Annotation of embedaddon/pcre/doc/pcreposix.3, revision 1.1.1.1
1.1 misho 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 to the PCRE regular expression
28: package. See the
29: .\" HREF
30: \fBpcreapi\fP
31: .\"
32: documentation for a description of PCRE's native API, which contains much
33: additional functionality.
34: .P
35: The functions described here are just wrapper functions that ultimately call
36: the PCRE native API. Their prototypes are defined in the \fBpcreposix.h\fP
37: header file, and on Unix systems the library itself is called
38: \fBpcreposix.a\fP, so can be accessed by adding \fB-lpcreposix\fP to the
39: command for linking an application that uses them. Because the POSIX functions
40: call the native ones, it is also necessary to add \fB-lpcre\fP.
41: .P
42: I have implemented only those POSIX option bits that can be reasonably mapped
43: to PCRE native options. In addition, the option REG_EXTENDED is defined with
44: the value zero. This has no effect, but since programs that are written to the
45: POSIX interface often use it, this makes it easier to slot in PCRE as a
46: replacement library. Other POSIX options are not even defined.
47: .P
48: There are also some other options that are not defined by POSIX. These have
49: been added at the request of users who want to make use of certain
50: PCRE-specific features via the POSIX calling interface.
51: .P
52: When PCRE is called via these functions, it is only the API that is POSIX-like
53: in style. The syntax and semantics of the regular expressions themselves are
54: still those of Perl, subject to the setting of various PCRE options, as
55: described below. "POSIX-like in style" means that the API approximates to the
56: POSIX definition; it is not fully POSIX-compatible, and in multi-byte encoding
57: domains it is probably even less compatible.
58: .P
59: The header for these functions is supplied as \fBpcreposix.h\fP to avoid any
60: potential clash with other POSIX libraries. It can, of course, be renamed or
61: aliased as \fBregex.h\fP, which is the "correct" name. It provides two
62: structure types, \fIregex_t\fP for compiled internal forms, and
63: \fIregmatch_t\fP for returning captured substrings. It also defines some
64: constants whose names start with "REG_"; these are used for setting options and
65: identifying error codes.
66: .
67: .
68: .SH "COMPILING A PATTERN"
69: .rs
70: .sp
71: The function \fBregcomp()\fP is called to compile a pattern into an
72: internal form. The pattern is a C string terminated by a binary zero, and
73: is passed in the argument \fIpattern\fP. The \fIpreg\fP argument is a pointer
74: to a \fBregex_t\fP structure that is used as a base for storing information
75: about the compiled regular expression.
76: .P
77: The argument \fIcflags\fP is either zero, or contains one or more of the bits
78: defined by the following macros:
79: .sp
80: REG_DOTALL
81: .sp
82: The PCRE_DOTALL option is set when the regular expression is passed for
83: compilation to the native function. Note that REG_DOTALL is not part of the
84: POSIX standard.
85: .sp
86: REG_ICASE
87: .sp
88: The PCRE_CASELESS option is set when the regular expression is passed for
89: compilation to the native function.
90: .sp
91: REG_NEWLINE
92: .sp
93: The PCRE_MULTILINE option is set when the regular expression is passed for
94: compilation to the native function. Note that this does \fInot\fP mimic the
95: defined POSIX behaviour for REG_NEWLINE (see the following section).
96: .sp
97: REG_NOSUB
98: .sp
99: The PCRE_NO_AUTO_CAPTURE option is set when the regular expression is passed
100: for compilation to the native function. In addition, when a pattern that is
101: compiled with this flag is passed to \fBregexec()\fP for matching, the
102: \fInmatch\fP and \fIpmatch\fP arguments are ignored, and no captured strings
103: are returned.
104: .sp
105: REG_UCP
106: .sp
107: The PCRE_UCP option is set when the regular expression is passed for
108: compilation to the native function. This causes PCRE to use Unicode properties
109: when matchine \ed, \ew, etc., instead of just recognizing ASCII values. Note
110: that REG_UTF8 is not part of the POSIX standard.
111: .sp
112: REG_UNGREEDY
113: .sp
114: The PCRE_UNGREEDY option is set when the regular expression is passed for
115: compilation to the native function. Note that REG_UNGREEDY is not part of the
116: POSIX standard.
117: .sp
118: REG_UTF8
119: .sp
120: The PCRE_UTF8 option is set when the regular expression is passed for
121: compilation to the native function. This causes the pattern itself and all data
122: strings used for matching it to be treated as UTF-8 strings. Note that REG_UTF8
123: is not part of the POSIX standard.
124: .P
125: In the absence of these flags, no options are passed to the native function.
126: This means the the regex is compiled with PCRE default semantics. In
127: particular, the way it handles newline characters in the subject string is the
128: Perl way, not the POSIX way. Note that setting PCRE_MULTILINE has only
129: \fIsome\fP of the effects specified for REG_NEWLINE. It does not affect the way
130: newlines are matched by . (they are not) or by a negative class such as [^a]
131: (they are).
132: .P
133: The yield of \fBregcomp()\fP is zero on success, and non-zero otherwise. The
134: \fIpreg\fP structure is filled in on success, and one member of the structure
135: is public: \fIre_nsub\fP contains the number of capturing subpatterns in
136: the regular expression. Various error codes are defined in the header file.
137: .P
138: NOTE: If the yield of \fBregcomp()\fP is non-zero, you must not attempt to
139: use the contents of the \fIpreg\fP structure. If, for example, you pass it to
140: \fBregexec()\fP, the result is undefined and your program is likely to crash.
