trunk/doc/pcreposix.3

.TH PCRE 3
.SH NAME
PCRE - Perl-compatible regular expressions.
.SH "SYNOPSIS OF POSIX API"
.rs
.sp
.B #include <pcreposix.h>
.PP
.SM
.br
.B int regcomp(regex_t *\fIpreg\fP, const char *\fIpattern\fP,
.ti +5n
.B int \fIcflags\fP);
.PP
.br
.B int regexec(regex_t *\fIpreg\fP, const char *\fIstring\fP,
.ti +5n
.B size_t \fInmatch\fP, regmatch_t \fIpmatch\fP[], int \fIeflags\fP);
.PP
.br
.B size_t regerror(int \fIerrcode\fP, const regex_t *\fIpreg\fP,
.ti +5n
.B char *\fIerrbuf\fP, size_t \fIerrbuf_size\fP);
.PP
.br
.B void regfree(regex_t *\fIpreg\fP);
.
.SH DESCRIPTION
.rs
.sp
This set of functions provides a POSIX-style API to the PCRE regular expression
package. See the
.\" HREF
\fBpcreapi\fP
.\"
documentation for a description of PCRE's native API, which contains much
additional functionality.
.P
The functions described here are just wrapper functions that ultimately call
the PCRE native API. Their prototypes are defined in the \fBpcreposix.h\fP
header file, and on Unix systems the library itself is called
\fBpcreposix.a\fP, so can be accessed by adding \fB-lpcreposix\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-lpcre\fP.
.P
I have implemented only those option bits that can be reasonably mapped to PCRE
native options. In addition, the options REG_EXTENDED and REG_NOSUB are defined
with the value zero. They have no effect, but since programs that are written
to the POSIX interface often use them, this makes it easier to slot in PCRE as
a replacement library. Other POSIX options are not even defined.
.P
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 expressions themselves are
still those of Perl, subject to the setting of various PCRE 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-byte encoding
domains it is probably even less compatible.
.P
The header for these functions is supplied as \fBpcreposix.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.
.P
.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 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 PCRE_DOTALL option is set when the 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 PCRE_CASELESS option is set when the expression is passed for compilation
to the native function.
.sp
  REG_NEWLINE
.sp
The PCRE_MULTILINE option is set when the 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).
.P
In the absence of these flags, no options are passed to the native function.
This means the the regex is compiled with PCRE 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 PCRE_MULTILINE has only
\fIsome\fP of the effects specified for REG_NEWLINE. It does not affect the way
newlines are matched by . (they aren't) 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.
.
.
.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 PCRE to obey POSIX semantics, but then PCRE was never
intended to be a POSIX engine. The following table lists the different
possibilities for matching newline characters in PCRE:
.sp
                          Default   Change with
.sp
  . matches newline          no     PCRE_DOTALL
  newline matches [^a]       yes    not changeable
  $ matches \en at end        yes    PCRE_DOLLARENDONLY
  $ matches \en in middle     no     PCRE_MULTILINE
  ^ matches \en in middle     no     PCRE_MULTILINE
.sp
This is the equivalent table for POSIX:
.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
PCRE's behaviour is the same as Perl's, except that there is no equivalent for
PCRE_DOLLAR_ENDONLY in Perl. In both PCRE and Perl, there is no way to stop
newline from matching [^a].
.P
The default POSIX newline handling can be obtained by setting PCRE_DOTALL and
PCRE_DOLLAR_ENDONLY, but there is no way to make PCRE behave exactly as for the
REG_NEWLINE action.
.
.
.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 terminated by a zero byte, subject to
the options in \fIeflags\fP. These can be:
.sp
  REG_NOTBOL
.sp
The PCRE_NOTBOL option is set when calling the underlying PCRE matching
function.
.sp
  REG_NOTEOL
.sp
The PCRE_NOTEOL option is set when calling the underlying PCRE matching
function.
.P
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 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. The length of the
message, including the zero, is limited to \fIerrbuf_size\fP. The yield of the
function is the size of buffer needed to hold the whole message.
.
.
.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
Philip Hazel
.br
University Computing Service,
.br
Cambridge CB2 3QG, England.
.P
.in 0
Last updated: 28 February 2005
.br
Copyright (c) 1997-2005 University of Cambridge.
1	nigel	41	.TH PCRE 3
2			.SH NAME
3	nigel	63	PCRE - Perl-compatible regular expressions.
4	nigel	75	.SH "SYNOPSIS OF POSIX API"
5			.rs
6			.sp
7	nigel	41	.B #include <pcreposix.h>
8			.PP
9			.SM
10			.br
11	nigel	75	.B int regcomp(regex_t \fIpreg\fP, const char \fIpattern\fP,
12	nigel	41	.ti +5n
13	nigel	75	.B int \fIcflags\fP);
14	nigel	41	.PP
15			.br
16	nigel	75	.B int regexec(regex_t \fIpreg\fP, const char \fIstring\fP,
17	nigel	41	.ti +5n
18	nigel	75	.B size_t \fInmatch\fP, regmatch_t \fIpmatch\fP[], int \fIeflags\fP);
19	nigel	41	.PP
20			.br
21	nigel	75	.B size_t regerror(int \fIerrcode\fP, const regex_t *\fIpreg\fP,
22	nigel	41	.ti +5n
23	nigel	75	.B char *\fIerrbuf\fP, size_t \fIerrbuf_size\fP);
24	nigel	41	.PP
25			.br
26	nigel	75	.B void regfree(regex_t *\fIpreg\fP);
27			.
