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revision 292 by ph10, Thu Dec 27 09:27:23 2007 UTC revision 548 by ph10, Fri Jun 25 14:42:00 2010 UTC
# Line 2  Line 2 
2  This file contains a concatenation of the PCRE man pages, converted to plain  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  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  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  synopses of each function in the library have not been included. Neither has
6  separate text files for the pcregrep and pcretest commands.  the pcredemo program. There are separate text files for the pcregrep and
7    pcretest commands.
8  -----------------------------------------------------------------------------  -----------------------------------------------------------------------------
9    
10    
# Line 18  INTRODUCTION Line 19  INTRODUCTION
19    
20         The  PCRE  library is a set of functions that implement regular expres-         The  PCRE  library is a set of functions that implement regular expres-
21         sion pattern matching using the same syntax and semantics as Perl, with         sion pattern matching using the same syntax and semantics as Perl, with
22         just  a  few differences. (Certain features that appeared in Python and         just  a few differences. Some features that appeared in Python and PCRE
23         PCRE before they appeared in Perl are also available using  the  Python         before they appeared in Perl are also available using the  Python  syn-
24         syntax.)         tax,  there  is  some  support for one or two .NET and Oniguruma syntax
25           items, and there is an option for requesting some  minor  changes  that
26         The  current  implementation of PCRE (release 7.x) corresponds approxi-         give better JavaScript compatibility.
27         mately with Perl 5.10, including support for UTF-8 encoded strings  and  
28         Unicode general category properties. However, UTF-8 and Unicode support         The  current implementation of PCRE corresponds approximately with Perl
29         has to be explicitly enabled; it is not the default. The Unicode tables         5.10/5.11, including support for UTF-8 encoded strings and Unicode gen-
30         correspond to Unicode release 5.0.0.         eral  category properties. However, UTF-8 and Unicode support has to be
31           explicitly enabled; it is not the default. The  Unicode  tables  corre-
32           spond to Unicode release 5.2.0.
33    
34         In  addition to the Perl-compatible matching function, PCRE contains an         In  addition to the Perl-compatible matching function, PCRE contains an
35         alternative matching function that matches the same  compiled  patterns         alternative function that matches the same compiled patterns in a  dif-
36         in  a different way. In certain circumstances, the alternative function         ferent way. In certain circumstances, the alternative function has some
37         has some advantages. For a discussion of the two  matching  algorithms,         advantages.  For a discussion of the two matching algorithms,  see  the
38         see the pcrematching page.         pcrematching page.
39    
40         PCRE  is  written  in C and released as a C library. A number of people         PCRE  is  written  in C and released as a C library. A number of people
41         have written wrappers and interfaces of various kinds.  In  particular,         have written wrappers and interfaces of various kinds.  In  particular,
# Line 52  INTRODUCTION Line 55  INTRODUCTION
55         library is built. The pcre_config() function makes it  possible  for  a         library is built. The pcre_config() function makes it  possible  for  a
56         client  to  discover  which  features are available. The features them-         client  to  discover  which  features are available. The features them-
57         selves are described in the pcrebuild page. Documentation about  build-         selves are described in the pcrebuild page. Documentation about  build-
58         ing  PCRE for various operating systems can be found in the README file         ing  PCRE  for various operating systems can be found in the README and
59         in the source distribution.         NON-UNIX-USE files in the source distribution.
60    
61         The library contains a number of undocumented  internal  functions  and         The library contains a number of undocumented  internal  functions  and
62         data  tables  that  are  used by more than one of the exported external         data  tables  that  are  used by more than one of the exported external
# Line 69  USER DOCUMENTATION Line 72  USER DOCUMENTATION
72         The user documentation for PCRE comprises a number  of  different  sec-         The user documentation for PCRE comprises a number  of  different  sec-
73         tions.  In the "man" format, each of these is a separate "man page". In         tions.  In the "man" format, each of these is a separate "man page". In
74         the HTML format, each is a separate page, linked from the  index  page.         the HTML format, each is a separate page, linked from the  index  page.
75         In  the  plain text format, all the sections are concatenated, for ease         In  the  plain  text format, all the sections, except the pcredemo sec-
76         of searching. The sections are as follows:         tion, are concatenated, for ease of searching. The sections are as fol-
77           lows:
78    
79           pcre              this document           pcre              this document
80           pcre-config       show PCRE installation configuration information           pcre-config       show PCRE installation configuration information
# Line 79  USER DOCUMENTATION Line 83  USER DOCUMENTATION
83           pcrecallout       details of the callout feature           pcrecallout       details of the callout feature
84           pcrecompat        discussion of Perl compatibility           pcrecompat        discussion of Perl compatibility
85           pcrecpp           details of the C++ wrapper           pcrecpp           details of the C++ wrapper
86             pcredemo          a demonstration C program that uses PCRE
87           pcregrep          description of the pcregrep command           pcregrep          description of the pcregrep command
88           pcrematching      discussion of the two matching algorithms           pcrematching      discussion of the two matching algorithms
89           pcrepartial       details of the partial matching facility           pcrepartial       details of the partial matching facility
90           pcrepattern       syntax and semantics of supported           pcrepattern       syntax and semantics of supported
91                               regular expressions                               regular expressions
          pcresyntax        quick syntax reference  
92           pcreperform       discussion of performance issues           pcreperform       discussion of performance issues
93           pcreposix         the POSIX-compatible C API           pcreposix         the POSIX-compatible C API
94           pcreprecompile    details of saving and re-using precompiled patterns           pcreprecompile    details of saving and re-using precompiled patterns
95           pcresample        discussion of the sample program           pcresample        discussion of the pcredemo program
96           pcrestack         discussion of stack usage           pcrestack         discussion of stack usage
97             pcresyntax        quick syntax reference
98           pcretest          description of the pcretest testing command           pcretest          description of the pcretest testing command
99    
100         In  addition,  in the "man" and HTML formats, there is a short page for         In  addition,  in the "man" and HTML formats, there is a short page for
# Line 134  UTF-8 AND UNICODE PROPERTY SUPPORT Line 139  UTF-8 AND UNICODE PROPERTY SUPPORT
139    
140         In  order  process  UTF-8 strings, you must build PCRE to include UTF-8         In  order  process  UTF-8 strings, you must build PCRE to include UTF-8
141         support in the code, and, in addition,  you  must  call  pcre_compile()         support in the code, and, in addition,  you  must  call  pcre_compile()
142         with  the PCRE_UTF8 option flag. When you do this, both the pattern and         with  the  PCRE_UTF8  option  flag,  or the pattern must start with the
143         any subject strings that are matched against it are  treated  as  UTF-8         sequence (*UTF8). When either of these is the case,  both  the  pattern
144         strings instead of just strings of bytes.         and  any  subject  strings  that  are matched against it are treated as
145           UTF-8 strings instead of strings of 1-byte characters.
146    
147         If  you compile PCRE with UTF-8 support, but do not use it at run time,         If you compile PCRE with UTF-8 support, but do not use it at run  time,
148         the library will be a bit bigger, but the additional run time  overhead         the  library will be a bit bigger, but the additional run time overhead
149         is limited to testing the PCRE_UTF8 flag occasionally, so should not be         is limited to testing the PCRE_UTF8 flag occasionally, so should not be
150         very big.         very big.
151    
152         If PCRE is built with Unicode character property support (which implies         If PCRE is built with Unicode character property support (which implies
153         UTF-8  support),  the  escape sequences \p{..}, \P{..}, and \X are sup-         UTF-8 support), the escape sequences \p{..}, \P{..}, and  \X  are  sup-
154         ported.  The available properties that can be tested are limited to the         ported.  The available properties that can be tested are limited to the
155         general  category  properties such as Lu for an upper case letter or Nd         general category properties such as Lu for an upper case letter  or  Nd
156         for a decimal number, the Unicode script names such as Arabic  or  Han,         for  a  decimal number, the Unicode script names such as Arabic or Han,
157         and  the  derived  properties  Any  and L&. A full list is given in the         and the derived properties Any and L&. A full  list  is  given  in  the
158         pcrepattern documentation. Only the short names for properties are sup-         pcrepattern documentation. Only the short names for properties are sup-
159         ported.  For example, \p{L} matches a letter. Its Perl synonym, \p{Let-         ported. For example, \p{L} matches a letter. Its Perl synonym,  \p{Let-
160         ter}, is not supported.  Furthermore,  in  Perl,  many  properties  may         ter},  is  not  supported.   Furthermore,  in Perl, many properties may
161         optionally  be  prefixed by "Is", for compatibility with Perl 5.6. PCRE         optionally be prefixed by "Is", for compatibility with Perl  5.6.  PCRE
162         does not support this.         does not support this.
163    
164     Validity of UTF-8 strings     Validity of UTF-8 strings
165    
166         When you set the PCRE_UTF8 flag, the strings  passed  as  patterns  and         When  you  set  the  PCRE_UTF8 flag, the strings passed as patterns and
167         subjects are (by default) checked for validity on entry to the relevant         subjects are (by default) checked for validity on entry to the relevant
168         functions. From release 7.3 of PCRE, the check is according  the  rules         functions.  From  release 7.3 of PCRE, the check is according the rules
169         of  RFC  3629, which are themselves derived from the Unicode specifica-         of RFC 3629, which are themselves derived from the  Unicode  specifica-
170         tion. Earlier releases of PCRE followed the rules of  RFC  2279,  which         tion.  Earlier  releases  of PCRE followed the rules of RFC 2279, which
171         allows  the  full range of 31-bit values (0 to 0x7FFFFFFF). The current         allows the full range of 31-bit values (0 to 0x7FFFFFFF).  The  current
172         check allows only values in the range U+0 to U+10FFFF, excluding U+D800         check allows only values in the range U+0 to U+10FFFF, excluding U+D800
173         to U+DFFF.         to U+DFFF.
174    
175         The  excluded  code  points are the "Low Surrogate Area" of Unicode, of         The excluded code points are the "Low Surrogate Area"  of  Unicode,  of
176         which the Unicode Standard says this: "The Low Surrogate Area does  not         which  the Unicode Standard says this: "The Low Surrogate Area does not
177         contain  any  character  assignments,  consequently  no  character code         contain any  character  assignments,  consequently  no  character  code
178         charts or namelists are provided for this area. Surrogates are reserved         charts or namelists are provided for this area. Surrogates are reserved
179         for  use  with  UTF-16 and then must be used in pairs." The code points         for use with UTF-16 and then must be used in pairs."  The  code  points
180         that are encoded by UTF-16 pairs  are  available  as  independent  code         that  are  encoded  by  UTF-16  pairs are available as independent code
181         points  in  the  UTF-8  encoding.  (In other words, the whole surrogate         points in the UTF-8 encoding. (In  other  words,  the  whole  surrogate
182         thing is a fudge for UTF-16 which unfortunately messes up UTF-8.)         thing is a fudge for UTF-16 which unfortunately messes up UTF-8.)
183    
184         If an  invalid  UTF-8  string  is  passed  to  PCRE,  an  error  return         If  an  invalid  UTF-8  string  is  passed  to  PCRE,  an  error return
185         (PCRE_ERROR_BADUTF8) is given. In some situations, you may already know         (PCRE_ERROR_BADUTF8) is given. In some situations, you may already know
186         that your strings are valid, and therefore want to skip these checks in         that your strings are valid, and therefore want to skip these checks in
187         order to improve performance. If you set the PCRE_NO_UTF8_CHECK flag at         order to improve performance. If you set the PCRE_NO_UTF8_CHECK flag at
188         compile time or at run time, PCRE assumes that the pattern  or  subject         compile  time  or at run time, PCRE assumes that the pattern or subject
189         it  is  given  (respectively)  contains only valid UTF-8 codes. In this         it is given (respectively) contains only valid  UTF-8  codes.  In  this
190         case, it does not diagnose an invalid UTF-8 string.         case, it does not diagnose an invalid UTF-8 string.
191    
192         If you pass an invalid UTF-8 string  when  PCRE_NO_UTF8_CHECK  is  set,         If  you  pass  an  invalid UTF-8 string when PCRE_NO_UTF8_CHECK is set,
193         what  happens  depends on why the string is invalid. If the string con-         what happens depends on why the string is invalid. If the  string  con-
194         forms to the "old" definition of UTF-8 (RFC 2279), it is processed as a         forms to the "old" definition of UTF-8 (RFC 2279), it is processed as a
195         string  of  characters  in  the  range 0 to 0x7FFFFFFF. In other words,         string of characters in the range 0  to  0x7FFFFFFF.  In  other  words,
196         apart from the initial validity test, PCRE (when in UTF-8 mode) handles         apart from the initial validity test, PCRE (when in UTF-8 mode) handles
197         strings  according  to  the more liberal rules of RFC 2279. However, if         strings according to the more liberal rules of RFC  2279.  However,  if
198         the string does not even conform to RFC 2279, the result is  undefined.         the  string does not even conform to RFC 2279, the result is undefined.
199         Your program may crash.         Your program may crash.
200    
201         If  you  want  to  process  strings  of  values  in the full range 0 to         If you want to process strings  of  values  in  the  full  range  0  to
202         0x7FFFFFFF, encoded in a UTF-8-like manner as per the old RFC, you  can         0x7FFFFFFF,  encoded in a UTF-8-like manner as per the old RFC, you can
203         set PCRE_NO_UTF8_CHECK to bypass the more restrictive test. However, in         set PCRE_NO_UTF8_CHECK to bypass the more restrictive test. However, in
204         this situation, you will have to apply your own validity check.         this situation, you will have to apply your own validity check.
205    
206     General comments about UTF-8 mode     General comments about UTF-8 mode
207    
208         1. An unbraced hexadecimal escape sequence (such  as  \xb3)  matches  a         1.  An  unbraced  hexadecimal  escape sequence (such as \xb3) matches a
209         two-byte UTF-8 character if the value is greater than 127.         two-byte UTF-8 character if the value is greater than 127.
210    
211         2.  Octal  numbers  up to \777 are recognized, and match two-byte UTF-8         2. Octal numbers up to \777 are recognized, and  match  two-byte  UTF-8
212         characters for values greater than \177.         characters for values greater than \177.
213    
214         3. Repeat quantifiers apply to complete UTF-8 characters, not to  indi-         3.  Repeat quantifiers apply to complete UTF-8 characters, not to indi-
215         vidual bytes, for example: \x{100}{3}.         vidual bytes, for example: \x{100}{3}.
216    
217         4.  The dot metacharacter matches one UTF-8 character instead of a sin-         4. The dot metacharacter matches one UTF-8 character instead of a  sin-
218         gle byte.         gle byte.
219    
220         5. The escape sequence \C can be used to match a single byte  in  UTF-8         5.  The  escape sequence \C can be used to match a single byte in UTF-8
221         mode,  but  its  use can lead to some strange effects. This facility is         mode, but its use can lead to some strange effects.  This  facility  is
222         not available in the alternative matching function, pcre_dfa_exec().         not available in the alternative matching function, pcre_dfa_exec().
223    
224         6. The character escapes \b, \B, \d, \D, \s, \S, \w, and  \W  correctly         6.  The  character escapes \b, \B, \d, \D, \s, \S, \w, and \W correctly
225         test  characters of any code value, but the characters that PCRE recog-         test characters of any code value, but, by default, the characters that
226         nizes as digits, spaces, or word characters  remain  the  same  set  as         PCRE  recognizes  as digits, spaces, or word characters remain the same
227         before, all with values less than 256. This remains true even when PCRE         set as before, all with values less than 256. This  remains  true  even
228         includes Unicode property support, because to do otherwise  would  slow         when  PCRE  is built to include Unicode property support, because to do
229         down  PCRE in many common cases. If you really want to test for a wider         otherwise would slow down PCRE in many common  cases.  Note  that  this
230         sense of, say, "digit", you must use Unicode  property  tests  such  as         also applies to \b, because it is defined in terms of \w and \W. If you
231         \p{Nd}.         really want to test for a wider sense of, say,  "digit",  you  can  use
232           explicit  Unicode property tests such as \p{Nd}.  Alternatively, if you
233           set the PCRE_UCP option, the way that the  character  escapes  work  is
234           changed  so that Unicode properties are used to determine which charac-
235           ters match. There are more details in the section on generic  character
236           types in the pcrepattern documentation.
237    
238         7.  Similarly,  characters that match the POSIX named character classes         7.  Similarly,  characters that match the POSIX named character classes
239         are all low-valued characters.         are all low-valued characters, unless the PCRE_UCP option is set.
240    
241         8. However, the Perl 5.10 horizontal and vertical  whitespace  matching         8. However, the Perl 5.10 horizontal and vertical  whitespace  matching
242         escapes (\h, \H, \v, and \V) do match all the appropriate Unicode char-         escapes (\h, \H, \v, and \V) do match all the appropriate Unicode char-
243         acters.         acters, whether or not PCRE_UCP is set.
244    
245         9. Case-insensitive matching applies only to  characters  whose  values         9. Case-insensitive matching applies only to  characters  whose  values
246         are  less than 128, unless PCRE is built with Unicode property support.         are  less than 128, unless PCRE is built with Unicode property support.
# Line 256  AUTHOR Line 267  AUTHOR
267    
268  REVISION  REVISION
269    
270         Last updated: 09 August 2007         Last updated: 12 May 2010
271         Copyright (c) 1997-2007 University of Cambridge.         Copyright (c) 1997-2010 University of Cambridge.
272  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
273    
274    
# Line 275  PCRE BUILD-TIME OPTIONS Line 286  PCRE BUILD-TIME OPTIONS
286         script,  where the optional features are selected or deselected by pro-         script,  where the optional features are selected or deselected by pro-
287         viding options to configure before running the make  command.  However,         viding options to configure before running the make  command.  However,
288         the  same  options  can be selected in both Unix-like and non-Unix-like         the  same  options  can be selected in both Unix-like and non-Unix-like
289         environments using the GUI facility of  CMakeSetup  if  you  are  using         environments using the GUI facility of cmake-gui if you are using CMake
290         CMake instead of configure to build PCRE.         instead of configure to build PCRE.
291    
292           There  is  a  lot more information about building PCRE in non-Unix-like
293           environments in the file called NON_UNIX_USE, which is part of the PCRE
294           distribution.  You  should consult this file as well as the README file
295           if you are building in a non-Unix-like environment.
296    
297         The complete list of options for configure (which includes the standard         The complete list of options for configure (which includes the standard
298         ones such as the  selection  of  the  installation  directory)  can  be         ones  such  as  the  selection  of  the  installation directory) can be
299         obtained by running         obtained by running
300    
301           ./configure --help           ./configure --help
302    
303         The  following  sections  include  descriptions  of options whose names         The following sections include  descriptions  of  options  whose  names
304         begin with --enable or --disable. These settings specify changes to the         begin with --enable or --disable. These settings specify changes to the
305         defaults  for  the configure command. Because of the way that configure         defaults for the configure command. Because of the way  that  configure
306         works, --enable and --disable always come in pairs, so  the  complemen-         works,  --enable  and --disable always come in pairs, so the complemen-
307         tary  option always exists as well, but as it specifies the default, it         tary option always exists as well, but as it specifies the default,  it
308         is not described.         is not described.
309    
310    
# Line 305  C++ SUPPORT Line 321  C++ SUPPORT
321    
322  UTF-8 SUPPORT  UTF-8 SUPPORT
323    
324         To build PCRE with support for UTF-8 character strings, add         To build PCRE with support for UTF-8 Unicode character strings, add
325    
326           --enable-utf8           --enable-utf8
327    
328         to the configure command. Of itself, this  does  not  make  PCRE  treat         to  the  configure  command.  Of  itself, this does not make PCRE treat
329         strings  as UTF-8. As well as compiling PCRE with this option, you also         strings as UTF-8. As well as compiling PCRE with this option, you  also
330         have have to set the PCRE_UTF8 option when you call the  pcre_compile()         have  have to set the PCRE_UTF8 option when you call the pcre_compile()
331         function.         or pcre_compile2() functions.
332    
333           If you set --enable-utf8 when compiling in an EBCDIC environment,  PCRE
334           expects its input to be either ASCII or UTF-8 (depending on the runtime
335           option). It is not possible to support both EBCDIC and UTF-8  codes  in
336           the  same  version  of  the  library.  Consequently,  --enable-utf8 and
337           --enable-ebcdic are mutually exclusive.
338    
339    
340  UNICODE CHARACTER PROPERTY SUPPORT  UNICODE CHARACTER PROPERTY SUPPORT
341    
342         UTF-8  support allows PCRE to process character values greater than 255         UTF-8 support allows PCRE to process character values greater than  255
343         in the strings that it handles. On its own, however, it does  not  pro-         in  the  strings that it handles. On its own, however, it does not pro-
344         vide any facilities for accessing the properties of such characters. If         vide any facilities for accessing the properties of such characters. If
345         you want to be able to use the pattern escapes \P, \p,  and  \X,  which         you  want  to  be able to use the pattern escapes \P, \p, and \X, which
346         refer to Unicode character properties, you must add         refer to Unicode character properties, you must add
347    
348           --enable-unicode-properties           --enable-unicode-properties
349    
350         to  the configure command. This implies UTF-8 support, even if you have         to the configure command. This implies UTF-8 support, even if you  have
351         not explicitly requested it.         not explicitly requested it.
352    
353         Including Unicode property support adds around 30K  of  tables  to  the         Including  Unicode  property  support  adds around 30K of tables to the
354         PCRE  library.  Only  the general category properties such as Lu and Nd         PCRE library. Only the general category properties such as  Lu  and  Nd
355         are supported. Details are given in the pcrepattern documentation.         are supported. Details are given in the pcrepattern documentation.
356    
357    
358  CODE VALUE OF NEWLINE  CODE VALUE OF NEWLINE
359    
360         By default, PCRE interprets character 10 (linefeed, LF)  as  indicating         By  default,  PCRE interprets the linefeed (LF) character as indicating
361         the  end  of  a line. This is the normal newline character on Unix-like         the end of a line. This is the normal newline  character  on  Unix-like
362         systems. You can compile PCRE to use character 13 (carriage return, CR)         systems.  You  can compile PCRE to use carriage return (CR) instead, by
363         instead, by adding         adding
364    
365           --enable-newline-is-cr           --enable-newline-is-cr
366    
367         to  the  configure  command.  There  is  also  a --enable-newline-is-lf         to the  configure  command.  There  is  also  a  --enable-newline-is-lf
368         option, which explicitly specifies linefeed as the newline character.         option, which explicitly specifies linefeed as the newline character.
369    
370         Alternatively, you can specify that line endings are to be indicated by         Alternatively, you can specify that line endings are to be indicated by
# Line 354  CODE VALUE OF NEWLINE Line 376  CODE VALUE OF NEWLINE
376    
377           --enable-newline-is-anycrlf           --enable-newline-is-anycrlf
378    
379         which  causes  PCRE  to recognize any of the three sequences CR, LF, or         which causes PCRE to recognize any of the three sequences  CR,  LF,  or
380         CRLF as indicating a line ending. Finally, a fifth option, specified by         CRLF as indicating a line ending. Finally, a fifth option, specified by
381    
382           --enable-newline-is-any           --enable-newline-is-any
# Line 414  HANDLING VERY LARGE PATTERNS Line 436  HANDLING VERY LARGE PATTERNS
436         nation metacharacter). By default, two-byte values are used  for  these         nation metacharacter). By default, two-byte values are used  for  these
437         offsets,  leading  to  a  maximum size for a compiled pattern of around         offsets,  leading  to  a  maximum size for a compiled pattern of around
438         64K. This is sufficient to handle all but the most  gigantic  patterns.         64K. This is sufficient to handle all but the most  gigantic  patterns.
439         Nevertheless,  some  people do want to process enormous patterns, so it         Nevertheless,  some  people do want to process truyl enormous patterns,
440         is possible to compile PCRE to use three-byte or four-byte  offsets  by         so it is possible to compile PCRE to use three-byte or  four-byte  off-
441         adding a setting such as         sets by adding a setting such as
442    
443           --with-link-size=3           --with-link-size=3
444    
# Line 443  AVOIDING EXCESSIVE STACK USAGE Line 465  AVOIDING EXCESSIVE STACK USAGE
465         to the configure command. With this configuration, PCRE  will  use  the         to the configure command. With this configuration, PCRE  will  use  the
466         pcre_stack_malloc  and pcre_stack_free variables to call memory manage-         pcre_stack_malloc  and pcre_stack_free variables to call memory manage-
467         ment functions. By default these point to malloc() and free(), but  you         ment functions. By default these point to malloc() and free(), but  you
468         can replace the pointers so that your own functions are used.         can replace the pointers so that your own functions are used instead.
469    
470         Separate  functions  are  provided  rather  than  using pcre_malloc and         Separate  functions  are  provided  rather  than  using pcre_malloc and
471         pcre_free because the  usage  is  very  predictable:  the  block  sizes         pcre_free because the  usage  is  very  predictable:  the  block  sizes
# Line 451  AVOIDING EXCESSIVE STACK USAGE Line 473  AVOIDING EXCESSIVE STACK USAGE
473         reverse order. A calling program might be able to  implement  optimized         reverse order. A calling program might be able to  implement  optimized
474         functions  that  perform  better  than  malloc()  and free(). PCRE runs         functions  that  perform  better  than  malloc()  and free(). PCRE runs
475         noticeably more slowly when built in this way. This option affects only         noticeably more slowly when built in this way. This option affects only
476         the   pcre_exec()   function;   it   is   not   relevant  for  the  the         the pcre_exec() function; it is not relevant for pcre_dfa_exec().
        pcre_dfa_exec() function.  
477    
478    
479  LIMITING PCRE RESOURCE USAGE  LIMITING PCRE RESOURCE USAGE
480    
481         Internally, PCRE has a function called match(), which it calls  repeat-         Internally,  PCRE has a function called match(), which it calls repeat-
482         edly   (sometimes   recursively)  when  matching  a  pattern  with  the         edly  (sometimes  recursively)  when  matching  a  pattern   with   the
483         pcre_exec() function. By controlling the maximum number of  times  this         pcre_exec()  function.  By controlling the maximum number of times this
484         function  may be called during a single matching operation, a limit can         function may be called during a single matching operation, a limit  can
485         be placed on the resources used by a single call  to  pcre_exec().  The         be  placed  on  the resources used by a single call to pcre_exec(). The
486         limit  can be changed at run time, as described in the pcreapi documen-         limit can be changed at run time, as described in the pcreapi  documen-
487         tation. The default is 10 million, but this can be changed by adding  a         tation.  The default is 10 million, but this can be changed by adding a
488         setting such as         setting such as
489    
490           --with-match-limit=500000           --with-match-limit=500000
491    
492         to   the   configure  command.  This  setting  has  no  effect  on  the         to  the  configure  command.  This  setting  has  no  effect   on   the
493         pcre_dfa_exec() matching function.         pcre_dfa_exec() matching function.
494    
495         In some environments it is desirable to limit the  depth  of  recursive         In  some  environments  it is desirable to limit the depth of recursive
496         calls of match() more strictly than the total number of calls, in order         calls of match() more strictly than the total number of calls, in order
497         to restrict the maximum amount of stack (or heap,  if  --disable-stack-         to  restrict  the maximum amount of stack (or heap, if --disable-stack-
498         for-recursion is specified) that is used. A second limit controls this;         for-recursion is specified) that is used. A second limit controls this;
499         it defaults to the value that  is  set  for  --with-match-limit,  which         it  defaults  to  the  value  that is set for --with-match-limit, which
500         imposes  no  additional constraints. However, you can set a lower limit         imposes no additional constraints. However, you can set a  lower  limit
501         by adding, for example,         by adding, for example,
502    
503           --with-match-limit-recursion=10000           --with-match-limit-recursion=10000
504    
505         to the configure command. This value can  also  be  overridden  at  run         to  the  configure  command.  This  value can also be overridden at run
506         time.         time.
507    
508    
509  CREATING CHARACTER TABLES AT BUILD TIME  CREATING CHARACTER TABLES AT BUILD TIME
510    
511         PCRE  uses fixed tables for processing characters whose code values are         PCRE uses fixed tables for processing characters whose code values  are
512         less than 256. By default, PCRE is built with a set of tables that  are         less  than 256. By default, PCRE is built with a set of tables that are
513         distributed  in  the  file pcre_chartables.c.dist. These tables are for         distributed in the file pcre_chartables.c.dist. These  tables  are  for
514         ASCII codes only. If you add         ASCII codes only. If you add
515    
516           --enable-rebuild-chartables           --enable-rebuild-chartables
517    
518         to the configure command, the distributed tables are  no  longer  used.         to  the  configure  command, the distributed tables are no longer used.