141: .
142: .
143: .SH "MATCHING NEWLINE CHARACTERS"
144: .rs
145: .sp
146: This area is not simple, because POSIX and Perl take different views of things.
147: It is not possible to get PCRE to obey POSIX semantics, but then PCRE was never
148: intended to be a POSIX engine. The following table lists the different
149: possibilities for matching newline characters in PCRE:
150: .sp
151: Default Change with
152: .sp
153: . matches newline no PCRE_DOTALL
154: newline matches [^a] yes not changeable
155: $ matches \en at end yes PCRE_DOLLARENDONLY
156: $ matches \en in middle no PCRE_MULTILINE
157: ^ matches \en in middle no PCRE_MULTILINE
158: .sp
159: This is the equivalent table for POSIX:
160: .sp
161: Default Change with
162: .sp
163: . matches newline yes REG_NEWLINE
164: newline matches [^a] yes REG_NEWLINE
165: $ matches \en at end no REG_NEWLINE
166: $ matches \en in middle no REG_NEWLINE
167: ^ matches \en in middle no REG_NEWLINE
168: .sp
169: PCRE's behaviour is the same as Perl's, except that there is no equivalent for
170: PCRE_DOLLAR_ENDONLY in Perl. In both PCRE and Perl, there is no way to stop
171: newline from matching [^a].
172: .P
173: The default POSIX newline handling can be obtained by setting PCRE_DOTALL and
174: PCRE_DOLLAR_ENDONLY, but there is no way to make PCRE behave exactly as for the
175: REG_NEWLINE action.
176: .
177: .
178: .SH "MATCHING A PATTERN"
179: .rs
180: .sp
181: The function \fBregexec()\fP is called to match a compiled pattern \fIpreg\fP
182: against a given \fIstring\fP, which is by default terminated by a zero byte
183: (but see REG_STARTEND below), subject to the options in \fIeflags\fP. These can
184: be:
185: .sp
186: REG_NOTBOL
187: .sp
188: The PCRE_NOTBOL option is set when calling the underlying PCRE matching
189: function.
190: .sp
191: REG_NOTEMPTY
192: .sp
193: The PCRE_NOTEMPTY option is set when calling the underlying PCRE matching
194: function. Note that REG_NOTEMPTY is not part of the POSIX standard. However,
195: setting this option can give more POSIX-like behaviour in some situations.
196: .sp
197: REG_NOTEOL
198: .sp
199: The PCRE_NOTEOL option is set when calling the underlying PCRE matching
200: function.
201: .sp
202: REG_STARTEND
203: .sp
204: The string is considered to start at \fIstring\fP + \fIpmatch[0].rm_so\fP and
205: to have a terminating NUL located at \fIstring\fP + \fIpmatch[0].rm_eo\fP
206: (there need not actually be a NUL at that location), regardless of the value of
207: \fInmatch\fP. This is a BSD extension, compatible with but not specified by
208: IEEE Standard 1003.2 (POSIX.2), and should be used with caution in software
209: intended to be portable to other systems. Note that a non-zero \fIrm_so\fP does
210: not imply REG_NOTBOL; REG_STARTEND affects only the location of the string, not
211: how it is matched.
212: .P
213: If the pattern was compiled with the REG_NOSUB flag, no data about any matched
214: strings is returned. The \fInmatch\fP and \fIpmatch\fP arguments of
215: \fBregexec()\fP are ignored.
216: .P
217: If the value of \fInmatch\fP is zero, or if the value \fIpmatch\fP is NULL,
218: no data about any matched strings is returned.
219: .P
220: Otherwise,the portion of the string that was matched, and also any captured
221: substrings, are returned via the \fIpmatch\fP argument, which points to an
222: array of \fInmatch\fP structures of type \fIregmatch_t\fP, containing the
223: members \fIrm_so\fP and \fIrm_eo\fP. These contain the offset to the first
224: character of each substring and the offset to the first character after the end
225: of each substring, respectively. The 0th element of the vector relates to the
226: entire portion of \fIstring\fP that was matched; subsequent elements relate to
227: the capturing subpatterns of the regular expression. Unused entries in the
228: array have both structure members set to -1.
229: .P
230: A successful match yields a zero return; various error codes are defined in the
231: header file, of which REG_NOMATCH is the "expected" failure code.
232: .
233: .
234: .SH "ERROR MESSAGES"
235: .rs
236: .sp
237: The \fBregerror()\fP function maps a non-zero errorcode from either
238: \fBregcomp()\fP or \fBregexec()\fP to a printable message. If \fIpreg\fP is not
239: NULL, the error should have arisen from the use of that structure. A message
240: terminated by a binary zero is placed in \fIerrbuf\fP. The length of the
241: message, including the zero, is limited to \fIerrbuf_size\fP. The yield of the
242: function is the size of buffer needed to hold the whole message.
243: .
244: .
245: .SH MEMORY USAGE
246: .rs
247: .sp
248: Compiling a regular expression causes memory to be allocated and associated
249: with the \fIpreg\fP structure. The function \fBregfree()\fP frees all such
250: memory, after which \fIpreg\fP may no longer be used as a compiled expression.
251: .
252: .
253: .SH AUTHOR
254: .rs
255: .sp
256: .nf
257: Philip Hazel
258: University Computing Service
259: Cambridge CB2 3QH, England.
260: .fi
261: .
262: .
263: .SH REVISION
264: .rs
265: .sp
266: .nf
267: Last updated: 16 May 2010
268: Copyright (c) 1997-2010 University of Cambridge.
269: .fi
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