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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) PCRE(3)
12
13
14 NAME
15 PCRE - Perl-compatible regular expressions
16
17
18 INTRODUCTION
19
20 The PCRE library is a set of functions that implement regular expres-
21 sion pattern matching using the same syntax and semantics as Perl, with
22 just a few differences. Some features that appeared in Python and PCRE
23 before they appeared in Perl are also available using the Python syn-
24 tax, there is some support for one or two .NET and Oniguruma syntax
25 items, and there is an option for requesting some minor changes that
26 give better JavaScript compatibility.
27
28 Starting with release 8.30, it is possible to compile two separate PCRE
29 libraries: the original, which supports 8-bit character strings
30 (including UTF-8 strings), and a second library that supports 16-bit
31 character strings (including UTF-16 strings). The build process allows
32 either one or both to be built. The majority of the work to make this
33 possible was done by Zoltan Herczeg.
34
35 Starting with release 8.32 it is possible to compile a third separate
36 PCRE library, which supports 32-bit character strings (including UTF-32
37 strings). The build process allows any set of the 8-, 16- and 32-bit
38 libraries. The work to make this possible was done by Christian Persch.
39
40 The three libraries contain identical sets of functions, except that
41 the names in the 16-bit library start with pcre16_ instead of pcre_,
42 and the names in the 32-bit library start with pcre32_ instead of
43 pcre_. To avoid over-complication and reduce the documentation mainte-
44 nance load, most of the documentation describes the 8-bit library, with
45 the differences for the 16-bit and 32-bit libraries described sepa-
46 rately in the pcre16 and pcre32 pages. References to functions or
47 structures of the form pcre[16|32]_xxx should be read as meaning
48 "pcre_xxx when using the 8-bit library, pcre16_xxx when using the
49 16-bit library, or pcre32_xxx when using the 32-bit library".
50
51 The current implementation of PCRE corresponds approximately with Perl
52 5.12, including support for UTF-8/16/32 encoded strings and Unicode
53 general category properties. However, UTF-8/16/32 and Unicode support
54 has to be explicitly enabled; it is not the default. The Unicode tables
55 correspond to Unicode release 6.2.0.
56
57 In addition to the Perl-compatible matching function, PCRE contains an
58 alternative function that matches the same compiled patterns in a dif-
59 ferent way. In certain circumstances, the alternative function has some
60 advantages. For a discussion of the two matching algorithms, see the
61 pcrematching page.
62
63 PCRE is written in C and released as a C library. A number of people
64 have written wrappers and interfaces of various kinds. In particular,
65 Google Inc. have provided a comprehensive C++ wrapper for the 8-bit
66 library. This is now included as part of the PCRE distribution. The
67 pcrecpp page has details of this interface. Other people's contribu-
68 tions can be found in the Contrib directory at the primary FTP site,
69 which is:
70
71 ftp://ftp.csx.cam.ac.uk/pub/software/programming/pcre
72
73 Details of exactly which Perl regular expression features are and are
74 not supported by PCRE are given in separate documents. See the pcrepat-
75 tern and pcrecompat pages. There is a syntax summary in the pcresyntax
76 page.
77
78 Some features of PCRE can be included, excluded, or changed when the
79 library is built. The pcre_config() function makes it possible for a
80 client to discover which features are available. The features them-
81 selves are described in the pcrebuild page. Documentation about build-
82 ing PCRE for various operating systems can be found in the README and
83 NON-AUTOTOOLS_BUILD files in the source distribution.
84
85 The libraries contains a number of undocumented internal functions and
86 data tables that are used by more than one of the exported external
87 functions, but which are not intended for use by external callers.
88 Their names all begin with "_pcre_" or "_pcre16_" or "_pcre32_", which
89 hopefully will not provoke any name clashes. In some environments, it
90 is possible to control which external symbols are exported when a
91 shared library is built, and in these cases the undocumented symbols
92 are not exported.
93
94
95 SECURITY CONSIDERATIONS
96
97 If you are using PCRE in a non-UTF application that permits users to
98 supply arbitrary patterns for compilation, you should be aware of a
99 feature that allows users to turn on UTF support from within a pattern,
100 provided that PCRE was built with UTF support. For example, an 8-bit
101 pattern that begins with "(*UTF8)" or "(*UTF)" turns on UTF-8 mode,
102 which interprets patterns and subjects as strings of UTF-8 characters
103 instead of individual 8-bit characters. This causes both the pattern
104 and any data against which it is matched to be checked for UTF-8 valid-
105 ity. If the data string is very long, such a check might use suffi-
106 ciently many resources as to cause your application to lose perfor-
107 mance.
108
109 The best way of guarding against this possibility is to use the
110 pcre_fullinfo() function to check the compiled pattern's options for
111 UTF.
112
113 If your application is one that supports UTF, be aware that validity
114 checking can take time. If the same data string is to be matched many
115 times, you can use the PCRE_NO_UTF[8|16|32]_CHECK option for the second
116 and subsequent matches to save redundant checks.
117
118 Another way that performance can be hit is by running a pattern that
119 has a very large search tree against a string that will never match.
120 Nested unlimited repeats in a pattern are a common example. PCRE pro-
121 vides some protection against this: see the PCRE_EXTRA_MATCH_LIMIT fea-
122 ture in the pcreapi page.
123
124
125 USER DOCUMENTATION
126
127 The user documentation for PCRE comprises a number of different sec-
128 tions. In the "man" format, each of these is a separate "man page". In
129 the HTML format, each is a separate page, linked from the index page.
130 In the plain text format, all the sections, except the pcredemo sec-
131 tion, are concatenated, for ease of searching. The sections are as fol-
132 lows:
133
134 pcre this document
135 pcre16 details of the 16-bit library
136 pcre32 details of the 32-bit library
137 pcre-config show PCRE installation configuration information
138 pcreapi details of PCRE's native C API
139 pcrebuild options for building PCRE
140 pcrecallout details of the callout feature
141 pcrecompat discussion of Perl compatibility
142 pcrecpp details of the C++ wrapper for the 8-bit library
143 pcredemo a demonstration C program that uses PCRE
144 pcregrep description of the pcregrep command (8-bit only)
145 pcrejit discussion of the just-in-time optimization support
146 pcrelimits details of size and other limits
147 pcrematching discussion of the two matching algorithms
148 pcrepartial details of the partial matching facility
149 pcrepattern syntax and semantics of supported
150 regular expressions
151 pcreperform discussion of performance issues
152 pcreposix the POSIX-compatible C API for the 8-bit library
153 pcreprecompile details of saving and re-using precompiled patterns
154 pcresample discussion of the pcredemo program
155 pcrestack discussion of stack usage
156 pcresyntax quick syntax reference
157 pcretest description of the pcretest testing command
158 pcreunicode discussion of Unicode and UTF-8/16/32 support
159
160 In addition, in the "man" and HTML formats, there is a short page for
161 each C library function, listing its arguments and results.
162
163
164 AUTHOR
165
166 Philip Hazel
167 University Computing Service
168 Cambridge CB2 3QH, England.
169
170 Putting an actual email address here seems to have been a spam magnet,
171 so I've taken it away. If you want to email me, use my two initials,
172 followed by the two digits 10, at the domain cam.ac.uk.
173
174
175 REVISION
176
177 Last updated: 11 November 2012
178 Copyright (c) 1997-2012 University of Cambridge.
179 ------------------------------------------------------------------------------
180
181
182 PCRE(3) PCRE(3)
183
184
185 NAME
186 PCRE - Perl-compatible regular expressions
187
188 #include <pcre.h>
189
190
191 PCRE 16-BIT API BASIC FUNCTIONS
192
193 pcre16 *pcre16_compile(PCRE_SPTR16 pattern, int options,
194 const char **errptr, int *erroffset,
195 const unsigned char *tableptr);
196
197 pcre16 *pcre16_compile2(PCRE_SPTR16 pattern, int options,
198 int *errorcodeptr,
199 const char **errptr, int *erroffset,
200 const unsigned char *tableptr);
201
202 pcre16_extra *pcre16_study(const pcre16 *code, int options,
203 const char **errptr);
204
205 void pcre16_free_study(pcre16_extra *extra);
206
207 int pcre16_exec(const pcre16 *code, const pcre16_extra *extra,
208 PCRE_SPTR16 subject, int length, int startoffset,
209 int options, int *ovector, int ovecsize);
210
211 int pcre16_dfa_exec(const pcre16 *code, const pcre16_extra *extra,
212 PCRE_SPTR16 subject, int length, int startoffset,
213 int options, int *ovector, int ovecsize,
214 int *workspace, int wscount);
215
216
217 PCRE 16-BIT API STRING EXTRACTION FUNCTIONS
218
219 int pcre16_copy_named_substring(const pcre16 *code,
220 PCRE_SPTR16 subject, int *ovector,
221 int stringcount, PCRE_SPTR16 stringname,
222 PCRE_UCHAR16 *buffer, int buffersize);
223
224 int pcre16_copy_substring(PCRE_SPTR16 subject, int *ovector,
225 int stringcount, int stringnumber, PCRE_UCHAR16 *buffer,
226 int buffersize);
227
228 int pcre16_get_named_substring(const pcre16 *code,
229 PCRE_SPTR16 subject, int *ovector,
230 int stringcount, PCRE_SPTR16 stringname,
231 PCRE_SPTR16 *stringptr);
232
233 int pcre16_get_stringnumber(const pcre16 *code,
234 PCRE_SPTR16 name);
235
236 int pcre16_get_stringtable_entries(const pcre16 *code,
237 PCRE_SPTR16 name, PCRE_UCHAR16 **first, PCRE_UCHAR16 **last);
238
239 int pcre16_get_substring(PCRE_SPTR16 subject, int *ovector,
240 int stringcount, int stringnumber,
241 PCRE_SPTR16 *stringptr);
242
243 int pcre16_get_substring_list(PCRE_SPTR16 subject,
244 int *ovector, int stringcount, PCRE_SPTR16 **listptr);
245
246 void pcre16_free_substring(PCRE_SPTR16 stringptr);
247
248 void pcre16_free_substring_list(PCRE_SPTR16 *stringptr);
249
250
251 PCRE 16-BIT API AUXILIARY FUNCTIONS
252
253 pcre16_jit_stack *pcre16_jit_stack_alloc(int startsize, int maxsize);
254
255 void pcre16_jit_stack_free(pcre16_jit_stack *stack);
256
257 void pcre16_assign_jit_stack(pcre16_extra *extra,
258 pcre16_jit_callback callback, void *data);
259
260 const unsigned char *pcre16_maketables(void);
261
262 int pcre16_fullinfo(const pcre16 *code, const pcre16_extra *extra,
263 int what, void *where);
264
265 int pcre16_refcount(pcre16 *code, int adjust);
266
267 int pcre16_config(int what, void *where);
268
269 const char *pcre16_version(void);
270
271 int pcre16_pattern_to_host_byte_order(pcre16 *code,
272 pcre16_extra *extra, const unsigned char *tables);
273
274
275 PCRE 16-BIT API INDIRECTED FUNCTIONS
276
277 void *(*pcre16_malloc)(size_t);
278
279 void (*pcre16_free)(void *);
280
281 void *(*pcre16_stack_malloc)(size_t);
282
283 void (*pcre16_stack_free)(void *);
284
285 int (*pcre16_callout)(pcre16_callout_block *);
286
287
288 PCRE 16-BIT API 16-BIT-ONLY FUNCTION
289
290 int pcre16_utf16_to_host_byte_order(PCRE_UCHAR16 *output,
291 PCRE_SPTR16 input, int length, int *byte_order,
292 int keep_boms);
293
294
295 THE PCRE 16-BIT LIBRARY
296
297 Starting with release 8.30, it is possible to compile a PCRE library
298 that supports 16-bit character strings, including UTF-16 strings, as
299 well as or instead of the original 8-bit library. The majority of the
300 work to make this possible was done by Zoltan Herczeg. The two
301 libraries contain identical sets of functions, used in exactly the same
302 way. Only the names of the functions and the data types of their argu-
303 ments and results are different. To avoid over-complication and reduce
304 the documentation maintenance load, most of the PCRE documentation
305 describes the 8-bit library, with only occasional references to the
306 16-bit library. This page describes what is different when you use the
307 16-bit library.
308
309 WARNING: A single application can be linked with both libraries, but
310 you must take care when processing any particular pattern to use func-
311 tions from just one library. For example, if you want to study a pat-
312 tern that was compiled with pcre16_compile(), you must do so with
313 pcre16_study(), not pcre_study(), and you must free the study data with
314 pcre16_free_study().
315
316
317 THE HEADER FILE
318
319 There is only one header file, pcre.h. It contains prototypes for all
320 the functions in all libraries, as well as definitions of flags, struc-
321 tures, error codes, etc.
322
323
324 THE LIBRARY NAME
325
326 In Unix-like systems, the 16-bit library is called libpcre16, and can
327 normally be accesss by adding -lpcre16 to the command for linking an
328 application that uses PCRE.
329
330
331 STRING TYPES
332
333 In the 8-bit library, strings are passed to PCRE library functions as
334 vectors of bytes with the C type "char *". In the 16-bit library,
335 strings are passed as vectors of unsigned 16-bit quantities. The macro
336 PCRE_UCHAR16 specifies an appropriate data type, and PCRE_SPTR16 is
337 defined as "const PCRE_UCHAR16 *". In very many environments, "short
338 int" is a 16-bit data type. When PCRE is built, it defines PCRE_UCHAR16
339 as "unsigned short int", but checks that it really is a 16-bit data
340 type. If it is not, the build fails with an error message telling the
341 maintainer to modify the definition appropriately.
342
343
344 STRUCTURE TYPES
345
346 The types of the opaque structures that are used for compiled 16-bit
347 patterns and JIT stacks are pcre16 and pcre16_jit_stack respectively.
348 The type of the user-accessible structure that is returned by
349 pcre16_study() is pcre16_extra, and the type of the structure that is
350 used for passing data to a callout function is pcre16_callout_block.
351 These structures contain the same fields, with the same names, as their
352 8-bit counterparts. The only difference is that pointers to character
353 strings are 16-bit instead of 8-bit types.
354
355
356 16-BIT FUNCTIONS
357
358 For every function in the 8-bit library there is a corresponding func-
359 tion in the 16-bit library with a name that starts with pcre16_ instead
360 of pcre_. The prototypes are listed above. In addition, there is one
361 extra function, pcre16_utf16_to_host_byte_order(). This is a utility
362 function that converts a UTF-16 character string to host byte order if
363 necessary. The other 16-bit functions expect the strings they are
364 passed to be in host byte order.
365
366 The input and output arguments of pcre16_utf16_to_host_byte_order() may
367 point to the same address, that is, conversion in place is supported.
368 The output buffer must be at least as long as the input.
369
370 The length argument specifies the number of 16-bit data units in the
371 input string; a negative value specifies a zero-terminated string.
372
373 If byte_order is NULL, it is assumed that the string starts off in host
374 byte order. This may be changed by byte-order marks (BOMs) anywhere in
375 the string (commonly as the first character).
376
377 If byte_order is not NULL, a non-zero value of the integer to which it
378 points means that the input starts off in host byte order, otherwise
379 the opposite order is assumed. Again, BOMs in the string can change
380 this. The final byte order is passed back at the end of processing.
381
382 If keep_boms is not zero, byte-order mark characters (0xfeff) are
383 copied into the output string. Otherwise they are discarded.
384
385 The result of the function is the number of 16-bit units placed into
386 the output buffer, including the zero terminator if the string was
387 zero-terminated.
388
389
390 SUBJECT STRING OFFSETS
391
392 The offsets within subject strings that are returned by the matching
393 functions are in 16-bit units rather than bytes.
394
395
396 NAMED SUBPATTERNS
397
398 The name-to-number translation table that is maintained for named sub-
399 patterns uses 16-bit characters. The pcre16_get_stringtable_entries()
400 function returns the length of each entry in the table as the number of
401 16-bit data units.
402
403
404 OPTION NAMES
405
406 There are two new general option names, PCRE_UTF16 and
407 PCRE_NO_UTF16_CHECK, which correspond to PCRE_UTF8 and
408 PCRE_NO_UTF8_CHECK in the 8-bit library. In fact, these new options
409 define the same bits in the options word. There is a discussion about
410 the validity of UTF-16 strings in the pcreunicode page.
411
412 For the pcre16_config() function there is an option PCRE_CONFIG_UTF16
413 that returns 1 if UTF-16 support is configured, otherwise 0. If this
414 option is given to pcre_config() or pcre32_config(), or if the
415 PCRE_CONFIG_UTF8 or PCRE_CONFIG_UTF32 option is given to pcre16_con-
416 fig(), the result is the PCRE_ERROR_BADOPTION error.
417
418
419 CHARACTER CODES
420
421 In 16-bit mode, when PCRE_UTF16 is not set, character values are
422 treated in the same way as in 8-bit, non UTF-8 mode, except, of course,
423 that they can range from 0 to 0xffff instead of 0 to 0xff. Character
424 types for characters less than 0xff can therefore be influenced by the
425 locale in the same way as before. Characters greater than 0xff have
426 only one case, and no "type" (such as letter or digit).
427
428 In UTF-16 mode, the character code is Unicode, in the range 0 to
429 0x10ffff, with the exception of values in the range 0xd800 to 0xdfff
430 because those are "surrogate" values that are used in pairs to encode
431 values greater than 0xffff.
432
433 A UTF-16 string can indicate its endianness by special code knows as a
434 byte-order mark (BOM). The PCRE functions do not handle this, expecting
435 strings to be in host byte order. A utility function called
436 pcre16_utf16_to_host_byte_order() is provided to help with this (see
437 above).
438
439
440 ERROR NAMES
441
442 The errors PCRE_ERROR_BADUTF16_OFFSET and PCRE_ERROR_SHORTUTF16 corre-
443 spond to their 8-bit counterparts. The error PCRE_ERROR_BADMODE is
444 given when a compiled pattern is passed to a function that processes
445 patterns in the other mode, for example, if a pattern compiled with
446 pcre_compile() is passed to pcre16_exec().
447
448 There are new error codes whose names begin with PCRE_UTF16_ERR for
449 invalid UTF-16 strings, corresponding to the PCRE_UTF8_ERR codes for
450 UTF-8 strings that are described in the section entitled "Reason codes
451 for invalid UTF-8 strings" in the main pcreapi page. The UTF-16 errors
452 are:
453
454 PCRE_UTF16_ERR1 Missing low surrogate at end of string
455 PCRE_UTF16_ERR2 Invalid low surrogate follows high surrogate
456 PCRE_UTF16_ERR3 Isolated low surrogate
457 PCRE_UTF16_ERR4 Non-character
458
459
460 ERROR TEXTS
461
462 If there is an error while compiling a pattern, the error text that is
463 passed back by pcre16_compile() or pcre16_compile2() is still an 8-bit
464 character string, zero-terminated.
465
466
467 CALLOUTS
468
469 The subject and mark fields in the callout block that is passed to a
470 callout function point to 16-bit vectors.
471
472
473 TESTING
474
475 The pcretest program continues to operate with 8-bit input and output
476 files, but it can be used for testing the 16-bit library. If it is run
477 with the command line option -16, patterns and subject strings are con-
478 verted from 8-bit to 16-bit before being passed to PCRE, and the 16-bit
479 library functions are used instead of the 8-bit ones. Returned 16-bit
480 strings are converted to 8-bit for output. If both the 8-bit and the
481 32-bit libraries were not compiled, pcretest defaults to 16-bit and the
482 -16 option is ignored.
483
484 When PCRE is being built, the RunTest script that is called by "make
485 check" uses the pcretest -C option to discover which of the 8-bit,
486 16-bit and 32-bit libraries has been built, and runs the tests appro-
487 priately.
488
489
490 NOT SUPPORTED IN 16-BIT MODE
491
492 Not all the features of the 8-bit library are available with the 16-bit
493 library. The C++ and POSIX wrapper functions support only the 8-bit
494 library, and the pcregrep program is at present 8-bit only.
495
496
497 AUTHOR
498
499 Philip Hazel
500 University Computing Service
501 Cambridge CB2 3QH, England.
502
503
504 REVISION
505
506 Last updated: 08 November 2012
507 Copyright (c) 1997-2012 University of Cambridge.
508 ------------------------------------------------------------------------------
509
510
511 PCRE(3) PCRE(3)
512
513
514 NAME
515 PCRE - Perl-compatible regular expressions
516
517 #include <pcre.h>
518
519
520 PCRE 32-BIT API BASIC FUNCTIONS
521
522 pcre32 *pcre32_compile(PCRE_SPTR32 pattern, int options,
523 const char **errptr, int *erroffset,
524 const unsigned char *tableptr);
525
526 pcre32 *pcre32_compile2(PCRE_SPTR32 pattern, int options,
527 int *errorcodeptr,
528 const char **errptr, int *erroffset,
529 const unsigned char *tableptr);
530
531 pcre32_extra *pcre32_study(const pcre32 *code, int options,
532 const char **errptr);
533
534 void pcre32_free_study(pcre32_extra *extra);
535
536 int pcre32_exec(const pcre32 *code, const pcre32_extra *extra,
537 PCRE_SPTR32 subject, int length, int startoffset,
538 int options, int *ovector, int ovecsize);
539
540 int pcre32_dfa_exec(const pcre32 *code, const pcre32_extra *extra,
541 PCRE_SPTR32 subject, int length, int startoffset,
542 int options, int *ovector, int ovecsize,
543 int *workspace, int wscount);
544
545
546 PCRE 32-BIT API STRING EXTRACTION FUNCTIONS
547
548 int pcre32_copy_named_substring(const pcre32 *code,
549 PCRE_SPTR32 subject, int *ovector,
550 int stringcount, PCRE_SPTR32 stringname,
551 PCRE_UCHAR32 *buffer, int buffersize);
552
553 int pcre32_copy_substring(PCRE_SPTR32 subject, int *ovector,
554 int stringcount, int stringnumber, PCRE_UCHAR32 *buffer,
555 int buffersize);
556
557 int pcre32_get_named_substring(const pcre32 *code,
558 PCRE_SPTR32 subject, int *ovector,
559 int stringcount, PCRE_SPTR32 stringname,
560 PCRE_SPTR32 *stringptr);
561
562 int pcre32_get_stringnumber(const pcre32 *code,
563 PCRE_SPTR32 name);
564
565 int pcre32_get_stringtable_entries(const pcre32 *code,
566 PCRE_SPTR32 name, PCRE_UCHAR32 **first, PCRE_UCHAR32 **last);
567
568 int pcre32_get_substring(PCRE_SPTR32 subject, int *ovector,
569 int stringcount, int stringnumber,
570 PCRE_SPTR32 *stringptr);
571
572 int pcre32_get_substring_list(PCRE_SPTR32 subject,
573 int *ovector, int stringcount, PCRE_SPTR32 **listptr);
574
575 void pcre32_free_substring(PCRE_SPTR32 stringptr);
576
577 void pcre32_free_substring_list(PCRE_SPTR32 *stringptr);
578
579
580 PCRE 32-BIT API AUXILIARY FUNCTIONS
581
582 pcre32_jit_stack *pcre32_jit_stack_alloc(int startsize, int maxsize);
583
584 void pcre32_jit_stack_free(pcre32_jit_stack *stack);
585
586 void pcre32_assign_jit_stack(pcre32_extra *extra,
587 pcre32_jit_callback callback, void *data);
588
589 const unsigned char *pcre32_maketables(void);
590
591 int pcre32_fullinfo(const pcre32 *code, const pcre32_extra *extra,
592 int what, void *where);
593
594 int pcre32_refcount(pcre32 *code, int adjust);
595
596 int pcre32_config(int what, void *where);
597
598 const char *pcre32_version(void);
599
600 int pcre32_pattern_to_host_byte_order(pcre32 *code,
601 pcre32_extra *extra, const unsigned char *tables);
602
603
604 PCRE 32-BIT API INDIRECTED FUNCTIONS
605
606 void *(*pcre32_malloc)(size_t);
607
608 void (*pcre32_free)(void *);
609
610 void *(*pcre32_stack_malloc)(size_t);
611
612 void (*pcre32_stack_free)(void *);
613
614 int (*pcre32_callout)(pcre32_callout_block *);
615
616
617 PCRE 32-BIT API 32-BIT-ONLY FUNCTION
618
619 int pcre32_utf32_to_host_byte_order(PCRE_UCHAR32 *output,
620 PCRE_SPTR32 input, int length, int *byte_order,
621 int keep_boms);
622
623
624 THE PCRE 32-BIT LIBRARY
625
626 Starting with release 8.32, it is possible to compile a PCRE library
627 that supports 32-bit character strings, including UTF-32 strings, as
628 well as or instead of the original 8-bit library. This work was done by
629 Christian Persch, based on the work done by Zoltan Herczeg for the
630 16-bit library. All three libraries contain identical sets of func-
631 tions, used in exactly the same way. Only the names of the functions
632 and the data types of their arguments and results are different. To
633 avoid over-complication and reduce the documentation maintenance load,
634 most of the PCRE documentation describes the 8-bit library, with only
635 occasional references to the 16-bit and 32-bit libraries. This page
636 describes what is different when you use the 32-bit library.
637
638 WARNING: A single application can be linked with all or any of the
639 three libraries, but you must take care when processing any particular
640 pattern to use functions from just one library. For example, if you
641 want to study a pattern that was compiled with pcre32_compile(), you
642 must do so with pcre32_study(), not pcre_study(), and you must free the
643 study data with pcre32_free_study().
644
645
646 THE HEADER FILE
647
648 There is only one header file, pcre.h. It contains prototypes for all
649 the functions in all libraries, as well as definitions of flags, struc-
650 tures, error codes, etc.
651
652
653 THE LIBRARY NAME
654
655 In Unix-like systems, the 32-bit library is called libpcre32, and can
656 normally be accesss by adding -lpcre32 to the command for linking an
657 application that uses PCRE.
658
659
660 STRING TYPES
661
662 In the 8-bit library, strings are passed to PCRE library functions as
663 vectors of bytes with the C type "char *". In the 32-bit library,
664 strings are passed as vectors of unsigned 32-bit quantities. The macro
665 PCRE_UCHAR32 specifies an appropriate data type, and PCRE_SPTR32 is
666 defined as "const PCRE_UCHAR32 *". In very many environments, "unsigned
667 int" is a 32-bit data type. When PCRE is built, it defines PCRE_UCHAR32
668 as "unsigned int", but checks that it really is a 32-bit data type. If
669 it is not, the build fails with an error message telling the maintainer
670 to modify the definition appropriately.
671
672
673 STRUCTURE TYPES
674
675 The types of the opaque structures that are used for compiled 32-bit
676 patterns and JIT stacks are pcre32 and pcre32_jit_stack respectively.
677 The type of the user-accessible structure that is returned by
678 pcre32_study() is pcre32_extra, and the type of the structure that is
679 used for passing data to a callout function is pcre32_callout_block.
680 These structures contain the same fields, with the same names, as their
681 8-bit counterparts. The only difference is that pointers to character
682 strings are 32-bit instead of 8-bit types.
683
684
685 32-BIT FUNCTIONS
686
687 For every function in the 8-bit library there is a corresponding func-
688 tion in the 32-bit library with a name that starts with pcre32_ instead
689 of pcre_. The prototypes are listed above. In addition, there is one
690 extra function, pcre32_utf32_to_host_byte_order(). This is a utility
691 function that converts a UTF-32 character string to host byte order if
692 necessary. The other 32-bit functions expect the strings they are
693 passed to be in host byte order.
694
695 The input and output arguments of pcre32_utf32_to_host_byte_order() may
696 point to the same address, that is, conversion in place is supported.
697 The output buffer must be at least as long as the input.
698
699 The length argument specifies the number of 32-bit data units in the
700 input string; a negative value specifies a zero-terminated string.
701
702 If byte_order is NULL, it is assumed that the string starts off in host
703 byte order. This may be changed by byte-order marks (BOMs) anywhere in
704 the string (commonly as the first character).
705
706 If byte_order is not NULL, a non-zero value of the integer to which it
707 points means that the input starts off in host byte order, otherwise
708 the opposite order is assumed. Again, BOMs in the string can change
709 this. The final byte order is passed back at the end of processing.
710
711 If keep_boms is not zero, byte-order mark characters (0xfeff) are
712 copied into the output string. Otherwise they are discarded.
713
714 The result of the function is the number of 32-bit units placed into
715 the output buffer, including the zero terminator if the string was
716 zero-terminated.
717
718
719 SUBJECT STRING OFFSETS
720
721 The offsets within subject strings that are returned by the matching
722 functions are in 32-bit units rather than bytes.
723
724
725 NAMED SUBPATTERNS
726
727 The name-to-number translation table that is maintained for named sub-
728 patterns uses 32-bit characters. The pcre32_get_stringtable_entries()
729 function returns the length of each entry in the table as the number of
730 32-bit data units.
731
732
733 OPTION NAMES
734
735 There are two new general option names, PCRE_UTF32 and
736 PCRE_NO_UTF32_CHECK, which correspond to PCRE_UTF8 and
737 PCRE_NO_UTF8_CHECK in the 8-bit library. In fact, these new options
738 define the same bits in the options word. There is a discussion about
739 the validity of UTF-32 strings in the pcreunicode page.
740
741 For the pcre32_config() function there is an option PCRE_CONFIG_UTF32
742 that returns 1 if UTF-32 support is configured, otherwise 0. If this
743 option is given to pcre_config() or pcre16_config(), or if the
744 PCRE_CONFIG_UTF8 or PCRE_CONFIG_UTF16 option is given to pcre32_con-
745 fig(), the result is the PCRE_ERROR_BADOPTION error.
746
747
748 CHARACTER CODES
749
750 In 32-bit mode, when PCRE_UTF32 is not set, character values are
751 treated in the same way as in 8-bit, non UTF-8 mode, except, of course,
752 that they can range from 0 to 0x7fffffff instead of 0 to 0xff. Charac-
753 ter types for characters less than 0xff can therefore be influenced by
754 the locale in the same way as before. Characters greater than 0xff
755 have only one case, and no "type" (such as letter or digit).
756
757 In UTF-32 mode, the character code is Unicode, in the range 0 to
758 0x10ffff, with the exception of values in the range 0xd800 to 0xdfff
759 because those are "surrogate" values that are ill-formed in UTF-32.
760
761 A UTF-32 string can indicate its endianness by special code knows as a
762 byte-order mark (BOM). The PCRE functions do not handle this, expecting
763 strings to be in host byte order. A utility function called
764 pcre32_utf32_to_host_byte_order() is provided to help with this (see
765 above).
766
767
768 ERROR NAMES
769
770 The error PCRE_ERROR_BADUTF32 corresponds to its 8-bit counterpart.
771 The error PCRE_ERROR_BADMODE is given when a compiled pattern is passed
772 to a function that processes patterns in the other mode, for example,
773 if a pattern compiled with pcre_compile() is passed to pcre32_exec().
774
775 There are new error codes whose names begin with PCRE_UTF32_ERR for
776 invalid UTF-32 strings, corresponding to the PCRE_UTF8_ERR codes for
777 UTF-8 strings that are described in the section entitled "Reason codes
778 for invalid UTF-8 strings" in the main pcreapi page. The UTF-32 errors
779 are:
780
781 PCRE_UTF32_ERR1 Surrogate character (range from 0xd800 to 0xdfff)
782 PCRE_UTF32_ERR2 Non-character
783 PCRE_UTF32_ERR3 Character > 0x10ffff
784
785
786 ERROR TEXTS
787
788 If there is an error while compiling a pattern, the error text that is
789 passed back by pcre32_compile() or pcre32_compile2() is still an 8-bit
790 character string, zero-terminated.
791
792
793 CALLOUTS
794
795 The subject and mark fields in the callout block that is passed to a
796 callout function point to 32-bit vectors.
797
798
799 TESTING
800
801 The pcretest program continues to operate with 8-bit input and output
802 files, but it can be used for testing the 32-bit library. If it is run
803 with the command line option -32, patterns and subject strings are con-
804 verted from 8-bit to 32-bit before being passed to PCRE, and the 32-bit
805 library functions are used instead of the 8-bit ones. Returned 32-bit
806 strings are converted to 8-bit for output. If both the 8-bit and the
807 16-bit libraries were not compiled, pcretest defaults to 32-bit and the
808 -32 option is ignored.
809
810 When PCRE is being built, the RunTest script that is called by "make
811 check" uses the pcretest -C option to discover which of the 8-bit,
812 16-bit and 32-bit libraries has been built, and runs the tests appro-
813 priately.
814
815
816 NOT SUPPORTED IN 32-BIT MODE
817
818 Not all the features of the 8-bit library are available with the 32-bit
819 library. The C++ and POSIX wrapper functions support only the 8-bit
820 library, and the pcregrep program is at present 8-bit only.
