trunk/doc/pcreposix.3

.TH PCREPOSIX 3
.SH NAME
PCRE - Perl-compatible regular expressions.
.SH "SYNOPSIS OF POSIX API"
.rs
.sp
.B #include <pcreposix.h>
.PP
.SM
.B int regcomp(regex_t *\fIpreg\fP, const char *\fIpattern\fP,
.ti +5n
.B int \fIcflags\fP);
.PP
.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
.B size_t regerror(int \fIerrcode\fP, const regex_t *\fIpreg\fP,
.ti +5n
.B char *\fIerrbuf\fP, size_t \fIerrbuf_size\fP);
.PP
.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 POSIX option bits that can be reasonably mapped
to PCRE native options. 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 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 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 PCRE_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 PCRE_CASELESS option is set when the regular expression is passed for
compilation to the native function.
.sp
  REG_NEWLINE
.sp
The PCRE_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
The PCRE_NO_AUTO_CAPTURE option is set when the regular expression is passed
for compilation to the native function. In addition, 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.
.sp
  REG_UTF8
.sp
The PCRE_UTF8 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_UTF8
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 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 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 PCRE_NOTBOL option is set when calling the underlying PCRE matching
function.
.sp
  REG_NOTEMPTY
.sp
The PCRE_NOTEMPTY option is set when calling the underlying PCRE 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 PCRE_NOTEOL option is set when calling the underlying PCRE 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.
.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.
.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 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
.nf
Philip Hazel
University Computing Service
Cambridge CB2 3QH, England.
.fi
.
.
.SH REVISION
.rs
.sp
.nf
Last updated: 11 March 2009
Copyright (c) 1997-2009 University of Cambridge.
.fi
1	nigel	79	.TH PCREPOSIX 3
2	nigel	41	.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	nigel	75	.B int regcomp(regex_t \fIpreg\fP, const char \fIpattern\fP,
11	nigel	41	.ti +5n
12	nigel	75	.B int \fIcflags\fP);
13	nigel	41	.PP
14	nigel	75	.B int regexec(regex_t \fIpreg\fP, const char \fIstring\fP,
15	nigel	41	.ti +5n
16	nigel	75	.B size_t \fInmatch\fP, regmatch_t \fIpmatch\fP[], int \fIeflags\fP);
17	nigel	41	.PP
18	nigel	75	.B size_t regerror(int \fIerrcode\fP, const regex_t *\fIpreg\fP,
19	nigel	41	.ti +5n
20	nigel	75	.B char *\fIerrbuf\fP, size_t \fIerrbuf_size\fP);
21	nigel	41	.PP
22	nigel	75	.B void regfree(regex_t *\fIpreg\fP);
23			.
24	nigel	41	.SH DESCRIPTION
25	nigel	63	.rs
26			.sp
27	nigel	41	This set of functions provides a POSIX-style API to the PCRE regular expression
28	nigel	63	package. See the
29			.\" HREF
30	nigel	75	\fBpcreapi\fP
31	nigel	63	.\"
32	nigel	77	documentation for a description of PCRE's native API, which contains much
33			additional functionality.
34	nigel	75	.P
35	nigel	41	The functions described here are just wrapper functions that ultimately call
36	nigel	75	the PCRE native API. Their prototypes are defined in the \fBpcreposix.h\fP
37	nigel	63	header file, and on Unix systems the library itself is called
38	nigel	75	\fBpcreposix.a\fP, so can be accessed by adding \fB-lpcreposix\fP to the
39			command for linking an application that uses them. Because the POSIX functions
40			call the native ones, it is also necessary to add \fB-lpcre\fP.
41			.P
42	ph10	388	I have implemented only those POSIX option bits that can be reasonably mapped
43			to PCRE native options. In addition, the option REG_EXTENDED is defined with
44			the value zero. This has no effect, but since programs that are written to the
45			POSIX interface often use it, this makes it easier to slot in PCRE as a
46			replacement library. Other POSIX options are not even defined.
47	nigel	75	.P
48	nigel	41	When PCRE is called via these functions, it is only the API that is POSIX-like
49			in style. The syntax and semantics of the regular expressions themselves are
50			still those of Perl, subject to the setting of various PCRE options, as
51	nigel	69	described below. "POSIX-like in style" means that the API approximates to the
52			POSIX definition; it is not fully POSIX-compatible, and in multi-byte encoding
53			domains it is probably even less compatible.
54	nigel	75	.P
55			The header for these functions is supplied as \fBpcreposix.h\fP to avoid any
56	nigel	41	potential clash with other POSIX libraries. It can, of course, be renamed or
57	nigel	75	aliased as \fBregex.h\fP, which is the "correct" name. It provides two
58			structure types, \fIregex_t\fP for compiled internal forms, and
59			\fIregmatch_t\fP for returning captured substrings. It also defines some
60	nigel	41	constants whose names start with "REG_"; these are used for setting options and
61			identifying error codes.
