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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. There are
6    separate text files for the pcregrep and pcretest commands.
7    -----------------------------------------------------------------------------
10    PCRE(3)                                                                PCRE(3)
13    NAME
14           PCRE - Perl-compatible regular expressions
19           The  PCRE  library is a set of functions that implement regular expres-
20           sion pattern matching using the same syntax and semantics as Perl, with
21           just  a  few  differences. Certain features that appeared in Python and
22           PCRE before they appeared in Perl are also available using  the  Python
23           syntax.  There is also some support for certain .NET and Oniguruma syn-
24           tax items, and there is an option for  requesting  some  minor  changes
25           that give better JavaScript compatibility.
27           The  current  implementation of PCRE (release 7.x) corresponds approxi-
28           mately with Perl 5.10, including support for UTF-8 encoded strings  and
29           Unicode general category properties. However, UTF-8 and Unicode support
30           has to be explicitly enabled; it is not the default. The Unicode tables
31           correspond to Unicode release 5.0.0.
33           In  addition to the Perl-compatible matching function, PCRE contains an
34           alternative matching function that matches the same  compiled  patterns
35           in  a different way. In certain circumstances, the alternative function
36           has some advantages. For a discussion of the two  matching  algorithms,
37           see the pcrematching page.
39           PCRE  is  written  in C and released as a C library. A number of people
40           have written wrappers and interfaces of various kinds.  In  particular,
41           Google  Inc.   have  provided  a comprehensive C++ wrapper. This is now
42           included as part of the PCRE distribution. The pcrecpp page has details
43           of  this  interface.  Other  people's contributions can be found in the
44           Contrib directory at the primary FTP site, which is:
46           ftp://ftp.csx.cam.ac.uk/pub/software/programming/pcre
48           Details of exactly which Perl regular expression features are  and  are
49           not supported by PCRE are given in separate documents. See the pcrepat-
50           tern and pcrecompat pages. There is a syntax summary in the  pcresyntax
51           page.
53           Some  features  of  PCRE can be included, excluded, or changed when the
54           library is built. The pcre_config() function makes it  possible  for  a
55           client  to  discover  which  features are available. The features them-
56           selves are described in the pcrebuild page. Documentation about  build-
57           ing  PCRE for various operating systems can be found in the README file
58           in the source distribution.
60           The library contains a number of undocumented  internal  functions  and
61           data  tables  that  are  used by more than one of the exported external
62           functions, but which are not intended  for  use  by  external  callers.
63           Their  names  all begin with "_pcre_", which hopefully will not provoke
64           any name clashes. In some environments, it is possible to control which
65           external  symbols  are  exported when a shared library is built, and in
66           these cases the undocumented symbols are not exported.
71           The user documentation for PCRE comprises a number  of  different  sec-
72           tions.  In the "man" format, each of these is a separate "man page". In
73           the HTML format, each is a separate page, linked from the  index  page.
74           In  the  plain text format, all the sections are concatenated, for ease
75           of searching. The sections are as follows:
77             pcre              this document
78             pcre-config       show PCRE installation configuration information
79             pcreapi           details of PCRE's native C API
80             pcrebuild         options for building PCRE
81             pcrecallout       details of the callout feature
82             pcrecompat        discussion of Perl compatibility
83             pcrecpp           details of the C++ wrapper
84             pcregrep          description of the pcregrep command
85             pcrematching      discussion of the two matching algorithms
86             pcrepartial       details of the partial matching facility
87             pcrepattern       syntax and semantics of supported
88                                 regular expressions
89             pcresyntax        quick syntax reference
90             pcreperform       discussion of performance issues
91             pcreposix         the POSIX-compatible C API
92             pcreprecompile    details of saving and re-using precompiled patterns
93             pcresample        discussion of the sample program
94             pcrestack         discussion of stack usage
95             pcretest          description of the pcretest testing command
97           In  addition,  in the "man" and HTML formats, there is a short page for
98           each C library function, listing its arguments and results.
103           There are some size limitations in PCRE but it is hoped that they  will
104           never in practice be relevant.
106           The  maximum  length of a compiled pattern is 65539 (sic) bytes if PCRE
107           is compiled with the default internal linkage size of 2. If you want to
108           process  regular  expressions  that are truly enormous, you can compile
109           PCRE with an internal linkage size of 3 or 4 (see the  README  file  in
110           the  source  distribution and the pcrebuild documentation for details).
111           In these cases the limit is substantially larger.  However,  the  speed
112           of execution is slower.
114           All values in repeating quantifiers must be less than 65536.
116           There is no limit to the number of parenthesized subpatterns, but there
117           can be no more than 65535 capturing subpatterns.
119           The maximum length of name for a named subpattern is 32 characters, and
120           the maximum number of named subpatterns is 10000.
122           The  maximum  length of a subject string is the largest positive number
123           that an integer variable can hold. However, when using the  traditional
124           matching function, PCRE uses recursion to handle subpatterns and indef-
125           inite repetition.  This means that the available stack space may  limit
126           the size of a subject string that can be processed by certain patterns.
127           For a discussion of stack issues, see the pcrestack documentation.
132           From release 3.3, PCRE has  had  some  support  for  character  strings
133           encoded  in the UTF-8 format. For release 4.0 this was greatly extended
134           to cover most common requirements, and in release 5.0  additional  sup-
135           port for Unicode general category properties was added.
137           In  order  process  UTF-8 strings, you must build PCRE to include UTF-8
138           support in the code, and, in addition,  you  must  call  pcre_compile()
139           with  the PCRE_UTF8 option flag. When you do this, both the pattern and
140           any subject strings that are matched against it are  treated  as  UTF-8
141           strings instead of just strings of bytes.
143           If  you compile PCRE with UTF-8 support, but do not use it at run time,
144           the library will be a bit bigger, but the additional run time  overhead
145           is limited to testing the PCRE_UTF8 flag occasionally, so should not be
146           very big.
148           If PCRE is built with Unicode character property support (which implies
149           UTF-8  support),  the  escape sequences \p{..}, \P{..}, and \X are sup-
150           ported.  The available properties that can be tested are limited to the
151           general  category  properties such as Lu for an upper case letter or Nd
152           for a decimal number, the Unicode script names such as Arabic  or  Han,
153           and  the  derived  properties  Any  and L&. A full list is given in the
154           pcrepattern documentation. Only the short names for properties are sup-
155           ported.  For example, \p{L} matches a letter. Its Perl synonym, \p{Let-
156           ter}, is not supported.  Furthermore,  in  Perl,  many  properties  may
157           optionally  be  prefixed by "Is", for compatibility with Perl 5.6. PCRE
158           does not support this.
160       Validity of UTF-8 strings
162           When you set the PCRE_UTF8 flag, the strings  passed  as  patterns  and
163           subjects are (by default) checked for validity on entry to the relevant
164           functions. From release 7.3 of PCRE, the check is according  the  rules
165           of  RFC  3629, which are themselves derived from the Unicode specifica-
166           tion. Earlier releases of PCRE followed the rules of  RFC  2279,  which
167           allows  the  full range of 31-bit values (0 to 0x7FFFFFFF). The current
168           check allows only values in the range U+0 to U+10FFFF, excluding U+D800
169           to U+DFFF.
171           The  excluded  code  points are the "Low Surrogate Area" of Unicode, of
172           which the Unicode Standard says this: "The Low Surrogate Area does  not
173           contain  any  character  assignments,  consequently  no  character code
174           charts or namelists are provided for this area. Surrogates are reserved
175           for  use  with  UTF-16 and then must be used in pairs." The code points
176           that are encoded by UTF-16 pairs  are  available  as  independent  code
177           points  in  the  UTF-8  encoding.  (In other words, the whole surrogate
178           thing is a fudge for UTF-16 which unfortunately messes up UTF-8.)
180           If an  invalid  UTF-8  string  is  passed  to  PCRE,  an  error  return
181           (PCRE_ERROR_BADUTF8) is given. In some situations, you may already know
182           that your strings are valid, and therefore want to skip these checks in
183           order to improve performance. If you set the PCRE_NO_UTF8_CHECK flag at
184           compile time or at run time, PCRE assumes that the pattern  or  subject
185           it  is  given  (respectively)  contains only valid UTF-8 codes. In this
186           case, it does not diagnose an invalid UTF-8 string.
188           If you pass an invalid UTF-8 string  when  PCRE_NO_UTF8_CHECK  is  set,
189           what  happens  depends on why the string is invalid. If the string con-
190           forms to the "old" definition of UTF-8 (RFC 2279), it is processed as a
191           string  of  characters  in  the  range 0 to 0x7FFFFFFF. In other words,
192           apart from the initial validity test, PCRE (when in UTF-8 mode) handles
193           strings  according  to  the more liberal rules of RFC 2279. However, if
194           the string does not even conform to RFC 2279, the result is  undefined.
195           Your program may crash.
197           If  you  want  to  process  strings  of  values  in the full range 0 to
198           0x7FFFFFFF, encoded in a UTF-8-like manner as per the old RFC, you  can
199           set PCRE_NO_UTF8_CHECK to bypass the more restrictive test. However, in
200           this situation, you will have to apply your own validity check.
202       General comments about UTF-8 mode
204           1. An unbraced hexadecimal escape sequence (such  as  \xb3)  matches  a
205           two-byte UTF-8 character if the value is greater than 127.
207           2.  Octal  numbers  up to \777 are recognized, and match two-byte UTF-8
208           characters for values greater than \177.
210           3. Repeat quantifiers apply to complete UTF-8 characters, not to  indi-
211           vidual bytes, for example: \x{100}{3}.
213           4.  The dot metacharacter matches one UTF-8 character instead of a sin-
214           gle byte.
216           5. The escape sequence \C can be used to match a single byte  in  UTF-8
217           mode,  but  its  use can lead to some strange effects. This facility is
218           not available in the alternative matching function, pcre_dfa_exec().
220           6. The character escapes \b, \B, \d, \D, \s, \S, \w, and  \W  correctly
221           test  characters of any code value, but the characters that PCRE recog-
222           nizes as digits, spaces, or word characters  remain  the  same  set  as
223           before, all with values less than 256. This remains true even when PCRE
224           includes Unicode property support, because to do otherwise  would  slow
225           down  PCRE in many common cases. If you really want to test for a wider
226           sense of, say, "digit", you must use Unicode  property  tests  such  as
227           \p{Nd}.
229           7.  Similarly,  characters that match the POSIX named character classes
230           are all low-valued characters.
232           8. However, the Perl 5.10 horizontal and vertical  whitespace  matching
233           escapes (\h, \H, \v, and \V) do match all the appropriate Unicode char-
234           acters.
236           9. Case-insensitive matching applies only to  characters  whose  values
237           are  less than 128, unless PCRE is built with Unicode property support.
238           Even when Unicode property support is available, PCRE  still  uses  its
239           own  character  tables when checking the case of low-valued characters,
240           so as not to degrade performance.  The Unicode property information  is
241           used only for characters with higher values. Even when Unicode property
242           support is available, PCRE supports case-insensitive matching only when
243           there  is  a  one-to-one  mapping between a letter's cases. There are a
244           small number of many-to-one mappings in Unicode;  these  are  not  sup-
245           ported by PCRE.
248    AUTHOR
250           Philip Hazel
251           University Computing Service
252           Cambridge CB2 3QH, England.
254           Putting  an actual email address here seems to have been a spam magnet,
255           so I've taken it away. If you want to email me, use  my  two  initials,
256           followed by the two digits 10, at the domain cam.ac.uk.
261           Last updated: 12 April 2008
262           Copyright (c) 1997-2008 University of Cambridge.
263    ------------------------------------------------------------------------------
266    PCREBUILD(3)                                                      PCREBUILD(3)
269    NAME
270           PCRE - Perl-compatible regular expressions
275           This  document  describes  the  optional  features  of PCRE that can be
276           selected when the library is compiled. It assumes use of the  configure
277           script,  where the optional features are selected or deselected by pro-
278           viding options to configure before running the make  command.  However,
279           the  same  options  can be selected in both Unix-like and non-Unix-like
280           environments using the GUI facility of  CMakeSetup  if  you  are  using
281           CMake instead of configure to build PCRE.
283           The complete list of options for configure (which includes the standard
284           ones such as the  selection  of  the  installation  directory)  can  be
285           obtained by running
287             ./configure --help
289           The  following  sections  include  descriptions  of options whose names
290           begin with --enable or --disable. These settings specify changes to the
291           defaults  for  the configure command. Because of the way that configure
292           works, --enable and --disable always come in pairs, so  the  complemen-
293           tary  option always exists as well, but as it specifies the default, it
294           is not described.
297    C++ SUPPORT
299           By default, the configure script will search for a C++ compiler and C++
300           header files. If it finds them, it automatically builds the C++ wrapper
301           library for PCRE. You can disable this by adding
303             --disable-cpp
305           to the configure command.
308    UTF-8 SUPPORT
310           To build PCRE with support for UTF-8 character strings, add
312             --enable-utf8
314           to the configure command. Of itself, this  does  not  make  PCRE  treat
315           strings  as UTF-8. As well as compiling PCRE with this option, you also
316           have have to set the PCRE_UTF8 option when you call the  pcre_compile()
317           function.
322           UTF-8  support allows PCRE to process character values greater than 255
323           in the strings that it handles. On its own, however, it does  not  pro-
324           vide any facilities for accessing the properties of such characters. If
325           you want to be able to use the pattern escapes \P, \p,  and  \X,  which
326           refer to Unicode character properties, you must add
328             --enable-unicode-properties
330           to  the configure command. This implies UTF-8 support, even if you have
331           not explicitly requested it.
333           Including Unicode property support adds around 30K  of  tables  to  the
334           PCRE  library.  Only  the general category properties such as Lu and Nd
335           are supported. Details are given in the pcrepattern documentation.
340           By default, PCRE interprets character 10 (linefeed, LF)  as  indicating
341           the  end  of  a line. This is the normal newline character on Unix-like
342           systems. You can compile PCRE to use character 13 (carriage return, CR)
343           instead, by adding
345             --enable-newline-is-cr
347           to  the  configure  command.  There  is  also  a --enable-newline-is-lf
348           option, which explicitly specifies linefeed as the newline character.
350           Alternatively, you can specify that line endings are to be indicated by
351           the two character sequence CRLF. If you want this, add
353             --enable-newline-is-crlf
355           to the configure command. There is a fourth option, specified by
357             --enable-newline-is-anycrlf
359           which  causes  PCRE  to recognize any of the three sequences CR, LF, or
360           CRLF as indicating a line ending. Finally, a fifth option, specified by
362             --enable-newline-is-any
364           causes PCRE to recognize any Unicode newline sequence.
366           Whatever  line  ending convention is selected when PCRE is built can be
367           overridden when the library functions are called. At build time  it  is
368           conventional to use the standard for your operating system.
373           By  default,  the  sequence \R in a pattern matches any Unicode newline
374           sequence, whatever has been selected as the line  ending  sequence.  If
375           you specify
377             --enable-bsr-anycrlf
379           the  default  is changed so that \R matches only CR, LF, or CRLF. What-
380           ever is selected when PCRE is built can be overridden when the  library
381           functions are called.
386           The  PCRE building process uses libtool to build both shared and static
387           Unix libraries by default. You can suppress one of these by adding  one
388           of
390             --disable-shared
391             --disable-static
393           to the configure command, as required.
398           When PCRE is called through the POSIX interface (see the pcreposix doc-
399           umentation), additional working storage is  required  for  holding  the
400           pointers  to capturing substrings, because PCRE requires three integers
401           per substring, whereas the POSIX interface provides only  two.  If  the
402           number of expected substrings is small, the wrapper function uses space
403           on the stack, because this is faster than using malloc() for each call.
404           The default threshold above which the stack is no longer used is 10; it
405           can be changed by adding a setting such as
407             --with-posix-malloc-threshold=20
409           to the configure command.
414           Within a compiled pattern, offset values are used  to  point  from  one
415           part  to another (for example, from an opening parenthesis to an alter-
416           nation metacharacter). By default, two-byte values are used  for  these
417           offsets,  leading  to  a  maximum size for a compiled pattern of around
418           64K. This is sufficient to handle all but the most  gigantic  patterns.
419           Nevertheless,  some  people do want to process enormous patterns, so it
420           is possible to compile PCRE to use three-byte or four-byte  offsets  by
421           adding a setting such as
423             --with-link-size=3
425           to  the  configure  command.  The value given must be 2, 3, or 4. Using
426           longer offsets slows down the operation of PCRE because it has to  load
427           additional bytes when handling them.
432           When matching with the pcre_exec() function, PCRE implements backtrack-
433           ing by making recursive calls to an internal function  called  match().
434           In  environments  where  the size of the stack is limited, this can se-
435           verely limit PCRE's operation. (The Unix environment does  not  usually
436           suffer from this problem, but it may sometimes be necessary to increase
437           the maximum stack size.  There is a discussion in the  pcrestack  docu-
438           mentation.)  An alternative approach to recursion that uses memory from
439           the heap to remember data, instead of using recursive  function  calls,
440           has  been  implemented to work round the problem of limited stack size.
441           If you want to build a version of PCRE that works this way, add
443             --disable-stack-for-recursion
445           to the configure command. With this configuration, PCRE  will  use  the
446           pcre_stack_malloc  and pcre_stack_free variables to call memory manage-
447           ment functions. By default these point to malloc() and free(), but  you
448           can replace the pointers so that your own functions are used.
450           Separate  functions  are  provided  rather  than  using pcre_malloc and
451           pcre_free because the  usage  is  very  predictable:  the  block  sizes
452           requested  are  always  the  same,  and  the blocks are always freed in
453           reverse order. A calling program might be able to  implement  optimized
454           functions  that  perform  better  than  malloc()  and free(). PCRE runs
455           noticeably more slowly when built in this way. This option affects only
456           the   pcre_exec()   function;   it   is   not   relevant  for  the  the
457           pcre_dfa_exec() function.