821
822
823 AUTHOR
824
825 Philip Hazel
826 University Computing Service
827 Cambridge CB2 3QH, England.
828
829
830 REVISION
831
832 Last updated: 08 November 2012
833 Copyright (c) 1997-2012 University of Cambridge.
834 ------------------------------------------------------------------------------
835
836
837 PCREBUILD(3) PCREBUILD(3)
838
839
840 NAME
841 PCRE - Perl-compatible regular expressions
842
843
844 PCRE BUILD-TIME OPTIONS
845
846 This document describes the optional features of PCRE that can be
847 selected when the library is compiled. It assumes use of the configure
848 script, where the optional features are selected or deselected by pro-
849 viding options to configure before running the make command. However,
850 the same options can be selected in both Unix-like and non-Unix-like
851 environments using the GUI facility of cmake-gui if you are using CMake
852 instead of configure to build PCRE.
853
854 There is a lot more information about building PCRE without using con-
855 figure (including information about using CMake or building "by hand")
856 in the file called NON-AUTOTOOLS-BUILD, which is part of the PCRE dis-
857 tribution. You should consult this file as well as the README file if
858 you are building in a non-Unix-like environment.
859
860 The complete list of options for configure (which includes the standard
861 ones such as the selection of the installation directory) can be
862 obtained by running
863
864 ./configure --help
865
866 The following sections include descriptions of options whose names
867 begin with --enable or --disable. These settings specify changes to the
868 defaults for the configure command. Because of the way that configure
869 works, --enable and --disable always come in pairs, so the complemen-
870 tary option always exists as well, but as it specifies the default, it
871 is not described.
872
873
874 BUILDING 8-BIT, 16-BIT AND 32-BIT LIBRARIES
875
876 By default, a library called libpcre is built, containing functions
877 that take string arguments contained in vectors of bytes, either as
878 single-byte characters, or interpreted as UTF-8 strings. You can also
879 build a separate library, called libpcre16, in which strings are con-
880 tained in vectors of 16-bit data units and interpreted either as sin-
881 gle-unit characters or UTF-16 strings, by adding
882
883 --enable-pcre16
884
885 to the configure command. You can also build a separate library, called
886 libpcre32, in which strings are contained in vectors of 32-bit data
887 units and interpreted either as single-unit characters or UTF-32
888 strings, by adding
889
890 --enable-pcre32
891
892 to the configure command. If you do not want the 8-bit library, add
893
894 --disable-pcre8
895
896 as well. At least one of the three libraries must be built. Note that
897 the C++ and POSIX wrappers are for the 8-bit library only, and that
898 pcregrep is an 8-bit program. None of these are built if you select
899 only the 16-bit or 32-bit libraries.
900
901
902 BUILDING SHARED AND STATIC LIBRARIES
903
904 The PCRE building process uses libtool to build both shared and static
905 Unix libraries by default. You can suppress one of these by adding one
906 of
907
908 --disable-shared
909 --disable-static
910
911 to the configure command, as required.
912
913
914 C++ SUPPORT
915
916 By default, if the 8-bit library is being built, the configure script
917 will search for a C++ compiler and C++ header files. If it finds them,
918 it automatically builds the C++ wrapper library (which supports only
919 8-bit strings). You can disable this by adding
920
921 --disable-cpp
922
923 to the configure command.
924
925
926 UTF-8, UTF-16 AND UTF-32 SUPPORT
927
928 To build PCRE with support for UTF Unicode character strings, add
929
930 --enable-utf
931
932 to the configure command. This setting applies to all three libraries,
933 adding support for UTF-8 to the 8-bit library, support for UTF-16 to
934 the 16-bit library, and support for UTF-32 to the to the 32-bit
935 library. There are no separate options for enabling UTF-8, UTF-16 and
936 UTF-32 independently because that would allow ridiculous settings such
937 as requesting UTF-16 support while building only the 8-bit library. It
938 is not possible to build one library with UTF support and another with-
939 out in the same configuration. (For backwards compatibility, --enable-
940 utf8 is a synonym of --enable-utf.)
941
942 Of itself, this setting does not make PCRE treat strings as UTF-8,
943 UTF-16 or UTF-32. As well as compiling PCRE with this option, you also
944 have have to set the PCRE_UTF8, PCRE_UTF16 or PCRE_UTF32 option (as
945 appropriate) when you call one of the pattern compiling functions.
946
947 If you set --enable-utf when compiling in an EBCDIC environment, PCRE
948 expects its input to be either ASCII or UTF-8 (depending on the run-
949 time option). It is not possible to support both EBCDIC and UTF-8 codes
950 in the same version of the library. Consequently, --enable-utf and
951 --enable-ebcdic are mutually exclusive.
952
953
954 UNICODE CHARACTER PROPERTY SUPPORT
955
956 UTF support allows the libraries to process character codepoints up to
957 0x10ffff in the strings that they handle. On its own, however, it does
958 not provide any facilities for accessing the properties of such charac-
959 ters. If you want to be able to use the pattern escapes \P, \p, and \X,
960 which refer to Unicode character properties, you must add
961
962 --enable-unicode-properties
963
964 to the configure command. This implies UTF support, even if you have
965 not explicitly requested it.
966
967 Including Unicode property support adds around 30K of tables to the
968 PCRE library. Only the general category properties such as Lu and Nd
969 are supported. Details are given in the pcrepattern documentation.
970
971
972 JUST-IN-TIME COMPILER SUPPORT
973
974 Just-in-time compiler support is included in the build by specifying
975
976 --enable-jit
977
978 This support is available only for certain hardware architectures. If
979 this option is set for an unsupported architecture, a compile time
980 error occurs. See the pcrejit documentation for a discussion of JIT
981 usage. When JIT support is enabled, pcregrep automatically makes use of
982 it, unless you add
983
984 --disable-pcregrep-jit
985
986 to the "configure" command.
987
988
989 CODE VALUE OF NEWLINE
990
991 By default, PCRE interprets the linefeed (LF) character as indicating
992 the end of a line. This is the normal newline character on Unix-like
993 systems. You can compile PCRE to use carriage return (CR) instead, by
994 adding
995
996 --enable-newline-is-cr
997
998 to the configure command. There is also a --enable-newline-is-lf
999 option, which explicitly specifies linefeed as the newline character.
1000
1001 Alternatively, you can specify that line endings are to be indicated by
1002 the two character sequence CRLF. If you want this, add
1003
1004 --enable-newline-is-crlf
1005
1006 to the configure command. There is a fourth option, specified by
1007
1008 --enable-newline-is-anycrlf
1009
1010 which causes PCRE to recognize any of the three sequences CR, LF, or
1011 CRLF as indicating a line ending. Finally, a fifth option, specified by
1012
1013 --enable-newline-is-any
1014
1015 causes PCRE to recognize any Unicode newline sequence.
1016
1017 Whatever line ending convention is selected when PCRE is built can be
1018 overridden when the library functions are called. At build time it is
1019 conventional to use the standard for your operating system.
1020
1021
1022 WHAT \R MATCHES
1023
1024 By default, the sequence \R in a pattern matches any Unicode newline
1025 sequence, whatever has been selected as the line ending sequence. If
1026 you specify
1027
1028 --enable-bsr-anycrlf
1029
1030 the default is changed so that \R matches only CR, LF, or CRLF. What-
1031 ever is selected when PCRE is built can be overridden when the library
1032 functions are called.
1033
1034
1035 POSIX MALLOC USAGE
1036
1037 When the 8-bit library is called through the POSIX interface (see the
1038 pcreposix documentation), additional working storage is required for
1039 holding the pointers to capturing substrings, because PCRE requires
1040 three integers per substring, whereas the POSIX interface provides only
1041 two. If the number of expected substrings is small, the wrapper func-
1042 tion uses space on the stack, because this is faster than using mal-
1043 loc() for each call. The default threshold above which the stack is no
1044 longer used is 10; it can be changed by adding a setting such as
1045
1046 --with-posix-malloc-threshold=20
1047
1048 to the configure command.
1049
1050
1051 HANDLING VERY LARGE PATTERNS
1052
1053 Within a compiled pattern, offset values are used to point from one
1054 part to another (for example, from an opening parenthesis to an alter-
1055 nation metacharacter). By default, in the 8-bit and 16-bit libraries,
1056 two-byte values are used for these offsets, leading to a maximum size
1057 for a compiled pattern of around 64K. This is sufficient to handle all
1058 but the most gigantic patterns. Nevertheless, some people do want to
1059 process truly enormous patterns, so it is possible to compile PCRE to
1060 use three-byte or four-byte offsets by adding a setting such as
1061
1062 --with-link-size=3
1063
1064 to the configure command. The value given must be 2, 3, or 4. For the
1065 16-bit library, a value of 3 is rounded up to 4. In these libraries,
1066 using longer offsets slows down the operation of PCRE because it has to
1067 load additional data when handling them. For the 32-bit library the
1068 value is always 4 and cannot be overridden; the value of --with-link-
1069 size is ignored.
1070
1071
1072 AVOIDING EXCESSIVE STACK USAGE
1073
1074 When matching with the pcre_exec() function, PCRE implements backtrack-
1075 ing by making recursive calls to an internal function called match().
1076 In environments where the size of the stack is limited, this can se-
1077 verely limit PCRE's operation. (The Unix environment does not usually
1078 suffer from this problem, but it may sometimes be necessary to increase
1079 the maximum stack size. There is a discussion in the pcrestack docu-
1080 mentation.) An alternative approach to recursion that uses memory from
1081 the heap to remember data, instead of using recursive function calls,
1082 has been implemented to work round the problem of limited stack size.
1083 If you want to build a version of PCRE that works this way, add
1084
1085 --disable-stack-for-recursion
1086
1087 to the configure command. With this configuration, PCRE will use the
1088 pcre_stack_malloc and pcre_stack_free variables to call memory manage-
1089 ment functions. By default these point to malloc() and free(), but you
1090 can replace the pointers so that your own functions are used instead.
1091
1092 Separate functions are provided rather than using pcre_malloc and
1093 pcre_free because the usage is very predictable: the block sizes
1094 requested are always the same, and the blocks are always freed in
1095 reverse order. A calling program might be able to implement optimized
1096 functions that perform better than malloc() and free(). PCRE runs
1097 noticeably more slowly when built in this way. This option affects only
1098 the pcre_exec() function; it is not relevant for pcre_dfa_exec().
1099
1100
1101 LIMITING PCRE RESOURCE USAGE
1102
1103 Internally, PCRE has a function called match(), which it calls repeat-
1104 edly (sometimes recursively) when matching a pattern with the
1105 pcre_exec() function. By controlling the maximum number of times this
1106 function may be called during a single matching operation, a limit can
1107 be placed on the resources used by a single call to pcre_exec(). The
1108 limit can be changed at run time, as described in the pcreapi documen-
1109 tation. The default is 10 million, but this can be changed by adding a
1110 setting such as
1111
1112 --with-match-limit=500000
1113
1114 to the configure command. This setting has no effect on the
1115 pcre_dfa_exec() matching function.
1116
1117 In some environments it is desirable to limit the depth of recursive
1118 calls of match() more strictly than the total number of calls, in order
1119 to restrict the maximum amount of stack (or heap, if --disable-stack-
1120 for-recursion is specified) that is used. A second limit controls this;
1121 it defaults to the value that is set for --with-match-limit, which
1122 imposes no additional constraints. However, you can set a lower limit
1123 by adding, for example,
1124
1125 --with-match-limit-recursion=10000
1126
1127 to the configure command. This value can also be overridden at run
1128 time.
1129
1130
1131 CREATING CHARACTER TABLES AT BUILD TIME
1132
1133 PCRE uses fixed tables for processing characters whose code values are
1134 less than 256. By default, PCRE is built with a set of tables that are
1135 distributed in the file pcre_chartables.c.dist. These tables are for
1136 ASCII codes only. If you add
1137
1138 --enable-rebuild-chartables
1139
1140 to the configure command, the distributed tables are no longer used.
1141 Instead, a program called dftables is compiled and run. This outputs
1142 the source for new set of tables, created in the default locale of your
1143 C run-time system. (This method of replacing the tables does not work
1144 if you are cross compiling, because dftables is run on the local host.
1145 If you need to create alternative tables when cross compiling, you will
1146 have to do so "by hand".)
1147
1148
1149 USING EBCDIC CODE
1150
1151 PCRE assumes by default that it will run in an environment where the
1152 character code is ASCII (or Unicode, which is a superset of ASCII).
1153 This is the case for most computer operating systems. PCRE can, how-
1154 ever, be compiled to run in an EBCDIC environment by adding
1155
1156 --enable-ebcdic
1157
1158 to the configure command. This setting implies --enable-rebuild-charta-
1159 bles. You should only use it if you know that you are in an EBCDIC
1160 environment (for example, an IBM mainframe operating system). The
1161 --enable-ebcdic option is incompatible with --enable-utf.
1162
1163 The EBCDIC character that corresponds to an ASCII LF is assumed to have
1164 the value 0x15 by default. However, in some EBCDIC environments, 0x25
1165 is used. In such an environment you should use
1166
1167 --enable-ebcdic-nl25
1168
1169 as well as, or instead of, --enable-ebcdic. The EBCDIC character for CR
1170 has the same value as in ASCII, namely, 0x0d. Whichever of 0x15 and
1171 0x25 is not chosen as LF is made to correspond to the Unicode NEL char-
1172 acter (which, in Unicode, is 0x85).
1173
1174 The options that select newline behaviour, such as --enable-newline-is-
1175 cr, and equivalent run-time options, refer to these character values in
1176 an EBCDIC environment.
1177
1178
1179 PCREGREP OPTIONS FOR COMPRESSED FILE SUPPORT
1180
1181 By default, pcregrep reads all files as plain text. You can build it so
1182 that it recognizes files whose names end in .gz or .bz2, and reads them
1183 with libz or libbz2, respectively, by adding one or both of
1184
1185 --enable-pcregrep-libz
1186 --enable-pcregrep-libbz2
1187
1188 to the configure command. These options naturally require that the rel-
1189 evant libraries are installed on your system. Configuration will fail
1190 if they are not.
1191
1192
1193 PCREGREP BUFFER SIZE
1194
1195 pcregrep uses an internal buffer to hold a "window" on the file it is
1196 scanning, in order to be able to output "before" and "after" lines when
1197 it finds a match. The size of the buffer is controlled by a parameter
1198 whose default value is 20K. The buffer itself is three times this size,
1199 but because of the way it is used for holding "before" lines, the long-
1200 est line that is guaranteed to be processable is the parameter size.
1201 You can change the default parameter value by adding, for example,
1202
1203 --with-pcregrep-bufsize=50K
1204
1205 to the configure command. The caller of pcregrep can, however, override
1206 this value by specifying a run-time option.
1207
1208
1209 PCRETEST OPTION FOR LIBREADLINE SUPPORT
1210
1211 If you add
1212
1213 --enable-pcretest-libreadline
1214
1215 to the configure command, pcretest is linked with the libreadline
1216 library, and when its input is from a terminal, it reads it using the
1217 readline() function. This provides line-editing and history facilities.
1218 Note that libreadline is GPL-licensed, so if you distribute a binary of
1219 pcretest linked in this way, there may be licensing issues.
1220
1221 Setting this option causes the -lreadline option to be added to the
1222 pcretest build. In many operating environments with a sytem-installed
1223 libreadline this is sufficient. However, in some environments (e.g. if
1224 an unmodified distribution version of readline is in use), some extra
1225 configuration may be necessary. The INSTALL file for libreadline says
1226 this:
1227
1228 "Readline uses the termcap functions, but does not link with the
1229 termcap or curses library itself, allowing applications which link
1230 with readline the to choose an appropriate library."
1231
1232 If your environment has not been set up so that an appropriate library
1233 is automatically included, you may need to add something like
1234
1235 LIBS="-ncurses"
1236
1237 immediately before the configure command.
1238
1239
1240 DEBUGGING WITH VALGRIND SUPPORT
1241
1242 By adding the
1243
1244 --enable-valgrind
1245
1246 option to to the configure command, PCRE will use valgrind annotations
1247 to mark certain memory regions as unaddressable. This allows it to
1248 detect invalid memory accesses, and is mostly useful for debugging PCRE
1249 itself.
1250
1251
1252 CODE COVERAGE REPORTING
1253
1254 If your C compiler is gcc, you can build a version of PCRE that can
1255 generate a code coverage report for its test suite. To enable this, you
1256 must install lcov version 1.6 or above. Then specify
1257
1258 --enable-coverage
1259
1260 to the configure command and build PCRE in the usual way.
1261
1262 Note that using ccache (a caching C compiler) is incompatible with code
1263 coverage reporting. If you have configured ccache to run automatically
1264 on your system, you must set the environment variable
1265
1266 CCACHE_DISABLE=1
1267
1268 before running make to build PCRE, so that ccache is not used.
1269
1270 When --enable-coverage is used, the following addition targets are
1271 added to the Makefile:
1272
1273 make coverage
1274
1275 This creates a fresh coverage report for the PCRE test suite. It is
1276 equivalent to running "make coverage-reset", "make coverage-baseline",
1277 "make check", and then "make coverage-report".
1278
1279 make coverage-reset
1280
1281 This zeroes the coverage counters, but does nothing else.
1282
1283 make coverage-baseline
1284
1285 This captures baseline coverage information.
1286
1287 make coverage-report
1288
1289 This creates the coverage report.
1290
1291 make coverage-clean-report
1292
1293 This removes the generated coverage report without cleaning the cover-
1294 age data itself.
1295
1296 make coverage-clean-data
1297
1298 This removes the captured coverage data without removing the coverage
1299 files created at compile time (*.gcno).
1300
1301 make coverage-clean
1302
1303 This cleans all coverage data including the generated coverage report.
1304 For more information about code coverage, see the gcov and lcov docu-
1305 mentation.
1306
1307
1308 SEE ALSO
1309
1310 pcreapi(3), pcre16, pcre32, pcre_config(3).
1311
1312
1313 AUTHOR
1314
1315 Philip Hazel
1316 University Computing Service
1317 Cambridge CB2 3QH, England.
1318
1319
1320 REVISION
1321
1322 Last updated: 30 October 2012
1323 Copyright (c) 1997-2012 University of Cambridge.
1324 ------------------------------------------------------------------------------
1325
1326
1327 PCREMATCHING(3) PCREMATCHING(3)
1328
1329
1330 NAME
1331 PCRE - Perl-compatible regular expressions
1332
1333
1334 PCRE MATCHING ALGORITHMS
1335
1336 This document describes the two different algorithms that are available
1337 in PCRE for matching a compiled regular expression against a given sub-
1338 ject string. The "standard" algorithm is the one provided by the
1339 pcre_exec(), pcre16_exec() and pcre32_exec() functions. These work in
1340 the same as as Perl's matching function, and provide a Perl-compatible
1341 matching operation. The just-in-time (JIT) optimization that is
1342 described in the pcrejit documentation is compatible with these func-
1343 tions.
1344
1345 An alternative algorithm is provided by the pcre_dfa_exec(),
1346 pcre16_dfa_exec() and pcre32_dfa_exec() functions; they operate in a
1347 different way, and are not Perl-compatible. This alternative has advan-
1348 tages and disadvantages compared with the standard algorithm, and these
1349 are described below.
1350
1351 When there is only one possible way in which a given subject string can
1352 match a pattern, the two algorithms give the same answer. A difference
1353 arises, however, when there are multiple possibilities. For example, if
1354 the pattern
1355
1356 ^<.*>
1357
1358 is matched against the string
1359
1360 <something> <something else> <something further>
1361
1362 there are three possible answers. The standard algorithm finds only one
1363 of them, whereas the alternative algorithm finds all three.
1364
1365
1366 REGULAR EXPRESSIONS AS TREES
1367
1368 The set of strings that are matched by a regular expression can be rep-
1369 resented as a tree structure. An unlimited repetition in the pattern
1370 makes the tree of infinite size, but it is still a tree. Matching the
1371 pattern to a given subject string (from a given starting point) can be
1372 thought of as a search of the tree. There are two ways to search a
1373 tree: depth-first and breadth-first, and these correspond to the two
1374 matching algorithms provided by PCRE.
1375
1376
1377 THE STANDARD MATCHING ALGORITHM
1378
1379 In the terminology of Jeffrey Friedl's book "Mastering Regular Expres-
1380 sions", the standard algorithm is an "NFA algorithm". It conducts a
1381 depth-first search of the pattern tree. That is, it proceeds along a
1382 single path through the tree, checking that the subject matches what is
1383 required. When there is a mismatch, the algorithm tries any alterna-
1384 tives at the current point, and if they all fail, it backs up to the
1385 previous branch point in the tree, and tries the next alternative
1386 branch at that level. This often involves backing up (moving to the
1387 left) in the subject string as well. The order in which repetition
1388 branches are tried is controlled by the greedy or ungreedy nature of
1389 the quantifier.
1390
1391 If a leaf node is reached, a matching string has been found, and at
1392 that point the algorithm stops. Thus, if there is more than one possi-
1393 ble match, this algorithm returns the first one that it finds. Whether
1394 this is the shortest, the longest, or some intermediate length depends
1395 on the way the greedy and ungreedy repetition quantifiers are specified
1396 in the pattern.
1397
1398 Because it ends up with a single path through the tree, it is rela-
1399 tively straightforward for this algorithm to keep track of the sub-
1400 strings that are matched by portions of the pattern in parentheses.
1401 This provides support for capturing parentheses and back references.
1402
1403
1404 THE ALTERNATIVE MATCHING ALGORITHM
1405
1406 This algorithm conducts a breadth-first search of the tree. Starting
1407 from the first matching point in the subject, it scans the subject
1408 string from left to right, once, character by character, and as it does
1409 this, it remembers all the paths through the tree that represent valid
1410 matches. In Friedl's terminology, this is a kind of "DFA algorithm",
1411 though it is not implemented as a traditional finite state machine (it
1412 keeps multiple states active simultaneously).
1413
1414 Although the general principle of this matching algorithm is that it
1415 scans the subject string only once, without backtracking, there is one
1416 exception: when a lookaround assertion is encountered, the characters
1417 following or preceding the current point have to be independently
1418 inspected.
1419
1420 The scan continues until either the end of the subject is reached, or
1421 there are no more unterminated paths. At this point, terminated paths
1422 represent the different matching possibilities (if there are none, the
1423 match has failed). Thus, if there is more than one possible match,
1424 this algorithm finds all of them, and in particular, it finds the long-
1425 est. The matches are returned in decreasing order of length. There is
1426 an option to stop the algorithm after the first match (which is neces-
1427 sarily the shortest) is found.
1428
1429 Note that all the matches that are found start at the same point in the
1430 subject. If the pattern
1431
1432 cat(er(pillar)?)?
1433
1434 is matched against the string "the caterpillar catchment", the result
1435 will be the three strings "caterpillar", "cater", and "cat" that start
1436 at the fifth character of the subject. The algorithm does not automati-
1437 cally move on to find matches that start at later positions.
1438
1439 There are a number of features of PCRE regular expressions that are not
1440 supported by the alternative matching algorithm. They are as follows:
1441
1442 1. Because the algorithm finds all possible matches, the greedy or
1443 ungreedy nature of repetition quantifiers is not relevant. Greedy and
1444 ungreedy quantifiers are treated in exactly the same way. However, pos-
1445 sessive quantifiers can make a difference when what follows could also
1446 match what is quantified, for example in a pattern like this:
1447
1448 ^a++\w!
1449
1450 This pattern matches "aaab!" but not "aaa!", which would be matched by
1451 a non-possessive quantifier. Similarly, if an atomic group is present,
1452 it is matched as if it were a standalone pattern at the current point,
1453 and the longest match is then "locked in" for the rest of the overall
1454 pattern.
1455
1456 2. When dealing with multiple paths through the tree simultaneously, it
1457 is not straightforward to keep track of captured substrings for the
1458 different matching possibilities, and PCRE's implementation of this
1459 algorithm does not attempt to do this. This means that no captured sub-
1460 strings are available.
1461
1462 3. Because no substrings are captured, back references within the pat-
1463 tern are not supported, and cause errors if encountered.
1464
1465 4. For the same reason, conditional expressions that use a backrefer-
1466 ence as the condition or test for a specific group recursion are not
1467 supported.
1468
1469 5. Because many paths through the tree may be active, the \K escape
1470 sequence, which resets the start of the match when encountered (but may
1471 be on some paths and not on others), is not supported. It causes an
1472 error if encountered.
1473
1474 6. Callouts are supported, but the value of the capture_top field is
1475 always 1, and the value of the capture_last field is always -1.
1476
1477 7. The \C escape sequence, which (in the standard algorithm) always
1478 matches a single data unit, even in UTF-8, UTF-16 or UTF-32 modes, is
1479 not supported in these modes, because the alternative algorithm moves
1480 through the subject string one character (not data unit) at a time, for
1481 all active paths through the tree.
1482
1483 8. Except for (*FAIL), the backtracking control verbs such as (*PRUNE)
1484 are not supported. (*FAIL) is supported, and behaves like a failing
1485 negative assertion.
1486
1487
1488 ADVANTAGES OF THE ALTERNATIVE ALGORITHM
1489
1490 Using the alternative matching algorithm provides the following advan-
1491 tages:
1492
1493 1. All possible matches (at a single point in the subject) are automat-
1494 ically found, and in particular, the longest match is found. To find
1495 more than one match using the standard algorithm, you have to do kludgy
1496 things with callouts.
1497
1498 2. Because the alternative algorithm scans the subject string just
1499 once, and never needs to backtrack (except for lookbehinds), it is pos-
1500 sible to pass very long subject strings to the matching function in
1501 several pieces, checking for partial matching each time. Although it is
1502 possible to do multi-segment matching using the standard algorithm by
1503 retaining partially matched substrings, it is more complicated. The
1504 pcrepartial documentation gives details of partial matching and dis-
1505 cusses multi-segment matching.
1506
1507
1508 DISADVANTAGES OF THE ALTERNATIVE ALGORITHM
1509
1510 The alternative algorithm suffers from a number of disadvantages:
1511
1512 1. It is substantially slower than the standard algorithm. This is
1513 partly because it has to search for all possible matches, but is also
1514 because it is less susceptible to optimization.
1515
1516 2. Capturing parentheses and back references are not supported.
1517
1518 3. Although atomic groups are supported, their use does not provide the
1519 performance advantage that it does for the standard algorithm.
1520
1521
1522 AUTHOR
1523
1524 Philip Hazel
1525 University Computing Service
1526 Cambridge CB2 3QH, England.
1527
1528
1529 REVISION
1530
1531 Last updated: 08 January 2012
1532 Copyright (c) 1997-2012 University of Cambridge.
1533 ------------------------------------------------------------------------------
1534
1535
1536 PCREAPI(3) PCREAPI(3)
1537
1538
1539 NAME
1540 PCRE - Perl-compatible regular expressions
1541
1542 #include <pcre.h>
1543
1544
1545 PCRE NATIVE API BASIC FUNCTIONS
1546
1547 pcre *pcre_compile(const char *pattern, int options,
1548 const char **errptr, int *erroffset,
1549 const unsigned char *tableptr);
1550
1551 pcre *pcre_compile2(const char *pattern, int options,
1552 int *errorcodeptr,
1553 const char **errptr, int *erroffset,
1554 const unsigned char *tableptr);
1555
1556 pcre_extra *pcre_study(const pcre *code, int options,
1557 const char **errptr);
1558
1559 void pcre_free_study(pcre_extra *extra);
1560
1561 int pcre_exec(const pcre *code, const pcre_extra *extra,
1562 const char *subject, int length, int startoffset,
1563 int options, int *ovector, int ovecsize);
1564
1565 int pcre_dfa_exec(const pcre *code, const pcre_extra *extra,
1566 const char *subject, int length, int startoffset,
1567 int options, int *ovector, int ovecsize,
1568 int *workspace, int wscount);
1569
1570
1571 PCRE NATIVE API STRING EXTRACTION FUNCTIONS
1572
1573 int pcre_copy_named_substring(const pcre *code,
1574 const char *subject, int *ovector,
1575 int stringcount, const char *stringname,
1576 char *buffer, int buffersize);
1577
1578 int pcre_copy_substring(const char *subject, int *ovector,
1579 int stringcount, int stringnumber, char *buffer,
1580 int buffersize);
1581
1582 int pcre_get_named_substring(const pcre *code,
1583 const char *subject, int *ovector,
1584 int stringcount, const char *stringname,
1585 const char **stringptr);
1586
1587 int pcre_get_stringnumber(const pcre *code,
1588 const char *name);
1589
1590 int pcre_get_stringtable_entries(const pcre *code,
1591 const char *name, char **first, char **last);
1592
1593 int pcre_get_substring(const char *subject, int *ovector,
1594 int stringcount, int stringnumber,
1595 const char **stringptr);
1596
1597 int pcre_get_substring_list(const char *subject,
1598 int *ovector, int stringcount, const char ***listptr);
1599
1600 void pcre_free_substring(const char *stringptr);
1601
1602 void pcre_free_substring_list(const char **stringptr);
1603
1604
1605 PCRE NATIVE API AUXILIARY FUNCTIONS
1606
1607 int pcre_jit_exec(const pcre *code, const pcre_extra *extra,
1608 const char *subject, int length, int startoffset,
1609 int options, int *ovector, int ovecsize,
1610 pcre_jit_stack *jstack);
1611
1612 pcre_jit_stack *pcre_jit_stack_alloc(int startsize, int maxsize);
1613
1614 void pcre_jit_stack_free(pcre_jit_stack *stack);
1615
1616 void pcre_assign_jit_stack(pcre_extra *extra,
1617 pcre_jit_callback callback, void *data);
1618
1619 const unsigned char *pcre_maketables(void);
1620
1621 int pcre_fullinfo(const pcre *code, const pcre_extra *extra,
1622 int what, void *where);
1623
1624 int pcre_refcount(pcre *code, int adjust);
1625
1626 int pcre_config(int what, void *where);
1627
1628 const char *pcre_version(void);
1629
1630 int pcre_pattern_to_host_byte_order(pcre *code,
1631 pcre_extra *extra, const unsigned char *tables);
1632
1633
1634 PCRE NATIVE API INDIRECTED FUNCTIONS
1635
1636 void *(*pcre_malloc)(size_t);
1637
1638 void (*pcre_free)(void *);
1639
1640 void *(*pcre_stack_malloc)(size_t);
1641
1642 void (*pcre_stack_free)(void *);
1643
1644 int (*pcre_callout)(pcre_callout_block *);
1645
1646
1647 PCRE 8-BIT, 16-BIT, AND 32-BIT LIBRARIES
1648
1649 As well as support for 8-bit character strings, PCRE also supports
1650 16-bit strings (from release 8.30) and 32-bit strings (from release
1651 8.32), by means of two additional libraries. They can be built as well
1652 as, or instead of, the 8-bit library. To avoid too much complication,
1653 this document describes the 8-bit versions of the functions, with only
1654 occasional references to the 16-bit and 32-bit libraries.
1655
1656 The 16-bit and 32-bit functions operate in the same way as their 8-bit
1657 counterparts; they just use different data types for their arguments
1658 and results, and their names start with pcre16_ or pcre32_ instead of
1659 pcre_. For every option that has UTF8 in its name (for example,
1660 PCRE_UTF8), there are corresponding 16-bit and 32-bit names with UTF8
1661 replaced by UTF16 or UTF32, respectively. This facility is in fact just
1662 cosmetic; the 16-bit and 32-bit option names define the same bit val-
1663 ues.
1664
1665 References to bytes and UTF-8 in this document should be read as refer-
1666 ences to 16-bit data quantities and UTF-16 when using the 16-bit
1667 library, or 32-bit data quantities and UTF-32 when using the 32-bit
1668 library, unless specified otherwise. More details of the specific dif-
1669 ferences for the 16-bit and 32-bit libraries are given in the pcre16
1670 and pcre32 pages.
1671
1672
1673 PCRE API OVERVIEW
1674
1675 PCRE has its own native API, which is described in this document. There
1676 are also some wrapper functions (for the 8-bit library only) that cor-
1677 respond to the POSIX regular expression API, but they do not give
1678 access to all the functionality. They are described in the pcreposix
1679 documentation. Both of these APIs define a set of C function calls. A
1680 C++ wrapper (again for the 8-bit library only) is also distributed with
1681 PCRE. It is documented in the pcrecpp page.
1682
1683 The native API C function prototypes are defined in the header file
1684 pcre.h, and on Unix-like systems the (8-bit) library itself is called
1685 libpcre. It can normally be accessed by adding -lpcre to the command
1686 for linking an application that uses PCRE. The header file defines the
1687 macros PCRE_MAJOR and PCRE_MINOR to contain the major and minor release
1688 numbers for the library. Applications can use these to include support
1689 for different releases of PCRE.
1690
1691 In a Windows environment, if you want to statically link an application
1692 program against a non-dll pcre.a file, you must define PCRE_STATIC
1693 before including pcre.h or pcrecpp.h, because otherwise the pcre_mal-
1694 loc() and pcre_free() exported functions will be declared
1695 __declspec(dllimport), with unwanted results.
