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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 that supports 32-bit character strings (including UTF-32
37 strings). The build process allows any combination of the 8-, 16- and
38 32-bit libraries. The work to make this possible was done by Christian
39 Persch.
40
41 The three libraries contain identical sets of functions, except that
42 the names in the 16-bit library start with pcre16_ instead of pcre_,
43 and the names in the 32-bit library start with pcre32_ instead of
44 pcre_. To avoid over-complication and reduce the documentation mainte-
45 nance load, most of the documentation describes the 8-bit library, with
46 the differences for the 16-bit and 32-bit libraries described sepa-
47 rately in the pcre16 and pcre32 pages. References to functions or
48 structures of the form pcre[16|32]_xxx should be read as meaning
49 "pcre_xxx when using the 8-bit library, pcre16_xxx when using the
50 16-bit library, or pcre32_xxx when using the 32-bit library".
51
52 The current implementation of PCRE corresponds approximately with Perl
53 5.12, including support for UTF-8/16/32 encoded strings and Unicode
54 general category properties. However, UTF-8/16/32 and Unicode support
55 has to be explicitly enabled; it is not the default. The Unicode tables
56 correspond to Unicode release 6.3.0.
57
58 In addition to the Perl-compatible matching function, PCRE contains an
59 alternative function that matches the same compiled patterns in a dif-
60 ferent way. In certain circumstances, the alternative function has some
61 advantages. For a discussion of the two matching algorithms, see the
62 pcrematching page.
63
64 PCRE is written in C and released as a C library. A number of people
65 have written wrappers and interfaces of various kinds. In particular,
66 Google Inc. have provided a comprehensive C++ wrapper for the 8-bit
67 library. This is now included as part of the PCRE distribution. The
68 pcrecpp page has details of this interface. Other people's contribu-
69 tions can be found in the Contrib directory at the primary FTP site,
70 which is:
71
72 ftp://ftp.csx.cam.ac.uk/pub/software/programming/pcre
73
74 Details of exactly which Perl regular expression features are and are
75 not supported by PCRE are given in separate documents. See the pcrepat-
76 tern and pcrecompat pages. There is a syntax summary in the pcresyntax
77 page.
78
79 Some features of PCRE can be included, excluded, or changed when the
80 library is built. The pcre_config() function makes it possible for a
81 client to discover which features are available. The features them-
82 selves are described in the pcrebuild page. Documentation about build-
83 ing PCRE for various operating systems can be found in the README and
84 NON-AUTOTOOLS_BUILD files in the source distribution.
85
86 The libraries contains a number of undocumented internal functions and
87 data tables that are used by more than one of the exported external
88 functions, but which are not intended for use by external callers.
89 Their names all begin with "_pcre_" or "_pcre16_" or "_pcre32_", which
90 hopefully will not provoke any name clashes. In some environments, it
91 is possible to control which external symbols are exported when a
92 shared library is built, and in these cases the undocumented symbols
93 are not exported.
94
95
96 SECURITY CONSIDERATIONS
97
98 If you are using PCRE in a non-UTF application that permits users to
99 supply arbitrary patterns for compilation, you should be aware of a
100 feature that allows users to turn on UTF support from within a pattern,
101 provided that PCRE was built with UTF support. For example, an 8-bit
102 pattern that begins with "(*UTF8)" or "(*UTF)" turns on UTF-8 mode,
103 which interprets patterns and subjects as strings of UTF-8 characters
104 instead of individual 8-bit characters. This causes both the pattern
105 and any data against which it is matched to be checked for UTF-8 valid-
106 ity. If the data string is very long, such a check might use suffi-
107 ciently many resources as to cause your application to lose perfor-
108 mance.
109
110 One way of guarding against this possibility is to use the
111 pcre_fullinfo() function to check the compiled pattern's options for
112 UTF. Alternatively, from release 8.33, you can set the PCRE_NEVER_UTF
113 option at compile time. This causes an compile time error if a pattern
114 contains a UTF-setting sequence.
115
116 If your application is one that supports UTF, be aware that validity
117 checking can take time. If the same data string is to be matched many
118 times, you can use the PCRE_NO_UTF[8|16|32]_CHECK option for the second
119 and subsequent matches to save redundant checks.
120
121 Another way that performance can be hit is by running a pattern that
122 has a very large search tree against a string that will never match.
123 Nested unlimited repeats in a pattern are a common example. PCRE pro-
124 vides some protection against this: see the PCRE_EXTRA_MATCH_LIMIT fea-
125 ture in the pcreapi page.
126
127
128 USER DOCUMENTATION
129
130 The user documentation for PCRE comprises a number of different sec-
131 tions. In the "man" format, each of these is a separate "man page". In
132 the HTML format, each is a separate page, linked from the index page.
133 In the plain text format, all the sections, except the pcredemo sec-
134 tion, are concatenated, for ease of searching. The sections are as fol-
135 lows:
136
137 pcre this document
138 pcre-config show PCRE installation configuration information
139 pcre16 details of the 16-bit library
140 pcre32 details of the 32-bit library
141 pcreapi details of PCRE's native C API
142 pcrebuild building PCRE
143 pcrecallout details of the callout feature
144 pcrecompat discussion of Perl compatibility
145 pcrecpp details of the C++ wrapper for the 8-bit library
146 pcredemo a demonstration C program that uses PCRE
147 pcregrep description of the pcregrep command (8-bit only)
148 pcrejit discussion of the just-in-time optimization support
149 pcrelimits details of size and other limits
150 pcrematching discussion of the two matching algorithms
151 pcrepartial details of the partial matching facility
152 pcrepattern syntax and semantics of supported
153 regular expressions
154 pcreperform discussion of performance issues
155 pcreposix the POSIX-compatible C API for the 8-bit library
156 pcreprecompile details of saving and re-using precompiled patterns
157 pcresample discussion of the pcredemo program
158 pcrestack discussion of stack usage
159 pcresyntax quick syntax reference
160 pcretest description of the pcretest testing command
161 pcreunicode discussion of Unicode and UTF-8/16/32 support
162
163 In addition, in the "man" and HTML formats, there is a short page for
164 each C library function, listing its arguments and results.
165
166
167 AUTHOR
168
169 Philip Hazel
170 University Computing Service
171 Cambridge CB2 3QH, England.
172
173 Putting an actual email address here seems to have been a spam magnet,
174 so I've taken it away. If you want to email me, use my two initials,
175 followed by the two digits 10, at the domain cam.ac.uk.
176
177
178 REVISION
179
180 Last updated: 13 May 2013
181 Copyright (c) 1997-2013 University of Cambridge.
182 ------------------------------------------------------------------------------
183
184
185 PCRE(3) Library Functions Manual PCRE(3)
186
187
188
189 NAME
190 PCRE - Perl-compatible regular expressions
191
192 #include <pcre.h>
193
194
195 PCRE 16-BIT API BASIC FUNCTIONS
196
197 pcre16 *pcre16_compile(PCRE_SPTR16 pattern, int options,
198 const char **errptr, int *erroffset,
199 const unsigned char *tableptr);
200
201 pcre16 *pcre16_compile2(PCRE_SPTR16 pattern, int options,
202 int *errorcodeptr,
203 const char **errptr, int *erroffset,
204 const unsigned char *tableptr);
205
206 pcre16_extra *pcre16_study(const pcre16 *code, int options,
207 const char **errptr);
208
209 void pcre16_free_study(pcre16_extra *extra);
210
211 int pcre16_exec(const pcre16 *code, const pcre16_extra *extra,
212 PCRE_SPTR16 subject, int length, int startoffset,
213 int options, int *ovector, int ovecsize);
214
215 int pcre16_dfa_exec(const pcre16 *code, const pcre16_extra *extra,
216 PCRE_SPTR16 subject, int length, int startoffset,
217 int options, int *ovector, int ovecsize,
218 int *workspace, int wscount);
219
220
221 PCRE 16-BIT API STRING EXTRACTION FUNCTIONS
222
223 int pcre16_copy_named_substring(const pcre16 *code,
224 PCRE_SPTR16 subject, int *ovector,
225 int stringcount, PCRE_SPTR16 stringname,
226 PCRE_UCHAR16 *buffer, int buffersize);
227
228 int pcre16_copy_substring(PCRE_SPTR16 subject, int *ovector,
229 int stringcount, int stringnumber, PCRE_UCHAR16 *buffer,
230 int buffersize);
231
232 int pcre16_get_named_substring(const pcre16 *code,
233 PCRE_SPTR16 subject, int *ovector,
234 int stringcount, PCRE_SPTR16 stringname,
235 PCRE_SPTR16 *stringptr);
236
237 int pcre16_get_stringnumber(const pcre16 *code,
238 PCRE_SPTR16 name);
239
240 int pcre16_get_stringtable_entries(const pcre16 *code,
241 PCRE_SPTR16 name, PCRE_UCHAR16 **first, PCRE_UCHAR16 **last);
242
243 int pcre16_get_substring(PCRE_SPTR16 subject, int *ovector,
244 int stringcount, int stringnumber,
245 PCRE_SPTR16 *stringptr);
246
247 int pcre16_get_substring_list(PCRE_SPTR16 subject,
248 int *ovector, int stringcount, PCRE_SPTR16 **listptr);
249
250 void pcre16_free_substring(PCRE_SPTR16 stringptr);
251
252 void pcre16_free_substring_list(PCRE_SPTR16 *stringptr);
253
254
255 PCRE 16-BIT API AUXILIARY FUNCTIONS
256
257 pcre16_jit_stack *pcre16_jit_stack_alloc(int startsize, int maxsize);
258
259 void pcre16_jit_stack_free(pcre16_jit_stack *stack);
260
261 void pcre16_assign_jit_stack(pcre16_extra *extra,
262 pcre16_jit_callback callback, void *data);
263
264 const unsigned char *pcre16_maketables(void);
265
266 int pcre16_fullinfo(const pcre16 *code, const pcre16_extra *extra,
267 int what, void *where);
268
269 int pcre16_refcount(pcre16 *code, int adjust);
270
271 int pcre16_config(int what, void *where);
272
273 const char *pcre16_version(void);
274
275 int pcre16_pattern_to_host_byte_order(pcre16 *code,
276 pcre16_extra *extra, const unsigned char *tables);
277
278
279 PCRE 16-BIT API INDIRECTED FUNCTIONS
280
281 void *(*pcre16_malloc)(size_t);
282
283 void (*pcre16_free)(void *);
284
285 void *(*pcre16_stack_malloc)(size_t);
286
287 void (*pcre16_stack_free)(void *);
288
289 int (*pcre16_callout)(pcre16_callout_block *);
290
291
292 PCRE 16-BIT API 16-BIT-ONLY FUNCTION
293
294 int pcre16_utf16_to_host_byte_order(PCRE_UCHAR16 *output,
295 PCRE_SPTR16 input, int length, int *byte_order,
296 int keep_boms);
297
298
299 THE PCRE 16-BIT LIBRARY
300
301 Starting with release 8.30, it is possible to compile a PCRE library
302 that supports 16-bit character strings, including UTF-16 strings, as
303 well as or instead of the original 8-bit library. The majority of the
304 work to make this possible was done by Zoltan Herczeg. The two
305 libraries contain identical sets of functions, used in exactly the same
306 way. Only the names of the functions and the data types of their argu-
307 ments and results are different. To avoid over-complication and reduce
308 the documentation maintenance load, most of the PCRE documentation
309 describes the 8-bit library, with only occasional references to the
310 16-bit library. This page describes what is different when you use the
311 16-bit library.
312
313 WARNING: A single application can be linked with both libraries, but
314 you must take care when processing any particular pattern to use func-
315 tions from just one library. For example, if you want to study a pat-
316 tern that was compiled with pcre16_compile(), you must do so with
317 pcre16_study(), not pcre_study(), and you must free the study data with
318 pcre16_free_study().
319
320
321 THE HEADER FILE
322
323 There is only one header file, pcre.h. It contains prototypes for all
324 the functions in all libraries, as well as definitions of flags, struc-
325 tures, error codes, etc.
326
327
328 THE LIBRARY NAME
329
330 In Unix-like systems, the 16-bit library is called libpcre16, and can
331 normally be accesss by adding -lpcre16 to the command for linking an
332 application that uses PCRE.
333
334
335 STRING TYPES
336
337 In the 8-bit library, strings are passed to PCRE library functions as
338 vectors of bytes with the C type "char *". In the 16-bit library,
339 strings are passed as vectors of unsigned 16-bit quantities. The macro
340 PCRE_UCHAR16 specifies an appropriate data type, and PCRE_SPTR16 is
341 defined as "const PCRE_UCHAR16 *". In very many environments, "short
342 int" is a 16-bit data type. When PCRE is built, it defines PCRE_UCHAR16
343 as "unsigned short int", but checks that it really is a 16-bit data
344 type. If it is not, the build fails with an error message telling the
345 maintainer to modify the definition appropriately.
346
347
348 STRUCTURE TYPES
349
350 The types of the opaque structures that are used for compiled 16-bit
351 patterns and JIT stacks are pcre16 and pcre16_jit_stack respectively.
352 The type of the user-accessible structure that is returned by
353 pcre16_study() is pcre16_extra, and the type of the structure that is
354 used for passing data to a callout function is pcre16_callout_block.
355 These structures contain the same fields, with the same names, as their
356 8-bit counterparts. The only difference is that pointers to character
357 strings are 16-bit instead of 8-bit types.
358
359
360 16-BIT FUNCTIONS
361
362 For every function in the 8-bit library there is a corresponding func-
363 tion in the 16-bit library with a name that starts with pcre16_ instead
364 of pcre_. The prototypes are listed above. In addition, there is one
365 extra function, pcre16_utf16_to_host_byte_order(). This is a utility
366 function that converts a UTF-16 character string to host byte order if
367 necessary. The other 16-bit functions expect the strings they are
368 passed to be in host byte order.
369
370 The input and output arguments of pcre16_utf16_to_host_byte_order() may
371 point to the same address, that is, conversion in place is supported.
372 The output buffer must be at least as long as the input.
373
374 The length argument specifies the number of 16-bit data units in the
375 input string; a negative value specifies a zero-terminated string.
376
377 If byte_order is NULL, it is assumed that the string starts off in host
378 byte order. This may be changed by byte-order marks (BOMs) anywhere in
379 the string (commonly as the first character).
380
381 If byte_order is not NULL, a non-zero value of the integer to which it
382 points means that the input starts off in host byte order, otherwise
383 the opposite order is assumed. Again, BOMs in the string can change
384 this. The final byte order is passed back at the end of processing.
385
386 If keep_boms is not zero, byte-order mark characters (0xfeff) are
387 copied into the output string. Otherwise they are discarded.
388
389 The result of the function is the number of 16-bit units placed into
390 the output buffer, including the zero terminator if the string was
391 zero-terminated.
392
393
394 SUBJECT STRING OFFSETS
395
396 The lengths and starting offsets of subject strings must be specified
397 in 16-bit data units, and the offsets within subject strings that are
398 returned by the matching functions are in also 16-bit units rather than
399 bytes.
400
401
402 NAMED SUBPATTERNS
403
404 The name-to-number translation table that is maintained for named sub-
405 patterns uses 16-bit characters. The pcre16_get_stringtable_entries()
406 function returns the length of each entry in the table as the number of
407 16-bit data units.
408
409
410 OPTION NAMES
411
412 There are two new general option names, PCRE_UTF16 and
413 PCRE_NO_UTF16_CHECK, which correspond to PCRE_UTF8 and
414 PCRE_NO_UTF8_CHECK in the 8-bit library. In fact, these new options
415 define the same bits in the options word. There is a discussion about
416 the validity of UTF-16 strings in the pcreunicode page.
417
418 For the pcre16_config() function there is an option PCRE_CONFIG_UTF16
419 that returns 1 if UTF-16 support is configured, otherwise 0. If this
420 option is given to pcre_config() or pcre32_config(), or if the
421 PCRE_CONFIG_UTF8 or PCRE_CONFIG_UTF32 option is given to pcre16_con-
422 fig(), the result is the PCRE_ERROR_BADOPTION error.
423
424
425 CHARACTER CODES
426
427 In 16-bit mode, when PCRE_UTF16 is not set, character values are
428 treated in the same way as in 8-bit, non UTF-8 mode, except, of course,
429 that they can range from 0 to 0xffff instead of 0 to 0xff. Character
430 types for characters less than 0xff can therefore be influenced by the
431 locale in the same way as before. Characters greater than 0xff have
432 only one case, and no "type" (such as letter or digit).
433
434 In UTF-16 mode, the character code is Unicode, in the range 0 to
435 0x10ffff, with the exception of values in the range 0xd800 to 0xdfff
436 because those are "surrogate" values that are used in pairs to encode
437 values greater than 0xffff.
438
439 A UTF-16 string can indicate its endianness by special code knows as a
440 byte-order mark (BOM). The PCRE functions do not handle this, expecting
441 strings to be in host byte order. A utility function called
442 pcre16_utf16_to_host_byte_order() is provided to help with this (see
443 above).
444
445
446 ERROR NAMES
447
448 The errors PCRE_ERROR_BADUTF16_OFFSET and PCRE_ERROR_SHORTUTF16 corre-
449 spond to their 8-bit counterparts. The error PCRE_ERROR_BADMODE is
450 given when a compiled pattern is passed to a function that processes
451 patterns in the other mode, for example, if a pattern compiled with
452 pcre_compile() is passed to pcre16_exec().
453
454 There are new error codes whose names begin with PCRE_UTF16_ERR for
455 invalid UTF-16 strings, corresponding to the PCRE_UTF8_ERR codes for
456 UTF-8 strings that are described in the section entitled "Reason codes
457 for invalid UTF-8 strings" in the main pcreapi page. The UTF-16 errors
458 are:
459
460 PCRE_UTF16_ERR1 Missing low surrogate at end of string
461 PCRE_UTF16_ERR2 Invalid low surrogate follows high surrogate
462 PCRE_UTF16_ERR3 Isolated low surrogate
463 PCRE_UTF16_ERR4 Non-character
464
465
466 ERROR TEXTS
467
468 If there is an error while compiling a pattern, the error text that is
469 passed back by pcre16_compile() or pcre16_compile2() is still an 8-bit
470 character string, zero-terminated.
471
472
473 CALLOUTS
474
475 The subject and mark fields in the callout block that is passed to a
476 callout function point to 16-bit vectors.
477
478
479 TESTING
480
481 The pcretest program continues to operate with 8-bit input and output
482 files, but it can be used for testing the 16-bit library. If it is run
483 with the command line option -16, patterns and subject strings are con-
484 verted from 8-bit to 16-bit before being passed to PCRE, and the 16-bit
485 library functions are used instead of the 8-bit ones. Returned 16-bit
486 strings are converted to 8-bit for output. If both the 8-bit and the
487 32-bit libraries were not compiled, pcretest defaults to 16-bit and the
488 -16 option is ignored.
489
490 When PCRE is being built, the RunTest script that is called by "make
491 check" uses the pcretest -C option to discover which of the 8-bit,
492 16-bit and 32-bit libraries has been built, and runs the tests appro-
493 priately.
494
495
496 NOT SUPPORTED IN 16-BIT MODE
497
498 Not all the features of the 8-bit library are available with the 16-bit
499 library. The C++ and POSIX wrapper functions support only the 8-bit
500 library, and the pcregrep program is at present 8-bit only.
501
502
503 AUTHOR
504
505 Philip Hazel
506 University Computing Service
507 Cambridge CB2 3QH, England.
508
509
510 REVISION
511
512 Last updated: 12 May 2013
513 Copyright (c) 1997-2013 University of Cambridge.
514 ------------------------------------------------------------------------------
515
516
517 PCRE(3) Library Functions Manual PCRE(3)
518
519
520
521 NAME
522 PCRE - Perl-compatible regular expressions
523
524 #include <pcre.h>
525
526
527 PCRE 32-BIT API BASIC FUNCTIONS
528
529 pcre32 *pcre32_compile(PCRE_SPTR32 pattern, int options,
530 const char **errptr, int *erroffset,
531 const unsigned char *tableptr);
532
533 pcre32 *pcre32_compile2(PCRE_SPTR32 pattern, int options,
534 int *errorcodeptr,
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 BUILDING PCRE
853
854 PCRE is distributed with a configure script that can be used to build
855 the library in Unix-like environments using the applications known as
856 Autotools. Also in the distribution are files to support building
857 using CMake instead of configure. The text file README contains general
858 information about building with Autotools (some of which is repeated
859 below), and also has some comments about building on various operating
860 systems. There is a lot more information about building PCRE without
861 using Autotools (including information about using CMake and building
862 "by hand") in the text file called NON-AUTOTOOLS-BUILD. You should
863 consult this file as well as the README file if you are building in a
864 non-Unix-like environment.
865
866
867 PCRE BUILD-TIME OPTIONS
868
869 The rest of this document describes the optional features of PCRE that
870 can be selected when the library is compiled. It assumes use of the
871 configure script, where the optional features are selected or dese-
872 lected by providing options to configure before running the make com-
873 mand. However, the same options can be selected in both Unix-like and
874 non-Unix-like environments using the GUI facility of cmake-gui if you
875 are using CMake instead of configure to build PCRE.
876
877 If you are not using Autotools or CMake, option selection can be done
878 by editing the config.h file, or by passing parameter settings to the
879 compiler, as described in NON-AUTOTOOLS-BUILD.
880
881 The complete list of options for configure (which includes the standard
882 ones such as the selection of the installation directory) can be
883 obtained by running
884
885 ./configure --help
886
887 The following sections include descriptions of options whose names
888 begin with --enable or --disable. These settings specify changes to the
889 defaults for the configure command. Because of the way that configure
890 works, --enable and --disable always come in pairs, so the complemen-
891 tary option always exists as well, but as it specifies the default, it
892 is not described.
893
894
895 BUILDING 8-BIT, 16-BIT AND 32-BIT LIBRARIES
896
897 By default, a library called libpcre is built, containing functions
898 that take string arguments contained in vectors of bytes, either as
899 single-byte characters, or interpreted as UTF-8 strings. You can also
900 build a separate library, called libpcre16, in which strings are con-
901 tained in vectors of 16-bit data units and interpreted either as sin-
902 gle-unit characters or UTF-16 strings, by adding
903
904 --enable-pcre16
905
906 to the configure command. You can also build yet another separate
907 library, called libpcre32, in which strings are contained in vectors of
908 32-bit data units and interpreted either as single-unit characters or
909 UTF-32 strings, by adding
910
911 --enable-pcre32
912
913 to the configure command. If you do not want the 8-bit library, add
914
915 --disable-pcre8
916
917 as well. At least one of the three libraries must be built. Note that
918 the C++ and POSIX wrappers are for the 8-bit library only, and that
919 pcregrep is an 8-bit program. None of these are built if you select
920 only the 16-bit or 32-bit libraries.
921
922
923 BUILDING SHARED AND STATIC LIBRARIES
924
925 The Autotools PCRE building process uses libtool to build both shared
926 and static libraries by default. You can suppress one of these by
927 adding one of
928
929 --disable-shared
930 --disable-static
931
932 to the configure command, as required.
933
934
935 C++ SUPPORT
936
937 By default, if the 8-bit library is being built, the configure script
938 will search for a C++ compiler and C++ header files. If it finds them,
939 it automatically builds the C++ wrapper library (which supports only
940 8-bit strings). You can disable this by adding
941
942 --disable-cpp
943
944 to the configure command.
945
946
947 UTF-8, UTF-16 AND UTF-32 SUPPORT
948
949 To build PCRE with support for UTF Unicode character strings, add
950
951 --enable-utf
952
953 to the configure command. This setting applies to all three libraries,
954 adding support for UTF-8 to the 8-bit library, support for UTF-16 to
955 the 16-bit library, and support for UTF-32 to the to the 32-bit
956 library. There are no separate options for enabling UTF-8, UTF-16 and
957 UTF-32 independently because that would allow ridiculous settings such
958 as requesting UTF-16 support while building only the 8-bit library. It
959 is not possible to build one library with UTF support and another with-
960 out in the same configuration. (For backwards compatibility, --enable-
961 utf8 is a synonym of --enable-utf.)
962
963 Of itself, this setting does not make PCRE treat strings as UTF-8,
964 UTF-16 or UTF-32. As well as compiling PCRE with this option, you also
965 have have to set the PCRE_UTF8, PCRE_UTF16 or PCRE_UTF32 option (as
966 appropriate) when you call one of the pattern compiling functions.
967
968 If you set --enable-utf when compiling in an EBCDIC environment, PCRE
969 expects its input to be either ASCII or UTF-8 (depending on the run-
970 time option). It is not possible to support both EBCDIC and UTF-8 codes
971 in the same version of the library. Consequently, --enable-utf and
972 --enable-ebcdic are mutually exclusive.
973
974
975 UNICODE CHARACTER PROPERTY SUPPORT
976
977 UTF support allows the libraries to process character codepoints up to
978 0x10ffff in the strings that they handle. On its own, however, it does
979 not provide any facilities for accessing the properties of such charac-
980 ters. If you want to be able to use the pattern escapes \P, \p, and \X,
981 which refer to Unicode character properties, you must add
982
983 --enable-unicode-properties
984
985 to the configure command. This implies UTF support, even if you have
986 not explicitly requested it.
987
988 Including Unicode property support adds around 30K of tables to the
989 PCRE library. Only the general category properties such as Lu and Nd
990 are supported. Details are given in the pcrepattern documentation.
991
992
993 JUST-IN-TIME COMPILER SUPPORT
994
995 Just-in-time compiler support is included in the build by specifying
996
997 --enable-jit
998
999 This support is available only for certain hardware architectures. If
1000 this option is set for an unsupported architecture, a compile time
1001 error occurs. See the pcrejit documentation for a discussion of JIT
1002 usage. When JIT support is enabled, pcregrep automatically makes use of
1003 it, unless you add
1004
1005 --disable-pcregrep-jit
1006
1007 to the "configure" command.
1008
1009
1010 CODE VALUE OF NEWLINE
1011
1012 By default, PCRE interprets the linefeed (LF) character as indicating
1013 the end of a line. This is the normal newline character on Unix-like
1014 systems. You can compile PCRE to use carriage return (CR) instead, by
1015 adding
1016
1017 --enable-newline-is-cr
1018
1019 to the configure command. There is also a --enable-newline-is-lf
1020 option, which explicitly specifies linefeed as the newline character.
1021
1022 Alternatively, you can specify that line endings are to be indicated by
1023 the two character sequence CRLF. If you want this, add
1024
1025 --enable-newline-is-crlf
1026
1027 to the configure command. There is a fourth option, specified by
1028
1029 --enable-newline-is-anycrlf
1030
1031 which causes PCRE to recognize any of the three sequences CR, LF, or
1032 CRLF as indicating a line ending. Finally, a fifth option, specified by
1033
1034 --enable-newline-is-any
1035
1036 causes PCRE to recognize any Unicode newline sequence.
1037
1038 Whatever line ending convention is selected when PCRE is built can be
1039 overridden when the library functions are called. At build time it is
1040 conventional to use the standard for your operating system.
1041
1042
1043 WHAT \R MATCHES
1044
1045 By default, the sequence \R in a pattern matches any Unicode newline
1046 sequence, whatever has been selected as the line ending sequence. If
1047 you specify
1048
1049 --enable-bsr-anycrlf
1050
1051 the default is changed so that \R matches only CR, LF, or CRLF. What-
1052 ever is selected when PCRE is built can be overridden when the library
1053 functions are called.
1054
1055
1056 POSIX MALLOC USAGE
1057
1058 When the 8-bit library is called through the POSIX interface (see the
1059 pcreposix documentation), additional working storage is required for
1060 holding the pointers to capturing substrings, because PCRE requires
1061 three integers per substring, whereas the POSIX interface provides only
1062 two. If the number of expected substrings is small, the wrapper func-
1063 tion uses space on the stack, because this is faster than using mal-
1064 loc() for each call. The default threshold above which the stack is no
1065 longer used is 10; it can be changed by adding a setting such as
1066
1067 --with-posix-malloc-threshold=20
1068
1069 to the configure command.
1070
1071
1072 HANDLING VERY LARGE PATTERNS
1073
1074 Within a compiled pattern, offset values are used to point from one
1075 part to another (for example, from an opening parenthesis to an alter-
1076 nation metacharacter). By default, in the 8-bit and 16-bit libraries,
1077 two-byte values are used for these offsets, leading to a maximum size
1078 for a compiled pattern of around 64K. This is sufficient to handle all
1079 but the most gigantic patterns. Nevertheless, some people do want to
1080 process truly enormous patterns, so it is possible to compile PCRE to
1081 use three-byte or four-byte offsets by adding a setting such as
1082
1083 --with-link-size=3
1084
1085 to the configure command. The value given must be 2, 3, or 4. For the
1086 16-bit library, a value of 3 is rounded up to 4. In these libraries,
1087 using longer offsets slows down the operation of PCRE because it has to
1088 load additional data when handling them. For the 32-bit library the
1089 value is always 4 and cannot be overridden; the value of --with-link-
1090 size is ignored.
1091
1092
1093 AVOIDING EXCESSIVE STACK USAGE
1094
1095 When matching with the pcre_exec() function, PCRE implements backtrack-
1096 ing by making recursive calls to an internal function called match().
1097 In environments where the size of the stack is limited, this can se-
1098 verely limit PCRE's operation. (The Unix environment does not usually
1099 suffer from this problem, but it may sometimes be necessary to increase
1100 the maximum stack size. There is a discussion in the pcrestack docu-
1101 mentation.) An alternative approach to recursion that uses memory from
1102 the heap to remember data, instead of using recursive function calls,
1103 has been implemented to work round the problem of limited stack size.
1104 If you want to build a version of PCRE that works this way, add
1105
1106 --disable-stack-for-recursion
1107
1108 to the configure command. With this configuration, PCRE will use the
1109 pcre_stack_malloc and pcre_stack_free variables to call memory manage-
1110 ment functions. By default these point to malloc() and free(), but you
1111 can replace the pointers so that your own functions are used instead.
1112
1113 Separate functions are provided rather than using pcre_malloc and
1114 pcre_free because the usage is very predictable: the block sizes
1115 requested are always the same, and the blocks are always freed in
1116 reverse order. A calling program might be able to implement optimized
1117 functions that perform better than malloc() and free(). PCRE runs
1118 noticeably more slowly when built in this way. This option affects only
1119 the pcre_exec() function; it is not relevant for pcre_dfa_exec().
1120
1121
1122 LIMITING PCRE RESOURCE USAGE
1123
1124 Internally, PCRE has a function called match(), which it calls repeat-
1125 edly (sometimes recursively) when matching a pattern with the
1126 pcre_exec() function. By controlling the maximum number of times this
1127 function may be called during a single matching operation, a limit can
1128 be placed on the resources used by a single call to pcre_exec(). The
1129 limit can be changed at run time, as described in the pcreapi documen-
1130 tation. The default is 10 million, but this can be changed by adding a
1131 setting such as
1132
1133 --with-match-limit=500000
1134
1135 to the configure command. This setting has no effect on the
1136 pcre_dfa_exec() matching function.