462           Internally, PCRE has a function called match(), which it calls  repeat-
463           edly   (sometimes   recursively)  when  matching  a  pattern  with  the
464           pcre_exec() function. By controlling the maximum number of  times  this
465           function  may be called during a single matching operation, a limit can
466           be placed on the resources used by a single call  to  pcre_exec().  The
467           limit  can be changed at run time, as described in the pcreapi documen-
468           tation. The default is 10 million, but this can be changed by adding  a
469           setting such as
471             --with-match-limit=500000
473           to   the   configure  command.  This  setting  has  no  effect  on  the
474           pcre_dfa_exec() matching function.
476           In some environments it is desirable to limit the  depth  of  recursive
477           calls of match() more strictly than the total number of calls, in order
478           to restrict the maximum amount of stack (or heap,  if  --disable-stack-
479           for-recursion is specified) that is used. A second limit controls this;
480           it defaults to the value that  is  set  for  --with-match-limit,  which
481           imposes  no  additional constraints. However, you can set a lower limit
482           by adding, for example,
484             --with-match-limit-recursion=10000
486           to the configure command. This value can  also  be  overridden  at  run
487           time.
492           PCRE  uses fixed tables for processing characters whose code values are
493           less than 256. By default, PCRE is built with a set of tables that  are
494           distributed  in  the  file pcre_chartables.c.dist. These tables are for
495           ASCII codes only. If you add
497             --enable-rebuild-chartables
499           to the configure command, the distributed tables are  no  longer  used.
500           Instead,  a  program  called dftables is compiled and run. This outputs
501           the source for new set of tables, created in the default locale of your
502           C runtime system. (This method of replacing the tables does not work if
503           you are cross compiling, because dftables is run on the local host.  If
504           you  need  to  create alternative tables when cross compiling, you will
505           have to do so "by hand".)
510           PCRE assumes by default that it will run in an  environment  where  the
511           character  code  is  ASCII  (or Unicode, which is a superset of ASCII).
512           This is the case for most computer operating systems.  PCRE  can,  how-
513           ever, be compiled to run in an EBCDIC environment by adding
515             --enable-ebcdic
517           to the configure command. This setting implies --enable-rebuild-charta-
518           bles. You should only use it if you know that  you  are  in  an  EBCDIC
519           environment (for example, an IBM mainframe operating system).
524           By default, pcregrep reads all files as plain text. You can build it so
525           that it recognizes files whose names end in .gz or .bz2, and reads them
526           with libz or libbz2, respectively, by adding one or both of
528             --enable-pcregrep-libz
529             --enable-pcregrep-libbz2
531           to the configure command. These options naturally require that the rel-
532           evant libraries are installed on your system. Configuration  will  fail
533           if they are not.
538           If you add
540             --enable-pcretest-libreadline
542           to  the  configure  command,  pcretest  is  linked with the libreadline
543           library, and when its input is from a terminal, it reads it  using  the
544           readline() function. This provides line-editing and history facilities.
545           Note that libreadline is GPL-licenced, so if you distribute a binary of
546           pcretest linked in this way, there may be licensing issues.
548           Setting  this  option  causes  the -lreadline option to be added to the
549           pcretest build. In many operating environments with  a  sytem-installed
550           libreadline this is sufficient. However, in some environments (e.g.  if
551           an unmodified distribution version of readline is in use),  some  extra
552           configuration  may  be necessary. The INSTALL file for libreadline says
553           this:
555             "Readline uses the termcap functions, but does not link with the
556             termcap or curses library itself, allowing applications which link
557             with readline the to choose an appropriate library."
559           If your environment has not been set up so that an appropriate  library
560           is automatically included, you may need to add something like
562             LIBS="-ncurses"
564           immediately before the configure command.
567    SEE ALSO
569           pcreapi(3), pcre_config(3).
572    AUTHOR
574           Philip Hazel
575           University Computing Service
576           Cambridge CB2 3QH, England.
581           Last updated: 13 April 2008
582           Copyright (c) 1997-2008 University of Cambridge.
583    ------------------------------------------------------------------------------
586    PCREMATCHING(3)                                                PCREMATCHING(3)
589    NAME
590           PCRE - Perl-compatible regular expressions
595           This document describes the two different algorithms that are available
596           in PCRE for matching a compiled regular expression against a given sub-
597           ject  string.  The  "standard"  algorithm  is  the  one provided by the
598           pcre_exec() function.  This works in the same was  as  Perl's  matching
599           function, and provides a Perl-compatible matching operation.
601           An  alternative  algorithm is provided by the pcre_dfa_exec() function;
602           this operates in a different way, and is not  Perl-compatible.  It  has
603           advantages  and disadvantages compared with the standard algorithm, and
604           these are described below.
606           When there is only one possible way in which a given subject string can
607           match  a pattern, the two algorithms give the same answer. A difference
608           arises, however, when there are multiple possibilities. For example, if
609           the pattern
611             ^<.*>
613           is matched against the string
615             <something> <something else> <something further>
617           there are three possible answers. The standard algorithm finds only one
618           of them, whereas the alternative algorithm finds all three.
623           The set of strings that are matched by a regular expression can be rep-
624           resented  as  a  tree structure. An unlimited repetition in the pattern
625           makes the tree of infinite size, but it is still a tree.  Matching  the
626           pattern  to a given subject string (from a given starting point) can be
627           thought of as a search of the tree.  There are two  ways  to  search  a
628           tree:  depth-first  and  breadth-first, and these correspond to the two
629           matching algorithms provided by PCRE.
634           In the terminology of Jeffrey Friedl's book "Mastering Regular  Expres-
635           sions",  the  standard  algorithm  is an "NFA algorithm". It conducts a
636           depth-first search of the pattern tree. That is, it  proceeds  along  a
637           single path through the tree, checking that the subject matches what is
638           required. When there is a mismatch, the algorithm  tries  any  alterna-
639           tives  at  the  current point, and if they all fail, it backs up to the
640           previous branch point in the  tree,  and  tries  the  next  alternative
641           branch  at  that  level.  This often involves backing up (moving to the
642           left) in the subject string as well.  The  order  in  which  repetition
643           branches  are  tried  is controlled by the greedy or ungreedy nature of
644           the quantifier.
646           If a leaf node is reached, a matching string has  been  found,  and  at
647           that  point the algorithm stops. Thus, if there is more than one possi-
648           ble match, this algorithm returns the first one that it finds.  Whether
649           this  is the shortest, the longest, or some intermediate length depends
650           on the way the greedy and ungreedy repetition quantifiers are specified
651           in the pattern.
653           Because  it  ends  up  with a single path through the tree, it is rela-
654           tively straightforward for this algorithm to keep  track  of  the  sub-
655           strings  that  are  matched  by portions of the pattern in parentheses.
656           This provides support for capturing parentheses and back references.
661           This algorithm conducts a breadth-first search of  the  tree.  Starting
662           from  the  first  matching  point  in the subject, it scans the subject
663           string from left to right, once, character by character, and as it does
664           this,  it remembers all the paths through the tree that represent valid
665           matches. In Friedl's terminology, this is a kind  of  "DFA  algorithm",
666           though  it is not implemented as a traditional finite state machine (it
667           keeps multiple states active simultaneously).
669           The scan continues until either the end of the subject is  reached,  or
670           there  are  no more unterminated paths. At this point, terminated paths
671           represent the different matching possibilities (if there are none,  the
672           match  has  failed).   Thus,  if there is more than one possible match,
673           this algorithm finds all of them, and in particular, it finds the long-
674           est.  In PCRE, there is an option to stop the algorithm after the first
675           match (which is necessarily the shortest) has been found.
677           Note that all the matches that are found start at the same point in the
678           subject. If the pattern
680             cat(er(pillar)?)
682           is  matched  against the string "the caterpillar catchment", the result
683           will be the three strings "cat", "cater", and "caterpillar" that  start
684           at the fourth character of the subject. The algorithm does not automat-
685           ically move on to find matches that start at later positions.
687           There are a number of features of PCRE regular expressions that are not
688           supported by the alternative matching algorithm. They are as follows:
690           1.  Because  the  algorithm  finds  all possible matches, the greedy or
691           ungreedy nature of repetition quantifiers is not relevant.  Greedy  and
692           ungreedy quantifiers are treated in exactly the same way. However, pos-
693           sessive quantifiers can make a difference when what follows could  also
694           match what is quantified, for example in a pattern like this:
696             ^a++\w!
698           This  pattern matches "aaab!" but not "aaa!", which would be matched by
699           a non-possessive quantifier. Similarly, if an atomic group is  present,
700           it  is matched as if it were a standalone pattern at the current point,
701           and the longest match is then "locked in" for the rest of  the  overall
702           pattern.
704           2. When dealing with multiple paths through the tree simultaneously, it
705           is not straightforward to keep track of  captured  substrings  for  the
706           different  matching  possibilities,  and  PCRE's implementation of this
707           algorithm does not attempt to do this. This means that no captured sub-
708           strings are available.
710           3.  Because no substrings are captured, back references within the pat-
711           tern are not supported, and cause errors if encountered.
713           4. For the same reason, conditional expressions that use  a  backrefer-
714           ence  as  the  condition or test for a specific group recursion are not
715           supported.
717           5. Because many paths through the tree may be  active,  the  \K  escape
718           sequence, which resets the start of the match when encountered (but may
719           be on some paths and not on others), is not  supported.  It  causes  an
720           error if encountered.
722           6.  Callouts  are  supported, but the value of the capture_top field is
723           always 1, and the value of the capture_last field is always -1.
725           7. The \C escape sequence, which (in the standard algorithm) matches  a
726           single  byte, even in UTF-8 mode, is not supported because the alterna-
727           tive algorithm moves through the subject  string  one  character  at  a
728           time, for all active paths through the tree.
730           8.  Except for (*FAIL), the backtracking control verbs such as (*PRUNE)
731           are not supported. (*FAIL) is supported, and  behaves  like  a  failing
732           negative assertion.
737           Using  the alternative matching algorithm provides the following advan-
738           tages:
740           1. All possible matches (at a single point in the subject) are automat-
741           ically  found,  and  in particular, the longest match is found. To find
742           more than one match using the standard algorithm, you have to do kludgy
743           things with callouts.
745           2.  There is much better support for partial matching. The restrictions
746           on the content of the pattern that apply when using the standard  algo-
747           rithm  for  partial matching do not apply to the alternative algorithm.
748           For non-anchored patterns, the starting position of a partial match  is
749           available.
751           3.  Because  the  alternative  algorithm  scans the subject string just
752           once, and never needs to backtrack, it is possible to  pass  very  long
753           subject  strings  to  the matching function in several pieces, checking
754           for partial matching each time.
759           The alternative algorithm suffers from a number of disadvantages:
761           1. It is substantially slower than  the  standard  algorithm.  This  is
762           partly  because  it has to search for all possible matches, but is also
763           because it is less susceptible to optimization.
765           2. Capturing parentheses and back references are not supported.
767           3. Although atomic groups are supported, their use does not provide the
768           performance advantage that it does for the standard algorithm.
771    AUTHOR
773           Philip Hazel
774           University Computing Service
775           Cambridge CB2 3QH, England.
780           Last updated: 19 April 2008
781           Copyright (c) 1997-2008 University of Cambridge.
782    ------------------------------------------------------------------------------
785    PCREAPI(3)                                                          PCREAPI(3)
788    NAME
789           PCRE - Perl-compatible regular expressions
794           #include <pcre.h>
796           pcre *pcre_compile(const char *pattern, int options,
797                const char **errptr, int *erroffset,
798                const unsigned char *tableptr);
800           pcre *pcre_compile2(const char *pattern, int options,
801                int *errorcodeptr,
802                const char **errptr, int *erroffset,
803                const unsigned char *tableptr);
805           pcre_extra *pcre_study(const pcre *code, int options,
806                const char **errptr);
808           int pcre_exec(const pcre *code, const pcre_extra *extra,
809                const char *subject, int length, int startoffset,
810                int options, int *ovector, int ovecsize);
812           int pcre_dfa_exec(const pcre *code, const pcre_extra *extra,
813                const char *subject, int length, int startoffset,
814                int options, int *ovector, int ovecsize,
815                int *workspace, int wscount);
817           int pcre_copy_named_substring(const pcre *code,
818                const char *subject, int *ovector,
819                int stringcount, const char *stringname,
820                char *buffer, int buffersize);
822           int pcre_copy_substring(const char *subject, int *ovector,
823                int stringcount, int stringnumber, char *buffer,
824                int buffersize);
826           int pcre_get_named_substring(const pcre *code,
827                const char *subject, int *ovector,
828                int stringcount, const char *stringname,
829                const char **stringptr);
831           int pcre_get_stringnumber(const pcre *code,
832                const char *name);
834           int pcre_get_stringtable_entries(const pcre *code,
835                const char *name, char **first, char **last);
837           int pcre_get_substring(const char *subject, int *ovector,
838                int stringcount, int stringnumber,
839                const char **stringptr);
841           int pcre_get_substring_list(const char *subject,
842                int *ovector, int stringcount, const char ***listptr);
844           void pcre_free_substring(const char *stringptr);
846           void pcre_free_substring_list(const char **stringptr);
848           const unsigned char *pcre_maketables(void);
850           int pcre_fullinfo(const pcre *code, const pcre_extra *extra,
851                int what, void *where);
853           int pcre_info(const pcre *code, int *optptr, int *firstcharptr);
855           int pcre_refcount(pcre *code, int adjust);
857           int pcre_config(int what, void *where);
859           char *pcre_version(void);
861           void *(*pcre_malloc)(size_t);
863           void (*pcre_free)(void *);
865           void *(*pcre_stack_malloc)(size_t);
867           void (*pcre_stack_free)(void *);
869           int (*pcre_callout)(pcre_callout_block *);
874           PCRE has its own native API, which is described in this document. There
875           are also some wrapper functions that correspond to  the  POSIX  regular
876           expression  API.  These  are  described in the pcreposix documentation.
877           Both of these APIs define a set of C function calls. A C++  wrapper  is
878           distributed with PCRE. It is documented in the pcrecpp page.
880           The  native  API  C  function prototypes are defined in the header file
881           pcre.h, and on Unix systems the library itself is called  libpcre.   It
882           can normally be accessed by adding -lpcre to the command for linking an
883           application  that  uses  PCRE.  The  header  file  defines  the  macros
884           PCRE_MAJOR  and  PCRE_MINOR to contain the major and minor release num-
885           bers for the library.  Applications can use these  to  include  support
886           for different releases of PCRE.
888           The   functions   pcre_compile(),  pcre_compile2(),  pcre_study(),  and
889           pcre_exec() are used for compiling and matching regular expressions  in
890           a  Perl-compatible  manner. A sample program that demonstrates the sim-
891           plest way of using them is provided in the file  called  pcredemo.c  in
892           the  source distribution. The pcresample documentation describes how to
893           compile and run it.
895           A second matching function, pcre_dfa_exec(), which is not Perl-compati-
896           ble,  is  also provided. This uses a different algorithm for the match-
897           ing. The alternative algorithm finds all possible matches (at  a  given
898           point  in  the subject), and scans the subject just once. However, this
899           algorithm does not return captured substrings. A description of the two
900           matching  algorithms and their advantages and disadvantages is given in
901           the pcrematching documentation.
903           In addition to the main compiling and  matching  functions,  there  are
904           convenience functions for extracting captured substrings from a subject
905           string that is matched by pcre_exec(). They are:
907             pcre_copy_substring()
908             pcre_copy_named_substring()
909             pcre_get_substring()
910             pcre_get_named_substring()
911             pcre_get_substring_list()
912             pcre_get_stringnumber()
913             pcre_get_stringtable_entries()
915           pcre_free_substring() and pcre_free_substring_list() are also provided,
916           to free the memory used for extracted strings.
918           The  function  pcre_maketables()  is  used  to build a set of character
919           tables  in  the  current  locale   for   passing   to   pcre_compile(),
920           pcre_exec(),  or  pcre_dfa_exec(). This is an optional facility that is
921           provided for specialist use.  Most  commonly,  no  special  tables  are
922           passed,  in  which case internal tables that are generated when PCRE is
923           built are used.
925           The function pcre_fullinfo() is used to find out  information  about  a
926           compiled  pattern; pcre_info() is an obsolete version that returns only
927           some of the available information, but is retained for  backwards  com-
928           patibility.   The function pcre_version() returns a pointer to a string
929           containing the version of PCRE and its date of release.
931           The function pcre_refcount() maintains a  reference  count  in  a  data
932           block  containing  a compiled pattern. This is provided for the benefit
933           of object-oriented applications.
935           The global variables pcre_malloc and pcre_free  initially  contain  the
936           entry  points  of  the  standard malloc() and free() functions, respec-
937           tively. PCRE calls the memory management functions via these variables,
938           so  a  calling  program  can replace them if it wishes to intercept the
939           calls. This should be done before calling any PCRE functions.
941           The global variables pcre_stack_malloc  and  pcre_stack_free  are  also
942           indirections  to  memory  management functions. These special functions
943           are used only when PCRE is compiled to use  the  heap  for  remembering
944           data, instead of recursive function calls, when running the pcre_exec()
945           function. See the pcrebuild documentation for  details  of  how  to  do
946           this.  It  is  a non-standard way of building PCRE, for use in environ-
947           ments that have limited stacks. Because of the greater  use  of  memory
948           management,  it  runs  more  slowly. Separate functions are provided so
949           that special-purpose external code can be  used  for  this  case.  When
950           used,  these  functions  are always called in a stack-like manner (last
951           obtained, first freed), and always for memory blocks of the same  size.
952           There  is  a discussion about PCRE's stack usage in the pcrestack docu-
953           mentation.
955           The global variable pcre_callout initially contains NULL. It can be set
956           by  the  caller  to  a "callout" function, which PCRE will then call at
957           specified points during a matching operation. Details are given in  the
958           pcrecallout documentation.
