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# 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.  There is also some support for certain .NET and Oniguruma syn-         tax,  there  is  some  support for one or two .NET and Oniguruma syntax
25         tax items, and there is an option for  requesting  some  minor  changes         items, and there is an option for requesting some  minor  changes  that
26         that give better JavaScript compatibility.         give better JavaScript compatibility.
27    
28         The  current  implementation of PCRE (release 7.x) corresponds approxi-         The  current implementation of PCRE corresponds approximately with Perl
29         mately with Perl 5.10, including support for UTF-8 encoded strings  and         5.12, including support for UTF-8 encoded strings and  Unicode  general
30         Unicode general category properties. However, UTF-8 and Unicode support         category  properties.  However,  UTF-8  and  Unicode  support has to be
31         has to be explicitly enabled; it is not the default. The Unicode tables         explicitly enabled; it is not the default. The  Unicode  tables  corre-
32         correspond to Unicode release 5.0.0.         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 54  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 71  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 81  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 136  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 in particular
230         sense of, say, "digit", you must use Unicode  property  tests  such  as         that this applies to \b and \B, because they are defined in terms of \w
231         \p{Nd}.         and \W. If you really want to test for a wider sense of, say,  "digit",
232           you  can  use  explicit Unicode property tests such as \p{Nd}. Alterna-
233           tively, if you set the PCRE_UCP option,  the  way  that  the  character
234           escapes  work  is changed so that Unicode properties are used to deter-
235           mine which characters match. There are more details in the  section  on
236           generic character 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 horizontal and  vertical  whitespace  matching  escapes
242         escapes (\h, \H, \v, and \V) do match all the appropriate Unicode char-         (\h,  \H,  \v, and \V) do match all the appropriate Unicode characters,
243         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.
247         Even when Unicode property support is available, PCRE  still  uses  its         Even when Unicode property support is available, PCRE  still  uses  its
248         own  character  tables when checking the case of low-valued characters,         own  character  tables when checking the case of low-valued characters,
249         so as not to degrade performance.  The Unicode property information  is         so as not to degrade performance.  The Unicode property information  is
250         used only for characters with higher values. Even when Unicode property         used only for characters with higher values. Furthermore, PCRE supports
251         support is available, PCRE supports case-insensitive matching only when         case-insensitive matching only  when  there  is  a  one-to-one  mapping
252         there  is  a  one-to-one  mapping between a letter's cases. There are a         between  a letter's cases. There are a small number of many-to-one map-
253         small number of many-to-one mappings in Unicode;  these  are  not  sup-         pings in Unicode; these are not supported by PCRE.
        ported by PCRE.  
254    
255    
256  AUTHOR  AUTHOR
# Line 251  AUTHOR Line 259  AUTHOR
259         University Computing Service         University Computing Service
260         Cambridge CB2 3QH, England.         Cambridge CB2 3QH, England.
261    
262         Putting  an actual email address here seems to have been a spam magnet,         Putting an actual email address here seems to have been a spam  magnet,
263         so I've taken it away. If you want to email me, use  my  two  initials,         so  I've  taken  it away. If you want to email me, use my two initials,
264         followed by the two digits 10, at the domain cam.ac.uk.         followed by the two digits 10, at the domain cam.ac.uk.
265    
266    
267  REVISION  REVISION
268    
269         Last updated: 12 April 2008         Last updated: 13 November 2010
270         Copyright (c) 1997-2008 University of Cambridge.         Copyright (c) 1997-2010 University of Cambridge.
271  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
272    
273    
274  PCREBUILD(3)                                                      PCREBUILD(3)  PCREBUILD(3)                                                      PCREBUILD(3)
275    
276    
# Line 277  PCRE BUILD-TIME OPTIONS Line 285  PCRE BUILD-TIME OPTIONS
285         script,  where the optional features are selected or deselected by pro-         script,  where the optional features are selected or deselected by pro-
286         viding options to configure before running the make  command.  However,         viding options to configure before running the make  command.  However,
287         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
288         environments using the GUI facility of  CMakeSetup  if  you  are  using         environments using the GUI facility of cmake-gui if you are using CMake
289         CMake instead of configure to build PCRE.         instead of configure to build PCRE.
290    
291           There  is  a  lot more information about building PCRE in non-Unix-like
292           environments in the file called NON_UNIX_USE, which is part of the PCRE
293           distribution.  You  should consult this file as well as the README file
294           if you are building in a non-Unix-like environment.
295    
296         The complete list of options for configure (which includes the standard         The complete list of options for configure (which includes the standard
297         ones such as the  selection  of  the  installation  directory)  can  be         ones  such  as  the  selection  of  the  installation directory) can be
298         obtained by running         obtained by running
299    
300           ./configure --help           ./configure --help
301    
302         The  following  sections  include  descriptions  of options whose names         The following sections include  descriptions  of  options  whose  names
303         begin with --enable or --disable. These settings specify changes to the         begin with --enable or --disable. These settings specify changes to the
304         defaults  for  the configure command. Because of the way that configure         defaults for the configure command. Because of the way  that  configure
305         works, --enable and --disable always come in pairs, so  the  complemen-         works,  --enable  and --disable always come in pairs, so the complemen-
306         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
307         is not described.         is not described.
308    
309    
# Line 307  C++ SUPPORT Line 320  C++ SUPPORT
320    
321  UTF-8 SUPPORT  UTF-8 SUPPORT
322    
323         To build PCRE with support for UTF-8 character strings, add         To build PCRE with support for UTF-8 Unicode character strings, add
324    
325           --enable-utf8           --enable-utf8
326    
327         to the configure command. Of itself, this  does  not  make  PCRE  treat         to  the  configure  command.  Of  itself, this does not make PCRE treat
328         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
329         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()
330         function.         or pcre_compile2() functions.
331    
332           If you set --enable-utf8 when compiling in an EBCDIC environment,  PCRE
333           expects its input to be either ASCII or UTF-8 (depending on the runtime
334           option). It is not possible to support both EBCDIC and UTF-8  codes  in
335           the  same  version  of  the  library.  Consequently,  --enable-utf8 and
336           --enable-ebcdic are mutually exclusive.
337    
338    
339  UNICODE CHARACTER PROPERTY SUPPORT  UNICODE CHARACTER PROPERTY SUPPORT
340    
341         UTF-8  support allows PCRE to process character values greater than 255         UTF-8 support allows PCRE to process character values greater than  255
342         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-
343         vide any facilities for accessing the properties of such characters. If         vide any facilities for accessing the properties of such characters. If
344         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
345         refer to Unicode character properties, you must add         refer to Unicode character properties, you must add
346    
347           --enable-unicode-properties           --enable-unicode-properties
348    
349         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
350         not explicitly requested it.         not explicitly requested it.
351    
352         Including Unicode property support adds around 30K  of  tables  to  the         Including  Unicode  property  support  adds around 30K of tables to the
353         PCRE  library.  Only  the general category properties such as Lu and Nd         PCRE library. Only the general category properties such as  Lu  and  Nd
354         are supported. Details are given in the pcrepattern documentation.         are supported. Details are given in the pcrepattern documentation.
355    
356    
357  CODE VALUE OF NEWLINE  CODE VALUE OF NEWLINE
358    
359         By default, PCRE interprets character 10 (linefeed, LF)  as  indicating         By  default,  PCRE interprets the linefeed (LF) character as indicating
360         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
361         systems. You can compile PCRE to use character 13 (carriage return, CR)         systems.  You  can compile PCRE to use carriage return (CR) instead, by
362         instead, by adding         adding
363    
364           --enable-newline-is-cr           --enable-newline-is-cr
365    
366         to  the  configure  command.  There  is  also  a --enable-newline-is-lf         to the  configure  command.  There  is  also  a  --enable-newline-is-lf
367         option, which explicitly specifies linefeed as the newline character.         option, which explicitly specifies linefeed as the newline character.
368    
369         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 356  CODE VALUE OF NEWLINE Line 375  CODE VALUE OF NEWLINE
375    
376           --enable-newline-is-anycrlf           --enable-newline-is-anycrlf
377    
378         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
379         CRLF as indicating a line ending. Finally, a fifth option, specified by         CRLF as indicating a line ending. Finally, a fifth option, specified by
380    
381           --enable-newline-is-any           --enable-newline-is-any
# Line 416  HANDLING VERY LARGE PATTERNS Line 435  HANDLING VERY LARGE PATTERNS
435         nation metacharacter). By default, two-byte values are used  for  these         nation metacharacter). By default, two-byte values are used  for  these
436         offsets,  leading  to  a  maximum size for a compiled pattern of around         offsets,  leading  to  a  maximum size for a compiled pattern of around
437         64K. This is sufficient to handle all but the most  gigantic  patterns.         64K. This is sufficient to handle all but the most  gigantic  patterns.
438         Nevertheless,  some  people do want to process enormous patterns, so it         Nevertheless,  some  people do want to process truyl enormous patterns,
439         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-
440         adding a setting such as         sets by adding a setting such as
441    
442           --with-link-size=3           --with-link-size=3
443    
# Line 445  AVOIDING EXCESSIVE STACK USAGE Line 464  AVOIDING EXCESSIVE STACK USAGE
464         to the configure command. With this configuration, PCRE  will  use  the         to the configure command. With this configuration, PCRE  will  use  the
465         pcre_stack_malloc  and pcre_stack_free variables to call memory manage-         pcre_stack_malloc  and pcre_stack_free variables to call memory manage-
466         ment functions. By default these point to malloc() and free(), but  you         ment functions. By default these point to malloc() and free(), but  you
467         can replace the pointers so that your own functions are used.         can replace the pointers so that your own functions are used instead.
468    
469         Separate  functions  are  provided  rather  than  using pcre_malloc and         Separate  functions  are  provided  rather  than  using pcre_malloc and
470         pcre_free because the  usage  is  very  predictable:  the  block  sizes         pcre_free because the  usage  is  very  predictable:  the  block  sizes
# Line 453  AVOIDING EXCESSIVE STACK USAGE Line 472  AVOIDING EXCESSIVE STACK USAGE
472         reverse order. A calling program might be able to  implement  optimized         reverse order. A calling program might be able to  implement  optimized
473         functions  that  perform  better  than  malloc()  and free(). PCRE runs         functions  that  perform  better  than  malloc()  and free(). PCRE runs
474         noticeably more slowly when built in this way. This option affects only         noticeably more slowly when built in this way. This option affects only
475         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.  
476    
477    
478  LIMITING PCRE RESOURCE USAGE  LIMITING PCRE RESOURCE USAGE
479    
480         Internally, PCRE has a function called match(), which it calls  repeat-         Internally,  PCRE has a function called match(), which it calls repeat-
481         edly   (sometimes   recursively)  when  matching  a  pattern  with  the         edly  (sometimes  recursively)  when  matching  a  pattern   with   the
482         pcre_exec() function. By controlling the maximum number of  times  this         pcre_exec()  function.  By controlling the maximum number of times this
483         function  may be called during a single matching operation, a limit can         function may be called during a single matching operation, a limit  can
484         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
485         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-
486         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
487         setting such as         setting such as
488    
489           --with-match-limit=500000           --with-match-limit=500000
490    
491         to   the   configure  command.  This  setting  has  no  effect  on  the         to  the  configure  command.  This  setting  has  no  effect   on   the
492         pcre_dfa_exec() matching function.         pcre_dfa_exec() matching function.
493    
494         In some environments it is desirable to limit the  depth  of  recursive         In  some  environments  it is desirable to limit the depth of recursive
495         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
496         to restrict the maximum amount of stack (or heap,  if  --disable-stack-         to  restrict  the maximum amount of stack (or heap, if --disable-stack-
497         for-recursion is specified) that is used. A second limit controls this;         for-recursion is specified) that is used. A second limit controls this;
498         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
499         imposes  no  additional constraints. However, you can set a lower limit         imposes no additional constraints. However, you can set a  lower  limit
500         by adding, for example,         by adding, for example,
501    
502           --with-match-limit-recursion=10000           --with-match-limit-recursion=10000
503    
504         to the configure command. This value can  also  be  overridden  at  run         to  the  configure  command.  This  value can also be overridden at run
505         time.         time.
506    
507    
508  CREATING CHARACTER TABLES AT BUILD TIME  CREATING CHARACTER TABLES AT BUILD TIME
509    
510         PCRE  uses fixed tables for processing characters whose code values are         PCRE uses fixed tables for processing characters whose code values  are
511         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
512         distributed  in  the  file pcre_chartables.c.dist. These tables are for         distributed in the file pcre_chartables.c.dist. These  tables  are  for
513         ASCII codes only. If you add         ASCII codes only. If you add
514    
515           --enable-rebuild-chartables           --enable-rebuild-chartables
516    
517         to the configure command, the distributed tables are  no  longer  used.         to  the  configure  command, the distributed tables are no longer used.
518         Instead,  a  program  called dftables is compiled and run. This outputs         Instead, a program called dftables is compiled and  run.  This  outputs
519         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
520         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
521         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
522         you  need  to  create alternative tables when cross compiling, you will         you need to create alternative tables when cross  compiling,  you  will
523         have to do so "by hand".)         have to do so "by hand".)
524    
525    
526  USING EBCDIC CODE  USING EBCDIC CODE
527    
528         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
529         character  code  is  ASCII  (or Unicode, which is a superset of ASCII).         character code is ASCII (or Unicode, which is  a  superset  of  ASCII).
530         This is the case for most computer operating systems.  PCRE  can,  how-         This  is  the  case for most computer operating systems. PCRE can, how-
531         ever, be compiled to run in an EBCDIC environment by adding         ever, be compiled to run in an EBCDIC environment by adding
532    
533           --enable-ebcdic           --enable-ebcdic
534    
535         to the configure command. This setting implies --enable-rebuild-charta-         to the configure command. This setting implies --enable-rebuild-charta-
536         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
537         environment (for example, an IBM mainframe operating system).         environment (for example,  an  IBM  mainframe  operating  system).  The
538           --enable-ebcdic option is incompatible with --enable-utf8.
539    
540    
541  PCREGREP OPTIONS FOR COMPRESSED FILE SUPPORT  PCREGREP OPTIONS FOR COMPRESSED FILE SUPPORT
# Line 542  PCRETEST OPTION FOR LIBREADLINE SUPPORT Line 561  PCRETEST OPTION FOR LIBREADLINE SUPPORT
561         to  the  configure  command,  pcretest  is  linked with the libreadline         to  the  configure  command,  pcretest  is  linked with the libreadline
562         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
563         readline() function. This provides line-editing and history facilities.         readline() function. This provides line-editing and history facilities.
564         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
565         pcretest linked in this way, there may be licensing issues.         pcretest linked in this way, there may be licensing issues.
566    
567         Setting  this  option  causes  the -lreadline option to be added to the         Setting  this  option  causes  the -lreadline option to be added to the
# Line 578  AUTHOR Line 597  AUTHOR
597    
598  REVISION  REVISION
599    
600         Last updated: 13 April 2008         Last updated: 29 September 2009
601         Copyright (c) 1997-2008 University of Cambridge.         Copyright (c) 1997-2009 University of Cambridge.
602  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
603    
604    
605  PCREMATCHING(3)                                                PCREMATCHING(3)  PCREMATCHING(3)                                                PCREMATCHING(3)
606    
607    
# Line 666  THE ALTERNATIVE MATCHING ALGORITHM Line 685  THE ALTERNATIVE MATCHING ALGORITHM
685         though  it is not implemented as a traditional finite state machine (it         though  it is not implemented as a traditional finite state machine (it
686         keeps multiple states active simultaneously).         keeps multiple states active simultaneously).
687    
688           Although the general principle of this matching algorithm  is  that  it
689           scans  the subject string only once, without backtracking, there is one
690           exception: when a lookaround assertion is encountered,  the  characters
691           following  or  preceding  the  current  point  have to be independently
692           inspected.
693    
694         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
695         there  are  no more unterminated paths. At this point, terminated paths         there  are  no more unterminated paths. At this point, terminated paths
696         represent the different matching possibilities (if there are none,  the         represent the different matching possibilities (if there are none,  the
697         match  has  failed).   Thus,  if there is more than one possible match,         match  has  failed).   Thus,  if there is more than one possible match,
698         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-
699         est.  In PCRE, there is an option to stop the algorithm after the first         est.  The  matches are returned in decreasing order of length. There is
700         match (which is necessarily the shortest) has been found.         an option to stop the algorithm after the first match (which is  neces-
701           sarily 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
705    
706           cat(er(pillar)?)           cat(er(pillar)?)?
707    
708         is  matched  against the string "the caterpillar catchment", the result         is matched against the string "the caterpillar catchment",  the  result
709         will be the three strings "cat", "cater", and "caterpillar" that  start         will  be the three strings "caterpillar", "cater", and "cat" that start
710         at the fourth character of the subject. The algorithm does not automat-         at the fifth character of the subject. The algorithm does not automati-
711         ically move on to find matches that start at later positions.         cally move on to find matches that start at later positions.
712    
713         There are a number of features of PCRE regular expressions that are not         There are a number of features of PCRE regular expressions that are not
714         supported by the alternative matching algorithm. They are as follows:         supported by the alternative matching algorithm. They are as follows:
715    
716         1.  Because  the  algorithm  finds  all possible matches, the greedy or         1. Because the algorithm finds all  possible  matches,  the  greedy  or
717         ungreedy nature of repetition quantifiers is not relevant.  Greedy  and         ungreedy  nature  of repetition quantifiers is not relevant. Greedy and
718         ungreedy quantifiers are treated in exactly the same way. However, pos-         ungreedy quantifiers are treated in exactly the same way. However, pos-
719         sessive quantifiers can make a difference when what follows could  also         sessive  quantifiers can make a difference when what follows could also
720         match what is quantified, for example in a pattern like this:         match what is quantified, for example in a pattern like this:
721    
722           ^a++\w!           ^a++\w!
723    
724         This  pattern matches "aaab!" but not "aaa!", which would be matched by         This pattern matches "aaab!" but not "aaa!", which would be matched  by
725         a non-possessive quantifier. Similarly, if an atomic group is  present,         a  non-possessive quantifier. Similarly, if an atomic group is present,
726         it  is matched as if it were a standalone pattern at the current point,         it is matched as if it were a standalone pattern at the current  point,
727         and the longest match is then "locked in" for the rest of  the  overall         and  the  longest match is then "locked in" for the rest of the overall
728         pattern.         pattern.
729    
730         2. When dealing with multiple paths through the tree simultaneously, it         2. When dealing with multiple paths through the tree simultaneously, it
731         is not straightforward to keep track of  captured  substrings  for  the         is  not  straightforward  to  keep track of captured substrings for the
732         different  matching  possibilities,  and  PCRE's implementation of this         different matching possibilities, and  PCRE's  implementation  of  this
733         algorithm does not attempt to do this. This means that no captured sub-         algorithm does not attempt to do this. This means that no captured sub-
734         strings are available.         strings are available.
735    
736         3.  Because no substrings are captured, back references within the pat-         3. Because no substrings are captured, back references within the  pat-
737         tern are not supported, and cause errors if encountered.         tern are not supported, and cause errors if encountered.
738    
739         4. For the same reason, conditional expressions that use  a  backrefer-         4.  For  the same reason, conditional expressions that use a backrefer-
740         ence  as  the  condition or test for a specific group recursion are not         ence as the condition or test for a specific group  recursion  are  not
741         supported.         supported.
742    
743         5. Because many paths through the tree may be  active,  the  \K  escape         5.  Because  many  paths  through the tree may be active, the \K escape
744         sequence, which resets the start of the match when encountered (but may         sequence, which resets the start of the match when encountered (but may
745         be on some paths and not on others), is not  supported.  It  causes  an         be  on  some  paths  and not on others), is not supported. It causes an
746         error if encountered.         error if encountered.
747    
748         6.  Callouts  are  supported, but the value of the capture_top field is         6. Callouts are supported, but the value of the  capture_top  field  is
749         always 1, and the value of the capture_last field is always -1.         always 1, and the value of the capture_last field is always -1.
750    
751         7. The \C escape sequence, which (in the standard algorithm) matches  a         7.  The \C escape sequence, which (in the standard algorithm) matches a
752         single  byte, even in UTF-8 mode, is not supported because the alterna-         single byte, even in UTF-8 mode, is not supported because the  alterna-
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.  Except for (*FAIL), the backtracking control verbs such as (*PRUNE)         8. Except for (*FAIL), the backtracking control verbs such as  (*PRUNE)
757         are not supported. (*FAIL) is supported, and  behaves  like  a  failing         are  not  supported.  (*FAIL)  is supported, and behaves like a failing
758         negative assertion.         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. Although it is possible to do multi-
775         available.         segment matching using the standard algorithm (pcre_exec()), by retain-
776           ing  partially matched substrings, it is more complicated. The pcrepar-
777         3.  Because  the  alternative  algorithm  scans the subject string just         tial documentation gives details  of  partial  matching  and  discusses
778         once, and never needs to backtrack, it is possible to  pass  very  long         multi-segment matching.
        subject  strings  to  the matching function in several pieces, checking  
        for partial matching each time.  
