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2: <head>
3: <title>pcreposix specification</title>
4: </head>
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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>
1.1.1.2 ! misho 47: This set of functions provides a POSIX-style API for the PCRE regular
! 48: expression 8-bit library. See the
1.1 misho 49: <a href="pcreapi.html"><b>pcreapi</b></a>
50: documentation for a description of PCRE's native API, which contains much
1.1.1.2 ! misho 51: additional functionality. There is no POSIX-style wrapper for PCRE's 16-bit
! 52: library.
1.1 misho 53: </P>
54: <P>
55: The functions described here are just wrapper functions that ultimately call
56: the PCRE native API. Their prototypes are defined in the <b>pcreposix.h</b>
57: header file, and on Unix systems the library itself is called
58: <b>pcreposix.a</b>, so can be accessed by adding <b>-lpcreposix</b> to the
59: command for linking an application that uses them. Because the POSIX functions
60: call the native ones, it is also necessary to add <b>-lpcre</b>.
61: </P>
62: <P>
63: I have implemented only those POSIX option bits that can be reasonably mapped
64: to PCRE native options. In addition, the option REG_EXTENDED is defined with
65: the value zero. This has no effect, but since programs that are written to the
66: POSIX interface often use it, this makes it easier to slot in PCRE as a
67: replacement library. Other POSIX options are not even defined.
68: </P>
69: <P>
70: There are also some other options that are not defined by POSIX. These have
71: been added at the request of users who want to make use of certain
72: PCRE-specific features via the POSIX calling interface.
73: </P>
74: <P>
75: When PCRE is called via these functions, it is only the API that is POSIX-like
76: in style. The syntax and semantics of the regular expressions themselves are
77: still those of Perl, subject to the setting of various PCRE options, as
78: described below. "POSIX-like in style" means that the API approximates to the
79: POSIX definition; it is not fully POSIX-compatible, and in multi-byte encoding
80: domains it is probably even less compatible.
81: </P>
82: <P>
83: The header for these functions is supplied as <b>pcreposix.h</b> to avoid any
84: potential clash with other POSIX libraries. It can, of course, be renamed or
85: aliased as <b>regex.h</b>, which is the "correct" name. It provides two
86: structure types, <i>regex_t</i> for compiled internal forms, and
87: <i>regmatch_t</i> for returning captured substrings. It also defines some
88: constants whose names start with "REG_"; these are used for setting options and
89: identifying error codes.
90: </P>
91: <br><a name="SEC3" href="#TOC1">COMPILING A PATTERN</a><br>
92: <P>
93: The function <b>regcomp()</b> is called to compile a pattern into an
94: internal form. The pattern is a C string terminated by a binary zero, and
95: is passed in the argument <i>pattern</i>. The <i>preg</i> argument is a pointer
96: to a <b>regex_t</b> structure that is used as a base for storing information
97: about the compiled regular expression.
98: </P>
99: <P>
100: The argument <i>cflags</i> is either zero, or contains one or more of the bits
101: defined by the following macros:
102: <pre>
103: REG_DOTALL
104: </pre>
105: The PCRE_DOTALL option is set when the regular expression is passed for
106: compilation to the native function. Note that REG_DOTALL is not part of the
107: POSIX standard.
108: <pre>
109: REG_ICASE
110: </pre>
111: The PCRE_CASELESS option is set when the regular expression is passed for
112: compilation to the native function.
113: <pre>
114: REG_NEWLINE
115: </pre>
116: The PCRE_MULTILINE option is set when the regular expression is passed for
117: compilation to the native function. Note that this does <i>not</i> mimic the
118: defined POSIX behaviour for REG_NEWLINE (see the following section).
119: <pre>
120: REG_NOSUB
121: </pre>
122: The PCRE_NO_AUTO_CAPTURE option is set when the regular expression is passed
123: for compilation to the native function. In addition, when a pattern that is
124: compiled with this flag is passed to <b>regexec()</b> for matching, the
125: <i>nmatch</i> and <i>pmatch</i> arguments are ignored, and no captured strings
126: are returned.
