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3: <title>pcreposix specification</title>
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6: <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: <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: <li><a name="TOC7" href="#SEC7">MEMORY USAGE</a>
23: <li><a name="TOC8" href="#SEC8">AUTHOR</a>
24: <li><a name="TOC9" href="#SEC9">REVISION</a>
25: </ul>
26: <br><a name="SEC1" href="#TOC1">SYNOPSIS OF POSIX API</a><br>
27: <P>
28: <b>#include <pcreposix.h></b>
29: </P>
30: <P>
31: <b>int regcomp(regex_t *<i>preg</i>, const char *<i>pattern</i>,</b>
32: <b>int <i>cflags</i>);</b>
33: </P>
34: <P>
35: <b>int regexec(regex_t *<i>preg</i>, const char *<i>string</i>,</b>
36: <b>size_t <i>nmatch</i>, regmatch_t <i>pmatch</i>[], int <i>eflags</i>);</b>
37: </P>
38: <P>
39: <b>size_t regerror(int <i>errcode</i>, const regex_t *<i>preg</i>,</b>
40: <b>char *<i>errbuf</i>, size_t <i>errbuf_size</i>);</b>
41: </P>
42: <P>
43: <b>void regfree(regex_t *<i>preg</i>);</b>
44: </P>
45: <br><a name="SEC2" href="#TOC1">DESCRIPTION</a><br>
46: <P>
47: This set of functions provides a POSIX-style API to the PCRE regular expression
48: package. See the
49: <a href="pcreapi.html"><b>pcreapi</b></a>
50: documentation for a description of PCRE's native API, which contains much
51: additional functionality.
52: </P>
53: <P>
54: The functions described here are just wrapper functions that ultimately call
55: the PCRE native API. Their prototypes are defined in the <b>pcreposix.h</b>
56: header file, and on Unix systems the library itself is called
57: <b>pcreposix.a</b>, so can be accessed by adding <b>-lpcreposix</b> to the
58: command for linking an application that uses them. Because the POSIX functions
59: call the native ones, it is also necessary to add <b>-lpcre</b>.
60: </P>
61: <P>
62: I have implemented only those POSIX option bits that can be reasonably mapped
63: to PCRE native options. In addition, the option REG_EXTENDED is defined with
64: the value zero. This has no effect, but since programs that are written to the
65: POSIX interface often use it, this makes it easier to slot in PCRE as a
66: replacement library. Other POSIX options are not even defined.
67: </P>
68: <P>
69: There are also some other options that are not defined by POSIX. These have
70: been added at the request of users who want to make use of certain
71: PCRE-specific features via the POSIX calling interface.
72: </P>
73: <P>
74: When PCRE is called via these functions, it is only the API that is POSIX-like
75: in style. The syntax and semantics of the regular expressions themselves are
76: still those of Perl, subject to the setting of various PCRE options, as
77: described below. "POSIX-like in style" means that the API approximates to the
78: POSIX definition; it is not fully POSIX-compatible, and in multi-byte encoding
79: domains it is probably even less compatible.
80: </P>
81: <P>
82: The header for these functions is supplied as <b>pcreposix.h</b> to avoid any
83: potential clash with other POSIX libraries. It can, of course, be renamed or
84: aliased as <b>regex.h</b>, which is the "correct" name. It provides two
85: structure types, <i>regex_t</i> for compiled internal forms, and
86: <i>regmatch_t</i> for returning captured substrings. It also defines some
87: constants whose names start with "REG_"; these are used for setting options and
88: identifying error codes.
89: </P>
90: <br><a name="SEC3" href="#TOC1">COMPILING A PATTERN</a><br>
91: <P>
92: The function <b>regcomp()</b> is called to compile a pattern into an
93: internal form. The pattern is a C string terminated by a binary zero, and
94: is passed in the argument <i>pattern</i>. The <i>preg</i> argument is a pointer
95: to a <b>regex_t</b> structure that is used as a base for storing information
96: about the compiled regular expression.
97: </P>
98: <P>
99: The argument <i>cflags</i> is either zero, or contains one or more of the bits
100: defined by the following macros:
101: <pre>
102: REG_DOTALL
103: </pre>
104: The PCRE_DOTALL option is set when the regular expression is passed for
105: compilation to the native function. Note that REG_DOTALL is not part of the
106: POSIX standard.