963           PCRE  supports five different conventions for indicating line breaks in
964           strings: a single CR (carriage return) character, a  single  LF  (line-
965           feed) character, the two-character sequence CRLF, any of the three pre-
966           ceding, or any Unicode newline sequence. The Unicode newline  sequences
967           are  the  three just mentioned, plus the single characters VT (vertical
968           tab, U+000B), FF (formfeed, U+000C), NEL (next line, U+0085), LS  (line
969           separator, U+2028), and PS (paragraph separator, U+2029).
971           Each  of  the first three conventions is used by at least one operating
972           system as its standard newline sequence. When PCRE is built, a  default
973           can  be  specified.  The default default is LF, which is the Unix stan-
974           dard. When PCRE is run, the default can be overridden,  either  when  a
975           pattern is compiled, or when it is matched.
977           At compile time, the newline convention can be specified by the options
978           argument of pcre_compile(), or it can be specified by special  text  at
979           the start of the pattern itself; this overrides any other settings. See
980           the pcrepattern page for details of the special character sequences.
982           In the PCRE documentation the word "newline" is used to mean "the char-
983           acter  or pair of characters that indicate a line break". The choice of
984           newline convention affects the handling of  the  dot,  circumflex,  and
985           dollar metacharacters, the handling of #-comments in /x mode, and, when
986           CRLF is a recognized line ending sequence, the match position  advance-
987           ment for a non-anchored pattern. There is more detail about this in the
988           section on pcre_exec() options below.
990           The choice of newline convention does not affect the interpretation  of
991           the  \n  or  \r  escape  sequences, nor does it affect what \R matches,
992           which is controlled in a similar way, but by separate options.
997           The PCRE functions can be used in  multi-threading  applications,  with
998           the  proviso  that  the  memory  management  functions  pointed  to  by
999           pcre_malloc, pcre_free, pcre_stack_malloc, and pcre_stack_free, and the
1000           callout function pointed to by pcre_callout, are shared by all threads.
1002           The compiled form of a regular expression is not altered during  match-
1003           ing, so the same compiled pattern can safely be used by several threads
1004           at once.
1009           The compiled form of a regular expression can be saved and re-used at a
1010           later  time,  possibly by a different program, and even on a host other
1011           than the one on which  it  was  compiled.  Details  are  given  in  the
1012           pcreprecompile  documentation.  However, compiling a regular expression
1013           with one version of PCRE for use with a different version is not  guar-
1014           anteed to work and may cause crashes.
1019           int pcre_config(int what, void *where);
1021           The  function pcre_config() makes it possible for a PCRE client to dis-
1022           cover which optional features have been compiled into the PCRE library.
1023           The  pcrebuild documentation has more details about these optional fea-
1024           tures.
1026           The first argument for pcre_config() is an  integer,  specifying  which
1027           information is required; the second argument is a pointer to a variable
1028           into which the information is  placed.  The  following  information  is
1029           available:
1031             PCRE_CONFIG_UTF8
1033           The  output is an integer that is set to one if UTF-8 support is avail-
1034           able; otherwise it is set to zero.
1038           The output is an integer that is set to  one  if  support  for  Unicode
1039           character properties is available; otherwise it is set to zero.
1041             PCRE_CONFIG_NEWLINE
1043           The  output  is  an integer whose value specifies the default character
1044           sequence that is recognized as meaning "newline". The four values  that
1045           are supported are: 10 for LF, 13 for CR, 3338 for CRLF, -2 for ANYCRLF,
1046           and -1 for ANY. The default should normally be  the  standard  sequence
1047           for your operating system.
1049             PCRE_CONFIG_BSR
1051           The output is an integer whose value indicates what character sequences
1052           the \R escape sequence matches by default. A value of 0 means  that  \R
1053           matches  any  Unicode  line ending sequence; a value of 1 means that \R
1054           matches only CR, LF, or CRLF. The default can be overridden when a pat-
1055           tern is compiled or matched.
1057             PCRE_CONFIG_LINK_SIZE
1059           The  output  is  an  integer that contains the number of bytes used for
1060           internal linkage in compiled regular expressions. The value is 2, 3, or
1061           4.  Larger  values  allow larger regular expressions to be compiled, at
1062           the expense of slower matching. The default value of  2  is  sufficient
1063           for  all  but  the  most massive patterns, since it allows the compiled
1064           pattern to be up to 64K in size.
1068           The output is an integer that contains the threshold  above  which  the
1069           POSIX  interface  uses malloc() for output vectors. Further details are
1070           given in the pcreposix documentation.
1072             PCRE_CONFIG_MATCH_LIMIT
1074           The output is an integer that gives the default limit for the number of
1075           internal  matching  function  calls in a pcre_exec() execution. Further
1076           details are given with pcre_exec() below.
1080           The output is an integer that gives the default limit for the depth  of
1081           recursion  when calling the internal matching function in a pcre_exec()
1082           execution. Further details are given with pcre_exec() below.
1086           The output is an integer that is set to one if internal recursion  when
1087           running pcre_exec() is implemented by recursive function calls that use
1088           the stack to remember their state. This is the usual way that  PCRE  is
1089           compiled. The output is zero if PCRE was compiled to use blocks of data
1090           on the  heap  instead  of  recursive  function  calls.  In  this  case,
1091           pcre_stack_malloc  and  pcre_stack_free  are  called  to  manage memory
1092           blocks on the heap, thus avoiding the use of the stack.
1097           pcre *pcre_compile(const char *pattern, int options,
1098                const char **errptr, int *erroffset,
1099                const unsigned char *tableptr);
1101           pcre *pcre_compile2(const char *pattern, int options,
1102                int *errorcodeptr,
1103                const char **errptr, int *erroffset,
1104                const unsigned char *tableptr);
1106           Either of the functions pcre_compile() or pcre_compile2() can be called
1107           to compile a pattern into an internal form. The only difference between
1108           the two interfaces is that pcre_compile2() has an additional  argument,
1109           errorcodeptr, via which a numerical error code can be returned.
1111           The pattern is a C string terminated by a binary zero, and is passed in
1112           the pattern argument. A pointer to a single block  of  memory  that  is
1113           obtained  via  pcre_malloc is returned. This contains the compiled code
1114           and related data. The pcre type is defined for the returned block; this
1115           is a typedef for a structure whose contents are not externally defined.
1116           It is up to the caller to free the memory (via pcre_free) when it is no
1117           longer required.
1119           Although  the compiled code of a PCRE regex is relocatable, that is, it
1120           does not depend on memory location, the complete pcre data block is not
1121           fully  relocatable, because it may contain a copy of the tableptr argu-
1122           ment, which is an address (see below).
1124           The options argument contains various bit settings that affect the com-
1125           pilation.  It  should be zero if no options are required. The available
1126           options are described below. Some of them, in  particular,  those  that
1127           are  compatible  with  Perl,  can also be set and unset from within the
1128           pattern (see the detailed description  in  the  pcrepattern  documenta-
1129           tion).  For  these options, the contents of the options argument speci-
1130           fies their initial settings at the start of compilation and  execution.
1131           The  PCRE_ANCHORED  and PCRE_NEWLINE_xxx options can be set at the time
1132           of matching as well as at compile time.
1134           If errptr is NULL, pcre_compile() returns NULL immediately.  Otherwise,
1135           if  compilation  of  a  pattern fails, pcre_compile() returns NULL, and
1136           sets the variable pointed to by errptr to point to a textual error mes-
1137           sage. This is a static string that is part of the library. You must not
1138           try to free it. The offset from the start of the pattern to the charac-
1139           ter where the error was discovered is placed in the variable pointed to
1140           by erroffset, which must not be NULL. If it is, an immediate  error  is
1141           given.
1143           If  pcre_compile2()  is  used instead of pcre_compile(), and the error-
1144           codeptr argument is not NULL, a non-zero error code number is  returned
1145           via  this argument in the event of an error. This is in addition to the
1146           textual error message. Error codes and messages are listed below.
1148           If the final argument, tableptr, is NULL, PCRE uses a  default  set  of
1149           character  tables  that  are  built  when  PCRE  is compiled, using the
1150           default C locale. Otherwise, tableptr must be an address  that  is  the
1151           result  of  a  call to pcre_maketables(). This value is stored with the
1152           compiled pattern, and used again by pcre_exec(), unless  another  table
1153           pointer is passed to it. For more discussion, see the section on locale
1154           support below.
1156           This code fragment shows a typical straightforward  call  to  pcre_com-
1157           pile():
1159             pcre *re;
1160             const char *error;
1161             int erroffset;
1162             re = pcre_compile(
1163               "^A.*Z",          /* the pattern */
1164               0,                /* default options */
1165               &error,           /* for error message */
1166               &erroffset,       /* for error offset */
1167               NULL);            /* use default character tables */
1169           The  following  names  for option bits are defined in the pcre.h header
1170           file:
1172             PCRE_ANCHORED
1174           If this bit is set, the pattern is forced to be "anchored", that is, it
1175           is  constrained to match only at the first matching point in the string
1176           that is being searched (the "subject string"). This effect can also  be
1177           achieved  by appropriate constructs in the pattern itself, which is the
1178           only way to do it in Perl.
1180             PCRE_AUTO_CALLOUT
1182           If this bit is set, pcre_compile() automatically inserts callout items,
1183           all  with  number  255, before each pattern item. For discussion of the
1184           callout facility, see the pcrecallout documentation.
1186             PCRE_BSR_ANYCRLF
1187             PCRE_BSR_UNICODE
1189           These options (which are mutually exclusive) control what the \R escape
1190           sequence  matches.  The choice is either to match only CR, LF, or CRLF,
1191           or to match any Unicode newline sequence. The default is specified when
1192           PCRE is built. It can be overridden from within the pattern, or by set-
1193           ting an option when a compiled pattern is matched.
1195             PCRE_CASELESS
1197           If this bit is set, letters in the pattern match both upper  and  lower
1198           case  letters.  It  is  equivalent  to  Perl's /i option, and it can be
1199           changed within a pattern by a (?i) option setting. In UTF-8 mode,  PCRE
1200           always  understands the concept of case for characters whose values are
1201           less than 128, so caseless matching is always possible. For  characters
1202           with  higher  values,  the concept of case is supported if PCRE is com-
1203           piled with Unicode property support, but not otherwise. If you want  to
1204           use  caseless  matching  for  characters 128 and above, you must ensure
1205           that PCRE is compiled with Unicode property support  as  well  as  with
1206           UTF-8 support.
1208             PCRE_DOLLAR_ENDONLY
1210           If  this bit is set, a dollar metacharacter in the pattern matches only
1211           at the end of the subject string. Without this option,  a  dollar  also
1212           matches  immediately before a newline at the end of the string (but not
1213           before any other newlines). The PCRE_DOLLAR_ENDONLY option  is  ignored
1214           if  PCRE_MULTILINE  is  set.   There is no equivalent to this option in
1215           Perl, and no way to set it within a pattern.
1217             PCRE_DOTALL
1219           If this bit is set, a dot metacharater in the pattern matches all char-
1220           acters,  including  those that indicate newline. Without it, a dot does
1221           not match when the current position is at a  newline.  This  option  is
1222           equivalent  to Perl's /s option, and it can be changed within a pattern
1223           by a (?s) option setting. A negative class such as [^a] always  matches
1224           newline characters, independent of the setting of this option.
1226             PCRE_DUPNAMES
1228           If  this  bit is set, names used to identify capturing subpatterns need
1229           not be unique. This can be helpful for certain types of pattern when it
1230           is  known  that  only  one instance of the named subpattern can ever be
1231           matched. There are more details of named subpatterns  below;  see  also
1232           the pcrepattern documentation.
1234             PCRE_EXTENDED
1236           If  this  bit  is  set,  whitespace  data characters in the pattern are
1237           totally ignored except when escaped or inside a character class. White-
1238           space does not include the VT character (code 11). In addition, charac-
1239           ters between an unescaped # outside a character class and the next new-
1240           line,  inclusive,  are  also  ignored.  This is equivalent to Perl's /x
1241           option, and it can be changed within a pattern by a  (?x)  option  set-
1242           ting.
1244           This  option  makes  it possible to include comments inside complicated
1245           patterns.  Note, however, that this applies only  to  data  characters.
1246           Whitespace   characters  may  never  appear  within  special  character
1247           sequences in a pattern, for  example  within  the  sequence  (?(  which
1248           introduces a conditional subpattern.
1250             PCRE_EXTRA
1252           This  option  was invented in order to turn on additional functionality
1253           of PCRE that is incompatible with Perl, but it  is  currently  of  very
1254           little  use. When set, any backslash in a pattern that is followed by a
1255           letter that has no special meaning  causes  an  error,  thus  reserving
1256           these  combinations  for  future  expansion.  By default, as in Perl, a
1257           backslash followed by a letter with no special meaning is treated as  a
1258           literal.  (Perl can, however, be persuaded to give a warning for this.)
1259           There are at present no other features controlled by  this  option.  It
1260           can also be set by a (?X) option setting within a pattern.
1262             PCRE_FIRSTLINE
1264           If  this  option  is  set,  an  unanchored pattern is required to match
1265           before or at the first  newline  in  the  subject  string,  though  the
1266           matched text may continue over the newline.
1270           If this option is set, PCRE's behaviour is changed in some ways so that
1271           it is compatible with JavaScript rather than Perl. The changes  are  as
1272           follows:
1274           (1)  A  lone  closing square bracket in a pattern causes a compile-time
1275           error, because this is illegal in JavaScript (by default it is  treated
1276           as a data character). Thus, the pattern AB]CD becomes illegal when this
1277           option is set.
1279           (2) At run time, a back reference to an unset subpattern group  matches
1280           an  empty  string (by default this causes the current matching alterna-
1281           tive to fail). A pattern such as (\1)(a) succeeds when this  option  is
1282           set  (assuming  it can find an "a" in the subject), whereas it fails by
1283           default, for Perl compatibility.
1285             PCRE_MULTILINE
1287           By default, PCRE treats the subject string as consisting  of  a  single
1288           line  of characters (even if it actually contains newlines). The "start
1289           of line" metacharacter (^) matches only at the  start  of  the  string,
1290           while  the  "end  of line" metacharacter ($) matches only at the end of
1291           the string, or before a terminating newline (unless PCRE_DOLLAR_ENDONLY
1292           is set). This is the same as Perl.
1294           When  PCRE_MULTILINE  it  is set, the "start of line" and "end of line"
1295           constructs match immediately following or immediately  before  internal
1296           newlines  in  the  subject string, respectively, as well as at the very
1297           start and end. This is equivalent to Perl's /m option, and  it  can  be
1298           changed within a pattern by a (?m) option setting. If there are no new-
1299           lines in a subject string, or no occurrences of ^ or $  in  a  pattern,
1300           setting PCRE_MULTILINE has no effect.
1302             PCRE_NEWLINE_CR
1303             PCRE_NEWLINE_LF
1304             PCRE_NEWLINE_CRLF
1305             PCRE_NEWLINE_ANYCRLF
1306             PCRE_NEWLINE_ANY
1308           These  options  override the default newline definition that was chosen
1309           when PCRE was built. Setting the first or the second specifies  that  a
1310           newline  is  indicated  by a single character (CR or LF, respectively).
1311           Setting PCRE_NEWLINE_CRLF specifies that a newline is indicated by  the
1312           two-character  CRLF  sequence.  Setting  PCRE_NEWLINE_ANYCRLF specifies
1313           that any of the three preceding sequences should be recognized. Setting
1314           PCRE_NEWLINE_ANY  specifies that any Unicode newline sequence should be
1315           recognized. The Unicode newline sequences are the three just mentioned,
1316           plus  the  single  characters  VT (vertical tab, U+000B), FF (formfeed,
1317           U+000C), NEL (next line, U+0085), LS (line separator, U+2028),  and  PS
1318           (paragraph  separator,  U+2029).  The  last  two are recognized only in
1319           UTF-8 mode.
1321           The newline setting in the  options  word  uses  three  bits  that  are
1322           treated as a number, giving eight possibilities. Currently only six are
1323           used (default plus the five values above). This means that if  you  set
1324           more  than one newline option, the combination may or may not be sensi-
1325           ble. For example, PCRE_NEWLINE_CR with PCRE_NEWLINE_LF is equivalent to
1326           PCRE_NEWLINE_CRLF,  but other combinations may yield unused numbers and
1327           cause an error.
1329           The only time that a line break is specially recognized when  compiling
1330           a  pattern  is  if  PCRE_EXTENDED  is set, and an unescaped # outside a
1331           character class is encountered. This indicates  a  comment  that  lasts
1332           until  after the next line break sequence. In other circumstances, line
1333           break  sequences  are  treated  as  literal  data,   except   that   in
1334           PCRE_EXTENDED mode, both CR and LF are treated as whitespace characters
1335           and are therefore ignored.
1337           The newline option that is set at compile time becomes the default that
1338           is  used for pcre_exec() and pcre_dfa_exec(), but it can be overridden.
1340             PCRE_NO_AUTO_CAPTURE
1342           If this option is set, it disables the use of numbered capturing paren-
1343           theses  in the pattern. Any opening parenthesis that is not followed by
1344           ? behaves as if it were followed by ?: but named parentheses can  still
1345           be  used  for  capturing  (and  they acquire numbers in the usual way).
1346           There is no equivalent of this option in Perl.
1348             PCRE_UNGREEDY
1350           This option inverts the "greediness" of the quantifiers  so  that  they
1351           are  not greedy by default, but become greedy if followed by "?". It is
1352           not compatible with Perl. It can also be set by a (?U)  option  setting
1353           within the pattern.
1355             PCRE_UTF8
1357           This  option  causes PCRE to regard both the pattern and the subject as
1358           strings of UTF-8 characters instead of single-byte  character  strings.
