1: .TH PCREPOSIX 3 "09 January 2012" "PCRE 8.30"
2: .SH NAME
3: PCRE - Perl-compatible regular expressions.
4: .SH "SYNOPSIS"
5: .rs
6: .sp
7: .B #include <pcreposix.h>
8: .PP
9: .nf
10: .B int regcomp(regex_t *\fIpreg\fP, const char *\fIpattern\fP,
11: .B " int \fIcflags\fP);"
12: .sp
13: .B int regexec(regex_t *\fIpreg\fP, const char *\fIstring\fP,
14: .B " size_t \fInmatch\fP, regmatch_t \fIpmatch\fP[], int \fIeflags\fP);"
15: .B " size_t regerror(int \fIerrcode\fP, const regex_t *\fIpreg\fP,"
16: .B " char *\fIerrbuf\fP, size_t \fIerrbuf_size\fP);"
17: .sp
18: .B void regfree(regex_t *\fIpreg\fP);
19: .fi
20: .
21: .SH DESCRIPTION
22: .rs
23: .sp
24: This set of functions provides a POSIX-style API for the PCRE regular
25: expression 8-bit library. See the
26: .\" HREF
27: \fBpcreapi\fP
28: .\"
29: documentation for a description of PCRE's native API, which contains much
30: additional functionality. There is no POSIX-style wrapper for PCRE's 16-bit
31: and 32-bit library.
32: .P
33: The functions described here are just wrapper functions that ultimately call
34: the PCRE native API. Their prototypes are defined in the \fBpcreposix.h\fP
35: header file, and on Unix systems the library itself is called
36: \fBpcreposix.a\fP, so can be accessed by adding \fB-lpcreposix\fP to the
37: command for linking an application that uses them. Because the POSIX functions
38: call the native ones, it is also necessary to add \fB-lpcre\fP.
39: .P
40: I have implemented only those POSIX option bits that can be reasonably mapped
41: to PCRE native options. In addition, the option REG_EXTENDED is defined with
42: the value zero. This has no effect, but since programs that are written to the
43: POSIX interface often use it, this makes it easier to slot in PCRE as a
44: replacement library. Other POSIX options are not even defined.
45: .P
46: There are also some other options that are not defined by POSIX. These have
47: been added at the request of users who want to make use of certain
48: PCRE-specific features via the POSIX calling interface.
49: .P
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. "POSIX-like in style" means that the API approximates to the
54: POSIX definition; it is not fully POSIX-compatible, and in multi-byte encoding
55: domains it is probably even less compatible.
56: .P
57: The header for these functions is supplied as \fBpcreposix.h\fP to avoid any
58: potential clash with other POSIX libraries. It can, of course, be renamed or
59: aliased as \fBregex.h\fP, which is the "correct" name. It provides two
60: structure types, \fIregex_t\fP for compiled internal forms, and
61: \fIregmatch_t\fP for returning captured substrings. It also defines some
62: constants whose names start with "REG_"; these are used for setting options and
63: identifying error codes.
64: .
65: .
66: .SH "COMPILING A PATTERN"
67: .rs
68: .sp
69: The function \fBregcomp()\fP is called to compile a pattern into an
70: internal form. The pattern is a C string terminated by a binary zero, and
71: is passed in the argument \fIpattern\fP. The \fIpreg\fP argument is a pointer
72: to a \fBregex_t\fP structure that is used as a base for storing information
73: about the compiled regular expression.
74: .P
75: The argument \fIcflags\fP is either zero, or contains one or more of the bits
76: defined by the following macros:
77: .sp
78: REG_DOTALL
79: .sp
80: The PCRE_DOTALL option is set when the regular expression is passed for
81: compilation to the native function. Note that REG_DOTALL is not part of the
82: POSIX standard.
83: .sp
84: REG_ICASE
85: .sp
86: The PCRE_CASELESS option is set when the regular expression is passed for
87: compilation to the native function.
