pcre-4.2/doc/pcreposix.3

.TH PCRE 3
.SH NAME
PCRE - Perl-compatible regular expressions.
.SH SYNOPSIS OF POSIX API
.B #include <pcreposix.h>
.PP
.SM
.br
.B int regcomp(regex_t *\fIpreg\fR, const char *\fIpattern\fR,
.ti +5n
.B int \fIcflags\fR);
.PP
.br
.B int regexec(regex_t *\fIpreg\fR, const char *\fIstring\fR,
.ti +5n
.B size_t \fInmatch\fR, regmatch_t \fIpmatch\fR[], int \fIeflags\fR);
.PP
.br
.B size_t regerror(int \fIerrcode\fR, const regex_t *\fIpreg\fR,
.ti +5n
.B char *\fIerrbuf\fR, size_t \fIerrbuf_size\fR);
.PP
.br
.B void regfree(regex_t *\fIpreg\fR);

.SH DESCRIPTION
.rs
.sp
This set of functions provides a POSIX-style API to the PCRE regular expression
package. See the
.\" HREF
\fBpcreapi\fR
.\"
documentation for a description of the native API, which contains additional
functionality.

The functions described here are just wrapper functions that ultimately call
the PCRE native API. Their prototypes are defined in the \fBpcreposix.h\fR
header file, and on Unix systems the library itself is called
\fBpcreposix.a\fR, so can be accessed by adding \fB-lpcreposix\fR to the
command for linking an application which uses them. Because the POSIX functions
call the native ones, it is also necessary to add \fR-lpcre\fR.

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.

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.

The header for these functions is supplied as \fBpcreposix.h\fR to avoid any
potential clash with other POSIX libraries. It can, of course, be renamed or
aliased as \fBregex.h\fR, which is the "correct" name. It provides two
structure types, \fIregex_t\fR for compiled internal forms, and
\fIregmatch_t\fR 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()\fR 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\fR. The \fIpreg\fR argument is a pointer
to a regex_t structure which is used as a base for storing information about
the compiled expression.

The argument \fIcflags\fR is either zero, or contains one or more of the bits
defined by the following macros:

  REG_ICASE

The PCRE_CASELESS option is set when the expression is passed for compilation
to the native function.

  REG_NEWLINE

The PCRE_MULTILINE option is set when the expression is passed for compilation
to the native function. Note that this does \fInot\fR mimic the defined POSIX
behaviour for REG_NEWLINE (see the following section).

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\fR 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).

The yield of \fBregcomp()\fR is zero on success, and non-zero otherwise. The
\fIpreg\fR structure is filled in on success, and one member of the structure
is public: \fIre_nsub\fR 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:

                          Default   Change with

  . matches newline          no     PCRE_DOTALL
  newline matches [^a]       yes    not changeable
  $ matches \\n at end        yes    PCRE_DOLLARENDONLY
  $ matches \\n in middle     no     PCRE_MULTILINE
  ^ matches \\n in middle     no     PCRE_MULTILINE

This is the equivalent table for POSIX:

                          Default   Change with

  . matches newline          yes      REG_NEWLINE
  newline matches [^a]       yes      REG_NEWLINE
  $ matches \\n at end        no       REG_NEWLINE
  $ matches \\n in middle     no       REG_NEWLINE
  ^ matches \\n in middle     no       REG_NEWLINE

PCRE's behaviour is the same as Perl's, except that there is no equivalent for
PCRE_DOLLARENDONLY in Perl. In both PCRE and Perl, there is no way to stop
newline from matching [^a].

The default POSIX newline handling can be obtained by setting PCRE_DOTALL and
PCRE_DOLLARENDONLY, 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()\fR is called to match a pre-compiled pattern
\fIpreg\fR against a given \fIstring\fR, which is terminated by a zero byte,
subject to the options in \fIeflags\fR. These can be:

  REG_NOTBOL

The PCRE_NOTBOL option is set when calling the underlying PCRE matching
function.

  REG_NOTEOL

The PCRE_NOTEOL option is set when calling the underlying PCRE matching
function.

The portion of the string that was matched, and also any captured substrings,
are returned via the \fIpmatch\fR argument, which points to an array of
\fInmatch\fR structures of type \fIregmatch_t\fR, containing the members
\fIrm_so\fR and \fIrm_eo\fR. 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\fR 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.