779    
780    
781  DISADVANTAGES OF THE ALTERNATIVE ALGORITHM  DISADVANTAGES OF THE ALTERNATIVE ALGORITHM
782    
783         The alternative algorithm suffers from a number of disadvantages:         The alternative algorithm suffers from a number of disadvantages:
784    
785         1. It is substantially slower than  the  standard  algorithm.  This  is         1.  It  is  substantially  slower  than the standard algorithm. This is
786         partly  because  it has to search for all possible matches, but is also         partly because it has to search for all possible matches, but  is  also
787         because it is less susceptible to optimization.         because it is less susceptible to optimization.
788    
789         2. Capturing parentheses and back references are not supported.         2. Capturing parentheses and back references are not supported.
# Line 777  AUTHOR Line 801  AUTHOR
801    
802  REVISION  REVISION
803    
804         Last updated: 19 April 2008         Last updated: 17 November 2010
805         Copyright (c) 1997-2008 University of Cambridge.         Copyright (c) 1997-2010 University of Cambridge.
806  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
807    
808    
809  PCREAPI(3)                                                          PCREAPI(3)  PCREAPI(3)                                                          PCREAPI(3)
810    
811    
# Line 885  PCRE API OVERVIEW Line 909  PCRE API OVERVIEW
909         bers for the library.  Applications can use these  to  include  support         bers for the library.  Applications can use these  to  include  support
910         for different releases of PCRE.         for different releases of PCRE.
911    
912           In a Windows environment, if you want to statically link an application
913           program against a non-dll pcre.a  file,  you  must  define  PCRE_STATIC
914           before  including  pcre.h or pcrecpp.h, because otherwise the pcre_mal-
915           loc()   and   pcre_free()   exported   functions   will   be   declared
916           __declspec(dllimport), with unwanted results.
917    
918         The   functions   pcre_compile(),  pcre_compile2(),  pcre_study(),  and         The   functions   pcre_compile(),  pcre_compile2(),  pcre_study(),  and
919         pcre_exec() are used for compiling and matching regular expressions  in         pcre_exec() are used for compiling and matching regular expressions  in
920         a  Perl-compatible  manner. A sample program that demonstrates the sim-         a  Perl-compatible  manner. A sample program that demonstrates the sim-
921         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
922         the  source distribution. The pcresample documentation describes how to         the PCRE source distribution. A listing of this program is given in the
923         compile and run it.         pcredemo documentation, and the pcresample documentation describes  how
924           to compile and run it.
925    
926         A second matching function, pcre_dfa_exec(), which is not Perl-compati-         A second matching function, pcre_dfa_exec(), which is not Perl-compati-
927         ble,  is  also provided. This uses a different algorithm for the match-         ble, is also provided. This uses a different algorithm for  the  match-
928         ing. The alternative algorithm finds all possible matches (at  a  given         ing.  The  alternative algorithm finds all possible matches (at a given
929         point  in  the subject), and scans the subject just once. However, this         point in the subject), and scans the subject just  once  (unless  there
930         algorithm does not return captured substrings. A description of the two         are  lookbehind  assertions).  However,  this algorithm does not return
931         matching  algorithms and their advantages and disadvantages is given in         captured substrings. A description of the two matching  algorithms  and
932         the pcrematching documentation.         their  advantages  and disadvantages is given in the pcrematching docu-
933           mentation.
934    
935         In addition to the main compiling and  matching  functions,  there  are         In addition to the main compiling and  matching  functions,  there  are
936         convenience functions for extracting captured substrings from a subject         convenience functions for extracting captured substrings from a subject
# Line 999  MULTITHREADING Line 1031  MULTITHREADING
1031         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
1032         callout function pointed to by pcre_callout, are shared by all threads.         callout function pointed to by pcre_callout, are shared by all threads.
1033    
1034         The compiled form of a regular expression is not altered during  match-         The  compiled form of a regular expression is not altered during match-
1035         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
1036         at once.         at once.
1037    
# Line 1007  MULTITHREADING Line 1039  MULTITHREADING
1039  SAVING PRECOMPILED PATTERNS FOR LATER USE  SAVING PRECOMPILED PATTERNS FOR LATER USE
1040    
1041         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
1042         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
1043         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
1044         pcreprecompile  documentation.  However, compiling a regular expression         pcreprecompile documentation. However, compiling a  regular  expression
1045         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-
1046         anteed to work and may cause crashes.         anteed to work and may cause crashes.
1047    
1048    
# Line 1018  CHECKING BUILD-TIME OPTIONS Line 1050  CHECKING BUILD-TIME OPTIONS
1050    
1051         int pcre_config(int what, void *where);         int pcre_config(int what, void *where);
1052    
1053         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-
1054         cover which optional features have been compiled into the PCRE library.         cover which optional features have been compiled into the PCRE library.
1055         The  pcrebuild documentation has more details about these optional fea-         The pcrebuild documentation has more details about these optional  fea-
1056         tures.         tures.
1057    
1058         The first argument for pcre_config() is an  integer,  specifying  which         The  first  argument  for pcre_config() is an integer, specifying which
1059         information is required; the second argument is a pointer to a variable         information is required; the second argument is a pointer to a variable
1060         into which the information is  placed.  The  following  information  is         into  which  the  information  is  placed. The following information is
1061         available:         available:
1062    
1063           PCRE_CONFIG_UTF8           PCRE_CONFIG_UTF8
1064    
1065         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-
1066         able; otherwise it is set to zero.         able; otherwise it is set to zero.
1067    
1068           PCRE_CONFIG_UNICODE_PROPERTIES           PCRE_CONFIG_UNICODE_PROPERTIES
1069    
1070         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
1071         character properties is available; otherwise it is set to zero.         character properties is available; otherwise it is set to zero.
1072    
1073           PCRE_CONFIG_NEWLINE           PCRE_CONFIG_NEWLINE
1074    
1075         The  output  is  an integer whose value specifies the default character         The output is an integer whose value specifies  the  default  character
1076         sequence that is recognized as meaning "newline". The four values  that         sequence  that is recognized as meaning "newline". The four values that
1077         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,
1078         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
1079         for your operating system.         are returned in EBCDIC environments. The default should normally corre-
1080           spond to the standard sequence for your operating system.
1081    
1082           PCRE_CONFIG_BSR           PCRE_CONFIG_BSR
1083    
# Line 1071  CHECKING BUILD-TIME OPTIONS Line 1104  CHECKING BUILD-TIME OPTIONS
1104    
1105           PCRE_CONFIG_MATCH_LIMIT           PCRE_CONFIG_MATCH_LIMIT
1106    
1107         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-
1108         internal  matching  function  calls in a pcre_exec() execution. Further         ber  of  internal  matching  function calls in a pcre_exec() execution.
1109         details are given with pcre_exec() below.         Further details are given with pcre_exec() below.
1110    
1111           PCRE_CONFIG_MATCH_LIMIT_RECURSION           PCRE_CONFIG_MATCH_LIMIT_RECURSION
1112    
1113         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
1114         recursion  when calling the internal matching function in a pcre_exec()         of   recursion  when  calling  the  internal  matching  function  in  a
1115         execution. Further details are given with pcre_exec() below.         pcre_exec() execution.  Further  details  are  given  with  pcre_exec()
1116           below.
1117    
1118           PCRE_CONFIG_STACKRECURSE           PCRE_CONFIG_STACKRECURSE
1119    
1120         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
1121         running pcre_exec() is implemented by recursive function calls that use         running pcre_exec() is implemented by recursive function calls that use
1122         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
1123         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
1124         on the  heap  instead  of  recursive  function  calls.  In  this  case,         on  the  heap  instead  of  recursive  function  calls.  In  this case,
1125         pcre_stack_malloc  and  pcre_stack_free  are  called  to  manage memory         pcre_stack_malloc and  pcre_stack_free  are  called  to  manage  memory
1126         blocks on the heap, thus avoiding the use of the stack.         blocks on the heap, thus avoiding the use of the stack.
1127    
1128    
# Line 1105  COMPILING A PATTERN Line 1139  COMPILING A PATTERN
1139    
1140         Either of the functions pcre_compile() or pcre_compile2() can be called         Either of the functions pcre_compile() or pcre_compile2() can be called
1141         to compile a pattern into an internal form. The only difference between         to compile a pattern into an internal form. The only difference between
1142         the two interfaces is that pcre_compile2() has an additional  argument,         the  two interfaces is that pcre_compile2() has an additional argument,
1143         errorcodeptr, via which a numerical error code can be returned.         errorcodeptr, via which a numerical error  code  can  be  returned.  To
1144           avoid  too  much repetition, we refer just to pcre_compile() below, but
1145           the information applies equally to pcre_compile2().
1146    
1147         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
1148         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
1149         obtained  via  pcre_malloc is returned. This contains the compiled code         obtained via pcre_malloc is returned. This contains the  compiled  code
1150         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
1151         is a typedef for a structure whose contents are not externally defined.         is a typedef for a structure whose contents are not externally defined.
1152         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
1153         longer required.         longer required.
1154    
1155         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
1156         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
1157         fully  relocatable, because it may contain a copy of the tableptr argu-         fully relocatable, because it may contain a copy of the tableptr  argu-
1158         ment, which is an address (see below).         ment, which is an address (see below).
1159    
1160         The options argument contains various bit settings that affect the com-         The options argument contains various bit settings that affect the com-
1161         pilation.  It  should be zero if no options are required. The available         pilation. It should be zero if no options are required.  The  available
1162         options are described below. Some of them, in  particular,  those  that         options  are  described  below. Some of them (in particular, those that
1163         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
1164         pattern (see the detailed description  in  the  pcrepattern  documenta-         unset  from  within  the  pattern  (see the detailed description in the
1165         tion).  For  these options, the contents of the options argument speci-         pcrepattern documentation). For those options that can be different  in
1166         fies their initial settings at the start of compilation and  execution.         different  parts  of  the pattern, the contents of the options argument
1167         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
1168         of matching as well as at compile time.         PCRE_ANCHORED, PCRE_BSR_xxx, and PCRE_NEWLINE_xxx options can be set at
1169           the time of matching as well as at compile time.
1170    
1171         If errptr is NULL, pcre_compile() returns NULL immediately.  Otherwise,         If errptr is NULL, pcre_compile() returns NULL immediately.  Otherwise,
1172         if  compilation  of  a  pattern fails, pcre_compile() returns NULL, and         if  compilation  of  a  pattern fails, pcre_compile() returns NULL, and
1173         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-
1174         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
1175         try to free it. The offset from the start of the pattern to the charac-         try to free it. The offset from the start of the pattern  to  the  byte
1176         ter where the error was discovered is placed in the variable pointed to         that was being processed when the error was discovered is placed in the
1177         by erroffset, which must not be NULL. If it is, an immediate  error  is         variable pointed to by erroffset, which must not be NULL. If it is,  an
1178         given.         immediate error is given. Some errors are not detected until checks are
1179           carried out when the whole pattern has been scanned; in this  case  the
1180           offset is set to the end of the pattern.
1181    
1182           Note  that  the offset is in bytes, not characters, even in UTF-8 mode.
1183           It may point into the middle of a UTF-8 character  (for  example,  when
1184           PCRE_ERROR_BADUTF8 is returned for an invalid UTF-8 string).
1185    
1186         If  pcre_compile2()  is  used instead of pcre_compile(), and the error-         If  pcre_compile2()  is  used instead of pcre_compile(), and the error-
1187         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 1216  COMPILING A PATTERN Line 1259  COMPILING A PATTERN
1259    
1260           PCRE_DOTALL           PCRE_DOTALL
1261    
1262         If this bit is set, a dot metacharater in the pattern matches all char-         If this bit is set, a dot metacharacter in the pattern matches a  char-
1263         acters,  including  those that indicate newline. Without it, a dot does         acter of any value, including one that indicates a newline. However, it
1264         not match when the current position is at a  newline.  This  option  is         only ever matches one character, even if newlines are  coded  as  CRLF.
1265         equivalent  to Perl's /s option, and it can be changed within a pattern         Without  this option, a dot does not match when the current position is
1266         by a (?s) option setting. A negative class such as [^a] always  matches         at a newline. This option is equivalent to Perl's /s option, and it can
1267         newline characters, independent of the setting of this option.         be  changed within a pattern by a (?s) option setting. A negative class
1268           such as [^a] always matches newline characters, independent of the set-
1269           ting of this option.
1270    
1271           PCRE_DUPNAMES           PCRE_DUPNAMES
1272    
# Line 1241  COMPILING A PATTERN Line 1286  COMPILING A PATTERN
1286         option, and it can be changed within a pattern by a  (?x)  option  set-         option, and it can be changed within a pattern by a  (?x)  option  set-
1287         ting.         ting.
1288    
1289         This  option  makes  it possible to include comments inside complicated         Which  characters  are  interpreted  as  newlines  is controlled by the
1290         patterns.  Note, however, that this applies only  to  data  characters.         options passed to pcre_compile() or by a special sequence at the  start
1291         Whitespace   characters  may  never  appear  within  special  character         of  the  pattern, as described in the section entitled "Newline conven-
1292         sequences in a pattern, for  example  within  the  sequence  (?(  which         tions" in the pcrepattern documentation. Note that the end of this type
1293         introduces a conditional subpattern.         of  comment  is  a  literal  newline  sequence  in  the pattern; escape
1294           sequences that happen to represent a newline do not count.
1295    
1296           This option makes it possible to include  comments  inside  complicated
1297           patterns.   Note,  however,  that this applies only to data characters.
1298           Whitespace  characters  may  never  appear  within  special   character
1299           sequences in a pattern, for example within the sequence (?( that intro-
1300           duces a conditional subpattern.
1301    
1302           PCRE_EXTRA           PCRE_EXTRA
1303    
1304         This  option  was invented in order to turn on additional functionality         This option was invented in order to turn on  additional  functionality
1305         of PCRE that is incompatible with Perl, but it  is  currently  of  very         of  PCRE  that  is  incompatible with Perl, but it is currently of very
1306         little  use. When set, any backslash in a pattern that is followed by a         little use. When set, any backslash in a pattern that is followed by  a
1307         letter that has no special meaning  causes  an  error,  thus  reserving         letter  that  has  no  special  meaning causes an error, thus reserving
1308         these  combinations  for  future  expansion.  By default, as in Perl, a         these combinations for future expansion. By  default,  as  in  Perl,  a
1309         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
1310         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
1311         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
1312         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
1313           within a pattern.
1314    
1315           PCRE_FIRSTLINE           PCRE_FIRSTLINE
1316    
# Line 1326  COMPILING A PATTERN Line 1379  COMPILING A PATTERN
1379         PCRE_NEWLINE_CRLF,  but other combinations may yield unused numbers and         PCRE_NEWLINE_CRLF,  but other combinations may yield unused numbers and
1380         cause an error.         cause an error.
1381    
1382         The only time that a line break is specially recognized when  compiling         The only time that a line break in a pattern  is  specially  recognized
1383         a  pattern  is  if  PCRE_EXTENDED  is set, and an unescaped # outside a         when  compiling  is when PCRE_EXTENDED is set. CR and LF are whitespace
1384         character class is encountered. This indicates  a  comment  that  lasts         characters, and so are ignored in this mode. Also, an unescaped #  out-
1385         until  after the next line break sequence. In other circumstances, line         side  a  character class indicates a comment that lasts until after the
1386         break  sequences  are  treated  as  literal  data,   except   that   in         next line break sequence. In other circumstances, line break  sequences
1387         PCRE_EXTENDED mode, both CR and LF are treated as whitespace characters         in patterns are treated as literal data.
        and are therefore ignored.  
1388    
1389         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
1390         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.
1391    
1392           PCRE_NO_AUTO_CAPTURE           PCRE_NO_AUTO_CAPTURE
1393    
# Line 1345  COMPILING A PATTERN Line 1397  COMPILING A PATTERN
1397         be  used  for  capturing  (and  they acquire numbers in the usual way).         be  used  for  capturing  (and  they acquire numbers in the usual way).
1398         There is no equivalent of this option in Perl.         There is no equivalent of this option in Perl.
1399    
1400             PCRE_UCP
1401    
1402           This option changes the way PCRE processes \B, \b, \D, \d, \S, \s,  \W,
1403           \w,  and  some  of  the POSIX character classes. By default, only ASCII
1404           characters are recognized, but if PCRE_UCP is set,  Unicode  properties
1405           are  used instead to classify characters. More details are given in the
1406           section on generic character types in the pcrepattern page. If you  set
1407           PCRE_UCP,  matching  one of the items it affects takes much longer. The
1408           option is available only if PCRE has been compiled with  Unicode  prop-
1409           erty support.
1410    
1411           PCRE_UNGREEDY           PCRE_UNGREEDY
1412    
1413         This option inverts the "greediness" of the quantifiers  so  that  they         This  option  inverts  the "greediness" of the quantifiers so that they
1414         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
1415         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
1416         within the pattern.         within the pattern.
1417    
1418           PCRE_UTF8           PCRE_UTF8
1419    
1420         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
1421         strings of UTF-8 characters instead of single-byte  character  strings.         strings  of  UTF-8 characters instead of single-byte character strings.
1422         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-
1423         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
1424         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
1425         UTF-8 support in the main pcre page.         UTF-8 support in the main pcre page.
1426    
1427           PCRE_NO_UTF8_CHECK           PCRE_NO_UTF8_CHECK
1428    
1429         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
1430         automatically  checked.  There  is  a  discussion about the validity of         automatically checked. There is a  discussion  about  the  validity  of
1431         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
1432         bytes  is  found,  pcre_compile() returns an error. If you already know         bytes is found, pcre_compile() returns an error. If  you  already  know
1433         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-
1434         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
1435         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
1436         undefined.  It  may  cause your program to crash. Note that this option         undefined. It may cause your program to crash. Note  that  this  option
1437         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
1438         UTF-8 validity checking of subject strings.         UTF-8 validity checking of subject strings.
1439    
1440    
1441  COMPILATION ERROR CODES  COMPILATION ERROR CODES
1442    
1443         The  following  table  lists  the  error  codes than may be returned by         The following table lists the error  codes  than  may  be  returned  by
1444         pcre_compile2(), along with the error messages that may be returned  by         pcre_compile2(),  along with the error messages that may be returned by
1445         both  compiling functions. As PCRE has developed, some error codes have         both compiling functions. As PCRE has developed, some error codes  have
1446         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.
1447    
1448            0  no error            0  no error
# Line 1435  COMPILATION ERROR CODES Line 1498  COMPILATION ERROR CODES
1498           50  [this code is not in use]           50  [this code is not in use]
1499           51  octal value is greater than \377 (not in UTF-8 mode)           51  octal value is greater than \377 (not in UTF-8 mode)
1500           52  internal error: overran compiling workspace           52  internal error: overran compiling workspace
1501           53  internal  error:  previously-checked  referenced  subpattern  not           53  internal error: previously-checked referenced subpattern
1502         found                 not found
1503           54  DEFINE group contains more than one branch           54  DEFINE group contains more than one branch
1504           55  repeating a DEFINE group is not allowed           55  repeating a DEFINE group is not allowed
1505           56  inconsistent NEWLINE options           56  inconsistent NEWLINE options
1506           57  \g is not followed by a braced, angle-bracketed, or quoted           57  \g is not followed by a braced, angle-bracketed, or quoted
1507                 name/number or by a plain number                 name/number or by a plain number
1508           58  a numbered reference must not be zero           58  a numbered reference must not be zero
1509           59  (*VERB) with an argument is not supported           59  an argument is not allowed for (*ACCEPT), (*FAIL), or (*COMMIT)
1510           60  (*VERB) not recognized           60  (*VERB) not recognized
1511           61  number is too big           61  number is too big
1512           62  subpattern name expected           62  subpattern name expected
1513           63  digit expected after (?+           63  digit expected after (?+
1514           64  ] is an invalid data character in JavaScript compatibility mode           64  ] is an invalid data character in JavaScript compatibility mode
1515             65  different names for subpatterns of the same number are
1516                   not allowed
1517             66  (*MARK) must have an argument
1518             67  this version of PCRE is not compiled with PCRE_UCP support
1519    
1520         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
1521         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 1468  STUDYING A PATTERN Line 1535  STUDYING A PATTERN
1535         the results of the study.         the results of the study.
1536    
1537         The  returned  value  from  pcre_study()  can  be  passed  directly  to         The  returned  value  from  pcre_study()  can  be  passed  directly  to
1538         pcre_exec().  However,  a  pcre_extra  block also contains other fields         pcre_exec()  or  pcre_dfa_exec(). However, a pcre_extra block also con-
1539         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
1540         described below in the section on matching a pattern.         passed; these are described below in the section on matching a pattern.