519         Instead,  a  program  called dftables is compiled and run. This outputs         Instead, a program called dftables is compiled and  run.  This  outputs
520         the source for new set of tables, created in the default locale of your         the source for new set of tables, created in the default locale of your
521         C runtime system. (This method of replacing the tables does not work if         C runtime system. (This method of replacing the tables does not work if
522         you are cross compiling, because dftables is run on the local host.  If         you  are cross compiling, because dftables is run on the local host. If
523         you  need  to  create alternative tables when cross compiling, you will         you need to create alternative tables when cross  compiling,  you  will
524         have to do so "by hand".)         have to do so "by hand".)
525    
526    
527  USING EBCDIC CODE  USING EBCDIC CODE
528    
529         PCRE assumes by default that it will run in an  environment  where  the         PCRE  assumes  by  default that it will run in an environment where the
530         character  code  is  ASCII  (or Unicode, which is a superset of ASCII).         character code is ASCII (or Unicode, which is  a  superset  of  ASCII).
531         This is the case for most computer operating systems.  PCRE  can,  how-         This  is  the  case for most computer operating systems. PCRE can, how-
532         ever, be compiled to run in an EBCDIC environment by adding         ever, be compiled to run in an EBCDIC environment by adding
533    
534           --enable-ebcdic           --enable-ebcdic
535    
536         to the configure command. This setting implies --enable-rebuild-charta-         to the configure command. This setting implies --enable-rebuild-charta-
537         bles. You should only use it if you know that  you  are  in  an  EBCDIC         bles.  You  should  only  use  it if you know that you are in an EBCDIC
538         environment (for example, an IBM mainframe operating system).         environment (for example,  an  IBM  mainframe  operating  system).  The
539           --enable-ebcdic option is incompatible with --enable-utf8.
540    
541    
542  PCREGREP OPTIONS FOR COMPRESSED FILE SUPPORT  PCREGREP OPTIONS FOR COMPRESSED FILE SUPPORT
# Line 540  PCRETEST OPTION FOR LIBREADLINE SUPPORT Line 562  PCRETEST OPTION FOR LIBREADLINE SUPPORT
562         to  the  configure  command,  pcretest  is  linked with the libreadline         to  the  configure  command,  pcretest  is  linked with the libreadline
563         library, and when its input is from a terminal, it reads it  using  the         library, and when its input is from a terminal, it reads it  using  the
564         readline() function. This provides line-editing and history facilities.         readline() function. This provides line-editing and history facilities.
565         Note that libreadline is GPL-licenced, so if you distribute a binary of         Note that libreadline is GPL-licensed, so if you distribute a binary of
566         pcretest linked in this way, there may be licensing issues.         pcretest linked in this way, there may be licensing issues.
567    
568           Setting  this  option  causes  the -lreadline option to be added to the
569           pcretest build. In many operating environments with  a  sytem-installed
570           libreadline this is sufficient. However, in some environments (e.g.  if
571           an unmodified distribution version of readline is in use),  some  extra
572           configuration  may  be necessary. The INSTALL file for libreadline says
573           this:
574    
575             "Readline uses the termcap functions, but does not link with the
576             termcap or curses library itself, allowing applications which link
577             with readline the to choose an appropriate library."
578    
579           If your environment has not been set up so that an appropriate  library
580           is automatically included, you may need to add something like
581    
582             LIBS="-ncurses"
583    
584           immediately before the configure command.
585    
586    
587  SEE ALSO  SEE ALSO
588    
# Line 558  AUTHOR Line 598  AUTHOR
598    
599  REVISION  REVISION
600    
601         Last updated: 18 December 2007         Last updated: 29 September 2009
602         Copyright (c) 1997-2007 University of Cambridge.         Copyright (c) 1997-2009 University of Cambridge.
603  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
604    
605    
# Line 646  THE ALTERNATIVE MATCHING ALGORITHM Line 686  THE ALTERNATIVE MATCHING ALGORITHM
686         though  it is not implemented as a traditional finite state machine (it         though  it is not implemented as a traditional finite state machine (it
687         keeps multiple states active simultaneously).         keeps multiple states active simultaneously).
688    
689           Although the general principle of this matching algorithm  is  that  it
690           scans  the subject string only once, without backtracking, there is one
691           exception: when a lookaround assertion is encountered,  the  characters
692           following  or  preceding  the  current  point  have to be independently
693           inspected.
694    
695         The scan continues until either the end of the subject is  reached,  or         The scan continues until either the end of the subject is  reached,  or
696         there  are  no more unterminated paths. At this point, terminated paths         there  are  no more unterminated paths. At this point, terminated paths
697         represent the different matching possibilities (if there are none,  the         represent the different matching possibilities (if there are none,  the
698         match  has  failed).   Thus,  if there is more than one possible match,         match  has  failed).   Thus,  if there is more than one possible match,
699         this algorithm finds all of them, and in particular, it finds the long-         this algorithm finds all of them, and in particular, it finds the long-
700         est.  In PCRE, there is an option to stop the algorithm after the first         est.  There  is  an  option to stop the algorithm after the first match
701         match (which is necessarily the shortest) has been found.         (which is necessarily the shortest) is found.
702    
703         Note that all the matches that are found start at the same point in the         Note that all the matches that are found start at the same point in the
704         subject. If the pattern         subject. If the pattern
# Line 707  THE ALTERNATIVE MATCHING ALGORITHM Line 753  THE ALTERNATIVE MATCHING ALGORITHM
753         tive algorithm moves through the subject  string  one  character  at  a         tive algorithm moves through the subject  string  one  character  at  a
754         time, for all active paths through the tree.         time, for all active paths through the tree.
755    
756         8.  None  of  the  backtracking control verbs such as (*PRUNE) are sup-         8.  Except for (*FAIL), the backtracking control verbs such as (*PRUNE)
757         ported.         are not supported. (*FAIL) is supported, and  behaves  like  a  failing
758           negative assertion.
759    
760    
761  ADVANTAGES OF THE ALTERNATIVE ALGORITHM  ADVANTAGES OF THE ALTERNATIVE ALGORITHM
762    
763         Using the alternative matching algorithm provides the following  advan-         Using  the alternative matching algorithm provides the following advan-
764         tages:         tages:
765    
766         1. All possible matches (at a single point in the subject) are automat-         1. All possible matches (at a single point in the subject) are automat-
767         ically found, and in particular, the longest match is  found.  To  find         ically  found,  and  in particular, the longest match is found. To find
768         more than one match using the standard algorithm, you have to do kludgy         more than one match using the standard algorithm, you have to do kludgy
769         things with callouts.         things with callouts.
770    
771         2. There is much better support for partial matching. The  restrictions         2.  Because  the  alternative  algorithm  scans the subject string just
772         on  the content of the pattern that apply when using the standard algo-         once, and never needs to backtrack, it is possible to  pass  very  long
773         rithm for partial matching do not apply to the  alternative  algorithm.         subject  strings  to  the matching function in several pieces, checking
774         For  non-anchored patterns, the starting position of a partial match is         for partial matching each time.  The  pcrepartial  documentation  gives
775         available.         details of partial matching.
   
        3. Because the alternative algorithm  scans  the  subject  string  just  
        once,  and  never  needs to backtrack, it is possible to pass very long  
        subject strings to the matching function in  several  pieces,  checking  
        for partial matching each time.  
776    
777    
778  DISADVANTAGES OF THE ALTERNATIVE ALGORITHM  DISADVANTAGES OF THE ALTERNATIVE ALGORITHM
# Line 756  AUTHOR Line 798  AUTHOR
798    
799  REVISION  REVISION
800    
801         Last updated: 08 August 2007         Last updated: 29 September 2009
802         Copyright (c) 1997-2007 University of Cambridge.         Copyright (c) 1997-2009 University of Cambridge.
803  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
804    
805    
# Line 864  PCRE API OVERVIEW Line 906  PCRE API OVERVIEW
906         bers for the library.  Applications can use these  to  include  support         bers for the library.  Applications can use these  to  include  support
907         for different releases of PCRE.         for different releases of PCRE.
908    
909           In a Windows environment, if you want to statically link an application
910           program against a non-dll pcre.a  file,  you  must  define  PCRE_STATIC
911           before  including  pcre.h or pcrecpp.h, because otherwise the pcre_mal-
912           loc()   and   pcre_free()   exported   functions   will   be   declared
913           __declspec(dllimport), with unwanted results.
914    
915         The   functions   pcre_compile(),  pcre_compile2(),  pcre_study(),  and         The   functions   pcre_compile(),  pcre_compile2(),  pcre_study(),  and
916         pcre_exec() are used for compiling and matching regular expressions  in         pcre_exec() are used for compiling and matching regular expressions  in
917         a  Perl-compatible  manner. A sample program that demonstrates the sim-         a  Perl-compatible  manner. A sample program that demonstrates the sim-
918         plest way of using them is provided in the file  called  pcredemo.c  in         plest way of using them is provided in the file  called  pcredemo.c  in
919         the  source distribution. The pcresample documentation describes how to         the PCRE source distribution. A listing of this program is given in the
920         run it.         pcredemo documentation, and the pcresample documentation describes  how
921           to compile and run it.
922    
923         A second matching function, pcre_dfa_exec(), which is not Perl-compati-         A second matching function, pcre_dfa_exec(), which is not Perl-compati-
924         ble,  is  also provided. This uses a different algorithm for the match-         ble, is also provided. This uses a different algorithm for  the  match-
925         ing. The alternative algorithm finds all possible matches (at  a  given         ing.  The  alternative algorithm finds all possible matches (at a given
926         point  in  the subject), and scans the subject just once. However, this         point in the subject), and scans the subject just  once  (unless  there
927         algorithm does not return captured substrings. A description of the two         are  lookbehind  assertions).  However,  this algorithm does not return
928         matching  algorithms and their advantages and disadvantages is given in         captured substrings. A description of the two matching  algorithms  and
929         the pcrematching documentation.         their  advantages  and disadvantages is given in the pcrematching docu-
930           mentation.
931    
932         In addition to the main compiling and  matching  functions,  there  are         In addition to the main compiling and  matching  functions,  there  are
933         convenience functions for extracting captured substrings from a subject         convenience functions for extracting captured substrings from a subject
# Line 978  MULTITHREADING Line 1028  MULTITHREADING
1028         pcre_malloc, pcre_free, pcre_stack_malloc, and pcre_stack_free, and the         pcre_malloc, pcre_free, pcre_stack_malloc, and pcre_stack_free, and the
1029         callout function pointed to by pcre_callout, are shared by all threads.         callout function pointed to by pcre_callout, are shared by all threads.
1030    
1031         The compiled form of a regular expression is not altered during  match-         The  compiled form of a regular expression is not altered during match-
1032         ing, so the same compiled pattern can safely be used by several threads         ing, so the same compiled pattern can safely be used by several threads
1033         at once.         at once.
1034    
# Line 986  MULTITHREADING Line 1036  MULTITHREADING
1036  SAVING PRECOMPILED PATTERNS FOR LATER USE  SAVING PRECOMPILED PATTERNS FOR LATER USE
1037    
1038         The compiled form of a regular expression can be saved and re-used at a         The compiled form of a regular expression can be saved and re-used at a
1039         later  time,  possibly by a different program, and even on a host other         later time, possibly by a different program, and even on a  host  other
1040         than the one on which  it  was  compiled.  Details  are  given  in  the         than  the  one  on  which  it  was  compiled.  Details are given in the
1041         pcreprecompile  documentation.  However, compiling a regular expression         pcreprecompile documentation. However, compiling a  regular  expression
1042         with one version of PCRE for use with a different version is not  guar-         with  one version of PCRE for use with a different version is not guar-
1043         anteed to work and may cause crashes.         anteed to work and may cause crashes.
1044    
1045    
# Line 997  CHECKING BUILD-TIME OPTIONS Line 1047  CHECKING BUILD-TIME OPTIONS
1047    
1048         int pcre_config(int what, void *where);         int pcre_config(int what, void *where);
1049    
1050         The  function pcre_config() makes it possible for a PCRE client to dis-         The function pcre_config() makes it possible for a PCRE client to  dis-
1051         cover which optional features have been compiled into the PCRE library.         cover which optional features have been compiled into the PCRE library.
1052         The  pcrebuild documentation has more details about these optional fea-         The pcrebuild documentation has more details about these optional  fea-
1053         tures.         tures.
1054    
1055         The first argument for pcre_config() is an  integer,  specifying  which         The  first  argument  for pcre_config() is an integer, specifying which
1056         information is required; the second argument is a pointer to a variable         information is required; the second argument is a pointer to a variable
1057         into which the information is  placed.  The  following  information  is         into  which  the  information  is  placed. The following information is
1058         available:         available:
1059    
1060           PCRE_CONFIG_UTF8           PCRE_CONFIG_UTF8
1061    
1062         The  output is an integer that is set to one if UTF-8 support is avail-         The output is an integer that is set to one if UTF-8 support is  avail-
1063         able; otherwise it is set to zero.         able; otherwise it is set to zero.
1064    
1065           PCRE_CONFIG_UNICODE_PROPERTIES           PCRE_CONFIG_UNICODE_PROPERTIES
1066    
1067         The output is an integer that is set to  one  if  support  for  Unicode         The  output  is  an  integer  that is set to one if support for Unicode
1068         character properties is available; otherwise it is set to zero.         character properties is available; otherwise it is set to zero.
1069    
1070           PCRE_CONFIG_NEWLINE           PCRE_CONFIG_NEWLINE
1071    
1072         The  output  is  an integer whose value specifies the default character         The output is an integer whose value specifies  the  default  character
1073         sequence that is recognized as meaning "newline". The four values  that         sequence  that is recognized as meaning "newline". The four values that
1074         are supported are: 10 for LF, 13 for CR, 3338 for CRLF, -2 for ANYCRLF,         are supported are: 10 for LF, 13 for CR, 3338 for CRLF, -2 for ANYCRLF,
1075         and -1 for ANY. The default should normally be  the  standard  sequence         and  -1  for  ANY.  Though they are derived from ASCII, the same values
1076         for your operating system.         are returned in EBCDIC environments. The default should normally corre-
1077           spond to the standard sequence for your operating system.
1078    
1079           PCRE_CONFIG_BSR           PCRE_CONFIG_BSR
1080    
# Line 1050  CHECKING BUILD-TIME OPTIONS Line 1101  CHECKING BUILD-TIME OPTIONS
1101    
1102           PCRE_CONFIG_MATCH_LIMIT           PCRE_CONFIG_MATCH_LIMIT
1103    
1104         The output is an integer that gives the default limit for the number of         The output is a long integer that gives the default limit for the  num-
1105         internal  matching  function  calls in a pcre_exec() execution. Further         ber  of  internal  matching  function calls in a pcre_exec() execution.
1106         details are given with pcre_exec() below.         Further details are given with pcre_exec() below.
1107    
1108           PCRE_CONFIG_MATCH_LIMIT_RECURSION           PCRE_CONFIG_MATCH_LIMIT_RECURSION
1109    
1110         The output is an integer that gives the default limit for the depth  of         The output is a long integer that gives the default limit for the depth
1111         recursion  when calling the internal matching function in a pcre_exec()         of   recursion  when  calling  the  internal  matching  function  in  a
1112         execution. Further details are given with pcre_exec() below.         pcre_exec() execution.  Further  details  are  given  with  pcre_exec()
1113           below.
1114    
1115           PCRE_CONFIG_STACKRECURSE           PCRE_CONFIG_STACKRECURSE
1116    
1117         The output is an integer that is set to one if internal recursion  when         The  output is an integer that is set to one if internal recursion when
1118         running pcre_exec() is implemented by recursive function calls that use         running pcre_exec() is implemented by recursive function calls that use
1119         the stack to remember their state. This is the usual way that  PCRE  is         the  stack  to remember their state. This is the usual way that PCRE is
1120         compiled. The output is zero if PCRE was compiled to use blocks of data         compiled. The output is zero if PCRE was compiled to use blocks of data
1121         on the  heap  instead  of  recursive  function  calls.  In  this  case,         on  the  heap  instead  of  recursive  function  calls.  In  this case,
1122         pcre_stack_malloc  and  pcre_stack_free  are  called  to  manage memory         pcre_stack_malloc and  pcre_stack_free  are  called  to  manage  memory
1123         blocks on the heap, thus avoiding the use of the stack.         blocks on the heap, thus avoiding the use of the stack.
1124    
1125    
# Line 1084  COMPILING A PATTERN Line 1136  COMPILING A PATTERN
1136    
1137         Either of the functions pcre_compile() or pcre_compile2() can be called         Either of the functions pcre_compile() or pcre_compile2() can be called
1138         to compile a pattern into an internal form. The only difference between         to compile a pattern into an internal form. The only difference between
1139         the two interfaces is that pcre_compile2() has an additional  argument,         the  two interfaces is that pcre_compile2() has an additional argument,
1140         errorcodeptr, via which a numerical error code can be returned.         errorcodeptr, via which a numerical error  code  can  be  returned.  To
1141           avoid  too  much repetition, we refer just to pcre_compile() below, but
1142           the information applies equally to pcre_compile2().
1143    
1144         The pattern is a C string terminated by a binary zero, and is passed in         The pattern is a C string terminated by a binary zero, and is passed in
1145         the pattern argument. A pointer to a single block  of  memory  that  is         the  pattern  argument.  A  pointer to a single block of memory that is
1146         obtained  via  pcre_malloc is returned. This contains the compiled code         obtained via pcre_malloc is returned. This contains the  compiled  code
1147         and related data. The pcre type is defined for the returned block; this         and related data. The pcre type is defined for the returned block; this
1148         is a typedef for a structure whose contents are not externally defined.         is a typedef for a structure whose contents are not externally defined.
1149         It is up to the caller to free the memory (via pcre_free) when it is no         It is up to the caller to free the memory (via pcre_free) when it is no
1150         longer required.         longer required.
1151    
1152         Although  the compiled code of a PCRE regex is relocatable, that is, it         Although the compiled code of a PCRE regex is relocatable, that is,  it
1153         does not depend on memory location, the complete pcre data block is not         does not depend on memory location, the complete pcre data block is not
1154         fully  relocatable, because it may contain a copy of the tableptr argu-         fully relocatable, because it may contain a copy of the tableptr  argu-
1155         ment, which is an address (see below).         ment, which is an address (see below).
1156    
1157         The options argument contains various bit settings that affect the com-         The options argument contains various bit settings that affect the com-
1158         pilation.  It  should be zero if no options are required. The available         pilation. It should be zero if no options are required.  The  available
1159         options are described below. Some of them, in  particular,  those  that         options  are  described  below. Some of them (in particular, those that
1160         are  compatible  with  Perl,  can also be set and unset from within the         are compatible with Perl, but some others as well) can also be set  and
1161         pattern (see the detailed description  in  the  pcrepattern  documenta-         unset  from  within  the  pattern  (see the detailed description in the
1162         tion).  For  these options, the contents of the options argument speci-         pcrepattern documentation). For those options that can be different  in
1163         fies their initial settings at the start of compilation and  execution.         different  parts  of  the pattern, the contents of the options argument
1164         The  PCRE_ANCHORED  and PCRE_NEWLINE_xxx options can be set at the time         specifies their settings at the start of compilation and execution. The
1165         of matching as well as at compile time.         PCRE_ANCHORED, PCRE_BSR_xxx, and PCRE_NEWLINE_xxx options can be set at
1166           the time of matching as well as at compile time.
1167    
1168         If errptr is NULL, pcre_compile() returns NULL immediately.  Otherwise,         If errptr is NULL, pcre_compile() returns NULL immediately.  Otherwise,
1169         if  compilation  of  a  pattern fails, pcre_compile() returns NULL, and         if  compilation  of  a  pattern fails, pcre_compile() returns NULL, and
1170         sets the variable pointed to by errptr to point to a textual error mes-         sets the variable pointed to by errptr to point to a textual error mes-
1171         sage. This is a static string that is part of the library. You must not         sage. This is a static string that is part of the library. You must not
1172         try to free it. The offset from the start of the pattern to the charac-         try to free it. The byte offset from the start of the  pattern  to  the
1173         ter where the error was discovered is placed in the variable pointed to         character  that  was  being  processed when the error was discovered is
1174         by erroffset, which must not be NULL. If it is, an immediate  error  is         placed in the variable pointed to by erroffset, which must not be NULL.
1175         given.         If  it  is,  an  immediate error is given. Some errors are not detected
1176           until checks are carried out when the whole pattern has  been  scanned;
1177           in this case the offset is set to the end of the pattern.
1178    
1179         If  pcre_compile2()  is  used instead of pcre_compile(), and the error-         If  pcre_compile2()  is  used instead of pcre_compile(), and the error-
1180         codeptr argument is not NULL, a non-zero error code number is  returned         codeptr argument is not NULL, a non-zero error code number is  returned
# Line 1234  COMPILING A PATTERN Line 1291  COMPILING A PATTERN
1291         letter that has no special meaning  causes  an  error,  thus  reserving         letter that has no special meaning  causes  an  error,  thus  reserving
1292         these  combinations  for  future  expansion.  By default, as in Perl, a         these  combinations  for  future  expansion.  By default, as in Perl, a
1293         backslash followed by a letter with no special meaning is treated as  a         backslash followed by a letter with no special meaning is treated as  a
1294         literal.  (Perl can, however, be persuaded to give a warning for this.)         literal. (Perl can, however, be persuaded to give an error for this, by
1295         There are at present no other features controlled by  this  option.  It         running it with the -w option.) There are at present no other  features
1296         can also be set by a (?X) option setting within a pattern.         controlled  by this option. It can also be set by a (?X) option setting
1297           within a pattern.
1298    
1299           PCRE_FIRSTLINE           PCRE_FIRSTLINE
1300    
1301         If  this  option  is  set,  an  unanchored pattern is required to match         If this option is set, an  unanchored  pattern  is  required  to  match
1302         before or at the first  newline  in  the  subject  string,  though  the         before  or  at  the  first  newline  in  the subject string, though the
1303         matched text may continue over the newline.         matched text may continue over the newline.
1304    
1305             PCRE_JAVASCRIPT_COMPAT
1306    
1307           If this option is set, PCRE's behaviour is changed in some ways so that
1308           it  is  compatible with JavaScript rather than Perl. The changes are as
1309           follows:
1310    
1311           (1) A lone closing square bracket in a pattern  causes  a  compile-time
1312           error,  because this is illegal in JavaScript (by default it is treated
1313           as a data character). Thus, the pattern AB]CD becomes illegal when this
1314           option is set.
1315    
1316           (2)  At run time, a back reference to an unset subpattern group matches
1317           an empty string (by default this causes the current  matching  alterna-
1318           tive  to  fail). A pattern such as (\1)(a) succeeds when this option is
1319           set (assuming it can find an "a" in the subject), whereas it  fails  by
1320           default, for Perl compatibility.
1321    
1322           PCRE_MULTILINE           PCRE_MULTILINE
1323    
1324         By  default,  PCRE  treats the subject string as consisting of a single         By  default,  PCRE  treats the subject string as consisting of a single
# Line 1297  COMPILING A PATTERN Line 1372  COMPILING A PATTERN
1372         and are therefore ignored.         and are therefore ignored.
1373    
1374         The newline option that is set at compile time becomes the default that         The newline option that is set at compile time becomes the default that
1375         is used for pcre_exec() and pcre_dfa_exec(), but it can be  overridden.         is used for pcre_exec() and pcre_dfa_exec(), but it can be overridden.
1376    
1377           PCRE_NO_AUTO_CAPTURE           PCRE_NO_AUTO_CAPTURE
1378    
1379         If this option is set, it disables the use of numbered capturing paren-         If this option is set, it disables the use of numbered capturing paren-
1380         theses in the pattern. Any opening parenthesis that is not followed  by         theses  in the pattern. Any opening parenthesis that is not followed by
1381         ?  behaves as if it were followed by ?: but named parentheses can still         ? behaves as if it were followed by ?: but named parentheses can  still
1382         be used for capturing (and they acquire  numbers  in  the  usual  way).         be  used  for  capturing  (and  they acquire numbers in the usual way).
1383         There is no equivalent of this option in Perl.         There is no equivalent of this option in Perl.
1384    
1385             PCRE_UCP
1386    
1387           This option changes the way PCRE processes \b, \d, \s, \w, and some  of
1388           the POSIX character classes. By default, only ASCII characters are rec-
1389           ognized, but if PCRE_UCP is set, Unicode properties are used instead to
1390           classify  characters.  More details are given in the section on generic
1391           character types in the pcrepattern page. If you set PCRE_UCP,  matching
1392           one  of the items it affects takes much longer. The option is available
1393           only if PCRE has been compiled with Unicode property support.
1394    
1395           PCRE_UNGREEDY           PCRE_UNGREEDY
1396    
1397         This  option  inverts  the "greediness" of the quantifiers so that they         This option inverts the "greediness" of the quantifiers  so  that  they
1398         are not greedy by default, but become greedy if followed by "?". It  is         are  not greedy by default, but become greedy if followed by "?". It is
1399         not  compatible  with Perl. It can also be set by a (?U) option setting         not compatible with Perl. It can also be set by a (?U)  option  setting
1400         within the pattern.         within the pattern.
1401    
1402           PCRE_UTF8           PCRE_UTF8
1403    
1404         This option causes PCRE to regard both the pattern and the  subject  as         This  option  causes PCRE to regard both the pattern and the subject as
1405         strings  of  UTF-8 characters instead of single-byte character strings.         strings of UTF-8 characters instead of single-byte  character  strings.
1406         However, it is available only when PCRE is built to include UTF-8  sup-         However,  it is available only when PCRE is built to include UTF-8 sup-
1407         port.  If not, the use of this option provokes an error. Details of how         port. If not, the use of this option provokes an error. Details of  how
1408         this option changes the behaviour of PCRE are given in the  section  on         this  option  changes the behaviour of PCRE are given in the section on
1409         UTF-8 support in the main pcre page.         UTF-8 support in the main pcre page.
1410    
1411           PCRE_NO_UTF8_CHECK           PCRE_NO_UTF8_CHECK
1412    
1413         When PCRE_UTF8 is set, the validity of the pattern as a UTF-8 string is         When PCRE_UTF8 is set, the validity of the pattern as a UTF-8 string is
1414         automatically checked. There is a  discussion  about  the  validity  of         automatically  checked.  There  is  a  discussion about the validity of
1415         UTF-8  strings  in  the main pcre page. If an invalid UTF-8 sequence of         UTF-8 strings in the main pcre page. If an invalid  UTF-8  sequence  of
1416         bytes is found, pcre_compile() returns an error. If  you  already  know         bytes  is  found,  pcre_compile() returns an error. If you already know
1417         that your pattern is valid, and you want to skip this check for perfor-         that your pattern is valid, and you want to skip this check for perfor-
1418         mance reasons, you can set the PCRE_NO_UTF8_CHECK option.  When  it  is         mance  reasons,  you  can set the PCRE_NO_UTF8_CHECK option. When it is
1419         set,  the  effect  of  passing  an invalid UTF-8 string as a pattern is         set, the effect of passing an invalid UTF-8  string  as  a  pattern  is
1420         undefined. It may cause your program to crash. Note  that  this  option         undefined.  It  may  cause your program to crash. Note that this option
1421         can  also be passed to pcre_exec() and pcre_dfa_exec(), to suppress the         can also be passed to pcre_exec() and pcre_dfa_exec(), to suppress  the
1422         UTF-8 validity checking of subject strings.         UTF-8 validity checking of subject strings.
1423    
1424    
1425  COMPILATION ERROR CODES  COMPILATION ERROR CODES
1426    
1427         The following table lists the error  codes  than  may  be  returned  by         The  following  table  lists  the  error  codes than may be returned by
1428         pcre_compile2(),  along with the error messages that may be returned by         pcre_compile2(), along with the error messages that may be returned  by
1429         both compiling functions. As PCRE has developed, some error codes  have         both  compiling functions. As PCRE has developed, some error codes have
1430         fallen out of use. To avoid confusion, they have not been re-used.         fallen out of use. To avoid confusion, they have not been re-used.