1696
1697 The functions pcre_compile(), pcre_compile2(), pcre_study(), and
1698 pcre_exec() are used for compiling and matching regular expressions in
1699 a Perl-compatible manner. A sample program that demonstrates the sim-
1700 plest way of using them is provided in the file called pcredemo.c in
1701 the PCRE source distribution. A listing of this program is given in the
1702 pcredemo documentation, and the pcresample documentation describes how
1703 to compile and run it.
1704
1705 Just-in-time compiler support is an optional feature of PCRE that can
1706 be built in appropriate hardware environments. It greatly speeds up the
1707 matching performance of many patterns. Simple programs can easily
1708 request that it be used if available, by setting an option that is
1709 ignored when it is not relevant. More complicated programs might need
1710 to make use of the functions pcre_jit_stack_alloc(),
1711 pcre_jit_stack_free(), and pcre_assign_jit_stack() in order to control
1712 the JIT code's memory usage.
1713
1714 From release 8.32 there is also a direct interface for JIT execution,
1715 which gives improved performance. The JIT-specific functions are dis-
1716 cussed in the pcrejit documentation.
1717
1718 A second matching function, pcre_dfa_exec(), which is not Perl-compati-
1719 ble, is also provided. This uses a different algorithm for the match-
1720 ing. The alternative algorithm finds all possible matches (at a given
1721 point in the subject), and scans the subject just once (unless there
1722 are lookbehind assertions). However, this algorithm does not return
1723 captured substrings. A description of the two matching algorithms and
1724 their advantages and disadvantages is given in the pcrematching docu-
1725 mentation.
1726
1727 In addition to the main compiling and matching functions, there are
1728 convenience functions for extracting captured substrings from a subject
1729 string that is matched by pcre_exec(). They are:
1730
1731 pcre_copy_substring()
1732 pcre_copy_named_substring()
1733 pcre_get_substring()
1734 pcre_get_named_substring()
1735 pcre_get_substring_list()
1736 pcre_get_stringnumber()
1737 pcre_get_stringtable_entries()
1738
1739 pcre_free_substring() and pcre_free_substring_list() are also provided,
1740 to free the memory used for extracted strings.
1741
1742 The function pcre_maketables() is used to build a set of character
1743 tables in the current locale for passing to pcre_compile(),
1744 pcre_exec(), or pcre_dfa_exec(). This is an optional facility that is
1745 provided for specialist use. Most commonly, no special tables are
1746 passed, in which case internal tables that are generated when PCRE is
1747 built are used.
1748
1749 The function pcre_fullinfo() is used to find out information about a
1750 compiled pattern. The function pcre_version() returns a pointer to a
1751 string containing the version of PCRE and its date of release.
1752
1753 The function pcre_refcount() maintains a reference count in a data
1754 block containing a compiled pattern. This is provided for the benefit
1755 of object-oriented applications.
1756
1757 The global variables pcre_malloc and pcre_free initially contain the
1758 entry points of the standard malloc() and free() functions, respec-
1759 tively. PCRE calls the memory management functions via these variables,
1760 so a calling program can replace them if it wishes to intercept the
1761 calls. This should be done before calling any PCRE functions.
1762
1763 The global variables pcre_stack_malloc and pcre_stack_free are also
1764 indirections to memory management functions. These special functions
1765 are used only when PCRE is compiled to use the heap for remembering
1766 data, instead of recursive function calls, when running the pcre_exec()
1767 function. See the pcrebuild documentation for details of how to do
1768 this. It is a non-standard way of building PCRE, for use in environ-
1769 ments that have limited stacks. Because of the greater use of memory
1770 management, it runs more slowly. Separate functions are provided so
1771 that special-purpose external code can be used for this case. When
1772 used, these functions are always called in a stack-like manner (last
1773 obtained, first freed), and always for memory blocks of the same size.
1774 There is a discussion about PCRE's stack usage in the pcrestack docu-
1775 mentation.
1776
1777 The global variable pcre_callout initially contains NULL. It can be set
1778 by the caller to a "callout" function, which PCRE will then call at
1779 specified points during a matching operation. Details are given in the
1780 pcrecallout documentation.
1781
1782
1783 NEWLINES
1784
1785 PCRE supports five different conventions for indicating line breaks in
1786 strings: a single CR (carriage return) character, a single LF (line-
1787 feed) character, the two-character sequence CRLF, any of the three pre-
1788 ceding, or any Unicode newline sequence. The Unicode newline sequences
1789 are the three just mentioned, plus the single characters VT (vertical
1790 tab, U+000B), FF (form feed, U+000C), NEL (next line, U+0085), LS (line
1791 separator, U+2028), and PS (paragraph separator, U+2029).
1792
1793 Each of the first three conventions is used by at least one operating
1794 system as its standard newline sequence. When PCRE is built, a default
1795 can be specified. The default default is LF, which is the Unix stan-
1796 dard. When PCRE is run, the default can be overridden, either when a
1797 pattern is compiled, or when it is matched.
1798
1799 At compile time, the newline convention can be specified by the options
1800 argument of pcre_compile(), or it can be specified by special text at
1801 the start of the pattern itself; this overrides any other settings. See
1802 the pcrepattern page for details of the special character sequences.
1803
1804 In the PCRE documentation the word "newline" is used to mean "the char-
1805 acter or pair of characters that indicate a line break". The choice of
1806 newline convention affects the handling of the dot, circumflex, and
1807 dollar metacharacters, the handling of #-comments in /x mode, and, when
1808 CRLF is a recognized line ending sequence, the match position advance-
1809 ment for a non-anchored pattern. There is more detail about this in the
1810 section on pcre_exec() options below.
1811
1812 The choice of newline convention does not affect the interpretation of
1813 the \n or \r escape sequences, nor does it affect what \R matches,
1814 which is controlled in a similar way, but by separate options.
1815
1816
1817 MULTITHREADING
1818
1819 The PCRE functions can be used in multi-threading applications, with
1820 the proviso that the memory management functions pointed to by
1821 pcre_malloc, pcre_free, pcre_stack_malloc, and pcre_stack_free, and the
1822 callout function pointed to by pcre_callout, are shared by all threads.
1823
1824 The compiled form of a regular expression is not altered during match-
1825 ing, so the same compiled pattern can safely be used by several threads
1826 at once.
1827
1828 If the just-in-time optimization feature is being used, it needs sepa-
1829 rate memory stack areas for each thread. See the pcrejit documentation
1830 for more details.
1831
1832
1833 SAVING PRECOMPILED PATTERNS FOR LATER USE
1834
1835 The compiled form of a regular expression can be saved and re-used at a
1836 later time, possibly by a different program, and even on a host other
1837 than the one on which it was compiled. Details are given in the
1838 pcreprecompile documentation, which includes a description of the
1839 pcre_pattern_to_host_byte_order() function. However, compiling a regu-
1840 lar expression with one version of PCRE for use with a different ver-
1841 sion is not guaranteed to work and may cause crashes.
1842
1843
1844 CHECKING BUILD-TIME OPTIONS
1845
1846 int pcre_config(int what, void *where);
1847
1848 The function pcre_config() makes it possible for a PCRE client to dis-
1849 cover which optional features have been compiled into the PCRE library.
1850 The pcrebuild documentation has more details about these optional fea-
1851 tures.
1852
1853 The first argument for pcre_config() is an integer, specifying which
1854 information is required; the second argument is a pointer to a variable
1855 into which the information is placed. The returned value is zero on
1856 success, or the negative error code PCRE_ERROR_BADOPTION if the value
1857 in the first argument is not recognized. The following information is
1858 available:
1859
1860 PCRE_CONFIG_UTF8
1861
1862 The output is an integer that is set to one if UTF-8 support is avail-
1863 able; otherwise it is set to zero. This value should normally be given
1864 to the 8-bit version of this function, pcre_config(). If it is given to
1865 the 16-bit or 32-bit version of this function, the result is
1866 PCRE_ERROR_BADOPTION.
1867
1868 PCRE_CONFIG_UTF16
1869
1870 The output is an integer that is set to one if UTF-16 support is avail-
1871 able; otherwise it is set to zero. This value should normally be given
1872 to the 16-bit version of this function, pcre16_config(). If it is given
1873 to the 8-bit or 32-bit version of this function, the result is
1874 PCRE_ERROR_BADOPTION.
1875
1876 PCRE_CONFIG_UTF32
1877
1878 The output is an integer that is set to one if UTF-32 support is avail-
1879 able; otherwise it is set to zero. This value should normally be given
1880 to the 32-bit version of this function, pcre32_config(). If it is given
1881 to the 8-bit or 16-bit version of this function, the result is
1882 PCRE_ERROR_BADOPTION.
1883
1884 PCRE_CONFIG_UNICODE_PROPERTIES
1885
1886 The output is an integer that is set to one if support for Unicode
1887 character properties is available; otherwise it is set to zero.
1888
1889 PCRE_CONFIG_JIT
1890
1891 The output is an integer that is set to one if support for just-in-time
1892 compiling is available; otherwise it is set to zero.
1893
1894 PCRE_CONFIG_JITTARGET
1895
1896 The output is a pointer to a zero-terminated "const char *" string. If
1897 JIT support is available, the string contains the name of the architec-
1898 ture for which the JIT compiler is configured, for example "x86 32bit
1899 (little endian + unaligned)". If JIT support is not available, the
1900 result is NULL.
1901
1902 PCRE_CONFIG_NEWLINE
1903
1904 The output is an integer whose value specifies the default character
1905 sequence that is recognized as meaning "newline". The values that are
1906 supported in ASCII/Unicode environments are: 10 for LF, 13 for CR, 3338
1907 for CRLF, -2 for ANYCRLF, and -1 for ANY. In EBCDIC environments, CR,
1908 ANYCRLF, and ANY yield the same values. However, the value for LF is
1909 normally 21, though some EBCDIC environments use 37. The corresponding
1910 values for CRLF are 3349 and 3365. The default should normally corre-
1911 spond to the standard sequence for your operating system.
1912
1913 PCRE_CONFIG_BSR
1914
1915 The output is an integer whose value indicates what character sequences
1916 the \R escape sequence matches by default. A value of 0 means that \R
1917 matches any Unicode line ending sequence; a value of 1 means that \R
1918 matches only CR, LF, or CRLF. The default can be overridden when a pat-
1919 tern is compiled or matched.
1920
1921 PCRE_CONFIG_LINK_SIZE
1922
1923 The output is an integer that contains the number of bytes used for
1924 internal linkage in compiled regular expressions. For the 8-bit
1925 library, the value can be 2, 3, or 4. For the 16-bit library, the value
1926 is either 2 or 4 and is still a number of bytes. For the 32-bit
1927 library, the value is either 2 or 4 and is still a number of bytes. The
1928 default value of 2 is sufficient for all but the most massive patterns,
1929 since it allows the compiled pattern to be up to 64K in size. Larger
1930 values allow larger regular expressions to be compiled, at the expense
1931 of slower matching.
1932
1933 PCRE_CONFIG_POSIX_MALLOC_THRESHOLD
1934
1935 The output is an integer that contains the threshold above which the
1936 POSIX interface uses malloc() for output vectors. Further details are
1937 given in the pcreposix documentation.
1938
1939 PCRE_CONFIG_MATCH_LIMIT
1940
1941 The output is a long integer that gives the default limit for the num-
1942 ber of internal matching function calls in a pcre_exec() execution.
1943 Further details are given with pcre_exec() below.
1944
1945 PCRE_CONFIG_MATCH_LIMIT_RECURSION
1946
1947 The output is a long integer that gives the default limit for the depth
1948 of recursion when calling the internal matching function in a
1949 pcre_exec() execution. Further details are given with pcre_exec()
1950 below.
1951
1952 PCRE_CONFIG_STACKRECURSE
1953
1954 The output is an integer that is set to one if internal recursion when
1955 running pcre_exec() is implemented by recursive function calls that use
1956 the stack to remember their state. This is the usual way that PCRE is
1957 compiled. The output is zero if PCRE was compiled to use blocks of data
1958 on the heap instead of recursive function calls. In this case,
1959 pcre_stack_malloc and pcre_stack_free are called to manage memory
1960 blocks on the heap, thus avoiding the use of the stack.
1961
1962
1963 COMPILING A PATTERN
1964
1965 pcre *pcre_compile(const char *pattern, int options,
1966 const char **errptr, int *erroffset,
1967 const unsigned char *tableptr);
1968
1969 pcre *pcre_compile2(const char *pattern, int options,
1970 int *errorcodeptr,
1971 const char **errptr, int *erroffset,
1972 const unsigned char *tableptr);
1973
1974 Either of the functions pcre_compile() or pcre_compile2() can be called
1975 to compile a pattern into an internal form. The only difference between
1976 the two interfaces is that pcre_compile2() has an additional argument,
1977 errorcodeptr, via which a numerical error code can be returned. To
1978 avoid too much repetition, we refer just to pcre_compile() below, but
1979 the information applies equally to pcre_compile2().
1980
1981 The pattern is a C string terminated by a binary zero, and is passed in
1982 the pattern argument. A pointer to a single block of memory that is
1983 obtained via pcre_malloc is returned. This contains the compiled code
1984 and related data. The pcre type is defined for the returned block; this
1985 is a typedef for a structure whose contents are not externally defined.
1986 It is up to the caller to free the memory (via pcre_free) when it is no
1987 longer required.
1988
1989 Although the compiled code of a PCRE regex is relocatable, that is, it
1990 does not depend on memory location, the complete pcre data block is not
1991 fully relocatable, because it may contain a copy of the tableptr argu-
1992 ment, which is an address (see below).
1993
1994 The options argument contains various bit settings that affect the com-
1995 pilation. It should be zero if no options are required. The available
1996 options are described below. Some of them (in particular, those that
1997 are compatible with Perl, but some others as well) can also be set and
1998 unset from within the pattern (see the detailed description in the
1999 pcrepattern documentation). For those options that can be different in
2000 different parts of the pattern, the contents of the options argument
2001 specifies their settings at the start of compilation and execution. The
2002 PCRE_ANCHORED, PCRE_BSR_xxx, PCRE_NEWLINE_xxx, PCRE_NO_UTF8_CHECK, and
2003 PCRE_NO_START_OPTIMIZE options can be set at the time of matching as
2004 well as at compile time.
2005
2006 If errptr is NULL, pcre_compile() returns NULL immediately. Otherwise,
2007 if compilation of a pattern fails, pcre_compile() returns NULL, and
2008 sets the variable pointed to by errptr to point to a textual error mes-
2009 sage. This is a static string that is part of the library. You must not
2010 try to free it. Normally, the offset from the start of the pattern to
2011 the byte that was being processed when the error was discovered is
2012 placed in the variable pointed to by erroffset, which must not be NULL
2013 (if it is, an immediate error is given). However, for an invalid UTF-8
2014 string, the offset is that of the first byte of the failing character.
2015
2016 Some errors are not detected until the whole pattern has been scanned;
2017 in these cases, the offset passed back is the length of the pattern.
2018 Note that the offset is in bytes, not characters, even in UTF-8 mode.
2019 It may sometimes point into the middle of a UTF-8 character.
2020
2021 If pcre_compile2() is used instead of pcre_compile(), and the error-
2022 codeptr argument is not NULL, a non-zero error code number is returned
2023 via this argument in the event of an error. This is in addition to the
2024 textual error message. Error codes and messages are listed below.
2025
2026 If the final argument, tableptr, is NULL, PCRE uses a default set of
2027 character tables that are built when PCRE is compiled, using the
2028 default C locale. Otherwise, tableptr must be an address that is the
2029 result of a call to pcre_maketables(). This value is stored with the
2030 compiled pattern, and used again by pcre_exec(), unless another table
2031 pointer is passed to it. For more discussion, see the section on locale
2032 support below.
2033
2034 This code fragment shows a typical straightforward call to pcre_com-
2035 pile():
2036
2037 pcre *re;
2038 const char *error;
2039 int erroffset;
2040 re = pcre_compile(
2041 "^A.*Z", /* the pattern */
2042 0, /* default options */
2043 &error, /* for error message */
2044 &erroffset, /* for error offset */
2045 NULL); /* use default character tables */
2046
2047 The following names for option bits are defined in the pcre.h header
2048 file:
2049
2050 PCRE_ANCHORED
2051
2052 If this bit is set, the pattern is forced to be "anchored", that is, it
2053 is constrained to match only at the first matching point in the string
2054 that is being searched (the "subject string"). This effect can also be
2055 achieved by appropriate constructs in the pattern itself, which is the
2056 only way to do it in Perl.
2057
2058 PCRE_AUTO_CALLOUT
2059
2060 If this bit is set, pcre_compile() automatically inserts callout items,
2061 all with number 255, before each pattern item. For discussion of the
2062 callout facility, see the pcrecallout documentation.
2063
2064 PCRE_BSR_ANYCRLF
2065 PCRE_BSR_UNICODE
2066
2067 These options (which are mutually exclusive) control what the \R escape
2068 sequence matches. The choice is either to match only CR, LF, or CRLF,
2069 or to match any Unicode newline sequence. The default is specified when
2070 PCRE is built. It can be overridden from within the pattern, or by set-
2071 ting an option when a compiled pattern is matched.
2072
2073 PCRE_CASELESS
2074
2075 If this bit is set, letters in the pattern match both upper and lower
2076 case letters. It is equivalent to Perl's /i option, and it can be
2077 changed within a pattern by a (?i) option setting. In UTF-8 mode, PCRE
2078 always understands the concept of case for characters whose values are
2079 less than 128, so caseless matching is always possible. For characters
2080 with higher values, the concept of case is supported if PCRE is com-
2081 piled with Unicode property support, but not otherwise. If you want to
2082 use caseless matching for characters 128 and above, you must ensure
2083 that PCRE is compiled with Unicode property support as well as with
2084 UTF-8 support.
2085
2086 PCRE_DOLLAR_ENDONLY
2087
2088 If this bit is set, a dollar metacharacter in the pattern matches only
2089 at the end of the subject string. Without this option, a dollar also
2090 matches immediately before a newline at the end of the string (but not
2091 before any other newlines). The PCRE_DOLLAR_ENDONLY option is ignored
2092 if PCRE_MULTILINE is set. There is no equivalent to this option in
2093 Perl, and no way to set it within a pattern.
2094
2095 PCRE_DOTALL
2096
2097 If this bit is set, a dot metacharacter in the pattern matches a char-
2098 acter of any value, including one that indicates a newline. However, it
2099 only ever matches one character, even if newlines are coded as CRLF.
2100 Without this option, a dot does not match when the current position is
2101 at a newline. This option is equivalent to Perl's /s option, and it can
2102 be changed within a pattern by a (?s) option setting. A negative class
2103 such as [^a] always matches newline characters, independent of the set-
2104 ting of this option.
2105
2106 PCRE_DUPNAMES
2107
2108 If this bit is set, names used to identify capturing subpatterns need
2109 not be unique. This can be helpful for certain types of pattern when it
2110 is known that only one instance of the named subpattern can ever be
2111 matched. There are more details of named subpatterns below; see also
2112 the pcrepattern documentation.
2113
2114 PCRE_EXTENDED
2115
2116 If this bit is set, white space data characters in the pattern are
2117 totally ignored except when escaped or inside a character class. White
2118 space does not include the VT character (code 11). In addition, charac-
2119 ters between an unescaped # outside a character class and the next new-
2120 line, inclusive, are also ignored. This is equivalent to Perl's /x
2121 option, and it can be changed within a pattern by a (?x) option set-
2122 ting.
2123
2124 Which characters are interpreted as newlines is controlled by the
2125 options passed to pcre_compile() or by a special sequence at the start
2126 of the pattern, as described in the section entitled "Newline conven-
2127 tions" in the pcrepattern documentation. Note that the end of this type
2128 of comment is a literal newline sequence in the pattern; escape
2129 sequences that happen to represent a newline do not count.
2130
2131 This option makes it possible to include comments inside complicated
2132 patterns. Note, however, that this applies only to data characters.
2133 White space characters may never appear within special character
2134 sequences in a pattern, for example within the sequence (?( that intro-
2135 duces a conditional subpattern.
2136
2137 PCRE_EXTRA
2138
2139 This option was invented in order to turn on additional functionality
2140 of PCRE that is incompatible with Perl, but it is currently of very
2141 little use. When set, any backslash in a pattern that is followed by a
2142 letter that has no special meaning causes an error, thus reserving
2143 these combinations for future expansion. By default, as in Perl, a
2144 backslash followed by a letter with no special meaning is treated as a
2145 literal. (Perl can, however, be persuaded to give an error for this, by
2146 running it with the -w option.) There are at present no other features
2147 controlled by this option. It can also be set by a (?X) option setting
2148 within a pattern.
2149
2150 PCRE_FIRSTLINE
2151
2152 If this option is set, an unanchored pattern is required to match
2153 before or at the first newline in the subject string, though the
2154 matched text may continue over the newline.
2155
2156 PCRE_JAVASCRIPT_COMPAT
2157
2158 If this option is set, PCRE's behaviour is changed in some ways so that
2159 it is compatible with JavaScript rather than Perl. The changes are as
2160 follows:
2161
2162 (1) A lone closing square bracket in a pattern causes a compile-time
2163 error, because this is illegal in JavaScript (by default it is treated
2164 as a data character). Thus, the pattern AB]CD becomes illegal when this
2165 option is set.
2166
2167 (2) At run time, a back reference to an unset subpattern group matches
2168 an empty string (by default this causes the current matching alterna-
2169 tive to fail). A pattern such as (\1)(a) succeeds when this option is
2170 set (assuming it can find an "a" in the subject), whereas it fails by
2171 default, for Perl compatibility.
2172
2173 (3) \U matches an upper case "U" character; by default \U causes a com-
2174 pile time error (Perl uses \U to upper case subsequent characters).
2175
2176 (4) \u matches a lower case "u" character unless it is followed by four
2177 hexadecimal digits, in which case the hexadecimal number defines the
2178 code point to match. By default, \u causes a compile time error (Perl
2179 uses it to upper case the following character).
2180
2181 (5) \x matches a lower case "x" character unless it is followed by two
2182 hexadecimal digits, in which case the hexadecimal number defines the
2183 code point to match. By default, as in Perl, a hexadecimal number is
2184 always expected after \x, but it may have zero, one, or two digits (so,
2185 for example, \xz matches a binary zero character followed by z).
2186
2187 PCRE_MULTILINE
2188
2189 By default, PCRE treats the subject string as consisting of a single
2190 line of characters (even if it actually contains newlines). The "start
2191 of line" metacharacter (^) matches only at the start of the string,
2192 while the "end of line" metacharacter ($) matches only at the end of
2193 the string, or before a terminating newline (unless PCRE_DOLLAR_ENDONLY
2194 is set). This is the same as Perl.
2195
2196 When PCRE_MULTILINE it is set, the "start of line" and "end of line"
2197 constructs match immediately following or immediately before internal
2198 newlines in the subject string, respectively, as well as at the very
2199 start and end. This is equivalent to Perl's /m option, and it can be
2200 changed within a pattern by a (?m) option setting. If there are no new-
2201 lines in a subject string, or no occurrences of ^ or $ in a pattern,
2202 setting PCRE_MULTILINE has no effect.
2203
2204 PCRE_NEWLINE_CR
2205 PCRE_NEWLINE_LF
2206 PCRE_NEWLINE_CRLF
2207 PCRE_NEWLINE_ANYCRLF
2208 PCRE_NEWLINE_ANY
2209
2210 These options override the default newline definition that was chosen
2211 when PCRE was built. Setting the first or the second specifies that a
2212 newline is indicated by a single character (CR or LF, respectively).
2213 Setting PCRE_NEWLINE_CRLF specifies that a newline is indicated by the
2214 two-character CRLF sequence. Setting PCRE_NEWLINE_ANYCRLF specifies
2215 that any of the three preceding sequences should be recognized. Setting
2216 PCRE_NEWLINE_ANY specifies that any Unicode newline sequence should be
2217 recognized.
2218
2219 In an ASCII/Unicode environment, the Unicode newline sequences are the
2220 three just mentioned, plus the single characters VT (vertical tab,
2221 U+000B), FF (form feed, U+000C), NEL (next line, U+0085), LS (line sep-
2222 arator, U+2028), and PS (paragraph separator, U+2029). For the 8-bit
2223 library, the last two are recognized only in UTF-8 mode.
2224
2225 When PCRE is compiled to run in an EBCDIC (mainframe) environment, the
2226 code for CR is 0x0d, the same as ASCII. However, the character code for
2227 LF is normally 0x15, though in some EBCDIC environments 0x25 is used.
2228 Whichever of these is not LF is made to correspond to Unicode's NEL
2229 character. EBCDIC codes are all less than 256. For more details, see
2230 the pcrebuild documentation.
2231
2232 The newline setting in the options word uses three bits that are
2233 treated as a number, giving eight possibilities. Currently only six are
2234 used (default plus the five values above). This means that if you set
2235 more than one newline option, the combination may or may not be sensi-
2236 ble. For example, PCRE_NEWLINE_CR with PCRE_NEWLINE_LF is equivalent to
2237 PCRE_NEWLINE_CRLF, but other combinations may yield unused numbers and
2238 cause an error.
2239
2240 The only time that a line break in a pattern is specially recognized
2241 when compiling is when PCRE_EXTENDED is set. CR and LF are white space
2242 characters, and so are ignored in this mode. Also, an unescaped # out-
2243 side a character class indicates a comment that lasts until after the
2244 next line break sequence. In other circumstances, line break sequences
2245 in patterns are treated as literal data.
2246
2247 The newline option that is set at compile time becomes the default that
2248 is used for pcre_exec() and pcre_dfa_exec(), but it can be overridden.
2249
2250 PCRE_NO_AUTO_CAPTURE
2251
2252 If this option is set, it disables the use of numbered capturing paren-
2253 theses in the pattern. Any opening parenthesis that is not followed by
2254 ? behaves as if it were followed by ?: but named parentheses can still
2255 be used for capturing (and they acquire numbers in the usual way).
2256 There is no equivalent of this option in Perl.
2257
2258 NO_START_OPTIMIZE
2259
2260 This is an option that acts at matching time; that is, it is really an
2261 option for pcre_exec() or pcre_dfa_exec(). If it is set at compile
2262 time, it is remembered with the compiled pattern and assumed at match-
2263 ing time. For details see the discussion of PCRE_NO_START_OPTIMIZE
2264 below.
2265
2266 PCRE_UCP
2267
2268 This option changes the way PCRE processes \B, \b, \D, \d, \S, \s, \W,
2269 \w, and some of the POSIX character classes. By default, only ASCII
2270 characters are recognized, but if PCRE_UCP is set, Unicode properties
2271 are used instead to classify characters. More details are given in the
2272 section on generic character types in the pcrepattern page. If you set
2273 PCRE_UCP, matching one of the items it affects takes much longer. The
2274 option is available only if PCRE has been compiled with Unicode prop-
2275 erty support.
2276
2277 PCRE_UNGREEDY
2278
2279 This option inverts the "greediness" of the quantifiers so that they
2280 are not greedy by default, but become greedy if followed by "?". It is
2281 not compatible with Perl. It can also be set by a (?U) option setting
2282 within the pattern.
2283
2284 PCRE_UTF8
2285
2286 This option causes PCRE to regard both the pattern and the subject as
2287 strings of UTF-8 characters instead of single-byte strings. However, it
2288 is available only when PCRE is built to include UTF support. If not,
2289 the use of this option provokes an error. Details of how this option
2290 changes the behaviour of PCRE are given in the pcreunicode page.
2291
2292 PCRE_NO_UTF8_CHECK
2293
2294 When PCRE_UTF8 is set, the validity of the pattern as a UTF-8 string is
2295 automatically checked. There is a discussion about the validity of
2296 UTF-8 strings in the pcreunicode page. If an invalid UTF-8 sequence is
2297 found, pcre_compile() returns an error. If you already know that your
2298 pattern is valid, and you want to skip this check for performance rea-
2299 sons, you can set the PCRE_NO_UTF8_CHECK option. When it is set, the
2300 effect of passing an invalid UTF-8 string as a pattern is undefined. It
2301 may cause your program to crash. Note that this option can also be
2302 passed to pcre_exec() and pcre_dfa_exec(), to suppress the validity
2303 checking of subject strings only. If the same string is being matched
2304 many times, the option can be safely set for the second and subsequent
2305 matchings to improve performance.
2306
2307
2308 COMPILATION ERROR CODES
2309
2310 The following table lists the error codes than may be returned by
2311 pcre_compile2(), along with the error messages that may be returned by
2312 both compiling functions. Note that error messages are always 8-bit
2313 ASCII strings, even in 16-bit or 32-bit mode. As PCRE has developed,
2314 some error codes have fallen out of use. To avoid confusion, they have
2315 not been re-used.
2316
2317 0 no error
2318 1 \ at end of pattern
2319 2 \c at end of pattern
2320 3 unrecognized character follows \
2321 4 numbers out of order in {} quantifier
2322 5 number too big in {} quantifier
2323 6 missing terminating ] for character class
2324 7 invalid escape sequence in character class
2325 8 range out of order in character class
2326 9 nothing to repeat
2327 10 [this code is not in use]
2328 11 internal error: unexpected repeat
2329 12 unrecognized character after (? or (?-
2330 13 POSIX named classes are supported only within a class
2331 14 missing )
2332 15 reference to non-existent subpattern
2333 16 erroffset passed as NULL
2334 17 unknown option bit(s) set
2335 18 missing ) after comment
2336 19 [this code is not in use]
2337 20 regular expression is too large
2338 21 failed to get memory
2339 22 unmatched parentheses
2340 23 internal error: code overflow
2341 24 unrecognized character after (?<
2342 25 lookbehind assertion is not fixed length
2343 26 malformed number or name after (?(
2344 27 conditional group contains more than two branches
2345 28 assertion expected after (?(
2346 29 (?R or (?[+-]digits must be followed by )
2347 30 unknown POSIX class name
2348 31 POSIX collating elements are not supported
2349 32 this version of PCRE is compiled without UTF support
2350 33 [this code is not in use]
2351 34 character value in \x{...} sequence is too large
2352 35 invalid condition (?(0)
2353 36 \C not allowed in lookbehind assertion
2354 37 PCRE does not support \L, \l, \N{name}, \U, or \u
2355 38 number after (?C is > 255
2356 39 closing ) for (?C expected
2357 40 recursive call could loop indefinitely
2358 41 unrecognized character after (?P
2359 42 syntax error in subpattern name (missing terminator)
2360 43 two named subpatterns have the same name
2361 44 invalid UTF-8 string (specifically UTF-8)
2362 45 support for \P, \p, and \X has not been compiled
2363 46 malformed \P or \p sequence
2364 47 unknown property name after \P or \p
2365 48 subpattern name is too long (maximum 32 characters)
2366 49 too many named subpatterns (maximum 10000)
2367 50 [this code is not in use]
2368 51 octal value is greater than \377 in 8-bit non-UTF-8 mode
2369 52 internal error: overran compiling workspace
2370 53 internal error: previously-checked referenced subpattern
2371 not found
2372 54 DEFINE group contains more than one branch
2373 55 repeating a DEFINE group is not allowed
2374 56 inconsistent NEWLINE options
2375 57 \g is not followed by a braced, angle-bracketed, or quoted
2376 name/number or by a plain number
2377 58 a numbered reference must not be zero
2378 59 an argument is not allowed for (*ACCEPT), (*FAIL), or (*COMMIT)
2379 60 (*VERB) not recognized
2380 61 number is too big
2381 62 subpattern name expected
2382 63 digit expected after (?+
2383 64 ] is an invalid data character in JavaScript compatibility mode
2384 65 different names for subpatterns of the same number are
2385 not allowed
2386 66 (*MARK) must have an argument
2387 67 this version of PCRE is not compiled with Unicode property
2388 support
2389 68 \c must be followed by an ASCII character
2390 69 \k is not followed by a braced, angle-bracketed, or quoted name
2391 70 internal error: unknown opcode in find_fixedlength()
2392 71 \N is not supported in a class
2393 72 too many forward references
2394 73 disallowed Unicode code point (>= 0xd800 && <= 0xdfff)
2395 74 invalid UTF-16 string (specifically UTF-16)
2396 75 name is too long in (*MARK), (*PRUNE), (*SKIP), or (*THEN)
2397 76 character value in \u.... sequence is too large
2398 77 invalid UTF-32 string (specifically UTF-32)
2399
2400 The numbers 32 and 10000 in errors 48 and 49 are defaults; different
2401 values may be used if the limits were changed when PCRE was built.
