trunk/doc/pcreposix.3

.TH PCREPOSIX 3 "09 January 2012" "PCRE 8.30"
.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 for the PCRE regular
expression 8-bit library. See the
.\" HREF
\fBpcreapi\fP
.\"
documentation for a description of PCRE's native API, which contains much
additional functionality. There is no POSIX-style wrapper for PCRE's 16-bit
library.
.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
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
PCRE-specific features via the POSIX calling interface.
.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.
.
.
.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_UCP
.sp
The PCRE_UCP option is set when the regular expression is passed for
compilation to the native function. This causes PCRE to use Unicode properties
when matchine \ed, \ew, etc., instead of just recognizing ASCII values. Note
that REG_UTF8 is not part of the POSIX standard.
.sp
  REG_UNGREEDY
.sp
The PCRE_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_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 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 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
If the value of \fInmatch\fP is zero, or if the value \fIpmatch\fP is NULL,
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 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: 09 January 2012
Copyright (c) 1997-2012 University of Cambridge.
.fi
1	.TH PCREPOSIX 3 "09 January 2012" "PCRE 8.30"
2	.SH NAME
3	PCRE - Perl-compatible regular expressions.
4	.SH "SYNOPSIS OF POSIX API"
5	.rs
6	.sp
7	.B #include <pcreposix.h>
8	.PP
9	.SM
10	.B int regcomp(regex_t \fIpreg\fP, const char \fIpattern\fP,
11	.ti +5n
12	.B int \fIcflags\fP);
13	.PP
14	.B int regexec(regex_t \fIpreg\fP, const char \fIstring\fP,
15	.ti +5n
16	.B size_t \fInmatch\fP, regmatch_t \fIpmatch\fP[], int \fIeflags\fP);
17	.PP
18	.B size_t regerror(int \fIerrcode\fP, const regex_t *\fIpreg\fP,
19	.ti +5n
20	.B char *\fIerrbuf\fP, size_t \fIerrbuf_size\fP);
21	.PP
22	.B void regfree(regex_t *\fIpreg\fP);
23	.
24	.SH DESCRIPTION
25	.rs
26	.sp
27	This set of functions provides a POSIX-style API for the PCRE regular
28	expression 8-bit library. See the
29	.\" HREF
30	\fBpcreapi\fP
31	.\"
32	documentation for a description of PCRE's native API, which contains much
33	additional functionality. There is no POSIX-style wrapper for PCRE's 16-bit
34	library.
35	.P
36	The functions described here are just wrapper functions that ultimately call
37	the PCRE native API. Their prototypes are defined in the \fBpcreposix.h\fP
38	header file, and on Unix systems the library itself is called
39	\fBpcreposix.a\fP, so can be accessed by adding \fB-lpcreposix\fP to the
40	command for linking an application that uses them. Because the POSIX functions
41	call the native ones, it is also necessary to add \fB-lpcre\fP.
42	.P
43	I have implemented only those POSIX option bits that can be reasonably mapped
44	to PCRE native options. In addition, the option REG_EXTENDED is defined with
45	the value zero. This has no effect, but since programs that are written to the
46	POSIX interface often use it, this makes it easier to slot in PCRE as a
47	replacement library. Other POSIX options are not even defined.
48	.P
49	There are also some other options that are not defined by POSIX. These have
50	been added at the request of users who want to make use of certain
51	PCRE-specific features via the POSIX calling interface.
52	.P
53	When PCRE is called via these functions, it is only the API that is POSIX-like
54	in style. The syntax and semantics of the regular expressions themselves are
55	still those of Perl, subject to the setting of various PCRE options, as
56	described below. "POSIX-like in style" means that the API approximates to the
57	POSIX definition; it is not fully POSIX-compatible, and in multi-byte encoding
58	domains it is probably even less compatible.
59	.P
60	The header for these functions is supplied as \fBpcreposix.h\fP to avoid any
61	potential clash with other POSIX libraries. It can, of course, be renamed or
62	aliased as \fBregex.h\fP, which is the "correct" name. It provides two
63	structure types, \fIregex_t\fP for compiled internal forms, and
64	\fIregmatch_t\fP for returning captured substrings. It also defines some
65	constants whose names start with "REG_"; these are used for setting options and
66	identifying error codes.
67	.
68	.