107: <pre>
108: REG_ICASE
109: </pre>
110: The PCRE_CASELESS option is set when the regular expression is passed for
111: compilation to the native function.
112: <pre>
113: REG_NEWLINE
114: </pre>
115: The PCRE_MULTILINE option is set when the regular expression is passed for
116: compilation to the native function. Note that this does <i>not</i> mimic the
117: defined POSIX behaviour for REG_NEWLINE (see the following section).
118: <pre>
119: REG_NOSUB
120: </pre>
121: The PCRE_NO_AUTO_CAPTURE option is set when the regular expression is passed
122: for compilation to the native function. In addition, when a pattern that is
123: compiled with this flag is passed to <b>regexec()</b> for matching, the
124: <i>nmatch</i> and <i>pmatch</i> arguments are ignored, and no captured strings
125: are returned.
126: <pre>
127: REG_UCP
128: </pre>
129: The PCRE_UCP option is set when the regular expression is passed for
130: compilation to the native function. This causes PCRE to use Unicode properties
131: when matchine \d, \w, etc., instead of just recognizing ASCII values. Note
132: that REG_UTF8 is not part of the POSIX standard.
133: <pre>
134: REG_UNGREEDY
135: </pre>
136: The PCRE_UNGREEDY option is set when the regular expression is passed for
137: compilation to the native function. Note that REG_UNGREEDY is not part of the
138: POSIX standard.
139: <pre>
140: REG_UTF8
141: </pre>
142: The PCRE_UTF8 option is set when the regular expression is passed for
143: compilation to the native function. This causes the pattern itself and all data
144: strings used for matching it to be treated as UTF-8 strings. Note that REG_UTF8
145: is not part of the POSIX standard.
146: </P>
147: <P>
148: In the absence of these flags, no options are passed to the native function.
149: This means the the regex is compiled with PCRE default semantics. In
150: particular, the way it handles newline characters in the subject string is the
151: Perl way, not the POSIX way. Note that setting PCRE_MULTILINE has only
152: <i>some</i> of the effects specified for REG_NEWLINE. It does not affect the way
153: newlines are matched by . (they are not) or by a negative class such as [^a]
154: (they are).
155: </P>
156: <P>
157: The yield of <b>regcomp()</b> is zero on success, and non-zero otherwise. The
158: <i>preg</i> structure is filled in on success, and one member of the structure
159: is public: <i>re_nsub</i> contains the number of capturing subpatterns in
160: the regular expression. Various error codes are defined in the header file.
161: </P>
162: <P>
163: NOTE: If the yield of <b>regcomp()</b> is non-zero, you must not attempt to
164: use the contents of the <i>preg</i> structure. If, for example, you pass it to
165: <b>regexec()</b>, the result is undefined and your program is likely to crash.
166: </P>
167: <br><a name="SEC4" href="#TOC1">MATCHING NEWLINE CHARACTERS</a><br>
168: <P>
169: This area is not simple, because POSIX and Perl take different views of things.
170: It is not possible to get PCRE to obey POSIX semantics, but then PCRE was never
171: intended to be a POSIX engine. The following table lists the different
172: possibilities for matching newline characters in PCRE:
173: <pre>
174: Default Change with
175:
176: . matches newline no PCRE_DOTALL
177: newline matches [^a] yes not changeable
178: $ matches \n at end yes PCRE_DOLLARENDONLY
179: $ matches \n in middle no PCRE_MULTILINE
180: ^ matches \n in middle no PCRE_MULTILINE
181: </pre>
182: This is the equivalent table for POSIX:
183: <pre>
184: Default Change with
185:
186: . matches newline yes REG_NEWLINE
187: newline matches [^a] yes REG_NEWLINE
188: $ matches \n at end no REG_NEWLINE
189: $ matches \n in middle no REG_NEWLINE
190: ^ matches \n in middle no REG_NEWLINE
191: </pre>
192: PCRE's behaviour is the same as Perl's, except that there is no equivalent for
193: PCRE_DOLLAR_ENDONLY in Perl. In both PCRE and Perl, there is no way to stop
194: newline from matching [^a].
195: </P>
196: <P>
197: The default POSIX newline handling can be obtained by setting PCRE_DOTALL and
198: PCRE_DOLLAR_ENDONLY, but there is no way to make PCRE behave exactly as for the
199: REG_NEWLINE action.
