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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
17
18 INTRODUCTION
19
20 The PCRE library is a set of functions that implement regular expres-
21 sion pattern matching using the same syntax and semantics as Perl, with
22 just a few differences. Some features that appeared in Python and PCRE
23 before they appeared in Perl are also available using the Python syn-
24 tax, there is some support for one or two .NET and Oniguruma syntax
25 items, and there is an option for requesting some minor changes that
26 give better JavaScript compatibility.
27
28 Starting with release 8.30, it is possible to compile two separate PCRE
29 libraries: the original, which supports 8-bit character strings
30 (including UTF-8 strings), and a second library that supports 16-bit
31 character strings (including UTF-16 strings). The build process allows
32 either one or both to be built. The majority of the work to make this
33 possible was done by Zoltan Herczeg.
34
35 Starting with release 8.32 it is possible to compile a third separate
36 PCRE library, which supports 32-bit character strings (including UTF-32
37 strings). The build process allows any set of the 8-, 16- and 32-bit
38 libraries. The work to make this possible was done by Christian Persch.
39
40 The three libraries contain identical sets of functions, except that
41 the names in the 16-bit library start with pcre16_ instead of pcre_,
42 and the names in the 32-bit library start with pcre32_ instead of
43 pcre_. To avoid over-complication and reduce the documentation mainte-
44 nance load, most of the documentation describes the 8-bit library, with
45 the differences for the 16-bit and 32-bit libraries described sepa-
46 rately in the pcre16 and pcre32 pages. References to functions or
47 structures of the form pcre[16|32]_xxx should be read as meaning
48 "pcre_xxx when using the 8-bit library, pcre16_xxx when using the
49 16-bit library, or pcre32_xxx when using the 32-bit library".
50
51 The current implementation of PCRE corresponds approximately with Perl
52 5.12, including support for UTF-8/16/32 encoded strings and Unicode
53 general category properties. However, UTF-8/16/32 and Unicode support
54 has to be explicitly enabled; it is not the default. The Unicode tables
55 correspond to Unicode release 6.2.0.
56
57 In addition to the Perl-compatible matching function, PCRE contains an
58 alternative function that matches the same compiled patterns in a dif-
59 ferent way. In certain circumstances, the alternative function has some
60 advantages. For a discussion of the two matching algorithms, see the
61 pcrematching page.
62
63 PCRE is written in C and released as a C library. A number of people
64 have written wrappers and interfaces of various kinds. In particular,
65 Google Inc. have provided a comprehensive C++ wrapper for the 8-bit
66 library. This is now included as part of the PCRE distribution. The
67 pcrecpp page has details of this interface. Other people's contribu-
68 tions can be found in the Contrib directory at the primary FTP site,
69 which is:
70
71 ftp://ftp.csx.cam.ac.uk/pub/software/programming/pcre
72
73 Details of exactly which Perl regular expression features are and are
74 not supported by PCRE are given in separate documents. See the pcrepat-
75 tern and pcrecompat pages. There is a syntax summary in the pcresyntax
76 page.
77
78 Some features of PCRE can be included, excluded, or changed when the
79 library is built. The pcre_config() function makes it possible for a
80 client to discover which features are available. The features them-
81 selves are described in the pcrebuild page. Documentation about build-
82 ing PCRE for various operating systems can be found in the README and
83 NON-AUTOTOOLS_BUILD files in the source distribution.
84
85 The libraries contains a number of undocumented internal functions and
86 data tables that are used by more than one of the exported external
87 functions, but which are not intended for use by external callers.
88 Their names all begin with "_pcre_" or "_pcre16_" or "_pcre32_", which
89 hopefully will not provoke any name clashes. In some environments, it
90 is possible to control which external symbols are exported when a
91 shared library is built, and in these cases the undocumented symbols
92 are not exported.
93
94
95 SECURITY CONSIDERATIONS
96
97 If you are using PCRE in a non-UTF application that permits users to
98 supply arbitrary patterns for compilation, you should be aware of a
99 feature that allows users to turn on UTF support from within a pattern,
100 provided that PCRE was built with UTF support. For example, an 8-bit
101 pattern that begins with "(*UTF8)" or "(*UTF)" turns on UTF-8 mode,
102 which interprets patterns and subjects as strings of UTF-8 characters
103 instead of individual 8-bit characters. This causes both the pattern
104 and any data against which it is matched to be checked for UTF-8 valid-
105 ity. If the data string is very long, such a check might use suffi-
106 ciently many resources as to cause your application to lose perfor-
107 mance.
108
109 One way of guarding against this possibility is to use the
110 pcre_fullinfo() function to check the compiled pattern's options for
111 UTF. Alternatively, from release 8.33, you can set the PCRE_NEVER_UTF
112 option at compile time. This causes an compile time error if a pattern
113 contains a UTF-setting sequence.
114
115 If your application is one that supports UTF, be aware that validity
116 checking can take time. If the same data string is to be matched many
117 times, you can use the PCRE_NO_UTF[8|16|32]_CHECK option for the second
118 and subsequent matches to save redundant checks.
119
120 Another way that performance can be hit is by running a pattern that
121 has a very large search tree against a string that will never match.
122 Nested unlimited repeats in a pattern are a common example. PCRE pro-
123 vides some protection against this: see the PCRE_EXTRA_MATCH_LIMIT fea-
124 ture in the pcreapi page.
125
126
127 USER DOCUMENTATION
128
129 The user documentation for PCRE comprises a number of different sec-
130 tions. In the "man" format, each of these is a separate "man page". In
131 the HTML format, each is a separate page, linked from the index page.
132 In the plain text format, all the sections, except the pcredemo sec-
133 tion, are concatenated, for ease of searching. The sections are as fol-
134 lows:
135
136 pcre this document
137 pcre16 details of the 16-bit library
138 pcre32 details of the 32-bit library
139 pcre-config show PCRE installation configuration information
140 pcreapi details of PCRE's native C API
141 pcrebuild options for building PCRE
142 pcrecallout details of the callout feature
143 pcrecompat discussion of Perl compatibility
144 pcrecpp details of the C++ wrapper for the 8-bit library
145 pcredemo a demonstration C program that uses PCRE
146 pcregrep description of the pcregrep command (8-bit only)
147 pcrejit discussion of the just-in-time optimization support
148 pcrelimits details of size and other limits
149 pcrematching discussion of the two matching algorithms
150 pcrepartial details of the partial matching facility
151 pcrepattern syntax and semantics of supported
152 regular expressions
153 pcreperform discussion of performance issues
154 pcreposix the POSIX-compatible C API for the 8-bit library
155 pcreprecompile details of saving and re-using precompiled patterns
156 pcresample discussion of the pcredemo program
157 pcrestack discussion of stack usage
158 pcresyntax quick syntax reference
159 pcretest description of the pcretest testing command
160 pcreunicode discussion of Unicode and UTF-8/16/32 support
161
162 In addition, in the "man" and HTML formats, there is a short page for
163 each C library function, listing its arguments and results.
164
165
166 AUTHOR
167
168 Philip Hazel
169 University Computing Service
170 Cambridge CB2 3QH, England.
171
172 Putting an actual email address here seems to have been a spam magnet,
173 so I've taken it away. If you want to email me, use my two initials,
174 followed by the two digits 10, at the domain cam.ac.uk.
175
176
177 REVISION
178
179 Last updated: 26 April 2013
180 Copyright (c) 1997-2013 University of Cambridge.
181 ------------------------------------------------------------------------------
182
183
184 PCRE(3) Library Functions Manual PCRE(3)
185
186
187
188 NAME
189 PCRE - Perl-compatible regular expressions
190
191 #include <pcre.h>
192
193
194 PCRE 16-BIT API BASIC FUNCTIONS
195
196 pcre16 *pcre16_compile(PCRE_SPTR16 pattern, int options,
197 const char **errptr, int *erroffset,
198 const unsigned char *tableptr);
199
200 pcre16 *pcre16_compile2(PCRE_SPTR16 pattern, int options,
201 int *errorcodeptr,
202 const char **errptr, int *erroffset,
203 const unsigned char *tableptr);
204
205 pcre16_extra *pcre16_study(const pcre16 *code, int options,
206 const char **errptr);
207
208 void pcre16_free_study(pcre16_extra *extra);
209
210 int pcre16_exec(const pcre16 *code, const pcre16_extra *extra,
211 PCRE_SPTR16 subject, int length, int startoffset,
212 int options, int *ovector, int ovecsize);
213
214 int pcre16_dfa_exec(const pcre16 *code, const pcre16_extra *extra,
215 PCRE_SPTR16 subject, int length, int startoffset,
216 int options, int *ovector, int ovecsize,
217 int *workspace, int wscount);
218
219
220 PCRE 16-BIT API STRING EXTRACTION FUNCTIONS
221
222 int pcre16_copy_named_substring(const pcre16 *code,
223 PCRE_SPTR16 subject, int *ovector,
224 int stringcount, PCRE_SPTR16 stringname,
225 PCRE_UCHAR16 *buffer, int buffersize);
226
227 int pcre16_copy_substring(PCRE_SPTR16 subject, int *ovector,
228 int stringcount, int stringnumber, PCRE_UCHAR16 *buffer,
229 int buffersize);
230
231 int pcre16_get_named_substring(const pcre16 *code,
232 PCRE_SPTR16 subject, int *ovector,
233 int stringcount, PCRE_SPTR16 stringname,
234 PCRE_SPTR16 *stringptr);
235
236 int pcre16_get_stringnumber(const pcre16 *code,
237 PCRE_SPTR16 name);
238
239 int pcre16_get_stringtable_entries(const pcre16 *code,
240 PCRE_SPTR16 name, PCRE_UCHAR16 **first, PCRE_UCHAR16 **last);
241
242 int pcre16_get_substring(PCRE_SPTR16 subject, int *ovector,
243 int stringcount, int stringnumber,
244 PCRE_SPTR16 *stringptr);
245
246 int pcre16_get_substring_list(PCRE_SPTR16 subject,
247 int *ovector, int stringcount, PCRE_SPTR16 **listptr);
248
249 void pcre16_free_substring(PCRE_SPTR16 stringptr);
250
251 void pcre16_free_substring_list(PCRE_SPTR16 *stringptr);
252
253
254 PCRE 16-BIT API AUXILIARY FUNCTIONS
255
256 pcre16_jit_stack *pcre16_jit_stack_alloc(int startsize, int maxsize);
257
258 void pcre16_jit_stack_free(pcre16_jit_stack *stack);
259
260 void pcre16_assign_jit_stack(pcre16_extra *extra,
261 pcre16_jit_callback callback, void *data);
262
263 const unsigned char *pcre16_maketables(void);
264
265 int pcre16_fullinfo(const pcre16 *code, const pcre16_extra *extra,
266 int what, void *where);
267
268 int pcre16_refcount(pcre16 *code, int adjust);
269
270 int pcre16_config(int what, void *where);
271
272 const char *pcre16_version(void);
273
274 int pcre16_pattern_to_host_byte_order(pcre16 *code,
275 pcre16_extra *extra, const unsigned char *tables);
276
277
278 PCRE 16-BIT API INDIRECTED FUNCTIONS
279
280 void *(*pcre16_malloc)(size_t);
281
282 void (*pcre16_free)(void *);
283
284 void *(*pcre16_stack_malloc)(size_t);
285
286 void (*pcre16_stack_free)(void *);
287
288 int (*pcre16_callout)(pcre16_callout_block *);
289
290
291 PCRE 16-BIT API 16-BIT-ONLY FUNCTION
292
293 int pcre16_utf16_to_host_byte_order(PCRE_UCHAR16 *output,
294 PCRE_SPTR16 input, int length, int *byte_order,
295 int keep_boms);
296
297
298 THE PCRE 16-BIT LIBRARY
299
300 Starting with release 8.30, it is possible to compile a PCRE library
301 that supports 16-bit character strings, including UTF-16 strings, as
302 well as or instead of the original 8-bit library. The majority of the
303 work to make this possible was done by Zoltan Herczeg. The two
304 libraries contain identical sets of functions, used in exactly the same
305 way. Only the names of the functions and the data types of their argu-
306 ments and results are different. To avoid over-complication and reduce
307 the documentation maintenance load, most of the PCRE documentation
308 describes the 8-bit library, with only occasional references to the
309 16-bit library. This page describes what is different when you use the
310 16-bit library.
311
312 WARNING: A single application can be linked with both libraries, but
313 you must take care when processing any particular pattern to use func-
314 tions from just one library. For example, if you want to study a pat-
315 tern that was compiled with pcre16_compile(), you must do so with
316 pcre16_study(), not pcre_study(), and you must free the study data with
317 pcre16_free_study().
318
319
320 THE HEADER FILE
321
322 There is only one header file, pcre.h. It contains prototypes for all
323 the functions in all libraries, as well as definitions of flags, struc-
324 tures, error codes, etc.
325
326
327 THE LIBRARY NAME
328
329 In Unix-like systems, the 16-bit library is called libpcre16, and can
330 normally be accesss by adding -lpcre16 to the command for linking an
331 application that uses PCRE.
332
333
334 STRING TYPES
335
336 In the 8-bit library, strings are passed to PCRE library functions as
337 vectors of bytes with the C type "char *". In the 16-bit library,
338 strings are passed as vectors of unsigned 16-bit quantities. The macro
339 PCRE_UCHAR16 specifies an appropriate data type, and PCRE_SPTR16 is
340 defined as "const PCRE_UCHAR16 *". In very many environments, "short
341 int" is a 16-bit data type. When PCRE is built, it defines PCRE_UCHAR16
342 as "unsigned short int", but checks that it really is a 16-bit data
343 type. If it is not, the build fails with an error message telling the
344 maintainer to modify the definition appropriately.
345
346
347 STRUCTURE TYPES
348
349 The types of the opaque structures that are used for compiled 16-bit
350 patterns and JIT stacks are pcre16 and pcre16_jit_stack respectively.
351 The type of the user-accessible structure that is returned by
352 pcre16_study() is pcre16_extra, and the type of the structure that is
353 used for passing data to a callout function is pcre16_callout_block.
354 These structures contain the same fields, with the same names, as their
355 8-bit counterparts. The only difference is that pointers to character
356 strings are 16-bit instead of 8-bit types.
357
358
359 16-BIT FUNCTIONS
360
361 For every function in the 8-bit library there is a corresponding func-
362 tion in the 16-bit library with a name that starts with pcre16_ instead
363 of pcre_. The prototypes are listed above. In addition, there is one
364 extra function, pcre16_utf16_to_host_byte_order(). This is a utility
365 function that converts a UTF-16 character string to host byte order if
366 necessary. The other 16-bit functions expect the strings they are
367 passed to be in host byte order.
368
369 The input and output arguments of pcre16_utf16_to_host_byte_order() may
370 point to the same address, that is, conversion in place is supported.
371 The output buffer must be at least as long as the input.
372
373 The length argument specifies the number of 16-bit data units in the
374 input string; a negative value specifies a zero-terminated string.
375
376 If byte_order is NULL, it is assumed that the string starts off in host
377 byte order. This may be changed by byte-order marks (BOMs) anywhere in
378 the string (commonly as the first character).
379
380 If byte_order is not NULL, a non-zero value of the integer to which it
381 points means that the input starts off in host byte order, otherwise
382 the opposite order is assumed. Again, BOMs in the string can change
383 this. The final byte order is passed back at the end of processing.
384
385 If keep_boms is not zero, byte-order mark characters (0xfeff) are
386 copied into the output string. Otherwise they are discarded.
387
388 The result of the function is the number of 16-bit units placed into
389 the output buffer, including the zero terminator if the string was
390 zero-terminated.
391
392
393 SUBJECT STRING OFFSETS
394
395 The lengths and starting offsets of subject strings must be specified
396 in 16-bit data units, and the offsets within subject strings that are
397 returned by the matching functions are in also 16-bit units rather than
398 bytes.
399
400
401 NAMED SUBPATTERNS
402
403 The name-to-number translation table that is maintained for named sub-
404 patterns uses 16-bit characters. The pcre16_get_stringtable_entries()
405 function returns the length of each entry in the table as the number of
406 16-bit data units.
407
408
409 OPTION NAMES
410
411 There are two new general option names, PCRE_UTF16 and
412 PCRE_NO_UTF16_CHECK, which correspond to PCRE_UTF8 and
413 PCRE_NO_UTF8_CHECK in the 8-bit library. In fact, these new options
414 define the same bits in the options word. There is a discussion about
415 the validity of UTF-16 strings in the pcreunicode page.
416
417 For the pcre16_config() function there is an option PCRE_CONFIG_UTF16
418 that returns 1 if UTF-16 support is configured, otherwise 0. If this
419 option is given to pcre_config() or pcre32_config(), or if the
420 PCRE_CONFIG_UTF8 or PCRE_CONFIG_UTF32 option is given to pcre16_con-
421 fig(), the result is the PCRE_ERROR_BADOPTION error.
422
423
424 CHARACTER CODES
425
426 In 16-bit mode, when PCRE_UTF16 is not set, character values are
427 treated in the same way as in 8-bit, non UTF-8 mode, except, of course,
428 that they can range from 0 to 0xffff instead of 0 to 0xff. Character
429 types for characters less than 0xff can therefore be influenced by the
430 locale in the same way as before. Characters greater than 0xff have
431 only one case, and no "type" (such as letter or digit).
432
433 In UTF-16 mode, the character code is Unicode, in the range 0 to
434 0x10ffff, with the exception of values in the range 0xd800 to 0xdfff
435 because those are "surrogate" values that are used in pairs to encode
436 values greater than 0xffff.
437
438 A UTF-16 string can indicate its endianness by special code knows as a
439 byte-order mark (BOM). The PCRE functions do not handle this, expecting
440 strings to be in host byte order. A utility function called
441 pcre16_utf16_to_host_byte_order() is provided to help with this (see
442 above).
443
444
445 ERROR NAMES
446
447 The errors PCRE_ERROR_BADUTF16_OFFSET and PCRE_ERROR_SHORTUTF16 corre-
448 spond to their 8-bit counterparts. The error PCRE_ERROR_BADMODE is
449 given when a compiled pattern is passed to a function that processes
450 patterns in the other mode, for example, if a pattern compiled with
451 pcre_compile() is passed to pcre16_exec().
452
453 There are new error codes whose names begin with PCRE_UTF16_ERR for
454 invalid UTF-16 strings, corresponding to the PCRE_UTF8_ERR codes for
455 UTF-8 strings that are described in the section entitled "Reason codes
456 for invalid UTF-8 strings" in the main pcreapi page. The UTF-16 errors
457 are:
458
459 PCRE_UTF16_ERR1 Missing low surrogate at end of string
460 PCRE_UTF16_ERR2 Invalid low surrogate follows high surrogate
461 PCRE_UTF16_ERR3 Isolated low surrogate
462 PCRE_UTF16_ERR4 Non-character
463
464
465 ERROR TEXTS
466
467 If there is an error while compiling a pattern, the error text that is
468 passed back by pcre16_compile() or pcre16_compile2() is still an 8-bit
469 character string, zero-terminated.
470
471
472 CALLOUTS
473
474 The subject and mark fields in the callout block that is passed to a
475 callout function point to 16-bit vectors.
476
477
478 TESTING
479
480 The pcretest program continues to operate with 8-bit input and output
481 files, but it can be used for testing the 16-bit library. If it is run
482 with the command line option -16, patterns and subject strings are con-
483 verted from 8-bit to 16-bit before being passed to PCRE, and the 16-bit
484 library functions are used instead of the 8-bit ones. Returned 16-bit
485 strings are converted to 8-bit for output. If both the 8-bit and the
486 32-bit libraries were not compiled, pcretest defaults to 16-bit and the
487 -16 option is ignored.
488
489 When PCRE is being built, the RunTest script that is called by "make
490 check" uses the pcretest -C option to discover which of the 8-bit,
491 16-bit and 32-bit libraries has been built, and runs the tests appro-
492 priately.
493
494
495 NOT SUPPORTED IN 16-BIT MODE
496
497 Not all the features of the 8-bit library are available with the 16-bit
498 library. The C++ and POSIX wrapper functions support only the 8-bit
499 library, and the pcregrep program is at present 8-bit only.
500
501
502 AUTHOR
503
504 Philip Hazel
505 University Computing Service
506 Cambridge CB2 3QH, England.
507
508
509 REVISION
510
511 Last updated: 12 May 2013
512 Copyright (c) 1997-2013 University of Cambridge.
513 ------------------------------------------------------------------------------
514
515
516 PCRE(3) Library Functions Manual PCRE(3)
517
518
519
520 NAME
521 PCRE - Perl-compatible regular expressions
522
523 #include <pcre.h>
524
525
526 PCRE 32-BIT API BASIC FUNCTIONS
527
528 pcre32 *pcre32_compile(PCRE_SPTR32 pattern, int options,
529 const char **errptr, int *erroffset,
530 const unsigned char *tableptr);
531
532 pcre32 *pcre32_compile2(PCRE_SPTR32 pattern, int options,
533 int *errorcodeptr,
534 const char **errptr, int *erroffset,
535 const unsigned char *tableptr);
536
537 pcre32_extra *pcre32_study(const pcre32 *code, int options,
538 const char **errptr);
539
540 void pcre32_free_study(pcre32_extra *extra);
541
542 int pcre32_exec(const pcre32 *code, const pcre32_extra *extra,
543 PCRE_SPTR32 subject, int length, int startoffset,
544 int options, int *ovector, int ovecsize);
545
546 int pcre32_dfa_exec(const pcre32 *code, const pcre32_extra *extra,
547 PCRE_SPTR32 subject, int length, int startoffset,
548 int options, int *ovector, int ovecsize,
549 int *workspace, int wscount);
550
551
552 PCRE 32-BIT API STRING EXTRACTION FUNCTIONS
553
554 int pcre32_copy_named_substring(const pcre32 *code,
555 PCRE_SPTR32 subject, int *ovector,
556 int stringcount, PCRE_SPTR32 stringname,
557 PCRE_UCHAR32 *buffer, int buffersize);
558
559 int pcre32_copy_substring(PCRE_SPTR32 subject, int *ovector,
560 int stringcount, int stringnumber, PCRE_UCHAR32 *buffer,
561 int buffersize);
562
563 int pcre32_get_named_substring(const pcre32 *code,
564 PCRE_SPTR32 subject, int *ovector,
565 int stringcount, PCRE_SPTR32 stringname,
566 PCRE_SPTR32 *stringptr);
567
568 int pcre32_get_stringnumber(const pcre32 *code,
569 PCRE_SPTR32 name);
570
571 int pcre32_get_stringtable_entries(const pcre32 *code,
572 PCRE_SPTR32 name, PCRE_UCHAR32 **first, PCRE_UCHAR32 **last);
573
574 int pcre32_get_substring(PCRE_SPTR32 subject, int *ovector,
575 int stringcount, int stringnumber,
576 PCRE_SPTR32 *stringptr);
577
578 int pcre32_get_substring_list(PCRE_SPTR32 subject,
579 int *ovector, int stringcount, PCRE_SPTR32 **listptr);
580
581 void pcre32_free_substring(PCRE_SPTR32 stringptr);
582
583 void pcre32_free_substring_list(PCRE_SPTR32 *stringptr);
584
585
586 PCRE 32-BIT API AUXILIARY FUNCTIONS
587
588 pcre32_jit_stack *pcre32_jit_stack_alloc(int startsize, int maxsize);
589
590 void pcre32_jit_stack_free(pcre32_jit_stack *stack);
591
592 void pcre32_assign_jit_stack(pcre32_extra *extra,
593 pcre32_jit_callback callback, void *data);
594
595 const unsigned char *pcre32_maketables(void);
596
597 int pcre32_fullinfo(const pcre32 *code, const pcre32_extra *extra,
598 int what, void *where);
599
600 int pcre32_refcount(pcre32 *code, int adjust);
601
602 int pcre32_config(int what, void *where);
603
604 const char *pcre32_version(void);
605
606 int pcre32_pattern_to_host_byte_order(pcre32 *code,
607 pcre32_extra *extra, const unsigned char *tables);
608
609
610 PCRE 32-BIT API INDIRECTED FUNCTIONS
611
612 void *(*pcre32_malloc)(size_t);
613
614 void (*pcre32_free)(void *);
615
616 void *(*pcre32_stack_malloc)(size_t);
617
618 void (*pcre32_stack_free)(void *);
619
620 int (*pcre32_callout)(pcre32_callout_block *);
621
622
623 PCRE 32-BIT API 32-BIT-ONLY FUNCTION
624
625 int pcre32_utf32_to_host_byte_order(PCRE_UCHAR32 *output,
626 PCRE_SPTR32 input, int length, int *byte_order,
627 int keep_boms);
628
629
630 THE PCRE 32-BIT LIBRARY
631
632 Starting with release 8.32, it is possible to compile a PCRE library
633 that supports 32-bit character strings, including UTF-32 strings, as
634 well as or instead of the original 8-bit library. This work was done by
635 Christian Persch, based on the work done by Zoltan Herczeg for the
636 16-bit library. All three libraries contain identical sets of func-
637 tions, used in exactly the same way. Only the names of the functions
638 and the data types of their arguments and results are different. To
639 avoid over-complication and reduce the documentation maintenance load,
640 most of the PCRE documentation describes the 8-bit library, with only
641 occasional references to the 16-bit and 32-bit libraries. This page
642 describes what is different when you use the 32-bit library.
643
644 WARNING: A single application can be linked with all or any of the
645 three libraries, but you must take care when processing any particular
646 pattern to use functions from just one library. For example, if you
647 want to study a pattern that was compiled with pcre32_compile(), you
648 must do so with pcre32_study(), not pcre_study(), and you must free the
649 study data with pcre32_free_study().
650
651
652 THE HEADER FILE
653
654 There is only one header file, pcre.h. It contains prototypes for all
655 the functions in all libraries, as well as definitions of flags, struc-
656 tures, error codes, etc.
657
658
659 THE LIBRARY NAME
660
661 In Unix-like systems, the 32-bit library is called libpcre32, and can
662 normally be accesss by adding -lpcre32 to the command for linking an
663 application that uses PCRE.
664
665
666 STRING TYPES
667
668 In the 8-bit library, strings are passed to PCRE library functions as
669 vectors of bytes with the C type "char *". In the 32-bit library,
670 strings are passed as vectors of unsigned 32-bit quantities. The macro
671 PCRE_UCHAR32 specifies an appropriate data type, and PCRE_SPTR32 is
672 defined as "const PCRE_UCHAR32 *". In very many environments, "unsigned
673 int" is a 32-bit data type. When PCRE is built, it defines PCRE_UCHAR32
674 as "unsigned int", but checks that it really is a 32-bit data type. If
675 it is not, the build fails with an error message telling the maintainer
676 to modify the definition appropriately.
677
678
679 STRUCTURE TYPES
680
681 The types of the opaque structures that are used for compiled 32-bit
682 patterns and JIT stacks are pcre32 and pcre32_jit_stack respectively.
683 The type of the user-accessible structure that is returned by
684 pcre32_study() is pcre32_extra, and the type of the structure that is
685 used for passing data to a callout function is pcre32_callout_block.
686 These structures contain the same fields, with the same names, as their
687 8-bit counterparts. The only difference is that pointers to character
688 strings are 32-bit instead of 8-bit types.
689
690
691 32-BIT FUNCTIONS
692
693 For every function in the 8-bit library there is a corresponding func-
694 tion in the 32-bit library with a name that starts with pcre32_ instead
695 of pcre_. The prototypes are listed above. In addition, there is one
696 extra function, pcre32_utf32_to_host_byte_order(). This is a utility
697 function that converts a UTF-32 character string to host byte order if
698 necessary. The other 32-bit functions expect the strings they are
699 passed to be in host byte order.
700
701 The input and output arguments of pcre32_utf32_to_host_byte_order() may
702 point to the same address, that is, conversion in place is supported.
703 The output buffer must be at least as long as the input.
704
705 The length argument specifies the number of 32-bit data units in the
706 input string; a negative value specifies a zero-terminated string.
707
708 If byte_order is NULL, it is assumed that the string starts off in host
709 byte order. This may be changed by byte-order marks (BOMs) anywhere in
710 the string (commonly as the first character).
711
712 If byte_order is not NULL, a non-zero value of the integer to which it
713 points means that the input starts off in host byte order, otherwise
714 the opposite order is assumed. Again, BOMs in the string can change
715 this. The final byte order is passed back at the end of processing.
716
717 If keep_boms is not zero, byte-order mark characters (0xfeff) are
718 copied into the output string. Otherwise they are discarded.
719
720 The result of the function is the number of 32-bit units placed into
721 the output buffer, including the zero terminator if the string was
722 zero-terminated.
723
724
725 SUBJECT STRING OFFSETS
726
727 The lengths and starting offsets of subject strings must be specified
728 in 32-bit data units, and the offsets within subject strings that are
729 returned by the matching functions are in also 32-bit units rather than
730 bytes.
731
732
733 NAMED SUBPATTERNS
734
735 The name-to-number translation table that is maintained for named sub-
736 patterns uses 32-bit characters. The pcre32_get_stringtable_entries()
737 function returns the length of each entry in the table as the number of
738 32-bit data units.
739
740
741 OPTION NAMES
742
743 There are two new general option names, PCRE_UTF32 and
744 PCRE_NO_UTF32_CHECK, which correspond to PCRE_UTF8 and
745 PCRE_NO_UTF8_CHECK in the 8-bit library. In fact, these new options
746 define the same bits in the options word. There is a discussion about
747 the validity of UTF-32 strings in the pcreunicode page.
748
749 For the pcre32_config() function there is an option PCRE_CONFIG_UTF32
750 that returns 1 if UTF-32 support is configured, otherwise 0. If this
751 option is given to pcre_config() or pcre16_config(), or if the
752 PCRE_CONFIG_UTF8 or PCRE_CONFIG_UTF16 option is given to pcre32_con-
753 fig(), the result is the PCRE_ERROR_BADOPTION error.
754
755
756 CHARACTER CODES
757
758 In 32-bit mode, when PCRE_UTF32 is not set, character values are
759 treated in the same way as in 8-bit, non UTF-8 mode, except, of course,
760 that they can range from 0 to 0x7fffffff instead of 0 to 0xff. Charac-
761 ter types for characters less than 0xff can therefore be influenced by
762 the locale in the same way as before. Characters greater than 0xff
763 have only one case, and no "type" (such as letter or digit).
764
765 In UTF-32 mode, the character code is Unicode, in the range 0 to
766 0x10ffff, with the exception of values in the range 0xd800 to 0xdfff
767 because those are "surrogate" values that are ill-formed in UTF-32.
768
769 A UTF-32 string can indicate its endianness by special code knows as a
770 byte-order mark (BOM). The PCRE functions do not handle this, expecting
771 strings to be in host byte order. A utility function called
772 pcre32_utf32_to_host_byte_order() is provided to help with this (see
773 above).
774
775
776 ERROR NAMES
777
778 The error PCRE_ERROR_BADUTF32 corresponds to its 8-bit counterpart.
779 The error PCRE_ERROR_BADMODE is given when a compiled pattern is passed
780 to a function that processes patterns in the other mode, for example,
781 if a pattern compiled with pcre_compile() is passed to pcre32_exec().
782
783 There are new error codes whose names begin with PCRE_UTF32_ERR for
784 invalid UTF-32 strings, corresponding to the PCRE_UTF8_ERR codes for
785 UTF-8 strings that are described in the section entitled "Reason codes
786 for invalid UTF-8 strings" in the main pcreapi page. The UTF-32 errors
787 are:
788
789 PCRE_UTF32_ERR1 Surrogate character (range from 0xd800 to 0xdfff)
790 PCRE_UTF32_ERR2 Non-character
791 PCRE_UTF32_ERR3 Character > 0x10ffff
792
793
794 ERROR TEXTS
795
796 If there is an error while compiling a pattern, the error text that is
797 passed back by pcre32_compile() or pcre32_compile2() is still an 8-bit
798 character string, zero-terminated.
799
800
801 CALLOUTS
802
803 The subject and mark fields in the callout block that is passed to a
804 callout function point to 32-bit vectors.
805
806
807 TESTING
808
809 The pcretest program continues to operate with 8-bit input and output
810 files, but it can be used for testing the 32-bit library. If it is run
811 with the command line option -32, patterns and subject strings are con-
812 verted from 8-bit to 32-bit before being passed to PCRE, and the 32-bit
813 library functions are used instead of the 8-bit ones. Returned 32-bit
814 strings are converted to 8-bit for output. If both the 8-bit and the
815 16-bit libraries were not compiled, pcretest defaults to 32-bit and the
816 -32 option is ignored.
817
818 When PCRE is being built, the RunTest script that is called by "make
819 check" uses the pcretest -C option to discover which of the 8-bit,
820 16-bit and 32-bit libraries has been built, and runs the tests appro-
821 priately.
