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1 -----------------------------------------------------------------------------
2 This file contains a concatenation of the PCRE man pages, converted to plain
3 text format for ease of searching with a text editor, or for use on systems
4 that do not have a man page processor. The small individual files that give
5 synopses of each function in the library have not been included. Neither has
6 the pcredemo program. There are separate text files for the pcregrep and
7 pcretest commands.
8 -----------------------------------------------------------------------------
9
10
11 PCRE(3) Library Functions Manual PCRE(3)
12
13
14
15 NAME
16 PCRE - Perl-compatible regular expressions
17
18 INTRODUCTION
19
20 The PCRE library is a set of functions that implement regular expres-
21 sion pattern matching using the same syntax and semantics as Perl, with
22 just a few differences. Some features that appeared in Python and PCRE
23 before they appeared in Perl are also available using the Python syn-
24 tax, there is some support for one or two .NET and Oniguruma syntax
25 items, and there is an option for requesting some minor changes that
26 give better JavaScript compatibility.
27
28 Starting with release 8.30, it is possible to compile two separate PCRE
29 libraries: the original, which supports 8-bit character strings
30 (including UTF-8 strings), and a second library that supports 16-bit
31 character strings (including UTF-16 strings). The build process allows
32 either one or both to be built. The majority of the work to make this
33 possible was done by Zoltan Herczeg.
34
35 Starting with release 8.32 it is possible to compile a third separate
36 PCRE library that supports 32-bit character strings (including UTF-32
37 strings). The build process allows any combination of the 8-, 16- and
38 32-bit libraries. The work to make this possible was done by Christian
39 Persch.
40
41 The three libraries contain identical sets of functions, except that
42 the names in the 16-bit library start with pcre16_ instead of pcre_,
43 and the names in the 32-bit library start with pcre32_ instead of
44 pcre_. To avoid over-complication and reduce the documentation mainte-
45 nance load, most of the documentation describes the 8-bit library, with
46 the differences for the 16-bit and 32-bit libraries described sepa-
47 rately in the pcre16 and pcre32 pages. References to functions or
48 structures of the form pcre[16|32]_xxx should be read as meaning
49 "pcre_xxx when using the 8-bit library, pcre16_xxx when using the
50 16-bit library, or pcre32_xxx when using the 32-bit library".
51
52 The current implementation of PCRE corresponds approximately with Perl
53 5.12, including support for UTF-8/16/32 encoded strings and Unicode
54 general category properties. However, UTF-8/16/32 and Unicode support
55 has to be explicitly enabled; it is not the default. The Unicode tables
56 correspond to Unicode release 6.3.0.
57
58 In addition to the Perl-compatible matching function, PCRE contains an
59 alternative function that matches the same compiled patterns in a dif-
60 ferent way. In certain circumstances, the alternative function has some
61 advantages. For a discussion of the two matching algorithms, see the
62 pcrematching page.
63
64 PCRE is written in C and released as a C library. A number of people
65 have written wrappers and interfaces of various kinds. In particular,
66 Google Inc. have provided a comprehensive C++ wrapper for the 8-bit
67 library. This is now included as part of the PCRE distribution. The
68 pcrecpp page has details of this interface. Other people's contribu-
69 tions can be found in the Contrib directory at the primary FTP site,
70 which is:
71
72 ftp://ftp.csx.cam.ac.uk/pub/software/programming/pcre
73
74 Details of exactly which Perl regular expression features are and are
75 not supported by PCRE are given in separate documents. See the pcrepat-
76 tern and pcrecompat pages. There is a syntax summary in the pcresyntax
77 page.
78
79 Some features of PCRE can be included, excluded, or changed when the
80 library is built. The pcre_config() function makes it possible for a
81 client to discover which features are available. The features them-
82 selves are described in the pcrebuild page. Documentation about build-
83 ing PCRE for various operating systems can be found in the README and
84 NON-AUTOTOOLS_BUILD files in the source distribution.
85
86 The libraries contains a number of undocumented internal functions and
87 data tables that are used by more than one of the exported external
88 functions, but which are not intended for use by external callers.
89 Their names all begin with "_pcre_" or "_pcre16_" or "_pcre32_", which
90 hopefully will not provoke any name clashes. In some environments, it
91 is possible to control which external symbols are exported when a
92 shared library is built, and in these cases the undocumented symbols
93 are not exported.
94
95
96 SECURITY CONSIDERATIONS
97
98 If you are using PCRE in a non-UTF application that permits users to
99 supply arbitrary patterns for compilation, you should be aware of a
100 feature that allows users to turn on UTF support from within a pattern,
101 provided that PCRE was built with UTF support. For example, an 8-bit
102 pattern that begins with "(*UTF8)" or "(*UTF)" turns on UTF-8 mode,
103 which interprets patterns and subjects as strings of UTF-8 characters
104 instead of individual 8-bit characters. This causes both the pattern
105 and any data against which it is matched to be checked for UTF-8 valid-
106 ity. If the data string is very long, such a check might use suffi-
107 ciently many resources as to cause your application to lose perfor-
108 mance.
109
110 One way of guarding against this possibility is to use the
111 pcre_fullinfo() function to check the compiled pattern's options for
112 UTF. Alternatively, from release 8.33, you can set the PCRE_NEVER_UTF
113 option at compile time. This causes an compile time error if a pattern
114 contains a UTF-setting sequence.
115
116 If your application is one that supports UTF, be aware that validity
117 checking can take time. If the same data string is to be matched many
118 times, you can use the PCRE_NO_UTF[8|16|32]_CHECK option for the second
119 and subsequent matches to save redundant checks.
120
121 Another way that performance can be hit is by running a pattern that
122 has a very large search tree against a string that will never match.
123 Nested unlimited repeats in a pattern are a common example. PCRE pro-
124 vides some protection against this: see the PCRE_EXTRA_MATCH_LIMIT fea-
125 ture in the pcreapi page.
126
127
128 USER DOCUMENTATION
129
130 The user documentation for PCRE comprises a number of different sec-
131 tions. In the "man" format, each of these is a separate "man page". In
132 the HTML format, each is a separate page, linked from the index page.
133 In the plain text format, the descriptions of the pcregrep and pcretest
134 programs are in files called pcregrep.txt and pcretest.txt, respec-
135 tively. The remaining sections, except for the pcredemo section (which
136 is a program listing), are concatenated in pcre.txt, for ease of
137 searching. The sections are as follows:
138
139 pcre this document
140 pcre-config show PCRE installation configuration information
141 pcre16 details of the 16-bit library
142 pcre32 details of the 32-bit library
143 pcreapi details of PCRE's native C API
144 pcrebuild building PCRE
145 pcrecallout details of the callout feature
146 pcrecompat discussion of Perl compatibility
147 pcrecpp details of the C++ wrapper for the 8-bit library
148 pcredemo a demonstration C program that uses PCRE
149 pcregrep description of the pcregrep command (8-bit only)
150 pcrejit discussion of the just-in-time optimization support
151 pcrelimits details of size and other limits
152 pcrematching discussion of the two matching algorithms
153 pcrepartial details of the partial matching facility
154 pcrepattern syntax and semantics of supported
155 regular expressions
156 pcreperform discussion of performance issues
157 pcreposix the POSIX-compatible C API for the 8-bit library
158 pcreprecompile details of saving and re-using precompiled patterns
159 pcresample discussion of the pcredemo program
160 pcrestack discussion of stack usage
161 pcresyntax quick syntax reference
162 pcretest description of the pcretest testing command
163 pcreunicode discussion of Unicode and UTF-8/16/32 support
164
165 In the "man" and HTML formats, there is also a short page for each C
166 library function, listing its arguments and results.
167
168
169 AUTHOR
170
171 Philip Hazel
172 University Computing Service
173 Cambridge CB2 3QH, England.
174
175 Putting an actual email address here seems to have been a spam magnet,
176 so I've taken it away. If you want to email me, use my two initials,
177 followed by the two digits 10, at the domain cam.ac.uk.
178
179
180 REVISION
181
182 Last updated: 08 January 2014
183 Copyright (c) 1997-2014 University of Cambridge.
184 ------------------------------------------------------------------------------
185
186
187 PCRE(3) Library Functions Manual PCRE(3)
188
189
190
191 NAME
192 PCRE - Perl-compatible regular expressions
193
194 #include <pcre.h>
195
196
197 PCRE 16-BIT API BASIC FUNCTIONS
198
199 pcre16 *pcre16_compile(PCRE_SPTR16 pattern, int options,
200 const char **errptr, int *erroffset,
201 const unsigned char *tableptr);
202
203 pcre16 *pcre16_compile2(PCRE_SPTR16 pattern, int options,
204 int *errorcodeptr,
205 const char **errptr, int *erroffset,
206 const unsigned char *tableptr);
207
208 pcre16_extra *pcre16_study(const pcre16 *code, int options,
209 const char **errptr);
210
211 void pcre16_free_study(pcre16_extra *extra);
212
213 int pcre16_exec(const pcre16 *code, const pcre16_extra *extra,
214 PCRE_SPTR16 subject, int length, int startoffset,
215 int options, int *ovector, int ovecsize);
216
217 int pcre16_dfa_exec(const pcre16 *code, const pcre16_extra *extra,
218 PCRE_SPTR16 subject, int length, int startoffset,
219 int options, int *ovector, int ovecsize,
220 int *workspace, int wscount);
221
222
223 PCRE 16-BIT API STRING EXTRACTION FUNCTIONS
224
225 int pcre16_copy_named_substring(const pcre16 *code,
226 PCRE_SPTR16 subject, int *ovector,
227 int stringcount, PCRE_SPTR16 stringname,
228 PCRE_UCHAR16 *buffer, int buffersize);
229
230 int pcre16_copy_substring(PCRE_SPTR16 subject, int *ovector,
231 int stringcount, int stringnumber, PCRE_UCHAR16 *buffer,
232 int buffersize);
233
234 int pcre16_get_named_substring(const pcre16 *code,
235 PCRE_SPTR16 subject, int *ovector,
236 int stringcount, PCRE_SPTR16 stringname,
237 PCRE_SPTR16 *stringptr);
238
239 int pcre16_get_stringnumber(const pcre16 *code,
240 PCRE_SPTR16 name);
241
242 int pcre16_get_stringtable_entries(const pcre16 *code,
243 PCRE_SPTR16 name, PCRE_UCHAR16 **first, PCRE_UCHAR16 **last);
244
245 int pcre16_get_substring(PCRE_SPTR16 subject, int *ovector,
246 int stringcount, int stringnumber,
247 PCRE_SPTR16 *stringptr);
248
249 int pcre16_get_substring_list(PCRE_SPTR16 subject,
250 int *ovector, int stringcount, PCRE_SPTR16 **listptr);
251
252 void pcre16_free_substring(PCRE_SPTR16 stringptr);
253
254 void pcre16_free_substring_list(PCRE_SPTR16 *stringptr);
255
256
257 PCRE 16-BIT API AUXILIARY FUNCTIONS
258
259 pcre16_jit_stack *pcre16_jit_stack_alloc(int startsize, int maxsize);
260
261 void pcre16_jit_stack_free(pcre16_jit_stack *stack);
262
263 void pcre16_assign_jit_stack(pcre16_extra *extra,
264 pcre16_jit_callback callback, void *data);
265
266 const unsigned char *pcre16_maketables(void);
267
268 int pcre16_fullinfo(const pcre16 *code, const pcre16_extra *extra,
269 int what, void *where);
270
271 int pcre16_refcount(pcre16 *code, int adjust);
272
273 int pcre16_config(int what, void *where);
274
275 const char *pcre16_version(void);
276
277 int pcre16_pattern_to_host_byte_order(pcre16 *code,
278 pcre16_extra *extra, const unsigned char *tables);
279
280
281 PCRE 16-BIT API INDIRECTED FUNCTIONS
282
283 void *(*pcre16_malloc)(size_t);
284
285 void (*pcre16_free)(void *);
286
287 void *(*pcre16_stack_malloc)(size_t);
288
289 void (*pcre16_stack_free)(void *);
290
291 int (*pcre16_callout)(pcre16_callout_block *);
292
293
294 PCRE 16-BIT API 16-BIT-ONLY FUNCTION
295
296 int pcre16_utf16_to_host_byte_order(PCRE_UCHAR16 *output,
297 PCRE_SPTR16 input, int length, int *byte_order,
298 int keep_boms);
299
300
301 THE PCRE 16-BIT LIBRARY
302
303 Starting with release 8.30, it is possible to compile a PCRE library
304 that supports 16-bit character strings, including UTF-16 strings, as
305 well as or instead of the original 8-bit library. The majority of the
306 work to make this possible was done by Zoltan Herczeg. The two
307 libraries contain identical sets of functions, used in exactly the same
308 way. Only the names of the functions and the data types of their argu-
309 ments and results are different. To avoid over-complication and reduce
310 the documentation maintenance load, most of the PCRE documentation
311 describes the 8-bit library, with only occasional references to the
312 16-bit library. This page describes what is different when you use the
313 16-bit library.
314
315 WARNING: A single application can be linked with both libraries, but
316 you must take care when processing any particular pattern to use func-
317 tions from just one library. For example, if you want to study a pat-
318 tern that was compiled with pcre16_compile(), you must do so with
319 pcre16_study(), not pcre_study(), and you must free the study data with
320 pcre16_free_study().
321
322
323 THE HEADER FILE
324
325 There is only one header file, pcre.h. It contains prototypes for all
326 the functions in all libraries, as well as definitions of flags, struc-
327 tures, error codes, etc.
328
329
330 THE LIBRARY NAME
331
332 In Unix-like systems, the 16-bit library is called libpcre16, and can
333 normally be accesss by adding -lpcre16 to the command for linking an
334 application that uses PCRE.
335
336
337 STRING TYPES
338
339 In the 8-bit library, strings are passed to PCRE library functions as
340 vectors of bytes with the C type "char *". In the 16-bit library,
341 strings are passed as vectors of unsigned 16-bit quantities. The macro
342 PCRE_UCHAR16 specifies an appropriate data type, and PCRE_SPTR16 is
343 defined as "const PCRE_UCHAR16 *". In very many environments, "short
344 int" is a 16-bit data type. When PCRE is built, it defines PCRE_UCHAR16
345 as "unsigned short int", but checks that it really is a 16-bit data
346 type. If it is not, the build fails with an error message telling the
347 maintainer to modify the definition appropriately.
348
349
350 STRUCTURE TYPES
351
352 The types of the opaque structures that are used for compiled 16-bit
353 patterns and JIT stacks are pcre16 and pcre16_jit_stack respectively.
354 The type of the user-accessible structure that is returned by
355 pcre16_study() is pcre16_extra, and the type of the structure that is
356 used for passing data to a callout function is pcre16_callout_block.
357 These structures contain the same fields, with the same names, as their
358 8-bit counterparts. The only difference is that pointers to character
359 strings are 16-bit instead of 8-bit types.
360
361
362 16-BIT FUNCTIONS
363
364 For every function in the 8-bit library there is a corresponding func-
365 tion in the 16-bit library with a name that starts with pcre16_ instead
366 of pcre_. The prototypes are listed above. In addition, there is one
367 extra function, pcre16_utf16_to_host_byte_order(). This is a utility
368 function that converts a UTF-16 character string to host byte order if
369 necessary. The other 16-bit functions expect the strings they are
370 passed to be in host byte order.
371
372 The input and output arguments of pcre16_utf16_to_host_byte_order() may
373 point to the same address, that is, conversion in place is supported.
374 The output buffer must be at least as long as the input.
375
376 The length argument specifies the number of 16-bit data units in the
377 input string; a negative value specifies a zero-terminated string.
378
379 If byte_order is NULL, it is assumed that the string starts off in host
380 byte order. This may be changed by byte-order marks (BOMs) anywhere in
381 the string (commonly as the first character).
382
383 If byte_order is not NULL, a non-zero value of the integer to which it
384 points means that the input starts off in host byte order, otherwise
385 the opposite order is assumed. Again, BOMs in the string can change
386 this. The final byte order is passed back at the end of processing.
387
388 If keep_boms is not zero, byte-order mark characters (0xfeff) are
389 copied into the output string. Otherwise they are discarded.
390
391 The result of the function is the number of 16-bit units placed into
392 the output buffer, including the zero terminator if the string was
393 zero-terminated.
394
395
396 SUBJECT STRING OFFSETS
397
398 The lengths and starting offsets of subject strings must be specified
399 in 16-bit data units, and the offsets within subject strings that are
400 returned by the matching functions are in also 16-bit units rather than
401 bytes.
402
403
404 NAMED SUBPATTERNS
405
406 The name-to-number translation table that is maintained for named sub-
407 patterns uses 16-bit characters. The pcre16_get_stringtable_entries()
408 function returns the length of each entry in the table as the number of
409 16-bit data units.
410
411
412 OPTION NAMES
413
414 There are two new general option names, PCRE_UTF16 and
415 PCRE_NO_UTF16_CHECK, which correspond to PCRE_UTF8 and
416 PCRE_NO_UTF8_CHECK in the 8-bit library. In fact, these new options
417 define the same bits in the options word. There is a discussion about
418 the validity of UTF-16 strings in the pcreunicode page.
419
420 For the pcre16_config() function there is an option PCRE_CONFIG_UTF16
421 that returns 1 if UTF-16 support is configured, otherwise 0. If this
422 option is given to pcre_config() or pcre32_config(), or if the
423 PCRE_CONFIG_UTF8 or PCRE_CONFIG_UTF32 option is given to pcre16_con-
424 fig(), the result is the PCRE_ERROR_BADOPTION error.
425
426
427 CHARACTER CODES
428
429 In 16-bit mode, when PCRE_UTF16 is not set, character values are
430 treated in the same way as in 8-bit, non UTF-8 mode, except, of course,
431 that they can range from 0 to 0xffff instead of 0 to 0xff. Character
432 types for characters less than 0xff can therefore be influenced by the
433 locale in the same way as before. Characters greater than 0xff have
434 only one case, and no "type" (such as letter or digit).
435
436 In UTF-16 mode, the character code is Unicode, in the range 0 to
437 0x10ffff, with the exception of values in the range 0xd800 to 0xdfff
438 because those are "surrogate" values that are used in pairs to encode
439 values greater than 0xffff.
440
441 A UTF-16 string can indicate its endianness by special code knows as a
442 byte-order mark (BOM). The PCRE functions do not handle this, expecting
443 strings to be in host byte order. A utility function called
444 pcre16_utf16_to_host_byte_order() is provided to help with this (see
445 above).
446
447
448 ERROR NAMES
449
450 The errors PCRE_ERROR_BADUTF16_OFFSET and PCRE_ERROR_SHORTUTF16 corre-
451 spond to their 8-bit counterparts. The error PCRE_ERROR_BADMODE is
452 given when a compiled pattern is passed to a function that processes
453 patterns in the other mode, for example, if a pattern compiled with
454 pcre_compile() is passed to pcre16_exec().
455
456 There are new error codes whose names begin with PCRE_UTF16_ERR for
457 invalid UTF-16 strings, corresponding to the PCRE_UTF8_ERR codes for
458 UTF-8 strings that are described in the section entitled "Reason codes
459 for invalid UTF-8 strings" in the main pcreapi page. The UTF-16 errors
460 are:
461
462 PCRE_UTF16_ERR1 Missing low surrogate at end of string
463 PCRE_UTF16_ERR2 Invalid low surrogate follows high surrogate
464 PCRE_UTF16_ERR3 Isolated low surrogate
465 PCRE_UTF16_ERR4 Non-character
466
467
468 ERROR TEXTS
469
470 If there is an error while compiling a pattern, the error text that is
471 passed back by pcre16_compile() or pcre16_compile2() is still an 8-bit
472 character string, zero-terminated.
473
474
475 CALLOUTS
476
477 The subject and mark fields in the callout block that is passed to a
478 callout function point to 16-bit vectors.
479
480
481 TESTING
482
483 The pcretest program continues to operate with 8-bit input and output
484 files, but it can be used for testing the 16-bit library. If it is run
485 with the command line option -16, patterns and subject strings are con-
486 verted from 8-bit to 16-bit before being passed to PCRE, and the 16-bit
487 library functions are used instead of the 8-bit ones. Returned 16-bit
488 strings are converted to 8-bit for output. If both the 8-bit and the
489 32-bit libraries were not compiled, pcretest defaults to 16-bit and the
490 -16 option is ignored.
491
492 When PCRE is being built, the RunTest script that is called by "make
493 check" uses the pcretest -C option to discover which of the 8-bit,
494 16-bit and 32-bit libraries has been built, and runs the tests appro-
495 priately.
496
497
498 NOT SUPPORTED IN 16-BIT MODE
499
500 Not all the features of the 8-bit library are available with the 16-bit
501 library. The C++ and POSIX wrapper functions support only the 8-bit
502 library, and the pcregrep program is at present 8-bit only.
503
504
505 AUTHOR
506
507 Philip Hazel
508 University Computing Service
509 Cambridge CB2 3QH, England.
510
511
512 REVISION
513
514 Last updated: 12 May 2013
515 Copyright (c) 1997-2013 University of Cambridge.
516 ------------------------------------------------------------------------------
517
518
519 PCRE(3) Library Functions Manual PCRE(3)
520
521
522
523 NAME
524 PCRE - Perl-compatible regular expressions
525
526 #include <pcre.h>
527
528
529 PCRE 32-BIT API BASIC FUNCTIONS
530
531 pcre32 *pcre32_compile(PCRE_SPTR32 pattern, int options,
532 const char **errptr, int *erroffset,
533 const unsigned char *tableptr);
534
535 pcre32 *pcre32_compile2(PCRE_SPTR32 pattern, int options,
536 int *errorcodeptr,
537 const unsigned char *tableptr);
538
539 pcre32_extra *pcre32_study(const pcre32 *code, int options,
540 const char **errptr);
541
542 void pcre32_free_study(pcre32_extra *extra);
543
544 int pcre32_exec(const pcre32 *code, const pcre32_extra *extra,
545 PCRE_SPTR32 subject, int length, int startoffset,
546 int options, int *ovector, int ovecsize);
547
548 int pcre32_dfa_exec(const pcre32 *code, const pcre32_extra *extra,
549 PCRE_SPTR32 subject, int length, int startoffset,
550 int options, int *ovector, int ovecsize,
551 int *workspace, int wscount);
552
553
554 PCRE 32-BIT API STRING EXTRACTION FUNCTIONS
555
556 int pcre32_copy_named_substring(const pcre32 *code,
557 PCRE_SPTR32 subject, int *ovector,
558 int stringcount, PCRE_SPTR32 stringname,
559 PCRE_UCHAR32 *buffer, int buffersize);
560
561 int pcre32_copy_substring(PCRE_SPTR32 subject, int *ovector,
562 int stringcount, int stringnumber, PCRE_UCHAR32 *buffer,
563 int buffersize);
564
565 int pcre32_get_named_substring(const pcre32 *code,
566 PCRE_SPTR32 subject, int *ovector,
567 int stringcount, PCRE_SPTR32 stringname,
568 PCRE_SPTR32 *stringptr);
569
570 int pcre32_get_stringnumber(const pcre32 *code,
571 PCRE_SPTR32 name);
572
573 int pcre32_get_stringtable_entries(const pcre32 *code,
574 PCRE_SPTR32 name, PCRE_UCHAR32 **first, PCRE_UCHAR32 **last);
575
576 int pcre32_get_substring(PCRE_SPTR32 subject, int *ovector,
577 int stringcount, int stringnumber,
578 PCRE_SPTR32 *stringptr);
579
580 int pcre32_get_substring_list(PCRE_SPTR32 subject,
581 int *ovector, int stringcount, PCRE_SPTR32 **listptr);
582
583 void pcre32_free_substring(PCRE_SPTR32 stringptr);
584
585 void pcre32_free_substring_list(PCRE_SPTR32 *stringptr);
586
587
588 PCRE 32-BIT API AUXILIARY FUNCTIONS
589
590 pcre32_jit_stack *pcre32_jit_stack_alloc(int startsize, int maxsize);
591
592 void pcre32_jit_stack_free(pcre32_jit_stack *stack);
593
594 void pcre32_assign_jit_stack(pcre32_extra *extra,
595 pcre32_jit_callback callback, void *data);
596
597 const unsigned char *pcre32_maketables(void);
598
599 int pcre32_fullinfo(const pcre32 *code, const pcre32_extra *extra,
600 int what, void *where);
601
602 int pcre32_refcount(pcre32 *code, int adjust);
603
604 int pcre32_config(int what, void *where);
605
606 const char *pcre32_version(void);
607
608 int pcre32_pattern_to_host_byte_order(pcre32 *code,
609 pcre32_extra *extra, const unsigned char *tables);
610
611
612 PCRE 32-BIT API INDIRECTED FUNCTIONS
613
614 void *(*pcre32_malloc)(size_t);
615
616 void (*pcre32_free)(void *);
617
618 void *(*pcre32_stack_malloc)(size_t);
619
620 void (*pcre32_stack_free)(void *);
621
622 int (*pcre32_callout)(pcre32_callout_block *);
623
624
625 PCRE 32-BIT API 32-BIT-ONLY FUNCTION
626
627 int pcre32_utf32_to_host_byte_order(PCRE_UCHAR32 *output,
628 PCRE_SPTR32 input, int length, int *byte_order,
629 int keep_boms);
630
631
632 THE PCRE 32-BIT LIBRARY
633
634 Starting with release 8.32, it is possible to compile a PCRE library
635 that supports 32-bit character strings, including UTF-32 strings, as
636 well as or instead of the original 8-bit library. This work was done by
637 Christian Persch, based on the work done by Zoltan Herczeg for the
638 16-bit library. All three libraries contain identical sets of func-
639 tions, used in exactly the same way. Only the names of the functions
640 and the data types of their arguments and results are different. To
641 avoid over-complication and reduce the documentation maintenance load,
642 most of the PCRE documentation describes the 8-bit library, with only
643 occasional references to the 16-bit and 32-bit libraries. This page
644 describes what is different when you use the 32-bit library.
645
646 WARNING: A single application can be linked with all or any of the
647 three libraries, but you must take care when processing any particular
648 pattern to use functions from just one library. For example, if you
649 want to study a pattern that was compiled with pcre32_compile(), you
650 must do so with pcre32_study(), not pcre_study(), and you must free the
651 study data with pcre32_free_study().
652
653
654 THE HEADER FILE
655
656 There is only one header file, pcre.h. It contains prototypes for all
657 the functions in all libraries, as well as definitions of flags, struc-
658 tures, error codes, etc.
659
660
661 THE LIBRARY NAME
662
663 In Unix-like systems, the 32-bit library is called libpcre32, and can
664 normally be accesss by adding -lpcre32 to the command for linking an
665 application that uses PCRE.
666
667
668 STRING TYPES
669
670 In the 8-bit library, strings are passed to PCRE library functions as
671 vectors of bytes with the C type "char *". In the 32-bit library,
672 strings are passed as vectors of unsigned 32-bit quantities. The macro
673 PCRE_UCHAR32 specifies an appropriate data type, and PCRE_SPTR32 is
674 defined as "const PCRE_UCHAR32 *". In very many environments, "unsigned
675 int" is a 32-bit data type. When PCRE is built, it defines PCRE_UCHAR32
676 as "unsigned int", but checks that it really is a 32-bit data type. If
677 it is not, the build fails with an error message telling the maintainer
678 to modify the definition appropriately.
679
680
681 STRUCTURE TYPES
682
683 The types of the opaque structures that are used for compiled 32-bit
684 patterns and JIT stacks are pcre32 and pcre32_jit_stack respectively.
685 The type of the user-accessible structure that is returned by
686 pcre32_study() is pcre32_extra, and the type of the structure that is
687 used for passing data to a callout function is pcre32_callout_block.
688 These structures contain the same fields, with the same names, as their
689 8-bit counterparts. The only difference is that pointers to character
690 strings are 32-bit instead of 8-bit types.
691
692
693 32-BIT FUNCTIONS
694
695 For every function in the 8-bit library there is a corresponding func-
696 tion in the 32-bit library with a name that starts with pcre32_ instead
697 of pcre_. The prototypes are listed above. In addition, there is one
698 extra function, pcre32_utf32_to_host_byte_order(). This is a utility
699 function that converts a UTF-32 character string to host byte order if
700 necessary. The other 32-bit functions expect the strings they are
701 passed to be in host byte order.
702
703 The input and output arguments of pcre32_utf32_to_host_byte_order() may
704 point to the same address, that is, conversion in place is supported.
705 The output buffer must be at least as long as the input.
706
707 The length argument specifies the number of 32-bit data units in the
708 input string; a negative value specifies a zero-terminated string.
709
710 If byte_order is NULL, it is assumed that the string starts off in host
711 byte order. This may be changed by byte-order marks (BOMs) anywhere in
712 the string (commonly as the first character).
713
714 If byte_order is not NULL, a non-zero value of the integer to which it
715 points means that the input starts off in host byte order, otherwise
716 the opposite order is assumed. Again, BOMs in the string can change
717 this. The final byte order is passed back at the end of processing.
718
719 If keep_boms is not zero, byte-order mark characters (0xfeff) are
720 copied into the output string. Otherwise they are discarded.
721
722 The result of the function is the number of 32-bit units placed into
723 the output buffer, including the zero terminator if the string was
724 zero-terminated.
725
726
727 SUBJECT STRING OFFSETS
728
729 The lengths and starting offsets of subject strings must be specified
730 in 32-bit data units, and the offsets within subject strings that are
731 returned by the matching functions are in also 32-bit units rather than
732 bytes.
733
734
735 NAMED SUBPATTERNS
736
737 The name-to-number translation table that is maintained for named sub-
738 patterns uses 32-bit characters. The pcre32_get_stringtable_entries()
739 function returns the length of each entry in the table as the number of
740 32-bit data units.
741
742
743 OPTION NAMES
744
745 There are two new general option names, PCRE_UTF32 and
746 PCRE_NO_UTF32_CHECK, which correspond to PCRE_UTF8 and
747 PCRE_NO_UTF8_CHECK in the 8-bit library. In fact, these new options
748 define the same bits in the options word. There is a discussion about
749 the validity of UTF-32 strings in the pcreunicode page.
750
751 For the pcre32_config() function there is an option PCRE_CONFIG_UTF32
752 that returns 1 if UTF-32 support is configured, otherwise 0. If this
753 option is given to pcre_config() or pcre16_config(), or if the
754 PCRE_CONFIG_UTF8 or PCRE_CONFIG_UTF16 option is given to pcre32_con-
755 fig(), the result is the PCRE_ERROR_BADOPTION error.
756
757
758 CHARACTER CODES
759
760 In 32-bit mode, when PCRE_UTF32 is not set, character values are
761 treated in the same way as in 8-bit, non UTF-8 mode, except, of course,
762 that they can range from 0 to 0x7fffffff instead of 0 to 0xff. Charac-
763 ter types for characters less than 0xff can therefore be influenced by
764 the locale in the same way as before. Characters greater than 0xff
765 have only one case, and no "type" (such as letter or digit).
766
767 In UTF-32 mode, the character code is Unicode, in the range 0 to
768 0x10ffff, with the exception of values in the range 0xd800 to 0xdfff
769 because those are "surrogate" values that are ill-formed in UTF-32.
770
771 A UTF-32 string can indicate its endianness by special code knows as a
772 byte-order mark (BOM). The PCRE functions do not handle this, expecting
773 strings to be in host byte order. A utility function called
774 pcre32_utf32_to_host_byte_order() is provided to help with this (see
775 above).
776
777
778 ERROR NAMES
779
780 The error PCRE_ERROR_BADUTF32 corresponds to its 8-bit counterpart.
781 The error PCRE_ERROR_BADMODE is given when a compiled pattern is passed
782 to a function that processes patterns in the other mode, for example,
783 if a pattern compiled with pcre_compile() is passed to pcre32_exec().
784
785 There are new error codes whose names begin with PCRE_UTF32_ERR for
786 invalid UTF-32 strings, corresponding to the PCRE_UTF8_ERR codes for
787 UTF-8 strings that are described in the section entitled "Reason codes
788 for invalid UTF-8 strings" in the main pcreapi page. The UTF-32 errors
789 are:
790
791 PCRE_UTF32_ERR1 Surrogate character (range from 0xd800 to 0xdfff)
792 PCRE_UTF32_ERR2 Non-character
793 PCRE_UTF32_ERR3 Character > 0x10ffff
794
795
796 ERROR TEXTS
797
798 If there is an error while compiling a pattern, the error text that is
799 passed back by pcre32_compile() or pcre32_compile2() is still an 8-bit
800 character string, zero-terminated.
801
802
803 CALLOUTS
804
805 The subject and mark fields in the callout block that is passed to a
806 callout function point to 32-bit vectors.
807
808
809 TESTING
810
811 The pcretest program continues to operate with 8-bit input and output
812 files, but it can be used for testing the 32-bit library. If it is run
813 with the command line option -32, patterns and subject strings are con-
814 verted from 8-bit to 32-bit before being passed to PCRE, and the 32-bit
815 library functions are used instead of the 8-bit ones. Returned 32-bit
816 strings are converted to 8-bit for output. If both the 8-bit and the
817 16-bit libraries were not compiled, pcretest defaults to 32-bit and the
818 -32 option is ignored.
