTION
	.rs
	.sp
	This set of functions provides a POSIX-style API for the PCRE2 regular
	expression 8-bit library. See the
	.\" HREF
	\fBpcre2api\fP
	.\"
	documentation for a description of PCRE2's native API, which contains much
	additional functionality. There are no POSIX-style wrappers for PCRE2's 16-bit
	and 32-bit libraries.
	.P
	The functions described here are just wrapper functions that ultimately call
	the PCRE2 native API. Their prototypes are defined in the \fBpcre2posix.h\fP
	header file, and on Unix systems the library itself is called
	\fBlibpcre2-posix.a\fP, so can be accessed by adding \fB-lpcre2-posix\fP to the
	command for linking an application that uses them. Because the POSIX functions
	call the native ones, it is also necessary to add \fB-lpcre2-8\fP.
	.P
	Those POSIX option bits that can reasonably be mapped to PCRE2 native options
	have been implemented. In addition, the option REG_EXTENDED is 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 easier to slot in PCRE2 as a
	replacement library. Other POSIX options are not even defined.
	.P
	There are also some options that are not defined by POSIX. These have been
	added at the request of users who want to make use of certain PCRE2-specific
	features via the POSIX calling interface.
	.P
	When PCRE2 is called via these functions, it is only the API that is POSIX-like
	in style. The syntax and semantics of the regular expressions themselves are
	still those of Perl, subject to the setting of various PCRE2 options, as
	described below. "POSIX-like in style" means that the API approximates to the
	POSIX definition; it is not fully POSIX-compatible, and in multi-unit encoding
	domains it is probably even less compatible.
	.P
	The header for these functions is supplied as \fBpcre2posix.h\fP to avoid any
	potential clash with other POSIX libraries. It can, of course, be renamed or
	aliased as \fBregex.h\fP, which is the "correct" name. It provides two
	structure types, \fIregex_t\fP for compiled internal forms, and
	\fIregmatch_t\fP for returning captured substrings. It also defines some
	constants whose names start with "REG_"; these are used for setting options and
	identifying error codes.
	.
	.
	.SH "COMPILING A PATTERN"
	.rs
	.sp
	The function \fBregcomp()\fP is called to compile a pattern into an
	internal form. The pattern is a C string terminated by a binary zero, and
	is passed in the argument \fIpattern\fP. The \fIpreg\fP argument is a pointer
	to a \fBregex_t\fP structure that is used as a base for storing information
	about the compiled regular expression.
	.P
	The argument \fIcflags\fP is either zero, or contains one or more of the bits
	defined by the following macros:
	.sp
	REG_DOTALL
	.sp
	The PCRE2_DOTALL option is set when the regular expression is passed for
	compilation to the native function. Note that REG_DOTALL is not part of the
	POSIX standard.
	.sp
	REG_ICASE
	.sp
	The PCRE2_CASELESS option is set when the regular expression is passed for
	compilation to the native function.
	.sp
	REG_NEWLINE
	.sp
	The PCRE2_MULTILINE option is set when the regular expression is passed for
	compilation to the native function. Note that this does \fInot\fP mimic the
	defined POSIX behaviour for REG_NEWLINE (see the following section).
	.sp
	REG_NOSUB
	.sp
	When a pattern that is compiled with this flag is passed to \fBregexec()\fP for
	matching, the \fInmatch\fP and \fIpmatch\fP arguments are ignored, and no
	captured strings are returned. Versions of the PCRE library prior to 10.22 used
	to set the PCRE2_NO_AUTO_CAPTURE compile option, but this no longer happens
	because it disables the use of back references.
	.sp
	REG_UCP
	.sp
	The PCRE2_UCP option is set when the regular expression is passed for
	compilation to the native function. This causes PCRE2 to use Unicode properties
	when matchine \ed, \ew, etc., instead of just recognizing ASCII values. Note
	that REG_UCP is not part of the POSIX standard.
	.sp
	REG_UNGREEDY
	.sp
	The PCRE2_UNGREEDY option is set when the regular expression is passed for
	compilation to the native function. Note that REG_UNGREEDY is not part of the
	POSIX standard.
	.sp
	REG_UTF
	.sp
	The PCRE2_UTF option is set when the regular expression is passed for
	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. Note that REG_UTF
	is not part of the POSIX standard.
	.P
	In the absence of these flags, no options are passed to the native function.
	This means the the regex is compiled with PCRE2 default semantics. In
	particular, the way it handles newline characters in the subject string is the
	Perl way, not the POSIX way. Note that setting PCRE2_MULTILINE has only
	\fIsome\fP of the effects specified for REG_NEWLINE. It does not affect the way
	newlines are matched by the dot metacharacter (they are not) or by a negative
	class such as [^a] (they are).
	.P
	The yield of \fBregcomp()\fP is zero on success, and non-zero otherwise. The
	\fIpreg\fP structure is filled in on success, and one member of the structure
	is public: \fIre_nsub\fP contains the number of capturing subpatterns in
	the regular expression. Various error codes are defined in the header file.
	.P
	NOTE: If the yield of \fBregcomp()\fP is non-zero, you must not attempt to
	use the contents of the \fIpreg\fP structure. If, for example, you pass it to
	\fBregexec()\fP, the result is undefined and your program is likely to crash.
	.
	.
	.SH "MATCHING NEWLINE CHARACTERS"
	.rs
	.sp
	This area is not simple, because POSIX and Perl take different views of things.
