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1 -----------------------------------------------------------------------------
2 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. Neither has
6 the pcredemo program. There are separate text files for the pcregrep and
7 pcretest commands.
8 -----------------------------------------------------------------------------
9
10
11 PCRE(3) Library Functions Manual PCRE(3)
12
13
14
15 NAME
16 PCRE - Perl-compatible regular expressions (original API)
17
18 PLEASE TAKE NOTE
19
20 This document relates to PCRE releases that use the original API, with
21 library names libpcre, libpcre16, and libpcre32. January 2015 saw the
22 first release of a new API, known as PCRE2, with release numbers start-
23 ing at 10.00 and library names libpcre2-8, libpcre2-16, and
24 libpcre2-32. The old libraries (now called PCRE1) are still being main-
25 tained for bug fixes, but there will be no new development. New
26 projects are advised to use the new PCRE2 libraries.
27
28
29 INTRODUCTION
30
31 The PCRE library is a set of functions that implement regular expres-
32 sion pattern matching using the same syntax and semantics as Perl, with
33 just a few differences. Some features that appeared in Python and PCRE
34 before they appeared in Perl are also available using the Python syn-
35 tax, there is some support for one or two .NET and Oniguruma syntax
36 items, and there is an option for requesting some minor changes that
37 give better JavaScript compatibility.
38
39 Starting with release 8.30, it is possible to compile two separate PCRE
40 libraries: the original, which supports 8-bit character strings
41 (including UTF-8 strings), and a second library that supports 16-bit
42 character strings (including UTF-16 strings). The build process allows
43 either one or both to be built. The majority of the work to make this
44 possible was done by Zoltan Herczeg.
45
46 Starting with release 8.32 it is possible to compile a third separate
47 PCRE library that supports 32-bit character strings (including UTF-32
48 strings). The build process allows any combination of the 8-, 16- and
49 32-bit libraries. The work to make this possible was done by Christian
50 Persch.
51
52 The three libraries contain identical sets of functions, except that
53 the names in the 16-bit library start with pcre16_ instead of pcre_,
54 and the names in the 32-bit library start with pcre32_ instead of
55 pcre_. To avoid over-complication and reduce the documentation mainte-
56 nance load, most of the documentation describes the 8-bit library, with
57 the differences for the 16-bit and 32-bit libraries described sepa-
58 rately in the pcre16 and pcre32 pages. References to functions or
59 structures of the form pcre[16|32]_xxx should be read as meaning
60 "pcre_xxx when using the 8-bit library, pcre16_xxx when using the
61 16-bit library, or pcre32_xxx when using the 32-bit library".
62
63 The current implementation of PCRE corresponds approximately with Perl
64 5.12, including support for UTF-8/16/32 encoded strings and Unicode
65 general category properties. However, UTF-8/16/32 and Unicode support
66 has to be explicitly enabled; it is not the default. The Unicode tables
67 correspond to Unicode release 6.3.0.
68
69 In addition to the Perl-compatible matching function, PCRE contains an
70 alternative function that matches the same compiled patterns in a dif-
71 ferent way. In certain circumstances, the alternative function has some
72 advantages. For a discussion of the two matching algorithms, see the
73 pcrematching page.
74
75 PCRE is written in C and released as a C library. A number of people
76 have written wrappers and interfaces of various kinds. In particular,
77 Google Inc. have provided a comprehensive C++ wrapper for the 8-bit
78 library. This is now included as part of the PCRE distribution. The
79 pcrecpp page has details of this interface. Other people's contribu-
80 tions can be found in the Contrib directory at the primary FTP site,
81 which is:
82
83 ftp://ftp.csx.cam.ac.uk/pub/software/programming/pcre
84
85 Details of exactly which Perl regular expression features are and are
86 not supported by PCRE are given in separate documents. See the pcrepat-
87 tern and pcrecompat pages. There is a syntax summary in the pcresyntax
88 page.
89
90 Some features of PCRE can be included, excluded, or changed when the
91 library is built. The pcre_config() function makes it possible for a
92 client to discover which features are available. The features them-
93 selves are described in the pcrebuild page. Documentation about build-
94 ing PCRE for various operating systems can be found in the README and
95 NON-AUTOTOOLS_BUILD files in the source distribution.
96
97 The libraries contains a number of undocumented internal functions and
98 data tables that are used by more than one of the exported external
99 functions, but which are not intended for use by external callers.
100 Their names all begin with "_pcre_" or "_pcre16_" or "_pcre32_", which
101 hopefully will not provoke any name clashes. In some environments, it
102 is possible to control which external symbols are exported when a
103 shared library is built, and in these cases the undocumented symbols
104 are not exported.
105
106
107 SECURITY CONSIDERATIONS
108
109 If you are using PCRE in a non-UTF application that permits users to
110 supply arbitrary patterns for compilation, you should be aware of a
111 feature that allows users to turn on UTF support from within a pattern,
112 provided that PCRE was built with UTF support. For example, an 8-bit
113 pattern that begins with "(*UTF8)" or "(*UTF)" turns on UTF-8 mode,
114 which interprets patterns and subjects as strings of UTF-8 characters
115 instead of individual 8-bit characters. This causes both the pattern
116 and any data against which it is matched to be checked for UTF-8 valid-
117 ity. If the data string is very long, such a check might use suffi-
118 ciently many resources as to cause your application to lose perfor-
119 mance.
120
121 One way of guarding against this possibility is to use the
122 pcre_fullinfo() function to check the compiled pattern's options for
123 UTF. Alternatively, from release 8.33, you can set the PCRE_NEVER_UTF
124 option at compile time. This causes an compile time error if a pattern
125 contains a UTF-setting sequence.
126
127 If your application is one that supports UTF, be aware that validity
128 checking can take time. If the same data string is to be matched many
129 times, you can use the PCRE_NO_UTF[8|16|32]_CHECK option for the second
130 and subsequent matches to save redundant checks.
131
132 Another way that performance can be hit is by running a pattern that
133 has a very large search tree against a string that will never match.
134 Nested unlimited repeats in a pattern are a common example. PCRE pro-
135 vides some protection against this: see the PCRE_EXTRA_MATCH_LIMIT fea-
136 ture in the pcreapi page.
137
138
139 USER DOCUMENTATION
140
141 The user documentation for PCRE comprises a number of different sec-
142 tions. In the "man" format, each of these is a separate "man page". In
143 the HTML format, each is a separate page, linked from the index page.
144 In the plain text format, the descriptions of the pcregrep and pcretest
145 programs are in files called pcregrep.txt and pcretest.txt, respec-
146 tively. The remaining sections, except for the pcredemo section (which
147 is a program listing), are concatenated in pcre.txt, for ease of
148 searching. The sections are as follows:
149
150 pcre this document
151 pcre-config show PCRE installation configuration information
152 pcre16 details of the 16-bit library
153 pcre32 details of the 32-bit library
154 pcreapi details of PCRE's native C API
155 pcrebuild building PCRE
156 pcrecallout details of the callout feature
157 pcrecompat discussion of Perl compatibility
158 pcrecpp details of the C++ wrapper for the 8-bit library
159 pcredemo a demonstration C program that uses PCRE
160 pcregrep description of the pcregrep command (8-bit only)
161 pcrejit discussion of the just-in-time optimization support
162 pcrelimits details of size and other limits
163 pcrematching discussion of the two matching algorithms
164 pcrepartial details of the partial matching facility
165 pcrepattern syntax and semantics of supported
166 regular expressions
167 pcreperform discussion of performance issues
168 pcreposix the POSIX-compatible C API for the 8-bit library
169 pcreprecompile details of saving and re-using precompiled patterns
170 pcresample discussion of the pcredemo program
171 pcrestack discussion of stack usage
172 pcresyntax quick syntax reference
173 pcretest description of the pcretest testing command
174 pcreunicode discussion of Unicode and UTF-8/16/32 support
175
176 In the "man" and HTML formats, there is also a short page for each C
177 library function, listing its arguments and results.
178
179
180 AUTHOR
181
182 Philip Hazel
183 University Computing Service
184 Cambridge CB2 3QH, England.
185
186 Putting an actual email address here seems to have been a spam magnet,
187 so I've taken it away. If you want to email me, use my two initials,
188 followed by the two digits 10, at the domain cam.ac.uk.
189
190
191 REVISION
192
193 Last updated: 10 February 2015
194 Copyright (c) 1997-2015 University of Cambridge.
195 ------------------------------------------------------------------------------
196
197
198 PCRE(3) Library Functions Manual PCRE(3)
199
200
201
202 NAME
203 PCRE - Perl-compatible regular expressions
204
205 #include <pcre.h>
206
207
208 PCRE 16-BIT API BASIC FUNCTIONS
209
210 pcre16 *pcre16_compile(PCRE_SPTR16 pattern, int options,
211 const char **errptr, int *erroffset,
212 const unsigned char *tableptr);
213
214 pcre16 *pcre16_compile2(PCRE_SPTR16 pattern, int options,
215 int *errorcodeptr,
216 const char **errptr, int *erroffset,
217 const unsigned char *tableptr);
218
219 pcre16_extra *pcre16_study(const pcre16 *code, int options,
220 const char **errptr);
221
222 void pcre16_free_study(pcre16_extra *extra);
223
224 int pcre16_exec(const pcre16 *code, const pcre16_extra *extra,
225 PCRE_SPTR16 subject, int length, int startoffset,
226 int options, int *ovector, int ovecsize);
227
228 int pcre16_dfa_exec(const pcre16 *code, const pcre16_extra *extra,
229 PCRE_SPTR16 subject, int length, int startoffset,
230 int options, int *ovector, int ovecsize,
231 int *workspace, int wscount);
232
233
234 PCRE 16-BIT API STRING EXTRACTION FUNCTIONS
235
236 int pcre16_copy_named_substring(const pcre16 *code,
237 PCRE_SPTR16 subject, int *ovector,
238 int stringcount, PCRE_SPTR16 stringname,
239 PCRE_UCHAR16 *buffer, int buffersize);
240
241 int pcre16_copy_substring(PCRE_SPTR16 subject, int *ovector,
242 int stringcount, int stringnumber, PCRE_UCHAR16 *buffer,
243 int buffersize);
244
245 int pcre16_get_named_substring(const pcre16 *code,
246 PCRE_SPTR16 subject, int *ovector,
247 int stringcount, PCRE_SPTR16 stringname,
248 PCRE_SPTR16 *stringptr);
249
250 int pcre16_get_stringnumber(const pcre16 *code,
251 PCRE_SPTR16 name);
252
253 int pcre16_get_stringtable_entries(const pcre16 *code,
254 PCRE_SPTR16 name, PCRE_UCHAR16 **first, PCRE_UCHAR16 **last);
255
256 int pcre16_get_substring(PCRE_SPTR16 subject, int *ovector,
257 int stringcount, int stringnumber,
258 PCRE_SPTR16 *stringptr);
259
260 int pcre16_get_substring_list(PCRE_SPTR16 subject,
261 int *ovector, int stringcount, PCRE_SPTR16 **listptr);
262
263 void pcre16_free_substring(PCRE_SPTR16 stringptr);
264
265 void pcre16_free_substring_list(PCRE_SPTR16 *stringptr);
266
267
268 PCRE 16-BIT API AUXILIARY FUNCTIONS
269
270 pcre16_jit_stack *pcre16_jit_stack_alloc(int startsize, int maxsize);
271
272 void pcre16_jit_stack_free(pcre16_jit_stack *stack);
273
274 void pcre16_assign_jit_stack(pcre16_extra *extra,
275 pcre16_jit_callback callback, void *data);
276
277 const unsigned char *pcre16_maketables(void);
278
279 int pcre16_fullinfo(const pcre16 *code, const pcre16_extra *extra,
280 int what, void *where);
281
282 int pcre16_refcount(pcre16 *code, int adjust);
283
284 int pcre16_config(int what, void *where);
285
286 const char *pcre16_version(void);
287
288 int pcre16_pattern_to_host_byte_order(pcre16 *code,
289 pcre16_extra *extra, const unsigned char *tables);
290
291
292 PCRE 16-BIT API INDIRECTED FUNCTIONS
293
294 void *(*pcre16_malloc)(size_t);
295
296 void (*pcre16_free)(void *);
297
298 void *(*pcre16_stack_malloc)(size_t);
299
300 void (*pcre16_stack_free)(void *);
301
302 int (*pcre16_callout)(pcre16_callout_block *);
303
304
305 PCRE 16-BIT API 16-BIT-ONLY FUNCTION
306
307 int pcre16_utf16_to_host_byte_order(PCRE_UCHAR16 *output,
308 PCRE_SPTR16 input, int length, int *byte_order,
309 int keep_boms);
310
311
312 THE PCRE 16-BIT LIBRARY
313
314 Starting with release 8.30, it is possible to compile a PCRE library
315 that supports 16-bit character strings, including UTF-16 strings, as
316 well as or instead of the original 8-bit library. The majority of the
317 work to make this possible was done by Zoltan Herczeg. The two
318 libraries contain identical sets of functions, used in exactly the same
319 way. Only the names of the functions and the data types of their argu-
320 ments and results are different. To avoid over-complication and reduce
321 the documentation maintenance load, most of the PCRE documentation
322 describes the 8-bit library, with only occasional references to the
323 16-bit library. This page describes what is different when you use the
324 16-bit library.
325
326 WARNING: A single application can be linked with both libraries, but
327 you must take care when processing any particular pattern to use func-
328 tions from just one library. For example, if you want to study a pat-
329 tern that was compiled with pcre16_compile(), you must do so with
330 pcre16_study(), not pcre_study(), and you must free the study data with
331 pcre16_free_study().
332
333
334 THE HEADER FILE
335
336 There is only one header file, pcre.h. It contains prototypes for all
337 the functions in all libraries, as well as definitions of flags, struc-
338 tures, error codes, etc.
339
340
341 THE LIBRARY NAME
342
343 In Unix-like systems, the 16-bit library is called libpcre16, and can
344 normally be accesss by adding -lpcre16 to the command for linking an
345 application that uses PCRE.
346
347
348 STRING TYPES
349
350 In the 8-bit library, strings are passed to PCRE library functions as
351 vectors of bytes with the C type "char *". In the 16-bit library,
352 strings are passed as vectors of unsigned 16-bit quantities. The macro
353 PCRE_UCHAR16 specifies an appropriate data type, and PCRE_SPTR16 is
354 defined as "const PCRE_UCHAR16 *". In very many environments, "short
355 int" is a 16-bit data type. When PCRE is built, it defines PCRE_UCHAR16
356 as "unsigned short int", but checks that it really is a 16-bit data
357 type. If it is not, the build fails with an error message telling the
358 maintainer to modify the definition appropriately.
359
360
361 STRUCTURE TYPES
362
363 The types of the opaque structures that are used for compiled 16-bit
364 patterns and JIT stacks are pcre16 and pcre16_jit_stack respectively.
365 The type of the user-accessible structure that is returned by
366 pcre16_study() is pcre16_extra, and the type of the structure that is
367 used for passing data to a callout function is pcre16_callout_block.
368 These structures contain the same fields, with the same names, as their
369 8-bit counterparts. The only difference is that pointers to character
370 strings are 16-bit instead of 8-bit types.
371
372
373 16-BIT FUNCTIONS
374
375 For every function in the 8-bit library there is a corresponding func-
376 tion in the 16-bit library with a name that starts with pcre16_ instead
377 of pcre_. The prototypes are listed above. In addition, there is one
378 extra function, pcre16_utf16_to_host_byte_order(). This is a utility
379 function that converts a UTF-16 character string to host byte order if
380 necessary. The other 16-bit functions expect the strings they are
381 passed to be in host byte order.
382
383 The input and output arguments of pcre16_utf16_to_host_byte_order() may
384 point to the same address, that is, conversion in place is supported.
385 The output buffer must be at least as long as the input.
386
387 The length argument specifies the number of 16-bit data units in the
388 input string; a negative value specifies a zero-terminated string.
389
390 If byte_order is NULL, it is assumed that the string starts off in host
391 byte order. This may be changed by byte-order marks (BOMs) anywhere in
392 the string (commonly as the first character).
393
394 If byte_order is not NULL, a non-zero value of the integer to which it
395 points means that the input starts off in host byte order, otherwise
396 the opposite order is assumed. Again, BOMs in the string can change
397 this. The final byte order is passed back at the end of processing.
398
399 If keep_boms is not zero, byte-order mark characters (0xfeff) are
400 copied into the output string. Otherwise they are discarded.
401
402 The result of the function is the number of 16-bit units placed into
403 the output buffer, including the zero terminator if the string was
404 zero-terminated.
405
406
407 SUBJECT STRING OFFSETS
408
409 The lengths and starting offsets of subject strings must be specified
410 in 16-bit data units, and the offsets within subject strings that are
411 returned by the matching functions are in also 16-bit units rather than
412 bytes.
413
414
415 NAMED SUBPATTERNS
416
417 The name-to-number translation table that is maintained for named sub-
418 patterns uses 16-bit characters. The pcre16_get_stringtable_entries()
419 function returns the length of each entry in the table as the number of
420 16-bit data units.
421
422
423 OPTION NAMES
424
425 There are two new general option names, PCRE_UTF16 and
426 PCRE_NO_UTF16_CHECK, which correspond to PCRE_UTF8 and
427 PCRE_NO_UTF8_CHECK in the 8-bit library. In fact, these new options
428 define the same bits in the options word. There is a discussion about
429 the validity of UTF-16 strings in the pcreunicode page.
430
431 For the pcre16_config() function there is an option PCRE_CONFIG_UTF16
432 that returns 1 if UTF-16 support is configured, otherwise 0. If this
433 option is given to pcre_config() or pcre32_config(), or if the
434 PCRE_CONFIG_UTF8 or PCRE_CONFIG_UTF32 option is given to pcre16_con-
435 fig(), the result is the PCRE_ERROR_BADOPTION error.
436
437
438 CHARACTER CODES
439
440 In 16-bit mode, when PCRE_UTF16 is not set, character values are
441 treated in the same way as in 8-bit, non UTF-8 mode, except, of course,
442 that they can range from 0 to 0xffff instead of 0 to 0xff. Character
443 types for characters less than 0xff can therefore be influenced by the
444 locale in the same way as before. Characters greater than 0xff have
445 only one case, and no "type" (such as letter or digit).
446
447 In UTF-16 mode, the character code is Unicode, in the range 0 to
448 0x10ffff, with the exception of values in the range 0xd800 to 0xdfff
449 because those are "surrogate" values that are used in pairs to encode
450 values greater than 0xffff.
451
452 A UTF-16 string can indicate its endianness by special code knows as a
453 byte-order mark (BOM). The PCRE functions do not handle this, expecting
454 strings to be in host byte order. A utility function called
455 pcre16_utf16_to_host_byte_order() is provided to help with this (see
456 above).
457
458
459 ERROR NAMES
460
461 The errors PCRE_ERROR_BADUTF16_OFFSET and PCRE_ERROR_SHORTUTF16 corre-
462 spond to their 8-bit counterparts. The error PCRE_ERROR_BADMODE is
463 given when a compiled pattern is passed to a function that processes
464 patterns in the other mode, for example, if a pattern compiled with
465 pcre_compile() is passed to pcre16_exec().
466
467 There are new error codes whose names begin with PCRE_UTF16_ERR for
468 invalid UTF-16 strings, corresponding to the PCRE_UTF8_ERR codes for
469 UTF-8 strings that are described in the section entitled "Reason codes
470 for invalid UTF-8 strings" in the main pcreapi page. The UTF-16 errors
471 are:
472
473 PCRE_UTF16_ERR1 Missing low surrogate at end of string
474 PCRE_UTF16_ERR2 Invalid low surrogate follows high surrogate
475 PCRE_UTF16_ERR3 Isolated low surrogate
476 PCRE_UTF16_ERR4 Non-character
477
478
479 ERROR TEXTS
480
481 If there is an error while compiling a pattern, the error text that is
482 passed back by pcre16_compile() or pcre16_compile2() is still an 8-bit
483 character string, zero-terminated.
484
485
486 CALLOUTS
487
488 The subject and mark fields in the callout block that is passed to a
489 callout function point to 16-bit vectors.
490
491
492 TESTING
493
494 The pcretest program continues to operate with 8-bit input and output
495 files, but it can be used for testing the 16-bit library. If it is run
496 with the command line option -16, patterns and subject strings are con-
497 verted from 8-bit to 16-bit before being passed to PCRE, and the 16-bit
498 library functions are used instead of the 8-bit ones. Returned 16-bit
499 strings are converted to 8-bit for output. If both the 8-bit and the
500 32-bit libraries were not compiled, pcretest defaults to 16-bit and the
501 -16 option is ignored.
502
503 When PCRE is being built, the RunTest script that is called by "make
504 check" uses the pcretest -C option to discover which of the 8-bit,
505 16-bit and 32-bit libraries has been built, and runs the tests appro-
506 priately.
507
508
509 NOT SUPPORTED IN 16-BIT MODE
510
511 Not all the features of the 8-bit library are available with the 16-bit
512 library. The C++ and POSIX wrapper functions support only the 8-bit
513 library, and the pcregrep program is at present 8-bit only.
514
515
516 AUTHOR
517
518 Philip Hazel
519 University Computing Service
520 Cambridge CB2 3QH, England.
521
522
523 REVISION
524
525 Last updated: 12 May 2013
526 Copyright (c) 1997-2013 University of Cambridge.
527 ------------------------------------------------------------------------------
528
529
530 PCRE(3) Library Functions Manual PCRE(3)
531
532
533
534 NAME
535 PCRE - Perl-compatible regular expressions
536
537 #include <pcre.h>
538
539
540 PCRE 32-BIT API BASIC FUNCTIONS
541
542 pcre32 *pcre32_compile(PCRE_SPTR32 pattern, int options,
543 const char **errptr, int *erroffset,
544 const unsigned char *tableptr);
545
546 pcre32 *pcre32_compile2(PCRE_SPTR32 pattern, int options,
547 int *errorcodeptr,
548 const unsigned char *tableptr);
549
550 pcre32_extra *pcre32_study(const pcre32 *code, int options,
551 const char **errptr);
552
553 void pcre32_free_study(pcre32_extra *extra);
554
555 int pcre32_exec(const pcre32 *code, const pcre32_extra *extra,
556 PCRE_SPTR32 subject, int length, int startoffset,
557 int options, int *ovector, int ovecsize);
558
559 int pcre32_dfa_exec(const pcre32 *code, const pcre32_extra *extra,
560 PCRE_SPTR32 subject, int length, int startoffset,
561 int options, int *ovector, int ovecsize,
562 int *workspace, int wscount);
563
564
565 PCRE 32-BIT API STRING EXTRACTION FUNCTIONS
566
567 int pcre32_copy_named_substring(const pcre32 *code,
568 PCRE_SPTR32 subject, int *ovector,
569 int stringcount, PCRE_SPTR32 stringname,
570 PCRE_UCHAR32 *buffer, int buffersize);
571
572 int pcre32_copy_substring(PCRE_SPTR32 subject, int *ovector,
573 int stringcount, int stringnumber, PCRE_UCHAR32 *buffer,
574 int buffersize);
575
576 int pcre32_get_named_substring(const pcre32 *code,
577 PCRE_SPTR32 subject, int *ovector,
578 int stringcount, PCRE_SPTR32 stringname,
579 PCRE_SPTR32 *stringptr);
580
581 int pcre32_get_stringnumber(const pcre32 *code,
582 PCRE_SPTR32 name);
583
584 int pcre32_get_stringtable_entries(const pcre32 *code,
585 PCRE_SPTR32 name, PCRE_UCHAR32 **first, PCRE_UCHAR32 **last);
586
587 int pcre32_get_substring(PCRE_SPTR32 subject, int *ovector,
588 int stringcount, int stringnumber,
589 PCRE_SPTR32 *stringptr);
590
591 int pcre32_get_substring_list(PCRE_SPTR32 subject,
592 int *ovector, int stringcount, PCRE_SPTR32 **listptr);
593
594 void pcre32_free_substring(PCRE_SPTR32 stringptr);
595
596 void pcre32_free_substring_list(PCRE_SPTR32 *stringptr);
597
598
599 PCRE 32-BIT API AUXILIARY FUNCTIONS
600
601 pcre32_jit_stack *pcre32_jit_stack_alloc(int startsize, int maxsize);
602
603 void pcre32_jit_stack_free(pcre32_jit_stack *stack);
604
605 void pcre32_assign_jit_stack(pcre32_extra *extra,
606 pcre32_jit_callback callback, void *data);
607
608 const unsigned char *pcre32_maketables(void);
609
610 int pcre32_fullinfo(const pcre32 *code, const pcre32_extra *extra,
611 int what, void *where);
612
613 int pcre32_refcount(pcre32 *code, int adjust);
614
615 int pcre32_config(int what, void *where);
616
617 const char *pcre32_version(void);
618
619 int pcre32_pattern_to_host_byte_order(pcre32 *code,
620 pcre32_extra *extra, const unsigned char *tables);
621
622
623 PCRE 32-BIT API INDIRECTED FUNCTIONS
624
625 void *(*pcre32_malloc)(size_t);
626
627 void (*pcre32_free)(void *);
628
629 void *(*pcre32_stack_malloc)(size_t);
630
631 void (*pcre32_stack_free)(void *);
632
633 int (*pcre32_callout)(pcre32_callout_block *);
634
635
636 PCRE 32-BIT API 32-BIT-ONLY FUNCTION
637
638 int pcre32_utf32_to_host_byte_order(PCRE_UCHAR32 *output,
639 PCRE_SPTR32 input, int length, int *byte_order,
640 int keep_boms);
641
642
643 THE PCRE 32-BIT LIBRARY
644
645 Starting with release 8.32, it is possible to compile a PCRE library
646 that supports 32-bit character strings, including UTF-32 strings, as
647 well as or instead of the original 8-bit library. This work was done by
648 Christian Persch, based on the work done by Zoltan Herczeg for the
649 16-bit library. All three libraries contain identical sets of func-
650 tions, used in exactly the same way. Only the names of the functions
651 and the data types of their arguments and results are different. To
652 avoid over-complication and reduce the documentation maintenance load,
653 most of the PCRE documentation describes the 8-bit library, with only
654 occasional references to the 16-bit and 32-bit libraries. This page
655 describes what is different when you use the 32-bit library.
656
657 WARNING: A single application can be linked with all or any of the
658 three libraries, but you must take care when processing any particular
659 pattern to use functions from just one library. For example, if you
660 want to study a pattern that was compiled with pcre32_compile(), you
661 must do so with pcre32_study(), not pcre_study(), and you must free the
662 study data with pcre32_free_study().
663
664
665 THE HEADER FILE
666
667 There is only one header file, pcre.h. It contains prototypes for all
668 the functions in all libraries, as well as definitions of flags, struc-
669 tures, error codes, etc.
670
671
672 THE LIBRARY NAME
673
674 In Unix-like systems, the 32-bit library is called libpcre32, and can
675 normally be accesss by adding -lpcre32 to the command for linking an
676 application that uses PCRE.
677
678
679 STRING TYPES
680
681 In the 8-bit library, strings are passed to PCRE library functions as
682 vectors of bytes with the C type "char *". In the 32-bit library,
683 strings are passed as vectors of unsigned 32-bit quantities. The macro
684 PCRE_UCHAR32 specifies an appropriate data type, and PCRE_SPTR32 is
685 defined as "const PCRE_UCHAR32 *". In very many environments, "unsigned
686 int" is a 32-bit data type. When PCRE is built, it defines PCRE_UCHAR32
687 as "unsigned int", but checks that it really is a 32-bit data type. If
688 it is not, the build fails with an error message telling the maintainer
689 to modify the definition appropriately.
690
691
692 STRUCTURE TYPES
693
694 The types of the opaque structures that are used for compiled 32-bit
695 patterns and JIT stacks are pcre32 and pcre32_jit_stack respectively.
696 The type of the user-accessible structure that is returned by
697 pcre32_study() is pcre32_extra, and the type of the structure that is
698 used for passing data to a callout function is pcre32_callout_block.
699 These structures contain the same fields, with the same names, as their
700 8-bit counterparts. The only difference is that pointers to character
701 strings are 32-bit instead of 8-bit types.
702
703
704 32-BIT FUNCTIONS
705
706 For every function in the 8-bit library there is a corresponding func-
707 tion in the 32-bit library with a name that starts with pcre32_ instead
708 of pcre_. The prototypes are listed above. In addition, there is one
709 extra function, pcre32_utf32_to_host_byte_order(). This is a utility
710 function that converts a UTF-32 character string to host byte order if
711 necessary. The other 32-bit functions expect the strings they are
712 passed to be in host byte order.
713
714 The input and output arguments of pcre32_utf32_to_host_byte_order() may
715 point to the same address, that is, conversion in place is supported.
716 The output buffer must be at least as long as the input.
717
718 The length argument specifies the number of 32-bit data units in the
719 input string; a negative value specifies a zero-terminated string.
720
721 If byte_order is NULL, it is assumed that the string starts off in host
722 byte order. This may be changed by byte-order marks (BOMs) anywhere in
723 the string (commonly as the first character).
724
725 If byte_order is not NULL, a non-zero value of the integer to which it
726 points means that the input starts off in host byte order, otherwise
727 the opposite order is assumed. Again, BOMs in the string can change
728 this. The final byte order is passed back at the end of processing.
729
730 If keep_boms is not zero, byte-order mark characters (0xfeff) are
731 copied into the output string. Otherwise they are discarded.
732
733 The result of the function is the number of 32-bit units placed into
734 the output buffer, including the zero terminator if the string was
735 zero-terminated.
736
737
738 SUBJECT STRING OFFSETS
739
740 The lengths and starting offsets of subject strings must be specified
741 in 32-bit data units, and the offsets within subject strings that are
742 returned by the matching functions are in also 32-bit units rather than
743 bytes.
744
745
746 NAMED SUBPATTERNS
747
748 The name-to-number translation table that is maintained for named sub-
749 patterns uses 32-bit characters. The pcre32_get_stringtable_entries()
750 function returns the length of each entry in the table as the number of
751 32-bit data units.
752
753
754 OPTION NAMES
755
756 There are two new general option names, PCRE_UTF32 and
757 PCRE_NO_UTF32_CHECK, which correspond to PCRE_UTF8 and
758 PCRE_NO_UTF8_CHECK in the 8-bit library. In fact, these new options
759 define the same bits in the options word. There is a discussion about
760 the validity of UTF-32 strings in the pcreunicode page.
761
762 For the pcre32_config() function there is an option PCRE_CONFIG_UTF32
763 that returns 1 if UTF-32 support is configured, otherwise 0. If this
764 option is given to pcre_config() or pcre16_config(), or if the
765 PCRE_CONFIG_UTF8 or PCRE_CONFIG_UTF16 option is given to pcre32_con-
766 fig(), the result is the PCRE_ERROR_BADOPTION error.
767
768
769 CHARACTER CODES
770
771 In 32-bit mode, when PCRE_UTF32 is not set, character values are
772 treated in the same way as in 8-bit, non UTF-8 mode, except, of course,
773 that they can range from 0 to 0x7fffffff instead of 0 to 0xff. Charac-
774 ter types for characters less than 0xff can therefore be influenced by
775 the locale in the same way as before. Characters greater than 0xff
776 have only one case, and no "type" (such as letter or digit).
777
778 In UTF-32 mode, the character code is Unicode, in the range 0 to
779 0x10ffff, with the exception of values in the range 0xd800 to 0xdfff
780 because those are "surrogate" values that are ill-formed in UTF-32.
781
782 A UTF-32 string can indicate its endianness by special code knows as a
783 byte-order mark (BOM). The PCRE functions do not handle this, expecting
784 strings to be in host byte order. A utility function called
785 pcre32_utf32_to_host_byte_order() is provided to help with this (see
786 above).
787
788
789 ERROR NAMES
790
791 The error PCRE_ERROR_BADUTF32 corresponds to its 8-bit counterpart.
792 The error PCRE_ERROR_BADMODE is given when a compiled pattern is passed
793 to a function that processes patterns in the other mode, for example,
794 if a pattern compiled with pcre_compile() is passed to pcre32_exec().
795
796 There are new error codes whose names begin with PCRE_UTF32_ERR for
797 invalid UTF-32 strings, corresponding to the PCRE_UTF8_ERR codes for
798 UTF-8 strings that are described in the section entitled "Reason codes
799 for invalid UTF-8 strings" in the main pcreapi page. The UTF-32 errors
800 are:
801
802 PCRE_UTF32_ERR1 Surrogate character (range from 0xd800 to 0xdfff)
803 PCRE_UTF32_ERR2 Non-character
804 PCRE_UTF32_ERR3 Character > 0x10ffff
805
806
807 ERROR TEXTS
808
809 If there is an error while compiling a pattern, the error text that is
810 passed back by pcre32_compile() or pcre32_compile2() is still an 8-bit
811 character string, zero-terminated.
812
813
814 CALLOUTS
815
816 The subject and mark fields in the callout block that is passed to a
817 callout function point to 32-bit vectors.
