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