	It is not possible to get PCRE2 to obey POSIX semantics, but then PCRE2 was
	never intended to be a POSIX engine. The following table lists the different
	possibilities for matching newline characters in Perl and PCRE2:
	.sp
	Default Change with
	.sp
	. matches newline no PCRE2_DOTALL
	newline matches [^a] yes not changeable
	$ matches \en at end yes PCRE2_DOLLAR_ENDONLY
	$ matches \en in middle no PCRE2_MULTILINE
	^ matches \en in middle no PCRE2_MULTILINE
	.sp
	This is the equivalent table for a POSIX-compatible pattern matcher:
	.sp
	Default Change with
	.sp
	. matches newline yes REG_NEWLINE
	newline matches [^a] yes REG_NEWLINE
	$ matches \en at end no REG_NEWLINE
	$ matches \en in middle no REG_NEWLINE
	^ matches \en in middle no REG_NEWLINE
	.sp
	This behaviour is not what happens when PCRE2 is called via its POSIX
	API. By default, PCRE2's behaviour is the same as Perl's, except that there is
	no equivalent for PCRE2_DOLLAR_ENDONLY in Perl. In both PCRE2 and Perl, there
	is no way to stop newline from matching [^a].
	.P
	Default POSIX newline handling can be obtained by setting PCRE2_DOTALL and
	PCRE2_DOLLAR_ENDONLY when calling \fBpcre2_compile()\fP directly, but there is
	no way to make PCRE2 behave exactly as for the REG_NEWLINE action. When using
	the POSIX API, passing REG_NEWLINE to PCRE2's \fBregcomp()\fP function
	causes PCRE2_MULTILINE to be passed to \fBpcre2_compile()\fP, and REG_DOTALL
	passes PCRE2_DOTALL. There is no way to pass PCRE2_DOLLAR_ENDONLY.
	.
	.
	.SH "MATCHING A PATTERN"
	.rs
	.sp
	The function \fBregexec()\fP is called to match a compiled pattern \fIpreg\fP
	against a given \fIstring\fP, which is by default terminated by a zero byte
	(but see REG_STARTEND below), subject to the options in \fIeflags\fP. These can
	be:
	.sp
	REG_NOTBOL
	.sp
	The PCRE2_NOTBOL option is set when calling the underlying PCRE2 matching
	function.
	.sp
	REG_NOTEMPTY
	.sp
	The PCRE2_NOTEMPTY option is set when calling the underlying PCRE2 matching
	function. Note that REG_NOTEMPTY is not part of the POSIX standard. However,
	setting this option can give more POSIX-like behaviour in some situations.
	.sp
	REG_NOTEOL
	.sp
	The PCRE2_NOTEOL option is set when calling the underlying PCRE2 matching
	function.
	.sp
	REG_STARTEND
	.sp
	The string is considered to start at \fIstring\fP + \fIpmatch[0].rm_so\fP and
	to have a terminating NUL located at \fIstring\fP + \fIpmatch[0].rm_eo\fP
	(there need not actually be a NUL at that location), regardless of the value of
	\fInmatch\fP. This is a BSD extension, compatible with but not specified by
	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 \fIrm_so\fP does
	not imply REG_NOTBOL; REG_STARTEND affects only the location of the string, not
	how it is matched. Setting REG_STARTEND and passing \fIpmatch\fP as NULL are
	mutually exclusive; the error REG_INVARG is returned.
	.P
	If the pattern was compiled with the REG_NOSUB flag, no data about any matched
	strings is returned. The \fInmatch\fP and \fIpmatch\fP arguments of
	\fBregexec()\fP are ignored (except possibly as input for REG_STARTEND).
	.P
	The value of \fInmatch\fP may be zero, and the value \fIpmatch\fP may be NULL
	(unless REG_STARTEND is set); in both these cases no data about any matched
	strings is returned.
	.P
	Otherwise, the portion of the string that was matched, and also any captured
	substrings, are returned via the \fIpmatch\fP argument, which points to an
	array of \fInmatch\fP structures of type \fIregmatch_t\fP, containing the
	members \fIrm_so\fP and \fIrm_eo\fP. These contain the byte offset to the first
	character of each substring and the offset to the first character after the end
	of each substring, respectively. The 0th element of the vector relates to the
	entire portion of \fIstring\fP that was matched; subsequent elements relate to
	the capturing subpatterns of the regular expression. Unused entries in the
	array have both structure members set to -1.
	.P
	A successful match yields a zero return; various error codes are defined in the
	header file, of which REG_NOMATCH is the "expected" failure code.
	.
	.
	.SH "ERROR MESSAGES"
	.rs
	.sp
	The \fBregerror()\fP function maps a non-zero errorcode from either
	\fBregcomp()\fP or \fBregexec()\fP to a printable message. If \fIpreg\fP is not
	NULL, the error should have arisen from the use of that structure. A message
	terminated by a binary zero is placed in \fIerrbuf\fP. If the buffer is too
	short, only the first \fIerrbuf_size\fP - 1 characters of the error message are
	used. The yield of the function is the size of buffer needed to hold the whole
	message, including the terminating zero. This value is greater than
	\fIerrbuf_size\fP if the message was truncated.
	.
	.
	.SH MEMORY USAGE
	.rs
	.sp
	Compiling a regular expression causes memory to be allocated and associated
	with the \fIpreg\fP structure. The function \fBregfree()\fP frees all such
	memory, after which \fIpreg\fP may no longer be used as a compiled expression.
	.
	.
	.SH AUTHOR
	.rs
	.sp
	.nf
	Philip Hazel
	University Computing Service
	Cambridge, England.
	.fi
	.
	.
	.SH REVISION
	.rs
	.sp
	.nf
	Last updated: 31 January 2016
	Copyright (c) 1997-2016 University of Cambridge.
	.fi