ViewVC logotype

Contents of /code/trunk/doc/pcre.txt

Parent Directory Parent Directory | Revision Log Revision Log

Revision 150 - (hide annotations) (download)
Tue Apr 17 08:22:40 2007 UTC (8 years ago) by ph10
File MIME type: text/plain
File size: 266746 byte(s)
Update HTML documentation.

1 nigel 75 -----------------------------------------------------------------------------
2 nigel 63 This file contains a concatenation of the PCRE man pages, converted to plain
3     text format for ease of searching with a text editor, or for use on systems
4     that do not have a man page processor. The small individual files that give
5     synopses of each function in the library have not been included. There are
6     separate text files for the pcregrep and pcretest commands.
7     -----------------------------------------------------------------------------
9 nigel 41
10 nigel 79 PCRE(3) PCRE(3)
11 nigel 41
12 nigel 79
13 nigel 73 NAME
14     PCRE - Perl-compatible regular expressions
16 nigel 77
17 nigel 75 INTRODUCTION
18 nigel 41
19 nigel 73 The PCRE library is a set of functions that implement regular expres-
20     sion pattern matching using the same syntax and semantics as Perl, with
21 nigel 93 just a few differences. (Certain features that appeared in Python and
22     PCRE before they appeared in Perl are also available using the Python
23     syntax.)
24 nigel 63
25 nigel 93 The current implementation of PCRE (release 7.x) corresponds approxi-
26     mately with Perl 5.10, including support for UTF-8 encoded strings and
27     Unicode general category properties. However, UTF-8 and Unicode support
28     has to be explicitly enabled; it is not the default. The Unicode tables
29     correspond to Unicode release 5.0.0.
30 nigel 77
31 nigel 93 In addition to the Perl-compatible matching function, PCRE contains an
32     alternative matching function that matches the same compiled patterns
33     in a different way. In certain circumstances, the alternative function
34     has some advantages. For a discussion of the two matching algorithms,
35     see the pcrematching page.
37     PCRE is written in C and released as a C library. A number of people
38     have written wrappers and interfaces of various kinds. In particular,
39     Google Inc. have provided a comprehensive C++ wrapper. This is now
40 nigel 77 included as part of the PCRE distribution. The pcrecpp page has details
41 nigel 93 of this interface. Other people's contributions can be found in the
42 nigel 77 Contrib directory at the primary FTP site, which is:
43 nigel 63
44 nigel 73 ftp://ftp.csx.cam.ac.uk/pub/software/programming/pcre
45 nigel 63
46 nigel 93 Details of exactly which Perl regular expression features are and are
47 nigel 73 not supported by PCRE are given in separate documents. See the pcrepat-
48     tern and pcrecompat pages.
49 nigel 63
50 nigel 93 Some features of PCRE can be included, excluded, or changed when the
51     library is built. The pcre_config() function makes it possible for a
52     client to discover which features are available. The features them-
53     selves are described in the pcrebuild page. Documentation about build-
54     ing PCRE for various operating systems can be found in the README file
55 nigel 75 in the source distribution.
56 nigel 63
57 nigel 93 The library contains a number of undocumented internal functions and
58     data tables that are used by more than one of the exported external
59     functions, but which are not intended for use by external callers.
60     Their names all begin with "_pcre_", which hopefully will not provoke
61 nigel 83 any name clashes. In some environments, it is possible to control which
62 nigel 93 external symbols are exported when a shared library is built, and in
63 nigel 83 these cases the undocumented symbols are not exported.
64 nigel 63
65 nigel 77
68 nigel 93 The user documentation for PCRE comprises a number of different sec-
69     tions. In the "man" format, each of these is a separate "man page". In
70     the HTML format, each is a separate page, linked from the index page.
71     In the plain text format, all the sections are concatenated, for ease
72 nigel 75 of searching. The sections are as follows:
73 nigel 63
74 nigel 73 pcre this document
75 nigel 77 pcreapi details of PCRE's native C API
76 nigel 73 pcrebuild options for building PCRE
77     pcrecallout details of the callout feature
78     pcrecompat discussion of Perl compatibility
79 nigel 77 pcrecpp details of the C++ wrapper
80 nigel 73 pcregrep description of the pcregrep command
81 nigel 77 pcrematching discussion of the two matching algorithms
82 nigel 75 pcrepartial details of the partial matching facility
83 nigel 73 pcrepattern syntax and semantics of supported
84     regular expressions
85     pcreperform discussion of performance issues
86 nigel 77 pcreposix the POSIX-compatible C API
87 nigel 75 pcreprecompile details of saving and re-using precompiled patterns
88 nigel 73 pcresample discussion of the sample program
89 nigel 91 pcrestack discussion of stack usage
90 nigel 75 pcretest description of the pcretest testing command
91 nigel 63
92 nigel 93 In addition, in the "man" and HTML formats, there is a short page for
93 nigel 77 each C library function, listing its arguments and results.
94 nigel 63
98 nigel 93 There are some size limitations in PCRE but it is hoped that they will
99 nigel 73 never in practice be relevant.
100 nigel 63
101 nigel 93 The maximum length of a compiled pattern is 65539 (sic) bytes if PCRE
102 nigel 73 is compiled with the default internal linkage size of 2. If you want to
103 nigel 93 process regular expressions that are truly enormous, you can compile
104     PCRE with an internal linkage size of 3 or 4 (see the README file in
105     the source distribution and the pcrebuild documentation for details).
106     In these cases the limit is substantially larger. However, the speed
107     of execution is slower.
108 nigel 63
109 nigel 93 All values in repeating quantifiers must be less than 65536. The maxi-
110     mum compiled length of subpattern with an explicit repeat count is
111 nigel 91 30000 bytes. The maximum number of capturing subpatterns is 65535.
112 nigel 63
113 nigel 93 There is no limit to the number of parenthesized subpatterns, but there
114     can be no more than 65535 capturing subpatterns.
115 nigel 63
116 nigel 93 The maximum length of name for a named subpattern is 32 characters, and
117     the maximum number of named subpatterns is 10000.
118 nigel 91
119 nigel 93 The maximum length of a subject string is the largest positive number
120     that an integer variable can hold. However, when using the traditional
121 nigel 77 matching function, PCRE uses recursion to handle subpatterns and indef-
122 nigel 93 inite repetition. This means that the available stack space may limit
123 nigel 77 the size of a subject string that can be processed by certain patterns.
124 nigel 91 For a discussion of stack issues, see the pcrestack documentation.
125 nigel 63
128 nigel 63
129 nigel 93 From release 3.3, PCRE has had some support for character strings
130     encoded in the UTF-8 format. For release 4.0 this was greatly extended
131     to cover most common requirements, and in release 5.0 additional sup-
132 nigel 75 port for Unicode general category properties was added.
133 nigel 63
134 nigel 93 In order process UTF-8 strings, you must build PCRE to include UTF-8
135     support in the code, and, in addition, you must call pcre_compile()
136     with the PCRE_UTF8 option flag. When you do this, both the pattern and
137     any subject strings that are matched against it are treated as UTF-8
138 nigel 73 strings instead of just strings of bytes.
139 nigel 63
140 nigel 93 If you compile PCRE with UTF-8 support, but do not use it at run time,
141     the library will be a bit bigger, but the additional run time overhead
142     is limited to testing the PCRE_UTF8 flag occasionally, so should not be
143     very big.
144 nigel 63
145 nigel 75 If PCRE is built with Unicode character property support (which implies
146 nigel 93 UTF-8 support), the escape sequences \p{..}, \P{..}, and \X are sup-
147 nigel 75 ported. The available properties that can be tested are limited to the
148 nigel 93 general category properties such as Lu for an upper case letter or Nd
149     for a decimal number, the Unicode script names such as Arabic or Han,
150     and the derived properties Any and L&. A full list is given in the
151 nigel 87 pcrepattern documentation. Only the short names for properties are sup-
152 nigel 93 ported. For example, \p{L} matches a letter. Its Perl synonym, \p{Let-
153     ter}, is not supported. Furthermore, in Perl, many properties may
154     optionally be prefixed by "Is", for compatibility with Perl 5.6. PCRE
155 nigel 87 does not support this.
156 nigel 75
157 nigel 73 The following comments apply when PCRE is running in UTF-8 mode:
158 nigel 63
159 nigel 93 1. When you set the PCRE_UTF8 flag, the strings passed as patterns and
160     subjects are checked for validity on entry to the relevant functions.
161 nigel 73 If an invalid UTF-8 string is passed, an error return is given. In some
162 nigel 93 situations, you may already know that your strings are valid, and
163 nigel 73 therefore want to skip these checks in order to improve performance. If
164 nigel 93 you set the PCRE_NO_UTF8_CHECK flag at compile time or at run time,
165     PCRE assumes that the pattern or subject it is given (respectively)
166     contains only valid UTF-8 codes. In this case, it does not diagnose an
167     invalid UTF-8 string. If you pass an invalid UTF-8 string to PCRE when
168     PCRE_NO_UTF8_CHECK is set, the results are undefined. Your program may
169 nigel 73 crash.
170 nigel 63
171 nigel 93 2. An unbraced hexadecimal escape sequence (such as \xb3) matches a
172 nigel 87 two-byte UTF-8 character if the value is greater than 127.
173 nigel 63
174 nigel 93 3. Octal numbers up to \777 are recognized, and match two-byte UTF-8
175 nigel 91 characters for values greater than \177.
177 nigel 93 4. Repeat quantifiers apply to complete UTF-8 characters, not to indi-
178 nigel 73 vidual bytes, for example: \x{100}{3}.
179 nigel 63
180 nigel 93 5. The dot metacharacter matches one UTF-8 character instead of a sin-
181 nigel 75 gle byte.
182 nigel 63
183 nigel 93 6. The escape sequence \C can be used to match a single byte in UTF-8
184     mode, but its use can lead to some strange effects. This facility is
185 nigel 77 not available in the alternative matching function, pcre_dfa_exec().
186 nigel 63
187 nigel 93 7. The character escapes \b, \B, \d, \D, \s, \S, \w, and \W correctly
188     test characters of any code value, but the characters that PCRE recog-
189     nizes as digits, spaces, or word characters remain the same set as
190 nigel 75 before, all with values less than 256. This remains true even when PCRE
191 nigel 93 includes Unicode property support, because to do otherwise would slow
192     down PCRE in many common cases. If you really want to test for a wider
193     sense of, say, "digit", you must use Unicode property tests such as
194 nigel 75 \p{Nd}.
195 nigel 63
196 nigel 93 8. Similarly, characters that match the POSIX named character classes
197 nigel 75 are all low-valued characters.
198 nigel 63
199 nigel 93 9. Case-insensitive matching applies only to characters whose values
200     are less than 128, unless PCRE is built with Unicode property support.
201     Even when Unicode property support is available, PCRE still uses its
202     own character tables when checking the case of low-valued characters,
203     so as not to degrade performance. The Unicode property information is
204 nigel 87 used only for characters with higher values. Even when Unicode property
205     support is available, PCRE supports case-insensitive matching only when
206 nigel 93 there is a one-to-one mapping between a letter's cases. There are a
207     small number of many-to-one mappings in Unicode; these are not sup-
208 nigel 87 ported by PCRE.
209 nigel 63
211     AUTHOR
213 nigel 77 Philip Hazel
214 ph10 99 University Computing Service
215 nigel 93 Cambridge CB2 3QH, England.
216 nigel 63
217 nigel 93 Putting an actual email address here seems to have been a spam magnet,
218 nigel 77 so I've taken it away. If you want to email me, use my initial and sur-
219     name, separated by a dot, at the domain ucs.cam.ac.uk.
221 nigel 63
222 ph10 99 REVISION
223 nigel 63
224 ph10 99 Last updated: 06 March 2007
225     Copyright (c) 1997-2007 University of Cambridge.
226     ------------------------------------------------------------------------------
227 ph10 111
229 nigel 79 PCREBUILD(3) PCREBUILD(3)
230 nigel 63
231 nigel 79
232 nigel 73 NAME
233     PCRE - Perl-compatible regular expressions
235 nigel 77
238 nigel 73 This document describes the optional features of PCRE that can be
239     selected when the library is compiled. They are all selected, or dese-
240 nigel 75 lected, by providing options to the configure script that is run before
241     the make command. The complete list of options for configure (which
242     includes the standard ones such as the selection of the installation
243     directory) can be obtained by running
244 nigel 63
245 nigel 73 ./configure --help
246 nigel 63
247 ph10 128 The following sections include descriptions of options whose names
248     begin with --enable or --disable. These settings specify changes to the
249     defaults for the configure command. Because of the way that configure
250     works, --enable and --disable always come in pairs, so the complemen-
251     tary option always exists as well, but as it specifies the default, it
252     is not described.
253 nigel 63
255 nigel 83 C++ SUPPORT
257     By default, the configure script will search for a C++ compiler and C++
258     header files. If it finds them, it automatically builds the C++ wrapper
259     library for PCRE. You can disable this by adding
261     --disable-cpp
263     to the configure command.
266 nigel 63 UTF-8 SUPPORT
268 nigel 73 To build PCRE with support for UTF-8 character strings, add
269 nigel 63
270 nigel 73 --enable-utf8
271 nigel 63
272 nigel 73 to the configure command. Of itself, this does not make PCRE treat
273     strings as UTF-8. As well as compiling PCRE with this option, you also
274     have have to set the PCRE_UTF8 option when you call the pcre_compile()
275     function.
276 nigel 63
280     UTF-8 support allows PCRE to process character values greater than 255
281     in the strings that it handles. On its own, however, it does not pro-
282     vide any facilities for accessing the properties of such characters. If
283     you want to be able to use the pattern escapes \P, \p, and \X, which
284     refer to Unicode character properties, you must add
286     --enable-unicode-properties
288     to the configure command. This implies UTF-8 support, even if you have
289     not explicitly requested it.
291 ph10 128 Including Unicode property support adds around 30K of tables to the
292     PCRE library. Only the general category properties such as Lu and Nd
293     are supported. Details are given in the pcrepattern documentation.
294 nigel 75
298 ph10 128 By default, PCRE interprets character 10 (linefeed, LF) as indicating
299     the end of a line. This is the normal newline character on Unix-like
300 nigel 91 systems. You can compile PCRE to use character 13 (carriage return, CR)
301     instead, by adding
302 nigel 63
303 nigel 73 --enable-newline-is-cr
304 nigel 63
305 ph10 128 to the configure command. There is also a --enable-newline-is-lf
306 nigel 91 option, which explicitly specifies linefeed as the newline character.
307 nigel 63
308 nigel 91 Alternatively, you can specify that line endings are to be indicated by
309     the two character sequence CRLF. If you want this, add
310 nigel 63
311 nigel 91 --enable-newline-is-crlf
313 nigel 93 to the configure command. There is a fourth option, specified by
314 nigel 91
315 ph10 150 --enable-newline-is-anycrlf
317     which causes PCRE to recognize any of the three sequences CR, LF, or
318     CRLF as indicating a line ending. Finally, a fifth option, specified by
320 nigel 93 --enable-newline-is-any
321 nigel 91
322 ph10 150 causes PCRE to recognize any Unicode newline sequence.
323 nigel 93
324 ph10 128 Whatever line ending convention is selected when PCRE is built can be
325     overridden when the library functions are called. At build time it is
326 nigel 93 conventional to use the standard for your operating system.
331 ph10 128 The PCRE building process uses libtool to build both shared and static
332     Unix libraries by default. You can suppress one of these by adding one
333 nigel 73 of
334 nigel 63
335 nigel 73 --disable-shared
336     --disable-static
337 nigel 63
338 nigel 73 to the configure command, as required.
339 nigel 63
343 nigel 75 When PCRE is called through the POSIX interface (see the pcreposix doc-
344 ph10 128 umentation), additional working storage is required for holding the
345     pointers to capturing substrings, because PCRE requires three integers
346     per substring, whereas the POSIX interface provides only two. If the
347 nigel 73 number of expected substrings is small, the wrapper function uses space
348     on the stack, because this is faster than using malloc() for each call.
349     The default threshold above which the stack is no longer used is 10; it
350     can be changed by adding a setting such as
351 nigel 63
352 nigel 73 --with-posix-malloc-threshold=20
353 nigel 63
354 nigel 73 to the configure command.
355 nigel 63
359 ph10 128 Within a compiled pattern, offset values are used to point from one
360     part to another (for example, from an opening parenthesis to an alter-
361     nation metacharacter). By default, two-byte values are used for these
362     offsets, leading to a maximum size for a compiled pattern of around
363     64K. This is sufficient to handle all but the most gigantic patterns.
364     Nevertheless, some people do want to process enormous patterns, so it
365     is possible to compile PCRE to use three-byte or four-byte offsets by
366 nigel 73 adding a setting such as
367 nigel 63
368 nigel 73 --with-link-size=3
369 nigel 63
370 ph10 128 to the configure command. The value given must be 2, 3, or 4. Using
371     longer offsets slows down the operation of PCRE because it has to load
372 nigel 73 additional bytes when handling them.
373 nigel 63
377 nigel 77 When matching with the pcre_exec() function, PCRE implements backtrack-
378 nigel 93 ing by making recursive calls to an internal function called match().
379     In environments where the size of the stack is limited, this can se-
380     verely limit PCRE's operation. (The Unix environment does not usually
381 nigel 91 suffer from this problem, but it may sometimes be necessary to increase
382 nigel 93 the maximum stack size. There is a discussion in the pcrestack docu-
383     mentation.) An alternative approach to recursion that uses memory from
384     the heap to remember data, instead of using recursive function calls,
385     has been implemented to work round the problem of limited stack size.
386 nigel 91 If you want to build a version of PCRE that works this way, add
387 nigel 73
388     --disable-stack-for-recursion
390 nigel 93 to the configure command. With this configuration, PCRE will use the
391     pcre_stack_malloc and pcre_stack_free variables to call memory manage-
392     ment functions. Separate functions are provided because the usage is
393     very predictable: the block sizes requested are always the same, and
394     the blocks are always freed in reverse order. A calling program might
395     be able to implement optimized functions that perform better than the
396     standard malloc() and free() functions. PCRE runs noticeably more
397 nigel 77 slowly when built in this way. This option affects only the pcre_exec()
398     function; it is not relevant for the the pcre_dfa_exec() function.
399 nigel 73
403 nigel 93 Internally, PCRE has a function called match(), which it calls repeat-
404     edly (sometimes recursively) when matching a pattern with the
405     pcre_exec() function. By controlling the maximum number of times this
406     function may be called during a single matching operation, a limit can
407     be placed on the resources used by a single call to pcre_exec(). The
408     limit can be changed at run time, as described in the pcreapi documen-
409     tation. The default is 10 million, but this can be changed by adding a
410 nigel 91 setting such as
412     --with-match-limit=500000
414 nigel 93 to the configure command. This setting has no effect on the
415 nigel 91 pcre_dfa_exec() matching function.
417 nigel 93 In some environments it is desirable to limit the depth of recursive
418 nigel 91 calls of match() more strictly than the total number of calls, in order
419 nigel 93 to restrict the maximum amount of stack (or heap, if --disable-stack-
420 nigel 91 for-recursion is specified) that is used. A second limit controls this;
421 nigel 93 it defaults to the value that is set for --with-match-limit, which
422     imposes no additional constraints. However, you can set a lower limit
423 nigel 91 by adding, for example,
425     --with-match-limit-recursion=10000
427 nigel 93 to the configure command. This value can also be overridden at run
428 nigel 91 time.
433     PCRE uses fixed tables for processing characters whose code values are
434     less than 256. By default, PCRE is built with a set of tables that are
435     distributed in the file pcre_chartables.c.dist. These tables are for
436     ASCII codes only. If you add
438     --enable-rebuild-chartables
440     to the configure command, the distributed tables are no longer used.
441     Instead, a program called dftables is compiled and run. This outputs
442     the source for new set of tables, created in the default locale of your
443     C runtime system. (This method of replacing the tables does not work if
444     you are cross compiling, because dftables is run on the local host. If
445     you need to create alternative tables when cross compiling, you will
446     have to do so "by hand".)
449 nigel 73 USING EBCDIC CODE
451 ph10 128 PCRE assumes by default that it will run in an environment where the
452     character code is ASCII (or Unicode, which is a superset of ASCII).