1137
1138 In some environments it is desirable to limit the depth of recursive
1139 calls of match() more strictly than the total number of calls, in order
1140 to restrict the maximum amount of stack (or heap, if --disable-stack-
1141 for-recursion is specified) that is used. A second limit controls this;
1142 it defaults to the value that is set for --with-match-limit, which
1143 imposes no additional constraints. However, you can set a lower limit
1144 by adding, for example,
1145
1146 --with-match-limit-recursion=10000
1147
1148 to the configure command. This value can also be overridden at run
1149 time.
1150
1151
1152 CREATING CHARACTER TABLES AT BUILD TIME
1153
1154 PCRE uses fixed tables for processing characters whose code values are
1155 less than 256. By default, PCRE is built with a set of tables that are
1156 distributed in the file pcre_chartables.c.dist. These tables are for
1157 ASCII codes only. If you add
1158
1159 --enable-rebuild-chartables
1160
1161 to the configure command, the distributed tables are no longer used.
1162 Instead, a program called dftables is compiled and run. This outputs
1163 the source for new set of tables, created in the default locale of your
1164 C run-time system. (This method of replacing the tables does not work
1165 if you are cross compiling, because dftables is run on the local host.
1166 If you need to create alternative tables when cross compiling, you will
1167 have to do so "by hand".)
1168
1169
1170 USING EBCDIC CODE
1171
1172 PCRE assumes by default that it will run in an environment where the
1173 character code is ASCII (or Unicode, which is a superset of ASCII).
1174 This is the case for most computer operating systems. PCRE can, how-
1175 ever, be compiled to run in an EBCDIC environment by adding
1176
1177 --enable-ebcdic
1178
1179 to the configure command. This setting implies --enable-rebuild-charta-
1180 bles. You should only use it if you know that you are in an EBCDIC
1181 environment (for example, an IBM mainframe operating system). The
1182 --enable-ebcdic option is incompatible with --enable-utf.
1183
1184 The EBCDIC character that corresponds to an ASCII LF is assumed to have
1185 the value 0x15 by default. However, in some EBCDIC environments, 0x25
1186 is used. In such an environment you should use
1187
1188 --enable-ebcdic-nl25
1189
1190 as well as, or instead of, --enable-ebcdic. The EBCDIC character for CR
1191 has the same value as in ASCII, namely, 0x0d. Whichever of 0x15 and
1192 0x25 is not chosen as LF is made to correspond to the Unicode NEL char-
1193 acter (which, in Unicode, is 0x85).
1194
1195 The options that select newline behaviour, such as --enable-newline-is-
1196 cr, and equivalent run-time options, refer to these character values in
1197 an EBCDIC environment.
1198
1199
1200 PCREGREP OPTIONS FOR COMPRESSED FILE SUPPORT
1201
1202 By default, pcregrep reads all files as plain text. You can build it so
1203 that it recognizes files whose names end in .gz or .bz2, and reads them
1204 with libz or libbz2, respectively, by adding one or both of
1205
1206 --enable-pcregrep-libz
1207 --enable-pcregrep-libbz2
1208
1209 to the configure command. These options naturally require that the rel-
1210 evant libraries are installed on your system. Configuration will fail
1211 if they are not.
1212
1213
1214 PCREGREP BUFFER SIZE
1215
1216 pcregrep uses an internal buffer to hold a "window" on the file it is
1217 scanning, in order to be able to output "before" and "after" lines when
1218 it finds a match. The size of the buffer is controlled by a parameter
1219 whose default value is 20K. The buffer itself is three times this size,
1220 but because of the way it is used for holding "before" lines, the long-
1221 est line that is guaranteed to be processable is the parameter size.
1222 You can change the default parameter value by adding, for example,
1223
1224 --with-pcregrep-bufsize=50K
1225
1226 to the configure command. The caller of pcregrep can, however, override
1227 this value by specifying a run-time option.
1228
1229
1230 PCRETEST OPTION FOR LIBREADLINE SUPPORT
1231
1232 If you add
1233
1234 --enable-pcretest-libreadline
1235
1236 to the configure command, pcretest is linked with the libreadline
1237 library, and when its input is from a terminal, it reads it using the
1238 readline() function. This provides line-editing and history facilities.
1239 Note that libreadline is GPL-licensed, so if you distribute a binary of
1240 pcretest linked in this way, there may be licensing issues.
1241
1242 Setting this option causes the -lreadline option to be added to the
1243 pcretest build. In many operating environments with a sytem-installed
1244 libreadline this is sufficient. However, in some environments (e.g. if
1245 an unmodified distribution version of readline is in use), some extra
1246 configuration may be necessary. The INSTALL file for libreadline says
1247 this:
1248
1249 "Readline uses the termcap functions, but does not link with the
1250 termcap or curses library itself, allowing applications which link
1251 with readline the to choose an appropriate library."
1252
1253 If your environment has not been set up so that an appropriate library
1254 is automatically included, you may need to add something like
1255
1256 LIBS="-ncurses"
1257
1258 immediately before the configure command.
1259
1260
1261 DEBUGGING WITH VALGRIND SUPPORT
1262
1263 By adding the
1264
1265 --enable-valgrind
1266
1267 option to to the configure command, PCRE will use valgrind annotations
1268 to mark certain memory regions as unaddressable. This allows it to
1269 detect invalid memory accesses, and is mostly useful for debugging PCRE
1270 itself.
1271
1272
1273 CODE COVERAGE REPORTING
1274
1275 If your C compiler is gcc, you can build a version of PCRE that can
1276 generate a code coverage report for its test suite. To enable this, you
1277 must install lcov version 1.6 or above. Then specify
1278
1279 --enable-coverage
1280
1281 to the configure command and build PCRE in the usual way.
1282
1283 Note that using ccache (a caching C compiler) is incompatible with code
1284 coverage reporting. If you have configured ccache to run automatically
1285 on your system, you must set the environment variable
1286
1287 CCACHE_DISABLE=1
1288
1289 before running make to build PCRE, so that ccache is not used.
1290
1291 When --enable-coverage is used, the following addition targets are
1292 added to the Makefile:
1293
1294 make coverage
1295
1296 This creates a fresh coverage report for the PCRE test suite. It is
1297 equivalent to running "make coverage-reset", "make coverage-baseline",
1298 "make check", and then "make coverage-report".
1299
1300 make coverage-reset
1301
1302 This zeroes the coverage counters, but does nothing else.
1303
1304 make coverage-baseline
1305
1306 This captures baseline coverage information.
1307
1308 make coverage-report
1309
1310 This creates the coverage report.
1311
1312 make coverage-clean-report
1313
1314 This removes the generated coverage report without cleaning the cover-
1315 age data itself.
1316
1317 make coverage-clean-data
1318
1319 This removes the captured coverage data without removing the coverage
1320 files created at compile time (*.gcno).
1321
1322 make coverage-clean
1323
1324 This cleans all coverage data including the generated coverage report.
1325 For more information about code coverage, see the gcov and lcov docu-
1326 mentation.
1327
1328
1329 SEE ALSO
1330
1331 pcreapi(3), pcre16, pcre32, pcre_config(3).
1332
1333
1334 AUTHOR
1335
1336 Philip Hazel
1337 University Computing Service
1338 Cambridge CB2 3QH, England.
1339
1340
1341 REVISION
1342
1343 Last updated: 12 May 2013
1344 Copyright (c) 1997-2013 University of Cambridge.
1345 ------------------------------------------------------------------------------
1346
1347
1348 PCREMATCHING(3) Library Functions Manual PCREMATCHING(3)
1349
1350
1351
1352 NAME
1353 PCRE - Perl-compatible regular expressions
1354
1355 PCRE MATCHING ALGORITHMS
1356
1357 This document describes the two different algorithms that are available
1358 in PCRE for matching a compiled regular expression against a given sub-
1359 ject string. The "standard" algorithm is the one provided by the
1360 pcre_exec(), pcre16_exec() and pcre32_exec() functions. These work in
1361 the same as as Perl's matching function, and provide a Perl-compatible
1362 matching operation. The just-in-time (JIT) optimization that is
1363 described in the pcrejit documentation is compatible with these func-
1364 tions.
1365
1366 An alternative algorithm is provided by the pcre_dfa_exec(),
1367 pcre16_dfa_exec() and pcre32_dfa_exec() functions; they operate in a
1368 different way, and are not Perl-compatible. This alternative has advan-
1369 tages and disadvantages compared with the standard algorithm, and these
1370 are described below.
1371
1372 When there is only one possible way in which a given subject string can
1373 match a pattern, the two algorithms give the same answer. A difference
1374 arises, however, when there are multiple possibilities. For example, if
1375 the pattern
1376
1377 ^<.*>
1378
1379 is matched against the string
1380
1381 <something> <something else> <something further>
1382
1383 there are three possible answers. The standard algorithm finds only one
1384 of them, whereas the alternative algorithm finds all three.
1385
1386
1387 REGULAR EXPRESSIONS AS TREES
1388
1389 The set of strings that are matched by a regular expression can be rep-
1390 resented as a tree structure. An unlimited repetition in the pattern
1391 makes the tree of infinite size, but it is still a tree. Matching the
1392 pattern to a given subject string (from a given starting point) can be
1393 thought of as a search of the tree. There are two ways to search a
1394 tree: depth-first and breadth-first, and these correspond to the two
1395 matching algorithms provided by PCRE.
1396
1397
1398 THE STANDARD MATCHING ALGORITHM
1399
1400 In the terminology of Jeffrey Friedl's book "Mastering Regular Expres-
1401 sions", the standard algorithm is an "NFA algorithm". It conducts a
1402 depth-first search of the pattern tree. That is, it proceeds along a
1403 single path through the tree, checking that the subject matches what is
1404 required. When there is a mismatch, the algorithm tries any alterna-
1405 tives at the current point, and if they all fail, it backs up to the
1406 previous branch point in the tree, and tries the next alternative
1407 branch at that level. This often involves backing up (moving to the
1408 left) in the subject string as well. The order in which repetition
1409 branches are tried is controlled by the greedy or ungreedy nature of
1410 the quantifier.
1411
1412 If a leaf node is reached, a matching string has been found, and at
1413 that point the algorithm stops. Thus, if there is more than one possi-
1414 ble match, this algorithm returns the first one that it finds. Whether
1415 this is the shortest, the longest, or some intermediate length depends
1416 on the way the greedy and ungreedy repetition quantifiers are specified
1417 in the pattern.
1418
1419 Because it ends up with a single path through the tree, it is rela-
1420 tively straightforward for this algorithm to keep track of the sub-
1421 strings that are matched by portions of the pattern in parentheses.
1422 This provides support for capturing parentheses and back references.
1423
1424
1425 THE ALTERNATIVE MATCHING ALGORITHM
1426
1427 This algorithm conducts a breadth-first search of the tree. Starting
1428 from the first matching point in the subject, it scans the subject
1429 string from left to right, once, character by character, and as it does
1430 this, it remembers all the paths through the tree that represent valid
1431 matches. In Friedl's terminology, this is a kind of "DFA algorithm",
1432 though it is not implemented as a traditional finite state machine (it
1433 keeps multiple states active simultaneously).
1434
1435 Although the general principle of this matching algorithm is that it
1436 scans the subject string only once, without backtracking, there is one
1437 exception: when a lookaround assertion is encountered, the characters
1438 following or preceding the current point have to be independently
1439 inspected.
1440
1441 The scan continues until either the end of the subject is reached, or
1442 there are no more unterminated paths. At this point, terminated paths
1443 represent the different matching possibilities (if there are none, the
1444 match has failed). Thus, if there is more than one possible match,
1445 this algorithm finds all of them, and in particular, it finds the long-
1446 est. The matches are returned in decreasing order of length. There is
1447 an option to stop the algorithm after the first match (which is neces-
1448 sarily the shortest) is found.
1449
1450 Note that all the matches that are found start at the same point in the
1451 subject. If the pattern
1452
1453 cat(er(pillar)?)?
1454
1455 is matched against the string "the caterpillar catchment", the result
1456 will be the three strings "caterpillar", "cater", and "cat" that start
1457 at the fifth character of the subject. The algorithm does not automati-
1458 cally move on to find matches that start at later positions.
1459
1460 PCRE's "auto-possessification" optimization usually applies to charac-
1461 ter repeats at the end of a pattern (as well as internally). For exam-
1462 ple, the pattern "a\d+" is compiled as if it were "a\d++" because there
1463 is no point even considering the possibility of backtracking into the
1464 repeated digits. For DFA matching, this means that only one possible
1465 match is found. If you really do want multiple matches in such cases,
1466 either use an ungreedy repeat ("a\d+?") or set the PCRE_NO_AUTO_POSSESS
1467 option when compiling.
1468
1469 There are a number of features of PCRE regular expressions that are not
1470 supported by the alternative matching algorithm. They are as follows:
1471
1472 1. Because the algorithm finds all possible matches, the greedy or
1473 ungreedy nature of repetition quantifiers is not relevant. Greedy and
1474 ungreedy quantifiers are treated in exactly the same way. However, pos-
1475 sessive quantifiers can make a difference when what follows could also
1476 match what is quantified, for example in a pattern like this:
1477
1478 ^a++\w!
1479
1480 This pattern matches "aaab!" but not "aaa!", which would be matched by
1481 a non-possessive quantifier. Similarly, if an atomic group is present,
1482 it is matched as if it were a standalone pattern at the current point,
1483 and the longest match is then "locked in" for the rest of the overall
1484 pattern.
1485
1486 2. When dealing with multiple paths through the tree simultaneously, it
1487 is not straightforward to keep track of captured substrings for the
1488 different matching possibilities, and PCRE's implementation of this
1489 algorithm does not attempt to do this. This means that no captured sub-
1490 strings are available.
1491
1492 3. Because no substrings are captured, back references within the pat-
1493 tern are not supported, and cause errors if encountered.
1494
1495 4. For the same reason, conditional expressions that use a backrefer-
1496 ence as the condition or test for a specific group recursion are not
1497 supported.
1498
1499 5. Because many paths through the tree may be active, the \K escape
1500 sequence, which resets the start of the match when encountered (but may
1501 be on some paths and not on others), is not supported. It causes an
1502 error if encountered.
1503
1504 6. Callouts are supported, but the value of the capture_top field is
1505 always 1, and the value of the capture_last field is always -1.
1506
1507 7. The \C escape sequence, which (in the standard algorithm) always
1508 matches a single data unit, even in UTF-8, UTF-16 or UTF-32 modes, is
1509 not supported in these modes, because the alternative algorithm moves
1510 through the subject string one character (not data unit) at a time, for
1511 all active paths through the tree.
1512
1513 8. Except for (*FAIL), the backtracking control verbs such as (*PRUNE)
1514 are not supported. (*FAIL) is supported, and behaves like a failing
1515 negative assertion.
1516
1517
1518 ADVANTAGES OF THE ALTERNATIVE ALGORITHM
1519
1520 Using the alternative matching algorithm provides the following advan-
1521 tages:
1522
1523 1. All possible matches (at a single point in the subject) are automat-
1524 ically found, and in particular, the longest match is found. To find
1525 more than one match using the standard algorithm, you have to do kludgy
1526 things with callouts.
1527
1528 2. Because the alternative algorithm scans the subject string just
1529 once, and never needs to backtrack (except for lookbehinds), it is pos-
1530 sible to pass very long subject strings to the matching function in
1531 several pieces, checking for partial matching each time. Although it is
1532 possible to do multi-segment matching using the standard algorithm by
1533 retaining partially matched substrings, it is more complicated. The
1534 pcrepartial documentation gives details of partial matching and dis-
1535 cusses multi-segment matching.
1536
1537
1538 DISADVANTAGES OF THE ALTERNATIVE ALGORITHM
1539
1540 The alternative algorithm suffers from a number of disadvantages:
1541
1542 1. It is substantially slower than the standard algorithm. This is
1543 partly because it has to search for all possible matches, but is also
1544 because it is less susceptible to optimization.
1545
1546 2. Capturing parentheses and back references are not supported.
1547
1548 3. Although atomic groups are supported, their use does not provide the
1549 performance advantage that it does for the standard algorithm.
1550
1551
1552 AUTHOR
1553
1554 Philip Hazel
1555 University Computing Service
1556 Cambridge CB2 3QH, England.
1557
1558
1559 REVISION
1560
1561 Last updated: 12 November 2013
1562 Copyright (c) 1997-2012 University of Cambridge.
1563 ------------------------------------------------------------------------------
1564
1565
1566 PCREAPI(3) Library Functions Manual PCREAPI(3)
1567
1568
1569
1570 NAME
1571 PCRE - Perl-compatible regular expressions
1572
1573 #include <pcre.h>
1574
1575
1576 PCRE NATIVE API BASIC FUNCTIONS
1577
1578 pcre *pcre_compile(const char *pattern, int options,
1579 const char **errptr, int *erroffset,
1580 const unsigned char *tableptr);
1581
1582 pcre *pcre_compile2(const char *pattern, int options,
1583 int *errorcodeptr,
1584 const char **errptr, int *erroffset,
1585 const unsigned char *tableptr);
1586
1587 pcre_extra *pcre_study(const pcre *code, int options,
1588 const char **errptr);
1589
1590 void pcre_free_study(pcre_extra *extra);
1591
1592 int pcre_exec(const pcre *code, const pcre_extra *extra,
1593 const char *subject, int length, int startoffset,
1594 int options, int *ovector, int ovecsize);
1595
1596 int pcre_dfa_exec(const pcre *code, const pcre_extra *extra,
1597 const char *subject, int length, int startoffset,
1598 int options, int *ovector, int ovecsize,
1599 int *workspace, int wscount);
1600
1601
1602 PCRE NATIVE API STRING EXTRACTION FUNCTIONS
1603
1604 int pcre_copy_named_substring(const pcre *code,
1605 const char *subject, int *ovector,
1606 int stringcount, const char *stringname,
1607 char *buffer, int buffersize);
1608
1609 int pcre_copy_substring(const char *subject, int *ovector,
1610 int stringcount, int stringnumber, char *buffer,
1611 int buffersize);
1612
1613 int pcre_get_named_substring(const pcre *code,
1614 const char *subject, int *ovector,
1615 int stringcount, const char *stringname,
1616 const char **stringptr);
1617
1618 int pcre_get_stringnumber(const pcre *code,
1619 const char *name);
1620
1621 int pcre_get_stringtable_entries(const pcre *code,
1622 const char *name, char **first, char **last);
1623
1624 int pcre_get_substring(const char *subject, int *ovector,
1625 int stringcount, int stringnumber,
1626 const char **stringptr);
1627
1628 int pcre_get_substring_list(const char *subject,
1629 int *ovector, int stringcount, const char ***listptr);
1630
1631 void pcre_free_substring(const char *stringptr);
1632
1633 void pcre_free_substring_list(const char **stringptr);
1634
1635
1636 PCRE NATIVE API AUXILIARY FUNCTIONS
1637
1638 int pcre_jit_exec(const pcre *code, const pcre_extra *extra,
1639 const char *subject, int length, int startoffset,
1640 int options, int *ovector, int ovecsize,
1641 pcre_jit_stack *jstack);
1642
1643 pcre_jit_stack *pcre_jit_stack_alloc(int startsize, int maxsize);
1644
1645 void pcre_jit_stack_free(pcre_jit_stack *stack);
1646
1647 void pcre_assign_jit_stack(pcre_extra *extra,
1648 pcre_jit_callback callback, void *data);
1649
1650 const unsigned char *pcre_maketables(void);
1651
1652 int pcre_fullinfo(const pcre *code, const pcre_extra *extra,
1653 int what, void *where);
1654
1655 int pcre_refcount(pcre *code, int adjust);
1656
1657 int pcre_config(int what, void *where);
1658
1659 const char *pcre_version(void);
1660
1661 int pcre_pattern_to_host_byte_order(pcre *code,
1662 pcre_extra *extra, const unsigned char *tables);
1663
1664
1665 PCRE NATIVE API INDIRECTED FUNCTIONS
1666
1667 void *(*pcre_malloc)(size_t);
1668
1669 void (*pcre_free)(void *);
1670
1671 void *(*pcre_stack_malloc)(size_t);
1672
1673 void (*pcre_stack_free)(void *);
1674
1675 int (*pcre_callout)(pcre_callout_block *);
1676
1677
1678 PCRE 8-BIT, 16-BIT, AND 32-BIT LIBRARIES
1679
1680 As well as support for 8-bit character strings, PCRE also supports
1681 16-bit strings (from release 8.30) and 32-bit strings (from release
1682 8.32), by means of two additional libraries. They can be built as well
1683 as, or instead of, the 8-bit library. To avoid too much complication,
1684 this document describes the 8-bit versions of the functions, with only
1685 occasional references to the 16-bit and 32-bit libraries.
1686
1687 The 16-bit and 32-bit functions operate in the same way as their 8-bit
1688 counterparts; they just use different data types for their arguments
1689 and results, and their names start with pcre16_ or pcre32_ instead of
1690 pcre_. For every option that has UTF8 in its name (for example,
1691 PCRE_UTF8), there are corresponding 16-bit and 32-bit names with UTF8
1692 replaced by UTF16 or UTF32, respectively. This facility is in fact just
1693 cosmetic; the 16-bit and 32-bit option names define the same bit val-
1694 ues.
1695
1696 References to bytes and UTF-8 in this document should be read as refer-
1697 ences to 16-bit data units and UTF-16 when using the 16-bit library, or
1698 32-bit data units and UTF-32 when using the 32-bit library, unless
1699 specified otherwise. More details of the specific differences for the
1700 16-bit and 32-bit libraries are given in the pcre16 and pcre32 pages.
1701
1702
1703 PCRE API OVERVIEW
1704
1705 PCRE has its own native API, which is described in this document. There
1706 are also some wrapper functions (for the 8-bit library only) that cor-
1707 respond to the POSIX regular expression API, but they do not give
1708 access to all the functionality. They are described in the pcreposix
1709 documentation. Both of these APIs define a set of C function calls. A
1710 C++ wrapper (again for the 8-bit library only) is also distributed with
1711 PCRE. It is documented in the pcrecpp page.
1712
1713 The native API C function prototypes are defined in the header file
1714 pcre.h, and on Unix-like systems the (8-bit) library itself is called
1715 libpcre. It can normally be accessed by adding -lpcre to the command
1716 for linking an application that uses PCRE. The header file defines the
1717 macros PCRE_MAJOR and PCRE_MINOR to contain the major and minor release
1718 numbers for the library. Applications can use these to include support
1719 for different releases of PCRE.
1720
1721 In a Windows environment, if you want to statically link an application
1722 program against a non-dll pcre.a file, you must define PCRE_STATIC
1723 before including pcre.h or pcrecpp.h, because otherwise the pcre_mal-
1724 loc() and pcre_free() exported functions will be declared
1725 __declspec(dllimport), with unwanted results.
1726
1727 The functions pcre_compile(), pcre_compile2(), pcre_study(), and
1728 pcre_exec() are used for compiling and matching regular expressions in
1729 a Perl-compatible manner. A sample program that demonstrates the sim-
1730 plest way of using them is provided in the file called pcredemo.c in
1731 the PCRE source distribution. A listing of this program is given in the
1732 pcredemo documentation, and the pcresample documentation describes how
1733 to compile and run it.
1734
1735 Just-in-time compiler support is an optional feature of PCRE that can
1736 be built in appropriate hardware environments. It greatly speeds up the
1737 matching performance of many patterns. Simple programs can easily
1738 request that it be used if available, by setting an option that is
1739 ignored when it is not relevant. More complicated programs might need
1740 to make use of the functions pcre_jit_stack_alloc(),
1741 pcre_jit_stack_free(), and pcre_assign_jit_stack() in order to control
1742 the JIT code's memory usage.
1743
1744 From release 8.32 there is also a direct interface for JIT execution,
1745 which gives improved performance. The JIT-specific functions are dis-
1746 cussed in the pcrejit documentation.
1747
1748 A second matching function, pcre_dfa_exec(), which is not Perl-compati-
1749 ble, is also provided. This uses a different algorithm for the match-
1750 ing. The alternative algorithm finds all possible matches (at a given
1751 point in the subject), and scans the subject just once (unless there
1752 are lookbehind assertions). However, this algorithm does not return
1753 captured substrings. A description of the two matching algorithms and
1754 their advantages and disadvantages is given in the pcrematching docu-
1755 mentation.
1756
1757 In addition to the main compiling and matching functions, there are
1758 convenience functions for extracting captured substrings from a subject
1759 string that is matched by pcre_exec(). They are:
1760
1761 pcre_copy_substring()
1762 pcre_copy_named_substring()
1763 pcre_get_substring()
1764 pcre_get_named_substring()
1765 pcre_get_substring_list()
1766 pcre_get_stringnumber()
1767 pcre_get_stringtable_entries()
1768
1769 pcre_free_substring() and pcre_free_substring_list() are also provided,
1770 to free the memory used for extracted strings.
1771
1772 The function pcre_maketables() is used to build a set of character
1773 tables in the current locale for passing to pcre_compile(),
1774 pcre_exec(), or pcre_dfa_exec(). This is an optional facility that is
1775 provided for specialist use. Most commonly, no special tables are
1776 passed, in which case internal tables that are generated when PCRE is
1777 built are used.
1778
1779 The function pcre_fullinfo() is used to find out information about a
1780 compiled pattern. The function pcre_version() returns a pointer to a
1781 string containing the version of PCRE and its date of release.
1782
1783 The function pcre_refcount() maintains a reference count in a data
1784 block containing a compiled pattern. This is provided for the benefit
1785 of object-oriented applications.
1786
1787 The global variables pcre_malloc and pcre_free initially contain the
1788 entry points of the standard malloc() and free() functions, respec-
1789 tively. PCRE calls the memory management functions via these variables,
1790 so a calling program can replace them if it wishes to intercept the
1791 calls. This should be done before calling any PCRE functions.
1792
1793 The global variables pcre_stack_malloc and pcre_stack_free are also
1794 indirections to memory management functions. These special functions
1795 are used only when PCRE is compiled to use the heap for remembering
1796 data, instead of recursive function calls, when running the pcre_exec()
1797 function. See the pcrebuild documentation for details of how to do
1798 this. It is a non-standard way of building PCRE, for use in environ-
1799 ments that have limited stacks. Because of the greater use of memory
1800 management, it runs more slowly. Separate functions are provided so
1801 that special-purpose external code can be used for this case. When
1802 used, these functions are always called in a stack-like manner (last
1803 obtained, first freed), and always for memory blocks of the same size.
1804 There is a discussion about PCRE's stack usage in the pcrestack docu-
1805 mentation.
1806
1807 The global variable pcre_callout initially contains NULL. It can be set
1808 by the caller to a "callout" function, which PCRE will then call at
1809 specified points during a matching operation. Details are given in the
1810 pcrecallout documentation.
1811
1812
1813 NEWLINES
1814
1815 PCRE supports five different conventions for indicating line breaks in
1816 strings: a single CR (carriage return) character, a single LF (line-
1817 feed) character, the two-character sequence CRLF, any of the three pre-
1818 ceding, or any Unicode newline sequence. The Unicode newline sequences
1819 are the three just mentioned, plus the single characters VT (vertical
1820 tab, U+000B), FF (form feed, U+000C), NEL (next line, U+0085), LS (line
1821 separator, U+2028), and PS (paragraph separator, U+2029).
1822
1823 Each of the first three conventions is used by at least one operating
1824 system as its standard newline sequence. When PCRE is built, a default
1825 can be specified. The default default is LF, which is the Unix stan-
1826 dard. When PCRE is run, the default can be overridden, either when a
1827 pattern is compiled, or when it is matched.
1828
1829 At compile time, the newline convention can be specified by the options
1830 argument of pcre_compile(), or it can be specified by special text at
1831 the start of the pattern itself; this overrides any other settings. See
1832 the pcrepattern page for details of the special character sequences.
1833
1834 In the PCRE documentation the word "newline" is used to mean "the char-
1835 acter or pair of characters that indicate a line break". The choice of
1836 newline convention affects the handling of the dot, circumflex, and
1837 dollar metacharacters, the handling of #-comments in /x mode, and, when
1838 CRLF is a recognized line ending sequence, the match position advance-
1839 ment for a non-anchored pattern. There is more detail about this in the
1840 section on pcre_exec() options below.
1841
1842 The choice of newline convention does not affect the interpretation of
1843 the \n or \r escape sequences, nor does it affect what \R matches,
1844 which is controlled in a similar way, but by separate options.
1845
1846
1847 MULTITHREADING
1848
1849 The PCRE functions can be used in multi-threading applications, with
1850 the proviso that the memory management functions pointed to by
1851 pcre_malloc, pcre_free, pcre_stack_malloc, and pcre_stack_free, and the
1852 callout function pointed to by pcre_callout, are shared by all threads.
1853
1854 The compiled form of a regular expression is not altered during match-
1855 ing, so the same compiled pattern can safely be used by several threads
1856 at once.
1857
1858 If the just-in-time optimization feature is being used, it needs sepa-
1859 rate memory stack areas for each thread. See the pcrejit documentation
1860 for more details.
1861
1862
1863 SAVING PRECOMPILED PATTERNS FOR LATER USE
1864
1865 The compiled form of a regular expression can be saved and re-used at a
1866 later time, possibly by a different program, and even on a host other
1867 than the one on which it was compiled. Details are given in the
1868 pcreprecompile documentation, which includes a description of the
1869 pcre_pattern_to_host_byte_order() function. However, compiling a regu-
1870 lar expression with one version of PCRE for use with a different ver-
1871 sion is not guaranteed to work and may cause crashes.
1872
1873
1874 CHECKING BUILD-TIME OPTIONS
1875
1876 int pcre_config(int what, void *where);
1877
1878 The function pcre_config() makes it possible for a PCRE client to dis-
1879 cover which optional features have been compiled into the PCRE library.
1880 The pcrebuild documentation has more details about these optional fea-
1881 tures.
1882
1883 The first argument for pcre_config() is an integer, specifying which
1884 information is required; the second argument is a pointer to a variable
1885 into which the information is placed. The returned value is zero on
1886 success, or the negative error code PCRE_ERROR_BADOPTION if the value
1887 in the first argument is not recognized. The following information is
1888 available:
1889
1890 PCRE_CONFIG_UTF8
1891
1892 The output is an integer that is set to one if UTF-8 support is avail-
1893 able; otherwise it is set to zero. This value should normally be given
1894 to the 8-bit version of this function, pcre_config(). If it is given to
1895 the 16-bit or 32-bit version of this function, the result is
1896 PCRE_ERROR_BADOPTION.
1897
1898 PCRE_CONFIG_UTF16
1899
1900 The output is an integer that is set to one if UTF-16 support is avail-
1901 able; otherwise it is set to zero. This value should normally be given
1902 to the 16-bit version of this function, pcre16_config(). If it is given
1903 to the 8-bit or 32-bit version of this function, the result is
1904 PCRE_ERROR_BADOPTION.
1905
1906 PCRE_CONFIG_UTF32
1907
1908 The output is an integer that is set to one if UTF-32 support is avail-
1909 able; otherwise it is set to zero. This value should normally be given
1910 to the 32-bit version of this function, pcre32_config(). If it is given
1911 to the 8-bit or 16-bit version of this function, the result is
1912 PCRE_ERROR_BADOPTION.
1913
1914 PCRE_CONFIG_UNICODE_PROPERTIES
1915
1916 The output is an integer that is set to one if support for Unicode
1917 character properties is available; otherwise it is set to zero.
1918
1919 PCRE_CONFIG_JIT
1920
1921 The output is an integer that is set to one if support for just-in-time
1922 compiling is available; otherwise it is set to zero.