822
823
824 NOT SUPPORTED IN 32-BIT MODE
825
826 Not all the features of the 8-bit library are available with the 32-bit
827 library. The C++ and POSIX wrapper functions support only the 8-bit
828 library, and the pcregrep program is at present 8-bit only.
829
830
831 AUTHOR
832
833 Philip Hazel
834 University Computing Service
835 Cambridge CB2 3QH, England.
836
837
838 REVISION
839
840 Last updated: 12 May 2013
841 Copyright (c) 1997-2013 University of Cambridge.
842 ------------------------------------------------------------------------------
843
844
845 PCREBUILD(3) Library Functions Manual PCREBUILD(3)
846
847
848
849 NAME
850 PCRE - Perl-compatible regular expressions
851
852 PCRE BUILD-TIME OPTIONS
853
854 This document describes the optional features of PCRE that can be
855 selected when the library is compiled. It assumes use of the configure
856 script, where the optional features are selected or deselected by pro-
857 viding options to configure before running the make command. However,
858 the same options can be selected in both Unix-like and non-Unix-like
859 environments using the GUI facility of cmake-gui if you are using CMake
860 instead of configure to build PCRE.
861
862 There is a lot more information about building PCRE without using con-
863 figure (including information about using CMake or building "by hand")
864 in the file called NON-AUTOTOOLS-BUILD, which is part of the PCRE dis-
865 tribution. You should consult this file as well as the README file if
866 you are building in a non-Unix-like environment.
867
868 The complete list of options for configure (which includes the standard
869 ones such as the selection of the installation directory) can be
870 obtained by running
871
872 ./configure --help
873
874 The following sections include descriptions of options whose names
875 begin with --enable or --disable. These settings specify changes to the
876 defaults for the configure command. Because of the way that configure
877 works, --enable and --disable always come in pairs, so the complemen-
878 tary option always exists as well, but as it specifies the default, it
879 is not described.
880
881
882 BUILDING 8-BIT, 16-BIT AND 32-BIT LIBRARIES
883
884 By default, a library called libpcre is built, containing functions
885 that take string arguments contained in vectors of bytes, either as
886 single-byte characters, or interpreted as UTF-8 strings. You can also
887 build a separate library, called libpcre16, in which strings are con-
888 tained in vectors of 16-bit data units and interpreted either as sin-
889 gle-unit characters or UTF-16 strings, by adding
890
891 --enable-pcre16
892
893 to the configure command. You can also build a separate library, called
894 libpcre32, in which strings are contained in vectors of 32-bit data
895 units and interpreted either as single-unit characters or UTF-32
896 strings, by adding
897
898 --enable-pcre32
899
900 to the configure command. If you do not want the 8-bit library, add
901
902 --disable-pcre8
903
904 as well. At least one of the three libraries must be built. Note that
905 the C++ and POSIX wrappers are for the 8-bit library only, and that
906 pcregrep is an 8-bit program. None of these are built if you select
907 only the 16-bit or 32-bit libraries.
908
909
910 BUILDING SHARED AND STATIC LIBRARIES
911
912 The PCRE building process uses libtool to build both shared and static
913 Unix libraries by default. You can suppress one of these by adding one
914 of
915
916 --disable-shared
917 --disable-static
918
919 to the configure command, as required.
920
921
922 C++ SUPPORT
923
924 By default, if the 8-bit library is being built, the configure script
925 will search for a C++ compiler and C++ header files. If it finds them,
926 it automatically builds the C++ wrapper library (which supports only
927 8-bit strings). You can disable this by adding
928
929 --disable-cpp
930
931 to the configure command.
932
933
934 UTF-8, UTF-16 AND UTF-32 SUPPORT
935
936 To build PCRE with support for UTF Unicode character strings, add
937
938 --enable-utf
939
940 to the configure command. This setting applies to all three libraries,
941 adding support for UTF-8 to the 8-bit library, support for UTF-16 to
942 the 16-bit library, and support for UTF-32 to the to the 32-bit
943 library. There are no separate options for enabling UTF-8, UTF-16 and
944 UTF-32 independently because that would allow ridiculous settings such
945 as requesting UTF-16 support while building only the 8-bit library. It
946 is not possible to build one library with UTF support and another with-
947 out in the same configuration. (For backwards compatibility, --enable-
948 utf8 is a synonym of --enable-utf.)
949
950 Of itself, this setting does not make PCRE treat strings as UTF-8,
951 UTF-16 or UTF-32. As well as compiling PCRE with this option, you also
952 have have to set the PCRE_UTF8, PCRE_UTF16 or PCRE_UTF32 option (as
953 appropriate) when you call one of the pattern compiling functions.
954
955 If you set --enable-utf when compiling in an EBCDIC environment, PCRE
956 expects its input to be either ASCII or UTF-8 (depending on the run-
957 time option). It is not possible to support both EBCDIC and UTF-8 codes
958 in the same version of the library. Consequently, --enable-utf and
959 --enable-ebcdic are mutually exclusive.
960
961
962 UNICODE CHARACTER PROPERTY SUPPORT
963
964 UTF support allows the libraries to process character codepoints up to
965 0x10ffff in the strings that they handle. On its own, however, it does
966 not provide any facilities for accessing the properties of such charac-
967 ters. If you want to be able to use the pattern escapes \P, \p, and \X,
968 which refer to Unicode character properties, you must add
969
970 --enable-unicode-properties
971
972 to the configure command. This implies UTF support, even if you have
973 not explicitly requested it.
974
975 Including Unicode property support adds around 30K of tables to the
976 PCRE library. Only the general category properties such as Lu and Nd
977 are supported. Details are given in the pcrepattern documentation.
978
979
980 JUST-IN-TIME COMPILER SUPPORT
981
982 Just-in-time compiler support is included in the build by specifying
983
984 --enable-jit
985
986 This support is available only for certain hardware architectures. If
987 this option is set for an unsupported architecture, a compile time
988 error occurs. See the pcrejit documentation for a discussion of JIT
989 usage. When JIT support is enabled, pcregrep automatically makes use of
990 it, unless you add
991
992 --disable-pcregrep-jit
993
994 to the "configure" command.
995
996
997 CODE VALUE OF NEWLINE
998
999 By default, PCRE interprets the linefeed (LF) character as indicating
1000 the end of a line. This is the normal newline character on Unix-like
1001 systems. You can compile PCRE to use carriage return (CR) instead, by
1002 adding
1003
1004 --enable-newline-is-cr
1005
1006 to the configure command. There is also a --enable-newline-is-lf
1007 option, which explicitly specifies linefeed as the newline character.
1008
1009 Alternatively, you can specify that line endings are to be indicated by
1010 the two character sequence CRLF. If you want this, add
1011
1012 --enable-newline-is-crlf
1013
1014 to the configure command. There is a fourth option, specified by
1015
1016 --enable-newline-is-anycrlf
1017
1018 which causes PCRE to recognize any of the three sequences CR, LF, or
1019 CRLF as indicating a line ending. Finally, a fifth option, specified by
1020
1021 --enable-newline-is-any
1022
1023 causes PCRE to recognize any Unicode newline sequence.
1024
1025 Whatever line ending convention is selected when PCRE is built can be
1026 overridden when the library functions are called. At build time it is
1027 conventional to use the standard for your operating system.
1028
1029
1030 WHAT \R MATCHES
1031
1032 By default, the sequence \R in a pattern matches any Unicode newline
1033 sequence, whatever has been selected as the line ending sequence. If
1034 you specify
1035
1036 --enable-bsr-anycrlf
1037
1038 the default is changed so that \R matches only CR, LF, or CRLF. What-
1039 ever is selected when PCRE is built can be overridden when the library
1040 functions are called.
1041
1042
1043 POSIX MALLOC USAGE
1044
1045 When the 8-bit library is called through the POSIX interface (see the
1046 pcreposix documentation), additional working storage is required for
1047 holding the pointers to capturing substrings, because PCRE requires
1048 three integers per substring, whereas the POSIX interface provides only
1049 two. If the number of expected substrings is small, the wrapper func-
1050 tion uses space on the stack, because this is faster than using mal-
1051 loc() for each call. The default threshold above which the stack is no
1052 longer used is 10; it can be changed by adding a setting such as
1053
1054 --with-posix-malloc-threshold=20
1055
1056 to the configure command.
1057
1058
1059 HANDLING VERY LARGE PATTERNS
1060
1061 Within a compiled pattern, offset values are used to point from one
1062 part to another (for example, from an opening parenthesis to an alter-
1063 nation metacharacter). By default, in the 8-bit and 16-bit libraries,
1064 two-byte values are used for these offsets, leading to a maximum size
1065 for a compiled pattern of around 64K. This is sufficient to handle all
1066 but the most gigantic patterns. Nevertheless, some people do want to
1067 process truly enormous patterns, so it is possible to compile PCRE to
1068 use three-byte or four-byte offsets by adding a setting such as
1069
1070 --with-link-size=3
1071
1072 to the configure command. The value given must be 2, 3, or 4. For the
1073 16-bit library, a value of 3 is rounded up to 4. In these libraries,
1074 using longer offsets slows down the operation of PCRE because it has to
1075 load additional data when handling them. For the 32-bit library the
1076 value is always 4 and cannot be overridden; the value of --with-link-
1077 size is ignored.
1078
1079
1080 AVOIDING EXCESSIVE STACK USAGE
1081
1082 When matching with the pcre_exec() function, PCRE implements backtrack-
1083 ing by making recursive calls to an internal function called match().
1084 In environments where the size of the stack is limited, this can se-
1085 verely limit PCRE's operation. (The Unix environment does not usually
1086 suffer from this problem, but it may sometimes be necessary to increase
1087 the maximum stack size. There is a discussion in the pcrestack docu-
1088 mentation.) An alternative approach to recursion that uses memory from
1089 the heap to remember data, instead of using recursive function calls,
1090 has been implemented to work round the problem of limited stack size.
1091 If you want to build a version of PCRE that works this way, add
1092
1093 --disable-stack-for-recursion
1094
1095 to the configure command. With this configuration, PCRE will use the
1096 pcre_stack_malloc and pcre_stack_free variables to call memory manage-
1097 ment functions. By default these point to malloc() and free(), but you
1098 can replace the pointers so that your own functions are used instead.
1099
1100 Separate functions are provided rather than using pcre_malloc and
1101 pcre_free because the usage is very predictable: the block sizes
1102 requested are always the same, and the blocks are always freed in
1103 reverse order. A calling program might be able to implement optimized
1104 functions that perform better than malloc() and free(). PCRE runs
1105 noticeably more slowly when built in this way. This option affects only
1106 the pcre_exec() function; it is not relevant for pcre_dfa_exec().
1107
1108
1109 LIMITING PCRE RESOURCE USAGE
1110
1111 Internally, PCRE has a function called match(), which it calls repeat-
1112 edly (sometimes recursively) when matching a pattern with the
1113 pcre_exec() function. By controlling the maximum number of times this
1114 function may be called during a single matching operation, a limit can
1115 be placed on the resources used by a single call to pcre_exec(). The
1116 limit can be changed at run time, as described in the pcreapi documen-
1117 tation. The default is 10 million, but this can be changed by adding a
1118 setting such as
1119
1120 --with-match-limit=500000
1121
1122 to the configure command. This setting has no effect on the
1123 pcre_dfa_exec() matching function.
1124
1125 In some environments it is desirable to limit the depth of recursive
1126 calls of match() more strictly than the total number of calls, in order
1127 to restrict the maximum amount of stack (or heap, if --disable-stack-
1128 for-recursion is specified) that is used. A second limit controls this;
1129 it defaults to the value that is set for --with-match-limit, which
1130 imposes no additional constraints. However, you can set a lower limit
1131 by adding, for example,
1132
1133 --with-match-limit-recursion=10000
1134
1135 to the configure command. This value can also be overridden at run
1136 time.
1137
1138
1139 CREATING CHARACTER TABLES AT BUILD TIME
1140
1141 PCRE uses fixed tables for processing characters whose code values are
1142 less than 256. By default, PCRE is built with a set of tables that are
1143 distributed in the file pcre_chartables.c.dist. These tables are for
1144 ASCII codes only. If you add
1145
1146 --enable-rebuild-chartables
1147
1148 to the configure command, the distributed tables are no longer used.
1149 Instead, a program called dftables is compiled and run. This outputs
1150 the source for new set of tables, created in the default locale of your
1151 C run-time system. (This method of replacing the tables does not work
1152 if you are cross compiling, because dftables is run on the local host.
1153 If you need to create alternative tables when cross compiling, you will
1154 have to do so "by hand".)
1155
1156
1157 USING EBCDIC CODE
1158
1159 PCRE assumes by default that it will run in an environment where the
1160 character code is ASCII (or Unicode, which is a superset of ASCII).
1161 This is the case for most computer operating systems. PCRE can, how-
1162 ever, be compiled to run in an EBCDIC environment by adding
1163
1164 --enable-ebcdic
1165
1166 to the configure command. This setting implies --enable-rebuild-charta-
1167 bles. You should only use it if you know that you are in an EBCDIC
1168 environment (for example, an IBM mainframe operating system). The
1169 --enable-ebcdic option is incompatible with --enable-utf.
1170
1171 The EBCDIC character that corresponds to an ASCII LF is assumed to have
1172 the value 0x15 by default. However, in some EBCDIC environments, 0x25
1173 is used. In such an environment you should use
1174
1175 --enable-ebcdic-nl25
1176
1177 as well as, or instead of, --enable-ebcdic. The EBCDIC character for CR
1178 has the same value as in ASCII, namely, 0x0d. Whichever of 0x15 and
1179 0x25 is not chosen as LF is made to correspond to the Unicode NEL char-
1180 acter (which, in Unicode, is 0x85).
1181
1182 The options that select newline behaviour, such as --enable-newline-is-
1183 cr, and equivalent run-time options, refer to these character values in
1184 an EBCDIC environment.
1185
1186
1187 PCREGREP OPTIONS FOR COMPRESSED FILE SUPPORT
1188
1189 By default, pcregrep reads all files as plain text. You can build it so
1190 that it recognizes files whose names end in .gz or .bz2, and reads them
1191 with libz or libbz2, respectively, by adding one or both of
1192
1193 --enable-pcregrep-libz
1194 --enable-pcregrep-libbz2
1195
1196 to the configure command. These options naturally require that the rel-
1197 evant libraries are installed on your system. Configuration will fail
1198 if they are not.
1199
1200
1201 PCREGREP BUFFER SIZE
1202
1203 pcregrep uses an internal buffer to hold a "window" on the file it is
1204 scanning, in order to be able to output "before" and "after" lines when
1205 it finds a match. The size of the buffer is controlled by a parameter
1206 whose default value is 20K. The buffer itself is three times this size,
1207 but because of the way it is used for holding "before" lines, the long-
1208 est line that is guaranteed to be processable is the parameter size.
1209 You can change the default parameter value by adding, for example,
1210
1211 --with-pcregrep-bufsize=50K
1212
1213 to the configure command. The caller of pcregrep can, however, override
1214 this value by specifying a run-time option.
1215
1216
1217 PCRETEST OPTION FOR LIBREADLINE SUPPORT
1218
1219 If you add
1220
1221 --enable-pcretest-libreadline
1222
1223 to the configure command, pcretest is linked with the libreadline
1224 library, and when its input is from a terminal, it reads it using the
1225 readline() function. This provides line-editing and history facilities.
1226 Note that libreadline is GPL-licensed, so if you distribute a binary of
1227 pcretest linked in this way, there may be licensing issues.
1228
1229 Setting this option causes the -lreadline option to be added to the
1230 pcretest build. In many operating environments with a sytem-installed
1231 libreadline this is sufficient. However, in some environments (e.g. if
1232 an unmodified distribution version of readline is in use), some extra
1233 configuration may be necessary. The INSTALL file for libreadline says
1234 this:
1235
1236 "Readline uses the termcap functions, but does not link with the
1237 termcap or curses library itself, allowing applications which link
1238 with readline the to choose an appropriate library."
1239
1240 If your environment has not been set up so that an appropriate library
1241 is automatically included, you may need to add something like
1242
1243 LIBS="-ncurses"
1244
1245 immediately before the configure command.
1246
1247
1248 DEBUGGING WITH VALGRIND SUPPORT
1249
1250 By adding the
1251
1252 --enable-valgrind
1253
1254 option to to the configure command, PCRE will use valgrind annotations
1255 to mark certain memory regions as unaddressable. This allows it to
1256 detect invalid memory accesses, and is mostly useful for debugging PCRE
1257 itself.
1258
1259
1260 CODE COVERAGE REPORTING
1261
1262 If your C compiler is gcc, you can build a version of PCRE that can
1263 generate a code coverage report for its test suite. To enable this, you
1264 must install lcov version 1.6 or above. Then specify
1265
1266 --enable-coverage
1267
1268 to the configure command and build PCRE in the usual way.
1269
1270 Note that using ccache (a caching C compiler) is incompatible with code
1271 coverage reporting. If you have configured ccache to run automatically
1272 on your system, you must set the environment variable
1273
1274 CCACHE_DISABLE=1
1275
1276 before running make to build PCRE, so that ccache is not used.
1277
1278 When --enable-coverage is used, the following addition targets are
1279 added to the Makefile:
1280
1281 make coverage
1282
1283 This creates a fresh coverage report for the PCRE test suite. It is
1284 equivalent to running "make coverage-reset", "make coverage-baseline",
1285 "make check", and then "make coverage-report".
1286
1287 make coverage-reset
1288
1289 This zeroes the coverage counters, but does nothing else.
1290
1291 make coverage-baseline
1292
1293 This captures baseline coverage information.
1294
1295 make coverage-report
1296
1297 This creates the coverage report.
1298
1299 make coverage-clean-report
1300
1301 This removes the generated coverage report without cleaning the cover-
1302 age data itself.
1303
1304 make coverage-clean-data
1305
1306 This removes the captured coverage data without removing the coverage
1307 files created at compile time (*.gcno).
1308
1309 make coverage-clean
1310
1311 This cleans all coverage data including the generated coverage report.
1312 For more information about code coverage, see the gcov and lcov docu-
1313 mentation.
1314
1315
1316 SEE ALSO
1317
1318 pcreapi(3), pcre16, pcre32, pcre_config(3).
1319
1320
1321 AUTHOR
1322
1323 Philip Hazel
1324 University Computing Service
1325 Cambridge CB2 3QH, England.
1326
1327
1328 REVISION
1329
1330 Last updated: 30 October 2012
1331 Copyright (c) 1997-2012 University of Cambridge.
1332 ------------------------------------------------------------------------------
1333
1334
1335 PCREMATCHING(3) Library Functions Manual PCREMATCHING(3)
1336
1337
1338
1339 NAME
1340 PCRE - Perl-compatible regular expressions
1341
1342 PCRE MATCHING ALGORITHMS
1343
1344 This document describes the two different algorithms that are available
1345 in PCRE for matching a compiled regular expression against a given sub-
1346 ject string. The "standard" algorithm is the one provided by the
1347 pcre_exec(), pcre16_exec() and pcre32_exec() functions. These work in
1348 the same as as Perl's matching function, and provide a Perl-compatible
1349 matching operation. The just-in-time (JIT) optimization that is
1350 described in the pcrejit documentation is compatible with these func-
1351 tions.
1352
1353 An alternative algorithm is provided by the pcre_dfa_exec(),
1354 pcre16_dfa_exec() and pcre32_dfa_exec() functions; they operate in a
1355 different way, and are not Perl-compatible. This alternative has advan-
1356 tages and disadvantages compared with the standard algorithm, and these
1357 are described below.
1358
1359 When there is only one possible way in which a given subject string can
1360 match a pattern, the two algorithms give the same answer. A difference
1361 arises, however, when there are multiple possibilities. For example, if
1362 the pattern
1363
1364 ^<.*>
1365
1366 is matched against the string
1367
1368 <something> <something else> <something further>
1369
1370 there are three possible answers. The standard algorithm finds only one
1371 of them, whereas the alternative algorithm finds all three.
1372
1373
1374 REGULAR EXPRESSIONS AS TREES
1375
1376 The set of strings that are matched by a regular expression can be rep-
1377 resented as a tree structure. An unlimited repetition in the pattern
1378 makes the tree of infinite size, but it is still a tree. Matching the
1379 pattern to a given subject string (from a given starting point) can be
1380 thought of as a search of the tree. There are two ways to search a
1381 tree: depth-first and breadth-first, and these correspond to the two
1382 matching algorithms provided by PCRE.
1383
1384
1385 THE STANDARD MATCHING ALGORITHM
1386
1387 In the terminology of Jeffrey Friedl's book "Mastering Regular Expres-
1388 sions", the standard algorithm is an "NFA algorithm". It conducts a
1389 depth-first search of the pattern tree. That is, it proceeds along a
1390 single path through the tree, checking that the subject matches what is
1391 required. When there is a mismatch, the algorithm tries any alterna-
1392 tives at the current point, and if they all fail, it backs up to the
1393 previous branch point in the tree, and tries the next alternative
1394 branch at that level. This often involves backing up (moving to the
1395 left) in the subject string as well. The order in which repetition
1396 branches are tried is controlled by the greedy or ungreedy nature of
1397 the quantifier.
1398
1399 If a leaf node is reached, a matching string has been found, and at
1400 that point the algorithm stops. Thus, if there is more than one possi-
1401 ble match, this algorithm returns the first one that it finds. Whether
1402 this is the shortest, the longest, or some intermediate length depends
1403 on the way the greedy and ungreedy repetition quantifiers are specified
1404 in the pattern.
1405
1406 Because it ends up with a single path through the tree, it is rela-
1407 tively straightforward for this algorithm to keep track of the sub-
1408 strings that are matched by portions of the pattern in parentheses.
1409 This provides support for capturing parentheses and back references.
1410
1411
1412 THE ALTERNATIVE MATCHING ALGORITHM
1413
1414 This algorithm conducts a breadth-first search of the tree. Starting
1415 from the first matching point in the subject, it scans the subject
1416 string from left to right, once, character by character, and as it does
1417 this, it remembers all the paths through the tree that represent valid
1418 matches. In Friedl's terminology, this is a kind of "DFA algorithm",
1419 though it is not implemented as a traditional finite state machine (it
1420 keeps multiple states active simultaneously).
1421
1422 Although the general principle of this matching algorithm is that it
1423 scans the subject string only once, without backtracking, there is one
1424 exception: when a lookaround assertion is encountered, the characters
1425 following or preceding the current point have to be independently
1426 inspected.
1427
1428 The scan continues until either the end of the subject is reached, or
1429 there are no more unterminated paths. At this point, terminated paths
1430 represent the different matching possibilities (if there are none, the
1431 match has failed). Thus, if there is more than one possible match,
1432 this algorithm finds all of them, and in particular, it finds the long-
1433 est. The matches are returned in decreasing order of length. There is
1434 an option to stop the algorithm after the first match (which is neces-
1435 sarily the shortest) is found.
1436
1437 Note that all the matches that are found start at the same point in the
1438 subject. If the pattern
1439
1440 cat(er(pillar)?)?
1441
1442 is matched against the string "the caterpillar catchment", the result
1443 will be the three strings "caterpillar", "cater", and "cat" that start
1444 at the fifth character of the subject. The algorithm does not automati-
1445 cally move on to find matches that start at later positions.
1446
1447 There are a number of features of PCRE regular expressions that are not
1448 supported by the alternative matching algorithm. They are as follows:
1449
1450 1. Because the algorithm finds all possible matches, the greedy or
1451 ungreedy nature of repetition quantifiers is not relevant. Greedy and
1452 ungreedy quantifiers are treated in exactly the same way. However, pos-
1453 sessive quantifiers can make a difference when what follows could also
1454 match what is quantified, for example in a pattern like this:
1455
1456 ^a++\w!
1457
1458 This pattern matches "aaab!" but not "aaa!", which would be matched by
1459 a non-possessive quantifier. Similarly, if an atomic group is present,
1460 it is matched as if it were a standalone pattern at the current point,
1461 and the longest match is then "locked in" for the rest of the overall
1462 pattern.
1463
1464 2. When dealing with multiple paths through the tree simultaneously, it
1465 is not straightforward to keep track of captured substrings for the
1466 different matching possibilities, and PCRE's implementation of this
1467 algorithm does not attempt to do this. This means that no captured sub-
1468 strings are available.
1469
1470 3. Because no substrings are captured, back references within the pat-
1471 tern are not supported, and cause errors if encountered.
1472
1473 4. For the same reason, conditional expressions that use a backrefer-
1474 ence as the condition or test for a specific group recursion are not
1475 supported.
1476
1477 5. Because many paths through the tree may be active, the \K escape
1478 sequence, which resets the start of the match when encountered (but may
1479 be on some paths and not on others), is not supported. It causes an
1480 error if encountered.
1481
1482 6. Callouts are supported, but the value of the capture_top field is
1483 always 1, and the value of the capture_last field is always -1.
1484
1485 7. The \C escape sequence, which (in the standard algorithm) always
1486 matches a single data unit, even in UTF-8, UTF-16 or UTF-32 modes, is
1487 not supported in these modes, because the alternative algorithm moves
1488 through the subject string one character (not data unit) at a time, for
1489 all active paths through the tree.
1490
1491 8. Except for (*FAIL), the backtracking control verbs such as (*PRUNE)
1492 are not supported. (*FAIL) is supported, and behaves like a failing
1493 negative assertion.
1494
1495
1496 ADVANTAGES OF THE ALTERNATIVE ALGORITHM
1497
1498 Using the alternative matching algorithm provides the following advan-
1499 tages:
1500
1501 1. All possible matches (at a single point in the subject) are automat-
1502 ically found, and in particular, the longest match is found. To find
1503 more than one match using the standard algorithm, you have to do kludgy
1504 things with callouts.
1505
1506 2. Because the alternative algorithm scans the subject string just
1507 once, and never needs to backtrack (except for lookbehinds), it is pos-
1508 sible to pass very long subject strings to the matching function in
1509 several pieces, checking for partial matching each time. Although it is
1510 possible to do multi-segment matching using the standard algorithm by
1511 retaining partially matched substrings, it is more complicated. The
1512 pcrepartial documentation gives details of partial matching and dis-
1513 cusses multi-segment matching.
1514
1515
1516 DISADVANTAGES OF THE ALTERNATIVE ALGORITHM
1517
1518 The alternative algorithm suffers from a number of disadvantages:
1519
1520 1. It is substantially slower than the standard algorithm. This is
1521 partly because it has to search for all possible matches, but is also
1522 because it is less susceptible to optimization.
1523
1524 2. Capturing parentheses and back references are not supported.
1525
1526 3. Although atomic groups are supported, their use does not provide the
1527 performance advantage that it does for the standard algorithm.
1528
1529
1530 AUTHOR
1531
1532 Philip Hazel
1533 University Computing Service
1534 Cambridge CB2 3QH, England.
1535
1536
1537 REVISION
1538
1539 Last updated: 08 January 2012
1540 Copyright (c) 1997-2012 University of Cambridge.
1541 ------------------------------------------------------------------------------
1542
1543
1544 PCREAPI(3) Library Functions Manual PCREAPI(3)
1545
1546
1547
1548 NAME
1549 PCRE - Perl-compatible regular expressions
1550
1551 #include <pcre.h>
1552
1553
1554 PCRE NATIVE API BASIC FUNCTIONS
1555
1556 pcre *pcre_compile(const char *pattern, int options,
1557 const char **errptr, int *erroffset,
1558 const unsigned char *tableptr);
1559
1560 pcre *pcre_compile2(const char *pattern, int options,
1561 int *errorcodeptr,
1562 const char **errptr, int *erroffset,
1563 const unsigned char *tableptr);
1564
1565 pcre_extra *pcre_study(const pcre *code, int options,
1566 const char **errptr);
1567
1568 void pcre_free_study(pcre_extra *extra);
1569
1570 int pcre_exec(const pcre *code, const pcre_extra *extra,
1571 const char *subject, int length, int startoffset,
1572 int options, int *ovector, int ovecsize);
1573
1574 int pcre_dfa_exec(const pcre *code, const pcre_extra *extra,
1575 const char *subject, int length, int startoffset,
1576 int options, int *ovector, int ovecsize,
1577 int *workspace, int wscount);
1578
1579
1580 PCRE NATIVE API STRING EXTRACTION FUNCTIONS
1581
1582 int pcre_copy_named_substring(const pcre *code,
1583 const char *subject, int *ovector,
1584 int stringcount, const char *stringname,
1585 char *buffer, int buffersize);
1586
1587 int pcre_copy_substring(const char *subject, int *ovector,
1588 int stringcount, int stringnumber, char *buffer,
1589 int buffersize);
1590
1591 int pcre_get_named_substring(const pcre *code,
1592 const char *subject, int *ovector,
1593 int stringcount, const char *stringname,
1594 const char **stringptr);
1595
1596 int pcre_get_stringnumber(const pcre *code,
1597 const char *name);
1598
1599 int pcre_get_stringtable_entries(const pcre *code,
1600 const char *name, char **first, char **last);
1601
1602 int pcre_get_substring(const char *subject, int *ovector,
1603 int stringcount, int stringnumber,
1604 const char **stringptr);
1605
1606 int pcre_get_substring_list(const char *subject,
1607 int *ovector, int stringcount, const char ***listptr);
1608
1609 void pcre_free_substring(const char *stringptr);
1610
1611 void pcre_free_substring_list(const char **stringptr);
1612
1613
1614 PCRE NATIVE API AUXILIARY FUNCTIONS
1615
1616 int pcre_jit_exec(const pcre *code, const pcre_extra *extra,
1617 const char *subject, int length, int startoffset,
1618 int options, int *ovector, int ovecsize,
1619 pcre_jit_stack *jstack);
1620
1621 pcre_jit_stack *pcre_jit_stack_alloc(int startsize, int maxsize);
1622
1623 void pcre_jit_stack_free(pcre_jit_stack *stack);
1624
1625 void pcre_assign_jit_stack(pcre_extra *extra,
1626 pcre_jit_callback callback, void *data);
1627
1628 const unsigned char *pcre_maketables(void);
1629
1630 int pcre_fullinfo(const pcre *code, const pcre_extra *extra,
1631 int what, void *where);
1632
1633 int pcre_refcount(pcre *code, int adjust);
1634
1635 int pcre_config(int what, void *where);
1636
1637 const char *pcre_version(void);
1638
1639 int pcre_pattern_to_host_byte_order(pcre *code,
1640 pcre_extra *extra, const unsigned char *tables);
1641
1642
1643 PCRE NATIVE API INDIRECTED FUNCTIONS
1644
1645 void *(*pcre_malloc)(size_t);
1646
1647 void (*pcre_free)(void *);
1648
1649 void *(*pcre_stack_malloc)(size_t);
1650
1651 void (*pcre_stack_free)(void *);
1652
1653 int (*pcre_callout)(pcre_callout_block *);
1654
1655
1656 PCRE 8-BIT, 16-BIT, AND 32-BIT LIBRARIES
1657
1658 As well as support for 8-bit character strings, PCRE also supports
1659 16-bit strings (from release 8.30) and 32-bit strings (from release
1660 8.32), by means of two additional libraries. They can be built as well
1661 as, or instead of, the 8-bit library. To avoid too much complication,
1662 this document describes the 8-bit versions of the functions, with only
1663 occasional references to the 16-bit and 32-bit libraries.
1664
1665 The 16-bit and 32-bit functions operate in the same way as their 8-bit
1666 counterparts; they just use different data types for their arguments
1667 and results, and their names start with pcre16_ or pcre32_ instead of
1668 pcre_. For every option that has UTF8 in its name (for example,
1669 PCRE_UTF8), there are corresponding 16-bit and 32-bit names with UTF8
1670 replaced by UTF16 or UTF32, respectively. This facility is in fact just
1671 cosmetic; the 16-bit and 32-bit option names define the same bit val-
1672 ues.
1673
1674 References to bytes and UTF-8 in this document should be read as refer-
1675 ences to 16-bit data units and UTF-16 when using the 16-bit library, or
1676 32-bit data units and UTF-32 when using the 32-bit library, unless
1677 specified otherwise. More details of the specific differences for the
1678 16-bit and 32-bit libraries are given in the pcre16 and pcre32 pages.
1679
1680
1681 PCRE API OVERVIEW
1682
1683 PCRE has its own native API, which is described in this document. There
1684 are also some wrapper functions (for the 8-bit library only) that cor-
1685 respond to the POSIX regular expression API, but they do not give
1686 access to all the functionality. They are described in the pcreposix
1687 documentation. Both of these APIs define a set of C function calls. A
1688 C++ wrapper (again for the 8-bit library only) is also distributed with
1689 PCRE. It is documented in the pcrecpp page.
1690
1691 The native API C function prototypes are defined in the header file
1692 pcre.h, and on Unix-like systems the (8-bit) library itself is called
1693 libpcre. It can normally be accessed by adding -lpcre to the command
1694 for linking an application that uses PCRE. The header file defines the
1695 macros PCRE_MAJOR and PCRE_MINOR to contain the major and minor release
1696 numbers for the library. Applications can use these to include support
1697 for different releases of PCRE.