453     PCRE can, however, be compiled to run in an EBCDIC environment by
454 nigel 75 adding
455 nigel 73
456     --enable-ebcdic
458 ph10 128 to the configure command. This setting implies --enable-rebuild-charta-
459     bles.
460 nigel 73
461 nigel 93
462     SEE ALSO
464     pcreapi(3), pcre_config(3).
466 nigel 63
467 ph10 99 AUTHOR
468 nigel 63
469 ph10 99 Philip Hazel
470     University Computing Service
471     Cambridge CB2 3QH, England.
474     REVISION
476 ph10 150 Last updated: 16 April 2007
477 ph10 99 Copyright (c) 1997-2007 University of Cambridge.
478     ------------------------------------------------------------------------------
479 ph10 111
482 nigel 63
483 nigel 79
484 nigel 77 NAME
485     PCRE - Perl-compatible regular expressions
486 nigel 73
487 nigel 77
490     This document describes the two different algorithms that are available
491     in PCRE for matching a compiled regular expression against a given sub-
492     ject string. The "standard" algorithm is the one provided by the
493     pcre_exec() function. This works in the same was as Perl's matching
494     function, and provides a Perl-compatible matching operation.
496     An alternative algorithm is provided by the pcre_dfa_exec() function;
497     this operates in a different way, and is not Perl-compatible. It has
498     advantages and disadvantages compared with the standard algorithm, and
499     these are described below.
501     When there is only one possible way in which a given subject string can
502     match a pattern, the two algorithms give the same answer. A difference
503     arises, however, when there are multiple possibilities. For example, if
504     the pattern
506     ^<.*>
508     is matched against the string
510     <something> <something else> <something further>
512     there are three possible answers. The standard algorithm finds only one
513 nigel 93 of them, whereas the alternative algorithm finds all three.
514 nigel 77
518     The set of strings that are matched by a regular expression can be rep-
519     resented as a tree structure. An unlimited repetition in the pattern
520     makes the tree of infinite size, but it is still a tree. Matching the
521     pattern to a given subject string (from a given starting point) can be
522 nigel 91 thought of as a search of the tree. There are two ways to search a
523     tree: depth-first and breadth-first, and these correspond to the two
524     matching algorithms provided by PCRE.
525 nigel 77
529 ph10 148 In the terminology of Jeffrey Friedl's book "Mastering Regular Expres-
530     sions", the standard algorithm is an "NFA algorithm". It conducts a
531 nigel 77 depth-first search of the pattern tree. That is, it proceeds along a
532     single path through the tree, checking that the subject matches what is
533     required. When there is a mismatch, the algorithm tries any alterna-
534     tives at the current point, and if they all fail, it backs up to the
535     previous branch point in the tree, and tries the next alternative
536     branch at that level. This often involves backing up (moving to the
537     left) in the subject string as well. The order in which repetition
538     branches are tried is controlled by the greedy or ungreedy nature of
539     the quantifier.
541     If a leaf node is reached, a matching string has been found, and at
542     that point the algorithm stops. Thus, if there is more than one possi-
543     ble match, this algorithm returns the first one that it finds. Whether
544     this is the shortest, the longest, or some intermediate length depends
545     on the way the greedy and ungreedy repetition quantifiers are specified
546     in the pattern.
548     Because it ends up with a single path through the tree, it is rela-
549     tively straightforward for this algorithm to keep track of the sub-
550     strings that are matched by portions of the pattern in parentheses.
551     This provides support for capturing parentheses and back references.
555 nigel 77
556 nigel 93 This algorithm conducts a breadth-first search of the tree. Starting
557     from the first matching point in the subject, it scans the subject
558     string from left to right, once, character by character, and as it does
559     this, it remembers all the paths through the tree that represent valid
560     matches. In Friedl's terminology, this is a kind of "DFA algorithm",
561     though it is not implemented as a traditional finite state machine (it
562     keeps multiple states active simultaneously).
563 nigel 77
564 nigel 93 The scan continues until either the end of the subject is reached, or
565     there are no more unterminated paths. At this point, terminated paths
566     represent the different matching possibilities (if there are none, the
567     match has failed). Thus, if there is more than one possible match,
568 nigel 77 this algorithm finds all of them, and in particular, it finds the long-
569 nigel 93 est. In PCRE, there is an option to stop the algorithm after the first
570 nigel 77 match (which is necessarily the shortest) has been found.
572     Note that all the matches that are found start at the same point in the
573     subject. If the pattern
575     cat(er(pillar)?)
577 nigel 93 is matched against the string "the caterpillar catchment", the result
578     will be the three strings "cat", "cater", and "caterpillar" that start
579 nigel 77 at the fourth character of the subject. The algorithm does not automat-
580     ically move on to find matches that start at later positions.
582     There are a number of features of PCRE regular expressions that are not
583 nigel 93 supported by the alternative matching algorithm. They are as follows:
584 nigel 77
585 nigel 93 1. Because the algorithm finds all possible matches, the greedy or
586     ungreedy nature of repetition quantifiers is not relevant. Greedy and
587     ungreedy quantifiers are treated in exactly the same way. However, pos-
588     sessive quantifiers can make a difference when what follows could also
589     match what is quantified, for example in a pattern like this:
590 nigel 77
591 nigel 93 ^a++\w!
593     This pattern matches "aaab!" but not "aaa!", which would be matched by
594     a non-possessive quantifier. Similarly, if an atomic group is present,
595     it is matched as if it were a standalone pattern at the current point,
596     and the longest match is then "locked in" for the rest of the overall
597     pattern.
599 nigel 77 2. When dealing with multiple paths through the tree simultaneously, it
600 nigel 93 is not straightforward to keep track of captured substrings for the
601     different matching possibilities, and PCRE's implementation of this
602 nigel 77 algorithm does not attempt to do this. This means that no captured sub-
603     strings are available.
605 nigel 93 3. Because no substrings are captured, back references within the pat-
606 nigel 77 tern are not supported, and cause errors if encountered.
608 nigel 93 4. For the same reason, conditional expressions that use a backrefer-
609     ence as the condition or test for a specific group recursion are not
610     supported.
611 nigel 77
612     5. Callouts are supported, but the value of the capture_top field is
613     always 1, and the value of the capture_last field is always -1.
615     6. The \C escape sequence, which (in the standard algorithm) matches a
616 nigel 93 single byte, even in UTF-8 mode, is not supported because the alterna-
617     tive algorithm moves through the subject string one character at a
618     time, for all active paths through the tree.
619 nigel 77
622 nigel 77
623 nigel 93 Using the alternative matching algorithm provides the following advan-
624     tages:
625 nigel 77
626     1. All possible matches (at a single point in the subject) are automat-
627 nigel 93 ically found, and in particular, the longest match is found. To find
628 nigel 77 more than one match using the standard algorithm, you have to do kludgy
629     things with callouts.
631 nigel 93 2. There is much better support for partial matching. The restrictions
632     on the content of the pattern that apply when using the standard algo-
633     rithm for partial matching do not apply to the alternative algorithm.
634     For non-anchored patterns, the starting position of a partial match is
635     available.
636 nigel 77
637 nigel 93 3. Because the alternative algorithm scans the subject string just
638     once, and never needs to backtrack, it is possible to pass very long
639     subject strings to the matching function in several pieces, checking
640     for partial matching each time.
641 nigel 77
644 nigel 77
645 nigel 93 The alternative algorithm suffers from a number of disadvantages:
646 nigel 77
647 nigel 93 1. It is substantially slower than the standard algorithm. This is
648     partly because it has to search for all possible matches, but is also
649 nigel 77 because it is less susceptible to optimization.
651     2. Capturing parentheses and back references are not supported.
653 nigel 93 3. Although atomic groups are supported, their use does not provide the
654     performance advantage that it does for the standard algorithm.
655 nigel 77
657 ph10 99 AUTHOR
658 nigel 77
659 ph10 99 Philip Hazel
660     University Computing Service
661     Cambridge CB2 3QH, England.
664     REVISION
666     Last updated: 06 March 2007
667     Copyright (c) 1997-2007 University of Cambridge.
668     ------------------------------------------------------------------------------
669 ph10 111
671 nigel 79 PCREAPI(3) PCREAPI(3)
672 nigel 77
673 nigel 79
674 nigel 73 NAME
675     PCRE - Perl-compatible regular expressions
677 nigel 77
678 nigel 75 PCRE NATIVE API
679 nigel 63
680 nigel 73 #include <pcre.h>
681 nigel 41
682 nigel 73 pcre *pcre_compile(const char *pattern, int options,
683     const char **errptr, int *erroffset,
684     const unsigned char *tableptr);
685 nigel 41
686 nigel 77 pcre *pcre_compile2(const char *pattern, int options,
687     int *errorcodeptr,
688     const char **errptr, int *erroffset,
689     const unsigned char *tableptr);
691 nigel 73 pcre_extra *pcre_study(const pcre *code, int options,
692     const char **errptr);
693 nigel 41
694 nigel 73 int pcre_exec(const pcre *code, const pcre_extra *extra,
695     const char *subject, int length, int startoffset,
696     int options, int *ovector, int ovecsize);
697 nigel 41
698 nigel 77 int pcre_dfa_exec(const pcre *code, const pcre_extra *extra,
699     const char *subject, int length, int startoffset,
700     int options, int *ovector, int ovecsize,
701     int *workspace, int wscount);
703 nigel 73 int pcre_copy_named_substring(const pcre *code,
704     const char *subject, int *ovector,
705     int stringcount, const char *stringname,
706     char *buffer, int buffersize);
707 nigel 63
708 nigel 73 int pcre_copy_substring(const char *subject, int *ovector,
709     int stringcount, int stringnumber, char *buffer,
710     int buffersize);
711 nigel 41
712 nigel 73 int pcre_get_named_substring(const pcre *code,
713     const char *subject, int *ovector,
714     int stringcount, const char *stringname,
715     const char **stringptr);
716 nigel 63
717 nigel 73 int pcre_get_stringnumber(const pcre *code,
718     const char *name);
719 nigel 63
720 nigel 91 int pcre_get_stringtable_entries(const pcre *code,
721     const char *name, char **first, char **last);
723 nigel 73 int pcre_get_substring(const char *subject, int *ovector,
724     int stringcount, int stringnumber,
725     const char **stringptr);
726 nigel 41
727 nigel 73 int pcre_get_substring_list(const char *subject,
728     int *ovector, int stringcount, const char ***listptr);
729 nigel 41
730 nigel 73 void pcre_free_substring(const char *stringptr);
731 nigel 49
732 nigel 73 void pcre_free_substring_list(const char **stringptr);
733 nigel 49
734 nigel 73 const unsigned char *pcre_maketables(void);
735 nigel 41
736 nigel 73 int pcre_fullinfo(const pcre *code, const pcre_extra *extra,
737     int what, void *where);
738 nigel 43
739 nigel 73 int pcre_info(const pcre *code, int *optptr, int *firstcharptr);
740 nigel 63
741 nigel 77 int pcre_refcount(pcre *code, int adjust);
743 nigel 73 int pcre_config(int what, void *where);
744 nigel 41
745 nigel 73 char *pcre_version(void);
746 nigel 63
747 nigel 73 void *(*pcre_malloc)(size_t);
748 nigel 41
749 nigel 73 void (*pcre_free)(void *);
750 nigel 41
751 nigel 73 void *(*pcre_stack_malloc)(size_t);
752 nigel 41
753 nigel 73 void (*pcre_stack_free)(void *);
754 nigel 41
755 nigel 73 int (*pcre_callout)(pcre_callout_block *);
756 nigel 41
757 nigel 73
758 nigel 75 PCRE API OVERVIEW
759 nigel 41
760 nigel 73 PCRE has its own native API, which is described in this document. There
761 nigel 93 are also some wrapper functions that correspond to the POSIX regular
762 nigel 77 expression API. These are described in the pcreposix documentation.
763     Both of these APIs define a set of C function calls. A C++ wrapper is
764     distributed with PCRE. It is documented in the pcrecpp page.
765 nigel 43
766 nigel 77 The native API C function prototypes are defined in the header file
767     pcre.h, and on Unix systems the library itself is called libpcre. It
768 nigel 75 can normally be accessed by adding -lpcre to the command for linking an
769     application that uses PCRE. The header file defines the macros
770     PCRE_MAJOR and PCRE_MINOR to contain the major and minor release num-
771     bers for the library. Applications can use these to include support
772     for different releases of PCRE.
773 nigel 41
774 nigel 77 The functions pcre_compile(), pcre_compile2(), pcre_study(), and
775     pcre_exec() are used for compiling and matching regular expressions in
776     a Perl-compatible manner. A sample program that demonstrates the sim-
777     plest way of using them is provided in the file called pcredemo.c in
778     the source distribution. The pcresample documentation describes how to
779     run it.
780 nigel 49
781 nigel 77 A second matching function, pcre_dfa_exec(), which is not Perl-compati-
782     ble, is also provided. This uses a different algorithm for the match-
783 nigel 91 ing. The alternative algorithm finds all possible matches (at a given
784 nigel 93 point in the subject), and scans the subject just once. However, this
785     algorithm does not return captured substrings. A description of the two
786     matching algorithms and their advantages and disadvantages is given in
787     the pcrematching documentation.
788 nigel 63
789 nigel 77 In addition to the main compiling and matching functions, there are
790     convenience functions for extracting captured substrings from a subject
791     string that is matched by pcre_exec(). They are:
793 nigel 73 pcre_copy_substring()
794     pcre_copy_named_substring()
795     pcre_get_substring()
796     pcre_get_named_substring()
797     pcre_get_substring_list()
798 nigel 75 pcre_get_stringnumber()
799 nigel 91 pcre_get_stringtable_entries()
800 nigel 63
801 nigel 73 pcre_free_substring() and pcre_free_substring_list() are also provided,
802     to free the memory used for extracted strings.
803 nigel 41
804 nigel 77 The function pcre_maketables() is used to build a set of character
805     tables in the current locale for passing to pcre_compile(),
806     pcre_exec(), or pcre_dfa_exec(). This is an optional facility that is
807     provided for specialist use. Most commonly, no special tables are
808     passed, in which case internal tables that are generated when PCRE is
809     built are used.
810 nigel 49
811 nigel 75 The function pcre_fullinfo() is used to find out information about a
812     compiled pattern; pcre_info() is an obsolete version that returns only
813     some of the available information, but is retained for backwards com-
814     patibility. The function pcre_version() returns a pointer to a string
815 nigel 73 containing the version of PCRE and its date of release.
816 nigel 41
817 nigel 77 The function pcre_refcount() maintains a reference count in a data
818     block containing a compiled pattern. This is provided for the benefit
819     of object-oriented applications.
821 nigel 75 The global variables pcre_malloc and pcre_free initially contain the
822     entry points of the standard malloc() and free() functions, respec-
823 nigel 73 tively. PCRE calls the memory management functions via these variables,
824 nigel 75 so a calling program can replace them if it wishes to intercept the
825 nigel 73 calls. This should be done before calling any PCRE functions.
826 nigel 41
827 nigel 75 The global variables pcre_stack_malloc and pcre_stack_free are also
828     indirections to memory management functions. These special functions
829     are used only when PCRE is compiled to use the heap for remembering
830 nigel 77 data, instead of recursive function calls, when running the pcre_exec()
831 nigel 91 function. See the pcrebuild documentation for details of how to do
832     this. It is a non-standard way of building PCRE, for use in environ-
833     ments that have limited stacks. Because of the greater use of memory
834     management, it runs more slowly. Separate functions are provided so
835     that special-purpose external code can be used for this case. When
836     used, these functions are always called in a stack-like manner (last
837     obtained, first freed), and always for memory blocks of the same size.
838     There is a discussion about PCRE's stack usage in the pcrestack docu-
839     mentation.
840 nigel 41
841 nigel 73 The global variable pcre_callout initially contains NULL. It can be set
842 nigel 77 by the caller to a "callout" function, which PCRE will then call at
843     specified points during a matching operation. Details are given in the
844 nigel 73 pcrecallout documentation.
845 nigel 41
846 nigel 73
847 nigel 91 NEWLINES
849 ph10 150 PCRE supports five different conventions for indicating line breaks in
850 nigel 93 strings: a single CR (carriage return) character, a single LF (line-
851 ph10 150 feed) character, the two-character sequence CRLF, any of the three pre-
852     ceding, or any Unicode newline sequence. The Unicode newline sequences
853     are the three just mentioned, plus the single characters VT (vertical
854     tab, U+000B), FF (formfeed, U+000C), NEL (next line, U+0085), LS (line
855     separator, U+2028), and PS (paragraph separator, U+2029).
856 nigel 93
857     Each of the first three conventions is used by at least one operating
858     system as its standard newline sequence. When PCRE is built, a default
859     can be specified. The default default is LF, which is the Unix stan-
860     dard. When PCRE is run, the default can be overridden, either when a
861     pattern is compiled, or when it is matched.
863 nigel 91 In the PCRE documentation the word "newline" is used to mean "the char-
864 nigel 93 acter or pair of characters that indicate a line break". The choice of
865     newline convention affects the handling of the dot, circumflex, and
866     dollar metacharacters, the handling of #-comments in /x mode, and, when
867     CRLF is a recognized line ending sequence, the match position advance-
868     ment for a non-anchored pattern. The choice of newline convention does
869     not affect the interpretation of the \n or \r escape sequences.
870 nigel 91
874 nigel 93 The PCRE functions can be used in multi-threading applications, with
875 nigel 73 the proviso that the memory management functions pointed to by
876     pcre_malloc, pcre_free, pcre_stack_malloc, and pcre_stack_free, and the
877     callout function pointed to by pcre_callout, are shared by all threads.
878 nigel 41
879 nigel 93 The compiled form of a regular expression is not altered during match-
880 nigel 73 ing, so the same compiled pattern can safely be used by several threads
881     at once.
882 nigel 41
886     The compiled form of a regular expression can be saved and re-used at a
887 nigel 93 later time, possibly by a different program, and even on a host other
888     than the one on which it was compiled. Details are given in the
889 nigel 75 pcreprecompile documentation.
893 nigel 41
894 nigel 73 int pcre_config(int what, void *where);
895 nigel 63
896 nigel 93 The function pcre_config() makes it possible for a PCRE client to dis-
897 nigel 73 cover which optional features have been compiled into the PCRE library.
898 nigel 93 The pcrebuild documentation has more details about these optional fea-
899 nigel 73 tures.
900 nigel 63
901 nigel 93 The first argument for pcre_config() is an integer, specifying which
902 nigel 73 information is required; the second argument is a pointer to a variable
903 nigel 93 into which the information is placed. The following information is
904 nigel 73 available:
905 nigel 63
906 nigel 73 PCRE_CONFIG_UTF8
907 nigel 63
908 nigel 93 The output is an integer that is set to one if UTF-8 support is avail-
909 nigel 73 able; otherwise it is set to zero.
910 nigel 63
913 nigel 93 The output is an integer that is set to one if support for Unicode
914 nigel 75 character properties is available; otherwise it is set to zero.
917 nigel 63
918 nigel 93 The output is an integer whose value specifies the default character
919     sequence that is recognized as meaning "newline". The four values that
920 ph10 150 are supported are: 10 for LF, 13 for CR, 3338 for CRLF, -2 for ANYCRLF,
921     and -1 for ANY. The default should normally be the standard sequence
922     for your operating system.
923 nigel 63
925 nigel 63
926 nigel 91 The output is an integer that contains the number of bytes used for
927 nigel 73 internal linkage in compiled regular expressions. The value is 2, 3, or
928 nigel 91 4. Larger values allow larger regular expressions to be compiled, at
929     the expense of slower matching. The default value of 2 is sufficient
930     for all but the most massive patterns, since it allows the compiled
931 nigel 73 pattern to be up to 64K in size.
932 nigel 63
934 nigel 63
935 nigel 91 The output is an integer that contains the threshold above which the
936     POSIX interface uses malloc() for output vectors. Further details are
937 nigel 73 given in the pcreposix documentation.
938 nigel 63
940 nigel 63
941 nigel 73 The output is an integer that gives the default limit for the number of
942 nigel 91 internal matching function calls in a pcre_exec() execution. Further
943 nigel 73 details are given with pcre_exec() below.
944 nigel 63
947 nigel 91 The output is an integer that gives the default limit for the depth of
948     recursion when calling the internal matching function in a pcre_exec()
949 nigel 87 execution. Further details are given with pcre_exec() below.