1541    
1542         If  studying  the  pattern  does not produce any additional information         If  studying  the  pattern  does  not  produce  any useful information,
1543         pcre_study() returns NULL. In that circumstance, if the calling program         pcre_study() returns NULL. In that circumstance, if the calling program
1544         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
1545         its own pcre_extra block.         pcre_dfa_exec(), it must set up its own pcre_extra block.
1546    
1547         The second argument of pcre_study() contains option bits.  At  present,         The second argument of pcre_study() contains option bits.  At  present,
1548         no options are defined, and this argument should always be zero.         no options are defined, and this argument should always be zero.
# Line 1495  STUDYING A PATTERN Line 1562  STUDYING A PATTERN
1562             0,              /* no options exist */             0,              /* no options exist */
1563             &error);        /* set to NULL or points to a message */             &error);        /* set to NULL or points to a message */
1564    
1565         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
1566         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
1567         ble starting bytes is created.         does not mean that there are any strings of that length that match, but
1568           it  does  guarantee that no shorter strings match. The value is used by
1569           pcre_exec() and pcre_dfa_exec() to avoid  wasting  time  by  trying  to
1570           match  strings  that are shorter than the lower bound. You can find out
1571           the value in a calling program via the pcre_fullinfo() function.
1572    
1573           Studying a pattern is also useful for non-anchored patterns that do not
1574           have  a  single fixed starting character. A bitmap of possible starting
1575           bytes is created. This speeds up finding a position in the  subject  at
1576           which to start matching.
1577    
1578           The  two  optimizations  just  described can be disabled by setting the
1579           PCRE_NO_START_OPTIMIZE   option    when    calling    pcre_exec()    or
1580           pcre_dfa_exec().  You  might  want  to do this if your pattern contains
1581           callouts or (*MARK), and you want to make use of  these  facilities  in
1582           cases  where  matching fails. See the discussion of PCRE_NO_START_OPTI-
1583           MIZE below.
1584    
1585    
1586  LOCALE SUPPORT  LOCALE SUPPORT
# Line 1505  LOCALE SUPPORT Line 1588  LOCALE SUPPORT
1588         PCRE handles caseless matching, and determines whether  characters  are         PCRE handles caseless matching, and determines whether  characters  are
1589         letters,  digits, or whatever, by reference to a set of tables, indexed         letters,  digits, or whatever, by reference to a set of tables, indexed
1590         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
1591         characters  with  codes  less than 128. Higher-valued codes never match         characters  with  codes  less than 128. By default, higher-valued codes
1592         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
1593         with  Unicode  character property support. The use of locales with Uni-         PCRE  is  built with Unicode character property support. Alternatively,
1594         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
1595         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
1596         not try to mix the two.         use of locales with Unicode is discouraged. If you are handling charac-
1597           ters  with codes greater than 128, you should either use UTF-8 and Uni-
1598           code, or use locales, but not try to mix the two.
1599    
1600         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
1601         argument  of  pcre_compile()  is  NULL.  These  are sufficient for many         argument  of  pcre_compile()  is  NULL.  These  are sufficient for many
# Line 1663  INFORMATION ABOUT A PATTERN Line 1748  INFORMATION ABOUT A PATTERN
1748         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
1749         /^a\dz\d/ the returned value is -1.         /^a\dz\d/ the returned value is -1.
1750    
1751             PCRE_INFO_MINLENGTH
1752    
1753           If the pattern was studied and a minimum length  for  matching  subject
1754           strings  was  computed,  its  value is returned. Otherwise the returned
1755           value is -1. The value is a number of characters, not bytes  (this  may
1756           be  relevant in UTF-8 mode). The fourth argument should point to an int
1757           variable. A non-negative value is a lower bound to the  length  of  any
1758           matching  string.  There  may not be any strings of that length that do
1759           actually match, but every string that does match is at least that long.
1760    
1761           PCRE_INFO_NAMECOUNT           PCRE_INFO_NAMECOUNT
1762           PCRE_INFO_NAMEENTRYSIZE           PCRE_INFO_NAMEENTRYSIZE
1763           PCRE_INFO_NAMETABLE           PCRE_INFO_NAMETABLE
# Line 1684  INFORMATION ABOUT A PATTERN Line 1779  INFORMATION ABOUT A PATTERN
1779         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
1780         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-
1781         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-
1782         sponding  name,  zero  terminated. The names are in alphabetical order.         sponding name, zero terminated.
1783         When PCRE_DUPNAMES is set, duplicate names are in order of their paren-  
1784         theses  numbers.  For  example,  consider the following pattern (assume         The  names are in alphabetical order. Duplicate names may appear if (?|
1785         PCRE_EXTENDED is  set,  so  white  space  -  including  newlines  -  is         is used to create multiple groups with the same number, as described in
1786         ignored):         the  section  on  duplicate subpattern numbers in the pcrepattern page.
1787           Duplicate names for subpatterns with different  numbers  are  permitted
1788           only  if  PCRE_DUPNAMES  is  set. In all cases of duplicate names, they
1789           appear in the table in the order in which they were found in  the  pat-
1790           tern.  In  the  absence  of (?| this is the order of increasing number;
1791           when (?| is used this is not necessarily the case because later subpat-
1792           terns may have lower numbers.
1793    
1794           As  a  simple  example of the name/number table, consider the following
1795           pattern (assume PCRE_EXTENDED is set, so white space -  including  new-
1796           lines - is ignored):
1797    
1798           (?<date> (?<year>(\d\d)?\d\d) -           (?<date> (?<year>(\d\d)?\d\d) -
1799           (?<month>\d\d) - (?<day>\d\d) )           (?<month>\d\d) - (?<day>\d\d) )
# Line 1709  INFORMATION ABOUT A PATTERN Line 1814  INFORMATION ABOUT A PATTERN
1814    
1815           PCRE_INFO_OKPARTIAL           PCRE_INFO_OKPARTIAL
1816    
1817         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
1818         The  fourth  argument  should point to an int variable. The pcrepartial         pcre_exec(),  otherwise  0.  The fourth argument should point to an int
1819         documentation lists the restrictions that apply to patterns  when  par-         variable. From  release  8.00,  this  always  returns  1,  because  the
1820         tial matching is used.         restrictions  that  previously  applied  to  partial matching have been
1821           lifted. The pcrepartial documentation gives details of  partial  match-
1822           ing.
1823    
1824           PCRE_INFO_OPTIONS           PCRE_INFO_OPTIONS
1825    
# Line 1749  INFORMATION ABOUT A PATTERN Line 1856  INFORMATION ABOUT A PATTERN
1856         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
1857         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
1858         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
1859         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
1860           data,  zero  is  returned. The fourth argument should point to a size_t
1861         variable.         variable.
1862    
1863    
# Line 1757  OBSOLETE INFO FUNCTION Line 1865  OBSOLETE INFO FUNCTION
1865    
1866         int pcre_info(const pcre *code, int *optptr, int *firstcharptr);         int pcre_info(const pcre *code, int *optptr, int *firstcharptr);
1867    
1868         The  pcre_info()  function is now obsolete because its interface is too         The pcre_info() function is now obsolete because its interface  is  too
1869         restrictive to return all the available data about a compiled  pattern.         restrictive  to return all the available data about a compiled pattern.
1870         New   programs   should  use  pcre_fullinfo()  instead.  The  yield  of         New  programs  should  use  pcre_fullinfo()  instead.  The   yield   of
1871         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-
1872         lowing negative numbers:         lowing negative numbers:
1873    
1874           PCRE_ERROR_NULL       the argument code was NULL           PCRE_ERROR_NULL       the argument code was NULL
1875           PCRE_ERROR_BADMAGIC   the "magic number" was not found           PCRE_ERROR_BADMAGIC   the "magic number" was not found
1876    
1877         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
1878         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
1879         PCRE_INFO_OPTIONS above).         PCRE_INFO_OPTIONS above).
1880    
1881         If  the  pattern  is  not anchored and the firstcharptr argument is not         If the pattern is not anchored and the  firstcharptr  argument  is  not
1882         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
1883         any matched string (see PCRE_INFO_FIRSTBYTE above).         any matched string (see PCRE_INFO_FIRSTBYTE above).
1884    
1885    
# Line 1779  REFERENCE COUNTS Line 1887  REFERENCE COUNTS
1887    
1888         int pcre_refcount(pcre *code, int adjust);         int pcre_refcount(pcre *code, int adjust);
1889    
1890         The  pcre_refcount()  function is used to maintain a reference count in         The pcre_refcount() function is used to maintain a reference  count  in
1891         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
1892         benefit  of  applications  that  operate  in an object-oriented manner,         benefit of applications that  operate  in  an  object-oriented  manner,
1893         where different parts of the application may be using the same compiled         where different parts of the application may be using the same compiled
1894         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.
1895    
1896         When a pattern is compiled, the reference count field is initialized to         When a pattern is compiled, the reference count field is initialized to
1897         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
1898         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
1899         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
1900         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
1901         is outside these limits, it is forced to the appropriate limit value.         is outside these limits, it is forced to the appropriate limit value.
1902    
1903         Except when it is zero, the reference count is not correctly  preserved         Except  when it is zero, the reference count is not correctly preserved
1904         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
1905         whose byte-order is different. (This seems a highly unlikely scenario.)         whose byte-order is different. (This seems a highly unlikely scenario.)
1906    
1907    
# Line 1805  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 1913  MATCHING A PATTERN: THE TRADITIONAL FUNC
1913    
1914         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
1915         compiled pattern, which is passed in the code argument. If the  pattern         compiled pattern, which is passed in the code argument. If the  pattern
1916         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
1917         argument. This function is the main matching facility of  the  library,         argument. This function is the main matching facility of  the  library,
1918         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
1919         an alternative matching function, which is described below in the  sec-         an alternative matching function, which is described below in the  sec-
# Line 1845  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 1953  MATCHING A PATTERN: THE TRADITIONAL FUNC
1953           unsigned long int match_limit_recursion;           unsigned long int match_limit_recursion;
1954           void *callout_data;           void *callout_data;
1955           const unsigned char *tables;           const unsigned char *tables;
1956             unsigned char **mark;
1957    
1958         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
1959         are set. The flag bits are:         are set. The flag bits are:
# Line 1854  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 1963  MATCHING A PATTERN: THE TRADITIONAL FUNC
1963           PCRE_EXTRA_MATCH_LIMIT_RECURSION           PCRE_EXTRA_MATCH_LIMIT_RECURSION
1964           PCRE_EXTRA_CALLOUT_DATA           PCRE_EXTRA_CALLOUT_DATA
1965           PCRE_EXTRA_TABLES           PCRE_EXTRA_TABLES
1966             PCRE_EXTRA_MARK
1967    
1968         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
1969         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 1864  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 1974  MATCHING A PATTERN: THE TRADITIONAL FUNC
1974         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
1975         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
1976         match, but which have a very large number  of  possibilities  in  their         match, but which have a very large number  of  possibilities  in  their
1977         search  trees.  The  classic  example  is  the  use of nested unlimited         search  trees. The classic example is a pattern that uses nested unlim-
1978         repeats.         ited repeats.
1979    
1980         Internally, PCRE uses a function called match() which it calls  repeat-         Internally, PCRE uses a function called match() which it calls  repeat-
1981         edly  (sometimes  recursively). The limit set by match_limit is imposed         edly  (sometimes  recursively). The limit set by match_limit is imposed
# Line 1887  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 1997  MATCHING A PATTERN: THE TRADITIONAL FUNC
1997         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-
1998         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.
1999    
2000         Limiting  the  recursion  depth  limits the amount of stack that can be         Limiting the recursion depth limits the amount of  stack  that  can  be
2001         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
2002         of the stack, the amount of heap memory that can be used.         of the stack, the amount of heap memory that can be used.
2003    
2004         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
2005         built; the default default  is  the  same  value  as  the  default  for         built;  the  default  default  is  the  same  value  as the default for
2006         match_limit.  You can override the default by suppling pcre_exec() with         match_limit. You can override the default by suppling pcre_exec()  with
2007         a  pcre_extra  block  in  which  match_limit_recursion  is   set,   and         a   pcre_extra   block  in  which  match_limit_recursion  is  set,  and
2008         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
2009         limit is exceeded, pcre_exec() returns PCRE_ERROR_RECURSIONLIMIT.         limit is exceeded, pcre_exec() returns PCRE_ERROR_RECURSIONLIMIT.
2010    
2011         The pcre_callout field is used in conjunction with the  "callout"  fea-         The  callout_data  field is used in conjunction with the "callout" fea-
2012         ture, which is described in the pcrecallout documentation.         ture, and is described in the pcrecallout documentation.
2013    
2014         The  tables  field  is  used  to  pass  a  character  tables pointer to         The tables field  is  used  to  pass  a  character  tables  pointer  to
2015         pcre_exec(); this overrides the value that is stored with the  compiled         pcre_exec();  this overrides the value that is stored with the compiled
2016         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
2017         custom tables were supplied to pcre_compile() via  its  tableptr  argu-         custom  tables  were  supplied to pcre_compile() via its tableptr argu-
2018         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
2019         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-
2020         using  patterns  that  have been saved after compiling with an external         using patterns that have been saved after compiling  with  an  external
2021         set of tables, because the external tables  might  be  at  a  different         set  of  tables,  because  the  external tables might be at a different
2022         address  when  pcre_exec() is called. See the pcreprecompile documenta-         address when pcre_exec() is called. See the  pcreprecompile  documenta-
2023         tion for a discussion of saving compiled patterns for later use.         tion for a discussion of saving compiled patterns for later use.
2024    
2025           If  PCRE_EXTRA_MARK  is  set in the flags field, the mark field must be
2026           set to point to a char * variable. If the pattern  contains  any  back-
2027           tracking  control verbs such as (*MARK:NAME), and the execution ends up
2028           with a name to pass back, a pointer to the  name  string  (zero  termi-
2029           nated)  is  placed  in  the  variable pointed to by the mark field. The
2030           names are within the compiled pattern; if you wish  to  retain  such  a
2031           name  you must copy it before freeing the memory of a compiled pattern.
2032           If there is no name to pass back, the variable pointed to by  the  mark
2033           field  set  to NULL. For details of the backtracking control verbs, see
2034           the section entitled "Backtracking control" in the pcrepattern documen-
2035           tation.
2036    
2037     Option bits for pcre_exec()     Option bits for pcre_exec()
2038    
2039         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.
2040         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,
2041         PCRE_NOTBOL,   PCRE_NOTEOL,   PCRE_NOTEMPTY,   PCRE_NO_UTF8_CHECK   and         PCRE_NOTBOL,    PCRE_NOTEOL,    PCRE_NOTEMPTY,   PCRE_NOTEMPTY_ATSTART,
2042         PCRE_PARTIAL.         PCRE_NO_START_OPTIMIZE,  PCRE_NO_UTF8_CHECK,   PCRE_PARTIAL_SOFT,   and
2043           PCRE_PARTIAL_HARD.
2044    
2045           PCRE_ANCHORED           PCRE_ANCHORED
2046    
# Line 1997  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 2120  MATCHING A PATTERN: THE TRADITIONAL FUNC
2120    
2121           a?b?           a?b?
2122    
2123         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
2124         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
2125         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-
2126         rences of "a" or "b".         rences of "a" or "b".
2127    
2128         Perl has no direct equivalent of PCRE_NOTEMPTY, but it does make a spe-           PCRE_NOTEMPTY_ATSTART
2129         cial case of a pattern match of the empty  string  within  its  split()  
2130         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
2131         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
2132         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.
2133         if that fails by advancing the starting offset (see below)  and  trying  
2134         an ordinary match again. There is some code that demonstrates how to do         Perl     has    no    direct    equivalent    of    PCRE_NOTEMPTY    or
2135         this in the pcredemo.c sample program.         PCRE_NOTEMPTY_ATSTART, but it does make a special  case  of  a  pattern
2136           match  of  the empty string within its split() function, and when using
2137           the /g modifier. It is  possible  to  emulate  Perl's  behaviour  after
2138           matching a null string by first trying the match again at the same off-
2139           set with PCRE_NOTEMPTY_ATSTART and  PCRE_ANCHORED,  and  then  if  that
2140           fails, by advancing the starting offset (see below) and trying an ordi-
2141           nary match again. There is some code that demonstrates how to  do  this
2142           in  the  pcredemo sample program. In the most general case, you have to
2143           check to see if the newline convention recognizes CRLF  as  a  newline,
2144           and  if so, and the current character is CR followed by LF, advance the
2145           starting offset by two characters instead of one.
2146    
2147             PCRE_NO_START_OPTIMIZE
2148    
2149           There are a number of optimizations that pcre_exec() uses at the  start
2150           of  a  match,  in  order to speed up the process. For example, if it is
2151           known that an unanchored match must start with a specific character, it
2152           searches  the  subject  for that character, and fails immediately if it
2153           cannot find it, without actually running the  main  matching  function.
2154           This means that a special item such as (*COMMIT) at the start of a pat-
2155           tern is not considered until after a suitable starting  point  for  the
2156           match  has been found. When callouts or (*MARK) items are in use, these
2157           "start-up" optimizations can cause them to be skipped if the pattern is
2158           never  actually  used.  The start-up optimizations are in effect a pre-
2159           scan of the subject that takes place before the pattern is run.
2160    
2161           The PCRE_NO_START_OPTIMIZE option disables the start-up  optimizations,
2162           possibly  causing  performance  to  suffer,  but ensuring that in cases
2163           where the result is "no match", the callouts do occur, and  that  items
2164           such as (*COMMIT) and (*MARK) are considered at every possible starting
2165           position in the subject  string.   Setting  PCRE_NO_START_OPTIMIZE  can
2166           change the outcome of a matching operation.  Consider the pattern
2167    
2168             (*COMMIT)ABC
2169    
2170           When  this  is  compiled, PCRE records the fact that a match must start
2171           with the character "A". Suppose the subject  string  is  "DEFABC".  The
2172           start-up  optimization  scans along the subject, finds "A" and runs the
2173           first match attempt from there. The (*COMMIT) item means that the  pat-
2174           tern  must  match the current starting position, which in this case, it
2175           does. However, if the same match  is  run  with  PCRE_NO_START_OPTIMIZE
2176           set,  the  initial  scan  along the subject string does not happen. The
2177           first match attempt is run starting  from  "D"  and  when  this  fails,
2178           (*COMMIT)  prevents  any  further  matches  being tried, so the overall
2179           result is "no match". If the pattern is studied,  more  start-up  opti-
2180           mizations  may  be  used. For example, a minimum length for the subject
2181           may be recorded. Consider the pattern
2182    
2183             (*MARK:A)(X|Y)
2184    
2185           The minimum length for a match is one  character.  If  the  subject  is
2186           "ABC",  there  will  be  attempts  to  match "ABC", "BC", "C", and then
2187           finally an empty string.  If the pattern is studied, the final  attempt
2188           does  not take place, because PCRE knows that the subject is too short,
2189           and so the (*MARK) is never encountered.  In this  case,  studying  the
2190           pattern  does  not  affect the overall match result, which is still "no
2191           match", but it does affect the auxiliary information that is returned.
2192    
2193           PCRE_NO_UTF8_CHECK           PCRE_NO_UTF8_CHECK
2194    
# Line 2019  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 2198  MATCHING A PATTERN: THE TRADITIONAL FUNC
2198         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
2199         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
2200         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,
2201         pcre_exec() returns the error PCRE_ERROR_BADUTF8. If  startoffset  con-         pcre_exec() returns  the  error  PCRE_ERROR_BADUTF8  or,  if  PCRE_PAR-
2202         tains an invalid value, PCRE_ERROR_BADUTF8_OFFSET is returned.         TIAL_HARD  is set and the problem is a truncated UTF-8 character at the
2203           end of the subject, PCRE_ERROR_SHORTUTF8.  If  startoffset  contains  a
2204           value  that does not point to the start of a UTF-8 character (or to the
2205           end of the subject), PCRE_ERROR_BADUTF8_OFFSET is returned.
2206    
2207           If you already know that your subject is valid, and you  want  to  skip
2208           these    checks    for   performance   reasons,   you   can   set   the
2209           PCRE_NO_UTF8_CHECK option when calling pcre_exec(). You might  want  to
2210           do  this  for the second and subsequent calls to pcre_exec() if you are
2211           making repeated calls to find all  the  matches  in  a  single  subject
2212           string.  However,  you  should  be  sure  that the value of startoffset
2213           points to the start of a UTF-8 character (or the end of  the  subject).
2214           When  PCRE_NO_UTF8_CHECK is set, the effect of passing an invalid UTF-8
2215           string as a subject or an invalid value of  startoffset  is  undefined.