1698
1699 In a Windows environment, if you want to statically link an application
1700 program against a non-dll pcre.a file, you must define PCRE_STATIC
1701 before including pcre.h or pcrecpp.h, because otherwise the pcre_mal-
1702 loc() and pcre_free() exported functions will be declared
1703 __declspec(dllimport), with unwanted results.
1704
1705 The functions pcre_compile(), pcre_compile2(), pcre_study(), and
1706 pcre_exec() are used for compiling and matching regular expressions in
1707 a Perl-compatible manner. A sample program that demonstrates the sim-
1708 plest way of using them is provided in the file called pcredemo.c in
1709 the PCRE source distribution. A listing of this program is given in the
1710 pcredemo documentation, and the pcresample documentation describes how
1711 to compile and run it.
1712
1713 Just-in-time compiler support is an optional feature of PCRE that can
1714 be built in appropriate hardware environments. It greatly speeds up the
1715 matching performance of many patterns. Simple programs can easily
1716 request that it be used if available, by setting an option that is
1717 ignored when it is not relevant. More complicated programs might need
1718 to make use of the functions pcre_jit_stack_alloc(),
1719 pcre_jit_stack_free(), and pcre_assign_jit_stack() in order to control
1720 the JIT code's memory usage.
1721
1722 From release 8.32 there is also a direct interface for JIT execution,
1723 which gives improved performance. The JIT-specific functions are dis-
1724 cussed in the pcrejit documentation.
1725
1726 A second matching function, pcre_dfa_exec(), which is not Perl-compati-
1727 ble, is also provided. This uses a different algorithm for the match-
1728 ing. The alternative algorithm finds all possible matches (at a given
1729 point in the subject), and scans the subject just once (unless there
1730 are lookbehind assertions). However, this algorithm does not return
1731 captured substrings. A description of the two matching algorithms and
1732 their advantages and disadvantages is given in the pcrematching docu-
1733 mentation.
1734
1735 In addition to the main compiling and matching functions, there are
1736 convenience functions for extracting captured substrings from a subject
1737 string that is matched by pcre_exec(). They are:
1738
1739 pcre_copy_substring()
1740 pcre_copy_named_substring()
1741 pcre_get_substring()
1742 pcre_get_named_substring()
1743 pcre_get_substring_list()
1744 pcre_get_stringnumber()
1745 pcre_get_stringtable_entries()
1746
1747 pcre_free_substring() and pcre_free_substring_list() are also provided,
1748 to free the memory used for extracted strings.
1749
1750 The function pcre_maketables() is used to build a set of character
1751 tables in the current locale for passing to pcre_compile(),
1752 pcre_exec(), or pcre_dfa_exec(). This is an optional facility that is
1753 provided for specialist use. Most commonly, no special tables are
1754 passed, in which case internal tables that are generated when PCRE is
1755 built are used.
1756
1757 The function pcre_fullinfo() is used to find out information about a
1758 compiled pattern. The function pcre_version() returns a pointer to a
1759 string containing the version of PCRE and its date of release.
1760
1761 The function pcre_refcount() maintains a reference count in a data
1762 block containing a compiled pattern. This is provided for the benefit
1763 of object-oriented applications.
1764
1765 The global variables pcre_malloc and pcre_free initially contain the
1766 entry points of the standard malloc() and free() functions, respec-
1767 tively. PCRE calls the memory management functions via these variables,
1768 so a calling program can replace them if it wishes to intercept the
1769 calls. This should be done before calling any PCRE functions.
1770
1771 The global variables pcre_stack_malloc and pcre_stack_free are also
1772 indirections to memory management functions. These special functions
1773 are used only when PCRE is compiled to use the heap for remembering
1774 data, instead of recursive function calls, when running the pcre_exec()
1775 function. See the pcrebuild documentation for details of how to do
1776 this. It is a non-standard way of building PCRE, for use in environ-
1777 ments that have limited stacks. Because of the greater use of memory
1778 management, it runs more slowly. Separate functions are provided so
1779 that special-purpose external code can be used for this case. When
1780 used, these functions are always called in a stack-like manner (last
1781 obtained, first freed), and always for memory blocks of the same size.
1782 There is a discussion about PCRE's stack usage in the pcrestack docu-
1783 mentation.
1784
1785 The global variable pcre_callout initially contains NULL. It can be set
1786 by the caller to a "callout" function, which PCRE will then call at
1787 specified points during a matching operation. Details are given in the
1788 pcrecallout documentation.
1789
1790
1791 NEWLINES
1792
1793 PCRE supports five different conventions for indicating line breaks in
1794 strings: a single CR (carriage return) character, a single LF (line-
1795 feed) character, the two-character sequence CRLF, any of the three pre-
1796 ceding, or any Unicode newline sequence. The Unicode newline sequences
1797 are the three just mentioned, plus the single characters VT (vertical
1798 tab, U+000B), FF (form feed, U+000C), NEL (next line, U+0085), LS (line
1799 separator, U+2028), and PS (paragraph separator, U+2029).
1800
1801 Each of the first three conventions is used by at least one operating
1802 system as its standard newline sequence. When PCRE is built, a default
1803 can be specified. The default default is LF, which is the Unix stan-
1804 dard. When PCRE is run, the default can be overridden, either when a
1805 pattern is compiled, or when it is matched.
1806
1807 At compile time, the newline convention can be specified by the options
1808 argument of pcre_compile(), or it can be specified by special text at
1809 the start of the pattern itself; this overrides any other settings. See
1810 the pcrepattern page for details of the special character sequences.
1811
1812 In the PCRE documentation the word "newline" is used to mean "the char-
1813 acter or pair of characters that indicate a line break". The choice of
1814 newline convention affects the handling of the dot, circumflex, and
1815 dollar metacharacters, the handling of #-comments in /x mode, and, when
1816 CRLF is a recognized line ending sequence, the match position advance-
1817 ment for a non-anchored pattern. There is more detail about this in the
1818 section on pcre_exec() options below.
1819
1820 The choice of newline convention does not affect the interpretation of
1821 the \n or \r escape sequences, nor does it affect what \R matches,
1822 which is controlled in a similar way, but by separate options.
1823
1824
1825 MULTITHREADING
1826
1827 The PCRE functions can be used in multi-threading applications, with
1828 the proviso that the memory management functions pointed to by
1829 pcre_malloc, pcre_free, pcre_stack_malloc, and pcre_stack_free, and the
1830 callout function pointed to by pcre_callout, are shared by all threads.
1831
1832 The compiled form of a regular expression is not altered during match-
1833 ing, so the same compiled pattern can safely be used by several threads
1834 at once.
1835
1836 If the just-in-time optimization feature is being used, it needs sepa-
1837 rate memory stack areas for each thread. See the pcrejit documentation
1838 for more details.
1839
1840
1841 SAVING PRECOMPILED PATTERNS FOR LATER USE
1842
1843 The compiled form of a regular expression can be saved and re-used at a
1844 later time, possibly by a different program, and even on a host other
1845 than the one on which it was compiled. Details are given in the
1846 pcreprecompile documentation, which includes a description of the
1847 pcre_pattern_to_host_byte_order() function. However, compiling a regu-
1848 lar expression with one version of PCRE for use with a different ver-
1849 sion is not guaranteed to work and may cause crashes.
1850
1851
1852 CHECKING BUILD-TIME OPTIONS
1853
1854 int pcre_config(int what, void *where);
1855
1856 The function pcre_config() makes it possible for a PCRE client to dis-
1857 cover which optional features have been compiled into the PCRE library.
1858 The pcrebuild documentation has more details about these optional fea-
1859 tures.
1860
1861 The first argument for pcre_config() is an integer, specifying which
1862 information is required; the second argument is a pointer to a variable
1863 into which the information is placed. The returned value is zero on
1864 success, or the negative error code PCRE_ERROR_BADOPTION if the value
1865 in the first argument is not recognized. The following information is
1866 available:
1867
1868 PCRE_CONFIG_UTF8
1869
1870 The output is an integer that is set to one if UTF-8 support is avail-
1871 able; otherwise it is set to zero. This value should normally be given
1872 to the 8-bit version of this function, pcre_config(). If it is given to
1873 the 16-bit or 32-bit version of this function, the result is
1874 PCRE_ERROR_BADOPTION.
1875
1876 PCRE_CONFIG_UTF16
1877
1878 The output is an integer that is set to one if UTF-16 support is avail-
1879 able; otherwise it is set to zero. This value should normally be given
1880 to the 16-bit version of this function, pcre16_config(). If it is given
1881 to the 8-bit or 32-bit version of this function, the result is
1882 PCRE_ERROR_BADOPTION.
1883
1884 PCRE_CONFIG_UTF32
1885
1886 The output is an integer that is set to one if UTF-32 support is avail-
1887 able; otherwise it is set to zero. This value should normally be given
1888 to the 32-bit version of this function, pcre32_config(). If it is given
1889 to the 8-bit or 16-bit version of this function, the result is
1890 PCRE_ERROR_BADOPTION.
1891
1892 PCRE_CONFIG_UNICODE_PROPERTIES
1893
1894 The output is an integer that is set to one if support for Unicode
1895 character properties is available; otherwise it is set to zero.
1896
1897 PCRE_CONFIG_JIT
1898
1899 The output is an integer that is set to one if support for just-in-time
1900 compiling is available; otherwise it is set to zero.
1901
1902 PCRE_CONFIG_JITTARGET
1903
1904 The output is a pointer to a zero-terminated "const char *" string. If
1905 JIT support is available, the string contains the name of the architec-
1906 ture for which the JIT compiler is configured, for example "x86 32bit
1907 (little endian + unaligned)". If JIT support is not available, the
1908 result is NULL.
1909
1910 PCRE_CONFIG_NEWLINE
1911
1912 The output is an integer whose value specifies the default character
1913 sequence that is recognized as meaning "newline". The values that are
1914 supported in ASCII/Unicode environments are: 10 for LF, 13 for CR, 3338
1915 for CRLF, -2 for ANYCRLF, and -1 for ANY. In EBCDIC environments, CR,
1916 ANYCRLF, and ANY yield the same values. However, the value for LF is
1917 normally 21, though some EBCDIC environments use 37. The corresponding
1918 values for CRLF are 3349 and 3365. The default should normally corre-
1919 spond to the standard sequence for your operating system.
1920
1921 PCRE_CONFIG_BSR
1922
1923 The output is an integer whose value indicates what character sequences
1924 the \R escape sequence matches by default. A value of 0 means that \R
1925 matches any Unicode line ending sequence; a value of 1 means that \R
1926 matches only CR, LF, or CRLF. The default can be overridden when a pat-
1927 tern is compiled or matched.
1928
1929 PCRE_CONFIG_LINK_SIZE
1930
1931 The output is an integer that contains the number of bytes used for
1932 internal linkage in compiled regular expressions. For the 8-bit
1933 library, the value can be 2, 3, or 4. For the 16-bit library, the value
1934 is either 2 or 4 and is still a number of bytes. For the 32-bit
1935 library, the value is either 2 or 4 and is still a number of bytes. The
1936 default value of 2 is sufficient for all but the most massive patterns,
1937 since it allows the compiled pattern to be up to 64K in size. Larger
1938 values allow larger regular expressions to be compiled, at the expense
1939 of slower matching.
1940
1941 PCRE_CONFIG_POSIX_MALLOC_THRESHOLD
1942
1943 The output is an integer that contains the threshold above which the
1944 POSIX interface uses malloc() for output vectors. Further details are
1945 given in the pcreposix documentation.
1946
1947 PCRE_CONFIG_MATCH_LIMIT
1948
1949 The output is a long integer that gives the default limit for the num-
1950 ber of internal matching function calls in a pcre_exec() execution.
1951 Further details are given with pcre_exec() below.
1952
1953 PCRE_CONFIG_MATCH_LIMIT_RECURSION
1954
1955 The output is a long integer that gives the default limit for the depth
1956 of recursion when calling the internal matching function in a
1957 pcre_exec() execution. Further details are given with pcre_exec()
1958 below.
1959
1960 PCRE_CONFIG_STACKRECURSE
1961
1962 The output is an integer that is set to one if internal recursion when
1963 running pcre_exec() is implemented by recursive function calls that use
1964 the stack to remember their state. This is the usual way that PCRE is
1965 compiled. The output is zero if PCRE was compiled to use blocks of data
1966 on the heap instead of recursive function calls. In this case,
1967 pcre_stack_malloc and pcre_stack_free are called to manage memory
1968 blocks on the heap, thus avoiding the use of the stack.
1969
1970
1971 COMPILING A PATTERN
1972
1973 pcre *pcre_compile(const char *pattern, int options,
1974 const char **errptr, int *erroffset,
1975 const unsigned char *tableptr);
1976
1977 pcre *pcre_compile2(const char *pattern, int options,
1978 int *errorcodeptr,
1979 const char **errptr, int *erroffset,
1980 const unsigned char *tableptr);
1981
1982 Either of the functions pcre_compile() or pcre_compile2() can be called
1983 to compile a pattern into an internal form. The only difference between
1984 the two interfaces is that pcre_compile2() has an additional argument,
1985 errorcodeptr, via which a numerical error code can be returned. To
1986 avoid too much repetition, we refer just to pcre_compile() below, but
1987 the information applies equally to pcre_compile2().
1988
1989 The pattern is a C string terminated by a binary zero, and is passed in
1990 the pattern argument. A pointer to a single block of memory that is
1991 obtained via pcre_malloc is returned. This contains the compiled code
1992 and related data. The pcre type is defined for the returned block; this
1993 is a typedef for a structure whose contents are not externally defined.
1994 It is up to the caller to free the memory (via pcre_free) when it is no
1995 longer required.
1996
1997 Although the compiled code of a PCRE regex is relocatable, that is, it
1998 does not depend on memory location, the complete pcre data block is not
1999 fully relocatable, because it may contain a copy of the tableptr argu-
2000 ment, which is an address (see below).
2001
2002 The options argument contains various bit settings that affect the com-
2003 pilation. It should be zero if no options are required. The available
2004 options are described below. Some of them (in particular, those that
2005 are compatible with Perl, but some others as well) can also be set and
2006 unset from within the pattern (see the detailed description in the
2007 pcrepattern documentation). For those options that can be different in
2008 different parts of the pattern, the contents of the options argument
2009 specifies their settings at the start of compilation and execution. The
2010 PCRE_ANCHORED, PCRE_BSR_xxx, PCRE_NEWLINE_xxx, PCRE_NO_UTF8_CHECK, and
2011 PCRE_NO_START_OPTIMIZE options can be set at the time of matching as
2012 well as at compile time.
2013
2014 If errptr is NULL, pcre_compile() returns NULL immediately. Otherwise,
2015 if compilation of a pattern fails, pcre_compile() returns NULL, and
2016 sets the variable pointed to by errptr to point to a textual error mes-
2017 sage. This is a static string that is part of the library. You must not
2018 try to free it. Normally, the offset from the start of the pattern to
2019 the data unit that was being processed when the error was discovered is
2020 placed in the variable pointed to by erroffset, which must not be NULL
2021 (if it is, an immediate error is given). However, for an invalid UTF-8
2022 or UTF-16 string, the offset is that of the first data unit of the
2023 failing character.
2024
2025 Some errors are not detected until the whole pattern has been scanned;
2026 in these cases, the offset passed back is the length of the pattern.
2027 Note that the offset is in data units, not characters, even in a UTF
2028 mode. It may sometimes point into the middle of a UTF-8 or UTF-16 char-
2029 acter.
2030
2031 If pcre_compile2() is used instead of pcre_compile(), and the error-
2032 codeptr argument is not NULL, a non-zero error code number is returned
2033 via this argument in the event of an error. This is in addition to the
2034 textual error message. Error codes and messages are listed below.
2035
2036 If the final argument, tableptr, is NULL, PCRE uses a default set of
2037 character tables that are built when PCRE is compiled, using the
2038 default C locale. Otherwise, tableptr must be an address that is the
2039 result of a call to pcre_maketables(). This value is stored with the
2040 compiled pattern, and used again by pcre_exec(), unless another table
2041 pointer is passed to it. For more discussion, see the section on locale
2042 support below.
2043
2044 This code fragment shows a typical straightforward call to pcre_com-
2045 pile():
2046
2047 pcre *re;
2048 const char *error;
2049 int erroffset;
2050 re = pcre_compile(
2051 "^A.*Z", /* the pattern */
2052 0, /* default options */
2053 &error, /* for error message */
2054 &erroffset, /* for error offset */
2055 NULL); /* use default character tables */
2056
2057 The following names for option bits are defined in the pcre.h header
2058 file:
2059
2060 PCRE_ANCHORED
2061
2062 If this bit is set, the pattern is forced to be "anchored", that is, it
2063 is constrained to match only at the first matching point in the string
2064 that is being searched (the "subject string"). This effect can also be
2065 achieved by appropriate constructs in the pattern itself, which is the
2066 only way to do it in Perl.
2067
2068 PCRE_AUTO_CALLOUT
2069
2070 If this bit is set, pcre_compile() automatically inserts callout items,
2071 all with number 255, before each pattern item. For discussion of the
2072 callout facility, see the pcrecallout documentation.
2073
2074 PCRE_BSR_ANYCRLF
2075 PCRE_BSR_UNICODE
2076
2077 These options (which are mutually exclusive) control what the \R escape
2078 sequence matches. The choice is either to match only CR, LF, or CRLF,
2079 or to match any Unicode newline sequence. The default is specified when
2080 PCRE is built. It can be overridden from within the pattern, or by set-
2081 ting an option when a compiled pattern is matched.
2082
2083 PCRE_CASELESS
2084
2085 If this bit is set, letters in the pattern match both upper and lower
2086 case letters. It is equivalent to Perl's /i option, and it can be
2087 changed within a pattern by a (?i) option setting. In UTF-8 mode, PCRE
2088 always understands the concept of case for characters whose values are
2089 less than 128, so caseless matching is always possible. For characters
2090 with higher values, the concept of case is supported if PCRE is com-
2091 piled with Unicode property support, but not otherwise. If you want to
2092 use caseless matching for characters 128 and above, you must ensure
2093 that PCRE is compiled with Unicode property support as well as with
2094 UTF-8 support.
2095
2096 PCRE_DOLLAR_ENDONLY
2097
2098 If this bit is set, a dollar metacharacter in the pattern matches only
2099 at the end of the subject string. Without this option, a dollar also
2100 matches immediately before a newline at the end of the string (but not
2101 before any other newlines). The PCRE_DOLLAR_ENDONLY option is ignored
2102 if PCRE_MULTILINE is set. There is no equivalent to this option in
2103 Perl, and no way to set it within a pattern.
2104
2105 PCRE_DOTALL
2106
2107 If this bit is set, a dot metacharacter in the pattern matches a char-
2108 acter of any value, including one that indicates a newline. However, it
2109 only ever matches one character, even if newlines are coded as CRLF.
2110 Without this option, a dot does not match when the current position is
2111 at a newline. This option is equivalent to Perl's /s option, and it can
2112 be changed within a pattern by a (?s) option setting. A negative class
2113 such as [^a] always matches newline characters, independent of the set-
2114 ting of this option.
2115
2116 PCRE_DUPNAMES
2117
2118 If this bit is set, names used to identify capturing subpatterns need
2119 not be unique. This can be helpful for certain types of pattern when it
2120 is known that only one instance of the named subpattern can ever be
2121 matched. There are more details of named subpatterns below; see also
2122 the pcrepattern documentation.
2123
2124 PCRE_EXTENDED
2125
2126 If this bit is set, white space data characters in the pattern are
2127 totally ignored except when escaped or inside a character class. White
2128 space does not include the VT character (code 11). In addition, charac-
2129 ters between an unescaped # outside a character class and the next new-
2130 line, inclusive, are also ignored. This is equivalent to Perl's /x
2131 option, and it can be changed within a pattern by a (?x) option set-
2132 ting.
2133
2134 Which characters are interpreted as newlines is controlled by the
2135 options passed to pcre_compile() or by a special sequence at the start
2136 of the pattern, as described in the section entitled "Newline conven-
2137 tions" in the pcrepattern documentation. Note that the end of this type
2138 of comment is a literal newline sequence in the pattern; escape
2139 sequences that happen to represent a newline do not count.
2140
2141 This option makes it possible to include comments inside complicated
2142 patterns. Note, however, that this applies only to data characters.
2143 White space characters may never appear within special character
2144 sequences in a pattern, for example within the sequence (?( that intro-
2145 duces a conditional subpattern.
2146
2147 PCRE_EXTRA
2148
2149 This option was invented in order to turn on additional functionality
2150 of PCRE that is incompatible with Perl, but it is currently of very
2151 little use. When set, any backslash in a pattern that is followed by a
2152 letter that has no special meaning causes an error, thus reserving
2153 these combinations for future expansion. By default, as in Perl, a
2154 backslash followed by a letter with no special meaning is treated as a
2155 literal. (Perl can, however, be persuaded to give an error for this, by
2156 running it with the -w option.) There are at present no other features
2157 controlled by this option. It can also be set by a (?X) option setting
2158 within a pattern.
2159
2160 PCRE_FIRSTLINE
2161
2162 If this option is set, an unanchored pattern is required to match
2163 before or at the first newline in the subject string, though the
2164 matched text may continue over the newline.
2165
2166 PCRE_JAVASCRIPT_COMPAT
2167
2168 If this option is set, PCRE's behaviour is changed in some ways so that
2169 it is compatible with JavaScript rather than Perl. The changes are as
2170 follows:
2171
2172 (1) A lone closing square bracket in a pattern causes a compile-time
2173 error, because this is illegal in JavaScript (by default it is treated
2174 as a data character). Thus, the pattern AB]CD becomes illegal when this
2175 option is set.
2176
2177 (2) At run time, a back reference to an unset subpattern group matches
2178 an empty string (by default this causes the current matching alterna-
2179 tive to fail). A pattern such as (\1)(a) succeeds when this option is
2180 set (assuming it can find an "a" in the subject), whereas it fails by
2181 default, for Perl compatibility.
2182
2183 (3) \U matches an upper case "U" character; by default \U causes a com-
2184 pile time error (Perl uses \U to upper case subsequent characters).
2185
2186 (4) \u matches a lower case "u" character unless it is followed by four
2187 hexadecimal digits, in which case the hexadecimal number defines the
2188 code point to match. By default, \u causes a compile time error (Perl
2189 uses it to upper case the following character).
2190
2191 (5) \x matches a lower case "x" character unless it is followed by two
2192 hexadecimal digits, in which case the hexadecimal number defines the
2193 code point to match. By default, as in Perl, a hexadecimal number is
2194 always expected after \x, but it may have zero, one, or two digits (so,
2195 for example, \xz matches a binary zero character followed by z).
2196
2197 PCRE_MULTILINE
2198
2199 By default, for the purposes of matching "start of line" and "end of
2200 line", PCRE treats the subject string as consisting of a single line of
2201 characters, even if it actually contains newlines. The "start of line"
2202 metacharacter (^) matches only at the start of the string, and the "end
2203 of line" metacharacter ($) matches only at the end of the string, or
2204 before a terminating newline (except when PCRE_DOLLAR_ENDONLY is set).
2205 Note, however, that unless PCRE_DOTALL is set, the "any character"
2206 metacharacter (.) does not match at a newline. This behaviour (for ^,
2207 $, and dot) is the same as Perl.
2208
2209 When PCRE_MULTILINE it is set, the "start of line" and "end of line"
2210 constructs match immediately following or immediately before internal
2211 newlines in the subject string, respectively, as well as at the very
2212 start and end. This is equivalent to Perl's /m option, and it can be
2213 changed within a pattern by a (?m) option setting. If there are no new-
2214 lines in a subject string, or no occurrences of ^ or $ in a pattern,
2215 setting PCRE_MULTILINE has no effect.
2216
2217 PCRE_NEVER_UTF
2218
2219 This option locks out interpretation of the pattern as UTF-8 (or UTF-16
2220 or UTF-32 in the 16-bit and 32-bit libraries). In particular, it pre-
2221 vents the creator of the pattern from switching to UTF interpretation
2222 by starting the pattern with (*UTF). This may be useful in applications
2223 that process patterns from external sources. The combination of
2224 PCRE_UTF8 and PCRE_NEVER_UTF also causes an error.
2225
2226 PCRE_NEWLINE_CR
2227 PCRE_NEWLINE_LF
2228 PCRE_NEWLINE_CRLF
2229 PCRE_NEWLINE_ANYCRLF
2230 PCRE_NEWLINE_ANY
2231
2232 These options override the default newline definition that was chosen
2233 when PCRE was built. Setting the first or the second specifies that a
2234 newline is indicated by a single character (CR or LF, respectively).
2235 Setting PCRE_NEWLINE_CRLF specifies that a newline is indicated by the
2236 two-character CRLF sequence. Setting PCRE_NEWLINE_ANYCRLF specifies
2237 that any of the three preceding sequences should be recognized. Setting
2238 PCRE_NEWLINE_ANY specifies that any Unicode newline sequence should be
2239 recognized.
2240
2241 In an ASCII/Unicode environment, the Unicode newline sequences are the
2242 three just mentioned, plus the single characters VT (vertical tab,
2243 U+000B), FF (form feed, U+000C), NEL (next line, U+0085), LS (line sep-
2244 arator, U+2028), and PS (paragraph separator, U+2029). For the 8-bit
2245 library, the last two are recognized only in UTF-8 mode.
2246
2247 When PCRE is compiled to run in an EBCDIC (mainframe) environment, the
2248 code for CR is 0x0d, the same as ASCII. However, the character code for
2249 LF is normally 0x15, though in some EBCDIC environments 0x25 is used.
2250 Whichever of these is not LF is made to correspond to Unicode's NEL
2251 character. EBCDIC codes are all less than 256. For more details, see
2252 the pcrebuild documentation.
2253
2254 The newline setting in the options word uses three bits that are
2255 treated as a number, giving eight possibilities. Currently only six are
2256 used (default plus the five values above). This means that if you set
2257 more than one newline option, the combination may or may not be sensi-
2258 ble. For example, PCRE_NEWLINE_CR with PCRE_NEWLINE_LF is equivalent to
2259 PCRE_NEWLINE_CRLF, but other combinations may yield unused numbers and
2260 cause an error.
2261
2262 The only time that a line break in a pattern is specially recognized
2263 when compiling is when PCRE_EXTENDED is set. CR and LF are white space
2264 characters, and so are ignored in this mode. Also, an unescaped # out-
2265 side a character class indicates a comment that lasts until after the
2266 next line break sequence. In other circumstances, line break sequences
2267 in patterns are treated as literal data.
2268
2269 The newline option that is set at compile time becomes the default that
2270 is used for pcre_exec() and pcre_dfa_exec(), but it can be overridden.
2271
2272 PCRE_NO_AUTO_CAPTURE
2273
2274 If this option is set, it disables the use of numbered capturing paren-
2275 theses in the pattern. Any opening parenthesis that is not followed by
2276 ? behaves as if it were followed by ?: but named parentheses can still
2277 be used for capturing (and they acquire numbers in the usual way).
2278 There is no equivalent of this option in Perl.
2279
2280 PCRE_NO_START_OPTIMIZE
2281
2282 This is an option that acts at matching time; that is, it is really an
2283 option for pcre_exec() or pcre_dfa_exec(). If it is set at compile
2284 time, it is remembered with the compiled pattern and assumed at match-
2285 ing time. This is necessary if you want to use JIT execution, because
2286 the JIT compiler needs to know whether or not this option is set. For
2287 details see the discussion of PCRE_NO_START_OPTIMIZE below.
2288
2289 PCRE_UCP
2290
2291 This option changes the way PCRE processes \B, \b, \D, \d, \S, \s, \W,
2292 \w, and some of the POSIX character classes. By default, only ASCII
2293 characters are recognized, but if PCRE_UCP is set, Unicode properties
2294 are used instead to classify characters. More details are given in the
2295 section on generic character types in the pcrepattern page. If you set
2296 PCRE_UCP, matching one of the items it affects takes much longer. The
2297 option is available only if PCRE has been compiled with Unicode prop-
2298 erty support.
2299
2300 PCRE_UNGREEDY
2301
2302 This option inverts the "greediness" of the quantifiers so that they
2303 are not greedy by default, but become greedy if followed by "?". It is
2304 not compatible with Perl. It can also be set by a (?U) option setting
2305 within the pattern.
2306
2307 PCRE_UTF8
2308
2309 This option causes PCRE to regard both the pattern and the subject as
2310 strings of UTF-8 characters instead of single-byte strings. However, it
2311 is available only when PCRE is built to include UTF support. If not,
2312 the use of this option provokes an error. Details of how this option
2313 changes the behaviour of PCRE are given in the pcreunicode page.
2314
2315 PCRE_NO_UTF8_CHECK
2316
2317 When PCRE_UTF8 is set, the validity of the pattern as a UTF-8 string is
2318 automatically checked. There is a discussion about the validity of
2319 UTF-8 strings in the pcreunicode page. If an invalid UTF-8 sequence is
2320 found, pcre_compile() returns an error. If you already know that your
2321 pattern is valid, and you want to skip this check for performance rea-
2322 sons, you can set the PCRE_NO_UTF8_CHECK option. When it is set, the
2323 effect of passing an invalid UTF-8 string as a pattern is undefined. It
2324 may cause your program to crash. Note that this option can also be
2325 passed to pcre_exec() and pcre_dfa_exec(), to suppress the validity
2326 checking of subject strings only. If the same string is being matched
2327 many times, the option can be safely set for the second and subsequent
2328 matchings to improve performance.
2329
2330
2331 COMPILATION ERROR CODES
2332
2333 The following table lists the error codes than may be returned by
2334 pcre_compile2(), along with the error messages that may be returned by
2335 both compiling functions. Note that error messages are always 8-bit
2336 ASCII strings, even in 16-bit or 32-bit mode. As PCRE has developed,
2337 some error codes have fallen out of use. To avoid confusion, they have
2338 not been re-used.
2339
2340 0 no error
2341 1 \ at end of pattern
2342 2 \c at end of pattern
2343 3 unrecognized character follows \
2344 4 numbers out of order in {} quantifier
2345 5 number too big in {} quantifier
2346 6 missing terminating ] for character class
2347 7 invalid escape sequence in character class
2348 8 range out of order in character class
2349 9 nothing to repeat
2350 10 [this code is not in use]
2351 11 internal error: unexpected repeat
2352 12 unrecognized character after (? or (?-
2353 13 POSIX named classes are supported only within a class
2354 14 missing )
2355 15 reference to non-existent subpattern
2356 16 erroffset passed as NULL
2357 17 unknown option bit(s) set
2358 18 missing ) after comment
2359 19 [this code is not in use]
2360 20 regular expression is too large
2361 21 failed to get memory
2362 22 unmatched parentheses
2363 23 internal error: code overflow
2364 24 unrecognized character after (?<
2365 25 lookbehind assertion is not fixed length
2366 26 malformed number or name after (?(
2367 27 conditional group contains more than two branches
2368 28 assertion expected after (?(
2369 29 (?R or (?[+-]digits must be followed by )
2370 30 unknown POSIX class name
2371 31 POSIX collating elements are not supported
2372 32 this version of PCRE is compiled without UTF support
2373 33 [this code is not in use]
2374 34 character value in \x{...} sequence is too large
2375 35 invalid condition (?(0)
2376 36 \C not allowed in lookbehind assertion
2377 37 PCRE does not support \L, \l, \N{name}, \U, or \u
2378 38 number after (?C is > 255
2379 39 closing ) for (?C expected
2380 40 recursive call could loop indefinitely
2381 41 unrecognized character after (?P
2382 42 syntax error in subpattern name (missing terminator)
2383 43 two named subpatterns have the same name
2384 44 invalid UTF-8 string (specifically UTF-8)
2385 45 support for \P, \p, and \X has not been compiled
2386 46 malformed \P or \p sequence
2387 47 unknown property name after \P or \p
2388 48 subpattern name is too long (maximum 32 characters)
2389 49 too many named subpatterns (maximum 10000)
2390 50 [this code is not in use]
2391 51 octal value is greater than \377 in 8-bit non-UTF-8 mode
2392 52 internal error: overran compiling workspace
2393 53 internal error: previously-checked referenced subpattern
2394 not found
2395 54 DEFINE group contains more than one branch
2396 55 repeating a DEFINE group is not allowed
2397 56 inconsistent NEWLINE options
2398 57 \g is not followed by a braced, angle-bracketed, or quoted
2399 name/number or by a plain number
2400 58 a numbered reference must not be zero
2401 59 an argument is not allowed for (*ACCEPT), (*FAIL), or (*COMMIT)
2402 60 (*VERB) not recognized or malformed
2403 61 number is too big
2404 62 subpattern name expected
2405 63 digit expected after (?+
2406 64 ] is an invalid data character in JavaScript compatibility mode
2407 65 different names for subpatterns of the same number are
2408 not allowed
2409 66 (*MARK) must have an argument
2410 67 this version of PCRE is not compiled with Unicode property
2411 support
2412 68 \c must be followed by an ASCII character
2413 69 \k is not followed by a braced, angle-bracketed, or quoted name
2414 70 internal error: unknown opcode in find_fixedlength()
2415 71 \N is not supported in a class
2416 72 too many forward references
2417 73 disallowed Unicode code point (>= 0xd800 && <= 0xdfff)
2418 74 invalid UTF-16 string (specifically UTF-16)
2419 75 name is too long in (*MARK), (*PRUNE), (*SKIP), or (*THEN)
2420 76 character value in \u.... sequence is too large
2421 77 invalid UTF-32 string (specifically UTF-32)
2422
2423 The numbers 32 and 10000 in errors 48 and 49 are defaults; different
2424 values may be used if the limits were changed when PCRE was built.