818
819
820 TESTING
821
822 The pcretest program continues to operate with 8-bit input and output
823 files, but it can be used for testing the 32-bit library. If it is run
824 with the command line option -32, patterns and subject strings are con-
825 verted from 8-bit to 32-bit before being passed to PCRE, and the 32-bit
826 library functions are used instead of the 8-bit ones. Returned 32-bit
827 strings are converted to 8-bit for output. If both the 8-bit and the
828 16-bit libraries were not compiled, pcretest defaults to 32-bit and the
829 -32 option is ignored.
830
831 When PCRE is being built, the RunTest script that is called by "make
832 check" uses the pcretest -C option to discover which of the 8-bit,
833 16-bit and 32-bit libraries has been built, and runs the tests appro-
834 priately.
835
836
837 NOT SUPPORTED IN 32-BIT MODE
838
839 Not all the features of the 8-bit library are available with the 32-bit
840 library. The C++ and POSIX wrapper functions support only the 8-bit
841 library, and the pcregrep program is at present 8-bit only.
842
843
844 AUTHOR
845
846 Philip Hazel
847 University Computing Service
848 Cambridge CB2 3QH, England.
849
850
851 REVISION
852
853 Last updated: 12 May 2013
854 Copyright (c) 1997-2013 University of Cambridge.
855 ------------------------------------------------------------------------------
856
857
858 PCREBUILD(3) Library Functions Manual PCREBUILD(3)
859
860
861
862 NAME
863 PCRE - Perl-compatible regular expressions
864
865 BUILDING PCRE
866
867 PCRE is distributed with a configure script that can be used to build
868 the library in Unix-like environments using the applications known as
869 Autotools. Also in the distribution are files to support building
870 using CMake instead of configure. The text file README contains general
871 information about building with Autotools (some of which is repeated
872 below), and also has some comments about building on various operating
873 systems. There is a lot more information about building PCRE without
874 using Autotools (including information about using CMake and building
875 "by hand") in the text file called NON-AUTOTOOLS-BUILD. You should
876 consult this file as well as the README file if you are building in a
877 non-Unix-like environment.
878
879
880 PCRE BUILD-TIME OPTIONS
881
882 The rest of this document describes the optional features of PCRE that
883 can be selected when the library is compiled. It assumes use of the
884 configure script, where the optional features are selected or dese-
885 lected by providing options to configure before running the make com-
886 mand. However, the same options can be selected in both Unix-like and
887 non-Unix-like environments using the GUI facility of cmake-gui if you
888 are using CMake instead of configure to build PCRE.
889
890 If you are not using Autotools or CMake, option selection can be done
891 by editing the config.h file, or by passing parameter settings to the
892 compiler, as described in NON-AUTOTOOLS-BUILD.
893
894 The complete list of options for configure (which includes the standard
895 ones such as the selection of the installation directory) can be
896 obtained by running
897
898 ./configure --help
899
900 The following sections include descriptions of options whose names
901 begin with --enable or --disable. These settings specify changes to the
902 defaults for the configure command. Because of the way that configure
903 works, --enable and --disable always come in pairs, so the complemen-
904 tary option always exists as well, but as it specifies the default, it
905 is not described.
906
907
908 BUILDING 8-BIT, 16-BIT AND 32-BIT LIBRARIES
909
910 By default, a library called libpcre is built, containing functions
911 that take string arguments contained in vectors of bytes, either as
912 single-byte characters, or interpreted as UTF-8 strings. You can also
913 build a separate library, called libpcre16, in which strings are con-
914 tained in vectors of 16-bit data units and interpreted either as sin-
915 gle-unit characters or UTF-16 strings, by adding
916
917 --enable-pcre16
918
919 to the configure command. You can also build yet another separate
920 library, called libpcre32, in which strings are contained in vectors of
921 32-bit data units and interpreted either as single-unit characters or
922 UTF-32 strings, by adding
923
924 --enable-pcre32
925
926 to the configure command. If you do not want the 8-bit library, add
927
928 --disable-pcre8
929
930 as well. At least one of the three libraries must be built. Note that
931 the C++ and POSIX wrappers are for the 8-bit library only, and that
932 pcregrep is an 8-bit program. None of these are built if you select
933 only the 16-bit or 32-bit libraries.
934
935
936 BUILDING SHARED AND STATIC LIBRARIES
937
938 The Autotools PCRE building process uses libtool to build both shared
939 and static libraries by default. You can suppress one of these by
940 adding one of
941
942 --disable-shared
943 --disable-static
944
945 to the configure command, as required.
946
947
948 C++ SUPPORT
949
950 By default, if the 8-bit library is being built, the configure script
951 will search for a C++ compiler and C++ header files. If it finds them,
952 it automatically builds the C++ wrapper library (which supports only
953 8-bit strings). You can disable this by adding
954
955 --disable-cpp
956
957 to the configure command.
958
959
960 UTF-8, UTF-16 AND UTF-32 SUPPORT
961
962 To build PCRE with support for UTF Unicode character strings, add
963
964 --enable-utf
965
966 to the configure command. This setting applies to all three libraries,
967 adding support for UTF-8 to the 8-bit library, support for UTF-16 to
968 the 16-bit library, and support for UTF-32 to the to the 32-bit
969 library. There are no separate options for enabling UTF-8, UTF-16 and
970 UTF-32 independently because that would allow ridiculous settings such
971 as requesting UTF-16 support while building only the 8-bit library. It
972 is not possible to build one library with UTF support and another with-
973 out in the same configuration. (For backwards compatibility, --enable-
974 utf8 is a synonym of --enable-utf.)
975
976 Of itself, this setting does not make PCRE treat strings as UTF-8,
977 UTF-16 or UTF-32. As well as compiling PCRE with this option, you also
978 have have to set the PCRE_UTF8, PCRE_UTF16 or PCRE_UTF32 option (as
979 appropriate) when you call one of the pattern compiling functions.
980
981 If you set --enable-utf when compiling in an EBCDIC environment, PCRE
982 expects its input to be either ASCII or UTF-8 (depending on the run-
983 time option). It is not possible to support both EBCDIC and UTF-8 codes
984 in the same version of the library. Consequently, --enable-utf and
985 --enable-ebcdic are mutually exclusive.
986
987
988 UNICODE CHARACTER PROPERTY SUPPORT
989
990 UTF support allows the libraries to process character codepoints up to
991 0x10ffff in the strings that they handle. On its own, however, it does
992 not provide any facilities for accessing the properties of such charac-
993 ters. If you want to be able to use the pattern escapes \P, \p, and \X,
994 which refer to Unicode character properties, you must add
995
996 --enable-unicode-properties
997
998 to the configure command. This implies UTF support, even if you have
999 not explicitly requested it.
1000
1001 Including Unicode property support adds around 30K of tables to the
1002 PCRE library. Only the general category properties such as Lu and Nd
1003 are supported. Details are given in the pcrepattern documentation.
1004
1005
1006 JUST-IN-TIME COMPILER SUPPORT
1007
1008 Just-in-time compiler support is included in the build by specifying
1009
1010 --enable-jit
1011
1012 This support is available only for certain hardware architectures. If
1013 this option is set for an unsupported architecture, a compile time
1014 error occurs. See the pcrejit documentation for a discussion of JIT
1015 usage. When JIT support is enabled, pcregrep automatically makes use of
1016 it, unless you add
1017
1018 --disable-pcregrep-jit
1019
1020 to the "configure" command.
1021
1022
1023 CODE VALUE OF NEWLINE
1024
1025 By default, PCRE interprets the linefeed (LF) character as indicating
1026 the end of a line. This is the normal newline character on Unix-like
1027 systems. You can compile PCRE to use carriage return (CR) instead, by
1028 adding
1029
1030 --enable-newline-is-cr
1031
1032 to the configure command. There is also a --enable-newline-is-lf
1033 option, which explicitly specifies linefeed as the newline character.
1034
1035 Alternatively, you can specify that line endings are to be indicated by
1036 the two character sequence CRLF. If you want this, add
1037
1038 --enable-newline-is-crlf
1039
1040 to the configure command. There is a fourth option, specified by
1041
1042 --enable-newline-is-anycrlf
1043
1044 which causes PCRE to recognize any of the three sequences CR, LF, or
1045 CRLF as indicating a line ending. Finally, a fifth option, specified by
1046
1047 --enable-newline-is-any
1048
1049 causes PCRE to recognize any Unicode newline sequence.
1050
1051 Whatever line ending convention is selected when PCRE is built can be
1052 overridden when the library functions are called. At build time it is
1053 conventional to use the standard for your operating system.
1054
1055
1056 WHAT \R MATCHES
1057
1058 By default, the sequence \R in a pattern matches any Unicode newline
1059 sequence, whatever has been selected as the line ending sequence. If
1060 you specify
1061
1062 --enable-bsr-anycrlf
1063
1064 the default is changed so that \R matches only CR, LF, or CRLF. What-
1065 ever is selected when PCRE is built can be overridden when the library
1066 functions are called.
1067
1068
1069 POSIX MALLOC USAGE
1070
1071 When the 8-bit library is called through the POSIX interface (see the
1072 pcreposix documentation), additional working storage is required for
1073 holding the pointers to capturing substrings, because PCRE requires
1074 three integers per substring, whereas the POSIX interface provides only
1075 two. If the number of expected substrings is small, the wrapper func-
1076 tion uses space on the stack, because this is faster than using mal-
1077 loc() for each call. The default threshold above which the stack is no
1078 longer used is 10; it can be changed by adding a setting such as
1079
1080 --with-posix-malloc-threshold=20
1081
1082 to the configure command.
1083
1084
1085 HANDLING VERY LARGE PATTERNS
1086
1087 Within a compiled pattern, offset values are used to point from one
1088 part to another (for example, from an opening parenthesis to an alter-
1089 nation metacharacter). By default, in the 8-bit and 16-bit libraries,
1090 two-byte values are used for these offsets, leading to a maximum size
1091 for a compiled pattern of around 64K. This is sufficient to handle all
1092 but the most gigantic patterns. Nevertheless, some people do want to
1093 process truly enormous patterns, so it is possible to compile PCRE to
1094 use three-byte or four-byte offsets by adding a setting such as
1095
1096 --with-link-size=3
1097
1098 to the configure command. The value given must be 2, 3, or 4. For the
1099 16-bit library, a value of 3 is rounded up to 4. In these libraries,
1100 using longer offsets slows down the operation of PCRE because it has to
1101 load additional data when handling them. For the 32-bit library the
1102 value is always 4 and cannot be overridden; the value of --with-link-
1103 size is ignored.
1104
1105
1106 AVOIDING EXCESSIVE STACK USAGE
1107
1108 When matching with the pcre_exec() function, PCRE implements backtrack-
1109 ing by making recursive calls to an internal function called match().
1110 In environments where the size of the stack is limited, this can se-
1111 verely limit PCRE's operation. (The Unix environment does not usually
1112 suffer from this problem, but it may sometimes be necessary to increase
1113 the maximum stack size. There is a discussion in the pcrestack docu-
1114 mentation.) An alternative approach to recursion that uses memory from
1115 the heap to remember data, instead of using recursive function calls,
1116 has been implemented to work round the problem of limited stack size.
1117 If you want to build a version of PCRE that works this way, add
1118
1119 --disable-stack-for-recursion
1120
1121 to the configure command. With this configuration, PCRE will use the
1122 pcre_stack_malloc and pcre_stack_free variables to call memory manage-
1123 ment functions. By default these point to malloc() and free(), but you
1124 can replace the pointers so that your own functions are used instead.
1125
1126 Separate functions are provided rather than using pcre_malloc and
1127 pcre_free because the usage is very predictable: the block sizes
1128 requested are always the same, and the blocks are always freed in
1129 reverse order. A calling program might be able to implement optimized
1130 functions that perform better than malloc() and free(). PCRE runs
1131 noticeably more slowly when built in this way. This option affects only
1132 the pcre_exec() function; it is not relevant for pcre_dfa_exec().
1133
1134
1135 LIMITING PCRE RESOURCE USAGE
1136
1137 Internally, PCRE has a function called match(), which it calls repeat-
1138 edly (sometimes recursively) when matching a pattern with the
1139 pcre_exec() function. By controlling the maximum number of times this
1140 function may be called during a single matching operation, a limit can
1141 be placed on the resources used by a single call to pcre_exec(). The
1142 limit can be changed at run time, as described in the pcreapi documen-
1143 tation. The default is 10 million, but this can be changed by adding a
1144 setting such as
1145
1146 --with-match-limit=500000
1147
1148 to the configure command. This setting has no effect on the
1149 pcre_dfa_exec() matching function.
1150
1151 In some environments it is desirable to limit the depth of recursive
1152 calls of match() more strictly than the total number of calls, in order
1153 to restrict the maximum amount of stack (or heap, if --disable-stack-
1154 for-recursion is specified) that is used. A second limit controls this;
1155 it defaults to the value that is set for --with-match-limit, which
1156 imposes no additional constraints. However, you can set a lower limit
1157 by adding, for example,
1158
1159 --with-match-limit-recursion=10000
1160
1161 to the configure command. This value can also be overridden at run
1162 time.
1163
1164
1165 CREATING CHARACTER TABLES AT BUILD TIME
1166
1167 PCRE uses fixed tables for processing characters whose code values are
1168 less than 256. By default, PCRE is built with a set of tables that are
1169 distributed in the file pcre_chartables.c.dist. These tables are for
1170 ASCII codes only. If you add
1171
1172 --enable-rebuild-chartables
1173
1174 to the configure command, the distributed tables are no longer used.
1175 Instead, a program called dftables is compiled and run. This outputs
1176 the source for new set of tables, created in the default locale of your
1177 C run-time system. (This method of replacing the tables does not work
1178 if you are cross compiling, because dftables is run on the local host.
1179 If you need to create alternative tables when cross compiling, you will
1180 have to do so "by hand".)
1181
1182
1183 USING EBCDIC CODE
1184
1185 PCRE assumes by default that it will run in an environment where the
1186 character code is ASCII (or Unicode, which is a superset of ASCII).
1187 This is the case for most computer operating systems. PCRE can, how-
1188 ever, be compiled to run in an EBCDIC environment by adding
1189
1190 --enable-ebcdic
1191
1192 to the configure command. This setting implies --enable-rebuild-charta-
1193 bles. You should only use it if you know that you are in an EBCDIC
1194 environment (for example, an IBM mainframe operating system). The
1195 --enable-ebcdic option is incompatible with --enable-utf.
1196
1197 The EBCDIC character that corresponds to an ASCII LF is assumed to have
1198 the value 0x15 by default. However, in some EBCDIC environments, 0x25
1199 is used. In such an environment you should use
1200
1201 --enable-ebcdic-nl25
1202
1203 as well as, or instead of, --enable-ebcdic. The EBCDIC character for CR
1204 has the same value as in ASCII, namely, 0x0d. Whichever of 0x15 and
1205 0x25 is not chosen as LF is made to correspond to the Unicode NEL char-
1206 acter (which, in Unicode, is 0x85).
1207
1208 The options that select newline behaviour, such as --enable-newline-is-
1209 cr, and equivalent run-time options, refer to these character values in
1210 an EBCDIC environment.
1211
1212
1213 PCREGREP OPTIONS FOR COMPRESSED FILE SUPPORT
1214
1215 By default, pcregrep reads all files as plain text. You can build it so
1216 that it recognizes files whose names end in .gz or .bz2, and reads them
1217 with libz or libbz2, respectively, by adding one or both of
1218
1219 --enable-pcregrep-libz
1220 --enable-pcregrep-libbz2
1221
1222 to the configure command. These options naturally require that the rel-
1223 evant libraries are installed on your system. Configuration will fail
1224 if they are not.
1225
1226
1227 PCREGREP BUFFER SIZE
1228
1229 pcregrep uses an internal buffer to hold a "window" on the file it is
1230 scanning, in order to be able to output "before" and "after" lines when
1231 it finds a match. The size of the buffer is controlled by a parameter
1232 whose default value is 20K. The buffer itself is three times this size,
1233 but because of the way it is used for holding "before" lines, the long-
1234 est line that is guaranteed to be processable is the parameter size.
1235 You can change the default parameter value by adding, for example,
1236
1237 --with-pcregrep-bufsize=50K
1238
1239 to the configure command. The caller of pcregrep can, however, override
1240 this value by specifying a run-time option.
1241
1242
1243 PCRETEST OPTION FOR LIBREADLINE SUPPORT
1244
1245 If you add
1246
1247 --enable-pcretest-libreadline
1248
1249 to the configure command, pcretest is linked with the libreadline
1250 library, and when its input is from a terminal, it reads it using the
1251 readline() function. This provides line-editing and history facilities.
1252 Note that libreadline is GPL-licensed, so if you distribute a binary of
1253 pcretest linked in this way, there may be licensing issues.
1254
1255 Setting this option causes the -lreadline option to be added to the
1256 pcretest build. In many operating environments with a sytem-installed
1257 libreadline this is sufficient. However, in some environments (e.g. if
1258 an unmodified distribution version of readline is in use), some extra
1259 configuration may be necessary. The INSTALL file for libreadline says
1260 this:
1261
1262 "Readline uses the termcap functions, but does not link with the
1263 termcap or curses library itself, allowing applications which link
1264 with readline the to choose an appropriate library."
1265
1266 If your environment has not been set up so that an appropriate library
1267 is automatically included, you may need to add something like
1268
1269 LIBS="-ncurses"
1270
1271 immediately before the configure command.
1272
1273
1274 DEBUGGING WITH VALGRIND SUPPORT
1275
1276 By adding the
1277
1278 --enable-valgrind
1279
1280 option to to the configure command, PCRE will use valgrind annotations
1281 to mark certain memory regions as unaddressable. This allows it to
1282 detect invalid memory accesses, and is mostly useful for debugging PCRE
1283 itself.
1284
1285
1286 CODE COVERAGE REPORTING
1287
1288 If your C compiler is gcc, you can build a version of PCRE that can
1289 generate a code coverage report for its test suite. To enable this, you
1290 must install lcov version 1.6 or above. Then specify
1291
1292 --enable-coverage
1293
1294 to the configure command and build PCRE in the usual way.
1295
1296 Note that using ccache (a caching C compiler) is incompatible with code
1297 coverage reporting. If you have configured ccache to run automatically
1298 on your system, you must set the environment variable
1299
1300 CCACHE_DISABLE=1
1301
1302 before running make to build PCRE, so that ccache is not used.
1303
1304 When --enable-coverage is used, the following addition targets are
1305 added to the Makefile:
1306
1307 make coverage
1308
1309 This creates a fresh coverage report for the PCRE test suite. It is
1310 equivalent to running "make coverage-reset", "make coverage-baseline",
1311 "make check", and then "make coverage-report".
1312
1313 make coverage-reset
1314
1315 This zeroes the coverage counters, but does nothing else.
1316
1317 make coverage-baseline
1318
1319 This captures baseline coverage information.
1320
1321 make coverage-report
1322
1323 This creates the coverage report.
1324
1325 make coverage-clean-report
1326
1327 This removes the generated coverage report without cleaning the cover-
1328 age data itself.
1329
1330 make coverage-clean-data
1331
1332 This removes the captured coverage data without removing the coverage
1333 files created at compile time (*.gcno).
1334
1335 make coverage-clean
1336
1337 This cleans all coverage data including the generated coverage report.
1338 For more information about code coverage, see the gcov and lcov docu-
1339 mentation.
1340
1341
1342 SEE ALSO
1343
1344 pcreapi(3), pcre16, pcre32, pcre_config(3).
1345
1346
1347 AUTHOR
1348
1349 Philip Hazel
1350 University Computing Service
1351 Cambridge CB2 3QH, England.
1352
1353
1354 REVISION
1355
1356 Last updated: 12 May 2013
1357 Copyright (c) 1997-2013 University of Cambridge.
1358 ------------------------------------------------------------------------------
1359
1360
1361 PCREMATCHING(3) Library Functions Manual PCREMATCHING(3)
1362
1363
1364
1365 NAME
1366 PCRE - Perl-compatible regular expressions
1367
1368 PCRE MATCHING ALGORITHMS
1369
1370 This document describes the two different algorithms that are available
1371 in PCRE for matching a compiled regular expression against a given sub-
1372 ject string. The "standard" algorithm is the one provided by the
1373 pcre_exec(), pcre16_exec() and pcre32_exec() functions. These work in
1374 the same as as Perl's matching function, and provide a Perl-compatible
1375 matching operation. The just-in-time (JIT) optimization that is
1376 described in the pcrejit documentation is compatible with these func-
1377 tions.
1378
1379 An alternative algorithm is provided by the pcre_dfa_exec(),
1380 pcre16_dfa_exec() and pcre32_dfa_exec() functions; they operate in a
1381 different way, and are not Perl-compatible. This alternative has advan-
1382 tages and disadvantages compared with the standard algorithm, and these
1383 are described below.
1384
1385 When there is only one possible way in which a given subject string can
1386 match a pattern, the two algorithms give the same answer. A difference
1387 arises, however, when there are multiple possibilities. For example, if
1388 the pattern
1389
1390 ^<.*>
1391
1392 is matched against the string
1393
1394 <something> <something else> <something further>
1395
1396 there are three possible answers. The standard algorithm finds only one
1397 of them, whereas the alternative algorithm finds all three.
1398
1399
1400 REGULAR EXPRESSIONS AS TREES
1401
1402 The set of strings that are matched by a regular expression can be rep-
1403 resented as a tree structure. An unlimited repetition in the pattern
1404 makes the tree of infinite size, but it is still a tree. Matching the
1405 pattern to a given subject string (from a given starting point) can be
1406 thought of as a search of the tree. There are two ways to search a
1407 tree: depth-first and breadth-first, and these correspond to the two
1408 matching algorithms provided by PCRE.
1409
1410
1411 THE STANDARD MATCHING ALGORITHM
1412
1413 In the terminology of Jeffrey Friedl's book "Mastering Regular Expres-
1414 sions", the standard algorithm is an "NFA algorithm". It conducts a
1415 depth-first search of the pattern tree. That is, it proceeds along a
1416 single path through the tree, checking that the subject matches what is
1417 required. When there is a mismatch, the algorithm tries any alterna-
1418 tives at the current point, and if they all fail, it backs up to the
1419 previous branch point in the tree, and tries the next alternative
1420 branch at that level. This often involves backing up (moving to the
1421 left) in the subject string as well. The order in which repetition
1422 branches are tried is controlled by the greedy or ungreedy nature of
1423 the quantifier.
1424
1425 If a leaf node is reached, a matching string has been found, and at
1426 that point the algorithm stops. Thus, if there is more than one possi-
1427 ble match, this algorithm returns the first one that it finds. Whether
1428 this is the shortest, the longest, or some intermediate length depends
1429 on the way the greedy and ungreedy repetition quantifiers are specified
1430 in the pattern.
1431
1432 Because it ends up with a single path through the tree, it is rela-
1433 tively straightforward for this algorithm to keep track of the sub-
1434 strings that are matched by portions of the pattern in parentheses.
1435 This provides support for capturing parentheses and back references.
1436
1437
1438 THE ALTERNATIVE MATCHING ALGORITHM
1439
1440 This algorithm conducts a breadth-first search of the tree. Starting
1441 from the first matching point in the subject, it scans the subject
1442 string from left to right, once, character by character, and as it does
1443 this, it remembers all the paths through the tree that represent valid
1444 matches. In Friedl's terminology, this is a kind of "DFA algorithm",
1445 though it is not implemented as a traditional finite state machine (it
1446 keeps multiple states active simultaneously).
1447
1448 Although the general principle of this matching algorithm is that it
1449 scans the subject string only once, without backtracking, there is one
1450 exception: when a lookaround assertion is encountered, the characters
1451 following or preceding the current point have to be independently
1452 inspected.
1453
1454 The scan continues until either the end of the subject is reached, or
1455 there are no more unterminated paths. At this point, terminated paths
1456 represent the different matching possibilities (if there are none, the
1457 match has failed). Thus, if there is more than one possible match,
1458 this algorithm finds all of them, and in particular, it finds the long-
1459 est. The matches are returned in decreasing order of length. There is
1460 an option to stop the algorithm after the first match (which is neces-
1461 sarily the shortest) is found.
1462
1463 Note that all the matches that are found start at the same point in the
1464 subject. If the pattern
1465
1466 cat(er(pillar)?)?
1467
1468 is matched against the string "the caterpillar catchment", the result
1469 will be the three strings "caterpillar", "cater", and "cat" that start
1470 at the fifth character of the subject. The algorithm does not automati-
1471 cally move on to find matches that start at later positions.
1472
1473 PCRE's "auto-possessification" optimization usually applies to charac-
1474 ter repeats at the end of a pattern (as well as internally). For exam-
1475 ple, the pattern "a\d+" is compiled as if it were "a\d++" because there
1476 is no point even considering the possibility of backtracking into the
1477 repeated digits. For DFA matching, this means that only one possible
1478 match is found. If you really do want multiple matches in such cases,
1479 either use an ungreedy repeat ("a\d+?") or set the PCRE_NO_AUTO_POSSESS
1480 option when compiling.
1481
1482 There are a number of features of PCRE regular expressions that are not
1483 supported by the alternative matching algorithm. They are as follows:
1484
1485 1. Because the algorithm finds all possible matches, the greedy or
1486 ungreedy nature of repetition quantifiers is not relevant. Greedy and
1487 ungreedy quantifiers are treated in exactly the same way. However, pos-
1488 sessive quantifiers can make a difference when what follows could also
1489 match what is quantified, for example in a pattern like this:
1490
1491 ^a++\w!
1492
1493 This pattern matches "aaab!" but not "aaa!", which would be matched by
1494 a non-possessive quantifier. Similarly, if an atomic group is present,
1495 it is matched as if it were a standalone pattern at the current point,
1496 and the longest match is then "locked in" for the rest of the overall
1497 pattern.
1498
1499 2. When dealing with multiple paths through the tree simultaneously, it
1500 is not straightforward to keep track of captured substrings for the
1501 different matching possibilities, and PCRE's implementation of this
1502 algorithm does not attempt to do this. This means that no captured sub-
1503 strings are available.
1504
1505 3. Because no substrings are captured, back references within the pat-
1506 tern are not supported, and cause errors if encountered.
1507
1508 4. For the same reason, conditional expressions that use a backrefer-
1509 ence as the condition or test for a specific group recursion are not
1510 supported.
1511
1512 5. Because many paths through the tree may be active, the \K escape
1513 sequence, which resets the start of the match when encountered (but may
1514 be on some paths and not on others), is not supported. It causes an
1515 error if encountered.
1516
1517 6. Callouts are supported, but the value of the capture_top field is
1518 always 1, and the value of the capture_last field is always -1.
1519
1520 7. The \C escape sequence, which (in the standard algorithm) always
1521 matches a single data unit, even in UTF-8, UTF-16 or UTF-32 modes, is
1522 not supported in these modes, because the alternative algorithm moves
1523 through the subject string one character (not data unit) at a time, for
1524 all active paths through the tree.
1525
1526 8. Except for (*FAIL), the backtracking control verbs such as (*PRUNE)
1527 are not supported. (*FAIL) is supported, and behaves like a failing
1528 negative assertion.
1529
1530
1531 ADVANTAGES OF THE ALTERNATIVE ALGORITHM
1532
1533 Using the alternative matching algorithm provides the following advan-
1534 tages:
1535
1536 1. All possible matches (at a single point in the subject) are automat-
1537 ically found, and in particular, the longest match is found. To find
1538 more than one match using the standard algorithm, you have to do kludgy
1539 things with callouts.
1540
1541 2. Because the alternative algorithm scans the subject string just
1542 once, and never needs to backtrack (except for lookbehinds), it is pos-
1543 sible to pass very long subject strings to the matching function in
1544 several pieces, checking for partial matching each time. Although it is
1545 possible to do multi-segment matching using the standard algorithm by
1546 retaining partially matched substrings, it is more complicated. The
1547 pcrepartial documentation gives details of partial matching and dis-
1548 cusses multi-segment matching.
1549
1550
1551 DISADVANTAGES OF THE ALTERNATIVE ALGORITHM
1552
1553 The alternative algorithm suffers from a number of disadvantages:
1554
1555 1. It is substantially slower than the standard algorithm. This is
1556 partly because it has to search for all possible matches, but is also
1557 because it is less susceptible to optimization.
1558
1559 2. Capturing parentheses and back references are not supported.
1560
1561 3. Although atomic groups are supported, their use does not provide the
1562 performance advantage that it does for the standard algorithm.
1563
1564
1565 AUTHOR
1566
1567 Philip Hazel
1568 University Computing Service
1569 Cambridge CB2 3QH, England.
1570
1571
1572 REVISION
1573
1574 Last updated: 12 November 2013
1575 Copyright (c) 1997-2012 University of Cambridge.
1576 ------------------------------------------------------------------------------
1577
1578
1579 PCREAPI(3) Library Functions Manual PCREAPI(3)
1580
1581
1582
1583 NAME
1584 PCRE - Perl-compatible regular expressions
1585
1586 #include <pcre.h>
1587
1588
1589 PCRE NATIVE API BASIC FUNCTIONS
1590
1591 pcre *pcre_compile(const char *pattern, int options,
1592 const char **errptr, int *erroffset,
1593 const unsigned char *tableptr);
1594
1595 pcre *pcre_compile2(const char *pattern, int options,
1596 int *errorcodeptr,
1597 const char **errptr, int *erroffset,
1598 const unsigned char *tableptr);
1599
1600 pcre_extra *pcre_study(const pcre *code, int options,
1601 const char **errptr);
1602
1603 void pcre_free_study(pcre_extra *extra);
1604
1605 int pcre_exec(const pcre *code, const pcre_extra *extra,
1606 const char *subject, int length, int startoffset,
1607 int options, int *ovector, int ovecsize);
1608
1609 int pcre_dfa_exec(const pcre *code, const pcre_extra *extra,
1610 const char *subject, int length, int startoffset,
1611 int options, int *ovector, int ovecsize,
1612 int *workspace, int wscount);
1613
1614
1615 PCRE NATIVE API STRING EXTRACTION FUNCTIONS
1616
1617 int pcre_copy_named_substring(const pcre *code,
1618 const char *subject, int *ovector,
1619 int stringcount, const char *stringname,
1620 char *buffer, int buffersize);
1621
1622 int pcre_copy_substring(const char *subject, int *ovector,
1623 int stringcount, int stringnumber, char *buffer,
1624 int buffersize);
1625
1626 int pcre_get_named_substring(const pcre *code,
1627 const char *subject, int *ovector,
1628 int stringcount, const char *stringname,
1629 const char **stringptr);
1630
1631 int pcre_get_stringnumber(const pcre *code,
1632 const char *name);
1633
1634 int pcre_get_stringtable_entries(const pcre *code,
1635 const char *name, char **first, char **last);
1636
1637 int pcre_get_substring(const char *subject, int *ovector,
1638 int stringcount, int stringnumber,
1639 const char **stringptr);
1640
1641 int pcre_get_substring_list(const char *subject,
1642 int *ovector, int stringcount, const char ***listptr);
1643
1644 void pcre_free_substring(const char *stringptr);
1645
1646 void pcre_free_substring_list(const char **stringptr);
1647
1648
1649 PCRE NATIVE API AUXILIARY FUNCTIONS
1650
1651 int pcre_jit_exec(const pcre *code, const pcre_extra *extra,
1652 const char *subject, int length, int startoffset,
1653 int options, int *ovector, int ovecsize,
1654 pcre_jit_stack *jstack);
1655
1656 pcre_jit_stack *pcre_jit_stack_alloc(int startsize, int maxsize);
1657
1658 void pcre_jit_stack_free(pcre_jit_stack *stack);
1659
1660 void pcre_assign_jit_stack(pcre_extra *extra,
1661 pcre_jit_callback callback, void *data);
1662
1663 const unsigned char *pcre_maketables(void);
1664
1665 int pcre_fullinfo(const pcre *code, const pcre_extra *extra,
1666 int what, void *where);
1667
1668 int pcre_refcount(pcre *code, int adjust);
1669
1670 int pcre_config(int what, void *where);
1671
1672 const char *pcre_version(void);
1673
1674 int pcre_pattern_to_host_byte_order(pcre *code,
1675 pcre_extra *extra, const unsigned char *tables);
1676
1677
1678 PCRE NATIVE API INDIRECTED FUNCTIONS
1679
1680 void *(*pcre_malloc)(size_t);
1681
1682 void (*pcre_free)(void *);
1683
1684 void *(*pcre_stack_malloc)(size_t);
1685
1686 void (*pcre_stack_free)(void *);
1687
1688 int (*pcre_callout)(pcre_callout_block *);
1689
1690 int (*pcre_stack_guard)(void);
1691
1692
1693 PCRE 8-BIT, 16-BIT, AND 32-BIT LIBRARIES
1694
1695 As well as support for 8-bit character strings, PCRE also supports
1696 16-bit strings (from release 8.30) and 32-bit strings (from release
1697 8.32), by means of two additional libraries. They can be built as well
1698 as, or instead of, the 8-bit library. To avoid too much complication,
1699 this document describes the 8-bit versions of the functions, with only
1700 occasional references to the 16-bit and 32-bit libraries.