1359           However,  it is available only when PCRE is built to include UTF-8 sup-
1360           port. If not, the use of this option provokes an error. Details of  how
1361           this  option  changes the behaviour of PCRE are given in the section on
1362           UTF-8 support in the main pcre page.
1364             PCRE_NO_UTF8_CHECK
1366           When PCRE_UTF8 is set, the validity of the pattern as a UTF-8 string is
1367           automatically  checked.  There  is  a  discussion about the validity of
1368           UTF-8 strings in the main pcre page. If an invalid  UTF-8  sequence  of
1369           bytes  is  found,  pcre_compile() returns an error. If you already know
1370           that your pattern is valid, and you want to skip this check for perfor-
1371           mance  reasons,  you  can set the PCRE_NO_UTF8_CHECK option. When it is
1372           set, the effect of passing an invalid UTF-8  string  as  a  pattern  is
1373           undefined.  It  may  cause your program to crash. Note that this option
1374           can also be passed to pcre_exec() and pcre_dfa_exec(), to suppress  the
1375           UTF-8 validity checking of subject strings.
1380           The  following  table  lists  the  error  codes than may be returned by
1381           pcre_compile2(), along with the error messages that may be returned  by
1382           both  compiling functions. As PCRE has developed, some error codes have
1383           fallen out of use. To avoid confusion, they have not been re-used.
1385              0  no error
1386              1  \ at end of pattern
1387              2  \c at end of pattern
1388              3  unrecognized character follows \
1389              4  numbers out of order in {} quantifier
1390              5  number too big in {} quantifier
1391              6  missing terminating ] for character class
1392              7  invalid escape sequence in character class
1393              8  range out of order in character class
1394              9  nothing to repeat
1395             10  [this code is not in use]
1396             11  internal error: unexpected repeat
1397             12  unrecognized character after (? or (?-
1398             13  POSIX named classes are supported only within a class
1399             14  missing )
1400             15  reference to non-existent subpattern
1401             16  erroffset passed as NULL
1402             17  unknown option bit(s) set
1403             18  missing ) after comment
1404             19  [this code is not in use]
1405             20  regular expression is too large
1406             21  failed to get memory
1407             22  unmatched parentheses
1408             23  internal error: code overflow
1409             24  unrecognized character after (?<
1410             25  lookbehind assertion is not fixed length
1411             26  malformed number or name after (?(
1412             27  conditional group contains more than two branches
1413             28  assertion expected after (?(
1414             29  (?R or (?[+-]digits must be followed by )
1415             30  unknown POSIX class name
1416             31  POSIX collating elements are not supported
1417             32  this version of PCRE is not compiled with PCRE_UTF8 support
1418             33  [this code is not in use]
1419             34  character value in \x{...} sequence is too large
1420             35  invalid condition (?(0)
1421             36  \C not allowed in lookbehind assertion
1422             37  PCRE does not support \L, \l, \N, \U, or \u
1423             38  number after (?C is > 255
1424             39  closing ) for (?C expected
1425             40  recursive call could loop indefinitely
1426             41  unrecognized character after (?P
1427             42  syntax error in subpattern name (missing terminator)
1428             43  two named subpatterns have the same name
1429             44  invalid UTF-8 string
1430             45  support for \P, \p, and \X has not been compiled
1431             46  malformed \P or \p sequence
1432             47  unknown property name after \P or \p
1433             48  subpattern name is too long (maximum 32 characters)
1434             49  too many named subpatterns (maximum 10000)
1435             50  [this code is not in use]
1436             51  octal value is greater than \377 (not in UTF-8 mode)
1437             52  internal error: overran compiling workspace
1438             53  internal  error:  previously-checked  referenced  subpattern  not
1439           found
1440             54  DEFINE group contains more than one branch
1441             55  repeating a DEFINE group is not allowed
1442             56  inconsistent NEWLINE options
1443             57  \g is not followed by a braced, angle-bracketed, or quoted
1444                   name/number or by a plain number
1445             58  a numbered reference must not be zero
1446             59  (*VERB) with an argument is not supported
1447             60  (*VERB) not recognized
1448             61  number is too big
1449             62  subpattern name expected
1450             63  digit expected after (?+
1451             64  ] is an invalid data character in JavaScript compatibility mode
1453           The  numbers  32  and 10000 in errors 48 and 49 are defaults; different
1454           values may be used if the limits were changed when PCRE was built.
1459           pcre_extra *pcre_study(const pcre *code, int options
1460                const char **errptr);
1462           If a compiled pattern is going to be used several times,  it  is  worth
1463           spending more time analyzing it in order to speed up the time taken for
1464           matching. The function pcre_study() takes a pointer to a compiled  pat-
1465           tern as its first argument. If studying the pattern produces additional
1466           information that will help speed up matching,  pcre_study()  returns  a
1467           pointer  to a pcre_extra block, in which the study_data field points to
1468           the results of the study.
1470           The  returned  value  from  pcre_study()  can  be  passed  directly  to
1471           pcre_exec().  However,  a  pcre_extra  block also contains other fields
1472           that can be set by the caller before the block  is  passed;  these  are
1473           described below in the section on matching a pattern.
1475           If  studying  the  pattern  does not produce any additional information
1476           pcre_study() returns NULL. In that circumstance, if the calling program
1477           wants  to  pass  any of the other fields to pcre_exec(), it must set up
1478           its own pcre_extra block.
1480           The second argument of pcre_study() contains option bits.  At  present,
1481           no options are defined, and this argument should always be zero.
1483           The  third argument for pcre_study() is a pointer for an error message.
1484           If studying succeeds (even if no data is  returned),  the  variable  it
1485           points  to  is  set  to NULL. Otherwise it is set to point to a textual
1486           error message. This is a static string that is part of the library. You
1487           must  not  try  to  free it. You should test the error pointer for NULL
1488           after calling pcre_study(), to be sure that it has run successfully.
1490           This is a typical call to pcre_study():
1492             pcre_extra *pe;
1493             pe = pcre_study(
1494               re,             /* result of pcre_compile() */
1495               0,              /* no options exist */
1496               &error);        /* set to NULL or points to a message */
1498           At present, studying a pattern is useful only for non-anchored patterns
1499           that  do not have a single fixed starting character. A bitmap of possi-
1500           ble starting bytes is created.
1505           PCRE handles caseless matching, and determines whether  characters  are
1506           letters,  digits, or whatever, by reference to a set of tables, indexed
1507           by character value. When running in UTF-8 mode, this  applies  only  to
1508           characters  with  codes  less than 128. Higher-valued codes never match
1509           escapes such as \w or \d, but can be tested with \p if  PCRE  is  built
1510           with  Unicode  character property support. The use of locales with Uni-
1511           code is discouraged. If you are handling characters with codes  greater
1512           than  128, you should either use UTF-8 and Unicode, or use locales, but
1513           not try to mix the two.
1515           PCRE contains an internal set of tables that are used  when  the  final
1516           argument  of  pcre_compile()  is  NULL.  These  are sufficient for many
1517           applications.  Normally, the internal tables recognize only ASCII char-
1518           acters. However, when PCRE is built, it is possible to cause the inter-
1519           nal tables to be rebuilt in the default "C" locale of the local system,
1520           which may cause them to be different.
1522           The  internal tables can always be overridden by tables supplied by the
1523           application that calls PCRE. These may be created in a different locale
1524           from  the  default.  As more and more applications change to using Uni-
1525           code, the need for this locale support is expected to die away.
1527           External tables are built by calling  the  pcre_maketables()  function,
1528           which  has no arguments, in the relevant locale. The result can then be
1529           passed to pcre_compile() or pcre_exec()  as  often  as  necessary.  For
1530           example,  to  build  and use tables that are appropriate for the French
1531           locale (where accented characters with  values  greater  than  128  are
1532           treated as letters), the following code could be used:
1534             setlocale(LC_CTYPE, "fr_FR");
1535             tables = pcre_maketables();
1536             re = pcre_compile(..., tables);
1538           The  locale  name "fr_FR" is used on Linux and other Unix-like systems;
1539           if you are using Windows, the name for the French locale is "french".
1541           When pcre_maketables() runs, the tables are built  in  memory  that  is
1542           obtained  via  pcre_malloc. It is the caller's responsibility to ensure
1543           that the memory containing the tables remains available for as long  as
1544           it is needed.
1546           The pointer that is passed to pcre_compile() is saved with the compiled
1547           pattern, and the same tables are used via this pointer by  pcre_study()
1548           and normally also by pcre_exec(). Thus, by default, for any single pat-
1549           tern, compilation, studying and matching all happen in the same locale,
1550           but different patterns can be compiled in different locales.
1552           It  is  possible to pass a table pointer or NULL (indicating the use of
1553           the internal tables) to pcre_exec(). Although  not  intended  for  this
1554           purpose,  this facility could be used to match a pattern in a different
1555           locale from the one in which it was compiled. Passing table pointers at
1556           run time is discussed below in the section on matching a pattern.
1561           int pcre_fullinfo(const pcre *code, const pcre_extra *extra,
1562                int what, void *where);
1564           The  pcre_fullinfo() function returns information about a compiled pat-
1565           tern. It replaces the obsolete pcre_info() function, which is neverthe-
1566           less retained for backwards compability (and is documented below).
1568           The  first  argument  for  pcre_fullinfo() is a pointer to the compiled
1569           pattern. The second argument is the result of pcre_study(), or NULL  if
1570           the  pattern  was not studied. The third argument specifies which piece
1571           of information is required, and the fourth argument is a pointer  to  a
1572           variable  to  receive  the  data. The yield of the function is zero for
1573           success, or one of the following negative numbers:
1575             PCRE_ERROR_NULL       the argument code was NULL
1576                                   the argument where was NULL
1577             PCRE_ERROR_BADMAGIC   the "magic number" was not found
1578             PCRE_ERROR_BADOPTION  the value of what was invalid
1580           The "magic number" is placed at the start of each compiled  pattern  as
1581           an  simple check against passing an arbitrary memory pointer. Here is a
1582           typical call of pcre_fullinfo(), to obtain the length of  the  compiled
1583           pattern:
1585             int rc;
1586             size_t length;
1587             rc = pcre_fullinfo(
1588               re,               /* result of pcre_compile() */
1589               pe,               /* result of pcre_study(), or NULL */
1590               PCRE_INFO_SIZE,   /* what is required */
1591               &length);         /* where to put the data */
1593           The  possible  values for the third argument are defined in pcre.h, and
1594           are as follows:
1596             PCRE_INFO_BACKREFMAX
1598           Return the number of the highest back reference  in  the  pattern.  The
1599           fourth  argument  should  point to an int variable. Zero is returned if
1600           there are no back references.
1604           Return the number of capturing subpatterns in the pattern.  The  fourth
1605           argument should point to an int variable.
1609           Return  a pointer to the internal default character tables within PCRE.
1610           The fourth argument should point to an unsigned char *  variable.  This
1611           information call is provided for internal use by the pcre_study() func-
1612           tion. External callers can cause PCRE to use  its  internal  tables  by
1613           passing a NULL table pointer.
1615             PCRE_INFO_FIRSTBYTE
1617           Return  information  about  the first byte of any matched string, for a
1618           non-anchored pattern. The fourth argument should point to an int  vari-
1619           able.  (This option used to be called PCRE_INFO_FIRSTCHAR; the old name
1620           is still recognized for backwards compatibility.)
1622           If there is a fixed first byte, for example, from  a  pattern  such  as
1623           (cat|cow|coyote), its value is returned. Otherwise, if either
1625           (a)  the pattern was compiled with the PCRE_MULTILINE option, and every
1626           branch starts with "^", or
1628           (b) every branch of the pattern starts with ".*" and PCRE_DOTALL is not
1629           set (if it were set, the pattern would be anchored),
1631           -1  is  returned, indicating that the pattern matches only at the start
1632           of a subject string or after any newline within the  string.  Otherwise
1633           -2 is returned. For anchored patterns, -2 is returned.
1635             PCRE_INFO_FIRSTTABLE
1637           If  the pattern was studied, and this resulted in the construction of a
1638           256-bit table indicating a fixed set of bytes for the first byte in any
1639           matching  string, a pointer to the table is returned. Otherwise NULL is
1640           returned. The fourth argument should point to an unsigned char *  vari-
1641           able.
1643             PCRE_INFO_HASCRORLF
1645           Return  1  if  the  pattern  contains any explicit matches for CR or LF
1646           characters, otherwise 0. The fourth argument should  point  to  an  int
1647           variable.  An explicit match is either a literal CR or LF character, or
1648           \r or \n.
1650             PCRE_INFO_JCHANGED
1652           Return 1 if the (?J) or (?-J) option setting is used  in  the  pattern,
1653           otherwise  0. The fourth argument should point to an int variable. (?J)
1654           and (?-J) set and unset the local PCRE_DUPNAMES option, respectively.
1656             PCRE_INFO_LASTLITERAL
1658           Return the value of the rightmost literal byte that must exist  in  any
1659           matched  string,  other  than  at  its  start,  if such a byte has been
1660           recorded. The fourth argument should point to an int variable. If there
1661           is  no such byte, -1 is returned. For anchored patterns, a last literal
1662           byte is recorded only if it follows something of variable  length.  For
1663           example, for the pattern /^a\d+z\d+/ the returned value is "z", but for
1664           /^a\dz\d/ the returned value is -1.
1666             PCRE_INFO_NAMECOUNT
1668             PCRE_INFO_NAMETABLE
1670           PCRE supports the use of named as well as numbered capturing  parenthe-
1671           ses.  The names are just an additional way of identifying the parenthe-
1672           ses, which still acquire numbers. Several convenience functions such as
1673           pcre_get_named_substring()  are  provided  for extracting captured sub-
1674           strings by name. It is also possible to extract the data  directly,  by
1675           first  converting  the  name to a number in order to access the correct
1676           pointers in the output vector (described with pcre_exec() below). To do
1677           the  conversion,  you  need  to  use  the  name-to-number map, which is
1678           described by these three values.
1680           The map consists of a number of fixed-size entries. PCRE_INFO_NAMECOUNT
1681           gives the number of entries, and PCRE_INFO_NAMEENTRYSIZE gives the size
1682           of each entry; both of these  return  an  int  value.  The  entry  size
1683           depends  on the length of the longest name. PCRE_INFO_NAMETABLE returns
1684           a pointer to the first entry of the table  (a  pointer  to  char).  The
1685           first two bytes of each entry are the number of the capturing parenthe-
1686           sis, most significant byte first. The rest of the entry is  the  corre-
1687           sponding  name,  zero  terminated. The names are in alphabetical order.
1688           When PCRE_DUPNAMES is set, duplicate names are in order of their paren-
1689           theses  numbers.  For  example,  consider the following pattern (assume
1690           PCRE_EXTENDED is  set,  so  white  space  -  including  newlines  -  is
1691           ignored):
1693             (?<date> (?<year>(\d\d)?\d\d) -
1694             (?<month>\d\d) - (?<day>\d\d) )
1696           There  are  four  named subpatterns, so the table has four entries, and
1697           each entry in the table is eight bytes long. The table is  as  follows,
1698           with non-printing bytes shows in hexadecimal, and undefined bytes shown
1699           as ??:
1701             00 01 d  a  t  e  00 ??
1702             00 05 d  a  y  00 ?? ??
1703             00 04 m  o  n  t  h  00
1704             00 02 y  e  a  r  00 ??
1706           When writing code to extract data  from  named  subpatterns  using  the
1707           name-to-number  map,  remember that the length of the entries is likely
1708           to be different for each compiled pattern.
1710             PCRE_INFO_OKPARTIAL
1712           Return 1 if the pattern can be used for partial matching, otherwise  0.
1713           The  fourth  argument  should point to an int variable. The pcrepartial
1714           documentation lists the restrictions that apply to patterns  when  par-
1715           tial matching is used.
1717             PCRE_INFO_OPTIONS
1719           Return  a  copy of the options with which the pattern was compiled. The
1720           fourth argument should point to an unsigned long  int  variable.  These
1721           option bits are those specified in the call to pcre_compile(), modified
1722           by any top-level option settings at the start of the pattern itself. In
1723           other  words,  they are the options that will be in force when matching
1724           starts. For example, if the pattern /(?im)abc(?-i)d/ is  compiled  with
1725           the  PCRE_EXTENDED option, the result is PCRE_CASELESS, PCRE_MULTILINE,
1726           and PCRE_EXTENDED.
1728           A pattern is automatically anchored by PCRE if  all  of  its  top-level
1729           alternatives begin with one of the following:
1731             ^     unless PCRE_MULTILINE is set
1732             \A    always
1733             \G    always
1734             .*    if PCRE_DOTALL is set and there are no back
1735                     references to the subpattern in which .* appears
1737           For such patterns, the PCRE_ANCHORED bit is set in the options returned
1738           by pcre_fullinfo().
1740             PCRE_INFO_SIZE
1742           Return the size of the compiled pattern, that is, the  value  that  was
1743           passed as the argument to pcre_malloc() when PCRE was getting memory in
1744           which to place the compiled data. The fourth argument should point to a
1745           size_t variable.
1747             PCRE_INFO_STUDYSIZE
1749           Return the size of the data block pointed to by the study_data field in
1750           a pcre_extra block. That is,  it  is  the  value  that  was  passed  to
1751           pcre_malloc() when PCRE was getting memory into which to place the data
1752           created by pcre_study(). The fourth argument should point to  a  size_t
1753           variable.
1758           int pcre_info(const pcre *code, int *optptr, int *firstcharptr);
1760           The  pcre_info()  function is now obsolete because its interface is too
1761           restrictive to return all the available data about a compiled  pattern.
1762           New   programs   should  use  pcre_fullinfo()  instead.  The  yield  of
1763           pcre_info() is the number of capturing subpatterns, or one of the  fol-
1764           lowing negative numbers:
1766             PCRE_ERROR_NULL       the argument code was NULL
1767             PCRE_ERROR_BADMAGIC   the "magic number" was not found
1769           If  the  optptr  argument is not NULL, a copy of the options with which
1770           the pattern was compiled is placed in the integer  it  points  to  (see
1771           PCRE_INFO_OPTIONS above).
1773           If  the  pattern  is  not anchored and the firstcharptr argument is not
1774           NULL, it is used to pass back information about the first character  of
1775           any matched string (see PCRE_INFO_FIRSTBYTE above).