2402
2403
2404 STUDYING A PATTERN
2405
2406 pcre_extra *pcre_study(const pcre *code, int options
2407 const char **errptr);
2408
2409 If a compiled pattern is going to be used several times, it is worth
2410 spending more time analyzing it in order to speed up the time taken for
2411 matching. The function pcre_study() takes a pointer to a compiled pat-
2412 tern as its first argument. If studying the pattern produces additional
2413 information that will help speed up matching, pcre_study() returns a
2414 pointer to a pcre_extra block, in which the study_data field points to
2415 the results of the study.
2416
2417 The returned value from pcre_study() can be passed directly to
2418 pcre_exec() or pcre_dfa_exec(). However, a pcre_extra block also con-
2419 tains other fields that can be set by the caller before the block is
2420 passed; these are described below in the section on matching a pattern.
2421
2422 If studying the pattern does not produce any useful information,
2423 pcre_study() returns NULL by default. In that circumstance, if the
2424 calling program wants to pass any of the other fields to pcre_exec() or
2425 pcre_dfa_exec(), it must set up its own pcre_extra block. However, if
2426 pcre_study() is called with the PCRE_STUDY_EXTRA_NEEDED option, it
2427 returns a pcre_extra block even if studying did not find any additional
2428 information. It may still return NULL, however, if an error occurs in
2429 pcre_study().
2430
2431 The second argument of pcre_study() contains option bits. There are
2432 three further options in addition to PCRE_STUDY_EXTRA_NEEDED:
2433
2434 PCRE_STUDY_JIT_COMPILE
2435 PCRE_STUDY_JIT_PARTIAL_HARD_COMPILE
2436 PCRE_STUDY_JIT_PARTIAL_SOFT_COMPILE
2437
2438 If any of these are set, and the just-in-time compiler is available,
2439 the pattern is further compiled into machine code that executes much
2440 faster than the pcre_exec() interpretive matching function. If the
2441 just-in-time compiler is not available, these options are ignored. All
2442 undefined bits in the options argument must be zero.
2443
2444 JIT compilation is a heavyweight optimization. It can take some time
2445 for patterns to be analyzed, and for one-off matches and simple pat-
2446 terns the benefit of faster execution might be offset by a much slower
2447 study time. Not all patterns can be optimized by the JIT compiler. For
2448 those that cannot be handled, matching automatically falls back to the
2449 pcre_exec() interpreter. For more details, see the pcrejit documenta-
2450 tion.
2451
2452 The third argument for pcre_study() is a pointer for an error message.
2453 If studying succeeds (even if no data is returned), the variable it
2454 points to is set to NULL. Otherwise it is set to point to a textual
2455 error message. This is a static string that is part of the library. You
2456 must not try to free it. You should test the error pointer for NULL
2457 after calling pcre_study(), to be sure that it has run successfully.
2458
2459 When you are finished with a pattern, you can free the memory used for
2460 the study data by calling pcre_free_study(). This function was added to
2461 the API for release 8.20. For earlier versions, the memory could be
2462 freed with pcre_free(), just like the pattern itself. This will still
2463 work in cases where JIT optimization is not used, but it is advisable
2464 to change to the new function when convenient.
2465
2466 This is a typical way in which pcre_study() is used (except that in a
2467 real application there should be tests for errors):
2468
2469 int rc;
2470 pcre *re;
2471 pcre_extra *sd;
2472 re = pcre_compile("pattern", 0, &error, &erroroffset, NULL);
2473 sd = pcre_study(
2474 re, /* result of pcre_compile() */
2475 0, /* no options */
2476 &error); /* set to NULL or points to a message */
2477 rc = pcre_exec( /* see below for details of pcre_exec() options */
2478 re, sd, "subject", 7, 0, 0, ovector, 30);
2479 ...
2480 pcre_free_study(sd);
2481 pcre_free(re);
2482
2483 Studying a pattern does two things: first, a lower bound for the length
2484 of subject string that is needed to match the pattern is computed. This
2485 does not mean that there are any strings of that length that match, but
2486 it does guarantee that no shorter strings match. The value is used to
2487 avoid wasting time by trying to match strings that are shorter than the
2488 lower bound. You can find out the value in a calling program via the
2489 pcre_fullinfo() function.
2490
2491 Studying a pattern is also useful for non-anchored patterns that do not
2492 have a single fixed starting character. A bitmap of possible starting
2493 bytes is created. This speeds up finding a position in the subject at
2494 which to start matching. (In 16-bit mode, the bitmap is used for 16-bit
2495 values less than 256. In 32-bit mode, the bitmap is used for 32-bit
2496 values less than 256.)
2497
2498 These two optimizations apply to both pcre_exec() and pcre_dfa_exec(),
2499 and the information is also used by the JIT compiler. The optimiza-
2500 tions can be disabled by setting the PCRE_NO_START_OPTIMIZE option when
2501 calling pcre_exec() or pcre_dfa_exec(), but if this is done, JIT execu-
2502 tion is also disabled. You might want to do this if your pattern con-
2503 tains callouts or (*MARK) and you want to make use of these facilities
2504 in cases where matching fails. See the discussion of
2505 PCRE_NO_START_OPTIMIZE below.
2506
2507
2508 LOCALE SUPPORT
2509
2510 PCRE handles caseless matching, and determines whether characters are
2511 letters, digits, or whatever, by reference to a set of tables, indexed
2512 by character value. When running in UTF-8 mode, this applies only to
2513 characters with codes less than 128. By default, higher-valued codes
2514 never match escapes such as \w or \d, but they can be tested with \p if
2515 PCRE is built with Unicode character property support. Alternatively,
2516 the PCRE_UCP option can be set at compile time; this causes \w and
2517 friends to use Unicode property support instead of built-in tables. The
2518 use of locales with Unicode is discouraged. If you are handling charac-
2519 ters with codes greater than 128, you should either use UTF-8 and Uni-
2520 code, or use locales, but not try to mix the two.
2521
2522 PCRE contains an internal set of tables that are used when the final
2523 argument of pcre_compile() is NULL. These are sufficient for many
2524 applications. Normally, the internal tables recognize only ASCII char-
2525 acters. However, when PCRE is built, it is possible to cause the inter-
2526 nal tables to be rebuilt in the default "C" locale of the local system,
2527 which may cause them to be different.
2528
2529 The internal tables can always be overridden by tables supplied by the
2530 application that calls PCRE. These may be created in a different locale
2531 from the default. As more and more applications change to using Uni-
2532 code, the need for this locale support is expected to die away.
2533
2534 External tables are built by calling the pcre_maketables() function,
2535 which has no arguments, in the relevant locale. The result can then be
2536 passed to pcre_compile() or pcre_exec() as often as necessary. For
2537 example, to build and use tables that are appropriate for the French
2538 locale (where accented characters with values greater than 128 are
2539 treated as letters), the following code could be used:
2540
2541 setlocale(LC_CTYPE, "fr_FR");
2542 tables = pcre_maketables();
2543 re = pcre_compile(..., tables);
2544
2545 The locale name "fr_FR" is used on Linux and other Unix-like systems;
2546 if you are using Windows, the name for the French locale is "french".
2547
2548 When pcre_maketables() runs, the tables are built in memory that is
2549 obtained via pcre_malloc. It is the caller's responsibility to ensure
2550 that the memory containing the tables remains available for as long as
2551 it is needed.
2552
2553 The pointer that is passed to pcre_compile() is saved with the compiled
2554 pattern, and the same tables are used via this pointer by pcre_study()
2555 and normally also by pcre_exec(). Thus, by default, for any single pat-
2556 tern, compilation, studying and matching all happen in the same locale,
2557 but different patterns can be compiled in different locales.
2558
2559 It is possible to pass a table pointer or NULL (indicating the use of
2560 the internal tables) to pcre_exec(). Although not intended for this
2561 purpose, this facility could be used to match a pattern in a different
2562 locale from the one in which it was compiled. Passing table pointers at
2563 run time is discussed below in the section on matching a pattern.
2564
2565
2566 INFORMATION ABOUT A PATTERN
2567
2568 int pcre_fullinfo(const pcre *code, const pcre_extra *extra,
2569 int what, void *where);
2570
2571 The pcre_fullinfo() function returns information about a compiled pat-
2572 tern. It replaces the pcre_info() function, which was removed from the
2573 library at version 8.30, after more than 10 years of obsolescence.
2574
2575 The first argument for pcre_fullinfo() is a pointer to the compiled
2576 pattern. The second argument is the result of pcre_study(), or NULL if
2577 the pattern was not studied. The third argument specifies which piece
2578 of information is required, and the fourth argument is a pointer to a
2579 variable to receive the data. The yield of the function is zero for
2580 success, or one of the following negative numbers:
2581
2582 PCRE_ERROR_NULL the argument code was NULL
2583 the argument where was NULL
2584 PCRE_ERROR_BADMAGIC the "magic number" was not found
2585 PCRE_ERROR_BADENDIANNESS the pattern was compiled with different
2586 endianness
2587 PCRE_ERROR_BADOPTION the value of what was invalid
2588
2589 The "magic number" is placed at the start of each compiled pattern as
2590 an simple check against passing an arbitrary memory pointer. The endi-
2591 anness error can occur if a compiled pattern is saved and reloaded on a
2592 different host. Here is a typical call of pcre_fullinfo(), to obtain
2593 the length of the compiled pattern:
2594
2595 int rc;
2596 size_t length;
2597 rc = pcre_fullinfo(
2598 re, /* result of pcre_compile() */
2599 sd, /* result of pcre_study(), or NULL */
2600 PCRE_INFO_SIZE, /* what is required */
2601 &length); /* where to put the data */
2602
2603 The possible values for the third argument are defined in pcre.h, and
2604 are as follows:
2605
2606 PCRE_INFO_BACKREFMAX
2607
2608 Return the number of the highest back reference in the pattern. The
2609 fourth argument should point to an int variable. Zero is returned if
2610 there are no back references.
2611
2612 PCRE_INFO_CAPTURECOUNT
2613
2614 Return the number of capturing subpatterns in the pattern. The fourth
2615 argument should point to an int variable.
2616
2617 PCRE_INFO_DEFAULT_TABLES
2618
2619 Return a pointer to the internal default character tables within PCRE.
2620 The fourth argument should point to an unsigned char * variable. This
2621 information call is provided for internal use by the pcre_study() func-
2622 tion. External callers can cause PCRE to use its internal tables by
2623 passing a NULL table pointer.
2624
2625 PCRE_INFO_FIRSTBYTE
2626
2627 Return information about the first data unit of any matched string, for
2628 a non-anchored pattern. (The name of this option refers to the 8-bit
2629 library, where data units are bytes.) The fourth argument should point
2630 to an int variable.
2631
2632 If there is a fixed first value, for example, the letter "c" from a
2633 pattern such as (cat|cow|coyote), its value is returned. In the 8-bit
2634 library, the value is always less than 256. In the 16-bit library the
2635 value can be up to 0xffff. In the 32-bit library the value can be up to
2636 0x10ffff.
2637
2638 If there is no fixed first value, and if either
2639
2640 (a) the pattern was compiled with the PCRE_MULTILINE option, and every
2641 branch starts with "^", or
2642
2643 (b) every branch of the pattern starts with ".*" and PCRE_DOTALL is not
2644 set (if it were set, the pattern would be anchored),
2645
2646 -1 is returned, indicating that the pattern matches only at the start
2647 of a subject string or after any newline within the string. Otherwise
2648 -2 is returned. For anchored patterns, -2 is returned.
2649
2650 Since for the 32-bit library using the non-UTF-32 mode, this function
2651 is unable to return the full 32-bit range of the character, this value
2652 is deprecated; instead the PCRE_INFO_FIRSTCHARACTERFLAGS and
2653 PCRE_INFO_FIRSTCHARACTER values should be used.
2654
2655 PCRE_INFO_FIRSTTABLE
2656
2657 If the pattern was studied, and this resulted in the construction of a
2658 256-bit table indicating a fixed set of values for the first data unit
2659 in any matching string, a pointer to the table is returned. Otherwise
2660 NULL is returned. The fourth argument should point to an unsigned char
2661 * variable.
2662
2663 PCRE_INFO_HASCRORLF
2664
2665 Return 1 if the pattern contains any explicit matches for CR or LF
2666 characters, otherwise 0. The fourth argument should point to an int
2667 variable. An explicit match is either a literal CR or LF character, or
2668 \r or \n.
2669
2670 PCRE_INFO_JCHANGED
2671
2672 Return 1 if the (?J) or (?-J) option setting is used in the pattern,
2673 otherwise 0. The fourth argument should point to an int variable. (?J)
2674 and (?-J) set and unset the local PCRE_DUPNAMES option, respectively.
2675
2676 PCRE_INFO_JIT
2677
2678 Return 1 if the pattern was studied with one of the JIT options, and
2679 just-in-time compiling was successful. The fourth argument should point
2680 to an int variable. A return value of 0 means that JIT support is not
2681 available in this version of PCRE, or that the pattern was not studied
2682 with a JIT option, or that the JIT compiler could not handle this par-
2683 ticular pattern. See the pcrejit documentation for details of what can
2684 and cannot be handled.
2685
2686 PCRE_INFO_JITSIZE
2687
2688 If the pattern was successfully studied with a JIT option, return the
2689 size of the JIT compiled code, otherwise return zero. The fourth argu-
2690 ment should point to a size_t variable.
2691
2692 PCRE_INFO_LASTLITERAL
2693
2694 Return the value of the rightmost literal data unit that must exist in
2695 any matched string, other than at its start, if such a value has been
2696 recorded. The fourth argument should point to an int variable. If there
2697 is no such value, -1 is returned. For anchored patterns, a last literal
2698 value is recorded only if it follows something of variable length. For
2699 example, for the pattern /^a\d+z\d+/ the returned value is "z", but for
2700 /^a\dz\d/ the returned value is -1.
2701
2702 Since for the 32-bit library using the non-UTF-32 mode, this function
2703 is unable to return the full 32-bit range of the character, this value
2704 is deprecated; instead the PCRE_INFO_REQUIREDCHARFLAGS and
2705 PCRE_INFO_REQUIREDCHAR values should be used.
2706
2707 PCRE_INFO_MAXLOOKBEHIND
2708
2709 Return the number of characters (NB not bytes) in the longest lookbe-
2710 hind assertion in the pattern. Note that the simple assertions \b and
2711 \B require a one-character lookbehind. This information is useful when
2712 doing multi-segment matching using the partial matching facilities.
2713
2714 PCRE_INFO_MINLENGTH
2715
2716 If the pattern was studied and a minimum length for matching subject
2717 strings was computed, its value is returned. Otherwise the returned
2718 value is -1. The value is a number of characters, which in UTF-8 mode
2719 may be different from the number of bytes. The fourth argument should
2720 point to an int variable. A non-negative value is a lower bound to the
2721 length of any matching string. There may not be any strings of that
2722 length that do actually match, but every string that does match is at
2723 least that long.
2724
2725 PCRE_INFO_NAMECOUNT
2726 PCRE_INFO_NAMEENTRYSIZE
2727 PCRE_INFO_NAMETABLE
2728
2729 PCRE supports the use of named as well as numbered capturing parenthe-
2730 ses. The names are just an additional way of identifying the parenthe-
2731 ses, which still acquire numbers. Several convenience functions such as
2732 pcre_get_named_substring() are provided for extracting captured sub-
2733 strings by name. It is also possible to extract the data directly, by
2734 first converting the name to a number in order to access the correct
2735 pointers in the output vector (described with pcre_exec() below). To do
2736 the conversion, you need to use the name-to-number map, which is
2737 described by these three values.
2738
2739 The map consists of a number of fixed-size entries. PCRE_INFO_NAMECOUNT
2740 gives the number of entries, and PCRE_INFO_NAMEENTRYSIZE gives the size
2741 of each entry; both of these return an int value. The entry size
2742 depends on the length of the longest name. PCRE_INFO_NAMETABLE returns
2743 a pointer to the first entry of the table. This is a pointer to char in
2744 the 8-bit library, where the first two bytes of each entry are the num-
2745 ber of the capturing parenthesis, most significant byte first. In the
2746 16-bit library, the pointer points to 16-bit data units, the first of
2747 which contains the parenthesis number. In the 32-bit library, the
2748 pointer points to 32-bit data units, the first of which contains the
2749 parenthesis number. The rest of the entry is the corresponding name,
2750 zero terminated.
2751
2752 The names are in alphabetical order. Duplicate names may appear if (?|
2753 is used to create multiple groups with the same number, as described in
2754 the section on duplicate subpattern numbers in the pcrepattern page.
2755 Duplicate names for subpatterns with different numbers are permitted
2756 only if PCRE_DUPNAMES is set. In all cases of duplicate names, they
2757 appear in the table in the order in which they were found in the pat-
2758 tern. In the absence of (?| this is the order of increasing number;
2759 when (?| is used this is not necessarily the case because later subpat-
2760 terns may have lower numbers.
2761
2762 As a simple example of the name/number table, consider the following
2763 pattern after compilation by the 8-bit library (assume PCRE_EXTENDED is
2764 set, so white space - including newlines - is ignored):
2765
2766 (?<date> (?<year>(\d\d)?\d\d) -
2767 (?<month>\d\d) - (?<day>\d\d) )
2768
2769 There are four named subpatterns, so the table has four entries, and
2770 each entry in the table is eight bytes long. The table is as follows,
2771 with non-printing bytes shows in hexadecimal, and undefined bytes shown
2772 as ??:
2773
2774 00 01 d a t e 00 ??
2775 00 05 d a y 00 ?? ??
2776 00 04 m o n t h 00
2777 00 02 y e a r 00 ??
2778
2779 When writing code to extract data from named subpatterns using the
2780 name-to-number map, remember that the length of the entries is likely
2781 to be different for each compiled pattern.
2782
2783 PCRE_INFO_OKPARTIAL
2784
2785 Return 1 if the pattern can be used for partial matching with
2786 pcre_exec(), otherwise 0. The fourth argument should point to an int
2787 variable. From release 8.00, this always returns 1, because the
2788 restrictions that previously applied to partial matching have been
2789 lifted. The pcrepartial documentation gives details of partial match-
2790 ing.
2791
2792 PCRE_INFO_OPTIONS
2793
2794 Return a copy of the options with which the pattern was compiled. The
2795 fourth argument should point to an unsigned long int variable. These
2796 option bits are those specified in the call to pcre_compile(), modified
2797 by any top-level option settings at the start of the pattern itself. In
2798 other words, they are the options that will be in force when matching
2799 starts. For example, if the pattern /(?im)abc(?-i)d/ is compiled with
2800 the PCRE_EXTENDED option, the result is PCRE_CASELESS, PCRE_MULTILINE,
2801 and PCRE_EXTENDED.
2802
2803 A pattern is automatically anchored by PCRE if all of its top-level
2804 alternatives begin with one of the following:
2805
2806 ^ unless PCRE_MULTILINE is set
2807 \A always
2808 \G always
2809 .* if PCRE_DOTALL is set and there are no back
2810 references to the subpattern in which .* appears
2811
2812 For such patterns, the PCRE_ANCHORED bit is set in the options returned
2813 by pcre_fullinfo().
2814
2815 PCRE_INFO_SIZE
2816
2817 Return the size of the compiled pattern in bytes (for both libraries).
2818 The fourth argument should point to a size_t variable. This value does
2819 not include the size of the pcre structure that is returned by
2820 pcre_compile(). The value that is passed as the argument to pcre_mal-
2821 loc() when pcre_compile() is getting memory in which to place the com-
2822 piled data is the value returned by this option plus the size of the
2823 pcre structure. Studying a compiled pattern, with or without JIT, does
2824 not alter the value returned by this option.
2825
2826 PCRE_INFO_STUDYSIZE
2827
2828 Return the size in bytes of the data block pointed to by the study_data
2829 field in a pcre_extra block. If pcre_extra is NULL, or there is no
2830 study data, zero is returned. The fourth argument should point to a
2831 size_t variable. The study_data field is set by pcre_study() to record
2832 information that will speed up matching (see the section entitled
2833 "Studying a pattern" above). The format of the study_data block is pri-
2834 vate, but its length is made available via this option so that it can
2835 be saved and restored (see the pcreprecompile documentation for
2836 details).
2837
2838 PCRE_INFO_FIRSTCHARACTERFLAGS
2839
2840 Return information about the first data unit of any matched string, for
2841 a non-anchored pattern. The fourth argument should point to an int
2842 variable.
2843
2844 If there is a fixed first value, for example, the letter "c" from a
2845 pattern such as (cat|cow|coyote), 1 is returned, and the character
2846 value can be retrieved using PCRE_INFO_FIRSTCHARACTER.
2847
2848 If there is no fixed first value, and if either
2849
2850 (a) the pattern was compiled with the PCRE_MULTILINE option, and every
2851 branch starts with "^", or
2852
2853 (b) every branch of the pattern starts with ".*" and PCRE_DOTALL is not
2854 set (if it were set, the pattern would be anchored),
2855
2856 2 is returned, indicating that the pattern matches only at the start of
2857 a subject string or after any newline within the string. Otherwise 0 is
2858 returned. For anchored patterns, 0 is returned.
2859
2860 PCRE_INFO_FIRSTCHARACTER
2861
2862 Return the fixed first character value, if PCRE_INFO_FIRSTCHARACTER-
2863 FLAGS returned 1; otherwise returns 0. The fourth argument should point
2864 to an uint_t variable.
2865
2866 In the 8-bit library, the value is always less than 256. In the 16-bit
2867 library the value can be up to 0xffff. In the 32-bit library in UTF-32
2868 mode the value can be up to 0x10ffff, and up to 0xffffffff when not
2869 using UTF-32 mode.
2870
2871 If there is no fixed first value, and if either
2872
2873 (a) the pattern was compiled with the PCRE_MULTILINE option, and every
2874 branch starts with "^", or
2875
2876 (b) every branch of the pattern starts with ".*" and PCRE_DOTALL is not
2877 set (if it were set, the pattern would be anchored),
2878
2879 -1 is returned, indicating that the pattern matches only at the start
2880 of a subject string or after any newline within the string. Otherwise
2881 -2 is returned. For anchored patterns, -2 is returned.
2882
2883 PCRE_INFO_REQUIREDCHARFLAGS
2884
2885 Returns 1 if there is a rightmost literal data unit that must exist in
2886 any matched string, other than at its start. The fourth argument should
2887 point to an int variable. If there is no such value, 0 is returned. If
2888 returning 1, the character value itself can be retrieved using
2889 PCRE_INFO_REQUIREDCHAR.
2890
2891 For anchored patterns, a last literal value is recorded only if it fol-
2892 lows something of variable length. For example, for the pattern
2893 /^a\d+z\d+/ the returned value 1 (with "z" returned from
2894 PCRE_INFO_REQUIREDCHAR), but for /^a\dz\d/ the returned value is 0.
2895
2896 PCRE_INFO_REQUIREDCHAR
2897
2898 Return the value of the rightmost literal data unit that must exist in
2899 any matched string, other than at its start, if such a value has been
2900 recorded. The fourth argument should point to an uint32_t variable. If
2901 there is no such value, 0 is returned.
2902
2903
2904 REFERENCE COUNTS
2905
2906 int pcre_refcount(pcre *code, int adjust);
2907
2908 The pcre_refcount() function is used to maintain a reference count in
2909 the data block that contains a compiled pattern. It is provided for the
2910 benefit of applications that operate in an object-oriented manner,
2911 where different parts of the application may be using the same compiled
2912 pattern, but you want to free the block when they are all done.
2913
2914 When a pattern is compiled, the reference count field is initialized to
2915 zero. It is changed only by calling this function, whose action is to
2916 add the adjust value (which may be positive or negative) to it. The
2917 yield of the function is the new value. However, the value of the count
2918 is constrained to lie between 0 and 65535, inclusive. If the new value
2919 is outside these limits, it is forced to the appropriate limit value.
2920
2921 Except when it is zero, the reference count is not correctly preserved
2922 if a pattern is compiled on one host and then transferred to a host
2923 whose byte-order is different. (This seems a highly unlikely scenario.)
2924
2925
2926 MATCHING A PATTERN: THE TRADITIONAL FUNCTION
2927
2928 int pcre_exec(const pcre *code, const pcre_extra *extra,
2929 const char *subject, int length, int startoffset,
2930 int options, int *ovector, int ovecsize);
2931
2932 The function pcre_exec() is called to match a subject string against a
2933 compiled pattern, which is passed in the code argument. If the pattern
2934 was studied, the result of the study should be passed in the extra
2935 argument. You can call pcre_exec() with the same code and extra argu-
2936 ments as many times as you like, in order to match different subject
2937 strings with the same pattern.
2938
2939 This function is the main matching facility of the library, and it
2940 operates in a Perl-like manner. For specialist use there is also an
2941 alternative matching function, which is described below in the section
2942 about the pcre_dfa_exec() function.
2943
2944 In most applications, the pattern will have been compiled (and option-
2945 ally studied) in the same process that calls pcre_exec(). However, it
2946 is possible to save compiled patterns and study data, and then use them
2947 later in different processes, possibly even on different hosts. For a
2948 discussion about this, see the pcreprecompile documentation.
2949
2950 Here is an example of a simple call to pcre_exec():
2951
2952 int rc;
2953 int ovector[30];
2954 rc = pcre_exec(
2955 re, /* result of pcre_compile() */
2956 NULL, /* we didn't study the pattern */
2957 "some string", /* the subject string */
2958 11, /* the length of the subject string */
2959 0, /* start at offset 0 in the subject */
2960 0, /* default options */
2961 ovector, /* vector of integers for substring information */
2962 30); /* number of elements (NOT size in bytes) */
2963
2964 Extra data for pcre_exec()
2965
2966 If the extra argument is not NULL, it must point to a pcre_extra data
2967 block. The pcre_study() function returns such a block (when it doesn't
2968 return NULL), but you can also create one for yourself, and pass addi-
2969 tional information in it. The pcre_extra block contains the following
2970 fields (not necessarily in this order):
2971
2972 unsigned long int flags;
2973 void *study_data;
2974 void *executable_jit;
2975 unsigned long int match_limit;
2976 unsigned long int match_limit_recursion;
2977 void *callout_data;
2978 const unsigned char *tables;
2979 unsigned char **mark;
2980
2981 In the 16-bit version of this structure, the mark field has type
2982 "PCRE_UCHAR16 **".
2983
2984 In the 32-bit version of this structure, the mark field has type
2985 "PCRE_UCHAR32 **".
2986
2987 The flags field is used to specify which of the other fields are set.
2988 The flag bits are:
2989
2990 PCRE_EXTRA_CALLOUT_DATA
2991 PCRE_EXTRA_EXECUTABLE_JIT
2992 PCRE_EXTRA_MARK
2993 PCRE_EXTRA_MATCH_LIMIT
2994 PCRE_EXTRA_MATCH_LIMIT_RECURSION
2995 PCRE_EXTRA_STUDY_DATA
2996 PCRE_EXTRA_TABLES
2997
2998 Other flag bits should be set to zero. The study_data field and some-
2999 times the executable_jit field are set in the pcre_extra block that is
3000 returned by pcre_study(), together with the appropriate flag bits. You
3001 should not set these yourself, but you may add to the block by setting
3002 other fields and their corresponding flag bits.
3003
3004 The match_limit field provides a means of preventing PCRE from using up
3005 a vast amount of resources when running patterns that are not going to
3006 match, but which have a very large number of possibilities in their
3007 search trees. The classic example is a pattern that uses nested unlim-
3008 ited repeats.
3009
3010 Internally, pcre_exec() uses a function called match(), which it calls
3011 repeatedly (sometimes recursively). The limit set by match_limit is
3012 imposed on the number of times this function is called during a match,
3013 which has the effect of limiting the amount of backtracking that can
3014 take place. For patterns that are not anchored, the count restarts from
3015 zero for each position in the subject string.
3016
3017 When pcre_exec() is called with a pattern that was successfully studied
3018 with a JIT option, the way that the matching is executed is entirely
3019 different. However, there is still the possibility of runaway matching
3020 that goes on for a very long time, and so the match_limit value is also
3021 used in this case (but in a different way) to limit how long the match-
3022 ing can continue.
3023
3024 The default value for the limit can be set when PCRE is built; the
3025 default default is 10 million, which handles all but the most extreme
3026 cases. You can override the default by suppling pcre_exec() with a
3027 pcre_extra block in which match_limit is set, and
3028 PCRE_EXTRA_MATCH_LIMIT is set in the flags field. If the limit is
3029 exceeded, pcre_exec() returns PCRE_ERROR_MATCHLIMIT.
3030
3031 The match_limit_recursion field is similar to match_limit, but instead
3032 of limiting the total number of times that match() is called, it limits
3033 the depth of recursion. The recursion depth is a smaller number than
3034 the total number of calls, because not all calls to match() are recur-
3035 sive. This limit is of use only if it is set smaller than match_limit.
3036
3037 Limiting the recursion depth limits the amount of machine stack that
3038 can be used, or, when PCRE has been compiled to use memory on the heap
3039 instead of the stack, the amount of heap memory that can be used. This
3040 limit is not relevant, and is ignored, when matching is done using JIT
3041 compiled code.
3042
3043 The default value for match_limit_recursion can be set when PCRE is
3044 built; the default default is the same value as the default for
3045 match_limit. You can override the default by suppling pcre_exec() with
3046 a pcre_extra block in which match_limit_recursion is set, and
3047 PCRE_EXTRA_MATCH_LIMIT_RECURSION is set in the flags field. If the
3048 limit is exceeded, pcre_exec() returns PCRE_ERROR_RECURSIONLIMIT.
3049
3050 The callout_data field is used in conjunction with the "callout" fea-
3051 ture, and is described in the pcrecallout documentation.
3052
3053 The tables field is used to pass a character tables pointer to
3054 pcre_exec(); this overrides the value that is stored with the compiled
3055 pattern. A non-NULL value is stored with the compiled pattern only if
3056 custom tables were supplied to pcre_compile() via its tableptr argu-
3057 ment. If NULL is passed to pcre_exec() using this mechanism, it forces
3058 PCRE's internal tables to be used. This facility is helpful when re-
3059 using patterns that have been saved after compiling with an external
3060 set of tables, because the external tables might be at a different
3061 address when pcre_exec() is called. See the pcreprecompile documenta-
3062 tion for a discussion of saving compiled patterns for later use.
3063
3064 If PCRE_EXTRA_MARK is set in the flags field, the mark field must be
3065 set to point to a suitable variable. If the pattern contains any back-
3066 tracking control verbs such as (*MARK:NAME), and the execution ends up
3067 with a name to pass back, a pointer to the name string (zero termi-
3068 nated) is placed in the variable pointed to by the mark field. The
3069 names are within the compiled pattern; if you wish to retain such a
3070 name you must copy it before freeing the memory of a compiled pattern.
3071 If there is no name to pass back, the variable pointed to by the mark
3072 field is set to NULL. For details of the backtracking control verbs,
3073 see the section entitled "Backtracking control" in the pcrepattern doc-
3074 umentation.
3075
3076 Option bits for pcre_exec()
3077
3078 The unused bits of the options argument for pcre_exec() must be zero.
3079 The only bits that may be set are PCRE_ANCHORED, PCRE_NEWLINE_xxx,
3080 PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, PCRE_NOTEMPTY_ATSTART,
3081 PCRE_NO_START_OPTIMIZE, PCRE_NO_UTF8_CHECK, PCRE_PARTIAL_HARD, and
3082 PCRE_PARTIAL_SOFT.
3083
3084 If the pattern was successfully studied with one of the just-in-time
3085 (JIT) compile options, the only supported options for JIT execution are
3086 PCRE_NO_UTF8_CHECK, PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY,
3087 PCRE_NOTEMPTY_ATSTART, PCRE_PARTIAL_HARD, and PCRE_PARTIAL_SOFT. If an
3088 unsupported option is used, JIT execution is disabled and the normal
3089 interpretive code in pcre_exec() is run.
3090
3091 PCRE_ANCHORED
3092
3093 The PCRE_ANCHORED option limits pcre_exec() to matching at the first
3094 matching position. If a pattern was compiled with PCRE_ANCHORED, or
3095 turned out to be anchored by virtue of its contents, it cannot be made
3096 unachored at matching time.
3097
3098 PCRE_BSR_ANYCRLF
3099 PCRE_BSR_UNICODE
3100
3101 These options (which are mutually exclusive) control what the \R escape
3102 sequence matches. The choice is either to match only CR, LF, or CRLF,
3103 or to match any Unicode newline sequence. These options override the
3104 choice that was made or defaulted when the pattern was compiled.
3105
3106 PCRE_NEWLINE_CR
3107 PCRE_NEWLINE_LF
3108 PCRE_NEWLINE_CRLF
3109 PCRE_NEWLINE_ANYCRLF
3110 PCRE_NEWLINE_ANY
3111
3112 These options override the newline definition that was chosen or
3113 defaulted when the pattern was compiled. For details, see the descrip-
3114 tion of pcre_compile() above. During matching, the newline choice
3115 affects the behaviour of the dot, circumflex, and dollar metacharac-
3116 ters. It may also alter the way the match position is advanced after a
3117 match failure for an unanchored pattern.