1923
1924 PCRE_CONFIG_JITTARGET
1925
1926 The output is a pointer to a zero-terminated "const char *" string. If
1927 JIT support is available, the string contains the name of the architec-
1928 ture for which the JIT compiler is configured, for example "x86 32bit
1929 (little endian + unaligned)". If JIT support is not available, the
1930 result is NULL.
1931
1932 PCRE_CONFIG_NEWLINE
1933
1934 The output is an integer whose value specifies the default character
1935 sequence that is recognized as meaning "newline". The values that are
1936 supported in ASCII/Unicode environments are: 10 for LF, 13 for CR, 3338
1937 for CRLF, -2 for ANYCRLF, and -1 for ANY. In EBCDIC environments, CR,
1938 ANYCRLF, and ANY yield the same values. However, the value for LF is
1939 normally 21, though some EBCDIC environments use 37. The corresponding
1940 values for CRLF are 3349 and 3365. The default should normally corre-
1941 spond to the standard sequence for your operating system.
1942
1943 PCRE_CONFIG_BSR
1944
1945 The output is an integer whose value indicates what character sequences
1946 the \R escape sequence matches by default. A value of 0 means that \R
1947 matches any Unicode line ending sequence; a value of 1 means that \R
1948 matches only CR, LF, or CRLF. The default can be overridden when a pat-
1949 tern is compiled or matched.
1950
1951 PCRE_CONFIG_LINK_SIZE
1952
1953 The output is an integer that contains the number of bytes used for
1954 internal linkage in compiled regular expressions. For the 8-bit
1955 library, the value can be 2, 3, or 4. For the 16-bit library, the value
1956 is either 2 or 4 and is still a number of bytes. For the 32-bit
1957 library, the value is either 2 or 4 and is still a number of bytes. The
1958 default value of 2 is sufficient for all but the most massive patterns,
1959 since it allows the compiled pattern to be up to 64K in size. Larger
1960 values allow larger regular expressions to be compiled, at the expense
1961 of slower matching.
1962
1963 PCRE_CONFIG_POSIX_MALLOC_THRESHOLD
1964
1965 The output is an integer that contains the threshold above which the
1966 POSIX interface uses malloc() for output vectors. Further details are
1967 given in the pcreposix documentation.
1968
1969 PCRE_CONFIG_PARENS_LIMIT
1970
1971 The output is a long integer that gives the maximum depth of nesting of
1972 parentheses (of any kind) in a pattern. This limit is imposed to cap
1973 the amount of system stack used when a pattern is compiled. It is spec-
1974 ified when PCRE is built; the default is 250.
1975
1976 PCRE_CONFIG_MATCH_LIMIT
1977
1978 The output is a long integer that gives the default limit for the num-
1979 ber of internal matching function calls in a pcre_exec() execution.
1980 Further details are given with pcre_exec() below.
1981
1982 PCRE_CONFIG_MATCH_LIMIT_RECURSION
1983
1984 The output is a long integer that gives the default limit for the depth
1985 of recursion when calling the internal matching function in a
1986 pcre_exec() execution. Further details are given with pcre_exec()
1987 below.
1988
1989 PCRE_CONFIG_STACKRECURSE
1990
1991 The output is an integer that is set to one if internal recursion when
1992 running pcre_exec() is implemented by recursive function calls that use
1993 the stack to remember their state. This is the usual way that PCRE is
1994 compiled. The output is zero if PCRE was compiled to use blocks of data
1995 on the heap instead of recursive function calls. In this case,
1996 pcre_stack_malloc and pcre_stack_free are called to manage memory
1997 blocks on the heap, thus avoiding the use of the stack.
1998
1999
2000 COMPILING A PATTERN
2001
2002 pcre *pcre_compile(const char *pattern, int options,
2003 const char **errptr, int *erroffset,
2004 const unsigned char *tableptr);
2005
2006 pcre *pcre_compile2(const char *pattern, int options,
2007 int *errorcodeptr,
2008 const char **errptr, int *erroffset,
2009 const unsigned char *tableptr);
2010
2011 Either of the functions pcre_compile() or pcre_compile2() can be called
2012 to compile a pattern into an internal form. The only difference between
2013 the two interfaces is that pcre_compile2() has an additional argument,
2014 errorcodeptr, via which a numerical error code can be returned. To
2015 avoid too much repetition, we refer just to pcre_compile() below, but
2016 the information applies equally to pcre_compile2().
2017
2018 The pattern is a C string terminated by a binary zero, and is passed in
2019 the pattern argument. A pointer to a single block of memory that is
2020 obtained via pcre_malloc is returned. This contains the compiled code
2021 and related data. The pcre type is defined for the returned block; this
2022 is a typedef for a structure whose contents are not externally defined.
2023 It is up to the caller to free the memory (via pcre_free) when it is no
2024 longer required.
2025
2026 Although the compiled code of a PCRE regex is relocatable, that is, it
2027 does not depend on memory location, the complete pcre data block is not
2028 fully relocatable, because it may contain a copy of the tableptr argu-
2029 ment, which is an address (see below).
2030
2031 The options argument contains various bit settings that affect the com-
2032 pilation. It should be zero if no options are required. The available
2033 options are described below. Some of them (in particular, those that
2034 are compatible with Perl, but some others as well) can also be set and
2035 unset from within the pattern (see the detailed description in the
2036 pcrepattern documentation). For those options that can be different in
2037 different parts of the pattern, the contents of the options argument
2038 specifies their settings at the start of compilation and execution. The
2039 PCRE_ANCHORED, PCRE_BSR_xxx, PCRE_NEWLINE_xxx, PCRE_NO_UTF8_CHECK, and
2040 PCRE_NO_START_OPTIMIZE options can be set at the time of matching as
2041 well as at compile time.
2042
2043 If errptr is NULL, pcre_compile() returns NULL immediately. Otherwise,
2044 if compilation of a pattern fails, pcre_compile() returns NULL, and
2045 sets the variable pointed to by errptr to point to a textual error mes-
2046 sage. This is a static string that is part of the library. You must not
2047 try to free it. Normally, the offset from the start of the pattern to
2048 the data unit that was being processed when the error was discovered is
2049 placed in the variable pointed to by erroffset, which must not be NULL
2050 (if it is, an immediate error is given). However, for an invalid UTF-8
2051 or UTF-16 string, the offset is that of the first data unit of the
2052 failing character.
2053
2054 Some errors are not detected until the whole pattern has been scanned;
2055 in these cases, the offset passed back is the length of the pattern.
2056 Note that the offset is in data units, not characters, even in a UTF
2057 mode. It may sometimes point into the middle of a UTF-8 or UTF-16 char-
2058 acter.
2059
2060 If pcre_compile2() is used instead of pcre_compile(), and the error-
2061 codeptr argument is not NULL, a non-zero error code number is returned
2062 via this argument in the event of an error. This is in addition to the
2063 textual error message. Error codes and messages are listed below.
2064
2065 If the final argument, tableptr, is NULL, PCRE uses a default set of
2066 character tables that are built when PCRE is compiled, using the
2067 default C locale. Otherwise, tableptr must be an address that is the
2068 result of a call to pcre_maketables(). This value is stored with the
2069 compiled pattern, and used again by pcre_exec() and pcre_dfa_exec()
2070 when the pattern is matched. For more discussion, see the section on
2071 locale support below.
2072
2073 This code fragment shows a typical straightforward call to pcre_com-
2074 pile():
2075
2076 pcre *re;
2077 const char *error;
2078 int erroffset;
2079 re = pcre_compile(
2080 "^A.*Z", /* the pattern */
2081 0, /* default options */
2082 &error, /* for error message */
2083 &erroffset, /* for error offset */
2084 NULL); /* use default character tables */
2085
2086 The following names for option bits are defined in the pcre.h header
2087 file:
2088
2089 PCRE_ANCHORED
2090
2091 If this bit is set, the pattern is forced to be "anchored", that is, it
2092 is constrained to match only at the first matching point in the string
2093 that is being searched (the "subject string"). This effect can also be
2094 achieved by appropriate constructs in the pattern itself, which is the
2095 only way to do it in Perl.
2096
2097 PCRE_AUTO_CALLOUT
2098
2099 If this bit is set, pcre_compile() automatically inserts callout items,
2100 all with number 255, before each pattern item. For discussion of the
2101 callout facility, see the pcrecallout documentation.
2102
2103 PCRE_BSR_ANYCRLF
2104 PCRE_BSR_UNICODE
2105
2106 These options (which are mutually exclusive) control what the \R escape
2107 sequence matches. The choice is either to match only CR, LF, or CRLF,
2108 or to match any Unicode newline sequence. The default is specified when
2109 PCRE is built. It can be overridden from within the pattern, or by set-
2110 ting an option when a compiled pattern is matched.
2111
2112 PCRE_CASELESS
2113
2114 If this bit is set, letters in the pattern match both upper and lower
2115 case letters. It is equivalent to Perl's /i option, and it can be
2116 changed within a pattern by a (?i) option setting. In UTF-8 mode, PCRE
2117 always understands the concept of case for characters whose values are
2118 less than 128, so caseless matching is always possible. For characters
2119 with higher values, the concept of case is supported if PCRE is com-
2120 piled with Unicode property support, but not otherwise. If you want to
2121 use caseless matching for characters 128 and above, you must ensure
2122 that PCRE is compiled with Unicode property support as well as with
2123 UTF-8 support.
2124
2125 PCRE_DOLLAR_ENDONLY
2126
2127 If this bit is set, a dollar metacharacter in the pattern matches only
2128 at the end of the subject string. Without this option, a dollar also
2129 matches immediately before a newline at the end of the string (but not
2130 before any other newlines). The PCRE_DOLLAR_ENDONLY option is ignored
2131 if PCRE_MULTILINE is set. There is no equivalent to this option in
2132 Perl, and no way to set it within a pattern.
2133
2134 PCRE_DOTALL
2135
2136 If this bit is set, a dot metacharacter in the pattern matches a char-
2137 acter of any value, including one that indicates a newline. However, it
2138 only ever matches one character, even if newlines are coded as CRLF.
2139 Without this option, a dot does not match when the current position is
2140 at a newline. This option is equivalent to Perl's /s option, and it can
2141 be changed within a pattern by a (?s) option setting. A negative class
2142 such as [^a] always matches newline characters, independent of the set-
2143 ting of this option.
2144
2145 PCRE_DUPNAMES
2146
2147 If this bit is set, names used to identify capturing subpatterns need
2148 not be unique. This can be helpful for certain types of pattern when it
2149 is known that only one instance of the named subpattern can ever be
2150 matched. There are more details of named subpatterns below; see also
2151 the pcrepattern documentation.
2152
2153 PCRE_EXTENDED
2154
2155 If this bit is set, most white space characters in the pattern are
2156 totally ignored except when escaped or inside a character class. How-
2157 ever, white space is not allowed within sequences such as (?> that
2158 introduce various parenthesized subpatterns, nor within a numerical
2159 quantifier such as {1,3}. However, ignorable white space is permitted
2160 between an item and a following quantifier and between a quantifier and
2161 a following + that indicates possessiveness.
2162
2163 White space did not used to include the VT character (code 11), because
2164 Perl did not treat this character as white space. However, Perl changed
2165 at release 5.18, so PCRE followed at release 8.34, and VT is now
2166 treated as white space.
2167
2168 PCRE_EXTENDED also causes characters between an unescaped # outside a
2169 character class and the next newline, inclusive, to be ignored.
2170 PCRE_EXTENDED is equivalent to Perl's /x option, and it can be changed
2171 within a pattern by a (?x) option setting.
2172
2173 Which characters are interpreted as newlines is controlled by the
2174 options passed to pcre_compile() or by a special sequence at the start
2175 of the pattern, as described in the section entitled "Newline conven-
2176 tions" in the pcrepattern documentation. Note that the end of this type
2177 of comment is a literal newline sequence in the pattern; escape
2178 sequences that happen to represent a newline do not count.
2179
2180 This option makes it possible to include comments inside complicated
2181 patterns. Note, however, that this applies only to data characters.
2182 White space characters may never appear within special character
2183 sequences in a pattern, for example within the sequence (?( that intro-
2184 duces a conditional subpattern.
2185
2186 PCRE_EXTRA
2187
2188 This option was invented in order to turn on additional functionality
2189 of PCRE that is incompatible with Perl, but it is currently of very
2190 little use. When set, any backslash in a pattern that is followed by a
2191 letter that has no special meaning causes an error, thus reserving
2192 these combinations for future expansion. By default, as in Perl, a
2193 backslash followed by a letter with no special meaning is treated as a
2194 literal. (Perl can, however, be persuaded to give an error for this, by
2195 running it with the -w option.) There are at present no other features
2196 controlled by this option. It can also be set by a (?X) option setting
2197 within a pattern.
2198
2199 PCRE_FIRSTLINE
2200
2201 If this option is set, an unanchored pattern is required to match
2202 before or at the first newline in the subject string, though the
2203 matched text may continue over the newline.
2204
2205 PCRE_JAVASCRIPT_COMPAT
2206
2207 If this option is set, PCRE's behaviour is changed in some ways so that
2208 it is compatible with JavaScript rather than Perl. The changes are as
2209 follows:
2210
2211 (1) A lone closing square bracket in a pattern causes a compile-time
2212 error, because this is illegal in JavaScript (by default it is treated
2213 as a data character). Thus, the pattern AB]CD becomes illegal when this
2214 option is set.
2215
2216 (2) At run time, a back reference to an unset subpattern group matches
2217 an empty string (by default this causes the current matching alterna-
2218 tive to fail). A pattern such as (\1)(a) succeeds when this option is
2219 set (assuming it can find an "a" in the subject), whereas it fails by
2220 default, for Perl compatibility.
2221
2222 (3) \U matches an upper case "U" character; by default \U causes a com-
2223 pile time error (Perl uses \U to upper case subsequent characters).
2224
2225 (4) \u matches a lower case "u" character unless it is followed by four
2226 hexadecimal digits, in which case the hexadecimal number defines the
2227 code point to match. By default, \u causes a compile time error (Perl
2228 uses it to upper case the following character).
2229
2230 (5) \x matches a lower case "x" character unless it is followed by two
2231 hexadecimal digits, in which case the hexadecimal number defines the
2232 code point to match. By default, as in Perl, a hexadecimal number is
2233 always expected after \x, but it may have zero, one, or two digits (so,
2234 for example, \xz matches a binary zero character followed by z).
2235
2236 PCRE_MULTILINE
2237
2238 By default, for the purposes of matching "start of line" and "end of
2239 line", PCRE treats the subject string as consisting of a single line of
2240 characters, even if it actually contains newlines. The "start of line"
2241 metacharacter (^) matches only at the start of the string, and the "end
2242 of line" metacharacter ($) matches only at the end of the string, or
2243 before a terminating newline (except when PCRE_DOLLAR_ENDONLY is set).
2244 Note, however, that unless PCRE_DOTALL is set, the "any character"
2245 metacharacter (.) does not match at a newline. This behaviour (for ^,
2246 $, and dot) is the same as Perl.
2247
2248 When PCRE_MULTILINE it is set, the "start of line" and "end of line"
2249 constructs match immediately following or immediately before internal
2250 newlines in the subject string, respectively, as well as at the very
2251 start and end. This is equivalent to Perl's /m option, and it can be
2252 changed within a pattern by a (?m) option setting. If there are no new-
2253 lines in a subject string, or no occurrences of ^ or $ in a pattern,
2254 setting PCRE_MULTILINE has no effect.
2255
2256 PCRE_NEVER_UTF
2257
2258 This option locks out interpretation of the pattern as UTF-8 (or UTF-16
2259 or UTF-32 in the 16-bit and 32-bit libraries). In particular, it pre-
2260 vents the creator of the pattern from switching to UTF interpretation
2261 by starting the pattern with (*UTF). This may be useful in applications
2262 that process patterns from external sources. The combination of
2263 PCRE_UTF8 and PCRE_NEVER_UTF also causes an error.
2264
2265 PCRE_NEWLINE_CR
2266 PCRE_NEWLINE_LF
2267 PCRE_NEWLINE_CRLF
2268 PCRE_NEWLINE_ANYCRLF
2269 PCRE_NEWLINE_ANY
2270
2271 These options override the default newline definition that was chosen
2272 when PCRE was built. Setting the first or the second specifies that a
2273 newline is indicated by a single character (CR or LF, respectively).
2274 Setting PCRE_NEWLINE_CRLF specifies that a newline is indicated by the
2275 two-character CRLF sequence. Setting PCRE_NEWLINE_ANYCRLF specifies
2276 that any of the three preceding sequences should be recognized. Setting
2277 PCRE_NEWLINE_ANY specifies that any Unicode newline sequence should be
2278 recognized.
2279
2280 In an ASCII/Unicode environment, the Unicode newline sequences are the
2281 three just mentioned, plus the single characters VT (vertical tab,
2282 U+000B), FF (form feed, U+000C), NEL (next line, U+0085), LS (line sep-
2283 arator, U+2028), and PS (paragraph separator, U+2029). For the 8-bit
2284 library, the last two are recognized only in UTF-8 mode.
2285
2286 When PCRE is compiled to run in an EBCDIC (mainframe) environment, the
2287 code for CR is 0x0d, the same as ASCII. However, the character code for
2288 LF is normally 0x15, though in some EBCDIC environments 0x25 is used.
2289 Whichever of these is not LF is made to correspond to Unicode's NEL
2290 character. EBCDIC codes are all less than 256. For more details, see
2291 the pcrebuild documentation.
2292
2293 The newline setting in the options word uses three bits that are
2294 treated as a number, giving eight possibilities. Currently only six are
2295 used (default plus the five values above). This means that if you set
2296 more than one newline option, the combination may or may not be sensi-
2297 ble. For example, PCRE_NEWLINE_CR with PCRE_NEWLINE_LF is equivalent to
2298 PCRE_NEWLINE_CRLF, but other combinations may yield unused numbers and
2299 cause an error.
2300
2301 The only time that a line break in a pattern is specially recognized
2302 when compiling is when PCRE_EXTENDED is set. CR and LF are white space
2303 characters, and so are ignored in this mode. Also, an unescaped # out-
2304 side a character class indicates a comment that lasts until after the
2305 next line break sequence. In other circumstances, line break sequences
2306 in patterns are treated as literal data.
2307
2308 The newline option that is set at compile time becomes the default that
2309 is used for pcre_exec() and pcre_dfa_exec(), but it can be overridden.
2310
2311 PCRE_NO_AUTO_CAPTURE
2312
2313 If this option is set, it disables the use of numbered capturing paren-
2314 theses in the pattern. Any opening parenthesis that is not followed by
2315 ? behaves as if it were followed by ?: but named parentheses can still
2316 be used for capturing (and they acquire numbers in the usual way).
2317 There is no equivalent of this option in Perl.
2318
2319 PCRE_NO_AUTO_POSSESS
2320
2321 If this option is set, it disables "auto-possessification". This is an
2322 optimization that, for example, turns a+b into a++b in order to avoid
2323 backtracks into a+ that can never be successful. However, if callouts
2324 are in use, auto-possessification means that some of them are never
2325 taken. You can set this option if you want the matching functions to do
2326 a full unoptimized search and run all the callouts, but it is mainly
2327 provided for testing purposes.
2328
2329 PCRE_NO_START_OPTIMIZE
2330
2331 This is an option that acts at matching time; that is, it is really an
2332 option for pcre_exec() or pcre_dfa_exec(). If it is set at compile
2333 time, it is remembered with the compiled pattern and assumed at match-
2334 ing time. This is necessary if you want to use JIT execution, because
2335 the JIT compiler needs to know whether or not this option is set. For
2336 details see the discussion of PCRE_NO_START_OPTIMIZE below.
2337
2338 PCRE_UCP
2339
2340 This option changes the way PCRE processes \B, \b, \D, \d, \S, \s, \W,
2341 \w, and some of the POSIX character classes. By default, only ASCII
2342 characters are recognized, but if PCRE_UCP is set, Unicode properties
2343 are used instead to classify characters. More details are given in the
2344 section on generic character types in the pcrepattern page. If you set
2345 PCRE_UCP, matching one of the items it affects takes much longer. The
2346 option is available only if PCRE has been compiled with Unicode prop-
2347 erty support.
2348
2349 PCRE_UNGREEDY
2350
2351 This option inverts the "greediness" of the quantifiers so that they
2352 are not greedy by default, but become greedy if followed by "?". It is
2353 not compatible with Perl. It can also be set by a (?U) option setting
2354 within the pattern.
2355
2356 PCRE_UTF8
2357
2358 This option causes PCRE to regard both the pattern and the subject as
2359 strings of UTF-8 characters instead of single-byte strings. However, it
2360 is available only when PCRE is built to include UTF support. If not,
2361 the use of this option provokes an error. Details of how this option
2362 changes the behaviour of PCRE are given in the pcreunicode page.
2363
2364 PCRE_NO_UTF8_CHECK
2365
2366 When PCRE_UTF8 is set, the validity of the pattern as a UTF-8 string is
2367 automatically checked. There is a discussion about the validity of
2368 UTF-8 strings in the pcreunicode page. If an invalid UTF-8 sequence is
2369 found, pcre_compile() returns an error. If you already know that your
2370 pattern is valid, and you want to skip this check for performance rea-
2371 sons, you can set the PCRE_NO_UTF8_CHECK option. When it is set, the
2372 effect of passing an invalid UTF-8 string as a pattern is undefined. It
2373 may cause your program to crash or loop. Note that this option can also
2374 be passed to pcre_exec() and pcre_dfa_exec(), to suppress the validity
2375 checking of subject strings only. If the same string is being matched
2376 many times, the option can be safely set for the second and subsequent
2377 matchings to improve performance.
2378
2379
2380 COMPILATION ERROR CODES
2381
2382 The following table lists the error codes than may be returned by
2383 pcre_compile2(), along with the error messages that may be returned by
2384 both compiling functions. Note that error messages are always 8-bit
2385 ASCII strings, even in 16-bit or 32-bit mode. As PCRE has developed,
2386 some error codes have fallen out of use. To avoid confusion, they have
2387 not been re-used.
2388
2389 0 no error
2390 1 \ at end of pattern
2391 2 \c at end of pattern
2392 3 unrecognized character follows \
2393 4 numbers out of order in {} quantifier
2394 5 number too big in {} quantifier
2395 6 missing terminating ] for character class
2396 7 invalid escape sequence in character class
2397 8 range out of order in character class
2398 9 nothing to repeat
2399 10 [this code is not in use]
2400 11 internal error: unexpected repeat
2401 12 unrecognized character after (? or (?-
2402 13 POSIX named classes are supported only within a class
2403 14 missing )
2404 15 reference to non-existent subpattern
2405 16 erroffset passed as NULL
2406 17 unknown option bit(s) set
2407 18 missing ) after comment
2408 19 [this code is not in use]
2409 20 regular expression is too large
2410 21 failed to get memory
2411 22 unmatched parentheses
2412 23 internal error: code overflow
2413 24 unrecognized character after (?<
2414 25 lookbehind assertion is not fixed length
2415 26 malformed number or name after (?(
2416 27 conditional group contains more than two branches
2417 28 assertion expected after (?(
2418 29 (?R or (?[+-]digits must be followed by )
2419 30 unknown POSIX class name
2420 31 POSIX collating elements are not supported
2421 32 this version of PCRE is compiled without UTF support
2422 33 [this code is not in use]
2423 34 character value in \x{} or \o{} is too large
2424 35 invalid condition (?(0)
2425 36 \C not allowed in lookbehind assertion
2426 37 PCRE does not support \L, \l, \N{name}, \U, or \u
2427 38 number after (?C is > 255
2428 39 closing ) for (?C expected
2429 40 recursive call could loop indefinitely
2430 41 unrecognized character after (?P
2431 42 syntax error in subpattern name (missing terminator)
2432 43 two named subpatterns have the same name
2433 44 invalid UTF-8 string (specifically UTF-8)
2434 45 support for \P, \p, and \X has not been compiled
2435 46 malformed \P or \p sequence
2436 47 unknown property name after \P or \p
2437 48 subpattern name is too long (maximum 32 characters)
2438 49 too many named subpatterns (maximum 10000)
2439 50 [this code is not in use]
2440 51 octal value is greater than \377 in 8-bit non-UTF-8 mode
2441 52 internal error: overran compiling workspace
2442 53 internal error: previously-checked referenced subpattern
2443 not found
2444 54 DEFINE group contains more than one branch
2445 55 repeating a DEFINE group is not allowed
2446 56 inconsistent NEWLINE options
2447 57 \g is not followed by a braced, angle-bracketed, or quoted
2448 name/number or by a plain number
2449 58 a numbered reference must not be zero
2450 59 an argument is not allowed for (*ACCEPT), (*FAIL), or (*COMMIT)
2451 60 (*VERB) not recognized or malformed
2452 61 number is too big
2453 62 subpattern name expected
2454 63 digit expected after (?+
2455 64 ] is an invalid data character in JavaScript compatibility mode
2456 65 different names for subpatterns of the same number are
2457 not allowed
2458 66 (*MARK) must have an argument
2459 67 this version of PCRE is not compiled with Unicode property
2460 support
2461 68 \c must be followed by an ASCII character
2462 69 \k is not followed by a braced, angle-bracketed, or quoted name
2463 70 internal error: unknown opcode in find_fixedlength()
2464 71 \N is not supported in a class
2465 72 too many forward references
2466 73 disallowed Unicode code point (>= 0xd800 && <= 0xdfff)
2467 74 invalid UTF-16 string (specifically UTF-16)
2468 75 name is too long in (*MARK), (*PRUNE), (*SKIP), or (*THEN)
2469 76 character value in \u.... sequence is too large
2470 77 invalid UTF-32 string (specifically UTF-32)
2471 78 setting UTF is disabled by the application
2472 79 non-hex character in \x{} (closing brace missing?)
2473 80 non-octal character in \o{} (closing brace missing?)
2474 81 missing opening brace after \o
2475 82 parentheses are too deeply nested
2476 83 invalid range in character class
2477
2478 The numbers 32 and 10000 in errors 48 and 49 are defaults; different
2479 values may be used if the limits were changed when PCRE was built.
2480
2481
2482 STUDYING A PATTERN
2483
2484 pcre_extra *pcre_study(const pcre *code, int options,
2485 const char **errptr);
2486
2487 If a compiled pattern is going to be used several times, it is worth
2488 spending more time analyzing it in order to speed up the time taken for
2489 matching. The function pcre_study() takes a pointer to a compiled pat-
2490 tern as its first argument. If studying the pattern produces additional
2491 information that will help speed up matching, pcre_study() returns a
2492 pointer to a pcre_extra block, in which the study_data field points to
2493 the results of the study.
2494
2495 The returned value from pcre_study() can be passed directly to
2496 pcre_exec() or pcre_dfa_exec(). However, a pcre_extra block also con-
2497 tains other fields that can be set by the caller before the block is
2498 passed; these are described below in the section on matching a pattern.
2499
2500 If studying the pattern does not produce any useful information,
2501 pcre_study() returns NULL by default. In that circumstance, if the
2502 calling program wants to pass any of the other fields to pcre_exec() or
2503 pcre_dfa_exec(), it must set up its own pcre_extra block. However, if
2504 pcre_study() is called with the PCRE_STUDY_EXTRA_NEEDED option, it
2505 returns a pcre_extra block even if studying did not find any additional
2506 information. It may still return NULL, however, if an error occurs in
2507 pcre_study().
2508
2509 The second argument of pcre_study() contains option bits. There are
2510 three further options in addition to PCRE_STUDY_EXTRA_NEEDED:
2511
2512 PCRE_STUDY_JIT_COMPILE
2513 PCRE_STUDY_JIT_PARTIAL_HARD_COMPILE
2514 PCRE_STUDY_JIT_PARTIAL_SOFT_COMPILE
2515
2516 If any of these are set, and the just-in-time compiler is available,
2517 the pattern is further compiled into machine code that executes much
2518 faster than the pcre_exec() interpretive matching function. If the
2519 just-in-time compiler is not available, these options are ignored. All
2520 undefined bits in the options argument must be zero.
2521
2522 JIT compilation is a heavyweight optimization. It can take some time
2523 for patterns to be analyzed, and for one-off matches and simple pat-
2524 terns the benefit of faster execution might be offset by a much slower
2525 study time. Not all patterns can be optimized by the JIT compiler. For
2526 those that cannot be handled, matching automatically falls back to the
2527 pcre_exec() interpreter. For more details, see the pcrejit documenta-
2528 tion.
2529
2530 The third argument for pcre_study() is a pointer for an error message.
2531 If studying succeeds (even if no data is returned), the variable it
2532 points to is set to NULL. Otherwise it is set to point to a textual
2533 error message. This is a static string that is part of the library. You
2534 must not try to free it. You should test the error pointer for NULL
2535 after calling pcre_study(), to be sure that it has run successfully.
2536
2537 When you are finished with a pattern, you can free the memory used for
2538 the study data by calling pcre_free_study(). This function was added to
2539 the API for release 8.20. For earlier versions, the memory could be
2540 freed with pcre_free(), just like the pattern itself. This will still
2541 work in cases where JIT optimization is not used, but it is advisable
2542 to change to the new function when convenient.
2543
2544 This is a typical way in which pcre_study() is used (except that in a
2545 real application there should be tests for errors):
2546
2547 int rc;
2548 pcre *re;
2549 pcre_extra *sd;
2550 re = pcre_compile("pattern", 0, &error, &erroroffset, NULL);
2551 sd = pcre_study(
2552 re, /* result of pcre_compile() */
2553 0, /* no options */
2554 &error); /* set to NULL or points to a message */
2555 rc = pcre_exec( /* see below for details of pcre_exec() options */
2556 re, sd, "subject", 7, 0, 0, ovector, 30);
2557 ...
2558 pcre_free_study(sd);
2559 pcre_free(re);
2560
2561 Studying a pattern does two things: first, a lower bound for the length
2562 of subject string that is needed to match the pattern is computed. This
2563 does not mean that there are any strings of that length that match, but
2564 it does guarantee that no shorter strings match. The value is used to
2565 avoid wasting time by trying to match strings that are shorter than the
2566 lower bound. You can find out the value in a calling program via the
2567 pcre_fullinfo() function.
2568
2569 Studying a pattern is also useful for non-anchored patterns that do not
2570 have a single fixed starting character. A bitmap of possible starting
2571 bytes is created. This speeds up finding a position in the subject at
2572 which to start matching. (In 16-bit mode, the bitmap is used for 16-bit
2573 values less than 256. In 32-bit mode, the bitmap is used for 32-bit
2574 values less than 256.)
2575
2576 These two optimizations apply to both pcre_exec() and pcre_dfa_exec(),
2577 and the information is also used by the JIT compiler. The optimiza-
2578 tions can be disabled by setting the PCRE_NO_START_OPTIMIZE option.
2579 You might want to do this if your pattern contains callouts or (*MARK)
2580 and you want to make use of these facilities in cases where matching
2581 fails.