1701
1702 The 16-bit and 32-bit functions operate in the same way as their 8-bit
1703 counterparts; they just use different data types for their arguments
1704 and results, and their names start with pcre16_ or pcre32_ instead of
1705 pcre_. For every option that has UTF8 in its name (for example,
1706 PCRE_UTF8), there are corresponding 16-bit and 32-bit names with UTF8
1707 replaced by UTF16 or UTF32, respectively. This facility is in fact just
1708 cosmetic; the 16-bit and 32-bit option names define the same bit val-
1709 ues.
1710
1711 References to bytes and UTF-8 in this document should be read as refer-
1712 ences to 16-bit data units and UTF-16 when using the 16-bit library, or
1713 32-bit data units and UTF-32 when using the 32-bit library, unless
1714 specified otherwise. More details of the specific differences for the
1715 16-bit and 32-bit libraries are given in the pcre16 and pcre32 pages.
1716
1717
1718 PCRE API OVERVIEW
1719
1720 PCRE has its own native API, which is described in this document. There
1721 are also some wrapper functions (for the 8-bit library only) that cor-
1722 respond to the POSIX regular expression API, but they do not give
1723 access to all the functionality. They are described in the pcreposix
1724 documentation. Both of these APIs define a set of C function calls. A
1725 C++ wrapper (again for the 8-bit library only) is also distributed with
1726 PCRE. It is documented in the pcrecpp page.
1727
1728 The native API C function prototypes are defined in the header file
1729 pcre.h, and on Unix-like systems the (8-bit) library itself is called
1730 libpcre. It can normally be accessed by adding -lpcre to the command
1731 for linking an application that uses PCRE. The header file defines the
1732 macros PCRE_MAJOR and PCRE_MINOR to contain the major and minor release
1733 numbers for the library. Applications can use these to include support
1734 for different releases of PCRE.
1735
1736 In a Windows environment, if you want to statically link an application
1737 program against a non-dll pcre.a file, you must define PCRE_STATIC
1738 before including pcre.h or pcrecpp.h, because otherwise the pcre_mal-
1739 loc() and pcre_free() exported functions will be declared
1740 __declspec(dllimport), with unwanted results.
1741
1742 The functions pcre_compile(), pcre_compile2(), pcre_study(), and
1743 pcre_exec() are used for compiling and matching regular expressions in
1744 a Perl-compatible manner. A sample program that demonstrates the sim-
1745 plest way of using them is provided in the file called pcredemo.c in
1746 the PCRE source distribution. A listing of this program is given in the
1747 pcredemo documentation, and the pcresample documentation describes how
1748 to compile and run it.
1749
1750 Just-in-time compiler support is an optional feature of PCRE that can
1751 be built in appropriate hardware environments. It greatly speeds up the
1752 matching performance of many patterns. Simple programs can easily
1753 request that it be used if available, by setting an option that is
1754 ignored when it is not relevant. More complicated programs might need
1755 to make use of the functions pcre_jit_stack_alloc(),
1756 pcre_jit_stack_free(), and pcre_assign_jit_stack() in order to control
1757 the JIT code's memory usage.
1758
1759 From release 8.32 there is also a direct interface for JIT execution,
1760 which gives improved performance. The JIT-specific functions are dis-
1761 cussed in the pcrejit documentation.
1762
1763 A second matching function, pcre_dfa_exec(), which is not Perl-compati-
1764 ble, is also provided. This uses a different algorithm for the match-
1765 ing. The alternative algorithm finds all possible matches (at a given
1766 point in the subject), and scans the subject just once (unless there
1767 are lookbehind assertions). However, this algorithm does not return
1768 captured substrings. A description of the two matching algorithms and
1769 their advantages and disadvantages is given in the pcrematching docu-
1770 mentation.
1771
1772 In addition to the main compiling and matching functions, there are
1773 convenience functions for extracting captured substrings from a subject
1774 string that is matched by pcre_exec(). They are:
1775
1776 pcre_copy_substring()
1777 pcre_copy_named_substring()
1778 pcre_get_substring()
1779 pcre_get_named_substring()
1780 pcre_get_substring_list()
1781 pcre_get_stringnumber()
1782 pcre_get_stringtable_entries()
1783
1784 pcre_free_substring() and pcre_free_substring_list() are also provided,
1785 to free the memory used for extracted strings.
1786
1787 The function pcre_maketables() is used to build a set of character
1788 tables in the current locale for passing to pcre_compile(),
1789 pcre_exec(), or pcre_dfa_exec(). This is an optional facility that is
1790 provided for specialist use. Most commonly, no special tables are
1791 passed, in which case internal tables that are generated when PCRE is
1792 built are used.
1793
1794 The function pcre_fullinfo() is used to find out information about a
1795 compiled pattern. The function pcre_version() returns a pointer to a
1796 string containing the version of PCRE and its date of release.
1797
1798 The function pcre_refcount() maintains a reference count in a data
1799 block containing a compiled pattern. This is provided for the benefit
1800 of object-oriented applications.
1801
1802 The global variables pcre_malloc and pcre_free initially contain the
1803 entry points of the standard malloc() and free() functions, respec-
1804 tively. PCRE calls the memory management functions via these variables,
1805 so a calling program can replace them if it wishes to intercept the
1806 calls. This should be done before calling any PCRE functions.
1807
1808 The global variables pcre_stack_malloc and pcre_stack_free are also
1809 indirections to memory management functions. These special functions
1810 are used only when PCRE is compiled to use the heap for remembering
1811 data, instead of recursive function calls, when running the pcre_exec()
1812 function. See the pcrebuild documentation for details of how to do
1813 this. It is a non-standard way of building PCRE, for use in environ-
1814 ments that have limited stacks. Because of the greater use of memory
1815 management, it runs more slowly. Separate functions are provided so
1816 that special-purpose external code can be used for this case. When
1817 used, these functions always allocate memory blocks of the same size.
1818 There is a discussion about PCRE's stack usage in the pcrestack docu-
1819 mentation.
1820
1821 The global variable pcre_callout initially contains NULL. It can be set
1822 by the caller to a "callout" function, which PCRE will then call at
1823 specified points during a matching operation. Details are given in the
1824 pcrecallout documentation.
1825
1826 The global variable pcre_stack_guard initially contains NULL. It can be
1827 set by the caller to a function that is called by PCRE whenever it
1828 starts to compile a parenthesized part of a pattern. When parentheses
1829 are nested, PCRE uses recursive function calls, which use up the system
1830 stack. This function is provided so that applications with restricted
1831 stacks can force a compilation error if the stack runs out. The func-
1832 tion should return zero if all is well, or non-zero to force an error.
1833
1834
1835 NEWLINES
1836
1837 PCRE supports five different conventions for indicating line breaks in
1838 strings: a single CR (carriage return) character, a single LF (line-
1839 feed) character, the two-character sequence CRLF, any of the three pre-
1840 ceding, or any Unicode newline sequence. The Unicode newline sequences
1841 are the three just mentioned, plus the single characters VT (vertical
1842 tab, U+000B), FF (form feed, U+000C), NEL (next line, U+0085), LS (line
1843 separator, U+2028), and PS (paragraph separator, U+2029).
1844
1845 Each of the first three conventions is used by at least one operating
1846 system as its standard newline sequence. When PCRE is built, a default
1847 can be specified. The default default is LF, which is the Unix stan-
1848 dard. When PCRE is run, the default can be overridden, either when a
1849 pattern is compiled, or when it is matched.
1850
1851 At compile time, the newline convention can be specified by the options
1852 argument of pcre_compile(), or it can be specified by special text at
1853 the start of the pattern itself; this overrides any other settings. See
1854 the pcrepattern page for details of the special character sequences.
1855
1856 In the PCRE documentation the word "newline" is used to mean "the char-
1857 acter or pair of characters that indicate a line break". The choice of
1858 newline convention affects the handling of the dot, circumflex, and
1859 dollar metacharacters, the handling of #-comments in /x mode, and, when
1860 CRLF is a recognized line ending sequence, the match position advance-
1861 ment for a non-anchored pattern. There is more detail about this in the
1862 section on pcre_exec() options below.
1863
1864 The choice of newline convention does not affect the interpretation of
1865 the \n or \r escape sequences, nor does it affect what \R matches,
1866 which is controlled in a similar way, but by separate options.
1867
1868
1869 MULTITHREADING
1870
1871 The PCRE functions can be used in multi-threading applications, with
1872 the proviso that the memory management functions pointed to by
1873 pcre_malloc, pcre_free, pcre_stack_malloc, and pcre_stack_free, and the
1874 callout and stack-checking functions pointed to by pcre_callout and
1875 pcre_stack_guard, are shared by all threads.
1876
1877 The compiled form of a regular expression is not altered during match-
1878 ing, so the same compiled pattern can safely be used by several threads
1879 at once.
1880
1881 If the just-in-time optimization feature is being used, it needs sepa-
1882 rate memory stack areas for each thread. See the pcrejit documentation
1883 for more details.
1884
1885
1886 SAVING PRECOMPILED PATTERNS FOR LATER USE
1887
1888 The compiled form of a regular expression can be saved and re-used at a
1889 later time, possibly by a different program, and even on a host other
1890 than the one on which it was compiled. Details are given in the
1891 pcreprecompile documentation, which includes a description of the
1892 pcre_pattern_to_host_byte_order() function. However, compiling a regu-
1893 lar expression with one version of PCRE for use with a different ver-
1894 sion is not guaranteed to work and may cause crashes.
1895
1896
1897 CHECKING BUILD-TIME OPTIONS
1898
1899 int pcre_config(int what, void *where);
1900
1901 The function pcre_config() makes it possible for a PCRE client to dis-
1902 cover which optional features have been compiled into the PCRE library.
1903 The pcrebuild documentation has more details about these optional fea-
1904 tures.
1905
1906 The first argument for pcre_config() is an integer, specifying which
1907 information is required; the second argument is a pointer to a variable
1908 into which the information is placed. The returned value is zero on
1909 success, or the negative error code PCRE_ERROR_BADOPTION if the value
1910 in the first argument is not recognized. The following information is
1911 available:
1912
1913 PCRE_CONFIG_UTF8
1914
1915 The output is an integer that is set to one if UTF-8 support is avail-
1916 able; otherwise it is set to zero. This value should normally be given
1917 to the 8-bit version of this function, pcre_config(). If it is given to
1918 the 16-bit or 32-bit version of this function, the result is
1919 PCRE_ERROR_BADOPTION.
1920
1921 PCRE_CONFIG_UTF16
1922
1923 The output is an integer that is set to one if UTF-16 support is avail-
1924 able; otherwise it is set to zero. This value should normally be given
1925 to the 16-bit version of this function, pcre16_config(). If it is given
1926 to the 8-bit or 32-bit version of this function, the result is
1927 PCRE_ERROR_BADOPTION.
1928
1929 PCRE_CONFIG_UTF32
1930
1931 The output is an integer that is set to one if UTF-32 support is avail-
1932 able; otherwise it is set to zero. This value should normally be given
1933 to the 32-bit version of this function, pcre32_config(). If it is given
1934 to the 8-bit or 16-bit version of this function, the result is
1935 PCRE_ERROR_BADOPTION.
1936
1937 PCRE_CONFIG_UNICODE_PROPERTIES
1938
1939 The output is an integer that is set to one if support for Unicode
1940 character properties is available; otherwise it is set to zero.
1941
1942 PCRE_CONFIG_JIT
1943
1944 The output is an integer that is set to one if support for just-in-time
1945 compiling is available; otherwise it is set to zero.
1946
1947 PCRE_CONFIG_JITTARGET
1948
1949 The output is a pointer to a zero-terminated "const char *" string. If
1950 JIT support is available, the string contains the name of the architec-
1951 ture for which the JIT compiler is configured, for example "x86 32bit
1952 (little endian + unaligned)". If JIT support is not available, the
1953 result is NULL.
1954
1955 PCRE_CONFIG_NEWLINE
1956
1957 The output is an integer whose value specifies the default character
1958 sequence that is recognized as meaning "newline". The values that are
1959 supported in ASCII/Unicode environments are: 10 for LF, 13 for CR, 3338
1960 for CRLF, -2 for ANYCRLF, and -1 for ANY. In EBCDIC environments, CR,
1961 ANYCRLF, and ANY yield the same values. However, the value for LF is
1962 normally 21, though some EBCDIC environments use 37. The corresponding
1963 values for CRLF are 3349 and 3365. The default should normally corre-
1964 spond to the standard sequence for your operating system.
1965
1966 PCRE_CONFIG_BSR
1967
1968 The output is an integer whose value indicates what character sequences
1969 the \R escape sequence matches by default. A value of 0 means that \R
1970 matches any Unicode line ending sequence; a value of 1 means that \R
1971 matches only CR, LF, or CRLF. The default can be overridden when a pat-
1972 tern is compiled or matched.
1973
1974 PCRE_CONFIG_LINK_SIZE
1975
1976 The output is an integer that contains the number of bytes used for
1977 internal linkage in compiled regular expressions. For the 8-bit
1978 library, the value can be 2, 3, or 4. For the 16-bit library, the value
1979 is either 2 or 4 and is still a number of bytes. For the 32-bit
1980 library, the value is either 2 or 4 and is still a number of bytes. The
1981 default value of 2 is sufficient for all but the most massive patterns,
1982 since it allows the compiled pattern to be up to 64K in size. Larger
1983 values allow larger regular expressions to be compiled, at the expense
1984 of slower matching.
1985
1986 PCRE_CONFIG_POSIX_MALLOC_THRESHOLD
1987
1988 The output is an integer that contains the threshold above which the
1989 POSIX interface uses malloc() for output vectors. Further details are
1990 given in the pcreposix documentation.
1991
1992 PCRE_CONFIG_PARENS_LIMIT
1993
1994 The output is a long integer that gives the maximum depth of nesting of
1995 parentheses (of any kind) in a pattern. This limit is imposed to cap
1996 the amount of system stack used when a pattern is compiled. It is spec-
1997 ified when PCRE is built; the default is 250. This limit does not take
1998 into account the stack that may already be used by the calling applica-
1999 tion. For finer control over compilation stack usage, you can set a
2000 pointer to an external checking function in pcre_stack_guard.
2001
2002 PCRE_CONFIG_MATCH_LIMIT
2003
2004 The output is a long integer that gives the default limit for the num-
2005 ber of internal matching function calls in a pcre_exec() execution.
2006 Further details are given with pcre_exec() below.
2007
2008 PCRE_CONFIG_MATCH_LIMIT_RECURSION
2009
2010 The output is a long integer that gives the default limit for the depth
2011 of recursion when calling the internal matching function in a
2012 pcre_exec() execution. Further details are given with pcre_exec()
2013 below.
2014
2015 PCRE_CONFIG_STACKRECURSE
2016
2017 The output is an integer that is set to one if internal recursion when
2018 running pcre_exec() is implemented by recursive function calls that use
2019 the stack to remember their state. This is the usual way that PCRE is
2020 compiled. The output is zero if PCRE was compiled to use blocks of data
2021 on the heap instead of recursive function calls. In this case,
2022 pcre_stack_malloc and pcre_stack_free are called to manage memory
2023 blocks on the heap, thus avoiding the use of the stack.
2024
2025
2026 COMPILING A PATTERN
2027
2028 pcre *pcre_compile(const char *pattern, int options,
2029 const char **errptr, int *erroffset,
2030 const unsigned char *tableptr);
2031
2032 pcre *pcre_compile2(const char *pattern, int options,
2033 int *errorcodeptr,
2034 const char **errptr, int *erroffset,
2035 const unsigned char *tableptr);
2036
2037 Either of the functions pcre_compile() or pcre_compile2() can be called
2038 to compile a pattern into an internal form. The only difference between
2039 the two interfaces is that pcre_compile2() has an additional argument,
2040 errorcodeptr, via which a numerical error code can be returned. To
2041 avoid too much repetition, we refer just to pcre_compile() below, but
2042 the information applies equally to pcre_compile2().
2043
2044 The pattern is a C string terminated by a binary zero, and is passed in
2045 the pattern argument. A pointer to a single block of memory that is
2046 obtained via pcre_malloc is returned. This contains the compiled code
2047 and related data. The pcre type is defined for the returned block; this
2048 is a typedef for a structure whose contents are not externally defined.
2049 It is up to the caller to free the memory (via pcre_free) when it is no
2050 longer required.
2051
2052 Although the compiled code of a PCRE regex is relocatable, that is, it
2053 does not depend on memory location, the complete pcre data block is not
2054 fully relocatable, because it may contain a copy of the tableptr argu-
2055 ment, which is an address (see below).
2056
2057 The options argument contains various bit settings that affect the com-
2058 pilation. It should be zero if no options are required. The available
2059 options are described below. Some of them (in particular, those that
2060 are compatible with Perl, but some others as well) can also be set and
2061 unset from within the pattern (see the detailed description in the
2062 pcrepattern documentation). For those options that can be different in
2063 different parts of the pattern, the contents of the options argument
2064 specifies their settings at the start of compilation and execution. The
2065 PCRE_ANCHORED, PCRE_BSR_xxx, PCRE_NEWLINE_xxx, PCRE_NO_UTF8_CHECK, and
2066 PCRE_NO_START_OPTIMIZE options can be set at the time of matching as
2067 well as at compile time.
2068
2069 If errptr is NULL, pcre_compile() returns NULL immediately. Otherwise,
2070 if compilation of a pattern fails, pcre_compile() returns NULL, and
2071 sets the variable pointed to by errptr to point to a textual error mes-
2072 sage. This is a static string that is part of the library. You must not
2073 try to free it. Normally, the offset from the start of the pattern to
2074 the data unit that was being processed when the error was discovered is
2075 placed in the variable pointed to by erroffset, which must not be NULL
2076 (if it is, an immediate error is given). However, for an invalid UTF-8
2077 or UTF-16 string, the offset is that of the first data unit of the
2078 failing character.
2079
2080 Some errors are not detected until the whole pattern has been scanned;
2081 in these cases, the offset passed back is the length of the pattern.
2082 Note that the offset is in data units, not characters, even in a UTF
2083 mode. It may sometimes point into the middle of a UTF-8 or UTF-16 char-
2084 acter.
2085
2086 If pcre_compile2() is used instead of pcre_compile(), and the error-
2087 codeptr argument is not NULL, a non-zero error code number is returned
2088 via this argument in the event of an error. This is in addition to the
2089 textual error message. Error codes and messages are listed below.
2090
2091 If the final argument, tableptr, is NULL, PCRE uses a default set of
2092 character tables that are built when PCRE is compiled, using the
2093 default C locale. Otherwise, tableptr must be an address that is the
2094 result of a call to pcre_maketables(). This value is stored with the
2095 compiled pattern, and used again by pcre_exec() and pcre_dfa_exec()
2096 when the pattern is matched. For more discussion, see the section on
2097 locale support below.
2098
2099 This code fragment shows a typical straightforward call to pcre_com-
2100 pile():
2101
2102 pcre *re;
2103 const char *error;
2104 int erroffset;
2105 re = pcre_compile(
2106 "^A.*Z", /* the pattern */
2107 0, /* default options */
2108 &error, /* for error message */
2109 &erroffset, /* for error offset */
2110 NULL); /* use default character tables */
2111
2112 The following names for option bits are defined in the pcre.h header
2113 file:
2114
2115 PCRE_ANCHORED
2116
2117 If this bit is set, the pattern is forced to be "anchored", that is, it
2118 is constrained to match only at the first matching point in the string
2119 that is being searched (the "subject string"). This effect can also be
2120 achieved by appropriate constructs in the pattern itself, which is the
2121 only way to do it in Perl.
2122
2123 PCRE_AUTO_CALLOUT
2124
2125 If this bit is set, pcre_compile() automatically inserts callout items,
2126 all with number 255, before each pattern item. For discussion of the
2127 callout facility, see the pcrecallout documentation.
2128
2129 PCRE_BSR_ANYCRLF
2130 PCRE_BSR_UNICODE
2131
2132 These options (which are mutually exclusive) control what the \R escape
2133 sequence matches. The choice is either to match only CR, LF, or CRLF,
2134 or to match any Unicode newline sequence. The default is specified when
2135 PCRE is built. It can be overridden from within the pattern, or by set-
2136 ting an option when a compiled pattern is matched.
2137
2138 PCRE_CASELESS
2139
2140 If this bit is set, letters in the pattern match both upper and lower
2141 case letters. It is equivalent to Perl's /i option, and it can be
2142 changed within a pattern by a (?i) option setting. In UTF-8 mode, PCRE
2143 always understands the concept of case for characters whose values are
2144 less than 128, so caseless matching is always possible. For characters
2145 with higher values, the concept of case is supported if PCRE is com-
2146 piled with Unicode property support, but not otherwise. If you want to
2147 use caseless matching for characters 128 and above, you must ensure
2148 that PCRE is compiled with Unicode property support as well as with
2149 UTF-8 support.
2150
2151 PCRE_DOLLAR_ENDONLY
2152
2153 If this bit is set, a dollar metacharacter in the pattern matches only
2154 at the end of the subject string. Without this option, a dollar also
2155 matches immediately before a newline at the end of the string (but not
2156 before any other newlines). The PCRE_DOLLAR_ENDONLY option is ignored
2157 if PCRE_MULTILINE is set. There is no equivalent to this option in
2158 Perl, and no way to set it within a pattern.
2159
2160 PCRE_DOTALL
2161
2162 If this bit is set, a dot metacharacter in the pattern matches a char-
2163 acter of any value, including one that indicates a newline. However, it
2164 only ever matches one character, even if newlines are coded as CRLF.
2165 Without this option, a dot does not match when the current position is
2166 at a newline. This option is equivalent to Perl's /s option, and it can
2167 be changed within a pattern by a (?s) option setting. A negative class
2168 such as [^a] always matches newline characters, independent of the set-
2169 ting of this option.
2170
2171 PCRE_DUPNAMES
2172
2173 If this bit is set, names used to identify capturing subpatterns need
2174 not be unique. This can be helpful for certain types of pattern when it
2175 is known that only one instance of the named subpattern can ever be
2176 matched. There are more details of named subpatterns below; see also
2177 the pcrepattern documentation.
2178
2179 PCRE_EXTENDED
2180
2181 If this bit is set, most white space characters in the pattern are
2182 totally ignored except when escaped or inside a character class. How-
2183 ever, white space is not allowed within sequences such as (?> that
2184 introduce various parenthesized subpatterns, nor within a numerical
2185 quantifier such as {1,3}. However, ignorable white space is permitted
2186 between an item and a following quantifier and between a quantifier and
2187 a following + that indicates possessiveness.
2188
2189 White space did not used to include the VT character (code 11), because
2190 Perl did not treat this character as white space. However, Perl changed
2191 at release 5.18, so PCRE followed at release 8.34, and VT is now
2192 treated as white space.
2193
2194 PCRE_EXTENDED also causes characters between an unescaped # outside a
2195 character class and the next newline, inclusive, to be ignored.
2196 PCRE_EXTENDED is equivalent to Perl's /x option, and it can be changed
2197 within a pattern by a (?x) option setting.
2198
2199 Which characters are interpreted as newlines is controlled by the
2200 options passed to pcre_compile() or by a special sequence at the start
2201 of the pattern, as described in the section entitled "Newline conven-
2202 tions" in the pcrepattern documentation. Note that the end of this type
2203 of comment is a literal newline sequence in the pattern; escape
2204 sequences that happen to represent a newline do not count.
2205
2206 This option makes it possible to include comments inside complicated
2207 patterns. Note, however, that this applies only to data characters.
2208 White space characters may never appear within special character
2209 sequences in a pattern, for example within the sequence (?( that intro-
2210 duces a conditional subpattern.
2211
2212 PCRE_EXTRA
2213
2214 This option was invented in order to turn on additional functionality
2215 of PCRE that is incompatible with Perl, but it is currently of very
2216 little use. When set, any backslash in a pattern that is followed by a
2217 letter that has no special meaning causes an error, thus reserving
2218 these combinations for future expansion. By default, as in Perl, a
2219 backslash followed by a letter with no special meaning is treated as a
2220 literal. (Perl can, however, be persuaded to give an error for this, by
2221 running it with the -w option.) There are at present no other features
2222 controlled by this option. It can also be set by a (?X) option setting
2223 within a pattern.
2224
2225 PCRE_FIRSTLINE
2226
2227 If this option is set, an unanchored pattern is required to match
2228 before or at the first newline in the subject string, though the
2229 matched text may continue over the newline.
2230
2231 PCRE_JAVASCRIPT_COMPAT
2232
2233 If this option is set, PCRE's behaviour is changed in some ways so that
2234 it is compatible with JavaScript rather than Perl. The changes are as
2235 follows:
2236
2237 (1) A lone closing square bracket in a pattern causes a compile-time
2238 error, because this is illegal in JavaScript (by default it is treated
2239 as a data character). Thus, the pattern AB]CD becomes illegal when this
2240 option is set.
2241
2242 (2) At run time, a back reference to an unset subpattern group matches
2243 an empty string (by default this causes the current matching alterna-
2244 tive to fail). A pattern such as (\1)(a) succeeds when this option is
2245 set (assuming it can find an "a" in the subject), whereas it fails by
2246 default, for Perl compatibility.
2247
2248 (3) \U matches an upper case "U" character; by default \U causes a com-
2249 pile time error (Perl uses \U to upper case subsequent characters).
2250
2251 (4) \u matches a lower case "u" character unless it is followed by four
2252 hexadecimal digits, in which case the hexadecimal number defines the
2253 code point to match. By default, \u causes a compile time error (Perl
2254 uses it to upper case the following character).
2255
2256 (5) \x matches a lower case "x" character unless it is followed by two
2257 hexadecimal digits, in which case the hexadecimal number defines the
2258 code point to match. By default, as in Perl, a hexadecimal number is
2259 always expected after \x, but it may have zero, one, or two digits (so,
2260 for example, \xz matches a binary zero character followed by z).
2261
2262 PCRE_MULTILINE
2263
2264 By default, for the purposes of matching "start of line" and "end of
2265 line", PCRE treats the subject string as consisting of a single line of
2266 characters, even if it actually contains newlines. The "start of line"
2267 metacharacter (^) matches only at the start of the string, and the "end
2268 of line" metacharacter ($) matches only at the end of the string, or
2269 before a terminating newline (except when PCRE_DOLLAR_ENDONLY is set).
2270 Note, however, that unless PCRE_DOTALL is set, the "any character"
2271 metacharacter (.) does not match at a newline. This behaviour (for ^,
2272 $, and dot) is the same as Perl.
2273
2274 When PCRE_MULTILINE it is set, the "start of line" and "end of line"
2275 constructs match immediately following or immediately before internal
2276 newlines in the subject string, respectively, as well as at the very
2277 start and end. This is equivalent to Perl's /m option, and it can be
2278 changed within a pattern by a (?m) option setting. If there are no new-
2279 lines in a subject string, or no occurrences of ^ or $ in a pattern,
2280 setting PCRE_MULTILINE has no effect.
2281
2282 PCRE_NEVER_UTF
2283
2284 This option locks out interpretation of the pattern as UTF-8 (or UTF-16
2285 or UTF-32 in the 16-bit and 32-bit libraries). In particular, it pre-
2286 vents the creator of the pattern from switching to UTF interpretation
2287 by starting the pattern with (*UTF). This may be useful in applications
2288 that process patterns from external sources. The combination of
2289 PCRE_UTF8 and PCRE_NEVER_UTF also causes an error.
2290
2291 PCRE_NEWLINE_CR
2292 PCRE_NEWLINE_LF
2293 PCRE_NEWLINE_CRLF
2294 PCRE_NEWLINE_ANYCRLF
2295 PCRE_NEWLINE_ANY
2296
2297 These options override the default newline definition that was chosen
2298 when PCRE was built. Setting the first or the second specifies that a
2299 newline is indicated by a single character (CR or LF, respectively).
2300 Setting PCRE_NEWLINE_CRLF specifies that a newline is indicated by the
2301 two-character CRLF sequence. Setting PCRE_NEWLINE_ANYCRLF specifies
2302 that any of the three preceding sequences should be recognized. Setting
2303 PCRE_NEWLINE_ANY specifies that any Unicode newline sequence should be
2304 recognized.
2305
2306 In an ASCII/Unicode environment, the Unicode newline sequences are the
2307 three just mentioned, plus the single characters VT (vertical tab,
2308 U+000B), FF (form feed, U+000C), NEL (next line, U+0085), LS (line sep-
2309 arator, U+2028), and PS (paragraph separator, U+2029). For the 8-bit
2310 library, the last two are recognized only in UTF-8 mode.
2311
2312 When PCRE is compiled to run in an EBCDIC (mainframe) environment, the
2313 code for CR is 0x0d, the same as ASCII. However, the character code for
2314 LF is normally 0x15, though in some EBCDIC environments 0x25 is used.
2315 Whichever of these is not LF is made to correspond to Unicode's NEL
2316 character. EBCDIC codes are all less than 256. For more details, see
2317 the pcrebuild documentation.
2318
2319 The newline setting in the options word uses three bits that are
2320 treated as a number, giving eight possibilities. Currently only six are
2321 used (default plus the five values above). This means that if you set
2322 more than one newline option, the combination may or may not be sensi-
2323 ble. For example, PCRE_NEWLINE_CR with PCRE_NEWLINE_LF is equivalent to
2324 PCRE_NEWLINE_CRLF, but other combinations may yield unused numbers and
2325 cause an error.
2326
2327 The only time that a line break in a pattern is specially recognized
2328 when compiling is when PCRE_EXTENDED is set. CR and LF are white space
2329 characters, and so are ignored in this mode. Also, an unescaped # out-
2330 side a character class indicates a comment that lasts until after the
2331 next line break sequence. In other circumstances, line break sequences
2332 in patterns are treated as literal data.
2333
2334 The newline option that is set at compile time becomes the default that
2335 is used for pcre_exec() and pcre_dfa_exec(), but it can be overridden.
2336
2337 PCRE_NO_AUTO_CAPTURE
2338
2339 If this option is set, it disables the use of numbered capturing paren-
2340 theses in the pattern. Any opening parenthesis that is not followed by
2341 ? behaves as if it were followed by ?: but named parentheses can still
2342 be used for capturing (and they acquire numbers in the usual way).
2343 There is no equivalent of this option in Perl.
2344
2345 PCRE_NO_AUTO_POSSESS
2346
2347 If this option is set, it disables "auto-possessification". This is an
2348 optimization that, for example, turns a+b into a++b in order to avoid
2349 backtracks into a+ that can never be successful. However, if callouts
2350 are in use, auto-possessification means that some of them are never
2351 taken. You can set this option if you want the matching functions to do
2352 a full unoptimized search and run all the callouts, but it is mainly
2353 provided for testing purposes.
2354
2355 PCRE_NO_START_OPTIMIZE
2356
2357 This is an option that acts at matching time; that is, it is really an
2358 option for pcre_exec() or pcre_dfa_exec(). If it is set at compile
2359 time, it is remembered with the compiled pattern and assumed at match-
2360 ing time. This is necessary if you want to use JIT execution, because
2361 the JIT compiler needs to know whether or not this option is set. For
2362 details see the discussion of PCRE_NO_START_OPTIMIZE below.
2363
2364 PCRE_UCP
2365
2366 This option changes the way PCRE processes \B, \b, \D, \d, \S, \s, \W,
2367 \w, and some of the POSIX character classes. By default, only ASCII
2368 characters are recognized, but if PCRE_UCP is set, Unicode properties
2369 are used instead to classify characters. More details are given in the
2370 section on generic character types in the pcrepattern page. If you set
2371 PCRE_UCP, matching one of the items it affects takes much longer. The
2372 option is available only if PCRE has been compiled with Unicode prop-
2373 erty support.
2374
2375 PCRE_UNGREEDY
2376
2377 This option inverts the "greediness" of the quantifiers so that they
2378 are not greedy by default, but become greedy if followed by "?". It is
2379 not compatible with Perl. It can also be set by a (?U) option setting
2380 within the pattern.
2381
2382 PCRE_UTF8
2383
2384 This option causes PCRE to regard both the pattern and the subject as
2385 strings of UTF-8 characters instead of single-byte strings. However, it
2386 is available only when PCRE is built to include UTF support. If not,
2387 the use of this option provokes an error. Details of how this option
2388 changes the behaviour of PCRE are given in the pcreunicode page.
2389
2390 PCRE_NO_UTF8_CHECK
2391
2392 When PCRE_UTF8 is set, the validity of the pattern as a UTF-8 string is
2393 automatically checked. There is a discussion about the validity of
2394 UTF-8 strings in the pcreunicode page. If an invalid UTF-8 sequence is
2395 found, pcre_compile() returns an error. If you already know that your
2396 pattern is valid, and you want to skip this check for performance rea-
2397 sons, you can set the PCRE_NO_UTF8_CHECK option. When it is set, the
2398 effect of passing an invalid UTF-8 string as a pattern is undefined. It
2399 may cause your program to crash or loop. Note that this option can also
2400 be passed to pcre_exec() and pcre_dfa_exec(), to suppress the validity
2401 checking of subject strings only. If the same string is being matched
2402 many times, the option can be safely set for the second and subsequent
2403 matchings to improve performance.