3118
3119 When PCRE_NEWLINE_CRLF, PCRE_NEWLINE_ANYCRLF, or PCRE_NEWLINE_ANY is
3120 set, and a match attempt for an unanchored pattern fails when the cur-
3121 rent position is at a CRLF sequence, and the pattern contains no
3122 explicit matches for CR or LF characters, the match position is
3123 advanced by two characters instead of one, in other words, to after the
3124 CRLF.
3125
3126 The above rule is a compromise that makes the most common cases work as
3127 expected. For example, if the pattern is .+A (and the PCRE_DOTALL
3128 option is not set), it does not match the string "\r\nA" because, after
3129 failing at the start, it skips both the CR and the LF before retrying.
3130 However, the pattern [\r\n]A does match that string, because it con-
3131 tains an explicit CR or LF reference, and so advances only by one char-
3132 acter after the first failure.
3133
3134 An explicit match for CR of LF is either a literal appearance of one of
3135 those characters, or one of the \r or \n escape sequences. Implicit
3136 matches such as [^X] do not count, nor does \s (which includes CR and
3137 LF in the characters that it matches).
3138
3139 Notwithstanding the above, anomalous effects may still occur when CRLF
3140 is a valid newline sequence and explicit \r or \n escapes appear in the
3141 pattern.
3142
3143 PCRE_NOTBOL
3144
3145 This option specifies that first character of the subject string is not
3146 the beginning of a line, so the circumflex metacharacter should not
3147 match before it. Setting this without PCRE_MULTILINE (at compile time)
3148 causes circumflex never to match. This option affects only the behav-
3149 iour of the circumflex metacharacter. It does not affect \A.
3150
3151 PCRE_NOTEOL
3152
3153 This option specifies that the end of the subject string is not the end
3154 of a line, so the dollar metacharacter should not match it nor (except
3155 in multiline mode) a newline immediately before it. Setting this with-
3156 out PCRE_MULTILINE (at compile time) causes dollar never to match. This
3157 option affects only the behaviour of the dollar metacharacter. It does
3158 not affect \Z or \z.
3159
3160 PCRE_NOTEMPTY
3161
3162 An empty string is not considered to be a valid match if this option is
3163 set. If there are alternatives in the pattern, they are tried. If all
3164 the alternatives match the empty string, the entire match fails. For
3165 example, if the pattern
3166
3167 a?b?
3168
3169 is applied to a string not beginning with "a" or "b", it matches an
3170 empty string at the start of the subject. With PCRE_NOTEMPTY set, this
3171 match is not valid, so PCRE searches further into the string for occur-
3172 rences of "a" or "b".
3173
3174 PCRE_NOTEMPTY_ATSTART
3175
3176 This is like PCRE_NOTEMPTY, except that an empty string match that is
3177 not at the start of the subject is permitted. If the pattern is
3178 anchored, such a match can occur only if the pattern contains \K.
3179
3180 Perl has no direct equivalent of PCRE_NOTEMPTY or
3181 PCRE_NOTEMPTY_ATSTART, but it does make a special case of a pattern
3182 match of the empty string within its split() function, and when using
3183 the /g modifier. It is possible to emulate Perl's behaviour after
3184 matching a null string by first trying the match again at the same off-
3185 set with PCRE_NOTEMPTY_ATSTART and PCRE_ANCHORED, and then if that
3186 fails, by advancing the starting offset (see below) and trying an ordi-
3187 nary match again. There is some code that demonstrates how to do this
3188 in the pcredemo sample program. In the most general case, you have to
3189 check to see if the newline convention recognizes CRLF as a newline,
3190 and if so, and the current character is CR followed by LF, advance the
3191 starting offset by two characters instead of one.
3192
3193 PCRE_NO_START_OPTIMIZE
3194
3195 There are a number of optimizations that pcre_exec() uses at the start
3196 of a match, in order to speed up the process. For example, if it is
3197 known that an unanchored match must start with a specific character, it
3198 searches the subject for that character, and fails immediately if it
3199 cannot find it, without actually running the main matching function.
3200 This means that a special item such as (*COMMIT) at the start of a pat-
3201 tern is not considered until after a suitable starting point for the
3202 match has been found. When callouts or (*MARK) items are in use, these
3203 "start-up" optimizations can cause them to be skipped if the pattern is
3204 never actually used. The start-up optimizations are in effect a pre-
3205 scan of the subject that takes place before the pattern is run.
3206
3207 The PCRE_NO_START_OPTIMIZE option disables the start-up optimizations,
3208 possibly causing performance to suffer, but ensuring that in cases
3209 where the result is "no match", the callouts do occur, and that items
3210 such as (*COMMIT) and (*MARK) are considered at every possible starting
3211 position in the subject string. If PCRE_NO_START_OPTIMIZE is set at
3212 compile time, it cannot be unset at matching time. The use of
3213 PCRE_NO_START_OPTIMIZE disables JIT execution; when it is set, matching
3214 is always done using interpretively.
3215
3216 Setting PCRE_NO_START_OPTIMIZE can change the outcome of a matching
3217 operation. Consider the pattern
3218
3219 (*COMMIT)ABC
3220
3221 When this is compiled, PCRE records the fact that a match must start
3222 with the character "A". Suppose the subject string is "DEFABC". The
3223 start-up optimization scans along the subject, finds "A" and runs the
3224 first match attempt from there. The (*COMMIT) item means that the pat-
3225 tern must match the current starting position, which in this case, it
3226 does. However, if the same match is run with PCRE_NO_START_OPTIMIZE
3227 set, the initial scan along the subject string does not happen. The
3228 first match attempt is run starting from "D" and when this fails,
3229 (*COMMIT) prevents any further matches being tried, so the overall
3230 result is "no match". If the pattern is studied, more start-up opti-
3231 mizations may be used. For example, a minimum length for the subject
3232 may be recorded. Consider the pattern
3233
3234 (*MARK:A)(X|Y)
3235
3236 The minimum length for a match is one character. If the subject is
3237 "ABC", there will be attempts to match "ABC", "BC", "C", and then
3238 finally an empty string. If the pattern is studied, the final attempt
3239 does not take place, because PCRE knows that the subject is too short,
3240 and so the (*MARK) is never encountered. In this case, studying the
3241 pattern does not affect the overall match result, which is still "no
3242 match", but it does affect the auxiliary information that is returned.
3243
3244 PCRE_NO_UTF8_CHECK
3245
3246 When PCRE_UTF8 is set at compile time, the validity of the subject as a
3247 UTF-8 string is automatically checked when pcre_exec() is subsequently
3248 called. The entire string is checked before any other processing takes
3249 place. The value of startoffset is also checked to ensure that it
3250 points to the start of a UTF-8 character. There is a discussion about
3251 the validity of UTF-8 strings in the pcreunicode page. If an invalid
3252 sequence of bytes is found, pcre_exec() returns the error
3253 PCRE_ERROR_BADUTF8 or, if PCRE_PARTIAL_HARD is set and the problem is a
3254 truncated character at the end of the subject, PCRE_ERROR_SHORTUTF8. In
3255 both cases, information about the precise nature of the error may also
3256 be returned (see the descriptions of these errors in the section enti-
3257 tled Error return values from pcre_exec() below). If startoffset con-
3258 tains a value that does not point to the start of a UTF-8 character (or
3259 to the end of the subject), PCRE_ERROR_BADUTF8_OFFSET is returned.
3260
3261 If you already know that your subject is valid, and you want to skip
3262 these checks for performance reasons, you can set the
3263 PCRE_NO_UTF8_CHECK option when calling pcre_exec(). You might want to
3264 do this for the second and subsequent calls to pcre_exec() if you are
3265 making repeated calls to find all the matches in a single subject
3266 string. However, you should be sure that the value of startoffset
3267 points to the start of a character (or the end of the subject). When
3268 PCRE_NO_UTF8_CHECK is set, the effect of passing an invalid string as a
3269 subject or an invalid value of startoffset is undefined. Your program
3270 may crash.
3271
3272 PCRE_PARTIAL_HARD
3273 PCRE_PARTIAL_SOFT
3274
3275 These options turn on the partial matching feature. For backwards com-
3276 patibility, PCRE_PARTIAL is a synonym for PCRE_PARTIAL_SOFT. A partial
3277 match occurs if the end of the subject string is reached successfully,
3278 but there are not enough subject characters to complete the match. If
3279 this happens when PCRE_PARTIAL_SOFT (but not PCRE_PARTIAL_HARD) is set,
3280 matching continues by testing any remaining alternatives. Only if no
3281 complete match can be found is PCRE_ERROR_PARTIAL returned instead of
3282 PCRE_ERROR_NOMATCH. In other words, PCRE_PARTIAL_SOFT says that the
3283 caller is prepared to handle a partial match, but only if no complete
3284 match can be found.
3285
3286 If PCRE_PARTIAL_HARD is set, it overrides PCRE_PARTIAL_SOFT. In this
3287 case, if a partial match is found, pcre_exec() immediately returns
3288 PCRE_ERROR_PARTIAL, without considering any other alternatives. In
3289 other words, when PCRE_PARTIAL_HARD is set, a partial match is consid-
3290 ered to be more important that an alternative complete match.
3291
3292 In both cases, the portion of the string that was inspected when the
3293 partial match was found is set as the first matching string. There is a
3294 more detailed discussion of partial and multi-segment matching, with
3295 examples, in the pcrepartial documentation.
3296
3297 The string to be matched by pcre_exec()
3298
3299 The subject string is passed to pcre_exec() as a pointer in subject, a
3300 length in bytes in length, and a starting byte offset in startoffset.
3301 If this is negative or greater than the length of the subject,
3302 pcre_exec() returns PCRE_ERROR_BADOFFSET. When the starting offset is
3303 zero, the search for a match starts at the beginning of the subject,
3304 and this is by far the most common case. In UTF-8 mode, the byte offset
3305 must point to the start of a UTF-8 character (or the end of the sub-
3306 ject). Unlike the pattern string, the subject may contain binary zero
3307 bytes.
3308
3309 A non-zero starting offset is useful when searching for another match
3310 in the same subject by calling pcre_exec() again after a previous suc-
3311 cess. Setting startoffset differs from just passing over a shortened
3312 string and setting PCRE_NOTBOL in the case of a pattern that begins
3313 with any kind of lookbehind. For example, consider the pattern
3314
3315 \Biss\B
3316
3317 which finds occurrences of "iss" in the middle of words. (\B matches
3318 only if the current position in the subject is not a word boundary.)
3319 When applied to the string "Mississipi" the first call to pcre_exec()
3320 finds the first occurrence. If pcre_exec() is called again with just
3321 the remainder of the subject, namely "issipi", it does not match,
3322 because \B is always false at the start of the subject, which is deemed
3323 to be a word boundary. However, if pcre_exec() is passed the entire
3324 string again, but with startoffset set to 4, it finds the second occur-
3325 rence of "iss" because it is able to look behind the starting point to
3326 discover that it is preceded by a letter.
3327
3328 Finding all the matches in a subject is tricky when the pattern can
3329 match an empty string. It is possible to emulate Perl's /g behaviour by
3330 first trying the match again at the same offset, with the
3331 PCRE_NOTEMPTY_ATSTART and PCRE_ANCHORED options, and then if that
3332 fails, advancing the starting offset and trying an ordinary match
3333 again. There is some code that demonstrates how to do this in the pcre-
3334 demo sample program. In the most general case, you have to check to see
3335 if the newline convention recognizes CRLF as a newline, and if so, and
3336 the current character is CR followed by LF, advance the starting offset
3337 by two characters instead of one.
3338
3339 If a non-zero starting offset is passed when the pattern is anchored,
3340 one attempt to match at the given offset is made. This can only succeed
3341 if the pattern does not require the match to be at the start of the
3342 subject.
3343
3344 How pcre_exec() returns captured substrings
3345
3346 In general, a pattern matches a certain portion of the subject, and in
3347 addition, further substrings from the subject may be picked out by
3348 parts of the pattern. Following the usage in Jeffrey Friedl's book,
3349 this is called "capturing" in what follows, and the phrase "capturing
3350 subpattern" is used for a fragment of a pattern that picks out a sub-
3351 string. PCRE supports several other kinds of parenthesized subpattern
3352 that do not cause substrings to be captured.
3353
3354 Captured substrings are returned to the caller via a vector of integers
3355 whose address is passed in ovector. The number of elements in the vec-
3356 tor is passed in ovecsize, which must be a non-negative number. Note:
3357 this argument is NOT the size of ovector in bytes.
3358
3359 The first two-thirds of the vector is used to pass back captured sub-
3360 strings, each substring using a pair of integers. The remaining third
3361 of the vector is used as workspace by pcre_exec() while matching cap-
3362 turing subpatterns, and is not available for passing back information.
3363 The number passed in ovecsize should always be a multiple of three. If
3364 it is not, it is rounded down.
3365
3366 When a match is successful, information about captured substrings is
3367 returned in pairs of integers, starting at the beginning of ovector,
3368 and continuing up to two-thirds of its length at the most. The first
3369 element of each pair is set to the byte offset of the first character
3370 in a substring, and the second is set to the byte offset of the first
3371 character after the end of a substring. Note: these values are always
3372 byte offsets, even in UTF-8 mode. They are not character counts.
3373
3374 The first pair of integers, ovector[0] and ovector[1], identify the
3375 portion of the subject string matched by the entire pattern. The next
3376 pair is used for the first capturing subpattern, and so on. The value
3377 returned by pcre_exec() is one more than the highest numbered pair that
3378 has been set. For example, if two substrings have been captured, the
3379 returned value is 3. If there are no capturing subpatterns, the return
3380 value from a successful match is 1, indicating that just the first pair
3381 of offsets has been set.
3382
3383 If a capturing subpattern is matched repeatedly, it is the last portion
3384 of the string that it matched that is returned.
3385
3386 If the vector is too small to hold all the captured substring offsets,
3387 it is used as far as possible (up to two-thirds of its length), and the
3388 function returns a value of zero. If neither the actual string matched
3389 nor any captured substrings are of interest, pcre_exec() may be called
3390 with ovector passed as NULL and ovecsize as zero. However, if the pat-
3391 tern contains back references and the ovector is not big enough to
3392 remember the related substrings, PCRE has to get additional memory for
3393 use during matching. Thus it is usually advisable to supply an ovector
3394 of reasonable size.
3395
3396 There are some cases where zero is returned (indicating vector over-
3397 flow) when in fact the vector is exactly the right size for the final
3398 match. For example, consider the pattern
3399
3400 (a)(?:(b)c|bd)
3401
3402 If a vector of 6 elements (allowing for only 1 captured substring) is
3403 given with subject string "abd", pcre_exec() will try to set the second
3404 captured string, thereby recording a vector overflow, before failing to
3405 match "c" and backing up to try the second alternative. The zero
3406 return, however, does correctly indicate that the maximum number of
3407 slots (namely 2) have been filled. In similar cases where there is tem-
3408 porary overflow, but the final number of used slots is actually less
3409 than the maximum, a non-zero value is returned.
3410
3411 The pcre_fullinfo() function can be used to find out how many capturing
3412 subpatterns there are in a compiled pattern. The smallest size for
3413 ovector that will allow for n captured substrings, in addition to the
3414 offsets of the substring matched by the whole pattern, is (n+1)*3.
3415
3416 It is possible for capturing subpattern number n+1 to match some part
3417 of the subject when subpattern n has not been used at all. For example,
3418 if the string "abc" is matched against the pattern (a|(z))(bc) the
3419 return from the function is 4, and subpatterns 1 and 3 are matched, but
3420 2 is not. When this happens, both values in the offset pairs corre-
3421 sponding to unused subpatterns are set to -1.
3422
3423 Offset values that correspond to unused subpatterns at the end of the
3424 expression are also set to -1. For example, if the string "abc" is
3425 matched against the pattern (abc)(x(yz)?)? subpatterns 2 and 3 are not
3426 matched. The return from the function is 2, because the highest used
3427 capturing subpattern number is 1, and the offsets for for the second
3428 and third capturing subpatterns (assuming the vector is large enough,
3429 of course) are set to -1.
3430
3431 Note: Elements in the first two-thirds of ovector that do not corre-
3432 spond to capturing parentheses in the pattern are never changed. That
3433 is, if a pattern contains n capturing parentheses, no more than ovec-
3434 tor[0] to ovector[2n+1] are set by pcre_exec(). The other elements (in
3435 the first two-thirds) retain whatever values they previously had.
3436
3437 Some convenience functions are provided for extracting the captured
3438 substrings as separate strings. These are described below.
3439
3440 Error return values from pcre_exec()
3441
3442 If pcre_exec() fails, it returns a negative number. The following are
3443 defined in the header file:
3444
3445 PCRE_ERROR_NOMATCH (-1)
3446
3447 The subject string did not match the pattern.
3448
3449 PCRE_ERROR_NULL (-2)
3450
3451 Either code or subject was passed as NULL, or ovector was NULL and
3452 ovecsize was not zero.
3453
3454 PCRE_ERROR_BADOPTION (-3)
3455
3456 An unrecognized bit was set in the options argument.
3457
3458 PCRE_ERROR_BADMAGIC (-4)
3459
3460 PCRE stores a 4-byte "magic number" at the start of the compiled code,
3461 to catch the case when it is passed a junk pointer and to detect when a
3462 pattern that was compiled in an environment of one endianness is run in
3463 an environment with the other endianness. This is the error that PCRE
3464 gives when the magic number is not present.
3465
3466 PCRE_ERROR_UNKNOWN_OPCODE (-5)
3467
3468 While running the pattern match, an unknown item was encountered in the
3469 compiled pattern. This error could be caused by a bug in PCRE or by
3470 overwriting of the compiled pattern.
3471
3472 PCRE_ERROR_NOMEMORY (-6)
3473
3474 If a pattern contains back references, but the ovector that is passed
3475 to pcre_exec() is not big enough to remember the referenced substrings,
3476 PCRE gets a block of memory at the start of matching to use for this
3477 purpose. If the call via pcre_malloc() fails, this error is given. The
3478 memory is automatically freed at the end of matching.
3479
3480 This error is also given if pcre_stack_malloc() fails in pcre_exec().
3481 This can happen only when PCRE has been compiled with --disable-stack-
3482 for-recursion.
3483
3484 PCRE_ERROR_NOSUBSTRING (-7)
3485
3486 This error is used by the pcre_copy_substring(), pcre_get_substring(),
3487 and pcre_get_substring_list() functions (see below). It is never
3488 returned by pcre_exec().
3489
3490 PCRE_ERROR_MATCHLIMIT (-8)
3491
3492 The backtracking limit, as specified by the match_limit field in a
3493 pcre_extra structure (or defaulted) was reached. See the description
3494 above.
3495
3496 PCRE_ERROR_CALLOUT (-9)
3497
3498 This error is never generated by pcre_exec() itself. It is provided for
3499 use by callout functions that want to yield a distinctive error code.
3500 See the pcrecallout documentation for details.
3501
3502 PCRE_ERROR_BADUTF8 (-10)
3503
3504 A string that contains an invalid UTF-8 byte sequence was passed as a
3505 subject, and the PCRE_NO_UTF8_CHECK option was not set. If the size of
3506 the output vector (ovecsize) is at least 2, the byte offset to the
3507 start of the the invalid UTF-8 character is placed in the first ele-
3508 ment, and a reason code is placed in the second element. The reason
3509 codes are listed in the following section. For backward compatibility,
3510 if PCRE_PARTIAL_HARD is set and the problem is a truncated UTF-8 char-
3511 acter at the end of the subject (reason codes 1 to 5),
3512 PCRE_ERROR_SHORTUTF8 is returned instead of PCRE_ERROR_BADUTF8.
3513
3514 PCRE_ERROR_BADUTF8_OFFSET (-11)
3515
3516 The UTF-8 byte sequence that was passed as a subject was checked and
3517 found to be valid (the PCRE_NO_UTF8_CHECK option was not set), but the
3518 value of startoffset did not point to the beginning of a UTF-8 charac-
3519 ter or the end of the subject.
3520
3521 PCRE_ERROR_PARTIAL (-12)
3522
3523 The subject string did not match, but it did match partially. See the
3524 pcrepartial documentation for details of partial matching.
3525
3526 PCRE_ERROR_BADPARTIAL (-13)
3527
3528 This code is no longer in use. It was formerly returned when the
3529 PCRE_PARTIAL option was used with a compiled pattern containing items
3530 that were not supported for partial matching. From release 8.00
3531 onwards, there are no restrictions on partial matching.
3532
3533 PCRE_ERROR_INTERNAL (-14)
3534
3535 An unexpected internal error has occurred. This error could be caused
3536 by a bug in PCRE or by overwriting of the compiled pattern.
3537
3538 PCRE_ERROR_BADCOUNT (-15)
3539
3540 This error is given if the value of the ovecsize argument is negative.
3541
3542 PCRE_ERROR_RECURSIONLIMIT (-21)
3543
3544 The internal recursion limit, as specified by the match_limit_recursion
3545 field in a pcre_extra structure (or defaulted) was reached. See the
3546 description above.
3547
3548 PCRE_ERROR_BADNEWLINE (-23)
3549
3550 An invalid combination of PCRE_NEWLINE_xxx options was given.
3551
3552 PCRE_ERROR_BADOFFSET (-24)
3553
3554 The value of startoffset was negative or greater than the length of the
3555 subject, that is, the value in length.
3556
3557 PCRE_ERROR_SHORTUTF8 (-25)
3558
3559 This error is returned instead of PCRE_ERROR_BADUTF8 when the subject
3560 string ends with a truncated UTF-8 character and the PCRE_PARTIAL_HARD
3561 option is set. Information about the failure is returned as for
3562 PCRE_ERROR_BADUTF8. It is in fact sufficient to detect this case, but
3563 this special error code for PCRE_PARTIAL_HARD precedes the implementa-
3564 tion of returned information; it is retained for backwards compatibil-
3565 ity.
3566
3567 PCRE_ERROR_RECURSELOOP (-26)
3568
3569 This error is returned when pcre_exec() detects a recursion loop within
3570 the pattern. Specifically, it means that either the whole pattern or a
3571 subpattern has been called recursively for the second time at the same
3572 position in the subject string. Some simple patterns that might do this
3573 are detected and faulted at compile time, but more complicated cases,
3574 in particular mutual recursions between two different subpatterns, can-
3575 not be detected until run time.
3576
3577 PCRE_ERROR_JIT_STACKLIMIT (-27)
3578
3579 This error is returned when a pattern that was successfully studied
3580 using a JIT compile option is being matched, but the memory available
3581 for the just-in-time processing stack is not large enough. See the
3582 pcrejit documentation for more details.
3583
3584 PCRE_ERROR_BADMODE (-28)
3585
3586 This error is given if a pattern that was compiled by the 8-bit library
3587 is passed to a 16-bit or 32-bit library function, or vice versa.
3588
3589 PCRE_ERROR_BADENDIANNESS (-29)
3590
3591 This error is given if a pattern that was compiled and saved is
3592 reloaded on a host with different endianness. The utility function
3593 pcre_pattern_to_host_byte_order() can be used to convert such a pattern
3594 so that it runs on the new host.
3595
3596 PCRE_ERROR_JIT_BADOPTION
3597
3598 This error is returned when a pattern that was successfully studied
3599 using a JIT compile option is being matched, but the matching mode
3600 (partial or complete match) does not correspond to any JIT compilation
3601 mode. When the JIT fast path function is used, this error may be also
3602 given for invalid options. See the pcrejit documentation for more
3603 details.
3604
3605 PCRE_ERROR_BADLENGTH (-32)
3606
3607 This error is given if pcre_exec() is called with a negative value for
3608 the length argument.
3609
3610 Error numbers -16 to -20, -22, and 30 are not used by pcre_exec().
3611
3612 Reason codes for invalid UTF-8 strings
3613
3614 This section applies only to the 8-bit library. The corresponding
3615 information for the 16-bit and 32-bit libraries is given in the pcre16
3616 and pcre32 pages.
3617
3618 When pcre_exec() returns either PCRE_ERROR_BADUTF8 or PCRE_ERROR_SHORT-
3619 UTF8, and the size of the output vector (ovecsize) is at least 2, the
3620 offset of the start of the invalid UTF-8 character is placed in the
3621 first output vector element (ovector[0]) and a reason code is placed in
3622 the second element (ovector[1]). The reason codes are given names in
3623 the pcre.h header file:
3624
3625 PCRE_UTF8_ERR1
3626 PCRE_UTF8_ERR2
3627 PCRE_UTF8_ERR3
3628 PCRE_UTF8_ERR4
3629 PCRE_UTF8_ERR5
3630
3631 The string ends with a truncated UTF-8 character; the code specifies
3632 how many bytes are missing (1 to 5). Although RFC 3629 restricts UTF-8
3633 characters to be no longer than 4 bytes, the encoding scheme (origi-
3634 nally defined by RFC 2279) allows for up to 6 bytes, and this is
3635 checked first; hence the possibility of 4 or 5 missing bytes.
3636
3637 PCRE_UTF8_ERR6
3638 PCRE_UTF8_ERR7
3639 PCRE_UTF8_ERR8
3640 PCRE_UTF8_ERR9
3641 PCRE_UTF8_ERR10
3642
3643 The two most significant bits of the 2nd, 3rd, 4th, 5th, or 6th byte of
3644 the character do not have the binary value 0b10 (that is, either the
3645 most significant bit is 0, or the next bit is 1).
3646
3647 PCRE_UTF8_ERR11
3648 PCRE_UTF8_ERR12
3649
3650 A character that is valid by the RFC 2279 rules is either 5 or 6 bytes
3651 long; these code points are excluded by RFC 3629.
3652
3653 PCRE_UTF8_ERR13
3654
3655 A 4-byte character has a value greater than 0x10fff; these code points
3656 are excluded by RFC 3629.
3657
3658 PCRE_UTF8_ERR14
3659
3660 A 3-byte character has a value in the range 0xd800 to 0xdfff; this
3661 range of code points are reserved by RFC 3629 for use with UTF-16, and
3662 so are excluded from UTF-8.
3663
3664 PCRE_UTF8_ERR15
3665 PCRE_UTF8_ERR16
3666 PCRE_UTF8_ERR17
3667 PCRE_UTF8_ERR18
3668 PCRE_UTF8_ERR19
3669
3670 A 2-, 3-, 4-, 5-, or 6-byte character is "overlong", that is, it codes
3671 for a value that can be represented by fewer bytes, which is invalid.
3672 For example, the two bytes 0xc0, 0xae give the value 0x2e, whose cor-
3673 rect coding uses just one byte.
3674
3675 PCRE_UTF8_ERR20
3676
3677 The two most significant bits of the first byte of a character have the
3678 binary value 0b10 (that is, the most significant bit is 1 and the sec-
3679 ond is 0). Such a byte can only validly occur as the second or subse-
3680 quent byte of a multi-byte character.
3681
3682 PCRE_UTF8_ERR21
3683
3684 The first byte of a character has the value 0xfe or 0xff. These values
3685 can never occur in a valid UTF-8 string.
3686
3687 PCRE_UTF8_ERR2
3688
3689 Non-character. These are the last two characters in each plane (0xfffe,
3690 0xffff, 0x1fffe, 0x1ffff .. 0x10fffe, 0x10ffff), and the characters
3691 0xfdd0..0xfdef.
3692
3693
3694 EXTRACTING CAPTURED SUBSTRINGS BY NUMBER
3695
3696 int pcre_copy_substring(const char *subject, int *ovector,
3697 int stringcount, int stringnumber, char *buffer,
3698 int buffersize);
3699
3700 int pcre_get_substring(const char *subject, int *ovector,
3701 int stringcount, int stringnumber,
3702 const char **stringptr);
3703
3704 int pcre_get_substring_list(const char *subject,
3705 int *ovector, int stringcount, const char ***listptr);
3706
3707 Captured substrings can be accessed directly by using the offsets
3708 returned by pcre_exec() in ovector. For convenience, the functions
3709 pcre_copy_substring(), pcre_get_substring(), and pcre_get_sub-
3710 string_list() are provided for extracting captured substrings as new,
3711 separate, zero-terminated strings. These functions identify substrings
3712 by number. The next section describes functions for extracting named
3713 substrings.
3714
3715 A substring that contains a binary zero is correctly extracted and has
3716 a further zero added on the end, but the result is not, of course, a C
3717 string. However, you can process such a string by referring to the
3718 length that is returned by pcre_copy_substring() and pcre_get_sub-
3719 string(). Unfortunately, the interface to pcre_get_substring_list() is
3720 not adequate for handling strings containing binary zeros, because the
3721 end of the final string is not independently indicated.
3722
3723 The first three arguments are the same for all three of these func-
3724 tions: subject is the subject string that has just been successfully
3725 matched, ovector is a pointer to the vector of integer offsets that was
3726 passed to pcre_exec(), and stringcount is the number of substrings that
3727 were captured by the match, including the substring that matched the
3728 entire regular expression. This is the value returned by pcre_exec() if
3729 it is greater than zero. If pcre_exec() returned zero, indicating that
3730 it ran out of space in ovector, the value passed as stringcount should
3731 be the number of elements in the vector divided by three.
3732
3733 The functions pcre_copy_substring() and pcre_get_substring() extract a
3734 single substring, whose number is given as stringnumber. A value of
3735 zero extracts the substring that matched the entire pattern, whereas
3736 higher values extract the captured substrings. For pcre_copy_sub-
3737 string(), the string is placed in buffer, whose length is given by
3738 buffersize, while for pcre_get_substring() a new block of memory is
3739 obtained via pcre_malloc, and its address is returned via stringptr.
3740 The yield of the function is the length of the string, not including
3741 the terminating zero, or one of these error codes:
3742
3743 PCRE_ERROR_NOMEMORY (-6)
3744
3745 The buffer was too small for pcre_copy_substring(), or the attempt to
3746 get memory failed for pcre_get_substring().
3747
3748 PCRE_ERROR_NOSUBSTRING (-7)
3749
3750 There is no substring whose number is stringnumber.
3751
3752 The pcre_get_substring_list() function extracts all available sub-
3753 strings and builds a list of pointers to them. All this is done in a
3754 single block of memory that is obtained via pcre_malloc. The address of
3755 the memory block is returned via listptr, which is also the start of
3756 the list of string pointers. The end of the list is marked by a NULL
3757 pointer. The yield of the function is zero if all went well, or the
3758 error code
3759
3760 PCRE_ERROR_NOMEMORY (-6)
3761
3762 if the attempt to get the memory block failed.
3763
3764 When any of these functions encounter a substring that is unset, which
3765 can happen when capturing subpattern number n+1 matches some part of
3766 the subject, but subpattern n has not been used at all, they return an
3767 empty string. This can be distinguished from a genuine zero-length sub-
3768 string by inspecting the appropriate offset in ovector, which is nega-
3769 tive for unset substrings.
3770
3771 The two convenience functions pcre_free_substring() and pcre_free_sub-
3772 string_list() can be used to free the memory returned by a previous
3773 call of pcre_get_substring() or pcre_get_substring_list(), respec-
3774 tively. They do nothing more than call the function pointed to by
3775 pcre_free, which of course could be called directly from a C program.
3776 However, PCRE is used in some situations where it is linked via a spe-
3777 cial interface to another programming language that cannot use
3778 pcre_free directly; it is for these cases that the functions are pro-
3779 vided.
3780
3781
3782 EXTRACTING CAPTURED SUBSTRINGS BY NAME
3783
3784 int pcre_get_stringnumber(const pcre *code,
3785 const char *name);
3786
3787 int pcre_copy_named_substring(const pcre *code,
3788 const char *subject, int *ovector,
3789 int stringcount, const char *stringname,
3790 char *buffer, int buffersize);
3791
3792 int pcre_get_named_substring(const pcre *code,
3793 const char *subject, int *ovector,
3794 int stringcount, const char *stringname,
3795 const char **stringptr);
3796
3797 To extract a substring by name, you first have to find associated num-
3798 ber. For example, for this pattern
3799
3800 (a+)b(?<xxx>\d+)...
3801
3802 the number of the subpattern called "xxx" is 2. If the name is known to
3803 be unique (PCRE_DUPNAMES was not set), you can find the number from the
3804 name by calling pcre_get_stringnumber(). The first argument is the com-
3805 piled pattern, and the second is the name. The yield of the function is
3806 the subpattern number, or PCRE_ERROR_NOSUBSTRING (-7) if there is no
3807 subpattern of that name.
3808
3809 Given the number, you can extract the substring directly, or use one of
3810 the functions described in the previous section. For convenience, there
3811 are also two functions that do the whole job.
3812
3813 Most of the arguments of pcre_copy_named_substring() and
3814 pcre_get_named_substring() are the same as those for the similarly
3815 named functions that extract by number. As these are described in the
3816 previous section, they are not re-described here. There are just two
3817 differences:
3818
3819 First, instead of a substring number, a substring name is given. Sec-
3820 ond, there is an extra argument, given at the start, which is a pointer
3821 to the compiled pattern. This is needed in order to gain access to the
3822 name-to-number translation table.