69	.SH "COMPILING A PATTERN"
70	.rs
71	.sp
72	The function \fBregcomp()\fP is called to compile a pattern into an
73	internal form. The pattern is a C string terminated by a binary zero, and
74	is passed in the argument \fIpattern\fP. The \fIpreg\fP argument is a pointer
75	to a \fBregex_t\fP structure that is used as a base for storing information
76	about the compiled regular expression.
77	.P
78	The argument \fIcflags\fP is either zero, or contains one or more of the bits
79	defined by the following macros:
80	.sp
81	REG_DOTALL
82	.sp
83	The PCRE_DOTALL option is set when the regular expression is passed for
84	compilation to the native function. Note that REG_DOTALL is not part of the
85	POSIX standard.
86	.sp
87	REG_ICASE
88	.sp
89	The PCRE_CASELESS option is set when the regular expression is passed for
90	compilation to the native function.
91	.sp
92	REG_NEWLINE
93	.sp
94	The PCRE_MULTILINE option is set when the regular expression is passed for
95	compilation to the native function. Note that this does \fInot\fP mimic the
96	defined POSIX behaviour for REG_NEWLINE (see the following section).
97	.sp
98	REG_NOSUB
99	.sp
100	The PCRE_NO_AUTO_CAPTURE option is set when the regular expression is passed
101	for compilation to the native function. In addition, when a pattern that is
102	compiled with this flag is passed to \fBregexec()\fP for matching, the
103	\fInmatch\fP and \fIpmatch\fP arguments are ignored, and no captured strings
104	are returned.
105	.sp
106	REG_UCP
107	.sp
108	The PCRE_UCP option is set when the regular expression is passed for
109	compilation to the native function. This causes PCRE to use Unicode properties
110	when matchine \ed, \ew, etc., instead of just recognizing ASCII values. Note
111	that REG_UTF8 is not part of the POSIX standard.
112	.sp
113	REG_UNGREEDY
114	.sp
115	The PCRE_UNGREEDY option is set when the regular expression is passed for
116	compilation to the native function. Note that REG_UNGREEDY is not part of the
117	POSIX standard.
118	.sp
119	REG_UTF8
120	.sp
121	The PCRE_UTF8 option is set when the regular expression is passed for
122	compilation to the native function. This causes the pattern itself and all data
123	strings used for matching it to be treated as UTF-8 strings. Note that REG_UTF8
124	is not part of the POSIX standard.
125	.P
126	In the absence of these flags, no options are passed to the native function.
127	This means the the regex is compiled with PCRE default semantics. In
128	particular, the way it handles newline characters in the subject string is the
129	Perl way, not the POSIX way. Note that setting PCRE_MULTILINE has only
130	\fIsome\fP of the effects specified for REG_NEWLINE. It does not affect the way
131	newlines are matched by . (they are not) or by a negative class such as [^a]
132	(they are).
133	.P
134	The yield of \fBregcomp()\fP is zero on success, and non-zero otherwise. The
135	\fIpreg\fP structure is filled in on success, and one member of the structure
136	is public: \fIre_nsub\fP contains the number of capturing subpatterns in
137	the regular expression. Various error codes are defined in the header file.
138	.P
139	NOTE: If the yield of \fBregcomp()\fP is non-zero, you must not attempt to
140	use the contents of the \fIpreg\fP structure. If, for example, you pass it to
141	\fBregexec()\fP, the result is undefined and your program is likely to crash.
142	.
143	.
144	.SH "MATCHING NEWLINE CHARACTERS"
145	.rs
146	.sp
147	This area is not simple, because POSIX and Perl take different views of things.
148	It is not possible to get PCRE to obey POSIX semantics, but then PCRE was never
149	intended to be a POSIX engine. The following table lists the different
150	possibilities for matching newline characters in PCRE:
151	.sp
152	Default Change with
153	.sp
154	. matches newline no PCRE_DOTALL
155	newline matches [^a] yes not changeable
156	$ matches \en at end yes PCRE_DOLLARENDONLY
157	$ matches \en in middle no PCRE_MULTILINE
158	^ matches \en in middle no PCRE_MULTILINE
159	.sp
160	This is the equivalent table for POSIX:
161	.sp
162	Default Change with
163	.sp
164	. matches newline yes REG_NEWLINE
165	newline matches [^a] yes REG_NEWLINE
166	$ matches \en at end no REG_NEWLINE
167	$ matches \en in middle no REG_NEWLINE
168	^ matches \en in middle no REG_NEWLINE
169	.sp
170	PCRE's behaviour is the same as Perl's, except that there is no equivalent for
171	PCRE_DOLLAR_ENDONLY in Perl. In both PCRE and Perl, there is no way to stop
172	newline from matching [^a].