1431    
1432            0  no error            0  no error
# Line 1397  COMPILATION ERROR CODES Line 1482  COMPILATION ERROR CODES
1482           50  [this code is not in use]           50  [this code is not in use]
1483           51  octal value is greater than \377 (not in UTF-8 mode)           51  octal value is greater than \377 (not in UTF-8 mode)
1484           52  internal error: overran compiling workspace           52  internal error: overran compiling workspace
1485           53   internal  error:  previously-checked  referenced  subpattern not           53  internal error: previously-checked referenced subpattern
1486         found                 not found
1487           54  DEFINE group contains more than one branch           54  DEFINE group contains more than one branch
1488           55  repeating a DEFINE group is not allowed           55  repeating a DEFINE group is not allowed
1489           56  inconsistent NEWLINE options           56  inconsistent NEWLINE options
1490           57  \g is not followed by a braced name or an optionally braced           57  \g is not followed by a braced, angle-bracketed, or quoted
1491                 non-zero number                 name/number or by a plain number
1492           58  (?+ or (?- or (?(+ or (?(- must be followed by a non-zero number           58  a numbered reference must not be zero
1493           59  (*VERB) with an argument is not supported           59  an argument is not allowed for (*ACCEPT), (*FAIL), or (*COMMIT)
1494           60  (*VERB) not recognized           60  (*VERB) not recognized
1495           61  number is too big           61  number is too big
1496           62  subpattern name expected           62  subpattern name expected
1497           63  digit expected after (?+           63  digit expected after (?+
1498             64  ] is an invalid data character in JavaScript compatibility mode
1499             65  different names for subpatterns of the same number are
1500                   not allowed
1501             66  (*MARK) must have an argument
1502             67  this version of PCRE is not compiled with PCRE_UCP support
1503    
1504         The numbers 32 and 10000 in errors 48 and 49  are  defaults;  different         The numbers 32 and 10000 in errors 48 and 49  are  defaults;  different
1505         values may be used if the limits were changed when PCRE was built.         values may be used if the limits were changed when PCRE was built.
# Line 1429  STUDYING A PATTERN Line 1519  STUDYING A PATTERN
1519         the results of the study.         the results of the study.
1520    
1521         The  returned  value  from  pcre_study()  can  be  passed  directly  to         The  returned  value  from  pcre_study()  can  be  passed  directly  to
1522         pcre_exec(). However, a pcre_extra block  also  contains  other  fields         pcre_exec() or pcre_dfa_exec(). However, a pcre_extra block  also  con-
1523         that  can  be  set  by the caller before the block is passed; these are         tains  other  fields  that can be set by the caller before the block is
1524         described below in the section on matching a pattern.         passed; these are described below in the section on matching a pattern.
1525    
1526         If studying the pattern does not  produce  any  additional  information         If studying the  pattern  does  not  produce  any  useful  information,
1527         pcre_study() returns NULL. In that circumstance, if the calling program         pcre_study() returns NULL. In that circumstance, if the calling program
1528         wants to pass any of the other fields to pcre_exec(), it  must  set  up         wants  to  pass  any  of   the   other   fields   to   pcre_exec()   or
1529         its own pcre_extra block.         pcre_dfa_exec(), it must set up its own pcre_extra block.
1530    
1531         The  second  argument of pcre_study() contains option bits. At present,         The  second  argument of pcre_study() contains option bits. At present,
1532         no options are defined, and this argument should always be zero.         no options are defined, and this argument should always be zero.
# Line 1456  STUDYING A PATTERN Line 1546  STUDYING A PATTERN
1546             0,              /* no options exist */             0,              /* no options exist */
1547             &error);        /* set to NULL or points to a message */             &error);        /* set to NULL or points to a message */
1548    
1549         At present, studying a pattern is useful only for non-anchored patterns         Studying a pattern does two things: first, a lower bound for the length
1550         that do not have a single fixed starting character. A bitmap of  possi-         of subject string that is needed to match the pattern is computed. This
1551         ble starting bytes is created.         does not mean that there are any strings of that length that match, but
1552           it does guarantee that no shorter strings match. The value is  used  by
1553           pcre_exec()  and  pcre_dfa_exec()  to  avoid  wasting time by trying to
1554           match strings that are shorter than the lower bound. You can  find  out
1555           the value in a calling program via the pcre_fullinfo() function.
1556    
1557           Studying a pattern is also useful for non-anchored patterns that do not
1558           have a single fixed starting character. A bitmap of  possible  starting
1559           bytes  is  created. This speeds up finding a position in the subject at
1560           which to start matching.
1561    
1562           The two optimizations just described can be  disabled  by  setting  the
1563           PCRE_NO_START_OPTIMIZE    option    when    calling    pcre_exec()   or
1564           pcre_dfa_exec(). You might want to do this  if  your  pattern  contains
1565           callouts,  or  make  use of (*MARK), and you make use of these in cases
1566           where matching fails.  See  the  discussion  of  PCRE_NO_START_OPTIMIZE
1567           below.
1568    
1569    
1570  LOCALE SUPPORT  LOCALE SUPPORT
# Line 1466  LOCALE SUPPORT Line 1572  LOCALE SUPPORT
1572         PCRE  handles  caseless matching, and determines whether characters are         PCRE  handles  caseless matching, and determines whether characters are
1573         letters, digits, or whatever, by reference to a set of tables,  indexed         letters, digits, or whatever, by reference to a set of tables,  indexed
1574         by  character  value.  When running in UTF-8 mode, this applies only to         by  character  value.  When running in UTF-8 mode, this applies only to
1575         characters with codes less than 128. Higher-valued  codes  never  match         characters with codes less than 128. By  default,  higher-valued  codes
1576         escapes  such  as  \w or \d, but can be tested with \p if PCRE is built         never match escapes such as \w or \d, but they can be tested with \p if
1577         with Unicode character property support. The use of locales  with  Uni-         PCRE is built with Unicode character property  support.  Alternatively,
1578         code  is discouraged. If you are handling characters with codes greater         the  PCRE_UCP  option  can  be  set at compile time; this causes \w and
1579         than 128, you should either use UTF-8 and Unicode, or use locales,  but         friends to use Unicode property support instead of built-in tables. The
1580         not try to mix the two.         use of locales with Unicode is discouraged. If you are handling charac-
1581           ters with codes greater than 128, you should either use UTF-8 and  Uni-
1582           code, or use locales, but not try to mix the two.
1583    
1584         PCRE  contains  an  internal set of tables that are used when the final         PCRE  contains  an  internal set of tables that are used when the final
1585         argument of pcre_compile() is  NULL.  These  are  sufficient  for  many         argument of pcre_compile() is  NULL.  These  are  sufficient  for  many
# Line 1624  INFORMATION ABOUT A PATTERN Line 1732  INFORMATION ABOUT A PATTERN
1732         example, for the pattern /^a\d+z\d+/ the returned value is "z", but for         example, for the pattern /^a\d+z\d+/ the returned value is "z", but for
1733         /^a\dz\d/ the returned value is -1.         /^a\dz\d/ the returned value is -1.
1734    
1735             PCRE_INFO_MINLENGTH
1736    
1737           If  the  pattern  was studied and a minimum length for matching subject
1738           strings was computed, its value is  returned.  Otherwise  the  returned
1739           value  is  -1. The value is a number of characters, not bytes (this may
1740           be relevant in UTF-8 mode). The fourth argument should point to an  int
1741           variable.  A  non-negative  value is a lower bound to the length of any
1742           matching string. There may not be any strings of that  length  that  do
1743           actually match, but every string that does match is at least that long.
1744    
1745           PCRE_INFO_NAMECOUNT           PCRE_INFO_NAMECOUNT
1746           PCRE_INFO_NAMEENTRYSIZE           PCRE_INFO_NAMEENTRYSIZE
1747           PCRE_INFO_NAMETABLE           PCRE_INFO_NAMETABLE
# Line 1645  INFORMATION ABOUT A PATTERN Line 1763  INFORMATION ABOUT A PATTERN
1763         a  pointer  to  the  first  entry of the table (a pointer to char). The         a  pointer  to  the  first  entry of the table (a pointer to char). The
1764         first two bytes of each entry are the number of the capturing parenthe-         first two bytes of each entry are the number of the capturing parenthe-
1765         sis,  most  significant byte first. The rest of the entry is the corre-         sis,  most  significant byte first. The rest of the entry is the corre-
1766         sponding name, zero terminated. The names are  in  alphabetical  order.         sponding name, zero terminated.
1767         When PCRE_DUPNAMES is set, duplicate names are in order of their paren-  
1768         theses numbers. For example, consider  the  following  pattern  (assume         The names are in alphabetical order. Duplicate names may appear if  (?|
1769         PCRE_EXTENDED  is  set,  so  white  space  -  including  newlines  - is         is used to create multiple groups with the same number, as described in
1770         ignored):         the section on duplicate subpattern numbers in  the  pcrepattern  page.
1771           Duplicate  names  for  subpatterns with different numbers are permitted
1772           only if PCRE_DUPNAMES is set. In all cases  of  duplicate  names,  they
1773           appear  in  the table in the order in which they were found in the pat-
1774           tern. In the absence of (?| this is the  order  of  increasing  number;
1775           when (?| is used this is not necessarily the case because later subpat-
1776           terns may have lower numbers.
1777    
1778           As a simple example of the name/number table,  consider  the  following
1779           pattern  (assume  PCRE_EXTENDED is set, so white space - including new-
1780           lines - is ignored):
1781    
1782           (?<date> (?<year>(\d\d)?\d\d) -           (?<date> (?<year>(\d\d)?\d\d) -
1783           (?<month>\d\d) - (?<day>\d\d) )           (?<month>\d\d) - (?<day>\d\d) )
# Line 1670  INFORMATION ABOUT A PATTERN Line 1798  INFORMATION ABOUT A PATTERN
1798    
1799           PCRE_INFO_OKPARTIAL           PCRE_INFO_OKPARTIAL
1800    
1801         Return  1 if the pattern can be used for partial matching, otherwise 0.         Return  1  if  the  pattern  can  be  used  for  partial  matching with
1802         The fourth argument should point to an int  variable.  The  pcrepartial         pcre_exec(), otherwise 0. The fourth argument should point  to  an  int
1803         documentation  lists  the restrictions that apply to patterns when par-         variable.  From  release  8.00,  this  always  returns  1,  because the
1804         tial matching is used.         restrictions that previously applied  to  partial  matching  have  been
1805           lifted.  The  pcrepartial documentation gives details of partial match-
1806           ing.
1807    
1808           PCRE_INFO_OPTIONS           PCRE_INFO_OPTIONS
1809    
# Line 1710  INFORMATION ABOUT A PATTERN Line 1840  INFORMATION ABOUT A PATTERN
1840         Return the size of the data block pointed to by the study_data field in         Return the size of the data block pointed to by the study_data field in
1841         a  pcre_extra  block.  That  is,  it  is  the  value that was passed to         a  pcre_extra  block.  That  is,  it  is  the  value that was passed to
1842         pcre_malloc() when PCRE was getting memory into which to place the data         pcre_malloc() when PCRE was getting memory into which to place the data
1843         created  by  pcre_study(). The fourth argument should point to a size_t         created  by  pcre_study().  If pcre_extra is NULL, or there is no study
1844           data, zero is returned. The fourth argument should point  to  a  size_t
1845         variable.         variable.
1846    
1847    
# Line 1718  OBSOLETE INFO FUNCTION Line 1849  OBSOLETE INFO FUNCTION
1849    
1850         int pcre_info(const pcre *code, int *optptr, int *firstcharptr);         int pcre_info(const pcre *code, int *optptr, int *firstcharptr);
1851    
1852         The pcre_info() function is now obsolete because its interface  is  too         The  pcre_info()  function is now obsolete because its interface is too
1853         restrictive  to return all the available data about a compiled pattern.         restrictive to return all the available data about a compiled  pattern.
1854         New  programs  should  use  pcre_fullinfo()  instead.  The   yield   of         New   programs   should  use  pcre_fullinfo()  instead.  The  yield  of
1855         pcre_info()  is the number of capturing subpatterns, or one of the fol-         pcre_info() is the number of capturing subpatterns, or one of the  fol-
1856         lowing negative numbers:         lowing negative numbers:
1857    
1858           PCRE_ERROR_NULL       the argument code was NULL           PCRE_ERROR_NULL       the argument code was NULL
1859           PCRE_ERROR_BADMAGIC   the "magic number" was not found           PCRE_ERROR_BADMAGIC   the "magic number" was not found
1860    
1861         If the optptr argument is not NULL, a copy of the  options  with  which         If  the  optptr  argument is not NULL, a copy of the options with which
1862         the  pattern  was  compiled  is placed in the integer it points to (see         the pattern was compiled is placed in the integer  it  points  to  (see
1863         PCRE_INFO_OPTIONS above).         PCRE_INFO_OPTIONS above).
1864    
1865         If the pattern is not anchored and the  firstcharptr  argument  is  not         If  the  pattern  is  not anchored and the firstcharptr argument is not
1866         NULL,  it is used to pass back information about the first character of         NULL, it is used to pass back information about the first character  of
1867         any matched string (see PCRE_INFO_FIRSTBYTE above).         any matched string (see PCRE_INFO_FIRSTBYTE above).
1868    
1869    
# Line 1740  REFERENCE COUNTS Line 1871  REFERENCE COUNTS
1871    
1872         int pcre_refcount(pcre *code, int adjust);         int pcre_refcount(pcre *code, int adjust);
1873    
1874         The pcre_refcount() function is used to maintain a reference  count  in         The  pcre_refcount()  function is used to maintain a reference count in
1875         the data block that contains a compiled pattern. It is provided for the         the data block that contains a compiled pattern. It is provided for the
1876         benefit of applications that  operate  in  an  object-oriented  manner,         benefit  of  applications  that  operate  in an object-oriented manner,
1877         where different parts of the application may be using the same compiled         where different parts of the application may be using the same compiled
1878         pattern, but you want to free the block when they are all done.         pattern, but you want to free the block when they are all done.
1879    
1880         When a pattern is compiled, the reference count field is initialized to         When a pattern is compiled, the reference count field is initialized to
1881         zero.   It is changed only by calling this function, whose action is to         zero.  It is changed only by calling this function, whose action is  to
1882         add the adjust value (which may be positive or  negative)  to  it.  The         add  the  adjust  value  (which may be positive or negative) to it. The
1883         yield of the function is the new value. However, the value of the count         yield of the function is the new value. However, the value of the count
1884         is constrained to lie between 0 and 65535, inclusive. If the new  value         is  constrained to lie between 0 and 65535, inclusive. If the new value
1885         is outside these limits, it is forced to the appropriate limit value.         is outside these limits, it is forced to the appropriate limit value.
1886    
1887         Except  when it is zero, the reference count is not correctly preserved         Except when it is zero, the reference count is not correctly  preserved
1888         if a pattern is compiled on one host and then  transferred  to  a  host         if  a  pattern  is  compiled on one host and then transferred to a host
1889         whose byte-order is different. (This seems a highly unlikely scenario.)         whose byte-order is different. (This seems a highly unlikely scenario.)
1890    
1891    
# Line 1766  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 1897  MATCHING A PATTERN: THE TRADITIONAL FUNC
1897    
1898         The function pcre_exec() is called to match a subject string against  a         The function pcre_exec() is called to match a subject string against  a
1899         compiled  pattern, which is passed in the code argument. If the pattern         compiled  pattern, which is passed in the code argument. If the pattern
1900         has been studied, the result of the study should be passed in the extra         was studied, the result of the study should  be  passed  in  the  extra
1901         argument.  This  function is the main matching facility of the library,         argument.  This  function is the main matching facility of the library,
1902         and it operates in a Perl-like manner. For specialist use there is also         and it operates in a Perl-like manner. For specialist use there is also
1903         an  alternative matching function, which is described below in the sec-         an  alternative matching function, which is described below in the sec-
# Line 1806  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 1937  MATCHING A PATTERN: THE TRADITIONAL FUNC
1937           unsigned long int match_limit_recursion;           unsigned long int match_limit_recursion;
1938           void *callout_data;           void *callout_data;
1939           const unsigned char *tables;           const unsigned char *tables;
1940             unsigned char **mark;
1941    
1942         The flags field is a bitmap that specifies which of  the  other  fields         The flags field is a bitmap that specifies which of  the  other  fields
1943         are set. The flag bits are:         are set. The flag bits are:
# Line 1815  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 1947  MATCHING A PATTERN: THE TRADITIONAL FUNC
1947           PCRE_EXTRA_MATCH_LIMIT_RECURSION           PCRE_EXTRA_MATCH_LIMIT_RECURSION
1948           PCRE_EXTRA_CALLOUT_DATA           PCRE_EXTRA_CALLOUT_DATA
1949           PCRE_EXTRA_TABLES           PCRE_EXTRA_TABLES
1950             PCRE_EXTRA_MARK
1951    
1952         Other  flag  bits should be set to zero. The study_data field is set in         Other  flag  bits should be set to zero. The study_data field is set in
1953         the pcre_extra block that is returned by  pcre_study(),  together  with         the pcre_extra block that is returned by  pcre_study(),  together  with
# Line 1825  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 1958  MATCHING A PATTERN: THE TRADITIONAL FUNC
1958         The match_limit field provides a means of preventing PCRE from using up         The match_limit field provides a means of preventing PCRE from using up
1959         a vast amount of resources when running patterns that are not going  to         a vast amount of resources when running patterns that are not going  to
1960         match,  but  which  have  a very large number of possibilities in their         match,  but  which  have  a very large number of possibilities in their
1961         search trees. The classic  example  is  the  use  of  nested  unlimited         search trees. The classic example is a pattern that uses nested  unlim-
1962         repeats.         ited repeats.
1963    
1964         Internally,  PCRE uses a function called match() which it calls repeat-         Internally,  PCRE uses a function called match() which it calls repeat-
1965         edly (sometimes recursively). The limit set by match_limit  is  imposed         edly (sometimes recursively). The limit set by match_limit  is  imposed
# Line 1848  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 1981  MATCHING A PATTERN: THE TRADITIONAL FUNC
1981         the total number of calls, because not all calls to match() are  recur-         the total number of calls, because not all calls to match() are  recur-
1982         sive.  This limit is of use only if it is set smaller than match_limit.         sive.  This limit is of use only if it is set smaller than match_limit.
1983    
1984         Limiting the recursion depth limits the amount of  stack  that  can  be         Limiting  the  recursion  depth  limits the amount of stack that can be
1985         used, or, when PCRE has been compiled to use memory on the heap instead         used, or, when PCRE has been compiled to use memory on the heap instead
1986         of the stack, the amount of heap memory that can be used.         of the stack, the amount of heap memory that can be used.
1987    
1988         The default value for match_limit_recursion can be  set  when  PCRE  is         The  default  value  for  match_limit_recursion can be set when PCRE is
1989         built;  the  default  default  is  the  same  value  as the default for         built; the default default  is  the  same  value  as  the  default  for
1990         match_limit. You can override the default by suppling pcre_exec()  with         match_limit.  You can override the default by suppling pcre_exec() with
1991         a   pcre_extra   block  in  which  match_limit_recursion  is  set,  and         a  pcre_extra  block  in  which  match_limit_recursion  is   set,   and
1992         PCRE_EXTRA_MATCH_LIMIT_RECURSION is set in  the  flags  field.  If  the         PCRE_EXTRA_MATCH_LIMIT_RECURSION  is  set  in  the  flags field. If the
1993         limit is exceeded, pcre_exec() returns PCRE_ERROR_RECURSIONLIMIT.         limit is exceeded, pcre_exec() returns PCRE_ERROR_RECURSIONLIMIT.
1994    
1995         The  pcre_callout  field is used in conjunction with the "callout" fea-         The callout_data field is used in conjunction with the  "callout"  fea-
1996         ture, which is described in the pcrecallout documentation.         ture, and is described in the pcrecallout documentation.
1997    
1998         The tables field  is  used  to  pass  a  character  tables  pointer  to         The  tables  field  is  used  to  pass  a  character  tables pointer to
1999         pcre_exec();  this overrides the value that is stored with the compiled         pcre_exec(); this overrides the value that is stored with the  compiled
2000         pattern. A non-NULL value is stored with the compiled pattern  only  if         pattern.  A  non-NULL value is stored with the compiled pattern only if
2001         custom  tables  were  supplied to pcre_compile() via its tableptr argu-         custom tables were supplied to pcre_compile() via  its  tableptr  argu-
2002         ment.  If NULL is passed to pcre_exec() using this mechanism, it forces         ment.  If NULL is passed to pcre_exec() using this mechanism, it forces
2003         PCRE's  internal  tables  to be used. This facility is helpful when re-         PCRE's internal tables to be used. This facility is  helpful  when  re-
2004         using patterns that have been saved after compiling  with  an  external         using  patterns  that  have been saved after compiling with an external
2005         set  of  tables,  because  the  external tables might be at a different         set of tables, because the external tables  might  be  at  a  different
2006         address when pcre_exec() is called. See the  pcreprecompile  documenta-         address  when  pcre_exec() is called. See the pcreprecompile documenta-
2007         tion for a discussion of saving compiled patterns for later use.         tion for a discussion of saving compiled patterns for later use.
2008    
2009           If PCRE_EXTRA_MARK is set in the flags field, the mark  field  must  be
2010           set  to  point  to a char * variable. If the pattern contains any back-
2011           tracking control verbs such as (*MARK:NAME), and the execution ends  up
2012           with  a  name  to  pass back, a pointer to the name string (zero termi-
2013           nated) is placed in the variable pointed to  by  the  mark  field.  The
2014           names  are  within  the  compiled pattern; if you wish to retain such a
2015           name you must copy it before freeing the memory of a compiled  pattern.
2016           If  there  is no name to pass back, the variable pointed to by the mark
2017           field set to NULL. For details of the backtracking control  verbs,  see
2018           the section entitled "Backtracking control" in the pcrepattern documen-
2019           tation.
2020    
2021     Option bits for pcre_exec()     Option bits for pcre_exec()
2022    
2023         The  unused  bits of the options argument for pcre_exec() must be zero.         The unused bits of the options argument for pcre_exec() must  be  zero.
2024         The only bits that may  be  set  are  PCRE_ANCHORED,  PCRE_NEWLINE_xxx,         The  only  bits  that  may  be set are PCRE_ANCHORED, PCRE_NEWLINE_xxx,
2025         PCRE_NOTBOL,   PCRE_NOTEOL,   PCRE_NOTEMPTY,   PCRE_NO_UTF8_CHECK   and         PCRE_NOTBOL,   PCRE_NOTEOL,    PCRE_NOTEMPTY,    PCRE_NOTEMPTY_ATSTART,
2026         PCRE_PARTIAL.         PCRE_NO_START_OPTIMIZE,   PCRE_NO_UTF8_CHECK,   PCRE_PARTIAL_SOFT,  and
2027           PCRE_PARTIAL_HARD.
2028    
2029           PCRE_ANCHORED           PCRE_ANCHORED
2030    
# Line 1958  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 2104  MATCHING A PATTERN: THE TRADITIONAL FUNC
2104    
2105           a?b?           a?b?
2106    
2107         is  applied  to  a string not beginning with "a" or "b", it matches the         is  applied  to  a  string not beginning with "a" or "b", it matches an
2108         empty string at the start of the subject. With PCRE_NOTEMPTY set,  this         empty string at the start of the subject. With PCRE_NOTEMPTY set,  this
2109         match is not valid, so PCRE searches further into the string for occur-         match is not valid, so PCRE searches further into the string for occur-
2110         rences of "a" or "b".         rences of "a" or "b".
2111    
2112         Perl has no direct equivalent of PCRE_NOTEMPTY, but it does make a spe-           PCRE_NOTEMPTY_ATSTART
2113         cial  case  of  a  pattern match of the empty string within its split()  
2114         function, and when using the /g modifier. It  is  possible  to  emulate         This is like PCRE_NOTEMPTY, except that an empty string match  that  is
2115         Perl's behaviour after matching a null string by first trying the match         not  at  the  start  of  the  subject  is  permitted. If the pattern is
2116         again at the same offset with PCRE_NOTEMPTY and PCRE_ANCHORED, and then         anchored, such a match can occur only if the pattern contains \K.
2117         if  that  fails by advancing the starting offset (see below) and trying  
2118         an ordinary match again. There is some code that demonstrates how to do         Perl    has    no    direct    equivalent    of    PCRE_NOTEMPTY     or
2119         this in the pcredemo.c sample program.         PCRE_NOTEMPTY_ATSTART,  but  it  does  make a special case of a pattern
2120           match of the empty string within its split() function, and  when  using
2121           the  /g  modifier.  It  is  possible  to emulate Perl's behaviour after
2122           matching a null string by first trying the match again at the same off-
2123           set  with  PCRE_NOTEMPTY_ATSTART  and  PCRE_ANCHORED,  and then if that
2124           fails, by advancing the starting offset (see below) and trying an ordi-
2125           nary  match  again. There is some code that demonstrates how to do this
2126           in the pcredemo sample program.
2127    
2128             PCRE_NO_START_OPTIMIZE
2129    
2130           There are a number of optimizations that pcre_exec() uses at the  start
2131           of  a  match,  in  order to speed up the process. For example, if it is
2132           known that an unanchored match must start with a specific character, it
2133           searches  the  subject  for that character, and fails immediately if it
2134           cannot find it, without actually running the  main  matching  function.
2135           This means that a special item such as (*COMMIT) at the start of a pat-
2136           tern is not considered until after a suitable starting  point  for  the
2137           match  has been found. When callouts or (*MARK) items are in use, these
2138           "start-up" optimizations can cause them to be skipped if the pattern is
2139           never  actually  used.  The start-up optimizations are in effect a pre-
2140           scan of the subject that takes place before the pattern is run.
2141    
2142           The PCRE_NO_START_OPTIMIZE option disables the start-up  optimizations,
2143           possibly  causing  performance  to  suffer,  but ensuring that in cases
2144           where the result is "no match", the callouts do occur, and  that  items
2145           such as (*COMMIT) and (*MARK) are considered at every possible starting
2146           position in the subject  string.   Setting  PCRE_NO_START_OPTIMIZE  can
2147           change the outcome of a matching operation.  Consider the pattern
2148    
2149             (*COMMIT)ABC
2150    
2151           When  this  is  compiled, PCRE records the fact that a match must start
2152           with the character "A". Suppose the subject  string  is  "DEFABC".  The
2153           start-up  optimization  scans along the subject, finds "A" and runs the
2154           first match attempt from there. The (*COMMIT) item means that the  pat-
2155           tern  must  match the current starting position, which in this case, it
2156           does. However, if the same match  is  run  with  PCRE_NO_START_OPTIMIZE
2157           set,  the  initial  scan  along the subject string does not happen. The
2158           first match attempt is run starting  from  "D"  and  when  this  fails,
2159           (*COMMIT)  prevents  any  further  matches  being tried, so the overall
2160           result is "no match". If the pattern is studied,  more  start-up  opti-
2161           mizations  may  be  used. For example, a minimum length for the subject
2162           may be recorded. Consider the pattern
2163    
2164             (*MARK:A)(X|Y)
2165    
2166           The minimum length for a match is one  character.  If  the  subject  is
2167           "ABC",  there  will  be  attempts  to  match "ABC", "BC", "C", and then
2168           finally an empty string.  If the pattern is studied, the final  attempt
2169           does  not take place, because PCRE knows that the subject is too short,
2170           and so the (*MARK) is never encountered.  In this  case,  studying  the
2171           pattern  does  not  affect the overall match result, which is still "no
2172           match", but it does affect the auxiliary information that is returned.
