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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         5.10/5.11, including support for UTF-8 encoded strings and Unicode gen-
30         Unicode general category properties. However, UTF-8 and Unicode support         eral  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 5.1.         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
101         each C library function, listing its arguments and results.         each C library function, listing its arguments and results.
102    
103    
104  LIMITATIONS  LIMITATIONS
105    
106         There  are some size limitations in PCRE but it is hoped that they will         There are some size limitations in PCRE but it is hoped that they  will
107         never in practice be relevant.         never in practice be relevant.
108    
109         The maximum length of a compiled pattern is 65539 (sic) bytes  if  PCRE         The  maximum  length of a compiled pattern is 65539 (sic) bytes if PCRE
110         is compiled with the default internal linkage size of 2. If you want to         is compiled with the default internal linkage size of 2. If you want to
111         process regular expressions that are truly enormous,  you  can  compile         process  regular  expressions  that are truly enormous, you can compile
112         PCRE  with  an  internal linkage size of 3 or 4 (see the README file in         PCRE with an internal linkage size of 3 or 4 (see the  README  file  in
113         the source distribution and the pcrebuild documentation  for  details).         the  source  distribution and the pcrebuild documentation for details).
114         In  these  cases the limit is substantially larger.  However, the speed         In these cases the limit is substantially larger.  However,  the  speed
115         of execution is slower.         of execution is slower.
116    
117         All values in repeating quantifiers must be less than 65536.         All values in repeating quantifiers must be less than 65536.
# Line 119  LIMITATIONS Line 122  LIMITATIONS
122         The maximum length of name for a named subpattern is 32 characters, and         The maximum length of name for a named subpattern is 32 characters, and
123         the maximum number of named subpatterns is 10000.         the maximum number of named subpatterns is 10000.
124    
125         The maximum length of a subject string is the largest  positive  number         The  maximum  length of a subject string is the largest positive number
126         that  an integer variable can hold. However, when using the traditional         that an integer variable can hold. However, when using the  traditional
127         matching function, PCRE uses recursion to handle subpatterns and indef-         matching function, PCRE uses recursion to handle subpatterns and indef-
128         inite  repetition.  This means that the available stack space may limit         inite repetition.  This means that the available stack space may  limit
129         the size of a subject string that can be processed by certain patterns.         the size of a subject string that can be processed by certain patterns.
130         For a discussion of stack issues, see the pcrestack documentation.         For a discussion of stack issues, see the pcrestack documentation.
131    
132    
133  UTF-8 AND UNICODE PROPERTY SUPPORT  UTF-8 AND UNICODE PROPERTY SUPPORT
134    
135         From  release  3.3,  PCRE  has  had  some support for character strings         From release 3.3, PCRE has  had  some  support  for  character  strings
136         encoded in the UTF-8 format. For release 4.0 this was greatly  extended         encoded  in the UTF-8 format. For release 4.0 this was greatly extended
137         to  cover  most common requirements, and in release 5.0 additional sup-         to cover most common requirements, and in release 5.0  additional  sup-
138         port for Unicode general category properties was added.         port for Unicode general category properties was added.
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, or the  pattern  must  start  with  the         with  the  PCRE_UTF8  option  flag,  or the pattern must start with the
143         sequence  (*UTF8).  When  either of these is the case, both the pattern         sequence (*UTF8). When either of these is the case,  both  the  pattern
144         and any subject strings that are matched  against  it  are  treated  as         and  any  subject  strings  that  are matched against it are treated as
145         UTF-8 strings instead of just strings of bytes.         UTF-8 strings instead of strings of 1-byte characters.
146    
147         If  you compile PCRE with UTF-8 support, but do not use it at run time,         If you compile PCRE with UTF-8 support, but do not use it at run  time,
148         the library will be a bit bigger, but the additional run time  overhead         the  library will be a bit bigger, but the additional run time overhead
149         is limited to testing the PCRE_UTF8 flag occasionally, so should not be         is limited to testing the PCRE_UTF8 flag occasionally, so should not be
150         very big.         very big.
151    
152         If PCRE is built with Unicode character property support (which implies         If PCRE is built with Unicode character property support (which implies
153         UTF-8  support),  the  escape sequences \p{..}, \P{..}, and \X are sup-         UTF-8 support), the escape sequences \p{..}, \P{..}, and  \X  are  sup-
154         ported.  The available properties that can be tested are limited to the         ported.  The available properties that can be tested are limited to the
155         general  category  properties such as Lu for an upper case letter or Nd         general category properties such as Lu for an upper case letter  or  Nd
156         for a decimal number, the Unicode script names such as Arabic  or  Han,         for  a  decimal number, the Unicode script names such as Arabic or Han,
157         and  the  derived  properties  Any  and L&. A full list is given in the         and the derived properties Any and L&. A full  list  is  given  in  the
158         pcrepattern documentation. Only the short names for properties are sup-         pcrepattern documentation. Only the short names for properties are sup-
159         ported.  For example, \p{L} matches a letter. Its Perl synonym, \p{Let-         ported. For example, \p{L} matches a letter. Its Perl synonym,  \p{Let-
160         ter}, is not supported.  Furthermore,  in  Perl,  many  properties  may         ter},  is  not  supported.   Furthermore,  in Perl, many properties may
161         optionally  be  prefixed by "Is", for compatibility with Perl 5.6. PCRE         optionally be prefixed by "Is", for compatibility with Perl  5.6.  PCRE
162         does not support this.         does not support this.
163    
164     Validity of UTF-8 strings     Validity of UTF-8 strings
165    
166         When you set the PCRE_UTF8 flag, the strings  passed  as  patterns  and         When  you  set  the  PCRE_UTF8 flag, the strings passed as patterns and
167         subjects are (by default) checked for validity on entry to the relevant         subjects are (by default) checked for validity on entry to the relevant
168         functions. From release 7.3 of PCRE, the check is according  the  rules         functions.  From  release 7.3 of PCRE, the check is according the rules
169         of  RFC  3629, which are themselves derived from the Unicode specifica-         of RFC 3629, which are themselves derived from the  Unicode  specifica-
170         tion. Earlier releases of PCRE followed the rules of  RFC  2279,  which         tion.  Earlier  releases  of PCRE followed the rules of RFC 2279, which
171         allows  the  full range of 31-bit values (0 to 0x7FFFFFFF). The current         allows the full range of 31-bit values (0 to 0x7FFFFFFF).  The  current
172         check allows only values in the range U+0 to U+10FFFF, excluding U+D800         check allows only values in the range U+0 to U+10FFFF, excluding U+D800
173         to U+DFFF.         to U+DFFF.
174    
175         The  excluded  code  points are the "Low Surrogate Area" of Unicode, of         The excluded code points are the "Low Surrogate Area"  of  Unicode,  of
176         which the Unicode Standard says this: "The Low Surrogate Area does  not         which  the Unicode Standard says this: "The Low Surrogate Area does not
177         contain  any  character  assignments,  consequently  no  character code         contain any  character  assignments,  consequently  no  character  code
178         charts or namelists are provided for this area. Surrogates are reserved         charts or namelists are provided for this area. Surrogates are reserved
179         for  use  with  UTF-16 and then must be used in pairs." The code points         for use with UTF-16 and then must be used in pairs."  The  code  points
180         that are encoded by UTF-16 pairs  are  available  as  independent  code         that  are  encoded  by  UTF-16  pairs are available as independent code
181         points  in  the  UTF-8  encoding.  (In other words, the whole surrogate         points in the UTF-8 encoding. (In  other  words,  the  whole  surrogate
182         thing is a fudge for UTF-16 which unfortunately messes up UTF-8.)         thing is a fudge for UTF-16 which unfortunately messes up UTF-8.)
183    
184         If an  invalid  UTF-8  string  is  passed  to  PCRE,  an  error  return         If  an  invalid  UTF-8  string  is  passed  to  PCRE,  an  error return
185         (PCRE_ERROR_BADUTF8) is given. In some situations, you may already know         (PCRE_ERROR_BADUTF8) is given. In some situations, you may already know
186         that your strings are valid, and therefore want to skip these checks in         that your strings are valid, and therefore want to skip these checks in
187         order to improve performance. If you set the PCRE_NO_UTF8_CHECK flag at         order to improve performance. If you set the PCRE_NO_UTF8_CHECK flag at
188         compile time or at run time, PCRE assumes that the pattern  or  subject         compile  time  or at run time, PCRE assumes that the pattern or subject
189         it  is  given  (respectively)  contains only valid UTF-8 codes. In this         it is given (respectively) contains only valid  UTF-8  codes.  In  this
190         case, it does not diagnose an invalid UTF-8 string.         case, it does not diagnose an invalid UTF-8 string.
191    
192         If you pass an invalid UTF-8 string  when  PCRE_NO_UTF8_CHECK  is  set,         If  you  pass  an  invalid UTF-8 string when PCRE_NO_UTF8_CHECK is set,
193         what  happens  depends on why the string is invalid. If the string con-         what happens depends on why the string is invalid. If the  string  con-
194         forms to the "old" definition of UTF-8 (RFC 2279), it is processed as a         forms to the "old" definition of UTF-8 (RFC 2279), it is processed as a
195         string  of  characters  in  the  range 0 to 0x7FFFFFFF. In other words,         string of characters in the range 0  to  0x7FFFFFFF.  In  other  words,
196         apart from the initial validity test, PCRE (when in UTF-8 mode) handles         apart from the initial validity test, PCRE (when in UTF-8 mode) handles
197         strings  according  to  the more liberal rules of RFC 2279. However, if         strings according to the more liberal rules of RFC  2279.  However,  if
198         the string does not even conform to RFC 2279, the result is  undefined.         the  string does not even conform to RFC 2279, the result is undefined.
199         Your program may crash.         Your program may crash.
200    
201         If  you  want  to  process  strings  of  values  in the full range 0 to         If you want to process strings  of  values  in  the  full  range  0  to
202         0x7FFFFFFF, encoded in a UTF-8-like manner as per the old RFC, you  can         0x7FFFFFFF,  encoded in a UTF-8-like manner as per the old RFC, you can
203         set PCRE_NO_UTF8_CHECK to bypass the more restrictive test. However, in         set PCRE_NO_UTF8_CHECK to bypass the more restrictive test. However, in
204         this situation, you will have to apply your own validity check.         this situation, you will have to apply your own validity check.
205    
206     General comments about UTF-8 mode     General comments about UTF-8 mode
207    
208         1. An unbraced hexadecimal escape sequence (such  as  \xb3)  matches  a         1.  An  unbraced  hexadecimal  escape sequence (such as \xb3) matches a
209         two-byte UTF-8 character if the value is greater than 127.         two-byte UTF-8 character if the value is greater than 127.
210    
211         2.  Octal  numbers  up to \777 are recognized, and match two-byte UTF-8         2. Octal numbers up to \777 are recognized, and  match  two-byte  UTF-8
212         characters for values greater than \177.         characters for values greater than \177.
213    
214         3. Repeat quantifiers apply to complete UTF-8 characters, not to  indi-         3.  Repeat quantifiers apply to complete UTF-8 characters, not to indi-
215         vidual bytes, for example: \x{100}{3}.         vidual bytes, for example: \x{100}{3}.
216    
217         4.  The dot metacharacter matches one UTF-8 character instead of a sin-         4. The dot metacharacter matches one UTF-8 character instead of a  sin-
218         gle byte.         gle byte.
219    
220         5. The escape sequence \C can be used to match a single byte  in  UTF-8         5.  The  escape sequence \C can be used to match a single byte in UTF-8
221         mode,  but  its  use can lead to some strange effects. This facility is         mode, but its use can lead to some strange effects.  This  facility  is
222         not available in the alternative matching function, pcre_dfa_exec().         not available in the alternative matching function, pcre_dfa_exec().
223    
224         6. The character escapes \b, \B, \d, \D, \s, \S, \w, and  \W  correctly         6.  The  character escapes \b, \B, \d, \D, \s, \S, \w, and \W correctly
225         test  characters of any code value, but the characters that PCRE recog-         test characters of any code value, but, by default, the characters that
226         nizes as digits, spaces, or word characters  remain  the  same  set  as         PCRE  recognizes  as digits, spaces, or word characters remain the same
227         before, all with values less than 256. This remains true even when PCRE         set as before, all with values less than 256. This  remains  true  even
228         includes Unicode property support, because to do otherwise  would  slow         when  PCRE  is built to include Unicode property support, because to do
229         down  PCRE in many common cases. If you really want to test for a wider         otherwise would slow down PCRE in many common  cases.  Note  that  this
230         sense of, say, "digit", you must use Unicode  property  tests  such  as         also applies to \b, because it is defined in terms of \w and \W. If you
231         \p{Nd}.  Note  that  this  also applies to \b, because it is defined in         really want to test for a wider sense of, say,  "digit",  you  can  use
232         terms of \w and \W.         explicit  Unicode property tests such as \p{Nd}.  Alternatively, if you
233           set the PCRE_UCP option, the way that the  character  escapes  work  is
234           changed  so that Unicode properties are used to determine which charac-
235           ters match. There are more details in the section on generic  character
236           types in the pcrepattern documentation.
237    
238         7. Similarly, characters that match the POSIX named  character  classes         7.  Similarly,  characters that match the POSIX named character classes
239         are all low-valued characters.         are all low-valued characters, unless the PCRE_UCP option is set.
240    
241         8.  However,  the Perl 5.10 horizontal and vertical whitespace matching         8. However, the Perl 5.10 horizontal and vertical  whitespace  matching
242         escapes (\h, \H, \v, and \V) do match all the appropriate Unicode char-         escapes (\h, \H, \v, and \V) do match all the appropriate Unicode char-
243         acters.         acters, whether or not PCRE_UCP is set.
244    
245         9.  Case-insensitive  matching  applies only to characters whose values         9. Case-insensitive matching applies only to  characters  whose  values
246         are less than 128, unless PCRE is built with Unicode property  support.         are  less than 128, unless PCRE is built with Unicode property support.
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. Even when Unicode property
251         support is available, PCRE supports case-insensitive matching only when         support is available, PCRE supports case-insensitive matching only when
252         there is a one-to-one mapping between a letter's  cases.  There  are  a         there  is  a  one-to-one  mapping between a letter's cases. There are a
253         small  number  of  many-to-one  mappings in Unicode; these are not sup-         small number of many-to-one mappings in Unicode;  these  are  not  sup-
254         ported by PCRE.         ported by PCRE.
255    
256    
# Line 253  AUTHOR Line 260  AUTHOR
260         University Computing Service         University Computing Service
261         Cambridge CB2 3QH, England.         Cambridge CB2 3QH, England.
262    
263         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,
264         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,
265         followed by the two digits 10, at the domain cam.ac.uk.         followed by the two digits 10, at the domain cam.ac.uk.
266    
267    
268  REVISION  REVISION
269    
270         Last updated: 11 April 2009         Last updated: 12 May 2010
271         Copyright (c) 1997-2009 University of Cambridge.         Copyright (c) 1997-2010 University of Cambridge.
272  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
273    
274    
# Line 279  PCRE BUILD-TIME OPTIONS Line 286  PCRE BUILD-TIME OPTIONS
286         script,  where the optional features are selected or deselected by pro-         script,  where the optional features are selected or deselected by pro-
287         viding options to configure before running the make  command.  However,         viding options to configure before running the make  command.  However,
288         the  same  options  can be selected in both Unix-like and non-Unix-like         the  same  options  can be selected in both Unix-like and non-Unix-like
289         environments using the GUI facility of  CMakeSetup  if  you  are  using         environments using the GUI facility of cmake-gui if you are using CMake
290         CMake instead of configure to build PCRE.         instead of configure to build PCRE.
291    
292           There  is  a  lot more information about building PCRE in non-Unix-like
293           environments in the file called NON_UNIX_USE, which is part of the PCRE
294           distribution.  You  should consult this file as well as the README file
295           if you are building in a non-Unix-like environment.
296    
297         The complete list of options for configure (which includes the standard         The complete list of options for configure (which includes the standard
298         ones such as the  selection  of  the  installation  directory)  can  be         ones  such  as  the  selection  of  the  installation directory) can be
299         obtained by running         obtained by running
300    
301           ./configure --help           ./configure --help
302    
303         The  following  sections  include  descriptions  of options whose names         The following sections include  descriptions  of  options  whose  names
304         begin with --enable or --disable. These settings specify changes to the         begin with --enable or --disable. These settings specify changes to the
305         defaults  for  the configure command. Because of the way that configure         defaults for the configure command. Because of the way  that  configure
306         works, --enable and --disable always come in pairs, so  the  complemen-         works,  --enable  and --disable always come in pairs, so the complemen-
307         tary  option always exists as well, but as it specifies the default, it         tary option always exists as well, but as it specifies the default,  it
308         is not described.         is not described.
309    
310    
# Line 313  UTF-8 SUPPORT Line 325  UTF-8 SUPPORT
325    
326           --enable-utf8           --enable-utf8
327    
328         to the configure command. Of itself, this  does  not  make  PCRE  treat         to  the  configure  command.  Of  itself, this does not make PCRE treat
329         strings  as UTF-8. As well as compiling PCRE with this option, you also         strings as UTF-8. As well as compiling PCRE with this option, you  also
330         have have to set the PCRE_UTF8 option when you call the  pcre_compile()         have  have to set the PCRE_UTF8 option when you call the pcre_compile()
331         function.         or pcre_compile2() functions.
332    
333         If  you set --enable-utf8 when compiling in an EBCDIC environment, PCRE         If you set --enable-utf8 when compiling in an EBCDIC environment,  PCRE
334         expects its input to be either ASCII or UTF-8 (depending on the runtime         expects its input to be either ASCII or UTF-8 (depending on the runtime
335         option).  It  is not possible to support both EBCDIC and UTF-8 codes in         option). It is not possible to support both EBCDIC and UTF-8  codes  in
336         the same  version  of  the  library.  Consequently,  --enable-utf8  and         the  same  version  of  the  library.  Consequently,  --enable-utf8 and
337         --enable-ebcdic are mutually exclusive.         --enable-ebcdic are mutually exclusive.
338    
339    
340  UNICODE CHARACTER PROPERTY SUPPORT  UNICODE CHARACTER PROPERTY SUPPORT
341    
342         UTF-8  support allows PCRE to process character values greater than 255         UTF-8 support allows PCRE to process character values greater than  255
343         in the strings that it handles. On its own, however, it does  not  pro-         in  the  strings that it handles. On its own, however, it does not pro-
344         vide any facilities for accessing the properties of such characters. If         vide any facilities for accessing the properties of such characters. If
345         you want to be able to use the pattern escapes \P, \p,  and  \X,  which         you  want  to  be able to use the pattern escapes \P, \p, and \X, which
346         refer to Unicode character properties, you must add         refer to Unicode character properties, you must add
347    
348           --enable-unicode-properties           --enable-unicode-properties
349    
350         to  the configure command. This implies UTF-8 support, even if you have         to the configure command. This implies UTF-8 support, even if you  have
351         not explicitly requested it.         not explicitly requested it.
352    
353         Including Unicode property support adds around 30K  of  tables  to  the         Including  Unicode  property  support  adds around 30K of tables to the
354         PCRE  library.  Only  the general category properties such as Lu and Nd         PCRE library. Only the general category properties such as  Lu  and  Nd
355         are supported. Details are given in the pcrepattern documentation.         are supported. Details are given in the pcrepattern documentation.
356    
357    
358  CODE VALUE OF NEWLINE  CODE VALUE OF NEWLINE
359    
360         By default, PCRE interprets the linefeed (LF) character  as  indicating         By  default,  PCRE interprets the linefeed (LF) character as indicating
361         the  end  of  a line. This is the normal newline character on Unix-like         the end of a line. This is the normal newline  character  on  Unix-like
362         systems. You can compile PCRE to use carriage return (CR)  instead,  by         systems.  You  can compile PCRE to use carriage return (CR) instead, by
363         adding         adding
364    
365           --enable-newline-is-cr           --enable-newline-is-cr
366    
367         to  the  configure  command.  There  is  also  a --enable-newline-is-lf         to the  configure  command.  There  is  also  a  --enable-newline-is-lf
368         option, which explicitly specifies linefeed as the newline character.         option, which explicitly specifies linefeed as the newline character.
369    
370         Alternatively, you can specify that line endings are to be indicated by         Alternatively, you can specify that line endings are to be indicated by
# Line 364  CODE VALUE OF NEWLINE Line 376  CODE VALUE OF NEWLINE
376    
377           --enable-newline-is-anycrlf           --enable-newline-is-anycrlf
378    
379         which  causes  PCRE  to recognize any of the three sequences CR, LF, or         which causes PCRE to recognize any of the three sequences  CR,  LF,  or
380         CRLF as indicating a line ending. Finally, a fifth option, specified by         CRLF as indicating a line ending. Finally, a fifth option, specified by
381    
382           --enable-newline-is-any           --enable-newline-is-any
383    
384         causes PCRE to recognize any Unicode newline sequence.         causes PCRE to recognize any Unicode newline sequence.
385    
386         Whatever line ending convention is selected when PCRE is built  can  be         Whatever  line  ending convention is selected when PCRE is built can be
387         overridden  when  the library functions are called. At build time it is         overridden when the library functions are called. At build time  it  is
388         conventional to use the standard for your operating system.         conventional to use the standard for your operating system.
389    
390    
391  WHAT \R MATCHES  WHAT \R MATCHES
392    
393         By default, the sequence \R in a pattern matches  any  Unicode  newline         By  default,  the  sequence \R in a pattern matches any Unicode newline
394         sequence,  whatever  has  been selected as the line ending sequence. If         sequence, whatever has been selected as the line  ending  sequence.  If
395         you specify         you specify
396    
397           --enable-bsr-anycrlf           --enable-bsr-anycrlf
398    
399         the default is changed so that \R matches only CR, LF, or  CRLF.  What-         the  default  is changed so that \R matches only CR, LF, or CRLF. What-
400         ever  is selected when PCRE is built can be overridden when the library         ever is selected when PCRE is built can be overridden when the  library
401         functions are called.         functions are called.
402    
403    
404  BUILDING SHARED AND STATIC LIBRARIES  BUILDING SHARED AND STATIC LIBRARIES
405    
406         The PCRE building process uses libtool to build both shared and  static         The  PCRE building process uses libtool to build both shared and static
407         Unix  libraries by default. You can suppress one of these by adding one         Unix libraries by default. You can suppress one of these by adding  one
408         of         of
409    
410           --disable-shared           --disable-shared
# Line 404  BUILDING SHARED AND STATIC LIBRARIES Line 416  BUILDING SHARED AND STATIC LIBRARIES
416  POSIX MALLOC USAGE  POSIX MALLOC USAGE
417    
418         When PCRE is called through the POSIX interface (see the pcreposix doc-         When PCRE is called through the POSIX interface (see the pcreposix doc-
419         umentation),  additional  working  storage  is required for holding the         umentation), additional working storage is  required  for  holding  the
420         pointers to capturing substrings, because PCRE requires three  integers         pointers  to capturing substrings, because PCRE requires three integers
421         per  substring,  whereas  the POSIX interface provides only two. If the         per substring, whereas the POSIX interface provides only  two.  If  the
422         number of expected substrings is small, the wrapper function uses space         number of expected substrings is small, the wrapper function uses space
423         on the stack, because this is faster than using malloc() for each call.         on the stack, because this is faster than using malloc() for each call.
424         The default threshold above which the stack is no longer used is 10; it         The default threshold above which the stack is no longer used is 10; it
# Line 419  POSIX MALLOC USAGE Line 431  POSIX MALLOC USAGE
431    
432  HANDLING VERY LARGE PATTERNS  HANDLING VERY LARGE PATTERNS
433    
434         Within  a  compiled  pattern,  offset values are used to point from one         Within a compiled pattern, offset values are used  to  point  from  one
435         part to another (for example, from an opening parenthesis to an  alter-         part  to another (for example, from an opening parenthesis to an alter-
436         nation  metacharacter).  By default, two-byte values are used for these         nation metacharacter). By default, two-byte values are used  for  these
437         offsets, leading to a maximum size for a  compiled  pattern  of  around         offsets,  leading  to  a  maximum size for a compiled pattern of around
438         64K.  This  is sufficient to handle all but the most gigantic patterns.         64K. This is sufficient to handle all but the most  gigantic  patterns.
439         Nevertheless, some people do want to process enormous patterns,  so  it         Nevertheless,  some  people do want to process truyl enormous patterns,
440         is  possible  to compile PCRE to use three-byte or four-byte offsets by         so it is possible to compile PCRE to use three-byte or  four-byte  off-
441         adding a setting such as         sets by adding a setting such as
442    
443           --with-link-size=3           --with-link-size=3
444    
445         to the configure command. The value given must be 2,  3,  or  4.  Using         to  the  configure  command.  The value given must be 2, 3, or 4. Using
446         longer  offsets slows down the operation of PCRE because it has to load         longer offsets slows down the operation of PCRE because it has to  load
447         additional bytes when handling them.         additional bytes when handling them.
448    
449    
450  AVOIDING EXCESSIVE STACK USAGE  AVOIDING EXCESSIVE STACK USAGE
451    
452         When matching with the pcre_exec() function, PCRE implements backtrack-         When matching with the pcre_exec() function, PCRE implements backtrack-
453         ing  by  making recursive calls to an internal function called match().         ing by making recursive calls to an internal function  called  match().
454         In environments where the size of the stack is limited,  this  can  se-         In  environments  where  the size of the stack is limited, this can se-
455         verely  limit  PCRE's operation. (The Unix environment does not usually         verely limit PCRE's operation. (The Unix environment does  not  usually
456         suffer from this problem, but it may sometimes be necessary to increase         suffer from this problem, but it may sometimes be necessary to increase
457         the  maximum  stack size.  There is a discussion in the pcrestack docu-         the maximum stack size.  There is a discussion in the  pcrestack  docu-
458         mentation.) An alternative approach to recursion that uses memory  from         mentation.)  An alternative approach to recursion that uses memory from
459         the  heap  to remember data, instead of using recursive function calls,         the heap to remember data, instead of using recursive  function  calls,
460         has been implemented to work round the problem of limited  stack  size.         has  been  implemented to work round the problem of limited stack size.
461         If you want to build a version of PCRE that works this way, add         If you want to build a version of PCRE that works this way, add
462    
463           --disable-stack-for-recursion           --disable-stack-for-recursion
464    
465         to  the  configure  command. With this configuration, PCRE will use the         to the configure command. With this configuration, PCRE  will  use  the
466         pcre_stack_malloc and pcre_stack_free variables to call memory  manage-         pcre_stack_malloc  and pcre_stack_free variables to call memory manage-
467         ment  functions. By default these point to malloc() and free(), but you         ment functions. By default these point to malloc() and free(), but  you
468         can replace the pointers so that your own functions are used.         can replace the pointers so that your own functions are used instead.