2216           Your program may crash.
2217    
2218         If  you  already  know that your subject is valid, and you want to skip           PCRE_PARTIAL_HARD
2219         these   checks   for   performance   reasons,   you   can    set    the           PCRE_PARTIAL_SOFT
2220         PCRE_NO_UTF8_CHECK  option  when calling pcre_exec(). You might want to  
2221         do this for the second and subsequent calls to pcre_exec() if  you  are         These  options turn on the partial matching feature. For backwards com-
2222         making  repeated  calls  to  find  all  the matches in a single subject         patibility, PCRE_PARTIAL is a synonym for PCRE_PARTIAL_SOFT. A  partial
2223         string. However, you should be  sure  that  the  value  of  startoffset         match  occurs if the end of the subject string is reached successfully,
2224         points  to  the  start of a UTF-8 character. When PCRE_NO_UTF8_CHECK is         but there are not enough subject characters to complete the  match.  If
2225         set, the effect of passing an invalid UTF-8 string as a subject,  or  a         this happens when PCRE_PARTIAL_SOFT (but not PCRE_PARTIAL_HARD) is set,
2226         value  of startoffset that does not point to the start of a UTF-8 char-         matching continues by testing any remaining alternatives.  Only  if  no
2227         acter, is undefined. Your program may crash.         complete  match  can be found is PCRE_ERROR_PARTIAL returned instead of
2228           PCRE_ERROR_NOMATCH. In other words,  PCRE_PARTIAL_SOFT  says  that  the
2229           PCRE_PARTIAL         caller  is  prepared to handle a partial match, but only if no complete
2230           match can be found.
2231         This option turns on the  partial  matching  feature.  If  the  subject  
2232         string  fails to match the pattern, but at some point during the match-         If PCRE_PARTIAL_HARD is set, it overrides  PCRE_PARTIAL_SOFT.  In  this
2233         ing process the end of the subject was reached (that  is,  the  subject         case,  if  a  partial  match  is found, pcre_exec() immediately returns
2234         partially  matches  the  pattern and the failure to match occurred only         PCRE_ERROR_PARTIAL, without  considering  any  other  alternatives.  In
2235         because there were not enough subject characters), pcre_exec()  returns         other  words, when PCRE_PARTIAL_HARD is set, a partial match is consid-
2236         PCRE_ERROR_PARTIAL  instead of PCRE_ERROR_NOMATCH. When PCRE_PARTIAL is         ered to be more important that an alternative complete match.
2237         used, there are restrictions on what may appear in the  pattern.  These  
2238         are discussed in the pcrepartial documentation.         In both cases, the portion of the string that was  inspected  when  the
2239           partial match was found is set as the first matching string. There is a
2240           more detailed discussion of partial and  multi-segment  matching,  with
2241           examples, in the pcrepartial documentation.
2242    
2243     The string to be matched by pcre_exec()     The string to be matched by pcre_exec()
2244    
2245         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
2246         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.
2247         mode,  the  byte  offset  must point to the start of a UTF-8 character.         If  this  is  negative  or  greater  than  the  length  of the subject,
2248         Unlike the pattern string, the subject may contain binary  zero  bytes.         pcre_exec() returns PCRE_ERROR_BADOFFSET. When the starting  offset  is
2249         When  the starting offset is zero, the search for a match starts at the         zero,  the  search  for a match starts at the beginning of the subject,
2250         beginning of the subject, and this is by far the most common case.         and this is by far the most common case. In UTF-8 mode, the byte offset
2251           must  point  to  the start of a UTF-8 character (or the end of the sub-
2252         A non-zero starting offset is useful when searching for  another  match         ject). Unlike the pattern string, the subject may contain  binary  zero
2253         in  the same subject by calling pcre_exec() again after a previous suc-         bytes.
2254         cess.  Setting startoffset differs from just passing over  a  shortened  
2255         string  and  setting  PCRE_NOTBOL  in the case of a pattern that begins         A  non-zero  starting offset is useful when searching for another match
2256           in the same subject by calling pcre_exec() again after a previous  suc-
2257           cess.   Setting  startoffset differs from just passing over a shortened
2258           string and setting PCRE_NOTBOL in the case of  a  pattern  that  begins
2259         with any kind of lookbehind. For example, consider the pattern         with any kind of lookbehind. For example, consider the pattern
2260    
2261           \Biss\B           \Biss\B
2262    
2263         which finds occurrences of "iss" in the middle of  words.  (\B  matches         which  finds  occurrences  of "iss" in the middle of words. (\B matches
2264         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.)
2265         When applied to the string "Mississipi" the first call  to  pcre_exec()         When  applied  to the string "Mississipi" the first call to pcre_exec()
2266         finds  the  first  occurrence. If pcre_exec() is called again with just         finds the first occurrence. If pcre_exec() is called  again  with  just
2267         the remainder of the subject,  namely  "issipi",  it  does  not  match,         the  remainder  of  the  subject,  namely  "issipi", it does not match,
2268         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
2269         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
2270         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-
2271         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
2272         discover that it is preceded by a letter.         discover that it is preceded by a letter.
2273    
2274           Finding all the matches in a subject is tricky  when  the  pattern  can
2275           match an empty string. It is possible to emulate Perl's /g behaviour by
2276           first  trying  the  match  again  at  the   same   offset,   with   the
2277           PCRE_NOTEMPTY_ATSTART  and  PCRE_ANCHORED  options,  and  then  if that
2278           fails, advancing the starting  offset  and  trying  an  ordinary  match
2279           again. There is some code that demonstrates how to do this in the pcre-
2280           demo sample program. In the most general case, you have to check to see
2281           if  the newline convention recognizes CRLF as a newline, and if so, and
2282           the current character is CR followed by LF, advance the starting offset
2283           by two characters instead of one.
2284    
2285         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,
2286         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
2287         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
# Line 2087  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 2297  MATCHING A PATTERN: THE TRADITIONAL FUNC
2297         string.  PCRE  supports several other kinds of parenthesized subpattern         string.  PCRE  supports several other kinds of parenthesized subpattern
2298         that do not cause substrings to be captured.         that do not cause substrings to be captured.
2299    
2300         Captured substrings are returned to the caller via a vector of  integer         Captured substrings are returned to the caller via a vector of integers
2301         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-
2302         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:
2303         Note: this argument is NOT the size of ovector in bytes.         this argument is NOT the size of ovector in bytes.
2304    
2305         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-
2306         strings, each substring using a pair of integers. The  remaining  third         strings, each substring using a pair of integers. The  remaining  third
2307         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-
2308         turing subpatterns, and is not available for passing back  information.         turing subpatterns, and is not available for passing back  information.
2309         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
2310         it is not, it is rounded down.         it is not, it is rounded down.
2311    
2312         When a match is successful, information about  captured  substrings  is         When a match is successful, information about  captured  substrings  is
2313         returned  in  pairs  of integers, starting at the beginning of ovector,         returned  in  pairs  of integers, starting at the beginning of ovector,
2314         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
2315         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
2316         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
2317         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
2318         tor[1], identify the portion of  the  subject  string  matched  by  the         byte offsets, even in UTF-8 mode. They are not character counts.
2319         entire  pattern.  The next pair is used for the first capturing subpat-  
2320         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
2321         highest numbered pair that has been set. For example, if two substrings         portion  of  the subject string matched by the entire pattern. The next
2322         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
2323         subpatterns,  the return value from a successful match is 1, indicating         returned by pcre_exec() is one more than the highest numbered pair that
2324         that just the first pair of offsets has been set.         has been set.  For example, if two substrings have been  captured,  the
2325           returned  value is 3. If there are no capturing subpatterns, the return
2326           value from a successful match is 1, indicating that just the first pair
2327           of offsets has been set.
2328    
2329         If a capturing subpattern is matched repeatedly, it is the last portion         If a capturing subpattern is matched repeatedly, it is the last portion
2330         of the string that it matched that is returned.         of the string that it matched that is returned.
2331    
2332         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,
2333         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
2334         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
2335         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
2336         as  NULL  and  ovecsize  as zero. However, if the pattern contains back         ovecsize as zero. However, if the pattern contains back references  and
2337         references and the ovector is not big enough to  remember  the  related         the  ovector is not big enough to remember the related substrings, PCRE
2338         substrings,  PCRE has to get additional memory for use during matching.         has to get additional memory for use during matching. Thus it  is  usu-
2339         Thus it is usually advisable to supply an ovector.         ally advisable to supply an ovector.
2340    
2341         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
2342         subpatterns  there  are  in  a  compiled pattern. The smallest size for         subpatterns there are in a compiled  pattern.  The  smallest  size  for
2343         ovector that will allow for n captured substrings, in addition  to  the         ovector  that  will allow for n captured substrings, in addition to the
2344         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.
2345    
2346         It  is  possible for capturing subpattern number n+1 to match some part         It is possible for capturing subpattern number n+1 to match  some  part
2347         of the subject when subpattern n has not been used at all. For example,         of the subject when subpattern n has not been used at all. For example,
2348         if  the  string  "abc"  is  matched against the pattern (a|(z))(bc) the         if the string "abc" is matched  against  the  pattern  (a|(z))(bc)  the
2349         return from the function is 4, and subpatterns 1 and 3 are matched, but         return from the function is 4, and subpatterns 1 and 3 are matched, but
2350         2  is  not.  When  this happens, both values in the offset pairs corre-         2 is not. When this happens, both values in  the  offset  pairs  corre-
2351         sponding to unused subpatterns are set to -1.         sponding to unused subpatterns are set to -1.
2352    
2353         Offset values that correspond to unused subpatterns at the end  of  the         Offset  values  that correspond to unused subpatterns at the end of the
2354         expression  are  also  set  to  -1. For example, if the string "abc" is         expression are also set to -1. For example,  if  the  string  "abc"  is
2355         matched against the pattern (abc)(x(yz)?)? subpatterns 2 and 3 are  not         matched  against the pattern (abc)(x(yz)?)? subpatterns 2 and 3 are not
2356         matched.  The  return  from the function is 2, because the highest used         matched. The return from the function is 2, because  the  highest  used
2357         capturing subpattern number is 1. However, you can refer to the offsets         capturing  subpattern  number  is 1, and the offsets for for the second
2358         for  the  second  and third capturing subpatterns if you wish (assuming         and third capturing subpatterns (assuming the vector is  large  enough,
2359         the vector is large enough, of course).         of course) are set to -1.
2360    
2361           Note: Elements of ovector that do not correspond to capturing parenthe-
2362           ses in the pattern are never changed. That is, if a pattern contains  n
2363           capturing parentheses, no more than ovector[0] to ovector[2n+1] are set
2364           by pcre_exec(). The other elements retain whatever values  they  previ-
2365           ously had.
2366    
2367         Some convenience functions are provided  for  extracting  the  captured         Some  convenience  functions  are  provided for extracting the captured
2368         substrings as separate strings. These are described below.         substrings as separate strings. These are described below.
2369    
2370     Error return values from pcre_exec()     Error return values from pcre_exec()
2371    
2372         If  pcre_exec()  fails, it returns a negative number. The following are         If pcre_exec() fails, it returns a negative number. The  following  are
2373         defined in the header file:         defined in the header file:
2374    
2375           PCRE_ERROR_NOMATCH        (-1)           PCRE_ERROR_NOMATCH        (-1)
# Line 2159  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 2378  MATCHING A PATTERN: THE TRADITIONAL FUNC
2378    
2379           PCRE_ERROR_NULL           (-2)           PCRE_ERROR_NULL           (-2)
2380    
2381         Either code or subject was passed as NULL,  or  ovector  was  NULL  and         Either  code  or  subject  was  passed as NULL, or ovector was NULL and
2382         ovecsize was not zero.         ovecsize was not zero.
2383    
2384           PCRE_ERROR_BADOPTION      (-3)           PCRE_ERROR_BADOPTION      (-3)
# Line 2168  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 2387  MATCHING A PATTERN: THE TRADITIONAL FUNC
2387    
2388           PCRE_ERROR_BADMAGIC       (-4)           PCRE_ERROR_BADMAGIC       (-4)
2389    
2390         PCRE  stores a 4-byte "magic number" at the start of the compiled code,         PCRE stores a 4-byte "magic number" at the start of the compiled  code,
2391         to catch the case when it is passed a junk pointer and to detect when a         to catch the case when it is passed a junk pointer and to detect when a
2392         pattern that was compiled in an environment of one endianness is run in         pattern that was compiled in an environment of one endianness is run in
2393         an environment with the other endianness. This is the error  that  PCRE         an  environment  with the other endianness. This is the error that PCRE
2394         gives when the magic number is not present.         gives when the magic number is not present.
2395    
2396           PCRE_ERROR_UNKNOWN_OPCODE (-5)           PCRE_ERROR_UNKNOWN_OPCODE (-5)
2397    
2398         While running the pattern match, an unknown item was encountered in the         While running the pattern match, an unknown item was encountered in the
2399         compiled pattern. This error could be caused by a bug  in  PCRE  or  by         compiled  pattern.  This  error  could be caused by a bug in PCRE or by
2400         overwriting of the compiled pattern.         overwriting of the compiled pattern.
2401    
2402           PCRE_ERROR_NOMEMORY       (-6)           PCRE_ERROR_NOMEMORY       (-6)
2403    
2404         If  a  pattern contains back references, but the ovector that is passed         If a pattern contains back references, but the ovector that  is  passed
2405         to pcre_exec() is not big enough to remember the referenced substrings,         to pcre_exec() is not big enough to remember the referenced substrings,
2406         PCRE  gets  a  block of memory at the start of matching to use for this         PCRE gets a block of memory at the start of matching to  use  for  this
2407         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
2408         memory is automatically freed at the end of matching.         memory is automatically freed at the end of matching.
2409    
2410           This error is also given if pcre_stack_malloc() fails  in  pcre_exec().
2411           This  can happen only when PCRE has been compiled with --disable-stack-
2412           for-recursion.
2413    
2414           PCRE_ERROR_NOSUBSTRING    (-7)           PCRE_ERROR_NOSUBSTRING    (-7)
2415    
2416         This  error is used by the pcre_copy_substring(), pcre_get_substring(),         This error is used by the pcre_copy_substring(),  pcre_get_substring(),
2417         and  pcre_get_substring_list()  functions  (see  below).  It  is  never         and  pcre_get_substring_list()  functions  (see  below).  It  is  never
2418         returned by pcre_exec().         returned by pcre_exec().
2419    
2420           PCRE_ERROR_MATCHLIMIT     (-8)           PCRE_ERROR_MATCHLIMIT     (-8)
2421    
2422         The  backtracking  limit,  as  specified  by the match_limit field in a         The backtracking limit, as specified by  the  match_limit  field  in  a
2423         pcre_extra structure (or defaulted) was reached.  See  the  description         pcre_extra  structure  (or  defaulted) was reached. See the description
2424         above.         above.
2425    
2426           PCRE_ERROR_CALLOUT        (-9)           PCRE_ERROR_CALLOUT        (-9)
2427    
2428         This error is never generated by pcre_exec() itself. It is provided for         This error is never generated by pcre_exec() itself. It is provided for
2429         use by callout functions that want to yield a distinctive  error  code.         use  by  callout functions that want to yield a distinctive error code.
2430         See the pcrecallout documentation for details.         See the pcrecallout documentation for details.
2431    
2432           PCRE_ERROR_BADUTF8        (-10)           PCRE_ERROR_BADUTF8        (-10)
2433    
2434         A  string  that contains an invalid UTF-8 byte sequence was passed as a         A string that contains an invalid UTF-8 byte sequence was passed  as  a
2435         subject.         subject.   However,  if  PCRE_PARTIAL_HARD  is set and the problem is a
2436           truncated UTF-8 character at the end of the subject,  PCRE_ERROR_SHORT-
2437           UTF8 is used instead.
2438    
2439           PCRE_ERROR_BADUTF8_OFFSET (-11)           PCRE_ERROR_BADUTF8_OFFSET (-11)
2440    
2441         The UTF-8 byte sequence that was passed as a subject was valid, but the         The UTF-8 byte sequence that was passed as a subject was valid, but the
2442         value  of startoffset did not point to the beginning of a UTF-8 charac-         value of startoffset did not point to the beginning of a UTF-8  charac-
2443         ter.         ter or the end of the subject.
2444    
2445           PCRE_ERROR_PARTIAL        (-12)           PCRE_ERROR_PARTIAL        (-12)
2446    
2447         The subject string did not match, but it did match partially.  See  the         The  subject  string did not match, but it did match partially. See the
2448         pcrepartial documentation for details of partial matching.         pcrepartial documentation for details of partial matching.
2449    
2450           PCRE_ERROR_BADPARTIAL     (-13)           PCRE_ERROR_BADPARTIAL     (-13)
2451    
2452         The  PCRE_PARTIAL  option  was  used with a compiled pattern containing         This code is no longer in  use.  It  was  formerly  returned  when  the
2453         items that are not supported for partial matching. See the  pcrepartial         PCRE_PARTIAL  option  was used with a compiled pattern containing items
2454         documentation for details of partial matching.         that were  not  supported  for  partial  matching.  From  release  8.00
2455           onwards, there are no restrictions on partial matching.
2456    
2457           PCRE_ERROR_INTERNAL       (-14)           PCRE_ERROR_INTERNAL       (-14)
2458    
# Line 2235  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 2461  MATCHING A PATTERN: THE TRADITIONAL FUNC
2461    
2462           PCRE_ERROR_BADCOUNT       (-15)           PCRE_ERROR_BADCOUNT       (-15)
2463    
2464         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.
2465    
2466           PCRE_ERROR_RECURSIONLIMIT (-21)           PCRE_ERROR_RECURSIONLIMIT (-21)
2467    
2468         The internal recursion limit, as specified by the match_limit_recursion         The internal recursion limit, as specified by the match_limit_recursion
2469         field in a pcre_extra structure (or defaulted)  was  reached.  See  the         field  in  a  pcre_extra  structure (or defaulted) was reached. See the
2470         description above.         description above.
2471    
2472           PCRE_ERROR_BADNEWLINE     (-23)           PCRE_ERROR_BADNEWLINE     (-23)
2473    
2474         An invalid combination of PCRE_NEWLINE_xxx options was given.         An invalid combination of PCRE_NEWLINE_xxx options was given.
2475    
2476             PCRE_ERROR_BADOFFSET      (-24)
2477    
2478           The value of startoffset was negative or greater than the length of the
2479           subject, that is, the value in length.
2480    
2481             PCRE_ERROR_SHORTUTF8      (-25)
2482    
2483           The  subject  string ended with an incomplete (truncated) UTF-8 charac-
2484           ter, and the PCRE_PARTIAL_HARD option was  set.  Without  this  option,
2485           PCRE_ERROR_BADUTF8 is returned in this situation.
2486    
2487         Error numbers -16 to -20 and -22 are not used by pcre_exec().         Error numbers -16 to -20 and -22 are not used by pcre_exec().
2488    
2489    
# Line 2385  EXTRACTING CAPTURED SUBSTRINGS BY NAME Line 2622  EXTRACTING CAPTURED SUBSTRINGS BY NAME
2622         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
2623         behaviour may not be what you want (see the next section).         behaviour may not be what you want (see the next section).
2624    
2625           Warning: If the pattern uses the (?| feature to set up multiple subpat-
2626           terns with the same number, as described in the  section  on  duplicate
2627           subpattern  numbers  in  the  pcrepattern page, you cannot use names to
2628           distinguish the different subpatterns, because names are  not  included
2629           in  the compiled code. The matching process uses only numbers. For this
2630           reason, the use of different names for subpatterns of the  same  number
2631           causes an error at compile time.
2632    
2633    
2634  DUPLICATE SUBPATTERN NAMES  DUPLICATE SUBPATTERN NAMES
2635    
# Line 2392  DUPLICATE SUBPATTERN NAMES Line 2637  DUPLICATE SUBPATTERN NAMES
2637              const char *name, char **first, char **last);              const char *name, char **first, char **last);
2638    
2639         When  a  pattern  is  compiled with the PCRE_DUPNAMES option, names for         When  a  pattern  is  compiled with the PCRE_DUPNAMES option, names for
2640         subpatterns are not required to  be  unique.  Normally,  patterns  with         subpatterns are not required to be unique. (Duplicate names are  always
2641         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 (?|
2642         subpatterns participates. An example is shown in the pcrepattern  docu-         feature. Indeed, if such subpatterns are named, they  are  required  to
2643         mentation.         use the same names.)
2644    
2645           Normally, patterns with duplicate names are such that in any one match,
2646           only one of the named subpatterns participates. An example is shown  in
2647           the pcrepattern documentation.