1780           int pcre_refcount(pcre *code, int adjust);
1782           The  pcre_refcount()  function is used to maintain a reference count in
1783           the data block that contains a compiled pattern. It is provided for the
1784           benefit  of  applications  that  operate  in an object-oriented manner,
1785           where different parts of the application may be using the same compiled
1786           pattern, but you want to free the block when they are all done.
1788           When a pattern is compiled, the reference count field is initialized to
1789           zero.  It is changed only by calling this function, whose action is  to
1790           add  the  adjust  value  (which may be positive or negative) to it. The
1791           yield of the function is the new value. However, the value of the count
1792           is  constrained to lie between 0 and 65535, inclusive. If the new value
1793           is outside these limits, it is forced to the appropriate limit value.
1795           Except when it is zero, the reference count is not correctly  preserved
1796           if  a  pattern  is  compiled on one host and then transferred to a host
1797           whose byte-order is different. (This seems a highly unlikely scenario.)
1802           int pcre_exec(const pcre *code, const pcre_extra *extra,
1803                const char *subject, int length, int startoffset,
1804                int options, int *ovector, int ovecsize);
1806           The  function pcre_exec() is called to match a subject string against a
1807           compiled pattern, which is passed in the code argument. If the  pattern
1808           has been studied, the result of the study should be passed in the extra
1809           argument. This function is the main matching facility of  the  library,
1810           and it operates in a Perl-like manner. For specialist use there is also
1811           an alternative matching function, which is described below in the  sec-
1812           tion about the pcre_dfa_exec() function.
1814           In  most applications, the pattern will have been compiled (and option-
1815           ally studied) in the same process that calls pcre_exec().  However,  it
1816           is possible to save compiled patterns and study data, and then use them
1817           later in different processes, possibly even on different hosts.  For  a
1818           discussion about this, see the pcreprecompile documentation.
1820           Here is an example of a simple call to pcre_exec():
1822             int rc;
1823             int ovector[30];
1824             rc = pcre_exec(
1825               re,             /* result of pcre_compile() */
1826               NULL,           /* we didn't study the pattern */
1827               "some string",  /* the subject string */
1828               11,             /* the length of the subject string */
1829               0,              /* start at offset 0 in the subject */
1830               0,              /* default options */
1831               ovector,        /* vector of integers for substring information */
1832               30);            /* number of elements (NOT size in bytes) */
1834       Extra data for pcre_exec()
1836           If  the  extra argument is not NULL, it must point to a pcre_extra data
1837           block. The pcre_study() function returns such a block (when it  doesn't
1838           return  NULL), but you can also create one for yourself, and pass addi-
1839           tional information in it. The pcre_extra block contains  the  following
1840           fields (not necessarily in this order):
1842             unsigned long int flags;
1843             void *study_data;
1844             unsigned long int match_limit;
1845             unsigned long int match_limit_recursion;
1846             void *callout_data;
1847             const unsigned char *tables;
1849           The  flags  field  is a bitmap that specifies which of the other fields
1850           are set. The flag bits are:
1852             PCRE_EXTRA_STUDY_DATA
1853             PCRE_EXTRA_MATCH_LIMIT
1855             PCRE_EXTRA_CALLOUT_DATA
1856             PCRE_EXTRA_TABLES
1858           Other flag bits should be set to zero. The study_data field is  set  in
1859           the  pcre_extra  block  that is returned by pcre_study(), together with
1860           the appropriate flag bit. You should not set this yourself, but you may
1861           add  to  the  block by setting the other fields and their corresponding
1862           flag bits.
1864           The match_limit field provides a means of preventing PCRE from using up
1865           a  vast amount of resources when running patterns that are not going to
1866           match, but which have a very large number  of  possibilities  in  their
1867           search  trees.  The  classic  example  is  the  use of nested unlimited
1868           repeats.
1870           Internally, PCRE uses a function called match() which it calls  repeat-
1871           edly  (sometimes  recursively). The limit set by match_limit is imposed
1872           on the number of times this function is called during  a  match,  which
1873           has  the  effect  of  limiting the amount of backtracking that can take
1874           place. For patterns that are not anchored, the count restarts from zero
1875           for each position in the subject string.
1877           The  default  value  for  the  limit can be set when PCRE is built; the
1878           default default is 10 million, which handles all but the  most  extreme
1879           cases.  You  can  override  the  default by suppling pcre_exec() with a
1880           pcre_extra    block    in    which    match_limit    is    set,     and
1881           PCRE_EXTRA_MATCH_LIMIT  is  set  in  the  flags  field. If the limit is
1882           exceeded, pcre_exec() returns PCRE_ERROR_MATCHLIMIT.
1884           The match_limit_recursion field is similar to match_limit, but  instead
1885           of limiting the total number of times that match() is called, it limits
1886           the depth of recursion. The recursion depth is a  smaller  number  than
1887           the  total number of calls, because not all calls to match() are recur-
1888           sive.  This limit is of use only if it is set smaller than match_limit.
1890           Limiting  the  recursion  depth  limits the amount of stack that can be
1891           used, or, when PCRE has been compiled to use memory on the heap instead
1892           of the stack, the amount of heap memory that can be used.
1894           The  default  value  for  match_limit_recursion can be set when PCRE is
1895           built; the default default  is  the  same  value  as  the  default  for
1896           match_limit.  You can override the default by suppling pcre_exec() with
1897           a  pcre_extra  block  in  which  match_limit_recursion  is   set,   and
1898           PCRE_EXTRA_MATCH_LIMIT_RECURSION  is  set  in  the  flags field. If the
1899           limit is exceeded, pcre_exec() returns PCRE_ERROR_RECURSIONLIMIT.
1901           The pcre_callout field is used in conjunction with the  "callout"  fea-
1902           ture, which is described in the pcrecallout documentation.
1904           The  tables  field  is  used  to  pass  a  character  tables pointer to
1905           pcre_exec(); this overrides the value that is stored with the  compiled
1906           pattern.  A  non-NULL value is stored with the compiled pattern only if
1907           custom tables were supplied to pcre_compile() via  its  tableptr  argu-
1908           ment.  If NULL is passed to pcre_exec() using this mechanism, it forces
1909           PCRE's internal tables to be used. This facility is  helpful  when  re-
1910           using  patterns  that  have been saved after compiling with an external
1911           set of tables, because the external tables  might  be  at  a  different
1912           address  when  pcre_exec() is called. See the pcreprecompile documenta-
1913           tion for a discussion of saving compiled patterns for later use.
1915       Option bits for pcre_exec()
1917           The unused bits of the options argument for pcre_exec() must  be  zero.
1918           The  only  bits  that  may  be set are PCRE_ANCHORED, PCRE_NEWLINE_xxx,
1920           PCRE_PARTIAL.
1922             PCRE_ANCHORED
1924           The  PCRE_ANCHORED  option  limits pcre_exec() to matching at the first
1925           matching position. If a pattern was  compiled  with  PCRE_ANCHORED,  or
1926           turned  out to be anchored by virtue of its contents, it cannot be made
1927           unachored at matching time.
1929             PCRE_BSR_ANYCRLF
1930             PCRE_BSR_UNICODE
1932           These options (which are mutually exclusive) control what the \R escape
1933           sequence  matches.  The choice is either to match only CR, LF, or CRLF,
1934           or to match any Unicode newline sequence. These  options  override  the
1935           choice that was made or defaulted when the pattern was compiled.
1937             PCRE_NEWLINE_CR
1938             PCRE_NEWLINE_LF
1939             PCRE_NEWLINE_CRLF
1940             PCRE_NEWLINE_ANYCRLF
1941             PCRE_NEWLINE_ANY
1943           These  options  override  the  newline  definition  that  was chosen or
1944           defaulted when the pattern was compiled. For details, see the  descrip-
1945           tion  of  pcre_compile()  above.  During  matching,  the newline choice
1946           affects the behaviour of the dot, circumflex,  and  dollar  metacharac-
1947           ters.  It may also alter the way the match position is advanced after a
1948           match failure for an unanchored pattern.
1951           set,  and a match attempt for an unanchored pattern fails when the cur-
1952           rent position is at a  CRLF  sequence,  and  the  pattern  contains  no
1953           explicit  matches  for  CR  or  LF  characters,  the  match position is
1954           advanced by two characters instead of one, in other words, to after the
1955           CRLF.
1957           The above rule is a compromise that makes the most common cases work as
1958           expected. For example, if the  pattern  is  .+A  (and  the  PCRE_DOTALL
1959           option is not set), it does not match the string "\r\nA" because, after
1960           failing at the start, it skips both the CR and the LF before  retrying.
1961           However,  the  pattern  [\r\n]A does match that string, because it con-
1962           tains an explicit CR or LF reference, and so advances only by one char-
1963           acter after the first failure.
1965           An explicit match for CR of LF is either a literal appearance of one of
1966           those characters, or one of the \r or  \n  escape  sequences.  Implicit
1967           matches  such  as [^X] do not count, nor does \s (which includes CR and
1968           LF in the characters that it matches).
1970           Notwithstanding the above, anomalous effects may still occur when  CRLF
1971           is a valid newline sequence and explicit \r or \n escapes appear in the
1972           pattern.
1974             PCRE_NOTBOL
1976           This option specifies that first character of the subject string is not
1977           the  beginning  of  a  line, so the circumflex metacharacter should not
1978           match before it. Setting this without PCRE_MULTILINE (at compile  time)
1979           causes  circumflex  never to match. This option affects only the behav-
1980           iour of the circumflex metacharacter. It does not affect \A.
1982             PCRE_NOTEOL
1984           This option specifies that the end of the subject string is not the end
1985           of  a line, so the dollar metacharacter should not match it nor (except
1986           in multiline mode) a newline immediately before it. Setting this  with-
1987           out PCRE_MULTILINE (at compile time) causes dollar never to match. This
1988           option affects only the behaviour of the dollar metacharacter. It  does
1989           not affect \Z or \z.
1991             PCRE_NOTEMPTY
1993           An empty string is not considered to be a valid match if this option is
1994           set. If there are alternatives in the pattern, they are tried.  If  all
1995           the  alternatives  match  the empty string, the entire match fails. For
1996           example, if the pattern
1998             a?b?
2000           is applied to a string not beginning with "a" or "b",  it  matches  the
2001           empty  string at the start of the subject. With PCRE_NOTEMPTY set, this
2002           match is not valid, so PCRE searches further into the string for occur-
2003           rences of "a" or "b".
2005           Perl has no direct equivalent of PCRE_NOTEMPTY, but it does make a spe-
2006           cial case of a pattern match of the empty  string  within  its  split()
2007           function,  and  when  using  the /g modifier. It is possible to emulate
2008           Perl's behaviour after matching a null string by first trying the match
2009           again at the same offset with PCRE_NOTEMPTY and PCRE_ANCHORED, and then
2010           if that fails by advancing the starting offset (see below)  and  trying
2011           an ordinary match again. There is some code that demonstrates how to do
2012           this in the pcredemo.c sample program.
2014             PCRE_NO_UTF8_CHECK
2016           When PCRE_UTF8 is set at compile time, the validity of the subject as a
2017           UTF-8  string is automatically checked when pcre_exec() is subsequently
2018           called.  The value of startoffset is also checked  to  ensure  that  it
2019           points  to  the start of a UTF-8 character. There is a discussion about
2020           the validity of UTF-8 strings in the section on UTF-8  support  in  the
2021           main  pcre  page.  If  an  invalid  UTF-8  sequence  of bytes is found,
2022           pcre_exec() returns the error PCRE_ERROR_BADUTF8. If  startoffset  con-
2023           tains an invalid value, PCRE_ERROR_BADUTF8_OFFSET is returned.
2025           If  you  already  know that your subject is valid, and you want to skip
2026           these   checks   for   performance   reasons,   you   can    set    the
2027           PCRE_NO_UTF8_CHECK  option  when calling pcre_exec(). You might want to
2028           do this for the second and subsequent calls to pcre_exec() if  you  are
2029           making  repeated  calls  to  find  all  the matches in a single subject
2030           string. However, you should be  sure  that  the  value  of  startoffset
2031           points  to  the  start of a UTF-8 character. When PCRE_NO_UTF8_CHECK is
2032           set, the effect of passing an invalid UTF-8 string as a subject,  or  a
2033           value  of startoffset that does not point to the start of a UTF-8 char-
2034           acter, is undefined. Your program may crash.
2036             PCRE_PARTIAL
2038           This option turns on the  partial  matching  feature.  If  the  subject
2039           string  fails to match the pattern, but at some point during the match-
2040           ing process the end of the subject was reached (that  is,  the  subject
2041           partially  matches  the  pattern and the failure to match occurred only
2042           because there were not enough subject characters), pcre_exec()  returns
2044           used, there are restrictions on what may appear in the  pattern.  These
2045           are discussed in the pcrepartial documentation.
2047       The string to be matched by pcre_exec()
2049           The  subject string is passed to pcre_exec() as a pointer in subject, a
2050           length in length, and a starting byte offset in startoffset.  In  UTF-8
2051           mode,  the  byte  offset  must point to the start of a UTF-8 character.
2052           Unlike the pattern string, the subject may contain binary  zero  bytes.
2053           When  the starting offset is zero, the search for a match starts at the
2054           beginning of the subject, and this is by far the most common case.
2056           A non-zero starting offset is useful when searching for  another  match
2057           in  the same subject by calling pcre_exec() again after a previous suc-
2058           cess.  Setting startoffset differs from just passing over  a  shortened
2059           string  and  setting  PCRE_NOTBOL  in the case of a pattern that begins
2060           with any kind of lookbehind. For example, consider the pattern
2062             \Biss\B
2064           which finds occurrences of "iss" in the middle of  words.  (\B  matches
2065           only  if  the  current position in the subject is not a word boundary.)
2066           When applied to the string "Mississipi" the first call  to  pcre_exec()
2067           finds  the  first  occurrence. If pcre_exec() is called again with just
2068           the remainder of the subject,  namely  "issipi",  it  does  not  match,
2069           because \B is always false at the start of the subject, which is deemed
2070           to be a word boundary. However, if pcre_exec()  is  passed  the  entire
2071           string again, but with startoffset set to 4, it finds the second occur-
2072           rence of "iss" because it is able to look behind the starting point  to
2073           discover that it is preceded by a letter.
2075           If  a  non-zero starting offset is passed when the pattern is anchored,
2076           one attempt to match at the given offset is made. This can only succeed
2077           if  the  pattern  does  not require the match to be at the start of the
2078           subject.
2080       How pcre_exec() returns captured substrings
2082           In general, a pattern matches a certain portion of the subject, and  in
2083           addition,  further  substrings  from  the  subject may be picked out by
2084           parts of the pattern. Following the usage  in  Jeffrey  Friedl's  book,
2085           this  is  called "capturing" in what follows, and the phrase "capturing
2086           subpattern" is used for a fragment of a pattern that picks out  a  sub-
2087           string.  PCRE  supports several other kinds of parenthesized subpattern
2088           that do not cause substrings to be captured.
2090           Captured substrings are returned to the caller via a vector of  integer
2091           offsets  whose  address is passed in ovector. The number of elements in
2092           the vector is passed in ovecsize, which must be a non-negative  number.
2093           Note: this argument is NOT the size of ovector in bytes.
2095           The  first  two-thirds of the vector is used to pass back captured sub-
2096           strings, each substring using a pair of integers. The  remaining  third
2097           of  the  vector is used as workspace by pcre_exec() while matching cap-
2098           turing subpatterns, and is not available for passing back  information.
2099           The  length passed in ovecsize should always be a multiple of three. If
2100           it is not, it is rounded down.
2102           When a match is successful, information about  captured  substrings  is
2103           returned  in  pairs  of integers, starting at the beginning of ovector,
2104           and continuing up to two-thirds of its length at the  most.  The  first
2105           element of a pair is set to the offset of the first character in a sub-
2106           string, and the second is set to the  offset  of  the  first  character
2107           after  the  end  of  a  substring. The first pair, ovector[0] and ovec-
2108           tor[1], identify the portion of  the  subject  string  matched  by  the
2109           entire  pattern.  The next pair is used for the first capturing subpat-
2110           tern, and so on. The value returned by pcre_exec() is one more than the
2111           highest numbered pair that has been set. For example, if two substrings
2112           have been captured, the returned value is 3. If there are no  capturing
2113           subpatterns,  the return value from a successful match is 1, indicating
2114           that just the first pair of offsets has been set.
2116           If a capturing subpattern is matched repeatedly, it is the last portion
2117           of the string that it matched that is returned.
2119           If  the vector is too small to hold all the captured substring offsets,
2120           it is used as far as possible (up to two-thirds of its length), and the
2121           function  returns a value of zero. In particular, if the substring off-
2122           sets are not of interest, pcre_exec() may be called with ovector passed
2123           as  NULL  and  ovecsize  as zero. However, if the pattern contains back
2124           references and the ovector is not big enough to  remember  the  related
2125           substrings,  PCRE has to get additional memory for use during matching.
2126           Thus it is usually advisable to supply an ovector.
2128           The pcre_info() function can be used to find  out  how  many  capturing
2129           subpatterns  there  are  in  a  compiled pattern. The smallest size for
2130           ovector that will allow for n captured substrings, in addition  to  the
2131           offsets of the substring matched by the whole pattern, is (n+1)*3.
2133           It  is  possible for capturing subpattern number n+1 to match some part
2134           of the subject when subpattern n has not been used at all. For example,
2135           if  the  string  "abc"  is  matched against the pattern (a|(z))(bc) the
2136           return from the function is 4, and subpatterns 1 and 3 are matched, but
2137           2  is  not.  When  this happens, both values in the offset pairs corre-
2138           sponding to unused subpatterns are set to -1.