469    
470         Separate functions are  provided  rather  than  using  pcre_malloc  and         Separate  functions  are  provided  rather  than  using pcre_malloc and
471         pcre_free  because  the  usage  is  very  predictable:  the block sizes         pcre_free because the  usage  is  very  predictable:  the  block  sizes
472         requested are always the same, and  the  blocks  are  always  freed  in         requested  are  always  the  same,  and  the blocks are always freed in
473         reverse  order.  A calling program might be able to implement optimized         reverse order. A calling program might be able to  implement  optimized
474         functions that perform better  than  malloc()  and  free().  PCRE  runs         functions  that  perform  better  than  malloc()  and free(). PCRE runs
475         noticeably more slowly when built in this way. This option affects only         noticeably more slowly when built in this way. This option affects only
476         the  pcre_exec()  function;  it   is   not   relevant   for   the   the         the pcre_exec() function; it is not relevant for pcre_dfa_exec().
        pcre_dfa_exec() function.  
477    
478    
479  LIMITING PCRE RESOURCE USAGE  LIMITING PCRE RESOURCE USAGE
# Line 551  PCRETEST OPTION FOR LIBREADLINE SUPPORT Line 562  PCRETEST OPTION FOR LIBREADLINE SUPPORT
562         to  the  configure  command,  pcretest  is  linked with the libreadline         to  the  configure  command,  pcretest  is  linked with the libreadline
563         library, and when its input is from a terminal, it reads it  using  the         library, and when its input is from a terminal, it reads it  using  the
564         readline() function. This provides line-editing and history facilities.         readline() function. This provides line-editing and history facilities.
565         Note that libreadline is GPL-licenced, so if you distribute a binary of         Note that libreadline is GPL-licensed, so if you distribute a binary of
566         pcretest linked in this way, there may be licensing issues.         pcretest linked in this way, there may be licensing issues.
567    
568         Setting  this  option  causes  the -lreadline option to be added to the         Setting  this  option  causes  the -lreadline option to be added to the
# Line 587  AUTHOR Line 598  AUTHOR
598    
599  REVISION  REVISION
600    
601         Last updated: 17 March 2009         Last updated: 29 September 2009
602         Copyright (c) 1997-2009 University of Cambridge.         Copyright (c) 1997-2009 University of Cambridge.
603  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
604    
# Line 675  THE ALTERNATIVE MATCHING ALGORITHM Line 686  THE ALTERNATIVE MATCHING ALGORITHM
686         though  it is not implemented as a traditional finite state machine (it         though  it is not implemented as a traditional finite state machine (it
687         keeps multiple states active simultaneously).         keeps multiple states active simultaneously).
688    
689           Although the general principle of this matching algorithm  is  that  it
690           scans  the subject string only once, without backtracking, there is one
691           exception: when a lookaround assertion is encountered,  the  characters
692           following  or  preceding  the  current  point  have to be independently
693           inspected.
694    
695         The scan continues until either the end of the subject is  reached,  or         The scan continues until either the end of the subject is  reached,  or
696         there  are  no more unterminated paths. At this point, terminated paths         there  are  no more unterminated paths. At this point, terminated paths
697         represent the different matching possibilities (if there are none,  the         represent the different matching possibilities (if there are none,  the
698         match  has  failed).   Thus,  if there is more than one possible match,         match  has  failed).   Thus,  if there is more than one possible match,
699         this algorithm finds all of them, and in particular, it finds the long-         this algorithm finds all of them, and in particular, it finds the long-
700         est.  In PCRE, there is an option to stop the algorithm after the first         est.  There  is  an  option to stop the algorithm after the first match
701         match (which is necessarily the shortest) has been found.         (which is necessarily the shortest) is found.
702    
703         Note that all the matches that are found start at the same point in the         Note that all the matches that are found start at the same point in the
704         subject. If the pattern         subject. If the pattern
# Line 751  ADVANTAGES OF THE ALTERNATIVE ALGORITHM Line 768  ADVANTAGES OF THE ALTERNATIVE ALGORITHM
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
        on the content of the pattern that apply when using the standard  algo-  
        rithm  for  partial matching do not apply to the alternative algorithm.  
        For non-anchored patterns, the starting position of a partial match  is  
        available.  
   
        3.  Because  the  alternative  algorithm  scans the subject string just  
772         once, and never needs to backtrack, it is possible to  pass  very  long         once, and never needs to backtrack, it is possible to  pass  very  long
773         subject  strings  to  the matching function in several pieces, checking         subject  strings  to  the matching function in several pieces, checking
774         for partial matching each time.         for partial matching each time.  The  pcrepartial  documentation  gives
775           details of partial matching.
776    
777    
778  DISADVANTAGES OF THE ALTERNATIVE ALGORITHM  DISADVANTAGES OF THE ALTERNATIVE ALGORITHM
779    
780         The alternative algorithm suffers from a number of disadvantages:         The alternative algorithm suffers from a number of disadvantages:
781    
782         1. It is substantially slower than  the  standard  algorithm.  This  is         1.  It  is  substantially  slower  than the standard algorithm. This is
783         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
784         because it is less susceptible to optimization.         because it is less susceptible to optimization.
785    
786         2. Capturing parentheses and back references are not supported.         2. Capturing parentheses and back references are not supported.
# Line 786  AUTHOR Line 798  AUTHOR
798    
799  REVISION  REVISION
800    
801         Last updated: 19 April 2008         Last updated: 29 September 2009
802         Copyright (c) 1997-2008 University of Cambridge.         Copyright (c) 1997-2009 University of Cambridge.
803  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
804    
805    
# Line 894  PCRE API OVERVIEW Line 906  PCRE API OVERVIEW
906         bers for the library.  Applications can use these  to  include  support         bers for the library.  Applications can use these  to  include  support
907         for different releases of PCRE.         for different releases of PCRE.
908    
909           In a Windows environment, if you want to statically link an application
910           program against a non-dll pcre.a  file,  you  must  define  PCRE_STATIC
911           before  including  pcre.h or pcrecpp.h, because otherwise the pcre_mal-
912           loc()   and   pcre_free()   exported   functions   will   be   declared
913           __declspec(dllimport), with unwanted results.
914    
915         The   functions   pcre_compile(),  pcre_compile2(),  pcre_study(),  and         The   functions   pcre_compile(),  pcre_compile2(),  pcre_study(),  and
916         pcre_exec() are used for compiling and matching regular expressions  in         pcre_exec() are used for compiling and matching regular expressions  in
917         a  Perl-compatible  manner. A sample program that demonstrates the sim-         a  Perl-compatible  manner. A sample program that demonstrates the sim-
918         plest way of using them is provided in the file  called  pcredemo.c  in         plest way of using them is provided in the file  called  pcredemo.c  in
919         the  source distribution. The pcresample documentation describes how to         the PCRE source distribution. A listing of this program is given in the
920         compile and run it.         pcredemo documentation, and the pcresample documentation describes  how
921           to compile and run it.
922    
923         A second matching function, pcre_dfa_exec(), which is not Perl-compati-         A second matching function, pcre_dfa_exec(), which is not Perl-compati-
924         ble,  is  also provided. This uses a different algorithm for the match-         ble, is also provided. This uses a different algorithm for  the  match-
925         ing. The alternative algorithm finds all possible matches (at  a  given         ing.  The  alternative algorithm finds all possible matches (at a given
926         point  in  the subject), and scans the subject just once. However, this         point in the subject), and scans the subject just  once  (unless  there
927         algorithm does not return captured substrings. A description of the two         are  lookbehind  assertions).  However,  this algorithm does not return
928         matching  algorithms and their advantages and disadvantages is given in         captured substrings. A description of the two matching  algorithms  and
929         the pcrematching documentation.         their  advantages  and disadvantages is given in the pcrematching docu-
930           mentation.
931    
932         In addition to the main compiling and  matching  functions,  there  are         In addition to the main compiling and  matching  functions,  there  are
933         convenience functions for extracting captured substrings from a subject         convenience functions for extracting captured substrings from a subject
# Line 1117  COMPILING A PATTERN Line 1137  COMPILING A PATTERN
1137         Either of the functions pcre_compile() or pcre_compile2() can be called         Either of the functions pcre_compile() or pcre_compile2() can be called
1138         to compile a pattern into an internal form. The only difference between         to compile a pattern into an internal form. The only difference between
1139         the  two interfaces is that pcre_compile2() has an additional argument,         the  two interfaces is that pcre_compile2() has an additional argument,
1140         errorcodeptr, via which a numerical error code can be returned.         errorcodeptr, via which a numerical error  code  can  be  returned.  To
1141           avoid  too  much repetition, we refer just to pcre_compile() below, but
1142           the information applies equally to pcre_compile2().
1143    
1144         The pattern is a C string terminated by a binary zero, and is passed in         The pattern is a C string terminated by a binary zero, and is passed in
1145         the  pattern  argument.  A  pointer to a single block of memory that is         the  pattern  argument.  A  pointer to a single block of memory that is
# Line 1135  COMPILING A PATTERN Line 1157  COMPILING A PATTERN
1157         The options argument contains various bit settings that affect the com-         The options argument contains various bit settings that affect the com-
1158         pilation. It should be zero if no options are required.  The  available         pilation. It should be zero if no options are required.  The  available
1159         options  are  described  below. Some of them (in particular, those that         options  are  described  below. Some of them (in particular, those that
1160         are compatible with Perl, but also some others) can  also  be  set  and         are compatible with Perl, but some others as well) can also be set  and
1161         unset  from  within  the  pattern  (see the detailed description in the         unset  from  within  the  pattern  (see the detailed description in the
1162         pcrepattern documentation). For those options that can be different  in         pcrepattern documentation). For those options that can be different  in
1163         different  parts  of  the pattern, the contents of the options argument         different  parts  of  the pattern, the contents of the options argument
1164         specifies their initial settings at the start of compilation and execu-         specifies their settings at the start of compilation and execution. The
1165         tion.  The PCRE_ANCHORED and PCRE_NEWLINE_xxx options can be set at the         PCRE_ANCHORED, PCRE_BSR_xxx, and PCRE_NEWLINE_xxx options can be set at
1166         time of matching as well as at compile time.         the time of matching as well as at compile time.
1167    
1168         If errptr is NULL, pcre_compile() returns NULL immediately.  Otherwise,         If errptr is NULL, pcre_compile() returns NULL immediately.  Otherwise,
1169         if  compilation  of  a  pattern fails, pcre_compile() returns NULL, and         if  compilation  of  a  pattern fails, pcre_compile() returns NULL, and
1170         sets the variable pointed to by errptr to point to a textual error mes-         sets the variable pointed to by errptr to point to a textual error mes-
1171         sage. This is a static string that is part of the library. You must not         sage. This is a static string that is part of the library. You must not
1172         try to free it. The offset from the start of the pattern to the charac-         try to free it. The byte offset from the start of the  pattern  to  the
1173         ter where the error was discovered is placed in the variable pointed to         character  that  was  being  processed when the error was discovered is
1174         by erroffset, which must not be NULL. If it is, an immediate  error  is         placed in the variable pointed to by erroffset, which must not be NULL.
1175         given.         If  it  is,  an  immediate error is given. Some errors are not detected
1176           until checks are carried out when the whole pattern has  been  scanned;
1177           in this case the offset is set to the end of the pattern.
1178    
1179         If  pcre_compile2()  is  used instead of pcre_compile(), and the error-         If  pcre_compile2()  is  used instead of pcre_compile(), and the error-
1180         codeptr argument is not NULL, a non-zero error code number is  returned         codeptr argument is not NULL, a non-zero error code number is  returned
# Line 1267  COMPILING A PATTERN Line 1291  COMPILING A PATTERN
1291         letter that has no special meaning  causes  an  error,  thus  reserving         letter that has no special meaning  causes  an  error,  thus  reserving
1292         these  combinations  for  future  expansion.  By default, as in Perl, a         these  combinations  for  future  expansion.  By default, as in Perl, a
1293         backslash followed by a letter with no special meaning is treated as  a         backslash followed by a letter with no special meaning is treated as  a
1294         literal.  (Perl can, however, be persuaded to give a warning for this.)         literal. (Perl can, however, be persuaded to give an error for this, by
1295         There are at present no other features controlled by  this  option.  It         running it with the -w option.) There are at present no other  features
1296         can also be set by a (?X) option setting within a pattern.         controlled  by this option. It can also be set by a (?X) option setting
1297           within a pattern.
1298    
1299           PCRE_FIRSTLINE           PCRE_FIRSTLINE
1300    
1301         If  this  option  is  set,  an  unanchored pattern is required to match         If this option is set, an  unanchored  pattern  is  required  to  match
1302         before or at the first  newline  in  the  subject  string,  though  the         before  or  at  the  first  newline  in  the subject string, though the
1303         matched text may continue over the newline.         matched text may continue over the newline.
1304    
1305           PCRE_JAVASCRIPT_COMPAT           PCRE_JAVASCRIPT_COMPAT
1306    
1307         If this option is set, PCRE's behaviour is changed in some ways so that         If this option is set, PCRE's behaviour is changed in some ways so that
1308         it is compatible with JavaScript rather than Perl. The changes  are  as         it  is  compatible with JavaScript rather than Perl. The changes are as
1309         follows:         follows:
1310    
1311         (1)  A  lone  closing square bracket in a pattern causes a compile-time         (1) A lone closing square bracket in a pattern  causes  a  compile-time
1312         error, because this is illegal in JavaScript (by default it is  treated         error,  because this is illegal in JavaScript (by default it is treated
1313         as a data character). Thus, the pattern AB]CD becomes illegal when this         as a data character). Thus, the pattern AB]CD becomes illegal when this
1314         option is set.         option is set.
1315    
1316         (2) At run time, a back reference to an unset subpattern group  matches         (2)  At run time, a back reference to an unset subpattern group matches
1317         an  empty  string (by default this causes the current matching alterna-         an empty string (by default this causes the current  matching  alterna-
1318         tive to fail). A pattern such as (\1)(a) succeeds when this  option  is         tive  to  fail). A pattern such as (\1)(a) succeeds when this option is
1319         set  (assuming  it can find an "a" in the subject), whereas it fails by         set (assuming it can find an "a" in the subject), whereas it  fails  by
1320         default, for Perl compatibility.         default, for Perl compatibility.
1321    
1322           PCRE_MULTILINE           PCRE_MULTILINE
1323    
1324         By default, PCRE treats the subject string as consisting  of  a  single         By  default,  PCRE  treats the subject string as consisting of a single
1325         line  of characters (even if it actually contains newlines). The "start         line of characters (even if it actually contains newlines). The  "start
1326         of line" metacharacter (^) matches only at the  start  of  the  string,         of  line"  metacharacter  (^)  matches only at the start of the string,
1327         while  the  "end  of line" metacharacter ($) matches only at the end of         while the "end of line" metacharacter ($) matches only at  the  end  of
1328         the string, or before a terminating newline (unless PCRE_DOLLAR_ENDONLY         the string, or before a terminating newline (unless PCRE_DOLLAR_ENDONLY
1329         is set). This is the same as Perl.         is set). This is the same as Perl.
1330    
1331         When  PCRE_MULTILINE  it  is set, the "start of line" and "end of line"         When PCRE_MULTILINE it is set, the "start of line" and  "end  of  line"
1332         constructs match immediately following or immediately  before  internal         constructs  match  immediately following or immediately before internal
1333         newlines  in  the  subject string, respectively, as well as at the very         newlines in the subject string, respectively, as well as  at  the  very
1334         start and end. This is equivalent to Perl's /m option, and  it  can  be         start  and  end.  This is equivalent to Perl's /m option, and it can be
1335         changed within a pattern by a (?m) option setting. If there are no new-         changed within a pattern by a (?m) option setting. If there are no new-
1336         lines in a subject string, or no occurrences of ^ or $  in  a  pattern,         lines  in  a  subject string, or no occurrences of ^ or $ in a pattern,
1337         setting PCRE_MULTILINE has no effect.         setting PCRE_MULTILINE has no effect.
1338    
1339           PCRE_NEWLINE_CR           PCRE_NEWLINE_CR
# Line 1317  COMPILING A PATTERN Line 1342  COMPILING A PATTERN
1342           PCRE_NEWLINE_ANYCRLF           PCRE_NEWLINE_ANYCRLF
1343           PCRE_NEWLINE_ANY           PCRE_NEWLINE_ANY
1344    
1345         These  options  override the default newline definition that was chosen         These options override the default newline definition that  was  chosen
1346         when PCRE was built. Setting the first or the second specifies  that  a         when  PCRE  was built. Setting the first or the second specifies that a
1347         newline  is  indicated  by a single character (CR or LF, respectively).         newline is indicated by a single character (CR  or  LF,  respectively).
1348         Setting PCRE_NEWLINE_CRLF specifies that a newline is indicated by  the         Setting  PCRE_NEWLINE_CRLF specifies that a newline is indicated by the
1349         two-character  CRLF  sequence.  Setting  PCRE_NEWLINE_ANYCRLF specifies         two-character CRLF  sequence.  Setting  PCRE_NEWLINE_ANYCRLF  specifies
1350         that any of the three preceding sequences should be recognized. Setting         that any of the three preceding sequences should be recognized. Setting
1351         PCRE_NEWLINE_ANY  specifies that any Unicode newline sequence should be         PCRE_NEWLINE_ANY specifies that any Unicode newline sequence should  be
1352         recognized. The Unicode newline sequences are the three just mentioned,         recognized. The Unicode newline sequences are the three just mentioned,
1353         plus  the  single  characters  VT (vertical tab, U+000B), FF (formfeed,         plus the single characters VT (vertical  tab,  U+000B),  FF  (formfeed,
1354         U+000C), NEL (next line, U+0085), LS (line separator, U+2028),  and  PS         U+000C),  NEL  (next line, U+0085), LS (line separator, U+2028), and PS
1355         (paragraph  separator,  U+2029).  The  last  two are recognized only in         (paragraph separator, U+2029). The last  two  are  recognized  only  in
1356         UTF-8 mode.         UTF-8 mode.
1357    
1358         The newline setting in the  options  word  uses  three  bits  that  are         The  newline  setting  in  the  options  word  uses three bits that are
1359         treated as a number, giving eight possibilities. Currently only six are         treated as a number, giving eight possibilities. Currently only six are
1360         used (default plus the five values above). This means that if  you  set         used  (default  plus the five values above). This means that if you set
1361         more  than one newline option, the combination may or may not be sensi-         more than one newline option, the combination may or may not be  sensi-
1362         ble. For example, PCRE_NEWLINE_CR with PCRE_NEWLINE_LF is equivalent to         ble. For example, PCRE_NEWLINE_CR with PCRE_NEWLINE_LF is equivalent to
1363         PCRE_NEWLINE_CRLF,  but other combinations may yield unused numbers and         PCRE_NEWLINE_CRLF, but other combinations may yield unused numbers  and
1364         cause an error.         cause an error.
1365    
1366         The only time that a line break is specially recognized when  compiling         The  only time that a line break is specially recognized when compiling
1367         a  pattern  is  if  PCRE_EXTENDED  is set, and an unescaped # outside a         a pattern is if PCRE_EXTENDED is set, and  an  unescaped  #  outside  a
1368         character class is encountered. This indicates  a  comment  that  lasts         character  class  is  encountered.  This indicates a comment that lasts
1369         until  after the next line break sequence. In other circumstances, line         until after the next line break sequence. In other circumstances,  line
1370         break  sequences  are  treated  as  literal  data,   except   that   in         break   sequences   are   treated  as  literal  data,  except  that  in
1371         PCRE_EXTENDED mode, both CR and LF are treated as whitespace characters         PCRE_EXTENDED mode, both CR and LF are treated as whitespace characters
1372         and are therefore ignored.         and are therefore ignored.
1373    
# Line 1352  COMPILING A PATTERN Line 1377  COMPILING A PATTERN
1377           PCRE_NO_AUTO_CAPTURE           PCRE_NO_AUTO_CAPTURE
1378    
1379         If this option is set, it disables the use of numbered capturing paren-         If this option is set, it disables the use of numbered capturing paren-
1380         theses in the pattern. Any opening parenthesis that is not followed  by         theses  in the pattern. Any opening parenthesis that is not followed by
1381         ?  behaves as if it were followed by ?: but named parentheses can still         ? behaves as if it were followed by ?: but named parentheses can  still
1382         be used for capturing (and they acquire  numbers  in  the  usual  way).         be  used  for  capturing  (and  they acquire numbers in the usual way).
1383         There is no equivalent of this option in Perl.         There is no equivalent of this option in Perl.
1384    
1385             PCRE_UCP
1386    
1387           This option changes the way PCRE processes \b, \d, \s, \w, and some  of
1388           the POSIX character classes. By default, only ASCII characters are rec-
1389           ognized, but if PCRE_UCP is set, Unicode properties are used instead to
1390           classify  characters.  More details are given in the section on generic
1391           character types in the pcrepattern page. If you set PCRE_UCP,  matching
1392           one  of the items it affects takes much longer. The option is available
1393           only if PCRE has been compiled with Unicode property support.
1394    
1395           PCRE_UNGREEDY           PCRE_UNGREEDY
1396    
1397         This  option  inverts  the "greediness" of the quantifiers so that they         This option inverts the "greediness" of the quantifiers  so  that  they
1398         are not greedy by default, but become greedy if followed by "?". It  is         are  not greedy by default, but become greedy if followed by "?". It is
1399         not  compatible  with Perl. It can also be set by a (?U) option setting         not compatible with Perl. It can also be set by a (?U)  option  setting
1400         within the pattern.         within the pattern.
1401    
1402           PCRE_UTF8           PCRE_UTF8
1403    
1404         This option causes PCRE to regard both the pattern and the  subject  as         This  option  causes PCRE to regard both the pattern and the subject as
1405         strings  of  UTF-8 characters instead of single-byte character strings.         strings of UTF-8 characters instead of single-byte  character  strings.
1406         However, it is available only when PCRE is built to include UTF-8  sup-         However,  it is available only when PCRE is built to include UTF-8 sup-
1407         port.  If not, the use of this option provokes an error. Details of how         port. If not, the use of this option provokes an error. Details of  how
1408         this option changes the behaviour of PCRE are given in the  section  on         this  option  changes the behaviour of PCRE are given in the section on
1409         UTF-8 support in the main pcre page.         UTF-8 support in the main pcre page.
1410    
1411           PCRE_NO_UTF8_CHECK           PCRE_NO_UTF8_CHECK
1412    
1413         When PCRE_UTF8 is set, the validity of the pattern as a UTF-8 string is         When PCRE_UTF8 is set, the validity of the pattern as a UTF-8 string is
1414         automatically checked. There is a  discussion  about  the  validity  of         automatically  checked.  There  is  a  discussion about the validity of
1415         UTF-8  strings  in  the main pcre page. If an invalid UTF-8 sequence of         UTF-8 strings in the main pcre page. If an invalid  UTF-8  sequence  of
1416         bytes is found, pcre_compile() returns an error. If  you  already  know         bytes  is  found,  pcre_compile() returns an error. If you already know
1417         that your pattern is valid, and you want to skip this check for perfor-         that your pattern is valid, and you want to skip this check for perfor-
1418         mance reasons, you can set the PCRE_NO_UTF8_CHECK option.  When  it  is         mance  reasons,  you  can set the PCRE_NO_UTF8_CHECK option. When it is
1419         set,  the  effect  of  passing  an invalid UTF-8 string as a pattern is         set, the effect of passing an invalid UTF-8  string  as  a  pattern  is
1420         undefined. It may cause your program to crash. Note  that  this  option         undefined.  It  may  cause your program to crash. Note that this option
1421         can  also be passed to pcre_exec() and pcre_dfa_exec(), to suppress the         can also be passed to pcre_exec() and pcre_dfa_exec(), to suppress  the
1422         UTF-8 validity checking of subject strings.         UTF-8 validity checking of subject strings.
1423    
1424    
1425  COMPILATION ERROR CODES  COMPILATION ERROR CODES
1426    
1427         The following table lists the error  codes  than  may  be  returned  by         The  following  table  lists  the  error  codes than may be returned by
1428         pcre_compile2(),  along with the error messages that may be returned by         pcre_compile2(), along with the error messages that may be returned  by
1429         both compiling functions. As PCRE has developed, some error codes  have         both  compiling functions. As PCRE has developed, some error codes have
1430         fallen out of use. To avoid confusion, they have not been re-used.         fallen out of use. To avoid confusion, they have not been re-used.
1431    
1432            0  no error            0  no error
# Line 1447  COMPILATION ERROR CODES Line 1482  COMPILATION ERROR CODES
1482           50  [this code is not in use]           50  [this code is not in use]
1483           51  octal value is greater than \377 (not in UTF-8 mode)           51  octal value is greater than \377 (not in UTF-8 mode)
1484           52  internal error: overran compiling workspace           52  internal error: overran compiling workspace
1485           53   internal  error:  previously-checked  referenced  subpattern not           53  internal error: previously-checked referenced subpattern
1486         found                 not found
1487           54  DEFINE group contains more than one branch           54  DEFINE group contains more than one branch
1488           55  repeating a DEFINE group is not allowed           55  repeating a DEFINE group is not allowed
1489           56  inconsistent NEWLINE options           56  inconsistent NEWLINE options
1490           57  \g is not followed by a braced, angle-bracketed, or quoted           57  \g is not followed by a braced, angle-bracketed, or quoted
1491                 name/number or by a plain number                 name/number or by a plain number
1492           58  a numbered reference must not be zero           58  a numbered reference must not be zero
1493           59  (*VERB) with an argument is not supported           59  an argument is not allowed for (*ACCEPT), (*FAIL), or (*COMMIT)
1494           60  (*VERB) not recognized           60  (*VERB) not recognized
1495           61  number is too big           61  number is too big
1496           62  subpattern name expected           62  subpattern name expected
1497           63  digit expected after (?+           63  digit expected after (?+
1498           64  ] is an invalid data character in JavaScript compatibility mode           64  ] is an invalid data character in JavaScript compatibility mode
1499             65  different names for subpatterns of the same number are
1500                   not allowed
1501             66  (*MARK) must have an argument
1502             67  this version of PCRE is not compiled with PCRE_UCP support
1503    
1504         The numbers 32 and 10000 in errors 48 and 49  are  defaults;  different         The numbers 32 and 10000 in errors 48 and 49  are  defaults;  different
1505         values may be used if the limits were changed when PCRE was built.         values may be used if the limits were changed when PCRE was built.
# Line 1480  STUDYING A PATTERN Line 1519  STUDYING A PATTERN
1519         the results of the study.         the results of the study.
1520    
1521         The  returned  value  from  pcre_study()  can  be  passed  directly  to         The  returned  value  from  pcre_study()  can  be  passed  directly  to
1522         pcre_exec(). However, a pcre_extra block  also  contains  other  fields         pcre_exec() or pcre_dfa_exec(). However, a pcre_extra block  also  con-
1523         that  can  be  set  by the caller before the block is passed; these are         tains  other  fields  that can be set by the caller before the block is
1524         described below in the section on matching a pattern.         passed; these are described below in the section on matching a pattern.
1525    
1526         If studying the pattern does not  produce  any  additional  information         If studying the  pattern  does  not  produce  any  useful  information,
1527         pcre_study() returns NULL. In that circumstance, if the calling program         pcre_study() returns NULL. In that circumstance, if the calling program
1528         wants to pass any of the other fields to pcre_exec(), it  must  set  up         wants  to  pass  any  of   the   other   fields   to   pcre_exec()   or
1529         its own pcre_extra block.         pcre_dfa_exec(), it must set up its own pcre_extra block.