952 nigel 63
953 nigel 91 The output is an integer that is set to one if internal recursion when
954 nigel 77 running pcre_exec() is implemented by recursive function calls that use
955 nigel 91 the stack to remember their state. This is the usual way that PCRE is
956 nigel 77 compiled. The output is zero if PCRE was compiled to use blocks of data
957 nigel 91 on the heap instead of recursive function calls. In this case,
958     pcre_stack_malloc and pcre_stack_free are called to manage memory
959 nigel 77 blocks on the heap, thus avoiding the use of the stack.
960 nigel 73
963 nigel 63
964 nigel 73 pcre *pcre_compile(const char *pattern, int options,
965     const char **errptr, int *erroffset,
966     const unsigned char *tableptr);
967 nigel 63
968 nigel 77 pcre *pcre_compile2(const char *pattern, int options,
969     int *errorcodeptr,
970     const char **errptr, int *erroffset,
971     const unsigned char *tableptr);
972 nigel 41
973 nigel 77 Either of the functions pcre_compile() or pcre_compile2() can be called
974     to compile a pattern into an internal form. The only difference between
975 nigel 91 the two interfaces is that pcre_compile2() has an additional argument,
976 nigel 77 errorcodeptr, via which a numerical error code can be returned.
978     The pattern is a C string terminated by a binary zero, and is passed in
979 nigel 91 the pattern argument. A pointer to a single block of memory that is
980     obtained via pcre_malloc is returned. This contains the compiled code
981 nigel 77 and related data. The pcre type is defined for the returned block; this
982     is a typedef for a structure whose contents are not externally defined.
983 nigel 91 It is up to the caller to free the memory (via pcre_free) when it is no
984     longer required.
985 nigel 77
986 nigel 91 Although the compiled code of a PCRE regex is relocatable, that is, it
987 nigel 73 does not depend on memory location, the complete pcre data block is not
988 nigel 91 fully relocatable, because it may contain a copy of the tableptr argu-
989 nigel 75 ment, which is an address (see below).
990 nigel 41
991 nigel 93 The options argument contains various bit settings that affect the com-
992     pilation. It should be zero if no options are required. The available
993 nigel 91 options are described below. Some of them, in particular, those that
994     are compatible with Perl, can also be set and unset from within the
995     pattern (see the detailed description in the pcrepattern documenta-
996     tion). For these options, the contents of the options argument speci-
997     fies their initial settings at the start of compilation and execution.
998     The PCRE_ANCHORED and PCRE_NEWLINE_xxx options can be set at the time
999     of matching as well as at compile time.
1000 nigel 41
1001 nigel 73 If errptr is NULL, pcre_compile() returns NULL immediately. Otherwise,
1002 nigel 91 if compilation of a pattern fails, pcre_compile() returns NULL, and
1003 nigel 73 sets the variable pointed to by errptr to point to a textual error mes-
1004 nigel 87 sage. This is a static string that is part of the library. You must not
1005     try to free it. The offset from the start of the pattern to the charac-
1006     ter where the error was discovered is placed in the variable pointed to
1007 nigel 91 by erroffset, which must not be NULL. If it is, an immediate error is
1008 nigel 73 given.
1009 nigel 53
1010 nigel 91 If pcre_compile2() is used instead of pcre_compile(), and the error-
1011     codeptr argument is not NULL, a non-zero error code number is returned
1012     via this argument in the event of an error. This is in addition to the
1013 nigel 77 textual error message. Error codes and messages are listed below.
1015 nigel 91 If the final argument, tableptr, is NULL, PCRE uses a default set of
1016     character tables that are built when PCRE is compiled, using the
1017     default C locale. Otherwise, tableptr must be an address that is the
1018     result of a call to pcre_maketables(). This value is stored with the
1019     compiled pattern, and used again by pcre_exec(), unless another table
1020 nigel 75 pointer is passed to it. For more discussion, see the section on locale
1021     support below.
1022 nigel 53
1023 nigel 91 This code fragment shows a typical straightforward call to pcre_com-
1024 nigel 73 pile():
1025 nigel 41
1026 nigel 73 pcre *re;
1027     const char *error;
1028     int erroffset;
1029     re = pcre_compile(
1030     "^A.*Z", /* the pattern */
1031     0, /* default options */
1032     &error, /* for error message */
1033     &erroffset, /* for error offset */
1034     NULL); /* use default character tables */
1035 nigel 41
1036 nigel 91 The following names for option bits are defined in the pcre.h header
1037 nigel 75 file:
1038 nigel 41
1039 nigel 73 PCRE_ANCHORED
1040 nigel 41
1041 nigel 73 If this bit is set, the pattern is forced to be "anchored", that is, it
1042 nigel 91 is constrained to match only at the first matching point in the string
1043     that is being searched (the "subject string"). This effect can also be
1044     achieved by appropriate constructs in the pattern itself, which is the
1045 nigel 73 only way to do it in Perl.
1046 nigel 41
1047 nigel 75 PCRE_AUTO_CALLOUT
1049     If this bit is set, pcre_compile() automatically inserts callout items,
1050 nigel 91 all with number 255, before each pattern item. For discussion of the
1051 nigel 75 callout facility, see the pcrecallout documentation.
1053 nigel 73 PCRE_CASELESS
1054 nigel 41
1055 nigel 91 If this bit is set, letters in the pattern match both upper and lower
1056     case letters. It is equivalent to Perl's /i option, and it can be
1057     changed within a pattern by a (?i) option setting. In UTF-8 mode, PCRE
1058     always understands the concept of case for characters whose values are
1059     less than 128, so caseless matching is always possible. For characters
1060     with higher values, the concept of case is supported if PCRE is com-
1061     piled with Unicode property support, but not otherwise. If you want to
1062     use caseless matching for characters 128 and above, you must ensure
1063     that PCRE is compiled with Unicode property support as well as with
1064 nigel 77 UTF-8 support.
1065 nigel 41
1067 nigel 41
1068 nigel 91 If this bit is set, a dollar metacharacter in the pattern matches only
1069     at the end of the subject string. Without this option, a dollar also
1070     matches immediately before a newline at the end of the string (but not
1071     before any other newlines). The PCRE_DOLLAR_ENDONLY option is ignored
1072     if PCRE_MULTILINE is set. There is no equivalent to this option in
1073     Perl, and no way to set it within a pattern.
1074 nigel 41
1075 nigel 73 PCRE_DOTALL
1076 nigel 41
1077 nigel 73 If this bit is set, a dot metacharater in the pattern matches all char-
1078 nigel 91 acters, including those that indicate newline. Without it, a dot does
1079     not match when the current position is at a newline. This option is
1080     equivalent to Perl's /s option, and it can be changed within a pattern
1081     by a (?s) option setting. A negative class such as [^a] always matches
1082 nigel 93 newline characters, independent of the setting of this option.
1083 nigel 63
1084 nigel 91 PCRE_DUPNAMES
1086     If this bit is set, names used to identify capturing subpatterns need
1087     not be unique. This can be helpful for certain types of pattern when it
1088     is known that only one instance of the named subpattern can ever be
1089     matched. There are more details of named subpatterns below; see also
1090     the pcrepattern documentation.
1092 nigel 73 PCRE_EXTENDED
1093 nigel 41
1094 nigel 91 If this bit is set, whitespace data characters in the pattern are
1095 nigel 77 totally ignored except when escaped or inside a character class. White-
1096     space does not include the VT character (code 11). In addition, charac-
1097     ters between an unescaped # outside a character class and the next new-
1098 nigel 91 line, inclusive, are also ignored. This is equivalent to Perl's /x
1099     option, and it can be changed within a pattern by a (?x) option set-
1100     ting.
1101 nigel 41
1102 nigel 91 This option makes it possible to include comments inside complicated
1103     patterns. Note, however, that this applies only to data characters.
1104     Whitespace characters may never appear within special character
1105     sequences in a pattern, for example within the sequence (?( which
1106 nigel 73 introduces a conditional subpattern.
1107 nigel 41
1108 nigel 73 PCRE_EXTRA
1109 nigel 41
1110 nigel 91 This option was invented in order to turn on additional functionality
1111     of PCRE that is incompatible with Perl, but it is currently of very
1112     little use. When set, any backslash in a pattern that is followed by a
1113     letter that has no special meaning causes an error, thus reserving
1114     these combinations for future expansion. By default, as in Perl, a
1115     backslash followed by a letter with no special meaning is treated as a
1116     literal. (Perl can, however, be persuaded to give a warning for this.)
1117     There are at present no other features controlled by this option. It
1118     can also be set by a (?X) option setting within a pattern.
1119 nigel 41
1120 nigel 77 PCRE_FIRSTLINE
1122 nigel 87 If this option is set, an unanchored pattern is required to match
1123 nigel 91 before or at the first newline in the subject string, though the
1124     matched text may continue over the newline.
1125 nigel 77
1126 nigel 73 PCRE_MULTILINE
1127 nigel 41
1128 nigel 87 By default, PCRE treats the subject string as consisting of a single
1129     line of characters (even if it actually contains newlines). The "start
1130     of line" metacharacter (^) matches only at the start of the string,
1131     while the "end of line" metacharacter ($) matches only at the end of
1132 nigel 75 the string, or before a terminating newline (unless PCRE_DOLLAR_ENDONLY
1133     is set). This is the same as Perl.
1134 nigel 63
1135 nigel 87 When PCRE_MULTILINE it is set, the "start of line" and "end of line"
1136 nigel 91 constructs match immediately following or immediately before internal
1137     newlines in the subject string, respectively, as well as at the very
1138     start and end. This is equivalent to Perl's /m option, and it can be
1139     changed within a pattern by a (?m) option setting. If there are no new-
1140     lines in a subject string, or no occurrences of ^ or $ in a pattern,
1141 nigel 73 setting PCRE_MULTILINE has no effect.
1142 nigel 63
1143 nigel 91 PCRE_NEWLINE_CR
1147 nigel 93 PCRE_NEWLINE_ANY
1148 nigel 91
1149     These options override the default newline definition that was chosen
1150     when PCRE was built. Setting the first or the second specifies that a
1151     newline is indicated by a single character (CR or LF, respectively).
1152 nigel 93 Setting PCRE_NEWLINE_CRLF specifies that a newline is indicated by the
1153 ph10 150 two-character CRLF sequence. Setting PCRE_NEWLINE_ANYCRLF specifies
1154     that any of the three preceding sequences should be recognized. Setting
1155     PCRE_NEWLINE_ANY specifies that any Unicode newline sequence should be
1156     recognized. The Unicode newline sequences are the three just mentioned,
1157     plus the single characters VT (vertical tab, U+000B), FF (formfeed,
1158     U+000C), NEL (next line, U+0085), LS (line separator, U+2028), and PS
1159     (paragraph separator, U+2029). The last two are recognized only in
1160     UTF-8 mode.
1161 nigel 91
1162 nigel 93 The newline setting in the options word uses three bits that are
1163 ph10 150 treated as a number, giving eight possibilities. Currently only six are
1164     used (default plus the five values above). This means that if you set
1165     more than one newline option, the combination may or may not be sensi-
1166     ble. For example, PCRE_NEWLINE_CR with PCRE_NEWLINE_LF is equivalent to
1167     PCRE_NEWLINE_CRLF, but other combinations may yield unused numbers and
1168     cause an error.
1169 nigel 91
1170 nigel 93 The only time that a line break is specially recognized when compiling
1171     a pattern is if PCRE_EXTENDED is set, and an unescaped # outside a
1172     character class is encountered. This indicates a comment that lasts
1173     until after the next line break sequence. In other circumstances, line
1174     break sequences are treated as literal data, except that in
1175     PCRE_EXTENDED mode, both CR and LF are treated as whitespace characters
1176     and are therefore ignored.
1178     The newline option that is set at compile time becomes the default that
1179     is used for pcre_exec() and pcre_dfa_exec(), but it can be overridden.
1181 nigel 73 PCRE_NO_AUTO_CAPTURE
1182 nigel 41
1183 nigel 73 If this option is set, it disables the use of numbered capturing paren-
1184 nigel 91 theses in the pattern. Any opening parenthesis that is not followed by
1185     ? behaves as if it were followed by ?: but named parentheses can still
1186     be used for capturing (and they acquire numbers in the usual way).
1187 nigel 73 There is no equivalent of this option in Perl.
1188 nigel 41
1189 nigel 73 PCRE_UNGREEDY
1190 nigel 41
1191 nigel 91 This option inverts the "greediness" of the quantifiers so that they
1192     are not greedy by default, but become greedy if followed by "?". It is
1193     not compatible with Perl. It can also be set by a (?U) option setting
1194 nigel 73 within the pattern.
1195 nigel 41
1196 nigel 73 PCRE_UTF8
1197 nigel 49
1198 nigel 91 This option causes PCRE to regard both the pattern and the subject as
1199     strings of UTF-8 characters instead of single-byte character strings.
1200     However, it is available only when PCRE is built to include UTF-8 sup-
1201     port. If not, the use of this option provokes an error. Details of how
1202     this option changes the behaviour of PCRE are given in the section on
1203 nigel 75 UTF-8 support in the main pcre page.
1204 nigel 71
1205 nigel 73 PCRE_NO_UTF8_CHECK
1206 nigel 71
1207 nigel 73 When PCRE_UTF8 is set, the validity of the pattern as a UTF-8 string is
1208 nigel 91 automatically checked. If an invalid UTF-8 sequence of bytes is found,
1209     pcre_compile() returns an error. If you already know that your pattern
1210     is valid, and you want to skip this check for performance reasons, you
1211     can set the PCRE_NO_UTF8_CHECK option. When it is set, the effect of
1212 nigel 73 passing an invalid UTF-8 string as a pattern is undefined. It may cause
1213 nigel 91 your program to crash. Note that this option can also be passed to
1214     pcre_exec() and pcre_dfa_exec(), to suppress the UTF-8 validity check-
1215 nigel 77 ing of subject strings.
1216 nigel 71
1217 nigel 73
1220 nigel 91 The following table lists the error codes than may be returned by
1221     pcre_compile2(), along with the error messages that may be returned by
1222 nigel 93 both compiling functions. As PCRE has developed, some error codes have
1223     fallen out of use. To avoid confusion, they have not been re-used.
1224 nigel 77
1225     0 no error
1226     1 \ at end of pattern
1227     2 \c at end of pattern
1228     3 unrecognized character follows \
1229     4 numbers out of order in {} quantifier
1230     5 number too big in {} quantifier
1231     6 missing terminating ] for character class
1232     7 invalid escape sequence in character class
1233     8 range out of order in character class
1234     9 nothing to repeat
1235 nigel 93 10 [this code is not in use]
1236 nigel 77 11 internal error: unexpected repeat
1237     12 unrecognized character after (?
1238     13 POSIX named classes are supported only within a class
1239     14 missing )
1240     15 reference to non-existent subpattern
1241     16 erroffset passed as NULL
1242     17 unknown option bit(s) set
1243     18 missing ) after comment
1244 nigel 93 19 [this code is not in use]
1245 nigel 77 20 regular expression too large
1246     21 failed to get memory
1247     22 unmatched parentheses
1248     23 internal error: code overflow
1249     24 unrecognized character after (?<
1250     25 lookbehind assertion is not fixed length
1251 nigel 91 26 malformed number or name after (?(
1252 nigel 77 27 conditional group contains more than two branches
1253     28 assertion expected after (?(
1254     29 (?R or (?digits must be followed by )
1255     30 unknown POSIX class name
1256     31 POSIX collating elements are not supported
1257     32 this version of PCRE is not compiled with PCRE_UTF8 support
1258 nigel 93 33 [this code is not in use]
1259 nigel 77 34 character value in \x{...} sequence is too large
1260     35 invalid condition (?(0)
1261     36 \C not allowed in lookbehind assertion
1262     37 PCRE does not support \L, \l, \N, \U, or \u
1263     38 number after (?C is > 255
1264     39 closing ) for (?C expected
1265     40 recursive call could loop indefinitely
1266     41 unrecognized character after (?P
1267 nigel 93 42 syntax error in subpattern name (missing terminator)
1268 nigel 91 43 two named subpatterns have the same name
1269 nigel 77 44 invalid UTF-8 string
1270     45 support for \P, \p, and \X has not been compiled
1271     46 malformed \P or \p sequence
1272     47 unknown property name after \P or \p
1273 nigel 91 48 subpattern name is too long (maximum 32 characters)
1274     49 too many named subpatterns (maximum 10,000)
1275     50 repeated subpattern is too long
1276     51 octal value is greater than \377 (not in UTF-8 mode)
1277 nigel 93 52 internal error: overran compiling workspace
1278     53 internal error: previously-checked referenced subpattern not
1279     found
1280     54 DEFINE group contains more than one branch
1281     55 repeating a DEFINE group is not allowed
1282     56 inconsistent NEWLINE options"
1283 nigel 77
1285 nigel 63 STUDYING A PATTERN
1286 nigel 49
1287 nigel 77 pcre_extra *pcre_study(const pcre *code, int options
1288 nigel 73 const char **errptr);
1289 nigel 63
1290 nigel 91 If a compiled pattern is going to be used several times, it is worth
1291 nigel 75 spending more time analyzing it in order to speed up the time taken for
1292 nigel 91 matching. The function pcre_study() takes a pointer to a compiled pat-
1293 nigel 75 tern as its first argument. If studying the pattern produces additional
1294 nigel 91 information that will help speed up matching, pcre_study() returns a
1295     pointer to a pcre_extra block, in which the study_data field points to
1296 nigel 75 the results of the study.
1297 nigel 41
1298 nigel 75 The returned value from pcre_study() can be passed directly to
1299 nigel 91 pcre_exec(). However, a pcre_extra block also contains other fields
1300     that can be set by the caller before the block is passed; these are
1301 nigel 75 described below in the section on matching a pattern.
1302 nigel 63
1303 nigel 91 If studying the pattern does not produce any additional information
1304 nigel 75 pcre_study() returns NULL. In that circumstance, if the calling program
1305 nigel 91 wants to pass any of the other fields to pcre_exec(), it must set up
1306 nigel 75 its own pcre_extra block.
1307 nigel 41
1308 nigel 91 The second argument of pcre_study() contains option bits. At present,
1309 nigel 75 no options are defined, and this argument should always be zero.
1311 nigel 91 The third argument for pcre_study() is a pointer for an error message.
1312     If studying succeeds (even if no data is returned), the variable it
1313     points to is set to NULL. Otherwise it is set to point to a textual
1314 nigel 87 error message. This is a static string that is part of the library. You
1315 nigel 91 must not try to free it. You should test the error pointer for NULL
1316 nigel 87 after calling pcre_study(), to be sure that it has run successfully.
1317 nigel 41
1318 nigel 73 This is a typical call to pcre_study():
1319 nigel 53
1320 nigel 73 pcre_extra *pe;
1321     pe = pcre_study(
1322     re, /* result of pcre_compile() */
1323     0, /* no options exist */
1324     &error); /* set to NULL or points to a message */
1325 nigel 53
1326 nigel 73 At present, studying a pattern is useful only for non-anchored patterns
1327 nigel 91 that do not have a single fixed starting character. A bitmap of possi-
1328 nigel 75 ble starting bytes is created.
1329 nigel 41
1331 nigel 63 LOCALE SUPPORT
1332 nigel 41
1333 nigel 91 PCRE handles caseless matching, and determines whether characters are
1334 ph10 142 letters, digits, or whatever, by reference to a set of tables, indexed
1335 nigel 91 by character value. When running in UTF-8 mode, this applies only to
1336     characters with codes less than 128. Higher-valued codes never match
1337     escapes such as \w or \d, but can be tested with \p if PCRE is built
1338     with Unicode character property support. The use of locales with Uni-
1339 ph10 142 code is discouraged. If you are handling characters with codes greater
1340     than 128, you should either use UTF-8 and Unicode, or use locales, but
1341     not try to mix the two.
1342 nigel 41
1343 ph10 142 PCRE contains an internal set of tables that are used when the final
1344     argument of pcre_compile() is NULL. These are sufficient for many
1345     applications. Normally, the internal tables recognize only ASCII char-
1346     acters. However, when PCRE is built, it is possible to cause the inter-
1347     nal tables to be rebuilt in the default "C" locale of the local system,
1348     which may cause them to be different.