2582
2583 PCRE_NO_START_OPTIMIZE can be specified at either compile time or exe-
2584 cution time. However, if PCRE_NO_START_OPTIMIZE is passed to
2585 pcre_exec(), (that is, after any JIT compilation has happened) JIT exe-
2586 cution is disabled. For JIT execution to work with PCRE_NO_START_OPTI-
2587 MIZE, the option must be set at compile time.
2588
2589 There is a longer discussion of PCRE_NO_START_OPTIMIZE below.
2590
2591
2592 LOCALE SUPPORT
2593
2594 PCRE handles caseless matching, and determines whether characters are
2595 letters, digits, or whatever, by reference to a set of tables, indexed
2596 by character code point. When running in UTF-8 mode, or in the 16- or
2597 32-bit libraries, this applies only to characters with code points less
2598 than 256. By default, higher-valued code points never match escapes
2599 such as \w or \d. However, if PCRE is built with Unicode property sup-
2600 port, all characters can be tested with \p and \P, or, alternatively,
2601 the PCRE_UCP option can be set when a pattern is compiled; this causes
2602 \w and friends to use Unicode property support instead of the built-in
2603 tables.
2604
2605 The use of locales with Unicode is discouraged. If you are handling
2606 characters with code points greater than 128, you should either use
2607 Unicode support, or use locales, but not try to mix the two.
2608
2609 PCRE contains an internal set of tables that are used when the final
2610 argument of pcre_compile() is NULL. These are sufficient for many
2611 applications. Normally, the internal tables recognize only ASCII char-
2612 acters. However, when PCRE is built, it is possible to cause the inter-
2613 nal tables to be rebuilt in the default "C" locale of the local system,
2614 which may cause them to be different.
2615
2616 The internal tables can always be overridden by tables supplied by the
2617 application that calls PCRE. These may be created in a different locale
2618 from the default. As more and more applications change to using Uni-
2619 code, the need for this locale support is expected to die away.
2620
2621 External tables are built by calling the pcre_maketables() function,
2622 which has no arguments, in the relevant locale. The result can then be
2623 passed to pcre_compile() as often as necessary. For example, to build
2624 and use tables that are appropriate for the French locale (where
2625 accented characters with values greater than 128 are treated as let-
2626 ters), the following code could be used:
2627
2628 setlocale(LC_CTYPE, "fr_FR");
2629 tables = pcre_maketables();
2630 re = pcre_compile(..., tables);
2631
2632 The locale name "fr_FR" is used on Linux and other Unix-like systems;
2633 if you are using Windows, the name for the French locale is "french".
2634
2635 When pcre_maketables() runs, the tables are built in memory that is
2636 obtained via pcre_malloc. It is the caller's responsibility to ensure
2637 that the memory containing the tables remains available for as long as
2638 it is needed.
2639
2640 The pointer that is passed to pcre_compile() is saved with the compiled
2641 pattern, and the same tables are used via this pointer by pcre_study()
2642 and also by pcre_exec() and pcre_dfa_exec(). Thus, for any single pat-
2643 tern, compilation, studying and matching all happen in the same locale,
2644 but different patterns can be processed in different locales.
2645
2646 It is possible to pass a table pointer or NULL (indicating the use of
2647 the internal tables) to pcre_exec() or pcre_dfa_exec() (see the discus-
2648 sion below in the section on matching a pattern). This facility is pro-
2649 vided for use with pre-compiled patterns that have been saved and
2650 reloaded. Character tables are not saved with patterns, so if a non-
2651 standard table was used at compile time, it must be provided again when
2652 the reloaded pattern is matched. Attempting to use this facility to
2653 match a pattern in a different locale from the one in which it was com-
2654 piled is likely to lead to anomalous (usually incorrect) results.
2655
2656
2657 INFORMATION ABOUT A PATTERN
2658
2659 int pcre_fullinfo(const pcre *code, const pcre_extra *extra,
2660 int what, void *where);
2661
2662 The pcre_fullinfo() function returns information about a compiled pat-
2663 tern. It replaces the pcre_info() function, which was removed from the
2664 library at version 8.30, after more than 10 years of obsolescence.
2665
2666 The first argument for pcre_fullinfo() is a pointer to the compiled
2667 pattern. The second argument is the result of pcre_study(), or NULL if
2668 the pattern was not studied. The third argument specifies which piece
2669 of information is required, and the fourth argument is a pointer to a
2670 variable to receive the data. The yield of the function is zero for
2671 success, or one of the following negative numbers:
2672
2673 PCRE_ERROR_NULL the argument code was NULL
2674 the argument where was NULL
2675 PCRE_ERROR_BADMAGIC the "magic number" was not found
2676 PCRE_ERROR_BADENDIANNESS the pattern was compiled with different
2677 endianness
2678 PCRE_ERROR_BADOPTION the value of what was invalid
2679 PCRE_ERROR_UNSET the requested field is not set
2680
2681 The "magic number" is placed at the start of each compiled pattern as
2682 an simple check against passing an arbitrary memory pointer. The endi-
2683 anness error can occur if a compiled pattern is saved and reloaded on a
2684 different host. Here is a typical call of pcre_fullinfo(), to obtain
2685 the length of the compiled pattern:
2686
2687 int rc;
2688 size_t length;
2689 rc = pcre_fullinfo(
2690 re, /* result of pcre_compile() */
2691 sd, /* result of pcre_study(), or NULL */
2692 PCRE_INFO_SIZE, /* what is required */
2693 &length); /* where to put the data */
2694
2695 The possible values for the third argument are defined in pcre.h, and
2696 are as follows:
2697
2698 PCRE_INFO_BACKREFMAX
2699
2700 Return the number of the highest back reference in the pattern. The
2701 fourth argument should point to an int variable. Zero is returned if
2702 there are no back references.
2703
2704 PCRE_INFO_CAPTURECOUNT
2705
2706 Return the number of capturing subpatterns in the pattern. The fourth
2707 argument should point to an int variable.
2708
2709 PCRE_INFO_DEFAULT_TABLES
2710
2711 Return a pointer to the internal default character tables within PCRE.
2712 The fourth argument should point to an unsigned char * variable. This
2713 information call is provided for internal use by the pcre_study() func-
2714 tion. External callers can cause PCRE to use its internal tables by
2715 passing a NULL table pointer.
2716
2717 PCRE_INFO_FIRSTBYTE
2718
2719 Return information about the first data unit of any matched string, for
2720 a non-anchored pattern. (The name of this option refers to the 8-bit
2721 library, where data units are bytes.) The fourth argument should point
2722 to an int variable.
2723
2724 If there is a fixed first value, for example, the letter "c" from a
2725 pattern such as (cat|cow|coyote), its value is returned. In the 8-bit
2726 library, the value is always less than 256. In the 16-bit library the
2727 value can be up to 0xffff. In the 32-bit library the value can be up to
2728 0x10ffff.
2729
2730 If there is no fixed first value, and if either
2731
2732 (a) the pattern was compiled with the PCRE_MULTILINE option, and every
2733 branch starts with "^", or
2734
2735 (b) every branch of the pattern starts with ".*" and PCRE_DOTALL is not
2736 set (if it were set, the pattern would be anchored),
2737
2738 -1 is returned, indicating that the pattern matches only at the start
2739 of a subject string or after any newline within the string. Otherwise
2740 -2 is returned. For anchored patterns, -2 is returned.
2741
2742 Since for the 32-bit library using the non-UTF-32 mode, this function
2743 is unable to return the full 32-bit range of the character, this value
2744 is deprecated; instead the PCRE_INFO_FIRSTCHARACTERFLAGS and
2745 PCRE_INFO_FIRSTCHARACTER values should be used.
2746
2747 PCRE_INFO_FIRSTTABLE
2748
2749 If the pattern was studied, and this resulted in the construction of a
2750 256-bit table indicating a fixed set of values for the first data unit
2751 in any matching string, a pointer to the table is returned. Otherwise
2752 NULL is returned. The fourth argument should point to an unsigned char
2753 * variable.
2754
2755 PCRE_INFO_HASCRORLF
2756
2757 Return 1 if the pattern contains any explicit matches for CR or LF
2758 characters, otherwise 0. The fourth argument should point to an int
2759 variable. An explicit match is either a literal CR or LF character, or
2760 \r or \n.
2761
2762 PCRE_INFO_JCHANGED
2763
2764 Return 1 if the (?J) or (?-J) option setting is used in the pattern,
2765 otherwise 0. The fourth argument should point to an int variable. (?J)
2766 and (?-J) set and unset the local PCRE_DUPNAMES option, respectively.
2767
2768 PCRE_INFO_JIT
2769
2770 Return 1 if the pattern was studied with one of the JIT options, and
2771 just-in-time compiling was successful. The fourth argument should point
2772 to an int variable. A return value of 0 means that JIT support is not
2773 available in this version of PCRE, or that the pattern was not studied
2774 with a JIT option, or that the JIT compiler could not handle this par-
2775 ticular pattern. See the pcrejit documentation for details of what can
2776 and cannot be handled.
2777
2778 PCRE_INFO_JITSIZE
2779
2780 If the pattern was successfully studied with a JIT option, return the
2781 size of the JIT compiled code, otherwise return zero. The fourth argu-
2782 ment should point to a size_t variable.
2783
2784 PCRE_INFO_LASTLITERAL
2785
2786 Return the value of the rightmost literal data unit that must exist in
2787 any matched string, other than at its start, if such a value has been
2788 recorded. The fourth argument should point to an int variable. If there
2789 is no such value, -1 is returned. For anchored patterns, a last literal
2790 value is recorded only if it follows something of variable length. For
2791 example, for the pattern /^a\d+z\d+/ the returned value is "z", but for
2792 /^a\dz\d/ the returned value is -1.
2793
2794 Since for the 32-bit library using the non-UTF-32 mode, this function
2795 is unable to return the full 32-bit range of characters, this value is
2796 deprecated; instead the PCRE_INFO_REQUIREDCHARFLAGS and
2797 PCRE_INFO_REQUIREDCHAR values should be used.
2798
2799 PCRE_INFO_MATCH_EMPTY
2800
2801 Return 1 if the pattern can match an empty string, otherwise 0. The
2802 fourth argument should point to an int variable.
2803
2804 PCRE_INFO_MATCHLIMIT
2805
2806 If the pattern set a match limit by including an item of the form
2807 (*LIMIT_MATCH=nnnn) at the start, the value is returned. The fourth
2808 argument should point to an unsigned 32-bit integer. If no such value
2809 has been set, the call to pcre_fullinfo() returns the error
2810 PCRE_ERROR_UNSET.
2811
2812 PCRE_INFO_MAXLOOKBEHIND
2813
2814 Return the number of characters (NB not data units) in the longest
2815 lookbehind assertion in the pattern. This information is useful when
2816 doing multi-segment matching using the partial matching facilities.
2817 Note that the simple assertions \b and \B require a one-character look-
2818 behind. \A also registers a one-character lookbehind, though it does
2819 not actually inspect the previous character. This is to ensure that at
2820 least one character from the old segment is retained when a new segment
2821 is processed. Otherwise, if there are no lookbehinds in the pattern, \A
2822 might match incorrectly at the start of a new segment.
2823
2824 PCRE_INFO_MINLENGTH
2825
2826 If the pattern was studied and a minimum length for matching subject
2827 strings was computed, its value is returned. Otherwise the returned
2828 value is -1. The value is a number of characters, which in UTF mode may
2829 be different from the number of data units. The fourth argument should
2830 point to an int variable. A non-negative value is a lower bound to the
2831 length of any matching string. There may not be any strings of that
2832 length that do actually match, but every string that does match is at
2833 least that long.
2834
2835 PCRE_INFO_NAMECOUNT
2836 PCRE_INFO_NAMEENTRYSIZE
2837 PCRE_INFO_NAMETABLE
2838
2839 PCRE supports the use of named as well as numbered capturing parenthe-
2840 ses. The names are just an additional way of identifying the parenthe-
2841 ses, which still acquire numbers. Several convenience functions such as
2842 pcre_get_named_substring() are provided for extracting captured sub-
2843 strings by name. It is also possible to extract the data directly, by
2844 first converting the name to a number in order to access the correct
2845 pointers in the output vector (described with pcre_exec() below). To do
2846 the conversion, you need to use the name-to-number map, which is
2847 described by these three values.
2848
2849 The map consists of a number of fixed-size entries. PCRE_INFO_NAMECOUNT
2850 gives the number of entries, and PCRE_INFO_NAMEENTRYSIZE gives the size
2851 of each entry; both of these return an int value. The entry size
2852 depends on the length of the longest name. PCRE_INFO_NAMETABLE returns
2853 a pointer to the first entry of the table. This is a pointer to char in
2854 the 8-bit library, where the first two bytes of each entry are the num-
2855 ber of the capturing parenthesis, most significant byte first. In the
2856 16-bit library, the pointer points to 16-bit data units, the first of
2857 which contains the parenthesis number. In the 32-bit library, the
2858 pointer points to 32-bit data units, the first of which contains the
2859 parenthesis number. The rest of the entry is the corresponding name,
2860 zero terminated.
2861
2862 The names are in alphabetical order. If (?| is used to create multiple
2863 groups with the same number, as described in the section on duplicate
2864 subpattern numbers in the pcrepattern page, the groups may be given the
2865 same name, but there is only one entry in the table. Different names
2866 for groups of the same number are not permitted. Duplicate names for
2867 subpatterns with different numbers are permitted, but only if PCRE_DUP-
2868 NAMES is set. They appear in the table in the order in which they were
2869 found in the pattern. In the absence of (?| this is the order of
2870 increasing number; when (?| is used this is not necessarily the case
2871 because later subpatterns may have lower numbers.
2872
2873 As a simple example of the name/number table, consider the following
2874 pattern after compilation by the 8-bit library (assume PCRE_EXTENDED is
2875 set, so white space - including newlines - is ignored):
2876
2877 (?<date> (?<year>(\d\d)?\d\d) -
2878 (?<month>\d\d) - (?<day>\d\d) )
2879
2880 There are four named subpatterns, so the table has four entries, and
2881 each entry in the table is eight bytes long. The table is as follows,
2882 with non-printing bytes shows in hexadecimal, and undefined bytes shown
2883 as ??:
2884
2885 00 01 d a t e 00 ??
2886 00 05 d a y 00 ?? ??
2887 00 04 m o n t h 00
2888 00 02 y e a r 00 ??
2889
2890 When writing code to extract data from named subpatterns using the
2891 name-to-number map, remember that the length of the entries is likely
2892 to be different for each compiled pattern.
2893
2894 PCRE_INFO_OKPARTIAL
2895
2896 Return 1 if the pattern can be used for partial matching with
2897 pcre_exec(), otherwise 0. The fourth argument should point to an int
2898 variable. From release 8.00, this always returns 1, because the
2899 restrictions that previously applied to partial matching have been
2900 lifted. The pcrepartial documentation gives details of partial match-
2901 ing.
2902
2903 PCRE_INFO_OPTIONS
2904
2905 Return a copy of the options with which the pattern was compiled. The
2906 fourth argument should point to an unsigned long int variable. These
2907 option bits are those specified in the call to pcre_compile(), modified
2908 by any top-level option settings at the start of the pattern itself. In
2909 other words, they are the options that will be in force when matching
2910 starts. For example, if the pattern /(?im)abc(?-i)d/ is compiled with
2911 the PCRE_EXTENDED option, the result is PCRE_CASELESS, PCRE_MULTILINE,
2912 and PCRE_EXTENDED.
2913
2914 A pattern is automatically anchored by PCRE if all of its top-level
2915 alternatives begin with one of the following:
2916
2917 ^ unless PCRE_MULTILINE is set
2918 \A always
2919 \G always
2920 .* if PCRE_DOTALL is set and there are no back
2921 references to the subpattern in which .* appears
2922
2923 For such patterns, the PCRE_ANCHORED bit is set in the options returned
2924 by pcre_fullinfo().
2925
2926 PCRE_INFO_RECURSIONLIMIT
2927
2928 If the pattern set a recursion limit by including an item of the form
2929 (*LIMIT_RECURSION=nnnn) at the start, the value is returned. The fourth
2930 argument should point to an unsigned 32-bit integer. If no such value
2931 has been set, the call to pcre_fullinfo() returns the error
2932 PCRE_ERROR_UNSET.
2933
2934 PCRE_INFO_SIZE
2935
2936 Return the size of the compiled pattern in bytes (for all three
2937 libraries). The fourth argument should point to a size_t variable. This
2938 value does not include the size of the pcre structure that is returned
2939 by pcre_compile(). The value that is passed as the argument to
2940 pcre_malloc() when pcre_compile() is getting memory in which to place
2941 the compiled data is the value returned by this option plus the size of
2942 the pcre structure. Studying a compiled pattern, with or without JIT,
2943 does not alter the value returned by this option.
2944
2945 PCRE_INFO_STUDYSIZE
2946
2947 Return the size in bytes (for all three libraries) of the data block
2948 pointed to by the study_data field in a pcre_extra block. If pcre_extra
2949 is NULL, or there is no study data, zero is returned. The fourth argu-
2950 ment should point to a size_t variable. The study_data field is set by
2951 pcre_study() to record information that will speed up matching (see the
2952 section entitled "Studying a pattern" above). The format of the
2953 study_data block is private, but its length is made available via this
2954 option so that it can be saved and restored (see the pcreprecompile
2955 documentation for details).
2956
2957 PCRE_INFO_FIRSTCHARACTERFLAGS
2958
2959 Return information about the first data unit of any matched string, for
2960 a non-anchored pattern. The fourth argument should point to an int
2961 variable.
2962
2963 If there is a fixed first value, for example, the letter "c" from a
2964 pattern such as (cat|cow|coyote), 1 is returned, and the character
2965 value can be retrieved using PCRE_INFO_FIRSTCHARACTER.
2966
2967 If there is no fixed first value, and if either
2968
2969 (a) the pattern was compiled with the PCRE_MULTILINE option, and every
2970 branch starts with "^", or
2971
2972 (b) every branch of the pattern starts with ".*" and PCRE_DOTALL is not
2973 set (if it were set, the pattern would be anchored),
2974
2975 2 is returned, indicating that the pattern matches only at the start of
2976 a subject string or after any newline within the string. Otherwise 0 is
2977 returned. For anchored patterns, 0 is returned.
2978
2979 PCRE_INFO_FIRSTCHARACTER
2980
2981 Return the fixed first character value in the situation where
2982 PCRE_INFO_FIRSTCHARACTERFLAGS returns 1; otherwise return 0. The fourth
2983 argument should point to an uint_t variable.
2984
2985 In the 8-bit library, the value is always less than 256. In the 16-bit
2986 library the value can be up to 0xffff. In the 32-bit library in UTF-32
2987 mode the value can be up to 0x10ffff, and up to 0xffffffff when not
2988 using UTF-32 mode.
2989
2990 PCRE_INFO_REQUIREDCHARFLAGS
2991
2992 Returns 1 if there is a rightmost literal data unit that must exist in
2993 any matched string, other than at its start. The fourth argument should
2994 point to an int variable. If there is no such value, 0 is returned. If
2995 returning 1, the character value itself can be retrieved using
2996 PCRE_INFO_REQUIREDCHAR.
2997
2998 For anchored patterns, a last literal value is recorded only if it fol-
2999 lows something of variable length. For example, for the pattern
3000 /^a\d+z\d+/ the returned value 1 (with "z" returned from
3001 PCRE_INFO_REQUIREDCHAR), but for /^a\dz\d/ the returned value is 0.
3002
3003 PCRE_INFO_REQUIREDCHAR
3004
3005 Return the value of the rightmost literal data unit that must exist in
3006 any matched string, other than at its start, if such a value has been
3007 recorded. The fourth argument should point to an uint32_t variable. If
3008 there is no such value, 0 is returned.
3009
3010
3011 REFERENCE COUNTS
3012
3013 int pcre_refcount(pcre *code, int adjust);
3014
3015 The pcre_refcount() function is used to maintain a reference count in
3016 the data block that contains a compiled pattern. It is provided for the
3017 benefit of applications that operate in an object-oriented manner,
3018 where different parts of the application may be using the same compiled
3019 pattern, but you want to free the block when they are all done.
3020
3021 When a pattern is compiled, the reference count field is initialized to
3022 zero. It is changed only by calling this function, whose action is to
3023 add the adjust value (which may be positive or negative) to it. The
3024 yield of the function is the new value. However, the value of the count
3025 is constrained to lie between 0 and 65535, inclusive. If the new value
3026 is outside these limits, it is forced to the appropriate limit value.
3027
3028 Except when it is zero, the reference count is not correctly preserved
3029 if a pattern is compiled on one host and then transferred to a host
3030 whose byte-order is different. (This seems a highly unlikely scenario.)
3031
3032
3033 MATCHING A PATTERN: THE TRADITIONAL FUNCTION
3034
3035 int pcre_exec(const pcre *code, const pcre_extra *extra,
3036 const char *subject, int length, int startoffset,
3037 int options, int *ovector, int ovecsize);
3038
3039 The function pcre_exec() is called to match a subject string against a
3040 compiled pattern, which is passed in the code argument. If the pattern
3041 was studied, the result of the study should be passed in the extra
3042 argument. You can call pcre_exec() with the same code and extra argu-
3043 ments as many times as you like, in order to match different subject
3044 strings with the same pattern.
3045
3046 This function is the main matching facility of the library, and it
3047 operates in a Perl-like manner. For specialist use there is also an
3048 alternative matching function, which is described below in the section
3049 about the pcre_dfa_exec() function.
3050
3051 In most applications, the pattern will have been compiled (and option-
3052 ally studied) in the same process that calls pcre_exec(). However, it
3053 is possible to save compiled patterns and study data, and then use them
3054 later in different processes, possibly even on different hosts. For a
3055 discussion about this, see the pcreprecompile documentation.
3056
3057 Here is an example of a simple call to pcre_exec():
3058
3059 int rc;
3060 int ovector[30];
3061 rc = pcre_exec(
3062 re, /* result of pcre_compile() */
3063 NULL, /* we didn't study the pattern */
3064 "some string", /* the subject string */
3065 11, /* the length of the subject string */
3066 0, /* start at offset 0 in the subject */
3067 0, /* default options */
3068 ovector, /* vector of integers for substring information */
3069 30); /* number of elements (NOT size in bytes) */
3070
3071 Extra data for pcre_exec()
3072
3073 If the extra argument is not NULL, it must point to a pcre_extra data
3074 block. The pcre_study() function returns such a block (when it doesn't
3075 return NULL), but you can also create one for yourself, and pass addi-
3076 tional information in it. The pcre_extra block contains the following
3077 fields (not necessarily in this order):
3078
3079 unsigned long int flags;
3080 void *study_data;
3081 void *executable_jit;
3082 unsigned long int match_limit;
3083 unsigned long int match_limit_recursion;
3084 void *callout_data;
3085 const unsigned char *tables;
3086 unsigned char **mark;
3087
3088 In the 16-bit version of this structure, the mark field has type
3089 "PCRE_UCHAR16 **".
3090
3091 In the 32-bit version of this structure, the mark field has type
3092 "PCRE_UCHAR32 **".
3093
3094 The flags field is used to specify which of the other fields are set.
3095 The flag bits are:
3096
3097 PCRE_EXTRA_CALLOUT_DATA
3098 PCRE_EXTRA_EXECUTABLE_JIT
3099 PCRE_EXTRA_MARK
3100 PCRE_EXTRA_MATCH_LIMIT
3101 PCRE_EXTRA_MATCH_LIMIT_RECURSION
3102 PCRE_EXTRA_STUDY_DATA
3103 PCRE_EXTRA_TABLES
3104
3105 Other flag bits should be set to zero. The study_data field and some-
3106 times the executable_jit field are set in the pcre_extra block that is
3107 returned by pcre_study(), together with the appropriate flag bits. You
3108 should not set these yourself, but you may add to the block by setting
3109 other fields and their corresponding flag bits.
3110
3111 The match_limit field provides a means of preventing PCRE from using up
3112 a vast amount of resources when running patterns that are not going to
3113 match, but which have a very large number of possibilities in their
3114 search trees. The classic example is a pattern that uses nested unlim-
3115 ited repeats.
3116
3117 Internally, pcre_exec() uses a function called match(), which it calls
3118 repeatedly (sometimes recursively). The limit set by match_limit is
3119 imposed on the number of times this function is called during a match,
3120 which has the effect of limiting the amount of backtracking that can
3121 take place. For patterns that are not anchored, the count restarts from
3122 zero for each position in the subject string.
3123
3124 When pcre_exec() is called with a pattern that was successfully studied
3125 with a JIT option, the way that the matching is executed is entirely
3126 different. However, there is still the possibility of runaway matching
3127 that goes on for a very long time, and so the match_limit value is also
3128 used in this case (but in a different way) to limit how long the match-
3129 ing can continue.
3130
3131 The default value for the limit can be set when PCRE is built; the
3132 default default is 10 million, which handles all but the most extreme
3133 cases. You can override the default by suppling pcre_exec() with a
3134 pcre_extra block in which match_limit is set, and
3135 PCRE_EXTRA_MATCH_LIMIT is set in the flags field. If the limit is
3136 exceeded, pcre_exec() returns PCRE_ERROR_MATCHLIMIT.
3137
3138 A value for the match limit may also be supplied by an item at the
3139 start of a pattern of the form
3140
3141 (*LIMIT_MATCH=d)
3142
3143 where d is a decimal number. However, such a setting is ignored unless
3144 d is less than the limit set by the caller of pcre_exec() or, if no
3145 such limit is set, less than the default.
3146
3147 The match_limit_recursion field is similar to match_limit, but instead
3148 of limiting the total number of times that match() is called, it limits
3149 the depth of recursion. The recursion depth is a smaller number than
3150 the total number of calls, because not all calls to match() are recur-
3151 sive. This limit is of use only if it is set smaller than match_limit.
3152
3153 Limiting the recursion depth limits the amount of machine stack that
3154 can be used, or, when PCRE has been compiled to use memory on the heap
3155 instead of the stack, the amount of heap memory that can be used. This
3156 limit is not relevant, and is ignored, when matching is done using JIT
3157 compiled code.
3158
3159 The default value for match_limit_recursion can be set when PCRE is
3160 built; the default default is the same value as the default for
3161 match_limit. You can override the default by suppling pcre_exec() with
3162 a pcre_extra block in which match_limit_recursion is set, and
3163 PCRE_EXTRA_MATCH_LIMIT_RECURSION is set in the flags field. If the
3164 limit is exceeded, pcre_exec() returns PCRE_ERROR_RECURSIONLIMIT.
3165
3166 A value for the recursion limit may also be supplied by an item at the
3167 start of a pattern of the form
3168
3169 (*LIMIT_RECURSION=d)
3170
3171 where d is a decimal number. However, such a setting is ignored unless
3172 d is less than the limit set by the caller of pcre_exec() or, if no
3173 such limit is set, less than the default.
3174
3175 The callout_data field is used in conjunction with the "callout" fea-
3176 ture, and is described in the pcrecallout documentation.
3177
3178 The tables field is provided for use with patterns that have been pre-
3179 compiled using custom character tables, saved to disc or elsewhere, and
3180 then reloaded, because the tables that were used to compile a pattern
3181 are not saved with it. See the pcreprecompile documentation for a dis-
3182 cussion of saving compiled patterns for later use. If NULL is passed
3183 using this mechanism, it forces PCRE's internal tables to be used.
3184
3185 Warning: The tables that pcre_exec() uses must be the same as those
3186 that were used when the pattern was compiled. If this is not the case,
3187 the behaviour of pcre_exec() is undefined. Therefore, when a pattern is
3188 compiled and matched in the same process, this field should never be
3189 set. In this (the most common) case, the correct table pointer is auto-
3190 matically passed with the compiled pattern from pcre_compile() to
3191 pcre_exec().
3192
3193 If PCRE_EXTRA_MARK is set in the flags field, the mark field must be
3194 set to point to a suitable variable. If the pattern contains any back-
3195 tracking control verbs such as (*MARK:NAME), and the execution ends up
3196 with a name to pass back, a pointer to the name string (zero termi-
3197 nated) is placed in the variable pointed to by the mark field. The
3198 names are within the compiled pattern; if you wish to retain such a
3199 name you must copy it before freeing the memory of a compiled pattern.
3200 If there is no name to pass back, the variable pointed to by the mark
3201 field is set to NULL. For details of the backtracking control verbs,
3202 see the section entitled "Backtracking control" in the pcrepattern doc-
3203 umentation.
3204
3205 Option bits for pcre_exec()
3206
3207 The unused bits of the options argument for pcre_exec() must be zero.
3208 The only bits that may be set are PCRE_ANCHORED, PCRE_NEWLINE_xxx,
3209 PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, PCRE_NOTEMPTY_ATSTART,
3210 PCRE_NO_START_OPTIMIZE, PCRE_NO_UTF8_CHECK, PCRE_PARTIAL_HARD, and
3211 PCRE_PARTIAL_SOFT.
3212
3213 If the pattern was successfully studied with one of the just-in-time
3214 (JIT) compile options, the only supported options for JIT execution are
3215 PCRE_NO_UTF8_CHECK, PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY,
3216 PCRE_NOTEMPTY_ATSTART, PCRE_PARTIAL_HARD, and PCRE_PARTIAL_SOFT. If an
3217 unsupported option is used, JIT execution is disabled and the normal
3218 interpretive code in pcre_exec() is run.
3219
3220 PCRE_ANCHORED
3221
3222 The PCRE_ANCHORED option limits pcre_exec() to matching at the first
3223 matching position. If a pattern was compiled with PCRE_ANCHORED, or
3224 turned out to be anchored by virtue of its contents, it cannot be made
3225 unachored at matching time.
3226
3227 PCRE_BSR_ANYCRLF
3228 PCRE_BSR_UNICODE
3229
3230 These options (which are mutually exclusive) control what the \R escape
3231 sequence matches. The choice is either to match only CR, LF, or CRLF,
3232 or to match any Unicode newline sequence. These options override the
3233 choice that was made or defaulted when the pattern was compiled.
3234
3235 PCRE_NEWLINE_CR
3236 PCRE_NEWLINE_LF
3237 PCRE_NEWLINE_CRLF
3238 PCRE_NEWLINE_ANYCRLF
3239 PCRE_NEWLINE_ANY
3240
3241 These options override the newline definition that was chosen or
3242 defaulted when the pattern was compiled. For details, see the descrip-
3243 tion of pcre_compile() above. During matching, the newline choice
3244 affects the behaviour of the dot, circumflex, and dollar metacharac-
3245 ters. It may also alter the way the match position is advanced after a
3246 match failure for an unanchored pattern.
3247
3248 When PCRE_NEWLINE_CRLF, PCRE_NEWLINE_ANYCRLF, or PCRE_NEWLINE_ANY is
3249 set, and a match attempt for an unanchored pattern fails when the cur-
3250 rent position is at a CRLF sequence, and the pattern contains no
3251 explicit matches for CR or LF characters, the match position is
3252 advanced by two characters instead of one, in other words, to after the
3253 CRLF.
3254
3255 The above rule is a compromise that makes the most common cases work as
3256 expected. For example, if the pattern is .+A (and the PCRE_DOTALL
3257 option is not set), it does not match the string "\r\nA" because, after
3258 failing at the start, it skips both the CR and the LF before retrying.
3259 However, the pattern [\r\n]A does match that string, because it con-
3260 tains an explicit CR or LF reference, and so advances only by one char-
3261 acter after the first failure.
