3
<title>pcreposix specification</title>
5
<body bgcolor="#FFFFFF" text="#00005A" link="#0066FF" alink="#3399FF" vlink="#2222BB">
6
This HTML document has been generated automatically from the original man page.
7
If there is any nonsense in it, please consult the man page, in case the
8
conversion went wrong.<br>
10
<li><a name="TOC1" href="#SEC1">SYNOPSIS OF POSIX API</a>
11
<li><a name="TOC2" href="#SEC2">DESCRIPTION</a>
12
<li><a name="TOC3" href="#SEC3">COMPILING A PATTERN</a>
13
<li><a name="TOC4" href="#SEC4">MATCHING NEWLINE CHARACTERS</a>
14
<li><a name="TOC5" href="#SEC5">MATCHING A PATTERN</a>
15
<li><a name="TOC6" href="#SEC6">ERROR MESSAGES</a>
16
<li><a name="TOC7" href="#SEC7">STORAGE</a>
17
<li><a name="TOC8" href="#SEC8">AUTHOR</a>
19
<br><a name="SEC1" href="#TOC1">SYNOPSIS OF POSIX API</a><br>
21
<b>#include <pcreposix.h></b>
24
<b>int regcomp(regex_t *<i>preg</i>, const char *<i>pattern</i>,</b>
25
<b>int <i>cflags</i>);</b>
28
<b>int regexec(regex_t *<i>preg</i>, const char *<i>string</i>,</b>
29
<b>size_t <i>nmatch</i>, regmatch_t <i>pmatch</i>[], int <i>eflags</i>);</b>
32
<b>size_t regerror(int <i>errcode</i>, const regex_t *<i>preg</i>,</b>
33
<b>char *<i>errbuf</i>, size_t <i>errbuf_size</i>);</b>
36
<b>void regfree(regex_t *<i>preg</i>);</b>
38
<br><a name="SEC2" href="#TOC1">DESCRIPTION</a><br>
40
This set of functions provides a POSIX-style API to the PCRE regular expression
42
<a href="pcreapi.html"><b>pcreapi</b></a>
43
documentation for a description of the native API, which contains additional
47
The functions described here are just wrapper functions that ultimately call
48
the PCRE native API. Their prototypes are defined in the <b>pcreposix.h</b>
49
header file, and on Unix systems the library itself is called
50
<b>pcreposix.a</b>, so can be accessed by adding <b>-lpcreposix</b> to the
51
command for linking an application which uses them. Because the POSIX functions
52
call the native ones, it is also necessary to add \fR-lpcre\fR.
55
I have implemented only those option bits that can be reasonably mapped to PCRE
56
native options. In addition, the options REG_EXTENDED and REG_NOSUB are defined
57
with the value zero. They have no effect, but since programs that are written
58
to the POSIX interface often use them, this makes it easier to slot in PCRE as
59
a replacement library. Other POSIX options are not even defined.
62
When PCRE is called via these functions, it is only the API that is POSIX-like
63
in style. The syntax and semantics of the regular expressions themselves are
64
still those of Perl, subject to the setting of various PCRE options, as
65
described below. "POSIX-like in style" means that the API approximates to the
66
POSIX definition; it is not fully POSIX-compatible, and in multi-byte encoding
67
domains it is probably even less compatible.
70
The header for these functions is supplied as <b>pcreposix.h</b> to avoid any
71
potential clash with other POSIX libraries. It can, of course, be renamed or
72
aliased as <b>regex.h</b>, which is the "correct" name. It provides two
73
structure types, <i>regex_t</i> for compiled internal forms, and
74
<i>regmatch_t</i> for returning captured substrings. It also defines some
75
constants whose names start with "REG_"; these are used for setting options and
76
identifying error codes.
78
<br><a name="SEC3" href="#TOC1">COMPILING A PATTERN</a><br>
80
The function <b>regcomp()</b> is called to compile a pattern into an
81
internal form. The pattern is a C string terminated by a binary zero, and
82
is passed in the argument <i>pattern</i>. The <i>preg</i> argument is a pointer
83
to a regex_t structure which is used as a base for storing information about
84
the compiled expression.
87
The argument <i>cflags</i> is either zero, or contains one or more of the bits
88
defined by the following macros:
96
The PCRE_CASELESS option is set when the expression is passed for compilation
97
to the native function.
105
The PCRE_MULTILINE option is set when the expression is passed for compilation
106
to the native function. Note that this does <i>not</i> mimic the defined POSIX
107
behaviour for REG_NEWLINE (see the following section).