1530    
1531         The  second  argument of pcre_study() contains option bits. At present,         The  second  argument of pcre_study() contains option bits. At present,
1532         no options are defined, and this argument should always be zero.         no options are defined, and this argument should always be zero.
# Line 1507  STUDYING A PATTERN Line 1546  STUDYING A PATTERN
1546             0,              /* no options exist */             0,              /* no options exist */
1547             &error);        /* set to NULL or points to a message */             &error);        /* set to NULL or points to a message */
1548    
1549         At present, studying a pattern is useful only for non-anchored patterns         Studying a pattern does two things: first, a lower bound for the length
1550         that do not have a single fixed starting character. A bitmap of  possi-         of subject string that is needed to match the pattern is computed. This
1551         ble starting bytes is created.         does not mean that there are any strings of that length that match, but
1552           it does guarantee that no shorter strings match. The value is  used  by
1553           pcre_exec()  and  pcre_dfa_exec()  to  avoid  wasting time by trying to
1554           match strings that are shorter than the lower bound. You can  find  out
1555           the value in a calling program via the pcre_fullinfo() function.
1556    
1557           Studying a pattern is also useful for non-anchored patterns that do not
1558           have a single fixed starting character. A bitmap of  possible  starting
1559           bytes  is  created. This speeds up finding a position in the subject at
1560           which to start matching.
1561    
1562           The two optimizations just described can be  disabled  by  setting  the
1563           PCRE_NO_START_OPTIMIZE    option    when    calling    pcre_exec()   or
1564           pcre_dfa_exec(). You might want to do this  if  your  pattern  contains
1565           callouts,  or  make  use of (*MARK), and you make use of these in cases
1566           where matching fails.  See  the  discussion  of  PCRE_NO_START_OPTIMIZE
1567           below.
1568    
1569    
1570  LOCALE SUPPORT  LOCALE SUPPORT
# Line 1517  LOCALE SUPPORT Line 1572  LOCALE SUPPORT
1572         PCRE  handles  caseless matching, and determines whether characters are         PCRE  handles  caseless matching, and determines whether characters are
1573         letters, digits, or whatever, by reference to a set of tables,  indexed         letters, digits, or whatever, by reference to a set of tables,  indexed
1574         by  character  value.  When running in UTF-8 mode, this applies only to         by  character  value.  When running in UTF-8 mode, this applies only to
1575         characters with codes less than 128. Higher-valued  codes  never  match         characters with codes less than 128. By  default,  higher-valued  codes
1576         escapes  such  as  \w or \d, but can be tested with \p if PCRE is built         never match escapes such as \w or \d, but they can be tested with \p if
1577         with Unicode character property support. The use of locales  with  Uni-         PCRE is built with Unicode character property  support.  Alternatively,
1578         code  is discouraged. If you are handling characters with codes greater         the  PCRE_UCP  option  can  be  set at compile time; this causes \w and
1579         than 128, you should either use UTF-8 and Unicode, or use locales,  but         friends to use Unicode property support instead of built-in tables. The
1580         not try to mix the two.         use of locales with Unicode is discouraged. If you are handling charac-
1581           ters with codes greater than 128, you should either use UTF-8 and  Uni-
1582           code, or use locales, but not try to mix the two.
1583    
1584         PCRE  contains  an  internal set of tables that are used when the final         PCRE  contains  an  internal set of tables that are used when the final
1585         argument of pcre_compile() is  NULL.  These  are  sufficient  for  many         argument of pcre_compile() is  NULL.  These  are  sufficient  for  many
# Line 1675  INFORMATION ABOUT A PATTERN Line 1732  INFORMATION ABOUT A PATTERN
1732         example, for the pattern /^a\d+z\d+/ the returned value is "z", but for         example, for the pattern /^a\d+z\d+/ the returned value is "z", but for
1733         /^a\dz\d/ the returned value is -1.         /^a\dz\d/ the returned value is -1.
1734    
1735             PCRE_INFO_MINLENGTH
1736    
1737           If  the  pattern  was studied and a minimum length for matching subject
1738           strings was computed, its value is  returned.  Otherwise  the  returned
1739           value  is  -1. The value is a number of characters, not bytes (this may
1740           be relevant in UTF-8 mode). The fourth argument should point to an  int
1741           variable.  A  non-negative  value is a lower bound to the length of any
1742           matching string. There may not be any strings of that  length  that  do
1743           actually match, but every string that does match is at least that long.
1744    
1745           PCRE_INFO_NAMECOUNT           PCRE_INFO_NAMECOUNT
1746           PCRE_INFO_NAMEENTRYSIZE           PCRE_INFO_NAMEENTRYSIZE
1747           PCRE_INFO_NAMETABLE           PCRE_INFO_NAMETABLE
# Line 1696  INFORMATION ABOUT A PATTERN Line 1763  INFORMATION ABOUT A PATTERN
1763         a  pointer  to  the  first  entry of the table (a pointer to char). The         a  pointer  to  the  first  entry of the table (a pointer to char). The
1764         first two bytes of each entry are the number of the capturing parenthe-         first two bytes of each entry are the number of the capturing parenthe-
1765         sis,  most  significant byte first. The rest of the entry is the corre-         sis,  most  significant byte first. The rest of the entry is the corre-
1766         sponding name, zero terminated. The names are  in  alphabetical  order.         sponding name, zero terminated.
1767         When PCRE_DUPNAMES is set, duplicate names are in order of their paren-  
1768         theses numbers. For example, consider  the  following  pattern  (assume         The names are in alphabetical order. Duplicate names may appear if  (?|
1769         PCRE_EXTENDED  is  set,  so  white  space  -  including  newlines  - is         is used to create multiple groups with the same number, as described in
1770         ignored):         the section on duplicate subpattern numbers in  the  pcrepattern  page.
1771           Duplicate  names  for  subpatterns with different numbers are permitted
1772           only if PCRE_DUPNAMES is set. In all cases  of  duplicate  names,  they
1773           appear  in  the table in the order in which they were found in the pat-
1774           tern. In the absence of (?| this is the  order  of  increasing  number;
1775           when (?| is used this is not necessarily the case because later subpat-
1776           terns may have lower numbers.
1777    
1778           As a simple example of the name/number table,  consider  the  following
1779           pattern  (assume  PCRE_EXTENDED is set, so white space - including new-
1780           lines - is ignored):
1781    
1782           (?<date> (?<year>(\d\d)?\d\d) -           (?<date> (?<year>(\d\d)?\d\d) -
1783           (?<month>\d\d) - (?<day>\d\d) )           (?<month>\d\d) - (?<day>\d\d) )
# Line 1721  INFORMATION ABOUT A PATTERN Line 1798  INFORMATION ABOUT A PATTERN
1798    
1799           PCRE_INFO_OKPARTIAL           PCRE_INFO_OKPARTIAL
1800    
1801         Return  1 if the pattern can be used for partial matching, otherwise 0.         Return  1  if  the  pattern  can  be  used  for  partial  matching with
1802         The fourth argument should point to an int  variable.  The  pcrepartial         pcre_exec(), otherwise 0. The fourth argument should point  to  an  int
1803         documentation  lists  the restrictions that apply to patterns when par-         variable.  From  release  8.00,  this  always  returns  1,  because the
1804         tial matching is used.         restrictions that previously applied  to  partial  matching  have  been
1805           lifted.  The  pcrepartial documentation gives details of partial match-
1806           ing.
1807    
1808           PCRE_INFO_OPTIONS           PCRE_INFO_OPTIONS
1809    
# Line 1761  INFORMATION ABOUT A PATTERN Line 1840  INFORMATION ABOUT A PATTERN
1840         Return the size of the data block pointed to by the study_data field in         Return the size of the data block pointed to by the study_data field in
1841         a  pcre_extra  block.  That  is,  it  is  the  value that was passed to         a  pcre_extra  block.  That  is,  it  is  the  value that was passed to
1842         pcre_malloc() when PCRE was getting memory into which to place the data         pcre_malloc() when PCRE was getting memory into which to place the data
1843         created  by  pcre_study(). The fourth argument should point to a size_t         created  by  pcre_study().  If pcre_extra is NULL, or there is no study
1844           data, zero is returned. The fourth argument should point  to  a  size_t
1845         variable.         variable.
1846    
1847    
# Line 1769  OBSOLETE INFO FUNCTION Line 1849  OBSOLETE INFO FUNCTION
1849    
1850         int pcre_info(const pcre *code, int *optptr, int *firstcharptr);         int pcre_info(const pcre *code, int *optptr, int *firstcharptr);
1851    
1852         The pcre_info() function is now obsolete because its interface  is  too         The  pcre_info()  function is now obsolete because its interface is too
1853         restrictive  to return all the available data about a compiled pattern.         restrictive to return all the available data about a compiled  pattern.
1854         New  programs  should  use  pcre_fullinfo()  instead.  The   yield   of         New   programs   should  use  pcre_fullinfo()  instead.  The  yield  of
1855         pcre_info()  is the number of capturing subpatterns, or one of the fol-         pcre_info() is the number of capturing subpatterns, or one of the  fol-
1856         lowing negative numbers:         lowing negative numbers:
1857    
1858           PCRE_ERROR_NULL       the argument code was NULL           PCRE_ERROR_NULL       the argument code was NULL
1859           PCRE_ERROR_BADMAGIC   the "magic number" was not found           PCRE_ERROR_BADMAGIC   the "magic number" was not found
1860    
1861         If the optptr argument is not NULL, a copy of the  options  with  which         If  the  optptr  argument is not NULL, a copy of the options with which
1862         the  pattern  was  compiled  is placed in the integer it points to (see         the pattern was compiled is placed in the integer  it  points  to  (see
1863         PCRE_INFO_OPTIONS above).         PCRE_INFO_OPTIONS above).
1864    
1865         If the pattern is not anchored and the  firstcharptr  argument  is  not         If  the  pattern  is  not anchored and the firstcharptr argument is not
1866         NULL,  it is used to pass back information about the first character of         NULL, it is used to pass back information about the first character  of
1867         any matched string (see PCRE_INFO_FIRSTBYTE above).         any matched string (see PCRE_INFO_FIRSTBYTE above).
1868    
1869    
# Line 1791  REFERENCE COUNTS Line 1871  REFERENCE COUNTS
1871    
1872         int pcre_refcount(pcre *code, int adjust);         int pcre_refcount(pcre *code, int adjust);
1873    
1874         The pcre_refcount() function is used to maintain a reference  count  in         The  pcre_refcount()  function is used to maintain a reference count in
1875         the data block that contains a compiled pattern. It is provided for the         the data block that contains a compiled pattern. It is provided for the
1876         benefit of applications that  operate  in  an  object-oriented  manner,         benefit  of  applications  that  operate  in an object-oriented manner,
1877         where different parts of the application may be using the same compiled         where different parts of the application may be using the same compiled
1878         pattern, but you want to free the block when they are all done.         pattern, but you want to free the block when they are all done.
1879    
1880         When a pattern is compiled, the reference count field is initialized to         When a pattern is compiled, the reference count field is initialized to
1881         zero.   It is changed only by calling this function, whose action is to         zero.  It is changed only by calling this function, whose action is  to
1882         add the adjust value (which may be positive or  negative)  to  it.  The         add  the  adjust  value  (which may be positive or negative) to it. The
1883         yield of the function is the new value. However, the value of the count         yield of the function is the new value. However, the value of the count
1884         is constrained to lie between 0 and 65535, inclusive. If the new  value         is  constrained to lie between 0 and 65535, inclusive. If the new value
1885         is outside these limits, it is forced to the appropriate limit value.         is outside these limits, it is forced to the appropriate limit value.
1886    
1887         Except  when it is zero, the reference count is not correctly preserved         Except when it is zero, the reference count is not correctly  preserved
1888         if a pattern is compiled on one host and then  transferred  to  a  host         if  a  pattern  is  compiled on one host and then transferred to a host
1889         whose byte-order is different. (This seems a highly unlikely scenario.)         whose byte-order is different. (This seems a highly unlikely scenario.)
1890    
1891    
# Line 1815  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 1895  MATCHING A PATTERN: THE TRADITIONAL FUNC
1895              const char *subject, int length, int startoffset,              const char *subject, int length, int startoffset,
1896              int options, int *ovector, int ovecsize);              int options, int *ovector, int ovecsize);
1897    
1898         The  function pcre_exec() is called to match a subject string against a         The function pcre_exec() is called to match a subject string against  a
1899         compiled pattern, which is passed in the code argument. If the  pattern         compiled  pattern, which is passed in the code argument. If the pattern
1900         has been studied, the result of the study should be passed in the extra         was studied, the result of the study should  be  passed  in  the  extra
1901         argument. This function is the main matching facility of  the  library,         argument.  This  function is the main matching facility of the library,
1902         and it operates in a Perl-like manner. For specialist use there is also         and it operates in a Perl-like manner. For specialist use there is also
1903         an alternative matching function, which is described below in the  sec-         an  alternative matching function, which is described below in the sec-
1904         tion about the pcre_dfa_exec() function.         tion about the pcre_dfa_exec() function.
1905    
1906         In  most applications, the pattern will have been compiled (and option-         In most applications, the pattern will have been compiled (and  option-
1907         ally studied) in the same process that calls pcre_exec().  However,  it         ally  studied)  in the same process that calls pcre_exec(). However, it
1908         is possible to save compiled patterns and study data, and then use them         is possible to save compiled patterns and study data, and then use them
1909         later in different processes, possibly even on different hosts.  For  a         later  in  different processes, possibly even on different hosts. For a
1910         discussion about this, see the pcreprecompile documentation.         discussion about this, see the pcreprecompile documentation.
1911    
1912         Here is an example of a simple call to pcre_exec():         Here is an example of a simple call to pcre_exec():
# Line 1845  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 1925  MATCHING A PATTERN: THE TRADITIONAL FUNC
1925    
1926     Extra data for pcre_exec()     Extra data for pcre_exec()
1927    
1928         If  the  extra argument is not NULL, it must point to a pcre_extra data         If the extra argument is not NULL, it must point to a  pcre_extra  data
1929         block. The pcre_study() function returns such a block (when it  doesn't         block.  The pcre_study() function returns such a block (when it doesn't
1930         return  NULL), but you can also create one for yourself, and pass addi-         return NULL), but you can also create one for yourself, and pass  addi-
1931         tional information in it. The pcre_extra block contains  the  following         tional  information  in it. The pcre_extra block contains the following
1932         fields (not necessarily in this order):         fields (not necessarily in this order):
1933    
1934           unsigned long int flags;           unsigned long int flags;
# Line 1857  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 1937  MATCHING A PATTERN: THE TRADITIONAL FUNC
1937           unsigned long int match_limit_recursion;           unsigned long int match_limit_recursion;
1938           void *callout_data;           void *callout_data;
1939           const unsigned char *tables;           const unsigned char *tables;
1940             unsigned char **mark;
1941    
1942         The  flags  field  is a bitmap that specifies which of the other fields         The flags field is a bitmap that specifies which of  the  other  fields
1943         are set. The flag bits are:         are set. The flag bits are:
1944    
1945           PCRE_EXTRA_STUDY_DATA           PCRE_EXTRA_STUDY_DATA
# Line 1866  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 1947  MATCHING A PATTERN: THE TRADITIONAL FUNC
1947           PCRE_EXTRA_MATCH_LIMIT_RECURSION           PCRE_EXTRA_MATCH_LIMIT_RECURSION
1948           PCRE_EXTRA_CALLOUT_DATA           PCRE_EXTRA_CALLOUT_DATA
1949           PCRE_EXTRA_TABLES           PCRE_EXTRA_TABLES
1950             PCRE_EXTRA_MARK
1951    
1952         Other flag bits should be set to zero. The study_data field is  set  in         Other  flag  bits should be set to zero. The study_data field is set in
1953         the  pcre_extra  block  that is returned by pcre_study(), together with         the pcre_extra block that is returned by  pcre_study(),  together  with
1954         the appropriate flag bit. You should not set this yourself, but you may         the appropriate flag bit. You should not set this yourself, but you may
1955         add  to  the  block by setting the other fields and their corresponding         add to the block by setting the other fields  and  their  corresponding
1956         flag bits.         flag bits.
1957    
1958         The match_limit field provides a means of preventing PCRE from using up         The match_limit field provides a means of preventing PCRE from using up
1959         a  vast amount of resources when running patterns that are not going to         a vast amount of resources when running patterns that are not going  to
1960         match, but which have a very large number  of  possibilities  in  their         match,  but  which  have  a very large number of possibilities in their
1961         search  trees.  The  classic  example  is  the  use of nested unlimited         search trees. The classic example is a pattern that uses nested  unlim-
1962         repeats.         ited repeats.
1963    
1964         Internally, PCRE uses a function called match() which it calls  repeat-         Internally,  PCRE uses a function called match() which it calls repeat-
1965         edly  (sometimes  recursively). The limit set by match_limit is imposed         edly (sometimes recursively). The limit set by match_limit  is  imposed
1966         on the number of times this function is called during  a  match,  which         on  the  number  of times this function is called during a match, which
1967         has  the  effect  of  limiting the amount of backtracking that can take         has the effect of limiting the amount of  backtracking  that  can  take
1968         place. For patterns that are not anchored, the count restarts from zero         place. For patterns that are not anchored, the count restarts from zero
1969         for each position in the subject string.         for each position in the subject string.
1970    
1971         The  default  value  for  the  limit can be set when PCRE is built; the         The default value for the limit can be set  when  PCRE  is  built;  the
1972         default default is 10 million, which handles all but the  most  extreme         default  default  is 10 million, which handles all but the most extreme
1973         cases.  You  can  override  the  default by suppling pcre_exec() with a         cases. You can override the default  by  suppling  pcre_exec()  with  a
1974         pcre_extra    block    in    which    match_limit    is    set,     and         pcre_extra     block    in    which    match_limit    is    set,    and
1975         PCRE_EXTRA_MATCH_LIMIT  is  set  in  the  flags  field. If the limit is         PCRE_EXTRA_MATCH_LIMIT is set in the  flags  field.  If  the  limit  is
1976         exceeded, pcre_exec() returns PCRE_ERROR_MATCHLIMIT.         exceeded, pcre_exec() returns PCRE_ERROR_MATCHLIMIT.
1977    
1978         The match_limit_recursion field is similar to match_limit, but  instead         The  match_limit_recursion field is similar to match_limit, but instead
1979         of limiting the total number of times that match() is called, it limits         of limiting the total number of times that match() is called, it limits
1980         the depth of recursion. The recursion depth is a  smaller  number  than         the  depth  of  recursion. The recursion depth is a smaller number than
1981         the  total number of calls, because not all calls to match() are recur-         the total number of calls, because not all calls to match() are  recur-
1982         sive.  This limit is of use only if it is set smaller than match_limit.         sive.  This limit is of use only if it is set smaller than match_limit.
1983    
1984         Limiting the recursion depth limits the amount of  stack  that  can  be         Limiting  the  recursion  depth  limits the amount of stack that can be
1985         used, or, when PCRE has been compiled to use memory on the heap instead         used, or, when PCRE has been compiled to use memory on the heap instead
1986         of the stack, the amount of heap memory that can be used.         of the stack, the amount of heap memory that can be used.
1987    
1988         The default value for match_limit_recursion can be  set  when  PCRE  is         The  default  value  for  match_limit_recursion can be set when PCRE is
1989         built;  the  default  default  is  the  same  value  as the default for         built; the default default  is  the  same  value  as  the  default  for
1990         match_limit. You can override the default by suppling pcre_exec()  with         match_limit.  You can override the default by suppling pcre_exec() with
1991         a   pcre_extra   block  in  which  match_limit_recursion  is  set,  and         a  pcre_extra  block  in  which  match_limit_recursion  is   set,   and
1992         PCRE_EXTRA_MATCH_LIMIT_RECURSION is set in  the  flags  field.  If  the         PCRE_EXTRA_MATCH_LIMIT_RECURSION  is  set  in  the  flags field. If the
1993         limit is exceeded, pcre_exec() returns PCRE_ERROR_RECURSIONLIMIT.         limit is exceeded, pcre_exec() returns PCRE_ERROR_RECURSIONLIMIT.
1994    
1995         The  pcre_callout  field is used in conjunction with the "callout" fea-         The callout_data field is used in conjunction with the  "callout"  fea-
1996         ture, which is described in the pcrecallout documentation.         ture, and is described in the pcrecallout documentation.
1997    
1998         The tables field  is  used  to  pass  a  character  tables  pointer  to         The  tables  field  is  used  to  pass  a  character  tables pointer to
1999         pcre_exec();  this overrides the value that is stored with the compiled         pcre_exec(); this overrides the value that is stored with the  compiled
2000         pattern. A non-NULL value is stored with the compiled pattern  only  if         pattern.  A  non-NULL value is stored with the compiled pattern only if
2001         custom  tables  were  supplied to pcre_compile() via its tableptr argu-         custom tables were supplied to pcre_compile() via  its  tableptr  argu-
2002         ment.  If NULL is passed to pcre_exec() using this mechanism, it forces         ment.  If NULL is passed to pcre_exec() using this mechanism, it forces
2003         PCRE's  internal  tables  to be used. This facility is helpful when re-         PCRE's internal tables to be used. This facility is  helpful  when  re-
2004         using patterns that have been saved after compiling  with  an  external         using  patterns  that  have been saved after compiling with an external
2005         set  of  tables,  because  the  external tables might be at a different         set of tables, because the external tables  might  be  at  a  different
2006         address when pcre_exec() is called. See the  pcreprecompile  documenta-         address  when  pcre_exec() is called. See the pcreprecompile documenta-
2007         tion for a discussion of saving compiled patterns for later use.         tion for a discussion of saving compiled patterns for later use.
2008    
2009           If PCRE_EXTRA_MARK is set in the flags field, the mark  field  must  be
2010           set  to  point  to a char * variable. If the pattern contains any back-
2011           tracking control verbs such as (*MARK:NAME), and the execution ends  up
2012           with  a  name  to  pass back, a pointer to the name string (zero termi-
2013           nated) is placed in the variable pointed to  by  the  mark  field.  The
2014           names  are  within  the  compiled pattern; if you wish to retain such a
2015           name you must copy it before freeing the memory of a compiled  pattern.
2016           If  there  is no name to pass back, the variable pointed to by the mark
2017           field set to NULL. For details of the backtracking control  verbs,  see
2018           the section entitled "Backtracking control" in the pcrepattern documen-
2019           tation.
2020    
2021     Option bits for pcre_exec()     Option bits for pcre_exec()
2022    
2023         The  unused  bits of the options argument for pcre_exec() must be zero.         The unused bits of the options argument for pcre_exec() must  be  zero.
2024         The only bits that may  be  set  are  PCRE_ANCHORED,  PCRE_NEWLINE_xxx,         The  only  bits  that  may  be set are PCRE_ANCHORED, PCRE_NEWLINE_xxx,
2025         PCRE_NOTBOL,    PCRE_NOTEOL,   PCRE_NOTEMPTY,   PCRE_NO_START_OPTIMIZE,         PCRE_NOTBOL,   PCRE_NOTEOL,    PCRE_NOTEMPTY,    PCRE_NOTEMPTY_ATSTART,
2026         PCRE_NO_UTF8_CHECK and PCRE_PARTIAL.         PCRE_NO_START_OPTIMIZE,   PCRE_NO_UTF8_CHECK,   PCRE_PARTIAL_SOFT,  and
2027           PCRE_PARTIAL_HARD.
2028    
2029           PCRE_ANCHORED           PCRE_ANCHORED
2030    
# Line 2009  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 2104  MATCHING A PATTERN: THE TRADITIONAL FUNC
2104    
2105           a?b?           a?b?
2106    
2107         is  applied  to  a string not beginning with "a" or "b", it matches the         is  applied  to  a  string not beginning with "a" or "b", it matches an
2108         empty string at the start of the subject. With PCRE_NOTEMPTY set,  this         empty string at the start of the subject. With PCRE_NOTEMPTY set,  this
2109         match is not valid, so PCRE searches further into the string for occur-         match is not valid, so PCRE searches further into the string for occur-
2110         rences of "a" or "b".         rences of "a" or "b".
2111    
2112         Perl has no direct equivalent of PCRE_NOTEMPTY, but it does make a spe-           PCRE_NOTEMPTY_ATSTART
2113         cial  case  of  a  pattern match of the empty string within its split()  
2114         function, and when using the /g modifier. It  is  possible  to  emulate         This is like PCRE_NOTEMPTY, except that an empty string match  that  is
2115         Perl's behaviour after matching a null string by first trying the match         not  at  the  start  of  the  subject  is  permitted. If the pattern is
2116         again at the same offset with PCRE_NOTEMPTY and PCRE_ANCHORED, and then         anchored, such a match can occur only if the pattern contains \K.
2117         if  that  fails by advancing the starting offset (see below) and trying  
2118         an ordinary match again. There is some code that demonstrates how to do         Perl    has    no    direct    equivalent    of    PCRE_NOTEMPTY     or
2119         this in the pcredemo.c sample program.         PCRE_NOTEMPTY_ATSTART,  but  it  does  make a special case of a pattern
2120           match of the empty string within its split() function, and  when  using
2121           the  /g  modifier.  It  is  possible  to emulate Perl's behaviour after
2122           matching a null string by first trying the match again at the same off-
2123           set  with  PCRE_NOTEMPTY_ATSTART  and  PCRE_ANCHORED,  and then if that
2124           fails, by advancing the starting offset (see below) and trying an ordi-
2125           nary  match  again. There is some code that demonstrates how to do this
2126           in the pcredemo sample program.
2127    
2128           PCRE_NO_START_OPTIMIZE           PCRE_NO_START_OPTIMIZE
2129    
2130         There  are a number of optimizations that pcre_exec() uses at the start         There are a number of optimizations that pcre_exec() uses at the  start
2131         of a match, in order to speed up the process. For  example,  if  it  is         of  a  match,  in  order to speed up the process. For example, if it is
2132         known  that  a  match must start with a specific character, it searches         known that an unanchored match must start with a specific character, it
2133         the subject for that character, and fails immediately if it cannot find         searches  the  subject  for that character, and fails immediately if it
2134         it,  without actually running the main matching function. When callouts         cannot find it, without actually running the  main  matching  function.
2135         are in use, these optimizations can cause  them  to  be  skipped.  This         This means that a special item such as (*COMMIT) at the start of a pat-
2136         option  disables  the  "start-up" optimizations, causing performance to         tern is not considered until after a suitable starting  point  for  the
2137         suffer, but ensuring that the callouts do occur.         match  has been found. When callouts or (*MARK) items are in use, these
2138           "start-up" optimizations can cause them to be skipped if the pattern is
2139           never  actually  used.  The start-up optimizations are in effect a pre-
2140           scan of the subject that takes place before the pattern is run.
