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2     <head>
3     <title>pcreposix specification</title>
4     </head>
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>
9     <ul>
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>
18     </ul>
19     <br><a name="SEC1" href="#TOC1">SYNOPSIS OF POSIX API</a><br>
20     <P>
21     <b>#include &#60;pcreposix.h&#62;</b>
22     </P>
23     <P>
24     <b>int regcomp(regex_t *<i>preg</i>, const char *<i>pattern</i>,</b>
25     <b>int <i>cflags</i>);</b>
26     </P>
27     <P>
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>
30     </P>
31     <P>
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>
34     </P>
35     <P>
36     <b>void regfree(regex_t *<i>preg</i>);</b>
37     </P>
38     <br><a name="SEC2" href="#TOC1">DESCRIPTION</a><br>
39     <P>
40     This set of functions provides a POSIX-style API to the PCRE regular expression
41     package. See the
42     <a href="pcreapi.html"><b>pcreapi</b></a>
43     documentation for a description of the native API, which contains additional
44     functionality.
45     </P>
46     <P>
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.
53     </P>
54     <P>
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.
60     </P>
61     <P>
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.
66     </P>
67     <P>
68     The header for these functions is supplied as <b>pcreposix.h</b> to avoid any
69     potential clash with other POSIX libraries. It can, of course, be renamed or
70     aliased as <b>regex.h</b>, which is the "correct" name. It provides two
71     structure types, <i>regex_t</i> for compiled internal forms, and
72     <i>regmatch_t</i> for returning captured substrings. It also defines some
73     constants whose names start with "REG_"; these are used for setting options and
74     identifying error codes.
75     </P>
76     <br><a name="SEC3" href="#TOC1">COMPILING A PATTERN</a><br>
77     <P>
78     The function <b>regcomp()</b> is called to compile a pattern into an
79     internal form. The pattern is a C string terminated by a binary zero, and
80     is passed in the argument <i>pattern</i>. The <i>preg</i> argument is a pointer
81     to a regex_t structure which is used as a base for storing information about
82     the compiled expression.
83     </P>
84     <P>
85     The argument <i>cflags</i> is either zero, or contains one or more of the bits
86     defined by the following macros:
87     </P>
88     <P>
89     <pre>
90     REG_ICASE
91     </PRE>
92     </P>
93     <P>
94     The PCRE_CASELESS option is set when the expression is passed for compilation
95     to the native function.
96     </P>
97     <P>
98     <pre>
99     REG_NEWLINE
100     </PRE>
101     </P>
102     <P>
103     The PCRE_MULTILINE option is set when the expression is passed for compilation
104     to the native function. Note that this does <i>not</i> mimic the defined POSIX
105     behaviour for REG_NEWLINE (see the following section).
106     </P>
107     <P>
108     In the absence of these flags, no options are passed to the native function.
109     This means the the regex is compiled with PCRE default semantics. In
110     particular, the way it handles newline characters in the subject string is the
111     Perl way, not the POSIX way. Note that setting PCRE_MULTILINE has only
112     <i>some</i> of the effects specified for REG_NEWLINE. It does not affect the way
113     newlines are matched by . (they aren't) or by a negative class such as [^a]
114     (they are).
115     </P>
116     <P>
117     The yield of <b>regcomp()</b> is zero on success, and non-zero otherwise. The
118     <i>preg</i> structure is filled in on success, and one member of the structure
119     is public: <i>re_nsub</i> contains the number of capturing subpatterns in
120     the regular expression. Various error codes are defined in the header file.