2404
2405
2406 COMPILATION ERROR CODES
2407
2408 The following table lists the error codes than may be returned by
2409 pcre_compile2(), along with the error messages that may be returned by
2410 both compiling functions. Note that error messages are always 8-bit
2411 ASCII strings, even in 16-bit or 32-bit mode. As PCRE has developed,
2412 some error codes have fallen out of use. To avoid confusion, they have
2413 not been re-used.
2414
2415 0 no error
2416 1 \ at end of pattern
2417 2 \c at end of pattern
2418 3 unrecognized character follows \
2419 4 numbers out of order in {} quantifier
2420 5 number too big in {} quantifier
2421 6 missing terminating ] for character class
2422 7 invalid escape sequence in character class
2423 8 range out of order in character class
2424 9 nothing to repeat
2425 10 [this code is not in use]
2426 11 internal error: unexpected repeat
2427 12 unrecognized character after (? or (?-
2428 13 POSIX named classes are supported only within a class
2429 14 missing )
2430 15 reference to non-existent subpattern
2431 16 erroffset passed as NULL
2432 17 unknown option bit(s) set
2433 18 missing ) after comment
2434 19 [this code is not in use]
2435 20 regular expression is too large
2436 21 failed to get memory
2437 22 unmatched parentheses
2438 23 internal error: code overflow
2439 24 unrecognized character after (?<
2440 25 lookbehind assertion is not fixed length
2441 26 malformed number or name after (?(
2442 27 conditional group contains more than two branches
2443 28 assertion expected after (?(
2444 29 (?R or (?[+-]digits must be followed by )
2445 30 unknown POSIX class name
2446 31 POSIX collating elements are not supported
2447 32 this version of PCRE is compiled without UTF support
2448 33 [this code is not in use]
2449 34 character value in \x{} or \o{} is too large
2450 35 invalid condition (?(0)
2451 36 \C not allowed in lookbehind assertion
2452 37 PCRE does not support \L, \l, \N{name}, \U, or \u
2453 38 number after (?C is > 255
2454 39 closing ) for (?C expected
2455 40 recursive call could loop indefinitely
2456 41 unrecognized character after (?P
2457 42 syntax error in subpattern name (missing terminator)
2458 43 two named subpatterns have the same name
2459 44 invalid UTF-8 string (specifically UTF-8)
2460 45 support for \P, \p, and \X has not been compiled
2461 46 malformed \P or \p sequence
2462 47 unknown property name after \P or \p
2463 48 subpattern name is too long (maximum 32 characters)
2464 49 too many named subpatterns (maximum 10000)
2465 50 [this code is not in use]
2466 51 octal value is greater than \377 in 8-bit non-UTF-8 mode
2467 52 internal error: overran compiling workspace
2468 53 internal error: previously-checked referenced subpattern
2469 not found
2470 54 DEFINE group contains more than one branch
2471 55 repeating a DEFINE group is not allowed
2472 56 inconsistent NEWLINE options
2473 57 \g is not followed by a braced, angle-bracketed, or quoted
2474 name/number or by a plain number
2475 58 a numbered reference must not be zero
2476 59 an argument is not allowed for (*ACCEPT), (*FAIL), or (*COMMIT)
2477 60 (*VERB) not recognized or malformed
2478 61 number is too big
2479 62 subpattern name expected
2480 63 digit expected after (?+
2481 64 ] is an invalid data character in JavaScript compatibility mode
2482 65 different names for subpatterns of the same number are
2483 not allowed
2484 66 (*MARK) must have an argument
2485 67 this version of PCRE is not compiled with Unicode property
2486 support
2487 68 \c must be followed by an ASCII character
2488 69 \k is not followed by a braced, angle-bracketed, or quoted name
2489 70 internal error: unknown opcode in find_fixedlength()
2490 71 \N is not supported in a class
2491 72 too many forward references
2492 73 disallowed Unicode code point (>= 0xd800 && <= 0xdfff)
2493 74 invalid UTF-16 string (specifically UTF-16)
2494 75 name is too long in (*MARK), (*PRUNE), (*SKIP), or (*THEN)
2495 76 character value in \u.... sequence is too large
2496 77 invalid UTF-32 string (specifically UTF-32)
2497 78 setting UTF is disabled by the application
2498 79 non-hex character in \x{} (closing brace missing?)
2499 80 non-octal character in \o{} (closing brace missing?)
2500 81 missing opening brace after \o
2501 82 parentheses are too deeply nested
2502 83 invalid range in character class
2503 84 group name must start with a non-digit
2504 85 parentheses are too deeply nested (stack check)
2505
2506 The numbers 32 and 10000 in errors 48 and 49 are defaults; different
2507 values may be used if the limits were changed when PCRE was built.
2508
2509
2510 STUDYING A PATTERN
2511
2512 pcre_extra *pcre_study(const pcre *code, int options,
2513 const char **errptr);
2514
2515 If a compiled pattern is going to be used several times, it is worth
2516 spending more time analyzing it in order to speed up the time taken for
2517 matching. The function pcre_study() takes a pointer to a compiled pat-
2518 tern as its first argument. If studying the pattern produces additional
2519 information that will help speed up matching, pcre_study() returns a
2520 pointer to a pcre_extra block, in which the study_data field points to
2521 the results of the study.
2522
2523 The returned value from pcre_study() can be passed directly to
2524 pcre_exec() or pcre_dfa_exec(). However, a pcre_extra block also con-
2525 tains other fields that can be set by the caller before the block is
2526 passed; these are described below in the section on matching a pattern.
2527
2528 If studying the pattern does not produce any useful information,
2529 pcre_study() returns NULL by default. In that circumstance, if the
2530 calling program wants to pass any of the other fields to pcre_exec() or
2531 pcre_dfa_exec(), it must set up its own pcre_extra block. However, if
2532 pcre_study() is called with the PCRE_STUDY_EXTRA_NEEDED option, it
2533 returns a pcre_extra block even if studying did not find any additional
2534 information. It may still return NULL, however, if an error occurs in
2535 pcre_study().
2536
2537 The second argument of pcre_study() contains option bits. There are
2538 three further options in addition to PCRE_STUDY_EXTRA_NEEDED:
2539
2540 PCRE_STUDY_JIT_COMPILE
2541 PCRE_STUDY_JIT_PARTIAL_HARD_COMPILE
2542 PCRE_STUDY_JIT_PARTIAL_SOFT_COMPILE
2543
2544 If any of these are set, and the just-in-time compiler is available,
2545 the pattern is further compiled into machine code that executes much
2546 faster than the pcre_exec() interpretive matching function. If the
2547 just-in-time compiler is not available, these options are ignored. All
2548 undefined bits in the options argument must be zero.
2549
2550 JIT compilation is a heavyweight optimization. It can take some time
2551 for patterns to be analyzed, and for one-off matches and simple pat-
2552 terns the benefit of faster execution might be offset by a much slower
2553 study time. Not all patterns can be optimized by the JIT compiler. For
2554 those that cannot be handled, matching automatically falls back to the
2555 pcre_exec() interpreter. For more details, see the pcrejit documenta-
2556 tion.
2557
2558 The third argument for pcre_study() is a pointer for an error message.
2559 If studying succeeds (even if no data is returned), the variable it
2560 points to is set to NULL. Otherwise it is set to point to a textual
2561 error message. This is a static string that is part of the library. You
2562 must not try to free it. You should test the error pointer for NULL
2563 after calling pcre_study(), to be sure that it has run successfully.
2564
2565 When you are finished with a pattern, you can free the memory used for
2566 the study data by calling pcre_free_study(). This function was added to
2567 the API for release 8.20. For earlier versions, the memory could be
2568 freed with pcre_free(), just like the pattern itself. This will still
2569 work in cases where JIT optimization is not used, but it is advisable
2570 to change to the new function when convenient.
2571
2572 This is a typical way in which pcre_study() is used (except that in a
2573 real application there should be tests for errors):
2574
2575 int rc;
2576 pcre *re;
2577 pcre_extra *sd;
2578 re = pcre_compile("pattern", 0, &error, &erroroffset, NULL);
2579 sd = pcre_study(
2580 re, /* result of pcre_compile() */
2581 0, /* no options */
2582 &error); /* set to NULL or points to a message */
2583 rc = pcre_exec( /* see below for details of pcre_exec() options */
2584 re, sd, "subject", 7, 0, 0, ovector, 30);
2585 ...
2586 pcre_free_study(sd);
2587 pcre_free(re);
2588
2589 Studying a pattern does two things: first, a lower bound for the length
2590 of subject string that is needed to match the pattern is computed. This
2591 does not mean that there are any strings of that length that match, but
2592 it does guarantee that no shorter strings match. The value is used to
2593 avoid wasting time by trying to match strings that are shorter than the
2594 lower bound. You can find out the value in a calling program via the
2595 pcre_fullinfo() function.
2596
2597 Studying a pattern is also useful for non-anchored patterns that do not
2598 have a single fixed starting character. A bitmap of possible starting
2599 bytes is created. This speeds up finding a position in the subject at
2600 which to start matching. (In 16-bit mode, the bitmap is used for 16-bit
2601 values less than 256. In 32-bit mode, the bitmap is used for 32-bit
2602 values less than 256.)
2603
2604 These two optimizations apply to both pcre_exec() and pcre_dfa_exec(),
2605 and the information is also used by the JIT compiler. The optimiza-
2606 tions can be disabled by setting the PCRE_NO_START_OPTIMIZE option.
2607 You might want to do this if your pattern contains callouts or (*MARK)
2608 and you want to make use of these facilities in cases where matching
2609 fails.
2610
2611 PCRE_NO_START_OPTIMIZE can be specified at either compile time or exe-
2612 cution time. However, if PCRE_NO_START_OPTIMIZE is passed to
2613 pcre_exec(), (that is, after any JIT compilation has happened) JIT exe-
2614 cution is disabled. For JIT execution to work with PCRE_NO_START_OPTI-
2615 MIZE, the option must be set at compile time.
2616
2617 There is a longer discussion of PCRE_NO_START_OPTIMIZE below.
2618
2619
2620 LOCALE SUPPORT
2621
2622 PCRE handles caseless matching, and determines whether characters are
2623 letters, digits, or whatever, by reference to a set of tables, indexed
2624 by character code point. When running in UTF-8 mode, or in the 16- or
2625 32-bit libraries, this applies only to characters with code points less
2626 than 256. By default, higher-valued code points never match escapes
2627 such as \w or \d. However, if PCRE is built with Unicode property sup-
2628 port, all characters can be tested with \p and \P, or, alternatively,
2629 the PCRE_UCP option can be set when a pattern is compiled; this causes
2630 \w and friends to use Unicode property support instead of the built-in
2631 tables.
2632
2633 The use of locales with Unicode is discouraged. If you are handling
2634 characters with code points greater than 128, you should either use
2635 Unicode support, or use locales, but not try to mix the two.
2636
2637 PCRE contains an internal set of tables that are used when the final
2638 argument of pcre_compile() is NULL. These are sufficient for many
2639 applications. Normally, the internal tables recognize only ASCII char-
2640 acters. However, when PCRE is built, it is possible to cause the inter-
2641 nal tables to be rebuilt in the default "C" locale of the local system,
2642 which may cause them to be different.
2643
2644 The internal tables can always be overridden by tables supplied by the
2645 application that calls PCRE. These may be created in a different locale
2646 from the default. As more and more applications change to using Uni-
2647 code, the need for this locale support is expected to die away.
2648
2649 External tables are built by calling the pcre_maketables() function,
2650 which has no arguments, in the relevant locale. The result can then be
2651 passed to pcre_compile() as often as necessary. For example, to build
2652 and use tables that are appropriate for the French locale (where
2653 accented characters with values greater than 128 are treated as let-
2654 ters), the following code could be used:
2655
2656 setlocale(LC_CTYPE, "fr_FR");
2657 tables = pcre_maketables();
2658 re = pcre_compile(..., tables);
2659
2660 The locale name "fr_FR" is used on Linux and other Unix-like systems;
2661 if you are using Windows, the name for the French locale is "french".
2662
2663 When pcre_maketables() runs, the tables are built in memory that is
2664 obtained via pcre_malloc. It is the caller's responsibility to ensure
2665 that the memory containing the tables remains available for as long as
2666 it is needed.
2667
2668 The pointer that is passed to pcre_compile() is saved with the compiled
2669 pattern, and the same tables are used via this pointer by pcre_study()
2670 and also by pcre_exec() and pcre_dfa_exec(). Thus, for any single pat-
2671 tern, compilation, studying and matching all happen in the same locale,
2672 but different patterns can be processed in different locales.
2673
2674 It is possible to pass a table pointer or NULL (indicating the use of
2675 the internal tables) to pcre_exec() or pcre_dfa_exec() (see the discus-
2676 sion below in the section on matching a pattern). This facility is pro-
2677 vided for use with pre-compiled patterns that have been saved and
2678 reloaded. Character tables are not saved with patterns, so if a non-
2679 standard table was used at compile time, it must be provided again when
2680 the reloaded pattern is matched. Attempting to use this facility to
2681 match a pattern in a different locale from the one in which it was com-
2682 piled is likely to lead to anomalous (usually incorrect) results.
2683
2684
2685 INFORMATION ABOUT A PATTERN
2686
2687 int pcre_fullinfo(const pcre *code, const pcre_extra *extra,
2688 int what, void *where);
2689
2690 The pcre_fullinfo() function returns information about a compiled pat-
2691 tern. It replaces the pcre_info() function, which was removed from the
2692 library at version 8.30, after more than 10 years of obsolescence.
2693
2694 The first argument for pcre_fullinfo() is a pointer to the compiled
2695 pattern. The second argument is the result of pcre_study(), or NULL if
2696 the pattern was not studied. The third argument specifies which piece
2697 of information is required, and the fourth argument is a pointer to a
2698 variable to receive the data. The yield of the function is zero for
2699 success, or one of the following negative numbers:
2700
2701 PCRE_ERROR_NULL the argument code was NULL
2702 the argument where was NULL
2703 PCRE_ERROR_BADMAGIC the "magic number" was not found
2704 PCRE_ERROR_BADENDIANNESS the pattern was compiled with different
2705 endianness
2706 PCRE_ERROR_BADOPTION the value of what was invalid
2707 PCRE_ERROR_UNSET the requested field is not set
2708
2709 The "magic number" is placed at the start of each compiled pattern as
2710 an simple check against passing an arbitrary memory pointer. The endi-
2711 anness error can occur if a compiled pattern is saved and reloaded on a
2712 different host. Here is a typical call of pcre_fullinfo(), to obtain
2713 the length of the compiled pattern:
2714
2715 int rc;
2716 size_t length;
2717 rc = pcre_fullinfo(
2718 re, /* result of pcre_compile() */
2719 sd, /* result of pcre_study(), or NULL */
2720 PCRE_INFO_SIZE, /* what is required */
2721 &length); /* where to put the data */
2722
2723 The possible values for the third argument are defined in pcre.h, and
2724 are as follows:
2725
2726 PCRE_INFO_BACKREFMAX
2727
2728 Return the number of the highest back reference in the pattern. The
2729 fourth argument should point to an int variable. Zero is returned if
2730 there are no back references.
2731
2732 PCRE_INFO_CAPTURECOUNT
2733
2734 Return the number of capturing subpatterns in the pattern. The fourth
2735 argument should point to an int variable.
2736
2737 PCRE_INFO_DEFAULT_TABLES
2738
2739 Return a pointer to the internal default character tables within PCRE.
2740 The fourth argument should point to an unsigned char * variable. This
2741 information call is provided for internal use by the pcre_study() func-
2742 tion. External callers can cause PCRE to use its internal tables by
2743 passing a NULL table pointer.
2744
2745 PCRE_INFO_FIRSTBYTE (deprecated)
2746
2747 Return information about the first data unit of any matched string, for
2748 a non-anchored pattern. The name of this option refers to the 8-bit
2749 library, where data units are bytes. The fourth argument should point
2750 to an int variable. Negative values are used for special cases. How-
2751 ever, this means that when the 32-bit library is in non-UTF-32 mode,
2752 the full 32-bit range of characters cannot be returned. For this rea-
2753 son, this value is deprecated; use PCRE_INFO_FIRSTCHARACTERFLAGS and
2754 PCRE_INFO_FIRSTCHARACTER instead.
2755
2756 If there is a fixed first value, for example, the letter "c" from a
2757 pattern such as (cat|cow|coyote), its value is returned. In the 8-bit
2758 library, the value is always less than 256. In the 16-bit library the
2759 value can be up to 0xffff. In the 32-bit library the value can be up to
2760 0x10ffff.
2761
2762 If there is no fixed first value, and if either
2763
2764 (a) the pattern was compiled with the PCRE_MULTILINE option, and every
2765 branch starts with "^", or
2766
2767 (b) every branch of the pattern starts with ".*" and PCRE_DOTALL is not
2768 set (if it were set, the pattern would be anchored),
2769
2770 -1 is returned, indicating that the pattern matches only at the start
2771 of a subject string or after any newline within the string. Otherwise
2772 -2 is returned. For anchored patterns, -2 is returned.
2773
2774 PCRE_INFO_FIRSTCHARACTER
2775
2776 Return the value of the first data unit (non-UTF character) of any
2777 matched string in the situation where PCRE_INFO_FIRSTCHARACTERFLAGS
2778 returns 1; otherwise return 0. The fourth argument should point to an
2779 uint_t variable.
2780
2781 In the 8-bit library, the value is always less than 256. In the 16-bit
2782 library the value can be up to 0xffff. In the 32-bit library in UTF-32
2783 mode the value can be up to 0x10ffff, and up to 0xffffffff when not
2784 using UTF-32 mode.
2785
2786 PCRE_INFO_FIRSTCHARACTERFLAGS
2787
2788 Return information about the first data unit of any matched string, for
2789 a non-anchored pattern. The fourth argument should point to an int
2790 variable.
2791
2792 If there is a fixed first value, for example, the letter "c" from a
2793 pattern such as (cat|cow|coyote), 1 is returned, and the character
2794 value can be retrieved using PCRE_INFO_FIRSTCHARACTER. If there is no
2795 fixed first value, and if either
2796
2797 (a) the pattern was compiled with the PCRE_MULTILINE option, and every
2798 branch starts with "^", or
2799
2800 (b) every branch of the pattern starts with ".*" and PCRE_DOTALL is not
2801 set (if it were set, the pattern would be anchored),
2802
2803 2 is returned, indicating that the pattern matches only at the start of
2804 a subject string or after any newline within the string. Otherwise 0 is
2805 returned. For anchored patterns, 0 is returned.
2806
2807 PCRE_INFO_FIRSTTABLE
2808
2809 If the pattern was studied, and this resulted in the construction of a
2810 256-bit table indicating a fixed set of values for the first data unit
2811 in any matching string, a pointer to the table is returned. Otherwise
2812 NULL is returned. The fourth argument should point to an unsigned char
2813 * variable.
2814
2815 PCRE_INFO_HASCRORLF
2816
2817 Return 1 if the pattern contains any explicit matches for CR or LF
2818 characters, otherwise 0. The fourth argument should point to an int
2819 variable. An explicit match is either a literal CR or LF character, or
2820 \r or \n.
2821
2822 PCRE_INFO_JCHANGED
2823
2824 Return 1 if the (?J) or (?-J) option setting is used in the pattern,
2825 otherwise 0. The fourth argument should point to an int variable. (?J)
2826 and (?-J) set and unset the local PCRE_DUPNAMES option, respectively.
2827
2828 PCRE_INFO_JIT
2829
2830 Return 1 if the pattern was studied with one of the JIT options, and
2831 just-in-time compiling was successful. The fourth argument should point
2832 to an int variable. A return value of 0 means that JIT support is not
2833 available in this version of PCRE, or that the pattern was not studied
2834 with a JIT option, or that the JIT compiler could not handle this par-
2835 ticular pattern. See the pcrejit documentation for details of what can
2836 and cannot be handled.
2837
2838 PCRE_INFO_JITSIZE
2839
2840 If the pattern was successfully studied with a JIT option, return the
2841 size of the JIT compiled code, otherwise return zero. The fourth argu-
2842 ment should point to a size_t variable.
2843
2844 PCRE_INFO_LASTLITERAL
2845
2846 Return the value of the rightmost literal data unit that must exist in
2847 any matched string, other than at its start, if such a value has been
2848 recorded. The fourth argument should point to an int variable. If there
2849 is no such value, -1 is returned. For anchored patterns, a last literal
2850 value is recorded only if it follows something of variable length. For
2851 example, for the pattern /^a\d+z\d+/ the returned value is "z", but for
2852 /^a\dz\d/ the returned value is -1.
2853
2854 Since for the 32-bit library using the non-UTF-32 mode, this function
2855 is unable to return the full 32-bit range of characters, this value is
2856 deprecated; instead the PCRE_INFO_REQUIREDCHARFLAGS and
2857 PCRE_INFO_REQUIREDCHAR values should be used.
2858
2859 PCRE_INFO_MATCH_EMPTY
2860
2861 Return 1 if the pattern can match an empty string, otherwise 0. The
2862 fourth argument should point to an int variable.
2863
2864 PCRE_INFO_MATCHLIMIT
2865
2866 If the pattern set a match limit by including an item of the form
2867 (*LIMIT_MATCH=nnnn) at the start, the value is returned. The fourth
2868 argument should point to an unsigned 32-bit integer. If no such value
2869 has been set, the call to pcre_fullinfo() returns the error
2870 PCRE_ERROR_UNSET.
2871
2872 PCRE_INFO_MAXLOOKBEHIND
2873
2874 Return the number of characters (NB not data units) in the longest
2875 lookbehind assertion in the pattern. This information is useful when
2876 doing multi-segment matching using the partial matching facilities.
2877 Note that the simple assertions \b and \B require a one-character look-
2878 behind. \A also registers a one-character lookbehind, though it does
2879 not actually inspect the previous character. This is to ensure that at
2880 least one character from the old segment is retained when a new segment
2881 is processed. Otherwise, if there are no lookbehinds in the pattern, \A
2882 might match incorrectly at the start of a new segment.
2883
2884 PCRE_INFO_MINLENGTH
2885
2886 If the pattern was studied and a minimum length for matching subject
2887 strings was computed, its value is returned. Otherwise the returned
2888 value is -1. The value is a number of characters, which in UTF mode may
2889 be different from the number of data units. The fourth argument should
2890 point to an int variable. A non-negative value is a lower bound to the
2891 length of any matching string. There may not be any strings of that
2892 length that do actually match, but every string that does match is at
2893 least that long.
2894
2895 PCRE_INFO_NAMECOUNT
2896 PCRE_INFO_NAMEENTRYSIZE
2897 PCRE_INFO_NAMETABLE
2898
2899 PCRE supports the use of named as well as numbered capturing parenthe-
2900 ses. The names are just an additional way of identifying the parenthe-
2901 ses, which still acquire numbers. Several convenience functions such as
2902 pcre_get_named_substring() are provided for extracting captured sub-
2903 strings by name. It is also possible to extract the data directly, by
2904 first converting the name to a number in order to access the correct
2905 pointers in the output vector (described with pcre_exec() below). To do
2906 the conversion, you need to use the name-to-number map, which is
2907 described by these three values.
2908
2909 The map consists of a number of fixed-size entries. PCRE_INFO_NAMECOUNT
2910 gives the number of entries, and PCRE_INFO_NAMEENTRYSIZE gives the size
2911 of each entry; both of these return an int value. The entry size
2912 depends on the length of the longest name. PCRE_INFO_NAMETABLE returns
2913 a pointer to the first entry of the table. This is a pointer to char in
2914 the 8-bit library, where the first two bytes of each entry are the num-
2915 ber of the capturing parenthesis, most significant byte first. In the
2916 16-bit library, the pointer points to 16-bit data units, the first of
2917 which contains the parenthesis number. In the 32-bit library, the
2918 pointer points to 32-bit data units, the first of which contains the
2919 parenthesis number. The rest of the entry is the corresponding name,
2920 zero terminated.
2921
2922 The names are in alphabetical order. If (?| is used to create multiple
2923 groups with the same number, as described in the section on duplicate
2924 subpattern numbers in the pcrepattern page, the groups may be given the
2925 same name, but there is only one entry in the table. Different names
2926 for groups of the same number are not permitted. Duplicate names for
2927 subpatterns with different numbers are permitted, but only if PCRE_DUP-
2928 NAMES is set. They appear in the table in the order in which they were
2929 found in the pattern. In the absence of (?| this is the order of
2930 increasing number; when (?| is used this is not necessarily the case
2931 because later subpatterns may have lower numbers.
2932
2933 As a simple example of the name/number table, consider the following
2934 pattern after compilation by the 8-bit library (assume PCRE_EXTENDED is
2935 set, so white space - including newlines - is ignored):
2936
2937 (?<date> (?<year>(\d\d)?\d\d) -
2938 (?<month>\d\d) - (?<day>\d\d) )
2939
2940 There are four named subpatterns, so the table has four entries, and
2941 each entry in the table is eight bytes long. The table is as follows,
2942 with non-printing bytes shows in hexadecimal, and undefined bytes shown
2943 as ??:
2944
2945 00 01 d a t e 00 ??
2946 00 05 d a y 00 ?? ??
2947 00 04 m o n t h 00
2948 00 02 y e a r 00 ??
2949
2950 When writing code to extract data from named subpatterns using the
2951 name-to-number map, remember that the length of the entries is likely
2952 to be different for each compiled pattern.
2953
2954 PCRE_INFO_OKPARTIAL
2955
2956 Return 1 if the pattern can be used for partial matching with
2957 pcre_exec(), otherwise 0. The fourth argument should point to an int
2958 variable. From release 8.00, this always returns 1, because the
2959 restrictions that previously applied to partial matching have been
2960 lifted. The pcrepartial documentation gives details of partial match-
2961 ing.
2962
2963 PCRE_INFO_OPTIONS
2964
2965 Return a copy of the options with which the pattern was compiled. The
2966 fourth argument should point to an unsigned long int variable. These
2967 option bits are those specified in the call to pcre_compile(), modified
2968 by any top-level option settings at the start of the pattern itself. In
2969 other words, they are the options that will be in force when matching
2970 starts. For example, if the pattern /(?im)abc(?-i)d/ is compiled with
2971 the PCRE_EXTENDED option, the result is PCRE_CASELESS, PCRE_MULTILINE,
2972 and PCRE_EXTENDED.
2973
2974 A pattern is automatically anchored by PCRE if all of its top-level
2975 alternatives begin with one of the following:
2976
2977 ^ unless PCRE_MULTILINE is set
2978 \A always
2979 \G always
2980 .* if PCRE_DOTALL is set and there are no back
2981 references to the subpattern in which .* appears
2982
2983 For such patterns, the PCRE_ANCHORED bit is set in the options returned
2984 by pcre_fullinfo().
2985
2986 PCRE_INFO_RECURSIONLIMIT
2987
2988 If the pattern set a recursion limit by including an item of the form
2989 (*LIMIT_RECURSION=nnnn) at the start, the value is returned. The fourth
2990 argument should point to an unsigned 32-bit integer. If no such value
2991 has been set, the call to pcre_fullinfo() returns the error
2992 PCRE_ERROR_UNSET.
2993
2994 PCRE_INFO_SIZE
2995
2996 Return the size of the compiled pattern in bytes (for all three
2997 libraries). The fourth argument should point to a size_t variable. This
2998 value does not include the size of the pcre structure that is returned
2999 by pcre_compile(). The value that is passed as the argument to
3000 pcre_malloc() when pcre_compile() is getting memory in which to place
3001 the compiled data is the value returned by this option plus the size of
3002 the pcre structure. Studying a compiled pattern, with or without JIT,
3003 does not alter the value returned by this option.
3004
3005 PCRE_INFO_STUDYSIZE
3006
3007 Return the size in bytes (for all three libraries) of the data block
3008 pointed to by the study_data field in a pcre_extra block. If pcre_extra
3009 is NULL, or there is no study data, zero is returned. The fourth argu-
3010 ment should point to a size_t variable. The study_data field is set by
3011 pcre_study() to record information that will speed up matching (see the
3012 section entitled "Studying a pattern" above). The format of the
3013 study_data block is private, but its length is made available via this
3014 option so that it can be saved and restored (see the pcreprecompile
3015 documentation for details).
3016
3017 PCRE_INFO_REQUIREDCHARFLAGS
3018
3019 Returns 1 if there is a rightmost literal data unit that must exist in
3020 any matched string, other than at its start. The fourth argument should
3021 point to an int variable. If there is no such value, 0 is returned. If
3022 returning 1, the character value itself can be retrieved using
3023 PCRE_INFO_REQUIREDCHAR.
3024
3025 For anchored patterns, a last literal value is recorded only if it fol-
3026 lows something of variable length. For example, for the pattern
3027 /^a\d+z\d+/ the returned value 1 (with "z" returned from
3028 PCRE_INFO_REQUIREDCHAR), but for /^a\dz\d/ the returned value is 0.
3029
3030 PCRE_INFO_REQUIREDCHAR
3031
3032 Return the value of the rightmost literal data unit that must exist in
3033 any matched string, other than at its start, if such a value has been
3034 recorded. The fourth argument should point to an uint32_t variable. If
3035 there is no such value, 0 is returned.
3036
3037
3038 REFERENCE COUNTS
3039
3040 int pcre_refcount(pcre *code, int adjust);
3041
3042 The pcre_refcount() function is used to maintain a reference count in
3043 the data block that contains a compiled pattern. It is provided for the
3044 benefit of applications that operate in an object-oriented manner,
3045 where different parts of the application may be using the same compiled
3046 pattern, but you want to free the block when they are all done.
3047
3048 When a pattern is compiled, the reference count field is initialized to
3049 zero. It is changed only by calling this function, whose action is to
3050 add the adjust value (which may be positive or negative) to it. The
3051 yield of the function is the new value. However, the value of the count
3052 is constrained to lie between 0 and 65535, inclusive. If the new value
3053 is outside these limits, it is forced to the appropriate limit value.
3054
3055 Except when it is zero, the reference count is not correctly preserved
3056 if a pattern is compiled on one host and then transferred to a host
3057 whose byte-order is different. (This seems a highly unlikely scenario.)
3058
3059
3060 MATCHING A PATTERN: THE TRADITIONAL FUNCTION
3061
3062 int pcre_exec(const pcre *code, const pcre_extra *extra,
3063 const char *subject, int length, int startoffset,
3064 int options, int *ovector, int ovecsize);
3065
3066 The function pcre_exec() is called to match a subject string against a
3067 compiled pattern, which is passed in the code argument. If the pattern
3068 was studied, the result of the study should be passed in the extra
3069 argument. You can call pcre_exec() with the same code and extra argu-
3070 ments as many times as you like, in order to match different subject
3071 strings with the same pattern.
3072
3073 This function is the main matching facility of the library, and it
3074 operates in a Perl-like manner. For specialist use there is also an
3075 alternative matching function, which is described below in the section
3076 about the pcre_dfa_exec() function.
3077
3078 In most applications, the pattern will have been compiled (and option-
3079 ally studied) in the same process that calls pcre_exec(). However, it
3080 is possible to save compiled patterns and study data, and then use them
3081 later in different processes, possibly even on different hosts. For a
3082 discussion about this, see the pcreprecompile documentation.
3083
3084 Here is an example of a simple call to pcre_exec():
3085
3086 int rc;
3087 int ovector[30];
3088 rc = pcre_exec(
3089 re, /* result of pcre_compile() */
3090 NULL, /* we didn't study the pattern */
3091 "some string", /* the subject string */
3092 11, /* the length of the subject string */
3093 0, /* start at offset 0 in the subject */
3094 0, /* default options */
3095 ovector, /* vector of integers for substring information */
3096 30); /* number of elements (NOT size in bytes) */
3097
3098 Extra data for pcre_exec()
3099
3100 If the extra argument is not NULL, it must point to a pcre_extra data
3101 block. The pcre_study() function returns such a block (when it doesn't
3102 return NULL), but you can also create one for yourself, and pass addi-
3103 tional information in it. The pcre_extra block contains the following
3104 fields (not necessarily in this order):
3105
3106 unsigned long int flags;
3107 void *study_data;
3108 void *executable_jit;
3109 unsigned long int match_limit;
3110 unsigned long int match_limit_recursion;
3111 void *callout_data;
3112 const unsigned char *tables;
3113 unsigned char **mark;
3114
3115 In the 16-bit version of this structure, the mark field has type
3116 "PCRE_UCHAR16 **".
3117
3118 In the 32-bit version of this structure, the mark field has type
3119 "PCRE_UCHAR32 **".
3120
3121 The flags field is used to specify which of the other fields are set.
3122 The flag bits are:
3123
3124 PCRE_EXTRA_CALLOUT_DATA
3125 PCRE_EXTRA_EXECUTABLE_JIT
3126 PCRE_EXTRA_MARK
3127 PCRE_EXTRA_MATCH_LIMIT
3128 PCRE_EXTRA_MATCH_LIMIT_RECURSION
3129 PCRE_EXTRA_STUDY_DATA
3130 PCRE_EXTRA_TABLES
3131
3132 Other flag bits should be set to zero. The study_data field and some-
3133 times the executable_jit field are set in the pcre_extra block that is
3134 returned by pcre_study(), together with the appropriate flag bits. You
3135 should not set these yourself, but you may add to the block by setting
3136 other fields and their corresponding flag bits.