2141    
2142           The PCRE_NO_START_OPTIMIZE option disables the start-up  optimizations,
2143           possibly  causing  performance  to  suffer,  but ensuring that in cases
2144           where the result is "no match", the callouts do occur, and  that  items
2145           such as (*COMMIT) and (*MARK) are considered at every possible starting
2146           position in the subject  string.   Setting  PCRE_NO_START_OPTIMIZE  can
2147           change the outcome of a matching operation.  Consider the pattern
2148    
2149             (*COMMIT)ABC
2150    
2151           When  this  is  compiled, PCRE records the fact that a match must start
2152           with the character "A". Suppose the subject  string  is  "DEFABC".  The
2153           start-up  optimization  scans along the subject, finds "A" and runs the
2154           first match attempt from there. The (*COMMIT) item means that the  pat-
2155           tern  must  match the current starting position, which in this case, it
2156           does. However, if the same match  is  run  with  PCRE_NO_START_OPTIMIZE
2157           set,  the  initial  scan  along the subject string does not happen. The
2158           first match attempt is run starting  from  "D"  and  when  this  fails,
2159           (*COMMIT)  prevents  any  further  matches  being tried, so the overall
2160           result is "no match". If the pattern is studied,  more  start-up  opti-
2161           mizations  may  be  used. For example, a minimum length for the subject
2162           may be recorded. Consider the pattern
2163    
2164             (*MARK:A)(X|Y)
2165    
2166           The minimum length for a match is one  character.  If  the  subject  is
2167           "ABC",  there  will  be  attempts  to  match "ABC", "BC", "C", and then
2168           finally an empty string.  If the pattern is studied, the final  attempt
2169           does  not take place, because PCRE knows that the subject is too short,
2170           and so the (*MARK) is never encountered.  In this  case,  studying  the
2171           pattern  does  not  affect the overall match result, which is still "no
2172           match", but it does affect the auxiliary information that is returned.
2173    
2174           PCRE_NO_UTF8_CHECK           PCRE_NO_UTF8_CHECK
2175    
# Line 2056  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 2193  MATCHING A PATTERN: THE TRADITIONAL FUNC
2193         value  of startoffset that does not point to the start of a UTF-8 char-         value  of startoffset that does not point to the start of a UTF-8 char-
2194         acter, is undefined. Your program may crash.         acter, is undefined. Your program may crash.
2195    
2196           PCRE_PARTIAL           PCRE_PARTIAL_HARD
2197             PCRE_PARTIAL_SOFT
2198    
2199         This option turns on the  partial  matching  feature.  If  the  subject         These options turn on the partial matching feature. For backwards  com-
2200         string  fails to match the pattern, but at some point during the match-         patibility,  PCRE_PARTIAL is a synonym for PCRE_PARTIAL_SOFT. A partial
2201         ing process the end of the subject was reached (that  is,  the  subject         match occurs if the end of the subject string is reached  successfully,
2202         partially  matches  the  pattern and the failure to match occurred only         but  there  are not enough subject characters to complete the match. If
2203         because there were not enough subject characters), pcre_exec()  returns         this happens when PCRE_PARTIAL_HARD  is  set,  pcre_exec()  immediately
2204         PCRE_ERROR_PARTIAL  instead of PCRE_ERROR_NOMATCH. When PCRE_PARTIAL is         returns  PCRE_ERROR_PARTIAL.  Otherwise,  if  PCRE_PARTIAL_SOFT is set,
2205         used, there are restrictions on what may appear in the  pattern.  These         matching continues by testing any other alternatives. Only if they  all
2206         are discussed in the pcrepartial documentation.         fail  is  PCRE_ERROR_PARTIAL  returned (instead of PCRE_ERROR_NOMATCH).
2207           The portion of the string that was inspected when the partial match was
2208           found  is  set  as  the first matching string. There is a more detailed
2209           discussion in the pcrepartial documentation.
2210    
2211     The string to be matched by pcre_exec()     The string to be matched by pcre_exec()
2212    
2213         The  subject string is passed to pcre_exec() as a pointer in subject, a         The subject string is passed to pcre_exec() as a pointer in subject,  a
2214         length (in bytes) in length, and a starting byte offset in startoffset.         length (in bytes) in length, and a starting byte offset in startoffset.
2215         In UTF-8 mode, the byte offset must point to the start of a UTF-8 char-         In UTF-8 mode, the byte offset must point to the start of a UTF-8 char-
2216         acter. Unlike the pattern string, the subject may contain  binary  zero         acter.  Unlike  the pattern string, the subject may contain binary zero
2217         bytes.  When the starting offset is zero, the search for a match starts         bytes. When the starting offset is zero, the search for a match  starts
2218         at the beginning of the subject, and this is by  far  the  most  common         at  the  beginning  of  the subject, and this is by far the most common
2219         case.         case.
2220    
2221         A  non-zero  starting offset is useful when searching for another match         A non-zero starting offset is useful when searching for  another  match
2222         in the same subject by calling pcre_exec() again after a previous  suc-         in  the same subject by calling pcre_exec() again after a previous suc-
2223         cess.   Setting  startoffset differs from just passing over a shortened         cess.  Setting startoffset differs from just passing over  a  shortened
2224         string and setting PCRE_NOTBOL in the case of  a  pattern  that  begins         string  and  setting  PCRE_NOTBOL  in the case of a pattern that begins
2225         with any kind of lookbehind. For example, consider the pattern         with any kind of lookbehind. For example, consider the pattern
2226    
2227           \Biss\B           \Biss\B
2228    
2229         which  finds  occurrences  of "iss" in the middle of words. (\B matches         which finds occurrences of "iss" in the middle of  words.  (\B  matches
2230         only if the current position in the subject is not  a  word  boundary.)         only  if  the  current position in the subject is not a word boundary.)
2231         When  applied  to the string "Mississipi" the first call to pcre_exec()         When applied to the string "Mississipi" the first call  to  pcre_exec()
2232         finds the first occurrence. If pcre_exec() is called  again  with  just         finds  the  first  occurrence. If pcre_exec() is called again with just
2233         the  remainder  of  the  subject,  namely  "issipi", it does not match,         the remainder of the subject,  namely  "issipi",  it  does  not  match,
2234         because \B is always false at the start of the subject, which is deemed         because \B is always false at the start of the subject, which is deemed
2235         to  be  a  word  boundary. However, if pcre_exec() is passed the entire         to be a word boundary. However, if pcre_exec()  is  passed  the  entire
2236         string again, but with startoffset set to 4, it finds the second occur-         string again, but with startoffset set to 4, it finds the second occur-
2237         rence  of "iss" because it is able to look behind the starting point to         rence of "iss" because it is able to look behind the starting point  to
2238         discover that it is preceded by a letter.         discover that it is preceded by a letter.
2239    
2240         If a non-zero starting offset is passed when the pattern  is  anchored,         If  a  non-zero starting offset is passed when the pattern is anchored,
2241         one attempt to match at the given offset is made. This can only succeed         one attempt to match at the given offset is made. This can only succeed
2242         if the pattern does not require the match to be at  the  start  of  the         if  the  pattern  does  not require the match to be at the start of the
2243         subject.         subject.
2244    
2245     How pcre_exec() returns captured substrings     How pcre_exec() returns captured substrings
2246    
2247         In  general, a pattern matches a certain portion of the subject, and in         In general, a pattern matches a certain portion of the subject, and  in
2248         addition, further substrings from the subject  may  be  picked  out  by         addition,  further  substrings  from  the  subject may be picked out by
2249         parts  of  the  pattern.  Following the usage in Jeffrey Friedl's book,         parts of the pattern. Following the usage  in  Jeffrey  Friedl's  book,
2250         this is called "capturing" in what follows, and the  phrase  "capturing         this  is  called "capturing" in what follows, and the phrase "capturing
2251         subpattern"  is  used for a fragment of a pattern that picks out a sub-         subpattern" is used for a fragment of a pattern that picks out  a  sub-
2252         string. PCRE supports several other kinds of  parenthesized  subpattern         string.  PCRE  supports several other kinds of parenthesized subpattern
2253         that do not cause substrings to be captured.         that do not cause substrings to be captured.
2254    
2255         Captured substrings are returned to the caller via a vector of integers         Captured substrings are returned to the caller via a vector of integers
2256         whose address is passed in ovector. The number of elements in the  vec-         whose  address is passed in ovector. The number of elements in the vec-
2257         tor  is  passed in ovecsize, which must be a non-negative number. Note:         tor is passed in ovecsize, which must be a non-negative  number.  Note:
2258         this argument is NOT the size of ovector in bytes.         this argument is NOT the size of ovector in bytes.
2259    
2260         The first two-thirds of the vector is used to pass back  captured  sub-         The  first  two-thirds of the vector is used to pass back captured sub-
2261         strings,  each  substring using a pair of integers. The remaining third         strings, each substring using a pair of integers. The  remaining  third
2262         of the vector is used as workspace by pcre_exec() while  matching  cap-         of  the  vector is used as workspace by pcre_exec() while matching cap-
2263         turing  subpatterns, and is not available for passing back information.         turing subpatterns, and is not available for passing back  information.
2264         The number passed in ovecsize should always be a multiple of three.  If         The  number passed in ovecsize should always be a multiple of three. If
2265         it is not, it is rounded down.         it is not, it is rounded down.
2266    
2267         When  a  match  is successful, information about captured substrings is         When a match is successful, information about  captured  substrings  is
2268         returned in pairs of integers, starting at the  beginning  of  ovector,         returned  in  pairs  of integers, starting at the beginning of ovector,
2269         and  continuing  up  to two-thirds of its length at the most. The first         and continuing up to two-thirds of its length at the  most.  The  first
2270         element of each pair is set to the byte offset of the  first  character         element  of  each pair is set to the byte offset of the first character
2271         in  a  substring, and the second is set to the byte offset of the first         in a substring, and the second is set to the byte offset of  the  first
2272         character after the end of a substring. Note: these values  are  always         character  after  the end of a substring. Note: these values are always
2273         byte offsets, even in UTF-8 mode. They are not character counts.         byte offsets, even in UTF-8 mode. They are not character counts.
2274    
2275         The  first  pair  of  integers, ovector[0] and ovector[1], identify the         The first pair of integers, ovector[0]  and  ovector[1],  identify  the
2276         portion of the subject string matched by the entire pattern.  The  next         portion  of  the subject string matched by the entire pattern. The next
2277         pair  is  used for the first capturing subpattern, and so on. The value         pair is used for the first capturing subpattern, and so on.  The  value
2278         returned by pcre_exec() is one more than the highest numbered pair that         returned by pcre_exec() is one more than the highest numbered pair that
2279         has  been  set.  For example, if two substrings have been captured, the         has been set.  For example, if two substrings have been  captured,  the
2280         returned value is 3. If there are no capturing subpatterns, the  return         returned  value is 3. If there are no capturing subpatterns, the return
2281         value from a successful match is 1, indicating that just the first pair         value from a successful match is 1, indicating that just the first pair
2282         of offsets has been set.         of offsets has been set.
2283    
2284         If a capturing subpattern is matched repeatedly, it is the last portion         If a capturing subpattern is matched repeatedly, it is the last portion
2285         of the string that it matched that is returned.         of the string that it matched that is returned.
2286    
2287         If  the vector is too small to hold all the captured substring offsets,         If the vector is too small to hold all the captured substring  offsets,
2288         it is used as far as possible (up to two-thirds of its length), and the         it is used as far as possible (up to two-thirds of its length), and the
2289         function  returns  a value of zero. If the substring offsets are not of         function returns a value of zero. If the substring offsets are  not  of
2290         interest, pcre_exec() may be called with ovector  passed  as  NULL  and         interest,  pcre_exec()  may  be  called with ovector passed as NULL and
2291         ovecsize  as zero. However, if the pattern contains back references and         ovecsize as zero. However, if the pattern contains back references  and
2292         the ovector is not big enough to remember the related substrings,  PCRE         the  ovector is not big enough to remember the related substrings, PCRE
2293         has  to  get additional memory for use during matching. Thus it is usu-         has to get additional memory for use during matching. Thus it  is  usu-
2294         ally advisable to supply an ovector.         ally advisable to supply an ovector.
2295    
2296         The pcre_info() function can be used to find  out  how  many  capturing         The pcre_fullinfo() function can be used to find out how many capturing
2297         subpatterns  there  are  in  a  compiled pattern. The smallest size for         subpatterns there are in a compiled  pattern.  The  smallest  size  for
2298         ovector that will allow for n captured substrings, in addition  to  the         ovector  that  will allow for n captured substrings, in addition to the
2299         offsets of the substring matched by the whole pattern, is (n+1)*3.         offsets of the substring matched by the whole pattern, is (n+1)*3.
2300    
2301         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
2302         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,
2303         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
2304         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
2305         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-
2306         sponding to unused subpatterns are set to -1.         sponding to unused subpatterns are set to -1.
2307    
2308         Offset values that correspond to unused subpatterns at the end  of  the         Offset  values  that correspond to unused subpatterns at the end of the
2309         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
2310         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
2311         matched.  The  return  from the function is 2, because the highest used         matched. The return from the function is 2, because  the  highest  used
2312         capturing subpattern number is 1. However, you can refer to the offsets         capturing subpattern number is 1. However, you can refer to the offsets
2313         for  the  second  and third capturing subpatterns if you wish (assuming         for the second and third capturing subpatterns if  you  wish  (assuming
2314         the vector is large enough, of course).         the vector is large enough, of course).
2315    
2316         Some convenience functions are provided  for  extracting  the  captured         Some  convenience  functions  are  provided for extracting the captured
2317         substrings as separate strings. These are described below.         substrings as separate strings. These are described below.
2318    
2319     Error return values from pcre_exec()     Error return values from pcre_exec()
2320    
2321         If  pcre_exec()  fails, it returns a negative number. The following are         If pcre_exec() fails, it returns a negative number. The  following  are
2322         defined in the header file:         defined in the header file:
2323    
2324           PCRE_ERROR_NOMATCH        (-1)           PCRE_ERROR_NOMATCH        (-1)
# Line 2186  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 2327  MATCHING A PATTERN: THE TRADITIONAL FUNC
2327    
2328           PCRE_ERROR_NULL           (-2)           PCRE_ERROR_NULL           (-2)
2329    
2330         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
2331         ovecsize was not zero.         ovecsize was not zero.
2332    
2333           PCRE_ERROR_BADOPTION      (-3)           PCRE_ERROR_BADOPTION      (-3)
# Line 2195  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 2336  MATCHING A PATTERN: THE TRADITIONAL FUNC
2336    
2337           PCRE_ERROR_BADMAGIC       (-4)           PCRE_ERROR_BADMAGIC       (-4)
2338    
2339         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,
2340         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
2341         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
2342         an environment with the other endianness. This is the error  that  PCRE         an  environment  with the other endianness. This is the error that PCRE
2343         gives when the magic number is not present.         gives when the magic number is not present.
2344    
2345           PCRE_ERROR_UNKNOWN_OPCODE (-5)           PCRE_ERROR_UNKNOWN_OPCODE (-5)
2346    
2347         While running the pattern match, an unknown item was encountered in the         While running the pattern match, an unknown item was encountered in the
2348         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
2349         overwriting of the compiled pattern.         overwriting of the compiled pattern.
2350    
2351           PCRE_ERROR_NOMEMORY       (-6)           PCRE_ERROR_NOMEMORY       (-6)
2352    
2353         If  a  pattern contains back references, but the ovector that is passed         If a pattern contains back references, but the ovector that  is  passed
2354         to pcre_exec() is not big enough to remember the referenced substrings,         to pcre_exec() is not big enough to remember the referenced substrings,
2355         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
2356         purpose. If the call via pcre_malloc() fails, this error is given.  The         purpose.  If the call via pcre_malloc() fails, this error is given. The
2357         memory is automatically freed at the end of matching.         memory is automatically freed at the end of matching.
2358    
2359           This error is also given if pcre_stack_malloc() fails  in  pcre_exec().
2360           This  can happen only when PCRE has been compiled with --disable-stack-
2361           for-recursion.
2362    
2363           PCRE_ERROR_NOSUBSTRING    (-7)           PCRE_ERROR_NOSUBSTRING    (-7)
2364    
2365         This  error is used by the pcre_copy_substring(), pcre_get_substring(),         This error is used by the pcre_copy_substring(),  pcre_get_substring(),
2366         and  pcre_get_substring_list()  functions  (see  below).  It  is  never         and  pcre_get_substring_list()  functions  (see  below).  It  is  never
2367         returned by pcre_exec().         returned by pcre_exec().
2368    
2369           PCRE_ERROR_MATCHLIMIT     (-8)           PCRE_ERROR_MATCHLIMIT     (-8)
2370    
2371         The  backtracking  limit,  as  specified  by the match_limit field in a         The backtracking limit, as specified by  the  match_limit  field  in  a
2372         pcre_extra structure (or defaulted) was reached.  See  the  description         pcre_extra  structure  (or  defaulted) was reached. See the description
2373         above.         above.
2374    
2375           PCRE_ERROR_CALLOUT        (-9)           PCRE_ERROR_CALLOUT        (-9)
2376    
2377         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
2378         use by callout functions that want to yield a distinctive  error  code.         use  by  callout functions that want to yield a distinctive error code.
2379         See the pcrecallout documentation for details.         See the pcrecallout documentation for details.
2380    
2381           PCRE_ERROR_BADUTF8        (-10)           PCRE_ERROR_BADUTF8        (-10)
2382    
2383         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
2384         subject.         subject.
2385    
2386           PCRE_ERROR_BADUTF8_OFFSET (-11)           PCRE_ERROR_BADUTF8_OFFSET (-11)
2387    
2388         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
2389         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-
2390         ter.         ter.
2391    
2392           PCRE_ERROR_PARTIAL        (-12)           PCRE_ERROR_PARTIAL        (-12)
2393    
2394         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
2395         pcrepartial documentation for details of partial matching.         pcrepartial documentation for details of partial matching.
2396    
2397           PCRE_ERROR_BADPARTIAL     (-13)           PCRE_ERROR_BADPARTIAL     (-13)
2398    
2399         The  PCRE_PARTIAL  option  was  used with a compiled pattern containing         This code is no longer in  use.  It  was  formerly  returned  when  the
2400         items that are not supported for partial matching. See the  pcrepartial         PCRE_PARTIAL  option  was used with a compiled pattern containing items
2401         documentation for details of partial matching.         that were  not  supported  for  partial  matching.  From  release  8.00
2402           onwards, there are no restrictions on partial matching.
2403    
2404           PCRE_ERROR_INTERNAL       (-14)           PCRE_ERROR_INTERNAL       (-14)
2405    
# Line 2412  EXTRACTING CAPTURED SUBSTRINGS BY NAME Line 2558  EXTRACTING CAPTURED SUBSTRINGS BY NAME
2558         ate.  NOTE:  If PCRE_DUPNAMES is set and there are duplicate names, the         ate.  NOTE:  If PCRE_DUPNAMES is set and there are duplicate names, the
2559         behaviour may not be what you want (see the next section).         behaviour may not be what you want (see the next section).
2560    
2561         Warning: If the pattern uses the "(?|" feature to set up multiple  sub-         Warning: If the pattern uses the (?| feature to set up multiple subpat-
2562         patterns  with  the  same  number,  you cannot use names to distinguish         terns  with  the  same number, as described in the section on duplicate
2563         them, because names are not included in the compiled code. The matching         subpattern numbers in the pcrepattern page, you  cannot  use  names  to
2564         process uses only numbers.         distinguish  the  different subpatterns, because names are not included
2565           in the compiled code. The matching process uses only numbers. For  this
2566           reason,  the  use of different names for subpatterns of the same number
2567           causes an error at compile time.
2568    
2569    
2570  DUPLICATE SUBPATTERN NAMES  DUPLICATE SUBPATTERN NAMES
# Line 2423  DUPLICATE SUBPATTERN NAMES Line 2572  DUPLICATE SUBPATTERN NAMES
2572         int pcre_get_stringtable_entries(const pcre *code,         int pcre_get_stringtable_entries(const pcre *code,
2573              const char *name, char **first, char **last);              const char *name, char **first, char **last);
2574    
2575         When  a  pattern  is  compiled with the PCRE_DUPNAMES option, names for         When a pattern is compiled with the  PCRE_DUPNAMES  option,  names  for
2576         subpatterns are not required to  be  unique.  Normally,  patterns  with         subpatterns  are not required to be unique. (Duplicate names are always
2577         duplicate  names  are such that in any one match, only one of the named         allowed for subpatterns with the same number, created by using the  (?|
2578         subpatterns participates. An example is shown in the pcrepattern  docu-         feature.  Indeed,  if  such subpatterns are named, they are required to
2579         mentation.         use the same names.)
2580    
2581         When    duplicates   are   present,   pcre_copy_named_substring()   and         Normally, patterns with duplicate names are such that in any one match,
2582         pcre_get_named_substring() return the first substring corresponding  to         only  one of the named subpatterns participates. An example is shown in
2583         the  given  name  that  is set. If none are set, PCRE_ERROR_NOSUBSTRING         the pcrepattern documentation.
2584         (-7) is returned; no  data  is  returned.  The  pcre_get_stringnumber()  
2585         function  returns one of the numbers that are associated with the name,         When   duplicates   are   present,   pcre_copy_named_substring()    and
2586           pcre_get_named_substring()  return the first substring corresponding to
2587           the given name that is set. If  none  are  set,  PCRE_ERROR_NOSUBSTRING
2588           (-7)  is  returned;  no  data  is returned. The pcre_get_stringnumber()
2589           function returns one of the numbers that are associated with the  name,
2590         but it is not defined which it is.         but it is not defined which it is.
2591    
2592         If you want to get full details of all captured substrings for a  given         If  you want to get full details of all captured substrings for a given
2593         name,  you  must  use  the pcre_get_stringtable_entries() function. The         name, you must use  the  pcre_get_stringtable_entries()  function.  The
2594         first argument is the compiled pattern, and the second is the name. The         first argument is the compiled pattern, and the second is the name. The
2595         third  and  fourth  are  pointers to variables which are updated by the         third and fourth are pointers to variables which  are  updated  by  the
2596         function. After it has run, they point to the first and last entries in         function. After it has run, they point to the first and last entries in
2597         the  name-to-number  table  for  the  given  name.  The function itself         the name-to-number table  for  the  given  name.  The  function  itself
2598         returns the length of each entry,  or  PCRE_ERROR_NOSUBSTRING  (-7)  if         returns  the  length  of  each entry, or PCRE_ERROR_NOSUBSTRING (-7) if
2599         there  are none. The format of the table is described above in the sec-         there are none. The format of the table is described above in the  sec-
2600         tion entitled Information about a  pattern.   Given  all  the  relevant         tion  entitled  Information  about  a  pattern.  Given all the relevant
2601         entries  for the name, you can extract each of their numbers, and hence         entries for the name, you can extract each of their numbers, and  hence
2602         the captured data, if any.         the captured data, if any.
2603    
2604    
2605  FINDING ALL POSSIBLE MATCHES  FINDING ALL POSSIBLE MATCHES
2606    
2607         The traditional matching function uses a  similar  algorithm  to  Perl,         The  traditional  matching  function  uses a similar algorithm to Perl,
2608         which stops when it finds the first match, starting at a given point in         which stops when it finds the first match, starting at a given point in
2609         the subject. If you want to find all possible matches, or  the  longest         the  subject.  If you want to find all possible matches, or the longest
2610         possible  match,  consider using the alternative matching function (see         possible match, consider using the alternative matching  function  (see
2611         below) instead. If you cannot use the alternative function,  but  still         below)  instead.  If you cannot use the alternative function, but still
2612         need  to  find all possible matches, you can kludge it up by making use         need to find all possible matches, you can kludge it up by  making  use
2613         of the callout facility, which is described in the pcrecallout documen-         of the callout facility, which is described in the pcrecallout documen-
2614         tation.         tation.
2615    
2616         What you have to do is to insert a callout right at the end of the pat-         What you have to do is to insert a callout right at the end of the pat-
2617         tern.  When your callout function is called, extract and save the  cur-         tern.   When your callout function is called, extract and save the cur-
2618         rent  matched  substring.  Then  return  1, which forces pcre_exec() to         rent matched substring. Then return  1,  which  forces  pcre_exec()  to
2619         backtrack and try other alternatives. Ultimately, when it runs  out  of         backtrack  and  try other alternatives. Ultimately, when it runs out of
2620         matches, pcre_exec() will yield PCRE_ERROR_NOMATCH.         matches, pcre_exec() will yield PCRE_ERROR_NOMATCH.
2621    
2622    
# Line 2474  MATCHING A PATTERN: THE ALTERNATIVE FUNC Line 2627  MATCHING A PATTERN: THE ALTERNATIVE FUNC
2627              int options, int *ovector, int ovecsize,              int options, int *ovector, int ovecsize,
2628              int *workspace, int wscount);              int *workspace, int wscount);
2629    
2630         The  function  pcre_dfa_exec()  is  called  to  match  a subject string         The function pcre_dfa_exec()  is  called  to  match  a  subject  string
2631         against a compiled pattern, using a matching algorithm that  scans  the         against  a  compiled pattern, using a matching algorithm that scans the
2632         subject  string  just  once, and does not backtrack. This has different         subject string just once, and does not backtrack.  This  has  different
2633         characteristics to the normal algorithm, and  is  not  compatible  with         characteristics  to  the  normal  algorithm, and is not compatible with
2634         Perl.  Some  of the features of PCRE patterns are not supported. Never-         Perl. Some of the features of PCRE patterns are not  supported.  Never-
2635         theless, there are times when this kind of matching can be useful.  For         theless,  there are times when this kind of matching can be useful. For
2636         a discussion of the two matching algorithms, see the pcrematching docu-         a discussion of the two matching algorithms, and  a  list  of  features
2637         mentation.         that  pcre_dfa_exec() does not support, see the pcrematching documenta-
2638           tion.