88: .sp
89: REG_NEWLINE
90: .sp
91: The PCRE_MULTILINE option is set when the regular expression is passed for
92: compilation to the native function. Note that this does \fInot\fP mimic the
93: defined POSIX behaviour for REG_NEWLINE (see the following section).
94: .sp
95: REG_NOSUB
96: .sp
97: The PCRE_NO_AUTO_CAPTURE option is set when the regular expression is passed
98: for compilation to the native function. In addition, when a pattern that is
99: compiled with this flag is passed to \fBregexec()\fP for matching, the
100: \fInmatch\fP and \fIpmatch\fP arguments are ignored, and no captured strings
101: are returned.
102: .sp
103: REG_UCP
104: .sp
105: The PCRE_UCP option is set when the regular expression is passed for
106: compilation to the native function. This causes PCRE to use Unicode properties
107: when matchine \ed, \ew, etc., instead of just recognizing ASCII values. Note
108: that REG_UTF8 is not part of the POSIX standard.
109: .sp
110: REG_UNGREEDY
111: .sp
112: The PCRE_UNGREEDY option is set when the regular expression is passed for
113: compilation to the native function. Note that REG_UNGREEDY is not part of the
114: POSIX standard.
115: .sp
116: REG_UTF8
117: .sp
118: The PCRE_UTF8 option is set when the regular expression is passed for
119: compilation to the native function. This causes the pattern itself and all data
120: strings used for matching it to be treated as UTF-8 strings. Note that REG_UTF8
121: is not part of the POSIX standard.
122: .P
123: In the absence of these flags, no options are passed to the native function.
124: This means the the regex is compiled with PCRE default semantics. In
125: particular, the way it handles newline characters in the subject string is the
126: Perl way, not the POSIX way. Note that setting PCRE_MULTILINE has only
127: \fIsome\fP of the effects specified for REG_NEWLINE. It does not affect the way
128: newlines are matched by . (they are not) or by a negative class such as [^a]
129: (they are).
130: .P
131: The yield of \fBregcomp()\fP is zero on success, and non-zero otherwise. The
132: \fIpreg\fP structure is filled in on success, and one member of the structure
133: is public: \fIre_nsub\fP contains the number of capturing subpatterns in
134: the regular expression. Various error codes are defined in the header file.
135: .P
136: NOTE: If the yield of \fBregcomp()\fP is non-zero, you must not attempt to
137: use the contents of the \fIpreg\fP structure. If, for example, you pass it to
138: \fBregexec()\fP, the result is undefined and your program is likely to crash.
139: .
140: .
141: .SH "MATCHING NEWLINE CHARACTERS"
142: .rs
143: .sp
144: This area is not simple, because POSIX and Perl take different views of things.
145: It is not possible to get PCRE to obey POSIX semantics, but then PCRE was never
146: intended to be a POSIX engine. The following table lists the different
147: possibilities for matching newline characters in PCRE:
148: .sp
149: Default Change with
150: .sp
151: . matches newline no PCRE_DOTALL
152: newline matches [^a] yes not changeable
153: $ matches \en at end yes PCRE_DOLLARENDONLY
154: $ matches \en in middle no PCRE_MULTILINE
155: ^ matches \en in middle no PCRE_MULTILINE
156: .sp
157: This is the equivalent table for POSIX:
158: .sp
159: Default Change with
160: .sp
161: . matches newline yes REG_NEWLINE
162: newline matches [^a] yes REG_NEWLINE
163: $ matches \en at end no REG_NEWLINE
164: $ matches \en in middle no REG_NEWLINE
165: ^ matches \en in middle no REG_NEWLINE
166: .sp
167: PCRE's behaviour is the same as Perl's, except that there is no equivalent for
168: PCRE_DOLLAR_ENDONLY in Perl. In both PCRE and Perl, there is no way to stop
169: newline from matching [^a].
170: .P
171: The default POSIX newline handling can be obtained by setting PCRE_DOTALL and
172: PCRE_DOLLAR_ENDONLY, but there is no way to make PCRE behave exactly as for the
173: REG_NEWLINE action.
174: .
