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	.TH PCRE 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	.br
11	.B int regcomp(regex_t \fIpreg\fP, const char \fIpattern\fP,
12	.ti +5n
13	.B int \fIcflags\fP);
14	.PP
15	.br
16	.B int regexec(regex_t \fIpreg\fP, const char \fIstring\fP,
17	.ti +5n
18	.B size_t \fInmatch\fP, regmatch_t \fIpmatch\fP[], int \fIeflags\fP);
19	.PP
20	.br
21	.B size_t regerror(int \fIerrcode\fP, const regex_t *\fIpreg\fP,
22	.ti +5n
23	.B char *\fIerrbuf\fP, size_t \fIerrbuf_size\fP);
24	.PP
25	.br
26	.B void regfree(regex_t *\fIpreg\fP);
27	.
28	.SH DESCRIPTION
29	.rs
30	.sp
31	This set of functions provides a POSIX-style API to the PCRE regular expression
32	package. See the
33	.\" HREF
34	\fBpcreapi\fP
35	.\"
36	documentation for a description of PCRE's native API, which contains much
37	additional functionality.
38	.P
39	The functions described here are just wrapper functions that ultimately call
40	the PCRE native API. Their prototypes are defined in the \fBpcreposix.h\fP
41	header file, and on Unix systems the library itself is called
42	\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	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	.P
52	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	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	.P
59	The header for these functions is supplied as \fBpcreposix.h\fP to avoid any
60	potential clash with other POSIX libraries. It can, of course, be renamed or
61	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	constants whose names start with "REG_"; these are used for setting options and
65	identifying error codes.
66	.P
67	.SH "COMPILING A PATTERN"
68	.rs
69	.sp
70	The function \fBregcomp()\fP is called to compile a pattern into an
71	internal form. The pattern is a C string terminated by a binary zero, and
72	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	defined by the following macros:
78	.sp
79	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	REG_ICASE
85	.sp
86	The PCRE_CASELESS option is set when the expression is passed for compilation
87	to the native function.
88	.sp
89	REG_NEWLINE
90	.sp
91	The PCRE_MULTILINE option is set when the expression is passed for compilation
92	to the native function. Note that this does \fInot\fP mimic the defined POSIX
93	behaviour for REG_NEWLINE (see the following section).
94	.P
95	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	\fIsome\fP of the effects specified for REG_NEWLINE. It does not affect the way
100	newlines are matched by . (they aren't) or by a negative class such as [^a]
101	(they are).
102	.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	the regular expression. Various error codes are defined in the header file.
107	.
108	.
109	.SH "MATCHING NEWLINE CHARACTERS"
110	.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	.sp
117	Default Change with
118	.sp
119	. matches newline no PCRE_DOTALL
120	newline matches [^a] yes not changeable
121	$ 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	This is the equivalent table for POSIX:
126	.sp
127	Default Change with
128	.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	PCRE's behaviour is the same as Perl's, except that there is no equivalent for
136	PCRE_DOLLAR_ENDONLY in Perl. In both PCRE and Perl, there is no way to stop
137	newline from matching [^a].
138	.P
139	The default POSIX newline handling can be obtained by setting PCRE_DOTALL and
140	PCRE_DOLLAR_ENDONLY, but there is no way to make PCRE behave exactly as for the
141	REG_NEWLINE action.
142	.
143	.
144	.SH "MATCHING A PATTERN"
145	.rs
146	.sp
147	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	REG_NOTBOL
152	.sp
153	The PCRE_NOTBOL option is set when calling the underlying PCRE matching
154	function.
155	.sp
156	REG_NOTEOL
157	.sp
158	The PCRE_NOTEOL option is set when calling the underlying PCRE matching
159	function.
160	.P
161	The portion of the string that was matched, and also any captured substrings,
162	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	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	portion of \fIstring\fP that was matched; subsequent elements relate to the
168	capturing subpatterns of the regular expression. Unused entries in the array
169	have both structure members set to -1.
170	.P
171	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	.
174	.
175	.SH "ERROR MESSAGES"
176	.rs
177	.sp
178	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	NULL, the error should have arisen from the use of that structure. A message
181	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	function is the size of buffer needed to hold the whole message.
184	.
185	.
186	.SH MEMORY USAGE
187	.rs
188	.sp
189	Compiling a regular expression causes memory to be allocated and associated
190	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	.SH AUTHOR
195	.rs
196	.sp
197	Philip Hazel
198	.br
199	University Computing Service,
200	.br
201	Cambridge CB2 3QG, England.
202	.P
203	.in 0
204	Last updated: 28 February 2005
205	.br
206	Copyright (c) 1997-2005 University of Cambridge.