2639    
2640         The arguments for the pcre_dfa_exec() function  are  the  same  as  for         The arguments for the pcre_dfa_exec() function  are  the  same  as  for
2641         pcre_exec(), plus two extras. The ovector argument is used in a differ-         pcre_exec(), plus two extras. The ovector argument is used in a differ-
# Line 2516  MATCHING A PATTERN: THE ALTERNATIVE FUNC Line 2670  MATCHING A PATTERN: THE ALTERNATIVE FUNC
2670    
2671         The unused bits of the options argument  for  pcre_dfa_exec()  must  be         The unused bits of the options argument  for  pcre_dfa_exec()  must  be
2672         zero.  The  only  bits  that  may  be  set are PCRE_ANCHORED, PCRE_NEW-         zero.  The  only  bits  that  may  be  set are PCRE_ANCHORED, PCRE_NEW-
2673         LINE_xxx, PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY,  PCRE_NO_UTF8_CHECK,         LINE_xxx,        PCRE_NOTBOL,        PCRE_NOTEOL,        PCRE_NOTEMPTY,
2674         PCRE_PARTIAL, PCRE_DFA_SHORTEST, and PCRE_DFA_RESTART. All but the last         PCRE_NOTEMPTY_ATSTART,       PCRE_NO_UTF8_CHECK,      PCRE_BSR_ANYCRLF,
2675         three of these are the same as for pcre_exec(), so their description is         PCRE_BSR_UNICODE, PCRE_NO_START_OPTIMIZE, PCRE_PARTIAL_HARD,  PCRE_PAR-
2676         not repeated here.         TIAL_SOFT,  PCRE_DFA_SHORTEST,  and PCRE_DFA_RESTART.  All but the last
2677           four of these are  exactly  the  same  as  for  pcre_exec(),  so  their
2678           PCRE_PARTIAL         description is not repeated here.
2679    
2680         This  has  the  same general effect as it does for pcre_exec(), but the           PCRE_PARTIAL_HARD
2681         details  are  slightly  different.  When  PCRE_PARTIAL   is   set   for           PCRE_PARTIAL_SOFT
2682         pcre_dfa_exec(),  the  return code PCRE_ERROR_NOMATCH is converted into  
2683         PCRE_ERROR_PARTIAL if the end of the subject  is  reached,  there  have         These  have the same general effect as they do for pcre_exec(), but the
2684         been no complete matches, but there is still at least one matching pos-         details are slightly  different.  When  PCRE_PARTIAL_HARD  is  set  for
2685         sibility. The portion of the string that provided the partial match  is         pcre_dfa_exec(),  it  returns PCRE_ERROR_PARTIAL if the end of the sub-
2686         set as the first matching string.         ject is reached and there is still at least  one  matching  possibility
2687           that requires additional characters. This happens even if some complete
2688           matches have also been found. When PCRE_PARTIAL_SOFT is set, the return
2689           code PCRE_ERROR_NOMATCH is converted into PCRE_ERROR_PARTIAL if the end
2690           of the subject is reached, there have been  no  complete  matches,  but
2691           there  is  still  at least one matching possibility. The portion of the
2692           string that was inspected when the longest partial match was  found  is
2693           set as the first matching string in both cases.
2694    
2695           PCRE_DFA_SHORTEST           PCRE_DFA_SHORTEST
2696    
# Line 2540  MATCHING A PATTERN: THE ALTERNATIVE FUNC Line 2701  MATCHING A PATTERN: THE ALTERNATIVE FUNC
2701    
2702           PCRE_DFA_RESTART           PCRE_DFA_RESTART
2703    
2704         When pcre_dfa_exec()  is  called  with  the  PCRE_PARTIAL  option,  and         When pcre_dfa_exec() returns a partial match, it is possible to call it
2705         returns  a  partial  match, it is possible to call it again, with addi-         again,  with  additional  subject characters, and have it continue with
2706         tional subject characters, and have it continue with  the  same  match.         the same match. The PCRE_DFA_RESTART option requests this action;  when
2707         The  PCRE_DFA_RESTART  option requests this action; when it is set, the         it  is  set,  the workspace and wscount options must reference the same
2708         workspace and wscount options must reference the same vector as  before         vector as before because data about the match so far is  left  in  them
2709         because  data  about  the  match so far is left in them after a partial         after a partial match. There is more discussion of this facility in the
2710         match. There is more discussion of this  facility  in  the  pcrepartial         pcrepartial documentation.
        documentation.  
2711    
2712     Successful returns from pcre_dfa_exec()     Successful returns from pcre_dfa_exec()
2713    
2714         When  pcre_dfa_exec()  succeeds, it may have matched more than one sub-         When pcre_dfa_exec() succeeds, it may have matched more than  one  sub-
2715         string in the subject. Note, however, that all the matches from one run         string in the subject. Note, however, that all the matches from one run
2716         of  the  function  start  at the same point in the subject. The shorter         of the function start at the same point in  the  subject.  The  shorter
2717         matches are all initial substrings of the longer matches. For  example,         matches  are all initial substrings of the longer matches. For example,
2718         if the pattern         if the pattern
2719    
2720           <.*>           <.*>
# Line 2569  MATCHING A PATTERN: THE ALTERNATIVE FUNC Line 2729  MATCHING A PATTERN: THE ALTERNATIVE FUNC
2729           <something> <something else>           <something> <something else>
2730           <something> <something else> <something further>           <something> <something else> <something further>
2731    
2732         On  success,  the  yield of the function is a number greater than zero,         On success, the yield of the function is a number  greater  than  zero,
2733         which is the number of matched substrings.  The  substrings  themselves         which  is  the  number of matched substrings. The substrings themselves
2734         are  returned  in  ovector. Each string uses two elements; the first is         are returned in ovector. Each string uses two elements;  the  first  is
2735         the offset to the start, and the second is the offset to  the  end.  In         the  offset  to  the start, and the second is the offset to the end. In
2736         fact,  all  the  strings  have the same start offset. (Space could have         fact, all the strings have the same start  offset.  (Space  could  have
2737         been saved by giving this only once, but it was decided to retain  some         been  saved by giving this only once, but it was decided to retain some
2738         compatibility  with  the  way pcre_exec() returns data, even though the         compatibility with the way pcre_exec() returns data,  even  though  the
2739         meaning of the strings is different.)         meaning of the strings is different.)
2740    
2741         The strings are returned in reverse order of length; that is, the long-         The strings are returned in reverse order of length; that is, the long-
2742         est  matching  string is given first. If there were too many matches to         est matching string is given first. If there were too many  matches  to
2743         fit into ovector, the yield of the function is zero, and the vector  is         fit  into ovector, the yield of the function is zero, and the vector is
2744         filled with the longest matches.         filled with the longest matches.
2745    
2746     Error returns from pcre_dfa_exec()     Error returns from pcre_dfa_exec()
2747    
2748         The  pcre_dfa_exec()  function returns a negative number when it fails.         The pcre_dfa_exec() function returns a negative number when  it  fails.
2749         Many of the errors are the same  as  for  pcre_exec(),  and  these  are         Many  of  the  errors  are  the  same as for pcre_exec(), and these are
2750         described  above.   There are in addition the following errors that are         described above.  There are in addition the following errors  that  are
2751         specific to pcre_dfa_exec():         specific to pcre_dfa_exec():
2752    
2753           PCRE_ERROR_DFA_UITEM      (-16)           PCRE_ERROR_DFA_UITEM      (-16)
2754    
2755         This return is given if pcre_dfa_exec() encounters an item in the  pat-         This  return is given if pcre_dfa_exec() encounters an item in the pat-
2756         tern  that  it  does not support, for instance, the use of \C or a back         tern that it does not support, for instance, the use of \C  or  a  back
2757         reference.         reference.
2758    
2759           PCRE_ERROR_DFA_UCOND      (-17)           PCRE_ERROR_DFA_UCOND      (-17)
2760    
2761         This return is given if pcre_dfa_exec()  encounters  a  condition  item         This  return  is  given  if pcre_dfa_exec() encounters a condition item
2762         that  uses  a back reference for the condition, or a test for recursion         that uses a back reference for the condition, or a test  for  recursion
2763         in a specific group. These are not supported.         in a specific group. These are not supported.
2764    
2765           PCRE_ERROR_DFA_UMLIMIT    (-18)           PCRE_ERROR_DFA_UMLIMIT    (-18)
2766    
2767         This return is given if pcre_dfa_exec() is called with an  extra  block         This  return  is given if pcre_dfa_exec() is called with an extra block
2768         that contains a setting of the match_limit field. This is not supported         that contains a setting of the match_limit field. This is not supported
2769         (it is meaningless).         (it is meaningless).
2770    
2771           PCRE_ERROR_DFA_WSSIZE     (-19)           PCRE_ERROR_DFA_WSSIZE     (-19)
2772    
2773         This return is given if  pcre_dfa_exec()  runs  out  of  space  in  the         This  return  is  given  if  pcre_dfa_exec()  runs  out of space in the
2774         workspace vector.         workspace vector.
2775    
2776           PCRE_ERROR_DFA_RECURSE    (-20)           PCRE_ERROR_DFA_RECURSE    (-20)
2777    
2778         When  a  recursive subpattern is processed, the matching function calls         When a recursive subpattern is processed, the matching  function  calls
2779         itself recursively, using private vectors for  ovector  and  workspace.         itself  recursively,  using  private vectors for ovector and workspace.
2780         This  error  is  given  if  the output vector is not large enough. This         This error is given if the output vector  is  not  large  enough.  This
2781         should be extremely rare, as a vector of size 1000 is used.         should be extremely rare, as a vector of size 1000 is used.
2782    
2783    
2784  SEE ALSO  SEE ALSO
2785    
2786         pcrebuild(3), pcrecallout(3), pcrecpp(3)(3), pcrematching(3),  pcrepar-         pcrebuild(3),  pcrecallout(3), pcrecpp(3)(3), pcrematching(3), pcrepar-
2787         tial(3), pcreposix(3), pcreprecompile(3), pcresample(3), pcrestack(3).         tial(3), pcreposix(3), pcreprecompile(3), pcresample(3), pcrestack(3).
2788    
2789    
# Line 2636  AUTHOR Line 2796  AUTHOR
2796    
2797  REVISION  REVISION
2798    
2799         Last updated: 11 April 2009         Last updated: 21 June 2010
2800         Copyright (c) 1997-2009 University of Cambridge.         Copyright (c) 1997-2010 University of Cambridge.
2801  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
2802    
2803    
# Line 2666  PCRE CALLOUTS Line 2826  PCRE CALLOUTS
2826    
2827           (?C1)abc(?C2)def           (?C1)abc(?C2)def
2828    
2829         If  the  PCRE_AUTO_CALLOUT  option  bit  is  set when pcre_compile() is         If  the  PCRE_AUTO_CALLOUT  option  bit  is  set when pcre_compile() or
2830         called, PCRE automatically  inserts  callouts,  all  with  number  255,         pcre_compile2() is called, PCRE  automatically  inserts  callouts,  all
2831         before  each  item in the pattern. For example, if PCRE_AUTO_CALLOUT is         with  number  255,  before  each  item  in the pattern. For example, if
2832         used with the pattern         PCRE_AUTO_CALLOUT is used with the pattern
2833    
2834           A(\d{2}|--)           A(\d{2}|--)
2835    
# Line 2698  MISSING CALLOUTS Line 2858  MISSING CALLOUTS
2858         ever  start,  and  the  callout is never reached. However, with "abyd",         ever  start,  and  the  callout is never reached. However, with "abyd",
2859         though the result is still no match, the callout is obeyed.         though the result is still no match, the callout is obeyed.
2860    
2861         You can disable these optimizations by passing the  PCRE_NO_START_OPTI-         If the pattern is studied, PCRE knows the minimum length of a  matching
2862         MIZE  option  to  pcre_exec()  or  pcre_dfa_exec(). This slows down the         string,  and will immediately give a "no match" return without actually
2863         matching process, but does ensure that callouts  such  as  the  example         running a match if the subject is not long enough, or,  for  unanchored
2864           patterns, if it has been scanned far enough.
2865    
2866           You  can disable these optimizations by passing the PCRE_NO_START_OPTI-
2867           MIZE option to pcre_exec() or  pcre_dfa_exec().  This  slows  down  the
2868           matching  process,  but  does  ensure that callouts such as the example
2869         above are obeyed.         above are obeyed.
2870    
2871    
2872  THE CALLOUT INTERFACE  THE CALLOUT INTERFACE
2873    
2874         During  matching, when PCRE reaches a callout point, the external func-         During matching, when PCRE reaches a callout point, the external  func-
2875         tion defined by pcre_callout is called (if it is set). This applies  to         tion  defined by pcre_callout is called (if it is set). This applies to
2876         both  the  pcre_exec()  and the pcre_dfa_exec() matching functions. The         both the pcre_exec() and the pcre_dfa_exec()  matching  functions.  The
2877         only argument to the callout function is a pointer  to  a  pcre_callout         only  argument  to  the callout function is a pointer to a pcre_callout
2878         block. This structure contains the following fields:         block. This structure contains the following fields:
2879    
2880           int          version;           int          version;
# Line 2725  THE CALLOUT INTERFACE Line 2890  THE CALLOUT INTERFACE
2890           int          pattern_position;           int          pattern_position;
2891           int          next_item_length;           int          next_item_length;
2892    
2893         The  version  field  is an integer containing the version number of the         The version field is an integer containing the version  number  of  the
2894         block format. The initial version was 0; the current version is 1.  The         block  format. The initial version was 0; the current version is 1. The
2895         version  number  will  change  again in future if additional fields are         version number will change again in future  if  additional  fields  are
2896         added, but the intention is never to remove any of the existing fields.         added, but the intention is never to remove any of the existing fields.
2897    
2898         The callout_number field contains the number of the  callout,  as  com-         The  callout_number  field  contains the number of the callout, as com-
2899         piled  into  the pattern (that is, the number after ?C for manual call-         piled into the pattern (that is, the number after ?C for  manual  call-
2900         outs, and 255 for automatically generated callouts).         outs, and 255 for automatically generated callouts).
2901    
2902         The offset_vector field is a pointer to the vector of offsets that  was         The  offset_vector field is a pointer to the vector of offsets that was
2903         passed   by   the   caller  to  pcre_exec()  or  pcre_dfa_exec().  When         passed  by  the  caller  to  pcre_exec()   or   pcre_dfa_exec().   When
2904         pcre_exec() is used, the contents can be inspected in order to  extract         pcre_exec()  is used, the contents can be inspected in order to extract
2905         substrings  that  have  been  matched  so  far,  in the same way as for         substrings that have been matched so  far,  in  the  same  way  as  for
2906         extracting substrings after a match has completed. For  pcre_dfa_exec()         extracting  substrings after a match has completed. For pcre_dfa_exec()
2907         this field is not useful.         this field is not useful.
2908    
2909         The subject and subject_length fields contain copies of the values that         The subject and subject_length fields contain copies of the values that
2910         were passed to pcre_exec().         were passed to pcre_exec().
2911    
2912         The start_match field normally contains the offset within  the  subject         The  start_match  field normally contains the offset within the subject
2913         at  which  the  current  match  attempt started. However, if the escape         at which the current match attempt  started.  However,  if  the  escape
2914         sequence \K has been encountered, this value is changed to reflect  the         sequence  \K has been encountered, this value is changed to reflect the
2915         modified  starting  point.  If the pattern is not anchored, the callout         modified starting point. If the pattern is not  anchored,  the  callout
2916         function may be called several times from the same point in the pattern         function may be called several times from the same point in the pattern
2917         for different starting points in the subject.         for different starting points in the subject.
2918    
2919         The  current_position  field  contains the offset within the subject of         The current_position field contains the offset within  the  subject  of
2920         the current match pointer.         the current match pointer.
2921    
2922         When the pcre_exec() function is used, the capture_top  field  contains         When  the  pcre_exec() function is used, the capture_top field contains
2923         one  more than the number of the highest numbered captured substring so         one more than the number of the highest numbered captured substring  so
2924         far. If no substrings have been captured, the value of  capture_top  is         far.  If  no substrings have been captured, the value of capture_top is
2925         one.  This  is always the case when pcre_dfa_exec() is used, because it         one. This is always the case when pcre_dfa_exec() is used,  because  it
2926         does not support captured substrings.         does not support captured substrings.
2927    
2928         The capture_last field contains the number of the  most  recently  cap-         The  capture_last  field  contains the number of the most recently cap-
2929         tured  substring. If no substrings have been captured, its value is -1.         tured substring. If no substrings have been captured, its value is  -1.
2930         This is always the case when pcre_dfa_exec() is used.         This is always the case when pcre_dfa_exec() is used.
2931    
2932         The callout_data field contains a value that is passed  to  pcre_exec()         The  callout_data  field contains a value that is passed to pcre_exec()
2933         or  pcre_dfa_exec() specifically so that it can be passed back in call-         or pcre_dfa_exec() specifically so that it can be passed back in  call-
2934         outs. It is passed in the pcre_callout field  of  the  pcre_extra  data         outs.  It  is  passed  in the pcre_callout field of the pcre_extra data
2935         structure.  If  no such data was passed, the value of callout_data in a         structure. If no such data was passed, the value of callout_data  in  a
2936         pcre_callout block is NULL. There is a description  of  the  pcre_extra         pcre_callout  block  is  NULL. There is a description of the pcre_extra
2937         structure in the pcreapi documentation.         structure in the pcreapi documentation.
2938    
2939         The  pattern_position field is present from version 1 of the pcre_call-         The pattern_position field is present from version 1 of the  pcre_call-
2940         out structure. It contains the offset to the next item to be matched in         out structure. It contains the offset to the next item to be matched in
2941         the pattern string.         the pattern string.
2942    
2943         The  next_item_length field is present from version 1 of the pcre_call-         The next_item_length field is present from version 1 of the  pcre_call-
2944         out structure. It contains the length of the next item to be matched in         out structure. It contains the length of the next item to be matched in
2945         the  pattern  string. When the callout immediately precedes an alterna-         the pattern string. When the callout immediately precedes  an  alterna-
2946         tion bar, a closing parenthesis, or the end of the pattern, the  length         tion  bar, a closing parenthesis, or the end of the pattern, the length
2947         is  zero.  When the callout precedes an opening parenthesis, the length         is zero. When the callout precedes an opening parenthesis,  the  length
2948         is that of the entire subpattern.         is that of the entire subpattern.
2949    
2950         The pattern_position and next_item_length fields are intended  to  help         The  pattern_position  and next_item_length fields are intended to help
2951         in  distinguishing between different automatic callouts, which all have         in distinguishing between different automatic callouts, which all  have
2952         the same callout number. However, they are set for all callouts.         the same callout number. However, they are set for all callouts.
2953    
2954    
2955  RETURN VALUES  RETURN VALUES
2956    
2957         The external callout function returns an integer to PCRE. If the  value         The  external callout function returns an integer to PCRE. If the value
2958         is  zero,  matching  proceeds  as  normal. If the value is greater than         is zero, matching proceeds as normal. If  the  value  is  greater  than
2959         zero, matching fails at the current point, but  the  testing  of  other         zero,  matching  fails  at  the current point, but the testing of other
2960         matching possibilities goes ahead, just as if a lookahead assertion had         matching possibilities goes ahead, just as if a lookahead assertion had
2961         failed. If the value is less than zero, the  match  is  abandoned,  and         failed.  If  the  value  is less than zero, the match is abandoned, and
2962         pcre_exec() (or pcre_dfa_exec()) returns the negative value.         pcre_exec() or pcre_dfa_exec() returns the negative value.
2963    
2964         Negative   values   should   normally   be   chosen  from  the  set  of         Negative  values  should  normally  be   chosen   from   the   set   of
2965         PCRE_ERROR_xxx values. In particular, PCRE_ERROR_NOMATCH forces a stan-         PCRE_ERROR_xxx values. In particular, PCRE_ERROR_NOMATCH forces a stan-
2966         dard  "no  match"  failure.   The  error  number  PCRE_ERROR_CALLOUT is         dard "no  match"  failure.   The  error  number  PCRE_ERROR_CALLOUT  is
2967         reserved for use by callout functions; it will never be  used  by  PCRE         reserved  for  use  by callout functions; it will never be used by PCRE
2968         itself.         itself.
2969    
2970    
# Line 2812  AUTHOR Line 2977  AUTHOR
2977    
2978  REVISION  REVISION
2979    
2980         Last updated: 15 March 2009         Last updated: 29 September 2009
2981         Copyright (c) 1997-2009 University of Cambridge.         Copyright (c) 1997-2009 University of Cambridge.
2982  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
2983    
# Line 2827  NAME Line 2992  NAME
2992  DIFFERENCES BETWEEN PCRE AND PERL  DIFFERENCES BETWEEN PCRE AND PERL
2993    
2994         This  document describes the differences in the ways that PCRE and Perl         This  document describes the differences in the ways that PCRE and Perl
2995         handle regular expressions. The differences described here  are  mainly         handle regular expressions. The differences  described  here  are  with
2996         with  respect  to  Perl 5.8, though PCRE versions 7.0 and later contain         respect to Perl 5.10/5.11.
        some features that are expected to be in the forthcoming Perl 5.10.  
2997    
2998         1. PCRE has only a subset of Perl's UTF-8 and Unicode support.  Details         1.  PCRE has only a subset of Perl's UTF-8 and Unicode support. Details
2999         of  what  it does have are given in the section on UTF-8 support in the         of what it does have are given in the section on UTF-8 support  in  the
3000         main pcre page.         main pcre page.
3001    
3002         2. PCRE does not allow repeat quantifiers on lookahead assertions. Perl         2. PCRE does not allow repeat quantifiers on lookahead assertions. Perl
3003         permits  them,  but they do not mean what you might think. For example,         permits them, but they do not mean what you might think.  For  example,
3004         (?!a){3} does not assert that the next three characters are not "a". It         (?!a){3} does not assert that the next three characters are not "a". It
3005         just asserts that the next character is not "a" three times.         just asserts that the next character is not "a" three times.
3006    
3007         3.  Capturing  subpatterns  that occur inside negative lookahead asser-         3. Capturing subpatterns that occur inside  negative  lookahead  asser-
3008         tions are counted, but their entries in the offsets  vector  are  never         tions  are  counted,  but their entries in the offsets vector are never
3009         set.  Perl sets its numerical variables from any such patterns that are         set. Perl sets its numerical variables from any such patterns that  are
3010         matched before the assertion fails to match something (thereby succeed-         matched before the assertion fails to match something (thereby succeed-
3011         ing),  but  only  if the negative lookahead assertion contains just one         ing), but only if the negative lookahead assertion  contains  just  one
3012         branch.         branch.
3013    
3014         4. Though binary zero characters are supported in the  subject  string,         4.  Though  binary zero characters are supported in the subject string,
3015         they are not allowed in a pattern string because it is passed as a nor-         they are not allowed in a pattern string because it is passed as a nor-
3016         mal C string, terminated by zero. The escape sequence \0 can be used in         mal C string, terminated by zero. The escape sequence \0 can be used in
3017         the pattern to represent a binary zero.         the pattern to represent a binary zero.
3018    
3019         5.  The  following Perl escape sequences are not supported: \l, \u, \L,         5. The following Perl escape sequences are not supported: \l,  \u,  \L,
3020         \U, and \N. In fact these are implemented by Perl's general string-han-         \U, and \N. In fact these are implemented by Perl's general string-han-
3021         dling  and are not part of its pattern matching engine. If any of these         dling and are not part of its pattern matching engine. If any of  these
3022         are encountered by PCRE, an error is generated.         are encountered by PCRE, an error is generated.
3023    
3024         6. The Perl escape sequences \p, \P, and \X are supported only if  PCRE         6.  The Perl escape sequences \p, \P, and \X are supported only if PCRE
3025         is  built  with Unicode character property support. The properties that         is built with Unicode character property support. The  properties  that
3026         can be tested with \p and \P are limited to the general category  prop-         can  be tested with \p and \P are limited to the general category prop-
3027         erties  such  as  Lu and Nd, script names such as Greek or Han, and the         erties such as Lu and Nd, script names such as Greek or  Han,  and  the
3028         derived properties Any and L&.         derived  properties  Any  and  L&. PCRE does support the Cs (surrogate)
3029           property, which Perl does not; the  Perl  documentation  says  "Because
3030           Perl hides the need for the user to understand the internal representa-
3031           tion of Unicode characters, there is no need to implement the  somewhat
3032           messy concept of surrogates."
3033    
3034         7. PCRE does support the \Q...\E escape for quoting substrings. Charac-         7. PCRE does support the \Q...\E escape for quoting substrings. Charac-
3035         ters  in  between  are  treated as literals. This is slightly different         ters in between are treated as literals.  This  is  slightly  different
3036         from Perl in that $ and @ are  also  handled  as  literals  inside  the         from  Perl  in  that  $  and  @ are also handled as literals inside the
3037         quotes.  In Perl, they cause variable interpolation (but of course PCRE         quotes. In Perl, they cause variable interpolation (but of course  PCRE
3038         does not have variables). Note the following examples:         does not have variables). Note the following examples:
3039    
3040             Pattern            PCRE matches      Perl matches             Pattern            PCRE matches      Perl matches
# Line 2876  DIFFERENCES BETWEEN PCRE AND PERL Line 3044  DIFFERENCES BETWEEN PCRE AND PERL
3044             \Qabc\$xyz\E       abc\$xyz          abc\$xyz             \Qabc\$xyz\E       abc\$xyz          abc\$xyz
3045             \Qabc\E\$\Qxyz\E   abc$xyz           abc$xyz             \Qabc\E\$\Qxyz\E   abc$xyz           abc$xyz
3046    
3047         The \Q...\E sequence is recognized both inside  and  outside  character         The  \Q...\E  sequence  is recognized both inside and outside character
3048         classes.         classes.
3049    
3050         8. Fairly obviously, PCRE does not support the (?{code}) and (??{code})         8. Fairly obviously, PCRE does not support the (?{code}) and (??{code})
3051         constructions. However, there is support for recursive  patterns.  This         constructions.  However,  there is support for recursive patterns. This
3052         is  not available in Perl 5.8, but will be in Perl 5.10. Also, the PCRE         is not available in Perl 5.8, but it is in Perl 5.10.  Also,  the  PCRE
3053         "callout" feature allows an external function to be called during  pat-         "callout"  feature allows an external function to be called during pat-
3054         tern matching. See the pcrecallout documentation for details.         tern matching. See the pcrecallout documentation for details.
3055    
3056         9.  Subpatterns  that  are  called  recursively or as "subroutines" are         9. Subpatterns that are called  recursively  or  as  "subroutines"  are
3057         always treated as atomic groups in  PCRE.  This  is  like  Python,  but         always  treated  as  atomic  groups  in  PCRE. This is like Python, but
3058         unlike Perl.         unlike Perl. There is a discussion of an example that explains this  in
3059           more  detail  in  the section on recursion differences from Perl in the
3060         10.  There are some differences that are concerned with the settings of         pcrepattern page.
3061         captured strings when part of  a  pattern  is  repeated.  For  example,  
3062         matching  "aba"  against  the  pattern  /^(a(b)?)+$/  in Perl leaves $2         10. There are some differences that are concerned with the settings  of
3063           captured  strings  when  part  of  a  pattern is repeated. For example,
3064           matching "aba" against the  pattern  /^(a(b)?)+$/  in  Perl  leaves  $2
3065         unset, but in PCRE it is set to "b".         unset, but in PCRE it is set to "b".
3066    
3067         11.  PCRE  does  support  Perl  5.10's  backtracking  verbs  (*ACCEPT),         11.  PCRE's handling of duplicate subpattern numbers and duplicate sub-
3068         (*FAIL),  (*F),  (*COMMIT), (*PRUNE), (*SKIP), and (*THEN), but only in         pattern names is not as general as Perl's. This is a consequence of the
3069         the forms without an  argument.  PCRE  does  not  support  (*MARK).  If         fact the PCRE works internally just with numbers, using an external ta-
3070         (*ACCEPT)  is within capturing parentheses, PCRE does not set that cap-         ble to translate between numbers and names. In  particular,  a  pattern
3071         ture group; this is different to Perl.         such  as  (?|(?<a>A)|(?<b)B),  where the two capturing parentheses have
3072           the same number but different names, is not supported,  and  causes  an
3073           error  at compile time. If it were allowed, it would not be possible to
3074           distinguish which parentheses matched, because both names map  to  cap-
3075           turing subpattern number 1. To avoid this confusing situation, an error
3076           is given at compile time.