3823
3824 These functions call pcre_get_stringnumber(), and if it succeeds, they
3825 then call pcre_copy_substring() or pcre_get_substring(), as appropri-
3826 ate. NOTE: If PCRE_DUPNAMES is set and there are duplicate names, the
3827 behaviour may not be what you want (see the next section).
3828
3829 Warning: If the pattern uses the (?| feature to set up multiple subpat-
3830 terns with the same number, as described in the section on duplicate
3831 subpattern numbers in the pcrepattern page, you cannot use names to
3832 distinguish the different subpatterns, because names are not included
3833 in the compiled code. The matching process uses only numbers. For this
3834 reason, the use of different names for subpatterns of the same number
3835 causes an error at compile time.
3836
3837
3838 DUPLICATE SUBPATTERN NAMES
3839
3840 int pcre_get_stringtable_entries(const pcre *code,
3841 const char *name, char **first, char **last);
3842
3843 When a pattern is compiled with the PCRE_DUPNAMES option, names for
3844 subpatterns are not required to be unique. (Duplicate names are always
3845 allowed for subpatterns with the same number, created by using the (?|
3846 feature. Indeed, if such subpatterns are named, they are required to
3847 use the same names.)
3848
3849 Normally, patterns with duplicate names are such that in any one match,
3850 only one of the named subpatterns participates. An example is shown in
3851 the pcrepattern documentation.
3852
3853 When duplicates are present, pcre_copy_named_substring() and
3854 pcre_get_named_substring() return the first substring corresponding to
3855 the given name that is set. If none are set, PCRE_ERROR_NOSUBSTRING
3856 (-7) is returned; no data is returned. The pcre_get_stringnumber()
3857 function returns one of the numbers that are associated with the name,
3858 but it is not defined which it is.
3859
3860 If you want to get full details of all captured substrings for a given
3861 name, you must use the pcre_get_stringtable_entries() function. The
3862 first argument is the compiled pattern, and the second is the name. The
3863 third and fourth are pointers to variables which are updated by the
3864 function. After it has run, they point to the first and last entries in
3865 the name-to-number table for the given name. The function itself
3866 returns the length of each entry, or PCRE_ERROR_NOSUBSTRING (-7) if
3867 there are none. The format of the table is described above in the sec-
3868 tion entitled Information about a pattern above. Given all the rele-
3869 vant entries for the name, you can extract each of their numbers, and
3870 hence the captured data, if any.
3871
3872
3873 FINDING ALL POSSIBLE MATCHES
3874
3875 The traditional matching function uses a similar algorithm to Perl,
3876 which stops when it finds the first match, starting at a given point in
3877 the subject. If you want to find all possible matches, or the longest
3878 possible match, consider using the alternative matching function (see
3879 below) instead. If you cannot use the alternative function, but still
3880 need to find all possible matches, you can kludge it up by making use
3881 of the callout facility, which is described in the pcrecallout documen-
3882 tation.
3883
3884 What you have to do is to insert a callout right at the end of the pat-
3885 tern. When your callout function is called, extract and save the cur-
3886 rent matched substring. Then return 1, which forces pcre_exec() to
3887 backtrack and try other alternatives. Ultimately, when it runs out of
3888 matches, pcre_exec() will yield PCRE_ERROR_NOMATCH.
3889
3890
3891 OBTAINING AN ESTIMATE OF STACK USAGE
3892
3893 Matching certain patterns using pcre_exec() can use a lot of process
3894 stack, which in certain environments can be rather limited in size.
3895 Some users find it helpful to have an estimate of the amount of stack
3896 that is used by pcre_exec(), to help them set recursion limits, as
3897 described in the pcrestack documentation. The estimate that is output
3898 by pcretest when called with the -m and -C options is obtained by call-
3899 ing pcre_exec with the values NULL, NULL, NULL, -999, and -999 for its
3900 first five arguments.
3901
3902 Normally, if its first argument is NULL, pcre_exec() immediately
3903 returns the negative error code PCRE_ERROR_NULL, but with this special
3904 combination of arguments, it returns instead a negative number whose
3905 absolute value is the approximate stack frame size in bytes. (A nega-
3906 tive number is used so that it is clear that no match has happened.)
3907 The value is approximate because in some cases, recursive calls to
3908 pcre_exec() occur when there are one or two additional variables on the
3909 stack.
3910
3911 If PCRE has been compiled to use the heap instead of the stack for
3912 recursion, the value returned is the size of each block that is
3913 obtained from the heap.
3914
3915
3916 MATCHING A PATTERN: THE ALTERNATIVE FUNCTION
3917
3918 int pcre_dfa_exec(const pcre *code, const pcre_extra *extra,
3919 const char *subject, int length, int startoffset,
3920 int options, int *ovector, int ovecsize,
3921 int *workspace, int wscount);
3922
3923 The function pcre_dfa_exec() is called to match a subject string
3924 against a compiled pattern, using a matching algorithm that scans the
3925 subject string just once, and does not backtrack. This has different
3926 characteristics to the normal algorithm, and is not compatible with
3927 Perl. Some of the features of PCRE patterns are not supported. Never-
3928 theless, there are times when this kind of matching can be useful. For
3929 a discussion of the two matching algorithms, and a list of features
3930 that pcre_dfa_exec() does not support, see the pcrematching documenta-
3931 tion.
3932
3933 The arguments for the pcre_dfa_exec() function are the same as for
3934 pcre_exec(), plus two extras. The ovector argument is used in a differ-
3935 ent way, and this is described below. The other common arguments are
3936 used in the same way as for pcre_exec(), so their description is not
3937 repeated here.
3938
3939 The two additional arguments provide workspace for the function. The
3940 workspace vector should contain at least 20 elements. It is used for
3941 keeping track of multiple paths through the pattern tree. More
3942 workspace will be needed for patterns and subjects where there are a
3943 lot of potential matches.
3944
3945 Here is an example of a simple call to pcre_dfa_exec():
3946
3947 int rc;
3948 int ovector[10];
3949 int wspace[20];
3950 rc = pcre_dfa_exec(
3951 re, /* result of pcre_compile() */
3952 NULL, /* we didn't study the pattern */
3953 "some string", /* the subject string */
3954 11, /* the length of the subject string */
3955 0, /* start at offset 0 in the subject */
3956 0, /* default options */
3957 ovector, /* vector of integers for substring information */
3958 10, /* number of elements (NOT size in bytes) */
3959 wspace, /* working space vector */
3960 20); /* number of elements (NOT size in bytes) */
3961
3962 Option bits for pcre_dfa_exec()
3963
3964 The unused bits of the options argument for pcre_dfa_exec() must be
3965 zero. The only bits that may be set are PCRE_ANCHORED, PCRE_NEW-
3966 LINE_xxx, PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY,
3967 PCRE_NOTEMPTY_ATSTART, PCRE_NO_UTF8_CHECK, PCRE_BSR_ANYCRLF,
3968 PCRE_BSR_UNICODE, PCRE_NO_START_OPTIMIZE, PCRE_PARTIAL_HARD, PCRE_PAR-
3969 TIAL_SOFT, PCRE_DFA_SHORTEST, and PCRE_DFA_RESTART. All but the last
3970 four of these are exactly the same as for pcre_exec(), so their
3971 description is not repeated here.
3972
3973 PCRE_PARTIAL_HARD
3974 PCRE_PARTIAL_SOFT
3975
3976 These have the same general effect as they do for pcre_exec(), but the
3977 details are slightly different. When PCRE_PARTIAL_HARD is set for
3978 pcre_dfa_exec(), it returns PCRE_ERROR_PARTIAL if the end of the sub-
3979 ject is reached and there is still at least one matching possibility
3980 that requires additional characters. This happens even if some complete
3981 matches have also been found. When PCRE_PARTIAL_SOFT is set, the return
3982 code PCRE_ERROR_NOMATCH is converted into PCRE_ERROR_PARTIAL if the end
3983 of the subject is reached, there have been no complete matches, but
3984 there is still at least one matching possibility. The portion of the
3985 string that was inspected when the longest partial match was found is
3986 set as the first matching string in both cases. There is a more
3987 detailed discussion of partial and multi-segment matching, with exam-
3988 ples, in the pcrepartial documentation.
3989
3990 PCRE_DFA_SHORTEST
3991
3992 Setting the PCRE_DFA_SHORTEST option causes the matching algorithm to
3993 stop as soon as it has found one match. Because of the way the alterna-
3994 tive algorithm works, this is necessarily the shortest possible match
3995 at the first possible matching point in the subject string.
3996
3997 PCRE_DFA_RESTART
3998
3999 When pcre_dfa_exec() returns a partial match, it is possible to call it
4000 again, with additional subject characters, and have it continue with
4001 the same match. The PCRE_DFA_RESTART option requests this action; when
4002 it is set, the workspace and wscount options must reference the same
4003 vector as before because data about the match so far is left in them
4004 after a partial match. There is more discussion of this facility in the
4005 pcrepartial documentation.
4006
4007 Successful returns from pcre_dfa_exec()
4008
4009 When pcre_dfa_exec() succeeds, it may have matched more than one sub-
4010 string in the subject. Note, however, that all the matches from one run
4011 of the function start at the same point in the subject. The shorter
4012 matches are all initial substrings of the longer matches. For example,
4013 if the pattern
4014
4015 <.*>
4016
4017 is matched against the string
4018
4019 This is <something> <something else> <something further> no more
4020
4021 the three matched strings are
4022
4023 <something>
4024 <something> <something else>
4025 <something> <something else> <something further>
4026
4027 On success, the yield of the function is a number greater than zero,
4028 which is the number of matched substrings. The substrings themselves
4029 are returned in ovector. Each string uses two elements; the first is
4030 the offset to the start, and the second is the offset to the end. In
4031 fact, all the strings have the same start offset. (Space could have
4032 been saved by giving this only once, but it was decided to retain some
4033 compatibility with the way pcre_exec() returns data, even though the
4034 meaning of the strings is different.)
4035
4036 The strings are returned in reverse order of length; that is, the long-
4037 est matching string is given first. If there were too many matches to
4038 fit into ovector, the yield of the function is zero, and the vector is
4039 filled with the longest matches. Unlike pcre_exec(), pcre_dfa_exec()
4040 can use the entire ovector for returning matched strings.
4041
4042 Error returns from pcre_dfa_exec()
4043
4044 The pcre_dfa_exec() function returns a negative number when it fails.
4045 Many of the errors are the same as for pcre_exec(), and these are
4046 described above. There are in addition the following errors that are
4047 specific to pcre_dfa_exec():
4048
4049 PCRE_ERROR_DFA_UITEM (-16)
4050
4051 This return is given if pcre_dfa_exec() encounters an item in the pat-
4052 tern that it does not support, for instance, the use of \C or a back
4053 reference.
4054
4055 PCRE_ERROR_DFA_UCOND (-17)
4056
4057 This return is given if pcre_dfa_exec() encounters a condition item
4058 that uses a back reference for the condition, or a test for recursion
4059 in a specific group. These are not supported.
4060
4061 PCRE_ERROR_DFA_UMLIMIT (-18)
4062
4063 This return is given if pcre_dfa_exec() is called with an extra block
4064 that contains a setting of the match_limit or match_limit_recursion
4065 fields. This is not supported (these fields are meaningless for DFA
4066 matching).
4067
4068 PCRE_ERROR_DFA_WSSIZE (-19)
4069
4070 This return is given if pcre_dfa_exec() runs out of space in the
4071 workspace vector.
4072
4073 PCRE_ERROR_DFA_RECURSE (-20)
4074
4075 When a recursive subpattern is processed, the matching function calls
4076 itself recursively, using private vectors for ovector and workspace.
4077 This error is given if the output vector is not large enough. This
4078 should be extremely rare, as a vector of size 1000 is used.
4079
4080 PCRE_ERROR_DFA_BADRESTART (-30)
4081
4082 When pcre_dfa_exec() is called with the PCRE_DFA_RESTART option, some
4083 plausibility checks are made on the contents of the workspace, which
4084 should contain data about the previous partial match. If any of these
4085 checks fail, this error is given.
4086
4087
4088 SEE ALSO
4089
4090 pcre16(3), pcre32(3), pcrebuild(3), pcrecallout(3), pcrecpp(3)(3),
4091 pcrematching(3), pcrepartial(3), pcreposix(3), pcreprecompile(3), pcre-
4092 sample(3), pcrestack(3).
4093
4094
4095 AUTHOR
4096
4097 Philip Hazel
4098 University Computing Service
4099 Cambridge CB2 3QH, England.
4100
4101
4102 REVISION
4103
4104 Last updated: 08 November 2012
4105 Copyright (c) 1997-2012 University of Cambridge.
4106 ------------------------------------------------------------------------------
4107
4108
4109 PCRECALLOUT(3) PCRECALLOUT(3)
4110
4111
4112 NAME
4113 PCRE - Perl-compatible regular expressions
4114
4115
4116 SYNOPSIS
4117
4118 #include <pcre.h>
4119
4120 int (*pcre_callout)(pcre_callout_block *);
4121
4122 int (*pcre16_callout)(pcre16_callout_block *);
4123
4124 int (*pcre32_callout)(pcre32_callout_block *);
4125
4126
4127 DESCRIPTION
4128
4129 PCRE provides a feature called "callout", which is a means of temporar-
4130 ily passing control to the caller of PCRE in the middle of pattern
4131 matching. The caller of PCRE provides an external function by putting
4132 its entry point in the global variable pcre_callout (pcre16_callout for
4133 the 16-bit library, pcre32_callout for the 32-bit library). By default,
4134 this variable contains NULL, which disables all calling out.
4135
4136 Within a regular expression, (?C) indicates the points at which the
4137 external function is to be called. Different callout points can be
4138 identified by putting a number less than 256 after the letter C. The
4139 default value is zero. For example, this pattern has two callout
4140 points:
4141
4142 (?C1)abc(?C2)def
4143
4144 If the PCRE_AUTO_CALLOUT option bit is set when a pattern is compiled,
4145 PCRE automatically inserts callouts, all with number 255, before each
4146 item in the pattern. For example, if PCRE_AUTO_CALLOUT is used with the
4147 pattern
4148
4149 A(\d{2}|--)
4150
4151 it is processed as if it were
4152
4153 (?C255)A(?C255)((?C255)\d{2}(?C255)|(?C255)-(?C255)-(?C255))(?C255)
4154
4155 Notice that there is a callout before and after each parenthesis and
4156 alternation bar. Automatic callouts can be used for tracking the
4157 progress of pattern matching. The pcretest command has an option that
4158 sets automatic callouts; when it is used, the output indicates how the
4159 pattern is matched. This is useful information when you are trying to
4160 optimize the performance of a particular pattern.
4161
4162 The use of callouts in a pattern makes it ineligible for optimization
4163 by the just-in-time compiler. Studying such a pattern with the
4164 PCRE_STUDY_JIT_COMPILE option always fails.
4165
4166
4167 MISSING CALLOUTS
4168
4169 You should be aware that, because of optimizations in the way PCRE
4170 matches patterns by default, callouts sometimes do not happen. For
4171 example, if the pattern is
4172
4173 ab(?C4)cd
4174
4175 PCRE knows that any matching string must contain the letter "d". If the
4176 subject string is "abyz", the lack of "d" means that matching doesn't
4177 ever start, and the callout is never reached. However, with "abyd",
4178 though the result is still no match, the callout is obeyed.
4179
4180 If the pattern is studied, PCRE knows the minimum length of a matching
4181 string, and will immediately give a "no match" return without actually
4182 running a match if the subject is not long enough, or, for unanchored
4183 patterns, if it has been scanned far enough.
4184
4185 You can disable these optimizations by passing the PCRE_NO_START_OPTI-
4186 MIZE option to the matching function, or by starting the pattern with
4187 (*NO_START_OPT). This slows down the matching process, but does ensure
4188 that callouts such as the example above are obeyed.
4189
4190
4191 THE CALLOUT INTERFACE
4192
4193 During matching, when PCRE reaches a callout point, the external func-
4194 tion defined by pcre_callout or pcre[16|32]_callout is called (if it is
4195 set). This applies to both normal and DFA matching. The only argument
4196 to the callout function is a pointer to a pcre_callout or
4197 pcre[16|32]_callout block. These structures contains the following
4198 fields:
4199
4200 int version;
4201 int callout_number;
4202 int *offset_vector;
4203 const char *subject; (8-bit version)
4204 PCRE_SPTR16 subject; (16-bit version)
4205 PCRE_SPTR32 subject; (32-bit version)
4206 int subject_length;
4207 int start_match;
4208 int current_position;
4209 int capture_top;
4210 int capture_last;
4211 void *callout_data;
4212 int pattern_position;
4213 int next_item_length;
4214 const unsigned char *mark; (8-bit version)
4215 const PCRE_UCHAR16 *mark; (16-bit version)
4216 const PCRE_UCHAR32 *mark; (32-bit version)
4217
4218 The version field is an integer containing the version number of the
4219 block format. The initial version was 0; the current version is 2. The
4220 version number will change again in future if additional fields are
4221 added, but the intention is never to remove any of the existing fields.
4222
4223 The callout_number field contains the number of the callout, as com-
4224 piled into the pattern (that is, the number after ?C for manual call-
4225 outs, and 255 for automatically generated callouts).
4226
4227 The offset_vector field is a pointer to the vector of offsets that was
4228 passed by the caller to the matching function. When pcre_exec() or
4229 pcre[16|32]_exec() is used, the contents can be inspected, in order to
4230 extract substrings that have been matched so far, in the same way as
4231 for extracting substrings after a match has completed. For the DFA
4232 matching functions, this field is not useful.
4233
4234 The subject and subject_length fields contain copies of the values that
4235 were passed to the matching function.
4236
4237 The start_match field normally contains the offset within the subject
4238 at which the current match attempt started. However, if the escape
4239 sequence \K has been encountered, this value is changed to reflect the
4240 modified starting point. If the pattern is not anchored, the callout
4241 function may be called several times from the same point in the pattern
4242 for different starting points in the subject.
4243
4244 The current_position field contains the offset within the subject of
4245 the current match pointer.
4246
4247 When the pcre_exec() or pcre[16|32]_exec() is used, the capture_top
4248 field contains one more than the number of the highest numbered cap-
4249 tured substring so far. If no substrings have been captured, the value
4250 of capture_top is one. This is always the case when the DFA functions
4251 are used, because they do not support captured substrings.
4252
4253 The capture_last field contains the number of the most recently cap-
4254 tured substring. If no substrings have been captured, its value is -1.
4255 This is always the case for the DFA matching functions.
4256
4257 The callout_data field contains a value that is passed to a matching
4258 function specifically so that it can be passed back in callouts. It is
4259 passed in the callout_data field of a pcre_extra or pcre[16|32]_extra
4260 data structure. If no such data was passed, the value of callout_data
4261 in a callout block is NULL. There is a description of the pcre_extra
4262 structure in the pcreapi documentation.
4263
4264 The pattern_position field is present from version 1 of the callout
4265 structure. It contains the offset to the next item to be matched in the
4266 pattern string.
4267
4268 The next_item_length field is present from version 1 of the callout
4269 structure. It contains the length of the next item to be matched in the
4270 pattern string. When the callout immediately precedes an alternation
4271 bar, a closing parenthesis, or the end of the pattern, the length is
4272 zero. When the callout precedes an opening parenthesis, the length is
4273 that of the entire subpattern.
4274
4275 The pattern_position and next_item_length fields are intended to help
4276 in distinguishing between different automatic callouts, which all have
4277 the same callout number. However, they are set for all callouts.
4278
4279 The mark field is present from version 2 of the callout structure. In
4280 callouts from pcre_exec() or pcre[16|32]_exec() it contains a pointer
4281 to the zero-terminated name of the most recently passed (*MARK),
4282 (*PRUNE), or (*THEN) item in the match, or NULL if no such items have
4283 been passed. Instances of (*PRUNE) or (*THEN) without a name do not
4284 obliterate a previous (*MARK). In callouts from the DFA matching func-
4285 tions this field always contains NULL.
4286
4287
4288 RETURN VALUES
4289
4290 The external callout function returns an integer to PCRE. If the value
4291 is zero, matching proceeds as normal. If the value is greater than
4292 zero, matching fails at the current point, but the testing of other
4293 matching possibilities goes ahead, just as if a lookahead assertion had
4294 failed. If the value is less than zero, the match is abandoned, the
4295 matching function returns the negative value.
4296
4297 Negative values should normally be chosen from the set of
4298 PCRE_ERROR_xxx values. In particular, PCRE_ERROR_NOMATCH forces a stan-
4299 dard "no match" failure. The error number PCRE_ERROR_CALLOUT is
4300 reserved for use by callout functions; it will never be used by PCRE
4301 itself.
4302
4303
4304 AUTHOR
4305
4306 Philip Hazel
4307 University Computing Service
4308 Cambridge CB2 3QH, England.
4309
4310
4311 REVISION
4312
4313 Last updated: 24 June 2012
4314 Copyright (c) 1997-2012 University of Cambridge.
4315 ------------------------------------------------------------------------------
4316
4317
4318 PCRECOMPAT(3) PCRECOMPAT(3)
4319
4320
4321 NAME
4322 PCRE - Perl-compatible regular expressions
4323
4324
4325 DIFFERENCES BETWEEN PCRE AND PERL
4326
4327 This document describes the differences in the ways that PCRE and Perl
4328 handle regular expressions. The differences described here are with
4329 respect to Perl versions 5.10 and above.
4330
4331 1. PCRE has only a subset of Perl's Unicode support. Details of what it
4332 does have are given in the pcreunicode page.
4333
4334 2. PCRE allows repeat quantifiers only on parenthesized assertions, but
4335 they do not mean what you might think. For example, (?!a){3} does not
4336 assert that the next three characters are not "a". It just asserts that
4337 the next character is not "a" three times (in principle: PCRE optimizes
4338 this to run the assertion just once). Perl allows repeat quantifiers on
4339 other assertions such as \b, but these do not seem to have any use.
4340
4341 3. Capturing subpatterns that occur inside negative lookahead asser-
4342 tions are counted, but their entries in the offsets vector are never
4343 set. Perl sets its numerical variables from any such patterns that are
4344 matched before the assertion fails to match something (thereby succeed-
4345 ing), but only if the negative lookahead assertion contains just one
4346 branch.
4347
4348 4. Though binary zero characters are supported in the subject string,
4349 they are not allowed in a pattern string because it is passed as a nor-
4350 mal C string, terminated by zero. The escape sequence \0 can be used in
4351 the pattern to represent a binary zero.
4352
4353 5. The following Perl escape sequences are not supported: \l, \u, \L,
4354 \U, and \N when followed by a character name or Unicode value. (\N on
4355 its own, matching a non-newline character, is supported.) In fact these
4356 are implemented by Perl's general string-handling and are not part of
4357 its pattern matching engine. If any of these are encountered by PCRE,
4358 an error is generated by default. However, if the PCRE_JAVASCRIPT_COM-
4359 PAT option is set, \U and \u are interpreted as JavaScript interprets
4360 them.
4361
4362 6. The Perl escape sequences \p, \P, and \X are supported only if PCRE
4363 is built with Unicode character property support. The properties that
4364 can be tested with \p and \P are limited to the general category prop-
4365 erties such as Lu and Nd, script names such as Greek or Han, and the
4366 derived properties Any and L&. PCRE does support the Cs (surrogate)
4367 property, which Perl does not; the Perl documentation says "Because
4368 Perl hides the need for the user to understand the internal representa-
4369 tion of Unicode characters, there is no need to implement the somewhat
4370 messy concept of surrogates."
4371
4372 7. PCRE does support the \Q...\E escape for quoting substrings. Charac-
4373 ters in between are treated as literals. This is slightly different
4374 from Perl in that $ and @ are also handled as literals inside the
4375 quotes. In Perl, they cause variable interpolation (but of course PCRE
4376 does not have variables). Note the following examples:
4377
4378 Pattern PCRE matches Perl matches
4379
4380 \Qabc$xyz\E abc$xyz abc followed by the
4381 contents of $xyz
4382 \Qabc\$xyz\E abc\$xyz abc\$xyz
4383 \Qabc\E\$\Qxyz\E abc$xyz abc$xyz
4384
4385 The \Q...\E sequence is recognized both inside and outside character
4386 classes.
4387
4388 8. Fairly obviously, PCRE does not support the (?{code}) and (??{code})
4389 constructions. However, there is support for recursive patterns. This
4390 is not available in Perl 5.8, but it is in Perl 5.10. Also, the PCRE
4391 "callout" feature allows an external function to be called during pat-
4392 tern matching. See the pcrecallout documentation for details.
4393
4394 9. Subpatterns that are called as subroutines (whether or not recur-
4395 sively) are always treated as atomic groups in PCRE. This is like
4396 Python, but unlike Perl. Captured values that are set outside a sub-
4397 routine call can be reference from inside in PCRE, but not in Perl.
4398 There is a discussion that explains these differences in more detail in
4399 the section on recursion differences from Perl in the pcrepattern page.
4400
4401 10. If any of the backtracking control verbs are used in an assertion
4402 or in a subpattern that is called as a subroutine (whether or not
4403 recursively), their effect is confined to that subpattern; it does not
4404 extend to the surrounding pattern. This is not always the case in Perl.
4405 In particular, if (*THEN) is present in a group that is called as a
4406 subroutine, its action is limited to that group, even if the group does
4407 not contain any | characters. There is one exception to this: the name
4408 from a *(MARK), (*PRUNE), or (*THEN) that is encountered in a success-
4409 ful positive assertion is passed back when a match succeeds (compare
4410 capturing parentheses in assertions). Note that such subpatterns are
4411 processed as anchored at the point where they are tested.
4412
4413 11. There are some differences that are concerned with the settings of
4414 captured strings when part of a pattern is repeated. For example,
4415 matching "aba" against the pattern /^(a(b)?)+$/ in Perl leaves $2
4416 unset, but in PCRE it is set to "b".
4417
4418 12. PCRE's handling of duplicate subpattern numbers and duplicate sub-
4419 pattern names is not as general as Perl's. This is a consequence of the
4420 fact the PCRE works internally just with numbers, using an external ta-
4421 ble to translate between numbers and names. In particular, a pattern
4422 such as (?|(?<a>A)|(?<b)B), where the two capturing parentheses have
4423 the same number but different names, is not supported, and causes an
4424 error at compile time. If it were allowed, it would not be possible to
4425 distinguish which parentheses matched, because both names map to cap-
4426 turing subpattern number 1. To avoid this confusing situation, an error
4427 is given at compile time.
4428
4429 13. Perl recognizes comments in some places that PCRE does not, for
4430 example, between the ( and ? at the start of a subpattern. If the /x
4431 modifier is set, Perl allows white space between ( and ? but PCRE never
4432 does, even if the PCRE_EXTENDED option is set.
4433
4434 14. PCRE provides some extensions to the Perl regular expression facil-
4435 ities. Perl 5.10 includes new features that are not in earlier ver-
4436 sions of Perl, some of which (such as named parentheses) have been in
4437 PCRE for some time. This list is with respect to Perl 5.10:
4438
4439 (a) Although lookbehind assertions in PCRE must match fixed length
4440 strings, each alternative branch of a lookbehind assertion can match a
4441 different length of string. Perl requires them all to have the same
4442 length.
4443
4444 (b) If PCRE_DOLLAR_ENDONLY is set and PCRE_MULTILINE is not set, the $
4445 meta-character matches only at the very end of the string.
4446
4447 (c) If PCRE_EXTRA is set, a backslash followed by a letter with no spe-
4448 cial meaning is faulted. Otherwise, like Perl, the backslash is quietly
4449 ignored. (Perl can be made to issue a warning.)
4450
4451 (d) If PCRE_UNGREEDY is set, the greediness of the repetition quanti-
4452 fiers is inverted, that is, by default they are not greedy, but if fol-
4453 lowed by a question mark they are.
4454
4455 (e) PCRE_ANCHORED can be used at matching time to force a pattern to be
4456 tried only at the first matching position in the subject string.
4457
4458 (f) The PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, PCRE_NOTEMPTY_ATSTART,
4459 and PCRE_NO_AUTO_CAPTURE options for pcre_exec() have no Perl equiva-
4460 lents.
4461
4462 (g) The \R escape sequence can be restricted to match only CR, LF, or
4463 CRLF by the PCRE_BSR_ANYCRLF option.
4464
4465 (h) The callout facility is PCRE-specific.
4466
4467 (i) The partial matching facility is PCRE-specific.
4468
4469 (j) Patterns compiled by PCRE can be saved and re-used at a later time,
4470 even on different hosts that have the other endianness. However, this
4471 does not apply to optimized data created by the just-in-time compiler.
4472
4473 (k) The alternative matching functions (pcre_dfa_exec(),
4474 pcre16_dfa_exec() and pcre32_dfa_exec(),) match in a different way and
4475 are not Perl-compatible.
4476
4477 (l) PCRE recognizes some special sequences such as (*CR) at the start
4478 of a pattern that set overall options that cannot be changed within the
4479 pattern.
4480
4481
4482 AUTHOR
4483
4484 Philip Hazel
4485 University Computing Service
4486 Cambridge CB2 3QH, England.
4487
4488
4489 REVISION
4490
4491 Last updated: 25 August 2012
4492 Copyright (c) 1997-2012 University of Cambridge.
4493 ------------------------------------------------------------------------------
4494
4495
4496 PCREPATTERN(3) PCREPATTERN(3)
4497
4498
4499 NAME
4500 PCRE - Perl-compatible regular expressions
4501
4502
4503 PCRE REGULAR EXPRESSION DETAILS
4504
4505 The syntax and semantics of the regular expressions that are supported
4506 by PCRE are described in detail below. There is a quick-reference syn-
4507 tax summary in the pcresyntax page. PCRE tries to match Perl syntax and
4508 semantics as closely as it can. PCRE also supports some alternative
4509 regular expression syntax (which does not conflict with the Perl syn-
4510 tax) in order to provide some compatibility with regular expressions in
4511 Python, .NET, and Oniguruma.
4512
4513 Perl's regular expressions are described in its own documentation, and
4514 regular expressions in general are covered in a number of books, some
4515 of which have copious examples. Jeffrey Friedl's "Mastering Regular
4516 Expressions", published by O'Reilly, covers regular expressions in
4517 great detail. This description of PCRE's regular expressions is
4518 intended as reference material.
4519
4520 The original operation of PCRE was on strings of one-byte characters.
4521 However, there is now also support for UTF-8 strings in the original
4522 library, an extra library that supports 16-bit and UTF-16 character
4523 strings, and a third library that supports 32-bit and UTF-32 character
4524 strings. To use these features, PCRE must be built to include appropri-
4525 ate support. When using UTF strings you must either call the compiling
4526 function with the PCRE_UTF8, PCRE_UTF16, or PCRE_UTF32 option, or the
4527 pattern must start with one of these special sequences:
4528
4529 (*UTF8)
4530 (*UTF16)
4531 (*UTF32)
4532 (*UTF)
4533
4534 (*UTF) is a generic sequence that can be used with any of the
4535 libraries. Starting a pattern with such a sequence is equivalent to
4536 setting the relevant option. This feature is not Perl-compatible. How
4537 setting a UTF mode affects pattern matching is mentioned in several
4538 places below. There is also a summary of features in the pcreunicode
4539 page.
4540
4541 Another special sequence that may appear at the start of a pattern or
4542 in combination with (*UTF8), (*UTF16), (*UTF32) or (*UTF) is:
4543
4544 (*UCP)
4545
4546 This has the same effect as setting the PCRE_UCP option: it causes
4547 sequences such as \d and \w to use Unicode properties to determine
4548 character types, instead of recognizing only characters with codes less
4549 than 128 via a lookup table.
4550
4551 If a pattern starts with (*NO_START_OPT), it has the same effect as
4552 setting the PCRE_NO_START_OPTIMIZE option either at compile or matching
4553 time. There are also some more of these special sequences that are con-
4554 cerned with the handling of newlines; they are described below.
4555
4556 The remainder of this document discusses the patterns that are sup-
4557 ported by PCRE when one its main matching functions, pcre_exec()
4558 (8-bit) or pcre[16|32]_exec() (16- or 32-bit), is used. PCRE also has
4559 alternative matching functions, pcre_dfa_exec() and
4560 pcre[16|32_dfa_exec(), which match using a different algorithm that is
4561 not Perl-compatible. Some of the features discussed below are not
4562 available when DFA matching is used. The advantages and disadvantages
4563 of the alternative functions, and how they differ from the normal func-
4564 tions, are discussed in the pcrematching page.