2140           Offset values that correspond to unused subpatterns at the end  of  the
2141           expression  are  also  set  to  -1. For example, if the string "abc" is
2142           matched against the pattern (abc)(x(yz)?)? subpatterns 2 and 3 are  not
2143           matched.  The  return  from the function is 2, because the highest used
2144           capturing subpattern number is 1. However, you can refer to the offsets
2145           for  the  second  and third capturing subpatterns if you wish (assuming
2146           the vector is large enough, of course).
2148           Some convenience functions are provided  for  extracting  the  captured
2149           substrings as separate strings. These are described below.
2151       Error return values from pcre_exec()
2153           If  pcre_exec()  fails, it returns a negative number. The following are
2154           defined in the header file:
2156             PCRE_ERROR_NOMATCH        (-1)
2158           The subject string did not match the pattern.
2160             PCRE_ERROR_NULL           (-2)
2162           Either code or subject was passed as NULL,  or  ovector  was  NULL  and
2163           ovecsize was not zero.
2165             PCRE_ERROR_BADOPTION      (-3)
2167           An unrecognized bit was set in the options argument.
2169             PCRE_ERROR_BADMAGIC       (-4)
2171           PCRE  stores a 4-byte "magic number" at the start of the compiled code,
2172           to catch the case when it is passed a junk pointer and to detect when a
2173           pattern that was compiled in an environment of one endianness is run in
2174           an environment with the other endianness. This is the error  that  PCRE
2175           gives when the magic number is not present.
2177             PCRE_ERROR_UNKNOWN_OPCODE (-5)
2179           While running the pattern match, an unknown item was encountered in the
2180           compiled pattern. This error could be caused by a bug  in  PCRE  or  by
2181           overwriting of the compiled pattern.
2183             PCRE_ERROR_NOMEMORY       (-6)
2185           If  a  pattern contains back references, but the ovector that is passed
2186           to pcre_exec() is not big enough to remember the referenced substrings,
2187           PCRE  gets  a  block of memory at the start of matching to use for this
2188           purpose. If the call via pcre_malloc() fails, this error is given.  The
2189           memory is automatically freed at the end of matching.
2191             PCRE_ERROR_NOSUBSTRING    (-7)
2193           This  error is used by the pcre_copy_substring(), pcre_get_substring(),
2194           and  pcre_get_substring_list()  functions  (see  below).  It  is  never
2195           returned by pcre_exec().
2197             PCRE_ERROR_MATCHLIMIT     (-8)
2199           The  backtracking  limit,  as  specified  by the match_limit field in a
2200           pcre_extra structure (or defaulted) was reached.  See  the  description
2201           above.
2203             PCRE_ERROR_CALLOUT        (-9)
2205           This error is never generated by pcre_exec() itself. It is provided for
2206           use by callout functions that want to yield a distinctive  error  code.
2207           See the pcrecallout documentation for details.
2209             PCRE_ERROR_BADUTF8        (-10)
2211           A  string  that contains an invalid UTF-8 byte sequence was passed as a
2212           subject.
2214             PCRE_ERROR_BADUTF8_OFFSET (-11)
2216           The UTF-8 byte sequence that was passed as a subject was valid, but the
2217           value  of startoffset did not point to the beginning of a UTF-8 charac-
2218           ter.
2220             PCRE_ERROR_PARTIAL        (-12)
2222           The subject string did not match, but it did match partially.  See  the
2223           pcrepartial documentation for details of partial matching.
2225             PCRE_ERROR_BADPARTIAL     (-13)
2227           The  PCRE_PARTIAL  option  was  used with a compiled pattern containing
2228           items that are not supported for partial matching. See the  pcrepartial
2229           documentation for details of partial matching.
2231             PCRE_ERROR_INTERNAL       (-14)
2233           An  unexpected  internal error has occurred. This error could be caused
2234           by a bug in PCRE or by overwriting of the compiled pattern.
2236             PCRE_ERROR_BADCOUNT       (-15)
2238           This error is given if the value of the ovecsize argument is  negative.
2240             PCRE_ERROR_RECURSIONLIMIT (-21)
2242           The internal recursion limit, as specified by the match_limit_recursion
2243           field in a pcre_extra structure (or defaulted)  was  reached.  See  the
2244           description above.
2246             PCRE_ERROR_BADNEWLINE     (-23)
2248           An invalid combination of PCRE_NEWLINE_xxx options was given.
2250           Error numbers -16 to -20 and -22 are not used by pcre_exec().
2255           int pcre_copy_substring(const char *subject, int *ovector,
2256                int stringcount, int stringnumber, char *buffer,
2257                int buffersize);
2259           int pcre_get_substring(const char *subject, int *ovector,
2260                int stringcount, int stringnumber,
2261                const char **stringptr);
2263           int pcre_get_substring_list(const char *subject,
2264                int *ovector, int stringcount, const char ***listptr);
2266           Captured  substrings  can  be  accessed  directly  by using the offsets
2267           returned by pcre_exec() in  ovector.  For  convenience,  the  functions
2268           pcre_copy_substring(),    pcre_get_substring(),    and    pcre_get_sub-
2269           string_list() are provided for extracting captured substrings  as  new,
2270           separate,  zero-terminated strings. These functions identify substrings
2271           by number. The next section describes functions  for  extracting  named
2272           substrings.
2274           A  substring that contains a binary zero is correctly extracted and has
2275           a further zero added on the end, but the result is not, of course, a  C
2276           string.   However,  you  can  process such a string by referring to the
2277           length that is  returned  by  pcre_copy_substring()  and  pcre_get_sub-
2278           string().  Unfortunately, the interface to pcre_get_substring_list() is
2279           not adequate for handling strings containing binary zeros, because  the
2280           end of the final string is not independently indicated.
2282           The  first  three  arguments  are the same for all three of these func-
2283           tions: subject is the subject string that has  just  been  successfully
2284           matched, ovector is a pointer to the vector of integer offsets that was
2285           passed to pcre_exec(), and stringcount is the number of substrings that
2286           were  captured  by  the match, including the substring that matched the
2287           entire regular expression. This is the value returned by pcre_exec() if
2288           it  is greater than zero. If pcre_exec() returned zero, indicating that
2289           it ran out of space in ovector, the value passed as stringcount  should
2290           be the number of elements in the vector divided by three.
2292           The  functions pcre_copy_substring() and pcre_get_substring() extract a
2293           single substring, whose number is given as  stringnumber.  A  value  of
2294           zero  extracts  the  substring that matched the entire pattern, whereas
2295           higher values  extract  the  captured  substrings.  For  pcre_copy_sub-
2296           string(),  the  string  is  placed  in buffer, whose length is given by
2297           buffersize, while for pcre_get_substring() a new  block  of  memory  is
2298           obtained  via  pcre_malloc,  and its address is returned via stringptr.
2299           The yield of the function is the length of the  string,  not  including
2300           the terminating zero, or one of these error codes:
2302             PCRE_ERROR_NOMEMORY       (-6)
2304           The  buffer  was too small for pcre_copy_substring(), or the attempt to
2305           get memory failed for pcre_get_substring().
2307             PCRE_ERROR_NOSUBSTRING    (-7)
2309           There is no substring whose number is stringnumber.
2311           The pcre_get_substring_list()  function  extracts  all  available  sub-
2312           strings  and  builds  a list of pointers to them. All this is done in a
2313           single block of memory that is obtained via pcre_malloc. The address of
2314           the  memory  block  is returned via listptr, which is also the start of
2315           the list of string pointers. The end of the list is marked  by  a  NULL
2316           pointer.  The  yield  of  the function is zero if all went well, or the
2317           error code
2319             PCRE_ERROR_NOMEMORY       (-6)
2321           if the attempt to get the memory block failed.
2323           When any of these functions encounter a substring that is unset,  which
2324           can  happen  when  capturing subpattern number n+1 matches some part of
2325           the subject, but subpattern n has not been used at all, they return  an
2326           empty string. This can be distinguished from a genuine zero-length sub-
2327           string by inspecting the appropriate offset in ovector, which is  nega-
2328           tive for unset substrings.
2330           The  two convenience functions pcre_free_substring() and pcre_free_sub-
2331           string_list() can be used to free the memory  returned  by  a  previous
2332           call  of  pcre_get_substring()  or  pcre_get_substring_list(),  respec-
2333           tively. They do nothing more than  call  the  function  pointed  to  by
2334           pcre_free,  which  of course could be called directly from a C program.
2335           However, PCRE is used in some situations where it is linked via a  spe-
2336           cial   interface  to  another  programming  language  that  cannot  use
2337           pcre_free directly; it is for these cases that the functions  are  pro-
2338           vided.
2343           int pcre_get_stringnumber(const pcre *code,
2344                const char *name);
2346           int pcre_copy_named_substring(const pcre *code,
2347                const char *subject, int *ovector,
2348                int stringcount, const char *stringname,
2349                char *buffer, int buffersize);
2351           int pcre_get_named_substring(const pcre *code,
2352                const char *subject, int *ovector,
2353                int stringcount, const char *stringname,
2354                const char **stringptr);
2356           To  extract a substring by name, you first have to find associated num-
2357           ber.  For example, for this pattern
2359             (a+)b(?<xxx>\d+)...
2361           the number of the subpattern called "xxx" is 2. If the name is known to
2362           be unique (PCRE_DUPNAMES was not set), you can find the number from the
2363           name by calling pcre_get_stringnumber(). The first argument is the com-
2364           piled pattern, and the second is the name. The yield of the function is
2365           the subpattern number, or PCRE_ERROR_NOSUBSTRING (-7) if  there  is  no
2366           subpattern of that name.
2368           Given the number, you can extract the substring directly, or use one of
2369           the functions described in the previous section. For convenience, there
2370           are also two functions that do the whole job.
2372           Most    of    the    arguments   of   pcre_copy_named_substring()   and
2373           pcre_get_named_substring() are the same  as  those  for  the  similarly
2374           named  functions  that extract by number. As these are described in the
2375           previous section, they are not re-described here. There  are  just  two
2376           differences:
2378           First,  instead  of a substring number, a substring name is given. Sec-
2379           ond, there is an extra argument, given at the start, which is a pointer
2380           to  the compiled pattern. This is needed in order to gain access to the
2381           name-to-number translation table.
2383           These functions call pcre_get_stringnumber(), and if it succeeds,  they
2384           then  call  pcre_copy_substring() or pcre_get_substring(), as appropri-
2385           ate. NOTE: If PCRE_DUPNAMES is set and there are duplicate  names,  the
2386           behaviour may not be what you want (see the next section).
2391           int pcre_get_stringtable_entries(const pcre *code,
2392                const char *name, char **first, char **last);
2394           When  a  pattern  is  compiled with the PCRE_DUPNAMES option, names for
2395           subpatterns are not required to  be  unique.  Normally,  patterns  with
2396           duplicate  names  are such that in any one match, only one of the named
2397           subpatterns participates. An example is shown in the pcrepattern  docu-
2398           mentation.
2400           When    duplicates   are   present,   pcre_copy_named_substring()   and
2401           pcre_get_named_substring() return the first substring corresponding  to
2402           the  given  name  that  is set. If none are set, PCRE_ERROR_NOSUBSTRING
2403           (-7) is returned; no  data  is  returned.  The  pcre_get_stringnumber()
2404           function  returns one of the numbers that are associated with the name,
2405           but it is not defined which it is.
2407           If you want to get full details of all captured substrings for a  given
2408           name,  you  must  use  the pcre_get_stringtable_entries() function. The
2409           first argument is the compiled pattern, and the second is the name. The
2410           third  and  fourth  are  pointers to variables which are updated by the
2411           function. After it has run, they point to the first and last entries in
2412           the  name-to-number  table  for  the  given  name.  The function itself
2413           returns the length of each entry,  or  PCRE_ERROR_NOSUBSTRING  (-7)  if
2414           there  are none. The format of the table is described above in the sec-
2415           tion entitled Information about a  pattern.   Given  all  the  relevant
2416           entries  for the name, you can extract each of their numbers, and hence
2417           the captured data, if any.
2422           The traditional matching function uses a  similar  algorithm  to  Perl,
2423           which stops when it finds the first match, starting at a given point in
2424           the subject. If you want to find all possible matches, or  the  longest
2425           possible  match,  consider using the alternative matching function (see
2426           below) instead. If you cannot use the alternative function,  but  still
2427           need  to  find all possible matches, you can kludge it up by making use
2428           of the callout facility, which is described in the pcrecallout documen-
2429           tation.
2431           What you have to do is to insert a callout right at the end of the pat-
2432           tern.  When your callout function is called, extract and save the  cur-
2433           rent  matched  substring.  Then  return  1, which forces pcre_exec() to
2434           backtrack and try other alternatives. Ultimately, when it runs  out  of
2435           matches, pcre_exec() will yield PCRE_ERROR_NOMATCH.
2440           int pcre_dfa_exec(const pcre *code, const pcre_extra *extra,
2441                const char *subject, int length, int startoffset,
2442                int options, int *ovector, int ovecsize,
2443                int *workspace, int wscount);
2445           The  function  pcre_dfa_exec()  is  called  to  match  a subject string
2446           against a compiled pattern, using a matching algorithm that  scans  the
2447           subject  string  just  once, and does not backtrack. This has different
2448           characteristics to the normal algorithm, and  is  not  compatible  with
2449           Perl.  Some  of the features of PCRE patterns are not supported. Never-
2450           theless, there are times when this kind of matching can be useful.  For
2451           a discussion of the two matching algorithms, see the pcrematching docu-
2452           mentation.
2454           The arguments for the pcre_dfa_exec() function  are  the  same  as  for
2455           pcre_exec(), plus two extras. The ovector argument is used in a differ-
2456           ent way, and this is described below. The other  common  arguments  are
2457           used  in  the  same way as for pcre_exec(), so their description is not
2458           repeated here.
2460           The two additional arguments provide workspace for  the  function.  The
2461           workspace  vector  should  contain at least 20 elements. It is used for
2462           keeping  track  of  multiple  paths  through  the  pattern  tree.  More
2463           workspace  will  be  needed for patterns and subjects where there are a
2464           lot of potential matches.
2466           Here is an example of a simple call to pcre_dfa_exec():
2468             int rc;
2469             int ovector[10];
2470             int wspace[20];
2471             rc = pcre_dfa_exec(
2472               re,             /* result of pcre_compile() */
2473               NULL,           /* we didn't study the pattern */
2474               "some string",  /* the subject string */
2475               11,             /* the length of the subject string */
2476               0,              /* start at offset 0 in the subject */
2477               0,              /* default options */
2478               ovector,        /* vector of integers for substring information */
2479               10,             /* number of elements (NOT size in bytes) */
2480               wspace,         /* working space vector */
2481               20);            /* number of elements (NOT size in bytes) */
2483       Option bits for pcre_dfa_exec()
2485           The unused bits of the options argument  for  pcre_dfa_exec()  must  be
2486           zero.  The  only  bits  that  may  be  set are PCRE_ANCHORED, PCRE_NEW-
2488           PCRE_PARTIAL, PCRE_DFA_SHORTEST, and PCRE_DFA_RESTART. All but the last
2489           three of these are the same as for pcre_exec(), so their description is
2490           not repeated here.
2492             PCRE_PARTIAL
2494           This  has  the  same general effect as it does for pcre_exec(), but the
2495           details  are  slightly  different.  When  PCRE_PARTIAL   is   set   for
2496           pcre_dfa_exec(),  the  return code PCRE_ERROR_NOMATCH is converted into
2497           PCRE_ERROR_PARTIAL if the end of the subject  is  reached,  there  have
2498           been no complete matches, but there is still at least one matching pos-
2499           sibility. The portion of the string that provided the partial match  is
2500           set as the first matching string.
2502             PCRE_DFA_SHORTEST
2504           Setting  the  PCRE_DFA_SHORTEST option causes the matching algorithm to
2505           stop as soon as it has found one match. Because of the way the alterna-
2506           tive  algorithm  works, this is necessarily the shortest possible match
2507           at the first possible matching point in the subject string.
2509             PCRE_DFA_RESTART
2511           When pcre_dfa_exec()  is  called  with  the  PCRE_PARTIAL  option,  and
2512           returns  a  partial  match, it is possible to call it again, with addi-
2513           tional subject characters, and have it continue with  the  same  match.
2514           The  PCRE_DFA_RESTART  option requests this action; when it is set, the
2515           workspace and wscount options must reference the same vector as  before
2516           because  data  about  the  match so far is left in them after a partial
2517           match. There is more discussion of this  facility  in  the  pcrepartial
2518           documentation.
2520       Successful returns from pcre_dfa_exec()
2522           When  pcre_dfa_exec()  succeeds, it may have matched more than one sub-
2523           string in the subject. Note, however, that all the matches from one run
2524           of  the  function  start  at the same point in the subject. The shorter
2525           matches are all initial substrings of the longer matches. For  example,
2526           if the pattern
2528             <.*>
2530           is matched against the string
2532             This is <something> <something else> <something further> no more
2534           the three matched strings are
2536             <something>
2537             <something> <something else>
2538             <something> <something else> <something further>
2540           On  success,  the  yield of the function is a number greater than zero,
2541           which is the number of matched substrings.  The  substrings  themselves
2542           are  returned  in  ovector. Each string uses two elements; the first is
2543           the offset to the start, and the second is the offset to  the  end.  In
2544           fact,  all  the  strings  have the same start offset. (Space could have
2545           been saved by giving this only once, but it was decided to retain  some
2546           compatibility  with  the  way pcre_exec() returns data, even though the
2547           meaning of the strings is different.)
2549           The strings are returned in reverse order of length; that is, the long-
2550           est  matching  string is given first. If there were too many matches to
2551           fit into ovector, the yield of the function is zero, and the vector  is
2552           filled with the longest matches.
2554       Error returns from pcre_dfa_exec()
2556           The  pcre_dfa_exec()  function returns a negative number when it fails.
2557           Many of the errors are the same  as  for  pcre_exec(),  and  these  are
2558           described  above.   There are in addition the following errors that are
2559           specific to pcre_dfa_exec():
2561             PCRE_ERROR_DFA_UITEM      (-16)
2563           This return is given if pcre_dfa_exec() encounters an item in the  pat-
2564           tern  that  it  does not support, for instance, the use of \C or a back
2565           reference.