28	nigel	41	.SH DESCRIPTION
29	nigel	63	.rs
30			.sp
31	nigel	41	This set of functions provides a POSIX-style API to the PCRE regular expression
32	nigel	63	package. See the
33			.\" HREF
34	nigel	75	\fBpcreapi\fP
35	nigel	63	.\"
36	nigel	77	documentation for a description of PCRE's native API, which contains much
37			additional functionality.
38	nigel	75	.P
39	nigel	41	The functions described here are just wrapper functions that ultimately call
40	nigel	75	the PCRE native API. Their prototypes are defined in the \fBpcreposix.h\fP
41	nigel	63	header file, and on Unix systems the library itself is called
42	nigel	75	\fBpcreposix.a\fP, so can be accessed by adding \fB-lpcreposix\fP to the
43			command for linking an application that uses them. Because the POSIX functions
44			call the native ones, it is also necessary to add \fB-lpcre\fP.
45			.P
46	nigel	43	I have implemented only those option bits that can be reasonably mapped to PCRE
47			native options. In addition, the options REG_EXTENDED and REG_NOSUB are defined
48			with the value zero. They have no effect, but since programs that are written
49			to the POSIX interface often use them, this makes it easier to slot in PCRE as
50			a replacement library. Other POSIX options are not even defined.
51	nigel	75	.P
52	nigel	41	When PCRE is called via these functions, it is only the API that is POSIX-like
53			in style. The syntax and semantics of the regular expressions themselves are
54			still those of Perl, subject to the setting of various PCRE options, as
55	nigel	69	described below. "POSIX-like in style" means that the API approximates to the
56			POSIX definition; it is not fully POSIX-compatible, and in multi-byte encoding
57			domains it is probably even less compatible.
58	nigel	75	.P
59			The header for these functions is supplied as \fBpcreposix.h\fP to avoid any
60	nigel	41	potential clash with other POSIX libraries. It can, of course, be renamed or
61	nigel	75	aliased as \fBregex.h\fP, which is the "correct" name. It provides two
62			structure types, \fIregex_t\fP for compiled internal forms, and
63			\fIregmatch_t\fP for returning captured substrings. It also defines some
64	nigel	41	constants whose names start with "REG_"; these are used for setting options and
65			identifying error codes.
66	nigel	75	.P
67			.SH "COMPILING A PATTERN"
68	nigel	63	.rs
69			.sp
70	nigel	75	The function \fBregcomp()\fP is called to compile a pattern into an
71	nigel	41	internal form. The pattern is a C string terminated by a binary zero, and
72	nigel	75	is passed in the argument \fIpattern\fP. The \fIpreg\fP argument is a pointer
73			to a \fBregex_t\fP structure that is used as a base for storing information
74			about the compiled expression.
75			.P
76			The argument \fIcflags\fP is either zero, or contains one or more of the bits
77	nigel	41	defined by the following macros:
78	nigel	75	.sp
79	nigel	77	REG_DOTALL
80			.sp
81			The PCRE_DOTALL option is set when the expression is passed for compilation to
82			the native function. Note that REG_DOTALL is not part of the POSIX standard.
83			.sp
84	nigel	41	REG_ICASE
85	nigel	75	.sp
86	nigel	41	The PCRE_CASELESS option is set when the expression is passed for compilation
87			to the native function.
88	nigel	75	.sp
89	nigel	41	REG_NEWLINE
90	nigel	75	.sp
91	nigel	41	The PCRE_MULTILINE option is set when the expression is passed for compilation
92	nigel	75	to the native function. Note that this does \fInot\fP mimic the defined POSIX
93	nigel	63	behaviour for REG_NEWLINE (see the following section).
94	nigel	75	.P
95	nigel	49	In the absence of these flags, no options are passed to the native function.
96			This means the the regex is compiled with PCRE default semantics. In
97			particular, the way it handles newline characters in the subject string is the
98			Perl way, not the POSIX way. Note that setting PCRE_MULTILINE has only
99	nigel	75	\fIsome\fP of the effects specified for REG_NEWLINE. It does not affect the way
100	nigel	63	newlines are matched by . (they aren't) or by a negative class such as [^a]
101			(they are).
102	nigel	75	.P
103			The yield of \fBregcomp()\fP is zero on success, and non-zero otherwise. The
104			\fIpreg\fP structure is filled in on success, and one member of the structure
105			is public: \fIre_nsub\fP contains the number of capturing subpatterns in
106	nigel	41	the regular expression. Various error codes are defined in the header file.