819
820 When PCRE is being built, the RunTest script that is called by "make
821 check" uses the pcretest -C option to discover which of the 8-bit,
822 16-bit and 32-bit libraries has been built, and runs the tests appro-
823 priately.
824
825
826 NOT SUPPORTED IN 32-BIT MODE
827
828 Not all the features of the 8-bit library are available with the 32-bit
829 library. The C++ and POSIX wrapper functions support only the 8-bit
830 library, and the pcregrep program is at present 8-bit only.
831
832
833 AUTHOR
834
835 Philip Hazel
836 University Computing Service
837 Cambridge CB2 3QH, England.
838
839
840 REVISION
841
842 Last updated: 12 May 2013
843 Copyright (c) 1997-2013 University of Cambridge.
844 ------------------------------------------------------------------------------
845
846
847 PCREBUILD(3) Library Functions Manual PCREBUILD(3)
848
849
850
851 NAME
852 PCRE - Perl-compatible regular expressions
853
854 BUILDING PCRE
855
856 PCRE is distributed with a configure script that can be used to build
857 the library in Unix-like environments using the applications known as
858 Autotools. Also in the distribution are files to support building
859 using CMake instead of configure. The text file README contains general
860 information about building with Autotools (some of which is repeated
861 below), and also has some comments about building on various operating
862 systems. There is a lot more information about building PCRE without
863 using Autotools (including information about using CMake and building
864 "by hand") in the text file called NON-AUTOTOOLS-BUILD. You should
865 consult this file as well as the README file if you are building in a
866 non-Unix-like environment.
867
868
869 PCRE BUILD-TIME OPTIONS
870
871 The rest of this document describes the optional features of PCRE that
872 can be selected when the library is compiled. It assumes use of the
873 configure script, where the optional features are selected or dese-
874 lected by providing options to configure before running the make com-
875 mand. However, the same options can be selected in both Unix-like and
876 non-Unix-like environments using the GUI facility of cmake-gui if you
877 are using CMake instead of configure to build PCRE.
878
879 If you are not using Autotools or CMake, option selection can be done
880 by editing the config.h file, or by passing parameter settings to the
881 compiler, as described in NON-AUTOTOOLS-BUILD.
882
883 The complete list of options for configure (which includes the standard
884 ones such as the selection of the installation directory) can be
885 obtained by running
886
887 ./configure --help
888
889 The following sections include descriptions of options whose names
890 begin with --enable or --disable. These settings specify changes to the
891 defaults for the configure command. Because of the way that configure
892 works, --enable and --disable always come in pairs, so the complemen-
893 tary option always exists as well, but as it specifies the default, it
894 is not described.
895
896
897 BUILDING 8-BIT, 16-BIT AND 32-BIT LIBRARIES
898
899 By default, a library called libpcre is built, containing functions
900 that take string arguments contained in vectors of bytes, either as
901 single-byte characters, or interpreted as UTF-8 strings. You can also
902 build a separate library, called libpcre16, in which strings are con-
903 tained in vectors of 16-bit data units and interpreted either as sin-
904 gle-unit characters or UTF-16 strings, by adding
905
906 --enable-pcre16
907
908 to the configure command. You can also build yet another separate
909 library, called libpcre32, in which strings are contained in vectors of
910 32-bit data units and interpreted either as single-unit characters or
911 UTF-32 strings, by adding
912
913 --enable-pcre32
914
915 to the configure command. If you do not want the 8-bit library, add
916
917 --disable-pcre8
918
919 as well. At least one of the three libraries must be built. Note that
920 the C++ and POSIX wrappers are for the 8-bit library only, and that
921 pcregrep is an 8-bit program. None of these are built if you select
922 only the 16-bit or 32-bit libraries.
923
924
925 BUILDING SHARED AND STATIC LIBRARIES
926
927 The Autotools PCRE building process uses libtool to build both shared
928 and static libraries by default. You can suppress one of these by
929 adding one of
930
931 --disable-shared
932 --disable-static
933
934 to the configure command, as required.
935
936
937 C++ SUPPORT
938
939 By default, if the 8-bit library is being built, the configure script
940 will search for a C++ compiler and C++ header files. If it finds them,
941 it automatically builds the C++ wrapper library (which supports only
942 8-bit strings). You can disable this by adding
943
944 --disable-cpp
945
946 to the configure command.
947
948
949 UTF-8, UTF-16 AND UTF-32 SUPPORT
950
951 To build PCRE with support for UTF Unicode character strings, add
952
953 --enable-utf
954
955 to the configure command. This setting applies to all three libraries,
956 adding support for UTF-8 to the 8-bit library, support for UTF-16 to
957 the 16-bit library, and support for UTF-32 to the to the 32-bit
958 library. There are no separate options for enabling UTF-8, UTF-16 and
959 UTF-32 independently because that would allow ridiculous settings such
960 as requesting UTF-16 support while building only the 8-bit library. It
961 is not possible to build one library with UTF support and another with-
962 out in the same configuration. (For backwards compatibility, --enable-
963 utf8 is a synonym of --enable-utf.)
964
965 Of itself, this setting does not make PCRE treat strings as UTF-8,
966 UTF-16 or UTF-32. As well as compiling PCRE with this option, you also
967 have have to set the PCRE_UTF8, PCRE_UTF16 or PCRE_UTF32 option (as
968 appropriate) when you call one of the pattern compiling functions.
969
970 If you set --enable-utf when compiling in an EBCDIC environment, PCRE
971 expects its input to be either ASCII or UTF-8 (depending on the run-
972 time option). It is not possible to support both EBCDIC and UTF-8 codes
973 in the same version of the library. Consequently, --enable-utf and
974 --enable-ebcdic are mutually exclusive.
975
976
977 UNICODE CHARACTER PROPERTY SUPPORT
978
979 UTF support allows the libraries to process character codepoints up to
980 0x10ffff in the strings that they handle. On its own, however, it does
981 not provide any facilities for accessing the properties of such charac-
982 ters. If you want to be able to use the pattern escapes \P, \p, and \X,
983 which refer to Unicode character properties, you must add
984
985 --enable-unicode-properties
986
987 to the configure command. This implies UTF support, even if you have
988 not explicitly requested it.
989
990 Including Unicode property support adds around 30K of tables to the
991 PCRE library. Only the general category properties such as Lu and Nd
992 are supported. Details are given in the pcrepattern documentation.
993
994
995 JUST-IN-TIME COMPILER SUPPORT
996
997 Just-in-time compiler support is included in the build by specifying
998
999 --enable-jit
1000
1001 This support is available only for certain hardware architectures. If
1002 this option is set for an unsupported architecture, a compile time
1003 error occurs. See the pcrejit documentation for a discussion of JIT
1004 usage. When JIT support is enabled, pcregrep automatically makes use of
1005 it, unless you add
1006
1007 --disable-pcregrep-jit
1008
1009 to the "configure" command.
1010
1011
1012 CODE VALUE OF NEWLINE
1013
1014 By default, PCRE interprets the linefeed (LF) character as indicating
1015 the end of a line. This is the normal newline character on Unix-like
1016 systems. You can compile PCRE to use carriage return (CR) instead, by
1017 adding
1018
1019 --enable-newline-is-cr
1020
1021 to the configure command. There is also a --enable-newline-is-lf
1022 option, which explicitly specifies linefeed as the newline character.
1023
1024 Alternatively, you can specify that line endings are to be indicated by
1025 the two character sequence CRLF. If you want this, add
1026
1027 --enable-newline-is-crlf
1028
1029 to the configure command. There is a fourth option, specified by
1030
1031 --enable-newline-is-anycrlf
1032
1033 which causes PCRE to recognize any of the three sequences CR, LF, or
1034 CRLF as indicating a line ending. Finally, a fifth option, specified by
1035
1036 --enable-newline-is-any
1037
1038 causes PCRE to recognize any Unicode newline sequence.
1039
1040 Whatever line ending convention is selected when PCRE is built can be
1041 overridden when the library functions are called. At build time it is
1042 conventional to use the standard for your operating system.
1043
1044
1045 WHAT \R MATCHES
1046
1047 By default, the sequence \R in a pattern matches any Unicode newline
1048 sequence, whatever has been selected as the line ending sequence. If
1049 you specify
1050
1051 --enable-bsr-anycrlf
1052
1053 the default is changed so that \R matches only CR, LF, or CRLF. What-
1054 ever is selected when PCRE is built can be overridden when the library
1055 functions are called.
1056
1057
1058 POSIX MALLOC USAGE
1059
1060 When the 8-bit library is called through the POSIX interface (see the
1061 pcreposix documentation), additional working storage is required for
1062 holding the pointers to capturing substrings, because PCRE requires
1063 three integers per substring, whereas the POSIX interface provides only
1064 two. If the number of expected substrings is small, the wrapper func-
1065 tion uses space on the stack, because this is faster than using mal-
1066 loc() for each call. The default threshold above which the stack is no
1067 longer used is 10; it can be changed by adding a setting such as
1068
1069 --with-posix-malloc-threshold=20
1070
1071 to the configure command.
1072
1073
1074 HANDLING VERY LARGE PATTERNS
1075
1076 Within a compiled pattern, offset values are used to point from one
1077 part to another (for example, from an opening parenthesis to an alter-
1078 nation metacharacter). By default, in the 8-bit and 16-bit libraries,
1079 two-byte values are used for these offsets, leading to a maximum size
1080 for a compiled pattern of around 64K. This is sufficient to handle all
1081 but the most gigantic patterns. Nevertheless, some people do want to
1082 process truly enormous patterns, so it is possible to compile PCRE to
1083 use three-byte or four-byte offsets by adding a setting such as
1084
1085 --with-link-size=3
1086
1087 to the configure command. The value given must be 2, 3, or 4. For the
1088 16-bit library, a value of 3 is rounded up to 4. In these libraries,
1089 using longer offsets slows down the operation of PCRE because it has to
1090 load additional data when handling them. For the 32-bit library the
1091 value is always 4 and cannot be overridden; the value of --with-link-
1092 size is ignored.
1093
1094
1095 AVOIDING EXCESSIVE STACK USAGE
1096
1097 When matching with the pcre_exec() function, PCRE implements backtrack-
1098 ing by making recursive calls to an internal function called match().
1099 In environments where the size of the stack is limited, this can se-
1100 verely limit PCRE's operation. (The Unix environment does not usually
1101 suffer from this problem, but it may sometimes be necessary to increase
1102 the maximum stack size. There is a discussion in the pcrestack docu-
1103 mentation.) An alternative approach to recursion that uses memory from
1104 the heap to remember data, instead of using recursive function calls,
1105 has been implemented to work round the problem of limited stack size.
1106 If you want to build a version of PCRE that works this way, add
1107
1108 --disable-stack-for-recursion
1109
1110 to the configure command. With this configuration, PCRE will use the
1111 pcre_stack_malloc and pcre_stack_free variables to call memory manage-
1112 ment functions. By default these point to malloc() and free(), but you
1113 can replace the pointers so that your own functions are used instead.
1114
1115 Separate functions are provided rather than using pcre_malloc and
1116 pcre_free because the usage is very predictable: the block sizes
1117 requested are always the same, and the blocks are always freed in
1118 reverse order. A calling program might be able to implement optimized
1119 functions that perform better than malloc() and free(). PCRE runs
1120 noticeably more slowly when built in this way. This option affects only
1121 the pcre_exec() function; it is not relevant for pcre_dfa_exec().
1122
1123
1124 LIMITING PCRE RESOURCE USAGE
1125
1126 Internally, PCRE has a function called match(), which it calls repeat-
1127 edly (sometimes recursively) when matching a pattern with the
1128 pcre_exec() function. By controlling the maximum number of times this
1129 function may be called during a single matching operation, a limit can
1130 be placed on the resources used by a single call to pcre_exec(). The
1131 limit can be changed at run time, as described in the pcreapi documen-
1132 tation. The default is 10 million, but this can be changed by adding a
1133 setting such as
1134
1135 --with-match-limit=500000
1136
1137 to the configure command. This setting has no effect on the
1138 pcre_dfa_exec() matching function.
1139
1140 In some environments it is desirable to limit the depth of recursive
1141 calls of match() more strictly than the total number of calls, in order
1142 to restrict the maximum amount of stack (or heap, if --disable-stack-
1143 for-recursion is specified) that is used. A second limit controls this;
1144 it defaults to the value that is set for --with-match-limit, which
1145 imposes no additional constraints. However, you can set a lower limit
1146 by adding, for example,
1147
1148 --with-match-limit-recursion=10000
1149
1150 to the configure command. This value can also be overridden at run
1151 time.
1152
1153
1154 CREATING CHARACTER TABLES AT BUILD TIME
1155
1156 PCRE uses fixed tables for processing characters whose code values are
1157 less than 256. By default, PCRE is built with a set of tables that are
1158 distributed in the file pcre_chartables.c.dist. These tables are for
1159 ASCII codes only. If you add
1160
1161 --enable-rebuild-chartables
1162
1163 to the configure command, the distributed tables are no longer used.
1164 Instead, a program called dftables is compiled and run. This outputs
1165 the source for new set of tables, created in the default locale of your
1166 C run-time system. (This method of replacing the tables does not work
1167 if you are cross compiling, because dftables is run on the local host.
1168 If you need to create alternative tables when cross compiling, you will
1169 have to do so "by hand".)
1170
1171
1172 USING EBCDIC CODE
1173
1174 PCRE assumes by default that it will run in an environment where the
1175 character code is ASCII (or Unicode, which is a superset of ASCII).
1176 This is the case for most computer operating systems. PCRE can, how-
1177 ever, be compiled to run in an EBCDIC environment by adding
1178
1179 --enable-ebcdic
1180
1181 to the configure command. This setting implies --enable-rebuild-charta-
1182 bles. You should only use it if you know that you are in an EBCDIC
1183 environment (for example, an IBM mainframe operating system). The
1184 --enable-ebcdic option is incompatible with --enable-utf.
1185
1186 The EBCDIC character that corresponds to an ASCII LF is assumed to have
1187 the value 0x15 by default. However, in some EBCDIC environments, 0x25
1188 is used. In such an environment you should use
1189
1190 --enable-ebcdic-nl25
1191
1192 as well as, or instead of, --enable-ebcdic. The EBCDIC character for CR
1193 has the same value as in ASCII, namely, 0x0d. Whichever of 0x15 and
1194 0x25 is not chosen as LF is made to correspond to the Unicode NEL char-
1195 acter (which, in Unicode, is 0x85).
1196
1197 The options that select newline behaviour, such as --enable-newline-is-
1198 cr, and equivalent run-time options, refer to these character values in
1199 an EBCDIC environment.
1200
1201
1202 PCREGREP OPTIONS FOR COMPRESSED FILE SUPPORT
1203
1204 By default, pcregrep reads all files as plain text. You can build it so
1205 that it recognizes files whose names end in .gz or .bz2, and reads them
1206 with libz or libbz2, respectively, by adding one or both of
1207
1208 --enable-pcregrep-libz
1209 --enable-pcregrep-libbz2
1210
1211 to the configure command. These options naturally require that the rel-
1212 evant libraries are installed on your system. Configuration will fail
1213 if they are not.
1214
1215
1216 PCREGREP BUFFER SIZE
1217
1218 pcregrep uses an internal buffer to hold a "window" on the file it is
1219 scanning, in order to be able to output "before" and "after" lines when
1220 it finds a match. The size of the buffer is controlled by a parameter
1221 whose default value is 20K. The buffer itself is three times this size,
1222 but because of the way it is used for holding "before" lines, the long-
1223 est line that is guaranteed to be processable is the parameter size.
1224 You can change the default parameter value by adding, for example,
1225
1226 --with-pcregrep-bufsize=50K
1227
1228 to the configure command. The caller of pcregrep can, however, override
1229 this value by specifying a run-time option.
1230
1231
1232 PCRETEST OPTION FOR LIBREADLINE SUPPORT
1233
1234 If you add
1235
1236 --enable-pcretest-libreadline
1237
1238 to the configure command, pcretest is linked with the libreadline
1239 library, and when its input is from a terminal, it reads it using the
1240 readline() function. This provides line-editing and history facilities.
1241 Note that libreadline is GPL-licensed, so if you distribute a binary of
1242 pcretest linked in this way, there may be licensing issues.
1243
1244 Setting this option causes the -lreadline option to be added to the
1245 pcretest build. In many operating environments with a sytem-installed
1246 libreadline this is sufficient. However, in some environments (e.g. if
1247 an unmodified distribution version of readline is in use), some extra
1248 configuration may be necessary. The INSTALL file for libreadline says
1249 this:
1250
1251 "Readline uses the termcap functions, but does not link with the
1252 termcap or curses library itself, allowing applications which link
1253 with readline the to choose an appropriate library."
1254
1255 If your environment has not been set up so that an appropriate library
1256 is automatically included, you may need to add something like
1257
1258 LIBS="-ncurses"
1259
1260 immediately before the configure command.
1261
1262
1263 DEBUGGING WITH VALGRIND SUPPORT
1264
1265 By adding the
1266
1267 --enable-valgrind
1268
1269 option to to the configure command, PCRE will use valgrind annotations
1270 to mark certain memory regions as unaddressable. This allows it to
1271 detect invalid memory accesses, and is mostly useful for debugging PCRE
1272 itself.
1273
1274
1275 CODE COVERAGE REPORTING
1276
1277 If your C compiler is gcc, you can build a version of PCRE that can
1278 generate a code coverage report for its test suite. To enable this, you
1279 must install lcov version 1.6 or above. Then specify
1280
1281 --enable-coverage
1282
1283 to the configure command and build PCRE in the usual way.
1284
1285 Note that using ccache (a caching C compiler) is incompatible with code
1286 coverage reporting. If you have configured ccache to run automatically
1287 on your system, you must set the environment variable
1288
1289 CCACHE_DISABLE=1
1290
1291 before running make to build PCRE, so that ccache is not used.
1292
1293 When --enable-coverage is used, the following addition targets are
1294 added to the Makefile:
1295
1296 make coverage
1297
1298 This creates a fresh coverage report for the PCRE test suite. It is
1299 equivalent to running "make coverage-reset", "make coverage-baseline",
1300 "make check", and then "make coverage-report".
1301
1302 make coverage-reset
1303
1304 This zeroes the coverage counters, but does nothing else.
1305
1306 make coverage-baseline
1307
1308 This captures baseline coverage information.
1309
1310 make coverage-report
1311
1312 This creates the coverage report.
1313
1314 make coverage-clean-report
1315
1316 This removes the generated coverage report without cleaning the cover-
1317 age data itself.
1318
1319 make coverage-clean-data
1320
1321 This removes the captured coverage data without removing the coverage
1322 files created at compile time (*.gcno).
1323
1324 make coverage-clean
1325
1326 This cleans all coverage data including the generated coverage report.
1327 For more information about code coverage, see the gcov and lcov docu-
1328 mentation.
1329
1330
1331 SEE ALSO
1332
1333 pcreapi(3), pcre16, pcre32, pcre_config(3).
1334
1335
1336 AUTHOR
1337
1338 Philip Hazel
1339 University Computing Service
1340 Cambridge CB2 3QH, England.
1341
1342
1343 REVISION
1344
1345 Last updated: 12 May 2013
1346 Copyright (c) 1997-2013 University of Cambridge.
1347 ------------------------------------------------------------------------------
1348
1349
1350 PCREMATCHING(3) Library Functions Manual PCREMATCHING(3)
1351
1352
1353
1354 NAME
1355 PCRE - Perl-compatible regular expressions
1356
1357 PCRE MATCHING ALGORITHMS
1358
1359 This document describes the two different algorithms that are available
1360 in PCRE for matching a compiled regular expression against a given sub-
1361 ject string. The "standard" algorithm is the one provided by the
1362 pcre_exec(), pcre16_exec() and pcre32_exec() functions. These work in
1363 the same as as Perl's matching function, and provide a Perl-compatible
1364 matching operation. The just-in-time (JIT) optimization that is
1365 described in the pcrejit documentation is compatible with these func-
1366 tions.
1367
1368 An alternative algorithm is provided by the pcre_dfa_exec(),
1369 pcre16_dfa_exec() and pcre32_dfa_exec() functions; they operate in a
1370 different way, and are not Perl-compatible. This alternative has advan-
1371 tages and disadvantages compared with the standard algorithm, and these
1372 are described below.
1373
1374 When there is only one possible way in which a given subject string can
1375 match a pattern, the two algorithms give the same answer. A difference
1376 arises, however, when there are multiple possibilities. For example, if
1377 the pattern
1378
1379 ^<.*>
1380
1381 is matched against the string
1382
1383 <something> <something else> <something further>
1384
1385 there are three possible answers. The standard algorithm finds only one
1386 of them, whereas the alternative algorithm finds all three.
1387
1388
1389 REGULAR EXPRESSIONS AS TREES
1390
1391 The set of strings that are matched by a regular expression can be rep-
1392 resented as a tree structure. An unlimited repetition in the pattern
1393 makes the tree of infinite size, but it is still a tree. Matching the
1394 pattern to a given subject string (from a given starting point) can be
1395 thought of as a search of the tree. There are two ways to search a
1396 tree: depth-first and breadth-first, and these correspond to the two
1397 matching algorithms provided by PCRE.
1398
1399
1400 THE STANDARD MATCHING ALGORITHM
1401
1402 In the terminology of Jeffrey Friedl's book "Mastering Regular Expres-
1403 sions", the standard algorithm is an "NFA algorithm". It conducts a
1404 depth-first search of the pattern tree. That is, it proceeds along a
1405 single path through the tree, checking that the subject matches what is
1406 required. When there is a mismatch, the algorithm tries any alterna-
1407 tives at the current point, and if they all fail, it backs up to the
1408 previous branch point in the tree, and tries the next alternative
1409 branch at that level. This often involves backing up (moving to the
1410 left) in the subject string as well. The order in which repetition
1411 branches are tried is controlled by the greedy or ungreedy nature of
1412 the quantifier.
1413
1414 If a leaf node is reached, a matching string has been found, and at
1415 that point the algorithm stops. Thus, if there is more than one possi-
1416 ble match, this algorithm returns the first one that it finds. Whether
1417 this is the shortest, the longest, or some intermediate length depends
1418 on the way the greedy and ungreedy repetition quantifiers are specified
1419 in the pattern.
1420
1421 Because it ends up with a single path through the tree, it is rela-
1422 tively straightforward for this algorithm to keep track of the sub-
1423 strings that are matched by portions of the pattern in parentheses.
1424 This provides support for capturing parentheses and back references.
1425
1426
1427 THE ALTERNATIVE MATCHING ALGORITHM
1428
1429 This algorithm conducts a breadth-first search of the tree. Starting
1430 from the first matching point in the subject, it scans the subject
1431 string from left to right, once, character by character, and as it does
1432 this, it remembers all the paths through the tree that represent valid
1433 matches. In Friedl's terminology, this is a kind of "DFA algorithm",
1434 though it is not implemented as a traditional finite state machine (it
1435 keeps multiple states active simultaneously).
1436
1437 Although the general principle of this matching algorithm is that it
1438 scans the subject string only once, without backtracking, there is one
1439 exception: when a lookaround assertion is encountered, the characters
1440 following or preceding the current point have to be independently
1441 inspected.
1442
1443 The scan continues until either the end of the subject is reached, or
1444 there are no more unterminated paths. At this point, terminated paths
1445 represent the different matching possibilities (if there are none, the
1446 match has failed). Thus, if there is more than one possible match,
1447 this algorithm finds all of them, and in particular, it finds the long-
1448 est. The matches are returned in decreasing order of length. There is
1449 an option to stop the algorithm after the first match (which is neces-
1450 sarily the shortest) is found.
1451
1452 Note that all the matches that are found start at the same point in the
1453 subject. If the pattern
1454
1455 cat(er(pillar)?)?
1456
1457 is matched against the string "the caterpillar catchment", the result
1458 will be the three strings "caterpillar", "cater", and "cat" that start
1459 at the fifth character of the subject. The algorithm does not automati-
1460 cally move on to find matches that start at later positions.
1461
1462 PCRE's "auto-possessification" optimization usually applies to charac-
1463 ter repeats at the end of a pattern (as well as internally). For exam-
1464 ple, the pattern "a\d+" is compiled as if it were "a\d++" because there
1465 is no point even considering the possibility of backtracking into the
1466 repeated digits. For DFA matching, this means that only one possible
1467 match is found. If you really do want multiple matches in such cases,
1468 either use an ungreedy repeat ("a\d+?") or set the PCRE_NO_AUTO_POSSESS
1469 option when compiling.
1470
1471 There are a number of features of PCRE regular expressions that are not
1472 supported by the alternative matching algorithm. They are as follows:
1473
1474 1. Because the algorithm finds all possible matches, the greedy or
1475 ungreedy nature of repetition quantifiers is not relevant. Greedy and
1476 ungreedy quantifiers are treated in exactly the same way. However, pos-
1477 sessive quantifiers can make a difference when what follows could also
1478 match what is quantified, for example in a pattern like this:
1479
1480 ^a++\w!
1481
1482 This pattern matches "aaab!" but not "aaa!", which would be matched by
1483 a non-possessive quantifier. Similarly, if an atomic group is present,
1484 it is matched as if it were a standalone pattern at the current point,
1485 and the longest match is then "locked in" for the rest of the overall
1486 pattern.
1487
1488 2. When dealing with multiple paths through the tree simultaneously, it
1489 is not straightforward to keep track of captured substrings for the
1490 different matching possibilities, and PCRE's implementation of this
1491 algorithm does not attempt to do this. This means that no captured sub-
1492 strings are available.
1493
1494 3. Because no substrings are captured, back references within the pat-
1495 tern are not supported, and cause errors if encountered.
1496
1497 4. For the same reason, conditional expressions that use a backrefer-
1498 ence as the condition or test for a specific group recursion are not
1499 supported.
1500
1501 5. Because many paths through the tree may be active, the \K escape
1502 sequence, which resets the start of the match when encountered (but may
1503 be on some paths and not on others), is not supported. It causes an
1504 error if encountered.
1505
1506 6. Callouts are supported, but the value of the capture_top field is
1507 always 1, and the value of the capture_last field is always -1.
1508
1509 7. The \C escape sequence, which (in the standard algorithm) always
1510 matches a single data unit, even in UTF-8, UTF-16 or UTF-32 modes, is
1511 not supported in these modes, because the alternative algorithm moves
1512 through the subject string one character (not data unit) at a time, for
1513 all active paths through the tree.
1514
1515 8. Except for (*FAIL), the backtracking control verbs such as (*PRUNE)
1516 are not supported. (*FAIL) is supported, and behaves like a failing
1517 negative assertion.
1518
1519
1520 ADVANTAGES OF THE ALTERNATIVE ALGORITHM
1521
1522 Using the alternative matching algorithm provides the following advan-
1523 tages:
1524
1525 1. All possible matches (at a single point in the subject) are automat-
1526 ically found, and in particular, the longest match is found. To find
1527 more than one match using the standard algorithm, you have to do kludgy
1528 things with callouts.
1529
1530 2. Because the alternative algorithm scans the subject string just
1531 once, and never needs to backtrack (except for lookbehinds), it is pos-
1532 sible to pass very long subject strings to the matching function in
1533 several pieces, checking for partial matching each time. Although it is
1534 possible to do multi-segment matching using the standard algorithm by
1535 retaining partially matched substrings, it is more complicated. The
1536 pcrepartial documentation gives details of partial matching and dis-
1537 cusses multi-segment matching.
1538
1539
1540 DISADVANTAGES OF THE ALTERNATIVE ALGORITHM
1541
1542 The alternative algorithm suffers from a number of disadvantages:
1543
1544 1. It is substantially slower than the standard algorithm. This is
1545 partly because it has to search for all possible matches, but is also
1546 because it is less susceptible to optimization.
1547
1548 2. Capturing parentheses and back references are not supported.
1549
1550 3. Although atomic groups are supported, their use does not provide the
1551 performance advantage that it does for the standard algorithm.
1552
1553
1554 AUTHOR
1555
1556 Philip Hazel
1557 University Computing Service
1558 Cambridge CB2 3QH, England.
1559
1560
1561 REVISION
1562
1563 Last updated: 12 November 2013
1564 Copyright (c) 1997-2012 University of Cambridge.
1565 ------------------------------------------------------------------------------
1566
1567
1568 PCREAPI(3) Library Functions Manual PCREAPI(3)
1569
1570
1571
1572 NAME
1573 PCRE - Perl-compatible regular expressions
1574
1575 #include <pcre.h>
1576
1577
1578 PCRE NATIVE API BASIC FUNCTIONS
1579
1580 pcre *pcre_compile(const char *pattern, int options,
1581 const char **errptr, int *erroffset,
1582 const unsigned char *tableptr);
1583
1584 pcre *pcre_compile2(const char *pattern, int options,
1585 int *errorcodeptr,
1586 const char **errptr, int *erroffset,
1587 const unsigned char *tableptr);
1588
1589 pcre_extra *pcre_study(const pcre *code, int options,
1590 const char **errptr);
1591
1592 void pcre_free_study(pcre_extra *extra);
1593
1594 int pcre_exec(const pcre *code, const pcre_extra *extra,
1595 const char *subject, int length, int startoffset,
1596 int options, int *ovector, int ovecsize);
1597
1598 int pcre_dfa_exec(const pcre *code, const pcre_extra *extra,
1599 const char *subject, int length, int startoffset,
1600 int options, int *ovector, int ovecsize,
1601 int *workspace, int wscount);
1602
1603
1604 PCRE NATIVE API STRING EXTRACTION FUNCTIONS
1605
1606 int pcre_copy_named_substring(const pcre *code,
1607 const char *subject, int *ovector,
1608 int stringcount, const char *stringname,
1609 char *buffer, int buffersize);
1610
1611 int pcre_copy_substring(const char *subject, int *ovector,
1612 int stringcount, int stringnumber, char *buffer,
1613 int buffersize);
1614
1615 int pcre_get_named_substring(const pcre *code,
1616 const char *subject, int *ovector,
1617 int stringcount, const char *stringname,
1618 const char **stringptr);
1619
1620 int pcre_get_stringnumber(const pcre *code,
1621 const char *name);
1622
1623 int pcre_get_stringtable_entries(const pcre *code,
1624 const char *name, char **first, char **last);
1625
1626 int pcre_get_substring(const char *subject, int *ovector,
1627 int stringcount, int stringnumber,
1628 const char **stringptr);
1629
1630 int pcre_get_substring_list(const char *subject,
1631 int *ovector, int stringcount, const char ***listptr);
1632
1633 void pcre_free_substring(const char *stringptr);
1634
1635 void pcre_free_substring_list(const char **stringptr);
1636
1637
1638 PCRE NATIVE API AUXILIARY FUNCTIONS
1639
1640 int pcre_jit_exec(const pcre *code, const pcre_extra *extra,
1641 const char *subject, int length, int startoffset,
1642 int options, int *ovector, int ovecsize,
1643 pcre_jit_stack *jstack);
1644
1645 pcre_jit_stack *pcre_jit_stack_alloc(int startsize, int maxsize);
1646
1647 void pcre_jit_stack_free(pcre_jit_stack *stack);
1648
1649 void pcre_assign_jit_stack(pcre_extra *extra,
1650 pcre_jit_callback callback, void *data);
1651
1652 const unsigned char *pcre_maketables(void);
1653
1654 int pcre_fullinfo(const pcre *code, const pcre_extra *extra,
1655 int what, void *where);
1656
1657 int pcre_refcount(pcre *code, int adjust);
1658
1659 int pcre_config(int what, void *where);
1660
1661 const char *pcre_version(void);
1662
1663 int pcre_pattern_to_host_byte_order(pcre *code,
1664 pcre_extra *extra, const unsigned char *tables);
1665
1666
1667 PCRE NATIVE API INDIRECTED FUNCTIONS
1668
1669 void *(*pcre_malloc)(size_t);
1670
1671 void (*pcre_free)(void *);
1672
1673 void *(*pcre_stack_malloc)(size_t);
1674
1675 void (*pcre_stack_free)(void *);
1676
1677 int (*pcre_callout)(pcre_callout_block *);
1678
1679 int (*pcre_stack_guard)(void);
1680
1681
1682 PCRE 8-BIT, 16-BIT, AND 32-BIT LIBRARIES
1683
1684 As well as support for 8-bit character strings, PCRE also supports
1685 16-bit strings (from release 8.30) and 32-bit strings (from release
1686 8.32), by means of two additional libraries. They can be built as well
1687 as, or instead of, the 8-bit library. To avoid too much complication,
1688 this document describes the 8-bit versions of the functions, with only
1689 occasional references to the 16-bit and 32-bit libraries.
1690
1691 The 16-bit and 32-bit functions operate in the same way as their 8-bit
1692 counterparts; they just use different data types for their arguments
1693 and results, and their names start with pcre16_ or pcre32_ instead of
1694 pcre_. For every option that has UTF8 in its name (for example,
1695 PCRE_UTF8), there are corresponding 16-bit and 32-bit names with UTF8
1696 replaced by UTF16 or UTF32, respectively. This facility is in fact just
1697 cosmetic; the 16-bit and 32-bit option names define the same bit val-
1698 ues.