200: </P>
201: <br><a name="SEC5" href="#TOC1">MATCHING A PATTERN</a><br>
202: <P>
203: The function <b>regexec()</b> is called to match a compiled pattern <i>preg</i>
204: against a given <i>string</i>, which is by default terminated by a zero byte
205: (but see REG_STARTEND below), subject to the options in <i>eflags</i>. These can
206: be:
207: <pre>
208: REG_NOTBOL
209: </pre>
210: The PCRE_NOTBOL option is set when calling the underlying PCRE matching
211: function.
212: <pre>
213: REG_NOTEMPTY
214: </pre>
215: The PCRE_NOTEMPTY option is set when calling the underlying PCRE matching
216: function. Note that REG_NOTEMPTY is not part of the POSIX standard. However,
217: setting this option can give more POSIX-like behaviour in some situations.
218: <pre>
219: REG_NOTEOL
220: </pre>
221: The PCRE_NOTEOL option is set when calling the underlying PCRE matching
222: function.
223: <pre>
224: REG_STARTEND
225: </pre>
226: The string is considered to start at <i>string</i> + <i>pmatch[0].rm_so</i> and
227: to have a terminating NUL located at <i>string</i> + <i>pmatch[0].rm_eo</i>
228: (there need not actually be a NUL at that location), regardless of the value of
229: <i>nmatch</i>. This is a BSD extension, compatible with but not specified by
230: IEEE Standard 1003.2 (POSIX.2), and should be used with caution in software
231: intended to be portable to other systems. Note that a non-zero <i>rm_so</i> does
232: not imply REG_NOTBOL; REG_STARTEND affects only the location of the string, not
233: how it is matched.
234: </P>
235: <P>
236: If the pattern was compiled with the REG_NOSUB flag, no data about any matched
237: strings is returned. The <i>nmatch</i> and <i>pmatch</i> arguments of
238: <b>regexec()</b> are ignored.
239: </P>
240: <P>
241: If the value of <i>nmatch</i> is zero, or if the value <i>pmatch</i> is NULL,
242: no data about any matched strings is returned.
243: </P>
244: <P>
245: Otherwise,the portion of the string that was matched, and also any captured
246: substrings, are returned via the <i>pmatch</i> argument, which points to an
247: array of <i>nmatch</i> structures of type <i>regmatch_t</i>, containing the
248: members <i>rm_so</i> and <i>rm_eo</i>. These contain the offset to the first
249: character of each substring and the offset to the first character after the end
250: of each substring, respectively. The 0th element of the vector relates to the
251: entire portion of <i>string</i> that was matched; subsequent elements relate to
252: the capturing subpatterns of the regular expression. Unused entries in the
253: array have both structure members set to -1.
254: </P>
255: <P>
256: A successful match yields a zero return; various error codes are defined in the
257: header file, of which REG_NOMATCH is the "expected" failure code.
258: </P>
259: <br><a name="SEC6" href="#TOC1">ERROR MESSAGES</a><br>
260: <P>
261: The <b>regerror()</b> function maps a non-zero errorcode from either
262: <b>regcomp()</b> or <b>regexec()</b> to a printable message. If <i>preg</i> is not
263: NULL, the error should have arisen from the use of that structure. A message
264: terminated by a binary zero is placed in <i>errbuf</i>. The length of the
265: message, including the zero, is limited to <i>errbuf_size</i>. The yield of the
266: function is the size of buffer needed to hold the whole message.
267: </P>
268: <br><a name="SEC7" href="#TOC1">MEMORY USAGE</a><br>
269: <P>
270: Compiling a regular expression causes memory to be allocated and associated
271: with the <i>preg</i> structure. The function <b>regfree()</b> frees all such
272: memory, after which <i>preg</i> may no longer be used as a compiled expression.
273: </P>
274: <br><a name="SEC8" href="#TOC1">AUTHOR</a><br>
275: <P>
276: Philip Hazel
277: <br>
278: University Computing Service
279: <br>
280: Cambridge CB2 3QH, England.
281: <br>
282: </P>
283: <br><a name="SEC9" href="#TOC1">REVISION</a><br>
284: <P>
285: Last updated: 16 May 2010
286: <br>
287: Copyright © 1997-2010 University of Cambridge.
288: <br>
289: <p>
290: Return to the <a href="index.html">PCRE index page</a>.
291: </p>
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