1349 nigel 41
1350 ph10 142 The internal tables can always be overridden by tables supplied by the
1351     application that calls PCRE. These may be created in a different locale
1352     from the default. As more and more applications change to using Uni-
1353     code, the need for this locale support is expected to die away.
1355     External tables are built by calling the pcre_maketables() function,
1356     which has no arguments, in the relevant locale. The result can then be
1357     passed to pcre_compile() or pcre_exec() as often as necessary. For
1358     example, to build and use tables that are appropriate for the French
1359     locale (where accented characters with values greater than 128 are
1360 nigel 75 treated as letters), the following code could be used:
1362     setlocale(LC_CTYPE, "fr_FR");
1363 nigel 73 tables = pcre_maketables();
1364     re = pcre_compile(..., tables);
1365 nigel 41
1366 ph10 142 The locale name "fr_FR" is used on Linux and other Unix-like systems;
1367     if you are using Windows, the name for the French locale is "french".
1369 nigel 91 When pcre_maketables() runs, the tables are built in memory that is
1370     obtained via pcre_malloc. It is the caller's responsibility to ensure
1371     that the memory containing the tables remains available for as long as
1372 nigel 75 it is needed.
1373 nigel 41
1374 nigel 75 The pointer that is passed to pcre_compile() is saved with the compiled
1375 nigel 91 pattern, and the same tables are used via this pointer by pcre_study()
1376 nigel 75 and normally also by pcre_exec(). Thus, by default, for any single pat-
1377     tern, compilation, studying and matching all happen in the same locale,
1378     but different patterns can be compiled in different locales.
1379 nigel 41
1380 nigel 91 It is possible to pass a table pointer or NULL (indicating the use of
1381     the internal tables) to pcre_exec(). Although not intended for this
1382     purpose, this facility could be used to match a pattern in a different
1383 nigel 75 locale from the one in which it was compiled. Passing table pointers at
1384     run time is discussed below in the section on matching a pattern.
1388 nigel 41
1389 nigel 73 int pcre_fullinfo(const pcre *code, const pcre_extra *extra,
1390     int what, void *where);
1391 nigel 63
1392 nigel 91 The pcre_fullinfo() function returns information about a compiled pat-
1393 nigel 73 tern. It replaces the obsolete pcre_info() function, which is neverthe-
1394     less retained for backwards compability (and is documented below).
1395 nigel 43
1396 nigel 91 The first argument for pcre_fullinfo() is a pointer to the compiled
1397     pattern. The second argument is the result of pcre_study(), or NULL if
1398     the pattern was not studied. The third argument specifies which piece
1399     of information is required, and the fourth argument is a pointer to a
1400     variable to receive the data. The yield of the function is zero for
1401 nigel 73 success, or one of the following negative numbers:
1402 nigel 41
1403 nigel 73 PCRE_ERROR_NULL the argument code was NULL
1404     the argument where was NULL
1405     PCRE_ERROR_BADMAGIC the "magic number" was not found
1406     PCRE_ERROR_BADOPTION the value of what was invalid
1407 nigel 53
1408 nigel 91 The "magic number" is placed at the start of each compiled pattern as
1409     an simple check against passing an arbitrary memory pointer. Here is a
1410     typical call of pcre_fullinfo(), to obtain the length of the compiled
1411 nigel 75 pattern:
1412 nigel 53
1413 nigel 73 int rc;
1414 nigel 91 size_t length;
1415 nigel 73 rc = pcre_fullinfo(
1416     re, /* result of pcre_compile() */
1417     pe, /* result of pcre_study(), or NULL */
1418     PCRE_INFO_SIZE, /* what is required */
1419     &length); /* where to put the data */
1420 nigel 43
1421 nigel 91 The possible values for the third argument are defined in pcre.h, and
1422 nigel 73 are as follows:
1423 nigel 43
1425 nigel 41
1426 nigel 91 Return the number of the highest back reference in the pattern. The
1427     fourth argument should point to an int variable. Zero is returned if
1428 nigel 73 there are no back references.
1429 nigel 43
1431 nigel 43
1432 nigel 91 Return the number of capturing subpatterns in the pattern. The fourth
1433 nigel 73 argument should point to an int variable.
1434 nigel 43
1436 nigel 75
1437 nigel 91 Return a pointer to the internal default character tables within PCRE.
1438     The fourth argument should point to an unsigned char * variable. This
1439 nigel 75 information call is provided for internal use by the pcre_study() func-
1440 nigel 91 tion. External callers can cause PCRE to use its internal tables by
1441 nigel 75 passing a NULL table pointer.
1444 nigel 43
1445 nigel 91 Return information about the first byte of any matched string, for a
1446     non-anchored pattern. The fourth argument should point to an int vari-
1447     able. (This option used to be called PCRE_INFO_FIRSTCHAR; the old name
1448     is still recognized for backwards compatibility.)
1449 nigel 41
1450 nigel 91 If there is a fixed first byte, for example, from a pattern such as
1451 nigel 93 (cat|cow|coyote), its value is returned. Otherwise, if either
1452 nigel 41
1453 nigel 87 (a) the pattern was compiled with the PCRE_MULTILINE option, and every
1454 nigel 73 branch starts with "^", or
1455 nigel 43
1456 nigel 73 (b) every branch of the pattern starts with ".*" and PCRE_DOTALL is not
1457     set (if it were set, the pattern would be anchored),
1458 nigel 41
1459 nigel 87 -1 is returned, indicating that the pattern matches only at the start
1460     of a subject string or after any newline within the string. Otherwise
1461 nigel 73 -2 is returned. For anchored patterns, -2 is returned.
1462 nigel 41
1464 nigel 41
1465 nigel 87 If the pattern was studied, and this resulted in the construction of a
1466 nigel 73 256-bit table indicating a fixed set of bytes for the first byte in any
1467 nigel 87 matching string, a pointer to the table is returned. Otherwise NULL is
1468     returned. The fourth argument should point to an unsigned char * vari-
1469 nigel 73 able.
1470 nigel 43
1472 nigel 43
1473 nigel 87 Return the value of the rightmost literal byte that must exist in any
1474     matched string, other than at its start, if such a byte has been
1475 nigel 73 recorded. The fourth argument should point to an int variable. If there
1476 nigel 87 is no such byte, -1 is returned. For anchored patterns, a last literal
1477     byte is recorded only if it follows something of variable length. For
1478 nigel 73 example, for the pattern /^a\d+z\d+/ the returned value is "z", but for
1479     /^a\dz\d/ the returned value is -1.
1480 nigel 63
1484 nigel 63
1485 nigel 87 PCRE supports the use of named as well as numbered capturing parenthe-
1486     ses. The names are just an additional way of identifying the parenthe-
1487 nigel 91 ses, which still acquire numbers. Several convenience functions such as
1488     pcre_get_named_substring() are provided for extracting captured sub-
1489     strings by name. It is also possible to extract the data directly, by
1490     first converting the name to a number in order to access the correct
1491     pointers in the output vector (described with pcre_exec() below). To do
1492     the conversion, you need to use the name-to-number map, which is
1493     described by these three values.
1494 nigel 63
1495 nigel 73 The map consists of a number of fixed-size entries. PCRE_INFO_NAMECOUNT
1496     gives the number of entries, and PCRE_INFO_NAMEENTRYSIZE gives the size
1497 nigel 87 of each entry; both of these return an int value. The entry size
1498     depends on the length of the longest name. PCRE_INFO_NAMETABLE returns
1499     a pointer to the first entry of the table (a pointer to char). The
1500 nigel 73 first two bytes of each entry are the number of the capturing parenthe-
1501 nigel 87 sis, most significant byte first. The rest of the entry is the corre-
1502     sponding name, zero terminated. The names are in alphabetical order.
1503 nigel 91 When PCRE_DUPNAMES is set, duplicate names are in order of their paren-
1504     theses numbers. For example, consider the following pattern (assume
1505     PCRE_EXTENDED is set, so white space - including newlines - is
1506     ignored):
1507 nigel 63
1508 nigel 93 (?<date> (?<year>(\d\d)?\d\d) -
1509     (?<month>\d\d) - (?<day>\d\d) )
1510 nigel 63
1511 nigel 87 There are four named subpatterns, so the table has four entries, and
1512     each entry in the table is eight bytes long. The table is as follows,
1513 nigel 75 with non-printing bytes shows in hexadecimal, and undefined bytes shown
1514     as ??:
1515 nigel 63
1516 nigel 73 00 01 d a t e 00 ??
1517     00 05 d a y 00 ?? ??
1518     00 04 m o n t h 00
1519     00 02 y e a r 00 ??
1520 nigel 63
1521 nigel 87 When writing code to extract data from named subpatterns using the
1522 nigel 91 name-to-number map, remember that the length of the entries is likely
1523     to be different for each compiled pattern.
1524 nigel 63
1525 nigel 73 PCRE_INFO_OPTIONS
1526 nigel 63
1527 nigel 87 Return a copy of the options with which the pattern was compiled. The
1528     fourth argument should point to an unsigned long int variable. These
1529 nigel 73 option bits are those specified in the call to pcre_compile(), modified
1530     by any top-level option settings within the pattern itself.
1531 nigel 63
1532 nigel 87 A pattern is automatically anchored by PCRE if all of its top-level
1533 nigel 73 alternatives begin with one of the following:
1534 nigel 63
1535 nigel 73 ^ unless PCRE_MULTILINE is set
1536     \A always
1537     \G always
1538     .* if PCRE_DOTALL is set and there are no back
1539     references to the subpattern in which .* appears
1540 nigel 63
1541 nigel 73 For such patterns, the PCRE_ANCHORED bit is set in the options returned
1542     by pcre_fullinfo().
1543 nigel 63
1544 nigel 73 PCRE_INFO_SIZE
1545 nigel 63
1546 nigel 87 Return the size of the compiled pattern, that is, the value that was
1547 nigel 73 passed as the argument to pcre_malloc() when PCRE was getting memory in
1548     which to place the compiled data. The fourth argument should point to a
1549     size_t variable.
1550 nigel 63
1552 nigel 63
1553 nigel 75 Return the size of the data block pointed to by the study_data field in
1554 nigel 87 a pcre_extra block. That is, it is the value that was passed to
1555 nigel 73 pcre_malloc() when PCRE was getting memory into which to place the data
1556 nigel 87 created by pcre_study(). The fourth argument should point to a size_t
1557 nigel 73 variable.
1558 nigel 63
1559 nigel 73
1562 nigel 73 int pcre_info(const pcre *code, int *optptr, int *firstcharptr);
1563 nigel 63
1564 nigel 87 The pcre_info() function is now obsolete because its interface is too
1565     restrictive to return all the available data about a compiled pattern.
1566     New programs should use pcre_fullinfo() instead. The yield of
1567     pcre_info() is the number of capturing subpatterns, or one of the fol-
1568 nigel 73 lowing negative numbers:
1569 nigel 43
1570 nigel 73 PCRE_ERROR_NULL the argument code was NULL
1571     PCRE_ERROR_BADMAGIC the "magic number" was not found
1572 nigel 43
1573 nigel 87 If the optptr argument is not NULL, a copy of the options with which
1574     the pattern was compiled is placed in the integer it points to (see
1575 nigel 73 PCRE_INFO_OPTIONS above).
1576 nigel 43
1577 nigel 87 If the pattern is not anchored and the firstcharptr argument is not
1578     NULL, it is used to pass back information about the first character of
1579 nigel 73 any matched string (see PCRE_INFO_FIRSTBYTE above).
1580 nigel 43
1582 nigel 77 REFERENCE COUNTS
1583 nigel 53
1584 nigel 77 int pcre_refcount(pcre *code, int adjust);
1586 nigel 87 The pcre_refcount() function is used to maintain a reference count in
1587 nigel 77 the data block that contains a compiled pattern. It is provided for the
1588 nigel 87 benefit of applications that operate in an object-oriented manner,
1589 nigel 77 where different parts of the application may be using the same compiled
1590     pattern, but you want to free the block when they are all done.
1592     When a pattern is compiled, the reference count field is initialized to
1593 nigel 87 zero. It is changed only by calling this function, whose action is to
1594     add the adjust value (which may be positive or negative) to it. The
1595 nigel 77 yield of the function is the new value. However, the value of the count
1596 nigel 87 is constrained to lie between 0 and 65535, inclusive. If the new value
1597 nigel 77 is outside these limits, it is forced to the appropriate limit value.
1599 nigel 87 Except when it is zero, the reference count is not correctly preserved
1600     if a pattern is compiled on one host and then transferred to a host
1601 nigel 77 whose byte-order is different. (This seems a highly unlikely scenario.)
1606 nigel 73 int pcre_exec(const pcre *code, const pcre_extra *extra,
1607     const char *subject, int length, int startoffset,
1608     int options, int *ovector, int ovecsize);
1609 nigel 53
1610 nigel 87 The function pcre_exec() is called to match a subject string against a
1611     compiled pattern, which is passed in the code argument. If the pattern
1612 nigel 75 has been studied, the result of the study should be passed in the extra
1613 nigel 87 argument. This function is the main matching facility of the library,
1614 nigel 77 and it operates in a Perl-like manner. For specialist use there is also
1615 nigel 87 an alternative matching function, which is described below in the sec-
1616 nigel 77 tion about the pcre_dfa_exec() function.
1617 nigel 41
1618 nigel 87 In most applications, the pattern will have been compiled (and option-
1619     ally studied) in the same process that calls pcre_exec(). However, it
1620 nigel 75 is possible to save compiled patterns and study data, and then use them
1621 nigel 87 later in different processes, possibly even on different hosts. For a
1622 nigel 75 discussion about this, see the pcreprecompile documentation.
1624 nigel 73 Here is an example of a simple call to pcre_exec():
1625 nigel 53
1626 nigel 73 int rc;
1627     int ovector[30];
1628     rc = pcre_exec(
1629     re, /* result of pcre_compile() */
1630     NULL, /* we didn't study the pattern */
1631     "some string", /* the subject string */
1632     11, /* the length of the subject string */
1633     0, /* start at offset 0 in the subject */
1634     0, /* default options */
1635 nigel 75 ovector, /* vector of integers for substring information */
1636 nigel 77 30); /* number of elements (NOT size in bytes) */
1637 nigel 53
1638 nigel 75 Extra data for pcre_exec()
1639 nigel 63
1640 nigel 87 If the extra argument is not NULL, it must point to a pcre_extra data
1641     block. The pcre_study() function returns such a block (when it doesn't
1642     return NULL), but you can also create one for yourself, and pass addi-
1643     tional information in it. The pcre_extra block contains the following
1644     fields (not necessarily in this order):
1645 nigel 75
1646 nigel 73 unsigned long int flags;
1647     void *study_data;
1648     unsigned long int match_limit;
1649 nigel 87 unsigned long int match_limit_recursion;
1650 nigel 73 void *callout_data;
1651 nigel 75 const unsigned char *tables;
1652 nigel 63
1653 nigel 87 The flags field is a bitmap that specifies which of the other fields
1654 nigel 73 are set. The flag bits are:
1655 nigel 63
1660 nigel 75 PCRE_EXTRA_TABLES
1661 nigel 63
1662 nigel 87 Other flag bits should be set to zero. The study_data field is set in
1663     the pcre_extra block that is returned by pcre_study(), together with
1664 nigel 75 the appropriate flag bit. You should not set this yourself, but you may
1665 nigel 87 add to the block by setting the other fields and their corresponding
1666 nigel 75 flag bits.
1667 nigel 63
1668 nigel 73 The match_limit field provides a means of preventing PCRE from using up
1669 nigel 87 a vast amount of resources when running patterns that are not going to
1670     match, but which have a very large number of possibilities in their
1671     search trees. The classic example is the use of nested unlimited
1672 nigel 75 repeats.
1673 nigel 63
1674 nigel 87 Internally, PCRE uses a function called match() which it calls repeat-
1675     edly (sometimes recursively). The limit set by match_limit is imposed
1676     on the number of times this function is called during a match, which
1677     has the effect of limiting the amount of backtracking that can take
1678     place. For patterns that are not anchored, the count restarts from zero
1679     for each position in the subject string.
1680 nigel 75
1681 nigel 87 The default value for the limit can be set when PCRE is built; the
1682     default default is 10 million, which handles all but the most extreme
1683     cases. You can override the default by suppling pcre_exec() with a
1684     pcre_extra block in which match_limit is set, and
1685     PCRE_EXTRA_MATCH_LIMIT is set in the flags field. If the limit is
1686 nigel 73 exceeded, pcre_exec() returns PCRE_ERROR_MATCHLIMIT.
1687 nigel 63
1688 nigel 87 The match_limit_recursion field is similar to match_limit, but instead
1689     of limiting the total number of times that match() is called, it limits
1690     the depth of recursion. The recursion depth is a smaller number than
1691     the total number of calls, because not all calls to match() are recur-
1692     sive. This limit is of use only if it is set smaller than match_limit.
1694     Limiting the recursion depth limits the amount of stack that can be
1695     used, or, when PCRE has been compiled to use memory on the heap instead
1696     of the stack, the amount of heap memory that can be used.
1698     The default value for match_limit_recursion can be set when PCRE is
1699     built; the default default is the same value as the default for
1700     match_limit. You can override the default by suppling pcre_exec() with
1701     a pcre_extra block in which match_limit_recursion is set, and
1702     PCRE_EXTRA_MATCH_LIMIT_RECURSION is set in the flags field. If the
1703     limit is exceeded, pcre_exec() returns PCRE_ERROR_RECURSIONLIMIT.
1705     The pcre_callout field is used in conjunction with the "callout" fea-
1706 nigel 73 ture, which is described in the pcrecallout documentation.
1707 nigel 63
1708 nigel 87 The tables field is used to pass a character tables pointer to
1709     pcre_exec(); this overrides the value that is stored with the compiled
1710     pattern. A non-NULL value is stored with the compiled pattern only if
1711     custom tables were supplied to pcre_compile() via its tableptr argu-
1712 nigel 75 ment. If NULL is passed to pcre_exec() using this mechanism, it forces
1713 nigel 87 PCRE's internal tables to be used. This facility is helpful when re-
1714     using patterns that have been saved after compiling with an external
1715     set of tables, because the external tables might be at a different
1716     address when pcre_exec() is called. See the pcreprecompile documenta-
1717 nigel 75 tion for a discussion of saving compiled patterns for later use.
1718 nigel 41
1719 nigel 75 Option bits for pcre_exec()
1720 nigel 71
1721 nigel 87 The unused bits of the options argument for pcre_exec() must be zero.
1722 nigel 91 The only bits that may be set are PCRE_ANCHORED, PCRE_NEWLINE_xxx,
1724     PCRE_PARTIAL.
1725 nigel 41
1726 nigel 75 PCRE_ANCHORED
1727 nigel 41
1728 nigel 91 The PCRE_ANCHORED option limits pcre_exec() to matching at the first
1729     matching position. If a pattern was compiled with PCRE_ANCHORED, or
1730     turned out to be anchored by virtue of its contents, it cannot be made
1731 nigel 75 unachored at matching time.
1733 nigel 91 PCRE_NEWLINE_CR
1737 nigel 93 PCRE_NEWLINE_ANY
1738 nigel 91
1739     These options override the newline definition that was chosen or
1740     defaulted when the pattern was compiled. For details, see the descrip-
1741 nigel 93 tion of pcre_compile() above. During matching, the newline choice
1742     affects the behaviour of the dot, circumflex, and dollar metacharac-
1743     ters. It may also alter the way the match position is advanced after a
1744 ph10 150 match failure for an unanchored pattern. When PCRE_NEWLINE_CRLF,
1745     PCRE_NEWLINE_ANYCRLF, or PCRE_NEWLINE_ANY is set, and a match attempt
1746     fails when the current position is at a CRLF sequence, the match posi-
1747     tion is advanced by two characters instead of one, in other words, to
1748     after the CRLF.
1749 nigel 91
1750 nigel 73 PCRE_NOTBOL
1751 nigel 41
1752 nigel 75 This option specifies that first character of the subject string is not
1753 ph10 150 the beginning of a line, so the circumflex metacharacter should not
1754     match before it. Setting this without PCRE_MULTILINE (at compile time)
1755     causes circumflex never to match. This option affects only the behav-
1756 nigel 77 iour of the circumflex metacharacter. It does not affect \A.