1699
1700 References to bytes and UTF-8 in this document should be read as refer-
1701 ences to 16-bit data units and UTF-16 when using the 16-bit library, or
1702 32-bit data units and UTF-32 when using the 32-bit library, unless
1703 specified otherwise. More details of the specific differences for the
1704 16-bit and 32-bit libraries are given in the pcre16 and pcre32 pages.
1705
1706
1707 PCRE API OVERVIEW
1708
1709 PCRE has its own native API, which is described in this document. There
1710 are also some wrapper functions (for the 8-bit library only) that cor-
1711 respond to the POSIX regular expression API, but they do not give
1712 access to all the functionality. They are described in the pcreposix
1713 documentation. Both of these APIs define a set of C function calls. A
1714 C++ wrapper (again for the 8-bit library only) is also distributed with
1715 PCRE. It is documented in the pcrecpp page.
1716
1717 The native API C function prototypes are defined in the header file
1718 pcre.h, and on Unix-like systems the (8-bit) library itself is called
1719 libpcre. It can normally be accessed by adding -lpcre to the command
1720 for linking an application that uses PCRE. The header file defines the
1721 macros PCRE_MAJOR and PCRE_MINOR to contain the major and minor release
1722 numbers for the library. Applications can use these to include support
1723 for different releases of PCRE.
1724
1725 In a Windows environment, if you want to statically link an application
1726 program against a non-dll pcre.a file, you must define PCRE_STATIC
1727 before including pcre.h or pcrecpp.h, because otherwise the pcre_mal-
1728 loc() and pcre_free() exported functions will be declared
1729 __declspec(dllimport), with unwanted results.
1730
1731 The functions pcre_compile(), pcre_compile2(), pcre_study(), and
1732 pcre_exec() are used for compiling and matching regular expressions in
1733 a Perl-compatible manner. A sample program that demonstrates the sim-
1734 plest way of using them is provided in the file called pcredemo.c in
1735 the PCRE source distribution. A listing of this program is given in the
1736 pcredemo documentation, and the pcresample documentation describes how
1737 to compile and run it.
1738
1739 Just-in-time compiler support is an optional feature of PCRE that can
1740 be built in appropriate hardware environments. It greatly speeds up the
1741 matching performance of many patterns. Simple programs can easily
1742 request that it be used if available, by setting an option that is
1743 ignored when it is not relevant. More complicated programs might need
1744 to make use of the functions pcre_jit_stack_alloc(),
1745 pcre_jit_stack_free(), and pcre_assign_jit_stack() in order to control
1746 the JIT code's memory usage.
1747
1748 From release 8.32 there is also a direct interface for JIT execution,
1749 which gives improved performance. The JIT-specific functions are dis-
1750 cussed in the pcrejit documentation.
1751
1752 A second matching function, pcre_dfa_exec(), which is not Perl-compati-
1753 ble, is also provided. This uses a different algorithm for the match-
1754 ing. The alternative algorithm finds all possible matches (at a given
1755 point in the subject), and scans the subject just once (unless there
1756 are lookbehind assertions). However, this algorithm does not return
1757 captured substrings. A description of the two matching algorithms and
1758 their advantages and disadvantages is given in the pcrematching docu-
1759 mentation.
1760
1761 In addition to the main compiling and matching functions, there are
1762 convenience functions for extracting captured substrings from a subject
1763 string that is matched by pcre_exec(). They are:
1764
1765 pcre_copy_substring()
1766 pcre_copy_named_substring()
1767 pcre_get_substring()
1768 pcre_get_named_substring()
1769 pcre_get_substring_list()
1770 pcre_get_stringnumber()
1771 pcre_get_stringtable_entries()
1772
1773 pcre_free_substring() and pcre_free_substring_list() are also provided,
1774 to free the memory used for extracted strings.
1775
1776 The function pcre_maketables() is used to build a set of character
1777 tables in the current locale for passing to pcre_compile(),
1778 pcre_exec(), or pcre_dfa_exec(). This is an optional facility that is
1779 provided for specialist use. Most commonly, no special tables are
1780 passed, in which case internal tables that are generated when PCRE is
1781 built are used.
1782
1783 The function pcre_fullinfo() is used to find out information about a
1784 compiled pattern. The function pcre_version() returns a pointer to a
1785 string containing the version of PCRE and its date of release.
1786
1787 The function pcre_refcount() maintains a reference count in a data
1788 block containing a compiled pattern. This is provided for the benefit
1789 of object-oriented applications.
1790
1791 The global variables pcre_malloc and pcre_free initially contain the
1792 entry points of the standard malloc() and free() functions, respec-
1793 tively. PCRE calls the memory management functions via these variables,
1794 so a calling program can replace them if it wishes to intercept the
1795 calls. This should be done before calling any PCRE functions.
1796
1797 The global variables pcre_stack_malloc and pcre_stack_free are also
1798 indirections to memory management functions. These special functions
1799 are used only when PCRE is compiled to use the heap for remembering
1800 data, instead of recursive function calls, when running the pcre_exec()
1801 function. See the pcrebuild documentation for details of how to do
1802 this. It is a non-standard way of building PCRE, for use in environ-
1803 ments that have limited stacks. Because of the greater use of memory
1804 management, it runs more slowly. Separate functions are provided so
1805 that special-purpose external code can be used for this case. When
1806 used, these functions are always called in a stack-like manner (last
1807 obtained, first freed), and always for memory blocks of the same size.
1808 There is a discussion about PCRE's stack usage in the pcrestack docu-
1809 mentation.
1810
1811 The global variable pcre_callout initially contains NULL. It can be set
1812 by the caller to a "callout" function, which PCRE will then call at
1813 specified points during a matching operation. Details are given in the
1814 pcrecallout documentation.
1815
1816 The global variable pcre_stack_guard initially contains NULL. It can be
1817 set by the caller to a function that is called by PCRE whenever it
1818 starts to compile a parenthesized part of a pattern. When parentheses
1819 are nested, PCRE uses recursive function calls, which use up the system
1820 stack. This function is provided so that applications with restricted
1821 stacks can force a compilation error if the stack runs out. The func-
1822 tion should return zero if all is well, or non-zero to force an error.
1823
1824
1825 NEWLINES
1826
1827 PCRE supports five different conventions for indicating line breaks in
1828 strings: a single CR (carriage return) character, a single LF (line-
1829 feed) character, the two-character sequence CRLF, any of the three pre-
1830 ceding, or any Unicode newline sequence. The Unicode newline sequences
1831 are the three just mentioned, plus the single characters VT (vertical
1832 tab, U+000B), FF (form feed, U+000C), NEL (next line, U+0085), LS (line
1833 separator, U+2028), and PS (paragraph separator, U+2029).
1834
1835 Each of the first three conventions is used by at least one operating
1836 system as its standard newline sequence. When PCRE is built, a default
1837 can be specified. The default default is LF, which is the Unix stan-
1838 dard. When PCRE is run, the default can be overridden, either when a
1839 pattern is compiled, or when it is matched.
1840
1841 At compile time, the newline convention can be specified by the options
1842 argument of pcre_compile(), or it can be specified by special text at
1843 the start of the pattern itself; this overrides any other settings. See
1844 the pcrepattern page for details of the special character sequences.
1845
1846 In the PCRE documentation the word "newline" is used to mean "the char-
1847 acter or pair of characters that indicate a line break". The choice of
1848 newline convention affects the handling of the dot, circumflex, and
1849 dollar metacharacters, the handling of #-comments in /x mode, and, when
1850 CRLF is a recognized line ending sequence, the match position advance-
1851 ment for a non-anchored pattern. There is more detail about this in the
1852 section on pcre_exec() options below.
1853
1854 The choice of newline convention does not affect the interpretation of
1855 the \n or \r escape sequences, nor does it affect what \R matches,
1856 which is controlled in a similar way, but by separate options.
1857
1858
1859 MULTITHREADING
1860
1861 The PCRE functions can be used in multi-threading applications, with
1862 the proviso that the memory management functions pointed to by
1863 pcre_malloc, pcre_free, pcre_stack_malloc, and pcre_stack_free, and the
1864 callout and stack-checking functions pointed to by pcre_callout and
1865 pcre_stack_guard, are shared by all threads.
1866
1867 The compiled form of a regular expression is not altered during match-
1868 ing, so the same compiled pattern can safely be used by several threads
1869 at once.
1870
1871 If the just-in-time optimization feature is being used, it needs sepa-
1872 rate memory stack areas for each thread. See the pcrejit documentation
1873 for more details.
1874
1875
1876 SAVING PRECOMPILED PATTERNS FOR LATER USE
1877
1878 The compiled form of a regular expression can be saved and re-used at a
1879 later time, possibly by a different program, and even on a host other
1880 than the one on which it was compiled. Details are given in the
1881 pcreprecompile documentation, which includes a description of the
1882 pcre_pattern_to_host_byte_order() function. However, compiling a regu-
1883 lar expression with one version of PCRE for use with a different ver-
1884 sion is not guaranteed to work and may cause crashes.
1885
1886
1887 CHECKING BUILD-TIME OPTIONS
1888
1889 int pcre_config(int what, void *where);
1890
1891 The function pcre_config() makes it possible for a PCRE client to dis-
1892 cover which optional features have been compiled into the PCRE library.
1893 The pcrebuild documentation has more details about these optional fea-
1894 tures.
1895
1896 The first argument for pcre_config() is an integer, specifying which
1897 information is required; the second argument is a pointer to a variable
1898 into which the information is placed. The returned value is zero on
1899 success, or the negative error code PCRE_ERROR_BADOPTION if the value
1900 in the first argument is not recognized. The following information is
1901 available:
1902
1903 PCRE_CONFIG_UTF8
1904
1905 The output is an integer that is set to one if UTF-8 support is avail-
1906 able; otherwise it is set to zero. This value should normally be given
1907 to the 8-bit version of this function, pcre_config(). If it is given to
1908 the 16-bit or 32-bit version of this function, the result is
1909 PCRE_ERROR_BADOPTION.
1910
1911 PCRE_CONFIG_UTF16
1912
1913 The output is an integer that is set to one if UTF-16 support is avail-
1914 able; otherwise it is set to zero. This value should normally be given
1915 to the 16-bit version of this function, pcre16_config(). If it is given
1916 to the 8-bit or 32-bit version of this function, the result is
1917 PCRE_ERROR_BADOPTION.
1918
1919 PCRE_CONFIG_UTF32
1920
1921 The output is an integer that is set to one if UTF-32 support is avail-
1922 able; otherwise it is set to zero. This value should normally be given
1923 to the 32-bit version of this function, pcre32_config(). If it is given
1924 to the 8-bit or 16-bit version of this function, the result is
1925 PCRE_ERROR_BADOPTION.
1926
1927 PCRE_CONFIG_UNICODE_PROPERTIES
1928
1929 The output is an integer that is set to one if support for Unicode
1930 character properties is available; otherwise it is set to zero.
1931
1932 PCRE_CONFIG_JIT
1933
1934 The output is an integer that is set to one if support for just-in-time
1935 compiling is available; otherwise it is set to zero.
1936
1937 PCRE_CONFIG_JITTARGET
1938
1939 The output is a pointer to a zero-terminated "const char *" string. If
1940 JIT support is available, the string contains the name of the architec-
1941 ture for which the JIT compiler is configured, for example "x86 32bit
1942 (little endian + unaligned)". If JIT support is not available, the
1943 result is NULL.
1944
1945 PCRE_CONFIG_NEWLINE
1946
1947 The output is an integer whose value specifies the default character
1948 sequence that is recognized as meaning "newline". The values that are
1949 supported in ASCII/Unicode environments are: 10 for LF, 13 for CR, 3338
1950 for CRLF, -2 for ANYCRLF, and -1 for ANY. In EBCDIC environments, CR,
1951 ANYCRLF, and ANY yield the same values. However, the value for LF is
1952 normally 21, though some EBCDIC environments use 37. The corresponding
1953 values for CRLF are 3349 and 3365. The default should normally corre-
1954 spond to the standard sequence for your operating system.
1955
1956 PCRE_CONFIG_BSR
1957
1958 The output is an integer whose value indicates what character sequences
1959 the \R escape sequence matches by default. A value of 0 means that \R
1960 matches any Unicode line ending sequence; a value of 1 means that \R
1961 matches only CR, LF, or CRLF. The default can be overridden when a pat-
1962 tern is compiled or matched.
1963
1964 PCRE_CONFIG_LINK_SIZE
1965
1966 The output is an integer that contains the number of bytes used for
1967 internal linkage in compiled regular expressions. For the 8-bit
1968 library, the value can be 2, 3, or 4. For the 16-bit library, the value
1969 is either 2 or 4 and is still a number of bytes. For the 32-bit
1970 library, the value is either 2 or 4 and is still a number of bytes. The
1971 default value of 2 is sufficient for all but the most massive patterns,
1972 since it allows the compiled pattern to be up to 64K in size. Larger
1973 values allow larger regular expressions to be compiled, at the expense
1974 of slower matching.
1975
1976 PCRE_CONFIG_POSIX_MALLOC_THRESHOLD
1977
1978 The output is an integer that contains the threshold above which the
1979 POSIX interface uses malloc() for output vectors. Further details are
1980 given in the pcreposix documentation.
1981
1982 PCRE_CONFIG_PARENS_LIMIT
1983
1984 The output is a long integer that gives the maximum depth of nesting of
1985 parentheses (of any kind) in a pattern. This limit is imposed to cap
1986 the amount of system stack used when a pattern is compiled. It is spec-
1987 ified when PCRE is built; the default is 250. This limit does not take
1988 into account the stack that may already be used by the calling applica-
1989 tion. For finer control over compilation stack usage, you can set a
1990 pointer to an external checking function in pcre_stack_guard.
1991
1992 PCRE_CONFIG_MATCH_LIMIT
1993
1994 The output is a long integer that gives the default limit for the num-
1995 ber of internal matching function calls in a pcre_exec() execution.
1996 Further details are given with pcre_exec() below.
1997
1998 PCRE_CONFIG_MATCH_LIMIT_RECURSION
1999
2000 The output is a long integer that gives the default limit for the depth
2001 of recursion when calling the internal matching function in a
2002 pcre_exec() execution. Further details are given with pcre_exec()
2003 below.
2004
2005 PCRE_CONFIG_STACKRECURSE
2006
2007 The output is an integer that is set to one if internal recursion when
2008 running pcre_exec() is implemented by recursive function calls that use
2009 the stack to remember their state. This is the usual way that PCRE is
2010 compiled. The output is zero if PCRE was compiled to use blocks of data
2011 on the heap instead of recursive function calls. In this case,
2012 pcre_stack_malloc and pcre_stack_free are called to manage memory
2013 blocks on the heap, thus avoiding the use of the stack.
2014
2015
2016 COMPILING A PATTERN
2017
2018 pcre *pcre_compile(const char *pattern, int options,
2019 const char **errptr, int *erroffset,
2020 const unsigned char *tableptr);
2021
2022 pcre *pcre_compile2(const char *pattern, int options,
2023 int *errorcodeptr,
2024 const char **errptr, int *erroffset,
2025 const unsigned char *tableptr);
2026
2027 Either of the functions pcre_compile() or pcre_compile2() can be called
2028 to compile a pattern into an internal form. The only difference between
2029 the two interfaces is that pcre_compile2() has an additional argument,
2030 errorcodeptr, via which a numerical error code can be returned. To
2031 avoid too much repetition, we refer just to pcre_compile() below, but
2032 the information applies equally to pcre_compile2().
2033
2034 The pattern is a C string terminated by a binary zero, and is passed in
2035 the pattern argument. A pointer to a single block of memory that is
2036 obtained via pcre_malloc is returned. This contains the compiled code
2037 and related data. The pcre type is defined for the returned block; this
2038 is a typedef for a structure whose contents are not externally defined.
2039 It is up to the caller to free the memory (via pcre_free) when it is no
2040 longer required.
2041
2042 Although the compiled code of a PCRE regex is relocatable, that is, it
2043 does not depend on memory location, the complete pcre data block is not
2044 fully relocatable, because it may contain a copy of the tableptr argu-
2045 ment, which is an address (see below).
2046
2047 The options argument contains various bit settings that affect the com-
2048 pilation. It should be zero if no options are required. The available
2049 options are described below. Some of them (in particular, those that
2050 are compatible with Perl, but some others as well) can also be set and
2051 unset from within the pattern (see the detailed description in the
2052 pcrepattern documentation). For those options that can be different in
2053 different parts of the pattern, the contents of the options argument
2054 specifies their settings at the start of compilation and execution. The
2055 PCRE_ANCHORED, PCRE_BSR_xxx, PCRE_NEWLINE_xxx, PCRE_NO_UTF8_CHECK, and
2056 PCRE_NO_START_OPTIMIZE options can be set at the time of matching as
2057 well as at compile time.
2058
2059 If errptr is NULL, pcre_compile() returns NULL immediately. Otherwise,
2060 if compilation of a pattern fails, pcre_compile() returns NULL, and
2061 sets the variable pointed to by errptr to point to a textual error mes-
2062 sage. This is a static string that is part of the library. You must not
2063 try to free it. Normally, the offset from the start of the pattern to
2064 the data unit that was being processed when the error was discovered is
2065 placed in the variable pointed to by erroffset, which must not be NULL
2066 (if it is, an immediate error is given). However, for an invalid UTF-8
2067 or UTF-16 string, the offset is that of the first data unit of the
2068 failing character.
2069
2070 Some errors are not detected until the whole pattern has been scanned;
2071 in these cases, the offset passed back is the length of the pattern.
2072 Note that the offset is in data units, not characters, even in a UTF
2073 mode. It may sometimes point into the middle of a UTF-8 or UTF-16 char-
2074 acter.
2075
2076 If pcre_compile2() is used instead of pcre_compile(), and the error-
2077 codeptr argument is not NULL, a non-zero error code number is returned
2078 via this argument in the event of an error. This is in addition to the
2079 textual error message. Error codes and messages are listed below.
2080
2081 If the final argument, tableptr, is NULL, PCRE uses a default set of
2082 character tables that are built when PCRE is compiled, using the
2083 default C locale. Otherwise, tableptr must be an address that is the
2084 result of a call to pcre_maketables(). This value is stored with the
2085 compiled pattern, and used again by pcre_exec() and pcre_dfa_exec()
2086 when the pattern is matched. For more discussion, see the section on
2087 locale support below.
2088
2089 This code fragment shows a typical straightforward call to pcre_com-
2090 pile():
2091
2092 pcre *re;
2093 const char *error;
2094 int erroffset;
2095 re = pcre_compile(
2096 "^A.*Z", /* the pattern */
2097 0, /* default options */
2098 &error, /* for error message */
2099 &erroffset, /* for error offset */
2100 NULL); /* use default character tables */
2101
2102 The following names for option bits are defined in the pcre.h header
2103 file:
2104
2105 PCRE_ANCHORED
2106
2107 If this bit is set, the pattern is forced to be "anchored", that is, it
2108 is constrained to match only at the first matching point in the string
2109 that is being searched (the "subject string"). This effect can also be
2110 achieved by appropriate constructs in the pattern itself, which is the
2111 only way to do it in Perl.
2112
2113 PCRE_AUTO_CALLOUT
2114
2115 If this bit is set, pcre_compile() automatically inserts callout items,
2116 all with number 255, before each pattern item. For discussion of the
2117 callout facility, see the pcrecallout documentation.
2118
2119 PCRE_BSR_ANYCRLF
2120 PCRE_BSR_UNICODE
2121
2122 These options (which are mutually exclusive) control what the \R escape
2123 sequence matches. The choice is either to match only CR, LF, or CRLF,
2124 or to match any Unicode newline sequence. The default is specified when
2125 PCRE is built. It can be overridden from within the pattern, or by set-
2126 ting an option when a compiled pattern is matched.
2127
2128 PCRE_CASELESS
2129
2130 If this bit is set, letters in the pattern match both upper and lower
2131 case letters. It is equivalent to Perl's /i option, and it can be
2132 changed within a pattern by a (?i) option setting. In UTF-8 mode, PCRE
2133 always understands the concept of case for characters whose values are
2134 less than 128, so caseless matching is always possible. For characters
2135 with higher values, the concept of case is supported if PCRE is com-
2136 piled with Unicode property support, but not otherwise. If you want to
2137 use caseless matching for characters 128 and above, you must ensure
2138 that PCRE is compiled with Unicode property support as well as with
2139 UTF-8 support.
2140
2141 PCRE_DOLLAR_ENDONLY
2142
2143 If this bit is set, a dollar metacharacter in the pattern matches only
2144 at the end of the subject string. Without this option, a dollar also
2145 matches immediately before a newline at the end of the string (but not
2146 before any other newlines). The PCRE_DOLLAR_ENDONLY option is ignored
2147 if PCRE_MULTILINE is set. There is no equivalent to this option in
2148 Perl, and no way to set it within a pattern.
2149
2150 PCRE_DOTALL
2151
2152 If this bit is set, a dot metacharacter in the pattern matches a char-
2153 acter of any value, including one that indicates a newline. However, it
2154 only ever matches one character, even if newlines are coded as CRLF.
2155 Without this option, a dot does not match when the current position is
2156 at a newline. This option is equivalent to Perl's /s option, and it can
2157 be changed within a pattern by a (?s) option setting. A negative class
2158 such as [^a] always matches newline characters, independent of the set-
2159 ting of this option.
2160
2161 PCRE_DUPNAMES
2162
2163 If this bit is set, names used to identify capturing subpatterns need
2164 not be unique. This can be helpful for certain types of pattern when it
2165 is known that only one instance of the named subpattern can ever be
2166 matched. There are more details of named subpatterns below; see also
2167 the pcrepattern documentation.
2168
2169 PCRE_EXTENDED
2170
2171 If this bit is set, most white space characters in the pattern are
2172 totally ignored except when escaped or inside a character class. How-
2173 ever, white space is not allowed within sequences such as (?> that
2174 introduce various parenthesized subpatterns, nor within a numerical
2175 quantifier such as {1,3}. However, ignorable white space is permitted
2176 between an item and a following quantifier and between a quantifier and
2177 a following + that indicates possessiveness.
2178
2179 White space did not used to include the VT character (code 11), because
2180 Perl did not treat this character as white space. However, Perl changed
2181 at release 5.18, so PCRE followed at release 8.34, and VT is now
2182 treated as white space.
2183
2184 PCRE_EXTENDED also causes characters between an unescaped # outside a
2185 character class and the next newline, inclusive, to be ignored.
2186 PCRE_EXTENDED is equivalent to Perl's /x option, and it can be changed
2187 within a pattern by a (?x) option setting.
2188
2189 Which characters are interpreted as newlines is controlled by the
2190 options passed to pcre_compile() or by a special sequence at the start
2191 of the pattern, as described in the section entitled "Newline conven-
2192 tions" in the pcrepattern documentation. Note that the end of this type
2193 of comment is a literal newline sequence in the pattern; escape
2194 sequences that happen to represent a newline do not count.
2195
2196 This option makes it possible to include comments inside complicated
2197 patterns. Note, however, that this applies only to data characters.
2198 White space characters may never appear within special character
2199 sequences in a pattern, for example within the sequence (?( that intro-
2200 duces a conditional subpattern.
2201
2202 PCRE_EXTRA
2203
2204 This option was invented in order to turn on additional functionality
2205 of PCRE that is incompatible with Perl, but it is currently of very
2206 little use. When set, any backslash in a pattern that is followed by a
2207 letter that has no special meaning causes an error, thus reserving
2208 these combinations for future expansion. By default, as in Perl, a
2209 backslash followed by a letter with no special meaning is treated as a
2210 literal. (Perl can, however, be persuaded to give an error for this, by
2211 running it with the -w option.) There are at present no other features
2212 controlled by this option. It can also be set by a (?X) option setting
2213 within a pattern.
2214
2215 PCRE_FIRSTLINE
2216
2217 If this option is set, an unanchored pattern is required to match
2218 before or at the first newline in the subject string, though the
2219 matched text may continue over the newline.
2220
2221 PCRE_JAVASCRIPT_COMPAT
2222
2223 If this option is set, PCRE's behaviour is changed in some ways so that
2224 it is compatible with JavaScript rather than Perl. The changes are as
2225 follows:
2226
2227 (1) A lone closing square bracket in a pattern causes a compile-time
2228 error, because this is illegal in JavaScript (by default it is treated
2229 as a data character). Thus, the pattern AB]CD becomes illegal when this
2230 option is set.
2231
2232 (2) At run time, a back reference to an unset subpattern group matches
2233 an empty string (by default this causes the current matching alterna-
2234 tive to fail). A pattern such as (\1)(a) succeeds when this option is
2235 set (assuming it can find an "a" in the subject), whereas it fails by
2236 default, for Perl compatibility.
2237
2238 (3) \U matches an upper case "U" character; by default \U causes a com-
2239 pile time error (Perl uses \U to upper case subsequent characters).
2240
2241 (4) \u matches a lower case "u" character unless it is followed by four
2242 hexadecimal digits, in which case the hexadecimal number defines the
2243 code point to match. By default, \u causes a compile time error (Perl
2244 uses it to upper case the following character).
2245
2246 (5) \x matches a lower case "x" character unless it is followed by two
2247 hexadecimal digits, in which case the hexadecimal number defines the
2248 code point to match. By default, as in Perl, a hexadecimal number is
2249 always expected after \x, but it may have zero, one, or two digits (so,
2250 for example, \xz matches a binary zero character followed by z).
2251
2252 PCRE_MULTILINE
2253
2254 By default, for the purposes of matching "start of line" and "end of
2255 line", PCRE treats the subject string as consisting of a single line of
2256 characters, even if it actually contains newlines. The "start of line"
2257 metacharacter (^) matches only at the start of the string, and the "end
2258 of line" metacharacter ($) matches only at the end of the string, or
2259 before a terminating newline (except when PCRE_DOLLAR_ENDONLY is set).
2260 Note, however, that unless PCRE_DOTALL is set, the "any character"
2261 metacharacter (.) does not match at a newline. This behaviour (for ^,
2262 $, and dot) is the same as Perl.
2263
2264 When PCRE_MULTILINE it is set, the "start of line" and "end of line"
2265 constructs match immediately following or immediately before internal
2266 newlines in the subject string, respectively, as well as at the very
2267 start and end. This is equivalent to Perl's /m option, and it can be
2268 changed within a pattern by a (?m) option setting. If there are no new-
2269 lines in a subject string, or no occurrences of ^ or $ in a pattern,
2270 setting PCRE_MULTILINE has no effect.
2271
2272 PCRE_NEVER_UTF
2273
2274 This option locks out interpretation of the pattern as UTF-8 (or UTF-16
2275 or UTF-32 in the 16-bit and 32-bit libraries). In particular, it pre-
2276 vents the creator of the pattern from switching to UTF interpretation
2277 by starting the pattern with (*UTF). This may be useful in applications
2278 that process patterns from external sources. The combination of
2279 PCRE_UTF8 and PCRE_NEVER_UTF also causes an error.
2280
2281 PCRE_NEWLINE_CR
2282 PCRE_NEWLINE_LF
2283 PCRE_NEWLINE_CRLF
2284 PCRE_NEWLINE_ANYCRLF
2285 PCRE_NEWLINE_ANY
2286
2287 These options override the default newline definition that was chosen
2288 when PCRE was built. Setting the first or the second specifies that a
2289 newline is indicated by a single character (CR or LF, respectively).
2290 Setting PCRE_NEWLINE_CRLF specifies that a newline is indicated by the
2291 two-character CRLF sequence. Setting PCRE_NEWLINE_ANYCRLF specifies
2292 that any of the three preceding sequences should be recognized. Setting
2293 PCRE_NEWLINE_ANY specifies that any Unicode newline sequence should be
2294 recognized.
2295
2296 In an ASCII/Unicode environment, the Unicode newline sequences are the
2297 three just mentioned, plus the single characters VT (vertical tab,
2298 U+000B), FF (form feed, U+000C), NEL (next line, U+0085), LS (line sep-
2299 arator, U+2028), and PS (paragraph separator, U+2029). For the 8-bit
2300 library, the last two are recognized only in UTF-8 mode.
2301
2302 When PCRE is compiled to run in an EBCDIC (mainframe) environment, the
2303 code for CR is 0x0d, the same as ASCII. However, the character code for
2304 LF is normally 0x15, though in some EBCDIC environments 0x25 is used.
2305 Whichever of these is not LF is made to correspond to Unicode's NEL
2306 character. EBCDIC codes are all less than 256. For more details, see
2307 the pcrebuild documentation.
2308
2309 The newline setting in the options word uses three bits that are
2310 treated as a number, giving eight possibilities. Currently only six are
2311 used (default plus the five values above). This means that if you set
2312 more than one newline option, the combination may or may not be sensi-
2313 ble. For example, PCRE_NEWLINE_CR with PCRE_NEWLINE_LF is equivalent to
2314 PCRE_NEWLINE_CRLF, but other combinations may yield unused numbers and
2315 cause an error.
2316
2317 The only time that a line break in a pattern is specially recognized
2318 when compiling is when PCRE_EXTENDED is set. CR and LF are white space
2319 characters, and so are ignored in this mode. Also, an unescaped # out-
2320 side a character class indicates a comment that lasts until after the
2321 next line break sequence. In other circumstances, line break sequences
2322 in patterns are treated as literal data.
2323
2324 The newline option that is set at compile time becomes the default that
2325 is used for pcre_exec() and pcre_dfa_exec(), but it can be overridden.
2326
2327 PCRE_NO_AUTO_CAPTURE
2328
2329 If this option is set, it disables the use of numbered capturing paren-
2330 theses in the pattern. Any opening parenthesis that is not followed by
2331 ? behaves as if it were followed by ?: but named parentheses can still
2332 be used for capturing (and they acquire numbers in the usual way).
2333 There is no equivalent of this option in Perl.
2334
2335 PCRE_NO_AUTO_POSSESS
2336
2337 If this option is set, it disables "auto-possessification". This is an
2338 optimization that, for example, turns a+b into a++b in order to avoid
2339 backtracks into a+ that can never be successful. However, if callouts
2340 are in use, auto-possessification means that some of them are never
2341 taken. You can set this option if you want the matching functions to do
2342 a full unoptimized search and run all the callouts, but it is mainly
2343 provided for testing purposes.
2344
2345 PCRE_NO_START_OPTIMIZE
2346
2347 This is an option that acts at matching time; that is, it is really an
2348 option for pcre_exec() or pcre_dfa_exec(). If it is set at compile
2349 time, it is remembered with the compiled pattern and assumed at match-
2350 ing time. This is necessary if you want to use JIT execution, because
2351 the JIT compiler needs to know whether or not this option is set. For
2352 details see the discussion of PCRE_NO_START_OPTIMIZE below.
2353
2354 PCRE_UCP
2355
2356 This option changes the way PCRE processes \B, \b, \D, \d, \S, \s, \W,
2357 \w, and some of the POSIX character classes. By default, only ASCII
2358 characters are recognized, but if PCRE_UCP is set, Unicode properties
2359 are used instead to classify characters. More details are given in the
2360 section on generic character types in the pcrepattern page. If you set
2361 PCRE_UCP, matching one of the items it affects takes much longer. The
2362 option is available only if PCRE has been compiled with Unicode prop-
2363 erty support.
2364
2365 PCRE_UNGREEDY
2366
2367 This option inverts the "greediness" of the quantifiers so that they
2368 are not greedy by default, but become greedy if followed by "?". It is
2369 not compatible with Perl. It can also be set by a (?U) option setting
2370 within the pattern.
2371
2372 PCRE_UTF8
2373
2374 This option causes PCRE to regard both the pattern and the subject as
2375 strings of UTF-8 characters instead of single-byte strings. However, it
2376 is available only when PCRE is built to include UTF support. If not,
2377 the use of this option provokes an error. Details of how this option
2378 changes the behaviour of PCRE are given in the pcreunicode page.
2379
2380 PCRE_NO_UTF8_CHECK
2381
2382 When PCRE_UTF8 is set, the validity of the pattern as a UTF-8 string is
2383 automatically checked. There is a discussion about the validity of
2384 UTF-8 strings in the pcreunicode page. If an invalid UTF-8 sequence is
2385 found, pcre_compile() returns an error. If you already know that your
2386 pattern is valid, and you want to skip this check for performance rea-
2387 sons, you can set the PCRE_NO_UTF8_CHECK option. When it is set, the
2388 effect of passing an invalid UTF-8 string as a pattern is undefined. It
2389 may cause your program to crash or loop. Note that this option can also
2390 be passed to pcre_exec() and pcre_dfa_exec(), to suppress the validity
2391 checking of subject strings only. If the same string is being matched
2392 many times, the option can be safely set for the second and subsequent
2393 matchings to improve performance.
2394
2395
2396 COMPILATION ERROR CODES
2397
2398 The following table lists the error codes than may be returned by
2399 pcre_compile2(), along with the error messages that may be returned by
2400 both compiling functions. Note that error messages are always 8-bit
2401 ASCII strings, even in 16-bit or 32-bit mode. As PCRE has developed,
2402 some error codes have fallen out of use. To avoid confusion, they have
2403 not been re-used.