3077    
3078         12. PCRE provides some extensions to the Perl regular expression facil-         12. PCRE provides some extensions to the Perl regular expression facil-
3079         ities.   Perl  5.10  will  include new features that are not in earlier         ities.   Perl  5.10  includes new features that are not in earlier ver-
3080         versions, some of which (such as named parentheses) have been  in  PCRE         sions of Perl, some of which (such as named parentheses) have  been  in
3081         for some time. This list is with respect to Perl 5.10:         PCRE for some time. This list is with respect to Perl 5.10:
3082    
3083         (a)  Although  lookbehind  assertions  must match fixed length strings,         (a)  Although  lookbehind  assertions  in  PCRE must match fixed length
3084         each alternative branch of a lookbehind assertion can match a different         strings, each alternative branch of a lookbehind assertion can match  a
3085         length of string. Perl requires them all to have the same length.         different  length  of  string.  Perl requires them all to have the same
3086           length.
3087    
3088         (b)  If PCRE_DOLLAR_ENDONLY is set and PCRE_MULTILINE is not set, the $         (b) If PCRE_DOLLAR_ENDONLY is set and PCRE_MULTILINE is not set, the  $
3089         meta-character matches only at the very end of the string.         meta-character matches only at the very end of the string.
3090    
3091         (c) If PCRE_EXTRA is set, a backslash followed by a letter with no spe-         (c) If PCRE_EXTRA is set, a backslash followed by a letter with no spe-
3092         cial meaning is faulted. Otherwise, like Perl, the backslash is quietly         cial meaning is faulted. Otherwise, like Perl, the backslash is quietly
3093         ignored.  (Perl can be made to issue a warning.)         ignored.  (Perl can be made to issue a warning.)
3094    
3095         (d) If PCRE_UNGREEDY is set, the greediness of the  repetition  quanti-         (d)  If  PCRE_UNGREEDY is set, the greediness of the repetition quanti-
3096         fiers is inverted, that is, by default they are not greedy, but if fol-         fiers is inverted, that is, by default they are not greedy, but if fol-
3097         lowed by a question mark they are.         lowed by a question mark they are.
3098    
3099         (e) PCRE_ANCHORED can be used at matching time to force a pattern to be         (e) PCRE_ANCHORED can be used at matching time to force a pattern to be
3100         tried only at the first matching position in the subject string.         tried only at the first matching position in the subject string.
3101    
3102         (f)  The PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, and PCRE_NO_AUTO_CAP-         (f) The PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, PCRE_NOTEMPTY_ATSTART,
3103         TURE options for pcre_exec() have no Perl equivalents.         and  PCRE_NO_AUTO_CAPTURE  options for pcre_exec() have no Perl equiva-
3104           lents.
3105    
3106         (g) The \R escape sequence can be restricted to match only CR,  LF,  or         (g) The \R escape sequence can be restricted to match only CR,  LF,  or
3107         CRLF by the PCRE_BSR_ANYCRLF option.         CRLF by the PCRE_BSR_ANYCRLF option.
# Line 2953  AUTHOR Line 3130  AUTHOR
3130    
3131  REVISION  REVISION
3132    
3133         Last updated: 11 September 2007         Last updated: 12 May 2010
3134         Copyright (c) 1997-2007 University of Cambridge.         Copyright (c) 1997-2010 University of Cambridge.
3135  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
3136    
3137    
# Line 2984  PCRE REGULAR EXPRESSION DETAILS Line 3161  PCRE REGULAR EXPRESSION DETAILS
3161    
3162         The original operation of PCRE was on strings of  one-byte  characters.         The original operation of PCRE was on strings of  one-byte  characters.
3163         However,  there is now also support for UTF-8 character strings. To use         However,  there is now also support for UTF-8 character strings. To use
3164         this, you must build PCRE to  include  UTF-8  support,  and  then  call         this, PCRE must be built to include UTF-8 support, and  you  must  call
3165         pcre_compile()  with  the  PCRE_UTF8  option.  There  is also a special         pcre_compile()  or  pcre_compile2() with the PCRE_UTF8 option. There is
3166         sequence that can be given at the start of a pattern:         also a special sequence that can be given at the start of a pattern:
3167    
3168           (*UTF8)           (*UTF8)
3169    
# Line 2996  PCRE REGULAR EXPRESSION DETAILS Line 3173  PCRE REGULAR EXPRESSION DETAILS
3173         below.  There  is  also  a  summary of UTF-8 features in the section on         below.  There  is  also  a  summary of UTF-8 features in the section on
3174         UTF-8 support in the main pcre page.         UTF-8 support in the main pcre page.
3175    
3176           Another special sequence that may appear at the start of a  pattern  or
3177           in combination with (*UTF8) is:
3178    
3179             (*UCP)
3180    
3181           This  has  the  same  effect  as setting the PCRE_UCP option: it causes
3182           sequences such as \d and \w to  use  Unicode  properties  to  determine
3183           character types, instead of recognizing only characters with codes less
3184           than 128 via a lookup table.
3185    
3186         The remainder of this document discusses the  patterns  that  are  sup-         The remainder of this document discusses the  patterns  that  are  sup-
3187         ported  by  PCRE when its main matching function, pcre_exec(), is used.         ported  by  PCRE when its main matching function, pcre_exec(), is used.
3188         From  release  6.0,   PCRE   offers   a   second   matching   function,         From  release  6.0,   PCRE   offers   a   second   matching   function,
# Line 3024  NEWLINE CONVENTIONS Line 3211  NEWLINE CONVENTIONS
3211           (*ANYCRLF)   any of the three above           (*ANYCRLF)   any of the three above
3212           (*ANY)       all Unicode newline sequences           (*ANY)       all Unicode newline sequences
3213    
3214         These override the default and the options given to pcre_compile(). For         These  override  the default and the options given to pcre_compile() or
3215         example, on a Unix system where LF is the default newline sequence, the         pcre_compile2(). For example, on a Unix system where LF is the  default
3216         pattern         newline sequence, the pattern
3217    
3218           (*CR)a.b           (*CR)a.b
3219    
# Line 3036  NEWLINE CONVENTIONS Line 3223  NEWLINE CONVENTIONS
3223         and that they must be in upper case.  If  more  than  one  of  them  is         and that they must be in upper case.  If  more  than  one  of  them  is
3224         present, the last one is used.         present, the last one is used.
3225    
3226         The  newline  convention  does  not  affect what the \R escape sequence         The  newline convention affects the interpretation of the dot metachar-
3227         matches. By default, this is any Unicode  newline  sequence,  for  Perl         acter when PCRE_DOTALL is not set, and also the behaviour of  \N.  How-
3228         compatibility.  However, this can be changed; see the description of \R         ever,  it  does  not  affect  what  the  \R escape sequence matches. By
3229         in the section entitled "Newline sequences" below. A change of \R  set-         default, this is any Unicode newline sequence, for Perl  compatibility.
3230         ting can be combined with a change of newline convention.         However,  this can be changed; see the description of \R in the section
3231           entitled "Newline sequences" below. A change of \R setting can be  com-
3232           bined with a change of newline convention.
3233    
3234    
3235  CHARACTERS AND METACHARACTERS  CHARACTERS AND METACHARACTERS
# Line 3143  BACKSLASH Line 3332  BACKSLASH
3332         acters  in patterns in a visible manner. There is no restriction on the         acters  in patterns in a visible manner. There is no restriction on the
3333         appearance of non-printing characters, apart from the binary zero  that         appearance of non-printing characters, apart from the binary zero  that
3334         terminates  a  pattern,  but  when  a pattern is being prepared by text         terminates  a  pattern,  but  when  a pattern is being prepared by text
3335         editing, it is usually easier  to  use  one  of  the  following  escape         editing, it is  often  easier  to  use  one  of  the  following  escape
3336         sequences than the binary character it represents:         sequences than the binary character it represents:
3337    
3338           \a        alarm, that is, the BEL character (hex 07)           \a        alarm, that is, the BEL character (hex 07)
# Line 3153  BACKSLASH Line 3342  BACKSLASH
3342           \n        linefeed (hex 0A)           \n        linefeed (hex 0A)
3343           \r        carriage return (hex 0D)           \r        carriage return (hex 0D)
3344           \t        tab (hex 09)           \t        tab (hex 09)
3345           \ddd      character with octal code ddd, or backreference           \ddd      character with octal code ddd, or back reference
3346           \xhh      character with hex code hh           \xhh      character with hex code hh
3347           \x{hhh..} character with hex code hhh..           \x{hhh..} character with hex code hhh..
3348    
# Line 3222  BACKSLASH Line 3411  BACKSLASH
3411         All the sequences that define a single character value can be used both         All the sequences that define a single character value can be used both
3412         inside  and  outside character classes. In addition, inside a character         inside  and  outside character classes. In addition, inside a character
3413         class, the sequence \b is interpreted as the backspace  character  (hex         class, the sequence \b is interpreted as the backspace  character  (hex
3414         08),  and the sequences \R and \X are interpreted as the characters "R"         08).  The sequences \B, \N, \R, and \X are not special inside a charac-
3415         and "X", respectively. Outside a character class, these sequences  have         ter class. Like any  other  unrecognized  escape  sequences,  they  are
3416         different meanings (see below).         treated  as  the  literal characters "B", "N", "R", and "X" by default,
3417           but cause an error if the PCRE_EXTRA option is set. Outside a character
3418           class, these sequences have different meanings.
3419    
3420     Absolute and relative back references     Absolute and relative back references
3421    
# Line 3244  BACKSLASH Line 3435  BACKSLASH
3435    
3436     Generic character types     Generic character types
3437    
3438         Another use of backslash is for specifying generic character types. The         Another use of backslash is for specifying generic character types:
        following are always recognized:  
3439    
3440           \d     any decimal digit           \d     any decimal digit
3441           \D     any character that is not a decimal digit           \D     any character that is not a decimal digit
# Line 3258  BACKSLASH Line 3448  BACKSLASH
3448           \w     any "word" character           \w     any "word" character
3449           \W     any "non-word" character           \W     any "non-word" character
3450    
3451         Each pair of escape sequences partitions the complete set of characters         There is also the single sequence \N, which matches a non-newline char-
3452         into  two disjoint sets. Any given character matches one, and only one,         acter.  This is the same as the "." metacharacter when  PCRE_DOTALL  is
3453         of each pair.         not set.
3454    
3455         These character type sequences can appear both inside and outside char-         Each  pair of lower and upper case escape sequences partitions the com-
3456         acter  classes.  They each match one character of the appropriate type.         plete set of characters into two disjoint  sets.  Any  given  character
3457         If the current matching point is at the end of the subject string,  all         matches  one, and only one, of each pair. The sequences can appear both
3458         of them fail, since there is no character to match.         inside and outside character classes. They each match one character  of
3459           the  appropriate  type.  If the current matching point is at the end of
3460           the subject string, all of them fail, because there is no character  to
3461           match.
3462    
3463         For  compatibility  with Perl, \s does not match the VT character (code         For  compatibility  with Perl, \s does not match the VT character (code
3464         11).  This makes it different from the the POSIX "space" class. The  \s         11).  This makes it different from the the POSIX "space" class. The  \s
# Line 3273  BACKSLASH Line 3466  BACKSLASH
3466         "use locale;" is included in a Perl script, \s may match the VT charac-         "use locale;" is included in a Perl script, \s may match the VT charac-
3467         ter. In PCRE, it never does.         ter. In PCRE, it never does.
3468    
3469         In  UTF-8 mode, characters with values greater than 128 never match \d,         A  "word"  character is an underscore or any character that is a letter
3470         \s, or \w, and always match \D, \S, and \W. This is true even when Uni-         or digit.  By default, the definition of letters  and  digits  is  con-
3471         code  character  property  support is available. These sequences retain         trolled  by PCRE's low-valued character tables, and may vary if locale-
3472         their original meanings from before UTF-8 support was available, mainly         specific matching is taking place (see "Locale support" in the  pcreapi
3473         for  efficiency  reasons. Note that this also affects \b, because it is         page).  For  example,  in  a French locale such as "fr_FR" in Unix-like
3474         defined in terms of \w and \W.         systems, or "french" in Windows, some character codes greater than  128
3475           are  used  for  accented letters, and these are then matched by \w. The
3476           use of locales with Unicode is discouraged.
3477    
3478           By default, in UTF-8 mode, characters  with  values  greater  than  128
3479           never  match  \d,  \s,  or  \w,  and always match \D, \S, and \W. These
3480           sequences retain their original meanings from before UTF-8 support  was
3481           available,  mainly for efficiency reasons. However, if PCRE is compiled
3482           with Unicode property support, and the PCRE_UCP option is set, the  be-
3483           haviour  is  changed  so  that Unicode properties are used to determine
3484           character types, as follows:
3485    
3486             \d  any character that \p{Nd} matches (decimal digit)
3487             \s  any character that \p{Z} matches, plus HT, LF, FF, CR
3488             \w  any character that \p{L} or \p{N} matches, plus underscore
3489    
3490           The upper case escapes match the inverse sets of characters. Note  that
3491           \d  matches  only decimal digits, whereas \w matches any Unicode digit,
3492           as well as any Unicode letter, and underscore. Note also that  PCRE_UCP
3493           affects  \b,  and  \B  because  they are defined in terms of \w and \W.
3494           Matching these sequences is noticeably slower when PCRE_UCP is set.
3495    
3496         The sequences \h, \H, \v, and \V are Perl 5.10 features. In contrast to         The sequences \h, \H, \v, and \V are Perl 5.10 features. In contrast to
3497         the  other  sequences, these do match certain high-valued codepoints in         the  other  sequences,  which  match  only ASCII characters by default,
3498         UTF-8 mode.  The horizontal space characters are:         these always  match  certain  high-valued  codepoints  in  UTF-8  mode,
3499           whether or not PCRE_UCP is set. The horizontal space characters are:
3500    
3501           U+0009     Horizontal tab           U+0009     Horizontal tab
3502           U+0020     Space           U+0020     Space
# Line 3314  BACKSLASH Line 3528  BACKSLASH
3528           U+2028     Line separator           U+2028     Line separator
3529           U+2029     Paragraph separator           U+2029     Paragraph separator
3530    
        A "word" character is an underscore or any character less than 256 that  
        is  a  letter  or  digit.  The definition of letters and digits is con-  
        trolled by PCRE's low-valued character tables, and may vary if  locale-  
        specific  matching is taking place (see "Locale support" in the pcreapi  
        page). For example, in a French locale such  as  "fr_FR"  in  Unix-like  
        systems,  or "french" in Windows, some character codes greater than 128  
        are used for accented letters, and these are matched by \w. The use  of  
        locales with Unicode is discouraged.  
   
3531     Newline sequences     Newline sequences
3532    
3533         Outside  a  character class, by default, the escape sequence \R matches         Outside  a  character class, by default, the escape sequence \R matches
# Line 3355  BACKSLASH Line 3560  BACKSLASH
3560           (*BSR_ANYCRLF)   CR, LF, or CRLF only           (*BSR_ANYCRLF)   CR, LF, or CRLF only
3561           (*BSR_UNICODE)   any Unicode newline sequence           (*BSR_UNICODE)   any Unicode newline sequence
3562    
3563         These override the default and the options given to pcre_compile(), but         These override the default and the options given to  pcre_compile()  or
3564         they can be overridden by options given to pcre_exec(). Note that these         pcre_compile2(),  but  they  can  be  overridden  by  options  given to
3565         special settings, which are not Perl-compatible, are recognized only at         pcre_exec() or pcre_dfa_exec(). Note that these special settings, which
3566         the  very  start  of a pattern, and that they must be in upper case. If         are  not  Perl-compatible,  are  recognized only at the very start of a
3567         more than one of them is present, the last one is  used.  They  can  be         pattern, and that they must be in upper case. If more than one of  them
3568         combined  with  a  change of newline convention, for example, a pattern         is present, the last one is used. They can be combined with a change of
3569         can start with:         newline convention; for example, a pattern can start with:
3570    
3571           (*ANY)(*BSR_ANYCRLF)           (*ANY)(*BSR_ANYCRLF)
3572    
3573         Inside a character class, \R matches the letter "R".         They can also be combined with the (*UTF8) or (*UCP) special sequences.
3574           Inside  a  character  class,  \R  is  treated as an unrecognized escape
3575           sequence, and so matches the letter "R" by default, but causes an error
3576           if PCRE_EXTRA is set.
3577    
3578     Unicode character properties     Unicode character properties
3579    
3580         When PCRE is built with Unicode character property support, three addi-         When PCRE is built with Unicode character property support, three addi-
3581         tional  escape sequences that match characters with specific properties         tional escape sequences that match characters with specific  properties
3582         are available.  When not in UTF-8 mode, these sequences are  of  course         are  available.   When not in UTF-8 mode, these sequences are of course
3583         limited  to  testing characters whose codepoints are less than 256, but         limited to testing characters whose codepoints are less than  256,  but
3584         they do work in this mode.  The extra escape sequences are:         they do work in this mode.  The extra escape sequences are:
3585    
3586           \p{xx}   a character with the xx property           \p{xx}   a character with the xx property
3587           \P{xx}   a character without the xx property           \P{xx}   a character without the xx property
3588           \X       an extended Unicode sequence           \X       an extended Unicode sequence
3589    
3590         The property names represented by xx above are limited to  the  Unicode         The  property  names represented by xx above are limited to the Unicode
3591         script names, the general category properties, and "Any", which matches         script names, the general category properties, "Any", which matches any
3592         any character (including newline). Other properties such as "InMusical-         character   (including  newline),  and  some  special  PCRE  properties
3593         Symbols"  are  not  currently supported by PCRE. Note that \P{Any} does         (described in the next section).  Other Perl properties such as  "InMu-
3594         not match any characters, so always causes a match failure.         sicalSymbols"  are  not  currently supported by PCRE. Note that \P{Any}
3595           does not match any characters, so always causes a match failure.
3596    
3597         Sets of Unicode characters are defined as belonging to certain scripts.         Sets of Unicode characters are defined as belonging to certain scripts.
3598         A  character from one of these sets can be matched using a script name.         A  character from one of these sets can be matched using a script name.
# Line 3395  BACKSLASH Line 3604  BACKSLASH
3604         Those that are not part of an identified script are lumped together  as         Those that are not part of an identified script are lumped together  as
3605         "Common". The current list of scripts is:         "Common". The current list of scripts is:
3606    
3607         Arabic,  Armenian,  Balinese,  Bengali,  Bopomofo,  Braille,  Buginese,         Arabic, Armenian, Avestan, Balinese, Bamum, Bengali, Bopomofo, Braille,
3608         Buhid,  Canadian_Aboriginal,  Cherokee,  Common,   Coptic,   Cuneiform,         Buginese, Buhid, Canadian_Aboriginal, Carian, Cham,  Cherokee,  Common,
3609         Cypriot, Cyrillic, Deseret, Devanagari, Ethiopic, Georgian, Glagolitic,         Coptic,   Cuneiform,  Cypriot,  Cyrillic,  Deseret,  Devanagari,  Egyp-
3610         Gothic, Greek, Gujarati, Gurmukhi, Han, Hangul, Hanunoo, Hebrew,  Hira-         tian_Hieroglyphs,  Ethiopic,  Georgian,  Glagolitic,   Gothic,   Greek,
3611         gana,  Inherited,  Kannada,  Katakana,  Kharoshthi,  Khmer, Lao, Latin,         Gujarati,  Gurmukhi,  Han,  Hangul,  Hanunoo,  Hebrew,  Hiragana, Impe-
3612         Limbu,  Linear_B,  Malayalam,  Mongolian,  Myanmar,  New_Tai_Lue,  Nko,         rial_Aramaic, Inherited, Inscriptional_Pahlavi, Inscriptional_Parthian,
3613         Ogham,  Old_Italic,  Old_Persian, Oriya, Osmanya, Phags_Pa, Phoenician,         Javanese,  Kaithi, Kannada, Katakana, Kayah_Li, Kharoshthi, Khmer, Lao,
3614         Runic,  Shavian,  Sinhala,  Syloti_Nagri,  Syriac,  Tagalog,  Tagbanwa,         Latin,  Lepcha,  Limbu,  Linear_B,  Lisu,  Lycian,  Lydian,  Malayalam,
3615         Tai_Le, Tamil, Telugu, Thaana, Thai, Tibetan, Tifinagh, Ugaritic, Yi.         Meetei_Mayek,  Mongolian, Myanmar, New_Tai_Lue, Nko, Ogham, Old_Italic,
3616           Old_Persian, Old_South_Arabian, Old_Turkic, Ol_Chiki,  Oriya,  Osmanya,
3617         Each  character has exactly one general category property, specified by         Phags_Pa,  Phoenician,  Rejang,  Runic, Samaritan, Saurashtra, Shavian,
3618         a two-letter abbreviation. For compatibility with Perl, negation can be         Sinhala, Sundanese, Syloti_Nagri, Syriac,  Tagalog,  Tagbanwa,  Tai_Le,
3619         specified  by  including a circumflex between the opening brace and the         Tai_Tham,  Tai_Viet,  Tamil,  Telugu,  Thaana, Thai, Tibetan, Tifinagh,
3620         property name. For example, \p{^Lu} is the same as \P{Lu}.         Ugaritic, Vai, Yi.
3621    
3622           Each character has exactly one Unicode general category property, spec-
3623           ified  by a two-letter abbreviation. For compatibility with Perl, nega-
3624           tion can be specified by including a  circumflex  between  the  opening
3625           brace  and  the  property  name.  For  example,  \p{^Lu} is the same as
3626           \P{Lu}.
3627    
3628         If only one letter is specified with \p or \P, it includes all the gen-         If only one letter is specified with \p or \P, it includes all the gen-
3629         eral  category properties that start with that letter. In this case, in         eral  category properties that start with that letter. In this case, in
# Line 3472  BACKSLASH Line 3687  BACKSLASH
3687         U+D800 to U+DFFF. Such characters are not valid in UTF-8  strings  (see         U+D800 to U+DFFF. Such characters are not valid in UTF-8  strings  (see
3688         RFC 3629) and so cannot be tested by PCRE, unless UTF-8 validity check-         RFC 3629) and so cannot be tested by PCRE, unless UTF-8 validity check-
3689         ing has been turned off (see the discussion  of  PCRE_NO_UTF8_CHECK  in         ing has been turned off (see the discussion  of  PCRE_NO_UTF8_CHECK  in
3690         the pcreapi page).         the pcreapi page). Perl does not support the Cs property.
3691    
3692         The  long  synonyms  for  these  properties that Perl supports (such as         The  long  synonyms  for  property  names  that  Perl supports (such as
3693         \p{Letter}) are not supported by PCRE, nor is it  permitted  to  prefix         \p{Letter}) are not supported by PCRE, nor is it  permitted  to  prefix
3694         any of these properties with "Is".         any of these properties with "Is".
3695    
# Line 3500  BACKSLASH Line 3715  BACKSLASH
3715         Matching characters by Unicode property is not fast, because  PCRE  has         Matching characters by Unicode property is not fast, because  PCRE  has
3716         to  search  a  structure  that  contains data for over fifteen thousand         to  search  a  structure  that  contains data for over fifteen thousand
3717         characters. That is why the traditional escape sequences such as \d and         characters. That is why the traditional escape sequences such as \d and
3718         \w do not use Unicode properties in PCRE.         \w  do  not  use  Unicode properties in PCRE by default, though you can
3719           make them do so by setting the PCRE_UCP option for pcre_compile() or by
3720           starting the pattern with (*UCP).
3721    
3722       PCRE's additional properties
3723    
3724           As  well  as  the standard Unicode properties described in the previous
3725           section, PCRE supports four more that make it possible to convert  tra-
3726           ditional escape sequences such as \w and \s and POSIX character classes
3727           to use Unicode properties. PCRE uses these non-standard, non-Perl prop-
3728           erties internally when PCRE_UCP is set. They are:
3729    
3730             Xan   Any alphanumeric character
3731             Xps   Any POSIX space character
3732             Xsp   Any Perl space character
3733             Xwd   Any Perl "word" character
3734    
3735           Xan  matches  characters that have either the L (letter) or the N (num-
3736           ber) property. Xps matches the characters tab, linefeed, vertical  tab,
3737           formfeed,  or  carriage  return, and any other character that has the Z
3738           (separator) property.  Xsp is the same as Xps, except that vertical tab
3739           is excluded. Xwd matches the same characters as Xan, plus underscore.
3740    
3741     Resetting the match start     Resetting the match start
3742    
# Line 3521  BACKSLASH Line 3757  BACKSLASH
3757    
3758         matches "foobar", the first substring is still set to "foo".         matches "foobar", the first substring is still set to "foo".
3759    
3760           Perl documents that the use  of  \K  within  assertions  is  "not  well
3761           defined".  In  PCRE,  \K  is  acted upon when it occurs inside positive
3762           assertions, but is ignored in negative assertions.
3763    
3764     Simple assertions     Simple assertions
3765    
3766         The final use of backslash is for certain simple assertions. An  asser-         The final use of backslash is for certain simple assertions. An  asser-
# Line 3537  BACKSLASH Line 3777  BACKSLASH
3777           \z     matches only at the end of the subject           \z     matches only at the end of the subject
3778           \G     matches at the first matching position in the subject           \G     matches at the first matching position in the subject
3779    
3780         These assertions may not appear in character classes (but note that  \b         Inside a character class, \b has a different meaning;  it  matches  the
3781         has a different meaning, namely the backspace character, inside a char-         backspace  character.  If  any  other  of these assertions appears in a
3782         acter class).         character class, by default it matches the corresponding literal  char-
3783           acter  (for  example,  \B  matches  the  letter  B).  However,  if  the
3784         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-
3785         character  and  the previous character do not both match \w or \W (i.e.         ated instead.
3786         one matches \w and the other matches \W), or the start or  end  of  the  
3787         string if the first or last character matches \w, respectively.         A  word  boundary is a position in the subject string where the current
3788           character and the previous character do not both match \w or  \W  (i.e.
3789           one  matches  \w  and the other matches \W), or the start or end of the
3790           string if the first or last  character  matches  \w,  respectively.  In
3791           UTF-8  mode,  the  meanings  of \w and \W can be changed by setting the
3792           PCRE_UCP option. When this is done, it also affects \b and \B.  Neither
3793           PCRE  nor  Perl has a separate "start of word" or "end of word" metase-
3794           quence. However, whatever follows \b normally determines which  it  is.
3795           For example, the fragment \ba matches "a" at the start of a word.
3796    
3797         The  \A,  \Z,  and \z assertions differ from the traditional circumflex         The  \A,  \Z,  and \z assertions differ from the traditional circumflex
3798         and dollar (described in the next section) in that they only ever match         and dollar (described in the next section) in that they only ever match
# Line 3627  CIRCUMFLEX AND DOLLAR Line 3875  CIRCUMFLEX AND DOLLAR
3875         set.         set.
3876    
3877    
3878  FULL STOP (PERIOD, DOT)  FULL STOP (PERIOD, DOT) AND \N
3879    
3880         Outside a character class, a dot in the pattern matches any one charac-         Outside a character class, a dot in the pattern matches any one charac-
3881         ter  in  the subject string except (by default) a character that signi-         ter  in  the subject string except (by default) a character that signi-
# Line 3650  FULL STOP (PERIOD, DOT) Line 3898  FULL STOP (PERIOD, DOT)
3898         flex and dollar, the only relationship being  that  they  both  involve         flex and dollar, the only relationship being  that  they  both  involve
3899         newlines. Dot has no special meaning in a character class.         newlines. Dot has no special meaning in a character class.