110
In the absence of these flags, no options are passed to the native function.
111
This means the the regex is compiled with PCRE default semantics. In
112
particular, the way it handles newline characters in the subject string is the
113
Perl way, not the POSIX way. Note that setting PCRE_MULTILINE has only
114
<i>some</i> of the effects specified for REG_NEWLINE. It does not affect the way
115
newlines are matched by . (they aren't) or by a negative class such as [^a]
119
The yield of <b>regcomp()</b> is zero on success, and non-zero otherwise. The
120
<i>preg</i> structure is filled in on success, and one member of the structure
121
is public: <i>re_nsub</i> contains the number of capturing subpatterns in
122
the regular expression. Various error codes are defined in the header file.
124
<br><a name="SEC4" href="#TOC1">MATCHING NEWLINE CHARACTERS</a><br>
126
This area is not simple, because POSIX and Perl take different views of things.
127
It is not possible to get PCRE to obey POSIX semantics, but then PCRE was never
128
intended to be a POSIX engine. The following table lists the different
129
possibilities for matching newline characters in PCRE:
138
. matches newline no PCRE_DOTALL
139
newline matches [^a] yes not changeable
140
$ matches \n at end yes PCRE_DOLLARENDONLY
141
$ matches \n in middle no PCRE_MULTILINE
142
^ matches \n in middle no PCRE_MULTILINE
146
This is the equivalent table for POSIX:
155
. matches newline yes REG_NEWLINE
156
newline matches [^a] yes REG_NEWLINE
157
$ matches \n at end no REG_NEWLINE
158
$ matches \n in middle no REG_NEWLINE
159
^ matches \n in middle no REG_NEWLINE
163
PCRE's behaviour is the same as Perl's, except that there is no equivalent for
164
PCRE_DOLLARENDONLY in Perl. In both PCRE and Perl, there is no way to stop
165
newline from matching [^a].
168
The default POSIX newline handling can be obtained by setting PCRE_DOTALL and
169
PCRE_DOLLARENDONLY, but there is no way to make PCRE behave exactly as for the
172
<br><a name="SEC5" href="#TOC1">MATCHING A PATTERN</a><br>
174
The function <b>regexec()</b> is called to match a pre-compiled pattern
175
<i>preg</i> against a given <i>string</i>, which is terminated by a zero byte,
176
subject to the options in <i>eflags</i>. These can be:
184
The PCRE_NOTBOL option is set when calling the underlying PCRE matching
193
The PCRE_NOTEOL option is set when calling the underlying PCRE matching
197
The portion of the string that was matched, and also any captured substrings,
198
are returned via the <i>pmatch</i> argument, which points to an array of
199
<i>nmatch</i> structures of type <i>regmatch_t</i>, containing the members
200
<i>rm_so</i> and <i>rm_eo</i>. These contain the offset to the first character of
201
each substring and the offset to the first character after the end of each
202
substring, respectively. The 0th element of the vector relates to the entire
203
portion of <i>string</i> that was matched; subsequent elements relate to the
204
capturing subpatterns of the regular expression. Unused entries in the array
205
have both structure members set to -1.
208
A successful match yields a zero return; various error codes are defined in the
209
header file, of which REG_NOMATCH is the "expected" failure code.
211
<br><a name="SEC6" href="#TOC1">ERROR MESSAGES</a><br>
213
The <b>regerror()</b> function maps a non-zero errorcode from either
214
<b>regcomp()</b> or <b>regexec()</b> to a printable message. If <i>preg</i> is not
215
NULL, the error should have arisen from the use of that structure. A message
216
terminated by a binary zero is placed in <i>errbuf</i>. The length of the
217
message, including the zero, is limited to <i>errbuf_size</i>. The yield of the
218
function is the size of buffer needed to hold the whole message.
220
<br><a name="SEC7" href="#TOC1">STORAGE</a><br>
222
Compiling a regular expression causes memory to be allocated and associated
223
with the <i>preg</i> structure. The function <b>regfree()</b> frees all such
224
memory, after which <i>preg</i> may no longer be used as a compiled expression.
226
<br><a name="SEC8" href="#TOC1">AUTHOR</a><br>
228
Philip Hazel <ph10@cam.ac.uk>
230
University Computing Service,
232
Cambridge CB2 3QG, England.
235
Last updated: 03 February 2003
237
Copyright © 1997-2003 University of Cambridge.
added
removed
doc/html/pcreposix.html