62	nigel	75	.P
63			.SH "COMPILING A PATTERN"
64	nigel	63	.rs
65			.sp
66	nigel	75	The function \fBregcomp()\fP is called to compile a pattern into an
67	nigel	41	internal form. The pattern is a C string terminated by a binary zero, and
68	nigel	75	is passed in the argument \fIpattern\fP. The \fIpreg\fP argument is a pointer
69			to a \fBregex_t\fP structure that is used as a base for storing information
70	nigel	87	about the compiled regular expression.
71	nigel	75	.P
72			The argument \fIcflags\fP is either zero, or contains one or more of the bits
73	nigel	41	defined by the following macros:
74	nigel	75	.sp
75	nigel	77	REG_DOTALL
76			.sp
77	nigel	87	The PCRE_DOTALL option is set when the regular expression is passed for
78			compilation to the native function. Note that REG_DOTALL is not part of the
79			POSIX standard.
80	nigel	77	.sp
81	nigel	41	REG_ICASE
82	nigel	75	.sp
83	nigel	87	The PCRE_CASELESS option is set when the regular expression is passed for
84			compilation to the native function.
85	nigel	75	.sp
86	nigel	41	REG_NEWLINE
87	nigel	75	.sp
88	nigel	87	The PCRE_MULTILINE option is set when the regular expression is passed for
89			compilation to the native function. Note that this does \fInot\fP mimic the
90			defined POSIX behaviour for REG_NEWLINE (see the following section).
91			.sp
92			REG_NOSUB
93			.sp
94			The PCRE_NO_AUTO_CAPTURE option is set when the regular expression is passed
95			for compilation to the native function. In addition, when a pattern that is
96			compiled with this flag is passed to \fBregexec()\fP for matching, the
97			\fInmatch\fP and \fIpmatch\fP arguments are ignored, and no captured strings
98			are returned.
99			.sp
100			REG_UTF8
101			.sp
102			The PCRE_UTF8 option is set when the regular expression is passed for
103			compilation to the native function. This causes the pattern itself and all data
104			strings used for matching it to be treated as UTF-8 strings. Note that REG_UTF8
105			is not part of the POSIX standard.
106	nigel	75	.P
107	nigel	49	In the absence of these flags, no options are passed to the native function.
108			This means the the regex is compiled with PCRE default semantics. In
109			particular, the way it handles newline characters in the subject string is the
110			Perl way, not the POSIX way. Note that setting PCRE_MULTILINE has only
111	nigel	75	\fIsome\fP of the effects specified for REG_NEWLINE. It does not affect the way
112	nigel	63	newlines are matched by . (they aren't) or by a negative class such as [^a]
113			(they are).
114	nigel	75	.P
115			The yield of \fBregcomp()\fP is zero on success, and non-zero otherwise. The
116			\fIpreg\fP structure is filled in on success, and one member of the structure
117			is public: \fIre_nsub\fP contains the number of capturing subpatterns in
118	nigel	41	the regular expression. Various error codes are defined in the header file.
119	nigel	75	.
120			.
121			.SH "MATCHING NEWLINE CHARACTERS"
122	nigel	63	.rs
123			.sp
124			This area is not simple, because POSIX and Perl take different views of things.
125			It is not possible to get PCRE to obey POSIX semantics, but then PCRE was never
126			intended to be a POSIX engine. The following table lists the different
127			possibilities for matching newline characters in PCRE:
128	nigel	75	.sp
129	nigel	63	Default Change with
130	nigel	75	.sp
131	nigel	63	. matches newline no PCRE_DOTALL
132			newline matches [^a] yes not changeable
133	nigel	75	$ matches \en at end yes PCRE_DOLLARENDONLY
134			$ matches \en in middle no PCRE_MULTILINE
135			^ matches \en in middle no PCRE_MULTILINE
136			.sp
137	nigel	63	This is the equivalent table for POSIX:
138	nigel	75	.sp
139	nigel	63	Default Change with
140	nigel	75	.sp
141			. matches newline yes REG_NEWLINE
142			newline matches [^a] yes REG_NEWLINE
143			$ matches \en at end no REG_NEWLINE
144			$ matches \en in middle no REG_NEWLINE
145			^ matches \en in middle no REG_NEWLINE
146			.sp
147	nigel	63	PCRE's behaviour is the same as Perl's, except that there is no equivalent for
148	nigel	75	PCRE_DOLLAR_ENDONLY in Perl. In both PCRE and Perl, there is no way to stop
149	nigel	63	newline from matching [^a].