2173    
2174           PCRE_NO_UTF8_CHECK           PCRE_NO_UTF8_CHECK
2175    
2176         When PCRE_UTF8 is set at compile time, the validity of the subject as a         When PCRE_UTF8 is set at compile time, the validity of the subject as a
2177         UTF-8 string is automatically checked when pcre_exec() is  subsequently         UTF-8  string is automatically checked when pcre_exec() is subsequently
2178         called.   The  value  of  startoffset is also checked to ensure that it         called.  The value of startoffset is also checked  to  ensure  that  it
2179         points to the start of a UTF-8 character. There is a  discussion  about         points  to  the start of a UTF-8 character. There is a discussion about
2180         the  validity  of  UTF-8 strings in the section on UTF-8 support in the         the validity of UTF-8 strings in the section on UTF-8  support  in  the
2181         main pcre page. If  an  invalid  UTF-8  sequence  of  bytes  is  found,         main  pcre  page.  If  an  invalid  UTF-8  sequence  of bytes is found,
2182         pcre_exec()  returns  the error PCRE_ERROR_BADUTF8. If startoffset con-         pcre_exec() returns the error PCRE_ERROR_BADUTF8. If  startoffset  con-
2183         tains an invalid value, PCRE_ERROR_BADUTF8_OFFSET is returned.         tains an invalid value, PCRE_ERROR_BADUTF8_OFFSET is returned.
2184    
2185         If you already know that your subject is valid, and you  want  to  skip         If  you  already  know that your subject is valid, and you want to skip
2186         these    checks    for   performance   reasons,   you   can   set   the         these   checks   for   performance   reasons,   you   can    set    the
2187         PCRE_NO_UTF8_CHECK option when calling pcre_exec(). You might  want  to         PCRE_NO_UTF8_CHECK  option  when calling pcre_exec(). You might want to
2188         do  this  for the second and subsequent calls to pcre_exec() if you are         do this for the second and subsequent calls to pcre_exec() if  you  are
2189         making repeated calls to find all  the  matches  in  a  single  subject         making  repeated  calls  to  find  all  the matches in a single subject
2190         string.  However,  you  should  be  sure  that the value of startoffset         string. However, you should be  sure  that  the  value  of  startoffset
2191         points to the start of a UTF-8 character.  When  PCRE_NO_UTF8_CHECK  is         points  to  the  start of a UTF-8 character. When PCRE_NO_UTF8_CHECK is
2192         set,  the  effect of passing an invalid UTF-8 string as a subject, or a         set, the effect of passing an invalid UTF-8 string as a subject,  or  a
2193         value of startoffset that does not point to the start of a UTF-8  char-         value  of startoffset that does not point to the start of a UTF-8 char-
2194         acter, is undefined. Your program may crash.         acter, is undefined. Your program may crash.
2195    
2196           PCRE_PARTIAL           PCRE_PARTIAL_HARD
2197             PCRE_PARTIAL_SOFT
2198    
2199         This  option  turns  on  the  partial  matching feature. If the subject         These options turn on the partial matching feature. For backwards  com-
2200         string fails to match the pattern, but at some point during the  match-         patibility,  PCRE_PARTIAL is a synonym for PCRE_PARTIAL_SOFT. A partial
2201         ing  process  the  end of the subject was reached (that is, the subject         match occurs if the end of the subject string is reached  successfully,
2202         partially matches the pattern and the failure to  match  occurred  only         but  there  are not enough subject characters to complete the match. If
2203         because  there were not enough subject characters), pcre_exec() returns         this happens when PCRE_PARTIAL_HARD  is  set,  pcre_exec()  immediately
2204         PCRE_ERROR_PARTIAL instead of PCRE_ERROR_NOMATCH. When PCRE_PARTIAL  is         returns  PCRE_ERROR_PARTIAL.  Otherwise,  if  PCRE_PARTIAL_SOFT is set,
2205         used,  there  are restrictions on what may appear in the pattern. These         matching continues by testing any other alternatives. Only if they  all
2206         are discussed in the pcrepartial documentation.         fail  is  PCRE_ERROR_PARTIAL  returned (instead of PCRE_ERROR_NOMATCH).
2207           The portion of the string that was inspected when the partial match was
2208           found  is  set  as  the first matching string. There is a more detailed
2209           discussion in the pcrepartial documentation.
2210    
2211     The string to be matched by pcre_exec()     The string to be matched by pcre_exec()
2212    
2213         The subject string is passed to pcre_exec() as a pointer in subject,  a         The subject string is passed to pcre_exec() as a pointer in subject,  a
2214         length  in  length, and a starting byte offset in startoffset. In UTF-8         length (in bytes) in length, and a starting byte offset in startoffset.
2215         mode, the byte offset must point to the start  of  a  UTF-8  character.         In UTF-8 mode, the byte offset must point to the start of a UTF-8 char-
2216         Unlike  the  pattern string, the subject may contain binary zero bytes.         acter.  Unlike  the pattern string, the subject may contain binary zero
2217         When the starting offset is zero, the search for a match starts at  the         bytes. When the starting offset is zero, the search for a match  starts
2218         beginning of the subject, and this is by far the most common case.         at  the  beginning  of  the subject, and this is by far the most common
2219           case.
2220         A  non-zero  starting offset is useful when searching for another match  
2221         in the same subject by calling pcre_exec() again after a previous  suc-         A non-zero starting offset is useful when searching for  another  match
2222         cess.   Setting  startoffset differs from just passing over a shortened         in  the same subject by calling pcre_exec() again after a previous suc-
2223         string and setting PCRE_NOTBOL in the case of  a  pattern  that  begins         cess.  Setting startoffset differs from just passing over  a  shortened
2224           string  and  setting  PCRE_NOTBOL  in the case of a pattern that begins
2225         with any kind of lookbehind. For example, consider the pattern         with any kind of lookbehind. For example, consider the pattern
2226    
2227           \Biss\B           \Biss\B
2228    
2229         which  finds  occurrences  of "iss" in the middle of words. (\B matches         which finds occurrences of "iss" in the middle of  words.  (\B  matches
2230         only if the current position in the subject is not  a  word  boundary.)         only  if  the  current position in the subject is not a word boundary.)
2231         When  applied  to the string "Mississipi" the first call to pcre_exec()         When applied to the string "Mississipi" the first call  to  pcre_exec()
2232         finds the first occurrence. If pcre_exec() is called  again  with  just         finds  the  first  occurrence. If pcre_exec() is called again with just
2233         the  remainder  of  the  subject,  namely  "issipi", it does not match,         the remainder of the subject,  namely  "issipi",  it  does  not  match,
2234         because \B is always false at the start of the subject, which is deemed         because \B is always false at the start of the subject, which is deemed
2235         to  be  a  word  boundary. However, if pcre_exec() is passed the entire         to be a word boundary. However, if pcre_exec()  is  passed  the  entire
2236         string again, but with startoffset set to 4, it finds the second occur-         string again, but with startoffset set to 4, it finds the second occur-
2237         rence  of "iss" because it is able to look behind the starting point to         rence of "iss" because it is able to look behind the starting point  to
2238         discover that it is preceded by a letter.         discover that it is preceded by a letter.
2239    
2240         If a non-zero starting offset is passed when the pattern  is  anchored,         If  a  non-zero starting offset is passed when the pattern is anchored,
2241         one attempt to match at the given offset is made. This can only succeed         one attempt to match at the given offset is made. This can only succeed
2242         if the pattern does not require the match to be at  the  start  of  the         if  the  pattern  does  not require the match to be at the start of the
2243         subject.         subject.
2244    
2245     How pcre_exec() returns captured substrings     How pcre_exec() returns captured substrings
2246    
2247         In  general, a pattern matches a certain portion of the subject, and in         In general, a pattern matches a certain portion of the subject, and  in
2248         addition, further substrings from the subject  may  be  picked  out  by         addition,  further  substrings  from  the  subject may be picked out by
2249         parts  of  the  pattern.  Following the usage in Jeffrey Friedl's book,         parts of the pattern. Following the usage  in  Jeffrey  Friedl's  book,
2250         this is called "capturing" in what follows, and the  phrase  "capturing         this  is  called "capturing" in what follows, and the phrase "capturing
2251         subpattern"  is  used for a fragment of a pattern that picks out a sub-         subpattern" is used for a fragment of a pattern that picks out  a  sub-
2252         string. PCRE supports several other kinds of  parenthesized  subpattern         string.  PCRE  supports several other kinds of parenthesized subpattern
2253         that do not cause substrings to be captured.         that do not cause substrings to be captured.
2254    
2255         Captured  substrings are returned to the caller via a vector of integer         Captured substrings are returned to the caller via a vector of integers
2256         offsets whose address is passed in ovector. The number of  elements  in         whose  address is passed in ovector. The number of elements in the vec-
2257         the  vector is passed in ovecsize, which must be a non-negative number.         tor is passed in ovecsize, which must be a non-negative  number.  Note:
2258         Note: this argument is NOT the size of ovector in bytes.         this argument is NOT the size of ovector in bytes.
2259    
2260         The first two-thirds of the vector is used to pass back  captured  sub-         The  first  two-thirds of the vector is used to pass back captured sub-
2261         strings,  each  substring using a pair of integers. The remaining third         strings, each substring using a pair of integers. The  remaining  third
2262         of the vector is used as workspace by pcre_exec() while  matching  cap-         of  the  vector is used as workspace by pcre_exec() while matching cap-
2263         turing  subpatterns, and is not available for passing back information.         turing subpatterns, and is not available for passing back  information.
2264         The length passed in ovecsize should always be a multiple of three.  If         The  number passed in ovecsize should always be a multiple of three. If
2265         it is not, it is rounded down.         it is not, it is rounded down.
2266    
2267         When  a  match  is successful, information about captured substrings is         When a match is successful, information about  captured  substrings  is
2268         returned in pairs of integers, starting at the  beginning  of  ovector,         returned  in  pairs  of integers, starting at the beginning of ovector,
2269         and  continuing  up  to two-thirds of its length at the most. The first         and continuing up to two-thirds of its length at the  most.  The  first
2270         element of a pair is set to the offset of the first character in a sub-         element  of  each pair is set to the byte offset of the first character
2271         string,  and  the  second  is  set to the offset of the first character         in a substring, and the second is set to the byte offset of  the  first
2272         after the end of a substring. The  first  pair,  ovector[0]  and  ovec-         character  after  the end of a substring. Note: these values are always
2273         tor[1],  identify  the  portion  of  the  subject string matched by the         byte offsets, even in UTF-8 mode. They are not character counts.
2274         entire pattern. The next pair is used for the first  capturing  subpat-  
2275         tern, and so on. The value returned by pcre_exec() is one more than the         The first pair of integers, ovector[0]  and  ovector[1],  identify  the
2276         highest numbered pair that has been set. For example, if two substrings         portion  of  the subject string matched by the entire pattern. The next
2277         have  been captured, the returned value is 3. If there are no capturing         pair is used for the first capturing subpattern, and so on.  The  value
2278         subpatterns, the return value from a successful match is 1,  indicating         returned by pcre_exec() is one more than the highest numbered pair that
2279         that just the first pair of offsets has been set.         has been set.  For example, if two substrings have been  captured,  the
2280           returned  value is 3. If there are no capturing subpatterns, the return
2281           value from a successful match is 1, indicating that just the first pair
2282           of offsets has been set.
2283    
2284         If a capturing subpattern is matched repeatedly, it is the last portion         If a capturing subpattern is matched repeatedly, it is the last portion
2285         of the string that it matched that is returned.         of the string that it matched that is returned.
2286    
2287         If the vector is too small to hold all the captured substring  offsets,         If the vector is too small to hold all the captured substring  offsets,
2288         it is used as far as possible (up to two-thirds of its length), and the         it is used as far as possible (up to two-thirds of its length), and the
2289         function returns a value of zero. In particular, if the substring  off-         function returns a value of zero. If the substring offsets are  not  of
2290         sets are not of interest, pcre_exec() may be called with ovector passed         interest,  pcre_exec()  may  be  called with ovector passed as NULL and
2291         as NULL and ovecsize as zero. However, if  the  pattern  contains  back         ovecsize as zero. However, if the pattern contains back references  and
2292         references  and  the  ovector is not big enough to remember the related         the  ovector is not big enough to remember the related substrings, PCRE
2293         substrings, PCRE has to get additional memory for use during  matching.         has to get additional memory for use during matching. Thus it  is  usu-
2294         Thus it is usually advisable to supply an ovector.         ally advisable to supply an ovector.
2295    
2296         The  pcre_info()  function  can  be used to find out how many capturing         The pcre_fullinfo() function can be used to find out how many capturing
2297         subpatterns there are in a compiled  pattern.  The  smallest  size  for         subpatterns there are in a compiled  pattern.  The  smallest  size  for
2298         ovector  that  will allow for n captured substrings, in addition to the         ovector  that  will allow for n captured substrings, in addition to the
2299         offsets of the substring matched by the whole pattern, is (n+1)*3.         offsets of the substring matched by the whole pattern, is (n+1)*3.
# Line 2149  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 2356  MATCHING A PATTERN: THE TRADITIONAL FUNC
2356         purpose.  If the call via pcre_malloc() fails, this error is given. The         purpose.  If the call via pcre_malloc() fails, this error is given. The
2357         memory is automatically freed at the end of matching.         memory is automatically freed at the end of matching.
2358    
2359           This error is also given if pcre_stack_malloc() fails  in  pcre_exec().
2360           This  can happen only when PCRE has been compiled with --disable-stack-
2361           for-recursion.
2362    
2363           PCRE_ERROR_NOSUBSTRING    (-7)           PCRE_ERROR_NOSUBSTRING    (-7)
2364    
2365         This error is used by the pcre_copy_substring(),  pcre_get_substring(),         This error is used by the pcre_copy_substring(),  pcre_get_substring(),
# Line 2185  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 2396  MATCHING A PATTERN: THE TRADITIONAL FUNC
2396    
2397           PCRE_ERROR_BADPARTIAL     (-13)           PCRE_ERROR_BADPARTIAL     (-13)
2398    
2399         The PCRE_PARTIAL option was used with  a  compiled  pattern  containing         This code is no longer in  use.  It  was  formerly  returned  when  the
2400         items  that are not supported for partial matching. See the pcrepartial         PCRE_PARTIAL  option  was used with a compiled pattern containing items
2401         documentation for details of partial matching.         that were  not  supported  for  partial  matching.  From  release  8.00
2402           onwards, there are no restrictions on partial matching.
2403    
2404           PCRE_ERROR_INTERNAL       (-14)           PCRE_ERROR_INTERNAL       (-14)
2405    
2406         An unexpected internal error has occurred. This error could  be  caused         An  unexpected  internal error has occurred. This error could be caused
2407         by a bug in PCRE or by overwriting of the compiled pattern.         by a bug in PCRE or by overwriting of the compiled pattern.
2408    
2409           PCRE_ERROR_BADCOUNT       (-15)           PCRE_ERROR_BADCOUNT       (-15)
2410    
2411         This  error is given if the value of the ovecsize argument is negative.         This error is given if the value of the ovecsize argument is negative.
2412    
2413           PCRE_ERROR_RECURSIONLIMIT (-21)           PCRE_ERROR_RECURSIONLIMIT (-21)
2414    
# Line 2346  EXTRACTING CAPTURED SUBSTRINGS BY NAME Line 2558  EXTRACTING CAPTURED SUBSTRINGS BY NAME
2558         ate.  NOTE:  If PCRE_DUPNAMES is set and there are duplicate names, the         ate.  NOTE:  If PCRE_DUPNAMES is set and there are duplicate names, the
2559         behaviour may not be what you want (see the next section).         behaviour may not be what you want (see the next section).
2560    
2561           Warning: If the pattern uses the (?| feature to set up multiple subpat-
2562           terns  with  the  same number, as described in the section on duplicate
2563           subpattern numbers in the pcrepattern page, you  cannot  use  names  to
2564           distinguish  the  different subpatterns, because names are not included
2565           in the compiled code. The matching process uses only numbers. For  this
2566           reason,  the  use of different names for subpatterns of the same number
2567           causes an error at compile time.
2568    
2569    
2570  DUPLICATE SUBPATTERN NAMES  DUPLICATE SUBPATTERN NAMES
2571    
# Line 2353  DUPLICATE SUBPATTERN NAMES Line 2573  DUPLICATE SUBPATTERN NAMES
2573              const char *name, char **first, char **last);              const char *name, char **first, char **last);
2574    
2575         When a pattern is compiled with the  PCRE_DUPNAMES  option,  names  for         When a pattern is compiled with the  PCRE_DUPNAMES  option,  names  for
2576         subpatterns  are  not  required  to  be unique. Normally, patterns with         subpatterns  are not required to be unique. (Duplicate names are always
2577         duplicate names are such that in any one match, only one of  the  named         allowed for subpatterns with the same number, created by using the  (?|
2578         subpatterns  participates. An example is shown in the pcrepattern docu-         feature.  Indeed,  if  such subpatterns are named, they are required to
2579         mentation.         use the same names.)
2580    
2581           Normally, patterns with duplicate names are such that in any one match,
2582           only  one of the named subpatterns participates. An example is shown in
2583           the pcrepattern documentation.
2584    
2585         When   duplicates   are   present,   pcre_copy_named_substring()    and         When   duplicates   are   present,   pcre_copy_named_substring()    and
2586         pcre_get_named_substring()  return the first substring corresponding to         pcre_get_named_substring()  return the first substring corresponding to
# Line 2409  MATCHING A PATTERN: THE ALTERNATIVE FUNC Line 2633  MATCHING A PATTERN: THE ALTERNATIVE FUNC
2633         characteristics  to  the  normal  algorithm, and is not compatible with         characteristics  to  the  normal  algorithm, and is not compatible with
2634         Perl. Some of the features of PCRE patterns are not  supported.  Never-         Perl. Some of the features of PCRE patterns are not  supported.  Never-
2635         theless,  there are times when this kind of matching can be useful. For         theless,  there are times when this kind of matching can be useful. For
2636         a discussion of the two matching algorithms, see the pcrematching docu-         a discussion of the two matching algorithms, and  a  list  of  features
2637         mentation.         that  pcre_dfa_exec() does not support, see the pcrematching documenta-
2638           tion.
2639    
2640         The  arguments  for  the  pcre_dfa_exec()  function are the same as for         The arguments for the pcre_dfa_exec() function  are  the  same  as  for
2641         pcre_exec(), plus two extras. The ovector argument is used in a differ-         pcre_exec(), plus two extras. The ovector argument is used in a differ-
2642         ent  way,  and  this is described below. The other common arguments are         ent way, and this is described below. The other  common  arguments  are
2643         used in the same way as for pcre_exec(), so their  description  is  not         used  in  the  same way as for pcre_exec(), so their description is not
2644         repeated here.         repeated here.
2645    
2646         The  two  additional  arguments provide workspace for the function. The         The two additional arguments provide workspace for  the  function.  The
2647         workspace vector should contain at least 20 elements. It  is  used  for         workspace  vector  should  contain at least 20 elements. It is used for
2648         keeping  track  of  multiple  paths  through  the  pattern  tree.  More         keeping  track  of  multiple  paths  through  the  pattern  tree.  More
2649         workspace will be needed for patterns and subjects where  there  are  a         workspace  will  be  needed for patterns and subjects where there are a
2650         lot of potential matches.         lot of potential matches.
2651    
2652         Here is an example of a simple call to pcre_dfa_exec():         Here is an example of a simple call to pcre_dfa_exec():
# Line 2443  MATCHING A PATTERN: THE ALTERNATIVE FUNC Line 2668  MATCHING A PATTERN: THE ALTERNATIVE FUNC
2668    
2669     Option bits for pcre_dfa_exec()     Option bits for pcre_dfa_exec()
2670    
2671         The  unused  bits  of  the options argument for pcre_dfa_exec() must be         The unused bits of the options argument  for  pcre_dfa_exec()  must  be
2672         zero. The only bits  that  may  be  set  are  PCRE_ANCHORED,  PCRE_NEW-         zero.  The  only  bits  that  may  be  set are PCRE_ANCHORED, PCRE_NEW-
2673         LINE_xxx,  PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, PCRE_NO_UTF8_CHECK,         LINE_xxx,        PCRE_NOTBOL,        PCRE_NOTEOL,        PCRE_NOTEMPTY,
2674         PCRE_PARTIAL, PCRE_DFA_SHORTEST, and PCRE_DFA_RESTART. All but the last         PCRE_NOTEMPTY_ATSTART,       PCRE_NO_UTF8_CHECK,      PCRE_BSR_ANYCRLF,
2675         three of these are the same as for pcre_exec(), so their description is         PCRE_BSR_UNICODE, PCRE_NO_START_OPTIMIZE, PCRE_PARTIAL_HARD,  PCRE_PAR-
2676         not repeated here.         TIAL_SOFT,  PCRE_DFA_SHORTEST,  and PCRE_DFA_RESTART.  All but the last
2677           four of these are  exactly  the  same  as  for  pcre_exec(),  so  their
2678           PCRE_PARTIAL         description is not repeated here.
2679    
2680         This has the same general effect as it does for  pcre_exec(),  but  the           PCRE_PARTIAL_HARD
2681         details   are   slightly   different.  When  PCRE_PARTIAL  is  set  for           PCRE_PARTIAL_SOFT
2682         pcre_dfa_exec(), the return code PCRE_ERROR_NOMATCH is  converted  into  
2683         PCRE_ERROR_PARTIAL  if  the  end  of the subject is reached, there have         These  have the same general effect as they do for pcre_exec(), but the
2684         been no complete matches, but there is still at least one matching pos-         details are slightly  different.  When  PCRE_PARTIAL_HARD  is  set  for
2685         sibility.  The portion of the string that provided the partial match is         pcre_dfa_exec(),  it  returns PCRE_ERROR_PARTIAL if the end of the sub-
2686         set as the first matching string.         ject is reached and there is still at least  one  matching  possibility
2687           that requires additional characters. This happens even if some complete
2688           matches have also been found. When PCRE_PARTIAL_SOFT is set, the return
2689           code PCRE_ERROR_NOMATCH is converted into PCRE_ERROR_PARTIAL if the end
2690           of the subject is reached, there have been  no  complete  matches,  but
2691           there  is  still  at least one matching possibility. The portion of the
2692           string that was inspected when the longest partial match was  found  is
2693           set as the first matching string in both cases.
2694    
2695           PCRE_DFA_SHORTEST           PCRE_DFA_SHORTEST
2696    
2697         Setting the PCRE_DFA_SHORTEST option causes the matching  algorithm  to         Setting  the  PCRE_DFA_SHORTEST option causes the matching algorithm to
2698         stop as soon as it has found one match. Because of the way the alterna-         stop as soon as it has found one match. Because of the way the alterna-
2699         tive algorithm works, this is necessarily the shortest  possible  match         tive  algorithm  works, this is necessarily the shortest possible match
2700         at the first possible matching point in the subject string.         at the first possible matching point in the subject string.
2701    
2702           PCRE_DFA_RESTART           PCRE_DFA_RESTART
2703    
2704         When  pcre_dfa_exec()  is  called  with  the  PCRE_PARTIAL  option, and         When pcre_dfa_exec() returns a partial match, it is possible to call it
2705         returns a partial match, it is possible to call it  again,  with  addi-         again,  with  additional  subject characters, and have it continue with
2706         tional  subject  characters,  and have it continue with the same match.         the same match. The PCRE_DFA_RESTART option requests this action;  when
2707         The PCRE_DFA_RESTART option requests this action; when it is  set,  the         it  is  set,  the workspace and wscount options must reference the same
2708         workspace  and wscount options must reference the same vector as before         vector as before because data about the match so far is  left  in  them
2709         because data about the match so far is left in  them  after  a  partial         after a partial match. There is more discussion of this facility in the
2710         match.  There  is  more  discussion of this facility in the pcrepartial         pcrepartial documentation.
        documentation.  
2711    
2712     Successful returns from pcre_dfa_exec()     Successful returns from pcre_dfa_exec()
2713    
# Line 2553  MATCHING A PATTERN: THE ALTERNATIVE FUNC Line 2784  MATCHING A PATTERN: THE ALTERNATIVE FUNC
2784  SEE ALSO  SEE ALSO
2785    
2786         pcrebuild(3),  pcrecallout(3), pcrecpp(3)(3), pcrematching(3), pcrepar-         pcrebuild(3),  pcrecallout(3), pcrecpp(3)(3), pcrematching(3), pcrepar-
2787         tial(3), pcreposix(3), pcreprecompile(3), pcresample(3),  pcrestack(3).         tial(3), pcreposix(3), pcreprecompile(3), pcresample(3), pcrestack(3).
2788    
2789    
2790  AUTHOR  AUTHOR
# Line 2565  AUTHOR Line 2796  AUTHOR
2796    
2797  REVISION  REVISION
2798    
2799         Last updated: 26 December 2007         Last updated: 21 June 2010
2800         Copyright (c) 1997-2007 University of Cambridge.         Copyright (c) 1997-2010 University of Cambridge.
2801  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
2802    
2803    
# Line 2595  PCRE CALLOUTS Line 2826  PCRE CALLOUTS
2826    
2827           (?C1)abc(?C2)def           (?C1)abc(?C2)def
2828    
2829         If  the  PCRE_AUTO_CALLOUT  option  bit  is  set when pcre_compile() is         If  the  PCRE_AUTO_CALLOUT  option  bit  is  set when pcre_compile() or
2830         called, PCRE automatically  inserts  callouts,  all  with  number  255,         pcre_compile2() is called, PCRE  automatically  inserts  callouts,  all
2831         before  each  item in the pattern. For example, if PCRE_AUTO_CALLOUT is         with  number  255,  before  each  item  in the pattern. For example, if
2832         used with the pattern         PCRE_AUTO_CALLOUT is used with the pattern
2833    
2834           A(\d{2}|--)           A(\d{2}|--)
2835    
# Line 2617  PCRE CALLOUTS Line 2848  PCRE CALLOUTS
2848  MISSING CALLOUTS  MISSING CALLOUTS
2849    
2850         You  should  be  aware  that,  because of optimizations in the way PCRE         You  should  be  aware  that,  because of optimizations in the way PCRE
2851         matches patterns, callouts sometimes do not happen. For example, if the         matches patterns by default, callouts  sometimes  do  not  happen.  For
2852         pattern is         example, if the pattern is
2853    
2854           ab(?C4)cd           ab(?C4)cd
2855    
# Line 2627  MISSING CALLOUTS Line 2858  MISSING CALLOUTS
2858         ever  start,  and  the  callout is never reached. However, with "abyd",         ever  start,  and  the  callout is never reached. However, with "abyd",
2859         though the result is still no match, the callout is obeyed.         though the result is still no match, the callout is obeyed.
2860    
2861           If the pattern is studied, PCRE knows the minimum length of a  matching
2862           string,  and will immediately give a "no match" return without actually
2863           running a match if the subject is not long enough, or,  for  unanchored
2864           patterns, if it has been scanned far enough.
2865    
2866           You  can disable these optimizations by passing the PCRE_NO_START_OPTI-
2867           MIZE option to pcre_exec() or  pcre_dfa_exec().  This  slows  down  the
2868           matching  process,  but  does  ensure that callouts such as the example
2869           above are obeyed.
2870    
2871    
2872  THE CALLOUT INTERFACE  THE CALLOUT INTERFACE
2873    
# Line 2654  THE CALLOUT INTERFACE Line 2895  THE CALLOUT INTERFACE
2895         version number will change again in future  if  additional  fields  are         version number will change again in future  if  additional  fields  are
2896         added, but the intention is never to remove any of the existing fields.         added, but the intention is never to remove any of the existing fields.
2897    
2898         The callout_number field contains the number of the  callout,  as  com-         The  callout_number  field  contains the number of the callout, as com-
2899         piled  into  the pattern (that is, the number after ?C for manual call-         piled into the pattern (that is, the number after ?C for  manual  call-
2900         outs, and 255 for automatically generated callouts).         outs, and 255 for automatically generated callouts).
2901    
2902         The offset_vector field is a pointer to the vector of offsets that  was         The  offset_vector field is a pointer to the vector of offsets that was
2903         passed   by   the   caller  to  pcre_exec()  or  pcre_dfa_exec().  When         passed  by  the  caller  to  pcre_exec()   or   pcre_dfa_exec().   When
2904         pcre_exec() is used, the contents can be inspected in order to  extract         pcre_exec()  is used, the contents can be inspected in order to extract
2905         substrings  that  have  been  matched  so  far,  in the same way as for         substrings that have been matched so  far,  in  the  same  way  as  for
2906         extracting substrings after a match has completed. For  pcre_dfa_exec()         extracting  substrings after a match has completed. For pcre_dfa_exec()
2907         this field is not useful.         this field is not useful.