4565
4566
4567 EBCDIC CHARACTER CODES
4568
4569 PCRE can be compiled to run in an environment that uses EBCDIC as its
4570 character code rather than ASCII or Unicode (typically a mainframe sys-
4571 tem). In the sections below, character code values are ASCII or Uni-
4572 code; in an EBCDIC environment these characters may have different code
4573 values, and there are no code points greater than 255.
4574
4575
4576 NEWLINE CONVENTIONS
4577
4578 PCRE supports five different conventions for indicating line breaks in
4579 strings: a single CR (carriage return) character, a single LF (line-
4580 feed) character, the two-character sequence CRLF, any of the three pre-
4581 ceding, or any Unicode newline sequence. The pcreapi page has further
4582 discussion about newlines, and shows how to set the newline convention
4583 in the options arguments for the compiling and matching functions.
4584
4585 It is also possible to specify a newline convention by starting a pat-
4586 tern string with one of the following five sequences:
4587
4588 (*CR) carriage return
4589 (*LF) linefeed
4590 (*CRLF) carriage return, followed by linefeed
4591 (*ANYCRLF) any of the three above
4592 (*ANY) all Unicode newline sequences
4593
4594 These override the default and the options given to the compiling func-
4595 tion. For example, on a Unix system where LF is the default newline
4596 sequence, the pattern
4597
4598 (*CR)a.b
4599
4600 changes the convention to CR. That pattern matches "a\nb" because LF is
4601 no longer a newline. Note that these special settings, which are not
4602 Perl-compatible, are recognized only at the very start of a pattern,
4603 and that they must be in upper case. If more than one of them is
4604 present, the last one is used.
4605
4606 The newline convention affects where the circumflex and dollar asser-
4607 tions are true. It also affects the interpretation of the dot metachar-
4608 acter when PCRE_DOTALL is not set, and the behaviour of \N. However, it
4609 does not affect what the \R escape sequence matches. By default, this
4610 is any Unicode newline sequence, for Perl compatibility. However, this
4611 can be changed; see the description of \R in the section entitled "New-
4612 line sequences" below. A change of \R setting can be combined with a
4613 change of newline convention.
4614
4615
4616 CHARACTERS AND METACHARACTERS
4617
4618 A regular expression is a pattern that is matched against a subject
4619 string from left to right. Most characters stand for themselves in a
4620 pattern, and match the corresponding characters in the subject. As a
4621 trivial example, the pattern
4622
4623 The quick brown fox
4624
4625 matches a portion of a subject string that is identical to itself. When
4626 caseless matching is specified (the PCRE_CASELESS option), letters are
4627 matched independently of case. In a UTF mode, PCRE always understands
4628 the concept of case for characters whose values are less than 128, so
4629 caseless matching is always possible. For characters with higher val-
4630 ues, the concept of case is supported if PCRE is compiled with Unicode
4631 property support, but not otherwise. If you want to use caseless
4632 matching for characters 128 and above, you must ensure that PCRE is
4633 compiled with Unicode property support as well as with UTF support.
4634
4635 The power of regular expressions comes from the ability to include
4636 alternatives and repetitions in the pattern. These are encoded in the
4637 pattern by the use of metacharacters, which do not stand for themselves
4638 but instead are interpreted in some special way.
4639
4640 There are two different sets of metacharacters: those that are recog-
4641 nized anywhere in the pattern except within square brackets, and those
4642 that are recognized within square brackets. Outside square brackets,
4643 the metacharacters are as follows:
4644
4645 \ general escape character with several uses
4646 ^ assert start of string (or line, in multiline mode)
4647 $ assert end of string (or line, in multiline mode)
4648 . match any character except newline (by default)
4649 [ start character class definition
4650 | start of alternative branch
4651 ( start subpattern
4652 ) end subpattern
4653 ? extends the meaning of (
4654 also 0 or 1 quantifier
4655 also quantifier minimizer
4656 * 0 or more quantifier
4657 + 1 or more quantifier
4658 also "possessive quantifier"
4659 { start min/max quantifier
4660
4661 Part of a pattern that is in square brackets is called a "character
4662 class". In a character class the only metacharacters are:
4663
4664 \ general escape character
4665 ^ negate the class, but only if the first character
4666 - indicates character range
4667 [ POSIX character class (only if followed by POSIX
4668 syntax)
4669 ] terminates the character class
4670
4671 The following sections describe the use of each of the metacharacters.
4672
4673
4674 BACKSLASH
4675
4676 The backslash character has several uses. Firstly, if it is followed by
4677 a character that is not a number or a letter, it takes away any special
4678 meaning that character may have. This use of backslash as an escape
4679 character applies both inside and outside character classes.
4680
4681 For example, if you want to match a * character, you write \* in the
4682 pattern. This escaping action applies whether or not the following
4683 character would otherwise be interpreted as a metacharacter, so it is
4684 always safe to precede a non-alphanumeric with backslash to specify
4685 that it stands for itself. In particular, if you want to match a back-
4686 slash, you write \\.
4687
4688 In a UTF mode, only ASCII numbers and letters have any special meaning
4689 after a backslash. All other characters (in particular, those whose
4690 codepoints are greater than 127) are treated as literals.
4691
4692 If a pattern is compiled with the PCRE_EXTENDED option, white space in
4693 the pattern (other than in a character class) and characters between a
4694 # outside a character class and the next newline are ignored. An escap-
4695 ing backslash can be used to include a white space or # character as
4696 part of the pattern.
4697
4698 If you want to remove the special meaning from a sequence of charac-
4699 ters, you can do so by putting them between \Q and \E. This is differ-
4700 ent from Perl in that $ and @ are handled as literals in \Q...\E
4701 sequences in PCRE, whereas in Perl, $ and @ cause variable interpola-
4702 tion. Note the following examples:
4703
4704 Pattern PCRE matches Perl matches
4705
4706 \Qabc$xyz\E abc$xyz abc followed by the
4707 contents of $xyz
4708 \Qabc\$xyz\E abc\$xyz abc\$xyz
4709 \Qabc\E\$\Qxyz\E abc$xyz abc$xyz
4710
4711 The \Q...\E sequence is recognized both inside and outside character
4712 classes. An isolated \E that is not preceded by \Q is ignored. If \Q
4713 is not followed by \E later in the pattern, the literal interpretation
4714 continues to the end of the pattern (that is, \E is assumed at the
4715 end). If the isolated \Q is inside a character class, this causes an
4716 error, because the character class is not terminated.
4717
4718 Non-printing characters
4719
4720 A second use of backslash provides a way of encoding non-printing char-
4721 acters in patterns in a visible manner. There is no restriction on the
4722 appearance of non-printing characters, apart from the binary zero that
4723 terminates a pattern, but when a pattern is being prepared by text
4724 editing, it is often easier to use one of the following escape
4725 sequences than the binary character it represents:
4726
4727 \a alarm, that is, the BEL character (hex 07)
4728 \cx "control-x", where x is any ASCII character
4729 \e escape (hex 1B)
4730 \f form feed (hex 0C)
4731 \n linefeed (hex 0A)
4732 \r carriage return (hex 0D)
4733 \t tab (hex 09)
4734 \ddd character with octal code ddd, or back reference
4735 \xhh character with hex code hh
4736 \x{hhh..} character with hex code hhh.. (non-JavaScript mode)
4737 \uhhhh character with hex code hhhh (JavaScript mode only)
4738
4739 The precise effect of \cx on ASCII characters is as follows: if x is a
4740 lower case letter, it is converted to upper case. Then bit 6 of the
4741 character (hex 40) is inverted. Thus \cA to \cZ become hex 01 to hex 1A
4742 (A is 41, Z is 5A), but \c{ becomes hex 3B ({ is 7B), and \c; becomes
4743 hex 7B (; is 3B). If the data item (byte or 16-bit value) following \c
4744 has a value greater than 127, a compile-time error occurs. This locks
4745 out non-ASCII characters in all modes.
4746
4747 The \c facility was designed for use with ASCII characters, but with
4748 the extension to Unicode it is even less useful than it once was. It
4749 is, however, recognized when PCRE is compiled in EBCDIC mode, where
4750 data items are always bytes. In this mode, all values are valid after
4751 \c. If the next character is a lower case letter, it is converted to
4752 upper case. Then the 0xc0 bits of the byte are inverted. Thus \cA
4753 becomes hex 01, as in ASCII (A is C1), but because the EBCDIC letters
4754 are disjoint, \cZ becomes hex 29 (Z is E9), and other characters also
4755 generate different values.
4756
4757 By default, after \x, from zero to two hexadecimal digits are read
4758 (letters can be in upper or lower case). Any number of hexadecimal dig-
4759 its may appear between \x{ and }, but the character code is constrained
4760 as follows:
4761
4762 8-bit non-UTF mode less than 0x100
4763 8-bit UTF-8 mode less than 0x10ffff and a valid codepoint
4764 16-bit non-UTF mode less than 0x10000
4765 16-bit UTF-16 mode less than 0x10ffff and a valid codepoint
4766 32-bit non-UTF mode less than 0x80000000
4767 32-bit UTF-32 mode less than 0x10ffff and a valid codepoint
4768
4769 Invalid Unicode codepoints are the range 0xd800 to 0xdfff (the so-
4770 called "surrogate" codepoints), and 0xffef.
4771
4772 If characters other than hexadecimal digits appear between \x{ and },
4773 or if there is no terminating }, this form of escape is not recognized.
4774 Instead, the initial \x will be interpreted as a basic hexadecimal
4775 escape, with no following digits, giving a character whose value is
4776 zero.
4777
4778 If the PCRE_JAVASCRIPT_COMPAT option is set, the interpretation of \x
4779 is as just described only when it is followed by two hexadecimal dig-
4780 its. Otherwise, it matches a literal "x" character. In JavaScript
4781 mode, support for code points greater than 256 is provided by \u, which
4782 must be followed by four hexadecimal digits; otherwise it matches a
4783 literal "u" character. Character codes specified by \u in JavaScript
4784 mode are constrained in the same was as those specified by \x in non-
4785 JavaScript mode.
4786
4787 Characters whose value is less than 256 can be defined by either of the
4788 two syntaxes for \x (or by \u in JavaScript mode). There is no differ-
4789 ence in the way they are handled. For example, \xdc is exactly the same
4790 as \x{dc} (or \u00dc in JavaScript mode).
4791
4792 After \0 up to two further octal digits are read. If there are fewer
4793 than two digits, just those that are present are used. Thus the
4794 sequence \0\x\07 specifies two binary zeros followed by a BEL character
4795 (code value 7). Make sure you supply two digits after the initial zero
4796 if the pattern character that follows is itself an octal digit.
4797
4798 The handling of a backslash followed by a digit other than 0 is compli-
4799 cated. Outside a character class, PCRE reads it and any following dig-
4800 its as a decimal number. If the number is less than 10, or if there
4801 have been at least that many previous capturing left parentheses in the
4802 expression, the entire sequence is taken as a back reference. A
4803 description of how this works is given later, following the discussion
4804 of parenthesized subpatterns.
4805
4806 Inside a character class, or if the decimal number is greater than 9
4807 and there have not been that many capturing subpatterns, PCRE re-reads
4808 up to three octal digits following the backslash, and uses them to gen-
4809 erate a data character. Any subsequent digits stand for themselves. The
4810 value of the character is constrained in the same way as characters
4811 specified in hexadecimal. For example:
4812
4813 \040 is another way of writing an ASCII space
4814 \40 is the same, provided there are fewer than 40
4815 previous capturing subpatterns
4816 \7 is always a back reference
4817 \11 might be a back reference, or another way of
4818 writing a tab
4819 \011 is always a tab
4820 \0113 is a tab followed by the character "3"
4821 \113 might be a back reference, otherwise the
4822 character with octal code 113
4823 \377 might be a back reference, otherwise
4824 the value 255 (decimal)
4825 \81 is either a back reference, or a binary zero
4826 followed by the two characters "8" and "1"
4827
4828 Note that octal values of 100 or greater must not be introduced by a
4829 leading zero, because no more than three octal digits are ever read.
4830
4831 All the sequences that define a single character value can be used both
4832 inside and outside character classes. In addition, inside a character
4833 class, \b is interpreted as the backspace character (hex 08).
4834
4835 \N is not allowed in a character class. \B, \R, and \X are not special
4836 inside a character class. Like other unrecognized escape sequences,
4837 they are treated as the literal characters "B", "R", and "X" by
4838 default, but cause an error if the PCRE_EXTRA option is set. Outside a
4839 character class, these sequences have different meanings.
4840
4841 Unsupported escape sequences
4842
4843 In Perl, the sequences \l, \L, \u, and \U are recognized by its string
4844 handler and used to modify the case of following characters. By
4845 default, PCRE does not support these escape sequences. However, if the
4846 PCRE_JAVASCRIPT_COMPAT option is set, \U matches a "U" character, and
4847 \u can be used to define a character by code point, as described in the
4848 previous section.
4849
4850 Absolute and relative back references
4851
4852 The sequence \g followed by an unsigned or a negative number, option-
4853 ally enclosed in braces, is an absolute or relative back reference. A
4854 named back reference can be coded as \g{name}. Back references are dis-
4855 cussed later, following the discussion of parenthesized subpatterns.
4856
4857 Absolute and relative subroutine calls
4858
4859 For compatibility with Oniguruma, the non-Perl syntax \g followed by a
4860 name or a number enclosed either in angle brackets or single quotes, is
4861 an alternative syntax for referencing a subpattern as a "subroutine".
4862 Details are discussed later. Note that \g{...} (Perl syntax) and
4863 \g<...> (Oniguruma syntax) are not synonymous. The former is a back
4864 reference; the latter is a subroutine call.
4865
4866 Generic character types
4867
4868 Another use of backslash is for specifying generic character types:
4869
4870 \d any decimal digit
4871 \D any character that is not a decimal digit
4872 \h any horizontal white space character
4873 \H any character that is not a horizontal white space character
4874 \s any white space character
4875 \S any character that is not a white space character
4876 \v any vertical white space character
4877 \V any character that is not a vertical white space character
4878 \w any "word" character
4879 \W any "non-word" character
4880
4881 There is also the single sequence \N, which matches a non-newline char-
4882 acter. This is the same as the "." metacharacter when PCRE_DOTALL is
4883 not set. Perl also uses \N to match characters by name; PCRE does not
4884 support this.
4885
4886 Each pair of lower and upper case escape sequences partitions the com-
4887 plete set of characters into two disjoint sets. Any given character
4888 matches one, and only one, of each pair. The sequences can appear both
4889 inside and outside character classes. They each match one character of
4890 the appropriate type. If the current matching point is at the end of
4891 the subject string, all of them fail, because there is no character to
4892 match.
4893
4894 For compatibility with Perl, \s does not match the VT character (code
4895 11). This makes it different from the the POSIX "space" class. The \s
4896 characters are HT (9), LF (10), FF (12), CR (13), and space (32). If
4897 "use locale;" is included in a Perl script, \s may match the VT charac-
4898 ter. In PCRE, it never does.
4899
4900 A "word" character is an underscore or any character that is a letter
4901 or digit. By default, the definition of letters and digits is con-
4902 trolled by PCRE's low-valued character tables, and may vary if locale-
4903 specific matching is taking place (see "Locale support" in the pcreapi
4904 page). For example, in a French locale such as "fr_FR" in Unix-like
4905 systems, or "french" in Windows, some character codes greater than 128
4906 are used for accented letters, and these are then matched by \w. The
4907 use of locales with Unicode is discouraged.
4908
4909 By default, in a UTF mode, characters with values greater than 128
4910 never match \d, \s, or \w, and always match \D, \S, and \W. These
4911 sequences retain their original meanings from before UTF support was
4912 available, mainly for efficiency reasons. However, if PCRE is compiled
4913 with Unicode property support, and the PCRE_UCP option is set, the be-
4914 haviour is changed so that Unicode properties are used to determine
4915 character types, as follows:
4916
4917 \d any character that \p{Nd} matches (decimal digit)
4918 \s any character that \p{Z} matches, plus HT, LF, FF, CR
4919 \w any character that \p{L} or \p{N} matches, plus underscore
4920
4921 The upper case escapes match the inverse sets of characters. Note that
4922 \d matches only decimal digits, whereas \w matches any Unicode digit,
4923 as well as any Unicode letter, and underscore. Note also that PCRE_UCP
4924 affects \b, and \B because they are defined in terms of \w and \W.
4925 Matching these sequences is noticeably slower when PCRE_UCP is set.
4926
4927 The sequences \h, \H, \v, and \V are features that were added to Perl
4928 at release 5.10. In contrast to the other sequences, which match only
4929 ASCII characters by default, these always match certain high-valued
4930 codepoints, whether or not PCRE_UCP is set. The horizontal space char-
4931 acters are:
4932
4933 U+0009 Horizontal tab (HT)
4934 U+0020 Space
4935 U+00A0 Non-break space
4936 U+1680 Ogham space mark
4937 U+180E Mongolian vowel separator
4938 U+2000 En quad
4939 U+2001 Em quad
4940 U+2002 En space
4941 U+2003 Em space
4942 U+2004 Three-per-em space
4943 U+2005 Four-per-em space
4944 U+2006 Six-per-em space
4945 U+2007 Figure space
4946 U+2008 Punctuation space
4947 U+2009 Thin space
4948 U+200A Hair space
4949 U+202F Narrow no-break space
4950 U+205F Medium mathematical space
4951 U+3000 Ideographic space
4952
4953 The vertical space characters are:
4954
4955 U+000A Linefeed (LF)
4956 U+000B Vertical tab (VT)
4957 U+000C Form feed (FF)
4958 U+000D Carriage return (CR)
4959 U+0085 Next line (NEL)
4960 U+2028 Line separator
4961 U+2029 Paragraph separator
4962
4963 In 8-bit, non-UTF-8 mode, only the characters with codepoints less than
4964 256 are relevant.
4965
4966 Newline sequences
4967
4968 Outside a character class, by default, the escape sequence \R matches
4969 any Unicode newline sequence. In 8-bit non-UTF-8 mode \R is equivalent
4970 to the following:
4971
4972 (?>\r\n|\n|\x0b|\f|\r|\x85)
4973
4974 This is an example of an "atomic group", details of which are given
4975 below. This particular group matches either the two-character sequence
4976 CR followed by LF, or one of the single characters LF (linefeed,
4977 U+000A), VT (vertical tab, U+000B), FF (form feed, U+000C), CR (car-
4978 riage return, U+000D), or NEL (next line, U+0085). The two-character
4979 sequence is treated as a single unit that cannot be split.
4980
4981 In other modes, two additional characters whose codepoints are greater
4982 than 255 are added: LS (line separator, U+2028) and PS (paragraph sepa-
4983 rator, U+2029). Unicode character property support is not needed for
4984 these characters to be recognized.
4985
4986 It is possible to restrict \R to match only CR, LF, or CRLF (instead of
4987 the complete set of Unicode line endings) by setting the option
4988 PCRE_BSR_ANYCRLF either at compile time or when the pattern is matched.
4989 (BSR is an abbrevation for "backslash R".) This can be made the default
4990 when PCRE is built; if this is the case, the other behaviour can be
4991 requested via the PCRE_BSR_UNICODE option. It is also possible to
4992 specify these settings by starting a pattern string with one of the
4993 following sequences:
4994
4995 (*BSR_ANYCRLF) CR, LF, or CRLF only
4996 (*BSR_UNICODE) any Unicode newline sequence
4997
4998 These override the default and the options given to the compiling func-
4999 tion, but they can themselves be overridden by options given to a
5000 matching function. Note that these special settings, which are not
5001 Perl-compatible, are recognized only at the very start of a pattern,
5002 and that they must be in upper case. If more than one of them is
5003 present, the last one is used. They can be combined with a change of
5004 newline convention; for example, a pattern can start with:
5005
5006 (*ANY)(*BSR_ANYCRLF)
5007
5008 They can also be combined with the (*UTF8), (*UTF16), (*UTF32), (*UTF)
5009 or (*UCP) special sequences. Inside a character class, \R is treated as
5010 an unrecognized escape sequence, and so matches the letter "R" by
5011 default, but causes an error if PCRE_EXTRA is set.
5012
5013 Unicode character properties
5014
5015 When PCRE is built with Unicode character property support, three addi-
5016 tional escape sequences that match characters with specific properties
5017 are available. When in 8-bit non-UTF-8 mode, these sequences are of
5018 course limited to testing characters whose codepoints are less than
5019 256, but they do work in this mode. The extra escape sequences are:
5020
5021 \p{xx} a character with the xx property
5022 \P{xx} a character without the xx property
5023 \X a Unicode extended grapheme cluster
5024
5025 The property names represented by xx above are limited to the Unicode
5026 script names, the general category properties, "Any", which matches any
5027 character (including newline), and some special PCRE properties
5028 (described in the next section). Other Perl properties such as "InMu-
5029 sicalSymbols" are not currently supported by PCRE. Note that \P{Any}
5030 does not match any characters, so always causes a match failure.
5031
5032 Sets of Unicode characters are defined as belonging to certain scripts.
5033 A character from one of these sets can be matched using a script name.
5034 For example:
5035
5036 \p{Greek}
5037 \P{Han}
5038
5039 Those that are not part of an identified script are lumped together as
5040 "Common". The current list of scripts is:
5041
5042 Arabic, Armenian, Avestan, Balinese, Bamum, Batak, Bengali, Bopomofo,
5043 Brahmi, Braille, Buginese, Buhid, Canadian_Aboriginal, Carian, Chakma,
5044 Cham, Cherokee, Common, Coptic, Cuneiform, Cypriot, Cyrillic, Deseret,
5045 Devanagari, Egyptian_Hieroglyphs, Ethiopic, Georgian, Glagolitic,
5046 Gothic, Greek, Gujarati, Gurmukhi, Han, Hangul, Hanunoo, Hebrew, Hira-
5047 gana, Imperial_Aramaic, Inherited, Inscriptional_Pahlavi, Inscrip-
5048 tional_Parthian, Javanese, Kaithi, Kannada, Katakana, Kayah_Li,
5049 Kharoshthi, Khmer, Lao, Latin, Lepcha, Limbu, Linear_B, Lisu, Lycian,
5050 Lydian, Malayalam, Mandaic, Meetei_Mayek, Meroitic_Cursive,
5051 Meroitic_Hieroglyphs, Miao, Mongolian, Myanmar, New_Tai_Lue, Nko,
5052 Ogham, Old_Italic, Old_Persian, Old_South_Arabian, Old_Turkic,
5053 Ol_Chiki, Oriya, Osmanya, Phags_Pa, Phoenician, Rejang, Runic, Samari-
5054 tan, Saurashtra, Sharada, Shavian, Sinhala, Sora_Sompeng, Sundanese,
5055 Syloti_Nagri, Syriac, Tagalog, Tagbanwa, Tai_Le, Tai_Tham, Tai_Viet,
5056 Takri, Tamil, Telugu, Thaana, Thai, Tibetan, Tifinagh, Ugaritic, Vai,
5057 Yi.
5058
5059 Each character has exactly one Unicode general category property, spec-
5060 ified by a two-letter abbreviation. For compatibility with Perl, nega-
5061 tion can be specified by including a circumflex between the opening
5062 brace and the property name. For example, \p{^Lu} is the same as
5063 \P{Lu}.
5064
5065 If only one letter is specified with \p or \P, it includes all the gen-
5066 eral category properties that start with that letter. In this case, in
5067 the absence of negation, the curly brackets in the escape sequence are
5068 optional; these two examples have the same effect:
5069
5070 \p{L}
5071 \pL
5072
5073 The following general category property codes are supported:
5074
5075 C Other
5076 Cc Control
5077 Cf Format
5078 Cn Unassigned
5079 Co Private use
5080 Cs Surrogate
5081
5082 L Letter
5083 Ll Lower case letter
5084 Lm Modifier letter
5085 Lo Other letter
5086 Lt Title case letter
5087 Lu Upper case letter
5088
5089 M Mark
5090 Mc Spacing mark
5091 Me Enclosing mark
5092 Mn Non-spacing mark
5093
5094 N Number
5095 Nd Decimal number
5096 Nl Letter number
5097 No Other number
5098
5099 P Punctuation
5100 Pc Connector punctuation
5101 Pd Dash punctuation
5102 Pe Close punctuation
5103 Pf Final punctuation
5104 Pi Initial punctuation
5105 Po Other punctuation
5106 Ps Open punctuation
5107
5108 S Symbol
5109 Sc Currency symbol
5110 Sk Modifier symbol
5111 Sm Mathematical symbol
5112 So Other symbol
5113
5114 Z Separator
5115 Zl Line separator
5116 Zp Paragraph separator
5117 Zs Space separator
5118
5119 The special property L& is also supported: it matches a character that
5120 has the Lu, Ll, or Lt property, in other words, a letter that is not
5121 classified as a modifier or "other".
5122
5123 The Cs (Surrogate) property applies only to characters in the range
5124 U+D800 to U+DFFF. Such characters are not valid in Unicode strings and
5125 so cannot be tested by PCRE, unless UTF validity checking has been
5126 turned off (see the discussion of PCRE_NO_UTF8_CHECK,
5127 PCRE_NO_UTF16_CHECK and PCRE_NO_UTF32_CHECK in the pcreapi page). Perl
5128 does not support the Cs property.
5129
5130 The long synonyms for property names that Perl supports (such as
5131 \p{Letter}) are not supported by PCRE, nor is it permitted to prefix
5132 any of these properties with "Is".
5133
5134 No character that is in the Unicode table has the Cn (unassigned) prop-
5135 erty. Instead, this property is assumed for any code point that is not
5136 in the Unicode table.
5137
5138 Specifying caseless matching does not affect these escape sequences.
5139 For example, \p{Lu} always matches only upper case letters.
5140
5141 Matching characters by Unicode property is not fast, because PCRE has
5142 to do a multistage table lookup in order to find a character's prop-
5143 erty. That is why the traditional escape sequences such as \d and \w do
5144 not use Unicode properties in PCRE by default, though you can make them
5145 do so by setting the PCRE_UCP option or by starting the pattern with
5146 (*UCP).
5147
5148 Extended grapheme clusters
5149
5150 The \X escape matches any number of Unicode characters that form an
5151 "extended grapheme cluster", and treats the sequence as an atomic group
5152 (see below). Up to and including release 8.31, PCRE matched an ear-
5153 lier, simpler definition that was equivalent to
5154
5155 (?>\PM\pM*)
5156
5157 That is, it matched a character without the "mark" property, followed
5158 by zero or more characters with the "mark" property. Characters with
5159 the "mark" property are typically non-spacing accents that affect the
5160 preceding character.
5161
5162 This simple definition was extended in Unicode to include more compli-
5163 cated kinds of composite character by giving each character a grapheme
5164 breaking property, and creating rules that use these properties to
5165 define the boundaries of extended grapheme clusters. In releases of
5166 PCRE later than 8.31, \X matches one of these clusters.
5167
5168 \X always matches at least one character. Then it decides whether to
5169 add additional characters according to the following rules for ending a
5170 cluster:
5171
5172 1. End at the end of the subject string.
5173
5174 2. Do not end between CR and LF; otherwise end after any control char-
5175 acter.
5176
5177 3. Do not break Hangul (a Korean script) syllable sequences. Hangul
5178 characters are of five types: L, V, T, LV, and LVT. An L character may
5179 be followed by an L, V, LV, or LVT character; an LV or V character may
5180 be followed by a V or T character; an LVT or T character may be follwed
5181 only by a T character.
5182
5183 4. Do not end before extending characters or spacing marks. Characters
5184 with the "mark" property always have the "extend" grapheme breaking
5185 property.
5186
5187 5. Do not end after prepend characters.
5188
5189 6. Otherwise, end the cluster.
5190
5191 PCRE's additional properties
5192
5193 As well as the standard Unicode properties described above, PCRE sup-
5194 ports four more that make it possible to convert traditional escape
5195 sequences such as \w and \s and POSIX character classes to use Unicode
5196 properties. PCRE uses these non-standard, non-Perl properties inter-
5197 nally when PCRE_UCP is set. They are:
5198
5199 Xan Any alphanumeric character
5200 Xps Any POSIX space character
5201 Xsp Any Perl space character
5202 Xwd Any Perl "word" character
5203
5204 Xan matches characters that have either the L (letter) or the N (num-
5205 ber) property. Xps matches the characters tab, linefeed, vertical tab,
5206 form feed, or carriage return, and any other character that has the Z
5207 (separator) property. Xsp is the same as Xps, except that vertical tab
5208 is excluded. Xwd matches the same characters as Xan, plus underscore.
5209
5210 Resetting the match start
5211
5212 The escape sequence \K causes any previously matched characters not to
5213 be included in the final matched sequence. For example, the pattern:
5214
5215 foo\Kbar
5216
5217 matches "foobar", but reports that it has matched "bar". This feature
5218 is similar to a lookbehind assertion (described below). However, in
5219 this case, the part of the subject before the real match does not have
5220 to be of fixed length, as lookbehind assertions do. The use of \K does
5221 not interfere with the setting of captured substrings. For example,
5222 when the pattern
5223
5224 (foo)\Kbar
5225
5226 matches "foobar", the first substring is still set to "foo".
5227
5228 Perl documents that the use of \K within assertions is "not well
5229 defined". In PCRE, \K is acted upon when it occurs inside positive
5230 assertions, but is ignored in negative assertions.
5231
5232 Simple assertions
5233
5234 The final use of backslash is for certain simple assertions. An asser-
5235 tion specifies a condition that has to be met at a particular point in
5236 a match, without consuming any characters from the subject string. The
5237 use of subpatterns for more complicated assertions is described below.
5238 The backslashed assertions are:
5239
5240 \b matches at a word boundary
5241 \B matches when not at a word boundary
5242 \A matches at the start of the subject
5243 \Z matches at the end of the subject
5244 also matches before a newline at the end of the subject
5245 \z matches only at the end of the subject
5246 \G matches at the first matching position in the subject
5247
5248 Inside a character class, \b has a different meaning; it matches the
5249 backspace character. If any other of these assertions appears in a
5250 character class, by default it matches the corresponding literal char-
5251 acter (for example, \B matches the letter B). However, if the
5252 PCRE_EXTRA option is set, an "invalid escape sequence" error is gener-
5253 ated instead.
5254
5255 A word boundary is a position in the subject string where the current
5256 character and the previous character do not both match \w or \W (i.e.
5257 one matches \w and the other matches \W), or the start or end of the
5258 string if the first or last character matches \w, respectively. In a
5259 UTF mode, the meanings of \w and \W can be changed by setting the
5260 PCRE_UCP option. When this is done, it also affects \b and \B. Neither
5261 PCRE nor Perl has a separate "start of word" or "end of word" metase-
5262 quence. However, whatever follows \b normally determines which it is.
5263 For example, the fragment \ba matches "a" at the start of a word.
5264
5265 The \A, \Z, and \z assertions differ from the traditional circumflex
5266 and dollar (described in the next section) in that they only ever match
5267 at the very start and end of the subject string, whatever options are
5268 set. Thus, they are independent of multiline mode. These three asser-
5269 tions are not affected by the PCRE_NOTBOL or PCRE_NOTEOL options, which
5270 affect only the behaviour of the circumflex and dollar metacharacters.
5271 However, if the startoffset argument of pcre_exec() is non-zero, indi-
5272 cating that matching is to start at a point other than the beginning of
5273 the subject, \A can never match. The difference between \Z and \z is
5274 that \Z matches before a newline at the end of the string as well as at
5275 the very end, whereas \z matches only at the end.
5276
5277 The \G assertion is true only when the current matching position is at
5278 the start point of the match, as specified by the startoffset argument
5279 of pcre_exec(). It differs from \A when the value of startoffset is
5280 non-zero. By calling pcre_exec() multiple times with appropriate argu-
5281 ments, you can mimic Perl's /g option, and it is in this kind of imple-
5282 mentation where \G can be useful.
5283
5284 Note, however, that PCRE's interpretation of \G, as the start of the
5285 current match, is subtly different from Perl's, which defines it as the
5286 end of the previous match. In Perl, these can be different when the
5287 previously matched string was empty. Because PCRE does just one match
5288 at a time, it cannot reproduce this behaviour.
5289
5290 If all the alternatives of a pattern begin with \G, the expression is
5291 anchored to the starting match position, and the "anchored" flag is set
5292 in the compiled regular expression.
5293
5294
5295 CIRCUMFLEX AND DOLLAR
5296
5297 The circumflex and dollar metacharacters are zero-width assertions.
5298 That is, they test for a particular condition being true without con-
5299 suming any characters from the subject string.
5300
5301 Outside a character class, in the default matching mode, the circumflex
5302 character is an assertion that is true only if the current matching
5303 point is at the start of the subject string. If the startoffset argu-
5304 ment of pcre_exec() is non-zero, circumflex can never match if the
5305 PCRE_MULTILINE option is unset. Inside a character class, circumflex
5306 has an entirely different meaning (see below).
