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1 nigel 63 <html>
2     <head>
3     <title>pcreposix specification</title>
4     </head>
5     <body bgcolor="#FFFFFF" text="#00005A" link="#0066FF" alink="#3399FF" vlink="#2222BB">
6 nigel 75 <h1>pcreposix man page</h1>
7     <p>
8     Return to the <a href="index.html">PCRE index page</a>.
9     </p>
10     <p>
11     This page is part of the PCRE HTML documentation. It was generated automatically
12     from the original man page. If there is any nonsense in it, please consult the
13     man page, in case the conversion went wrong.
14     <br>
15 nigel 63 <ul>
16     <li><a name="TOC1" href="#SEC1">SYNOPSIS OF POSIX API</a>
17     <li><a name="TOC2" href="#SEC2">DESCRIPTION</a>
18     <li><a name="TOC3" href="#SEC3">COMPILING A PATTERN</a>
19     <li><a name="TOC4" href="#SEC4">MATCHING NEWLINE CHARACTERS</a>
20     <li><a name="TOC5" href="#SEC5">MATCHING A PATTERN</a>
21     <li><a name="TOC6" href="#SEC6">ERROR MESSAGES</a>
22 nigel 75 <li><a name="TOC7" href="#SEC7">MEMORY USAGE</a>
23 nigel 63 <li><a name="TOC8" href="#SEC8">AUTHOR</a>
24     </ul>
25     <br><a name="SEC1" href="#TOC1">SYNOPSIS OF POSIX API</a><br>
26     <P>
27     <b>#include &#60;pcreposix.h&#62;</b>
28     </P>
29     <P>
30     <b>int regcomp(regex_t *<i>preg</i>, const char *<i>pattern</i>,</b>
31     <b>int <i>cflags</i>);</b>
32     </P>
33     <P>
34     <b>int regexec(regex_t *<i>preg</i>, const char *<i>string</i>,</b>
35     <b>size_t <i>nmatch</i>, regmatch_t <i>pmatch</i>[], int <i>eflags</i>);</b>
36     </P>
37     <P>
38     <b>size_t regerror(int <i>errcode</i>, const regex_t *<i>preg</i>,</b>
39     <b>char *<i>errbuf</i>, size_t <i>errbuf_size</i>);</b>
40     </P>
41     <P>
42     <b>void regfree(regex_t *<i>preg</i>);</b>
43     </P>
44     <br><a name="SEC2" href="#TOC1">DESCRIPTION</a><br>
45     <P>
46     This set of functions provides a POSIX-style API to the PCRE regular expression
47     package. See the
48     <a href="pcreapi.html"><b>pcreapi</b></a>
49 nigel 75 documentation for a description of PCRE's native API, which contains additional
50 nigel 63 functionality.
51     </P>
52     <P>
53     The functions described here are just wrapper functions that ultimately call
54     the PCRE native API. Their prototypes are defined in the <b>pcreposix.h</b>
55     header file, and on Unix systems the library itself is called
56     <b>pcreposix.a</b>, so can be accessed by adding <b>-lpcreposix</b> to the
57 nigel 75 command for linking an application that uses them. Because the POSIX functions
58     call the native ones, it is also necessary to add <b>-lpcre</b>.
59 nigel 63 </P>
60     <P>
61     I have implemented only those option bits that can be reasonably mapped to PCRE
62     native options. In addition, the options REG_EXTENDED and REG_NOSUB are defined
63     with the value zero. They have no effect, but since programs that are written
64     to the POSIX interface often use them, this makes it easier to slot in PCRE as
65     a replacement library. Other POSIX options are not even defined.
66     </P>
67     <P>
68     When PCRE is called via these functions, it is only the API that is POSIX-like
69     in style. The syntax and semantics of the regular expressions themselves are
70     still those of Perl, subject to the setting of various PCRE options, as
71 nigel 69 described below. "POSIX-like in style" means that the API approximates to the
72     POSIX definition; it is not fully POSIX-compatible, and in multi-byte encoding
73     domains it is probably even less compatible.
74 nigel 63 </P>
75     <P>
76     The header for these functions is supplied as <b>pcreposix.h</b> to avoid any
77     potential clash with other POSIX libraries. It can, of course, be renamed or
78     aliased as <b>regex.h</b>, which is the "correct" name. It provides two
79     structure types, <i>regex_t</i> for compiled internal forms, and
80     <i>regmatch_t</i> for returning captured substrings. It also defines some
81     constants whose names start with "REG_"; these are used for setting options and
82     identifying error codes.
83     </P>
84 nigel 75 <P>
85     </P>
86 nigel 63 <br><a name="SEC3" href="#TOC1">COMPILING A PATTERN</a><br>
87     <P>
88     The function <b>regcomp()</b> is called to compile a pattern into an
89     internal form. The pattern is a C string terminated by a binary zero, and
90     is passed in the argument <i>pattern</i>. The <i>preg</i> argument is a pointer
91 nigel 75 to a <b>regex_t</b> structure that is used as a base for storing information
92     about the compiled expression.