127: <pre>
128: REG_UCP
129: </pre>
130: The PCRE_UCP option is set when the regular expression is passed for
131: compilation to the native function. This causes PCRE to use Unicode properties
132: when matchine \d, \w, etc., instead of just recognizing ASCII values. Note
133: that REG_UTF8 is not part of the POSIX standard.
134: <pre>
135: REG_UNGREEDY
136: </pre>
137: The PCRE_UNGREEDY option is set when the regular expression is passed for
138: compilation to the native function. Note that REG_UNGREEDY is not part of the
139: POSIX standard.
140: <pre>
141: REG_UTF8
142: </pre>
143: The PCRE_UTF8 option is set when the regular expression is passed for
144: compilation to the native function. This causes the pattern itself and all data
145: strings used for matching it to be treated as UTF-8 strings. Note that REG_UTF8
146: is not part of the POSIX standard.
147: </P>
148: <P>
149: In the absence of these flags, no options are passed to the native function.
150: This means the the regex is compiled with PCRE default semantics. In
151: particular, the way it handles newline characters in the subject string is the
152: Perl way, not the POSIX way. Note that setting PCRE_MULTILINE has only
153: <i>some</i> of the effects specified for REG_NEWLINE. It does not affect the way
154: newlines are matched by . (they are not) or by a negative class such as [^a]
155: (they are).
156: </P>
157: <P>
158: The yield of <b>regcomp()</b> is zero on success, and non-zero otherwise. The
159: <i>preg</i> structure is filled in on success, and one member of the structure
160: is public: <i>re_nsub</i> contains the number of capturing subpatterns in
161: the regular expression. Various error codes are defined in the header file.
162: </P>
163: <P>
164: NOTE: If the yield of <b>regcomp()</b> is non-zero, you must not attempt to
165: use the contents of the <i>preg</i> structure. If, for example, you pass it to
166: <b>regexec()</b>, the result is undefined and your program is likely to crash.
167: </P>
168: <br><a name="SEC4" href="#TOC1">MATCHING NEWLINE CHARACTERS</a><br>
169: <P>
170: This area is not simple, because POSIX and Perl take different views of things.
171: It is not possible to get PCRE to obey POSIX semantics, but then PCRE was never
172: intended to be a POSIX engine. The following table lists the different
173: possibilities for matching newline characters in PCRE:
174: <pre>
175: Default Change with
176:
177: . matches newline no PCRE_DOTALL
178: newline matches [^a] yes not changeable
179: $ matches \n at end yes PCRE_DOLLARENDONLY
180: $ matches \n in middle no PCRE_MULTILINE
181: ^ matches \n in middle no PCRE_MULTILINE
182: </pre>
183: This is the equivalent table for POSIX:
184: <pre>
185: Default Change with
186:
187: . matches newline yes REG_NEWLINE
188: newline matches [^a] yes REG_NEWLINE
189: $ matches \n at end no REG_NEWLINE
190: $ matches \n in middle no REG_NEWLINE
191: ^ matches \n in middle no REG_NEWLINE
192: </pre>
193: PCRE's behaviour is the same as Perl's, except that there is no equivalent for
194: PCRE_DOLLAR_ENDONLY in Perl. In both PCRE and Perl, there is no way to stop
195: newline from matching [^a].
196: </P>
197: <P>
198: The default POSIX newline handling can be obtained by setting PCRE_DOTALL and
199: PCRE_DOLLAR_ENDONLY, but there is no way to make PCRE behave exactly as for the
200: REG_NEWLINE action.
201: </P>
202: <br><a name="SEC5" href="#TOC1">MATCHING A PATTERN</a><br>
203: <P>
204: The function <b>regexec()</b> is called to match a compiled pattern <i>preg</i>
205: against a given <i>string</i>, which is by default terminated by a zero byte
206: (but see REG_STARTEND below), subject to the options in <i>eflags</i>. These can
207: be:
208: <pre>
209: REG_NOTBOL
210: </pre>
211: The PCRE_NOTBOL option is set when calling the underlying PCRE matching
212: function.