173	.P
174	The default POSIX newline handling can be obtained by setting PCRE_DOTALL and
175	PCRE_DOLLAR_ENDONLY, but there is no way to make PCRE behave exactly as for the
176	REG_NEWLINE action.
177	.
178	.
179	.SH "MATCHING A PATTERN"
180	.rs
181	.sp
182	The function \fBregexec()\fP is called to match a compiled pattern \fIpreg\fP
183	against a given \fIstring\fP, which is by default terminated by a zero byte
184	(but see REG_STARTEND below), subject to the options in \fIeflags\fP. These can
185	be:
186	.sp
187	REG_NOTBOL
188	.sp
189	The PCRE_NOTBOL option is set when calling the underlying PCRE matching
190	function.
191	.sp
192	REG_NOTEMPTY
193	.sp
194	The PCRE_NOTEMPTY option is set when calling the underlying PCRE matching
195	function. Note that REG_NOTEMPTY is not part of the POSIX standard. However,
196	setting this option can give more POSIX-like behaviour in some situations.
197	.sp
198	REG_NOTEOL
199	.sp
200	The PCRE_NOTEOL option is set when calling the underlying PCRE matching
201	function.
202	.sp
203	REG_STARTEND
204	.sp
205	The string is considered to start at \fIstring\fP + \fIpmatch[0].rm_so\fP and
206	to have a terminating NUL located at \fIstring\fP + \fIpmatch[0].rm_eo\fP
207	(there need not actually be a NUL at that location), regardless of the value of
208	\fInmatch\fP. This is a BSD extension, compatible with but not specified by
209	IEEE Standard 1003.2 (POSIX.2), and should be used with caution in software
210	intended to be portable to other systems. Note that a non-zero \fIrm_so\fP does
211	not imply REG_NOTBOL; REG_STARTEND affects only the location of the string, not
212	how it is matched.
213	.P
214	If the pattern was compiled with the REG_NOSUB flag, no data about any matched
215	strings is returned. The \fInmatch\fP and \fIpmatch\fP arguments of
216	\fBregexec()\fP are ignored.
217	.P
218	If the value of \fInmatch\fP is zero, or if the value \fIpmatch\fP is NULL,
219	no data about any matched strings is returned.
220	.P
221	Otherwise,the portion of the string that was matched, and also any captured
222	substrings, are returned via the \fIpmatch\fP argument, which points to an
223	array of \fInmatch\fP structures of type \fIregmatch_t\fP, containing the
224	members \fIrm_so\fP and \fIrm_eo\fP. These contain the offset to the first
225	character of each substring and the offset to the first character after the end
226	of each substring, respectively. The 0th element of the vector relates to the
227	entire portion of \fIstring\fP that was matched; subsequent elements relate to
228	the capturing subpatterns of the regular expression. Unused entries in the
229	array have both structure members set to -1.
230	.P
231	A successful match yields a zero return; various error codes are defined in the
232	header file, of which REG_NOMATCH is the "expected" failure code.
233	.
234	.
235	.SH "ERROR MESSAGES"
236	.rs
237	.sp
238	The \fBregerror()\fP function maps a non-zero errorcode from either
239	\fBregcomp()\fP or \fBregexec()\fP to a printable message. If \fIpreg\fP is not
240	NULL, the error should have arisen from the use of that structure. A message
241	terminated by a binary zero is placed in \fIerrbuf\fP. The length of the
242	message, including the zero, is limited to \fIerrbuf_size\fP. The yield of the
243	function is the size of buffer needed to hold the whole message.
244	.
245	.
246	.SH MEMORY USAGE
247	.rs
248	.sp
249	Compiling a regular expression causes memory to be allocated and associated
250	with the \fIpreg\fP structure. The function \fBregfree()\fP frees all such
251	memory, after which \fIpreg\fP may no longer be used as a compiled expression.
252	.
253	.
254	.SH AUTHOR
255	.rs
256	.sp
257	.nf
258	Philip Hazel
259	University Computing Service
260	Cambridge CB2 3QH, England.
261	.fi
262	.
263	.
264	.SH REVISION
265	.rs
266	.sp
267	.nf
268	Last updated: 09 January 2012
269	Copyright (c) 1997-2012 University of Cambridge.
270	.fi
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