175: .
176: .SH "MATCHING A PATTERN"
177: .rs
178: .sp
179: The function \fBregexec()\fP is called to match a compiled pattern \fIpreg\fP
180: against a given \fIstring\fP, which is by default terminated by a zero byte
181: (but see REG_STARTEND below), subject to the options in \fIeflags\fP. These can
182: be:
183: .sp
184: REG_NOTBOL
185: .sp
186: The PCRE_NOTBOL option is set when calling the underlying PCRE matching
187: function.
188: .sp
189: REG_NOTEMPTY
190: .sp
191: The PCRE_NOTEMPTY option is set when calling the underlying PCRE matching
192: function. Note that REG_NOTEMPTY is not part of the POSIX standard. However,
193: setting this option can give more POSIX-like behaviour in some situations.
194: .sp
195: REG_NOTEOL
196: .sp
197: The PCRE_NOTEOL option is set when calling the underlying PCRE matching
198: function.
199: .sp
200: REG_STARTEND
201: .sp
202: The string is considered to start at \fIstring\fP + \fIpmatch[0].rm_so\fP and
203: to have a terminating NUL located at \fIstring\fP + \fIpmatch[0].rm_eo\fP
204: (there need not actually be a NUL at that location), regardless of the value of
205: \fInmatch\fP. This is a BSD extension, compatible with but not specified by
206: IEEE Standard 1003.2 (POSIX.2), and should be used with caution in software
207: intended to be portable to other systems. Note that a non-zero \fIrm_so\fP does
208: not imply REG_NOTBOL; REG_STARTEND affects only the location of the string, not
209: how it is matched.
210: .P
211: If the pattern was compiled with the REG_NOSUB flag, no data about any matched
212: strings is returned. The \fInmatch\fP and \fIpmatch\fP arguments of
213: \fBregexec()\fP are ignored.
214: .P
215: If the value of \fInmatch\fP is zero, or if the value \fIpmatch\fP is NULL,
216: no data about any matched strings is returned.
217: .P
218: Otherwise,the portion of the string that was matched, and also any captured
219: substrings, are returned via the \fIpmatch\fP argument, which points to an
220: array of \fInmatch\fP structures of type \fIregmatch_t\fP, containing the
221: members \fIrm_so\fP and \fIrm_eo\fP. These contain the offset to the first
222: character of each substring and the offset to the first character after the end
223: of each substring, respectively. The 0th element of the vector relates to the
224: entire portion of \fIstring\fP that was matched; subsequent elements relate to
225: the capturing subpatterns of the regular expression. Unused entries in the
226: array have both structure members set to -1.
227: .P
228: A successful match yields a zero return; various error codes are defined in the
229: header file, of which REG_NOMATCH is the "expected" failure code.
230: .
231: .
232: .SH "ERROR MESSAGES"
233: .rs
234: .sp
235: The \fBregerror()\fP function maps a non-zero errorcode from either
236: \fBregcomp()\fP or \fBregexec()\fP to a printable message. If \fIpreg\fP is not
237: NULL, the error should have arisen from the use of that structure. A message
238: terminated by a binary zero is placed in \fIerrbuf\fP. The length of the
239: message, including the zero, is limited to \fIerrbuf_size\fP. The yield of the
240: function is the size of buffer needed to hold the whole message.
241: .
242: .
243: .SH MEMORY USAGE
244: .rs
245: .sp
246: Compiling a regular expression causes memory to be allocated and associated
247: with the \fIpreg\fP structure. The function \fBregfree()\fP frees all such
248: memory, after which \fIpreg\fP may no longer be used as a compiled expression.
249: .
250: .
251: .SH AUTHOR
252: .rs
253: .sp
254: .nf
255: Philip Hazel
256: University Computing Service
257: Cambridge CB2 3QH, England.
258: .fi
259: .
260: .
261: .SH REVISION
262: .rs
263: .sp
264: .nf
265: Last updated: 09 January 2012
266: Copyright (c) 1997-2012 University of Cambridge.
267: .fi
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