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()\fR function maps a non-zero errorcode from either
\fBregcomp()\fR or \fBregexec()\fR to a printable message. If \fIpreg\fR 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\fR. The length of the
message, including the zero, is limited to \fIerrbuf_size\fR. The yield of the
function is the size of buffer needed to hold the whole message.

.SH STORAGE
.rs
.sp
Compiling a regular expression causes memory to be allocated and associated
with the \fIpreg\fR structure. The function \fBregfree()\fR frees all such
memory, after which \fIpreg\fR may no longer be used as a compiled expression.

.SH AUTHOR
.rs
.sp
Philip Hazel <ph10@cam.ac.uk>
.br
University Computing Service,
.br
Cambridge CB2 3QG, England.

.in 0
Last updated: 03 February 2003
.br
Copyright (c) 1997-2003 University of Cambridge.
1	.TH PCRE 3
2	.SH NAME
3	PCRE - Perl-compatible regular expressions.
4	.SH SYNOPSIS OF POSIX API
5	.B #include <pcreposix.h>
6	.PP
7	.SM
8	.br
9	.B int regcomp(regex_t \fIpreg\fR, const char \fIpattern\fR,
10	.ti +5n
11	.B int \fIcflags\fR);
12	.PP
13	.br
14	.B int regexec(regex_t \fIpreg\fR, const char \fIstring\fR,
15	.ti +5n
16	.B size_t \fInmatch\fR, regmatch_t \fIpmatch\fR[], int \fIeflags\fR);
17	.PP
18	.br
19	.B size_t regerror(int \fIerrcode\fR, const regex_t *\fIpreg\fR,
20	.ti +5n
21	.B char *\fIerrbuf\fR, size_t \fIerrbuf_size\fR);
22	.PP
23	.br
24	.B void regfree(regex_t *\fIpreg\fR);
25
26	.SH DESCRIPTION
27	.rs
28	.sp
29	This set of functions provides a POSIX-style API to the PCRE regular expression
30	package. See the
31	.\" HREF
32	\fBpcreapi\fR
33	.\"
34	documentation for a description of the native API, which contains additional
35	functionality.
36
37	The functions described here are just wrapper functions that ultimately call
38	the PCRE native API. Their prototypes are defined in the \fBpcreposix.h\fR
39	header file, and on Unix systems the library itself is called
40	\fBpcreposix.a\fR, so can be accessed by adding \fB-lpcreposix\fR to the
41	command for linking an application which uses them. Because the POSIX functions
42	call the native ones, it is also necessary to add \fR-lpcre\fR.
43
44	I have implemented only those option bits that can be reasonably mapped to PCRE
45	native options. In addition, the options REG_EXTENDED and REG_NOSUB are defined
46	with the value zero. They have no effect, but since programs that are written
47	to the POSIX interface often use them, this makes it easier to slot in PCRE as
48	a replacement library. Other POSIX options are not even defined.
49
50	When PCRE is called via these functions, it is only the API that is POSIX-like
51	in style. The syntax and semantics of the regular expressions themselves are
52	still those of Perl, subject to the setting of various PCRE options, as
53	described below.
54
55	The header for these functions is supplied as \fBpcreposix.h\fR to avoid any
56	potential clash with other POSIX libraries. It can, of course, be renamed or
57	aliased as \fBregex.h\fR, which is the "correct" name. It provides two
58	structure types, \fIregex_t\fR for compiled internal forms, and
59	\fIregmatch_t\fR 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
63	.SH COMPILING A PATTERN
64	.rs
65	.sp
66	The function \fBregcomp()\fR 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\fR. The \fIpreg\fR argument is a pointer
69	to a regex_t structure which is used as a base for storing information about
70	the compiled expression.
71
72	The argument \fIcflags\fR is either zero, or contains one or more of the bits
73	defined by the following macros:
74
75	REG_ICASE
76
77	The PCRE_CASELESS option is set when the expression is passed for compilation
78	to the native function.
79
80	REG_NEWLINE
81
82	The PCRE_MULTILINE option is set when the expression is passed for compilation
83	to the native function. Note that this does \fInot\fR mimic the defined POSIX
84	behaviour for REG_NEWLINE (see the following section).
85
86	In the absence of these flags, no options are passed to the native function.
87	This means the the regex is compiled with PCRE default semantics. In
88	particular, the way it handles newline characters in the subject string is the
