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Revision 99 - (show annotations)
Tue Mar 6 12:27:42 2007 UTC (14 years, 2 months ago) by ph10
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1. Move the comment about version numbers from pcre.h.in to configure.ac 
because that's where they are now set.
2. Update all the man pages to remove the use of .br and .in because this
causes trouble for some HTML converters. Also standardised the final sections 
giving author information and revision date.
3. Update the maintain/132html man page converter to handle .nf/.fi and to barf 
at .br/.in.
1 .TH PCRE 3
3 PCRE - Perl-compatible regular expressions
5 .rs
6 .sp
7 The PCRE library is a set of functions that implement regular expression
8 pattern matching using the same syntax and semantics as Perl, with just a few
9 differences. (Certain features that appeared in Python and PCRE before they
10 appeared in Perl are also available using the Python syntax.)
11 .P
12 The current implementation of PCRE (release 7.x) corresponds approximately with
13 Perl 5.10, including support for UTF-8 encoded strings and Unicode general
14 category properties. However, UTF-8 and Unicode support has to be explicitly
15 enabled; it is not the default. The Unicode tables correspond to Unicode
16 release 5.0.0.
17 .P
18 In addition to the Perl-compatible matching function, PCRE contains an
19 alternative matching function that matches the same compiled patterns in a
20 different way. In certain circumstances, the alternative function has some
21 advantages. For a discussion of the two matching algorithms, see the
22 .\" HREF
23 \fBpcrematching\fP
24 .\"
25 page.
26 .P
27 PCRE is written in C and released as a C library. A number of people have
28 written wrappers and interfaces of various kinds. In particular, Google Inc.
29 have provided a comprehensive C++ wrapper. This is now included as part of the
30 PCRE distribution. The
31 .\" HREF
32 \fBpcrecpp\fP
33 .\"
34 page has details of this interface. Other people's contributions can be found
35 in the \fIContrib\fR directory at the primary FTP site, which is:
36 .sp
37 .\" HTML <a href="ftp://ftp.csx.cam.ac.uk/pub/software/programming/pcre">
38 .\" </a>
39 ftp://ftp.csx.cam.ac.uk/pub/software/programming/pcre
40 .P
41 Details of exactly which Perl regular expression features are and are not
42 supported by PCRE are given in separate documents. See the
43 .\" HREF
44 \fBpcrepattern\fR
45 .\"
46 and
47 .\" HREF
48 \fBpcrecompat\fR
49 .\"
50 pages.
51 .P
52 Some features of PCRE can be included, excluded, or changed when the library is
53 built. The
54 .\" HREF
55 \fBpcre_config()\fR
56 .\"
57 function makes it possible for a client to discover which features are
58 available. The features themselves are described in the
59 .\" HREF
60 \fBpcrebuild\fP
61 .\"
62 page. Documentation about building PCRE for various operating systems can be
63 found in the \fBREADME\fP file in the source distribution.
64 .P
65 The library contains a number of undocumented internal functions and data
66 tables that are used by more than one of the exported external functions, but
67 which are not intended for use by external callers. Their names all begin with
68 "_pcre_", which hopefully will not provoke any name clashes. In some
69 environments, it is possible to control which external symbols are exported
70 when a shared library is built, and in these cases the undocumented symbols are
71 not exported.
72 .
73 .
75 .rs
76 .sp
77 The user documentation for PCRE comprises a number of different sections. In
78 the "man" format, each of these is a separate "man page". In the HTML format,
79 each is a separate page, linked from the index page. In the plain text format,
80 all the sections are concatenated, for ease of searching. The sections are as
81 follows:
82 .sp
83 pcre this document
84 pcreapi details of PCRE's native C API
85 pcrebuild options for building PCRE
86 pcrecallout details of the callout feature
87 pcrecompat discussion of Perl compatibility
88 pcrecpp details of the C++ wrapper
89 pcregrep description of the \fBpcregrep\fP command
90 pcrematching discussion of the two matching algorithms
91 pcrepartial details of the partial matching facility
92 .\" JOIN
93 pcrepattern syntax and semantics of supported
94 regular expressions
95 pcreperform discussion of performance issues
96 pcreposix the POSIX-compatible C API
97 pcreprecompile details of saving and re-using precompiled patterns
98 pcresample discussion of the sample program
99 pcrestack discussion of stack usage
100 pcretest description of the \fBpcretest\fP testing command
101 .sp
102 In addition, in the "man" and HTML formats, there is a short page for each
103 C library function, listing its arguments and results.
104 .
105 .
107 .rs
108 .sp
109 There are some size limitations in PCRE but it is hoped that they will never in
110 practice be relevant.
111 .P
112 The maximum length of a compiled pattern is 65539 (sic) bytes if PCRE is
113 compiled with the default internal linkage size of 2. If you want to process
114 regular expressions that are truly enormous, you can compile PCRE with an
115 internal linkage size of 3 or 4 (see the \fBREADME\fP file in the source
116 distribution and the
117 .\" HREF
118 \fBpcrebuild\fP
119 .\"
120 documentation for details). In these cases the limit is substantially larger.
121 However, the speed of execution is slower.
122 .P
123 All values in repeating quantifiers must be less than 65536. The maximum
124 compiled length of subpattern with an explicit repeat count is 30000 bytes. The
125 maximum number of capturing subpatterns is 65535.
126 .P
127 There is no limit to the number of parenthesized subpatterns, but there can be
128 no more than 65535 capturing subpatterns.