2648    
2649         When    duplicates   are   present,   pcre_copy_named_substring()   and         When    duplicates   are   present,   pcre_copy_named_substring()   and
2650         pcre_get_named_substring() return the first substring corresponding  to         pcre_get_named_substring() return the first substring corresponding  to
# Line 2448  MATCHING A PATTERN: THE ALTERNATIVE FUNC Line 2697  MATCHING A PATTERN: THE ALTERNATIVE FUNC
2697         characteristics to the normal algorithm, and  is  not  compatible  with         characteristics to the normal algorithm, and  is  not  compatible  with
2698         Perl.  Some  of the features of PCRE patterns are not supported. Never-         Perl.  Some  of the features of PCRE patterns are not supported. Never-
2699         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
2700         a discussion of the two matching algorithms, see the pcrematching docu-         a  discussion  of  the  two matching algorithms, and a list of features
2701         mentation.         that pcre_dfa_exec() does not support, see the pcrematching  documenta-
2702           tion.
2703    
2704         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
2705         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-
2706         ent way, and this is described below. The other  common  arguments  are         ent  way,  and  this is described below. The other common arguments are
2707         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
2708         repeated here.         repeated here.
2709    
2710         The two additional arguments provide workspace for  the  function.  The         The  two  additional  arguments provide workspace for the function. The
2711         workspace  vector  should  contain at least 20 elements. It is used for         workspace vector should contain at least 20 elements. It  is  used  for
2712         keeping  track  of  multiple  paths  through  the  pattern  tree.  More         keeping  track  of  multiple  paths  through  the  pattern  tree.  More
2713         workspace  will  be  needed for patterns and subjects where there are a         workspace will be needed for patterns and subjects where  there  are  a
2714         lot of potential matches.         lot of potential matches.
2715    
2716         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 2482  MATCHING A PATTERN: THE ALTERNATIVE FUNC Line 2732  MATCHING A PATTERN: THE ALTERNATIVE FUNC
2732    
2733     Option bits for pcre_dfa_exec()     Option bits for pcre_dfa_exec()
2734    
2735         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
2736         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-
2737         LINE_xxx, PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY,  PCRE_NO_UTF8_CHECK,         LINE_xxx,        PCRE_NOTBOL,        PCRE_NOTEOL,        PCRE_NOTEMPTY,
2738         PCRE_PARTIAL, PCRE_DFA_SHORTEST, and PCRE_DFA_RESTART. All but the last         PCRE_NOTEMPTY_ATSTART,      PCRE_NO_UTF8_CHECK,       PCRE_BSR_ANYCRLF,
2739         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-
2740         not repeated here.         TIAL_SOFT, PCRE_DFA_SHORTEST, and PCRE_DFA_RESTART.  All but  the  last
2741           four  of  these  are  exactly  the  same  as  for pcre_exec(), so their
2742           PCRE_PARTIAL         description is not repeated here.
2743    
2744         This  has  the  same general effect as it does for pcre_exec(), but the           PCRE_PARTIAL_HARD
2745         details  are  slightly  different.  When  PCRE_PARTIAL   is   set   for           PCRE_PARTIAL_SOFT
2746         pcre_dfa_exec(),  the  return code PCRE_ERROR_NOMATCH is converted into  
2747         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
2748         been no complete matches, but there is still at least one matching pos-         details  are  slightly  different.  When  PCRE_PARTIAL_HARD  is set for
2749         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-
2750         set as the first matching string.         ject  is  reached  and there is still at least one matching possibility
2751           that requires additional characters. This happens even if some complete
2752           matches have also been found. When PCRE_PARTIAL_SOFT is set, the return
2753           code PCRE_ERROR_NOMATCH is converted into PCRE_ERROR_PARTIAL if the end
2754           of  the  subject  is  reached, there have been no complete matches, but
2755           there is still at least one matching possibility. The  portion  of  the
2756           string  that  was inspected when the longest partial match was found is
2757           set as the first matching string  in  both  cases.   There  is  a  more
2758           detailed  discussion  of partial and multi-segment matching, with exam-
2759           ples, in the pcrepartial documentation.
2760    
2761           PCRE_DFA_SHORTEST           PCRE_DFA_SHORTEST
2762    
2763         Setting  the  PCRE_DFA_SHORTEST option causes the matching algorithm to         Setting the PCRE_DFA_SHORTEST option causes the matching  algorithm  to
2764         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-
2765         tive  algorithm  works, this is necessarily the shortest possible match         tive algorithm works, this is necessarily the shortest  possible  match
2766         at the first possible matching point in the subject string.         at the first possible matching point in the subject string.
2767    
2768           PCRE_DFA_RESTART           PCRE_DFA_RESTART
2769    
2770         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
2771         returns  a  partial  match, it is possible to call it again, with addi-         again, with additional subject characters, and have  it  continue  with
2772         tional subject characters, and have it continue with  the  same  match.         the  same match. The PCRE_DFA_RESTART option requests this action; when
2773         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
2774         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
2775         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
2776         match. There is more discussion of this  facility  in  the  pcrepartial         pcrepartial documentation.
        documentation.  
2777    
2778     Successful returns from pcre_dfa_exec()     Successful returns from pcre_dfa_exec()
2779    
# Line 2592  MATCHING A PATTERN: THE ALTERNATIVE FUNC Line 2850  MATCHING A PATTERN: THE ALTERNATIVE FUNC
2850  SEE ALSO  SEE ALSO
2851    
2852         pcrebuild(3), pcrecallout(3), pcrecpp(3)(3), pcrematching(3),  pcrepar-         pcrebuild(3), pcrecallout(3), pcrecpp(3)(3), pcrematching(3),  pcrepar-
2853         tial(3),  pcreposix(3), pcreprecompile(3), pcresample(3), pcrestack(3).         tial(3), pcreposix(3), pcreprecompile(3), pcresample(3), pcrestack(3).
2854    
2855    
2856  AUTHOR  AUTHOR
# Line 2604  AUTHOR Line 2862  AUTHOR
2862    
2863  REVISION  REVISION
2864    
2865         Last updated: 12 April 2008         Last updated: 13 November 2010
2866         Copyright (c) 1997-2008 University of Cambridge.         Copyright (c) 1997-2010 University of Cambridge.
2867  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
2868    
2869    
2870  PCRECALLOUT(3)                                                  PCRECALLOUT(3)  PCRECALLOUT(3)                                                  PCRECALLOUT(3)
2871    
2872    
# Line 2634  PCRE CALLOUTS Line 2892  PCRE CALLOUTS
2892    
2893           (?C1)abc(?C2)def           (?C1)abc(?C2)def
2894    
2895         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
2896         called, PCRE automatically  inserts  callouts,  all  with  number  255,         pcre_compile2() is called, PCRE  automatically  inserts  callouts,  all
2897         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
2898         used with the pattern         PCRE_AUTO_CALLOUT is used with the pattern
2899    
2900           A(\d{2}|--)           A(\d{2}|--)
2901    
# Line 2656  PCRE CALLOUTS Line 2914  PCRE CALLOUTS
2914  MISSING CALLOUTS  MISSING CALLOUTS
2915    
2916         You  should  be  aware  that,  because of optimizations in the way PCRE         You  should  be  aware  that,  because of optimizations in the way PCRE
2917         matches patterns, callouts sometimes do not happen. For example, if the         matches patterns by default, callouts  sometimes  do  not  happen.  For
2918         pattern is         example, if the pattern is
2919    
2920           ab(?C4)cd           ab(?C4)cd
2921    
# Line 2666  MISSING CALLOUTS Line 2924  MISSING CALLOUTS
2924         ever  start,  and  the  callout is never reached. However, with "abyd",         ever  start,  and  the  callout is never reached. However, with "abyd",
2925         though the result is still no match, the callout is obeyed.         though the result is still no match, the callout is obeyed.
2926    
2927           If the pattern is studied, PCRE knows the minimum length of a  matching
2928           string,  and will immediately give a "no match" return without actually
2929           running a match if the subject is not long enough, or,  for  unanchored
2930           patterns, if it has been scanned far enough.
2931    
2932           You  can disable these optimizations by passing the PCRE_NO_START_OPTI-
2933           MIZE option to pcre_exec() or  pcre_dfa_exec().  This  slows  down  the
2934           matching  process,  but  does  ensure that callouts such as the example
2935           above are obeyed.
2936    
2937    
2938  THE CALLOUT INTERFACE  THE CALLOUT INTERFACE
2939    
# Line 2693  THE CALLOUT INTERFACE Line 2961  THE CALLOUT INTERFACE
2961         version number will change again in future  if  additional  fields  are         version number will change again in future  if  additional  fields  are
2962         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.
2963    
2964         The callout_number field contains the number of the  callout,  as  com-         The  callout_number  field  contains the number of the callout, as com-
2965         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-
2966         outs, and 255 for automatically generated callouts).         outs, and 255 for automatically generated callouts).
2967    
2968         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
2969         passed   by   the   caller  to  pcre_exec()  or  pcre_dfa_exec().  When         passed  by  the  caller  to  pcre_exec()   or   pcre_dfa_exec().   When
2970         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
2971         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
2972         extracting substrings after a match has completed. For  pcre_dfa_exec()         extracting  substrings after a match has completed. For pcre_dfa_exec()
2973         this field is not useful.         this field is not useful.
2974    
2975         The subject and subject_length fields contain copies of the values that         The subject and subject_length fields contain copies of the values that
2976         were passed to pcre_exec().         were passed to pcre_exec().
2977    
2978         The start_match field normally contains the offset within  the  subject         The  start_match  field normally contains the offset within the subject
2979         at  which  the  current  match  attempt started. However, if the escape         at which the current match attempt  started.  However,  if  the  escape
2980         sequence \K has been encountered, this value is changed to reflect  the         sequence  \K has been encountered, this value is changed to reflect the
2981         modified  starting  point.  If the pattern is not anchored, the callout         modified starting point. If the pattern is not  anchored,  the  callout
2982         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
2983         for different starting points in the subject.         for different starting points in the subject.
2984    
2985         The  current_position  field  contains the offset within the subject of         The current_position field contains the offset within  the  subject  of
2986         the current match pointer.         the current match pointer.
2987    
2988         When the pcre_exec() function is used, the capture_top  field  contains         When  the  pcre_exec() function is used, the capture_top field contains
2989         one  more than the number of the highest numbered captured substring so         one more than the number of the highest numbered captured substring  so
2990         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
2991         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
2992         does not support captured substrings.         does not support captured substrings.
2993    
2994         The capture_last field contains the number of the  most  recently  cap-         The  capture_last  field  contains the number of the most recently cap-
2995         tured  substring. If no substrings have been captured, its value is -1.         tured substring. If no substrings have been captured, its value is  -1.
2996         This is always the case when pcre_dfa_exec() is used.         This is always the case when pcre_dfa_exec() is used.
2997    
2998         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()
2999         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-
3000         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
3001         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
3002         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
3003         structure in the pcreapi documentation.         structure in the pcreapi documentation.
3004    
3005         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-
3006         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
3007         the pattern string.         the pattern string.
3008    
3009         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-
3010         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
3011         the  pattern  string. When the callout immediately precedes an alterna-         the pattern string. When the callout immediately precedes  an  alterna-
3012         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
3013         is  zero.  When the callout precedes an opening parenthesis, the length         is zero. When the callout precedes an opening parenthesis,  the  length
3014         is that of the entire subpattern.         is that of the entire subpattern.
3015    
3016         The pattern_position and next_item_length fields are intended  to  help         The  pattern_position  and next_item_length fields are intended to help
3017         in  distinguishing between different automatic callouts, which all have         in distinguishing between different automatic callouts, which all  have
3018         the same callout number. However, they are set for all callouts.         the same callout number. However, they are set for all callouts.
3019    
3020    
3021  RETURN VALUES  RETURN VALUES
3022    
3023         The external callout function returns an integer to PCRE. If the  value         The  external callout function returns an integer to PCRE. If the value
3024         is  zero,  matching  proceeds  as  normal. If the value is greater than         is zero, matching proceeds as normal. If  the  value  is  greater  than
3025         zero, matching fails at the current point, but  the  testing  of  other         zero,  matching  fails  at  the current point, but the testing of other
3026         matching possibilities goes ahead, just as if a lookahead assertion had         matching possibilities goes ahead, just as if a lookahead assertion had
3027         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
3028         pcre_exec() (or pcre_dfa_exec()) returns the negative value.         pcre_exec() or pcre_dfa_exec() returns the negative value.
3029    
3030         Negative   values   should   normally   be   chosen  from  the  set  of         Negative  values  should  normally  be   chosen   from   the   set   of
3031         PCRE_ERROR_xxx values. In particular, PCRE_ERROR_NOMATCH forces a stan-         PCRE_ERROR_xxx values. In particular, PCRE_ERROR_NOMATCH forces a stan-
3032         dard  "no  match"  failure.   The  error  number  PCRE_ERROR_CALLOUT is         dard "no  match"  failure.   The  error  number  PCRE_ERROR_CALLOUT  is
3033         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
3034         itself.         itself.
3035    
3036    
# Line 2775  AUTHOR Line 3043  AUTHOR
3043    
3044  REVISION  REVISION
3045    
3046         Last updated: 29 May 2007         Last updated: 29 September 2009
3047         Copyright (c) 1997-2007 University of Cambridge.         Copyright (c) 1997-2009 University of Cambridge.
3048  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
3049    
3050    
3051  PCRECOMPAT(3)                                                    PCRECOMPAT(3)  PCRECOMPAT(3)                                                    PCRECOMPAT(3)
3052    
3053    
# Line 2790  NAME Line 3058  NAME
3058  DIFFERENCES BETWEEN PCRE AND PERL  DIFFERENCES BETWEEN PCRE AND PERL
3059    
3060         This  document describes the differences in the ways that PCRE and Perl         This  document describes the differences in the ways that PCRE and Perl
3061         handle regular expressions. The differences described here  are  mainly         handle regular expressions. The differences  described  here  are  with
3062         with  respect  to  Perl 5.8, though PCRE versions 7.0 and later contain         respect to Perl versions 5.10 and above.
        some features that are expected to be in the forthcoming Perl 5.10.  
3063    
3064         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
3065         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
3066         main pcre page.         main pcre page.
3067    
3068         2. PCRE does not allow repeat quantifiers on lookahead assertions. Perl         2. PCRE does not allow repeat quantifiers on lookahead assertions. Perl
3069         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,
3070         (?!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
3071         just asserts that the next character is not "a" three times.         just asserts that the next character is not "a" three times.
3072    
3073         3.  Capturing  subpatterns  that occur inside negative lookahead asser-         3. Capturing subpatterns that occur inside  negative  lookahead  asser-
3074         tions are counted, but their entries in the offsets  vector  are  never         tions  are  counted,  but their entries in the offsets vector are never
3075         set.  Perl sets its numerical variables from any such patterns that are         set. Perl sets its numerical variables from any such patterns that  are
3076         matched before the assertion fails to match something (thereby succeed-         matched before the assertion fails to match something (thereby succeed-
3077         ing),  but  only  if the negative lookahead assertion contains just one         ing), but only if the negative lookahead assertion  contains  just  one
3078         branch.         branch.
3079    
3080         4. Though binary zero characters are supported in the  subject  string,         4.  Though  binary zero characters are supported in the subject string,
3081         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-
3082         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
3083         the pattern to represent a binary zero.         the pattern to represent a binary zero.
3084    
3085         5.  The  following Perl escape sequences are not supported: \l, \u, \L,         5. The following Perl escape sequences are not supported: \l,  \u,  \L,
3086         \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-
3087         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
3088         are encountered by PCRE, an error is generated.         are encountered by PCRE, an error is generated.
3089    
3090         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
3091         is  built  with Unicode character property support. The properties that         is built with Unicode character property support. The  properties  that
3092         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-
3093         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
3094         derived properties Any and L&.         derived  properties  Any  and  L&. PCRE does support the Cs (surrogate)
3095           property, which Perl does not; the  Perl  documentation  says  "Because
3096           Perl hides the need for the user to understand the internal representa-
3097           tion of Unicode characters, there is no need to implement the  somewhat
3098           messy concept of surrogates."
3099    
3100         7. PCRE does support the \Q...\E escape for quoting substrings. Charac-         7. PCRE does support the \Q...\E escape for quoting substrings. Charac-
3101         ters  in  between  are  treated as literals. This is slightly different         ters in between are treated as literals.  This  is  slightly  different
3102         from Perl in that $ and @ are  also  handled  as  literals  inside  the         from  Perl  in  that  $  and  @ are also handled as literals inside the
3103         quotes.  In Perl, they cause variable interpolation (but of course PCRE         quotes. In Perl, they cause variable interpolation (but of course  PCRE
3104         does not have variables). Note the following examples:         does not have variables). Note the following examples:
3105    
3106             Pattern            PCRE matches      Perl matches             Pattern            PCRE matches      Perl matches
# Line 2839  DIFFERENCES BETWEEN PCRE AND PERL Line 3110  DIFFERENCES BETWEEN PCRE AND PERL
3110             \Qabc\$xyz\E       abc\$xyz          abc\$xyz             \Qabc\$xyz\E       abc\$xyz          abc\$xyz
3111             \Qabc\E\$\Qxyz\E   abc$xyz           abc$xyz             \Qabc\E\$\Qxyz\E   abc$xyz           abc$xyz
3112    
3113         The \Q...\E sequence is recognized both inside  and  outside  character         The  \Q...\E  sequence  is recognized both inside and outside character
3114         classes.         classes.
3115    
3116         8. Fairly obviously, PCRE does not support the (?{code}) and (??{code})         8. Fairly obviously, PCRE does not support the (?{code}) and (??{code})
3117         constructions. However, there is support for recursive  patterns.  This         constructions.  However,  there is support for recursive patterns. This
3118         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
3119         "callout" feature allows an external function to be called during  pat-         "callout"  feature allows an external function to be called during pat-
3120         tern matching. See the pcrecallout documentation for details.         tern matching. See the pcrecallout documentation for details.
3121    
3122         9.  Subpatterns  that  are  called  recursively or as "subroutines" are         9. Subpatterns that are called  recursively  or  as  "subroutines"  are
3123         always treated as atomic groups in  PCRE.  This  is  like  Python,  but         always  treated  as  atomic  groups  in  PCRE. This is like Python, but
3124         unlike Perl.         unlike Perl. There is a discussion of an example that explains this  in
3125           more  detail  in  the section on recursion differences from Perl in the
3126         10.  There are some differences that are concerned with the settings of         pcrepattern page.
3127         captured strings when part of  a  pattern  is  repeated.  For  example,  
3128         matching  "aba"  against  the  pattern  /^(a(b)?)+$/  in Perl leaves $2         10. There are some differences that are concerned with the settings  of
3129           captured  strings  when  part  of  a  pattern is repeated. For example,
3130           matching "aba" against the  pattern  /^(a(b)?)+$/  in  Perl  leaves  $2
3131         unset, but in PCRE it is set to "b".         unset, but in PCRE it is set to "b".
3132    
3133         11.  PCRE  does  support  Perl  5.10's  backtracking  verbs  (*ACCEPT),         11.  PCRE's handling of duplicate subpattern numbers and duplicate sub-
3134         (*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
3135         the forms without an  argument.  PCRE  does  not  support  (*MARK).  If         fact the PCRE works internally just with numbers, using an external ta-
3136         (*ACCEPT)  is within capturing parentheses, PCRE does not set that cap-         ble to translate between numbers and names. In  particular,  a  pattern
3137         ture group; this is different to Perl.         such  as  (?|(?<a>A)|(?<b)B),  where the two capturing parentheses have
3138           the same number but different names, is not supported,  and  causes  an
3139         12. PCRE provides some extensions to the Perl regular expression facil-         error  at compile time. If it were allowed, it would not be possible to
3140         ities.   Perl  5.10  will  include new features that are not in earlier         distinguish which parentheses matched, because both names map  to  cap-
3141         versions, some of which (such as named parentheses) have been  in  PCRE         turing subpattern number 1. To avoid this confusing situation, an error
3142         for some time. This list is with respect to Perl 5.10:         is given at compile time.
3143    
3144         (a)  Although  lookbehind  assertions  must match fixed length strings,         12. Perl recognizes comments in some  places  that  PCRE  doesn't,  for
3145         each alternative branch of a lookbehind assertion can match a different         example, between the ( and ? at the start of a subpattern.
3146         length of string. Perl requires them all to have the same length.  
3147           13. PCRE provides some extensions to the Perl regular expression facil-
3148           ities.  Perl 5.10 includes new features that are not  in  earlier  ver-
3149           sions  of  Perl, some of which (such as named parentheses) have been in
3150           PCRE for some time. This list is with respect to Perl 5.10:
3151    
3152           (a) Although lookbehind assertions in  PCRE  must  match  fixed  length
3153           strings,  each alternative branch of a lookbehind assertion can match a
3154           different length of string. Perl requires them all  to  have  the  same
3155           length.
3156    
3157         (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 $
3158         meta-character matches only at the very end of the string.         meta-character matches only at the very end of the string.
# Line 2886  DIFFERENCES BETWEEN PCRE AND PERL Line 3168  DIFFERENCES BETWEEN PCRE AND PERL
3168         (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
3169         tried only at the first matching position in the subject string.         tried only at the first matching position in the subject string.