213: <pre>
214: REG_NOTEMPTY
215: </pre>
216: The PCRE_NOTEMPTY option is set when calling the underlying PCRE matching
217: function. Note that REG_NOTEMPTY is not part of the POSIX standard. However,
218: setting this option can give more POSIX-like behaviour in some situations.
219: <pre>
220: REG_NOTEOL
221: </pre>
222: The PCRE_NOTEOL option is set when calling the underlying PCRE matching
223: function.
224: <pre>
225: REG_STARTEND
226: </pre>
227: The string is considered to start at <i>string</i> + <i>pmatch[0].rm_so</i> and
228: to have a terminating NUL located at <i>string</i> + <i>pmatch[0].rm_eo</i>
229: (there need not actually be a NUL at that location), regardless of the value of
230: <i>nmatch</i>. This is a BSD extension, compatible with but not specified by
231: IEEE Standard 1003.2 (POSIX.2), and should be used with caution in software
232: intended to be portable to other systems. Note that a non-zero <i>rm_so</i> does
233: not imply REG_NOTBOL; REG_STARTEND affects only the location of the string, not
234: how it is matched.
235: </P>
236: <P>
237: If the pattern was compiled with the REG_NOSUB flag, no data about any matched
238: strings is returned. The <i>nmatch</i> and <i>pmatch</i> arguments of
239: <b>regexec()</b> are ignored.
240: </P>
241: <P>
242: If the value of <i>nmatch</i> is zero, or if the value <i>pmatch</i> is NULL,
243: no data about any matched strings is returned.
244: </P>
245: <P>
246: Otherwise,the portion of the string that was matched, and also any captured
247: substrings, are returned via the <i>pmatch</i> argument, which points to an
248: array of <i>nmatch</i> structures of type <i>regmatch_t</i>, containing the
249: members <i>rm_so</i> and <i>rm_eo</i>. These contain the offset to the first
250: character of each substring and the offset to the first character after the end
251: of each substring, respectively. The 0th element of the vector relates to the
252: entire portion of <i>string</i> that was matched; subsequent elements relate to
253: the capturing subpatterns of the regular expression. Unused entries in the
254: array have both structure members set to -1.
255: </P>
256: <P>
257: A successful match yields a zero return; various error codes are defined in the
258: header file, of which REG_NOMATCH is the "expected" failure code.
259: </P>
260: <br><a name="SEC6" href="#TOC1">ERROR MESSAGES</a><br>
261: <P>
262: The <b>regerror()</b> function maps a non-zero errorcode from either
263: <b>regcomp()</b> or <b>regexec()</b> to a printable message. If <i>preg</i> is not
264: NULL, the error should have arisen from the use of that structure. A message
265: terminated by a binary zero is placed in <i>errbuf</i>. The length of the
266: message, including the zero, is limited to <i>errbuf_size</i>. The yield of the
267: function is the size of buffer needed to hold the whole message.
268: </P>
269: <br><a name="SEC7" href="#TOC1">MEMORY USAGE</a><br>
270: <P>
271: Compiling a regular expression causes memory to be allocated and associated
272: with the <i>preg</i> structure. The function <b>regfree()</b> frees all such
273: memory, after which <i>preg</i> may no longer be used as a compiled expression.
274: </P>
275: <br><a name="SEC8" href="#TOC1">AUTHOR</a><br>
276: <P>
277: Philip Hazel
278: <br>
279: University Computing Service
280: <br>
281: Cambridge CB2 3QH, England.
282: <br>
283: </P>
284: <br><a name="SEC9" href="#TOC1">REVISION</a><br>
285: <P>
1.1.1.2 ! misho 286: Last updated: 09 January 2012
1.1 misho 287: <br>
1.1.1.2 ! misho 288: Copyright © 1997-2012 University of Cambridge.
1.1 misho 289: <br>
290: <p>
291: Return to the <a href="index.html">PCRE index page</a>.
292: </p>
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