2567             PCRE_ERROR_DFA_UCOND      (-17)
2569           This return is given if pcre_dfa_exec()  encounters  a  condition  item
2570           that  uses  a back reference for the condition, or a test for recursion
2571           in a specific group. These are not supported.
2573             PCRE_ERROR_DFA_UMLIMIT    (-18)
2575           This return is given if pcre_dfa_exec() is called with an  extra  block
2576           that contains a setting of the match_limit field. This is not supported
2577           (it is meaningless).
2579             PCRE_ERROR_DFA_WSSIZE     (-19)
2581           This return is given if  pcre_dfa_exec()  runs  out  of  space  in  the
2582           workspace vector.
2584             PCRE_ERROR_DFA_RECURSE    (-20)
2586           When  a  recursive subpattern is processed, the matching function calls
2587           itself recursively, using private vectors for  ovector  and  workspace.
2588           This  error  is  given  if  the output vector is not large enough. This
2589           should be extremely rare, as a vector of size 1000 is used.
2592    SEE ALSO
2594           pcrebuild(3), pcrecallout(3), pcrecpp(3)(3), pcrematching(3),  pcrepar-
2595           tial(3),  pcreposix(3), pcreprecompile(3), pcresample(3), pcrestack(3).
2598    AUTHOR
2600           Philip Hazel
2601           University Computing Service
2602           Cambridge CB2 3QH, England.
2605    REVISION
2607           Last updated: 12 April 2008
2608           Copyright (c) 1997-2008 University of Cambridge.
2609    ------------------------------------------------------------------------------
2612    PCRECALLOUT(3)                                                  PCRECALLOUT(3)
2615    NAME
2616           PCRE - Perl-compatible regular expressions
2621           int (*pcre_callout)(pcre_callout_block *);
2623           PCRE provides a feature called "callout", which is a means of temporar-
2624           ily passing control to the caller of PCRE  in  the  middle  of  pattern
2625           matching.  The  caller of PCRE provides an external function by putting
2626           its entry point in the global variable pcre_callout. By  default,  this
2627           variable contains NULL, which disables all calling out.
2629           Within  a  regular  expression,  (?C) indicates the points at which the
2630           external function is to be called.  Different  callout  points  can  be
2631           identified  by  putting  a number less than 256 after the letter C. The
2632           default value is zero.  For  example,  this  pattern  has  two  callout
2633           points:
2635             (?C1)abc(?C2)def
2637           If  the  PCRE_AUTO_CALLOUT  option  bit  is  set when pcre_compile() is
2638           called, PCRE automatically  inserts  callouts,  all  with  number  255,
2639           before  each  item in the pattern. For example, if PCRE_AUTO_CALLOUT is
2640           used with the pattern
2642             A(\d{2}|--)
2644           it is processed as if it were
2646           (?C255)A(?C255)((?C255)\d{2}(?C255)|(?C255)-(?C255)-(?C255))(?C255)
2648           Notice that there is a callout before and after  each  parenthesis  and
2649           alternation  bar.  Automatic  callouts  can  be  used  for tracking the
2650           progress of pattern matching. The pcretest command has an  option  that
2651           sets  automatic callouts; when it is used, the output indicates how the
2652           pattern is matched. This is useful information when you are  trying  to
2653           optimize the performance of a particular pattern.
2658           You  should  be  aware  that,  because of optimizations in the way PCRE
2659           matches patterns, callouts sometimes do not happen. For example, if the
2660           pattern is
2662             ab(?C4)cd
2664           PCRE knows that any matching string must contain the letter "d". If the
2665           subject string is "abyz", the lack of "d" means that  matching  doesn't
2666           ever  start,  and  the  callout is never reached. However, with "abyd",
2667           though the result is still no match, the callout is obeyed.
2672           During matching, when PCRE reaches a callout point, the external  func-
2673           tion  defined by pcre_callout is called (if it is set). This applies to
2674           both the pcre_exec() and the pcre_dfa_exec()  matching  functions.  The
2675           only  argument  to  the callout function is a pointer to a pcre_callout
2676           block. This structure contains the following fields:
2678             int          version;
2679             int          callout_number;
2680             int         *offset_vector;
2681             const char  *subject;
2682             int          subject_length;
2683             int          start_match;
2684             int          current_position;
2685             int          capture_top;
2686             int          capture_last;
2687             void        *callout_data;
2688             int          pattern_position;
2689             int          next_item_length;
2691           The version field is an integer containing the version  number  of  the
2692           block  format. The initial version was 0; the current version is 1. The
2693           version number will change again in future  if  additional  fields  are
2694           added, but the intention is never to remove any of the existing fields.
2696           The callout_number field contains the number of the  callout,  as  com-
2697           piled  into  the pattern (that is, the number after ?C for manual call-
2698           outs, and 255 for automatically generated callouts).
2700           The offset_vector field is a pointer to the vector of offsets that  was
2701           passed   by   the   caller  to  pcre_exec()  or  pcre_dfa_exec().  When
2702           pcre_exec() is used, the contents can be inspected in order to  extract
2703           substrings  that  have  been  matched  so  far,  in the same way as for
2704           extracting substrings after a match has completed. For  pcre_dfa_exec()
2705           this field is not useful.
2707           The subject and subject_length fields contain copies of the values that
2708           were passed to pcre_exec().
2710           The start_match field normally contains the offset within  the  subject
2711           at  which  the  current  match  attempt started. However, if the escape
2712           sequence \K has been encountered, this value is changed to reflect  the
2713           modified  starting  point.  If the pattern is not anchored, the callout
2714           function may be called several times from the same point in the pattern
2715           for different starting points in the subject.
2717           The  current_position  field  contains the offset within the subject of
2718           the current match pointer.
2720           When the pcre_exec() function is used, the capture_top  field  contains
2721           one  more than the number of the highest numbered captured substring so
2722           far. If no substrings have been captured, the value of  capture_top  is
2723           one.  This  is always the case when pcre_dfa_exec() is used, because it
2724           does not support captured substrings.
2726           The capture_last field contains the number of the  most  recently  cap-
2727           tured  substring. If no substrings have been captured, its value is -1.
2728           This is always the case when pcre_dfa_exec() is used.
2730           The callout_data field contains a value that is passed  to  pcre_exec()
2731           or  pcre_dfa_exec() specifically so that it can be passed back in call-
2732           outs. It is passed in the pcre_callout field  of  the  pcre_extra  data
2733           structure.  If  no such data was passed, the value of callout_data in a
2734           pcre_callout block is NULL. There is a description  of  the  pcre_extra
2735           structure in the pcreapi documentation.
2737           The  pattern_position field is present from version 1 of the pcre_call-
2738           out structure. It contains the offset to the next item to be matched in
2739           the pattern string.
2741           The  next_item_length field is present from version 1 of the pcre_call-
2742           out structure. It contains the length of the next item to be matched in
2743           the  pattern  string. When the callout immediately precedes an alterna-
2744           tion bar, a closing parenthesis, or the end of the pattern, the  length
2745           is  zero.  When the callout precedes an opening parenthesis, the length
2746           is that of the entire subpattern.
2748           The pattern_position and next_item_length fields are intended  to  help
2749           in  distinguishing between different automatic callouts, which all have
2750           the same callout number. However, they are set for all callouts.
2755           The external callout function returns an integer to PCRE. If the  value
2756           is  zero,  matching  proceeds  as  normal. If the value is greater than
2757           zero, matching fails at the current point, but  the  testing  of  other
2758           matching possibilities goes ahead, just as if a lookahead assertion had
2759           failed. If the value is less than zero, the  match  is  abandoned,  and
2760           pcre_exec() (or pcre_dfa_exec()) returns the negative value.
2762           Negative   values   should   normally   be   chosen  from  the  set  of
2763           PCRE_ERROR_xxx values. In particular, PCRE_ERROR_NOMATCH forces a stan-
2764           dard  "no  match"  failure.   The  error  number  PCRE_ERROR_CALLOUT is
2765           reserved for use by callout functions; it will never be  used  by  PCRE
2766           itself.
2769    AUTHOR
2771           Philip Hazel
2772           University Computing Service
2773           Cambridge CB2 3QH, England.
2776    REVISION
2778           Last updated: 29 May 2007
2779           Copyright (c) 1997-2007 University of Cambridge.
2780    ------------------------------------------------------------------------------
2783    PCRECOMPAT(3)                                                    PCRECOMPAT(3)
2786    NAME
2787           PCRE - Perl-compatible regular expressions
2792           This  document describes the differences in the ways that PCRE and Perl
2793           handle regular expressions. The differences described here  are  mainly
2794           with  respect  to  Perl 5.8, though PCRE versions 7.0 and later contain
2795           some features that are expected to be in the forthcoming Perl 5.10.
2797           1. PCRE has only a subset of Perl's UTF-8 and Unicode support.  Details
2798           of  what  it does have are given in the section on UTF-8 support in the
2799           main pcre page.
2801           2. PCRE does not allow repeat quantifiers on lookahead assertions. Perl
2802           permits  them,  but they do not mean what you might think. For example,
2803           (?!a){3} does not assert that the next three characters are not "a". It
2804           just asserts that the next character is not "a" three times.
2806           3.  Capturing  subpatterns  that occur inside negative lookahead asser-
2807           tions are counted, but their entries in the offsets  vector  are  never
2808           set.  Perl sets its numerical variables from any such patterns that are
2809           matched before the assertion fails to match something (thereby succeed-
2810           ing),  but  only  if the negative lookahead assertion contains just one
2811           branch.
2813           4. Though binary zero characters are supported in the  subject  string,
2814           they are not allowed in a pattern string because it is passed as a nor-
2815           mal C string, terminated by zero. The escape sequence \0 can be used in
2816           the pattern to represent a binary zero.
2818           5.  The  following Perl escape sequences are not supported: \l, \u, \L,
2819           \U, and \N. In fact these are implemented by Perl's general string-han-
2820           dling  and are not part of its pattern matching engine. If any of these
2821           are encountered by PCRE, an error is generated.
2823           6. The Perl escape sequences \p, \P, and \X are supported only if  PCRE
2824           is  built  with Unicode character property support. The properties that
2825           can be tested with \p and \P are limited to the general category  prop-
2826           erties  such  as  Lu and Nd, script names such as Greek or Han, and the
2827           derived properties Any and L&.
2829           7. PCRE does support the \Q...\E escape for quoting substrings. Charac-
2830           ters  in  between  are  treated as literals. This is slightly different
2831           from Perl in that $ and @ are  also  handled  as  literals  inside  the
2832           quotes.  In Perl, they cause variable interpolation (but of course PCRE
2833           does not have variables). Note the following examples:
2835               Pattern            PCRE matches      Perl matches
2837               \Qabc$xyz\E        abc$xyz           abc followed by the
2838                                                      contents of $xyz
2839               \Qabc\$xyz\E       abc\$xyz          abc\$xyz
2840               \Qabc\E\$\Qxyz\E   abc$xyz           abc$xyz
2842           The \Q...\E sequence is recognized both inside  and  outside  character
2843           classes.
2845           8. Fairly obviously, PCRE does not support the (?{code}) and (??{code})
2846           constructions. However, there is support for recursive  patterns.  This
2847           is  not available in Perl 5.8, but will be in Perl 5.10. Also, the PCRE
2848           "callout" feature allows an external function to be called during  pat-
2849           tern matching. See the pcrecallout documentation for details.
2851           9.  Subpatterns  that  are  called  recursively or as "subroutines" are
2852           always treated as atomic groups in  PCRE.  This  is  like  Python,  but
2853           unlike Perl.
2855           10.  There are some differences that are concerned with the settings of
2856           captured strings when part of  a  pattern  is  repeated.  For  example,
2857           matching  "aba"  against  the  pattern  /^(a(b)?)+$/  in Perl leaves $2
2858           unset, but in PCRE it is set to "b".
2860           11.  PCRE  does  support  Perl  5.10's  backtracking  verbs  (*ACCEPT),
2861           (*FAIL),  (*F),  (*COMMIT), (*PRUNE), (*SKIP), and (*THEN), but only in
2862           the forms without an  argument.  PCRE  does  not  support  (*MARK).  If
2863           (*ACCEPT)  is within capturing parentheses, PCRE does not set that cap-
2864           ture group; this is different to Perl.
2866           12. PCRE provides some extensions to the Perl regular expression facil-
2867           ities.   Perl  5.10  will  include new features that are not in earlier
2868           versions, some of which (such as named parentheses) have been  in  PCRE
2869           for some time. This list is with respect to Perl 5.10:
2871           (a)  Although  lookbehind  assertions  must match fixed length strings,
2872           each alternative branch of a lookbehind assertion can match a different
2873           length of string. Perl requires them all to have the same length.
2875           (b)  If PCRE_DOLLAR_ENDONLY is set and PCRE_MULTILINE is not set, the $
2876           meta-character matches only at the very end of the string.
2878           (c) If PCRE_EXTRA is set, a backslash followed by a letter with no spe-
2879           cial meaning is faulted. Otherwise, like Perl, the backslash is quietly
2880           ignored.  (Perl can be made to issue a warning.)
2882           (d) If PCRE_UNGREEDY is set, the greediness of the  repetition  quanti-
2883           fiers is inverted, that is, by default they are not greedy, but if fol-
2884           lowed by a question mark they are.
2886           (e) PCRE_ANCHORED can be used at matching time to force a pattern to be
2887           tried only at the first matching position in the subject string.
2890           TURE options for pcre_exec() have no Perl equivalents.
2892           (g) The \R escape sequence can be restricted to match only CR,  LF,  or
2893           CRLF by the PCRE_BSR_ANYCRLF option.
2895           (h) The callout facility is PCRE-specific.
2897           (i) The partial matching facility is PCRE-specific.
2899           (j) Patterns compiled by PCRE can be saved and re-used at a later time,
2900           even on different hosts that have the other endianness.
2902           (k) The alternative matching function (pcre_dfa_exec())  matches  in  a
2903           different way and is not Perl-compatible.
2905           (l)  PCRE  recognizes some special sequences such as (*CR) at the start
2906           of a pattern that set overall options that cannot be changed within the
2907           pattern.
2910    AUTHOR
2912           Philip Hazel
2913           University Computing Service
2914           Cambridge CB2 3QH, England.
2917    REVISION
2919           Last updated: 11 September 2007
2920           Copyright (c) 1997-2007 University of Cambridge.
2921    ------------------------------------------------------------------------------
2924    PCREPATTERN(3)                                                  PCREPATTERN(3)
2927    NAME
2928           PCRE - Perl-compatible regular expressions
2933           The  syntax and semantics of the regular expressions that are supported
2934           by PCRE are described in detail below. There is a quick-reference  syn-
2935           tax summary in the pcresyntax page. PCRE tries to match Perl syntax and
2936           semantics as closely as it can. PCRE  also  supports  some  alternative
2937           regular  expression  syntax (which does not conflict with the Perl syn-
2938           tax) in order to provide some compatibility with regular expressions in
2939           Python, .NET, and Oniguruma.
2941           Perl's  regular expressions are described in its own documentation, and
2942           regular expressions in general are covered in a number of  books,  some
2943           of  which  have  copious  examples. Jeffrey Friedl's "Mastering Regular
2944           Expressions", published by  O'Reilly,  covers  regular  expressions  in
2945           great  detail.  This  description  of  PCRE's  regular  expressions  is
2946           intended as reference material.
2948           The original operation of PCRE was on strings of  one-byte  characters.
2949           However,  there is now also support for UTF-8 character strings. To use
2950           this, you must build PCRE to  include  UTF-8  support,  and  then  call
2951           pcre_compile()  with  the  PCRE_UTF8  option.  How this affects pattern
2952           matching is mentioned in several places below. There is also a  summary
2953           of  UTF-8  features  in  the  section on UTF-8 support in the main pcre
2954           page.
2956           The remainder of this document discusses the  patterns  that  are  sup-
2957           ported  by  PCRE when its main matching function, pcre_exec(), is used.
2958           From  release  6.0,   PCRE   offers   a   second   matching   function,
2959           pcre_dfa_exec(),  which matches using a different algorithm that is not
2960           Perl-compatible. Some of the features discussed below are not available
2961           when  pcre_dfa_exec()  is used. The advantages and disadvantages of the
2962           alternative function, and how it differs from the normal function,  are
2963           discussed in the pcrematching page.
2968           PCRE  supports five different conventions for indicating line breaks in
2969           strings: a single CR (carriage return) character, a  single  LF  (line-
2970           feed) character, the two-character sequence CRLF, any of the three pre-
2971           ceding, or any Unicode newline sequence. The pcreapi page  has  further
2972           discussion  about newlines, and shows how to set the newline convention
2973           in the options arguments for the compiling and matching functions.
2975           It is also possible to specify a newline convention by starting a  pat-
2976           tern string with one of the following five sequences:
2978             (*CR)        carriage return
2979             (*LF)        linefeed
2980             (*CRLF)      carriage return, followed by linefeed
2981             (*ANYCRLF)   any of the three above
2982             (*ANY)       all Unicode newline sequences
2984           These override the default and the options given to pcre_compile(). For
2985           example, on a Unix system where LF is the default newline sequence, the
2986           pattern
2988             (*CR)a.b
2990           changes the convention to CR. That pattern matches "a\nb" because LF is
2991           no longer a newline. Note that these special settings,  which  are  not
2992           Perl-compatible,  are  recognized  only at the very start of a pattern,
2993           and that they must be in upper case.  If  more  than  one  of  them  is
2994           present, the last one is used.
2996           The  newline  convention  does  not  affect what the \R escape sequence
2997           matches. By default, this is any Unicode  newline  sequence,  for  Perl
2998           compatibility.  However, this can be changed; see the description of \R
2999           in the section entitled "Newline sequences" below. A change of \R  set-
3000           ting can be combined with a change of newline convention.