3170    
3171         (f)  The PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, and PCRE_NO_AUTO_CAP-         (f) The PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, PCRE_NOTEMPTY_ATSTART,
3172         TURE options for pcre_exec() have no Perl equivalents.         and PCRE_NO_AUTO_CAPTURE options for pcre_exec() have no  Perl  equiva-
3173           lents.
3174    
3175         (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
3176         CRLF by the PCRE_BSR_ANYCRLF option.         CRLF by the PCRE_BSR_ANYCRLF option.
3177    
3178         (h) The callout facility is PCRE-specific.         (h) The callout facility is PCRE-specific.
# Line 2899  DIFFERENCES BETWEEN PCRE AND PERL Line 3182  DIFFERENCES BETWEEN PCRE AND PERL
3182         (j) Patterns compiled by PCRE can be saved and re-used at a later time,         (j) Patterns compiled by PCRE can be saved and re-used at a later time,
3183         even on different hosts that have the other endianness.         even on different hosts that have the other endianness.
3184    
3185         (k) The alternative matching function (pcre_dfa_exec())  matches  in  a         (k)  The  alternative  matching function (pcre_dfa_exec()) matches in a
3186         different way and is not Perl-compatible.         different way and is not Perl-compatible.
3187    
3188         (l)  PCRE  recognizes some special sequences such as (*CR) at the start         (l) PCRE recognizes some special sequences such as (*CR) at  the  start
3189         of a pattern that set overall options that cannot be changed within the         of a pattern that set overall options that cannot be changed within the
3190         pattern.         pattern.
3191    
# Line 2916  AUTHOR Line 3199  AUTHOR
3199    
3200  REVISION  REVISION
3201    
3202         Last updated: 11 September 2007         Last updated: 31 October 2010
3203         Copyright (c) 1997-2007 University of Cambridge.         Copyright (c) 1997-2010 University of Cambridge.
3204  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
3205    
3206    
3207  PCREPATTERN(3)                                                  PCREPATTERN(3)  PCREPATTERN(3)                                                  PCREPATTERN(3)
3208    
3209    
# Line 2947  PCRE REGULAR EXPRESSION DETAILS Line 3230  PCRE REGULAR EXPRESSION DETAILS
3230    
3231         The original operation of PCRE was on strings of  one-byte  characters.         The original operation of PCRE was on strings of  one-byte  characters.
3232         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
3233         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
3234         pcre_compile()  with  the  PCRE_UTF8  option.  How this affects pattern         pcre_compile()  or  pcre_compile2() with the PCRE_UTF8 option. There is
3235         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:
3236         of  UTF-8  features  in  the  section on UTF-8 support in the main pcre  
3237         page.           (*UTF8)
3238    
3239           Starting a pattern with this sequence  is  equivalent  to  setting  the
3240           PCRE_UTF8  option.  This  feature  is  not Perl-compatible. How setting
3241           UTF-8 mode affects pattern matching  is  mentioned  in  several  places
3242           below.  There  is  also  a  summary of UTF-8 features in the section on
3243           UTF-8 support in the main pcre page.
3244    
3245           Another special sequence that may appear at the start of a  pattern  or
3246           in combination with (*UTF8) is:
3247    
3248             (*UCP)
3249    
3250           This  has  the  same  effect  as setting the PCRE_UCP option: it causes
3251           sequences such as \d and \w to  use  Unicode  properties  to  determine
3252           character types, instead of recognizing only characters with codes less
3253           than 128 via a lookup table.
3254    
3255         The remainder of this document discusses the  patterns  that  are  sup-         The remainder of this document discusses the  patterns  that  are  sup-
3256         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 2981  NEWLINE CONVENTIONS Line 3280  NEWLINE CONVENTIONS
3280           (*ANYCRLF)   any of the three above           (*ANYCRLF)   any of the three above
3281           (*ANY)       all Unicode newline sequences           (*ANY)       all Unicode newline sequences
3282    
3283         These override the default and the options given to pcre_compile(). For         These  override  the default and the options given to pcre_compile() or
3284         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
3285         pattern         newline sequence, the pattern
3286    
3287           (*CR)a.b           (*CR)a.b
3288    
# Line 2993  NEWLINE CONVENTIONS Line 3292  NEWLINE CONVENTIONS
3292         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
3293         present, the last one is used.         present, the last one is used.
3294    
3295         The  newline  convention  does  not  affect what the \R escape sequence         The  newline convention affects the interpretation of the dot metachar-
3296         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-
3297         compatibility.  However, this can be changed; see the description of \R         ever,  it  does  not  affect  what  the  \R escape sequence matches. By
3298         in the section entitled "Newline sequences" below. A change of \R  set-         default, this is any Unicode newline sequence, for Perl  compatibility.
3299         ting can be combined with a change of newline convention.         However,  this can be changed; see the description of \R in the section
3300           entitled "Newline sequences" below. A change of \R setting can be  com-
3301           bined with a change of newline convention.
3302    
3303    
3304  CHARACTERS AND METACHARACTERS  CHARACTERS AND METACHARACTERS
# Line 3055  CHARACTERS AND METACHARACTERS Line 3356  CHARACTERS AND METACHARACTERS
3356                    syntax)                    syntax)
3357           ]      terminates the character class           ]      terminates the character class
3358    
3359         The  following sections describe the use of each of the metacharacters.         The following sections describe the use of each of the metacharacters.
3360    
3361    
3362  BACKSLASH  BACKSLASH
3363    
3364         The backslash character has several uses. Firstly, if it is followed by         The backslash character has several uses. Firstly, if it is followed by
3365         a  non-alphanumeric  character,  it takes away any special meaning that         a non-alphanumeric character, it takes away any  special  meaning  that
3366         character may have. This  use  of  backslash  as  an  escape  character         character  may  have.  This  use  of  backslash  as an escape character
3367         applies both inside and outside character classes.         applies both inside and outside character classes.
3368    
3369         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
3370         pattern.  This escaping action applies whether  or  not  the  following         pattern.   This  escaping  action  applies whether or not the following
3371         character  would  otherwise be interpreted as a metacharacter, so it is         character would otherwise be interpreted as a metacharacter, so  it  is
3372         always safe to precede a non-alphanumeric  with  backslash  to  specify         always  safe  to  precede  a non-alphanumeric with backslash to specify
3373         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-
3374         slash, you write \\.         slash, you write \\.
3375    
3376         If a pattern is compiled with the PCRE_EXTENDED option,  whitespace  in         If  a  pattern is compiled with the PCRE_EXTENDED option, whitespace in
3377         the  pattern (other than in a character class) and characters between a         the pattern (other than in a character class) and characters between  a
3378         # outside a character class and the next newline are ignored. An escap-         # outside a character class and the next newline are ignored. An escap-
3379         ing  backslash  can  be  used to include a whitespace or # character as         ing backslash can be used to include a whitespace  or  #  character  as
3380         part of the pattern.         part of the pattern.
3381    
3382         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-
3383         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-
3384         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
3385         sequences  in  PCRE, whereas in Perl, $ and @ cause variable interpola-         sequences in PCRE, whereas in Perl, $ and @ cause  variable  interpola-
3386         tion. Note the following examples:         tion. Note the following examples:
3387    
3388           Pattern            PCRE matches   Perl matches           Pattern            PCRE matches   Perl matches
# Line 3091  BACKSLASH Line 3392  BACKSLASH
3392           \Qabc\$xyz\E       abc\$xyz       abc\$xyz           \Qabc\$xyz\E       abc\$xyz       abc\$xyz
3393           \Qabc\E\$\Qxyz\E   abc$xyz        abc$xyz           \Qabc\E\$\Qxyz\E   abc$xyz        abc$xyz
3394    
3395         The \Q...\E sequence is recognized both inside  and  outside  character         The  \Q...\E  sequence  is recognized both inside and outside character
3396         classes.         classes.  An isolated \E that is not preceded by \Q is ignored.
3397    
3398     Non-printing characters     Non-printing characters
3399    
3400         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-
3401         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
3402         appearance  of non-printing characters, apart from the binary zero that         appearance of non-printing characters, apart from the binary zero  that
3403         terminates a pattern, but when a pattern  is  being  prepared  by  text         terminates  a  pattern,  but  when  a pattern is being prepared by text
3404         editing,  it  is  usually  easier  to  use  one of the following escape         editing, it is  often  easier  to  use  one  of  the  following  escape
3405         sequences than the binary character it represents:         sequences than the binary character it represents:
3406    
3407           \a        alarm, that is, the BEL character (hex 07)           \a        alarm, that is, the BEL character (hex 07)
# Line 3110  BACKSLASH Line 3411  BACKSLASH
3411           \n        linefeed (hex 0A)           \n        linefeed (hex 0A)
3412           \r        carriage return (hex 0D)           \r        carriage return (hex 0D)
3413           \t        tab (hex 09)           \t        tab (hex 09)
3414           \ddd      character with octal code ddd, or backreference           \ddd      character with octal code ddd, or back reference
3415           \xhh      character with hex code hh           \xhh      character with hex code hh
3416           \x{hhh..} character with hex code hhh..           \x{hhh..} character with hex code hhh..
3417    
3418         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,
3419         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
3420         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;
3421         becomes hex 7B.         becomes hex 7B.
3422    
3423         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
3424         in upper or lower case). Any number of hexadecimal  digits  may  appear         in  upper  or  lower case). Any number of hexadecimal digits may appear
3425         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
3426         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,
3427         the  maximum value in hexadecimal is 7FFFFFFF. Note that this is bigger         the maximum value in hexadecimal is 7FFFFFFF. Note that this is  bigger
3428         than the largest Unicode code point, which is 10FFFF.         than the largest Unicode code point, which is 10FFFF.
3429    
3430         If characters other than hexadecimal digits appear between \x{  and  },         If  characters  other than hexadecimal digits appear between \x{ and },
3431         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.
3432         Instead, the initial \x will be  interpreted  as  a  basic  hexadecimal         Instead,  the  initial  \x  will  be interpreted as a basic hexadecimal
3433         escape,  with  no  following  digits, giving a character whose value is         escape, with no following digits, giving a  character  whose  value  is
3434         zero.         zero.
3435    
3436         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
3437         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-
3438         dled. For example, \xdc is exactly the same as \x{dc}.         dled. For example, \xdc is exactly the same as \x{dc}.
3439    
3440         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
3441         than  two  digits,  just  those  that  are  present  are used. Thus the         than two digits, just  those  that  are  present  are  used.  Thus  the
3442         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
3443         (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
3444         if the pattern character that follows is itself an octal digit.         if the pattern character that follows is itself an octal digit.
3445    
3446         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-
3447         cated.  Outside a character class, PCRE reads it and any following dig-         cated.  Outside a character class, PCRE reads it and any following dig-
3448         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
3449         have been at least that many previous capturing left parentheses in the         have been at least that many previous capturing left parentheses in the
3450         expression, the entire  sequence  is  taken  as  a  back  reference.  A         expression,  the  entire  sequence  is  taken  as  a  back reference. A
3451         description  of how this works is given later, following the discussion         description of how this works is given later, following the  discussion
3452         of parenthesized subpatterns.         of parenthesized subpatterns.
3453    
3454         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
3455         and  there have not been that many capturing subpatterns, PCRE re-reads         and there have not been that many capturing subpatterns, PCRE  re-reads
3456         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-
3457         erate  a data character. Any subsequent digits stand for themselves. In         erate a data character. Any subsequent digits stand for themselves.  In
3458         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
3459         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
3460         example:         example:
3461    
3462           \040   is another way of writing a space           \040   is another way of writing a space
# Line 3173  BACKSLASH Line 3474  BACKSLASH
3474           \81    is either a back reference, or a binary zero           \81    is either a back reference, or a binary zero
3475                     followed by the two characters "8" and "1"                     followed by the two characters "8" and "1"
3476    
3477         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
3478         leading zero, because no more than three octal digits are ever read.         leading zero, because no more than three octal digits are ever read.
3479    
3480         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
3481         inside and outside character classes. In addition, inside  a  character         inside  and  outside character classes. In addition, inside a character
3482         class,  the  sequence \b is interpreted as the backspace character (hex         class, the sequence \b is interpreted as the backspace  character  (hex
3483         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-
3484         and  "X", respectively. Outside a character class, these sequences have         ter class. Like any  other  unrecognized  escape  sequences,  they  are
3485         different meanings (see below).         treated  as  the  literal characters "B", "N", "R", and "X" by default,
3486           but cause an error if the PCRE_EXTRA option is set. Outside a character
3487           class, these sequences have different meanings.
3488    
3489     Absolute and relative back references     Absolute and relative back references
3490    
3491         The sequence \g followed by an unsigned or a negative  number,  option-         The  sequence  \g followed by an unsigned or a negative number, option-
3492         ally  enclosed  in braces, is an absolute or relative back reference. A         ally enclosed in braces, is an absolute or relative back  reference.  A
3493         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-
3494         cussed later, following the discussion of parenthesized subpatterns.         cussed later, following the discussion of parenthesized subpatterns.
3495    
3496     Absolute and relative subroutine calls     Absolute and relative subroutine calls
3497    
3498         For  compatibility with Oniguruma, the non-Perl syntax \g followed by a         For compatibility with Oniguruma, the non-Perl syntax \g followed by  a
3499         name or a number enclosed either in angle brackets or single quotes, is         name or a number enclosed either in angle brackets or single quotes, is
3500         an  alternative  syntax for referencing a subpattern as a "subroutine".         an alternative syntax for referencing a subpattern as  a  "subroutine".
3501         Details are discussed later.   Note  that  \g{...}  (Perl  syntax)  and         Details  are  discussed  later.   Note  that  \g{...} (Perl syntax) and
3502         \g<...>  (Oniguruma  syntax)  are  not synonymous. The former is a back         \g<...> (Oniguruma syntax) are not synonymous. The  former  is  a  back
3503         reference; the latter is a subroutine call.         reference; the latter is a subroutine call.
3504    
3505     Generic character types     Generic character types
3506    
3507         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:  
3508    
3509           \d     any decimal digit           \d     any decimal digit
3510           \D     any character that is not a decimal digit           \D     any character that is not a decimal digit
# Line 3215  BACKSLASH Line 3517  BACKSLASH
3517           \w     any "word" character           \w     any "word" character
3518           \W     any "non-word" character           \W     any "non-word" character
3519    
3520         Each pair of escape sequences partitions the complete set of characters         There is also the single sequence \N, which matches a non-newline char-
3521         into two disjoint sets. Any given character matches one, and only  one,         acter.  This is the same as the "." metacharacter when  PCRE_DOTALL  is
3522         of each pair.         not set.
3523    
3524         These character type sequences can appear both inside and outside char-         Each  pair of lower and upper case escape sequences partitions the com-
3525         acter classes. They each match one character of the  appropriate  type.         plete set of characters into two disjoint  sets.  Any  given  character
3526         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
3527         of them fail, since there is no character to match.         inside and outside character classes. They each match one character  of
3528           the  appropriate  type.  If the current matching point is at the end of
3529         For compatibility with Perl, \s does not match the VT  character  (code         the subject string, all of them fail, because there is no character  to
3530         11).   This makes it different from the the POSIX "space" class. The \s         match.
3531         characters are HT (9), LF (10), FF (12), CR (13), and  space  (32).  If  
3532           For  compatibility  with Perl, \s does not match the VT character (code
3533           11).  This makes it different from the the POSIX "space" class. The  \s
3534           characters  are  HT  (9), LF (10), FF (12), CR (13), and space (32). If
3535         "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-
3536         ter. In PCRE, it never does.         ter. In PCRE, it never does.
3537    
3538         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
3539         \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-
3540         code character property support is available.  These  sequences  retain         trolled  by PCRE's low-valued character tables, and may vary if locale-
3541         their original meanings from before UTF-8 support was available, mainly         specific matching is taking place (see "Locale support" in the  pcreapi
3542         for efficiency reasons.         page).  For  example,  in  a French locale such as "fr_FR" in Unix-like
3543           systems, or "french" in Windows, some character codes greater than  128
3544         The sequences \h, \H, \v, and \V are Perl 5.10 features. In contrast to         are  used  for  accented letters, and these are then matched by \w. The
3545         the  other  sequences, these do match certain high-valued codepoints in         use of locales with Unicode is discouraged.
3546         UTF-8 mode.  The horizontal space characters are:  
3547           By default, in UTF-8 mode, characters  with  values  greater  than  128
3548           never  match  \d,  \s,  or  \w,  and always match \D, \S, and \W. These
3549           sequences retain their original meanings from before UTF-8 support  was
3550           available,  mainly for efficiency reasons. However, if PCRE is compiled
3551           with Unicode property support, and the PCRE_UCP option is set, the  be-
3552           haviour  is  changed  so  that Unicode properties are used to determine
3553           character types, as follows:
3554    
3555             \d  any character that \p{Nd} matches (decimal digit)
3556             \s  any character that \p{Z} matches, plus HT, LF, FF, CR
3557             \w  any character that \p{L} or \p{N} matches, plus underscore
3558    
3559           The upper case escapes match the inverse sets of characters. Note  that
3560           \d  matches  only decimal digits, whereas \w matches any Unicode digit,
3561           as well as any Unicode letter, and underscore. Note also that  PCRE_UCP
3562           affects  \b,  and  \B  because  they are defined in terms of \w and \W.
3563           Matching these sequences is noticeably slower when PCRE_UCP is set.
3564    
3565           The sequences \h, \H, \v, and \V are features that were added  to  Perl
3566           at  release  5.10. In contrast to the other sequences, which match only
3567           ASCII characters by default, these  always  match  certain  high-valued
3568           codepoints  in UTF-8 mode, whether or not PCRE_UCP is set. The horizon-
3569           tal space characters are:
3570    
3571           U+0009     Horizontal tab           U+0009     Horizontal tab
3572           U+0020     Space           U+0020     Space
# Line 3270  BACKSLASH Line 3598  BACKSLASH
3598           U+2028     Line separator           U+2028     Line separator
3599           U+2029     Paragraph separator           U+2029     Paragraph separator
3600    
        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.  
   
3601     Newline sequences     Newline sequences
3602    
3603         Outside  a  character class, by default, the escape sequence \R matches         Outside a character class, by default, the escape sequence  \R  matches
3604         any Unicode newline sequence. This is a Perl 5.10 feature. In non-UTF-8         any Unicode newline sequence. In non-UTF-8 mode \R is equivalent to the
3605         mode \R is equivalent to the following:         following:
3606    
3607           (?>\r\n|\n|\x0b|\f|\r|\x85)           (?>\r\n|\n|\x0b|\f|\r|\x85)
3608    
3609         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
3610         below.  This particular group matches either the two-character sequence         below.  This particular group matches either the two-character sequence
3611         CR  followed  by  LF,  or  one  of  the single characters LF (linefeed,         CR followed by LF, or  one  of  the  single  characters  LF  (linefeed,
3612         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
3613         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
3614         is treated as a single unit that cannot be split.         is treated as a single unit that cannot be split.
3615    
3616         In UTF-8 mode, two additional characters whose codepoints  are  greater         In  UTF-8  mode, two additional characters whose codepoints are greater
3617         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-
3618         rator, U+2029).  Unicode character property support is not  needed  for         rator,  U+2029).   Unicode character property support is not needed for
3619         these characters to be recognized.         these characters to be recognized.
3620    
3621         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
3622         the complete set  of  Unicode  line  endings)  by  setting  the  option         the  complete  set  of  Unicode  line  endings)  by  setting the option
3623         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.
3624         (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
3625         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
3626         requested via the PCRE_BSR_UNICODE option.   It  is  also  possible  to         requested  via  the  PCRE_BSR_UNICODE  option.   It is also possible to
3627         specify  these  settings  by  starting a pattern string with one of the         specify these settings by starting a pattern string  with  one  of  the
3628         following sequences:         following sequences:
3629    
3630           (*BSR_ANYCRLF)   CR, LF, or CRLF only           (*BSR_ANYCRLF)   CR, LF, or CRLF only
3631           (*BSR_UNICODE)   any Unicode newline sequence           (*BSR_UNICODE)   any Unicode newline sequence
3632    
3633         These override the default and the options given to pcre_compile(), but         These  override  the default and the options given to pcre_compile() or
3634         they can be overridden by options given to pcre_exec(). Note that these         pcre_compile2(), but  they  can  be  overridden  by  options  given  to
3635         special settings, which are not Perl-compatible, are recognized only at         pcre_exec() or pcre_dfa_exec(). Note that these special settings, which
3636         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
3637         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
3638         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
3639         can start with:         newline convention; for example, a pattern can start with:
3640    
3641           (*ANY)(*BSR_ANYCRLF)           (*ANY)(*BSR_ANYCRLF)
3642    
3643         Inside a character class, \R matches the letter "R".         They can also be combined with the (*UTF8) or (*UCP) special sequences.
