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 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_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: 05 April 2008
Copyright (c) 1997-2008 University of Cambridge.
.fi
1	.TH PCREPOSIX 3
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 to the PCRE regular expression
28	package. See the
29	.\" HREF
30	\fBpcreapi\fP
31	.\"
32	documentation for a description of PCRE's native API, which contains much
33	additional functionality.
34	.P
35	The functions described here are just wrapper functions that ultimately call
36	the PCRE native API. Their prototypes are defined in the \fBpcreposix.h\fP
37	header file, and on Unix systems the library itself is called
38	\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	I have implemented only those option bits that can be reasonably mapped to PCRE
43	native options. In addition, the option REG_EXTENDED is defined with the value
44	zero. This has no effect, but since programs that are written to the POSIX
45	interface often use it, this makes it easier to slot in PCRE as a replacement
46	library. Other POSIX options are not even defined.
47	.P
48	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	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	.P
55	The header for these functions is supplied as \fBpcreposix.h\fP to avoid any
56	potential clash with other POSIX libraries. It can, of course, be renamed or
57	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	constants whose names start with "REG_"; these are used for setting options and
61	identifying error codes.
62	.P
63	.SH "COMPILING A PATTERN"
64	.rs
65	.sp
66	The function \fBregcomp()\fP is called to compile a pattern into an
67	internal form. The pattern is a C string terminated by a binary zero, and
68	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	about the compiled regular expression.
71	.P
72	The argument \fIcflags\fP is either zero, or contains one or more of the bits
73	defined by the following macros:
74	.sp
75	REG_DOTALL
76	.sp
77	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	.sp
81	REG_ICASE
82	.sp
83	The PCRE_CASELESS option is set when the regular expression is passed for
84	compilation to the native function.
85	.sp
86	REG_NEWLINE
87	.sp
88	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	.P
107	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	\fIsome\fP of the effects specified for REG_NEWLINE. It does not affect the way
112	newlines are matched by . (they aren't) or by a negative class such as [^a]
113	(they are).
114	.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	the regular expression. Various error codes are defined in the header file.
119	.
120	.
121	.SH "MATCHING NEWLINE CHARACTERS"
122	.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	.sp
129	Default Change with
130	.sp
131	. matches newline no PCRE_DOTALL
132	newline matches [^a] yes not changeable
133	$ 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	This is the equivalent table for POSIX:
138	.sp
139	Default Change with
140	.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	PCRE's behaviour is the same as Perl's, except that there is no equivalent for
148	PCRE_DOLLAR_ENDONLY in Perl. In both PCRE and Perl, there is no way to stop
149	newline from matching [^a].
150	.P
151	The default POSIX newline handling can be obtained by setting PCRE_DOTALL and
152	PCRE_DOLLAR_ENDONLY, but there is no way to make PCRE behave exactly as for the
153	REG_NEWLINE action.
154	.
155	.
156	.SH "MATCHING A PATTERN"
157	.rs
158	.sp
159	The function \fBregexec()\fP is called to match a compiled pattern \fIpreg\fP
160	against a given \fIstring\fP, which is by default terminated by a zero byte
161	(but see REG_STARTEND below), subject to the options in \fIeflags\fP. These can
162	be:
163	.sp
164	REG_NOTBOL
165	.sp
166	The PCRE_NOTBOL option is set when calling the underlying PCRE matching
167	function.
168	.sp
169	REG_NOTEOL
170	.sp
171	The PCRE_NOTEOL option is set when calling the underlying PCRE matching
172	function.
173	.sp
174	REG_STARTEND
175	.sp
176	The string is considered to start at \fIstring\fP + \fIpmatch[0].rm_so\fP and
177	to have a terminating NUL located at \fIstring\fP + \fIpmatch[0].rm_eo\fP
178	(there need not actually be a NUL at that location), regardless of the value of
179	\fInmatch\fP. This is a BSD extension, compatible with but not specified by
180	IEEE Standard 1003.2 (POSIX.2), and should be used with caution in software
181	intended to be portable to other systems. Note that a non-zero \fIrm_so\fP does
182	not imply REG_NOTBOL; REG_STARTEND affects only the location of the string, not
183	how it is matched.
184	.P
185	If the pattern was compiled with the REG_NOSUB flag, no data about any matched
186	strings is returned. The \fInmatch\fP and \fIpmatch\fP arguments of
187	\fBregexec()\fP are ignored.
188	.P
189	Otherwise,the portion of the string that was matched, and also any captured
190	substrings, are returned via the \fIpmatch\fP argument, which points to an
191	array of \fInmatch\fP structures of type \fIregmatch_t\fP, containing the
192	members \fIrm_so\fP and \fIrm_eo\fP. These contain the offset to the first
193	character of each substring and the offset to the first character after the end
194	of each substring, respectively. The 0th element of the vector relates to the
195	entire portion of \fIstring\fP that was matched; subsequent elements relate to
196	the capturing subpatterns of the regular expression. Unused entries in the
197	array have both structure members set to -1.
198	.P
199	A successful match yields a zero return; various error codes are defined in the
200	header file, of which REG_NOMATCH is the "expected" failure code.
201	.
202	.
203	.SH "ERROR MESSAGES"
204	.rs
205	.sp
206	The \fBregerror()\fP function maps a non-zero errorcode from either
207	\fBregcomp()\fP or \fBregexec()\fP to a printable message. If \fIpreg\fP is not
208	NULL, the error should have arisen from the use of that structure. A message
209	terminated by a binary zero is placed in \fIerrbuf\fP. The length of the
210	message, including the zero, is limited to \fIerrbuf_size\fP. The yield of the
211	function is the size of buffer needed to hold the whole message.
212	.
213	.
214	.SH MEMORY USAGE
215	.rs
216	.sp
217	Compiling a regular expression causes memory to be allocated and associated
218	with the \fIpreg\fP structure. The function \fBregfree()\fP frees all such
219	memory, after which \fIpreg\fP may no longer be used as a compiled expression.
220	.
221	.
222	.SH AUTHOR
223	.rs
224	.sp
225	.nf
226	Philip Hazel
227	University Computing Service
228	Cambridge CB2 3QH, England.
229	.fi
230	.
231	.
232	.SH REVISION
233	.rs
234	.sp
235	.nf
236	Last updated: 05 April 2008
237	Copyright (c) 1997-2008 University of Cambridge.
238	.fi
Name	Value
svn:eol-style	native
svn:keywords	"Author Date Id Revision Url"