1757 nigel 41
1758 nigel 73 PCRE_NOTEOL
1759 nigel 41
1760 nigel 75 This option specifies that the end of the subject string is not the end
1761 ph10 150 of a line, so the dollar metacharacter should not match it nor (except
1762     in multiline mode) a newline immediately before it. Setting this with-
1763 nigel 75 out PCRE_MULTILINE (at compile time) causes dollar never to match. This
1764 ph10 150 option affects only the behaviour of the dollar metacharacter. It does
1765 nigel 75 not affect \Z or \z.
1766 nigel 41
1767 nigel 73 PCRE_NOTEMPTY
1768 nigel 41
1769 nigel 73 An empty string is not considered to be a valid match if this option is
1770 ph10 150 set. If there are alternatives in the pattern, they are tried. If all
1771     the alternatives match the empty string, the entire match fails. For
1772 nigel 73 example, if the pattern
1773 nigel 41
1774 nigel 73 a?b?
1775 nigel 41
1776 ph10 150 is applied to a string not beginning with "a" or "b", it matches the
1777     empty string at the start of the subject. With PCRE_NOTEMPTY set, this
1778 nigel 73 match is not valid, so PCRE searches further into the string for occur-
1779     rences of "a" or "b".
1780 nigel 41
1781 nigel 73 Perl has no direct equivalent of PCRE_NOTEMPTY, but it does make a spe-
1782 ph10 150 cial case of a pattern match of the empty string within its split()
1783     function, and when using the /g modifier. It is possible to emulate
1784 nigel 73 Perl's behaviour after matching a null string by first trying the match
1785 nigel 75 again at the same offset with PCRE_NOTEMPTY and PCRE_ANCHORED, and then
1786 ph10 150 if that fails by advancing the starting offset (see below) and trying
1787 nigel 75 an ordinary match again. There is some code that demonstrates how to do
1788     this in the pcredemo.c sample program.
1789 nigel 41
1790 nigel 75 PCRE_NO_UTF8_CHECK
1792     When PCRE_UTF8 is set at compile time, the validity of the subject as a
1793 ph10 150 UTF-8 string is automatically checked when pcre_exec() is subsequently
1794     called. The value of startoffset is also checked to ensure that it
1795     points to the start of a UTF-8 character. If an invalid UTF-8 sequence
1796 nigel 75 of bytes is found, pcre_exec() returns the error PCRE_ERROR_BADUTF8. If
1797 ph10 150 startoffset contains an invalid value, PCRE_ERROR_BADUTF8_OFFSET is
1798 nigel 75 returned.
1800 ph10 150 If you already know that your subject is valid, and you want to skip
1801     these checks for performance reasons, you can set the
1802     PCRE_NO_UTF8_CHECK option when calling pcre_exec(). You might want to
1803     do this for the second and subsequent calls to pcre_exec() if you are
1804     making repeated calls to find all the matches in a single subject
1805     string. However, you should be sure that the value of startoffset
1806     points to the start of a UTF-8 character. When PCRE_NO_UTF8_CHECK is
1807     set, the effect of passing an invalid UTF-8 string as a subject, or a
1808     value of startoffset that does not point to the start of a UTF-8 char-
1809 nigel 75 acter, is undefined. Your program may crash.
1813 ph10 150 This option turns on the partial matching feature. If the subject
1814     string fails to match the pattern, but at some point during the match-
1815     ing process the end of the subject was reached (that is, the subject
1816     partially matches the pattern and the failure to match occurred only
1817     because there were not enough subject characters), pcre_exec() returns
1819     used, there are restrictions on what may appear in the pattern. These
1820 nigel 75 are discussed in the pcrepartial documentation.
1822     The string to be matched by pcre_exec()
1824 ph10 150 The subject string is passed to pcre_exec() as a pointer in subject, a
1825     length in length, and a starting byte offset in startoffset. In UTF-8
1826     mode, the byte offset must point to the start of a UTF-8 character.
1827     Unlike the pattern string, the subject may contain binary zero bytes.
1828     When the starting offset is zero, the search for a match starts at the
1829 nigel 75 beginning of the subject, and this is by far the most common case.
1830 nigel 63
1831 ph10 150 A non-zero starting offset is useful when searching for another match
1832     in the same subject by calling pcre_exec() again after a previous suc-
1833     cess. Setting startoffset differs from just passing over a shortened
1834     string and setting PCRE_NOTBOL in the case of a pattern that begins
1835 nigel 73 with any kind of lookbehind. For example, consider the pattern
1836 nigel 41
1837 nigel 73 \Biss\B
1838 nigel 41
1839 ph10 150 which finds occurrences of "iss" in the middle of words. (\B matches
1840     only if the current position in the subject is not a word boundary.)
1841     When applied to the string "Mississipi" the first call to pcre_exec()
1842     finds the first occurrence. If pcre_exec() is called again with just
1843     the remainder of the subject, namely "issipi", it does not match,
1844 nigel 73 because \B is always false at the start of the subject, which is deemed
1845 ph10 150 to be a word boundary. However, if pcre_exec() is passed the entire
1846 nigel 75 string again, but with startoffset set to 4, it finds the second occur-
1847 ph10 150 rence of "iss" because it is able to look behind the starting point to
1848 nigel 75 discover that it is preceded by a letter.
1849 nigel 41
1850 ph10 150 If a non-zero starting offset is passed when the pattern is anchored,
1851 nigel 75 one attempt to match at the given offset is made. This can only succeed
1852 ph10 150 if the pattern does not require the match to be at the start of the
1853 nigel 75 subject.
1854 nigel 41
1855 nigel 75 How pcre_exec() returns captured substrings
1857 ph10 150 In general, a pattern matches a certain portion of the subject, and in
1858     addition, further substrings from the subject may be picked out by
1859     parts of the pattern. Following the usage in Jeffrey Friedl's book,
1860     this is called "capturing" in what follows, and the phrase "capturing
1861     subpattern" is used for a fragment of a pattern that picks out a sub-
1862     string. PCRE supports several other kinds of parenthesized subpattern
1863 nigel 73 that do not cause substrings to be captured.
1864 nigel 65
1865 ph10 150 Captured substrings are returned to the caller via a vector of integer
1866     offsets whose address is passed in ovector. The number of elements in
1867     the vector is passed in ovecsize, which must be a non-negative number.
1868 nigel 75 Note: this argument is NOT the size of ovector in bytes.
1869 nigel 41
1870 ph10 150 The first two-thirds of the vector is used to pass back captured sub-
1871     strings, each substring using a pair of integers. The remaining third
1872     of the vector is used as workspace by pcre_exec() while matching cap-
1873     turing subpatterns, and is not available for passing back information.
1874     The length passed in ovecsize should always be a multiple of three. If
1875 nigel 75 it is not, it is rounded down.
1877 ph10 150 When a match is successful, information about captured substrings is
1878     returned in pairs of integers, starting at the beginning of ovector,
1879     and continuing up to two-thirds of its length at the most. The first
1880 nigel 73 element of a pair is set to the offset of the first character in a sub-
1881 ph10 150 string, and the second is set to the offset of the first character
1882     after the end of a substring. The first pair, ovector[0] and ovec-
1883     tor[1], identify the portion of the subject string matched by the
1884     entire pattern. The next pair is used for the first capturing subpat-
1885 nigel 91 tern, and so on. The value returned by pcre_exec() is one more than the
1886     highest numbered pair that has been set. For example, if two substrings
1887 ph10 150 have been captured, the returned value is 3. If there are no capturing
1888     subpatterns, the return value from a successful match is 1, indicating
1889 nigel 91 that just the first pair of offsets has been set.
1890 nigel 41
1891 nigel 73 If a capturing subpattern is matched repeatedly, it is the last portion
1892 nigel 75 of the string that it matched that is returned.
1893 nigel 41
1894 ph10 150 If the vector is too small to hold all the captured substring offsets,
1895 nigel 75 it is used as far as possible (up to two-thirds of its length), and the
1896 ph10 150 function returns a value of zero. In particular, if the substring off-
1897 nigel 75 sets are not of interest, pcre_exec() may be called with ovector passed
1898 ph10 150 as NULL and ovecsize as zero. However, if the pattern contains back
1899     references and the ovector is not big enough to remember the related
1900     substrings, PCRE has to get additional memory for use during matching.
1901 nigel 73 Thus it is usually advisable to supply an ovector.
1902 nigel 41
1903 ph10 150 The pcre_info() function can be used to find out how many capturing
1904     subpatterns there are in a compiled pattern. The smallest size for
1905     ovector that will allow for n captured substrings, in addition to the
1906 nigel 91 offsets of the substring matched by the whole pattern, is (n+1)*3.
1907 nigel 41
1908 ph10 150 It is possible for capturing subpattern number n+1 to match some part
1909 nigel 91 of the subject when subpattern n has not been used at all. For example,
1910 ph10 150 if the string "abc" is matched against the pattern (a|(z))(bc) the
1911 nigel 91 return from the function is 4, and subpatterns 1 and 3 are matched, but
1912 ph10 150 2 is not. When this happens, both values in the offset pairs corre-
1913 nigel 91 sponding to unused subpatterns are set to -1.
1914 nigel 75
1915 ph10 150 Offset values that correspond to unused subpatterns at the end of the
1916     expression are also set to -1. For example, if the string "abc" is
1917     matched against the pattern (abc)(x(yz)?)? subpatterns 2 and 3 are not
1918     matched. The return from the function is 2, because the highest used
1919 nigel 91 capturing subpattern number is 1. However, you can refer to the offsets
1920 ph10 150 for the second and third capturing subpatterns if you wish (assuming
1921 nigel 91 the vector is large enough, of course).
1923 ph10 150 Some convenience functions are provided for extracting the captured
1924 nigel 91 substrings as separate strings. These are described below.
1926     Error return values from pcre_exec()
1928 ph10 150 If pcre_exec() fails, it returns a negative number. The following are
1929 nigel 73 defined in the header file:
1930 nigel 41
1931 nigel 73 PCRE_ERROR_NOMATCH (-1)
1932 nigel 41
1933 nigel 73 The subject string did not match the pattern.
1934 nigel 41
1935 nigel 73 PCRE_ERROR_NULL (-2)
1936 nigel 41
1937 ph10 150 Either code or subject was passed as NULL, or ovector was NULL and
1938 nigel 73 ovecsize was not zero.
1939 nigel 41
1940 nigel 73 PCRE_ERROR_BADOPTION (-3)
1941 nigel 41
1942 nigel 73 An unrecognized bit was set in the options argument.
1943 nigel 41
1944 nigel 73 PCRE_ERROR_BADMAGIC (-4)
1945 nigel 41
1946 ph10 150 PCRE stores a 4-byte "magic number" at the start of the compiled code,
1947 nigel 75 to catch the case when it is passed a junk pointer and to detect when a
1948     pattern that was compiled in an environment of one endianness is run in
1949 ph10 150 an environment with the other endianness. This is the error that PCRE
1950 nigel 75 gives when the magic number is not present.
1951 nigel 41
1952 nigel 93 PCRE_ERROR_UNKNOWN_OPCODE (-5)
1953 nigel 41
1954 nigel 73 While running the pattern match, an unknown item was encountered in the
1955 ph10 150 compiled pattern. This error could be caused by a bug in PCRE or by
1956 nigel 73 overwriting of the compiled pattern.
1957 nigel 41
1958 nigel 73 PCRE_ERROR_NOMEMORY (-6)
1959 nigel 41
1960 ph10 150 If a pattern contains back references, but the ovector that is passed
1961 nigel 73 to pcre_exec() is not big enough to remember the referenced substrings,
1962 ph10 150 PCRE gets a block of memory at the start of matching to use for this
1963     purpose. If the call via pcre_malloc() fails, this error is given. The
1964 nigel 75 memory is automatically freed at the end of matching.
1965 nigel 41
1966 nigel 73 PCRE_ERROR_NOSUBSTRING (-7)
1967 nigel 53
1968 ph10 150 This error is used by the pcre_copy_substring(), pcre_get_substring(),
1969 nigel 73 and pcre_get_substring_list() functions (see below). It is never
1970     returned by pcre_exec().
1971 nigel 63
1972 nigel 73 PCRE_ERROR_MATCHLIMIT (-8)
1973 nigel 63
1974 ph10 150 The backtracking limit, as specified by the match_limit field in a
1975     pcre_extra structure (or defaulted) was reached. See the description
1976 nigel 87 above.
1978 nigel 73 PCRE_ERROR_CALLOUT (-9)
1979 nigel 63
1980 nigel 73 This error is never generated by pcre_exec() itself. It is provided for
1981 ph10 150 use by callout functions that want to yield a distinctive error code.
1982 nigel 73 See the pcrecallout documentation for details.
1983 nigel 71
1984 nigel 73 PCRE_ERROR_BADUTF8 (-10)
1985 nigel 71
1986 ph10 150 A string that contains an invalid UTF-8 byte sequence was passed as a
1987 nigel 73 subject.
1991     The UTF-8 byte sequence that was passed as a subject was valid, but the
1992 ph10 150 value of startoffset did not point to the beginning of a UTF-8 charac-
1993 nigel 73 ter.
1995 nigel 77 PCRE_ERROR_PARTIAL (-12)
1996 nigel 73
1997 ph10 150 The subject string did not match, but it did match partially. See the
1998 nigel 75 pcrepartial documentation for details of partial matching.
2000 nigel 77 PCRE_ERROR_BADPARTIAL (-13)
2001 nigel 75
2002 ph10 150 The PCRE_PARTIAL option was used with a compiled pattern containing
2003     items that are not supported for partial matching. See the pcrepartial
2004 nigel 75 documentation for details of partial matching.
2006 nigel 77 PCRE_ERROR_INTERNAL (-14)
2007 nigel 75
2008 ph10 150 An unexpected internal error has occurred. This error could be caused
2009 nigel 75 by a bug in PCRE or by overwriting of the compiled pattern.
2011 nigel 77 PCRE_ERROR_BADCOUNT (-15)
2012 nigel 75
2013 ph10 150 This error is given if the value of the ovecsize argument is negative.
2014 nigel 75
2016 nigel 75
2017 nigel 93 The internal recursion limit, as specified by the match_limit_recursion
2018 ph10 150 field in a pcre_extra structure (or defaulted) was reached. See the
2019 nigel 93 description above.
2023 ph10 150 When a group that can match an empty substring is repeated with an
2024     unbounded upper limit, the subject position at the start of the group
2025 nigel 93 must be remembered, so that a test for an empty string can be made when
2026 ph10 150 the end of the group is reached. Some workspace is required for this;
2027 nigel 93 if it runs out, this error is given.
2031     An invalid combination of PCRE_NEWLINE_xxx options was given.
2033     Error numbers -16 to -20 are not used by pcre_exec().
2038 nigel 73 int pcre_copy_substring(const char *subject, int *ovector,
2039     int stringcount, int stringnumber, char *buffer,
2040     int buffersize);
2041 nigel 63
2042 nigel 73 int pcre_get_substring(const char *subject, int *ovector,
2043     int stringcount, int stringnumber,
2044     const char **stringptr);
2045 nigel 63
2046 nigel 73 int pcre_get_substring_list(const char *subject,
2047     int *ovector, int stringcount, const char ***listptr);
2048 nigel 63
2049 ph10 150 Captured substrings can be accessed directly by using the offsets
2050     returned by pcre_exec() in ovector. For convenience, the functions
2051 nigel 73 pcre_copy_substring(), pcre_get_substring(), and pcre_get_sub-
2052 ph10 150 string_list() are provided for extracting captured substrings as new,
2053     separate, zero-terminated strings. These functions identify substrings
2054     by number. The next section describes functions for extracting named
2055 nigel 91 substrings.
2056 nigel 41
2057 ph10 150 A substring that contains a binary zero is correctly extracted and has
2058     a further zero added on the end, but the result is not, of course, a C
2059     string. However, you can process such a string by referring to the
2060     length that is returned by pcre_copy_substring() and pcre_get_sub-
2061 nigel 91 string(). Unfortunately, the interface to pcre_get_substring_list() is
2062 ph10 150 not adequate for handling strings containing binary zeros, because the
2063 nigel 91 end of the final string is not independently indicated.
2065 ph10 150 The first three arguments are the same for all three of these func-
2066     tions: subject is the subject string that has just been successfully
2067 nigel 73 matched, ovector is a pointer to the vector of integer offsets that was
2068     passed to pcre_exec(), and stringcount is the number of substrings that
2069 ph10 150 were captured by the match, including the substring that matched the
2070 nigel 75 entire regular expression. This is the value returned by pcre_exec() if
2071 ph10 150 it is greater than zero. If pcre_exec() returned zero, indicating that
2072     it ran out of space in ovector, the value passed as stringcount should
2073 nigel 75 be the number of elements in the vector divided by three.
2074 nigel 41
2075 ph10 150 The functions pcre_copy_substring() and pcre_get_substring() extract a
2076     single substring, whose number is given as stringnumber. A value of
2077     zero extracts the substring that matched the entire pattern, whereas
2078     higher values extract the captured substrings. For pcre_copy_sub-
2079     string(), the string is placed in buffer, whose length is given by
2080     buffersize, while for pcre_get_substring() a new block of memory is
2081     obtained via pcre_malloc, and its address is returned via stringptr.
2082     The yield of the function is the length of the string, not including
2083 nigel 93 the terminating zero, or one of these error codes:
2084 nigel 41
2085 nigel 73 PCRE_ERROR_NOMEMORY (-6)
2086 nigel 41
2087 ph10 150 The buffer was too small for pcre_copy_substring(), or the attempt to
2088 nigel 73 get memory failed for pcre_get_substring().
2089 nigel 41
2090 nigel 73 PCRE_ERROR_NOSUBSTRING (-7)
2091 nigel 41
2092 nigel 73 There is no substring whose number is stringnumber.
2093 nigel 41
2094 ph10 150 The pcre_get_substring_list() function extracts all available sub-
2095     strings and builds a list of pointers to them. All this is done in a
2096 nigel 75 single block of memory that is obtained via pcre_malloc. The address of
2097 ph10 150 the memory block is returned via listptr, which is also the start of
2098     the list of string pointers. The end of the list is marked by a NULL
2099     pointer. The yield of the function is zero if all went well, or the
2100 nigel 93 error code
2101 nigel 41
2102 nigel 73 PCRE_ERROR_NOMEMORY (-6)
2103 nigel 41
2104 nigel 73 if the attempt to get the memory block failed.
2105 nigel 41
2106 ph10 150 When any of these functions encounter a substring that is unset, which
2107     can happen when capturing subpattern number n+1 matches some part of
2108     the subject, but subpattern n has not been used at all, they return an
2109 nigel 73 empty string. This can be distinguished from a genuine zero-length sub-
2110 ph10 150 string by inspecting the appropriate offset in ovector, which is nega-
2111 nigel 73 tive for unset substrings.
2112 nigel 41
2113 ph10 150 The two convenience functions pcre_free_substring() and pcre_free_sub-
2114     string_list() can be used to free the memory returned by a previous
2115 nigel 75 call of pcre_get_substring() or pcre_get_substring_list(), respec-
2116 ph10 150 tively. They do nothing more than call the function pointed to by
2117     pcre_free, which of course could be called directly from a C program.
2118     However, PCRE is used in some situations where it is linked via a spe-
2119     cial interface to another programming language that cannot use
2120     pcre_free directly; it is for these cases that the functions are pro-
2121 nigel 77 vided.
2122 nigel 41
2123 nigel 73
2125 nigel 41
2126 nigel 75 int pcre_get_stringnumber(const pcre *code,
2127     const char *name);
2129 nigel 73 int pcre_copy_named_substring(const pcre *code,
2130     const char *subject, int *ovector,
2131     int stringcount, const char *stringname,
2132     char *buffer, int buffersize);
2133 nigel 41
2134 nigel 73 int pcre_get_named_substring(const pcre *code,
2135     const char *subject, int *ovector,
2136     int stringcount, const char *stringname,
2137     const char **stringptr);
2138 nigel 41
2139 ph10 150 To extract a substring by name, you first have to find associated num-
2140 nigel 75 ber. For example, for this pattern
2141 nigel 41
2142 nigel 93 (a+)b(?<xxx>\d+)...