3644           Inside a character class, \R  is  treated  as  an  unrecognized  escape
3645           sequence, and so matches the letter "R" by default, but causes an error
3646           if PCRE_EXTRA is set.
3647    
3648     Unicode character properties     Unicode character properties
3649    
# Line 3336  BACKSLASH Line 3658  BACKSLASH
3658           \X       an extended Unicode sequence           \X       an extended Unicode sequence
3659    
3660         The property names represented by xx above are limited to  the  Unicode         The property names represented by xx above are limited to  the  Unicode
3661         script names, the general category properties, and "Any", which matches         script names, the general category properties, "Any", which matches any
3662         any character (including newline). Other properties such as "InMusical-         character  (including  newline),  and  some  special  PCRE   properties
3663         Symbols"  are  not  currently supported by PCRE. Note that \P{Any} does         (described  in the next section).  Other Perl properties such as "InMu-
3664         not match any characters, so always causes a match failure.         sicalSymbols" are not currently supported by PCRE.  Note  that  \P{Any}
3665           does not match any characters, so always causes a match failure.
3666    
3667         Sets of Unicode characters are defined as belonging to certain scripts.         Sets of Unicode characters are defined as belonging to certain scripts.
3668         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.
3669         For example:         For example:
3670    
3671           \p{Greek}           \p{Greek}
3672           \P{Han}           \P{Han}
3673    
3674         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
3675         "Common". The current list of scripts is:         "Common". The current list of scripts is:
3676    
3677         Arabic,  Armenian,  Balinese,  Bengali,  Bopomofo,  Braille,  Buginese,         Arabic, Armenian, Avestan, Balinese, Bamum, Bengali, Bopomofo, Braille,
3678         Buhid,  Canadian_Aboriginal,  Cherokee,  Common,   Coptic,   Cuneiform,         Buginese,  Buhid,  Canadian_Aboriginal, Carian, Cham, Cherokee, Common,
3679         Cypriot, Cyrillic, Deseret, Devanagari, Ethiopic, Georgian, Glagolitic,         Coptic,  Cuneiform,  Cypriot,  Cyrillic,  Deseret,  Devanagari,   Egyp-
3680         Gothic, Greek, Gujarati, Gurmukhi, Han, Hangul, Hanunoo, Hebrew,  Hira-         tian_Hieroglyphs,   Ethiopic,   Georgian,  Glagolitic,  Gothic,  Greek,
3681         gana,  Inherited,  Kannada,  Katakana,  Kharoshthi,  Khmer, Lao, Latin,         Gujarati, Gurmukhi,  Han,  Hangul,  Hanunoo,  Hebrew,  Hiragana,  Impe-
3682         Limbu,  Linear_B,  Malayalam,  Mongolian,  Myanmar,  New_Tai_Lue,  Nko,         rial_Aramaic, Inherited, Inscriptional_Pahlavi, Inscriptional_Parthian,
3683         Ogham,  Old_Italic,  Old_Persian, Oriya, Osmanya, Phags_Pa, Phoenician,         Javanese, Kaithi, Kannada, Katakana, Kayah_Li, Kharoshthi, Khmer,  Lao,
3684         Runic,  Shavian,  Sinhala,  Syloti_Nagri,  Syriac,  Tagalog,  Tagbanwa,         Latin,  Lepcha,  Limbu,  Linear_B,  Lisu,  Lycian,  Lydian,  Malayalam,
3685         Tai_Le, Tamil, Telugu, Thaana, Thai, Tibetan, Tifinagh, Ugaritic, Yi.         Meetei_Mayek, Mongolian, Myanmar, New_Tai_Lue, Nko, Ogham,  Old_Italic,
3686           Old_Persian,  Old_South_Arabian,  Old_Turkic, Ol_Chiki, Oriya, Osmanya,
3687         Each  character has exactly one general category property, specified by         Phags_Pa, Phoenician, Rejang, Runic,  Samaritan,  Saurashtra,  Shavian,
3688         a two-letter abbreviation. For compatibility with Perl, negation can be         Sinhala,  Sundanese,  Syloti_Nagri,  Syriac, Tagalog, Tagbanwa, Tai_Le,
3689         specified  by  including a circumflex between the opening brace and the         Tai_Tham, Tai_Viet, Tamil, Telugu,  Thaana,  Thai,  Tibetan,  Tifinagh,
3690         property name. For example, \p{^Lu} is the same as \P{Lu}.         Ugaritic, Vai, Yi.
3691    
3692           Each character has exactly one Unicode general category property, spec-
3693           ified by a two-letter abbreviation. For compatibility with Perl,  nega-
3694           tion  can  be  specified  by including a circumflex between the opening
3695           brace and the property name.  For  example,  \p{^Lu}  is  the  same  as
3696           \P{Lu}.
3697    
3698         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-
3699         eral  category properties that start with that letter. In this case, in         eral category properties that start with that letter. In this case,  in
3700         the absence of negation, the curly brackets in the escape sequence  are         the  absence of negation, the curly brackets in the escape sequence are
3701         optional; these two examples have the same effect:         optional; these two examples have the same effect:
3702    
3703           \p{L}           \p{L}
# Line 3420  BACKSLASH Line 3749  BACKSLASH
3749           Zp    Paragraph separator           Zp    Paragraph separator
3750           Zs    Space separator           Zs    Space separator
3751    
3752         The  special property L& is also supported: it matches a character that         The special property L& is also supported: it matches a character  that
3753         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
3754         classified as a modifier or "other".         classified as a modifier or "other".
3755    
3756         The  Cs  (Surrogate)  property  applies only to characters in the range         The Cs (Surrogate) property applies only to  characters  in  the  range
3757         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
3758         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-
3759         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
3760         the pcreapi page).         the pcreapi page). Perl does not support the Cs property.
3761    
3762         The  long  synonyms  for  these  properties that Perl supports (such as         The long synonyms for  property  names  that  Perl  supports  (such  as
3763         \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
3764         any of these properties with "Is".         any of these properties with "Is".
3765    
3766         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-
3767         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
3768         in the Unicode table.         in the Unicode table.
3769    
3770         Specifying  caseless  matching  does not affect these escape sequences.         Specifying caseless matching does not affect  these  escape  sequences.
3771         For example, \p{Lu} always matches only upper case letters.         For example, \p{Lu} always matches only upper case letters.
3772    
3773         The \X escape matches any number of Unicode  characters  that  form  an         The  \X  escape  matches  any number of Unicode characters that form an
3774         extended Unicode sequence. \X is equivalent to         extended Unicode sequence. \X is equivalent to
3775    
3776           (?>\PM\pM*)           (?>\PM\pM*)
3777    
3778         That  is,  it matches a character without the "mark" property, followed         That is, it matches a character without the "mark"  property,  followed
3779         by zero or more characters with the "mark"  property,  and  treats  the         by  zero  or  more  characters with the "mark" property, and treats the
3780         sequence  as  an  atomic group (see below).  Characters with the "mark"         sequence as an atomic group (see below).  Characters  with  the  "mark"
3781         property are typically accents that  affect  the  preceding  character.         property  are  typically  accents  that affect the preceding character.
3782         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
3783         matches any one character.         matches any one character.
3784    
3785         Matching characters by Unicode property is not fast, because  PCRE  has         Matching  characters  by Unicode property is not fast, because PCRE has
3786         to  search  a  structure  that  contains data for over fifteen thousand         to search a structure that contains  data  for  over  fifteen  thousand
3787         characters. That is why the traditional escape sequences such as \d and         characters. That is why the traditional escape sequences such as \d and
3788         \w do not use Unicode properties in PCRE.         \w do not use Unicode properties in PCRE by  default,  though  you  can
3789           make them do so by setting the PCRE_UCP option for pcre_compile() or by
3790           starting the pattern with (*UCP).
3791    
3792       PCRE's additional properties
3793    
3794           As well as the standard Unicode properties described  in  the  previous
3795           section,  PCRE supports four more that make it possible to convert tra-
3796           ditional escape sequences such as \w and \s and POSIX character classes
3797           to use Unicode properties. PCRE uses these non-standard, non-Perl prop-
3798           erties internally when PCRE_UCP is set. They are:
3799    
3800             Xan   Any alphanumeric character
3801             Xps   Any POSIX space character
3802             Xsp   Any Perl space character
3803             Xwd   Any Perl "word" character
3804    
3805           Xan matches characters that have either the L (letter) or the  N  (num-
3806           ber)  property. Xps matches the characters tab, linefeed, vertical tab,
3807           formfeed, or carriage return, and any other character that  has  the  Z
3808           (separator) property.  Xsp is the same as Xps, except that vertical tab
3809           is excluded. Xwd matches the same characters as Xan, plus underscore.
3810    
3811     Resetting the match start     Resetting the match start
3812    
3813         The escape sequence \K, which is a Perl 5.10 feature, causes any previ-         The escape sequence \K causes any previously matched characters not  to
3814         ously matched characters not  to  be  included  in  the  final  matched         be included in the final matched sequence. For example, the pattern:
        sequence. For example, the pattern:  
3815    
3816           foo\Kbar           foo\Kbar
3817    
# Line 3477  BACKSLASH Line 3826  BACKSLASH
3826    
3827         matches "foobar", the first substring is still set to "foo".         matches "foobar", the first substring is still set to "foo".
3828    
3829           Perl documents that the use  of  \K  within  assertions  is  "not  well
3830           defined".  In  PCRE,  \K  is  acted upon when it occurs inside positive
3831           assertions, but is ignored in negative assertions.
3832    
3833     Simple assertions     Simple assertions
3834    
3835         The final use of backslash is for certain simple assertions. An  asser-         The final use of backslash is for certain simple assertions. An  asser-
# Line 3493  BACKSLASH Line 3846  BACKSLASH
3846           \z     matches only at the end of the subject           \z     matches only at the end of the subject
3847           \G     matches at the first matching position in the subject           \G     matches at the first matching position in the subject
3848    
3849         These assertions may not appear in character classes (but note that  \b         Inside a character class, \b has a different meaning;  it  matches  the
3850         has a different meaning, namely the backspace character, inside a char-         backspace  character.  If  any  other  of these assertions appears in a
3851         acter class).         character class, by default it matches the corresponding literal  char-
3852           acter  (for  example,  \B  matches  the  letter  B).  However,  if  the
3853         A word boundary is a position in the subject string where  the  current         PCRE_EXTRA option is set, an "invalid escape sequence" error is  gener-
3854         character  and  the previous character do not both match \w or \W (i.e.         ated instead.
3855         one matches \w and the other matches \W), or the start or  end  of  the  
3856         string if the first or last character matches \w, respectively.         A  word  boundary is a position in the subject string where the current
3857           character and the previous character do not both match \w or  \W  (i.e.
3858           one  matches  \w  and the other matches \W), or the start or end of the
3859           string if the first or last  character  matches  \w,  respectively.  In
3860           UTF-8  mode,  the  meanings  of \w and \W can be changed by setting the
3861           PCRE_UCP option. When this is done, it also affects \b and \B.  Neither
3862           PCRE  nor  Perl has a separate "start of word" or "end of word" metase-
3863           quence. However, whatever follows \b normally determines which  it  is.
3864           For example, the fragment \ba matches "a" at the start of a word.
3865    
3866         The  \A,  \Z,  and \z assertions differ from the traditional circumflex         The  \A,  \Z,  and \z assertions differ from the traditional circumflex
3867         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
# Line 3583  CIRCUMFLEX AND DOLLAR Line 3944  CIRCUMFLEX AND DOLLAR
3944         set.         set.
3945    
3946    
3947  FULL STOP (PERIOD, DOT)  FULL STOP (PERIOD, DOT) AND \N
3948    
3949         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-
3950         ter  in  the subject string except (by default) a character that signi-         ter  in  the subject string except (by default) a character that signi-
# Line 3606  FULL STOP (PERIOD, DOT) Line 3967  FULL STOP (PERIOD, DOT)
3967         flex and dollar, the only relationship being  that  they  both  involve         flex and dollar, the only relationship being  that  they  both  involve
3968         newlines. Dot has no special meaning in a character class.         newlines. Dot has no special meaning in a character class.
3969    
3970           The  escape  sequence  \N  behaves  like  a  dot, except that it is not
3971           affected by the PCRE_DOTALL option. In  other  words,  it  matches  any
3972           character except one that signifies the end of a line.
3973    
3974    
3975  MATCHING A SINGLE BYTE  MATCHING A SINGLE BYTE
3976    
# Line 3613  MATCHING A SINGLE BYTE Line 3978  MATCHING A SINGLE BYTE
3978         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
3979         line-ending  characters.  The  feature  is provided in Perl in order to         line-ending  characters.  The  feature  is provided in Perl in order to
3980         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-
3981         acters  into individual bytes, what remains in the string may be a mal-         acters  into  individual bytes, the rest of the string may start with a
3982         formed UTF-8 string. For this reason, the \C escape  sequence  is  best         malformed UTF-8 character. For this reason, the \C escape  sequence  is
3983         avoided.         best avoided.
3984    
3985         PCRE  does  not  allow \C to appear in lookbehind assertions (described         PCRE  does  not  allow \C to appear in lookbehind assertions (described
3986         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-
# Line 3626  SQUARE BRACKETS AND CHARACTER CLASSES Line 3991  SQUARE BRACKETS AND CHARACTER CLASSES
3991    
3992         An opening square bracket introduces a character class, terminated by a         An opening square bracket introduces a character class, terminated by a
3993         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-
3994         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,
3995         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
3996         circumflex, if present) or escaped with a backslash.         square  bracket  is required as a member of the class, it should be the
3997           first data character in the class  (after  an  initial  circumflex,  if
3998           present) or escaped with a backslash.
3999    
4000         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
4001         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
4002         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
4003         character in the class definition is a circumflex, in  which  case  the         character in the class definition is a circumflex, in  which  case  the
4004         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
# Line 3642  SQUARE BRACKETS AND CHARACTER CLASSES Line 4009  SQUARE BRACKETS AND CHARACTER CLASSES
4009         while [^aeiou] matches any character that is not a  lower  case  vowel.         while [^aeiou] matches any character that is not a  lower  case  vowel.
4010         Note that a circumflex is just a convenient notation for specifying the         Note that a circumflex is just a convenient notation for specifying the
4011         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
4012         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-
4013         sumes a character from the subject string, and therefore  it  fails  if         sumes a character from the subject string, and therefore  it  fails  if
4014         the current pointer is at the end of the string.         the current pointer is at the end of the string.
4015    
# Line 3658  SQUARE BRACKETS AND CHARACTER CLASSES Line 4025  SQUARE BRACKETS AND CHARACTER CLASSES
4025         than 128, so caseless matching is always possible. For characters  with         than 128, so caseless matching is always possible. For characters  with
4026         higher  values,  the  concept  of case is supported if PCRE is compiled         higher  values,  the  concept  of case is supported if PCRE is compiled
4027         with Unicode property support, but not otherwise.  If you want  to  use         with Unicode property support, but not otherwise.  If you want  to  use
4028         caseless  matching  for  characters 128 and above, you must ensure that         caseless  matching  in UTF8-mode for characters 128 and above, you must
4029         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
4030         support.         with UTF-8 support.
4031    
4032         Characters  that  might  indicate  line breaks are never treated in any         Characters  that  might  indicate  line breaks are never treated in any
4033         special way  when  matching  character  classes,  whatever  line-ending         special way  when  matching  character  classes,  whatever  line-ending
# Line 3697  SQUARE BRACKETS AND CHARACTER CLASSES Line 4064  SQUARE BRACKETS AND CHARACTER CLASSES
4064         concept  of  case for characters with values greater than 128 only when         concept  of  case for characters with values greater than 128 only when
4065         it is compiled with Unicode property support.         it is compiled with Unicode property support.
4066    
4067         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
4068         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
4069         class. For example, [\dABCDEF] matches any hexadecimal digit. A circum-         match to the class. For example,  [\dABCDEF]  matches  any  hexadecimal
4070         flex  can  conveniently  be used with the upper case character types to         digit.  A circumflex can conveniently be used with the upper case char-
4071         specify a more restricted set of characters  than  the  matching  lower         acter types to specify a more restricted set  of  characters  than  the
4072         case  type.  For example, the class [^\W_] matches any letter or digit,         matching  lower  case  type.  For example, the class [^\W_] matches any
4073         but not underscore.         letter or digit, but not underscore.
4074    
4075         The only metacharacters that are recognized in  character  classes  are         The only metacharacters that are recognized in  character  classes  are
4076         backslash,  hyphen  (only  where  it can be interpreted as specifying a         backslash,  hyphen  (only  where  it can be interpreted as specifying a
# Line 3722  POSIX CHARACTER CLASSES Line 4089  POSIX CHARACTER CLASSES
4089           [01[:alpha:]%]           [01[:alpha:]%]
4090    
4091         matches "0", "1", any alphabetic character, or "%". The supported class         matches "0", "1", any alphabetic character, or "%". The supported class
4092         names are         names are:
4093    
4094           alnum    letters and digits           alnum    letters and digits
4095           alpha    letters           alpha    letters
# Line 3733  POSIX CHARACTER CLASSES Line 4100  POSIX CHARACTER CLASSES
4100           graph    printing characters, excluding space           graph    printing characters, excluding space
4101           lower    lower case letters           lower    lower case letters
4102           print    printing characters, including space           print    printing characters, including space
4103           punct    printing characters, excluding letters and digits           punct    printing characters, excluding letters and digits and space
4104           space    white space (not quite the same as \s)           space    white space (not quite the same as \s)
4105           upper    upper case letters           upper    upper case letters
4106           word     "word" characters (same as \w)           word     "word" characters (same as \w)
# Line 3754  POSIX CHARACTER CLASSES Line 4121  POSIX CHARACTER CLASSES
4121         POSIX syntax [.ch.] and [=ch=] where "ch" is a "collating element", but         POSIX syntax [.ch.] and [=ch=] where "ch" is a "collating element", but
4122         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.
4123    
4124         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
4125         of the POSIX character classes.         not match any of the POSIX character classes. However, if the  PCRE_UCP
4126           option  is passed to pcre_compile(), some of the classes are changed so
4127           that Unicode character properties are used. This is achieved by replac-
4128           ing the POSIX classes by other sequences, as follows:
4129    
4130             [:alnum:]  becomes  \p{Xan}
4131             [:alpha:]  becomes  \p{L}
4132             [:blank:]  becomes  \h
4133             [:digit:]  becomes  \p{Nd}
4134             [:lower:]  becomes  \p{Ll}
4135             [:space:]  becomes  \p{Xps}
4136             [:upper:]  becomes  \p{Lu}
4137             [:word:]   becomes  \p{Xwd}
4138    
4139           Negated  versions,  such  as [:^alpha:] use \P instead of \p. The other
4140           POSIX classes are unchanged, and match only characters with code points
4141           less than 128.
4142    
4143    
4144  VERTICAL BAR  VERTICAL BAR
# Line 3770  VERTICAL BAR Line 4153  VERTICAL BAR
4153         string). The matching process tries each alternative in turn, from left         string). The matching process tries each alternative in turn, from left
4154         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
4155         are within a subpattern (defined below), "succeeds" means matching  the         are within a subpattern (defined below), "succeeds" means matching  the
4156         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.
4157    
4158    
4159  INTERNAL OPTION SETTING  INTERNAL OPTION SETTING
4160    
4161         The settings of the  PCRE_CASELESS,  PCRE_MULTILINE,  PCRE_DOTALL,  and         The  settings  of  the  PCRE_CASELESS, PCRE_MULTILINE, PCRE_DOTALL, and
4162         PCRE_EXTENDED  options  (which are Perl-compatible) can be changed from         PCRE_EXTENDED options (which are Perl-compatible) can be  changed  from
4163         within the pattern by  a  sequence  of  Perl  option  letters  enclosed         within  the  pattern  by  a  sequence  of  Perl option letters enclosed
4164         between "(?" and ")".  The option letters are         between "(?" and ")".  The option letters are
4165    
4166           i  for PCRE_CASELESS           i  for PCRE_CASELESS
# Line 3787  INTERNAL OPTION SETTING Line 4170  INTERNAL OPTION SETTING
4170    
4171         For example, (?im) sets caseless, multiline matching. It is also possi-         For example, (?im) sets caseless, multiline matching. It is also possi-
4172         ble to unset these options by preceding the letter with a hyphen, and a         ble to unset these options by preceding the letter with a hyphen, and a
4173         combined  setting and unsetting such as (?im-sx), which sets PCRE_CASE-         combined setting and unsetting such as (?im-sx), which sets  PCRE_CASE-
4174         LESS and PCRE_MULTILINE while unsetting PCRE_DOTALL and  PCRE_EXTENDED,         LESS  and PCRE_MULTILINE while unsetting PCRE_DOTALL and PCRE_EXTENDED,
4175         is  also  permitted.  If  a  letter  appears  both before and after the         is also permitted. If a  letter  appears  both  before  and  after  the
4176         hyphen, the option is unset.         hyphen, the option is unset.