3262
3263 An explicit match for CR of LF is either a literal appearance of one of
3264 those characters, or one of the \r or \n escape sequences. Implicit
3265 matches such as [^X] do not count, nor does \s (which includes CR and
3266 LF in the characters that it matches).
3267
3268 Notwithstanding the above, anomalous effects may still occur when CRLF
3269 is a valid newline sequence and explicit \r or \n escapes appear in the
3270 pattern.
3271
3272 PCRE_NOTBOL
3273
3274 This option specifies that first character of the subject string is not
3275 the beginning of a line, so the circumflex metacharacter should not
3276 match before it. Setting this without PCRE_MULTILINE (at compile time)
3277 causes circumflex never to match. This option affects only the behav-
3278 iour of the circumflex metacharacter. It does not affect \A.
3279
3280 PCRE_NOTEOL
3281
3282 This option specifies that the end of the subject string is not the end
3283 of a line, so the dollar metacharacter should not match it nor (except
3284 in multiline mode) a newline immediately before it. Setting this with-
3285 out PCRE_MULTILINE (at compile time) causes dollar never to match. This
3286 option affects only the behaviour of the dollar metacharacter. It does
3287 not affect \Z or \z.
3288
3289 PCRE_NOTEMPTY
3290
3291 An empty string is not considered to be a valid match if this option is
3292 set. If there are alternatives in the pattern, they are tried. If all
3293 the alternatives match the empty string, the entire match fails. For
3294 example, if the pattern
3295
3296 a?b?
3297
3298 is applied to a string not beginning with "a" or "b", it matches an
3299 empty string at the start of the subject. With PCRE_NOTEMPTY set, this
3300 match is not valid, so PCRE searches further into the string for occur-
3301 rences of "a" or "b".
3302
3303 PCRE_NOTEMPTY_ATSTART
3304
3305 This is like PCRE_NOTEMPTY, except that an empty string match that is
3306 not at the start of the subject is permitted. If the pattern is
3307 anchored, such a match can occur only if the pattern contains \K.
3308
3309 Perl has no direct equivalent of PCRE_NOTEMPTY or
3310 PCRE_NOTEMPTY_ATSTART, but it does make a special case of a pattern
3311 match of the empty string within its split() function, and when using
3312 the /g modifier. It is possible to emulate Perl's behaviour after
3313 matching a null string by first trying the match again at the same off-
3314 set with PCRE_NOTEMPTY_ATSTART and PCRE_ANCHORED, and then if that
3315 fails, by advancing the starting offset (see below) and trying an ordi-
3316 nary match again. There is some code that demonstrates how to do this
3317 in the pcredemo sample program. In the most general case, you have to
3318 check to see if the newline convention recognizes CRLF as a newline,
3319 and if so, and the current character is CR followed by LF, advance the
3320 starting offset by two characters instead of one.
3321
3322 PCRE_NO_START_OPTIMIZE
3323
3324 There are a number of optimizations that pcre_exec() uses at the start
3325 of a match, in order to speed up the process. For example, if it is
3326 known that an unanchored match must start with a specific character, it
3327 searches the subject for that character, and fails immediately if it
3328 cannot find it, without actually running the main matching function.
3329 This means that a special item such as (*COMMIT) at the start of a pat-
3330 tern is not considered until after a suitable starting point for the
3331 match has been found. Also, when callouts or (*MARK) items are in use,
3332 these "start-up" optimizations can cause them to be skipped if the pat-
3333 tern is never actually used. The start-up optimizations are in effect a
3334 pre-scan of the subject that takes place before the pattern is run.
3335
3336 The PCRE_NO_START_OPTIMIZE option disables the start-up optimizations,
3337 possibly causing performance to suffer, but ensuring that in cases
3338 where the result is "no match", the callouts do occur, and that items
3339 such as (*COMMIT) and (*MARK) are considered at every possible starting
3340 position in the subject string. If PCRE_NO_START_OPTIMIZE is set at
3341 compile time, it cannot be unset at matching time. The use of
3342 PCRE_NO_START_OPTIMIZE at matching time (that is, passing it to
3343 pcre_exec()) disables JIT execution; in this situation, matching is
3344 always done using interpretively.
3345
3346 Setting PCRE_NO_START_OPTIMIZE can change the outcome of a matching
3347 operation. Consider the pattern
3348
3349 (*COMMIT)ABC
3350
3351 When this is compiled, PCRE records the fact that a match must start
3352 with the character "A". Suppose the subject string is "DEFABC". The
3353 start-up optimization scans along the subject, finds "A" and runs the
3354 first match attempt from there. The (*COMMIT) item means that the pat-
3355 tern must match the current starting position, which in this case, it
3356 does. However, if the same match is run with PCRE_NO_START_OPTIMIZE
3357 set, the initial scan along the subject string does not happen. The
3358 first match attempt is run starting from "D" and when this fails,
3359 (*COMMIT) prevents any further matches being tried, so the overall
3360 result is "no match". If the pattern is studied, more start-up opti-
3361 mizations may be used. For example, a minimum length for the subject
3362 may be recorded. Consider the pattern
3363
3364 (*MARK:A)(X|Y)
3365
3366 The minimum length for a match is one character. If the subject is
3367 "ABC", there will be attempts to match "ABC", "BC", "C", and then
3368 finally an empty string. If the pattern is studied, the final attempt
3369 does not take place, because PCRE knows that the subject is too short,
3370 and so the (*MARK) is never encountered. In this case, studying the
3371 pattern does not affect the overall match result, which is still "no
3372 match", but it does affect the auxiliary information that is returned.
3373
3374 PCRE_NO_UTF8_CHECK
3375
3376 When PCRE_UTF8 is set at compile time, the validity of the subject as a
3377 UTF-8 string is automatically checked when pcre_exec() is subsequently
3378 called. The entire string is checked before any other processing takes
3379 place. The value of startoffset is also checked to ensure that it
3380 points to the start of a UTF-8 character. There is a discussion about
3381 the validity of UTF-8 strings in the pcreunicode page. If an invalid
3382 sequence of bytes is found, pcre_exec() returns the error
3383 PCRE_ERROR_BADUTF8 or, if PCRE_PARTIAL_HARD is set and the problem is a
3384 truncated character at the end of the subject, PCRE_ERROR_SHORTUTF8. In
3385 both cases, information about the precise nature of the error may also
3386 be returned (see the descriptions of these errors in the section enti-
3387 tled Error return values from pcre_exec() below). If startoffset con-
3388 tains a value that does not point to the start of a UTF-8 character (or
3389 to the end of the subject), PCRE_ERROR_BADUTF8_OFFSET is returned.
3390
3391 If you already know that your subject is valid, and you want to skip
3392 these checks for performance reasons, you can set the
3393 PCRE_NO_UTF8_CHECK option when calling pcre_exec(). You might want to
3394 do this for the second and subsequent calls to pcre_exec() if you are
3395 making repeated calls to find all the matches in a single subject
3396 string. However, you should be sure that the value of startoffset
3397 points to the start of a character (or the end of the subject). When
3398 PCRE_NO_UTF8_CHECK is set, the effect of passing an invalid string as a
3399 subject or an invalid value of startoffset is undefined. Your program
3400 may crash or loop.
3401
3402 PCRE_PARTIAL_HARD
3403 PCRE_PARTIAL_SOFT
3404
3405 These options turn on the partial matching feature. For backwards com-
3406 patibility, PCRE_PARTIAL is a synonym for PCRE_PARTIAL_SOFT. A partial
3407 match occurs if the end of the subject string is reached successfully,
3408 but there are not enough subject characters to complete the match. If
3409 this happens when PCRE_PARTIAL_SOFT (but not PCRE_PARTIAL_HARD) is set,
3410 matching continues by testing any remaining alternatives. Only if no
3411 complete match can be found is PCRE_ERROR_PARTIAL returned instead of
3412 PCRE_ERROR_NOMATCH. In other words, PCRE_PARTIAL_SOFT says that the
3413 caller is prepared to handle a partial match, but only if no complete
3414 match can be found.
3415
3416 If PCRE_PARTIAL_HARD is set, it overrides PCRE_PARTIAL_SOFT. In this
3417 case, if a partial match is found, pcre_exec() immediately returns
3418 PCRE_ERROR_PARTIAL, without considering any other alternatives. In
3419 other words, when PCRE_PARTIAL_HARD is set, a partial match is consid-
3420 ered to be more important that an alternative complete match.
3421
3422 In both cases, the portion of the string that was inspected when the
3423 partial match was found is set as the first matching string. There is a
3424 more detailed discussion of partial and multi-segment matching, with
3425 examples, in the pcrepartial documentation.
3426
3427 The string to be matched by pcre_exec()
3428
3429 The subject string is passed to pcre_exec() as a pointer in subject, a
3430 length in length, and a starting offset in startoffset. The units for
3431 length and startoffset are bytes for the 8-bit library, 16-bit data
3432 items for the 16-bit library, and 32-bit data items for the 32-bit
3433 library.
3434
3435 If startoffset is negative or greater than the length of the subject,
3436 pcre_exec() returns PCRE_ERROR_BADOFFSET. When the starting offset is
3437 zero, the search for a match starts at the beginning of the subject,
3438 and this is by far the most common case. In UTF-8 or UTF-16 mode, the
3439 offset must point to the start of a character, or the end of the sub-
3440 ject (in UTF-32 mode, one data unit equals one character, so all off-
3441 sets are valid). Unlike the pattern string, the subject may contain
3442 binary zeroes.
3443
3444 A non-zero starting offset is useful when searching for another match
3445 in the same subject by calling pcre_exec() again after a previous suc-
3446 cess. Setting startoffset differs from just passing over a shortened
3447 string and setting PCRE_NOTBOL in the case of a pattern that begins
3448 with any kind of lookbehind. For example, consider the pattern
3449
3450 \Biss\B
3451
3452 which finds occurrences of "iss" in the middle of words. (\B matches
3453 only if the current position in the subject is not a word boundary.)
3454 When applied to the string "Mississipi" the first call to pcre_exec()
3455 finds the first occurrence. If pcre_exec() is called again with just
3456 the remainder of the subject, namely "issipi", it does not match,
3457 because \B is always false at the start of the subject, which is deemed
3458 to be a word boundary. However, if pcre_exec() is passed the entire
3459 string again, but with startoffset set to 4, it finds the second occur-
3460 rence of "iss" because it is able to look behind the starting point to
3461 discover that it is preceded by a letter.
3462
3463 Finding all the matches in a subject is tricky when the pattern can
3464 match an empty string. It is possible to emulate Perl's /g behaviour by
3465 first trying the match again at the same offset, with the
3466 PCRE_NOTEMPTY_ATSTART and PCRE_ANCHORED options, and then if that
3467 fails, advancing the starting offset and trying an ordinary match
3468 again. There is some code that demonstrates how to do this in the pcre-
3469 demo sample program. In the most general case, you have to check to see
3470 if the newline convention recognizes CRLF as a newline, and if so, and
3471 the current character is CR followed by LF, advance the starting offset
3472 by two characters instead of one.
3473
3474 If a non-zero starting offset is passed when the pattern is anchored,
3475 one attempt to match at the given offset is made. This can only succeed
3476 if the pattern does not require the match to be at the start of the
3477 subject.
3478
3479 How pcre_exec() returns captured substrings
3480
3481 In general, a pattern matches a certain portion of the subject, and in
3482 addition, further substrings from the subject may be picked out by
3483 parts of the pattern. Following the usage in Jeffrey Friedl's book,
3484 this is called "capturing" in what follows, and the phrase "capturing
3485 subpattern" is used for a fragment of a pattern that picks out a sub-
3486 string. PCRE supports several other kinds of parenthesized subpattern
3487 that do not cause substrings to be captured.
3488
3489 Captured substrings are returned to the caller via a vector of integers
3490 whose address is passed in ovector. The number of elements in the vec-
3491 tor is passed in ovecsize, which must be a non-negative number. Note:
3492 this argument is NOT the size of ovector in bytes.
3493
3494 The first two-thirds of the vector is used to pass back captured sub-
3495 strings, each substring using a pair of integers. The remaining third
3496 of the vector is used as workspace by pcre_exec() while matching cap-
3497 turing subpatterns, and is not available for passing back information.
3498 The number passed in ovecsize should always be a multiple of three. If
3499 it is not, it is rounded down.
3500
3501 When a match is successful, information about captured substrings is
3502 returned in pairs of integers, starting at the beginning of ovector,
3503 and continuing up to two-thirds of its length at the most. The first
3504 element of each pair is set to the offset of the first character in a
3505 substring, and the second is set to the offset of the first character
3506 after the end of a substring. These values are always data unit off-
3507 sets, even in UTF mode. They are byte offsets in the 8-bit library,
3508 16-bit data item offsets in the 16-bit library, and 32-bit data item
3509 offsets in the 32-bit library. Note: they are not character counts.
3510
3511 The first pair of integers, ovector[0] and ovector[1], identify the
3512 portion of the subject string matched by the entire pattern. The next
3513 pair is used for the first capturing subpattern, and so on. The value
3514 returned by pcre_exec() is one more than the highest numbered pair that
3515 has been set. For example, if two substrings have been captured, the
3516 returned value is 3. If there are no capturing subpatterns, the return
3517 value from a successful match is 1, indicating that just the first pair
3518 of offsets has been set.
3519
3520 If a capturing subpattern is matched repeatedly, it is the last portion
3521 of the string that it matched that is returned.
3522
3523 If the vector is too small to hold all the captured substring offsets,
3524 it is used as far as possible (up to two-thirds of its length), and the
3525 function returns a value of zero. If neither the actual string matched
3526 nor any captured substrings are of interest, pcre_exec() may be called
3527 with ovector passed as NULL and ovecsize as zero. However, if the pat-
3528 tern contains back references and the ovector is not big enough to
3529 remember the related substrings, PCRE has to get additional memory for
3530 use during matching. Thus it is usually advisable to supply an ovector
3531 of reasonable size.
3532
3533 There are some cases where zero is returned (indicating vector over-
3534 flow) when in fact the vector is exactly the right size for the final
3535 match. For example, consider the pattern
3536
3537 (a)(?:(b)c|bd)
3538
3539 If a vector of 6 elements (allowing for only 1 captured substring) is
3540 given with subject string "abd", pcre_exec() will try to set the second
3541 captured string, thereby recording a vector overflow, before failing to
3542 match "c" and backing up to try the second alternative. The zero
3543 return, however, does correctly indicate that the maximum number of
3544 slots (namely 2) have been filled. In similar cases where there is tem-
3545 porary overflow, but the final number of used slots is actually less
3546 than the maximum, a non-zero value is returned.
3547
3548 The pcre_fullinfo() function can be used to find out how many capturing
3549 subpatterns there are in a compiled pattern. The smallest size for
3550 ovector that will allow for n captured substrings, in addition to the
3551 offsets of the substring matched by the whole pattern, is (n+1)*3.
3552
3553 It is possible for capturing subpattern number n+1 to match some part
3554 of the subject when subpattern n has not been used at all. For example,
3555 if the string "abc" is matched against the pattern (a|(z))(bc) the
3556 return from the function is 4, and subpatterns 1 and 3 are matched, but
3557 2 is not. When this happens, both values in the offset pairs corre-
3558 sponding to unused subpatterns are set to -1.
3559
3560 Offset values that correspond to unused subpatterns at the end of the
3561 expression are also set to -1. For example, if the string "abc" is
3562 matched against the pattern (abc)(x(yz)?)? subpatterns 2 and 3 are not
3563 matched. The return from the function is 2, because the highest used
3564 capturing subpattern number is 1, and the offsets for for the second
3565 and third capturing subpatterns (assuming the vector is large enough,
3566 of course) are set to -1.
3567
3568 Note: Elements in the first two-thirds of ovector that do not corre-
3569 spond to capturing parentheses in the pattern are never changed. That
3570 is, if a pattern contains n capturing parentheses, no more than ovec-
3571 tor[0] to ovector[2n+1] are set by pcre_exec(). The other elements (in
3572 the first two-thirds) retain whatever values they previously had.
3573
3574 Some convenience functions are provided for extracting the captured
3575 substrings as separate strings. These are described below.
3576
3577 Error return values from pcre_exec()
3578
3579 If pcre_exec() fails, it returns a negative number. The following are
3580 defined in the header file:
3581
3582 PCRE_ERROR_NOMATCH (-1)
3583
3584 The subject string did not match the pattern.
3585
3586 PCRE_ERROR_NULL (-2)
3587
3588 Either code or subject was passed as NULL, or ovector was NULL and
3589 ovecsize was not zero.
3590
3591 PCRE_ERROR_BADOPTION (-3)
3592
3593 An unrecognized bit was set in the options argument.
3594
3595 PCRE_ERROR_BADMAGIC (-4)
3596
3597 PCRE stores a 4-byte "magic number" at the start of the compiled code,
3598 to catch the case when it is passed a junk pointer and to detect when a
3599 pattern that was compiled in an environment of one endianness is run in
3600 an environment with the other endianness. This is the error that PCRE
3601 gives when the magic number is not present.
3602
3603 PCRE_ERROR_UNKNOWN_OPCODE (-5)
3604
3605 While running the pattern match, an unknown item was encountered in the
3606 compiled pattern. This error could be caused by a bug in PCRE or by
3607 overwriting of the compiled pattern.
3608
3609 PCRE_ERROR_NOMEMORY (-6)
3610
3611 If a pattern contains back references, but the ovector that is passed
3612 to pcre_exec() is not big enough to remember the referenced substrings,
3613 PCRE gets a block of memory at the start of matching to use for this
3614 purpose. If the call via pcre_malloc() fails, this error is given. The
3615 memory is automatically freed at the end of matching.
3616
3617 This error is also given if pcre_stack_malloc() fails in pcre_exec().
3618 This can happen only when PCRE has been compiled with --disable-stack-
3619 for-recursion.
3620
3621 PCRE_ERROR_NOSUBSTRING (-7)
3622
3623 This error is used by the pcre_copy_substring(), pcre_get_substring(),
3624 and pcre_get_substring_list() functions (see below). It is never
3625 returned by pcre_exec().
3626
3627 PCRE_ERROR_MATCHLIMIT (-8)
3628
3629 The backtracking limit, as specified by the match_limit field in a
3630 pcre_extra structure (or defaulted) was reached. See the description
3631 above.
3632
3633 PCRE_ERROR_CALLOUT (-9)
3634
3635 This error is never generated by pcre_exec() itself. It is provided for
3636 use by callout functions that want to yield a distinctive error code.
3637 See the pcrecallout documentation for details.
3638
3639 PCRE_ERROR_BADUTF8 (-10)
3640
3641 A string that contains an invalid UTF-8 byte sequence was passed as a
3642 subject, and the PCRE_NO_UTF8_CHECK option was not set. If the size of
3643 the output vector (ovecsize) is at least 2, the byte offset to the
3644 start of the the invalid UTF-8 character is placed in the first ele-
3645 ment, and a reason code is placed in the second element. The reason
3646 codes are listed in the following section. For backward compatibility,
3647 if PCRE_PARTIAL_HARD is set and the problem is a truncated UTF-8 char-
3648 acter at the end of the subject (reason codes 1 to 5),
3649 PCRE_ERROR_SHORTUTF8 is returned instead of PCRE_ERROR_BADUTF8.
3650
3651 PCRE_ERROR_BADUTF8_OFFSET (-11)
3652
3653 The UTF-8 byte sequence that was passed as a subject was checked and
3654 found to be valid (the PCRE_NO_UTF8_CHECK option was not set), but the
3655 value of startoffset did not point to the beginning of a UTF-8 charac-
3656 ter or the end of the subject.
3657
3658 PCRE_ERROR_PARTIAL (-12)
3659
3660 The subject string did not match, but it did match partially. See the
3661 pcrepartial documentation for details of partial matching.
3662
3663 PCRE_ERROR_BADPARTIAL (-13)
3664
3665 This code is no longer in use. It was formerly returned when the
3666 PCRE_PARTIAL option was used with a compiled pattern containing items
3667 that were not supported for partial matching. From release 8.00
3668 onwards, there are no restrictions on partial matching.
3669
3670 PCRE_ERROR_INTERNAL (-14)
3671
3672 An unexpected internal error has occurred. This error could be caused
3673 by a bug in PCRE or by overwriting of the compiled pattern.
3674
3675 PCRE_ERROR_BADCOUNT (-15)
3676
3677 This error is given if the value of the ovecsize argument is negative.
3678
3679 PCRE_ERROR_RECURSIONLIMIT (-21)
3680
3681 The internal recursion limit, as specified by the match_limit_recursion
3682 field in a pcre_extra structure (or defaulted) was reached. See the
3683 description above.
3684
3685 PCRE_ERROR_BADNEWLINE (-23)
3686
3687 An invalid combination of PCRE_NEWLINE_xxx options was given.
3688
3689 PCRE_ERROR_BADOFFSET (-24)
3690
3691 The value of startoffset was negative or greater than the length of the
3692 subject, that is, the value in length.
3693
3694 PCRE_ERROR_SHORTUTF8 (-25)
3695
3696 This error is returned instead of PCRE_ERROR_BADUTF8 when the subject
3697 string ends with a truncated UTF-8 character and the PCRE_PARTIAL_HARD
3698 option is set. Information about the failure is returned as for
3699 PCRE_ERROR_BADUTF8. It is in fact sufficient to detect this case, but
3700 this special error code for PCRE_PARTIAL_HARD precedes the implementa-
3701 tion of returned information; it is retained for backwards compatibil-
3702 ity.
3703
3704 PCRE_ERROR_RECURSELOOP (-26)
3705
3706 This error is returned when pcre_exec() detects a recursion loop within
3707 the pattern. Specifically, it means that either the whole pattern or a
3708 subpattern has been called recursively for the second time at the same
3709 position in the subject string. Some simple patterns that might do this
3710 are detected and faulted at compile time, but more complicated cases,
3711 in particular mutual recursions between two different subpatterns, can-
3712 not be detected until run time.
3713
3714 PCRE_ERROR_JIT_STACKLIMIT (-27)
3715
3716 This error is returned when a pattern that was successfully studied
3717 using a JIT compile option is being matched, but the memory available
3718 for the just-in-time processing stack is not large enough. See the
3719 pcrejit documentation for more details.
3720
3721 PCRE_ERROR_BADMODE (-28)
3722
3723 This error is given if a pattern that was compiled by the 8-bit library
3724 is passed to a 16-bit or 32-bit library function, or vice versa.
3725
3726 PCRE_ERROR_BADENDIANNESS (-29)
3727
3728 This error is given if a pattern that was compiled and saved is
3729 reloaded on a host with different endianness. The utility function
3730 pcre_pattern_to_host_byte_order() can be used to convert such a pattern
3731 so that it runs on the new host.
3732
3733 PCRE_ERROR_JIT_BADOPTION
3734
3735 This error is returned when a pattern that was successfully studied
3736 using a JIT compile option is being matched, but the matching mode
3737 (partial or complete match) does not correspond to any JIT compilation
3738 mode. When the JIT fast path function is used, this error may be also
3739 given for invalid options. See the pcrejit documentation for more
3740 details.
3741
3742 PCRE_ERROR_BADLENGTH (-32)
3743
3744 This error is given if pcre_exec() is called with a negative value for
3745 the length argument.
3746
3747 Error numbers -16 to -20, -22, and 30 are not used by pcre_exec().
3748
3749 Reason codes for invalid UTF-8 strings
3750
3751 This section applies only to the 8-bit library. The corresponding
3752 information for the 16-bit and 32-bit libraries is given in the pcre16
3753 and pcre32 pages.
3754
3755 When pcre_exec() returns either PCRE_ERROR_BADUTF8 or PCRE_ERROR_SHORT-
3756 UTF8, and the size of the output vector (ovecsize) is at least 2, the
3757 offset of the start of the invalid UTF-8 character is placed in the
3758 first output vector element (ovector[0]) and a reason code is placed in
3759 the second element (ovector[1]). The reason codes are given names in
3760 the pcre.h header file:
3761
3762 PCRE_UTF8_ERR1
3763 PCRE_UTF8_ERR2
3764 PCRE_UTF8_ERR3
3765 PCRE_UTF8_ERR4
3766 PCRE_UTF8_ERR5
3767
3768 The string ends with a truncated UTF-8 character; the code specifies
3769 how many bytes are missing (1 to 5). Although RFC 3629 restricts UTF-8
3770 characters to be no longer than 4 bytes, the encoding scheme (origi-
3771 nally defined by RFC 2279) allows for up to 6 bytes, and this is
3772 checked first; hence the possibility of 4 or 5 missing bytes.
3773
3774 PCRE_UTF8_ERR6
3775 PCRE_UTF8_ERR7
3776 PCRE_UTF8_ERR8
3777 PCRE_UTF8_ERR9
3778 PCRE_UTF8_ERR10
3779
3780 The two most significant bits of the 2nd, 3rd, 4th, 5th, or 6th byte of
3781 the character do not have the binary value 0b10 (that is, either the
3782 most significant bit is 0, or the next bit is 1).
3783
3784 PCRE_UTF8_ERR11
3785 PCRE_UTF8_ERR12
3786
3787 A character that is valid by the RFC 2279 rules is either 5 or 6 bytes
3788 long; these code points are excluded by RFC 3629.
3789
3790 PCRE_UTF8_ERR13
3791
3792 A 4-byte character has a value greater than 0x10fff; these code points
3793 are excluded by RFC 3629.
3794
3795 PCRE_UTF8_ERR14
3796
3797 A 3-byte character has a value in the range 0xd800 to 0xdfff; this
3798 range of code points are reserved by RFC 3629 for use with UTF-16, and
3799 so are excluded from UTF-8.
3800
3801 PCRE_UTF8_ERR15
3802 PCRE_UTF8_ERR16
3803 PCRE_UTF8_ERR17
3804 PCRE_UTF8_ERR18
3805 PCRE_UTF8_ERR19
3806
3807 A 2-, 3-, 4-, 5-, or 6-byte character is "overlong", that is, it codes
3808 for a value that can be represented by fewer bytes, which is invalid.
3809 For example, the two bytes 0xc0, 0xae give the value 0x2e, whose cor-
3810 rect coding uses just one byte.
3811
3812 PCRE_UTF8_ERR20
3813
3814 The two most significant bits of the first byte of a character have the
3815 binary value 0b10 (that is, the most significant bit is 1 and the sec-
3816 ond is 0). Such a byte can only validly occur as the second or subse-
3817 quent byte of a multi-byte character.
3818
3819 PCRE_UTF8_ERR21
3820
3821 The first byte of a character has the value 0xfe or 0xff. These values
3822 can never occur in a valid UTF-8 string.
3823
3824 PCRE_UTF8_ERR22
3825
3826 This error code was formerly used when the presence of a so-called
3827 "non-character" caused an error. Unicode corrigendum #9 makes it clear
3828 that such characters should not cause a string to be rejected, and so
3829 this code is no longer in use and is never returned.
3830
3831
3832 EXTRACTING CAPTURED SUBSTRINGS BY NUMBER
3833
3834 int pcre_copy_substring(const char *subject, int *ovector,
3835 int stringcount, int stringnumber, char *buffer,
3836 int buffersize);
3837
3838 int pcre_get_substring(const char *subject, int *ovector,
3839 int stringcount, int stringnumber,
3840 const char **stringptr);
3841
3842 int pcre_get_substring_list(const char *subject,
3843 int *ovector, int stringcount, const char ***listptr);
3844
3845 Captured substrings can be accessed directly by using the offsets
3846 returned by pcre_exec() in ovector. For convenience, the functions
3847 pcre_copy_substring(), pcre_get_substring(), and pcre_get_sub-
3848 string_list() are provided for extracting captured substrings as new,
3849 separate, zero-terminated strings. These functions identify substrings
3850 by number. The next section describes functions for extracting named
3851 substrings.
3852
3853 A substring that contains a binary zero is correctly extracted and has
3854 a further zero added on the end, but the result is not, of course, a C
3855 string. However, you can process such a string by referring to the
3856 length that is returned by pcre_copy_substring() and pcre_get_sub-
3857 string(). Unfortunately, the interface to pcre_get_substring_list() is
3858 not adequate for handling strings containing binary zeros, because the
3859 end of the final string is not independently indicated.
3860
3861 The first three arguments are the same for all three of these func-
3862 tions: subject is the subject string that has just been successfully
3863 matched, ovector is a pointer to the vector of integer offsets that was
3864 passed to pcre_exec(), and stringcount is the number of substrings that
3865 were captured by the match, including the substring that matched the
3866 entire regular expression. This is the value returned by pcre_exec() if
3867 it is greater than zero. If pcre_exec() returned zero, indicating that
3868 it ran out of space in ovector, the value passed as stringcount should
3869 be the number of elements in the vector divided by three.
3870
3871 The functions pcre_copy_substring() and pcre_get_substring() extract a
3872 single substring, whose number is given as stringnumber. A value of
3873 zero extracts the substring that matched the entire pattern, whereas
3874 higher values extract the captured substrings. For pcre_copy_sub-
3875 string(), the string is placed in buffer, whose length is given by
3876 buffersize, while for pcre_get_substring() a new block of memory is
3877 obtained via pcre_malloc, and its address is returned via stringptr.
3878 The yield of the function is the length of the string, not including
3879 the terminating zero, or one of these error codes:
3880
3881 PCRE_ERROR_NOMEMORY (-6)
3882
3883 The buffer was too small for pcre_copy_substring(), or the attempt to
3884 get memory failed for pcre_get_substring().
3885
3886 PCRE_ERROR_NOSUBSTRING (-7)
3887
3888 There is no substring whose number is stringnumber.
3889
3890 The pcre_get_substring_list() function extracts all available sub-
3891 strings and builds a list of pointers to them. All this is done in a
3892 single block of memory that is obtained via pcre_malloc. The address of
3893 the memory block is returned via listptr, which is also the start of
3894 the list of string pointers. The end of the list is marked by a NULL
3895 pointer. The yield of the function is zero if all went well, or the
3896 error code
3897
3898 PCRE_ERROR_NOMEMORY (-6)
3899
3900 if the attempt to get the memory block failed.
3901
3902 When any of these functions encounter a substring that is unset, which
3903 can happen when capturing subpattern number n+1 matches some part of
3904 the subject, but subpattern n has not been used at all, they return an
3905 empty string. This can be distinguished from a genuine zero-length sub-
3906 string by inspecting the appropriate offset in ovector, which is nega-
3907 tive for unset substrings.
3908
3909 The two convenience functions pcre_free_substring() and pcre_free_sub-
3910 string_list() can be used to free the memory returned by a previous
3911 call of pcre_get_substring() or pcre_get_substring_list(), respec-
3912 tively. They do nothing more than call the function pointed to by
3913 pcre_free, which of course could be called directly from a C program.
3914 However, PCRE is used in some situations where it is linked via a spe-
3915 cial interface to another programming language that cannot use
3916 pcre_free directly; it is for these cases that the functions are pro-
3917 vided.
3918
3919
3920 EXTRACTING CAPTURED SUBSTRINGS BY NAME
3921
3922 int pcre_get_stringnumber(const pcre *code,
3923 const char *name);
3924
3925 int pcre_copy_named_substring(const pcre *code,
3926 const char *subject, int *ovector,
3927 int stringcount, const char *stringname,
3928 char *buffer, int buffersize);
3929
3930 int pcre_get_named_substring(const pcre *code,
3931 const char *subject, int *ovector,
3932 int stringcount, const char *stringname,
3933 const char **stringptr);
3934
3935 To extract a substring by name, you first have to find associated num-
3936 ber. For example, for this pattern
3937
3938 (a+)b(?<xxx>\d+)...
