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1 nigel 41 .TH PCRE 3
2     .SH NAME
3 nigel 63 PCRE - Perl-compatible regular expressions.
4     .SH SYNOPSIS OF POSIX API
5 nigel 41 .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 nigel 63 .rs
28     .sp
29 nigel 41 This set of functions provides a POSIX-style API to the PCRE regular expression
30 nigel 63 package. See the
31     .\" HREF
32     \fBpcreapi\fR
33     .\"
34     documentation for a description of the native API, which contains additional
35     functionality.
36 nigel 41
37     The functions described here are just wrapper functions that ultimately call
38 nigel 63 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 nigel 41
44 nigel 43 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 nigel 41
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 nigel 69 described below. "POSIX-like in style" means that the API approximates to the
54     POSIX definition; it is not fully POSIX-compatible, and in multi-byte encoding
55     domains it is probably even less compatible.
56 nigel 41
57     The header for these functions is supplied as \fBpcreposix.h\fR to avoid any
58     potential clash with other POSIX libraries. It can, of course, be renamed or
59     aliased as \fBregex.h\fR, which is the "correct" name. It provides two
60     structure types, \fIregex_t\fR for compiled internal forms, and
61     \fIregmatch_t\fR for returning captured substrings. It also defines some
62     constants whose names start with "REG_"; these are used for setting options and
63     identifying error codes.
64    
65     .SH COMPILING A PATTERN
66 nigel 63 .rs
67     .sp
68 nigel 41 The function \fBregcomp()\fR is called to compile a pattern into an
69     internal form. The pattern is a C string terminated by a binary zero, and
70     is passed in the argument \fIpattern\fR. The \fIpreg\fR argument is a pointer
71     to a regex_t structure which is used as a base for storing information about
72     the compiled expression.
73    
74     The argument \fIcflags\fR is either zero, or contains one or more of the bits
75     defined by the following macros:
76    
77     REG_ICASE
78    
79     The PCRE_CASELESS option is set when the expression is passed for compilation
80     to the native function.
81    
82     REG_NEWLINE
83    
84     The PCRE_MULTILINE option is set when the expression is passed for compilation
85 nigel 63 to the native function. Note that this does \fInot\fR mimic the defined POSIX
86     behaviour for REG_NEWLINE (see the following section).
87 nigel 41
88 nigel 49 In the absence of these flags, no options are passed to the native function.
89     This means the the regex is compiled with PCRE default semantics. In
90     particular, the way it handles newline characters in the subject string is the
91     Perl way, not the POSIX way. Note that setting PCRE_MULTILINE has only
92     \fIsome\fR of the effects specified for REG_NEWLINE. It does not affect the way
93 nigel 63 newlines are matched by . (they aren't) or by a negative class such as [^a]
94     (they are).
95 nigel 49
96 nigel 41 The yield of \fBregcomp()\fR is zero on success, and non-zero otherwise. The
97     \fIpreg\fR structure is filled in on success, and one member of the structure
98 nigel 63 is public: \fIre_nsub\fR contains the number of capturing subpatterns in
99 nigel 41 the regular expression. Various error codes are defined in the header file.
100    
101 nigel 63 .SH MATCHING NEWLINE CHARACTERS
102     .rs
103     .sp
104     This area is not simple, because POSIX and Perl take different views of things.
105     It is not possible to get PCRE to obey POSIX semantics, but then PCRE was never
106     intended to be a POSIX engine. The following table lists the different
107     possibilities for matching newline characters in PCRE:
108 nigel 41
109 nigel 63 Default Change with
110    
111     . matches newline no PCRE_DOTALL
112     newline matches [^a] yes not changeable
113     $ matches \\n at end yes PCRE_DOLLARENDONLY
114     $ matches \\n in middle no PCRE_MULTILINE
115     ^ matches \\n in middle no PCRE_MULTILINE
116    
117     This is the equivalent table for POSIX:
118    
119     Default Change with
120    
121     . matches newline yes REG_NEWLINE
122     newline matches [^a] yes REG_NEWLINE
123     $ matches \\n at end no REG_NEWLINE
124     $ matches \\n in middle no REG_NEWLINE
125     ^ matches \\n in middle no REG_NEWLINE
126    
127     PCRE's behaviour is the same as Perl's, except that there is no equivalent for
128     PCRE_DOLLARENDONLY in Perl. In both PCRE and Perl, there is no way to stop
129     newline from matching [^a].
130    
131     The default POSIX newline handling can be obtained by setting PCRE_DOTALL and
132     PCRE_DOLLARENDONLY, but there is no way to make PCRE behave exactly as for the
133     REG_NEWLINE action.
134    
135 nigel 41 .SH MATCHING A PATTERN
136 nigel 63 .rs
137     .sp
138 nigel 41 The function \fBregexec()\fR is called to match a pre-compiled pattern
139     \fIpreg\fR against a given \fIstring\fR, which is terminated by a zero byte,
140     subject to the options in \fIeflags\fR. These can be:
141    
142     REG_NOTBOL
143    
144     The PCRE_NOTBOL option is set when calling the underlying PCRE matching
145     function.
146    
147     REG_NOTEOL
148    
149     The PCRE_NOTEOL option is set when calling the underlying PCRE matching
150     function.
151    
152     The portion of the string that was matched, and also any captured substrings,
153     are returned via the \fIpmatch\fR argument, which points to an array of
154     \fInmatch\fR structures of type \fIregmatch_t\fR, containing the members
155     \fIrm_so\fR and \fIrm_eo\fR. These contain the offset to the first character of
156     each substring and the offset to the first character after the end of each
157     substring, respectively. The 0th element of the vector relates to the entire
158     portion of \fIstring\fR that was matched; subsequent elements relate to the
159     capturing subpatterns of the regular expression. Unused entries in the array
160     have both structure members set to -1.
161    
162     A successful match yields a zero return; various error codes are defined in the
163     header file, of which REG_NOMATCH is the "expected" failure code.
164    
165     .SH ERROR MESSAGES
166 nigel 63 .rs
167     .sp
168 nigel 41 The \fBregerror()\fR function maps a non-zero errorcode from either
169 nigel 63 \fBregcomp()\fR or \fBregexec()\fR to a printable message. If \fIpreg\fR is not
170 nigel 41 NULL, the error should have arisen from the use of that structure. A message
171     terminated by a binary zero is placed in \fIerrbuf\fR. The length of the
172     message, including the zero, is limited to \fIerrbuf_size\fR. The yield of the
173     function is the size of buffer needed to hold the whole message.
174    
175     .SH STORAGE
176 nigel 63 .rs
177     .sp
178 nigel 41 Compiling a regular expression causes memory to be allocated and associated
179     with the \fIpreg\fR structure. The function \fBregfree()\fR frees all such
180     memory, after which \fIpreg\fR may no longer be used as a compiled expression.
181    
182     .SH AUTHOR
183 nigel 63 .rs
184     .sp
185 nigel 41 Philip Hazel <ph10@cam.ac.uk>
186     .br
187     University Computing Service,
188     .br
189     Cambridge CB2 3QG, England.
190 nigel 63
191     .in 0
192     Last updated: 03 February 2003
193 nigel 41 .br
194 nigel 63 Copyright (c) 1997-2003 University of Cambridge.

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