2425
2426
2427 STUDYING A PATTERN
2428
2429 pcre_extra *pcre_study(const pcre *code, int options
2430 const char **errptr);
2431
2432 If a compiled pattern is going to be used several times, it is worth
2433 spending more time analyzing it in order to speed up the time taken for
2434 matching. The function pcre_study() takes a pointer to a compiled pat-
2435 tern as its first argument. If studying the pattern produces additional
2436 information that will help speed up matching, pcre_study() returns a
2437 pointer to a pcre_extra block, in which the study_data field points to
2438 the results of the study.
2439
2440 The returned value from pcre_study() can be passed directly to
2441 pcre_exec() or pcre_dfa_exec(). However, a pcre_extra block also con-
2442 tains other fields that can be set by the caller before the block is
2443 passed; these are described below in the section on matching a pattern.
2444
2445 If studying the pattern does not produce any useful information,
2446 pcre_study() returns NULL by default. In that circumstance, if the
2447 calling program wants to pass any of the other fields to pcre_exec() or
2448 pcre_dfa_exec(), it must set up its own pcre_extra block. However, if
2449 pcre_study() is called with the PCRE_STUDY_EXTRA_NEEDED option, it
2450 returns a pcre_extra block even if studying did not find any additional
2451 information. It may still return NULL, however, if an error occurs in
2452 pcre_study().
2453
2454 The second argument of pcre_study() contains option bits. There are
2455 three further options in addition to PCRE_STUDY_EXTRA_NEEDED:
2456
2457 PCRE_STUDY_JIT_COMPILE
2458 PCRE_STUDY_JIT_PARTIAL_HARD_COMPILE
2459 PCRE_STUDY_JIT_PARTIAL_SOFT_COMPILE
2460
2461 If any of these are set, and the just-in-time compiler is available,
2462 the pattern is further compiled into machine code that executes much
2463 faster than the pcre_exec() interpretive matching function. If the
2464 just-in-time compiler is not available, these options are ignored. All
2465 undefined bits in the options argument must be zero.
2466
2467 JIT compilation is a heavyweight optimization. It can take some time
2468 for patterns to be analyzed, and for one-off matches and simple pat-
2469 terns the benefit of faster execution might be offset by a much slower
2470 study time. Not all patterns can be optimized by the JIT compiler. For
2471 those that cannot be handled, matching automatically falls back to the
2472 pcre_exec() interpreter. For more details, see the pcrejit documenta-
2473 tion.
2474
2475 The third argument for pcre_study() is a pointer for an error message.
2476 If studying succeeds (even if no data is returned), the variable it
2477 points to is set to NULL. Otherwise it is set to point to a textual
2478 error message. This is a static string that is part of the library. You
2479 must not try to free it. You should test the error pointer for NULL
2480 after calling pcre_study(), to be sure that it has run successfully.
2481
2482 When you are finished with a pattern, you can free the memory used for
2483 the study data by calling pcre_free_study(). This function was added to
2484 the API for release 8.20. For earlier versions, the memory could be
2485 freed with pcre_free(), just like the pattern itself. This will still
2486 work in cases where JIT optimization is not used, but it is advisable
2487 to change to the new function when convenient.
2488
2489 This is a typical way in which pcre_study() is used (except that in a
2490 real application there should be tests for errors):
2491
2492 int rc;
2493 pcre *re;
2494 pcre_extra *sd;
2495 re = pcre_compile("pattern", 0, &error, &erroroffset, NULL);
2496 sd = pcre_study(
2497 re, /* result of pcre_compile() */
2498 0, /* no options */
2499 &error); /* set to NULL or points to a message */
2500 rc = pcre_exec( /* see below for details of pcre_exec() options */
2501 re, sd, "subject", 7, 0, 0, ovector, 30);
2502 ...
2503 pcre_free_study(sd);
2504 pcre_free(re);
2505
2506 Studying a pattern does two things: first, a lower bound for the length
2507 of subject string that is needed to match the pattern is computed. This
2508 does not mean that there are any strings of that length that match, but
2509 it does guarantee that no shorter strings match. The value is used to
2510 avoid wasting time by trying to match strings that are shorter than the
2511 lower bound. You can find out the value in a calling program via the
2512 pcre_fullinfo() function.
2513
2514 Studying a pattern is also useful for non-anchored patterns that do not
2515 have a single fixed starting character. A bitmap of possible starting
2516 bytes is created. This speeds up finding a position in the subject at
2517 which to start matching. (In 16-bit mode, the bitmap is used for 16-bit
2518 values less than 256. In 32-bit mode, the bitmap is used for 32-bit
2519 values less than 256.)
2520
2521 These two optimizations apply to both pcre_exec() and pcre_dfa_exec(),
2522 and the information is also used by the JIT compiler. The optimiza-
2523 tions can be disabled by setting the PCRE_NO_START_OPTIMIZE option.
2524 You might want to do this if your pattern contains callouts or (*MARK)
2525 and you want to make use of these facilities in cases where matching
2526 fails.
2527
2528 PCRE_NO_START_OPTIMIZE can be specified at either compile time or exe-
2529 cution time. However, if PCRE_NO_START_OPTIMIZE is passed to
2530 pcre_exec(), (that is, after any JIT compilation has happened) JIT exe-
2531 cution is disabled. For JIT execution to work with PCRE_NO_START_OPTI-
2532 MIZE, the option must be set at compile time.
2533
2534 There is a longer discussion of PCRE_NO_START_OPTIMIZE below.
2535
2536
2537 LOCALE SUPPORT
2538
2539 PCRE handles caseless matching, and determines whether characters are
2540 letters, digits, or whatever, by reference to a set of tables, indexed
2541 by character value. When running in UTF-8 mode, this applies only to
2542 characters with codes less than 128. By default, higher-valued codes
2543 never match escapes such as \w or \d, but they can be tested with \p if
2544 PCRE is built with Unicode character property support. Alternatively,
2545 the PCRE_UCP option can be set at compile time; this causes \w and
2546 friends to use Unicode property support instead of built-in tables. The
2547 use of locales with Unicode is discouraged. If you are handling charac-
2548 ters with codes greater than 128, you should either use UTF-8 and Uni-
2549 code, or use locales, but not try to mix the two.
2550
2551 PCRE contains an internal set of tables that are used when the final
2552 argument of pcre_compile() is NULL. These are sufficient for many
2553 applications. Normally, the internal tables recognize only ASCII char-
2554 acters. However, when PCRE is built, it is possible to cause the inter-
2555 nal tables to be rebuilt in the default "C" locale of the local system,
2556 which may cause them to be different.
2557
2558 The internal tables can always be overridden by tables supplied by the
2559 application that calls PCRE. These may be created in a different locale
2560 from the default. As more and more applications change to using Uni-
2561 code, the need for this locale support is expected to die away.
2562
2563 External tables are built by calling the pcre_maketables() function,
2564 which has no arguments, in the relevant locale. The result can then be
2565 passed to pcre_compile() or pcre_exec() as often as necessary. For
2566 example, to build and use tables that are appropriate for the French
2567 locale (where accented characters with values greater than 128 are
2568 treated as letters), the following code could be used:
2569
2570 setlocale(LC_CTYPE, "fr_FR");
2571 tables = pcre_maketables();
2572 re = pcre_compile(..., tables);
2573
2574 The locale name "fr_FR" is used on Linux and other Unix-like systems;
2575 if you are using Windows, the name for the French locale is "french".
2576
2577 When pcre_maketables() runs, the tables are built in memory that is
2578 obtained via pcre_malloc. It is the caller's responsibility to ensure
2579 that the memory containing the tables remains available for as long as
2580 it is needed.
2581
2582 The pointer that is passed to pcre_compile() is saved with the compiled
2583 pattern, and the same tables are used via this pointer by pcre_study()
2584 and normally also by pcre_exec(). Thus, by default, for any single pat-
2585 tern, compilation, studying and matching all happen in the same locale,
2586 but different patterns can be compiled in different locales.
2587
2588 It is possible to pass a table pointer or NULL (indicating the use of
2589 the internal tables) to pcre_exec(). Although not intended for this
2590 purpose, this facility could be used to match a pattern in a different
2591 locale from the one in which it was compiled. Passing table pointers at
2592 run time is discussed below in the section on matching a pattern.
2593
2594
2595 INFORMATION ABOUT A PATTERN
2596
2597 int pcre_fullinfo(const pcre *code, const pcre_extra *extra,
2598 int what, void *where);
2599
2600 The pcre_fullinfo() function returns information about a compiled pat-
2601 tern. It replaces the pcre_info() function, which was removed from the
2602 library at version 8.30, after more than 10 years of obsolescence.
2603
2604 The first argument for pcre_fullinfo() is a pointer to the compiled
2605 pattern. The second argument is the result of pcre_study(), or NULL if
2606 the pattern was not studied. The third argument specifies which piece
2607 of information is required, and the fourth argument is a pointer to a
2608 variable to receive the data. The yield of the function is zero for
2609 success, or one of the following negative numbers:
2610
2611 PCRE_ERROR_NULL the argument code was NULL
2612 the argument where was NULL
2613 PCRE_ERROR_BADMAGIC the "magic number" was not found
2614 PCRE_ERROR_BADENDIANNESS the pattern was compiled with different
2615 endianness
2616 PCRE_ERROR_BADOPTION the value of what was invalid
2617 PCRE_ERROR_UNSET the requested field is not set
2618
2619 The "magic number" is placed at the start of each compiled pattern as
2620 an simple check against passing an arbitrary memory pointer. The endi-
2621 anness error can occur if a compiled pattern is saved and reloaded on a
2622 different host. Here is a typical call of pcre_fullinfo(), to obtain
2623 the length of the compiled pattern:
2624
2625 int rc;
2626 size_t length;
2627 rc = pcre_fullinfo(
2628 re, /* result of pcre_compile() */
2629 sd, /* result of pcre_study(), or NULL */
2630 PCRE_INFO_SIZE, /* what is required */
2631 &length); /* where to put the data */
2632
2633 The possible values for the third argument are defined in pcre.h, and
2634 are as follows:
2635
2636 PCRE_INFO_BACKREFMAX
2637
2638 Return the number of the highest back reference in the pattern. The
2639 fourth argument should point to an int variable. Zero is returned if
2640 there are no back references.
2641
2642 PCRE_INFO_CAPTURECOUNT
2643
2644 Return the number of capturing subpatterns in the pattern. The fourth
2645 argument should point to an int variable.
2646
2647 PCRE_INFO_DEFAULT_TABLES
2648
2649 Return a pointer to the internal default character tables within PCRE.
2650 The fourth argument should point to an unsigned char * variable. This
2651 information call is provided for internal use by the pcre_study() func-
2652 tion. External callers can cause PCRE to use its internal tables by
2653 passing a NULL table pointer.
2654
2655 PCRE_INFO_FIRSTBYTE
2656
2657 Return information about the first data unit of any matched string, for
2658 a non-anchored pattern. (The name of this option refers to the 8-bit
2659 library, where data units are bytes.) The fourth argument should point
2660 to an int variable.
2661
2662 If there is a fixed first value, for example, the letter "c" from a
2663 pattern such as (cat|cow|coyote), its value is returned. In the 8-bit
2664 library, the value is always less than 256. In the 16-bit library the
2665 value can be up to 0xffff. In the 32-bit library the value can be up to
2666 0x10ffff.
2667
2668 If there is no fixed first value, and if either
2669
2670 (a) the pattern was compiled with the PCRE_MULTILINE option, and every
2671 branch starts with "^", or
2672
2673 (b) every branch of the pattern starts with ".*" and PCRE_DOTALL is not
2674 set (if it were set, the pattern would be anchored),
2675
2676 -1 is returned, indicating that the pattern matches only at the start
2677 of a subject string or after any newline within the string. Otherwise
2678 -2 is returned. For anchored patterns, -2 is returned.
2679
2680 Since for the 32-bit library using the non-UTF-32 mode, this function
2681 is unable to return the full 32-bit range of the character, this value
2682 is deprecated; instead the PCRE_INFO_FIRSTCHARACTERFLAGS and
2683 PCRE_INFO_FIRSTCHARACTER values should be used.
2684
2685 PCRE_INFO_FIRSTTABLE
2686
2687 If the pattern was studied, and this resulted in the construction of a
2688 256-bit table indicating a fixed set of values for the first data unit
2689 in any matching string, a pointer to the table is returned. Otherwise
2690 NULL is returned. The fourth argument should point to an unsigned char
2691 * variable.
2692
2693 PCRE_INFO_HASCRORLF
2694
2695 Return 1 if the pattern contains any explicit matches for CR or LF
2696 characters, otherwise 0. The fourth argument should point to an int
2697 variable. An explicit match is either a literal CR or LF character, or
2698 \r or \n.
2699
2700 PCRE_INFO_JCHANGED
2701
2702 Return 1 if the (?J) or (?-J) option setting is used in the pattern,
2703 otherwise 0. The fourth argument should point to an int variable. (?J)
2704 and (?-J) set and unset the local PCRE_DUPNAMES option, respectively.
2705
2706 PCRE_INFO_JIT
2707
2708 Return 1 if the pattern was studied with one of the JIT options, and
2709 just-in-time compiling was successful. The fourth argument should point
2710 to an int variable. A return value of 0 means that JIT support is not
2711 available in this version of PCRE, or that the pattern was not studied
2712 with a JIT option, or that the JIT compiler could not handle this par-
2713 ticular pattern. See the pcrejit documentation for details of what can
2714 and cannot be handled.
2715
2716 PCRE_INFO_JITSIZE
2717
2718 If the pattern was successfully studied with a JIT option, return the
2719 size of the JIT compiled code, otherwise return zero. The fourth argu-
2720 ment should point to a size_t variable.
2721
2722 PCRE_INFO_LASTLITERAL
2723
2724 Return the value of the rightmost literal data unit that must exist in
2725 any matched string, other than at its start, if such a value has been
2726 recorded. The fourth argument should point to an int variable. If there
2727 is no such value, -1 is returned. For anchored patterns, a last literal
2728 value is recorded only if it follows something of variable length. For
2729 example, for the pattern /^a\d+z\d+/ the returned value is "z", but for
2730 /^a\dz\d/ the returned value is -1.
2731
2732 Since for the 32-bit library using the non-UTF-32 mode, this function
2733 is unable to return the full 32-bit range of the character, this value
2734 is deprecated; instead the PCRE_INFO_REQUIREDCHARFLAGS and
2735 PCRE_INFO_REQUIREDCHAR values should be used.
2736
2737 PCRE_INFO_MATCHLIMIT
2738
2739 If the pattern set a match limit by including an item of the form
2740 (*LIMIT_MATCH=nnnn) at the start, the value is returned. The fourth
2741 argument should point to an unsigned 32-bit integer. If no such value
2742 has been set, the call to pcre_fullinfo() returns the error
2743 PCRE_ERROR_UNSET.
2744
2745 PCRE_INFO_MAXLOOKBEHIND
2746
2747 Return the number of characters (NB not data units) in the longest
2748 lookbehind assertion in the pattern. This information is useful when
2749 doing multi-segment matching using the partial matching facilities.
2750 Note that the simple assertions \b and \B require a one-character look-
2751 behind. \A also registers a one-character lookbehind, though it does
2752 not actually inspect the previous character. This is to ensure that at
2753 least one character from the old segment is retained when a new segment
2754 is processed. Otherwise, if there are no lookbehinds in the pattern, \A
2755 might match incorrectly at the start of a new segment.
2756
2757 PCRE_INFO_MINLENGTH
2758
2759 If the pattern was studied and a minimum length for matching subject
2760 strings was computed, its value is returned. Otherwise the returned
2761 value is -1. The value is a number of characters, which in UTF mode may
2762 be different from the number of data units. The fourth argument should
2763 point to an int variable. A non-negative value is a lower bound to the
2764 length of any matching string. There may not be any strings of that
2765 length that do actually match, but every string that does match is at
2766 least that long.
2767
2768 PCRE_INFO_NAMECOUNT
2769 PCRE_INFO_NAMEENTRYSIZE
2770 PCRE_INFO_NAMETABLE
2771
2772 PCRE supports the use of named as well as numbered capturing parenthe-
2773 ses. The names are just an additional way of identifying the parenthe-
2774 ses, which still acquire numbers. Several convenience functions such as
2775 pcre_get_named_substring() are provided for extracting captured sub-
2776 strings by name. It is also possible to extract the data directly, by
2777 first converting the name to a number in order to access the correct
2778 pointers in the output vector (described with pcre_exec() below). To do
2779 the conversion, you need to use the name-to-number map, which is
2780 described by these three values.
2781
2782 The map consists of a number of fixed-size entries. PCRE_INFO_NAMECOUNT
2783 gives the number of entries, and PCRE_INFO_NAMEENTRYSIZE gives the size
2784 of each entry; both of these return an int value. The entry size
2785 depends on the length of the longest name. PCRE_INFO_NAMETABLE returns
2786 a pointer to the first entry of the table. This is a pointer to char in
2787 the 8-bit library, where the first two bytes of each entry are the num-
2788 ber of the capturing parenthesis, most significant byte first. In the
2789 16-bit library, the pointer points to 16-bit data units, the first of
2790 which contains the parenthesis number. In the 32-bit library, the
2791 pointer points to 32-bit data units, the first of which contains the
2792 parenthesis number. The rest of the entry is the corresponding name,
2793 zero terminated.
2794
2795 The names are in alphabetical order. Duplicate names may appear if (?|
2796 is used to create multiple groups with the same number, as described in
2797 the section on duplicate subpattern numbers in the pcrepattern page.
2798 Duplicate names for subpatterns with different numbers are permitted
2799 only if PCRE_DUPNAMES is set. In all cases of duplicate names, they
2800 appear in the table in the order in which they were found in the pat-
2801 tern. In the absence of (?| this is the order of increasing number;
2802 when (?| is used this is not necessarily the case because later subpat-
2803 terns may have lower numbers.
2804
2805 As a simple example of the name/number table, consider the following
2806 pattern after compilation by the 8-bit library (assume PCRE_EXTENDED is
2807 set, so white space - including newlines - is ignored):
2808
2809 (?<date> (?<year>(\d\d)?\d\d) -
2810 (?<month>\d\d) - (?<day>\d\d) )
2811
2812 There are four named subpatterns, so the table has four entries, and
2813 each entry in the table is eight bytes long. The table is as follows,
2814 with non-printing bytes shows in hexadecimal, and undefined bytes shown
2815 as ??:
2816
2817 00 01 d a t e 00 ??
2818 00 05 d a y 00 ?? ??
2819 00 04 m o n t h 00
2820 00 02 y e a r 00 ??
2821
2822 When writing code to extract data from named subpatterns using the
2823 name-to-number map, remember that the length of the entries is likely
2824 to be different for each compiled pattern.
2825
2826 PCRE_INFO_OKPARTIAL
2827
2828 Return 1 if the pattern can be used for partial matching with
2829 pcre_exec(), otherwise 0. The fourth argument should point to an int
2830 variable. From release 8.00, this always returns 1, because the
2831 restrictions that previously applied to partial matching have been
2832 lifted. The pcrepartial documentation gives details of partial match-
2833 ing.
2834
2835 PCRE_INFO_OPTIONS
2836
2837 Return a copy of the options with which the pattern was compiled. The
2838 fourth argument should point to an unsigned long int variable. These
2839 option bits are those specified in the call to pcre_compile(), modified
2840 by any top-level option settings at the start of the pattern itself. In
2841 other words, they are the options that will be in force when matching
2842 starts. For example, if the pattern /(?im)abc(?-i)d/ is compiled with
2843 the PCRE_EXTENDED option, the result is PCRE_CASELESS, PCRE_MULTILINE,
2844 and PCRE_EXTENDED.
2845
2846 A pattern is automatically anchored by PCRE if all of its top-level
2847 alternatives begin with one of the following:
2848
2849 ^ unless PCRE_MULTILINE is set
2850 \A always
2851 \G always
2852 .* if PCRE_DOTALL is set and there are no back
2853 references to the subpattern in which .* appears
2854
2855 For such patterns, the PCRE_ANCHORED bit is set in the options returned
2856 by pcre_fullinfo().
2857
2858 PCRE_INFO_RECURSIONLIMIT
2859
2860 If the pattern set a recursion limit by including an item of the form
2861 (*LIMIT_RECURSION=nnnn) at the start, the value is returned. The fourth
2862 argument should point to an unsigned 32-bit integer. If no such value
2863 has been set, the call to pcre_fullinfo() returns the error
2864 PCRE_ERROR_UNSET.
2865
2866 PCRE_INFO_SIZE
2867
2868 Return the size of the compiled pattern in bytes (for all three
2869 libraries). The fourth argument should point to a size_t variable. This
2870 value does not include the size of the pcre structure that is returned
2871 by pcre_compile(). The value that is passed as the argument to
2872 pcre_malloc() when pcre_compile() is getting memory in which to place
2873 the compiled data is the value returned by this option plus the size of
2874 the pcre structure. Studying a compiled pattern, with or without JIT,
2875 does not alter the value returned by this option.
2876
2877 PCRE_INFO_STUDYSIZE
2878
2879 Return the size in bytes (for all three libraries) of the data block
2880 pointed to by the study_data field in a pcre_extra block. If pcre_extra
2881 is NULL, or there is no study data, zero is returned. The fourth argu-
2882 ment should point to a size_t variable. The study_data field is set by
2883 pcre_study() to record information that will speed up matching (see the
2884 section entitled "Studying a pattern" above). The format of the
2885 study_data block is private, but its length is made available via this
2886 option so that it can be saved and restored (see the pcreprecompile
2887 documentation for details).
2888
2889 PCRE_INFO_FIRSTCHARACTERFLAGS
2890
2891 Return information about the first data unit of any matched string, for
2892 a non-anchored pattern. The fourth argument should point to an int
2893 variable.
2894
2895 If there is a fixed first value, for example, the letter "c" from a
2896 pattern such as (cat|cow|coyote), 1 is returned, and the character
2897 value can be retrieved using PCRE_INFO_FIRSTCHARACTER.
2898
2899 If there is no fixed first value, and if either
2900
2901 (a) the pattern was compiled with the PCRE_MULTILINE option, and every
2902 branch starts with "^", or
2903
2904 (b) every branch of the pattern starts with ".*" and PCRE_DOTALL is not
2905 set (if it were set, the pattern would be anchored),
2906
2907 2 is returned, indicating that the pattern matches only at the start of
2908 a subject string or after any newline within the string. Otherwise 0 is
2909 returned. For anchored patterns, 0 is returned.
2910
2911 PCRE_INFO_FIRSTCHARACTER
2912
2913 Return the fixed first character value, if PCRE_INFO_FIRSTCHARACTER-
2914 FLAGS returned 1; otherwise returns 0. The fourth argument should point
2915 to an uint_t variable.
2916
2917 In the 8-bit library, the value is always less than 256. In the 16-bit
2918 library the value can be up to 0xffff. In the 32-bit library in UTF-32
2919 mode the value can be up to 0x10ffff, and up to 0xffffffff when not
2920 using UTF-32 mode.
2921
2922 If there is no fixed first value, and if either
2923
2924 (a) the pattern was compiled with the PCRE_MULTILINE option, and every
2925 branch starts with "^", or
2926
2927 (b) every branch of the pattern starts with ".*" and PCRE_DOTALL is not
2928 set (if it were set, the pattern would be anchored),
2929
2930 -1 is returned, indicating that the pattern matches only at the start
2931 of a subject string or after any newline within the string. Otherwise
2932 -2 is returned. For anchored patterns, -2 is returned.
2933
2934 PCRE_INFO_REQUIREDCHARFLAGS
2935
2936 Returns 1 if there is a rightmost literal data unit that must exist in
2937 any matched string, other than at its start. The fourth argument should
2938 point to an int variable. If there is no such value, 0 is returned. If
2939 returning 1, the character value itself can be retrieved using
2940 PCRE_INFO_REQUIREDCHAR.
2941
2942 For anchored patterns, a last literal value is recorded only if it fol-
2943 lows something of variable length. For example, for the pattern
2944 /^a\d+z\d+/ the returned value 1 (with "z" returned from
2945 PCRE_INFO_REQUIREDCHAR), but for /^a\dz\d/ the returned value is 0.
2946
2947 PCRE_INFO_REQUIREDCHAR
2948
2949 Return the value of the rightmost literal data unit that must exist in
2950 any matched string, other than at its start, if such a value has been
2951 recorded. The fourth argument should point to an uint32_t variable. If
2952 there is no such value, 0 is returned.
2953
2954
2955 REFERENCE COUNTS
2956
2957 int pcre_refcount(pcre *code, int adjust);
2958
2959 The pcre_refcount() function is used to maintain a reference count in
2960 the data block that contains a compiled pattern. It is provided for the
2961 benefit of applications that operate in an object-oriented manner,
2962 where different parts of the application may be using the same compiled
2963 pattern, but you want to free the block when they are all done.
2964
2965 When a pattern is compiled, the reference count field is initialized to
2966 zero. It is changed only by calling this function, whose action is to
2967 add the adjust value (which may be positive or negative) to it. The
2968 yield of the function is the new value. However, the value of the count
2969 is constrained to lie between 0 and 65535, inclusive. If the new value
2970 is outside these limits, it is forced to the appropriate limit value.
2971
2972 Except when it is zero, the reference count is not correctly preserved
2973 if a pattern is compiled on one host and then transferred to a host
2974 whose byte-order is different. (This seems a highly unlikely scenario.)
2975
2976
2977 MATCHING A PATTERN: THE TRADITIONAL FUNCTION
2978
2979 int pcre_exec(const pcre *code, const pcre_extra *extra,
2980 const char *subject, int length, int startoffset,
2981 int options, int *ovector, int ovecsize);
2982
2983 The function pcre_exec() is called to match a subject string against a
2984 compiled pattern, which is passed in the code argument. If the pattern
2985 was studied, the result of the study should be passed in the extra
2986 argument. You can call pcre_exec() with the same code and extra argu-
2987 ments as many times as you like, in order to match different subject
2988 strings with the same pattern.
2989
2990 This function is the main matching facility of the library, and it
2991 operates in a Perl-like manner. For specialist use there is also an
2992 alternative matching function, which is described below in the section
2993 about the pcre_dfa_exec() function.
2994
2995 In most applications, the pattern will have been compiled (and option-
2996 ally studied) in the same process that calls pcre_exec(). However, it
2997 is possible to save compiled patterns and study data, and then use them
2998 later in different processes, possibly even on different hosts. For a
2999 discussion about this, see the pcreprecompile documentation.
3000
3001 Here is an example of a simple call to pcre_exec():
3002
3003 int rc;
3004 int ovector[30];
3005 rc = pcre_exec(
3006 re, /* result of pcre_compile() */
3007 NULL, /* we didn't study the pattern */
3008 "some string", /* the subject string */
3009 11, /* the length of the subject string */
3010 0, /* start at offset 0 in the subject */
3011 0, /* default options */
3012 ovector, /* vector of integers for substring information */
3013 30); /* number of elements (NOT size in bytes) */
3014
3015 Extra data for pcre_exec()
3016
3017 If the extra argument is not NULL, it must point to a pcre_extra data
3018 block. The pcre_study() function returns such a block (when it doesn't
3019 return NULL), but you can also create one for yourself, and pass addi-
3020 tional information in it. The pcre_extra block contains the following
3021 fields (not necessarily in this order):
3022
3023 unsigned long int flags;
3024 void *study_data;
3025 void *executable_jit;
3026 unsigned long int match_limit;
3027 unsigned long int match_limit_recursion;
3028 void *callout_data;
3029 const unsigned char *tables;
3030 unsigned char **mark;
3031
3032 In the 16-bit version of this structure, the mark field has type
3033 "PCRE_UCHAR16 **".
3034
3035 In the 32-bit version of this structure, the mark field has type
3036 "PCRE_UCHAR32 **".
3037
3038 The flags field is used to specify which of the other fields are set.
3039 The flag bits are:
3040
3041 PCRE_EXTRA_CALLOUT_DATA
3042 PCRE_EXTRA_EXECUTABLE_JIT
3043 PCRE_EXTRA_MARK
3044 PCRE_EXTRA_MATCH_LIMIT
3045 PCRE_EXTRA_MATCH_LIMIT_RECURSION
3046 PCRE_EXTRA_STUDY_DATA
3047 PCRE_EXTRA_TABLES
3048
3049 Other flag bits should be set to zero. The study_data field and some-
3050 times the executable_jit field are set in the pcre_extra block that is
3051 returned by pcre_study(), together with the appropriate flag bits. You
3052 should not set these yourself, but you may add to the block by setting
3053 other fields and their corresponding flag bits.
3054
3055 The match_limit field provides a means of preventing PCRE from using up
3056 a vast amount of resources when running patterns that are not going to
3057 match, but which have a very large number of possibilities in their
3058 search trees. The classic example is a pattern that uses nested unlim-
3059 ited repeats.
3060
3061 Internally, pcre_exec() uses a function called match(), which it calls
3062 repeatedly (sometimes recursively). The limit set by match_limit is
3063 imposed on the number of times this function is called during a match,
3064 which has the effect of limiting the amount of backtracking that can
3065 take place. For patterns that are not anchored, the count restarts from
3066 zero for each position in the subject string.
3067
3068 When pcre_exec() is called with a pattern that was successfully studied
3069 with a JIT option, the way that the matching is executed is entirely
3070 different. However, there is still the possibility of runaway matching
3071 that goes on for a very long time, and so the match_limit value is also
3072 used in this case (but in a different way) to limit how long the match-
3073 ing can continue.
3074
3075 The default value for the limit can be set when PCRE is built; the
3076 default default is 10 million, which handles all but the most extreme
3077 cases. You can override the default by suppling pcre_exec() with a
3078 pcre_extra block in which match_limit is set, and
3079 PCRE_EXTRA_MATCH_LIMIT is set in the flags field. If the limit is
3080 exceeded, pcre_exec() returns PCRE_ERROR_MATCHLIMIT.
3081
3082 A value for the match limit may also be supplied by an item at the
3083 start of a pattern of the form
3084
3085 (*LIMIT_MATCH=d)
3086
3087 where d is a decimal number. However, such a setting is ignored unless
3088 d is less than the limit set by the caller of pcre_exec() or, if no
3089 such limit is set, less than the default.
3090
3091 The match_limit_recursion field is similar to match_limit, but instead
3092 of limiting the total number of times that match() is called, it limits
3093 the depth of recursion. The recursion depth is a smaller number than
3094 the total number of calls, because not all calls to match() are recur-
3095 sive. This limit is of use only if it is set smaller than match_limit.
3096
3097 Limiting the recursion depth limits the amount of machine stack that
3098 can be used, or, when PCRE has been compiled to use memory on the heap
3099 instead of the stack, the amount of heap memory that can be used. This
3100 limit is not relevant, and is ignored, when matching is done using JIT
3101 compiled code.
3102
3103 The default value for match_limit_recursion can be set when PCRE is
3104 built; the default default is the same value as the default for
3105 match_limit. You can override the default by suppling pcre_exec() with
3106 a pcre_extra block in which match_limit_recursion is set, and
3107 PCRE_EXTRA_MATCH_LIMIT_RECURSION is set in the flags field. If the
3108 limit is exceeded, pcre_exec() returns PCRE_ERROR_RECURSIONLIMIT.
3109
3110 A value for the recursion limit may also be supplied by an item at the
3111 start of a pattern of the form
3112
3113 (*LIMIT_RECURSION=d)
3114
3115 where d is a decimal number. However, such a setting is ignored unless
3116 d is less than the limit set by the caller of pcre_exec() or, if no
3117 such limit is set, less than the default.
3118
3119 The callout_data field is used in conjunction with the "callout" fea-
3120 ture, and is described in the pcrecallout documentation.
3121
3122 The tables field is used to pass a character tables pointer to
3123 pcre_exec(); this overrides the value that is stored with the compiled
3124 pattern. A non-NULL value is stored with the compiled pattern only if
3125 custom tables were supplied to pcre_compile() via its tableptr argu-
3126 ment. If NULL is passed to pcre_exec() using this mechanism, it forces
3127 PCRE's internal tables to be used. This facility is helpful when re-
3128 using patterns that have been saved after compiling with an external
3129 set of tables, because the external tables might be at a different
3130 address when pcre_exec() is called. See the pcreprecompile documenta-
3131 tion for a discussion of saving compiled patterns for later use.