3939
3940 the number of the subpattern called "xxx" is 2. If the name is known to
3941 be unique (PCRE_DUPNAMES was not set), you can find the number from the
3942 name by calling pcre_get_stringnumber(). The first argument is the com-
3943 piled pattern, and the second is the name. The yield of the function is
3944 the subpattern number, or PCRE_ERROR_NOSUBSTRING (-7) if there is no
3945 subpattern of that name.
3946
3947 Given the number, you can extract the substring directly, or use one of
3948 the functions described in the previous section. For convenience, there
3949 are also two functions that do the whole job.
3950
3951 Most of the arguments of pcre_copy_named_substring() and
3952 pcre_get_named_substring() are the same as those for the similarly
3953 named functions that extract by number. As these are described in the
3954 previous section, they are not re-described here. There are just two
3955 differences:
3956
3957 First, instead of a substring number, a substring name is given. Sec-
3958 ond, there is an extra argument, given at the start, which is a pointer
3959 to the compiled pattern. This is needed in order to gain access to the
3960 name-to-number translation table.
3961
3962 These functions call pcre_get_stringnumber(), and if it succeeds, they
3963 then call pcre_copy_substring() or pcre_get_substring(), as appropri-
3964 ate. NOTE: If PCRE_DUPNAMES is set and there are duplicate names, the
3965 behaviour may not be what you want (see the next section).
3966
3967 Warning: If the pattern uses the (?| feature to set up multiple subpat-
3968 terns with the same number, as described in the section on duplicate
3969 subpattern numbers in the pcrepattern page, you cannot use names to
3970 distinguish the different subpatterns, because names are not included
3971 in the compiled code. The matching process uses only numbers. For this
3972 reason, the use of different names for subpatterns of the same number
3973 causes an error at compile time.
3974
3975
3976 DUPLICATE SUBPATTERN NAMES
3977
3978 int pcre_get_stringtable_entries(const pcre *code,
3979 const char *name, char **first, char **last);
3980
3981 When a pattern is compiled with the PCRE_DUPNAMES option, names for
3982 subpatterns are not required to be unique. (Duplicate names are always
3983 allowed for subpatterns with the same number, created by using the (?|
3984 feature. Indeed, if such subpatterns are named, they are required to
3985 use the same names.)
3986
3987 Normally, patterns with duplicate names are such that in any one match,
3988 only one of the named subpatterns participates. An example is shown in
3989 the pcrepattern documentation.
3990
3991 When duplicates are present, pcre_copy_named_substring() and
3992 pcre_get_named_substring() return the first substring corresponding to
3993 the given name that is set. If none are set, PCRE_ERROR_NOSUBSTRING
3994 (-7) is returned; no data is returned. The pcre_get_stringnumber()
3995 function returns one of the numbers that are associated with the name,
3996 but it is not defined which it is.
3997
3998 If you want to get full details of all captured substrings for a given
3999 name, you must use the pcre_get_stringtable_entries() function. The
4000 first argument is the compiled pattern, and the second is the name. The
4001 third and fourth are pointers to variables which are updated by the
4002 function. After it has run, they point to the first and last entries in
4003 the name-to-number table for the given name. The function itself
4004 returns the length of each entry, or PCRE_ERROR_NOSUBSTRING (-7) if
4005 there are none. The format of the table is described above in the sec-
4006 tion entitled Information about a pattern above. Given all the rele-
4007 vant entries for the name, you can extract each of their numbers, and
4008 hence the captured data, if any.
4009
4010
4011 FINDING ALL POSSIBLE MATCHES
4012
4013 The traditional matching function uses a similar algorithm to Perl,
4014 which stops when it finds the first match, starting at a given point in
4015 the subject. If you want to find all possible matches, or the longest
4016 possible match, consider using the alternative matching function (see
4017 below) instead. If you cannot use the alternative function, but still
4018 need to find all possible matches, you can kludge it up by making use
4019 of the callout facility, which is described in the pcrecallout documen-
4020 tation.
4021
4022 What you have to do is to insert a callout right at the end of the pat-
4023 tern. When your callout function is called, extract and save the cur-
4024 rent matched substring. Then return 1, which forces pcre_exec() to
4025 backtrack and try other alternatives. Ultimately, when it runs out of
4026 matches, pcre_exec() will yield PCRE_ERROR_NOMATCH.
4027
4028
4029 OBTAINING AN ESTIMATE OF STACK USAGE
4030
4031 Matching certain patterns using pcre_exec() can use a lot of process
4032 stack, which in certain environments can be rather limited in size.
4033 Some users find it helpful to have an estimate of the amount of stack
4034 that is used by pcre_exec(), to help them set recursion limits, as
4035 described in the pcrestack documentation. The estimate that is output
4036 by pcretest when called with the -m and -C options is obtained by call-
4037 ing pcre_exec with the values NULL, NULL, NULL, -999, and -999 for its
4038 first five arguments.
4039
4040 Normally, if its first argument is NULL, pcre_exec() immediately
4041 returns the negative error code PCRE_ERROR_NULL, but with this special
4042 combination of arguments, it returns instead a negative number whose
4043 absolute value is the approximate stack frame size in bytes. (A nega-
4044 tive number is used so that it is clear that no match has happened.)
4045 The value is approximate because in some cases, recursive calls to
4046 pcre_exec() occur when there are one or two additional variables on the
4047 stack.
4048
4049 If PCRE has been compiled to use the heap instead of the stack for
4050 recursion, the value returned is the size of each block that is
4051 obtained from the heap.
4052
4053
4054 MATCHING A PATTERN: THE ALTERNATIVE FUNCTION
4055
4056 int pcre_dfa_exec(const pcre *code, const pcre_extra *extra,
4057 const char *subject, int length, int startoffset,
4058 int options, int *ovector, int ovecsize,
4059 int *workspace, int wscount);
4060
4061 The function pcre_dfa_exec() is called to match a subject string
4062 against a compiled pattern, using a matching algorithm that scans the
4063 subject string just once, and does not backtrack. This has different
4064 characteristics to the normal algorithm, and is not compatible with
4065 Perl. Some of the features of PCRE patterns are not supported. Never-
4066 theless, there are times when this kind of matching can be useful. For
4067 a discussion of the two matching algorithms, and a list of features
4068 that pcre_dfa_exec() does not support, see the pcrematching documenta-
4069 tion.
4070
4071 The arguments for the pcre_dfa_exec() function are the same as for
4072 pcre_exec(), plus two extras. The ovector argument is used in a differ-
4073 ent way, and this is described below. The other common arguments are
4074 used in the same way as for pcre_exec(), so their description is not
4075 repeated here.
4076
4077 The two additional arguments provide workspace for the function. The
4078 workspace vector should contain at least 20 elements. It is used for
4079 keeping track of multiple paths through the pattern tree. More
4080 workspace will be needed for patterns and subjects where there are a
4081 lot of potential matches.
4082
4083 Here is an example of a simple call to pcre_dfa_exec():
4084
4085 int rc;
4086 int ovector[10];
4087 int wspace[20];
4088 rc = pcre_dfa_exec(
4089 re, /* result of pcre_compile() */
4090 NULL, /* we didn't study the pattern */
4091 "some string", /* the subject string */
4092 11, /* the length of the subject string */
4093 0, /* start at offset 0 in the subject */
4094 0, /* default options */
4095 ovector, /* vector of integers for substring information */
4096 10, /* number of elements (NOT size in bytes) */
4097 wspace, /* working space vector */
4098 20); /* number of elements (NOT size in bytes) */
4099
4100 Option bits for pcre_dfa_exec()
4101
4102 The unused bits of the options argument for pcre_dfa_exec() must be
4103 zero. The only bits that may be set are PCRE_ANCHORED, PCRE_NEW-
4104 LINE_xxx, PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY,
4105 PCRE_NOTEMPTY_ATSTART, PCRE_NO_UTF8_CHECK, PCRE_BSR_ANYCRLF,
4106 PCRE_BSR_UNICODE, PCRE_NO_START_OPTIMIZE, PCRE_PARTIAL_HARD, PCRE_PAR-
4107 TIAL_SOFT, PCRE_DFA_SHORTEST, and PCRE_DFA_RESTART. All but the last
4108 four of these are exactly the same as for pcre_exec(), so their
4109 description is not repeated here.
4110
4111 PCRE_PARTIAL_HARD
4112 PCRE_PARTIAL_SOFT
4113
4114 These have the same general effect as they do for pcre_exec(), but the
4115 details are slightly different. When PCRE_PARTIAL_HARD is set for
4116 pcre_dfa_exec(), it returns PCRE_ERROR_PARTIAL if the end of the sub-
4117 ject is reached and there is still at least one matching possibility
4118 that requires additional characters. This happens even if some complete
4119 matches have also been found. When PCRE_PARTIAL_SOFT is set, the return
4120 code PCRE_ERROR_NOMATCH is converted into PCRE_ERROR_PARTIAL if the end
4121 of the subject is reached, there have been no complete matches, but
4122 there is still at least one matching possibility. The portion of the
4123 string that was inspected when the longest partial match was found is
4124 set as the first matching string in both cases. There is a more
4125 detailed discussion of partial and multi-segment matching, with exam-
4126 ples, in the pcrepartial documentation.
4127
4128 PCRE_DFA_SHORTEST
4129
4130 Setting the PCRE_DFA_SHORTEST option causes the matching algorithm to
4131 stop as soon as it has found one match. Because of the way the alterna-
4132 tive algorithm works, this is necessarily the shortest possible match
4133 at the first possible matching point in the subject string.
4134
4135 PCRE_DFA_RESTART
4136
4137 When pcre_dfa_exec() returns a partial match, it is possible to call it
4138 again, with additional subject characters, and have it continue with
4139 the same match. The PCRE_DFA_RESTART option requests this action; when
4140 it is set, the workspace and wscount options must reference the same
4141 vector as before because data about the match so far is left in them
4142 after a partial match. There is more discussion of this facility in the
4143 pcrepartial documentation.
4144
4145 Successful returns from pcre_dfa_exec()
4146
4147 When pcre_dfa_exec() succeeds, it may have matched more than one sub-
4148 string in the subject. Note, however, that all the matches from one run
4149 of the function start at the same point in the subject. The shorter
4150 matches are all initial substrings of the longer matches. For example,
4151 if the pattern
4152
4153 <.*>
4154
4155 is matched against the string
4156
4157 This is <something> <something else> <something further> no more
4158
4159 the three matched strings are
4160
4161 <something>
4162 <something> <something else>
4163 <something> <something else> <something further>
4164
4165 On success, the yield of the function is a number greater than zero,
4166 which is the number of matched substrings. The substrings themselves
4167 are returned in ovector. Each string uses two elements; the first is
4168 the offset to the start, and the second is the offset to the end. In
4169 fact, all the strings have the same start offset. (Space could have
4170 been saved by giving this only once, but it was decided to retain some
4171 compatibility with the way pcre_exec() returns data, even though the
4172 meaning of the strings is different.)
4173
4174 The strings are returned in reverse order of length; that is, the long-
4175 est matching string is given first. If there were too many matches to
4176 fit into ovector, the yield of the function is zero, and the vector is
4177 filled with the longest matches. Unlike pcre_exec(), pcre_dfa_exec()
4178 can use the entire ovector for returning matched strings.
4179
4180 NOTE: PCRE's "auto-possessification" optimization usually applies to
4181 character repeats at the end of a pattern (as well as internally). For
4182 example, the pattern "a\d+" is compiled as if it were "a\d++" because
4183 there is no point even considering the possibility of backtracking into
4184 the repeated digits. For DFA matching, this means that only one possi-
4185 ble match is found. If you really do want multiple matches in such
4186 cases, either use an ungreedy repeat ("a\d+?") or set the
4187 PCRE_NO_AUTO_POSSESS option when compiling.
4188
4189 Error returns from pcre_dfa_exec()
4190
4191 The pcre_dfa_exec() function returns a negative number when it fails.
4192 Many of the errors are the same as for pcre_exec(), and these are
4193 described above. There are in addition the following errors that are
4194 specific to pcre_dfa_exec():
4195
4196 PCRE_ERROR_DFA_UITEM (-16)
4197
4198 This return is given if pcre_dfa_exec() encounters an item in the pat-
4199 tern that it does not support, for instance, the use of \C or a back
4200 reference.
4201
4202 PCRE_ERROR_DFA_UCOND (-17)
4203
4204 This return is given if pcre_dfa_exec() encounters a condition item
4205 that uses a back reference for the condition, or a test for recursion
4206 in a specific group. These are not supported.
4207
4208 PCRE_ERROR_DFA_UMLIMIT (-18)
4209
4210 This return is given if pcre_dfa_exec() is called with an extra block
4211 that contains a setting of the match_limit or match_limit_recursion
4212 fields. This is not supported (these fields are meaningless for DFA
4213 matching).
4214
4215 PCRE_ERROR_DFA_WSSIZE (-19)
4216
4217 This return is given if pcre_dfa_exec() runs out of space in the
4218 workspace vector.
4219
4220 PCRE_ERROR_DFA_RECURSE (-20)
4221
4222 When a recursive subpattern is processed, the matching function calls
4223 itself recursively, using private vectors for ovector and workspace.
4224 This error is given if the output vector is not large enough. This
4225 should be extremely rare, as a vector of size 1000 is used.
4226
4227 PCRE_ERROR_DFA_BADRESTART (-30)
4228
4229 When pcre_dfa_exec() is called with the PCRE_DFA_RESTART option, some
4230 plausibility checks are made on the contents of the workspace, which
4231 should contain data about the previous partial match. If any of these
4232 checks fail, this error is given.
4233
4234
4235 SEE ALSO
4236
4237 pcre16(3), pcre32(3), pcrebuild(3), pcrecallout(3), pcrecpp(3)(3),
4238 pcrematching(3), pcrepartial(3), pcreposix(3), pcreprecompile(3), pcre-
4239 sample(3), pcrestack(3).
4240
4241
4242 AUTHOR
4243
4244 Philip Hazel
4245 University Computing Service
4246 Cambridge CB2 3QH, England.
4247
4248
4249 REVISION
4250
4251 Last updated: 12 November 2013
4252 Copyright (c) 1997-2013 University of Cambridge.
4253 ------------------------------------------------------------------------------
4254
4255
4256 PCRECALLOUT(3) Library Functions Manual PCRECALLOUT(3)
4257
4258
4259
4260 NAME
4261 PCRE - Perl-compatible regular expressions
4262
4263 SYNOPSIS
4264
4265 #include <pcre.h>
4266
4267 int (*pcre_callout)(pcre_callout_block *);
4268
4269 int (*pcre16_callout)(pcre16_callout_block *);
4270
4271 int (*pcre32_callout)(pcre32_callout_block *);
4272
4273
4274 DESCRIPTION
4275
4276 PCRE provides a feature called "callout", which is a means of temporar-
4277 ily passing control to the caller of PCRE in the middle of pattern
4278 matching. The caller of PCRE provides an external function by putting
4279 its entry point in the global variable pcre_callout (pcre16_callout for
4280 the 16-bit library, pcre32_callout for the 32-bit library). By default,
4281 this variable contains NULL, which disables all calling out.
4282
4283 Within a regular expression, (?C) indicates the points at which the
4284 external function is to be called. Different callout points can be
4285 identified by putting a number less than 256 after the letter C. The
4286 default value is zero. For example, this pattern has two callout
4287 points:
4288
4289 (?C1)abc(?C2)def
4290
4291 If the PCRE_AUTO_CALLOUT option bit is set when a pattern is compiled,
4292 PCRE automatically inserts callouts, all with number 255, before each
4293 item in the pattern. For example, if PCRE_AUTO_CALLOUT is used with the
4294 pattern
4295
4296 A(\d{2}|--)
4297
4298 it is processed as if it were
4299
4300 (?C255)A(?C255)((?C255)\d{2}(?C255)|(?C255)-(?C255)-(?C255))(?C255)
4301
4302 Notice that there is a callout before and after each parenthesis and
4303 alternation bar. If the pattern contains a conditional group whose con-
4304 dition is an assertion, an automatic callout is inserted immediately
4305 before the condition. Such a callout may also be inserted explicitly,
4306 for example:
4307
4308 (?(?C9)(?=a)ab|de)
4309
4310 This applies only to assertion conditions (because they are themselves
4311 independent groups).
4312
4313 Automatic callouts can be used for tracking the progress of pattern
4314 matching. The pcretest program has a pattern qualifier (/C) that sets
4315 automatic callouts; when it is used, the output indicates how the pat-
4316 tern is being matched. This is useful information when you are trying
4317 to optimize the performance of a particular pattern.
4318
4319
4320 MISSING CALLOUTS
4321
4322 You should be aware that, because of optimizations in the way PCRE com-
4323 piles and matches patterns, callouts sometimes do not happen exactly as
4324 you might expect.
4325
4326 At compile time, PCRE "auto-possessifies" repeated items when it knows
4327 that what follows cannot be part of the repeat. For example, a+[bc] is
4328 compiled as if it were a++[bc]. The pcretest output when this pattern
4329 is anchored and then applied with automatic callouts to the string
4330 "aaaa" is:
4331
4332 --->aaaa
4333 +0 ^ ^
4334 +1 ^ a+
4335 +3 ^ ^ [bc]
4336 No match
4337
4338 This indicates that when matching [bc] fails, there is no backtracking
4339 into a+ and therefore the callouts that would be taken for the back-
4340 tracks do not occur. You can disable the auto-possessify feature by
4341 passing PCRE_NO_AUTO_POSSESS to pcre_compile(), or starting the pattern
4342 with (*NO_AUTO_POSSESS). If this is done in pcretest (using the /O
4343 qualifier), the output changes to this:
4344
4345 --->aaaa
4346 +0 ^ ^
4347 +1 ^ a+
4348 +3 ^ ^ [bc]
4349 +3 ^ ^ [bc]
4350 +3 ^ ^ [bc]
4351 +3 ^^ [bc]
4352 No match
4353
4354 This time, when matching [bc] fails, the matcher backtracks into a+ and
4355 tries again, repeatedly, until a+ itself fails.
4356
4357 Other optimizations that provide fast "no match" results also affect
4358 callouts. For example, if the pattern is
4359
4360 ab(?C4)cd
4361
4362 PCRE knows that any matching string must contain the letter "d". If the
4363 subject string is "abyz", the lack of "d" means that matching doesn't
4364 ever start, and the callout is never reached. However, with "abyd",
4365 though the result is still no match, the callout is obeyed.
4366
4367 If the pattern is studied, PCRE knows the minimum length of a matching
4368 string, and will immediately give a "no match" return without actually
4369 running a match if the subject is not long enough, or, for unanchored
4370 patterns, if it has been scanned far enough.
4371
4372 You can disable these optimizations by passing the PCRE_NO_START_OPTI-
4373 MIZE option to the matching function, or by starting the pattern with
4374 (*NO_START_OPT). This slows down the matching process, but does ensure
4375 that callouts such as the example above are obeyed.
4376
4377
4378 THE CALLOUT INTERFACE
4379
4380 During matching, when PCRE reaches a callout point, the external func-
4381 tion defined by pcre_callout or pcre[16|32]_callout is called (if it is
4382 set). This applies to both normal and DFA matching. The only argument
4383 to the callout function is a pointer to a pcre_callout or
4384 pcre[16|32]_callout block. These structures contains the following
4385 fields:
4386
4387 int version;
4388 int callout_number;
4389 int *offset_vector;
4390 const char *subject; (8-bit version)
4391 PCRE_SPTR16 subject; (16-bit version)
4392 PCRE_SPTR32 subject; (32-bit version)
4393 int subject_length;
4394 int start_match;
4395 int current_position;
4396 int capture_top;
4397 int capture_last;
4398 void *callout_data;
4399 int pattern_position;
4400 int next_item_length;
4401 const unsigned char *mark; (8-bit version)
4402 const PCRE_UCHAR16 *mark; (16-bit version)
4403 const PCRE_UCHAR32 *mark; (32-bit version)
4404
4405 The version field is an integer containing the version number of the
4406 block format. The initial version was 0; the current version is 2. The
4407 version number will change again in future if additional fields are
4408 added, but the intention is never to remove any of the existing fields.
4409
4410 The callout_number field contains the number of the callout, as com-
4411 piled into the pattern (that is, the number after ?C for manual call-
4412 outs, and 255 for automatically generated callouts).
4413
4414 The offset_vector field is a pointer to the vector of offsets that was
4415 passed by the caller to the matching function. When pcre_exec() or
4416 pcre[16|32]_exec() is used, the contents can be inspected, in order to
4417 extract substrings that have been matched so far, in the same way as
4418 for extracting substrings after a match has completed. For the DFA
4419 matching functions, this field is not useful.
4420
4421 The subject and subject_length fields contain copies of the values that
4422 were passed to the matching function.
4423
4424 The start_match field normally contains the offset within the subject
4425 at which the current match attempt started. However, if the escape
4426 sequence \K has been encountered, this value is changed to reflect the
4427 modified starting point. If the pattern is not anchored, the callout
4428 function may be called several times from the same point in the pattern
4429 for different starting points in the subject.
4430
4431 The current_position field contains the offset within the subject of
4432 the current match pointer.
4433
4434 When the pcre_exec() or pcre[16|32]_exec() is used, the capture_top
4435 field contains one more than the number of the highest numbered cap-
4436 tured substring so far. If no substrings have been captured, the value
4437 of capture_top is one. This is always the case when the DFA functions
4438 are used, because they do not support captured substrings.
4439
4440 The capture_last field contains the number of the most recently cap-
4441 tured substring. However, when a recursion exits, the value reverts to
4442 what it was outside the recursion, as do the values of all captured
4443 substrings. If no substrings have been captured, the value of cap-
4444 ture_last is -1. This is always the case for the DFA matching func-
4445 tions.
4446
4447 The callout_data field contains a value that is passed to a matching
4448 function specifically so that it can be passed back in callouts. It is
4449 passed in the callout_data field of a pcre_extra or pcre[16|32]_extra
4450 data structure. If no such data was passed, the value of callout_data
4451 in a callout block is NULL. There is a description of the pcre_extra
4452 structure in the pcreapi documentation.
4453
4454 The pattern_position field is present from version 1 of the callout
4455 structure. It contains the offset to the next item to be matched in the
4456 pattern string.
4457
4458 The next_item_length field is present from version 1 of the callout
4459 structure. It contains the length of the next item to be matched in the
4460 pattern string. When the callout immediately precedes an alternation
4461 bar, a closing parenthesis, or the end of the pattern, the length is
4462 zero. When the callout precedes an opening parenthesis, the length is
4463 that of the entire subpattern.
4464
4465 The pattern_position and next_item_length fields are intended to help
4466 in distinguishing between different automatic callouts, which all have
4467 the same callout number. However, they are set for all callouts.
4468
4469 The mark field is present from version 2 of the callout structure. In
4470 callouts from pcre_exec() or pcre[16|32]_exec() it contains a pointer
4471 to the zero-terminated name of the most recently passed (*MARK),
4472 (*PRUNE), or (*THEN) item in the match, or NULL if no such items have
4473 been passed. Instances of (*PRUNE) or (*THEN) without a name do not
4474 obliterate a previous (*MARK). In callouts from the DFA matching func-
4475 tions this field always contains NULL.
4476
4477
4478 RETURN VALUES
4479
4480 The external callout function returns an integer to PCRE. If the value
4481 is zero, matching proceeds as normal. If the value is greater than
4482 zero, matching fails at the current point, but the testing of other
4483 matching possibilities goes ahead, just as if a lookahead assertion had
4484 failed. If the value is less than zero, the match is abandoned, the
4485 matching function returns the negative value.
4486
4487 Negative values should normally be chosen from the set of
4488 PCRE_ERROR_xxx values. In particular, PCRE_ERROR_NOMATCH forces a stan-
4489 dard "no match" failure. The error number PCRE_ERROR_CALLOUT is
4490 reserved for use by callout functions; it will never be used by PCRE
4491 itself.
4492
4493
4494 AUTHOR
4495
4496 Philip Hazel
4497 University Computing Service
4498 Cambridge CB2 3QH, England.
4499
4500
4501 REVISION
4502
4503 Last updated: 12 November 2013
4504 Copyright (c) 1997-2013 University of Cambridge.
4505 ------------------------------------------------------------------------------
4506
4507
4508 PCRECOMPAT(3) Library Functions Manual PCRECOMPAT(3)
4509
4510
4511
4512 NAME
4513 PCRE - Perl-compatible regular expressions
4514
4515 DIFFERENCES BETWEEN PCRE AND PERL
4516
4517 This document describes the differences in the ways that PCRE and Perl
4518 handle regular expressions. The differences described here are with
4519 respect to Perl versions 5.10 and above.
4520
4521 1. PCRE has only a subset of Perl's Unicode support. Details of what it
4522 does have are given in the pcreunicode page.
4523
4524 2. PCRE allows repeat quantifiers only on parenthesized assertions, but
4525 they do not mean what you might think. For example, (?!a){3} does not
4526 assert that the next three characters are not "a". It just asserts that
4527 the next character is not "a" three times (in principle: PCRE optimizes
4528 this to run the assertion just once). Perl allows repeat quantifiers on
4529 other assertions such as \b, but these do not seem to have any use.
4530
4531 3. Capturing subpatterns that occur inside negative lookahead asser-
4532 tions are counted, but their entries in the offsets vector are never
4533 set. Perl sometimes (but not always) sets its numerical variables from
4534 inside negative assertions.
4535
4536 4. Though binary zero characters are supported in the subject string,
4537 they are not allowed in a pattern string because it is passed as a nor-
4538 mal C string, terminated by zero. The escape sequence \0 can be used in
4539 the pattern to represent a binary zero.
4540
4541 5. The following Perl escape sequences are not supported: \l, \u, \L,
4542 \U, and \N when followed by a character name or Unicode value. (\N on
4543 its own, matching a non-newline character, is supported.) In fact these
4544 are implemented by Perl's general string-handling and are not part of
4545 its pattern matching engine. If any of these are encountered by PCRE,
4546 an error is generated by default. However, if the PCRE_JAVASCRIPT_COM-
4547 PAT option is set, \U and \u are interpreted as JavaScript interprets
4548 them.
4549
4550 6. The Perl escape sequences \p, \P, and \X are supported only if PCRE
4551 is built with Unicode character property support. The properties that
4552 can be tested with \p and \P are limited to the general category prop-
4553 erties such as Lu and Nd, script names such as Greek or Han, and the
4554 derived properties Any and L&. PCRE does support the Cs (surrogate)
4555 property, which Perl does not; the Perl documentation says "Because
4556 Perl hides the need for the user to understand the internal representa-
4557 tion of Unicode characters, there is no need to implement the somewhat
4558 messy concept of surrogates."
4559
4560 7. PCRE does support the \Q...\E escape for quoting substrings. Charac-
4561 ters in between are treated as literals. This is slightly different
4562 from Perl in that $ and @ are also handled as literals inside the
4563 quotes. In Perl, they cause variable interpolation (but of course PCRE
4564 does not have variables). Note the following examples:
4565
4566 Pattern PCRE matches Perl matches
4567
4568 \Qabc$xyz\E abc$xyz abc followed by the
4569 contents of $xyz
4570 \Qabc\$xyz\E abc\$xyz abc\$xyz
4571 \Qabc\E\$\Qxyz\E abc$xyz abc$xyz
4572
4573 The \Q...\E sequence is recognized both inside and outside character
4574 classes.
4575
4576 8. Fairly obviously, PCRE does not support the (?{code}) and (??{code})
4577 constructions. However, there is support for recursive patterns. This
4578 is not available in Perl 5.8, but it is in Perl 5.10. Also, the PCRE
4579 "callout" feature allows an external function to be called during pat-
4580 tern matching. See the pcrecallout documentation for details.
4581
4582 9. Subpatterns that are called as subroutines (whether or not recur-
4583 sively) are always treated as atomic groups in PCRE. This is like
4584 Python, but unlike Perl. Captured values that are set outside a sub-
4585 routine call can be reference from inside in PCRE, but not in Perl.
4586 There is a discussion that explains these differences in more detail in
4587 the section on recursion differences from Perl in the pcrepattern page.
4588
4589 10. If any of the backtracking control verbs are used in a subpattern
4590 that is called as a subroutine (whether or not recursively), their
4591 effect is confined to that subpattern; it does not extend to the sur-
4592 rounding pattern. This is not always the case in Perl. In particular,
4593 if (*THEN) is present in a group that is called as a subroutine, its
4594 action is limited to that group, even if the group does not contain any
4595 | characters. Note that such subpatterns are processed as anchored at
4596 the point where they are tested.
4597
4598 11. If a pattern contains more than one backtracking control verb, the
4599 first one that is backtracked onto acts. For example, in the pattern
4600 A(*COMMIT)B(*PRUNE)C a failure in B triggers (*COMMIT), but a failure
4601 in C triggers (*PRUNE). Perl's behaviour is more complex; in many cases
4602 it is the same as PCRE, but there are examples where it differs.
4603
4604 12. Most backtracking verbs in assertions have their normal actions.
4605 They are not confined to the assertion.
4606
4607 13. There are some differences that are concerned with the settings of
4608 captured strings when part of a pattern is repeated. For example,
4609 matching "aba" against the pattern /^(a(b)?)+$/ in Perl leaves $2
4610 unset, but in PCRE it is set to "b".
4611
4612 14. PCRE's handling of duplicate subpattern numbers and duplicate sub-
4613 pattern names is not as general as Perl's. This is a consequence of the
4614 fact the PCRE works internally just with numbers, using an external ta-
4615 ble to translate between numbers and names. In particular, a pattern
4616 such as (?|(?<a>A)|(?<b)B), where the two capturing parentheses have
4617 the same number but different names, is not supported, and causes an
4618 error at compile time. If it were allowed, it would not be possible to
4619 distinguish which parentheses matched, because both names map to cap-
4620 turing subpattern number 1. To avoid this confusing situation, an error
4621 is given at compile time.
4622
4623 15. Perl recognizes comments in some places that PCRE does not, for
4624 example, between the ( and ? at the start of a subpattern. If the /x
4625 modifier is set, Perl allows white space between ( and ? (though cur-
4626 rent Perls warn that this is deprecated) but PCRE never does, even if
4627 the PCRE_EXTENDED option is set.
4628
4629 16. Perl, when in warning mode, gives warnings for character classes
4630 such as [A-\d] or [a-[:digit:]]. It then treats the hyphens as liter-
4631 als. PCRE has no warning features, so it gives an error in these cases
4632 because they are almost certainly user mistakes.
4633
4634 17. In PCRE, the upper/lower case character properties Lu and Ll are
4635 not affected when case-independent matching is specified. For example,
4636 \p{Lu} always matches an upper case letter. I think Perl has changed in
4637 this respect; in the release at the time of writing (5.16), \p{Lu} and
4638 \p{Ll} match all letters, regardless of case, when case independence is
4639 specified.
4640
4641 18. PCRE provides some extensions to the Perl regular expression facil-
4642 ities. Perl 5.10 includes new features that are not in earlier ver-
4643 sions of Perl, some of which (such as named parentheses) have been in
4644 PCRE for some time. This list is with respect to Perl 5.10:
4645
4646 (a) Although lookbehind assertions in PCRE must match fixed length
4647 strings, each alternative branch of a lookbehind assertion can match a
4648 different length of string. Perl requires them all to have the same
4649 length.