2143 nigel 63
2144 nigel 91 the number of the subpattern called "xxx" is 2. If the name is known to
2145     be unique (PCRE_DUPNAMES was not set), you can find the number from the
2146     name by calling pcre_get_stringnumber(). The first argument is the com-
2147     piled pattern, and the second is the name. The yield of the function is
2148 ph10 150 the subpattern number, or PCRE_ERROR_NOSUBSTRING (-7) if there is no
2149 nigel 91 subpattern of that name.
2150 nigel 63
2151 nigel 75 Given the number, you can extract the substring directly, or use one of
2152     the functions described in the previous section. For convenience, there
2153     are also two functions that do the whole job.
2155 ph10 150 Most of the arguments of pcre_copy_named_substring() and
2156     pcre_get_named_substring() are the same as those for the similarly
2157     named functions that extract by number. As these are described in the
2158     previous section, they are not re-described here. There are just two
2159 nigel 75 differences:
2160 nigel 63
2161 ph10 150 First, instead of a substring number, a substring name is given. Sec-
2162 nigel 73 ond, there is an extra argument, given at the start, which is a pointer
2163 ph10 150 to the compiled pattern. This is needed in order to gain access to the
2164 nigel 73 name-to-number translation table.
2165 nigel 63
2166 ph10 150 These functions call pcre_get_stringnumber(), and if it succeeds, they
2167     then call pcre_copy_substring() or pcre_get_substring(), as appropri-
2168     ate. NOTE: If PCRE_DUPNAMES is set and there are duplicate names, the
2169 ph10 128 behaviour may not be what you want (see the next section).
2170 nigel 63
2171 nigel 77
2174     int pcre_get_stringtable_entries(const pcre *code,
2175     const char *name, char **first, char **last);
2177 ph10 150 When a pattern is compiled with the PCRE_DUPNAMES option, names for
2178     subpatterns are not required to be unique. Normally, patterns with
2179     duplicate names are such that in any one match, only one of the named
2180     subpatterns participates. An example is shown in the pcrepattern docu-
2181 nigel 91 mentation. When duplicates are present, pcre_copy_named_substring() and
2182 ph10 150 pcre_get_named_substring() return the first substring corresponding to
2183     the given name that is set. If none are set, an empty string is
2184 nigel 91 returned. The pcre_get_stringnumber() function returns one of the num-
2185 ph10 150 bers that are associated with the name, but it is not defined which it
2186 nigel 91 is.
2188 ph10 150 If you want to get full details of all captured substrings for a given
2189     name, you must use the pcre_get_stringtable_entries() function. The
2190 nigel 91 first argument is the compiled pattern, and the second is the name. The
2191 ph10 150 third and fourth are pointers to variables which are updated by the
2192 nigel 91 function. After it has run, they point to the first and last entries in
2193 ph10 150 the name-to-number table for the given name. The function itself
2194     returns the length of each entry, or PCRE_ERROR_NOSUBSTRING (-7) if
2195     there are none. The format of the table is described above in the sec-
2196     tion entitled Information about a pattern. Given all the relevant
2197     entries for the name, you can extract each of their numbers, and hence
2198 nigel 93 the captured data, if any.
2199 nigel 91
2203 ph10 150 The traditional matching function uses a similar algorithm to Perl,
2204 nigel 77 which stops when it finds the first match, starting at a given point in
2205 ph10 150 the subject. If you want to find all possible matches, or the longest
2206     possible match, consider using the alternative matching function (see
2207     below) instead. If you cannot use the alternative function, but still
2208     need to find all possible matches, you can kludge it up by making use
2209 nigel 77 of the callout facility, which is described in the pcrecallout documen-
2210     tation.
2212     What you have to do is to insert a callout right at the end of the pat-
2213 ph10 150 tern. When your callout function is called, extract and save the cur-
2214     rent matched substring. Then return 1, which forces pcre_exec() to
2215     backtrack and try other alternatives. Ultimately, when it runs out of
2216 nigel 77 matches, pcre_exec() will yield PCRE_ERROR_NOMATCH.
2221     int pcre_dfa_exec(const pcre *code, const pcre_extra *extra,
2222     const char *subject, int length, int startoffset,
2223     int options, int *ovector, int ovecsize,
2224     int *workspace, int wscount);
2226 ph10 150 The function pcre_dfa_exec() is called to match a subject string
2227     against a compiled pattern, using a matching algorithm that scans the
2228     subject string just once, and does not backtrack. This has different
2229     characteristics to the normal algorithm, and is not compatible with
2230     Perl. Some of the features of PCRE patterns are not supported. Never-
2231     theless, there are times when this kind of matching can be useful. For
2232 nigel 93 a discussion of the two matching algorithms, see the pcrematching docu-
2233     mentation.
2234 nigel 77
2235 ph10 150 The arguments for the pcre_dfa_exec() function are the same as for
2236 nigel 77 pcre_exec(), plus two extras. The ovector argument is used in a differ-
2237 ph10 150 ent way, and this is described below. The other common arguments are
2238     used in the same way as for pcre_exec(), so their description is not
2239 nigel 77 repeated here.
2241 ph10 150 The two additional arguments provide workspace for the function. The
2242     workspace vector should contain at least 20 elements. It is used for
2243 nigel 77 keeping track of multiple paths through the pattern tree. More
2244 ph10 150 workspace will be needed for patterns and subjects where there are a
2245 nigel 91 lot of potential matches.
2246 nigel 77
2247 nigel 87 Here is an example of a simple call to pcre_dfa_exec():
2248 nigel 77
2249     int rc;
2250     int ovector[10];
2251     int wspace[20];
2252 nigel 87 rc = pcre_dfa_exec(
2253 nigel 77 re, /* result of pcre_compile() */
2254     NULL, /* we didn't study the pattern */
2255     "some string", /* the subject string */
2256     11, /* the length of the subject string */
2257     0, /* start at offset 0 in the subject */
2258     0, /* default options */
2259     ovector, /* vector of integers for substring information */
2260     10, /* number of elements (NOT size in bytes) */
2261     wspace, /* working space vector */
2262     20); /* number of elements (NOT size in bytes) */
2264     Option bits for pcre_dfa_exec()
2266 ph10 150 The unused bits of the options argument for pcre_dfa_exec() must be
2267     zero. The only bits that may be set are PCRE_ANCHORED, PCRE_NEW-
2269 nigel 91 PCRE_PARTIAL, PCRE_DFA_SHORTEST, and PCRE_DFA_RESTART. All but the last
2270     three of these are the same as for pcre_exec(), so their description is
2271     not repeated here.
2272 nigel 77
2275 ph10 150 This has the same general effect as it does for pcre_exec(), but the
2276     details are slightly different. When PCRE_PARTIAL is set for
2277     pcre_dfa_exec(), the return code PCRE_ERROR_NOMATCH is converted into
2278     PCRE_ERROR_PARTIAL if the end of the subject is reached, there have
2279 nigel 77 been no complete matches, but there is still at least one matching pos-
2280 ph10 150 sibility. The portion of the string that provided the partial match is
2281 nigel 77 set as the first matching string.
2285 ph10 150 Setting the PCRE_DFA_SHORTEST option causes the matching algorithm to
2286 nigel 93 stop as soon as it has found one match. Because of the way the alterna-
2287 ph10 150 tive algorithm works, this is necessarily the shortest possible match
2288 nigel 93 at the first possible matching point in the subject string.
2289 nigel 77
2292 ph10 150 When pcre_dfa_exec() is called with the PCRE_PARTIAL option, and
2293     returns a partial match, it is possible to call it again, with addi-
2294     tional subject characters, and have it continue with the same match.
2295     The PCRE_DFA_RESTART option requests this action; when it is set, the
2296     workspace and wscount options must reference the same vector as before
2297     because data about the match so far is left in them after a partial
2298     match. There is more discussion of this facility in the pcrepartial
2299 nigel 77 documentation.
2301     Successful returns from pcre_dfa_exec()
2303 ph10 150 When pcre_dfa_exec() succeeds, it may have matched more than one sub-
2304 nigel 77 string in the subject. Note, however, that all the matches from one run
2305 ph10 150 of the function start at the same point in the subject. The shorter
2306     matches are all initial substrings of the longer matches. For example,
2307 nigel 77 if the pattern
2309     <.*>
2311     is matched against the string
2313     This is <something> <something else> <something further> no more
2315     the three matched strings are
2317     <something>
2318     <something> <something else>
2319     <something> <something else> <something further>
2321 ph10 150 On success, the yield of the function is a number greater than zero,
2322     which is the number of matched substrings. The substrings themselves
2323     are returned in ovector. Each string uses two elements; the first is
2324     the offset to the start, and the second is the offset to the end. In
2325     fact, all the strings have the same start offset. (Space could have
2326     been saved by giving this only once, but it was decided to retain some
2327     compatibility with the way pcre_exec() returns data, even though the
2328 nigel 93 meaning of the strings is different.)
2329 nigel 77
2330     The strings are returned in reverse order of length; that is, the long-
2331 ph10 150 est matching string is given first. If there were too many matches to
2332     fit into ovector, the yield of the function is zero, and the vector is
2333 nigel 77 filled with the longest matches.
2335     Error returns from pcre_dfa_exec()
2337 ph10 150 The pcre_dfa_exec() function returns a negative number when it fails.
2338     Many of the errors are the same as for pcre_exec(), and these are
2339     described above. There are in addition the following errors that are
2340 nigel 77 specific to pcre_dfa_exec():
2342     PCRE_ERROR_DFA_UITEM (-16)
2344 ph10 150 This return is given if pcre_dfa_exec() encounters an item in the pat-
2345     tern that it does not support, for instance, the use of \C or a back
2346 nigel 77 reference.
2348     PCRE_ERROR_DFA_UCOND (-17)
2350 ph10 150 This return is given if pcre_dfa_exec() encounters a condition item
2351     that uses a back reference for the condition, or a test for recursion
2352 nigel 93 in a specific group. These are not supported.
2353 nigel 77
2356 ph10 150 This return is given if pcre_dfa_exec() is called with an extra block
2357 nigel 77 that contains a setting of the match_limit field. This is not supported
2358     (it is meaningless).
2360     PCRE_ERROR_DFA_WSSIZE (-19)
2362 ph10 150 This return is given if pcre_dfa_exec() runs out of space in the
2363 nigel 77 workspace vector.
2367 ph10 150 When a recursive subpattern is processed, the matching function calls
2368     itself recursively, using private vectors for ovector and workspace.
2369     This error is given if the output vector is not large enough. This
2370 nigel 77 should be extremely rare, as a vector of size 1000 is used.
2372 nigel 93
2373     SEE ALSO
2375 ph10 150 pcrebuild(3), pcrecallout(3), pcrecpp(3)(3), pcrematching(3), pcrepar-
2376     tial(3), pcreposix(3), pcreprecompile(3), pcresample(3), pcrestack(3).
2377 nigel 93
2378 nigel 63
2379 ph10 99 AUTHOR
2380 nigel 63
2381 ph10 99 Philip Hazel
2382     University Computing Service
2383     Cambridge CB2 3QH, England.
2386     REVISION
2388 ph10 150 Last updated: 16 April 2007
2389 ph10 99 Copyright (c) 1997-2007 University of Cambridge.
2390     ------------------------------------------------------------------------------
2391 ph10 111
2394 nigel 63
2395 nigel 79
2396 nigel 73 NAME
2397     PCRE - Perl-compatible regular expressions
2399 nigel 77
2400 nigel 63 PCRE CALLOUTS
2402 nigel 73 int (*pcre_callout)(pcre_callout_block *);
2403 nigel 63
2404 nigel 73 PCRE provides a feature called "callout", which is a means of temporar-
2405     ily passing control to the caller of PCRE in the middle of pattern
2406     matching. The caller of PCRE provides an external function by putting
2407     its entry point in the global variable pcre_callout. By default, this
2408     variable contains NULL, which disables all calling out.
2409 nigel 63
2410 nigel 73 Within a regular expression, (?C) indicates the points at which the
2411     external function is to be called. Different callout points can be
2412     identified by putting a number less than 256 after the letter C. The
2413     default value is zero. For example, this pattern has two callout
2414     points:
2415 nigel 63
2416 nigel 75 (?C1)eabc(?C2)def
2417 nigel 63
2418 nigel 75 If the PCRE_AUTO_CALLOUT option bit is set when pcre_compile() is
2419     called, PCRE automatically inserts callouts, all with number 255,
2420     before each item in the pattern. For example, if PCRE_AUTO_CALLOUT is
2421     used with the pattern
2422 nigel 63
2423 nigel 75 A(\d{2}|--)
2425     it is processed as if it were
2427     (?C255)A(?C255)((?C255)\d{2}(?C255)|(?C255)-(?C255)-(?C255))(?C255)
2429     Notice that there is a callout before and after each parenthesis and
2430     alternation bar. Automatic callouts can be used for tracking the
2431     progress of pattern matching. The pcretest command has an option that
2432     sets automatic callouts; when it is used, the output indicates how the
2433     pattern is matched. This is useful information when you are trying to
2434     optimize the performance of a particular pattern.
2439     You should be aware that, because of optimizations in the way PCRE
2440     matches patterns, callouts sometimes do not happen. For example, if the
2441     pattern is
2443     ab(?C4)cd
2445     PCRE knows that any matching string must contain the letter "d". If the
2446     subject string is "abyz", the lack of "d" means that matching doesn't
2447     ever start, and the callout is never reached. However, with "abyd",
2448     though the result is still no match, the callout is obeyed.
2453     During matching, when PCRE reaches a callout point, the external func-
2454 nigel 77 tion defined by pcre_callout is called (if it is set). This applies to
2455     both the pcre_exec() and the pcre_dfa_exec() matching functions. The
2456     only argument to the callout function is a pointer to a pcre_callout
2457     block. This structure contains the following fields:
2458 nigel 75
2459 nigel 73 int version;
2460     int callout_number;
2461     int *offset_vector;
2462     const char *subject;
2463     int subject_length;
2464     int start_match;
2465     int current_position;
2466     int capture_top;
2467     int capture_last;
2468     void *callout_data;
2469 nigel 75 int pattern_position;
2470     int next_item_length;
2471 nigel 63
2472 nigel 77 The version field is an integer containing the version number of the
2473     block format. The initial version was 0; the current version is 1. The
2474     version number will change again in future if additional fields are
2475 nigel 75 added, but the intention is never to remove any of the existing fields.
2476 nigel 63
2477 nigel 77 The callout_number field contains the number of the callout, as com-
2478     piled into the pattern (that is, the number after ?C for manual call-
2479 nigel 75 outs, and 255 for automatically generated callouts).
2480 nigel 63
2481 nigel 77 The offset_vector field is a pointer to the vector of offsets that was
2482     passed by the caller to pcre_exec() or pcre_dfa_exec(). When
2483     pcre_exec() is used, the contents can be inspected in order to extract
2484     substrings that have been matched so far, in the same way as for
2485     extracting substrings after a match has completed. For pcre_dfa_exec()
2486     this field is not useful.
2487 nigel 63
2488 nigel 75 The subject and subject_length fields contain copies of the values that
2489 nigel 73 were passed to pcre_exec().
2490 nigel 63
2491 nigel 77 The start_match field contains the offset within the subject at which
2492     the current match attempt started. If the pattern is not anchored, the
2493 nigel 75 callout function may be called several times from the same point in the
2494     pattern for different starting points in the subject.
2495 nigel 63
2496 nigel 77 The current_position field contains the offset within the subject of
2497 nigel 73 the current match pointer.
2498 nigel 63
2499 nigel 77 When the pcre_exec() function is used, the capture_top field contains
2500     one more than the number of the highest numbered captured substring so
2501     far. If no substrings have been captured, the value of capture_top is
2502     one. This is always the case when pcre_dfa_exec() is used, because it
2503     does not support captured substrings.
2504 nigel 63
2505 nigel 77 The capture_last field contains the number of the most recently cap-
2506     tured substring. If no substrings have been captured, its value is -1.
2507     This is always the case when pcre_dfa_exec() is used.
2508 nigel 63
2509 nigel 77 The callout_data field contains a value that is passed to pcre_exec()
2510     or pcre_dfa_exec() specifically so that it can be passed back in call-
2511     outs. It is passed in the pcre_callout field of the pcre_extra data
2512     structure. If no such data was passed, the value of callout_data in a
2513     pcre_callout block is NULL. There is a description of the pcre_extra
2514 nigel 73 structure in the pcreapi documentation.
2515 nigel 63
2516 nigel 77 The pattern_position field is present from version 1 of the pcre_call-
2517 nigel 75 out structure. It contains the offset to the next item to be matched in
2518     the pattern string.
2519 nigel 63
2520 nigel 77 The next_item_length field is present from version 1 of the pcre_call-
2521 nigel 75 out structure. It contains the length of the next item to be matched in
2522 nigel 77 the pattern string. When the callout immediately precedes an alterna-
2523     tion bar, a closing parenthesis, or the end of the pattern, the length
2524     is zero. When the callout precedes an opening parenthesis, the length
2525 nigel 75 is that of the entire subpattern.
2526 nigel 73
2527 nigel 77 The pattern_position and next_item_length fields are intended to help
2528     in distinguishing between different automatic callouts, which all have
2529 nigel 75 the same callout number. However, they are set for all callouts.
2532 nigel 63 RETURN VALUES
2534 nigel 77 The external callout function returns an integer to PCRE. If the value
2535     is zero, matching proceeds as normal. If the value is greater than
2536     zero, matching fails at the current point, but the testing of other
2537     matching possibilities goes ahead, just as if a lookahead assertion had
2538     failed. If the value is less than zero, the match is abandoned, and
2539     pcre_exec() (or pcre_dfa_exec()) returns the negative value.
2540 nigel 63
2541 nigel 77 Negative values should normally be chosen from the set of
2542 nigel 73 PCRE_ERROR_xxx values. In particular, PCRE_ERROR_NOMATCH forces a stan-
2543 nigel 77 dard "no match" failure. The error number PCRE_ERROR_CALLOUT is
2544     reserved for use by callout functions; it will never be used by PCRE
2545 nigel 73 itself.
2546 nigel 63
2548 ph10 99 AUTHOR
2549 nigel 63
2550 ph10 99 Philip Hazel
2551     University Computing Service
2552     Cambridge CB2 3QH, England.
2555     REVISION
2557     Last updated: 06 March 2007
2558     Copyright (c) 1997-2007 University of Cambridge.
2559     ------------------------------------------------------------------------------
2560 ph10 111
2562 nigel 79 PCRECOMPAT(3) PCRECOMPAT(3)
2563 nigel 63
2564 nigel 79
2565 nigel 73 NAME
2566     PCRE - Perl-compatible regular expressions
2568 nigel 77
2570 nigel 41
2571 nigel 73 This document describes the differences in the ways that PCRE and Perl
2572 nigel 93 handle regular expressions. The differences described here are mainly
2573     with respect to Perl 5.8, though PCRE version 7.0 contains some fea-
2574     tures that are expected to be in the forthcoming Perl 5.10.
2575 nigel 41
2576 nigel 93 1. PCRE has only a subset of Perl's UTF-8 and Unicode support. Details
2577     of what it does have are given in the section on UTF-8 support in the
2578 nigel 87 main pcre page.
2579 nigel 41
2580 nigel 73 2. PCRE does not allow repeat quantifiers on lookahead assertions. Perl
2581 nigel 93 permits them, but they do not mean what you might think. For example,
2582 nigel 73 (?!a){3} does not assert that the next three characters are not "a". It
2583     just asserts that the next character is not "a" three times.
2584 nigel 41
2585 nigel 93 3. Capturing subpatterns that occur inside negative lookahead asser-
2586     tions are counted, but their entries in the offsets vector are never
2587     set. Perl sets its numerical variables from any such patterns that are
2588 nigel 73 matched before the assertion fails to match something (thereby succeed-
2589 nigel 93 ing), but only if the negative lookahead assertion contains just one
2590 nigel 73 branch.
2591 nigel 41
2592 nigel 93 4. Though binary zero characters are supported in the subject string,
2593 nigel 73 they are not allowed in a pattern string because it is passed as a nor-
2594 nigel 75 mal C string, terminated by zero. The escape sequence \0 can be used in
2595     the pattern to represent a binary zero.