4177    
4178         The PCRE-specific options PCRE_DUPNAMES, PCRE_UNGREEDY, and  PCRE_EXTRA         The  PCRE-specific options PCRE_DUPNAMES, PCRE_UNGREEDY, and PCRE_EXTRA
4179         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
4180         the characters J, U and X respectively.         the characters J, U and X respectively.
4181    
4182         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
4183         tern  parentheses),  the change applies to the remainder of the pattern         inside subpattern parentheses), the change applies to the remainder  of
4184         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
4185         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-
4186         in data extracted by the pcre_fullinfo() function).         fore show up in data extracted by the pcre_fullinfo() function).
4187    
4188         An option change within a subpattern (see below for  a  description  of         An  option  change  within a subpattern (see below for a description of
4189         subpatterns) affects only that part of the current pattern that follows         subpatterns) affects only that part of the subpattern that follows  it,
4190         it, so         so
4191    
4192           (a(?i)b)c           (a(?i)b)c
4193    
4194         matches abc and aBc and no other strings (assuming PCRE_CASELESS is not         matches abc and aBc and no other strings (assuming PCRE_CASELESS is not
4195         used).   By  this means, options can be made to have different settings         used).  By this means, options can be made to have  different  settings
4196         in different parts of the pattern. Any changes made in one  alternative         in  different parts of the pattern. Any changes made in one alternative
4197         do  carry  on  into subsequent branches within the same subpattern. For         do carry on into subsequent branches within the  same  subpattern.  For
4198         example,         example,
4199    
4200           (a(?i)b|c)           (a(?i)b|c)
4201    
4202         matches "ab", "aB", "c", and "C", even though  when  matching  "C"  the         matches  "ab",  "aB",  "c",  and "C", even though when matching "C" the
4203         first  branch  is  abandoned before the option setting. This is because         first branch is abandoned before the option setting.  This  is  because
4204         the effects of option settings happen at compile time. There  would  be         the  effects  of option settings happen at compile time. There would be
4205         some very weird behaviour otherwise.         some very weird behaviour otherwise.
4206    
4207         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
4208         application when the compile or match functions  are  called.  In  some         application  when  the  compile  or match functions are called. In some
4209         cases  the  pattern  can  contain special leading sequences to override         cases the pattern can contain special leading sequences such as (*CRLF)
4210         what the application has set or what has been  defaulted.  Details  are         to  override  what  the application has set or what has been defaulted.
4211         given in the section entitled "Newline sequences" above.         Details are given in the section entitled  "Newline  sequences"  above.
4212           There  are  also  the  (*UTF8) and (*UCP) leading sequences that can be
4213           used to set UTF-8 and Unicode property modes; they  are  equivalent  to
4214           setting the PCRE_UTF8 and the PCRE_UCP options, respectively.
4215    
4216    
4217  SUBPATTERNS  SUBPATTERNS
# Line 3837  SUBPATTERNS Line 4223  SUBPATTERNS
4223    
4224           cat(aract|erpillar|)           cat(aract|erpillar|)
4225    
4226         matches one of the words "cat", "cataract", or  "caterpillar".  Without         matches "cataract", "caterpillar", or "cat". Without  the  parentheses,
4227         the  parentheses,  it  would  match  "cataract", "erpillar" or an empty         it would match "cataract", "erpillar" or an empty string.
        string.  
4228    
4229         2. It sets up the subpattern as  a  capturing  subpattern.  This  means         2.  It  sets  up  the  subpattern as a capturing subpattern. This means
4230         that,  when  the  whole  pattern  matches,  that portion of the subject         that, when the whole pattern  matches,  that  portion  of  the  subject
4231         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
4232         ovector  argument  of pcre_exec(). Opening parentheses are counted from         ovector argument of pcre_exec(). Opening parentheses are  counted  from
4233         left to right (starting from 1) to obtain  numbers  for  the  capturing         left  to  right  (starting  from 1) to obtain numbers for the capturing
4234         subpatterns.         subpatterns. For example, if the  string  "the  red  king"  is  matched
4235           against the pattern
        For  example,  if the string "the red king" is matched against the pat-  
        tern  
4236    
4237           the ((red|white) (king|queen))           the ((red|white) (king|queen))
4238    
4239         the captured substrings are "red king", "red", and "king", and are num-         the captured substrings are "red king", "red", and "king", and are num-
4240         bered 1, 2, and 3, respectively.         bered 1, 2, and 3, respectively.
4241    
4242         The  fact  that  plain  parentheses  fulfil two functions is not always         The fact that plain parentheses fulfil  two  functions  is  not  always
4243         helpful.  There are often times when a grouping subpattern is  required         helpful.   There are often times when a grouping subpattern is required
4244         without  a capturing requirement. If an opening parenthesis is followed         without a capturing requirement. If an opening parenthesis is  followed
4245         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-
4246         ing,  and  is  not  counted when computing the number of any subsequent         ing, and is not counted when computing the  number  of  any  subsequent
4247         capturing subpatterns. For example, if the string "the white queen"  is         capturing  subpatterns. For example, if the string "the white queen" is
4248         matched against the pattern         matched against the pattern
4249    
4250           the ((?:red|white) (king|queen))           the ((?:red|white) (king|queen))
# Line 3869  SUBPATTERNS Line 4252  SUBPATTERNS
4252         the captured substrings are "white queen" and "queen", and are numbered         the captured substrings are "white queen" and "queen", and are numbered
4253         1 and 2. The maximum number of capturing subpatterns is 65535.         1 and 2. The maximum number of capturing subpatterns is 65535.
4254    
4255         As a convenient shorthand, if any option settings are required  at  the         As  a  convenient shorthand, if any option settings are required at the
4256         start  of  a  non-capturing  subpattern,  the option letters may appear         start of a non-capturing subpattern,  the  option  letters  may  appear
4257         between the "?" and the ":". Thus the two patterns         between the "?" and the ":". Thus the two patterns
4258    
4259           (?i:saturday|sunday)           (?i:saturday|sunday)
4260           (?:(?i)saturday|sunday)           (?:(?i)saturday|sunday)
4261    
4262         match exactly the same set of strings. Because alternative branches are         match exactly the same set of strings. Because alternative branches are
4263         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
4264         the subpattern is reached, an option setting in one branch does  affect         the  subpattern is reached, an option setting in one branch does affect
4265         subsequent  branches,  so  the above patterns match "SUNDAY" as well as         subsequent branches, so the above patterns match "SUNDAY"  as  well  as
4266         "Saturday".         "Saturday".
4267    
4268    
4269  DUPLICATE SUBPATTERN NUMBERS  DUPLICATE SUBPATTERN NUMBERS
4270    
4271         Perl 5.10 introduced a feature whereby each alternative in a subpattern         Perl 5.10 introduced a feature whereby each alternative in a subpattern
4272         uses  the same numbers for its capturing parentheses. Such a subpattern         uses the same numbers for its capturing parentheses. Such a  subpattern
4273         starts with (?| and is itself a non-capturing subpattern. For  example,         starts  with (?| and is itself a non-capturing subpattern. For example,
4274         consider this pattern:         consider this pattern:
4275    
4276           (?|(Sat)ur|(Sun))day           (?|(Sat)ur|(Sun))day
4277    
4278         Because  the two alternatives are inside a (?| group, both sets of cap-         Because the two alternatives are inside a (?| group, both sets of  cap-
4279         turing parentheses are numbered one. Thus, when  the  pattern  matches,         turing  parentheses  are  numbered one. Thus, when the pattern matches,
4280         you  can  look  at captured substring number one, whichever alternative         you can look at captured substring number  one,  whichever  alternative
4281         matched. This construct is useful when you want to  capture  part,  but         matched.  This  construct  is useful when you want to capture part, but
4282         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-
4283         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
4284         each  branch. The numbers of any capturing buffers that follow the sub-         each branch. The numbers of any capturing parentheses that  follow  the
4285         pattern start after the highest number used in any branch. The  follow-         subpattern  start after the highest number used in any branch. The fol-
4286         ing  example  is taken from the Perl documentation.  The numbers under-         lowing example is taken from the Perl documentation. The numbers under-
4287         neath show in which buffer the captured content will be stored.         neath show in which buffer the captured content will be stored.
4288    
4289           # before  ---------------branch-reset----------- after           # before  ---------------branch-reset----------- after
4290           / ( a )  (?| x ( y ) z | (p (q) r) | (t) u (v) ) ( z ) /x           / ( a )  (?| x ( y ) z | (p (q) r) | (t) u (v) ) ( z ) /x
4291           # 1            2         2  3        2     3     4           # 1            2         2  3        2     3     4
4292    
4293         A backreference or a recursive call to  a  numbered  subpattern  always         A  back  reference  to a numbered subpattern uses the most recent value
4294         refers to the first one in the pattern with the given number.         that is set for that number by any subpattern.  The  following  pattern
4295           matches "abcabc" or "defdef":
4296    
4297             /(?|(abc)|(def))\1/
4298    
4299           In  contrast, a recursive or "subroutine" call to a numbered subpattern
4300           always refers to the first one in the pattern with  the  given  number.
4301           The following pattern matches "abcabc" or "defabc":
4302    
4303             /(?|(abc)|(def))(?1)/
4304    
4305           If  a condition test for a subpattern's having matched refers to a non-
4306           unique number, the test is true if any of the subpatterns of that  num-
4307           ber have matched.
4308    
4309         An  alternative approach to using this "branch reset" feature is to use         An  alternative approach to using this "branch reset" feature is to use
4310         duplicate named subpatterns, as described in the next section.         duplicate named subpatterns, as described in the next section.
# Line 3923  NAMED SUBPATTERNS Line 4319  NAMED SUBPATTERNS
4319         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
4320         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
4321         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-
4322         tax.         tax.  Perl  allows  identically  numbered subpatterns to have different
4323           names, but PCRE does not.
4324    
4325         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>...)
4326         or (?'name'...) as in Perl, or (?P<name>...) as in  Python.  References         or  (?'name'...)  as in Perl, or (?P<name>...) as in Python. References
4327         to capturing parentheses from other parts of the pattern, such as back-         to capturing parentheses from other parts of the pattern, such as  back
4328         references, recursion, and conditions, can be made by name as  well  as         references,  recursion,  and conditions, can be made by name as well as
4329         by number.         by number.
4330    
4331         Names  consist  of  up  to  32 alphanumeric characters and underscores.         Names consist of up to  32  alphanumeric  characters  and  underscores.
4332         Named capturing parentheses are still  allocated  numbers  as  well  as         Named  capturing  parentheses  are  still  allocated numbers as well as
4333         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
4334         function calls for extracting the name-to-number translation table from         function calls for extracting the name-to-number translation table from
4335         a compiled pattern. There is also a convenience function for extracting         a compiled pattern. There is also a convenience function for extracting
4336         a captured substring by name.         a captured substring by name.
4337    
4338         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
4339         to relax this constraint by setting the PCRE_DUPNAMES option at compile         to relax this constraint by setting the PCRE_DUPNAMES option at compile
4340         time. This can be useful for patterns where only one  instance  of  the         time.  (Duplicate  names are also always permitted for subpatterns with
4341         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-
4342         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
4343           named parentheses can match. Suppose you want to match the  name  of  a
4344           weekday,  either as a 3-letter abbreviation or as the full name, and in
4345         both cases you want to extract the abbreviation. This pattern (ignoring         both cases you want to extract the abbreviation. This pattern (ignoring
4346         the line breaks) does the job:         the line breaks) does the job:
4347    
# Line 3952  NAMED SUBPATTERNS Line 4351  NAMED SUBPATTERNS
4351           (?<DN>Thu)(?:rsday)?|           (?<DN>Thu)(?:rsday)?|
4352           (?<DN>Sat)(?:urday)?           (?<DN>Sat)(?:urday)?
4353    
4354         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
4355         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
4356         reset" subpattern, as described in the previous section.)         reset" subpattern, as described in the previous section.)
4357    
4358         The convenience function for extracting the data by  name  returns  the         The  convenience  function  for extracting the data by name returns the
4359         substring  for  the first (and in this example, the only) subpattern of         substring for the first (and in this example, the only)  subpattern  of
4360         that name that matched. This saves searching  to  find  which  numbered         that  name  that  matched.  This saves searching to find which numbered
4361         subpattern  it  was. If you make a reference to a non-unique named sub-         subpattern it was.
4362         pattern from elsewhere in the pattern, the one that corresponds to  the  
4363         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
4364         dling named subpatterns, see the pcreapi documentation.         elsewhere  in the pattern, the one that corresponds to the first occur-
4365           rence of the name is used. In the absence of duplicate numbers (see the
4366           previous  section) this is the one with the lowest number. If you use a
4367           named reference in a condition test (see the section  about  conditions
4368           below),  either  to check whether a subpattern has matched, or to check
4369           for recursion, all subpatterns with the same name are  tested.  If  the
4370           condition  is  true for any one of them, the overall condition is true.
4371           This is the same behaviour as testing by number. For further details of
4372           the interfaces for handling named subpatterns, see the pcreapi documen-
4373           tation.
4374    
4375           Warning: You cannot use different names to distinguish between two sub-
4376           patterns  with  the same number because PCRE uses only the numbers when
4377           matching. For this reason, an error is given at compile time if differ-
4378           ent  names  are given to subpatterns with the same number. However, you
4379           can give the same name to subpatterns with the same number,  even  when
4380           PCRE_DUPNAMES is not set.
4381    
4382    
4383  REPETITION  REPETITION
4384    
4385         Repetition is specified by quantifiers, which can  follow  any  of  the         Repetition  is  specified  by  quantifiers, which can follow any of the
4386         following items:         following items:
4387    
4388           a literal data character           a literal data character
# Line 3975  REPETITION Line 4390  REPETITION
4390           the \C escape sequence           the \C escape sequence
4391           the \X escape sequence (in UTF-8 mode with Unicode properties)           the \X escape sequence (in UTF-8 mode with Unicode properties)
4392           the \R escape sequence           the \R escape sequence
4393           an escape such as \d that matches a single character           an escape such as \d or \pL that matches a single character
4394           a character class           a character class
4395           a back reference (see next section)           a back reference (see next section)
4396           a parenthesized subpattern (unless it is an assertion)           a parenthesized subpattern (unless it is an assertion)
4397             a recursive or "subroutine" call to a subpattern
4398    
4399         The  general repetition quantifier specifies a minimum and maximum num-         The general repetition quantifier specifies a minimum and maximum  num-
4400         ber of permitted matches, by giving the two numbers in  curly  brackets         ber  of  permitted matches, by giving the two numbers in curly brackets
4401         (braces),  separated  by  a comma. The numbers must be less than 65536,         (braces), separated by a comma. The numbers must be  less  than  65536,
4402         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:
4403    
4404           z{2,4}           z{2,4}
4405    
4406         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
4407         special  character.  If  the second number is omitted, but the comma is         special character. If the second number is omitted, but  the  comma  is
4408         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
4409         are  both omitted, the quantifier specifies an exact number of required         are both omitted, the quantifier specifies an exact number of  required
4410         matches. Thus         matches. Thus
4411    
4412           [aeiou]{3,}           [aeiou]{3,}
# Line 3999  REPETITION Line 4415  REPETITION
4415    
4416           \d{8}           \d{8}
4417    
4418         matches exactly 8 digits. An opening curly bracket that  appears  in  a         matches  exactly  8  digits. An opening curly bracket that appears in a
4419         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
4420         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-
4421         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.
4422    
4423         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 4014  REPETITION Line 4430  REPETITION
4430         The quantifier {0} is permitted, causing the expression to behave as if         The quantifier {0} is permitted, causing the expression to behave as if
4431         the previous item and the quantifier were not present. This may be use-         the previous item and the quantifier were not present. This may be use-
4432         ful  for  subpatterns that are referenced as subroutines from elsewhere         ful  for  subpatterns that are referenced as subroutines from elsewhere
4433         in the pattern. Items other than subpatterns that have a {0} quantifier         in the pattern (but see also the section entitled "Defining subpatterns
4434         are omitted from the compiled pattern.         for  use  by  reference only" below). Items other than subpatterns that
4435           have a {0} quantifier are omitted from the compiled pattern.
4436    
4437         For  convenience, the three most common quantifiers have single-charac-         For convenience, the three most common quantifiers have  single-charac-
4438         ter abbreviations:         ter abbreviations:
4439    
4440           *    is equivalent to {0,}           *    is equivalent to {0,}
4441           +    is equivalent to {1,}           +    is equivalent to {1,}
4442           ?    is equivalent to {0,1}           ?    is equivalent to {0,1}
4443    
4444         It is possible to construct infinite loops by  following  a  subpattern         It  is  possible  to construct infinite loops by following a subpattern
4445         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,
4446         for example:         for example:
4447    
4448           (a?)*           (a?)*
4449    
4450         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
4451         for  such  patterns. However, because there are cases where this can be         for such patterns. However, because there are cases where this  can  be
4452         useful, such patterns are now accepted, but if any  repetition  of  the         useful,  such  patterns  are now accepted, but if any repetition of the
4453         subpattern  does in fact match no characters, the loop is forcibly bro-         subpattern does in fact match no characters, the loop is forcibly  bro-
4454         ken.         ken.
4455    
4456         By default, the quantifiers are "greedy", that is, they match  as  much         By  default,  the quantifiers are "greedy", that is, they match as much
4457         as  possible  (up  to  the  maximum number of permitted times), without         as possible (up to the maximum  number  of  permitted  times),  without
4458         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
4459         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
4460         appear between /* and */ and within the comment,  individual  *  and  /         appear  between  /*  and  */ and within the comment, individual * and /
4461         characters  may  appear. An attempt to match C comments by applying the         characters may appear. An attempt to match C comments by  applying  the
4462         pattern         pattern
4463    
4464           /\*.*\*/           /\*.*\*/
# Line 4050  REPETITION Line 4467  REPETITION
4467    
4468           /* first comment */  not comment  /* second comment */           /* first comment */  not comment  /* second comment */
4469    
4470         fails, because it matches the entire string owing to the greediness  of         fails,  because it matches the entire string owing to the greediness of
4471         the .*  item.         the .*  item.
4472    
4473         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
4474         be greedy, and instead matches the minimum number of times possible, so         be greedy, and instead matches the minimum number of times possible, so
4475         the pattern         the pattern
4476    
4477           /\*.*?\*/           /\*.*?\*/
4478    
4479         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
4480         quantifiers is not otherwise changed,  just  the  preferred  number  of         quantifiers  is  not  otherwise  changed,  just the preferred number of
4481         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
4482         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
4483         appear doubled, as in         appear doubled, as in
4484    
4485           \d??\d           \d??\d
# Line 4070  REPETITION Line 4487  REPETITION
4487         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
4488         only way the rest of the pattern matches.         only way the rest of the pattern matches.
4489    
4490         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
4491         Perl),  the  quantifiers are not greedy by default, but individual ones         Perl), the quantifiers are not greedy by default, but  individual  ones
4492         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
4493         words, it inverts the default behaviour.         words, it inverts the default behaviour.
4494    
4495         When  a  parenthesized  subpattern  is quantified with a minimum repeat         When a parenthesized subpattern is quantified  with  a  minimum  repeat
4496         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
4497         required  for  the  compiled  pattern, in proportion to the size of the         required for the compiled pattern, in proportion to  the  size  of  the
4498         minimum or maximum.         minimum or maximum.
4499    
4500         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-
4501         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,
4502         the pattern is implicitly anchored, because whatever  follows  will  be         the  pattern  is  implicitly anchored, because whatever follows will be
4503         tried  against every character position in the subject string, so there         tried against every character position in the subject string, so  there
4504         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
4505         first.  PCRE  normally treats such a pattern as though it were preceded         first. PCRE normally treats such a pattern as though it  were  preceded
4506         by \A.         by \A.
4507    
4508         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-
4509         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-
4510         mization, or alternatively using ^ to indicate anchoring explicitly.         mization, or alternatively using ^ to indicate anchoring explicitly.
4511    
4512         However, there is one situation where the optimization cannot be  used.         However,  there is one situation where the optimization cannot be used.
4513         When  .*   is  inside  capturing  parentheses that are the subject of a         When .*  is inside capturing parentheses that are the subject of a back
4514         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
4515         where a later one succeeds. Consider, for example:         a later one succeeds. Consider, for example:
4516    
4517           (.*)abc\1           (.*)abc\1
4518    
4519         If  the subject is "xyz123abc123" the match point is the fourth charac-         If the subject is "xyz123abc123" the match point is the fourth  charac-
4520         ter. For this reason, such a pattern is not implicitly anchored.         ter. For this reason, such a pattern is not implicitly anchored.
4521    
4522         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 4108  REPETITION Line 4525  REPETITION
4525           (tweedle[dume]{3}\s*)+