2404
2405 0 no error
2406 1 \ at end of pattern
2407 2 \c at end of pattern
2408 3 unrecognized character follows \
2409 4 numbers out of order in {} quantifier
2410 5 number too big in {} quantifier
2411 6 missing terminating ] for character class
2412 7 invalid escape sequence in character class
2413 8 range out of order in character class
2414 9 nothing to repeat
2415 10 [this code is not in use]
2416 11 internal error: unexpected repeat
2417 12 unrecognized character after (? or (?-
2418 13 POSIX named classes are supported only within a class
2419 14 missing )
2420 15 reference to non-existent subpattern
2421 16 erroffset passed as NULL
2422 17 unknown option bit(s) set
2423 18 missing ) after comment
2424 19 [this code is not in use]
2425 20 regular expression is too large
2426 21 failed to get memory
2427 22 unmatched parentheses
2428 23 internal error: code overflow
2429 24 unrecognized character after (?<
2430 25 lookbehind assertion is not fixed length
2431 26 malformed number or name after (?(
2432 27 conditional group contains more than two branches
2433 28 assertion expected after (?(
2434 29 (?R or (?[+-]digits must be followed by )
2435 30 unknown POSIX class name
2436 31 POSIX collating elements are not supported
2437 32 this version of PCRE is compiled without UTF support
2438 33 [this code is not in use]
2439 34 character value in \x{} or \o{} is too large
2440 35 invalid condition (?(0)
2441 36 \C not allowed in lookbehind assertion
2442 37 PCRE does not support \L, \l, \N{name}, \U, or \u
2443 38 number after (?C is > 255
2444 39 closing ) for (?C expected
2445 40 recursive call could loop indefinitely
2446 41 unrecognized character after (?P
2447 42 syntax error in subpattern name (missing terminator)
2448 43 two named subpatterns have the same name
2449 44 invalid UTF-8 string (specifically UTF-8)
2450 45 support for \P, \p, and \X has not been compiled
2451 46 malformed \P or \p sequence
2452 47 unknown property name after \P or \p
2453 48 subpattern name is too long (maximum 32 characters)
2454 49 too many named subpatterns (maximum 10000)
2455 50 [this code is not in use]
2456 51 octal value is greater than \377 in 8-bit non-UTF-8 mode
2457 52 internal error: overran compiling workspace
2458 53 internal error: previously-checked referenced subpattern
2459 not found
2460 54 DEFINE group contains more than one branch
2461 55 repeating a DEFINE group is not allowed
2462 56 inconsistent NEWLINE options
2463 57 \g is not followed by a braced, angle-bracketed, or quoted
2464 name/number or by a plain number
2465 58 a numbered reference must not be zero
2466 59 an argument is not allowed for (*ACCEPT), (*FAIL), or (*COMMIT)
2467 60 (*VERB) not recognized or malformed
2468 61 number is too big
2469 62 subpattern name expected
2470 63 digit expected after (?+
2471 64 ] is an invalid data character in JavaScript compatibility mode
2472 65 different names for subpatterns of the same number are
2473 not allowed
2474 66 (*MARK) must have an argument
2475 67 this version of PCRE is not compiled with Unicode property
2476 support
2477 68 \c must be followed by an ASCII character
2478 69 \k is not followed by a braced, angle-bracketed, or quoted name
2479 70 internal error: unknown opcode in find_fixedlength()
2480 71 \N is not supported in a class
2481 72 too many forward references
2482 73 disallowed Unicode code point (>= 0xd800 && <= 0xdfff)
2483 74 invalid UTF-16 string (specifically UTF-16)
2484 75 name is too long in (*MARK), (*PRUNE), (*SKIP), or (*THEN)
2485 76 character value in \u.... sequence is too large
2486 77 invalid UTF-32 string (specifically UTF-32)
2487 78 setting UTF is disabled by the application
2488 79 non-hex character in \x{} (closing brace missing?)
2489 80 non-octal character in \o{} (closing brace missing?)
2490 81 missing opening brace after \o
2491 82 parentheses are too deeply nested
2492 83 invalid range in character class
2493 84 group name must start with a non-digit
2494 85 parentheses are too deeply nested (stack check)
2495
2496 The numbers 32 and 10000 in errors 48 and 49 are defaults; different
2497 values may be used if the limits were changed when PCRE was built.
2498
2499
2500 STUDYING A PATTERN
2501
2502 pcre_extra *pcre_study(const pcre *code, int options,
2503 const char **errptr);
2504
2505 If a compiled pattern is going to be used several times, it is worth
2506 spending more time analyzing it in order to speed up the time taken for
2507 matching. The function pcre_study() takes a pointer to a compiled pat-
2508 tern as its first argument. If studying the pattern produces additional
2509 information that will help speed up matching, pcre_study() returns a
2510 pointer to a pcre_extra block, in which the study_data field points to
2511 the results of the study.
2512
2513 The returned value from pcre_study() can be passed directly to
2514 pcre_exec() or pcre_dfa_exec(). However, a pcre_extra block also con-
2515 tains other fields that can be set by the caller before the block is
2516 passed; these are described below in the section on matching a pattern.
2517
2518 If studying the pattern does not produce any useful information,
2519 pcre_study() returns NULL by default. In that circumstance, if the
2520 calling program wants to pass any of the other fields to pcre_exec() or
2521 pcre_dfa_exec(), it must set up its own pcre_extra block. However, if
2522 pcre_study() is called with the PCRE_STUDY_EXTRA_NEEDED option, it
2523 returns a pcre_extra block even if studying did not find any additional
2524 information. It may still return NULL, however, if an error occurs in
2525 pcre_study().
2526
2527 The second argument of pcre_study() contains option bits. There are
2528 three further options in addition to PCRE_STUDY_EXTRA_NEEDED:
2529
2530 PCRE_STUDY_JIT_COMPILE
2531 PCRE_STUDY_JIT_PARTIAL_HARD_COMPILE
2532 PCRE_STUDY_JIT_PARTIAL_SOFT_COMPILE
2533
2534 If any of these are set, and the just-in-time compiler is available,
2535 the pattern is further compiled into machine code that executes much
2536 faster than the pcre_exec() interpretive matching function. If the
2537 just-in-time compiler is not available, these options are ignored. All
2538 undefined bits in the options argument must be zero.
2539
2540 JIT compilation is a heavyweight optimization. It can take some time
2541 for patterns to be analyzed, and for one-off matches and simple pat-
2542 terns the benefit of faster execution might be offset by a much slower
2543 study time. Not all patterns can be optimized by the JIT compiler. For
2544 those that cannot be handled, matching automatically falls back to the
2545 pcre_exec() interpreter. For more details, see the pcrejit documenta-
2546 tion.
2547
2548 The third argument for pcre_study() is a pointer for an error message.
2549 If studying succeeds (even if no data is returned), the variable it
2550 points to is set to NULL. Otherwise it is set to point to a textual
2551 error message. This is a static string that is part of the library. You
2552 must not try to free it. You should test the error pointer for NULL
2553 after calling pcre_study(), to be sure that it has run successfully.
2554
2555 When you are finished with a pattern, you can free the memory used for
2556 the study data by calling pcre_free_study(). This function was added to
2557 the API for release 8.20. For earlier versions, the memory could be
2558 freed with pcre_free(), just like the pattern itself. This will still
2559 work in cases where JIT optimization is not used, but it is advisable
2560 to change to the new function when convenient.
2561
2562 This is a typical way in which pcre_study() is used (except that in a
2563 real application there should be tests for errors):
2564
2565 int rc;
2566 pcre *re;
2567 pcre_extra *sd;
2568 re = pcre_compile("pattern", 0, &error, &erroroffset, NULL);
2569 sd = pcre_study(
2570 re, /* result of pcre_compile() */
2571 0, /* no options */
2572 &error); /* set to NULL or points to a message */
2573 rc = pcre_exec( /* see below for details of pcre_exec() options */
2574 re, sd, "subject", 7, 0, 0, ovector, 30);
2575 ...
2576 pcre_free_study(sd);
2577 pcre_free(re);
2578
2579 Studying a pattern does two things: first, a lower bound for the length
2580 of subject string that is needed to match the pattern is computed. This
2581 does not mean that there are any strings of that length that match, but
2582 it does guarantee that no shorter strings match. The value is used to
2583 avoid wasting time by trying to match strings that are shorter than the
2584 lower bound. You can find out the value in a calling program via the
2585 pcre_fullinfo() function.
2586
2587 Studying a pattern is also useful for non-anchored patterns that do not
2588 have a single fixed starting character. A bitmap of possible starting
2589 bytes is created. This speeds up finding a position in the subject at
2590 which to start matching. (In 16-bit mode, the bitmap is used for 16-bit
2591 values less than 256. In 32-bit mode, the bitmap is used for 32-bit
2592 values less than 256.)
2593
2594 These two optimizations apply to both pcre_exec() and pcre_dfa_exec(),
2595 and the information is also used by the JIT compiler. The optimiza-
2596 tions can be disabled by setting the PCRE_NO_START_OPTIMIZE option.
2597 You might want to do this if your pattern contains callouts or (*MARK)
2598 and you want to make use of these facilities in cases where matching
2599 fails.
2600
2601 PCRE_NO_START_OPTIMIZE can be specified at either compile time or exe-
2602 cution time. However, if PCRE_NO_START_OPTIMIZE is passed to
2603 pcre_exec(), (that is, after any JIT compilation has happened) JIT exe-
2604 cution is disabled. For JIT execution to work with PCRE_NO_START_OPTI-
2605 MIZE, the option must be set at compile time.
2606
2607 There is a longer discussion of PCRE_NO_START_OPTIMIZE below.
2608
2609
2610 LOCALE SUPPORT
2611
2612 PCRE handles caseless matching, and determines whether characters are
2613 letters, digits, or whatever, by reference to a set of tables, indexed
2614 by character code point. When running in UTF-8 mode, or in the 16- or
2615 32-bit libraries, this applies only to characters with code points less
2616 than 256. By default, higher-valued code points never match escapes
2617 such as \w or \d. However, if PCRE is built with Unicode property sup-
2618 port, all characters can be tested with \p and \P, or, alternatively,
2619 the PCRE_UCP option can be set when a pattern is compiled; this causes
2620 \w and friends to use Unicode property support instead of the built-in
2621 tables.
2622
2623 The use of locales with Unicode is discouraged. If you are handling
2624 characters with code points greater than 128, you should either use
2625 Unicode support, or use locales, but not try to mix the two.
2626
2627 PCRE contains an internal set of tables that are used when the final
2628 argument of pcre_compile() is NULL. These are sufficient for many
2629 applications. Normally, the internal tables recognize only ASCII char-
2630 acters. However, when PCRE is built, it is possible to cause the inter-
2631 nal tables to be rebuilt in the default "C" locale of the local system,
2632 which may cause them to be different.
2633
2634 The internal tables can always be overridden by tables supplied by the
2635 application that calls PCRE. These may be created in a different locale
2636 from the default. As more and more applications change to using Uni-
2637 code, the need for this locale support is expected to die away.
2638
2639 External tables are built by calling the pcre_maketables() function,
2640 which has no arguments, in the relevant locale. The result can then be
2641 passed to pcre_compile() as often as necessary. For example, to build
2642 and use tables that are appropriate for the French locale (where
2643 accented characters with values greater than 128 are treated as let-
2644 ters), the following code could be used:
2645
2646 setlocale(LC_CTYPE, "fr_FR");
2647 tables = pcre_maketables();
2648 re = pcre_compile(..., tables);
2649
2650 The locale name "fr_FR" is used on Linux and other Unix-like systems;
2651 if you are using Windows, the name for the French locale is "french".
2652
2653 When pcre_maketables() runs, the tables are built in memory that is
2654 obtained via pcre_malloc. It is the caller's responsibility to ensure
2655 that the memory containing the tables remains available for as long as
2656 it is needed.
2657
2658 The pointer that is passed to pcre_compile() is saved with the compiled
2659 pattern, and the same tables are used via this pointer by pcre_study()
2660 and also by pcre_exec() and pcre_dfa_exec(). Thus, for any single pat-
2661 tern, compilation, studying and matching all happen in the same locale,
2662 but different patterns can be processed in different locales.
2663
2664 It is possible to pass a table pointer or NULL (indicating the use of
2665 the internal tables) to pcre_exec() or pcre_dfa_exec() (see the discus-
2666 sion below in the section on matching a pattern). This facility is pro-
2667 vided for use with pre-compiled patterns that have been saved and
2668 reloaded. Character tables are not saved with patterns, so if a non-
2669 standard table was used at compile time, it must be provided again when
2670 the reloaded pattern is matched. Attempting to use this facility to
2671 match a pattern in a different locale from the one in which it was com-
2672 piled is likely to lead to anomalous (usually incorrect) results.
2673
2674
2675 INFORMATION ABOUT A PATTERN
2676
2677 int pcre_fullinfo(const pcre *code, const pcre_extra *extra,
2678 int what, void *where);
2679
2680 The pcre_fullinfo() function returns information about a compiled pat-
2681 tern. It replaces the pcre_info() function, which was removed from the
2682 library at version 8.30, after more than 10 years of obsolescence.
2683
2684 The first argument for pcre_fullinfo() is a pointer to the compiled
2685 pattern. The second argument is the result of pcre_study(), or NULL if
2686 the pattern was not studied. The third argument specifies which piece
2687 of information is required, and the fourth argument is a pointer to a
2688 variable to receive the data. The yield of the function is zero for
2689 success, or one of the following negative numbers:
2690
2691 PCRE_ERROR_NULL the argument code was NULL
2692 the argument where was NULL
2693 PCRE_ERROR_BADMAGIC the "magic number" was not found
2694 PCRE_ERROR_BADENDIANNESS the pattern was compiled with different
2695 endianness
2696 PCRE_ERROR_BADOPTION the value of what was invalid
2697 PCRE_ERROR_UNSET the requested field is not set
2698
2699 The "magic number" is placed at the start of each compiled pattern as
2700 an simple check against passing an arbitrary memory pointer. The endi-
2701 anness error can occur if a compiled pattern is saved and reloaded on a
2702 different host. Here is a typical call of pcre_fullinfo(), to obtain
2703 the length of the compiled pattern:
2704
2705 int rc;
2706 size_t length;
2707 rc = pcre_fullinfo(
2708 re, /* result of pcre_compile() */
2709 sd, /* result of pcre_study(), or NULL */
2710 PCRE_INFO_SIZE, /* what is required */
2711 &length); /* where to put the data */
2712
2713 The possible values for the third argument are defined in pcre.h, and
2714 are as follows:
2715
2716 PCRE_INFO_BACKREFMAX
2717
2718 Return the number of the highest back reference in the pattern. The
2719 fourth argument should point to an int variable. Zero is returned if
2720 there are no back references.
2721
2722 PCRE_INFO_CAPTURECOUNT
2723
2724 Return the number of capturing subpatterns in the pattern. The fourth
2725 argument should point to an int variable.
2726
2727 PCRE_INFO_DEFAULT_TABLES
2728
2729 Return a pointer to the internal default character tables within PCRE.
2730 The fourth argument should point to an unsigned char * variable. This
2731 information call is provided for internal use by the pcre_study() func-
2732 tion. External callers can cause PCRE to use its internal tables by
2733 passing a NULL table pointer.
2734
2735 PCRE_INFO_FIRSTBYTE (deprecated)
2736
2737 Return information about the first data unit of any matched string, for
2738 a non-anchored pattern. The name of this option refers to the 8-bit
2739 library, where data units are bytes. The fourth argument should point
2740 to an int variable. Negative values are used for special cases. How-
2741 ever, this means that when the 32-bit library is in non-UTF-32 mode,
2742 the full 32-bit range of characters cannot be returned. For this rea-
2743 son, this value is deprecated; use PCRE_INFO_FIRSTCHARACTERFLAGS and
2744 PCRE_INFO_FIRSTCHARACTER instead.
2745
2746 If there is a fixed first value, for example, the letter "c" from a
2747 pattern such as (cat|cow|coyote), its value is returned. In the 8-bit
2748 library, the value is always less than 256. In the 16-bit library the
2749 value can be up to 0xffff. In the 32-bit library the value can be up to
2750 0x10ffff.
2751
2752 If there is no fixed first value, and if either
2753
2754 (a) the pattern was compiled with the PCRE_MULTILINE option, and every
2755 branch starts with "^", or
2756
2757 (b) every branch of the pattern starts with ".*" and PCRE_DOTALL is not
2758 set (if it were set, the pattern would be anchored),
2759
2760 -1 is returned, indicating that the pattern matches only at the start
2761 of a subject string or after any newline within the string. Otherwise
2762 -2 is returned. For anchored patterns, -2 is returned.
2763
2764 PCRE_INFO_FIRSTCHARACTER
2765
2766 Return the value of the first data unit (non-UTF character) of any
2767 matched string in the situation where PCRE_INFO_FIRSTCHARACTERFLAGS
2768 returns 1; otherwise return 0. The fourth argument should point to an
2769 uint_t variable.
2770
2771 In the 8-bit library, the value is always less than 256. In the 16-bit
2772 library the value can be up to 0xffff. In the 32-bit library in UTF-32
2773 mode the value can be up to 0x10ffff, and up to 0xffffffff when not
2774 using UTF-32 mode.
2775
2776 PCRE_INFO_FIRSTCHARACTERFLAGS
2777
2778 Return information about the first data unit of any matched string, for
2779 a non-anchored pattern. The fourth argument should point to an int
2780 variable.
2781
2782 If there is a fixed first value, for example, the letter "c" from a
2783 pattern such as (cat|cow|coyote), 1 is returned, and the character
2784 value can be retrieved using PCRE_INFO_FIRSTCHARACTER. If there is no
2785 fixed first value, and if either
2786
2787 (a) the pattern was compiled with the PCRE_MULTILINE option, and every
2788 branch starts with "^", or
2789
2790 (b) every branch of the pattern starts with ".*" and PCRE_DOTALL is not
2791 set (if it were set, the pattern would be anchored),
2792
2793 2 is returned, indicating that the pattern matches only at the start of
2794 a subject string or after any newline within the string. Otherwise 0 is
2795 returned. For anchored patterns, 0 is returned.
2796
2797 PCRE_INFO_FIRSTTABLE
2798
2799 If the pattern was studied, and this resulted in the construction of a
2800 256-bit table indicating a fixed set of values for the first data unit
2801 in any matching string, a pointer to the table is returned. Otherwise
2802 NULL is returned. The fourth argument should point to an unsigned char
2803 * variable.
2804
2805 PCRE_INFO_HASCRORLF
2806
2807 Return 1 if the pattern contains any explicit matches for CR or LF
2808 characters, otherwise 0. The fourth argument should point to an int
2809 variable. An explicit match is either a literal CR or LF character, or
2810 \r or \n.
2811
2812 PCRE_INFO_JCHANGED
2813
2814 Return 1 if the (?J) or (?-J) option setting is used in the pattern,
2815 otherwise 0. The fourth argument should point to an int variable. (?J)
2816 and (?-J) set and unset the local PCRE_DUPNAMES option, respectively.
2817
2818 PCRE_INFO_JIT
2819
2820 Return 1 if the pattern was studied with one of the JIT options, and
2821 just-in-time compiling was successful. The fourth argument should point
2822 to an int variable. A return value of 0 means that JIT support is not
2823 available in this version of PCRE, or that the pattern was not studied
2824 with a JIT option, or that the JIT compiler could not handle this par-
2825 ticular pattern. See the pcrejit documentation for details of what can
2826 and cannot be handled.
2827
2828 PCRE_INFO_JITSIZE
2829
2830 If the pattern was successfully studied with a JIT option, return the
2831 size of the JIT compiled code, otherwise return zero. The fourth argu-
2832 ment should point to a size_t variable.
2833
2834 PCRE_INFO_LASTLITERAL
2835
2836 Return the value of the rightmost literal data unit that must exist in
2837 any matched string, other than at its start, if such a value has been
2838 recorded. The fourth argument should point to an int variable. If there
2839 is no such value, -1 is returned. For anchored patterns, a last literal
2840 value is recorded only if it follows something of variable length. For
2841 example, for the pattern /^a\d+z\d+/ the returned value is "z", but for
2842 /^a\dz\d/ the returned value is -1.
2843
2844 Since for the 32-bit library using the non-UTF-32 mode, this function
2845 is unable to return the full 32-bit range of characters, this value is
2846 deprecated; instead the PCRE_INFO_REQUIREDCHARFLAGS and
2847 PCRE_INFO_REQUIREDCHAR values should be used.
2848
2849 PCRE_INFO_MATCH_EMPTY
2850
2851 Return 1 if the pattern can match an empty string, otherwise 0. The
2852 fourth argument should point to an int variable.
2853
2854 PCRE_INFO_MATCHLIMIT
2855
2856 If the pattern set a match limit by including an item of the form
2857 (*LIMIT_MATCH=nnnn) at the start, the value is returned. The fourth
2858 argument should point to an unsigned 32-bit integer. If no such value
2859 has been set, the call to pcre_fullinfo() returns the error
2860 PCRE_ERROR_UNSET.
2861
2862 PCRE_INFO_MAXLOOKBEHIND
2863
2864 Return the number of characters (NB not data units) in the longest
2865 lookbehind assertion in the pattern. This information is useful when
2866 doing multi-segment matching using the partial matching facilities.
2867 Note that the simple assertions \b and \B require a one-character look-
2868 behind. \A also registers a one-character lookbehind, though it does
2869 not actually inspect the previous character. This is to ensure that at
2870 least one character from the old segment is retained when a new segment
2871 is processed. Otherwise, if there are no lookbehinds in the pattern, \A
2872 might match incorrectly at the start of a new segment.
2873
2874 PCRE_INFO_MINLENGTH
2875
2876 If the pattern was studied and a minimum length for matching subject
2877 strings was computed, its value is returned. Otherwise the returned
2878 value is -1. The value is a number of characters, which in UTF mode may
2879 be different from the number of data units. The fourth argument should
2880 point to an int variable. A non-negative value is a lower bound to the
2881 length of any matching string. There may not be any strings of that
2882 length that do actually match, but every string that does match is at
2883 least that long.
2884
2885 PCRE_INFO_NAMECOUNT
2886 PCRE_INFO_NAMEENTRYSIZE
2887 PCRE_INFO_NAMETABLE
2888
2889 PCRE supports the use of named as well as numbered capturing parenthe-
2890 ses. The names are just an additional way of identifying the parenthe-
2891 ses, which still acquire numbers. Several convenience functions such as
2892 pcre_get_named_substring() are provided for extracting captured sub-
2893 strings by name. It is also possible to extract the data directly, by
2894 first converting the name to a number in order to access the correct
2895 pointers in the output vector (described with pcre_exec() below). To do
2896 the conversion, you need to use the name-to-number map, which is
2897 described by these three values.
2898
2899 The map consists of a number of fixed-size entries. PCRE_INFO_NAMECOUNT
2900 gives the number of entries, and PCRE_INFO_NAMEENTRYSIZE gives the size
2901 of each entry; both of these return an int value. The entry size
2902 depends on the length of the longest name. PCRE_INFO_NAMETABLE returns
2903 a pointer to the first entry of the table. This is a pointer to char in
2904 the 8-bit library, where the first two bytes of each entry are the num-
2905 ber of the capturing parenthesis, most significant byte first. In the
2906 16-bit library, the pointer points to 16-bit data units, the first of
2907 which contains the parenthesis number. In the 32-bit library, the
2908 pointer points to 32-bit data units, the first of which contains the
2909 parenthesis number. The rest of the entry is the corresponding name,
2910 zero terminated.
2911
2912 The names are in alphabetical order. If (?| is used to create multiple
2913 groups with the same number, as described in the section on duplicate
2914 subpattern numbers in the pcrepattern page, the groups may be given the
2915 same name, but there is only one entry in the table. Different names
2916 for groups of the same number are not permitted. Duplicate names for
2917 subpatterns with different numbers are permitted, but only if PCRE_DUP-
2918 NAMES is set. They appear in the table in the order in which they were
2919 found in the pattern. In the absence of (?| this is the order of
2920 increasing number; when (?| is used this is not necessarily the case
2921 because later subpatterns may have lower numbers.
2922
2923 As a simple example of the name/number table, consider the following
2924 pattern after compilation by the 8-bit library (assume PCRE_EXTENDED is
2925 set, so white space - including newlines - is ignored):
2926
2927 (?<date> (?<year>(\d\d)?\d\d) -
2928 (?<month>\d\d) - (?<day>\d\d) )
2929
2930 There are four named subpatterns, so the table has four entries, and
2931 each entry in the table is eight bytes long. The table is as follows,
2932 with non-printing bytes shows in hexadecimal, and undefined bytes shown
2933 as ??:
2934
2935 00 01 d a t e 00 ??
2936 00 05 d a y 00 ?? ??
2937 00 04 m o n t h 00
2938 00 02 y e a r 00 ??
2939
2940 When writing code to extract data from named subpatterns using the
2941 name-to-number map, remember that the length of the entries is likely
2942 to be different for each compiled pattern.
2943
2944 PCRE_INFO_OKPARTIAL
2945
2946 Return 1 if the pattern can be used for partial matching with
2947 pcre_exec(), otherwise 0. The fourth argument should point to an int
2948 variable. From release 8.00, this always returns 1, because the
2949 restrictions that previously applied to partial matching have been
2950 lifted. The pcrepartial documentation gives details of partial match-
2951 ing.
2952
2953 PCRE_INFO_OPTIONS
2954
2955 Return a copy of the options with which the pattern was compiled. The
2956 fourth argument should point to an unsigned long int variable. These
2957 option bits are those specified in the call to pcre_compile(), modified
2958 by any top-level option settings at the start of the pattern itself. In
2959 other words, they are the options that will be in force when matching
2960 starts. For example, if the pattern /(?im)abc(?-i)d/ is compiled with
2961 the PCRE_EXTENDED option, the result is PCRE_CASELESS, PCRE_MULTILINE,
2962 and PCRE_EXTENDED.
2963
2964 A pattern is automatically anchored by PCRE if all of its top-level
2965 alternatives begin with one of the following:
2966
2967 ^ unless PCRE_MULTILINE is set
2968 \A always
2969 \G always
2970 .* if PCRE_DOTALL is set and there are no back
2971 references to the subpattern in which .* appears
2972
2973 For such patterns, the PCRE_ANCHORED bit is set in the options returned
2974 by pcre_fullinfo().
2975
2976 PCRE_INFO_RECURSIONLIMIT
2977
2978 If the pattern set a recursion limit by including an item of the form
2979 (*LIMIT_RECURSION=nnnn) at the start, the value is returned. The fourth
2980 argument should point to an unsigned 32-bit integer. If no such value
2981 has been set, the call to pcre_fullinfo() returns the error
2982 PCRE_ERROR_UNSET.
2983
2984 PCRE_INFO_SIZE
2985
2986 Return the size of the compiled pattern in bytes (for all three
2987 libraries). The fourth argument should point to a size_t variable. This
2988 value does not include the size of the pcre structure that is returned
2989 by pcre_compile(). The value that is passed as the argument to
2990 pcre_malloc() when pcre_compile() is getting memory in which to place
2991 the compiled data is the value returned by this option plus the size of
2992 the pcre structure. Studying a compiled pattern, with or without JIT,
2993 does not alter the value returned by this option.
2994
2995 PCRE_INFO_STUDYSIZE
2996
2997 Return the size in bytes (for all three libraries) of the data block
2998 pointed to by the study_data field in a pcre_extra block. If pcre_extra
2999 is NULL, or there is no study data, zero is returned. The fourth argu-
3000 ment should point to a size_t variable. The study_data field is set by
3001 pcre_study() to record information that will speed up matching (see the
3002 section entitled "Studying a pattern" above). The format of the
3003 study_data block is private, but its length is made available via this
3004 option so that it can be saved and restored (see the pcreprecompile
3005 documentation for details).
3006
3007 PCRE_INFO_REQUIREDCHARFLAGS
3008
3009 Returns 1 if there is a rightmost literal data unit that must exist in
3010 any matched string, other than at its start. The fourth argument should
3011 point to an int variable. If there is no such value, 0 is returned. If
3012 returning 1, the character value itself can be retrieved using
3013 PCRE_INFO_REQUIREDCHAR.
3014
3015 For anchored patterns, a last literal value is recorded only if it fol-
3016 lows something of variable length. For example, for the pattern
3017 /^a\d+z\d+/ the returned value 1 (with "z" returned from
3018 PCRE_INFO_REQUIREDCHAR), but for /^a\dz\d/ the returned value is 0.
3019
3020 PCRE_INFO_REQUIREDCHAR
3021
3022 Return the value of the rightmost literal data unit that must exist in
3023 any matched string, other than at its start, if such a value has been
3024 recorded. The fourth argument should point to an uint32_t variable. If
3025 there is no such value, 0 is returned.
3026
3027
3028 REFERENCE COUNTS
3029
3030 int pcre_refcount(pcre *code, int adjust);
3031
3032 The pcre_refcount() function is used to maintain a reference count in
3033 the data block that contains a compiled pattern. It is provided for the
3034 benefit of applications that operate in an object-oriented manner,
3035 where different parts of the application may be using the same compiled
3036 pattern, but you want to free the block when they are all done.
3037
3038 When a pattern is compiled, the reference count field is initialized to
3039 zero. It is changed only by calling this function, whose action is to
3040 add the adjust value (which may be positive or negative) to it. The
3041 yield of the function is the new value. However, the value of the count
3042 is constrained to lie between 0 and 65535, inclusive. If the new value
3043 is outside these limits, it is forced to the appropriate limit value.
3044
3045 Except when it is zero, the reference count is not correctly preserved
3046 if a pattern is compiled on one host and then transferred to a host
3047 whose byte-order is different. (This seems a highly unlikely scenario.)
3048
3049
3050 MATCHING A PATTERN: THE TRADITIONAL FUNCTION
3051
3052 int pcre_exec(const pcre *code, const pcre_extra *extra,
3053 const char *subject, int length, int startoffset,
3054 int options, int *ovector, int ovecsize);
3055
3056 The function pcre_exec() is called to match a subject string against a
3057 compiled pattern, which is passed in the code argument. If the pattern
3058 was studied, the result of the study should be passed in the extra
3059 argument. You can call pcre_exec() with the same code and extra argu-
3060 ments as many times as you like, in order to match different subject
3061 strings with the same pattern.
3062
3063 This function is the main matching facility of the library, and it
3064 operates in a Perl-like manner. For specialist use there is also an
3065 alternative matching function, which is described below in the section
3066 about the pcre_dfa_exec() function.
3067
3068 In most applications, the pattern will have been compiled (and option-
3069 ally studied) in the same process that calls pcre_exec(). However, it
3070 is possible to save compiled patterns and study data, and then use them
3071 later in different processes, possibly even on different hosts. For a
3072 discussion about this, see the pcreprecompile documentation.
3073
3074 Here is an example of a simple call to pcre_exec():
3075
3076 int rc;
3077 int ovector[30];
3078 rc = pcre_exec(
3079 re, /* result of pcre_compile() */
3080 NULL, /* we didn't study the pattern */
3081 "some string", /* the subject string */
3082 11, /* the length of the subject string */
3083 0, /* start at offset 0 in the subject */
3084 0, /* default options */
3085 ovector, /* vector of integers for substring information */
3086 30); /* number of elements (NOT size in bytes) */
3087
3088 Extra data for pcre_exec()
3089
3090 If the extra argument is not NULL, it must point to a pcre_extra data
3091 block. The pcre_study() function returns such a block (when it doesn't
3092 return NULL), but you can also create one for yourself, and pass addi-
3093 tional information in it. The pcre_extra block contains the following
3094 fields (not necessarily in this order):
3095
3096 unsigned long int flags;
3097 void *study_data;
3098 void *executable_jit;
3099 unsigned long int match_limit;
3100 unsigned long int match_limit_recursion;
3101 void *callout_data;
3102 const unsigned char *tables;
3103 unsigned char **mark;
3104
3105 In the 16-bit version of this structure, the mark field has type
3106 "PCRE_UCHAR16 **".
3107
3108 In the 32-bit version of this structure, the mark field has type
3109 "PCRE_UCHAR32 **".
3110
3111 The flags field is used to specify which of the other fields are set.
3112 The flag bits are:
3113
3114 PCRE_EXTRA_CALLOUT_DATA
3115 PCRE_EXTRA_EXECUTABLE_JIT
3116 PCRE_EXTRA_MARK
3117 PCRE_EXTRA_MATCH_LIMIT
3118 PCRE_EXTRA_MATCH_LIMIT_RECURSION
3119 PCRE_EXTRA_STUDY_DATA
3120 PCRE_EXTRA_TABLES
3121
3122 Other flag bits should be set to zero. The study_data field and some-
3123 times the executable_jit field are set in the pcre_extra block that is
3124 returned by pcre_study(), together with the appropriate flag bits. You
3125 should not set these yourself, but you may add to the block by setting
3126 other fields and their corresponding flag bits.
