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