3132
3133 If PCRE_EXTRA_MARK is set in the flags field, the mark field must be
3134 set to point to a suitable variable. If the pattern contains any back-
3135 tracking control verbs such as (*MARK:NAME), and the execution ends up
3136 with a name to pass back, a pointer to the name string (zero termi-
3137 nated) is placed in the variable pointed to by the mark field. The
3138 names are within the compiled pattern; if you wish to retain such a
3139 name you must copy it before freeing the memory of a compiled pattern.
3140 If there is no name to pass back, the variable pointed to by the mark
3141 field is set to NULL. For details of the backtracking control verbs,
3142 see the section entitled "Backtracking control" in the pcrepattern doc-
3143 umentation.
3144
3145 Option bits for pcre_exec()
3146
3147 The unused bits of the options argument for pcre_exec() must be zero.
3148 The only bits that may be set are PCRE_ANCHORED, PCRE_NEWLINE_xxx,
3149 PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, PCRE_NOTEMPTY_ATSTART,
3150 PCRE_NO_START_OPTIMIZE, PCRE_NO_UTF8_CHECK, PCRE_PARTIAL_HARD, and
3151 PCRE_PARTIAL_SOFT.
3152
3153 If the pattern was successfully studied with one of the just-in-time
3154 (JIT) compile options, the only supported options for JIT execution are
3155 PCRE_NO_UTF8_CHECK, PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY,
3156 PCRE_NOTEMPTY_ATSTART, PCRE_PARTIAL_HARD, and PCRE_PARTIAL_SOFT. If an
3157 unsupported option is used, JIT execution is disabled and the normal
3158 interpretive code in pcre_exec() is run.
3159
3160 PCRE_ANCHORED
3161
3162 The PCRE_ANCHORED option limits pcre_exec() to matching at the first
3163 matching position. If a pattern was compiled with PCRE_ANCHORED, or
3164 turned out to be anchored by virtue of its contents, it cannot be made
3165 unachored at matching time.
3166
3167 PCRE_BSR_ANYCRLF
3168 PCRE_BSR_UNICODE
3169
3170 These options (which are mutually exclusive) control what the \R escape
3171 sequence matches. The choice is either to match only CR, LF, or CRLF,
3172 or to match any Unicode newline sequence. These options override the
3173 choice that was made or defaulted when the pattern was compiled.
3174
3175 PCRE_NEWLINE_CR
3176 PCRE_NEWLINE_LF
3177 PCRE_NEWLINE_CRLF
3178 PCRE_NEWLINE_ANYCRLF
3179 PCRE_NEWLINE_ANY
3180
3181 These options override the newline definition that was chosen or
3182 defaulted when the pattern was compiled. For details, see the descrip-
3183 tion of pcre_compile() above. During matching, the newline choice
3184 affects the behaviour of the dot, circumflex, and dollar metacharac-
3185 ters. It may also alter the way the match position is advanced after a
3186 match failure for an unanchored pattern.
3187
3188 When PCRE_NEWLINE_CRLF, PCRE_NEWLINE_ANYCRLF, or PCRE_NEWLINE_ANY is
3189 set, and a match attempt for an unanchored pattern fails when the cur-
3190 rent position is at a CRLF sequence, and the pattern contains no
3191 explicit matches for CR or LF characters, the match position is
3192 advanced by two characters instead of one, in other words, to after the
3193 CRLF.
3194
3195 The above rule is a compromise that makes the most common cases work as
3196 expected. For example, if the pattern is .+A (and the PCRE_DOTALL
3197 option is not set), it does not match the string "\r\nA" because, after
3198 failing at the start, it skips both the CR and the LF before retrying.
3199 However, the pattern [\r\n]A does match that string, because it con-
3200 tains an explicit CR or LF reference, and so advances only by one char-
3201 acter after the first failure.
3202
3203 An explicit match for CR of LF is either a literal appearance of one of
3204 those characters, or one of the \r or \n escape sequences. Implicit
3205 matches such as [^X] do not count, nor does \s (which includes CR and
3206 LF in the characters that it matches).
3207
3208 Notwithstanding the above, anomalous effects may still occur when CRLF
3209 is a valid newline sequence and explicit \r or \n escapes appear in the
3210 pattern.
3211
3212 PCRE_NOTBOL
3213
3214 This option specifies that first character of the subject string is not
3215 the beginning of a line, so the circumflex metacharacter should not
3216 match before it. Setting this without PCRE_MULTILINE (at compile time)
3217 causes circumflex never to match. This option affects only the behav-
3218 iour of the circumflex metacharacter. It does not affect \A.
3219
3220 PCRE_NOTEOL
3221
3222 This option specifies that the end of the subject string is not the end
3223 of a line, so the dollar metacharacter should not match it nor (except
3224 in multiline mode) a newline immediately before it. Setting this with-
3225 out PCRE_MULTILINE (at compile time) causes dollar never to match. This
3226 option affects only the behaviour of the dollar metacharacter. It does
3227 not affect \Z or \z.
3228
3229 PCRE_NOTEMPTY
3230
3231 An empty string is not considered to be a valid match if this option is
3232 set. If there are alternatives in the pattern, they are tried. If all
3233 the alternatives match the empty string, the entire match fails. For
3234 example, if the pattern
3235
3236 a?b?
3237
3238 is applied to a string not beginning with "a" or "b", it matches an
3239 empty string at the start of the subject. With PCRE_NOTEMPTY set, this
3240 match is not valid, so PCRE searches further into the string for occur-
3241 rences of "a" or "b".
3242
3243 PCRE_NOTEMPTY_ATSTART
3244
3245 This is like PCRE_NOTEMPTY, except that an empty string match that is
3246 not at the start of the subject is permitted. If the pattern is
3247 anchored, such a match can occur only if the pattern contains \K.
3248
3249 Perl has no direct equivalent of PCRE_NOTEMPTY or
3250 PCRE_NOTEMPTY_ATSTART, but it does make a special case of a pattern
3251 match of the empty string within its split() function, and when using
3252 the /g modifier. It is possible to emulate Perl's behaviour after
3253 matching a null string by first trying the match again at the same off-
3254 set with PCRE_NOTEMPTY_ATSTART and PCRE_ANCHORED, and then if that
3255 fails, by advancing the starting offset (see below) and trying an ordi-
3256 nary match again. There is some code that demonstrates how to do this
3257 in the pcredemo sample program. In the most general case, you have to
3258 check to see if the newline convention recognizes CRLF as a newline,
3259 and if so, and the current character is CR followed by LF, advance the
3260 starting offset by two characters instead of one.
3261
3262 PCRE_NO_START_OPTIMIZE
3263
3264 There are a number of optimizations that pcre_exec() uses at the start
3265 of a match, in order to speed up the process. For example, if it is
3266 known that an unanchored match must start with a specific character, it
3267 searches the subject for that character, and fails immediately if it
3268 cannot find it, without actually running the main matching function.
3269 This means that a special item such as (*COMMIT) at the start of a pat-
3270 tern is not considered until after a suitable starting point for the
3271 match has been found. Also, when callouts or (*MARK) items are in use,
3272 these "start-up" optimizations can cause them to be skipped if the pat-
3273 tern is never actually used. The start-up optimizations are in effect a
3274 pre-scan of the subject that takes place before the pattern is run.
3275
3276 The PCRE_NO_START_OPTIMIZE option disables the start-up optimizations,
3277 possibly causing performance to suffer, but ensuring that in cases
3278 where the result is "no match", the callouts do occur, and that items
3279 such as (*COMMIT) and (*MARK) are considered at every possible starting
3280 position in the subject string. If PCRE_NO_START_OPTIMIZE is set at
3281 compile time, it cannot be unset at matching time. The use of
3282 PCRE_NO_START_OPTIMIZE at matching time (that is, passing it to
3283 pcre_exec()) disables JIT execution; in this situation, matching is
3284 always done using interpretively.
3285
3286 Setting PCRE_NO_START_OPTIMIZE can change the outcome of a matching
3287 operation. Consider the pattern
3288
3289 (*COMMIT)ABC
3290
3291 When this is compiled, PCRE records the fact that a match must start
3292 with the character "A". Suppose the subject string is "DEFABC". The
3293 start-up optimization scans along the subject, finds "A" and runs the
3294 first match attempt from there. The (*COMMIT) item means that the pat-
3295 tern must match the current starting position, which in this case, it
3296 does. However, if the same match is run with PCRE_NO_START_OPTIMIZE
3297 set, the initial scan along the subject string does not happen. The
3298 first match attempt is run starting from "D" and when this fails,
3299 (*COMMIT) prevents any further matches being tried, so the overall
3300 result is "no match". If the pattern is studied, more start-up opti-
3301 mizations may be used. For example, a minimum length for the subject
3302 may be recorded. Consider the pattern
3303
3304 (*MARK:A)(X|Y)
3305
3306 The minimum length for a match is one character. If the subject is
3307 "ABC", there will be attempts to match "ABC", "BC", "C", and then
3308 finally an empty string. If the pattern is studied, the final attempt
3309 does not take place, because PCRE knows that the subject is too short,
3310 and so the (*MARK) is never encountered. In this case, studying the
3311 pattern does not affect the overall match result, which is still "no
3312 match", but it does affect the auxiliary information that is returned.
3313
3314 PCRE_NO_UTF8_CHECK
3315
3316 When PCRE_UTF8 is set at compile time, the validity of the subject as a
3317 UTF-8 string is automatically checked when pcre_exec() is subsequently
3318 called. The entire string is checked before any other processing takes
3319 place. The value of startoffset is also checked to ensure that it
3320 points to the start of a UTF-8 character. There is a discussion about
3321 the validity of UTF-8 strings in the pcreunicode page. If an invalid
3322 sequence of bytes is found, pcre_exec() returns the error
3323 PCRE_ERROR_BADUTF8 or, if PCRE_PARTIAL_HARD is set and the problem is a
3324 truncated character at the end of the subject, PCRE_ERROR_SHORTUTF8. In
3325 both cases, information about the precise nature of the error may also
3326 be returned (see the descriptions of these errors in the section enti-
3327 tled Error return values from pcre_exec() below). If startoffset con-
3328 tains a value that does not point to the start of a UTF-8 character (or
3329 to the end of the subject), PCRE_ERROR_BADUTF8_OFFSET is returned.
3330
3331 If you already know that your subject is valid, and you want to skip
3332 these checks for performance reasons, you can set the
3333 PCRE_NO_UTF8_CHECK option when calling pcre_exec(). You might want to
3334 do this for the second and subsequent calls to pcre_exec() if you are
3335 making repeated calls to find all the matches in a single subject
3336 string. However, you should be sure that the value of startoffset
3337 points to the start of a character (or the end of the subject). When
3338 PCRE_NO_UTF8_CHECK is set, the effect of passing an invalid string as a
3339 subject or an invalid value of startoffset is undefined. Your program
3340 may crash.
3341
3342 PCRE_PARTIAL_HARD
3343 PCRE_PARTIAL_SOFT
3344
3345 These options turn on the partial matching feature. For backwards com-
3346 patibility, PCRE_PARTIAL is a synonym for PCRE_PARTIAL_SOFT. A partial
3347 match occurs if the end of the subject string is reached successfully,
3348 but there are not enough subject characters to complete the match. If
3349 this happens when PCRE_PARTIAL_SOFT (but not PCRE_PARTIAL_HARD) is set,
3350 matching continues by testing any remaining alternatives. Only if no
3351 complete match can be found is PCRE_ERROR_PARTIAL returned instead of
3352 PCRE_ERROR_NOMATCH. In other words, PCRE_PARTIAL_SOFT says that the
3353 caller is prepared to handle a partial match, but only if no complete
3354 match can be found.
3355
3356 If PCRE_PARTIAL_HARD is set, it overrides PCRE_PARTIAL_SOFT. In this
3357 case, if a partial match is found, pcre_exec() immediately returns
3358 PCRE_ERROR_PARTIAL, without considering any other alternatives. In
3359 other words, when PCRE_PARTIAL_HARD is set, a partial match is consid-
3360 ered to be more important that an alternative complete match.
3361
3362 In both cases, the portion of the string that was inspected when the
3363 partial match was found is set as the first matching string. There is a
3364 more detailed discussion of partial and multi-segment matching, with
3365 examples, in the pcrepartial documentation.
3366
3367 The string to be matched by pcre_exec()
3368
3369 The subject string is passed to pcre_exec() as a pointer in subject, a
3370 length in length, and a starting offset in startoffset. The units for
3371 length and startoffset are bytes for the 8-bit library, 16-bit data
3372 items for the 16-bit library, and 32-bit data items for the 32-bit
3373 library.
3374
3375 If startoffset is negative or greater than the length of the subject,
3376 pcre_exec() returns PCRE_ERROR_BADOFFSET. When the starting offset is
3377 zero, the search for a match starts at the beginning of the subject,
3378 and this is by far the most common case. In UTF-8 or UTF-16 mode, the
3379 offset must point to the start of a character, or the end of the sub-
3380 ject (in UTF-32 mode, one data unit equals one character, so all off-
3381 sets are valid). Unlike the pattern string, the subject may contain
3382 binary zeroes.
3383
3384 A non-zero starting offset is useful when searching for another match
3385 in the same subject by calling pcre_exec() again after a previous suc-
3386 cess. Setting startoffset differs from just passing over a shortened
3387 string and setting PCRE_NOTBOL in the case of a pattern that begins
3388 with any kind of lookbehind. For example, consider the pattern
3389
3390 \Biss\B
3391
3392 which finds occurrences of "iss" in the middle of words. (\B matches
3393 only if the current position in the subject is not a word boundary.)
3394 When applied to the string "Mississipi" the first call to pcre_exec()
3395 finds the first occurrence. If pcre_exec() is called again with just
3396 the remainder of the subject, namely "issipi", it does not match,
3397 because \B is always false at the start of the subject, which is deemed
3398 to be a word boundary. However, if pcre_exec() is passed the entire
3399 string again, but with startoffset set to 4, it finds the second occur-
3400 rence of "iss" because it is able to look behind the starting point to
3401 discover that it is preceded by a letter.
3402
3403 Finding all the matches in a subject is tricky when the pattern can
3404 match an empty string. It is possible to emulate Perl's /g behaviour by
3405 first trying the match again at the same offset, with the
3406 PCRE_NOTEMPTY_ATSTART and PCRE_ANCHORED options, and then if that
3407 fails, advancing the starting offset and trying an ordinary match
3408 again. There is some code that demonstrates how to do this in the pcre-
3409 demo sample program. In the most general case, you have to check to see
3410 if the newline convention recognizes CRLF as a newline, and if so, and
3411 the current character is CR followed by LF, advance the starting offset
3412 by two characters instead of one.
3413
3414 If a non-zero starting offset is passed when the pattern is anchored,
3415 one attempt to match at the given offset is made. This can only succeed
3416 if the pattern does not require the match to be at the start of the
3417 subject.
3418
3419 How pcre_exec() returns captured substrings
3420
3421 In general, a pattern matches a certain portion of the subject, and in
3422 addition, further substrings from the subject may be picked out by
3423 parts of the pattern. Following the usage in Jeffrey Friedl's book,
3424 this is called "capturing" in what follows, and the phrase "capturing
3425 subpattern" is used for a fragment of a pattern that picks out a sub-
3426 string. PCRE supports several other kinds of parenthesized subpattern
3427 that do not cause substrings to be captured.
3428
3429 Captured substrings are returned to the caller via a vector of integers
3430 whose address is passed in ovector. The number of elements in the vec-
3431 tor is passed in ovecsize, which must be a non-negative number. Note:
3432 this argument is NOT the size of ovector in bytes.
3433
3434 The first two-thirds of the vector is used to pass back captured sub-
3435 strings, each substring using a pair of integers. The remaining third
3436 of the vector is used as workspace by pcre_exec() while matching cap-
3437 turing subpatterns, and is not available for passing back information.
3438 The number passed in ovecsize should always be a multiple of three. If
3439 it is not, it is rounded down.
3440
3441 When a match is successful, information about captured substrings is
3442 returned in pairs of integers, starting at the beginning of ovector,
3443 and continuing up to two-thirds of its length at the most. The first
3444 element of each pair is set to the offset of the first character in a
3445 substring, and the second is set to the offset of the first character
3446 after the end of a substring. These values are always data unit off-
3447 sets, even in UTF mode. They are byte offsets in the 8-bit library,
3448 16-bit data item offsets in the 16-bit library, and 32-bit data item
3449 offsets in the 32-bit library. Note: they are not character counts.
3450
3451 The first pair of integers, ovector[0] and ovector[1], identify the
3452 portion of the subject string matched by the entire pattern. The next
3453 pair is used for the first capturing subpattern, and so on. The value
3454 returned by pcre_exec() is one more than the highest numbered pair that
3455 has been set. For example, if two substrings have been captured, the
3456 returned value is 3. If there are no capturing subpatterns, the return
3457 value from a successful match is 1, indicating that just the first pair
3458 of offsets has been set.
3459
3460 If a capturing subpattern is matched repeatedly, it is the last portion
3461 of the string that it matched that is returned.
3462
3463 If the vector is too small to hold all the captured substring offsets,
3464 it is used as far as possible (up to two-thirds of its length), and the
3465 function returns a value of zero. If neither the actual string matched
3466 nor any captured substrings are of interest, pcre_exec() may be called
3467 with ovector passed as NULL and ovecsize as zero. However, if the pat-
3468 tern contains back references and the ovector is not big enough to
3469 remember the related substrings, PCRE has to get additional memory for
3470 use during matching. Thus it is usually advisable to supply an ovector
3471 of reasonable size.
3472
3473 There are some cases where zero is returned (indicating vector over-
3474 flow) when in fact the vector is exactly the right size for the final
3475 match. For example, consider the pattern
3476
3477 (a)(?:(b)c|bd)
3478
3479 If a vector of 6 elements (allowing for only 1 captured substring) is
3480 given with subject string "abd", pcre_exec() will try to set the second
3481 captured string, thereby recording a vector overflow, before failing to
3482 match "c" and backing up to try the second alternative. The zero
3483 return, however, does correctly indicate that the maximum number of
3484 slots (namely 2) have been filled. In similar cases where there is tem-
3485 porary overflow, but the final number of used slots is actually less
3486 than the maximum, a non-zero value is returned.
3487
3488 The pcre_fullinfo() function can be used to find out how many capturing
3489 subpatterns there are in a compiled pattern. The smallest size for
3490 ovector that will allow for n captured substrings, in addition to the
3491 offsets of the substring matched by the whole pattern, is (n+1)*3.
3492
3493 It is possible for capturing subpattern number n+1 to match some part
3494 of the subject when subpattern n has not been used at all. For example,
3495 if the string "abc" is matched against the pattern (a|(z))(bc) the
3496 return from the function is 4, and subpatterns 1 and 3 are matched, but
3497 2 is not. When this happens, both values in the offset pairs corre-
3498 sponding to unused subpatterns are set to -1.
3499
3500 Offset values that correspond to unused subpatterns at the end of the
3501 expression are also set to -1. For example, if the string "abc" is
3502 matched against the pattern (abc)(x(yz)?)? subpatterns 2 and 3 are not
3503 matched. The return from the function is 2, because the highest used
3504 capturing subpattern number is 1, and the offsets for for the second
3505 and third capturing subpatterns (assuming the vector is large enough,
3506 of course) are set to -1.
3507
3508 Note: Elements in the first two-thirds of ovector that do not corre-
3509 spond to capturing parentheses in the pattern are never changed. That
3510 is, if a pattern contains n capturing parentheses, no more than ovec-
3511 tor[0] to ovector[2n+1] are set by pcre_exec(). The other elements (in
3512 the first two-thirds) retain whatever values they previously had.
3513
3514 Some convenience functions are provided for extracting the captured
3515 substrings as separate strings. These are described below.
3516
3517 Error return values from pcre_exec()
3518
3519 If pcre_exec() fails, it returns a negative number. The following are
3520 defined in the header file:
3521
3522 PCRE_ERROR_NOMATCH (-1)
3523
3524 The subject string did not match the pattern.
3525
3526 PCRE_ERROR_NULL (-2)
3527
3528 Either code or subject was passed as NULL, or ovector was NULL and
3529 ovecsize was not zero.
3530
3531 PCRE_ERROR_BADOPTION (-3)
3532
3533 An unrecognized bit was set in the options argument.
3534
3535 PCRE_ERROR_BADMAGIC (-4)
3536
3537 PCRE stores a 4-byte "magic number" at the start of the compiled code,
3538 to catch the case when it is passed a junk pointer and to detect when a
3539 pattern that was compiled in an environment of one endianness is run in
3540 an environment with the other endianness. This is the error that PCRE
3541 gives when the magic number is not present.
3542
3543 PCRE_ERROR_UNKNOWN_OPCODE (-5)
3544
3545 While running the pattern match, an unknown item was encountered in the
3546 compiled pattern. This error could be caused by a bug in PCRE or by
3547 overwriting of the compiled pattern.
3548
3549 PCRE_ERROR_NOMEMORY (-6)
3550
3551 If a pattern contains back references, but the ovector that is passed
3552 to pcre_exec() is not big enough to remember the referenced substrings,
3553 PCRE gets a block of memory at the start of matching to use for this
3554 purpose. If the call via pcre_malloc() fails, this error is given. The
3555 memory is automatically freed at the end of matching.
3556
3557 This error is also given if pcre_stack_malloc() fails in pcre_exec().
3558 This can happen only when PCRE has been compiled with --disable-stack-
3559 for-recursion.
3560
3561 PCRE_ERROR_NOSUBSTRING (-7)
3562
3563 This error is used by the pcre_copy_substring(), pcre_get_substring(),
3564 and pcre_get_substring_list() functions (see below). It is never
3565 returned by pcre_exec().
3566
3567 PCRE_ERROR_MATCHLIMIT (-8)
3568
3569 The backtracking limit, as specified by the match_limit field in a
3570 pcre_extra structure (or defaulted) was reached. See the description
3571 above.
3572
3573 PCRE_ERROR_CALLOUT (-9)
3574
3575 This error is never generated by pcre_exec() itself. It is provided for
3576 use by callout functions that want to yield a distinctive error code.
3577 See the pcrecallout documentation for details.
3578
3579 PCRE_ERROR_BADUTF8 (-10)
3580
3581 A string that contains an invalid UTF-8 byte sequence was passed as a
3582 subject, and the PCRE_NO_UTF8_CHECK option was not set. If the size of
3583 the output vector (ovecsize) is at least 2, the byte offset to the
3584 start of the the invalid UTF-8 character is placed in the first ele-
3585 ment, and a reason code is placed in the second element. The reason
3586 codes are listed in the following section. For backward compatibility,
3587 if PCRE_PARTIAL_HARD is set and the problem is a truncated UTF-8 char-
3588 acter at the end of the subject (reason codes 1 to 5),
3589 PCRE_ERROR_SHORTUTF8 is returned instead of PCRE_ERROR_BADUTF8.
3590
3591 PCRE_ERROR_BADUTF8_OFFSET (-11)
3592
3593 The UTF-8 byte sequence that was passed as a subject was checked and
3594 found to be valid (the PCRE_NO_UTF8_CHECK option was not set), but the
3595 value of startoffset did not point to the beginning of a UTF-8 charac-
3596 ter or the end of the subject.
3597
3598 PCRE_ERROR_PARTIAL (-12)
3599
3600 The subject string did not match, but it did match partially. See the
3601 pcrepartial documentation for details of partial matching.
3602
3603 PCRE_ERROR_BADPARTIAL (-13)
3604
3605 This code is no longer in use. It was formerly returned when the
3606 PCRE_PARTIAL option was used with a compiled pattern containing items
3607 that were not supported for partial matching. From release 8.00
3608 onwards, there are no restrictions on partial matching.
3609
3610 PCRE_ERROR_INTERNAL (-14)
3611
3612 An unexpected internal error has occurred. This error could be caused
3613 by a bug in PCRE or by overwriting of the compiled pattern.
3614
3615 PCRE_ERROR_BADCOUNT (-15)
3616
3617 This error is given if the value of the ovecsize argument is negative.
3618
3619 PCRE_ERROR_RECURSIONLIMIT (-21)
3620
3621 The internal recursion limit, as specified by the match_limit_recursion
3622 field in a pcre_extra structure (or defaulted) was reached. See the
3623 description above.
3624
3625 PCRE_ERROR_BADNEWLINE (-23)
3626
3627 An invalid combination of PCRE_NEWLINE_xxx options was given.
3628
3629 PCRE_ERROR_BADOFFSET (-24)
3630
3631 The value of startoffset was negative or greater than the length of the
3632 subject, that is, the value in length.
3633
3634 PCRE_ERROR_SHORTUTF8 (-25)
3635
3636 This error is returned instead of PCRE_ERROR_BADUTF8 when the subject
3637 string ends with a truncated UTF-8 character and the PCRE_PARTIAL_HARD
3638 option is set. Information about the failure is returned as for
3639 PCRE_ERROR_BADUTF8. It is in fact sufficient to detect this case, but
3640 this special error code for PCRE_PARTIAL_HARD precedes the implementa-
3641 tion of returned information; it is retained for backwards compatibil-
3642 ity.
3643
3644 PCRE_ERROR_RECURSELOOP (-26)
3645
3646 This error is returned when pcre_exec() detects a recursion loop within
3647 the pattern. Specifically, it means that either the whole pattern or a
3648 subpattern has been called recursively for the second time at the same
3649 position in the subject string. Some simple patterns that might do this
3650 are detected and faulted at compile time, but more complicated cases,
3651 in particular mutual recursions between two different subpatterns, can-
3652 not be detected until run time.
3653
3654 PCRE_ERROR_JIT_STACKLIMIT (-27)
3655
3656 This error is returned when a pattern that was successfully studied
3657 using a JIT compile option is being matched, but the memory available
3658 for the just-in-time processing stack is not large enough. See the
3659 pcrejit documentation for more details.
3660
3661 PCRE_ERROR_BADMODE (-28)
3662
3663 This error is given if a pattern that was compiled by the 8-bit library
3664 is passed to a 16-bit or 32-bit library function, or vice versa.
3665
3666 PCRE_ERROR_BADENDIANNESS (-29)
3667
3668 This error is given if a pattern that was compiled and saved is
3669 reloaded on a host with different endianness. The utility function
3670 pcre_pattern_to_host_byte_order() can be used to convert such a pattern
3671 so that it runs on the new host.
3672
3673 PCRE_ERROR_JIT_BADOPTION
3674
3675 This error is returned when a pattern that was successfully studied
3676 using a JIT compile option is being matched, but the matching mode
3677 (partial or complete match) does not correspond to any JIT compilation
3678 mode. When the JIT fast path function is used, this error may be also
3679 given for invalid options. See the pcrejit documentation for more
3680 details.
3681
3682 PCRE_ERROR_BADLENGTH (-32)
3683
3684 This error is given if pcre_exec() is called with a negative value for
3685 the length argument.
3686
3687 Error numbers -16 to -20, -22, and 30 are not used by pcre_exec().
3688
3689 Reason codes for invalid UTF-8 strings
3690
3691 This section applies only to the 8-bit library. The corresponding
3692 information for the 16-bit and 32-bit libraries is given in the pcre16
3693 and pcre32 pages.
3694
3695 When pcre_exec() returns either PCRE_ERROR_BADUTF8 or PCRE_ERROR_SHORT-
3696 UTF8, and the size of the output vector (ovecsize) is at least 2, the
3697 offset of the start of the invalid UTF-8 character is placed in the
3698 first output vector element (ovector[0]) and a reason code is placed in
3699 the second element (ovector[1]). The reason codes are given names in
3700 the pcre.h header file:
3701
3702 PCRE_UTF8_ERR1
3703 PCRE_UTF8_ERR2
3704 PCRE_UTF8_ERR3
3705 PCRE_UTF8_ERR4
3706 PCRE_UTF8_ERR5
3707
3708 The string ends with a truncated UTF-8 character; the code specifies
3709 how many bytes are missing (1 to 5). Although RFC 3629 restricts UTF-8
3710 characters to be no longer than 4 bytes, the encoding scheme (origi-
3711 nally defined by RFC 2279) allows for up to 6 bytes, and this is
3712 checked first; hence the possibility of 4 or 5 missing bytes.
3713
3714 PCRE_UTF8_ERR6
3715 PCRE_UTF8_ERR7
3716 PCRE_UTF8_ERR8
3717 PCRE_UTF8_ERR9
3718 PCRE_UTF8_ERR10
3719
3720 The two most significant bits of the 2nd, 3rd, 4th, 5th, or 6th byte of
3721 the character do not have the binary value 0b10 (that is, either the
3722 most significant bit is 0, or the next bit is 1).
3723
3724 PCRE_UTF8_ERR11
3725 PCRE_UTF8_ERR12
3726
3727 A character that is valid by the RFC 2279 rules is either 5 or 6 bytes
3728 long; these code points are excluded by RFC 3629.
3729
3730 PCRE_UTF8_ERR13
3731
3732 A 4-byte character has a value greater than 0x10fff; these code points
3733 are excluded by RFC 3629.
3734
3735 PCRE_UTF8_ERR14
3736
3737 A 3-byte character has a value in the range 0xd800 to 0xdfff; this
3738 range of code points are reserved by RFC 3629 for use with UTF-16, and
3739 so are excluded from UTF-8.
3740
3741 PCRE_UTF8_ERR15
3742 PCRE_UTF8_ERR16
3743 PCRE_UTF8_ERR17
3744 PCRE_UTF8_ERR18
3745 PCRE_UTF8_ERR19
3746
3747 A 2-, 3-, 4-, 5-, or 6-byte character is "overlong", that is, it codes
3748 for a value that can be represented by fewer bytes, which is invalid.
3749 For example, the two bytes 0xc0, 0xae give the value 0x2e, whose cor-
3750 rect coding uses just one byte.
3751
3752 PCRE_UTF8_ERR20
3753
3754 The two most significant bits of the first byte of a character have the
3755 binary value 0b10 (that is, the most significant bit is 1 and the sec-
3756 ond is 0). Such a byte can only validly occur as the second or subse-
3757 quent byte of a multi-byte character.
3758
3759 PCRE_UTF8_ERR21
3760
3761 The first byte of a character has the value 0xfe or 0xff. These values
3762 can never occur in a valid UTF-8 string.
3763
3764 PCRE_UTF8_ERR22
3765
3766 This error code was formerly used when the presence of a so-called
3767 "non-character" caused an error. Unicode corrigendum #9 makes it clear
3768 that such characters should not cause a string to be rejected, and so
3769 this code is no longer in use and is never returned.
3770
3771
3772 EXTRACTING CAPTURED SUBSTRINGS BY NUMBER
3773
3774 int pcre_copy_substring(const char *subject, int *ovector,
3775 int stringcount, int stringnumber, char *buffer,
3776 int buffersize);
3777
3778 int pcre_get_substring(const char *subject, int *ovector,
3779 int stringcount, int stringnumber,
3780 const char **stringptr);
3781
3782 int pcre_get_substring_list(const char *subject,
3783 int *ovector, int stringcount, const char ***listptr);
3784
3785 Captured substrings can be accessed directly by using the offsets
3786 returned by pcre_exec() in ovector. For convenience, the functions
3787 pcre_copy_substring(), pcre_get_substring(), and pcre_get_sub-
3788 string_list() are provided for extracting captured substrings as new,
3789 separate, zero-terminated strings. These functions identify substrings
3790 by number. The next section describes functions for extracting named
3791 substrings.
3792
3793 A substring that contains a binary zero is correctly extracted and has
3794 a further zero added on the end, but the result is not, of course, a C
3795 string. However, you can process such a string by referring to the
3796 length that is returned by pcre_copy_substring() and pcre_get_sub-
3797 string(). Unfortunately, the interface to pcre_get_substring_list() is
3798 not adequate for handling strings containing binary zeros, because the
3799 end of the final string is not independently indicated.
3800
3801 The first three arguments are the same for all three of these func-
3802 tions: subject is the subject string that has just been successfully
3803 matched, ovector is a pointer to the vector of integer offsets that was
3804 passed to pcre_exec(), and stringcount is the number of substrings that
3805 were captured by the match, including the substring that matched the
3806 entire regular expression. This is the value returned by pcre_exec() if
3807 it is greater than zero. If pcre_exec() returned zero, indicating that
3808 it ran out of space in ovector, the value passed as stringcount should
3809 be the number of elements in the vector divided by three.
3810
3811 The functions pcre_copy_substring() and pcre_get_substring() extract a
3812 single substring, whose number is given as stringnumber. A value of
3813 zero extracts the substring that matched the entire pattern, whereas
3814 higher values extract the captured substrings. For pcre_copy_sub-
3815 string(), the string is placed in buffer, whose length is given by
3816 buffersize, while for pcre_get_substring() a new block of memory is
3817 obtained via pcre_malloc, and its address is returned via stringptr.