3137
3138 The match_limit field provides a means of preventing PCRE from using up
3139 a vast amount of resources when running patterns that are not going to
3140 match, but which have a very large number of possibilities in their
3141 search trees. The classic example is a pattern that uses nested unlim-
3142 ited repeats.
3143
3144 Internally, pcre_exec() uses a function called match(), which it calls
3145 repeatedly (sometimes recursively). The limit set by match_limit is
3146 imposed on the number of times this function is called during a match,
3147 which has the effect of limiting the amount of backtracking that can
3148 take place. For patterns that are not anchored, the count restarts from
3149 zero for each position in the subject string.
3150
3151 When pcre_exec() is called with a pattern that was successfully studied
3152 with a JIT option, the way that the matching is executed is entirely
3153 different. However, there is still the possibility of runaway matching
3154 that goes on for a very long time, and so the match_limit value is also
3155 used in this case (but in a different way) to limit how long the match-
3156 ing can continue.
3157
3158 The default value for the limit can be set when PCRE is built; the
3159 default default is 10 million, which handles all but the most extreme
3160 cases. You can override the default by suppling pcre_exec() with a
3161 pcre_extra block in which match_limit is set, and
3162 PCRE_EXTRA_MATCH_LIMIT is set in the flags field. If the limit is
3163 exceeded, pcre_exec() returns PCRE_ERROR_MATCHLIMIT.
3164
3165 A value for the match limit may also be supplied by an item at the
3166 start of a pattern of the form
3167
3168 (*LIMIT_MATCH=d)
3169
3170 where d is a decimal number. However, such a setting is ignored unless
3171 d is less than the limit set by the caller of pcre_exec() or, if no
3172 such limit is set, less than the default.
3173
3174 The match_limit_recursion field is similar to match_limit, but instead
3175 of limiting the total number of times that match() is called, it limits
3176 the depth of recursion. The recursion depth is a smaller number than
3177 the total number of calls, because not all calls to match() are recur-
3178 sive. This limit is of use only if it is set smaller than match_limit.
3179
3180 Limiting the recursion depth limits the amount of machine stack that
3181 can be used, or, when PCRE has been compiled to use memory on the heap
3182 instead of the stack, the amount of heap memory that can be used. This
3183 limit is not relevant, and is ignored, when matching is done using JIT
3184 compiled code.
3185
3186 The default value for match_limit_recursion can be set when PCRE is
3187 built; the default default is the same value as the default for
3188 match_limit. You can override the default by suppling pcre_exec() with
3189 a pcre_extra block in which match_limit_recursion is set, and
3190 PCRE_EXTRA_MATCH_LIMIT_RECURSION is set in the flags field. If the
3191 limit is exceeded, pcre_exec() returns PCRE_ERROR_RECURSIONLIMIT.
3192
3193 A value for the recursion limit may also be supplied by an item at the
3194 start of a pattern of the form
3195
3196 (*LIMIT_RECURSION=d)
3197
3198 where d is a decimal number. However, such a setting is ignored unless
3199 d is less than the limit set by the caller of pcre_exec() or, if no
3200 such limit is set, less than the default.
3201
3202 The callout_data field is used in conjunction with the "callout" fea-
3203 ture, and is described in the pcrecallout documentation.
3204
3205 The tables field is provided for use with patterns that have been pre-
3206 compiled using custom character tables, saved to disc or elsewhere, and
3207 then reloaded, because the tables that were used to compile a pattern
3208 are not saved with it. See the pcreprecompile documentation for a dis-
3209 cussion of saving compiled patterns for later use. If NULL is passed
3210 using this mechanism, it forces PCRE's internal tables to be used.
3211
3212 Warning: The tables that pcre_exec() uses must be the same as those
3213 that were used when the pattern was compiled. If this is not the case,
3214 the behaviour of pcre_exec() is undefined. Therefore, when a pattern is
3215 compiled and matched in the same process, this field should never be
3216 set. In this (the most common) case, the correct table pointer is auto-
3217 matically passed with the compiled pattern from pcre_compile() to
3218 pcre_exec().
3219
3220 If PCRE_EXTRA_MARK is set in the flags field, the mark field must be
3221 set to point to a suitable variable. If the pattern contains any back-
3222 tracking control verbs such as (*MARK:NAME), and the execution ends up
3223 with a name to pass back, a pointer to the name string (zero termi-
3224 nated) is placed in the variable pointed to by the mark field. The
3225 names are within the compiled pattern; if you wish to retain such a
3226 name you must copy it before freeing the memory of a compiled pattern.
3227 If there is no name to pass back, the variable pointed to by the mark
3228 field is set to NULL. For details of the backtracking control verbs,
3229 see the section entitled "Backtracking control" in the pcrepattern doc-
3230 umentation.
3231
3232 Option bits for pcre_exec()
3233
3234 The unused bits of the options argument for pcre_exec() must be zero.
3235 The only bits that may be set are PCRE_ANCHORED, PCRE_NEWLINE_xxx,
3236 PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, PCRE_NOTEMPTY_ATSTART,
3237 PCRE_NO_START_OPTIMIZE, PCRE_NO_UTF8_CHECK, PCRE_PARTIAL_HARD, and
3238 PCRE_PARTIAL_SOFT.
3239
3240 If the pattern was successfully studied with one of the just-in-time
3241 (JIT) compile options, the only supported options for JIT execution are
3242 PCRE_NO_UTF8_CHECK, PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY,
3243 PCRE_NOTEMPTY_ATSTART, PCRE_PARTIAL_HARD, and PCRE_PARTIAL_SOFT. If an
3244 unsupported option is used, JIT execution is disabled and the normal
3245 interpretive code in pcre_exec() is run.
3246
3247 PCRE_ANCHORED
3248
3249 The PCRE_ANCHORED option limits pcre_exec() to matching at the first
3250 matching position. If a pattern was compiled with PCRE_ANCHORED, or
3251 turned out to be anchored by virtue of its contents, it cannot be made
3252 unachored at matching time.
3253
3254 PCRE_BSR_ANYCRLF
3255 PCRE_BSR_UNICODE
3256
3257 These options (which are mutually exclusive) control what the \R escape
3258 sequence matches. The choice is either to match only CR, LF, or CRLF,
3259 or to match any Unicode newline sequence. These options override the
3260 choice that was made or defaulted when the pattern was compiled.
3261
3262 PCRE_NEWLINE_CR
3263 PCRE_NEWLINE_LF
3264 PCRE_NEWLINE_CRLF
3265 PCRE_NEWLINE_ANYCRLF
3266 PCRE_NEWLINE_ANY
3267
3268 These options override the newline definition that was chosen or
3269 defaulted when the pattern was compiled. For details, see the descrip-
3270 tion of pcre_compile() above. During matching, the newline choice
3271 affects the behaviour of the dot, circumflex, and dollar metacharac-
3272 ters. It may also alter the way the match position is advanced after a
3273 match failure for an unanchored pattern.
3274
3275 When PCRE_NEWLINE_CRLF, PCRE_NEWLINE_ANYCRLF, or PCRE_NEWLINE_ANY is
3276 set, and a match attempt for an unanchored pattern fails when the cur-
3277 rent position is at a CRLF sequence, and the pattern contains no
3278 explicit matches for CR or LF characters, the match position is
3279 advanced by two characters instead of one, in other words, to after the
3280 CRLF.
3281
3282 The above rule is a compromise that makes the most common cases work as
3283 expected. For example, if the pattern is .+A (and the PCRE_DOTALL
3284 option is not set), it does not match the string "\r\nA" because, after
3285 failing at the start, it skips both the CR and the LF before retrying.
3286 However, the pattern [\r\n]A does match that string, because it con-
3287 tains an explicit CR or LF reference, and so advances only by one char-
3288 acter after the first failure.
3289
3290 An explicit match for CR of LF is either a literal appearance of one of
3291 those characters, or one of the \r or \n escape sequences. Implicit
3292 matches such as [^X] do not count, nor does \s (which includes CR and
3293 LF in the characters that it matches).
3294
3295 Notwithstanding the above, anomalous effects may still occur when CRLF
3296 is a valid newline sequence and explicit \r or \n escapes appear in the
3297 pattern.
3298
3299 PCRE_NOTBOL
3300
3301 This option specifies that first character of the subject string is not
3302 the beginning of a line, so the circumflex metacharacter should not
3303 match before it. Setting this without PCRE_MULTILINE (at compile time)
3304 causes circumflex never to match. This option affects only the behav-
3305 iour of the circumflex metacharacter. It does not affect \A.
3306
3307 PCRE_NOTEOL
3308
3309 This option specifies that the end of the subject string is not the end
3310 of a line, so the dollar metacharacter should not match it nor (except
3311 in multiline mode) a newline immediately before it. Setting this with-
3312 out PCRE_MULTILINE (at compile time) causes dollar never to match. This
3313 option affects only the behaviour of the dollar metacharacter. It does
3314 not affect \Z or \z.
3315
3316 PCRE_NOTEMPTY
3317
3318 An empty string is not considered to be a valid match if this option is
3319 set. If there are alternatives in the pattern, they are tried. If all
3320 the alternatives match the empty string, the entire match fails. For
3321 example, if the pattern
3322
3323 a?b?
3324
3325 is applied to a string not beginning with "a" or "b", it matches an
3326 empty string at the start of the subject. With PCRE_NOTEMPTY set, this
3327 match is not valid, so PCRE searches further into the string for occur-
3328 rences of "a" or "b".
3329
3330 PCRE_NOTEMPTY_ATSTART
3331
3332 This is like PCRE_NOTEMPTY, except that an empty string match that is
3333 not at the start of the subject is permitted. If the pattern is
3334 anchored, such a match can occur only if the pattern contains \K.
3335
3336 Perl has no direct equivalent of PCRE_NOTEMPTY or
3337 PCRE_NOTEMPTY_ATSTART, but it does make a special case of a pattern
3338 match of the empty string within its split() function, and when using
3339 the /g modifier. It is possible to emulate Perl's behaviour after
3340 matching a null string by first trying the match again at the same off-
3341 set with PCRE_NOTEMPTY_ATSTART and PCRE_ANCHORED, and then if that
3342 fails, by advancing the starting offset (see below) and trying an ordi-
3343 nary match again. There is some code that demonstrates how to do this
3344 in the pcredemo sample program. In the most general case, you have to
3345 check to see if the newline convention recognizes CRLF as a newline,
3346 and if so, and the current character is CR followed by LF, advance the
3347 starting offset by two characters instead of one.
3348
3349 PCRE_NO_START_OPTIMIZE
3350
3351 There are a number of optimizations that pcre_exec() uses at the start
3352 of a match, in order to speed up the process. For example, if it is
3353 known that an unanchored match must start with a specific character, it
3354 searches the subject for that character, and fails immediately if it
3355 cannot find it, without actually running the main matching function.
3356 This means that a special item such as (*COMMIT) at the start of a pat-
3357 tern is not considered until after a suitable starting point for the
3358 match has been found. Also, when callouts or (*MARK) items are in use,
3359 these "start-up" optimizations can cause them to be skipped if the pat-
3360 tern is never actually used. The start-up optimizations are in effect a
3361 pre-scan of the subject that takes place before the pattern is run.
3362
3363 The PCRE_NO_START_OPTIMIZE option disables the start-up optimizations,
3364 possibly causing performance to suffer, but ensuring that in cases
3365 where the result is "no match", the callouts do occur, and that items
3366 such as (*COMMIT) and (*MARK) are considered at every possible starting
3367 position in the subject string. If PCRE_NO_START_OPTIMIZE is set at
3368 compile time, it cannot be unset at matching time. The use of
3369 PCRE_NO_START_OPTIMIZE at matching time (that is, passing it to
3370 pcre_exec()) disables JIT execution; in this situation, matching is
3371 always done using interpretively.
3372
3373 Setting PCRE_NO_START_OPTIMIZE can change the outcome of a matching
3374 operation. Consider the pattern
3375
3376 (*COMMIT)ABC
3377
3378 When this is compiled, PCRE records the fact that a match must start
3379 with the character "A". Suppose the subject string is "DEFABC". The
3380 start-up optimization scans along the subject, finds "A" and runs the
3381 first match attempt from there. The (*COMMIT) item means that the pat-
3382 tern must match the current starting position, which in this case, it
3383 does. However, if the same match is run with PCRE_NO_START_OPTIMIZE
3384 set, the initial scan along the subject string does not happen. The
3385 first match attempt is run starting from "D" and when this fails,
3386 (*COMMIT) prevents any further matches being tried, so the overall
3387 result is "no match". If the pattern is studied, more start-up opti-
3388 mizations may be used. For example, a minimum length for the subject
3389 may be recorded. Consider the pattern
3390
3391 (*MARK:A)(X|Y)
3392
3393 The minimum length for a match is one character. If the subject is
3394 "ABC", there will be attempts to match "ABC", "BC", "C", and then
3395 finally an empty string. If the pattern is studied, the final attempt
3396 does not take place, because PCRE knows that the subject is too short,
3397 and so the (*MARK) is never encountered. In this case, studying the
3398 pattern does not affect the overall match result, which is still "no
3399 match", but it does affect the auxiliary information that is returned.
3400
3401 PCRE_NO_UTF8_CHECK
3402
3403 When PCRE_UTF8 is set at compile time, the validity of the subject as a
3404 UTF-8 string is automatically checked when pcre_exec() is subsequently
3405 called. The entire string is checked before any other processing takes
3406 place. The value of startoffset is also checked to ensure that it
3407 points to the start of a UTF-8 character. There is a discussion about
3408 the validity of UTF-8 strings in the pcreunicode page. If an invalid
3409 sequence of bytes is found, pcre_exec() returns the error
3410 PCRE_ERROR_BADUTF8 or, if PCRE_PARTIAL_HARD is set and the problem is a
3411 truncated character at the end of the subject, PCRE_ERROR_SHORTUTF8. In
3412 both cases, information about the precise nature of the error may also
3413 be returned (see the descriptions of these errors in the section enti-
3414 tled Error return values from pcre_exec() below). If startoffset con-
3415 tains a value that does not point to the start of a UTF-8 character (or
3416 to the end of the subject), PCRE_ERROR_BADUTF8_OFFSET is returned.
3417
3418 If you already know that your subject is valid, and you want to skip
3419 these checks for performance reasons, you can set the
3420 PCRE_NO_UTF8_CHECK option when calling pcre_exec(). You might want to
3421 do this for the second and subsequent calls to pcre_exec() if you are
3422 making repeated calls to find all the matches in a single subject
3423 string. However, you should be sure that the value of startoffset
3424 points to the start of a character (or the end of the subject). When
3425 PCRE_NO_UTF8_CHECK is set, the effect of passing an invalid string as a
3426 subject or an invalid value of startoffset is undefined. Your program
3427 may crash or loop.
3428
3429 PCRE_PARTIAL_HARD
3430 PCRE_PARTIAL_SOFT
3431
3432 These options turn on the partial matching feature. For backwards com-
3433 patibility, PCRE_PARTIAL is a synonym for PCRE_PARTIAL_SOFT. A partial
3434 match occurs if the end of the subject string is reached successfully,
3435 but there are not enough subject characters to complete the match. If
3436 this happens when PCRE_PARTIAL_SOFT (but not PCRE_PARTIAL_HARD) is set,
3437 matching continues by testing any remaining alternatives. Only if no
3438 complete match can be found is PCRE_ERROR_PARTIAL returned instead of
3439 PCRE_ERROR_NOMATCH. In other words, PCRE_PARTIAL_SOFT says that the
3440 caller is prepared to handle a partial match, but only if no complete
3441 match can be found.
3442
3443 If PCRE_PARTIAL_HARD is set, it overrides PCRE_PARTIAL_SOFT. In this
3444 case, if a partial match is found, pcre_exec() immediately returns
3445 PCRE_ERROR_PARTIAL, without considering any other alternatives. In
3446 other words, when PCRE_PARTIAL_HARD is set, a partial match is consid-
3447 ered to be more important that an alternative complete match.
3448
3449 In both cases, the portion of the string that was inspected when the
3450 partial match was found is set as the first matching string. There is a
3451 more detailed discussion of partial and multi-segment matching, with
3452 examples, in the pcrepartial documentation.
3453
3454 The string to be matched by pcre_exec()
3455
3456 The subject string is passed to pcre_exec() as a pointer in subject, a
3457 length in length, and a starting offset in startoffset. The units for
3458 length and startoffset are bytes for the 8-bit library, 16-bit data
3459 items for the 16-bit library, and 32-bit data items for the 32-bit
3460 library.
3461
3462 If startoffset is negative or greater than the length of the subject,
3463 pcre_exec() returns PCRE_ERROR_BADOFFSET. When the starting offset is
3464 zero, the search for a match starts at the beginning of the subject,
3465 and this is by far the most common case. In UTF-8 or UTF-16 mode, the
3466 offset must point to the start of a character, or the end of the sub-
3467 ject (in UTF-32 mode, one data unit equals one character, so all off-
3468 sets are valid). Unlike the pattern string, the subject may contain
3469 binary zeroes.
3470
3471 A non-zero starting offset is useful when searching for another match
3472 in the same subject by calling pcre_exec() again after a previous suc-
3473 cess. Setting startoffset differs from just passing over a shortened
3474 string and setting PCRE_NOTBOL in the case of a pattern that begins
3475 with any kind of lookbehind. For example, consider the pattern
3476
3477 \Biss\B
3478
3479 which finds occurrences of "iss" in the middle of words. (\B matches
3480 only if the current position in the subject is not a word boundary.)
3481 When applied to the string "Mississipi" the first call to pcre_exec()
3482 finds the first occurrence. If pcre_exec() is called again with just
3483 the remainder of the subject, namely "issipi", it does not match,
3484 because \B is always false at the start of the subject, which is deemed
3485 to be a word boundary. However, if pcre_exec() is passed the entire
3486 string again, but with startoffset set to 4, it finds the second occur-
3487 rence of "iss" because it is able to look behind the starting point to
3488 discover that it is preceded by a letter.
3489
3490 Finding all the matches in a subject is tricky when the pattern can
3491 match an empty string. It is possible to emulate Perl's /g behaviour by
3492 first trying the match again at the same offset, with the
3493 PCRE_NOTEMPTY_ATSTART and PCRE_ANCHORED options, and then if that
3494 fails, advancing the starting offset and trying an ordinary match
3495 again. There is some code that demonstrates how to do this in the pcre-
3496 demo sample program. In the most general case, you have to check to see
3497 if the newline convention recognizes CRLF as a newline, and if so, and
3498 the current character is CR followed by LF, advance the starting offset
3499 by two characters instead of one.
3500
3501 If a non-zero starting offset is passed when the pattern is anchored,
3502 one attempt to match at the given offset is made. This can only succeed
3503 if the pattern does not require the match to be at the start of the
3504 subject.
3505
3506 How pcre_exec() returns captured substrings
3507
3508 In general, a pattern matches a certain portion of the subject, and in
3509 addition, further substrings from the subject may be picked out by
3510 parts of the pattern. Following the usage in Jeffrey Friedl's book,
3511 this is called "capturing" in what follows, and the phrase "capturing
3512 subpattern" is used for a fragment of a pattern that picks out a sub-
3513 string. PCRE supports several other kinds of parenthesized subpattern
3514 that do not cause substrings to be captured.
3515
3516 Captured substrings are returned to the caller via a vector of integers
3517 whose address is passed in ovector. The number of elements in the vec-
3518 tor is passed in ovecsize, which must be a non-negative number. Note:
3519 this argument is NOT the size of ovector in bytes.
3520
3521 The first two-thirds of the vector is used to pass back captured sub-
3522 strings, each substring using a pair of integers. The remaining third
3523 of the vector is used as workspace by pcre_exec() while matching cap-
3524 turing subpatterns, and is not available for passing back information.
3525 The number passed in ovecsize should always be a multiple of three. If
3526 it is not, it is rounded down.
3527
3528 When a match is successful, information about captured substrings is
3529 returned in pairs of integers, starting at the beginning of ovector,
3530 and continuing up to two-thirds of its length at the most. The first
3531 element of each pair is set to the offset of the first character in a
3532 substring, and the second is set to the offset of the first character
3533 after the end of a substring. These values are always data unit off-
3534 sets, even in UTF mode. They are byte offsets in the 8-bit library,
3535 16-bit data item offsets in the 16-bit library, and 32-bit data item
3536 offsets in the 32-bit library. Note: they are not character counts.
3537
3538 The first pair of integers, ovector[0] and ovector[1], identify the
3539 portion of the subject string matched by the entire pattern. The next
3540 pair is used for the first capturing subpattern, and so on. The value
3541 returned by pcre_exec() is one more than the highest numbered pair that
3542 has been set. For example, if two substrings have been captured, the
3543 returned value is 3. If there are no capturing subpatterns, the return
3544 value from a successful match is 1, indicating that just the first pair
3545 of offsets has been set.
3546
3547 If a capturing subpattern is matched repeatedly, it is the last portion
3548 of the string that it matched that is returned.
3549
3550 If the vector is too small to hold all the captured substring offsets,
3551 it is used as far as possible (up to two-thirds of its length), and the
3552 function returns a value of zero. If neither the actual string matched
3553 nor any captured substrings are of interest, pcre_exec() may be called
3554 with ovector passed as NULL and ovecsize as zero. However, if the pat-
3555 tern contains back references and the ovector is not big enough to
3556 remember the related substrings, PCRE has to get additional memory for
3557 use during matching. Thus it is usually advisable to supply an ovector
3558 of reasonable size.
3559
3560 There are some cases where zero is returned (indicating vector over-
3561 flow) when in fact the vector is exactly the right size for the final
3562 match. For example, consider the pattern
3563
3564 (a)(?:(b)c|bd)
3565
3566 If a vector of 6 elements (allowing for only 1 captured substring) is
3567 given with subject string "abd", pcre_exec() will try to set the second
3568 captured string, thereby recording a vector overflow, before failing to
3569 match "c" and backing up to try the second alternative. The zero
3570 return, however, does correctly indicate that the maximum number of
3571 slots (namely 2) have been filled. In similar cases where there is tem-
3572 porary overflow, but the final number of used slots is actually less
3573 than the maximum, a non-zero value is returned.
3574
3575 The pcre_fullinfo() function can be used to find out how many capturing
3576 subpatterns there are in a compiled pattern. The smallest size for
3577 ovector that will allow for n captured substrings, in addition to the
3578 offsets of the substring matched by the whole pattern, is (n+1)*3.
3579
3580 It is possible for capturing subpattern number n+1 to match some part
3581 of the subject when subpattern n has not been used at all. For example,
3582 if the string "abc" is matched against the pattern (a|(z))(bc) the
3583 return from the function is 4, and subpatterns 1 and 3 are matched, but
3584 2 is not. When this happens, both values in the offset pairs corre-
3585 sponding to unused subpatterns are set to -1.
3586
3587 Offset values that correspond to unused subpatterns at the end of the
3588 expression are also set to -1. For example, if the string "abc" is
3589 matched against the pattern (abc)(x(yz)?)? subpatterns 2 and 3 are not
3590 matched. The return from the function is 2, because the highest used
3591 capturing subpattern number is 1, and the offsets for for the second
3592 and third capturing subpatterns (assuming the vector is large enough,
3593 of course) are set to -1.
3594
3595 Note: Elements in the first two-thirds of ovector that do not corre-
3596 spond to capturing parentheses in the pattern are never changed. That
3597 is, if a pattern contains n capturing parentheses, no more than ovec-
3598 tor[0] to ovector[2n+1] are set by pcre_exec(). The other elements (in
3599 the first two-thirds) retain whatever values they previously had.
3600
3601 Some convenience functions are provided for extracting the captured
3602 substrings as separate strings. These are described below.
3603
3604 Error return values from pcre_exec()
3605
3606 If pcre_exec() fails, it returns a negative number. The following are
3607 defined in the header file:
3608
3609 PCRE_ERROR_NOMATCH (-1)
3610
3611 The subject string did not match the pattern.
3612
3613 PCRE_ERROR_NULL (-2)
3614
3615 Either code or subject was passed as NULL, or ovector was NULL and
3616 ovecsize was not zero.
3617
3618 PCRE_ERROR_BADOPTION (-3)
3619
3620 An unrecognized bit was set in the options argument.
3621
3622 PCRE_ERROR_BADMAGIC (-4)
3623
3624 PCRE stores a 4-byte "magic number" at the start of the compiled code,
3625 to catch the case when it is passed a junk pointer and to detect when a
3626 pattern that was compiled in an environment of one endianness is run in
3627 an environment with the other endianness. This is the error that PCRE
3628 gives when the magic number is not present.
3629
3630 PCRE_ERROR_UNKNOWN_OPCODE (-5)
3631
3632 While running the pattern match, an unknown item was encountered in the
3633 compiled pattern. This error could be caused by a bug in PCRE or by
3634 overwriting of the compiled pattern.
3635
3636 PCRE_ERROR_NOMEMORY (-6)
3637
3638 If a pattern contains back references, but the ovector that is passed
3639 to pcre_exec() is not big enough to remember the referenced substrings,
3640 PCRE gets a block of memory at the start of matching to use for this
3641 purpose. If the call via pcre_malloc() fails, this error is given. The
3642 memory is automatically freed at the end of matching.
3643
3644 This error is also given if pcre_stack_malloc() fails in pcre_exec().
3645 This can happen only when PCRE has been compiled with --disable-stack-
3646 for-recursion.
3647
3648 PCRE_ERROR_NOSUBSTRING (-7)
3649
3650 This error is used by the pcre_copy_substring(), pcre_get_substring(),
3651 and pcre_get_substring_list() functions (see below). It is never
3652 returned by pcre_exec().
3653
3654 PCRE_ERROR_MATCHLIMIT (-8)
3655
3656 The backtracking limit, as specified by the match_limit field in a
3657 pcre_extra structure (or defaulted) was reached. See the description
3658 above.
3659
3660 PCRE_ERROR_CALLOUT (-9)
3661
3662 This error is never generated by pcre_exec() itself. It is provided for
3663 use by callout functions that want to yield a distinctive error code.
3664 See the pcrecallout documentation for details.
3665
3666 PCRE_ERROR_BADUTF8 (-10)
3667
3668 A string that contains an invalid UTF-8 byte sequence was passed as a
3669 subject, and the PCRE_NO_UTF8_CHECK option was not set. If the size of
3670 the output vector (ovecsize) is at least 2, the byte offset to the
3671 start of the the invalid UTF-8 character is placed in the first ele-
3672 ment, and a reason code is placed in the second element. The reason
3673 codes are listed in the following section. For backward compatibility,
3674 if PCRE_PARTIAL_HARD is set and the problem is a truncated UTF-8 char-
3675 acter at the end of the subject (reason codes 1 to 5),
3676 PCRE_ERROR_SHORTUTF8 is returned instead of PCRE_ERROR_BADUTF8.
3677
3678 PCRE_ERROR_BADUTF8_OFFSET (-11)
3679
3680 The UTF-8 byte sequence that was passed as a subject was checked and
3681 found to be valid (the PCRE_NO_UTF8_CHECK option was not set), but the
3682 value of startoffset did not point to the beginning of a UTF-8 charac-
3683 ter or the end of the subject.
3684
3685 PCRE_ERROR_PARTIAL (-12)
3686
3687 The subject string did not match, but it did match partially. See the
3688 pcrepartial documentation for details of partial matching.
3689
3690 PCRE_ERROR_BADPARTIAL (-13)
3691
3692 This code is no longer in use. It was formerly returned when the
3693 PCRE_PARTIAL option was used with a compiled pattern containing items
3694 that were not supported for partial matching. From release 8.00
3695 onwards, there are no restrictions on partial matching.
3696
3697 PCRE_ERROR_INTERNAL (-14)
3698
3699 An unexpected internal error has occurred. This error could be caused
3700 by a bug in PCRE or by overwriting of the compiled pattern.
3701
3702 PCRE_ERROR_BADCOUNT (-15)
3703
3704 This error is given if the value of the ovecsize argument is negative.
3705
3706 PCRE_ERROR_RECURSIONLIMIT (-21)
3707
3708 The internal recursion limit, as specified by the match_limit_recursion
3709 field in a pcre_extra structure (or defaulted) was reached. See the
3710 description above.
3711
3712 PCRE_ERROR_BADNEWLINE (-23)
3713
3714 An invalid combination of PCRE_NEWLINE_xxx options was given.
3715
3716 PCRE_ERROR_BADOFFSET (-24)
3717
3718 The value of startoffset was negative or greater than the length of the
3719 subject, that is, the value in length.
3720
3721 PCRE_ERROR_SHORTUTF8 (-25)
3722
3723 This error is returned instead of PCRE_ERROR_BADUTF8 when the subject
3724 string ends with a truncated UTF-8 character and the PCRE_PARTIAL_HARD
3725 option is set. Information about the failure is returned as for
3726 PCRE_ERROR_BADUTF8. It is in fact sufficient to detect this case, but
3727 this special error code for PCRE_PARTIAL_HARD precedes the implementa-
3728 tion of returned information; it is retained for backwards compatibil-
3729 ity.
3730
3731 PCRE_ERROR_RECURSELOOP (-26)
3732
3733 This error is returned when pcre_exec() detects a recursion loop within
3734 the pattern. Specifically, it means that either the whole pattern or a
3735 subpattern has been called recursively for the second time at the same
3736 position in the subject string. Some simple patterns that might do this
3737 are detected and faulted at compile time, but more complicated cases,
3738 in particular mutual recursions between two different subpatterns, can-
3739 not be detected until run time.
3740
3741 PCRE_ERROR_JIT_STACKLIMIT (-27)
3742
3743 This error is returned when a pattern that was successfully studied
3744 using a JIT compile option is being matched, but the memory available
3745 for the just-in-time processing stack is not large enough. See the
3746 pcrejit documentation for more details.
3747
3748 PCRE_ERROR_BADMODE (-28)
3749
3750 This error is given if a pattern that was compiled by the 8-bit library
3751 is passed to a 16-bit or 32-bit library function, or vice versa.
3752
3753 PCRE_ERROR_BADENDIANNESS (-29)
3754
3755 This error is given if a pattern that was compiled and saved is
3756 reloaded on a host with different endianness. The utility function
3757 pcre_pattern_to_host_byte_order() can be used to convert such a pattern
3758 so that it runs on the new host.
3759
3760 PCRE_ERROR_JIT_BADOPTION
3761
3762 This error is returned when a pattern that was successfully studied
3763 using a JIT compile option is being matched, but the matching mode
3764 (partial or complete match) does not correspond to any JIT compilation
3765 mode. When the JIT fast path function is used, this error may be also
3766 given for invalid options. See the pcrejit documentation for more
3767 details.
3768
3769 PCRE_ERROR_BADLENGTH (-32)
3770
3771 This error is given if pcre_exec() is called with a negative value for
3772 the length argument.
3773
3774 Error numbers -16 to -20, -22, and 30 are not used by pcre_exec().
3775
3776 Reason codes for invalid UTF-8 strings
3777
3778 This section applies only to the 8-bit library. The corresponding
3779 information for the 16-bit and 32-bit libraries is given in the pcre16
3780 and pcre32 pages.
3781
3782 When pcre_exec() returns either PCRE_ERROR_BADUTF8 or PCRE_ERROR_SHORT-
3783 UTF8, and the size of the output vector (ovecsize) is at least 2, the
3784 offset of the start of the invalid UTF-8 character is placed in the
3785 first output vector element (ovector[0]) and a reason code is placed in
3786 the second element (ovector[1]). The reason codes are given names in
3787 the pcre.h header file:
3788
3789 PCRE_UTF8_ERR1
3790 PCRE_UTF8_ERR2
3791 PCRE_UTF8_ERR3
3792 PCRE_UTF8_ERR4
3793 PCRE_UTF8_ERR5
3794
3795 The string ends with a truncated UTF-8 character; the code specifies
3796 how many bytes are missing (1 to 5). Although RFC 3629 restricts UTF-8
3797 characters to be no longer than 4 bytes, the encoding scheme (origi-
3798 nally defined by RFC 2279) allows for up to 6 bytes, and this is
3799 checked first; hence the possibility of 4 or 5 missing bytes.
3800
3801 PCRE_UTF8_ERR6
3802 PCRE_UTF8_ERR7
3803 PCRE_UTF8_ERR8
3804 PCRE_UTF8_ERR9
3805 PCRE_UTF8_ERR10
3806
3807 The two most significant bits of the 2nd, 3rd, 4th, 5th, or 6th byte of
3808 the character do not have the binary value 0b10 (that is, either the
3809 most significant bit is 0, or the next bit is 1).
3810
3811 PCRE_UTF8_ERR11
3812 PCRE_UTF8_ERR12
3813
3814 A character that is valid by the RFC 2279 rules is either 5 or 6 bytes
3815 long; these code points are excluded by RFC 3629.
3816
3817 PCRE_UTF8_ERR13
3818
3819 A 4-byte character has a value greater than 0x10fff; these code points
3820 are excluded by RFC 3629.