3127
3128 The match_limit field provides a means of preventing PCRE from using up
3129 a vast amount of resources when running patterns that are not going to
3130 match, but which have a very large number of possibilities in their
3131 search trees. The classic example is a pattern that uses nested unlim-
3132 ited repeats.
3133
3134 Internally, pcre_exec() uses a function called match(), which it calls
3135 repeatedly (sometimes recursively). The limit set by match_limit is
3136 imposed on the number of times this function is called during a match,
3137 which has the effect of limiting the amount of backtracking that can
3138 take place. For patterns that are not anchored, the count restarts from
3139 zero for each position in the subject string.
3140
3141 When pcre_exec() is called with a pattern that was successfully studied
3142 with a JIT option, the way that the matching is executed is entirely
3143 different. However, there is still the possibility of runaway matching
3144 that goes on for a very long time, and so the match_limit value is also
3145 used in this case (but in a different way) to limit how long the match-
3146 ing can continue.
3147
3148 The default value for the limit can be set when PCRE is built; the
3149 default default is 10 million, which handles all but the most extreme
3150 cases. You can override the default by suppling pcre_exec() with a
3151 pcre_extra block in which match_limit is set, and
3152 PCRE_EXTRA_MATCH_LIMIT is set in the flags field. If the limit is
3153 exceeded, pcre_exec() returns PCRE_ERROR_MATCHLIMIT.
3154
3155 A value for the match limit may also be supplied by an item at the
3156 start of a pattern of the form
3157
3158 (*LIMIT_MATCH=d)
3159
3160 where d is a decimal number. However, such a setting is ignored unless
3161 d is less than the limit set by the caller of pcre_exec() or, if no
3162 such limit is set, less than the default.
3163
3164 The match_limit_recursion field is similar to match_limit, but instead
3165 of limiting the total number of times that match() is called, it limits
3166 the depth of recursion. The recursion depth is a smaller number than
3167 the total number of calls, because not all calls to match() are recur-
3168 sive. This limit is of use only if it is set smaller than match_limit.
3169
3170 Limiting the recursion depth limits the amount of machine stack that
3171 can be used, or, when PCRE has been compiled to use memory on the heap
3172 instead of the stack, the amount of heap memory that can be used. This
3173 limit is not relevant, and is ignored, when matching is done using JIT
3174 compiled code.
3175
3176 The default value for match_limit_recursion can be set when PCRE is
3177 built; the default default is the same value as the default for
3178 match_limit. You can override the default by suppling pcre_exec() with
3179 a pcre_extra block in which match_limit_recursion is set, and
3180 PCRE_EXTRA_MATCH_LIMIT_RECURSION is set in the flags field. If the
3181 limit is exceeded, pcre_exec() returns PCRE_ERROR_RECURSIONLIMIT.
3182
3183 A value for the recursion limit may also be supplied by an item at the
3184 start of a pattern of the form
3185
3186 (*LIMIT_RECURSION=d)
3187
3188 where d is a decimal number. However, such a setting is ignored unless
3189 d is less than the limit set by the caller of pcre_exec() or, if no
3190 such limit is set, less than the default.
3191
3192 The callout_data field is used in conjunction with the "callout" fea-
3193 ture, and is described in the pcrecallout documentation.
3194
3195 The tables field is provided for use with patterns that have been pre-
3196 compiled using custom character tables, saved to disc or elsewhere, and
3197 then reloaded, because the tables that were used to compile a pattern
3198 are not saved with it. See the pcreprecompile documentation for a dis-
3199 cussion of saving compiled patterns for later use. If NULL is passed
3200 using this mechanism, it forces PCRE's internal tables to be used.
3201
3202 Warning: The tables that pcre_exec() uses must be the same as those
3203 that were used when the pattern was compiled. If this is not the case,
3204 the behaviour of pcre_exec() is undefined. Therefore, when a pattern is
3205 compiled and matched in the same process, this field should never be
3206 set. In this (the most common) case, the correct table pointer is auto-
3207 matically passed with the compiled pattern from pcre_compile() to
3208 pcre_exec().
3209
3210 If PCRE_EXTRA_MARK is set in the flags field, the mark field must be
3211 set to point to a suitable variable. If the pattern contains any back-
3212 tracking control verbs such as (*MARK:NAME), and the execution ends up
3213 with a name to pass back, a pointer to the name string (zero termi-
3214 nated) is placed in the variable pointed to by the mark field. The
3215 names are within the compiled pattern; if you wish to retain such a
3216 name you must copy it before freeing the memory of a compiled pattern.
3217 If there is no name to pass back, the variable pointed to by the mark
3218 field is set to NULL. For details of the backtracking control verbs,
3219 see the section entitled "Backtracking control" in the pcrepattern doc-
3220 umentation.
3221
3222 Option bits for pcre_exec()
3223
3224 The unused bits of the options argument for pcre_exec() must be zero.
3225 The only bits that may be set are PCRE_ANCHORED, PCRE_NEWLINE_xxx,
3226 PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, PCRE_NOTEMPTY_ATSTART,
3227 PCRE_NO_START_OPTIMIZE, PCRE_NO_UTF8_CHECK, PCRE_PARTIAL_HARD, and
3228 PCRE_PARTIAL_SOFT.
3229
3230 If the pattern was successfully studied with one of the just-in-time
3231 (JIT) compile options, the only supported options for JIT execution are
3232 PCRE_NO_UTF8_CHECK, PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY,
3233 PCRE_NOTEMPTY_ATSTART, PCRE_PARTIAL_HARD, and PCRE_PARTIAL_SOFT. If an
3234 unsupported option is used, JIT execution is disabled and the normal
3235 interpretive code in pcre_exec() is run.
3236
3237 PCRE_ANCHORED
3238
3239 The PCRE_ANCHORED option limits pcre_exec() to matching at the first
3240 matching position. If a pattern was compiled with PCRE_ANCHORED, or
3241 turned out to be anchored by virtue of its contents, it cannot be made
3242 unachored at matching time.
3243
3244 PCRE_BSR_ANYCRLF
3245 PCRE_BSR_UNICODE
3246
3247 These options (which are mutually exclusive) control what the \R escape
3248 sequence matches. The choice is either to match only CR, LF, or CRLF,
3249 or to match any Unicode newline sequence. These options override the
3250 choice that was made or defaulted when the pattern was compiled.
3251
3252 PCRE_NEWLINE_CR
3253 PCRE_NEWLINE_LF
3254 PCRE_NEWLINE_CRLF
3255 PCRE_NEWLINE_ANYCRLF
3256 PCRE_NEWLINE_ANY
3257
3258 These options override the newline definition that was chosen or
3259 defaulted when the pattern was compiled. For details, see the descrip-
3260 tion of pcre_compile() above. During matching, the newline choice
3261 affects the behaviour of the dot, circumflex, and dollar metacharac-
3262 ters. It may also alter the way the match position is advanced after a
3263 match failure for an unanchored pattern.
3264
3265 When PCRE_NEWLINE_CRLF, PCRE_NEWLINE_ANYCRLF, or PCRE_NEWLINE_ANY is
3266 set, and a match attempt for an unanchored pattern fails when the cur-
3267 rent position is at a CRLF sequence, and the pattern contains no
3268 explicit matches for CR or LF characters, the match position is
3269 advanced by two characters instead of one, in other words, to after the
3270 CRLF.
3271
3272 The above rule is a compromise that makes the most common cases work as
3273 expected. For example, if the pattern is .+A (and the PCRE_DOTALL
3274 option is not set), it does not match the string "\r\nA" because, after
3275 failing at the start, it skips both the CR and the LF before retrying.
3276 However, the pattern [\r\n]A does match that string, because it con-
3277 tains an explicit CR or LF reference, and so advances only by one char-
3278 acter after the first failure.
3279
3280 An explicit match for CR of LF is either a literal appearance of one of
3281 those characters, or one of the \r or \n escape sequences. Implicit
3282 matches such as [^X] do not count, nor does \s (which includes CR and
3283 LF in the characters that it matches).
3284
3285 Notwithstanding the above, anomalous effects may still occur when CRLF
3286 is a valid newline sequence and explicit \r or \n escapes appear in the
3287 pattern.
3288
3289 PCRE_NOTBOL
3290
3291 This option specifies that first character of the subject string is not
3292 the beginning of a line, so the circumflex metacharacter should not
3293 match before it. Setting this without PCRE_MULTILINE (at compile time)
3294 causes circumflex never to match. This option affects only the behav-
3295 iour of the circumflex metacharacter. It does not affect \A.
3296
3297 PCRE_NOTEOL
3298
3299 This option specifies that the end of the subject string is not the end
3300 of a line, so the dollar metacharacter should not match it nor (except
3301 in multiline mode) a newline immediately before it. Setting this with-
3302 out PCRE_MULTILINE (at compile time) causes dollar never to match. This
3303 option affects only the behaviour of the dollar metacharacter. It does
3304 not affect \Z or \z.
3305
3306 PCRE_NOTEMPTY
3307
3308 An empty string is not considered to be a valid match if this option is
3309 set. If there are alternatives in the pattern, they are tried. If all
3310 the alternatives match the empty string, the entire match fails. For
3311 example, if the pattern
3312
3313 a?b?
3314
3315 is applied to a string not beginning with "a" or "b", it matches an
3316 empty string at the start of the subject. With PCRE_NOTEMPTY set, this
3317 match is not valid, so PCRE searches further into the string for occur-
3318 rences of "a" or "b".
3319
3320 PCRE_NOTEMPTY_ATSTART
3321
3322 This is like PCRE_NOTEMPTY, except that an empty string match that is
3323 not at the start of the subject is permitted. If the pattern is
3324 anchored, such a match can occur only if the pattern contains \K.
3325
3326 Perl has no direct equivalent of PCRE_NOTEMPTY or
3327 PCRE_NOTEMPTY_ATSTART, but it does make a special case of a pattern
3328 match of the empty string within its split() function, and when using
3329 the /g modifier. It is possible to emulate Perl's behaviour after
3330 matching a null string by first trying the match again at the same off-
3331 set with PCRE_NOTEMPTY_ATSTART and PCRE_ANCHORED, and then if that
3332 fails, by advancing the starting offset (see below) and trying an ordi-
3333 nary match again. There is some code that demonstrates how to do this
3334 in the pcredemo sample program. In the most general case, you have to
3335 check to see if the newline convention recognizes CRLF as a newline,
3336 and if so, and the current character is CR followed by LF, advance the
3337 starting offset by two characters instead of one.
3338
3339 PCRE_NO_START_OPTIMIZE
3340
3341 There are a number of optimizations that pcre_exec() uses at the start
3342 of a match, in order to speed up the process. For example, if it is
3343 known that an unanchored match must start with a specific character, it
3344 searches the subject for that character, and fails immediately if it
3345 cannot find it, without actually running the main matching function.
3346 This means that a special item such as (*COMMIT) at the start of a pat-
3347 tern is not considered until after a suitable starting point for the
3348 match has been found. Also, when callouts or (*MARK) items are in use,
3349 these "start-up" optimizations can cause them to be skipped if the pat-
3350 tern is never actually used. The start-up optimizations are in effect a
3351 pre-scan of the subject that takes place before the pattern is run.
3352
3353 The PCRE_NO_START_OPTIMIZE option disables the start-up optimizations,
3354 possibly causing performance to suffer, but ensuring that in cases
3355 where the result is "no match", the callouts do occur, and that items
3356 such as (*COMMIT) and (*MARK) are considered at every possible starting
3357 position in the subject string. If PCRE_NO_START_OPTIMIZE is set at
3358 compile time, it cannot be unset at matching time. The use of
3359 PCRE_NO_START_OPTIMIZE at matching time (that is, passing it to
3360 pcre_exec()) disables JIT execution; in this situation, matching is
3361 always done using interpretively.
3362
3363 Setting PCRE_NO_START_OPTIMIZE can change the outcome of a matching
3364 operation. Consider the pattern
3365
3366 (*COMMIT)ABC
3367
3368 When this is compiled, PCRE records the fact that a match must start
3369 with the character "A". Suppose the subject string is "DEFABC". The
3370 start-up optimization scans along the subject, finds "A" and runs the
3371 first match attempt from there. The (*COMMIT) item means that the pat-
3372 tern must match the current starting position, which in this case, it
3373 does. However, if the same match is run with PCRE_NO_START_OPTIMIZE
3374 set, the initial scan along the subject string does not happen. The
3375 first match attempt is run starting from "D" and when this fails,
3376 (*COMMIT) prevents any further matches being tried, so the overall
3377 result is "no match". If the pattern is studied, more start-up opti-
3378 mizations may be used. For example, a minimum length for the subject
3379 may be recorded. Consider the pattern
3380
3381 (*MARK:A)(X|Y)
3382
3383 The minimum length for a match is one character. If the subject is
3384 "ABC", there will be attempts to match "ABC", "BC", "C", and then
3385 finally an empty string. If the pattern is studied, the final attempt
3386 does not take place, because PCRE knows that the subject is too short,
3387 and so the (*MARK) is never encountered. In this case, studying the
3388 pattern does not affect the overall match result, which is still "no
3389 match", but it does affect the auxiliary information that is returned.
3390
3391 PCRE_NO_UTF8_CHECK
3392
3393 When PCRE_UTF8 is set at compile time, the validity of the subject as a
3394 UTF-8 string is automatically checked when pcre_exec() is subsequently
3395 called. The entire string is checked before any other processing takes
3396 place. The value of startoffset is also checked to ensure that it
3397 points to the start of a UTF-8 character. There is a discussion about
3398 the validity of UTF-8 strings in the pcreunicode page. If an invalid
3399 sequence of bytes is found, pcre_exec() returns the error
3400 PCRE_ERROR_BADUTF8 or, if PCRE_PARTIAL_HARD is set and the problem is a
3401 truncated character at the end of the subject, PCRE_ERROR_SHORTUTF8. In
3402 both cases, information about the precise nature of the error may also
3403 be returned (see the descriptions of these errors in the section enti-
3404 tled Error return values from pcre_exec() below). If startoffset con-
3405 tains a value that does not point to the start of a UTF-8 character (or
3406 to the end of the subject), PCRE_ERROR_BADUTF8_OFFSET is returned.
3407
3408 If you already know that your subject is valid, and you want to skip
3409 these checks for performance reasons, you can set the
3410 PCRE_NO_UTF8_CHECK option when calling pcre_exec(). You might want to
3411 do this for the second and subsequent calls to pcre_exec() if you are
3412 making repeated calls to find all the matches in a single subject
3413 string. However, you should be sure that the value of startoffset
3414 points to the start of a character (or the end of the subject). When
3415 PCRE_NO_UTF8_CHECK is set, the effect of passing an invalid string as a
3416 subject or an invalid value of startoffset is undefined. Your program
3417 may crash or loop.
3418
3419 PCRE_PARTIAL_HARD
3420 PCRE_PARTIAL_SOFT
3421
3422 These options turn on the partial matching feature. For backwards com-
3423 patibility, PCRE_PARTIAL is a synonym for PCRE_PARTIAL_SOFT. A partial
3424 match occurs if the end of the subject string is reached successfully,
3425 but there are not enough subject characters to complete the match. If
3426 this happens when PCRE_PARTIAL_SOFT (but not PCRE_PARTIAL_HARD) is set,
3427 matching continues by testing any remaining alternatives. Only if no
3428 complete match can be found is PCRE_ERROR_PARTIAL returned instead of
3429 PCRE_ERROR_NOMATCH. In other words, PCRE_PARTIAL_SOFT says that the
3430 caller is prepared to handle a partial match, but only if no complete
3431 match can be found.
3432
3433 If PCRE_PARTIAL_HARD is set, it overrides PCRE_PARTIAL_SOFT. In this
3434 case, if a partial match is found, pcre_exec() immediately returns
3435 PCRE_ERROR_PARTIAL, without considering any other alternatives. In
3436 other words, when PCRE_PARTIAL_HARD is set, a partial match is consid-
3437 ered to be more important that an alternative complete match.
3438
3439 In both cases, the portion of the string that was inspected when the
3440 partial match was found is set as the first matching string. There is a
3441 more detailed discussion of partial and multi-segment matching, with
3442 examples, in the pcrepartial documentation.
3443
3444 The string to be matched by pcre_exec()
3445
3446 The subject string is passed to pcre_exec() as a pointer in subject, a
3447 length in length, and a starting offset in startoffset. The units for
3448 length and startoffset are bytes for the 8-bit library, 16-bit data
3449 items for the 16-bit library, and 32-bit data items for the 32-bit
3450 library.
3451
3452 If startoffset is negative or greater than the length of the subject,
3453 pcre_exec() returns PCRE_ERROR_BADOFFSET. When the starting offset is
3454 zero, the search for a match starts at the beginning of the subject,
3455 and this is by far the most common case. In UTF-8 or UTF-16 mode, the
3456 offset must point to the start of a character, or the end of the sub-
3457 ject (in UTF-32 mode, one data unit equals one character, so all off-
3458 sets are valid). Unlike the pattern string, the subject may contain
3459 binary zeroes.
3460
3461 A non-zero starting offset is useful when searching for another match
3462 in the same subject by calling pcre_exec() again after a previous suc-
3463 cess. Setting startoffset differs from just passing over a shortened
3464 string and setting PCRE_NOTBOL in the case of a pattern that begins
3465 with any kind of lookbehind. For example, consider the pattern
3466
3467 \Biss\B
3468
3469 which finds occurrences of "iss" in the middle of words. (\B matches
3470 only if the current position in the subject is not a word boundary.)
3471 When applied to the string "Mississipi" the first call to pcre_exec()
3472 finds the first occurrence. If pcre_exec() is called again with just
3473 the remainder of the subject, namely "issipi", it does not match,
3474 because \B is always false at the start of the subject, which is deemed
3475 to be a word boundary. However, if pcre_exec() is passed the entire
3476 string again, but with startoffset set to 4, it finds the second occur-
3477 rence of "iss" because it is able to look behind the starting point to
3478 discover that it is preceded by a letter.
3479
3480 Finding all the matches in a subject is tricky when the pattern can
3481 match an empty string. It is possible to emulate Perl's /g behaviour by
3482 first trying the match again at the same offset, with the
3483 PCRE_NOTEMPTY_ATSTART and PCRE_ANCHORED options, and then if that
3484 fails, advancing the starting offset and trying an ordinary match
3485 again. There is some code that demonstrates how to do this in the pcre-
3486 demo sample program. In the most general case, you have to check to see
3487 if the newline convention recognizes CRLF as a newline, and if so, and
3488 the current character is CR followed by LF, advance the starting offset
3489 by two characters instead of one.
3490
3491 If a non-zero starting offset is passed when the pattern is anchored,
3492 one attempt to match at the given offset is made. This can only succeed
3493 if the pattern does not require the match to be at the start of the
3494 subject.
3495
3496 How pcre_exec() returns captured substrings
3497
3498 In general, a pattern matches a certain portion of the subject, and in
3499 addition, further substrings from the subject may be picked out by
3500 parts of the pattern. Following the usage in Jeffrey Friedl's book,
3501 this is called "capturing" in what follows, and the phrase "capturing
3502 subpattern" is used for a fragment of a pattern that picks out a sub-
3503 string. PCRE supports several other kinds of parenthesized subpattern
3504 that do not cause substrings to be captured.
3505
3506 Captured substrings are returned to the caller via a vector of integers
3507 whose address is passed in ovector. The number of elements in the vec-
3508 tor is passed in ovecsize, which must be a non-negative number. Note:
3509 this argument is NOT the size of ovector in bytes.
3510
3511 The first two-thirds of the vector is used to pass back captured sub-
3512 strings, each substring using a pair of integers. The remaining third
3513 of the vector is used as workspace by pcre_exec() while matching cap-
3514 turing subpatterns, and is not available for passing back information.
3515 The number passed in ovecsize should always be a multiple of three. If
3516 it is not, it is rounded down.
3517
3518 When a match is successful, information about captured substrings is
3519 returned in pairs of integers, starting at the beginning of ovector,
3520 and continuing up to two-thirds of its length at the most. The first
3521 element of each pair is set to the offset of the first character in a
3522 substring, and the second is set to the offset of the first character
3523 after the end of a substring. These values are always data unit off-
3524 sets, even in UTF mode. They are byte offsets in the 8-bit library,
3525 16-bit data item offsets in the 16-bit library, and 32-bit data item
3526 offsets in the 32-bit library. Note: they are not character counts.
3527
3528 The first pair of integers, ovector[0] and ovector[1], identify the
3529 portion of the subject string matched by the entire pattern. The next
3530 pair is used for the first capturing subpattern, and so on. The value
3531 returned by pcre_exec() is one more than the highest numbered pair that
3532 has been set. For example, if two substrings have been captured, the
3533 returned value is 3. If there are no capturing subpatterns, the return
3534 value from a successful match is 1, indicating that just the first pair
3535 of offsets has been set.
3536
3537 If a capturing subpattern is matched repeatedly, it is the last portion
3538 of the string that it matched that is returned.
3539
3540 If the vector is too small to hold all the captured substring offsets,
3541 it is used as far as possible (up to two-thirds of its length), and the
3542 function returns a value of zero. If neither the actual string matched
3543 nor any captured substrings are of interest, pcre_exec() may be called
3544 with ovector passed as NULL and ovecsize as zero. However, if the pat-
3545 tern contains back references and the ovector is not big enough to
3546 remember the related substrings, PCRE has to get additional memory for
3547 use during matching. Thus it is usually advisable to supply an ovector
3548 of reasonable size.
3549
3550 There are some cases where zero is returned (indicating vector over-
3551 flow) when in fact the vector is exactly the right size for the final
3552 match. For example, consider the pattern
3553
3554 (a)(?:(b)c|bd)
3555
3556 If a vector of 6 elements (allowing for only 1 captured substring) is
3557 given with subject string "abd", pcre_exec() will try to set the second
3558 captured string, thereby recording a vector overflow, before failing to
3559 match "c" and backing up to try the second alternative. The zero
3560 return, however, does correctly indicate that the maximum number of
3561 slots (namely 2) have been filled. In similar cases where there is tem-
3562 porary overflow, but the final number of used slots is actually less
3563 than the maximum, a non-zero value is returned.
3564
3565 The pcre_fullinfo() function can be used to find out how many capturing
3566 subpatterns there are in a compiled pattern. The smallest size for
3567 ovector that will allow for n captured substrings, in addition to the
3568 offsets of the substring matched by the whole pattern, is (n+1)*3.
3569
3570 It is possible for capturing subpattern number n+1 to match some part
3571 of the subject when subpattern n has not been used at all. For example,
3572 if the string "abc" is matched against the pattern (a|(z))(bc) the
3573 return from the function is 4, and subpatterns 1 and 3 are matched, but
3574 2 is not. When this happens, both values in the offset pairs corre-
3575 sponding to unused subpatterns are set to -1.
3576
3577 Offset values that correspond to unused subpatterns at the end of the
3578 expression are also set to -1. For example, if the string "abc" is
3579 matched against the pattern (abc)(x(yz)?)? subpatterns 2 and 3 are not
3580 matched. The return from the function is 2, because the highest used
3581 capturing subpattern number is 1, and the offsets for for the second
3582 and third capturing subpatterns (assuming the vector is large enough,
3583 of course) are set to -1.
3584
3585 Note: Elements in the first two-thirds of ovector that do not corre-
3586 spond to capturing parentheses in the pattern are never changed. That
3587 is, if a pattern contains n capturing parentheses, no more than ovec-
3588 tor[0] to ovector[2n+1] are set by pcre_exec(). The other elements (in
3589 the first two-thirds) retain whatever values they previously had.
3590
3591 Some convenience functions are provided for extracting the captured
3592 substrings as separate strings. These are described below.
3593
3594 Error return values from pcre_exec()
3595
3596 If pcre_exec() fails, it returns a negative number. The following are
3597 defined in the header file:
3598
3599 PCRE_ERROR_NOMATCH (-1)
3600
3601 The subject string did not match the pattern.
3602
3603 PCRE_ERROR_NULL (-2)
3604
3605 Either code or subject was passed as NULL, or ovector was NULL and
3606 ovecsize was not zero.
3607
3608 PCRE_ERROR_BADOPTION (-3)
3609
3610 An unrecognized bit was set in the options argument.
3611
3612 PCRE_ERROR_BADMAGIC (-4)
3613
3614 PCRE stores a 4-byte "magic number" at the start of the compiled code,
3615 to catch the case when it is passed a junk pointer and to detect when a
3616 pattern that was compiled in an environment of one endianness is run in
3617 an environment with the other endianness. This is the error that PCRE
3618 gives when the magic number is not present.
3619
3620 PCRE_ERROR_UNKNOWN_OPCODE (-5)
3621
3622 While running the pattern match, an unknown item was encountered in the
3623 compiled pattern. This error could be caused by a bug in PCRE or by
3624 overwriting of the compiled pattern.
3625
3626 PCRE_ERROR_NOMEMORY (-6)
3627
3628 If a pattern contains back references, but the ovector that is passed
3629 to pcre_exec() is not big enough to remember the referenced substrings,
3630 PCRE gets a block of memory at the start of matching to use for this
3631 purpose. If the call via pcre_malloc() fails, this error is given. The
3632 memory is automatically freed at the end of matching.
3633
3634 This error is also given if pcre_stack_malloc() fails in pcre_exec().
3635 This can happen only when PCRE has been compiled with --disable-stack-
3636 for-recursion.
3637
3638 PCRE_ERROR_NOSUBSTRING (-7)
3639
3640 This error is used by the pcre_copy_substring(), pcre_get_substring(),
3641 and pcre_get_substring_list() functions (see below). It is never
3642 returned by pcre_exec().
3643
3644 PCRE_ERROR_MATCHLIMIT (-8)
3645
3646 The backtracking limit, as specified by the match_limit field in a
3647 pcre_extra structure (or defaulted) was reached. See the description
3648 above.
3649
3650 PCRE_ERROR_CALLOUT (-9)
3651
3652 This error is never generated by pcre_exec() itself. It is provided for
3653 use by callout functions that want to yield a distinctive error code.
3654 See the pcrecallout documentation for details.
3655
3656 PCRE_ERROR_BADUTF8 (-10)
3657
3658 A string that contains an invalid UTF-8 byte sequence was passed as a
3659 subject, and the PCRE_NO_UTF8_CHECK option was not set. If the size of
3660 the output vector (ovecsize) is at least 2, the byte offset to the
3661 start of the the invalid UTF-8 character is placed in the first ele-
3662 ment, and a reason code is placed in the second element. The reason
3663 codes are listed in the following section. For backward compatibility,
3664 if PCRE_PARTIAL_HARD is set and the problem is a truncated UTF-8 char-
3665 acter at the end of the subject (reason codes 1 to 5),
3666 PCRE_ERROR_SHORTUTF8 is returned instead of PCRE_ERROR_BADUTF8.
3667
3668 PCRE_ERROR_BADUTF8_OFFSET (-11)
3669
3670 The UTF-8 byte sequence that was passed as a subject was checked and
3671 found to be valid (the PCRE_NO_UTF8_CHECK option was not set), but the
3672 value of startoffset did not point to the beginning of a UTF-8 charac-
3673 ter or the end of the subject.
3674
3675 PCRE_ERROR_PARTIAL (-12)
3676
3677 The subject string did not match, but it did match partially. See the
3678 pcrepartial documentation for details of partial matching.
3679
3680 PCRE_ERROR_BADPARTIAL (-13)
3681
3682 This code is no longer in use. It was formerly returned when the
3683 PCRE_PARTIAL option was used with a compiled pattern containing items
3684 that were not supported for partial matching. From release 8.00
3685 onwards, there are no restrictions on partial matching.
3686
3687 PCRE_ERROR_INTERNAL (-14)
3688
3689 An unexpected internal error has occurred. This error could be caused
3690 by a bug in PCRE or by overwriting of the compiled pattern.
3691
3692 PCRE_ERROR_BADCOUNT (-15)
3693
3694 This error is given if the value of the ovecsize argument is negative.
3695
3696 PCRE_ERROR_RECURSIONLIMIT (-21)
3697
3698 The internal recursion limit, as specified by the match_limit_recursion
3699 field in a pcre_extra structure (or defaulted) was reached. See the
3700 description above.
3701
3702 PCRE_ERROR_BADNEWLINE (-23)
3703
3704 An invalid combination of PCRE_NEWLINE_xxx options was given.
3705
3706 PCRE_ERROR_BADOFFSET (-24)
3707
3708 The value of startoffset was negative or greater than the length of the
3709 subject, that is, the value in length.
3710
3711 PCRE_ERROR_SHORTUTF8 (-25)
3712
3713 This error is returned instead of PCRE_ERROR_BADUTF8 when the subject
3714 string ends with a truncated UTF-8 character and the PCRE_PARTIAL_HARD
3715 option is set. Information about the failure is returned as for
3716 PCRE_ERROR_BADUTF8. It is in fact sufficient to detect this case, but
3717 this special error code for PCRE_PARTIAL_HARD precedes the implementa-
3718 tion of returned information; it is retained for backwards compatibil-
3719 ity.
3720
3721 PCRE_ERROR_RECURSELOOP (-26)
3722
3723 This error is returned when pcre_exec() detects a recursion loop within
3724 the pattern. Specifically, it means that either the whole pattern or a
3725 subpattern has been called recursively for the second time at the same
3726 position in the subject string. Some simple patterns that might do this
3727 are detected and faulted at compile time, but more complicated cases,
3728 in particular mutual recursions between two different subpatterns, can-
3729 not be detected until run time.
3730
3731 PCRE_ERROR_JIT_STACKLIMIT (-27)
3732
3733 This error is returned when a pattern that was successfully studied
3734 using a JIT compile option is being matched, but the memory available
3735 for the just-in-time processing stack is not large enough. See the
3736 pcrejit documentation for more details.
3737
3738 PCRE_ERROR_BADMODE (-28)
3739
3740 This error is given if a pattern that was compiled by the 8-bit library
3741 is passed to a 16-bit or 32-bit library function, or vice versa.
3742
3743 PCRE_ERROR_BADENDIANNESS (-29)
3744
3745 This error is given if a pattern that was compiled and saved is
3746 reloaded on a host with different endianness. The utility function
3747 pcre_pattern_to_host_byte_order() can be used to convert such a pattern
3748 so that it runs on the new host.
3749
3750 PCRE_ERROR_JIT_BADOPTION
3751
3752 This error is returned when a pattern that was successfully studied
3753 using a JIT compile option is being matched, but the matching mode
3754 (partial or complete match) does not correspond to any JIT compilation
3755 mode. When the JIT fast path function is used, this error may be also
3756 given for invalid options. See the pcrejit documentation for more
3757 details.
3758
3759 PCRE_ERROR_BADLENGTH (-32)
3760
3761 This error is given if pcre_exec() is called with a negative value for
3762 the length argument.
3763
3764 Error numbers -16 to -20, -22, and 30 are not used by pcre_exec().
3765
3766 Reason codes for invalid UTF-8 strings
3767
3768 This section applies only to the 8-bit library. The corresponding
3769 information for the 16-bit and 32-bit libraries is given in the pcre16
3770 and pcre32 pages.
3771
3772 When pcre_exec() returns either PCRE_ERROR_BADUTF8 or PCRE_ERROR_SHORT-
3773 UTF8, and the size of the output vector (ovecsize) is at least 2, the
3774 offset of the start of the invalid UTF-8 character is placed in the
3775 first output vector element (ovector[0]) and a reason code is placed in
3776 the second element (ovector[1]). The reason codes are given names in
3777 the pcre.h header file:
3778
3779 PCRE_UTF8_ERR1
3780 PCRE_UTF8_ERR2
3781 PCRE_UTF8_ERR3
3782 PCRE_UTF8_ERR4
3783 PCRE_UTF8_ERR5
3784
3785 The string ends with a truncated UTF-8 character; the code specifies
3786 how many bytes are missing (1 to 5). Although RFC 3629 restricts UTF-8
3787 characters to be no longer than 4 bytes, the encoding scheme (origi-
3788 nally defined by RFC 2279) allows for up to 6 bytes, and this is
3789 checked first; hence the possibility of 4 or 5 missing bytes.
3790
3791 PCRE_UTF8_ERR6
3792 PCRE_UTF8_ERR7
3793 PCRE_UTF8_ERR8
3794 PCRE_UTF8_ERR9
3795 PCRE_UTF8_ERR10
3796
3797 The two most significant bits of the 2nd, 3rd, 4th, 5th, or 6th byte of
3798 the character do not have the binary value 0b10 (that is, either the
3799 most significant bit is 0, or the next bit is 1).
3800
3801 PCRE_UTF8_ERR11
3802 PCRE_UTF8_ERR12
3803
3804 A character that is valid by the RFC 2279 rules is either 5 or 6 bytes
3805 long; these code points are excluded by RFC 3629.
3806
3807 PCRE_UTF8_ERR13
3808
3809 A 4-byte character has a value greater than 0x10fff; these code points
3810 are excluded by RFC 3629.
3811
3812 PCRE_UTF8_ERR14
3813
3814 A 3-byte character has a value in the range 0xd800 to 0xdfff; this
3815 range of code points are reserved by RFC 3629 for use with UTF-16, and
3816 so are excluded from UTF-8.