3818 The yield of the function is the length of the string, not including
3819 the terminating zero, or one of these error codes:
3820
3821 PCRE_ERROR_NOMEMORY (-6)
3822
3823 The buffer was too small for pcre_copy_substring(), or the attempt to
3824 get memory failed for pcre_get_substring().
3825
3826 PCRE_ERROR_NOSUBSTRING (-7)
3827
3828 There is no substring whose number is stringnumber.
3829
3830 The pcre_get_substring_list() function extracts all available sub-
3831 strings and builds a list of pointers to them. All this is done in a
3832 single block of memory that is obtained via pcre_malloc. The address of
3833 the memory block is returned via listptr, which is also the start of
3834 the list of string pointers. The end of the list is marked by a NULL
3835 pointer. The yield of the function is zero if all went well, or the
3836 error code
3837
3838 PCRE_ERROR_NOMEMORY (-6)
3839
3840 if the attempt to get the memory block failed.
3841
3842 When any of these functions encounter a substring that is unset, which
3843 can happen when capturing subpattern number n+1 matches some part of
3844 the subject, but subpattern n has not been used at all, they return an
3845 empty string. This can be distinguished from a genuine zero-length sub-
3846 string by inspecting the appropriate offset in ovector, which is nega-
3847 tive for unset substrings.
3848
3849 The two convenience functions pcre_free_substring() and pcre_free_sub-
3850 string_list() can be used to free the memory returned by a previous
3851 call of pcre_get_substring() or pcre_get_substring_list(), respec-
3852 tively. They do nothing more than call the function pointed to by
3853 pcre_free, which of course could be called directly from a C program.
3854 However, PCRE is used in some situations where it is linked via a spe-
3855 cial interface to another programming language that cannot use
3856 pcre_free directly; it is for these cases that the functions are pro-
3857 vided.
3858
3859
3860 EXTRACTING CAPTURED SUBSTRINGS BY NAME
3861
3862 int pcre_get_stringnumber(const pcre *code,
3863 const char *name);
3864
3865 int pcre_copy_named_substring(const pcre *code,
3866 const char *subject, int *ovector,
3867 int stringcount, const char *stringname,
3868 char *buffer, int buffersize);
3869
3870 int pcre_get_named_substring(const pcre *code,
3871 const char *subject, int *ovector,
3872 int stringcount, const char *stringname,
3873 const char **stringptr);
3874
3875 To extract a substring by name, you first have to find associated num-
3876 ber. For example, for this pattern
3877
3878 (a+)b(?<xxx>\d+)...
3879
3880 the number of the subpattern called "xxx" is 2. If the name is known to
3881 be unique (PCRE_DUPNAMES was not set), you can find the number from the
3882 name by calling pcre_get_stringnumber(). The first argument is the com-
3883 piled pattern, and the second is the name. The yield of the function is
3884 the subpattern number, or PCRE_ERROR_NOSUBSTRING (-7) if there is no
3885 subpattern of that name.
3886
3887 Given the number, you can extract the substring directly, or use one of
3888 the functions described in the previous section. For convenience, there
3889 are also two functions that do the whole job.
3890
3891 Most of the arguments of pcre_copy_named_substring() and
3892 pcre_get_named_substring() are the same as those for the similarly
3893 named functions that extract by number. As these are described in the
3894 previous section, they are not re-described here. There are just two
3895 differences:
3896
3897 First, instead of a substring number, a substring name is given. Sec-
3898 ond, there is an extra argument, given at the start, which is a pointer
3899 to the compiled pattern. This is needed in order to gain access to the
3900 name-to-number translation table.
3901
3902 These functions call pcre_get_stringnumber(), and if it succeeds, they
3903 then call pcre_copy_substring() or pcre_get_substring(), as appropri-
3904 ate. NOTE: If PCRE_DUPNAMES is set and there are duplicate names, the
3905 behaviour may not be what you want (see the next section).
3906
3907 Warning: If the pattern uses the (?| feature to set up multiple subpat-
3908 terns with the same number, as described in the section on duplicate
3909 subpattern numbers in the pcrepattern page, you cannot use names to
3910 distinguish the different subpatterns, because names are not included
3911 in the compiled code. The matching process uses only numbers. For this
3912 reason, the use of different names for subpatterns of the same number
3913 causes an error at compile time.
3914
3915
3916 DUPLICATE SUBPATTERN NAMES
3917
3918 int pcre_get_stringtable_entries(const pcre *code,
3919 const char *name, char **first, char **last);
3920
3921 When a pattern is compiled with the PCRE_DUPNAMES option, names for
3922 subpatterns are not required to be unique. (Duplicate names are always
3923 allowed for subpatterns with the same number, created by using the (?|
3924 feature. Indeed, if such subpatterns are named, they are required to
3925 use the same names.)
3926
3927 Normally, patterns with duplicate names are such that in any one match,
3928 only one of the named subpatterns participates. An example is shown in
3929 the pcrepattern documentation.
3930
3931 When duplicates are present, pcre_copy_named_substring() and
3932 pcre_get_named_substring() return the first substring corresponding to
3933 the given name that is set. If none are set, PCRE_ERROR_NOSUBSTRING
3934 (-7) is returned; no data is returned. The pcre_get_stringnumber()
3935 function returns one of the numbers that are associated with the name,
3936 but it is not defined which it is.
3937
3938 If you want to get full details of all captured substrings for a given
3939 name, you must use the pcre_get_stringtable_entries() function. The
3940 first argument is the compiled pattern, and the second is the name. The
3941 third and fourth are pointers to variables which are updated by the
3942 function. After it has run, they point to the first and last entries in
3943 the name-to-number table for the given name. The function itself
3944 returns the length of each entry, or PCRE_ERROR_NOSUBSTRING (-7) if
3945 there are none. The format of the table is described above in the sec-
3946 tion entitled Information about a pattern above. Given all the rele-
3947 vant entries for the name, you can extract each of their numbers, and
3948 hence the captured data, if any.
3949
3950
3951 FINDING ALL POSSIBLE MATCHES
3952
3953 The traditional matching function uses a similar algorithm to Perl,
3954 which stops when it finds the first match, starting at a given point in
3955 the subject. If you want to find all possible matches, or the longest
3956 possible match, consider using the alternative matching function (see
3957 below) instead. If you cannot use the alternative function, but still
3958 need to find all possible matches, you can kludge it up by making use
3959 of the callout facility, which is described in the pcrecallout documen-
3960 tation.
3961
3962 What you have to do is to insert a callout right at the end of the pat-
3963 tern. When your callout function is called, extract and save the cur-
3964 rent matched substring. Then return 1, which forces pcre_exec() to
3965 backtrack and try other alternatives. Ultimately, when it runs out of
3966 matches, pcre_exec() will yield PCRE_ERROR_NOMATCH.
3967
3968
3969 OBTAINING AN ESTIMATE OF STACK USAGE
3970
3971 Matching certain patterns using pcre_exec() can use a lot of process
3972 stack, which in certain environments can be rather limited in size.
3973 Some users find it helpful to have an estimate of the amount of stack
3974 that is used by pcre_exec(), to help them set recursion limits, as
3975 described in the pcrestack documentation. The estimate that is output
3976 by pcretest when called with the -m and -C options is obtained by call-
3977 ing pcre_exec with the values NULL, NULL, NULL, -999, and -999 for its
3978 first five arguments.
3979
3980 Normally, if its first argument is NULL, pcre_exec() immediately
3981 returns the negative error code PCRE_ERROR_NULL, but with this special
3982 combination of arguments, it returns instead a negative number whose
3983 absolute value is the approximate stack frame size in bytes. (A nega-
3984 tive number is used so that it is clear that no match has happened.)
3985 The value is approximate because in some cases, recursive calls to
3986 pcre_exec() occur when there are one or two additional variables on the
3987 stack.
3988
3989 If PCRE has been compiled to use the heap instead of the stack for
3990 recursion, the value returned is the size of each block that is
3991 obtained from the heap.
3992
3993
3994 MATCHING A PATTERN: THE ALTERNATIVE FUNCTION
3995
3996 int pcre_dfa_exec(const pcre *code, const pcre_extra *extra,
3997 const char *subject, int length, int startoffset,
3998 int options, int *ovector, int ovecsize,
3999 int *workspace, int wscount);
4000
4001 The function pcre_dfa_exec() is called to match a subject string
4002 against a compiled pattern, using a matching algorithm that scans the
4003 subject string just once, and does not backtrack. This has different
4004 characteristics to the normal algorithm, and is not compatible with
4005 Perl. Some of the features of PCRE patterns are not supported. Never-
4006 theless, there are times when this kind of matching can be useful. For
4007 a discussion of the two matching algorithms, and a list of features
4008 that pcre_dfa_exec() does not support, see the pcrematching documenta-
4009 tion.
4010
4011 The arguments for the pcre_dfa_exec() function are the same as for
4012 pcre_exec(), plus two extras. The ovector argument is used in a differ-
4013 ent way, and this is described below. The other common arguments are
4014 used in the same way as for pcre_exec(), so their description is not
4015 repeated here.
4016
4017 The two additional arguments provide workspace for the function. The
4018 workspace vector should contain at least 20 elements. It is used for
4019 keeping track of multiple paths through the pattern tree. More
4020 workspace will be needed for patterns and subjects where there are a
4021 lot of potential matches.
4022
4023 Here is an example of a simple call to pcre_dfa_exec():
4024
4025 int rc;
4026 int ovector[10];
4027 int wspace[20];
4028 rc = pcre_dfa_exec(
4029 re, /* result of pcre_compile() */
4030 NULL, /* we didn't study the pattern */
4031 "some string", /* the subject string */
4032 11, /* the length of the subject string */
4033 0, /* start at offset 0 in the subject */
4034 0, /* default options */
4035 ovector, /* vector of integers for substring information */
4036 10, /* number of elements (NOT size in bytes) */
4037 wspace, /* working space vector */
4038 20); /* number of elements (NOT size in bytes) */
4039
4040 Option bits for pcre_dfa_exec()
4041
4042 The unused bits of the options argument for pcre_dfa_exec() must be
4043 zero. The only bits that may be set are PCRE_ANCHORED, PCRE_NEW-
4044 LINE_xxx, PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY,
4045 PCRE_NOTEMPTY_ATSTART, PCRE_NO_UTF8_CHECK, PCRE_BSR_ANYCRLF,
4046 PCRE_BSR_UNICODE, PCRE_NO_START_OPTIMIZE, PCRE_PARTIAL_HARD, PCRE_PAR-
4047 TIAL_SOFT, PCRE_DFA_SHORTEST, and PCRE_DFA_RESTART. All but the last
4048 four of these are exactly the same as for pcre_exec(), so their
4049 description is not repeated here.
4050
4051 PCRE_PARTIAL_HARD
4052 PCRE_PARTIAL_SOFT
4053
4054 These have the same general effect as they do for pcre_exec(), but the
4055 details are slightly different. When PCRE_PARTIAL_HARD is set for
4056 pcre_dfa_exec(), it returns PCRE_ERROR_PARTIAL if the end of the sub-
4057 ject is reached and there is still at least one matching possibility
4058 that requires additional characters. This happens even if some complete
4059 matches have also been found. When PCRE_PARTIAL_SOFT is set, the return
4060 code PCRE_ERROR_NOMATCH is converted into PCRE_ERROR_PARTIAL if the end
4061 of the subject is reached, there have been no complete matches, but
4062 there is still at least one matching possibility. The portion of the
4063 string that was inspected when the longest partial match was found is
4064 set as the first matching string in both cases. There is a more
4065 detailed discussion of partial and multi-segment matching, with exam-
4066 ples, in the pcrepartial documentation.
4067
4068 PCRE_DFA_SHORTEST
4069
4070 Setting the PCRE_DFA_SHORTEST option causes the matching algorithm to
4071 stop as soon as it has found one match. Because of the way the alterna-
4072 tive algorithm works, this is necessarily the shortest possible match
4073 at the first possible matching point in the subject string.
4074
4075 PCRE_DFA_RESTART
4076
4077 When pcre_dfa_exec() returns a partial match, it is possible to call it
4078 again, with additional subject characters, and have it continue with
4079 the same match. The PCRE_DFA_RESTART option requests this action; when
4080 it is set, the workspace and wscount options must reference the same
4081 vector as before because data about the match so far is left in them
4082 after a partial match. There is more discussion of this facility in the
4083 pcrepartial documentation.
4084
4085 Successful returns from pcre_dfa_exec()
4086
4087 When pcre_dfa_exec() succeeds, it may have matched more than one sub-
4088 string in the subject. Note, however, that all the matches from one run
4089 of the function start at the same point in the subject. The shorter
4090 matches are all initial substrings of the longer matches. For example,
4091 if the pattern
4092
4093 <.*>
4094
4095 is matched against the string
4096
4097 This is <something> <something else> <something further> no more
4098
4099 the three matched strings are
4100
4101 <something>
4102 <something> <something else>
4103 <something> <something else> <something further>
4104
4105 On success, the yield of the function is a number greater than zero,
4106 which is the number of matched substrings. The substrings themselves
4107 are returned in ovector. Each string uses two elements; the first is
4108 the offset to the start, and the second is the offset to the end. In
4109 fact, all the strings have the same start offset. (Space could have
4110 been saved by giving this only once, but it was decided to retain some
4111 compatibility with the way pcre_exec() returns data, even though the
4112 meaning of the strings is different.)
4113
4114 The strings are returned in reverse order of length; that is, the long-
4115 est matching string is given first. If there were too many matches to
4116 fit into ovector, the yield of the function is zero, and the vector is
4117 filled with the longest matches. Unlike pcre_exec(), pcre_dfa_exec()
4118 can use the entire ovector for returning matched strings.
4119
4120 Error returns from pcre_dfa_exec()
4121
4122 The pcre_dfa_exec() function returns a negative number when it fails.
4123 Many of the errors are the same as for pcre_exec(), and these are
4124 described above. There are in addition the following errors that are
4125 specific to pcre_dfa_exec():
4126
4127 PCRE_ERROR_DFA_UITEM (-16)
4128
4129 This return is given if pcre_dfa_exec() encounters an item in the pat-
4130 tern that it does not support, for instance, the use of \C or a back
4131 reference.
4132
4133 PCRE_ERROR_DFA_UCOND (-17)
4134
4135 This return is given if pcre_dfa_exec() encounters a condition item
4136 that uses a back reference for the condition, or a test for recursion
4137 in a specific group. These are not supported.
4138
4139 PCRE_ERROR_DFA_UMLIMIT (-18)
4140
4141 This return is given if pcre_dfa_exec() is called with an extra block
4142 that contains a setting of the match_limit or match_limit_recursion
4143 fields. This is not supported (these fields are meaningless for DFA
4144 matching).
4145
4146 PCRE_ERROR_DFA_WSSIZE (-19)
4147
4148 This return is given if pcre_dfa_exec() runs out of space in the
4149 workspace vector.
4150
4151 PCRE_ERROR_DFA_RECURSE (-20)
4152
4153 When a recursive subpattern is processed, the matching function calls
4154 itself recursively, using private vectors for ovector and workspace.
4155 This error is given if the output vector is not large enough. This
4156 should be extremely rare, as a vector of size 1000 is used.
4157
4158 PCRE_ERROR_DFA_BADRESTART (-30)
4159
4160 When pcre_dfa_exec() is called with the PCRE_DFA_RESTART option, some
4161 plausibility checks are made on the contents of the workspace, which
4162 should contain data about the previous partial match. If any of these
4163 checks fail, this error is given.
4164
4165
4166 SEE ALSO
4167
4168 pcre16(3), pcre32(3), pcrebuild(3), pcrecallout(3), pcrecpp(3)(3),
4169 pcrematching(3), pcrepartial(3), pcreposix(3), pcreprecompile(3), pcre-
4170 sample(3), pcrestack(3).
4171
4172
4173 AUTHOR
4174
4175 Philip Hazel
4176 University Computing Service
4177 Cambridge CB2 3QH, England.
4178
4179
4180 REVISION
4181
4182 Last updated: 12 May 2013
4183 Copyright (c) 1997-2013 University of Cambridge.
4184 ------------------------------------------------------------------------------
4185
4186
4187 PCRECALLOUT(3) Library Functions Manual PCRECALLOUT(3)
4188
4189
4190
4191 NAME
4192 PCRE - Perl-compatible regular expressions
4193
4194 SYNOPSIS
4195
4196 #include <pcre.h>
4197
4198 int (*pcre_callout)(pcre_callout_block *);
4199
4200 int (*pcre16_callout)(pcre16_callout_block *);
4201
4202 int (*pcre32_callout)(pcre32_callout_block *);
4203
4204
4205 DESCRIPTION
4206
4207 PCRE provides a feature called "callout", which is a means of temporar-
4208 ily passing control to the caller of PCRE in the middle of pattern
4209 matching. The caller of PCRE provides an external function by putting
4210 its entry point in the global variable pcre_callout (pcre16_callout for
4211 the 16-bit library, pcre32_callout for the 32-bit library). By default,
4212 this variable contains NULL, which disables all calling out.
4213
4214 Within a regular expression, (?C) indicates the points at which the
4215 external function is to be called. Different callout points can be
4216 identified by putting a number less than 256 after the letter C. The
4217 default value is zero. For example, this pattern has two callout
4218 points:
4219
4220 (?C1)abc(?C2)def
4221
4222 If the PCRE_AUTO_CALLOUT option bit is set when a pattern is compiled,
4223 PCRE automatically inserts callouts, all with number 255, before each
4224 item in the pattern. For example, if PCRE_AUTO_CALLOUT is used with the
4225 pattern
4226
4227 A(\d{2}|--)
4228
4229 it is processed as if it were
4230
4231 (?C255)A(?C255)((?C255)\d{2}(?C255)|(?C255)-(?C255)-(?C255))(?C255)
4232
4233 Notice that there is a callout before and after each parenthesis and
4234 alternation bar. If the pattern contains a conditional group whose con-
4235 dition is an assertion, an automatic callout is inserted immediately
4236 before the condition. Such a callout may also be inserted explicitly,
4237 for example:
4238
4239 (?(?C9)(?=a)ab|de)
4240
4241 This applies only to assertion conditions (because they are themselves
4242 independent groups).
4243
4244 Automatic callouts can be used for tracking the progress of pattern
4245 matching. The pcretest command has an option that sets automatic call-
4246 outs; when it is used, the output indicates how the pattern is matched.
4247 This is useful information when you are trying to optimize the perfor-
4248 mance of a particular pattern.
4249
4250
4251 MISSING CALLOUTS
4252
4253 You should be aware that, because of optimizations in the way PCRE
4254 matches patterns by default, callouts sometimes do not happen. For
4255 example, if the pattern is
4256
4257 ab(?C4)cd
4258
4259 PCRE knows that any matching string must contain the letter "d". If the
4260 subject string is "abyz", the lack of "d" means that matching doesn't
4261 ever start, and the callout is never reached. However, with "abyd",
4262 though the result is still no match, the callout is obeyed.
4263
4264 If the pattern is studied, PCRE knows the minimum length of a matching
4265 string, and will immediately give a "no match" return without actually
4266 running a match if the subject is not long enough, or, for unanchored
4267 patterns, if it has been scanned far enough.
4268
4269 You can disable these optimizations by passing the PCRE_NO_START_OPTI-
4270 MIZE option to the matching function, or by starting the pattern with
4271 (*NO_START_OPT). This slows down the matching process, but does ensure
4272 that callouts such as the example above are obeyed.
4273
4274
4275 THE CALLOUT INTERFACE
4276
4277 During matching, when PCRE reaches a callout point, the external func-
4278 tion defined by pcre_callout or pcre[16|32]_callout is called (if it is
4279 set). This applies to both normal and DFA matching. The only argument
4280 to the callout function is a pointer to a pcre_callout or
4281 pcre[16|32]_callout block. These structures contains the following
4282 fields:
4283
4284 int version;
4285 int callout_number;
4286 int *offset_vector;
4287 const char *subject; (8-bit version)
4288 PCRE_SPTR16 subject; (16-bit version)
4289 PCRE_SPTR32 subject; (32-bit version)
4290 int subject_length;
4291 int start_match;
4292 int current_position;
4293 int capture_top;
4294 int capture_last;
4295 void *callout_data;
4296 int pattern_position;
4297 int next_item_length;
4298 const unsigned char *mark; (8-bit version)
4299 const PCRE_UCHAR16 *mark; (16-bit version)
4300 const PCRE_UCHAR32 *mark; (32-bit version)
4301
4302 The version field is an integer containing the version number of the
4303 block format. The initial version was 0; the current version is 2. The
4304 version number will change again in future if additional fields are
4305 added, but the intention is never to remove any of the existing fields.
4306
4307 The callout_number field contains the number of the callout, as com-
4308 piled into the pattern (that is, the number after ?C for manual call-
4309 outs, and 255 for automatically generated callouts).
4310
4311 The offset_vector field is a pointer to the vector of offsets that was
4312 passed by the caller to the matching function. When pcre_exec() or
4313 pcre[16|32]_exec() is used, the contents can be inspected, in order to
4314 extract substrings that have been matched so far, in the same way as
4315 for extracting substrings after a match has completed. For the DFA
4316 matching functions, this field is not useful.
4317
4318 The subject and subject_length fields contain copies of the values that
4319 were passed to the matching function.
4320
4321 The start_match field normally contains the offset within the subject
4322 at which the current match attempt started. However, if the escape
4323 sequence \K has been encountered, this value is changed to reflect the
4324 modified starting point. If the pattern is not anchored, the callout
4325 function may be called several times from the same point in the pattern
4326 for different starting points in the subject.
4327
4328 The current_position field contains the offset within the subject of
4329 the current match pointer.
4330
4331 When the pcre_exec() or pcre[16|32]_exec() is used, the capture_top
4332 field contains one more than the number of the highest numbered cap-
4333 tured substring so far. If no substrings have been captured, the value
4334 of capture_top is one. This is always the case when the DFA functions
4335 are used, because they do not support captured substrings.
4336
4337 The capture_last field contains the number of the most recently cap-
4338 tured substring. However, when a recursion exits, the value reverts to
4339 what it was outside the recursion, as do the values of all captured
4340 substrings. If no substrings have been captured, the value of cap-
4341 ture_last is -1. This is always the case for the DFA matching func-
4342 tions.
4343
4344 The callout_data field contains a value that is passed to a matching
4345 function specifically so that it can be passed back in callouts. It is
4346 passed in the callout_data field of a pcre_extra or pcre[16|32]_extra
4347 data structure. If no such data was passed, the value of callout_data
4348 in a callout block is NULL. There is a description of the pcre_extra
4349 structure in the pcreapi documentation.
4350
4351 The pattern_position field is present from version 1 of the callout
4352 structure. It contains the offset to the next item to be matched in the
4353 pattern string.
4354
4355 The next_item_length field is present from version 1 of the callout
4356 structure. It contains the length of the next item to be matched in the
4357 pattern string. When the callout immediately precedes an alternation
4358 bar, a closing parenthesis, or the end of the pattern, the length is
4359 zero. When the callout precedes an opening parenthesis, the length is
4360 that of the entire subpattern.
4361
4362 The pattern_position and next_item_length fields are intended to help
4363 in distinguishing between different automatic callouts, which all have
4364 the same callout number. However, they are set for all callouts.
4365
4366 The mark field is present from version 2 of the callout structure. In
4367 callouts from pcre_exec() or pcre[16|32]_exec() it contains a pointer
4368 to the zero-terminated name of the most recently passed (*MARK),
4369 (*PRUNE), or (*THEN) item in the match, or NULL if no such items have
4370 been passed. Instances of (*PRUNE) or (*THEN) without a name do not
4371 obliterate a previous (*MARK). In callouts from the DFA matching func-
4372 tions this field always contains NULL.
4373
4374
4375 RETURN VALUES
4376
4377 The external callout function returns an integer to PCRE. If the value
4378 is zero, matching proceeds as normal. If the value is greater than
4379 zero, matching fails at the current point, but the testing of other
4380 matching possibilities goes ahead, just as if a lookahead assertion had
4381 failed. If the value is less than zero, the match is abandoned, the
4382 matching function returns the negative value.
4383
4384 Negative values should normally be chosen from the set of
4385 PCRE_ERROR_xxx values. In particular, PCRE_ERROR_NOMATCH forces a stan-
4386 dard "no match" failure. The error number PCRE_ERROR_CALLOUT is
4387 reserved for use by callout functions; it will never be used by PCRE
4388 itself.
4389
4390
4391 AUTHOR
4392
4393 Philip Hazel
4394 University Computing Service
4395 Cambridge CB2 3QH, England.
4396
4397
4398 REVISION
4399
4400 Last updated: 03 March 2013
4401 Copyright (c) 1997-2013 University of Cambridge.
4402 ------------------------------------------------------------------------------
4403
4404
4405 PCRECOMPAT(3) Library Functions Manual PCRECOMPAT(3)
4406
4407
4408
4409 NAME
4410 PCRE - Perl-compatible regular expressions
4411
4412 DIFFERENCES BETWEEN PCRE AND PERL
4413
4414 This document describes the differences in the ways that PCRE and Perl
4415 handle regular expressions. The differences described here are with
4416 respect to Perl versions 5.10 and above.
4417
4418 1. PCRE has only a subset of Perl's Unicode support. Details of what it
4419 does have are given in the pcreunicode page.
4420
4421 2. PCRE allows repeat quantifiers only on parenthesized assertions, but
4422 they do not mean what you might think. For example, (?!a){3} does not
4423 assert that the next three characters are not "a". It just asserts that
4424 the next character is not "a" three times (in principle: PCRE optimizes
4425 this to run the assertion just once). Perl allows repeat quantifiers on
4426 other assertions such as \b, but these do not seem to have any use.
4427
4428 3. Capturing subpatterns that occur inside negative lookahead asser-
4429 tions are counted, but their entries in the offsets vector are never
4430 set. Perl sometimes (but not always) sets its numerical variables from
4431 inside negative assertions.
4432
4433 4. Though binary zero characters are supported in the subject string,
4434 they are not allowed in a pattern string because it is passed as a nor-
4435 mal C string, terminated by zero. The escape sequence \0 can be used in
4436 the pattern to represent a binary zero.
4437
4438 5. The following Perl escape sequences are not supported: \l, \u, \L,
4439 \U, and \N when followed by a character name or Unicode value. (\N on
4440 its own, matching a non-newline character, is supported.) In fact these
4441 are implemented by Perl's general string-handling and are not part of
4442 its pattern matching engine. If any of these are encountered by PCRE,
4443 an error is generated by default. However, if the PCRE_JAVASCRIPT_COM-
4444 PAT option is set, \U and \u are interpreted as JavaScript interprets
4445 them.
4446
4447 6. The Perl escape sequences \p, \P, and \X are supported only if PCRE
4448 is built with Unicode character property support. The properties that
4449 can be tested with \p and \P are limited to the general category prop-
4450 erties such as Lu and Nd, script names such as Greek or Han, and the
4451 derived properties Any and L&. PCRE does support the Cs (surrogate)
4452 property, which Perl does not; the Perl documentation says "Because
4453 Perl hides the need for the user to understand the internal representa-
4454 tion of Unicode characters, there is no need to implement the somewhat
4455 messy concept of surrogates."
4456
4457 7. PCRE does support the \Q...\E escape for quoting substrings. Charac-
4458 ters in between are treated as literals. This is slightly different
4459 from Perl in that $ and @ are also handled as literals inside the
4460 quotes. In Perl, they cause variable interpolation (but of course PCRE
4461 does not have variables). Note the following examples:
4462
4463 Pattern PCRE matches Perl matches
4464
4465 \Qabc$xyz\E abc$xyz abc followed by the
4466 contents of $xyz
4467 \Qabc\$xyz\E abc\$xyz abc\$xyz
4468 \Qabc\E\$\Qxyz\E abc$xyz abc$xyz
4469
4470 The \Q...\E sequence is recognized both inside and outside character
4471 classes.
4472
4473 8. Fairly obviously, PCRE does not support the (?{code}) and (??{code})
4474 constructions. However, there is support for recursive patterns. This
4475 is not available in Perl 5.8, but it is in Perl 5.10. Also, the PCRE
4476 "callout" feature allows an external function to be called during pat-
4477 tern matching. See the pcrecallout documentation for details.
4478
4479 9. Subpatterns that are called as subroutines (whether or not recur-
4480 sively) are always treated as atomic groups in PCRE. This is like
4481 Python, but unlike Perl. Captured values that are set outside a sub-
4482 routine call can be reference from inside in PCRE, but not in Perl.
4483 There is a discussion that explains these differences in more detail in
4484 the section on recursion differences from Perl in the pcrepattern page.
4485
4486 10. If any of the backtracking control verbs are used in a subpattern
4487 that is called as a subroutine (whether or not recursively), their
4488 effect is confined to that subpattern; it does not extend to the sur-
4489 rounding pattern. This is not always the case in Perl. In particular,
4490 if (*THEN) is present in a group that is called as a subroutine, its
4491 action is limited to that group, even if the group does not contain any
4492 | characters. Note that such subpatterns are processed as anchored at
4493 the point where they are tested.
4494
4495 11. If a pattern contains more than one backtracking control verb, the
4496 first one that is backtracked onto acts. For example, in the pattern
4497 A(*COMMIT)B(*PRUNE)C a failure in B triggers (*COMMIT), but a failure
4498 in C triggers (*PRUNE). Perl's behaviour is more complex; in many cases
4499 it is the same as PCRE, but there are examples where it differs.
4500
4501 12. Most backtracking verbs in assertions have their normal actions.
4502 They are not confined to the assertion.
4503
4504 13. There are some differences that are concerned with the settings of
4505 captured strings when part of a pattern is repeated. For example,
4506 matching "aba" against the pattern /^(a(b)?)+$/ in Perl leaves $2
4507 unset, but in PCRE it is set to "b".
4508
4509 14. PCRE's handling of duplicate subpattern numbers and duplicate sub-
4510 pattern names is not as general as Perl's. This is a consequence of the
4511 fact the PCRE works internally just with numbers, using an external ta-
4512 ble to translate between numbers and names. In particular, a pattern
4513 such as (?|(?<a>A)|(?<b)B), where the two capturing parentheses have
4514 the same number but different names, is not supported, and causes an
4515 error at compile time. If it were allowed, it would not be possible to
4516 distinguish which parentheses matched, because both names map to cap-
4517 turing subpattern number 1. To avoid this confusing situation, an error
4518 is given at compile time.
4519
4520 15. Perl recognizes comments in some places that PCRE does not, for
4521 example, between the ( and ? at the start of a subpattern. If the /x
4522 modifier is set, Perl allows white space between ( and ? but PCRE never
4523 does, even if the PCRE_EXTENDED option is set.
4524
4525 16. In PCRE, the upper/lower case character properties Lu and Ll are
4526 not affected when case-independent matching is specified. For example,
4527 \p{Lu} always matches an upper case letter. I think Perl has changed in
4528 this respect; in the release at the time of writing (5.16), \p{Lu} and
4529 \p{Ll} match all letters, regardless of case, when case independence is
4530 specified.
4531
4532 17. PCRE provides some extensions to the Perl regular expression facil-
4533 ities. Perl 5.10 includes new features that are not in earlier ver-
4534 sions of Perl, some of which (such as named parentheses) have been in
4535 PCRE for some time. This list is with respect to Perl 5.10:
4536
4537 (a) Although lookbehind assertions in PCRE must match fixed length
4538 strings, each alternative branch of a lookbehind assertion can match a
4539 different length of string. Perl requires them all to have the same
4540 length.
4541
4542 (b) If PCRE_DOLLAR_ENDONLY is set and PCRE_MULTILINE is not set, the $
4543 meta-character matches only at the very end of the string.
4544
4545 (c) If PCRE_EXTRA is set, a backslash followed by a letter with no spe-
4546 cial meaning is faulted. Otherwise, like Perl, the backslash is quietly
4547 ignored. (Perl can be made to issue a warning.)
4548
4549 (d) If PCRE_UNGREEDY is set, the greediness of the repetition quanti-
4550 fiers is inverted, that is, by default they are not greedy, but if fol-
4551 lowed by a question mark they are.
4552
4553 (e) PCRE_ANCHORED can be used at matching time to force a pattern to be
4554 tried only at the first matching position in the subject string.
4555
4556 (f) The PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, PCRE_NOTEMPTY_ATSTART,
4557 and PCRE_NO_AUTO_CAPTURE options for pcre_exec() have no Perl equiva-
4558 lents.
4559
4560 (g) The \R escape sequence can be restricted to match only CR, LF, or
4561 CRLF by the PCRE_BSR_ANYCRLF option.
4562
4563 (h) The callout facility is PCRE-specific.
4564
4565 (i) The partial matching facility is PCRE-specific.