93 nigel 63 </P>
94     <P>
95     The argument <i>cflags</i> is either zero, or contains one or more of the bits
96     defined by the following macros:
97     <pre>
98     REG_ICASE
99 nigel 75 </pre>
100 nigel 63 The PCRE_CASELESS option is set when the expression is passed for compilation
101     to the native function.
102     <pre>
104 nigel 75 </pre>
105 nigel 63 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).
108     </P>
109     <P>
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]
116     (they are).
117     </P>
118     <P>
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.
123     </P>
124     <br><a name="SEC4" href="#TOC1">MATCHING NEWLINE CHARACTERS</a><br>
125     <P>
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:
130     <pre>
131     Default Change with
132 nigel 75
133 nigel 63 . matches newline no PCRE_DOTALL
134     newline matches [^a] yes not changeable
135     $ matches \n at end yes PCRE_DOLLARENDONLY
136     $ matches \n in middle no PCRE_MULTILINE
137     ^ matches \n in middle no PCRE_MULTILINE
138 nigel 75 </pre>
139 nigel 63 This is the equivalent table for POSIX:
140     <pre>
141     Default Change with
142 nigel 75
143     . matches newline yes REG_NEWLINE
144     newline matches [^a] yes REG_NEWLINE
145     $ matches \n at end no REG_NEWLINE
146     $ matches \n in middle no REG_NEWLINE
147     ^ matches \n in middle no REG_NEWLINE
148     </pre>
149 nigel 63 PCRE's behaviour is the same as Perl's, except that there is no equivalent for
150 nigel 75 PCRE_DOLLAR_ENDONLY in Perl. In both PCRE and Perl, there is no way to stop
151 nigel 63 newline from matching [^a].
152     </P>
153     <P>
154     The default POSIX newline handling can be obtained by setting PCRE_DOTALL and
155 nigel 75 PCRE_DOLLAR_ENDONLY, but there is no way to make PCRE behave exactly as for the
156 nigel 63 REG_NEWLINE action.
157     </P>
158     <br><a name="SEC5" href="#TOC1">MATCHING A PATTERN</a><br>
159     <P>
160 nigel 75 The function <b>regexec()</b> is called to match a compiled pattern <i>preg</i>
161     against a given <i>string</i>, which is terminated by a zero byte, subject to
162     the options in <i>eflags</i>. These can be:
163 nigel 63 <pre>
164     REG_NOTBOL
165 nigel 75 </pre>
166 nigel 63 The PCRE_NOTBOL option is set when calling the underlying PCRE matching
167     function.
168     <pre>
169     REG_NOTEOL
170 nigel 75 </pre>
171 nigel 63 The PCRE_NOTEOL option is set when calling the underlying PCRE matching
172     function.
173     </P>
174     <P>
175     The portion of the string that was matched, and also any captured substrings,
176     are returned via the <i>pmatch</i> argument, which points to an array of
177     <i>nmatch</i> structures of type <i>regmatch_t</i>, containing the members
178     <i>rm_so</i> and <i>rm_eo</i>. These contain the offset to the first character of
179     each substring and the offset to the first character after the end of each
180     substring, respectively. The 0th element of the vector relates to the entire
181     portion of <i>string</i> that was matched; subsequent elements relate to the
182     capturing subpatterns of the regular expression. Unused entries in the array
183     have both structure members set to -1.
184     </P>
185     <P>
186     A successful match yields a zero return; various error codes are defined in the
187     header file, of which REG_NOMATCH is the "expected" failure code.
188     </P>
189     <br><a name="SEC6" href="#TOC1">ERROR MESSAGES</a><br>
190     <P>
191     The <b>regerror()</b> function maps a non-zero errorcode from either
192     <b>regcomp()</b> or <b>regexec()</b> to a printable message. If <i>preg</i> is not
193     NULL, the error should have arisen from the use of that structure. A message
194     terminated by a binary zero is placed in <i>errbuf</i>. The length of the
195     message, including the zero, is limited to <i>errbuf_size</i>. The yield of the
196     function is the size of buffer needed to hold the whole message.
197     </P>
198 nigel 75 <br><a name="SEC7" href="#TOC1">MEMORY USAGE</a><br>
199 nigel 63 <P>
200     Compiling a regular expression causes memory to be allocated and associated
201     with the <i>preg</i> structure. The function <b>regfree()</b> frees all such
202     memory, after which <i>preg</i> may no longer be used as a compiled expression.
203     </P>
204     <br><a name="SEC8" href="#TOC1">AUTHOR</a><br>
205     <P>
206     Philip Hazel &#60;ph10@cam.ac.uk&#62;
207     <br>
208     University Computing Service,
209     <br>
210     Cambridge CB2 3QG, England.
211     </P>
212     <P>
213 nigel 75 Last updated: 07 September 2004
214 nigel 63 <br>
215 nigel 75 Copyright &copy; 1997-2004 University of Cambridge.
216     <p>
217     Return to the <a href="index.html">PCRE index page</a>.
218     </p>

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