2908    
2909         The subject and subject_length fields contain copies of the values that         The subject and subject_length fields contain copies of the values that
2910         were passed to pcre_exec().         were passed to pcre_exec().
2911    
2912         The start_match field normally contains the offset within  the  subject         The  start_match  field normally contains the offset within the subject
2913         at  which  the  current  match  attempt started. However, if the escape         at which the current match attempt  started.  However,  if  the  escape
2914         sequence \K has been encountered, this value is changed to reflect  the         sequence  \K has been encountered, this value is changed to reflect the
2915         modified  starting  point.  If the pattern is not anchored, the callout         modified starting point. If the pattern is not  anchored,  the  callout
2916         function may be called several times from the same point in the pattern         function may be called several times from the same point in the pattern
2917         for different starting points in the subject.         for different starting points in the subject.
2918    
2919         The  current_position  field  contains the offset within the subject of         The current_position field contains the offset within  the  subject  of
2920         the current match pointer.         the current match pointer.
2921    
2922         When the pcre_exec() function is used, the capture_top  field  contains         When  the  pcre_exec() function is used, the capture_top field contains
2923         one  more than the number of the highest numbered captured substring so         one more than the number of the highest numbered captured substring  so
2924         far. If no substrings have been captured, the value of  capture_top  is         far.  If  no substrings have been captured, the value of capture_top is
2925         one.  This  is always the case when pcre_dfa_exec() is used, because it         one. This is always the case when pcre_dfa_exec() is used,  because  it
2926         does not support captured substrings.         does not support captured substrings.
2927    
2928         The capture_last field contains the number of the  most  recently  cap-         The  capture_last  field  contains the number of the most recently cap-
2929         tured  substring. If no substrings have been captured, its value is -1.         tured substring. If no substrings have been captured, its value is  -1.
2930         This is always the case when pcre_dfa_exec() is used.         This is always the case when pcre_dfa_exec() is used.
2931    
2932         The callout_data field contains a value that is passed  to  pcre_exec()         The  callout_data  field contains a value that is passed to pcre_exec()
2933         or  pcre_dfa_exec() specifically so that it can be passed back in call-         or pcre_dfa_exec() specifically so that it can be passed back in  call-
2934         outs. It is passed in the pcre_callout field  of  the  pcre_extra  data         outs.  It  is  passed  in the pcre_callout field of the pcre_extra data
2935         structure.  If  no such data was passed, the value of callout_data in a         structure. If no such data was passed, the value of callout_data  in  a
2936         pcre_callout block is NULL. There is a description  of  the  pcre_extra         pcre_callout  block  is  NULL. There is a description of the pcre_extra
2937         structure in the pcreapi documentation.         structure in the pcreapi documentation.
2938    
2939         The  pattern_position field is present from version 1 of the pcre_call-         The pattern_position field is present from version 1 of the  pcre_call-
2940         out structure. It contains the offset to the next item to be matched in         out structure. It contains the offset to the next item to be matched in
2941         the pattern string.         the pattern string.
2942    
2943         The  next_item_length field is present from version 1 of the pcre_call-         The next_item_length field is present from version 1 of the  pcre_call-
2944         out structure. It contains the length of the next item to be matched in         out structure. It contains the length of the next item to be matched in
2945         the  pattern  string. When the callout immediately precedes an alterna-         the pattern string. When the callout immediately precedes  an  alterna-
2946         tion bar, a closing parenthesis, or the end of the pattern, the  length         tion  bar, a closing parenthesis, or the end of the pattern, the length
2947         is  zero.  When the callout precedes an opening parenthesis, the length         is zero. When the callout precedes an opening parenthesis,  the  length
2948         is that of the entire subpattern.         is that of the entire subpattern.
2949    
2950         The pattern_position and next_item_length fields are intended  to  help         The  pattern_position  and next_item_length fields are intended to help
2951         in  distinguishing between different automatic callouts, which all have         in distinguishing between different automatic callouts, which all  have
2952         the same callout number. However, they are set for all callouts.         the same callout number. However, they are set for all callouts.
2953    
2954    
2955  RETURN VALUES  RETURN VALUES
2956    
2957         The external callout function returns an integer to PCRE. If the  value         The  external callout function returns an integer to PCRE. If the value
2958         is  zero,  matching  proceeds  as  normal. If the value is greater than         is zero, matching proceeds as normal. If  the  value  is  greater  than
2959         zero, matching fails at the current point, but  the  testing  of  other         zero,  matching  fails  at  the current point, but the testing of other
2960         matching possibilities goes ahead, just as if a lookahead assertion had         matching possibilities goes ahead, just as if a lookahead assertion had
2961         failed. If the value is less than zero, the  match  is  abandoned,  and         failed.  If  the  value  is less than zero, the match is abandoned, and
2962         pcre_exec() (or pcre_dfa_exec()) returns the negative value.         pcre_exec() or pcre_dfa_exec() returns the negative value.
2963    
2964         Negative   values   should   normally   be   chosen  from  the  set  of         Negative  values  should  normally  be   chosen   from   the   set   of
2965         PCRE_ERROR_xxx values. In particular, PCRE_ERROR_NOMATCH forces a stan-         PCRE_ERROR_xxx values. In particular, PCRE_ERROR_NOMATCH forces a stan-
2966         dard  "no  match"  failure.   The  error  number  PCRE_ERROR_CALLOUT is         dard "no  match"  failure.   The  error  number  PCRE_ERROR_CALLOUT  is
2967         reserved for use by callout functions; it will never be  used  by  PCRE         reserved  for  use  by callout functions; it will never be used by PCRE
2968         itself.         itself.
2969    
2970    
# Line 2736  AUTHOR Line 2977  AUTHOR
2977    
2978  REVISION  REVISION
2979    
2980         Last updated: 29 May 2007         Last updated: 29 September 2009
2981         Copyright (c) 1997-2007 University of Cambridge.         Copyright (c) 1997-2009 University of Cambridge.
2982  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
2983    
2984    
# Line 2751  NAME Line 2992  NAME
2992  DIFFERENCES BETWEEN PCRE AND PERL  DIFFERENCES BETWEEN PCRE AND PERL
2993    
2994         This  document describes the differences in the ways that PCRE and Perl         This  document describes the differences in the ways that PCRE and Perl
2995         handle regular expressions. The differences described here  are  mainly         handle regular expressions. The differences  described  here  are  with
2996         with  respect  to  Perl 5.8, though PCRE versions 7.0 and later contain         respect to Perl 5.10/5.11.
        some features that are expected to be in the forthcoming Perl 5.10.  
2997    
2998         1. PCRE has only a subset of Perl's UTF-8 and Unicode support.  Details         1.  PCRE has only a subset of Perl's UTF-8 and Unicode support. Details
2999         of  what  it does have are given in the section on UTF-8 support in the         of what it does have are given in the section on UTF-8 support  in  the
3000         main pcre page.         main pcre page.
3001    
3002         2. PCRE does not allow repeat quantifiers on lookahead assertions. Perl         2. PCRE does not allow repeat quantifiers on lookahead assertions. Perl
3003         permits  them,  but they do not mean what you might think. For example,         permits them, but they do not mean what you might think.  For  example,
3004         (?!a){3} does not assert that the next three characters are not "a". It         (?!a){3} does not assert that the next three characters are not "a". It
3005         just asserts that the next character is not "a" three times.         just asserts that the next character is not "a" three times.
3006    
3007         3.  Capturing  subpatterns  that occur inside negative lookahead asser-         3. Capturing subpatterns that occur inside  negative  lookahead  asser-
3008         tions are counted, but their entries in the offsets  vector  are  never         tions  are  counted,  but their entries in the offsets vector are never
3009         set.  Perl sets its numerical variables from any such patterns that are         set. Perl sets its numerical variables from any such patterns that  are
3010         matched before the assertion fails to match something (thereby succeed-         matched before the assertion fails to match something (thereby succeed-
3011         ing),  but  only  if the negative lookahead assertion contains just one         ing), but only if the negative lookahead assertion  contains  just  one
3012         branch.         branch.
3013    
3014         4. Though binary zero characters are supported in the  subject  string,         4.  Though  binary zero characters are supported in the subject string,
3015         they are not allowed in a pattern string because it is passed as a nor-         they are not allowed in a pattern string because it is passed as a nor-
3016         mal C string, terminated by zero. The escape sequence \0 can be used in         mal C string, terminated by zero. The escape sequence \0 can be used in
3017         the pattern to represent a binary zero.         the pattern to represent a binary zero.
3018    
3019         5.  The  following Perl escape sequences are not supported: \l, \u, \L,         5. The following Perl escape sequences are not supported: \l,  \u,  \L,
3020         \U, and \N. In fact these are implemented by Perl's general string-han-         \U, and \N. In fact these are implemented by Perl's general string-han-
3021         dling  and are not part of its pattern matching engine. If any of these         dling and are not part of its pattern matching engine. If any of  these
3022         are encountered by PCRE, an error is generated.         are encountered by PCRE, an error is generated.
3023    
3024         6. The Perl escape sequences \p, \P, and \X are supported only if  PCRE         6.  The Perl escape sequences \p, \P, and \X are supported only if PCRE
3025         is  built  with Unicode character property support. The properties that         is built with Unicode character property support. The  properties  that
3026         can be tested with \p and \P are limited to the general category  prop-         can  be tested with \p and \P are limited to the general category prop-
3027         erties  such  as  Lu and Nd, script names such as Greek or Han, and the         erties such as Lu and Nd, script names such as Greek or  Han,  and  the
3028         derived properties Any and L&.         derived  properties  Any  and  L&. PCRE does support the Cs (surrogate)
3029           property, which Perl does not; the  Perl  documentation  says  "Because
3030           Perl hides the need for the user to understand the internal representa-
3031           tion of Unicode characters, there is no need to implement the  somewhat
3032           messy concept of surrogates."
3033    
3034         7. PCRE does support the \Q...\E escape for quoting substrings. Charac-         7. PCRE does support the \Q...\E escape for quoting substrings. Charac-
3035         ters  in  between  are  treated as literals. This is slightly different         ters in between are treated as literals.  This  is  slightly  different
3036         from Perl in that $ and @ are  also  handled  as  literals  inside  the         from  Perl  in  that  $  and  @ are also handled as literals inside the
3037         quotes.  In Perl, they cause variable interpolation (but of course PCRE         quotes. In Perl, they cause variable interpolation (but of course  PCRE
3038         does not have variables). Note the following examples:         does not have variables). Note the following examples:
3039    
3040             Pattern            PCRE matches      Perl matches             Pattern            PCRE matches      Perl matches
# Line 2800  DIFFERENCES BETWEEN PCRE AND PERL Line 3044  DIFFERENCES BETWEEN PCRE AND PERL
3044             \Qabc\$xyz\E       abc\$xyz          abc\$xyz             \Qabc\$xyz\E       abc\$xyz          abc\$xyz
3045             \Qabc\E\$\Qxyz\E   abc$xyz           abc$xyz             \Qabc\E\$\Qxyz\E   abc$xyz           abc$xyz
3046    
3047         The \Q...\E sequence is recognized both inside  and  outside  character         The  \Q...\E  sequence  is recognized both inside and outside character
3048         classes.         classes.
3049    
3050         8. Fairly obviously, PCRE does not support the (?{code}) and (??{code})         8. Fairly obviously, PCRE does not support the (?{code}) and (??{code})
3051         constructions. However, there is support for recursive  patterns.  This         constructions.  However,  there is support for recursive patterns. This
3052         is  not available in Perl 5.8, but will be in Perl 5.10. Also, the PCRE         is not available in Perl 5.8, but it is in Perl 5.10.  Also,  the  PCRE
3053         "callout" feature allows an external function to be called during  pat-         "callout"  feature allows an external function to be called during pat-
3054         tern matching. See the pcrecallout documentation for details.         tern matching. See the pcrecallout documentation for details.
3055    
3056         9.  Subpatterns  that  are  called  recursively or as "subroutines" are         9. Subpatterns that are called  recursively  or  as  "subroutines"  are
3057         always treated as atomic groups in  PCRE.  This  is  like  Python,  but         always  treated  as  atomic  groups  in  PCRE. This is like Python, but
3058         unlike Perl.         unlike Perl. There is a discussion of an example that explains this  in
3059           more  detail  in  the section on recursion differences from Perl in the
3060         10.  There are some differences that are concerned with the settings of         pcrepattern page.
3061         captured strings when part of  a  pattern  is  repeated.  For  example,  
3062         matching  "aba"  against  the  pattern  /^(a(b)?)+$/  in Perl leaves $2         10. There are some differences that are concerned with the settings  of
3063           captured  strings  when  part  of  a  pattern is repeated. For example,
3064           matching "aba" against the  pattern  /^(a(b)?)+$/  in  Perl  leaves  $2
3065         unset, but in PCRE it is set to "b".         unset, but in PCRE it is set to "b".
3066    
3067         11.  PCRE  does  support  Perl  5.10's  backtracking  verbs  (*ACCEPT),         11.  PCRE's handling of duplicate subpattern numbers and duplicate sub-
3068         (*FAIL),  (*F),  (*COMMIT), (*PRUNE), (*SKIP), and (*THEN), but only in         pattern names is not as general as Perl's. This is a consequence of the
3069         the forms without an  argument.  PCRE  does  not  support  (*MARK).  If         fact the PCRE works internally just with numbers, using an external ta-
3070         (*ACCEPT)  is within capturing parentheses, PCRE does not set that cap-         ble to translate between numbers and names. In  particular,  a  pattern
3071         ture group; this is different to Perl.         such  as  (?|(?<a>A)|(?<b)B),  where the two capturing parentheses have
3072           the same number but different names, is not supported,  and  causes  an
3073           error  at compile time. If it were allowed, it would not be possible to
3074           distinguish which parentheses matched, because both names map  to  cap-
3075           turing subpattern number 1. To avoid this confusing situation, an error
3076           is given at compile time.
3077    
3078         12. PCRE provides some extensions to the Perl regular expression facil-         12. PCRE provides some extensions to the Perl regular expression facil-
3079         ities.   Perl  5.10  will  include new features that are not in earlier         ities.   Perl  5.10  includes new features that are not in earlier ver-
3080         versions, some of which (such as named parentheses) have been  in  PCRE         sions of Perl, some of which (such as named parentheses) have  been  in
3081         for some time. This list is with respect to Perl 5.10:         PCRE for some time. This list is with respect to Perl 5.10:
3082    
3083         (a)  Although  lookbehind  assertions  must match fixed length strings,         (a)  Although  lookbehind  assertions  in  PCRE must match fixed length
3084         each alternative branch of a lookbehind assertion can match a different         strings, each alternative branch of a lookbehind assertion can match  a
3085         length of string. Perl requires them all to have the same length.         different  length  of  string.  Perl requires them all to have the same
3086           length.
3087    
3088         (b)  If PCRE_DOLLAR_ENDONLY is set and PCRE_MULTILINE is not set, the $         (b) If PCRE_DOLLAR_ENDONLY is set and PCRE_MULTILINE is not set, the  $
3089         meta-character matches only at the very end of the string.         meta-character matches only at the very end of the string.
3090    
3091         (c) If PCRE_EXTRA is set, a backslash followed by a letter with no spe-         (c) If PCRE_EXTRA is set, a backslash followed by a letter with no spe-
3092         cial meaning is faulted. Otherwise, like Perl, the backslash is quietly         cial meaning is faulted. Otherwise, like Perl, the backslash is quietly
3093         ignored.  (Perl can be made to issue a warning.)         ignored.  (Perl can be made to issue a warning.)
3094    
3095         (d) If PCRE_UNGREEDY is set, the greediness of the  repetition  quanti-         (d)  If  PCRE_UNGREEDY is set, the greediness of the repetition quanti-
3096         fiers is inverted, that is, by default they are not greedy, but if fol-         fiers is inverted, that is, by default they are not greedy, but if fol-
3097         lowed by a question mark they are.         lowed by a question mark they are.
3098    
3099         (e) PCRE_ANCHORED can be used at matching time to force a pattern to be         (e) PCRE_ANCHORED can be used at matching time to force a pattern to be
3100         tried only at the first matching position in the subject string.         tried only at the first matching position in the subject string.
3101    
3102         (f)  The PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, and PCRE_NO_AUTO_CAP-         (f) The PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, PCRE_NOTEMPTY_ATSTART,
3103         TURE options for pcre_exec() have no Perl equivalents.         and  PCRE_NO_AUTO_CAPTURE  options for pcre_exec() have no Perl equiva-
3104           lents.
3105    
3106         (g) The \R escape sequence can be restricted to match only CR,  LF,  or         (g) The \R escape sequence can be restricted to match only CR,  LF,  or
3107         CRLF by the PCRE_BSR_ANYCRLF option.         CRLF by the PCRE_BSR_ANYCRLF option.
# Line 2877  AUTHOR Line 3130  AUTHOR
3130    
3131  REVISION  REVISION
3132    
3133         Last updated: 11 September 2007         Last updated: 12 May 2010
3134         Copyright (c) 1997-2007 University of Cambridge.         Copyright (c) 1997-2010 University of Cambridge.
3135  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
3136    
3137    
# Line 2893  PCRE REGULAR EXPRESSION DETAILS Line 3146  PCRE REGULAR EXPRESSION DETAILS
3146    
3147         The  syntax and semantics of the regular expressions that are supported         The  syntax and semantics of the regular expressions that are supported
3148         by PCRE are described in detail below. There is a quick-reference  syn-         by PCRE are described in detail below. There is a quick-reference  syn-
3149         tax  summary  in  the  pcresyntax  page. Perl's regular expressions are         tax summary in the pcresyntax page. PCRE tries to match Perl syntax and
3150         described in its own documentation, and regular expressions in  general         semantics as closely as it can. PCRE  also  supports  some  alternative
3151         are  covered in a number of books, some of which have copious examples.         regular  expression  syntax (which does not conflict with the Perl syn-
3152         Jeffrey  Friedl's  "Mastering  Regular   Expressions",   published   by         tax) in order to provide some compatibility with regular expressions in
3153         O'Reilly,  covers regular expressions in great detail. This description         Python, .NET, and Oniguruma.
3154         of PCRE's regular expressions is intended as reference material.  
3155           Perl's  regular expressions are described in its own documentation, and
3156           regular expressions in general are covered in a number of  books,  some
3157           of  which  have  copious  examples. Jeffrey Friedl's "Mastering Regular
3158           Expressions", published by  O'Reilly,  covers  regular  expressions  in
3159           great  detail.  This  description  of  PCRE's  regular  expressions  is
3160           intended as reference material.
3161    
3162         The original operation of PCRE was on strings of  one-byte  characters.         The original operation of PCRE was on strings of  one-byte  characters.
3163         However,  there is now also support for UTF-8 character strings. To use         However,  there is now also support for UTF-8 character strings. To use
3164         this, you must build PCRE to  include  UTF-8  support,  and  then  call         this, PCRE must be built to include UTF-8 support, and  you  must  call
3165         pcre_compile()  with  the  PCRE_UTF8  option.  How this affects pattern         pcre_compile()  or  pcre_compile2() with the PCRE_UTF8 option. There is
3166         matching is mentioned in several places below. There is also a  summary         also a special sequence that can be given at the start of a pattern:
3167         of  UTF-8  features  in  the  section on UTF-8 support in the main pcre  
3168         page.           (*UTF8)
3169    
3170           Starting a pattern with this sequence  is  equivalent  to  setting  the
3171           PCRE_UTF8  option.  This  feature  is  not Perl-compatible. How setting
3172           UTF-8 mode affects pattern matching  is  mentioned  in  several  places
3173           below.  There  is  also  a  summary of UTF-8 features in the section on
3174           UTF-8 support in the main pcre page.
3175    
3176           Another special sequence that may appear at the start of a  pattern  or
3177           in combination with (*UTF8) is:
3178    
3179             (*UCP)
3180    
3181           This  has  the  same  effect  as setting the PCRE_UCP option: it causes
3182           sequences such as \d and \w to  use  Unicode  properties  to  determine
3183           character types, instead of recognizing only characters with codes less
3184           than 128 via a lookup table.
3185    
3186         The remainder of this document discusses the  patterns  that  are  sup-         The remainder of this document discusses the  patterns  that  are  sup-
3187         ported  by  PCRE when its main matching function, pcre_exec(), is used.         ported  by  PCRE when its main matching function, pcre_exec(), is used.
# Line 2936  NEWLINE CONVENTIONS Line 3211  NEWLINE CONVENTIONS
3211           (*ANYCRLF)   any of the three above           (*ANYCRLF)   any of the three above
3212           (*ANY)       all Unicode newline sequences           (*ANY)       all Unicode newline sequences
3213    
3214         These override the default and the options given to pcre_compile(). For         These  override  the default and the options given to pcre_compile() or
3215         example, on a Unix system where LF is the default newline sequence, the         pcre_compile2(). For example, on a Unix system where LF is the  default
3216         pattern         newline sequence, the pattern
3217    
3218           (*CR)a.b           (*CR)a.b
3219    
# Line 2948  NEWLINE CONVENTIONS Line 3223  NEWLINE CONVENTIONS
3223         and that they must be in upper case.  If  more  than  one  of  them  is         and that they must be in upper case.  If  more  than  one  of  them  is
3224         present, the last one is used.         present, the last one is used.
3225    
3226         The  newline  convention  does  not  affect what the \R escape sequence         The  newline convention affects the interpretation of the dot metachar-
3227         matches. By default, this is any Unicode  newline  sequence,  for  Perl         acter when PCRE_DOTALL is not set, and also the behaviour of  \N.  How-
3228         compatibility.  However, this can be changed; see the description of \R         ever,  it  does  not  affect  what  the  \R escape sequence matches. By
3229         in the section entitled "Newline sequences" below. A change of \R  set-         default, this is any Unicode newline sequence, for Perl  compatibility.
3230         ting can be combined with a change of newline convention.         However,  this can be changed; see the description of \R in the section
3231           entitled "Newline sequences" below. A change of \R setting can be  com-
3232           bined with a change of newline convention.
3233    
3234    
3235  CHARACTERS AND METACHARACTERS  CHARACTERS AND METACHARACTERS
# Line 3010  CHARACTERS AND METACHARACTERS Line 3287  CHARACTERS AND METACHARACTERS
3287                    syntax)                    syntax)
3288           ]      terminates the character class           ]      terminates the character class
3289    
3290         The  following sections describe the use of each of the metacharacters.         The following sections describe the use of each of the metacharacters.
3291    
3292    
3293  BACKSLASH  BACKSLASH
3294    
3295         The backslash character has several uses. Firstly, if it is followed by         The backslash character has several uses. Firstly, if it is followed by
3296         a  non-alphanumeric  character,  it takes away any special meaning that         a non-alphanumeric character, it takes away any  special  meaning  that
3297         character may have. This  use  of  backslash  as  an  escape  character         character  may  have.  This  use  of  backslash  as an escape character
3298         applies both inside and outside character classes.         applies both inside and outside character classes.
3299    
3300         For  example,  if  you want to match a * character, you write \* in the         For example, if you want to match a * character, you write  \*  in  the
3301         pattern.  This escaping action applies whether  or  not  the  following         pattern.   This  escaping  action  applies whether or not the following
3302         character  would  otherwise be interpreted as a metacharacter, so it is         character would otherwise be interpreted as a metacharacter, so  it  is
3303         always safe to precede a non-alphanumeric  with  backslash  to  specify         always  safe  to  precede  a non-alphanumeric with backslash to specify
3304         that  it stands for itself. In particular, if you want to match a back-         that it stands for itself. In particular, if you want to match a  back-
3305         slash, you write \\.         slash, you write \\.
3306    
3307         If a pattern is compiled with the PCRE_EXTENDED option,  whitespace  in         If  a  pattern is compiled with the PCRE_EXTENDED option, whitespace in
3308         the  pattern (other than in a character class) and characters between a         the pattern (other than in a character class) and characters between  a
3309         # outside a character class and the next newline are ignored. An escap-         # outside a character class and the next newline are ignored. An escap-
3310         ing  backslash  can  be  used to include a whitespace or # character as         ing backslash can be used to include a whitespace  or  #  character  as
3311         part of the pattern.         part of the pattern.
3312    
3313         If you want to remove the special meaning from a  sequence  of  charac-         If  you  want  to remove the special meaning from a sequence of charac-
3314         ters,  you can do so by putting them between \Q and \E. This is differ-         ters, you can do so by putting them between \Q and \E. This is  differ-
3315         ent from Perl in that $ and  @  are  handled  as  literals  in  \Q...\E         ent  from  Perl  in  that  $  and  @ are handled as literals in \Q...\E
3316         sequences  in  PCRE, whereas in Perl, $ and @ cause variable interpola-         sequences in PCRE, whereas in Perl, $ and @ cause  variable  interpola-
3317         tion. Note the following examples:         tion. Note the following examples:
3318    
3319           Pattern            PCRE matches   Perl matches           Pattern            PCRE matches   Perl matches
# Line 3046  BACKSLASH Line 3323  BACKSLASH
3323           \Qabc\$xyz\E       abc\$xyz       abc\$xyz           \Qabc\$xyz\E       abc\$xyz       abc\$xyz
3324           \Qabc\E\$\Qxyz\E   abc$xyz        abc$xyz           \Qabc\E\$\Qxyz\E   abc$xyz        abc$xyz
3325    
3326         The \Q...\E sequence is recognized both inside  and  outside  character         The  \Q...\E  sequence  is recognized both inside and outside character
3327         classes.         classes.
3328    
3329     Non-printing characters     Non-printing characters
3330    
3331         A second use of backslash provides a way of encoding non-printing char-         A second use of backslash provides a way of encoding non-printing char-
3332         acters in patterns in a visible manner. There is no restriction on  the         acters  in patterns in a visible manner. There is no restriction on the
3333         appearance  of non-printing characters, apart from the binary zero that         appearance of non-printing characters, apart from the binary zero  that
3334         terminates a pattern, but when a pattern  is  being  prepared  by  text         terminates  a  pattern,  but  when  a pattern is being prepared by text
3335         editing,  it  is  usually  easier  to  use  one of the following escape         editing, it is  often  easier  to  use  one  of  the  following  escape
3336         sequences than the binary character it represents:         sequences than the binary character it represents:
3337    
3338           \a        alarm, that is, the BEL character (hex 07)           \a        alarm, that is, the BEL character (hex 07)
# Line 3065  BACKSLASH Line 3342  BACKSLASH
3342           \n        linefeed (hex 0A)           \n        linefeed (hex 0A)
3343           \r        carriage return (hex 0D)           \r        carriage return (hex 0D)
3344           \t        tab (hex 09)           \t        tab (hex 09)
3345           \ddd      character with octal code ddd, or backreference           \ddd      character with octal code ddd, or back reference
3346           \xhh      character with hex code hh           \xhh      character with hex code hh
3347           \x{hhh..} character with hex code hhh..           \x{hhh..} character with hex code hhh..
3348    
3349         The precise effect of \cx is as follows: if x is a lower  case  letter,         The  precise  effect of \cx is as follows: if x is a lower case letter,
3350         it  is converted to upper case. Then bit 6 of the character (hex 40) is         it is converted to upper case. Then bit 6 of the character (hex 40)  is
3351         inverted.  Thus \cz becomes hex 1A, but \c{ becomes hex 3B,  while  \c;         inverted.   Thus  \cz becomes hex 1A, but \c{ becomes hex 3B, while \c;
3352         becomes hex 7B.         becomes hex 7B.
3353    
3354         After  \x, from zero to two hexadecimal digits are read (letters can be         After \x, from zero to two hexadecimal digits are read (letters can  be
3355         in upper or lower case). Any number of hexadecimal  digits  may  appear         in  upper  or  lower case). Any number of hexadecimal digits may appear
3356         between  \x{  and  },  but the value of the character code must be less         between \x{ and }, but the value of the character  code  must  be  less
3357         than 256 in non-UTF-8 mode, and less than 2**31 in UTF-8 mode. That is,         than 256 in non-UTF-8 mode, and less than 2**31 in UTF-8 mode. That is,
3358         the  maximum value in hexadecimal is 7FFFFFFF. Note that this is bigger         the maximum value in hexadecimal is 7FFFFFFF. Note that this is  bigger
3359         than the largest Unicode code point, which is 10FFFF.         than the largest Unicode code point, which is 10FFFF.