3900    
3901           The escape sequence \N always behaves as a dot does when PCRE_DOTALL is
3902           not set. In other words, it matches any one character except  one  that
3903           signifies the end of a line.
3904    
3905    
3906  MATCHING A SINGLE BYTE  MATCHING A SINGLE BYTE
3907    
# Line 3670  SQUARE BRACKETS AND CHARACTER CLASSES Line 3922  SQUARE BRACKETS AND CHARACTER CLASSES
3922    
3923         An opening square bracket introduces a character class, terminated by a         An opening square bracket introduces a character class, terminated by a
3924         closing square bracket. A closing square bracket on its own is not spe-         closing square bracket. A closing square bracket on its own is not spe-
3925         cial. If a closing square bracket is required as a member of the class,         cial by default.  However, if the PCRE_JAVASCRIPT_COMPAT option is set,
3926         it should be the first data character in the class  (after  an  initial         a lone closing square bracket causes a compile-time error. If a closing
3927         circumflex, if present) or escaped with a backslash.         square  bracket  is required as a member of the class, it should be the
3928           first data character in the class  (after  an  initial  circumflex,  if
3929           present) or escaped with a backslash.
3930    
3931         A  character  class matches a single character in the subject. In UTF-8         A  character  class matches a single character in the subject. In UTF-8
3932         mode, the character may occupy more than one byte. A matched  character         mode, the character may be more than one byte long. A matched character
3933         must be in the set of characters defined by the class, unless the first         must be in the set of characters defined by the class, unless the first
3934         character in the class definition is a circumflex, in  which  case  the         character in the class definition is a circumflex, in  which  case  the
3935         subject  character  must  not  be in the set defined by the class. If a         subject  character  must  not  be in the set defined by the class. If a
# Line 3686  SQUARE BRACKETS AND CHARACTER CLASSES Line 3940  SQUARE BRACKETS AND CHARACTER CLASSES
3940         while [^aeiou] matches any character that is not a  lower  case  vowel.         while [^aeiou] matches any character that is not a  lower  case  vowel.
3941         Note that a circumflex is just a convenient notation for specifying the         Note that a circumflex is just a convenient notation for specifying the
3942         characters that are in the class by enumerating those that are  not.  A         characters that are in the class by enumerating those that are  not.  A
3943         class  that starts with a circumflex is not an assertion: it still con-         class  that starts with a circumflex is not an assertion; it still con-
3944         sumes a character from the subject string, and therefore  it  fails  if         sumes a character from the subject string, and therefore  it  fails  if
3945         the current pointer is at the end of the string.         the current pointer is at the end of the string.
3946    
# Line 3702  SQUARE BRACKETS AND CHARACTER CLASSES Line 3956  SQUARE BRACKETS AND CHARACTER CLASSES
3956         than 128, so caseless matching is always possible. For characters  with         than 128, so caseless matching is always possible. For characters  with
3957         higher  values,  the  concept  of case is supported if PCRE is compiled         higher  values,  the  concept  of case is supported if PCRE is compiled
3958         with Unicode property support, but not otherwise.  If you want  to  use         with Unicode property support, but not otherwise.  If you want  to  use
3959         caseless  matching  for  characters 128 and above, you must ensure that         caseless  matching  in UTF8-mode for characters 128 and above, you must
3960         PCRE is compiled with Unicode property support as well  as  with  UTF-8         ensure that PCRE is compiled with Unicode property support as  well  as
3961         support.         with UTF-8 support.
3962    
3963         Characters  that  might  indicate  line breaks are never treated in any         Characters  that  might  indicate  line breaks are never treated in any
3964         special way  when  matching  character  classes,  whatever  line-ending         special way  when  matching  character  classes,  whatever  line-ending
# Line 3741  SQUARE BRACKETS AND CHARACTER CLASSES Line 3995  SQUARE BRACKETS AND CHARACTER CLASSES
3995         concept  of  case for characters with values greater than 128 only when         concept  of  case for characters with values greater than 128 only when
3996         it is compiled with Unicode property support.         it is compiled with Unicode property support.
3997    
3998         The character types \d, \D, \p, \P, \s, \S, \w, and \W may also  appear         The character types \d, \D, \h, \H, \p, \P, \s, \S, \v, \V, \w, and  \W
3999         in  a  character  class,  and add the characters that they match to the         may  also appear in a character class, and add the characters that they
4000         class. For example, [\dABCDEF] matches any hexadecimal digit. A circum-         match to the class. For example,  [\dABCDEF]  matches  any  hexadecimal
4001         flex  can  conveniently  be used with the upper case character types to         digit.  A circumflex can conveniently be used with the upper case char-
4002         specify a more restricted set of characters  than  the  matching  lower         acter types to specify a more restricted set  of  characters  than  the
4003         case  type.  For example, the class [^\W_] matches any letter or digit,         matching  lower  case  type.  For example, the class [^\W_] matches any
4004         but not underscore.         letter or digit, but not underscore.
4005    
4006         The only metacharacters that are recognized in  character  classes  are         The only metacharacters that are recognized in  character  classes  are
4007         backslash,  hyphen  (only  where  it can be interpreted as specifying a         backslash,  hyphen  (only  where  it can be interpreted as specifying a
# Line 3766  POSIX CHARACTER CLASSES Line 4020  POSIX CHARACTER CLASSES
4020           [01[:alpha:]%]           [01[:alpha:]%]
4021    
4022         matches "0", "1", any alphabetic character, or "%". The supported class         matches "0", "1", any alphabetic character, or "%". The supported class
4023         names are         names are:
4024    
4025           alnum    letters and digits           alnum    letters and digits
4026           alpha    letters           alpha    letters
# Line 3777  POSIX CHARACTER CLASSES Line 4031  POSIX CHARACTER CLASSES
4031           graph    printing characters, excluding space           graph    printing characters, excluding space
4032           lower    lower case letters           lower    lower case letters
4033           print    printing characters, including space           print    printing characters, including space
4034           punct    printing characters, excluding letters and digits           punct    printing characters, excluding letters and digits and space
4035           space    white space (not quite the same as \s)           space    white space (not quite the same as \s)
4036           upper    upper case letters           upper    upper case letters
4037           word     "word" characters (same as \w)           word     "word" characters (same as \w)
# Line 3798  POSIX CHARACTER CLASSES Line 4052  POSIX CHARACTER CLASSES
4052         POSIX syntax [.ch.] and [=ch=] where "ch" is a "collating element", but         POSIX syntax [.ch.] and [=ch=] where "ch" is a "collating element", but
4053         these are not supported, and an error is given if they are encountered.         these are not supported, and an error is given if they are encountered.
4054    
4055         In UTF-8 mode, characters with values greater than 128 do not match any         By  default,  in UTF-8 mode, characters with values greater than 128 do
4056         of the POSIX character classes.         not match any of the POSIX character classes. However, if the  PCRE_UCP
4057           option  is passed to pcre_compile(), some of the classes are changed so
4058           that Unicode character properties are used. This is achieved by replac-
4059           ing the POSIX classes by other sequences, as follows:
4060    
4061             [:alnum:]  becomes  \p{Xan}
4062             [:alpha:]  becomes  \p{L}
4063             [:blank:]  becomes  \h
4064             [:digit:]  becomes  \p{Nd}
4065             [:lower:]  becomes  \p{Ll}
4066             [:space:]  becomes  \p{Xps}
4067             [:upper:]  becomes  \p{Lu}
4068             [:word:]   becomes  \p{Xwd}
4069    
4070           Negated  versions,  such  as [:^alpha:] use \P instead of \p. The other
4071           POSIX classes are unchanged, and match only characters with code points
4072           less than 128.
4073    
4074    
4075  VERTICAL BAR  VERTICAL BAR
4076    
4077         Vertical bar characters are used to separate alternative patterns.  For         Vertical  bar characters are used to separate alternative patterns. For
4078         example, the pattern         example, the pattern
4079    
4080           gilbert|sullivan           gilbert|sullivan
4081    
4082         matches  either "gilbert" or "sullivan". Any number of alternatives may         matches either "gilbert" or "sullivan". Any number of alternatives  may
4083         appear, and an empty  alternative  is  permitted  (matching  the  empty         appear,  and  an  empty  alternative  is  permitted (matching the empty
4084         string). The matching process tries each alternative in turn, from left         string). The matching process tries each alternative in turn, from left
4085         to right, and the first one that succeeds is used. If the  alternatives         to  right, and the first one that succeeds is used. If the alternatives
4086         are  within a subpattern (defined below), "succeeds" means matching the         are within a subpattern (defined below), "succeeds" means matching  the
4087         rest of the main pattern as well as the alternative in the subpattern.         rest of the main pattern as well as the alternative in the subpattern.
4088    
4089    
4090  INTERNAL OPTION SETTING  INTERNAL OPTION SETTING
4091    
4092         The settings of the  PCRE_CASELESS,  PCRE_MULTILINE,  PCRE_DOTALL,  and         The  settings  of  the  PCRE_CASELESS, PCRE_MULTILINE, PCRE_DOTALL, and
4093         PCRE_EXTENDED  options  (which are Perl-compatible) can be changed from         PCRE_EXTENDED options (which are Perl-compatible) can be  changed  from
4094         within the pattern by  a  sequence  of  Perl  option  letters  enclosed         within  the  pattern  by  a  sequence  of  Perl option letters enclosed
4095         between "(?" and ")".  The option letters are         between "(?" and ")".  The option letters are
4096    
4097           i  for PCRE_CASELESS           i  for PCRE_CASELESS
# Line 3831  INTERNAL OPTION SETTING Line 4101  INTERNAL OPTION SETTING
4101    
4102         For example, (?im) sets caseless, multiline matching. It is also possi-         For example, (?im) sets caseless, multiline matching. It is also possi-
4103         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
4104         combined  setting and unsetting such as (?im-sx), which sets PCRE_CASE-         combined setting and unsetting such as (?im-sx), which sets  PCRE_CASE-
4105         LESS and PCRE_MULTILINE while unsetting PCRE_DOTALL and  PCRE_EXTENDED,         LESS  and PCRE_MULTILINE while unsetting PCRE_DOTALL and PCRE_EXTENDED,
4106         is  also  permitted.  If  a  letter  appears  both before and after the         is also permitted. If a  letter  appears  both  before  and  after  the
4107         hyphen, the option is unset.         hyphen, the option is unset.
4108    
4109         The PCRE-specific options PCRE_DUPNAMES, PCRE_UNGREEDY, and  PCRE_EXTRA         The  PCRE-specific options PCRE_DUPNAMES, PCRE_UNGREEDY, and PCRE_EXTRA
4110         can  be changed in the same way as the Perl-compatible options by using         can be changed in the same way as the Perl-compatible options by  using
4111         the characters J, U and X respectively.         the characters J, U and X respectively.
4112    
4113         When one of these option changes occurs at  top  level  (that  is,  not         When  one  of  these  option  changes occurs at top level (that is, not
4114         inside  subpattern parentheses), the change applies to the remainder of         inside subpattern parentheses), the change applies to the remainder  of
4115         the pattern that follows. If the change is placed right at the start of         the pattern that follows. If the change is placed right at the start of
4116         a pattern, PCRE extracts it into the global options (and it will there-         a pattern, PCRE extracts it into the global options (and it will there-
4117         fore show up in data extracted by the pcre_fullinfo() function).         fore show up in data extracted by the pcre_fullinfo() function).
4118    
4119         An option change within a subpattern (see below for  a  description  of         An  option  change  within a subpattern (see below for a description of
4120         subpatterns) affects only that part of the current pattern that follows         subpatterns) affects only that part of the current pattern that follows
4121         it, so         it, so
4122    
4123           (a(?i)b)c           (a(?i)b)c
4124    
4125         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
4126         used).   By  this means, options can be made to have different settings         used).  By this means, options can be made to have  different  settings
4127         in different parts of the pattern. Any changes made in one  alternative         in  different parts of the pattern. Any changes made in one alternative
4128         do  carry  on  into subsequent branches within the same subpattern. For         do carry on into subsequent branches within the  same  subpattern.  For
4129         example,         example,
4130    
4131           (a(?i)b|c)           (a(?i)b|c)
4132    
4133         matches "ab", "aB", "c", and "C", even though  when  matching  "C"  the         matches  "ab",  "aB",  "c",  and "C", even though when matching "C" the
4134         first  branch  is  abandoned before the option setting. This is because         first branch is abandoned before the option setting.  This  is  because
4135         the effects of option settings happen at compile time. There  would  be         the  effects  of option settings happen at compile time. There would be
4136         some very weird behaviour otherwise.         some very weird behaviour otherwise.
4137    
4138         Note:  There  are  other  PCRE-specific  options that can be set by the         Note: There are other PCRE-specific options that  can  be  set  by  the
4139         application when the compile or match functions  are  called.  In  some         application  when  the  compile  or match functions are called. In some
4140         cases the pattern can contain special leading sequences such as (*CRLF)         cases the pattern can contain special leading sequences such as (*CRLF)
4141         to override what the application has set or what  has  been  defaulted.         to  override  what  the application has set or what has been defaulted.
4142         Details  are  given  in the section entitled "Newline sequences" above.         Details are given in the section entitled  "Newline  sequences"  above.
4143         There is also the (*UTF8) leading sequence that  can  be  used  to  set         There  are  also  the  (*UTF8) and (*UCP) leading sequences that can be
4144         UTF-8 mode; this is equivalent to setting the PCRE_UTF8 option.         used to set UTF-8 and Unicode property modes; they  are  equivalent  to
4145           setting the PCRE_UTF8 and the PCRE_UCP options, respectively.
4146    
4147    
4148  SUBPATTERNS  SUBPATTERNS
# Line 3953  DUPLICATE SUBPATTERN NUMBERS Line 4224  DUPLICATE SUBPATTERN NUMBERS
4224           / ( a )  (?| x ( y ) z | (p (q) r) | (t) u (v) ) ( z ) /x           / ( a )  (?| x ( y ) z | (p (q) r) | (t) u (v) ) ( z ) /x
4225           # 1            2         2  3        2     3     4           # 1            2         2  3        2     3     4
4226    
4227         A backreference or a recursive call to  a  numbered  subpattern  always         A back reference to a numbered subpattern uses the  most  recent  value
4228         refers to the first one in the pattern with the given number.         that  is  set  for that number by any subpattern. The following pattern
4229           matches "abcabc" or "defdef":
4230    
4231             /(?|(abc)|(def))\1/
4232    
4233           In contrast, a recursive or "subroutine" call to a numbered  subpattern
4234           always  refers  to  the first one in the pattern with the given number.
4235           The following pattern matches "abcabc" or "defabc":
4236    
4237         An  alternative approach to using this "branch reset" feature is to use           /(?|(abc)|(def))(?1)/
4238    
4239           If a condition test for a subpattern's having matched refers to a  non-
4240           unique  number, the test is true if any of the subpatterns of that num-
4241           ber have matched.
4242    
4243           An alternative approach to using this "branch reset" feature is to  use
4244         duplicate named subpatterns, as described in the next section.         duplicate named subpatterns, as described in the next section.
4245    
4246    
4247  NAMED SUBPATTERNS  NAMED SUBPATTERNS
4248    
4249         Identifying capturing parentheses by number is simple, but  it  can  be         Identifying  capturing  parentheses  by number is simple, but it can be
4250         very  hard  to keep track of the numbers in complicated regular expres-         very hard to keep track of the numbers in complicated  regular  expres-
4251         sions. Furthermore, if an  expression  is  modified,  the  numbers  may         sions.  Furthermore,  if  an  expression  is  modified, the numbers may
4252         change.  To help with this difficulty, PCRE supports the naming of sub-         change. To help with this difficulty, PCRE supports the naming of  sub-
4253         patterns. This feature was not added to Perl until release 5.10. Python         patterns. This feature was not added to Perl until release 5.10. Python
4254         had  the  feature earlier, and PCRE introduced it at release 4.0, using         had the feature earlier, and PCRE introduced it at release  4.0,  using
4255         the Python syntax. PCRE now supports both the Perl and the Python  syn-         the  Python syntax. PCRE now supports both the Perl and the Python syn-
4256         tax.         tax. Perl allows identically numbered  subpatterns  to  have  different
4257           names, but PCRE does not.
4258    
4259         In  PCRE,  a subpattern can be named in one of three ways: (?<name>...)         In  PCRE,  a subpattern can be named in one of three ways: (?<name>...)
4260         or (?'name'...) as in Perl, or (?P<name>...) as in  Python.  References         or (?'name'...) as in Perl, or (?P<name>...) as in  Python.  References
4261         to capturing parentheses from other parts of the pattern, such as back-         to  capturing parentheses from other parts of the pattern, such as back
4262         references, recursion, and conditions, can be made by name as  well  as         references, recursion, and conditions, can be made by name as  well  as
4263         by number.         by number.
4264    
# Line 3986  NAMED SUBPATTERNS Line 4271  NAMED SUBPATTERNS
4271    
4272         By default, a name must be unique within a pattern, but it is  possible         By default, a name must be unique within a pattern, but it is  possible
4273         to relax this constraint by setting the PCRE_DUPNAMES option at compile         to relax this constraint by setting the PCRE_DUPNAMES option at compile
4274         time. This can be useful for patterns where only one  instance  of  the         time. (Duplicate names are also always permitted for  subpatterns  with
4275           the  same  number, set up as described in the previous section.) Dupli-
4276           cate names can be useful for patterns where only one  instance  of  the
4277         named  parentheses  can  match. Suppose you want to match the name of a         named  parentheses  can  match. Suppose you want to match the name of a
4278         weekday, either as a 3-letter abbreviation or as the full name, and  in         weekday, either as a 3-letter abbreviation or as the full name, and  in
4279         both cases you want to extract the abbreviation. This pattern (ignoring         both cases you want to extract the abbreviation. This pattern (ignoring
# Line 4005  NAMED SUBPATTERNS Line 4292  NAMED SUBPATTERNS
4292         The convenience function for extracting the data by  name  returns  the         The convenience function for extracting the data by  name  returns  the
4293         substring  for  the first (and in this example, the only) subpattern of         substring  for  the first (and in this example, the only) subpattern of
4294         that name that matched. This saves searching  to  find  which  numbered         that name that matched. This saves searching  to  find  which  numbered
4295         subpattern  it  was. If you make a reference to a non-unique named sub-         subpattern it was.
4296         pattern from elsewhere in the pattern, the one that corresponds to  the  
4297         lowest  number  is used. For further details of the interfaces for han-         If  you  make  a  back  reference to a non-unique named subpattern from
4298         dling named subpatterns, see the pcreapi documentation.         elsewhere in the pattern, the one that corresponds to the first  occur-
4299           rence of the name is used. In the absence of duplicate numbers (see the
4300           previous section) this is the one with the lowest number. If you use  a
4301           named  reference  in a condition test (see the section about conditions
4302           below), either to check whether a subpattern has matched, or  to  check
4303           for  recursion,  all  subpatterns with the same name are tested. If the
4304           condition is true for any one of them, the overall condition  is  true.
4305           This is the same behaviour as testing by number. For further details of
4306           the interfaces for handling named subpatterns, see the pcreapi documen-
4307           tation.
4308    
4309         Warning: You cannot use different names to distinguish between two sub-         Warning: You cannot use different names to distinguish between two sub-
4310         patterns  with  the same number (see the previous section) because PCRE         patterns with the same number because PCRE uses only the  numbers  when
4311         uses only the numbers when matching.         matching. For this reason, an error is given at compile time if differ-
4312           ent names are given to subpatterns with the same number.  However,  you
4313           can  give  the same name to subpatterns with the same number, even when
4314           PCRE_DUPNAMES is not set.
4315    
4316    
4317  REPETITION  REPETITION
# Line 4029  REPETITION Line 4328  REPETITION
4328           a character class           a character class
4329           a back reference (see next section)           a back reference (see next section)
4330           a parenthesized subpattern (unless it is an assertion)           a parenthesized subpattern (unless it is an assertion)
4331             a recursive or "subroutine" call to a subpattern
4332    
4333         The  general repetition quantifier specifies a minimum and maximum num-         The  general repetition quantifier specifies a minimum and maximum num-
4334         ber of permitted matches, by giving the two numbers in  curly  brackets         ber of permitted matches, by giving the two numbers in  curly  brackets
# Line 4143  REPETITION Line 4443  REPETITION
4443         mization, or alternatively using ^ to indicate anchoring explicitly.         mization, or alternatively using ^ to indicate anchoring explicitly.
4444    
4445         However,  there is one situation where the optimization cannot be used.         However,  there is one situation where the optimization cannot be used.
4446         When .*  is inside capturing parentheses that  are  the  subject  of  a         When .*  is inside capturing parentheses that are the subject of a back
4447         backreference  elsewhere  in the pattern, a match at the start may fail         reference elsewhere in the pattern, a match at the start may fail where
4448         where a later one succeeds. Consider, for example:         a later one succeeds. Consider, for example:
4449    
4450           (.*)abc\1           (.*)abc\1
4451    
# Line 4352  BACK REFERENCES Line 4652  BACK REFERENCES
4652    
4653         There may be more than one back reference to the same subpattern. If  a         There may be more than one back reference to the same subpattern. If  a
4654         subpattern  has  not actually been used in a particular match, any back         subpattern  has  not actually been used in a particular match, any back
4655         references to it always fail. For example, the pattern         references to it always fail by default. For example, the pattern
4656    
4657           (a|(bc))\2           (a|(bc))\2
4658    
4659         always fails if it starts to match "a" rather than "bc". Because  there         always fails if it starts to match "a" rather than  "bc".  However,  if
4660         may  be  many  capturing parentheses in a pattern, all digits following         the PCRE_JAVASCRIPT_COMPAT option is set at compile time, a back refer-
4661         the backslash are taken as part of a potential back  reference  number.         ence to an unset value matches an empty string.
4662         If the pattern continues with a digit character, some delimiter must be  
4663         used to terminate the back reference. If the  PCRE_EXTENDED  option  is         Because there may be many capturing parentheses in a pattern, all  dig-
4664         set,  this  can  be  whitespace.  Otherwise an empty comment (see "Com-         its  following a backslash are taken as part of a potential back refer-
4665         ments" below) can be used.         ence number.  If the pattern continues with  a  digit  character,  some
4666           delimiter  must  be  used  to  terminate  the  back  reference.  If the
4667         A back reference that occurs inside the parentheses to which it  refers         PCRE_EXTENDED option is set, this can be whitespace. Otherwise, the \g{
4668         fails  when  the subpattern is first used, so, for example, (a\1) never         syntax or an empty comment (see "Comments" below) can be used.
4669         matches.  However, such references can be useful inside  repeated  sub-  
4670       Recursive back references
4671    
4672           A  back reference that occurs inside the parentheses to which it refers
4673           fails when the subpattern is first used, so, for example,  (a\1)  never
4674           matches.   However,  such references can be useful inside repeated sub-
4675         patterns. For example, the pattern         patterns. For example, the pattern
4676    
4677           (a|b\1)+           (a|b\1)+
4678    
4679         matches any number of "a"s and also "aba", "ababbaa" etc. At each iter-         matches any number of "a"s and also "aba", "ababbaa" etc. At each iter-
4680         ation of the subpattern,  the  back  reference  matches  the  character         ation  of  the  subpattern,  the  back  reference matches the character
4681         string  corresponding  to  the previous iteration. In order for this to         string corresponding to the previous iteration. In order  for  this  to
4682         work, the pattern must be such that the first iteration does  not  need         work,  the  pattern must be such that the first iteration does not need
4683         to  match the back reference. This can be done using alternation, as in         to match the back reference. This can be done using alternation, as  in
4684         the example above, or by a quantifier with a minimum of zero.         the example above, or by a quantifier with a minimum of zero.
4685    
4686           Back  references of this type cause the group that they reference to be
4687           treated as an atomic group.  Once the whole group has been  matched,  a
4688           subsequent  matching  failure cannot cause backtracking into the middle
4689           of the group.
4690    
4691    
4692  ASSERTIONS  ASSERTIONS
4693    
# Line 4425  ASSERTIONS Line 4735  ASSERTIONS
4735         If you want to force a matching failure at some point in a pattern, the         If you want to force a matching failure at some point in a pattern, the
4736         most convenient way to do it is  with  (?!)  because  an  empty  string         most convenient way to do it is  with  (?!)  because  an  empty  string
4737         always  matches, so an assertion that requires there not to be an empty         always  matches, so an assertion that requires there not to be an empty
4738         string must always fail.         string must always fail.   The  Perl  5.10  backtracking  control  verb
4739           (*FAIL) or (*F) is essentially a synonym for (?!).
4740    
4741     Lookbehind assertions     Lookbehind assertions
4742    
4743         Lookbehind assertions start with (?<= for positive assertions and  (?<!         Lookbehind  assertions start with (?<= for positive assertions and (?<!
4744         for negative assertions. For example,         for negative assertions. For example,
4745    
4746           (?<!foo)bar           (?<!foo)bar
4747    
4748         does  find  an  occurrence  of "bar" that is not preceded by "foo". The         does find an occurrence of "bar" that is not  preceded  by  "foo".  The
4749         contents of a lookbehind assertion are restricted  such  that  all  the         contents  of  a  lookbehind  assertion are restricted such that all the
4750         strings it matches must have a fixed length. However, if there are sev-         strings it matches must have a fixed length. However, if there are sev-
4751         eral top-level alternatives, they do not all  have  to  have  the  same         eral  top-level  alternatives,  they  do  not all have to have the same
4752         fixed length. Thus         fixed length. Thus
4753    
4754           (?<=bullock|donkey)           (?<=bullock|donkey)
# Line 4446  ASSERTIONS Line 4757  ASSERTIONS
4757    
4758           (?<!dogs?|cats?)           (?<!dogs?|cats?)
4759    
4760         causes  an  error at compile time. Branches that match different length         causes an error at compile time. Branches that match  different  length
4761         strings are permitted only at the top level of a lookbehind  assertion.         strings  are permitted only at the top level of a lookbehind assertion.
4762         This  is  an  extension  compared  with  Perl (at least for 5.8), which         This is an extension compared with Perl (5.8 and 5.10), which  requires
4763         requires all branches to match the same length of string. An  assertion         all branches to match the same length of string. An assertion such as
        such as  
4764    
4765           (?<=ab(c|de))           (?<=ab(c|de))
4766    
4767         is  not  permitted,  because  its single top-level branch can match two         is  not  permitted,  because  its single top-level branch can match two
4768         different lengths, but it is acceptable if rewritten to  use  two  top-         different lengths, but it is acceptable to PCRE if rewritten to use two
4769         level branches:         top-level branches:
4770    
4771           (?<=abc|abde)           (?<=abc|abde)
4772    
4773         In some cases, the Perl 5.10 escape sequence \K (see above) can be used         In some cases, the Perl 5.10 escape sequence \K (see above) can be used
4774         instead of a lookbehind assertion; this is not restricted to  a  fixed-         instead of  a  lookbehind  assertion  to  get  round  the  fixed-length
4775         length.         restriction.