121     </P>
122     <br><a name="SEC4" href="#TOC1">MATCHING NEWLINE CHARACTERS</a><br>
123     <P>
124     This area is not simple, because POSIX and Perl take different views of things.
125     It is not possible to get PCRE to obey POSIX semantics, but then PCRE was never
126     intended to be a POSIX engine. The following table lists the different
127     possibilities for matching newline characters in PCRE:
128     </P>
129     <P>
130     <pre>
131     Default Change with
132     </PRE>
133     </P>
134     <P>
135     <pre>
136     . matches newline no PCRE_DOTALL
137     newline matches [^a] yes not changeable
138     $ matches \n at end yes PCRE_DOLLARENDONLY
139     $ matches \n in middle no PCRE_MULTILINE
140     ^ matches \n in middle no PCRE_MULTILINE
141     </PRE>
142     </P>
143     <P>
144     This is the equivalent table for POSIX:
145     </P>
146     <P>
147     <pre>
148     Default Change with
149     </PRE>
150     </P>
151     <P>
152     <pre>
153     . matches newline yes REG_NEWLINE
154     newline matches [^a] yes REG_NEWLINE
155     $ matches \n at end no REG_NEWLINE
156     $ matches \n in middle no REG_NEWLINE
157     ^ matches \n in middle no REG_NEWLINE
158     </PRE>
159     </P>
160     <P>
161     PCRE's behaviour is the same as Perl's, except that there is no equivalent for
162     PCRE_DOLLARENDONLY in Perl. In both PCRE and Perl, there is no way to stop
163     newline from matching [^a].
164     </P>
165     <P>
166     The default POSIX newline handling can be obtained by setting PCRE_DOTALL and
167     PCRE_DOLLARENDONLY, but there is no way to make PCRE behave exactly as for the
168     REG_NEWLINE action.
169     </P>
170     <br><a name="SEC5" href="#TOC1">MATCHING A PATTERN</a><br>
171     <P>
172     The function <b>regexec()</b> is called to match a pre-compiled pattern
173     <i>preg</i> against a given <i>string</i>, which is terminated by a zero byte,
174     subject to the options in <i>eflags</i>. These can be:
175     </P>
176     <P>
177     <pre>
178     REG_NOTBOL
179     </PRE>
180     </P>
181     <P>
182     The PCRE_NOTBOL option is set when calling the underlying PCRE matching
183     function.
184     </P>
185     <P>
186     <pre>
187     REG_NOTEOL
188     </PRE>
189     </P>
190     <P>
191     The PCRE_NOTEOL option is set when calling the underlying PCRE matching
192     function.
193     </P>
194     <P>
195     The portion of the string that was matched, and also any captured substrings,
196     are returned via the <i>pmatch</i> argument, which points to an array of
197     <i>nmatch</i> structures of type <i>regmatch_t</i>, containing the members
198     <i>rm_so</i> and <i>rm_eo</i>. These contain the offset to the first character of
199     each substring and the offset to the first character after the end of each
200     substring, respectively. The 0th element of the vector relates to the entire
201     portion of <i>string</i> that was matched; subsequent elements relate to the
202     capturing subpatterns of the regular expression. Unused entries in the array
203     have both structure members set to -1.
204     </P>
205     <P>
206     A successful match yields a zero return; various error codes are defined in the
207     header file, of which REG_NOMATCH is the "expected" failure code.
208     </P>
209     <br><a name="SEC6" href="#TOC1">ERROR MESSAGES</a><br>
210     <P>
211     The <b>regerror()</b> function maps a non-zero errorcode from either
212     <b>regcomp()</b> or <b>regexec()</b> to a printable message. If <i>preg</i> is not
213     NULL, the error should have arisen from the use of that structure. A message
214     terminated by a binary zero is placed in <i>errbuf</i>. The length of the
215     message, including the zero, is limited to <i>errbuf_size</i>. The yield of the
216     function is the size of buffer needed to hold the whole message.
217     </P>
218     <br><a name="SEC7" href="#TOC1">STORAGE</a><br>
219     <P>
220     Compiling a regular expression causes memory to be allocated and associated
221     with the <i>preg</i> structure. The function <b>regfree()</b> frees all such
222     memory, after which <i>preg</i> may no longer be used as a compiled expression.
223     </P>
224     <br><a name="SEC8" href="#TOC1">AUTHOR</a><br>
225     <P>
226     Philip Hazel &#60;ph10@cam.ac.uk&#62;
227     <br>
228     University Computing Service,
229     <br>
230     Cambridge CB2 3QG, England.
231     </P>
232     <P>
233     Last updated: 03 February 2003
234     <br>
235     Copyright &copy; 1997-2003 University of Cambridge.

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