107	nigel	75	.
108			.
109			.SH "MATCHING NEWLINE CHARACTERS"
110	nigel	63	.rs
111			.sp
112			This area is not simple, because POSIX and Perl take different views of things.
113			It is not possible to get PCRE to obey POSIX semantics, but then PCRE was never
114			intended to be a POSIX engine. The following table lists the different
115			possibilities for matching newline characters in PCRE:
116	nigel	75	.sp
117	nigel	63	Default Change with
118	nigel	75	.sp
119	nigel	63	. matches newline no PCRE_DOTALL
120			newline matches [^a] yes not changeable
121	nigel	75	$ matches \en at end yes PCRE_DOLLARENDONLY
122			$ matches \en in middle no PCRE_MULTILINE
123			^ matches \en in middle no PCRE_MULTILINE
124			.sp
125	nigel	63	This is the equivalent table for POSIX:
126	nigel	75	.sp
127	nigel	63	Default Change with
128	nigel	75	.sp
129			. matches newline yes REG_NEWLINE
130			newline matches [^a] yes REG_NEWLINE
131			$ matches \en at end no REG_NEWLINE
132			$ matches \en in middle no REG_NEWLINE
133			^ matches \en in middle no REG_NEWLINE
134			.sp
135	nigel	63	PCRE's behaviour is the same as Perl's, except that there is no equivalent for
136	nigel	75	PCRE_DOLLAR_ENDONLY in Perl. In both PCRE and Perl, there is no way to stop
137	nigel	63	newline from matching [^a].
138	nigel	75	.P
139	nigel	63	The default POSIX newline handling can be obtained by setting PCRE_DOTALL and
140	nigel	75	PCRE_DOLLAR_ENDONLY, but there is no way to make PCRE behave exactly as for the
141	nigel	63	REG_NEWLINE action.
142	nigel	75	.
143			.
144			.SH "MATCHING A PATTERN"
145	nigel	63	.rs
146			.sp
147	nigel	75	The function \fBregexec()\fP is called to match a compiled pattern \fIpreg\fP
148			against a given \fIstring\fP, which is terminated by a zero byte, subject to
149			the options in \fIeflags\fP. These can be:
150			.sp
151	nigel	41	REG_NOTBOL
152	nigel	75	.sp
153	nigel	41	The PCRE_NOTBOL option is set when calling the underlying PCRE matching
154			function.
155	nigel	75	.sp
156	nigel	41	REG_NOTEOL
157	nigel	75	.sp
158	nigel	41	The PCRE_NOTEOL option is set when calling the underlying PCRE matching
159			function.
160	nigel	75	.P
161	nigel	41	The portion of the string that was matched, and also any captured substrings,
162	nigel	75	are returned via the \fIpmatch\fP argument, which points to an array of
163			\fInmatch\fP structures of type \fIregmatch_t\fP, containing the members
164			\fIrm_so\fP and \fIrm_eo\fP. These contain the offset to the first character of
165	nigel	41	each substring and the offset to the first character after the end of each
166			substring, respectively. The 0th element of the vector relates to the entire
167	nigel	75	portion of \fIstring\fP that was matched; subsequent elements relate to the
168	nigel	41	capturing subpatterns of the regular expression. Unused entries in the array
169			have both structure members set to -1.
170	nigel	75	.P
171	nigel	41	A successful match yields a zero return; various error codes are defined in the
172			header file, of which REG_NOMATCH is the "expected" failure code.
173	nigel	75	.
174			.
175			.SH "ERROR MESSAGES"
176	nigel	63	.rs
177			.sp
178	nigel	75	The \fBregerror()\fP function maps a non-zero errorcode from either
179			\fBregcomp()\fP or \fBregexec()\fP to a printable message. If \fIpreg\fP is not
180	nigel	41	NULL, the error should have arisen from the use of that structure. A message
181	nigel	75	terminated by a binary zero is placed in \fIerrbuf\fP. The length of the
182			message, including the zero, is limited to \fIerrbuf_size\fP. The yield of the
183	nigel	41	function is the size of buffer needed to hold the whole message.
184	nigel	75	.
185			.
186			.SH MEMORY USAGE
187	nigel	63	.rs
188			.sp
189	nigel	41	Compiling a regular expression causes memory to be allocated and associated
190	nigel	75	with the \fIpreg\fP structure. The function \fBregfree()\fP frees all such
191			memory, after which \fIpreg\fP may no longer be used as a compiled expression.
192			.
193			.
194	nigel	41	.SH AUTHOR
195	nigel	63	.rs
196			.sp
197	nigel	77	Philip Hazel
198	nigel	41	.br
199			University Computing Service,
200			.br
201			Cambridge CB2 3QG, England.
202	nigel	75	.P
203	nigel	63	.in 0
204	nigel	77	Last updated: 28 February 2005
205	nigel	41	.br
206	nigel	77	Copyright (c) 1997-2005 University of Cambridge.