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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     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 nigel 63 .rs
65     .sp
66 nigel 41 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 nigel 63 to the native function. Note that this does \fInot\fR mimic the defined POSIX
84     behaviour for REG_NEWLINE (see the following section).
85 nigel 41
86 nigel 49 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 nigel 63 newlines are matched by . (they aren't) or by a negative class such as [^a]
92     (they are).
93 nigel 49
94 nigel 41 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 nigel 63 is public: \fIre_nsub\fR contains the number of capturing subpatterns in
97 nigel 41 the regular expression. Various error codes are defined in the header file.
98    
99 nigel 63 .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 nigel 41
107 nigel 63 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 nigel 41 .SH MATCHING A PATTERN
134 nigel 63 .rs
135     .sp
136 nigel 41 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 nigel 63 .rs
165     .sp
166 nigel 41 The \fBregerror()\fR function maps a non-zero errorcode from either
167 nigel 63 \fBregcomp()\fR or \fBregexec()\fR to a printable message. If \fIpreg\fR is not
168 nigel 41 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 nigel 63 .rs
175     .sp
176 nigel 41 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 nigel 63 .rs
182     .sp
183 nigel 41 Philip Hazel <ph10@cam.ac.uk>
184     .br
185     University Computing Service,
186     .br
187     Cambridge CB2 3QG, England.
188 nigel 63
189     .in 0
190     Last updated: 03 February 2003
191 nigel 41 .br
192 nigel 63 Copyright (c) 1997-2003 University of Cambridge.

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