89	Perl way, not the POSIX way. Note that setting PCRE_MULTILINE has only
90	\fIsome\fR of the effects specified for REG_NEWLINE. It does not affect the way
91	newlines are matched by . (they aren't) or by a negative class such as [^a]
92	(they are).
93
94	The yield of \fBregcomp()\fR is zero on success, and non-zero otherwise. The
95	\fIpreg\fR structure is filled in on success, and one member of the structure
96	is public: \fIre_nsub\fR contains the number of capturing subpatterns in
97	the regular expression. Various error codes are defined in the header file.
98
99	.SH MATCHING NEWLINE CHARACTERS
100	.rs
101	.sp
102	This area is not simple, because POSIX and Perl take different views of things.
103	It is not possible to get PCRE to obey POSIX semantics, but then PCRE was never
104	intended to be a POSIX engine. The following table lists the different
105	possibilities for matching newline characters in PCRE:
106
107	Default Change with
108
109	. matches newline no PCRE_DOTALL
110	newline matches [^a] yes not changeable
111	$ matches \\n at end yes PCRE_DOLLARENDONLY
112	$ matches \\n in middle no PCRE_MULTILINE
113	^ matches \\n in middle no PCRE_MULTILINE
114
115	This is the equivalent table for POSIX:
116
117	Default Change with
118
119	. matches newline yes REG_NEWLINE
120	newline matches [^a] yes REG_NEWLINE
121	$ matches \\n at end no REG_NEWLINE
122	$ matches \\n in middle no REG_NEWLINE
123	^ matches \\n in middle no REG_NEWLINE
124
125	PCRE's behaviour is the same as Perl's, except that there is no equivalent for
126	PCRE_DOLLARENDONLY in Perl. In both PCRE and Perl, there is no way to stop
127	newline from matching [^a].
128
129	The default POSIX newline handling can be obtained by setting PCRE_DOTALL and
130	PCRE_DOLLARENDONLY, but there is no way to make PCRE behave exactly as for the
131	REG_NEWLINE action.
132
133	.SH MATCHING A PATTERN
134	.rs
135	.sp
136	The function \fBregexec()\fR is called to match a pre-compiled pattern
137	\fIpreg\fR against a given \fIstring\fR, which is terminated by a zero byte,
138	subject to the options in \fIeflags\fR. These can be:
139
140	REG_NOTBOL
141
142	The PCRE_NOTBOL option is set when calling the underlying PCRE matching
143	function.
144
145	REG_NOTEOL
146
147	The PCRE_NOTEOL option is set when calling the underlying PCRE matching
148	function.
149
150	The portion of the string that was matched, and also any captured substrings,
151	are returned via the \fIpmatch\fR argument, which points to an array of
152	\fInmatch\fR structures of type \fIregmatch_t\fR, containing the members
153	\fIrm_so\fR and \fIrm_eo\fR. These contain the offset to the first character of
154	each substring and the offset to the first character after the end of each
155	substring, respectively. The 0th element of the vector relates to the entire
156	portion of \fIstring\fR that was matched; subsequent elements relate to the
157	capturing subpatterns of the regular expression. Unused entries in the array
158	have both structure members set to -1.
159
160	A successful match yields a zero return; various error codes are defined in the
161	header file, of which REG_NOMATCH is the "expected" failure code.
162
163	.SH ERROR MESSAGES
164	.rs
165	.sp
166	The \fBregerror()\fR function maps a non-zero errorcode from either
167	\fBregcomp()\fR or \fBregexec()\fR to a printable message. If \fIpreg\fR is not
168	NULL, the error should have arisen from the use of that structure. A message
169	terminated by a binary zero is placed in \fIerrbuf\fR. The length of the
170	message, including the zero, is limited to \fIerrbuf_size\fR. The yield of the
171	function is the size of buffer needed to hold the whole message.
172
173	.SH STORAGE
174	.rs
175	.sp
176	Compiling a regular expression causes memory to be allocated and associated
177	with the \fIpreg\fR structure. The function \fBregfree()\fR frees all such
178	memory, after which \fIpreg\fR may no longer be used as a compiled expression.
179
180	.SH AUTHOR
181	.rs
182	.sp
183	Philip Hazel <ph10@cam.ac.uk>
184	.br
185	University Computing Service,
186	.br
187	Cambridge CB2 3QG, England.
188
189	.in 0
190	Last updated: 03 February 2003
191	.br
192	Copyright (c) 1997-2003 University of Cambridge.