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