3817
3818 PCRE_UTF8_ERR15
3819 PCRE_UTF8_ERR16
3820 PCRE_UTF8_ERR17
3821 PCRE_UTF8_ERR18
3822 PCRE_UTF8_ERR19
3823
3824 A 2-, 3-, 4-, 5-, or 6-byte character is "overlong", that is, it codes
3825 for a value that can be represented by fewer bytes, which is invalid.
3826 For example, the two bytes 0xc0, 0xae give the value 0x2e, whose cor-
3827 rect coding uses just one byte.
3828
3829 PCRE_UTF8_ERR20
3830
3831 The two most significant bits of the first byte of a character have the
3832 binary value 0b10 (that is, the most significant bit is 1 and the sec-
3833 ond is 0). Such a byte can only validly occur as the second or subse-
3834 quent byte of a multi-byte character.
3835
3836 PCRE_UTF8_ERR21
3837
3838 The first byte of a character has the value 0xfe or 0xff. These values
3839 can never occur in a valid UTF-8 string.
3840
3841 PCRE_UTF8_ERR22
3842
3843 This error code was formerly used when the presence of a so-called
3844 "non-character" caused an error. Unicode corrigendum #9 makes it clear
3845 that such characters should not cause a string to be rejected, and so
3846 this code is no longer in use and is never returned.
3847
3848
3849 EXTRACTING CAPTURED SUBSTRINGS BY NUMBER
3850
3851 int pcre_copy_substring(const char *subject, int *ovector,
3852 int stringcount, int stringnumber, char *buffer,
3853 int buffersize);
3854
3855 int pcre_get_substring(const char *subject, int *ovector,
3856 int stringcount, int stringnumber,
3857 const char **stringptr);
3858
3859 int pcre_get_substring_list(const char *subject,
3860 int *ovector, int stringcount, const char ***listptr);
3861
3862 Captured substrings can be accessed directly by using the offsets
3863 returned by pcre_exec() in ovector. For convenience, the functions
3864 pcre_copy_substring(), pcre_get_substring(), and pcre_get_sub-
3865 string_list() are provided for extracting captured substrings as new,
3866 separate, zero-terminated strings. These functions identify substrings
3867 by number. The next section describes functions for extracting named
3868 substrings.
3869
3870 A substring that contains a binary zero is correctly extracted and has
3871 a further zero added on the end, but the result is not, of course, a C
3872 string. However, you can process such a string by referring to the
3873 length that is returned by pcre_copy_substring() and pcre_get_sub-
3874 string(). Unfortunately, the interface to pcre_get_substring_list() is
3875 not adequate for handling strings containing binary zeros, because the
3876 end of the final string is not independently indicated.
3877
3878 The first three arguments are the same for all three of these func-
3879 tions: subject is the subject string that has just been successfully
3880 matched, ovector is a pointer to the vector of integer offsets that was
3881 passed to pcre_exec(), and stringcount is the number of substrings that
3882 were captured by the match, including the substring that matched the
3883 entire regular expression. This is the value returned by pcre_exec() if
3884 it is greater than zero. If pcre_exec() returned zero, indicating that
3885 it ran out of space in ovector, the value passed as stringcount should
3886 be the number of elements in the vector divided by three.
3887
3888 The functions pcre_copy_substring() and pcre_get_substring() extract a
3889 single substring, whose number is given as stringnumber. A value of
3890 zero extracts the substring that matched the entire pattern, whereas
3891 higher values extract the captured substrings. For pcre_copy_sub-
3892 string(), the string is placed in buffer, whose length is given by
3893 buffersize, while for pcre_get_substring() a new block of memory is
3894 obtained via pcre_malloc, and its address is returned via stringptr.
3895 The yield of the function is the length of the string, not including
3896 the terminating zero, or one of these error codes:
3897
3898 PCRE_ERROR_NOMEMORY (-6)
3899
3900 The buffer was too small for pcre_copy_substring(), or the attempt to
3901 get memory failed for pcre_get_substring().
3902
3903 PCRE_ERROR_NOSUBSTRING (-7)
3904
3905 There is no substring whose number is stringnumber.
3906
3907 The pcre_get_substring_list() function extracts all available sub-
3908 strings and builds a list of pointers to them. All this is done in a
3909 single block of memory that is obtained via pcre_malloc. The address of
3910 the memory block is returned via listptr, which is also the start of
3911 the list of string pointers. The end of the list is marked by a NULL
3912 pointer. The yield of the function is zero if all went well, or the
3913 error code
3914
3915 PCRE_ERROR_NOMEMORY (-6)
3916
3917 if the attempt to get the memory block failed.
3918
3919 When any of these functions encounter a substring that is unset, which
3920 can happen when capturing subpattern number n+1 matches some part of
3921 the subject, but subpattern n has not been used at all, they return an
3922 empty string. This can be distinguished from a genuine zero-length sub-
3923 string by inspecting the appropriate offset in ovector, which is nega-
3924 tive for unset substrings.
3925
3926 The two convenience functions pcre_free_substring() and pcre_free_sub-
3927 string_list() can be used to free the memory returned by a previous
3928 call of pcre_get_substring() or pcre_get_substring_list(), respec-
3929 tively. They do nothing more than call the function pointed to by
3930 pcre_free, which of course could be called directly from a C program.
3931 However, PCRE is used in some situations where it is linked via a spe-
3932 cial interface to another programming language that cannot use
3933 pcre_free directly; it is for these cases that the functions are pro-
3934 vided.
3935
3936
3937 EXTRACTING CAPTURED SUBSTRINGS BY NAME
3938
3939 int pcre_get_stringnumber(const pcre *code,
3940 const char *name);
3941
3942 int pcre_copy_named_substring(const pcre *code,
3943 const char *subject, int *ovector,
3944 int stringcount, const char *stringname,
3945 char *buffer, int buffersize);
3946
3947 int pcre_get_named_substring(const pcre *code,
3948 const char *subject, int *ovector,
3949 int stringcount, const char *stringname,
3950 const char **stringptr);
3951
3952 To extract a substring by name, you first have to find associated num-
3953 ber. For example, for this pattern
3954
3955 (a+)b(?<xxx>\d+)...
3956
3957 the number of the subpattern called "xxx" is 2. If the name is known to
3958 be unique (PCRE_DUPNAMES was not set), you can find the number from the
3959 name by calling pcre_get_stringnumber(). The first argument is the com-
3960 piled pattern, and the second is the name. The yield of the function is
3961 the subpattern number, or PCRE_ERROR_NOSUBSTRING (-7) if there is no
3962 subpattern of that name.
3963
3964 Given the number, you can extract the substring directly, or use one of
3965 the functions described in the previous section. For convenience, there
3966 are also two functions that do the whole job.
3967
3968 Most of the arguments of pcre_copy_named_substring() and
3969 pcre_get_named_substring() are the same as those for the similarly
3970 named functions that extract by number. As these are described in the
3971 previous section, they are not re-described here. There are just two
3972 differences:
3973
3974 First, instead of a substring number, a substring name is given. Sec-
3975 ond, there is an extra argument, given at the start, which is a pointer
3976 to the compiled pattern. This is needed in order to gain access to the
3977 name-to-number translation table.
3978
3979 These functions call pcre_get_stringnumber(), and if it succeeds, they
3980 then call pcre_copy_substring() or pcre_get_substring(), as appropri-
3981 ate. NOTE: If PCRE_DUPNAMES is set and there are duplicate names, the
3982 behaviour may not be what you want (see the next section).
3983
3984 Warning: If the pattern uses the (?| feature to set up multiple subpat-
3985 terns with the same number, as described in the section on duplicate
3986 subpattern numbers in the pcrepattern page, you cannot use names to
3987 distinguish the different subpatterns, because names are not included
3988 in the compiled code. The matching process uses only numbers. For this
3989 reason, the use of different names for subpatterns of the same number
3990 causes an error at compile time.
3991
3992
3993 DUPLICATE SUBPATTERN NAMES
3994
3995 int pcre_get_stringtable_entries(const pcre *code,
3996 const char *name, char **first, char **last);
3997
3998 When a pattern is compiled with the PCRE_DUPNAMES option, names for
3999 subpatterns are not required to be unique. (Duplicate names are always
4000 allowed for subpatterns with the same number, created by using the (?|
4001 feature. Indeed, if such subpatterns are named, they are required to
4002 use the same names.)
4003
4004 Normally, patterns with duplicate names are such that in any one match,
4005 only one of the named subpatterns participates. An example is shown in
4006 the pcrepattern documentation.
4007
4008 When duplicates are present, pcre_copy_named_substring() and
4009 pcre_get_named_substring() return the first substring corresponding to
4010 the given name that is set. If none are set, PCRE_ERROR_NOSUBSTRING
4011 (-7) is returned; no data is returned. The pcre_get_stringnumber()
4012 function returns one of the numbers that are associated with the name,
4013 but it is not defined which it is.
4014
4015 If you want to get full details of all captured substrings for a given
4016 name, you must use the pcre_get_stringtable_entries() function. The
4017 first argument is the compiled pattern, and the second is the name. The
4018 third and fourth are pointers to variables which are updated by the
4019 function. After it has run, they point to the first and last entries in
4020 the name-to-number table for the given name. The function itself
4021 returns the length of each entry, or PCRE_ERROR_NOSUBSTRING (-7) if
4022 there are none. The format of the table is described above in the sec-
4023 tion entitled Information about a pattern above. Given all the rele-
4024 vant entries for the name, you can extract each of their numbers, and
4025 hence the captured data, if any.
4026
4027
4028 FINDING ALL POSSIBLE MATCHES
4029
4030 The traditional matching function uses a similar algorithm to Perl,
4031 which stops when it finds the first match, starting at a given point in
4032 the subject. If you want to find all possible matches, or the longest
4033 possible match, consider using the alternative matching function (see
4034 below) instead. If you cannot use the alternative function, but still
4035 need to find all possible matches, you can kludge it up by making use
4036 of the callout facility, which is described in the pcrecallout documen-
4037 tation.
4038
4039 What you have to do is to insert a callout right at the end of the pat-
4040 tern. When your callout function is called, extract and save the cur-
4041 rent matched substring. Then return 1, which forces pcre_exec() to
4042 backtrack and try other alternatives. Ultimately, when it runs out of
4043 matches, pcre_exec() will yield PCRE_ERROR_NOMATCH.
4044
4045
4046 OBTAINING AN ESTIMATE OF STACK USAGE
4047
4048 Matching certain patterns using pcre_exec() can use a lot of process
4049 stack, which in certain environments can be rather limited in size.
4050 Some users find it helpful to have an estimate of the amount of stack
4051 that is used by pcre_exec(), to help them set recursion limits, as
4052 described in the pcrestack documentation. The estimate that is output
4053 by pcretest when called with the -m and -C options is obtained by call-
4054 ing pcre_exec with the values NULL, NULL, NULL, -999, and -999 for its
4055 first five arguments.
4056
4057 Normally, if its first argument is NULL, pcre_exec() immediately
4058 returns the negative error code PCRE_ERROR_NULL, but with this special
4059 combination of arguments, it returns instead a negative number whose
4060 absolute value is the approximate stack frame size in bytes. (A nega-
4061 tive number is used so that it is clear that no match has happened.)
4062 The value is approximate because in some cases, recursive calls to
4063 pcre_exec() occur when there are one or two additional variables on the
4064 stack.
4065
4066 If PCRE has been compiled to use the heap instead of the stack for
4067 recursion, the value returned is the size of each block that is
4068 obtained from the heap.
4069
4070
4071 MATCHING A PATTERN: THE ALTERNATIVE FUNCTION
4072
4073 int pcre_dfa_exec(const pcre *code, const pcre_extra *extra,
4074 const char *subject, int length, int startoffset,
4075 int options, int *ovector, int ovecsize,
4076 int *workspace, int wscount);
4077
4078 The function pcre_dfa_exec() is called to match a subject string
4079 against a compiled pattern, using a matching algorithm that scans the
4080 subject string just once, and does not backtrack. This has different
4081 characteristics to the normal algorithm, and is not compatible with
4082 Perl. Some of the features of PCRE patterns are not supported. Never-
4083 theless, there are times when this kind of matching can be useful. For
4084 a discussion of the two matching algorithms, and a list of features
4085 that pcre_dfa_exec() does not support, see the pcrematching documenta-
4086 tion.
4087
4088 The arguments for the pcre_dfa_exec() function are the same as for
4089 pcre_exec(), plus two extras. The ovector argument is used in a differ-
4090 ent way, and this is described below. The other common arguments are
4091 used in the same way as for pcre_exec(), so their description is not
4092 repeated here.
4093
4094 The two additional arguments provide workspace for the function. The
4095 workspace vector should contain at least 20 elements. It is used for
4096 keeping track of multiple paths through the pattern tree. More
4097 workspace will be needed for patterns and subjects where there are a
4098 lot of potential matches.
4099
4100 Here is an example of a simple call to pcre_dfa_exec():
4101
4102 int rc;
4103 int ovector[10];
4104 int wspace[20];
4105 rc = pcre_dfa_exec(
4106 re, /* result of pcre_compile() */
4107 NULL, /* we didn't study the pattern */
4108 "some string", /* the subject string */
4109 11, /* the length of the subject string */
4110 0, /* start at offset 0 in the subject */
4111 0, /* default options */
4112 ovector, /* vector of integers for substring information */
4113 10, /* number of elements (NOT size in bytes) */
4114 wspace, /* working space vector */
4115 20); /* number of elements (NOT size in bytes) */
4116
4117 Option bits for pcre_dfa_exec()
4118
4119 The unused bits of the options argument for pcre_dfa_exec() must be
4120 zero. The only bits that may be set are PCRE_ANCHORED, PCRE_NEW-
4121 LINE_xxx, PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY,
4122 PCRE_NOTEMPTY_ATSTART, PCRE_NO_UTF8_CHECK, PCRE_BSR_ANYCRLF,
4123 PCRE_BSR_UNICODE, PCRE_NO_START_OPTIMIZE, PCRE_PARTIAL_HARD, PCRE_PAR-
4124 TIAL_SOFT, PCRE_DFA_SHORTEST, and PCRE_DFA_RESTART. All but the last
4125 four of these are exactly the same as for pcre_exec(), so their
4126 description is not repeated here.
4127
4128 PCRE_PARTIAL_HARD
4129 PCRE_PARTIAL_SOFT
4130
4131 These have the same general effect as they do for pcre_exec(), but the
4132 details are slightly different. When PCRE_PARTIAL_HARD is set for
4133 pcre_dfa_exec(), it returns PCRE_ERROR_PARTIAL if the end of the sub-
4134 ject is reached and there is still at least one matching possibility
4135 that requires additional characters. This happens even if some complete
4136 matches have also been found. When PCRE_PARTIAL_SOFT is set, the return
4137 code PCRE_ERROR_NOMATCH is converted into PCRE_ERROR_PARTIAL if the end
4138 of the subject is reached, there have been no complete matches, but
4139 there is still at least one matching possibility. The portion of the
4140 string that was inspected when the longest partial match was found is
4141 set as the first matching string in both cases. There is a more
4142 detailed discussion of partial and multi-segment matching, with exam-
4143 ples, in the pcrepartial documentation.
4144
4145 PCRE_DFA_SHORTEST
4146
4147 Setting the PCRE_DFA_SHORTEST option causes the matching algorithm to
4148 stop as soon as it has found one match. Because of the way the alterna-
4149 tive algorithm works, this is necessarily the shortest possible match
4150 at the first possible matching point in the subject string.
4151
4152 PCRE_DFA_RESTART
4153
4154 When pcre_dfa_exec() returns a partial match, it is possible to call it
4155 again, with additional subject characters, and have it continue with
4156 the same match. The PCRE_DFA_RESTART option requests this action; when
4157 it is set, the workspace and wscount options must reference the same
4158 vector as before because data about the match so far is left in them
4159 after a partial match. There is more discussion of this facility in the
4160 pcrepartial documentation.
4161
4162 Successful returns from pcre_dfa_exec()
4163
4164 When pcre_dfa_exec() succeeds, it may have matched more than one sub-
4165 string in the subject. Note, however, that all the matches from one run
4166 of the function start at the same point in the subject. The shorter
4167 matches are all initial substrings of the longer matches. For example,
4168 if the pattern
4169
4170 <.*>
4171
4172 is matched against the string
4173
4174 This is <something> <something else> <something further> no more
4175
4176 the three matched strings are
4177
4178 <something>
4179 <something> <something else>
4180 <something> <something else> <something further>
4181
4182 On success, the yield of the function is a number greater than zero,
4183 which is the number of matched substrings. The substrings themselves
4184 are returned in ovector. Each string uses two elements; the first is
4185 the offset to the start, and the second is the offset to the end. In
4186 fact, all the strings have the same start offset. (Space could have
4187 been saved by giving this only once, but it was decided to retain some
4188 compatibility with the way pcre_exec() returns data, even though the
4189 meaning of the strings is different.)
4190
4191 The strings are returned in reverse order of length; that is, the long-
4192 est matching string is given first. If there were too many matches to
4193 fit into ovector, the yield of the function is zero, and the vector is
4194 filled with the longest matches. Unlike pcre_exec(), pcre_dfa_exec()
4195 can use the entire ovector for returning matched strings.
4196
4197 NOTE: PCRE's "auto-possessification" optimization usually applies to
4198 character repeats at the end of a pattern (as well as internally). For
4199 example, the pattern "a\d+" is compiled as if it were "a\d++" because
4200 there is no point even considering the possibility of backtracking into
4201 the repeated digits. For DFA matching, this means that only one possi-
4202 ble match is found. If you really do want multiple matches in such
4203 cases, either use an ungreedy repeat ("a\d+?") or set the
4204 PCRE_NO_AUTO_POSSESS option when compiling.
4205
4206 Error returns from pcre_dfa_exec()
4207
4208 The pcre_dfa_exec() function returns a negative number when it fails.
4209 Many of the errors are the same as for pcre_exec(), and these are
4210 described above. There are in addition the following errors that are
4211 specific to pcre_dfa_exec():
4212
4213 PCRE_ERROR_DFA_UITEM (-16)
4214
4215 This return is given if pcre_dfa_exec() encounters an item in the pat-
4216 tern that it does not support, for instance, the use of \C or a back
4217 reference.
4218
4219 PCRE_ERROR_DFA_UCOND (-17)
4220
4221 This return is given if pcre_dfa_exec() encounters a condition item
4222 that uses a back reference for the condition, or a test for recursion
4223 in a specific group. These are not supported.
4224
4225 PCRE_ERROR_DFA_UMLIMIT (-18)
4226
4227 This return is given if pcre_dfa_exec() is called with an extra block
4228 that contains a setting of the match_limit or match_limit_recursion
4229 fields. This is not supported (these fields are meaningless for DFA
4230 matching).
4231
4232 PCRE_ERROR_DFA_WSSIZE (-19)
4233
4234 This return is given if pcre_dfa_exec() runs out of space in the
4235 workspace vector.
4236
4237 PCRE_ERROR_DFA_RECURSE (-20)
4238
4239 When a recursive subpattern is processed, the matching function calls
4240 itself recursively, using private vectors for ovector and workspace.
4241 This error is given if the output vector is not large enough. This
4242 should be extremely rare, as a vector of size 1000 is used.
4243
4244 PCRE_ERROR_DFA_BADRESTART (-30)
4245
4246 When pcre_dfa_exec() is called with the PCRE_DFA_RESTART option, some
4247 plausibility checks are made on the contents of the workspace, which
4248 should contain data about the previous partial match. If any of these
4249 checks fail, this error is given.
4250
4251
4252 SEE ALSO
4253
4254 pcre16(3), pcre32(3), pcrebuild(3), pcrecallout(3), pcrecpp(3)(3),
4255 pcrematching(3), pcrepartial(3), pcreposix(3), pcreprecompile(3), pcre-
4256 sample(3), pcrestack(3).
4257
4258
4259 AUTHOR
4260
4261 Philip Hazel
4262 University Computing Service
4263 Cambridge CB2 3QH, England.
4264
4265
4266 REVISION
4267
4268 Last updated: 09 February 2014
4269 Copyright (c) 1997-2014 University of Cambridge.
4270 ------------------------------------------------------------------------------
4271
4272
4273 PCRECALLOUT(3) Library Functions Manual PCRECALLOUT(3)
4274
4275
4276
4277 NAME
4278 PCRE - Perl-compatible regular expressions
4279
4280 SYNOPSIS
4281
4282 #include <pcre.h>
4283
4284 int (*pcre_callout)(pcre_callout_block *);
4285
4286 int (*pcre16_callout)(pcre16_callout_block *);
4287
4288 int (*pcre32_callout)(pcre32_callout_block *);
4289
4290
4291 DESCRIPTION
4292
4293 PCRE provides a feature called "callout", which is a means of temporar-
4294 ily passing control to the caller of PCRE in the middle of pattern
4295 matching. The caller of PCRE provides an external function by putting
4296 its entry point in the global variable pcre_callout (pcre16_callout for
4297 the 16-bit library, pcre32_callout for the 32-bit library). By default,
4298 this variable contains NULL, which disables all calling out.
4299
4300 Within a regular expression, (?C) indicates the points at which the
4301 external function is to be called. Different callout points can be
4302 identified by putting a number less than 256 after the letter C. The
4303 default value is zero. For example, this pattern has two callout
4304 points:
4305
4306 (?C1)abc(?C2)def
4307
4308 If the PCRE_AUTO_CALLOUT option bit is set when a pattern is compiled,
4309 PCRE automatically inserts callouts, all with number 255, before each
4310 item in the pattern. For example, if PCRE_AUTO_CALLOUT is used with the
4311 pattern
4312
4313 A(\d{2}|--)
4314
4315 it is processed as if it were
4316
4317 (?C255)A(?C255)((?C255)\d{2}(?C255)|(?C255)-(?C255)-(?C255))(?C255)
4318
4319 Notice that there is a callout before and after each parenthesis and
4320 alternation bar. If the pattern contains a conditional group whose con-
4321 dition is an assertion, an automatic callout is inserted immediately
4322 before the condition. Such a callout may also be inserted explicitly,
4323 for example:
4324
4325 (?(?C9)(?=a)ab|de)
4326
4327 This applies only to assertion conditions (because they are themselves
4328 independent groups).
4329
4330 Automatic callouts can be used for tracking the progress of pattern
4331 matching. The pcretest program has a pattern qualifier (/C) that sets
4332 automatic callouts; when it is used, the output indicates how the pat-
4333 tern is being matched. This is useful information when you are trying
4334 to optimize the performance of a particular pattern.
4335
4336
4337 MISSING CALLOUTS
4338
4339 You should be aware that, because of optimizations in the way PCRE com-
4340 piles and matches patterns, callouts sometimes do not happen exactly as
4341 you might expect.
4342
4343 At compile time, PCRE "auto-possessifies" repeated items when it knows
4344 that what follows cannot be part of the repeat. For example, a+[bc] is
4345 compiled as if it were a++[bc]. The pcretest output when this pattern
4346 is anchored and then applied with automatic callouts to the string
4347 "aaaa" is:
4348
4349 --->aaaa
4350 +0 ^ ^
4351 +1 ^ a+
4352 +3 ^ ^ [bc]
4353 No match
4354
4355 This indicates that when matching [bc] fails, there is no backtracking
4356 into a+ and therefore the callouts that would be taken for the back-
4357 tracks do not occur. You can disable the auto-possessify feature by
4358 passing PCRE_NO_AUTO_POSSESS to pcre_compile(), or starting the pattern
4359 with (*NO_AUTO_POSSESS). If this is done in pcretest (using the /O
4360 qualifier), the output changes to this:
4361
4362 --->aaaa
4363 +0 ^ ^
4364 +1 ^ a+
4365 +3 ^ ^ [bc]
4366 +3 ^ ^ [bc]
4367 +3 ^ ^ [bc]
4368 +3 ^^ [bc]
4369 No match
4370
4371 This time, when matching [bc] fails, the matcher backtracks into a+ and
4372 tries again, repeatedly, until a+ itself fails.
4373
4374 Other optimizations that provide fast "no match" results also affect
4375 callouts. For example, if the pattern is
4376
4377 ab(?C4)cd
4378
4379 PCRE knows that any matching string must contain the letter "d". If the
4380 subject string is "abyz", the lack of "d" means that matching doesn't
4381 ever start, and the callout is never reached. However, with "abyd",
4382 though the result is still no match, the callout is obeyed.
4383
4384 If the pattern is studied, PCRE knows the minimum length of a matching
4385 string, and will immediately give a "no match" return without actually
4386 running a match if the subject is not long enough, or, for unanchored
4387 patterns, if it has been scanned far enough.
4388
4389 You can disable these optimizations by passing the PCRE_NO_START_OPTI-
4390 MIZE option to the matching function, or by starting the pattern with
4391 (*NO_START_OPT). This slows down the matching process, but does ensure
4392 that callouts such as the example above are obeyed.
4393
4394
4395 THE CALLOUT INTERFACE
4396
4397 During matching, when PCRE reaches a callout point, the external func-
4398 tion defined by pcre_callout or pcre[16|32]_callout is called (if it is
4399 set). This applies to both normal and DFA matching. The only argument
4400 to the callout function is a pointer to a pcre_callout or
4401 pcre[16|32]_callout block. These structures contains the following
4402 fields:
4403
4404 int version;
4405 int callout_number;
4406 int *offset_vector;
4407 const char *subject; (8-bit version)
4408 PCRE_SPTR16 subject; (16-bit version)
4409 PCRE_SPTR32 subject; (32-bit version)
4410 int subject_length;
4411 int start_match;
4412 int current_position;
4413 int capture_top;
4414 int capture_last;
4415 void *callout_data;
4416 int pattern_position;
4417 int next_item_length;
4418 const unsigned char *mark; (8-bit version)
4419 const PCRE_UCHAR16 *mark; (16-bit version)
4420 const PCRE_UCHAR32 *mark; (32-bit version)
4421
4422 The version field is an integer containing the version number of the
4423 block format. The initial version was 0; the current version is 2. The
4424 version number will change again in future if additional fields are
4425 added, but the intention is never to remove any of the existing fields.
4426
4427 The callout_number field contains the number of the callout, as com-
4428 piled into the pattern (that is, the number after ?C for manual call-
4429 outs, and 255 for automatically generated callouts).
4430
4431 The offset_vector field is a pointer to the vector of offsets that was
4432 passed by the caller to the matching function. When pcre_exec() or
4433 pcre[16|32]_exec() is used, the contents can be inspected, in order to
4434 extract substrings that have been matched so far, in the same way as
4435 for extracting substrings after a match has completed. For the DFA
4436 matching functions, this field is not useful.
4437
4438 The subject and subject_length fields contain copies of the values that
4439 were passed to the matching function.
4440
4441 The start_match field normally contains the offset within the subject
4442 at which the current match attempt started. However, if the escape
4443 sequence \K has been encountered, this value is changed to reflect the
4444 modified starting point. If the pattern is not anchored, the callout
4445 function may be called several times from the same point in the pattern
4446 for different starting points in the subject.
4447
4448 The current_position field contains the offset within the subject of
4449 the current match pointer.
4450
4451 When the pcre_exec() or pcre[16|32]_exec() is used, the capture_top
4452 field contains one more than the number of the highest numbered cap-
4453 tured substring so far. If no substrings have been captured, the value
4454 of capture_top is one. This is always the case when the DFA functions
4455 are used, because they do not support captured substrings.
4456
4457 The capture_last field contains the number of the most recently cap-
4458 tured substring. However, when a recursion exits, the value reverts to
4459 what it was outside the recursion, as do the values of all captured
4460 substrings. If no substrings have been captured, the value of cap-
4461 ture_last is -1. This is always the case for the DFA matching func-
4462 tions.
4463
4464 The callout_data field contains a value that is passed to a matching
4465 function specifically so that it can be passed back in callouts. It is
4466 passed in the callout_data field of a pcre_extra or pcre[16|32]_extra
4467 data structure. If no such data was passed, the value of callout_data
4468 in a callout block is NULL. There is a description of the pcre_extra
4469 structure in the pcreapi documentation.
4470
4471 The pattern_position field is present from version 1 of the callout
4472 structure. It contains the offset to the next item to be matched in the
4473 pattern string.
4474
4475 The next_item_length field is present from version 1 of the callout
4476 structure. It contains the length of the next item to be matched in the
4477 pattern string. When the callout immediately precedes an alternation
4478 bar, a closing parenthesis, or the end of the pattern, the length is
4479 zero. When the callout precedes an opening parenthesis, the length is
4480 that of the entire subpattern.
4481
4482 The pattern_position and next_item_length fields are intended to help
4483 in distinguishing between different automatic callouts, which all have
4484 the same callout number. However, they are set for all callouts.
4485
4486 The mark field is present from version 2 of the callout structure. In
4487 callouts from pcre_exec() or pcre[16|32]_exec() it contains a pointer
4488 to the zero-terminated name of the most recently passed (*MARK),
4489 (*PRUNE), or (*THEN) item in the match, or NULL if no such items have
4490 been passed. Instances of (*PRUNE) or (*THEN) without a name do not
4491 obliterate a previous (*MARK). In callouts from the DFA matching func-
4492 tions this field always contains NULL.
4493
4494
4495 RETURN VALUES
4496
4497 The external callout function returns an integer to PCRE. If the value
4498 is zero, matching proceeds as normal. If the value is greater than
4499 zero, matching fails at the current point, but the testing of other
4500 matching possibilities goes ahead, just as if a lookahead assertion had
4501 failed. If the value is less than zero, the match is abandoned, the
4502 matching function returns the negative value.
4503
4504 Negative values should normally be chosen from the set of
4505 PCRE_ERROR_xxx values. In particular, PCRE_ERROR_NOMATCH forces a stan-
4506 dard "no match" failure. The error number PCRE_ERROR_CALLOUT is
4507 reserved for use by callout functions; it will never be used by PCRE
4508 itself.
4509
4510
4511 AUTHOR
4512
4513 Philip Hazel
4514 University Computing Service
4515 Cambridge CB2 3QH, England.
4516
4517
4518 REVISION
4519
4520 Last updated: 12 November 2013
4521 Copyright (c) 1997-2013 University of Cambridge.
4522 ------------------------------------------------------------------------------
4523
4524
4525 PCRECOMPAT(3) Library Functions Manual PCRECOMPAT(3)
4526
4527
4528
4529 NAME
4530 PCRE - Perl-compatible regular expressions
4531
4532 DIFFERENCES BETWEEN PCRE AND PERL
4533
4534 This document describes the differences in the ways that PCRE and Perl
4535 handle regular expressions. The differences described here are with
4536 respect to Perl versions 5.10 and above.
4537
4538 1. PCRE has only a subset of Perl's Unicode support. Details of what it
4539 does have are given in the pcreunicode page.
4540
4541 2. PCRE allows repeat quantifiers only on parenthesized assertions, but
4542 they do not mean what you might think. For example, (?!a){3} does not
4543 assert that the next three characters are not "a". It just asserts that
4544 the next character is not "a" three times (in principle: PCRE optimizes
4545 this to run the assertion just once). Perl allows repeat quantifiers on
4546 other assertions such as \b, but these do not seem to have any use.
4547
4548 3. Capturing subpatterns that occur inside negative lookahead asser-
4549 tions are counted, but their entries in the offsets vector are never
4550 set. Perl sometimes (but not always) sets its numerical variables from
4551 inside negative assertions.
4552
4553 4. Though binary zero characters are supported in the subject string,
4554 they are not allowed in a pattern string because it is passed as a nor-
4555 mal C string, terminated by zero. The escape sequence \0 can be used in
4556 the pattern to represent a binary zero.
4557
4558 5. The following Perl escape sequences are not supported: \l, \u, \L,
4559 \U, and \N when followed by a character name or Unicode value. (\N on
4560 its own, matching a non-newline character, is supported.) In fact these
4561 are implemented by Perl's general string-handling and are not part of
4562 its pattern matching engine. If any of these are encountered by PCRE,
4563 an error is generated by default. However, if the PCRE_JAVASCRIPT_COM-
4564 PAT option is set, \U and \u are interpreted as JavaScript interprets
4565 them.
4566
4567 6. The Perl escape sequences \p, \P, and \X are supported only if PCRE
4568 is built with Unicode character property support. The properties that
4569 can be tested with \p and \P are limited to the general category prop-
4570 erties such as Lu and Nd, script names such as Greek or Han, and the
4571 derived properties Any and L&. PCRE does support the Cs (surrogate)
4572 property, which Perl does not; the Perl documentation says "Because
4573 Perl hides the need for the user to understand the internal representa-
4574 tion of Unicode characters, there is no need to implement the somewhat
4575 messy concept of surrogates."
4576
4577 7. PCRE does support the \Q...\E escape for quoting substrings. Charac-
4578 ters in between are treated as literals. This is slightly different
4579 from Perl in that $ and @ are also handled as literals inside the
4580 quotes. In Perl, they cause variable interpolation (but of course PCRE
4581 does not have variables). Note the following examples:
4582
4583 Pattern PCRE matches Perl matches
4584
4585 \Qabc$xyz\E abc$xyz abc followed by the
4586 contents of $xyz
4587 \Qabc\$xyz\E abc\$xyz abc\$xyz
4588 \Qabc\E\$\Qxyz\E abc$xyz abc$xyz
4589
4590 The \Q...\E sequence is recognized both inside and outside character
4591 classes.