3005           A  regular  expression  is  a pattern that is matched against a subject
3006           string from left to right. Most characters stand for  themselves  in  a
3007           pattern,  and  match  the corresponding characters in the subject. As a
3008           trivial example, the pattern
3010             The quick brown fox
3012           matches a portion of a subject string that is identical to itself. When
3013           caseless  matching is specified (the PCRE_CASELESS option), letters are
3014           matched independently of case. In UTF-8 mode, PCRE  always  understands
3015           the  concept  of case for characters whose values are less than 128, so
3016           caseless matching is always possible. For characters with  higher  val-
3017           ues,  the concept of case is supported if PCRE is compiled with Unicode
3018           property support, but not otherwise.   If  you  want  to  use  caseless
3019           matching  for  characters  128  and above, you must ensure that PCRE is
3020           compiled with Unicode property support as well as with UTF-8 support.
3022           The power of regular expressions comes  from  the  ability  to  include
3023           alternatives  and  repetitions in the pattern. These are encoded in the
3024           pattern by the use of metacharacters, which do not stand for themselves
3025           but instead are interpreted in some special way.
3027           There  are  two different sets of metacharacters: those that are recog-
3028           nized anywhere in the pattern except within square brackets, and  those
3029           that  are  recognized  within square brackets. Outside square brackets,
3030           the metacharacters are as follows:
3032             \      general escape character with several uses
3033             ^      assert start of string (or line, in multiline mode)
3034             $      assert end of string (or line, in multiline mode)
3035             .      match any character except newline (by default)
3036             [      start character class definition
3037             |      start of alternative branch
3038             (      start subpattern
3039             )      end subpattern
3040             ?      extends the meaning of (
3041                    also 0 or 1 quantifier
3042                    also quantifier minimizer
3043             *      0 or more quantifier
3044             +      1 or more quantifier
3045                    also "possessive quantifier"
3046             {      start min/max quantifier
3048           Part of a pattern that is in square brackets  is  called  a  "character
3049           class". In a character class the only metacharacters are:
3051             \      general escape character
3052             ^      negate the class, but only if the first character
3053             -      indicates character range
3054             [      POSIX character class (only if followed by POSIX
3055                      syntax)
3056             ]      terminates the character class
3058           The  following sections describe the use of each of the metacharacters.
3063           The backslash character has several uses. Firstly, if it is followed by
3064           a  non-alphanumeric  character,  it takes away any special meaning that
3065           character may have. This  use  of  backslash  as  an  escape  character
3066           applies both inside and outside character classes.
3068           For  example,  if  you want to match a * character, you write \* in the
3069           pattern.  This escaping action applies whether  or  not  the  following
3070           character  would  otherwise be interpreted as a metacharacter, so it is
3071           always safe to precede a non-alphanumeric  with  backslash  to  specify
3072           that  it stands for itself. In particular, if you want to match a back-
3073           slash, you write \\.
3075           If a pattern is compiled with the PCRE_EXTENDED option,  whitespace  in
3076           the  pattern (other than in a character class) and characters between a
3077           # outside a character class and the next newline are ignored. An escap-
3078           ing  backslash  can  be  used to include a whitespace or # character as
3079           part of the pattern.
3081           If you want to remove the special meaning from a  sequence  of  charac-
3082           ters,  you can do so by putting them between \Q and \E. This is differ-
3083           ent from Perl in that $ and  @  are  handled  as  literals  in  \Q...\E
3084           sequences  in  PCRE, whereas in Perl, $ and @ cause variable interpola-
3085           tion. Note the following examples:
3087             Pattern            PCRE matches   Perl matches
3089             \Qabc$xyz\E        abc$xyz        abc followed by the
3090                                                 contents of $xyz
3091             \Qabc\$xyz\E       abc\$xyz       abc\$xyz
3092             \Qabc\E\$\Qxyz\E   abc$xyz        abc$xyz
3094           The \Q...\E sequence is recognized both inside  and  outside  character
3095           classes.
3097       Non-printing characters
3099           A second use of backslash provides a way of encoding non-printing char-
3100           acters in patterns in a visible manner. There is no restriction on  the
3101           appearance  of non-printing characters, apart from the binary zero that
3102           terminates a pattern, but when a pattern  is  being  prepared  by  text
3103           editing,  it  is  usually  easier  to  use  one of the following escape
3104           sequences than the binary character it represents:
3106             \a        alarm, that is, the BEL character (hex 07)
3107             \cx       "control-x", where x is any character
3108             \e        escape (hex 1B)
3109             \f        formfeed (hex 0C)
3110             \n        linefeed (hex 0A)
3111             \r        carriage return (hex 0D)
3112             \t        tab (hex 09)
3113             \ddd      character with octal code ddd, or backreference
3114             \xhh      character with hex code hh
3115             \x{hhh..} character with hex code hhh..
3117           The precise effect of \cx is as follows: if x is a lower  case  letter,
3118           it  is converted to upper case. Then bit 6 of the character (hex 40) is
3119           inverted.  Thus \cz becomes hex 1A, but \c{ becomes hex 3B,  while  \c;
3120           becomes hex 7B.
3122           After  \x, from zero to two hexadecimal digits are read (letters can be
3123           in upper or lower case). Any number of hexadecimal  digits  may  appear
3124           between  \x{  and  },  but the value of the character code must be less
3125           than 256 in non-UTF-8 mode, and less than 2**31 in UTF-8 mode. That is,
3126           the  maximum value in hexadecimal is 7FFFFFFF. Note that this is bigger
3127           than the largest Unicode code point, which is 10FFFF.
3129           If characters other than hexadecimal digits appear between \x{  and  },
3130           or if there is no terminating }, this form of escape is not recognized.
3131           Instead, the initial \x will be  interpreted  as  a  basic  hexadecimal
3132           escape,  with  no  following  digits, giving a character whose value is
3133           zero.
3135           Characters whose value is less than 256 can be defined by either of the
3136           two  syntaxes  for  \x. There is no difference in the way they are han-
3137           dled. For example, \xdc is exactly the same as \x{dc}.
3139           After \0 up to two further octal digits are read. If  there  are  fewer
3140           than  two  digits,  just  those  that  are  present  are used. Thus the
3141           sequence \0\x\07 specifies two binary zeros followed by a BEL character
3142           (code  value 7). Make sure you supply two digits after the initial zero
3143           if the pattern character that follows is itself an octal digit.
3145           The handling of a backslash followed by a digit other than 0 is compli-
3146           cated.  Outside a character class, PCRE reads it and any following dig-
3147           its as a decimal number. If the number is less than  10,  or  if  there
3148           have been at least that many previous capturing left parentheses in the
3149           expression, the entire  sequence  is  taken  as  a  back  reference.  A
3150           description  of how this works is given later, following the discussion
3151           of parenthesized subpatterns.
3153           Inside a character class, or if the decimal number is  greater  than  9
3154           and  there have not been that many capturing subpatterns, PCRE re-reads
3155           up to three octal digits following the backslash, and uses them to gen-
3156           erate  a data character. Any subsequent digits stand for themselves. In
3157           non-UTF-8 mode, the value of a character specified  in  octal  must  be
3158           less  than  \400.  In  UTF-8 mode, values up to \777 are permitted. For
3159           example:
3161             \040   is another way of writing a space
3162             \40    is the same, provided there are fewer than 40
3163                       previous capturing subpatterns
3164             \7     is always a back reference
3165             \11    might be a back reference, or another way of
3166                       writing a tab
3167             \011   is always a tab
3168             \0113  is a tab followed by the character "3"
3169             \113   might be a back reference, otherwise the
3170                       character with octal code 113
3171             \377   might be a back reference, otherwise
3172                       the byte consisting entirely of 1 bits
3173             \81    is either a back reference, or a binary zero
3174                       followed by the two characters "8" and "1"
3176           Note that octal values of 100 or greater must not be  introduced  by  a
3177           leading zero, because no more than three octal digits are ever read.
3179           All the sequences that define a single character value can be used both
3180           inside and outside character classes. In addition, inside  a  character
3181           class,  the  sequence \b is interpreted as the backspace character (hex
3182           08), and the sequences \R and \X are interpreted as the characters  "R"
3183           and  "X", respectively. Outside a character class, these sequences have
3184           different meanings (see below).
3186       Absolute and relative back references
3188           The sequence \g followed by an unsigned or a negative  number,  option-
3189           ally  enclosed  in braces, is an absolute or relative back reference. A
3190           named back reference can be coded as \g{name}. Back references are dis-
3191           cussed later, following the discussion of parenthesized subpatterns.
3193       Absolute and relative subroutine calls
3195           For  compatibility with Oniguruma, the non-Perl syntax \g followed by a
3196           name or a number enclosed either in angle brackets or single quotes, is
3197           an  alternative  syntax for referencing a subpattern as a "subroutine".
3198           Details are discussed later.   Note  that  \g{...}  (Perl  syntax)  and
3199           \g<...>  (Oniguruma  syntax)  are  not synonymous. The former is a back
3200           reference; the latter is a subroutine call.
3202       Generic character types
3204           Another use of backslash is for specifying generic character types. The
3205           following are always recognized:
3207             \d     any decimal digit
3208             \D     any character that is not a decimal digit
3209             \h     any horizontal whitespace character
3210             \H     any character that is not a horizontal whitespace character
3211             \s     any whitespace character
3212             \S     any character that is not a whitespace character
3213             \v     any vertical whitespace character
3214             \V     any character that is not a vertical whitespace character
3215             \w     any "word" character
3216             \W     any "non-word" character
3218           Each pair of escape sequences partitions the complete set of characters
3219           into two disjoint sets. Any given character matches one, and only  one,
3220           of each pair.
3222           These character type sequences can appear both inside and outside char-
3223           acter classes. They each match one character of the  appropriate  type.
3224           If  the current matching point is at the end of the subject string, all
3225           of them fail, since there is no character to match.
3227           For compatibility with Perl, \s does not match the VT  character  (code
3228           11).   This makes it different from the the POSIX "space" class. The \s
3229           characters are HT (9), LF (10), FF (12), CR (13), and  space  (32).  If
3230           "use locale;" is included in a Perl script, \s may match the VT charac-
3231           ter. In PCRE, it never does.
3233           In UTF-8 mode, characters with values greater than 128 never match  \d,
3234           \s, or \w, and always match \D, \S, and \W. This is true even when Uni-
3235           code character property support is available.  These  sequences  retain
3236           their original meanings from before UTF-8 support was available, mainly
3237           for efficiency reasons.
3239           The sequences \h, \H, \v, and \V are Perl 5.10 features. In contrast to
3240           the  other  sequences, these do match certain high-valued codepoints in
3241           UTF-8 mode.  The horizontal space characters are:
3243             U+0009     Horizontal tab
3244             U+0020     Space
3245             U+00A0     Non-break space
3246             U+1680     Ogham space mark
3247             U+180E     Mongolian vowel separator
3248             U+2000     En quad
3249             U+2001     Em quad
3250             U+2002     En space
3251             U+2003     Em space
3252             U+2004     Three-per-em space
3253             U+2005     Four-per-em space
3254             U+2006     Six-per-em space
3255             U+2007     Figure space
3256             U+2008     Punctuation space
3257             U+2009     Thin space
3258             U+200A     Hair space
3259             U+202F     Narrow no-break space
3260             U+205F     Medium mathematical space
3261             U+3000     Ideographic space
3263           The vertical space characters are:
3265             U+000A     Linefeed
3266             U+000B     Vertical tab
3267             U+000C     Formfeed
3268             U+000D     Carriage return
3269             U+0085     Next line
3270             U+2028     Line separator
3271             U+2029     Paragraph separator
3273           A "word" character is an underscore or any character less than 256 that
3274           is  a  letter  or  digit.  The definition of letters and digits is con-
3275           trolled by PCRE's low-valued character tables, and may vary if  locale-
3276           specific  matching is taking place (see "Locale support" in the pcreapi
3277           page). For example, in a French locale such  as  "fr_FR"  in  Unix-like
3278           systems,  or "french" in Windows, some character codes greater than 128
3279           are used for accented letters, and these are matched by \w. The use  of
3280           locales with Unicode is discouraged.
3282       Newline sequences
3284           Outside  a  character class, by default, the escape sequence \R matches
3285           any Unicode newline sequence. This is a Perl 5.10 feature. In non-UTF-8
3286           mode \R is equivalent to the following:
3288             (?>\r\n|\n|\x0b|\f|\r|\x85)
3290           This  is  an  example  of an "atomic group", details of which are given
3291           below.  This particular group matches either the two-character sequence
3292           CR  followed  by  LF,  or  one  of  the single characters LF (linefeed,
3293           U+000A), VT (vertical tab, U+000B), FF (formfeed, U+000C), CR (carriage
3294           return, U+000D), or NEL (next line, U+0085). The two-character sequence
3295           is treated as a single unit that cannot be split.
3297           In UTF-8 mode, two additional characters whose codepoints  are  greater
3298           than 255 are added: LS (line separator, U+2028) and PS (paragraph sepa-
3299           rator, U+2029).  Unicode character property support is not  needed  for
3300           these characters to be recognized.
3302           It is possible to restrict \R to match only CR, LF, or CRLF (instead of
3303           the complete set  of  Unicode  line  endings)  by  setting  the  option
3304           PCRE_BSR_ANYCRLF either at compile time or when the pattern is matched.
3305           (BSR is an abbrevation for "backslash R".) This can be made the default
3306           when  PCRE  is  built;  if this is the case, the other behaviour can be
3307           requested via the PCRE_BSR_UNICODE option.   It  is  also  possible  to
3308           specify  these  settings  by  starting a pattern string with one of the
3309           following sequences:
3311             (*BSR_ANYCRLF)   CR, LF, or CRLF only
3312             (*BSR_UNICODE)   any Unicode newline sequence
3314           These override the default and the options given to pcre_compile(), but
3315           they can be overridden by options given to pcre_exec(). Note that these
3316           special settings, which are not Perl-compatible, are recognized only at
3317           the  very  start  of a pattern, and that they must be in upper case. If
3318           more than one of them is present, the last one is  used.  They  can  be
3319           combined  with  a  change of newline convention, for example, a pattern
3320           can start with:
3322             (*ANY)(*BSR_ANYCRLF)
3324           Inside a character class, \R matches the letter "R".
3326       Unicode character properties
3328           When PCRE is built with Unicode character property support, three addi-
3329           tional  escape sequences that match characters with specific properties
3330           are available.  When not in UTF-8 mode, these sequences are  of  course
3331           limited  to  testing characters whose codepoints are less than 256, but
3332           they do work in this mode.  The extra escape sequences are:
3334             \p{xx}   a character with the xx property
3335             \P{xx}   a character without the xx property
3336             \X       an extended Unicode sequence
3338           The property names represented by xx above are limited to  the  Unicode
3339           script names, the general category properties, and "Any", which matches
3340           any character (including newline). Other properties such as "InMusical-
3341           Symbols"  are  not  currently supported by PCRE. Note that \P{Any} does
3342           not match any characters, so always causes a match failure.
3344           Sets of Unicode characters are defined as belonging to certain scripts.
3345           A  character from one of these sets can be matched using a script name.
3346           For example:
3348             \p{Greek}
3349             \P{Han}
3351           Those that are not part of an identified script are lumped together  as
3352           "Common". The current list of scripts is:
3354           Arabic,  Armenian,  Balinese,  Bengali,  Bopomofo,  Braille,  Buginese,
3355           Buhid,  Canadian_Aboriginal,  Cherokee,  Common,   Coptic,   Cuneiform,
3356           Cypriot, Cyrillic, Deseret, Devanagari, Ethiopic, Georgian, Glagolitic,
3357           Gothic, Greek, Gujarati, Gurmukhi, Han, Hangul, Hanunoo, Hebrew,  Hira-
3358           gana,  Inherited,  Kannada,  Katakana,  Kharoshthi,  Khmer, Lao, Latin,
3359           Limbu,  Linear_B,  Malayalam,  Mongolian,  Myanmar,  New_Tai_Lue,  Nko,
3360           Ogham,  Old_Italic,  Old_Persian, Oriya, Osmanya, Phags_Pa, Phoenician,
3361           Runic,  Shavian,  Sinhala,  Syloti_Nagri,  Syriac,  Tagalog,  Tagbanwa,
3362           Tai_Le, Tamil, Telugu, Thaana, Thai, Tibetan, Tifinagh, Ugaritic, Yi.
3364           Each  character has exactly one general category property, specified by
3365           a two-letter abbreviation. For compatibility with Perl, negation can be
3366           specified  by  including a circumflex between the opening brace and the
3367           property name. For example, \p{^Lu} is the same as \P{Lu}.
3369           If only one letter is specified with \p or \P, it includes all the gen-
3370           eral  category properties that start with that letter. In this case, in
3371           the absence of negation, the curly brackets in the escape sequence  are
3372           optional; these two examples have the same effect:
3374             \p{L}
3375             \pL
3377           The following general category property codes are supported:
3379             C     Other
3380             Cc    Control
3381             Cf    Format
3382             Cn    Unassigned
3383             Co    Private use
3384             Cs    Surrogate
3386             L     Letter
3387             Ll    Lower case letter
3388             Lm    Modifier letter
3389             Lo    Other letter
3390             Lt    Title case letter
3391             Lu    Upper case letter
3393             M     Mark
3394             Mc    Spacing mark
3395             Me    Enclosing mark
3396             Mn    Non-spacing mark
3398             N     Number
3399             Nd    Decimal number
3400             Nl    Letter number
3401             No    Other number
3403             P     Punctuation
3404             Pc    Connector punctuation
3405             Pd    Dash punctuation
3406             Pe    Close punctuation
3407             Pf    Final punctuation
3408             Pi    Initial punctuation
3409             Po    Other punctuation
3410             Ps    Open punctuation
3412             S     Symbol
3413             Sc    Currency symbol
3414             Sk    Modifier symbol