3821
3822 PCRE_UTF8_ERR14
3823
3824 A 3-byte character has a value in the range 0xd800 to 0xdfff; this
3825 range of code points are reserved by RFC 3629 for use with UTF-16, and
3826 so are excluded from UTF-8.
3827
3828 PCRE_UTF8_ERR15
3829 PCRE_UTF8_ERR16
3830 PCRE_UTF8_ERR17
3831 PCRE_UTF8_ERR18
3832 PCRE_UTF8_ERR19
3833
3834 A 2-, 3-, 4-, 5-, or 6-byte character is "overlong", that is, it codes
3835 for a value that can be represented by fewer bytes, which is invalid.
3836 For example, the two bytes 0xc0, 0xae give the value 0x2e, whose cor-
3837 rect coding uses just one byte.
3838
3839 PCRE_UTF8_ERR20
3840
3841 The two most significant bits of the first byte of a character have the
3842 binary value 0b10 (that is, the most significant bit is 1 and the sec-
3843 ond is 0). Such a byte can only validly occur as the second or subse-
3844 quent byte of a multi-byte character.
3845
3846 PCRE_UTF8_ERR21
3847
3848 The first byte of a character has the value 0xfe or 0xff. These values
3849 can never occur in a valid UTF-8 string.
3850
3851 PCRE_UTF8_ERR22
3852
3853 This error code was formerly used when the presence of a so-called
3854 "non-character" caused an error. Unicode corrigendum #9 makes it clear
3855 that such characters should not cause a string to be rejected, and so
3856 this code is no longer in use and is never returned.
3857
3858
3859 EXTRACTING CAPTURED SUBSTRINGS BY NUMBER
3860
3861 int pcre_copy_substring(const char *subject, int *ovector,
3862 int stringcount, int stringnumber, char *buffer,
3863 int buffersize);
3864
3865 int pcre_get_substring(const char *subject, int *ovector,
3866 int stringcount, int stringnumber,
3867 const char **stringptr);
3868
3869 int pcre_get_substring_list(const char *subject,
3870 int *ovector, int stringcount, const char ***listptr);
3871
3872 Captured substrings can be accessed directly by using the offsets
3873 returned by pcre_exec() in ovector. For convenience, the functions
3874 pcre_copy_substring(), pcre_get_substring(), and pcre_get_sub-
3875 string_list() are provided for extracting captured substrings as new,
3876 separate, zero-terminated strings. These functions identify substrings
3877 by number. The next section describes functions for extracting named
3878 substrings.
3879
3880 A substring that contains a binary zero is correctly extracted and has
3881 a further zero added on the end, but the result is not, of course, a C
3882 string. However, you can process such a string by referring to the
3883 length that is returned by pcre_copy_substring() and pcre_get_sub-
3884 string(). Unfortunately, the interface to pcre_get_substring_list() is
3885 not adequate for handling strings containing binary zeros, because the
3886 end of the final string is not independently indicated.
3887
3888 The first three arguments are the same for all three of these func-
3889 tions: subject is the subject string that has just been successfully
3890 matched, ovector is a pointer to the vector of integer offsets that was
3891 passed to pcre_exec(), and stringcount is the number of substrings that
3892 were captured by the match, including the substring that matched the
3893 entire regular expression. This is the value returned by pcre_exec() if
3894 it is greater than zero. If pcre_exec() returned zero, indicating that
3895 it ran out of space in ovector, the value passed as stringcount should
3896 be the number of elements in the vector divided by three.
3897
3898 The functions pcre_copy_substring() and pcre_get_substring() extract a
3899 single substring, whose number is given as stringnumber. A value of
3900 zero extracts the substring that matched the entire pattern, whereas
3901 higher values extract the captured substrings. For pcre_copy_sub-
3902 string(), the string is placed in buffer, whose length is given by
3903 buffersize, while for pcre_get_substring() a new block of memory is
3904 obtained via pcre_malloc, and its address is returned via stringptr.
3905 The yield of the function is the length of the string, not including
3906 the terminating zero, or one of these error codes:
3907
3908 PCRE_ERROR_NOMEMORY (-6)
3909
3910 The buffer was too small for pcre_copy_substring(), or the attempt to
3911 get memory failed for pcre_get_substring().
3912
3913 PCRE_ERROR_NOSUBSTRING (-7)
3914
3915 There is no substring whose number is stringnumber.
3916
3917 The pcre_get_substring_list() function extracts all available sub-
3918 strings and builds a list of pointers to them. All this is done in a
3919 single block of memory that is obtained via pcre_malloc. The address of
3920 the memory block is returned via listptr, which is also the start of
3921 the list of string pointers. The end of the list is marked by a NULL
3922 pointer. The yield of the function is zero if all went well, or the
3923 error code
3924
3925 PCRE_ERROR_NOMEMORY (-6)
3926
3927 if the attempt to get the memory block failed.
3928
3929 When any of these functions encounter a substring that is unset, which
3930 can happen when capturing subpattern number n+1 matches some part of
3931 the subject, but subpattern n has not been used at all, they return an
3932 empty string. This can be distinguished from a genuine zero-length sub-
3933 string by inspecting the appropriate offset in ovector, which is nega-
3934 tive for unset substrings.
3935
3936 The two convenience functions pcre_free_substring() and pcre_free_sub-
3937 string_list() can be used to free the memory returned by a previous
3938 call of pcre_get_substring() or pcre_get_substring_list(), respec-
3939 tively. They do nothing more than call the function pointed to by
3940 pcre_free, which of course could be called directly from a C program.
3941 However, PCRE is used in some situations where it is linked via a spe-
3942 cial interface to another programming language that cannot use
3943 pcre_free directly; it is for these cases that the functions are pro-
3944 vided.
3945
3946
3947 EXTRACTING CAPTURED SUBSTRINGS BY NAME
3948
3949 int pcre_get_stringnumber(const pcre *code,
3950 const char *name);
3951
3952 int pcre_copy_named_substring(const pcre *code,
3953 const char *subject, int *ovector,
3954 int stringcount, const char *stringname,
3955 char *buffer, int buffersize);
3956
3957 int pcre_get_named_substring(const pcre *code,
3958 const char *subject, int *ovector,
3959 int stringcount, const char *stringname,
3960 const char **stringptr);
3961
3962 To extract a substring by name, you first have to find associated num-
3963 ber. For example, for this pattern
3964
3965 (a+)b(?<xxx>\d+)...
3966
3967 the number of the subpattern called "xxx" is 2. If the name is known to
3968 be unique (PCRE_DUPNAMES was not set), you can find the number from the
3969 name by calling pcre_get_stringnumber(). The first argument is the com-
3970 piled pattern, and the second is the name. The yield of the function is
3971 the subpattern number, or PCRE_ERROR_NOSUBSTRING (-7) if there is no
3972 subpattern of that name.
3973
3974 Given the number, you can extract the substring directly, or use one of
3975 the functions described in the previous section. For convenience, there
3976 are also two functions that do the whole job.
3977
3978 Most of the arguments of pcre_copy_named_substring() and
3979 pcre_get_named_substring() are the same as those for the similarly
3980 named functions that extract by number. As these are described in the
3981 previous section, they are not re-described here. There are just two
3982 differences:
3983
3984 First, instead of a substring number, a substring name is given. Sec-
3985 ond, there is an extra argument, given at the start, which is a pointer
3986 to the compiled pattern. This is needed in order to gain access to the
3987 name-to-number translation table.
3988
3989 These functions call pcre_get_stringnumber(), and if it succeeds, they
3990 then call pcre_copy_substring() or pcre_get_substring(), as appropri-
3991 ate. NOTE: If PCRE_DUPNAMES is set and there are duplicate names, the
3992 behaviour may not be what you want (see the next section).
3993
3994 Warning: If the pattern uses the (?| feature to set up multiple subpat-
3995 terns with the same number, as described in the section on duplicate
3996 subpattern numbers in the pcrepattern page, you cannot use names to
3997 distinguish the different subpatterns, because names are not included
3998 in the compiled code. The matching process uses only numbers. For this
3999 reason, the use of different names for subpatterns of the same number
4000 causes an error at compile time.
4001
4002
4003 DUPLICATE SUBPATTERN NAMES
4004
4005 int pcre_get_stringtable_entries(const pcre *code,
4006 const char *name, char **first, char **last);
4007
4008 When a pattern is compiled with the PCRE_DUPNAMES option, names for
4009 subpatterns are not required to be unique. (Duplicate names are always
4010 allowed for subpatterns with the same number, created by using the (?|
4011 feature. Indeed, if such subpatterns are named, they are required to
4012 use the same names.)
4013
4014 Normally, patterns with duplicate names are such that in any one match,
4015 only one of the named subpatterns participates. An example is shown in
4016 the pcrepattern documentation.
4017
4018 When duplicates are present, pcre_copy_named_substring() and
4019 pcre_get_named_substring() return the first substring corresponding to
4020 the given name that is set. If none are set, PCRE_ERROR_NOSUBSTRING
4021 (-7) is returned; no data is returned. The pcre_get_stringnumber()
4022 function returns one of the numbers that are associated with the name,
4023 but it is not defined which it is.
4024
4025 If you want to get full details of all captured substrings for a given
4026 name, you must use the pcre_get_stringtable_entries() function. The
4027 first argument is the compiled pattern, and the second is the name. The
4028 third and fourth are pointers to variables which are updated by the
4029 function. After it has run, they point to the first and last entries in
4030 the name-to-number table for the given name. The function itself
4031 returns the length of each entry, or PCRE_ERROR_NOSUBSTRING (-7) if
4032 there are none. The format of the table is described above in the sec-
4033 tion entitled Information about a pattern above. Given all the rele-
4034 vant entries for the name, you can extract each of their numbers, and
4035 hence the captured data, if any.
4036
4037
4038 FINDING ALL POSSIBLE MATCHES
4039
4040 The traditional matching function uses a similar algorithm to Perl,
4041 which stops when it finds the first match, starting at a given point in
4042 the subject. If you want to find all possible matches, or the longest
4043 possible match, consider using the alternative matching function (see
4044 below) instead. If you cannot use the alternative function, but still
4045 need to find all possible matches, you can kludge it up by making use
4046 of the callout facility, which is described in the pcrecallout documen-
4047 tation.
4048
4049 What you have to do is to insert a callout right at the end of the pat-
4050 tern. When your callout function is called, extract and save the cur-
4051 rent matched substring. Then return 1, which forces pcre_exec() to
4052 backtrack and try other alternatives. Ultimately, when it runs out of
4053 matches, pcre_exec() will yield PCRE_ERROR_NOMATCH.
4054
4055
4056 OBTAINING AN ESTIMATE OF STACK USAGE
4057
4058 Matching certain patterns using pcre_exec() can use a lot of process
4059 stack, which in certain environments can be rather limited in size.
4060 Some users find it helpful to have an estimate of the amount of stack
4061 that is used by pcre_exec(), to help them set recursion limits, as
4062 described in the pcrestack documentation. The estimate that is output
4063 by pcretest when called with the -m and -C options is obtained by call-
4064 ing pcre_exec with the values NULL, NULL, NULL, -999, and -999 for its
4065 first five arguments.
4066
4067 Normally, if its first argument is NULL, pcre_exec() immediately
4068 returns the negative error code PCRE_ERROR_NULL, but with this special
4069 combination of arguments, it returns instead a negative number whose
4070 absolute value is the approximate stack frame size in bytes. (A nega-
4071 tive number is used so that it is clear that no match has happened.)
4072 The value is approximate because in some cases, recursive calls to
4073 pcre_exec() occur when there are one or two additional variables on the
4074 stack.
4075
4076 If PCRE has been compiled to use the heap instead of the stack for
4077 recursion, the value returned is the size of each block that is
4078 obtained from the heap.
4079
4080
4081 MATCHING A PATTERN: THE ALTERNATIVE FUNCTION
4082
4083 int pcre_dfa_exec(const pcre *code, const pcre_extra *extra,
4084 const char *subject, int length, int startoffset,
4085 int options, int *ovector, int ovecsize,
4086 int *workspace, int wscount);
4087
4088 The function pcre_dfa_exec() is called to match a subject string
4089 against a compiled pattern, using a matching algorithm that scans the
4090 subject string just once, and does not backtrack. This has different
4091 characteristics to the normal algorithm, and is not compatible with
4092 Perl. Some of the features of PCRE patterns are not supported. Never-
4093 theless, there are times when this kind of matching can be useful. For
4094 a discussion of the two matching algorithms, and a list of features
4095 that pcre_dfa_exec() does not support, see the pcrematching documenta-
4096 tion.
4097
4098 The arguments for the pcre_dfa_exec() function are the same as for
4099 pcre_exec(), plus two extras. The ovector argument is used in a differ-
4100 ent way, and this is described below. The other common arguments are
4101 used in the same way as for pcre_exec(), so their description is not
4102 repeated here.
4103
4104 The two additional arguments provide workspace for the function. The
4105 workspace vector should contain at least 20 elements. It is used for
4106 keeping track of multiple paths through the pattern tree. More
4107 workspace will be needed for patterns and subjects where there are a
4108 lot of potential matches.
4109
4110 Here is an example of a simple call to pcre_dfa_exec():
4111
4112 int rc;
4113 int ovector[10];
4114 int wspace[20];
4115 rc = pcre_dfa_exec(
4116 re, /* result of pcre_compile() */
4117 NULL, /* we didn't study the pattern */
4118 "some string", /* the subject string */
4119 11, /* the length of the subject string */
4120 0, /* start at offset 0 in the subject */
4121 0, /* default options */
4122 ovector, /* vector of integers for substring information */
4123 10, /* number of elements (NOT size in bytes) */
4124 wspace, /* working space vector */
4125 20); /* number of elements (NOT size in bytes) */
4126
4127 Option bits for pcre_dfa_exec()
4128
4129 The unused bits of the options argument for pcre_dfa_exec() must be
4130 zero. The only bits that may be set are PCRE_ANCHORED, PCRE_NEW-
4131 LINE_xxx, PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY,
4132 PCRE_NOTEMPTY_ATSTART, PCRE_NO_UTF8_CHECK, PCRE_BSR_ANYCRLF,
4133 PCRE_BSR_UNICODE, PCRE_NO_START_OPTIMIZE, PCRE_PARTIAL_HARD, PCRE_PAR-
4134 TIAL_SOFT, PCRE_DFA_SHORTEST, and PCRE_DFA_RESTART. All but the last
4135 four of these are exactly the same as for pcre_exec(), so their
4136 description is not repeated here.
4137
4138 PCRE_PARTIAL_HARD
4139 PCRE_PARTIAL_SOFT
4140
4141 These have the same general effect as they do for pcre_exec(), but the
4142 details are slightly different. When PCRE_PARTIAL_HARD is set for
4143 pcre_dfa_exec(), it returns PCRE_ERROR_PARTIAL if the end of the sub-
4144 ject is reached and there is still at least one matching possibility
4145 that requires additional characters. This happens even if some complete
4146 matches have also been found. When PCRE_PARTIAL_SOFT is set, the return
4147 code PCRE_ERROR_NOMATCH is converted into PCRE_ERROR_PARTIAL if the end
4148 of the subject is reached, there have been no complete matches, but
4149 there is still at least one matching possibility. The portion of the
4150 string that was inspected when the longest partial match was found is
4151 set as the first matching string in both cases. There is a more
4152 detailed discussion of partial and multi-segment matching, with exam-
4153 ples, in the pcrepartial documentation.
4154
4155 PCRE_DFA_SHORTEST
4156
4157 Setting the PCRE_DFA_SHORTEST option causes the matching algorithm to
4158 stop as soon as it has found one match. Because of the way the alterna-
4159 tive algorithm works, this is necessarily the shortest possible match
4160 at the first possible matching point in the subject string.
4161
4162 PCRE_DFA_RESTART
4163
4164 When pcre_dfa_exec() returns a partial match, it is possible to call it
4165 again, with additional subject characters, and have it continue with
4166 the same match. The PCRE_DFA_RESTART option requests this action; when
4167 it is set, the workspace and wscount options must reference the same
4168 vector as before because data about the match so far is left in them
4169 after a partial match. There is more discussion of this facility in the
4170 pcrepartial documentation.
4171
4172 Successful returns from pcre_dfa_exec()
4173
4174 When pcre_dfa_exec() succeeds, it may have matched more than one sub-
4175 string in the subject. Note, however, that all the matches from one run
4176 of the function start at the same point in the subject. The shorter
4177 matches are all initial substrings of the longer matches. For example,
4178 if the pattern
4179
4180 <.*>
4181
4182 is matched against the string
4183
4184 This is <something> <something else> <something further> no more
4185
4186 the three matched strings are
4187
4188 <something>
4189 <something> <something else>
4190 <something> <something else> <something further>
4191
4192 On success, the yield of the function is a number greater than zero,
4193 which is the number of matched substrings. The substrings themselves
4194 are returned in ovector. Each string uses two elements; the first is
4195 the offset to the start, and the second is the offset to the end. In
4196 fact, all the strings have the same start offset. (Space could have
4197 been saved by giving this only once, but it was decided to retain some
4198 compatibility with the way pcre_exec() returns data, even though the
4199 meaning of the strings is different.)
4200
4201 The strings are returned in reverse order of length; that is, the long-
4202 est matching string is given first. If there were too many matches to
4203 fit into ovector, the yield of the function is zero, and the vector is
4204 filled with the longest matches. Unlike pcre_exec(), pcre_dfa_exec()
4205 can use the entire ovector for returning matched strings.
4206
4207 NOTE: PCRE's "auto-possessification" optimization usually applies to
4208 character repeats at the end of a pattern (as well as internally). For
4209 example, the pattern "a\d+" is compiled as if it were "a\d++" because
4210 there is no point even considering the possibility of backtracking into
4211 the repeated digits. For DFA matching, this means that only one possi-
4212 ble match is found. If you really do want multiple matches in such
4213 cases, either use an ungreedy repeat ("a\d+?") or set the
4214 PCRE_NO_AUTO_POSSESS option when compiling.
4215
4216 Error returns from pcre_dfa_exec()
4217
4218 The pcre_dfa_exec() function returns a negative number when it fails.
4219 Many of the errors are the same as for pcre_exec(), and these are
4220 described above. There are in addition the following errors that are
4221 specific to pcre_dfa_exec():
4222
4223 PCRE_ERROR_DFA_UITEM (-16)
4224
4225 This return is given if pcre_dfa_exec() encounters an item in the pat-
4226 tern that it does not support, for instance, the use of \C or a back
4227 reference.
4228
4229 PCRE_ERROR_DFA_UCOND (-17)
4230
4231 This return is given if pcre_dfa_exec() encounters a condition item
4232 that uses a back reference for the condition, or a test for recursion
4233 in a specific group. These are not supported.
4234
4235 PCRE_ERROR_DFA_UMLIMIT (-18)
4236
4237 This return is given if pcre_dfa_exec() is called with an extra block
4238 that contains a setting of the match_limit or match_limit_recursion
4239 fields. This is not supported (these fields are meaningless for DFA
4240 matching).
4241
4242 PCRE_ERROR_DFA_WSSIZE (-19)
4243
4244 This return is given if pcre_dfa_exec() runs out of space in the
4245 workspace vector.
4246
4247 PCRE_ERROR_DFA_RECURSE (-20)
4248
4249 When a recursive subpattern is processed, the matching function calls
4250 itself recursively, using private vectors for ovector and workspace.
4251 This error is given if the output vector is not large enough. This
4252 should be extremely rare, as a vector of size 1000 is used.
4253
4254 PCRE_ERROR_DFA_BADRESTART (-30)
4255
4256 When pcre_dfa_exec() is called with the PCRE_DFA_RESTART option, some
4257 plausibility checks are made on the contents of the workspace, which
4258 should contain data about the previous partial match. If any of these
4259 checks fail, this error is given.
4260
4261
4262 SEE ALSO
4263
4264 pcre16(3), pcre32(3), pcrebuild(3), pcrecallout(3), pcrecpp(3)(3),
4265 pcrematching(3), pcrepartial(3), pcreposix(3), pcreprecompile(3), pcre-
4266 sample(3), pcrestack(3).
4267
4268
4269 AUTHOR
4270
4271 Philip Hazel
4272 University Computing Service
4273 Cambridge CB2 3QH, England.
4274
4275
4276 REVISION
4277
4278 Last updated: 18 December 2015
4279 Copyright (c) 1997-2015 University of Cambridge.
4280 ------------------------------------------------------------------------------
4281
4282
4283 PCRECALLOUT(3) Library Functions Manual PCRECALLOUT(3)
4284
4285
4286
4287 NAME
4288 PCRE - Perl-compatible regular expressions
4289
4290 SYNOPSIS
4291
4292 #include <pcre.h>
4293
4294 int (*pcre_callout)(pcre_callout_block *);
4295
4296 int (*pcre16_callout)(pcre16_callout_block *);
4297
4298 int (*pcre32_callout)(pcre32_callout_block *);
4299
4300
4301 DESCRIPTION
4302
4303 PCRE provides a feature called "callout", which is a means of temporar-
4304 ily passing control to the caller of PCRE in the middle of pattern
4305 matching. The caller of PCRE provides an external function by putting
4306 its entry point in the global variable pcre_callout (pcre16_callout for
4307 the 16-bit library, pcre32_callout for the 32-bit library). By default,
4308 this variable contains NULL, which disables all calling out.
4309
4310 Within a regular expression, (?C) indicates the points at which the
4311 external function is to be called. Different callout points can be
4312 identified by putting a number less than 256 after the letter C. The
4313 default value is zero. For example, this pattern has two callout
4314 points:
4315
4316 (?C1)abc(?C2)def
4317
4318 If the PCRE_AUTO_CALLOUT option bit is set when a pattern is compiled,
4319 PCRE automatically inserts callouts, all with number 255, before each
4320 item in the pattern. For example, if PCRE_AUTO_CALLOUT is used with the
4321 pattern
4322
4323 A(\d{2}|--)
4324
4325 it is processed as if it were
4326
4327 (?C255)A(?C255)((?C255)\d{2}(?C255)|(?C255)-(?C255)-(?C255))(?C255)
4328
4329 Notice that there is a callout before and after each parenthesis and
4330 alternation bar. If the pattern contains a conditional group whose con-
4331 dition is an assertion, an automatic callout is inserted immediately
4332 before the condition. Such a callout may also be inserted explicitly,
4333 for example:
4334
4335 (?(?C9)(?=a)ab|de)
4336
4337 This applies only to assertion conditions (because they are themselves
4338 independent groups).
4339
4340 Automatic callouts can be used for tracking the progress of pattern
4341 matching. The pcretest program has a pattern qualifier (/C) that sets
4342 automatic callouts; when it is used, the output indicates how the pat-
4343 tern is being matched. This is useful information when you are trying
4344 to optimize the performance of a particular pattern.
4345
4346
4347 MISSING CALLOUTS
4348
4349 You should be aware that, because of optimizations in the way PCRE com-
4350 piles and matches patterns, callouts sometimes do not happen exactly as
4351 you might expect.
4352
4353 At compile time, PCRE "auto-possessifies" repeated items when it knows
4354 that what follows cannot be part of the repeat. For example, a+[bc] is
4355 compiled as if it were a++[bc]. The pcretest output when this pattern
4356 is anchored and then applied with automatic callouts to the string
4357 "aaaa" is:
4358
4359 --->aaaa
4360 +0 ^ ^
4361 +1 ^ a+
4362 +3 ^ ^ [bc]
4363 No match
4364
4365 This indicates that when matching [bc] fails, there is no backtracking
4366 into a+ and therefore the callouts that would be taken for the back-
4367 tracks do not occur. You can disable the auto-possessify feature by
4368 passing PCRE_NO_AUTO_POSSESS to pcre_compile(), or starting the pattern
4369 with (*NO_AUTO_POSSESS). If this is done in pcretest (using the /O
4370 qualifier), the output changes to this:
4371
4372 --->aaaa
4373 +0 ^ ^
4374 +1 ^ a+
4375 +3 ^ ^ [bc]
4376 +3 ^ ^ [bc]
4377 +3 ^ ^ [bc]
4378 +3 ^^ [bc]
4379 No match
4380
4381 This time, when matching [bc] fails, the matcher backtracks into a+ and
4382 tries again, repeatedly, until a+ itself fails.
4383
4384 Other optimizations that provide fast "no match" results also affect
4385 callouts. For example, if the pattern is
4386
4387 ab(?C4)cd
4388
4389 PCRE knows that any matching string must contain the letter "d". If the
4390 subject string is "abyz", the lack of "d" means that matching doesn't
4391 ever start, and the callout is never reached. However, with "abyd",
4392 though the result is still no match, the callout is obeyed.
4393
4394 If the pattern is studied, PCRE knows the minimum length of a matching
4395 string, and will immediately give a "no match" return without actually
4396 running a match if the subject is not long enough, or, for unanchored
4397 patterns, if it has been scanned far enough.
4398
4399 You can disable these optimizations by passing the PCRE_NO_START_OPTI-
4400 MIZE option to the matching function, or by starting the pattern with
4401 (*NO_START_OPT). This slows down the matching process, but does ensure
4402 that callouts such as the example above are obeyed.
4403
4404
4405 THE CALLOUT INTERFACE
4406
4407 During matching, when PCRE reaches a callout point, the external func-
4408 tion defined by pcre_callout or pcre[16|32]_callout is called (if it is
4409 set). This applies to both normal and DFA matching. The only argument
4410 to the callout function is a pointer to a pcre_callout or
4411 pcre[16|32]_callout block. These structures contains the following
4412 fields:
4413
4414 int version;
4415 int callout_number;
4416 int *offset_vector;
4417 const char *subject; (8-bit version)
4418 PCRE_SPTR16 subject; (16-bit version)
4419 PCRE_SPTR32 subject; (32-bit version)
4420 int subject_length;
4421 int start_match;
4422 int current_position;
4423 int capture_top;
4424 int capture_last;
4425 void *callout_data;
4426 int pattern_position;
4427 int next_item_length;
4428 const unsigned char *mark; (8-bit version)
4429 const PCRE_UCHAR16 *mark; (16-bit version)
4430 const PCRE_UCHAR32 *mark; (32-bit version)
4431
4432 The version field is an integer containing the version number of the
4433 block format. The initial version was 0; the current version is 2. The
4434 version number will change again in future if additional fields are
4435 added, but the intention is never to remove any of the existing fields.
4436
4437 The callout_number field contains the number of the callout, as com-
4438 piled into the pattern (that is, the number after ?C for manual call-
4439 outs, and 255 for automatically generated callouts).
4440
4441 The offset_vector field is a pointer to the vector of offsets that was
4442 passed by the caller to the matching function. When pcre_exec() or
4443 pcre[16|32]_exec() is used, the contents can be inspected, in order to
4444 extract substrings that have been matched so far, in the same way as
4445 for extracting substrings after a match has completed. For the DFA
4446 matching functions, this field is not useful.
4447
4448 The subject and subject_length fields contain copies of the values that
4449 were passed to the matching function.
4450
4451 The start_match field normally contains the offset within the subject
4452 at which the current match attempt started. However, if the escape
4453 sequence \K has been encountered, this value is changed to reflect the
4454 modified starting point. If the pattern is not anchored, the callout
4455 function may be called several times from the same point in the pattern
4456 for different starting points in the subject.
4457
4458 The current_position field contains the offset within the subject of
4459 the current match pointer.
4460
4461 When the pcre_exec() or pcre[16|32]_exec() is used, the capture_top
4462 field contains one more than the number of the highest numbered cap-
4463 tured substring so far. If no substrings have been captured, the value
4464 of capture_top is one. This is always the case when the DFA functions
4465 are used, because they do not support captured substrings.
4466
4467 The capture_last field contains the number of the most recently cap-
4468 tured substring. However, when a recursion exits, the value reverts to
4469 what it was outside the recursion, as do the values of all captured
4470 substrings. If no substrings have been captured, the value of cap-
4471 ture_last is -1. This is always the case for the DFA matching func-
4472 tions.
4473
4474 The callout_data field contains a value that is passed to a matching
4475 function specifically so that it can be passed back in callouts. It is
4476 passed in the callout_data field of a pcre_extra or pcre[16|32]_extra
4477 data structure. If no such data was passed, the value of callout_data
4478 in a callout block is NULL. There is a description of the pcre_extra
4479 structure in the pcreapi documentation.
4480
4481 The pattern_position field is present from version 1 of the callout
4482 structure. It contains the offset to the next item to be matched in the
4483 pattern string.
4484
4485 The next_item_length field is present from version 1 of the callout
4486 structure. It contains the length of the next item to be matched in the
4487 pattern string. When the callout immediately precedes an alternation
4488 bar, a closing parenthesis, or the end of the pattern, the length is
4489 zero. When the callout precedes an opening parenthesis, the length is
4490 that of the entire subpattern.
4491
4492 The pattern_position and next_item_length fields are intended to help
4493 in distinguishing between different automatic callouts, which all have
4494 the same callout number. However, they are set for all callouts.
4495
4496 The mark field is present from version 2 of the callout structure. In
4497 callouts from pcre_exec() or pcre[16|32]_exec() it contains a pointer
4498 to the zero-terminated name of the most recently passed (*MARK),
4499 (*PRUNE), or (*THEN) item in the match, or NULL if no such items have
4500 been passed. Instances of (*PRUNE) or (*THEN) without a name do not
4501 obliterate a previous (*MARK). In callouts from the DFA matching func-
4502 tions this field always contains NULL.
4503
4504
4505 RETURN VALUES
4506
4507 The external callout function returns an integer to PCRE. If the value
4508 is zero, matching proceeds as normal. If the value is greater than
4509 zero, matching fails at the current point, but the testing of other
4510 matching possibilities goes ahead, just as if a lookahead assertion had
4511 failed. If the value is less than zero, the match is abandoned, the
4512 matching function returns the negative value.
4513
4514 Negative values should normally be chosen from the set of
4515 PCRE_ERROR_xxx values. In particular, PCRE_ERROR_NOMATCH forces a stan-
4516 dard "no match" failure. The error number PCRE_ERROR_CALLOUT is
4517 reserved for use by callout functions; it will never be used by PCRE
4518 itself.
4519
4520
4521 AUTHOR
4522
4523 Philip Hazel
4524 University Computing Service
4525 Cambridge CB2 3QH, England.
4526
4527
4528 REVISION
4529
4530 Last updated: 12 November 2013
4531 Copyright (c) 1997-2013 University of Cambridge.
4532 ------------------------------------------------------------------------------
4533
4534
4535 PCRECOMPAT(3) Library Functions Manual PCRECOMPAT(3)
4536
4537
4538
4539 NAME
4540 PCRE - Perl-compatible regular expressions
4541
4542 DIFFERENCES BETWEEN PCRE AND PERL
4543
4544 This document describes the differences in the ways that PCRE and Perl
4545 handle regular expressions. The differences described here are with
4546 respect to Perl versions 5.10 and above.
4547
4548 1. PCRE has only a subset of Perl's Unicode support. Details of what it
4549 does have are given in the pcreunicode page.
4550
4551 2. PCRE allows repeat quantifiers only on parenthesized assertions, but
4552 they do not mean what you might think. For example, (?!a){3} does not
4553 assert that the next three characters are not "a". It just asserts that
4554 the next character is not "a" three times (in principle: PCRE optimizes
4555 this to run the assertion just once). Perl allows repeat quantifiers on
4556 other assertions such as \b, but these do not seem to have any use.
4557
4558 3. Capturing subpatterns that occur inside negative lookahead asser-
4559 tions are counted, but their entries in the offsets vector are never
4560 set. Perl sometimes (but not always) sets its numerical variables from
4561 inside negative assertions.
4562
4563 4. Though binary zero characters are supported in the subject string,
4564 they are not allowed in a pattern string because it is passed as a nor-
4565 mal C string, terminated by zero. The escape sequence \0 can be used in
4566 the pattern to represent a binary zero.
4567
4568 5. The following Perl escape sequences are not supported: \l, \u, \L,
4569 \U, and \N when followed by a character name or Unicode value. (\N on
4570 its own, matching a non-newline character, is supported.) In fact these
4571 are implemented by Perl's general string-handling and are not part of
4572 its pattern matching engine. If any of these are encountered by PCRE,
4573 an error is generated by default. However, if the PCRE_JAVASCRIPT_COM-
4574 PAT option is set, \U and \u are interpreted as JavaScript interprets
4575 them.
4576
4577 6. The Perl escape sequences \p, \P, and \X are supported only if PCRE
4578 is built with Unicode character property support. The properties that
4579 can be tested with \p and \P are limited to the general category prop-
4580 erties such as Lu and Nd, script names such as Greek or Han, and the
4581 derived properties Any and L&. PCRE does support the Cs (surrogate)
4582 property, which Perl does not; the Perl documentation says "Because
4583 Perl hides the need for the user to understand the internal representa-
4584 tion of Unicode characters, there is no need to implement the somewhat
4585 messy concept of surrogates."