129 .P
130 The maximum length of name for a named subpattern is 32 characters, and the
131 maximum number of named subpatterns is 10000.
132 .P
133 The maximum length of a subject string is the largest positive number that an
134 integer variable can hold. However, when using the traditional matching
135 function, PCRE uses recursion to handle subpatterns and indefinite repetition.
136 This means that the available stack space may limit the size of a subject
137 string that can be processed by certain patterns. For a discussion of stack
138 issues, see the
139 .\" HREF
140 \fBpcrestack\fP
141 .\"
142 documentation.
143 .sp
144 .\" HTML <a name="utf8support"></a>
145 .
146 .
148 .rs
149 .sp
150 From release 3.3, PCRE has had some support for character strings encoded in
151 the UTF-8 format. For release 4.0 this was greatly extended to cover most
152 common requirements, and in release 5.0 additional support for Unicode general
153 category properties was added.
154 .P
155 In order process UTF-8 strings, you must build PCRE to include UTF-8 support in
156 the code, and, in addition, you must call
157 .\" HREF
158 \fBpcre_compile()\fP
159 .\"
160 with the PCRE_UTF8 option flag. When you do this, both the pattern and any
161 subject strings that are matched against it are treated as UTF-8 strings
162 instead of just strings of bytes.
163 .P
164 If you compile PCRE with UTF-8 support, but do not use it at run time, the
165 library will be a bit bigger, but the additional run time overhead is limited
166 to testing the PCRE_UTF8 flag occasionally, so should not be very big.
167 .P
168 If PCRE is built with Unicode character property support (which implies UTF-8
169 support), the escape sequences \ep{..}, \eP{..}, and \eX are supported.
170 The available properties that can be tested are limited to the general
171 category properties such as Lu for an upper case letter or Nd for a decimal
172 number, the Unicode script names such as Arabic or Han, and the derived
173 properties Any and L&. A full list is given in the
174 .\" HREF
175 \fBpcrepattern\fP
176 .\"
177 documentation. Only the short names for properties are supported. For example,
178 \ep{L} matches a letter. Its Perl synonym, \ep{Letter}, is not supported.
179 Furthermore, in Perl, many properties may optionally be prefixed by "Is", for
180 compatibility with Perl 5.6. PCRE does not support this.
181 .P
182 The following comments apply when PCRE is running in UTF-8 mode:
183 .P
184 1. When you set the PCRE_UTF8 flag, the strings passed as patterns and subjects
185 are checked for validity on entry to the relevant functions. If an invalid
186 UTF-8 string is passed, an error return is given. In some situations, you may
187 already know that your strings are valid, and therefore want to skip these
188 checks in order to improve performance. If you set the PCRE_NO_UTF8_CHECK flag
189 at compile time or at run time, PCRE assumes that the pattern or subject it
190 is given (respectively) contains only valid UTF-8 codes. In this case, it does
191 not diagnose an invalid UTF-8 string. If you pass an invalid UTF-8 string to
192 PCRE when PCRE_NO_UTF8_CHECK is set, the results are undefined. Your program
193 may crash.
194 .P
195 2. An unbraced hexadecimal escape sequence (such as \exb3) matches a two-byte
196 UTF-8 character if the value is greater than 127.
197 .P
198 3. Octal numbers up to \e777 are recognized, and match two-byte UTF-8
199 characters for values greater than \e177.
200 .P
201 4. Repeat quantifiers apply to complete UTF-8 characters, not to individual
202 bytes, for example: \ex{100}{3}.
203 .P
204 5. The dot metacharacter matches one UTF-8 character instead of a single byte.
205 .P
206 6. The escape sequence \eC can be used to match a single byte in UTF-8 mode,
207 but its use can lead to some strange effects. This facility is not available in
208 the alternative matching function, \fBpcre_dfa_exec()\fP.
209 .P
210 7. The character escapes \eb, \eB, \ed, \eD, \es, \eS, \ew, and \eW correctly
211 test characters of any code value, but the characters that PCRE recognizes as
212 digits, spaces, or word characters remain the same set as before, all with
213 values less than 256. This remains true even when PCRE includes Unicode
214 property support, because to do otherwise would slow down PCRE in many common
215 cases. If you really want to test for a wider sense of, say, "digit", you
216 must use Unicode property tests such as \ep{Nd}.
217 .P
218 8. Similarly, characters that match the POSIX named character classes are all
219 low-valued characters.
220 .P
221 9. Case-insensitive matching applies only to characters whose values are less
222 than 128, unless PCRE is built with Unicode property support. Even when Unicode
223 property support is available, PCRE still uses its own character tables when
224 checking the case of low-valued characters, so as not to degrade performance.
225 The Unicode property information is used only for characters with higher
226 values. Even when Unicode property support is available, PCRE supports
227 case-insensitive matching only when there is a one-to-one mapping between a
228 letter's cases. There are a small number of many-to-one mappings in Unicode;
229 these are not supported by PCRE.
230 .
231 .
233 .rs
234 .sp
235 .nf
236 Philip Hazel
237 University Computing Service
238 Cambridge CB2 3QH, England.
239 .fi
240 .P
241 Putting an actual email address here seems to have been a spam magnet, so I've
242 taken it away. If you want to email me, use my initial and surname, separated
243 by a dot, at the domain ucs.cam.ac.uk.
244 .
245 .
247 .rs
248 .sp
249 .nf
250 Last updated: 06 March 2007
251 Copyright (c) 1997-2007 University of Cambridge.
252 .fi


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