3360    
3361         If characters other than hexadecimal digits appear between \x{  and  },         If  characters  other than hexadecimal digits appear between \x{ and },
3362         or if there is no terminating }, this form of escape is not recognized.         or if there is no terminating }, this form of escape is not recognized.
3363         Instead, the initial \x will be  interpreted  as  a  basic  hexadecimal         Instead,  the  initial  \x  will  be interpreted as a basic hexadecimal
3364         escape,  with  no  following  digits, giving a character whose value is         escape, with no following digits, giving a  character  whose  value  is
3365         zero.         zero.
3366    
3367         Characters whose value is less than 256 can be defined by either of the         Characters whose value is less than 256 can be defined by either of the
3368         two  syntaxes  for  \x. There is no difference in the way they are han-         two syntaxes for \x. There is no difference in the way  they  are  han-
3369         dled. For example, \xdc is exactly the same as \x{dc}.         dled. For example, \xdc is exactly the same as \x{dc}.
3370    
3371         After \0 up to two further octal digits are read. If  there  are  fewer         After  \0  up  to two further octal digits are read. If there are fewer
3372         than  two  digits,  just  those  that  are  present  are used. Thus the         than two digits, just  those  that  are  present  are  used.  Thus  the
3373         sequence \0\x\07 specifies two binary zeros followed by a BEL character         sequence \0\x\07 specifies two binary zeros followed by a BEL character
3374         (code  value 7). Make sure you supply two digits after the initial zero         (code value 7). Make sure you supply two digits after the initial  zero
3375         if the pattern character that follows is itself an octal digit.         if the pattern character that follows is itself an octal digit.
3376    
3377         The handling of a backslash followed by a digit other than 0 is compli-         The handling of a backslash followed by a digit other than 0 is compli-
3378         cated.  Outside a character class, PCRE reads it and any following dig-         cated.  Outside a character class, PCRE reads it and any following dig-
3379         its as a decimal number. If the number is less than  10,  or  if  there         its  as  a  decimal  number. If the number is less than 10, or if there
3380         have been at least that many previous capturing left parentheses in the         have been at least that many previous capturing left parentheses in the
3381         expression, the entire  sequence  is  taken  as  a  back  reference.  A         expression,  the  entire  sequence  is  taken  as  a  back reference. A
3382         description  of how this works is given later, following the discussion         description of how this works is given later, following the  discussion
3383         of parenthesized subpatterns.         of parenthesized subpatterns.
3384    
3385         Inside a character class, or if the decimal number is  greater  than  9         Inside  a  character  class, or if the decimal number is greater than 9
3386         and  there have not been that many capturing subpatterns, PCRE re-reads         and there have not been that many capturing subpatterns, PCRE  re-reads
3387         up to three octal digits following the backslash, and uses them to gen-         up to three octal digits following the backslash, and uses them to gen-
3388         erate  a data character. Any subsequent digits stand for themselves. In         erate a data character. Any subsequent digits stand for themselves.  In
3389         non-UTF-8 mode, the value of a character specified  in  octal  must  be         non-UTF-8  mode,  the  value  of a character specified in octal must be
3390         less  than  \400.  In  UTF-8 mode, values up to \777 are permitted. For         less than \400. In UTF-8 mode, values up to  \777  are  permitted.  For
3391         example:         example:
3392    
3393           \040   is another way of writing a space           \040   is another way of writing a space
# Line 3128  BACKSLASH Line 3405  BACKSLASH
3405           \81    is either a back reference, or a binary zero           \81    is either a back reference, or a binary zero
3406                     followed by the two characters "8" and "1"                     followed by the two characters "8" and "1"
3407    
3408         Note that octal values of 100 or greater must not be  introduced  by  a         Note  that  octal  values of 100 or greater must not be introduced by a
3409         leading zero, because no more than three octal digits are ever read.         leading zero, because no more than three octal digits are ever read.
3410    
3411         All the sequences that define a single character value can be used both         All the sequences that define a single character value can be used both
3412         inside and outside character classes. In addition, inside  a  character         inside  and  outside character classes. In addition, inside a character
3413         class,  the  sequence \b is interpreted as the backspace character (hex         class, the sequence \b is interpreted as the backspace  character  (hex
3414         08), and the sequences \R and \X are interpreted as the characters  "R"         08).  The sequences \B, \N, \R, and \X are not special inside a charac-
3415         and  "X", respectively. Outside a character class, these sequences have         ter class. Like any  other  unrecognized  escape  sequences,  they  are
3416         different meanings (see below).         treated  as  the  literal characters "B", "N", "R", and "X" by default,
3417           but cause an error if the PCRE_EXTRA option is set. Outside a character
3418           class, these sequences have different meanings.
3419    
3420     Absolute and relative back references     Absolute and relative back references
3421    
3422         The sequence \g followed by an unsigned or a negative  number,  option-         The  sequence  \g followed by an unsigned or a negative number, option-
3423         ally  enclosed  in braces, is an absolute or relative back reference. A         ally enclosed in braces, is an absolute or relative back  reference.  A
3424         named back reference can be coded as \g{name}. Back references are dis-         named back reference can be coded as \g{name}. Back references are dis-
3425         cussed later, following the discussion of parenthesized subpatterns.         cussed later, following the discussion of parenthesized subpatterns.
3426    
3427       Absolute and relative subroutine calls
3428    
3429           For compatibility with Oniguruma, the non-Perl syntax \g followed by  a
3430           name or a number enclosed either in angle brackets or single quotes, is
3431           an alternative syntax for referencing a subpattern as  a  "subroutine".
3432           Details  are  discussed  later.   Note  that  \g{...} (Perl syntax) and
3433           \g<...> (Oniguruma syntax) are not synonymous. The  former  is  a  back
3434           reference; the latter is a subroutine call.
3435    
3436     Generic character types     Generic character types
3437    
3438         Another use of backslash is for specifying generic character types. The         Another use of backslash is for specifying generic character types:
        following are always recognized:  
3439    
3440           \d     any decimal digit           \d     any decimal digit
3441           \D     any character that is not a decimal digit           \D     any character that is not a decimal digit
# Line 3161  BACKSLASH Line 3448  BACKSLASH
3448           \w     any "word" character           \w     any "word" character
3449           \W     any "non-word" character           \W     any "non-word" character
3450    
3451         Each pair of escape sequences partitions the complete set of characters         There is also the single sequence \N, which matches a non-newline char-
3452         into  two disjoint sets. Any given character matches one, and only one,         acter.  This is the same as the "." metacharacter when  PCRE_DOTALL  is
3453         of each pair.         not set.
3454    
3455         These character type sequences can appear both inside and outside char-         Each  pair of lower and upper case escape sequences partitions the com-
3456         acter  classes.  They each match one character of the appropriate type.         plete set of characters into two disjoint  sets.  Any  given  character
3457         If the current matching point is at the end of the subject string,  all         matches  one, and only one, of each pair. The sequences can appear both
3458         of them fail, since there is no character to match.         inside and outside character classes. They each match one character  of
3459           the  appropriate  type.  If the current matching point is at the end of
3460           the subject string, all of them fail, because there is no character  to
3461           match.
3462    
3463         For  compatibility  with Perl, \s does not match the VT character (code         For  compatibility  with Perl, \s does not match the VT character (code
3464         11).  This makes it different from the the POSIX "space" class. The  \s         11).  This makes it different from the the POSIX "space" class. The  \s
# Line 3176  BACKSLASH Line 3466  BACKSLASH
3466         "use locale;" is included in a Perl script, \s may match the VT charac-         "use locale;" is included in a Perl script, \s may match the VT charac-
3467         ter. In PCRE, it never does.         ter. In PCRE, it never does.
3468    
3469         In  UTF-8 mode, characters with values greater than 128 never match \d,         A  "word"  character is an underscore or any character that is a letter
3470         \s, or \w, and always match \D, \S, and \W. This is true even when Uni-         or digit.  By default, the definition of letters  and  digits  is  con-
3471         code  character  property  support is available. These sequences retain         trolled  by PCRE's low-valued character tables, and may vary if locale-
3472         their original meanings from before UTF-8 support was available, mainly         specific matching is taking place (see "Locale support" in the  pcreapi
3473         for efficiency reasons.         page).  For  example,  in  a French locale such as "fr_FR" in Unix-like
3474           systems, or "french" in Windows, some character codes greater than  128
3475           are  used  for  accented letters, and these are then matched by \w. The
3476           use of locales with Unicode is discouraged.
3477    
3478           By default, in UTF-8 mode, characters  with  values  greater  than  128
3479           never  match  \d,  \s,  or  \w,  and always match \D, \S, and \W. These
3480           sequences retain their original meanings from before UTF-8 support  was
3481           available,  mainly for efficiency reasons. However, if PCRE is compiled
3482           with Unicode property support, and the PCRE_UCP option is set, the  be-
3483           haviour  is  changed  so  that Unicode properties are used to determine
3484           character types, as follows:
3485    
3486             \d  any character that \p{Nd} matches (decimal digit)
3487             \s  any character that \p{Z} matches, plus HT, LF, FF, CR
3488             \w  any character that \p{L} or \p{N} matches, plus underscore
3489    
3490           The upper case escapes match the inverse sets of characters. Note  that
3491           \d  matches  only decimal digits, whereas \w matches any Unicode digit,
3492           as well as any Unicode letter, and underscore. Note also that  PCRE_UCP
3493           affects  \b,  and  \B  because  they are defined in terms of \w and \W.
3494           Matching these sequences is noticeably slower when PCRE_UCP is set.
3495    
3496         The sequences \h, \H, \v, and \V are Perl 5.10 features. In contrast to         The sequences \h, \H, \v, and \V are Perl 5.10 features. In contrast to
3497         the other sequences, these do match certain high-valued  codepoints  in         the  other  sequences,  which  match  only ASCII characters by default,
3498         UTF-8 mode.  The horizontal space characters are:         these always  match  certain  high-valued  codepoints  in  UTF-8  mode,
3499           whether or not PCRE_UCP is set. The horizontal space characters are:
3500    
3501           U+0009     Horizontal tab           U+0009     Horizontal tab
3502           U+0020     Space           U+0020     Space
# Line 3216  BACKSLASH Line 3528  BACKSLASH
3528           U+2028     Line separator           U+2028     Line separator
3529           U+2029     Paragraph separator           U+2029     Paragraph separator
3530    
        A "word" character is an underscore or any character less than 256 that  
        is a letter or digit. The definition of  letters  and  digits  is  con-  
        trolled  by PCRE's low-valued character tables, and may vary if locale-  
        specific matching is taking place (see "Locale support" in the  pcreapi  
        page).  For  example,  in  a French locale such as "fr_FR" in Unix-like  
        systems, or "french" in Windows, some character codes greater than  128  
        are  used for accented letters, and these are matched by \w. The use of  
        locales with Unicode is discouraged.  
   
3531     Newline sequences     Newline sequences
3532    
3533         Outside a character class, by default, the escape sequence  \R  matches         Outside  a  character class, by default, the escape sequence \R matches
3534         any Unicode newline sequence. This is a Perl 5.10 feature. In non-UTF-8         any Unicode newline sequence. This is a Perl 5.10 feature. In non-UTF-8
3535         mode \R is equivalent to the following:         mode \R is equivalent to the following:
3536    
3537           (?>\r\n|\n|\x0b|\f|\r|\x85)           (?>\r\n|\n|\x0b|\f|\r|\x85)
3538    
3539         This is an example of an "atomic group", details  of  which  are  given         This  is  an  example  of an "atomic group", details of which are given
3540         below.  This particular group matches either the two-character sequence         below.  This particular group matches either the two-character sequence
3541         CR followed by LF, or  one  of  the  single  characters  LF  (linefeed,         CR  followed  by  LF,  or  one  of  the single characters LF (linefeed,
3542         U+000A), VT (vertical tab, U+000B), FF (formfeed, U+000C), CR (carriage         U+000A), VT (vertical tab, U+000B), FF (formfeed, U+000C), CR (carriage
3543         return, U+000D), or NEL (next line, U+0085). The two-character sequence         return, U+000D), or NEL (next line, U+0085). The two-character sequence
3544         is treated as a single unit that cannot be split.         is treated as a single unit that cannot be split.
3545    
3546         In  UTF-8  mode, two additional characters whose codepoints are greater         In UTF-8 mode, two additional characters whose codepoints  are  greater
3547         than 255 are added: LS (line separator, U+2028) and PS (paragraph sepa-         than 255 are added: LS (line separator, U+2028) and PS (paragraph sepa-
3548         rator,  U+2029).   Unicode character property support is not needed for         rator, U+2029).  Unicode character property support is not  needed  for
3549         these characters to be recognized.         these characters to be recognized.
3550    
3551         It is possible to restrict \R to match only CR, LF, or CRLF (instead of         It is possible to restrict \R to match only CR, LF, or CRLF (instead of
3552         the  complete  set  of  Unicode  line  endings)  by  setting the option         the complete set  of  Unicode  line  endings)  by  setting  the  option
3553         PCRE_BSR_ANYCRLF either at compile time or when the pattern is matched.         PCRE_BSR_ANYCRLF either at compile time or when the pattern is matched.
3554         (BSR is an abbrevation for "backslash R".) This can be made the default         (BSR is an abbrevation for "backslash R".) This can be made the default
3555         when PCRE is built; if this is the case, the  other  behaviour  can  be         when  PCRE  is  built;  if this is the case, the other behaviour can be
3556         requested  via  the  PCRE_BSR_UNICODE  option.   It is also possible to         requested via the PCRE_BSR_UNICODE option.   It  is  also  possible  to
3557         specify these settings by starting a pattern string  with  one  of  the         specify  these  settings  by  starting a pattern string with one of the
3558         following sequences:         following sequences:
3559    
3560           (*BSR_ANYCRLF)   CR, LF, or CRLF only           (*BSR_ANYCRLF)   CR, LF, or CRLF only
3561           (*BSR_UNICODE)   any Unicode newline sequence           (*BSR_UNICODE)   any Unicode newline sequence
3562    
3563         These override the default and the options given to pcre_compile(), but         These override the default and the options given to  pcre_compile()  or
3564         they can be overridden by options given to pcre_exec(). Note that these         pcre_compile2(),  but  they  can  be  overridden  by  options  given to
3565         special settings, which are not Perl-compatible, are recognized only at         pcre_exec() or pcre_dfa_exec(). Note that these special settings, which
3566         the very start of a pattern, and that they must be in  upper  case.  If         are  not  Perl-compatible,  are  recognized only at the very start of a
3567         more  than  one  of  them is present, the last one is used. They can be         pattern, and that they must be in upper case. If more than one of  them
3568         combined with a change of newline convention, for  example,  a  pattern         is present, the last one is used. They can be combined with a change of
3569         can start with:         newline convention; for example, a pattern can start with:
3570    
3571           (*ANY)(*BSR_ANYCRLF)           (*ANY)(*BSR_ANYCRLF)
3572    
3573         Inside a character class, \R matches the letter "R".         They can also be combined with the (*UTF8) or (*UCP) special sequences.
3574           Inside  a  character  class,  \R  is  treated as an unrecognized escape
3575           sequence, and so matches the letter "R" by default, but causes an error
3576           if PCRE_EXTRA is set.
3577    
3578     Unicode character properties     Unicode character properties
3579    
# Line 3282  BACKSLASH Line 3588  BACKSLASH
3588           \X       an extended Unicode sequence           \X       an extended Unicode sequence
3589    
3590         The  property  names represented by xx above are limited to the Unicode         The  property  names represented by xx above are limited to the Unicode
3591         script names, the general category properties, and "Any", which matches         script names, the general category properties, "Any", which matches any
3592         any character (including newline). Other properties such as "InMusical-         character   (including  newline),  and  some  special  PCRE  properties
3593         Symbols" are not currently supported by PCRE. Note  that  \P{Any}  does         (described in the next section).  Other Perl properties such as  "InMu-
3594         not match any characters, so always causes a match failure.         sicalSymbols"  are  not  currently supported by PCRE. Note that \P{Any}
3595           does not match any characters, so always causes a match failure.
3596    
3597         Sets of Unicode characters are defined as belonging to certain scripts.         Sets of Unicode characters are defined as belonging to certain scripts.
3598         A character from one of these sets can be matched using a script  name.         A  character from one of these sets can be matched using a script name.
3599         For example:         For example:
3600    
3601           \p{Greek}           \p{Greek}
3602           \P{Han}           \P{Han}
3603    
3604         Those  that are not part of an identified script are lumped together as         Those that are not part of an identified script are lumped together  as
3605         "Common". The current list of scripts is:         "Common". The current list of scripts is:
3606    
3607         Arabic,  Armenian,  Balinese,  Bengali,  Bopomofo,  Braille,  Buginese,         Arabic, Armenian, Avestan, Balinese, Bamum, Bengali, Bopomofo, Braille,
3608         Buhid,   Canadian_Aboriginal,   Cherokee,  Common,  Coptic,  Cuneiform,         Buginese, Buhid, Canadian_Aboriginal, Carian, Cham,  Cherokee,  Common,
3609         Cypriot, Cyrillic, Deseret, Devanagari, Ethiopic, Georgian, Glagolitic,         Coptic,   Cuneiform,  Cypriot,  Cyrillic,  Deseret,  Devanagari,  Egyp-
3610         Gothic,  Greek, Gujarati, Gurmukhi, Han, Hangul, Hanunoo, Hebrew, Hira-         tian_Hieroglyphs,  Ethiopic,  Georgian,  Glagolitic,   Gothic,   Greek,
3611         gana, Inherited, Kannada,  Katakana,  Kharoshthi,  Khmer,  Lao,  Latin,         Gujarati,  Gurmukhi,  Han,  Hangul,  Hanunoo,  Hebrew,  Hiragana, Impe-
3612         Limbu,  Linear_B,  Malayalam,  Mongolian,  Myanmar,  New_Tai_Lue,  Nko,         rial_Aramaic, Inherited, Inscriptional_Pahlavi, Inscriptional_Parthian,
3613         Ogham, Old_Italic, Old_Persian, Oriya, Osmanya,  Phags_Pa,  Phoenician,         Javanese,  Kaithi, Kannada, Katakana, Kayah_Li, Kharoshthi, Khmer, Lao,
3614         Runic,  Shavian,  Sinhala,  Syloti_Nagri,  Syriac,  Tagalog,  Tagbanwa,         Latin,  Lepcha,  Limbu,  Linear_B,  Lisu,  Lycian,  Lydian,  Malayalam,
3615         Tai_Le, Tamil, Telugu, Thaana, Thai, Tibetan, Tifinagh, Ugaritic, Yi.         Meetei_Mayek,  Mongolian, Myanmar, New_Tai_Lue, Nko, Ogham, Old_Italic,
3616           Old_Persian, Old_South_Arabian, Old_Turkic, Ol_Chiki,  Oriya,  Osmanya,
3617         Each character has exactly one general category property, specified  by         Phags_Pa,  Phoenician,  Rejang,  Runic, Samaritan, Saurashtra, Shavian,
3618         a two-letter abbreviation. For compatibility with Perl, negation can be         Sinhala, Sundanese, Syloti_Nagri, Syriac,  Tagalog,  Tagbanwa,  Tai_Le,
3619         specified by including a circumflex between the opening brace  and  the         Tai_Tham,  Tai_Viet,  Tamil,  Telugu,  Thaana, Thai, Tibetan, Tifinagh,
3620         property name. For example, \p{^Lu} is the same as \P{Lu}.         Ugaritic, Vai, Yi.
3621    
3622           Each character has exactly one Unicode general category property, spec-
3623           ified  by a two-letter abbreviation. For compatibility with Perl, nega-
3624           tion can be specified by including a  circumflex  between  the  opening
3625           brace  and  the  property  name.  For  example,  \p{^Lu} is the same as
3626           \P{Lu}.
3627    
3628         If only one letter is specified with \p or \P, it includes all the gen-         If only one letter is specified with \p or \P, it includes all the gen-
3629         eral category properties that start with that letter. In this case,  in         eral  category properties that start with that letter. In this case, in
3630         the  absence of negation, the curly brackets in the escape sequence are         the absence of negation, the curly brackets in the escape sequence  are
3631         optional; these two examples have the same effect:         optional; these two examples have the same effect:
3632    
3633           \p{L}           \p{L}
# Line 3366  BACKSLASH Line 3679  BACKSLASH
3679           Zp    Paragraph separator           Zp    Paragraph separator
3680           Zs    Space separator           Zs    Space separator
3681    
3682         The special property L& is also supported: it matches a character  that         The  special property L& is also supported: it matches a character that
3683         has  the  Lu,  Ll, or Lt property, in other words, a letter that is not         has the Lu, Ll, or Lt property, in other words, a letter  that  is  not
3684         classified as a modifier or "other".         classified as a modifier or "other".
3685    
3686         The Cs (Surrogate) property applies only to  characters  in  the  range         The  Cs  (Surrogate)  property  applies only to characters in the range
3687         U+D800  to  U+DFFF. Such characters are not valid in UTF-8 strings (see         U+D800 to U+DFFF. Such characters are not valid in UTF-8  strings  (see
3688         RFC 3629) and so cannot be tested by PCRE, unless UTF-8 validity check-         RFC 3629) and so cannot be tested by PCRE, unless UTF-8 validity check-
3689         ing  has  been  turned off (see the discussion of PCRE_NO_UTF8_CHECK in         ing has been turned off (see the discussion  of  PCRE_NO_UTF8_CHECK  in
3690         the pcreapi page).         the pcreapi page). Perl does not support the Cs property.
3691    
3692         The long synonyms for these properties  that  Perl  supports  (such  as         The  long  synonyms  for  property  names  that  Perl supports (such as
3693         \p{Letter})  are  not  supported by PCRE, nor is it permitted to prefix         \p{Letter}) are not supported by PCRE, nor is it  permitted  to  prefix
3694         any of these properties with "Is".         any of these properties with "Is".
3695    
3696         No character that is in the Unicode table has the Cn (unassigned) prop-         No character that is in the Unicode table has the Cn (unassigned) prop-
3697         erty.  Instead, this property is assumed for any code point that is not         erty.  Instead, this property is assumed for any code point that is not
3698         in the Unicode table.         in the Unicode table.
3699    
3700         Specifying caseless matching does not affect  these  escape  sequences.         Specifying  caseless  matching  does not affect these escape sequences.
3701         For example, \p{Lu} always matches only upper case letters.         For example, \p{Lu} always matches only upper case letters.
3702    
3703         The  \X  escape  matches  any number of Unicode characters that form an         The \X escape matches any number of Unicode  characters  that  form  an
3704         extended Unicode sequence. \X is equivalent to         extended Unicode sequence. \X is equivalent to
3705    
3706           (?>\PM\pM*)           (?>\PM\pM*)
3707    
3708         That is, it matches a character without the "mark"  property,  followed         That  is,  it matches a character without the "mark" property, followed
3709         by  zero  or  more  characters with the "mark" property, and treats the         by zero or more characters with the "mark"  property,  and  treats  the
3710         sequence as an atomic group (see below).  Characters  with  the  "mark"         sequence  as  an  atomic group (see below).  Characters with the "mark"
3711         property  are  typically  accents  that affect the preceding character.         property are typically accents that  affect  the  preceding  character.
3712         None of them have codepoints less than 256, so  in  non-UTF-8  mode  \X         None  of  them  have  codepoints less than 256, so in non-UTF-8 mode \X
3713         matches any one character.         matches any one character.
3714    
3715         Matching  characters  by Unicode property is not fast, because PCRE has         Matching characters by Unicode property is not fast, because  PCRE  has
3716         to search a structure that contains  data  for  over  fifteen  thousand         to  search  a  structure  that  contains data for over fifteen thousand
3717         characters. That is why the traditional escape sequences such as \d and         characters. That is why the traditional escape sequences such as \d and
3718         \w do not use Unicode properties in PCRE.         \w  do  not  use  Unicode properties in PCRE by default, though you can
3719           make them do so by setting the PCRE_UCP option for pcre_compile() or by
3720           starting the pattern with (*UCP).
3721    
3722       PCRE's additional properties
3723    
3724           As  well  as  the standard Unicode properties described in the previous
3725           section, PCRE supports four more that make it possible to convert  tra-
3726           ditional escape sequences such as \w and \s and POSIX character classes
3727           to use Unicode properties. PCRE uses these non-standard, non-Perl prop-
3728           erties internally when PCRE_UCP is set. They are:
3729    
3730             Xan   Any alphanumeric character
3731             Xps   Any POSIX space character
3732             Xsp   Any Perl space character
3733             Xwd   Any Perl "word" character
3734    
3735           Xan  matches  characters that have either the L (letter) or the N (num-
3736           ber) property. Xps matches the characters tab, linefeed, vertical  tab,
3737           formfeed,  or  carriage  return, and any other character that has the Z
3738           (separator) property.  Xsp is the same as Xps, except that vertical tab
3739           is excluded. Xwd matches the same characters as Xan, plus underscore.
3740    
3741     Resetting the match start     Resetting the match start
3742    
3743         The escape sequence \K, which is a Perl 5.10 feature, causes any previ-         The escape sequence \K, which is a Perl 5.10 feature, causes any previ-
3744         ously  matched  characters  not  to  be  included  in the final matched         ously matched characters not  to  be  included  in  the  final  matched
3745         sequence. For example, the pattern:         sequence. For example, the pattern:
3746    
3747           foo\Kbar           foo\Kbar
3748    
3749         matches "foobar", but reports that it has matched "bar".  This  feature         matches  "foobar",  but reports that it has matched "bar". This feature
3750         is  similar  to  a lookbehind assertion (described below).  However, in         is similar to a lookbehind assertion (described  below).   However,  in
3751         this case, the part of the subject before the real match does not  have         this  case, the part of the subject before the real match does not have
3752         to  be of fixed length, as lookbehind assertions do. The use of \K does         to be of fixed length, as lookbehind assertions do. The use of \K  does
3753         not interfere with the setting of captured  substrings.   For  example,         not  interfere  with  the setting of captured substrings.  For example,
3754         when the pattern         when the pattern
3755    
3756           (foo)\Kbar           (foo)\Kbar
3757    
3758         matches "foobar", the first substring is still set to "foo".         matches "foobar", the first substring is still set to "foo".
3759    
3760           Perl documents that the use  of  \K  within  assertions  is  "not  well
3761           defined".  In  PCRE,  \K  is  acted upon when it occurs inside positive
3762           assertions, but is ignored in negative assertions.
3763    
3764     Simple assertions     Simple assertions
3765    
3766         The  final use of backslash is for certain simple assertions. An asser-         The final use of backslash is for certain simple assertions. An  asser-
3767         tion specifies a condition that has to be met at a particular point  in         tion  specifies a condition that has to be met at a particular point in
3768         a  match, without consuming any characters from the subject string. The         a match, without consuming any characters from the subject string.  The
3769         use of subpatterns for more complicated assertions is described  below.         use  of subpatterns for more complicated assertions is described below.
3770         The backslashed assertions are:         The backslashed assertions are:
3771    
3772           \b     matches at a word boundary           \b     matches at a word boundary
# Line 3439  BACKSLASH Line 3777  BACKSLASH
3777           \z     matches only at the end of the subject           \z     matches only at the end of the subject
3778           \G     matches at the first matching position in the subject           \G     matches at the first matching position in the subject
3779    
3780         These  assertions may not appear in character classes (but note that \b         Inside a character class, \b has a different meaning;  it  matches  the
3781         has a different meaning, namely the backspace character, inside a char-         backspace  character.  If  any  other  of these assertions appears in a
3782         acter class).         character class, by default it matches the corresponding literal  char-
3783           acter  (for  example,  \B  matches  the  letter  B).  However,  if  the
3784           PCRE_EXTRA option is set, an "invalid escape sequence" error is  gener-
3785           ated instead.
3786    
3787         A  word  boundary is a position in the subject string where the current         A  word  boundary is a position in the subject string where the current
3788         character and the previous character do not both match \w or  \W  (i.e.         character and the previous character do not both match \w or  \W  (i.e.
3789         one  matches  \w  and the other matches \W), or the start or end of the         one  matches  \w  and the other matches \W), or the start or end of the
3790         string if the first or last character matches \w, respectively.         string if the first or last  character  matches  \w,  respectively.  In
3791           UTF-8  mode,  the  meanings  of \w and \W can be changed by setting the
3792           PCRE_UCP option. When this is done, it also affects \b and \B.  Neither
3793           PCRE  nor  Perl has a separate "start of word" or "end of word" metase-
3794           quence. However, whatever follows \b normally determines which  it  is.