4566
4567 (j) Patterns compiled by PCRE can be saved and re-used at a later time,
4568 even on different hosts that have the other endianness. However, this
4569 does not apply to optimized data created by the just-in-time compiler.
4570
4571 (k) The alternative matching functions (pcre_dfa_exec(),
4572 pcre16_dfa_exec() and pcre32_dfa_exec(),) match in a different way and
4573 are not Perl-compatible.
4574
4575 (l) PCRE recognizes some special sequences such as (*CR) at the start
4576 of a pattern that set overall options that cannot be changed within the
4577 pattern.
4578
4579
4580 AUTHOR
4581
4582 Philip Hazel
4583 University Computing Service
4584 Cambridge CB2 3QH, England.
4585
4586
4587 REVISION
4588
4589 Last updated: 19 March 2013
4590 Copyright (c) 1997-2013 University of Cambridge.
4591 ------------------------------------------------------------------------------
4592
4593
4594 PCREPATTERN(3) Library Functions Manual PCREPATTERN(3)
4595
4596
4597
4598 NAME
4599 PCRE - Perl-compatible regular expressions
4600
4601 PCRE REGULAR EXPRESSION DETAILS
4602
4603 The syntax and semantics of the regular expressions that are supported
4604 by PCRE are described in detail below. There is a quick-reference syn-
4605 tax summary in the pcresyntax page. PCRE tries to match Perl syntax and
4606 semantics as closely as it can. PCRE also supports some alternative
4607 regular expression syntax (which does not conflict with the Perl syn-
4608 tax) in order to provide some compatibility with regular expressions in
4609 Python, .NET, and Oniguruma.
4610
4611 Perl's regular expressions are described in its own documentation, and
4612 regular expressions in general are covered in a number of books, some
4613 of which have copious examples. Jeffrey Friedl's "Mastering Regular
4614 Expressions", published by O'Reilly, covers regular expressions in
4615 great detail. This description of PCRE's regular expressions is
4616 intended as reference material.
4617
4618 This document discusses the patterns that are supported by PCRE when
4619 one its main matching functions, pcre_exec() (8-bit) or
4620 pcre[16|32]_exec() (16- or 32-bit), is used. PCRE also has alternative
4621 matching functions, pcre_dfa_exec() and pcre[16|32_dfa_exec(), which
4622 match using a different algorithm that is not Perl-compatible. Some of
4623 the features discussed below are not available when DFA matching is
4624 used. The advantages and disadvantages of the alternative functions,
4625 and how they differ from the normal functions, are discussed in the
4626 pcrematching page.
4627
4628
4629 SPECIAL START-OF-PATTERN ITEMS
4630
4631 A number of options that can be passed to pcre_compile() can also be
4632 set by special items at the start of a pattern. These are not Perl-com-
4633 patible, but are provided to make these options accessible to pattern
4634 writers who are not able to change the program that processes the pat-
4635 tern. Any number of these items may appear, but they must all be
4636 together right at the start of the pattern string, and the letters must
4637 be in upper case.
4638
4639 UTF support
4640
4641 The original operation of PCRE was on strings of one-byte characters.
4642 However, there is now also support for UTF-8 strings in the original
4643 library, an extra library that supports 16-bit and UTF-16 character
4644 strings, and a third library that supports 32-bit and UTF-32 character
4645 strings. To use these features, PCRE must be built to include appropri-
4646 ate support. When using UTF strings you must either call the compiling
4647 function with the PCRE_UTF8, PCRE_UTF16, or PCRE_UTF32 option, or the
4648 pattern must start with one of these special sequences:
4649
4650 (*UTF8)
4651 (*UTF16)
4652 (*UTF32)
4653 (*UTF)
4654
4655 (*UTF) is a generic sequence that can be used with any of the
4656 libraries. Starting a pattern with such a sequence is equivalent to
4657 setting the relevant option. How setting a UTF mode affects pattern
4658 matching is mentioned in several places below. There is also a summary
4659 of features in the pcreunicode page.
4660
4661 Some applications that allow their users to supply patterns may wish to
4662 restrict them to non-UTF data for security reasons. If the
4663 PCRE_NEVER_UTF option is set at compile time, (*UTF) etc. are not
4664 allowed, and their appearance causes an error.
4665
4666 Unicode property support
4667
4668 Another special sequence that may appear at the start of a pattern is
4669
4670 (*UCP)
4671
4672 This has the same effect as setting the PCRE_UCP option: it causes
4673 sequences such as \d and \w to use Unicode properties to determine
4674 character types, instead of recognizing only characters with codes less
4675 than 128 via a lookup table.
4676
4677 Disabling start-up optimizations
4678
4679 If a pattern starts with (*NO_START_OPT), it has the same effect as
4680 setting the PCRE_NO_START_OPTIMIZE option either at compile or matching
4681 time.
4682
4683 Newline conventions
4684
4685 PCRE supports five different conventions for indicating line breaks in
4686 strings: a single CR (carriage return) character, a single LF (line-
4687 feed) character, the two-character sequence CRLF, any of the three pre-
4688 ceding, or any Unicode newline sequence. The pcreapi page has further
4689 discussion about newlines, and shows how to set the newline convention
4690 in the options arguments for the compiling and matching functions.
4691
4692 It is also possible to specify a newline convention by starting a pat-
4693 tern string with one of the following five sequences:
4694
4695 (*CR) carriage return
4696 (*LF) linefeed
4697 (*CRLF) carriage return, followed by linefeed
4698 (*ANYCRLF) any of the three above
4699 (*ANY) all Unicode newline sequences
4700
4701 These override the default and the options given to the compiling func-
4702 tion. For example, on a Unix system where LF is the default newline
4703 sequence, the pattern
4704
4705 (*CR)a.b
4706
4707 changes the convention to CR. That pattern matches "a\nb" because LF is
4708 no longer a newline. If more than one of these settings is present, the
4709 last one is used.
4710
4711 The newline convention affects where the circumflex and dollar asser-
4712 tions are true. It also affects the interpretation of the dot metachar-
4713 acter when PCRE_DOTALL is not set, and the behaviour of \N. However, it
4714 does not affect what the \R escape sequence matches. By default, this
4715 is any Unicode newline sequence, for Perl compatibility. However, this
4716 can be changed; see the description of \R in the section entitled "New-
4717 line sequences" below. A change of \R setting can be combined with a
4718 change of newline convention.
4719
4720 Setting match and recursion limits
4721
4722 The caller of pcre_exec() can set a limit on the number of times the
4723 internal match() function is called and on the maximum depth of recur-
4724 sive calls. These facilities are provided to catch runaway matches that
4725 are provoked by patterns with huge matching trees (a typical example is
4726 a pattern with nested unlimited repeats) and to avoid running out of
4727 system stack by too much recursion. When one of these limits is
4728 reached, pcre_exec() gives an error return. The limits can also be set
4729 by items at the start of the pattern of the form
4730
4731 (*LIMIT_MATCH=d)
4732 (*LIMIT_RECURSION=d)
4733
4734 where d is any number of decimal digits. However, the value of the set-
4735 ting must be less than the value set by the caller of pcre_exec() for
4736 it to have any effect. In other words, the pattern writer can lower the
4737 limit set by the programmer, but not raise it. If there is more than
4738 one setting of one of these limits, the lower value is used.
4739
4740
4741 EBCDIC CHARACTER CODES
4742
4743 PCRE can be compiled to run in an environment that uses EBCDIC as its
4744 character code rather than ASCII or Unicode (typically a mainframe sys-
4745 tem). In the sections below, character code values are ASCII or Uni-
4746 code; in an EBCDIC environment these characters may have different code
4747 values, and there are no code points greater than 255.
4748
4749
4750 CHARACTERS AND METACHARACTERS
4751
4752 A regular expression is a pattern that is matched against a subject
4753 string from left to right. Most characters stand for themselves in a
4754 pattern, and match the corresponding characters in the subject. As a
4755 trivial example, the pattern
4756
4757 The quick brown fox
4758
4759 matches a portion of a subject string that is identical to itself. When
4760 caseless matching is specified (the PCRE_CASELESS option), letters are
4761 matched independently of case. In a UTF mode, PCRE always understands
4762 the concept of case for characters whose values are less than 128, so
4763 caseless matching is always possible. For characters with higher val-
4764 ues, the concept of case is supported if PCRE is compiled with Unicode
4765 property support, but not otherwise. If you want to use caseless
4766 matching for characters 128 and above, you must ensure that PCRE is
4767 compiled with Unicode property support as well as with UTF support.
4768
4769 The power of regular expressions comes from the ability to include
4770 alternatives and repetitions in the pattern. These are encoded in the
4771 pattern by the use of metacharacters, which do not stand for themselves
4772 but instead are interpreted in some special way.
4773
4774 There are two different sets of metacharacters: those that are recog-
4775 nized anywhere in the pattern except within square brackets, and those
4776 that are recognized within square brackets. Outside square brackets,
4777 the metacharacters are as follows:
4778
4779 \ general escape character with several uses
4780 ^ assert start of string (or line, in multiline mode)
4781 $ assert end of string (or line, in multiline mode)
4782 . match any character except newline (by default)
4783 [ start character class definition
4784 | start of alternative branch
4785 ( start subpattern
4786 ) end subpattern
4787 ? extends the meaning of (
4788 also 0 or 1 quantifier
4789 also quantifier minimizer
4790 * 0 or more quantifier
4791 + 1 or more quantifier
4792 also "possessive quantifier"
4793 { start min/max quantifier
4794
4795 Part of a pattern that is in square brackets is called a "character
4796 class". In a character class the only metacharacters are:
4797
4798 \ general escape character
4799 ^ negate the class, but only if the first character
4800 - indicates character range
4801 [ POSIX character class (only if followed by POSIX
4802 syntax)
4803 ] terminates the character class
4804
4805 The following sections describe the use of each of the metacharacters.
4806
4807
4808 BACKSLASH
4809
4810 The backslash character has several uses. Firstly, if it is followed by
4811 a character that is not a number or a letter, it takes away any special
4812 meaning that character may have. This use of backslash as an escape
4813 character applies both inside and outside character classes.
4814
4815 For example, if you want to match a * character, you write \* in the
4816 pattern. This escaping action applies whether or not the following
4817 character would otherwise be interpreted as a metacharacter, so it is
4818 always safe to precede a non-alphanumeric with backslash to specify
4819 that it stands for itself. In particular, if you want to match a back-
4820 slash, you write \\.
4821
4822 In a UTF mode, only ASCII numbers and letters have any special meaning
4823 after a backslash. All other characters (in particular, those whose
4824 codepoints are greater than 127) are treated as literals.
4825
4826 If a pattern is compiled with the PCRE_EXTENDED option, white space in
4827 the pattern (other than in a character class) and characters between a
4828 # outside a character class and the next newline are ignored. An escap-
4829 ing backslash can be used to include a white space or # character as
4830 part of the pattern.
4831
4832 If you want to remove the special meaning from a sequence of charac-
4833 ters, you can do so by putting them between \Q and \E. This is differ-
4834 ent from Perl in that $ and @ are handled as literals in \Q...\E
4835 sequences in PCRE, whereas in Perl, $ and @ cause variable interpola-
4836 tion. Note the following examples:
4837
4838 Pattern PCRE matches Perl matches
4839
4840 \Qabc$xyz\E abc$xyz abc followed by the
4841 contents of $xyz
4842 \Qabc\$xyz\E abc\$xyz abc\$xyz
4843 \Qabc\E\$\Qxyz\E abc$xyz abc$xyz
4844
4845 The \Q...\E sequence is recognized both inside and outside character
4846 classes. An isolated \E that is not preceded by \Q is ignored. If \Q
4847 is not followed by \E later in the pattern, the literal interpretation
4848 continues to the end of the pattern (that is, \E is assumed at the
4849 end). If the isolated \Q is inside a character class, this causes an
4850 error, because the character class is not terminated.
4851
4852 Non-printing characters
4853
4854 A second use of backslash provides a way of encoding non-printing char-
4855 acters in patterns in a visible manner. There is no restriction on the
4856 appearance of non-printing characters, apart from the binary zero that
4857 terminates a pattern, but when a pattern is being prepared by text
4858 editing, it is often easier to use one of the following escape
4859 sequences than the binary character it represents:
4860
4861 \a alarm, that is, the BEL character (hex 07)
4862 \cx "control-x", where x is any ASCII character
4863 \e escape (hex 1B)
4864 \f form feed (hex 0C)
4865 \n linefeed (hex 0A)
4866 \r carriage return (hex 0D)
4867 \t tab (hex 09)
4868 \ddd character with octal code ddd, or back reference
4869 \xhh character with hex code hh
4870 \x{hhh..} character with hex code hhh.. (non-JavaScript mode)
4871 \uhhhh character with hex code hhhh (JavaScript mode only)
4872
4873 The precise effect of \cx on ASCII characters is as follows: if x is a
4874 lower case letter, it is converted to upper case. Then bit 6 of the
4875 character (hex 40) is inverted. Thus \cA to \cZ become hex 01 to hex 1A
4876 (A is 41, Z is 5A), but \c{ becomes hex 3B ({ is 7B), and \c; becomes
4877 hex 7B (; is 3B). If the data item (byte or 16-bit value) following \c
4878 has a value greater than 127, a compile-time error occurs. This locks
4879 out non-ASCII characters in all modes.
4880
4881 The \c facility was designed for use with ASCII characters, but with
4882 the extension to Unicode it is even less useful than it once was. It
4883 is, however, recognized when PCRE is compiled in EBCDIC mode, where
4884 data items are always bytes. In this mode, all values are valid after
4885 \c. If the next character is a lower case letter, it is converted to
4886 upper case. Then the 0xc0 bits of the byte are inverted. Thus \cA
4887 becomes hex 01, as in ASCII (A is C1), but because the EBCDIC letters
4888 are disjoint, \cZ becomes hex 29 (Z is E9), and other characters also
4889 generate different values.
4890
4891 By default, after \x, from zero to two hexadecimal digits are read
4892 (letters can be in upper or lower case). Any number of hexadecimal dig-
4893 its may appear between \x{ and }, but the character code is constrained
4894 as follows:
4895
4896 8-bit non-UTF mode less than 0x100
4897 8-bit UTF-8 mode less than 0x10ffff and a valid codepoint
4898 16-bit non-UTF mode less than 0x10000
4899 16-bit UTF-16 mode less than 0x10ffff and a valid codepoint
4900 32-bit non-UTF mode less than 0x80000000
4901 32-bit UTF-32 mode less than 0x10ffff and a valid codepoint
4902
4903 Invalid Unicode codepoints are the range 0xd800 to 0xdfff (the so-
4904 called "surrogate" codepoints), and 0xffef.
4905
4906 If characters other than hexadecimal digits appear between \x{ and },
4907 or if there is no terminating }, this form of escape is not recognized.
4908 Instead, the initial \x will be interpreted as a basic hexadecimal
4909 escape, with no following digits, giving a character whose value is
4910 zero.
4911
4912 If the PCRE_JAVASCRIPT_COMPAT option is set, the interpretation of \x
4913 is as just described only when it is followed by two hexadecimal dig-
4914 its. Otherwise, it matches a literal "x" character. In JavaScript
4915 mode, support for code points greater than 256 is provided by \u, which
4916 must be followed by four hexadecimal digits; otherwise it matches a
4917 literal "u" character. Character codes specified by \u in JavaScript
4918 mode are constrained in the same was as those specified by \x in non-
4919 JavaScript mode.
4920
4921 Characters whose value is less than 256 can be defined by either of the
4922 two syntaxes for \x (or by \u in JavaScript mode). There is no differ-
4923 ence in the way they are handled. For example, \xdc is exactly the same
4924 as \x{dc} (or \u00dc in JavaScript mode).
4925
4926 After \0 up to two further octal digits are read. If there are fewer
4927 than two digits, just those that are present are used. Thus the
4928 sequence \0\x\07 specifies two binary zeros followed by a BEL character
4929 (code value 7). Make sure you supply two digits after the initial zero
4930 if the pattern character that follows is itself an octal digit.
4931
4932 The handling of a backslash followed by a digit other than 0 is compli-
4933 cated. Outside a character class, PCRE reads it and any following dig-
4934 its as a decimal number. If the number is less than 10, or if there
4935 have been at least that many previous capturing left parentheses in the
4936 expression, the entire sequence is taken as a back reference. A
4937 description of how this works is given later, following the discussion
4938 of parenthesized subpatterns.
4939
4940 Inside a character class, or if the decimal number is greater than 9
4941 and there have not been that many capturing subpatterns, PCRE re-reads
4942 up to three octal digits following the backslash, and uses them to gen-
4943 erate a data character. Any subsequent digits stand for themselves. The
4944 value of the character is constrained in the same way as characters
4945 specified in hexadecimal. For example:
4946
4947 \040 is another way of writing an ASCII space
4948 \40 is the same, provided there are fewer than 40
4949 previous capturing subpatterns
4950 \7 is always a back reference
4951 \11 might be a back reference, or another way of
4952 writing a tab
4953 \011 is always a tab
4954 \0113 is a tab followed by the character "3"
4955 \113 might be a back reference, otherwise the
4956 character with octal code 113
4957 \377 might be a back reference, otherwise
4958 the value 255 (decimal)
4959 \81 is either a back reference, or a binary zero
4960 followed by the two characters "8" and "1"
4961
4962 Note that octal values of 100 or greater must not be introduced by a
4963 leading zero, because no more than three octal digits are ever read.
4964
4965 All the sequences that define a single character value can be used both
4966 inside and outside character classes. In addition, inside a character
4967 class, \b is interpreted as the backspace character (hex 08).
4968
4969 \N is not allowed in a character class. \B, \R, and \X are not special
4970 inside a character class. Like other unrecognized escape sequences,
4971 they are treated as the literal characters "B", "R", and "X" by
4972 default, but cause an error if the PCRE_EXTRA option is set. Outside a
4973 character class, these sequences have different meanings.
4974
4975 Unsupported escape sequences
4976
4977 In Perl, the sequences \l, \L, \u, and \U are recognized by its string
4978 handler and used to modify the case of following characters. By
4979 default, PCRE does not support these escape sequences. However, if the
4980 PCRE_JAVASCRIPT_COMPAT option is set, \U matches a "U" character, and
4981 \u can be used to define a character by code point, as described in the
4982 previous section.
4983
4984 Absolute and relative back references
4985
4986 The sequence \g followed by an unsigned or a negative number, option-
4987 ally enclosed in braces, is an absolute or relative back reference. A
4988 named back reference can be coded as \g{name}. Back references are dis-
4989 cussed later, following the discussion of parenthesized subpatterns.
4990
4991 Absolute and relative subroutine calls
4992
4993 For compatibility with Oniguruma, the non-Perl syntax \g followed by a
4994 name or a number enclosed either in angle brackets or single quotes, is
4995 an alternative syntax for referencing a subpattern as a "subroutine".
4996 Details are discussed later. Note that \g{...} (Perl syntax) and
4997 \g<...> (Oniguruma syntax) are not synonymous. The former is a back
4998 reference; the latter is a subroutine call.
4999
5000 Generic character types
5001
5002 Another use of backslash is for specifying generic character types:
5003
5004 \d any decimal digit
5005 \D any character that is not a decimal digit
5006 \h any horizontal white space character
5007 \H any character that is not a horizontal white space character
5008 \s any white space character
5009 \S any character that is not a white space character
5010 \v any vertical white space character
5011 \V any character that is not a vertical white space character
5012 \w any "word" character
5013 \W any "non-word" character
5014
5015 There is also the single sequence \N, which matches a non-newline char-
5016 acter. This is the same as the "." metacharacter when PCRE_DOTALL is
5017 not set. Perl also uses \N to match characters by name; PCRE does not
5018 support this.
5019
5020 Each pair of lower and upper case escape sequences partitions the com-
5021 plete set of characters into two disjoint sets. Any given character
5022 matches one, and only one, of each pair. The sequences can appear both
5023 inside and outside character classes. They each match one character of
5024 the appropriate type. If the current matching point is at the end of
5025 the subject string, all of them fail, because there is no character to
5026 match.
5027
5028 For compatibility with Perl, \s does not match the VT character (code
5029 11). This makes it different from the the POSIX "space" class. The \s
5030 characters are HT (9), LF (10), FF (12), CR (13), and space (32). If
5031 "use locale;" is included in a Perl script, \s may match the VT charac-
5032 ter. In PCRE, it never does.
5033
5034 A "word" character is an underscore or any character that is a letter
5035 or digit. By default, the definition of letters and digits is con-
5036 trolled by PCRE's low-valued character tables, and may vary if locale-
5037 specific matching is taking place (see "Locale support" in the pcreapi
5038 page). For example, in a French locale such as "fr_FR" in Unix-like
5039 systems, or "french" in Windows, some character codes greater than 128
5040 are used for accented letters, and these are then matched by \w. The
5041 use of locales with Unicode is discouraged.
5042
5043 By default, in a UTF mode, characters with values greater than 128
5044 never match \d, \s, or \w, and always match \D, \S, and \W. These
5045 sequences retain their original meanings from before UTF support was
5046 available, mainly for efficiency reasons. However, if PCRE is compiled
5047 with Unicode property support, and the PCRE_UCP option is set, the be-
5048 haviour is changed so that Unicode properties are used to determine
5049 character types, as follows:
5050
5051 \d any character that \p{Nd} matches (decimal digit)
5052 \s any character that \p{Z} matches, plus HT, LF, FF, CR
5053 \w any character that \p{L} or \p{N} matches, plus underscore
5054
5055 The upper case escapes match the inverse sets of characters. Note that
5056 \d matches only decimal digits, whereas \w matches any Unicode digit,
5057 as well as any Unicode letter, and underscore. Note also that PCRE_UCP
5058 affects \b, and \B because they are defined in terms of \w and \W.
5059 Matching these sequences is noticeably slower when PCRE_UCP is set.
5060
5061 The sequences \h, \H, \v, and \V are features that were added to Perl
5062 at release 5.10. In contrast to the other sequences, which match only
5063 ASCII characters by default, these always match certain high-valued
5064 codepoints, whether or not PCRE_UCP is set. The horizontal space char-
5065 acters are:
5066
5067 U+0009 Horizontal tab (HT)
5068 U+0020 Space
5069 U+00A0 Non-break space
5070 U+1680 Ogham space mark
5071 U+180E Mongolian vowel separator
5072 U+2000 En quad
5073 U+2001 Em quad
5074 U+2002 En space
5075 U+2003 Em space
5076 U+2004 Three-per-em space
5077 U+2005 Four-per-em space
5078 U+2006 Six-per-em space
5079 U+2007 Figure space
5080 U+2008 Punctuation space
5081 U+2009 Thin space
5082 U+200A Hair space
5083 U+202F Narrow no-break space
5084 U+205F Medium mathematical space
5085 U+3000 Ideographic space
5086
5087 The vertical space characters are:
5088
5089 U+000A Linefeed (LF)
5090 U+000B Vertical tab (VT)
5091 U+000C Form feed (FF)
5092 U+000D Carriage return (CR)
5093 U+0085 Next line (NEL)
5094 U+2028 Line separator
5095 U+2029 Paragraph separator
5096
5097 In 8-bit, non-UTF-8 mode, only the characters with codepoints less than
5098 256 are relevant.
5099
5100 Newline sequences
5101
5102 Outside a character class, by default, the escape sequence \R matches
5103 any Unicode newline sequence. In 8-bit non-UTF-8 mode \R is equivalent
5104 to the following:
5105
5106 (?>\r\n|\n|\x0b|\f|\r|\x85)
5107
5108 This is an example of an "atomic group", details of which are given
5109 below. This particular group matches either the two-character sequence
5110 CR followed by LF, or one of the single characters LF (linefeed,
5111 U+000A), VT (vertical tab, U+000B), FF (form feed, U+000C), CR (car-
5112 riage return, U+000D), or NEL (next line, U+0085). The two-character
5113 sequence is treated as a single unit that cannot be split.
5114
5115 In other modes, two additional characters whose codepoints are greater
5116 than 255 are added: LS (line separator, U+2028) and PS (paragraph sepa-
5117 rator, U+2029). Unicode character property support is not needed for
5118 these characters to be recognized.
5119
5120 It is possible to restrict \R to match only CR, LF, or CRLF (instead of
5121 the complete set of Unicode line endings) by setting the option
5122 PCRE_BSR_ANYCRLF either at compile time or when the pattern is matched.
5123 (BSR is an abbrevation for "backslash R".) This can be made the default
5124 when PCRE is built; if this is the case, the other behaviour can be
5125 requested via the PCRE_BSR_UNICODE option. It is also possible to
5126 specify these settings by starting a pattern string with one of the
5127 following sequences:
5128
5129 (*BSR_ANYCRLF) CR, LF, or CRLF only
5130 (*BSR_UNICODE) any Unicode newline sequence
5131
5132 These override the default and the options given to the compiling func-
5133 tion, but they can themselves be overridden by options given to a
5134 matching function. Note that these special settings, which are not
5135 Perl-compatible, are recognized only at the very start of a pattern,
5136 and that they must be in upper case. If more than one of them is
5137 present, the last one is used. They can be combined with a change of
5138 newline convention; for example, a pattern can start with:
5139
5140 (*ANY)(*BSR_ANYCRLF)
5141
5142 They can also be combined with the (*UTF8), (*UTF16), (*UTF32), (*UTF)
5143 or (*UCP) special sequences. Inside a character class, \R is treated as
5144 an unrecognized escape sequence, and so matches the letter "R" by
5145 default, but causes an error if PCRE_EXTRA is set.
5146
5147 Unicode character properties
5148
5149 When PCRE is built with Unicode character property support, three addi-
5150 tional escape sequences that match characters with specific properties
5151 are available. When in 8-bit non-UTF-8 mode, these sequences are of
5152 course limited to testing characters whose codepoints are less than
5153 256, but they do work in this mode. The extra escape sequences are:
5154
5155 \p{xx} a character with the xx property
5156 \P{xx} a character without the xx property
5157 \X a Unicode extended grapheme cluster
5158
5159 The property names represented by xx above are limited to the Unicode
5160 script names, the general category properties, "Any", which matches any
5161 character (including newline), and some special PCRE properties
5162 (described in the next section). Other Perl properties such as "InMu-
5163 sicalSymbols" are not currently supported by PCRE. Note that \P{Any}
5164 does not match any characters, so always causes a match failure.
5165
5166 Sets of Unicode characters are defined as belonging to certain scripts.
5167 A character from one of these sets can be matched using a script name.
5168 For example:
5169
5170 \p{Greek}
5171 \P{Han}
5172
5173 Those that are not part of an identified script are lumped together as
5174 "Common". The current list of scripts is:
5175
5176 Arabic, Armenian, Avestan, Balinese, Bamum, Batak, Bengali, Bopomofo,
5177 Brahmi, Braille, Buginese, Buhid, Canadian_Aboriginal, Carian, Chakma,
5178 Cham, Cherokee, Common, Coptic, Cuneiform, Cypriot, Cyrillic, Deseret,
5179 Devanagari, Egyptian_Hieroglyphs, Ethiopic, Georgian, Glagolitic,
5180 Gothic, Greek, Gujarati, Gurmukhi, Han, Hangul, Hanunoo, Hebrew, Hira-
5181 gana, Imperial_Aramaic, Inherited, Inscriptional_Pahlavi, Inscrip-
5182 tional_Parthian, Javanese, Kaithi, Kannada, Katakana, Kayah_Li,
5183 Kharoshthi, Khmer, Lao, Latin, Lepcha, Limbu, Linear_B, Lisu, Lycian,
5184 Lydian, Malayalam, Mandaic, Meetei_Mayek, Meroitic_Cursive,
5185 Meroitic_Hieroglyphs, Miao, Mongolian, Myanmar, New_Tai_Lue, Nko,
5186 Ogham, Old_Italic, Old_Persian, Old_South_Arabian, Old_Turkic,
5187 Ol_Chiki, Oriya, Osmanya, Phags_Pa, Phoenician, Rejang, Runic, Samari-
5188 tan, Saurashtra, Sharada, Shavian, Sinhala, Sora_Sompeng, Sundanese,
5189 Syloti_Nagri, Syriac, Tagalog, Tagbanwa, Tai_Le, Tai_Tham, Tai_Viet,
5190 Takri, Tamil, Telugu, Thaana, Thai, Tibetan, Tifinagh, Ugaritic, Vai,
5191 Yi.
5192
5193 Each character has exactly one Unicode general category property, spec-
5194 ified by a two-letter abbreviation. For compatibility with Perl, nega-
5195 tion can be specified by including a circumflex between the opening
5196 brace and the property name. For example, \p{^Lu} is the same as
5197 \P{Lu}.
5198
5199 If only one letter is specified with \p or \P, it includes all the gen-
5200 eral category properties that start with that letter. In this case, in
5201 the absence of negation, the curly brackets in the escape sequence are
5202 optional; these two examples have the same effect:
5203
5204 \p{L}
5205 \pL
5206
5207 The following general category property codes are supported:
5208
5209 C Other
5210 Cc Control
5211 Cf Format
5212 Cn Unassigned
5213 Co Private use
5214 Cs Surrogate
5215
5216 L Letter
5217 Ll Lower case letter
5218 Lm Modifier letter
5219 Lo Other letter
5220 Lt Title case letter
5221 Lu Upper case letter
5222
5223 M Mark
5224 Mc Spacing mark
5225 Me Enclosing mark
5226 Mn Non-spacing mark
5227
5228 N Number
5229 Nd Decimal number
5230 Nl Letter number
5231 No Other number
5232
5233 P Punctuation
5234 Pc Connector punctuation
5235 Pd Dash punctuation
5236 Pe Close punctuation
5237 Pf Final punctuation
5238 Pi Initial punctuation
5239 Po Other punctuation
5240 Ps Open punctuation
5241
5242 S Symbol
5243 Sc Currency symbol
5244 Sk Modifier symbol
5245 Sm Mathematical symbol
5246 So Other symbol
5247
5248 Z Separator
5249 Zl Line separator
5250 Zp Paragraph separator
5251 Zs Space separator
5252
5253 The special property L& is also supported: it matches a character that
5254 has the Lu, Ll, or Lt property, in other words, a letter that is not
5255 classified as a modifier or "other".
5256
5257 The Cs (Surrogate) property applies only to characters in the range
5258 U+D800 to U+DFFF. Such characters are not valid in Unicode strings and
5259 so cannot be tested by PCRE, unless UTF validity checking has been
5260 turned off (see the discussion of PCRE_NO_UTF8_CHECK,
5261 PCRE_NO_UTF16_CHECK and PCRE_NO_UTF32_CHECK in the pcreapi page). Perl
5262 does not support the Cs property.
5263
5264 The long synonyms for property names that Perl supports (such as
5265 \p{Letter}) are not supported by PCRE, nor is it permitted to prefix
5266 any of these properties with "Is".
5267
5268 No character that is in the Unicode table has the Cn (unassigned) prop-
5269 erty. Instead, this property is assumed for any code point that is not
5270 in the Unicode table.
5271
5272 Specifying caseless matching does not affect these escape sequences.
5273 For example, \p{Lu} always matches only upper case letters. This is
5274 different from the behaviour of current versions of Perl.
5275
5276 Matching characters by Unicode property is not fast, because PCRE has
5277 to do a multistage table lookup in order to find a character's prop-
5278 erty. That is why the traditional escape sequences such as \d and \w do
5279 not use Unicode properties in PCRE by default, though you can make them
5280 do so by setting the PCRE_UCP option or by starting the pattern with
5281 (*UCP).
5282
5283 Extended grapheme clusters
5284
5285 The \X escape matches any number of Unicode characters that form an
5286 "extended grapheme cluster", and treats the sequence as an atomic group
5287 (see below). Up to and including release 8.31, PCRE matched an ear-
5288 lier, simpler definition that was equivalent to
5289
5290 (?>\PM\pM*)
5291
5292 That is, it matched a character without the "mark" property, followed
5293 by zero or more characters with the "mark" property. Characters with
5294 the "mark" property are typically non-spacing accents that affect the
5295 preceding character.
5296
5297 This simple definition was extended in Unicode to include more compli-
5298 cated kinds of composite character by giving each character a grapheme
5299 breaking property, and creating rules that use these properties to
5300 define the boundaries of extended grapheme clusters. In releases of
5301 PCRE later than 8.31, \X matches one of these clusters.
5302
5303 \X always matches at least one character. Then it decides whether to
5304 add additional characters according to the following rules for ending a
5305 cluster:
5306
5307 1. End at the end of the subject string.
5308
5309 2. Do not end between CR and LF; otherwise end after any control char-
5310 acter.
5311
5312 3. Do not break Hangul (a Korean script) syllable sequences. Hangul
5313 characters are of five types: L, V, T, LV, and LVT. An L character may
5314 be followed by an L, V, LV, or LVT character; an LV or V character may
5315 be followed by a V or T character; an LVT or T character may be follwed
5316 only by a T character.
5317
5318 4. Do not end before extending characters or spacing marks. Characters
5319 with the "mark" property always have the "extend" grapheme breaking
5320 property.