4592
4593 8. Fairly obviously, PCRE does not support the (?{code}) and (??{code})
4594 constructions. However, there is support for recursive patterns. This
4595 is not available in Perl 5.8, but it is in Perl 5.10. Also, the PCRE
4596 "callout" feature allows an external function to be called during pat-
4597 tern matching. See the pcrecallout documentation for details.
4598
4599 9. Subpatterns that are called as subroutines (whether or not recur-
4600 sively) are always treated as atomic groups in PCRE. This is like
4601 Python, but unlike Perl. Captured values that are set outside a sub-
4602 routine call can be reference from inside in PCRE, but not in Perl.
4603 There is a discussion that explains these differences in more detail in
4604 the section on recursion differences from Perl in the pcrepattern page.
4605
4606 10. If any of the backtracking control verbs are used in a subpattern
4607 that is called as a subroutine (whether or not recursively), their
4608 effect is confined to that subpattern; it does not extend to the sur-
4609 rounding pattern. This is not always the case in Perl. In particular,
4610 if (*THEN) is present in a group that is called as a subroutine, its
4611 action is limited to that group, even if the group does not contain any
4612 | characters. Note that such subpatterns are processed as anchored at
4613 the point where they are tested.
4614
4615 11. If a pattern contains more than one backtracking control verb, the
4616 first one that is backtracked onto acts. For example, in the pattern
4617 A(*COMMIT)B(*PRUNE)C a failure in B triggers (*COMMIT), but a failure
4618 in C triggers (*PRUNE). Perl's behaviour is more complex; in many cases
4619 it is the same as PCRE, but there are examples where it differs.
4620
4621 12. Most backtracking verbs in assertions have their normal actions.
4622 They are not confined to the assertion.
4623
4624 13. There are some differences that are concerned with the settings of
4625 captured strings when part of a pattern is repeated. For example,
4626 matching "aba" against the pattern /^(a(b)?)+$/ in Perl leaves $2
4627 unset, but in PCRE it is set to "b".
4628
4629 14. PCRE's handling of duplicate subpattern numbers and duplicate sub-
4630 pattern names is not as general as Perl's. This is a consequence of the
4631 fact the PCRE works internally just with numbers, using an external ta-
4632 ble to translate between numbers and names. In particular, a pattern
4633 such as (?|(?<a>A)|(?<b)B), where the two capturing parentheses have
4634 the same number but different names, is not supported, and causes an
4635 error at compile time. If it were allowed, it would not be possible to
4636 distinguish which parentheses matched, because both names map to cap-
4637 turing subpattern number 1. To avoid this confusing situation, an error
4638 is given at compile time.
4639
4640 15. Perl recognizes comments in some places that PCRE does not, for
4641 example, between the ( and ? at the start of a subpattern. If the /x
4642 modifier is set, Perl allows white space between ( and ? (though cur-
4643 rent Perls warn that this is deprecated) but PCRE never does, even if
4644 the PCRE_EXTENDED option is set.
4645
4646 16. Perl, when in warning mode, gives warnings for character classes
4647 such as [A-\d] or [a-[:digit:]]. It then treats the hyphens as liter-
4648 als. PCRE has no warning features, so it gives an error in these cases
4649 because they are almost certainly user mistakes.
4650
4651 17. In PCRE, the upper/lower case character properties Lu and Ll are
4652 not affected when case-independent matching is specified. For example,
4653 \p{Lu} always matches an upper case letter. I think Perl has changed in
4654 this respect; in the release at the time of writing (5.16), \p{Lu} and
4655 \p{Ll} match all letters, regardless of case, when case independence is
4656 specified.
4657
4658 18. PCRE provides some extensions to the Perl regular expression facil-
4659 ities. Perl 5.10 includes new features that are not in earlier ver-
4660 sions of Perl, some of which (such as named parentheses) have been in
4661 PCRE for some time. This list is with respect to Perl 5.10:
4662
4663 (a) Although lookbehind assertions in PCRE must match fixed length
4664 strings, each alternative branch of a lookbehind assertion can match a
4665 different length of string. Perl requires them all to have the same
4666 length.
4667
4668 (b) If PCRE_DOLLAR_ENDONLY is set and PCRE_MULTILINE is not set, the $
4669 meta-character matches only at the very end of the string.
4670
4671 (c) If PCRE_EXTRA is set, a backslash followed by a letter with no spe-
4672 cial meaning is faulted. Otherwise, like Perl, the backslash is quietly
4673 ignored. (Perl can be made to issue a warning.)
4674
4675 (d) If PCRE_UNGREEDY is set, the greediness of the repetition quanti-
4676 fiers is inverted, that is, by default they are not greedy, but if fol-
4677 lowed by a question mark they are.
4678
4679 (e) PCRE_ANCHORED can be used at matching time to force a pattern to be
4680 tried only at the first matching position in the subject string.
4681
4682 (f) The PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, PCRE_NOTEMPTY_ATSTART,
4683 and PCRE_NO_AUTO_CAPTURE options for pcre_exec() have no Perl equiva-
4684 lents.
4685
4686 (g) The \R escape sequence can be restricted to match only CR, LF, or
4687 CRLF by the PCRE_BSR_ANYCRLF option.
4688
4689 (h) The callout facility is PCRE-specific.
4690
4691 (i) The partial matching facility is PCRE-specific.
4692
4693 (j) Patterns compiled by PCRE can be saved and re-used at a later time,
4694 even on different hosts that have the other endianness. However, this
4695 does not apply to optimized data created by the just-in-time compiler.
4696
4697 (k) The alternative matching functions (pcre_dfa_exec(),
4698 pcre16_dfa_exec() and pcre32_dfa_exec(),) match in a different way and
4699 are not Perl-compatible.
4700
4701 (l) PCRE recognizes some special sequences such as (*CR) at the start
4702 of a pattern that set overall options that cannot be changed within the
4703 pattern.
4704
4705
4706 AUTHOR
4707
4708 Philip Hazel
4709 University Computing Service
4710 Cambridge CB2 3QH, England.
4711
4712
4713 REVISION
4714
4715 Last updated: 10 November 2013
4716 Copyright (c) 1997-2013 University of Cambridge.
4717 ------------------------------------------------------------------------------
4718
4719
4720 PCREPATTERN(3) Library Functions Manual PCREPATTERN(3)
4721
4722
4723
4724 NAME
4725 PCRE - Perl-compatible regular expressions
4726
4727 PCRE REGULAR EXPRESSION DETAILS
4728
4729 The syntax and semantics of the regular expressions that are supported
4730 by PCRE are described in detail below. There is a quick-reference syn-
4731 tax summary in the pcresyntax page. PCRE tries to match Perl syntax and
4732 semantics as closely as it can. PCRE also supports some alternative
4733 regular expression syntax (which does not conflict with the Perl syn-
4734 tax) in order to provide some compatibility with regular expressions in
4735 Python, .NET, and Oniguruma.
4736
4737 Perl's regular expressions are described in its own documentation, and
4738 regular expressions in general are covered in a number of books, some
4739 of which have copious examples. Jeffrey Friedl's "Mastering Regular
4740 Expressions", published by O'Reilly, covers regular expressions in
4741 great detail. This description of PCRE's regular expressions is
4742 intended as reference material.
4743
4744 This document discusses the patterns that are supported by PCRE when
4745 one its main matching functions, pcre_exec() (8-bit) or
4746 pcre[16|32]_exec() (16- or 32-bit), is used. PCRE also has alternative
4747 matching functions, pcre_dfa_exec() and pcre[16|32_dfa_exec(), which
4748 match using a different algorithm that is not Perl-compatible. Some of
4749 the features discussed below are not available when DFA matching is
4750 used. The advantages and disadvantages of the alternative functions,
4751 and how they differ from the normal functions, are discussed in the
4752 pcrematching page.
4753
4754
4755 SPECIAL START-OF-PATTERN ITEMS
4756
4757 A number of options that can be passed to pcre_compile() can also be
4758 set by special items at the start of a pattern. These are not Perl-com-
4759 patible, but are provided to make these options accessible to pattern
4760 writers who are not able to change the program that processes the pat-
4761 tern. Any number of these items may appear, but they must all be
4762 together right at the start of the pattern string, and the letters must
4763 be in upper case.
4764
4765 UTF support
4766
4767 The original operation of PCRE was on strings of one-byte characters.
4768 However, there is now also support for UTF-8 strings in the original
4769 library, an extra library that supports 16-bit and UTF-16 character
4770 strings, and a third library that supports 32-bit and UTF-32 character
4771 strings. To use these features, PCRE must be built to include appropri-
4772 ate support. When using UTF strings you must either call the compiling
4773 function with the PCRE_UTF8, PCRE_UTF16, or PCRE_UTF32 option, or the
4774 pattern must start with one of these special sequences:
4775
4776 (*UTF8)
4777 (*UTF16)
4778 (*UTF32)
4779 (*UTF)
4780
4781 (*UTF) is a generic sequence that can be used with any of the
4782 libraries. Starting a pattern with such a sequence is equivalent to
4783 setting the relevant option. How setting a UTF mode affects pattern
4784 matching is mentioned in several places below. There is also a summary
4785 of features in the pcreunicode page.
4786
4787 Some applications that allow their users to supply patterns may wish to
4788 restrict them to non-UTF data for security reasons. If the
4789 PCRE_NEVER_UTF option is set at compile time, (*UTF) etc. are not
4790 allowed, and their appearance causes an error.
4791
4792 Unicode property support
4793
4794 Another special sequence that may appear at the start of a pattern is
4795 (*UCP). This has the same effect as setting the PCRE_UCP option: it
4796 causes sequences such as \d and \w to use Unicode properties to deter-
4797 mine character types, instead of recognizing only characters with codes
4798 less than 128 via a lookup table.
4799
4800 Disabling auto-possessification
4801
4802 If a pattern starts with (*NO_AUTO_POSSESS), it has the same effect as
4803 setting the PCRE_NO_AUTO_POSSESS option at compile time. This stops
4804 PCRE from making quantifiers possessive when what follows cannot match
4805 the repeated item. For example, by default a+b is treated as a++b. For
4806 more details, see the pcreapi documentation.
4807
4808 Disabling start-up optimizations
4809
4810 If a pattern starts with (*NO_START_OPT), it has the same effect as
4811 setting the PCRE_NO_START_OPTIMIZE option either at compile or matching
4812 time. This disables several optimizations for quickly reaching "no
4813 match" results. For more details, see the pcreapi documentation.
4814
4815 Newline conventions
4816
4817 PCRE supports five different conventions for indicating line breaks in
4818 strings: a single CR (carriage return) character, a single LF (line-
4819 feed) character, the two-character sequence CRLF, any of the three pre-
4820 ceding, or any Unicode newline sequence. The pcreapi page has further
4821 discussion about newlines, and shows how to set the newline convention
4822 in the options arguments for the compiling and matching functions.
4823
4824 It is also possible to specify a newline convention by starting a pat-
4825 tern string with one of the following five sequences:
4826
4827 (*CR) carriage return
4828 (*LF) linefeed
4829 (*CRLF) carriage return, followed by linefeed
4830 (*ANYCRLF) any of the three above
4831 (*ANY) all Unicode newline sequences
4832
4833 These override the default and the options given to the compiling func-
4834 tion. For example, on a Unix system where LF is the default newline
4835 sequence, the pattern
4836
4837 (*CR)a.b
4838
4839 changes the convention to CR. That pattern matches "a\nb" because LF is
4840 no longer a newline. If more than one of these settings is present, the
4841 last one is used.
4842
4843 The newline convention affects where the circumflex and dollar asser-
4844 tions are true. It also affects the interpretation of the dot metachar-
4845 acter when PCRE_DOTALL is not set, and the behaviour of \N. However, it
4846 does not affect what the \R escape sequence matches. By default, this
4847 is any Unicode newline sequence, for Perl compatibility. However, this
4848 can be changed; see the description of \R in the section entitled "New-
4849 line sequences" below. A change of \R setting can be combined with a
4850 change of newline convention.
4851
4852 Setting match and recursion limits
4853
4854 The caller of pcre_exec() can set a limit on the number of times the
4855 internal match() function is called and on the maximum depth of recur-
4856 sive calls. These facilities are provided to catch runaway matches that
4857 are provoked by patterns with huge matching trees (a typical example is
4858 a pattern with nested unlimited repeats) and to avoid running out of
4859 system stack by too much recursion. When one of these limits is
4860 reached, pcre_exec() gives an error return. The limits can also be set
4861 by items at the start of the pattern of the form
4862
4863 (*LIMIT_MATCH=d)
4864 (*LIMIT_RECURSION=d)
4865
4866 where d is any number of decimal digits. However, the value of the set-
4867 ting must be less than the value set (or defaulted) by the caller of
4868 pcre_exec() for it to have any effect. In other words, the pattern
4869 writer can lower the limits set by the programmer, but not raise them.
4870 If there is more than one setting of one of these limits, the lower
4871 value is used.
4872
4873
4874 EBCDIC CHARACTER CODES
4875
4876 PCRE can be compiled to run in an environment that uses EBCDIC as its
4877 character code rather than ASCII or Unicode (typically a mainframe sys-
4878 tem). In the sections below, character code values are ASCII or Uni-
4879 code; in an EBCDIC environment these characters may have different code
4880 values, and there are no code points greater than 255.
4881
4882
4883 CHARACTERS AND METACHARACTERS
4884
4885 A regular expression is a pattern that is matched against a subject
4886 string from left to right. Most characters stand for themselves in a
4887 pattern, and match the corresponding characters in the subject. As a
4888 trivial example, the pattern
4889
4890 The quick brown fox
4891
4892 matches a portion of a subject string that is identical to itself. When
4893 caseless matching is specified (the PCRE_CASELESS option), letters are
4894 matched independently of case. In a UTF mode, PCRE always understands
4895 the concept of case for characters whose values are less than 128, so
4896 caseless matching is always possible. For characters with higher val-
4897 ues, the concept of case is supported if PCRE is compiled with Unicode
4898 property support, but not otherwise. If you want to use caseless
4899 matching for characters 128 and above, you must ensure that PCRE is
4900 compiled with Unicode property support as well as with UTF support.
4901
4902 The power of regular expressions comes from the ability to include
4903 alternatives and repetitions in the pattern. These are encoded in the
4904 pattern by the use of metacharacters, which do not stand for themselves
4905 but instead are interpreted in some special way.
4906
4907 There are two different sets of metacharacters: those that are recog-
4908 nized anywhere in the pattern except within square brackets, and those
4909 that are recognized within square brackets. Outside square brackets,
4910 the metacharacters are as follows:
4911
4912 \ general escape character with several uses
4913 ^ assert start of string (or line, in multiline mode)
4914 $ assert end of string (or line, in multiline mode)
4915 . match any character except newline (by default)
4916 [ start character class definition
4917 | start of alternative branch
4918 ( start subpattern
4919 ) end subpattern
4920 ? extends the meaning of (
4921 also 0 or 1 quantifier
4922 also quantifier minimizer
4923 * 0 or more quantifier
4924 + 1 or more quantifier
4925 also "possessive quantifier"
4926 { start min/max quantifier
4927
4928 Part of a pattern that is in square brackets is called a "character
4929 class". In a character class the only metacharacters are:
4930
4931 \ general escape character
4932 ^ negate the class, but only if the first character
4933 - indicates character range
4934 [ POSIX character class (only if followed by POSIX
4935 syntax)
4936 ] terminates the character class
4937
4938 The following sections describe the use of each of the metacharacters.
4939
4940
4941 BACKSLASH
4942
4943 The backslash character has several uses. Firstly, if it is followed by
4944 a character that is not a number or a letter, it takes away any special
4945 meaning that character may have. This use of backslash as an escape
4946 character applies both inside and outside character classes.
4947
4948 For example, if you want to match a * character, you write \* in the
4949 pattern. This escaping action applies whether or not the following
4950 character would otherwise be interpreted as a metacharacter, so it is
4951 always safe to precede a non-alphanumeric with backslash to specify
4952 that it stands for itself. In particular, if you want to match a back-
4953 slash, you write \\.
4954
4955 In a UTF mode, only ASCII numbers and letters have any special meaning
4956 after a backslash. All other characters (in particular, those whose
4957 codepoints are greater than 127) are treated as literals.
4958
4959 If a pattern is compiled with the PCRE_EXTENDED option, most white
4960 space in the pattern (other than in a character class), and characters
4961 between a # outside a character class and the next newline, inclusive,
4962 are ignored. An escaping backslash can be used to include a white space
4963 or # character as part of the pattern.
4964
4965 If you want to remove the special meaning from a sequence of charac-
4966 ters, you can do so by putting them between \Q and \E. This is differ-
4967 ent from Perl in that $ and @ are handled as literals in \Q...\E
4968 sequences in PCRE, whereas in Perl, $ and @ cause variable interpola-
4969 tion. Note the following examples:
4970
4971 Pattern PCRE matches Perl matches
4972
4973 \Qabc$xyz\E abc$xyz abc followed by the
4974 contents of $xyz
4975 \Qabc\$xyz\E abc\$xyz abc\$xyz
4976 \Qabc\E\$\Qxyz\E abc$xyz abc$xyz
4977
4978 The \Q...\E sequence is recognized both inside and outside character
4979 classes. An isolated \E that is not preceded by \Q is ignored. If \Q
4980 is not followed by \E later in the pattern, the literal interpretation
4981 continues to the end of the pattern (that is, \E is assumed at the
4982 end). If the isolated \Q is inside a character class, this causes an
4983 error, because the character class is not terminated.
4984
4985 Non-printing characters
4986
4987 A second use of backslash provides a way of encoding non-printing char-
4988 acters in patterns in a visible manner. There is no restriction on the
4989 appearance of non-printing characters, apart from the binary zero that
4990 terminates a pattern, but when a pattern is being prepared by text
4991 editing, it is often easier to use one of the following escape
4992 sequences than the binary character it represents:
4993
4994 \a alarm, that is, the BEL character (hex 07)
4995 \cx "control-x", where x is any ASCII character
4996 \e escape (hex 1B)
4997 \f form feed (hex 0C)
4998 \n linefeed (hex 0A)
4999 \r carriage return (hex 0D)
5000 \t tab (hex 09)
5001 \0dd character with octal code 0dd
5002 \ddd character with octal code ddd, or back reference
5003 \o{ddd..} character with octal code ddd..
5004 \xhh character with hex code hh
5005 \x{hhh..} character with hex code hhh.. (non-JavaScript mode)
5006 \uhhhh character with hex code hhhh (JavaScript mode only)
5007
5008 The precise effect of \cx on ASCII characters is as follows: if x is a
5009 lower case letter, it is converted to upper case. Then bit 6 of the
5010 character (hex 40) is inverted. Thus \cA to \cZ become hex 01 to hex 1A
5011 (A is 41, Z is 5A), but \c{ becomes hex 3B ({ is 7B), and \c; becomes
5012 hex 7B (; is 3B). If the data item (byte or 16-bit value) following \c
5013 has a value greater than 127, a compile-time error occurs. This locks
5014 out non-ASCII characters in all modes.
5015
5016 The \c facility was designed for use with ASCII characters, but with
5017 the extension to Unicode it is even less useful than it once was. It
5018 is, however, recognized when PCRE is compiled in EBCDIC mode, where
5019 data items are always bytes. In this mode, all values are valid after
5020 \c. If the next character is a lower case letter, it is converted to
5021 upper case. Then the 0xc0 bits of the byte are inverted. Thus \cA
5022 becomes hex 01, as in ASCII (A is C1), but because the EBCDIC letters
5023 are disjoint, \cZ becomes hex 29 (Z is E9), and other characters also
5024 generate different values.
5025
5026 After \0 up to two further octal digits are read. If there are fewer
5027 than two digits, just those that are present are used. Thus the
5028 sequence \0\x\07 specifies two binary zeros followed by a BEL character
5029 (code value 7). Make sure you supply two digits after the initial zero
5030 if the pattern character that follows is itself an octal digit.
5031
5032 The escape \o must be followed by a sequence of octal digits, enclosed
5033 in braces. An error occurs if this is not the case. This escape is a
5034 recent addition to Perl; it provides way of specifying character code
5035 points as octal numbers greater than 0777, and it also allows octal
5036 numbers and back references to be unambiguously specified.
5037
5038 For greater clarity and unambiguity, it is best to avoid following \ by
5039 a digit greater than zero. Instead, use \o{} or \x{} to specify charac-
5040 ter numbers, and \g{} to specify back references. The following para-
5041 graphs describe the old, ambiguous syntax.
5042
5043 The handling of a backslash followed by a digit other than 0 is compli-
5044 cated, and Perl has changed in recent releases, causing PCRE also to
5045 change. Outside a character class, PCRE reads the digit and any follow-
5046 ing digits as a decimal number. If the number is less than 8, or if
5047 there have been at least that many previous capturing left parentheses
5048 in the expression, the entire sequence is taken as a back reference. A
5049 description of how this works is given later, following the discussion
5050 of parenthesized subpatterns.
5051
5052 Inside a character class, or if the decimal number following \ is
5053 greater than 7 and there have not been that many capturing subpatterns,
5054 PCRE handles \8 and \9 as the literal characters "8" and "9", and oth-
5055 erwise re-reads up to three octal digits following the backslash, using
5056 them to generate a data character. Any subsequent digits stand for
5057 themselves. For example:
5058
5059 \040 is another way of writing an ASCII space
5060 \40 is the same, provided there are fewer than 40
5061 previous capturing subpatterns
5062 \7 is always a back reference
5063 \11 might be a back reference, or another way of
5064 writing a tab
5065 \011 is always a tab
5066 \0113 is a tab followed by the character "3"
5067 \113 might be a back reference, otherwise the
5068 character with octal code 113
5069 \377 might be a back reference, otherwise
5070 the value 255 (decimal)
5071 \81 is either a back reference, or the two
5072 characters "8" and "1"
5073
5074 Note that octal values of 100 or greater that are specified using this
5075 syntax must not be introduced by a leading zero, because no more than
5076 three octal digits are ever read.
5077
5078 By default, after \x that is not followed by {, from zero to two hexa-
5079 decimal digits are read (letters can be in upper or lower case). Any
5080 number of hexadecimal digits may appear between \x{ and }. If a charac-
5081 ter other than a hexadecimal digit appears between \x{ and }, or if
5082 there is no terminating }, an error occurs.
5083
5084 If the PCRE_JAVASCRIPT_COMPAT option is set, the interpretation of \x
5085 is as just described only when it is followed by two hexadecimal dig-
5086 its. Otherwise, it matches a literal "x" character. In JavaScript
5087 mode, support for code points greater than 256 is provided by \u, which
5088 must be followed by four hexadecimal digits; otherwise it matches a
5089 literal "u" character.
5090
5091 Characters whose value is less than 256 can be defined by either of the
5092 two syntaxes for \x (or by \u in JavaScript mode). There is no differ-
5093 ence in the way they are handled. For example, \xdc is exactly the same
5094 as \x{dc} (or \u00dc in JavaScript mode).
5095
5096 Constraints on character values
5097
5098 Characters that are specified using octal or hexadecimal numbers are
5099 limited to certain values, as follows:
5100
5101 8-bit non-UTF mode less than 0x100
5102 8-bit UTF-8 mode less than 0x10ffff and a valid codepoint
5103 16-bit non-UTF mode less than 0x10000
5104 16-bit UTF-16 mode less than 0x10ffff and a valid codepoint
5105 32-bit non-UTF mode less than 0x100000000
5106 32-bit UTF-32 mode less than 0x10ffff and a valid codepoint
5107
5108 Invalid Unicode codepoints are the range 0xd800 to 0xdfff (the so-
5109 called "surrogate" codepoints), and 0xffef.
5110
5111 Escape sequences in character classes
5112
5113 All the sequences that define a single character value can be used both
5114 inside and outside character classes. In addition, inside a character
5115 class, \b is interpreted as the backspace character (hex 08).
5116
5117 \N is not allowed in a character class. \B, \R, and \X are not special
5118 inside a character class. Like other unrecognized escape sequences,
5119 they are treated as the literal characters "B", "R", and "X" by
5120 default, but cause an error if the PCRE_EXTRA option is set. Outside a
5121 character class, these sequences have different meanings.
5122
5123 Unsupported escape sequences
5124
5125 In Perl, the sequences \l, \L, \u, and \U are recognized by its string
5126 handler and used to modify the case of following characters. By
5127 default, PCRE does not support these escape sequences. However, if the
5128 PCRE_JAVASCRIPT_COMPAT option is set, \U matches a "U" character, and
5129 \u can be used to define a character by code point, as described in the
5130 previous section.
5131
5132 Absolute and relative back references
5133
5134 The sequence \g followed by an unsigned or a negative number, option-
5135 ally enclosed in braces, is an absolute or relative back reference. A
5136 named back reference can be coded as \g{name}. Back references are dis-
5137 cussed later, following the discussion of parenthesized subpatterns.
5138
5139 Absolute and relative subroutine calls
5140
5141 For compatibility with Oniguruma, the non-Perl syntax \g followed by a
5142 name or a number enclosed either in angle brackets or single quotes, is
5143 an alternative syntax for referencing a subpattern as a "subroutine".
5144 Details are discussed later. Note that \g{...} (Perl syntax) and
5145 \g<...> (Oniguruma syntax) are not synonymous. The former is a back
5146 reference; the latter is a subroutine call.
5147
5148 Generic character types
5149
5150 Another use of backslash is for specifying generic character types:
5151
5152 \d any decimal digit
5153 \D any character that is not a decimal digit
5154 \h any horizontal white space character
5155 \H any character that is not a horizontal white space character
5156 \s any white space character
5157 \S any character that is not a white space character
5158 \v any vertical white space character
5159 \V any character that is not a vertical white space character
5160 \w any "word" character
5161 \W any "non-word" character
5162
5163 There is also the single sequence \N, which matches a non-newline char-
5164 acter. This is the same as the "." metacharacter when PCRE_DOTALL is
5165 not set. Perl also uses \N to match characters by name; PCRE does not
5166 support this.
5167
5168 Each pair of lower and upper case escape sequences partitions the com-
5169 plete set of characters into two disjoint sets. Any given character
5170 matches one, and only one, of each pair. The sequences can appear both
5171 inside and outside character classes. They each match one character of
5172 the appropriate type. If the current matching point is at the end of
5173 the subject string, all of them fail, because there is no character to
5174 match.
5175
5176 For compatibility with Perl, \s did not used to match the VT character
5177 (code 11), which made it different from the the POSIX "space" class.
5178 However, Perl added VT at release 5.18, and PCRE followed suit at
5179 release 8.34. The default \s characters are now HT (9), LF (10), VT
5180 (11), FF (12), CR (13), and space (32), which are defined as white
5181 space in the "C" locale. This list may vary if locale-specific matching
5182 is taking place. For example, in some locales the "non-breaking space"
5183 character (\xA0) is recognized as white space, and in others the VT
5184 character is not.
5185
5186 A "word" character is an underscore or any character that is a letter
5187 or digit. By default, the definition of letters and digits is con-
5188 trolled by PCRE's low-valued character tables, and may vary if locale-
5189 specific matching is taking place (see "Locale support" in the pcreapi
5190 page). For example, in a French locale such as "fr_FR" in Unix-like
5191 systems, or "french" in Windows, some character codes greater than 127
5192 are used for accented letters, and these are then matched by \w. The
5193 use of locales with Unicode is discouraged.
5194
5195 By default, characters whose code points are greater than 127 never
5196 match \d, \s, or \w, and always match \D, \S, and \W, although this may
5197 vary for characters in the range 128-255 when locale-specific matching
5198 is happening. These escape sequences retain their original meanings
5199 from before Unicode support was available, mainly for efficiency rea-
5200 sons. If PCRE is compiled with Unicode property support, and the
5201 PCRE_UCP option is set, the behaviour is changed so that Unicode prop-
5202 erties are used to determine character types, as follows:
5203
5204 \d any character that matches \p{Nd} (decimal digit)
5205 \s any character that matches \p{Z} or \h or \v
5206 \w any character that matches \p{L} or \p{N}, plus underscore
5207
5208 The upper case escapes match the inverse sets of characters. Note that
5209 \d matches only decimal digits, whereas \w matches any Unicode digit,
5210 as well as any Unicode letter, and underscore. Note also that PCRE_UCP
5211 affects \b, and \B because they are defined in terms of \w and \W.
5212 Matching these sequences is noticeably slower when PCRE_UCP is set.
5213
5214 The sequences \h, \H, \v, and \V are features that were added to Perl
5215 at release 5.10. In contrast to the other sequences, which match only
5216 ASCII characters by default, these always match certain high-valued
5217 code points, whether or not PCRE_UCP is set. The horizontal space char-
5218 acters are:
5219
5220 U+0009 Horizontal tab (HT)
5221 U+0020 Space
5222 U+00A0 Non-break space
5223 U+1680 Ogham space mark
5224 U+180E Mongolian vowel separator
5225 U+2000 En quad
5226 U+2001 Em quad
5227 U+2002 En space
5228 U+2003 Em space
5229 U+2004 Three-per-em space
5230 U+2005 Four-per-em space
5231 U+2006 Six-per-em space
5232 U+2007 Figure space
5233 U+2008 Punctuation space
5234 U+2009 Thin space
5235 U+200A Hair space
5236 U+202F Narrow no-break space
5237 U+205F Medium mathematical space
5238 U+3000 Ideographic space
5239
5240 The vertical space characters are:
5241
5242 U+000A Linefeed (LF)
5243 U+000B Vertical tab (VT)
5244 U+000C Form feed (FF)
5245 U+000D Carriage return (CR)
5246 U+0085 Next line (NEL)
5247 U+2028 Line separator
5248 U+2029 Paragraph separator
5249
5250 In 8-bit, non-UTF-8 mode, only the characters with codepoints less than
5251 256 are relevant.
5252
5253 Newline sequences
5254
5255 Outside a character class, by default, the escape sequence \R matches
5256 any Unicode newline sequence. In 8-bit non-UTF-8 mode \R is equivalent
5257 to the following:
5258
5259 (?>\r\n|\n|\x0b|\f|\r|\x85)
5260
5261 This is an example of an "atomic group", details of which are given
5262 below. This particular group matches either the two-character sequence
5263 CR followed by LF, or one of the single characters LF (linefeed,
5264 U+000A), VT (vertical tab, U+000B), FF (form feed, U+000C), CR (car-
5265 riage return, U+000D), or NEL (next line, U+0085). The two-character
5266 sequence is treated as a single unit that cannot be split.
5267
5268 In other modes, two additional characters whose codepoints are greater
5269 than 255 are added: LS (line separator, U+2028) and PS (paragraph sepa-
5270 rator, U+2029). Unicode character property support is not needed for
5271 these characters to be recognized.
5272
5273 It is possible to restrict \R to match only CR, LF, or CRLF (instead of
5274 the complete set of Unicode line endings) by setting the option
5275 PCRE_BSR_ANYCRLF either at compile time or when the pattern is matched.
5276 (BSR is an abbrevation for "backslash R".) This can be made the default
5277 when PCRE is built; if this is the case, the other behaviour can be
5278 requested via the PCRE_BSR_UNICODE option. It is also possible to
5279 specify these settings by starting a pattern string with one of the
5280 following sequences:
5281
5282 (*BSR_ANYCRLF) CR, LF, or CRLF only
5283 (*BSR_UNICODE) any Unicode newline sequence
5284
5285 These override the default and the options given to the compiling func-
5286 tion, but they can themselves be overridden by options given to a
5287 matching function. Note that these special settings, which are not
5288 Perl-compatible, are recognized only at the very start of a pattern,
5289 and that they must be in upper case. If more than one of them is
5290 present, the last one is used. They can be combined with a change of
5291 newline convention; for example, a pattern can start with:
5292
5293 (*ANY)(*BSR_ANYCRLF)
5294
5295 They can also be combined with the (*UTF8), (*UTF16), (*UTF32), (*UTF)
5296 or (*UCP) special sequences. Inside a character class, \R is treated as
5297 an unrecognized escape sequence, and so matches the letter "R" by
5298 default, but causes an error if PCRE_EXTRA is set.
5299
5300 Unicode character properties
5301
5302 When PCRE is built with Unicode character property support, three addi-
5303 tional escape sequences that match characters with specific properties
5304 are available. When in 8-bit non-UTF-8 mode, these sequences are of
5305 course limited to testing characters whose codepoints are less than
5306 256, but they do work in this mode. The extra escape sequences are:
5307
5308 \p{xx} a character with the xx property
5309 \P{xx} a character without the xx property
5310 \X a Unicode extended grapheme cluster
5311
5312 The property names represented by xx above are limited to the Unicode
5313 script names, the general category properties, "Any", which matches any
5314 character (including newline), and some special PCRE properties
5315 (described in the next section). Other Perl properties such as "InMu-
5316 sicalSymbols" are not currently supported by PCRE. Note that \P{Any}
5317 does not match any characters, so always causes a match failure.