4586
4587 7. PCRE does support the \Q...\E escape for quoting substrings. Charac-
4588 ters in between are treated as literals. This is slightly different
4589 from Perl in that $ and @ are also handled as literals inside the
4590 quotes. In Perl, they cause variable interpolation (but of course PCRE
4591 does not have variables). Note the following examples:
4592
4593 Pattern PCRE matches Perl matches
4594
4595 \Qabc$xyz\E abc$xyz abc followed by the
4596 contents of $xyz
4597 \Qabc\$xyz\E abc\$xyz abc\$xyz
4598 \Qabc\E\$\Qxyz\E abc$xyz abc$xyz
4599
4600 The \Q...\E sequence is recognized both inside and outside character
4601 classes.
4602
4603 8. Fairly obviously, PCRE does not support the (?{code}) and (??{code})
4604 constructions. However, there is support for recursive patterns. This
4605 is not available in Perl 5.8, but it is in Perl 5.10. Also, the PCRE
4606 "callout" feature allows an external function to be called during pat-
4607 tern matching. See the pcrecallout documentation for details.
4608
4609 9. Subpatterns that are called as subroutines (whether or not recur-
4610 sively) are always treated as atomic groups in PCRE. This is like
4611 Python, but unlike Perl. Captured values that are set outside a sub-
4612 routine call can be reference from inside in PCRE, but not in Perl.
4613 There is a discussion that explains these differences in more detail in
4614 the section on recursion differences from Perl in the pcrepattern page.
4615
4616 10. If any of the backtracking control verbs are used in a subpattern
4617 that is called as a subroutine (whether or not recursively), their
4618 effect is confined to that subpattern; it does not extend to the sur-
4619 rounding pattern. This is not always the case in Perl. In particular,
4620 if (*THEN) is present in a group that is called as a subroutine, its
4621 action is limited to that group, even if the group does not contain any
4622 | characters. Note that such subpatterns are processed as anchored at
4623 the point where they are tested.
4624
4625 11. If a pattern contains more than one backtracking control verb, the
4626 first one that is backtracked onto acts. For example, in the pattern
4627 A(*COMMIT)B(*PRUNE)C a failure in B triggers (*COMMIT), but a failure
4628 in C triggers (*PRUNE). Perl's behaviour is more complex; in many cases
4629 it is the same as PCRE, but there are examples where it differs.
4630
4631 12. Most backtracking verbs in assertions have their normal actions.
4632 They are not confined to the assertion.
4633
4634 13. There are some differences that are concerned with the settings of
4635 captured strings when part of a pattern is repeated. For example,
4636 matching "aba" against the pattern /^(a(b)?)+$/ in Perl leaves $2
4637 unset, but in PCRE it is set to "b".
4638
4639 14. PCRE's handling of duplicate subpattern numbers and duplicate sub-
4640 pattern names is not as general as Perl's. This is a consequence of the
4641 fact the PCRE works internally just with numbers, using an external ta-
4642 ble to translate between numbers and names. In particular, a pattern
4643 such as (?|(?<a>A)|(?<b>B), where the two capturing parentheses have
4644 the same number but different names, is not supported, and causes an
4645 error at compile time. If it were allowed, it would not be possible to
4646 distinguish which parentheses matched, because both names map to cap-
4647 turing subpattern number 1. To avoid this confusing situation, an error
4648 is given at compile time.
4649
4650 15. Perl recognizes comments in some places that PCRE does not, for
4651 example, between the ( and ? at the start of a subpattern. If the /x
4652 modifier is set, Perl allows white space between ( and ? (though cur-
4653 rent Perls warn that this is deprecated) but PCRE never does, even if
4654 the PCRE_EXTENDED option is set.
4655
4656 16. Perl, when in warning mode, gives warnings for character classes
4657 such as [A-\d] or [a-[:digit:]]. It then treats the hyphens as liter-
4658 als. PCRE has no warning features, so it gives an error in these cases
4659 because they are almost certainly user mistakes.
4660
4661 17. In PCRE, the upper/lower case character properties Lu and Ll are
4662 not affected when case-independent matching is specified. For example,
4663 \p{Lu} always matches an upper case letter. I think Perl has changed in
4664 this respect; in the release at the time of writing (5.16), \p{Lu} and
4665 \p{Ll} match all letters, regardless of case, when case independence is
4666 specified.
4667
4668 18. PCRE provides some extensions to the Perl regular expression facil-
4669 ities. Perl 5.10 includes new features that are not in earlier ver-
4670 sions of Perl, some of which (such as named parentheses) have been in
4671 PCRE for some time. This list is with respect to Perl 5.10:
4672
4673 (a) Although lookbehind assertions in PCRE must match fixed length
4674 strings, each alternative branch of a lookbehind assertion can match a
4675 different length of string. Perl requires them all to have the same
4676 length.
4677
4678 (b) If PCRE_DOLLAR_ENDONLY is set and PCRE_MULTILINE is not set, the $
4679 meta-character matches only at the very end of the string.
4680
4681 (c) If PCRE_EXTRA is set, a backslash followed by a letter with no spe-
4682 cial meaning is faulted. Otherwise, like Perl, the backslash is quietly
4683 ignored. (Perl can be made to issue a warning.)
4684
4685 (d) If PCRE_UNGREEDY is set, the greediness of the repetition quanti-
4686 fiers is inverted, that is, by default they are not greedy, but if fol-
4687 lowed by a question mark they are.
4688
4689 (e) PCRE_ANCHORED can be used at matching time to force a pattern to be
4690 tried only at the first matching position in the subject string.
4691
4692 (f) The PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, PCRE_NOTEMPTY_ATSTART,
4693 and PCRE_NO_AUTO_CAPTURE options for pcre_exec() have no Perl equiva-
4694 lents.
4695
4696 (g) The \R escape sequence can be restricted to match only CR, LF, or
4697 CRLF by the PCRE_BSR_ANYCRLF option.
4698
4699 (h) The callout facility is PCRE-specific.
4700
4701 (i) The partial matching facility is PCRE-specific.
4702
4703 (j) Patterns compiled by PCRE can be saved and re-used at a later time,
4704 even on different hosts that have the other endianness. However, this
4705 does not apply to optimized data created by the just-in-time compiler.
4706
4707 (k) The alternative matching functions (pcre_dfa_exec(),
4708 pcre16_dfa_exec() and pcre32_dfa_exec(),) match in a different way and
4709 are not Perl-compatible.
4710
4711 (l) PCRE recognizes some special sequences such as (*CR) at the start
4712 of a pattern that set overall options that cannot be changed within the
4713 pattern.
4714
4715
4716 AUTHOR
4717
4718 Philip Hazel
4719 University Computing Service
4720 Cambridge CB2 3QH, England.
4721
4722
4723 REVISION
4724
4725 Last updated: 10 November 2013
4726 Copyright (c) 1997-2013 University of Cambridge.
4727 ------------------------------------------------------------------------------
4728
4729
4730 PCREPATTERN(3) Library Functions Manual PCREPATTERN(3)
4731
4732
4733
4734 NAME
4735 PCRE - Perl-compatible regular expressions
4736
4737 PCRE REGULAR EXPRESSION DETAILS
4738
4739 The syntax and semantics of the regular expressions that are supported
4740 by PCRE are described in detail below. There is a quick-reference syn-
4741 tax summary in the pcresyntax page. PCRE tries to match Perl syntax and
4742 semantics as closely as it can. PCRE also supports some alternative
4743 regular expression syntax (which does not conflict with the Perl syn-
4744 tax) in order to provide some compatibility with regular expressions in
4745 Python, .NET, and Oniguruma.
4746
4747 Perl's regular expressions are described in its own documentation, and
4748 regular expressions in general are covered in a number of books, some
4749 of which have copious examples. Jeffrey Friedl's "Mastering Regular
4750 Expressions", published by O'Reilly, covers regular expressions in
4751 great detail. This description of PCRE's regular expressions is
4752 intended as reference material.
4753
4754 This document discusses the patterns that are supported by PCRE when
4755 one its main matching functions, pcre_exec() (8-bit) or
4756 pcre[16|32]_exec() (16- or 32-bit), is used. PCRE also has alternative
4757 matching functions, pcre_dfa_exec() and pcre[16|32_dfa_exec(), which
4758 match using a different algorithm that is not Perl-compatible. Some of
4759 the features discussed below are not available when DFA matching is
4760 used. The advantages and disadvantages of the alternative functions,
4761 and how they differ from the normal functions, are discussed in the
4762 pcrematching page.
4763
4764
4765 SPECIAL START-OF-PATTERN ITEMS
4766
4767 A number of options that can be passed to pcre_compile() can also be
4768 set by special items at the start of a pattern. These are not Perl-com-
4769 patible, but are provided to make these options accessible to pattern
4770 writers who are not able to change the program that processes the pat-
4771 tern. Any number of these items may appear, but they must all be
4772 together right at the start of the pattern string, and the letters must
4773 be in upper case.
4774
4775 UTF support
4776
4777 The original operation of PCRE was on strings of one-byte characters.
4778 However, there is now also support for UTF-8 strings in the original
4779 library, an extra library that supports 16-bit and UTF-16 character
4780 strings, and a third library that supports 32-bit and UTF-32 character
4781 strings. To use these features, PCRE must be built to include appropri-
4782 ate support. When using UTF strings you must either call the compiling
4783 function with the PCRE_UTF8, PCRE_UTF16, or PCRE_UTF32 option, or the
4784 pattern must start with one of these special sequences:
4785
4786 (*UTF8)
4787 (*UTF16)
4788 (*UTF32)
4789 (*UTF)
4790
4791 (*UTF) is a generic sequence that can be used with any of the
4792 libraries. Starting a pattern with such a sequence is equivalent to
4793 setting the relevant option. How setting a UTF mode affects pattern
4794 matching is mentioned in several places below. There is also a summary
4795 of features in the pcreunicode page.
4796
4797 Some applications that allow their users to supply patterns may wish to
4798 restrict them to non-UTF data for security reasons. If the
4799 PCRE_NEVER_UTF option is set at compile time, (*UTF) etc. are not
4800 allowed, and their appearance causes an error.
4801
4802 Unicode property support
4803
4804 Another special sequence that may appear at the start of a pattern is
4805 (*UCP). This has the same effect as setting the PCRE_UCP option: it
4806 causes sequences such as \d and \w to use Unicode properties to deter-
4807 mine character types, instead of recognizing only characters with codes
4808 less than 128 via a lookup table.
4809
4810 Disabling auto-possessification
4811
4812 If a pattern starts with (*NO_AUTO_POSSESS), it has the same effect as
4813 setting the PCRE_NO_AUTO_POSSESS option at compile time. This stops
4814 PCRE from making quantifiers possessive when what follows cannot match
4815 the repeated item. For example, by default a+b is treated as a++b. For
4816 more details, see the pcreapi documentation.
4817
4818 Disabling start-up optimizations
4819
4820 If a pattern starts with (*NO_START_OPT), it has the same effect as
4821 setting the PCRE_NO_START_OPTIMIZE option either at compile or matching
4822 time. This disables several optimizations for quickly reaching "no
4823 match" results. For more details, see the pcreapi documentation.
4824
4825 Newline conventions
4826
4827 PCRE supports five different conventions for indicating line breaks in
4828 strings: a single CR (carriage return) character, a single LF (line-
4829 feed) character, the two-character sequence CRLF, any of the three pre-
4830 ceding, or any Unicode newline sequence. The pcreapi page has further
4831 discussion about newlines, and shows how to set the newline convention
4832 in the options arguments for the compiling and matching functions.
4833
4834 It is also possible to specify a newline convention by starting a pat-
4835 tern string with one of the following five sequences:
4836
4837 (*CR) carriage return
4838 (*LF) linefeed
4839 (*CRLF) carriage return, followed by linefeed
4840 (*ANYCRLF) any of the three above
4841 (*ANY) all Unicode newline sequences
4842
4843 These override the default and the options given to the compiling func-
4844 tion. For example, on a Unix system where LF is the default newline
4845 sequence, the pattern
4846
4847 (*CR)a.b
4848
4849 changes the convention to CR. That pattern matches "a\nb" because LF is
4850 no longer a newline. If more than one of these settings is present, the
4851 last one is used.
4852
4853 The newline convention affects where the circumflex and dollar asser-
4854 tions are true. It also affects the interpretation of the dot metachar-
4855 acter when PCRE_DOTALL is not set, and the behaviour of \N. However, it
4856 does not affect what the \R escape sequence matches. By default, this
4857 is any Unicode newline sequence, for Perl compatibility. However, this
4858 can be changed; see the description of \R in the section entitled "New-
4859 line sequences" below. A change of \R setting can be combined with a
4860 change of newline convention.
4861
4862 Setting match and recursion limits
4863
4864 The caller of pcre_exec() can set a limit on the number of times the
4865 internal match() function is called and on the maximum depth of recur-
4866 sive calls. These facilities are provided to catch runaway matches that
4867 are provoked by patterns with huge matching trees (a typical example is
4868 a pattern with nested unlimited repeats) and to avoid running out of
4869 system stack by too much recursion. When one of these limits is
4870 reached, pcre_exec() gives an error return. The limits can also be set
4871 by items at the start of the pattern of the form
4872
4873 (*LIMIT_MATCH=d)
4874 (*LIMIT_RECURSION=d)
4875
4876 where d is any number of decimal digits. However, the value of the set-
4877 ting must be less than the value set (or defaulted) by the caller of
4878 pcre_exec() for it to have any effect. In other words, the pattern
4879 writer can lower the limits set by the programmer, but not raise them.
4880 If there is more than one setting of one of these limits, the lower
4881 value is used.
4882
4883
4884 EBCDIC CHARACTER CODES
4885
4886 PCRE can be compiled to run in an environment that uses EBCDIC as its
4887 character code rather than ASCII or Unicode (typically a mainframe sys-
4888 tem). In the sections below, character code values are ASCII or Uni-
4889 code; in an EBCDIC environment these characters may have different code
4890 values, and there are no code points greater than 255.
4891
4892
4893 CHARACTERS AND METACHARACTERS
4894
4895 A regular expression is a pattern that is matched against a subject
4896 string from left to right. Most characters stand for themselves in a
4897 pattern, and match the corresponding characters in the subject. As a
4898 trivial example, the pattern
4899
4900 The quick brown fox
4901
4902 matches a portion of a subject string that is identical to itself. When
4903 caseless matching is specified (the PCRE_CASELESS option), letters are
4904 matched independently of case. In a UTF mode, PCRE always understands
4905 the concept of case for characters whose values are less than 128, so
4906 caseless matching is always possible. For characters with higher val-
4907 ues, the concept of case is supported if PCRE is compiled with Unicode
4908 property support, but not otherwise. If you want to use caseless
4909 matching for characters 128 and above, you must ensure that PCRE is
4910 compiled with Unicode property support as well as with UTF support.
4911
4912 The power of regular expressions comes from the ability to include
4913 alternatives and repetitions in the pattern. These are encoded in the
4914 pattern by the use of metacharacters, which do not stand for themselves
4915 but instead are interpreted in some special way.
4916
4917 There are two different sets of metacharacters: those that are recog-
4918 nized anywhere in the pattern except within square brackets, and those
4919 that are recognized within square brackets. Outside square brackets,
4920 the metacharacters are as follows:
4921
4922 \ general escape character with several uses
4923 ^ assert start of string (or line, in multiline mode)
4924 $ assert end of string (or line, in multiline mode)
4925 . match any character except newline (by default)
4926 [ start character class definition
4927 | start of alternative branch
4928 ( start subpattern
4929 ) end subpattern
4930 ? extends the meaning of (
4931 also 0 or 1 quantifier
4932 also quantifier minimizer
4933 * 0 or more quantifier
4934 + 1 or more quantifier
4935 also "possessive quantifier"
4936 { start min/max quantifier
4937
4938 Part of a pattern that is in square brackets is called a "character
4939 class". In a character class the only metacharacters are:
4940
4941 \ general escape character
4942 ^ negate the class, but only if the first character
4943 - indicates character range
4944 [ POSIX character class (only if followed by POSIX
4945 syntax)
4946 ] terminates the character class
4947
4948 The following sections describe the use of each of the metacharacters.
4949
4950
4951 BACKSLASH
4952
4953 The backslash character has several uses. Firstly, if it is followed by
4954 a character that is not a number or a letter, it takes away any special
4955 meaning that character may have. This use of backslash as an escape
4956 character applies both inside and outside character classes.
4957
4958 For example, if you want to match a * character, you write \* in the
4959 pattern. This escaping action applies whether or not the following
4960 character would otherwise be interpreted as a metacharacter, so it is
4961 always safe to precede a non-alphanumeric with backslash to specify
4962 that it stands for itself. In particular, if you want to match a back-
4963 slash, you write \\.
4964
4965 In a UTF mode, only ASCII numbers and letters have any special meaning
4966 after a backslash. All other characters (in particular, those whose
4967 codepoints are greater than 127) are treated as literals.
4968
4969 If a pattern is compiled with the PCRE_EXTENDED option, most white
4970 space in the pattern (other than in a character class), and characters
4971 between a # outside a character class and the next newline, inclusive,
4972 are ignored. An escaping backslash can be used to include a white space
4973 or # character as part of the pattern.
4974
4975 If you want to remove the special meaning from a sequence of charac-
4976 ters, you can do so by putting them between \Q and \E. This is differ-
4977 ent from Perl in that $ and @ are handled as literals in \Q...\E
4978 sequences in PCRE, whereas in Perl, $ and @ cause variable interpola-
4979 tion. Note the following examples:
4980
4981 Pattern PCRE matches Perl matches
4982
4983 \Qabc$xyz\E abc$xyz abc followed by the
4984 contents of $xyz
4985 \Qabc\$xyz\E abc\$xyz abc\$xyz
4986 \Qabc\E\$\Qxyz\E abc$xyz abc$xyz
4987
4988 The \Q...\E sequence is recognized both inside and outside character
4989 classes. An isolated \E that is not preceded by \Q is ignored. If \Q
4990 is not followed by \E later in the pattern, the literal interpretation
4991 continues to the end of the pattern (that is, \E is assumed at the
4992 end). If the isolated \Q is inside a character class, this causes an
4993 error, because the character class is not terminated.
4994
4995 Non-printing characters
4996
4997 A second use of backslash provides a way of encoding non-printing char-
4998 acters in patterns in a visible manner. There is no restriction on the
4999 appearance of non-printing characters, apart from the binary zero that
5000 terminates a pattern, but when a pattern is being prepared by text
5001 editing, it is often easier to use one of the following escape
5002 sequences than the binary character it represents. In an ASCII or Uni-
5003 code environment, these escapes are as follows:
5004
5005 \a alarm, that is, the BEL character (hex 07)
5006 \cx "control-x", where x is any ASCII character
5007 \e escape (hex 1B)
5008 \f form feed (hex 0C)
5009 \n linefeed (hex 0A)
5010 \r carriage return (hex 0D)
5011 \t tab (hex 09)
5012 \0dd character with octal code 0dd
5013 \ddd character with octal code ddd, or back reference
5014 \o{ddd..} character with octal code ddd..
5015 \xhh character with hex code hh
5016 \x{hhh..} character with hex code hhh.. (non-JavaScript mode)
5017 \uhhhh character with hex code hhhh (JavaScript mode only)
5018
5019 The precise effect of \cx on ASCII characters is as follows: if x is a
5020 lower case letter, it is converted to upper case. Then bit 6 of the
5021 character (hex 40) is inverted. Thus \cA to \cZ become hex 01 to hex 1A
5022 (A is 41, Z is 5A), but \c{ becomes hex 3B ({ is 7B), and \c; becomes
5023 hex 7B (; is 3B). If the data item (byte or 16-bit value) following \c
5024 has a value greater than 127, a compile-time error occurs. This locks
5025 out non-ASCII characters in all modes.
5026
5027 When PCRE is compiled in EBCDIC mode, \a, \e, \f, \n, \r, and \t gener-
5028 ate the appropriate EBCDIC code values. The \c escape is processed as
5029 specified for Perl in the perlebcdic document. The only characters that
5030 are allowed after \c are A-Z, a-z, or one of @, [, \, ], ^, _, or ?.
5031 Any other character provokes a compile-time error. The sequence \c@
5032 encodes character code 0; after \c the letters (in either case) encode
5033 characters 1-26 (hex 01 to hex 1A); [, \, ], ^, and _ encode characters
5034 27-31 (hex 1B to hex 1F), and \c? becomes either 255 (hex FF) or 95
5035 (hex 5F).
5036
5037 Thus, apart from \c?, these escapes generate the same character code
5038 values as they do in an ASCII environment, though the meanings of the
5039 values mostly differ. For example, \cG always generates code value 7,
5040 which is BEL in ASCII but DEL in EBCDIC.
5041
5042 The sequence \c? generates DEL (127, hex 7F) in an ASCII environment,
5043 but because 127 is not a control character in EBCDIC, Perl makes it
5044 generate the APC character. Unfortunately, there are several variants
5045 of EBCDIC. In most of them the APC character has the value 255 (hex
5046 FF), but in the one Perl calls POSIX-BC its value is 95 (hex 5F). If
5047 certain other characters have POSIX-BC values, PCRE makes \c? generate
5048 95; otherwise it generates 255.
5049
5050 After \0 up to two further octal digits are read. If there are fewer
5051 than two digits, just those that are present are used. Thus the
5052 sequence \0\x\015 specifies two binary zeros followed by a CR character
5053 (code value 13). Make sure you supply two digits after the initial zero
5054 if the pattern character that follows is itself an octal digit.
5055
5056 The escape \o must be followed by a sequence of octal digits, enclosed
5057 in braces. An error occurs if this is not the case. This escape is a
5058 recent addition to Perl; it provides way of specifying character code
5059 points as octal numbers greater than 0777, and it also allows octal
5060 numbers and back references to be unambiguously specified.
5061
5062 For greater clarity and unambiguity, it is best to avoid following \ by
5063 a digit greater than zero. Instead, use \o{} or \x{} to specify charac-
5064 ter numbers, and \g{} to specify back references. The following para-
5065 graphs describe the old, ambiguous syntax.
5066
5067 The handling of a backslash followed by a digit other than 0 is compli-
5068 cated, and Perl has changed in recent releases, causing PCRE also to
5069 change. Outside a character class, PCRE reads the digit and any follow-
5070 ing digits as a decimal number. If the number is less than 8, or if
5071 there have been at least that many previous capturing left parentheses
5072 in the expression, the entire sequence is taken as a back reference. A
5073 description of how this works is given later, following the discussion
5074 of parenthesized subpatterns.
5075
5076 Inside a character class, or if the decimal number following \ is
5077 greater than 7 and there have not been that many capturing subpatterns,
5078 PCRE handles \8 and \9 as the literal characters "8" and "9", and oth-
5079 erwise re-reads up to three octal digits following the backslash, using
5080 them to generate a data character. Any subsequent digits stand for
5081 themselves. For example:
5082
5083 \040 is another way of writing an ASCII space
5084 \40 is the same, provided there are fewer than 40
5085 previous capturing subpatterns
5086 \7 is always a back reference
5087 \11 might be a back reference, or another way of
5088 writing a tab
5089 \011 is always a tab
5090 \0113 is a tab followed by the character "3"
5091 \113 might be a back reference, otherwise the
5092 character with octal code 113
5093 \377 might be a back reference, otherwise
5094 the value 255 (decimal)
5095 \81 is either a back reference, or the two
5096 characters "8" and "1"
5097
5098 Note that octal values of 100 or greater that are specified using this
5099 syntax must not be introduced by a leading zero, because no more than
5100 three octal digits are ever read.
5101
5102 By default, after \x that is not followed by {, from zero to two hexa-
5103 decimal digits are read (letters can be in upper or lower case). Any
5104 number of hexadecimal digits may appear between \x{ and }. If a charac-
5105 ter other than a hexadecimal digit appears between \x{ and }, or if
5106 there is no terminating }, an error occurs.
5107
5108 If the PCRE_JAVASCRIPT_COMPAT option is set, the interpretation of \x
5109 is as just described only when it is followed by two hexadecimal dig-
5110 its. Otherwise, it matches a literal "x" character. In JavaScript
5111 mode, support for code points greater than 256 is provided by \u, which
5112 must be followed by four hexadecimal digits; otherwise it matches a
5113 literal "u" character.
5114
5115 Characters whose value is less than 256 can be defined by either of the
5116 two syntaxes for \x (or by \u in JavaScript mode). There is no differ-
5117 ence in the way they are handled. For example, \xdc is exactly the same
5118 as \x{dc} (or \u00dc in JavaScript mode).
5119
5120 Constraints on character values
5121
5122 Characters that are specified using octal or hexadecimal numbers are
5123 limited to certain values, as follows:
5124
5125 8-bit non-UTF mode less than 0x100
5126 8-bit UTF-8 mode less than 0x10ffff and a valid codepoint
5127 16-bit non-UTF mode less than 0x10000
5128 16-bit UTF-16 mode less than 0x10ffff and a valid codepoint
5129 32-bit non-UTF mode less than 0x100000000
5130 32-bit UTF-32 mode less than 0x10ffff and a valid codepoint
5131
5132 Invalid Unicode codepoints are the range 0xd800 to 0xdfff (the so-
5133 called "surrogate" codepoints), and 0xffef.
5134
5135 Escape sequences in character classes
5136
5137 All the sequences that define a single character value can be used both
5138 inside and outside character classes. In addition, inside a character
5139 class, \b is interpreted as the backspace character (hex 08).
5140
5141 \N is not allowed in a character class. \B, \R, and \X are not special
5142 inside a character class. Like other unrecognized escape sequences,
5143 they are treated as the literal characters "B", "R", and "X" by
5144 default, but cause an error if the PCRE_EXTRA option is set. Outside a
5145 character class, these sequences have different meanings.
5146
5147 Unsupported escape sequences
5148
5149 In Perl, the sequences \l, \L, \u, and \U are recognized by its string
5150 handler and used to modify the case of following characters. By
5151 default, PCRE does not support these escape sequences. However, if the
5152 PCRE_JAVASCRIPT_COMPAT option is set, \U matches a "U" character, and
5153 \u can be used to define a character by code point, as described in the
5154 previous section.
5155
5156 Absolute and relative back references
5157
5158 The sequence \g followed by an unsigned or a negative number, option-
5159 ally enclosed in braces, is an absolute or relative back reference. A
5160 named back reference can be coded as \g{name}. Back references are dis-
5161 cussed later, following the discussion of parenthesized subpatterns.
5162
5163 Absolute and relative subroutine calls
5164
5165 For compatibility with Oniguruma, the non-Perl syntax \g followed by a
5166 name or a number enclosed either in angle brackets or single quotes, is
5167 an alternative syntax for referencing a subpattern as a "subroutine".
5168 Details are discussed later. Note that \g{...} (Perl syntax) and
5169 \g<...> (Oniguruma syntax) are not synonymous. The former is a back
5170 reference; the latter is a subroutine call.
5171
5172 Generic character types
5173
5174 Another use of backslash is for specifying generic character types:
5175
5176 \d any decimal digit
5177 \D any character that is not a decimal digit
5178 \h any horizontal white space character
5179 \H any character that is not a horizontal white space character
5180 \s any white space character
5181 \S any character that is not a white space character
5182 \v any vertical white space character
5183 \V any character that is not a vertical white space character
5184 \w any "word" character
5185 \W any "non-word" character
5186
5187 There is also the single sequence \N, which matches a non-newline char-
5188 acter. This is the same as the "." metacharacter when PCRE_DOTALL is
5189 not set. Perl also uses \N to match characters by name; PCRE does not
5190 support this.
5191
5192 Each pair of lower and upper case escape sequences partitions the com-
5193 plete set of characters into two disjoint sets. Any given character
5194 matches one, and only one, of each pair. The sequences can appear both
5195 inside and outside character classes. They each match one character of
5196 the appropriate type. If the current matching point is at the end of
5197 the subject string, all of them fail, because there is no character to
5198 match.
5199
5200 For compatibility with Perl, \s did not used to match the VT character
5201 (code 11), which made it different from the the POSIX "space" class.
5202 However, Perl added VT at release 5.18, and PCRE followed suit at
5203 release 8.34. The default \s characters are now HT (9), LF (10), VT
5204 (11), FF (12), CR (13), and space (32), which are defined as white
5205 space in the "C" locale. This list may vary if locale-specific matching
5206 is taking place. For example, in some locales the "non-breaking space"
5207 character (\xA0) is recognized as white space, and in others the VT
5208 character is not.
5209
5210 A "word" character is an underscore or any character that is a letter
5211 or digit. By default, the definition of letters and digits is con-
5212 trolled by PCRE's low-valued character tables, and may vary if locale-
5213 specific matching is taking place (see "Locale support" in the pcreapi
5214 page). For example, in a French locale such as "fr_FR" in Unix-like
5215 systems, or "french" in Windows, some character codes greater than 127
5216 are used for accented letters, and these are then matched by \w. The
5217 use of locales with Unicode is discouraged.
5218
5219 By default, characters whose code points are greater than 127 never
5220 match \d, \s, or \w, and always match \D, \S, and \W, although this may
5221 vary for characters in the range 128-255 when locale-specific matching
5222 is happening. These escape sequences retain their original meanings
5223 from before Unicode support was available, mainly for efficiency rea-
5224 sons. If PCRE is compiled with Unicode property support, and the
5225 PCRE_UCP option is set, the behaviour is changed so that Unicode prop-
5226 erties are used to determine character types, as follows:
5227
5228 \d any character that matches \p{Nd} (decimal digit)
5229 \s any character that matches \p{Z} or \h or \v
5230 \w any character that matches \p{L} or \p{N}, plus underscore
5231
5232 The upper case escapes match the inverse sets of characters. Note that
5233 \d matches only decimal digits, whereas \w matches any Unicode digit,
5234 as well as any Unicode letter, and underscore. Note also that PCRE_UCP
5235 affects \b, and \B because they are defined in terms of \w and \W.
5236 Matching these sequences is noticeably slower when PCRE_UCP is set.
5237
5238 The sequences \h, \H, \v, and \V are features that were added to Perl
5239 at release 5.10. In contrast to the other sequences, which match only
5240 ASCII characters by default, these always match certain high-valued
5241 code points, whether or not PCRE_UCP is set. The horizontal space char-
5242 acters are:
5243
5244 U+0009 Horizontal tab (HT)
5245 U+0020 Space
5246 U+00A0 Non-break space
5247 U+1680 Ogham space mark
5248 U+180E Mongolian vowel separator
5249 U+2000 En quad
5250 U+2001 Em quad
5251 U+2002 En space
5252 U+2003 Em space
5253 U+2004 Three-per-em space
5254 U+2005 Four-per-em space
5255 U+2006 Six-per-em space
5256 U+2007 Figure space
5257 U+2008 Punctuation space
5258 U+2009 Thin space
5259 U+200A Hair space
5260 U+202F Narrow no-break space
5261 U+205F Medium mathematical space
5262 U+3000 Ideographic space
5263
5264 The vertical space characters are:
5265
5266 U+000A Linefeed (LF)
5267 U+000B Vertical tab (VT)
5268 U+000C Form feed (FF)
5269 U+000D Carriage return (CR)
5270 U+0085 Next line (NEL)
5271 U+2028 Line separator
5272 U+2029 Paragraph separator
5273
5274 In 8-bit, non-UTF-8 mode, only the characters with codepoints less than
5275 256 are relevant.
5276
5277 Newline sequences
5278
5279 Outside a character class, by default, the escape sequence \R matches
5280 any Unicode newline sequence. In 8-bit non-UTF-8 mode \R is equivalent
5281 to the following:
5282
5283 (?>\r\n|\n|\x0b|\f|\r|\x85)
5284
5285 This is an example of an "atomic group", details of which are given
5286 below. This particular group matches either the two-character sequence
5287 CR followed by LF, or one of the single characters LF (linefeed,
5288 U+000A), VT (vertical tab, U+000B), FF (form feed, U+000C), CR (car-
5289 riage return, U+000D), or NEL (next line, U+0085). The two-character
5290 sequence is treated as a single unit that cannot be split.
5291
5292 In other modes, two additional characters whose codepoints are greater
5293 than 255 are added: LS (line separator, U+2028) and PS (paragraph sepa-
5294 rator, U+2029). Unicode character property support is not needed for
5295 these characters to be recognized.
5296
5297 It is possible to restrict \R to match only CR, LF, or CRLF (instead of
5298 the complete set of Unicode line endings) by setting the option
5299 PCRE_BSR_ANYCRLF either at compile time or when the pattern is matched.
5300 (BSR is an abbrevation for "backslash R".) This can be made the default
5301 when PCRE is built; if this is the case, the other behaviour can be
5302 requested via the PCRE_BSR_UNICODE option. It is also possible to
5303 specify these settings by starting a pattern string with one of the
5304 following sequences:
5305
5306 (*BSR_ANYCRLF) CR, LF, or CRLF only
5307 (*BSR_UNICODE) any Unicode newline sequence
5308
5309 These override the default and the options given to the compiling func-
5310 tion, but they can themselves be overridden by options given to a
5311 matching function. Note that these special settings, which are not
5312 Perl-compatible, are recognized only at the very start of a pattern,
5313 and that they must be in upper case. If more than one of them is
5314 present, the last one is used. They can be combined with a change of
5315 newline convention; for example, a pattern can start with:
5316
5317 (*ANY)(*BSR_ANYCRLF)
5318
5319 They can also be combined with the (*UTF8), (*UTF16), (*UTF32), (*UTF)
5320 or (*UCP) special sequences. Inside a character class, \R is treated as
5321 an unrecognized escape sequence, and so matches the letter "R" by
5322 default, but causes an error if PCRE_EXTRA is set.