150	nigel	75	.P
151	nigel	63	The default POSIX newline handling can be obtained by setting PCRE_DOTALL and
152	nigel	75	PCRE_DOLLAR_ENDONLY, but there is no way to make PCRE behave exactly as for the
153	nigel	63	REG_NEWLINE action.
154	nigel	75	.
155			.
156			.SH "MATCHING A PATTERN"
157	nigel	63	.rs
158			.sp
159	nigel	75	The function \fBregexec()\fP is called to match a compiled pattern \fIpreg\fP
160	ph10	345	against a given \fIstring\fP, which is by default terminated by a zero byte
161	ph10	332	(but see REG_STARTEND below), subject to the options in \fIeflags\fP. These can
162			be:
163	nigel	75	.sp
164	nigel	41	REG_NOTBOL
165	nigel	75	.sp
166	nigel	41	The PCRE_NOTBOL option is set when calling the underlying PCRE matching
167			function.
168	nigel	75	.sp
169	ph10	388	REG_NOTEMPTY
170	ph10	392	.sp
171	ph10	388	The PCRE_NOTEMPTY option is set when calling the underlying PCRE matching
172	ph10	392	function. Note that REG_NOTEMPTY is not part of the POSIX standard. However,
173	ph10	388	setting this option can give more POSIX-like behaviour in some situations.
174			.sp
175	nigel	41	REG_NOTEOL
176	nigel	75	.sp
177	nigel	41	The PCRE_NOTEOL option is set when calling the underlying PCRE matching
178			function.
179	ph10	332	.sp
180			REG_STARTEND
181			.sp
182			The string is considered to start at \fIstring\fP + \fIpmatch[0].rm_so\fP and
183			to have a terminating NUL located at \fIstring\fP + \fIpmatch[0].rm_eo\fP
184			(there need not actually be a NUL at that location), regardless of the value of
185			\fInmatch\fP. This is a BSD extension, compatible with but not specified by
186			IEEE Standard 1003.2 (POSIX.2), and should be used with caution in software
187			intended to be portable to other systems. Note that a non-zero \fIrm_so\fP does
188			not imply REG_NOTBOL; REG_STARTEND affects only the location of the string, not
189			how it is matched.
190	nigel	75	.P
191	nigel	87	If the pattern was compiled with the REG_NOSUB flag, no data about any matched
192			strings is returned. The \fInmatch\fP and \fIpmatch\fP arguments of
193			\fBregexec()\fP are ignored.
194	nigel	75	.P
195	nigel	87	Otherwise,the portion of the string that was matched, and also any captured
196			substrings, are returned via the \fIpmatch\fP argument, which points to an
197			array of \fInmatch\fP structures of type \fIregmatch_t\fP, containing the
198			members \fIrm_so\fP and \fIrm_eo\fP. These contain the offset to the first
199			character of each substring and the offset to the first character after the end
200			of each substring, respectively. The 0th element of the vector relates to the
201			entire portion of \fIstring\fP that was matched; subsequent elements relate to
202			the capturing subpatterns of the regular expression. Unused entries in the
203			array have both structure members set to -1.
204			.P
205	nigel	41	A successful match yields a zero return; various error codes are defined in the
206			header file, of which REG_NOMATCH is the "expected" failure code.
207	nigel	75	.
208			.
209			.SH "ERROR MESSAGES"
210	nigel	63	.rs
211			.sp
212	nigel	75	The \fBregerror()\fP function maps a non-zero errorcode from either
213			\fBregcomp()\fP or \fBregexec()\fP to a printable message. If \fIpreg\fP is not
214	nigel	41	NULL, the error should have arisen from the use of that structure. A message
215	nigel	75	terminated by a binary zero is placed in \fIerrbuf\fP. The length of the
216			message, including the zero, is limited to \fIerrbuf_size\fP. The yield of the
217	nigel	41	function is the size of buffer needed to hold the whole message.
218	nigel	75	.
219			.
220			.SH MEMORY USAGE
221	nigel	63	.rs
222			.sp
223	nigel	41	Compiling a regular expression causes memory to be allocated and associated
224	nigel	75	with the \fIpreg\fP structure. The function \fBregfree()\fP frees all such
225			memory, after which \fIpreg\fP may no longer be used as a compiled expression.
226			.
227			.
228	nigel	41	.SH AUTHOR
229	nigel	63	.rs
230			.sp
231	ph10	99	.nf
232	nigel	77	Philip Hazel
233	ph10	99	University Computing Service
234	nigel	93	Cambridge CB2 3QH, England.
235	ph10	99	.fi
236			.
237			.
238			.SH REVISION
239			.rs
240			.sp
241			.nf
242	ph10	388	Last updated: 11 March 2009
243			Copyright (c) 1997-2009 University of Cambridge.
244	ph10	99	.fi
Name	Value
svn:eol-style	native
svn:keywords	"Author Date Id Revision Url"