4650
4651 (b) If PCRE_DOLLAR_ENDONLY is set and PCRE_MULTILINE is not set, the $
4652 meta-character matches only at the very end of the string.
4653
4654 (c) If PCRE_EXTRA is set, a backslash followed by a letter with no spe-
4655 cial meaning is faulted. Otherwise, like Perl, the backslash is quietly
4656 ignored. (Perl can be made to issue a warning.)
4657
4658 (d) If PCRE_UNGREEDY is set, the greediness of the repetition quanti-
4659 fiers is inverted, that is, by default they are not greedy, but if fol-
4660 lowed by a question mark they are.
4661
4662 (e) PCRE_ANCHORED can be used at matching time to force a pattern to be
4663 tried only at the first matching position in the subject string.
4664
4665 (f) The PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, PCRE_NOTEMPTY_ATSTART,
4666 and PCRE_NO_AUTO_CAPTURE options for pcre_exec() have no Perl equiva-
4667 lents.
4668
4669 (g) The \R escape sequence can be restricted to match only CR, LF, or
4670 CRLF by the PCRE_BSR_ANYCRLF option.
4671
4672 (h) The callout facility is PCRE-specific.
4673
4674 (i) The partial matching facility is PCRE-specific.
4675
4676 (j) Patterns compiled by PCRE can be saved and re-used at a later time,
4677 even on different hosts that have the other endianness. However, this
4678 does not apply to optimized data created by the just-in-time compiler.
4679
4680 (k) The alternative matching functions (pcre_dfa_exec(),
4681 pcre16_dfa_exec() and pcre32_dfa_exec(),) match in a different way and
4682 are not Perl-compatible.
4683
4684 (l) PCRE recognizes some special sequences such as (*CR) at the start
4685 of a pattern that set overall options that cannot be changed within the
4686 pattern.
4687
4688
4689 AUTHOR
4690
4691 Philip Hazel
4692 University Computing Service
4693 Cambridge CB2 3QH, England.
4694
4695
4696 REVISION
4697
4698 Last updated: 10 November 2013
4699 Copyright (c) 1997-2013 University of Cambridge.
4700 ------------------------------------------------------------------------------
4701
4702
4703 PCREPATTERN(3) Library Functions Manual PCREPATTERN(3)
4704
4705
4706
4707 NAME
4708 PCRE - Perl-compatible regular expressions
4709
4710 PCRE REGULAR EXPRESSION DETAILS
4711
4712 The syntax and semantics of the regular expressions that are supported
4713 by PCRE are described in detail below. There is a quick-reference syn-
4714 tax summary in the pcresyntax page. PCRE tries to match Perl syntax and
4715 semantics as closely as it can. PCRE also supports some alternative
4716 regular expression syntax (which does not conflict with the Perl syn-
4717 tax) in order to provide some compatibility with regular expressions in
4718 Python, .NET, and Oniguruma.
4719
4720 Perl's regular expressions are described in its own documentation, and
4721 regular expressions in general are covered in a number of books, some
4722 of which have copious examples. Jeffrey Friedl's "Mastering Regular
4723 Expressions", published by O'Reilly, covers regular expressions in
4724 great detail. This description of PCRE's regular expressions is
4725 intended as reference material.
4726
4727 This document discusses the patterns that are supported by PCRE when
4728 one its main matching functions, pcre_exec() (8-bit) or
4729 pcre[16|32]_exec() (16- or 32-bit), is used. PCRE also has alternative
4730 matching functions, pcre_dfa_exec() and pcre[16|32_dfa_exec(), which
4731 match using a different algorithm that is not Perl-compatible. Some of
4732 the features discussed below are not available when DFA matching is
4733 used. The advantages and disadvantages of the alternative functions,
4734 and how they differ from the normal functions, are discussed in the
4735 pcrematching page.
4736
4737
4738 SPECIAL START-OF-PATTERN ITEMS
4739
4740 A number of options that can be passed to pcre_compile() can also be
4741 set by special items at the start of a pattern. These are not Perl-com-
4742 patible, but are provided to make these options accessible to pattern
4743 writers who are not able to change the program that processes the pat-
4744 tern. Any number of these items may appear, but they must all be
4745 together right at the start of the pattern string, and the letters must
4746 be in upper case.
4747
4748 UTF support
4749
4750 The original operation of PCRE was on strings of one-byte characters.
4751 However, there is now also support for UTF-8 strings in the original
4752 library, an extra library that supports 16-bit and UTF-16 character
4753 strings, and a third library that supports 32-bit and UTF-32 character
4754 strings. To use these features, PCRE must be built to include appropri-
4755 ate support. When using UTF strings you must either call the compiling
4756 function with the PCRE_UTF8, PCRE_UTF16, or PCRE_UTF32 option, or the
4757 pattern must start with one of these special sequences:
4758
4759 (*UTF8)
4760 (*UTF16)
4761 (*UTF32)
4762 (*UTF)
4763
4764 (*UTF) is a generic sequence that can be used with any of the
4765 libraries. Starting a pattern with such a sequence is equivalent to
4766 setting the relevant option. How setting a UTF mode affects pattern
4767 matching is mentioned in several places below. There is also a summary
4768 of features in the pcreunicode page.
4769
4770 Some applications that allow their users to supply patterns may wish to
4771 restrict them to non-UTF data for security reasons. If the
4772 PCRE_NEVER_UTF option is set at compile time, (*UTF) etc. are not
4773 allowed, and their appearance causes an error.
4774
4775 Unicode property support
4776
4777 Another special sequence that may appear at the start of a pattern is
4778 (*UCP). This has the same effect as setting the PCRE_UCP option: it
4779 causes sequences such as \d and \w to use Unicode properties to deter-
4780 mine character types, instead of recognizing only characters with codes
4781 less than 128 via a lookup table.
4782
4783 Disabling auto-possessification
4784
4785 If a pattern starts with (*NO_AUTO_POSSESS), it has the same effect as
4786 setting the PCRE_NO_AUTO_POSSESS option at compile time. This stops
4787 PCRE from making quantifiers possessive when what follows cannot match
4788 the repeated item. For example, by default a+b is treated as a++b. For
4789 more details, see the pcreapi documentation.
4790
4791 Disabling start-up optimizations
4792
4793 If a pattern starts with (*NO_START_OPT), it has the same effect as
4794 setting the PCRE_NO_START_OPTIMIZE option either at compile or matching
4795 time. This disables several optimizations for quickly reaching "no
4796 match" results. For more details, see the pcreapi documentation.
4797
4798 Newline conventions
4799
4800 PCRE supports five different conventions for indicating line breaks in
4801 strings: a single CR (carriage return) character, a single LF (line-
4802 feed) character, the two-character sequence CRLF, any of the three pre-
4803 ceding, or any Unicode newline sequence. The pcreapi page has further
4804 discussion about newlines, and shows how to set the newline convention
4805 in the options arguments for the compiling and matching functions.
4806
4807 It is also possible to specify a newline convention by starting a pat-
4808 tern string with one of the following five sequences:
4809
4810 (*CR) carriage return
4811 (*LF) linefeed
4812 (*CRLF) carriage return, followed by linefeed
4813 (*ANYCRLF) any of the three above
4814 (*ANY) all Unicode newline sequences
4815
4816 These override the default and the options given to the compiling func-
4817 tion. For example, on a Unix system where LF is the default newline
4818 sequence, the pattern
4819
4820 (*CR)a.b
4821
4822 changes the convention to CR. That pattern matches "a\nb" because LF is
4823 no longer a newline. If more than one of these settings is present, the
4824 last one is used.
4825
4826 The newline convention affects where the circumflex and dollar asser-
4827 tions are true. It also affects the interpretation of the dot metachar-
4828 acter when PCRE_DOTALL is not set, and the behaviour of \N. However, it
4829 does not affect what the \R escape sequence matches. By default, this
4830 is any Unicode newline sequence, for Perl compatibility. However, this
4831 can be changed; see the description of \R in the section entitled "New-
4832 line sequences" below. A change of \R setting can be combined with a
4833 change of newline convention.
4834
4835 Setting match and recursion limits
4836
4837 The caller of pcre_exec() can set a limit on the number of times the
4838 internal match() function is called and on the maximum depth of recur-
4839 sive calls. These facilities are provided to catch runaway matches that
4840 are provoked by patterns with huge matching trees (a typical example is
4841 a pattern with nested unlimited repeats) and to avoid running out of
4842 system stack by too much recursion. When one of these limits is
4843 reached, pcre_exec() gives an error return. The limits can also be set
4844 by items at the start of the pattern of the form
4845
4846 (*LIMIT_MATCH=d)
4847 (*LIMIT_RECURSION=d)
4848
4849 where d is any number of decimal digits. However, the value of the set-
4850 ting must be less than the value set (or defaulted) by the caller of
4851 pcre_exec() for it to have any effect. In other words, the pattern
4852 writer can lower the limits set by the programmer, but not raise them.
4853 If there is more than one setting of one of these limits, the lower
4854 value is used.
4855
4856
4857 EBCDIC CHARACTER CODES
4858
4859 PCRE can be compiled to run in an environment that uses EBCDIC as its
4860 character code rather than ASCII or Unicode (typically a mainframe sys-
4861 tem). In the sections below, character code values are ASCII or Uni-
4862 code; in an EBCDIC environment these characters may have different code
4863 values, and there are no code points greater than 255.
4864
4865
4866 CHARACTERS AND METACHARACTERS
4867
4868 A regular expression is a pattern that is matched against a subject
4869 string from left to right. Most characters stand for themselves in a
4870 pattern, and match the corresponding characters in the subject. As a
4871 trivial example, the pattern
4872
4873 The quick brown fox
4874
4875 matches a portion of a subject string that is identical to itself. When
4876 caseless matching is specified (the PCRE_CASELESS option), letters are
4877 matched independently of case. In a UTF mode, PCRE always understands
4878 the concept of case for characters whose values are less than 128, so
4879 caseless matching is always possible. For characters with higher val-
4880 ues, the concept of case is supported if PCRE is compiled with Unicode
4881 property support, but not otherwise. If you want to use caseless
4882 matching for characters 128 and above, you must ensure that PCRE is
4883 compiled with Unicode property support as well as with UTF support.
4884
4885 The power of regular expressions comes from the ability to include
4886 alternatives and repetitions in the pattern. These are encoded in the
4887 pattern by the use of metacharacters, which do not stand for themselves
4888 but instead are interpreted in some special way.
4889
4890 There are two different sets of metacharacters: those that are recog-
4891 nized anywhere in the pattern except within square brackets, and those
4892 that are recognized within square brackets. Outside square brackets,
4893 the metacharacters are as follows:
4894
4895 \ general escape character with several uses
4896 ^ assert start of string (or line, in multiline mode)
4897 $ assert end of string (or line, in multiline mode)
4898 . match any character except newline (by default)
4899 [ start character class definition
4900 | start of alternative branch
4901 ( start subpattern
4902 ) end subpattern
4903 ? extends the meaning of (
4904 also 0 or 1 quantifier
4905 also quantifier minimizer
4906 * 0 or more quantifier
4907 + 1 or more quantifier
4908 also "possessive quantifier"
4909 { start min/max quantifier
4910
4911 Part of a pattern that is in square brackets is called a "character
4912 class". In a character class the only metacharacters are:
4913
4914 \ general escape character
4915 ^ negate the class, but only if the first character
4916 - indicates character range
4917 [ POSIX character class (only if followed by POSIX
4918 syntax)
4919 ] terminates the character class
4920
4921 The following sections describe the use of each of the metacharacters.
4922
4923
4924 BACKSLASH
4925
4926 The backslash character has several uses. Firstly, if it is followed by
4927 a character that is not a number or a letter, it takes away any special
4928 meaning that character may have. This use of backslash as an escape
4929 character applies both inside and outside character classes.
4930
4931 For example, if you want to match a * character, you write \* in the
4932 pattern. This escaping action applies whether or not the following
4933 character would otherwise be interpreted as a metacharacter, so it is
4934 always safe to precede a non-alphanumeric with backslash to specify
4935 that it stands for itself. In particular, if you want to match a back-
4936 slash, you write \\.
4937
4938 In a UTF mode, only ASCII numbers and letters have any special meaning
4939 after a backslash. All other characters (in particular, those whose
4940 codepoints are greater than 127) are treated as literals.
4941
4942 If a pattern is compiled with the PCRE_EXTENDED option, most white
4943 space in the pattern (other than in a character class), and characters
4944 between a # outside a character class and the next newline, inclusive,
4945 are ignored. An escaping backslash can be used to include a white space
4946 or # character as part of the pattern.
4947
4948 If you want to remove the special meaning from a sequence of charac-
4949 ters, you can do so by putting them between \Q and \E. This is differ-
4950 ent from Perl in that $ and @ are handled as literals in \Q...\E
4951 sequences in PCRE, whereas in Perl, $ and @ cause variable interpola-
4952 tion. Note the following examples:
4953
4954 Pattern PCRE matches Perl matches
4955
4956 \Qabc$xyz\E abc$xyz abc followed by the
4957 contents of $xyz
4958 \Qabc\$xyz\E abc\$xyz abc\$xyz
4959 \Qabc\E\$\Qxyz\E abc$xyz abc$xyz
4960
4961 The \Q...\E sequence is recognized both inside and outside character
4962 classes. An isolated \E that is not preceded by \Q is ignored. If \Q
4963 is not followed by \E later in the pattern, the literal interpretation
4964 continues to the end of the pattern (that is, \E is assumed at the
4965 end). If the isolated \Q is inside a character class, this causes an
4966 error, because the character class is not terminated.
4967
4968 Non-printing characters
4969
4970 A second use of backslash provides a way of encoding non-printing char-
4971 acters in patterns in a visible manner. There is no restriction on the
4972 appearance of non-printing characters, apart from the binary zero that
4973 terminates a pattern, but when a pattern is being prepared by text
4974 editing, it is often easier to use one of the following escape
4975 sequences than the binary character it represents:
4976
4977 \a alarm, that is, the BEL character (hex 07)
4978 \cx "control-x", where x is any ASCII character
4979 \e escape (hex 1B)
4980 \f form feed (hex 0C)
4981 \n linefeed (hex 0A)
4982 \r carriage return (hex 0D)
4983 \t tab (hex 09)
4984 \0dd character with octal code 0dd
4985 \ddd character with octal code ddd, or back reference
4986 \o{ddd..} character with octal code ddd..
4987 \xhh character with hex code hh
4988 \x{hhh..} character with hex code hhh.. (non-JavaScript mode)
4989 \uhhhh character with hex code hhhh (JavaScript mode only)
4990
4991 The precise effect of \cx on ASCII characters is as follows: if x is a
4992 lower case letter, it is converted to upper case. Then bit 6 of the
4993 character (hex 40) is inverted. Thus \cA to \cZ become hex 01 to hex 1A
4994 (A is 41, Z is 5A), but \c{ becomes hex 3B ({ is 7B), and \c; becomes
4995 hex 7B (; is 3B). If the data item (byte or 16-bit value) following \c
4996 has a value greater than 127, a compile-time error occurs. This locks
4997 out non-ASCII characters in all modes.
4998
4999 The \c facility was designed for use with ASCII characters, but with
5000 the extension to Unicode it is even less useful than it once was. It
5001 is, however, recognized when PCRE is compiled in EBCDIC mode, where
5002 data items are always bytes. In this mode, all values are valid after
5003 \c. If the next character is a lower case letter, it is converted to
5004 upper case. Then the 0xc0 bits of the byte are inverted. Thus \cA
5005 becomes hex 01, as in ASCII (A is C1), but because the EBCDIC letters
5006 are disjoint, \cZ becomes hex 29 (Z is E9), and other characters also
5007 generate different values.
5008
5009 After \0 up to two further octal digits are read. If there are fewer
5010 than two digits, just those that are present are used. Thus the
5011 sequence \0\x\07 specifies two binary zeros followed by a BEL character
5012 (code value 7). Make sure you supply two digits after the initial zero
5013 if the pattern character that follows is itself an octal digit.
5014
5015 The escape \o must be followed by a sequence of octal digits, enclosed
5016 in braces. An error occurs if this is not the case. This escape is a
5017 recent addition to Perl; it provides way of specifying character code
5018 points as octal numbers greater than 0777, and it also allows octal
5019 numbers and back references to be unambiguously specified.
5020
5021 For greater clarity and unambiguity, it is best to avoid following \ by
5022 a digit greater than zero. Instead, use \o{} or \x{} to specify charac-
5023 ter numbers, and \g{} to specify back references. The following para-
5024 graphs describe the old, ambiguous syntax.
5025
5026 The handling of a backslash followed by a digit other than 0 is compli-
5027 cated, and Perl has changed in recent releases, causing PCRE also to
5028 change. Outside a character class, PCRE reads the digit and any follow-
5029 ing digits as a decimal number. If the number is less than 8, or if
5030 there have been at least that many previous capturing left parentheses
5031 in the expression, the entire sequence is taken as a back reference. A
5032 description of how this works is given later, following the discussion
5033 of parenthesized subpatterns.
5034
5035 Inside a character class, or if the decimal number following \ is
5036 greater than 7 and there have not been that many capturing subpatterns,
5037 PCRE handles \8 and \9 as the literal characters "8" and "9", and oth-
5038 erwise re-reads up to three octal digits following the backslash, using
5039 them to generate a data character. Any subsequent digits stand for
5040 themselves. For example:
5041
5042 \040 is another way of writing an ASCII space
5043 \40 is the same, provided there are fewer than 40
5044 previous capturing subpatterns
5045 \7 is always a back reference
5046 \11 might be a back reference, or another way of
5047 writing a tab
5048 \011 is always a tab
5049 \0113 is a tab followed by the character "3"
5050 \113 might be a back reference, otherwise the
5051 character with octal code 113
5052 \377 might be a back reference, otherwise
5053 the value 255 (decimal)
5054 \81 is either a back reference, or the two
5055 characters "8" and "1"
5056
5057 Note that octal values of 100 or greater that are specified using this
5058 syntax must not be introduced by a leading zero, because no more than
5059 three octal digits are ever read.
5060
5061 By default, after \x that is not followed by {, from zero to two hexa-
5062 decimal digits are read (letters can be in upper or lower case). Any
5063 number of hexadecimal digits may appear between \x{ and }. If a charac-
5064 ter other than a hexadecimal digit appears between \x{ and }, or if
5065 there is no terminating }, an error occurs.
5066
5067 If the PCRE_JAVASCRIPT_COMPAT option is set, the interpretation of \x
5068 is as just described only when it is followed by two hexadecimal dig-
5069 its. Otherwise, it matches a literal "x" character. In JavaScript
5070 mode, support for code points greater than 256 is provided by \u, which
5071 must be followed by four hexadecimal digits; otherwise it matches a
5072 literal "u" character.
5073
5074 Characters whose value is less than 256 can be defined by either of the
5075 two syntaxes for \x (or by \u in JavaScript mode). There is no differ-
5076 ence in the way they are handled. For example, \xdc is exactly the same
5077 as \x{dc} (or \u00dc in JavaScript mode).
5078
5079 Constraints on character values
5080
5081 Characters that are specified using octal or hexadecimal numbers are
5082 limited to certain values, as follows:
5083
5084 8-bit non-UTF mode less than 0x100
5085 8-bit UTF-8 mode less than 0x10ffff and a valid codepoint
5086 16-bit non-UTF mode less than 0x10000
5087 16-bit UTF-16 mode less than 0x10ffff and a valid codepoint
5088 32-bit non-UTF mode less than 0x100000000
5089 32-bit UTF-32 mode less than 0x10ffff and a valid codepoint
5090
5091 Invalid Unicode codepoints are the range 0xd800 to 0xdfff (the so-
5092 called "surrogate" codepoints), and 0xffef.
5093
5094 Escape sequences in character classes
5095
5096 All the sequences that define a single character value can be used both
5097 inside and outside character classes. In addition, inside a character
5098 class, \b is interpreted as the backspace character (hex 08).
5099
5100 \N is not allowed in a character class. \B, \R, and \X are not special
5101 inside a character class. Like other unrecognized escape sequences,
5102 they are treated as the literal characters "B", "R", and "X" by
5103 default, but cause an error if the PCRE_EXTRA option is set. Outside a
5104 character class, these sequences have different meanings.
5105
5106 Unsupported escape sequences
5107
5108 In Perl, the sequences \l, \L, \u, and \U are recognized by its string
5109 handler and used to modify the case of following characters. By
5110 default, PCRE does not support these escape sequences. However, if the
5111 PCRE_JAVASCRIPT_COMPAT option is set, \U matches a "U" character, and
5112 \u can be used to define a character by code point, as described in the
5113 previous section.
5114
5115 Absolute and relative back references
5116
5117 The sequence \g followed by an unsigned or a negative number, option-
5118 ally enclosed in braces, is an absolute or relative back reference. A
5119 named back reference can be coded as \g{name}. Back references are dis-
5120 cussed later, following the discussion of parenthesized subpatterns.
5121
5122 Absolute and relative subroutine calls
5123
5124 For compatibility with Oniguruma, the non-Perl syntax \g followed by a
5125 name or a number enclosed either in angle brackets or single quotes, is
5126 an alternative syntax for referencing a subpattern as a "subroutine".
5127 Details are discussed later. Note that \g{...} (Perl syntax) and
5128 \g<...> (Oniguruma syntax) are not synonymous. The former is a back
5129 reference; the latter is a subroutine call.
5130
5131 Generic character types
5132
5133 Another use of backslash is for specifying generic character types:
5134
5135 \d any decimal digit
5136 \D any character that is not a decimal digit
5137 \h any horizontal white space character
5138 \H any character that is not a horizontal white space character
5139 \s any white space character
5140 \S any character that is not a white space character
5141 \v any vertical white space character
5142 \V any character that is not a vertical white space character
5143 \w any "word" character
5144 \W any "non-word" character
5145
5146 There is also the single sequence \N, which matches a non-newline char-
5147 acter. This is the same as the "." metacharacter when PCRE_DOTALL is
5148 not set. Perl also uses \N to match characters by name; PCRE does not
5149 support this.
5150
5151 Each pair of lower and upper case escape sequences partitions the com-
5152 plete set of characters into two disjoint sets. Any given character
5153 matches one, and only one, of each pair. The sequences can appear both
5154 inside and outside character classes. They each match one character of
5155 the appropriate type. If the current matching point is at the end of
5156 the subject string, all of them fail, because there is no character to
5157 match.
5158
5159 For compatibility with Perl, \s did not used to match the VT character
5160 (code 11), which made it different from the the POSIX "space" class.
5161 However, Perl added VT at release 5.18, and PCRE followed suit at
5162 release 8.34. The default \s characters are now HT (9), LF (10), VT
5163 (11), FF (12), CR (13), and space (32), which are defined as white
5164 space in the "C" locale. This list may vary if locale-specific matching
5165 is taking place; in particular, in some locales the "non-breaking
5166 space" character (\xA0) is recognized as white space.
5167
5168 A "word" character is an underscore or any character that is a letter
5169 or digit. By default, the definition of letters and digits is con-
5170 trolled by PCRE's low-valued character tables, and may vary if locale-
5171 specific matching is taking place (see "Locale support" in the pcreapi
5172 page). For example, in a French locale such as "fr_FR" in Unix-like
5173 systems, or "french" in Windows, some character codes greater than 127
5174 are used for accented letters, and these are then matched by \w. The
5175 use of locales with Unicode is discouraged.
5176
5177 By default, characters whose code points are greater than 127 never
5178 match \d, \s, or \w, and always match \D, \S, and \W, although this may
5179 vary for characters in the range 128-255 when locale-specific matching
5180 is happening. These escape sequences retain their original meanings
5181 from before Unicode support was available, mainly for efficiency rea-
5182 sons. If PCRE is compiled with Unicode property support, and the
5183 PCRE_UCP option is set, the behaviour is changed so that Unicode prop-
5184 erties are used to determine character types, as follows:
5185
5186 \d any character that matches \p{Nd} (decimal digit)
5187 \s any character that matches \p{Z} or \h or \v
5188 \w any character that matches \p{L} or \p{N}, plus underscore
5189
5190 The upper case escapes match the inverse sets of characters. Note that
5191 \d matches only decimal digits, whereas \w matches any Unicode digit,
5192 as well as any Unicode letter, and underscore. Note also that PCRE_UCP
5193 affects \b, and \B because they are defined in terms of \w and \W.
5194 Matching these sequences is noticeably slower when PCRE_UCP is set.
5195
5196 The sequences \h, \H, \v, and \V are features that were added to Perl
5197 at release 5.10. In contrast to the other sequences, which match only
5198 ASCII characters by default, these always match certain high-valued
5199 code points, whether or not PCRE_UCP is set. The horizontal space char-
5200 acters are:
5201
5202 U+0009 Horizontal tab (HT)
5203 U+0020 Space
5204 U+00A0 Non-break space
5205 U+1680 Ogham space mark
5206 U+180E Mongolian vowel separator
5207 U+2000 En quad
5208 U+2001 Em quad
5209 U+2002 En space
5210 U+2003 Em space
5211 U+2004 Three-per-em space
5212 U+2005 Four-per-em space
5213 U+2006 Six-per-em space
5214 U+2007 Figure space
5215 U+2008 Punctuation space
5216 U+2009 Thin space
5217 U+200A Hair space
5218 U+202F Narrow no-break space
5219 U+205F Medium mathematical space
5220 U+3000 Ideographic space
5221
5222 The vertical space characters are:
5223
5224 U+000A Linefeed (LF)
5225 U+000B Vertical tab (VT)
5226 U+000C Form feed (FF)
5227 U+000D Carriage return (CR)
5228 U+0085 Next line (NEL)
5229 U+2028 Line separator
5230 U+2029 Paragraph separator
5231
5232 In 8-bit, non-UTF-8 mode, only the characters with codepoints less than
5233 256 are relevant.
5234
5235 Newline sequences
5236
5237 Outside a character class, by default, the escape sequence \R matches
5238 any Unicode newline sequence. In 8-bit non-UTF-8 mode \R is equivalent
5239 to the following:
5240
5241 (?>\r\n|\n|\x0b|\f|\r|\x85)
5242
5243 This is an example of an "atomic group", details of which are given
5244 below. This particular group matches either the two-character sequence
5245 CR followed by LF, or one of the single characters LF (linefeed,
5246 U+000A), VT (vertical tab, U+000B), FF (form feed, U+000C), CR (car-
5247 riage return, U+000D), or NEL (next line, U+0085). The two-character
5248 sequence is treated as a single unit that cannot be split.
5249
5250 In other modes, two additional characters whose codepoints are greater
5251 than 255 are added: LS (line separator, U+2028) and PS (paragraph sepa-
5252 rator, U+2029). Unicode character property support is not needed for
5253 these characters to be recognized.
5254
5255 It is possible to restrict \R to match only CR, LF, or CRLF (instead of
5256 the complete set of Unicode line endings) by setting the option
5257 PCRE_BSR_ANYCRLF either at compile time or when the pattern is matched.
5258 (BSR is an abbrevation for "backslash R".) This can be made the default
5259 when PCRE is built; if this is the case, the other behaviour can be
5260 requested via the PCRE_BSR_UNICODE option. It is also possible to
5261 specify these settings by starting a pattern string with one of the
5262 following sequences:
5263
5264 (*BSR_ANYCRLF) CR, LF, or CRLF only
5265 (*BSR_UNICODE) any Unicode newline sequence
5266
5267 These override the default and the options given to the compiling func-
5268 tion, but they can themselves be overridden by options given to a
5269 matching function. Note that these special settings, which are not
5270 Perl-compatible, are recognized only at the very start of a pattern,
5271 and that they must be in upper case. If more than one of them is
5272 present, the last one is used. They can be combined with a change of
5273 newline convention; for example, a pattern can start with:
5274
5275 (*ANY)(*BSR_ANYCRLF)
5276
5277 They can also be combined with the (*UTF8), (*UTF16), (*UTF32), (*UTF)
5278 or (*UCP) special sequences. Inside a character class, \R is treated as
5279 an unrecognized escape sequence, and so matches the letter "R" by
5280 default, but causes an error if PCRE_EXTRA is set.
5281
5282 Unicode character properties
5283
5284 When PCRE is built with Unicode character property support, three addi-
5285 tional escape sequences that match characters with specific properties
5286 are available. When in 8-bit non-UTF-8 mode, these sequences are of
5287 course limited to testing characters whose codepoints are less than
5288 256, but they do work in this mode. The extra escape sequences are:
5289
5290 \p{xx} a character with the xx property
5291 \P{xx} a character without the xx property
5292 \X a Unicode extended grapheme cluster
5293
5294 The property names represented by xx above are limited to the Unicode
5295 script names, the general category properties, "Any", which matches any
5296 character (including newline), and some special PCRE properties
5297 (described in the next section). Other Perl properties such as "InMu-
5298 sicalSymbols" are not currently supported by PCRE. Note that \P{Any}
5299 does not match any characters, so always causes a match failure.
5300
5301 Sets of Unicode characters are defined as belonging to certain scripts.
5302 A character from one of these sets can be matched using a script name.
5303 For example:
5304
5305 \p{Greek}
5306 \P{Han}
5307
5308 Those that are not part of an identified script are lumped together as
5309 "Common". The current list of scripts is:
5310
5311 Arabic, Armenian, Avestan, Balinese, Bamum, Batak, Bengali, Bopomofo,
5312 Brahmi, Braille, Buginese, Buhid, Canadian_Aboriginal, Carian, Chakma,
5313 Cham, Cherokee, Common, Coptic, Cuneiform, Cypriot, Cyrillic, Deseret,
5314 Devanagari, Egyptian_Hieroglyphs, Ethiopic, Georgian, Glagolitic,
5315 Gothic, Greek, Gujarati, Gurmukhi, Han, Hangul, Hanunoo, Hebrew, Hira-
5316 gana, Imperial_Aramaic, Inherited, Inscriptional_Pahlavi, Inscrip-
5317 tional_Parthian, Javanese, Kaithi, Kannada, Katakana, Kayah_Li,
5318 Kharoshthi, Khmer, Lao, Latin, Lepcha, Limbu, Linear_B, Lisu, Lycian,
5319 Lydian, Malayalam, Mandaic, Meetei_Mayek, Meroitic_Cursive,
5320 Meroitic_Hieroglyphs, Miao, Mongolian, Myanmar, New_Tai_Lue, Nko,
5321 Ogham, Old_Italic, Old_Persian, Old_South_Arabian, Old_Turkic,
5322 Ol_Chiki, Oriya, Osmanya, Phags_Pa, Phoenician, Rejang, Runic, Samari-
5323 tan, Saurashtra, Sharada, Shavian, Sinhala, Sora_Sompeng, Sundanese,
5324 Syloti_Nagri, Syriac, Tagalog, Tagbanwa, Tai_Le, Tai_Tham, Tai_Viet,
5325 Takri, Tamil, Telugu, Thaana, Thai, Tibetan, Tifinagh, Ugaritic, Vai,
5326 Yi.
5327
5328 Each character has exactly one Unicode general category property, spec-
5329 ified by a two-letter abbreviation. For compatibility with Perl, nega-
5330 tion can be specified by including a circumflex between the opening
5331 brace and the property name. For example, \p{^Lu} is the same as
5332 \P{Lu}.