3795           For example, the fragment \ba matches "a" at the start of a word.
3796    
3797         The \A, \Z, and \z assertions differ from  the  traditional  circumflex         The  \A,  \Z,  and \z assertions differ from the traditional circumflex
3798         and dollar (described in the next section) in that they only ever match         and dollar (described in the next section) in that they only ever match
3799         at the very start and end of the subject string, whatever  options  are         at  the  very start and end of the subject string, whatever options are
3800         set.  Thus,  they are independent of multiline mode. These three asser-         set. Thus, they are independent of multiline mode. These  three  asser-
3801         tions are not affected by the PCRE_NOTBOL or PCRE_NOTEOL options, which         tions are not affected by the PCRE_NOTBOL or PCRE_NOTEOL options, which
3802         affect  only the behaviour of the circumflex and dollar metacharacters.         affect only the behaviour of the circumflex and dollar  metacharacters.
3803         However, if the startoffset argument of pcre_exec() is non-zero,  indi-         However,  if the startoffset argument of pcre_exec() is non-zero, indi-
3804         cating that matching is to start at a point other than the beginning of         cating that matching is to start at a point other than the beginning of
3805         the subject, \A can never match. The difference between \Z  and  \z  is         the  subject,  \A  can never match. The difference between \Z and \z is
3806         that \Z matches before a newline at the end of the string as well as at         that \Z matches before a newline at the end of the string as well as at
3807         the very end, whereas \z matches only at the end.         the very end, whereas \z matches only at the end.
3808    
3809         The \G assertion is true only when the current matching position is  at         The  \G assertion is true only when the current matching position is at
3810         the  start point of the match, as specified by the startoffset argument         the start point of the match, as specified by the startoffset  argument
3811         of pcre_exec(). It differs from \A when the  value  of  startoffset  is         of  pcre_exec().  It  differs  from \A when the value of startoffset is
3812         non-zero.  By calling pcre_exec() multiple times with appropriate argu-         non-zero. By calling pcre_exec() multiple times with appropriate  argu-
3813         ments, you can mimic Perl's /g option, and it is in this kind of imple-         ments, you can mimic Perl's /g option, and it is in this kind of imple-
3814         mentation where \G can be useful.         mentation where \G can be useful.
3815    
3816         Note,  however,  that  PCRE's interpretation of \G, as the start of the         Note, however, that PCRE's interpretation of \G, as the  start  of  the
3817         current match, is subtly different from Perl's, which defines it as the         current match, is subtly different from Perl's, which defines it as the
3818         end  of  the  previous  match. In Perl, these can be different when the         end of the previous match. In Perl, these can  be  different  when  the
3819         previously matched string was empty. Because PCRE does just  one  match         previously  matched  string was empty. Because PCRE does just one match
3820         at a time, it cannot reproduce this behaviour.         at a time, it cannot reproduce this behaviour.
3821    
3822         If  all  the alternatives of a pattern begin with \G, the expression is         If all the alternatives of a pattern begin with \G, the  expression  is
3823         anchored to the starting match position, and the "anchored" flag is set         anchored to the starting match position, and the "anchored" flag is set
3824         in the compiled regular expression.         in the compiled regular expression.
3825    
# Line 3481  BACKSLASH Line 3827  BACKSLASH
3827  CIRCUMFLEX AND DOLLAR  CIRCUMFLEX AND DOLLAR
3828    
3829         Outside a character class, in the default matching mode, the circumflex         Outside a character class, in the default matching mode, the circumflex
3830         character is an assertion that is true only  if  the  current  matching         character  is  an  assertion  that is true only if the current matching
3831         point  is  at the start of the subject string. If the startoffset argu-         point is at the start of the subject string. If the  startoffset  argu-
3832         ment of pcre_exec() is non-zero, circumflex  can  never  match  if  the         ment  of  pcre_exec()  is  non-zero,  circumflex can never match if the
3833         PCRE_MULTILINE  option  is  unset. Inside a character class, circumflex         PCRE_MULTILINE option is unset. Inside a  character  class,  circumflex
3834         has an entirely different meaning (see below).         has an entirely different meaning (see below).
3835    
3836         Circumflex need not be the first character of the pattern if  a  number         Circumflex  need  not be the first character of the pattern if a number
3837         of  alternatives are involved, but it should be the first thing in each         of alternatives are involved, but it should be the first thing in  each
3838         alternative in which it appears if the pattern is ever  to  match  that         alternative  in  which  it appears if the pattern is ever to match that
3839         branch.  If all possible alternatives start with a circumflex, that is,         branch. If all possible alternatives start with a circumflex, that  is,
3840         if the pattern is constrained to match only at the start  of  the  sub-         if  the  pattern  is constrained to match only at the start of the sub-
3841         ject,  it  is  said  to be an "anchored" pattern. (There are also other         ject, it is said to be an "anchored" pattern.  (There  are  also  other
3842         constructs that can cause a pattern to be anchored.)         constructs that can cause a pattern to be anchored.)
3843    
3844         A dollar character is an assertion that is true  only  if  the  current         A  dollar  character  is  an assertion that is true only if the current
3845         matching  point  is  at  the  end of the subject string, or immediately         matching point is at the end of  the  subject  string,  or  immediately
3846         before a newline at the end of the string (by default). Dollar need not         before a newline at the end of the string (by default). Dollar need not
3847         be  the  last  character of the pattern if a number of alternatives are         be the last character of the pattern if a number  of  alternatives  are
3848         involved, but it should be the last item in  any  branch  in  which  it         involved,  but  it  should  be  the last item in any branch in which it
3849         appears. Dollar has no special meaning in a character class.         appears. Dollar has no special meaning in a character class.
3850    
3851         The  meaning  of  dollar  can be changed so that it matches only at the         The meaning of dollar can be changed so that it  matches  only  at  the
3852         very end of the string, by setting the  PCRE_DOLLAR_ENDONLY  option  at         very  end  of  the string, by setting the PCRE_DOLLAR_ENDONLY option at
3853         compile time. This does not affect the \Z assertion.         compile time. This does not affect the \Z assertion.
3854    
3855         The meanings of the circumflex and dollar characters are changed if the         The meanings of the circumflex and dollar characters are changed if the
3856         PCRE_MULTILINE option is set. When  this  is  the  case,  a  circumflex         PCRE_MULTILINE  option  is  set.  When  this  is the case, a circumflex
3857         matches  immediately after internal newlines as well as at the start of         matches immediately after internal newlines as well as at the start  of
3858         the subject string. It does not match after a  newline  that  ends  the         the  subject  string.  It  does not match after a newline that ends the
3859         string.  A dollar matches before any newlines in the string, as well as         string. A dollar matches before any newlines in the string, as well  as
3860         at the very end, when PCRE_MULTILINE is set. When newline is  specified         at  the very end, when PCRE_MULTILINE is set. When newline is specified
3861         as  the  two-character  sequence CRLF, isolated CR and LF characters do         as the two-character sequence CRLF, isolated CR and  LF  characters  do
3862         not indicate newlines.         not indicate newlines.
3863    
3864         For example, the pattern /^abc$/ matches the subject string  "def\nabc"         For  example, the pattern /^abc$/ matches the subject string "def\nabc"
3865         (where  \n  represents a newline) in multiline mode, but not otherwise.         (where \n represents a newline) in multiline mode, but  not  otherwise.
3866         Consequently, patterns that are anchored in single  line  mode  because         Consequently,  patterns  that  are anchored in single line mode because
3867         all  branches  start  with  ^ are not anchored in multiline mode, and a         all branches start with ^ are not anchored in  multiline  mode,  and  a
3868         match for circumflex is  possible  when  the  startoffset  argument  of         match  for  circumflex  is  possible  when  the startoffset argument of
3869         pcre_exec()  is  non-zero. The PCRE_DOLLAR_ENDONLY option is ignored if         pcre_exec() is non-zero. The PCRE_DOLLAR_ENDONLY option is  ignored  if
3870         PCRE_MULTILINE is set.         PCRE_MULTILINE is set.
3871    
3872         Note that the sequences \A, \Z, and \z can be used to match  the  start         Note  that  the sequences \A, \Z, and \z can be used to match the start
3873         and  end of the subject in both modes, and if all branches of a pattern         and end of the subject in both modes, and if all branches of a  pattern
3874         start with \A it is always anchored, whether or not  PCRE_MULTILINE  is         start  with  \A it is always anchored, whether or not PCRE_MULTILINE is
3875         set.         set.
3876    
3877    
3878  FULL STOP (PERIOD, DOT)  FULL STOP (PERIOD, DOT) AND \N
3879    
3880         Outside a character class, a dot in the pattern matches any one charac-         Outside a character class, a dot in the pattern matches any one charac-
3881         ter in the subject string except (by default) a character  that  signi-         ter  in  the subject string except (by default) a character that signi-
3882         fies  the  end  of  a line. In UTF-8 mode, the matched character may be         fies the end of a line. In UTF-8 mode, the  matched  character  may  be
3883         more than one byte long.         more than one byte long.
3884    
3885         When a line ending is defined as a single character, dot never  matches         When  a line ending is defined as a single character, dot never matches
3886         that  character; when the two-character sequence CRLF is used, dot does         that character; when the two-character sequence CRLF is used, dot  does
3887         not match CR if it is immediately followed  by  LF,  but  otherwise  it         not  match  CR  if  it  is immediately followed by LF, but otherwise it
3888         matches  all characters (including isolated CRs and LFs). When any Uni-         matches all characters (including isolated CRs and LFs). When any  Uni-
3889         code line endings are being recognized, dot does not match CR or LF  or         code  line endings are being recognized, dot does not match CR or LF or
3890         any of the other line ending characters.         any of the other line ending characters.
3891    
3892         The  behaviour  of  dot  with regard to newlines can be changed. If the         The behaviour of dot with regard to newlines can  be  changed.  If  the
3893         PCRE_DOTALL option is set, a dot matches  any  one  character,  without         PCRE_DOTALL  option  is  set,  a dot matches any one character, without
3894         exception. If the two-character sequence CRLF is present in the subject         exception. If the two-character sequence CRLF is present in the subject
3895         string, it takes two dots to match it.         string, it takes two dots to match it.
3896    
3897         The handling of dot is entirely independent of the handling of  circum-         The  handling of dot is entirely independent of the handling of circum-
3898         flex  and  dollar,  the  only relationship being that they both involve         flex and dollar, the only relationship being  that  they  both  involve
3899         newlines. Dot has no special meaning in a character class.         newlines. Dot has no special meaning in a character class.
3900    
3901           The escape sequence \N always behaves as a dot does when PCRE_DOTALL is
3902           not set. In other words, it matches any one character except  one  that
3903           signifies the end of a line.
3904    
3905    
3906  MATCHING A SINGLE BYTE  MATCHING A SINGLE BYTE
3907    
3908         Outside a character class, the escape sequence \C matches any one byte,         Outside a character class, the escape sequence \C matches any one byte,
3909         both  in  and  out  of  UTF-8 mode. Unlike a dot, it always matches any         both in and out of UTF-8 mode. Unlike a  dot,  it  always  matches  any
3910         line-ending characters. The feature is provided in  Perl  in  order  to         line-ending  characters.  The  feature  is provided in Perl in order to
3911         match  individual bytes in UTF-8 mode. Because it breaks up UTF-8 char-         match individual bytes in UTF-8 mode. Because it breaks up UTF-8  char-
3912         acters into individual bytes, what remains in the string may be a  mal-         acters  into individual bytes, what remains in the string may be a mal-
3913         formed  UTF-8  string.  For this reason, the \C escape sequence is best         formed UTF-8 string. For this reason, the \C escape  sequence  is  best
3914         avoided.         avoided.
3915    
3916         PCRE does not allow \C to appear in  lookbehind  assertions  (described         PCRE  does  not  allow \C to appear in lookbehind assertions (described
3917         below),  because  in UTF-8 mode this would make it impossible to calcu-         below), because in UTF-8 mode this would make it impossible  to  calcu-
3918         late the length of the lookbehind.         late the length of the lookbehind.
3919    
3920    
# Line 3572  SQUARE BRACKETS AND CHARACTER CLASSES Line 3922  SQUARE BRACKETS AND CHARACTER CLASSES
3922    
3923         An opening square bracket introduces a character class, terminated by a         An opening square bracket introduces a character class, terminated by a
3924         closing square bracket. A closing square bracket on its own is not spe-         closing square bracket. A closing square bracket on its own is not spe-
3925         cial. If a closing square bracket is required as a member of the class,         cial by default.  However, if the PCRE_JAVASCRIPT_COMPAT option is set,
3926         it  should  be  the first data character in the class (after an initial         a lone closing square bracket causes a compile-time error. If a closing
3927         circumflex, if present) or escaped with a backslash.         square  bracket  is required as a member of the class, it should be the
3928           first data character in the class  (after  an  initial  circumflex,  if
3929           present) or escaped with a backslash.
3930    
3931         A character class matches a single character in the subject.  In  UTF-8         A  character  class matches a single character in the subject. In UTF-8
3932         mode,  the character may occupy more than one byte. A matched character         mode, the character may be more than one byte long. A matched character
3933         must be in the set of characters defined by the class, unless the first         must be in the set of characters defined by the class, unless the first
3934         character  in  the  class definition is a circumflex, in which case the         character in the class definition is a circumflex, in  which  case  the
3935         subject character must not be in the set defined by  the  class.  If  a         subject  character  must  not  be in the set defined by the class. If a
3936         circumflex  is actually required as a member of the class, ensure it is         circumflex is actually required as a member of the class, ensure it  is
3937         not the first character, or escape it with a backslash.         not the first character, or escape it with a backslash.
3938    
3939         For example, the character class [aeiou] matches any lower case  vowel,         For  example, the character class [aeiou] matches any lower case vowel,
3940         while  [^aeiou]  matches  any character that is not a lower case vowel.         while [^aeiou] matches any character that is not a  lower  case  vowel.
3941         Note that a circumflex is just a convenient notation for specifying the         Note that a circumflex is just a convenient notation for specifying the
3942         characters  that  are in the class by enumerating those that are not. A         characters that are in the class by enumerating those that are  not.  A
3943         class that starts with a circumflex is not an assertion: it still  con-         class  that starts with a circumflex is not an assertion; it still con-
3944         sumes  a  character  from the subject string, and therefore it fails if         sumes a character from the subject string, and therefore  it  fails  if
3945         the current pointer is at the end of the string.         the current pointer is at the end of the string.
3946    
3947         In UTF-8 mode, characters with values greater than 255 can be  included         In  UTF-8 mode, characters with values greater than 255 can be included
3948         in  a  class as a literal string of bytes, or by using the \x{ escaping         in a class as a literal string of bytes, or by using the  \x{  escaping
3949         mechanism.         mechanism.
3950    
3951         When caseless matching is set, any letters in a  class  represent  both         When  caseless  matching  is set, any letters in a class represent both
3952         their  upper  case  and lower case versions, so for example, a caseless         their upper case and lower case versions, so for  example,  a  caseless
3953         [aeiou] matches "A" as well as "a", and a caseless  [^aeiou]  does  not         [aeiou]  matches  "A"  as well as "a", and a caseless [^aeiou] does not
3954         match  "A", whereas a caseful version would. In UTF-8 mode, PCRE always         match "A", whereas a caseful version would. In UTF-8 mode, PCRE  always
3955         understands the concept of case for characters whose  values  are  less         understands  the  concept  of case for characters whose values are less
3956         than  128, so caseless matching is always possible. For characters with         than 128, so caseless matching is always possible. For characters  with
3957         higher values, the concept of case is supported  if  PCRE  is  compiled         higher  values,  the  concept  of case is supported if PCRE is compiled
3958         with  Unicode  property support, but not otherwise.  If you want to use         with Unicode property support, but not otherwise.  If you want  to  use
3959         caseless matching for characters 128 and above, you  must  ensure  that         caseless  matching  in UTF8-mode for characters 128 and above, you must
3960         PCRE  is  compiled  with Unicode property support as well as with UTF-8         ensure that PCRE is compiled with Unicode property support as  well  as
3961         support.         with UTF-8 support.
3962    
3963         Characters that might indicate line breaks are  never  treated  in  any         Characters  that  might  indicate  line breaks are never treated in any
3964         special  way  when  matching  character  classes,  whatever line-ending         special way  when  matching  character  classes,  whatever  line-ending
3965         sequence is in  use,  and  whatever  setting  of  the  PCRE_DOTALL  and         sequence  is  in  use,  and  whatever  setting  of  the PCRE_DOTALL and
3966         PCRE_MULTILINE options is used. A class such as [^a] always matches one         PCRE_MULTILINE options is used. A class such as [^a] always matches one
3967         of these characters.         of these characters.
3968    
3969         The minus (hyphen) character can be used to specify a range of  charac-         The  minus (hyphen) character can be used to specify a range of charac-
3970         ters  in  a  character  class.  For  example,  [d-m] matches any letter         ters in a character  class.  For  example,  [d-m]  matches  any  letter
3971         between d and m, inclusive. If a  minus  character  is  required  in  a         between  d  and  m,  inclusive.  If  a minus character is required in a
3972         class,  it  must  be  escaped  with a backslash or appear in a position         class, it must be escaped with a backslash  or  appear  in  a  position
3973         where it cannot be interpreted as indicating a range, typically as  the         where  it cannot be interpreted as indicating a range, typically as the
3974         first or last character in the class.         first or last character in the class.
3975    
3976         It is not possible to have the literal character "]" as the end charac-         It is not possible to have the literal character "]" as the end charac-
3977         ter of a range. A pattern such as [W-]46] is interpreted as a class  of         ter  of a range. A pattern such as [W-]46] is interpreted as a class of
3978         two  characters ("W" and "-") followed by a literal string "46]", so it         two characters ("W" and "-") followed by a literal string "46]", so  it
3979         would match "W46]" or "-46]". However, if the "]"  is  escaped  with  a         would  match  "W46]"  or  "-46]". However, if the "]" is escaped with a
3980         backslash  it is interpreted as the end of range, so [W-\]46] is inter-         backslash it is interpreted as the end of range, so [W-\]46] is  inter-
3981         preted as a class containing a range followed by two other  characters.         preted  as a class containing a range followed by two other characters.
3982         The  octal or hexadecimal representation of "]" can also be used to end         The octal or hexadecimal representation of "]" can also be used to  end
3983         a range.         a range.
3984    
3985         Ranges operate in the collating sequence of character values. They  can         Ranges  operate in the collating sequence of character values. They can
3986         also   be  used  for  characters  specified  numerically,  for  example         also  be  used  for  characters  specified  numerically,  for   example
3987         [\000-\037]. In UTF-8 mode, ranges can include characters whose  values         [\000-\037].  In UTF-8 mode, ranges can include characters whose values
3988         are greater than 255, for example [\x{100}-\x{2ff}].         are greater than 255, for example [\x{100}-\x{2ff}].
3989    
3990         If a range that includes letters is used when caseless matching is set,         If a range that includes letters is used when caseless matching is set,
3991         it matches the letters in either case. For example, [W-c] is equivalent         it matches the letters in either case. For example, [W-c] is equivalent
3992         to  [][\\^_`wxyzabc],  matched  caselessly,  and  in non-UTF-8 mode, if         to [][\\^_`wxyzabc], matched caselessly,  and  in  non-UTF-8  mode,  if
3993         character tables for a French locale are in  use,  [\xc8-\xcb]  matches         character  tables  for  a French locale are in use, [\xc8-\xcb] matches
3994         accented  E  characters in both cases. In UTF-8 mode, PCRE supports the         accented E characters in both cases. In UTF-8 mode, PCRE  supports  the
3995         concept of case for characters with values greater than 128  only  when         concept  of  case for characters with values greater than 128 only when
3996         it is compiled with Unicode property support.         it is compiled with Unicode property support.
3997    
3998         The  character types \d, \D, \p, \P, \s, \S, \w, and \W may also appear         The character types \d, \D, \h, \H, \p, \P, \s, \S, \v, \V, \w, and  \W
3999         in a character class, and add the characters that  they  match  to  the         may  also appear in a character class, and add the characters that they
4000         class. For example, [\dABCDEF] matches any hexadecimal digit. A circum-         match to the class. For example,  [\dABCDEF]  matches  any  hexadecimal
4001         flex can conveniently be used with the upper case  character  types  to         digit.  A circumflex can conveniently be used with the upper case char-
4002         specify  a  more  restricted  set of characters than the matching lower         acter types to specify a more restricted set  of  characters  than  the
4003         case type. For example, the class [^\W_] matches any letter  or  digit,         matching  lower  case  type.  For example, the class [^\W_] matches any
4004         but not underscore.         letter or digit, but not underscore.
4005    
4006         The  only  metacharacters  that are recognized in character classes are         The only metacharacters that are recognized in  character  classes  are
4007         backslash, hyphen (only where it can be  interpreted  as  specifying  a         backslash,  hyphen  (only  where  it can be interpreted as specifying a
4008         range),  circumflex  (only  at the start), opening square bracket (only         range), circumflex (only at the start), opening  square  bracket  (only
4009         when it can be interpreted as introducing a POSIX class name - see  the         when  it can be interpreted as introducing a POSIX class name - see the
4010         next  section),  and  the  terminating closing square bracket. However,         next section), and the terminating  closing  square  bracket.  However,
4011         escaping other non-alphanumeric characters does no harm.         escaping other non-alphanumeric characters does no harm.
4012    
4013    
4014  POSIX CHARACTER CLASSES  POSIX CHARACTER CLASSES
4015    
4016         Perl supports the POSIX notation for character classes. This uses names         Perl supports the POSIX notation for character classes. This uses names
4017         enclosed  by  [: and :] within the enclosing square brackets. PCRE also         enclosed by [: and :] within the enclosing square brackets.  PCRE  also
4018         supports this notation. For example,         supports this notation. For example,
4019    
4020           [01[:alpha:]%]           [01[:alpha:]%]
4021    
4022         matches "0", "1", any alphabetic character, or "%". The supported class         matches "0", "1", any alphabetic character, or "%". The supported class
4023         names are         names are:
4024    
4025           alnum    letters and digits           alnum    letters and digits
4026           alpha    letters           alpha    letters
# Line 3679  POSIX CHARACTER CLASSES Line 4031  POSIX CHARACTER CLASSES
4031           graph    printing characters, excluding space           graph    printing characters, excluding space
4032           lower    lower case letters           lower    lower case letters
4033           print    printing characters, including space           print    printing characters, including space
4034           punct    printing characters, excluding letters and digits           punct    printing characters, excluding letters and digits and space
4035           space    white space (not quite the same as \s)           space    white space (not quite the same as \s)
4036           upper    upper case letters           upper    upper case letters
4037           word     "word" characters (same as \w)           word     "word" characters (same as \w)
4038           xdigit   hexadecimal digits           xdigit   hexadecimal digits
4039    
4040         The  "space" characters are HT (9), LF (10), VT (11), FF (12), CR (13),         The "space" characters are HT (9), LF (10), VT (11), FF (12), CR  (13),
4041         and space (32). Notice that this list includes the VT  character  (code         and  space  (32). Notice that this list includes the VT character (code
4042         11). This makes "space" different to \s, which does not include VT (for         11). This makes "space" different to \s, which does not include VT (for
4043         Perl compatibility).         Perl compatibility).
4044    
4045         The name "word" is a Perl extension, and "blank"  is  a  GNU  extension         The  name  "word"  is  a Perl extension, and "blank" is a GNU extension
4046         from  Perl  5.8. Another Perl extension is negation, which is indicated         from Perl 5.8. Another Perl extension is negation, which  is  indicated
4047         by a ^ character after the colon. For example,         by a ^ character after the colon. For example,
4048    
4049           [12[:^digit:]]           [12[:^digit:]]
4050    
4051         matches "1", "2", or any non-digit. PCRE (and Perl) also recognize  the         matches  "1", "2", or any non-digit. PCRE (and Perl) also recognize the
4052         POSIX syntax [.ch.] and [=ch=] where "ch" is a "collating element", but         POSIX syntax [.ch.] and [=ch=] where "ch" is a "collating element", but
4053         these are not supported, and an error is given if they are encountered.         these are not supported, and an error is given if they are encountered.
4054    
4055         In UTF-8 mode, characters with values greater than 128 do not match any         By  default,  in UTF-8 mode, characters with values greater than 128 do
4056         of the POSIX character classes.         not match any of the POSIX character classes. However, if the  PCRE_UCP
4057           option  is passed to pcre_compile(), some of the classes are changed so
4058           that Unicode character properties are used. This is achieved by replac-
4059           ing the POSIX classes by other sequences, as follows:
4060    
4061             [:alnum:]  becomes  \p{Xan}
4062             [:alpha:]  becomes  \p{L}
4063             [:blank:]  becomes  \h
4064             [:digit:]  becomes  \p{Nd}
4065             [:lower:]  becomes  \p{Ll}
4066             [:space:]  becomes  \p{Xps}
4067             [:upper:]  becomes  \p{Lu}
4068             [:word:]   becomes  \p{Xwd}
4069    
4070           Negated  versions,  such  as [:^alpha:] use \P instead of \p. The other
4071           POSIX classes are unchanged, and match only characters with code points
4072           less than 128.
4073    
4074    
4075  VERTICAL BAR  VERTICAL BAR
4076    
4077         Vertical bar characters are used to separate alternative patterns.  For         Vertical  bar characters are used to separate alternative patterns. For
4078         example, the pattern         example, the pattern
4079    
4080           gilbert|sullivan           gilbert|sullivan
4081    
4082         matches  either "gilbert" or "sullivan". Any number of alternatives may         matches either "gilbert" or "sullivan". Any number of alternatives  may
4083         appear, and an empty  alternative  is  permitted  (matching  the  empty         appear,  and  an  empty  alternative  is  permitted (matching the empty
4084         string). The matching process tries each alternative in turn, from left         string). The matching process tries each alternative in turn, from left
4085         to right, and the first one that succeeds is used. If the  alternatives         to  right, and the first one that succeeds is used. If the alternatives
4086         are  within a subpattern (defined below), "succeeds" means matching the         are within a subpattern (defined below), "succeeds" means matching  the
4087         rest of the main pattern as well as the alternative in the  subpattern.         rest of the main pattern as well as the alternative in the subpattern.
4088    
4089    
4090  INTERNAL OPTION SETTING  INTERNAL OPTION SETTING
# Line 3742  INTERNAL OPTION SETTING Line 4110  INTERNAL OPTION SETTING
4110         can be changed in the same way as the Perl-compatible options by  using         can be changed in the same way as the Perl-compatible options by  using
4111         the characters J, U and X respectively.         the characters J, U and X respectively.
4112    
4113         When  an option change occurs at top level (that is, not inside subpat-         When  one  of  these  option  changes occurs at top level (that is, not
4114         tern parentheses), the change applies to the remainder of  the  pattern         inside subpattern parentheses), the change applies to the remainder  of
4115         that follows.  If the change is placed right at the start of a pattern,         the pattern that follows. If the change is placed right at the start of
4116         PCRE extracts it into the global options (and it will therefore show up         a pattern, PCRE extracts it into the global options (and it will there-
4117         in data extracted by the pcre_fullinfo() function).         fore show up in data extracted by the pcre_fullinfo() function).
4118    
4119         An  option  change  within a subpattern (see below for a description of         An  option  change  within a subpattern (see below for a description of
4120         subpatterns) affects only that part of the current pattern that follows         subpatterns) affects only that part of the current pattern that follows
# Line 3769  INTERNAL OPTION SETTING Line 4137  INTERNAL OPTION SETTING
4137    
4138         Note: There are other PCRE-specific options that  can  be  set  by  the         Note: There are other PCRE-specific options that  can  be  set  by  the
4139         application  when  the  compile  or match functions are called. In some         application  when  the  compile  or match functions are called. In some
4140         cases the pattern can contain special  leading  sequences  to  override         cases the pattern can contain special leading sequences such as (*CRLF)
4141         what  the  application  has set or what has been defaulted. Details are         to  override  what  the application has set or what has been defaulted.