5318
5319 Sets of Unicode characters are defined as belonging to certain scripts.
5320 A character from one of these sets can be matched using a script name.
5321 For example:
5322
5323 \p{Greek}
5324 \P{Han}
5325
5326 Those that are not part of an identified script are lumped together as
5327 "Common". The current list of scripts is:
5328
5329 Arabic, Armenian, Avestan, Balinese, Bamum, Bassa_Vah, Batak, Bengali,
5330 Bopomofo, Brahmi, Braille, Buginese, Buhid, Canadian_Aboriginal, Car-
5331 ian, Caucasian_Albanian, Chakma, Cham, Cherokee, Common, Coptic, Cunei-
5332 form, Cypriot, Cyrillic, Deseret, Devanagari, Duployan, Egyptian_Hiero-
5333 glyphs, Elbasan, Ethiopic, Georgian, Glagolitic, Gothic, Grantha,
5334 Greek, Gujarati, Gurmukhi, Han, Hangul, Hanunoo, Hebrew, Hiragana,
5335 Imperial_Aramaic, Inherited, Inscriptional_Pahlavi, Inscrip-
5336 tional_Parthian, Javanese, Kaithi, Kannada, Katakana, Kayah_Li,
5337 Kharoshthi, Khmer, Khojki, Khudawadi, Lao, Latin, Lepcha, Limbu, Lin-
5338 ear_A, Linear_B, Lisu, Lycian, Lydian, Mahajani, Malayalam, Mandaic,
5339 Manichaean, Meetei_Mayek, Mende_Kikakui, Meroitic_Cursive,
5340 Meroitic_Hieroglyphs, Miao, Modi, Mongolian, Mro, Myanmar, Nabataean,
5341 New_Tai_Lue, Nko, Ogham, Ol_Chiki, Old_Italic, Old_North_Arabian,
5342 Old_Permic, Old_Persian, Old_South_Arabian, Old_Turkic, Oriya, Osmanya,
5343 Pahawh_Hmong, Palmyrene, Pau_Cin_Hau, Phags_Pa, Phoenician,
5344 Psalter_Pahlavi, Rejang, Runic, Samaritan, Saurashtra, Sharada, Sha-
5345 vian, Siddham, Sinhala, Sora_Sompeng, Sundanese, Syloti_Nagri, Syriac,
5346 Tagalog, Tagbanwa, Tai_Le, Tai_Tham, Tai_Viet, Takri, Tamil, Telugu,
5347 Thaana, Thai, Tibetan, Tifinagh, Tirhuta, Ugaritic, Vai, Warang_Citi,
5348 Yi.
5349
5350 Each character has exactly one Unicode general category property, spec-
5351 ified by a two-letter abbreviation. For compatibility with Perl, nega-
5352 tion can be specified by including a circumflex between the opening
5353 brace and the property name. For example, \p{^Lu} is the same as
5354 \P{Lu}.
5355
5356 If only one letter is specified with \p or \P, it includes all the gen-
5357 eral category properties that start with that letter. In this case, in
5358 the absence of negation, the curly brackets in the escape sequence are
5359 optional; these two examples have the same effect:
5360
5361 \p{L}
5362 \pL
5363
5364 The following general category property codes are supported:
5365
5366 C Other
5367 Cc Control
5368 Cf Format
5369 Cn Unassigned
5370 Co Private use
5371 Cs Surrogate
5372
5373 L Letter
5374 Ll Lower case letter
5375 Lm Modifier letter
5376 Lo Other letter
5377 Lt Title case letter
5378 Lu Upper case letter
5379
5380 M Mark
5381 Mc Spacing mark
5382 Me Enclosing mark
5383 Mn Non-spacing mark
5384
5385 N Number
5386 Nd Decimal number
5387 Nl Letter number
5388 No Other number
5389
5390 P Punctuation
5391 Pc Connector punctuation
5392 Pd Dash punctuation
5393 Pe Close punctuation
5394 Pf Final punctuation
5395 Pi Initial punctuation
5396 Po Other punctuation
5397 Ps Open punctuation
5398
5399 S Symbol
5400 Sc Currency symbol
5401 Sk Modifier symbol
5402 Sm Mathematical symbol
5403 So Other symbol
5404
5405 Z Separator
5406 Zl Line separator
5407 Zp Paragraph separator
5408 Zs Space separator
5409
5410 The special property L& is also supported: it matches a character that
5411 has the Lu, Ll, or Lt property, in other words, a letter that is not
5412 classified as a modifier or "other".
5413
5414 The Cs (Surrogate) property applies only to characters in the range
5415 U+D800 to U+DFFF. Such characters are not valid in Unicode strings and
5416 so cannot be tested by PCRE, unless UTF validity checking has been
5417 turned off (see the discussion of PCRE_NO_UTF8_CHECK,
5418 PCRE_NO_UTF16_CHECK and PCRE_NO_UTF32_CHECK in the pcreapi page). Perl
5419 does not support the Cs property.
5420
5421 The long synonyms for property names that Perl supports (such as
5422 \p{Letter}) are not supported by PCRE, nor is it permitted to prefix
5423 any of these properties with "Is".
5424
5425 No character that is in the Unicode table has the Cn (unassigned) prop-
5426 erty. Instead, this property is assumed for any code point that is not
5427 in the Unicode table.
5428
5429 Specifying caseless matching does not affect these escape sequences.
5430 For example, \p{Lu} always matches only upper case letters. This is
5431 different from the behaviour of current versions of Perl.
5432
5433 Matching characters by Unicode property is not fast, because PCRE has
5434 to do a multistage table lookup in order to find a character's prop-
5435 erty. That is why the traditional escape sequences such as \d and \w do
5436 not use Unicode properties in PCRE by default, though you can make them
5437 do so by setting the PCRE_UCP option or by starting the pattern with
5438 (*UCP).
5439
5440 Extended grapheme clusters
5441
5442 The \X escape matches any number of Unicode characters that form an
5443 "extended grapheme cluster", and treats the sequence as an atomic group
5444 (see below). Up to and including release 8.31, PCRE matched an ear-
5445 lier, simpler definition that was equivalent to
5446
5447 (?>\PM\pM*)
5448
5449 That is, it matched a character without the "mark" property, followed
5450 by zero or more characters with the "mark" property. Characters with
5451 the "mark" property are typically non-spacing accents that affect the
5452 preceding character.
5453
5454 This simple definition was extended in Unicode to include more compli-
5455 cated kinds of composite character by giving each character a grapheme
5456 breaking property, and creating rules that use these properties to
5457 define the boundaries of extended grapheme clusters. In releases of
5458 PCRE later than 8.31, \X matches one of these clusters.
5459
5460 \X always matches at least one character. Then it decides whether to
5461 add additional characters according to the following rules for ending a
5462 cluster:
5463
5464 1. End at the end of the subject string.
5465
5466 2. Do not end between CR and LF; otherwise end after any control char-
5467 acter.
5468
5469 3. Do not break Hangul (a Korean script) syllable sequences. Hangul
5470 characters are of five types: L, V, T, LV, and LVT. An L character may
5471 be followed by an L, V, LV, or LVT character; an LV or V character may
5472 be followed by a V or T character; an LVT or T character may be follwed
5473 only by a T character.
5474
5475 4. Do not end before extending characters or spacing marks. Characters
5476 with the "mark" property always have the "extend" grapheme breaking
5477 property.
5478
5479 5. Do not end after prepend characters.
5480
5481 6. Otherwise, end the cluster.
5482
5483 PCRE's additional properties
5484
5485 As well as the standard Unicode properties described above, PCRE sup-
5486 ports four more that make it possible to convert traditional escape
5487 sequences such as \w and \s to use Unicode properties. PCRE uses these
5488 non-standard, non-Perl properties internally when PCRE_UCP is set. How-
5489 ever, they may also be used explicitly. These properties are:
5490
5491 Xan Any alphanumeric character
5492 Xps Any POSIX space character
5493 Xsp Any Perl space character
5494 Xwd Any Perl "word" character
5495
5496 Xan matches characters that have either the L (letter) or the N (num-
5497 ber) property. Xps matches the characters tab, linefeed, vertical tab,
5498 form feed, or carriage return, and any other character that has the Z
5499 (separator) property. Xsp is the same as Xps; it used to exclude ver-
5500 tical tab, for Perl compatibility, but Perl changed, and so PCRE fol-
5501 lowed at release 8.34. Xwd matches the same characters as Xan, plus
5502 underscore.
5503
5504 There is another non-standard property, Xuc, which matches any charac-
5505 ter that can be represented by a Universal Character Name in C++ and
5506 other programming languages. These are the characters $, @, ` (grave
5507 accent), and all characters with Unicode code points greater than or
5508 equal to U+00A0, except for the surrogates U+D800 to U+DFFF. Note that
5509 most base (ASCII) characters are excluded. (Universal Character Names
5510 are of the form \uHHHH or \UHHHHHHHH where H is a hexadecimal digit.
5511 Note that the Xuc property does not match these sequences but the char-
5512 acters that they represent.)
5513
5514 Resetting the match start
5515
5516 The escape sequence \K causes any previously matched characters not to
5517 be included in the final matched sequence. For example, the pattern:
5518
5519 foo\Kbar
5520
5521 matches "foobar", but reports that it has matched "bar". This feature
5522 is similar to a lookbehind assertion (described below). However, in
5523 this case, the part of the subject before the real match does not have
5524 to be of fixed length, as lookbehind assertions do. The use of \K does
5525 not interfere with the setting of captured substrings. For example,
5526 when the pattern
5527
5528 (foo)\Kbar
5529
5530 matches "foobar", the first substring is still set to "foo".
5531
5532 Perl documents that the use of \K within assertions is "not well
5533 defined". In PCRE, \K is acted upon when it occurs inside positive
5534 assertions, but is ignored in negative assertions. Note that when a
5535 pattern such as (?=ab\K) matches, the reported start of the match can
5536 be greater than the end of the match.
5537
5538 Simple assertions
5539
5540 The final use of backslash is for certain simple assertions. An asser-
5541 tion specifies a condition that has to be met at a particular point in
5542 a match, without consuming any characters from the subject string. The
5543 use of subpatterns for more complicated assertions is described below.
5544 The backslashed assertions are:
5545
5546 \b matches at a word boundary
5547 \B matches when not at a word boundary
5548 \A matches at the start of the subject
5549 \Z matches at the end of the subject
5550 also matches before a newline at the end of the subject
5551 \z matches only at the end of the subject
5552 \G matches at the first matching position in the subject
5553
5554 Inside a character class, \b has a different meaning; it matches the
5555 backspace character. If any other of these assertions appears in a
5556 character class, by default it matches the corresponding literal char-
5557 acter (for example, \B matches the letter B). However, if the
5558 PCRE_EXTRA option is set, an "invalid escape sequence" error is gener-
5559 ated instead.
5560
5561 A word boundary is a position in the subject string where the current
5562 character and the previous character do not both match \w or \W (i.e.
5563 one matches \w and the other matches \W), or the start or end of the
5564 string if the first or last character matches \w, respectively. In a
5565 UTF mode, the meanings of \w and \W can be changed by setting the
5566 PCRE_UCP option. When this is done, it also affects \b and \B. Neither
5567 PCRE nor Perl has a separate "start of word" or "end of word" metase-
5568 quence. However, whatever follows \b normally determines which it is.
5569 For example, the fragment \ba matches "a" at the start of a word.
5570
5571 The \A, \Z, and \z assertions differ from the traditional circumflex
5572 and dollar (described in the next section) in that they only ever match
5573 at the very start and end of the subject string, whatever options are
5574 set. Thus, they are independent of multiline mode. These three asser-
5575 tions are not affected by the PCRE_NOTBOL or PCRE_NOTEOL options, which
5576 affect only the behaviour of the circumflex and dollar metacharacters.
5577 However, if the startoffset argument of pcre_exec() is non-zero, indi-
5578 cating that matching is to start at a point other than the beginning of
5579 the subject, \A can never match. The difference between \Z and \z is
5580 that \Z matches before a newline at the end of the string as well as at
5581 the very end, whereas \z matches only at the end.
5582
5583 The \G assertion is true only when the current matching position is at
5584 the start point of the match, as specified by the startoffset argument
5585 of pcre_exec(). It differs from \A when the value of startoffset is
5586 non-zero. By calling pcre_exec() multiple times with appropriate argu-
5587 ments, you can mimic Perl's /g option, and it is in this kind of imple-
5588 mentation where \G can be useful.
5589
5590 Note, however, that PCRE's interpretation of \G, as the start of the
5591 current match, is subtly different from Perl's, which defines it as the
5592 end of the previous match. In Perl, these can be different when the
5593 previously matched string was empty. Because PCRE does just one match
5594 at a time, it cannot reproduce this behaviour.
5595
5596 If all the alternatives of a pattern begin with \G, the expression is
5597 anchored to the starting match position, and the "anchored" flag is set
5598 in the compiled regular expression.
5599
5600
5601 CIRCUMFLEX AND DOLLAR
5602
5603 The circumflex and dollar metacharacters are zero-width assertions.
5604 That is, they test for a particular condition being true without con-
5605 suming any characters from the subject string.
5606
5607 Outside a character class, in the default matching mode, the circumflex
5608 character is an assertion that is true only if the current matching
5609 point is at the start of the subject string. If the startoffset argu-
5610 ment of pcre_exec() is non-zero, circumflex can never match if the
5611 PCRE_MULTILINE option is unset. Inside a character class, circumflex
5612 has an entirely different meaning (see below).
5613
5614 Circumflex need not be the first character of the pattern if a number
5615 of alternatives are involved, but it should be the first thing in each
5616 alternative in which it appears if the pattern is ever to match that
5617 branch. If all possible alternatives start with a circumflex, that is,
5618 if the pattern is constrained to match only at the start of the sub-
5619 ject, it is said to be an "anchored" pattern. (There are also other
5620 constructs that can cause a pattern to be anchored.)
5621
5622 The dollar character is an assertion that is true only if the current
5623 matching point is at the end of the subject string, or immediately
5624 before a newline at the end of the string (by default). Note, however,
5625 that it does not actually match the newline. Dollar need not be the
5626 last character of the pattern if a number of alternatives are involved,
5627 but it should be the last item in any branch in which it appears. Dol-
5628 lar has no special meaning in a character class.
5629
5630 The meaning of dollar can be changed so that it matches only at the
5631 very end of the string, by setting the PCRE_DOLLAR_ENDONLY option at
5632 compile time. This does not affect the \Z assertion.
5633
5634 The meanings of the circumflex and dollar characters are changed if the
5635 PCRE_MULTILINE option is set. When this is the case, a circumflex
5636 matches immediately after internal newlines as well as at the start of
5637 the subject string. It does not match after a newline that ends the
5638 string. A dollar matches before any newlines in the string, as well as
5639 at the very end, when PCRE_MULTILINE is set. When newline is specified
5640 as the two-character sequence CRLF, isolated CR and LF characters do
5641 not indicate newlines.
5642
5643 For example, the pattern /^abc$/ matches the subject string "def\nabc"
5644 (where \n represents a newline) in multiline mode, but not otherwise.
5645 Consequently, patterns that are anchored in single line mode because
5646 all branches start with ^ are not anchored in multiline mode, and a
5647 match for circumflex is possible when the startoffset argument of
5648 pcre_exec() is non-zero. The PCRE_DOLLAR_ENDONLY option is ignored if
5649 PCRE_MULTILINE is set.
5650
5651 Note that the sequences \A, \Z, and \z can be used to match the start
5652 and end of the subject in both modes, and if all branches of a pattern
5653 start with \A it is always anchored, whether or not PCRE_MULTILINE is
5654 set.
5655
5656
5657 FULL STOP (PERIOD, DOT) AND \N
5658
5659 Outside a character class, a dot in the pattern matches any one charac-
5660 ter in the subject string except (by default) a character that signi-
5661 fies the end of a line.
5662
5663 When a line ending is defined as a single character, dot never matches
5664 that character; when the two-character sequence CRLF is used, dot does
5665 not match CR if it is immediately followed by LF, but otherwise it
5666 matches all characters (including isolated CRs and LFs). When any Uni-
5667 code line endings are being recognized, dot does not match CR or LF or
5668 any of the other line ending characters.
5669
5670 The behaviour of dot with regard to newlines can be changed. If the
5671 PCRE_DOTALL option is set, a dot matches any one character, without
5672 exception. If the two-character sequence CRLF is present in the subject
5673 string, it takes two dots to match it.
5674
5675 The handling of dot is entirely independent of the handling of circum-
5676 flex and dollar, the only relationship being that they both involve
5677 newlines. Dot has no special meaning in a character class.
5678
5679 The escape sequence \N behaves like a dot, except that it is not
5680 affected by the PCRE_DOTALL option. In other words, it matches any
5681 character except one that signifies the end of a line. Perl also uses
5682 \N to match characters by name; PCRE does not support this.
5683
5684
5685 MATCHING A SINGLE DATA UNIT
5686
5687 Outside a character class, the escape sequence \C matches any one data
5688 unit, whether or not a UTF mode is set. In the 8-bit library, one data
5689 unit is one byte; in the 16-bit library it is a 16-bit unit; in the
5690 32-bit library it is a 32-bit unit. Unlike a dot, \C always matches
5691 line-ending characters. The feature is provided in Perl in order to
5692 match individual bytes in UTF-8 mode, but it is unclear how it can use-
5693 fully be used. Because \C breaks up characters into individual data
5694 units, matching one unit with \C in a UTF mode means that the rest of
5695 the string may start with a malformed UTF character. This has undefined
5696 results, because PCRE assumes that it is dealing with valid UTF strings
5697 (and by default it checks this at the start of processing unless the
5698 PCRE_NO_UTF8_CHECK, PCRE_NO_UTF16_CHECK or PCRE_NO_UTF32_CHECK option
5699 is used).
5700
5701 PCRE does not allow \C to appear in lookbehind assertions (described
5702 below) in a UTF mode, because this would make it impossible to calcu-
5703 late the length of the lookbehind.
5704
5705 In general, the \C escape sequence is best avoided. However, one way of
5706 using it that avoids the problem of malformed UTF characters is to use
5707 a lookahead to check the length of the next character, as in this pat-
5708 tern, which could be used with a UTF-8 string (ignore white space and
5709 line breaks):
5710
5711 (?| (?=[\x00-\x7f])(\C) |
5712 (?=[\x80-\x{7ff}])(\C)(\C) |
5713 (?=[\x{800}-\x{ffff}])(\C)(\C)(\C) |
5714 (?=[\x{10000}-\x{1fffff}])(\C)(\C)(\C)(\C))
5715
5716 A group that starts with (?| resets the capturing parentheses numbers
5717 in each alternative (see "Duplicate Subpattern Numbers" below). The
5718 assertions at the start of each branch check the next UTF-8 character
5719 for values whose encoding uses 1, 2, 3, or 4 bytes, respectively. The
5720 character's individual bytes are then captured by the appropriate num-
5721 ber of groups.
5722
5723
5724 SQUARE BRACKETS AND CHARACTER CLASSES
5725
5726 An opening square bracket introduces a character class, terminated by a
5727 closing square bracket. A closing square bracket on its own is not spe-
5728 cial by default. However, if the PCRE_JAVASCRIPT_COMPAT option is set,
5729 a lone closing square bracket causes a compile-time error. If a closing
5730 square bracket is required as a member of the class, it should be the
5731 first data character in the class (after an initial circumflex, if
5732 present) or escaped with a backslash.
5733
5734 A character class matches a single character in the subject. In a UTF
5735 mode, the character may be more than one data unit long. A matched
5736 character must be in the set of characters defined by the class, unless
5737 the first character in the class definition is a circumflex, in which
5738 case the subject character must not be in the set defined by the class.
5739 If a circumflex is actually required as a member of the class, ensure
5740 it is not the first character, or escape it with a backslash.
5741
5742 For example, the character class [aeiou] matches any lower case vowel,
5743 while [^aeiou] matches any character that is not a lower case vowel.
5744 Note that a circumflex is just a convenient notation for specifying the
5745 characters that are in the class by enumerating those that are not. A
5746 class that starts with a circumflex is not an assertion; it still con-
5747 sumes a character from the subject string, and therefore it fails if
5748 the current pointer is at the end of the string.
5749
5750 In UTF-8 (UTF-16, UTF-32) mode, characters with values greater than 255
5751 (0xffff) can be included in a class as a literal string of data units,
5752 or by using the \x{ escaping mechanism.
5753
5754 When caseless matching is set, any letters in a class represent both
5755 their upper case and lower case versions, so for example, a caseless
5756 [aeiou] matches "A" as well as "a", and a caseless [^aeiou] does not
5757 match "A", whereas a caseful version would. In a UTF mode, PCRE always
5758 understands the concept of case for characters whose values are less
5759 than 128, so caseless matching is always possible. For characters with
5760 higher values, the concept of case is supported if PCRE is compiled
5761 with Unicode property support, but not otherwise. If you want to use
5762 caseless matching in a UTF mode for characters 128 and above, you must
5763 ensure that PCRE is compiled with Unicode property support as well as
5764 with UTF support.
5765
5766 Characters that might indicate line breaks are never treated in any
5767 special way when matching character classes, whatever line-ending
5768 sequence is in use, and whatever setting of the PCRE_DOTALL and
5769 PCRE_MULTILINE options is used. A class such as [^a] always matches one
5770 of these characters.
5771
5772 The minus (hyphen) character can be used to specify a range of charac-
5773 ters in a character class. For example, [d-m] matches any letter
5774 between d and m, inclusive. If a minus character is required in a
5775 class, it must be escaped with a backslash or appear in a position
5776 where it cannot be interpreted as indicating a range, typically as the
5777 first or last character in the class, or immediately after a range. For
5778 example, [b-d-z] matches letters in the range b to d, a hyphen charac-
5779 ter, or z.
5780
5781 It is not possible to have the literal character "]" as the end charac-
5782 ter of a range. A pattern such as [W-]46] is interpreted as a class of
5783 two characters ("W" and "-") followed by a literal string "46]", so it
5784 would match "W46]" or "-46]". However, if the "]" is escaped with a
5785 backslash it is interpreted as the end of range, so [W-\]46] is inter-
5786 preted as a class containing a range followed by two other characters.
5787 The octal or hexadecimal representation of "]" can also be used to end
5788 a range.
5789
5790 An error is generated if a POSIX character class (see below) or an
5791 escape sequence other than one that defines a single character appears
5792 at a point where a range ending character is expected. For example,
5793 [z-\xff] is valid, but [A-\d] and [A-[:digit:]] are not.
5794
5795 Ranges operate in the collating sequence of character values. They can
5796 also be used for characters specified numerically, for example
5797 [\000-\037]. Ranges can include any characters that are valid for the
5798 current mode.
5799
5800 If a range that includes letters is used when caseless matching is set,
5801 it matches the letters in either case. For example, [W-c] is equivalent
5802 to [][\\^_`wxyzabc], matched caselessly, and in a non-UTF mode, if
5803 character tables for a French locale are in use, [\xc8-\xcb] matches
5804 accented E characters in both cases. In UTF modes, PCRE supports the
5805 concept of case for characters with values greater than 128 only when
5806 it is compiled with Unicode property support.
5807
5808 The character escape sequences \d, \D, \h, \H, \p, \P, \s, \S, \v, \V,
5809 \w, and \W may appear in a character class, and add the characters that
5810 they match to the class. For example, [\dABCDEF] matches any hexadeci-
5811 mal digit. In UTF modes, the PCRE_UCP option affects the meanings of
5812 \d, \s, \w and their upper case partners, just as it does when they
5813 appear outside a character class, as described in the section entitled
5814 "Generic character types" above. The escape sequence \b has a different
5815 meaning inside a character class; it matches the backspace character.
5816 The sequences \B, \N, \R, and \X are not special inside a character
5817 class. Like any other unrecognized escape sequences, they are treated
5818 as the literal characters "B", "N", "R", and "X" by default, but cause
5819 an error if the PCRE_EXTRA option is set.
5820
5821 A circumflex can conveniently be used with the upper case character
5822 types to specify a more restricted set of characters than the matching
5823 lower case type. For example, the class [^\W_] matches any letter or
5824 digit, but not underscore, whereas [\w] includes underscore. A positive
5825 character class should be read as "something OR something OR ..." and a
5826 negative class as "NOT something AND NOT something AND NOT ...".
5827
5828 The only metacharacters that are recognized in character classes are
5829 backslash, hyphen (only where it can be interpreted as specifying a
5830 range), circumflex (only at the start), opening square bracket (only
5831 when it can be interpreted as introducing a POSIX class name, or for a
5832 special compatibility feature - see the next two sections), and the
5833 terminating closing square bracket. However, escaping other non-
5834 alphanumeric characters does no harm.
5835
5836
5837 POSIX CHARACTER CLASSES
5838
5839 Perl supports the POSIX notation for character classes. This uses names
5840 enclosed by [: and :] within the enclosing square brackets. PCRE also
5841 supports this notation. For example,
5842
5843 [01[:alpha:]%]
5844
5845 matches "0", "1", any alphabetic character, or "%". The supported class
5846 names are:
5847
5848 alnum letters and digits
5849 alpha letters
5850 ascii character codes 0 - 127
5851 blank space or tab only
5852 cntrl control characters
5853 digit decimal digits (same as \d)
5854 graph printing characters, excluding space
5855 lower lower case letters
5856 print printing characters, including space
5857 punct printing characters, excluding letters and digits and space
5858 space white space (the same as \s from PCRE 8.34)
5859 upper upper case letters
5860 word "word" characters (same as \w)
5861 xdigit hexadecimal digits
5862
5863 The default "space" characters are HT (9), LF (10), VT (11), FF (12),
5864 CR (13), and space (32). If locale-specific matching is taking place,
5865 the list of space characters may be different; there may be fewer or
5866 more of them. "Space" used to be different to \s, which did not include
5867 VT, for Perl compatibility. However, Perl changed at release 5.18, and
5868 PCRE followed at release 8.34. "Space" and \s now match the same set
5869 of characters.
5870
5871 The name "word" is a Perl extension, and "blank" is a GNU extension
5872 from Perl 5.8. Another Perl extension is negation, which is indicated
5873 by a ^ character after the colon. For example,
5874
5875 [12[:^digit:]]
5876
5877 matches "1", "2", or any non-digit. PCRE (and Perl) also recognize the
5878 POSIX syntax [.ch.] and [=ch=] where "ch" is a "collating element", but
5879 these are not supported, and an error is given if they are encountered.
5880
5881 By default, characters with values greater than 128 do not match any of
5882 the POSIX character classes. However, if the PCRE_UCP option is passed
5883 to pcre_compile(), some of the classes are changed so that Unicode
5884 character properties are used. This is achieved by replacing certain
5885 POSIX classes by other sequences, as follows:
5886
5887 [:alnum:] becomes \p{Xan}
5888 [:alpha:] becomes \p{L}
5889 [:blank:] becomes \h
5890 [:digit:] becomes \p{Nd}
5891 [:lower:] becomes \p{Ll}
5892 [:space:] becomes \p{Xps}
5893 [:upper:] becomes \p{Lu}
5894 [:word:] becomes \p{Xwd}
5895
5896 Negated versions, such as [:^alpha:] use \P instead of \p. Three other
5897 POSIX classes are handled specially in UCP mode:
5898
5899 [:graph:] This matches characters that have glyphs that mark the page
5900 when printed. In Unicode property terms, it matches all char-
5901 acters with the L, M, N, P, S, or Cf properties, except for:
5902
5903 U+061C Arabic Letter Mark
5904 U+180E Mongolian Vowel Separator
5905 U+2066 - U+2069 Various "isolate"s
5906
5907
5908 [:print:] This matches the same characters as [:graph:] plus space
5909 characters that are not controls, that is, characters with
5910 the Zs property.
5911
5912 [:punct:] This matches all characters that have the Unicode P (punctua-
5913 tion) property, plus those characters whose code points are
5914 less than 128 that have the S (Symbol) property.
5915
5916 The other POSIX classes are unchanged, and match only characters with
5917 code points less than 128.
5918
5919
5920 COMPATIBILITY FEATURE FOR WORD BOUNDARIES
5921
5922 In the POSIX.2 compliant library that was included in 4.4BSD Unix, the
5923 ugly syntax [[:<:]] and [[:>:]] is used for matching "start of word"
5924 and "end of word". PCRE treats these items as follows:
5925
5926 [[:<:]] is converted to \b(?=\w)
5927 [[:>:]] is converted to \b(?<=\w)
5928
5929 Only these exact character sequences are recognized. A sequence such as
5930 [a[:<:]b] provokes error for an unrecognized POSIX class name. This
5931 support is not compatible with Perl. It is provided to help migrations
5932 from other environments, and is best not used in any new patterns. Note
5933 that \b matches at the start and the end of a word (see "Simple asser-
5934 tions" above), and in a Perl-style pattern the preceding or following
5935 character normally shows which is wanted, without the need for the
5936 assertions that are used above in order to give exactly the POSIX be-
5937 haviour.
5938
5939
5940 VERTICAL BAR
5941
5942 Vertical bar characters are used to separate alternative patterns. For
5943 example, the pattern
5944
5945 gilbert|sullivan
5946
5947 matches either "gilbert" or "sullivan". Any number of alternatives may
5948 appear, and an empty alternative is permitted (matching the empty
5949 string). The matching process tries each alternative in turn, from left
5950 to right, and the first one that succeeds is used. If the alternatives
5951 are within a subpattern (defined below), "succeeds" means matching the
5952 rest of the main pattern as well as the alternative in the subpattern.
5953
5954
5955 INTERNAL OPTION SETTING
5956
5957 The settings of the PCRE_CASELESS, PCRE_MULTILINE, PCRE_DOTALL, and
5958 PCRE_EXTENDED options (which are Perl-compatible) can be changed from
5959 within the pattern by a sequence of Perl option letters enclosed
5960 between "(?" and ")". The option letters are
5961
5962 i for PCRE_CASELESS
5963 m for PCRE_MULTILINE
5964 s for PCRE_DOTALL
5965 x for PCRE_EXTENDED
5966
5967 For example, (?im) sets caseless, multiline matching. It is also possi-
5968 ble to unset these options by preceding the letter with a hyphen, and a
5969 combined setting and unsetting such as (?im-sx), which sets PCRE_CASE-
5970 LESS and PCRE_MULTILINE while unsetting PCRE_DOTALL and PCRE_EXTENDED,
5971 is also permitted. If a letter appears both before and after the
5972 hyphen, the option is unset.
5973
5974 The PCRE-specific options PCRE_DUPNAMES, PCRE_UNGREEDY, and PCRE_EXTRA
5975 can be changed in the same way as the Perl-compatible options by using
5976 the characters J, U and X respectively.
5977
5978 When one of these option changes occurs at top level (that is, not
5979 inside subpattern parentheses), the change applies to the remainder of
5980 the pattern that follows. If the change is placed right at the start of
5981 a pattern, PCRE extracts it into the global options (and it will there-
5982 fore show up in data extracted by the pcre_fullinfo() function).
5983
5984 An option change within a subpattern (see below for a description of
5985 subpatterns) affects only that part of the subpattern that follows it,
5986 so
5987
5988 (a(?i)b)c
5989
5990 matches abc and aBc and no other strings (assuming PCRE_CASELESS is not
5991 used). By this means, options can be made to have different settings
5992 in different parts of the pattern. Any changes made in one alternative
5993 do carry on into subsequent branches within the same subpattern. For
5994 example,
5995
5996 (a(?i)b|c)
5997
5998 matches "ab", "aB", "c", and "C", even though when matching "C" the
5999 first branch is abandoned before the option setting. This is because
6000 the effects of option settings happen at compile time. There would be
6001 some very weird behaviour otherwise.
6002
6003 Note: There are other PCRE-specific options that can be set by the
6004 application when the compiling or matching functions are called. In
6005 some cases the pattern can contain special leading sequences such as
6006 (*CRLF) to override what the application has set or what has been
6007 defaulted. Details are given in the section entitled "Newline
6008 sequences" above. There are also the (*UTF8), (*UTF16),(*UTF32), and
6009 (*UCP) leading sequences that can be used to set UTF and Unicode prop-
6010 erty modes; they are equivalent to setting the PCRE_UTF8, PCRE_UTF16,
6011 PCRE_UTF32 and the PCRE_UCP options, respectively. The (*UTF) sequence
6012 is a generic version that can be used with any of the libraries. How-
6013 ever, the application can set the PCRE_NEVER_UTF option, which locks
6014 out the use of the (*UTF) sequences.
6015
6016
6017 SUBPATTERNS
6018
6019 Subpatterns are delimited by parentheses (round brackets), which can be
6020 nested. Turning part of a pattern into a subpattern does two things:
6021
6022 1. It localizes a set of alternatives. For example, the pattern
6023
6024 cat(aract|erpillar|)
6025
6026 matches "cataract", "caterpillar", or "cat". Without the parentheses,
6027 it would match "cataract", "erpillar" or an empty string.
6028
6029 2. It sets up the subpattern as a capturing subpattern. This means
6030 that, when the whole pattern matches, that portion of the subject
6031 string that matched the subpattern is passed back to the caller via the
6032