5333
5334 If only one letter is specified with \p or \P, it includes all the gen-
5335 eral category properties that start with that letter. In this case, in
5336 the absence of negation, the curly brackets in the escape sequence are
5337 optional; these two examples have the same effect:
5338
5339 \p{L}
5340 \pL
5341
5342 The following general category property codes are supported:
5343
5344 C Other
5345 Cc Control
5346 Cf Format
5347 Cn Unassigned
5348 Co Private use
5349 Cs Surrogate
5350
5351 L Letter
5352 Ll Lower case letter
5353 Lm Modifier letter
5354 Lo Other letter
5355 Lt Title case letter
5356 Lu Upper case letter
5357
5358 M Mark
5359 Mc Spacing mark
5360 Me Enclosing mark
5361 Mn Non-spacing mark
5362
5363 N Number
5364 Nd Decimal number
5365 Nl Letter number
5366 No Other number
5367
5368 P Punctuation
5369 Pc Connector punctuation
5370 Pd Dash punctuation
5371 Pe Close punctuation
5372 Pf Final punctuation
5373 Pi Initial punctuation
5374 Po Other punctuation
5375 Ps Open punctuation
5376
5377 S Symbol
5378 Sc Currency symbol
5379 Sk Modifier symbol
5380 Sm Mathematical symbol
5381 So Other symbol
5382
5383 Z Separator
5384 Zl Line separator
5385 Zp Paragraph separator
5386 Zs Space separator
5387
5388 The special property L& is also supported: it matches a character that
5389 has the Lu, Ll, or Lt property, in other words, a letter that is not
5390 classified as a modifier or "other".
5391
5392 The Cs (Surrogate) property applies only to characters in the range
5393 U+D800 to U+DFFF. Such characters are not valid in Unicode strings and
5394 so cannot be tested by PCRE, unless UTF validity checking has been
5395 turned off (see the discussion of PCRE_NO_UTF8_CHECK,
5396 PCRE_NO_UTF16_CHECK and PCRE_NO_UTF32_CHECK in the pcreapi page). Perl
5397 does not support the Cs property.
5398
5399 The long synonyms for property names that Perl supports (such as
5400 \p{Letter}) are not supported by PCRE, nor is it permitted to prefix
5401 any of these properties with "Is".
5402
5403 No character that is in the Unicode table has the Cn (unassigned) prop-
5404 erty. Instead, this property is assumed for any code point that is not
5405 in the Unicode table.
5406
5407 Specifying caseless matching does not affect these escape sequences.
5408 For example, \p{Lu} always matches only upper case letters. This is
5409 different from the behaviour of current versions of Perl.
5410
5411 Matching characters by Unicode property is not fast, because PCRE has
5412 to do a multistage table lookup in order to find a character's prop-
5413 erty. That is why the traditional escape sequences such as \d and \w do
5414 not use Unicode properties in PCRE by default, though you can make them
5415 do so by setting the PCRE_UCP option or by starting the pattern with
5416 (*UCP).
5417
5418 Extended grapheme clusters
5419
5420 The \X escape matches any number of Unicode characters that form an
5421 "extended grapheme cluster", and treats the sequence as an atomic group
5422 (see below). Up to and including release 8.31, PCRE matched an ear-
5423 lier, simpler definition that was equivalent to
5424
5425 (?>\PM\pM*)
5426
5427 That is, it matched a character without the "mark" property, followed
5428 by zero or more characters with the "mark" property. Characters with
5429 the "mark" property are typically non-spacing accents that affect the
5430 preceding character.
5431
5432 This simple definition was extended in Unicode to include more compli-
5433 cated kinds of composite character by giving each character a grapheme
5434 breaking property, and creating rules that use these properties to
5435 define the boundaries of extended grapheme clusters. In releases of
5436 PCRE later than 8.31, \X matches one of these clusters.
5437
5438 \X always matches at least one character. Then it decides whether to
5439 add additional characters according to the following rules for ending a
5440 cluster:
5441
5442 1. End at the end of the subject string.
5443
5444 2. Do not end between CR and LF; otherwise end after any control char-
5445 acter.
5446
5447 3. Do not break Hangul (a Korean script) syllable sequences. Hangul
5448 characters are of five types: L, V, T, LV, and LVT. An L character may
5449 be followed by an L, V, LV, or LVT character; an LV or V character may
5450 be followed by a V or T character; an LVT or T character may be follwed
5451 only by a T character.
5452
5453 4. Do not end before extending characters or spacing marks. Characters
5454 with the "mark" property always have the "extend" grapheme breaking
5455 property.
5456
5457 5. Do not end after prepend characters.
5458
5459 6. Otherwise, end the cluster.
5460
5461 PCRE's additional properties
5462
5463 As well as the standard Unicode properties described above, PCRE sup-
5464 ports four more that make it possible to convert traditional escape
5465 sequences such as \w and \s to use Unicode properties. PCRE uses these
5466 non-standard, non-Perl properties internally when PCRE_UCP is set. How-
5467 ever, they may also be used explicitly. These properties are:
5468
5469 Xan Any alphanumeric character
5470 Xps Any POSIX space character
5471 Xsp Any Perl space character
5472 Xwd Any Perl "word" character
5473
5474 Xan matches characters that have either the L (letter) or the N (num-
5475 ber) property. Xps matches the characters tab, linefeed, vertical tab,
5476 form feed, or carriage return, and any other character that has the Z
5477 (separator) property. Xsp is the same as Xps; it used to exclude ver-
5478 tical tab, for Perl compatibility, but Perl changed, and so PCRE fol-
5479 lowed at release 8.34. Xwd matches the same characters as Xan, plus
5480 underscore.
5481
5482 There is another non-standard property, Xuc, which matches any charac-
5483 ter that can be represented by a Universal Character Name in C++ and
5484 other programming languages. These are the characters $, @, ` (grave
5485 accent), and all characters with Unicode code points greater than or
5486 equal to U+00A0, except for the surrogates U+D800 to U+DFFF. Note that
5487 most base (ASCII) characters are excluded. (Universal Character Names
5488 are of the form \uHHHH or \UHHHHHHHH where H is a hexadecimal digit.
5489 Note that the Xuc property does not match these sequences but the char-
5490 acters that they represent.)
5491
5492 Resetting the match start
5493
5494 The escape sequence \K causes any previously matched characters not to
5495 be included in the final matched sequence. For example, the pattern:
5496
5497 foo\Kbar
5498
5499 matches "foobar", but reports that it has matched "bar". This feature
5500 is similar to a lookbehind assertion (described below). However, in
5501 this case, the part of the subject before the real match does not have
5502 to be of fixed length, as lookbehind assertions do. The use of \K does
5503 not interfere with the setting of captured substrings. For example,
5504 when the pattern
5505
5506 (foo)\Kbar
5507
5508 matches "foobar", the first substring is still set to "foo".
5509
5510 Perl documents that the use of \K within assertions is "not well
5511 defined". In PCRE, \K is acted upon when it occurs inside positive
5512 assertions, but is ignored in negative assertions.
5513
5514 Simple assertions
5515
5516 The final use of backslash is for certain simple assertions. An asser-
5517 tion specifies a condition that has to be met at a particular point in
5518 a match, without consuming any characters from the subject string. The
5519 use of subpatterns for more complicated assertions is described below.
5520 The backslashed assertions are:
5521
5522 \b matches at a word boundary
5523 \B matches when not at a word boundary
5524 \A matches at the start of the subject
5525 \Z matches at the end of the subject
5526 also matches before a newline at the end of the subject
5527 \z matches only at the end of the subject
5528 \G matches at the first matching position in the subject
5529
5530 Inside a character class, \b has a different meaning; it matches the
5531 backspace character. If any other of these assertions appears in a
5532 character class, by default it matches the corresponding literal char-
5533 acter (for example, \B matches the letter B). However, if the
5534 PCRE_EXTRA option is set, an "invalid escape sequence" error is gener-
5535 ated instead.
5536
5537 A word boundary is a position in the subject string where the current
5538 character and the previous character do not both match \w or \W (i.e.
5539 one matches \w and the other matches \W), or the start or end of the
5540 string if the first or last character matches \w, respectively. In a
5541 UTF mode, the meanings of \w and \W can be changed by setting the
5542 PCRE_UCP option. When this is done, it also affects \b and \B. Neither
5543 PCRE nor Perl has a separate "start of word" or "end of word" metase-
5544 quence. However, whatever follows \b normally determines which it is.
5545 For example, the fragment \ba matches "a" at the start of a word.
5546
5547 The \A, \Z, and \z assertions differ from the traditional circumflex
5548 and dollar (described in the next section) in that they only ever match
5549 at the very start and end of the subject string, whatever options are
5550 set. Thus, they are independent of multiline mode. These three asser-
5551 tions are not affected by the PCRE_NOTBOL or PCRE_NOTEOL options, which
5552 affect only the behaviour of the circumflex and dollar metacharacters.
5553 However, if the startoffset argument of pcre_exec() is non-zero, indi-
5554 cating that matching is to start at a point other than the beginning of
5555 the subject, \A can never match. The difference between \Z and \z is
5556 that \Z matches before a newline at the end of the string as well as at
5557 the very end, whereas \z matches only at the end.
5558
5559 The \G assertion is true only when the current matching position is at
5560 the start point of the match, as specified by the startoffset argument
5561 of pcre_exec(). It differs from \A when the value of startoffset is
5562 non-zero. By calling pcre_exec() multiple times with appropriate argu-
5563 ments, you can mimic Perl's /g option, and it is in this kind of imple-
5564 mentation where \G can be useful.
5565
5566 Note, however, that PCRE's interpretation of \G, as the start of the
5567 current match, is subtly different from Perl's, which defines it as the
5568 end of the previous match. In Perl, these can be different when the
5569 previously matched string was empty. Because PCRE does just one match
5570 at a time, it cannot reproduce this behaviour.
5571
5572 If all the alternatives of a pattern begin with \G, the expression is
5573 anchored to the starting match position, and the "anchored" flag is set
5574 in the compiled regular expression.
5575
5576
5577 CIRCUMFLEX AND DOLLAR
5578
5579 The circumflex and dollar metacharacters are zero-width assertions.
5580 That is, they test for a particular condition being true without con-
5581 suming any characters from the subject string.
5582
5583 Outside a character class, in the default matching mode, the circumflex
5584 character is an assertion that is true only if the current matching
5585 point is at the start of the subject string. If the startoffset argu-
5586 ment of pcre_exec() is non-zero, circumflex can never match if the
5587 PCRE_MULTILINE option is unset. Inside a character class, circumflex
5588 has an entirely different meaning (see below).
5589
5590 Circumflex need not be the first character of the pattern if a number
5591 of alternatives are involved, but it should be the first thing in each
5592 alternative in which it appears if the pattern is ever to match that
5593 branch. If all possible alternatives start with a circumflex, that is,
5594 if the pattern is constrained to match only at the start of the sub-
5595 ject, it is said to be an "anchored" pattern. (There are also other
5596 constructs that can cause a pattern to be anchored.)
5597
5598 The dollar character is an assertion that is true only if the current
5599 matching point is at the end of the subject string, or immediately
5600 before a newline at the end of the string (by default). Note, however,
5601 that it does not actually match the newline. Dollar need not be the
5602 last character of the pattern if a number of alternatives are involved,
5603 but it should be the last item in any branch in which it appears. Dol-
5604 lar has no special meaning in a character class.
5605
5606 The meaning of dollar can be changed so that it matches only at the
5607 very end of the string, by setting the PCRE_DOLLAR_ENDONLY option at
5608 compile time. This does not affect the \Z assertion.
5609
5610 The meanings of the circumflex and dollar characters are changed if the
5611 PCRE_MULTILINE option is set. When this is the case, a circumflex
5612 matches immediately after internal newlines as well as at the start of
5613 the subject string. It does not match after a newline that ends the
5614 string. A dollar matches before any newlines in the string, as well as
5615 at the very end, when PCRE_MULTILINE is set. When newline is specified
5616 as the two-character sequence CRLF, isolated CR and LF characters do
5617 not indicate newlines.
5618
5619 For example, the pattern /^abc$/ matches the subject string "def\nabc"
5620 (where \n represents a newline) in multiline mode, but not otherwise.
5621 Consequently, patterns that are anchored in single line mode because
5622 all branches start with ^ are not anchored in multiline mode, and a
5623 match for circumflex is possible when the startoffset argument of
5624 pcre_exec() is non-zero. The PCRE_DOLLAR_ENDONLY option is ignored if
5625 PCRE_MULTILINE is set.
5626
5627 Note that the sequences \A, \Z, and \z can be used to match the start
5628 and end of the subject in both modes, and if all branches of a pattern
5629 start with \A it is always anchored, whether or not PCRE_MULTILINE is
5630 set.
5631
5632
5633 FULL STOP (PERIOD, DOT) AND \N
5634
5635 Outside a character class, a dot in the pattern matches any one charac-
5636 ter in the subject string except (by default) a character that signi-
5637 fies the end of a line.
5638
5639 When a line ending is defined as a single character, dot never matches
5640 that character; when the two-character sequence CRLF is used, dot does
5641 not match CR if it is immediately followed by LF, but otherwise it
5642 matches all characters (including isolated CRs and LFs). When any Uni-
5643 code line endings are being recognized, dot does not match CR or LF or
5644 any of the other line ending characters.
5645
5646 The behaviour of dot with regard to newlines can be changed. If the
5647 PCRE_DOTALL option is set, a dot matches any one character, without
5648 exception. If the two-character sequence CRLF is present in the subject
5649 string, it takes two dots to match it.
5650
5651 The handling of dot is entirely independent of the handling of circum-
5652 flex and dollar, the only relationship being that they both involve
5653 newlines. Dot has no special meaning in a character class.
5654
5655 The escape sequence \N behaves like a dot, except that it is not
5656 affected by the PCRE_DOTALL option. In other words, it matches any
5657 character except one that signifies the end of a line. Perl also uses
5658 \N to match characters by name; PCRE does not support this.
5659
5660
5661 MATCHING A SINGLE DATA UNIT
5662
5663 Outside a character class, the escape sequence \C matches any one data
5664 unit, whether or not a UTF mode is set. In the 8-bit library, one data
5665 unit is one byte; in the 16-bit library it is a 16-bit unit; in the
5666 32-bit library it is a 32-bit unit. Unlike a dot, \C always matches
5667 line-ending characters. The feature is provided in Perl in order to
5668 match individual bytes in UTF-8 mode, but it is unclear how it can use-
5669 fully be used. Because \C breaks up characters into individual data
5670 units, matching one unit with \C in a UTF mode means that the rest of
5671 the string may start with a malformed UTF character. This has undefined
5672 results, because PCRE assumes that it is dealing with valid UTF strings
5673 (and by default it checks this at the start of processing unless the
5674 PCRE_NO_UTF8_CHECK, PCRE_NO_UTF16_CHECK or PCRE_NO_UTF32_CHECK option
5675 is used).
5676
5677 PCRE does not allow \C to appear in lookbehind assertions (described
5678 below) in a UTF mode, because this would make it impossible to calcu-
5679 late the length of the lookbehind.
5680
5681 In general, the \C escape sequence is best avoided. However, one way of
5682 using it that avoids the problem of malformed UTF characters is to use
5683 a lookahead to check the length of the next character, as in this pat-
5684 tern, which could be used with a UTF-8 string (ignore white space and
5685 line breaks):
5686
5687 (?| (?=[\x00-\x7f])(\C) |
5688 (?=[\x80-\x{7ff}])(\C)(\C) |
5689 (?=[\x{800}-\x{ffff}])(\C)(\C)(\C) |
5690 (?=[\x{10000}-\x{1fffff}])(\C)(\C)(\C)(\C))
5691
5692 A group that starts with (?| resets the capturing parentheses numbers
5693 in each alternative (see "Duplicate Subpattern Numbers" below). The
5694 assertions at the start of each branch check the next UTF-8 character
5695 for values whose encoding uses 1, 2, 3, or 4 bytes, respectively. The
5696 character's individual bytes are then captured by the appropriate num-
5697 ber of groups.
5698
5699
5700 SQUARE BRACKETS AND CHARACTER CLASSES
5701
5702 An opening square bracket introduces a character class, terminated by a
5703 closing square bracket. A closing square bracket on its own is not spe-
5704 cial by default. However, if the PCRE_JAVASCRIPT_COMPAT option is set,
5705 a lone closing square bracket causes a compile-time error. If a closing
5706 square bracket is required as a member of the class, it should be the
5707 first data character in the class (after an initial circumflex, if
5708 present) or escaped with a backslash.
5709
5710 A character class matches a single character in the subject. In a UTF
5711 mode, the character may be more than one data unit long. A matched
5712 character must be in the set of characters defined by the class, unless
5713 the first character in the class definition is a circumflex, in which
5714 case the subject character must not be in the set defined by the class.
5715 If a circumflex is actually required as a member of the class, ensure
5716 it is not the first character, or escape it with a backslash.
5717
5718 For example, the character class [aeiou] matches any lower case vowel,
5719 while [^aeiou] matches any character that is not a lower case vowel.
5720 Note that a circumflex is just a convenient notation for specifying the
5721 characters that are in the class by enumerating those that are not. A
5722 class that starts with a circumflex is not an assertion; it still con-
5723 sumes a character from the subject string, and therefore it fails if
5724 the current pointer is at the end of the string.
5725
5726 In UTF-8 (UTF-16, UTF-32) mode, characters with values greater than 255
5727 (0xffff) can be included in a class as a literal string of data units,
5728 or by using the \x{ escaping mechanism.
5729
5730 When caseless matching is set, any letters in a class represent both
5731 their upper case and lower case versions, so for example, a caseless
5732 [aeiou] matches "A" as well as "a", and a caseless [^aeiou] does not
5733 match "A", whereas a caseful version would. In a UTF mode, PCRE always
5734 understands the concept of case for characters whose values are less
5735 than 128, so caseless matching is always possible. For characters with
5736 higher values, the concept of case is supported if PCRE is compiled
5737 with Unicode property support, but not otherwise. If you want to use
5738 caseless matching in a UTF mode for characters 128 and above, you must
5739 ensure that PCRE is compiled with Unicode property support as well as
5740 with UTF support.
5741
5742 Characters that might indicate line breaks are never treated in any
5743 special way when matching character classes, whatever line-ending
5744 sequence is in use, and whatever setting of the PCRE_DOTALL and
5745 PCRE_MULTILINE options is used. A class such as [^a] always matches one
5746 of these characters.
5747
5748 The minus (hyphen) character can be used to specify a range of charac-
5749 ters in a character class. For example, [d-m] matches any letter
5750 between d and m, inclusive. If a minus character is required in a
5751 class, it must be escaped with a backslash or appear in a position
5752 where it cannot be interpreted as indicating a range, typically as the
5753 first or last character in the class, or immediately after a range. For
5754 example, [b-d-z] matches letters in the range b to d, a hyphen charac-
5755 ter, or z.
5756
5757 It is not possible to have the literal character "]" as the end charac-
5758 ter of a range. A pattern such as [W-]46] is interpreted as a class of
5759 two characters ("W" and "-") followed by a literal string "46]", so it
5760 would match "W46]" or "-46]". However, if the "]" is escaped with a
5761 backslash it is interpreted as the end of range, so [W-\]46] is inter-
5762 preted as a class containing a range followed by two other characters.
5763 The octal or hexadecimal representation of "]" can also be used to end
5764 a range.
5765
5766 An error is generated if a POSIX character class (see below) or an
5767 escape sequence other than one that defines a single character appears
5768 at a point where a range ending character is expected. For example,
5769 [z-\xff] is valid, but [A-\d] and [A-[:digit:]] are not.
5770
5771 Ranges operate in the collating sequence of character values. They can
5772 also be used for characters specified numerically, for example
5773 [\000-\037]. Ranges can include any characters that are valid for the
5774 current mode.
5775
5776 If a range that includes letters is used when caseless matching is set,
5777 it matches the letters in either case. For example, [W-c] is equivalent
5778 to [][\\^_`wxyzabc], matched caselessly, and in a non-UTF mode, if
5779 character tables for a French locale are in use, [\xc8-\xcb] matches
5780 accented E characters in both cases. In UTF modes, PCRE supports the
5781 concept of case for characters with values greater than 128 only when
5782 it is compiled with Unicode property support.
5783
5784 The character escape sequences \d, \D, \h, \H, \p, \P, \s, \S, \v, \V,
5785 \w, and \W may appear in a character class, and add the characters that
5786 they match to the class. For example, [\dABCDEF] matches any hexadeci-
5787 mal digit. In UTF modes, the PCRE_UCP option affects the meanings of
5788 \d, \s, \w and their upper case partners, just as it does when they
5789 appear outside a character class, as described in the section entitled
5790 "Generic character types" above. The escape sequence \b has a different
5791 meaning inside a character class; it matches the backspace character.
5792 The sequences \B, \N, \R, and \X are not special inside a character
5793 class. Like any other unrecognized escape sequences, they are treated
5794 as the literal characters "B", "N", "R", and "X" by default, but cause
5795 an error if the PCRE_EXTRA option is set.
5796
5797 A circumflex can conveniently be used with the upper case character
5798 types to specify a more restricted set of characters than the matching
5799 lower case type. For example, the class [^\W_] matches any letter or
5800 digit, but not underscore, whereas [\w] includes underscore. A positive
5801 character class should be read as "something OR something OR ..." and a
5802 negative class as "NOT something AND NOT something AND NOT ...".
5803
5804 The only metacharacters that are recognized in character classes are
5805 backslash, hyphen (only where it can be interpreted as specifying a
5806 range), circumflex (only at the start), opening square bracket (only
5807 when it can be interpreted as introducing a POSIX class name - see the
5808 next section), and the terminating closing square bracket. However,
5809 escaping other non-alphanumeric characters does no harm.
5810
5811
5812 POSIX CHARACTER CLASSES
5813
5814 Perl supports the POSIX notation for character classes. This uses names
5815 enclosed by [: and :] within the enclosing square brackets. PCRE also
5816 supports this notation. For example,
5817
5818 [01[:alpha:]%]
5819
5820 matches "0", "1", any alphabetic character, or "%". The supported class
5821 names are:
5822
5823 alnum letters and digits
5824 alpha letters
5825 ascii character codes 0 - 127
5826 blank space or tab only
5827 cntrl control characters
5828 digit decimal digits (same as \d)
5829 graph printing characters, excluding space
5830 lower lower case letters
5831 print printing characters, including space
5832 punct printing characters, excluding letters and digits and space
5833 space white space (the same as \s from PCRE 8.34)
5834 upper upper case letters
5835 word "word" characters (same as \w)
5836 xdigit hexadecimal digits
5837
5838 The default "space" characters are HT (9), LF (10), VT (11), FF (12),
5839 CR (13), and space (32). If locale-specific matching is taking place,
5840 there may be additional space characters. "Space" used to be different
5841 to \s, which did not include VT, for Perl compatibility. However, Perl
5842 changed at release 5.18, and PCRE followed at release 8.34. "Space" and
5843 \s now match the same set of characters.
5844
5845 The name "word" is a Perl extension, and "blank" is a GNU extension
5846 from Perl 5.8. Another Perl extension is negation, which is indicated
5847 by a ^ character after the colon. For example,
5848
5849 [12[:^digit:]]
5850
5851 matches "1", "2", or any non-digit. PCRE (and Perl) also recognize the
5852 POSIX syntax [.ch.] and [=ch=] where "ch" is a "collating element", but
5853 these are not supported, and an error is given if they are encountered.
5854
5855 By default, characters with values greater than 128 do not match any of
5856 the POSIX character classes. However, if the PCRE_UCP option is passed
5857 to pcre_compile(), some of the classes are changed so that Unicode
5858 character properties are used. This is achieved by replacing certain
5859 POSIX classes by other sequences, as follows:
5860
5861 [:alnum:] becomes \p{Xan}
5862 [:alpha:] becomes \p{L}
5863 [:blank:] becomes \h
5864 [:digit:] becomes \p{Nd}
5865 [:lower:] becomes \p{Ll}
5866 [:space:] becomes \p{Xps}
5867 [:upper:] becomes \p{Lu}
5868 [:word:] becomes \p{Xwd}
5869
5870 Negated versions, such as [:^alpha:] use \P instead of \p. Three other
5871 POSIX classes are handled specially in UCP mode:
5872
5873 [:graph:] This matches characters that have glyphs that mark the page
5874 when printed. In Unicode property terms, it matches all char-
5875 acters with the L, M, N, P, S, or Cf properties, except for:
5876
5877 U+061C Arabic Letter Mark
5878 U+180E Mongolian Vowel Separator
5879 U+2066 - U+2069 Various "isolate"s
5880
5881
5882 [:print:] This matches the same characters as [:graph:] plus space
5883 characters that are not controls, that is, characters with
5884 the Zs property.
5885
5886 [:punct:] This matches all characters that have the Unicode P (punctua-
5887 tion) property, plus those characters whose code points are
5888 less than 128 that have the S (Symbol) property.
5889
5890 The other POSIX classes are unchanged, and match only characters with
5891 code points less than 128.
5892
5893
5894 VERTICAL BAR
5895
5896 Vertical bar characters are used to separate alternative patterns. For
5897 example, the pattern
5898
5899 gilbert|sullivan
5900
5901 matches either "gilbert" or "sullivan". Any number of alternatives may
5902 appear, and an empty alternative is permitted (matching the empty
5903 string). The matching process tries each alternative in turn, from left
5904 to right, and the first one that succeeds is used. If the alternatives
5905 are within a subpattern (defined below), "succeeds" means matching the
5906 rest of the main pattern as well as the alternative in the subpattern.
5907
5908
5909 INTERNAL OPTION SETTING
5910
5911 The settings of the PCRE_CASELESS, PCRE_MULTILINE, PCRE_DOTALL, and
5912 PCRE_EXTENDED options (which are Perl-compatible) can be changed from
5913 within the pattern by a sequence of Perl option letters enclosed
5914 between "(?" and ")". The option letters are
5915
5916 i for PCRE_CASELESS
5917 m for PCRE_MULTILINE
5918 s for PCRE_DOTALL
5919 x for PCRE_EXTENDED
5920
5921 For example, (?im) sets caseless, multiline matching. It is also possi-
5922 ble to unset these options by preceding the letter with a hyphen, and a
5923 combined setting and unsetting such as (?im-sx), which sets PCRE_CASE-
5924 LESS and PCRE_MULTILINE while unsetting PCRE_DOTALL and PCRE_EXTENDED,
5925 is also permitted. If a letter appears both before and after the
5926 hyphen, the option is unset.
5927
5928 The PCRE-specific options PCRE_DUPNAMES, PCRE_UNGREEDY, and PCRE_EXTRA
5929 can be changed in the same way as the Perl-compatible options by using
5930 the characters J, U and X respectively.
5931
5932 When one of these option changes occurs at top level (that is, not
5933 inside subpattern parentheses), the change applies to the remainder of
5934 the pattern that follows. If the change is placed right at the start of
5935 a pattern, PCRE extracts it into the global options (and it will there-
5936 fore show up in data extracted by the pcre_fullinfo() function).
5937
5938 An option change within a subpattern (see below for a description of
5939 subpatterns) affects only that part of the subpattern that follows it,
5940 so
5941
5942 (a(?i)b)c
5943
5944 matches abc and aBc and no other strings (assuming PCRE_CASELESS is not
5945 used). By this means, options can be made to have different settings
5946 in different parts of the pattern. Any changes made in one alternative
5947 do carry on into subsequent branches within the same subpattern. For
5948 example,
5949
5950 (a(?i)b|c)
5951
5952 matches "ab", "aB", "c", and "C", even though when matching "C" the
5953 first branch is abandoned before the option setting. This is because
5954 the effects of option settings happen at compile time. There would be
5955 some very weird behaviour otherwise.
5956
5957 Note: There are other PCRE-specific options that can be set by the
5958 application when the compiling or matching functions are called. In
5959 some cases the pattern can contain special leading sequences such as
5960 (*CRLF) to override what the application has set or what has been
5961 defaulted. Details are given in the section entitled "Newline
5962 sequences" above. There are also the (*UTF8), (*UTF16),(*UTF32), and
5963 (*UCP) leading sequences that can be used to set UTF and Unicode prop-
5964 erty modes; they are equivalent to setting the PCRE_UTF8, PCRE_UTF16,
5965 PCRE_UTF32 and the PCRE_UCP options, respectively. The (*UTF) sequence
5966 is a generic version that can be used with any of the libraries. How-
5967 ever, the application can set the PCRE_NEVER_UTF option, which locks
5968 out the use of the (*UTF) sequences.
5969
5970
5971 SUBPATTERNS
5972
5973 Subpatterns are delimited by parentheses (round brackets), which can be
5974 nested. Turning part of a pattern into a subpattern does two things:
5975
5976 1. It localizes a set of alternatives. For example, the pattern
5977
5978 cat(aract|erpillar|)
5979
5980 matches "cataract", "caterpillar", or "cat". Without the parentheses,
5981 it would match "cataract", "erpillar" or an empty string.
5982
5983 2. It sets up the subpattern as a capturing subpattern. This means
5984 that, when the whole pattern matches, that portion of the subject
5985 string that matched the subpattern is passed back to the caller via the
5986 ovector argument of the matching function. (This applies only to the
5987 traditional matching functions; the DFA matching functions do not sup-
5988 port capturing.)
5989
5990 Opening parentheses are counted from left to right (starting from 1) to
5991 obtain numbers for the capturing subpatterns. For example, if the
5992 string "the red king" is matched against the pattern
5993
5994 the ((red|white) (king|queen))
5995
5996 the captured substrings are "red king", "red", and "king", and are num-
5997 bered 1, 2, and 3, respectively.
5998
5999 The fact that plain parentheses fulfil two functions is not always
6000 helpful. There are often times when a grouping subpattern is required
6001 without a capturing requirement. If an opening parenthesis is followed
6002 by a question mark and a colon, the subpattern does not do any captur-
6003 ing, and is not counted when computing the number of any subsequent
6004 capturing subpatterns. For example, if the string "the white queen" is
6005 matched against the pattern
6006
6007 the ((?:red|white) (king|queen))
6008
6009 the captured substrings are "white queen" and "queen", and are numbered
6010 1 and 2. The maximum number of capturing subpatterns is 65535.
6011
6012 As a convenient shorthand, if any option settings are required at the
6013 start of a non-capturing subpattern, the option letters may appear
6014 between the "?" and the ":". Thus the two patterns
6015
6016 (?i:saturday|sunday)
6017 (?:(?i)saturday|sunday)
6018
6019 match exactly the same set of strings. Because alternative branches are
6020 tried from left to right, and options are not reset until the end of
6021 the subpattern is reached, an option setting in one branch does affect
6022 subsequent branches, so the above patterns match "SUNDAY" as well as
6023 "Saturday".
6024
6025
6026 DUPLICATE SUBPATTERN NUMBERS
6027
6028 Perl 5.10 introduced a feature whereby each alternative in a subpattern
6029 uses the same numbers for its capturing parentheses. Such a subpattern
6030 starts with (?| and is itself a non-capturing subpattern. For example,
6031 consider this pattern:
6032
6033 (?|(Sat)ur|(Sun))day
6034
6035 Because the two alternatives are inside a (?| group, both sets of cap-
6036 turing parentheses are numbered one. Thus, when the pattern matches,