5323
5324 Unicode character properties
5325
5326 When PCRE is built with Unicode character property support, three addi-
5327 tional escape sequences that match characters with specific properties
5328 are available. When in 8-bit non-UTF-8 mode, these sequences are of
5329 course limited to testing characters whose codepoints are less than
5330 256, but they do work in this mode. The extra escape sequences are:
5331
5332 \p{xx} a character with the xx property
5333 \P{xx} a character without the xx property
5334 \X a Unicode extended grapheme cluster
5335
5336 The property names represented by xx above are limited to the Unicode
5337 script names, the general category properties, "Any", which matches any
5338 character (including newline), and some special PCRE properties
5339 (described in the next section). Other Perl properties such as "InMu-
5340 sicalSymbols" are not currently supported by PCRE. Note that \P{Any}
5341 does not match any characters, so always causes a match failure.
5342
5343 Sets of Unicode characters are defined as belonging to certain scripts.
5344 A character from one of these sets can be matched using a script name.
5345 For example:
5346
5347 \p{Greek}
5348 \P{Han}
5349
5350 Those that are not part of an identified script are lumped together as
5351 "Common". The current list of scripts is:
5352
5353 Arabic, Armenian, Avestan, Balinese, Bamum, Bassa_Vah, Batak, Bengali,
5354 Bopomofo, Brahmi, Braille, Buginese, Buhid, Canadian_Aboriginal, Car-
5355 ian, Caucasian_Albanian, Chakma, Cham, Cherokee, Common, Coptic, Cunei-
5356 form, Cypriot, Cyrillic, Deseret, Devanagari, Duployan, Egyptian_Hiero-
5357 glyphs, Elbasan, Ethiopic, Georgian, Glagolitic, Gothic, Grantha,
5358 Greek, Gujarati, Gurmukhi, Han, Hangul, Hanunoo, Hebrew, Hiragana,
5359 Imperial_Aramaic, Inherited, Inscriptional_Pahlavi, Inscrip-
5360 tional_Parthian, Javanese, Kaithi, Kannada, Katakana, Kayah_Li,
5361 Kharoshthi, Khmer, Khojki, Khudawadi, Lao, Latin, Lepcha, Limbu, Lin-
5362 ear_A, Linear_B, Lisu, Lycian, Lydian, Mahajani, Malayalam, Mandaic,
5363 Manichaean, Meetei_Mayek, Mende_Kikakui, Meroitic_Cursive,
5364 Meroitic_Hieroglyphs, Miao, Modi, Mongolian, Mro, Myanmar, Nabataean,
5365 New_Tai_Lue, Nko, Ogham, Ol_Chiki, Old_Italic, Old_North_Arabian,
5366 Old_Permic, Old_Persian, Old_South_Arabian, Old_Turkic, Oriya, Osmanya,
5367 Pahawh_Hmong, Palmyrene, Pau_Cin_Hau, Phags_Pa, Phoenician,
5368 Psalter_Pahlavi, Rejang, Runic, Samaritan, Saurashtra, Sharada, Sha-
5369 vian, Siddham, Sinhala, Sora_Sompeng, Sundanese, Syloti_Nagri, Syriac,
5370 Tagalog, Tagbanwa, Tai_Le, Tai_Tham, Tai_Viet, Takri, Tamil, Telugu,
5371 Thaana, Thai, Tibetan, Tifinagh, Tirhuta, Ugaritic, Vai, Warang_Citi,
5372 Yi.
5373
5374 Each character has exactly one Unicode general category property, spec-
5375 ified by a two-letter abbreviation. For compatibility with Perl, nega-
5376 tion can be specified by including a circumflex between the opening
5377 brace and the property name. For example, \p{^Lu} is the same as
5378 \P{Lu}.
5379
5380 If only one letter is specified with \p or \P, it includes all the gen-
5381 eral category properties that start with that letter. In this case, in
5382 the absence of negation, the curly brackets in the escape sequence are
5383 optional; these two examples have the same effect:
5384
5385 \p{L}
5386 \pL
5387
5388 The following general category property codes are supported:
5389
5390 C Other
5391 Cc Control
5392 Cf Format
5393 Cn Unassigned
5394 Co Private use
5395 Cs Surrogate
5396
5397 L Letter
5398 Ll Lower case letter
5399 Lm Modifier letter
5400 Lo Other letter
5401 Lt Title case letter
5402 Lu Upper case letter
5403
5404 M Mark
5405 Mc Spacing mark
5406 Me Enclosing mark
5407 Mn Non-spacing mark
5408
5409 N Number
5410 Nd Decimal number
5411 Nl Letter number
5412 No Other number
5413
5414 P Punctuation
5415 Pc Connector punctuation
5416 Pd Dash punctuation
5417 Pe Close punctuation
5418 Pf Final punctuation
5419 Pi Initial punctuation
5420 Po Other punctuation
5421 Ps Open punctuation
5422
5423 S Symbol
5424 Sc Currency symbol
5425 Sk Modifier symbol
5426 Sm Mathematical symbol
5427 So Other symbol
5428
5429 Z Separator
5430 Zl Line separator
5431 Zp Paragraph separator
5432 Zs Space separator
5433
5434 The special property L& is also supported: it matches a character that
5435 has the Lu, Ll, or Lt property, in other words, a letter that is not
5436 classified as a modifier or "other".
5437
5438 The Cs (Surrogate) property applies only to characters in the range
5439 U+D800 to U+DFFF. Such characters are not valid in Unicode strings and
5440 so cannot be tested by PCRE, unless UTF validity checking has been
5441 turned off (see the discussion of PCRE_NO_UTF8_CHECK,
5442 PCRE_NO_UTF16_CHECK and PCRE_NO_UTF32_CHECK in the pcreapi page). Perl
5443 does not support the Cs property.
5444
5445 The long synonyms for property names that Perl supports (such as
5446 \p{Letter}) are not supported by PCRE, nor is it permitted to prefix
5447 any of these properties with "Is".
5448
5449 No character that is in the Unicode table has the Cn (unassigned) prop-
5450 erty. Instead, this property is assumed for any code point that is not
5451 in the Unicode table.
5452
5453 Specifying caseless matching does not affect these escape sequences.
5454 For example, \p{Lu} always matches only upper case letters. This is
5455 different from the behaviour of current versions of Perl.
5456
5457 Matching characters by Unicode property is not fast, because PCRE has
5458 to do a multistage table lookup in order to find a character's prop-
5459 erty. That is why the traditional escape sequences such as \d and \w do
5460 not use Unicode properties in PCRE by default, though you can make them
5461 do so by setting the PCRE_UCP option or by starting the pattern with
5462 (*UCP).
5463
5464 Extended grapheme clusters
5465
5466 The \X escape matches any number of Unicode characters that form an
5467 "extended grapheme cluster", and treats the sequence as an atomic group
5468 (see below). Up to and including release 8.31, PCRE matched an ear-
5469 lier, simpler definition that was equivalent to
5470
5471 (?>\PM\pM*)
5472
5473 That is, it matched a character without the "mark" property, followed
5474 by zero or more characters with the "mark" property. Characters with
5475 the "mark" property are typically non-spacing accents that affect the
5476 preceding character.
5477
5478 This simple definition was extended in Unicode to include more compli-
5479 cated kinds of composite character by giving each character a grapheme
5480 breaking property, and creating rules that use these properties to
5481 define the boundaries of extended grapheme clusters. In releases of
5482 PCRE later than 8.31, \X matches one of these clusters.
5483
5484 \X always matches at least one character. Then it decides whether to
5485 add additional characters according to the following rules for ending a
5486 cluster:
5487
5488 1. End at the end of the subject string.
5489
5490 2. Do not end between CR and LF; otherwise end after any control char-
5491 acter.
5492
5493 3. Do not break Hangul (a Korean script) syllable sequences. Hangul
5494 characters are of five types: L, V, T, LV, and LVT. An L character may
5495 be followed by an L, V, LV, or LVT character; an LV or V character may
5496 be followed by a V or T character; an LVT or T character may be follwed
5497 only by a T character.
5498
5499 4. Do not end before extending characters or spacing marks. Characters
5500 with the "mark" property always have the "extend" grapheme breaking
5501 property.
5502
5503 5. Do not end after prepend characters.
5504
5505 6. Otherwise, end the cluster.
5506
5507 PCRE's additional properties
5508
5509 As well as the standard Unicode properties described above, PCRE sup-
5510 ports four more that make it possible to convert traditional escape
5511 sequences such as \w and \s to use Unicode properties. PCRE uses these
5512 non-standard, non-Perl properties internally when PCRE_UCP is set. How-
5513 ever, they may also be used explicitly. These properties are:
5514
5515 Xan Any alphanumeric character
5516 Xps Any POSIX space character
5517 Xsp Any Perl space character
5518 Xwd Any Perl "word" character
5519
5520 Xan matches characters that have either the L (letter) or the N (num-
5521 ber) property. Xps matches the characters tab, linefeed, vertical tab,
5522 form feed, or carriage return, and any other character that has the Z
5523 (separator) property. Xsp is the same as Xps; it used to exclude ver-
5524 tical tab, for Perl compatibility, but Perl changed, and so PCRE fol-
5525 lowed at release 8.34. Xwd matches the same characters as Xan, plus
5526 underscore.
5527
5528 There is another non-standard property, Xuc, which matches any charac-
5529 ter that can be represented by a Universal Character Name in C++ and
5530 other programming languages. These are the characters $, @, ` (grave
5531 accent), and all characters with Unicode code points greater than or
5532 equal to U+00A0, except for the surrogates U+D800 to U+DFFF. Note that
5533 most base (ASCII) characters are excluded. (Universal Character Names
5534 are of the form \uHHHH or \UHHHHHHHH where H is a hexadecimal digit.
5535 Note that the Xuc property does not match these sequences but the char-
5536 acters that they represent.)
5537
5538 Resetting the match start
5539
5540 The escape sequence \K causes any previously matched characters not to
5541 be included in the final matched sequence. For example, the pattern:
5542
5543 foo\Kbar
5544
5545 matches "foobar", but reports that it has matched "bar". This feature
5546 is similar to a lookbehind assertion (described below). However, in
5547 this case, the part of the subject before the real match does not have
5548 to be of fixed length, as lookbehind assertions do. The use of \K does
5549 not interfere with the setting of captured substrings. For example,
5550 when the pattern
5551
5552 (foo)\Kbar
5553
5554 matches "foobar", the first substring is still set to "foo".
5555
5556 Perl documents that the use of \K within assertions is "not well
5557 defined". In PCRE, \K is acted upon when it occurs inside positive
5558 assertions, but is ignored in negative assertions. Note that when a
5559 pattern such as (?=ab\K) matches, the reported start of the match can
5560 be greater than the end of the match.
5561
5562 Simple assertions
5563
5564 The final use of backslash is for certain simple assertions. An asser-
5565 tion specifies a condition that has to be met at a particular point in
5566 a match, without consuming any characters from the subject string. The
5567 use of subpatterns for more complicated assertions is described below.
5568 The backslashed assertions are:
5569
5570 \b matches at a word boundary
5571 \B matches when not at a word boundary
5572 \A matches at the start of the subject
5573 \Z matches at the end of the subject
5574 also matches before a newline at the end of the subject
5575 \z matches only at the end of the subject
5576 \G matches at the first matching position in the subject
5577
5578 Inside a character class, \b has a different meaning; it matches the
5579 backspace character. If any other of these assertions appears in a
5580 character class, by default it matches the corresponding literal char-
5581 acter (for example, \B matches the letter B). However, if the
5582 PCRE_EXTRA option is set, an "invalid escape sequence" error is gener-
5583 ated instead.
5584
5585 A word boundary is a position in the subject string where the current
5586 character and the previous character do not both match \w or \W (i.e.
5587 one matches \w and the other matches \W), or the start or end of the
5588 string if the first or last character matches \w, respectively. In a
5589 UTF mode, the meanings of \w and \W can be changed by setting the
5590 PCRE_UCP option. When this is done, it also affects \b and \B. Neither
5591 PCRE nor Perl has a separate "start of word" or "end of word" metase-
5592 quence. However, whatever follows \b normally determines which it is.
5593 For example, the fragment \ba matches "a" at the start of a word.
5594
5595 The \A, \Z, and \z assertions differ from the traditional circumflex
5596 and dollar (described in the next section) in that they only ever match
5597 at the very start and end of the subject string, whatever options are
5598 set. Thus, they are independent of multiline mode. These three asser-
5599 tions are not affected by the PCRE_NOTBOL or PCRE_NOTEOL options, which
5600 affect only the behaviour of the circumflex and dollar metacharacters.
5601 However, if the startoffset argument of pcre_exec() is non-zero, indi-
5602 cating that matching is to start at a point other than the beginning of
5603 the subject, \A can never match. The difference between \Z and \z is
5604 that \Z matches before a newline at the end of the string as well as at
5605 the very end, whereas \z matches only at the end.
5606
5607 The \G assertion is true only when the current matching position is at
5608 the start point of the match, as specified by the startoffset argument
5609 of pcre_exec(). It differs from \A when the value of startoffset is
5610 non-zero. By calling pcre_exec() multiple times with appropriate argu-
5611 ments, you can mimic Perl's /g option, and it is in this kind of imple-
5612 mentation where \G can be useful.
5613
5614 Note, however, that PCRE's interpretation of \G, as the start of the
5615 current match, is subtly different from Perl's, which defines it as the
5616 end of the previous match. In Perl, these can be different when the
5617 previously matched string was empty. Because PCRE does just one match
5618 at a time, it cannot reproduce this behaviour.
5619
5620 If all the alternatives of a pattern begin with \G, the expression is
5621 anchored to the starting match position, and the "anchored" flag is set
5622 in the compiled regular expression.
5623
5624
5625 CIRCUMFLEX AND DOLLAR
5626
5627 The circumflex and dollar metacharacters are zero-width assertions.
5628 That is, they test for a particular condition being true without con-
5629 suming any characters from the subject string.
5630
5631 Outside a character class, in the default matching mode, the circumflex
5632 character is an assertion that is true only if the current matching
5633 point is at the start of the subject string. If the startoffset argu-
5634 ment of pcre_exec() is non-zero, circumflex can never match if the
5635 PCRE_MULTILINE option is unset. Inside a character class, circumflex
5636 has an entirely different meaning (see below).
5637
5638 Circumflex need not be the first character of the pattern if a number
5639 of alternatives are involved, but it should be the first thing in each
5640 alternative in which it appears if the pattern is ever to match that
5641 branch. If all possible alternatives start with a circumflex, that is,
5642 if the pattern is constrained to match only at the start of the sub-
5643 ject, it is said to be an "anchored" pattern. (There are also other
5644 constructs that can cause a pattern to be anchored.)
5645
5646 The dollar character is an assertion that is true only if the current
5647 matching point is at the end of the subject string, or immediately
5648 before a newline at the end of the string (by default). Note, however,
5649 that it does not actually match the newline. Dollar need not be the
5650 last character of the pattern if a number of alternatives are involved,
5651 but it should be the last item in any branch in which it appears. Dol-
5652 lar has no special meaning in a character class.
5653
5654 The meaning of dollar can be changed so that it matches only at the
5655 very end of the string, by setting the PCRE_DOLLAR_ENDONLY option at
5656 compile time. This does not affect the \Z assertion.
5657
5658 The meanings of the circumflex and dollar characters are changed if the
5659 PCRE_MULTILINE option is set. When this is the case, a circumflex
5660 matches immediately after internal newlines as well as at the start of
5661 the subject string. It does not match after a newline that ends the
5662 string. A dollar matches before any newlines in the string, as well as
5663 at the very end, when PCRE_MULTILINE is set. When newline is specified
5664 as the two-character sequence CRLF, isolated CR and LF characters do
5665 not indicate newlines.
5666
5667 For example, the pattern /^abc$/ matches the subject string "def\nabc"
5668 (where \n represents a newline) in multiline mode, but not otherwise.
5669 Consequently, patterns that are anchored in single line mode because
5670 all branches start with ^ are not anchored in multiline mode, and a
5671 match for circumflex is possible when the startoffset argument of
5672 pcre_exec() is non-zero. The PCRE_DOLLAR_ENDONLY option is ignored if
5673 PCRE_MULTILINE is set.
5674
5675 Note that the sequences \A, \Z, and \z can be used to match the start
5676 and end of the subject in both modes, and if all branches of a pattern
5677 start with \A it is always anchored, whether or not PCRE_MULTILINE is
5678 set.
5679
5680
5681 FULL STOP (PERIOD, DOT) AND \N
5682
5683 Outside a character class, a dot in the pattern matches any one charac-
5684 ter in the subject string except (by default) a character that signi-
5685 fies the end of a line.
5686
5687 When a line ending is defined as a single character, dot never matches
5688 that character; when the two-character sequence CRLF is used, dot does
5689 not match CR if it is immediately followed by LF, but otherwise it
5690 matches all characters (including isolated CRs and LFs). When any Uni-
5691 code line endings are being recognized, dot does not match CR or LF or
5692 any of the other line ending characters.
5693
5694 The behaviour of dot with regard to newlines can be changed. If the
5695 PCRE_DOTALL option is set, a dot matches any one character, without
5696 exception. If the two-character sequence CRLF is present in the subject
5697 string, it takes two dots to match it.
5698
5699 The handling of dot is entirely independent of the handling of circum-
5700 flex and dollar, the only relationship being that they both involve
5701 newlines. Dot has no special meaning in a character class.
5702
5703 The escape sequence \N behaves like a dot, except that it is not
5704 affected by the PCRE_DOTALL option. In other words, it matches any
5705 character except one that signifies the end of a line. Perl also uses
5706 \N to match characters by name; PCRE does not support this.
5707
5708
5709 MATCHING A SINGLE DATA UNIT
5710
5711 Outside a character class, the escape sequence \C matches any one data
5712 unit, whether or not a UTF mode is set. In the 8-bit library, one data
5713 unit is one byte; in the 16-bit library it is a 16-bit unit; in the
5714 32-bit library it is a 32-bit unit. Unlike a dot, \C always matches
5715 line-ending characters. The feature is provided in Perl in order to
5716 match individual bytes in UTF-8 mode, but it is unclear how it can use-
5717 fully be used. Because \C breaks up characters into individual data
5718 units, matching one unit with \C in a UTF mode means that the rest of
5719 the string may start with a malformed UTF character. This has undefined
5720 results, because PCRE assumes that it is dealing with valid UTF strings
5721 (and by default it checks this at the start of processing unless the
5722 PCRE_NO_UTF8_CHECK, PCRE_NO_UTF16_CHECK or PCRE_NO_UTF32_CHECK option
5723 is used).
5724
5725 PCRE does not allow \C to appear in lookbehind assertions (described
5726 below) in a UTF mode, because this would make it impossible to calcu-
5727 late the length of the lookbehind.
5728
5729 In general, the \C escape sequence is best avoided. However, one way of
5730 using it that avoids the problem of malformed UTF characters is to use
5731 a lookahead to check the length of the next character, as in this pat-
5732 tern, which could be used with a UTF-8 string (ignore white space and
5733 line breaks):
5734
5735 (?| (?=[\x00-\x7f])(\C) |
5736 (?=[\x80-\x{7ff}])(\C)(\C) |
5737 (?=[\x{800}-\x{ffff}])(\C)(\C)(\C) |
5738 (?=[\x{10000}-\x{1fffff}])(\C)(\C)(\C)(\C))
5739
5740 A group that starts with (?| resets the capturing parentheses numbers
5741 in each alternative (see "Duplicate Subpattern Numbers" below). The
5742 assertions at the start of each branch check the next UTF-8 character
5743 for values whose encoding uses 1, 2, 3, or 4 bytes, respectively. The
5744 character's individual bytes are then captured by the appropriate num-
5745 ber of groups.
5746
5747
5748 SQUARE BRACKETS AND CHARACTER CLASSES
5749
5750 An opening square bracket introduces a character class, terminated by a
5751 closing square bracket. A closing square bracket on its own is not spe-
5752 cial by default. However, if the PCRE_JAVASCRIPT_COMPAT option is set,
5753 a lone closing square bracket causes a compile-time error. If a closing
5754 square bracket is required as a member of the class, it should be the
5755 first data character in the class (after an initial circumflex, if
5756 present) or escaped with a backslash.
5757
5758 A character class matches a single character in the subject. In a UTF
5759 mode, the character may be more than one data unit long. A matched
5760 character must be in the set of characters defined by the class, unless
5761 the first character in the class definition is a circumflex, in which
5762 case the subject character must not be in the set defined by the class.
5763 If a circumflex is actually required as a member of the class, ensure
5764 it is not the first character, or escape it with a backslash.
5765
5766 For example, the character class [aeiou] matches any lower case vowel,
5767 while [^aeiou] matches any character that is not a lower case vowel.
5768 Note that a circumflex is just a convenient notation for specifying the
5769 characters that are in the class by enumerating those that are not. A
5770 class that starts with a circumflex is not an assertion; it still con-
5771 sumes a character from the subject string, and therefore it fails if
5772 the current pointer is at the end of the string.
5773
5774 In UTF-8 (UTF-16, UTF-32) mode, characters with values greater than 255
5775 (0xffff) can be included in a class as a literal string of data units,
5776 or by using the \x{ escaping mechanism.
5777
5778 When caseless matching is set, any letters in a class represent both
5779 their upper case and lower case versions, so for example, a caseless
5780 [aeiou] matches "A" as well as "a", and a caseless [^aeiou] does not
5781 match "A", whereas a caseful version would. In a UTF mode, PCRE always
5782 understands the concept of case for characters whose values are less
5783 than 128, so caseless matching is always possible. For characters with
5784 higher values, the concept of case is supported if PCRE is compiled
5785 with Unicode property support, but not otherwise. If you want to use
5786 caseless matching in a UTF mode for characters 128 and above, you must
5787 ensure that PCRE is compiled with Unicode property support as well as
5788 with UTF support.
5789
5790 Characters that might indicate line breaks are never treated in any
5791 special way when matching character classes, whatever line-ending
5792 sequence is in use, and whatever setting of the PCRE_DOTALL and
5793 PCRE_MULTILINE options is used. A class such as [^a] always matches one
5794 of these characters.
5795
5796 The minus (hyphen) character can be used to specify a range of charac-
5797 ters in a character class. For example, [d-m] matches any letter
5798 between d and m, inclusive. If a minus character is required in a
5799 class, it must be escaped with a backslash or appear in a position
5800 where it cannot be interpreted as indicating a range, typically as the
5801 first or last character in the class, or immediately after a range. For
5802 example, [b-d-z] matches letters in the range b to d, a hyphen charac-
5803 ter, or z.
5804
5805 It is not possible to have the literal character "]" as the end charac-
5806 ter of a range. A pattern such as [W-]46] is interpreted as a class of
5807 two characters ("W" and "-") followed by a literal string "46]", so it
5808 would match "W46]" or "-46]". However, if the "]" is escaped with a
5809 backslash it is interpreted as the end of range, so [W-\]46] is inter-
5810 preted as a class containing a range followed by two other characters.
5811 The octal or hexadecimal representation of "]" can also be used to end
5812 a range.
5813
5814 An error is generated if a POSIX character class (see below) or an
5815 escape sequence other than one that defines a single character appears
5816 at a point where a range ending character is expected. For example,
5817 [z-\xff] is valid, but [A-\d] and [A-[:digit:]] are not.
5818
5819 Ranges operate in the collating sequence of character values. They can
5820 also be used for characters specified numerically, for example
5821 [\000-\037]. Ranges can include any characters that are valid for the
5822 current mode.
5823
5824 If a range that includes letters is used when caseless matching is set,
5825 it matches the letters in either case. For example, [W-c] is equivalent
5826 to [][\\^_`wxyzabc], matched caselessly, and in a non-UTF mode, if
5827 character tables for a French locale are in use, [\xc8-\xcb] matches
5828 accented E characters in both cases. In UTF modes, PCRE supports the
5829 concept of case for characters with values greater than 128 only when
5830 it is compiled with Unicode property support.
5831
5832 The character escape sequences \d, \D, \h, \H, \p, \P, \s, \S, \v, \V,
5833 \w, and \W may appear in a character class, and add the characters that
5834 they match to the class. For example, [\dABCDEF] matches any hexadeci-
5835 mal digit. In UTF modes, the PCRE_UCP option affects the meanings of
5836 \d, \s, \w and their upper case partners, just as it does when they
5837 appear outside a character class, as described in the section entitled
5838 "Generic character types" above. The escape sequence \b has a different
5839 meaning inside a character class; it matches the backspace character.
5840 The sequences \B, \N, \R, and \X are not special inside a character
5841 class. Like any other unrecognized escape sequences, they are treated
5842 as the literal characters "B", "N", "R", and "X" by default, but cause
5843 an error if the PCRE_EXTRA option is set.
5844
5845 A circumflex can conveniently be used with the upper case character
5846 types to specify a more restricted set of characters than the matching
5847 lower case type. For example, the class [^\W_] matches any letter or
5848 digit, but not underscore, whereas [\w] includes underscore. A positive
5849 character class should be read as "something OR something OR ..." and a
5850 negative class as "NOT something AND NOT something AND NOT ...".
5851
5852 The only metacharacters that are recognized in character classes are
5853 backslash, hyphen (only where it can be interpreted as specifying a
5854 range), circumflex (only at the start), opening square bracket (only
5855 when it can be interpreted as introducing a POSIX class name, or for a
5856 special compatibility feature - see the next two sections), and the
5857 terminating closing square bracket. However, escaping other non-
5858 alphanumeric characters does no harm.
5859
5860
5861 POSIX CHARACTER CLASSES
5862
5863 Perl supports the POSIX notation for character classes. This uses names
5864 enclosed by [: and :] within the enclosing square brackets. PCRE also
5865 supports this notation. For example,
5866
5867 [01[:alpha:]%]
5868
5869 matches "0", "1", any alphabetic character, or "%". The supported class
5870 names are:
5871
5872 alnum letters and digits
5873 alpha letters
5874 ascii character codes 0 - 127
5875 blank space or tab only
5876 cntrl control characters
5877 digit decimal digits (same as \d)
5878 graph printing characters, excluding space
5879 lower lower case letters
5880 print printing characters, including space
5881 punct printing characters, excluding letters and digits and space
5882 space white space (the same as \s from PCRE 8.34)
5883 upper upper case letters
5884 word "word" characters (same as \w)
5885 xdigit hexadecimal digits
5886
5887 The default "space" characters are HT (9), LF (10), VT (11), FF (12),
5888 CR (13), and space (32). If locale-specific matching is taking place,
5889 the list of space characters may be different; there may be fewer or
5890 more of them. "Space" used to be different to \s, which did not include
5891 VT, for Perl compatibility. However, Perl changed at release 5.18, and
5892 PCRE followed at release 8.34. "Space" and \s now match the same set
5893 of characters.
5894
5895 The name "word" is a Perl extension, and "blank" is a GNU extension
5896 from Perl 5.8. Another Perl extension is negation, which is indicated
5897 by a ^ character after the colon. For example,
5898
5899 [12[:^digit:]]
5900
5901 matches "1", "2", or any non-digit. PCRE (and Perl) also recognize the
5902 POSIX syntax [.ch.] and [=ch=] where "ch" is a "collating element", but
5903 these are not supported, and an error is given if they are encountered.
5904
5905 By default, characters with values greater than 128 do not match any of
5906 the POSIX character classes. However, if the PCRE_UCP option is passed
5907 to pcre_compile(), some of the classes are changed so that Unicode
5908 character properties are used. This is achieved by replacing certain
5909 POSIX classes by other sequences, as follows:
5910
5911 [:alnum:] becomes \p{Xan}
5912 [:alpha:] becomes \p{L}
5913 [:blank:] becomes \h
5914 [:digit:] becomes \p{Nd}
5915 [:lower:] becomes \p{Ll}
5916 [:space:] becomes \p{Xps}
5917 [:upper:] becomes \p{Lu}
5918 [:word:] becomes \p{Xwd}
5919
5920 Negated versions, such as [:^alpha:] use \P instead of \p. Three other
5921 POSIX classes are handled specially in UCP mode:
5922
5923 [:graph:] This matches characters that have glyphs that mark the page
5924 when printed. In Unicode property terms, it matches all char-
5925 acters with the L, M, N, P, S, or Cf properties, except for:
5926
5927 U+061C Arabic Letter Mark
5928 U+180E Mongolian Vowel Separator
5929 U+2066 - U+2069 Various "isolate"s
5930
5931
5932 [:print:] This matches the same characters as [:graph:] plus space
5933 characters that are not controls, that is, characters with
5934 the Zs property.
5935
5936 [:punct:] This matches all characters that have the Unicode P (punctua-
5937 tion) property, plus those characters whose code points are
5938 less than 128 that have the S (Symbol) property.
5939
5940 The other POSIX classes are unchanged, and match only characters with
5941 code points less than 128.
5942
5943
5944 COMPATIBILITY FEATURE FOR WORD BOUNDARIES
5945
5946 In the POSIX.2 compliant library that was included in 4.4BSD Unix, the
5947 ugly syntax [[:<:]] and [[:>:]] is used for matching "start of word"
5948 and "end of word". PCRE treats these items as follows:
5949
5950 [[:<:]] is converted to \b(?=\w)
5951 [[:>:]] is converted to \b(?<=\w)
5952
5953 Only these exact character sequences are recognized. A sequence such as
5954 [a[:<:]b] provokes error for an unrecognized POSIX class name. This
5955 support is not compatible with Perl. It is provided to help migrations
5956 from other environments, and is best not used in any new patterns. Note
5957 that \b matches at the start and the end of a word (see "Simple asser-
5958 tions" above), and in a Perl-style pattern the preceding or following
5959 character normally shows which is wanted, without the need for the
5960 assertions that are used above in order to give exactly the POSIX be-
5961 haviour.
5962
5963
5964 VERTICAL BAR
5965
5966 Vertical bar characters are used to separate alternative patterns. For
5967 example, the pattern
5968
5969 gilbert|sullivan
5970
5971 matches either "gilbert" or "sullivan". Any number of alternatives may
5972 appear, and an empty alternative is permitted (matching the empty
5973 string). The matching process tries each alternative in turn, from left
5974 to right, and the first one that succeeds is used. If the alternatives
5975 are within a subpattern (defined below), "succeeds" means matching the
5976 rest of the main pattern as well as the alternative in the subpattern.
5977
5978
5979 INTERNAL OPTION SETTING
5980
5981 The settings of the PCRE_CASELESS, PCRE_MULTILINE, PCRE_DOTALL, and
5982 PCRE_EXTENDED options (which are Perl-compatible) can be changed from
5983 within the pattern by a sequence of Perl option letters enclosed
5984 between "(?" and ")". The option letters are
5985
5986 i for PCRE_CASELESS
5987 m for PCRE_MULTILINE
5988 s for PCRE_DOTALL
5989 x for PCRE_EXTENDED
5990
5991 For example, (?im) sets caseless, multiline matching. It is also possi-
5992 ble to unset these options by preceding the letter with a hyphen, and a
5993 combined setting and unsetting such as (?im-sx), which sets PCRE_CASE-
5994 LESS and PCRE_MULTILINE while unsetting PCRE_DOTALL and PCRE_EXTENDED,
5995 is also permitted. If a letter appears both before and after the
5996 hyphen, the option is unset.
5997
5998 The PCRE-specific options PCRE_DUPNAMES, PCRE_UNGREEDY, and PCRE_EXTRA
5999 can be changed in the same way as the Perl-compatible options by using
6000 the characters J, U and X respectively.
6001
6002 When one of these option changes occurs at top level (that is, not
6003 inside subpattern parentheses), the change applies to the remainder of
6004 the pattern that follows. An option change within a subpattern (see
6005 below for a description of subpatterns) affects only that part of the
6006 subpattern that follows it, so
6007
6008 (a(?i)b)c
6009
6010 matches abc and aBc and no other strings (assuming PCRE_CASELESS is not
6011 used). By this means, options can be made to have different settings
6012 in different parts of the pattern. Any changes made in one alternative
6013 do carry on into subsequent branches within the same subpattern. For
6014 example,
6015
6016 (a(?i)b|c)
6017
6018 matches "ab", "aB", "c", and "C", even though when matching "C" the
6019 first branch is abandoned before the option setting. This is because
6020 the effects of option settings happen at compile time. There would be
6021 some very weird behaviour otherwise.
6022
6023 Note: There are other PCRE-specific options that can be set by the
6024 application when the compiling or matching functions are called. In
6025 some cases the pattern can contain special leading sequences such as
6026 (*CRLF) to override what the application has set or what has been
6027 defaulted. Details are given in the section entitled "Newline
6028 sequences" above. There are also the (*UTF8), (*UTF16),(*UTF32), and
6029 (*UCP) leading sequences that can be used to set UTF and Unicode prop-
6030 erty modes; they are equivalent to setting the PCRE_UTF8, PCRE_UTF16,
6031 PCRE_UTF32 and the PCRE_UCP options, respectively. The (*UTF) sequen