4142         given in the section entitled "Newline sequences" above.         Details are given in the section entitled  "Newline  sequences"  above.
4143           There  are  also  the  (*UTF8) and (*UCP) leading sequences that can be
4144           used to set UTF-8 and Unicode property modes; they  are  equivalent  to
4145           setting the PCRE_UTF8 and the PCRE_UCP options, respectively.
4146    
4147    
4148  SUBPATTERNS  SUBPATTERNS
# Line 3783  SUBPATTERNS Line 4154  SUBPATTERNS
4154    
4155           cat(aract|erpillar|)           cat(aract|erpillar|)
4156    
4157         matches  one  of the words "cat", "cataract", or "caterpillar". Without         matches one of the words "cat", "cataract", or  "caterpillar".  Without
4158         the parentheses, it would match  "cataract",  "erpillar"  or  an  empty         the  parentheses,  it  would  match  "cataract", "erpillar" or an empty
4159         string.         string.
4160    
4161         2.  It  sets  up  the  subpattern as a capturing subpattern. This means         2. It sets up the subpattern as  a  capturing  subpattern.  This  means
4162         that, when the whole pattern  matches,  that  portion  of  the  subject         that,  when  the  whole  pattern  matches,  that portion of the subject
4163         string that matched the subpattern is passed back to the caller via the         string that matched the subpattern is passed back to the caller via the
4164         ovector argument of pcre_exec(). Opening parentheses are  counted  from         ovector  argument  of pcre_exec(). Opening parentheses are counted from
4165         left  to  right  (starting  from 1) to obtain numbers for the capturing         left to right (starting from 1) to obtain  numbers  for  the  capturing
4166         subpatterns.         subpatterns.
4167    
4168         For example, if the string "the red king" is matched against  the  pat-         For  example,  if the string "the red king" is matched against the pat-
4169         tern         tern
4170    
4171           the ((red|white) (king|queen))           the ((red|white) (king|queen))
# Line 3802  SUBPATTERNS Line 4173  SUBPATTERNS
4173         the captured substrings are "red king", "red", and "king", and are num-         the captured substrings are "red king", "red", and "king", and are num-
4174         bered 1, 2, and 3, respectively.         bered 1, 2, and 3, respectively.
4175    
4176         The fact that plain parentheses fulfil  two  functions  is  not  always         The  fact  that  plain  parentheses  fulfil two functions is not always
4177         helpful.   There are often times when a grouping subpattern is required         helpful.  There are often times when a grouping subpattern is  required
4178         without a capturing requirement. If an opening parenthesis is  followed         without  a capturing requirement. If an opening parenthesis is followed
4179         by  a question mark and a colon, the subpattern does not do any captur-         by a question mark and a colon, the subpattern does not do any  captur-
4180         ing, and is not counted when computing the  number  of  any  subsequent         ing,  and  is  not  counted when computing the number of any subsequent
4181         capturing  subpatterns. For example, if the string "the white queen" is         capturing subpatterns. For example, if the string "the white queen"  is
4182         matched against the pattern         matched against the pattern
4183    
4184           the ((?:red|white) (king|queen))           the ((?:red|white) (king|queen))
# Line 3815  SUBPATTERNS Line 4186  SUBPATTERNS
4186         the captured substrings are "white queen" and "queen", and are numbered         the captured substrings are "white queen" and "queen", and are numbered
4187         1 and 2. The maximum number of capturing subpatterns is 65535.         1 and 2. The maximum number of capturing subpatterns is 65535.
4188    
4189         As  a  convenient shorthand, if any option settings are required at the         As a convenient shorthand, if any option settings are required  at  the
4190         start of a non-capturing subpattern,  the  option  letters  may  appear         start  of  a  non-capturing  subpattern,  the option letters may appear
4191         between the "?" and the ":". Thus the two patterns         between the "?" and the ":". Thus the two patterns
4192    
4193           (?i:saturday|sunday)           (?i:saturday|sunday)
4194           (?:(?i)saturday|sunday)           (?:(?i)saturday|sunday)
4195    
4196         match exactly the same set of strings. Because alternative branches are         match exactly the same set of strings. Because alternative branches are
4197         tried from left to right, and options are not reset until  the  end  of         tried  from  left  to right, and options are not reset until the end of
4198         the  subpattern is reached, an option setting in one branch does affect         the subpattern is reached, an option setting in one branch does  affect
4199         subsequent branches, so the above patterns match "SUNDAY"  as  well  as         subsequent  branches,  so  the above patterns match "SUNDAY" as well as
4200         "Saturday".         "Saturday".
4201    
4202    
4203  DUPLICATE SUBPATTERN NUMBERS  DUPLICATE SUBPATTERN NUMBERS
4204    
4205         Perl 5.10 introduced a feature whereby each alternative in a subpattern         Perl 5.10 introduced a feature whereby each alternative in a subpattern
4206         uses the same numbers for its capturing parentheses. Such a  subpattern         uses  the same numbers for its capturing parentheses. Such a subpattern
4207         starts  with (?| and is itself a non-capturing subpattern. For example,         starts with (?| and is itself a non-capturing subpattern. For  example,
4208         consider this pattern:         consider this pattern:
4209    
4210           (?|(Sat)ur|(Sun))day           (?|(Sat)ur|(Sun))day
4211    
4212         Because the two alternatives are inside a (?| group, both sets of  cap-         Because  the two alternatives are inside a (?| group, both sets of cap-
4213         turing  parentheses  are  numbered one. Thus, when the pattern matches,         turing parentheses are numbered one. Thus, when  the  pattern  matches,
4214         you can look at captured substring number  one,  whichever  alternative         you  can  look  at captured substring number one, whichever alternative
4215         matched.  This  construct  is useful when you want to capture part, but         matched. This construct is useful when you want to  capture  part,  but
4216         not all, of one of a number of alternatives. Inside a (?| group, paren-         not all, of one of a number of alternatives. Inside a (?| group, paren-
4217         theses  are  numbered as usual, but the number is reset at the start of         theses are numbered as usual, but the number is reset at the  start  of
4218         each branch. The numbers of any capturing buffers that follow the  sub-         each  branch. The numbers of any capturing buffers that follow the sub-
4219         pattern  start after the highest number used in any branch. The follow-         pattern start after the highest number used in any branch. The  follow-
4220         ing example is taken from the Perl documentation.  The  numbers  under-         ing  example  is taken from the Perl documentation.  The numbers under-
4221         neath show in which buffer the captured content will be stored.         neath show in which buffer the captured content will be stored.
4222    
4223           # before  ---------------branch-reset----------- after           # before  ---------------branch-reset----------- after
4224           / ( a )  (?| x ( y ) z | (p (q) r) | (t) u (v) ) ( z ) /x           / ( a )  (?| x ( y ) z | (p (q) r) | (t) u (v) ) ( z ) /x
4225           # 1            2         2  3        2     3     4           # 1            2         2  3        2     3     4
4226    
4227         A  backreference  or  a  recursive call to a numbered subpattern always         A back reference to a numbered subpattern uses the  most  recent  value
4228         refers to the first one in the pattern with the given number.         that  is  set  for that number by any subpattern. The following pattern
4229           matches "abcabc" or "defdef":
4230    
4231             /(?|(abc)|(def))\1/
4232    
4233           In contrast, a recursive or "subroutine" call to a numbered  subpattern
4234           always  refers  to  the first one in the pattern with the given number.
4235           The following pattern matches "abcabc" or "defabc":
4236    
4237             /(?|(abc)|(def))(?1)/
4238    
4239           If a condition test for a subpattern's having matched refers to a  non-
4240           unique  number, the test is true if any of the subpatterns of that num-
4241           ber have matched.
4242    
4243         An alternative approach to using this "branch reset" feature is to  use         An alternative approach to using this "branch reset" feature is to  use
4244         duplicate named subpatterns, as described in the next section.         duplicate named subpatterns, as described in the next section.
# Line 3869  NAMED SUBPATTERNS Line 4253  NAMED SUBPATTERNS
4253         patterns. This feature was not added to Perl until release 5.10. Python         patterns. This feature was not added to Perl until release 5.10. Python
4254         had the feature earlier, and PCRE introduced it at release  4.0,  using         had the feature earlier, and PCRE introduced it at release  4.0,  using
4255         the  Python syntax. PCRE now supports both the Perl and the Python syn-         the  Python syntax. PCRE now supports both the Perl and the Python syn-
4256         tax.         tax. Perl allows identically numbered  subpatterns  to  have  different
4257           names, but PCRE does not.
4258    
4259         In PCRE, a subpattern can be named in one of three  ways:  (?<name>...)         In  PCRE,  a subpattern can be named in one of three ways: (?<name>...)
4260         or  (?'name'...)  as in Perl, or (?P<name>...) as in Python. References         or (?'name'...) as in Perl, or (?P<name>...) as in  Python.  References
4261         to capturing parentheses from other parts of the pattern, such as back-         to  capturing parentheses from other parts of the pattern, such as back
4262         references,  recursion,  and conditions, can be made by name as well as         references, recursion, and conditions, can be made by name as  well  as
4263         by number.         by number.
4264    
4265         Names consist of up to  32  alphanumeric  characters  and  underscores.         Names  consist  of  up  to  32 alphanumeric characters and underscores.
4266         Named  capturing  parentheses  are  still  allocated numbers as well as         Named capturing parentheses are still  allocated  numbers  as  well  as
4267         names, exactly as if the names were not present. The PCRE API  provides         names,  exactly as if the names were not present. The PCRE API provides
4268         function calls for extracting the name-to-number translation table from         function calls for extracting the name-to-number translation table from
4269         a compiled pattern. There is also a convenience function for extracting         a compiled pattern. There is also a convenience function for extracting
4270         a captured substring by name.         a captured substring by name.
4271    
4272         By  default, a name must be unique within a pattern, but it is possible         By default, a name must be unique within a pattern, but it is  possible
4273         to relax this constraint by setting the PCRE_DUPNAMES option at compile         to relax this constraint by setting the PCRE_DUPNAMES option at compile
4274         time.  This  can  be useful for patterns where only one instance of the         time. (Duplicate names are also always permitted for  subpatterns  with
4275         named parentheses can match. Suppose you want to match the  name  of  a         the  same  number, set up as described in the previous section.) Dupli-
4276         weekday,  either as a 3-letter abbreviation or as the full name, and in         cate names can be useful for patterns where only one  instance  of  the
4277           named  parentheses  can  match. Suppose you want to match the name of a
4278           weekday, either as a 3-letter abbreviation or as the full name, and  in
4279         both cases you want to extract the abbreviation. This pattern (ignoring         both cases you want to extract the abbreviation. This pattern (ignoring
4280         the line breaks) does the job:         the line breaks) does the job:
4281    
# Line 3898  NAMED SUBPATTERNS Line 4285  NAMED SUBPATTERNS
4285           (?<DN>Thu)(?:rsday)?|           (?<DN>Thu)(?:rsday)?|
4286           (?<DN>Sat)(?:urday)?           (?<DN>Sat)(?:urday)?
4287    
4288         There  are  five capturing substrings, but only one is ever set after a         There are five capturing substrings, but only one is ever set  after  a
4289         match.  (An alternative way of solving this problem is to use a "branch         match.  (An alternative way of solving this problem is to use a "branch
4290         reset" subpattern, as described in the previous section.)         reset" subpattern, as described in the previous section.)
4291    
4292         The  convenience  function  for extracting the data by name returns the         The convenience function for extracting the data by  name  returns  the
4293         substring for the first (and in this example, the only)  subpattern  of         substring  for  the first (and in this example, the only) subpattern of
4294         that  name  that  matched.  This saves searching to find which numbered         that name that matched. This saves searching  to  find  which  numbered
4295         subpattern it was. If you make a reference to a non-unique  named  sub-         subpattern it was.
4296         pattern  from elsewhere in the pattern, the one that corresponds to the  
4297         lowest number is used. For further details of the interfaces  for  han-         If  you  make  a  back  reference to a non-unique named subpattern from
4298         dling named subpatterns, see the pcreapi documentation.         elsewhere in the pattern, the one that corresponds to the first  occur-
4299           rence of the name is used. In the absence of duplicate numbers (see the
4300           previous section) this is the one with the lowest number. If you use  a
4301           named  reference  in a condition test (see the section about conditions
4302           below), either to check whether a subpattern has matched, or  to  check
4303           for  recursion,  all  subpatterns with the same name are tested. If the
4304           condition is true for any one of them, the overall condition  is  true.
4305           This is the same behaviour as testing by number. For further details of
4306           the interfaces for handling named subpatterns, see the pcreapi documen-
4307           tation.
4308    
4309           Warning: You cannot use different names to distinguish between two sub-
4310           patterns with the same number because PCRE uses only the  numbers  when
4311           matching. For this reason, an error is given at compile time if differ-
4312           ent names are given to subpatterns with the same number.  However,  you
4313           can  give  the same name to subpatterns with the same number, even when
4314           PCRE_DUPNAMES is not set.
4315    
4316    
4317  REPETITION  REPETITION
4318    
4319         Repetition  is  specified  by  quantifiers, which can follow any of the         Repetition is specified by quantifiers, which can  follow  any  of  the
4320         following items:         following items:
4321    
4322           a literal data character           a literal data character
# Line 3925  REPETITION Line 4328  REPETITION
4328           a character class           a character class
4329           a back reference (see next section)           a back reference (see next section)
4330           a parenthesized subpattern (unless it is an assertion)           a parenthesized subpattern (unless it is an assertion)
4331             a recursive or "subroutine" call to a subpattern
4332    
4333         The general repetition quantifier specifies a minimum and maximum  num-         The  general repetition quantifier specifies a minimum and maximum num-
4334         ber  of  permitted matches, by giving the two numbers in curly brackets         ber of permitted matches, by giving the two numbers in  curly  brackets
4335         (braces), separated by a comma. The numbers must be  less  than  65536,         (braces),  separated  by  a comma. The numbers must be less than 65536,
4336         and the first must be less than or equal to the second. For example:         and the first must be less than or equal to the second. For example:
4337    
4338           z{2,4}           z{2,4}
4339    
4340         matches  "zz",  "zzz",  or  "zzzz". A closing brace on its own is not a         matches "zz", "zzz", or "zzzz". A closing brace on its  own  is  not  a
4341         special character. If the second number is omitted, but  the  comma  is         special  character.  If  the second number is omitted, but the comma is
4342         present,  there  is  no upper limit; if the second number and the comma         present, there is no upper limit; if the second number  and  the  comma
4343         are both omitted, the quantifier specifies an exact number of  required         are  both omitted, the quantifier specifies an exact number of required
4344         matches. Thus         matches. Thus
4345    
4346           [aeiou]{3,}           [aeiou]{3,}
# Line 3945  REPETITION Line 4349  REPETITION
4349    
4350           \d{8}           \d{8}
4351    
4352         matches  exactly  8  digits. An opening curly bracket that appears in a         matches exactly 8 digits. An opening curly bracket that  appears  in  a
4353         position where a quantifier is not allowed, or one that does not  match         position  where a quantifier is not allowed, or one that does not match
4354         the  syntax of a quantifier, is taken as a literal character. For exam-         the syntax of a quantifier, is taken as a literal character. For  exam-
4355         ple, {,6} is not a quantifier, but a literal string of four characters.         ple, {,6} is not a quantifier, but a literal string of four characters.
4356    
4357         In  UTF-8  mode,  quantifiers  apply to UTF-8 characters rather than to         In  UTF-8  mode,  quantifiers  apply to UTF-8 characters rather than to
# Line 3958  REPETITION Line 4362  REPETITION
4362         may be of different lengths).         may be of different lengths).
4363    
4364         The quantifier {0} is permitted, causing the expression to behave as if         The quantifier {0} is permitted, causing the expression to behave as if
4365         the previous item and the quantifier were not present.         the previous item and the quantifier were not present. This may be use-
4366           ful for subpatterns that are referenced as subroutines  from  elsewhere
4367           in the pattern. Items other than subpatterns that have a {0} quantifier
4368           are omitted from the compiled pattern.
4369    
4370         For  convenience, the three most common quantifiers have single-charac-         For convenience, the three most common quantifiers have  single-charac-
4371         ter abbreviations:         ter abbreviations:
4372    
4373           *    is equivalent to {0,}           *    is equivalent to {0,}
4374           +    is equivalent to {1,}           +    is equivalent to {1,}
4375           ?    is equivalent to {0,1}           ?    is equivalent to {0,1}
4376    
4377         It is possible to construct infinite loops by  following  a  subpattern         It  is  possible  to construct infinite loops by following a subpattern
4378         that can match no characters with a quantifier that has no upper limit,         that can match no characters with a quantifier that has no upper limit,
4379         for example:         for example:
4380    
4381           (a?)*           (a?)*
4382    
4383         Earlier versions of Perl and PCRE used to give an error at compile time         Earlier versions of Perl and PCRE used to give an error at compile time
4384         for  such  patterns. However, because there are cases where this can be         for such patterns. However, because there are cases where this  can  be
4385         useful, such patterns are now accepted, but if any  repetition  of  the         useful,  such  patterns  are now accepted, but if any repetition of the
4386         subpattern  does in fact match no characters, the loop is forcibly bro-         subpattern does in fact match no characters, the loop is forcibly  bro-
4387         ken.         ken.
4388    
4389         By default, the quantifiers are "greedy", that is, they match  as  much         By  default,  the quantifiers are "greedy", that is, they match as much
4390         as  possible  (up  to  the  maximum number of permitted times), without         as possible (up to the maximum  number  of  permitted  times),  without
4391         causing the rest of the pattern to fail. The classic example  of  where         causing  the  rest of the pattern to fail. The classic example of where
4392         this gives problems is in trying to match comments in C programs. These         this gives problems is in trying to match comments in C programs. These
4393         appear between /* and */ and within the comment,  individual  *  and  /         appear  between  /*  and  */ and within the comment, individual * and /
4394         characters  may  appear. An attempt to match C comments by applying the         characters may appear. An attempt to match C comments by  applying  the
4395         pattern         pattern
4396    
4397           /\*.*\*/           /\*.*\*/
# Line 3993  REPETITION Line 4400  REPETITION
4400    
4401           /* first comment */  not comment  /* second comment */           /* first comment */  not comment  /* second comment */
4402    
4403         fails, because it matches the entire string owing to the greediness  of         fails,  because it matches the entire string owing to the greediness of
4404         the .*  item.         the .*  item.
4405    
4406         However,  if  a quantifier is followed by a question mark, it ceases to         However, if a quantifier is followed by a question mark, it  ceases  to
4407         be greedy, and instead matches the minimum number of times possible, so         be greedy, and instead matches the minimum number of times possible, so
4408         the pattern         the pattern
4409    
4410           /\*.*?\*/           /\*.*?\*/
4411    
4412         does  the  right  thing with the C comments. The meaning of the various         does the right thing with the C comments. The meaning  of  the  various
4413         quantifiers is not otherwise changed,  just  the  preferred  number  of         quantifiers  is  not  otherwise  changed,  just the preferred number of
4414         matches.   Do  not  confuse this use of question mark with its use as a         matches.  Do not confuse this use of question mark with its  use  as  a
4415         quantifier in its own right. Because it has two uses, it can  sometimes         quantifier  in its own right. Because it has two uses, it can sometimes
4416         appear doubled, as in         appear doubled, as in
4417    
4418           \d??\d           \d??\d
# Line 4013  REPETITION Line 4420  REPETITION
4420         which matches one digit by preference, but can match two if that is the         which matches one digit by preference, but can match two if that is the
4421         only way the rest of the pattern matches.         only way the rest of the pattern matches.
4422    
4423         If the PCRE_UNGREEDY option is set (an option that is not available  in         If  the PCRE_UNGREEDY option is set (an option that is not available in
4424         Perl),  the  quantifiers are not greedy by default, but individual ones         Perl), the quantifiers are not greedy by default, but  individual  ones
4425         can be made greedy by following them with a  question  mark.  In  other         can  be  made  greedy  by following them with a question mark. In other
4426         words, it inverts the default behaviour.         words, it inverts the default behaviour.
4427    
4428         When  a  parenthesized  subpattern  is quantified with a minimum repeat         When a parenthesized subpattern is quantified  with  a  minimum  repeat
4429         count that is greater than 1 or with a limited maximum, more memory  is         count  that is greater than 1 or with a limited maximum, more memory is
4430         required  for  the  compiled  pattern, in proportion to the size of the         required for the compiled pattern, in proportion to  the  size  of  the
4431         minimum or maximum.         minimum or maximum.
4432    
4433         If a pattern starts with .* or .{0,} and the PCRE_DOTALL option (equiv-         If a pattern starts with .* or .{0,} and the PCRE_DOTALL option (equiv-
4434         alent  to  Perl's  /s) is set, thus allowing the dot to match newlines,         alent to Perl's /s) is set, thus allowing the dot  to  match  newlines,
4435         the pattern is implicitly anchored, because whatever  follows  will  be         the  pattern  is  implicitly anchored, because whatever follows will be
4436         tried  against every character position in the subject string, so there         tried against every character position in the subject string, so  there
4437         is no point in retrying the overall match at  any  position  after  the         is  no  point  in  retrying the overall match at any position after the
4438         first.  PCRE  normally treats such a pattern as though it were preceded         first. PCRE normally treats such a pattern as though it  were  preceded
4439         by \A.         by \A.
4440    
4441         In cases where it is known that the subject  string  contains  no  new-         In  cases  where  it  is known that the subject string contains no new-
4442         lines,  it  is  worth setting PCRE_DOTALL in order to obtain this opti-         lines, it is worth setting PCRE_DOTALL in order to  obtain  this  opti-
4443         mization, or alternatively using ^ to indicate anchoring explicitly.         mization, or alternatively using ^ to indicate anchoring explicitly.
4444    
4445         However, there is one situation where the optimization cannot be  used.         However,  there is one situation where the optimization cannot be used.
4446         When  .*   is  inside  capturing  parentheses that are the subject of a         When .*  is inside capturing parentheses that are the subject of a back
4447         backreference elsewhere in the pattern, a match at the start  may  fail         reference elsewhere in the pattern, a match at the start may fail where
4448         where a later one succeeds. Consider, for example:         a later one succeeds. Consider, for example:
4449    
4450           (.*)abc\1           (.*)abc\1
4451    
4452         If  the subject is "xyz123abc123" the match point is the fourth charac-         If the subject is "xyz123abc123" the match point is the fourth  charac-
4453         ter. For this reason, such a pattern is not implicitly anchored.         ter. For this reason, such a pattern is not implicitly anchored.
4454    
4455         When a capturing subpattern is repeated, the value captured is the sub-         When a capturing subpattern is repeated, the value captured is the sub-
# Line 4051  REPETITION Line 4458  REPETITION
4458           (tweedle[dume]{3}\s*)+           (tweedle[dume]{3}\s*)+
4459    
4460         has matched "tweedledum tweedledee" the value of the captured substring         has matched "tweedledum tweedledee" the value of the captured substring
4461         is "tweedledee". However, if there are  nested  capturing  subpatterns,         is  "tweedledee".  However,  if there are nested capturing subpatterns,
4462         the  corresponding captured values may have been set in previous itera-         the corresponding captured values may have been set in previous  itera-
4463         tions. For example, after         tions. For example, after
4464    
4465           /(a|(b))+/           /(a|(b))+/
# Line 4062  REPETITION Line 4469  REPETITION
4469    
4470  ATOMIC GROUPING AND POSSESSIVE QUANTIFIERS  ATOMIC GROUPING AND POSSESSIVE QUANTIFIERS
4471    
4472         With both maximizing ("greedy") and minimizing ("ungreedy"  or  "lazy")         With  both  maximizing ("greedy") and minimizing ("ungreedy" or "lazy")
4473         repetition,  failure  of what follows normally causes the repeated item         repetition, failure of what follows normally causes the  repeated  item
4474         to be re-evaluated to see if a different number of repeats  allows  the         to  be  re-evaluated to see if a different number of repeats allows the
4475         rest  of  the pattern to match. Sometimes it is useful to prevent this,         rest of the pattern to match. Sometimes it is useful to  prevent  this,
4476         either to change the nature of the match, or to cause it  fail  earlier         either  to  change the nature of the match, or to cause it fail earlier
4477         than  it otherwise might, when the author of the pattern knows there is         than it otherwise might, when the author of the pattern knows there  is
4478         no point in carrying on.         no point in carrying on.
4479    
4480         Consider, for example, the pattern \d+foo when applied to  the  subject         Consider,  for  example, the pattern \d+foo when applied to the subject
4481         line         line
4482    
4483           123456bar           123456bar
4484    
4485         After matching all 6 digits and then failing to match "foo", the normal         After matching all 6 digits and then failing to match "foo", the normal
4486         action of the matcher is to try again with only 5 digits  matching  the         action  of  the matcher is to try again with only 5 digits matching the
4487         \d+  item,  and  then  with  4,  and  so on, before ultimately failing.         \d+ item, and then with  4,  and  so  on,  before  ultimately  failing.
4488         "Atomic grouping" (a term taken from Jeffrey  Friedl's  book)  provides         "Atomic  grouping"  (a  term taken from Jeffrey Friedl's book) provides
4489         the  means for specifying that once a subpattern has matched, it is not         the means for specifying that once a subpattern has matched, it is  not
4490         to be re-evaluated in this way.         to be re-evaluated in this way.
4491    
4492         If we use atomic grouping for the previous example, the  matcher  gives         If  we  use atomic grouping for the previous example, the matcher gives
4493         up  immediately  on failing to match "foo" the first time. The notation         up immediately on failing to match "foo" the first time.  The  notation
4494         is a kind of special parenthesis, starting with (?> as in this example:         is a kind of special parenthesis, starting with (?> as in this example:
4495    
4496           (?>\d+)foo           (?>\d+)foo
# Line 4161  ATOMIC GROUPING AND POSSESSIVE QUANTIFIE Line 4568  ATOMIC GROUPING AND POSSESSIVE QUANTIFIE
4568    
4569           ((?>\D+)|<\d+>)*[!?]           ((?>\D+)|<\d+>)*[!?]
4570    
4571         sequences of non-digits cannot be broken, and failure happens  quickly.         sequences of non-digits cannot be broken, and failure happens quickly.
4572    
4573    
4574  BACK REFERENCES  BACK REFERENCES
4575    
4576         Outside a character class, a backslash followed by a digit greater than         Outside a character class, a backslash followed by a digit greater than
4577         0 (and possibly further digits) is a back reference to a capturing sub-         0 (and possibly further digits) is a back reference to a capturing sub-
4578         pattern  earlier  (that is, to its left) in the pattern, provided there         pattern earlier (that is, to its left) in the pattern,  provided  there
4579         have been that many previous capturing left parentheses.         have been that many previous capturing left parentheses.
4580    
4581         However, if the decimal number following the backslash is less than 10,         However, if the decimal number following the backslash is less than 10,
4582         it  is  always  taken  as a back reference, and causes an error only if         it is always taken as a back reference, and causes  an  error  only  if
4583         there are not that many capturing left parentheses in the  entire  pat-         there  are  not that many capturing left parentheses in the entire pat-
4584         tern.  In  other words, the parentheses that are referenced need not be         tern. In other words, the parentheses that are referenced need  not  be
4585         to the left of the reference for numbers less than 10. A "forward  back         to  the left of the reference for numbers less than 10. A "forward back
4586         reference"  of  this  type can make sense when a repetition is involved         reference" of this type can make sense when a  repetition  is  involved
4587         and the subpattern to the right has participated in an  earlier  itera-         and  the  subpattern to the right has participated in an earlier itera-
4588         tion.         tion.
4589    
4590         It  is  not  possible to have a numerical "forward back reference" to a         It is not possible to have a numerical "forward back  reference"  to  a
4591         subpattern whose number is 10 or  more  using  this  syntax  because  a         subpattern  whose  number  is  10  or  more using this syntax because a
4592         sequence  such  as  \50 is interpreted as a character defined in octal.         sequence such as \50 is interpreted as a character  defined  in  octal.
4593         See the subsection entitled "Non-printing characters" above for further         See the subsection entitled "Non-printing characters" above for further
4594         details  of  the  handling of digits following a backslash. There is no         details of the handling of digits following a backslash.  There  is  no
4595         such problem when named parentheses are used. A back reference  to  any         such  problem  when named parentheses are used. A back reference to any
4596