2596 nigel 41
2597 nigel 93 5. The following Perl escape sequences are not supported: \l, \u, \L,
2598 nigel 75 \U, and \N. In fact these are implemented by Perl's general string-han-
2599 nigel 93 dling and are not part of its pattern matching engine. If any of these
2600 nigel 75 are encountered by PCRE, an error is generated.
2601 nigel 41
2602 nigel 93 6. The Perl escape sequences \p, \P, and \X are supported only if PCRE
2603     is built with Unicode character property support. The properties that
2604     can be tested with \p and \P are limited to the general category prop-
2605     erties such as Lu and Nd, script names such as Greek or Han, and the
2606 nigel 87 derived properties Any and L&.
2607 nigel 75
2608     7. PCRE does support the \Q...\E escape for quoting substrings. Charac-
2609 nigel 93 ters in between are treated as literals. This is slightly different
2610     from Perl in that $ and @ are also handled as literals inside the
2611     quotes. In Perl, they cause variable interpolation (but of course PCRE
2612 nigel 73 does not have variables). Note the following examples:
2613 nigel 49
2614 nigel 73 Pattern PCRE matches Perl matches
2615 nigel 41
2616 nigel 73 \Qabc$xyz\E abc$xyz abc followed by the
2617     contents of $xyz
2618     \Qabc\$xyz\E abc\$xyz abc\$xyz
2619     \Qabc\E\$\Qxyz\E abc$xyz abc$xyz
2620 nigel 41
2621 nigel 93 The \Q...\E sequence is recognized both inside and outside character
2622 nigel 73 classes.
2623 nigel 41
2624 nigel 93 8. Fairly obviously, PCRE does not support the (?{code}) and (??{code})
2625     constructions. However, there is support for recursive patterns. This
2626     is not available in Perl 5.8, but will be in Perl 5.10. Also, the PCRE
2627     "callout" feature allows an external function to be called during pat-
2628 nigel 75 tern matching. See the pcrecallout documentation for details.
2629 nigel 63
2630 nigel 93 9. Subpatterns that are called recursively or as "subroutines" are
2631     always treated as atomic groups in PCRE. This is like Python, but
2632     unlike Perl.
2634     10. There are some differences that are concerned with the settings of
2635     captured strings when part of a pattern is repeated. For example,
2636     matching "aba" against the pattern /^(a(b)?)+$/ in Perl leaves $2
2637 nigel 73 unset, but in PCRE it is set to "b".
2638 nigel 41
2639 nigel 93 11. PCRE provides some extensions to the Perl regular expression facil-
2640     ities. Perl 5.10 will include new features that are not in earlier
2641     versions, some of which (such as named parentheses) have been in PCRE
2642     for some time. This list is with respect to Perl 5.10:
2643 nigel 41
2644 nigel 93 (a) Although lookbehind assertions must match fixed length strings,
2645 nigel 73 each alternative branch of a lookbehind assertion can match a different
2646     length of string. Perl requires them all to have the same length.
2647 nigel 41
2648 nigel 93 (b) If PCRE_DOLLAR_ENDONLY is set and PCRE_MULTILINE is not set, the $
2649 nigel 73 meta-character matches only at the very end of the string.
2650 nigel 41
2651 nigel 73 (c) If PCRE_EXTRA is set, a backslash followed by a letter with no spe-
2652 nigel 93 cial meaning is faulted. Otherwise, like Perl, the backslash is
2653 nigel 91 ignored. (Perl can be made to issue a warning.)
2654 nigel 41
2655 nigel 93 (d) If PCRE_UNGREEDY is set, the greediness of the repetition quanti-
2656 nigel 73 fiers is inverted, that is, by default they are not greedy, but if fol-
2657     lowed by a question mark they are.
2658 nigel 41
2659 nigel 75 (e) PCRE_ANCHORED can be used at matching time to force a pattern to be
2660     tried only at the first matching position in the subject string.
2661 nigel 41
2663 nigel 73 TURE options for pcre_exec() have no Perl equivalents.
2664 nigel 41
2665 nigel 93 (g) The callout facility is PCRE-specific.
2666 nigel 41
2667 nigel 93 (h) The partial matching facility is PCRE-specific.
2668 nigel 43
2669 nigel 93 (i) Patterns compiled by PCRE can be saved and re-used at a later time,
2670 nigel 75 even on different hosts that have the other endianness.
2672 nigel 93 (j) The alternative matching function (pcre_dfa_exec()) matches in a
2673 nigel 77 different way and is not Perl-compatible.
2675 nigel 63
2676 ph10 99 AUTHOR
2677 nigel 63
2678 ph10 99 Philip Hazel
2679     University Computing Service
2680     Cambridge CB2 3QH, England.
2683     REVISION
2685     Last updated: 06 March 2007
2686     Copyright (c) 1997-2007 University of Cambridge.
2687     ------------------------------------------------------------------------------
2688 ph10 111
2691 nigel 63
2692 nigel 79
2693 nigel 73 NAME
2694     PCRE - Perl-compatible regular expressions
2696 nigel 77
2699 nigel 73 The syntax and semantics of the regular expressions supported by PCRE
2700     are described below. Regular expressions are also described in the Perl
2701 nigel 75 documentation and in a number of books, some of which have copious
2702     examples. Jeffrey Friedl's "Mastering Regular Expressions", published
2703     by O'Reilly, covers regular expressions in great detail. This descrip-
2704     tion of PCRE's regular expressions is intended as reference material.
2705 nigel 49
2706 nigel 75 The original operation of PCRE was on strings of one-byte characters.
2707     However, there is now also support for UTF-8 character strings. To use
2708     this, you must build PCRE to include UTF-8 support, and then call
2709     pcre_compile() with the PCRE_UTF8 option. How this affects pattern
2710     matching is mentioned in several places below. There is also a summary
2711     of UTF-8 features in the section on UTF-8 support in the main pcre
2712     page.
2713 nigel 41
2714 nigel 77 The remainder of this document discusses the patterns that are sup-
2715     ported by PCRE when its main matching function, pcre_exec(), is used.
2716     From release 6.0, PCRE offers a second matching function,
2717     pcre_dfa_exec(), which matches using a different algorithm that is not
2718     Perl-compatible. The advantages and disadvantages of the alternative
2719     function, and how it differs from the normal function, are discussed in
2720     the pcrematching page.
2722 nigel 93
2725 nigel 75 A regular expression is a pattern that is matched against a subject
2726     string from left to right. Most characters stand for themselves in a
2727     pattern, and match the corresponding characters in the subject. As a
2728 nigel 73 trivial example, the pattern
2729 nigel 41
2730 nigel 73 The quick brown fox
2731 nigel 41
2732 nigel 77 matches a portion of a subject string that is identical to itself. When
2733     caseless matching is specified (the PCRE_CASELESS option), letters are
2734     matched independently of case. In UTF-8 mode, PCRE always understands
2735     the concept of case for characters whose values are less than 128, so
2736     caseless matching is always possible. For characters with higher val-
2737     ues, the concept of case is supported if PCRE is compiled with Unicode
2738     property support, but not otherwise. If you want to use caseless
2739     matching for characters 128 and above, you must ensure that PCRE is
2740     compiled with Unicode property support as well as with UTF-8 support.
2741 nigel 41
2742 nigel 77 The power of regular expressions comes from the ability to include
2743     alternatives and repetitions in the pattern. These are encoded in the
2744     pattern by the use of metacharacters, which do not stand for themselves
2745     but instead are interpreted in some special way.
2747     There are two different sets of metacharacters: those that are recog-
2748     nized anywhere in the pattern except within square brackets, and those
2749 nigel 93 that are recognized within square brackets. Outside square brackets,
2750     the metacharacters are as follows:
2751 nigel 41
2752 nigel 73 \ general escape character with several uses
2753     ^ assert start of string (or line, in multiline mode)
2754     $ assert end of string (or line, in multiline mode)
2755     . match any character except newline (by default)
2756     [ start character class definition
2757     | start of alternative branch
2758     ( start subpattern
2759     ) end subpattern
2760     ? extends the meaning of (
2761     also 0 or 1 quantifier
2762     also quantifier minimizer
2763     * 0 or more quantifier
2764     + 1 or more quantifier
2765     also "possessive quantifier"
2766     { start min/max quantifier
2767 nigel 41
2768 nigel 77 Part of a pattern that is in square brackets is called a "character
2769 nigel 75 class". In a character class the only metacharacters are:
2770 nigel 41
2771 nigel 73 \ general escape character
2772     ^ negate the class, but only if the first character
2773     - indicates character range
2774     [ POSIX character class (only if followed by POSIX
2775     syntax)
2776     ] terminates the character class
2777 nigel 41
2778 nigel 77 The following sections describe the use of each of the metacharacters.
2779 nigel 41
2781 nigel 63 BACKSLASH
2782 nigel 41
2783 nigel 73 The backslash character has several uses. Firstly, if it is followed by
2784 nigel 77 a non-alphanumeric character, it takes away any special meaning that
2785     character may have. This use of backslash as an escape character
2786 nigel 73 applies both inside and outside character classes.
2787 nigel 41
2788 nigel 77 For example, if you want to match a * character, you write \* in the
2789     pattern. This escaping action applies whether or not the following
2790     character would otherwise be interpreted as a metacharacter, so it is
2791     always safe to precede a non-alphanumeric with backslash to specify
2792     that it stands for itself. In particular, if you want to match a back-
2793 nigel 75 slash, you write \\.
2794 nigel 41
2795 nigel 77 If a pattern is compiled with the PCRE_EXTENDED option, whitespace in
2796     the pattern (other than in a character class) and characters between a
2797 nigel 91 # outside a character class and the next newline are ignored. An escap-
2798     ing backslash can be used to include a whitespace or # character as
2799     part of the pattern.
2800 nigel 41
2801 nigel 77 If you want to remove the special meaning from a sequence of charac-
2802     ters, you can do so by putting them between \Q and \E. This is differ-
2803     ent from Perl in that $ and @ are handled as literals in \Q...\E
2804     sequences in PCRE, whereas in Perl, $ and @ cause variable interpola-
2805 nigel 73 tion. Note the following examples:
2806 nigel 63
2807 nigel 73 Pattern PCRE matches Perl matches
2808 nigel 63
2809 nigel 73 \Qabc$xyz\E abc$xyz abc followed by the
2810     contents of $xyz
2811     \Qabc\$xyz\E abc\$xyz abc\$xyz
2812     \Qabc\E\$\Qxyz\E abc$xyz abc$xyz
2813 nigel 63
2814 nigel 77 The \Q...\E sequence is recognized both inside and outside character
2815 nigel 73 classes.
2816 nigel 63
2817 nigel 75 Non-printing characters
2819 nigel 73 A second use of backslash provides a way of encoding non-printing char-
2820 nigel 77 acters in patterns in a visible manner. There is no restriction on the
2821     appearance of non-printing characters, apart from the binary zero that
2822     terminates a pattern, but when a pattern is being prepared by text
2823     editing, it is usually easier to use one of the following escape
2824 nigel 73 sequences than the binary character it represents:
2825 nigel 63
2826 nigel 73 \a alarm, that is, the BEL character (hex 07)
2827     \cx "control-x", where x is any character
2828     \e escape (hex 1B)
2829     \f formfeed (hex 0C)
2830     \n newline (hex 0A)
2831     \r carriage return (hex 0D)
2832     \t tab (hex 09)
2833     \ddd character with octal code ddd, or backreference
2834     \xhh character with hex code hh
2835 nigel 87 \x{hhh..} character with hex code hhh..
2836 nigel 41
2837 nigel 77 The precise effect of \cx is as follows: if x is a lower case letter,
2838     it is converted to upper case. Then bit 6 of the character (hex 40) is
2839     inverted. Thus \cz becomes hex 1A, but \c{ becomes hex 3B, while \c;
2840 nigel 73 becomes hex 7B.
2841 nigel 41
2842 nigel 77 After \x, from zero to two hexadecimal digits are read (letters can be
2843 nigel 87 in upper or lower case). Any number of hexadecimal digits may appear
2844     between \x{ and }, but the value of the character code must be less
2845     than 256 in non-UTF-8 mode, and less than 2**31 in UTF-8 mode (that is,
2846     the maximum hexadecimal value is 7FFFFFFF). If characters other than
2847     hexadecimal digits appear between \x{ and }, or if there is no termi-
2848     nating }, this form of escape is not recognized. Instead, the initial
2849     \x will be interpreted as a basic hexadecimal escape, with no following
2850     digits, giving a character whose value is zero.
2851 nigel 41
2852 nigel 73 Characters whose value is less than 256 can be defined by either of the
2853 nigel 87 two syntaxes for \x. There is no difference in the way they are han-
2854     dled. For example, \xdc is exactly the same as \x{dc}.
2855 nigel 41
2856 nigel 91 After \0 up to two further octal digits are read. If there are fewer
2857     than two digits, just those that are present are used. Thus the
2858     sequence \0\x\07 specifies two binary zeros followed by a BEL character
2859     (code value 7). Make sure you supply two digits after the initial zero
2860     if the pattern character that follows is itself an octal digit.
2861 nigel 63
2862 nigel 73 The handling of a backslash followed by a digit other than 0 is compli-
2863     cated. Outside a character class, PCRE reads it and any following dig-
2864 nigel 91 its as a decimal number. If the number is less than 10, or if there
2865 nigel 73 have been at least that many previous capturing left parentheses in the
2866 nigel 91 expression, the entire sequence is taken as a back reference. A
2867     description of how this works is given later, following the discussion
2868 nigel 73 of parenthesized subpatterns.
2869 nigel 41
2870 nigel 91 Inside a character class, or if the decimal number is greater than 9
2871     and there have not been that many capturing subpatterns, PCRE re-reads
2872 nigel 93 up to three octal digits following the backslash, and uses them to gen-
2873 nigel 91 erate a data character. Any subsequent digits stand for themselves. In
2874     non-UTF-8 mode, the value of a character specified in octal must be
2875     less than \400. In UTF-8 mode, values up to \777 are permitted. For
2876     example:
2877 nigel 41
2878 nigel 73 \040 is another way of writing a space
2879     \40 is the same, provided there are fewer than 40
2880     previous capturing subpatterns
2881     \7 is always a back reference
2882     \11 might be a back reference, or another way of
2883     writing a tab
2884     \011 is always a tab
2885     \0113 is a tab followed by the character "3"
2886     \113 might be a back reference, otherwise the
2887     character with octal code 113
2888     \377 might be a back reference, otherwise
2889     the byte consisting entirely of 1 bits
2890     \81 is either a back reference, or a binary zero
2891     followed by the two characters "8" and "1"
2892 nigel 41
2893 nigel 91 Note that octal values of 100 or greater must not be introduced by a
2894 nigel 73 leading zero, because no more than three octal digits are ever read.
2895 nigel 41
2896 nigel 91 All the sequences that define a single character value can be used both
2897     inside and outside character classes. In addition, inside a character
2898     class, the sequence \b is interpreted as the backspace character (hex
2899 nigel 93 08), and the sequences \R and \X are interpreted as the characters "R"
2900     and "X", respectively. Outside a character class, these sequences have
2901     different meanings (see below).
2902 nigel 43
2903 nigel 93 Absolute and relative back references
2905     The sequence \g followed by a positive or negative number, optionally
2906     enclosed in braces, is an absolute or relative back reference. Back
2907     references are discussed later, following the discussion of parenthe-
2908     sized subpatterns.
2910 nigel 75 Generic character types
2911 nigel 41
2912 nigel 93 Another use of backslash is for specifying generic character types. The
2913     following are always recognized:
2914 nigel 75
2915 nigel 73 \d any decimal digit
2916     \D any character that is not a decimal digit
2917     \s any whitespace character
2918     \S any character that is not a whitespace character
2919     \w any "word" character
2920     \W any "non-word" character
2921 nigel 41
2922 nigel 73 Each pair of escape sequences partitions the complete set of characters
2923 nigel 87 into two disjoint sets. Any given character matches one, and only one,
2924 nigel 73 of each pair.
2925 nigel 41
2926 nigel 75 These character type sequences can appear both inside and outside char-
2927 nigel 87 acter classes. They each match one character of the appropriate type.
2928     If the current matching point is at the end of the subject string, all
2929 nigel 75 of them fail, since there is no character to match.
2930 nigel 41
2931 nigel 87 For compatibility with Perl, \s does not match the VT character (code
2932     11). This makes it different from the the POSIX "space" class. The \s
2933 nigel 91 characters are HT (9), LF (10), FF (12), CR (13), and space (32). (If
2934     "use locale;" is included in a Perl script, \s may match the VT charac-
2935     ter. In PCRE, it never does.)
2936 nigel 63
2937 nigel 75 A "word" character is an underscore or any character less than 256 that
2938 nigel 87 is a letter or digit. The definition of letters and digits is con-
2939     trolled by PCRE's low-valued character tables, and may vary if locale-
2940     specific matching is taking place (see "Locale support" in the pcreapi
2941 ph10 142 page). For example, in a French locale such as "fr_FR" in Unix-like
2942     systems, or "french" in Windows, some character codes greater than 128
2943     are used for accented letters, and these are matched by \w.
2944 nigel 63
2945 nigel 87 In UTF-8 mode, characters with values greater than 128 never match \d,
2946 nigel 75 \s, or \w, and always match \D, \S, and \W. This is true even when Uni-
2947 nigel 87 code character property support is available. The use of locales with
2948     Unicode is discouraged.
2949 nigel 41
2950 nigel 93 Newline sequences
2952     Outside a character class, the escape sequence \R matches any Unicode
2953     newline sequence. This is an extension to Perl. In non-UTF-8 mode \R is
2954     equivalent to the following:
2956     (?>\r\n|\n|\x0b|\f|\r|\x85)
2958     This is an example of an "atomic group", details of which are given
2959     below. This particular group matches either the two-character sequence
2960     CR followed by LF, or one of the single characters LF (linefeed,
2961     U+000A), VT (vertical tab, U+000B), FF (formfeed, U+000C), CR (carriage
2962     return, U+000D), or NEL (next line, U+0085). The two-character sequence
2963     is treated as a single unit that cannot be split.
2965     In UTF-8 mode, two additional characters whose codepoints are greater
2966     than 255 are added: LS (line separator, U+2028) and PS (paragraph sepa-
2967     rator, U+2029). Unicode character property support is not needed for
2968     these characters to be recognized.
2970     Inside a character class, \R matches the letter "R".
2972 nigel 75 Unicode character properties
2974     When PCRE is built with Unicode character property support, three addi-
2975 nigel 87 tional escape sequences to match character properties are available
2976 nigel 75 when UTF-8 mode is selected. They are:
2978 nigel 87 \p{xx} a character with the xx property
2979     \P{xx} a character without the xx property
2980     \X an extended Unicode sequence
2981 nigel 75
2982 nigel 77 The property names represented by xx above are limited to the Unicode
2983 nigel 87 script names, the general category properties, and "Any", which matches
2984     any character (including newline). Other properties such as "InMusical-
2985     Symbols" are not currently supported by PCRE. Note that \P{Any} does
2986     not match any characters, so always causes a match failure.
2987 nigel 75
2988 nigel 87 Sets of Unicode characters are defined as belonging to certain scripts.
2989     A character from one of these sets can be matched using a script name.
2990     For example:
2991 nigel 75
2992 nigel 87 \p{Greek}
2993     \P{Han}
2995     Those that are not part of an identified script are lumped together as
2996     "Common". The current list of scripts is:
2998 nigel 93 Arabic, Armenian, Balinese, Bengali, Bopomofo, Braille, Buginese,
2999     Buhid, Canadian_Aboriginal, Cherokee, Common, Coptic, Cuneiform,
3000     Cypriot, Cyrillic, Deseret, Devanagari, Ethiopic, Georgian, Glagolitic,
3001     Gothic, Greek, Gujarati, Gurmukhi, Han, Hangul, Hanunoo, Hebrew, Hira-
3002     gana, Inherited, Kannada, Katakana, Kharoshthi, Khmer, Lao, Latin,
3003     Limbu, Linear_B, Malayalam, Mongolian, Myanmar, New_Tai_Lue, Nko,
3004     Ogham, Old_Italic, Old_Persian, Oriya, Osmanya, Phags_Pa, Phoenician,
3005     Runic, Shavian, Sinhala, Syloti_Nagri, Syriac, Tagalog, Tagbanwa,
3006     Tai_Le, Tamil, Telugu, Thaana, Thai, Tibetan, Tifinagh, Ugaritic, Yi.
3007 nigel 87
3008     Each character has exactly one general category property, specified by
3009     a two-letter abbreviation. For compatibility with Perl, negation can be
3010     specified by including a circumflex between the opening brace and the
3011     property name. For example, \p{^Lu} is the same as \P{Lu}.