4776    
4777         The  implementation  of lookbehind assertions is, for each alternative,         The  implementation  of lookbehind assertions is, for each alternative,
4778         to temporarily move the current position back by the fixed  length  and         to temporarily move the current position back by the fixed  length  and
# Line 4474  ASSERTIONS Line 4784  ASSERTIONS
4784         ble to calculate the length of the lookbehind. The \X and  \R  escapes,         ble to calculate the length of the lookbehind. The \X and  \R  escapes,
4785         which can match different numbers of bytes, are also not permitted.         which can match different numbers of bytes, are also not permitted.
4786    
4787           "Subroutine"  calls  (see below) such as (?2) or (?&X) are permitted in
4788           lookbehinds, as long as the subpattern matches a  fixed-length  string.
4789           Recursion, however, is not supported.
4790    
4791         Possessive  quantifiers  can  be  used  in  conjunction with lookbehind         Possessive  quantifiers  can  be  used  in  conjunction with lookbehind
4792         assertions to specify efficient matching at  the  end  of  the  subject         assertions to specify efficient matching of fixed-length strings at the
4793         string. Consider a simple pattern such as         end of subject strings. Consider a simple pattern such as
4794    
4795           abcd$           abcd$
4796    
# Line 4539  CONDITIONAL SUBPATTERNS Line 4853  CONDITIONAL SUBPATTERNS
4853    
4854         It  is possible to cause the matching process to obey a subpattern con-         It  is possible to cause the matching process to obey a subpattern con-
4855         ditionally or to choose between two alternative subpatterns,  depending         ditionally or to choose between two alternative subpatterns,  depending
4856         on  the result of an assertion, or whether a previous capturing subpat-         on  the result of an assertion, or whether a specific capturing subpat-
4857         tern matched or not. The two possible forms of  conditional  subpattern         tern has already been matched. The two possible  forms  of  conditional
4858         are         subpattern are:
4859    
4860           (?(condition)yes-pattern)           (?(condition)yes-pattern)
4861           (?(condition)yes-pattern|no-pattern)           (?(condition)yes-pattern|no-pattern)
# Line 4556  CONDITIONAL SUBPATTERNS Line 4870  CONDITIONAL SUBPATTERNS
4870     Checking for a used subpattern by number     Checking for a used subpattern by number
4871    
4872         If the text between the parentheses consists of a sequence  of  digits,         If the text between the parentheses consists of a sequence  of  digits,
4873         the  condition  is  true if the capturing subpattern of that number has         the condition is true if a capturing subpattern of that number has pre-
4874         previously matched. An alternative notation is to  precede  the  digits         viously matched. If there is more than one  capturing  subpattern  with
4875         with a plus or minus sign. In this case, the subpattern number is rela-         the  same  number  (see  the earlier section about duplicate subpattern
4876         tive rather than absolute.  The most recently opened parentheses can be         numbers), the condition is true if any of them have been set. An alter-
4877         referenced  by  (?(-1),  the  next most recent by (?(-2), and so on. In         native  notation is to precede the digits with a plus or minus sign. In
4878         looping constructs it can also make sense to refer to subsequent groups         this case, the subpattern number is relative rather than absolute.  The
4879         with constructs such as (?(+2).         most  recently opened parentheses can be referenced by (?(-1), the next
4880           most recent by (?(-2), and so on. In looping  constructs  it  can  also
4881           make  sense  to  refer  to  subsequent  groups  with constructs such as
4882           (?(+2).
4883    
4884         Consider  the  following  pattern, which contains non-significant white         Consider the following pattern, which  contains  non-significant  white
4885         space to make it more readable (assume the PCRE_EXTENDED option) and to         space to make it more readable (assume the PCRE_EXTENDED option) and to
4886         divide it into three parts for ease of discussion:         divide it into three parts for ease of discussion:
4887    
4888           ( \( )?    [^()]+    (?(1) \) )           ( \( )?    [^()]+    (?(1) \) )
4889    
4890         The  first  part  matches  an optional opening parenthesis, and if that         The first part matches an optional opening  parenthesis,  and  if  that
4891         character is present, sets it as the first captured substring. The sec-         character is present, sets it as the first captured substring. The sec-
4892         ond  part  matches one or more characters that are not parentheses. The         ond part matches one or more characters that are not  parentheses.  The
4893         third part is a conditional subpattern that tests whether the first set         third part is a conditional subpattern that tests whether the first set
4894         of parentheses matched or not. If they did, that is, if subject started         of parentheses matched or not. If they did, that is, if subject started
4895         with an opening parenthesis, the condition is true, and so the yes-pat-         with an opening parenthesis, the condition is true, and so the yes-pat-
4896         tern  is  executed  and  a  closing parenthesis is required. Otherwise,         tern is executed and a  closing  parenthesis  is  required.  Otherwise,
4897         since no-pattern is not present, the  subpattern  matches  nothing.  In         since  no-pattern  is  not  present, the subpattern matches nothing. In
4898         other  words,  this  pattern  matches  a  sequence  of non-parentheses,         other words,  this  pattern  matches  a  sequence  of  non-parentheses,
4899         optionally enclosed in parentheses.         optionally enclosed in parentheses.
4900    
4901         If you were embedding this pattern in a larger one,  you  could  use  a         If  you  were  embedding  this pattern in a larger one, you could use a
4902         relative reference:         relative reference:
4903    
4904           ...other stuff... ( \( )?    [^()]+    (?(-1) \) ) ...           ...other stuff... ( \( )?    [^()]+    (?(-1) \) ) ...
4905    
4906         This  makes  the  fragment independent of the parentheses in the larger         This makes the fragment independent of the parentheses  in  the  larger
4907         pattern.         pattern.
4908    
4909     Checking for a used subpattern by name     Checking for a used subpattern by name
4910    
4911         Perl uses the syntax (?(<name>)...) or (?('name')...)  to  test  for  a         Perl  uses  the  syntax  (?(<name>)...) or (?('name')...) to test for a
4912         used  subpattern  by  name.  For compatibility with earlier versions of         used subpattern by name. For compatibility  with  earlier  versions  of
4913         PCRE, which had this facility before Perl, the syntax  (?(name)...)  is         PCRE,  which  had this facility before Perl, the syntax (?(name)...) is
4914         also  recognized. However, there is a possible ambiguity with this syn-         also recognized. However, there is a possible ambiguity with this  syn-
4915         tax, because subpattern names may  consist  entirely  of  digits.  PCRE         tax,  because  subpattern  names  may  consist entirely of digits. PCRE
4916         looks  first for a named subpattern; if it cannot find one and the name         looks first for a named subpattern; if it cannot find one and the  name
4917         consists entirely of digits, PCRE looks for a subpattern of  that  num-         consists  entirely  of digits, PCRE looks for a subpattern of that num-
4918         ber,  which must be greater than zero. Using subpattern names that con-         ber, which must be greater than zero. Using subpattern names that  con-
4919         sist entirely of digits is not recommended.         sist entirely of digits is not recommended.
4920    
4921         Rewriting the above example to use a named subpattern gives this:         Rewriting the above example to use a named subpattern gives this:
4922    
4923           (?<OPEN> \( )?    [^()]+    (?(<OPEN>) \) )           (?<OPEN> \( )?    [^()]+    (?(<OPEN>) \) )
4924    
4925           If  the  name used in a condition of this kind is a duplicate, the test
4926           is applied to all subpatterns of the same name, and is true if any  one
4927           of them has matched.
4928    
4929     Checking for pattern recursion     Checking for pattern recursion
4930    
4931         If the condition is the string (R), and there is no subpattern with the         If the condition is the string (R), and there is no subpattern with the
4932         name  R, the condition is true if a recursive call to the whole pattern         name R, the condition is true if a recursive call to the whole  pattern
4933         or any subpattern has been made. If digits or a name preceded by amper-         or any subpattern has been made. If digits or a name preceded by amper-
4934         sand follow the letter R, for example:         sand follow the letter R, for example:
4935    
4936           (?(R3)...) or (?(R&name)...)           (?(R3)...) or (?(R&name)...)
4937    
4938         the  condition is true if the most recent recursion is into the subpat-         the condition is true if the most recent recursion is into a subpattern
4939         tern whose number or name is given. This condition does not  check  the         whose number or name is given. This condition does not check the entire
4940         entire recursion stack.         recursion stack. If the name used in a condition  of  this  kind  is  a
4941           duplicate, the test is applied to all subpatterns of the same name, and
4942           is true if any one of them is the most recent recursion.
4943    
4944         At  "top  level", all these recursion test conditions are false. Recur-         At "top level", all these recursion test  conditions  are  false.   The
4945         sive patterns are described below.         syntax for recursive patterns is described below.
4946    
4947     Defining subpatterns for use by reference only     Defining subpatterns for use by reference only
4948    
4949         If the condition is the string (DEFINE), and  there  is  no  subpattern         If  the  condition  is  the string (DEFINE), and there is no subpattern
4950         with  the  name  DEFINE,  the  condition is always false. In this case,         with the name DEFINE, the condition is  always  false.  In  this  case,
4951         there may be only one alternative  in  the  subpattern.  It  is  always         there  may  be  only  one  alternative  in the subpattern. It is always
4952         skipped  if  control  reaches  this  point  in the pattern; the idea of         skipped if control reaches this point  in  the  pattern;  the  idea  of
4953         DEFINE is that it can be used to define "subroutines" that can be  ref-         DEFINE  is that it can be used to define "subroutines" that can be ref-
4954         erenced  from elsewhere. (The use of "subroutines" is described below.)         erenced from elsewhere. (The use of "subroutines" is described  below.)
4955         For example, a pattern to match an IPv4 address could be  written  like         For  example,  a pattern to match an IPv4 address could be written like
4956         this (ignore whitespace and line breaks):         this (ignore whitespace and line breaks):
4957    
4958           (?(DEFINE) (?<byte> 2[0-4]\d | 25[0-5] | 1\d\d | [1-9]?\d) )           (?(DEFINE) (?<byte> 2[0-4]\d | 25[0-5] | 1\d\d | [1-9]?\d) )
4959           \b (?&byte) (\.(?&byte)){3} \b           \b (?&byte) (\.(?&byte)){3} \b
4960    
4961         The  first part of the pattern is a DEFINE group inside which a another         The first part of the pattern is a DEFINE group inside which a  another
4962         group named "byte" is defined. This matches an individual component  of         group  named "byte" is defined. This matches an individual component of
4963         an  IPv4  address  (a number less than 256). When matching takes place,         an IPv4 address (a number less than 256). When  matching  takes  place,
4964         this part of the pattern is skipped because DEFINE acts  like  a  false         this  part  of  the pattern is skipped because DEFINE acts like a false
4965         condition.         condition. The rest of the pattern uses references to the  named  group
4966           to  match the four dot-separated components of an IPv4 address, insist-
4967         The rest of the pattern uses references to the named group to match the         ing on a word boundary at each end.
        four dot-separated components of an IPv4 address, insisting on  a  word  
        boundary at each end.  
4968    
4969     Assertion conditions     Assertion conditions
4970    
4971         If  the  condition  is  not  in any of the above formats, it must be an         If the condition is not in any of the above  formats,  it  must  be  an
4972         assertion.  This may be a positive or negative lookahead or  lookbehind         assertion.   This may be a positive or negative lookahead or lookbehind
4973         assertion.  Consider  this  pattern,  again  containing non-significant         assertion. Consider  this  pattern,  again  containing  non-significant
4974         white space, and with the two alternatives on the second line:         white space, and with the two alternatives on the second line:
4975    
4976           (?(?=[^a-z]*[a-z])           (?(?=[^a-z]*[a-z])
4977           \d{2}-[a-z]{3}-\d{2}  |  \d{2}-\d{2}-\d{2} )           \d{2}-[a-z]{3}-\d{2}  |  \d{2}-\d{2}-\d{2} )
4978    
4979         The condition  is  a  positive  lookahead  assertion  that  matches  an         The  condition  is  a  positive  lookahead  assertion  that  matches an
4980         optional  sequence of non-letters followed by a letter. In other words,         optional sequence of non-letters followed by a letter. In other  words,
4981         it tests for the presence of at least one letter in the subject.  If  a         it  tests  for the presence of at least one letter in the subject. If a
4982         letter  is found, the subject is matched against the first alternative;         letter is found, the subject is matched against the first  alternative;
4983         otherwise it is  matched  against  the  second.  This  pattern  matches         otherwise  it  is  matched  against  the  second.  This pattern matches
4984         strings  in  one  of the two forms dd-aaa-dd or dd-dd-dd, where aaa are         strings in one of the two forms dd-aaa-dd or dd-dd-dd,  where  aaa  are
4985         letters and dd are digits.         letters and dd are digits.
4986    
4987    
4988  COMMENTS  COMMENTS
4989    
4990         The sequence (?# marks the start of a comment that continues up to  the         The  sequence (?# marks the start of a comment that continues up to the
4991         next  closing  parenthesis.  Nested  parentheses are not permitted. The         next closing parenthesis. Nested parentheses  are  not  permitted.  The
4992         characters that make up a comment play no part in the pattern  matching         characters  that make up a comment play no part in the pattern matching
4993         at all.         at all.
4994    
4995         If  the PCRE_EXTENDED option is set, an unescaped # character outside a         If the PCRE_EXTENDED option is set, an unescaped # character outside  a
4996         character class introduces a  comment  that  continues  to  immediately         character  class  introduces  a  comment  that continues to immediately
4997         after the next newline in the pattern.         after the next newline in the pattern.
4998    
4999    
5000  RECURSIVE PATTERNS  RECURSIVE PATTERNS
5001    
5002         Consider  the problem of matching a string in parentheses, allowing for         Consider the problem of matching a string in parentheses, allowing  for
5003         unlimited nested parentheses. Without the use of  recursion,  the  best         unlimited  nested  parentheses.  Without the use of recursion, the best
5004         that  can  be  done  is  to use a pattern that matches up to some fixed         that can be done is to use a pattern that  matches  up  to  some  fixed
5005         depth of nesting. It is not possible to  handle  an  arbitrary  nesting         depth  of  nesting.  It  is not possible to handle an arbitrary nesting
5006         depth.         depth.
5007    
5008         For some time, Perl has provided a facility that allows regular expres-         For some time, Perl has provided a facility that allows regular expres-
5009         sions to recurse (amongst other things). It does this by  interpolating         sions  to recurse (amongst other things). It does this by interpolating
5010         Perl  code in the expression at run time, and the code can refer to the         Perl code in the expression at run time, and the code can refer to  the
5011         expression itself. A Perl pattern using code interpolation to solve the         expression itself. A Perl pattern using code interpolation to solve the
5012         parentheses problem can be created like this:         parentheses problem can be created like this:
5013    
# Line 4697  RECURSIVE PATTERNS Line 5017  RECURSIVE PATTERNS
5017         refers recursively to the pattern in which it appears.         refers recursively to the pattern in which it appears.
5018    
5019         Obviously, PCRE cannot support the interpolation of Perl code. Instead,         Obviously, PCRE cannot support the interpolation of Perl code. Instead,
5020         it  supports  special  syntax  for recursion of the entire pattern, and         it supports special syntax for recursion of  the  entire  pattern,  and
5021         also for individual subpattern recursion.  After  its  introduction  in         also  for  individual  subpattern  recursion. After its introduction in
5022         PCRE  and  Python,  this  kind of recursion was introduced into Perl at         PCRE and Python, this kind of  recursion  was  subsequently  introduced
5023         release 5.10.         into Perl at release 5.10.
5024    
5025         A special item that consists of (? followed by a  number  greater  than         A  special  item  that consists of (? followed by a number greater than
5026         zero and a closing parenthesis is a recursive call of the subpattern of         zero and a closing parenthesis is a recursive call of the subpattern of
5027         the given number, provided that it occurs inside that  subpattern.  (If         the  given  number, provided that it occurs inside that subpattern. (If
5028         not,  it  is  a  "subroutine" call, which is described in the next sec-         not, it is a "subroutine" call, which is described  in  the  next  sec-
5029         tion.) The special item (?R) or (?0) is a recursive call of the  entire         tion.)  The special item (?R) or (?0) is a recursive call of the entire
5030         regular expression.         regular expression.
5031    
        In  PCRE (like Python, but unlike Perl), a recursive subpattern call is  
        always treated as an atomic group. That is, once it has matched some of  
        the subject string, it is never re-entered, even if it contains untried  
        alternatives and there is a subsequent matching failure.  
   
5032         This PCRE pattern solves the nested  parentheses  problem  (assume  the         This PCRE pattern solves the nested  parentheses  problem  (assume  the
5033         PCRE_EXTENDED option is set so that white space is ignored):         PCRE_EXTENDED option is set so that white space is ignored):
5034    
5035           \( ( (?>[^()]+) | (?R) )* \)           \( ( [^()]++ | (?R) )* \)
5036    
5037         First  it matches an opening parenthesis. Then it matches any number of         First  it matches an opening parenthesis. Then it matches any number of
5038         substrings which can either be a  sequence  of  non-parentheses,  or  a         substrings which can either be a  sequence  of  non-parentheses,  or  a
5039         recursive  match  of the pattern itself (that is, a correctly parenthe-         recursive  match  of the pattern itself (that is, a correctly parenthe-
5040         sized substring).  Finally there is a closing parenthesis.         sized substring).  Finally there is a closing parenthesis. Note the use
5041           of a possessive quantifier to avoid backtracking into sequences of non-
5042           parentheses.
5043    
5044         If this were part of a larger pattern, you would not  want  to  recurse         If this were part of a larger pattern, you would not  want  to  recurse
5045         the entire pattern, so instead you could use this:         the entire pattern, so instead you could use this:
5046    
5047           ( \( ( (?>[^()]+) | (?1) )* \) )           ( \( ( [^()]++ | (?1) )* \) )
5048    
5049         We  have  put the pattern into parentheses, and caused the recursion to         We  have  put the pattern into parentheses, and caused the recursion to
5050         refer to them instead of the whole pattern.         refer to them instead of the whole pattern.
5051    
5052         In a larger pattern,  keeping  track  of  parenthesis  numbers  can  be         In a larger pattern,  keeping  track  of  parenthesis  numbers  can  be
5053         tricky.  This is made easier by the use of relative references. (A Perl         tricky.  This  is made easier by the use of relative references (a Perl
5054         5.10 feature.)  Instead of (?1) in the  pattern  above  you  can  write         5.10 feature).  Instead of (?1) in the  pattern  above  you  can  write
5055         (?-2) to refer to the second most recently opened parentheses preceding         (?-2) to refer to the second most recently opened parentheses preceding
5056         the recursion. In other  words,  a  negative  number  counts  capturing         the recursion. In other  words,  a  negative  number  counts  capturing
5057         parentheses leftwards from the point at which it is encountered.         parentheses leftwards from the point at which it is encountered.
# Line 4749  RECURSIVE PATTERNS Line 5066  RECURSIVE PATTERNS
5066         syntax for this is (?&name); PCRE's earlier syntax  (?P>name)  is  also         syntax for this is (?&name); PCRE's earlier syntax  (?P>name)  is  also
5067         supported. We could rewrite the above example as follows:         supported. We could rewrite the above example as follows:
5068    
5069           (?<pn> \( ( (?>[^()]+) | (?&pn) )* \) )           (?<pn> \( ( [^()]++ | (?&pn) )* \) )
5070    
5071         If  there  is more than one subpattern with the same name, the earliest         If  there  is more than one subpattern with the same name, the earliest
5072         one is used.         one is used.
5073    
5074         This particular example pattern that we have been looking  at  contains         This particular example pattern that we have been looking  at  contains
5075         nested  unlimited repeats, and so the use of atomic grouping for match-         nested unlimited repeats, and so the use of a possessive quantifier for
5076         ing strings of non-parentheses is important when applying  the  pattern         matching strings of non-parentheses is important when applying the pat-
5077         to strings that do not match. For example, when this pattern is applied         tern  to  strings  that do not match. For example, when this pattern is
5078         to         applied to
5079    
5080           (aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa()           (aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa()
5081    
5082         it yields "no match" quickly. However, if atomic grouping is not  used,         it yields "no match" quickly. However, if a  possessive  quantifier  is
5083         the  match  runs  for a very long time indeed because there are so many         not  used, the match runs for a very long time indeed because there are
5084         different ways the + and * repeats can carve up the  subject,  and  all         so many different ways the + and * repeats can carve  up  the  subject,
5085         have to be tested before failure can be reported.         and all have to be tested before failure can be reported.
5086    
5087         At the end of a match, the values set for any capturing subpatterns are         At  the  end  of a match, the values of capturing parentheses are those
5088         those from the outermost level of the recursion at which the subpattern         from the outermost level. If you want to obtain intermediate values,  a
5089         value  is  set.   If  you want to obtain intermediate values, a callout         callout  function can be used (see below and the pcrecallout documenta-
5090         function can be used (see below and the pcrecallout documentation).  If         tion). If the pattern above is matched against
        the pattern above is matched against  
5091    
5092           (ab(cd)ef)           (ab(cd)ef)
5093    
5094         the  value  for  the  capturing  parentheses is "ef", which is the last         the value for the inner capturing parentheses  (numbered  2)  is  "ef",
5095         value taken on at the top level. If additional parentheses  are  added,         which  is the last value taken on at the top level. If a capturing sub-
5096         giving         pattern is not matched at the top level, its final value is unset, even
5097           if it is (temporarily) set at a deeper level.
5098           \( ( ( (?>[^()]+) | (?R) )* ) \)  
5099              ^                        ^         If  there are more than 15 capturing parentheses in a pattern, PCRE has
5100              ^                        ^         to obtain extra memory to store data during a recursion, which it  does
5101           by using pcre_malloc, freeing it via pcre_free afterwards. If no memory
5102         the  string  they  capture is "ab(cd)ef", the contents of the top level         can be obtained, the match fails with the PCRE_ERROR_NOMEMORY error.
        parentheses. If there are more than 15 capturing parentheses in a  pat-  
        tern, PCRE has to obtain extra memory to store data during a recursion,  
        which it does by using pcre_malloc, freeing  it  via  pcre_free  after-  
        wards.  If  no  memory  can  be  obtained,  the  match  fails  with the  
        PCRE_ERROR_NOMEMORY error.  
5103    
5104         Do not confuse the (?R) item with the condition (R),  which  tests  for         Do not confuse the (?R) item with the condition (R),  which  tests  for
5105         recursion.   Consider  this pattern, which matches text in angle brack-         recursion.   Consider  this pattern, which matches text in angle brack-
# Line 4802  RECURSIVE PATTERNS Line 5113  RECURSIVE PATTERNS
5113         two  different  alternatives for the recursive and non-recursive cases.         two  different  alternatives for the recursive and non-recursive cases.
5114         The (?R) item is the actual recursive call.         The (?R) item is the actual recursive call.
5115    
5116       Recursion difference from Perl
5117    
5118           In PCRE (like Python, but unlike Perl), a recursive subpattern call  is
5119           always treated as an atomic group. That is, once it has matched some of
5120           the subject string, it is never re-entered, even if it contains untried
5121           alternatives  and  there  is a subsequent matching failure. This can be
5122           illustrated by the following pattern, which purports to match a  palin-
5123           dromic  string  that contains an odd number of characters (for example,
5124           "a", "aba", "abcba", "abcdcba"):
5125    
5126             ^(.|(.)(?1)\2)$
5127    
5128           The idea is that it either matches a single character, or two identical
5129           characters  surrounding  a sub-palindrome. In Perl, this pattern works;
5130           in PCRE it does not if the pattern is  longer  than  three  characters.
5131           Consider the subject string "abcba":
5132    
5133           At  the  top level, the first character is matched, but as it is not at
5134           the end of the string, the first alternative fails; the second alterna-
5135           tive is taken and the recursion kicks in. The recursive call to subpat-
5136           tern 1 successfully matches the next character ("b").  (Note  that  the
5137           beginning and end of line tests are not part of the recursion).
5138    
5139           Back  at  the top level, the next character ("c") is compared with what
5140           subpattern 2 matched, which was "a". This fails. Because the  recursion
5141           is  treated  as  an atomic group, there are now no backtracking points,
5142           and so the entire match fails. (Perl is able, at  this  point,  to  re-
5143           enter  the  recursion  and try the second alternative.) However, if the
5144           pattern is written with the alternatives in the other order, things are
5145           different:
5146    
5147             ^((.)(?1)\2|.)$
5148    
5149           This  time,  the recursing alternative is tried first, and continues to
5150           recurse until it runs out of characters, at which point  the  recursion
5151           fails.  But  this  time  we  do  have another alternative to try at the
5152           higher level. That is the big difference:  in  the  previous  case  the
5153           remaining alternative is at a deeper recursion level, which PCRE cannot
5154           use.
5155    
5156           To change the pattern so that matches all palindromic strings, not just
5157           those  with  an  odd number of characters, it is tempting to change the
5158           pattern to this:
5159    
5160             ^((.)(?1)\2|.?)$
5161    
5162           Again, this works in Perl, but not in PCRE, and for  the  same  reason.
5163           When  a  deeper  recursion has matched a single character, it cannot be
5164           entered again in order to match an empty string.  The  solution  is  to
5165           separate  the two cases, and write out the odd and even cases as alter-
5166           natives at the higher level:
5167    
5168             ^(?:((.)(?1)\2|)|((.)(?3)\4|.))
5169    
5170           If you want to match typical palindromic phrases, the  pattern  has  to
5171           ignore all non-word characters, which can be done like this:
5172    
5173             ^\W*+(?:((.)\W*+(?1)\W*+\2|)|((.)\W*+(?3)\W*+\4|\W*+.\W*+))\W*+$
5174    
5175           If run with the PCRE_CASELESS option, this pattern matches phrases such
5176           as "A man, a plan, a canal: Panama!" and it works well in both PCRE and
5177           Perl.  Note the use of the possessive quantifier *+ to avoid backtrack-
5178           ing into sequences of non-word characters. Without this, PCRE  takes  a
5179           great  deal  longer  (ten  times or more) to match typical phrases, and
5180           Perl takes so long that you think it has gone into a loop.
5181    
5182           WARNING: The palindrome-matching patterns above work only if  the  sub-
5183           ject  string  does not start with a palindrome that is shorter than the
5184           entire string.  For example, although "abcba" is correctly matched,  if
5185           the  subject  is "ababa", PCRE finds the palindrome "aba" at the start,
5186           then fails at top level because the end of the string does not  follow.
5187           Once  again, it cannot jump back into the recursion to try other alter-
5188           natives, so the entire match fails.
5189    
5190    
5191  SUBPATTERNS AS SUBROUTINES  SUBPATTERNS AS SUBROUTINES
5192    
# Line 4828  SUBPATTERNS AS SUBROUTINES Line 5213  SUBPATTERNS AS SUBROUTINES
5213         two strings. Another example is  given  in  the  discussion  of  DEFINE         two strings. Another example is  given  in  the  discussion  of  DEFINE
5214         above.         above.
5215    
5216         Like recursive subpatterns, a "subroutine" call is always treated as an         Like  recursive  subpatterns, a subroutine call is always treated as an
5217