5307
5308 Circumflex need not be the first character of the pattern if a number
5309 of alternatives are involved, but it should be the first thing in each
5310 alternative in which it appears if the pattern is ever to match that
5311 branch. If all possible alternatives start with a circumflex, that is,
5312 if the pattern is constrained to match only at the start of the sub-
5313 ject, it is said to be an "anchored" pattern. (There are also other
5314 constructs that can cause a pattern to be anchored.)
5315
5316 The dollar character is an assertion that is true only if the current
5317 matching point is at the end of the subject string, or immediately
5318 before a newline at the end of the string (by default). Note, however,
5319 that it does not actually match the newline. Dollar need not be the
5320 last character of the pattern if a number of alternatives are involved,
5321 but it should be the last item in any branch in which it appears. Dol-
5322 lar has no special meaning in a character class.
5323
5324 The meaning of dollar can be changed so that it matches only at the
5325 very end of the string, by setting the PCRE_DOLLAR_ENDONLY option at
5326 compile time. This does not affect the \Z assertion.
5327
5328 The meanings of the circumflex and dollar characters are changed if the
5329 PCRE_MULTILINE option is set. When this is the case, a circumflex
5330 matches immediately after internal newlines as well as at the start of
5331 the subject string. It does not match after a newline that ends the
5332 string. A dollar matches before any newlines in the string, as well as
5333 at the very end, when PCRE_MULTILINE is set. When newline is specified
5334 as the two-character sequence CRLF, isolated CR and LF characters do
5335 not indicate newlines.
5336
5337 For example, the pattern /^abc$/ matches the subject string "def\nabc"
5338 (where \n represents a newline) in multiline mode, but not otherwise.
5339 Consequently, patterns that are anchored in single line mode because
5340 all branches start with ^ are not anchored in multiline mode, and a
5341 match for circumflex is possible when the startoffset argument of
5342 pcre_exec() is non-zero. The PCRE_DOLLAR_ENDONLY option is ignored if
5343 PCRE_MULTILINE is set.
5344
5345 Note that the sequences \A, \Z, and \z can be used to match the start
5346 and end of the subject in both modes, and if all branches of a pattern
5347 start with \A it is always anchored, whether or not PCRE_MULTILINE is
5348 set.
5349
5350
5351 FULL STOP (PERIOD, DOT) AND \N
5352
5353 Outside a character class, a dot in the pattern matches any one charac-
5354 ter in the subject string except (by default) a character that signi-
5355 fies the end of a line.
5356
5357 When a line ending is defined as a single character, dot never matches
5358 that character; when the two-character sequence CRLF is used, dot does
5359 not match CR if it is immediately followed by LF, but otherwise it
5360 matches all characters (including isolated CRs and LFs). When any Uni-
5361 code line endings are being recognized, dot does not match CR or LF or
5362 any of the other line ending characters.
5363
5364 The behaviour of dot with regard to newlines can be changed. If the
5365 PCRE_DOTALL option is set, a dot matches any one character, without
5366 exception. If the two-character sequence CRLF is present in the subject
5367 string, it takes two dots to match it.
5368
5369 The handling of dot is entirely independent of the handling of circum-
5370 flex and dollar, the only relationship being that they both involve
5371 newlines. Dot has no special meaning in a character class.
5372
5373 The escape sequence \N behaves like a dot, except that it is not
5374 affected by the PCRE_DOTALL option. In other words, it matches any
5375 character except one that signifies the end of a line. Perl also uses
5376 \N to match characters by name; PCRE does not support this.
5377
5378
5379 MATCHING A SINGLE DATA UNIT
5380
5381 Outside a character class, the escape sequence \C matches any one data
5382 unit, whether or not a UTF mode is set. In the 8-bit library, one data
5383 unit is one byte; in the 16-bit library it is a 16-bit unit; in the
5384 32-bit library it is a 32-bit unit. Unlike a dot, \C always matches
5385 line-ending characters. The feature is provided in Perl in order to
5386 match individual bytes in UTF-8 mode, but it is unclear how it can use-
5387 fully be used. Because \C breaks up characters into individual data
5388 units, matching one unit with \C in a UTF mode means that the rest of
5389 the string may start with a malformed UTF character. This has undefined
5390 results, because PCRE assumes that it is dealing with valid UTF strings
5391 (and by default it checks this at the start of processing unless the
5392 PCRE_NO_UTF8_CHECK, PCRE_NO_UTF16_CHECK or PCRE_NO_UTF32_CHECK option
5393 is used).
5394
5395 PCRE does not allow \C to appear in lookbehind assertions (described
5396 below) in a UTF mode, because this would make it impossible to calcu-
5397 late the length of the lookbehind.
5398
5399 In general, the \C escape sequence is best avoided. However, one way of
5400 using it that avoids the problem of malformed UTF characters is to use
5401 a lookahead to check the length of the next character, as in this pat-
5402 tern, which could be used with a UTF-8 string (ignore white space and
5403 line breaks):
5404
5405 (?| (?=[\x00-\x7f])(\C) |
5406 (?=[\x80-\x{7ff}])(\C)(\C) |
5407 (?=[\x{800}-\x{ffff}])(\C)(\C)(\C) |
5408 (?=[\x{10000}-\x{1fffff}])(\C)(\C)(\C)(\C))
5409
5410 A group that starts with (?| resets the capturing parentheses numbers
5411 in each alternative (see "Duplicate Subpattern Numbers" below). The
5412 assertions at the start of each branch check the next UTF-8 character
5413 for values whose encoding uses 1, 2, 3, or 4 bytes, respectively. The
5414 character's individual bytes are then captured by the appropriate num-
5415 ber of groups.
5416
5417
5418 SQUARE BRACKETS AND CHARACTER CLASSES
5419
5420 An opening square bracket introduces a character class, terminated by a
5421 closing square bracket. A closing square bracket on its own is not spe-
5422 cial by default. However, if the PCRE_JAVASCRIPT_COMPAT option is set,
5423 a lone closing square bracket causes a compile-time error. If a closing
5424 square bracket is required as a member of the class, it should be the
5425 first data character in the class (after an initial circumflex, if
5426 present) or escaped with a backslash.
5427
5428 A character class matches a single character in the subject. In a UTF
5429 mode, the character may be more than one data unit long. A matched
5430 character must be in the set of characters defined by the class, unless
5431 the first character in the class definition is a circumflex, in which
5432 case the subject character must not be in the set defined by the class.
5433 If a circumflex is actually required as a member of the class, ensure
5434 it is not the first character, or escape it with a backslash.
5435
5436 For example, the character class [aeiou] matches any lower case vowel,
5437 while [^aeiou] matches any character that is not a lower case vowel.
5438 Note that a circumflex is just a convenient notation for specifying the
5439 characters that are in the class by enumerating those that are not. A
5440 class that starts with a circumflex is not an assertion; it still con-
5441 sumes a character from the subject string, and therefore it fails if
5442 the current pointer is at the end of the string.
5443
5444 In UTF-8 (UTF-16, UTF-32) mode, characters with values greater than 255
5445 (0xffff) can be included in a class as a literal string of data units,
5446 or by using the \x{ escaping mechanism.
5447
5448 When caseless matching is set, any letters in a class represent both
5449 their upper case and lower case versions, so for example, a caseless
5450 [aeiou] matches "A" as well as "a", and a caseless [^aeiou] does not
5451 match "A", whereas a caseful version would. In a UTF mode, PCRE always
5452 understands the concept of case for characters whose values are less
5453 than 128, so caseless matching is always possible. For characters with
5454 higher values, the concept of case is supported if PCRE is compiled
5455 with Unicode property support, but not otherwise. If you want to use
5456 caseless matching in a UTF mode for characters 128 and above, you must
5457 ensure that PCRE is compiled with Unicode property support as well as
5458 with UTF support.
5459
5460 Characters that might indicate line breaks are never treated in any
5461 special way when matching character classes, whatever line-ending
5462 sequence is in use, and whatever setting of the PCRE_DOTALL and
5463 PCRE_MULTILINE options is used. A class such as [^a] always matches one
5464 of these characters.
5465
5466 The minus (hyphen) character can be used to specify a range of charac-
5467 ters in a character class. For example, [d-m] matches any letter
5468 between d and m, inclusive. If a minus character is required in a
5469 class, it must be escaped with a backslash or appear in a position
5470 where it cannot be interpreted as indicating a range, typically as the
5471 first or last character in the class.
5472
5473 It is not possible to have the literal character "]" as the end charac-
5474 ter of a range. A pattern such as [W-]46] is interpreted as a class of
5475 two characters ("W" and "-") followed by a literal string "46]", so it
5476 would match "W46]" or "-46]". However, if the "]" is escaped with a
5477 backslash it is interpreted as the end of range, so [W-\]46] is inter-
5478 preted as a class containing a range followed by two other characters.
5479 The octal or hexadecimal representation of "]" can also be used to end
5480 a range.
5481
5482 Ranges operate in the collating sequence of character values. They can
5483 also be used for characters specified numerically, for example
5484 [\000-\037]. Ranges can include any characters that are valid for the
5485 current mode.
5486
5487 If a range that includes letters is used when caseless matching is set,
5488 it matches the letters in either case. For example, [W-c] is equivalent
5489 to [][\\^_`wxyzabc], matched caselessly, and in a non-UTF mode, if
5490 character tables for a French locale are in use, [\xc8-\xcb] matches
5491 accented E characters in both cases. In UTF modes, PCRE supports the
5492 concept of case for characters with values greater than 128 only when
5493 it is compiled with Unicode property support.
5494
5495 The character escape sequences \d, \D, \h, \H, \p, \P, \s, \S, \v, \V,
5496 \w, and \W may appear in a character class, and add the characters that
5497 they match to the class. For example, [\dABCDEF] matches any hexadeci-
5498 mal digit. In UTF modes, the PCRE_UCP option affects the meanings of
5499 \d, \s, \w and their upper case partners, just as it does when they
5500 appear outside a character class, as described in the section entitled
5501 "Generic character types" above. The escape sequence \b has a different
5502 meaning inside a character class; it matches the backspace character.
5503 The sequences \B, \N, \R, and \X are not special inside a character
5504 class. Like any other unrecognized escape sequences, they are treated
5505 as the literal characters "B", "N", "R", and "X" by default, but cause
5506 an error if the PCRE_EXTRA option is set.
5507
5508 A circumflex can conveniently be used with the upper case character
5509 types to specify a more restricted set of characters than the matching
5510 lower case type. For example, the class [^\W_] matches any letter or
5511 digit, but not underscore, whereas [\w] includes underscore. A positive
5512 character class should be read as "something OR something OR ..." and a
5513 negative class as "NOT something AND NOT something AND NOT ...".
5514
5515 The only metacharacters that are recognized in character classes are
5516 backslash, hyphen (only where it can be interpreted as specifying a
5517 range), circumflex (only at the start), opening square bracket (only
5518 when it can be interpreted as introducing a POSIX class name - see the
5519 next section), and the terminating closing square bracket. However,
5520 escaping other non-alphanumeric characters does no harm.
5521
5522
5523 POSIX CHARACTER CLASSES
5524
5525 Perl supports the POSIX notation for character classes. This uses names
5526 enclosed by [: and :] within the enclosing square brackets. PCRE also
5527 supports this notation. For example,
5528
5529 [01[:alpha:]%]
5530
5531 matches "0", "1", any alphabetic character, or "%". The supported class
5532 names are:
5533
5534 alnum letters and digits
5535 alpha letters
5536 ascii character codes 0 - 127
5537 blank space or tab only
5538 cntrl control characters
5539 digit decimal digits (same as \d)
5540 graph printing characters, excluding space
5541 lower lower case letters
5542 print printing characters, including space
5543 punct printing characters, excluding letters and digits and space
5544 space white space (not quite the same as \s)
5545 upper upper case letters
5546 word "word" characters (same as \w)
5547 xdigit hexadecimal digits
5548
5549 The "space" characters are HT (9), LF (10), VT (11), FF (12), CR (13),
5550 and space (32). Notice that this list includes the VT character (code
5551 11). This makes "space" different to \s, which does not include VT (for
5552 Perl compatibility).
5553
5554 The name "word" is a Perl extension, and "blank" is a GNU extension
5555 from Perl 5.8. Another Perl extension is negation, which is indicated
5556 by a ^ character after the colon. For example,
5557
5558 [12[:^digit:]]
5559
5560 matches "1", "2", or any non-digit. PCRE (and Perl) also recognize the
5561 POSIX syntax [.ch.] and [=ch=] where "ch" is a "collating element", but
5562 these are not supported, and an error is given if they are encountered.
5563
5564 By default, in UTF modes, characters with values greater than 128 do
5565 not match any of the POSIX character classes. However, if the PCRE_UCP
5566 option is passed to pcre_compile(), some of the classes are changed so
5567 that Unicode character properties are used. This is achieved by replac-
5568 ing the POSIX classes by other sequences, as follows:
5569
5570 [:alnum:] becomes \p{Xan}
5571 [:alpha:] becomes \p{L}
5572 [:blank:] becomes \h
5573 [:digit:] becomes \p{Nd}
5574 [:lower:] becomes \p{Ll}
5575 [:space:] becomes \p{Xps}
5576 [:upper:] becomes \p{Lu}
5577 [:word:] becomes \p{Xwd}
5578
5579 Negated versions, such as [:^alpha:] use \P instead of \p. The other
5580 POSIX classes are unchanged, and match only characters with code points
5581 less than 128.
5582
5583
5584 VERTICAL BAR
5585
5586 Vertical bar characters are used to separate alternative patterns. For
5587 example, the pattern
5588
5589 gilbert|sullivan
5590
5591 matches either "gilbert" or "sullivan". Any number of alternatives may
5592 appear, and an empty alternative is permitted (matching the empty
5593 string). The matching process tries each alternative in turn, from left
5594 to right, and the first one that succeeds is used. If the alternatives
5595 are within a subpattern (defined below), "succeeds" means matching the
5596 rest of the main pattern as well as the alternative in the subpattern.
5597
5598
5599 INTERNAL OPTION SETTING
5600
5601 The settings of the PCRE_CASELESS, PCRE_MULTILINE, PCRE_DOTALL, and
5602 PCRE_EXTENDED options (which are Perl-compatible) can be changed from
5603 within the pattern by a sequence of Perl option letters enclosed
5604 between "(?" and ")". The option letters are
5605
5606 i for PCRE_CASELESS
5607 m for PCRE_MULTILINE
5608 s for PCRE_DOTALL
5609 x for PCRE_EXTENDED
5610
5611 For example, (?im) sets caseless, multiline matching. It is also possi-
5612 ble to unset these options by preceding the letter with a hyphen, and a
5613 combined setting and unsetting such as (?im-sx), which sets PCRE_CASE-
5614 LESS and PCRE_MULTILINE while unsetting PCRE_DOTALL and PCRE_EXTENDED,
5615 is also permitted. If a letter appears both before and after the
5616 hyphen, the option is unset.
5617
5618 The PCRE-specific options PCRE_DUPNAMES, PCRE_UNGREEDY, and PCRE_EXTRA
5619 can be changed in the same way as the Perl-compatible options by using
5620 the characters J, U and X respectively.
5621
5622 When one of these option changes occurs at top level (that is, not
5623 inside subpattern parentheses), the change applies to the remainder of
5624 the pattern that follows. If the change is placed right at the start of
5625 a pattern, PCRE extracts it into the global options (and it will there-
5626 fore show up in data extracted by the pcre_fullinfo() function).
5627
5628 An option change within a subpattern (see below for a description of
5629 subpatterns) affects only that part of the subpattern that follows it,
5630 so
5631
5632 (a(?i)b)c
5633
5634 matches abc and aBc and no other strings (assuming PCRE_CASELESS is not
5635 used). By this means, options can be made to have different settings
5636 in different parts of the pattern. Any changes made in one alternative
5637 do carry on into subsequent branches within the same subpattern. For
5638 example,
5639
5640 (a(?i)b|c)
5641
5642 matches "ab", "aB", "c", and "C", even though when matching "C" the
5643 first branch is abandoned before the option setting. This is because
5644 the effects of option settings happen at compile time. There would be
5645 some very weird behaviour otherwise.
5646
5647 Note: There are other PCRE-specific options that can be set by the
5648 application when the compiling or matching functions are called. In
5649 some cases the pattern can contain special leading sequences such as
5650 (*CRLF) to override what the application has set or what has been
5651 defaulted. Details are given in the section entitled "Newline
5652 sequences" above. There are also the (*UTF8), (*UTF16),(*UTF32), and
5653 (*UCP) leading sequences that can be used to set UTF and Unicode prop-
5654 erty modes; they are equivalent to setting the PCRE_UTF8, PCRE_UTF16,
5655 PCRE_UTF32 and the PCRE_UCP options, respectively. The (*UTF) sequence
5656 is a generic version that can be used with any of the libraries.
5657
5658
5659 SUBPATTERNS
5660
5661 Subpatterns are delimited by parentheses (round brackets), which can be
5662 nested. Turning part of a pattern into a subpattern does two things:
5663
5664 1. It localizes a set of alternatives. For example, the pattern
5665
5666 cat(aract|erpillar|)
5667
5668 matches "cataract", "caterpillar", or "cat". Without the parentheses,
5669 it would match "cataract", "erpillar" or an empty string.
5670
5671 2. It sets up the subpattern as a capturing subpattern. This means
5672 that, when the whole pattern matches, that portion of the subject
5673 string that matched the subpattern is passed back to the caller via the
5674 ovector argument of the matching function. (This applies only to the
5675 traditional matching functions; the DFA matching functions do not sup-
5676 port capturing.)
5677
5678 Opening parentheses are counted from left to right (starting from 1) to
5679 obtain numbers for the capturing subpatterns. For example, if the
5680 string "the red king" is matched against the pattern
5681
5682 the ((red|white) (king|queen))
5683
5684 the captured substrings are "red king", "red", and "king", and are num-
5685 bered 1, 2, and 3, respectively.
5686
5687 The fact that plain parentheses fulfil two functions is not always
5688 helpful. There are often times when a grouping subpattern is required
5689 without a capturing requirement. If an opening parenthesis is followed
5690 by a question mark and a colon, the subpattern does not do any captur-
5691 ing, and is not counted when computing the number of any subsequent
5692 capturing subpatterns. For example, if the string "the white queen" is
5693 matched against the pattern
5694
5695 the ((?:red|white) (king|queen))
5696
5697 the captured substrings are "white queen" and "queen", and are numbered
5698 1 and 2. The maximum number of capturing subpatterns is 65535.
5699
5700 As a convenient shorthand, if any option settings are required at the
5701 start of a non-capturing subpattern, the option letters may appear
5702 between the "?" and the ":". Thus the two patterns
5703
5704 (?i:saturday|sunday)
5705 (?:(?i)saturday|sunday)
5706
5707 match exactly the same set of strings. Because alternative branches are
5708 tried from left to right, and options are not reset until the end of
5709 the subpattern is reached, an option setting in one branch does affect
5710 subsequent branches, so the above patterns match "SUNDAY" as well as
5711 "Saturday".
5712
5713
5714 DUPLICATE SUBPATTERN NUMBERS
5715
5716 Perl 5.10 introduced a feature whereby each alternative in a subpattern
5717 uses the same numbers for its capturing parentheses. Such a subpattern
5718 starts with (?| and is itself a non-capturing subpattern. For example,
5719 consider this pattern:
5720
5721 (?|(Sat)ur|(Sun))day
5722
5723 Because the two alternatives are inside a (?| group, both sets of cap-
5724 turing parentheses are numbered one. Thus, when the pattern matches,
5725 you can look at captured substring number one, whichever alternative
5726 matched. This construct is useful when you want to capture part, but
5727 not all, of one of a number of alternatives. Inside a (?| group, paren-
5728 theses are numbered as usual, but the number is reset at the start of
5729 each branch. The numbers of any capturing parentheses that follow the
5730 subpattern start after the highest number used in any branch. The fol-
5731 lowing example is taken from the Perl documentation. The numbers under-
5732 neath show in which buffer the captured content will be stored.
5733
5734 # before ---------------branch-reset----------- after
5735 / ( a ) (?| x ( y ) z | (p (q) r) | (t) u (v) ) ( z ) /x
5736 # 1 2 2 3 2 3 4
5737
5738 A back reference to a numbered subpattern uses the most recent value
5739 that is set for that number by any subpattern. The following pattern
5740 matches "abcabc" or "defdef":
5741
5742 /(?|(abc)|(def))\1/
5743
5744 In contrast, a subroutine call to a numbered subpattern always refers
5745 to the first one in the pattern with the given number. The following
5746 pattern matches "abcabc" or "defabc":
5747
5748 /(?|(abc)|(def))(?1)/
5749
5750 If a condition test for a subpattern's having matched refers to a non-
5751 unique number, the test is true if any of the subpatterns of that num-
5752 ber have matched.
5753
5754 An alternative approach to using this "branch reset" feature is to use
5755 duplicate named subpatterns, as described in the next section.
5756
5757
5758 NAMED SUBPATTERNS
5759
5760 Identifying capturing parentheses by number is simple, but it can be
5761 very hard to keep track of the numbers in complicated regular expres-
5762 sions. Furthermore, if an expression is modified, the numbers may
5763 change. To help with this difficulty, PCRE supports the naming of sub-
5764 patterns. This feature was not added to Perl until release 5.10. Python
5765 had the feature earlier, and PCRE introduced it at release 4.0, using
5766 the Python syntax. PCRE now supports both the Perl and the Python syn-
5767 tax. Perl allows identically numbered subpatterns to have different
5768 names, but PCRE does not.
5769
5770 In PCRE, a subpattern can be named in one of three ways: (?<name>...)
5771 or (?'name'...) as in Perl, or (?P<name>...) as in Python. References
5772 to capturing parentheses from other parts of the pattern, such as back
5773 references, recursion, and conditions, can be made by name as well as
5774 by number.
5775
5776 Names consist of up to 32 alphanumeric characters and underscores.
5777 Named capturing parentheses are still allocated numbers as well as
5778 names, exactly as if the names were not present. The PCRE API provides
5779 function calls for extracting the name-to-number translation table from
5780 a compiled pattern. There is also a convenience function for extracting
5781 a captured substring by name.
5782
5783 By default, a name must be unique within a pattern, but it is possible
5784 to relax this constraint by setting the PCRE_DUPNAMES option at compile
5785 time. (Duplicate names are also always permitted for subpatterns with
5786 the same number, set up as described in the previous section.) Dupli-
5787 cate names can be useful for patterns where only one instance of the
5788 named parentheses can match. Suppose you want to match the name of a
5789 weekday, either as a 3-letter abbreviation or as the full name, and in
5790 both cases you want to extract the abbreviation. This pattern (ignoring
5791 the line breaks) does the job:
5792
5793 (?<DN>Mon|Fri|Sun)(?:day)?|
5794 (?<DN>Tue)(?:sday)?|
5795 (?<DN>Wed)(?:nesday)?|
5796 (?<DN>Thu)(?:rsday)?|
5797 (?<DN>Sat)(?:urday)?
5798
5799 There are five capturing substrings, but only one is ever set after a
5800 match. (An alternative way of solving this problem is to use a "branch
5801 reset" subpattern, as described in the previous section.)
5802
5803 The convenience function for extracting the data by name returns the
5804 substring for the first (and in this example, the only) subpattern of
5805 that name that matched. This saves searching to find which numbered
5806 subpattern it was.
5807
5808 If you make a back reference to a non-unique named subpattern from
5809 elsewhere in the pattern, the one that corresponds to the first occur-
5810 rence of the name is used. In the absence of duplicate numbers (see the
5811 previous section) this is the one with the lowest number. If you use a
5812 named reference in a condition test (see the section about conditions
5813 below), either to check whether a subpattern has matched, or to check
5814 for recursion, all subpatterns with the same name are tested. If the
5815 condition is true for any one of them, the overall condition is true.
5816 This is the same behaviour as testing by number. For further details of
5817 the interfaces for handling named subpatterns, see the pcreapi documen-
5818 tation.
5819
5820 Warning: You cannot use different names to distinguish between two sub-
5821 patterns with the same number because PCRE uses only the numbers when
5822 matching. For this reason, an error is given at compile time if differ-
5823 ent names are given to subpatterns with the same number. However, you
5824 can give the same name to subpatterns with the same number, even when
5825 PCRE_DUPNAMES is not set.
5826
5827
5828 REPETITION
5829
5830 Repetition is specified by quantifiers, which can follow any of the
5831 following items:
5832
5833 a literal data character
5834 the dot metacharacter
5835 the \C escape sequence
5836 the \X escape sequence
5837 the \R escape sequence
5838 an escape such as \d or \pL that matches a single character
5839 a character class
5840 a back reference (see next section)
5841 a parenthesized subpattern (including assertions)
5842 a subroutine call to a subpattern (recursive or otherwise)
5843
5844 The general repetition quantifier specifies a minimum and maximum num-
5845 ber of permitted matches, by giving the two numbers in curly brackets
5846 (braces), separated by a comma. The numbers must be less than 65536,
5847 and the first must be less than or equal to the second. For example:
5848
5849 z{2,4}
5850
5851 matches "zz", "zzz", or "zzzz". A closing brace on its own is not a
5852 special character. If the second number is omitted, but the comma is
5853 present, there is no upper limit; if the second number and the comma
5854 are both omitted, the quantifier specifies an exact number of required
5855 matches. Thus
5856
5857 [aeiou]{3,}
5858
5859 matches at least 3 successive vowels, but may match many more, while
5860
5861 \d{8}
5862
5863 matches exactly 8 digits. An opening curly bracket that appears in a
5864 position where a quantifier is not allowed, or one that does not match
5865 the syntax of a quantifier, is taken as a literal character. For exam-
5866 ple, {,6} is not a quantifier, but a literal string of four characters.
5867
5868 In UTF modes, quantifiers apply to characters rather than to individual
5869 data units. Thus, for example, \x{100}{2} matches two characters, each
5870 of which is represented by a two-byte sequence in a UTF-8 string. Simi-
5871 larly, \X{3} matches three Unicode extended grapheme clusters, each of
5872 which may be several data units long (and they may be of different
5873 lengths).
5874
5875 The quantifier {0} is permitted, causing the expression to behave as if
5876 the previous item and the quantifier were not present. This may be use-
5877 ful for subpatterns that are referenced as subroutines from elsewhere
5878 in the pattern (but see also the section entitled "Defining subpatterns
5879 for use by reference only" below). Items other than subpatterns that
5880 have a {0} quantifier are omitted from the compiled pattern.
5881
5882 For convenience, the three most common quantifiers have single-charac-
5883 ter abbreviations:
5884
5885 * is equivalent to {0,}
5886 + is equivalent to {1,}
5887 ? is equivalent to {0,1}
5888
5889 It is possible to construct infinite loops by following a subpattern
5890 that can match no characters with a quantifier that has no upper limit,
5891 for example:
5892
5893 (a?)*
5894
5895 Earlier versions of Perl and PCRE used to give an error at compile time
5896 for such patterns. However, because there are cases where this can be
5897 useful, such patterns are now accepted, but if any repetition of the
5898 subpattern does in fact match no characters, the loop is forcibly bro-
5899 ken.
5900
5901 By default, the quantifiers are "greedy", that is, they match as much
5902 as possible (up to the maximum number of permitted times), without
5903 causing the rest of the pattern to fail. The classic example of where
5904 this gives problems is in trying to match comments in C programs. These
5905 appear between /* and */ and within the comment, individual * and /
5906 characters may appear. An attempt to match C comments by applying the
5907 pattern
5908
5909 /\*.*\*/
5910
5911 to the string
5912
5913 /* first comment */ not comment /* second comment */
5914
5915 fails, because it matches the entire string owing to the greediness of
5916 the .* item.
5917
5918 However, if a quantifier is followed by a question mark, it ceases to
5919 be greedy, and instead matches the minimum number of times possible, so
5920 the pattern
5921
5922 /\*.*?\*/
5923
5924 does the right thing with the C comments. The meaning of the various
5925 quantifiers is not otherwise changed, just the preferred number of
5926 matches. Do not confuse this use of question mark with its use as a
5927 quantifier in its own right. Because it has two uses, it can sometimes
5928 appear doubled, as in
5929
5930 \d??\d
5931
5932 which matches one digit by preference, but can match two if that is the
5933 only way the rest of the pattern matches.
5934
5935 If the PCRE_UNGREEDY option is set (an option that is not available in
5936 Perl), the quantifiers are not greedy by default, but individual ones
5937 can be made greedy by following them with a question mark. In other
5938 words, it inverts the default behaviour.
5939
5940 When a parenthesized subpattern is quantified with a minimum repeat
5941 count that is greater than 1 or with a limited maximum, more memory is
5942 required for the compiled pattern, in proportion to the size of the
5943 minimum or maximum.
5944
5945 If a pattern starts with .* or .{0,} and the PCRE_DOTALL option (equiv-
5946 alent to Perl's /s) is set, thus allowing the dot to match newlines,
5947 the pattern is implicitly anchored, because whatever follows will be
5948 tried against every character position in the subject string, so there
5949 is no point in retrying the overall match at any position after the
5950 first. PCRE normally treats such a pattern as though it were preceded
5951 by \A.
5952
5953 In cases where it is known that the subject string contains no new-
5954 lines, it is worth setting PCRE_DOTALL in order to obtain this opti-
5955 mization, or alternatively using ^ to indicate anchoring explicitly.
5956
5957 However, there are some cases where the optimization cannot be used.
5958 When .* is inside capturing parentheses that are the subject of a back
5959 reference elsewhere in the pattern, a match at the start may fail where
5960 a later one succeeds. Consider, for example:
5961
5962 (.*)abc\1
5963
5964 If the subject is "xyz123abc123" the match point is the fourth charac-
5965 ter. For this reason, such a pattern is not implicitly anchored.
5966
5967 Another case where implicit anchoring is not applied is when the lead-
5968 ing .* is inside an atomic group. Once again, a match at the start may
5969 fail where a later one succeeds. Consider this pattern:
5970
5971 (?>.*?a)b
5972
5973 It matches "ab" in the subject "aab". The use of the backtracking con-
5974 trol verbs (*PRUNE) and (*SKIP) also disable this optimization.
5975
5976 When a capturing subpattern is repeated, the value captured is the sub-
5977 string that matched the final iteration. For example, after
5978
5979 (tweedle[dume]{3}\s*)+
5980
5981 has matched "tweedledum tweedledee" the value of the captured substring
5982 is "tweedledee". However, if there are nested capturing subpatterns,
5983 the corresponding captured values may have been set in previous itera-
5984 tions. For example, after
5985
5986 /(a|(b))+/
5987
5988 matches "aba" the value of the second captured substring is "b".
5989
5990
5991 ATOMIC GROUPING AND POSSESSIVE QUANTIFIERS
5992
5993 With both maximizing ("greedy") and minimizing ("ungreedy" or "lazy")
5994 repetition, failure of what follows normally causes the repeated item
5995 to be re-evaluated to see if a different number of repeats allows the
5996 rest of the pattern to match. Sometimes it is useful to prevent this,
5997 either to change the nature of the match, or to cause it fail earlier
5998 than it otherwise might, when the author of the pattern knows there is
5999 no point in carrying on.
6000
6001 Consider, for example, the pattern \d+foo when applied to the subject
6002 line
6003
6004 123456bar
6005
6006 After matching all 6 digits and then failing to match "foo", the normal
6007 action of the matcher is to try again with only 5 digits matching the
6008 \d+ item, and then with 4, and so on, before ultimately failing.
6009 "Atomic grouping" (a term taken from Jeffrey Friedl's book) provides
6010 the means for specifying that once a subpattern has matched, it is not
6011 to be re-evaluated in this way.
6012
6013 If we use atomic grouping for the previous example, the matcher gives
6014 up immediately on failing to match "foo" the first time. The notation
6015 is a kind of special parenthesis, starting with (?> as in this example:
6016
6017 (?>\d+)foo
6018
6019 This kind of parenthesis "locks up" the part of the pattern it con-
6020 tains once it has matched, and a failure further into the pattern is
6021 prevented from backtracking into it. Backtracking past it to previous
6022 items, however, works as normal.
6023
6024 An alternative description is that a subpattern of this type matches
6025 the string of characters that an identical standalone pattern would
6026 match, if anchored at the current point in the subject string.
6027
6028 Atomic grouping subpatterns are not capturing subpatterns. Simple cases
6029 such as the above example can be thought of as a maximizing repeat that
6030 must swallow everything it can. So, while both \d+ and \d+? are pre-
6031 pared to adjust the number of digits they match in order to make the
6032 rest of the pattern match, (?>\d+) can only match an entire sequence of
6033 digits.
6034
6035 Atomic groups in general can of course contain arbitrarily complicated
6036 subpatterns, and can be nested. However, when the subpattern for an
6037 atomic group is just a single repeated item, as in the example above, a
6038 simpler notation, called a "possessive quantifier" can be used. This
6039 consists of an additional + character following a quantifier. Using
6040 this notation, the previous example can be rewritten as
6041