3013     If only one letter is specified with \p or \P, it includes all the gen-
3014     eral category properties that start with that letter. In this case, in
3015     the absence of negation, the curly brackets in the escape sequence are
3016     optional; these two examples have the same effect:
3018 nigel 75 \p{L}
3019     \pL
3021 nigel 87 The following general category property codes are supported:
3022 nigel 75
3023     C Other
3024     Cc Control
3025     Cf Format
3026     Cn Unassigned
3027     Co Private use
3028     Cs Surrogate
3030     L Letter
3031     Ll Lower case letter
3032     Lm Modifier letter
3033     Lo Other letter
3034     Lt Title case letter
3035     Lu Upper case letter
3037     M Mark
3038     Mc Spacing mark
3039     Me Enclosing mark
3040     Mn Non-spacing mark
3042     N Number
3043     Nd Decimal number
3044     Nl Letter number
3045     No Other number
3047     P Punctuation
3048     Pc Connector punctuation
3049     Pd Dash punctuation
3050     Pe Close punctuation
3051     Pf Final punctuation
3052     Pi Initial punctuation
3053     Po Other punctuation
3054     Ps Open punctuation
3056     S Symbol
3057     Sc Currency symbol
3058     Sk Modifier symbol
3059     Sm Mathematical symbol
3060     So Other symbol
3062     Z Separator
3063     Zl Line separator
3064     Zp Paragraph separator
3065     Zs Space separator
3067 nigel 87 The special property L& is also supported: it matches a character that
3068     has the Lu, Ll, or Lt property, in other words, a letter that is not
3069     classified as a modifier or "other".
3070 nigel 75
3071 nigel 87 The long synonyms for these properties that Perl supports (such as
3072 nigel 91 \p{Letter}) are not supported by PCRE, nor is it permitted to prefix
3073 nigel 87 any of these properties with "Is".
3075     No character that is in the Unicode table has the Cn (unassigned) prop-
3076     erty. Instead, this property is assumed for any code point that is not
3077     in the Unicode table.
3079 nigel 77 Specifying caseless matching does not affect these escape sequences.
3080 nigel 75 For example, \p{Lu} always matches only upper case letters.
3082 nigel 77 The \X escape matches any number of Unicode characters that form an
3083 nigel 75 extended Unicode sequence. \X is equivalent to
3085     (?>\PM\pM*)
3087 nigel 77 That is, it matches a character without the "mark" property, followed
3088     by zero or more characters with the "mark" property, and treats the
3089     sequence as an atomic group (see below). Characters with the "mark"
3090 nigel 75 property are typically accents that affect the preceding character.
3092 nigel 77 Matching characters by Unicode property is not fast, because PCRE has
3093     to search a structure that contains data for over fifteen thousand
3094 nigel 75 characters. That is why the traditional escape sequences such as \d and
3095     \w do not use Unicode properties in PCRE.
3097     Simple assertions
3099 nigel 93 The final use of backslash is for certain simple assertions. An asser-
3100 nigel 77 tion specifies a condition that has to be met at a particular point in
3101     a match, without consuming any characters from the subject string. The
3102     use of subpatterns for more complicated assertions is described below.
3103 nigel 75 The backslashed assertions are:
3104 nigel 41
3105 nigel 73 \b matches at a word boundary
3106     \B matches when not at a word boundary
3107 nigel 93 \A matches at the start of the subject
3108     \Z matches at the end of the subject
3109     also matches before a newline at the end of the subject
3110     \z matches only at the end of the subject
3111     \G matches at the first matching position in the subject
3112 nigel 41
3113 nigel 77 These assertions may not appear in character classes (but note that \b
3114 nigel 73 has a different meaning, namely the backspace character, inside a char-
3115     acter class).
3116 nigel 41
3117 nigel 77 A word boundary is a position in the subject string where the current
3118     character and the previous character do not both match \w or \W (i.e.
3119     one matches \w and the other matches \W), or the start or end of the
3120 nigel 73 string if the first or last character matches \w, respectively.
3121 nigel 43
3122 nigel 77 The \A, \Z, and \z assertions differ from the traditional circumflex
3123 nigel 75 and dollar (described in the next section) in that they only ever match
3124 nigel 77 at the very start and end of the subject string, whatever options are
3125     set. Thus, they are independent of multiline mode. These three asser-
3126 nigel 75 tions are not affected by the PCRE_NOTBOL or PCRE_NOTEOL options, which
3127 nigel 77 affect only the behaviour of the circumflex and dollar metacharacters.
3128     However, if the startoffset argument of pcre_exec() is non-zero, indi-
3129 nigel 75 cating that matching is to start at a point other than the beginning of
3130 nigel 77 the subject, \A can never match. The difference between \Z and \z is
3131 nigel 91 that \Z matches before a newline at the end of the string as well as at
3132     the very end, whereas \z matches only at the end.
3133 nigel 63
3134 nigel 91 The \G assertion is true only when the current matching position is at
3135     the start point of the match, as specified by the startoffset argument
3136     of pcre_exec(). It differs from \A when the value of startoffset is
3137     non-zero. By calling pcre_exec() multiple times with appropriate argu-
3138 nigel 73 ments, you can mimic Perl's /g option, and it is in this kind of imple-
3139     mentation where \G can be useful.
3140 nigel 41
3141 nigel 91 Note, however, that PCRE's interpretation of \G, as the start of the
3142 nigel 73 current match, is subtly different from Perl's, which defines it as the
3143 nigel 91 end of the previous match. In Perl, these can be different when the
3144     previously matched string was empty. Because PCRE does just one match
3145 nigel 73 at a time, it cannot reproduce this behaviour.
3146 nigel 41
3147 nigel 91 If all the alternatives of a pattern begin with \G, the expression is
3148 nigel 73 anchored to the starting match position, and the "anchored" flag is set
3149     in the compiled regular expression.
3150 nigel 63
3153 nigel 63
3154 nigel 73 Outside a character class, in the default matching mode, the circumflex
3155 nigel 91 character is an assertion that is true only if the current matching
3156     point is at the start of the subject string. If the startoffset argu-
3157     ment of pcre_exec() is non-zero, circumflex can never match if the
3158     PCRE_MULTILINE option is unset. Inside a character class, circumflex
3159 nigel 73 has an entirely different meaning (see below).
3160 nigel 41
3161 nigel 91 Circumflex need not be the first character of the pattern if a number
3162     of alternatives are involved, but it should be the first thing in each
3163     alternative in which it appears if the pattern is ever to match that
3164     branch. If all possible alternatives start with a circumflex, that is,
3165     if the pattern is constrained to match only at the start of the sub-
3166     ject, it is said to be an "anchored" pattern. (There are also other
3167 nigel 73 constructs that can cause a pattern to be anchored.)
3168 nigel 41
3169 nigel 91 A dollar character is an assertion that is true only if the current
3170     matching point is at the end of the subject string, or immediately
3171     before a newline at the end of the string (by default). Dollar need not
3172     be the last character of the pattern if a number of alternatives are
3173     involved, but it should be the last item in any branch in which it
3174     appears. Dollar has no special meaning in a character class.
3175 nigel 41
3176 nigel 77 The meaning of dollar can be changed so that it matches only at the
3177     very end of the string, by setting the PCRE_DOLLAR_ENDONLY option at
3178 nigel 73 compile time. This does not affect the \Z assertion.
3179 nigel 41
3180 nigel 73 The meanings of the circumflex and dollar characters are changed if the
3181 nigel 91 PCRE_MULTILINE option is set. When this is the case, a circumflex
3182     matches immediately after internal newlines as well as at the start of
3183     the subject string. It does not match after a newline that ends the
3184     string. A dollar matches before any newlines in the string, as well as
3185     at the very end, when PCRE_MULTILINE is set. When newline is specified
3186     as the two-character sequence CRLF, isolated CR and LF characters do
3187     not indicate newlines.
3188 nigel 41
3189 nigel 91 For example, the pattern /^abc$/ matches the subject string "def\nabc"
3190     (where \n represents a newline) in multiline mode, but not otherwise.
3191     Consequently, patterns that are anchored in single line mode because
3192     all branches start with ^ are not anchored in multiline mode, and a
3193     match for circumflex is possible when the startoffset argument of
3194     pcre_exec() is non-zero. The PCRE_DOLLAR_ENDONLY option is ignored if
3195     PCRE_MULTILINE is set.
3196 nigel 41
3197 nigel 91 Note that the sequences \A, \Z, and \z can be used to match the start
3198     and end of the subject in both modes, and if all branches of a pattern
3199     start with \A it is always anchored, whether or not PCRE_MULTILINE is
3200     set.
3201 nigel 41
3202 nigel 91
3203 nigel 63 FULL STOP (PERIOD, DOT)
3204 nigel 41
3205 nigel 73 Outside a character class, a dot in the pattern matches any one charac-
3206 nigel 91 ter in the subject string except (by default) a character that signi-
3207     fies the end of a line. In UTF-8 mode, the matched character may be
3208 nigel 93 more than one byte long.
3209 nigel 41
3210 nigel 93 When a line ending is defined as a single character, dot never matches
3211     that character; when the two-character sequence CRLF is used, dot does
3212     not match CR if it is immediately followed by LF, but otherwise it
3213     matches all characters (including isolated CRs and LFs). When any Uni-
3214     code line endings are being recognized, dot does not match CR or LF or
3215     any of the other line ending characters.
3216 nigel 41
3217 nigel 93 The behaviour of dot with regard to newlines can be changed. If the
3218     PCRE_DOTALL option is set, a dot matches any one character, without
3219     exception. If the two-character sequence CRLF is present in the subject
3220     string, it takes two dots to match it.
3222     The handling of dot is entirely independent of the handling of circum-
3223     flex and dollar, the only relationship being that they both involve
3224 nigel 91 newlines. Dot has no special meaning in a character class.
3229 nigel 73 Outside a character class, the escape sequence \C matches any one byte,
3230 nigel 93 both in and out of UTF-8 mode. Unlike a dot, it always matches any
3231     line-ending characters. The feature is provided in Perl in order to
3232     match individual bytes in UTF-8 mode. Because it breaks up UTF-8 char-
3233     acters into individual bytes, what remains in the string may be a mal-
3234     formed UTF-8 string. For this reason, the \C escape sequence is best
3235     avoided.
3236 nigel 63
3237 nigel 77 PCRE does not allow \C to appear in lookbehind assertions (described
3238     below), because in UTF-8 mode this would make it impossible to calcu-
3239 nigel 75 late the length of the lookbehind.
3240 nigel 63
3243 nigel 63
3244 nigel 73 An opening square bracket introduces a character class, terminated by a
3245     closing square bracket. A closing square bracket on its own is not spe-
3246     cial. If a closing square bracket is required as a member of the class,
3247 nigel 77 it should be the first data character in the class (after an initial
3248 nigel 73 circumflex, if present) or escaped with a backslash.
3249 nigel 41
3250 nigel 77 A character class matches a single character in the subject. In UTF-8
3251     mode, the character may occupy more than one byte. A matched character
3252 nigel 73 must be in the set of characters defined by the class, unless the first
3253 nigel 77 character in the class definition is a circumflex, in which case the
3254     subject character must not be in the set defined by the class. If a
3255     circumflex is actually required as a member of the class, ensure it is
3256 nigel 73 not the first character, or escape it with a backslash.
3257 nigel 41
3258 nigel 77 For example, the character class [aeiou] matches any lower case vowel,
3259     while [^aeiou] matches any character that is not a lower case vowel.
3260 nigel 73 Note that a circumflex is just a convenient notation for specifying the
3261 nigel 77 characters that are in the class by enumerating those that are not. A
3262     class that starts with a circumflex is not an assertion: it still con-
3263     sumes a character from the subject string, and therefore it fails if
3264 nigel 75 the current pointer is at the end of the string.
3265 nigel 41
3266 nigel 77 In UTF-8 mode, characters with values greater than 255 can be included
3267     in a class as a literal string of bytes, or by using the \x{ escaping
3268 nigel 73 mechanism.
3269 nigel 63
3270 nigel 77 When caseless matching is set, any letters in a class represent both
3271     their upper case and lower case versions, so for example, a caseless
3272     [aeiou] matches "A" as well as "a", and a caseless [^aeiou] does not
3273     match "A", whereas a caseful version would. In UTF-8 mode, PCRE always
3274     understands the concept of case for characters whose values are less
3275     than 128, so caseless matching is always possible. For characters with
3276     higher values, the concept of case is supported if PCRE is compiled
3277     with Unicode property support, but not otherwise. If you want to use
3278     caseless matching for characters 128 and above, you must ensure that
3279     PCRE is compiled with Unicode property support as well as with UTF-8
3280     support.
3281 nigel 41
3282 nigel 93 Characters that might indicate line breaks are never treated in any
3283     special way when matching character classes, whatever line-ending
3284     sequence is in use, and whatever setting of the PCRE_DOTALL and
3285     PCRE_MULTILINE options is used. A class such as [^a] always matches one
3286     of these characters.
3287 nigel 41
3288 nigel 75 The minus (hyphen) character can be used to specify a range of charac-
3289     ters in a character class. For example, [d-m] matches any letter
3290     between d and m, inclusive. If a minus character is required in a
3291     class, it must be escaped with a backslash or appear in a position
3292     where it cannot be interpreted as indicating a range, typically as the
3293 nigel 73 first or last character in the class.
3294 nigel 41
3295 nigel 73 It is not possible to have the literal character "]" as the end charac-
3296 nigel 75 ter of a range. A pattern such as [W-]46] is interpreted as a class of
3297     two characters ("W" and "-") followed by a literal string "46]", so it
3298     would match "W46]" or "-46]". However, if the "]" is escaped with a
3299     backslash it is interpreted as the end of range, so [W-\]46] is inter-
3300     preted as a class containing a range followed by two other characters.
3301     The octal or hexadecimal representation of "]" can also be used to end
3302     a range.
3303 nigel 41
3304 nigel 75 Ranges operate in the collating sequence of character values. They can
3305     also be used for characters specified numerically, for example
3306     [\000-\037]. In UTF-8 mode, ranges can include characters whose values
3307 nigel 73 are greater than 255, for example [\x{100}-\x{2ff}].
3308 nigel 63
3309 nigel 73 If a range that includes letters is used when caseless matching is set,
3310     it matches the letters in either case. For example, [W-c] is equivalent
3311 nigel 75 to [][\\^_`wxyzabc], matched caselessly, and in non-UTF-8 mode, if
3312 ph10 142 character tables for a French locale are in use, [\xc8-\xcb] matches
3313 nigel 75 accented E characters in both cases. In UTF-8 mode, PCRE supports the
3314     concept of case for characters with values greater than 128 only when
3315     it is compiled with Unicode property support.
3316 nigel 41
3317 nigel 75 The character types \d, \D, \p, \P, \s, \S, \w, and \W may also appear
3318     in a character class, and add the characters that they match to the
3319     class. For example, [\dABCDEF] matches any hexadecimal digit. A circum-
3320     flex can conveniently be used with the upper case character types to
3321     specify a more restricted set of characters than the matching lower
3322     case type. For example, the class [^\W_] matches any letter or digit,
3323     but not underscore.
3324 nigel 41
3325 nigel 75 The only metacharacters that are recognized in character classes are
3326     backslash, hyphen (only where it can be interpreted as specifying a
3327     range), circumflex (only at the start), opening square bracket (only
3328     when it can be interpreted as introducing a POSIX class name - see the
3329     next section), and the terminating closing square bracket. However,
3330     escaping other non-alphanumeric characters does no harm.
3331 nigel 41
3332 nigel 73
3335 nigel 75 Perl supports the POSIX notation for character classes. This uses names
3336     enclosed by [: and :] within the enclosing square brackets. PCRE also
3337     supports this notation. For example,
3338 nigel 63
3339 nigel 73 [01[:alpha:]%]
3340 nigel 43
3341 nigel 73 matches "0", "1", any alphabetic character, or "%". The supported class
3342     names are
3343 nigel 43
3344 nigel 73 alnum letters and digits
3345     alpha letters
3346     ascii character codes 0 - 127
3347     blank space or tab only
3348     cntrl control characters
3349     digit decimal digits (same as \d)
3350     graph printing characters, excluding space
3351     lower lower case letters
3352     print printing characters, including space
3353     punct printing characters, excluding letters and digits
3354     space white space (not quite the same as \s)
3355     upper upper case letters
3356     word "word" characters (same as \w)
3357     xdigit hexadecimal digits
3358 nigel 43
3359 nigel 73 The "space" characters are HT (9), LF (10), VT (11), FF (12), CR (13),
3360     and space (32). Notice that this list includes the VT character (code
3361     11). This makes "space" different to \s, which does not include VT (for
3362     Perl compatibility).
3363 nigel 43
3364 nigel 73 The name "word" is a Perl extension, and "blank" is a GNU extension
3365     from Perl 5.8. Another Perl extension is negation, which is indicated
3366     by a ^ character after the colon. For example,
3367 nigel 63
3368 nigel 73 [12[:^digit:]]
3369 nigel 43
3370 nigel 73 matches "1", "2", or any non-digit. PCRE (and Perl) also recognize the
3371     POSIX syntax [.ch.] and [=ch=] where "ch" is a "collating element", but
3372     these are not supported, and an error is given if they are encountered.
3373 nigel 43
3374 nigel 75 In UTF-8 mode, characters with values greater than 128 do not match any
3375 nigel 73 of the POSIX character classes.
3376 nigel 43
3378 nigel 41 VERTICAL BAR
3379 nigel 63
3380 nigel 73 Vertical bar characters are used to separate alternative patterns. For
3381     example, the pattern
3382 nigel 41
3383 nigel 73 gilbert|sullivan
3384 nigel 41
3385 nigel 73 matches either "gilbert" or "sullivan". Any number of alternatives may
3386     appear, and an empty alternative is permitted (matching the empty
3387 nigel 91 string). The matching process tries each alternative in turn, from left
3388     to right, and the first one that succeeds is used. If the alternatives
3389     are within a subpattern (defined below), "succeeds" means matching the
3390     rest of the main pattern as well as the alternative in the subpattern.
3391 nigel 41
3395 nigel 73 The settings of the PCRE_CASELESS, PCRE_MULTILINE, PCRE_DOTALL, and
3396     PCRE_EXTENDED options can be changed from within the pattern by a
3397     sequence of Perl option letters enclosed between "(?" and ")". The
3398     option letters are
3399 nigel 63
3400 nigel 73 i for PCRE_CASELESS
3401     m for PCRE_MULTILINE
3402     s for PCRE_DOTALL
3403     x for PCRE_EXTENDED
3404 nigel 41
3405 nigel 73 For example, (?im) sets caseless, multiline matching. It is also possi-
3406     ble to unset these options by preceding the letter with a hyphen, and a
3407     combined setting and unsetting such as (?im-sx), which sets PCRE_CASE-
3408     LESS and PCRE_MULTILINE while unsetting PCRE_DOTALL and PCRE_EXTENDED,
3409     is also permitted. If a letter appears both before and after the
3410     hyphen, the option is unset.
3411 nigel 41
3412 nigel 73 When an option change occurs at top level (that is, not inside subpat-
3413     tern parentheses), the change applies to the remainder of the pattern
3414     that follows. If the change is placed right at the start of a pattern,
3415     PCRE extracts it into the global options (and it will therefore show up
3416     in data extracted by the pcre_fullinfo() function).
3417 nigel 41
3418 nigel 93 An option change within a subpattern (see below for a description of
3419     subpatterns) affects only that part of the current pattern that follows
3420     it, so
3421 nigel 41
3422 nigel 73 (a(?i)b)c
3423 nigel 41
3424 nigel 73 matches abc and aBc and no other strings (assuming PCRE_CASELESS is not
3425 nigel 93 used). By this means, options can be made to have different settings
3426     in different parts of the pattern. Any changes made in one alternative
3427     do carry on into subsequent branches within the same subpattern. For
3428 nigel 73 example,
3429 nigel 41
3430 nigel