5321
5322 5. Do not end after prepend characters.
5323
5324 6. Otherwise, end the cluster.
5325
5326 PCRE's additional properties
5327
5328 As well as the standard Unicode properties described above, PCRE sup-
5329 ports four more that make it possible to convert traditional escape
5330 sequences such as \w and \s and POSIX character classes to use Unicode
5331 properties. PCRE uses these non-standard, non-Perl properties inter-
5332 nally when PCRE_UCP is set. However, they may also be used explicitly.
5333 These properties are:
5334
5335 Xan Any alphanumeric character
5336 Xps Any POSIX space character
5337 Xsp Any Perl space character
5338 Xwd Any Perl "word" character
5339
5340 Xan matches characters that have either the L (letter) or the N (num-
5341 ber) property. Xps matches the characters tab, linefeed, vertical tab,
5342 form feed, or carriage return, and any other character that has the Z
5343 (separator) property. Xsp is the same as Xps, except that vertical tab
5344 is excluded. Xwd matches the same characters as Xan, plus underscore.
5345
5346 There is another non-standard property, Xuc, which matches any charac-
5347 ter that can be represented by a Universal Character Name in C++ and
5348 other programming languages. These are the characters $, @, ` (grave
5349 accent), and all characters with Unicode code points greater than or
5350 equal to U+00A0, except for the surrogates U+D800 to U+DFFF. Note that
5351 most base (ASCII) characters are excluded. (Universal Character Names
5352 are of the form \uHHHH or \UHHHHHHHH where H is a hexadecimal digit.
5353 Note that the Xuc property does not match these sequences but the char-
5354 acters that they represent.)
5355
5356 Resetting the match start
5357
5358 The escape sequence \K causes any previously matched characters not to
5359 be included in the final matched sequence. For example, the pattern:
5360
5361 foo\Kbar
5362
5363 matches "foobar", but reports that it has matched "bar". This feature
5364 is similar to a lookbehind assertion (described below). However, in
5365 this case, the part of the subject before the real match does not have
5366 to be of fixed length, as lookbehind assertions do. The use of \K does
5367 not interfere with the setting of captured substrings. For example,
5368 when the pattern
5369
5370 (foo)\Kbar
5371
5372 matches "foobar", the first substring is still set to "foo".
5373
5374 Perl documents that the use of \K within assertions is "not well
5375 defined". In PCRE, \K is acted upon when it occurs inside positive
5376 assertions, but is ignored in negative assertions.
5377
5378 Simple assertions
5379
5380 The final use of backslash is for certain simple assertions. An asser-
5381 tion specifies a condition that has to be met at a particular point in
5382 a match, without consuming any characters from the subject string. The
5383 use of subpatterns for more complicated assertions is described below.
5384 The backslashed assertions are:
5385
5386 \b matches at a word boundary
5387 \B matches when not at a word boundary
5388 \A matches at the start of the subject
5389 \Z matches at the end of the subject
5390 also matches before a newline at the end of the subject
5391 \z matches only at the end of the subject
5392 \G matches at the first matching position in the subject
5393
5394 Inside a character class, \b has a different meaning; it matches the
5395 backspace character. If any other of these assertions appears in a
5396 character class, by default it matches the corresponding literal char-
5397 acter (for example, \B matches the letter B). However, if the
5398 PCRE_EXTRA option is set, an "invalid escape sequence" error is gener-
5399 ated instead.
5400
5401 A word boundary is a position in the subject string where the current
5402 character and the previous character do not both match \w or \W (i.e.
5403 one matches \w and the other matches \W), or the start or end of the
5404 string if the first or last character matches \w, respectively. In a
5405 UTF mode, the meanings of \w and \W can be changed by setting the
5406 PCRE_UCP option. When this is done, it also affects \b and \B. Neither
5407 PCRE nor Perl has a separate "start of word" or "end of word" metase-
5408 quence. However, whatever follows \b normally determines which it is.
5409 For example, the fragment \ba matches "a" at the start of a word.
5410
5411 The \A, \Z, and \z assertions differ from the traditional circumflex
5412 and dollar (described in the next section) in that they only ever match
5413 at the very start and end of the subject string, whatever options are
5414 set. Thus, they are independent of multiline mode. These three asser-
5415 tions are not affected by the PCRE_NOTBOL or PCRE_NOTEOL options, which
5416 affect only the behaviour of the circumflex and dollar metacharacters.
5417 However, if the startoffset argument of pcre_exec() is non-zero, indi-
5418 cating that matching is to start at a point other than the beginning of
5419 the subject, \A can never match. The difference between \Z and \z is
5420 that \Z matches before a newline at the end of the string as well as at
5421 the very end, whereas \z matches only at the end.
5422
5423 The \G assertion is true only when the current matching position is at
5424 the start point of the match, as specified by the startoffset argument
5425 of pcre_exec(). It differs from \A when the value of startoffset is
5426 non-zero. By calling pcre_exec() multiple times with appropriate argu-
5427 ments, you can mimic Perl's /g option, and it is in this kind of imple-
5428 mentation where \G can be useful.
5429
5430 Note, however, that PCRE's interpretation of \G, as the start of the
5431 current match, is subtly different from Perl's, which defines it as the
5432 end of the previous match. In Perl, these can be different when the
5433 previously matched string was empty. Because PCRE does just one match
5434 at a time, it cannot reproduce this behaviour.
5435
5436 If all the alternatives of a pattern begin with \G, the expression is
5437 anchored to the starting match position, and the "anchored" flag is set
5438 in the compiled regular expression.
5439
5440
5441 CIRCUMFLEX AND DOLLAR
5442
5443 The circumflex and dollar metacharacters are zero-width assertions.
5444 That is, they test for a particular condition being true without con-
5445 suming any characters from the subject string.
5446
5447 Outside a character class, in the default matching mode, the circumflex
5448 character is an assertion that is true only if the current matching
5449 point is at the start of the subject string. If the startoffset argu-
5450 ment of pcre_exec() is non-zero, circumflex can never match if the
5451 PCRE_MULTILINE option is unset. Inside a character class, circumflex
5452 has an entirely different meaning (see below).
5453
5454 Circumflex need not be the first character of the pattern if a number
5455 of alternatives are involved, but it should be the first thing in each
5456 alternative in which it appears if the pattern is ever to match that
5457 branch. If all possible alternatives start with a circumflex, that is,
5458 if the pattern is constrained to match only at the start of the sub-
5459 ject, it is said to be an "anchored" pattern. (There are also other
5460 constructs that can cause a pattern to be anchored.)
5461
5462 The dollar character is an assertion that is true only if the current
5463 matching point is at the end of the subject string, or immediately
5464 before a newline at the end of the string (by default). Note, however,
5465 that it does not actually match the newline. Dollar need not be the
5466 last character of the pattern if a number of alternatives are involved,
5467 but it should be the last item in any branch in which it appears. Dol-
5468 lar has no special meaning in a character class.
5469
5470 The meaning of dollar can be changed so that it matches only at the
5471 very end of the string, by setting the PCRE_DOLLAR_ENDONLY option at
5472 compile time. This does not affect the \Z assertion.
5473
5474 The meanings of the circumflex and dollar characters are changed if the
5475 PCRE_MULTILINE option is set. When this is the case, a circumflex
5476 matches immediately after internal newlines as well as at the start of
5477 the subject string. It does not match after a newline that ends the
5478 string. A dollar matches before any newlines in the string, as well as
5479 at the very end, when PCRE_MULTILINE is set. When newline is specified
5480 as the two-character sequence CRLF, isolated CR and LF characters do
5481 not indicate newlines.
5482
5483 For example, the pattern /^abc$/ matches the subject string "def\nabc"
5484 (where \n represents a newline) in multiline mode, but not otherwise.
5485 Consequently, patterns that are anchored in single line mode because
5486 all branches start with ^ are not anchored in multiline mode, and a
5487 match for circumflex is possible when the startoffset argument of
5488 pcre_exec() is non-zero. The PCRE_DOLLAR_ENDONLY option is ignored if
5489 PCRE_MULTILINE is set.
5490
5491 Note that the sequences \A, \Z, and \z can be used to match the start
5492 and end of the subject in both modes, and if all branches of a pattern
5493 start with \A it is always anchored, whether or not PCRE_MULTILINE is
5494 set.
5495
5496
5497 FULL STOP (PERIOD, DOT) AND \N
5498
5499 Outside a character class, a dot in the pattern matches any one charac-
5500 ter in the subject string except (by default) a character that signi-
5501 fies the end of a line.
5502
5503 When a line ending is defined as a single character, dot never matches
5504 that character; when the two-character sequence CRLF is used, dot does
5505 not match CR if it is immediately followed by LF, but otherwise it
5506 matches all characters (including isolated CRs and LFs). When any Uni-
5507 code line endings are being recognized, dot does not match CR or LF or
5508 any of the other line ending characters.
5509
5510 The behaviour of dot with regard to newlines can be changed. If the
5511 PCRE_DOTALL option is set, a dot matches any one character, without
5512 exception. If the two-character sequence CRLF is present in the subject
5513 string, it takes two dots to match it.
5514
5515 The handling of dot is entirely independent of the handling of circum-
5516 flex and dollar, the only relationship being that they both involve
5517 newlines. Dot has no special meaning in a character class.
5518
5519 The escape sequence \N behaves like a dot, except that it is not
5520 affected by the PCRE_DOTALL option. In other words, it matches any
5521 character except one that signifies the end of a line. Perl also uses
5522 \N to match characters by name; PCRE does not support this.
5523
5524
5525 MATCHING A SINGLE DATA UNIT
5526
5527 Outside a character class, the escape sequence \C matches any one data
5528 unit, whether or not a UTF mode is set. In the 8-bit library, one data
5529 unit is one byte; in the 16-bit library it is a 16-bit unit; in the
5530 32-bit library it is a 32-bit unit. Unlike a dot, \C always matches
5531 line-ending characters. The feature is provided in Perl in order to
5532 match individual bytes in UTF-8 mode, but it is unclear how it can use-
5533 fully be used. Because \C breaks up characters into individual data
5534 units, matching one unit with \C in a UTF mode means that the rest of
5535 the string may start with a malformed UTF character. This has undefined
5536 results, because PCRE assumes that it is dealing with valid UTF strings
5537 (and by default it checks this at the start of processing unless the
5538 PCRE_NO_UTF8_CHECK, PCRE_NO_UTF16_CHECK or PCRE_NO_UTF32_CHECK option
5539 is used).
5540
5541 PCRE does not allow \C to appear in lookbehind assertions (described
5542 below) in a UTF mode, because this would make it impossible to calcu-
5543 late the length of the lookbehind.
5544
5545 In general, the \C escape sequence is best avoided. However, one way of
5546 using it that avoids the problem of malformed UTF characters is to use
5547 a lookahead to check the length of the next character, as in this pat-
5548 tern, which could be used with a UTF-8 string (ignore white space and
5549 line breaks):
5550
5551 (?| (?=[\x00-\x7f])(\C) |
5552 (?=[\x80-\x{7ff}])(\C)(\C) |
5553 (?=[\x{800}-\x{ffff}])(\C)(\C)(\C) |
5554 (?=[\x{10000}-\x{1fffff}])(\C)(\C)(\C)(\C))
5555
5556 A group that starts with (?| resets the capturing parentheses numbers
5557 in each alternative (see "Duplicate Subpattern Numbers" below). The
5558 assertions at the start of each branch check the next UTF-8 character
5559 for values whose encoding uses 1, 2, 3, or 4 bytes, respectively. The
5560 character's individual bytes are then captured by the appropriate num-
5561 ber of groups.
5562
5563
5564 SQUARE BRACKETS AND CHARACTER CLASSES
5565
5566 An opening square bracket introduces a character class, terminated by a
5567 closing square bracket. A closing square bracket on its own is not spe-
5568 cial by default. However, if the PCRE_JAVASCRIPT_COMPAT option is set,
5569 a lone closing square bracket causes a compile-time error. If a closing
5570 square bracket is required as a member of the class, it should be the
5571 first data character in the class (after an initial circumflex, if
5572 present) or escaped with a backslash.
5573
5574 A character class matches a single character in the subject. In a UTF
5575 mode, the character may be more than one data unit long. A matched
5576 character must be in the set of characters defined by the class, unless
5577 the first character in the class definition is a circumflex, in which
5578 case the subject character must not be in the set defined by the class.
5579 If a circumflex is actually required as a member of the class, ensure
5580 it is not the first character, or escape it with a backslash.
5581
5582 For example, the character class [aeiou] matches any lower case vowel,
5583 while [^aeiou] matches any character that is not a lower case vowel.
5584 Note that a circumflex is just a convenient notation for specifying the
5585 characters that are in the class by enumerating those that are not. A
5586 class that starts with a circumflex is not an assertion; it still con-
5587 sumes a character from the subject string, and therefore it fails if
5588 the current pointer is at the end of the string.
5589
5590 In UTF-8 (UTF-16, UTF-32) mode, characters with values greater than 255
5591 (0xffff) can be included in a class as a literal string of data units,
5592 or by using the \x{ escaping mechanism.
5593
5594 When caseless matching is set, any letters in a class represent both
5595 their upper case and lower case versions, so for example, a caseless
5596 [aeiou] matches "A" as well as "a", and a caseless [^aeiou] does not
5597 match "A", whereas a caseful version would. In a UTF mode, PCRE always
5598 understands the concept of case for characters whose values are less
5599 than 128, so caseless matching is always possible. For characters with
5600 higher values, the concept of case is supported if PCRE is compiled
5601 with Unicode property support, but not otherwise. If you want to use
5602 caseless matching in a UTF mode for characters 128 and above, you must
5603 ensure that PCRE is compiled with Unicode property support as well as
5604 with UTF support.
5605
5606 Characters that might indicate line breaks are never treated in any
5607 special way when matching character classes, whatever line-ending
5608 sequence is in use, and whatever setting of the PCRE_DOTALL and
5609 PCRE_MULTILINE options is used. A class such as [^a] always matches one
5610 of these characters.
5611
5612 The minus (hyphen) character can be used to specify a range of charac-
5613 ters in a character class. For example, [d-m] matches any letter
5614 between d and m, inclusive. If a minus character is required in a
5615 class, it must be escaped with a backslash or appear in a position
5616 where it cannot be interpreted as indicating a range, typically as the
5617 first or last character in the class.
5618
5619 It is not possible to have the literal character "]" as the end charac-
5620 ter of a range. A pattern such as [W-]46] is interpreted as a class of
5621 two characters ("W" and "-") followed by a literal string "46]", so it
5622 would match "W46]" or "-46]". However, if the "]" is escaped with a
5623 backslash it is interpreted as the end of range, so [W-\]46] is inter-
5624 preted as a class containing a range followed by two other characters.
5625 The octal or hexadecimal representation of "]" can also be used to end
5626 a range.
5627
5628 Ranges operate in the collating sequence of character values. They can
5629 also be used for characters specified numerically, for example
5630 [\000-\037]. Ranges can include any characters that are valid for the
5631 current mode.
5632
5633 If a range that includes letters is used when caseless matching is set,
5634 it matches the letters in either case. For example, [W-c] is equivalent
5635 to [][\\^_`wxyzabc], matched caselessly, and in a non-UTF mode, if
5636 character tables for a French locale are in use, [\xc8-\xcb] matches
5637 accented E characters in both cases. In UTF modes, PCRE supports the
5638 concept of case for characters with values greater than 128 only when
5639 it is compiled with Unicode property support.
5640
5641 The character escape sequences \d, \D, \h, \H, \p, \P, \s, \S, \v, \V,
5642 \w, and \W may appear in a character class, and add the characters that
5643 they match to the class. For example, [\dABCDEF] matches any hexadeci-
5644 mal digit. In UTF modes, the PCRE_UCP option affects the meanings of
5645 \d, \s, \w and their upper case partners, just as it does when they
5646 appear outside a character class, as described in the section entitled
5647 "Generic character types" above. The escape sequence \b has a different
5648 meaning inside a character class; it matches the backspace character.
5649 The sequences \B, \N, \R, and \X are not special inside a character
5650 class. Like any other unrecognized escape sequences, they are treated
5651 as the literal characters "B", "N", "R", and "X" by default, but cause
5652 an error if the PCRE_EXTRA option is set.
5653
5654 A circumflex can conveniently be used with the upper case character
5655 types to specify a more restricted set of characters than the matching
5656 lower case type. For example, the class [^\W_] matches any letter or
5657 digit, but not underscore, whereas [\w] includes underscore. A positive
5658 character class should be read as "something OR something OR ..." and a
5659 negative class as "NOT something AND NOT something AND NOT ...".
5660
5661 The only metacharacters that are recognized in character classes are
5662 backslash, hyphen (only where it can be interpreted as specifying a
5663 range), circumflex (only at the start), opening square bracket (only
5664 when it can be interpreted as introducing a POSIX class name - see the
5665 next section), and the terminating closing square bracket. However,
5666 escaping other non-alphanumeric characters does no harm.
5667
5668
5669 POSIX CHARACTER CLASSES
5670
5671 Perl supports the POSIX notation for character classes. This uses names
5672 enclosed by [: and :] within the enclosing square brackets. PCRE also
5673 supports this notation. For example,
5674
5675 [01[:alpha:]%]
5676
5677 matches "0", "1", any alphabetic character, or "%". The supported class
5678 names are:
5679
5680 alnum letters and digits
5681 alpha letters
5682 ascii character codes 0 - 127
5683 blank space or tab only
5684 cntrl control characters
5685 digit decimal digits (same as \d)
5686 graph printing characters, excluding space
5687 lower lower case letters
5688 print printing characters, including space
5689 punct printing characters, excluding letters and digits and space
5690 space white space (not quite the same as \s)
5691 upper upper case letters
5692 word "word" characters (same as \w)
5693 xdigit hexadecimal digits
5694
5695 The "space" characters are HT (9), LF (10), VT (11), FF (12), CR (13),
5696 and space (32). Notice that this list includes the VT character (code
5697 11). This makes "space" different to \s, which does not include VT (for
5698 Perl compatibility).
5699
5700 The name "word" is a Perl extension, and "blank" is a GNU extension
5701 from Perl 5.8. Another Perl extension is negation, which is indicated
5702 by a ^ character after the colon. For example,
5703
5704 [12[:^digit:]]
5705
5706 matches "1", "2", or any non-digit. PCRE (and Perl) also recognize the
5707 POSIX syntax [.ch.] and [=ch=] where "ch" is a "collating element", but
5708 these are not supported, and an error is given if they are encountered.
5709
5710 By default, in UTF modes, characters with values greater than 128 do
5711 not match any of the POSIX character classes. However, if the PCRE_UCP
5712 option is passed to pcre_compile(), some of the classes are changed so
5713 that Unicode character properties are used. This is achieved by replac-
5714 ing the POSIX classes by other sequences, as follows:
5715
5716 [:alnum:] becomes \p{Xan}
5717 [:alpha:] becomes \p{L}
5718 [:blank:] becomes \h
5719 [:digit:] becomes \p{Nd}
5720 [:lower:] becomes \p{Ll}
5721 [:space:] becomes \p{Xps}
5722 [:upper:] becomes \p{Lu}
5723 [:word:] becomes \p{Xwd}
5724
5725 Negated versions, such as [:^alpha:] use \P instead of \p. The other
5726 POSIX classes are unchanged, and match only characters with code points
5727 less than 128.
5728
5729
5730 VERTICAL BAR
5731
5732 Vertical bar characters are used to separate alternative patterns. For
5733 example, the pattern
5734
5735 gilbert|sullivan
5736
5737 matches either "gilbert" or "sullivan". Any number of alternatives may
5738 appear, and an empty alternative is permitted (matching the empty
5739 string). The matching process tries each alternative in turn, from left
5740 to right, and the first one that succeeds is used. If the alternatives
5741 are within a subpattern (defined below), "succeeds" means matching the
5742 rest of the main pattern as well as the alternative in the subpattern.
5743
5744
5745 INTERNAL OPTION SETTING
5746
5747 The settings of the PCRE_CASELESS, PCRE_MULTILINE, PCRE_DOTALL, and
5748 PCRE_EXTENDED options (which are Perl-compatible) can be changed from
5749 within the pattern by a sequence of Perl option letters enclosed
5750 between "(?" and ")". The option letters are
5751
5752 i for PCRE_CASELESS
5753 m for PCRE_MULTILINE
5754 s for PCRE_DOTALL
5755 x for PCRE_EXTENDED
5756
5757 For example, (?im) sets caseless, multiline matching. It is also possi-
5758 ble to unset these options by preceding the letter with a hyphen, and a
5759 combined setting and unsetting such as (?im-sx), which sets PCRE_CASE-
5760 LESS and PCRE_MULTILINE while unsetting PCRE_DOTALL and PCRE_EXTENDED,
5761 is also permitted. If a letter appears both before and after the
5762 hyphen, the option is unset.
5763
5764 The PCRE-specific options PCRE_DUPNAMES, PCRE_UNGREEDY, and PCRE_EXTRA
5765 can be changed in the same way as the Perl-compatible options by using
5766 the characters J, U and X respectively.
5767
5768 When one of these option changes occurs at top level (that is, not
5769 inside subpattern parentheses), the change applies to the remainder of
5770 the pattern that follows. If the change is placed right at the start of
5771 a pattern, PCRE extracts it into the global options (and it will there-
5772 fore show up in data extracted by the pcre_fullinfo() function).
5773
5774 An option change within a subpattern (see below for a description of
5775 subpatterns) affects only that part of the subpattern that follows it,
5776 so
5777
5778 (a(?i)b)c
5779
5780 matches abc and aBc and no other strings (assuming PCRE_CASELESS is not
5781 used). By this means, options can be made to have different settings
5782 in different parts of the pattern. Any changes made in one alternative
5783 do carry on into subsequent branches within the same subpattern. For
5784 example,
5785
5786 (a(?i)b|c)
5787
5788 matches "ab", "aB", "c", and "C", even though when matching "C" the
5789 first branch is abandoned before the option setting. This is because
5790 the effects of option settings happen at compile time. There would be
5791 some very weird behaviour otherwise.
5792
5793 Note: There are other PCRE-specific options that can be set by the
5794 application when the compiling or matching functions are called. In
5795 some cases the pattern can contain special leading sequences such as
5796 (*CRLF) to override what the application has set or what has been
5797 defaulted. Details are given in the section entitled "Newline
5798 sequences" above. There are also the (*UTF8), (*UTF16),(*UTF32), and
5799 (*UCP) leading sequences that can be used to set UTF and Unicode prop-
5800 erty modes; they are equivalent to setting the PCRE_UTF8, PCRE_UTF16,
5801 PCRE_UTF32 and the PCRE_UCP options, respectively. The (*UTF) sequence
5802 is a generic version that can be used with any of the libraries. How-
5803 ever, the application can set the PCRE_NEVER_UTF option, which locks
5804 out the use of the (*UTF) sequences.
5805
5806
5807 SUBPATTERNS
5808
5809 Subpatterns are delimited by parentheses (round brackets), which can be
5810 nested. Turning part of a pattern into a subpattern does two things:
5811
5812 1. It localizes a set of alternatives. For example, the pattern
5813
5814 cat(aract|erpillar|)
5815
5816 matches "cataract", "caterpillar", or "cat". Without the parentheses,
5817 it would match "cataract", "erpillar" or an empty string.
5818
5819 2. It sets up the subpattern as a capturing subpattern. This means
5820 that, when the whole pattern matches, that portion of the subject
5821 string that matched the subpattern is passed back to the caller via the
5822 ovector argument of the matching function. (This applies only to the
5823 traditional matching functions; the DFA matching functions do not sup-
5824 port capturing.)
5825
5826 Opening parentheses are counted from left to right (starting from 1) to
5827 obtain numbers for the capturing subpatterns. For example, if the
5828 string "the red king" is matched against the pattern
5829
5830 the ((red|white) (king|queen))
5831
5832 the captured substrings are "red king", "red", and "king", and are num-
5833 bered 1, 2, and 3, respectively.
5834
5835 The fact that plain parentheses fulfil two functions is not always
5836 helpful. There are often times when a grouping subpattern is required
5837 without a capturing requirement. If an opening parenthesis is followed
5838 by a question mark and a colon, the subpattern does not do any captur-
5839 ing, and is not counted when computing the number of any subsequent
5840 capturing subpatterns. For example, if the string "the white queen" is
5841 matched against the pattern
5842
5843 the ((?:red|white) (king|queen))
5844
5845 the captured substrings are "white queen" and "queen", and are numbered
5846 1 and 2. The maximum number of capturing subpatterns is 65535.
5847
5848 As a convenient shorthand, if any option settings are required at the
5849 start of a non-capturing subpattern, the option letters may appear
5850 between the "?" and the ":". Thus the two patterns
5851
5852 (?i:saturday|sunday)
5853 (?:(?i)saturday|sunday)
5854
5855 match exactly the same set of strings. Because alternative branches are
5856 tried from left to right, and options are not reset until the end of
5857 the subpattern is reached, an option setting in one branch does affect
5858 subsequent branches, so the above patterns match "SUNDAY" as well as
5859 "Saturday".
5860
5861
5862 DUPLICATE SUBPATTERN NUMBERS
5863
5864 Perl 5.10 introduced a feature whereby each alternative in a subpattern
5865 uses the same numbers for its capturing parentheses. Such a subpattern
5866 starts with (?| and is itself a non-capturing subpattern. For example,
5867 consider this pattern:
5868
5869 (?|(Sat)ur|(Sun))day
5870
5871 Because the two alternatives are inside a (?| group, both sets of cap-
5872 turing parentheses are numbered one. Thus, when the pattern matches,
5873 you can look at captured substring number one, whichever alternative
5874 matched. This construct is useful when you want to capture part, but
5875 not all, of one of a number of alternatives. Inside a (?| group, paren-
5876 theses are numbered as usual, but the number is reset at the start of
5877 each branch. The numbers of any capturing parentheses that follow the
5878 subpattern start after the highest number used in any branch. The fol-
5879 lowing example is taken from the Perl documentation. The numbers under-
5880 neath show in which buffer the captured content will be stored.
5881
5882 # before ---------------branch-reset----------- after
5883 / ( a ) (?| x ( y ) z | (p (q) r) | (t) u (v) ) ( z ) /x
5884 # 1 2 2 3 2 3 4
5885
5886 A back reference to a numbered subpattern uses the most recent value
5887 that is set for that number by any subpattern. The following pattern
5888 matches "abcabc" or "defdef":
5889
5890 /(?|(abc)|(def))\1/
5891
5892 In contrast, a subroutine call to a numbered subpattern always refers
5893 to the first one in the pattern with the given number. The following
5894 pattern matches "abcabc" or "defabc":
5895
5896 /(?|(abc)|(def))(?1)/
5897
5898 If a condition test for a subpattern's having matched refers to a non-
5899 unique number, the test is true if any of the subpatterns of that num-
5900 ber have matched.
5901
5902 An alternative approach to using this "branch reset" feature is to use
5903 duplicate named subpatterns, as described in the next section.
5904
5905
5906 NAMED SUBPATTERNS
5907
5908 Identifying capturing parentheses by number is simple, but it can be
5909 very hard to keep track of the numbers in complicated regular expres-
5910 sions. Furthermore, if an expression is modified, the numbers may
5911 change. To help with this difficulty, PCRE supports the naming of sub-
5912 patterns. This feature was not added to Perl until release 5.10. Python
5913 had the feature earlier, and PCRE introduced it at release 4.0, using
5914 the Python syntax. PCRE now supports both the Perl and the Python syn-
5915 tax. Perl allows identically numbered subpatterns to have different
5916 names, but PCRE does not.
5917
5918 In PCRE, a subpattern can be named in one of three ways: (?<name>...)
5919 or (?'name'...) as in Perl, or (?P<name>...) as in Python. References
5920 to capturing parentheses from other parts of the pattern, such as back
5921 references, recursion, and conditions, can be made by name as well as
5922 by number.
5923
5924 Names consist of up to 32 alphanumeric characters and underscores.
5925 Named capturing parentheses are still allocated numbers as well as
5926 names, exactly as if the names were not present. The PCRE API provides
5927 function calls for extracting the name-to-number translation table from
5928 a compiled pattern. There is also a convenience function for extracting
5929 a captured substring by name.
5930
5931 By default, a name must be unique within a pattern, but it is possible
5932 to relax this constraint by setting the PCRE_DUPNAMES option at compile
5933 time. (Duplicate names are also always permitted for subpatterns with
5934 the same number, set up as described in the previous section.) Dupli-
5935 cate names can be useful for patterns where only one instance of the
5936 named parentheses can match. Suppose you want to match the name of a
5937 weekday, either as a 3-letter abbreviation or as the full name, and in
5938 both cases you want to extract the abbreviation. This pattern (ignoring
5939 the line breaks) does the job:
5940
5941 (?<DN>Mon|Fri|Sun)(?:day)?|
5942 (?<DN>Tue)(?:sday)?|
5943 (?<DN>Wed)(?:nesday)?|
5944 (?<DN>Thu)(?:rsday)?|
5945 (?<DN>Sat)(?:urday)?
5946
5947 There are five capturing substrings, but only one is ever set after a
5948 match. (An alternative way of solving this problem is to use a "branch
5949 reset" subpattern, as described in the previous section.)
5950
5951 The convenience function for extracting the data by name returns the
5952 substring for the first (and in this example, the only) subpattern of
5953 that name that matched. This saves searching to find which numbered
5954 subpattern it was.
5955
5956 If you make a back reference to a non-unique named subpattern from
5957 elsewhere in the pattern, the one that corresponds to the first occur-
5958 rence of the name is used. In the absence of duplicate numbers (see the
5959 previous section) this is the one with the lowest number. If you use a
5960 named reference in a condition test (see the section about conditions
5961 below), either to check whether a subpattern has matched, or to check
5962 for recursion, all subpatterns with the same name are tested. If the
5963 condition is true for any one of them, the overall condition is true.
5964 This is the same behaviour as testing by number. For further details of
5965 the interfaces for handling named subpatterns, see the pcreapi documen-
5966 tation.
5967
5968 Warning: You cannot use different names to distinguish between two sub-
5969 patterns with the same number because PCRE uses only the numbers when
5970 matching. For this reason, an error is given at compile time if differ-
5971 ent names are given to subpatterns with the same number. However, you
5972 can give the same name to subpatterns with the same number, even when
5973 PCRE_DUPNAMES is not set.
5974
5975
5976 REPETITION
5977
5978 Repetition is specified by quantifiers, which can follow any of the
5979 following items:
5980
5981 a literal data character
5982 the dot metacharacter
5983 the \C escape sequence
5984 the \X escape sequence
5985 the \R escape sequence
5986 an escape such as \d or \pL that matches a single character
5987 a character class
5988 a back reference (see next section)
5989 a parenthesized subpattern (including assertions)
5990 a subroutine call to a subpattern (recursive or otherwise)
5991
5992 The general repetition quantifier specifies a minimum and maximum num-
5993 ber of permitted matches, by giving the two numbers in curly brackets
5994 (braces), separated by a comma. The numbers must be less than 65536,
5995 and the first must be less than or equal to the second. For example:
5996
5997 z{2,4}
5998
5999 matches "zz", "zzz", or "zzzz". A closing brace on its own is not a
6000 special character. If the second number is omitted, but the comma is
6001 present, there is no upper limit; if the second number and the comma
6002 are both omitted, the quantifier specifies an exact number of required
6003 matches. Thus
6004
6005 [aeiou]{3,}
6006
6007 matches at least 3 successive vowels, but may match many more, while
6008
6009 \d{8}
6010
6011 matches exactly 8 digits. An opening curly bracket that appears in a
6012 position where a quantifier is not allowed, or one that does not match
6013 the syntax of a quantifier, is taken as a literal character. For exam-
6014 ple, {,6} is not a quantifier, but a literal string of four characters.
6015
6016 In UTF modes, quantifiers apply to characters rather than to individual
6017 data units. Thus, for example, \x{100}{2} matches two characters, each
6018 of which is represented by a two-byte sequence in a UTF-8 string. Simi-
6019 larly, \X{3} matches three Unicode extended grapheme clusters, each of
6020 which may be several data units long (and they may be of different
6021 lengths).
6022
6023 The quantifier {0} is permitted, causing the expression to behave as if
6024 the previous item and the quantifier were not present. This may be use-
6025 ful for subpatterns that are referenced as subroutines from elsewhere
6026 in the pattern (but see also the section entitled "Defining subpatterns
6027 for use by reference only" below). Items other than subpatterns that
6028 have a {0} quantifier are omitted from the compiled pattern.
6029
6030 For convenience, the three most common quantifiers have single-charac-
6031 ter abbreviations:
6032
6033 * is equivalent to {0,}
6034 + is equivalent to {1,}
6035 ? is equivalent to {0,1}
6036
6037 It is possible to construct infinite loops by following a subpattern
6038 that can match no characters with a quantifier that has no upper limit,
6039 for example:
6040<